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.     

Structural, microstructural and transport properties study of lanthanum lithium titanium perovskite thin films grown by Pulsed Laser Deposition

Lanthanum lithium titanate thin films were grown by Pulsed Laser Deposition. La_0.57Li_0.29TiO₃ dense films with smooth surfaces were obtained after optimization of the growth parameters. Such films deposited at 700 °C under 15 Pa are nano-crystalline with domains corresponding to the cubic and tetragonal modifications of this phase. In relation to the measured conductivities/activation energy and to previous works, we clearly underlined that the films of practical interest, prepared at relatively low temperature, are predominantly formed from the tetragonal ordered phase.     

Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

Palladium colloidal nanoparticles with an average size of approximately 2.4 nm have been incorporated into mesoporous inorganic thin films following a multistep approach. This involves the deposition of mesoporous titania thin films with a thickness of 200 nm by spin-coating on titanium plates with a superhydrophilic titania outer layer and activation by calcination in a vacuum furnace at 573 K. Nanoparticles have been confined within the porous titania network by dip-coating noble metal suspensions onto these mesoporous thin films. Finally, the resulting nanoconfined systems were used as substrates for the growth of oriented carbon nanotubes (CNTs) using plasma-enhanced chemical vapour deposition at 923 K in order to enhance their surface area. These CNTs were tested in the hydrogenation of phenylacetylene by hydrogen in a batch reactor. The initial reaction rate observed on a CNT/TiO₂ structured catalyst was considerably higher than that on 1 wt% Pd/TiO₂ thin films.     

Fabrication of porous TiO2 film via hydrothermal method and its photocatalytic performances

Porous anatase (TiO₂) films were fabricated onto stainless steel substrates with Ti(OC₄H₉)₄ as a precursor via hydrothermal process. The crystallization and porous structure of TiO₂ film were dependent on the time and temperature of the hydrothermal reaction. A TiO₂ film with orderly porous structure and high crystallization was obtained upon treatment at 150 °C for 2 h. The grain size of TiO₂ is ca. 6 nm, and pore diameter is ca. 10 nm. Diffusion of Fe into the porous TiO₂ film occurred; Fe also diffused onto the surface of the film with the extension of hydrothermal reaction time or increase of the reaction temperature. The diffusion reaction has a large effect on the formation of porous TiO₂ film as well as its interface texture. However, it does not change the crystal phase of the TiO₂. The resultant TiO₂ film showed high photocatalytic activity towards degradation of gaseous formaldehyde.     

Effect of plasma treatment on chemical bonding states of porous TiO2 thin films prepared from polymer-blended solution

Dense TiO₂ (D-TiO₂) thin films and porous TiO₂ (P-TiO₂) thin films were prepared by using a polymer-blended solution. The film porosity decreased gradually or disappeared with an increase in the polyethylene glycol (PEG) or TiO₂ content of the solution. To modify their surface properties, the thin films were treated with atmospheric pressure (AP) plasma by using a reactive gas. The surface morphologies of the O₂-plasma-treated TiO₂ (O-TiO₂) thin films were smooth and did not change significantly. The decolorization efficiency of the P-TiO₂ thin films was found to be enhanced when compared to that of the D-TiO₂ thin films. The enhancement was due to an increase in the specific surface area and the number of hydroxyl groups, and a decrease of Ti₂O₃ states.     

Nanocrystalline TiO2 thin films for NH3 monitoring: microstructural and physical characterization

Nanocrystalline titanium oxide thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH₃ gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of titanium oxide thin films. The structure and the morphology of such material have been investigated by X ray diffraction, Scanning microscopy, high resolution electron microscopy and selected area electron diffraction. The X-ray diffraction measurements confirmed that the films grown by this technique have good crystalline tetragonal mixed anatase and rutile phase structure. The HRTEM image of TiO₂ thin film showed grains of about 50–60 nm in size with aggregation of 10–15 nm crystallites. Selected area electron diffraction pattern shows that the TiO₂ films exhibited tetragonal structure. The surface morphology (SEM) of the TiO₂ film showed that the nanoparticles are fine with an average grain size of about 50–60 nm. The optical band gap of TiO₂ film is 3.26 eV. Gas sensing properties showed that TiO₂ films were sensitive as well as fast in responding to NH₃. A high sensitivity for ammonia indicates that the TiO₂ films are selective for this gas.     

Hydrothermal growth of ferromagnetic Fe-doped TiO2 films

Polycrystalline Fe-doped TiO₂ anatase films were deposited on (001) oriented SrTiO₃ single crystal substrates at temperatures less than 200 °C from acidic aqueous solutions of titanyl sulfate and iron (III) nitrate. Epitaxial anatase TiO₂ films were obtained when the films were annealed in air at 900 °C. Room-temperature ferromagnetic Fe-doped TiO₂ thin films were obtained after repeated deposition and annealing steps. The observed saturation magnetization (>0.28μ_B/Fe) could not be attributed to the presence of secondary phase magnetic iron oxides or iron clusters.     

