Removal of Rhodamine B from aqueous solution by ZnFe₂O₄ nanocomposite with magnetic separation performance

Magnetic ZnFe₂O₄ nanocomposite (ZnFe-NC) was used as an adsorbent for the removal of Rhodamine B (RB) from aqueous solution. The synthesized nanocomposite was characterized by XRD, SEM, HRTEM, BET and FTIR. The effects of various parameters such as initial RB concentration (5–25 mg L⁻¹), pH (3.4–11.1) and temperature (20–60°C) were investigated. The adsorption capacity at equilibrium increased from 5.02 to 9.83 mg g⁻¹, with the increase in the initial concentration of RB from 5 to 25 mg L⁻¹ at pH 7.0 and at 20°C. The experimental results indicated that the maximum RB removal could be attained at a solution pH of 4.4 and the adsorption capacity obtained was 6.02 mg g⁻¹. Kinetic adsorption data were analyzed using the pseudo-first-order kinetic model, the pseudo-second-order model and the intraparticle diffusion model. The adsorption kinetics well fitted using a pseudo-second-order kinetic model. The experimental isotherm data were analyzed using two isotherm models, namely, Langmuir and Freundlich. The results revealed that the adsorption behavior of the RB onto ZnFe-NC fitted well with the Langmuir isotherm model. In addition, various thermodynamic parameters, such as standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) have been calculated.