Carbonated layered double hydroxides were fully characterized by vibrational spectroscopies, powder X-ray diffraction and solid-state NMR tuning the cations, the layer charge density, and the preparation method to get original structural and dynamical features within the materials. It clearly appears that carbonate and hydrogenocarbonate coexist in the same interlayer after contact with air and also that the hydrogenocarbonate quantity is correlated to the M II /M III molar ratio constituting a strong pH probe of the interlayer space. Likewise, these two species are involved in an exchange process with atmospheric carbon dioxide, and hydrogenocarbonate proves to be the key parameter of exchange kinetics. These crucial results, extended to various cationic couples, could lead to new alternatives for carbon dioxide storage.
In
order to shed light on molecular dynamics and structure in layered
materials, 27Al NMR spectra of layered double hydroxides
(LDHs) were investigated by varying the layer charge density, the
cations of the sheets, the interlayer anions, the hydration state,
and the temperature. This study reveals that most of the broadening
of 27Al satellite transitions in LDHs is due to dynamics
within the interlayer space rather than the chemical environment of 27Al in the sheets, i.e., cation disorder. This finding provides
a new solid-state NMR tool to probe dynamics in aluminum-bearing layered
materials which does not require tensor calculations, which is based
on direct acquisition spectra and which provides long-range information
as the 27Al spectra are sensitive to dynamics that occur
3–5 Å away from the observed nuclei.
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