ZnS Nanospheres Coated with ZnSe/MoSe2 Shells as Dual Heterojunctions with Wide Spectral Responses for the Photoreduction of Cr(VI)

Cr(VI) is a kind of heavy metal ion with strong toxicity to the environment. A better treatment strategy is to reduce Cr(VI) to low toxic Cr(III). However, how to implement this process cleanly and efficiently is still a challenge. In this study, ZnS/ZnSe/MoSe2 (ZZM) nanocomposites with dual type-II heterojunctions are synthesized by solvothermal and ion exchange methods for the first time. The photocatalytic performance of ZZM nanocomposites is evaluated by the photocatalytic reduction of Cr(VI) under visible light irradiation. The ZZM-1:1 nanocomposites can reduce 96.0% of Cr(VI), and the reaction rate constant is 2.476 × 10–2 min–1, which is 3.67, 3.44, and 10.49 times higher than those of MoSe2, ZnSe, and ZnS, respectively. The improved photocatalytic activity can be assigned to the dual heterostructures, which effectively promotes the separation and transmission of photogenerated charge carriers. Meanwhile, the extended light response range and the increased specific surface area also contribute to the improvement of the photocatalytic efficiency. After five cycles, the ZZM-1:1 nanomaterial still shows an 81.1% photoreduction efficiency for Cr(VI). The experimental results show that the ZZM nanocomposites have great potential in removing Cr(VI) from wastewater.