Adsorption behaviors of Congo red onto Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles prepared via an alcohol-assisted combustion process

Magnetic Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles were prepared through an alcohol-assisted combustion process. The composition, morphology and magnetic properties of the nanomaterials were characterized by XRD, TEM and VSM techniques. The magnetic Fe₂O₃/Fe₃O₄ heterogeneous nanomaterials were soft magnetic nanoparticles with a saturation magnetization of 38.6 emu g⁻¹ and an average particle size of approximate 29 nm. The adsorption behavior of Congo red (CR) onto Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles was examined by UV-visible absorption spectroscopy, and the data for the kinetics and the isotherm of CR adsorption onto Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles were in good agreement with the pseudo-second-order model and Langmuir model, respectively, which suggested that the adsorption mechanism of CR onto Fe₂O₃/Fe₃O₄ heterogeneous nanoparticles was the chemical and monolayer adsorption. Moreover, the influence of pH on the adsorption process was investigated, and when pH was equal to and less than 7, there would be larger adsorbances. (paper)