Reconsideration about the competitive adsorption of H2O and CO2 on carbon surfaces: The influence of oxygen functional groups

The primary challenge that hampers the widespread use of carbon-based adsorbents for CO2 storage is their low adsorption efficiency. There has been a disagreement among researchers regarding how H2O influences CO2 adsorption in these adsorbents. To address this, a detailed study was conducted by density functional theory and adsorption experiments. The adsorption of CO2 by H2O was examined on carbon surfaces modified with different oxygen functional groups at the molecular level. The results demonstrated that carboxyl and hydroxyl groups, improved the polarity of the carbon surfaces. This enhancement facilitated the adsorption of CO2. The introduction of carboxyl groups increased van der Waals interactions between the carbon surface and CO2, while the introduction of hydroxyl groups facilitated the formation of hydrogen bonds between hydroxyl and CO2. These interactions stabilized the adsorption configuration of CO2. Since the local polarity of H2O exceeds that of CO2, H2O preferentially adsorbs, potentially occupying the adsorption site of CO2. Furthermore, the van der Waals interaction formed between H2O and CO2 might impede CO2 adsorption, thereby reducing co-adsorption energy. The experimental results align with the simulation outcomes. This study presents a novel approach for developing carbon-based adsorbents that efficiently capture CO2 under wet conditions.