Peanut Shell Biochar From Oxygen-Limited and Nitrogen Pyrolysis for SO2 and Toluene Adsorption

This study evaluated peanut shell-derived biochars prepared via oxygen-limited pyrolysis (PSA, 300°C–600°C) and nitrogen-pyrolysis (PSN, 300°C–700°C) as adsorbents for SO₂ and toluene removal from dry flue gas. Increasing pyrolysis temperature enhanced textural properties, with surface areas reaching 281.6 m²·g⁻¹ (PSA600) and 222.73 m²·g⁻¹ (PSN700), while oxygen-containing groups decreased and aromatic carbon and crystalline minerals (SiO₂, CaCO₃) increased. XPS confirmed stabilized active sites (pyridinic N, C–O/C–N) at higher temperatures, facilitating pollutant capture. Adsorption performance improved with temperature: PSA600 achieved a toluene adsorption capacity of 50.6 mg·g⁻¹ (2.37× PSA300), and PSN700 achieved an SO₂ adsorption capacity of 24.8 mg·g⁻¹ (11.26 × PSN300). Kinetic modeling showed temperature-dependent rate-limiting steps, but high R² values for both pseudo-first-order and pseudo-second-order models indicated that kinetics alone cannot unambiguously reveal the mechanism, requiring complementary characterization. Overall, pyrolysis temperature and atmosphere jointly govern the trade-off between pore development and surface chemistry, providing a basis for the rational design of low-cost biochars for multi-pollutant control and agricultural waste valorization.