Magnetically Separable PVA-functionalized Mn-Fe Oxide Uniform Nanoparticles for Effective Removal of Cationic Dyes from Aqueous Medium

Uniform nanoparticles of Mn-Fe oxide (MF) were prepared by the coprecipitation process under optimum experimental conditions. These particles acquired magnetism (MF_mag) by the controlled heat treatment at 900 ◦C, which are then characterized by x-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) for their structural, morphological, and elemental analysis, respectively. The same particles were functionalized with polyvinyl alcohol (PVA) and used as adsorbent for the removal of a model dye “Methylene Blue (MB)” from aqueous solutions. Effect of pH, concentration of dye adsorbent, temperature, contact time of the adsorbent with the adsorbate dye molecules was evaluated on the adsorption process. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption, among them Langmuir model was found best fit to equilibrium data. The adsorption kinetics was found to follow the pseudo-second-order kinetic model. Thermodynamics parameters, ΔG°, ΔH° and ΔS°, indicated that the adsorption of MB onto PVA-functionalized MFmag was spontaneous, exothermic and physical in nature. It was noted that the adsorption process understudy is very effective, since in most of the cases the adsorbate solutions became colourless and up to 99% dye was removed under optimum conditions. Similarly, in all cases, the adsorbents were easily separated from the adsorption mixtures by a permanent magnet. With the advantages of effective adsorption of dye and magnetic separation, the PVA-functionalized MF nanoparticles could prove to be a promising adsorbent in the wastewater treatment processes.