Advertisement

Advanced Composites and Hybrid Materials

, Volume 1, Issue 2, pp 269–299 | Cite as

Regulations of silver halide nanostructure and composites on photocatalysis

  • Yingying Fan
  • Dongxue Han
  • Zhongqian Song
  • Zhonghui Sun
  • Xiandui Dong
  • Li Niu
Review

Abstract

The silver halides and their corresponding composites would constitute remarkable photocatalytic systems not only in energy production but also in environmental remediation. The major advantage in these silver halides system is that plasma metal Ag0 species would be spontaneously generated by silver halides under light irradiation, which play dual roles of expanding light absorption range and charge carriers separation. In this tutorial review, the origin and development of silver halides, synthesis methods, construction of composite structures with other materials, photocatalytic applications, and various and controversial mechanisms are all exhaustively described.

Graphical abstract

The silver halides and their corresponding composites would constitute remarkable photocatalytic systems not only in energy production but also in environmental remediation.

Keywords

Silver halide Photocatalysis Composites materials 

1 Introduction

From the past to the present, the continued population growth combing with sustainable industry development have bring about beyond controlled environment containments and avaricious power requirements. Among multiple contaminations, the water pollution government is considered as one of the critical events that intimately associate with human’s livelihood [1, 2].

Thus, urgent conductions are demanded to be applied on the treatment approaches of water pollution especially the organic dye component, which is difficult to be decomposed no matter through chemical or biological methods. In the energy demand aspects, most of the energy production is supplied by the depletion of the fossil resources, such as oil, coal and natural gas. It is well known that these fossil sources are stored limited and environment troubles would be yield following the combustion of the traditional fuels, which urgently demand for a developing sustainable energy technologies [3, 4, 5, 6, 7, 8].

Inexhaustible solar energy is the most important sustainable resource, whose annual energy output for Earth is capable for satisfying mankind’s yearly energy consumption with 5% UV, 43% visible, and 52% IR [9, 10]. For today, many applications of solar energy have been proposed, such as photoelectrochemical reaction and various solar cells [5, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27], which are all indirect utilization depending on meticulous devices. Photocatalysis is a direct conversion technique between solar and chemical energy in presence of catalyst and accelerates the photoreaction [16, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37]. The corresponding applications are mainly exhibited in photocatalytic hydrogen evolution from water splitting [38, 39, 40, 41, 42], organic contaminants degradation [43, 44, 45, 46, 47, 48, 49, 50], water disinfection [51, 52, 53, 54], CO2 photoreduction, and surface self-cleaning [55, 56, 57, 58, 59, 60, 61]. Nowadays, photocatalysis energy conversion technology based on the semiconductor with suitable bandgap has emerged as one of the saviors for the traditional power mode, which could utilize the solar energy to degrade the water pollutions and produce clean energy [62, 63, 64, 65, 66, 67]. Alien to the metal possessing a continuous electronic state, semiconductor possesses a bandgap with a void electron region, which extends from the top of filled VB to the bottom of vacant CB. Thus, when the light irradiates on the semiconductor nanoparticles, pairs of electrons and holes would be generated and have sufficient time (nanosecond) for arrival at the surface reaction before recombination owning to the existence of bandgap [68, 69]. For environment cleanup, the electrons and holes would integrate with oxygen molecules (O2) or water molecules (H2O) to form the radicals, which play a vital role in organic dyes degradation. While in clean energy aspect, mainly the electrons are delivered to the precursor reactants (such as H2O and CO2) to generate the hydrogen (H2) and hydrocarbon fuels, which are actively regarded as energy vectors for converting solar to chemical and electrical energy. The requirement for transforming the irradiation energy to hydrogen and hydrocarbon fuels could be generalized into two reasons. First, amplitude diversifications of solar irradiation, according to daily and seasonal changes, are incompatible with the successive energy supplying in life and industry demand. Thus, conversion of the solar energy into hydrogen and hydrocarbon fuels becomes necessary. Second, due to H2O and CO2 as raw materials and combustion product, hydrogen and hydrocarbon fuels are pragmatic for large-scale operations because of its sustainable properties and readily available resource.

1.1 The development origin of AgX

In 1972, Fujishima and Honda discovered that TiO2 was able to photoelectron-splitting water under light, which opened new era for photocatalysis [70]. Since then, large number of metal oxides similar to TiO2 with large bandgap has been focused as photocatalysts. As well known, although large bandgap is enable to maintain semiconductor’s stability during reaction process, low solar energy absorption (only ultraviolet light) creates poor photocatalysis efficiency. Therefore, remedies for enhancing solar energy utilization have been devoted, such as doping various non-metal or transition metal atoms into large-band semiconductor’s crystal [71, 72, 73]. Based on many reports on doping methods, even though certain promotions are detected in both irradiation absorption and catalytic ability, large distance is still required to catch up [74, 75].

The photocatalytic capability could be determined by many factors. Especially, the light utilization characteristics for controlling the charge carrier generation and the corresponding charge carriers separation, both of which are critical important toward the photoinduced chemistry efficiency. In this perspective, plasmon-enhanced photocatalyst constituting by plasmon and semiconductor is able to vividly express its superiority in these two photocatalytic enhancement aspects. First, plasmonic metal nanoparticles can act as an antenna to localize the irradiation energy and then transfers it to the semiconductor, which makes the photocatalyst a high absorption coefficient [76, 77, 78, 79]. Second, irradiation light is likely to be scattered by larger metal particles on the semiconductor surface, thus the path length of light through the semiconductor is expanded [80, 81, 82]. Hereafter, a significant proportion of scattered light tends to be trapped and absorbed by the semiconductor. Third, bulk recombination of electrons and holes in semiconductor is regularly happen due to the fact that the minority carrier distance (L) is shorter than the physical size of semiconductor structure [83, 84, 85]. As the plasmon could localize the optical confining to the near-surface region of a semiconductor, the electrons and holes generated in there only need traveling less than L to engage the reaction, which greatly minimize the recombination ratio. In addition, plasmonic metal nanoparticle is able to sensitize the semiconductor to below-band gap light through transferring its own excited electrons into the CB of semiconductor so that the photocatalysis activity of semiconductor can be apparently improved [86]. Moreover, in plasmonics, metal or even noble metal are the noumenon particles (such as Cu, Au, and Ag), which promises their resistance to decomposition. Based on these two advantages, plasmonic nanoparticles (NPs) are considered as favorable photosensitive materials for enhancing the light absorption coefficient of large bandgap semiconductors and could also maintain their stabilities [87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102]. Great quantities of works on constituting plasmonic NPs and large-bandgap semiconductors have already achieved. For instance, Cu NPs dispersed on TiO2 supports and mesoporous Au/TiO2 nanocomposite have been prepared for H2 production and wastewater treatment reactions, respectively [103, 104, 105]. However, assemble efficiency between plasmonic NPs and semiconductor is not able to get well controlled due to the external precursors introduction, leading to uncertain sensitive efficiency of plasmonic NPs on semiconductor photocatalysts. If the semiconductor photocatalysts act as the precursor to generate plasmonic NPs, then seamlessly integration between semiconductor photocatalysts and plasmonic NPs will be realized and result in high charge transport efficiency among them. Throughout all photocatalysts, only AgX semiconductors can be in situ partially converted to plasmonic Ag NPs under light irradiation constituting Ag/AgX hybrid particles with clean and well-define metal/semiconductor interfaces.

1.2 What is silver halide and its development in nanotechnology

Silver halides (AgX) are related to one kind of semiconductor crystal constituted by positively charged silver ion (Ag+) and negative halogen ions (X = Cl, Br and I) [106, 107]. The key characteristic of AgX is the photosensitivity, as photolytic silver could be formed under light exposure, which make AgX become pivotal source material in photographic film. In photographic aspects, microscopic sized AgX grains are integrated into gelation to form photographic emulsions, in which negative emulsion is built up by AgBr containing a small percentage of AgI while AgCl grains constitute the positive emulsion [108, 109]. Through certain light exposure, pairs of electron and positive hole could be liberated within AgX crystal. Due to the important role of crystal defect, positive holes likely recombining with electrons would be captured by X traps, which create higher merge opportunity for the generation of Ag0 particles by the combination of interstitial Ag+ and photoelectrons. In this way, the term of “latent image” is developed accounting for the photographic emulsion exposure [110]. However, these beneficial features of silver halide in photographic process simultaneously reflect that the silver halides are unstable under irradiation of light, which inhibit their application in the photocatalysis aspects. In 1921, Baur and Rebmann investigated the photochemical properties of AgCl in water splitting and discovered minor O2 evolution under UV irradiation [111]. In order to take insight into the oxygen evolution, Chandrasekaran and Thomas in 1983 opened a mechanism exploration work and elucidated that water oxidation by AgCl/Ag+ system under irradiation was not catalytic though a similarity between this system and photosynthetic energy storage was existed [112]. However, in 1996, one more time Calzaferri et al. carried out a photochemical oxidation of water to O2 with thin AgCl layer on SnO2-coated glass plate in small excess presence of Ag+ ions in aqueous solution under different illumination conditions [113]. This work revealed that the role of Ag+ ion was to repair the damaged AgCl species during the photochemical oxidation of water, which ensured an intact AgCl composition before and after the reaction. Simultaneously, convincing mechanism was proposed explaining the reasons of acidic condition, an excess of Cl, chlorine and oxygen formation during the water decomposition combining with a thoroughly reaction process analysis. And this mechanism indirectly indicated the photochemical oxidation of water on AgCl layers was a photocatalytic process. After that in 1999, Noriyoshi Kakuta et al. used a AgBr/SiO2 composite prepared from Schumann emulsion to generate hydrogen (H2) from CH3OH/H2O photolysis under UV illumination and this reaction was continued for 200 h without destruction of AgBr although Ag0 was observed [114]. Maybe it was the first time to confessedly recognize the silver halide as photocatalyst. In 2006, a visible-light-induced photocatalyst AgI/TiO2 was prepared by Chun Hu et al. and was found to show high efficiency for the degradation of azodyes, which based on their previous work visible-light-driven photocatalyst AgBr/TiO2 [115]. The above-mentioned is primary regarding the origin of silver halides on the photocatalysis application. From then on, tremendous works with respect to the property and morphology modification on silver halides sprang up to advance their photocatalytic performance [114, 115, 116, 117, 118, 119, 120, 121].

2 Preparation of silver halide

As AgX is composited by Ag+ and Cl, common features for synthesis are definitely existed among them, such as a precipitation reaction of Ag+ and X and ion-exchange between silver salt and HX [122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135]. The architecture and morphology of AgX, especially with high-surface-energy crystalline facets, are able to manage and define their unique photocatalytic properties [136, 137, 138, 139, 140, 141, 142, 143, 144]. And some photocatalytic performance discussed in Section 3.1 is exactly in accordance with the well-designed architectures of AgX. At present, various types of synthesis modus have been created for fabricating AgX crystals with different architectures and shapes. Table 1 listed an overview of many respective AgX architectures that prepared in various synthesis methods, including polyvinylpyrrolidone-assisted precipitation, ion-exchange, and template-direction. [1, 145, 146, 147]. Here, several synthetic approaches have been partitioned to systematically analyze the reaction process and mechanisms.
Table 1

Summary of the shapes, morphology illustrations, photocatalyst kinds, methods for synthesis and photocatalytic applications of AgX nanostructures discussed in this review

2.1 Polyvinylpyrrolidone-assisted precipitation

The most convenient way to synthesize AgX crystal is the chemical precipitation between Ag+ and X [148, 149, 150]. However, violent reaction rate of direct precipitation likely to cause particles aggregation into bulk, which wrecks the desired nano-size properties. Thus, restraint tactics should be exerted in precipitation process to obtain uniform nano or micro level particles [151]. As an excellent capping agent, polyvinylpyrrolidone (PVP) has been widely applied in morphology control of many inorganic crystals, such as metal single crystal, metallic salts and inorganic semiconductors [152, 153, 154, 155, 156, 157, 158]. For examples, tetrahedral Pt nanoparticles (NPs) stabilized by PVP has been synthesized employing H2 reduction method [159]. Applying a facile solvothermal technology in presence of PVP, controllable CdS colloidal spheres with monodisperse submicrometer have been prepared [160]. Especially in silver composition aspect, PVP has been taking as dominant morphology agent to form large-scale silver crystals with uniform distribution [1, 161]. This selectivity can be ascribed to the preferred binding tendency between PVP and Ag+, which forms PVP-Ag+ complex and plays a vital role in Ag+ stabilization. Within unite structure from PVP molecule chain, electron clouds are inclined to show partiality for polar groups (C = O) and ligands -N, which property enable interaction between Ag+ and C = O as well as N atom in the pyrrole ring. As shown in Fourier transform-infrared spectroscopy (FT-IR) spectra of PVP-Ag+ and pure PVP in Fig. 1a, the interaction between Ag+ and pyrrole N was reflected at 1388 cm−1, and the strong band generated at 2436 cm−1 was attributed to the formation of Ag+…-O = C, respecting the PVP-Ag+ configuration [162]. Due to steric effect of PVP, the chemical reaction of Ag+ and X become sluggish and controllable. With reaction occurrence, crystal diameter gradually increases and steric effect is strengthened. Finally, the PVP molecule cover layer generated on the surface of AgX crystal succeeds in prohibiting growth and agglomeration of crystal particles. More significant, each crystal face is terminated with different ion states. Some surfaces are mainly constituted with Ag+ that mass PVP molecules would attach, thus suppressed growth on these planes would happen. While other planes dominated by X would gain less influence from PVP and wanton growth is extended. Finally, a morphology management is achieved based on PVP adjustment as shown in Fig. 1b, c [162, 163].
Fig. 1

a FT-IR spectrum of the freeze-dried PVP–Ag+ hybrid precursor with RPVP/Ag = 0.05. Reproduced with permission from ref. [162]. Copyright 2014 Elsevier. b, c SEM images of Ag/AgCl crystal particles synthesized in the presence of PVP. b Reproduced with permission from ref. [164]. Copyright 2011 Royal Society of Chemistry. c Reproduced with permission from ref. [163]. Copyright 2014 Royal Society of Chemistry

Monodispersed cubic AgCl NPs were synthesized by Yugang Sun group through a typical precipitation reaction between Ag+ ions and Cl ions, in which PVP was added to assist the morphology control [6]. This approach points a vital role of PVP in AgX architecture construction and is received as popular approach to design various AgX architectures. In a similar cube-like AgCl crystal synthesis (Fig. 1b), Shaojun Dong’s group has investigated the crystal morphology changes with increasing amounts of PVP founding reduced crystal size and more structured architecture [164]. Besides the regular cube shapes, cube-tetrapod-like AgCl constructions assembled by four cubes were also synthesized through higher reaction temperatures (Fig. 1c) [61, 163, 164]. In AgBr system, hexagonal nanoplates exposed with high energy facets were fabricated using PVP as capping agent as well, first revealing facet effect on AgBr photocatalytic properties [61, 142]. On the other hand, polar-faceted AgI microplates with [143] surfaces were prepared in a facile PVP-assisted precipitation, whose archetypes demonstrated preferred diametric migration of charge carriers [143]. In these typical synthesis, Ag+ cations and X anions are dissolved into viscous solvents with addition of PVP (such as ethylene glycol, glycerol or deionized water with P-tolyl sulfonic acid), respectively, before the stages of reaction. In this process, PVP mainly serves as stabilizer of both ions, and may also complex with Ag+. Then, both solutions are injected into each other under vigorous stirring generating milky dispersions, in which several or tens nanometers sized particles would be formed. Alternatively, such processes are proceeded in certain temperatures, larger crystals under micron level would be synthesized with uniform morphologies.

2.2 Template-directed formation

Since appropriate templates are able to defined both architectures and sizes of target productions, template-directed methods have been regarded as a versatile method in designing various desired nanostructures [165, 166, 167]. Similar to other general NPs composites, template-based AgX synthesis can also be divided into two types of hard template and soft template.

2.2.1 Hard templates

The morphology of AgX nanostructures based on hard template is only affected by original template morphology and their dimensions can also be tight controlled with rigid growth along templates [168, 169]. Commonly used hard templates are anodic aluminum oxide (AAO) and water-soluble sacrificial salt-crystal-template, the latter serves as both reactants and templates during synthesis process. Anodic aluminum oxide (AAO) containing uniform and tunable pore distribution can be used to efficiently guide the synthesis of AgCl nanoparticle nanowires and various AgI nanowires [170, 171, 172, 173, 174], in which electrochemical deposition and electroless precipitation approaches play major roles in embedding AgX into the pores of AAO templates. In Fig. 2a, representative AgI nanowire synthesis is listed based on a highly ordered AAO membrane [173]. Initially, a layer of metal (such as Ag, Au or Pt) is sputtered onto one side of membrane to enable AAO conductive and serve as working electrode. After that, high-orientated Ag nanowire array along template channel direction is electrodeposited within nonporous AAO membrane and subsequent iodination is carried out in an electrochemical cell to obtain the final AgI product. For AgCl nanowire synthesis, a direct precipitation of Ag+ and Cl also can offer uniform deposition for filling AAO membrane pores in high yield [170]. Outstanding advantages of this AAO-template direct synthesis are that desired AgX nanowires or nanorods can homogeneously and periodically aligned among AAO matrix with diameter and length changes in accordance with template pore size. However, with AAO in product, extra template elimination step must be added after synthesis which increases the experiment’s complexity. Water-soluble sacrificial salt-crystal-template-directed synthesis is capable of generating AgX crystal structures with hollow interior morphologies and achieved successful cases including AgCl nanoframe, Ag/AgCl and Ag/AgBr cubic cage [175, 176, 177]. In these materials, salt-crystal-templates (such as KBr, NaCl) are first prepared through injecting their saturated aqueous solution into low solubility alcohol solution leading to salt crystal precipitation in Fig. 2b. Subsequently, AgNO3 solution is added along with ion exchange diffusion reaction between X and Ag+ to form AgX crystal on the surface of salt crystal. When the AgX crystal growth is completed, the obtained salt crystal/AgX samples are washed with water to remove and dissolve the inside salt crystal corn; thus, AgX hollow interior architectures are acquired.
Fig. 2

Schematic illustration for the synthesis process of AgI/Ag hetero-nanowire structure using AAO membrane with electrochemical method (a), and the water-soluble sacrificial salt-crystal-template route for the formation of Ag/AgCl cubic cages (b). a Reproduced with permission from ref. [174]. Copyright 2015 American Chemical Society. b Reproduced with permission from ref. [252]. Copyright 2013 Wiley

2.2.2 Soft templates

Generally, microemulsions composited with various micelles and reverse micelles are the most common soft templates in nanoparticles synthesis of inorganic crystals, noble metals and metal oxides [116, 178, 179, 180, 181, 182, 183, 184, 185]. The professional term of “microemulsion” was proposed by J. H. Schulman, who introduced the “micro emulsion” systems describing a stable transition between oil-rich and water-rich mixture [186, 187]. The surfactant molecules, containing amphiphilic groups, aggregate to form direct and reversed micelles in oil/water (O/W) and water/oil (W/O) microemulsions with hydrophilic groups oriented to water while hydrophobic groups associated with organic solvent [188]. Since then, numbers of nanoparticles practical synthesis on this topic have carried out and attained significance in basic research area. So far, quantities of nanoparticles with variable architectures have been successfully fabricated including nanorods [189, 190, 191], nanocubes [192], nanowires [193, 194], nanoplates [195, 196, 197], and feather or dendrite-like crystal structures [198]. Initially, micelle-based synthesis is capable of preparing AgX nanoparticles through mixing two identical reverse micelles each containing silver ions or halide ions [188, 199, 200, 201, 202, 203, 204]. Two kinds of reverse micelles after mixing rapidly repeat collide with association and dissociation processes companying reaction ions exchanges.

