Fabrication of ZnIn2S4/2.0 wt% I–Bi2S3 heterostructured composite for photocatalytic degradation of methyl orange and rhodamine B dyes under visible light irradiation

In this study, we explored the photocatalytic degradation of methyl orange (MO) and Rhodamine B (RhB) via 2.0 wt% I–Bi 2 S 3 , ZnIn 2 S 4 , and their composite ZnIn 2 S 4 /2.0 wt% I–Bi 2 S 3 under visible light irradiation. While 2.0 wt% I–Bi 2 S 3 revealed insignificant photocatalytic activity, ZnIn 2 S 4 showed outstanding efficiency, degrading 94.7% of MO in 150 min and 98.9% of RhB in just 35 min. The composite achieved even better performance, 95% MO degradation (150 min) and 99.7% RhB degradation (35 min), demonstrating a synergistic effect between 2.0 wt% I–Bi 2 S 3 and ZnIn 2 S 4 . TEM, SEM, XRD, XPS, UV–Vis DRS, ESR, photoelectrochemistry, and PL tests were performed to characterize the structure, morphology, and separation efficiency of the products. According to kinetic studies, the photocatalytic degradation kinetics of rhodamine B and methyl orange exhibited various patterns. For Rhodamine B (RhB), a nonlinear exponential decay function was applied to obtain the rate constants, yielding k = 0.17186 ± 0.00147 min⁻ 1 for ZnIn 2 S 4 and k = 0.25567 ± 0.00405 min⁻ 1 for the composite with R 2  = 0.99. This outcome indicates that RhB degradation follows first order kinetics closely. While the degradation of methyl orange fulfills R 2  ≈ 0.93, which means it is less consistent with the first order model. The computed rate constants were k = 0.01171 ± 0.00157 min⁻ 1 for ZnIn 2 S 4 and k = 0.01362 ± 0.00184 min⁻ 1 for the composite. MO degradation is characterized by pseudo-first order behavior due to the deviation from linearity of a first order reaction. The boost in photocatalytic degradation was related to the reduction in electron–hole recombination that resulted from the creation of a heterostructure and a doping strategy. This study shows the potential of ZnIn 2 S 4 -based composites as high-performance photocatalysts for environmental remediation, displaying an exceptional solution for effectively eliminating hazardous organic dyes from wastewater.