PHOTOOXIDATION OF CERTAIN ORGANICS USING TiO2 SUSPENSION AS CATALYST

Abstract

TiO2 sensitized photochemical reaction of ethanolamine has been studied under different experimental conditions and reaction environments. The irradiation of TiO2 - ethanolamine reaction mixture by the light of wavelength > the band gap energy of TiO2 (3.2 ev) results in the oxidation of adsorbed substrate to produce HCHO via C-C bond cleavage. In the studied concentration range of ethanolamine, the reaction follows first-order kinetics with respect to ethanolamine. This reaction has been carried out in oxygenated, aerated and nitrogen atmosphere. Oxygen acts as an electron scavenger and enhances the photocatalytic efficiency by about 3 times to that of the aerated reaction samples. In nitrogen atmosphere no reaction product could be detected. In the acidic medium at pH 2.5 the protonation of ethanolamine and TiO2 surface does not lead to the formation of C-C bond cleavage product. However, the hydroxylation of TiO2 surface increases the yield of HCHO by about 4 times to that of observed at pH 5.6. The presence of acrylonitrile reduces the reaction yield indicating the operation of free radical mechanism. This reaction could also be initiated by sunlight efficiently. About 12 wt% of silver is found to be the optimum concentration of Ag4- as a co-catalyst for the photooxidation of ethanolamine. At high concentration of silver the rate of reaction is retarted. On the basis of these observations a reaction scheme is suggested.