Preparation and CO₂ adsorption of N-doped biochar and effect of acetone on its adsorption performance

CO₂ adsorption is a promising carbon capture technology. Boiler flue gas is a major source of CO₂ emissions, with a complex composition. The influence of coexisting components (especially VOCs) on CO₂ adsorption performance is an urgent problem to be explored. In this study, wheat stalk and wood were selected as the raw materials, and urea and melamine as nitrogen sources, a series of N-doped biochars were prepared. They were characterized by SEM, BET, FTIR, and XPS, and their adsorption properties and mechanism for single-component CO₂ and binary-component CO₂ and acetone were systematically studied. The results show that CO₂ adsorption increase by melamine modification (26.96%-48.58%) was better than urea modification (2.98%-43.60%). The N-doped biochar had a high specific surface area (1753.445 m² g^-1) and ultramicropores structure, and the CO₂ adsorption capacity was up to 3.17 mmol g^-1 under normal pressure and 40 °C. The adsorption process was well fitted to the R-P model (R² = 0.9999) and the PSO model (R² = 0.998), respectively, indicating that the CO₂ adsorption on biochar was the multi-layer adsorption, which could be determined by both physical and chemical adsorption. CO₂ and acetone in the binary-component had a certain competitive synergistic effect on the N-doped biochar, and acetone had a synergistic effect on the CO₂ adsorption, while CO₂ was not conducive to the acetone adsorption. The schematic diagram of possible adsorption mechanism for binary-component CO₂ and acetone on the N-doped biochar was given. The findings further improved the theoretical system of CO₂ adsorption by biochar.