ABSTRACT
With a view on adding to their use in trace gas sensing, we perform a combined experimental and theoretical study of the change of the conductivity of a metal organic framework (iron (1,2,3)-triazolate, Fe(ta)2) with the uptake of chemically inert gases. To align our first-principles calculations with experimental measurements, we perform an ensemble average over different microscopic arrangements of the gas molecules in the pores of the metal-organic framework (MOF). Up to the experimentally reachable limit of gas uptake, we find a good agreement between both approaches. Thus, we can employ theory to further interpret our experimental results in terms of changes to the parameters of the Bardeen-Shockley band theory, electron-phonon coupling (in the form of the deformation potential), bulk modulus, and carrier effective mass. We find the first of these to be most strongly influenced through the gas uptake. Furthermore, we find the changes to the deformation potential to strongly depend on the individual microscopic arrangements of molecules in the pores of the MOF. This hints at a possible synthetic engineering of the material, e.g., by closing off certain pores, for a stronger, more interpretable electric response upon gas sorption.
ABSTRACT
The cubic SBU Ni8X6L6 (X = OH-/H2O, L = ligand) is of great interest due to its stability and potential applications when integrated in MOFs. Here, we investigate by detailed DRIFTS measurements and exchange reactions whether it is found to be neutral in MOFs, as previously assumed in the literature, or whether it can show anionic character, as observed in complexes.
ABSTRACT
In this work, a metal-organic framework (MOF), namely MFU-4, which is comprised of zinc cations and benzotriazolate ligands, was used to entrap SF6 gas molecules inside its pores, and thus a new scheme for long-term leakproof storage of dangerous gasses is demonstrated. The SF6 gas was introduced into the pores at an elevated gas pressure and temperature. Upon cooling down and release of the gas pressure, we discovered that the gas was well-trapped inside the pores and did not leak out - not even after two months of exposure to air at room temperature. The material was thoroughly analyzed before and after the loading as well as after given periods of time (1, 3, 7, 14 or 60 days) after the loading. The studies included powder X-ray diffraction measurements, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy, 19F nuclear magnetic resonance spectroscopy and computational simulations. In addition, the possibility to release the gas guest by applying elevated temperature, vacuum and acid-induced framework decomposition was also investigated. The controlled gas release using elevated temperature has the additional benefit that the host MOF can be reused for further gas capture cycles.
ABSTRACT
One of the main problems of gas storage in porous materials is that many molecules of interest adsorb too weakly to be retained effectively. To enhance gas storage in metal-organic frameworks (MOFs), we propose the use of kinetic trapping, i.e., a process where the guest gas is captured in the voids at loading conditions and not released immediately at normal conditions. In this approach, the diffusion-limiting pore size and the framework flexibility have to be matched to the gas, requiring flexible pore apertures to be smaller than the van der Waals diameter of the trapped guest. We selected the Metal-Organic Framework Ulm University-4 (MFU-4) with a pore aperture of 2.52 Å as a model coordination framework and used it for storage of xenon (with van der Waals diameter of 4.4 Å). Although xenon atoms are substantially larger than the MOF pore aperture, MFU-4 could be loaded with xenon by applying moderately high gas pressures. This is demonstrated to be due to the pore flexibility as confirmed by computational studies. The xenon loading could be tuned (from 0 wt % to more than 44.5 wt %) by changing the loading parameters such as pressure, temperature, and time, and the xenon atoms remained inside the pores upon exposing the material to air atmosphere at room temperature. To understand the material behavior, TGA, XRPD, and 129Xe NMR spectroscopy and computational studies were carried out.
ABSTRACT
Two organometallic pentanuclear zinc complexes, namely [Zn5Et4(Me2bta)6] and [Zn5Me4(Me2bta)6], containing tridentate N-donor ligands (5,6-dimethylbenzotriazolate, Me2bta) were prepared by a one-pot synthesis. These compounds represent the first examples of organometallic complexes featuring a Kuratowski-type bond topology. Zinc ions were introduced as organometallic precursors (either diethylzinc or dimethylzinc was used), which upon mixing with the ligand yielded the desired complexes spontaneously. The organometallic complexes were characterized by a range of analytical techniques including NMR- and FT-IR spectroscopy, mass spectrometry, and elemental analysis. In addition, the structure of [Zn5Et4(Me2bta)6] could be solved by single-crystal X-ray analysis. The thermal and chemical stability of the complexes was studied by TGA, VT-XRPD and DRIFT, in addition to NMR and mass spectrometric investigations. The compounds were found to be unexpectedly stable under various conditions and to lack any reactivity with electrophilic reactants such as aldehydes, which commonly react easily with organozinc compounds. However, the basic alkyl groups could be reacted with strongly acidic compounds such as trifluoroacetic acid.
ABSTRACT
Plasma-enhanced chemical vapor deposited polymers (plasma polymers) are promising candidates for biomaterials applications. In the present study, plasma deposition as a fast and easily scalable method was adapted to deposit coatings from n-heptane and methyl methacrylate monomers onto glass substrates. Linear patterns with line and groove widths between 1.25 and 160 µm were introduced by degrative UV-lithography for cell alignment. Differential interference contrast optical microscopy, profilometry and atomic force microscopy revealed that the patterned surfaces had a smooth, homogeneous appearance and a pattern height of 8 and 45 nm for plasma deposited n-heptane and methyl methacrylate, respectively. UV-lithography increased the oxygen content on the surface drastically as shown by X-ray photoelectron spectroscopy. After immersion in simulated body fluid for 21 days, the pattern was still intact, and the ester groups were also maintained for the most part as shown by infrared spectroscopy. To test the coatings' potential applicability for biomaterial surfaces in a preliminary experiment, we cultured murine preosteoblastic MC3T3-E1 cells on these coatings. Light and electron microscopically, a normal spindle-shaped and aligned cell morphology was observed. At the mRNA level, cells showed no signs of diminished proliferation or elevated expression of apoptosis markers. In conclusion, plasma-enhanced chemical vapor deposited polymers can be patterned with a fast and feasible method and might be suitable materials to guide cell alignment.