Titania photocatalytic reactions with

In our experiment, photocatalytic decomposition of ethylene was utilized to probe the surface defect. Photocatalytic properties of all titania samples are shown in table 2. From these results, conversions of ethylene at 5 min and 3 hr were apparently constant (not different in order) due to the equilibrium between the adsorption of gaseous (i.e. ethylene and/or O2) on the titania surface and the consumption of surface species. Moreover it can be concluded that photoactivity of titania increased with increasing of Ti site present in titania surface. It was found that surface area of titania did not control photoactivity of TiOa, but it was the surface defect in titania surface. Although, the lattice oxygen ions are active site of this photocatalytic reaction since it is the site for trapping holes [4], this work showed that the presence of oxygen vacancy site (Ti site) on surface titania can enhance activity of photocatdyst, too. It revealed that oxygen vacancy can increase the life time of separated electron-hole pairs. 

Figure 4.11 Schematic representation of a photocatalytic reaction occurring on a titania particle on which Pt nanoparticles have been deposited. Adapted from [160] with permission from Springer Science and Business Media.

Watanabe et al. have reported similar action spectrum analysis of photoin-duced degradation of Rhodamine B with a cadmium sulfide suspension and pointed out a similar dye-sensitization mechanism Watanabe, T. Takizawa, T. Honda, K. J. Phys. Chem. 1977, 81, 1845. Photocatalytic reaction of MB in aerated titania suspensions was reported in 1937 by a Japanese photochemist Horio, M. Nihon Gakujutsu Kyokai Hokoku 1937, 12, 204 (in Japanese). As far as the author knows, this is the first report on titania photocatalysis. 

The influence of surface hydrophihcity of catalyst on the oxidation of benzylal-cohol to benzaldehyde in aqueous solution has been investigated by Augugliaro et al. [34] using a synthetic titania catalyst with predominant anatase phase and titania P25. More hydrophilic catalyst was prepared by hydrolysis using TiCl4 as precursor. The comparative in situ ATR-FTIR results show that the selectivity to benzaldehyde is increased over the more hydrophilic catalyst. This is attributed to a lower ability of photocatalytic reaction products to adsorb at the surface. 

Hydrolysis. Ultrasound assistance to hydrolysis reactions largely involves organic systems — both liquids and solid-liquid systems, which are dealt with here simply to reduce the number of subheadings — but also in inorganic systems — mostly heterogeneous. One example of the latter is the improved photocatalytic activity of titania-only materials fabricated by an ultrasound-assisted hydrolysis process, on which US has an elusive effect [41]. In any case, organic hydrolysis is by far a much common application of US. These reaotions almost invariably require high-intensity ultrasound [42,43]. When two immiscible phases are involved — which is most often — the authors consider the liquid-liquid interphase as interface [44]. 

Anpo M., Shima T., Kodama S. and Kubokawa Y. (1987), Photocatalytic hydrogenation of propyne with water on small-particle titania size quantization effects and reaction intermediates , J. Phys. Chem. 91, 4305-4310. 

The infiuence of supported Au particles on the photoconversion of NO2 has been investigated by simultaneous detection of gas phase and surface species using DRIFTS by Ramakrishnan et al. [24]. The nanosized Au-supported catalyst was prepared by deposition of pre-prepared Au nanoparticle precursor solution onto titania. The catalysts were illuminated in the in situ reaction chamber by a 365 nm 50 mW LED UV source coupled with fiber optics while simultaneously collecting the diffuse reflectance spectra. Adsorption of NO2 is negligible in dark however, new absorption bands arose between 1200 and 1800 cm after starting illumination of the catalyst (Figure 4.1). The band intensities observed with Au-supported catalysts increase markedly with N O2 photocatalytic conversion in the quadrupled gas phase. Marked increase of activity has also been confirmed for the photooxidation of phenol in parallel batch experiments. 

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