Thus, Ag+ and X combine together and nucleate with AgX nanoparticles formation within the water pools of reverse micelles. In these reverse micelles reaction for AgX, the surfactant molecules have a strong effect on the morphologies of AgX nanostructures through acting as soft templates as well as affecting reaction parameters, such as precursor ions reaction trace and reaction rate [199]. In addition, taking advantage of Br and Cl that existed in molecules of cetyltrimethylammonium (CTAB) and cetyltrimethylammonium chloride (CTAC), AgBr and AgCl can be facilely fabricated without addition of external X resource [147, 202, 205, 206, 207]. Liu group used an oil-in-water mixture microemulsion of CTAC chloroform solution and AgNO3 aqueous solution to one-pot synthesize two controllable morphology Ag/AgCl nanostructures (sphere and cube) through the changes of CTAC concentration in chloroform solution [147]. When CTAC chloroform solution was injected dropwise into a bulk aqueous solution of AgNO3, microemulsion of oil-in-water could be form with the hydrophobic tail of CTAC toward micro-oil core while hydrophilic point directing bulk water phase. In this direct micelles, solution concentration of CTAC was shown to induce a change to the Ag/AgCl morphology (Fig. 3a), forming cube-like (Fig. 3b) or sphere-like (Fig. 3c) nanospecies by adding diluted or highly concentrated CTAC chloroform solution, respectively. The regulation effect of CTAC surfactant was the reasonable illustration for such reaction phenomenon proving that high surfactant concentration facilitated cube-like architecture manufacture and low concentration favored sphere structure formation. In addition, different surface content of metallic Ag0 was observed comparing this oil-in-water synthesis process with previous water-in-oil Ag/AgCl preparation [205]. This is attributed to reaction discrepancy of direct micelles and reverse micelles for the Ag/AgCl preparation: Nanostructured AgCl crystals were generated owning to the collision of Ag+ and Cl ions both in oil-in-water and water-in-oil system and the surface metallic Ag0 grains were induced by ambient light irradiation. However, in oil-in-water case, the collision reaction was mainly occurred at the outer interface of micro-oil phase, in which reactant Ag+ for AgCl and extra Ag+ reduced to produce Ag0 could both constantly provided from the bulk water phase. As a result, comparatively more enriched Ag species could prone to be generated in oil-in-water than water-in-oil microemulsion system. What more important is that ternary alloyed AgClxBr1-x nanocrystals (NCs) with tunable bandgaps can be obtained with CTAC and CTAB selected as both halogen sources and surfactants [208]. In Fig. 3d, non-polar solvent chloroform solution of CTAC/CTAB was injected dropwise to polar aqueous solution of AgNO3 leading to the formation of microemulsion [208]. Surfactant CTAC/CTAB molecules with amphiphilic groups tended to agglomerate at the interface with hydrophilic halogen ion end toward water phase while hydrophobic alkyl chains contacting with chloroform solution. Ag+ dissolved in water phase would like to collide with X within the same phase immediately generating AgX species, whose aging process was controlled by diffusion states of CTAC and CTAB from non-polar phase. Consequently, well-defined ternary alloys of AgClxBr1-x nanocrystals, such as AgCl0.75Br0.25 (Fig. 3e), AgCl0.5Br0.5 (Fig. 3f), and AgCl0.25Br0.75 (Fig. 3g), were obtained by competitive reaction between CTAC and CTAB with Ag+. However, apart from these advantages in the soft-template technique, many challenges remain: Comparing with hard-template technology, the nanostructures produced via soft-template method are still difficult to achieve uniform distributions no matter in size or shapes; The surfactants served as adjuvants or used as precursors during synthesis are not easy to be removed especially in light- and heat-sensitive materials, which ultimately turn into impurities.
Fig. 3

a Possible explanation of the one-pot controllable synthesis of Ag/AgCl-based nanospheres and quasi-nanocubes via an oil-in-water medium. bc SEM images of the bare Ag/AgCl quasi-nanocubes (b) and bare Ag/AgCl nanospheres (c). d Schematic illustration of the synthesis procedure of AgClxBr1-x NCs. eg Typical SEM images of AgClxBr1-x samples. ac Reproduced with permission from ref. [147]. Copyright 2011 Royal Society of Chemistry. dg Reproduced with permission from ref. [208]. Copyright 2013 Royal Society of Chemistry

2.3 In situ ion exchange

Similar with hard template directed synthesis, in situ ion exchange of nanofabrication offer precious control on the placement of silver halide nanostructures over the preformed anion or cation salts, which acts as both templates and silver ion or halide ion sources [209]. Conventional in situ anion exchange synthesis method utilizes silver-based compounds such as Ag3PO4, Ag2CO3 and Ag2Mo2O7 as templates as well as silver source for fabricating heterostructured silver-based compound/silver halide structure [1, 44, 210, 211]. In general, as shown in Fig. 4a, large number of silver-based compounds (Ag-based compounds) acte as templates are first prepared or purchased to simplify experimental process and save time. After adding halide ions (X), ion-exchange reaction between anion from Ag-based compound and X occur resulting AgX crystals formation and depositing on the surface of substrate precursors. During this anion exchange process, AgX generation on Ag-based compounds surface in hybrid system can be tuned by varying X ion concentration with high resolution. In addition, benefiting from the heterostructure of Ag-based compounds/AgX material system, photocorrosion obstacle occurring in practical application can be eliminated. Shown in Fig. 4b–d, Ag3PO4/AgBr cubic crystals (Fig. 4b), Ag2CO3/AgBr.
Fig. 4

a Schematic diagram of the proposed basic anion exchange mechanism of Ag-based compound into Ag-based compound/AgX composite. Exposing Ag-based compound with halide ion (X) led to ion exchange between anion ions from Ag-based compound and X, which was then grown into Ag-based compound/AgX composite. Using anion exchange reaction, cubic Ag3PO4/AgBr/Ag heterostructures (b), Ag2CO3/Ag/AgBr ternary nanorods (c) and Ag2CO3/AgBr/Ag nanorods (the inset was the corresponding photographs) (d) have all been successfully synthesized. e Schematic illustration of the conversion processes from Ag2CO3 nanorods to AgnX nanotubes via an acid-etching anion exchange reaction. And the corresponding prepared Ag2S, AgCl, Ag3PO4, and Ag2C2O4 nanotubes (f). b Reproduced with permission from ref. [1]. Copyright 2013 Royal Society of Chemistry. c Reproduced with permission from ref. [44]. Copyright 2015 Royal Society of Chemistry. d Reproduced with permission from ref. [210]. Copyright 2015 Royal Society of Chemistry. (e, f) Reproduced with permission from ref. [214]. Copyright 2014 Royal Society of Chemistry

nanorods (Fig. 4c) and Ag2Mo2O7/AgBr rods (Fig. 4d) were all prepared through anionic ion exchange synthesis method between PO4 3−, CO3 2− and Mo2O7 with Br, and showed higher photocatalytic stability than pristine Ag3PO4, Ag2CO3 and Ag2Mo2O7 [1, 7, 8, 44, 210, 212]. However, this point is also regarded as its major drawback, as single silver halide component is difficult to be formed. Another acid-etching anion exchange reaction can also be used to fabricate series of AgX nanostructures [213]. While differ from conventional anion exchange reaction comparing Fig. 4a, typical silver halides rather than mixtures of Ag-based compounds/silver halides can be created. In this section as shown in Fig. 4e [214], pregrown Ag2CO3 nanorods were taken as templates, hydrogen ion (H+) from various acid was injected to react with Ag2CO3 releasing Ag+ ions around vicinity of templates. The released Ag+ ions surrounding Ag2CO3 templates were again reacted with the acid radical ions (Xn-) to generate a thin layer AgnX coating over the substrates, which resulted in intermediate formation of Ag2CO3-AgnX yolk-shell nanostructures. Furthermore, the resist made by local shell of AgnX could change the reaction progress by altering diffusion condition. A common ionic radius of Xn- is much larger than H+; thus, most of Xn- ions could be delayed out of shell while H+ smoothly went across reacting with Ag2CO3 core to generate large amount of Ag+. Due to concentration difference between internal and external, Ag+ ion tended to diffuse from core region to outside and react with Xn- with more AgnX directly precipitated above the tubular surface. After removal of the core region of Ag2CO3 with acid etching, an ordered hollow interior structure was finally patterned. Acid-etching anion exchange reaction allows for precise control over the structure and placement of silver halides, including external architecture preservation, size and pure phase acquisition. It can generate a wide range of AgnX, such as Ag2S, AgCl, Ag3PO4 and Ag2C2O4 (Fig. 4f). In addition, as a major advantage, anion ion-exchange reaction can produce double anion silver halide, such as Ag(Br, Cl) and Ag(Br, I), just taking the formed AgX as Ag-based compound to anion exchange with another halide ion [213, 215, 216].

Cation exchange reaction is similar to anion exchange in that halide-based compound is used as template for the formation of silver halide with silver nitrate. Copper nitrate (CuBr) microspheres were used in cation exchange reaction with silver nitrate and employed as chemical template, similar to Ag-based compound in anion exchange reaction, which could provide Br source and then be applied as a matrix for the deposition of AgBr [217]. The drawback of cation exchange reaction is also semblance with anion exchange reaction: single silver halide component is difficult to be obtained as original core materials cannot be removed entirely [218].

3 Engineering silver halide for photocatalysis applications

The ability to engineer the physical parameters of AgX, including morphology control and energy band regulation, or composite with other materials provide great promise for performance improvement in photocatalysis [219, 220]. This section will concentrate on the connection between the photocatalytic properties of AgX composite with their configuration organizations. Physical parameters will also be linked with their engineering method in Section 2. In addition, we will also discuss the photocatalysis enhancement of well-regulated AgX composite with corresponding reaction mechanism in specific application, which is another important section to illustrate AgX in Section 4.

3.1 Modification of morphology

The typical approach to engineer the photocatalytic properties of a single AgX component is to manipulate its morphology [221]. The morphology modification, including controls of the size, shape, and surface structures, determines the chemical reactions efficiency and selectivity in heterogeneous photocatalysis through changing some physicochemical properties, such as face-specific reactant molecular adsorption and interfacial charge transfer [222, 223, 224, 225, 226, 227, 228, 229]. Therefore, morphology modification is an important variable that should be deliberately designed to achieve prompted photocatalytic properties.

Highly reactive crystal plane is difficult to be formed due to the surface energy minimizing trends in crystal growth process. However, Lu group reported a successful synthesis of uniform anatase TiO2 single crystals with a large percentage of more active facets exposure rather than thermodynamically stable {101} facets [230]. Since then, nano- or micro-sized photocatalyst crystals with high specific facets exposure have been devoted significant efforts demonstrating superior activity no matter in organic compounds degradation, hydrogen evolution or CO2 reduction [231, 232]. When polyhedral nanostructure is fabrication, more active catalytic sites are emerged including specific facets, edges, corners and steps, where more reactive intensity can be gained. Figure 5 shows the photocatalytic activities of AgX nanostructures (AgCl, AgBr, and AgI) with a set of controlled geometries (near-spherical, cube, concave cube, hierarchically superstructure, and nanoplates), which have been calculated using organic dye degradation and oxygen evolution from water oxidation under light irradiation [233]. From methyl orange (MO) degradation effect (Fig. 5 a, c, d) and O2 evolution comparisons (Fig. 5b), a general theme can be observed, that the photocatalytic performance improves as the crystal surface complexity increases. Thus, it can be inferred that the configuration and quality of crystal surface play a pivotal role in determining their performances in photocatalytic applications.
Fig. 5

a Photodecomposition of MO 20 mg L−1 dye in solution over cubic Ag@AgCl, near-spherical Ag@AgCl and N-doped TiO2 under visible light (≥ 400 nm) irradiation. Reproduced with permission from ref. [146]. Copyright 2011 Royal Society of Chemistry. b Amount of oxygen evolved during photocatalytic oxidation of water with 3D AgCl hierarchical superstructures, concave cubes, and AgCl cubes as catalysts under irradiation by visible light provided by a 300 W Xe arc lamp. Reproduced with permission from ref. [392]. Copyright 2012 Wiley. c Over concave and spherical AgI particles. The result clearly shows that the concave particles exhibit superior performance to the spherical counterparts. Reproduced with permission from ref. [154]. Copyright 2014 Elsevier. d Photodegradation of MO dyes over the AgBr nanoplates, irregular AgBr particles and Ag3PO4. Reproduced with permission from ref. [142]. Copyright 2012 Royal Society of Chemistry

In morphology control aspect, adequate understanding of crystal surface properties is regarded as the necessary conditions [234, 235, 236]. In AgBr crystal, the surface energy of {111} facets has been calculated to be higher than ordinary {110} and {100} facets [61, 142, 237]. Thus, AgBr nanoplates with {111} facets exposure has been designed using PVP as capping agent. And the photocatalytic performance investigation of AgBr with {111} facets in organic dye degradation was manifested to be 4 times higher than the irregular AgBr microspheres which were generally constituted by stable {110} and {100} facets. Besides, high-purity wurtzite-type β-AgI microplates with polar {0001} facets demonstrated preferential diametric migration of photogenerated charge carriers (electrons, holes) along the c axis indicating an effective vectorial electron–hole separation [143]. Thus, dramatically enhanced photocatalytic ability was achieved in organic dye degradation aspect [238, 239, 240, 241]. Concave structures enclosed by high-index facets regularly draw much more interest than general flat faces attributing to the large number of active sites. Based on the overgrowth preference of corners and edges along <111> and <110> directions, a AgCl concave nanocube structure has been formed from it cubic seeds, and showed much higher photocatalytic performance in O2 evolution comparing with original cube structure [242].

3.2 Regulation of energy level

For certain photocatalytic reaction, the band position of semiconductor should fulfill the corresponding reaction potential requirements [243]. That is, the energy of conduction band (CB) satisfies the required reduction potential while valence band (VB) should be positive than the oxidation potential. Thus, in order to refine the redox potentials, many strategies have been developed to engineer the energy band of semiconductors. Three main tactics have always been explored; first, substituting the cations with alkali metal or alkaline earth metal elements to low the levels of the CB; [244, 245] Second, doping with cations with d10 or d10s2 configurations, 3d-transition elements, and nonmetal elements for lifting VB position; [74, 246, 247, 248] Third, fabrication of a solid solution, which can tune the CB and VB simultaneously [249, 250]. However, as superior photo-sensitive materials with the ability to produce plasmonic metal Ag0, the introduction of other elements will destroy the original performance; thus, the first two methods have been rarely applied in AgX. Solid solution of semiconductor nanomaterials constituted by parent AgX materials can not only maintain their original high photocatalytic ability but also construct new composite energy band [251].

Ternary alloyed photocatalytic silver halide AgX (AgClxBr1-x, 0 ≤ x ≤ 1) nanocrystals with uniform cubic morphology could engineer their energy bandgap from 2.5 to 3.0 eV via tuning the ratio of Cl and Br ions (Fig. 6a), which was calculated from the UV-Visible absorption spectra in Fig. 6b [208]. In AgClxBr1-x alloys, the energy bands (VB and CB) are both constituted by Cl3p, Br 4d, and Ag 4d states, while the ratio changes of halogen ions (Cl, Br) mainly influence the CB rather than VB levels [208]. As shown in Fig. 6c, the proportion increase of Cl rather than Br ion gives rise to a negative shift for the CB minimum, subsequently leading to the bandgap narrowing. In the light of theoretical and experimental results, the absorption efficiency of incident light can be augmented by a smaller bandgap value. Consequently, the photocatalytic performance on dye degradation and CO2 reduction were both found to depend on the chemical compositions of AgClxBr1-x, and AgCl0.75Br0.25 sample exhibited the highest activity. On the other hand, the higher VB and CB dispersion of AgClxBr1-x comparing with pristine AgCl and AgBr indicated more charge carriers’ transmission convenience [252], which was another guarantee for photocatalytic activity promotion. Furthermore, plasmonic Ag@AgBr/AgCl heterostructured nanocashews and Ag@AgCl-AgI photocatalysts with highly efficient visible light activity has also been prepared through ion-exchange process [215, 253].
Fig. 6

a The experimental lattice constants and indirect bandgap values of AgClxBr1-x NCs depending on the composition changes. b UV-Visible absorption spectra of AgClxBr1-x nanocrystals. c Electronic structures of the ternary alloyed AgClxBr1-x NCs (x = 1, 0.75, 0.5, 0.25, 0). Reproduced with permission from ref. [208].2018 Copyright 2013 Royal Society of Chemistry

3.3 Composited with other materials

3.3.1 Other photoactive semiconductor

Heterogeneous system constituted by photoactive semiconductors is regarded as an effective method to facilitate the photoexcited electron-hole separation with enhanced photocatalytic activity [254, 255, 256, 257, 258, 259, 260, 261, 262, 263, 264, 265, 266, 267, 268, 269]. Various metallic semiconductor (such as TiO2, ZnO, BiVO4) and metal-free nitrogen-doped graphene semiconductors have been considered as preferred substances to composite with AgX, shown as Table 2. As photosensitive materials, AgX and Ag/AgX (especially X = Cl and Br) are regarded as suitable semiconductor selections to modify photocatalytic composition system, which can produce efficient coupling photocatalysts with higher activity and stability compared with the single component [270, 271, 272, 273, 274, 275, 276]. Among them, the hybridization between AgX and other metallic semiconductor would significantly improve the light absorption efficiency and facilitate the photoinduced charge carrier separation with similar transmission routes [277, 278, 279, 280, 281, 282, 283, 284, 285, 286]. Such as in TiO2 coupling system, the spectral absorption range tuning of TiO2 is the key factor for its visible light photocatalytic performance modification [287, 288, 289, 290, 291, 292]. The introduction of narrow bandgap AgBr plays a major role in spectral absorption range extension of AgBr/TiO2 system [293], and especially with plasmonic Ag0 generation, further intensive visible light utilization can be obtained [294, 295, 296]. In charge transfer mechanism for photoconversion efficiency enhancement, the photogenerated electrons generated in photo-excited AgBr were all transferred into TiO2 nanoparticles as the CB of AgBr is more negative than TiO2, which promised the effective separation of charge carriers [297, 298].
Table 2

Examples of composite photocatalysts constituted by AgX and other semiconductors

Composite photocatalyst

Synthesized strategy

Applications

References

Ag/AgCl/ZnO

Deposition and precipitation

Degradation of rhodamine B (RhB) and MO as model dyes

[276]

Ag/AgCl/TiO2

Deposition and photoreduction

Photocatalytic decolorization of MO aqueous solution at ambient temperature

[266, 287]

CuO/Ag/AgCl/TiO2

Precipitation

Visible light degradation of MO and phenol

[288]

Ag/AgCl/TiO2/hierarchical porous magnesian

Precipitation

Photocatalytic degradation of gaseous benzene

[289]

Ag-AgCl/WO3

deposition–precipitation–photoreduction method

Photodegradation of 4-CP

[294]

Ag@AgCl/BiVO4

In situ oxidation reaction

degradation of dye RhB

[295]

Ag@AgCl/g-C3N4

In situ ion exchange approach

Photocatalytic degradation of RhB, MB, MO.

[301]

g-C3N4/ZnO/AgCl

Precipitation

Photocatalytic degradation of RhB

[302]

Ag–AgBr/TiO2

Sol-gel and solvothermal route

Photocatalytic degradation of ibuprofen (IBP) over the as-prepared photocatalysts under white LED irradiation

[290]

Ag–AgBr/TiO2 tubes

Deposition and precipitation

Photocatalytic degradation of phenol

[291]

AgBr/ZnO

Chemical precipitation

Photocatalytic degradation of azo dyes

[297]

AgX (X = Br, I)/g-C3N4

Precipitation

Photocatalytic degradation of MO

[303]

AgBr supported on g-C3N4-decorated CN ternary nanocomposites

Deposition

water purification and CO2 reduction

[299]

Ag@AgBr/g-C3N4

Deposition

Photocatalytic degradation of MO

[304]

NG–AgX@Ag, X = Br, Cl

Deposition and precipitation

Photocatalytic degradation of RhB under visible light

[305]

AgI/AgVO3 nanoribbon

In situ ion-exchange approach

Photocatalytic selective oxidation of benzylamine

[209]

MoS2/BiOI/AgI

Precipitation

Photocatalytic degradation of RhB

[267]

Bi2SiO5/AgI nanoplate

in situ precipitation

Degradation of ARG aqueous

[268]

three-dimensional AgI@TiO2

Deposition

Photodegradation of organic pollutants

[292]

In AgBr-supported metal-free g-C3N4-decorated Nitrogen-doped graphene (CN) ternary nanocomposites (ACNNG-x), Z-scheme heterogeneous structure consisting of AgBr and CN with different energy level has been proved to be an effective rule to photocatalytic degradation of MO and CO2 photoreduction under visible light [299, 300, 301, 302, 303, 304, 305]. Two charge carriers separation mechanisms were involved in this system before and after the generation of metallic Ag0 nanoparticles. Before the metallic Ag0 generation, the photoinduced electrons from the CB of CN would inject into the CB of AgBr while the photoinduced holes remaining in VB would transfer from AgBr to CN. Following this process, high electron-holes separation was obtained and promote the photocatalytic performance. According to the intrinsic photosensitive property of AgBr, the accumulated electrons on the surface of AgBr generated from the repeated absorption of photons will combine with Ag+ to form Ag0 species on the crystal surface. Thus, a AgBr–Ag–CN system with Ag0 species as a conductor was achieved, which formed the known Ohmic contact with low contact resistance and opened a faster charge between AgBr and CN. In this type, the photoinduced electrons generated on the CB of AgBr could directly combine with the holes from CN using metallic Ag0 as reactive sites. Finally, the reserving holes in AgBr and electrons in CN were participated into the forward degradation and reduction reactions.

3.3.2 Other non-photoactive materials

The hybridization of AgX or Ag/AgX with other non-photocatalytic materials (shown in Table 3) specially the carbon-based conductive matters has attracted extensive concerns due to their unique electronic properties and high specific surface area [306, 307, 308, 309, 310, 311, 312, 313, 314, 315]. In hybridization aspect between AgX and photocatalytic substrates, the photocatalysis elevation is based on the Z-scheme heterogeneous structure formation in order to gain high charge separation efficiency [316, 317, 318, 319, 320, 321]. While incorporation of AgX in high specific surface area substrate is another promising strategy in photocatalytic activity promotion, especially in wastewater treatment [322, 323, 324, 325, 326]. With the substrates as dispersing templates, homogeneous and uniform semiconductor crystal morphology could be formed, which in turn can enhance their photocatalytic performance [327, 328, 329, 330, 331, 332, 333, 334]. The graphene sheets with high optical transmittance, large 2D specific surface area, unique electronic properties and locally conjugated aromatic system has regarded as one kind of ideal substrate candidates for photocatalytic deposition. Especially, the 2D planar structure framed by sp 2 hybrid carbon atoms facilitates large amount of dye molecules adsorption through π-π conjugation, which can be a key driving force to promote photocatalytic activity [72]. Among these graphene-based composite photocatalysts, graphene oxide (GO) is generally utilized as a precursor to be reduced as reduced-graphene oxide (rGO), and sometimes it is also applied as a substrate for photocatalysts deposition as well [335, 336]. Furthermore, water-soluble sulfonated graphene (SGE), one kind of graphene sheets with p-phenyl-SO3H groups covalently bonded to their edges, can also be synthesized from GO precursor [72, 337]. Due to the perfect preservation of graphene structure at sheet center and water-soluble groups binding at edges, SGE displays complete combination of great water solubility, aromatic molecules adsorption and photo-induced electron reservoir these features together [338]. Thus, the binding of AgX and SGE together confirmed superior photodegradation ability and high stability.
Table 3

Examples of composite photocatalysts constituted by AgX and other non-photoactive materials

Composite photocatalyst

Synthesized strategy

Applications

References

Ag/AgX-CNTs (X = Cl, Br, I)

An ultrasonic assistant deposition-precipitation method

Photocatalytic degradation of TBP

[327]

Ag@AgCl/reduced GO

Deposition-precipitation and photoreduction

Photodegradation of RhB dye

[319]

Ag@AgX@Graphene

Deposition

Photodegradation of acridine orange (AO) pollutant

[308]

Ag@AgCl–RGO.

