Unveiling the role of pentagonal topological defects in lignocellulose-derived self-assembled N/O co-doped micro-mesoporous biochar for enhanced CO₂ adsorption

• Convert red waxberry pits to self-assembled mesoporous biochar with pentagonal topological defects. • NWBC-900 exhibits high CO 2 adsorption capacity. • Distinct CO 2 adsorption capacities due to various N-N-Oconfigurations and synergies. • Pearson heatmaps show defects strongly enhance CO 2 adsorption of graphitic-N, C-C-O-C. • Pentagonal topological defects boost CO 2 adsorption of biochar by enhancing electron transfer. The physicochemical properties of biochar are critical for CO 2 adsorption; however, the synergistic effect of doped nitrogen and topological defect in biochar on CO 2 adsorption capacity remains uncertain. Here, N/O coupled topological defect co-doped biochars (NWBCs-T) were successfully synthesized via self-assembly temperature-controlled carbonization/annealing within 500–900 °C from red bayberry pits. The influence mechanism of temperature on the formation, transformation, and interaction of N/O and pentagonal topological defect functionalities, as well as their impact on CO 2 adsorption, was systematically investigated. The results revealed that NWBC-900 exhibited the highest CO 2 adsorption capacity of 60 mg/g, primarily attributed to the prominent synergistic effect between N/O active sites and topological defect, rather than the physical adsorption force from micro-mesoporous pores, as evidenced by relevant analyses and Pearson heatmaps. Notably, the presence of pentagonal topological defects exerts a profound enhancing effect on CO 2 adsorption of edge graphitic-N and C-O-C sites, yet exerts weaker or opposite effects on other N/O configurations. Further insights from XPS and NMR analyses indicated a notable surge in pentagonal topological defects at elevated annealing temperatures, along with a reduction in total and pyrrolic nitrogen content. DFT calculation findings confirmed that pentagonal topological defects introduced at elevated temperatures adjust electron distribution, thereby facilitating improved electron transfer and boosting adsorption binding of NWBC-900 for CO 2 . This work provides new insights into the conversion of waste biomass into green-efficient biochar for carbon capture.