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

The removal of TcO4- from aqueous solutions has attracted more and more attention recently, and ReO4 has been widely used as its natural analog. In this work, polymeric ionic liquid gel adsorbents, PC2-C(12)vimBr, with high adsorption capacity and selectivity towards ReO4- were synthesized by radiation-induced polymerization and crosslinking. PC2-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 PC2-C-12 vimBr gels for ReO4- was evaluated by batch adsorption. The PC2-C(12)vimBr gel containing 20 mol% hydrophilic unit (named PC2-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 NO3 was 33.4 +/- 1.9, which was more than 10 times higher than that of PC(2)vimBr, and it could maintain ReO4- uptake as high as 100 mg g(-1) in 0.5 mol kg(-1) HNO3. The Delta H-Theta and Delta S-Theta of the NO3/ReO4- ion-exchange reaction of PC2-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 ReO4- onto PC2-C(12)vimBr-A gel was ion-exchange, and it could be recovered using 5.4 mol kg(-1) HNO3.