1 Introduction

Marine biofouling has resulted in significant economic losses to ship transportation [1], oil platforms, and aquaculture industries [2]. The application of antifouling coating on surface of protected materials is an effective approach to combat marine biofouling. Previously, tributyltin-based self-polishing antifouling paint was considered the most efficient option. However, it posed serious threats to the normal physiological activities of marine organisms. Consequently, in 2008, Internaitonal Maritime Organization completely banned the utilization of tributyltin-based self-polishing coatings. Subsequently, copper-based or zinc-based tin-free self-polishing antifouling coatings became commonly commercial antifouling coatings. Nevertheless, these metal-based self-polishing coatings still possess toxicity and can cause harm to the marine environment with long-term usage. Therefore, emerging antifouling coatings have garnered considerable attention, such as environmentally friendly self-polishing antifouling coatings [3], low surface energy antifouling coatings [4], bionic antifouling coatings [5], etc. Environmentally friendly self-polishing coatings primarily achieve their antifouling properties through release natural organic antifouling agent. Low surface energy antifouling coatings exhibit reduced attachment by marine organisms due to the presence of functional groups with low surface energy characteristics. Bionic antifouling coatings replicate unique surface structures found in organisms and thereby achieve excellent performance against marine fouler. The low surface energy antifouling coating has garnered significant attention due to its non-release nature, straightforward preparation process and stable structure [6].

Siloxane is a polymer composed of -Si–O- as the basic repeating unit, which gives it unique properties compared to other carbon-based polymers. The Si–O-Si bond angle and length are higher than those of C–O–C, resulting in greater rotational freedom for methyl group towards the interface and a larger exclusion or free volume of the polymer chain, leading to low elastic modulus [7]. In addition, the high dissociation energy of -Si–O- (460 kJ·mol−1) contributes to silicone’s excellent thermal and chemical stability [8]. Polydimethylsiloxane (PDMS), an important product in siloxane coatings, exhibits low surface energy due to its silicon-oxygen bonds and silicon atoms connecting methyl groups with low steric hindrance effect. Due to the low surface energy characteristics of the coating, it becomes challenging for most marine organisms to effectively adhere to its surface. Moreover, under the hydrodynamic forces exerted by water flow, facilitated by its low elastic modulus, the PDMS coating surface forms a dynamic interfacial structure that promotes efficient removal of surface-attached microorganisms. This unique structure plays a crucial role in facilitating efficient removal of surface-attached microorganisms.

Despite the inherent antifouling properties of siloxane coatings, certain challenges persist in its practical application as an antifouling coating [9]: 1) Due to the low surface energy characteristics of the siloxane coating, its adhesion strength to metals and other materials is insufficient, rendering it prone to detachment. 2) While the antifouling performance of siloxane coatings is enhanced in water flow scenarios, achieving superior antifouling effects solely through low surface energy under static conditions remains challenging. 3) The mechanical properties of siloxane materials are inadequate, and they are prone to the formation of micro-cracks when subjected to external forces, leading to coating damage and a reduction in its service life. In view of these limitations aforementioned associated with siloxanes, researchers have employed various methodologies to modify them, resulting in significant enhancements in adhesion strength, static antifouling efficacy, and self-healing capabilities, as shown in Fig. 1.

Fig. 1
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Schematic diagram of challenges and modification strategies of siloxane antifouling coatings

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This review presents a comprehensive summary and analysis of recent advancements in siloxane antifouling coatings. Firstly, the commonly employed synthetic preparation methods for these coatings are summarized. Secondly, the modification strategies for improving the comprehensive properties of siloxane antifouling coatings are outline. The modification strategies encompass enhancing the coating's adhesion, improving its static antifouling performance, and augmenting its self-healing capabilities. Finally, the research methods and directions for improving the performance of siloxane antifouling coatings in the future are discussed and analyzed. This study presents a pioneering and comprehensive analysis of siloxane antifouling coatings, shedding light on the current research status, and offering insights into future development trends.

2 Synthesis method of siloxane coating

Despite its unique structure and excellent antifouling performance, the exclusive reliance on siloxane in antifouling coatings fails to meet the practical requirements of industrial applications. To better cater to marine antifouling requirements, novel antifouling coatings can be developed by compounding siloxane with other materials through diverse chemical reactions. Different materials exhibit distinct chemical reactivity, necessitating diverse preparation and processing methodologies. In this regard, this study provides a comprehensive summary of various preparation methods for siloxane-based antifouling coatings, encompassing surface modification techniques, diisocyanate polymerization approaches, click chemistry strategies, and other polymerization reaction methodologies.

A common approach for the preparation of modified siloxane antifouling coatings involves the utilization of a curing agent to synthesize amino or hydroxyl terminated polysiloxane. As depicted in Fig. 2(a), Liu et. al [10] developed a self-healing coating based polyurea consisting of PDMS and diisocyanate. Similarly, Wang et al. [11] prepared a self-healing PDMS coating by curing amino-terminated PDMS with 4,4’–methylenebis-(cyclohexyl lisocyanate) and isophthaladehyde, thereby introducing additional hydrogen bonds into the coating. The presence of diisocyanates and other chain extenders further enhances the number of hydrogen bonds, which surpass the influence of van der Waals forces between molecular chains and ultimately improving the mechanical properties of the siloxane coating. In addition to 4,4’–methylenebis-(cyclohexyl lisocyanate), commonly used diisocyanates include isophorone dissocyanate [12], toluene diisocyanate [13], 4,4’-diphenylmethane diisocyanate [14], and 1,6-disocyanatohexane [15] etc. Triisocyanates such as isophorone dissocyanate-tris also serve as important curing agents for enhancing the mechanical properties of siloxane coatings [16]. Tripolyisocyanate significantly promotes network crosslinking density within siloxane coating, leading to improve the mechanical properties of polysiloxane coatings [17]. Furthermore, other chain extenders like glycerol [18], 3-Aminophenylboronic acid [19], boric acid [20], and other ternary chain extenders can also enhance the mechanical properties of the polymer. The modified functional groups of the siloxane coating prepared by this method are primarily located at the end of the siloxane molecular chain, thereby retaining the fundamental properties of the siloxane coating. However, due to limitations in the amount of curing agent added, there exists an upper limit to performance enhancement for coatings produced using this method.

