Competitive adsorption-driven CO₂/N₂ separation in monolayer fullerene membranes with funnel-shaped pores

Efficient CO₂/N₂ separation is critical for advancing carbon capture technologies to mitigate climate impacts from industrial emissions. In this study, we model an idealized, defect-free monolayer fullerene membrane featuring funnel-shaped nanochannels to investigate the CO₂/N₂ separation mechanism by combining first-principles calculations and molecular dynamics simulations. The unique nanochannel geometry induces a dual mechanism: (1) competitive adsorption preferentially enriches CO₂ at the membrane surface and (2) nanopore confinement creates a pronounced difference in free energy barriers for translocation (25.89 kJ mol^-1 for CO₂vs. 47.81 kJ mol^-1 for N₂), facilitating highly selective CO₂ permeation. This synergistic interplay yields exceptional performance, with a CO₂/N₂ selectivity of 3564 and a CO₂ permeance of 2.11 × 10^-5 mol m^-2 s^-1 Pa^-1 at 300 K, representing an upper-bound prediction or an idealized, defect-free sheet that surpasses conventional membrane benchmarks. Additionally, rotational density of states analysis reveals that both CO₂ and N₂ exhibit notably enhanced high-frequency rotational modes when traversing the funnel-shaped nanochannels, but stronger rotational constraints significantly restrict N₂ diffusion compared to CO₂. These findings highlight the promise of monolayer fullerene membranes as sustainable, high-performance solutions for gas separation and provide mechanistic insights for the rational design of advanced nanochannel architectures for future separation technologies.