Synthesis of magnetic chromium substituted cobalt ferrite Co(CrxFe1–x)2O4 adsorbents for phosphate removal

Abstract

In this work, we aimed to prepare chromium substituted cobalt ferrite Co(CrxFe1–x)2O4 powders by a simple coprecipitationannealing method with different Cr contents to create novel magnetic adsorbents for the removal of phosphate ions from water. The effects of Cr substitution on the crystal structure, phase composition, morphology, surface atomic composition, surface area and magnetic properties of our adsorbents were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller nitrogen adsorption-desorption and vibrating sample magnetometry. According to the results, all our Co(CrxFe1–x)2O4 samples exhibited higher phosphate adsorption than CoFe2O4 powder but their magnetic properties were reduced for increasing Cr substitution. Among them, the Co(Cr0.25Fe0.75)2O4 sample was found to be the most promising material since its magnetic properties are still high to allow it to be easily separated from the solution and its maximum P adsorption capacity (according to the Langmuir model) was estimated to be 4.84 times higher than CoFe2O4, which can be attributed to the presence of Cr3+ ions on the surface and the enhanced surface specific area of this substituted sample. Moreover, the adsorption data of Co(Cr0.25Fe0.75)2O4 sample also fitted well to the pseudo second order kinetic model, revealing the adsorption rate constant of 0.87 mgP–1s–1, two times superior to CoFe2O4.

Keywords

• chromium substitution
• cobalt ferrite
• phosphate removal
• magnetic adsorbent
• surface cr 3 content