Fig. 2
figure 2

Several methods for preparing modified siloxane coatings. Modified PDMS coating based on diisocyanate curing strategy (a) [10]. Copyright 2017, Royal Society of Chemistry. Modified siloxane antifouling coating based on block copolymerization (b) [21]. Copyright 2016, Elsevier. Modified PDMS antifouling coatings based on ABA-type block polymerization (c) [22]. Copyright 2020, American Chemical Society. Modified PDMS coating based on surface treatment (d) [23]. Copyright 2015, American Chemical Society. Modified PDMS coating based on hyperbranched polymerization (e) [24]. Copyright 2021 John 2021 Wiley‐VCH GmbH. Modified PDMS coating based on side-chain branching polymerization (f) [25]. Copyright 2022, Elsevier. Modified PDMS coating based on click chemistry side-link branch (g) [26]. Copyright 2021, Elsevier

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In contrast, the block copolymerization derived polymer is not constrained by the relative proportions of its constituents. According to the structural characteristics of block copolymers, block copolymerization methods can be classified into two categories: random block copolymerization and ABA block copolymerization. Figure 2(b) illustrates the preparation of siloxane antifouling coatings through random block copolymerization [21]. Binary block copolymers were synthesized by olefin polymerization of poly(dimethyl siloxane)propoxyethyl 4-vinylbenzoate and 2,3,4,5,6-pentafluorostyrene. Due to the distinct physical and chemical properties of different blocks, phase separation occurs in the resulting block polymers. The phase separation structure obscures the surface morphology of the coating and effectively impedes the adhesion of fouling organisms. Similarly, Kim et al. [27] also formed silicon-based block polymers via 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane and cyclohexyl methacrylate block polymerization under tert-butylperoxy-2-ethylhecanoate catalytic conditions. However, it is evident that these polymers possess a main chain consisting of -C–C- bonds rather than -Si–O- bonds, thereby impeding the optimization of siloxane antifouling performance. The conventional block polymerization method fails to manifest the inherent low surface energy antifouling advantages associated with siloxane materials. On the other hand, ABA block polymerization employs siloxane as the main chain with modified groups such as poly(ethylene glycol) (PEG) [28], poly(N-vinylpyrrolidone) (PVP) [29], and zwitterionic polymers [30] being polymerized at both ends. Guo et al. [22] prepared a novel type of block copolymer coating. As shown in Fig. 2(c), the hydroxyl-terminated PDMS serves as the center while 1-(1H,1H,2H,2H-perfluorodecyloxy)-3-(3,6,9-trioxadecyloxy)-propan-2-yl acrylate and 2, 2’ Azobis-(isobutyronitrile) function as end groups in this structure. The amphiphilic copolymer was blended into the cross-linked PDMS matrix to form a set of controllable surface composition and surface renewal coatings with effective antifouling and decontamination properties. Both types of block polymerizations effectively introduce appropriate modified groups. However, the traditional block polymerization does not make use of the main chain characteristics of siloxane, while the modified groups of ABA block polymerization are still concentrated at both ends of the molecular chain.

The surface modification of the cured siloxane coating can enhance the dispersion of the modified groups, thereby ensuring direct interaction between the modified functional groups and the coating interface. As depicted in Fig. 2(d), Shivapooja et al. [23] grafted onto the PVDS surface, followed by the growth of sulfobetaine methacrylate (SBMA) zwitterionic polymer through atom transfer radical polymerization reaction on the coating surface. This approach solely modifies the surface of coating without affecting its internal structure. Depending on the hydration level of the modifier, it significantly enhances the antifouling efficacy of the siloxane coating. The mechanical properties within the siloxane remain unaffected by surface modification. By subjecting the elastomer substrate to mechanical strain, facile detachment of the biofilm accumulated during prolonged exposure is achieved. Similarly, Shen et al. [31] activated PDMS surface using benzophenone to generate free radicals and subsequently polymerized a mixed zwitterionic polymer comprising carboxybetaine methacrylate (CBMA), SBMA, and 2-hydroxyethyl methacrylate on its surface. The modified siloxane coating effectively mitigated bacterial adhesion and proliferation. Regrettably, although this method yields high performance antifouling coatings, its preparation process is intricate and challenging for industrial application.

Hyperbranched polymerization is a straightforward and efficient method for enhancing material properties [32]. As depicted in Fig. 2(e), Chen et al. [24] employed hyperbranched polymerization to fabricate a siloxane antifouling coating with amino end. This hyperbranched siloxane polymer not only enhances its own mechanical properties but also improves the adhesion between the coating and substrate. The incorporation of zwitterionic silane imparts both oleophobic and antibacterial characteristics to the coating. The terminal single-molecule structure of the hyperbranched siloxane polymer significantly influences its overall performance. Apart from to PDMS-NH2 [33], other commonly used single molecules such as PDMS-SH [34] and PDMS-OH [35] are utilized as raw materials. However, one drawback of the hyperbranched polymerization method lies in its limited control over molecular weight, thereby reducing controllability.

Compared with the afore mentioned polymerization methods, the side chain modification approach can enhance the additional properties of the siloxane coating by incorporating suitable side chain groups. Moreover, this method ensures that main polymer backbone remains -Si–O-, thereby preserving the original coating properties. Side chain modification strategies can be categorized into two types: one involves forming polymer modifications through specific strategies, while the other entails attaching small molecular groups to the side chains using click chemistry. Generally, in side chain polymerization modification methods, a modified side chain polymer is first prepared and then further reacted via polycondensation or anionic polymerization to form the main chain compound. As illustrated in Fig. 2(f), Hu et al. [25] synthesized an amphiphilic antifouling coating through a multistep polymerization reaction.. Initially, under the 2, 2’ Azobis-(isobutyronitrile) initiation conditions, poly(ethylene glycol) methyl ether methacrylate and dodecafluoroheptyl methacrylate were copolymerized within the branched structure of 3-(Dimethoxy(methyl)silyl)-propane-1-thiol via free radical polymerization. Subsequently, employing polycondensation reaction techniques led to preparation of an amphiphilic siloxane-based polymer as the main backbone component. This method for modifying siloxane through side chain polymerization enables diverse modification approaches for developing antifouling coatings and exhibits promising application prospects.

Click chemistry offers the advantages of a straightforward reaction, absence of by-products, and easy synthesis control. It also an effective method for modifying special siloxane polymers through click chemical side chain modification. As illustrated in Fig. 2(g), Hu et al. [26] utilized the thiol group of 2-(2-benzimidazolyl)ethanethiol (BET) small molecule to react with the olefin bond in polymethylvinylsiloxane (PMVS), resulting in a BET modified polysiloxane coating. This side chain modification introduces metal coordination bonds into the coating, enhancing both its mechanical properties and antifouling performance. Click chemistry represents a controllable reaction principle where two functional groups react upon contact. Among siloxane polymers, PMVS is particularly suitable for click chemical side chain modification due to the presence of olefin bonds in its side chains. Commonly used click chemical modification groups for side chains include thiol groups such as 2-mercapto-ethanesulfonate (MESNA) [36], N-Acetyl-L-cysteine [37], silanol [38], 1,3-propanedithiol [39]. Additionally, other groups, like Si–H [40], 3-Chloroper benzoic acid [41] can be modified through side-chain branching as well. The main drawback of click chemical side chain modification lies in its high requirements for reactants. However, this does not affect the strategy of utilizing chemically modified side chains via clicking to prepare antifouling coatings since PMVS is widely available with mature preparation methods and excellent antifouling performance.

