Photocatalysed degradation of a herbicide derivative, bromacil, in aqueous suspensions of titanium dioxide

Abstract

The photocatalysed degradation of a herbicide, 5-bromo-3-sec-butyl-6-methyl uracil (bromacil, 1) has been investigated in aqueous suspensions of titanium dioxide under a variety of conditions. The degradation was studied by monitoring the depletion in total organic carbon (TOC) content as a function of irradiation time. The degradation kinetics of the model compound was studied under different conditions such as pH, catalyst concentration, substrate concentration, different types of TiO₂ and in the presence of electron acceptors such as hydrogen peroxide (H₂O₂) and potassium bromate (KBrO₃) besides molecular oxygen. The degradation rate was found to be strongly influenced by all the above factors. Higher degradation rate was observed with Degussa P25 as compared with other photocatalysts. The addition of bromate ion has been found to enhance the degradation rate markedly. 5-Hydroxy-3-sec-butyl-6-methyl uracil (2) and diisopropyl urea (16) were identified as the degradation products by GC-MS analysis and probable pathways for the formation of the products have been proposed.