Influence of oxygen flow rate on photocatalytic TiO2 films deposited by rf magnetron sputtering

Titanium dioxide (TiO₂) thin films having anatase (1 0 1) crystal structure were prepared on non-alkali glass substrates by rf (13.56 MHz) magnetron sputtering using a TiO₂ ceramic target under various oxygen partial pressures. At a fixed substrate temperature of 400 °C and total gas pressure of 1 Pa after 3 h deposition. Effects of oxygen partial pressure on the structural, surface morphology, and photocatalytic activities of the TiO₂ thin films were investigated. We performed both photoinduced decomposition of methylene blue (MB) and photoinduced hydrophilicity under UV light illumination. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO₂ thin films. The results showed that when the [O₂/(Ar + O₂)] flow rate increased to 50%, the photoinduced decomposition of MB and photoinduced hydrophilicity were enhanced. The water contact angle after 9 min UV illumination was approximately 4.5°, and the methylene blue (MB) solution decomposition from 12 down to 3.34 μ mol/L for 240 min UV irradiation.     

Li2O–ZnO–Co3O4–TiO2 composite thin-film electrocatalyst for efficient water oxidation catalysis

Thin films of different Li₂O–ZnO–Co₃O₄–TiO₂ (LZCT) compositions were prepared and employed as electrocatalysts (i.e., anodes) to perform water oxidation reaction (WOR). The electrocatalytic activities of these thin films were compared with those exhibited by the sodium salt of cobalt phosphate (Na₂CoP₂O₇) (CP) thin-film electrocatalyst, which is a well-known water oxidation catalyst (WOC). These results suggest that the 10Li₂O–10ZnO–40Co₃O₄–40TiO₂ composition exhibits a better catalytic activity in terms of higher faradaic efficiency (>98%), lower over potentials (<400?mV), higher reaction stability (up to 30 continuous cyclic voltammetry (CV) cycles), and the rate of O₂ and H₂ gas evolution in terms of current density (about 1?mA/cm²) in comparison with those exhibited by CP thin-film electrocatalyst. Furthermore, these LZCT thin films exhibited very high specific surface area values and due to the unique microstructure of ZnCo₂O₄ phase evolved out of these LZCT compositions at a calcination temperature of 550°C for 30?min it has been found to be responsible for the higher specific surface area values measured for these thin-film compositions.     

Improved dielectric properties of chemical solution derived Pb0.5Sr0.5TiO3 thin films by a layer-by-layer annealing method

Pb_0.5Sr_0.5TiO₃ thin films were prepared on Pt/TiO₂/SiO₂/Si and LaNiO₃ (LNO)/Si substrates by using chemical solution deposition technique, and a layer-by-layer annealing method was used in an attempt to improve the dielectric properties of the thin films. The structure, dielectric, and ferroelectric properties of the thin films were investigated. Improved dielectric properties of the thin films were clearly confirmed: the dielectric constant and dielectric loss for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 1064 and 0.027, respectively, at 1 kHz, with a dielectric tunability of more than 50%; similarly, the films prepared on LNO/Si substrates, showed a high dielectric constant of 1280 and a low dielectric loss of 0.023, at 1 kHz. P-E hysteresis loop measurements indicated that the remanent polarization and coercive field for the films on Pt/TiO₂/SiO₂/Si substrates annealed at 650 °C were 15.7 μC/cm² and 51 kV/cm, respectively.     

Enhanced photocatalytic activity of silver nanoparticles modified TiO2 thin films prepared by RF magnetron sputtering

Ag-TiO₂ nanostructured thin films with silver volume fraction of 0–40% were prepared by RF magnetron sputtering. The microstructure, surface topography, and optical properties of the films were characterized by X-ray diffractometer, transmission electron microscope, and ultraviolet–visible spectrophotometer. 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 silver content was studied in detail. It is found that silver content influences microstructure of TiO₂ thin films, and silver in the films is metallic Ag (Ag⁰). Photocatalytic activity of the films increases with increasing silver content up to 5 vol.% Ag and then decreases to values significantly still bigger than that of pure TiO₂ thin films. Silver nanoparticles significantly enhance the photocatalytic activity of TiO₂ films. The better separation between electrons and holes on silver modified TiO₂ thin films surface allowed more efficiency for the oxidation and reduction reactions. The enhanced photocatalytic activity was mainly attributed to the decrease of energy gap of the films and the increase of oxygen anion radicals O₂⁻ and reactive center of surface Ti³⁺ on silver modified TiO₂ thin films surface.     

