Stability Of Zeolitic Imidazolate Frameworks Research Articles

Vibrational dynamics as an essential determinant of the thermal stability of zinc zeolitic imidazolate lattices.

Thermal stability and kinetics of zeolitic imidazolate frameworks (ZIFs) are crucial for their applications as energetic materials. Here, the effect of microscopic vibrational dynamics on the thermal stability of ZIFs is demonstrated by using simple tools. Specifically, we explored the thermal kinetics based on Flynn-Wall-Ozawa and Kissinger's methods. The study comprises a combination of structure-related effects such as topology, density, and alkyl substitution with respect to vibrational dynamics in ZIFs. The results exhibit a linear correlation between the vibrational dynamics of the linkers and activation energy, I.E. stabilization of ZIFs, in the polymorphic Zn(EtIm)2 series. At the same time, thermal destabilization was observed with the growing alkyl chain and was further probed by IR spectroscopy.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Stability of zeolitic imidazolate frameworks (ZIF-7) under high pressures and its implications on storage applications of ZIFs

We report the chemical stability of ZIF-7 under pressure using Raman spectroscopy. Our results show a reversible pressure response of ZIF-7 in non-penetrating media up to 8 ​GPa. Increasing pressures above 12 ​GPa leads to an irreversible ring-opening polymerization to a disordered phase. The lower chemical stability of ZIF-7 over prototypic ZIF-8 is explained to be due to hydrogen bonding C–H-π interaction. This study highlights the role of various substituents in the imidazole linkers in ZIFs for their gas storage applications under pressure.

Improving the Acidic Stability of Zeolitic Imidazolate Frameworks by Biofunctional Molecules

Summary Zeolitic imidazolate frameworks (ZIFs) have been widely investigated for their use in separation, gas adsorption, catalysis, and biotechnology. Their practical applications, however, can be hampered by their structural instability in humid acidic conditions. Here, guided by density functional theory calculations, we demonstrate that the acidic stability of two polymorphic ZIFs (i.e., ZIF-8 and ZIF-L) can be enhanced by the incorporation of functional groups on polypeptides or DNA. A range of complementary synchrotron investigations into the local chemical structure and bonding environment suggest that the enhanced acidic stability arises from the newly established coordinative interactions between the Zn centers and the inserted carboxylate (for polypeptides) or phosphate (for DNA) groups, both of which have lower pKas than the imidazolate ligand. With functional biomolecular homologs (i.e., enzymes), we demonstrate a symbiotic stability reinforcement effect, i.e., the encapsulated biomolecules stabilize the ZIF matrix while the ZIF exoskeleton protects the enzyme from denaturation.

Stability of Zeolitic Imidazolate Frameworks in NO2

The use of nanoporous zeolitic imidazolate frameworks (ZIFs) in separation processes is attractive, but the presence of acid gases such as SOx or NOx in process streams can have detrimental effects. While we have recently developed a mechanistic picture of SOx–ZIF interactions, here we describe the remarkably different effects of NO2 on ZIFs. ZIFs with a representative range of SOx stabilities are all unstable—as defined by loss of crystallinity and porosity—in dry and humid NO2, whereas most ZIFs are stable in dry SOx and some even in humid SOx. A detailed mechanism is developed based on Fourier transform infrared spectroscopy and density functional theory calculations. H-abstraction by free radical NO2 and subsequent acidic species formation are the major degradation pathways, while adsorbed HNO3 formation in humid conditions is an additional pathway in hydrophilic ZIFs. These findings strongly suggest that new strategies to stabilize ZIFs/metal–organic frameworks toward NO2 attack are required.

Acid Gas Stability of Zeolitic Imidazolate Frameworks: Generalized Kinetic and Thermodynamic Characteristics

Acid gases such as SO2 and CO2 are present in many environments in which the use of nanoporous metal–organic frameworks (MOFs) is envisaged. Among metal–organic frameworks, zeolitic imidazolate frameworks (ZIFs) have been extensively explored as membranes or adsorbents. However, there is little systematic knowledge of the effects of acid gas exposure on the structure of ZIFs, in particular the mechanistic aspects of ZIF degradation by acid gases as well as the effects of ZIF crystal topology and linker composition on their stability. Here we present a generalized and quantitative investigation of the kinetic and thermodynamic acid gas stability of a diverse range of ZIF materials. The stability of 16 ZIFs (of SOD, RHO, ANA, and GME topologies) under different environments—humid air, liquid water, and acid gases CO2 and SO2 (dry, humid, and aqueous)—is investigated by a suite of experimental and computational methods. The kinetics of ZIF degradation under exposure to humid SO2 is studied in detail, and eff...

