Enhanced CO2 capturing over ultra-microporous carbon with nitrogen-active species prepared using one-step carbonization of polybenzoxazine for a sustainable environment.

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.

Oxidative upgrade of furfural to succinic acid using SO3H-carbocatalysts with nitrogen functionalities based on polybenzoxazine.

SO3H-carbocatalysts with nitrogen functionalities were prepared using the carbonization of polybenzoxazine derived from four different amines (aniline, ethylenediamine, triethylenetetramine, and tetraethylenepentamine) and then sulfonation. The obtained SO3H-carbocatalysts underwent catalytic testing for furfural oxidation with H2O2 to produce succinic acid. The effects of nitrogen functionalities were reported for the first time. The results showed that all carbon samples exhibited a microporous characteristic with comparable textural properties and contained various nitrogen functionalities (N-6, N-5, N-Q, and N-X). After sulfonation, the SO3H-carbocatalyst prepared from tetraethylenepentamine-based polybenzoxazine had the highest amount of sulfonic acid groups (1.45 mmol g-1) and a high nitrogen content (4.23%), providing a maximum succinic acid yield of 93.0% within a rapid reaction time of 60 min under the optimized conditions. This was higher than from Amberlyst-type catalysts and SO3H-carbocatalyst without nitrogen functionalities and was ascribed to the synergistic activity of the sulfonic acid groups and nitrogen functionalities. The XPS spectra and computational study confirmed that such nitrogen functionalities, especially N-5, are capable of forming hydrogen bonding with furfural, facilitating the formation of an intermediate compound and thereby enhancing the catalytic efficiency. However, after four cycles, the succinic acid yield decreased to 40% due to leaching of the sulfonic acid groups.