Preparation of sesame straw-derived hierarchical porous biochar via in-situ pyrolysis pressure tuning coupled with post-acid leaching for enhanced CO2 capture

Conventional biochar production lacks precise control over pore architecture, limiting its CO 2 capture performance. Here, we introduce pyrolysis pressure as a powerful and environmentally benign design lever to engineer hierarchical porous biochar from agricultural waste. By simply switching between negative (−0.1 MPa), atmospheric (0 MPa), and positive (0.1 MPa) pressure during pyrolysis, we systematically regulate volatile escape, suppress secondary reactions, and achieve tunable micro–/mesoporosity. This pressure–tuning strategy, combined with post–synthesis acid leaching, offers a scalable route to high–performance biochar adsorbents. The optimized acid-leached negative-pressure biochar (HNSB) exhibits a specific surface area of 638.45 m 2 /g, a micropore volume of 0.2940 cm 3 /g, and a CO 2 uptake of 155.74 mg/g at 0 °C and 1 bar, 1.37 times that of atmospheric–pressure biochar. Kinetic and isotherm analyses confirm micropore–filling physical adsorption as the dominant mechanism, well described by Avrami and Freundlich models. Notably, the adsorbent shows exceptional cyclic stability (99.10 % retention after 10 cycles) and robust resistance to flue gas impurities (only 3.93 % capacity loss in dry simulated flue gas). This work establishes pressure–tuned pyrolysis as a new, environmentally benign platform for designing high–performance, low–cost biochar adsorbents, bridging the gap between agricultural residue valorization and practical carbon capture.