Mono-/Bi-valent anion resource recovery via electrodialysis using dual-side-chain functionalized poly(aryl ether sulfone) anion exchange membranes†

Abstract

The ion separation performance of polymer membrane can be significantly enhanced by constructing suitable and stable ion channels within the dense matrix. In this work, we fabricated four anion exchange membranes (AEMs) based on a type of distorted poly(aryl ether sulfone) bearing dual-side-chains and explored the influence of these dual-side-chains by tuning the ratio of the two on the separation performance of Cl⁻/F⁻ and Cl⁻/SO₄²⁻. Small-angle X-ray scattering analysis indicated that the as-prepared AEMs in wet state possessed sub-nanometer ion channels with a size of 0.334 nm, which resulted from the synergetic modification of the distorted main chains and dual-side-chains. In addition, the stability of the ion channels could be verified by a very low swelling ratio of 5.3%. The AEM with the smallest ion channel demonstrated superior perm-selectivity (Cl⁻/SO₄²⁻) of 52.21 during the electrodialysis (ED) process, compared to other AEMs, such as ACS AEM, which showed a selectivity of 18.63. In addition, the optimum AEM (PPH-sIm_10−X-5N_X) also exhibited selectivity for Cl⁻/F⁻ due to its dense structure and hydrophobic side chains. By using free volume and electrostatics-driven simulations, it was inferred that the ion-blocking effect of the dense membrane structure on the transport of larger ions was effective. As a result, this dual-side-chain polymer with a distorted backbone is conducive to constructing stable sub-nanometer ion channels in AEMs for mono-/bi-valent anion resource recovery.