Study on the influence of inductive groups on the performance of carboxylate-based hydrogel polymer network

Abstract

We report study on the effect of Br and CH3 inductive groups on the loading capacity of carboxylate-based hydrogel adsorbent. Synthesized sodium acrylate (NaAc) and 2-Bromoacrylic acid (BrAc) copolymer hydrogels for metal ion capture were characterized using FTIR, UV–Vis, 13C NMR, and DSC methods for structural and functional properties. Both FTIR and UV–Vis spectra indicated formation of a charge transfer complex between Br, CH3 groups and the carbonyl (C═O) group whereas solid-state NMR evidenced Br group appearance as an appendage on hydrogel backbone. By incorporating Br group on the hydrogel matrix and consequently exploiting the high electronegativity potential and inductive effect chemistry of this group, there was a significant increase in dissociation of H+ ions and hence higher loading capacity of carboxylate group. This facilitated higher ion exchange ability, resulting in up to 4 times increase in adsorption capacity during adsorption from multi-element metal ion competitive solution. Separately, when applied on single ion non-competitive solution, its adsorption capacity on vanadium increased three-fold from 119 mg/g to 373 mg/g due to the effect of Br group. However, the CH3 had a negating effect instead lowering the adsorption capacity (below 119 mg/g); while also caused lower swelling ratio of carboxylate-functionalized hydrogel adsorbents.