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

Abstract

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.