Adsorptive Behavior of Corn-Cob- and Straw-Derived Biochar for Polycyclic Aromatic Hydrocarbon Removal from Aqueous Systems

This study investigates the potential of biochar derived from agricultural residues—corn cob and wheat straw—for removing polycyclic aromatic hydrocarbons (PAHs) from aqueous systems. Biochars were produced via pyrolysis at 700 °C and characterized using BET, SEM, EDS, FTIR, and pXRD to evaluate physicochemical properties. Adsorption experiments with naphthalene, fluorene, fluoranthene, and pyrene revealed high adsorption affinities (Log Kd = 4.35–5.69 L/kg), with Freundlich isotherm modeling indicating nonlinear behavior (n = 0.732–0.923), suggesting a combination of pore filling and chemical interactions such as π-π stacking and hydrogen bonding. Corn-cob biochar, rich in lignin, exhibited a higher surface area (111 m2/g) and greater affinity for fluorene, while wheat-straw biochar, with a higher oxygen content and more functional groups, performed better for naphthalene and pyrene. FTIR and pXRD confirmed aromatic and graphitic structures facilitating PAH interactions. These results underscore the importance of feedstock selection and pyrolysis conditions in tailoring biochar properties for specific pollutants. While both biochars compare favorably with conventional adsorbents like activated carbon, further research on long-term stability in complex matrices is needed. Overall, the findings support the development of cost-effective, scalable, and eco-friendly biochar-based technologies for water remediation.