Structural Characterisation of Complex Layered Double Hydroxides and TGA-GC-MS Study on Thermal Response and Carbonate Contamination in Nitrate- and Organic-Exchanged Hydrotalcites.
Layered double hydroxides (LDHs) are versatile materials used for intercalating bioactive molecules in the fields of pharmaceuticals, nutraceuticals and cosmetics, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability and improving their pharmacokinetic properties and formulation stability. Moreover, LDHs are used in various technological applications to improve stability and processability. The crystal chemistry of hydrotalcite-like compounds was investigated by X-ray powder diffraction (XRPD), automated electron diffraction tomography (ADT) and thermogravimetric analysis (TGA)-GC-MS to shed light on the mechanisms involved in ion exchange and absorption of contaminants, mainly carbonate anions. For the first time, ADT allowed a structural model of LDH_NO3 to be obtained from experiment, shedding light on the conformation of nitrate inside LDH and on the loss of crystallinity due to the layer morphology. The ADT analysis of a hybrid LDH sample (LDH_EUS) clearly revealed an increase in defectivity in this material. XRPD demonstrated that the presence of carbonate can influence the intercalation of organic molecules into LDH, since CO3 -contaminated samples tend to adopt d spacings that are approximate multiples of the d spacing of LDH_CO3 . TGA-GC-MS allowed intercalated and surface- adsorbed organic molecules to be distinguished and quantified, the presence and amount of carbonate to be confirmed, especially at low concentrations (<2 wt %), and the different types and strengths of adsorption to be classified with respect to the temperature of elimination.
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy).
Eleonora
E
Conterosito
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy).
Luca
L
Palin
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy).
Diego
D
Antonioli
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy).
Davide
D
Viterbo
Dipartimento di Scienze Fisiche, della Terra e dell'Ambiente, Università degli Studi di Siena, Via Laterino 8, 53100 Siena (Italy).|Institut für Physikalische Chemie, Johannes Gutenberg Universität, Jakob-Welder-Weg 11, 55099 Mainz (Germany).
Enrico
E
Mugnaioli
Institut für Physikalische Chemie, Johannes Gutenberg Universität, Jakob-Welder-Weg 11, 55099 Mainz (Germany).
Ute
U
Kolb
Dipartimento di Scienze Farmaceutiche, Università degli Studi di Perugia, Via del Liceo 1, 06123 Perugia (Italy).
Luana
L
Perioli
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy). marco.milanesio@uniupo.it.
Marco
M
Milanesio
Dipartimento di Scienze e Innovazione Tecnologica, Università del Piemonte Orientale "A. Avogadro", Via T. Michel 11, 15121 Alessandria (Italy). valentina.gianotti@uniupo.it.
Valentina
V
Gianotti
electron diffraction; intercations; ion exchange; layered compounds; structure elucidation