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Coordination of aluminum in saponite-like material as a function of synthesis pH
Published online by Cambridge University Press: 28 February 2025
Abstract
Saponite-like materials have a wide range of potential applications, especially in heterogeneous catalysis. Despite the simplicity of the synthesis, the mechanisms of the formation of saponite are not well understood yet. The aim of the present study was to investigate a possible correlation between the coordination of Al in the solid phase and in the solution. For this, samples were prepared by varying the initial OH:Si molar ratio from 0.18 to 2.14, leading to a pH in the supernatant after the hydrothermal treatment of 6.7 to 12.7, respectively. The characterization of the material was performed by combining nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) spectroscopies, and good agreement was obtained between the two techniques. Between pH7 and pH10, 60–65% of aluminum was found to be in tetrahedral coordination, while this percentage increased above pH10 (up to 81%). These results correlated with the speciation of the aluminum in aqueous solution. Indeed, above pH10, all available aluminum was in the soluble form Al(OH)4–.
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- © The Author(s), 2025. Published by Cambridge University Press on behalf of The Clay Minerals Society