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 (CO₂, H₂, methane, and ethane) adsorption inside an interconnected porous network of carbon. This was achieved by synthesizing novel macro-meso-microporous carbon (M³C) nanospheres with interconnected pore structures. The M³Cs showed a CO₂ capture capacity of 5.3 mmol/g at atmospheric CO₂ pressure, with excellent kinetics. This was due to fast CO₂ adsorption within the interconnected hierarchical macro-meso-microporous M³C. In situ small-angle neutron scattering (SANS) under various CO₂ pressures indicated that the macro- and mesopores of M³C enable fast diffusion of CO₂ molecules inside the micropores, where adsorbed CO₂ molecules densify into a liquid-like state. This strong densification of CO₂ molecules causes fast CO₂ diffusion in the macro- and mesopores of M³C, restarting the adsorption cycle for fresh CO₂ molecules until all pores are completely filled. Notably, M³C also showed good capture capacities for hydrogen and various hydrocarbons, with excellent selectivity toward ethane over methane.