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

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 ??) 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.

Automated summary

This study developed ion-imprinted membranes with a six-coordinated and semi-rigid imprinted nanocage structure. These membranes exhibited excellent Nd(III) adsorption capacity and higher selectivity to Y(III) compared to other rare earth elements. Both experimental measurements and theoretical calculations showed that Nd(III) had shorter average coordination bond and stronger binding energy in the nanocage, which was attributed to the symmetrical crab-type structure and specific cavity size of the nanocage. The limited decomposition of the nanocage and the anti-swelling property of the rGO framework allowed for better selective adsorption.