<p>In this study, we explored the photocatalytic degradation of methyl orange (MO) and Rhodamine B (RhB) via 2.0&#xa0;wt% I–Bi₂S₃, ZnIn₂S₄, and their composite ZnIn₂S₄/2.0&#xa0;wt% I–Bi₂S₃ under visible light irradiation. While 2.0&#xa0;wt% I–Bi₂S₃ revealed insignificant photocatalytic activity, ZnIn₂S₄ showed outstanding efficiency, degrading 94.7% of MO in 150&#xa0;min and 98.9% of RhB in just 35&#xa0;min. The composite achieved even better performance, 95% MO degradation (150&#xa0;min) and 99.7% RhB degradation (35&#xa0;min), demonstrating a synergistic effect between 2.0&#xa0;wt% I–Bi₂S₃ and ZnIn₂S₄. 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&#xa0;min⁻¹ for ZnIn₂S₄ and k = 0.25567 ± 0.00405&#xa0;min⁻¹ for the composite with R² = 0.99. This outcome indicates that RhB degradation follows first order kinetics closely. While the degradation of methyl orange fulfills R² ≈ 0.93, which means it is less consistent with the first order model. The computed rate constants were k = 0.01171 ± 0.00157&#xa0;min⁻¹ for ZnIn₂S₄ and k = 0.01362 ± 0.00184&#xa0;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 ZnIn₂S₄-based composites as high-performance photocatalysts for environmental remediation, displaying an exceptional solution for effectively eliminating hazardous organic dyes from wastewater.</p>