| Various radioactive nuclides and heavy metals are inevitably produced in the process of nuclear energy utilization,seriously harming the ecological environment.Adsorption is considered as one of the promising methods for removal of radioactive pollutants and developing efficient absorbents is its critical point.Metal organic framework material(MOF)is a kind of ideal material for adsorption of radioactive contaminants,because it has the advantages of large surface area and high porosity.However,the research results show that many MOF materials cannot meet the requirement of radioactive pollution remediation,and the adsorption performance of many MOF materials still needs to be further improved.By means of modifying MOF materials,the purpose of this research is to improve their adsorption performance of radioactive nuclides and heavy metal ions,to study its adsorption mechanism in detail,and to preparing the MOF composites that meet the needs of practical engineering applications.The content of the paper mainly includes:Ethylenediaminetetraacetic acid(EDTA)was modified in the pores of the metal organic framework(UiO-66),synthesizing EDTA modified UiO-66(UiO-66-EDTA).Extensive characterization data revealed its stable octahedral structure and carboxyl and amine functional groups on the surface.The batch experiment results proved that UiO-66-EDTA can efficiently adsorb "hard acid" Eu3+,“soft acid" Hg2+and"boundary acid" Pb2+.The main reason is that the EDTA functional group has "hard"and“soft" chemical properties.The maximum adsorption capacity of UiO-66-EDTA for "hard acid" Eu3+,"soft acid" Hg2+and "boundary acid" Pb2+is 195.2,371.6 and 357.9 mg·g-1.Competitive adsorption experiments showed that the removal efficiency of 11 metal ions in the coexisting system reached more than 99%.The results of X-ray photoelectron spectroscopy(XPS)analysis showed that the complexation of Eu3+,Hg2+and Pb2+with carboxyl group(-COOH)and tertiary amine group(C-N(C)-C)was the main mechanism for adsorption of metal ions by UiO-66-EDTA.Aiming at adsorption of radioactive pollutants with Sr2+and Cs+,an existing synthetic method was improved to further modify UiO-66-NH2 with-SO3H functional group and a MOF(UiO-66-NH-SO3H)was synthesized.The batch experiment results showed that the modified MOF material can selectively adsorb nuclides Sr2+and Cs+,and the maximum adsorption capacity at 298 K is 173.3 and 218.0 mg·g-1,respectively.By means of technical analysis X-ray photoelectron spectroscopy(XPS)and Infrared spectroscopy(IR),combined with the analysis of batch experiment results,it was confirmed that the mechanism of adsorption was the complexation of nuclide and-SO3H functional group,electrostatic attraction and ion exchange.Aiming at adsorption of radioactive pollutants with 99Tc which is hard to remove,Th-Ni MOFs were synthesized using a scalable tactic in this study,and the Th-Ni MOFs were further modified to obtain a composite of Th-Ni MOF and PP(Th-Ni MOF@PP)with a simple method.The results of batch experiments show that Th-Ni@PP has excellent selective adsorption performance for Re(VII)(an analog of radioactive 99Tc).The maximum adsorption capacity of the material for Re(VII)at 298 K is 286.6 mg·g-1.The results of batch experiments and microscopic characterization prove that ion exchange,coordination complexation and electrostatic adsorption are the mechanisms of Re(VII)adsorption by the composite.The synthesis method of MOF composite and the results of highly efficient adsorption of Re(VII)provide an important reference for the engineering application of MOF materials for the removal of 99Tc and other nuclides. |
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