ZIF-8 membrane: the synthesis technique and nanofiltration application

Abstract

Membrane technology for water treatment is growing due to the increased demand for clean water and the stringent standard for water quality. Nanofiltration (NF) is widely used in membranes for water treatment due to lower energy consumption and higher flux rates. The application was not limited to only water treatment, yet NF showed excellent potential for solvent nanofiltration application. The utilization of MOF materials for the preparation of NF membranes to produce composite membranes has attracted more attention among researchers due to the advantages offered by the material. Zeolitic imidazolate framework-8 (ZIF-8) membrane has been considered a promising MOF membrane with its capabilities and promising performance due to the small aperture size of the compounds and the stability towards harsh chemical condition. The purpose of this review is to present the synthesis approaches on the preparation of ZIF-8 membranes and the application of ZIF-8 membrane for NF application. The challenges and prospects of ZIF-8 membranes are also discussed to further stimulate the development and the application of ZIF-8 membrane for NF.

Structural Chemistry of Zeolitic Imidazolate Frameworks

“…In ZIFs, the metal ions serve as nodes that are connected by imidazole-based linkers to form a three-dimensional framework . ZIFs have a high degree of tunability in their structures and properties due to the ability to vary connection of metal ions and linkers used in their synthesis, and they have shown great potential in applications such as gas storage, separation, and sensing. ,− Metal–organic molecular cages (MOCs), on the other hand, are discrete, self-assembled structures made up of organic linkers and metal ions that form a cage-like structure around a central cavity. − The behavior of these cages in solution is dominated by Brownian motion, the random movement of particles in a fluid due to their collisions with other fast-moving molecules in the solution. This characteristic can be coupled with their structural design to selectively capture and release guest molecules based on the size, shape, and polarity of the cavity and linkers used.…”

Zeolite Imidazolate Frameworks-8@SiO2–ZrO2 Crystal–Amorphous Hybrid Core–Shell Structure as a Building Block for Water Purification Membranes

“…The measured salt rejections, following the order of Na 2 SO 4 > MgSO 4 > NaCl, are attributed to a combination of size sieving and Donnan exclusion, 17,18 consistently with the silanol-covered surface of the S−Z gel. 28 The membrane prepared by coating 1 layer of ZIF-8@S−Z, namely the ZIF-8@S−Z(1) membrane, presents higher salt rejections (13.5% for NaCl, 26.5% for MgSO 4 , and 35.6% for Na 2 SO 4 ) compared to the S−Z membrane, despite an active layer with thickness of only 0.5 μm (vs 2.7 μm of S−Z), and a permeance of 3.2 L m −2 h −1 bar −1 .…”

“…13 In this respect, MOF-based active layers provide important advantages comparted to other postmodification techniques (e.g., layer-bylayer deposition of polyelectrolytes or carbonaceous materials) in terms of versatility, structural regularity and enhanced selectivity. 13 ZIF-8, 14 MIL-101, 15 MOF-303 16 and UiO-66 17,18 are among the few MOFs that have recently been used for this scope, which shows the good water stability. MOF structure can be designed and optimized for NF applications.…”

“…Indeed, the voids and defects between nanocrystals allow for the permeation of dissolved ions and organic species through the membrane. Thus, continuous and selective layers were achieved only at a thickness of several micrometers, ,, and this is detrimental to the membrane permeance. An alternative approach consists of the dispersion of MOFs nanocrystals in a continuous matrix to form defect-free NF active layers.…”