Study On The Construction Of Micro-electric Field On The Surface Of Iron-based Composites And The Mechanism Of Degradation Of Organic Pollutants

Water pollution poses a great threat to both human health and aquatic ecosystems,which is a hotspot and difficult problem of current international research.As a novel and efficient wastewater purification technology,heterogeneous Fenton reactions have attracted a widespread attention in wastewater treatment in recent years.However,due to the dependency on redox reactions at a single metal to achieve the activation of H₂O₂in the heterogeneous Fenton reaction,it still suffers from poor stability of the catalyst,unsatisfactory catalytic activity under neutral condition and low utilization efficiency of H₂O₂.Aiming at the removal of emerging refractory organic pollutants and the shortcomings of the Fenton reaction system,this paper starts from the construction of microelectric fields and cation-?interaction on the catalyst surface,and further trys to explore the solutions through the in-depth research of the development of novel efficient and stable iron-based heterogeneous catalysts and their pollutant degradation mechanisms.The work and results are summarized as follows:(1)Carbon nitride compounds(g-C₃N₄)complexed with the in-situ-produced Fe(d-g-C₃N₄-Fe)was synthesized via an organic ligand complexation method.The X-ray photoelectron spectroscopy(XPS)and extended X-ray absorption fine structure(EXAFS)analysis and density functional theory(DFT)calculations confirm the formation of Fe(III)-?interaction and Fe–N complexation between the Fe of iron oxides and the pyridinic N of g-C₃N₄,which induced the production of more oxygen vacancies(OVs)with more electrons in iron oxides and uneven electron distribution(micro-electric field)on the surface of d-g-C₃N₄-Fe.d-g-C₃N₄-Fe exhibits high Fenton-like efficiency and stability for the degradation of hydroxyl-containing pollutants and hydrophobic pollutants mixing with the former.(2)Based on the results of Fourier Transform infrared spectroscopy(FTIR),in situ Raman and DFT calculations,a novel reaction mechanism of the enhanced Fenton-like efficiency by the synergistic effect of oxygen vacancies and organics adsorption in the d-g-C₃N₄-Fe system has been proposed.As the electron donors,the adsorbed hydroxyl-containing pollutants were mainly complexed with surface Fe(III)through their hydroxyl group,which resulted in the efficient reduction of H₂O₂to^·OH at the electron-rich OV centers,leading to almost all of the energy of H₂O₂being applied to the degradation of pollutants.However,the adsorbed hydrophobic pollutants at peripheral structure in g-C₃N₄can lead to the rapid invalid decomposition of H₂O₂to O₂by the synergistic effect of iron species and OV.These results demonstrate that the Fe(III)-?interaction could carry out the oxidation of pollutants on the catalyst surface and decreasing the consumption of H₂O₂,and the role of OV in the Fenton reaction system depends on pollutant adsorption patterns.(3)To further enhance the electrons uniform distribution on the catalyst surface,a novel iron-based catalyst(Fe⁰-Fe_yC_z/Fe_x-GZIF-8-r GO)was creatively developed.The X-ray diffraction(XRD),XPS,M(?)ssbauer spectra(MS),EXAFS and Raman analysis demonstrate that three phases(Fe⁰-Fe_yC_z/Fe_x,GZIF-8 and r GO)were formed and interconnected with each other through Fe–O–C,Fe–N and C–O–Zn–N chemical coordination bonds in Fe⁰-Fe_yC_z/Fe_x-GZIF-8-r GO,which resulted in the production of strong(Fe or Zn)-?interaction in Fe⁰-Fe_yC_z/Fe_x-GZIF-8-r GO.The DFT calculations further reveal the formation of micro-electric field(electron-rich Fe area and electron-poor r GO area)on the Fe_yC_z/Fe_x-GZIF-8-r GO surface.Based on the structural and chemical properties,in the case of O₂/Fe³⁺as electron acceptor,Fe⁰-Fe_yC_z/Fe_x-GZIF-8-r GO is able to efficiently mineralize and degrade organic pollutants through interfacial strong(Fe or Zn)-?interaction without any energy input.Thus,Fe⁰-Fe_yC_z/Fe_x-GZIF-8-r GO shows excellent catalytic activity and stability for the degradation of various organic pollutants in water.