Synthesis of 3D hierarchical porous iron oxides for adsorption of Congo red from dye wastewater

In this study, 3D hierarchical porous iron oxides were prepared by a precursor thermal conversion method and their adsorption properties for Congo red were reported. The products were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), electron microscopy (EM) and nitrogen adsorption-desorption isotherms. Results demonstrated that the 3D magnetic bowknot-like iron oxides were constructed by three-dimensional self-assembly of nanorods with porous nanostructures. The effect of experimental parameters including polymer concentration, reaction temperature, reaction time and heat treatment atmosphere were studied. Bowknot-like α-Fe2O3, Fe3O4 and γ-Fe2O3 superstructures were obtained by the thermal transformation of the oxalate precursor under the various atmosphere. These porous iron oxide superstructures exhibited ferromagnetic property at room temperature. Adsorption of Congo red (CR) onto the as-prepared samples from aqueous solutions was investigated and discussed. The results indicated that pseudo-second-order kinetic equation model can better describe the adsorption kinetics of CR onto α-Fe2O3 and γ-Fe2O3, and Lagergren-first-order kinetic model is better fitted for the adsorption of CR onto Fe3O4. The hierarchically α-Fe2O3 bowknots showed better adsorption ability for CR than Fe3O4 and γ-Fe2O3 superstructure.