Monovalent Cation Exchange Membranes with Janus Charged Structure for Ion Separation

Monovalent cation exchange membranes (M-CEMs) have been extensively applied in environmental remediation and energy harvesting such as the extraction of Na+ or Li+ from brine and seawater. However, owing to the limitations of membrane structures and materials, M-CEMs have a low perm-selectivity issue. Herein, we proposed a facile approach to construct a novel M-CEM with a Janus-charged structure, consisting of a positively-charged trimesic acid/polyethylenimine surface thin layer and a negatively charged commercial cation exchange membrane (CEM). Selectrodialysis results indi-cated that the Janus-charged M-CEMs could effectively suppress the migration of anions, which often occurred in porous CEMs, thereby enabling the novel Janus-charged M-CEMs to possess high perm-selectivity and high total cation fluxes. Compared with state-of-the-art M-CEMs, the Janus-charged M-CEM exhibited the highest perm-selectivity of 145.77 for Na+/Mg2+ beyond the contemporary "Upper Bound" plot as well as the excellent perm-selectivity of 14.11 for Li+/Mg2+, indicating its great potentials in ion separation. This study can provide novel insights into the design of Janus-charged M-CEMs for ion separation in diverse environmental and energy applications.(c) 2022 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).