Diffusion in nanoporous materials in the focus of an IUPAC Initiative: The innovative power of “Microscopic” measuring techniques

The diffusion of guest molecules in the interior of nanoporous materials is a phenomenon of great interest for both fundamental research and practical application. This concerns, in particular, the use of these materials for matter-upgrading by separation, purification and conversion, since the gain in value-added products can never be faster than allowed by the rate of mass transfer between the interior of such systems and their surroundings. In view of the complexity of these systems, the quantitation of diffusion in their interior is far from trivial and requires, as a rule, the introduction and consideration of a series of parameters. Measurement of these parameters often necessitates, in turn, a number of different measuring techniques. The present paper introduces into this multitude of parameters and the options of their measurement. It follows the classification as recently presented in an IUPAC Technical Report, dealing with the measurement of the determining parameters of diffusion in nanoporous materials. Particular attention is given to the so-called microscopic techniques and their distinguished role within the arsenal of measuring techniques.