Adsorption of Azo Dye on Magnetically Separable Fe3O4/CeO2 Nanocomposite: Kinetics, Isotherm, Mechanism

Abstract

In this study, magnetically separable Fe₃O₄/CeO₂ nanocomposite (F/CNc) was first synthesized in hydrothermal and sol-precipitation methods and characterized by techniques including SEM-EDS, XRD, BET, FT-IR and VSM. The adsorption experiments of acid black dye (AB210) onto F/CNc were carried out under the conditions of temperature (30 – 60 ℃), solution pH (1 – 11), Fe-Ce molar ratio (1:2.5 – 4) and initial dye concentrations (20 – 80 mg/L). The adsorption capacity of AB210 increased with increasing initial dye concentration and temperature, and decreased with increasing solution pH. The maximum adsorption capacity of F/CNc for AB210 reached 124.5 mg/g when Fe-Ce molar ratio was 1:3. Pseudo-first-order and pseudo-second-order models were then used to describe the kinetics of adsorption, of which the latter fitted the adsorption process well, and the adsorption process complied also with the intra-particle diffusion model. The isothermal adsorption was described using Langmuir, Freundlich and Temkin models and the Langmuir model matched. FT-IR and Zeta-potential measurement proved the physical adsorption process of AB210 onto F/CNc. The saturation magnetizations of Fe₃O₄ nanospheres and F/CNc were measured to be 69.1 emu/g and 22.9 emu/g respectively, indicating the coating layer reduced the magnetization of Fe₃O₄ nanospheres, but F/CNc were still separated easily by applying a magnetic field, keeping easy separability. Being easy to recover and remaining adsorption efficiency 90 % in comparison to the original even after four adsorption cycles, demonstrate the effectiveness and practical application of F/CNc as an adsorbent.