Activity Of TiO2 Thin Films Research Articles

Hydrophilic and photocatalytic activities of Nd-doped titanium dioxide thin films

The Nd-doped TiO2 thin films with higher hydrophilic and photocatalytic activities were prepared on glass slides by an acid-catalyzed sol–gel method. The effects of Nd doping on crystalline phase, surface composition and optical property were investigated by means of techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), optical contact angle tester and UV-Vis spectroscopy. The results show that Nd doping obviously influences the hydrophilic and photocatalytic activities of TiO2 thin films. Nd doping could cause the TiO2 lattice distortion, inhibit phase transition from anatase to rutile, cause red shift of the absorption spectrum edge, produce hydroxyl radicals (·OH), and accelerate surface hydroxylation, which result in a significant improvement in the hydrophilicity and photoreactivity of Nd-doped TiO2 thin films. When the content of Nd is 0.1% (mass fraction), TiO2 thin films achieve the smallest grain size (about 15 nm), and the hydrophilic and photocatalytic activities of TiO2 thin film reach the maximum, the contact angle is only 8.1°, and 92% of methylene blue is finally degraded. Moreover, the modification mechanism of Nd doping was also discussed.

Photocatalytic property of titanium dioxide thin films deposited by radio frequency magnetron sputtering in argon and water vapour plasma

The present work is investigating the photocatalytic activity of TiO2 thin films deposited by radiofrequency magnetron sputtering of a pure TiO2 target in Ar and Ar/H2O (pressure ratio 40/3) plasmas. Optical absorption, structure, surface morphology and chemical structure of the deposited films were comparatively studied. The films were amorphous and included a large amount of hydroxyl groups (about 5% of oxygen atoms were bounded to hydrogen) irrespective of the intentional content of water in the deposition chamber. Incorporation of hydroxyl groups in the film deposited in pure Ar plasma is explained as contamination of the working gas with water molecules desorbed by plasma from the deposition chamber walls. However, intentional input of water vapour into the discharge chamber decreased the deposition speed and roughness of the deposited films. The good photocatalytic activity of the deposited films could be attributed hydroxyl groups in their structures.

Photocatalytic activity of TiO2 thin films by hydrogen DC plasma

Thin layers of anatase titanium dioxide were coated on glass by spray pyrolysis method. The layers were hydrogenated by DC plasma from room temperature up to 350°C. Hydrogen plasma treatment at low temperatures, leads to decrease the surface roughness, while surface roughness is increased by enhancing plasma temperature. Layers’ band gap was decreased 0.13eV by plasma treatment at highest temperature. Hydrophilicity and photocatalytic properties of the layers under plasma treatment at 150 and 200°C, were improved noticeably. However, plasma treatment at temperatures above 200°C was lead to decrease hydrophilicity and photocatalytic activity of TiO2 layers. The reason seems formation of oxygen vacancies in the interior layers that act as charge carriers’ recombination centers.

Effect of annealing treatment on the photocatalytic activity of TiO2 thin films deposited by dc reactive magnetron sputtering

Titanium dioxide (TiO2) thin films have been deposited by DC reactive magnetron sputtering on silicon and quartz substrates with different Ar/O2 ratios in the gas mixture. Substrate temperature was kept constant at 400 °C during the deposition process, and the TiO2 thin films were later annealed at 700 °C for 3 h. The effect of the Ar/O2 ratio in the gas flow and the annealing treatment on the phase composition, deposition rate, crystallinity, surface morphology and the resulting photocatalytic properties were investigated. For photocatalytic measurements, the variation of the concentration of the methylene blue (MB) dye under UV irradiation was followed by a change in the intensity of the characteristic MB band in the UV- Vis transmittance spectra. We report here that the as-grown TiO2 films showed only the anatase phase, whereas after annealing, the samples exhibited both the anatase and rutile phases in proportions that varied with the Ar/O2 ratio in the mixture of gases used during growth. In particular, the annealed TiO2 thin film deposited at a 50/50 ratio of Ar/O2, composed of both anatase (80%) and rutile phases (20%), exhibited the highest photocatalytic activity (30% of MB degradation) compared with the samples without annealing and composed of only the anatase phase.

