Magnetically recoverable Fusarium oxysporum–CuFe₂O₄/ZIF-67 biocomposite for efficient Cd²⁺ removal from aquatic systems

This study reports the development of a magnetically recoverable biosorbent based on Fusarium oxysporum (F. oxy) biomass functionalized with CuFe₂O₄ (CFO) nanoparticles and ZIF-67 for Cd²⁺ removal from synthetic solutions and real industrial wastewaters. Structural characterization using SEM, EDX-mapping, BET, VSM, and XRD confirmed the successful formation of the F. oxy/CFO/ZIF-67 composite, with the specific surface area increasing from 1.569 to 123 m² g⁻¹ after magnetic and MOF modification. FTIR analysis revealed the presence of hydroxyl, carboxyl, amine, and metal–oxygen functional groups, while the point of zero charge (pHpzc ≈ 6.5) indicated favorable electrostatic interactions with Cd²⁺ at near-neutral pH. The composite exhibited saturation magnetization of 11.179 emu g⁻¹, enabling rapid magnetic separation. Process optimization using response surface methodology based on a central composite design (RSM–CCD) showed excellent predictive accuracy of the quadratic model (R² = 0.9994, Adjusted R² = 0.999, Predicted R² = 0.9982), achieving Cd²⁺ removal efficiencies up to 99.17%. Adsorption onto F. oxy/CFO/ZIF-67 followed Freundlich isotherm behavior and pseudo-second-order kinetics, with a maximum adsorption capacity of 33.64 mg g⁻¹. Thermodynamic parameters (ΔG° < 0; ΔH° = 67.6–75.9 kJ mol⁻¹) indicated a spontaneous and endothermic process. Evaluation in electroplating, battery, and pigment wastewaters demonstrated Cd²⁺ reduction from 2.35 ± 0.12–0.94 ± 0.05 mg L⁻¹ to 0.41 ± 0.03–0.28 ± 0.02 mg L⁻¹, corresponding to removal efficiencies of 70.2–82.6% despite the presence of competing ions. The treated effluents exhibited a shift toward near-neutral pH values (≈ 6.6–6.9), suggesting amphoteric buffering behavior of the composite surface. Regeneration tests showed that the adsorbent retained over 90% of its initial efficiency after multiple reuse cycles, highlighting its applicability for Cd²⁺ removal from complex industrial wastewater systems. MOF-modified magnetic fungal biomass achieved up to 99.17% Cd²⁺ removal under optimized conditions. Surface area increased from 1.569 to 123 m² g⁻¹ after CFO/ZIF-67 functionalization. Cd²⁺ reduced from 2.35 ± 0.12 to 0.41 ± 0.03 mg L⁻¹ in electroplating wastewater. Composite retained >90% removal efficiency after four adsorption–desorption cycles. Effluent pH shifted to ~6.6–6.9, indicating amphoteric buffering of the adsorbent surface.