Composite TiO2 Films Research Articles

Composite TiO2-SiO2-REOs photocatalysts for water treatment: Degradation kinetics of monuron and its intermediates

Modifying a hydrophilic TiO2 photocatalyst by hydrophobic rare-earth oxides (REOs) may promote affinity to hydrophobic non-polar species, thus improving photocatalytic activity. The present work was focused on the kinetics of photocatalytic degradation of the polar Acid Orange 7 (AO7) and of the non-polar herbicide monuron (3-(4-chlorophenyl)-1, 1-dimethylurea) and its degradation intermediates in the presence of composite TiO2 films containing SiO2 binder and different REOs (CeO2, La2O3, Er2O3, Yb2O3). The addition of REOs particles into the TiO2/SiO2 composite matrix resulted in an increase in the initial degradation rate of monuron from 2.1 nmol min−1cm−2 to 2.7–3.0 nmol min−1cm−2. Furthermore, the ratios between the initial degradation rates of monuron to those of AO7 were significantly higher for composite films containing REOs showing a positive effect on the removal of the non-polar monuron molecules for all REOs. A comparison between the kinetics with the various types of photocatalysts reveals that the positive impact of SiO2 and that of SiO2/REOs on the kinetics was not limited to the conversion of monuron but to the overall mineralization. The main novelty represents the fact although the rate of TOC decrease varied among photocatalysts, the kinetics of intermediates is not significantly influenced.

Composite TiO2 films modified by CeO2 and SiO2 for the photocatalytic removal of water pollutants.

TiO2 particles of high photocatalytic activity immobilised on various substrates usually suffer from low mechanical stability. This can be overcome by the utilisation of an inorganic binder and/or incorporation in a robust hydrophobic matrix based on rare-earth metal oxides (REOs). Furthermore, intrinsic hydrophobicity of REOs may result in an increased affinity of TiO2-REOs composites to non-polar aqueous pollutants. Therefore, in the present work, three methods were used for the fabrication of composite TiO2/CeO2 films for photocatalytic removal of dye Acid Orange 7 and the herbicide monuron, as representing polar and non-polar pollutants, respectively. In the first method, the composition of a paste containing photoactive TiO2 particles and CeCl3 or Ce(NO3)3 as CeO2 precursors was optimised. This paste was deposited on glass by doctor blading. The second method consisted of the deposition of thin layers of CeO2 by spray coating over a particulate TiO2 photocatalyst layer (prepared by drop casting or electrophoresis). Both approaches lead to composite films of similar photoactivity that of the pure TiO2 layer, nevertheless films made by the first approach revealed better mechanical stability. The third method comprised of modifying a particulate TiO2 film by an overlayer based on colloidal SiO2 and tetraethoxysilane serving as binders, TiO2 particles and cerium oxide precursors at varying concentrations. It was found that such an overlayer significantly improved the mechanical properties of the resulting coating. The use of cerium acetylacetonate as a CeO2 precursor showed only a small increase in photocatalytic activity. On the other hand, deposition of SiO2/TiO2 dispersions containing CeO2 nanoparticles resulted in significant improvement in the rate of photocatalytic removal of the herbicide monuron.

On the Role of γ-Fe2O3 Nanoparticles and Reduced Graphene Oxide Nanosheets in Enhancing Self-Cleaning Properties of Composite TiO2 for Cultural Heritage Protection

