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Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO 2 Using DRS, PL, and EPR
Author(s) -
Zhang Zizhong,
Long Jinlin,
Xie Xiuqiang,
Lin Huan,
Zhou Yangen,
Yuan Rusheng,
Dai Wenxin,
Ding Zhengxin,
Wang Xuxu,
Fu Xianzhi
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100991
Subject(s) - electron paramagnetic resonance , photoluminescence , dopant , doping , photochemistry , materials science , absorption (acoustics) , absorption spectroscopy , visible spectrum , absorption band , analytical chemistry (journal) , irradiation , spectroscopy , diffuse reflectance infrared fourier transform , chemistry , photocatalysis , optoelectronics , nuclear magnetic resonance , optics , catalysis , physics , nuclear physics , composite material , biochemistry , chromatography , quantum mechanics
The electronic structure and photoactivation process in N‐doped TiO 2 is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO 2 catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti 3+ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO 2 , the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N s . ), oxygen vacancies with one electron (V o . ), and Ti 3+ ions are produced with light irradiation and the intensity of N s . species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO 2 corresponding to the main absorption band at 410 nm of N‐doped TiO 2 , but oxygen vacancies and Ti 3+ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO 2 is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N s . species but they stabilize the active nitrogen species N s − .