Based On Fe-MOFs(MIL-68 And MIL-53) To Construct Highly Effective Fenton-like AOPs For Degrading Organic Pollutants In Water

Advanced oxidation technology is considered to be an effective method to remove refractory organic pollutants from the environment.Among various advanced oxidation processes（AOPs）,Fenton and its derivative Fenton-like have attracted much attention due to their advantages of simplicity and effectiveness.Heterogeneous Fenton,alleviating some disadvantages of homogeneous Fenton,such as the formation of iron sludge,narrow pH range and difficult recovery of catalyst,has become the research focus of Fenton type advanced oxidation technology.Fe-based metal-organic frameworks（Fe-MOFs）have great potential in heterogeneous Fenton catalysis due to wide distribution of single iron sites,porous structures,and large surface areas.However,in the heterogeneous Fenton catalytic system constructed by Fe-MOFs alone,the slow Fe（Ⅲ）/Fe（Ⅱ）redox cycle and low H₂O₂ utilization efficiency result in low catalytic activity,limiting their practical application.Therefore,it is still an urgent and challenging problem to design a highly efficient Fe-MOFs Fenton-like catalyst or catalytic system to minimize the amount of reagents and maximize the utilization of H₂O₂.Herein,the following strategies were proposed to improve the Fenton-like activity of Fe-MOFs catalysis and explore the mechanism of catalytic activity enhancement,so as to provide a basis for the construction of an efficient Fe-MOFs Fenton-like catalytic system.（1）MIL-68（Fe）was chosen as Fenton-like catalyst,and a small amount of Na HSO₃ was added to MIL-68（Fe）/H₂O₂ system to improve the Fenton-like performance.The factors affecting the catalytic oxidation capacity of the MIL-68（Fe）/HSO₃^-/H₂O₂ system were investigated using methyl orange（MO）as model pollutant.Under the optimal condition,the degradation rate of MO could be increased by 11.5 times,and the TOC（Total Organic Carbon）removal in 120 min reached 46.8%.The MIL-68（Fe）/HSO₃^-/H₂O₂ system also displayed a wide applicable pH range.Besides MO,other organic contaminants such as AR18（acid red 18）,Rh B（rhodamine B）,MB（methylene blue）,XO（xylenol orange）and TC（tetracycline）could be effectively degraded in the MIL-68（Fe）/HSO₃^-/H₂O₂ system as well.The quenching tests and EPR（Electron Paramagnetic Resonance）spectrometry confirmed that·OH,SO₄^·-,HO₂^·,and ¹O₂ were the main reactive species for MO degradation in the MIL-68（Fe）/HSO₃^-/H₂O₂ system.The coumarin fluorometry further disclosed that relative to the MIL-68（Fe）/H₂O₂ system,much more hydroxyl radicals were generated in the MIL-68（Fe）/HSO₃^-/H₂O₂ system.Cyclic voltammetry analysis,on the other hand,indicated that the presence of HSO₃^-facilitated the Fe（Ⅲ）/Fe（Ⅱ）cycle in the MIL-68（Fe）/HSO₃^-/H₂O₂ system.Based on these results,the enhanced mechanism of the Fenton-like MIL-68（Fe）/HSO₃^-/H₂O₂ system was proposed.Finally,the cyclic experiments manifested the MIL-68（Fe）/HSO₃^-/H₂O₂system had good stability and reusability.This study suggests that the addition of bisulfite was an excellent way to construct the Fe-MOFs mediated Fenton systems for eliminating organic contaminants in water with high efficiency.（2）MoS₂/MIL-53（Fe）/FeMO₄（MMFO）composite catalyst was synthesized by hydrothermal method,and optimal loading of MoS₂ was determined to be 30%by degradation of MO.By optimizing the reaction conditions,it was found that 30%MMFO-H₂O₂ system performed the best catalytic effect when pH=4.0 and H₂O₂concentration was 8 m M,and the first-order kinetic rate constant was 0.4409 min^-1.In addition to MoS₂ and MIL-53（Fe）,the peak of FeMoO₄ in the complex was characterized by XRD,and the peak of FeMoO₄ was enhanced with the gradual increase of MoS₂ content,which could promote the rapid degradation of MO.XPS revealed that the redox reaction occurred in the composite process of MoS₂ and MIL-53（Fe）.Mo（Ⅳ）in MoS₂ was oxidized to Mo（Ⅵ）by Fe（Ⅲ）on the surface of MIL-53（Fe）,while Fe（Ⅲ）was reduced to Fe（Ⅱ）.The presence of Fe（Ⅱ）on the surface of the complex was conducive to the generation of reactive oxygen species,which accelerated the degradation of MO.EPR and capture experiments showed that the main reactive oxygen species in the system were O₂^·-and ¹O₂.Finally,it is speculated that in the Fenton-like system with H₂O₂,there are both free radical pathways(O₂^·-)and non-free radical pathways（¹O₂）,and free radical degradation plays a dominant role.The stability and recyclability of 30%MMFO was proved by the cycle experiment and the comparison of the catalysts before and after reaction.This study provides a means to improve the Fenton-like efficiency,which not only enables the simultaneous recycling of catalyst and promoter,but also reduces the amount of H₂O₂ used.