Abstract:Amorphous
metal–organic frameworks (MOFs) have the potential
for applications such as controlled drug delivery and hazardous material
encapsulation. Moreover, their distinct mechanical properties may
facilitate fabrication of industrial-scale adsorbents for gas uptake
applications. However, the dense amorphous phase has less capacity
for gas adsorption compared to its parent crystalline structure because
for the majority of MOFs, amorphization drops their accessible porosity
and negatively affects their gas ad… Show more
“…Unlike other CPs/MOFs, where recrystallisation induced less than 100% recovery of the gas uptake compared with their pristine states would be expected 24 , we find an increase in the N 2 uptake of Cu[Fe] 2/3 -c' with a BET surface area of 585 m 2 g −1 . The partial retention of the amorphous phase and the elimination of CN − linkers during the mechanical milling process, described in the previous section, would generate local bypassing routes, resulting in a more accessible/connective porous network 33 , 38 , 39 . Fig.…”
Section: Resultsmentioning
confidence: 99%
“…Partial amorphisation of some crystalline MOFs through a lightly shear/uniaxial deformation has been demonstrated to open up these closed pockets through the formation of dangling linkers in computational studies. Up to 48.5% and 20.8% increases in the accessible surface area have been demonstrated, theoretically, under shear and compression strain in Cu 3 (1,3,5-tris(1H-pyrazol-4-yl)benzene) 2 39 . Moreover, the presence of ligand vacancy also leads to the accessibility of hidden pore cavities 38 .…”
Section: Enhanced Porosity Via Crystal-glass-crystal Transformationmentioning
Prussian blue analogues (PBAs) are archetypes of microporous coordination polymers/metal–organic frameworks whose versatile composition allows for diverse functionalities. However, developments in PBAs have centred solely on their crystalline state, and the glassy state of PBAs has not been explored. Here we describe the preparation of the glassy state of PBAs via a mechanically induced crystal-to-glass transformation and explore their properties. The preservation of short-range metal–ligand–metal connectivity is confirmed, enabling the framework-based functionality and semiconductivity in the glass. The transformation also generates unconventional CN− vacancies, followed by the reduction of metal sites. This leads to significant porosity enhancement in recrystallised PBA, enabled by further accessibility of isolated micropores. Finally, mechanical stability under stress for successful vitrification is correlated to defect contents and interstitial water. Our results demonstrate how mechanochemistry provides opportunities to explore glassy states of molecular framework materials in which the stable liquid state is absent.
“…Unlike other CPs/MOFs, where recrystallisation induced less than 100% recovery of the gas uptake compared with their pristine states would be expected 24 , we find an increase in the N 2 uptake of Cu[Fe] 2/3 -c' with a BET surface area of 585 m 2 g −1 . The partial retention of the amorphous phase and the elimination of CN − linkers during the mechanical milling process, described in the previous section, would generate local bypassing routes, resulting in a more accessible/connective porous network 33 , 38 , 39 . Fig.…”
Section: Resultsmentioning
confidence: 99%
“…Partial amorphisation of some crystalline MOFs through a lightly shear/uniaxial deformation has been demonstrated to open up these closed pockets through the formation of dangling linkers in computational studies. Up to 48.5% and 20.8% increases in the accessible surface area have been demonstrated, theoretically, under shear and compression strain in Cu 3 (1,3,5-tris(1H-pyrazol-4-yl)benzene) 2 39 . Moreover, the presence of ligand vacancy also leads to the accessibility of hidden pore cavities 38 .…”
Section: Enhanced Porosity Via Crystal-glass-crystal Transformationmentioning
Prussian blue analogues (PBAs) are archetypes of microporous coordination polymers/metal–organic frameworks whose versatile composition allows for diverse functionalities. However, developments in PBAs have centred solely on their crystalline state, and the glassy state of PBAs has not been explored. Here we describe the preparation of the glassy state of PBAs via a mechanically induced crystal-to-glass transformation and explore their properties. The preservation of short-range metal–ligand–metal connectivity is confirmed, enabling the framework-based functionality and semiconductivity in the glass. The transformation also generates unconventional CN− vacancies, followed by the reduction of metal sites. This leads to significant porosity enhancement in recrystallised PBA, enabled by further accessibility of isolated micropores. Finally, mechanical stability under stress for successful vitrification is correlated to defect contents and interstitial water. Our results demonstrate how mechanochemistry provides opportunities to explore glassy states of molecular framework materials in which the stable liquid state is absent.
