Pyrolysis temperature-regulated physicochemical structural evolution of flower-like N-doped biochar and the relevance for CO2 adsorption behavior

Biomass-derived N-doped porous carbons are promising adsorbents for CO 2 capture because of their tunable pore structures and nitrogen-containing surface groups. Pyrolysis temperature is known to strongly affect their physicochemical properties, yet its role in regulating CO 2 adsorption, particularly diffusion behavior, remains unclear. Herein, flower-like N-doped biochars were fabricated from a biomass/ZIF-8 composite precursor via a solvothermal-assisted pyrolysis route. By integrating thermogravimetric kinetic/thermodynamic analysis, multiscale structural and surface chemical characterizations, and adsorption kinetic modeling, the relationship between pyrolysis temperature, biochar structural evolution, and CO 2 adsorption behavior was systematically examined. The results show that pyrolysis temperature directs the conversion of the composite precursor by regulating framework degradation, Zn-derived pore-forming reactions, carbon matrix reconstruction, and nitrogen-species evolution. The CO 2 uptake increased markedly from 39 mg/g for the sample prepared at 500 °C to a maximum of 134 mg/g for the sample prepared at 900 °C, owing to the more favorable combination of developed microporosity and retained nitrogen functionalities. Further kinetic analysis revealed that CO 2 adsorption involved external diffusion, intraparticle diffusion, and near-equilibrium adsorption stages. The adsorption kinetics were closely associated with the temperature-regulated evolution of surface accessibility, nitrogen functionalities, and pore structures. This study provides a process-level understanding of how pyrolysis temperature tailors N-doped biochar structures and their CO 2 adsorption behavior, offering guidance for the design of efficient biomass-derived carbon adsorbents.