Analytical monitoring of photocatalytic treatments. Degradation of 2,3,6-trichlorobenzoic acid in aqueous TiO2 dispersions

The photocatalytic degradation of 2,3,6-trichlorobenzoic acid (2,3,6-TBA) i n aqueous TiO2 dispersions irradiated with simulated solar light was invest igated. Fast primary degradation of the herbicide, which obeys a pseudo-fir st order law, was observed. Complete mineralisation of the organic carbon t o CO2 was obtained after long term irradiation, with corresponding stoichio metric transformation of organic chlorine into chloride ion. Various aromat ic intermediates, originating from 2,3,6-TBA, were detected during the trea tment and identified using GC-MS. From the analytical data, a possible mult i-step degradation scheme was proposed. The photocatalytic treatment of the pesticide was also performed in the presence of Brij 35 micellar solutions , although strong inhibition of the process was observed. When surfactant a ggregates are present the photocatalytic destruction of 2,3,6-TBA is still possible at reasonable rates only after a proper dilution of the waste and by increasing significantly the semiconductor/pollutant ratio. (C) 1999 Els evier Science B.V. All rights reserved.