Zeolitic imidazolate framework
[3][4] Due to their robust porosity, resistance to thermal changes, and chemical stability, ZIFs are being investigated for applications such as carbon dioxide capture.
[9] Yaghi introduced ZIFs as a novel class of materials that combined the structural characteristics of zeolites — such as their tetrahedral coordination and robust chemical stability— with the tunability and porosity of MOFs.
By linking metal ions (typically zinc or cobalt) with imidazolate linkers, ZIFs achieved the zeolite-like topology while maintaining the modularity and versatility of MOF chemistry.
This innovation significantly broadened the potential applications of porous materials in areas such as gas storage, separation, and catalysis.
ZIF-8 demonstrated exceptional chemical and thermal stability, coupled with a highly selective pore system, making it suitable for demanding applications like carbon dioxide capture and hydrocarbon separation.
The short-range structural disorder of the tetrahedral ligand environment around metal nodes in the ZIF glass was detected for the first time by performing zinc-67 nuclear magnetic resonance.
Crystals slowly grow from a heated solution of a hydrated metal salt, an ImH (imidazole with acidic proton), a solvent, and base.
[15][16] A wide range of solvents, bases, and conditions have been explored, with an eye towards improving crystal functionality, morphology, and dispersity.
Due to their promising material properties, significant interest lies in economical large-scale production methods.
[36][37] Chemical vapor deposition is of particular promise due to the high degree of uniformity and aspect ratio control it can offer, and its ability to be integrated into traditional lithographic workflows for functional thin films (e.g. microelectronics).
Environmentally-friendly synthesis based on supercritical carbon dioxide (scCO2) have been also reported as a feasible procedure for the preparation of ZIF-8 at an industrial scale.
[38] Working under stoichiometric conditions, ZIF-8 could be obtained in 10 hours and does not require the use of ligand excess, additives, organic solvents or cleaning steps.
[6] Those carefully selected ZIF crystals are able to form a glassy solid after heating and cooling in an argon atmosphere.
The crystal form of ZIF, or MOF in general, is known for its porosity, but is difficult to mass-produce and incorporate in actual applications due to unavoidable intercrystalline defects.
The first intriguing one is that ZIF glass maintains the porous structure as its crystalline form after melt-quench process, which means it can be applied for applications such as gas separation and storage.
ZIFs exhibit some properties relevant to carbon dioxide capture,[40] while commercial technology still centers around amine solvents.
ZIFs 68, 69, 70, 78, 81, 82, 95, and 100 have been found to have very high uptake capacity, meaning that they can store a lot of carbon dioxide, though their affinity to it is not always strong.
[42] ZIF-62 was made into a glassy membrane on the nanoporous alumina support for gas separation for the first time by Yuhan et al in 2020.
[43] The vitrification process effectively eliminates grain boundaries formation within the glass, and the molecular sieving ability of such membrane is significantly improved.
[3] Oxidation of aldehyde groups Hydrogenation of n-hexene ZIF’s are also good candidates for chemical sensors because of their tunable adsorbance properties.
Despite these similarities with other MOFs, ZIFs have significant properties that distinguish these structures as uniquely applicable to carbon capture processes.
ZIFs, however, have nearly identical performance in dry vs humid conditions, showing much higher CO2 selectivity over water, allowing the adsorbent to store more carbon before saturation is reached.
When this saturation and regeneration tests were run at these conditions, ZIFs also showed minimal to no structural degradation, a good indication of the adsorbent’s re-usability.
