Efficiency And Mechanism Of FeOCl And G-C₃N₄/FeOCl Composite On Peroxymonosulfate Activation For 2,4-dichlorophenol Removal From Water

With the rapid development of our economy,water pollution is becoming more and more serious.The widely used 2,4-dichlorophenol（2,4-DCP）has a high concentration and great harm in the aquatic environment,seriously endangering the safety of human beings and the ecological environment.Advanced oxidation technologies based on sulfate radical radicals（SR-AOPs）have the characteristics of strong oxidation ability and can effectively purify refractory organic pollutants in water.Iron oxychloride（Fe OCl）,as a heterogeneous iron based catalyst,has the advantage of rich surface active sites and can be used to activate peroxymonosulfate（PMS）for the degradation of 2,4-DCP.However,the current,the activation properties of Fe OCl for PMS need to be improved and the activation mechanism is still unclear,which limits the directional research and development of Fe OCl based materials.In view of the above situation,this paper prepared Fe OCl and graphite carbon nitride（g-C₃N₄）modified Fe OCl（recorded as CNFe OCl）,explored their PMS activation properties and activation mechanism,and analyzed the mechanism of catalytic performance improvement of CNFe OCl.The main conclusions of this paper are as follows:（1）The L25（5⁴）orthogonal test results showed that the order of influence of the four factors in the Fe OCl/PMS system was:initial pollutant concentration>catalyst dosage>initial p H>PMS dosage;The order of influence of the four factors in the CNFe OCl/PMS system was:catalyst dosage>initial pollutant concentration>initial p H>PMS dosage;The optimal experimental conditions for the system were:initial pollutant concentration C₀=10.00 mg/L,catalyst dosage=0.50 g/L,initial p H=3,and PMS dosage=4.00 m M.（2）The adsorption experimental results of the catalyst under the optimal experimental conditions showed that the adsorption and removal rates of 2,4-DCP by Fe OCl and CNFe OCl were 9.8%and 13.2%,respectively.（3）The degradation experiment results of the catalyst under the optimal experimental conditions showed that the PMS activation performance of CNFe OCl composite catalyst was better than that of Fe OCl catalyst;The TOC removal experimental results of Fe OCl/PMS/2,4-DCP（30.00 mg/L）and CNFe OCl/PMS/2,4-DCP（30.00 mg/L）systems indicated that the mineralization ability of the CNFe OCl system was superior to that of the Fe OCl system.（4）XRD,FT-IR,and XPS characterization of the catalyst showed that Fe OCl and CNFe OCl were successfully prepared by thermal annealing;The reuse experiments of Fe OCl and CNFe OCl and the XRD and FT-IR characterization results of the two catalysts before and after the reaction indicated that the catalyst had good stability.（5）The ESR analysis and quenching experiments of Fe OCl/PMS and CNFe OCl/PMS systems showed that there were SO₄^·-,O₂^·-,¹O₂,and a small amount of·OH in the system.The oxidation of ¹O₂was the main pathway for the degradation of 2,4-DCP;Combining the XPS characterization results of Fe OCl and CNFe OCl before and after the reaction,it was proposed that Fe（Ⅲ）-OH and Fe（Ⅱ）-OH on the surface of the catalyst activated PMS to produce SO₄^·-and O₂^·-,which reacted to produce a large amount of ¹O₂in the system.（6）Based on the XPS,EIS,and BET characterization results of Fe OCl and CNFe OCl before the reaction,it was proposed that the Fe（Ⅱ）/Fe（Ⅲ）ratio and the Fe（Ⅱ）/Fe（Ⅲ）conversion rate of the catalyst determined the activation performance of the catalyst.The increased Fe（II）/Fe（III）ratio,specific surface area,surface hydroxyl content,and reduced charge transfer resistance in CNFe OCl are the reasons for its significant PMS activation properties.