Fungal mycelium enhanced magnetic biochar from rice straw for efficient tetracycline adsorption: A sustainable strategy for agricultural waste valorization

This study presents a sustainable fungal-biochar refinery approach to convert rice straw into a high-performance magnetic adsorbent. The material was synthesized via solid-state fermentation using Pleurotus ostreatus followed by carbonization and KHCO₃ activation at 900 °C. The fungal pretreatment significantly enhanced porosity, yielding a specific surface area of 2587.51 m² g⁻¹ (a 22 % increase over conventional pyrolysis). Characterization by SEM, XRD, FT-IR, XPS, and N₂ physisorption confirmed a highly porous architecture and abundant surface chemistry. After Fe₃O₄ loading, the biochar retained exceptional adsorption capacity for tetracycline hydrochloride, outperforming most reported agricultural waste-based adsorbents, and achieved facile magnetic recovery (>92 %). Adsorption kinetics and isotherms were best described by the Elovich and Redlich-Peterson models, respectively. The adsorbent performed robustly across a broad pH range (e.g., 99.31 % removal at pH 4) and exhibited excellent reusability with < 15 % capacity loss over five cycles. This work offers an effective strategy for biomass waste into functional materials and a closed-loop solution for simultaneous agricultural waste management and water remediation, aligning with circular bioeconomy principles.