Comprehensive Molecular-level Understanding of MgO Hydration through Computational Chemistry

Taichi Inagaki; Miho Hatanaka

doi:10.1021/acs.jpcc.5c06767

paper

Comprehensive Molecular-level Understanding of MgO Hydration through Computational Chemistry

arXiv:2601.10186 · doi:10.1021/acs.jpcc.5c06767

Abstract

The hydration of magnesium oxide (MgO) to magnesium hydroxide (Mg(OH) $_{2}$ ) is a fundamental solid-surface chemical reaction with significant implications for materials science. Yet its molecular-level mechanism from water adsorption to Mg(OH) $_{2}$ nucleation and growth remains elusive due to its complex and multi-step nature. Here, we elucidate the molecular process of MgO hydration based on structures of the MgO/water interface obtained by a combined computational chemistry approach of potential-scaling molecular dynamics simulations and first-principles calculations without any a priori assumptions about reaction pathways. The result shows that the Mg $^{2 +}$ dissolution follows the dissociative water adsorption. We find that this initial dissolution can proceed exothermically even from the defect-free surface with an average activation barrier of $\sim$ 12 kcal/mol. This exothermicity depends crucially on the stabilization of the resulting surface vacancy, achieved by proton adsorption onto neighboring surface oxygen atoms. Further Mg $^{2 +}$ dissolution then occurs in correlation with proton penetration into the solid. Moreover, we find that the Mg(OH) $_{2}$ nucleation and growth proceeds according to the dissolution-precipitation mechanism, rather than a solid-state reaction mechanism involving a direct topotactic transformation. In this process, Mg $^{2 +}$ ions migrate away from the surface and form amorphous Mg-OH chains as precursors for Mg(OH) $_{2}$ nucleation. We also demonstrate that sufficient water facilitates the formation of more ordered crystalline nuclei. This computational study provides a comprehensive molecular-level understanding of MgO hydration, representing a foundational step toward elucidating the mechanisms of this class of complex and multi-step solid-surface chemical reactions.

This document is the unedited Author's version of a Submitted Manuscript subsequently accepted for publication in The Journal of Physical Chemistry C, copyright \c{opyright} American Chemical Society. To access the final edited and published work see https://doi.org/10.1021/acs.jpcc.5c06767