Preparation and Characterization of Mn_0.4Zn_0.6Fe₂O₄ Nanoparticles Supported on Dead Cells of Yarrowia lipolytica as a Novel and Efficient Adsorbent/Biosorbent Composite for the Removal of Azo Food Dyes: Central Composite Design Optimization Study

The removal of hazardous dyes is of great importance to making healthy and drinkable water. Here, a new ferromagnetic composite based on Mn_0.4Zn_0.6Fe₂O₄ nanoparticles (NPs) supported on dead Yarrowia lipolytica ISF7 (D-YL-ISF7) was prepared. Nanoparticle aggregation was inhibited using D-YL-ISF7, which causes the availability of more active sites. The dead D-YL-ISF7-supported Mn_0.4Zn_0.6Fe₂O₄ nanoparticles (NPs) were characterized by Fourier transform infrared (FT-IR), <i>X</i>-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive <i>X</i>-ray (EDX), Brunuaer–Emmett–Teller (BET), and vibrating sample magnetometer (VSM) analysis and used as robust adsorbents/biosorbents to simultaneously remove tartrazine (TA) and ponceau 4R (P4R) azo food dyes in their binary solution. First-order derivative spectrophotometry was implemented for the simultaneous analysis of dyes in binary mixtures. Central composite design (CCD) was used to evaluate the influence of pH, sonication time, Mn_0.4Zn_0.6Fe₂O₄-NPs-D-YL-ISF7 mass, and initial TA and P4R concentrations on the efficiency for the removal of the studied dyes. At optimum conditions (pH 2.0, sonication time 5 min, Mn_0.4Zn_0.6Fe₂O₄-NPs-D-YL-ISF7 mass 0.015 g, TA concentration 12 mg L^–1 and P4R concentration 16 mg L^–1), high removal efficiencies (>99.0%) were obtained for TA and P4R dyes, reasonably well predicted by the model. The CCD allowed the optimization and the scale-up of the process, which presented a good correlation between large and small scales. Adsorption isotherm data fitted well to the Langmuir model. Under ultrasound, the Langmuir adsorption capacity of Mn_0.4Zn_0.6Fe₂O₄-NPs-D-YL-ISF7 was obtained to be 90.827 mg g^–1 for TA and 101.461 mg g^–1 for P4R. A pseudo-second-order reaction model was chosen for kinetic study