Templated synthesis of ordered porous TiO2 films and their application in dye-sensitized solar cell

Ordered porous TiO₂ thin films were fabricated on conductive glass by using colloid crystal template of polystyrene (PS) spheres. Microstructural characterization by scanning electron microscopy techniques was carried out to explore the porous structural changes due to the PS templates which could be controlled by adjusting the drawing rate. Photovoltaic performance was measured and this revealed the effect of microstructural changes. The results showed that monolayer porous TiO₂ films and multilayer porous TiO₂ films could be successfully prepared. And multilayer porous TiO₂ films provided large surface area for dye absorption to increase the efficiency of dye-sensitized solar cells (DSSCs) which were assembled by porous TiO₂ films.     

Preparation and characterization of Co-doped TiO2 materials for solar light induced current and photocatalytic applications

Different amounts of Co-doped TiO₂ powders and thin films were prepared by following a conventional co-precipitation and sol–gel dip coating technique, respectively. The synthesized powders and thin films were subjected to thermal treatments from 400 to 800 °C and were thoroughly investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive analysis with X-rays, FT-infrared, FT-Raman, diffuse reflectance spectroscopy, ultraviolet–visible spectroscopy, BET surface area, zeta potential, flat band potential measurements, band-gap energy, etc. The photocatalytic ability of the powders was evaluated by methylene blue (MB) degradation studies. The thin films were characterized by photocurrent and ultraviolet–visible (UV–Vis) spectroscopy techniques. The characterization results suggest that the Co-doped TiO₂ powders synthesized in this study consist mainly anatase phase, and possess reasonably high specific surface area, low band gap energy and flat band potentials amenable to water oxidation in photoelectrochemical (PEC) cells. The photocatalytic degradation of MB over Co-doped TiO₂ powders followed the Langmuir–Hinshelwood first order reaction rate relationship. The 0.1 wt.% Co-doped TiO₂ composition provided the higher photocurrent, n-type semi-conducting behavior and higher photocatalytic activity among various Co-doped TiO₂ compositions and pure TiO₂ investigated.     

Hydrophilic properties of nano-TiO2 thin films deposited by RF magnetron sputtering

Microstructure and hydrophilicity of nano-titanium dioxide (TiO₂) thin films, deposited by radio frequency magnetron sputtering, annealed at different temperatures, were studied by field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and water contact angle methods. It is found that the crystal phase transforms from amorphous to rutile structure with increase of annealing temperature from room temperature to 800 °C. It is also indicated that the organic contaminants on the surface of the films can be removed and the oxygen vacancies can be reduced by the annealing treatment. Annealed at the temperature below 300 °C, amorphous TiO₂ thin films show rather poor hydrophilicity, and annealed at the temperature range from 400 to 650 °C, the super hydrophilicity anatase of TiO₂ thin films can be observed. However, when the annealing temperature reaches 800 °C, the hydrophilicity of the films declines mainly derived from the appearance of rutile.     

Fabrication of large-area and high-quality colloidal crystal films on nanocrystalline porous substrates by a room temperature floating self-assembly method

When colloidal crystal films are deposited onto nanocrystalline porous substrates by the commonly used colloidal crystallization method of vertical deposition self-assembly, the colloidal crystal tends to be poorly adhered to the porous film. Herein, we present a fabrication of large-area, three-dimensional (3D) colloidal crystal thin films on nanocrystalline porous substrates by a room temperature floating self-assembly method that has recently been developed for colloidal crystal deposition. Firstly, colloidal suspensions were prepared by dispersing monodisperse colloidal microspheres at high volume fraction in a mixture of ethanol and water. At room temperature, these suspensions were spread onto nanocrystalline porous TiO₂ films. The colloidal particles assembled into 3D ordered structures at the air−liquid interface of the suspensions as a result of rapid evaporation of the solvents. After the solvents (water and ethanol) had evaporated completely, the colloidal crystals were directly deposited on the nanocrystalline porous TiO₂ films. Scanning electron microscopy images and normal-incidence transmission spectra of the samples showed that the colloidal crystal films deposited on the nanocrystalline porous TiO₂ substrates by this method had very high crystalline quality. In addition, the effect of the degree of surface roughness of the nanocrystalline porous substrate on the crystalline quality of the colloidal crystals has been studied.     

Reticulated macroporous ceramic foam supported TiO2 for photocatalytic applications

Ceramic macroporous reticular alumina foams with a pore size of 15, 20 and 25 pores per inch (ppi) were prepared by the Schwartzwalder method and sintered at 1200 °C to preserve a high porosity. TiO₂ thick films were supported on the foam surface by a wash coating process, using Degussa P25 as a TiO₂ nanopowder source. After annealing at 600 °C, films with an adequate adhesion and with a thickness of 5–10 μm were obtained. An increasing pore size of the supported foams improves the specific photocatalytic activity of the TiO₂ coated scaffolds, the flow of solution through the highly active porous foam structure and the better access of light to the active TiO₂ surface.     

