Semiconductor Mediated Photocatalysed Reaction of Two Selected Organic Compounds in Aqueous Suspensions of Titanium Dioxide

Abstract

Semiconductor mediated hydrogen peroxide-assisted photocatalytic degradation of two selected pesticide compounds, chloramben (1) and cyanazine (2) has been investigated in aqueous suspensions under a variety of conditions. The degradation was studied by monitoring the depletion in total organic carbon (TOC) content and decrease in substrate concentration as a function of irradiation time. The degradation kinetics of pesticide compounds 1 and 2 were investigated under different conditions such as type of TiO₂ (Anatase/Anatase-Rutile mixture), reaction pH, catalyst dosage and hydrogen peroxide (H₂O₂) concentration. The degradation rates were found to be strongly influenced by all the above parameters. Titanium dioxide Degussa P25 was found to be more efficient as compared with other two commercially available TiO₂ powders like Hombikat UV100 and PC500 from Millennium Inorganic Chemicals. GC-MS analysis of the irradiated mixture of pesticide compounds 1 and 2 indicate the formation of several intermediate products which have been characterized on the basis of molecular ion/mass fragmentation pattern and also on comparison with the NIST library. Plausible mechanism for the formation of different products involving the reaction of hydroxyl and super oxide radical anions with 1 and 2 has been proposed.