Photocatalytic activity of TiO2 thin films deposited by RF magnetron sputtering

Nano-TiO₂ thin films were deposited on silicon and glass substrates by radio-frequency (RF) magnetron sputtering using TiO₂ ceramic target and characterized by X-ray diffractometer, X-ray photoelectron spectrometer, atomic force microscope, and ultraviolet-visible spectrophotometer. Photocatalytic activity was evaluated by light induced degradation of 5 ppm methyl orange solution using a high pressure mercury lamp as lamp-house. It was found that the film as deposited is polymorph, with energy gap of 3.02 eV, and can absorb visible light. The film was repeatedly used for six times in degradation of 5 ppm methyl orange, and the degradation rates of methyl orange solution are 36.566%, 33.112%, 32.824%, 32.248%, 30.521% and 28.794%, respectively. After ultrasonic treatment in de-ionized water for ten minutes, the degradation rate of methyl orange solution resumes to 33.975%.     

Photocatalytic Zn-doped TiO2 films prepared by DC reactive magnetron sputtering

Zn-doped TiO₂ films were prepared by means of pulsed DC reactive magnetron sputtering method using Ti and Zn mixed target. The deposition condition was optimized to produce uniform and transparent TiO₂ films. Titanium was in the Ti⁴⁺ oxidation state in all Zn-doped TiO₂ films. The zinc oxide deposited on the substrate was in the fully oxidized state of ZnO. Increase of zinc concentration inhibited the crystal growth in the TiO₂ films. The surface morphology gradually changed from crystalline to amorphous along with the increase of doped zinc concentration. The optical transmittances of these films decreased only slightly with increasing zinc concentration due to very similar band edges of ZnO and anatase TiO₂. The doped ZnO had weak influence on light absorption of the TiO₂ films. When zinc concentration was very low (<1 at%), the photocatalytic activities of the doped films had nearly no difference from that of pure TiO₂ film. Photocatalytic activities decreased obviously in the films containing high amount of zinc oxide.     

Photocatalytic properties of porous TiO2/Ag thin films

In this study, nanocrystalline TiO₂/Ag composite thin films were prepared by a sol-gel spin-coating technique. By introducing polystyrene (PS) spheres into the precursor solution, porous TiO₂/Ag thin films were prepared after calcination at a temperature of 500 °C for 4 h. Three different sizes (50, 200, and 400 nm) of PS spheres were used to prepare porous TiO₂ films. The as-prepared TiO₂ and TiO₂/Ag thin films were characterized by X-ray diffractometry (XRD) and by scanning electron microscopy to reveal structural and morphological differences. In addition, the photocatalytic properties of these films were investigated by degrading methylene blue under UV irradiation.When PS spheres of different sizes were introduced after calcination, the as-prepared TiO₂ films exhibited different porous structures. XRD results showed that all TiO₂/Ag films exhibited a major anatase phase. The photodegradation of porous TiO₂ thin films prepared with 200 nm PS spheres and doped with 1 mol% Ag exhibited the best photocatalytic efficiency where ∼ 100% methylene blue was decomposed within 8 h under UV exposure.     

Photo-fixation of SO2 in nanocrystalline TiO2 films prepared by reactive DC magnetron sputtering

We report on photo-fixation of SO₂ onto nanostructured TiO₂ thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 ppm SO₂ gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SO_x species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO₂ uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO_x complexes. The total SO_x uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be ~ 2.2 at.% at 473 K. These films were pale yellowish and had an optical absorption coefficient being ~ 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO₂ to achieve combined anti-grease and photocatalytic properties.     

Characterization and photocatalytic activity of TiO2 thin films prepared by RF magnetron sputtering

TiO₂ nano-structured thin films were prepared by RF magnetron sputtering and annealed in ambient air for 1 h at 400, 600, 800, 1000, and 1200 °C, respectively. Their phase structure, surface topography, and energy gap were characterized by X-ray diffractometer, atomic force microscope, and fluorescence spectrometer. Photocatalytic activity of the films was evaluated by light induced degradation of methyl orange (C₁₄H₁₄N₃NaO₃S) solution using a high pressure mercury lamp as lamp-house. The relation of photocatalytic activity and annealed temperature was studied in detail. It is found that the crystal phase transforms from amorphous to anatase, and rutile structure with annealing temperature increasing from room temperature to 1200 °C. Energy gap varies with annealing temperature. Photocatalytic activity is dependent on energy gap and grain size. Suitable energy gap from 2.97 to 3.07 eV is favorable for creation of electronic-hole pairs that make the films show excellent photocatalytic activity.     