Self-assembled encapsulation

Photodegradation of MB pollutant

[322]

Ag/AgCl/GO

Oxidation-chloridization process

Photodegradation of MO pollutant

[323]

Ag/AgBr/RGO

Sequent double-jet precipitation, hydrothermal, and UV light reduction

Photodegradation of MO pollutant

[324]

GO/AgBr

One-step solution-mixing method

Photodegradation of RhB, MB and MO pollutant

[325]

Ag@AgBr/SGE (water soluble sulfonated graphene)

Microemulsion method

Degradation of MO

[338]

Ag/AgBr/Co–Ni–NO3

anion-exchange precipitation method

Degradation of MO

[334]

Ag/AgBr/Graphene Oxide

a surfactant-assisted assembly protocol

Degradation of MO

[206]

3D AgX/Graphene Aerogels (X = Br, Cl)

In situ growth

Photocatalytic degradation of MO and reduction of CrVI

[207]

GO@AgBr

2D coupling route

Degradation of RhB and H2 evolution

[366]

Ag-AgI-TiO2/CNFs

Chemical oxidation method

Photocatalytic decomposition of MO, acid red 18 and MB

[297]

AgI-RGO

Template-free ultrasound-assisted method

Photocatalytic decomposition of RhB

[326]

AgI-RGO

Co-assembly

Photocatalytic decomposition ofRhB

[340]

3D graphene aerogels (GAs), with cross-linking framework structure and macroscopic block appearance, can be constructed through the graphene sheets overlapping and coalescence [339, 340]. The hierarchically porous structure widespread through the 3D GAs is considered as an ideal support for the deposition of photocatalyst NPs. Low mass density of GAs enable its block structure suspends within the solution without any assistance of external force. Therefore, the photocatalyst uniformly distributed throughout hierarchically porous surface ensures effective contact between the photocatalysts and contaminant molecules. In 3D AgX/GAs (X = Br, Cl) [207], the AgBr and AgCl nanoparticles have been homogeneously in situ grown on the surface of the hierarchical pores of the GAs. The synergistic effect between the large dye molecules adsorption and photocatalytic degradation ability of AgX (X = Br, Cl) make AgX/GAs superior photocatalytic performance of organic dye molecules degradation. On the other hand, macroscopic block appearance of AgX/GAs make it an easily and conveniently recycling operation, which can be treated just using tweezers. It is another advantage of AgX/GAs for photocatalytic applications.

4 Photocatalytic application of silver halides

Photocatalysis encompasses a fundamental solar light-photocatalyst-matter interaction; as result, many practical and scientific fields have stood to benefit from it. Already, many photocatalytic applications have emerged since Fujishima and Honda achieved the photolysis splitting of water in 1972 [70], which are divided into three categories: (i) remediation of contaminants, (ii) water splitting, and (iii) artificial photosynthesis. The first area reflects the environment application of photocatalysis and has been successfully used for a wide arrange of compounds [341, 342, 343, 344, 345, 346, 347, 348], like phenols, dyes, surfactants, aromatic carboxylic acids, aliphatic alcohols, simple aromatics, pesticides, and alkanes as well as a variety of high oxidative state of heavy metals (such as CrVI, Au3+, Pt4+, and Rh3+) [349, 350, 351, 352]. Among these organism or metal ions degradation cases, complete mineralization and metal reduction have been reported. The second and third exploit the energy-related application of photocatalyst, that is hydrogen evolution from water splitting and reduction of CO2 into carbohydrates [55, 212, 250, 353, 354, 355, 356].

4.1 Organic compound degradation

4.1.1 Advantage analysis of photocatalysis on mechanism aspect

Direct oxidative combust of organic dye molecules by O2 is environmentally friendly and thermodynamically favorable as the entire degradation is exothermic. However, such non-catalytic reaction between triplet ground state O2 (S = 1) and singlet ground state organic dye molecule (S = 0) is kinetically slow in which a high-energy barrier should be conquered during reaction (Fig. 7 Path A). Two main reasons can explain such kinetic resistance [357, 358]: One is spin-forbidden. As mentioned above, the electrons in oxidant O2 molecule is spin-parallel (triple ground state), while organic dye molecule is singlet ground state with spin-paired electrons and some products are usually also spin-paired. Such situation indicates that one of electrons is inevitably spin-reversed during reaction process and this process is spin-forbidden with slow kinetics. Another is unfavorable one-electron reduction potential of O2 molecule. Although O2 molecule has rather high multielectron reduction potential (E(O2/H2O) = +1.229 V and E(O2/H2O) = +0.695 V, NHE, PH = 0) during reaction, its one-electron reduction potential is low (E(O2/O2 -•) = − 0.16 V) meaning the first electron acquirement is difficult during oxidation reaction [359, 360].
Fig. 7

a Three respective reaction paths for the combustion of organic dyes in the presence of triplet ground state O2 (S = 1). Path A is the direct non-catalytic reaction with a high-energy barrier; Path B is the thermal-catalytic degradation process with low energy barrier; Path C is the brief illustration of photocatalytic degradation process with energy supplying. b Corresponding mechanism in photocatalytic reaction. Reproduced with permission from ref. [360]. Copyright 2010 Royal Society of Chemistry

As shown in Fig. 7a, apart from the non-catalytic reaction (path A), other two approaches are also able to achieve reaction target with favorable kinetics that can accelerate overall reaction process between O2 and organic dyes [360]. The first approach is to substitute the noncatalytic reaction with catalytic approach, that is transforming the high-energy barrier into multiple low-energy barrier. The introduction of catalyst can provide some active sites to bound with one of or both of reactants forming intermediates. Then as shown in path B, following the reaction a series of transitional intermediates (T1 and T2) and stationary (S1) are generated with much lower activation energies than the non-catalytic reaction barrier. Therefore, besides thermodynamically favorable, such catalytic reaction is also kinetically satisfied. The second approach is exhibited in Fig. 7 path C. External energy is supplied in the catalytic system constituted by organic compounds, O2 and catalyst, which enable reaction circumvent or overcome the intrinsic barrier during the degradation process. Photocatalytic reaction exactly illustrates this type of process. Under irradiation at ambient circumstance, the semiconductor photocatalyst can absorb the photons with energy matching or exceeding its bandgap, to excite the electrons (ecb ) from VB to CB leaving holes (hvb +) behind as shown in Fig. 7b. The VB holes can capture electrons from the absorbed H2O to generate OH radicals (Eq. (1)) or directly react with organic dye molecules to make them oxidized (Eq. (2)). In open system, dissolved oxygen can scavenge electrons from the CB of semiconductor to produce O2 -• radicals shown as Eq. (3). These activation radicals with oxygen atom are more reactive than the corresponding oxygen molecule O2 and can deliver their energy or electrons into other species or reactants to make chemical changes. Explaining as Eqs. (4)–(6), such reactions always hold low- or non-energy barriers, which guarantee high reaction rate. Overall the entire photocatalytic reaction, only O2 and H2O engage to combust the organic dyes into other degradation products under light irradiation, no photocatalyst component is consumed.
$$ {\mathrm{H}}_2\mathrm{O}+{h}_{vb}^{+}\to {\mathrm{OH}}^{\cdotp }+{\mathrm{H}}^{+} $$
(1)
$$ \mathrm{R}-\mathrm{H}+{h}_{vb}^{+}\to {\mathrm{R}\mathrm{H}}^{+\bullet}\rightleftharpoons {\mathrm{R}}^{\bullet }+{\mathrm{H}}^{+}\to \to $$
(2)
$$ {\mathrm{O}}_2+{\mathrm{e}}_{\mathrm{cb}}^{-}\to {\mathrm{O}}_2^{-\bullet } $$
(3)
$$ \mathrm{R}-\mathrm{H}+{\mathrm{OH}}^{\bullet}\to {\mathrm{R}}^{\bullet }+{\mathrm{H}}_2\mathrm{O} $$
(4)
$$ {\mathrm{R}}^{\bullet }+{\mathrm{O}}_2\to {\mathrm{R}\mathrm{OO}}^{\bullet}\overset{{\mathrm{O}}_2/}{\to}\overset{{\mathrm{H}}_2\mathrm{O}}{\to}\mathrm{Degradation} $$
(5)
$$ \mathrm{H}-\mathrm{R}+{\mathrm{O}\mathrm{H}}^{\bullet}\to {\mathrm{H}\mathrm{ROH}}^{\bullet}\overset{{\mathrm{O}}_2/}{\to}\overset{{\mathrm{H}}_2\mathrm{O}}{\to }\ \mathrm{Degradation} $$
(6)

4.1.2 Performance evaluation modes of silver halide in organic degradation

Some of the first, and most successful, applications of AgX in photocatalysis are the degradation of organic dye molecules [361]. Similar to previously mentioned degradation compounds, general classes of organic substance, though cannot be entirely mineralized have been degraded by AgX. A partial tabulation of various organic compounds that photodegraded by illuminated AgX or AgX-based composites is provided in Table 4. Besides providing these organic matter references, some representative parameters for photocatalysis evaluation have also been summarized and analyzed, such as the apparent rate constant (kapp) and total organic carbon (TOC).
Table 4

Various organic compounds that photodegraded by AgX or AgX-based composites

Substrate

Photocatalyst composites

References

Penicillin G (PG)

Ag-AgBr/TiO2/RGO;

[362]

Phenol

AgBr/Bi2WO6; Ag–AgBr/TiO2; AgBr/Ag; AgCl

[217, 291, 367, 369]

Methylene blue (MB)

AgBr/Bi2WO6; Ag/AgCl; graphene oxide/Ag@AgCl

[6, 124, 322, 367]

Methyl orange (MO)

AgBr@Ag; AgCl@Ag; AgBr; Ag2Mo2O7@AgBr; Ag/AgCl; CNNs/Ag/AgCl; Ag/AgCl/TiO2; Ag/AgBr/TiO2; AgI

[122, 123, 125, 142, 143, 147, 163, 164, 207, 210, 213, 217, 233, 236, 237, 288, 298, 299, 320, 321, 335, 348, 365, 370]

Rhodamin B (RhB)

AgBr; Ag2Mo2O7@AgBr; Ag/AgCl/PrGO; Ag@AgBr/AgCl; Ag/AgCl; CNNs/Ag/AgCl; Ag@AgBr/AgCl; Ag/AgX/BiOX (X = Cl, Br); MoS2/BiOI/AgI

[124, 210, 215, 238, 267, 269, 321, 336, 364, 366]

Ibuprofen (IBP)

Ag–AgBr/TiO2

[290]

p-nitrophenol (PNP)

Ag–AgBr/γ-Al2O3

[239]

17-β-ethinylestradiol (EE2)

Ag/AgCl@helical chiral TiO2;’

[239]

the azo dye acid orange 7 (AO7)

AgCl

[369]

2,4-dichlorophenol (2,4-DCP)

AgCl; AgI/BiOI

[241, 369]

4-chlorophenol

Ag/AgCl@TiO2

[240]

benzene

Ag/AgCl/TiO2/PM

[289]

acridine orange (AO)

Ag@AgX (X = Cl, Br)

[308]

acid red G aqueous solution

Bi2SiO5/AgI

[268]

The real-time concentration changes of organic pollutants during photocatalytic degradation are detected through their UV-visible absorbance. According to Lambert-Beer law, actual concentration changes of colored dye molecules (C/C0) are directly proportional to their corresponding normalized UV-vis absorption values (A/A0). Consequently, through tracing the light absorbance changes, we can successfully monitor photocatalytic degradation states of organic dyes. The pollutant degradation kinetics in heterogeneous photocatalysis from aqueous phase has been widely analyzed in Langmuir-Hinshelwood model (Eq. (7)): [362, 363]
$$ {r}_0=-\frac{\mathrm{d}C}{\mathrm{d}t}=-\frac{kKC}{1+ KC} $$
(7)
There, r0 represents the initial reaction rate (mg L−1 min−1), t is the reaction time (min), C is denoted as the real-time concentration of pollutants (mg L−1), K expresses the Langmuir adsorption equilibrium constant (L mg−1), and k signifies the Langmuir-Hinshelwood reaction rate constant (mg L−1 min−1). Under dilute concentration cases (KC < < 1) of water pollutants, a pseudo-first-order kinetics model can be deduced from Eq. (7) through Eq. (8) and (9):
$$ {r}_0=-\frac{\mathrm{d}C}{\mathrm{d}t}=- kKC $$
(8)
$$ \ln \left(\frac{C}{C_0}\right)=- kKC=-{k}_{app}t $$
(9)
where C 0 represents the original concentration of water pollutants (mg L−1) and k app is the apparent rate constant (min−1). During the overall dye degradation process of AgX, the normalized concentration of dye molecules (ln(C0/C)) show linear relationship with irradiation time indicating that these degradations follow the first-order kinetics (Eq. (9)) [299, 364, 365]. Shown as Fig. 8a, based on the curve state (Ct/C0 ~ t) and time consumption along the entire degradation, an overall degradation process can be obtained. Via pseudo-first-order linear fitting between ln(C0/C) and t, kapp can be determined from linear slop and applied to evaluate the degradation rate among different photocatalyst in the same experiment (Fig. 8b). Besides, one more degradation index, total organic carbon (TOC) is taken to assess the mineralization effect of organic pollutants [366]. The loss value of TOC after the photodegradation, expressing as the percentage of original quantity, suggests the mineralization degree of organic matters as shown Fig. 8c [290, 367].
Fig. 8

a Degradation curve on Ct/C0 against reaction time (t), and the derived linear plots between ln(Ct/C0) and t for determination of kapp. Reproduced with permission from ref. [175], Copyright 2014 Elsevier. b Performance comparison of photocatalytic degradation by the slops (kapp) of ln(C0/C) ~ t. Reproduced with permission from ref. [364], Copyright 2015 Royal Society of Chemistry. c TOC changes during the photocatalytic degradation. Reproduced with permission from ref. [367], Copyright 2014 Royal Society of Chemistry

4.1.3 Photocatalytic mechanism based on different charge transfer modes

Heterogeneous photocatalysis of AgX on organic degradation is a process, similar to general photocatalysis mechanism, where illuminated AgX semiconductors generate photoexcited electrons and holes. Then, H2O and dissolved O2 molecules as well as X ions will react with these charge carriers to produce many radicals (OH, O2 -•) or oxidative X atom, who can oxide the organic contaminants. As mentioned above, photosensitive AgX can absorb photons and excite electrons from its VB to CB leaving holes in VB. The photogenerated electrons migrate to AgX surface and combines with interstitial Ag+ ions producing Ag0 atom. Upton repeated absorption of photons and continue generation of Ag0 on AgX, ultimately silver clusters are able to be produced who can promote their photocatalysis through the localized surface plasmon effect. The localized surface plasmon effect of metallic Ag0 not merely trigger the self-generated electrons and holes engaging in the photocatalytic degradation. On the other hand, the electric field enhancement around Ag/AgX interface can promote incident light absorbance for AgX when Ag0 nanoparticles in plasmon resonance. [368]Ag/AgCl hybrid structure (Fig. 9a), metallic Ag0 nanoparticles deposited on AgCl cube surface, was calculated by 3D finite-difference time-domain simulations (FDTD) to show the electric fields enhancement result under 550 nm excitation. Significant increase of electric field intensity around Ag/AgCl interface has been observed in Fig. 9a right image and Fig. 9b, which can promote the light absorption of AgCl crystal. Thus, photocatalytic promotion effect can also be raised on original AgCl semiconductor due to the metallic Ag0 nanoparticles generation. In accordance with previous studies, two carriers transport modes have been proposed with the introduction of Ag0 in AgX system.
Fig. 9

a Left: 3D FDTD simulation model of a 4 × 4 array of metallic Ag0 nanoparticles deposited on the surface of AgCl substrate under 550 nm excitation. Right: Large magnification on the side view image of (b)

Two of the first, the surface plasmon resonance (SPR) electrons generated in Ag/AgX system remain in the Ag nanoparticles instead of being transferred to AgX, which are mainly reflected in Ag/AgCl and Ag/AgBr composite [6, 237, 348]. The surface of AgX particles are most likely negative charged with X ions termination, and therefore polarize the modified metallic Ag into two opposite charge carriers regions, in which the positive and negative charges is close to or far away from the Ag/AgX interface shown as Fig. 10a [6]. Thus, the SPR electrons generated in metallic Ag0 nanograins are forced to transfer into the negative charged region far away from Ag/AgX interface and react with O2 to from active substance O2 -•. While the remaining holes in metallic Ag0 nanograins migrate into AgX and oxidize X ions and H2O molecules to X atoms and OH, who are also both reactive radical species. It is worth mentioning that through directly oxidizing the dye molecules, X atoms can be again reduced back to X ions, which ensures the stability of AgX [369]. On the other hand, narrow bandgap AgBr also can excite electrons under visible light irradiation (Fig. 10b). Fortunately, due to the excellent conductivity of Ag nanoparticles synergetic with the polarization field of AgBr core, these electrons are able to migrate from AgBr surface to Ag nanoparticles, which reduce the recombination probability of e and Ag+ ions and one more time promise the stability of Ag/AgBr hybrid system [122, 164, 239, 370]. The second mode, contrary to the first explanation above, involves the SPR electrons of metallic Ag0 nanoparticles transferring to the CBs of AgX semiconductors [207, 313, 371]. To elucidate the underlying photocatalysis mechanism in Ag/AgCl composite system, transient absorption (TA) spectroscopy has been taken to investigate the photoelectron migration dynamics between Ag nanoparticles and AgCl semiconductor [252]. Through monitoring the state filling kinetics on the 1s electron level, TA spectroscopy can explore the corresponding electronic transmission status from AgX semiconductor to Ag nanoparticles [372, 373]. Taken Ag/AgCl hybrid structure as analysis object, no photon-induced-electron-plasmon-bleaching (Fig. 11a, iii) and hot-electron-cooling (Fig. 11a, iv) signals can be observed in Ag0 nanoparticles deposited on AgCl substrate comparing single Ag0 nanoparticles (Fig. 11a, i and ii), indicating that a strong electronic coupling exists between metallic Ag0 nanoparticles and AgCl substrate. That is the photon-induced SPR electrons in metallic Ag0 nanoparticles can efficiently inject into the CB of AgCl (Fig. 11a, v) and the injection time is far beyond the TA time resolution, which consist with the previous electron coupling result of other semiconductors [313, 374, 375]. Based on analysis results from TA spectroscopy, the second charge transfer mode from metallic Ag0 nanoparticles to AgCl substrate is proposed under light illumination and shown in Fig. 11b. When the frequency of visible irradiation light matches the intrinsic electron oscillation on metallic Ag0 nanoparticle surface, the corresponding electromagnetic wave intensity will be amplified and confined within certain interfacial hot spots. These produced hot electrons from plasmon-excited Ag nanoparticles can fast inject into the CB of AgCl [320, 376], whose feature is similar to dye sensitization [284]. Afterward, the electrons arrived at the CB of AgCl can be consumed by O2 molecules to produce oxidative radicals or molecules (O2 -•, H2O2) [210, 377]. The positive holes remaining in Ag0 nanoparticles can directly oxide the organic dyes or trapped by H2O to generate OH [124, 378]. These radicals and oxidative molecules (O2 -•, H2O2 and OH) are considered as powerful force to destruct the dye molecules structure [321].
Fig. 10

Schematic illustration of photocatalytic mechanism on Ag/AgCl composite (a) and Ag-AgBr part from Ag-AgBr/γ-Al2O3 nanostructures (b) under illumination. a Reproduced with permission from [122], Copyright 2011 Wiley. b Reproduced with permission from ref. [370], Copyright 2011 Royal Society of Chemistry

Fig. 11

a 470 nm transient absorption kinetics of metallic Ag0 nanoparticles alone (i, ii) and coupled with AgCl substrate (iii, iv) at different delay time after 400 nm excitation. (v) Schematic illustration of electron transfer from metallic Ag0 nanoparticle to AgCl substrate after excitation. b Mechanism illustration of Ag/AgCl hybrid structure for photocatalytic organic dye degradation. a, b Reproduced with permission from [252], Copyright 2013 Wiley. c Energy level distribution on Ag/AgBr interface under dark condition. d With visible light irradiation, energy level changes and charge transfer pathway between metallic Ag0 nanoparticles and AgBr crystal substrates. c, d Reproduced with permission from [380], Copyright 2012 Wiley

Another interpretation for the second mode is from work function perspective of metallic Ag0 nanoparticles and their depositing AgX substrate, taking Ag/AgBr for instance. As shown in Fig. 11c, due to the different work functions between Ag0 nanoparticle (ΦAg = 4.25 eV) and AgBr crystal (ΦAgBr = 5.3 eV) [379, 380], a Schottky barrier can be formed at interface when both sides are attached together. Then electrons from low work function Ag0 nanoparticle will transfer to AgBr crystal with high work function until two Fermi level equilibrium. Under light illumination, the strong SPR enable high electron density generated and enriched on the surface of metallic Ag0 nanoparticle [39, 381], which can raise itself Fermi level and facilitate the electrons injected into the CBof AgBr (Fig. 11d) [382].

