Construction of Mg-doped ZnO/g-C3N4@ZIF-8 multi-component catalyst with superior catalytic performance for the degradation of illicit drug under visible light

Methadone (MET) as a synthetic opioid agonist drug found in sewage as well as in treated wastewater from treatment plants was selected as a representative illicit drug in the present study. A pathway was developed for the fabrication of Mg-ZnO/g-C3N4@ZIF-8 and the photocatalytic degradation of MET from water under LED light. The morphology, porous properties and structure of the nanocomposite catalyst was characterized using UV–vis DRS, PL, XPS, XRD, FTIR, SEM-EDX, TEM, and BET techniques. Mg-ZnO/g-C3N4@ZIF-8 semiconductor nanostructure has shown great potential toward the efficient photodegradation of MET under visible light irradiation. Approximately complete degradation of MET takes place in just 10 min at initial drug concentration of 50 mg/l, pH of 9, catalyst dosage of 0.5 g/l and the presence of 0.3 g/l of NaBH4. The as-prepared nanocomposite catalyst showed long-term stability and excellent recyclability for six cycles. Additionally, phototransformation intermediates generated during photocatalysis reaction were investigated by LC-MS/MS. The photodegradation of pollutants by Mg-ZnO/g-C3N4@ZIF-8 nanocomposite photocatalyst benefits from better charge separation efficiency, the highly porous structure and more absorption of pollutant molecules as well as molecular transport of both products and reactants, the production of additional oxidant radicals in the presence of BH4−ions and finally the synergistic effects due to the heterojunction or interface between Mg-ZnO and g-C3N4. The Mg-ZnO/g-C3N4@ZIF-8 nanocomposite with remarkable catalytic performance under visible light and great stability is a promising catalyst for efficient wastewater treatment applications.