Eco-friendly synthesis of nitrogen-doped carbon dots from Cochlospermum regium for efficient photocatalytic removal of pharmaceutical contaminants and antibacterial performance

Nitrogen-doped carbon dots (NCDs) were successfully synthesized from Cochlospermum regium petals via a facile hydrothermal method using L-phenylalanine as a nitrogen source. The structural, morphological, optical, and electrochemical properties of the prepared materials were systematically characterized using XRD, SEM–EDX, TEM, UV–Vis spectroscopy, XPS, BET, and electrochemical impedance spectroscopy. Compared with undoped carbon dots (CDs), the NCDs exhibited enhanced visible-light absorption, improved charge transfer capability, and a larger surface area, which significantly promoted their photocatalytic performance. Under visible light irradiation, the NCDs achieved 82% degradation of amoxicillin and 68% degradation of ciprofloxacin, outperforming CDs under identical conditions. Optimization studies revealed that catalyst dosage, pollutant concentration, and light intensity strongly influenced degradation efficiency, with maximum degradation reaching 99% for amoxicillin and 82% for ciprofloxacin under optimal conditions (45 W visible light). Reactive species trapping experiments confirmed that superoxide radicals (O₂⁻•) played a dominant role in ciprofloxacin degradation, whereas hydroxyl radicals (•OH) were primarily responsible for amoxicillin decomposition. In addition, NCDs exhibited strong antibacterial activity against both Gram-positive and Gram-negative bacteria, good biocompatibility in MTT assays, and moderate antioxidant properties. Photodegradation experiments conducted in real water samples demonstrated stable and consistent removal efficiencies, confirming the robustness of the system. These findings highlight NCDs as a promising green nanomaterial for antibiotic removal and sustainable wastewater treatment under visible-light conditions.