4.1.4 Role of dye molecules in organic degradation

When organism degradation mechanism is investigated in photocatalysis, semiconductor photocatalysts are generally regarded as the first objective, that is semiconductor is excited by light and engaged in degradation process. Owning to acting as degradation substance, though dye molecules are found to have sensitizing effect in prompting itself degradation, few works have listed their roles in mechanism illustration. In dye-sensitized perspective, the semiconductor is not acted as photocatalyst to absorb light but as an electron transfer medium from the excited dye molecules pass the CB of semiconductor and then electrons are scavenged by electron acceptors [383, 384, 385]. As shown in Fig. 12a and Eq. (10–12), dye molecules absorb visible light and become excited (path a, Dye*), and then the activated electrons from Dye* are injected into their adjoining CB of semiconductor (ecb , path b), where the ecb can be scavenged by absorbed electron acceptors to produce radicals (path c and d), such as the O2 -•. These radicals, actually the product of dye excitation, will turn over to decompose the dyes (path e), and dyes will also self-decompose due to the loss of electrons (path e). Simultaneously, Fig. 12a clearly
$$ \mathrm{Dye}+\mathrm{hv}\left(\mathrm{visible}\right)\to {\mathrm{Dye}}^{\ast } $$
(10)
$$ {\mathrm{Dye}}^{\ast }+\mathrm{Photocatalyst}\to {\mathrm{Dye}}^{+\bullet }+\mathrm{Photocatalyst}\left({\mathrm{e}}_{\mathrm{cb}}^{-}\right) $$
(11)
$$ {\mathrm{O}}_2+{\mathrm{e}}_{\mathrm{cb}}^{-}\to {\mathrm{O}}_2^{-\bullet } $$
(12)
manifests that the semiconductor just play a medium role for electron transfer. In Fig. 12b, wide and continuously unoccupied electron-acceptor states have distributed among semiconductor CB [386], which ensures adequate space and matched energy level for the electron injection from excited dyes [360]. Besides, the magnitude of density states within CBcan block the back-transfer of electrons from the CBto oxidized dyes, as this backward recombination will lead to an entropy decrease of entire reaction system [387], which is considered as thermodynamically unfavorable. In addition, reduction potential of the oxidized dye is located at forbidden zone of semiconductor, where no energy states exist. Consequently, there is no energy state overlap between the semiconductor and oxidized dye molecules meaning large force intensity should be exerted to drive the back-electron transfer with a low ratio [388, 389].
Fig. 12

a Photodegradation process explained in dye-sensitized perspective. b Electrons injection from vibrational levels of excited dye molecules into the continuously distributed energy states within CB of absorbed semiconductor. Reproduced with permission from ref. [360], Copyright 2010 Royal Society of Chemistry

Although dye sensitization effect enable a photocatalytic activity promotion, such influence will disappear as the dye molecules discolor. As well known, color disappearance just can represent the destruction of chromogenic function group in dye molecules rather than the sufficient degradation. Therefore, photocatalytic activity based on photocatalyst absorbing light is still needed to completely degrade the remaining colorless organic products.

4.2 Other applications of AgX

Large-scale emission of CO2 has created global warming troubles around the world and aroused considerable public concerns. One potential approach to reducing the atmosphere CO2 is photocatalytic reduction of CO2 with H2O to generate hydrocarbon resources (such as methanol and ethanol) utilizing solar energy [390]. Shown as in Fig. 13, the CB edges of AgCl and AgBr nanoparticles are estimated to be − 0.516 and − 0.571 eV (vs NHE), which are more negative than the reduction potential of CO2Θ(CO2/CH3OH) = − 0.38 eV) [61]. These band energy calculation results indicate that the photoexcited electrons in CB of AgBr and AgCl are capable to convert the CO2 molecules into carbohydrate CH3OH [391]. Actually, many works have manifested that the AgX was more suitable for catalytically reducing CO2 into ethanol as φΘ(CO2/C2H5OH) = − 0.085 eV [163, 208, 215]. In alloyed AgClxBr1-x (x = 0, 0.25, 0.5, 0.75 and 1) photocatalysts, the maximum conversion efficiency has been achieved by AgCl0.75Br0.25 sample with methanol and ethanol yields are 181 and 362 mmol g−1, respectively. The corresponding apparent quantum efficiency was calculated to be 3.781% [208].
Fig. 13

Photocatalytic mechanism of Ag/AgX (X = Br, Cl) for visible-light reduction of CO2. Reproduced with permission from ref. [61], Copyright 2012 Royal Society of Chemistry

In addition, under UV/visible light irradiation, the photocatalytic oxidation of H2O to O2 can be realized by AgCl nanoparticles with the presence of a small excess of silver ions in solution [242, 392, 393]. The overall reaction process can be summarized as the following equations: [394].

$$ \left[{nAg}^{+}, mAgCl\right]+\frac{r}{2}{H}_2O\overset{light}{\to }\ \left[\left(n-r\right){Ag}^{+}, mAgCl,{rAg}^0\right]+{rH}^{+}+\frac{r}{4}{O}_2 $$
(13)

According to this redox reaction, oxygen can be generated under light illumination by AgCl while the excess of Ag+ is reduced to Ag0, which is also the reason of the necessary existence of Ag+. However, for the same reason, the application of photocatalytic O2 evolution has been expanded.

5 Concluding and perspective

The extensive research based on AgX into photocatalytic applications in recent years has been confirmed as a powerful platform on the utilization of light for environment remediation and energy output. Because of the metallic Ag0 nanoparticles automatic generation under light irradiation, whose plasmonic effect can promote light absorption and charge carriers’ separation, AgX has been the semiconductor of choice for the photocatalytic applications. Due to the progress in both the synthesis and assembly of AgX nanostructures, many advances in performance improvement have been made possible. Through PVP-assisted precipitation, template-directed formation and in situ ion exchange methods et. al, large numbers of nanostructures with various morphologies can be produced. Among them, the uniform nanoparticles with fundamental morphologies (including spheres, near-spheres, cubes, plates and tubes), complex geometries with precisely controlled facets and corners, and hybrid composites constituted by AgX with other substrates have all been investigated and summarized. On the other hand, the growth mechanism during the synthesis has illuminated many critical factors for the various morphology formation, such as surfactant assisting, template directing, and molecules capping [217]. These mechanism insights are benefit for further accurate controlling of AgX geometry in the further researches. The reasons for the large content length on the synthesis of AgX nanostructures is that the photocatalytic responses of single AgX materials are mainly controlled and manipulated by their featured shapes with many active sites. And a number of experimental characterizations and theoretical calculation modes have manifested that much more high-active reaction sites can be exposed in various nanostructure geometry with different synthesis processes. Furthermore, energy band regulation and composition constitution between different AgX species or with other substrates are also considered as critical factors in determining the photocatalytic properties.

Aside from the AgX nanostructure investigations from a fundamental science angle, photocatalytic properties in the final applications are the real purpose, including organic dye degradation, CO2 reduction and O2 evolution. Among them, the most prominent application of AgX at current time is in organic dye degradation. Due to the photosensitivity of dye molecules and spontaneous generation of Ag0 under light irradiation, different reaction mechanisms with various charge carriers transfer pathways are exhaustively analyzed one by one. For instance, the photoinduced electrons from sensitized dye molecules to semiconductors, plasma electrons in metallic Ag0 nanoparticles injecting into adjacent AgX semiconductor or inversely transfer from AgX to metallic Ag0. Some contradictions and conflicts are existed in the field of reaction mechanism under different perspectives, as microscopic reaction process during photocatalytic has not be entirely grasped by scientists. That also a research hotspot in photocatalytic researches. In summary, a rapid development can be observed in the research topic of photocatalysis, and it is promised to be applied to more new scientific and technical fields.

Nevertheless, there is still considerable space for photocatalytic applications of AgX especially in stability aspect. The inevitable integration of Ag+ ions and photogenerated electrons in AgX system would destruct the original crystal construction in a certain extent. Particularly, when special morphology has been exhaustively designed and specific crystal plane should be investigated, the formation of metallic Ag0 substance on AgX surface make experimental program default. Therefore, an urgent probe should be conducted to reduce the combination between Ag+ ions and electrons. Overall, this review is aimed to provide a comprehensive assistance for the further development of AgX and their corresponding composites, so that high efficiency in photocatalytic performance would be constructed.

Notes

Funding

This work was supported by NSFC, China (21622509, 21527806 and 21475122), Department of Science and Techniques of Jilin Province (20150201001GX and 20150203002YY), Jilin Province Development and Reform Commission (2016C014, 2017C053-1), Science and Technology Bureau of Changchun (15SS05).