The durability of novel metallic artifacts and buildings is an open issue, and the role of smart protecting coatings in extending these artifacts’ lifetimes is crucial. In this paper, the role of γ-Fe2O3 nanoparticles and reduced graphene oxide (rGO) nanosheets on enhancing the self-cleaning properties of composite TiO2 films and reducing metal alterations due to contact with acid rain and pollutants is investigated. The photocatalytic assessment of the TiO2 based films indicates that there are optimum contents for γ-Fe2O3 and rGO, which confer the film lower bandgap and tune the TiO2 anatase/rutile ratio. By adding a proper content of γ-Fe2O3, wettability is reduced both in dark and under illumination, which could be related to higher roughness. γ-Fe2O3 overloading causes increasing crack density and eventually a fully cracked structure. Adding an appropriate amount of rGO causes a sharp increase in roughness, due to the stacking of rGO nanosheets, while simultaneously avoiding cracking. At higher contents of rGO, wettability further decreases due to higher amounts of hydroxyl groups bound onto rGO; also in this case, overloading causes film cracking. Evaluation of self-cleaning performance and discoloration resistance under soiling and acid rain simulated tests demonstrates that proper loadings of γ-Fe2O3 and rGO present higher efficiency thanks to higher superhydrophilic tendency and higher photocatalytic activities, as well as an efficient barrier effect.

Light management in TiO2 thin films integrated with Au plasmonic nanoparticles

The light-harvesting properties of metal oxide thin films can be remarkably increased by the introduction of plasmonic nanostructures, leading to higher efficiencies in photovoltaic or photoelectrochemical devices. In the prototypical material combination, Au-TiO2, nano- and mesoscale porosity of TiO2 is desirable to improve not only the light-harvesting, but also the available surface area for chemical reactions. Moreover, great attention has been given to the control of size and shape of Au nanoparticles (NPs) to tune the overall optical properties of the film. In this work, we investigate the optical properties of composite Au-TiO2 films exhibiting remarkable light scattering properties. TiO2 is characterized by a tree-like hierarchical morphology produced by pulsed laser deposition, and two different configurations for Au integration, namely Au on top and at the bottom of TiO2, are explored while varying the size of Au NPs. The hierarchical oxide morphology allows to achieve superior scattering properties after the combination with Au NPs with respect to films obtained from a commercial paste deposition. Both the Au-top and Au-bottom configurations enable to tune the plasmonic properties of Au NPs. Specifically, outstanding scattering properties are exhibited by the composite TiO2 film grown on top of large (∼100 nm) Au NPs. These results show the potential interest of employing such integrated films as photoanodes in dye-sensitized or perovskite-based solar cells, or in photoelectrochemical cells for water splitting. An analogous approach can be employed for alternative materials, both considering the plasmonic structures as well as the semiconductor layer.

Hydrophilic, antibacterial and photocatalytic properties of TiO2 composite films modified by the methods of N+ ion implantation and doping of CNTs under visible light irradiation

The carbon nanotubes (CNTs) doped TiO2 films were synthesized using the sol-gel method. To obtain better visible light induced properties, the CNTs-TiO2 composite films were implanted by nitrogen ions (N+ ions) with ions energy of 40 keV and doses of 5 × 1015, 1 × 1016, 5 × 1016, and 1 × 1017 ions/cm2 using an implanter equipped with Freeman ion source. SEM, XRD, XPS and UV–Vis spectra were utilized to explore the surface morphology, crystal structure, chemical composition and optical characteristics of the composite films respectively. The visible light induced properties of the composite films were examined by the experiments of degradation of methylene orange, water contact angle measurements and sterilization of E. coli. The XPS results showed the replacement of oxygen by implanted N+ ions in TiO2 lattice. The UV–Vis spectra exhibited the red-shift for all implanted samples. Meanwhile, the results of visible light induced experiments showed that the photocatalytic degradation efficiency and antibacterial activity of TiO2 composite films were enhanced, and the water contact angle decreased, which indicates that those properties of TiO2 composite films were improved. The best performance of hydrophilic, photocatalytic and antibacterial properties of the composite TiO2 films was corresponding to the implanted dose of 1 × 1016, 5 × 1016 and 1 × 1017 ions/cm2 respectively.

