The majority of research into metal-organic frameworks (MOFs) focuses on their crystalline nature. Recent research has revealed solid-liquid transitions within the family, which we use here to create ...a class of functional, stable and porous composite materials. Described herein is the design, synthesis, and characterisation of MOF crystal-glass composites, formed by dispersing crystalline MOFs within a MOF-glass matrix. The coordinative bonding and chemical structure of a MIL-53 crystalline phase are preserved within the ZIF-62 glass matrix. Whilst separated phases, the interfacial interactions between the closely contacted microdomains improve the mechanical properties of the composite glass. More significantly, the high temperature open pore phase of MIL-53, which spontaneously transforms to a narrow pore upon cooling in the presence of water, is stabilised at room temperature in the crystal-glass composite. This leads to a significant improvement of CO
adsorption capacity.
Over the past decade, the zirconium-terephthalate UiO-66 has evolved into one of the most intensely studied metal–organic frameworks (MOFs) to date. Among the most fascinating and pervasive features ...of this material are defects, and their influence on a multitude of its properties. However, the simultaneous occurrence of two defect types, missing linkers and missing nodes, limits the extent to which certain material properties can be accurately matched to the framework’s defect structure. In this contribution, we present a strategy to unequivocally create missing linker defects in UiO-66, by first synthesizing terephthalate frameworks doped with a thermolabile linker, trans-1,4-cyclohexane-dicarboxylate (cdc), followed by postsynthetic thermal decomposition of the latter. Characterization of the mixed-linker materials before and after cdc removal by powder X-ray diffraction, thermogravimetric analysis, N2 physisorption, and NMR spectroscopy confirmed a homogeneous distribution of cdc, and thus also of the formed defects, throughout the materials. The UiO-66 structure is shown to tolerate up to 4.3 missing linker defects per Zr6O4(OH)412+ node, with higher defect densities compromising the framework’s structural integrity and porosity. Importantly, no increase in specific surface area was seen after additional missing linker defects were formed, providing compelling evidence that high porosity often observed in modulated UiO-66 samples should rather be attributed to missing cluster defects.
Perfluorinated alkylated substances (PFASs) are widely used in industrial and commercial applications, leading to a widespread occurrence of these persistent and harmful contaminants in our ...environment. Removal of these compounds from surface and waste waters is being mandated by European and U.S. governments. Currently, there are no treatment techniques available that lower the concentrations of these compounds for large water bodies in a cost‐ and energy‐efficient way. We hereby propose a hydrophobic, all‐silica zeolite Beta material that is a highly selective and high‐capacity adsorbent for PFASs, even in the presence of organic competitors. Advanced characterization data demonstrate that the adsorption process is driven by a very negative adsorption enthalpy and favorable steric factors.
Perfluorinated compounds have found wide application but have adverse effects on health and environment. There is a need to selectively recover them from process and surface waters. We now show that a microporous zeolite Beta, in its all‐silica form, shows outstanding capacity and affinity for the uptake of PFASs like perfluorooctanoic acid and perfluorooctanesulfonic acid, even in the presence of other organics.
Lead halide perovskite (LHP) semiconductors show exceptional optoelectronic properties. Barriers for their applications, however, lie in their polymorphism, instability to polar solvents, phase ...segregation, and susceptibility to the leaching of lead ions. We report a family of scalable composites fabricated through liquid-phase sintering of LHPs and metal-organic framework glasses. The glass acts as a matrix for LHPs, effectively stabilizing nonequilibrium perovskite phases through interfacial interactions. These interactions also passivate LHP surface defects and impart bright, narrow-band photoluminescence with a wide gamut for creating white light-emitting diodes (LEDs). The processable composites show high stability against immersion in water and organic solvents as well as exposure to heat, light, air, and ambient humidity. These properties, together with their lead self-sequestration capability, can enable breakthrough applications for LHPs.
Magnesium–sulfur batteries are considered as attractive energy-storage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the ...mechanism of a Mg–S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS (resonant inelastic X-ray scattering), and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystallizes in the rock-salt structure with octahedral coordination of magnesium.
To date, only several microporous, and even fewer nanoporous, glasses have been produced, always via post synthesis acid treatment of phase separated dense materials, e.g. Vycor glass. In contrast, ...high internal surface areas are readily achieved in crystalline materials, such as metal-organic frameworks (MOFs). It has recently been discovered that a new family of melt quenched glasses can be produced from MOFs, though they have thus far lacked the accessible and intrinsic porosity of their crystalline precursors. Here, we report the first glasses that are permanently and reversibly porous toward incoming gases, without post-synthetic treatment. We characterize the structure of these glasses using a range of experimental techniques, and demonstrate pores in the range of 4 - 8 Å. The discovery of MOF glasses with permanent accessible porosity reveals a new category of porous glass materials that are elevated beyond conventional inorganic and organic porous glasses by their diversity and tunability.
UiO-66 is known as one of the most robust metal–organic framework materials. Nevertheless, UiO-66 has also been shown to undergo postsynthetic exchange of structural linkers with surprising ease in ...some solvents. To date, the exchange mechanism has not yet been fully elucidated. Here, we show how time-resolved monitoring grants insight into the selected case of exchanging 2-aminoterephthalate into UiO-66 in methanol. Analysis of both the solid and liquid phases, complemented by computational insights, revealed the active role of methanol in the creation and stabilization of dangling linkers. Similar to monocarboxylate defects that can be introduced during UiO-66 synthesis, such dangling linkers undergo fast exchange. The presence of missing-linker or missing-cluster defects at the start of the exchange process was shown to have no considerable impact on the equilibrium composition. After the exchange process, the incoming 2-aminoterephthalate and remaining terephthalate linkers were distributed homogeneously in the framework for the typical submicron size of UiO-66 crystallites.
We present a method for high temperature stabilization of bulk amorphous aluminium oxide. The stabilization is achieved by dispersing polysilane dendritic molecules in aluminium hydroxide gel, which ...upon thermal treatment gives amorphous aluminium oxide stable up to 900 °C. The dispersed macromolecules covalently bind to the alumina matrix and induce homogeneously distributed strain fields that keep the alumina amorphous. The thermal conversion of the precursor system was followed by thermogravimetry with an evolved gas analysis, infrared spectroscopy and 29Si NMR. The amorphous structure of aluminium oxide was confirmed with an X-ray and electron diffraction. Additionally, the amorphous state was supported by presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by a UV–visible absorption spectroscopy.
The fast adsorption kinetics of zeolitic imidazolate frameworks (ZIFs) enable a wide range of sorption applications. The most commonly used framework, ZIF-8, is relatively non-polar. Increasing the ...polarity of ZIF-8 through the encapsulation of different polar species shows promise for enhancing the sorption performance for pure CO2. Recently, the outlook has re-focused on gas mixtures, mostly in the context of post-combustion CO2 capture from wet flue gasses. While water is known to sometimes have a synergistic effect on CO2 sorption, we still face the potential problem of preferential water vapor adsorption. Herein, we report the preparation of three ZIF-8/organic dye (OD) composites using Congo red, Xylenol orange, and Bromothymol blue, and their impact on the sorption properties for CO2, water, and a model wet CO2 system at 50% RH. The results show that the preparation of OD composites can be a promising way to optimize adsorbents for single gasses, but further work is needed to find superior ZIF@OD for the selective sorption of CO2 from wet gas mixtures.
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