Development of an adsorption–desorption technique for the recovery of rare-earth metal ions using the phase transition behavior of zwitterionic polymer brushes

Abstract

This study synthesized a sulfobetaine-type zwitterionic polymer brush on a porous silica particle (P-SiO₂-poly(DMAPS)) through surface-initiated atom transfer radical polymerization (SI-ATRP) and demonstrated its applicability as an adsorption–desorption material for lanthanide (Ln) ions in aqueous solutions. Appropriate Ln adsorption conditions for P-SiO₂-poly(DMAPS) were established according to the effects of various Ln metal ions on the thermo-responsive behavior of poly(DMAPS) in aqueous solutions. From the adsorption experiments, it was confirmed that P-SiO₂-poly(DMAPS) enabled the complete recovery of all Ln ions from aqueous solutions. The regression analyses of the Langmuir adsorption isotherm curves of Ln ions at 50 °C–70 °C showed that the chemisorption processes of all Ln ions on P-SiO₂-poly(DMAPS) were entropy-driven and occurred spontaneously, while the maximum adsorption capacities of Ln ions decreased as the ionic radii decreased from light to heavy Ln ions. Furthermore, 100% of all Ln ions adsorbed on P-SiO₂-poly(DMAPS) desorbed by simple shaking in a certain concentration of ethylenediaminetetraacetic acid (EDTA) solution. These results prove that this novel Ln adsorption–desorption technique using a zwitterionic polymer brush has great potential in chemical, environmental, and energy fields.