Research On The Performance And Mechanism Of Iron And Nitrogen Co-doped Carbon Nanomaterials To Activate Peroxymonosulfate To Degrade Organic Pollutants

Tetracycline（TC）is widely used in the fields of medical treatment,animal husbandry and aquaculture.Most tetracycline directly enters the environment in Active form through excretion,causing serious pollution.Traditional water treatment technology cannot achieve effective degradation of tetracycline.Recently,advanced oxidation technology based on peroxymonosulfate（SR-AOPs）has been favored due to its higher redox potential and longer life cycle.Various iron-based materials are widely used in the activation of peroxymonosulfate,owing to the advantage low price,wide sources,safety and non-toxicity.However,problems such as iron leaching and harsh p H range restrict its practical application.Anchoring the iron element on the carbon nanomaterial to form a carbon-coated iron core-shell structure is a feasible strategy that can effectively avoid the above shortcomings.In addition,due to the introduction of heteroatomic nitrogen with high electronegativity,nitrogen-doped carbon nanocomposites had displaied more and more odds,such as more active sites and stronger electrical conductivity.Therefore,using carbon materials as the matrix,incorporating iron and nitrogen into the interlayers of the carbon materials through a simple process and an appropriate framework,not only can avoid the loss of iron elements,but also can use a synergistic effect to enhance the catalytic activity.Based on this,the iron-nitrogen co-doped carbon nanomaterials were successful prepared by the one-pot pyrolysis method.Here,FeCl₃?6H₂O was the iron source and chelating agent,L-glutamic acid acted as the nitrogen source,and Cs served as the carbon source.The optimum synthesis conditions were determined by changing the Fe/N molar ratio and pyrolysis temperatures.The iron-nitrogen co-doped carbon nanomaterials were characterized through SEM,XRD,TGA,Raman,BET,FT-IR,XPS.The characterization results demonstrated that the microscopic morphology of Fe,N@Cs-800 was a coral-like structure composed of stacked nanosheets.The main forms of iron in Fe,N@Cs-800 were Fe⁰ and Fe₃C.TGA analysis showed that the iron content was 3.33%.Fe,N@Cs-800 had a specific surface area of 74.068 m²/g and pore size distribution between 2-15nm,belonging to a mesoporous structure.The influence of various reaction conditions such as catalyst dosage,PMS concentration,initial p H and TC concentration on the degradation of TC by Fe,N@Cs-800/PMS system was systematically investigated.The larger the catalyst dosage led to the higher the TC removal rate.As the concentration of PMS increased,the removal of TC had a tendency to promote first and then inhibit,ascribed to the self-quenching effect of excessive PMS.When the initial p H was 3-9,value the removal of TC had a negligible effect in the Fe,N@Cs-800/PMS system,revealing that it was suitable for a wide p H range.Moreover,the effects of common inorganic anions（Cl^─,NO₃^─,H₂PO₄^─,HCO₃^─）and humic acid（HA）on the removal of TC were explored.All of Cl^─,H₂PO₄^─,HCO₃^─,HA revealed different degrees of inhibition,and HCO₃^─had the most significant inhibition.Furthermore,the degradation experiments of different pollutants suggested that Fe,N@Cs-800 had selective oxidation and the dye removal effect was better than antibiotics.the active substances in the system were confirmed to be SO₄^?─,?OH,O₂^?─and ¹O₂ via free radical quenching experiment and ESR examination,and ¹O₂ was dominant.Pyridine N,graphite N,C=O were identified as the main active sites by the XPS analysis of used Fe,N@Cs-800.And Fe0,the cycle of Fe²⁺/Fe³⁺were also one of the sources of SO₄^?─and?OH.Besides,there are eleven major intermediates identified by LC-MS.Based on these intermediate products,three possible degradation pathways were proposed.Among them,part of the small molecular substances were directly mineralized into carbon dioxide and water.