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

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Abstract
Solid-state 29Si and 27Al NMR spectroscopy with magic-angle spinning was used to study two smectites, two illites and a vermiculite. 27Al NMR was able to directly observe the coordination of aluminium. 29Si 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 Q3(2Al), Q3(1Al) and Q3(0Al) respectively. The smectites exhibited single resonances centred at δ = −93 (Q3(0Al)). The illites displayed broad resonances between δ = −80 and −105. The 29Si spectrum of a smectite complexed with alkylammonium cations showed a shielding of up to 1 ppm relative to the untreated sample.