New family of ‘hybrid glasses’ expand metal-organic framework field

Novel materials could move us closer to industrial gas storage solutions and tuneable glasses

The experimental set up on I22, a small-angle scattering and diffraction beamline
The experimental set up on I22, a small-angle scattering and diffraction beamline
 An international team of scientists have used Diamond to develop a new manufacturing method which produces glass-like materials incorporating both organic, and inorganic elements. The novel materials are malleable and easy to shape, meaning that they could have important industrial applications in a range of fields, including advanced photonics and carbon capture.
Prof Trevor Rayment is Physical Science Director at Diamond. He comments: "This work is an exciting example of how Diamond’s techniques can deepen our fundamental understanding of the properties of glasses and produce tantalising prospects of practical applications of new materials. This work could have a lasting impact on both frontiers of knowledge.”
Metal-organic frameworks (MOFs) are a type of compound that are currently generating a lot of interest because of their ability to capture certain molecules. MOFs are cage-like structures consisting of metal ions, linked by organic bonds. They work like chemical sponges, absorbing specific elements from the atmosphere; and by altering the composition of the MOF, scientists can manipulate which particular gas it will absorb and store.
This chemical variability could make MOFs useful in industrial settings where gas storage or separations are particularly important; examples include hydrogen storage, which is particularly important for hydrogen-powered cars, and flue gases, in which toxic gases can be selectively absorbed by MOFs and removed from the atmosphere.
However it has proved challenging to utilise MOFs in an industrial setting, due to difficulties in altering their physical form to create a different shapes. The compounds themselves have poor mechanical and thermal properties, and so are prone to falling apart when exposed to post-processing techniques that are usually used to change a material’s shape, like sintering or melt-casting. This is a problem for industrial applications which may call for different forms of material, like thin films or fibres; if MOF structures can’t be easily adapted then their use is limited.
But scientists may now have found a solution. Using Diamond, the team were able to scrutinise the MOFs in atomic detail. Scientists from Europe, China, and Japan used Diamond’s extreme conditions beamline, I15, which offers X-ray powder and single-crystal diffraction under extreme pressures and temperatures. They also used I22, a small-angle scattering and diffraction beamline with a high brilliance insertion device source that allows structural investigation of materials under extreme environments on millisecond and shorter time scales. With this level of insight, they were able to understand the structural changes which took place after transitions from crystalline to amorphous and glass phases.
Beamline set up on I15, Diamond’s extreme conditions beamline
Beamline set up on I15, Diamond’s extreme conditions beamline
The group found that by heating MOFs under argon, they were able to melt the material into a liquid that could then be cooled into a glass, with a chemical composition identical to the crystalline MOF. The new class of materials this process creates could help combine the absorbency and gas storage properties of MOFs with the structural malleability of glass and formability of the liquid phase.
Dr Thomas Bennett from the Department of Materials Science and Metallurgy at the University of Cambridge says: “Traditional methods used in melt-casting of metals or sintering of ceramics usually cause the structural collapse of MOFs due to the structures thermally degrading at low temperatures. Through exploring the interface between melting, recrystallisation and thermal decomposition, we should now be able to manufacture a variety of shapes and structures that were previously impossible, both expanding the range of applications for MOFs, and making those already existing more industrially relevant.”
The new hybrid glass materials are particularly useful because, by altering the elemental composition of the MOF prior to the heating and cooling process, it will be possible to alter the material’s properties and tailor its chemical functionality. This would result in ‘chemically designed’ glasses, useful for a vast range of different applications.
The new hybrid glass materials could impact on a vast range of different industrial sectors, due to the properties of the glasses themselves, or through utilisation of the solid-liquid transitions involved in their formation. There’s still work to be done, but the materials provide a new facet to existing metal-organic frameworks, and suggest that MOFs might be interesting for reasons other than their porosity.