Effects of heterogeneity on diffusion in nanopores—From inorganic materials to protein crystals and ion channels

The diffusion of molecules in nanopores (micropores and narrow mesopores) is influenced by the structure of the pore walls, as well as by the presence of other diffusing molecules. The heterogeneous environment leads to deviations from bulk diffusion, which can be quantified via molecular simulations. The heterogeneity may be geometrical or chemical in nature. Increasing computational capabilities present a more and more detailed picture. Such information can be used in the analysis and design of porous media. Applications include mesoporous catalysts and sorbents, zeolites, supports for controlled release or uptake, protein crystals and ion channels. To bridge the gap between microscopic computer simulations and engineering applications, as well as to improve our fundamental insight, analytical or semi-analytical expressions that capture the main effects are desirable. Our analysis reveals a remarkable similarity between the effects of heterogeneity on diffusion in very disparate nanoporous media, although caution should be exercised in the interpretation of this seemingly universal behavior.