KINETICS OF HETEROGENEOUS PHOTOCATALYTIC DECOMPOSITION OF MONURON OVER ANATASE TITANIUM-DIOXIDE POWDER

The photocatalytic degradation of Monuron (3-(4-chlorophenyl)-1-1-dime thylurea) in aqueous TiO2 dispersions irradiated in the near-UV region has been investigated by using a Pyrex batch photoreactor. The Monuro n and total organic carbon concentrations were determined; several rea ction intermediates were also identified using HPLC. The influence on the degradation kinetics of the initial Monuron concentration, of the TiO2 concentration, and of the initial pH of dispersion was studied. A pseudo-first order kinetics of Langmuir-Hinshelwood type was found to satisfactorily describe the Monuron degradation. The mineralization o f the pollutant was virtually complete in the 3-9 pH range while at pH = 1.0 and 11.0 only a partial mineralization was reached even after a long irradiation time. The quantum yield values of Monuron degradatio n were determined by measuring the photon flow transmitted by the disp ersion and applying a macroscopic photon balance on the photoreactor. The quantum yields were found to increase by increasing the pH of the dispersion.