Impact of TiO2 Surface Defects on the Mechanism of Acetaldehyde Decomposition under Irradiation of a Fluorescent Lamp

TiO2 was placed in heat-treatment at the temperature of 400–500 °C under flow of hydrogen gas in order to introduce some titania surface defects. It was observed that hole centers in TiO2 were created during its heat treatment up to 450 °C, whereas at 500 °C some Ti3+ electron surface defects appeared. The type of titania surface defects had a great impact on the mechanism of acetaldehyde decomposition under irradiation of artificial visible light. Formation of O•− defects improved both acetaldehyde decomposition and mineralization due to the increased oxidation of adsorbed acetaldehyde molecules by holes. Contrary to that, the presence of electron traps and oxygen vacancies in titania (Ti3+ centers) was detrimental for its photocatalytic properties towards acetaldehyde decomposition. It was proved that transformation of acetaldehyde on the TiO2 with Ti3+ defects proceeded through formation of butene complexes, similar as on rutile-type TiO2. Formed acetic acid, upon further oxidation of butene complexes, was strongly bound with the titania surface and showed high stability under photocatalytic process. Therefore, titania sample heat-treated with H2 at 500 °C showed much lower photocatalytic activity than that prepared at 450 °C. This study indicated the great impact of titania surface defects (hole traps) in the oxidation of acetaldehyde and opposed one in the case of defects in the form of Ti3+ and oxygen vacancies. Oxidation abilities of TiO2 seem to be important in the photocatalytic decomposition of volatile organic compounds (VOCs) such as acetaldehyde.

Synthesis, Characterizations and Photocatalytic Activity of Mesoporous TiO2 Using Typha Latifolia as Template

Typha latifolia were successfully used as template to synthesize mesoporous titania and silica with efficient photocatalytic activity under solar and visible light. Both two titania and silica samples were characterized by a combination of various physicochemical techniques, such as, N2 adsorption/ desorption isotherm, diffuse reflectance UV-vis, and X-ray diffraction. It was found that both two synthesized samples exhibited similar morphologies to the original templates. The presence of the residual carbon species of mesoporous titania and silica strongly affects their photocatalytic activity. The photoactivity of P25 TiO2 could not almost exhibit while both mesoporous titania and silica samples exhibited varied photoactivities for dyes under visible light, due to the presence of the residual carbon species. Moreover, as a whole the titania sample enhanced the higher photocatalytic activity than the silica sample under both solar and visible light.

Improvement of Orange II Photobleaching by Moderate Ga3+Doping of Titania and Detrimental Effect of Structural Disorder on Ga Overloading

Highly photoactive Ga3+-doped anatase modification of titania was prepared by homogeneous hydrolysis of aqueous solutions mixture of titanium oxo-sulphate TiOSO4and gallium(III) nitrate with urea. Incorporation of Ga3+into the anatase lattice has a clear positive effect on the photocatalytic activity under UV and Vis light irradiation up to a certain extent of Ga. Ga3+doping decreased the size of the crystallites, increased surface area, and affected texture of the samples. Higher amount of gallium leads to the formation of a nondiffractive phase, probably photocatalytically inactive. The titania sample with 2.18 wt.% Ge3+had the highest activity during the photocatalysed degradation in the UV and visible light regions; the total bleaching of dye Orange II was achieved within 29 minutes. Ga concentration larger than 5% (up to 15%) significantly inhibited the growth of the anatase crystal domains which formed the nondiffractive phase content and led to remarkable worsening of the photobleaching efficiency.

Photoactivity of Anatase–Rutile TiO2 Nanocrystalline Mixtures Obtained by Heat Treatment of Titanium Peroxide Gel

ABSTRACTNanosized titanium dioxide photocatalysts with anatase structure or mixture of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO4 and ammonia and following treatment with H2O2 was used to prepare porous yellowish (Ti-Per) gel. The gel was lyophilized for 48h and (Ti-Per)LYO-powder was obtained. Single phase anatase TiO2 samples were prepared by heating of the (Ti-Per)LYO powder. The lamella-like particle morphology of TiO2 samples determined by SEM were stable in air up to 950°C.The structure evolution during heating of the starting (Ti-Per)LYO powder was studied by DTA and XRD analyses in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM and BET methods. The photocatalytic activity of the sample titania TI-LYO/950 heated to 950ºC in air contained 78.4% anatase and 21.6% rutile was higher than standard Degussa P25. Titania sample TI-LYO/950 reveals the highest catalytic activity during the photocatalyzed degradation course of 4-chlorophenol in aqueous suspension under UV-irradiation.