Self-assembled fabrication of superparamagnetic highly stable mesoporous amorphous iron oxides

In this article, we report the fabrication of highly stable amorphous mesoporous iron oxides (AMIOs) with surface tunable properties by a template-free method. AMIOs with surface areas from 264 to 43 m²/g and mesopore sizes from 5 to 11 nm were synthesized. The synthesized AMIOs were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectra, and nitrogen adsorption analysis. The XRD patterns indicated that the thermal decomposition of the ferric oxalate complex under open atmospheric conditions at low temperature (200-275 °C) and in inert atmospheric conditions at high temperature (400 °C) facilitates formation of crystallographically amorphous iron oxides. Χ-potential analyses of AMIOs indicated that they have almost similar points of zero charge. Magnetic measurements revealed superparamagnetic behavior, with magnetization values around 20 emu/g. The capacities of various amorphous iron oxides to remove As(V) and Cr(VI) by adsorption were investigated. The efficiencies of removal of Cr(VI) and As(V) were found to be 24 and 81 mg/g, respectively. We propose a plausible mechanism for the stability of AMIOs.