PHOTOCATALYTICALLY ASSISTED HYDROLYSIS OF CHLORINATED METHANES UNDER ANAEROBIC CONDITIONS

The photocatalytic degradation of CCl4, CHCl3, and CH2Cl2 over irradia ted TiO2 has been investigated at pH 5 and pH 11 under anaerobic condi tions. Chloromethanes degrade through combined reductive and oxidative processes. Photocatalytically assisted hydrolysis, given by sequentia l reactions involving (OH)-O-./e-/H+, is 10(6)-10(8) times faster than the corresponding thermal process. Dechlorination of chloromethanes i s achieved with degradation rates in the order CCl4 > CHCl3 > CH2Cl2. Stable intermediates, either chlorinated (chloromethanes, C2Cl6, and C 2Cl4)or dechlorinated (formic acid, formaldehyde, and methanol) have b een quantified. The average carbon oxidation number n(C) remains almos t unchanged at the end of the degradation process, although for CCl4 i n the early stages it is markedly reduced with slow regrowth of n(C) t oward the initial value. Reaction pathways accounting for the observed results are presented based on literature data concerning transient i ntermediates.