The influence of manganese ions doping on nanosheet assembly NiFe2O4 for the removal of Congo red

Highlights: • Ni_0.98Mn_0.02Fe₂O₄ show the more superior characteristic and adsorption capacity. • With the Mn²⁺ ions doping, the groups and charge distributions might be changed. • Adsorption mechanism is illustrated via adsorption isotherms and kinetics models. In this work, it is successfully achieved to synthesize the three-dimensional flowerlike Ni_(1-x)Mn_xFe₂O₄ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1) by an environmental hydrothermal method. The morphology and structure of as-prepared Ni_(1-x)Mn_xFe₂O₄ are characterized via X-ray diffraction, scanning electronic microscopy and nitrogen adsorption-desorption isotherms, besides, the magnetic properties of the samples is revealed by vibrating sample magnetometer. The results show that the Ni_(1-x)Mn_xFe₂O₄ are cubic spinel phase with three-dimensional flowerlike microspheres structure assembled by nanosheets, which is exhibited the good performance to remove Congo red (CR). Besides, the samples with good magnetic properties facilitates magnetic separation for CR solution. The kinetics and isotherm of adsorption process are studied via a UV–visible spectrophotometer. The adsorption process is found to fit the pseudo-second-order kinetic model and Freundlich isotherm model better. Moreover, the adsorption capability of CR on Ni_(1-x)Mn_xFe₂O₄ has a great enhancement by the appropriate doping of Mn²⁺ ions. In order to research the mechanism of the CR adsorption process, the effect of pH value and the surface group of the samples and CR are measured. Due to the doping of Mn²⁺ ions, the surface activity of Ni_(1-x)Mn_xFe₂O₄ has been changed and the adsorption capability (231.74546 mg g⁻¹) of CR on Ni_0.98Mn_0.02Fe₂O₄ is maximum in the all samples at pH 5. This research suggests that appropriate doping of Mn²⁺ ions could enhance the adsorption performance for CR, which provides a new idea for the development of adsorbent.