Iron-Doped Titania: Synthesis, Structural, Magnetic and Photocatalytic Properties

Ultrafine Fe-doped TiO2 (Fe content of 0, 0.5, 2, 5, 10, and 20 wt. %) was prepared using two-stage TiCl4 and FeCl3(6H2O hydrolysis at final pH ( 3.5. The effect of the Fe ion weight concentration on the phase composition and morphology was investigated using XRD, FTIR, Mossbauer spectroscopy, thermal analysis, and low-temperature nitrogen adsorption. Increasing the content of Fe3+ ions in the range of 0-10 wt. % causes an increase in the amount of the anatase phase from 0 to 85-90 %. The average size of anatase particles decreases from 31 nm for a Fe content of 0.5 wt. % to about 4 nm for a Fe content of 10 wt. %. The material synthesized at an Fe ion concentration of 20 wt. % is amorphous (XRD data) without any magnetically ordered iron-containing phase. The Mossbauer spectra of all Fe-doped TiO2 samples consist of doublets only, with isomer shift values of 0.55-0.57 mm/s corresponding to Fe3+ in a high-spin state in octahedral coordination, so isomorphic substitution of Ti4+ ions for Fe3+ is highly probable. Annealing of Fe-doped TiO2 sample with a maximum doping degree (20 wt. %) at 900 (C leads to the formation of the Fe2TiO5 pseudobrookite phase and the transition of amorphous anatase to monoclinic titania (space group symmetry С12/m1). The BET specific surface area values of Fe-doped titania increase linearly from 70 to 350 m2/g with increasing iron content from 0 to 5 wt. %. Further increase in the iron content does not affect the BET surface area. The growth of oxygen vacancies concentration with increasing Fe3+ content was observed by FTIR that corresponds to the reduction of the rutile lattice constant. The anatase-rutile transition temperature (thermal analysis data) is the highest (about 575 (C) for the material with the maximum Fe ion content. Photocatalytic activity of Fe-doped TiO2 samples in reaction of methylene blue degradation increases with an increase in the Fe content and correlates with the anatase phase relative concentration. The reaction rate increases from about 0.008 to 0.028 min – 1, while the reaction rate for commercial photocatalyst Degussa P25 under the same experimental conditions is about 0.029 min – 1.