Background: Among different pollutants released into the environment, dyes are considered as one of the most dangerous contaminants. In recent years, magnetic nanomaterials have attracted much attention for their dye removal capacity. The aim of this study was to explore the adsorption kinetics of an anionic dye (Reactive Orange 13 (RO)) by NiFe₂O₄ nanoparticles (NiFe₂O₄ NPs) under various conditions.

Methods: NiFe₂O₄ nanoparticles (NiFe₂O₄ NPs) were prepared and characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), pH_pzc and BET methods. The adsorption characteristics of the NiFe₂O₄ NPs adsorbent were examined using Reactive Orange 13 as an adsorbate. The influences of parameters including pH, dose of adsorbent and contact time were investigated to find the optimum adsorption conditions.

Results: Decreasing solution pH and increasing contact time were favorable for improving adsorption efficiency. The kinetic and isotherm data of RO adsorption on NiFe₂O₄ NPs were well fitted by pseudo-second-order and Langmuir models, respectively.

Conclusion: The maximal adsorption capacity of RO was 243.9 mg g^-1 at 25^◦C and pH 3.0 and the adsorption of RO on the NiFe₂O₄ NPs follows a monolayer coverage model. NiFe₂O₄ NPs might be an effective and potential adsorbent for removing anionic dyes from aqueous solutions.