Zeolitic imidazolate framework-8 as a reverse osmosis membrane for water desalination: Insight from molecular simulation

Abstract

A molecular simulation study is reported for water desalination in zeolitic imidazolate framework-8 (ZIF-8) membrane. The simulation demonstrates that water desalination occurs under external pressure, and Na(+) and Cl(-) ions cannot transport across the membrane due to the sieving effect of small apertures in ZIF-8. The flux of water permeating the membrane scales linearly with the external pressure, and exhibits an Arrhenius-type relation with temperature (activation energy of 24.4 kJ∕mol). Compared with bulk phase, water molecules in ZIF-8 membrane are less hydrogen-bonded and the lifetime of hydrogen-bonding is considerably longer, as attributed to the surface interactions and geometrical confinement. This simulation study suggests that ZIF-8 might be potentially used as a reverse osmosis membrane for water purification.

Structural effects on SAPO-34 and ZIF-8 materials exposed to seawater solutions, and their potential as desalination membranes

“…This is the first known reverse osmosis test in a ZIF-8 membrane, however the result is not promising for practical desalination applications requiring >90% rejection of NaCl. As presented in Figure 1, the aperture size of ZIF-8 that is widely reported of 0.34nm [15] leads to the intuitive view that ZIF-8 should block ions and permeate water, which was also determined by simulation [29]. We measured a pore size by PALS of 0.55nm which may be indicative of the mean pore size that is more relevant to permeation.…”

“…In particular, ZIF-8 (Composition Zn(MeIM)2), is known to be highly stable in aqueous environments [15,28] and thus a suitable candidate for water treatment application. To validate ZIF-8 as a candidate for a desalination membrane material, Hu and co-workers simulated that it possesses the correct intrinsic porosity to permeate water, but block Na + and Cl -ions [29]. The concept for this mechanism is highlighted by the size of the ZIF-8 aperture relative to the water and ions is shown in Figure 1.…”

Two-dimensional covalent triazine framework as an ultrathin-film nanoporous membrane for desalination

“…In particular, new membranes with enhanced water permeability compared to currently available polyamide--based membranes may have an important role to play in lowering energy consumption. 4 Several nanostructured materials have been previously investigated as promising membrane candidates such as carbon nanotubes (CNTs) 5,6,7 and zeolites 8,9 . Despite CNTs' high water permeability, 5 membranes based on CNTs exhibit poor salt rejection, and it remains challenging to fabricate membranes with dense, well--aligned nanotubes.…”

“…6,7 Zeolite membranes, on the other hand, possess three--dimensional networks that can effectively reject salt ions 8 but show relatively low water permeability. 9 Recently, nanoporous one--atom--thick graphene, the thinnest possible membrane made from matter, has drawn considerable attention and been shown computationally to provide significantly enhanced permeability compared to polyamide while maintaining excellent ability to reject salt. 10 Moreover, recent work of Surwade et al has further experimentally realized such single--layered nanoporous graphene membranes and demonstrated their potential in desalination at the lab scale.…”

Novel nanomaterials for water desalination technology

“…Membranes based on CNTs have been limited by low salt rejection rates and the difficulty of producing highly aligned and high-density CNT arrays [7], [8]. As for zeolites, studies suggest that their relatively low water permeability may pose a challenge for desalination applications [9].…”