Interlayer grafting of kaolinite using trimethylphosphate (TMP), a phosphoric acid triester, was achieved using a methoxy-modified kaolinite (MeO-Kaol) as an intermediate. First, TMP was intercalated between the layers of MeO-Kaol upon dispersing MeO-Kaol to TMP at room temperature (TMP/MeO-Kaol-RT). The X-ray diffraction (XRD) pattern of TMP/MeO-Kaol-RT revealed that the basal spacing of MeO-Kaol was increased from 0.86 to 1.28 nm. The 1.28 nm diffraction line disappeared and the 0.86 nm diffraction line appeared upon washing of TMP/MeO-Kaol-RT with an excess of ethanol. The thermogravimetry (TG) curve of TMP/MeO-Kaol-RT showed mass loss at 50-180 °C. Solid-state 13C nuclear magnetic resonance spectroscopy with cross polarization and magic angle spinning techniques (13C CP/MAS NMR) and Fourier transform infrared spectroscopy (FT-IR) spectra showed the presence of methoxy groups in TMP/MeO-Kaol-RT. The C/P molar ratio of TMP/MeO-Kaol-RT was 3.0. The liquid-state 31P NMR spectrum of the guest species extracted with CDCl3 showed one signal at 3.0 ppm, which was the same as the chemical shift of TMP in CDCl3. These results clearly indicate intercalation of TMP between the layers of MeO-Kaol. Next, the dispersion of MeO-Kaol in TMP was heated at 150 °C under a nitrogen atmosphere (TMP/MeO-Kaol-150). The XRD pattern of TMP/MeO-Kaol-150 revealed that the basal spacing was increased from 0.86 to 1.12 nm. The 1.12 nm diffraction line was scarcely changed upon washing of TMP/MeO-Kaol-150 with an excess of ethanol and water. The TG curve of TMP/MeO-Kaol-150 showed mass loss at 300-400 °C. The 13C CP/MAS NMR and IR spectra showed the presence of TMP moieties in TMP/MeO-Kaol-150. The C/P molar ratio of TMP/MeO-Kaol-150 was 1.7. The solid-state 1H MAS NMR spectrum of TMP/MeO-Kaol-150 revealed the presence of POH groups. SEM images, 27Al MAS NMR spectra and Al/Si molar ratios observed for kaolinite and TMP/MeO-Kaol-150 indicate preservation of the kaolinite structure. These results clearly indicate the proceeding of interlayer grafting of kaolinite using TMP with hydrolysis of a limited amount of P-OMe groups.
ASJC Scopus subject areas
- Inorganic Chemistry