Photocatalysis Performance of Nb-doped TiO2 Film in Situ Growth Prepared by a Micro Plasma Method

Abstract Thin TiO2 films in-situ grown on titanium alloy substrate were prepared in 0.05 mol/L H2SO4 electrolyte using the micro plasma oxidation method. The photocatalytic properties of the prepared thin TiO2 films were investigated using Rhodamine B solution as a target pollutant. In order to improve the photocatalytic properties of the obtained TiO2 films, different contents of Nb(NO3)3 were added into the H2SO4 electrolyte and the Nb-doped TiO2 films in situ growth were obtained. The influences of the doping ions on the surface morphologies, the crystal phase compositions and microstructures of the TiO2 films were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results show that doping of Nb ions can refine the mesoporous TiO2 grain and increase the specific surface area. But doping of Nb ions has little influence on the crystal phase composition and the lattice parameters. Otherwise, doping of Nb ions can improve the photocatalytic activity of TiO2 thin films, when the Nb(NO3)3 is 1.2 g/L, the degradation rate of Rhodamine B solution in 90 min reaches 85%, showing the strongest light degradation ability.

Cr-Doped TiO<sub>2</sub> Thin Films Prepared by Means of a Magnetron Co-Sputtering Process: Photocatalytic Application

This paper deals with the effect of Cr content on photocatalytic activity of TiO2 thin films deposited on quartz and intrinsic silicon substrates by using the RF magnetron co-sputtering process. Some physical investigations on such sputtered films were made by means of X-ray Diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy as well as UV-Vis-IR absorption techniques. The heat treatment under oxygen atmosphere at 550°C reveals that the crystalline structure of TiO2: Cr depends on Cr content. Anatase-to-rutile phase transformation occurs at a Cr content of about 7%. On the other hand, the band gap energy value of annealed TiO2: Cr films varies in terms of Cr doping and a transition around 7% of Cr is accrued. The photocatalytic activity of undoped and doped TiO2 films was evaluated by photo-degrading of the amido black under UV light irradiation. Modification of the chemical structure of titanium dioxide by Cr doping allows moving the photocatalytic activity of titanium dioxide towards visible light. The results indicate that films doped with 2% Cr exhibit the highest UV and visible light photocatalytic activity.

How to modify the photocatalytic activity of TiO2 thin films through their roughness by using additives. A relation between kinetics, morphology and synthesis

The possibility to improve the photocatalytic activity of TiO2 thin films by using organic additives is investigated. Two non-aqueous sol–gel routes (In Situ and Ex Situ) have been selected to obtain organic/inorganic stable sols and TiO2 thin films have been produced using the dip-coating process optimized in a previous study. The influence of the additive on the physico-chemical properties of the catalysts has been evaluated using XRD, GIXRD, UV–Vis spectroscopy, krypton and nitrogen adsorption–desorption, profilometry and SEM. The photocatalytic activity has been assessed by monitoring the degradation of 4-nitrophenol (4-NP) under UV light and UV–Visible light over time. The performances of the catalysts have been evaluated using the values of the reaction rate coefficient estimated through the adjustment of the first order kinetic model taking in account the variation of the volume inside the reactor due to sampling. The results highlight that the performances of the catalysts were better that the performances of the commercial photocatalytic coating (Saint Gobain Glass Bioclean®) which constitutes a significant step forwards for the production of photocatalytic coating. Moreover, the results highlight that the organic additive induces an alteration of the surface roughness and hence, a modification of the active surface of the films. In the case of the In Situ synthesis an increase of the active surface is associated to a 100% improvement of the photocatalytic activity. On the opposite, for the Ex Situ synthesis, a decrease of the active surface is associated to a 50% decrease of the photocatalytic activity due to the presence of the additive.

Enhanced photocatalytic activity of TiO2 thin films on plasma-pretreated organic polymers

Organic polymers are excellent substrates for photocatalytic applications of TiO2 thin films, which can be easily prepared by sol–gel synthesis followed by dip coating. However, the wettability of the hydrophobic surface of polymers should be improved. In this work, commercial poly(vinyl chloride) (PVC), poly(methyl methacrylate) (PMMA) and polystyrene (PS) were selected according to their high transmittance in the TiO2 activation range for the immobilization of the semiconductor. Low pressure (LPP) and atmospheric pressure (APP) plasma were used to modify the surface properties of the organic polymers to improve the affinity for TiO2 aqueous sols and solutions. The characterization of the materials was performed by atomic force microscopy (AFM), UV–Vis spectroscopy, and contact angle and surface tension measurements, employed to evaluate wettability of the samples. The effect of the power of discharge and treatment time on the induced surface properties was analyzed. LPP at 300W during 600s was found as adequate treatment to promote the hydrophilicity of all samples without damage to the bulk. The adhesion of TiO2 thin films on the polymers was improved with the plasma pre-treatment due to the generation of roughness and specific polar functional groups. Accordingly, the photocatalytic performance increased with respect to the non-treated substrates, reaching similar conversion values than the reference photocatalyst where glass, a hydrophilyc substrate, was used as support.

