Impacts of different activation processes on the carbon stability of biochar for oxidation resistance

Biochar modification is widely used to improve its capability for environmental application, while its impact on carbon sequestration potential is unknown. Herein, the oxidation-resistance stability of biochar with different activation processes was first evaluated, which is crucial for sustainable production of engineered biochar. Thermal activation enhanced the thermal stability of biochar with a higher R₅₀ as 61.5–62.7%, whereas a higher carbon loss of 15.2–17.2% was revealed after chemical oxidation. Physical activation of biochar had marginal effect on thermal stability, but it still weakened its chemical stability. By contrast, chemical activation with H₂SO₄ improved the stability in terms of chemical-oxidation (6.7% carbon loss) and thermal-oxidation (R₅₀ as 66.2%). Further analysis revealed that the thermal stability of engineered biochar was controlled by aromaticity, while the surface area was a vital factor correlating to the chemical stability. Our findings serve as an important reference to understand trade-off between biochar stability and broader application.