Synthesis of manganese dioxide/iron oxide/graphene oxide magnetic nanocomposites for hexavalent chromium removal

Effective removal of heavy metal ions from wastewater is one of the important environment issues. Here, manganese dioxide/iron oxide/graphene-based magnetic nanocomposites (MnO2/Fe3O4/graphene oxide and MnO2/Fe3O4/graphene) were prepared by an easy and effective two-step reaction and investigated for the removal of hexavalent chromium ion from water. The materials were characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, and Brunauer-Emmett-Teller surface area measurement. MnO2/Fe3O4/graphene oxide (MnO2/Fe3O4/GO) synthesized at pH 5.0 was the most effective adsorption material among other samples synthesized under different conditions. The Langmuir isotherm model was consistent with the experimental data at different pH values. MnO2/Fe3O4/GO showed excellent adsorption capacities both at pH 5.0 (q(max) = 175.4 mg g(-1)) and pH 2.0 (q(max) = 193.1 mg g(-1)). Hexavalent chromium adsorption by MnO2/Fe3O4/GO was pH dependent. The adsorption kinetic data were best described by a pseudo-second-order model. MnO2/Fe3O4/GO was stable and easily recovered. These experimental results suggested that MnO2/Fe3O4/GO had great potential as an economic and efficient adsorbent of heavy metals from wastewater.