The above discussion summarized the diverse range of preparation methods available for siloxane antifouling coatings. Depending on the chemical properties of the modified functional molecule and the designed coating structure, an appropriate method can be selected to achieve a modified siloxane antifouling coating.

3 Modification strategy of siloxane antifouling coating

As previously mentioned, a single siloxane coating alone fails to meet the demands of antifouling applications. Consequently, researchers have endeavored to enhance the antifouling performance of siloxane coatings in marine environments through diverse modification methods and strategies. Herein, this article categorizes and summarizes the research progress on modification strategies for siloxane antifouling coatings conducted this year. These three strategies are devised based on addressing the respective limitations of siloxane coatings: 1) Enhancing adhesion strength between the siloxane coating and substrate; 2) Improving static antifouling efficacy of siloxane coating; 3) Augmenting self-healing properties of siloxane coatings.

3.1 Strong adhesion siloxane antifouling coating

Although the siloxane coating reduces the adhesion of marine fouling organisms due to its low surface energy, it is also attributed to this property that the adhesion between the coating and the protected metal substrate is compromised [42]. The conventional approach in marine coatings involves a layered system, where the primer primarily enhances adhesion, intermediate paint provides corrosion resistance, and topcoat exhibits antifouling performance [43]. Therefore, traditionally, a siloxane antifouling coating is applied over an epoxy anticorrosive coating to leverage interfacial forces for improved adhesion [44]. However, with advancements in research on novel antifouling coatings, alternative strategies have been developed to enhance the adhesive properties of siloxane coatings.

The mechanical properties of the coating can be enhanced by inorganic nano-fillers, which can also improve the adhesion between the coating and substrate [45]. As depicted in Fig. 3(a), Xie et al. [46] demonstrated that perfluorosilys nanodiamond modification of PDMS coating resulted in improved adhesion strength from 1.5 MPa to 2.1 MPa. This is due to hydrogen bonding between the nanodiamond and substrate facilitated by residual hydroxyl groups on the nanodiamond surface. At the same time, these hydrogen bonding interactions also improve the self-healing properties of PDMS coatings at room temperature. Furthermore, inorganic nanomaterials with abundant surface functional groups such as graphene oxide [47] and carbon nanotubes [48] have been employed to enhance siloxane adhesion strength. However, it should be noted that there is an upper limit for incorporating each type of inorganic filler into the coating, as excessive amounts may lead to agglomeration within the coating matrix and significantly compromise its mechanical properties. Enhancing the dispersion of inorganic fillers in siloxane coatings and augmenting the performance of these coatings through surface treatment of the fillers have emerged as pivotal research avenues for developing antifouling coatings with inorganic fillers.

Fig. 3
figure 3

Several strategies to improve the adhesion of siloxane antifouling coatings. A strategy for improving the adhesion strength of PDMS coatings modified by fluorinated nanodiamonds (a) [46]. Copyright 2020, American Chemical Society. A strategy for improving the adhesion strength based on self-stratification of AR and PDMS resin (b) [49]. A strategy for improving the adhesion strength based on bionic mussels (c) [50]. Copyright 2022, Elsevier. A strategy for improving the adhesion strength based on amino and epoxy end groups (d) [51]. Copyright 2021, Elsevier

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Self-stratified hybrid coatings have been proven to be an effective approach for enhancing the adhesion of siloxane coatings. After the stratification of heterogeneous substances, a defined topological structure emerges at the interface between them, thereby enhancing the interfacial mechanical properties. As depicted in Fig. 3(b), Xue et al. [49] successfully achieved a self-stratified acrylic resin (AR) /PDMS coating by blending AR and PDMS together. Due to the distinct forces and physical properties of these components, AR predominantly distributes on the metal surface while PDMS mainly resides on the outermost layer, resulting in a chemical gradient and topological structure between them. The antifouling performance of the composite coating is ensured by PDMS, while the adhesion strength of the coating is guaranteed by AR. Apart from self-stratification, another method to improve adhesion is through segmental differentiation within siloxane copolymers. Liu et al. [52] synthesized a siloxane polymer with separated soft segments (PDMS) and hard segments (HMDA). The presence of HMDA enables effective hydrogen bonding with the substrate, thereby enhancing the adhesive strength of modified siloxane coatings. The strategy of employing self-stratified hybrid coatings to enhance adhesion in siloxane systems is highly convenient due to the unique physical and chemical properties associated with Si–O bonds, which render them less compatible with most other organic coatings and prone to microphase separation or interlayer delamination.

The method of inorganic filler or hierarchical structure modification primarily enhances adhesion strength by forming weak physical bonds, such as hydrogen bonds, with the substrate. However, the potential for improvement using this modification method is limited [53]. Alternatively, adhesion strength can be significantly enhanced through other methods like chemical bonding [54]. For instance, Lin et al. [50] developed a high-adhesion siloxane coating based on strong bond cooperation inspired by the exceptional adhesive performance of bionic mussels, as shown in Fig. 3(c). By modifying the siloxane chain segment with natural phenolic organic small molecules, an abundance of phenolic hydroxyl groups is incorporated into the siloxane chain to facilitate bonding with various metal substrates. This unique segment structure results in an enrichment of hydrophilic phenolic hydroxyl groups near the matrix and predominantly hydrophobic siloxanes on the surface. The multiple phenolic hydroxyl groups form hydrogen bonds and metal coordination bonds with the metal matrix surface, thereby enhancing adhesion. Under dry conditions, the modified coating exhibits an adhesion strength of 3.6 MPa, which is six times that of unmodified coatings, and even under wet conditions, it achieves a remarkable adhesion strength to the substrate at 3.0 MPa.

Similarly, the adhesion strength between different coatings can be enhanced through the formation of robust bonding. Zheng et al. [51] mproved the adhesion strength between PDMS and epoxy coating by employing a bridging agent to bond them together, as illustrated in Fig. 3(d). The bridging agent used is a small molecular material with a significant gap between its two ends. One end consists of siloxane while the other end comprises either amino or epoxy groups, such as (3-aminopropyl) triethoxysilane (KH550) and γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) respectively. These bridging agents facilitate the formation of bonding bridges at the interface between siloxane and epoxy coatings, thereby enhancing their adhesion. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane, which shares similarities with KH550 due to having one end composed of siloxane and another end consisting of an amino group, was also utilized as a bridging agent by Zhang et al. [54] to improve interfacial adhesion between PDMS and epoxy coating. By establishing a weak or strong interaction bond between the internal group of the coating and the substrate, it is possible to enhance the adhesion strength of the siloxane coating on the substrate surface, thereby overcoming environmental limitations associated.