Comparison of hydrophilic properties of TiO2 thin films prepared by sol-gel method and reactive magnetron sputtering system

This article reports on preparation, characterization and comparison of TiO₂ films prepared by sol-gel method using the titanium isopropoxide sol (TiO₂ coating sol 3%) as solvent precursor and reactive magnetron sputtering from substoichiometric TiO_2 − x targets of 50 mm in diameter. Dual magnetron supplied by dc bipolar pulsed power source was used for reactive magnetron sputtering. Depositions were performed on unheated glass substrates. Comparison of photocatalytic properties was based on measurements of hydrophilicity, i.e. evaluation of water contact angle on the film surface after UV irradiation. It is shown, that TiO₂ films prepared by the sol-gel method exhibited higher hydrophilicity in the as-deposited state but has significant deterioration of hydrophilicity during aging, compared to TiO₂ films prepared by magnetron sputtering. To explain this effect AFM, SEM and high resolution XPS measurements were performed. It is shown that the deterioration of hydrophilicity of sol-gel TiO₂ films can be suppressed if as-deposited films are exposed to the plasma of microwave oxygen discharge.     

Photocatalytic performance of very thin TiO2/SnO2 stacked-film prepared by magnetron sputtering

TiO₂/SnO₂ stacked-layers are synthesized by reactive sputter deposition on the glass substrate. Very thin TiO₂/SnO₂ bilayer-photocatalysts exhibited a very high photocatalytic activity for a degradation of gaseous acetaldehyde. Both the control of an electronic structure of TiO₂ overlayer in the near-surface region and the interfacial separation of photogenerated electrons/holes in the TiO₂/SnO₂ stacked-layer are keys to improve the photocatalytic performance.     

Mesoporous TiO2 thin films embedded with Au nanoparticles for the enhancement of the photocatalytic properties

Mesoporous TiO₂ thin films were prepared by hydrothermal-oxidation of titanium metal thin films, which were obtained by DC magnetron sputtering technique. Gold nanoparticles, which were prepared by reduction of HAuCl₄, were embedded into the holes of the mesoporous TiO₂ films by capillary method followed by annealing in air up to 400 °C. The size of pore of TiO₂ films is about 100 nm and that of Au nanoparticles is about 10 nm in average. The morphology of the films was analyzed by field emission scanning electron microscope (FE-SEM) and scanning probe microscopes (SPMs). Subsequently, the photocatalytic performances of the obtained nanosystems in the decomposition of methylene blue solution are discussed. The obtained results show that the dispersion of Au nanoparticles on the mesoporous TiO2 matrix will help enhancing the photocatalytic activity with respect to pure TiO₂ under visible light irradiation.     

Etch damage characteristics of TiO2 thin films by capacitively coupled RF Ar plasmas

Etch damage of TiO₂ thin films with the anatase phase by capacitively coupled RF Ar plasmas has been investigated. The plasma etching causes a mixed phase of anatase and rutile or the rutile phase. The effect of Ar plasma etching damage on degenerating TiO₂ thin films is dependent on gas pressure and etching time. The physical etching effect at a low gas pressure (1.3 Pa) contributes to the degradation: the atomic O concentration at the thin film surface is strongly increased. At a high gas pressure (13-27 Pa) and long etching time (60 min), there are a variety of surface defects or pits, which seem to be similar to those for GaN resulting from synergy effect between particle and UV radiation from the plasmas. For the hydrophilicity, the thin film etched at the high gas pressure and a short etching time (5 min) seems to have no etch damage: its contact angle property is almost similar to that for the as-grown thin film, and is independent of the black light irradiation. This result would probably result from formation of donor-like surface defects such as oxygen vacancy.     

Photocatalytic properties of Cr-doped TiO2 films prepared by oxygen cluster ion beam assisted deposition

We prepared Cr-doped titanium dioxide (TiO₂) films by oxygen (O₂) cluster ion beam assisted deposition method, and investigated photocatalytic properties of the films as well as crystallographic property, optical property and surface morphology. The films prepared at a substrate temperature below 200 °C were found to be amorphous from the X-ray diffraction measurement. For the substrate temperatures such as 300 °C and 400 °C, the films exhibited rutile and/or anatase structures. The film surface measured by the atomic force microscope (AFM) was smooth at an atomic level. Furthermore, the optical band gap decreased with increase of Cr-composition, and it was approximately 3.3 eV for the non-doped films, 3.2 eV for the 1% Cr-doped films and 3.1 eV for the 10% Cr-doped films, respectively. With regard to the photocatalytic properties of the Cr-doped TiO₂ films, we measured the change of contact angle as well as the photocatalytic degradation of methylene blue by the UV light irradiation. Compared with the non-doped films, the 1% Cr-doped films prepared at a substrate temperature of 400 °C showed high degradation efficiency. In addition, the contact angle of the 1% Cr-doped films with an initial value of 60° decreased to 10° by the UV light irradiation for 20 min, and the films exhibited the predominant properties of photocatalytic hydrophilicity even for the UV light irradiation with longer wavelengths.     

