Removal Of Antibiotics By The Activated PMS With Two Dimensional Cobalt-based Catalyst And Its Mechanism

As the ever-increasing population and fast economic development,more antibiotics have been broadly used and released into the environment,which could cause serious ecotoxicological effects on the aquatic environment.Due to their long-term stability and refractory biodegradability,antibiotics are frequently detected in different water sources.Residues of antibiotics and their derivatives not only cause serious environmental problems,but also have potential impacts on human health.Therefore,it is of great significance to remove such refractory biological pollutants from wastewater.The advanced oxidation method based on persulfate mainly activates persulfate（PS）through different activation methods to generate SO₄^·-.In the various catalytic activation methods of PMS,the heterogeneous activation of PMS by transition metal catalysts has favorable features including high catalytic efficiency,mild reaction conditions and easy recovery,among which,cobalt-based catalysts are considered to be the transition metal catalysts with the best catalytic performance.Especially,Co₃O₄ has attracted much attention because of its excellent stability and cost-effectiveness.However,Co₃O₄ usually has a poor electrical conductivity and insufficient active sites.This seriously hinders its practical application in AOPs.Therefore,the construction of high catalytic performance Co₃O₄-based catalysts with rapid charge transfer and abundant active sites for PMS activation is of significance.In this context,two different synthesis methods were used to prepare Co₃O₄ catalyst with two-dimensional structure.Because two-dimensional structure can expose more reactive sites;at the same time,the electron transport capacity of Co₃O₄ is regulated by magnesium doping strategy.The target material was applied to the catalytic activation of peroxymonosulfate to degrade levofloxacin and tetracycline hydrochloride in water,and its efficiency and mechanism were investigated.Finally,the intermediate products of pollutants in the degradation process were further explored by LC-MS.The simple preparation method enriches the synthesis method of two-dimensional Co₃O₄ and also provides a new idea for the research of efficient Co₃O₄catalyst.The main research contents and results are as follows:（1）Co₃O₄/MgO nanosheet for efficient PMS activation to rapidly degrade levofloxacinUsing CoCl₂·6H₂O,MgCl₂·6H₂O and Na₂CO₃ as raw materials,Co₃O₄/MgO catalysts were synthesized through the one-pot MgO-mediated synthesis method and obtained by calcining in a muffle furnace at 500℃for 3h in air.SEM and TEM results showed that Co₃O₄/MgO presents a thinner nanosheet structure with abundant pores,which is beneficial to the diffusion and migration of electrons.XPS analysis results showed that compared with Co₃O₄,Co₃O₄/MgO had higher content of Co²⁺and surface hydroxy-oxygen,which was conducive to the efficient degradation of antibiotics.Co₃O₄/MgO/PMS system exhibited excellent LEV removal efficiency(1.1738 min^-1),which exhibited superior performance over single Co₃O₄(0.0366 min^-1)and MgO(0.0080 min^-1)catalyst.The effects of reaction temperature,catalyst dosage,PMS concentration,initial p H on the catalytic reaction were investigated.The removal efficiencies of LEV can still be maintained under wide p H of 3.0～11.0 and was unaffected by the interference of common anions.Additionally,the MgO/Co₃O₄/PMS system can also effectively degrade malachite green（MG）,rhodamine B（Rh B）,pefloxacin（PEF）,ciprofloxacin（CIP）and tetracycline（TC）,showing excellent universality.Through radical quenching experiments and electron paramagnetic resonance（EPR）analysis,it was confirmed that the generation of radicals(^·OH and SO₄^·-)and the non-radical（¹O₂）pathways collectively contributed to catalytic LEV oxidation.Three LEV degradation pathways were speculated based on the determination of the LEV degradation intermediate according to LC-MS.（2）PMS activation by oxygen vacancies rich Mg-doped Co₃O₄-r nanosheets for fast tetracycline degradationThe Mg-doped Co₃O₄precursor was fabricated by one-pot solvo-thermal method and calcinated in a muffle furnace at 500°C,then precursor was ultrasonically dispersed into Na BH₄ solution for 1 h.The morphologies and properties of the Mg-doped Co₃O₄-r were characterized by various technologies,demonstrating that the Mg-doping and Na BH₄ reduction endowed the resultant Mg-doped Co₃O₄-r more reduced Co²⁺species,higher surface area and more oxygen vacancies.The Mg-doped Co₃O₄-r exhibited high PMS activation ability,which greatly enhanced the TC degradation.Specifically,over1.96-fold and 8.26-fold reaction kinetic rate promotion were achieved for the Mg-doped Co₃O₄-r relative to the Co₃O₄-r and Mg-doped Co₃O₄ without Na BH₄ reduction.The effects of catalyst dosage,PMS concentration,reaction temperature,initial p H on the catalytic reaction were investigated.In addition,high TC removal efficiencies were maintained under wide p H of 3.0～11.0 and in the presence of common anions(SO₄^2-,HCO₃^-and H₂PO₄^-)and humic acid.The main XPS peaks and XRD patterns of the fresh and used Mg-doped Co₃O₄-r are identical,this implies that the Mg-doped Co₃O₄-r not only possesses high performance TC degradation capacity,but also exhibits good reusability and stability.The radical quenching trials,EPR outcome and electrochemical analysis suggested that radical and non-radical were the main pathway for TC degradation in the Mg-doped Co₃O₄-r/PMS system.In a word,two-dimensional structure Mg-doped Co₃O₄-r is favorable to accelerating mass transport and facilitating exposure of more active sites.Also,abundant oxygen vacancy and Mg doping improve material conductivity ability and facilitate electron transfer of the Mg-doped Co₃O₄-r.Success of this work demonstrates the potential of the Mg-doped Co₃O₄-r as PMS activator for the degradation of TC.Finally,the TC degradation pathway is speculated based on the determination of the TC degradation intermediate according to LC-MS.