Removal of cationic dyes from aqueous solutions using NiFe₂O₄ nanoparticles

In this study, NiFe₂O₄ nanoparticles (NiFe₂O₄ NPs) were synthesized and characterized by X-ray diffraction, transmission electronic microscopy (TEM), pH_pzc and Brunauer, Emmett, and Teller methods. The size of the nanostructures according to TEM was obtained and found to be around 12 nm. The adsorption capacity of NiFe₂O₄ NPs was examined using cationic dyes of malachite green (MG), Nile blue A (NB) and Janus green B (JG) as the pollutant (adsorbate). The results demonstrated that the optimum pH, adsorbent dose and temperature were 7.0, 0.05 g and 25 °C, respectively. Adsorption equilibrium experiments were performed, and the results of fitting by the non-linear models signify that the Langmuir–Freundlich model can describe the isotherm of adsorption. Also, the kinetic data were modeled with recently developed models, and the data indicate that the adsorption kinetics follow the fractal-like pseudo-second order (r²>0.99). The method was applied to the removal of dyes in real samples. It was found that NiFe₂O₄ NPs is a highly efficient adsorbent for MG, NB and JG from aqueous solution, with a maximum capacity of 210 mg g^–1, 167.8 mg g^–1 and 102.6 mg g^–1, respectively.