Sunlight-activated BiOCl@ZnO core-shell-like heterostructures for the efficient removal of dye pollutants

In this study, we report the successful synthesis of BiOCl@ZnO core-shell-like heterostructures designed to harness solar energy for the efficient removal of hazardous dyes. The BiOCl@ZnO heterostructures were synthesised using a reflux-assisted precipitation method, and their structural, morphological, surface, and compositional properties were systematically characterised using HRTEM, SEM, XRD, FTIR, UV-vis spectroscopy, EDX, thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) surface area analysis. The sunlight-driven photocatalytic activity of BiOCl@ZnO was evaluated against the cationic dyes methylene blue (MB) and rhodamine 6G (Rh6G), the anionic dye Congo red (CR), and their ternary mixture simulating real wastewater. The photocatalyst exhibited high degradation efficiencies, achieving 94.39% for MB, 63.76% for Rh6G, and 92.78% for CR individually, while the corresponding efficiencies in the ternary dye system were 92.20%, 85.73%, and 72.98%, respectively. The effect of pH on photocatalytic activity was also investigated, revealing optimal degradation of MB and CR at pH 7, and Rh6G at pH 11. Radical-scavenging experiments confirmed that photogenerated holes (h + ) are the dominant reactive species driving the dye degradation, thereby elucidating the photocatalytic mechanism.