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Synthesis and microstructural properties of Fe-TiO2 nanocrystalline particles obtained by the modified sol-gel method

A series of iron/titanium oxide nanocrystalline particles with the Fe/Ti molar ratio up to 0.15 was synthesized by the modified sol-gel procedure. Ti(IV)-isopropoxide and anhydrous Fe(II)-acetate were used as precursors of titanium and iron. The precursors were mixed and subsequently hydrolyzed with water molecules generated “in situ” by an esterification reaction between acetic acid and ethanol. FT-IR spectra showed that acetate groups were chemically bound to the metal cation. The Raman spectra of as-synthesized samples exhibited relative strong and sharp band at 2937 cm-1 associated with bands at 3022 and 2985 cm-1, as a result of stretching vibrations of CH2 and CH3 groups of unhydrolyzed organic precursor. Thermogravimetric analysis (TGA) showed that the weight loss was accelerated and completed at a lower temperature as the relative concentration of iron in Fe-TiO2 samples increased. Thermal analysis proved the evaporation of solvents and thermal degradation of loosely bound organic molecules at a temperature up to 260oC. The strong exothermic peak in DTA curve between 300-450oC was due to the amorphous-anatase transition related to the thermal degradation of strongly bound organic molecules, condensation of unhydrolyzed –OR groups, sintering and growth of particles and a rearrangement of newly formed chemical bonds. With the addition of iron this exothermic peak shifted to lower temperatures, became more asymmetric and was completed in a narrower temperature range. As-synthesized samples were amorphous for XRD independently of the relative amount of doped iron. The undoped samples and samples doped with 1 mol% of iron, thermally treated up to 500oC, contained anatase as the dominant phase and rutile as the minor phase. The samples having 15 mol% of iron, thermally treated at the same temperature, contained anatase (major phase), rutile (minor phase) and a very small amount of an unidentified phase. The crystallite size of the dominant phase in samples was estimated from the XRD line broadening using the Scherrer formula. Scanning electron micrographs of undoped samples heated at 500oC showed large irregular aggregates of nanocrystalline TiO2 particles with a relatively flat surface. On the contrary, the samples doped with 5 and 15 mol% of iron and treated at the same temperature exhibited a non-uniform sponge-like surface with rather uniformly distributed micrometer holes. Also, much smaller aggregates growing up from the surface of big ones were visible. The present result showed a remarkable influence of iron on the morphology of iron-doped TiO2 samples. In addition, XRD results differed from many similar investigations that considered only the presence of hematite or pseudobrookite as segregated iron phases in iron-doped TiO2 powder samples.

Fe-TiO2; sol-gel

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