Photocatalytic Decomposition of Formic Acid Under Visible Light Irradiation Over V-ion-implanted TiO2 Thin Film Photocatalysts Prepared on Quartz Substrate by Ionized Cluster Beam (ICB) Deposition Method

Unique visible-light-responsive TiO₂ photocatalysts (λ>450 nm) were successfully developed by implantation of V ions into the TiO₂ thin films prepared on a quartz substrate by an ionized cluster beam (ICB) deposition method. After V ions implantation into TiO₂ thin film, the photocatalytic activity of the thin films for the decomposition of formic acid into CO₂ and H₂O was found to proceed efficiently under visible light irradiation longer than 450 nm. The TiO₂ thin film photocatalysts were characterized by XRD, UV-vis, XPS, FE-SEM and AFM.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

Photocatalytic functional coatings of TiO2 thin films on polymer substrate by plasma enhanced atomic layer deposition

We prepared photocatalytic TiO₂ thin films which exhibited relatively high growth rate and low impurity on polymer substrate by plasma enhanced atomic layer deposition (PE-ALD) from Ti(NMe₂)₄ [tetrakis (dimethylamido) Ti, TDMAT] and O₂ plasma to show the self-cleaning effect. The TiO₂ thin films with anatase phase and bandgap energy about 3.3 eV were deposited at growth temperature of 250 °C and the photocatalytic effects were compared with commercial Activ glass. From contact angles measurement of water droplet and photo-induced degradation test of organic liquid, TiO₂ thin films with anatase phases showed superhydrophilic phenomena and decomposed organic liquid after UV irradiation. The anatase TiO₂ thin film on polymer substrate showed highest photocatalytic efficiency after 5 h UV irradiation. We attribute the highest photocatalytic efficiency of TiO₂ thin film with anatase structure to the formation of suitable crystalline phase and large surface area.     

Photocatalytic decomposition of NO on titanium oxide thin film photocatalysts prepared by an ionized cluster beam technique

Transparent TiO₂ thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by an ionized cluster beam (ICB) method. The UV‐VIS absorption spectra of these films show specific interference fringes, indicating that uniform and transparent TiO₂ thin films are formed. The results of XRD measurements indicate that these TiO₂ thin films consist of both anatase and rutile structures. UV light (λ > 270 nm) irradiation of these TiO₂ thin films in the presence of NO led to the photocatalytic decomposition of NO into N₂, O₂ and N₂O. The reactivity of these TiO₂ thin films for the photocatalytic decomposition of NO is strongly dependent on the film thickness, i.e., the thinner the TiO₂ thin films, the higher the reactivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of V and Zn codoping on the microstructures and photocatalytic activities of nanocrystalline TiO2 films

To enhance the photocatalytic activity of TiO₂, V and Zn co-doped TiO₂ films were synthesized by the sol–gel method. The experimental results indicated that the films were composed of round-like nano-particles or aggregates. V and Zn codoping could not only obviously increase the specific surface area of TiO₂ but also result in the narrowed band gap of TiO₂ sample. The photocatalytic activities of the TiO₂ films were evaluated by the photocatalytic decomposition of organic dyes in aqueous solution. Compared with un-doped TiO₂ film or single doped TiO₂ film, V and Zn co-doped TiO₂ film exhibited excellent photocatalytic activities under both UV light and visible light. The improvement mechanism by V and Zn codoping was also discussed.     

AUGMENTATION OF PHOTOCATALYTIC ACTIVITY OF TiO2 THIN FILMS PREPARED BY A SOL-GEL TECHNIQUE

In order to increase the photocatalytic activity on TiO₂ thin film per its external surface area, the structure of flat thin film was modified by adding a small amount of polyethylene glycol (PEG) to TiO₂ sol solution. By firing PEG contained in a TiO₂ gel film, a porous structure was developed. The photocatalytic activities of the thin films prepared thus were evaluated by the degradation of 2-propanol in the aqueous solutions under black light illumination. The photocatalytic activity of TiO₂ thin film prepared with added PEG 400 by 2.6 wt% or PEG 2000 by 9.5 wt% was increased by about 30% as compared to that prepared without added PEG.     

