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 ·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·g −1 at 0 and 25 °C, respectively. In addition, the CO 2 /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 CO 2 /N 2 selectivity, and pyrrole-N and hydroxy groups contribute more to the CO 2 adsorption. In situ Fourier 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 Avramís fractional-order kinetic model.