Activation Of Persulfate By Biochar Catalyst For The Degradation Of Tetracycline Hydrochloride

In recent decades,with the continuous improvement of human economic and living standards,environmental pollution caused by refractory organic substances such as tetracyclines（TC）has become an increasingly serious and concerned problem.Biochar is a new type of environmental remediation material produced from waste biomass under limited oxygen conditions.In recent years,us ing waste biomass as a low-cost carbon precursor to synthesize functional materials to activate persulfate（PS）to eliminate organic pollutants such as TC has been extensively studied.However,the sources of biochar are very wide,and the biochar catalysts prepared from different precursors have different structural properties and catalytic performance.Therefore,it is crucial to discuss different sources of biochar and select suitable precursors to prepare biochar catalysts.In this paper,a novel N,P co-doped biochar catalyst（FS-BC）was successfully prepared by selecting fish scales as raw materials,and it was applied to activation peroxymonosulfate（PMS）and peroxodisulfate（PDS）at the same time for the first time,and the TC was successful degraded.At the same time,peanut shell and coffee grounds were selected as raw materials to successfully prepare peanut shell biochar（PS-BC）and coffee ground biochar catalysts（CG-BC）.The differences of the three different sources of biochar catalysts to activation PMS and PDS for the degradation of TC were systematically studied.The specific research contents and discussions are as follows:（1）FS-BC,PC-BC and CG-BC were successfully prepared by direct one-step pyrolysis.Different morphologies pore structures,specific surface areas,defect structures and elemental compositions of the three catalysts were identified by means of SEM,XRD,FTIR,BET,Raman,XPS and other characterization methods.The results showed that PS-BC was dominated by non-porous structure,FS-BC had microporous and mesoporous structures,and CG-BC was dominated by mesoporous structure.The specific surface area of FS-BC（89.8761 m²/g）was between PS-BC（299.0649 m²/g）and CG-BC（71.5392 m²/g）,but it had the highest degree of defects.FS-BC was rich in mineral elements such as P and Ca,which were not contained in PS-BC and CG-BC.（2）The differences of PS-BC,FS-BC and CG-BC on PMS and PDS activation and degradation of TC were explored.Among them,FS-BC exhibited the best catalytic performance due to its excellent defect structure（I _D/I_G=1.225）and the synergistic effect of N and P heteroatoms.When using PMS as oxidant,the degradation efficiencies of PS-BC,FS-BC and CG-BC to TC were 86.26%,99.71%and 84.41%,respectively.When using PDS,the degradation efficiencies of PS-BC,FS-BC and CG-BC for TC degradation were 56.79%,93.99%and 49.12%,respectively.In the FS-BC/PMS system,almost complete degradation of TC was achieved.In addition,the degradation efficiency of TC in the PMS system was significantly higher than that in the PDS system,indicating that PMS ha d better activation properties.The initial p H and anions（HCO₃^―,H₂PO₄^―,Cl^―and NO₃^―）had no obvious effect on the degradation of TC in the FS-BC/PMS system and the FS-BC/PDS system.After three cycles of FS-BC,the degradation efficiency of TC in FS-BC/PMS system and FS-BC/PDS system can still reach 95.64%and 91.99%.Meanwhile,the total organic carbon（TOC）removal efficiencies of the FS-BC/PMS and FS-BC/PDS systems can reach 62.34%and 54%,respectively.It show ed that FS-BC had very broad practical application scenarios.（3）The mechanism of PMS and PDS activation to degrade TC was explored by means of quenching experiments,electron paramagnetic resonance（ESR）characterization,and electrochemical characterization.In the FS-BC/PMS and FS-BC/PDS systems,the presence of a radical pathway was not detec ted,but a non-radical pathway involving surface-bound reactive species,singlet oxygen（¹O₂）,and direct electron transfer was involved.Structural defects,N species（graphitic N and pyridine N）,P-C groups,and positively charged sp² hybrid C adjacent to graphitic N were all important active sites.（4）The degradation pathway of TC was explored,and the intermediate products of TC were detected by liquid chromatography-mass spectrometry（HPLC-MS）.TC is finally mineralized to carbon dioxide（CO₂）and water（H₂O）through processes such as hydroxylation,demethylation process,and dehydration.