New layered calcium organosilicate hybrids with covalently linked organic functionalities

A series of layered calcium organosilicate hybrids containing covalently linked organic functionalities was synthesized by a sol-gel process from the reaction of calcium salt and organotrialkoxysilane with alkyl (from methyl to octadecyl) and phenyl functionalities in an aqueous/ethanolic basic solution at room temperature. These hybrid organic-inorganic materials were characterized by XRD, TEM, FTIR, and solid state Si-29, H-1, and C-13 NMR spectroscopy. The comparison of the basal distance measured by XRD and the length of the alkyl groups is consistent with a bilayer arrangement of the organic group inside the interlayer. The degree of basal ordering does not depend on the alkyl group length. Broad in-plane diffraction peaks are best explained by a smectite-like layer than by the parent inorganic calcium silicate hydrate (C-S-H) structure. This suggests the existence of edge-sharing Ca(O,OH)(6) layers separated by well-organized organosilicates. FTIR, C-13, and Si-29 NMR spectra exhibit the typical features of Si-C bonds, showing that the organic groups have not been cleaved. Moreover, the Si-29 NMR spectrum shows that silanes are fully hydrolyzed but weakly condensated. To our knowledge, this is the first report of the synthesis and characterization of layered calcium silicate with organic functionalities directly bonded to the inorganic framework via Si-C bonds.