The Study About The Mechanisms Of Metal-organic Frameworks Derived Bi₂O₂CO₃/porous Carbon Nitrid For The Photodegradation Of Wastewater Contaminated With Antibiotics

In recent years,tetracyclines and sulfonamides are widely used as pharmaceutical and personal care products,leaving their residues in the surface water,groundwater,and wastewater treatment plants effluents more serious.They are hazardous for the ecosystem and cause growing concerns to public health,even at low concentrations,but conventional water treatment techniques cannot fully remove them.Up to now,great efforts have been dedicated to developing photocatalysts with efficient solar-driven catalytic processes owing to their intriguing prospects for addressing the energy crisis and environmental pollution.Lately,the photocatalysts derived from metal–organic frameworks have been attracting widespread attention due to their controllable structure and open diffusion channels.Therefore,in this study,bismuth-based MOFs derived Bi₂O₂CO₃/porous carbon nitrid have been synthesized for the photodegradation of tetracyclines and sulfonamides.Furthermore,the reaction mechanism and degrdation pathway have been deeply investigated.Specific research contents are as follows:（1）In the past five years,bismuth-based MOFs have received steadily rising interests in the application of smart photonic devices,sensors,and catalysts.However,to our best knowledge,the possibility of using Bi-MOF derived products as photocatalysts has never been explored.In this study,we designed a novel composite composed of Bi₂O₂CO₃ anchored in porous g-C₃N₄ hybrids via one-shot calcination of the CAU-17/melamine precursor.The composition,morphologies and surface areas are characterized by X-ray diffraction,scanning electron microscopy and transmission electron microscopy.Meanwhile,the interface properties between Bi₂O₂CO₃ and g-C₃N₄ are investigated by the high-resolution transmission electron microscopy,flourier transform infrared spectra,X-ray photoelectron spectroscopy and electron spin resonance measurements.Theory calculations demonstrate that this kind of chemical bond could provide an electron shuttle pathway to accelerate the interfacial charge flow（decreased the energy barrier and transfer distance by 5?e V and 1.4??）.（2）The photocatalytic performance was estimated by the degradation of antibiotics under visible light irradiation,including TC and SMT.For SMT,all composites displayed superior photocatalytic decomposition efficiency compared to g-C₃N₄,Bi₂O₂CO₃ and Bi₂O₃.Among them,the BO/CN-3 exhibited the highest photocatalytic performance（90.31%）for the degradation of SMT in 90 min.As for TC,the BO/CN-3 effectively degraded more than 83%of TC within 60?min of visible light illumination in comparison with 42%by pristine g-C₃N₄.The photocatalytic degradation efficiency of TC and SMT slightly reduced by 5%and 6%after four cycles,respectively,indicating good stability of composites.（3）To accurately investigate the different photocatalytic activities,the corresponding rate constant k to the specific surface area was also normalized.The results indicate the synergistic effects between BO and CN rather than the increased surface area reinforced the photocatalytic capacities under visible light.Time-resolved fluorescence spectra were further performed at their corresponding steady-state emission peaks yield to calculate the average radiative lifetime.A double-exponential function fits the decay,yielding the radiative average lifetime of≈7.24?ns and 4.97?ns for CN and BO/CN-3.Species trapping experiments and EPR spin-trapping experiments shows ¹O₂and h⁺are the main reactive species.This could be ascribed to the strong interaction and formation of Bi-N bonds at the interface,thus promoting spatial charge separation and the oxidation of·O₂^-by holes.