Exploring the nature of surface barriers on MOF Zn(tbip) by applying IR microscopy in high temporal and spatial resolution

The options of IR microscopy for monitoring the evolution of guest (propane) profiles in nanoporous materials (MOF Zn(tbip)) during transient sorption experiments are exploited in a phenomenological study of the formation and variation of transport resistances on the surface of these materials (“surface barriers”). Novel crystal faces, produced by a simple breaking of the crystals, are found to exhibit notably reduced surface resistances while, with increasing time of storage under ambient atmosphere, the surface resistances are found to be enhanced. Differences in the permeabilities on opposite crystal faces appear in a notable asymmetry in the transient concentration profiles. Symmetry is re-established in crystals with two fresh fracture faces.