Nanoporous Glass as a Model System for a Consistency Check of the Different Techniques of Diffusion Measurement

Abstract

The remarkable differences in the guest diffusivities in nanoporous materials commonly found with the application of different measuring techniques are usually ascribed to the existence of a hierarchy of transport resistances in addition to the diffusional resistance of the pore system and their differing influence due to the differing diffusion path lengths covered by the different measuring techniques. We report diffusion measurements with nanoporous glasses where the existence of such resistances could be avoided. Molecular propagation over diffusion path lengths from hundreds of nanometers up to millimeters was thus found to be controlled by a uniform mechanism, appearing in coinciding results of microscopic and macroscopic diffusion measurement.

Transport in Nanoporous Materials Including MOFs: The Applicability of Fick’s Laws

“…Examples for which exactly this behavior has been observed include purely microporous and mesoporous zeolites [12] , activated carbon [13] , nanoporous glass [14] and ordered mesoporous silica of type SBA-15. [15] The validity of the Fickian model and the physical meaning of the diffusivity appearing in Eq.…”

Flux response technology applied in zero length column diffusivity measurements

“…With these factors in mind, it must be ac- knowledged that the diffusion coefficients reported in literature for microporous materials often vary with differences as large as five orders of magnitude being reported for different techniques (Kärger 2012). The discrepancies between different techniques have since been resolved and can be traced to the different length scales over which diffusion is measured (Chmelik et al 2011). Measured diffusivities were found to be smaller when the path length covered in the measurement is large (macro-measurements) suggesting the intrusion of extra-crystalline transport resistances in addition to the diffusional resistance of the pore system (Ruthven 2001;Chmelik et al 2011;García-Sánchez et al 2012).…”

“…The discrepancies between different techniques have since been resolved and can be traced to the different length scales over which diffusion is measured (Chmelik et al 2011). Measured diffusivities were found to be smaller when the path length covered in the measurement is large (macro-measurements) suggesting the intrusion of extra-crystalline transport resistances in addition to the diffusional resistance of the pore system (Ruthven 2001;Chmelik et al 2011;García-Sánchez et al 2012). The purpose of this paper is to measure propane diffusivity in the washcoat of monolith samples using Flux Response Technology (FRT) and to show that this method can be used to compare and contrast with other micro and macroporous techniques in one experiment by analysing the adsorption and desorption transients in the FRT profile.…”

Single‐Particle and Ensemble Diffusivities—Test of Ergodicity

“…[10] This limitation has now been overcome by a modified roller-quenching process [11] in combination with an optical fine cooling [12] so that the fabrication of nanoporous glasses with a homogeneous pore surface and pore diameters down to 1 nm have now become possible. [13] Here we used such glasses with a random threedimensional pore structure and pore sizes of 3 nm as determined from nitrogen adsorption at 77 K (see the Supporting Information).…”