Abstract
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(iPrO)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 °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 °C), but an exclusion to the surface occurred when the annealing temperature was increased to 700 °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.
Highlights
Titania (TiO2) is one of the most investigated semiconductor nanomaterials, primarily because of its photocatalytic activity, chemical stability, low toxicity, and facile synthesis.[1,2] The discovery of its ability to split water in the 1970s by Fujishima and Honda[3] encouraged intensive research for applications in the photocatalytic degradation of organic pollutants[4] and hydrogen production from water.[5]
The band gap of anatase is ca. 3.2 eV, and UV radiation is required to promote an electron from the valence band (VB) to the conduction band (CB)
This compound absorbs in the visible spectrum and can transfer an excited electron into the CB of titania.[7−9] This is used in dye-sensitized solar cells.[10]
Summary
Titania (TiO2) is one of the most investigated semiconductor nanomaterials, primarily because of its photocatalytic activity, chemical stability, low toxicity, and facile synthesis.[1,2] The discovery of its ability to split water in the 1970s by Fujishima and Honda[3] encouraged intensive research for applications in the photocatalytic degradation of organic pollutants[4] and hydrogen production from water.[5]. 3.2 eV, and UV radiation is required to promote an electron from the valence band (VB) to the conduction band (CB). An organic or inorganic compound is attached to the surface of titania. This compound absorbs in the visible spectrum and can transfer an excited electron into the CB of titania.[7−9] This is used in dye-sensitized solar cells.[10] Doping of metals or nonmetals into the titania lattice may generate intermediate energy levels between the VBTiO2 and CBTiO2 and redshift the absorption spectrum into the visible region. For substitutional doping of titania, it is a requirement that the cation that replaces Ti has a similar ionic radius
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