Mg/Al Ordering in Layered Double Hydroxides Revealed by Multinuclear NMR Spectroscopy

The anion-exchange ability of layered double hydroxides (LDHs) has been exploited to create materials for use in catalysis, drug delivery, and environmental remediation. The specific cation arrangements in the hydroxide layers of hydrotalcite-like LDHs, of general formula Mg²⁺₁₋xAl³⁺xOH₂(Anionn⁻x/n)...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2008-07, Vol.321 (5885), p.113-117
Main Authors: Sideris, Paul J, Nielsen, Ulla Gro, Gan, Zhehong, Grey, Clare P
Format: Article
Language:English
Subjects:
Anions
Cations
Chemistry
Hydrogen
Hydroxides
Hydroxyls
Materials
Materials science
Minerals
NMR
Nuclear magnetic resonance
Resonance
Sheet metal
Spectroscopy
Spectrum analysis
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Summary:The anion-exchange ability of layered double hydroxides (LDHs) has been exploited to create materials for use in catalysis, drug delivery, and environmental remediation. The specific cation arrangements in the hydroxide layers of hydrotalcite-like LDHs, of general formula Mg²⁺₁₋xAl³⁺xOH₂(Anionn⁻x/n)·yH₂O, have, however, remained elusive, and their elucidation could enhance the functional optimization of these materials. We applied rapid (60 kilohertz) magic angle spinning (MAS) to obtain high-resolution hydrogen-1 nuclear magnetic resonance (¹H NMR) spectra and characterize the magnesium and aluminum distribution. These data, in combination with ¹H-²⁷Al double-resonance and ²⁵Mg triple-quantum MAS NMR data, show that the cations are fully ordered for magnesium:aluminum ratios of 2:1 and that at lower aluminum content, a nonrandom distribution of cations persists, with no Al³⁺-Al³⁺ close contacts. The application of rapid MAS NMR methods to investigate proton distributions in a wide range of materials is readily envisaged.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1157581