Investigation on sustainable phosphate release in agriculture: Structural and thermodynamic study of stability, dehydration and anionic exchange of Mg-Al-HPO4 layered double hydroxide by DFT calculations

This work is mainly focused on investigating the conformation of the interlayer HPO42− anions in a Mg-Al layered double hydroxide, as well as their characteristic interactions, and the thermodynamic features of the dehydration process and the anion exchange of these phosphate-intercalated structures. Different anion conformations were tested and compared by means of DFT calculations. It could be observed that the anion configuration in the interlayer region affects the basal spacing of these layered materials, also presenting a clear distinction between their electronic energies. The phase diagram of the studied material indicated a strong stabilization of the hydration water molecules in the interlayer region, mainly driven by hydrogen bonds. Thermodynamic potentials for the anion exchange reaction with CO32− were calculated in order to investigate the possible nutrient release of this material. The process was thermodynamically spontaneous for the studied LDH, thus making it suitable for agricultural applications.