Combined Application of Tracer Zero Length Column Technique and Pulsed Field Gradient Nuclear Magnetic Resonance for Studies of Diffusion of Small Sorbate Molecules in Mesoporous Silica SBA-15

Abstract

Tracer zero length column (TZLC) and pulsed field gradient (PFG) NMR techniques were used to study self-diffusion of toluene in two samples of SBA-15 silica. Analysis of the diffusion data allowed us to assign evaluated diffusivities to diffusion of toluene in pore systems of SBA-15 particles. It was observed that there is a large discrepancy between the values of the diffusivities obtained by the two techniques under very similar experimental conditions. The most likely reason of this discrepancy is related to the particular morphology of the SBA-15 particles, which form stringlike aggregates with lengths close to 20−30 μm. As a consequence of the formation of such aggregate structures some mesoporous channels can be as long as the length of these structures. These long channels are expected to have transport barriers at the points of intergrowth of primary particles. Other channels are much shorter and are not expected to exhibit any significant transport barriers. Under the experimental conditions used...