Bis-terpyridine imprinted nanocage in the confined two-dimensional lamellar membrane for selective adsorption of Nd(III)

Abstract

Nd is a strategic metal, but its extraction and separation process remains a challenging task. Here, ion-imprinted membranes with six-coordinated and semi-rigid imprinted nanocage structure were developed by self-assembling terpyridine monomers in the confined reduced graphene oxide (rGO) nanochannels. The obtained membranes displayed excellent Nd(III) adsorption capacity of 20.6 mg g−1 in the solution including seven rare earth elements (REEs), together with a 7.68 times higher selectivity to Y(III). Experimental measurements and theoretical calculations revealed that Nd(III) was well coordinated to the six pyridine-nitrogen in the nanocage, which showed shorter average coordination bond (0.77 Å) and stronger binding energy (-10.52 eV) than other REEs. These were mainly attributed to the rigid symmetrical crab-type architecture and specific cavity size of bis-terpyridine nanocage. Meanwhile, the limited decomposition of these metastable nanocage derived from 2D confined effect and nanochannel walls with few groups reduced the interference of groups at non-imprinted sites on selective adsorption. The excellent anti-swelling property of rGO framework endowed 7 static adsorption cycles and maintained high selectivity (K'(Nd/Y) > 7). Integrated into account the well-defined semi-rigid sites constituted by non-covalent interactions, this strategy provided a new idea for facile synthesis of imprinted sites with higher selectivity.