Pulsed field gradient NMR study of the diffusion of n-hexane confined in hydroxylated and dehydroxylated MCM-41 of various pore diameters

The pore dimension of a reference MCM-41 material was reduced in a controll ed manner by successive silylation with tetrachlorosilane. Also, the surfac e of these materials was modified by temperature treatment, resulting in a reduction of the concentration of surface silanol groups. Pulsed field grad ient (PFG) NMR diffusion measurements of n-hexane confined in these modifie d MCM-41 samples have been performed and the results discussed within the G aussian phase distribution and short gradient pulse approximations. The obs erved increase of the mean residence time with increasing diffusion time of the confined n-hexane suggests a distribution of channel lengths to exist. (C) 2000 Elsevier Science B.V. All rights reserved.