| Background90Sr is a fission product of 235U and 239Pu in nuclear materials,which is commonly used as a signal radionuclide to be monitored.When 90Sr ingested by human body in the environment,it is easy to deposit in skeleton and hematopoietic system because of its biochemical behavior similar to calcium,and causes radiation damage to human body.So it is one of the key radionuclides to evaluate the health effects.90Sr is a beta radionuclide,the monitoring or decontamination of 90Sr in environment and biological samples are mainly achieved by radiochemical separation.Traditional separation of strontium are co-precipitation,solvent extraction,extraction chromatography,etc.However the process of these methods are time-consuming and complex.Therefore,it is important to de.velop and establish a new efficient and rapid technology for the monitoring and decontamination of 90Sr.In recent years,with the rapid development of new materials and technologies in the field of chemistry,the research of new materials for radionuclide separation has created broad prospects.Metal Organic Frame Complexes(MOF)is a new porous material which has been developed rapidly in the field of coordination chemistry.It has the characteristics of large specific surface area,strong molecular designability and easy modification of structure,and can be used as excellent adsorption materials.At present,due to few research on the separation of radionuclides with MOF materials,it is possible to make a breakthrough by combining MOF materials with magnetic nanoparticles to develop new materials with high efficiency and rapid separation of strontium.ObjectiveThe preparation of magnetic functionalized MOF material with specific selectivity,high efficiency,rapidity and simplicity for 90Sr was studied.Various factors affecting its separation performance and adsorption mechanism were studied,which provided new ideas and scientific basis for the application of magnetic adsorbents in the field of radionuclide separation.MethodsIn this study,UiO-66 derivatives with good chemical stability were selected to synthesize MMOF.Then.18 crown-6 derivatives with special selectivity for strontium were functionalized to MMOF surface by chemical derivation and physical encapsulation respectively,and their adsorption properties for strontium were studied.The main methods are as following:(1)Fe3O4 magnetic nanoparticles were prepared by coprecipitation method,the surface of Fe3O4 particles was modified by thioglycolic acid,and then the magnetic particles were added to the UiO-66-NH2 growth mixture by encapsulation method to make MOF grow around the magnetic particles,forming MMOF(Fe3O4＠UiO-66-NH2，M-UiO for short)centered on magnetic particles.Subsequently,4-aminodibenzo-18-crown-6 was bridged on M-UiO by glutaraldehyde to synthesize ADB18C6-Fe3O4@UiO-66-NH2(AM-UiO for short)using Schiff base reaction.In addition,M-UiO was dispersed in chloroform solution and 1-octanol was used as diluent to synthesize 4’.4"(5")-di-tert-butyl dicyclohexano-18-crown-6 coated MMOF DtBuCH18C6@Fe3O4@UiO-66-NH2(DM-UiO for short).(2)The crystal structure,morphology,chemical composition,specific surface area and magnetic properties of AM-UiO and DM-UiO were analyzed by PXRD,SEM,TEM,FT-IR,XPS,VSM and micropore analysis.(3)AM-UiO and DM-UiO were used to adsorb 90Sr in solution.The effects of nitric acid concentration,reaction time,initial strontium concentration,temperature,adsorbent dosage and co-existing cations on the adsorption of strontium by AM-UiO and DM-UiO were investigated.The adsorption kinetics,thermodynamics and isothermal adsorption model were also studied.Finally,the adsorption properties and stability of the two adsorbents were compared in acidic system.Results(1)New functional magnetic MOF materials AM-UiO and DM-UiO were synthesized.AM-UiO and DM-UiO both have UiO-66-NH2 crystal structure.The surface morphology of AM-UiO is regular and the surface of DM-UiO is swelling.The carbon-nitrogen double bond(C=N)formed in AM-UiO indicated that ADB18C6 was modified on the surface of M-UiO by chemical bond,and the grafting amount was about 0.5 mmol/g by elemental analysis.Both of them had the C-O-C characteristic of ether ring,indicating that both ADB18C6 and DtBuCH18C6 introduced M-UiO.The specific surface areas of AM-UiO and DM-UiO are 755 m2·g-1 and 708 m2·g-1 and 0.64 cm3·g-1.The pore sizes are 0.85 cm3·g-1 respectively,which belong to microporous structural materials.VSM magnetization curves show that AM-UiO and DM-UiO are superparamagnetic,with saturation magnetization Ms of 6.6 emu/g and 5.2 emu/g,respectively.(2)The separation of Sr solution by AM-UiO reached equilibrium in about 60 minutes.The distribution coefficient of adsorbent was the highest in 4 mol/L HNO3 medium,and the adsorption capacity increased with the initial concentration of strontium.The adsorption behavior was analyzed.AM-UiO conformed to the isothermal adsorption Freundich model,and the kinetic analysis conformed to the quasi-second-order kinetic model.(3)The separation of Sr solution by DM-UiO reached equilibrium in about 60 minutes.The distribution coefficient of adsorbent in 7 mol/L HNO3 medium was the highest.The adsorption capacity increased with the initial concentration of strontium,which had a special selective adsorption for strontium.The recovery of strontium can reach 99%after three times of desorption in 0.01 mol/L HNO3 medium after the adsorption of 1 mg/L solution of strontium ion concentration.The adsorption behavior of DM-UiO conforms to the Freundich model of isothermal adsorption.The adsorption thermodynamic study shows that the adsorption of strontium is an endothermic reaction and the reaction is spontaneous.The kinetic analysis conforms to the quasi-second-order kinetic model.ConclusionIn this paper,a novel functional material of crown ether modified MOF was synthesized by combining magnetic assisted separation technology with MOF materials which are developing rapidly in the field of materials.The magnetic adsorption material has the characteristics of strong selectivity to 90Sr,high efficiency and rapid separation.This study provides a new idea for the research and development of new materials for the separation of radionuclides,and has great potential and research value in this field. |
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