A SIMULATION STUDY OF WATER AND IONS IN ZEOLITIC IMIDZOLATE FRAMEWORKS

Abstract

Recently metal-organic frameworks (MOFs) have emerged as a new class of nanoporous crystalline materials. They have been studied in storage, separation, catalysis and drug delivery. However very few has studied its potential as a membrane for reverse osmosis.

In this paper, the fundamental properties of water and ions in a sub-class of MOFs named zeolitic imidazolate frameworks (ZIFs) are studied by molecular simulations. Specifically, six different ZIFs (ZIF-68, 69, 71, 78, 79, and 81) with varying topology and functional group are considered as potential membrane for reverse osmosis. It is found that Na+ and Cl- ions cannot diffuse in all the six ZIFs, and water diffusion is affected by various extents upon adding NaCl, with water in ZIF-71 being affected the least. ZIF-71 also gives the highest diffusion coefficient of water in the presence and absence of NaCl. Among the six ZIFs, only ZIF-71 allows the multi-directional diffusion of water.