Photo-Generated Activities of Nanocrystalline TiO<Subscript>2</Subscript> Thin Films

Transparent nanocrystalline TiO₂ thin films with high photocatalytic activity and photo-induced wettability were successfully deposited on a glass slide. Crystal phase transformations and particle size of TiO₂ were investigated. Structural and morphological properties of the films were investigated. The photocatalytic activity of the TiO₂ films was evaluated. It is found that the photocatalytic activity of TiO₂ thin films is significantly decreased by increasing the annealing temperature, which results in a decrease in BET surface area and an increase in crystal size. In addition, increasing film thickness within a certain range significantly improves the photocatalytic activity without causing crack formation of the TiO₂ films. Photocatalytic oxidation and photo-induced wettability conversion on the films were investigated. It is found that photo-induced hydrophilic conversion is observed even on the samples annealed at high temperature. The best photo-generated activities are obtained by optimization of dip-coating cycles and annealing temperatures.     

Enhanced photocatalytic activity of highly transparent superhydrophilic doped TiO2 thin films for improving the self-cleaning property of solar panel covers

Undoped and metal doped nanocrystalline TiO₂ transparent thin films were synthesized on glass substrates via sol-gel/dip-coating method. TiO₂ thin film coatings can be applied to the surfaces of solar panels to impart self-cleaning properties to them. The structural and optical properties of few nanometer-thick films were characterized by XRD, SEM, CA, AFM, XPS, and UV–Vis spectrophotometry techniques. The stoichiometric TiO₂ films crystallized in anatase phase, with a particle size of ～100 nm, which were uniformly distributed on the surface. The prepared films with a roughness of ～1–5 nm, increased the hydrophilicity of the glass surface. Reducing the amount of Ti precursor (X) favored the improvement of film quality. To improve the photocatalytic activity of the TiO₂ thin film, it was doped with Ni, Cd, Mo, Bi and Sr metal ions. The effect of metal doping on the photocatalytic activity of the films was investigated using the degradation process of methylene blue (MB) dye as the model contaminant. Among the prepared coatings, the Sr–TiO₂ film showed the highest efficiency for MB degradation. It increased the dye degradation efficiency of the films under both UV and Vis lights. The kinetic investigations also showed that the degradation of MB by TiO₂ and M ? TiO₂ films obeyed the pseudo-first order kinetics.     

Thickness effect in the photocatalytic activity of TiO2 thin films derived from sol-gel process

TiO₂ films in various thicknesses were prepared by sol-gel method, and their photocatalytic activities in the decomposition of gaseous 2-propanol were evaluated. It was found that the photocatalytic activities of transparent TiO₂ films increase with the increase of film thickness: The photocatalytic activity of TiO₂ films in 670 nm-thickness was 3.7 times that of films in 70 nm-thickness. We proposed that the higher photocatalytic activities for the thicker TiO₂ films originate from the greater amount of photogenerated electron and hole pairs, which are transferred from the inside to the surface of TiO₂ films. We also provided some experimental evidences supporting this mechanism.     

Photoelectrocatalytic degradation of bisphenol A in aqueous solution using a Au–TiO2/ITO film

A series of Au–TiO₂/ITO films with nanocrystaline structure was prepared by a procedure of photo-deposition and subsequent dip-coating. The Au–TiO₂/ITO films were characterized by X-ray diffraction, scanning electronic microscopy, electron diffraction, X-ray photoelectron spectroscopy, and UV–VIS diffuse reflectance spectroscopy to examine the surface structure, chemical composition, the chemical state of metal, and the light absorption properties. The photocatalytic activity of the Au–TiO₂/ITO films was evaluated in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of bisphenol A (BPA) in aqueous solution. Compared with a TiO₂/ITO film, the degree of BPA degradation using the Au–TiO₂/ITO films was significantly higher in both the PC and PEC processes. The enhancement is attributed to the action of Au deposits on the TiO₂ surface, which play a key role by attracting conduction band photoelectrons. In the PEC process, the anodic bias externally applied on the illuminated Au–TiO₂/ITO film can further drive away the accumulated photoelectrons from the metal deposits and promote a process of interfacial charge transfer.     