References

  1. 1.
    Wang W-S, Du H, Wang R-X, Wen T, Xu A-W (2013) Heterostructured Ag3PO4/AgBr/Ag plasmonic photocatalyst with enhanced photocatalytic activity and stability under visible light. Nanoscale 5:3315–3321Google Scholar
  2. 2.
    Martin DJ, Liu G, Moniz SJA, Bi Y, Beale AM, Ye J, Tang J (2015) Efficient visible driven photocatalyst, silver phosphate: performance, understanding and perspective. Chem Soc Rev 44:7808–7828Google Scholar
  3. 3.
    Cheng Y-J, Yang S-H, Hsu C-S (2009) Synthesis of conjugated polymers for organic solar cell applications. Chem Rev 109:5868–5923Google Scholar
  4. 4.
    Chu S, Cui Y, Liu N (2017) The path towards sustainable energy. Nat Mater 16:16–22Google Scholar
  5. 5.
    Calkins JO, Umasankar Y, O’Neill H, Ramasamy RP (2013) High photo-electrochemical activity of thylakoid-carbon nanotube composites for photosynthetic energy conversion. Energy Environ Sci 6:1891–1900Google Scholar
  6. 6.
    An C, Peng S, Sun Y (2010) Facile synthesis of sunlight-driven AgCl:Ag plasmonic nanophotocatalyst. Adv Mater 22:2570–2574Google Scholar
  7. 7.
    Zhao W, Ma W, Chen C, Zhao J, Shuai Z (2004) Efficient degradation of toxic organic pollutants with Ni2O3/TiO2-xBx under visible irradiation. J Am Chem Soc 126:4782–4783Google Scholar
  8. 8.
    Zberg B, Uggowitzer PJ, Loffler JF (2009) MgZnCa glasses without clinically observable hydrogen evolution for biodegradable implants. Nat Mater 8:887–891Google Scholar
  9. 9.
    Wöhrle D, Meissner D (1991) Organic solar cells. Adv Mater 3:129–138Google Scholar
  10. 10.
    Schultz DM, Yoon TP (2014) Solar synthesis: prospects in visible light photocatalysis. Science 343:980–993Google Scholar
  11. 11.
    Gratzel M (2001) Photoelectrochemical cells. Nature 414:338–344Google Scholar
  12. 12.
    Law M, Greene LE, Johnson JC, Saykally R, Yang P (2005) Nanowire dye-sensitized solar cells. Nat Mater 4:455–459Google Scholar
  13. 13.
    Li G, Shrotriya V, Huang J, Yao Y, Moriarty T, Emery K, Yang Y (2005) High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat Mater 4:864–868Google Scholar
  14. 14.
    Kim JY, Kim SH, Lee HH, Lee K, Ma W, Gong X, Heeger AJ (2006) New architecture for high-efficiency polymer photovoltaic cells using solution-based titanium oxide as an optical spacer. Adv Mater 18:572–576Google Scholar
  15. 15.
    Kojima A, Teshima K, Shirai Y, Miyasaka T (2009) Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. J Am Chem Soc 131:6050–6051Google Scholar
  16. 16.
    Fitzner R, Mena-Osteritz E, Mishra A, Schulz G, Reinold E, Weil M, Korner C, Ziehlke H, Elschner C, Leo K, Riede M, Pfeiffer M, Uhrich C, Bauerle P (2012) Correlation of pi-conjugated oligomer structure with film morphology and organic solar cell performance. J Am Chem Soc 134:11064–11067Google Scholar
  17. 17.
    Tong L, Iwase A, Nattestad A, Bach U, Weidelener M, Gotz G, Mishra A, Bauerle P, Amal R, Wallace GG, Mozer AJ (2012) Sustained solar hydrogen generation using a dye-sensitised NiO photocathode/BiVO4 tandem photo-electrochemical device. Energy Environ Sci 5:9472–9475Google Scholar
  18. 18.
    Liu M, Johnston MB, Snaith HJ (2013) Efficient planar heterojunction perovskite solar cells by vapour deposition. Nature 501:395–398Google Scholar
  19. 19.
    Jeon NJ, Noh JH, Kim YC, Yang WS, Ryu S, Seok SI (2014) Solvent engineering for high-performance inorganic–organic hybrid perovskite solar cells. Nat Mater 13:897–903Google Scholar
  20. 20.
    Mei A, Li X, Liu L, Ku Z, Liu T, Rong Y, Xu M, Hu M, Chen J, Yang Y, Grätzel M, Han H (2014) A hole-conductor–free, fully printable mesoscopic perovskite solar cell with high stability. Science 345:295–298Google Scholar
  21. 21.
    Wang X, Liow C, Qi D, Zhu B, Leow WR, Wang H, Xue C, Chen X, Li S (2014) Programmable photo-electrochemical hydrogen evolution based on multi-segmented CdS-Au nanorod arrays. Adv Mater 26:3506–3512Google Scholar
  22. 22.
    Montoya JH, Seitz LC, Chakthranont P, Vojvodic A, Jaramillo TF, Norskov JK (2017) Materials for solar fuels and chemicals. Nat Mater 16:70–81Google Scholar
  23. 23.
    Wu H, Huang Y, Xu F, Duan Y, Yin Z (2016) Energy harvesters for wearable and stretchable electronics: From flexibility to stretchability. Adv Mater 28:9881–9919Google Scholar
  24. 24.
    Smith EL, Abbott AP, Ryder KS (2014) Deep eutectic solvents (DESs) and their applications. Chem Rev 114:11060–11082Google Scholar
  25. 25.
    Stamenkovic VR, Strmcnik D, Lopes PP, Markovic NM (2016) Energy and fuels from electrochemical interfaces. Nat Mater 16:57–69Google Scholar
  26. 26.
    Green MA, Bremner SP (2017) Energy conversion approaches and materials for high-efficiency photovoltaics. Nat Mater 16:23–34Google Scholar
  27. 27.
    Bredas J-L, Sargent EH, Scholes GD (2017) Photovoltaic concepts inspired by coherence effects in photosynthetic systems. Nat Mater 16:35–44Google Scholar
  28. 28.
    Zhang G, Choi W (2012) A low-cost sensitizer based on a phenolic resin for charge-transfer type photocatalysts working under visible light. Chem Commun 48:10621–10623Google Scholar
  29. 29.
    Serpone N, Emeline AV (2012) Semiconductor photocatalysis — past, present, and future outlook. J Phys Chem Lett 3:673–677Google Scholar
  30. 30.
    Tang J, Liu Y, Li H, Tan Z, Li D (2013) A novel Ag3AsO4 visible-light-responsive photocatalyst: facile synthesis and exceptional photocatalytic performance. Chem Commun 49:5498–5500Google Scholar
  31. 31.
    Qiu X, Zhao Y, Burda C (2007) Synthesis and characterization of nitrogen-doped group IVB visible-light-photoactive metal oxide nanoparticles. Adv Mater 19:3995–3999Google Scholar
  32. 32.
    Morales W, Cason M, Aina O, de Tacconi NR, Rajeshwar K (2008) Combustion synthesis and characterization of nanocrystalline WO3. J Am Chem Soc 130:6318–6319Google Scholar
  33. 33.
    Putri LK, Ong W-J, Chang WS, Chai S-P (2016) Enhancement in the photocatalytic activity of carbon nitride through hybridization with light-sensitive AgCl for carbon dioxide reduction to methane. Catal Sci Technol 6:744–754Google Scholar
  34. 34.
    Liu J, Zhang G (2014) Recent advances in synthesis and applications of clay-based photocatalysts: a review. Phys Chem Chem Phys 16:8178–8192Google Scholar
  35. 35.
    Garlisi C, Scandura G, Szlachetko J, Ahmadi S, Sa J, Palmisano G (2016) E-beam evaporated TiO2 and Cu-TiO2 on glass: Performance in the discoloration of methylene blue and 2-propanol oxidation. Appl Catal A Gen 526:191–199Google Scholar
  36. 36.
    Lou Z, Huang B, Qin X, Zhang X, Wang Z, Zheng Z, Cheng H, Wang P, Dai Y (2011) One-step synthesis of AgBr microcrystals with different morphologies by ILs-assisted hydrothermal method. CrystEngComm 13:1789–1793Google Scholar
  37. 37.
    Li Y, Zhang H, Guo Z, Han J, Zhao X, Zhao Q, Kim S-J (2008) Highly efficient visible-light-induced photocatalytic activity of nanostructured AgI/TiO2 photocatalyst. Langmuir 24:8351–8357Google Scholar
  38. 38.
    Khan SUM, Al-Shahry M, Ingler WB (2002) Efficient photochemical water splitting by a chemically modified n-TiO2. Science 297:2243–2245Google Scholar
  39. 39.
    Liu Z, Hou W, Pavaskar P, Aykol M, Cronin SB (2011) Plasmon resonant enhancement of photocatalytic water splitting under visible illumination. Nano Lett 11:1111–1116Google Scholar
  40. 40.
    Yi Z, Withers RL, Liu Y (2011) A two-step approach towards solar-driven water splitting. Electrochem Commun 13:28–30Google Scholar
  41. 41.
    Xie G, Zhang K, Guo B, Liu Q, Fang L, Gong JR (2013) Graphene-based materials for hydrogen generation from light-driven water splitting. Adv Mater 25:3820–3839Google Scholar
  42. 42.
    Xiang Q, Cheng B, Yu J (2013) Hierarchical porous CdS nanosheet-assembled flowers with enhanced visible-light photocatalytic H2-production performance. Appl Catal B 138–139:299–303Google Scholar
  43. 43.
    Tang J, Zou Z, Ye J (2004) Efficient photocatalytic decomposition of organic contaminants over CaBi2O4 under visible-light irradiation. Angew Chem Int Ed 43:4463–4466Google Scholar
  44. 44.
    Li J, Xie Y, Zhong Y, Hu Y (2015) Facile synthesis of Z-scheme Ag2CO3/Ag/AgBr ternary heterostructured nanorods with improved photostability and photoactivity. J Mater Chem A 3:5474–5481Google Scholar
  45. 45.
    Tong H, Ouyang S, Bi Y, Umezawa N, Oshikiri M, Ye J (2012) Nano-photocatalytic materials: possibilities and challenges. Adv Mater 24:229–251Google Scholar
  46. 46.
    Wang P, Huang B, Zhang X, Qin X, Jin H, Dai Y, Wang Z, Wei J, Zhan J, Wang S, Wang J, Whangbo M-H (2009) Highly efficient visible-light plasmonic photocatalyst Ag@AgBr. Chem Eur J 15:1821–1824Google Scholar
  47. 47.
    Sancier KM, Morrison SR (1973) Oxidation of organic molecules by photoproduced holes of ZnO. Surf Sci 36:622–629Google Scholar
  48. 48.
    Park Y, Lee S-H, Kang SO, Choi W (2010) Organic dye-sensitized TiO2 for the redox conversion of water pollutants under visible light. Chem Commun 46:2477–2479Google Scholar
  49. 49.
    Kulkarni AA, Bhanage BM (2014) Ag@AgCl nanomaterial synthesis using sugar cane juice and its application in degradation of azo dyes. ACS Sustain Chem Eng 2:1007–1013Google Scholar
  50. 50.
    Li G, Wong KH, Zhang X, Hu C, Yu JC, Chan RCY, Wong PK (2009) Degradation of Acid Orange 7 using magnetic AgBr under visible light: The roles of oxidizing species. Chemosphere 76:1185–1191Google Scholar
  51. 51.
    Hu C, Guo J, Qu J, Hu X (2007) Photocatalytic degradation of pathogenic bacteria with AgI/TiO2 under visible light irradiation. Langmuir 23:4982–4987Google Scholar
  52. 52.
    Akhavan O, Ghaderi E (2009) Photocatalytic reduction of graphene oxide nanosheets on TiO2 thin film for photoinactivation of bacteria in solar light irradiation. J Phys Chem C 113:20214–20220Google Scholar
  53. 53.
    Legrini O, Oliveros E, Braun AM (1993) Photochemical processes for water treatment. Chem Rev 93:671–698Google Scholar
  54. 54.
    Lan Y, Hu C, Hu X, Qu J (2007) Efficient destruction of pathogenic bacteria with AgBr/TiO2 under visible light irradiation. Appl Catal B 73:354–360Google Scholar
  55. 55.
    Fu Y, Sun D, Chen Y, Huang R, Ding Z, Fu X, Li Z (2012) An amine-functionalized titanium metal–organic framework photocatalyst with visible-light-induced activity for CO2 reduction. Angew Chem 124:3420–3423Google Scholar
  56. 56.
    Bozzi A, Yuranova T, Kiwi J (2005) Self-cleaning of wool-polyamide and polyester textiles by TiO2-rutile modification under daylight irradiation at ambient temperature. J Photochem Photobiol A Chem 172:27–34Google Scholar
  57. 57.
    Kafizas A, Kellici S, Darr JA, Parkin IP (2009) Titanium dioxide and composite metal/metal oxide titania thin films on glass: A comparative study of photocatalytic activity. J Photochem Photobiol A Chem 204:183–190Google Scholar
  58. 58.
    Protti S, Albini A, Serpone N (2014) Photocatalytic generation of solar fuels from the reduction of H2O and CO2: a look at the patent literature. Phys Chem Chem Phys 16:19790–19827Google Scholar
  59. 59.
    Tu W, Zhou Y, Zou Z (2014) Photocatalytic conversion of CO2 into renewable hydrocarbon fuels: state-of-the-art accomplishment, challenges, and prospects. Adv Mater 26:4607–4626Google Scholar
  60. 60.
    Habisreutinger SN, Schmidt-Mende L, Stolarczyk JK (2013) Photocatalytic reduction of CO2 on TiO2 and other semiconductors. Angew Chem Int Ed 52:7372–7408Google Scholar
  61. 61.
    An C, Wang J, Jiang W, Zhang M, Ming X, Wang S, Zhang Q (2012) Strongly visible-light responsive plasmonic shaped AgX:Ag (X = Cl, Br) nanoparticles for reduction of CO2 to methanol. Nano 4:5646–5650Google Scholar
  62. 62.
    Yu H, Shi R, Zhao Y, Waterhouse GIN, Wu L-Z, Tung C-H, Zhang T (2016) Smart utilization of carbon dots in semiconductor photocatalysis. Adv Mater 28:9454–9477Google Scholar
  63. 63.
    Yu H, Liu L, Wang X, Wang P, Yu J, Wang Y (2012) The dependence of photocatalytic activity and photoinduced self-stability of photosensitive AgI nanoparticles. Dalton Trans 41:10405–10411Google Scholar
  64. 64.
    Yu C, Li G, Kumar S, Yang K, Jin R (2014) Phase transformation synthesis of novel Ag2O/Ag2CO3 heterostructures with high visible light efficiency in photocatalytic degradation of pollutants. Adv Mater 26:892–898Google Scholar
  65. 65.
    Yao W, Zhang B, Huang C, Ma C, Song X, Xu Q (2012) Synthesis and characterization of high efficiency and stable Ag3PO4/TiO2 visible light photocatalyst for the degradation of methylene blue and rhodamine B solutions. J Mater Chem 22:4050–4055Google Scholar
  66. 66.
    Yamashita Y, Gao Y, Yoshida K, Kakuta N, Petrykin V, Kakihana M (2005) Photocatalytic conversion of NO on AgCl/Al2O3 mixed with ZSM-5. J Ceram Soc Jpn 113:509–512Google Scholar
  67. 67.
    Xu Y, Xu H, Li H, Xia J, Liu C, Liu L (2011) Enhanced photocatalytic activity of new photocatalyst Ag/AgCl/ZnO. J Alloy Compd 509:3286–3292Google Scholar
  68. 68.
    He K, Zhu K, Chen W (2011) Photocatalytic behavior of PdCl2-modified nanostructured AgI/TiO2 photocatalyst. Rare Metals 30:131–134Google Scholar
  69. 69.
    Zang Y, Farnood R (2008) Photocatalytic activity of AgBr/TiO2 in water under simulated sunlight irradiation. Appl Catal B 79:334–340Google Scholar
  70. 70.
    Fujishima A, Honda K (1972) Electrochemical photolysis of water at a semiconductor electrode. Nature 238:37–38Google Scholar
  71. 71.
    Bae E, Choi W, Park J, Shin HS, Kim SB, Lee JS (2004) Effects of surface anchoring groups (carboxylate vs phosphonate) in ruthenium-complex-sensitized TiO2 on visible light reactivity in aqueous suspensions. J Phys Chem B 108:14093–14101Google Scholar
  72. 72.
    Fan Y, Han D, Cai B, Ma W, Javed M, Gan S, Wu T, Siddiq M, Dong X, Niu L (2014) Ce-/S-codoped TiO2/Sulfonated graphene for photocatalytic degradation of organic dyes. J Mater Chem A 2:13565–13570Google Scholar
  73. 73.
    Tajima T, Sakata W, Wada T, Tsutsui A, Nishimoto S, Miyake M, Takaguchi Y (2011) Photosensitized hydrogen evolution from water using a single-walled carbon nanotube/fullerodendron/SiO2 coaxial nanohybrid. Adv Mater 23:5750–5754Google Scholar
  74. 74.
    Asahi R, Morikawa T, Ohwaki T, Aoki K, Taga Y (2001) Visible-light photocatalysis in nitrogen-doped titanium oxides. Science 293:269–271Google Scholar
  75. 75.
    Klosek S, Raftery D (2001) Visible light driven V-doped TiO2 photocatalyst and its photooxidation of ethanol. J Phys Chem B 105:2815–2819Google Scholar
  76. 76.
    Zhou X, Liu G, Yu J, Fan W (2012) Surface plasmon resonance-mediated photocatalysis by noble metal-based composites under visible light. J Mater Chem 22:21337–21354Google Scholar
  77. 77.
    Elahifard MR, Rahimnejad S, Haghighi S, Gholami MR (2007) Apatite-coated Ag/AgBr/TiO2 visible-light photocatalyst for destruction of bacteria. J Am Chem Soc 129:9552–9553Google Scholar
  78. 78.
    Zhou W, Cao M, Li N, Su S, Zhao X, Wang J, Li X, Hu C (2013) Ag@AgHPW as a plasmonic catalyst for visible-light photocatalytic degradation of environmentally harmful organic pollutants. Mater Res Bull 48:2308–2316Google Scholar
  79. 79.
    Dombi P, Hörl A, Rácz P, Márton I, Trügler A, Krenn JR, Hohenester U (2013) Ultrafast strong-field photoemission from plasmonic nanoparticles. Nano Lett 13:674–678Google Scholar
  80. 80.
    Chen H, Shao L, Li Q, Wang J (2013) Gold nanorods and their plasmonic properties. Chem Soc Rev 42:2679–2724Google Scholar
  81. 81.
    Zhang P, Wang T, Gong J (2015) Understanding of the plasmonic enhancement for solar water splitting. Adv Mater 27:5328–5342Google Scholar
  82. 82.
    Rycenga M, Cobley CM, Zeng J, Li W, Moran CH, Zhang Q, Qin D, Xia Y (2011) Controlling the synthesis and assembly of silver nanostructures for plasmonic applications. Chem Rev 111:3669–3712Google Scholar
  83. 83.
    Kuai L, Geng B, Chen X, Zhao Y, Luo Y (2010) Facile subsequently light-induced route to highly efficient and stable sunlight-driven Ag−AgBr plasmonic photocatalyst. Langmuir 26:18723–18727Google Scholar
  84. 84.
    Chi Y, Zhao L, Lu X, An C, Guo W, Liu Y, Wu C-ML (2015) Effects of subnanometer silver clusters on the AgBr(110) photocatalyst surface: a theoretical investigation. Catal Sci Technol 5:4821–4829Google Scholar
  85. 85.
    Link S, El-Sayed MA (1999) Spectral properties and relaxation dynamics of surface plasmon electronic oscillations in gold and silver nanodots and nanorods. J Phys Chem B 103:8410–8426Google Scholar
  86. 86.
    Yang P, Zheng J, Xu Y, Zhang Q and Jiang L (2016) Colloidal synthesis and applications of plasmonic metal nanoparticles. Adv Mater 28:10508–10517Google Scholar
  87. 87.
    Tsukamoto D, Shiraishi Y, Sugano Y, Ichikawa S, Tanaka S, Hirai T (2012) Gold nanoparticles located at the interface of anatase/rutile TiO2 particles as active plasmonic photocatalysts for aerobic oxidation. J Am Chem Soc 134:6309–6315Google Scholar
  88. 88.
    Tian Y, Tatsuma T (2005) Mechanisms and applications of plasmon-induced charge separation at TiO2 films loaded with gold nanoparticles. J Am Chem Soc 127:7632–7637Google Scholar
  89. 89.
    Wang P, Huang B, Dai Y, Whangbo M-H (2012) Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles. Phys Chem Chem Phys 14:9813–9825Google Scholar
  90. 90.
    Sun Y (2010) Conversion of Ag nanowires to AgCl nanowires decorated with Au nanoparticles and their photocatalytic activity. J Phys Chem C 114:2127–2133Google Scholar
  91. 91.
    Xie W, Schlücker S (2015) Hot electron-induced reduction of small molecules on photorecycling metal surfaces. Nat Commun 6:7570Google Scholar
  92. 92.
    Wang P, Xia Y, Wu P, Wang X, Yu H, Yu J (2014) Cu(II) as a general cocatalyst for improved visible-light photocatalytic performance of photosensitive Ag-based compounds. J Phys Chem C 118:8891–8898Google Scholar
  93. 93.
    Su R, Tiruvalam R, He Q, Dimitratos N, Kesavan L, Hammond C, Lopez-Sanchez JA, Bechstein R, Kiely CJ, Hutchings GJ, Besenbacher F (2012) Promotion of phenol photodecomposition over TiO2 using Au, Pd, and Au–Pd nanoparticles. ACS Nano 6:6284–6292Google Scholar
  94. 94.
    Seo JH, Jeon WI, Dembereldorj U, Lee SY, Joo S-W (2011) Cytotoxicity of serum protein-adsorbed visible-light photocatalytic Ag/AgBr/TiO2 nanoparticles. J Hazard Mater 198:347–355Google Scholar
  95. 95.
    Jin L, Zhu G, Hojamberdiev M, Luo X, Tan C, Peng J, Wei X, Li J, Liu P (2014) A plasmonic Ag–AgBr/Bi2O2CO3 composite photocatalyst with enhanced visible-light photocatalytic activity. Ind Eng Chem Res 53:13718–13727Google Scholar
  96. 96.
    Jiang R, Li B, Fang C, Wang J (2014) Metal/semiconductor hybrid nanostructures for plasmon-enhanced applications. Adv Mater 26:5274–5309Google Scholar
  97. 97.
    Colón G, Maicu M, Hidalgo MC, Navío JA (2006) Cu-doped TiO2 systems with improved photocatalytic activity. Appl Catal B 67:41–51Google Scholar
  98. 98.
    Irie H, Kamiya K, Shibanuma T, Miura S, Tryk DA, Yokoyama T, Hashimoto K (2009) Visible light-sensitive Cu(II)-grafted TiO2 photocatalysts: activities and x-ray absorption fine structure analyses. J Phys Chem C 113:10761–10766Google Scholar
  99. 99.
    He J, Ichinose I, Kunitake T, Nakao A, Shiraishi Y, Toshima N (2003) Facile fabrication of Ag−Pd bimetallic nanoparticles in ultrathin TiO2-gel films: nanoparticle morphology and catalytic activity. J Am Chem Soc 125:11034–11040Google Scholar
  100. 100.
    Liu J, Raveendran P, Shervani Z, Ikushima Y, Hakuta Y (2005) Synthesis of Ag and AgI quantum dots in AOT-stabilized water-in-CO2 microemulsions. Chem Eur J 11:1854–1860Google Scholar
  101. 101.
    Cao J, Xu B, Luo B, Lin H, Chen S (2011) Preparation, characterization and visible-light photocatalytic activity of AgI/AgCl/TiO2. Appl Surf Sci 257:7083–7089Google Scholar
  102. 102.
    Hirakawa T, Kamat PV (2005) Charge separation and catalytic activity of Ag@TiO2 core−shell composite clusters under UV−irradiation. J Am Chem Soc 127:3928–3934Google Scholar
  103. 103.
    Montini T, Gombac V, Sordelli L, Delgado JJ, Chen X, Adami G, Fornasiero P (2011) Nanostructured Cu/TiO2 photocatalysts for H2 production from ethanol and glycerol aqueous solutions. ChemCatChem 3:574–577Google Scholar
  104. 104.
    Li H, Bian Z, Zhu J, Huo Y, Li H, Lu Y (2007) Mesoporous Au/TiO2 nanocomposites with enhanced photocatalytic activity. J Am Chem Soc 129:4538–4539Google Scholar
  105. 105.
