Effect of N-Containing Functional Groups on CO2 Adsorption of Carbonaceous Materials: A Density Functional Theory Approach

The amount of anthropogenic CO2 emission keeps increasing worldwide, and it urges the development of efficient CO2 capture technologies. Among various CO2 capture methods, adsorption is receiving more interest, and carbonaceous materials are considered good CO2 adsorbents. There have been many studies of N-containing carbon materials that have enhanced surface interaction with CO2; however, various N-containing functional groups existing in the carbon surface have not been investigated in detail. In this study, first principle calculations were conducted for carbon models having various N-functional groups to distinguish N-containing heterogeneity and understand carbon surface chemistry for CO2 adsorption. Among N-functional groups tested, the highest adsorption energies of -0.224 and -0.218 eV were observed in pyridone and pyridine groups, respectively. Structural parameters including bond angle and length revealed an exceptional hydrogen-bonding interaction between CO2 and pyridone group. Charge accumulation on CO2 during interaction with pyridine-functionalized surface was confirmed by Bader charge analysis. Also, the peak shift of CO2 near Fermi level in the DOS calculation and the presence of HOMO on pyridinic-N in the frontier orbital calculation determined that the interaction of pyridinic-N is weak Lewis acid base interaction by charge transfer. Furthermore, adsorption energies of N-2 were calculated and compared to those of CO2 to find its selective adsorption ability. Our results suggest that pyridone and pyridine groups are most effective for enhancing the interaction with CO2 and have potential for selective CO2 adsorption.