Effect of organic capping agents on the optical and photocatalytic activity of mesoporous TiO2 nanoparticles by sol–gel method
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In this work, the effect of capping agent effects on the structural, morphological, optical properties and photocatalytic removal of Rhodamine B (RhB) dye has been investigated. TiO2 nanoparticles were synthesized by a simple, fast and eco-friendly sol–gel method, in the presence of various capping agents, including ethylenediamine, polyvinyl alcohol (PVA), ethylene glycol, glucose and valine. The obtained TiO2 nanoparticles have been characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis, high resolution scanning electron microscopy and transmission electron microscopy, UV–visible absorption and photoluminescence (PL) spectroscopy. XRD pattern reveals the polycrystalline nature of TiO2 with anatase structure. The results revealed that the optical absorption band of TiO2 nanoparticles varied by capping agents. PL spectra exhibited visible emissions due to the formation of defects in the band gap region of TiO2 nanoparticles. The photocatalytic degradation of RhB dye by synthesized TiO2 nanoparticles using different capping agents was investigated under UV irradiation and the results demonstrated that TiO2 nanoparticles have appreciable photocatalytic activity for decomposing RhB dye when PVA was used as a capping agent. The results explained that the preparation of TiO2 nanoparticles showed a high efficiency in the removal of organic dyes.
KeywordsTiO2 UV-light Photoluminescence Capping agents RhB dye PVA
Transparent semiconducting metal oxide with high quality crystalline shape and size have much attention among the researchers due to their unique physical and chemical properties . They were utilized in numerous important industrial applications such as temperature sensor, solar energy conversion, gas sensor, photocatalysis and electrochemistry etc., due to their structural stability and properties are very different to those of bulk counterparts [2, 3, 4, 5]. Transition metal oxides are well known photocatalysts owing to their ability to generate hole-electron pairs . Titanium dioxide (TiO2) is one of the most extensively studied materials due to its thermal stability and harmless nature. It is multi-functional, cheap abundant and low cast materials. TiO2 is a n-type semiconductor  that can be formed in three different polymorphs rutile, brookite and antase [8, 9]. This different polymorphs exhibits different bandgap energies with 3.0 eV (rutile), 3.2 eV (anatase) and ≈ 3.2 eV (brookite) .
Various methods have been employed to synthesize metal oxide nanoparticles, such as microwave method , hydrothermal method , solid-state , solution route method , sol–gel method . Among these methods, the sol–gel method has low a temperature for crystallization resulting in large crystalline size and small surface area. Although, the final product would contain high carbon content when organic reagents are used during the process. The solvents used for sol–gel preparation method can be classified into aqueous or organic methods. In organic method solvents like, ethanol, methanol or ethylene glycol is widely used as solvents for metal oxide preparation [15, 16, 17]. However, these organic solvents are costly, inflammable and dangerous to the environment. In aqueous method, DI (deionized) water can be used as a solvent to from more stable, uniform and eco-friendly solution that is easy to prepare metal oxide nanoparticles . Hydrothermal and precipitation methods have been used to synthesize semiconductor metal oxides directly from solution, which resulted in the formation of a various range of particle size powder. This process is the most well-known method for the production of various metal oxides. Even if this process is able to synthesize crystals of substances which are unstable near the melting point, and the ability to synthesize large crystals of high quality.
Up to date, various surface modifications of metal oxides has been investigated by various capping agents, such as triethanolamine , trioctylphosphine oxide , triethanolamine , gelatin , l-cysteine . Functionalizing of TMOS surface by chemical agents can alter particle size, morphology, thermodynamic stability, optical properties, photocatalytic activity as well as antibacterial activity.
Various types of the photocatalyst can inhibit the quick recombination of electron–hole pairs the through different mechanism [24, 25]. Among all, organic capped metal oxide semiconductor photocatalyst, more efficiently involved in the suppression of electron–hole recombination via Schottky barriers to the Fermi energy of the selected metals usually being lower than that of the semiconductors. Cozzoli et al.  synthesized TiO2 in the presence of organic capping agents and compared the photocatalytic behavior by using Uniblue A as a pollutant. The results indicated that the photocatalytic effect was higher in the sample with both anatase and rutile structure. This is due to transfer of electrons from the anatase phase to the rutile phase which reduced the excitons recombination. In the present work, the photocatalytic performance of five samples of TiO2 nanoparticles was investigated by the photocatalytic degradation of RhB under UV–visible lighting. The structure, morphology, optical and photocatalytic activity of synthesized TiO2 nanoparticles were investigated in detail.
