Microporous metal imidazolates : synthesis and characterization of nano- and microcrystals as well as membranes and investigation of the mechanisms of crystallization

[no abstract

In situ static and dynamic light scattering and scanning electron microscopy study on the crystallization of the dense zinc imidazolate framework ZIF-zni

The kinetics and mechanism of crystallization of the dense zinc imidazolate framework with zni topology, from comparatively dilute methanol solutions containing Zn(NO3)·6H2O and imidazole with variation of the zinc-to-imidazole ratio, were followed in situ by time-resolved static and dynamic light scattering. The light scattering data revealed that metastable primary particles of about 100 nm in diameter form rapidly upon mixing the component solutions. After a lag time that is dependent on the imidazole concentration, the primary particles aggregate into secondary particles by a monomer addition mechanism with the primary particles as the monomers. Complementary scanning electron microscopy revealed that further evolution of the secondary particles is a complex process involving polycrystalline intermediates, the non-spherical morphologies of which depend on the initial zinc-to-imidazole ratio. Time and location of the first appearance of crystalline order could so far not be established. The pure-phase ZIF-zni crystals obtained after 240 min are twins. The aspect ratio of the tetragonal crystals can be controlled via the zinc-to-imidazole ratio. © 2011 The Owner Societies

Metal-organic framework nanofibers via electrospinning

A hierarchical system of highly porous nanofibers has been prepared by electrospinning MOF (metal-organic framework) nanoparticles with suitable carrier polymers. Nitrogen adsorption proved the MOF nanoparticles to be fully accessible inside the polymeric fibers. © 2011 The Royal Society of Chemistry

Post-Synthetic Anisotropic Wet-Chemical Etching of Colloidal Sodalite ZIF Crystals

Controlling the shape of metal-organic framework (MOF) crystals is important for understanding their crystallization and useful for myriad applications. However, despite the many advances in shaping of inorganic nanoparticles, post-synthetic shape control of MOFs and, in general, molecular crystals remains embryonic. Herein, we report using a simple wet-chemistry process at room temperature to control the anisotropic etching of colloidal ZIF-8 and ZIF-67 crystals. Our work enables uniform reshaping of these porous materials into unprecedented morphologies, including cubic and tetrahedral crystals, and even hollow boxes, by an acid-base reaction and subsequent sequestration of leached metal ions. Etching tests on these ZIFs reveal that etching occurs preferentially in the crystallographic directions richer in metal-ligand bonds; that, along these directions, the etching rate tends to be faster on the crystal surfaces of higher dimensionality; and that the etching can be modulated by adjusting the pH of the etchant solution

Water-based synthesis of zeolitic imidazolate framework-8 with high morphology level at room temperature

In this study, the synthesis of zeolitic imidazole framework (ZIF-8) in water was systematically studied using 6 zinc sources (Zn(OAc)(2), ZnSO4, Zn(NO3)(2), ZnCl2, ZnBr2, ZnI2), respectively, under different conditions at room temperature without using any additives. It was found that Zn(OAc)(2) is the best precursor and the resultant ZIF-8 particles have the best quality with rhombic dodecahedron morphology. The concentration of 2-methylimidazole (Hmim), molar ratio Hmim/Zn and water content all have significant impacts on the morphology, particle size, and crystallinity of ZIF-8. Further result analysis reveals that 3 key reactions are involved in the ZIF-8 formation which needs five steps in ZIF-8 structural evolution. This study provides a deep understanding of the crystallization process of ZIF-8 particles in a waterbased system

One-dimensional metal-organic framework photonic crystals used as platforms for vapor sorption.

