Pulsed field gradient NMR studies of diffusion in MCM-41 mesoporous solids

✍ Scribed by F. Stallmach; A. Gräser; J. Kärger; C. Krause; M. Jeschke; U. Oberhagemann; S. Spange

• Publisher: Elsevier Science
• Year: 2001
• Tongue: English
• Weight: 332 KB
• Volume: 44-45
• Category: Article
• ISSN: 1387-1811
• DOI: 10.1016/s1387-1811(01)00256-6

✦ Synopsis

Pulsed ®eld gradient NMR is able to monitor the displacement of guest molecules in porous materials without interfering with the microstructure and microdynamics of the system under study. Using this technique, the propagation pattern of benzene, n-hexadecane, propylenecarbonate, ethylbenzene and diethyl ether in ordered mesoporous materials of type MCM-41 was studied.

The evaluation of the self-diusion of benzene allows a quick and easy assessment of the transport resistance in the nanoporous material acting over diusion length scales of 1±10 lm. The fast diusivities observed with benzene, ethylbenzene and diethyl ether in MCM-41 suggest that the transport processes for these sorbate molecules are governed by gas or vapour phase diusion, which is reduced by interactions with the silica walls.

Measurements over shorter diusion lengths ( 6 1 lm), which were realised using n-hexadecane, showed that the selfdiusion in the hexagonal channels of MCM-41 is anisotropic. The ®nite value of the self-diusion component perpendicular to the channel axis indicates the existence of permeable defects like ``windows'' in the silica matrix.