Mussel-inspired polyphenol/polyethyleneimine assembled membranes with highly positive charged surface for unprecedented high cation perm-selectivity

Mono/multivalent cation separation techniques have shown increasing importance in diverse environmental and energy applications. The separation performance of emerging monovalent cation exchange membranes (MCEMs) is greatly determined by the architecture and charge property of MCEMs, which should be finely tuned for the energy efficiency applications. Herein, a series of mussel-inspired polyphenol/polyethyleneimine assembled membranes (PPAMs) with highly positively-charged surfaces were elegantly constructed through a facile layer-by-layer assembly method. Based on the synergetic reactions between polyphenols with multiple reactive groups and PEI with abundant amino groups, the denser membrane surfaces with a higher crosslinking degree and more positive charges were readily formed. As a result, the Na+/Mg2+ and Li+/Mg2+ perm-selectivities of PPAMs with such surface architecture and charge property followed the same order as gallic acid/polyethyleneimine membrane (M-GA/PEI) > pyrogallic/polyethyleneimine membrane (M-Pyrogallic/PEI) > protocatechuic acid/polyethyleneimine membrane (M-PA/PEI) > caffeic acid/polyethyleneimine membrane (M-CA/PEI). Most interestingly, the M-GA/PEI fabricated exhibited the unprecedented perm-selectivity (Na+/Mg2+) up to 180.4 with Na+ flux of 6.01 × 10−8 mol cm−2 s−1, which exceeded the current “Upper Bound” plot of MCEMs. The low membrane resistance and excellent separation performance of PPAMs brought great potential for resource recovery and environmental remediation.