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The porosities of three mesoporous silica materials were characterized with 129Xe NMR spectroscopy. The materials were sythesized by a sol-gel process with r = 0, 25, and 70% methanol by weight in an aqueous cetyltrimethylammonium bromide solution. Temperature dependent chemical shifts and spin lattice relaxation times reveal that xenon does not penetrate the pores of the largely disordered (r = 70%) silica. 129Xe NMR spectra of the silica with r = 0 are shown on the left. For both r = 0 and 25%, temperature dependent resonances corresponding to physisorbed xenon were observed. An additional resonance for the r = 25% sample was attributed to xenon between the disordered cylindrical pores. 2D NMR exchange experiments corroborate the spin lattice relaxation data which show that xenon is in rapid exchange between the adsorbed and the gas phase. |
T. Pietraß, J. M. Kneller, R. A. Assink and M. T. Anderson, J. Phys. Chem. B 103, 8837-8841 (1999).
