A STUDY OF THE PRIMARY STEP IN THE PHOTOCHEMICAL DEGRADATION OF ACETIC-ACID AND CHLOROACETIC ACIDS ON A TIO2 PHOTOCATALYST

The photocatalytic degradation of the four acids ClxCH3-xCOOH (x = 0-3) in the presence of UV-irradiated TiO2 was studied under O2, N2 and N2O. The formation of CO2, Cl- and CH2O with time was monitored. The decomposition rate depends strongly on the value of x and on the gas under which the reaction takes place. It is much higher under O2 than under N2O if hydrogen is bound to the α-carbon atom of the acid. The fast reaction under O2 is inhibited by addition of H2O2. Information on the nature of the intermediate free radicals was obtained from spin-trap experiments. Mechanisms involving several reactive species are deduced from the differences in reactivity of the acids. © 1990.