Synthesis, Structure, and Carbon Dioxide Capture Properties of Zeolitic Imidazolate Frameworks

Abstract

Zeolites are one of humanity's most important synthetic products. These aluminosilicate-based materials represent a large segment of the global economy. Indeed, the value of zeolites used in petroleum refining as catalysts and in detergents as water softeners is estimated at $350 billion per year. A major current goal in zeolite chemistry is to create a structure in which metal ions and functionalizable organic units make up an integral part of the framework. Such a structure, by virtue of the flexibility with which metal ions and organic moieties can be varied, is viewed as a key to further improving zeolite properties and accessing new applications. Recently, it was recognized that the Si-O-Si preferred angle in zeolites (145 degrees ) is coincident with that of the bridging angle in the M-Im-M fragment (where M is Zn or Co and Im is imidazolate), and therefore it should be possible to make new zeolitic imidazolate frameworks (ZIFs) with topologies based on those of tetrahedral zeolites. This idea was successful and proved to be quite fruitful; within the last 5 years over 90 new ZIF structures have been reported. The recent application of high-throughput synthesis and characterization of ZIFs has expanded this structure space significantly: it is now possible to make ZIFs with topologies previously unknown in zeolites, in addition to mimicking known structures. In this Account, we describe the general preparation of crystalline ZIFs, discussing the methods that have been developed to create and analyze the variety of materials afforded. We include a comprehensive list of all known ZIFs, including structure, topology, and pore metrics. We also examine how complexity might be introduced into new structures, highlighting how link-link interactions might be exploited to effect particular cage sizes, create polarity variations between pores, or adjust framework robustness, for example. The chemical and thermal stability of ZIFs permit many applications, such as the capture of CO(2) and its selective separation from industrially relevant gas mixtures. Currently, ZIFs are the best porous materials for the selective capture of CO(2); furthermore, they show exceptionally high capacity for CO(2) among adsorbents operating by physisorption. The stability of ZIFs has also enabled organic transformations to be carried out on the crystals, yielding covalently functionalized isoreticular structures wherein the topology, crystallinity, and porosity of the ZIF structure are maintained throughout the reaction process. These reactions, being carried out on macroscopic crystals that behave as single molecules, have enabled the realization of the chemist's dream of using "crystals as molecules", opening the way for the application of the extensive library of organic reactions to the functionalization of useful extended porous structures.

Modelling a Linker Mix‐and‐Match Approach for Controlling the Optical Excitation Gaps and Band Alignment of Zeolitic Imidazolate Frameworks

“…ZIF structures with some of these linkers have been reported before, including Cu(Im) 2 , Zn(Ica) 2 , Zn(bIm) 2 , Zn(mIm) 2 and Co(nIm) 2 with SOD topology, as well as Zn(abIm) 2 and Zn(pur) 2 with LTA topology 6b. To date, no ZIFs have been synthesized with tIm and fIm linkers, although these molecular units are reported in the patent literature 8…”

“…ZIF structures with the same topology (SOD) and tetrahedral metal (Zn), but different imidazolate‐based linkers or combination of linkers, were computationally generated. The SOD topology (Figure 1) was chosen because of its flexibility to accept a wide range of chemical compositions, in terms of both linkers and metals 6b. Recently, ZIFs with SOD topology have been experimentally investigated and shown promise in the context of photocatalytic applications 7.…”

Addressing Challenges of Identifying Geometrically Diverse Sets of Crystalline Porous Materials

“…The zeolite class of these materials is the most well-known, as they have found wide use in industry since the late 1950s, with common applications as chemical catalysts and membranes for separations and water softeners; 1À4 their value is estimated at $350 billion per year. 5 There is increasing interest in utilizing zeolites as membranes or adsorbents for CO 2 capture applications. 3 In addition to zeolites, metal organic frameworks (MOFs) 6,7 and their subfamily of zeolitic imidazolate frameworks (ZIFs) 8 have recently generated interest for their potential use in gas separation or storage.…”

Microporous metal-organic framework with potential for carbon dioxide capture at ambient conditions

“…The regeneration energy cost to utilize these porous materials for CO 2 capture by the implementation of temperature swing adsorption, pressure swing adsorption (PSA) and vacuum swing adsorption is significantly lower than the abovementioned alkanolamine technology. More importantly, the rapid development over the past decade in this research field to target some porous MOFs for their extremely high uptake of CO 2 at high pressure 11,12 and to immobilize functional sites, such as open metal sites [13][14][15][16][17][18][19][20][21][22][23] , -NH 2 and -OH organic sites into the pore surfaces to enhance their interactions and thus enforce their efficient CO 2 separation selectivity have principally ensured the feasibility of porous MOFs for CO 2 capture [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] .…”