Dependence of phase distribution and magnetic properties of milled and annealed ZnO·Fe₂O₃ nanostructures as efficient adsorbents of heavy metals

Mixed oxides and ferrites nanoparticles (NPs) have shown a considerable potential in environmental applications of purifying wastewater from heavy metal by adsorption. In this paper, ZnO·Fe₂O₃ powders mixture were mechanical milled followed by annealing at 500, 600 and 700 °C. X-ray diffraction characterization confirmed the phase composition and showed crystal growth from 7 to 11 nm due to annealing. Scanning electron microscope revealed agglomerated and spherical particles that increased in size with same trend as XRD results. These nanopowders exhibited a ferromagnetic behavior with varying magnetization and coercivity, the saturation magnetization was found to decrease from 1.45 to 0.09 emu/g with increasing annealing temperature. This was explained due to phase transition and the allocation of A and B atoms in the tetrahedral and octahedral sites in ferrites as a result of annealing. Moreover, BET surface calculations showed an un-patterned pore size distribution with a maximum surface area of 1.84 m²/g obtained after annealing at 500 °C. This sample also demonstrated the highest adsorption capacity at 49.42, 54.69 and 12.34 mg/g for heavy metals ions of nickel, cadmium and chromium, respectively.