Waste-derived carbon dots as interfacial defect modulators in ZnO for robust UV photocatalytic antibiotic degradation

A sustainable ZnO/carbon dots (ZnO/CDs) nanocomposite was synthesized via a one-step hydrothermal route using carbon dots derived from oil palm empty fruit bunch waste. High-resolution XPS analysis confirms deliberate interfacial defect engineering through the formation of Zn-C bonds (283.6 eV), an increased oxygen vacancy concentration (531.6 eV), and chemisorbed oxygen species, which collectively regulate charge transfer and defect-mediated reactivity. As a result, the ZnO/CDs composite exhibits exceptional UV-driven tetracycline degradation, achieving 92.67% removal of 5 mg L−1 within 180 min using 1 g L−1 catalyst at neutral pH, outperforming most reported undoped biomass-derived CDs/ZnO systems. Reactive species trapping experiments identify hydroxyl radicals as the dominant active species, with degradation reduced to 39.28% in the presence of tert-butanol, alongside a significant contribution from superoxide radicals, reduced to 58.10% with p-benzoquinone. These findings are consistent with a mechanism in which biomass-derived carbon dots function as efficient electron acceptors, suppressing charge recombination, and enhancing reactive oxygen species generation. The degradation process follows pseudo-first-order kinetics, and the ZnO/CDs nanocomposite demonstrates excellent stability, with more than 87% efficiency retained after five cycles, together with a competitive pilot-scale treatment cost of US$7.09 m−3. These results demonstrate a green, efficient, and economically viable photocatalyst for antibiotic wastewater remediation.