Hydration behavior of MgO surface: A first-principles study

Abstract

The easy hydration of magnesium oxide (MgO) largely limits its potential applications. Understanding the hydration mechanism of MgO will be helpful to solve this problem. Herein, density functional theory (DFT) calculations and ab initio molecular simulations (AIMD) were used to investigate the hydration behavior of the MgO surface at the molecular or atomic scale and the mechanism behind the effect of the anti-hydration agent (citric acid) on MgO hydration. The calculated results show that a defective surface with low coordinated Mg atom is more easily hydrated than the perfect MgO (001) surface. H2O reacts quickly with unsaturated 3-coordinated Mg atoms and the increasing of H2O content facilitates the hydration. In the late stage of hydration, the Mg(OH)2 layer formed with low mechanical strength easily peels off, exposing fresh MgO surface for further reaction with H2O. Nevertheless, citric acid can coordinate with the unsaturated Mg atoms by forming bonds, increasing the coordination number, thus reducing the reactivity with H2O and protecting MgO from being hydrated. These findings provide a theoretical insight into the hydration behavior of MgO and important guidances for the development of new anti-hydration agents.