Preparation and photovoltaic properties of N-doped TiO 2 nanocrystals in vacuum
- PDF / 442,706 Bytes
- 7 Pages / 584.957 x 782.986 pts Page_size
- 74 Downloads / 128 Views
Fang Lei School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
Jing-Tai Zhao Key Laboratory of Transparent Opto-Functional Inorganic Materials of Chinese Academy of Science, Shanghai Institute of Ceramics, Shanghai 200050, China
Ying Shi and Jian-Jun Xie School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China (Received 10 April 2012; accepted 24 October 2012)
This work presents the preparation and characterization of N-doped TiO2 nanocrystals obtained by a solid-state reaction in vacuum with urea as the nitrogen source. The particle sizes of the products are smaller than 20 nm from the x-ray powder diffraction patterns and the transmission electron microscopy images. Different from the reported samples obtained in air or under dry N2 or NH3 gas flow, the doped nitrogen exists mainly as absorbed NOx groups but as smaller incorporated species in the nanocrystals, which is supported by the results from x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Dependent on the nitrogen amount, the surface photovoltage (SPV) response reaches the maximum at the mediate molar ratio of 5:4 (urea to TiO2), which can be explained that proper nitrogen concentration can enhance the separation of the photogenerated carriers to improve the SPV intensity, but excess nitrogen can spread the impurity energy levels to narrow energy gaps, which reinforces the combination of the photogenerated electrons and holes and then decreases the SPV signal. The corresponding detailed discussion is also reported.
I. INTRODUCTION
In recent years, semiconductor-based photocatalysis has attracted extensive interest for basic and applied chemical utilization of solar energy.1–7 One of the most commonly used materials is anatase.8–10 But suffering from its large band gap of 3.2 eV, pure anatase has to work in ultraviolet (UV) range and only use about 3% of solar radiation.6 Therefore, it is important to develop novel anatase-based materials with appropriate band gap fit for the visible spectral region to realize visible light photocatalysis. Since Asahi et al.7 reported N-doped anatase with high reactivity under visible light in 2001, the origin of its visible light photocatalysis was explored by numerous theoretical and experimental researches.6,11–14 Variable nitrogen species such as O–Ti–N, Ti–NH2, N–C, and NOx groups were assumed according to the results from x-ray photoelectron spectroscopy (XPS), nuclear magnetic a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.371 468
J. Mater. Res., Vol. 28, No. 3, Feb 14, 2013
http://journals.cambridge.org
Downloaded: 12 Mar 2015
resonance, and electron paramagnetic resonance measurements,6,15–19 while the influences of nano-/microarchitecture were also discussed.20–22 The theoretical calculations suggested that the narrowed band gap was caused by mixing N 2p states with O 2p bands.6,23 Furthermore, Li et al.24
Data Loading...
