Fundamental Understanding of Negative Gas Adsorption in Mesoporous Solids: Towards threshold sensitive mechanical actuators – FUN
As a preliminary step, a few MOF DUT-49 derivatives were synthesized for the development and validation of the innovative concept of NGA in porous materials. All these materials were finely characterized by using in situ X-ray diffraction (XRD), Hg porosimetry, High-pressure Xe NMR, microcalorimetry and simulations (Hybrid Osmotic Monte Carlo based on accurate flexible force field as well as thermodynamic models). The adsorption-induced response of an isoreticular series of MOF DUT-49 was evaluated under a wide range of conditions, i.e. nature of the gas molecules, temperature and gas pressure. The structural change of the free-guest MOF DUT-49s upon mechanical pressure was further assessed by using Hg-porosimetry, calorimetry and high-pressure XRD again assisted by state-of-the art computations to gain insight into the microscopic mechanisms that govern the mechanical pressure-driven contraction of the structure. The knowledge gained at this stage of the project enabled to tune the MOF DUT-49s to boost their performances in terms of pressure amplification.
The project gains an unprecedented understanding of the synergistic interplay between the dynamics of the MOF framework, the confinement of the guest molecules and the microscopic origin of the NGA phenomenon. A systematic exploration of the ligand length and functionalization enabled to tune the elastic and inelastic properties of the MOFs at the molecular level to modulate the NGA properties. This critical design principles for molecular building blocks led to the synthesis of a novel framework DUT-160 incorporating acetylene in the ligand backbone that exhibited the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K.
From an applications standpoint, the conclusions of the project are expected in the near future to pave the way towards a proof of concept for pressure amplification using flexible MOFs that has not been envisaged so far for any class of porous materials.
The experimental and computational data and the resulting knowledge produced throughout the duration of the project were disseminated via publications in top quality journals in the field of Chemistry and Material Science (Nature Commun, Chem. Mater., Chem.Sci….) as well as via invited talks in several international conferences.
One fascinating property of certain porous Metal-Organic Frameworks (MOFs) is their stimulus-induced breathing, a unique feature in the field of nanoporous adsorbents as compared to other reference materials such as activated carbons and zeolites. Recently, Technische Universität Dresden (TUD) discovered a novel breathing MOF, i.e. DUT-49, showing an exceptional counter-intuitive phenomenon upon guest-adsorption, the so-called Negative Gas Adsorption that causes a massive response of the mesoporous framework in terms of both amount of gas expelled and pressure increase. Besides the fundamental interest of this intriguing phenomenon triggered by a massive structural transition associated with more than 50% of unit cell volume change, there are many possible technological applications in terms of mechanical actuators that react selectively to changes in environmental pressure and capable of transforming a large amount of latent strain into pressure. The highly challenging objectives of FUN are to (i) systematically investigate the impact of chemical modification of this MOF framework, i.e. nature of the metal and the organic linker (different lengths and functional groups), on the NGA response (amount of gas expelled, pressure threshold, pressure amplification) and the associated changes of the MOF framework, (ii) gain an in-depth understanding of the driving force that governs the guest-induced structural contraction of the DUT-49s at the origin of the NGA phenomenon by combining simulations, calorimetric measurements and in situ structural analyses, (iii) anticipate refined DUT-49s and further showcase their optimal NGA performances primarily in terms of high pressure amplification and (iv) finally propose a novel concept for advanced instrumentation development with potential partners in a more applied project in a second stage.
This interdisciplinary project calls for highly interlinked activities in synthesis/characterization of high quality MOF samples, advanced adsorption, energetic and structure methodology, and state-of-the-art molecular simulations, during all stages of the screening, understanding and optimization of the NGA phenomena in breathing MOFs. To address these highly challenging objectives, FUN assembles three highly dedicated groups with complementary expertise comprising MOF synthesis/structure/adsorption (TUD), experimental adsorption/microcalorimetry (MADIREL, Marseille), experimental molecular dynamics exploration and in situ high-pressure structure characterization (Institut Charles Gerhardt Montpellier–ICGM) and modelling (ICGM), with ICGM/TUD ensuring project coordination. These groups have invested much effort together over the last few years in developing research infrastructure with complementary expertise to achieve breakthroughs in the understanding and further exploitation of abnormal phenomena in breathing MOFs. This integrated approach of the consortium involves the required modules to attack this exploratory multidisciplinary project with the objectives to understand complex behaviours of “Novel Nanomaterials” and further anticipate their potential applications in “Nanotechnologies for the future” which fits very well within the scope of Challenge 3-Axis 4. The outcomes of this research are expected to attract external partners for a potential transfer into the domains of pressure sensors and mechanical actuators.
Madame SABINE DEVAUTOUR-VINOT (Institut Charles Gerhardt Montpellier)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
ICGM Institut Charles Gerhardt Montpellier
CNRS DR12_MADIREL Centre national de la recherche scientifique, Délégation Provence et Corse_MADIREL
TUD Anorganische Chemie Technische Universitat Dresden
Help of the ANR 316,440 euros
Beginning and duration of the scientific project: - 36 Months