Effect of surface structure on photocatalytic activity of TiO2 thin films prepared by sol-gel method

Transparent anatase mesoporous TiO2 (MTiO2) and TiO2 nanometer thin films were prepared on soda-lime glass and fused quartz via the reverse micellar method and sol–gel method, respectively. The as-prepared MTiO2 and TiO2 films were then treated by dipping them in a H2SO4 solution. The MTiO2 and TiO2 films before and after surface acid treatment were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), BET surface area and UV–VIS spectrophotometry. The photocatalytic activity of the samples was evaluated by photocatalytic oxidation of acetone in air. It was found that MTiO2 thin films showed higher photocatalytic activity than that of the TiO2 thin films. This was attributed to the fact that MTiO2 thin films were composed of smaller monodisperse spherical particles about 15 nm and had higher specific surface areas. Furthermore, the monodispersity of TiO2 particles was beneficial to transfer and separation of photo-generated electrons and holes in the inner of and on the surface of TiO2 particle and reduced the recombination of photo-generated electrons and holes. The films deposited on quartz showed the highest photocatalytic activity because films deposited on quartz exhibited a better crystallization and had no sodium contaminant. The photocatalytic activity of MTiO2 and TiO2 thin films deposited on different substrates after treated with H2SO4 solution was significantly enhanced. Acid treatment was particularly effective for MTiO2/glass and TiO2/glass, which showed activity enhancement of four and over two times, respectively. This increase in activity has been correlated with the reduction of sodium ions and the increase in the adsorbed hydroxyl content on the surface of TiO2 films.

Enhanced photocatalytic activity of mesoporous and ordinary TiO2 thin films by sulfuric acid treatment

Highly ordered TiO2 nanotube arrays (TNs) are prepared by electrochemical anodization of titanium foil in a mixed electrolyte solution of glycerol and NH4F and then calcined at various temperatures The prepared samples are characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy The photocatalytic activity is evaluated by photocatalytic degradation of methyl orange (MO) aqueous solution under UV light irradiation The production of hydroxyl radicals ( OH) on the surface of UV-irradiated samples is detected by a photoluminescence (PL) technique using terephthalic acid (TA) as a probe molecule The transient photocurrent response is measured by several on–off cycles of intermittent irradiation The results show that low temperatures (below 600 °C) have no great influence on surface morphology and architecture of the TNs sample and the prepared TNs can be stable up to ca 600 °C At 800 °C, the nanotube arrays are completely destroyed and only dense rutile crystallites are observed The photocatalytic activity, formation rate of hydroxyl radicals and photocurrent of the TNs increases with increasing temperatures (from 300 to 600 °C) due to the enhancement of crystallization Especially, at 600 °C, the sample shows the highest photocatalytic activity due to its bi-phase composition, good crystallization and remaining tubular structures With further increase in the calcination temperature from 600 to 800 °C, the photocatalytic activity rapidly decreases due to the vanishing of anatase phase, collapse of nanotube structures and decrease of surface areas

Effect of calcination temperature on morphology and photoelectrochemical properties of anodized titanium dioxide nanotube arrays

Novel thin films of titanium dioxide dispersed in a polymeric matrix have been prepared by a chemically modified sol–gel technique. Nanostructured films of pure TiO2 in the anatase form are obtained after annealing at 500°C. SEM, TEM and TG/DTA are used for the structure characterisation of TiO2 films. The role of the polymer in controlling the microstructure is confirmed. The first application of this technique in gas sensor field is presented in this work. Ethanol and methanol sensing properties are tested and reported. TiO2 sensors can detect very well concentration required for breath analysers.

