Study on recognition and separation of rare earth ions at picometre scale by using efficient ion-surface imprinted polymer materials

Abstract

The graft-polymerization of hydroxyethyl methylacrylate (HEMA) on micro-sized silica gel particles was first conducted by initiating of a surface-initiating system, which was constituted by the bonded amino groups on the modified silica gel particles and persulfate in the solution, obtaining the grafted particles PHEMA/SiO2 with a high grafting degree of 40g/100g. Subsequently, 8-hydroxyquinoline as a ligand with strong chelating ability for metal ions was bonded on the side chains of the grafted macromolecule PHEMA through the substitution reaction between 5-chloromethyl-8-hydroxyquinoline (CHQ) and the hydroxyl group of the grafted macromolecule PHEMA, preparing the functional grafted particles HQ-PHEMA/SiO2. On the basis of examining the chelating adsorption property of HQ-PHEMA/SiO2 particles for Pr3+ ion, the Pr3+ ion surface-imprinting was carried out by using the effective surface-imprinting technique of “pre-grafting and post-crosslinking/imprinting” established by our group. During the surface-imprinting process, Pr3+ ion was used as a template ion, and 2,2′-dichlorodiethyl ether was used crosslinked, resulting in the Pr3+ ion surface-imprinted material IIP-HQP/SiO2. The recognition and binding characters of IIP-HQP/SiO2 towards Pr3+ ion were investigated in-depth with La3+ and Ce3+ ions as two contrast ions. The experimental results show that the IIP-HQP/SiO2 particles possess special recognition selectivity and high binding ability for Pr3+ ion. The binding capacity of IIP-HQP/SiO2 for Pr3+ ion reaches 0.13mmol/g, and relative to La3+ and Ce3+ ions, the selectivity coefficients of IIP-HQP/SiO2 for Pr3+ ion are 5.22 and 5.12, respectively. La, Ce and Pr are three neighbouring rare earth elements, and the ion radius differences between La3+, Ce3+ and Pr3+ ions are only in a range of 2–5pm. Obviously, in this investigation, the mutual separation of La3+, Ce3+ and Pr3+ ions at picometre scale is realized successfully by using the ion surface-imprinted polymer material with high performance.