Structural and photocatalytic properties of iron- and europium-doped TiO2 nanoparticles obtained under hydrothermal conditions
Introduction
Titanium dioxide (titania) is a cheap, nontoxic and highly efficient photocatalyst being extensively applied for the degradation of organic pollutants, air purification, water splitting, and reduction of nitrogen to ammonia [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. However, only a small UV fraction of solar light (<5%) can be utilised because of large band gap (∼3 eV) of titanium dioxide semiconductor structure. Recently, a considerable number of studies were devoted to the development of efficient visible light sensitive photocatalysts and to photocatalytic properties improvement [11], [12], [13], [14], [15]. Transition metal selective doping is one of the common approaches to extend the spectral response of titania to the visible light region. In particular the iron doping was found to increase the photocatalytic activity up to 2.5 times [12]. Investigation on chloroform photodegradation revealed a significant photocatalytic reactivity increase over nanocrystalline TiO2 codoped with Fe3+ and Eu3+ by sol–gel method, as compared with undoped or monodoped TiO2 nanoparticles [16].
It is already established that material properties depend strongly on precursors and synthesis methods in correlation with the thermodynamic process parameters. For the synthesis of nanoparticle systems the hydrothermal method was intensively utilised in the last decade [17], [18], [19], [20], [21]. However, no reports on the hydrothermal synthesis of iron- and europium-codoped TiO2 materials have been published, by our knowledge.
It is the aim of this work to present the hydrothermal synthesis of iron- and europium-doped and -codoped TiO2 nanoparticle systems, their microstructure, morphology and catalytic properties in the photodegradation of phenol, in both UV and visible light region.
Section snippets
Hydrothermal synthesis
Fe3+- and Eu3+-doped and -codoped nanocrystalline titania samples have been synthesized by a hydrothermal route, starting with titanium (IV), iron (III) and europium (III) chlorides in solution. Titanium tetrachloride has been obtained by air oxidation under vigorous stirring (30 h) from a 15% titanium trichloride in hydrochloric acid solution. Europium trichloride has been prepared by dissolving the corresponding europium oxide amount in 2N hydrochloric acid. A 25% ammonium hydroxide solution
X-ray diffraction
Primary structural information was given by XRD patterns of the hydrothermal samples (Fig. 1a–d).
All spectra display the characteristic patterns of TiO2 in tetragonal anatase phase (the anatase characteristic lines are indexed in Fig. 1a). No relevant differentiation can be observed by changing the doping element (Fig. 1b–d) except for small line intensity variations and a slight increase of diffraction line widths from undoped (Fig. 1a) to codoped (Fig. 1d) samples. Rietveld refinement of XRD
Conclusions
Iron- and europium-doped TiO2 nanoparticles were obtained by a hydrothermal route, at mild temperature and pressure (∼200 °C and ∼15 atm, for 1 h). Rietveld refinements of the XRD patterns reveal the exclusive presence of iron- and europium-doped anatase phase in hydrothermally synthesized samples; the particle mean size was less than 15 nm and the morphology was found to depend on doping element. EXAFS analysis strongly support that both Fe3+ and Eu3+ ions enter the TiO2 lattice, by substituting
Acknowledgements
This work was supported by the Romanian Ministry of Education and Research through Contract CEEX-Matnantech no. 23/2005. We gratefully acknowledge the valuable assistance of Dr. Edmund Welter and Dr. Dariusz Zajac (HASYLAB) during the EXAFS experiments, as well as the whole scientific support of Prof. Eberhardt Burkel and Dr. Radu Nicula (University of Rostock).
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