Facile Synthesis of Hierarchically Structured Bi₂S₃/Bi₂WO₆ Photocatalysts for Highly Efficient Reduction of Cr(VI)

Varied morphologies and compositions of bismuth tungstate nanocomposites have been investigated as promising materials for photocatalytic applications. Among these nanocomposites, hierarchically structured bismuth sulfide (Bi₂S₃)/bismuth tungstate (Bi₂WO₆) hybrids have significant photocatalytic efficiency toward heavy metal ions. To simplify the synthetic procedure for this desirable composite, we developed a robust single-step hydrothermal synthesis for the formation of hierarchically structured heterocatalysts of Bi₂S₃/Bi₂WO₆ with a high yield (>95%). The synthesized heterostructures were characterized by various spectroscopic, microscopic, and surface area analysis techniques, which confirmed the successful incorporation of Bi₂S₃ into the Bi₂WO₆ matrix and were used to optimize pore size for enhanced catalytic activity. The resulting Bi₂S₃/Bi₂WO₆ heterocatalysts were used to remove toxic Cr(VI) ions via reduction to water insoluble Cr(III) utilizing visible-light irradiation. We also investigated the role of citric acid as a hole scavenger in the reduction of Cr(VI) with minimizing the rate of electron-hole recombination during photocatalysis. Likewise, the observed catalytic activity was significantly enhanced under a condition of an appropriate balance between hierarchical structure of catalysts and the amount of hole scavenger.