Coconut Shell Biochar: Physicochemical Textural Properties, Morphology, and Carbon Sequestration Potential

Background and Objective: Coconut shell biochar (CSB) is a promising soil amendment and carbon sequestration material, yet its physicochemical and textural properties, stability, and carbon sequestration potential under different pyrolysis temperatures remain underexplored. This study aimed to investigate the effects of slow pyrolysis temperature on the physicochemical, textural, and morphological characteristics of coconut shell biochars, and to assess their carbon sequestration potential. Materials and Methods: Coconut shells were pyrolyzed at 350, 450, and 700°C to produce biochars, which were characterized for yield (%), pH, bulk density, cation exchange capacity, electrical conductivity, surface functional groups, and BET textural properties (specific surface area, pore volume, and pore size). Surface morphology and elemental composition were analyzed using SEM/EDX. Carbon sequestration potential was estimated from ultimate analysis and validated via accelerated chemical oxidation using KMnO₄. Results: Biochar properties were strongly temperature-dependent. Increasing pyrolysis temperature enhanced pH, electrical conductivity, and cation exchange capacity, while decreasing yield and bulk density. Total surface functional groups declined from 4.04 mmol/g (CSB350) to 2.17 mmol/g (CSB700). Specific surface area increased from 282.0 m²/g (CSB350) to 712.0 m²/g (CSB450) before decreasing to 320.7 m/g (CSB700). Pore diameter increased from 2.80 nm to 4.85 nm, and pore volume peaked at 0.36 cm³/g for CSB450. H:C and O:C ratios decreased with pyrolysis, from 0.71 and 0.58 in raw shell to 0.40 and 0.30 in CSB700, indicating high long-term stability (>100 years) on the IBI scale. Accelerated chemical oxidation results corroborated these findings, confirming the relationship between pyrolysis temperature and biochar stability. Conclusion: Coconut shell biochar exhibits temperature-dependent physicochemical and textural properties, with higher pyrolysis temperatures favoring stability and carbon sequestration. These findings support the use of CSB as a long-lasting soil amendment and highlight its potential to mitigate atmospheric carbon. Future studies should explore field-scale impacts on soil properties and crop productivity.