Fabrication Of Metal-organic Frameworks Photocatalysts For Photocatalytic Degradation Of Fluoroquinolone Antibiotics And Their Mechanism

Antibiotics are used to treat human and animal diseases and are frequently detected in the environment as a new class of pollutants.By inducing the generation of drug-resistant bacteria and resistance genes,it destroys the micro-ecological environment and microbial community structure,and seriously threatens human health and ecological security.The treatment of emerging pollutants,including antibiotics,has not only received extensive attention from researchers,but has also been written into the"14th Five-Year Plan".Among the many antibiotic removal methods,green,energy-saving and efficient photocatalytic technology has been given high hopes.In recent years,metal-organic frameworks（MOFs）,as an emerging type of inorganic-organic hybrid material constituted with functional metal-oxo clusters and organic linkers,have demonstrated broad application prospects in photocatalysis.MOFs have high specific surface area and tunable porous structure.It has abundant active sites and can efficiently degrade antibiotics,which has become a research hotspot.In order to further improve the photocatalytic performance,MOFs and other materials are used to construct a heterojunction structure.In this paper,two MOFs heterojunction materials,g-C₃N₄/NH₂-MIL-88B（Fe）and Bi₂Mo O₆/Ui O-66-NH₂ were used for visible light photocatalytic degradation of fluoroquinolone antibiotics ofloxacin（OFL）and ciprofloxacin（CIP）.The main findings are as follows: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 visible light degradation performance toward ofloxacin in aqueous solution.The photodegradation rate of ofloxacin by MCN-60 under visible light reaches 97.5%in 150 min,and the apparent first-order kinetics rate constant reaches 0.0217 min^-1,4.5 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·O₂^-radical has a more dominant role than·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.In order to further improve the degradation efficiency of OFL and the adaptability of materials,direct Z-scheme Bi₂Mo O₆/Ui O-66-NH₂（BUN-x）heterostructures were successfully prepared using a facile solvothermal method.Z-scheme heterostructure was successfully formed between Bi₂Mo O₆ and Ui O-66-NH₂,which promoted transfer of electrons and holes.And BUN-x composites have smaller band gap and a stronger visible light absorption capacity,which elevate photocatalytic performance.Among them,the removal rates of OFL and CIP by BUN-100 composite were highest,which reached 100.0%and 95.0%within 90 min,respectively.In addition,the photocatalytic performance in OFL and CIP mixed systems was evaluated.The degradation of antibiotics in actual water was inhibited to some extent,and the overall decrease was not large.The cyclic experiment also proved good water stability of BUN-100 composite.In addition,the active species（·OH,h⁺and·O₂^-）generated by BUN-100 were certified.The active sites and degradation products of the two antibiotics were compared,and an identical degradation product was found.Finally,the degradation process of OFL and CIP could both gradually reduce toxicity.These two works provided new insights for synthesis of MOF-based photocatalysts and application in efficient and green antibiotic wastewater treatment.