Performance,Mechanism And Products Toxicity Of Tetracycline Degradation By Persulfate Activation With Fe,Co And O Co-doped G-C₃N₄

Antibiotics are complex molecular compounds with potent antibacterial abilities,which have been widely used as therapeutic drugs for bacterial infections and growth promoters in animal breeding.As one of the most widely used antibiotics in the world,tetracycline has the characteristics of stable chemical structure,high biological activity and strong persistence.Its long-term residue in the ecological environment poses a serious threat to human health and ecological environment security,and even leads to the emergence of superbugs has triggered an international public health crisis.Therefore,the pollution of antibiotics such as tetracycline and its treatment have attracted much attention.Oxidative degradation technology based on persulfate activation is a typical representative of chemical advanced oxidation technology.It can in situ generate SO₄·^-radicals with high potential,long half-life,wide p H adaptability and high selectivity to degrade antibiotics such as tetracycline.The field shows good application prospects.In recent years,carbon nitride（g-C₃N₄）,as a new type of two-dimensional organic polymer material,has been favored in the study of persulfate activation for wastewater treatment.However,pure g-C₃N₄ is limited in its ability to activate persulfate to degrade tetracycline due to the lack of freeπelectrons,low electron mobility,and low specific surface area in the conjugated system.Therefore,in this study,g-C₃N₄was doped with heteroatoms to improve its activity of activating persulfate to degrade tetracycline in wastewater containing tetracycline and to explore the potential biological toxicity risk of its degradation products.The main research contents and results are as follows:（1）Fe,Co and O co-doped thin-layer porous g-CN（FCOCN）was synthesized by one-step calcination method using metal source and urea as raw materials,The characterization results show that the heteroatoms Fe,Co and O are successfully doped into the g-C₃N₄structure through C-O-Fe-N or CO-Co-N bonds,so that the g-C₃N₄ planar structure is partially broken into smaller microstructures.crystal,forming an active network structure of edge defects and cavities,increasing its reactive sites,pollutant mass transfer capacity and electron transport capacity,its specific surface area increased from 28.59 m²/g to 55.66 m²/g,and the work function It is reduced from 4.94 e V to 4.85 e V,and the charge transfer resistance is reduced from 637.6Ωto 364.0Ω.（2）Fe,Co and O co-doped g-C₃N₄ can effectively activate sodium persulfate to degrade tetracycline in wastewater,and the degradation process is affected by the amount of sodium persulfate,catalyst amount,initial tetracycline concentration,p H and reaction temperature.When the amount of sodium persulfate and catalyst amount are 2500 mg/L and300 mg/L,respectively,the stoichiometric efficiency of Fe,Co and O co-doped g-C₃N₄ to activate persulfate and the degradation efficiency of tetracycline can reach 5.2%,respectively and 90.1%,and the first-order degradation kinetic constant(0.021 min^-1)was2.67 times that of pure g-C₃N₄,indicating that co-doping had a synergistic effect on persulfate activation;at the same time,with the decrease of initial tetracycline concentration and reaction p H,and the increase of the reaction temperature,the degradation efficiency of tetracycline was continuously enhanced,and the activation energy was 23.88 k J.mol^-1;after five consecutive cycles of Fe,Co and O co-doped g-C₃N₄,the degradation efficiency of tetracycline was still 72.7%,indicating that it has good recycling stability.（3）During the degradation of tetracycline by Fe,Co,and O co-doped g-C₃N₄/sodium persulfate system,sodium persulfate is mainly due to the synergistic transformation and enrichment of valence states between Fe³⁺/Fe²⁺and Co³⁺/Co²⁺redox pairs.Electron O/N and electron-deficient C act as catalytic centers to promote electron transfer and are activated to generate active species SO₄·^-,·OH,·O₂^-,¹O₂ and SO₅·^-to oxidize tetracycline;in decarboxylation,C decarboxylation bonds are broken,open Under the action of cyclization and/or hydroxylation,tetracycline is decomposed into 18 major transition products through 5possible pathways;quantitative structure-toxicity relationship prediction of transition intermediates and acute toxicity results of treated solutions indicate that Fe,Co and O are co-incorporated The mixed g-C₃N₄/sodium persulfate system had a good detoxification effect on tetracycline,and the toxicity of most intermediate products was significantly reduced,and the growth inhibition of Vibrio fischeri,Escherichia coli and Bacillus subtilis was significantly weakened in the treated water.