Spatially ordered chelating resin based on liquid-crystal phase with highly selective removal of metal ions

In this study, an ordered spatial chelating resin was synthesized, and its selective adsorption of various cations was investigated. By using polyethyleneimine (PEI) as the main chain, methoxy biphenyl group as the rigid group, and methylene units as the flexible chains, a series of side-chain liquid crystal chelating resins were synthesized (labeled as POMen, where n is the spacer length varying between three to six methylene units). The analysis of the thermal properties of POMens showed that they are thermotropic liquid crystals with smectic structure. In its liquid state, out of all POMens, POMe6 demonstrated excellent adsorption capacity relative to Pb2+ with maximum value equal to 387 mg/g. In particular, L-POMe6 demonstrates an excellent selectivity for the removal of Pb2+ in the presence of competitive heavy metal ions. Density functional theory (DFT) calculations were carried out to analyze the binding energies of L-POMe6 structures and their corresponding metal ion complexes. L-POMe6 demonstrated the lowest binding energy with Pb2+ complexes compared other complexes. Furthermore, the adsorption of Pb2+ onto L-POMe6 adsorbents fitted to the Langmuir adsorption and pseudo-second-order kinetic model. The regeneration capacities of L-POMe6 were studied, that the adsorption capability remains high after several cycles of adsorption-desorption process.