Synthesis of MnFe 2 O 4 and Mn 3 O 4 magnetic nano-composites with enhanced properties for adsorption of Cr(VI): artificial neural network modeling.

This study reports adsorptive removal of Cr(VI) by magnetic manganese ferrite and manganese oxide nano-particles (MnF-MO-NPs) composite from aqueous media. The X-ray diffraction pattern of MnF-MO-NPs revealed a polycrystalline nature with nanoscale crystallite size. The prepared adsorbent with high Brunauer-Emmett-Teller specific surface area of 100.62 m2 /g and saturation magnetization of 30.12 emu/g exhibited maximum Cr(VI) removal at solution pH 2.0 and was easily separated from water under an external magnetic field. Adsorption capacity as much as 91.24 mg/g is reported and electrostatic interaction between positively charged adsorbent surface and anionic metal ion species is the main driving force in this adsorption. Adsorption experimental data followed Langmuir isotherm and second order kinetics. Partial involvement of intra-particle diffusion was also observed due to the mesoporous nature of MnF-MO-NPs. The thermodynamic studies revealed that the process was favorable, spontaneous and exothermic in nature. An artificial neural network model was developed for accurate prediction of Cr(VI) ions removal with minimum mean squared error (MSE) of 15.4 × 10-4 and maximum R2 of 0.98. Owing to large surface to volume ratio, advantage of easy magnetic separation, and high adsorption capacity towards Cr(VI), the reported MnF-MO-NPs appear to be a potential candidate in Cr(VI) contaminated wastewater remediation.