Photocatalytically Assisted Hydrolysis of Chlorinated Methanes under Anaerobic Conditions

The photocatalytic degradation of CCl 4, CHCl 3, and CH 2 Cl 2 over irradiated TiO 2 has been investigated at pH 5 and pH 11 under anaerobic conditions. Chloromethanes degrade through combined reductive and oxidative processes. Photocatalytically assisted hydrolysis, given by sequential reactions involving • OH/e - /H +, is 10 6 −10 8 times faster than the corresponding thermal process. Dechlorination of chloromethanes is achieved with degradation rates in the order CCl 4 > CHCl 3 > CH 2 Cl 2 . Stable intermediates, either chlorinated (chloromethanes, C 2 Cl 6, and C 2 Cl 4 ) or dechlorinated (formic acid, formaldehyde, and methanol) have been quantified. The average carbon oxidation number n C remains almost unchanged at the end of the degradation process, although for CCl 4 in the early stages it is markedly reduced with slow regrowth of n C toward the initial value. Reaction pathways accounting for the observed results are presented based on literature data concerning transient intermediates.