3.2 Static antifouling siloxane antifouling coating

The siloxane coating possesses not only a low surface energy but also an excellent elastic modulus. When subjected to water flow, the dynamic nature of the siloxane coating allows it to form a responsive surface, effectively shedding attached organisms. However, in stagnant water conditions, relying solely on low surface energy for antifouling purposes proves unfavorable. The attachment of marine fouling organisms onto object surfaces is a complex process involving two steps: initial adsorption of small organic molecules such as proteoglycans to form an organic film layer and subsequent attraction of microorganisms like bacteria and algae leading to biofilm formation. It is advisable to proactively mitigate marine biofouling from the initial stage. The antifouling efficacy under static conditions can be achieved by strategically designing the interfacial structure between the coating and small organic molecules. Therefore, constructing a static antifouling coating can be approached from three perspectives: 1) establishing a physical barrier interface that impedes the adsorption of organic molecules onto the coating; 2) creating a dynamic coating surface capable of self-renewal; 3) eliminating microorganisms on the coating's surface while preventing biofilm formation.

Establishing a physical barrier interface that impedes the adsorption of organic molecules onto the coating. In an aqueous environment, certain hydrophilic molecules can engage in weak interactions, which is called hydration. Presently, the modification of siloxane coatings entails integrating hydrophilic components in order to attain amphiphilic antifouling characteristics. Amphiphilic coatings refer to polymer-based coatings comprising both hydrophilic and hydrophobic constituents. These hydrophilic segments can form a dense hydration layer with water, effectively preventing non-specific adsorption of organic molecules such as proteoglycans through physical interactions and thereby enhancing the static antifouling performance of the coating. Commonly used hydrophilic segments for PDMS modification include zwitterionic polymers, PVP, polyols, among others. Table 1 summarizes the classification and modified groups of amphiphilic siloxane coatings.

Table 1 Classification and modified groups of amphiphilic siloxane coatings
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The binding of PEG to PDMS is widely recognized as the most suitable among polyols for achieving effective PDMS binding [67]. Kil et al. [76] developed a bifunctional brush copolymer incorporating both antifouling PEG and antifouling PDMS, as illustrated in Fig. 4(a). Compared to single polymer antifouling coatings, this amphiphilic copolymer coating exhibits superior resistance against protein and algae fouling. Polysilane amphiphilic modified organosilicones were prepared by Grunlan et al. [77], resulting in a significant decrease in the water contact angle from 114° to 16°, which remained stable for a minimum of three months. Currently, the exact mechanism underlying the antifouling properties of PEG-modified PDMS coatings remains unclear. On one hand, the hydrophilic PEG segment can form a hydration layer with water at the interface to hinder non-specific protein adsorption [78]. On the other hand, due to immiscibility between PEG and PDMS segments, microphase separation occurs [68], which enables adjustment of surface morphology and wettability of the coating, thereby preventing fouling substance adsorption such as proteins. The antifouling performance of the coating surface is significantly influenced by the ratio between PDMS and PEG, indicating that a clear mechanism to explain this phenomenon remains elusive [16]. Meanwhile, PEG is susceptible to oxidation during usage, leading to a decline in its antifouling performance over time.

Fig. 4
figure 4

Several strategies for preparing amphiphilic PDMS composite antifouling coatings. PDMS amphiphilic antifouling coating based on PEG modification (a) [76]. Copyright 2023, Royal Society of Chemistry. PDMS amphiphilic antifouling coating based on zwitterionic polymer modification (b) [62]. Copyright 2022, American Chemical Society. PDMS amphiphilic network antifouling coating based on PVP modification (c) [65]. Copyright 2019, Elsevier

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The zwitterionic polymer exhibits enhanced hydration effects and forms a more robust hydration layer compared to PEG, thereby enhancing the antifouling performance of the coating. Ma et al. employed zwitterionic polymer methacryloxyethyl dimethyl butyl ammonium bromide (MDBAB) to modify the siloxane coating and achieved an amphiphilic antifouling coating, as depicted in Fig. 4(b) [60]. The antifouling mechanism of zwitterionic polymers primarily stems from the formation of a dense hydration layer with water after hydrolysis of zwitterions. In aqueous environments, the hydrophilic quaternary ammonium groups on the coating surface form a dense physical layer, conferring anti-fogging, underwater oleophobicity, self-cleaning ability, antibacterial properties, friction-resistant electrification characteristics, super-lubrication capabilities and other desirable attributes. At present, the commonly used zwitterionic polymers include CBMA, SBMA, 2-methacryloyloxyethyl phosphorylcholine (MPC) and other materials. Nevertheless, factors influencing the hydrolytic strength of zwitterionic polymer materials remain unclear [79]. With the discovery of ploy(trimethylamine N-oxide) (PTMAO) new zwitterionic polymers and advancements in molecular dynamics simulation methods, a clearer understanding of the factors influencing the hydration strength of zwitterionic polymers has emerged.

Due to the formation of a water barrier created by polar pyrrolidone units, PVP exhibits remarkable anti-biofouling properties against protein adsorption and cell adhesion. Moreover, PVP demonstrates exceptional stability and has been extensively investigated for its application in modified siloxane antifouling coatings. Zhang Lei's research team [65] successfully developed an amphiphilic antifouling coating by incorporating PVP into PDMS, as illustrated in Fig. 3(c). The modified coating demonstrates enhanced hydrophilicity and exerts a significant inhibitory effect on the adhesion of bacteria, chlorella, and barnacles. Remarkably, after undergoing a 123 days seawater test, the PVP-modified PDMS antifouling coating exhibits remarkable efficacy against fouling. The hydrophilic pyrrolidone unit within PVP effectively captures water molecules through surface-preferential interface aggregation, forming a water layer that efficiently eliminates electrostatic adsorption between the coating and biomolecules. To further investigate the potential value of PVP modified PDMS coatings, our team conducted a comprehensive study on the diverse applications of PDMS and PVP [22], N-vinyl-2-pyrrolidone [66], and other modified groups in amphiphilic siloxane coatings for marine antifouling [29], medical antibacterial purposes, and other surface engineering.

Develop a self-renewing coating surface with dynamic properties to prevent the attachment of fouling organisms. Currently, copper acrylic acid-based self-polishing copolymers is primarily utilized in marine antifouling coatings. This coating creates a dynamic surface through molecular chain hydrolysis, which releases antifouling agents to prevent the attachment of marine fouling organisms. The hydrolysis rate of this coating is influenced by the velocity of water flow. The hydrolysis rate of its molecular chain is accelerated under the process of water flow, leading to an enhanced antifouling efficacy. However, when exposed to static water conditions, the hydrolysis rate becomes significantly slower than the growth rate of fouling organisms, leading to a diminished static antifouling effect. Reaching static antifouling performance can be accomplished by developing antifouling coatings with enhanced hydrolysis rates or precisely controlled release of hydrolytic agents.

