Study On Activation Of Peroxymonosulfate By Calcium-Cobalt Catalyst For Degrading Organic Pollutants

In recent years,peroxymonosulfate（PMS）has attracted extensive attention in the degradation of organic pollutants in wastewater.Among them,cobalt-based catalysts are the earliest and most studied catalysts in the field of PMS activation.However,due to the toxicity of cobalt ions,reducing the amount of catalyst and improving the catalytic activity is a problem that needs attention.In this paper,acid orange 7（AO7）was used as the target pollutant,and the effect of lewis acid（LA）ions represented by Ca²⁺on promoting the degradation of organic pollutants by Co²⁺activated PMS was studied under neutral p H conditions.Calcium cobaltate（Ca₂Co₂O₅）was prepared to realize heterogeneous catalysis,and the catalytic performance and reaction mechanism of calcium synergistic catalyst activated PMS to degrade organic pollutants were studied.The research carried out in this paper is as follows:（1）The addition of Ca²⁺to the Co²⁺/PMS system promotes the degradation of AO7.For example,the degradation rate of AO7 in the Co²⁺/Ca²⁺/PMS system is 0.14min^-1,which is 1.75 times and 23.3 times that of the Co²⁺/PMS(0.08 min^-1)and Ca²⁺/PMS(0.006 min^-1)systems,respectively.As the acidity of LA increases,the degradation of AO7 first increases and then decreases,and the addition of K⁺,Na⁺,Ba²⁺and Ca²⁺increases it,while the addition of Mg²⁺,La³⁺,and Y³⁺inhibits the degradation.The rate of PMS decomposition will increase with the increase of the Lewis acidity of LA.Through the characterization results of Raman spectroscopy and cyclic voltammetry,as well as decomposition experiments,it was found that LA,as an electron withdrawing species,increased the oxidation ability of PMS,the Co²⁺as a single-electron reducing agent,can reduce PMS more quickly to form active radical species;while La³⁺and Y³⁺act as strong LA,PMS undergoes a two-electron transfer process to form dioxygen.（2）Because the presence of Co²⁺in the homogeneous system will cause water pollution,in order to further explore the role of calcium and cobalt synergistic catalytic oxidation,we prepared Ca₂Co₂O₅ catalysts by sol-gel method to realize heterogeneous calcium synergistic catalyst activation of PMS to degrade organic pollutants.From the characterization results of XRD and XPS,it is found that Ca₂Co₂O₅ has a unique layered structure and multiple cobalt oxidation states,consisting of hexagonal Co O₂ layers and deformed rock salt Ca₂Co O₃,there are three valence states of Co（II）,Co（III）and Co（IV）.The Ca₂Co₂O₅/PMS system can degrade up to 93%of AO7 within 7.5 min with a reaction rate of 0.58 min^-1,which is2.6 times and 3.9 times that of the Co₃O₄/PMS and Co²⁺/PMS systems,respectively.The removal efficiency of the catalyst was still 80%after 5 cycles of use,and the analysis found that the leaching of Ca²⁺was the cause of the slight loss of catalyst activity.Through quenching experiments and electrochemical characterization,it was found that the activation of PMS by Ca₂Co₂O₅ reflects the generation of active species in two ways:One is that PMS is activated to generate SO₄^·-and·OH,and these radicals then degrade the substrate;The other is that the catalyst forms complexes with PMS and AO7,and direct electron transfer occurs between them,so that the substrate is decomposed.Based on the above research results,it is found that the addition of Ca²⁺can increase the reaction rate of the Co²⁺/PMS/AO7 system,and with the increase of the acidity of LA ions,the reaction rate first increases and then decreases,and the decomposition rate of PMS increases continuously.The Ca₂Co₂O₅ catalyst can efficiently and stably degrade organic pollutants,and we further studied the reaction mechanism of calcium and cobalt synergistic catalytic activation of PMS.It provides innovative ideas and theoretical basis for the modification of cobalt-based catalysts and the principle of PMS activation.