Abstract
Different phases of iron oxide were obtained by hydrothermal treatment of ferric solution at 200°C with the addition of either KOH, ethylenediamine (EDA), or KOH and EDA into the reaction system. As usually observed, the α-Fe2O3 hexagonal plates and hexagonal bipyramids were obtained for reaction with KOH and EDA, respectively. When both KOH and EDA were added into the reaction system, we observed an interesting phase transformation from α-Fe2O3 to Fe3O4 at low-temperature hydrothermal conditions. The phase transformation involves the formation of α-Fe2O3 hexagonal plates, the dissolution of the α-Fe2O3 hexagonal plates, the reduction of Fe3+ to Fe2+, and the nucleation and growth of new Fe3O4 polyhedral particles.
Highlights
The more stable phases in iron oxides are hematite and magnetite
We explore the role of ethylenediamine (EDA or en in ligand form) on the phases of iron oxide in hydrothermal condition
The phase can be identified to be α-Fe2O3 when either KOH or EDA alone was added to the reaction system despite different morphologies
Summary
The more stable phases in iron oxides are hematite and magnetite. Studies about the nano/microstructures of iron oxides and their properties, which are related to the intrinsic structure and crystal shapes, have been intensively engaged, especially for hematite and magnetite. Magnetite has unique electric and magnetic properties because its intrinsic crystal structure allows electrons to be transferred between Fe2+ and Fe3+ in the octahedral sites [15]. Many researches have demonstrated the capability of using chemical syntheses to control particle morphologies of iron oxide by surfactants [16,17,18]. Morphologies like wires [19], rods [20], tubes [21], rings [22], disks [23], cubes [24], spheres [25], hexagonal plates of α-Fe2O3 [26,27], and polyhedral particles of Fe3O4 [28,29] have been synthesized successfully
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