Functional Group Spatial Arrangement in Cationic Polymeric Nanotraps for Selective Perrhenate Anion Capture

The selective capture of specific anions from complex wastewater remains a critical challenge in resource recovery. Although cationic polymers can adsorb anions through ion exchange, the influence of the spatial arrangement of the functional group on their selectivity is not well understood. In this study, two imidazolium-based cationic polymers with ortho- and para-substituted spatial arrangements (denoted as CPN-oVIm-Cl and CPN-pVIm-Cl) were synthesized, and their efficacy in the selective adsorption of perrhenate was comparatively studied. Both materials exhibit high adsorption capacities for perrhenate, reaching over 1200 mg g^-1, along with rapid adsorption kinetics. A key finding is that CPN-pVIm-Cl shows significantly superior selectivity toward ReO₄ ^- in the presence of multicharged competing anions such as SO₄ ^2- and AsO₄ ^3-, compared to CPN-oVIm-Cl. Mechanistic studies indicate that the uniformly distributed charges in the para-substituted polymer enhance specific recognition, whereas the locally concentrated charges in the ortho-substituted analogue reduce selectivity. This work highlights the spatial arrangement of functional groups as a key factor in tuning ion selectivity, offering a new perspective for designing high-performance adsorbents.