29Si MAS solid state and 129Xe NMR of porous silica

The condensation of surface hydroxyl groups of silica after high-temperature treatment has been studied by 29Si MAS solid state and 129Xe NMR spectroscopy. Above 500°C, the number of surface hydroxyl groups is diminished and intraparticle 129Xe species, which reside in the pores of silica and rapidly exchange between pores of different size, are increasingly shielded. Chemical exchange between intraparticle xenon with xenon in interparticle voids is also enhanced upon thermal treatment of silica and can be monitored by 2D EXSY spectroscopy.