Hydrothermal syntheses and characterization of alkylammonium phyllosilicates containing CSiO3 and SiO4 units

Alkylammonium phyllosilicate hybrids were synthesized hydrothermally from mixtures of Mg(OH)2, LiF and Si-containing reagents without using any layered silicates. Octadecyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, silica sol and tetraethoxysilane (TEOS) were used as silica sources. A formation of a covalent bonding between an inorganic moiety and an organic moiety and a formation of a layered structure took place simultaneously in one pot. The structure of the hybrids was revealed by means of elemental analysis, X-ray diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED), high-resolution solid-state nuclear magnetic resonance (NMR) and infrared (IR). The inorganic moiety of the hybrids is a magnesium phyllosilicate analogous to Mg-trioctahedral smectites. The organic moiety is analogous to alkylammonium (C18H37N+(CH3)2C3H6–) and exists between layers of the inorganic moiety, being combined with the inorganic moiety through Si–C covalent bonds. Furthermore, solid-state 29Si NMR and XRD revealed that there are some defects in the inorganic moiety because of substitution of CSiO3 for the Si tetrahedral site. The lateral dimension of the inorganic moiety is closer to that of an Mg-trioctahedral sheet in a free state as the organic/inorganic ratio is higher.