Mechanisms of CO2 and H2O Co-adsorption Behavior on Functionalized Porous Carbons: Perspectives of Molecular Clustering Effect

Abstract

Efficiently and selectively capturing carbon dioxide in humid environments has emerged as a pivotal aspect in carbon capture, utilization and storage (CCUS) technology. Herein, the adsorption properties and mechanism of porous carbons for CO2 and H2O gas mixture were investigated. It focused on the co-adsorption behavior of CO2 and H2O in M-doped (M=N, P, S, and O) surface-functionalized graphene models, and explored its competitive and synergistic mechanism at a microscopic level. In the relatively low pressure range, all G-Rs (functionalized-graphene surfaces) exhibit a similar superior CO2 adsorption performance than G-None (pristine graphene surface) for both dry and humidity conditions. However, at high pressures, G-None, G-NH2 and especially G-C3─P maintain a high CO2 adsorption capacity under humidity condition, while the CO2 uptakes on G-C═O, G-SO3H and G-(CO)C2PO show a significant reduction at humidity condition. For example, at humidity condition, the CO2 uptake on G-C3─P was 15.8 mmol/cm3 at 300 kPa, while the adsorption capacity of CO2 on G-(CO)C2PO decreases to 2.9 mmol/cm3. These results were caused by the different aggregation effects of water on G-Rs at high pressures. In addition, the adsorption behaviors and intrinsic mechanism of CO2 and H2O between G-Rs were analyzed through two different clustering effects for H2O, including centralized clustering and decentralized clustering. This work precisely disentangles the co-adsorption process and mechanism of CO2 and H2O and offers an innovative perspective to the development of high-performance porous carbon adsorbents for optimal CO2 capture.