Microporous carbon foams: The effect of nitrogen-doping on CO2 capture and separation via pressure swing adsorption

Abstract

This work investigates the effect of nitrogen doping on the porous structure and CO2 adsorption properties of hierarchically porous carbon foams, at different temperatures and pressures. A series of carbon foams with nitrogen contents of ∼7 to 13 at % is prepared by reaction of sodium ethoxide with different amino alcohols (namely monoethanolamine, diethanolamine, and triethanolamine), followed by thermal decomposition of the reaction product. The structure, morphology, porosity and chemical composition are studied using appropriate methods. The resulting material comprises micron-scale macropores combined with unrestricted micropores and mesopores embedded in the carbon walls. It is found that both nitrogen species and ultra-micropores contribute positively to CO2 uptake. The carbon foam with a nitrogen content of ∼7 at % (as well as an ultra-micropore volume of 0.44 cm3 g−1 and a specific surface area of 1549 m2 g-1) displays the highest CO2 uptake, adsorbing 5.14 mmol g−1 at 273 K, 3.22 mmol g−1 at 298 K, or 1.93 mmol g−1 at 323 K. This nitrogen-doped carbon foam adsorbs more CO2 than the undoped carbon foam reference, despite having significantly lower ultra-micropore volume and higher specific surface area. This highlights the importance of nitrogen species in CO2 capture. However, increasing the nitrogen content leads to suppression of the micropore volume, resulting in poor CO2 uptake. High CO2/N2 selectivity with good separation of CO2 from the CO2-N2 gas mixture, fast adsorption via physisorption, and excellent cycling durability are also observed, pointing towards the high regenerative ability of these materials.