Degradation Efficiency And Mechanism Of Levofloxacin Via Peroxymonosulfate Catalyzed By Hierachical Hollow Cobalt Molybdenum In Wastewater

Antibiotics are widely used in bacterial infections all over the world.Levofloxacin（Lev）is one of the most widely used antibiotics because of its broad-spectrum antibacterial properties and strong antibacterial activity.Antibiotics widely exist in natural water,which will improve the drug resistance of microorganisms,and pose a great threat to the ecology and human health.Among many methods to remove antibiotics,persulfate advanced oxidation technology has made achievements in the degradation of refractory organic compounds.Method of activating peroxymonosulfate（PMS）with heterogeneous transition metals has been widely concerned because of its high activation efficiency,simple operation and recyclable catalyst.Among them,Co-based catalyst is considered to be the best PMS activator among all transition metals.However,there are still some defects in the cobalt-based catalysts,such as few active sites,slow Co³⁺/Co²⁺circulation,lack of favorable physical structure on the surface of the materials.In view of the above problems,this study intends to synthesize a highly efficient cobalt-based catalyst to activate PMS to degrade levofloxacin rapidly.In this paper,hierachical hollow Mo/Co bimetallic oxide（Mo/Co HHBON）with excellent catalytic performance was synthesized by coupling polyoxometalates（POM）with zeolites imidazole framework（ZIF-67）to form precursors,and then calcined at high temperature to realize efficient activation of PMS and rapid degradation of Lev.The physical and chemical properties of the materials were obtained by various characterization,and the degradation efficiency and mechanism of Lev by Mo/Co HHBON/PMS system were studied.In conclusion,the following conclusions are obtained.（1）The Mo/Co HHBON is successfully synthesized.The material has hollow and micro/meso/macroporous structure with open cavity.The specific surface area of the material is 69.37 m²/g,which is 3 times than that of the sample without PMA（Co₃O₄,22.15 m²/g）.PMA is successfully embedded into ZIF-67 cavity,realizing the nano level contact of Mo and Co atoms,which is conducive to the electron conduction and changes the electronic structure of the material.The content of Co²⁺is increased,indicating the oxygen vacancy is promoted after PMA doping.（2）The system Mo/Co HHBON/PMS/Lev has excellent catalytic ability,wide p H adaptability,good recycling performance and strong chemical stability.The system has good catalytic activity in wide p H range（3-11）(pseudo first order reaction rate k_obs=0.558-0.859 min^-1).With the increase of PMS,catalyst concentration,the reaction rate increases first and then decreases.In the low concentration range（[PMS]=0.5-1.0 m M,[catalyst]=40-100 mg/L）,the higher the concentration,the better the catalytic effect.If the concentration is too high,the quenching effect will affect the catalytic performance.In the reaction conditions of p H=7,[PMS]=1.0 m M,[catalyst]=100 mg/L,reaction temperature=25℃,91%Lev is removed in 15 min with k_obs=0.652 min^-1,which is 6-10 times of the previous study.The interfering substances such as Cl^-,HCO₃^-,HPO₄^-and HA have different degrees of inhibition effects.Mo/Co HHBON/PMS system has excellent degradation ability for PEF,PNP,RHB and MB and removal rate is up to 85%after 6^th run,indicating good universal application the excellent cycle stability performance.（3）The improvement of Lev degradation by Mo/Co HHBON/PMS system,active oxygen generation mechanisms and the potential pathway of Lev degradation are revealed.The results shows that k_obs of Mo/Co HHBON/PMS/Lev is16 times higher than the system Co₃O₄/PMS/Lev.From the perspective of radicals,Mo/Co HHBON/PMS produces more active oxygen,benefitting to the degradation of Lev.From the perspective of electron transfer,Mo/Co HHBON/PMS has better PMS adsorption ability,stronger electron transfer ability,the O-O bond is easier to break to produce active intermediate to degrade lev.Three active oxygen production mechanisms are as follows.Mechanism 1:oxidation reduction cycle of transition metal(Co²⁺/Co³⁺,Mo⁴⁺/Mo⁶⁺).Mechanism 2:bimetallic synergism.Mechanism 3:oxygen vacancy promotes the production of ¹O₂.Based on the 27 kinds intermediate products of Lev,the 6 transformation pathways are deduced,invovling decarboxylation,quinolone ring opening,piperazine ring opening,ammoniation,hydroxylation,defluorination,dehydrogenation.And biological toxicity of Lev degradation intermediates decrease.