NATURE AND PROPERTIES OF PURE AND NB-DOPED TIO2 CERAMIC MEMBRANES AFFECTING THE PHOTOCATALYTIC DEGRADATION OF 3-CHLOROSALICYLIC ACID AS A MODEL OF HALOGENATED ORGANIC-COMPOUNDS

Pure and Nb-doped TiO2 ceramic membranes supported on glass were prepared by sol-gel techniques. When irradiated with near-UV light, these membranes brought about the photocatalytic degradation of 3-chlorosalicylic acid (3-CSA). Relationships between preparation conditions and the characteristics and efficiencies of the different membranes have been inferred. The changes in the physical-chemical characteristics of these membranes when they are fired at high temperatures are retarded by both the Nb-doping and the coating on glass supports. Doping does not improve the rate of degradation of 3-CSA, despite the fact that light absorbance is higher. The increase of firing temperature causes an increase in the size of membrane particles and a remarkable drop in the specific surface area, resulting in a substantial decrease in photochemical efficiency. A discussion based on the hypothesis of e-/h+ recombination at grain boundaries and point defects of the membranes is presented. © 1992.