Significantly increased CO ₂ adsorption performance of nanostructured templated carbon by tuning surface area and nitrogen doping

Carbon dioxide adsorption properties of a series of templated carbon adsorbents with high Brunauer-Emmett-Teller surface areas (1361-3840 m ²/g) and with/without nitrogen doping (6-7 wt % N) were systematically studied. Two linear relationships between CO ₂ adsorption capacities and surface areas of nitrogen-doped/undoped nanostructured templated carbons were first established. The doped nitrogen was present in the forms of pyridinic nitrogen, pyrrolic/pyridonic nitrogen, quaternary nitrogen, and an oxidized form of nitrogen. The interaction energies with CO ₂, as approximated by the isosteric heats of adsorption, were increased from 30 kJ/mol on the undoped carbon to 50 kJ/mol on the N-doped carbon as a result of these nitrogen sites. The increased interactions led to an enhancement in CO ₂ adsorption capacity by a factor of 2, while N ₂ uptake was not enhanced. The optimized N-doped templated carbon, N-TC-EMC, possessed remarkable CO ₂ capacity (4 mmol/g at 1 atm and 298 K) and selectivity (CO ₂/N ₂ at 1 atm = 14). Postdoping ammonia treatment was found beneficial to CO ₂ adsorption. CO ₂ performance of N-doped carbon under wet condition and conditions relevant to flue gas, rates of adsorption, and regeneration requirement, which are important for practical applications, were also investigated. The results showed that N-doped templated carbon exhibited all prerequisite attributes for CO ₂ capture and storage applications: high CO ₂ capacity and CO ₂/N ₂ selectivity, fast and reversible adsorption, thermal and moisture stabilities, and ease in CO ₂ desorption.