Preparation and CO2 Adsorption Performance of the B–Cu Codoping Walnut Shell Biochar

Biochar has garnered increasing attention in the field of CO₂ adsorption. The B–Cu codoping activated carbon was prepared. Many characterization techniques were used to analyze the effects of the Cu loading temperature and loading amount on the microstructure and physicochemical properties of the activated carbon. The CO₂ adsorption performance of the activated carbon was evaluated, and its adsorption mechanism was analyzed. The results indicated that Cu doping enriched the pore structure and surface functional groups of the activated carbon. As the Cu loading temperature (200 ∼ 500 °C) and Cu loading amount (5 ∼ 20 wt %) increased, the CO₂ adsorption capacity of the activated carbon first increased and then decreased. The M15-400 activated carbon exhibited the highest specific surface area (1572.80 m²/g) and microporosity (93.91%). The CO₂ adsorption capacity of the B–Cu codoping activated carbon M15-400 was 18.35% higher than that of the undoped activated carbon CK1-1-700, and it showed satisfactory cyclic performance. Both physical and chemical adsorptions were involved. Both monolayer and multilayer adsorption coexisted. This study revealed the synergistic mechanism of nonmetal and metal element coupling on the structure and CO₂ adsorption performance of a walnut shell biochar. This study will provide a reference for the efficient adsorption of the biochar.