(585d) Structure Characteristics of Hydration Layer Confined to Slab Geometry of Rutile(110)

The surface science of metal oxides enjoys an increasing interest, and many researchers develop attentions on oxide surface. This is motivated by the applications where oxide surfaces play an important role because of most metals being oxidized immediately when exposed to ambient, and because of metal oxides being used in many fields of chemical engineering such as catalyst, inorganic membrane, solar cell, and so on. Recently, research on single-crystalline TiO2 surfaces is pursued because the wide range of its applications and the expectation that insight into surface properties on fundamental level will develop materials and device performance in many fields including heterogeneous catalysis, solar energy.

Rutile (110) is well accepted as the representative bulk model oxide and is used to discover the distinct phenomena on metal oxide surfaces. From an experimental point of view, rutile (110) is a wonderful sample to work with, but hard to prepare. Furthermore the surface effect will be enhanced in nano-scale pores and gaps, which are difficult to characterize in experiments. However, molecular simulation offers an alternative method to get insight on the molecular level information about the fluid around the surfaces. In this work, we study the static structure properties of water confined to slab geometry of rutile (110) with molecular dynamics simulation.

We build a model that contains two slabs of rutile(110) opposite to each other with water molecules between them, and their distance is ranging from 0.4 to 2.0 nm by NVT-ensemble (T=300K) MD simulations. The long-range electrostatic interaction plays an important role on the interactions between atoms of the slabs and water molecules. Significant water layers were observed along the normal direction of the surface. The Water molecules in the closest layer are absorbed at the five-coordinated Ti and two-coordinated O (or bridging O) atoms on the surfaces. Further, the dipole of water molecules in the second layer was found to have considerable preferential orientation, mainly because of the synergistic effects of the water molecules in the first layer and long-rang electrostatic interactions of the surface atoms. The water molecules are more concentrated with the decrease of the distance between slabs.