Adsorption of acid red 88 anionic dye from aqueous solution onto ZnO/ZnMn2O4 nanocomposite: Equilibrium, kinetics, and thermodynamics

Abstract

The adsorption of acid red 88 (AR88) anionic dye onto ZnO/ZnMn2O4 nanocomposite (ZnMn-NC) prepared by the hydrothermal method was carried out. The adsorbent was characterized by means of XRD, SEM, HRTEM, Raman spectroscopy, FTIR, BET, and zeta potential measurements. We investigated the influence of dye initial concentration, temperature, and pH on AR88 adsorption onto ZnMn-NC. Equilibrium data were analyzed by model equations such as Langmuir and Freundlich isotherms and were best represented by the Freundlich isotherm model. The experimental kinetic data were analyzed using pseudo first-order, pseudo second-order, and intraparticle diffusion kinetic models. The adsorption kinetics was best fitted to the pseudo second-order kinetic model. Thermodynamic parameters, change in free energy ΔGº, enthalpy ΔHº, and entropy ΔSº were also evaluated, indicating the spontaneous and exothermic character of the adsorption of AR88 onto ZnMn-NC.