Visible light-assisted photocatalytic mineralization of diuron pesticide using novel type II CuS/Bi2W2O9 heterojunctions with a hierarchical microspherical structure

In this study, a series of CuS/Bi2W2O9 type II heterojunction photocatalysts with a hierarchical microspherical structure were prepared by a two-step process involving the combustion synthesis of Bi2W2O9 followed by CuS modification using a hydrothermal method. The heterojunctions were characterized by XRD, XPS, FESEM, TEM, IR, UV-vis-DRS and PL techniques. During synthesis, Cu2+ ions replaced W6+ ions to form Bi2CuxW2-xO9-2x as a nonstoichiometric solid solution phase. Pure Bi2W2O9 exhibited plate-like micron-sized particles. Under hydrothermal treatment, the desegregation of the Bi2W2O9 plates to nanosheets and the concurrent formation of CuS nanorods were noticed leading to their hierarchical reorganisation to microspherical structures. The heterojunction materials exhibited enhanced visible light absorption with an improved charge carrier separation ability. The CuS/Bi2W2O9 heterojunction materials were studied as an efficient photocatalyst for the degradation of diuron pesticide under visible light irradiation achieving 95% mineralization within 3 h. A mechanistic study indicated that the mineralization of diuron occurred in a cascade manner over the catalyst surface involving dechlorination, alkyl oxidation and oxidative ring-opening steps. In this study, a highly efficient visible light active photocatalytic system has been developed for the first time that is a viable alternative to a TiO2-based UV active photocatalyst for the mineralization of diuron pesticide.