Construction of zwitterionic ion imprinted polymer brushes on mixed matrix membranes for the separation of rare earth ions

Abstract

In this article, zwitterionic ion imprinted polymer brushes were constructed on mixed matrix membranes (MMMs) for the separation of rare earth ions. A multi-step chemical grafting strategy to anchor amino groups and double bonds sequentially on the oxygen-containing sites at the edge of GO nanosheets were established at first. After incorporating these modified GO nanosheets into MMMs, the imprinting process was constructed via in-situ free radical polymerization initiated by oxidize-reduction initiators on these double bond sites of GO nanosheets in the MMMs. [2-(methylacryloxy)ethyl] dimethyl-(3-propyl sulfonate) ammonium hydroxide was firstly applied as functional monomers to generate the zwitterionic polymer brushes on the GO-mixed matrix membranes, together with the aid of ligand bis (2,4,4-trimethylpentyl) phosphonic acid (Cyanex272) in the MMMs matrix. Benefiting from these specific designed imprinted sites, the imprinted membranes had the highest adsorption capacity for Y3+, which was nearly twice as much as that of Ho3+ and Er3+. The significant difference in adsorption capacity and permeation efficiency between imprinted and non-imprinted membranes proved this imprinting strategy realized valid Y3+ imprinting sites construction. The separation coefficients of Y3+/Ho3+ and Y3+/Er3+ calculated from permeation experiments were 2.16 and 2.77, which were much higher than those of MMMs and NIMs. Imprinted factor βr of Y3+/Ho3+ and Y3+/Er3+ were calculated as 2.63 and 1.97.