Copper Oxide-Doped Bismuth Oxychloride Heterostructures for Heterogeneous Photocatalysis: Design, Kinetics, and Photocatalytic Degradation Mechanism for Water Decontamination

Bismuth oxychloride (BiOCl)- copper oxide (CuO) heterostructures were synthesized via a solvothermal route and assessed as visible-light-driven photocatalysts for methyl orange (MO) degradation. Different CuO loadings deposited on BiOCl microspheres were investigated to identify the optimal composition. Structural and physicochemical characterization revealed that low CuO content (0.6 wt. %) promoted uniform dispersion and enhanced surface area, whereas higher loadings led to nonuniform coverage and reduced photocatalytic efficiency. Operating conditions were optimized using response surface methodology based on a central composite design, considering catalyst dosage (0.1-0.8 g L^-1) and pH (4-9). The highest degradation efficiency (~50% after 60 min irradiation) was achieved at pH = 4 and a catalyst dosage of 0.8 g L^-1 using the BiOCl surface modified with 0.6% CuO. Kinetic analysis followed a pseudo-first-order model. Mass spectrometry identified transient intermediates associated with demethylation and desulfonation pathways, while radical scavenger experiments confirmed hydroxyl radicals (^•OH) as the dominant oxidizing species, with a secondary contribution from superoxide radicals (^•O₂^-). These results highlight the critical role of CuO dispersion and interfacial quality in enhancing charge separation and photocatalytic performance, providing practical guidelines for the rational design of BiOX-CuO heterostructures for water remediation applications.