²³Na 2D 3QMAS NMR and ²⁹Si, ²⁷Al MAS NMR investigation of Laponite and synthetic saponites of variable interlayer charge

Abstract

Abstract29Si, 27Al MAS NMR is used to characterize Laponite RD and synthetic saponites of variable interlayer charge. The Si/Al ratios are in good agreement with the calculated charge from chemical analysis except for the lowest-charged saponite. In contrast to the 29Si MAS NMR spectra in which resolved signals are detected, the 27Al MAS NMR spectra show one signal whose linewidth increases with the clay charge. The water content of the clay samples was obtained from 1H MAS NMR.The 2D MQMAS NMR technique is required to obtain a high-resolution spectrum of nuclei with strong quadrupolar interaction. This method was applied to the 23Na nucleus of clay counterions and to the 27Al structural nucleus. One well-defined 23Na NMR signal is observed for all the clays studied except the highest-charged saponite. Possible explanations for this different behaviour are discussed. The calculated isotropic chemical shift evolves progressively with the clay charge whereas the deduced quadrupolar interaction does not change significantly. The 27Al 2D 3QMAS technique was not able to resolve more than one signal.

Aluminum ion occupancy in the structure of synthetic saponites: Effect on crystallinity

“…A decrease of Si/Al ratio reflects more Al ions were incorporated into the saponite structure, resulting in an increase of the Q 3 Si(1Al) signal intensity. In the 29 Si CPMAS NMR spectra of all samples, a signal at -84 to -86 ppm was recorded, which was attributed to Q 3 Si(2Al) in the previous studies (Lipsicas et al 1984;Delevoye et al 2003). Interestingly, this signal has never been reported for natural clay minerals.…”

Edge-modification of laponite with dimethyl-octylmethoxysilane

“…The Gauss-Lorentz ratio was maintained at values greater than 0.7 and fitting was undertaken until reproducible results were obtained with r 2 values greater than 0.995. 29 Si NMR spectra were recorded on a double-channel Varian Infinity Plus 400 spectrometer, equipped with a 7.5 mm crosspolarization (CP)-MAS probehead, working at 79.44 MHz. 29 Si single pulse excitation spectra were recorded for samples Laponite, Si-L0-72 and Si-L80-72 with a recycle delay of 100 s.…”

“…The aim of this paper is to describe the silylation of laponite with the monoalkoxysilane, dimethyl-octylmethoxysilane, and to examine the effect of synthesis conditions on the resultant properties of the material using infrared emission absorption, 29 Si NMR, thermogravimetric analysis, BET N 2 sorption, and X-ray diffraction.…”

Silylation of saponite with 3-aminopropyltriethoxysilane

“…6). The resonance at − 83.8 ppm can be attributed to either Q 3 Si(2Al) (Lipsicas et al, 1984;Delevoye et al, 2003) environment or to the Q 2 Si(OAl) environment at the layer edges of clay minerals (Vogels et al, 2005) or both. The intensity of the resonance at − 83.8 ppm decreased with decreasing Si/Al ratio (Fig.…”