Visible-light-driven photocatalytic degradation of ofloxacin by g-C3N4/NH2-MIL-88B(Fe) heterostructure: Mechanisms, DFT calculation, degradation pathway and toxicity evolution

In this study, g-C3N4/NH2-MIL-88B(Fe) (MCN-x) heterostructures were successfully prepared using a facile solvothermal method. MCN-x composites exhibit excellent degradation performance toward ofloxacin in aqueous solution under visible light (lambda > 420 nm). The photodegradation rate of ofloxacin by MCN-60 under visible light reaches 96.5% in 150 min, and the apparent first-order kinetics rate constant reaches 0.0217 min(-1), 3.7 and 4.7 times that of pristine g-C3N4 and NH2-MIL-88(Fe), respectively. This decent photocatalytic performance is principally attributed that the introduction of g-C3N4 can notably promote the separation of photogenerated electron-hole pairs. Besides, the photocatalytic efficiency and structure of the MCN-60 composite basically show no change after three reuse cycles. Furthermore, trapping experiments and ESR analyses confirm that the center dot O-2(-) radical has a more dominant role than center dot OH and holes (h(+)). The ofloxacin degradation mechanism and pathway are predicted by density functional theory (DFT) calculations and an intermediate analysis. Quantitative structure-activity relationship (QSAR) predictions reveal that the ofloxacin photocatalytic degradation process can reduce toxicity in a step-by-step manner. MOF-based materials have been confirmed to show high potential for practical application in removing emerging pollutants from wastewater.