Simultaneous diazinon removal and toxicity reduction from real wastewater using a starch-assisted CuCoFe₂O₄ magnetic...

The separation of organophosphate pesticides from complex water matrices remains challenging due to matrix interference and the limited operational robustness of conventional adsorbents. In this work, a multifunctional magnetic biochar-metal-organic frameworks (MOFs) composite was developed from fish-scale-derived biochar through sequential modification with starch, CuCoFe₂O₄ magnetic nanoparticles, and MOF-5 to enable efficient diazinon (DZ) removal and rapid solid-liquid separation. The resulting composite exhibited a substantially increased specific surface area (≈200 m² g^-1) and sufficient magnetic responsiveness (saturation magnetization ≈16.6 emu g^-1), allowing fast recovery using an external magnetic field. Controlled batch experiments demonstrated that the prepared composite achieved ∼99% DZ removal, with a maximum removal capacity of approximately 40 mg g^-1. Under optimized operational parameters, the removal process rapidly progressed and reached a steady state in less than 75 min. Kinetic evaluation indicated that the removal behavior conformed closely to a second-order rate expression, while equilibrium modeling showed strong agreement with the Langmuir framework, suggesting uniform surface coverage via single-layer removal. Thermodynamic parameters further verified that the removal proceeded favorably without external energy input and released heat, with physisorption being the predominant mechanism. In addition, the material maintained a high removal capability after repeated regeneration, remaining stable across seven consecutive removal-desorption cycles. Importantly, consistent DZ removal was achieved in real wastewater matrices without pH adjustment, underscoring the operational practicality of the developed material. Mechanistic analysis revealed that pore filling, electrostatic interactions, hydrogen bonding, and π-related interactions jointly governed DZ uptake. Overall, this study presents a magnetic biochar-MOF composite with integrated separation efficiency, reusability, and applicability in realistic water systems for pesticide removal.