Peroxymonosulfate Activation By The MOFs-derived Bimetallic Oxides For The Degradation Of Pefloxacin And Its Mechanism

Pefloxacin（PEF）is a representative third-generation fluoroquinolone antibiotic extensively used for the treatment of bacterial infections in both humans and animals,rendering it capable of entering the environment via various pathways.Nonetheless,the persistent occurrence of PEF in the environment potentially endangers human health and ecological safety.As municipal secondary biochemical treatment systems rely mainly on microbial-based biological treatment methods that cannot effectively remove antibiotics such as PEF,there are urgent need for research into effective methods of PEF removal.The advanced oxidation technology based on peroxymonosulfate（PMS）is characterized by strong oxidation capacity,an applicable p H range,operational simplicity,etc.Its principle is to activate PMS by various means to produce highly active sulfate radicals and hydroxyl radicals to achieve pollutant removal.Among the various activation methods,the non-homogeneous activation method based on transition metal oxides has attracted much attention,but it faces problems such as easy agglomeration of catalysts,single active sites and high leaching of active metals.In this study,transition metal doping was achieved by simple Lewis acid etching of cobalt-and zinc-based metal organic frameworks（MOFs）to obtain bimetallic precursors,which were then carbonized in an air atmosphere to obtain MOFs-derived bimetallic oxides,with the aim of increasing the active sites on the catalyst surface,improving catalytic activity and reducing active metal leaching.Systematically investigated the performance and mechanism of the obtained Co₃O₄/Zn O p-n heterojunction bimetallic oxide and Cu O/Zn O bimetallic oxide catalysts for the activation of PMS for the degradation of PEF,focusing on the mechanism of the action of the active sites on the surface during PMS activation,and explored the possible pathways for the activation of PMS for the degradation of PEF by the two catalysts.The major research contents and results are as follows:（1）MOFs-derived Co₃O₄/Zn O p-n heterojunction bimetallic oxide activated PMS for PEF degradationZIF-67 MOFs precursors were synthesized with cobalt acetate tetrahydrate（Co（OAc）₂·4H₂O）and 2-methylimidazole（2-Me IM）as raw materials and cetyltrimethylammonium bromide（CTAB）as a structural director.ZIF-67 MOFs were etched with anhydrous zinc chloride（Zn Cl₂）solution as Lewis acid and finally carbonized in air to obtain oxygen vacancy（O_V）-rich Co₃O₄/Zn O p-n heterojunction bimetallic oxides（ZOCO-X）.The synthesis conditions of the catalyst ZOCO-X were optimized to obtain the optimal catalyst,namely ZOCO-2.Characterization results from XRD,Raman,XPS,EPR and electrochemical experiments show that p-Co₃O₄/n-Zn O heterojunctions are formed in ZOCO-2 compared to single metal oxides and have more O_V,thus having a higher electron transfer efficiency and facilitating the activation of PMS.The catalytic degradation experiments showed that the ZOCO-2/PMS system was able to achieve 94.81%removal of PEF within 20 min.XPS analysis showed that the O_V content and the valence ratio of cobalt in ZOCO-2 changed after the reaction,implying that O_V,Co（Ⅱ）and Co（Ⅲ）were all involved in the degradation of PEF.The PFE degradation rate constant for the ZOCO-2/PMS system was(k_app=1.3500 min^-1),which was 151.8 and 84.4 times higher than that of the Zn O/PMS(k_app=0.0089 min^-1)and Co₃O₄/PMS(k_app=0.0160 min^-1)systems,respectively,and the formation of Zn O and Co₃O₄ p-n heterojunctions in the ZOCO-2 and the high content of O_Vin the ZOCO-2 played an important role in the rapid degradation of PEF.The catalytic degradation performance of the ZOCO-2/PMS system for PEF was investigated under different conditions of initial solution p H,reaction temperature,PMS concentration,catalyst dosage and aqueous matrix.The results showed that the system exhibited good removal rates for PEF in the p H range of 3.00 to 10.00and showed good immunity to various anionic influences.ZOCO-2 is still effective in activating PMS to remove 90%of PEF after 5 repeated applications.Additionally,the system exhibits favorable removal efficacy toward several other antibiotics as well as dyes.Reactive oxygen scavenging assay and electron paramagnetic resonance（EPR）analysis showed that the activation of PMS by ZOCO-2 produced reactive oxygen species such as^·OH,SO₄^·-,O₂^·-and ¹O₂,but^·OH and SO₄^·-played major roles in the degradation of PEF.Combined with the degradation intermediates obtained by HPLC-MS analysis,the mechanism of PMS activation by ZOCO-2 and the degradation pathway of PEF were proposed.（2）MOFs derived Cu O/Zn O bimetallic oxide activated PMS degradation of PEFZIF-8 MOFs precursors were synthesized with zinc nitrate hexahydrate（Zn（NO）₃·6H₂O）and 2-methylimidazole（2-Me IM）as raw materials,and ZIF-8 was etched by Cu Cl₂ solution as Lewis acid,and finally carbonized at high temperature under an air atmosphere to prepare O_V-rich Cu O/Zn O bimetallic oxides（CUZNOX）.The preparation conditions of the catalysts,including the amount of copper doping and calcination temperature,were optimised.The results indicated that the carbonisation temperature had a strong influence on the performance of the final catalysts,and the best catalytic degradation performance was obtained at 400℃（CUZNO3）.The crystal structure,elemental composition,valence,morphology,specific surface area and electron transfer properties of CUZNO3 were characterised and analysed by XRD,XPS,SEM,TEM,BET and electrochemical experiments.The catalytic degradation experiments demonstrated that the CUZNO3/PMS system could remove 94.45%of PEF at 20 min with a k_app of 0.4541 min^-1,which was 47.8 and 14.7 times higher than those of the Zn O/PMS(k_app=0.0095 min^-1)and the Cu O/PMS(k_app=0.0310 min^-1)systems,respectively.The greater amount of O_V in CUZNO3 gives it better PMS activation efficiency compared to Cu O and significantly lower Cu ion leaching during the reaction.The effects of catalyst dosage,the initial p H of the solution,PMS concentration and reaction temperature on the performance of the CUZNO3/PMS system for PEF removal were investigated.The results showed that the system exhibited good performance in removing PEF in the p H range of 3.00～11.00.The effect of co-existing substances(e.g.,Cl^-,HCO₃^-,SO₄^2-,NO₃^-and humic acids)in the water was investigated.Repeated use experiments have shown that CUZNO3 is still effective in activating PMS to remove around 90%of PEF after 5 applications.Additionally,the system exhibits favorable removal efficacy toward several other antibiotics as well as dyes.The activation of PMS by the CUZNO3 catalyst generated various reactive oxygen species,among which^·OH,SO₄^·-and ¹O₂ were crucial in decomposing PEF.18 intermediate products were detected during the degradation process via HPLC-MS analysis.These findings enabled the elucidation of the mechanism of PMS activation by CUZNO3 and the degradation pathway of PEF.