PHOTOCATALYTIC DEGRADATION OF POLLUTANT OVER TIO2 IN DIFFERENT CRYSTAL-STRUCTURES

TiO2 samples of different crystal forms and crystal sizes were prepare d by calcining the hydrolysis product of titanium tetraisopropoxide at different temperatures. The photocatalytic degradation rate of severa l compounds over TiO2 was either dependent on the calcination temperat ure (group I) or independent of it up to 500 degrees C (group II), Gro up I compounds are sparsely water-soluble, whereas group II compounds are water-soluble. For group I compounds there was a proportional rela tionship between the degradation rate and crystal size of anatase. A h ypothesis explaining the mechanism of the photocatalytic processes of the two groups was proposed on the basis of their different adsorption modes. The addition of H2O2 accelerated the photocatalytic degradatio n. This effect was more pronounced for rutile than anatase.