Synthesis, characterization and optimization of a bionanocomposite for methylene blue removal from aqueous solutions

This study developed and characterized a magnetic bionanocomposite (BNC) by immobilizing cobalt ferrite nanoparticles (CoFe₂O₄) onto fungal biomass of Actinomucor elegans LBM 290 and evaluated its efficacy in removing methylene blue (MB) dye from aqueous solutions. Characterization via X-ray diffraction (XRD) and Rietveld refinement confirmed the synthesis of highly crystalline nanoparticles approximately 70 nm in size. Fourier-transform infrared spectroscopy (FTIR) revealed interactions between fungal functional groups (hydroxyl, amide) and the nanoparticles, while scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) demonstrated homogeneous surface functionalization. Vibrating sample magnetometry (VSM) confirmed the preservation of magnetic properties, enabling easy recovery using an external magnetic field. The BNC demonstrated superior efficacy, achieving 49% MB removal, significantly higher than the 1.57% achieved by NPs alone. The adsorption experiments of MB were conducted under different conditions (contact time, adsorbent dosage, initial pH solution, solution temperature, and initial dye concentration). The experimental conditions were optimized, establishing the maximum removal (51.2%) at pH 7.7 mg/L of MB, 70 mg of BNC, 48 h of contact and 25 °C. Adsorption kinetics followed a pseudo-second-order model, and equilibrium data fit the Langmuir isotherm, indicating monolayer physisorption. Thermodynamic analysis revealed a spontaneous and exothermic process. The BNC maintained high removal efficiency during multiple reuse cycles and reduced post-treatment phytotoxicity, as demonstrated by Lactuca sativa germination trials. These results highlight the BNC as a sustainable, recoverable, and effective adsorbent for the bioremediation of dye-contaminated from aqueous solutions.