Comparative Study of the Photocatalytic Degradation of the Herbicide 2,4-D Using WO.sub.3/TiO.sub.2 and Fe.sub.2O.sub.3/TiO.sub.2 as Catalysts

In this study, a comparison of the photocatalytic activity efficiency of the catalysts WO.sub.3/TiO.sub.2, Fe.sub.2O.sub.3/TiO.sub.2, and TiO.sub.2 in the degradation of the herbicide 2,4-D and its main by-product (2,4-dichlorophenol, 2,4-DCP), under natural sunlight, visible, and UV light, was carried out. The catalysts were synthesized by the sol-gel method. All the catalysts showed anatase crystalline phase, and they exhibited similar values of band gap, specific surface area, and crystallite size; however, different photocatalytic activity was observed under the different light sources. Complete degradation of 2,4-D and near to 89% of mineralization using WO.sub.3/TiO.sub.2 and Fe.sub.2O.sub.3/TiO.sub.2 was achieved after 150 min under solar light, while using TiO.sub.2 sol-gel, lower degradation rate was obtained. By using artificial light (UV and visible lamp), the degradation and mineralization rates were lower than those obtained under natural sunlight. The produced 2,4-DCP intermediate was completely degraded after 240 min under sunlight only with the modified catalysts.