    Xuming Z, Lim CY, Ru-Shi L, Din Ping T (2013) Plasmonic photocatalysis. Rep Prog Phys 76:046401Google Scholar
  106. 106.
    An C, Wang J, Liu J, Wang S, Zhang Q-H (2014) Plasmonic enhancement of photocatalysis over Ag incorporated AgI hollow nanostructures. RSC Adv 4:2409–2413Google Scholar
  107. 107.
    An C, Wang S, Sun Y, Zhang Q, Zhang J, Wang C, Fang J (2016) Plasmonic silver incorporated silver halides for efficient photocatalysis. J Mater Chem A 4:4336–4352Google Scholar
  108. 108.
    Tani T (2007) Review of mechanisms of photographic sensitivity. Imaging Sci J 55:65–79Google Scholar
  109. 109.
    Smith PV (1976) A tight-binding approach to the electronic structure of the silver halides—II. J Phys Chem Solids 37:589–597Google Scholar
  110. 110.
    James TH, Kornfeld G (1942) Reduction of silver halides and the mechanism of photographic development. Chem Rev 30:1–32Google Scholar
  111. 111.
    Emil Baur AR (1921) Über versuche zur photolyse des wassers. Helv Chim Acta 4:256–262Google Scholar
  112. 112.
    Chandrasekaran K, Thomas JK (1983) The mechanism of the photochemical oxidation of water to oxygen with silver chloride colloids. Chem Phys Lett 97:357–360Google Scholar
  113. 113.
    Pfanner K, Gfeller N, Calzaferri G (1996) Photochemical oxidation of water with thin AgCl layers. J Photochem Photobiol A Chem 95:175–180Google Scholar
  114. 114.
    Kakuta N, Goto N, Ohkita H, Mizushima T (1999) Silver bromide as a photocatalyst for hydrogen generation from CH3OH/H2O solution. J Phys Chem B 103:5917–5919Google Scholar
  115. 115.
    Hu C, Hu X, Wang L, Qu J, Wang A (2006) Visible-light-induced photocatalytic degradation of azodyes in aqueous AgI/TiO2 dispersion. Environ Sci Technol 40:7903–7907Google Scholar
  116. 116.
    Liang Y, Lin S, Liu L, Hu J, Cui W (2015) Oil-in-water self-assembled Ag@AgCl QDs sensitized Bi2WO6: Enhanced photocatalytic degradation under visible light irradiation. Appl Catal B 164:192–203Google Scholar
  117. 117.
    Krishnakumar B, Swaminathan M (2012) Photodegradation of acid violet 7 with AgBr–ZnO under highly alkaline conditions. Spectrochim Acta A Mol Biomol Spectrosc 99:160–165Google Scholar
  118. 118.
    Hu C, Lan Y, Qu J, Hu X, Wang A (2006) Ag/AgBr/TiO2 visible light photocatalyst for destruction of azodyes and bacteria. J Phys Chem B 110:4066–4072Google Scholar
  119. 119.
    Gamage McEvoy J, Cui W, Zhang Z (2014) Synthesis and characterization of Ag/AgCl–activated carbon composites for enhanced visible light photocatalysis. Appl Catal B 144:702–712Google Scholar
  120. 120.
    Krishnakumar B, Subash B, Swaminathan M (2012) AgBr–ZnO – An efficient nano-photocatalyst for the mineralization of Acid Black 1 with UV light. Sep Purif Technol 85:35–44Google Scholar
  121. 121.
    Li G, Wang Y, Mao L (2014) Recent progress in highly efficient Ag-based visible-light photocatalysts. RSC Adv 4:53649–53661Google Scholar
  122. 122.
    Jiang J, Zhang L (2011) Rapid microwave-assisted nonaqueous synthesis and growth mechanism of AgCl/Ag, and its daylight-driven plasmonic photocatalysis. Chem Eur J 17:3710–3717Google Scholar
  123. 123.
    Li Y, Ding Y (2010) Porous AgCl/Ag nanocomposites with enhanced visible light photocatalytic properties. J Phys Chem C 114:3175–3179Google Scholar
  124. 124.
    Lin ZY, Xiao J, Yan JH, Liu P, Li LH, Yang GW (2015) Ag/AgCl plasmonic cubes with ultrahigh activity as advanced visible-light photocatalysts for photodegrading dyes. J Mater Chem A 3:7649–7658Google Scholar
  125. 125.
    Xu Z, Han L, Hu P, Dong S (2014) Facile synthesis of small Ag@AgCl nanoparticles via a vapor diffusion strategy and their highly efficient visible-light-driven photocatalytic performance. Catal Sci Technol 4:3615–3619Google Scholar
  126. 126.
    Wang D, Duan Y, Luo Q, Li X, Bao L (2011) Visible light photocatalytic activities of plasmonic Ag/AgBr particles synthesized by a double jet method. Desalination 270:174–180Google Scholar
  127. 127.
    Validžić IL, Janković IA, Mitrić M, Bibić N, Nedeljković JM (2007) Growth and quantum confinement in AgI nanowires. Mater Lett 61:3522–3525Google Scholar
  128. 128.
    Xu H, Li H, Xia J, Yin S, Luo Z, Liu L, Xu L (2011) One-pot synthesis of visible-light-driven plasmonic photocatalyst Ag/AgCl in ionic liquid. ACS Appl Mater Interfaces 3:22–29Google Scholar
  129. 129.
    Yamada H, Saruwatari I, Kuwata N, Kawamura J (2014) Local structure of thermally stable super ionic conducting AgI confined in mesopores. J Phys Chem C 118:23845–23852Google Scholar
  130. 130.
    Sanson A, Rocca F, Armellini C, Dalba G, Fornasini P, Grisenti R (2008) Correlation between I-Ag distance and ionic conductivity in AgI fast-ion-conducting glasses. Phys Rev Lett 101:155901Google Scholar
  131. 131.
    Yamada H, Bhattacharyya AJ, Maier J (2006) Extremely high silver ionic conductivity in composites of silver halide (AgBr, AgI) and mesoporous alumina. Adv Funct Mater 16:525–530Google Scholar
  132. 132.
    Wu F, Wang W, Xu Z, Li F (2015) Bromide (Br) - based synthesis of Ag nanocubes with high-yield. Sci Rep 5:10772Google Scholar
  133. 133.
    Li B, Wang H, Zhang B, Hu P, Chen C, Guo L (2013) Facile synthesis of one dimensional AgBr@Ag nanostructures and their visible light photocatalytic properties. ACS Appl Mater Interfaces 5:12283–12287Google Scholar
  134. 134.
    Ng CHB, Fan WY (2007) Controlled synthesis of β-AgI nanoplatelets from selective nucleation of twinned Ag seeds in a tandem reaction. J Phys Chem C 111:2953–2958Google Scholar
  135. 135.
    Jiang W, An C, Liu J, Wang S, Zhao L, Guo W, Liu J (2014) Facile aqueous synthesis of [small beta]-AgI nanoplates as efficient visible-light-responsive photocatalyst. Dalton Trans 43:300–305Google Scholar
  136. 136.
    Bi Y, Ye J (2010) Direct conversion of commercial silver foils into high aspect ratio AgBr nanowires with enhanced photocatalytic properties. Chem Eur J 16:10327–10331Google Scholar
  137. 137.
    Purbia R, Paria S (2015) Yolk/shell nanoparticles: classifications, synthesis, properties, and applications. Nano 7:19789–19873Google Scholar
  138. 138.
    Ma X, Dai Y, Lu J, Guo M, Huang B (2012) Tuning of the surface-exposing and photocatalytic activity for AgX (X = Cl and Br): a theoretical study. J Phys Chem C 116:19372–19378Google Scholar
  139. 139.
    Wang K, Murahari P, Yokoyama K, Lord JS, Pratt FL, He J, Schulz L, Willis M, Anthony JE, Morley NA, Nuccio L, Misquitta A, Dunstan DJ, Shimomura K, Watanabe I, Zhang S, Heathcote P and Drew AJ (2017) Temporal mapping of photochemical reactions and molecular excited states with carbon specificity. Nat Mater 16(4):467–473Google Scholar
  140. 140.
    Morgan BJ, Madden PA (2011) Effects of lattice polarity on interfacial space charges and defect disorder in ionically conducting AgI heterostructures. Phys Rev Lett 107:206102Google Scholar
  141. 141.
    Makiura R, Yonemura T, Yamada T, Yamauchi M, Ikeda R, Kitagawa H, Kato K, Takata M (2009) Size-controlled stabilization of the superionic phase to room temperature in polymer-coated AgI nanoparticles. Nat Mater 8:476–480Google Scholar
  142. 142.
    Wang H, Gao J, Guo T, Wang R, Guo L, Liu Y, Li J (2012) Facile synthesis of AgBr nanoplates with exposed {111} facets and enhanced photocatalytic properties. Chem Commun 48:275–277Google Scholar
  143. 143.
    Kuang Q, Zheng X, Yang S (2014) AgI microplate monocrystals with polar {0001} facets: spontaneous photocarrier separation and enhanced photocatalytic activity. Chem Eur J 20:2637–2645Google Scholar
  144. 144.
    Xu Y, Xu H, Li H, Yan J, Xia J, Yin S, Zhang Q (2013) Ionic liquid oxidation synthesis of Ag@AgCl core–shell structure for photocatalytic application under visible-light irradiation. Colloids Surf A Physicochem Eng Asp 416:80–85Google Scholar
  145. 145.
    Ma B, Guo J, Dai W-L and Fan K (2013) Highly stable and efficient Ag/AgCl core–shell sphere: Controllable synthesis, characterization, and photocatalytic application. Appl Catal B 130–131:257–263Google Scholar
  146. 146.
    Lou Z, Huang B, Wang P, Wang Z, Qin X, Zhang X, Cheng H, Zheng Z, Dai Y (2011) The synthesis of the near-spherical AgCl crystal for visible light photocatalytic applications. Dalton Trans 40:4104–4110Google Scholar
  147. 147.
    Zhu M, Chen P, Liu M (2011) Sunlight-driven plasmonic photocatalysts based on Ag/AgCl nanostructures synthesized via an oil-in-water medium: enhanced catalytic performance by morphology selection. J Mater Chem 21:16413–16419Google Scholar
  148. 148.
    Bashouti MY, Talebi R, Kassar T, Nahal A, Ristein J, Unruh T, Christiansen SH (2016) Systematic surface phase transition of Ag thin films by iodine functionalization at room temperature: evolution of optoelectronic and texture properties. Sci Rep 6:21439Google Scholar
  149. 149.
    Belloni J, Treguer M, Remita H, De Keyzer R (1999) Enhanced yield of photoinduced electrons in doped silver halide crystals. Nature 402:865–867Google Scholar
  150. 150.
    Chen D, Yoo SH, Huang Q, Ali G, Cho SO (2012) Sonochemical synthesis of Ag/AgCl nanocubes and their efficient visible-light-driven photocatalytic performance. Chem Eur J 18:5192–5200Google Scholar
  151. 151.
    Zhang D, Qi L, Ma J, Cheng H (2001) Formation of silver nanowires in aqueous solutions of a double-hydrophilic block copolymer. Chem Mater 13:2753–2755Google Scholar
  152. 152.
    Zeng J, Zheng Y, Rycenga M, Tao J, Li Z-Y, Zhang Q, Zhu Y, Xia Y (2010) Controlling the shapes of silver nanocrystals with different capping agents. J Am Chem Soc 132:8552–8553Google Scholar
  153. 153.
    Wiley BJ, Chen Y, McLellan JM, Xiong Y, Li Z-Y, Ginger D, Xia Y (2007) Synthesis and optical properties of silver nanobars and nanorice. Nano Lett 7:1032–1036Google Scholar
  154. 154.
    An C, Liu J, Wang S, Zhang J, Wang Z, Long R, Sun Y (2014) Concaving AgI sub-microparticles for enhanced photocatalysis. Nano Energy 9:204–211Google Scholar
  155. 155.
    Chen D, Chen Q, Zhang W, Ge L, Shao G, Fan B, Lu H, Zhang R, Yang D, Shao G (2015) Freeze-dried PVP–Ag+ precursors to novel AgBr/AgCl–Ag hybrid nanocrystals for visible-light-driven photodegradation of organic pollutants. Superlattice Microstruct 80:136–150Google Scholar
  156. 156.
    Wang H, Qiao X, Chen J, Wang X, Ding S (2005) Mechanisms of PVP in the preparation of silver nanoparticles. Mater Chem Phys 94:449–453Google Scholar
  157. 157.
    Zhang Z, Zhao B, Hu L (1996) PVP protective mechanism of ultrafine silver powder synthesized by chemical reduction processes. J Solid State Chem 121:105–110Google Scholar
  158. 158.
    Pastoriza-Santos I, Liz-Marzán LM (2002) Formation of PVP-protected metal nanoparticles in DMF. Langmuir 18:2888–2894Google Scholar
  159. 159.
    Narayanan R, El-Sayed MA (2004) Changing catalytic activity during colloidal platinum nanocatalysis due to shape changes: electron-transfer reaction. J Am Chem Soc 126:7194–7195Google Scholar
  160. 160.
    Li X-H, Li J-X, Li G-D, Liu D-P, Chen J-S (2007) Controlled synthesis, growth mechanism, and properties of monodisperse CdS colloidal spheres. Chem Eur J 13:8754–8761Google Scholar
  161. 161.
    Sun Y, Mayers B, Herricks T, Xia Y (2003) Polyol synthesis of uniform silver nanowires: a plausible growth mechanism and the supporting evidence. Nano Lett 3:955–960Google Scholar
  162. 162.
    Chen D, Liu M, Chen Q, Ge L, Fan B, Wang H, Lu H, Yang D, Zhang R, Yan Q, Shao G, Sun J, Gao L (2014) Large-scale synthesis and enhanced visible-light-driven photocatalytic performance of hierarchical Ag/AgCl nanocrystals derived from freeze-dried PVP–Ag+ hybrid precursors with porosity. Appl Catal B 144:394–407Google Scholar
  163. 163.
    Cai B, Wang J, Gan S, Han D, Wu Z, Niu L (2014) A distinctive red Ag/AgCl photocatalyst with efficient photocatalytic oxidative and reductive activities. J Mater Chem A 2:5280–5286Google Scholar
  164. 164.
    Han L, Wang P, Zhu C, Zhai Y, Dong S (2011) Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst. Nano 3:2931–2935Google Scholar
  165. 165.
    Han J, Liu Y, Guo R (2009) Reactive template method to synthesize gold nanoparticles with controllable size and morphology supported on shells of polymer hollow microspheres and their application for aerobic alcohol oxidation in water. Adv Funct Mater 19:1112–1117Google Scholar
  166. 166.
    Aldaye FA, Sleiman HF (2006) Sequential self-assembly of a DNA hexagon as a template for the organization of gold nanoparticles. Angew Chem Int Ed 45:2204–2209Google Scholar
  167. 167.
    Wang G, Mitomo H, Matsuo Y, Shimamoto N, Niikura K, Ijiro K (2013) DNA-templated plasmonic Ag/AgCl nanostructures for molecular selective photocatalysis and photocatalytic inactivation of cancer cells. J Mater Chem B 1:5899–5907Google Scholar
  168. 168.
    Yan Z, Compagnini G, Chrisey DB (2011) Generation of AgCl cubes by excimer laser ablation of bulk Ag in aqueous NaCl solutions. J Phys Chem C 115:5058–5062Google Scholar
  169. 169.
    Xiong W, Zhao Q, Li X, Zhang D (2011) One-step synthesis of flower-like Ag/AgCl/BiOCl composite with enhanced visible-light photocatalytic activity. Catal Commun 16:229–233Google Scholar
  170. 170.
    Sun C, Chen P, Zhou S (2007) AgCl nanoparticle nanowires fabricated by template method. Mater Lett 61:1645–1648Google Scholar
  171. 171.
    Lee W, Yoo H.-I and Lee J.-K (2001) Template route toward a novel nanostructured superionic conductor film; AgI nanorod/γ-Al2O3. Chem Commun 0(24):2530–2531Google Scholar
  172. 172.
    Piao Y and Kim H (2003) Paired cell for the preparation of AgI nanowires using nanoporous alumina membrane templates. Chem Commun 9:2898–2899Google Scholar
  173. 173.
    Zhang H, Tsuchiya T, Liang C, Terabe K (2015) Size-controlled AgI/Ag heteronanowires in highly ordered alumina membranes: superionic phase stabilization and conductivity. Nano Lett 15:5161–5167Google Scholar
  174. 174.
    El-Kouedi M, Foss CA, Bodolosky-Bettis SA, Bachman RE (2002) Structural analysis of AgI and Au/AgI nanocomposite films by powder x-ray diffraction: evidence for preferential orientation. J Phys Chem B 106:7205–7209Google Scholar
  175. 175.
    Li H, Wu T, Cai B, Ma W, Sun Y, Gan S, Han D and Niu L (2015) Efficiently photocatalytic reduction of carcinogenic contaminant Cr (VI) upon robust AgCl:Ag hollow nanocrystals. Appl Catal B 164:344–351Google Scholar
  176. 176.
    Han C, Ge L, Chen C, Li Y, Zhao Z, Xiao X, Li Z, Zhang J (2014) Site-selected synthesis of novel Ag@AgCl nanoframes with efficient visible light induced photocatalytic activity. J Mater Chem A 2:12594–12600Google Scholar
  177. 177.
    Xiao X, Ge L, Han C, Li Y, Zhao Z, Xin Y, Fang S, Wu L, Qiu P (2015) A facile way to synthesize Ag@AgBr cubic cages with efficient visible-light-induced photocatalytic activity. Appl Catal B 163:564–572Google Scholar
  178. 178.
    Kurihara K, Kizling J, Stenius P, Fendler JH (1983) Laser and pulse radiolytically induced colloidal gold formation in water and in water-in-oil microemulsions. J Am Chem Soc 105:2574–2579Google Scholar
  179. 179.
    Zarur AJ, Ying JY (2000) Reverse microemulsion synthesis of nanostructured complex oxides for catalytic combustion. Nature 403:65–67Google Scholar
  180. 180.
    Yoon B, Wai CM (2005) Microemulsion-templated synthesis of carbon nanotube-supported Pd and Rh nanoparticles for catalytic applications. J Am Chem Soc 127:17174–17175Google Scholar
  181. 181.
    Vaucher S, Fielden J, Li M, Dujardin E, Mann S (2002) Molecule-based magnetic nanoparticles: synthesis of cobalt hexacyanoferrate, cobalt pentacyanonitrosylferrate, and chromium hexacyanochromate coordination polymers in water-in-oil microemulsions. Nano Lett 2:225–229Google Scholar
  182. 182.
    Mo Z, Zuo D, Chen H, Sun Y, Zhang P (2007) Synthesis of graphite nanosheets/AgCl/polypyrrole composites via two-step inverse microemulsion method. Eur Polym J 43:300–306Google Scholar
  183. 183.
    Husein MM, Rodil E, Vera JH (2006) A novel approach for the preparation of AgBr nanoparticles from their bulk solid precursor using CTAB microemulsions. Langmuir 22:2264–2272Google Scholar
  184. 184.
    Husein MM, Rodil E, Vera JH (2005) A novel method for the preparation of silver chloride nanoparticles starting from their solid powder using microemulsions. J Colloid Interface Sci 288:457–467Google Scholar
  185. 185.
    Jones MR, Osberg KD, Macfarlane RJ, Langille MR, Mirkin CA (2011) Templated techniques for the synthesis and assembly of plasmonic nanostructures. Chem Rev 111:3736–3827Google Scholar
  186. 186.
    Hoar TP and Schulman JH (1943) Transparent water-in-oil disperdions: the oleopathic hydro-micelle. Nature 152:102Google Scholar
  187. 187.
    Schulman JH, Stoeckenius W, Prince LM (1959) Mechanism of formation and structure of Micro emulsions by electron microscopy. J Phys Chem 63:1677–1680Google Scholar
  188. 188.
    Xu S, Li Y (2003) Different morphology at different reactant molar ratios: synthesis of silver halide low-dimensional nanomaterials in microemulsions. J Mater Chem 13:163–165Google Scholar
  189. 189.
    Jana NR, Gearheart L, Murphy CJ (2001) Seed-mediated growth approach for shape-controlled synthesis of spheroidal and rod-like gold nanoparticles using a surfactant template. Adv Mater 13:1389–1393Google Scholar
  190. 190.
    Liu Y, Chu Y, Yang L, Han D, Lü Z (2005) A novel solution-phase route for the synthesis of crystalline silver nanowires. Mater Res Bull 40:1796–1801Google Scholar
  191. 191.
    Ni C, Hassan PA, Kaler EW (2005) Structural characteristics and growth of pentagonal silver nanorods prepared by a surfactant method. Langmuir 21:3334–3337Google Scholar
  192. 192.
    Vaidya S, Rastogi P, Agarwal S, Gupta SK, Ahmad T, Antonelli AM, Ramanujachary KV, Lofland SE, Ganguli AK (2008) Nanospheres, nanocubes, and nanorods of nickel oxalate: control of shape and size by surfactant and solvent. J Phys Chem C 112:12610–12615Google Scholar
  193. 193.
    Zheng X, Zhu L, Yan A, Wang X, Xie Y (2003) Controlling synthesis of silver nanowires and dendrites in mixed surfactant solutions. J Colloid Interface Sci 268:357–361Google Scholar
  194. 194.
    Zhang J, Han B, Liu M, Liu D, Dong Z, Liu J, Li D, Wang J, Dong B, Zhao H, Rong L (2003) Ultrasonication-induced formation of silver nanofibers in reverse micelles and small-angle x-ray scattering studies. J Phys Chem B 107:3679–3683Google Scholar
  195. 195.
    Wang D, Song C, Hu Z, Zhou X (2005) Synthesis of silver nanoparticles with flake-like shapes. Mater Lett 59:1760–1763Google Scholar
  196. 196.
    Maillard M, Giorgio S, Pileni M-P (2003) Tuning the size of silver nanodisks with similar aspect ratios: synthesis and optical properties. J Phys Chem B 107:2466–2470Google Scholar
  197. 197.
    Doruk JS, Yener O, Randall CA, Adair JH (2002) Synthesis of nanosized silver platelets in octylamine-water bilayer systems. Langmuir 18:8692–8699Google Scholar
  198. 198.
    Zheng X, Zhu L, Wang X, Yan A, Xie Y (2004) A simple mixed surfactant route for the preparation of noble metal dendrites. J Cryst Growth 260:255–262Google Scholar
  199. 199.
    Schwuger M-J, Stickdorn K, Schomaecker R (1995) Microemulsions in technical processes. Chem Rev 95:849–864Google Scholar
  200. 200.
    Debuigne F, Jeunieau L, Wiame M, Nagy JB (2000) Synthesis of organic nanoparticles in different W/O microemulsions. Langmuir 16:7605–7611Google Scholar
  201. 201.
    Ohde H, Rodriguez J M, Ye X-R and Wai C M (2000) Synthesizing silver halide nanoparticles in supercritical carbon dioxide utilizing a water-in-CO2 microemulsion. Chem Commun 23:2353–2354Google Scholar
  202. 202.
    Husein M, Rodil E, Vera J (2003) Formation of silver chloride nanoparticles in microemulsions by direct precipitation with the surfactant counterion. Langmuir 19:8467–8474Google Scholar
  203. 203.
    Sugimoto T, Kimijima KI (2003) New approach to the formation mechanism of AgCl nanoparticles in a reverse micelle system. J Phys Chem B 107:10753–10759Google Scholar
  204. 204.
    Kimijima KI, Sugimoto T (2004) Growth mechanism of AgCl nanoparticles in a reverse micelle system. J Phys Chem B 108:3735–3738Google Scholar
  205. 205.
    Zhu M, Chen P, Liu M (2011) Graphene oxide enwrapped Ag/AgX (X = Br, Cl) nanocomposite as a highly efficient visible-light plasmonic photocatalyst. ACS Nano 5:4529–4536Google Scholar
  206. 206.
