²⁹Si and ²⁷Al nuclear magnetic resonance spectroscopy of 2:1 clay minerals

Solid-state 29 Si and 27 Al NMR spectroscopy with magic-angle spinning was used to study two smectites, two illites and a vermiculite. 27 Al NMR was able to directly observe the coordination of aluminium. 29 Si NMR was sensitive to both the chemical nature of the interlayer species and the presence of aluminium in the tetrahedral sheet. Well-resolved resonances in the vermiculite at δ = −84·6, −88·7 and −92·9 (ppm relative to TMS) were assigned to Q 3 (2Al), Q 3 (1Al) and Q 3 (0Al) respectively. The smectites exhibited single resonances centred at δ = −93 ( Q 3 (0Al)). The illites displayed broad resonances between δ = −80 and −105. The 29 Si spectrum of a smectite complexed with alkylammonium cations showed a shielding of up to 1 ppm relative to the untreated sample.