Degradation Of Acetaminophen By Phosphorus-doped Cyanobacterial Carbon/persulfate/thiosulfate System

With the development of the economy and the increase of public health awareness,the demand for pharmaceuticals and personal care products(PPCPs)has surged.With the mass production and use of PPCP_S,PPCPs and their metabolites were continuously discharged into the environment through such pathways as production wastewater or domestic sewage.Persulfate(PS)oxidation technology based on activation of carbon materials can degrade many PPCPs through free radical or non-free radical pathways,without additional energy and metal ion pollution problems,which had a broad development prospect.Biochar was a kind of typical non-metallic carbon material with low price and abundant oxygen-containing functional groups.Due to the influence of raw materials and preparation conditions,the activation efficiency of biochar on persulfate was limited.Improving the activation efficiency of biochar on persulfate through heteroatom doping modification has been a hotspot in current research.In this study,phosphorous doped cyanobacteria biochar(CPB)was prepared out of cyanobacteria and carbonized after phosphorus-doped modification.The effects of phosphorus source and phosphorus addition amount on the specific surface area,surface functional groups,heteroatom distribution of phosphorus and other atoms of biochar were analyzed.Based on the optimized screening,this study constructed a phosphorus-doped cyanobacterial biochar/persulfate/thiosulfate system and carried out the degradation experiment with acetaminophen(ATP),a typical PPCPs,as the target substance.The effects of biochar dosage,persulfate concentration,solution p H,temperature,dissolved oxygen,typical anions and natural organic matter on the degradation of ATP in the system were investigated.The active species and active sites in the system were verified by electron paramagnetic resonance(EPR)and experiments.The intermediates were analyzed by gas chromatography-mass spectrometry(GC-MS)The specific conclusions are as follows:(1)Phosphorus doping changed the pore structure,content of surface phosphorus functional groups,carbon and oxygen functional groups of cyanobacteria biochar,and persulfate activation performance of cyanobacterial biochar were significantly improved.Phosphorus source and addition amount also affected the physical and chemical properties of biochar and its activation performance.Sodium dihydrogen phosphate was used as phosphorus source.Phosphorus-doped biochar prepared by high impregnation concentration(3.5 mol/L)showed good activation performance.(2)The degradation of ATP in biochar/persulfate/thiosulfate system was achieved under the synergistic action of biochar,persulfate and thiosulfate.In a certain range,increasing biochar dosage,persulfate and thiosulfate concentration,prolongation of reaction time and the rise of temperature can promote the degradation of ATP in the system.The degradation process of ATP conformed to the quasi first-order kinetic model.Under alkaline conditions(p H=11),the degradation of ATP was significantly decreased,and the degradation effect was also significantly inhibited by carbonate,bicarbonate and humic acid.In addition,the system was less affected by dissolved oxygen,chloride ion and nitrate in water.With the increase in biochar use times,the efficiency of the system decreased,which may be related to the loss of biochar surface active sites.(3)There may be free radical and non-free radical pathways in biochar/persulfate/thiosulfate system.In the free radical pathway,hydroxyl radical and sulfate radical may play a certain role in the degradation of the system,while in the non-free radical pathway,singlet oxygen and the electron transfer between ATP and PS together promote the degradation of ATP.By analyzing the surface chemical composition of biochar before and after the reaction,it was inferred that C=O and phosphor-containing groups play a certain role in the activation mechanism.By analysis of the intermediates,it was speculated that the phenol was formed into the degradation of acetaminophen,and then it was oxidized to form other small molecules.This study will provide a theoretical basis and technical support for the development of new persulfate activators and the resource utilization of cyanobacteria.