Enhanced photocatalytic and antibacterial performance of ZnO/CuO nanocomposites via carbon dot decoration

Abstract Zinc oxide nanoparticles (ZnO-NPs) are gaining popularity due to their low toxicity, cost-effective production, and environmentally friendly profile. However, their practical use is limited by inherent challenges such as a large energy bandgap, high exciton binding energy, rapid electron–hole recombination, poor absorption of visible light, and low photocatalytic efficiency. To address these issues, our study introduces an innovative approach: incorporating small amounts of transition metal oxides like copper (II) oxide (CuO) along with trace amounts of carbon nanomaterials, specifically carbon dots (C-dots). We demonstrate that adding just 9% CuO nanoparticles and 2% C-dots to ZnO-NPs significantly enhances their properties. This modification reduces the energy bandgap from 3.08 eV to 2.51 eV, improving visible light absorption and boosting photocatalytic activity. In practical application, the optimized composite achieved an impressive 98.7% removal of methylene blue (MB) dye within 60 min under visible light, far surpassing pure ZnO-NPs, which only removed 62% in the same period. Additionally, the modified nanocomposites exhibit markedly improved antibacterial activity. The zones of inhibition against bacteria such as Bacillus Seraus, Escherichia coli, Salmonella typhi, and Staphylococcus aureus increased significantly from 8–13 mm for pure ZnO-NPs to 14–18 mm for the ZnO/CuO@C-dot composites, indicating stronger antimicrobial effects driven by enhanced surface charge and stability. Overall, our findings reveal that even minimal integration of C-dots into ZnO/CuO nanocomposites can dramatically elevate their photocatalytic and antibacterial performance. To our knowledge, this represents one of the most significant improvements achieved through such small additive modifications, opening new avenues for efficient environmental remediation and biomedical applications.