“…Partial amorphization of some crystalline MOFs through a lightly shear/uniaxial deformation has been demonstrated to open up these closed pockets through the formation of dangling linkers in computational studies. Up to 48.5% and 20.8% increases in the accessible surface area have been demonstrated, theoretically, under shear and compression strain in Cu3(1,3,5-tris(1H-pyrazol-4-yl)benzene)2 50 . Moreover, the presence of ligand vacancy also leads to the accessibility of hidden pore cavities 49 .…”
Section: Resultsmentioning
confidence: 93%
“…Unlike other CPs/MOFs, where recrystallization induced less than 100% recovery of the gas uptake compared with their pristine states would be expected 30 , we find an increase in the N2 uptake of Cu[Fe]2/3-c' with a BET surface area of 585 m 2 g −1 . The partial retention of the amorphous phase and the elimination of CN − linkers during the mechanical milling process, described in the previous section, would generate local bypassing routes, resulting in a more accessible/connective porous network 46,49,50 .…”
Prussian blue analogues (PBAs), a class of microporous crystalline coordination frameworks, are long known for their diverse properties in porosity, magnetic, charge transport, catalysis, optics, and more. Versatile structural composition and the ability to control defect ordering through synthetic conditions offer opportunities to manipulate the functionality in the crystalline state. However, developments in Prussian blue analogues (PBAs) have primarily revolved around the ordered crystalline state, and the glassy state of PBAs has not yet been explored. Here we report the discovery of a disordered glassy state of the PBA via mechanically induced crystal–glass transformation. We found the preservation of metal–ligand–metal connectivity, confirming the short-range order and semiconductor behaviour, exhibiting an electronic conductivity value of 0.31 mS cm−1 at 50 ˚C. Mechanical-induced glass transformation also triggers changes in electronic states, where electroneutrality is compensated by introducing unconventional CN− vacancies. Partial disorders and ligand vacancies in recrystallized PBA give rise to an enhanced porosity, inaccessible in the crystalline parent. The present work also established a correlation between the mechanical stress required to initiate crystal–glass transformation and intrinsic mechanical properties, which are controlled by the vacancy/defect content, the presence of interstitial water, and the overall composition of PBAs.
“…These approaches must include a description of the bond breaking and forming events present during amorphization, which has been achieved in aMOFs using the reactive force field ReaxFF in classical simulations or, alternatively, using ab initio MD simulations. 12,[43][44][45][46] The first approach is limited in the number of MOF chemistries the force field covers, while the second, although very useful for providing mechanistic insights, is too computationally expensive to be used as a routine method to produce structures of aMOFs given the system size needed to reproduce the amorphous system.…”
Amorphous metal−organic frameworks (aMOFs) are a class of disordered framework materials with a defined local order given by the connectivity between inorganic nodes and organic linkers, but absent longer-range order. The rational development of function for aMOFs is hindered by our limited understanding of the underlying structure-property relationships in these systems, a consequence of the absence of long-range order, which makes experimental characterization particularly challenging. Here, we use a versatile modelling approach to generate in-silico structural models for an aMOF based on Fe trimers and 1,3,5-benzenetricarboxylate (BTC) linkers, Fe-BTC. We build a phase space for this material that includes nine amorphous phases with different degrees of defects and local order. These models are analyzed through a combination of structural analysis, pore analysis and pair distribution functions. Therefore, we are able to systematically explore the effects of the variation of each of these features, both in isolation and combined, for a disordered MOF system, something that would not be possible through experiment alone. We find that the degree of local order has a greater impact on structure and properties than the degree of defects. The approach presented here is versatile and allows for the study of different structural features and MOF chemistries, enabling the development of design rules for the rational design of aMOFs.
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