Influence of pH and chloride anion on the photocatalytic degradation of organic compounds - Part I. Effect on the benzamide and para-hydroxybenzoic acid in TiO2 aqueous solution

In the present work. we have studied the influence of pH (in the range 3-11 ) and chloride anions (in the range 0-0.8 mol/l) on the photocatalytic degr adation (PCD), with titanium dioxide (TiO2), in aqueous solution of two aro matic compounds: benzamide (BA) and para-hydroxybenzoic acid (4-HBZ). No si gnificant adsorption is detected for the BA; further the pH input has a ver y low effect on this photodegradation rate. However, the pH effect on the a dsorption of 4-HBZ on TiO2 Surface is significant and this is a factor to t ake into account in relation the photocatalytic decomposition of organic po llutants in water. For this compound, the degradation rate increases when t he pH decreases. The effect of the pH on the degradation rate of 4-HBZ is n ot only dependent on the TiO2 charge surface but also on the formation of h ydroxyl free radicals. At low chloride concentration, the behaviours of BA and 4-HBZ are sensitively different ([Cl-] < 0.02 mol/l). 4-HBZ is only wea kly dependent on the chloride concentration. By contrast, the degradation o f BA is strongly affected by the chloride ions concentration. (C) 2001 Else vier Science B.V. All rights reserved.