In recent years, rapid degradation of water and antifouling materials such as poly(ε-caprolactone) (PCL) and poly(lactic acid) have emerged as a prominent research area. Ma's team has made significant contributions in this field [80, 81]. They have extensively explored the modification of siloxane coatings using degradable PCL to address the limitations of static antifouling properties. By utilizing hyperbranched PCL and siloxane as raw materials, they successfully developed biodegradable network crosslinked siloxane coatings [82], as illustrated in Fig. 5(a). The continuous degradation of the PCL segment in marine environments creates a dynamic surface that effectively prevents marine biofouling from adhering to the coating surface. Moreover, this degradable dynamic surface also forms a rough texture, which enhances its ability to deter attachment by marine organisms. The key focus of their research lies in coordinating the type and content of both main chains and branched chains to regulate the degradation rate of the coating, thereby achieving optimal antifouling performance while prolonging its service life span. As depicted in Fig. 6(b), Ma's team investigated the antifouling properties of chemically modified methylsilyl acrylate copolymers by manipulating variations in main chain types and side chain contents. Compared with traditional methylsilane acrylate copolymers, those containing polyester segments within their main chains exhibited higher degradation rates along with reduced swelling characteristics. This can be attributed to hydrolysis occurring within the polyester segment of the main chain, consequently accelerating coating degradation while ensuring sustained antifouling efficacy even under static conditions. Grunlan and his team have reported on the incorporation of PDMS segments into PCL/PDMS shape-memory polymer scaffolds for cranial defect healing [83, 84]. It has been demonstrated that when combined with organic cross-linked networks, PDMS exhibits inherent bioactivity and can modify degradation rates, addressing the lack of innate bioactivity and slow degradation observed in poly(ε-caprolactone) diacrylate scaffolds. Drawing inspiration from the controlled-release external self-healing anticorrosive coating, it was proposed to incorporate controllable degradation segments into degradable static antifouling coatings. In the presence of fouling biological aggregation [85], the pH [86], enzyme activity [87], and other factors in the coating surface environment undergo alterations. By employing molecular design strategies, the degradation rate of degradable coatings under such environmental conditions can be enhanced. This controlled degradation coating effectively prevents ineffective degradation and extends its service life, making it more suitable for engineering applications.

Fig. 5
figure 5

PDMS static antifouling coating based on degradation of hyperbranched polycaprolactone side chain (a) [82]. Copyright 2020, American Chemical Society. Static antifouling coatings based on main chain degradation of 2-methylene-1,3-dioxepane-tributylsilyl methacrylate-methyl methacrylate copolymer (b) [81]. Copyright 2015, American Chemical Society

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Fig. 6
figure 6

Several strategies to improve the antifouling performance of PDMS coatings based on the addition of antifouling agents. Preparation method of PDMS antifouling coating based on inorganic nano-filler release (a) [88]. Copyright 2015, Royal Society of Chemistry. An antifouling strategy based on natural organic antifouling agents (b) [89]. Copyright 2021, Elsevier. A strategy to improve the static antifouling ability of PDMS coating based on non-releasing antifouling agent (c) [90]. Copyright 2019 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim. A strategy to improve the antifouling performance of PDMS coatings based on ionic liquid release (d) [91]. Copyright 2022, American Chemical Society

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Eliminating microorganisms on the coating's surface while preventing biofilm formation. Adding antifouling agent to the siloxane coating is also a viable strategy for enhancing the static antifouling performance of the coating. While this coating may not entirely prevent the attachment process of marine organisms, it can actively eradicate attached organisms and achieve a static antifouling effect. However, it should be noted that the release of antifouling agents inevitably poses risks to the marine environment. Consequently, there has been an increasing awareness among individuals regarding marine environmental protection, leading to the development of novel environmentally-friendly antifouling agents. Currently, antifouling agents can be categorized into four types: release-type inorganic heavy metal-based agents, release-type organic agents, non-release-type organic agents, and ion-release-based agents.

Copper based oxides, including Cu2O [92] and CuO, are commonly employed as antifouling agents in marine coatings [93]. Selim et al. [88] synthesized PDMS composite coatings with varying concentrations of nanofillers, as depicted in Fig. 6(a). The mechanical properties of the PDMS coating remained unaffected, while the incorporation of Cu2O nanofillers enhanced the static antifouling performance of the coating. Given the evident impact of heavy metal ions on marine pollution, there is a growing trend towards replacing traditional copper-based antifouling agents with low-copper alternatives that are more environmentally friendly.

4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) represents a broad-spectrum fungicide and eco-friendly antifouling agent capable of effectively preventing marine organisms from adhering to hull surfaces [10]. Pan et al. [89] investigated the antifouling mechanism of organic agents like DCOIT and butenolide in coatings, as illustrated in Fig. 6(b). In comparison to DCOIT, butenolide demonstrated efficient prevention against bacterial adhesion on coating surfaces without exerting bactericidal effects. DCOIT primarily achieves its static antifouling effect by deactivating bacteria adhered to coating surfaces. However, similar as inorganic antifouling agents, releasing antifouling agents are always fully consumed whereas non-release counterparts not only require smaller quantities for usage but also offer long-term effectiveness.

Non-releasing antifouling agents are small molecular materials that are grafted onto the coating chain or surface, effectively preventing fouling on the coated surface. As depicted in Fig. 6(c), Xie et al. [90] developed a coating with enduring and static antifouling properties by grafting antifouling groups onto the PDMS side chain. Two non-releasing antifouling groups, dodecafluoroheptyl methacrylate and triclosan acrylate, along with 3-mercaptopropyl trimethoxysilane (KH590), were incorporated into PDMS through grafting. The inherent immiscibility between the antifouling group and PDMS leads to self-stratification phenomenon, resulting in enrichment of the antifouling group on the coating surface. The exceptional static antifouling performance is attributed to the anti-adhesion effect of these two antifouling groups against bacteria and diatoms. Following a real sea-based antifouling test for 3 months, the modified coating exhibited outstanding static antifouling performance. In addition to antifouling agents, ionic liquids have emerged as a promising strategy for enhancing the antifouling performance of coatings. As depicted in Fig. 6(d), yuan et al. [91] developed a polydimethylsiloxane-based coating incorporating a quaternary ammonium ionic liquid that releases nitric oxide gas. This innovative coating effectively impedes the adsorption of bovine serum albumin and bacteria by releasing nitric oxide. Similarly, Sun et al. [94] grafted imidazolium ionic liquid onto PDMS to fabricate a siloxane coating with antibacterial adhesion properties. Ionic liquid-based antifouling coatings exhibit remarkable resistance against bacterial and protein fouling, making them highly suitable for medical material applications. However, their efficacy in large-scale antifouling of marine environments remains unverified.

