| In recent years,radionuclide pollution and organic pollution in the environment have threatened the ecological security and human health.In order to understand the migration and transformation mechanism of pollutants and to protect environment effectively,the development of novel environmental materials and the analysis of their reaction mechanism at the microscopic solid-liquid interface are extremely necessary.Nanoscale zero-valent iron(NZVI)is a novel nanomaterial with low price,facile fabrication method,high reactivity,and mutiple reaction mechanism towards pollutants.It has gradually a promising material for the removal of many pollutants from environment,and has shown great potential environmental management.However,NZVI is easy to be oxidized,corroded,and agglomerated because it possesses strong magetism and reducibility,which significantly restrit its environmental application.Therefore,the functionalization of NZVI has become the key point of recent investigations.In this paper,surface sulfidation and matrix supporting methods are utilized for the modification of NZVI.Functional NZVIs are applied for the elimination of radionuclides and chlorinated organic compounds.The microscopic mechanism of pollutants towards NZVI-based materials are explored,while the practical application values in environmental management are evaluated.The specific work is as follows:(1)Elimination of radionuclide by using ternary layered double hydroxides.Nanoscale zero valent iron(NZVI),which was supported on Ca-Mg-Al-layered double hydroxide(Ca-Mg-Al-LDH/NZVI)was fabricated via an in-situ growth way.Macroscopic batch experiments and microscopic spetrum characterization were conducted to analysis the process of U(Ⅵ)decontamination from aqueous solutions.The results demonstrated that Ca-Mg-Al-LDH/NZVI had remarkable BET surface(426.8 m2·g-1),abundant functional groups(M-O,-OH,etc.),and high efficiency(4 h to achieve 216.1 mg·g-1)for U(Ⅵ)removal.The removal process was dominated by inner-sphere surface coordination and reductive reaction.The XPS study indicated that Ca-Mg-Al-LDH not only enhanced the dispersity of NZVI,but improved the U(Ⅵ)capacity due to their instinct adsorptive ability.(2)Efficient enrichment of MXene-supported nanoscale zero-valent iron towards uranium(Ⅵ).MXene,a representative class of two-dimensional material,had been employed to support NZVI and the composite(MXFe)was applied in U(Ⅵ)decontamination.Moreover,serial characterization techniques(scanning/transmission electron microscope,XRD,FTIR,VSM,etc)were utilized,and the outstanding stability,high surface area,abundant functional group,and magnetism of MxFe was confirmed.The result of batch experiments indicated that the excellent performance of U(Ⅵ)elimination(10 mg·L-1)by MXFe,and all pollutant could be removed in 15 min.In addition,the elimination efficiency of U(Ⅵ)was maintained well in typical univalent/bivalent ion background,and achieved～60%in real seawater system.Finally,XPS and pH analyses were applied to explore the removal mechanism of U(Ⅵ)onto MXFe.The result demonstrated that inner-sphere complex adsorption and reduction reactions dominated the U(Ⅵ)decontamination.(3)Precursor impact of uranium elimination by biochar supported sulfurized nanoscale zero-valent iron.Serial biochar-based sulfide NZVIs(BC-SNZVIs)with different C/Fe and S/Fe were synthesized and applied to the elimination of U(Ⅵ)in order to investigate the effect of iron,sulfur,and biochar precursor.The result showed that the best ratio of C/Fe and S/Fe were determined to be 1.0 and 0.14.The precursor played an essential role towards BC-SNZVIs on their dispersibility and structure.The XRD analyses were conducted to study their crystalline structure and the BC1.0S0.14NZVI showed outstanding stability after 10-day exposure under atmosphere.The excellent magnetism was confirmed via VSM study and BC1.0-S0.14NZVI could be easily and rapidly separated from aqueous solution.The batch kinetic and isothermal studies illustrated the superior performances towards U(Ⅵ),and the results revealed the fast kinetics and high capacities of BC-SNZVIs,which was benificial to further investigations of NZVI-based and biochar-based materials.(4)Adsorptive and reductive removal of U(Ⅵ)by biochar supported sulfide NZVI from wastewater.Surface sulfidation and matrix supporting techniques were combined and biochar supported sulfide NZVI(DI-SNZVI)was synthesized.The precursor ratio of C/Fe and S/Fe were selected to be 1.0 and 0.14.The removal of U(Ⅵ)by DI-SNZVI can reach the maximum adsorption capacity of 427.9 mg·g-1 within 3 h.The cycle experiments and different water system investigations further illustrated its potential ability for real applications.Moreover,the abundant functional groups and FeSx shell of DI-SNZVI were proved to be responsible for the enhanced removal of U(Ⅵ).In the end,XPS study revealed that U(Ⅵ)elimination mechanisms were synergistic attributed to the adsorptive and reductive processes.(5)Fabrication of sulfide nanoscale zero-valent iron and heterogeneous Fentonlike degradation of 2,4-Dichlorophenol.SNZVI was fabricated via one-step dithionitemethod and applied it for heterogeneous Fenton-like elimination of 2,4Dichlorophenol(DCP).Serial characterization methods such as XPS,FTIR,BET,XRD,VSM,and EPR were applied.The result indicated that the sulfidation technique greatly improved the stability,specific area,oxidized resistance,hydrophobicity,and functionality.The efficiency of degradation(86.3%)was approximately 7 times higher than adsorption(12.6%)under N2 condition,indicating the promising potential of SNZVI in environmental governance.Moreover,Fenton-like reaction and reactive oxygen species(ROS)were confirmed to dominate the degradation process,and the generated radicals by introducing H2O2 had priority to degrade DCP rather than corroded SNZVI.Finally,the result of gas chromatography-mass spectrometry(GCMS)confirmed that DCP was mainly decomposed into harmless alkanes and inorganic matters,which significantly reduced the perniciousness of DCP.Overall,the physicochemical properties,such as microstructure,crystal form,and surface functional groups,of different functionalized NZVIs were studied.The removal effect of U(Ⅵ)and chlorinated organics DCP was investigated,and the reaction mechanism was explored.It can be shown that both surface sulfidation and substrate supporting can be used as effective ways to functionalize NZVI.The results can provide important references for the correlational studies... |
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