Photocatalytic activity of pulsed laser deposited TiO2 thin films in N2, O2 and CH4

We report on pulsed laser deposition of TiO₂ films on glass substrates in oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmosphere. The nitrogen incorporation into TiO₂ lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO₂ films was red-shifted up to ∼ 480 nm from 360 nm in case of undoped ones.The photocatalytic activity of TiO₂ films was investigated during toxic Cr(VI) ions photoreduction to Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, TiO₂ films deposited in nitrogen atmosphere showed the highest photocatalytic activity, whereas by UV light exposure the best results were obtained for the TiO₂ structures deposited in pure methane and oxygen atmosphere.     

Photocatalytic TiO2 films deposited on cenosphere particles by pulse magnetron sputtering method

In the present study, TiO₂ films were deposited on the surface of cenosphere particles using the modified magnetron sputtering equipment under different working conditions. The resulting films were characterized by field emission scanning electron microscopy (FE-SEM), Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The FE-SEM and AFM results show that the grain sizes and root-mean-square (RMS) roughness values of the TiO₂ films increase with the increase in deposition time and film thickness. The XRD results indicate that the film was TiO₂ film and sputtering time is an importance condition to influence the films crystal. With the increasing of sputtering time, the crystallization of the TiO₂ film was increased. The XPS results show that only TiO₂ films existed on the surface of cenosphere particles. In addition, the photocatalytic activities of these films were investigated by degrading methyl orange under UV irradiation. The results suggest that the photocatalytic activity of cenosphere particles with anatase TiO₂ films is remarkable and this catalyst can be applicable for the photocatalytic degradation of other organic compounds under UV lights.     

Photocatalytic degradation of 2,4-dichlorophenol wastewater using porphyrin/TiO2 complexes activated by visible light

The use of TiO₂ as photocatalyst to degrade the organic compounds is an effective method of oxidation process and has been widely studied in environmental engineering. However, TiO₂ absorbed the UV light which is only small part of sunlight reaching earth surface to activate photocatalytic procedure effectively is a major disadvantage. Therefore, studies on the development of new TiO₂ wherein its photocatalytic activity can be activated by visible light which is the major part of sunlight will be valuable for field application. In this study, we evaluate the photocatalytic degrading efficiency of porphyrins/TiO₂ complexes on the organic pollutants under irradiation with visible light (λ = 419 nm). The results showed that the photodecomposition efficiency of 2,4-dichlorophenol (2,4-DCP) wastewater by using porphyrin/TiO₂ irradiated under visible light for 4 h was up to 42-81% at pH 10. These evidences reveal that the system of porphyrin/TiO₂ complexes has also significantly efficiency of photocatalytic degradation for some hazardous or recalcitrant pollutants under visible light irradiation.     

Characterization of SiO2 and TiO2 films prepared using rf magnetron sputtering and their application to anti-reflection coating

Preparation of TiO₂ and SiO₂ films for optical applications was attempted using conventional rf magnetron sputtering in the sputtering ambient with various O₂/Ar+O₂ ratios and at substrate temperatures between room temperature and 400 °C. X-ray photoelectron spectroscopy (XPS) and optical spectroscopy investigations indicated that oxygen addition in the sputtering ambient was essential for growing TiO₂ films with stoichiometric compositions and good transmittance, while SiO₂ films had a stoichiometric composition of O/Si ratio=2.1-2.2 and were highly transparent in the visible wavelength region, independent of gas composition in the growing ambient. It was also identified from scanning electron microscope (SEM), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) measurements that the structural characteristics of both TiO₂ and SiO₂ films were significantly improved with O₂ addition in the sputtering ambient, showing smoother surface morphologies and higher resistances to water absorption when compared with films grown without O₂ addition. Heating of the substrate between 200 and 400 °C considerably increased the refractive index of TiO₂ layers, resulting in dense structures along with an improvement of crystallinity. For optical applications, AR coatings composed of 2-4 multi-layers on glass were designed and manufactured by stacking in turn the SiO₂ and TiO₂ films at room temperature and O₂/Ar+O₂=10%, and the performance of the produced coatings was compared with simulation results.     

