CRYSTAL GROWTH OF LAYERED SILICATE GRAFTED WITH ORGANIC GROUPS ON MONODISPERSE SPHERICAL SILICA PARTICLES

Control of the structure and morphology of clay crystals presents a challenge in the synthesis of materials for adsorption and catalysis. In the present study, direct crystallization of a phyllosilicate grafted with organosilyl (methylsilyl and phenylsilyl) groups on the surface of monodisperse spherical silica particles (2.6 mu m) is reported. Methyl-and phenyltriethoxysilanes were allowed to react hydrothermally in a Teflon-lined autoclave with silica, MgCl2, and LiF in the presence of urea for 2 or 4 days. X-ray diffraction patterns revealed that the fine platy particles formed were a trioctahedral hectorite-like layered silicate. Greater temperature (150 degrees C) was required to achieve homogeneous coverage of the original spherical silica particles with the hectorite-like particles. The diameter of the initial silica grains increased slightly to 3.0 mu m after the hydrothermal reactions, while the original spherical shape and size distribution were maintained. Solid-state Si-29 nuclear magnetic resonance analyses confirmed that the presence of resonances attributed to the RSi(OMg)(OSi)(2) and RSi(OMg)(OH)(OSi) (R = methyl or phenyl) environments of the silicon proved the formation of covalent bonds between phyllosilicate sheets and the organic moieties. The crystallinity of the layered silicates increased when the reactions ran for a longer time (4 days).