Investigations of TiO 2 Nanoparticles Surface-Doped with Eu in Aqueous Fluids to High P-T Conditions
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Investigations of TiO2 Nanoparticles Surface-Doped with Eu in Aqueous Fluids to High PT Conditions Phillip A. McCart, Laurel Farris, Robert A. Mayanovic, Hao Yan. Department of Physics, Astronomy and Materials Science, Missouri State University, Springfield, MO 65897, USA ABSTRACT A hydrothermal reactor has been used for surface doping of anatase TiO2 nanoparticles (~ 13 nm across) with Eu3+ ions in aqueous fluids to 370 ˚C and ~20 MPa. XRD and Raman measurements made both before and after hydrothermal treatment with Eu show that the anatase structure of the TiO2 nanoparticles (NPs) is preserved. SEM imaging, combined with XRD indicates that the size and overall morphology of the TiO2 nanoparticles is preserved subsequent to hydrothermal treatment in the presence of Eu. The photoluminescence occurring in the 400 to ~700 nm range of the (as prepared) Eu surface-doped TiO2 NPs are red-shifted by ~ 50 nm and reduced in intensity relative to the photoluminescence of TiO2 NPs. INTRODUCTION Materials suitable for photocatalysis show promise for applications such as conversion of sunlight into renewable energy and for decomposition of organic waste. Previous work has demonstrated that UV-irradiated TiO2 has potential for use in photocatalysis, anticorrosion metal coating, and indoor pollutant self-cleaning [1, 2]. Because of the much greater surface area to volume ratio, many of the physical and chemical properties, including catalytic activity, of TiO2 nanoparticles (NPs) is enhanced on the nanoscale in comparison to that of bulk TiO2. However, there are two issues that prevent widespread use of TiO2 for photocatalysis: 1) Low catalytic efficiency, and 2) absorption by the material during photocatalytic reactions in the near UV region of the solar spectrum (i.e., absorption of less than 5% of the total) due to its wide energy band gap. Bulk doping with rare earth element (REE) ions has been shown to improve the photocatalytic efficiency of TiO2 NPs [2-5]. However, because of the considerably greater ionic radii of the REE, conversion of structural phase from anatase to rutile, where the rutile phase does not have as suitable properties for photocatalysis, of the TiO2 NPs is common [2-4]. Our previous studies show that precipitation (i.e. chemisorption) of transition metal ions onto the surface of Fe3O4 NPs can be accomplished in aqueous fluids at high temperatures and pressures [6,7]. The objective of our research is to cause surface-doping with Eu3+ under hydrothermal conditions and to determine how localized REE doping of this nature affects the structural, vibrational and optical (i.e., photoluminescence) characteristics of TiO2 NPs. EXPERIMENT Hydrothermal Treatment of TiO2 Nanoparticles The TiO2 nanoparticles were treated under hydrothermal conditions in order to provide doping of the nanoparticle surface with Eu3+ ions. The solution was prepared using HPLC water.
The HPLC water was deoxygenated for approximately15 minutes with percolating N2 gas. TiO2 NPs were loaded in our hydrothermal reactor along with 0.02 m E
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