Roles of Mo dopant in Bi₂WO₆ for enhancing photocatalytic activities

We present the investigation of the roles of molybdenum (Mo) dopant with a concentration of 0.0625% to 1.0% Mo into bismuth tungstate (Bi₂WO₆) by a one-step hydrothermal method for the enhancement of photocatalytic activities. The obtained materials and doping effects were characterized by the morphology, crystal structure, chemical states, and optical properties. By combining XRD, XANES, and EXAFS studies, the distortion of the local structure with substitutional doping was revealed as doping with Mo ions was located at the lattice sites of the tungsten ions. Photocatalytic reactions of Mo-doped Bi₂WO₆ were studied by the degradation of methyl orange dye under visible light irradiation. The results show that the optimal concentration of Mo dopant is 0.25%, with the highest photocatalytic activity up to ∼2-fold compared to the bare Bi₂WO₆. From our investigation, we propose that the impurity level is located below the conduction band edge of Bi₂WO₆ after doping with Mo⁶⁺ ions. This impurity level acts as an electron trapping site to prevent the transition of excited electrons from the conduction band to the valence band. By trapping experiments, the superoxide anion radicals (O₂˙^-) as the main active species to enhance photocatalytic efficiency was established.