Preparation, crystal structure, and photocatalytic activity of TiO2 films by chemical vapor deposition

Photocatalytic activities of TiO₂ films were experimentally studied. TiO₂ films with different crystal structures (amorphous, anatase, rutile) were prepared by a Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD) at different reaction temperatures and also by a Sol-Gel method using TTIP (Titanium Tetra Iso-Pro-poxyde). The Effect of CVD preparation method, CVD reaction conditions, crystal structure and wave-length of UV light on the photocatalytic decomposition rate of methylene blue in aqueous solution were studied. First, the characteristics of CVD preparation of TiO₂ films, such as the CVD film growth rate, crystal structure and morphology of the grown TiO₂ films, were experimentally studied as a function of CVD reaction temperature. Secondly, photocatalytic activities of TiO₂ films were evaluated by using two types of photo-reactors. The results indicated that TiO₂ films prepared by CVD exhibit higher photocatalytic activity than a catalyst prepared by the Sol-Gel method. Among the CVD grown TiO₂ films, anatase and rutile showed high photocatalytic activities. However, amorphous TiO₂ films showed lower activities. The activity of the photocatalysts of anatase films was excellent under all types of UV-lamps. The activity of CVD-prepared anatase films was four to seven times higher than that of photocatalyst films prepared by the Sol-Gel method.     

Photocatalytic decomposition of NO under visible light irradiation on the Cr‐ion‐implanted TiO2 thin film photocatalyst

Transparent TiO₂ thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by the ionized cluster beam (ICB) method. In order to improve the photocatalytic performance of these thin films under visible light irradiation, transition metal ions such as Cr and V were implanted into the deep bulk inside of the films using an advanced metal‐ion‐implantation technique. The UV‐vis absorption spectra of these metal‐ion‐implanted TiO₂ thin films were found to shift smoothly toward visible light regions, its extent depending on the amount and kinds of metal ions implanted. Using these metal‐ion‐implanted TiO₂ thin films as photocatalysts, the photocatalytic decomposition of NO_x into N₂ and O₂ was successfully carried out under visible light (λ 450 nm) irradiation at 275 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optical and photoelectrochemical properties of a TiO2 thin film doped with a ruthenium–tungsten bimetallic complex

Optical and photoelectrochemical (PEC) properties of a TiO₂ thin film electrode doped with a new variation of ruthenium–(4,4′dimethyl-2,2′-bipyridine)–isothiocyanato–tungsten[bis-(phenyl-1,2-ethilenodithiolenic)] bimetallic complex (BM) were investigated. Physical adsorption process was used to immobilise the BM on the TiO₂ thin film. Crystalline structure and surface morphology of the thin films were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) techniques. N3 commercial dye was also used as a dopant to the TiO₂ films for comparison. Light absorption spectra and bandgap energy of the thin films were determined using UV–vis spectroscopy. Light absorption of the TiO₂ thin film doped with BM was better than the TiO₂ doped with the N3 commercial dye. Band edges of the TiO₂ thin film and the BM were determined via cyclic voltammetry (CV) measurements. Top-edge of the BM valence band (VB) was more positive than the bottom edge of the conduction band (CB) of the TiO₂ film (vs. NHE). PEC analysis indicated that photocurrent of TiO₂ doped with the BM electrode was higher than TiO₂ doped with the N3 in the beginning of illumination process, but the performance was defeated after a while. Based on the optical properties and the PEC analyses, BM has potential to be used as dye sensitisers for a PEC cell.     

Influence of Metal (Au, Ag) Micro-Grid on the Photocatalytic Activity of TiO2 Film

In this paper, we prepared TiO₂ thin film with the surface modified by a connected Au micro-grid via a microsphere lithography strategy, and the modified films show higher photocatalytic activity than the pure TiO₂ film. The photocatalytic activity improved as Au loading increased, obtaining the best performance at a certain loading amount, and then decreased at higher loading amount. This behavior, not observed in TiO₂ films modified with Ag micro-grid, can be attributed to the relationship between the energetic positions and the metal clusters size.     

