Polymeric ionic liquid gels composed of hydrophilic and hydrophobic units for high adsorption selectivity of perrhenate

The removal of TcO(4)(−) from aqueous solutions has attracted more and more attention recently, and ReO(4)(−) has been widely used as its natural analog. In this work, polymeric ionic liquid gel adsorbents, PC(2)-C(12)vimBr, with high adsorption capacity and selectivity towards ReO(4)(−) were synthesized by radiation-induced polymerization and crosslinking. PC(2)-C(12)vimBr was composed of two monomers: a hydrophobic unit, 1-vinyl-3-dodecylimidazolium bromide for high selectivity, and a hydrophilic unit, 1-vinyl-3-ethylimidazolium bromide for improved kinetics. A gel fraction up to 90% could be achieved under 40 kGy with varied monomer ratios. The adsorption of PC(2)-C(12)vimBr gels for ReO(4)(−) was evaluated by batch adsorption. The PC(2)-C(12)vimBr gel containing 20 mol% hydrophilic unit (named PC(2)-C(12)vimBr-A) could significantly improve the adsorption kinetics, which had an equilibrium time of ca. 24 h. The adsorption capacity obtained from the Langmuir model was 559 mg g(−1) (Re/gel). The selective factor against NO(3)(−) was 33.4 ± 1.9, which was more than 10 times higher than that of PC(2)vimBr, and it could maintain ReO(4)(−) uptake as high as 100 mg g(−1) in 0.5 mol kg(−1) HNO(3). The ΔH(Θ) and ΔS(Θ) of the NO(3)(−)/ReO(4)(−) ion-exchange reaction of PC(2)-C(12)vimNO(3)-A were −16.9 kJ mol(−1) and 29 J mol(−1) K(−1), respectively, indicating physical adsorption. The adsorption mechanism of ReO(4)(−) onto PC(2)-C(12)vimBr-A gel was ion-exchange, and it could be recovered using 5.4 mol kg(−1) HNO(3).