Chemistry and Physics of Materials Unit, New Chemistry Unit, Theoretical Sciences Unit, and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research , Jakkur P.O., Bangalore-560064, India.
Inorg Chem. 2013 Sep 16;52(18):10512-9. doi: 10.1021/ic401426q. Epub 2013 Sep 5.
TiO2 (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 (NH4)2TiF6 for comparison, has been characterized by various techniques. XPS analysis shows the composition to be TiO1.7N0.18F0.12 for urea-based method (N, F-TiO2-urea) and TiO1.9N0.04F0.06 for complex decomposition method (N, F-TiO2-complex). Both the materials are defect-free as revealed by photoluminescence spectroscopy. Thus, N, F-TiO2-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-TiO2-urea. It exhibits enhanced photocatalytic activity and also significant hydrogen evolution (400 μmol/g) on interaction with visible light in the absence of any cocatalyst, which is much higher compared to N, F-TiO2-complex and N-TiO2. First-principles calculations show significant local distortions on codoping TiO2 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 TiO2 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-TiO2 and predict enhanced photocatalytic activity on codoping of TiO2 by N and F.
采用简单的固态法，分别以尿素和氟化铵为氮源和氟源，以及（NH4）2TiF6 分解作为对比，合成了掺氮掺氟锐钛矿 TiO2（用尿素和氟化铵分别作为氮源和氟源，合成的掺氮掺氟 TiO2 分别记为 N，F-TiO2-urea 和 N，F-TiO2-complex）。通过各种技术对其进行了表征。XPS 分析表明，尿素基法（N，F-TiO2-urea）的组成为 TiO1.7N0.18F0.12，而复杂分解法（N，F-TiO2-complex）的组成为 TiO1.9N0.04F0.06。光致发光光谱表明两种材料均无缺陷。因此，与氮掺杂样品相比，N，F-TiO2-urea 表现出较小的缺陷诱导磁化。N 和 F 的共取代伴随着可见光吸收的增强，导致黄色，并在 N，F-TiO2-urea 的情况下产生约 2.2 eV 的带隙。在没有任何助催化剂的情况下，它在可见光照射下表现出增强的光催化活性和显著的析氢（400 μmol/g），与 N，F-TiO2-complex 和 N-TiO2 相比，这要高得多。第一性原理计算表明，在 TiO2 中掺 N 和 F 会导致局部显著变形，每对 N，F 会使能量降低 1.93 eV。氮和氟分别带有虚拟正负电荷，掺杂剂倾向于成对聚集。我们的计算预测 TiO2 共掺氮和氟会导致带隙减小。计算的能带结构表明，氮 2p 态在价带上方形成单独的子带，而掺入氟后会增强。我们的计算还表明，N，F-TiO2 中的反常 Born 有效电荷，并预测共掺杂 TiO2 中的氮和氟会增强光催化活性。
