Formation of CO₂ Hydrates within Single-Walled Carbon Nanotubes at Ambient Pressure: CO₂ Capture and Selective Separation of a CO₂/H₂ Mixture in Water

Carbon dioxide (CO₂) capture and separation are two currently accepted strategies to mitigate increasing CO₂ emissions into the atmosphere due to the burning of fossil fuels. Here, we show the simulation results of hydrate-based CO₂ capture and selective separation from the CO₂/H₂ mixture dissolved in water, both using single-walled carbon nanotubes (SW-CNTs). The spontaneous formation of quasi-one-dimensional (Q1D) polygonal CO₂ hydrates under ambient pressure was observed within SW-CNTs immersed in CO₂ aqueous solution. Moreover, highly selective adsorption of a CO₂ over a H₂ molecule is observed in the Q1D polygonal ice nanotube due to a much lower value of the potential mean force (PMF) difference for a CO₂ molecule than for a H₂ molecule enclosed in the corresponding hydrate. The simulation results indicate that the formation of Q1D hydrates can be an effective approach for CO₂ capture or for the separation of CO₂ from H₂ in the mixture.