Revisiting kaolinite dehydroxylation: A sup 29 Si and sup 27 Al MAS NMR study

• Published in: Journal of the American Chemical Society 1989-05, Vol.111:10
• Main Authors: Lambert, J.F., Millman, W.S., Fripiat, J.J.
• Format: Article
• Language: English
• Subjects: 360602 > Other Materials-- Structure & Phase Studies; 400101 > Activation, Nuclear Reaction, Radiometric & Radiochemical Procedures; ALUMINIUM 27; ALUMINIUM COMPOUNDS; ALUMINIUM ISOTOPES; ALUMINIUM SILICATES; DATA; DATA ANALYSIS; EVEN-ODD NUCLEI; EXPERIMENTAL DATA; INFORMATION; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ISOTOPES; KAOLINITE; LIGHT NUCLEI; MAGNETIC RESONANCE; MATERIALS SCIENCE; MEASURING INSTRUMENTS; MEASURING METHODS; MINERALS; NUCLEAR MAGNETIC RESONANCE; NUCLEI; NUMERICAL DATA; ODD-EVEN NUCLEI; OXYGEN COMPOUNDS; RESONANCE; SILICATE MINERALS; SILICATES; SILICON 29; SILICON COMPOUNDS; SILICON ISOTOPES; STABLE ISOTOPES 360000 > Materials
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja00192a005

The {sup 29}Si and {sup 27}Al MAS NMR spectra of kaolinite are easily interpreted in terms of a Q{sup 3} environment for silicon and of an octahedral configuration of aluminum. Upon progressive dehydroxylation, these spectra become more complex. For a degree of dehydroxylation ({alpha}) between 1/10 and 9/10, three {sup 27}Al resonances are observed at +3, +28, and +55 ppm. The octahedral component decreases in intensity as {alpha} increases, whereas the other two become dominant. The line at +28 ppm is assigned to pentacoordinated Al, as suggested by Gilson et al. The +55-ppm line is attributed to tetrahedrally coordinated Al. Simultaneously, the {minus}91-ppm (initial) component of the {sup 29}Si spectrum decreases in intensity, while at least two components corresponding to more shielded Si nuclei grow in intensity. As {alpha} increases beyond 9/10, further shifts are observed in the {sup 29}Si spectra as mentioned by Meinhold et al. Ultimately a line at {minus}109 ppm suggests a significant proportion of the {sup 29}Si nuclei being in a Q{sup 4} environment, while the {sup 27}Al spectrum is reminiscent of that of a spinel-like material. The relationships between the {sup 29}Si and {sup 27}Al spectra are discussed and compared with IR data in the 1,200-400-cm{sup {minus}1} range and with earlier results on {sup 1}H (static) NMR.