Novel Core-Shell Structured Megnatic Nanomaterials For Uranium Sepration:Synthesis And Adsorption Study

Uranium resource is the foundation for development of China's nuclear industry,and uranium reserves are crucial for stable operation of nuclear power.Due to limited uranium in terrestrial crust,it is urged to develop alternative methods to secure uranium resource for sustainability of nuclear industry.Separation of uranium from seawater or radioactive wastes has been considered as a supplementary approach,which can also benefit environmental protection and volume reduction of radioactive wastes.Because of easy operation,lower energy cost and less secondary waste,magnetically assisted chemical separation has been widely recognized as an effective way for uranium enrichment.In this respect,magnetic composite materials play a core role.Structure and performance of the magnetic composite materials significantly influence the separation efficiency.However,traditional magnetic composite materials have chemically inert surfaces with poor number of functional groups,leading to a relatively lower adsorption capacity toward uranium.To address this problem,this study was dedicated to preparing new kinds of core-shell structured magnetic nanomaterials via surface initiated living radical polymerization integrated with bio-inspired polydopamine chemistry.Through controlled architecture of functional polymer shells on the surfaces of magnetic nanoparticles,as well as tuning of the molecular weight and distribution,efficient adsorption of uranium was realized.Achievements of this thesis include:Firstly,highly water-dispersible Fe₃O₄ magnetic nanoparticles?MNPs?with tunable size was synthesized by using a modified solvothermal method.By manipulating the selfpolymerization of dopamine in alkaline environment,polydopamine?PDA?was deposited on the surfaces of Fe₃O₄ MNPs.Thickness of the PDA layers could be adjusted by controlling reaction time.With abundant catechol and amine groups,the PDA layer could serve as a favorable platform for efficient anchoring of initiators.Then,surface initiated single electron transfer-living radical polymerization?SET-LRP?was used for controlled growth of poly?acrylonitrile??PAN?brushes from the surfaces of Fe₃O₄@PDA.After hydroxylamine treatment,cyano groups in the PAN brushes were transformed to amidoxime groups,showing adsorption ability to uranium.Performance for uranium enrichment and adsorption kinetics was investigated.Besides,metal-free photoinduced electron transfer-atom transfer radical polymerization?PET-ATRP?was employed for growing poly?glycidyl methacrylate??PGMA?brushes from the surfaces of Fe₃O₄@PDA.The PGMA brushes were further modified by ethylenediamine.The obtained composite material showed improved hydrophilicity and efficient adsorption toward uranium with an adsorption capacity 260 mg/g.Influences of light,catalyst,polymerization period on the growth behavior of PGMA brushes from surfaces of Fe₃O₄@PDA were detailed.Overall,the thesis established the method by integrating polydopamine chemistry with surface initiated living radical polymerization,such as SET-LRP and PET-ATRP,to synthesize functional core-shell structured magnetic nanocomposites.The method was well controlled and easily operated under mild conditions,and could greatly increase degree of functionalization on surfaces of magnetic nanomaterials,resulting in highly efficient adsorption toward uranium.The findings in this thesis would provide a novel methodology for synthesis of new kinds of functional adsorption materials of uranium.