Time-, spectral- and spatially resolved EPR spectroscopy enables simultaneous monitoring of diffusion of different guest molecules in nano-pores

Abstract

Diffusion in porous materials is under ongoing active investigation due to its major role in practical applications such as catalysis and chromatography. The complexity of these systems limits the use of the Einstein-Stokes diffusion theory, and it must be distinguished between the microscopic scale of diffusion at a molecular level, which is sensitive to the local surroundings of a diffusing molecule, and the macroscopic scale which takes into account diffusion spanning multiple pores, grain boundaries and inhomogeneity within the material. Here, we employ an in situ approach for quantitative measurements of the diffusion on a macroscopic length scale. For the first time, full time-resolved spectral spatial EPR imaging in combination with the simultaneous iterative reconstruction technique (SIRT) allows the simultaneous observation of the diffusion of two different molecular species inside of an aerogel in a single experiment.