Magnetic FeO/g-CN/ZnO@Bentonite quaternary heterojunction for solar-light-driven photocatalytic removal of clomipramine drug.

This study presents the fabrication of a novel quaternary heterostructure nano-photocatalyst, FeO/g-CN/ZnO@Bentonite, designed for the efficient photocatalysis of Clomipramine hydrochloride (CMP), a persistent pharmaceutical contaminant. The properties of the catalyst were thoroughly characterized using various techniques. Band edge positions of FeO, g-CN, and ZnO were estimated from UV-Vis DRS data using absolute electronegativity and band gap calculations, confirming the formation of a direct Z-scheme heterojunction with CB and VB potentials facilitating effective spatial charge separation. XPS analysis further revealed strong interfacial interactions, including Fe-C bonding and Zn-O-Fe linkages, as well as oxygen vacancies that promote enhanced surface activity and electron mobility. These structural features support the proposed charge-transfer mechanism, wherein electrons in ZnO and FeO recombine with holes in g-CN, while retained electrons in g-CN and holes in FeO drive redox reactions, leading to enhanced reactive oxygen species (ROS) generation. Optimization of operational parameters via RSM-CCD identified optimal conditions (0.03 g/L catalyst dosage, pH 6, 60 min irradiation, 30 mg/L CMP), achieving 98.02 ± 1.89 % degradation efficiency. The quadratic regression model showed strong correlation (R = 0.96, AIC = 234.46). LC-MS analysis confirmed the transformation of CMP into non-toxic intermediates, while scavenger experiments identified hydroxyl and superoxide radicals as the key reactive oxygen species (ROS) in the degradation mechanism. The photocatalyst exhibited remarkable reusability over 15 consecutive cycles, with negligible performance loss and maintained structural integrity confirmed by post-treatment XRD and FTIR. With a low synthesis cost of $43.12/kg, this nano-photocatalyst offers a sustainable, structurally robust, and economically viable solution for pharmaceutical wastewater treatment.