Add time:07/11/2019         Source:sciencedirect.com

Iron/titanium oxide nanoparticles with the initial molar ratio [FeIII/(FeIII + TiIV)] ≤ 0.50 were hydrothermally synthesized at 180 °C in an aqueous ammonia solution (pH ≅ 9.6). The titanium and iron precursors were TiCl4 and FeCl3, respectively. The amount of doped iron strongly affected microstructural properties as well as the degree of dispersion of iron in the Fe-Ti-O system. Anatase was the dominant phase in the iron/titanium oxide samples with [Fe/(Fe + Ti)] ≤ 0.25. The average crystallite size of the anatase phase in iron/titanium oxide samples decreased with the increase of iron doping. The results of precise unit-cell parameters measurement, obtained using Rietveld refinements of the powder diffraction patterns with added silicon indicated that the solid solubility limit of FeIII inside the anatase lattice was ∼8 mol%. The appearance of hematite (α-Fe2O3) sextet in the Mössbauer spectrum in the sample doped with 10 mol% of iron confirmed that the solid solubility limit of FeIII in the TiO2 lattice has been overreached. The relative concentrations of α-Fe2O3 in the samples increased with FeIII doping up to 15 mol% of added FeIII and then, quite unexpectedly, the XRD 104 line and Mössbauer sextet of α-Fe2O3 completely disappeared at 0.20 < [Fe/(Fe + Ti)] < 0.30. The EELS (electron energy-loss spectroscopy) analysis confirmed that the sample doped with 30 mol% of FeIII contained no hematite. The FeIII in the samples at 0.20 < [Fe/(Fe + Ti)] < 0.30 segregated not in the form of hematite, but in the form of iron/titanium oxide phase that was poorly crystallized or even amorphous. The α-Fe2O3 again appeared at [Fe/(Fe + Ti)] = 0.50. The diffuse reflectance spectra were used for band gap energy calculations. The band gap energy of the undoped TiO2 sample was 3.1 eV, whereas the band gap energy of Fe-Ti-O samples doped with up to 10% showed a blue shift (3.2 eV). The significant red shift (from 3.2 to 2.4 eV) was observed in the samples with higher iron content (from 10 to 50 mol%).

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