Rare-Earth-Modified Titania Nanoparticles: Molecular Insight into Synthesis and Photochemical Properties

A molecular precursor approach to titania (anatase) nanopowders modified with different amounts of rare-earth elements (REEs: Eu, Sm, and Y) was developed using the interaction of REE nitrates with titanium alkoxides by a two-step solvothermal-combustion method. The nature of an emerging intermetallic intermediate was revealed unexpectedly for the applied conditions via a single-crystal study of the isolated bimetallic isopropoxide nitrate complex [Ti2Y((PrO)-Pr-i)(9)(NO3)(2)], a nonoxo-substituted compound. Powders of the final reaction products were characterized by powder X-ray diffraction, scanning electron microscopy-energy-dispersive spectroscopy, Fourier transform infrared, X- ray photoelectron spectroscopy, Raman spectroscopy, and photoluminescence (PL). The addition of REEs stabilized the anatase phase up to ca. 700 degrees C before phase transformation into rutile became evident. The photocatalytic activity of titania modified with Eu3+ and Sm3+ was compared with that of Degussa P25 titania as the control. PL studies indicated the incorporation of Eu and Sm cations into titania (anatase) at lower annealing temperatures (500 degrees C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 degrees C. The efficiency of the modified titania was inferior to the control titania while illuminated within narrow wavelength intervals (445-465 and 510-530 nm), but when subjected to a wide range of visible radiation, the Eu3+- and Sm3+-modified titania outperformed the control, which was attributed both to doping of the band structure of TiO2 with additional energy levels and to the surface chemistry of the REE-modified titania.

Automated summary

A molecular precursor approach was developed for titania nanopowders modified with rare-earth elements. The addition of Eu3+ and Sm3+ stabilized the anatase phase and improved photocatalytic activity under visible light illumination, attributing to doping of the band structure of TiO2 and to the surface chemistry of the REE-modified titania.