The cation-exchange resin loaded with ferrous ion (CERF) catalyzes the photochemical oxidation of 2,4-D. The co-existence of UV light and oxalate is the key to initiating the attack by hydroxyl radicals of 2,4-D in the presence of CERF and H2O2. In addition to oxalate, citrate and EDTA may also drive the CERF-induced photooxidation that is more favorable in an acidic environment. The solid catalyst can easily be separated from the solution by filtration after the reaction, and then reused. The removal rate of 2,4-D with the reused CERF was found to be faster than that with the fresh CERF This can be explained by the presence of a higher amount of ferrous ions in the recycled resin, thus speeding up the production of hydroxyl radicals. The effect of oxalate concentration on the recycling efficiency of the catalyst was studied. For the first cycle, the rate constants increased as the oxalate concentration increased. The removal rate was strongly dependent on the concentration of the oxalate. For practical purposes, a model was derived to evaluate the capacity of the catalyst and to predict the cumulative mass of 2,4-D removed at any reaction time of any cycle. In a series of four runs conducted with the same catalyst, the optimal concentration of oxalate was found to be 2.4 mm, and 74.7% of 2,4-D (total 0.099468 mg) was transformed. (c) 2007 Elsevier B.V. All rights reserved.