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. (C) 2013 Elsevier B.V. All rights reserved.