Underlying mechanism of CO2 uptake onto biomass-based porous carbons: Do adsorbents capture CO2 chiefly through narrow micropores?

Biomass-based porous carbon materials, as promising CO2 adsorbents, have demonstrated their superiority and inherent potential. However, most of the previous reports simply attributed the unprecedented CO2 capture of porous carbon to the presence of abundant narrow micropores of less than 0.7 nm. Here, we have successfully prepared microporous carbons with analogous textural properties and oxygen functional groups by KOH activated from hydrothermally treated biomass. Based on the experimental results and theoretical calculations, we have found that the oxygen-containing functional groups on porous carbons are critically sensitive to CO2 uptake, especially with carboxyl and hydroxyl groups. We can roughly estimate that oxygen groups and pore structure of OC700 contribute 37% and 63% respectively to the CO2 capture, which can be elucidated by grand canonical Monte Carlo (GCMC) simulations. The introduction of oxygen functional groups into porous carbon materials firmly grasps CO2 through electrostatic interactions by density function theory (DFT) calculations. These oxygen groups provide new adsorption sites for the efficient CO2 capture. The OC700 achieves an extremely high CO2 adsorption capacity of 8.0 mmol g−1 and 4.8 mmol g−1 at 0° C and 25 °C (1 bar), respectively.