Dielectric Spectroscopy Study of Water Behavior in Calcined Upsalite: A Mesoporous Magnesium Carbonate without Organic Surface Groups

The water sorption properties and the dielectric spectroscopy response of calcined Upsalite, a novel mesoporous and amorphous magnesium carbonate material candidate for several life-science-based application areas, were investigated. The calcination of Upsalite at 250 °C, which removes organic groups present in the uncalcined material, is found to significantly affect the behavior of adsorbed water. The proportion of free to bound water is considerably higher in the calcined material as compared to the uncalcined counterpart for relative humidities above ∼80%. The amount of free water in calcined Upsalite remains high even when the relative humidity is subsequently decreased and is the most likely cause of crystallization of the material into nesquehonite upon high humidity storage. In chorus, the presence of organic groups in uncalcined Upalite most likely accounts for the higher binding degree of adsorbed water and, thus, the less likelihood of water-induced crystallization of this version of the material. Two dielectric relaxation processes were observed in calcined Upsalite and were attributed to a Maxwell–Wagner and a Stern-layer relaxation process. The presented results create a fundamental understanding of water interaction properties in the novel mesoporous magnesium carbonate material Upsalite and are expected to facilitate optimization of the stability of the material while simultaneously ensuring the lack of toxic surface groupsproperties of importance for novel drug formulations and other life-science applications.