Nitrogen-doped porous carbons from polyacrylonitrile fiber as effective CO₂ adsorbents

In this report, nitrogen-doped porous carbons were synthesized from polyacrylonitrile fiber by a facile two-step synthesis process i.e. carbonization followed by KOH activation. Activation temperature and KOH/carbon ratio are two parameters to tune the porosity and surface chemical properties of sorbents. The as-obtained sorbents were carefully characterized. Special attention was paid concerning the change of sorbents' morphology with respect to synthesis conditions. Under the activation temperatures of this study, the sorbents can still retain their fibrous structure when the KOH/carbon mass ratio is 1. Further increasing the KOH amount will destroy the original morphology of polyacrylonitrile fiber. CO₂ adsorption performance tests show that a sorbent retaining the fibrous shape possesses the highest CO₂ uptake of 3.95 mmol/g at 25°C and 1 bar. Comprehensive investigation found that the mutual effect of narrow microporosity and doped N content govern the CO₂ adsorption capacity of these adsorbents. Furthermore, these polyacrylonitrile fiber-derived carbons present multiple outstanding CO₂ capture properties such as excellent recyclability, high CO₂/N₂ selectivity, fast adsorption kinetics, suitable heat of adsorption, and good dynamic adsorption capacity. Hence, nitrogen-doped porous carbons with fibrous structure are promising in CO₂ capture.