Well-connected microsphere-nanoparticulate TiO2 composites as high performance photoanode for dye sensitized solar cell

Anatase TiO2 microspheres with smooth and fibrous morphology (SμS and FμS) resembling laddu and dandelion are synthesized by solvothermal and hydrothermal methods, respectively. A detailed analysis of these two microstructures using XRD, UV–vis spectroscopy, electron microscopy and surface area measurement techniques are presented. Photoanodes fabricated using these microspheres and their composites with nanoparticles (Degussa P25) are tested for photovoltaic (PV) performance using a standard Grätzel-type dye-sensitized solar cell (DSSC) configuration. The DSSC made up of SμS and FμS microspheres exhibit an efficiency (η) of 8.4% and 6.4% respectively, in comparison to η≈7.1% for nanoparticulate P25. Further enhancement in η is realized in the composite photoanode films made of porous SμS/FμS microspheres filled with nanoparticulate P25 TiO2. High power conversion efficiency of 8.9% (for cell area of 0.5cm2 and thickness of ~25µm) was achieved in composite photoanode film consisting of 80wt% SμS and 20wt% P25. Electrochemical impedance spectroscopy studies reveal a low interfacial resistance in composite photoanodes, which is desired for efficient electron generation and transport. Composite microspheres filled with P25 nanoparticles in their voids show enhanced efficiency than the mesoporous TiO2 microspheres. Thus, SμS-nanoparticle composite TiO2 film possesses essential attributes necessary for an efficient photoanode viz. large surface area for dye adsorption, good connectivity between nanocrystallites for the efficient electron transport, and higher scattering properties for better light harvesting efficiency.

The Effect of Scattering Layer on the Performance of Dye-Sensitized Solar Cells Using TiO2 Hollow Spheres/TiO2 Nanoparticles Films as Photoanodes.

TiO2 hollow spheres were successfully synthesized using poly styrene as the template. Dye-sensitized solar cells are fabricated based on double-layered composite films of TiO2 nanoparticles and TiO2 hollow spheres. The photoelectric conversion performances of Dye-sensitized solar cells based on TiO2 nanoparticles/TiO2 nanoparticles, TiO2 nanoparticles/TiO2 hollow spheres and TiO2 hollow spheres/TiO2 hollow spheres double-layered films are investigated, and their photoelectric conversion efficiencies were determined to 4.52, 7.10 and 5.48%, respectively. Dye-sensitized solar cells based on double layered composite films of TiO2 nanoparticles and TiO2 hollow spheres exhibit the highest photo-electric conversion efficiency mainly due to the combined effect of two factors, the high light scattering of over-layer hollow spheres that enhance harvesting light of the Dye-sensitized solar cells and the under-layer TiO2 nanoparticle layer that ensures good electronic contact between TiO2 film and FTO conducting glass. The double layered composite TiO2 film electrodes are a promising development in enhancing the performance of dye-sensitized solar cells.

TiO<sub>2</sub>-Based Composite Film for the Photodegradation of Methyl Green

A simple process was developed for preparation of highly photoactive Fe and S codoped TiO2-SiO2-ZnO composite film. The Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the composite TiO2 sample was 432.5m2g-1, while that of the pure TiO2 was 103.4m2g-1. The diffuse reflectance measurements exhibited an extension of light absorption into the visible region for the composite TiO2. The photoluminescence (PL) spectra analysis indicated that the electron-hole recombination rate was effectively inhibited in the composite TiO2. The photocatalytic activities of the TiO2 films were evaluated by the photocatalytic decomposition of methyl green in aqueous solution. The composite TiO2 film exhibited excellent photocatalytic activities compared to pure TiO2 film.

Improved performance of dye-sensitized solar cells using TiO2 nanotubes infiltrated by TiO2 nanoparticles using a dipping–rinsing–hydrolysis process

An efficient back-illuminated dye-sensitized solar cell (DSSC) is made with a flexible Ti-foil based photoanode composed of a composite TiO2 film with TiO2 nanotubes (TNT) and TiO2 nanoparticles (TNP). The composite TiO2 film is fabricated through a novel dipping–rinsing–hydrolysis (DRH) process by inserting TiO2 into TNT and sintering the product to form TNP inside TNT. By directly placing TiO2 nanoparticles into TNT, the former grow internally from the base of TNT to occupy it completely. This solves previous problems of incomplete filling of TNP into TNT, which used partial penetration of TiCl4 reactant from the top of the TNT. In the present case, the TNP are grown from the base of TNT. A DSSC containing TNT and TNP prepared in this way shows a photoelectric efficiency of 6.45%, which is much higher than that (4.21%) of a DSSC with untreated TNT. The films are characterized by using scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The improvement in the photoelectric efficiency is explained by using electrochemical impedance spectroscopy (EIS), incident photon-to-current conversion efficiency (IPCE) analysis, and UV-absorption spectra analysis.

