Water Transport in Periodic Mesoporous Organosilica Materials

Abstract

Water transport in periodic mesoporous organosilicas (PMOs) was studied using pulsed field gradient NMR. A series of isogeometric PMO materials with different chemical compositions of the pore walls were investigated and compared to a purely siliceous MCM-41 material with an identical pore size. The long-range water diffusivities measured were found to be largely controlled by the macroscopic textural properties of the materials, namely, by the particle geometry and a degree of the particle agglomeration, and by thermodynamic conditions under which the experiments were performed. It is shown that their combined effect caused water molecules either to propagate predominantly along the capillary-condensed water domains or to frequently alternate their trajectories between these domains and the water phase in the interparticle space. Because the transport rates in these two regimes differ substantially, it is suggested that by a purposeful choice of the PMO composition, both the long-range transport rate and...