Xe-129 NMR of mesoporous silicas

The porosities of three mesoporous silica materials were characterized with Xe-129 NMR spectroscopy. The materials were sythesized by a sol-gel proces s with r = 0, 25, and 70% methanol by weight in an aqueous cetyltrimethylam monium bromide solution. Temperature-dependent chemical shifts and spin-lat tice relaxation times reveal that xenon does not penetrate the pores of the largely disordered (r = 70%) silica. For both r = 0 and 25%, temperature-d ependent resonances corresponding to physisorbed xenon were observed. An ad ditional resonance for the r = 25% sample was attributed to xenon between t he disordered cylindrical pores. 2D NMR exchange experiments corroborate th e spin-lattice relaxation data, which show that xenon is in rapid exchange between the adsorbed and the gas phase.