Composite TiO<SUB>2</SUB> Film with Quantum Dots Fabricated Through a Sol–Gel Process

A novel strategy has been developed to fabricate composite TiO2 films with CdTe quantum dots (QDs). Aqueous CdTe QDs with green-, yellow-, and red-emitting were prepared using thioglycolic acid as a capping agent. The QDs revealed high photoluminescence (PL) efficiencies under optimal preparation conditions. TiO2 sol was obtained by the controlling hydrolysis of tetrabutyl titanate in ethanol with poly(vinyl pyrrolidone). Diethanolamine was added to prevent the QDs from PL quenching generated by surface defects. After embedding the QDs in composite TiO2 film, the PL intensity of the QDs decreased because of the excitation and recombination between the QDs and TiO2. The PL peak wavelength of the QDs in films revealed a slight blue shift compared with their initial ones. The blue shift degree of the PL peaks depended on the properties of the QDs. Red-emitting CdTe QDs revealed a small blue shift of 1 nm while green-emitting ones revealed a blue shift of 7 nm. This indicated red-emitting QDs with high stability against incorporation. Facile preparation and excellent properties including high PL brightness, multicolor emission, and high stability make these films important applications in various fields.

Improvement of Performance of Dye-Sensitized Solar Cell by Using Composite Nanoparticulate Photoelectrode Films

Photoelectrodes using different nanoparticle size and film thickness of TiO2 were prepared by screen-printing and post annealing method with the objective of optimizing the photovoltaic performance of dye-sensitized solar cells (DSSCs). The effect of nanoparticle size and film thickness of the TiO2 on the performance of DSSCs was investigated. Based on the effect investigation, composite nanoparticulate TiO2 film electrodes were designed and fabricated to improve the photovoltaic performance of the DSSCs. The enhanced conversion efficiency was achieved in the DSSCs by introducing light scattering layer and additional dye adsorption nanoparticle layer to form composite TiO2 films, and by optimizing the nanoparticle size and film thickness. The improvement mechanism was also discussed.

The Preparation of Composite TiO2 Electrodes for Dye‐Sensitized Solar Cells

AbstractIn this work, the 1D titania nanorods (Tnr) were successfully prepared from commercial Degussa P25 powders (DP25) by alkaline hydrothermal method and applied to fabricate the composite TiO2 photoanodes for DSSCs. The morphology of the obtained 1D titania nanomaterials is controllable and is dependent on the post heat treatment. Anatase Tnr (a‐Tnr) with diameters of 50‐200 nm and lengths of several hundreds nanomaters was obtained after calcination at 600 °C. The BET surface area was 20 m2/g. For DSSCs study, the composite TiO2 pastes with a range of DP25/Tnr weight ratio were used for photoanodes. It was found that by adding the Tnr, the photoconversion efficiency (η) increases, yet, due to the lower surface area of a‐Tnr, the DSSC efficiency is deteriorated for higher Tnr content. The DSSC performance also largely depends on the thickness of composite TiO2 films. The best efficiency of ∼7.56% (Voc = 0.81V, Jsc = 14.9 mA/cm2, FF = 0.63) was achieved for the D80a20 sample (80% DP25, 20% Tnr) with film thickness of 20 μm. To realize the electron transport properties of composite film, the DSSCs were investigated by electrochemical impedance spectroscopy. The results indicated that the electron transport efficiency is affected by the morphology and composition of the composite TiO2 electrodes.

