Large-surface-area carbons derived from lotus stem waste for efficient CO₂ capture

Porous carbons with a large number of micropores were obtained by the hydrothermal carbonization of lotus stems followed by KOH activation, and their CO₂ capture performance was evaluated. The influence of KOH/char ratio on the pore texture and surface chemistry of the carbons was investigated by N₂ adsorption, SEM, TEM and elemental analysis. Results indicate that as-prepared carbons had surface areas up to 2 893 m²/g and pore volumes up to 1.59 cm³/g, and that KOH activation increased their surface areas by forming large micropores and small mesopores. The CO₂ uptake in the carbons at ambient pressure was up to 3.85 and 6.17 mmol/g at 25 and 0℃, respectively, which are among the highest values for biomass-derived carbons reported in the literature. The porous carbon with the highest surface area did not show the highest CO₂ uptake. The decisive factor for their CO₂ uptake at ambient pressure is not the surface area but the microporosity and micropore size distribution. This result provides guidance for further searches for porous adsorbents for CO₂ capture. The porous carbons from lotus stem waste have the advantages of low cost and high capture ability for CO₂.