Insights into the Transport of Aqueous Quaternary Ammonium Cations: A Combined Experimental and Computational Study

Roles of Anion-Cation Coupling Transport and Dehydration-Induced Ion-Membrane Interaction in Precise Separation of Ions by Nanofiltration Membranes

Nanofiltration (NF) membranes are playing increasingly crucial roles in addressing emerging environmental challenges by precise separation, yet understanding of the selective transport mechanism is still limited. In this work, the underlying mechanisms governing precise selectivity of the polyamide NF membrane were elucidated using a series of monovalent cations with minor hydrated radius difference. The observed selectivity of a single cation was neither correlated with the hydrated radius nor hydration energy, which could not be explained by the widely accepted NF model or ion dehydration theory. Herein, we employed an Arrhenius approach combined with Monte Carlo simulation to unravel that the transmembrane process of the cation would be dominated by its pairing anion, if the anion has a greater transmembrane energy barrier, due to the constraint of anion-cation coupling transport. Molecular dynamics simulations further revealed that the distinct hydration structure was the primary origin of the energy barrier difference of cations. The cation having a larger incompressible structure after partial dehydration through subnanopores would induce a more significant ion-membrane interaction and consequently a higher energy barrier. Moreover, to validate our proposed mechanisms, a membrane grafting modification toward enlarging the energy barrier difference of dominant ions achieved a 3-fold enhancement in ion separation efficiency. Our work provides insights into the precise separation of ionic species by NF membranes.

Role of cationic groups on structural and dynamical correlations in hydrated quaternary ammonium-functionalized poly(p-phenylene oxide)-based anion exchange membranes

Extensive atomistic molecular dynamics simulations were conducted using a polarizable force field to study hydroxide and water dynamics in anion exchange membranes.

Parameterization of a coarse-grained model with short-ranged interactions for modeling fuel cell membranes with controlled water uptake

The coarse-grained model FF_pvap reproduces the experimental activity coefficient of water in tetramethylammonium chloride solutions over a wide range of concentrations, with a hundred-fold gain in computing efficiency with respect to atomistic models.

Atomistic simulations of ammonium-based protic ionic liquids: steric effects on structure, low frequency vibrational modes and electrical conductivity

Structural correlations and signature of cation–anion hydrogen bonding in ammonium triflate protic ionic liquids at varying length of the alkyl tail.

Electrochemical conversion of CO2 to fuels: tuning of the reaction zone using suitable functional groups in a solid polymer electrolyte

The electrochemical reduction of gaseous CO₂ is studied for the first time using sterically hindered bulky quaternary ammonium ions in a solid polymer matrix at room temperature and atmospheric pressure in a developed electrochemical reactor.