One-step facile synthesis of pomelo peel biochar activated by KOH under air atmosphere for adsorptive removal of methylene blue and oxytetracycline

BACKGROUND: In this work, a biochar was synthesized from pomelo (Citrus maxima) peel (PBC) which is one of the popular biomass wastes, and enhanced in texture structure and surface-active functional groups via chemical activation with potassium hydroxide (KOH) under air environment. The optimal concentration of KOH solution and pyrolysis temperatures were determined. The morphology and physicochemical properties of the material were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and Brunauer–Emmett–Teller analysis. The activated biochar was applied to the removal of methylene blue (MB) and oxytetracycline (OTC) in water samples. RESULTS: The adsorption of MB and OTC on the prepared biochar obeyed the Langmuir model (R² = 0.9598 and 0.9891, respectively), and the highest adsorption capacity for MB and OTC reached 268.0 and 95.6 mg g⁻¹, respectively. An isotherm study also indicated that MB followed monolayer adsorption while OTC underwent multilayer adsorption. The kinetic results suggest possible adsorption mechanisms involving electrostatic attraction, pore adsorption, hydrogen bonding and π–π interaction. High removal of MB and OTC could be obtained in solutions with a wide range of pH. CONCLUSION: The present study revealed that PBC could be prepared under air environment with KOH activation and be an efficient adsorbent for the removal of organic pollutants from wastewater.