Effect of Moisture Content, System Pressure, and Temperature on the Adsorption of Carbon Dioxide in Carbon Nanotube and Graphite Composite Structures Using Molecular Dynamics Simulations

This work investigated the adsorption of carbon dioxide within the composite structure of graphite-carbon nanotubes (Gr-CNT) using molecular dynamics simulation. Our main focus was determining the effects of system temperature, pressure, and moisture content on local density distribution, interaction energy, and the adsorption isotherms associated with CO2 adsorbed within Gr-CNT slits. Various adsorption conformations of CO2 on Gr-CNT surfaces are also discussed. Simulation results show that the adsorption of CO2 in Gr-CNT nanoslits exhibits the characteristics of a Langmuir monolayer. The calculated interaction energies for CO2 and H2O on GR surfaces were -16.67 and -11.18 kJ/mol, respectively. These values are in good agreement with the results of calculations based on density functional theory. The interaction energy between the CO2 monolayer and Gr-CNT decreased with an increase in system temperature and moisture coverage in Gr-CNTs. The adsorption isotherm of CO2 decreased significantly with an increase in moisture coverage, due to the fact that many of the adsorption sites were occupied by water molecules. Moreover, CO2 has low solubility in water and the electrostatic potential of H2O molecules affect the adsorption conformation of CO2; therefore, the average interaction energy and the amount of CO2 that was adsorbed decreased substantially with an increase in the moisture coverage of the adsorbents.