Abstract:
A new synthesis route for producing nanosized crystallites of acicular goethite particles using ferric nitrate, hydrazine sulphate and sodium hydroxide is reported. The process steps essentially consist of a four-step procedure: (i) partial reduction of Fe(III) to Fe(II) due to the addition of hydrazine sulphate to ferric nitrate solution, (ii) formation of ferrihydrite primary particles, (iii) their transformation to goethite, and (iv) the growth of the goethite nuclei. X-ray diffraction, transmission electron microscopy and infrared spectroscopy data have been used to determine the phase formation under different pH and temperature conditions. Depending on the pH of precipitation ferrihydrite (pH 2-5), goethite (pH 7) or a mixture of goethite and magnetite (pH 9-12) was obtained when precipitation was carried out in the presence of hydrazine sulphate whereas in its absence under similar conditions only ferrihydrite was formed up to a pH of 9 and at pH 12 a mixture of ferrihydrite and goethite was observed. Addition of hydrazine sulphate reduced the pH formation of goethite. Precipitation was also carried out by maintaining temperature in the range of 300-353 K at a pH of 3. The results show that uniform goethite particles of 200-400 nm length with a high axial ratio of 10, can be obtained at a pH of 7 at room temperature and pure goethite can also be obtained at 353 K at a pH of 3. (C) 2009 Elsevier B.V. All rights reserved.