The effect of iron ions on the anatase–rutile phase transformation of titania (TiO2) in mica–titania pigments

Rutile TiO2-coated mica–titania pigments were prepared by hydrolysis of titanium tetrachloride in the presence of Fe3+. After calcination at 700 °C for 2 h, TiO2 nanolayers in rutile phase were formed on the mica surfaces. The morphology and the anatase–rutile transformation were probed by scanning electronic microscopy (SEM) and X-ray diffraction (XRD) respectively. SEM micrographs show that the dopants enhance the growth of particles of TiO2 thin layers. The change of lattice parameters confirms that Fe3+ enter anatase structure and affect the anatase–rutile transformation. For the iron loading regime studied here, the anatase–rutile transformation is inhibited at low dopant levels with respect to undoped titania. While the anatase–rutile transformation is promoted as iron loading is increased. Moreover, synthesized pH value also has a pronounced effect on the anatase–rutile transformation and a highly acidic environment favors the formation of rutile.

► Rutile TiO2-coated mica–titania pigments were prepared by Fe3+ doping.
► The anatase–rutile transformation is inhibited at low dopant levels.
►  The inhibition becomes less pronounced as iron loading is increased.
► A highly acidic environment favors the formation of rutile.