Regularities of formation of iron(III) nanocrystalline oxides and oxyhydroxides during oxidation of iron(II) compounds in an alkaline medium |
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Authors: | V V Popov A I Gorbunov |
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Institution: | 1.Moscow Engineering Physics Institute (State University),Moscow,Russia;2.State Research Institute of Chemistry and Technology of Organoelement Compounds,Moscow,Russia |
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Abstract: | Regularities of formation of nanocrystalline iron(III) oxides and oxyhydroxides via oxidation of iron(II) compounds in an
alkaline pH range (pH ≥ 12) were studied using pH and E
h
measurements, chemical analysis, electron microscopy, and X-ray diffraction. When the molar ratio OH−]/FeII] ∼ 2 (pH ∼ 12–12.5), the oxidation process yields cube-shaped magnetite Fe3O4 particles. An excess of an alkaline agent with an overstoichiometric concentration equal to or higher than 0.5 mol/L (pH
≥ 13.5) induces the formation of anisotropic particles of nanocrystalline goethite α-FeOOH over the entire range of the synthesis
parameters studied. Reaction products (Fe3O4 and/or α-FeOOH) are formed immediately as the initial Fe(OH)2 starts oxidizing by the dissolution-oxidation-precipitation mechanism near the surface of Fe(OH)2 precursor particles. Carbonate ions considerably change the structure and shape of newly formed α-FeOOH particles. |
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