| In order to alleviate the tension of energy shortage,vigorously developing clean and green nuclear energy has become an inevitable trend.The application of nuclear technology undoubtedly aggravates the radioactive pollution in water.The adsorption method is an economical,efficient,flexible method that can almost completely remove radioactive pollutants in water.In recent years,zeolite imidazole frameworks(ZIFs)with adjustable physicochemical properties have become a new generation of adsorbent materials with great development prospects.Herein,the research progress in the removal of uranium(U(Ⅵ))from water by ZIFs was reviewed.First,the introduction systematically summarized the development history,structure and properties,synthesis technology and modification methods of ZIFs,and summarized recent research reports on ZIFs used as water purification materials to remove pollutants from water.Subsequently,Subsequently,in this research work,four kinds of ZIFs were synthesized successively and used to adsorb U(Ⅵ)in water.Through a series of microscopic characterization techniques,the crystal structure and surface characteristics of the four ZIFs were observed.The adsorption behavior and mechanism of U(Ⅵ)on ZIF materials were further ekplored through macroscopic batch experiments and microscopic spectral analyses.Finally,the possible challenges and opportunities of ZIFs in the field of environmental governance were briefly discussed,hoping to provide references for the practical application of ZIFs materials in the future.The main work and innovations of this research are summarized as follows:(1)Four low-cost and environmentally friendly ZIFs were successfully synthesized.At room temperature,ZIF-8,ZIF-9,ZIF-67 and Zn/Co-ZIF were successfully prepared by stirring the mixture of transition metal salt(Zn(NO3)2·6H2O or Co(NO3)2·6H2O)and organic ligand(2-methylimidazole or benzimidazole).The synthesis process avoided the heat energy input of the traditional solvothermal method,which not only reduced the cost but also made the preparation process more environmentally friendly.Combined with SEM,BET,XRD,FTIR,XPS and other analysis techniques,four kinds of ZIFs were observed to have regular crystal morphology,abundant nitrogen and oxygen functional groups(such as C-N,C=N,Zn-N,Co-N,etc.),considerable specific surface area and good material stability.(2)The adsorption behavior of ZIFs for U(Ⅵ)was investigated by the combination of macroscopic batch experiments and microscopic spectroscopic analyses.The adsorption isotherms of four ZIFs for U(Ⅵ)were measured at room temperature.Langmuir model could better describe the adsorption behavior of ZIFs for U(Ⅵ).According to the model,the maximum adsorption amounts of the four ZIFs were sorted from largest to smallest:ZIF-8(540.4 mg/g)>Zn/Co-ZIF(527.5 mg/g)>ZIF-9(448.6 mg/g)>ZIF-67(368.2 mg/g).Kinetic experiments showed that ZIFs had faster adsorption rates for U(Ⅵ),and the reaction equilibrium could be reached within 1 hour.In summary,ZIFs had fast equilibrium time and excellent U(Ⅵ)adsorption capacity,indicating that ZIFs have enormous potential in purifying radioactive wastewater.In addition,according to the influence of pH and ionic strength,FTIR and XPS spectra,the mechanism of action between ZIFs and U(Ⅵ)could be attributed to surface complexation and electrostatic interaction.(3)The reasons for the different adsorption capacities of different ZIFs for U(Ⅵ)were analyzed in detail.Different from previous reports,this work was not limited to the study of improving the abilities of ZIFs to remove pollutants,but more in-depth exploration of the chemical affinity of the active adsorption sites on the surface of ZIFs to U(Ⅵ).Herein,ZIFs with different metal nodes(ZIF-8 and ZIF-67),organic connectors(ZIF-9 and ZIF-67)and single/double metal nodes(ZIF-8,ZIF-67 and Zn/Co-ZIF)were employed to remove U(Ⅵ)in water and the mechanism have been clarified in detail.Specifically,ZIF-8 had a larger specific surface area and more abundant adsorption sites than ZIF-67,resulting in a stronger adsorption capacity of ZIF-8 than ZIF-67.In addition,Co-N and C-N on ZIF-9 were both involved in the adsorption process of U(Ⅵ),and the oxygen-containing functional groups on ZIF-9 were much more abundant than those on ZIF-67,which might be the main reason why ZIF-9 had better adsorption performance than ZIF-67.However,the influence of single metal node and double metal node on ZIFs adsorption of U(Ⅵ)could be attributed to the higher participation of Zn-N bond than Co-N bond. |
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