Bionics is a pivotal scientific field that has yielded diverse inspirations from nature, including the development of bionic antifouling coatings [95]. The bionic antifouling coating can meet the static antifouling performance of the coating. It is a basic bionic modification method to structurally modify the surface structure of the siloxane coating and prevent the adhesion of algae and other provincial committees on the surface of the coating from a microscopic distance [96]. Another bionic strategy for antifouling coatings involves slippery liquid-infused porous surface, wherein lubricating antifouling agents like silicone oil are encapsulated within the coating, gradually releasing and ensuring short-term antifouling effects on the coated surface [97]. However, controversies persist regarding bionic antifouling coatings. On one hand, fouling organisms such as barnacles can still attach themselves to marine structures. On the other hand, concerns arise about potential environmental impacts resulting from the release of lubricating antifouling agents. Addressing the static antifouling performance of coatings relies on understanding the interface between the coating and fouling organisms. The static antifouling issue of the coating can be addressed from three perspectives: the surface of the coating, fouling organisms, and the two-phase interface. In future research, there should be a focus on developing novel antifouling interfaces that are both scientifically advanced and environmentally friendly.

3.3 Self-healing siloxane antifouling coating

Siloxane antifouling coatings, serving as topcoats for direct exposure to seawater, are inevitably subjected to external mechanical forces during the application process [98]. These forces can easily induce micro cracks in the coating, subsequently impacting its service life [99]. Endowing siloxane coatings with self-healing properties emerges as a crucial strategy for prolonging their durability [100]. At present, self-healing coatings can be divided into external self-healing coatings and intrinsic self-healing coatings. The external self-healing coating primarily relies on the incorporation of microcapsule materials within the coating for repair purposes. Conversely, the intrinsic self-healing coating depends on dynamic bonding mechanisms within the coating to facilitate structural self-healing. The compatibility of the siloxane coating with most materials is limited, making it challenging to repair using foreign aid materials. Consequently, it is commonly employed to enhance the internal structure of the siloxane coating, augment internal dynamic bonding, and improve its self-healing capabilities [101].

Recently, by harnessing the advantages of supramolecular chemistry to regulate mechanical integrity through reversible cross-linking mechanisms such as dynamic covalent bonds, hydrogen bonds, and metal chelation, silicon-based supramolecular materials have been developed with distinctive functionalities including intrinsic self-healing capabilities, stimuli-responsive behavior, and recyclability [102]. Liu et al. [103] modified PDMS by incorporating urea-pyridone as a functional group, as depicted in Fig. 7 (a). The introduction of these modified groups facilitated multiple hydrogen bonding interactions between molecular chains and enhanced the self-healing properties of the coating. Moreover, the multivalent hydrogen bonds confer exceptional mechanical strength upon the developed siloxane materials. It is noteworthy that the author investigated the influence of water molecules on the self-healing of hydrogen bonds. The presence of water facilitates both dissociation and recombination processes, thereby enhancing the mobility efficiency of hydrogen bonds within the modified siloxane polymer and ultimately improving the coating's self-healing performance. The water-promoted self-healing strategy of siloxane coatings presented herein offers significant advantages for the development of underwater antifouling coatings. Metal coordination bond is another effective modification strategy for self-healing siloxane coatings. Hu et al. [26] developed a side chain-modified siloxane coating on PVMS with BET as the side linker, as shown in Fig. 7(b). The unsaturated N atom of BET forms a metal coordination bond with zinc ions, which not only imparts self-healing properties but also enhances the antifouling performance of the coating. Similarly, Tan et al. [104] prepared self-healing siloxanes using amino-terminated PDMS and cerium ions, as illustrated in Fig. 7(c). The supramolecular structure and reversible metal coordination bonds contribute to improved self-healing properties of the polymer material. Furthermore, the metal coordination bond plays a pivotal role in enhancing the adhesion between the coating and the metal substrate by facilitating chemical interactions between group from the coating and functional groups on the surface of the metal substrate [11, 105, 106]. Therefore, it is foreseeable that the design of metal coordination bonds in siloxane antifouling coatings holds significant potential value. By precisely engineering the molecular structure of metal coordination bonds, it becomes possible to develop siloxane antifouling coatings with exceptional adhesion, static antifouling performance, and self-healing capabilities simultaneously. Additional dynamic covalent bonds, such as disulfide bonds, have been further explored for the self-healing performance of the siloxane coating. Kang et al. [107] fabricated a dynamic disulfide-containing siloxane coating where thermal stimulation triggers rapid cleavage and reformation of disulfide bonds among molecular chains, facilitating movement and enabling efficient healing. In summary, the incorporation of dynamic bonding to enhance the self-healing properties of siloxane coatings holds significant implications for the restoration of their mechanical and antifouling characteristics.

Fig. 7
figure 7

Several strategies for improving the self-healing properties of siloxane coatings. A self-healing siloxane coating based on multiple hydrogen bonds (a) [103]. Copyright 2018 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim. A self-healing siloxane coating based on metal coordination bonds (b) [26]. Copyright 2021, Elsevier. A self-healing siloxane coating based on nanofillers and metal coordination bond (c) [104]. Copyright 2018 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

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4 Future research strategies for siloxane antifouling coatings

Microstructure designable and environmentally friendly antifouling coatings are the development trend of future research. In this context, the future research strategies for siloxane antifouling coatings are emphasized. 1) Theoretical calculations, such as molecular dynamics, can explain the mechanism of organic coatings from a molecular perspective, which facilitates in-depth research on siloxane antifouling coatings. 2) By combining with siloxane coating, the use of new photocatalytic materials can achieve environmentally friendly static antifouling performance and enable environmentally friendly antifouling.

4.1 Theoretical calculation

The advancement of new technology profoundly impacts the research methodologies employed in materials science. With the increasing application of theoretical calculations, a greater understanding of reaction dynamics at both molecular and atomic levels is being unveiled. The utilization of theoretical calculation methods has also gained significant traction within the field of coating science, revealing interfacial interaction mechanisms between coatings and metals, water, as well as proteins at a molecular level. This enhanced comprehension facilitates the design of chemically structured coatings tailored to specific requirements.

