ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012) P 07
X-RAY ABSORPTION AND EMISSION SPECTROSCOPY OF TITANIUM DIOXIDE WITH MODIFIED ANIONIC SUBLATTICE
K. Biernacka1∗, M. Sikora1, Cz. Kapusta1, A. Brudnik2, K. Zakrzewska2, and M. Radecka3
1Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, 30, Mickiewicza Av, 30–059 Krakow, Poland
2Faculty of Electrical Engineering, Automatics, Computer Science and Electronics, AGH University of Science and Technology, 30, Mickiewicza Av, 30–059 Krakow, Poland
3Faculty of Materials Science and Ceramics, AGH University of Science and Technology, 30, Mickiewicza Av, 30–059 Krakow, Poland
Keywords: titanium dioxide, photoelectrolysis, hydrogen, XANES, XES
∗e-mail : biernack@agh.edu.pl
TiO2 based thin films are very promising mate- rials for an efficient conversion of solar energy into hydrogen in the process of water photolysis. Hydro- gen is considered as a prospective energy carrier to replace traditional fossil fuels. TiO2 with modified anionic sublattice is considered for potential appli- cations as photoanode for hydrogen generation due to its reported photocatalytic activity in the visible light [1, 2].
Modification of anionic sublattices presented in this work consists in deviation from stoichiometric composition towards oxygen deficiency and nitrogen doping. Thin films of TiO2−x and TiO2−x:N were deposited by dc pulsed magnetron sputtering under
Figure 1 : HERFD-XANES (upper) and XES (lower) spectra of TiO2−x:N thin films and reference samples (TiO2P25, TiN) at Ti-K-edge and Kβ emission line, re- spectively. Insets show the close-up of the pre-edge and Kβ satellite regions.
optical emission spectroscopy as a function of con-
trollable technological parameter I/I0related to the sputtering rate. The efficiency of solar energy con- version into chemical energy is determined by the intrinsic properties of the photoanode material.
The aim of this work is to study local atomic en- vironment and its changes upon doping of titanium dioxide by N as well as to understand the structural changes in nonstoichiometric TiO2−xcaused by oxy- gen deficiency. HERFD-XANES measurements at the Ti K-edge measurements give direct information on the location of N dopant in the TiO2 structure.
Spectra show a significant change in the pre-edge structure and shift of the edge to lower photon en- ergy upon increasing nitrogen flow [3]. A significant evolution of the Kβ satellite region from valence- to-core Ti Kβ XES measurements is attributed to evolution in the local structure around Ti species and change in the character of electronic structure.
The spin value and valence state have been derived from Kβ main emission lines that were correlated to the energy shift of respective K absorption edge (Fig. 1). The results from synchrotron measure- ments are correlated with XRD and optical mea- surements in order to obtain the full interpretation of the changes in local atomic/ionic structure and their influence on photo-electrical and optical prop- erties.
Acknowledgments: The financial support of the Pol- ish Ministry of Science and Higher Education (2009–
2012) within the project NN515 080 637 is highly ac- knowledged. K.B. has been partly supported by the EU Human Capital Operation Program, Polish Project No.
POKL.04.0101-00-434/08-00.
References
[1] A. Brudnik et al., “Microstructure and optical prop- erties of photoactive TiO2:N thin films,” Vacuum 82 (2008) 936 – 941.
[2] S. Sakthivel et al., “Photocatalytic and photoelec- trochemical properties of nitrogen-doped titanium dioxide,” Chem. Phys. Chem. 4 (2003) 487 – 490.
[3] A. Braun et al., “Nitrogen doping of TiO2 pho- tocatalyst forms a second eg state in the oxygen 1s NEXAFS pre-edge,” J. Phys. Chem. 114 (2010) 516 – 519.
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