The endowment of monovalent anion selectivity and antifouling property to cross-linked ion-exchange membranes by constructing amphoteric structure

Ion exchange membranes (IEMs) with high monovalent-ion selectivity show promising application in ion resource recovery. In this work, we report a kind of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based on amphoteric ion exchange membranes (AIEMs) having cross-linked structure. Therein, four imidazolium-terminated aliphatic chains (2IM-nC, n = 3, 6, 9, and 12) with varied number of −CH2− were used as crosslinker for cross-linking membrane matrix. Small-angle X-ray scattering tests indicate that the ion cluster sizes of the four AIEMs are evaluated with values of 0.378, 0.384, 0.388 to 0.408 nm, which possibly render the enhanced mono-valent anion selectivity of as-prepared AIEMs. Tested in the electrodialysis (ED) filled with a mixture solution of 0.05 M NaCl + 0.05 M Na2SO4, at current densities of 2.5 mA·cm−2 and 5.0 mA·cm−2, the PSO42-Cl- values of cross-linked AIEM having longer alkyl chains are 20.41 and 22.51, respectively, which are higher than AIEM with shorter cross-linker alkyl chain under the same conditions (3.5). Due to the hydrophilic surface and hydrophilic/negatively charged zwitterionic surface of AIEM, act as useful barriers via physical blocking and electrostatic repulsion, respectively, the anti-fouling performance of IEMs is improved simultaneously. In view of the superior performance, it is believed that the structure–property relationship of AIEM developed here can serve as a guideline for advanced IEMs.