Potentially toxic elements removal from aqueous solution using green synthesized ZnCo2O4 nanoparticles: a comparative study of adsorption isotherm and kinetic using linear and non-linear models

Abstract

ZnCo₂O₄ nanoparticles were synthesized by Aloe vera extract, and its characteristic was investigated using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Also, the thermal characteristic of ZnCo₂O₄ nanoparticles was studied by thermogravimetric analysis (TGA). The capacity of ZnCo₂O₄ nanoparticles toward elimination of potentially toxic elements from aqueous media have been investigated by atomic absorption spectroscopy (AAS). The effect of various parameters including contact time, adsorbent mass, pH and initial metal concentration on the adsorption process have been investigated. Potentially toxic elements were removed using ZnCo₂O₄ nanoparticles, achieving maximum removal efficiencies of 92, 84, 60, and 50 % for Ni²⁺, Co²⁺, Cd²⁺, and Pb²⁺, respectively. A comparative analysis of linear and non-linear regression techniques for predicting optimal isotherms was conducted utilizing experimental adsorption equilibrium data. Various adsorption isotherm models, including Langmuir, Freundlich, Redlich-Peterson and Temkin were employed to analyze the experimental data. The findings indicated that the Langmuir equation provided a superior fit for the adsorption isotherms in the context of linear regression, whereas the Redlich-Peterson model demonstrated better fitting in non-linear regression. Kinetic modeling revealed that non-linear pseudo-second-order and Elovich models best describe the adsorption behavior of potentially toxic metal ions onto ZnCo₂O₄ nanoparticles, with contributions from both chemisorption and intraparticle diffusion mechanisms.