Insights into the CO₂ Capture Characteristics within the Hierarchical Pores of Carbon Nanospheres Using Small-Angle Neutron Scattering

Understanding adsorption processes at the molecular level has transformed the discovery of engineered materials for maximizing gas storage capacity and kinetics in adsorption-based carbon capture applications. In this work, we studied the molecular mechanism of gas (CO 2, H 2, methane, and ethane) adsorption inside an interconnected porous network of carbon. This was achieved by synthesizing novel macro–meso–microporous carbon (M 3 C) nanospheres with interconnected pore structures. The M 3 Cs showed a CO 2 capture capacity of 5.3 mmol/g at atmospheric CO 2 pressure, with excellent kinetics. This was due to fast CO 2 adsorption within the interconnected hierarchical macro–meso–microporous M 3 C. In situ small-angle neutron scattering (SANS) under various CO 2 pressures indicated that the macro- and mesopores of M 3 C enable fast diffusion of CO 2 molecules inside the micropores, where adsorbed CO 2 molecules densify into a liquid-like state. This strong densification of CO 2 molecules causes fast CO 2 diffusion in the macro- and mesopores of M 3 C, restarting the adsorption cycle for fresh CO 2 molecules until all pores are completely filled. Notably, M 3 C also showed good capture capacities for hydrogen and various hydrocarbons, with excellent selectivity toward ethane over methane.