Synthesis of Fe3O4@SiO2@MnO2 composite magnetic submicrospheres as adsorbent for methyl orange decolouration

Core-shell-shell composite (Fe₃O₄@SiO₂@MnO₂) submicrospheres were successfully synthesised by homogeneous precipitation of MnO₂ on Fe₃O₄@SiO₂ spheres, which were prepared by a modified sol-gel method with the presence of Fe₃O₄ particles. The synthesised multilayer-structured nanocomposites were characterised by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and using a vibrating sample magnetometer. The results show that the magnetic Fe₃O₄ cores were well wrapped by the intermediate layer of SiO₂ with a thickness of 40 nm in the amorphous phase, and the MnO₂ nanoparticles with a diameter not exceeding 10 nm were attached on the SiO₂ shell. The magnetic measurements indicated that the Fe₃O₄@SiO₂@MnO₂ submicrospheres were of superparamagnetism with the saturation magnetisation of 29.41 eum/g. At the same time, the submicrospheres demonstrated a high chemical adsorption activity for methyl orange (MO) decolouration with efficiency of up to 93.76% within 1 h. Moreover, the submicrospheres were found to be stable under repeated applications of up to five successive cycles with a near constant adsorption activity after regeneration. It is expected that the adsorbent could be used for trace pollutants (MO) removal from water and recycled owing to its superparamagnetism properties and high adsorption activity.