Metal-organic Framework-derived CoFe₂O₄ Activated Permonosulfate（PMS） Treatment Of Dye Wastewater

The advanced oxidation technology based on sulfate radicals（SO₄·^-）has been widely concerned by researchers due to its high efficiency and strong applicability,and it is an effective method for treating dye wastewater.The technology of producing SO₄·^-with permonosulfate（PMS）as oxidant is the current research focus.The existing research found that the use of cobalt ions to activate PMS to produce SO₄·^-is highly efficient,but there is secondary pollution of cobalt.And the traditional cobalt-based catalysts limit the secondary pollution of cobalt ions to a certain extent,but catalytic activity is low.Therefore,it is of great significance to develop novel and efficient catalysts.The cobalt-iron oxides with metal organic frameworks（MOFs）as the precursor not only inherit the porous and nanostructures with large specific surface area of MOFs,but also introduce bimetallic sites,which improves the traditional cobalt-based oxides from two aspects.The catalysts have both the advantages of high catalytic activity and less secondary pollution of metal ions.In this subject,the nano-CoFe₂O₄ catalyst（M-CoFe₂O₄）derived from CoFe-MOF by heat treatment was prepared,and the effect of activating PMS to treat dye wastewater was studied.In the absence of catalyst,the thesis researches and analyzes the self-activation of PMS itself.Three typical dyes,methylene blue（MB）,acid orange 7（AO7）,and rhodamine B（RhB）were treated by base catalysis of PMS in this study to investigate the optimal degradation conditions and the mechanism.Studies have shown that under alkaline conditions,PMS has strong activation properties and can effectively process AO7and MB,but has a poorer effect on RhB.PMS has poor self-activation performance under neutral conditions and cannot effectively treat dye contaminants.Under the optimal condition（p H=10.8～11.5（MB）or p H=10.0～10.8（AO7 or RhB）,PMS dosage=100mg/L）,the decolorization rate constants of MB,AO7 and RhB were 0.097,0.074,and 0.004min^-1,respectively,and the decolorization efficiency were 95.1%,93.3%,and 30.1%,respectively.The scavenging tests indicated that singlet oxygen played a critical role in the treatment by self-activation of PMS for all of the three dyes.Based on the results of UV-Vis spectra analysis,it could be speculated that the faster decolorization rates of MB and acid AO7 could be due to the more efficient oxidation of the thiazide chromophore group and the azo bond by singlet oxygen.Based on the study of PMS self-activation performance,the simulated wastewater treatment with RhB dye was used to study the effect of catalyst M-CoFe₂O₄ on PMS.Under the optimal conditions of p H=5.0,PMS dosage of 200 mg/L,and catalyst dosage of 200 mg/L,complete degradation of RhB can be achieved after 20 minutes of reaction.M-CoFe₂O₄/PMS system could also degrade AO7 and MB quickly.After the catalyst was recycled for 4 times,the removal rate of RhB by M-CoFe₂O₄/PMS system in 60 minutes could still reach 91.7%,indicating the catalyst had strong durability.The effects of Cl^-,H₂PO₄^-and HCO₃^-on the degradation of RhB by M-CoFe₂O₄/PMS system were studied.H₂PO₄^-and HCO₃^-can promote the reaction,and the reaction can achieve complete degradation of RhB in 10 minutes.Cl^-has an inhibitory effect on the reaction.After 20minutes of reaction,the RhB removal rate was reduced to 91.6%.Studies have shown that M-CoFe₂O₄ has broad application prospects in the treatment of dye wastewater.