Study On Photo-Assisted N-rGO/Fe₃O₄ Catalyzed S₂O₈^2- Degradation Of Antibiotics

The advanced oxidation technology based on SO₄^-·?SR-AOPs?is a newly arisen advanced oxidation technology?AOPs?that has been rapidly developed recently.Under certain conditions?heat,light radiation,ultrasound,microwave,transition metal ions,etc.?,the peroxy bond in the persulfate?peroxymonosulfate?PMS?/peroxydisulfate?PDS??is broken to produce SO₄^-·,thereby achieving the degradation and mineralization of pollutants.However,most of the activation methods in SR-AOPs are susceptible to the constraints of equipment conditions and energy consumption,or cause the disadvantages of secondary pollution at different levels.Heterogeneous catalysts have huge development prospects and application potential in research of SR-AOPs due to the low ion dissolution rate and convenient separation and recovery.Therefore,research on relating issues has important practical significance.This study proposed that SR-AOPs and photocatalysis were combined in the form of heterogeneous catalysis to constituted an oxidation system in which SO₄^-· and ·OH exist simultaneously.The utilization efficiency of the ultraviolet and visible light of the catalytic system was improved by the persulfate oxidant as an electron acceptor and the electron transfer between the light-induced ligand and the heterogeneous catalyst.In this paper,the composite catalyst?N-rGO/Fe₃O₄?was synthesized by hydrolysis process with N atom-doped graphene oxide?GO?loaded with Fe₃O₄.N-rGO/Fe₃O₄ overcame the agglomeration phenomenon of Fe₃O₄ and N-rGO laminates,increased defect edges and active sites,improved catalytic activity,and realized the recovery and reuse of composite catalysts by magnetic separation.The degradation efficiency of N-rGO/Fe₃O₄ activated PDS system,ultraviolet assisted N-rGO/Fe₃O₄ activated PDS system and visible light assisted N-rGO/Fe₃O₄ activated PDS system to tetracycline?TC?,oxytetracycline?OTC?and norfloxacin?NOR?were investigated respectively.Analyze the catalytic mechanism and explore the degradation pathways of antibiotic pollutants.Specific research contents include the following aspects:?1?GO was prepared by an improved hummers method,and GO was doped with N atoms and simultaneously loaded with Fe₃O₄ to synthesize a composite material N-rGO/Fe₃O₄.The microstructure,surface functional group and phase structure were characterized by scanning electron microscopy?SEM?,Fourier transform infrared?FTIR?and X-ray diffraction?XRD?.It was indicated that N atoms were successfully doped into the carbon skeleton and Fe₃O₄ particles are evenly distributed on the surface of N-rGO.The catalytic reaction mechanism,degradation kinetics and degradation pathways of N-rGO/Fe₃O₄ activated PDS catalytic system to degrade TC were explored.In addition,the effects of reaction time,N-rGO/Fe₃O₄ and PDS addition ratio,initial TC concentration and pH value on catalytic activity and reuse stability were studied.The results showed that under the optimized conditions?PDS=2 mM;m?N-rGO/Fe₃O₄?:m?PDS?=6:1;pH=3?,the 60 mg/L TC degradation efficiency at 120 min reached 100%.Moreover,the degradation efficiency of OTC was still up to 90.79%in 5 repeated cycles.?2?On this basis,the N-rGO/Fe₃O₄ activated PDS system was combined with photocatalytic form,and the photocatalytic efficiency was improved by using PDS and N-rGO/Fe₃O₄ as electron acceptors.Further explored the effect of UV-assisted N-rGO/Fe₃O₄ activated PDS system on the degradation efficiency of NOR,and proved that the UV-assisted N-rGO/Fe₃O₄ activated PDS system has a 10.8-fold increased in the reaction rate constant of NOR compared to N-rGO/Fe₃O₄ activated PDS system.The results showed that under the optimal conditions?PDS=1 mM;m?N-rGO/Fe₃O₄?:m?PDS?=4:1;pH=3?,the 100 mg/L NOR degradation efficiency reached 100%in 13 minutes,and N-rGO/Fe₃O₄ showed stable catalytic activity in cycling experiments.The main active radicals in the UV-assisted N-rGO/Fe₃O₄ activated PDS system were ·OH and SO₄^-·,and there may be a non-radical catalytic mechanism that occurred in the outer layer of N-rGO/Fe₃O₄.In addition,five possible degradation pathways of NOR were deduced based on HPLC-MS.?3?The effect of Vis on the degradation of OTC in N-rGO/Fe₃O₄ activated PDS systems was investigated based on the dominance of Vis in the solar spectrum,and based on the characteristic that tetracycline antibiotics are prone to direct photolysis.The results showed that under the optimal conditions?PDS=1 mm;m?N-rGO/Fe₃O₄?:m?PDS?=4:1;pH=3?,the 50 mg/L OTC degradation efficiency reached 100%in 32.5 minutes,and there was no significant decrease after five cycles.·OH and SO₄^-· were the main active oxides for OTC degradation in this system.In addition,according to HPLC-MS analysis,four OTC degradation pathways were proposed,namely hydroxylation,dehydration,decarbonylation and demethylation.