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 micrometer 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⁺/V⁵⁺ 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.