The preparation of a novel iron/manganese binary oxide for the efficient removal of hexavalent chromium [Cr()] from aqueous solutions

To remove hexavalent chromium Cr( vi ) efficiently, a novel Fe-Mn binary oxide adsorbent was prepared via a "two-step method" combined with a co-precipitation method and hydrothermal method. The as-prepared Fe-Mn binary oxide absorbent was characterized via transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectra (FTIR), thermogravimetric analysis (TGA), zeta potential, BET and X-ray photoelectron spectroscopy (XPS). The results indicated that the morphology of the adsorbent was rod-like with length of about 100 nm and width of about 50-60 nm, specific surface area was 63.297 m 2 g −1 , has the composition of α-Fe 2 O 3 , β-MnO 2 and MnFe 2 O 4 and isoelectric point was observed at pH value of 4.81. The removal of Cr( vi ) was chosen as a model reaction to evaluate the adsorption capacity of the Fe-Mn binary oxide adsorbent, indicating that the Fe-Mn binary oxide adsorbent showed high adsorption performance (removal rate = 99%) and excellent adsorption stability (removal rate > 90% after six rounds of adsorption). The adsorption behavior of the Fe-Mn binary oxide was better represented by the Freundlich model (adsorption isotherm) and the pseudo-second-order model (adsorption kinetic), suggesting that the adsorption process was multi-molecular layer chemical adsorption. The possible adsorption mechanism of the Fe-Mn binary oxide for the removal of Cr( vi ) included the protonation process and the electrostatic attraction interactions. A novel Fe-Mn binary oxide adsorbent prepared via "co-precipitation and hydrothermal" method, for the efficient and fast removal of Cr( vi ).