No abstract

Two series of saponites with fixed (Si+Al)/Mg and Si/Mg ratios, respectively, were synthesized by using hydrothermal methods. The obtained products were characterized by XRD, XRF, 27 Al, and 29 Si MAS NMR, SEM, and TEM. XRD patterns showed that well-ordered saponites were obtained in the initial Si/Al ratio range of 5. 43-7.89. Beyond this Si/Al ratio range, poorly crystallized saponites were obtained with small crystallized particles, which can be seen from TEM images. When intercalating saponite with surfactant, the intercalated products displayed strong and well-ordered (00l) reflections, indicating that layered saponite has been successfully synthesized in the present study. 27Al MAS NMR spectra demonstrated that well-crystallized synthetic saponites had a higher Al(IV)/Al(VI) ratio than the poorly crystallized samples, which is an important factor affecting the crystallinity of synthetic saponite. A one-to-one substitution (i.e., 1 Al 3+ → 1 Mg 2+) actually occurred in the octahedral sheet and this substitution had a negative effect on the crystallinity of the synthetic saponites. After grafting the synthetic saponites with silane, the decreased intensity of the 29 Si NMR signal at -86 ppm and the increased intensity of Q 3 Si(0Al) and Q 3 Si(1Al) signals strongly suggested that the signal at ca. -86 ppm corresponded to Q 2 Si at the layer edges of saponite.

AB ST R ACT : Silylated kaolinites were synthesized at 80ºC without the use of inert gas protection. The method presented started with mechanical grinding of kaolinite, followed by grafting with 3-aminopropyltriethoxysilane (APTES). The mechanical grinding treatment destroyed the ordered sheets of kaolinite, formed fine fragments and generated broken bonds (undercoordinated metal ions). These broken bonds served as new sites for the condensation with APTES. Fourier transform infrared spectroscopy (FTIR) confirmed the existence of ÀCH 2 from APTES. 29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ( 29 Si CP/MAS NMR) showed that the principal bonding mechanism between APTES and kaolinite fitted a tridentate silylation model (T 3 ) with a chemical shift at À66.7 ppm. The silane loadings of the silylated samples were estimated from the mass loss obtained by TG-DTG curves. The results showed that the 6-hour ground kaolinite could be grafted with the most APTES (7.0%) using cyclohexane as solvent. The loaded amount of APTES in the silylated samples obtained in different solvents decreased in the order as: nonpolar solvent > polar solvent with low dielectric constant (toluene) > polar solvent with high dielectric constant (ethanol).