Photodegradation of aqueous imidacloprid by CuS@TiO2 under solar-simulated light: complete mineralization, catalyst efficiency, recovery, and reuse

This work aims to investigate the photocatalytic degradation of imidacloprid (IM) via copper(II) sulfide (CuS) attached to a titanium dioxide (CuS@TiO₂) composite catalyst under solar-simulated light and to evaluate its efficiency compared with that of pure titanium dioxide (TiO₂) and other TiO₂ sensitizers. The CuS@TiO₂ composite demonstrated superior photocatalytic performance, achieving up to 96% degradation of IM under UV–visible irradiation and up to 70% under visible light alone. The primary objective was to determine the optimal parameters for maximum degradation efficiency, with the highest efficiency observed at pH 7.5, which is attributed to the balanced surface charge that would enhance IM adsorption. Additionally, this study examines the effects of the IM concentration and photocatalyst loading. Higher concentrations of IM reduce the efficiency due to competition for active sites, even though the quantum yields increase. The optimum photocatalyst loading was between 0.15 and 0.20 g, at which a peak removal efficiency of 93% was noted. The study also confirmed the complete mineralization of IM through high-performance liquid chromatography (HPLC), total organic carbon (TOC), and UV–visible spectroscopy analyses, which revealed significant reductions in organic carbon and its conversion to by-products that are much less harmful by-products, such as carbon dioxide (CO₂) and chloride ions (Cl⁻). During five cycles of reuse, the CuS@TiO₂ catalyst maintained a degradation efficiency of 91–96%, highlighting its robustness and long-term potential. These findings suggest that the CuS@TiO₂ composite is a promising, environmentally friendly, and effective alternative for large-scale environmental remediation.