Molecular simulation combined with DFT calculation guided heteroatom-doped biochar rational design for highly selective and efficient CO2 capture

Abstract

Using solid sorbents for post-combustion CO2 capture from flue gas have shown many potential advantages. The heteroatom doping technique can significantly enhance the CO2 adsorption performance of biochar. However, the diverse forms of heteroatom doping make the development process complex and expensive. To address this, this work firstly used density functional theory (DFT) calculations to screen out three kinds of doping forms (BCO2, P-C, and C-S-C) on biochar, which can improve the CO2 adsorption energy and the theoretical selectivity. Subsequently, the adsorption isotherms simulated by grand canonical Monte Carlo (GCMC) showed the CO2 adsorption capacity on heteroatom-doped biochar at low pressure (≤1 bar) was higher than that of the pristine biochar, which can show excellent performance in flue gas CO2 trapping. Then, three types of heteroatom-doped biochar were synthesized based on theoretical calculations. Among them, P-doped biochar exhibited superior CO2 adsorption capacity (1.34 mmol/g) at 72 °C and 1 bar, which was 10.7 % higher than the pristine biochar. Through adsorption isotherm experiments, it was found that the performance of materials under low pressure is dominated by heteroatom doping, while under high pressure, it is dominated by pore structure, which is consistent with the conclusion obtained from GCMC simulation. And adsorption kinetics experiments revealed that the impact of heteroatom doping becomes more pronounced as the temperature increases, and heteroatom doping can optimize CO2 adsorption kinetics. Furthermore, the heteroatom-doped biochar exhibits exceptional thermal, chemical, and cyclic stability.