In-Depth Study of Mass Transfer in Nanoporous Materials by Micro-Imaging

The first application of interference microscopy to monitoring mass transfer in nanoporous materials dates back to late 1970s when Caro and colleagues reported results of investigations of water uptake by LTA type zeolites. It was, however, not before the beginning of the new millennium that the developments in both the measuring technique and computational power have enabled the recording of transient guest profiles during molecular uptake and release under well-defined conditions, leading to the establishment of a novel access to diffusion studies, now referred to as micro-imaging. In the present contribution, the thus accessible novel type of information is illustrated by an in-depth analysis of the uptake kinetics of methanol in an all-silica ferrierite. In particular, two remarkable experimental findings are reported, which may be tracked back to their microstructural and/or microdynamic origin, namely a pronounced asymmetry in the transient concentration profiles and a slowing down of guest uptake with increasing temperature.