Nanostructure Thin Films of Titanium Dioxide Coated on Glass and Its Anti UV Effect for Living Organisms

The increasing use of ultraviolet (UV) light in medicine, industrial environments, for cosmetic use, and even in consumer products necessitates that greater attention be paid to the potential hazards of this type of electromagnetic radiation. To avoid any adverse effects of exposure to this type of radiation, suitable protection filters were produced to block UV bands. Nanostructure composite and thin film of titanium dioxide coatings on glass have been prepared by the sol—gel method. TiO2 sol suspension was prepared by first adding titanium tetra isopropoxide (Ti(OPr)4 or TTP) to a mixture of ethanol and HCl (molar ratio TTP:HCl:EtOH:H2O = 1:1.1:10:10) and then adding a 2 wt.% solution of hydroxyl ethyl cellulose (HEC) as dispersant followed by of stirring. Precalcined TiO2 nanopowder was mixed with a sol and heat treated. Thin and composite films were deposited on the glass substrate (microscope glass slide) by spincoating them at ambient conditions. After drying, samples were heated to 500 °C. The resulting films were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). The purpose of our study was to determine if thin and composite TiO2 films with ultraviolet light have any effect on the growth of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus) and Bacillus species (Bacillus sp.) We have seen unusual results in which TiO2 thin and composite films protect E. coli, S. aureus and Bacillus sp from UV light. The survival of E. coli with UV alone was 3.2 % while with UV and TiO2 composite film was 91%. The UVabsorbing coatings are transparent, colorless, and exhibit high optical quality. The UV-protective coatings offer an easy method to protect the living organisms against UV.

A comparative study on physicochemical properties and photocatalytic behavior of two different nanostructure composite TiO2 films coated on glass substrate

Two types of composite films (MPC500SGF-MC and ANPSGF-MC) have been synthesized by a modified sol-gel method using different particle sizes of TiO2 powder. Methyl cellulose was added as a template to the sol for stress reduction which improved not only the amount of crystalline material immobilized on the support, but also the nanosize of the films calcined at 500°C. The physicochemical properties, including surface morphology, crystal size and adhesion on the glass substrate, were investigated by SEM and XRD. The photocatalytic activities of the films were compared using methyl orange (MO) as a model organic contaminant in water. The results on photocatalytic degradation of MO showed that the increase in photocatalytic activity for Aldrich TiO2 powder (ANP) calcined at 500°C, compared with that of Millenium PC500 composite film. The optimum degradation conditions of MO solution are determined. This study proves that particle size of starting TiO2 material is important for the preparation of nanostructure...

Preparation of self-supporting hierarchical nanostructured anatase/rutile composite TiO2 film

Via the combination of an electrospinning method with a hydrothermal reaction, a large-scale cedar-like hierarchical nanostructured TiO(2) film with an anatase/rutile composite phase was fabricated.

Organization of supramolecular assembly of 9-mesityl-10-carboxymethylacridinium ion and fullerene clusters on TiO2 nanoparticles for light energy conversion

TiO2 nanoparticles modified with composite nanoclusters of 9-mesityl-10-carboxymethylacridinium ion (Mes–Acr+–COOH) and fullerene (C60) in acetonitrile–toluene (3 : 1, v/v) were deposited as thin films on nanostructured SnO2 electrode using an electrophoretic technique. The composite TiO2 films have broad as well as high absorbance properties, exhibiting a photoactive response under visible light excitation using I3−/I− redox couple, in contrast with the reference multilayer films composed of the single component. This indicates that the composite cluster TiO2 film based on 9-mesityl-10-carboxymethylacridinium ion and fullerene harvests light widely in the visible region due to organization of the supramolecular assembly. In the case of a monolayer system of TiO2 nanocrystallites modified with Mes–Acr+–COOH, however, no net photocurrent is observed in the photocurrent action spectrum. This indicates that TiO2 nanoparticles act as materials to organize composite molecules rather than as those to accept electrons. An incident photon-to-photocurrent generation efficiency (IPCE) of 37% has been achieved at an applied bias potential of 0.2 V vs. SCE in the Mes–Acr+–COOH/C60 composite system using TiO2 nanoparticles.