Use of organo- and alkoxysilanes in the synthesis of grafted and pristine clays

A one-step, direct method is described for the creation of synthetic smectite clays grafted with organics on the interlayer surfaces using an organotrialkoxysilane as the silica source. The silane employed most successfully is phenyltriethoxysilane (PTES). Aqueous slurries of LiF, magnesium hydroxide, and the silane are refluxed for 2-5 days, and desirable molar compositions are determined. X-ray powder diffraction, thermal analysis, IR, TEM, N-2 sorption isotherms, and solid-state C-13 and Si-29 NMR techniques are used to characterize the products. The loading of organics on the PTES-hectorites is determined at 20-25% and is comprised of phenyl groups as Si-C linkages. Evidence of this linkage includes an IR peak at 1430 cm(-1) and Si-29 NMR assignments at -79 and -66 ppm for RSi(OMg)(OSi)(2) and RSi(OMg)(OSi)(OH) species, respectively. The use of tetraethoxysilane (TEOS) resulted in a pure hectorite and comprises the first report of the successful use of a tetraalkoxysilane silicon source for crystallizing hectorite from an aqueous solution.