Efficient CO2 adsorption and mechanism on nitrogen-doped porous carbons

In this work, nitrogen-doped porous carbons (NACs) were fabricated as an adsorbent by urea modification and KOH activation. The CO(2)adsorption mechanism for the NACs was then explored. The NACs are found to present a large specific surface area (1920.72-3078.99 m(2)center dot g(-1)) and high micropore percentage (61.60%-76.23%). Under a pressure of 1 bar, sample NAC-650-650 shows the highest CO(2)adsorption capacity up to 5.96 and 3.92 mmol center dot g(-1)at 0 and 25 degrees C, respectively. In addition, the CO2/N(2)selectivity of NAC-650-650 is 79.93, much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650. The CO(2)adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles. Analysis of the results show that the CO(2)capacity of the NACs has a linear correlation (R-2= 0.9633) with the cumulative pore volume for a pore size less than 1.02 nm. The presence of nitrogen and oxygen enhances the CO2/N(2)selectivity, and pyrrole-N and hydroxy groups contribute more to the CO(2)adsorption. InsituFourier transform infrared spectra analysis indicates that CO(2)is adsorbed onto the NACs as a gas. Furthermore, the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat, and it is found to be controlled by CO(2)diffusion. The CO(2)adsorption kinetics for NACs at room temperature and in pure CO(2)is in accordance with the pseudo-first-order model and Avramis fractional-order kinetic model.

Automated summary

NACs were fabricated as an adsorbent with large specific surface area and high micropore percentage. The sample NAC-650-650 showed the highest CO(2) adsorption capacity and selectivity under 1 bar pressure, maintaining over 97% capacity after ten cycles. The CO(2) capacity of NACs has a linear correlation with the cumulative pore volume for pores less than 1.02 nm, and the presence of nitrogen and oxygen enhances CO2/N2 selectivity.