Inert-gas-free thermochemical conversion of banana pseudostem under oxygen-limited conditions into functional biochar for naphthenic acid removal

Banana pseudostem waste is an abundant agro-industrial residue with potential as a sustainable precursor for biochar production. This study evaluates an inert-gas-free thermochemical conducted under oxygen-limited conditions for producing banana pseudostem-derived biochars and compares it with conventional pyrolysis under continuous N 2 flow at 300 and 600 °C. Biochars obtained at 300 °C exhibited similar physicochemical properties regardless of the conversion atmosphere, whereas significant structural and textural evolution was observed at 600 °C, highlighting the influence of thermal conditions on biochar development. Adsorption performance toward naphthenic acids was assessed using benzoic acid (BA) and cyclohexanecarboxylic acid (CHCA) as model compounds. Molecular modeling predicted stronger adsorption affinity for BA, consistent with experimental results. The air-treated biochar produced at 600 °C showed enhanced surface area, improved thermal stability, and superior adsorption performance. Adsorption kinetics followed the Elovich model, suggesting heterogeneous surface interactions, with pollutant removal exceeding 80% within 3 h. Equilibrium data were well described by the Langmuir model, yielding a maximum BA adsorption capacity of 0.95 mmol g ₋1 . The results demonstrate that oxygen-limited thermochemical conversion can be used as a simplified and sustainable route to produce functional biochars from banana pseudostem, supporting their application for naphthenic acid-related compound removal from produced water.