Mass transport behavior of nanoconfined supercritical water–aromatic hydrocarbon mixtures

Understanding mass transport in nanoconfined supercritical fluids is essential for advancing technologies such as energy conversion, chemical extraction, and biomass valorization under extreme conditions. In this study, molecular dynamics simulations were conducted to investigate the mass transport behavior of a supercritical water–aromatic hydrocarbon binary mixture confined within armchair carbon nanotubes. The simulations covered temperatures from 673.15 to 973.15 K, solute molar concentrations from 1% to 30%, and nanotube diameters between 12.20 and 40.68 Å, representing typical conditions for supercritical water applications. The results indicate that aromatic solutes preferentially adsorb near the inner walls of carbon nanotubes, forming stable adsorption layers that significantly reduce overall molecular diffusion. Furthermore, temperature, solute molar concentration, and nanotube diameter collectively affect the mass transport behavior of the confined fluid by altering hydrogen bonding structures, solute–water and fluid–nanotube interaction energies, and molecular spatial distributions. These findings provide molecular-level insights into the relationship between structure and transport in nanoconfined supercritical systems.