Diffusion of Tetrafluoromethane in Single-Walled Aluminosilicate Nanotubes: Pulsed Field Gradient NMR and Molecular Dynamics Simulations

作者：Dvoyashkin Muslim; Zang Ji; Yucelen G Ipek; Katihar Aakanksha; Nair Sankar; Sholl David S; Bowers Clifford R; Vasenkov Sergey^*

来源：Journal of Physical Chemistry C, 2012, 116(40): 21350-21355.

DOI：10.1021/jp3054247

Diffusion of tetrafluoromethane (CF4) in single-walled aluminosilicate nanotubes was studied by means of pulsed field gradient (PFG) NMR and molecular dynamics (MD) simulations. The application of a high magnetic field and high magnetic field gradients allowed C-13 PFG NMR measurements of diffusion to be performed under conditions of sufficiently large signal-to-noise ratios for a broad range of CF4 loadings. The PFG NMR data were analyzed to obtain the diffusivities for diffusion of CF4 inside the nanotube aggregates, in which the sorbate displacements exceeded the average length of individual nanotubes. In addition, the corresponding diffusivities under conditions of fast exchange of CF4 molecules between nanotubes or nanotube aggregates and the surrounding gas phase in a nanotube bed were also estimated. The experimental CF4 diffusivities inside the nanotube aggregates were found to be several times smaller than the corresponding diffusivities obtained by MD for diffusion inside the defect-free nanotubes. This difference points to the existence of additional transport resistances inside the nanotube aggregates under the conditions of the reported PFG NMR measurements, i.e., when the gas molecules diffuse through several nanotubes interconnected along the nanotube lengths inside the aggregates. Such additional transport resistances are likely to originate from diffusion through thin layers of microporous material, which is expected to connect the individual nanorubes in the aggregates.

• 出版日期2012-10-11