Photoactivity of brookite–rutile TiO2 nanocrystalline mixtures obtained by heat treatment of hydrothermally prepared brookite

Pure brookite phase was prepared by hydrothermal synthesis of titanium peroxo-complex in the presence of glycolic acid at 220 °C. The structure of prepared brookite samples was determined by X-ray powder diffraction (XRD) and selected area electron diffraction (SAED). The prepared brookite was studied by in situ high temperature XRD in air. The morphology and microstructure characteristics were also obtained by transmission electron microscopy (TEM). The nitrogen adsorption–desorption was used for determination of surface area (BET) and porosity. The method of UV–vis diffuse reflectance spectroscopy was employed to estimate band-gap energies of prepared brookite. The photocatalytic activity of the prepared titania samples were assessed by photocatalytic decomposition of Orange II dye in an aqueous slurry under UV irradiation at 365 nm wavelength. The photocatalytic activity of the prepared sample brookite heated to 800 °C in air was higher than nanocrystalline unheated brookite powder.

► Brookite–rutile transformation begin at 825 °C.
► With increasing annealing temperature the specific surface area decreased and the mesoporous character of heated samples increased.
► Origin rutile phase has a negative effect on the photocatalytic activity.