Activation Of Peroxymonosulfate By Non-metal Doped Cobalt Oxide For Antibiotic Removal And Its Mechanism

The discovery of antibiotics has played an important role in agricultural development and human disease control,but their irrational and even abusive use has led to their increasing accumulation in the environment,and the resulting ecological impact can no longer be ignored.Due to the antibacterial activity of antibiotics,typical municipal wastewater treatment processes have very limited effect on their removal.Therefore,it is of great value to study methods for efficient degradation of antibiotics in water.In recent years,sulfate radical(SO₄^·-)based advanced oxidation processes（SR-AOPs）,especially peroxymonosulfate（PMS）,have shown great potential for antibiotic removal due to their advantages of stronger oxidation capacity and wider p H application range.Activation of PMS is the key to the study of advanced oxidation process based on PMS.Among various methods of activation of PMS,activation methods based on transition metal catalysts have been widely concerned,especially cobalt-based catalysts.However,the catalytic activity of cobalt oxides（e.g.,cobalt tetroxide）to PMS is hindered by several factors,such as fewer reactive sites,low electron transport efficiency and limited redox cycle between different valence cobalt ions.Doping non-metallic elements into cobalt oxides can effectively regulate the electronic structure of cobalt oxides and improve the catalytic performance.However,the current research work mainly focuses on sulfur doping and phosphorus doping,and the other non-metallic elements researches are relatively small.Therefore,in order to further explore the role of nonmetals in persulfate activation,the contents of nonmetallic doped cobalt oxide in persulfate activation are enriched.In this paper,B-Co₃O₄ and CoO_X-Se-C catalysts were prepared by adding boron（B）and selenium（Se）to cobalt oxide respectively,and an advanced oxidation system for persulfate activated degradation of Pefloxacin（PEF）was constructed.The catalytic performance,catalytic mechanism and influence of reaction conditions of the two materials were investigated.The main research and results of this thesis are as follows:（1）PMS activation by the MOF-derived B-doped Co₃O₄ catalyst for the degradation of pefloxacinThe precursor of B-t ZIF-67 was formed by etching t ZIF-67 with B₄O₇^2-/B₃O₃^3-solution,and then calcined at high temperature in air.The diamond-shaped dodecahedron B-Co₃O₄ nanomaterial with cross section was prepared successfully.The catalytic degradation experiment showed that under the optimal conditions,B-Co₃O₄ could catalytically activate PMS within 30 min to remove 91.3%PEF,and the kinetic constant was 0.085 min^-1,while Co₃O₄ without boron could only remove 5.7%PEF,and the kinetic constant was 0.003 min^-1,which was much lower than the effect of boron doping.The effects of catalyst dosage,PMS concentration,reaction temperature,initial p H and coexisting anions on the degradation of PEF by B-Co₃O₄/PMS were investigated.The results showed that B-Co₃O₄ exhibited good PMS activation ability in the p H range of3.0-10.0.In addition,the B-Co₃O₄/PMS system can also rapidly degrade antibiotics and dyes such as levofloxacin（LEV）,ciprofloxacin（CIP）,gatifloxacin（GAT）and rhodamine B（Rh B）,which has good universality.The effect of boron doping was discussed.X-ray photoelectron spectroscopy（XPS）analysis showed that the addition of boron significantly increased the content of Co²⁺and chemisorbed oxygen in Co₃O₄.Electrochemical experiments have demonstrated that B-Co₃O₄ has a lower charge transfer resistance,which facilitates the transfer of electrons.The reaction mechanism of PMS activation by B-Co₃O₄ for PEF degradation was investigated,and the results showed that the redox cycle of Co²⁺/Co³⁺was the main reason for PMS activation,and the presence of chemisorbed oxygen facilitated the adsorption of PMS on the material surface.Radical scavenging experiments and EPR analysis showed that SO₄^·-、^·OH、O₂^·-and ¹O₂ were the main reactive oxygen species in the system.Based on the analysis of the degradation intermediates,the possible path of PEF degradation by activating PMS with B-Co₃O₄ was proposed.（2）PMS activation by the carbon-loaded Se doped cobalt oxide for the degradation of pefloxacinUsing the chelation between tannic acid and cobalt ions,a Co-Se-TA precursor was synthesized using selenium dioxide（Se O₂）as the selenium source,and carbon-loaded selenium-doped cobalt oxide nanoparticles（CoO_X-Se-C）were prepared under nitrogen atomosphere at 1000°C.Physicochemical analysis of CoO_X-Se-C was carried out using various characterizations,and the results showed that CoO_X-Se-C had higher specific surface area,larger pore volume and pore size compared with Co₃O₄-C without selenium,and the incorporation of Se promoted the formation of CoO.In terms of catalytic activation of PMS for pollutant degradation,the CoO_X-Se-C/PMS system was able to remove 96.2%of PEF in 30 min with a reaction kinetic constant of 0.250 min^-1,which was three times higher than that of Co₃O₄-C,indicating that the incorporation of Se accelerated the reaction.The effects of catalyst dosage,PMS concentration,reaction temperature,initial p H and coexisting anions on the degradation of PEF by CoO_X-Se-C/PMS were investigated.The results showed that CoO_X-Se-C exhibited excellent PMS activation in a wide p H range from 3.0 to 11.0.In addition,the CoO_X-Se-C/PMS system showed good universality with removal rates above 90.0%for other antibiotics and dyes,such as levofloxacin,ciprofloxacin,tetracycline hydrochloride and rhodamine B.After four cycles,the CoO_X-Se-C/PMS system could still remove 77.1%PEF,indicating that the material has good cycling stability.The mechanism of CoO_X-Se-C activated PMS to degrade PEF was investigated.The results showed that the Co²⁺/Co³⁺redox cycle was the main reason for the activation of PMS,and the presence of Se-Se promoted the reduction of Co³⁺.Radical scavenging experiments and EPR tests proved that the non-radical pathway dominated by ¹O₂ and the radical pathway dominated by SO₄^·-were the main mechanisms of the degradation of PEF.Based on the results of HPLC-MS analysis,a possible pathway for the degradation of PEF by CoO_X-Se-C-activated PMS was proposed.