Synthesis, Characterization, Photocatalysis, and Varied Properties of TiO2 Cosubstituted with Nitrogen and Fluorine

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• 作者：Nitesh Kumar ; Urmimala Maitra ; Vinay I. Hegde ; Umesh V. Waghmare ; A. Sundaresan ; C. N. R. Rao
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：September 16, 2013
• 年：2013
• 卷：52
• 期：18
• 页码：10512-10519
• 全文大小：486K
• 年卷期：v.52,no.18(September 16, 2013)
• ISSN：1520-510X

文摘

TiO<sub>2sub> (anatase) codoped with nitrogen and fluorine, synthesized by a simple solid state route, using urea and ammonium fluoride as sources of nitrogen and fluorine, respectively, as well as by decomposition of (NH<sub>4sub>)<sub>2sub>TiF<sub>6sub> for comparison, has been characterized by various techniques. XPS analysis shows the composition to be TiO<sub>1.7sub>N<sub>0.18sub>F<sub>0.12sub> for urea-based method (N, F-TiO<sub>2sub>-urea) and TiO<sub>1.9sub>N<sub>0.04sub>F<sub>0.06sub> for complex decomposition method (N, F-TiO<sub>2sub>-complex). Both the materials are defect-free as revealed by photoluminescence spectroscopy. Thus, N, F-TiO<sub>2sub>-urea exhibits smaller defect-induced magnetization compared to the nitrogen-doped sample. Cosubstitution of N and F is accompanied with an enhancement of the absorption of light in the visible region giving rise to yellow color and with a band gap of 2.2 eV in the case of N, F-TiO<sub>2sub>-urea. It exhibits enhanced photocatalytic activity and also significant hydrogen evolution (400 渭mol/g) on interaction with visible light in the absence of any cocatalyst, which is much higher compared to N, F-TiO<sub>2sub>-complex and N-TiO<sub>2sub>. First-principles calculations show significant local distortions on codoping TiO<sub>2sub> with N and F and a lowering of energy by 1.93 eV per N, F pair. With virtual negative and positive charges on nitrogen and fluorine, respectively, the dopants prefer pairwise clustering. Our calculations predict a reduction in the band gap in TiO<sub>2sub> cosubstituted with nitrogen and fluorine. The calculated band structure shows that nitrogen 2p states form a separate subband just above the valence band which is enhanced on incorporation of fluorine. Our calculations also indicate anomalous Born effective charges in N, F-TiO<sub>2sub> and predict enhanced photocatalytic activity on codoping of TiO<sub>2sub> by N and F.