Photoinduced reduction of aquatic Cr(VI) on CdS/MoS 2 heterostructures

Abstract

Among the aquatic pollutant remediation reactions, the reduction of oncogenic Cr(VI) to a benign Cr(III) is a reaction of high interest. Among different remediation methods, photocatalysis is considered the best because of efficiency, eco-and environment-friendly nature. So, 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. Herein, a facile two-step method, solvothermal and hydrothermal, was used to synthesise visible-light responsive CdS/MoS2 heterostructures (CM-HSs). Extensive structural characterizations were performed to assess the crystal structure (XRD and XPS), morphology (SEM and BET), and optical (UV-Vis) properties of the as-synthesized photocatalysts (CM-HSs). Aquatic Cr(VI) photoreduction was carried out over these photocatalysts using visible light. The results revealed high photocatalytic activity and photostability of CM-HSs regarding Cr(VI) reduction compared to that of the bare CdS. Among the heterostructures, CM-10 (2 wt % of MoS2) was the most active, reducing 99.04% of Cr(VI) within just 60 min. The enhanced photocatalytic activity for CM-10 was attributed to its high light harvesting capability, 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 upon literature and experimental evidence, a photocatalytic mechanism for the photoreduction of Cr(VI) is also discussed in detail. The effect of different parameters, like amount of photocatalyst, amount of Cr(VI) and pH, were also evaluated. Like other good catalysts, CM-10 (2 wt % of MoS2) owe good photostability and recyclability.