The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering

This paper seeks to determine the optimal settings for the deposition parameters, for TiO2 thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO2 target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (°C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO2. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (110) and (200) peaks of the rutile structure and the (200) peak of the anatase structure were observed, at 2θ∼27.4°, 39.2° and 48°, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO2 film, because of the increased strength of the interface of micro-blasted tools.

Influence of annealing temperature on structure and photocatalytic activity of TiO2 thin films prepared by DC reactive magnetron sputtering method

Transparent TiO2 thin films were successfully prepared on high purity silica substrates by DC reactive magnetron sputtering method and annealed at different temperatures. The effects of the annealing temperature (300–600 °C) on crystalline structure, morphology, and photocatalytic activity of the TiO2 thin films were discussed. The photocatalytic activity of the films was evaluated by photodegradation of methylene blue solution. With increasing annealing temperature, the photocatalytic activity of the TiO2 thin films gradually increased because of the improvement of crystallization of anatase TiO2 thin films. At 500 °C, the TiO2 thin film shows the highest photocatalytic activity due to the improvement of crystallization of anatase TiO2 thin films. When the annealing temperature increases to 600 °C, the photocatalytic activity of thin film decreases owing to the formation of rutile phase and the decrease of surface area.

Enhanced photocatalytic activity of TiO2 thin film coating on microstructured silicon substrate

Photocatalytic TiO2 thin film is prepared by sol-gel technique on microstructured silicon substrate produced by femtosecond laser cumulative irradiation. The photocatalytic activity is evaluated by the degradation of methylene blue (MB) solution under ultraviolet (UV) irradiation. For 6-ml MB solution with initial concentration of 3.0 \times 10^{-5} mol/L, the degradation rate caused by TiO2 thin film of 2-cm2 area is higher than 70% after 10-h UV irradiation. Microstructured silicon substrate is found to enhance photocatalytic activity of the TiO2 thin film remarkably. The femtosecond laser microstructured silicon substrate is suitable to support TiO2 thin film photocatalysts.

Effect of Crystal Structure and Grain Size on Photo-Catalytic Activities of Remote-Plasma Atomic Layer Deposited Titanium Oxide Thin Film

The photo-catalytic activities of TiO2 thin films grown by remote plasma atomic layer deposition (RPALD) were investigated as a function of grain size and crystal structure. As the deposition temperature increased, it was shown that grain size of the anatase phase in the as-deposited TiO2 thin films progressively decreased. When the TiO2 films grown by RPALD were annealed at 900°C, the anatase TiO2 phase with relatively small grains provided large number of nucleation sites for formation of more stable rutile phase. On the other hand, the phase transition to rutile was retarded due to the reduction in grain boundaries in the case of the anatase TiO2 films with large grains. Thus, the anatase TiO2 phase with large grains has excellent thermal stability against the phase transition to rutile. Because the large grain boundary volume is a primary cause of degradation of photo-catalytic activity, the photo-catalytic activity of the TiO2 thin film was maximized when the anatase phase with large grains was formed in the TiO2 thin film. Therefore, RPALD can be effectively utilized to control the grain size of the as-deposited anatase TiO2 thin film with high thermal stability for potential application of photo-catalysts.

Effects of Fe-Doping on the Structures and Photocatalytic Activities of TiO2 Thin Films

The Fe-doped TiO2 films were prepared by sol-gel method and characterized by X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),confocal microscope Raman spectrometer(Raman),UV-Vis absorption spectroscopy(UV-Vis) and atomic force microscopy(AFM).The photocatalytic activities of the films were evaluated by using the degradation of the methyl orange.The results showed that TiO2 in Fe/TiO2 films took an anatase structure when calcinated between 300 ℃ and 600 ℃.Increasing the calcination temperature up to 700 ℃,TiO2 transformed to rutile phase.The roughness and the grain size of Fe/TiO2 films grew gradually with the increases of the doping amount of Fe content and the calcination temperature.The photon excited wavelength of the Fe/TiO2 films moved to the visible light gradually with the increase of number of coating layer.Low levels of Fe-doping improved the photocatalytic activities of the TiO2 thin films,while higher doping decreased the photocatalytic activities of TiO2 thin films.The optimal Fe-doping was found to be 0.1% for the maximum degradation of methyl orange.

Photocatalytic Activities of Mo Ions Implanted TiO<sub>2</sub> Thin Films

Transparent TiO2 thin films were deposited onto microscope glass slides by means of d.c. magnetron sputtering method. In order to enhance the photocatalytic activity of TiO2 thin films, Mo ions with different nominal doses were implanted into the TiO2 thin films. The samples were characterized by different technologies including X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS) and UV-VIS-NIR spectrophotometer. The photodegradation results of methylene blue dye solution indicated that optimal dose of 2×1012ions/cm2 Mo ion-implantation resulted in a higher photocatalytic activity in the implanted TiO2 thin films.

