Mechanisms of the CO₂ and H₂O co-adsorption behavior of functionalized porous carbons: perspectives of the molecular...

The efficient and selective capture of 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 a CO₂ and H₂O gas mixture were investigated. This study 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 the competitive and synergistic mechanisms at a microscopic level. In the relatively low pressure range, all G-Rs (functionalized-graphene surfaces) exhibit a similar superior CO₂ adsorption performance for both dry and humid conditions when compared with G-None (pristine graphene surface). However, at high pressures, G-None, G-NH₂ and especially G-C₃-P maintain a high CO₂ adsorption capacity under the humid condition, while the CO₂ uptakes on G-CO, G-SO₃H and G-(CO)C₂PO show a significant reduction under humid condition. For example, under humid condition, the CO₂ uptake on G-C₃-P is 15.8 mmol cm^-3 at 300 kPa, while the adsorption capacity of CO₂ on G-(CO)C₂PO decreases to 2.9 mmol cm^-3. These results were obtained owing to 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 on the development of high-performance porous carbon adsorbents for optimal CO₂ capture.