    Zhu M, Chen P, Liu M (2012) Ag/AgBr/graphene oxide nanocomposite synthesized via oil/water and water/iil microemulsions: a comparison of sunlight energized plasmonic photocatalytic activity. Langmuir 28:3385–3390Google Scholar
  207. 207.
    Fan Y, Ma W, Han D, Gan S, Dong X, Niu L (2015) Convenient recycling of 3D AgX/graphene aerogels (X = Br, Cl) for efficient photocatalytic degradation of water pollutants. Adv Mater 27:3767–3773Google Scholar
  208. 208.
    Cai B, Wang J, Han D, Gan S, Zhang Q, Wu Z, Niu L (2013) Ternary alloyed AgCl(x)Br(1-x) nanocrystals: facile modulation of electronic structures toward advancedphotocatalytic performance. Nano 5:10989–10995Google Scholar
  209. 209.
    Wang X, Yang J, Ma S, Zhao D, Dai J, Zhang D (2016) In situ fabrication of AgI/AgVO3 nanoribbon composites with enhanced visible photocatalytic activity for redox reactions. Catal Sci Technol 6:243–253Google Scholar
  210. 210.
    Shen C-C, Zhu Q, Zhao Z-W, Wen T, Wang X, Xu A-W (2015) Plasmon enhanced visible light photocatalytic activity of ternary Ag2Mo2O7@AgBr-Ag rod-like heterostructures. J Mater Chem A 3:14661–14668Google Scholar
  211. 211.
    Yang M, Zhou K (2011) Synthesis and characterizations of spherical hollow composed of AgI nanoparticle using AgBr as the precursor. Appl Surf Sci 257:2503–2507Google Scholar
  212. 212.
    Abou Asi M, He C, Su M, Xia D, Lin L, Deng H, Xiong Y, Qiu R, Li X-z (2011) Photocatalytic reduction of CO2 to hydrocarbons using AgBr/TiO2 nanocomposites under visible light. Catal Today 175:256–263Google Scholar
  213. 213.
    Wang P, Huang B, Zhang Q, Zhang X, Qin X, Dai Y, Zhan J, Yu J, Liu H, Lou Z (2010) Highly efficient visible light plasmonic photocatalyst Ag@Ag(Br,I). Chem Eur J 16:10042–10047Google Scholar
  214. 214.
    Li J, Yang W, Ning J, Zhong Y, Hu Y (2014) Rapid formation of AgnX(X = S, Cl, PO4, C2O4) nanotubes via an acid-etching anion exchange reaction. Nano 6:5612–5615Google Scholar
  215. 215.
    An C, Wang J, Qin C, Jiang W, Wang S, Li Y, Zhang Q (2012) Synthesis of Ag@AgBr/AgCl heterostructured nanocashews with enhanced photocatalytic performance via anion exchange. J Mater Chem 22:13153–13158Google Scholar
  216. 216.
    Choi WS, Byun GY, Bae TS, Lee H-J (2013) Evolution of AgX nanowires into Ag derivative nano/microtubes for highly efficient visible-light photocatalysts. ACS Appl Mater Interfaces 5:11225–11233Google Scholar
  217. 217.
    Lou S, Jia X, Wang Y, Zhou S (2015) Template-assisted in-situ synthesis of porous AgBr/Ag composite microspheres as highly efficient visible-light photocatalyst. Appl Catal B 176–177:586–593Google Scholar
  218. 218.
    Cheng H, Huang B, Wang P, Wang Z, Lou Z, Wang J, Qin X, Zhang X, Dai Y (2011) In situ ion exchange synthesis of the novel Ag/AgBr/BiOBr hybrid with highly efficient decontamination of pollutants. Chem Commun 47:7054–7056Google Scholar
  219. 219.
    Bai S, Li X, Kong Q, Long R, Wang C, Jiang J, Xiong Y (2015) Toward enhanced photocatalytic oxygen evolution: synergetic utilization of plasmonic effect and schottky junction via interfacing facet selection. Adv Mater 27:3444–3452Google Scholar
  220. 220.
    Berry CR (1967) Effects of crystal surface on the optical absorption edge of AgBr. Phys Rev 153:989–992Google Scholar
  221. 221.
    Wang P, Huang B, Lou Z, Zhang X, Qin X, Dai Y, Zheng Z, Wang X (2010) Synthesis of highly efficient Ag@AgCl plasmonic photocatalysts with various structures. Chem Eur J 16:538–544Google Scholar
  222. 222.
    Tachikawa T, Yamashita S, Majima T (2011) Evidence for crystal-face-dependent TiO2 photocatalysis from single-molecule imaging and kinetic analysis. J Am Chem Soc 133:7197–7204Google Scholar
  223. 223.
    Yin Y, Alivisatos AP (2005) Colloidal nanocrystal synthesis and the organic-inorganic interface. Nature 437:664–670Google Scholar
  224. 224.
    Burda C, Chen X, Narayanan R, El-Sayed MA (2005) Chemistry and properties of nanocrystals of different shapes. Chem Rev 105:1025–1102Google Scholar
  225. 225.
    Ardo S, Meyer GJ (2009) Photodriven heterogeneous charge transfer with transition-metal compounds anchored to TiO2 semiconductor surfaces. Chem Soc Rev 38:115–164Google Scholar
  226. 226.
    Ma X, Dai Y, Guo M, Zhu Y, Huang B (2013) Insights into the adsorption and energy transfer of Ag clusters on the AgCl(100) surface. Phys Chem Chem Phys 15:8722–8731Google Scholar
  227. 227.
    Kisch H (2013) Semiconductor photocatalysis—mechanistic and synthetic aspects. Angew Chem Int Ed 52:812–847Google Scholar
  228. 228.
    Bi Y, Ouyang S, Cao J, Ye J (2011) Facile synthesis of rhombic dodecahedral AgX/Ag3PO4 (X = Cl, Br, I) heterocrystals with enhanced photocatalytic properties and stabilities. Phys Chem Chem Phys 13:10071–10075Google Scholar
  229. 229.
    Huo P, Yan Y, Li S, Li H, Huang W (2010) Floating photocatalysts of fly-ash cenospheres supported AgCl/TiO2 films with enhanced Rhodamine B photodecomposition activity. Desalination 256:196–200Google Scholar
  230. 230.
    Yang HG, Sun CH, Qiao SZ, Zou J, Liu G, Smith SC, Cheng HM, Lu GQ (2008) Anatase TiO2 single crystals with a large percentage of reactive facets. Nature 453:638–641Google Scholar
  231. 231.
    Jang ES, Won JH, Hwang SJ, Choy JH (2006) Fine tuning of the face orientation of ZnO crystals to optimize their photocatalytic activity. Adv Mater 18:3309–3312Google Scholar
  232. 232.
    Liu G, Yu JC, Lu GQ, Cheng H-M (2011) Crystal facet engineering of semiconductor photocatalysts: motivations, advances and unique properties. Chem Commun 47:6763–6783Google Scholar
  233. 233.
    Zhang H, Lu Y, Liu H, Fang J (2015) One-pot synthesis of high-index faceted AgCl nanocrystals with trapezohedral, concave hexoctahedral structures and their photocatalytic activity. Nano 7:11591–11601Google Scholar
  234. 234.
    Chen J, Lim B, Lee EP, Xia Y (2009) Shape-controlled synthesis of platinum nanocrystals for catalytic and electrocatalytic applications. Nano Today 4:81–95Google Scholar
  235. 235.
    Xia Y, Xiong Y, Lim B, Skrabalak SE (2009) Shape-controlled synthesis of metal nanocrystals: simple chemistry meets complex physics? Angew Chem Int Ed 48:60–103Google Scholar
  236. 236.
    Wang H, Yang J, Li X, Zhang H, Li J, Guo L (2012) Facet-dependent photocatalytic properties of AgBr nanocrystals. Small 8:2802–2806Google Scholar
  237. 237.
    Wang H, Lang X, Gao J, Liu W, Wu D, Wu Y, Guo L, Li J (2012) Polyhedral AgBr microcrystals with an increased percentage of exposed {111} facets as a highly efficient visible-light photocatalyst. Chem Eur J 18:4620–4626Google Scholar
  238. 238.
    Pica M, Nocchetti M, Ridolfi B, Donnadio A, Costantino F, Gentili PL, Casciola M (2015) Nanosized zirconium phosphate/AgCl composite materials: a new synergy for efficient photocatalytic degradation of organic dye pollutants. J Mater Chem A 3:5525–5534Google Scholar
  239. 239.
    Zhao Y, Kuai L, Geng B (2012) Low-cost and highly efficient composite visible light-driven Ag-AgBr/[gamma]-Al2O3 plasmonic photocatalyst for degrading organic pollutants. Catal. Sci. Technol. 2:1269–1274Google Scholar
  240. 240.
    Guo J-F, Ma B, Yin A, Fan K, Dai W-L (2012) Highly stable and efficient Ag/AgCl@TiO2 photocatalyst: preparation, characterization, and application in the treatment of aqueous hazardous pollutants. J Hazard Mater 211–212:77–82Google Scholar
  241. 241.
    Cheng H, Wang W, Huang B, Wang Z, Zhan J, Qin X, Zhang X, Dai Y (2013) Tailoring AgI nanoparticles for the assembly of AgI/BiOI hierarchical hybrids with size-dependent photocatalytic activities. J Mater Chem A 1:7131–7136Google Scholar
  242. 242.
    Lou Z, Huang B, Qin X, Zhang X, Cheng H, Liu Y, Wang S, Wang J, Dai Y (2012) One-step synthesis of AgCl concave cubes by preferential overgrowth along <111> and <110> directions. Chem Commun 48:3488–3490Google Scholar
  243. 243.
    Chen X, Mao SS (2007) Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications. Chem Rev 107:2891–2959Google Scholar
  244. 244.
    Yi Z, Ye J, Kikugawa N, Kako T, Ouyang S, Stuart-Williams H, Yang H, Cao J, Luo W, Li Z, Liu Y, Withers RL (2010) An orthophosphate semiconductor with photooxidation properties under visible-light irradiation. Nat Mater 9:559–564Google Scholar
  245. 245.
    Ouyang S, Kikugawa N, Chen D, Zou Z, Ye J (2009) A systematical study on photocatalytic properties of AgMO2 (M = Al, Ga, In): effects of chemical compositions, crystal structures, and electronic structures. J Phys Chem C 113:1560–1566Google Scholar
  246. 246.
    Chen X, Burda C (2008) The electronic origin of the visible-light absorption properties of C-, N- and S-Doped TiO2 nanomaterials. J Am Chem Soc 130:5018–5019Google Scholar
  247. 247.
    Hosogi Y, Kato H, Kudo A (2008) Photocatalytic activities of layered titanates and niobates Ion-exchanged with Sn2+ under visible light irradiation. J Phys Chem C 112:17678–17682Google Scholar
  248. 248.
    Nasir M, Xi Z, Xing M, Zhang J, Chen F, Tian B, Bagwasi S (2013) Study of synergistic effect of Ce- and S-codoping on the enhancement of visible-light photocatalytic activity of TiO2. J Phys Chem C 117:9520–9528Google Scholar
  249. 249.
    Ouyang S, Ye J (2011) β-AgAl1-xGaxO2 solid-solution photocatalysts: continuous modulation of electronic structure toward high-performance visible-light photoactivity. J Am Chem Soc 133:7757–7763Google Scholar
  250. 250.
    Maeda K, Teramura K, Lu D, Takata T, Saito N, Inoue Y, Domen K (2006) Photocatalyst releasing hydrogen from water. Nature 440:295–295Google Scholar
  251. 251.
    Gotlib IY, Ivanov-Schitz AK, Murin IV, Petrov AV, Zakalyukin RM (2012) Structure and ionic transport properties of AgI1–xBrx within single-wall carbon nanotubes from molecular dynamics simulation. J Phys Chem C 116:19554–19570Google Scholar
  252. 252.
    Tang Y, Jiang Z, Xing G, Li A, Kanhere PD, Zhang Y, Sum TC, Li S, Chen X, Dong Z, Chen Z (2013) Efficient Ag@AgCl cubic cage photocatalysts profit from ultrafast plasmon-induced electron transfer processes. Adv Funct Mater 23:2932–2940Google Scholar
  253. 253.
    Wang P, Huang B, Zhang X, Qin X, Dai Y, Wang Z, Lou Z (2011) Highly efficient visible light plasmonic photocatalysts Ag@Ag(Cl,Br) and Ag@AgCl-AgI. ChemCatChem 3:360–364Google Scholar
  254. 254.
    Zhang Z, Yates JT (2012) Band bending in semiconductors: chemical and physical consequences at surfaces and interfaces. Chem Rev 112:5520–5551Google Scholar
  255. 255.
    Chen X, Shen S, Guo L, Mao SS (2010) Semiconductor-based photocatalytic hydrogen generation. Chem Rev 110:6503–6570Google Scholar
  256. 256.
    Yang Y, Zhang G, Xu W (2012) Facile synthesis and photocatalytic properties of AgAgClTiO2/rectorite composite. J Colloid Interface Sci 376:217–223Google Scholar
  257. 257.
    Wang P, Huang B, Qin X, Zhang X, Dai Y, Whangbo M-H (2009) Ag/AgBr/WO3·H2O: visible-light photocatalyst for bacteria destruction. Inorg Chem 48:10697–10702Google Scholar
  258. 258.
    Wang X, Li S, Ma Y, Yu H, Yu J (2011) H2WO4·H2O/Ag/AgCl composite nanoplates: a plasmonic Z-scheme visible-light photocatalyst. J Phys Chem C 115:14648–14655Google Scholar
  259. 259.
    Sun W, Li Y, Shi W, Zhao X, Fang P (2011) Formation of AgI/TiO2 nanocomposite leads to excellent thermochromic reversibility and photostability. J Mater Chem 21:9263–9270Google Scholar
  260. 260.
    Wang P, Huang B, Zhang X, Qin X, Dai Y, Jin H, Wei J, Whangbo M-H (2008) Composite semiconductor H2WO4⋅H2O/AgCl as an efficient and stable photocatalyst under visible light. Chem Eur J 14:10543–10546Google Scholar
  261. 261.
    Vignesh K, Suganthi A, Rajarajan M, Sara SA (2012) Photocatalytic activity of AgI sensitized ZnO nanoparticles under visible light irradiation. Powder Technol 224:331–337Google Scholar
  262. 262.
    Tada H, Mitsui T, Kiyonaga T, Akita T, Tanaka K (2006) All-solid-state Z-scheme in CdS-Au-TiO2 three-component nanojunction system. Nat Mater 5:782–786Google Scholar
  263. 263.
    Tian B, Dong R, Zhang J, Bao S, Yang F, Zhang (2014) Sandwich-structured AgCl@Ag@TiO2 with excellent visible-light photocatalytic activity for organic pollutant degradation and E. coli K12 inactivation. J Appl Catal B 158–159:76–84Google Scholar
  264. 264.
    Hou J, Wang Z, Yang C, Zhou W, Jiao S, Zhu H (2013) Hierarchically plasmonic Z-scheme photocatalyst of Ag/AgCl nanocrystals decorated mesoporous single-crystalline metastable Bi20TiO32 nanosheets. J Phys Chem C 117:5132–5141Google Scholar
  265. 265.
    Fox MA, Dulay MT (1993) Heterogeneous photocatalysis. Chem Rev 93:341–357Google Scholar
  266. 266.
    Yu J, Dai G, Huang B (2009) Fabrication and characterization of visible-light-driven plasmonic photocatalyst Ag/AgCl/TiO2 nanotube arrays. J Phys Chem C 113:16394–16401Google Scholar
  267. 267.
    Jahurul Islam M, Amaranatha Reddy D, Han NS, Choi J, Song JK, Kim TK (2016) An oxygen-vacancy rich 3D novel hierarchical MoS2/BiOI/AgI ternary nanocomposite: enhanced photocatalytic activity through photogenerated electron shuttling in a Z-scheme manner. Phys Chem Chem Phys 18:24984–24993Google Scholar
  268. 268.
    Wan Z, Zhang G (2015) Synthesis and facet-dependent enhanced photocatalytic activity of Bi2SiO5/AgI nanoplate photocatalysts. J Mater Chem A 3:16737–16745Google Scholar
  269. 269.
    Chen D, Li T, Chen Q, Gao J, Fan B, Li J, Li X, Zhang R, Sun J, Gao L (2012) Hierarchically plasmonic photocatalysts of Ag/AgCl nanocrystals coupled with single-crystalline WO3 nanoplates. Nano 4:5431–5439Google Scholar
  270. 270.
    Zhou Z, Long M, Cai W, Cai J (2012) Synthesis and photocatalytic performance of the efficient visible light photocatalyst Ag–AgCl/BiVO4. J Mol Catal A Chem 353–354:22–28Google Scholar
  271. 271.
    Feng N, Wang Q, Zheng A, Zhang Z, Fan J, Liu S-B, Amoureux J-P, Deng F (2013) Understanding the high photocatalytic activity of (B, Ag)-codoped TiO2 under solar-light irradiation with XPS, solid-state NMR, and DFT calculations. J Am Chem Soc 135:1607–1616Google Scholar
  272. 272.
    Zhou J, Cheng Y, Yu J (2011) Preparation and characterization of visible-light-driven plasmonic photocatalyst Ag/AgCl/TiO2 nanocomposite thin films. J Photochem Photobiol A Chem 223:82–87Google Scholar
  273. 273.
    Zhang Y, Tang Z-R, Fu X, Xu Y-J (2011) Nanocomposite of Ag–AgBr–TiO2 as a photoactive and durable catalyst for degradation of volatile organic compounds in the gas phase. Appl Catal B 106:445–452Google Scholar
  274. 274.
    Cheng H, Huang B, Dai Y, Qin X, Zhang X (2010) One-step synthesis of the nanostructured AgI/BiOI composites with highly enhanced visible-light photocatalytic performances. Langmuir 26:6618–6624Google Scholar
  275. 275.
    Wu D, Long M (2011) Enhancing visible-light activity of the self-cleaning TiO2-coated cotton fabrics by loading AgI particles. Surf Coat Technol 206:1175–1179Google Scholar
  276. 276.
    Begum G, Manna J, Rana RK (2012) Controlled orientation in a bio-inspired assembly of Ag/AgCl/ZnO nanostructures enables enhancement in visible-light-induced photocatalytic performance. Chem Eur J 18:6847–6853Google Scholar
  277. 277.
    Cao J, Luo B, Lin H, Xu B, Chen S (2012) Visible light photocatalytic activity enhancement and mechanism of AgBr/Ag3PO4 hybrids for degradation of methyl orange. J Hazard Mater 217–218:107–115Google Scholar
  278. 278.
    Zhang L-S, Wong K-H, Yip H-Y, Hu C, Yu JC, Chan C-Y, Wong P-K (2010) Effective photocatalytic disinfection of E. coli K-12 using AgBr−Ag−Bi2WO6 nanojunction system irradiated by visible light: the role of diffusing hydroxyl Radicals. Environ Sci Technol 44:1392–1398Google Scholar
  279. 279.
    Cao J, Luo B, Lin H, Chen S (2011) Synthesis, characterization and photocatalytic activity of AgBr/H2WO4 composite photocatalyst. J Mol Catal A Chem 344:138–144Google Scholar
  280. 280.
    Zhang L, Wong K-H, Chen Z, Yu JC, Zhao J, Hu C, Chan C-Y, Wong P-K (2009) AgBr-Ag-Bi2WO6 nanojunction system: a novel and efficient photocatalyst with double visible-light active components. Appl Catal A Gen 363:221–229Google Scholar
  281. 281.
    Cao J, Luo B, Lin H, Chen S (2011) Photocatalytic activity of novel AgBr/WO3 composite photocatalyst under visible light irradiation for methyl orange degradation. J Hazard Mater 190:700–706Google Scholar
  282. 282.
    Marchetti AP, Muenter AA, Baetzold RC, McCleary RT (1998) Formation and spectroscopic manifestation of silver clusters on silver bromide surfaces. J Phys Chem B 102:5287–5297Google Scholar
  283. 283.
    Ma X, Dai Y, Guo M, Huang B (2012) The role of effective mass of carrier in the photocatalytic behavior of silver halide-based Ag@AgX (X=Cl, Br, I): a theoretical study. ChemPhysChem 13:2304–2309Google Scholar
  284. 284.
    Linic S, Christopher P, Ingram DB (2011) Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy. Nat Mater 10:911–921Google Scholar
  285. 285.
    Lan J, Zhou X, Liu G, Yu J, Zhang J, Zhi L, Nie G (2011) Enhancing photocatalytic activity of one-dimensional KNbO3 nanowires by Au nanoparticles under ultraviolet and visible-light. Nano 3:5161–5167Google Scholar
  286. 286.
    Hailstone RK (1995) Computer simulation studies of Silver cluster formation on AgBr microcrystals. J Phys Chem 99:4414–4428Google Scholar
  287. 287.
    Andersson M, Birkedal H, Franklin NR, Ostomel T, Boettcher S, Palmqvist AEC, Stucky GD (2005) Ag/AgCl-loaded ordered mesoporous anatase for photocatalysis. Chem Mater 17:1409–1415Google Scholar
  288. 288.
    Shah ZH, Wang J, Ge Y, Wang C, Mao W, Zhang S, Lu R (2015) Highly enhanced plasmonic photocatalytic activity of Ag/AgCl/TiO2 by CuO co-catalyst. J Mater Chem A 3:3568–3575Google Scholar
  289. 289.
    Yang L, Wang F, Shu C, Liu P, Zhang W, Hu S (2016) An in-situ synthesis of Ag/AgCl/TiO2/hierarchical porous magnesian material and its photocatalytic performance. Sci Rep 6:21617Google Scholar
  290. 290.
    Wang X, Tang Y, Chen Z, Lim T-T (2012) Highly stable heterostructured Ag-AgBr/TiO2 composite: a bifunctional visible-light active photocatalyst for destruction of ibuprofen and bacteria. J Mater Chem 22:23149–23158Google Scholar
  291. 291.
    Tian G, Chen Y, Bao H-L, Meng X, Pan K, Zhou W, Tian C, Wang J-Q, Fu H (2012) Controlled synthesis of thorny anatase TiO2 tubes for construction of Ag-AgBr/TiO2 composites as highly efficient simulated solar-light photocatalyst. J Mater Chem 22:2081–2088Google Scholar
  292. 292.
    An C, Jiang W, Wang J, Wang S, Ma Z, Li Y (2013) Synthesis of three-dimensional AgI@TiO2 nanoparticles with improved photocatalytic performance. Dalton Trans 42:8796–8801Google Scholar
  293. 293.
    Hou Y, Li X, Zhao Q, Quan X, Chen G (2011) TiO2 nanotube/Ag-AgBr three-component nanojunction for efficient photoconversion. J Mater Chem 21:18067–18076Google Scholar
  294. 294.
    Ma B, Guo J, Dai W-L, Fan K (2012) Ag-AgCl/WO3 hollow sphere with flower-like structure and superior visible photocatalytic activity. Appl Catal B 123–124:193–199Google Scholar
  295. 295.
    Li H, Sun Y, Cai B, Gan S, Han D, Niu L, Wu T (2015) Hierarchically Z-scheme photocatalyst of Ag@AgCl decorated on BiVO4 (0 4 0) with enhancing photoelectrochemical and photocatalytic performance. Appl Catal B 170–171:206–214Google Scholar
  296. 296.
    Wu C, Shen L, Zhang YC, Huang Q (2012) Synthesis of AgBr/ZnO nanocomposite with visible light-driven photocatalytic activity. Mater Lett 66:83–85Google Scholar
  297. 297.
    Yu D, Bai J, Liang H, Wang J, Li C (2015) Fabrication of a novel visible-light-driven photocatalyst Ag-AgI-TiO2 nanoparticles supported on carbon nanofibers. Appl Surf Sci 349:241–250Google Scholar
  298. 298.
    Wang D, Duan Y, Luo Q, Li X, An J, Bao L, Shi L (2012) Novel preparation method for a new visible light photocatalyst: mesoporous TiO2 supported Ag/AgBr. J Mater Chem 22:4847–4854Google Scholar
  299. 299.
    Li H, Gan S, Wang H, Han D, Niu L (2015) Intercorrelated superhybrid of AgBr supported on graphitic-C3N4-decorated nitrogen-doped graphene: high engineering photocatalytic activities for water purification and CO2 reduction. Adv Mater 27:6906–6913Google Scholar
  300. 300.
    Zhou P, Yu J, Jaroniec M (2014) All-solid-state Z-scheme photocatalytic systems. Adv Mater 26:4920–4935Google Scholar
  301. 301.
    Zhang S, Li J, Wang X, Huang Y, Zeng M, Xu J (2014) In situ ion exchange synthesis of strongly coupled Ag@AgCl/g-C3N4 porous nanosheets as plasmonic photocatalyst for highly efficient visible-light photocatalysis. ACS Appl Mater Interfaces 6:22116–22125Google Scholar
