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 .