Functionality-Induced Locking of Zeolitic Imidazolate Frameworks

Abstract

Zeolitic imidazolate frameworks (ZIFs) are metal–organic analogues of zeolites that have attracted considerable interest for gas separation applications. However, the inherent framework flexibility of ZIFs during gas adsorption complicates their designed and desired performance. Herein, we report functionality-induced locking of ZIFs undergoing irreversible structural transformations, which leads to exceptional framework rigidity. Specifically, an isoreticular series of zeolite GME-type CoII-ZIFs were prepared and proven to have dynamic, flexible, and rigid behaviors after thermal activation, depending on their functional groups (i.e., −H, −CH3, and −NO2). Molecular insights into the irreversible, functionality-induced locking were determined to occur as a consequence of framework flexibility for maximizing the linker–linker interactions from π–π interaction to hydrogen bonding. The practical impact of functionality-induced locking in ZIFs was evaluated through high-pressure CO2/CH4 adsorptive separation for realizing more efficient methane purification. The present findings shed light on the deliberate control over the inherent flexibility observed in many porous materials to optimize their performance in practical applications.

Popping and Locking: Balanced Rigidity and Porosity of Zeolitic Imidazolate Frameworks for High-Productivity Methane Purification

“…(e) The purification productivity of CH 4 calculated by integrating the CO 2 /CH 4 breakthrough curve (CO 2 /CH 4 = 50:50) at 298 K, with CH 4 purity of 99%. (f) Comparison of CH 4 purification productivity calculated from CO 2 /CH 4 breakthrough curve (CO 2 /CH 4 = 50:50) at 298 K for ZIFs in this work with our previous work as well as MOFs, zeolites, and carbon materials − previously reported. The blue, orange, and red pentagrams represented ZIF-78-lt, ZIF-78-ht1, and ZIF-78-ht2, respectively; the orange, red, and blue hollow circles represented ZIF-68-Co, ZIF-78-Co, and ZIF-79-Co, respectively; the green triangles represent MOFs, and the gray diamonds represent zeolites (solid diamonds indicate the breakthrough test conducted at 298 K, while hollow diamonds represent test at 303 K).…”

“…194). Each tetrahedral Zn­(II) center is connected to two nIMs and two nbIMs that were interconnected to form a three-dimensional framework with GME net, which is isoreticular to the Co­(II)-based structures . To handle the substantial disorder of nbIM, the activated structures were refined in lower symmetry space group P 6 3 (No.…”

A Hydrogen-Bonded Organic Framework Equipped with a Molecular Nanovalve

“…Configuring materials to predictably respond to an external stimulus (i.e., light, pH, temperature, chemical and/or biological environment, electric field, among others) for carrying out a specific function at the bulk level is the fundamental basis of molecular machinery. − Indeed, the chemistry of incorporating movable elements into biomolecular, molecular, supramolecular, and inorganic and/or hybrid inorganic–organic systems has been duly explored and developed in this regard, examples of which include mechanically interlocked molecules (e.g., catenanes, rotaxanes), pseudorotaxanes, porous inorganic materials (e.g., mesoporous silica), and metal–organic frameworks (MOFs). − The latter examples are of particular interest as control over access to and from the internal pore environments of porous inorganic materials and MOFs provides significant advantages for applications in molecular transport, chemical sensing, gas separation and storage, catalysis, and drug delivery. − Given that such systems are often endowed with accessible pore apertures, it appears obvious that installing a stimuli-responsive valve composed of movable elements is a critical step for controlling access of molecules to and from the internal pore environment . Although mesoporous silica and MOFs have had “molecular nanovalves or valves” installed, noted examples are often overengineered with respect to extensive synthesis being required (i.e., tethering functional, movable molecules on the inorganic walls or organic building units) or remain at the mercy of the self-assembly and/or template-driven synthesis process. − , Furthermore, often as a result of overengineering, facile control over the movable elements is relatively limited, thereby hindering overall performance.…”

Crown Ether Nanopores in Graphene Membranes for Highly Efficient CO2/CH4 and CO2/CO Separation: A Theoretical Study

“…Due to the significant advancements in nanotechnology, nanomaterials have emerged as promising candidates for gas separation applications. Intrinsic porous nanomaterials such as metal–organic frameworks, covalent organic frameworks, and zeolite imidazolate frameworks have demonstrated excellent separation performance in CO 2 /CH 4 separation with experimental or theoretical approaches. − Polymeric membranes have also been experimentally and theoretically explored for this purpose. − Hybrid matrix films combining MOF nanosheets and polymer matrices have shown excellent CO 2 /CH 4 selectivity in natural gas and the ability to remove H 2 S using experimental method . Beyond above porous materials, 2D nanomaterials also offer distinct advantages over 3D porous materials.…”