College of Chemistry, Chemical and Environmental Engineering, Laboratory of Fiber Materials and Modern Textile, Qingdao University, Qingdao 266071, P.R. China.
Chemistry. 2013 Apr 15;19(16):5113-9. doi: 10.1002/chem.201202719. Epub 2013 Feb 18.
Cerium ions (Ce(3+)) can be selectively doped into the TiO2(B) core of TiO2(B)/anatase core-shell nanofibers by means of a simple one-pot hydrothermal treatment of a starting material of hydrogen trititanate (H2Ti3O7) nanofibers. These Ce(3+) ions (≈0.202 nm) are located on the (110) lattice planes of the TiO2(B) core in tunnels (width≈0.297 nm). The introduction of Ce(3+) ions reduces the defects of the TiO2(B) core by inhibiting the faster growth of (110) lattice planes. More importantly, the redox potential of the Ce(3+)/Ce(4+) couple (E°(Ce(3+)/Ce(4+))=1.715 V versus the normal hydrogen electrode) is more negative than the valence band of TiO2(B). Therefore, once the Ce(3+)-doped nanofibers are irradiated by UV light, the doped Ce(3+) ions--in close vicinity to the interface between the TiO2(B) core and anatase nanoshell--can efficiently trap the photogenerated holes. This facilitates the migration of holes from the anatase shell and leaves more photogenerated electrons in the anatase nanoshell, which results in a highly efficient separation of photogenerated charges in the anatase nanoshell. Hence, this enhanced charge-separation mechanism accelerates dye degradation and alcohol oxidation processes. The one-pot treatment doping strategy is also used to selectively dope other metal ions with variable oxidation states such as Co(2+/3+) and Cu(+/2+) ions. The doping substantially improves the photocatalytic activity of the mixed-phase nanofibers. In contrast, the doping of ions with an invariable oxidation state, such as Zn(2+), Ca(2+), or Mg(2+), does not enhance the photoactivity of the mixed-phase nanofibers as the ions could not trap the photogenerated holes.
铈离子（Ce(3+)）可以通过简单的一步水热处理氢钛酸（H2Ti3O7）纳米纤维的起始材料，选择性地掺杂到 TiO2(B)/锐钛矿核壳纳米纤维的 TiO2(B)核中。这些 Ce(3+)离子（≈0.202nm）位于 TiO2(B)核的（110）晶格平面的隧道中（宽度≈0.297nm）。Ce(3+)离子的引入通过抑制（110）晶格平面的更快生长，减少了 TiO2(B)核的缺陷。更重要的是，Ce(3+)/Ce(4+) 电对的氧化还原电位（E°(Ce(3+)/Ce(4+))=1.715V 相对于标准氢电极）比 TiO2(B)的价带更负。因此，一旦 Ce(3+）掺杂的纳米纤维受到紫外光照射，掺杂的 Ce(3+)离子——在 TiO2(B)核和锐钛矿纳米壳之间的界面附近——可以有效地捕获光生空穴。这促进了空穴从锐钛矿壳的迁移，并使更多的光生电子留在锐钛矿纳米壳中，从而导致锐钛矿纳米壳中光生电荷的高效分离。因此，这种增强的电荷分离机制加速了染料降解和醇氧化过程。一锅处理掺杂策略也用于选择性地掺杂其他具有可变氧化态的金属离子，如 Co(2+/3+)和 Cu(+/2+)离子。掺杂显著提高了混合相纳米纤维的光催化活性。相比之下，掺杂具有不变氧化态的离子，如 Zn(2+)、Ca(2+)或 Mg(2+)，不会增强混合相纳米纤维的光活性，因为这些离子无法捕获光生空穴。