Effects of ambient oxygen pressures and substrate temperatures in pulsed laser deposited Zn0.85Li0.15O thin films

Li doped zinc oxide Zn_1−xLi_xO (x = 0.15) thin films were grown by using the pulsed laser deposition method. The depositions were done onto Pt(111)/Ti/SiO₂/Si(100) substrate set at temperatures ranging from 300 °C to 700 °C, with varying the ambient O₂ pressure range of 3-20 mTorr. The effects of substrate temperatures and ambient O₂ pressures on the surface morphology and structural properties of the Zn_0.85Li_0.15O thin films were investigated by using the scanning probe microscopy and X-ray diffraction spectra, respectively. Also the chemical structures of the films were investigated by observing the X-ray photoelectron spectra of the core and shallower levels. We observed the deep blue PL emissions centered at about 390 nm (3.20 eV) from the Zn_0.85Li_0.15O thin films. It was investigated with respect to the ambient O₂ pressures during the deposition. It is considered that the deep blue PL emission in the Zn_0.85Li_0.15O thin film may be related to the incorporation of oxygen vacancies.     

Preparation and characterization of nanocrystalline porous TiO2/WO3 composite thin films

TiO₂ materials possessing not only photocatalytic but also electrochromic properties have attracted many research and development interests. Though WO₃ exhibits excellent electrochromic properties, the much higher cost and water-sensitivity of WO₃ as compared with the TiO₂ may restrict the practical application of WO₃ materials. In the present study, the feasibility of preparing nanocrystalline porous TiO₂/WO₃ composite thin films was investigated.Precursors of sols TiO₂ and/or WO₃ and polystyrene microspheres were used to prepare nanocrystalline pure TiO₂, WO₃, and composite TiO₂/WO₃ thin films by spin coating. The spin-coated thin films were amorphous and, after heat treating at a temperature of 500 °C, nanocrystalline TiO₂, TiO₂/WO₃, and WO₃ thin films with or without pores were prepared successfully. The heat-treated thin films were colorless and coloration-bleaching phenomena can be observed during cyclic voltammetry tests. The heat-treated thin films exhibited good reversible electrochromic behavior while the porous TiO₂/WO₃ composite film exhibited improved electrochromic properties.     

Chemical–hydrothermal combined surface modification of titanium for improvement of osteointegration

The chemical–hydrothermal combined synthesis of TiO₂ and CaTiO₃ films on pure Ti substrates was examined with a focus on crystallinity and surface morphology of the films. Pure Ti disks were chemically treated with H₂O₂/HNO₃ solutions at 353 K for 5–60 min in order to introduce a TiO₂ layer with low crystallinity on the surface. The samples were then hydrothermally treated in an autoclave at 453 K for 12 h. Anatase-type TiO₂ and perovskite-type CaTiO₃ films with high crystallinity were obtained upon treatment with distilled water and an aqueous solution of Ca(OH)₂, respectively. Cracks in the TiO₂ precursor films disappeared after hydrothermal treatment. Uniform and crack-free films could be obtained by the present process. In addition, in vitro formation of hydroxyapatite (HAp) on the films was investigated. Obtained samples were immersed in SBF (Simulated Body Fluid), adjusted to 310 K. A light HAp precipitate could be observed on non-surface modified Ti after 6 days of immersion. In contrast, precipitate formed after only 2 days on the present oxide films. The present surface modification was confirmed to drastically promote deposition of HAp on the surface of Ti.     

Ag surfactant effects of TiO2 films prepared by sputter deposition

The surfactant effect of Ag on the thin film structure of TiO₂ by radio frequency magnetron sputtering has been investigated. Comparisons between the atomic force microscopy images revealed that the surface roughness of TiO₂ film mediated by Ag was smaller than that of the TiO₂ film without Ag. The surface segregation effect of Ag was confirmed using X-ray photoelectron spectroscopy. The results of X-ray diffraction revealed that the initial deposition of a 0.4 nm thick Ag surfactant layer onto a Fe buffer layer prior to the deposition of the TiO₂ film reduced the rutile (110) growth and enhanced the anatase (100) growth. It was concluded that Ag was an effective surfactant for changing the thin film structure of TiO₂ on the Fe buffer layer. The photocatalytic effect of the fabricated TiO₂ film was also investigated using the remote oxidation process. TiO₂ films with the Ag surfactant exhibited higher photocatalytic activity than conventionally deposited TiO₂ films.