Nanoporous silica grown in organic media: Absorption and NMR characterization

Pure silica of high surface area was prepd. by the slow evapn. of colloidal solns. of silicic acid in org. solvents. The porous silica materials were characterized by nitrogen adsorption, adsorption of volatile org. mols., and 29Si magic angle spinning (MAS) NMR. The absorption properties and the high concn. of silanols, detected by 29Si NMR resonances, are consistent with a surface area of 600-700 m2/g. The high surface area and the virtual lack of long-range order suggest the model of a "sponge" contg. open and interconnected pores. The size of the pores or channels is relatively homogeneous and is affected quite markedly by the org. prepn. medium. The pores of the structure obtained using tetrahydrofurane are on the subnanometer scale, an indication that the diffusive phenomena must be influenced by intimate org.-inorg. interactions during the slow evapn. of the solvent.