The photocatalyic degradation and modeling of 2,4-Dichlorophenoxyacetic acid by bismuth tungstate/peroxide

Abstract

The photodegradation of herbicide 2,4-Dichlorophenoxyacetic acid (2,4-D) by bismuth tungstate with or without hydrogen peroxide by visible light was investigated. The photocatalytical reactions were studied under various conditions including the examination of the effects of initial pH, 2,4-D concentrations, light intensities, and hydrogen peroxide. Photocatalytic reactions were optimized at pH 5, higher or lower pH levels will reduce the decay rate due to the phase change of 2,4-D molecules and/or bismuth tungstate. The increase of catalyst/[2,4-D] ratio and light intensity were found to improve the 2,4-D decay rates, due to the increment of number of active sites and electron–holes on the Bi2WO6 surface, respectively. The involvement of H2O2 in the Bi2WO6 photocatalytic process can effectively double the 2,4-D decay rate, however, this was observed within a narrow gap of H2O2 dosages and easily overdosed, a precise control of H2O2 dosing is critical for a successful application. Kinetic models were derived successfully, so that the process performance is predictable by incorporating initial pH level, 2,4-D concentration, light intensities, and hydrogen peroxide.