Removal of Methylene Blue from Aqueous Solutions using Nano-Magnetic Adsorbent Based on Zinc-Doped Cobalt Ferrite

In this study, Zn-substituted cobalt ferrite nanoparticles (CoFe1.9Zn 0.1O4, CFZ) were successfully synthesized via a combined EDTA-citrate sol-gel process. The synthesized CoFe1.9Zn 0.1O4 nanoparticles were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), point zero charge (pHpzc) and scanning electron microscopy (SEM). The adsorption experiments of methylene blue (MB) onto CFZ surface were conducted in batch mode.  The experiments were conducted under different conditions (contact time, adsorbent dosage, initial pH solution, solution temperature and initial dye concentration). The experimental data were better fitted to pseudo-second-order (PSO) kinetic model (R2=0.9990).  In addition, Langmuir isotherm (R2=0.9906) was the best model to describe the experimental adsorption data. The maximum adsorbed amount of MB (qmax) per unit mass of adsorbent was about 27.79 mg/g. The adsorption thermodynamics (i.e., ΔG°, ΔH°, ΔS°) revealed that the proposed adsorption process is feasible, spontaneous and exothermic in nature. The obtained results suggest that CFZ is a promising material used as an adsorbent for very toxic pollutants from aqueous solutions.