Two-step self-assembly of iron oxide into three-dimensional hollow magnetic porous microspheres and their toxic ion adsorption mechanism

Hollow magnetic porous Fe3O4/alpha-FeOOH microspheres, with abundant surface hydroxyl groups and carbonate-like species, were prepared using a simple template free solution method. The obtained magnetic microspheres were characterized by field emission scanning electron microscopy, transmission electron microscopy, nitrogen adsorption-desorption isotherms, vibrating sample magnetometry and X-ray diffraction. A two-step self-assembly mechanism for the microspheres was proposed based on the morphology of the products produced with different reaction times and the X-ray diffraction of the raw product grown at the initial stage. The toxic ion adsorption properties of the microspheres were investigated for As(V), Cr(VI), Cd(II) and Hg(II) ion removal. The adsorption mechanism was studied by an X-ray photoelectron spectrometer and Fourier transform infrared absorption spectroscopy. The results suggest that both the surface hydroxyl groups and the carbonate-like species participated in the ion-exchange process.