Dipeptide Crystals as Reverse Osmosis Membranes for Water Desalination: Atomistic Simulation

An atomistic simulation study is reported to investigate the capability of dipeptide crystals as reverse osmosis (RO) membranes for water desalination. Eight dipeptides are considered, namely, Ala-Val (AV), Val-Ala (VA), Ala-Ile (AI), Ile-Ala (IA), Val-Ile (VI), Ile-Val (IV), Val-Val (VV), and Leu-Ser (LS). It is revealed that water flux is governed by both pore size and helicity. With a relatively larger pore size, AV, AI, VV, and LS exhibit a higher water flux than VA, IA, VI, and IV. Despite similar pore size in AI and VA, a higher flux is observed in AI because of a lower helicity. On the other hand, VI, LS, IV, and IA possess higher salt rejection (>90%, and 100% for VI) than the rest (<70%). The salt rejection is determined by the electric potential difference across the membrane, induced by the staggered arrangement of −NH3+ and −COO– groups in the dipeptides. This unique arrangement of charge groups is not observed in other types of RO membranes. A higher electric potential difference allows more ...