Enhanced CO₂ capturing over ultra-microporous carbon with nitrogen-active species prepared using one-step...

Nitrogen-enriched porous carbon has been a promising material for CO₂ capture in the recent decades. To enhance the performance of CO₂ adsorption, both an N-active site and the textural properties are crucial determinants. Herein, ultra-microporous carbon with N-active species was prepared using two synthesis procedures: 1) one-step carbonization of a polybenzoxazine (PBZ) precursor at 800 °C, and 2) the CO₂ activation process at 900 °C. The activated porous carbon had the higher specific surface area (943 m²/g) and a total pore volume (0.51 cm³/g) compared to un-activated porous carbon (335 m²/g and 0.19 cm³/g, respectively). In addition, the presence of N-active species such as pyridine-N, secondary-N, pyridone-N, and oxide-N in the carbon structures could be clearly observed in the high-resolution XPS spectra. The CO₂ adsorption measurement was performed at 30 and 50 °C under a wide range of pressures (1-7 bar). The maximum amount of CO₂ uptake was ca. 3.59 mmol/g for the activated porous carbon operated at 30 °C and a CO₂ pressure of 7 bar, which was due to the high specific surface area and the large micropore volume. Specifically, carbon with a 3D interconnected pore structure, derived from the sol-gel process of the PBZ precursor, exhibited good structural stability and consequently led to better absorption capability under the high atmospheric pressure of CO₂. The enhanced CO₂ adsorption capability for the as-prepared porous carbon was based on two mechanisms: physisorption as a result of textural properties and chemisorption as a result of the acid-base interaction between the basic N functionality and the acidic CO₂ gas. All results suggested that ultra-microporous carbon with N-active species prepared from polybenzoxazine is a promising adsorbent for CO₂ capture and storage, which can be used at a wide range of pressures and in many applications e.g. flue gas adsorption and natural gas production.