Surface properties of doped and undoped TiO2 thin films deposited by magnetron sputtering

In this work, transparent titanium dioxide (TiO₂) thin films were deposited onto microscope glass slides by means of the d.c. reactive magnetron sputtering method. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectroscopy (UV) and contact angle analysis using the Owens-Wendt method for the surface energy calculation. The photocatalytic activity of the films was tested by measuring the photodegradation of Rhodamine-B (RhB) dye under radiation of UV light. Iron-doped TiO₂ films were also prepared in order to study the Fe-doping effect on TiO₂ photocatalytic activity. The influences of different iron concentrations on the contact angle of the series of Fe-doped TiO₂ thin films, were investigated. The influences of total sputtering pressures on TiO₂ photocatalytic activity were also investigated. It was observed that the photocatalytic activity of the TiO₂ thin films was slightly improved by increasing the total sputtering pressure. Moreover, it was also observed that in general, iron-doping was detrimental for photocatalytic activity, nevertheless the films with low iron concentrations showed better photocatalytic activity than those with high iron concentrations. It was found that iron-doping has changed the wettability appetency of TiO₂ coated surfaces.     

Microstructure of sol-gel derived TiO2 thin films characterized by atmospheric ellipsometric porosimetry

Adsorption of water vapor during ellipsometric measurements was performed in-situ for the characterization of sol-gel derived TiO₂ thin films. The data obtained were compared with complementary results derived from scanning electron microscopy and photocatalytic degradation measurements. Results indicate that a less permeable surface layer encapsulates the porous interior of the films which may become more accessible by defects such as cracks. Atmospheric ellipsometric porosimetry provides a valuable tool for the microstructural characterization of sol-gel films.     

Effects of internal stress on photocatalytic properties of TiO2 films

Effects of internal stress on photocatalytic properties have been investigated on titanium dioxide films deposited by reactive magnetron sputtering. Atomic peening effects by bombardments of high-energy particles in sputtering processes should generate not only compressive stress, but also oxygen defects in the films. Therefore, the films with higher compressive stress performed almost no photocatalytic activity. Furthermore, compressive or tensile stress was applied on the films deposited on curved micro sheet glasses by flattening the substrates after the deposition by external force. It was found that the photodecomposition activity of the films applied the slight compressive stress improved clearly, whereas the one of the films applied the tensile stress degraded.     

Electrochromic properties of TiO2 anatase thin films prepared by a dipping sol-gel method

Electrochromic TiO₂ anatase thin films on ITO were prepared by the sol-gel dipping method using a solution of titanium tetraisopropoxide, diethanolamine and ethanol. The films were transparent in the visible range and can be colored in a solution of LiClO₄ in propylene carbonate. The transmittances of the colored films were found to be strongly dependent on the Li⁺ inserted charge. Combining the experimental data obtained from in situ Raman and in situ transmittance spectra with the data from chronoamperometic measurements, it was demonstrated that the fully colorated state of the TiO₂ anatase films is Li_0.5TiO₂ with a crystalline structure of Imma space group symmetry. In the Raman spectra this coloration state exhibits five characteristic bands at 176, 224, 316, 531 and 629 cm⁻¹.     

High transparent sol-gel derived nanostructured TiO2 thin film

In this investigation, high transparent nanostructured TiO₂ thin film has been prepared by a dip-coating method. The prepared sol was obtained through the hydrolysis of titanium isopropoxide under the selected pH. The transmission of film as an optical parameter was characterized by spectrophotometer. With respect to other experimental results, a high transmission spectrum without any fluctuation in visible wavelength region has been recorded. According to transmission spectrum of film the refractive index and extinction coefficient has been determined. Experimental result has shown that the prepared film has high transmission and good optical parameters. SEM and AFM have been applied for morphology characterization of the film surface.     

The properties of Ba0.5Sr0.5TiO3 thin film prepared by RF magnetron sputtering from powder target

The Ba_0.5Sr_0.5TiO₃ (BST) thin film with the thickness of 400 nm deposited from powder target is prepared by the radio-frequency magnetron sputtering technique. The deposition rate of BST film is estimated to be 45 nm/min, which is very fast for ferroelectric materials. The dielectric properties of the as-prepared BST thin film are demonstrated. High dielectric tunability up to 42.7% and low dielectric loss small to 0.01 are achieved at a low applied voltage of 5 V. The results demonstrate that the RF magnetron sputtering from powder target is a versatile, novel technique for the deposition of high-quality ferroelectric thin films.