Photocatalytic properties of TiO2 sol-gel modified nanocomposite films

TiO₂ nanocomposite films with different concentrations of TiO₂ MT-150A nanoparticles were immobilized on glass substrates using a dip coating process. The crystalline structure and surface chemical state of nanocomposite film properties were examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The specific surface area and morphology of TiO₂ MT-150A nanoparticles were evaluated by the BET method and Field Emission Scanning Electron Microscopy (FE-SEM). The photocatalytic activities of films were evaluated by the methyl orange decoloring rate. XPS measurements showed that the oxygen amount (%) was related to the film composition. The composite film with 10 g/L MT-150A loading yielded the highest amount of surface oxygen (26.82%) and TiO₂ rutile showed the lowest amount of surface oxygen (13.67%) in the form of surface hydroxyl groups. The remaining oxygen was identified as lattice oxygen. In addition, the nanocomposite film with 10 g/L MT-150A loading yielded the highest photocatalytic activity.     

Preparation and photocatalytic activity of Keggin-ion tungstate and TiO2 hybrid layer-by-layer film composites

Keggin ions (PW₁₂O₄₀³⁻ (PW₁₂), SiW₁₂O₄₀⁴⁻ (SiW₁₂), H₂W₁₂O₄₀⁶⁻ (H₂W₁₂)) and TiO₂ hybrid thin films were prepared using the layer-by-layer method. Their photocatalytic activities were investigated using gaseous 2-propanol decomposition. All films were transparent in the visible wavelength range. For 2-propanol decomposition, H₂W₁₂ was the most effective for the combination with TiO₂ despite having the smallest TiO₂ deposition amount. The photocatalytic activity of the PW₁₂–TiO₂ hybrid film was increased 2.3 times by visible light with UV illumination. This increase was less remarkable for hybrid films of other Keggin ions, suggesting that the visible light excitation of reduced PW₁₂ plays an important role in the enhancement of 2-propanol decomposition.     

Microwave photocatalysis III. Transition metal ion‐doped TiO2 thin films on mercury electrodeless discharge lamps: preparation,characterization and their effect on the photocatalytic degradation of mono‐chloroacetic acid and Rhodamine B

BACKGROUND: Mercury electrodeless discharge lamps (Hg‐EDLs) were used to generate UV radiation when exposed to a microwave field. EDLs were coated with doped TiO₂ in the form of thin films containing transition metal ions Mⁿ⁺ (M = Fe, Co, Ni, V, Cr, Mn, Zr, Ag). Photocatalytic degradation of mono‐chloroacetic acid (MCAA) to HCl, CO₂, and H₂O, and decomposition of Rhodamine B on the thin films were investigated in detail. RESULTS: Polycrystalline thin doped TiO₂ films were prepared by dip‐coating of EDL via a sol–gel method using titanium n‐butoxide, acetylacetone, and a transition metal acetylacetonate. The films were characterized by Raman spectroscopy, UV/Vis absorption spectroscopy, X‐ray photoelectron spectroscopy (XPS), electron microprobe analysis and by atomic force microscopy (AFM). The photocatalytic activity of doped TiO₂ films was monitored in the decomposition of Rhodamine B in water. Compared with the pure TiO₂ film, the UV/Vis spectra of V, Zr and Ag‐doped TiO₂ showed significant absorption in the visible region, and hence the photocatalytic degradation of MCAA had increased. The best apparent degradation rate constant (0.0125 min^?1), which was higher than that on the pure TiO₂ film by a factor of 1.7, was obtained with the Ag(3%)/TiO₂ photocatalyst. The effect of doping level of vanadium acetylacetonate on the photocatalytic efficiency of the V‐doped TiO₂ was determined. CONCLUSIONS: Transition metal ion‐doped TiO₂ thin films showed significant absorption in the visible region. The metal doped TiO₂ photocatalyst (with an appropriate amount of V, Zr and Ag) on the Hg‐EDLs increased the degradation efficiency of MCAA in a microwave field. Copyright © 2009 Society of Chemical Industry     

