Precursor-engineered solar-responsive biochars from agricultural residues for low-energy CO2 capture and regeneration

Developing biochars that combine high CO 2 adsorption performance and low-temperature regenerability is crucial for integrating carbon capture into a low-carbon circular bioeconomy. Herein, solar-responsive biochars were prepared from five agricultural residues via mechanical-compaction-assisted KOH activation, and multi-technique characterization with Pearson correlation analysis established correlations between precursor composition, pore structure/surface chemistry, and CO 2 capture/regeneration performance. Precursors enriched in hemicellulose and lignin favor the development of ultramicropores (<0.7 nm) and oxygen groups, which synergistically govern CO 2 capture performance. The wheat-straw-derived biochar WS600–3T shows the highest ultramicropore volume and N/O contents, delivering CO 2 adsorption capacities of 6.71 and 4.44 mmol·g −1 at 0 and 25 °C (1 bar), respectively. Under 1 sun irradiation, biochar surface temperatures rise to 48.8–63.1 °C within 41 min. The rapeseed-cake-derived RSC600–3T, with a high integrated solar-light absorption capability, reached a CO 2 desorption ratio of ∼90%. Meanwhile, WS600–3T provided the highest desorbed amount (3.04 mmol·g −1 ) at 25 °C, evidencing a favourable balance between adsorption capacity and regeneration efficiency. Overall, precursor-composition-programmed design is demonstrated as an efficient route to solar-responsive biochars with integrated high-capacity CO 2 capture and low-energy regeneration, and as a guiding strategy for the high-value utilization of agricultural residues as functional sorbents for solar-driven post-combustion CO 2 mitigation.