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

Abstract 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 2893 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 °C, 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.