(366i) Water Desalination through Zeolitic-Imidazolate Framework Membranes: A Molecular Simulation Study
In this work, water desalination through ZIF-25, -71, -93, -96 and -97 membranes is investigated by molecular simulation. The ZIFs possess identical rho-topology, but differ in functional groups. Due to the presence of various functional groups, the aperture size and polarity differ in the five ZIFs. The rejection of salt (NaCl) is found to be around 97% in ZIF-25, and 100% in the other four ZIFs. The permeance ranges from 27 to 710 kg/(m2.hr.bar), about one ~ two orders of magnitude higher compared to commercial RO membranes. Because of a larger aperture size da, ZIF-25, -71 and -96 exhibit much higher water flux than ZIF-93 and -97. The flux in ZIF-25, -71 and -96 is governed by the polarity of functional group rather than da. With hydrophobic â??CH3 group, ZIF-25 has the highest flux despite the smallest daamong ZIF-25, -71 and -96. With the highest flux, the life time of hydrogen bonding in ZIF-25 is shorter than in ZIF-71 and -96. Furthermore, water molecules undergo fast flushing motion in ZIF-25, but frequent jumping in ZIF-96 and particularly in ZIF-97. An Arrhenius-type relationship is found between water flux in ZIF-25 and temperature, and the activation energy is predicted to be 6.5 kJ/mol. This simulation study provides a microscopic insight into water desalination in a series of ZIFs, reveals the key factors governing water flux, and suggests that ZIF-25 might be an interesting reverse osmosis membrane for high-performance water desalination.