Adsorption of Congo red on magnetic cobalt-manganese ferrite nanoparticles: Adsorption kinetic, isotherm, thermodynamics, and electrochemistry.

Magnetic Co0.5Mn0.5Fe2O4 nanoparticles were successfully prepared via the combustion and calcination process, with an average particle diameter of 31.5 nm and a saturation magnetization of 25.25 emu·g-1, they were employed to adsorbe Congo red (CR) from wastewater, the Pseudo-second-order kinetic and Freundlich isotherm were consistent with the adsorption data, indicating that their adsorption was a multilayer chemisorption process, the thermodynamic investigation showed that the adsorption was a favored exothermic process. The ionic strength of Cl- in CR solution had no obvious effect on the adsorption efficiency of Co0.5Mn0.5Fe2O4 nanoparticles, and the maximum adsorbance was 58.3 mg·g-1 at pH 2, decreasing as the pH of the CR solutions increased from 2 to 12. The ion leaching experiment and XRD demonstrated that Co0.5Mn0.5Fe2O4 nanoparticles had excellent stability, and the relative removal rate was 93.85% of the first time after 7 cycles. Cyclic voltammetry and electrochemical impedance spectroscopy demonstrated that CR was adsorbed onto Co0.5Mn0.5Fe2O4 nanoparticles, and the electrical conductivity of Co0.5Mn0.5Fe2O4 nanoparticles decreased after adsorption of CR. Magnetic Co0.5Mn0.5Fe2O4 nanoparticles displayed a promising application in wastewater treatment.