Photocatalytic Activity of Ag<sup>+</sup>-Doped TiO<sub>2</sub> Thin Films Prepared by Sol-Gel Method

TiO2and Ag+-doped TiO2thin films were successfully obtained on microscope glass slides by means of sol-gel method. Then the photocatalytic activity of the TiO2and Ag+-doped TiO2thin films was evaluated by the degradation of rhodamine B dye solution. The effects of both annealing temperatures and Ag+contents on the photocatalytic activity of TiO2thin films were examined. The results indicated that the TiO2thin films with an atomic ratio of Ti:Ag=10:1 annealed at 300°C had a higher photocatalytic activity.

The effect of Sn dopant on crystal structure and photocatalytic behavior of nanostructured titania thin films

In this study, preparation of Sn doped (0–30 mol % Sn) TiO2 dip-coated thin films on glazed porcelain substrates via sol–gel process have been investigated. The effects of Sn content on the structural, optical, and photo-catalytic properties of applied thin films have been studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission SEM (FE-SEM), and high resolution transmission electron microscopy (HR-TEM). Surface topography and surface chemical state of thin films were examined by atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). XRD patterns showed an increase in peak intensities of the rutile crystalline phase by increasing the Sn dopant. The prepared Sn-doped TiO2 photo-catalyst films showed optical absorption edge in the visible light area and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photo-catalytic activity of TiO2 thin films, and the optimum dopant amount is found to be 15 mol%. The Sn4+ dopants substituted Ti4+ in the lattice of TiO2 and increased surface oxygen vacancies and the surface hydroxyl groups. TEM results showed small increase in planar spacing (was detected by HR-TEM caused by Sn dopants in titania based crystals).

Photocatalytic Activities of Fe<sup>3+</sup>-Doped TiO<sub>2</sub> Thin Films Prepared by Sol-Gel Method

TiO2 and different contents Fe3+-doped TiO2 thin films were successfully obtained on microscope glass slides by Sol-Gel method. Then the photocatalytic activities of the samples were evaluated by the degradation of Rhodamine B dye solution. The effects of both annealing temperatures and Fe3+ contents on the photocatalytic activities of TiO2 thin films were examined. The results indicated that the sample with an atomic ratio of Ti:Fe=7:3 annealed at 500°C had a higher photocatalytic activity.

The Photocatalytic Activity of TiO2 Thin Film Deposited on Al Plate Together with Cu(II) and Ag(I)

Cu (II) and Ag(I) together with TiO(2) powder were deposited on conducting support substrates to enhance the photocatalytic ability. The catalytic efficiency was tested by monitoring the photocatalytic degradation and detriment of methylene blue (MB) and bovine serum albumin (BSA). The conformational change of BSA induced by catalysts was also observed by circular dichroism spectroscopy.The antibacterial activities were studied by Escherichia coli. Both MB and BSA could be degraded more efficiently than pure TiO(2). After treatment with catalyst, the morphology of cells became twisted and rougher. Regular wrinkles were damaged and groove-like rift appeared on the surface. The fluorescence polarization has shown a significant decrease in membrane fluidity and the increase of permeability of cell membrane. Changes of the spectral profile of E. coli were observed, which suggested the damages of surface groups on the cell membrane.

Photocatalytic activity of TiO2 thin films deposited by cathodic arc

In this work, the photocatalytic activity and the kinetic behavior of anatase TiO2 films deposited by cathodic arc (CA films) on glass substrates are reported and compared with those of TiO2 Degussa P-25 films obtained by dip-coating immersion (DC films). The mass density of films, determined by X-ray reflectometry was 20% lower for DC films compared with CA films, indicating a higher porosity of DC samples. The activity was evaluated from the efficiency to reduce Cr(VI) in the presence of EDTA. Although the response of CA films resulted lower compared with that of P-25 films of the same TiO2 content (e.g. 90% vs. 50% Cr(VI) reduction after 180min irradiation for samples with 0.03mgcm−2 of TiO2), a fact associated to the lower porosity, adhesion properties of the new materials were much better. CA film photoactivity improved by increasing the coating thickness; after 180min, a sample with 0.03mgcm−2 of TiO2 presented 50% of Cr(VI) reduction vs. 80% for a sample with 0.28mgcm−2. These photocatalysts, whose preparation is simple and affordable, are very promising to be used as immobilized materials in photoreactors for the treatment of pollutants in gaseous and aqueous systems.

Evaluation of Photocatalytic Activity of TiO2 Thin Films by Spin-Trap ESR Spectroscopy

Evaluation of Photocatalytic Activity of TiO₂ Thin Films by Spin-Trap ESR Spectroscopy