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In this work, graphene-derived N-enriched porous carbons were synthesized by urea modification and KOH activation of thermally shocked graphene oxide. The prepared sorbents were characterized by various techniques and investigated as potential CO2 capture materials. The as-prepared sorbents possess high CO2 adsorption capacity of 2.40 mmol/g (25 °C) and 3.24 mmol/g (0 °C) at 1 bar, which is higher than most graphene-based carbons reported previously. The nitrogen incorporation and narrow microporosity are the two major factors that determine CO2 uptake for these graphene-derived carbonaceous adsorbents under ambient conditions. The adsorption kinetic data of the optimized sample were well-described by the classical Fick’s diffusion model with a high CO2 diffusion rate. The fast CO2 adsorption kinetics can be attributed to the short diffusion paths of this sample, which is composed of thin layers of graphene sheets. Moreover, these graphene-derived sorbents also demonstrate excellent stability and recyclability, high selectivity of CO2 over N2, suitable heat of adsorption, and excellent dynamic CO2 capture capacity. As a result, these graphene-derived porous carbons deserve consideration for removal of CO2 from exhausted flue gas.

The synthesis of carbonaceous CO2 adsorbents doped with nitrogen were carried out via a hydrothermal reaction of biomass d-glucose, followed by urea treatment and K2CO3 activation. These carbons display high uptake of CO2 at 1 bar and 25 and 0 °C, up to 3.92 and 6.23 mmol g–1, respectively. Additionally, the as-synthesized materials exhibit superior reusability, high CO2/N2 selectivity, fast CO2 adsorption kinetics, and excellent dynamic capture capacity at the experimental conditions used. The synthetic effect of the nitrogen content and narrow microporosity decide the capture capacity for CO2 at 1 bar and 25 °C for these N-enriched carbonaceous adsorbents. This study provides a viable method to prepare high-performance CO2 carbonaceous sorbents without using caustic KOH. In addition, this work gives further insights into the CO2 adsorption mechanism for nitrogen-doped porous carbon sorbents and, hence, inspires ways to synthesize novel carbonaceous materials for removing CO2 from combustion exhaust gases.

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In this study, N-enriched porous carbons were prepared by a facile synthesis method at low temperatures ranging from 400 to 500 °C. Sodium amide was used as both activator and nitridation reagent, and lotus stalk was used as the carbon precursor. The as-synthesized samples demonstrate the maximum CO2 uptake of 3.88 and 5.62 mmol/g at 25 and 0 °C, respectively, at atmospheric pressure. Moreover, these lotus stalk-derived adsorbents exhibit a rapid CO2 adsorption rate, high CO2/N2 selectivity, moderate CO2 isosteric heat of adsorption, stable cyclic ability, and excellent dynamic CO2 capture capacity. Systematic research shows that, besides the volume of narrow micropore and nitrogen content, the pore size distribution is also a non-negligible factor in determining CO2 adsorption capacity under ambient condition for these adsorbents. The good CO2 adsorption performance together with single-step and low-temperature preparation indicates that these sorbents are very promising for CO2 capture from flue gas.