  302. 302.
    Akhundi A, Habibi-Yangjeh A (2015) Ternary g-C3N4/ZnO/AgCl nanocomposites: Synergistic collaboration on visible-light-driven activity in photodegradation of an organic pollutant. Appl Surf Sci 358(Part A):261–269Google Scholar
  303. 303.
    Xu H, Yan J, Xu Y, Song Y, Li H, Xia J, Huang C, Wan H (2013) Novel visible-light-driven AgX/graphite-like C3N4 (X = Br, I) hybrid materials with synergistic photocatalytic activity. Appl Catal B 129:182–193Google Scholar
  304. 304.
    Yang Y, Guo W, Guo Y, Zhao Y, Yuan X, Guo Y (2014) Fabrication of Z-scheme plasmonic photocatalyst Ag@AgBr/g-C3N4 with enhanced visible-light photocatalytic activity. J Hazard Mater 271:150–159Google Scholar
  305. 305.
    Dong C, Wu K-L, Wei X-W, Wang J, Liu L, Jiang B-B (2014) Nitrogen-doped graphene modified AgX@Ag (X = Br, Cl) composites with improved visible light photocatalytic activity and stability. Appl Catal A Gen 488:11–18Google Scholar
  306. 306.
    Zhang N, Zhang Y, Xu Y-J (2012) Recent progress on graphene-based photocatalysts: current status and future perspectives. Nano 4:5792–5813Google Scholar
  307. 307.
    Zhang H, Lv X, Li Y, Wang Y, Li J (2010) P25-graphene composite as a high performance photocatalyst. ACS Nano 4:380–386Google Scholar
  308. 308.
    Wang Y, Sun L, Fugetsu B (2013) Morphology-controlled synthesis of sunlight-driven plasmonic photocatalysts Ag@AgX (X = Cl, Br) with graphene oxide template. J Mater ChemA 1:12536–12544Google Scholar
  309. 309.
    Sohrabnezhad S, Pourahmad A (2012) AgBr/Al-MCM-41 visible-light photocatalyst for gas-phase decomposition of CH3CHO. Spectrochim Acta A Mol Biomol Spectrosc 86:271–275Google Scholar
  310. 310.
    Rodrigues S, Uma S, Martyanov IN, Klabunde KJ (2005) AgBr/Al-MCM-41 visible-light photocatalyst for gas-phase decomposition of CH3CHO. J Catal 233:405–410Google Scholar
  311. 311.
    Reddy VR, Currao A, Calzaferri G (2007) Zeolite A and zeolite L monolayers modified with AgCl as photocatalyst for water oxidation to O2. J Mater Chem 17:3603–3609Google Scholar
  312. 312.
    Qu Y, Duan X (2013) Progress, challenge and perspective of heterogeneous photocatalysts. Chem Soc Rev 42:2568–2580Google Scholar
  313. 313.
    Tang Y, Jiang Z, Deng J, Gong D, Lai Y, Tay HT, Joo IT, Lau TH, Dong Z, Chen Z (2012) Synthesis of nanostructured silver/silver halides on titanate surfaces and their visible-light photocatalytic performance. ACS Appl Mater Interfaces 4:438–446Google Scholar
  314. 314.
    Tang Y, Subramaniam VP, Lau TH, Lai Y, Gong D, Kanhere PD, Cheng YH, Chen Z, Dong Z (2011) In situ formation of large-scale Ag/AgCl nanoparticles on layered titanate honeycomb by gas phase reaction for visible light degradation of phenol solution. Appl Catal B 106:577–585Google Scholar
  315. 315.
    Pourahmad A, Sohrabnezhad S, Kashefian E (2010) AgBr/nanoAlMCM-41 visible light photocatalyst for degradation of methylene blue dye. Spectrochim Acta A Mol Biomol Spectrosc 77:1108–1114Google Scholar
  316. 316.
    Song S, Hong F, He Z, Cai Q, Chen J (2012) AgIO3-modified AgI/TiO2 composites for photocatalytic degradation of p-chlorophenol under visible light irradiation. J Colloid Interface Sci 378:159–166Google Scholar
  317. 317.
    Sekizawa K, Maeda K, Domen K, Koike K, Ishitani O (2013) Artificial Z-scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO2. J Am Chem Soc 135:4596–4599Google Scholar
  318. 318.
    Qi H, Wolfe J, Fichou D, Chen Z (2016) Cu2O photocathode for low bias photoelectrochemical water splitting enabled by NiFe-layered double hydroxide co-catalyst. Sci Rep 6:30882Google Scholar
  319. 319.
    Zhang H, Fan X, Quan X, Chen S, Yu H (2011) Graphene sheets grafted Ag@AgCl hybrid with enhanced plasmonic photocatalytic activity under visible light. Environ Sci Technol 45:5731–5736Google Scholar
  320. 320.
    Xu Y, Xu H, Yan J, Li H, Huang L, Zhang Q, Huang C, Wan H (2013) A novel visible-light-response plasmonic photocatalyst CNT/Ag/AgBr and its photocatalytic properties. Phys Chem Chem Phys 15:5821–5830Google Scholar
  321. 321.
    Wang Y, Xia M, Li K, Shen X, Muhanmood T, Wang F (2016) Facile solvothermal synthesis of a high-efficiency CNNs/Ag/AgCl plasmonic photocatalyst. Phys Chem Chem Phys 18:27257–27264Google Scholar
  322. 322.
    Min Y, He G, Xu Q, Chen Y (2014) Self-assembled encapsulation of graphene oxide/Ag@AgCl as a Z-scheme photocatalytic system for pollutant removal. J Mater Chem A 2:1294–1301Google Scholar
  323. 323.
    Zhu M, Chen P, Liu M (2012) Highly efficient visible-light-driven plasmonic photocatalysts based on graphene oxide-hybridized one-dimensional Ag/AgCl heteroarchitectures. J Mater Chem 22:21487–21494Google Scholar
  324. 324.
    Zeng C, Guo M, Tian B, Zhang J (2013) Reduced graphene oxide modified Ag/AgBr with enhanced visible light photocatalytic activity for methyl orange degradation. Chem Phys Lett 575:81–85Google Scholar
  325. 325.
    Zhang D, Tang H, Wang Y, Wu K, Huang H, Tang G, Yang J (2014) Synthesis and characterization of graphene oxide modified AgBr nanocomposites with enhanced photocatalytic activity and stability under visible light. Appl Surf Sci 319:306–311Google Scholar
  326. 326.
    Reddy DA, Lee S, Choi J, Park S, Ma R, Yang H, Kim TK (2015) Green synthesis of AgI-reduced graphene oxide nanocomposites: Toward enhanced visible-light photocatalytic activity for organic dye removal. Appl Surf Sci 341:175–184Google Scholar
  327. 327.
    Shi H, Chen J, Li G, Nie X, Zhao H, Wong P-K, An T (2013) Synthesis and characterization of novel plasmonic Ag/AgX-CNTs (X = Cl, Br, I) nanocomposite photocatalysts and synergetic degradation of organic pollutant under visible light. ACS Appl Mater Interfaces 5:6959–6967Google Scholar
  328. 328.
    Xiao X, Zhang W, Yu J, Sun Y, Zhang Y, Dong F (2016) Mechanistic understanding of ternary Ag/AgCl@La(OH)3 nanorods as novel visible light plasmonic photocatalysts. Catal Sci Technol 6:5003–5010Google Scholar
  329. 329.
    Xu H, Xu Y, Li H, Xia J, Xiong J, Yin S, Huang C, Wan H (2012) Synthesis, characterization and photocatalytic property of AgBr/BiPO4 heterojunction photocatalyst. Dalton Trans 41:3387–3394Google Scholar
  330. 330.
    Peng T, Hu C, Hu X, Zhou X, Qu J (2012) Enhanced photodegradation of toxic pollutants on plasmonic Au–Ag–AgI/Al2O3 under visible irradiation. Catal Lett 142:646–654Google Scholar
  331. 331.
    Padervand M, Reza Elahifard M, Vatan Meidanshahi R, Ghasemi S, Haghighi S, Reza Gholami M (2012) Investigation of the antibacterial and photocatalytic properties of the zeolitic nanosized AgBr/TiO2 composites. Mater Sci Semicon Process 15:73–79Google Scholar
  332. 332.
    Lin H, Cao J, Luo B, Xu B, Chen S (2012) Synthesis of novel Z-scheme AgI/Ag/AgBr composite with enhanced visible light photocatalytic activity. Catal Commun 21:91–95Google Scholar
  333. 333.
    Li X, Yu J, Low J, Fang Y, Xiao J, Chen X (2015) Engineering heterogeneous semiconductors for solar water splitting. J Mater Chem A 3:2485–2534Google Scholar
  334. 334.
    Fan H, Zhu J, Sun J, Zhang S, Ai S (2013) Ag/AgBr/Co–Ni–NO3 layered double hydroxide nanocomposites with highly adsorptive and photocatalytic properties. Chem Eur J 19:2523–2530Google Scholar
  335. 335.
    Vinoth R, Karthik P, Muthamizhchelvan C, Neppolian B, Ashokkumar M (2016) Carrier separation and charge transport characteristics of reduced graphene oxide supported visible-light active photocatalysts. Phys Chem Chem Phys 18:5179–5191Google Scholar
  336. 336.
    Gao W, Ran C, Wang M, Li L, Sun Z, Yao X (2016) The role of reduction extent of graphene oxide in the photocatalytic performance of Ag/AgX (X = Cl, Br)/rGO composites and the pseudo-second-order kinetics reaction nature of the Ag/AgBr system. Phys Chem Chem Phys 18:18219–18226Google Scholar
  337. 337.
    Zhao G, Jiang L, He Y, Li J, Dong H, Wang X, Hu W (2011) Sulfonated graphene for persistent aromatic pollutant management. Adv Mater 23:3959–3963Google Scholar
  338. 338.
    Cai B, Lv X, Gan S, Zhou M, Ma W, Wu T, Li F, Han D, Niu L (2013) Advanced visible-light-driven photocatalyst upon the incorporation of sulfonated graphene. Nano 5:1910Google Scholar
  339. 339.
    Hu H, Zhao Z, Wan W, Gogotsi Y, Qiu J (2013) Ultralight and highly compressible graphene aerogels. Adv Mater 25:2219–2223Google Scholar
  340. 340.
    Reddy DA, Choi J, Lee S, Ma R, Kim TK (2015) Green synthesis of AgI nanoparticle-functionalized reduced graphene oxide aerogels with enhanced catalytic performance and facile recycling. RSC Adv 5:67394–67404Google Scholar
  341. 341.
    Chemseddine A, Boehm HP (1990) A study of the primary step in the photochemical degradation of acetic acid and chloroacetic acids on a TiO2 photocatalyst. J Mol Catal 60:295–311Google Scholar
  342. 342.
    D’Oliveira J-C, Minero C, Pelizzetti E, Pichat P (1993) Photodegradation of dichlorophenols and trichlorophenols in TiO2 aqueous suspensions: kinetic effects of the positions of the Cl atoms and identification of the intermediates. J Photochem Photobiol A Chem 72:261–267Google Scholar
  343. 343.
    Mills G, Hoffmann MR (1993) Photocatalytic degradation of pentachlorophenol on titanium dioxide particles: identification of intermediates and mechanism of reaction. Environ Sci Technol 27:1681–1689Google Scholar
  344. 344.
    Kormann C, Bahnemann DW, Hoffmann MR (1991) Photolysis of chloroform and other organic molecules in aqueous titanium dioxide suspensions. Environ Sci Technol 25:494–500Google Scholar
  345. 345.
    Carraway ER, Hoffman AJ, Hoffmann MR (1994) Photocatalytic oxidation of organic acids on quantum-sized semiconductor colloids. Environ Sci Technol 28:786–793Google Scholar
  346. 346.
    D’Oliveira JC, Al-Sayyed G, Pichat P (1990) Photodegradation of 2- and 3-chlorophenol in titanium dioxide aqueous suspensions. Environ Sci Technol 24:990–996Google Scholar
  347. 347.
    Hidaka H, Zhao J, Pelizzetti E, Serpone N (1992) Photodegradation of surfactants. 8. Comparison of photocatalytic processes between anionic DBS and cationic BDDAC on the titania surface. J Phys Chem 96:2226–2230Google Scholar
  348. 348.
    Wang P, Huang B, Qin X, Zhang X, Dai Y, Wei J, Whangbo M-H (2008) Ag@AgCl: A highly efficient and stable photocatalyst active under visible light. Angew Chem Int Ed 47:7931–7933Google Scholar
  349. 349.
    Ollis DF, Pelizzetti E, Serpone N (1991) Photocatalyzed destruction of water contaminants. Environ Sci Technol 25:1522–1529Google Scholar
  350. 350.
    Albert M, Gao YM, Toft D, Dwight K, Wold A (1992) Photoassisted gold deposition of titanium dioxide. Mater Res Bull 27:961–966Google Scholar
  351. 351.
    Dominguez A, Tardajos G, Aicart E, Perez-Casas S, Trejo LM, Costas M, Patterson D, van Tra H (1993) Van der Waals liquids, Flory theory and mixing functions for chlorobenzene with linear and branched alkanes. J Chem Soc Faraday Trans 89:89–93Google Scholar
  352. 352.
    Borgarello E, Serpone N, Emo G, Harris R, Pelizzetti E, Minero C (1986) Light-induced reduction of rhodium(III) and palladium(II) on titanium dioxide dispersions and the selective photochemical separation and recovery of gold(III), platinum(IV), and rhodium(III) in chloride media. Inorg Chem 25:4499–4503Google Scholar
  353. 353.
    Kudo A, Miseki Y (2009) Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 38:253–278Google Scholar
  354. 354.
    Maeda K, Takata T, Hara M, Saito N, Inoue Y, Kobayashi H, Domen K (2005) GaN:ZnO solid solution as a photocatalyst for visible-light-driven overall water splitting. J Am Chem Soc 127:8286–8287Google Scholar
  355. 355.
    Sato S, Morikawa T, Kajino T, Ishitani O (2013) A highly efficient mononuclear iridium complex photocatalyst for CO2 reduction under visible light. Angew Chem 125:1022–1026Google Scholar
  356. 356.
    Wang C, Xie Z, deKrafft KE, Lin W (2011) Doping metal–organic frameworks for water oxidation, carbon dioxide reduction, and organic photocatalysis. J Am Chem Soc 133:13445–13454Google Scholar
  357. 357.
    Pau MYM, Lipscomb JD, Solomon EI (2007) Substrate activation for O2 reactions by oxidized metal centers in biology. Proc Natl Acad Sci 104:18355–18362Google Scholar
  358. 358.
    Mallat T, Baiker A (2004) Oxidation of alcohols with molecular oxygen on solid catalysts. Chem Rev 104:3037–3058Google Scholar
  359. 359.
    Sawyer DT, Valentine JS (1981) How super is superoxide? Accounts Chem Res 14:393–400Google Scholar
  360. 360.
    Chen C, Ma W, Zhao J (2010) Semiconductor-mediated photodegradation of pollutants under visible-light irradiation. Chem Soc Rev 39:4206–4219Google Scholar
  361. 361.
    Zheng Z, Chen C, Bo A, Zavahir FS, Waclawik ER, Zhao J, Yang D, Zhu H (2014) Visible-light-induced selective photocatalytic oxidation of benzylamine into imine over supported Ag/AgI photocatalysts. ChemCatChem 6:1210–1214Google Scholar
  362. 362.
    Wang P, Tang Y, Dong Z, Chen Z, Lim T-T (2013) Ag-AgBr/TiO2/RGO nanocomposite for visible-light photocatalytic degradation of penicillin G. J Mater Chem A 1:4718–4727Google Scholar
  363. 363.
    Hoffmann MR, Martin ST, Choi W, Bahnemann DW (1995) Environmental applications of semiconductor photocatalysis. Chem Rev 95:69–96Google Scholar
  364. 364.
    Ye L, Liu J, Gong C, Tian L, Peng T, Zan L (2012) Two different roles of metallic Ag on Ag/AgX/BiOX (X = Cl, Br) visible light photocatalysts: surface plasmon resonance and Z-scheme bridge. ACS Catal 2:1677–1683Google Scholar
  365. 365.
    Hu P, Cao Y, Jia D, Li Q, Liu R (2014) Engineering the metathesis and oxidation-reduction reaction in solid state at room temperature for nanosynthesis. Sci Rep 4:4153Google Scholar
  366. 366.
    Wang J, An C, Liu J, Xi G, Jiang W, Wang S, Zhang Q-H (2013) Graphene oxide coupled AgBr nanosheets: an efficient dual-functional visible-light-responsive nanophotocatalyst with enhanced performance. J Mater Chem A 1:2827–2832Google Scholar
  367. 367.
    Wang D, Guo L, Zhen Y, Yue L, Xue G, Fu F (2014) AgBr quantum dots decorated mesoporous Bi2WO6 architectures with enhanced photocatalytic activities for methylene blue. J Mater Chem A 2:11716–11727Google Scholar
  368. 368.
    Baetzold RC (1997) Calculated properties of Ag clusters on silver halide cubic surface sites. J Phys Chem B 101:8180–8190Google Scholar
  369. 369.
    Dong R, Tian B, Zeng C, Li T, Wang T, Zhang J (2013) Ecofriendly synthesis and photocatalytic activity of uniform cubic Ag@AgCl plasmonic photocatalyst. J Phys Chem C 117:213–220Google Scholar
  370. 370.
    An C, Wang R, Wang S, Zhang X (2011) Converting AgCl nanocubes to sunlight-driven plasmonic AgCl: Ag nanophotocatalyst with high activity and durability. J Mater Chem 21:11532–11536Google Scholar
  371. 371.
    Hu C, Peng T, Hu X, Nie Y, Zhou X, Qu J, He H (2010) Plasmon-induced photodegradation of toxic pollutants with Ag−AgI/Al2O3 under visible-light irradiation. J Am Chem Soc 132:857–862Google Scholar
  372. 372.
    Muskens OL, Del Fatti N, Vallée F (2006) Femtosecond response of a single metal nanoparticle. Nano Lett 6:552–556Google Scholar
  373. 373.
    Inouye H, Tanaka K, Tanahashi I, Hirao K (1998) Ultrafast dynamics of nonequilibrium electrons in a gold nanoparticle system. Phys Rev B 57:11334–11340Google Scholar
  374. 374.
    Tisdale WA, Williams KJ, Timp BA, Norris DJ, Aydil ES, Zhu X-Y (2010) Hot-electron transfer from semiconductor nanocrystals. Science 328:1543–1547Google Scholar
  375. 375.
    Kaelberer T, Fedotov VA, Papasimakis N, Tsai DP, Zheludev NI (2010) Toroidal dipolar response in a metamaterial. Science 330:1510–1512Google Scholar
  376. 376.
    Wang D, Li Y, Li Puma G, Wang C, Wang P, Zhang W, Wang Q (2013) Ag/AgCl@helical chiral TiO2 nanofibers as a visible-light driven plasmon photocatalyst. Chem Commun 49:10367–10369Google Scholar
  377. 377.
    Zhou X, Hu C, Hu X, Peng T (2012) Enhanced electron transfer and silver-releasing suppression in Ag–AgBr/titanium-doped Al2O3 suspensions with visible-light irradiation. J Hazard Mater 219–220:276–282Google Scholar
  378. 378.
    Zhou X, Hu C, Hu X, Peng T, Qu J (2010) Plasmon-assisted degradation of toxic pollutants with Ag−AgBr/Al2O3 under visible-light irradiation. J Phys Chem C 114:2746–2750Google Scholar
  379. 379.
    Seki K, Yanagi H, Kobayashi Y, Ohta T, Tani T (1994) UV photoemission study of dye/AgBr interfaces in relation to spectral sensitization. Phys Rev B 49:2760–2767Google Scholar
  380. 380.
    Jiang J, Li H, Zhang L (2012) New insight into daylight photocatalysis of AgBr@Ag: Synergistic effect between semiconductor photocatalysis and plasmonic photocatalysis. Chem Eur J 18:6360–6369Google Scholar
  381. 381.
    Ingram DB, Linic S (2011) Water splitting on composite plasmonic-metal/semiconductor photoelectrodes: Evidence for selective plasmon-induced formation of charge carriers near the semiconductor surface. J Am Chem Soc 133:5202–5205Google Scholar
  382. 382.
    Chang Y, Xu J, Zhang Y, Ma S, Xin L, Zhu L, Xu C (2009) Optical properties and photocatalytic performances of Pd modified ZnO samples. J Phys Chem C 113:18761–18767Google Scholar
  383. 383.
    Ravelli D, Dondi D, Fagnoni M, Albini A (2009) Photocatalysis. A multi-faceted concept for green chemistry. Chem Soc Rev 38:1999–2011Google Scholar
  384. 384.
    Bae E, Choi W (2003) Highly enhanced photoreductive degradation of perchlorinated compounds on dye-sensitized metal/TiO2 under visible light. Environ Sci Technol 37:147–152Google Scholar
  385. 385.
    Wu T, Liu G, Zhao J, Hidaka H, Serpone N (1998) Photoassisted degradation of dye pollutants. V. self-photosensitized oxidative transformation of Rhodamine B under visible light irradiation in aqueous TiO2 dispersions. J Phys Chem B 102:5845–5851Google Scholar
  386. 386.
    Takeshita K, Sasaki Y, Kobashi M, Tanaka Y, Maeda S, Yamakata A, Ishibashi T-a, Onishi H (2004) Effect of annealing temperature on back electron transfer and distribution of deep trap sites in dye-sensitized TiO2, studied by time-resolved infrared spectroscopy. J Phys Chem B 108:2963–2969Google Scholar
  387. 387.
    Hagfeldt A, Graetzel M (1995) Light-induced redox reactions in nanocrystalline systems. Chem Rev 95:49–68Google Scholar
  388. 388.
    Moser JE, Grätzel M (1993) Observation of temperature independent heterogeneous electron transfer reactions in the inverted Marcus region. Chem Phys 176:493–500Google Scholar
  389. 389.
    Kuciauskas D, Freund MS, Gray HB, Winkler JR, Lewis NS (2001) Electron transfer dynamics in nanocrystalline titanium dioxide solar cells sensitized with ruthenium or osmium polypyridyl complexes. J Phys Chem B 105:392–403Google Scholar
  390. 390.
    Zhang X, Li J, Lu X, Tang C, Lu G (2012) Visible light induced CO2 reduction and Rh B decolorization over electrostatic-assembled AgBr/palygorskite. J Colloid Interface Sci 377:277–283Google Scholar
  391. 391.
    Glaus S, Calzaferri G (2003) The band structures of the silver halides AgF, AgCl, and AgBr: A comparative study. Photochem Photobiol Sci 2:398–401Google Scholar
  392. 392.
    Lou Z, Huang B, Ma X, Zhang X, Qin X, Wang Z, Dai Y, Liu Y (2012) A 3D AgCl hierarchical superstructure synthesized by a wet chemical oxidation method. Chem Eur J 18:16090–16096Google Scholar
  393. 393.
    Hou Y, Zuo F, Ma Q, Wang C, Bartels L, Feng P (2012) Ag3PO4 oxygen evolution photocatalyst employing synergistic action of Ag/AgBr nanoparticles and graphene sheets. J Phys Chem C 116:20132–20139Google Scholar
  394. 394.
    Schürch D, Currao A, Sarkar S, Hodes G, Calzaferri G (2002) The silver chloride photoanode in photoelectrochemical water splitting. J Phys Chem B 106:12764–12775Google Scholar

Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Yingying Fan
    • 1
    • 2
  • Dongxue Han
    • 1
  • Zhongqian Song
    • 1
    • 2
  • Zhonghui Sun
    • 1
    • 2
  • Xiandui Dong
    • 1
  • Li Niu
    • 1
  1. 1.Center for Advanced Research on Analytical Science, School of Chemistry and Chemical EngineeringGuangzhou UniversityGuangzhouPeople’s Republic of China
  2. 2.Engineering Laboratory for Modern Analytical Techniques, Changchun Institute of Applied Chemistry, Chinese Academy of SciencesChangchunPeople’s Republic of China

Personalised recommendations