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A series of porous carbons for CO2 capture were developed by simple carbonization and KOH activation of coconut shells under very mild conditions. Different techniques such as nitrogen sorption, X-ray diffraction, scanning emission microscopy, and transmission electron microscopy were used to characterize these sorbents. Owing to the high amount of narrow micropores within the carbon framework, the porous carbon prepared at a KOH/precursor ratio of 3 and 600 °C exhibits an enhanced CO2 adsorption capacity of 4.23 and 6.04 mmol/g at 25 and 0 °C under 1 bar, respectively. In addition to the high CO2 uptake, these samples also show fast adsorption kinetics, moderate heat of adsorption, high CO2 over N2 selectivity, excellent recyclability and stability, and superior dynamic CO2 capture capacity. The application of coconut shell as precursors for porous carbons provides a cost-effective way for the development of better adsorbents for CO2 capture.

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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