Sorbate Diffusion On Different Length Scales in SBA-15 Porous Solids by Pulsed Field Gradient NMR and Zero Length Column Techniques

Silicates SBA-15 containing mesopores and micropores are promising materials for a variety of applications including catalysis, sensor development and drug delivery. Transport of sorbate molecules in the pore networks of SBA-15 particles is expected to play a notable role in these applications. Despite a general consensus on the importance of sorbate transport in SBA-15 materials, properties of this transport have not been investigated as thoroughly as those of zeolites. Here we report results of diffusion studies of guest molecules in selected SBA-15 samples for different length scales of molecular displacements. The diffusion data were obtained by pulsed field gradient (PFG) NMR method under conditions of application of large (up to 30 T/m) gradients as well as by zero length column (ZLC) technique. Comparison of the data obtained by these two techniques for the same sorbate/SBA-15 systems can provide some new insights on the diffusion behavior. In addition, analysis of the dependence of effective diffusivities on the length scale of molecular displacements measured by PFG NMR has the potential to reveal important information on details of molecular transport in SBA-15 materials.