An efficient biochar adsorbent for CO2 capture: Combined experimental and theoretical study on the promotion mechanism of N-doping

The N-doped carbon material is one of the most efficient adsorption materials in the field of carbon capture. Although many N-doped carbon materials have been prepared for CO2 adsorption in recent years, the promotion mechanism of N-doping has not been clearly proposed. In this study, a series of N-doped biochars were successfully prepared by a facile solvent-free method. Among them, the biochar prepared with corncob powder, K2CO3 and urea at 800 °C showed the highest adsorption capacity (5.69 mmol/g at 0 °C and 1 bar) and selectivity (38.24 at CO2/N2 = 10/90). The biochar also exhibited excellent thermal stability and cycle performance. Notable, correlation analysis showed that ultra-micropores were the decisive factor for CO2 adsorption at low temperatures; nevertheless, the effect of N-doping would gradually appear with the increase of adsorption temperature. By fitting the kinetics of CO2 adsorption, it was found experimentally that N-doping could increase the activation energy between biochar and CO2. Next, through constructing biochar models with different nitrogen contents and different N-doping forms, it was found from theoretical calculation that N-doping could increase the adsorption energy between CO2 and biochar. Further theoretical analysis found that N-doping mainly enhanced the dispersion interaction between the biochar surface and CO2 to improve the adsorption performance, and the higher the nitrogen content, the more obvious the improvement. This work not only prepared a N-doped biochar with excellent CO2 adsorption performance from waste biomass, but also revealed the promotion mechanism of N-doping in detail by combining theoretical calculations with experiments.