Crystalline structure, surface chemistry and catalytic properties of Fe3+ doped TiO2 sol-gel catalysts for photooxidation of 2,4-dichlorophenoxyacetic acid

Highly active Fe3+ doped TiO2 (xFe-TiO2 where x = 3 or 5 wt%) photocatalysts were synthesized by the sol-gel method and their structures were refined with the Rietveld method. Several important effects of calcination temperature on the crystalline structure, textural features, phase concentration, Fe3+ distribution, optical properties, and photocatalytic activity were determined. When Fe-TiO2 materials were calcined at 400 degrees C, most of Fe3+ were formed alpha-Fe2O3 and some of them were incorporated in the network of TiO2 anatase; as calcination temperature increased to 800 degrees C, alpha-Fe2O3 and FeTiO3 coexisted on the TiO2 rutile phase. High calcination temperature also led to surface area sharply diminishing and the surface oxygen reducibility significantly decreasing. The interatomic distances of Fe-TiO2 catalysts obtained from the method of radial distribution function (RDF) were: Ti...O = 1.93 angstrom (anatase), Fe...O = 2.59 angstrom, Ti...Ti = 3.08 angstrom, Ti...Fe = 3.69 angstrom, Ti...Ti = 3.79 angstrom, Ti...O = 4.83 angstrom (rutile). In the photooxidation of 2,4-dichlorophenoxyacetic acid (2,4-DA), the photocatalytic activity of Fe-TiO2 catalyst increased with increase of Fe3+ content in anatase phase. The 2,4-DA photooxidation followed the first-order kinetic reaction model and favored under acidic condition. Approximately 95% 2,4-DA were photooxidized with the best catalyst 5Fe-TiO2-400 after 120 min of reaction under UV irradiation. TiO2 phase transformation from anatase to rutile and FeTiO3 formation at 800 degrees C negatively impacted on the photocatalytic performance. The catalytic activity of the catalysts correlated well with variations of textural properties, phase concentration, and surface oxygen reducibility that were all controlled by the calcination temperature. (C) 2018 Elsevier B.V. All rights reserved.