Insights into the Stability of Zeolitic Imidazolate Frameworks in Humid Acidic Environments from First-Principles Calculations

Understanding the degradation mechanisms of zeolitic imidazolate frameworks (ZIFs) is crucial to improve their chemical stability and realize their potential industrial applications. Here, we conduct a comprehensive study utilizing dispersion-corrected density functional theory calculations to investigate the chemical stability of bulk ZIFs and their external surfaces under conditions of acid-gas exposure. We examine the influence of steric factors such as topology and ligand functionalization on the relative chemical stability of prototypical ZIFs (ZIF-2 and ZIF-8), including their hypothetical polymorphs. We find that defect formation is more thermodynamically and kinetically favorable at ZIF external surfaces versus the bulk, and that both topology and ligand functionalization impact defect formation. In addition, we provide a detailed mechanism for the reaction of ZIFs with sulfurous and sulfuric acids, of which the latter serves as a catalyst in potential degradation reactions of ZIFs. We also provide information about the adsorption strength of a range of acid gases to defective ZIF structures, which can inform potential strategies to regenerate ZIFs and/or achieve defect engineering in these materials.

Recovery of Acid-Gas-Degraded Zeolitic Imidazolate Frameworks by Solvent-Assisted Crystal Redemption (SACRed).

The acid stability of zeolitic imidazolate frameworks (ZIFs) is an important issue hindering their application. Acid-gas damage of ZIFs has been considered irreversible. However, we demonstrate a methodology called solvent-assisted crystal redemption (SACRed) to reverse acid-gas damage to ZIFs with a high degree of structural and functional recovery. For example, post-SACRed ZIF-8 is shown to be structurally and chemically near-identical with the original pristine ZIF-8 that suffered a large loss of surface area, porosity, and crystallinity during acid-gas exposure. We also provide mechanistic insight into the recovery process using deuterium-labeled linkers and 2H NMR spectroscopy. SACRed treatments could allow large extensions in the lifetime of ZIF-based membranes and adsorbents that degrade over time.

Stability of ZIF-8 membranes and crystalline powders in water at room temperature

The perceived robust stability of zeolitic imidazolate frameworks (ZIFs) was regarded as an important feature of ZIFs that have intrigued intensive research efforts. However, hydrolysis of ZIF crystals was recently identified under hydrothermal conditions. In this work, the dynamic stability of α-alumina supported ZIF-8 membranes and static stability of both ZIF-8 membranes and powder in water were studied via pervaporation and batch durability tests at room temperature. The sharp increase in water pervaporation flux from 0.04kgm−2h−1 to 1.39kgm−2h−1 and the disappearance of ZIF-8 structure after pervaporation are consistent with morphology and phase structure data showing that ZIF-8 layer on the α-alumina support underwent degradation during water pervaporation. The gradual degradation of ZIF-8 layer was also experimentally observed in batch durability tests in pure water. To better understand the mechanism of stability of ZIF-8 structure, control experiments on hydrolysis of ZIF-8 powder in aqueous conditions were designed and performed. The continuous release of Zn2+ from ZIF-8 structure to the aqueous solution was detected along with the change in pH value of the aqueous system. The presence of 2-methylimidazolate in aqueous solution can stabilize the ZIF-8 structure of both membrane and crystals. These evidences confirm that ZIF-8 crystals can degrade in water due to the dissolution of ZIF-8. The rate and extent of the dissolution depends on the ZIF-8 crystal to water mass ratio.

Stability of zeolitic imidazolate frameworks: effect of forced water intrusion and framework flexibility dynamics

Synergistic effect of temperature and pressure upon forced water intrusion strongly affects metal–organic frameworks stability.

Zeolitic Imidazolate Frameworks: Synthesis, Functionalization, and Catalytic/Adsorption Applications

Zeolitic imidazolate frameworks (ZIFs) are comprised of transition metal ions (Zn, Co) and a range of imidazolate linkers in a tetrahedral coordination similar to that in crystalline aluminosilicate zeolites. The high surface area, tunable nanoporosity that can be subject to functionalization and the excellent thermal/chemical stability of ZIFs are attractive for heterogeneous catalysis and selective gas adsorption/separation. This review presents the current trends in synthesis, surface modification and catalytic reactions/adsorption of ZIF-based materials with particular emphasis on ZIF-8, which is the most widely studied structure among ZIFs.

Improvement of hydrothermal stability of zeolitic imidazolate frameworks

The metal-organic framework ZIF-8, which undergoes hydrolysis under hydrothermal conditions, is endowed with high water-resistance after a shell-ligand-exchange-reaction. The stabilized ZIF-8 retains its structural characteristics with improved application performances in adsorption and membrane separation.

Exceptional chemical and thermal stability of zeolitic imidazolate frameworks.

Twelve zeolitic imidazolate frameworks (ZIFs; termed ZIF-1 to -12) have been synthesized as crystals by copolymerization of either Zn(II) (ZIF-1 to -4, -6 to -8, and -10 to -11) or Co(II) (ZIF-9 and -12) with imidazolate-type links. The ZIF crystal structures are based on the nets of seven distinct aluminosilicate zeolites: tetrahedral Si(Al) and the bridging O are replaced with transition metal ion and imidazolate link, respectively. In addition, one example of mixed-coordination imidazolate of Zn(II) and In(III) (ZIF-5) based on the garnet net is reported. Study of the gas adsorption and thermal and chemical stability of two prototypical members, ZIF-8 and -11, demonstrated their permanent porosity (Langmuir surface area = 1,810 m(2)/g), high thermal stability (up to 550 degrees C), and remarkable chemical resistance to boiling alkaline water and organic solvents.