High Throughput Simulations of Monovalent Cation Selectivity in Nanoporous Membranes

Membranes with tunable selectivity are crucial for the recovery of important elements from waste and saltwater brines. Among various ion separations of technological interest, separating alkali metal ions for recovery of lithium is difficult due to their similar charge densities and hydration radii. Zeolites have shown promise as reverse osmosis membranes for water filtration and are an attractive prospect for use as ion-selective membranes. Here, we propose a high-throughput molecular simulations approach for determining ion selectivity. The technique involves a charge gradient between the feed and permeate sides of the membrane which is achieved by redistributing anions evenly and cations asymmetrically. The result is fast transport of cations toward reduction of the charge imbalance, favoring the cations that encounter smaller free energy and/or kinetic barriers. This approach has been used to calculate the selectivity for monovalent cations through several nanoporous frameworks covering different geometries and chemistries. With this approach, we can systematically study relevant zeolite structures to examine their solute selectivity and identify crucial factors contributing to this selectivity.