Carbonate–Hydrogenocarbonate Coexistence and Dynamics in Layered Double Hydroxides

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

Probing the Dynamics of Layered Double Hydroxides by Solid-State ²⁷Al NMR Spectroscopy

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

Zero-Field NMR Enhanced by Parahydrogen in Reversible Exchange

We have recently demonstrated that sensitive and chemically specific NMR spectra can be recorded in the absence of a magnetic field using hydrogenative parahydrogen induced polarization (PHIP)− and detection with an optical atomic magnetometer. Here, we show that non-hydrogenative parahydrogen-induced polarization− (NH-PHIP) can also dramatically enhance the sensitivity of zero-field NMR. We demonstrate the detection of pyridine, at concentrations as low as 6 mM in a sample volume of 250 μL, with sufficient sensitivity to resolve all identifying spectral features, as supported by numerical simulations. Because the NH-PHIP mechanism is nonreactive, operates in situ, and eliminates the need for a prepolarizing magnet, its combination with optical atomic magnetometry will greatly broaden the analytical capabilities of zero-field and low-field NMR