Vibrational analysis of gas adsorption in metal-organic frameworks

Metal-organic frameworks (MOFs) are reticular materials with large pore volume, high surface area, molecular selectivity, and chemical tunability [1]. MOFs stand out as promising solid sorbents for gas separation applications in a sustainability context such as in, for example, CO2 capture and storage. Adsorbates can bind to a MOF either through physisorption [2] or chemisorption mechanisms, where coordinatively unsaturated metal sites within a MOF enable chemical bond formation [3]. Gas adsorption isotherms are typically analyzed for information on the gas uptake and binding energies. However, microscopic insights into the nature of the guest-host interaction are not readily available in these measurements. Raman micro-spectroscopy in combination with ab-initio computational simulations based on density-functional theory (DFT) can potentially provide molecular scale information on adsorbate-adsorbent interaction MOF pores [4,5]. In this contribution, we investigate $CO_2$ and $N_2$ adsorption in HKUST-1 and $ZnBDC(TED)_{0.5} under variable temperature and pressure conditions. We compare the experimental Raman spectra with spectra simulated based on Molecular Dynamics and DFT calculations, assuming the experimentally verified pressures and temperatures. By quantifiying the spectral modifications occurring in experimental and simulated spectra, we evaluate the gas density at pore scale and discuss the specifics of adsorbate-adsorbent interaction in HKUST-1 and$ZnBDC(TED)_{0.5}.$

References

[1] T. Ghanbari et al. Science of The Total Environment 707, 135090 (2020). [2] Nour Nijem et al, J. Phys.: Condens. Matter 24, 424203 (2012). [3] N. Li et al., Small 15, 1900426 (2019). [4] K. I. Hadjiivanov et al., Chemical Reviews 121(3), 1286 (2021). [5] M. E. Ferreira et al., arXiv:2411.14644 (2024).