PH effect in the photocatalytic transformation of a phenyi-urea herbicide

The photocatalytic transformation 0f the herbicide 1,1-dimethyl-3-phenylurea 0n aqueous TiO2 and ZnO suspensions was investigated at several pH. In neutral TiO2 and ZnO suspensions four main products are observed : both the aromatic ring and the methyl groups are oxidized. In acidic TiO2 suspensions (pH = 2), the main reaction is the oxidation 0f the methyl groups and the attack 0f the aromatic ring is a very minor process. This change at low pH in the distribution 0f products may result from changes in adsorption 0f fenuron onto the photoactive pigment.