Removal Of Antibiotics By The Activated Peroxymonosulfate With Alkaline Earth Metal Modified Cobalt Tetraoxide And Its Mechanism

Antibiotics are widely used in medical,aquaculture and animal husbandry,and have become a widespread pollutant in the water environment.It is difficult to remove antibiotics effectively with traditional secondary biochemical treatment owing to the antimicrobial properties of antibiotics,resulting in their cumulative residues in the water environment,which can further cause intractable environmental problems such as antibiotic resistance genes.Hence,it is urgent to study effective methods for removing antibiotics.Compared to conventional Fenton and Fenton-like technologies,advanced oxidation processes based on peroxymonosulfate（PMS）is of great attention because of its high efficiency and wide pH adaptability.In numerous ways to activate PMS,the heterogeneous activation of PMS by transition metal oxides has the advantages of high efficiency and easy recovery,especially cobalt tetraoxide are regarded as one of the most effective catalyst.Nevertheless,cobalt oxides alone often have problems such as particle agglomeration,poor stability,resulting in unsatisfactory catalytic activity.Non-metallic elements and transition metal doping have been proven to be the effective strategies to enhance the activity of cobalt oxides such as Co₃O₄,while there are few alkaline earth metal modified cobalt oxide catalysts have been studied.Alkaline earth metal materials can regulate the catalyst surface properties to produce surface hydroxyl groups and defects that are favorable for PMS activation.It can also act as carriers to enhance catalyst dispersion,thus improving the utilization efficiency of active sites.Thus,in this thesis,MgO/Co₃O₄ with aboudant hydroxyl and oxygen vacancy（O_v）and CaCO₃（from eggshell）loaded Co₃O₄ were successfully prepared from the aspects of regulating surface properties and dispersibility of Co₃O₄.The performance and mechanism of PMS activation by two catalysts for the degradation of levofloxacin（LEV）and pefloxacin（PEF）were investigated.The main studies and results are as follows:（1）MgO/Co₃O₄ catalyst with abundant hydroxyl and oxygen vacancies activated PMS to degrade levofloxacinThe hydroxyl on the catalyst surface is one of the rate-limiting factors for PMS activation.The MgO/Co₃O₄ composites was obtained by modifying Co₃O₄ with alkaline earth metal oxide MgO.The morphology,crystal structure,elemental composition,surface defects and functional groups of the catalysts were analyzed by various characterization methods.X-ray photoelectron spectroscopy（XPS）and electrochemical characterization show that MgO/Co₃O₄ possess higher surface hydroxyl level and electronic transfer ability.Solid electron paramagnetic resonance（EPR）demonstrates a large amount of O_v was existed in the MgO/Co₃O₄ composites.MgO/Co₃O₄ was employed to activate PMS for LEV degradation.The experimental results showed that the removal rate of LEV in the MgO/Co₃O₄-PMS system was as high as 96.93%within20 min,and the LEV degradation rate constant in(0.9077 min^-1)was about 142 times that of Co₃O₄-PMS(0.0064 min^-1)system.The comprehensive performance of MgO/Co₃O₄ has been systematically evaluated and the results show that the catalyst has a strong anti-interference ability,and possess excellent stability and universality.Radical quenching tests and EPR trials prove that the combined action of radicals(SO₄^·-,^·OH)and non-radical（¹O₂）pathways achieved the degradation of LEV.Various experimental and characterization results demonstrate that Co²⁺/Co³⁺is the main active center of PMS activation,and O_v can accelerate the Co²⁺/Co³⁺cycle and improve the PMS activation efficiency.The intermediates of LEV degradation were analyzed by high performance liquid chromatography-mass spectrometry（HPLC-MS）,and the possible pathways of LEV degradation were proposed.The above results indicate that the MgO modification enhances the hydroxyl concentration and electron transfer efficiency of the material and consequently improves the ability of the catalyst to activate PMS.（2）Removal of pefloxacin by eggshell-origined CaCO₃ loaded Co₃O₄ activated PMS.Based on the work of the previous chapter,the eggshell-derived CaCO₃ loaded Co₃O₄,i.e.Co₃O₄@EG,was prepared by waste eggshells as the calcium source from the perspective of optimising the raw material,saving the cost of material preparation.The properties of the material such as morphology,crystal structure and elemental composition are revealed by various characterization methods.Scanning electron microscope（SEM）and transmission electron microscope（TEM）show that,compared with Co₃O₄ spherical particles agglomerated together,Co₃O₄@EG composites have lamellar structure and Co₃O₄ nanoparticles are evenly distributed on the surface of eggshell,which is conducive to the full utilization of active sites.The XPS demonstrates that the higher ratio of surface hydroxyl groups and Co²⁺in Co₃O₄@EG compared with Co₃O₄,which facilitates the rapid activation of PMS.Co₃O₄@EG was used to activate PMS to degrade PEF,and the removal rate of PEF in the catalytic system was as high as95.29%after 20 min reaction,indicating that Co₃O₄@EG has good PMS activation ability.Degradation kinetic constants of PEF in Co₃O₄@EG/PMS system was 0.3376 min^-1,which was much higher than that for the Co₃O₄/PMS(0.0051 min^-1)and EG/PMS(0.0048 min^-1)systems.The influencing factors of the Co₃O₄@EG/PMS system were investigated in detail and the comprehensive performance of the catalyst was evaluated.According to the experimental results showed that the catalyst has strong resistance to interference and good stability and universality.Radical scavenging and trapping experiments demonstrate that radical pathways dominated by SO₄^·-and^·OH and non-radical pathways dominated by ¹O₂ have important roles in the degradation of PEF.The mechanism of PMS activation by Co₃O₄@EG and the possible degradation pathway of PEF were proposed by combining the results of catalyst XPS before and after the reaction and the HPLC-MS analysis of the reaction products.The above results show that the preparation of Co₃O₄@EG using eggshell as raw material can solve the agglomeration of Co₃O₄ particles and cobalt ion leaching.The obtained Co₃O₄@EG can efficiently activate PMS to degrade antibiotics such as PEF,which has application potential.