Photocatalytic Hydrogen Evolution Activity of Anatase-Brookite Nanoparticles Modified with Rare Earth Metals (Gd, Lu, Tm, Tb, Pr)

Rare earth elements (Gd, Lu, Tm, Tb, Pr) modification effects on two-phased TiO2 (anatase-brookite) were analyzed. The powders were synthesized by a one-step hydrothermal method. The phase composition, crystalline size, and shape of the samples were studied by X-ray diffractometry, transmission and scanning electron microscopies, and energy-dispersive X-ray spectroscopy. The decrease of the crystallite size and increase of the lattice strain due to the modification were confirmed by the Scherrer, modified Scherrer, Williamson-Hall, Size-strain plot (SSP), and Halder-Wagner methods. The textural characteristics of the samples were determined from N2 adsorption-desorption isotherms using the methods of Brunauer–Emmet–Teller and Barret–Joiner–Halenda and revealed their mesoporous structure. UV-Vis diffuse reflectance spectra of the modified samples showed a blue shift compared to the unmodified sample. The values of band gap energy of the modified powders increased due to a phenomenon of quantum confinement or size quantization. The modification with rare earth elements improved the photocatalytic activity of the anatase-brookite composite in the hydrogen evolution reaction, which was ascribed to physico-chemical properties.