Water on the MgO(001) Surface: Surface Reconstruction and Ion Solvation

Abstract

The interaction of water with the MgO(001) surface under ambient conditions is investigated by density functional theory combined with statistical thermodynamics. For water loadings of more than one monolayer, we show that the standard structure model, a fully hydroxylated surface, needs to be revised. Reconstructed surfaces, involving hydrated/hydroxylated Mg(2+) ions above the surface, are more stable. These findings provide a consistent picture for surface hydroxylation between low and high water coverage that is in agreement with available XPS data.

Thin water films and particle morphology evolution in nanocrystalline MgO

“…Ab initio molecular dynamics simulations of multilayer water adsorption on BaO(100) have revealed facile cation dissolution and formation of hydroxylated structures . Similar phenomena were recently studied for MgO(100), where a Mg(OH) 2 ‐layered structure was predicted to be thermodynamically preferred at high chemical potentials of water . Although the barriers for Mg(OH) 2 formation or detachment of solvated Mg 2+ from the surface are unknown, it can be assumed that these processes are facile at room temperature.…”

Water dissociation on the low-coordinated sites of MgO nanopowders

“…This study demonstrates the necessity of experiments performed in ultra-high vacuum conditions on oxide powders in order to understand the reactive behavior of surface defects. This is particularly relevant when, as in the present case for MgO, the oxide is hygroscopic and can undergo deep restructuring after exposure at a pressure beyond a material-specific threshold [14].…”

“…The previous findings indicate that a fine analysis of the reactivity of defective MgO surfaces and nanopowders with respect to water vapor imperatively requires ultra-high vacuum (UHV) conditions. Exposure to water vapor at higher pressure than 10 -5 mbar can indeed induce profound restructuring of the MgO surfaces [6,[12][13][14] and may cause mass transport [15]. Further, the marginal fraction of the surface occupied by defects suggests to study their hydroxylation on powders by infrared spectroscopy in transmission, in such way that the high specific surface area of the samples should compensate for the scarcity of the sites under study.…”

Chromium Adsorption Reveals a Persistent Hydroxylation of Vacuum-Annealed α-Al2O3(0001)

“…An additional motivation came from the ease with which the α-Al 2 O 3 (0001) surface hydroxylates by dissociative adsorption of water. Unlike some other common oxides such as MgO whose hydroxylation is still the subject of debate 7,8 , there was an early consensus between photoemission 9,10 , high-resolution electron energy loss spectroscopy 9,[11][12][13] , thermal desorption 14 , ab initio molecular dynamics 15 and density functional approaches 16,17 , that α-Al 2 O 3 (0001) adsorbs dissociatively isolated water molecules. This is because the out-of-plane 2p orbitals of the coordinatively unsaturated aluminum ions that terminate the α-Al 2 O 3 (0001) surface give those sites a strong acidic Lewis character [15][16][17] .…”