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Selenium-Doped Cobalt Single Atom Catalysts For Magnesium Sulfite Oxidation And Wastewater Degradation

Posted on:2024-05-15Degree:MasterType:Thesis
Country:ChinaCandidate:S N XuFull Text:PDF
GTID:2531307142953259Subject:Chemical Engineering and Technology
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In recent years,thermal power generation has dominated the energy sector,leading to the generation of large amounts of SO2.To allow SO2 to meet emission standards,wet desulfurization technology has been widely used.Among the wet desulfurization technologies,magnesium desulfurization has received more and more attention because of its advantages of low equipment cost,small footprint and high desulfurization efficiency.At present,the most commonly used treatment method of magnesium desulfurization byproducts is oxidation recovery of the magnesium sulfite method,catalytic oxidation of magnesium sulfite into a higher economic value and better stability of magnesium sulfate.Meanwhile,sulfite activation in advanced oxidation is often used to degrade organic pollutants such as printing and dyeing wastewater and antibiotic wastewater.Electrocatalytic oxidation technology is widely used in the field of catalysis due to its advantages of fast catalytic rate and environmental friendliness.Single-atom catalysts have the advantages of high atom utilization and excellent catalytic performance,while selenium atoms are rich in d electrons and have high polarizability,and can significantly increase the electron transport rate of the material.Therefore,this work investigated the doping of selenium into monoatomic catalysts to enhance their electrocatalytic oxidation performance.In this paper,Co-SAs@NC and Co-SAs@Se-NC catalysts were prepared using CoZn-ZIFs as precursors and characterized for their structural morphology and properties.HAADF-STEM,EDS and XAFS results showed that Co existed in monoatomic form and the XAFS results indicated that the coordination structure of the Co active site in Co-SAs@Se-NC catalysts was Co-N4.The XRD,XPS and Raman results showed that Se was successfully doped in Co-SAs@Se-NC and that Se doping could increase the defects of the catalyst,break the electrical neutrality of the carbon matrix and improve the electrical conductivity of the carbon material,thus enhancing the electrochemical performance of the catalyst.The current density of the SO32oxidation peak was found to increase after Se doping by CV,indicating that CoSAs@Se-NC has better catalytic performance for MgSO3 oxidation compared to CoSAs@NC under the action of the electric field.At a lower current density(8.9 mA cm"2),the MgSO3 oxidation rate can reach 0.1134 mmol·L-1·s-1,which increases with the enhancement of current density.Based on the effects of different reaction conditions on the oxidation efficiency of MgSO3,a reaction kinetic model of the reaction was obtained,and oxygen diffusion was identified as the controlling step of the reaction.The burst experiments,as well as the EPR characterization results,showed that the ·O2-,·SO4-,and·SO5-radicals generated from the adsorption of dissolved oxygen by the electricfield-enhanced catalyst had a significant effect on the MgSO3 oxidation.Meanwhile,the catalytic capacity of Co-SAs@Se-NC decreased by 5.8%after ten cycling experiments,which proved the good cycling performance of the catalyst under the action of the electric field.Investigating the degradation behavior of the Co-SAs@Se-NC electrocatalytic MgSO3 oxidation system for different concentrations of MB and OTC simulated wastewater,it was found that the degradation rate of MB and OTC increased significantly in this system.When the concentrations of MB and OTC in the initial wastewater were 50 mg/L,the degradation efficiency was 97.9%and 91.7%,respectively,and the degradation efficiency of MB and OTC decreased by only 2.9%and 4.3%after five cycles in the Co-SAs@Se-NC electrocatalytic MgSO3 oxidation system,which once again proved the excellent degradation performance of electric field coupled single-atom catalyst for simulated wastewater.The burst experiments demonstrated that the ·O2-,·SO4-,and·SO5-radicals generated during the electrocatalytic MgSO3 oxidation by Co-SAs@Se-NC under the action of electric field significantly promoted the degradation rates of MB and OTC.The LC-MS characterization of the products in the degradation of MB and OTC,respectively,led to The possible degradation pathways of MB were inferred to be:decomposition or demethylation reaction after successive addition of hydroxyl groups;the possible degradation pathways of OTC included:demethylation,dehydration,decarbonization,deamination,and hydroxylation reaction.
Keywords/Search Tags:electrocatalysis, single-atom catalysts, magnesium sulfite oxidation, wastewater degradation
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