The mass distribution and hydrogen bond characteristics of nano-confined supercritical water

In technologies such as supercritical water (SCW) gasification, SCW can infiltrate the nanopores of materials, resulting in nano-confined SCW. The interaction between SCW and the nanopore walls can alter the properties of water. This study utilizes the “carbon nanotube (CNT) connected bulk water” model to calculate the confined density of SCW across a broad range. Subsequently, the CNT is extended and subjected to secondary molecular dynamics (MD) simulations to investigate the mass distribution and hydrogen bond (HB) characteristics of confined SCW. The results show that the ratio of confined density to bulk density in SCW is influenced by the CNT diameter, increasing from 0.52 to 0.82 as the CNT diameter changes from approximately 10 Å to 20 Å. Additionally, the average number of HBs per SCW molecule in confinement is lower than that in bulk water, and it strongly correlates with the confined density. Furthermore, based on the unique mass and energy distributions of SCW within CNTs, three typical positions and four distinct layers can be identified. These positions include the vacuum layer position, the water peak position, and the HB peak position, with respective distances from the wall of approximately 1.84 Å, 3.47 Å, and 4.43 Å.