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.