Molecular Simulation Study on Factors Affecting Carbon Dioxide Adsorption on Amorphous Silica Surfaces

Adsorption of CO2 molecules on amorphous silica surface in the absence/presence of Si-H defects and KCI nanoparticles under various humidity and temperature conditions is investigated using grand-canonical Monte Carlo simulation. This investigation reveals that the CO2 uptake capability of the amorphous silica material would strongly rely on the external and internal conditions. It is found that the performance of the adsorbent surface is consistently weakened under external (environmental) conditions such as high humidity and high temperature, owing to the steric deactivation of active surface silanols and the increase in the kinetic energy of CO2 molecules, respectively. The presence of Si-H defects also has a detrimental effect on its CO2 uptake capability as an internal condition, primarily due to the intrinsically weak reactivity of the defects arising from the absence of frontier orbitals on Si-H bonds. It is highlighted that the presence of small-sized KCI nanoparticles embedded in the amorphous silica surface has a potential to improve the CO2 uptake capability of the amorphous silica surface. The enhanced performance is originated from the synergistic effect of the KCI-induced surface optimization and the minimized KCI particle size.