Study On The Preparation Of Crown Ether-like Solid-supported Polymer And Its Lithium Adsorption And Separation Performance

Crown ethers exhibit excellent selectivity to adsorb alkali metal ions and are widely used in the field of adsorption and separation of lithium isotopes because of their unique macrocyclic structures.The traditional method of separating lithium isotopes with crown ethers was liquid-liquid extraction.However,a large amount of organic solvents are used in this method and it is not easy to separate toxic crown ethers from the system.Since then,researchers have shifted their direction to solid-liquid extraction based on composites functionalized with crown ethers.But till now,these composites still have some limitations,for instance,the utilization of crown ethers is low and the lithium isotope separation factor is not high enough.In this paper,B15C5 and DB18C6 were selected as functional groups for the adsorption and separation of lithium isotopes,and AB15C5 and ADB18C6 were synthesized to be immobilized on the surface of PVDF microspheres.In addition,model crown peptides were designed properly to access the thermodynamic parameters of M--crown peptide complexes by density functional theory(DFT).C4 and C6 exhibits excellent selectivity to adsorb lithium ions.Then,the experiment was carried out,and C6 did not exhibit the selectivity to adsorb metal ions(Li÷,Na+ and Cs-).The reason is that the water solubility of C6 is good and metal ions can not be taken out of the water phase.Thus,crown peptides need to be immobilized on the substrate surface for further exploration.Two different synthetic routes were designed for B15C5,DB18C6 and C6.For B15C5 and DB18C6,PVDF microspheres functionalized with B15C5 or DB18C6(PGB5 or PGB6)were prepared via pre-irradiation emulsion grafting polymerization of GMA and the reaction between amino and epoxy groups.For C6,PVDF microspheres functionalized with C6(PHC6)were prepared via pre-irradiation emulsion grafting polymerization of HEMA,the reaction between hydroxy and acroleyl chloride and thiol-ene click reaction.And the loading capacity of B15C5 was near 1.20 mmol/g for PGB5 and DB18C6 was near 0.86 mmol/g for PGB6.All products were verified by FT-IR,1H-NMR,TG,SEM and XPS.The performance on the lithium isotope separation of PGB5 microspheres was characterized.The equilibrium adsorption time of PGB5 microspheres for Li+ in aqueous solutions is about 20 hours.The electrostatic interaction of counteranion affected the stability of Li+-crown ether complex.That is to say,Li+-crown ether complex is more easily formed if the counteranion is softer.The maximum adsorption capacity for Li+ can reach 3.5 mg/g in a CH3COOLi solution,and the maximum isotope separation factor is achieved as high as 1.05 ± 0.02 in a CH3COOLi solution.The effect of solvent and PH in separation lithium isotopes is also important.The lithium adsorption capacity and separation factor are higher in water than in organic solvents.PGB5 microspheres shows better ability of adsorbing and separating lithium isotopes in weak acidity condition,i.e.,0.1 M HNO3.