The effect of pore surface hydrophilic/hydrophobic character upon n-hexane diffusion within MCM-41 particles was investigated (table 25) using PFG NMR for various pore fillings. Starting with totally filled pores, the n-hexane diffusivity within MCM-41 particles was significantly enhanced as pore filling decreased until it reached a maximum value. The diffusivity was shown to decline again at very low pore-filling. This was explained in terms of a three-component parallel diffusion mechanism in which surface diffusion, interface diffusion and liquid-phase diffusion were involved. The influence of surface property variations upon the molecular diffusivity in MCM-41 was enhanced in partially filled samples.
Enhanced n-Hexane Diffusion in Partially Filled MCM-41 of Different Surface Hydrophobicity Probed by NMR. F.Courivaud, E.W.Hansen, S.Kolboe, A.Karlsson, M.Stöcker: Microporous and Mesoporous Materials, 2000, 37[1–2], 223–32
Table 25
Diffusion of Hexane in MCM-41 Zeolite
Tout-gassing(C) | Pore-Filling | Do(m2/s) |
180-200 | 1 | 1.61 x 10-9 |
180-200 | 0.446 | 3.05 x 10-9 |
180-200 | 0.214 | 5.81 x 10-9 |
180-200 | 0.089 | 3.75 x 10-9 |
50 | 1 | 1.55 x 10-9 |
50 | 0.333 | 2.53 x 10-19 |