Mechanism of surface hydration of potassium carbonate: Insights from first-principles simulations

In this work, the density functional theory simulations were performed to analyze the hydration mechanism of single and multiple water molecules over K2CO3(0 0 1) surface. A single water molecule preferentially adsorbed on the hollow site through a hydrogen bond and an ionic bond. Mulliken charge analysis showed that electrons were transferred from the potassium atom on K2CO3(0 0 1) surface to the H2O molecule. To investigate the impact of water molecule coverage, the configurations of multiple water molecules adsorbed on K2CO3(0 0 1) surface at different coverages (from 0.5 to 1.5 monolayers) were optimized. The results indicated that one monolayer of water molecules adsorbed on K2CO3(0 0 1) surface is the most stable configuration because of well water-water and water-surface interactions, where four water molecules generate a head-to-tail water chain by hydrogen bonding. Interestingly, the distances between the adjacent molecule layers increased with increasing water coverage, suggesting that the potassium carbonate expands during the earlier hydration process. In addition, the geometric parameters of the hydrogen bonds were obtained and we found that the hydrogen bonds formed by the combination of water molecules on substrate obeyed the bond valence model.