TiO2 thin films by a novel sol–gel processing for gas sensor applications

Nanosized titanium dioxide photocatalysts with varying amount of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO 4 with urea was used to prepare porous spherical clusters of anatase TiO 2. Photoactive titania powders with variable amount of anatase and rutile phases were prepared by heating of pure anatase in the temperatutre range 800–1150 °C. The structure evolution during heating of the starting anatase powders was studied by XRD analysis in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM, BET and BJH. The spherical particle morphology of TiO 2 mixtures determined by SEM was stable in air up to 900 °C. The photocatalytic activity of the sample titania TIT85/825 heated to 825 °C in air, contained 77.4% anatase and 22.6% rutile was higher than that nanocrystalline anatase powder. Titania sample TIT85/825 reveals the highest catalytic activity during the photocatalyzed degradation of 4-chlorophenol in aqueous suspension.

Photoactivity of anatase–rutile TiO2 nanocrystalline mixtures obtained by heat treatment of homogeneously precipitated anatase

TiO2 coatings with different crystal structures were prepared from alkoxide solutions via the dip-coating technique. The physical properties, except the crystal structure, were adjusted to distinguish the effect of crystal structure on their photocatalytic property. The results of photocatalytic measurements using TiO2 coatings with different crystal structures showed that the decomposition of aqueous acetic acid was enhanced by the content of anatase phase.

Crystal structures of TiO2 thin coatings prepared from the alkoxide solution via the dip-coating technique affecting the photocatalytic decomposition of aqueous acetic acid

Porous anatase coatings were prepared from alkoxide solutions containing organic polymer by a dip-coating technique. The morphology of the coatings, such as pore size, pore distribution and thickness, was controlled. The effects of the morphology of the porous anatase coatings on the photocatalytic activity for the photocatalytic decomposition of aqueous acetic acid were examined.

Morphology of thin anatase coatings prepared from alkoxide solutions containing organic polymer, affecting the photocatalytic decomposition of aqueous acetic acid

TiO2 coatings are attractive materials for use as photocatalysts, photoelectrodes and solar cells. Structural modification, quantum size effects, and large surface-to-volume make the coatings interesting. We have described the effects of crystal strucmre [1], crystallinity [2] and morphology [3] of TiO2 coatings on photocatalytic properties, and shown that a TiO2 coating prepared from a chemically-modified alkoxide solution had characteristic structur.es [4]. Here we report the photocatalytic properties of TiO2 coatings prepared by the chemically modified alkoxide method, which have nanostructure and show preferred orientation along the c axis. We also report the effect of oxygen vacancies in the TiO2 coatings on the photocatalytic properties. Decomposition of acetic acid is a very important reaction because during decomposition acetic acid usually generates organic compounds containing more than two carbons. Decomposition of aqueous acetic acid by use of oxygen and photocatalysts is lcnown to proceed differently from the photo-Kolbe reaction [5] with a product of ethane. During the photocatalytic decomposition of aqueous acetic acid with oxygen, formaldehyde is generated as an intermediate compound and this oxidizes readily to carbon dioxide. Chemical oxygen demand (COD) decreases to zero characteristically in the process. Therefore, the photocatalytic decomposition of aqueous acetic acid with oxygen is a key reaction for purification and treatment of water. T iQ coatings were prepared by the chemically modified alkoxide method. The method has been described in detail elsewhere [4]. The precursor solution for the coatings was prepared from titanium tetraisopropoxide, anhydrous el:hanol, diethanol amine, water and polyethylene glycol (molecular weight; Mw = 2000). The concentration of titanium tetraisopropoxide in ethanol was 0.5 mol dm -3. The molar ratios of water and diethanolamine to titanium tetraisopropoxide were 1 and 2, respectively. The concentration of polyethylene glycol to titanium tetraisopropoxide was 20 wt%. Gel coating, which was prepared on a quartz glass plate by a dip-coating method, crystallized to anatase during elevation on

Y. Butsugan

Papers

Crystal structures of TiO2 thin coatings prepared from the alkoxide solution via the dip-coating technique affecting the photocatalytic decomposition of aqueous acetic acid

Morphology of thin anatase coatings prepared from alkoxide solutions containing organic polymer, affecting the photocatalytic decomposition of aqueous acetic acid

TiO2 coating photocatalysts with nanostructure and preferred orientation showing excellent activity for decomposition of aqueous acetic acid