A chemically assembled anion exchange membrane surface for monovalent anion selectivity and fouling reduction

Separation and extraction of monovalent anions from salt lakes or oceans is very important in view of a sustainable supply of industrial chemical compounds. In this work, a novel anion exchange membrane (AEM) with simultaneously enhanced monovalent anion selectivity and reduced organic fouling properties was synthesized through oxidative self-polymerization and an amide condensation reaction. Using a rapid deposition and polymerization procedure, L-dopa was coated on a commercial AEM surface to form an L-dopa polymer layer (L-PDA) by using CuSO4 and H2O2 as a trigger. This layer was chemically assembled with a 4-amino-benzenesulfonic acid monosodium salt (ABS) via an amide condensation reaction. The resulting anion exchange membrane L-PDA#ABS, with a unique hydrophilic characteristic and negatively charged thin layer, was found to have a high monovalent anion permselectivity of 5.29 (SO42−/Br−) and 4.66 (SO42−/Cl−) in electrodialysis (ED) (10 min, initial concentration of 50 mM Br−, Cl− and SO42−, and current density of 10.00 mA cm−2), while the original AEM had corresponding permselectivities of 1.22 and 1.00. Furthermore, the selective separation efficiency parameter of the L-PDA#ABS AEM in SO42−/Br− and SO42−/Cl− was 66% and 63%, which is higher than those of the original AEM (8% and 2%). Sodium dodecyl benzene sulfonate, bovine serum albumin and humic acid were used as model organic fouling materials; the L-PDA#ABS AEM has a much higher antifouling potential than a commercial reference AEM. The work also demonstrated that the chemically assembled functional layer with high stability was suitable for long term application.