Transport Phenomena in Nanoporous Materials

Abstract

Diffusion, that is, the irregular movement of atoms and molecules, is a universal phenomenon of mass transfer occurring in all states of matter. It is of equal importance for fundamental research and technological applications. The present review deals with the challenges of the reliable observation of these phenomena in nanoporous materials. Starting with a survey of the different variants of diffusion measurement, it highlights the potentials of "microscopic" techniques, notably the pulsed field gradient (PFG) technique of NMR and the techniques of microimaging by interference microscopy (IFM) and IR microscopy (IRM). Considering ensembles of guest molecules, these techniques are able to directly record mass transfer phenomena over distances of typically micrometers. Their concerted application has given rise to the clarification of long-standing discrepancies, notably between microscopic equilibrium and macroscopic non-equilibrium measurements, and to a wealth of new information about molecular transport under confinement, hitherto often inaccessible and sometimes even unimaginable.

Structure–performance descriptors and the role of Lewis acidity in the methanol-to-propylene process

“…Preparation of M4 involved extraction of framework Al by steaming, leading to the formation of "inefficient" occluded mesopores barely impacting intracrystalline diffusion. 31,32,33 Milina et al 6 have…”

Diffusion in quasi-one-dimensional channels: A small system n, p, T, transition state theory for hopping times

“…Single file diffusion occurs in a variety of natural and engineered systems, including ion and water transport through biological membranes [8][9][10][11], diffusion in molecular sieves such as zeolites [12][13][14], carbon nanotubes [15], * richard.bowles@usask.ca or metal organic frameworks [16,17], and charge-carrier diffusion in one dimensional channels [18]. At the molecular level, pulsed field gradient nuclear magnetic resonance (NMR) techniques have been used to study SFD in adsorbate molecules confined in zeolites [19][20][21] and gas mixtures confined to polycrystalline dipeptide channels [22].…”

Stochastic Modelling of Solution Particle Movement: An Individual Case of Coupled Concentration Gradient Dependent and Independent Movements of Efavirenz

“…Other researchers have been able to correlate self and transport forms of diffusion from experimental observations [8]. Transport diffusion has been shown to thrive in neighbouring solution particles that have zero relative drift.…”

“…This was because for transport diffusion to occur the particles should be in such an orientation which enables progression of that process [8]. The extent of the transport diffu-sion of a solution particle was projected to decrease with increasing relative drift to an active neighbourhood.…”

“…The transport diffusion can further be studied from Fick's laws by use of partial differential equations, however reseachers have used different variable spaces to study this flow [6] [7] [8]. Furthermore, in this work we tracked the transport diffusion by making use of the one to one function relationship between secondary saturation and concentration [9].…”