Environment-Friendly Carbon Quantum Dots/ZnFeO Photocatalysts: Characterization, Biocompatibility, and Mechanisms for NO Removal.

A highly efficient and environmentally-friendly oxidation process is always desirable for air purification. This study reported a novel carbon quantum dots (CQDs)/ZnFeO composite photocatalyst for the first time through a facile hydrothermal process. The CQDs/ZnFeO (15 vol %) composite demonstrates stronger transient photocurrent response, approximately 8 times higher than that of ZnFeO, indicating superior transfer efficiency of photogenerated electrons and separation efficiency of photogenerated electron-hole pairs. Compared with pristine ZnFeO nanoparticles, CQDs/ZnFeO displayed enhanced photocatalytic activities on gaseous NO removal and high selectivity for nitrate formation under visible light (λ > 420 nm) irradiation. Electron spin resonance analysis and a series of radical-trapping experiments showed that the reactive species contributing to NO elimination were ·O and ·OH radicals. The possible mechanisms were proposed regarding how CQDs improve the photocatalytic performance of ZnFeO. The CQDs are believed to act as an electron reservoir and transporter as well as a powerful energy-transfer component during the photocatalysis processes over CQDs/ZnFeO samples. Furthermore, the toxicity assessment authenticated good biocompatibility and low cytotoxity of CQDs/ZnFeO. The results of this study indicate that CQDs/ZnFeO is a promising photocatalyst for air purification.