Characterization of Iron Oxide and Doped Iron-Oxide Nanocomposites for Photocatalytic Degradation of Organic Compounds

The industrial wastewater containing the various dyes is responsible for water pollution, due to their carcinogenic properties. Iron oxides are a kind of natural minerals and photocatalysts, naturally existing in the earth’s crust with huge content. However, the secondary iron oxides such as hematite (α-Fe2O3), goethite (α-FeOOH), maghemite (γ-Fe2O3), ferrihydrite (Fe5HO8·4H2O), and magnetite (Fe3O4) were found in aqueous streams as suspended materials with a significant amount. Hematite and maghemite are two common iron oxides to show semiconductor properties with a narrow band gap of 2.0–2.3 eV and presumed to be photoactive under solar irradiation as photocatalysts or photosensitizers. Hematite is of particular fundamental interest as it transforms from an antiferromagnetic (AF) to a weakly ferromagnetic (WF) state at about 265 K, known as Morin transition (TM). In this chapter, we compare the photocatalytic ability of iron oxides obtained from Japanese municipal waste slag (MWS) to the ones obtained from simple iron silicate and alumina-doped iron silicate glass-ceramics prepared by chemicals. We aim to clarify the relationship between the structure and photocatalytic performance of the iron oxides under different preparation and reaction conditions. For the main structural characterization, we have chosen 57Fe Mössbauer spectroscopy, X-ray powder diffraction (XRD), Fourier transform infrared spectra (FTIR), transmission electron microscope (TEM), UV–vis diffuse reflectance spectra (DRS), and impedance spectroscopy (IS).