Nitrogen-doped microporous carbon with high CO2 sorption by KOH activation of black gram

Nitrogen-doped microporous carbon materials were synthesized by KOH activation of char produced by heating powdered black gram at 300 °C in an inert atmosphere. The carbohydrate and protein present in the black gram were converted to nitrogen-enriched carbon structures during the charring as evidenced by elemental analysis and Raman spectrum. The black gram char derived activated carbon materials (BGC) were characterized by elemental analysis, XRD, Raman spectroscopy, SEM, TEM, XPS and N2 gas adsorption-desorption studies. The nitrogen content, textural properties and CO2 adsorption capacities of the black gram derived activated carbon (BGC-x-y) depend on the KOH to black gram char ratio (x) and activation temperature (y). The highest surface area (2305 m2 g−1) and total pore volume (1.23 cm3 g−1) were exhibited by BGC-3-800 whereas the highest micropore volume (0.397 cm3 g−1) was obtained for BGC-1-700. The nitrogen (1.78 to 5.34 wt%) in the amorphous BGC-x-y materials was present in the pyrolic, pyridinic, quaternary and N-oxide forms. The highest CO2 adsorption capacity of 3.46 and 5.3 mmol g−1 at 25 and 0 °C, respectively, at 1 atmosphere was achieved for BGC-1-700. The physical adsorption (heat of adsorption: −39 to −35 kJ mol−1) of CO2 is mainly due to micropore filling as the adsorption capacity increases with micropore volume. The CO2 adsorption on BGC-1-700 showed very good selectivity over nitrogen adsorption and excellent recyclability over five adsorption-desorption cycles.