Porous Fe3O4 and gamma-Fe2O3 foams synthesized in air by sol-gel autocombustion

Porous magnetite (Fe3O4) and maghemite (γ-Fe2O3) foams were synthesized by a sol-gel autocombustion method in air atmosphere. Citric acid, ferric nitrate, and ammonia were used as the starting materials. The gels were ignited at a low temperature of 200 °C. Synthetic mechanism of Fe3O4 was studied by coupling mass spectrometry, thermogravimetry, and differential scanning calorimetry (MS-TG-DSC). The phase structures and the phase transformation of the samples were investigated by X-ray diffraction (XRD). Porous morphologies of the Fe3O4 and γ-Fe2O3 foams with micron-size pores were characterized by scanning electron microscopy (SEM). Magnetic properties of the Fe3O4 and γ-Fe2O3 samples were studied by vibration sample magnetometer (VSM) measurements at room temperature, which showed tunable saturation magnetization values and small coercivities. The highest saturation magnetization of the porous Fe3O4 sample is about 90% of its bulk value, implying that the purity of the products is quite good.