Enhancing photoactivity of TiO_2(B)/anatase core-shell nanofibers by selectively doping cerium ions into the TiO_2(B) core

摘要

Cerium ions (Ce~(3+)) can be selectively doped into the TiO2(B) core of TiO2(B)/anatase core-shell nanofi- bers 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 TiO_2(B) core in tunnels (width0.297 nm). The introduction of Ce3+ 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+)/Ce4+ couple (E8(Ce3+/Ce4+)=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 TiO_2(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.