Photocatalytic degradation of antibiotics using Cu doped-SnO2/CQDs nanocomposites

In this study, a copper-doped tin oxide/carbon quantum dot (CuSCs) nanocomposite was developed and applied for the photocatalytic degradation of antibiotics, specifically tetracycline (TCH) and sulfamethazine (SMT). The nanocomposite was characterized by the presence of metallic, carboxyl, and hydroxyl functional groups, with copper and CQDs uniformly distributed on the SnO₂ surface. The incorporation of Cu reduced the bandgap of the material, enhancing its visible-light absorption and photocatalytic activity. At an optimal dose of 40 mg/100 mL, the nanocomposite achieved 100 % degradation of TCH and 72 % degradation of SMT within 120 min. The variation in degradation efficiency was attributed to reactive species generated during photocatalysis, which preferentially disrupted the benzene ring in TCH over the sulfur-nitrogen bond in SMT. Maximum degradation was observed at an initial antibiotic concentration of 10 ppm. Light absorption by the solution was found to limit the production of oxidizing species, while pH optimization studies showed the highest degradation efficiencies at neutral pH (6.7–7.0). High-performance liquid chromatography-mass spectrometry (HPLC-MS) identified possible TCH degradation pathways, and mineralization experiments demonstrated a 47 % reduction in total organic carbon (TOC) for TCH within 120 min. Reactive species trapping experiments revealed that h⁺ and O₂•⁻ were the primary contributors to TCH degradation. These findings highlight the potential of CuSCs nanocomposites for the efficient degradation of antibiotic pollutants under visible-light irradiation.