From Layered Double Hydroxides to Layered Double Hydroxide-Based Nanocomposites—A Solid-State NMR Study

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• 作者：Anastasia Vyalikh ; Francis Reny Costa ; Udo Wagenknecht ; Gert Heinrich ; Dominique Massiot ; Ulrich Scheler
• 刊名：Journal of Physical Chemistry C
• 出版年：2009
• 出版时间：December 24, 2009
• 年：2009
• 卷：113
• 期：51
• 页码：21308-21313
• 全文大小：143K
• 年卷期：v.113,no.51(December 24, 2009)
• ISSN：1932-7455

文摘

The local structure of pristine and surfactant-modified aluminum layered double hydroxides (LDH) has been characterized by ²⁷Al and ¹H solid-state NMR. Values for the ²⁷Al quadrupole coupling constants and the isotropic chemical shifts obtained from ²⁷Al triple-quantum (3Q)MAS NMR have been applied to fit the one-dimensional ²⁷Al MAS spectra and to characterize the structural changes in the different stages of LDH modification by the regeneration method quantitatively. Six-coordinated (octahedral) aluminum is found in all LDHs studied, indicating that the LDH structure is composed of octahedra formed by six hydroxyl groups. Two octahedral Al sites with different local environments have been distinguished in the ²⁷Al 3QMAS NMR spectra. The calcined and subsequently surfactant-treated LDHs show additionally a considerable fraction of 4-fold coordinated (tetrahedral) aluminum. The quantitative analysis shows that ca. 29% of aluminum has been converted from octahedral to tetrahedral sites in bis(2-ethylhexyl)phosphate (BEHP)-modified LDH, while modification with sodium dodecyl benzenesulfonate (SDBS) leads to formation of only ca. 17% tetrahedral Al sites. The presence of tetrahedral aluminum is attributed to calcination products, which are not converted after rehydration. Differences in the relative contents of AlO₄ in surfactant-modified LDH is explained by the presence of interlayer water molecules in SDBS−LDH that is confirmed by ¹H MAS NMR.