Temperature-dependent structural properties of water molecules confined in TiO2 nanoslits: Insights from molecular dynamics simulations

The confinement of titanium dioxide (TiO2) significantly affects the nanoconfined water molecules behaviors, manifested structurally as fluid layering and dynamically as slowing down of fluid mobility near the confining surface. In this work, we carried out molecular dynamics simulations to investigate temperature-dependent structural characteristics of water molecules confined in rutile (110) nanoslits. Specifically, we studied the microstructure of two layers of water molecules near TiO2 surface under temperatures ranging from 27 to 800 degrees C. The simulation results showed that the mean residence time of the first layer of water molecules decreased with temperature. A dramatic decreasing rate occurred when the temperature went beyond 300 degrees C. Detailed microstructural investigation of confined water molecules showed that with the increase of temperature, the orientation of some water molecules changed. The possible reason is that water molecules obtained more kinetic energy due to the higher interfacial temperature, so as to increase the probability of forming hydrogen bonds between water molecules in layer I. Moreover, dimers of water molecules, which exhibit higher mobility than water monomers near TiO2 surfaces, began to form at about 300 degrees C. The formation of hydrogen bonds within the first layer of water molecules is largely responsible for the reduction of mean residence time. The results of this work provide perceptive guidelines for the application of TiO2 at high temperatures, such as TiO2-supported catalysts. (C) 2016 Elsevier B.V. All rights reserved.