Highly porous nitrogen-doped activated carbons (NACs) were prepared by the chemical activation of chitosan using alkali carbonates. The NACs exhibited extremely high CO2 capacities of 1.6 mmol g(-1) (15 kPa) and 4.9 mmol g(-1) (100 kPa) at 25 °C. Nitrogen atoms doped into carbon frameworks clearly enhanced CO2 adsorption at low partial pressures.
Polyethylenimine-functionalized porous chitosan (PEI−CS) beads were prepared and their CO 2 adsorption performance was evaluated. The CO 2 adsorption capacity of PEI−CS was dependent upon both the amine content and surface area of the functionalized beads. PEI−CS showed a CO 2 adsorption capacity of 2.3 mmol/g at 313 K and 15 kPa of CO 2 in the absence of water vapor that considerably increased to 3.6 mmol/g in the presence of water vapor. To rationalize this phenomenon, the CO 2 adsorption mechanisms in the absence and presence of water vapor were investigated by diffuse reflectance infrared Fourier transform spectroscopy. The results indicated that the mechanism of CO 2 adsorption onto PEI−CS, in both the absence and presence of water vapor, involved the formation of carbamate. Therefore, the higher CO 2 adsorption capacity in the presence of water vapor was attributed to the increased accessibility to amino groups of PEI−CS, owing to swelling of the polyethylenimine chain and/or chitosan framework upon adsorption of water. The herein reported chitosan-based material displays high CO 2 adsorption capacity as well as excellent regenerability and, thereby, shows potential as an adsorbent for CO 2 capture.
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