X-Nuclei NMR Self-Diffusion Studies in Mesoporous Silica Foam and Microporous MOF CuBTC

作者：Schlayer Stefan; Pusch Anne Kristin; Pielenz Friederike; Beckert Steffen; Peksa Mikulas; Horch Carsten; Moschkowitz Lutz; Einicke Wolf Dietrich; Stallmach Frank^*

来源：Materials, 2012, 5(4): 617-633.

DOI：10.3390/ma5040617

• probe design
• diffusion
• Li-7
• C-13
• Cs-133
• PFG NMR
• CuBTC
• MCF

A standard X-observe NMR probe was equipped with a z-gradient coil to enable high-sensitivity pulsed field gradient NMR diffusion studies of Li+ and Cs+ cations of aqueous salt solutions in a high-porosity mesocellular silica foam (MCF) and of CO2 adsorbed in metal-organic frameworks (MOF). The coil design and the necessary probe modifications, which yield pulsed field gradients of up to +/- 16.2 Tm-1, are introduced. The system was calibrated at H-2 resonance frequency and successfully applied for diffusion studies at Li-7, Na-23, C-13 and Cs-133 frequencies. Significant reductions of the diffusivities of the cations in LiClac and CsClac solution introduced into MCFs are observed. By comparison of the diffusion behavior with the bulk solutions, a tortuosity of the silica foam of 4.5 +/- 0.6 was derived. Single component self-diffusion of CO2 and CH4 (measured by H-1 NMR) as well as self-diffusion of the individual components in CO2/CH4 mixtures was studied in the MOF CuBTC. The experimental results confirm high mobilities of the adsorbed gases and trends for diffusion separation factors predicted by MD simulations.

• 出版日期2012-4