Preparation of polyaniline membranes considering hydration energy effects for the selective separation of monovalent cations

Low-temperature plasma polymerization enabled stable PANI grafting onto CEMs. • Membrane surface hydrophobicity was tuned to regulate the hydration-energy barrier. • Na + /Ca 2+ permselectivity increased from 0.70 to 6.06 after modification. • Hydration-mediated transport and concentration polarization jointly governed ion selectivity. • The modified membrane achieved high selectivity with only a slight loss of Na + flux. Monovalent-selective cation exchange membranes are crucial for water softening and resource recovery via electrodialysis (ED). However, effective separation of monovalent and divalent ions remains challenging due to small differences in charge and ionic size. This study employed low-temperature plasma grafting to covalently graft polyaniline onto cation exchange membrane substrates. Iodinated linear alkanes with varying carbon chain lengths were used to quaternize the polyaniline layer, modulating surface hydration energy. Increasing the carbon chain length enhanced membrane hydrophobicity, and the Na + /Ca 2+ permselectivity of the PANI-C 5 CEM increased from 0.70 to 6.06. In mixed-salt systems, Ca 2+ experienced stronger electrostatic repulsion and additional migration resistance due to the interception effect of surrounding Na + ions. This work demonstrates that integrating surface hydration energy regulation with ionic competition effects is an effective strategy for developing high-performance monovalent-selective membranes. Download: Download high-res image (199KB) Download: Download full-size image