Currently, various theories regarding adhesion strength have been proposed [108]. Among them, the most widely accepted theory is based on adsorption and intermolecular interactions through chemical bonds [109]. Through theoretical calculations, the adhesion mechanism between the coating and the substrate can be elucidated from a molecular interaction perspective. Yoshizawa et al. [110] investigated the adhesion between epoxy resin and hydroxylated alumina surface (001) using a micromodel of density functional theory calculation, as depicted in Fig. 8(a). The presence of hydrogen bond interaction between epoxy resin containing OH and ether groups and alumina facilitates effective stretching of epoxy resin at the alumina interface. Furthermore, water molecules present at the interface between these two phases influence their adhesion strength. This occurs due to rearrangement of hydrogen bond networks by water molecular layers, consequently reducing the adhesive properties between both phases. As illustrated in Fig. 8(b), they [111] also examined 4,4’-diaminodiphenyl sulfone and diglycidyl ether of bisphenol A interaction with hydroxylated alumina surface (001) within epoxy coatings using molecular dynamics (MD) and density functional theory methods. Notably, hydroxyl and phenyl ether components within diglycidyl ether of bisphenol A significantly contribute to enhancing adhesive characteristics of epoxy resin. In order to gain further insights into the peeling process between epoxy resin and treatment, the change in adhesion strength of the epoxy resin-silica interface was investigated at different angles, as shown in Fig. 8(c) [ 112]. Additionally, theoretical calculations were performed to determine the adhesion strength of epoxy resin with carbon fiber [108], copper surface [112] and other materials. The transition from horizontal to vertical orientation revealed two inflection points in the interaction force between epoxy resin molecules and silica interface, indicating the loss of influence from two oriented molecules on interfacial forces. Theoretical calculations can serve as a valuable guide for optimizing the structural design of the coating, thereby facilitating the development of a highly adhesive coating. Notably, there is a lack of relevant simulations through theoretical calculations regarding siloxane coating's interface interaction in siloxane modification research. Therefore, Yoshizawa's team's investigation on epoxy resin's interface interaction can serve as valuable reference experience for related studies on siloxane coatings.

Fig. 8
figure 8

Several cases of molecular dynamics study of adhesion mechanism between resin and substrate. Study on the molecular mechanism of adhesion interaction between epoxy resin and hydroxylated alumina surface in the presence of interfacial water molecules (a) [110]. Copyright 2018, American Chemical Society. Adhesion energy calculation of adhesion interaction between various functional groups of epoxy resin and hydroxylated alumina surface (b) [111]. Copyright 2022, American Chemical Society. The adhesion strength between hydroxylated silica (001) surface and epoxy resin was calculated (c) [113]. Copyright 2022 The Authors

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The Zwitterionic polymer antifouling coating represents a promising novel approach in the field of antifouling coatings. Zwitterionic polymers undergo ionization in aqueous environments, resulting in the formation of positive and negative functional groups that weakly interact with water molecules to create a dense hydration layer. Currently, hydration is considered as the primary mechanism behind the antifouling properties of zwitterionic polymer coatings. Surface sum frequency generation vibrational spectroscopy (SFGVS) and MD simulations are widely employed to characterize hydration at the interface between zwitterionic polymers and water. SFGVS-based tests are more rigorous [114], while MD simulations offer a microscopic understanding of hydration mechanisms [115]. TMAO is a natural zwitterionic molecule that exists in a small organic penetrant in a saltwater fish. Its oppositely charged groups are directly connected without spacers and may be the best zwitterion for antifouling materials. The antifouling performance of PTAMO was demonstrated by integrating theoretical calculations with experimental validation. Huang et al. [116] investigated the influence of salt and protein on surface hydration using SFGVS and MD techniques, as depicted in Fig. 9(a). The shorter distance between positive and negative charge groups in PTMAO results in stronger interaction with O atoms from water molecules but weaker repulsion with N atoms from water molecules. Metal ions have minimal impact on PTMAO's hydration behavior, ensuring its effectiveness even in high salinity seawater conditions. The hydration strength of PTMAO was compared with that of other zwitterionic polymers, such as CBMA and SBMA, highlighting the superior hydration properties of PTAMO in antifouling applications. As illustrated in Fig. 9(b), Ye et al. [117] studied the effects of two cysteine-terminal heptapeptide molecules on the antifouling mechanism. One is a molecule with alternating hydrophobic and hydrophilic groups, and the other is a zwitterionic molecule. Molecular dynamics results show that zwitterionic peptides can form more hydrogen bonds with water to form stronger hydration, thereby resisting the interaction between surface and protein. This also proves the limitation of the application of the antifouling mechanism of hydration to amphiphilic polymers. To elucidate the relationship between interfacial hydration of zwitterionic polymers and their molecular structure, Liu et al. [118] conducted various MD simulations. As shown in Fig. 9(c), compared to PEG brushes, the three zwitterionic brushes exhibited stronger interaction with water molecules. Moreover, chain length between zwitterionic groups and properties of positive and negative ionic groups significantly affect antifouling properties. Based on these microscopic mechanisms and conclusions, MD calculations can be employed as a preferential screening tool for identifying excellent modification strategies prior to the preparation of siloxane antifouling coatings. The molecular-level selection of modified groups exhibiting enhanced antifouling properties provides valuable guidance for the structural design of macroscopic coatings.

Fig. 9
figure 9

Several cases of molecular dynamics simulation coating hydration layer. Study on the molecular dynamics mechanism of super-hydration on PTMAO surface (a) [115]. Copyright 2019 The Authors. Molecular dynamics study of antifouling mechanism based on strong surface hydration of peptide self-assembled monolayers (b) [117]. Copyright 2015, American Chemical Society. Molecular Dynamics Study on Hydration Intensity of Different Zwitterionic Polymers (c) [118]. Copyright 2020 Royal Society of Chemistry

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The self-healing siloxane coating is currently a prominent area of research, with applications spanning various fields such as electronic skin and protective coatings. Molecular dynamics provides insights into the microscopic process of material self-healing through molecular chain bonding. Bao 's team has done a lot of research in the field of electronic skin. In the latest research, they [119] studied the self-healing process of PDMS/PEG layered self-healing coating by theoretical simulation, as depicted in Fig. 10(a). The PDMS/PEG multilayer electronic skin material breaks and dislocates after being scratched. Since the two have the same dynamic bonds and immiscible main chains, the broken interface can be rearranged through the movement of the molecular chain and restored to the performance of the adult. In addition, they also found that temperature can affect the self-healing rate. However, the enhanced healing ability at higher temperatures is not due to faster polymer kinetics, but to increased miscibility. However, in incompatible polymer types, the effect of temperature on the self-healing of the coating still depends on the interaction of polymer molecular chains and hydrogen bonds. In our previous work [120, 121], we simulated the self-healing behavior of PDMS at different temperatures. As shown in Fig. 10(c), the results show that the PDMS coating can have faster self-healing behavior at higher temperatures. However, our research may not be accurate enough. Chen et al. [122] studied the variation of hydrogen bonding with temperature in PU, as illustrated in Fig. 10(c). They determined that the main contribution of self-healing of PU materials is due to the movement of hydrogen bonds. Under different temperatures, the motion activity of hydrogen bonds is different. There is an appropriate temperature for hydrogen bonds. If the temperature is too high, the activity of hydrogen bonds will decrease and the self-healing efficiency of the coating will be reduced. In short, the self-healing process of organic coatings is not the same due to the different types and quantities of bonding. Therefore, through molecular dynamics simulation of siloxane antifouling coatings, the self-healing mechanism of siloxane coatings with different modification strategies can be clarified at the molecular level, which can enhance people 's understanding of self-healing siloxane coatings.

