CdS/MoS2 Heterojunctions: Facile Synthesis and Photocatalytic Reduction of the Toxic Cr(VI) to Cr(III) Micronutrient

Abstract

Among the aquatic pollutant remediation reactions, the reduction of toxic Cr(VI) to a benign Cr(III) is of significant interest. Among the avrious remediation methods, photocatalysis is considered optimal due to its efficiency and eco-friendly nature. Therefore, the development of highly active, visible-light-responsive, and noble-metal-free photocatalysts for the elimination of toxic heavy metal ions from wastewater is highly desirable. In this study, a facile two-step method, comprising solvothermal and hydrothermal, was used to synthesize visible-light-responsive CdS/MoS₂ heterojunctions (CM-HJs). Extensive structural characterization was performed to assess the crystal structure (XRD and XPS), morphology (SEM and BET), and optical (UV-Vis) properties of the as-synthesized photocatalysts. Aquatic Cr(VI) photoreduction was conducted on these photocatalysts under visible light irradiation. The results revealed the high photocatalytic activity and photostability of CM-HJs for Cr(VI) reduction compared to the bare CdS. Among the heterojunctions, CM-10 (10 wt % MoS₂) exhibted the highest acvtivty, reducing 99.04% of Cr(VI) within 60 min. The enhanced photocatalytic activity can be attributed to its high light harvesting capability and efficient separation and transportation of the produced electron-hole pairs due to the intimate contact interfaces and matching band potentials of CdS with MoS₂. Based on the literature and experimental evidence, a photocatalytic mechanism for the photoreduction of Cr(VI) is discussed in detail. The effect of different parameters; like the amount of photocatalyst, amount of Cr(VI), and pH were also evaluated. Like other good photocatalysts, CM-10 owes good photostability and recyclability.