Synthesis, Properties, and Applications of Iron Oxides: Versatility and Challenges

Iron (III) oxide is a compound that appears in at least four different polymorphs: α-Fe2O3, β-Fe2O3, γ-Fe2O3, and e-Fe2O3. However, Fe3+ ions are also present in another form of iron oxide: Fe3O4, which is an iron crystal structure with both Fe2+ and Fe3+ ions. And in its turn, Fe2+ ions are also present in the FeO form of iron oxide. Each of these six different structures presents distinctive physical properties and, therefore, diverse applications. The different crystalline forms of iron oxide have found fertile ground in the field of nanotechnology, and therefore, became popular among researchers who have proven a wide variety of biomedicine, electronics, construction, environmental remediation, and energy harvesting applications. In this regard, the main technological challenge is related to control of its physical characteristics such as morphology, size distribution, dispersion, crystallinity, structural defects, porosity, active area, as well as impurities. All of these influence the physical and optical properties of the synthesized material and will determine its field of application. As such, the synthesized material characteristics depend on the synthesis method employed. Thereby, in this chapter, we will cover the main characteristics of iron oxides with a focus on preparation processes, physicochemical properties, and their relationship with their main applications.