Flowerlike Sm-ZnIn2S4 as a Susceptible Visible-Light Photocatalyst for Cr6+ Reduction: Experimental Design, RSM, and ANN Modeling

Since Cr6+ compounds are introduced among the first category of hypertoxic water contaminants, efforts to find the most effective methods for removing such pollutants are research priorities. This study aims to convert Cr6+ into the less toxic oxidation state Cr3+ through an efficient photocatalytic process. To this end, samarium-doped ZnIn2S4 (Sm-ZnIn2S4) was synthesized via a one-pot solvothermal method and its flowerlike structure in the hexagonal crystal phase was validated through various characterization techniques. The photocatalytic performance of Sm-ZnIn2S4 exposed to visible light was systematically studied through experimental design and optimization by response surface methodology (RSM) and modeling by an artificial neural network (ANN). A Cr6+ reduction of 97.18% was attained under RSM-based optimal conditions ([Cr6+](0): 40 mg L-1; [Catalyst](0): 0.4 g L-1; pH 5; t: 60 min). According to ANN's results, solution pH was the most effective operational parameter. The kinetics of the process indicated a good fit with the quasi-first-order Langmuir-Hinshelwood model with a rate constant value of 0.034 min(-1), which is 4.3-fold compared with pristine ZnIn2S4. The good stability and long-term use of Sm-ZnIn2S4 were also proved through four consecutive cycles. The superior performance of Sm-ZnIn2S4 originated from the modulating the electronic structure of ZnIn2S4 through Sm doping and its flowerlike hierarchical structure, leading to increasing light harvesting, separating charge carriers, and adsorbing more Cr6+ ions. The results indicate that flowerlike Sm-ZnIn2S4 could be employed as a susceptible visible-light photocatalyst for wastewater treatment with high efficiency and operation speed.

Automated summary

This study focuses on using an efficient photocatalytic process to convert Cr6+ into its less toxic oxidation state Cr3+. Samarium-doped ZnIn2S4 was synthesized and its flowerlike structure was validated. The photocatalytic performance of Sm-ZnIn2S4 under visible light was systematically studied, achieving a Cr6+ reduction of 97.18%. The results suggest that Sm-ZnIn2S4 can be employed as an efficient visible-light photocatalyst for wastewater treatment.