Constructing gradient porosity beyond sieving-kinetics trade-off: Rapidly precise CO2/CH4 separation on carbon nanofibers

Abstract

Adsorption-based capture of carbon dioxide (CO2) to upgrade natural gas offer a promising solution for energy crisis and the reduction of CO2 emission. However, trade-off between high adsorption selectivity and rapid kinetic is an inherent shortcoming of size-sieving based adsorptive separation of gas molecules at similar sizes, hindering the launch of sieving adsorbent for practical challenging selective gas capture. Herein, a gradiently porous carbon nanofiber PCF-800 with interconnected sieving ultramicropores and low-proportion surficial mesopores is tailor-made to simultaneously realize the exclusive and rapid capture of CO2 from CH4. Arising from the unique interconnected micro-mesoporous structure, the as-prepared PCF-800 not only achieves remarkable uptake ratio of 45 (298 K, 1 bar) for CO2/CH4 separation via size-sieving effect but also shows fast kinetic with diffusion rate of 1.35 × 10-3 s−1, outperforming the conventional ultramicroporous counterpart. Moreover, the impressive dynamic CO2/CH4 separation factor up to 21.7 and satisfying cycling durability revealed by the breakthrough experiments further imply the industrial potential of PCF-800 in practical CH4 purification. This work may shed light on the design of gradient sieving carbonaceous adsorbent with high selectivity and fast kinetic for extensive high-performance small gas separation.