Tailored biochar from oil palm trunk via controlled carbonization for efficient dye adsorption

Oil palm trunks (OPT) represent an underutilized agricultural byproduct that poses significant environmental challenges. The effectiveness of OPT as feedstock for biochar production will be depends on carbonization conditions, yet the relationship between process parameters and biochar properties remains insufficiently explored. This study investigates the potential of converting OPT into micropores bioadsorbent through controlled carbonization. Biochar was produced at temperatures of 300, 400, and 500 °C, with residence times of 2, 3, and 4 h, and subsequently characterized for its physicochemical properties and adsorption capacity. The results indicate that biochar produced at 300 °C for 2 h exhibited the highest surface area (10.24 m²/g), while the carbon content peaked at 79.9% in biochar synthesized at 500 °C for 4 h. Notably, although the maximum surface area was observed at 300 °C for 2 h, superior MB removal (52.5%) at longer residence time (4 h) indicates that adsorption performance was governed primarily by surface functional chemistry and pore accessibility rather than surface area alone. The enhanced adsorption at mild carbonization was attributed to the preservation of oxygen-containing surface functional groups rather than surface area alone. Langmuir isotherm analysis provided the best fit (R² > 0.9), yielding a maximum monolayer adsorption capacity of 3.57 mg g^-1 and a favourable separation factor (R_L < 1). These results demonstrate that adsorption performance of OPT-derived biochar is governed by surface chemistry controlled through carbonization severity, positioning OPT as a promising low-cost precursor for sustainable dye adsorption applications.