2 Materials and methods
2.1 Sample preparation
2.2 Characterization techniques
The X-ray diffraction (XRD) patterns of the sample were measured by using Philips X’pert PRO X-ray Diffractometer (PW3040/60) with CuKα radiation (45 kV, 40 mA). XRD patterns for the samples, examine were recorded in the region of 2 (= 10°–80°. The surface morphology and the size of the sample were characterized by (FESEM) Leica Cambridge S3600 and transmission electron microscopes (TEM) were taken with Philips CM12. The UV–visible optical absorption study was carried out using UV–visible spectrophotometer (Varian, Carry-50 Bio) in the wavelength range from 250 to 600 nm using quartz cuvette at room temperature. The excitation and photoluminescence (PL) spectra of the sample were measured by Perkin Elmer LS-45 luminescence spectrometer.
2.3 Photocatalytic experiment
To investigate the photocatalytic activity of the synthesized samples, degradation of RhB was performed under UV light irradiation at room temperature. A Hg lamp (UV) metal halide lamp with a 420 nm cutoff fleeter was used as the light source. An aqueous solution of RhB (100 mL 10 ppm) was prepared in a container and then 100 mg of the photocatalyst was dispersed in this solution. Before the irradiation, the catalyst/dye solution was kept in dark condition with constant magnetic stirring for 1 h to reach complete adsorption- desorption equilibrium. pH of the catalyst/dye solution was not adjusted. After 30 min intervals, 5 mL of the solution was taken and centrifuged to remove the photocatalyst particles before the photocatalytic experiment. The photo-reacted the solutions of the centrifuged sample were analyzed by measuring the change in absorption band maximum using the UV–visible spectrophotometer. After each photocatalytic reaction, the same materials were being centrifuged and dried to recycle for another test.
3 Results and discussion
3.1 Structure and structural analysis
Crystal size and band gab of TiO2 nanoparticles
Synthesized of TiO2 with different capping agents
Crystal size (nm)
Band gap energy (eV)
3.1.3 TEM analysis
3.1.4 Photoluminescence (PL) studies
3.1.5 Band gap energy
3.2 Photocatalytic studies
The potential UV light-driven photocatalyt of measporous TiO2 nanoparticles were synthesized by a sol–gel method for photodegradation of RhB dye. The UV–visible spectra showed that the band gap values of the photocatalyst decreased in the range 3.25–3.10 eV as capped with glucose, valine, EDA, EG and PVA. For rod-like TiO2 nanoparticles, the enhanced intensity of the PL band in blue and green emission rang results from the higher crystallinity, morphology, defects in surface gradually reduce the electron–hole recombination and consequently increase the photocatalytic degradation activity. The rod-like PVA capped measporous TiO2 nanoparticles demonstrated rapid and efficient RhB dye decomposition with a degradation rate of 70% within the initial 120 min, owing to the higher adsorption capacity and the better electron–hole pair separation under UV light leads to the generation of less harmless chemical.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
- 7.Nadzirah S, Hashim U (2013) Effects of annealing temperature on current-voltage characteristics of TiO2 thin film by sol–gel process on silicon substrate for biosensor application. In: 2013 IEEE regional symposium on micro and nanoelectronics (RSM), pp 167–170Google Scholar
- 21.Ayob MTA, Ahmad AR, Mohd HMK, Abdul Rahman I, Radiman S (2014) Effect of triethanolamine: ethylenediamine ratios on CuO nanoparticles prepared by ultrasound irradiation. In: AIP conference proceeding, vol 1614, pp 8–13Google Scholar
- 38.Magdalane CM, Kaviyarasu K, Vijaya JJ, Siddhardha B, Jeyaraj B, Kennedy J, Maaza M (2017) Evaluation on the heterostructured CeO2/Y2O3 binary metal oxide nanocomposites for UV/Vis light induced photocatalytic degradation of Rhodamine-B dye for textile engineering application. J Alloys Compd 727:1324–1337CrossRefGoogle Scholar
- 44.Magdalane CM, Kaviyarasu K, Raja A, Arularasu MV, Mola GT, Isaev AB, Al-Dhabi NA, Arasu MV, Jeyaraj B, Kennedy J, Maaza M (2018) Photocatalytic decomposition effect of erbium doped cerium oxide nanostructures driven by visible light irradiation: investigation of cytotoxicity, antibacterial growth inhibition using catalyst. J Photochem Photobiol B Biol 185:275–282CrossRefGoogle Scholar