Structural characterization of porous solids by simultaneously monitoring the low-temperature phase equilibria and diffusion of intrapore fluids using nuclear magnetic resonance

Nuclear magnetic resonance (NMR) provides a variety of tools for the structural characterization of porous solids. In this paper, we discuss a relatively novel approach called NMR cryodiffusometry, which is based on a simultaneous assessment of both the phase state of intraporous liquids at low temperatures, using NMR cryoporometry, and their transport properties, using NMR diffusometry. Choosing two model porous materials with ordered and disordered pore structures as the host systems, we discuss the methodological and fundamental aspects of the method. Thus, with the use of an intentionally micro-structured mesoporous silicon, we demonstrate how its structural features give rise to specific patterns in the effective molecular diffusivities measured upon progressive melting of a frozen liquid in the mesopores. We then present the results of a detailed study of the transport properties of the same liquid during both melting and freezing processes in Vycor porous glass, a material with a random pore structure.

Gas transport in aluminosilicate nanotubes by diffusion NMR

Diffusion of tetrafluoromethane in aluminosilicate nanotubes was studied by means of 13C pulsed field gradient (PFG) NMR at 297 K. The measured data allow the estimation of the diffusivity of tetrafluoromethane inside the nanotubes as well as the diffusivity for these molecules undergoing fast exchange between many nanotubes. The results support the assumption about the one-dimensional nature of the tetrafluoromethane diffusion inside nanotubes