Fig. 10
figure 10

Molecular dynamics simulation of self-healing process of several PDMS-based materials. Simulation of self-healing process of PDMS/PEG immiscible dynamic polymer (a) [119]. Copyright 2023 The Authors. Molecular dynamics simulation of the effect of temperature on the self-healing behavior of PDMS coating (b) [120]. Copyright 2022, Elsevier. Molecular dynamics study of the effect of temperature on hydrogen bond self-healing behavior (c) [122]. Copyright 2020 Royal Society of Chemistry

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4.2 Photocatalytic nontoxic antifouling coating

Photocatalytic technology represents a novel environmentally friendly approach. Ever since Mastsunaga [123] first reported the photocatalytic sterilization effect of TiO2, the potential advantages of this technology in marine antifouling have been convincingly demonstrated. The photocatalytic antifouling mechanism of semiconductor materials originates from their photovoltaic effect, which involves the generation of hole-electron pairs upon light excitation and subsequent photolysis of water to produce reactive oxygen species (ROS), thereby achieving bactericidal and antifouling effects.

With the advancement of photocatalytic antifouling technology, photocatalytic antifouling materials can be categorized into three groups. The first group comprises titanium dioxide-based photocatalysts, the second group consists of Bi-based semiconductor heterojunction photocatalysts, and the third group includes porphyrin covalent organic framework photocatalysts. Huang et al. [124] have successfully fabricated a polyethersulfone-TiO2/MXene composite film with exceptional antifouling properties. As depicted in Fig. 11(a), upon ultraviolet light irradiation, valence band electrons in TiO2 semiconductors are excited to the conduction band, generating photogenerated hole-electron pairs. Active electrons and holes interact with water to produce various ROS, thereby achieving bactericidal and antifouling effects. However, TiO2 semiconductors possess a wide band gap and only absorb light within the ultraviolet region. In recent years, Bi-based photocatalytic semiconductors have garnered extensive attention as novel materials due to their diverse range, non-toxicity, and stability. As illustrated in Fig. 11(b), a novel BiVO4/InVO4 heterojunction composite material was proposed by Hou's team [125] for photocatalytic antifouling and sterilization purposes. This semiconductor heterojunction not only possesses a reduced band gap but also effectively facilitates the separation of photogenerated electron–hole pairs through the heterojunction interface. Under visible light irradiation, this material demonstrates exceptional antifouling properties and holds great potential as a new type of photocatalytic antifouling agent for marine coatings. Li et al. [126] designed a Schottky heterojunction based on Bi2S3 and Ti3C2Tx, which exhibits a lower band gap. Ti3C2Tx can effectively separate photogenerated hole electron pairs [127]. The incorporation of T can effectively suppress electron backflow and enhance the separation efficiency of electron–hole pairs. By leveraging the difference in work function between components, they engineered a biocompatible Schottky junction with enhanced near-infrared response sterilization ability through improved photocatalytic and photothermal properties.

Fig. 11
figure 11

Three types of photocatalytic antifouling materials. Photocatalytic mechanism of polyethersulfone-TiO2/MXene composite film (a) [124]. Copyright 2021, Elsevier. Photocatalytic antifouling mechanism diagram of Bi-based semiconductor heterojunction (b) [125]. Copyright 2018, Elsevier. Photocatalytic antifouling mechanism diagram of porphyrin covalent organic framework semiconductor heterojunction (c) [128]. Copyright 2022, American Chemical Society

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The light absorption ability of materials is influenced by the band gap of semiconductor materials. To achieve a more controllable semiconductor band gap, research has been conducted on porphyrin organic small molecule polymer semiconductors. In our study [128], an organic photocatalytic semiconductor was successfully prepared by modifying covalent organic framework materials with metal organic framework materials. By constructing a heterojunction framework, the dissociation of singlet excitons at the heterojunction interface is accelerated, leading to the formation of a direct Z-type heterojunction. This facilitates the separation and transfer of photogenerated carriers while inhibiting exciton annihilation, thereby enhancing overall molecular oxygen activation efficiency. Furthermore, the porous structure of the heterojunction provides numerous active sites and reactant transport channels, which further promotes the generation of various active substances. The abundant production of ROS contributes to enhanced antibacterial and antifouling properties in this heterojunction.

Photocatalytic antifouling antibacterial materials have been incorporated into the design of antifouling coatings [129]. Although current experimental results demonstrate the effective antifouling properties of photocatalytic antifouling agents, not all released ROS are utilized for antibacterial purposes within the coating. The migration mechanism of various ROS in the coating remains unclear; however, their impact on the coating is undeniable. Siloxane coatings exhibit promising potential as photocatalytic antifouling coatings due to their exceptional chemical and physical stability.

5 Summary and outlook

This article presents recent advancements in siloxane antifouling coatings and provide a comprehensive overview of the preparation methods and modification strategies employed for these coatings. Despite the development of various antifouling materials with exceptional durability, there remains ample scope for the exploration of novel materials exhibiting superior antifouling properties based on innovative concepts. This paper provides several clear conclusions regarding the current siloxane coating modification strategy, which may serve as a valuable direction for future research in this field. Furthermore, we contend that future research endeavors in the realm of siloxane antifouling coatings should prioritize the subsequent aspects.

  1. 1)

    Functional modified groups. Functional modification group is the key factor to improve the siloxane antifouling coating. On the one hand, it is important to develop and discover new functional groups. The dopamine group obtained by bionics can improve the adhesion strength of the coating. The PTMAO obtained by fish can improve the static antifouling performance. On the other hand, the development of multiple functional groups is also important. The utilization of metal coordination bonds has demonstrated significant potential in augmenting coating adhesion, antifouling performance, self-healing capability, and photocatalytic processes. Therefore, rational use and development of functional modification groups can improve the comprehensive properties of coatings.

  2. 2)

    Microstructure design. Microstructure design is a method based on theoretical calculation. The bottom-up design is carried out from the molecular level, and the macroscopic structure design of the siloxane coating is guided by theoretical calculation. In addition, based on theoretical calculations, a databased of coating structure-performance can be better established, thereby enriching structural design ideas.

  3. 3)

    Photocatalytic antifouling. As an environmentally friendly antifouling strategy, photocatalytic antifouling has shown potential advantages. However, whether ROS-based photocatalytic antifouling can be implemented in coatings is still unknown. It is imperative to conduct further investigations into the diffusion mechanism of diverse reactive oxygen species in environmentally-friendly photocatalytic antifouling coatings.

In conclusion, siloxane antifouling coatings hold significant potential for further exploration. Through new research methods and research strategies, it may be a new way to improve the comprehensive antifouling performance of siloxane coatings. This article provides readers with the latest updates on siloxane antifouling coating developments through this article, enabling them to develop enhanced solutions for marine industrial environments.