Detailed Characterization of Surface Ln-Doped Anatase TiO 2 Nanoparticles by Hydrothermal Treatment for Photocatalysis a
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Detailed Characterization of Surface Ln-Doped Anatase TiO2 Nanoparticles by Hydrothermal Treatment for Photocatalysis and Gas Sensing Applications Rezwanur Rahman, Sean T. Anderson, Sonal Dey, Robert A. Mayanovic. Department of Physics, Astronomy, and Materials Science, Missouri State University, 901 South National Avenue, Springfield, MO 65897 ABSTRACT Nanostructured anatase TiO2 is a promising material for gas sensing and photocatalysis. In order to modify its catalytic properties, the lanthanide (Ln) ions Eu3+, Gd3+, Nd3+ and Yb3+ were precipitated on the surface of TiO2 nanoparticles (NPs) by hydrothermal treatment. Results from Raman spectroscopy and X-ray diffraction (XRD) measurements show that the anatase structure of the TiO2 nanoparticles was preserved after hydrothermal treatment. SEM and TEM show a heterogeneous distribution in size and a nanocrystallite morphology of the TiO2 NPs (~ 14 nm in size) and EDX confirmed the presence of the Ln-ion surface doping after hydrothermal treatment. An increase in photoluminescence (PL) was observed for the Lnsurface-doped TiO2 NPs when measurements were made in forming gas (5% H2 + 95% Ar) at 520 °C. In contrast, the PL measurements made at room temperature did not show any noticeable difference in forming gas or in ambient air. Our temperature-dependent PL results obtained in different gas environments are consistent with modification of oxygen-vacancies and holedefects due to a combination of hydrothermal treatment and surface Ln-doping. INTRODUCTION TiO2 nanostructured materials are being investigated for a number of applications, including photocatalysis, gas sensing, solar cell devices, antibacterial agents, and self-cleaning coatings [1]. Photocatalytic activity, as well as other physical and chemical properties, are enhanced by the higher surface area to volume ratio of the nanocrystalline material. Of the common TiO2 phases, anatase is the most photocatalytic, having highly suitable energy band vs normal hydrogen electrode (NHE) potential characteristics [1]. However, anatase TiO2 is an inefficient material, absorbing primarily UV light due to its wide bandgap energy (3.2 eV) [2]. Doping with lanthanide (Ln) ions has been found to be advantageous for enhancing the optical and catalytic properties of TiO2 nanoparticles (NPs) [3], including enhancing the photoreceptivity to visible light [4]. However, incorporation of amounts greater than doping levels of Ln ions results in substantial disruption of the crystalline phase of anatase TiO2 NPs. Hydrothermal Ln-incorporated overgrowth of TiO2 NPs and nanostructures may result in less disruption of the original atomic structure of the material. In this work, we have fabricated TiO2LnxTi1-xO2 core-shell nanoparticles (Ln = Nd, Eu, Gd, Yb) using hydrothermal methods. The NPs were characterized using in situ photoluminescence (PL) spectroscopy under different gas atmospheres and to high temperatures. Because greater PL intensity in indirect bandgap semiconductors has been found to correspond to increased photocatalyti
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