(321ab) Temperature and Pressure Effects on Hydrogen Bonds of Supercritical Water Confined in Carbon Nanotube---a Molecular Dynamics Study

Supercritical water is widely used in a variety of chemical processes such as hydrothermal synthesis, hydrolysis reaction and environmental friendly treatment of wastes. And it is widely accepted that many anomalous properties of water as a solvent arise as a consequence of specific hydrogen bonding interactions of its molecules. Despite of the importance, direct experimental investigation of water molecules at high temperature, high pressure and nano-scale confinement represents a very challenging task. In this work we have performed a series of MD simulations of supercritical water confined in (6, 6) CNT, to investigate the temperature and the pressure effects on the static properties of confined water molecules. The results showed that at the supercritical conditions, the temperature and pressure would break down the hydrogen-bonded network of water molecules. Therefore, though the water molecules can still enter the (6, 6) CNT, the existence of sigle-file water chain connected by hydrogen bonds in the CNT's interior, which is firstly reported by Hummer et al, is not observed in this work. Furthermore, the fluctuation of the number of water molecules in (6, 6) CNT demonstrates the water molecules could move freely inside the (6, 6) CNT, compared with our previous researches on water molecules confined in (6, 6) CNT at ambient conditions.