Application of NMR spectroscopy for the investigation of structure-mobility relations in nanoporous host-guest systems in concerted action with IR Micro-Imaging

• Applicants: Professor Dr. Jürgen Haase; Professor Dr. Jörg Kärger
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 277602929

With the focus on instrument-based and methodical work, in the course of the project KA 953/20-1,2, the background was set for new micro-imaging methods (measurement of transient concentration profiles with IR and interference microscopy). They provide a new approach to the exploration of molecular dynamics in nanoporous host-guest systems. NMR diffusometry with pulsed field gradients (PFG NMR) constitutes another microscopic method, which is complementary in a double fashion. First, it is applied under equilibrium conditions and, second, in the variation of temperature and pressure (and thereby of the guest loading) a much wider range can be covered (moreover, the variation is achieved with much less experimental effort). The potential offered by the concerted application of PFG NMR and Micro-Imaging shall be purposefully employed in this project to deepen our knowledge on molecular dynamics in nanoporous materials. The proposal is submitted in parallel with the application of C. Chmelik on "Micro-Imaging for the exploration of diffusion and reaction in nanoporous materials". A successful approach of the posed questions will be achieved only by the concerted use of both techniques. Besides technical and instrument-based developments for the use of PFG NMR in the particular fields (including the variation of temperature, pressure and observation time above the current limits), the work will be centered on the following three topics: (i) The combined measurement of self-diffusion (PFG NMR, this project) and transport diffusion (Micro-Imaging) establishes unprecedented options for the investigation of the interrelation of transport phenomena under equilibrium and non-equilibrium conditions. This is one of the fundamental questions of current research in the investigation of mesoscopic molecular systems under spatial confinement, which shall be in the focus of the studies within the first topic. (ii) We are, second, going to examine and to exploit the options of PFG NMR to study the impact of host-guest interactions on host structure and guest dynamics. This includes, in particular, the option of temperature variation over a wide range, in which drastic changes in the characteristics are expected. For the understanding of these processes and, possibly, even for their mere detection, a particular wide variation is essential. (iii) While the host-guest interactions considered in the second topic was found to give rise to a completely new type of hysteresis phenomena sorption hysteresis in mesoporous materials is known since over 100 years. However, the origin of this phenomenon and the intrinsic mechanisms determining its time dependence are still a topic of controversial discussion. With the information obtained by the combined application of PFG NMR and Micro-Imaging on the intrinsic dynamics of such systems we hope to contribute, within a third topic of our research plan, with so far inaccessible experimental evidence.

• DFG Programme: Research Grants