We present the fabrication of one-dimensional photonic crystals (Bragg stacks) based on a microporous metal–organic framework material and mesoporous titanium dioxide. The Bragg stack heterostructures were obtained using two complementary synthesis approaches utilizing the bottom-up assembly of heterogeneous, i.e. two-component photonic crystal multilayer structures. Zeolitic imidazolate framework ZIF-8 and mesoporous titanium dioxide were chosen as functional components with different refractive indices. While ZIF-8 is intended to impart molecular selectivity, mesoporous TiO2 is used to ensure high refractive index contrast and to guarantee molecular diffusion within the Bragg stack. The combination of micro- and mesoporosity within one scaffold endows the 1D-MOF PC with characteristic adsorption properties upon exposure to various organic vapors. In this context, the sorption behavior of the photonic material was studied as a function of partial pressure of organic vapors. The results show that the multilayered photonic heterostructures are sensitive and selective towards a series of chemically similar solvent vapors. It is thus anticipated that the concept of multilayer heterogeneous photonic structures will provide a versatile platform for future selective, label-free optical sensors

Processing of thermally stable 3D hierarchical ZIF-8@ZnO structures and their CO2 adsorption studies

Core-shell hybrid structures of ZnO-Zeolitic Imidazolate Framework-8 (ZIF@ZnO) were obtained by the solvothermal treatment of ZnO hierarchical structures having an average cluster size of ~3 µm and surface area of ~19 m2/g. The surface area and pore volume of these supported structures could be tailored as a function of reaction time and temperature. Solvothermal treatment of ZnO structures in the presence of imidazole at 95 °C for 24 h induced extremely large surface area of 733 m2/g for the ZIF@ZnO samples. Samples thus obtained demonstrated a CO2 adsorption capacity of 0.34 mmol/g at 25 °C compared to the value of 0.052 mmol/g measured for the ZnO structures. More significantly, the ZnO core helped the ZIF-8 surface fractal assemblies to significantly improve the thermal stability and retain their near spherical shapes allowing better handling in any practical adsorption application. The results validate that surface conversion of ZnO microstructures to ZIF-8 could be an efficient pathway towards the development of ZIF based supported adsorbents for CO2 separation. © 2016 Elsevier Ltd. All rights reserved

One-step synthesis of 2,5-bis(chloromethyl)-1,4-dioxane from epichlorohydrin using ZIF-8, taking advantage of structural defects

We demonstrate herein the ZIF-8-only-mediated catalysis of the cyclodimerization of epichlorohydrin to 2,5-bis(chloromethyl)-1,4-dioxane in the absence of co-catalyst and solvent. The easy handling and economic aspects of ZIF-8, in addition to the one-step reaction to produce the cyclodimer, make this catalyst attractive even for industry. It has been clearly illustrated that the nature of the method used to synthesize ZIF-8 affected the yields of the cyclodimers. Specifically, the method employed to produce ZIF-8 directly influences the amount of crystal structural defects, which in turn impacts their performance as catalysts. To emphasize the role of defects, other physical properties, such as surface area and particle size, were controlled during the synthesis of the ZIF-8 catalysts. Remarkably, the amount of structural defects was quantified by temperature program desorption analysis

Nanoimprinted, Submicrometric, MOF-Based 2D Photonic Structures: Toward Easy Selective Vapors Sensing by a Smartphone Camera

International audience2D photonic metal–oxide-framework-based homo- and hetero-structures are fabricated by soft lithographic approaches. As shown by A. Cattoni, M. Faustini and co-workers, these materials can be used as selective photonic sensing platforms. Detection of toxic vapors such as styrene are performed using an easy transduction method, compatible with smart-phone camera technologies

Ultrapermeable Thin Film ZIF-8/Polyamide Membrane for H-2/CO2 Separation at High Temperature without Using Sweep Gas

The use of thin film composites containing metal-organic frameworks (MOFs) as filler is of widespread interest for nanofiltration issues, since their thin selective layer allows a high permeation flow. The application of this kind of membranes for gas separation should provide a better permeance in comparison with other polymeric membranes and a reduction in the amount of MOF required for their fabrication. Here, the preparation of 50-100 nm thick polyamide flat membranes containing zeolitic imidazolate framework-8 (ZIF-8) nanoparticles is shown via interfacial polymerization, containing a lower amount of MOF (0.013 g m(-2) membrane) as compared to other membranes used for gas separation. The membranes are applied for H-2/CO2 separation at high temperatures and pressures, showing a stable performance at 180 degrees C for at least seven days. Outstanding separation values are 328 GPU of H-2 and a H-2/CO2 selectivity of 18.1 at 180 degrees C and 6 bar feed without transmembrane pressure. These membranes, also measurable without sweep gas, are highly suitable for industrial application