12 research outputs found
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
Metal Organic Framework Containing Mixed Matrix Membranes for Gas Separation: A Different Approach to Mmm Preparation Methods
Formate modulated solvothermal synthesis of ZIF-8 investigated using time-resolved in situ X-ray diffraction and scanning electron microscopy
Time-resolved investigations using in situ energy-dispersive X-ray diffraction in tandem with ex situscanning electron microscopy revealed that solvothermal crystallisation of ZIF-8 in methanol solvent and in the presence of sodium formate as a simple monodentate ligand (modulator) is a rapid process yielding big, high-quality single crystals in short time (<4 h). Kinetic analysis of crystallisation curves was performed by applying the Avrami–Erofe'ev and Gualtieri models. The analyses revealed that the weakly basic formate modulator acts as a base in deprotonation equilibria (deprotonation of the bridging 2-methylimidazole ligand) rather than as a competitive ligand in coordination equilibria at the metal (Zn2+) centres. This is in contrast to the coordination modulation function of formate in ZIF-8 synthesis at room temperature. Crystal shape evolves with time in the presence of formate from cubes with truncated edges to rhombic dodecahedra. The latter shape represents most likely the stable equilibrium morphology of ZIF-8
NMR studies of carbon dioxide and methane self-diffusion in ZIF-8 at elevated gas pressures
Self-diffusion measurements with methane and
carbon dioxide adsorbed in the Zeolitic Imidazolate Framework-
8 (ZIF-8) were performed by 1H and 13C pulsed field
gradient nuclear magnetic resonance (PFG NMR). The experiments
were conducted at 298 K and variable pressures
of 7 to 15 bar in the gas phase above the ZIF-8 bed. Via
known adsorption isotherms these pressures were converted
to loadings of the adsorbed molecules. The self-diffusion
coefficients of carbon dioxide measured by PFG NMR are
found to be independent of loading. They are in good agreement
with results from molecular dynamic (MD) simulations
and resume the trend previously found by IR microscopy
at lower loadings. Methane diffuses in ZIF-8 only
slightly slower than carbon dioxide. Its experimentally obtained
self-diffusion coefficients are about a factor of two
smaller than the corresponding values determined by MD
simulations using flexible framework
Hull of H.M.A.S. Australia with three workers beneath, Cockatoo Island Dock, Sydney, 4 June 1930 [picture].
Title devised from accompanying information where available.; Part of the: Fairfax archive of glass plate negatives.; Fairfax number: 6945.; Also available online at: http://nla.gov.au/nla.pic-vn6266612; Acquired from Fairfax Media, 2012