In situ synthesis of Au-decorated BiOCl/BiVO4 hybrid ternary system with enhanced visible-light photocatalytic behavior

BiOCl/BiVO4 photocatalysts with different ratios of gold particles were synthesized by a facile method at room temperature. The gold was in situ incorporated on the BiOCl/BiVO4 powders through the chemical reduction of HAuCl4 using ascorbic acid as reducing agent. X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis diffuse reflectance spectroscopy were conducted to perform the textural, structural and composition characterizations of the materials; while their photoactivities were evaluated using the methyl orange degradation under visible-light irradiation. The detailed morphology and microstructure of the 1.50Au-(BiOCl/BiVO4 ) catalyst reveals nanometer and micro-meter sized particles in a range from 20 to 500 nm with sphere and elongated-like shapes. Polycrystalline features are observed with preferred (121) surface orientation and interplanar distance values corresponding to (112), (004) and (022) planes of monoclinic BiVO4, while (011), (110), (102) planes can be related to tetragonal BiOCl with the direction (111). The surface chemical analysis showed that the most active Au-(BiOCl/BiVO4) catalyst presents the highest V4+/V(5+ )ratio (0.85), a 43 at.% BiOCl content and a percentage of Au-decoration of about 1 at.%. A synergic behavior between these chemical compositions enhances the MO photocatalytic degradation. It was found that photodegradation rates strongly relied on the gold content, and the Au-(BiOCl/ BiVO4) photocatalyst was highly stable after six reuses and easy to be recovered by centrifugation. A possible electronic transfer mechanism in the different as-synthesized photocatalysts upon visible illumination is proposed, thus elucidating the roles of Au, BiOCl and BiVO4 components. Presumably, the synergistic interaction arising between semiconducting and metallic nanoparticles induces the charge separation responsible for the enhanced photocatalytic behavior.