Degradation Of Phenolic Organic Pollutants In Water By Iron-based Metal Organic Framework-derived Materials Activated With Permonosulphate

To address the scientific problems of low selectivity and poor stability of non-homogeneous catalysts in permonosulphate(PMS)advanced oxidation technology,it is of great theoretical significance and practical prospect to develop efficient and stable PMS activation catalysts with clear conformational relationships at the molecular level.In this study,we designed and constructed stable and efficient Fe-MOFs and derivatives for advanced oxidation catalysts based on the excellent structural and easy-to-regulate characteristics of Fe-based metal-organic frameworks(Fe-MOFs).The intrinsic mechanisms of ligand-unsaturated metal and ligand site electronic structures on the catalytic performance of Fe-MOFs were systematically investigated,the process and mechanism of the stability of catalytic materials regulated by pyrolysis process parameters and hydrophobic modification were studied,the degradation process and the reaction path of(non-)radical binding were elucidated for Fe-MOFs-based catalytic systems.This study provides scientific support and research basis for the advanced oxidation of phenolic organic pollutants by Fe-MOFs-based functional materials with PMS.The specific research contents and main findings are as follows:(1)Process and mechanism of Mn-Fe bimetallic site-modified organic framework-catalyzed activation of PMS for the degradation of mono-phenols.Start with metal loci,the degradation process and reaction mechanism of phenol by a series of transition metal Mn-doped MIL-101(Fe0.96Mn0.04),MIL-101(Fe0.94Mn0.06),MIL-101(Fe0.92Mn0.08)and MIL-101(Fe0.90Mn0.10)catalyst systems were investigated.The results showed that the degradation ability of MIL-101(Fe0.92Mn0.08)for phenol increased from 80%to 100%in 30 min,and total organic carbon(TOC)removal rate(64%)is 1.8 times higher than MIL-101(Fe)(36%),showing excellent catalytic activity.The high activity originates from the presence of abundant Lewis density(4.97 mmol g-1)on the surface of MIL-101(Fe0.92Mn0.08)catalyst material,and Mn successfully replaces part of Fe metal centers,forming new Fe-O-Mn metal nodes,constructing abundant unsaturated coordination defects,providing a large number of active centers,accelerating the valence cycling of Fe(Ⅲ)and Fe(Ⅱ),and further enhanced the generation of active species and exhibited excellent synergistic catalytic performance.The results of the burst reaction and degradation mechanism showed that SO4-·played a major role in the degradation during the activation of PMS,and the breakage of the O-O bond in PMS triggered the generation of active species,followed by the oxidative degradation of phenol by SO4-·,which mineralized it into degradable small molecular fragments.(2)Organic ligand constructs modulate the degradation of dibasic phenolic pollutants catalyzed by Fe based metal framework.Starting from organic ligand regulation,based on the structural properties of the organic ligands in MIL-101(Fe),two different electronegative functional groups-NO2 and-NH2 were introduced to prepare NO2-MIL-101(Fe)and NH2-MIL-101(Fe)respectively for the catalytic degradation of bisphenol A,a typical phenolic organic pollutant in water.The results showed that the PMS dosage was 8 mmol L-1,the reaction temperature was 25℃,and the NO2-MIL-101(Fe)dosage was 0.1 g L-1,after 60 min of reaction,the removal rate of BPA reached 100%,which was 18%higher than the degradation efficiency of MIL-101(Fe)(85%),and the reaction rate constant(0.42 min-1)was 2.3 times higher than MIL-101(Fe)(0.18 min-1).The difference in activity originated from the introduction of the strong electronegative group-NO2 in NO2-MIL-101(Fe)could regulate the electron density around the metal center Fe(Ⅲ)and change the electronic structure of the metal center,and both electrostatic potential and adsorption energy calculations show that the introduction of functional groups with strong electronegativity leads to a decrease in electron cloud density on the metal center Fe(Ⅲ)in MOFs and increases the adsorption energy,which facilitates the adsorption and enrichment of organic pollutants with reactive oxygen species.The electrochemical reaction mechanism shows that NO2-MIL-101(Fe)has the smallest interfacial charge transfer resistance value and the largest exchange current density,in which the enhanced catalytic activity of redox ability is the key factor for the improvement of catalytic activity,and also can effectively catalyze the degradation of phenol and other multi-species typical organic pollutants.(3)Process and mechanism of catalytic degradation of dibasic phenolic pollutants by FeCe bimetallic oxides prepared by MIL-101(Fe)derivatization.To address the problem of difficult separation and poor stability of powder MOFs in practical applications,the spatial structure properties of MIL-101(Fe)in the pyrolysis preparation process were investigated.The new rod catalyst CUMSs/Ce-500 had the best degradation activity at 500℃ under nitrogen atmosphere.The results showed that bisphenol A was effectively removed and mineralized in the PMS/CUMSs/Ce-500/bisphenol A advanced oxidation system,the degradation reaction rate constant was 0.816 min-1.Combined with the results of Fukui function calculations,the degradation pathway of BPA was further refined based on the intermediates identified by UHPLC-MS technique.The CUMSs/Ce-500 material was also formed with strong magnetic properties,which made it easy to separate and reuse the catalyst after the advanced oxidation reaction,and the efficient catalytic performance was maintained after five cycles of experiments.The effect of potential inorganic anions in the actual wastewater was investigated,and the data showed that both CUMSs/Ce-500 are resistant to inorganic anions(NO3-、SO42-、HCO3-、Na+)and have potential value in wastewater treatment applications.(4)Reaction mechanism and degradation mechanism of hollow carbon-coated H-C@Fe3O4 activated PMS for removal of dibasic phenols.Optimization and modification on the basis of the above study,inorganic hydrophobic material silica(mSiO2)was introduced.Based on the structural characteristics of mSiO2,hollow Fe3O4 nanomaterials(H-C@Fe3O4)encapsulated by carbon layer were prepared for the activation reaction of PMS by two-step calcination with MIL-101(Fe)as the precursor.The results combined with theoretical calculations showed that the strong interaction between Fe3O4 nanoparticles and the outer carbon shell in the H-C@Fe3O4 catalytic material improved the adsorption energy of the material(-1.31 eV),which was much larger than the carbon layer alone(-0.71 eV),contributed to the growth of the O-O bond of the PMS molecule(1.59 A)and promoted the charge transfer between the carbon shell,and the H-C@Fe3O4 bisphenol A removal rate reached 100%within 40 min with a high reaction rate constant(0.43 min-1).Through the study of the reaction process and mechanism,the results indicate that a fast ternary electron transfer system is established between bisphenol A,H-C@Fe3O4 and PMS during PMS activation.Strong interactions between the metal nanoparticles Fe3O4 in H-C@Fe3O4/PMS and the outer carbon shell promote the free radical(SO4-·and ·OH)reaction process,while generating the non-free radical 1O2.The carbon-encapsulated hollow structure can further reinforce the material and ensure the structural stability of the material even during repeated catalytic processes.H-C@Fe3O4 maintains efficient organic pollutant degradation efficiency after five cycles of testing.This work demonstrates that reasonable structural design and component modulation is an effective way to solve the low cycling stability and low utilization of reactive oxygen species.