Excellent antimicrobial properties of mesoporous anatase TiO2 and Ag/TiO2 composite films

Optically transparent, crack-free, mesoporous anatase TiO₂ thin films were fabricated. The Ag/TiO₂ composite films were prepared by incorporating Ag in the pores of TiO₂ films with an impregnation method via photoreduction. The as-prepared composite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectronic spectra (XPS) and N₂ adsorption. The release behavior of silver ions in the mesoporous composite film was also studied. Moreover, the antimicrobial behaviors of the mesoporous film were also investigated by confocal laser scanning microscopy. The antibacterial activities of the composite films were studied by a fluorescence label method using Escherichia coli (E. coli) as a model. The as-prepared mesoporous TiO₂ films showed much higher antimicrobial efficiency than that of glass and commercial P25 TiO₂ spinning film. The facts would result from the high surface area, small crystal size and more active sites for the mesoporous catalysis. After the doping of Ag, a significant improvement for the antimicrobial ability was obtained. To elucidate the roles of the membrane photocatalyst and the doped silver in the antimicrobial activity, cells from a silver-resistant E. coli were used. These results indicated that Ag nanoparticles in the mesoporous were not only an antimicrobial but also an intensifier for photocatalysis. The as-prepared mesoporous composite film is promising in application of photocatalysis, antimicrobial and self-clean technologies.     

Synthesis, characterization and photocatalytic properties of sol-gel TiO2 films

The application of heterogeneous photocatalysis is described as an advanced oxidation process (AOP) for the degradation of the diazo reactive dye using immobilized TiO₂ as a photocatalyst. Starting TiO₂ solutions were prepared with and without the addition of polyethylene glycol (PEG) and TiO₂ films were directly deposited on a borosilicate glass substrate using the sol-gel dip-coating method. The surface morphology and the nanoscale roughness of TiO₂ films were studied by means of atomic force microscopy (AFM). Structural properties of TiO₂ were identified by X-ray diffraction (XRD). The decomposition behaviour of organic compounds from the gels was investigated using thermal gravimetry (TG) and differential scanning calorimetry (DSC). Photocatalytic activities of TiO₂ films in the process of degradation of the commercial diazo textile dye Congo red (CR), used as a model pollutant, were monitored by means of UV/vis spectrophotometry. The kinetics of the degradation of the CR dye was described with the Langmuir-Hinshelwood (L-H) kinetic model.The addition of PEG to the TiO₂ solution resulted in the changes in the film surface morphology, and affected the ratio of anatase-rutile crystal phases and the photocatalytic activity of TiO₂. The TiO₂ film prepared with PEG is characterized by higher roughness parameters (R_a, R_max, R_q, R_z and Z_max), a lower amount of the rutile phase of TiO₂, a higher amount of the anatase phase of TiO₂ and a better photocatalytic activity compared to the TiO₂ film without the addition of PEG.     

Preparation of Ti/SnO2-Sb2O4 photoanode by electrodeposition and dip coating for PEC oxidations

Thin films of antimony-doped SnO₂ on titanium substrate with a doping range of 1.5-8 mol% were prepared by an electrodeposition and dip coating method. The prepared Ti/SnO₂-Sb₂O₄ thin films were tested as a photoanode in the photoelectrocatalytic(PEC) experiments to degrade phenol in aqueous solution in order to evaluate their PEC performance. The photocatalytic (PC), electrocatalytic (EC) and PEC activity of Ti/SnO₂-Sb₂O₄ thin films was compared in the degradation processes. And the effect of annealing temperature on their PEC activity was also investigated. The experimental results confirmed that the Sb-doped Ti/SnO₂ thin films enhanced the phenol degradation and the Ti/SnO₂-Sb₂O₄ film containing 6 mol% of Sb calcinated at 450 °C achieved the best performance for phenol degradation. The degradation experiments also demonstrated that the Ti/SnO₂-Sb₂O₄ film achieved faster degradation of phenol in the PEC process than in the PC and EC processes. Compared with Ti/TiO₂ and Ti/SnO₂ photoanodes, the Ti/SnO₂-Sb₂O₄ photoanode showed higher activity.