Sustainable porous carbons have been prepared by chemical activation of hydrothermally carbonized polysaccharides (starch and cellulose) and biomass (sawdust). These materials were investigated as sorbents for CO2 capture. The activation process was carried out under severe (KOH/precursor = 4) or mild (KOH/precursor = 2) activation conditions at different temperatures in the 600–800 °C range. Textural characterization of the porous carbons showed that the samples obtained under mild activating conditions exhibit smaller surface areas and pore sizes than those prepared by employing a greater amount of KOH. However, the mildly activated carbons exhibit a good capacity to store CO2, which is mainly due to the presence of a large number of narrow micropores (<1 nm). A very high CO2 uptake of 4.8 mmol·g−1 (212 mg CO2·g−1) was registered at room temperature (25 °C) for a carbon activated at 600 °C using KOH/precursor = 2. To the best of our knowledge, this result constitutes the largest ever recorded CO2 uptake at room temperature for any activated carbon. Furthermore, we observed that these porous carbons have fast CO2adsorption rates, a good selectivity for CO2–N2 separation and they can be easily regenerated.
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