Mechanochemistry of Metal–Organic Frameworks under Pressure and Shock

Abstract

Metrics & MoreArticle Recommendations CONSPECTUS: Metal−organic framework solids (MOFs) are synthetic nanoporous materials that have drawn intense efforts in synthesis and characterization of chemical properties, most notably for their ability to adsorb liquids and gases. They are constructed as "node−spacer" nanostructured materials: metal centers (ions or clusters) connected by organic linkers (commonly containing carboxylate or imidazolate groups) to form crystalline, extended, often highly nanoporous structures. MOFs exhibit a variety of advantages over conventional porous materials: rationally designed synthesis of desired crystal structures and crystal engineering become feasible; great synthetic versatility and ease of incorporating different chemical functionalities are realized; and the use of lightweight organic linkers allows for ultrahigh surface area and porosity previously not accessible to conventional materials (i.e., zeolites and porous carbon). As a consequence, MOFs show great promise for a rapidly expanding collection of applications such as gas storage, separations, catalysis, sensing, and drug delivery.The mechanochemistry of MOFs and their response to shock waves, which we discuss in this Account, have been only partially explored. Mechanochemistry, the connection between the mechanical and the chemical worlds, has ancient origins. Rubbing sticks together to start a fire is mechanochemistry. Only in the past decade or so, however, has mechanochemistry gained a notable focus in the chemical community. In the following discussion, we present a general introduction to the complex mechanochemical behavior of MOFs both under quasi-static compression and under shock loading created by high-speed impact. During elastic deformation, MOFs undergo reversible structural or phase transitions. Plastic deformation of MOFs can result in mechanochemistry and can permanently modify the crystal structure, the pore dimensions and configuration, and the chemical bonding. The large energies required to induce bond rearrangement during plastic deformation suggest an interesting potential of MOFs for shock wave mitigation applications. MOFs are promising materials for shock energy dissipation because of the high density of nanopores which can absorb shock energy as they collapse. We have recently developed a platform to assess shock wave energy attenuation by MOFs and other powdered materials. It uses a tabletop laser-driven flyer plate to impact MOF samples at velocities of up to 2.0 km/s. The pressure of the shock waves that break out from the MOF sample can be measured by photon Doppler velocimetry. By measuring the shock profiles of MOF layers with different thicknesses, we can determine the shock pressure attenuation by the MOF layer. We have identified the two-wave structure of shocks in MOFs caused by nanopore collapse. Electron micrographs of recovered shocked MOFs show distinct zones in the shocked material corresponding to shock powder compaction, nanopore collapse, and chemical bond destruction.

Tribochemistry, Mechanical Alloying, Mechanochemistry: What is in a Name?

“…The rate of pulsing can vary significantly, from e.g. 30 Hz in a conventional ball mill to tens of kHz using ultrasound radiation ( Zhou et al, 2020 ). The types of mechanical action can be also different, including impact, shear stress, friction, rubbing, and cleavage, or any combination thereof, Figure 5B .…”

“…30 Hz in a conventional ball mill to tens of kHz using ultrasound radiation. 48 The types of mechanical action can be also different, including impact, shear stress, friction, rubbing, and cleavage, or any combination thereof, Figure 5B. Moreover, different types of action can be applied to fractions of the sample located at different sites within the same milling jar, 198 or can vary between successive pulses.…”

“…To date, mechanochemical approaches being applied to transformations from across the chemical sciences have been reported, spanning from the synthesis of inorganic and organic compounds [including those as complex as peptides ( Hernández et al, 2017 ; Maurin et al, 2017 )] through to the preparation of large porous frameworks such as metal-organic frameworks [MOFs( Stolar et al, 2017 ; Stolar and Užarević, 2020 ; Wang et al, 2020 ; Zhou et al, 2020 ; Głowniak et al, 2021 ; Stolar et al, 2021 )]. Moreover, the scale of mechanochemical reactions has ranged from the mechanical manipulation of single atoms and molecules (predominantly, synthetic and natural polymers) using atomic force microscopy ( Kaupp, 2009 ; Ribas-Arino and Marx, 2012 ; Makarov, 2016 ; Li et al, 2017 ) to the induction of reactions in multi-component inorganic and organic powder mixtures in ball milling reactors or extruders ( Iwasaki et al, 2010 ; Am Ende et al, 2014 ; Oliveira et al, 2017 ; Andersen and Mack, 2018b ; Egleston et al, 2020 ).…”

“…5,42,43 To date, mechano-chemical approaches being applied to transformations from across the chemical sciences have been reported, spanning from the synthesis of organic compounds (e.g. peptides 44,45 ) through to the preparation of large porous frameworks such as metal-organic frameworks (MOFs [46][47][48][49][50][51] ). Moreover, the scale of mechano-chemical reactions has ranged from the mechanical manipulation of single atoms and molecules (predominantly, synthetic and natural polymers) using atomic force microscopy [52][53][54][55] to the induction of reactions in multi-component powder mixtures in ball milling reactors or extruders.…”

Observations on Detonation Growth of Lead Azide at Microscale

“…Due to the high pressure, high temperature, and destruction of detonation products, the direct measurement of detonation pressure is difficult to perform. At present, several measurements can be applied to detonation or shock-pressure tests at regular size [ 13 , 14 ]. Experimental determination of detonation pressure with microgeometries is, however, not widespread; most determinations are calculated based on data at the macroscale rather than measured.…”