Water desalination through FAU zeolite studied by using molecular dynamics simulations

JS Song and L Liu and SY Cai, JOURNAL OF MOLECULAR LIQUIDS, 380, 121683 (2023).

DOI: 10.1016/j.molliq.2023.121683

Zeolite possesses some superior properties such as huge specific area and proper aperture, endowing it with wide applications in water remediation. Non-equilibrium molecular dynamics (NEMD) simulations were performed to explore the desalination mechanisms of three monovalent salt solutions (including LiCl, NaCl and KCl) in FAU zeolites, associated with the effects of driving pressure and temperature on purification performance being discussed. The fluxes and rejections of three solutions increase and decrease with pressure respectively, and consistently follow the same order, LiCl < NaCl approximate to= KCl. In the desalination process, cation ions form hydration shells both in the bulk and confined zeolite channel. However, Li+, Na+, K+ hydrates lose approximately 0.005176, 0.28356 and 0.25515 water molecules respectively when entering from bulk region into zeolite, which implies the hydrogen bonding (HB) networks displacing process is energy-consuming and closely related to rejection performance. Attributed to the smallest radius and the minimum displacing numbers, Li+ ions possess stable hydration layer and receive the lowest rejection. With proximal water molecules displacing numbers, Na+ and K+ ions show similar purification properties. We find it is the enhanced kinetic energy and more fragile HB networks in solutions at high temperature that endow it more likely for ions to have an access to faujasite (FAU) zeolite. Therefore, the flux and rejection of NaCl and LiCl solutions show a trade-off effect, that is the former property increases and the latter one decreases with temperature, respectively. Our study provides fundamental insights into FAU zeolite purification, and is in favor of guidelines for optimal design of nanoporous medium membrane in water desalination. (c) 2023 Elsevier B.V. All rights reserved.

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