Enhancing Photoactivity of TiO₂(B)/Anatase Core–Shell Nanofibers by Selectively Doping Cerium Ions into the TiO₂(B) Core

Abstract

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.

Enhanced photodynamic therapy of mixed phase TiO2(B)/anatase nanofibers for killing of HeLa cells

“…These diffraction patterns reveal that both mixed-phase anatase and TiO 2 (B) are not in a balanced volume ratio, as T(B) is always the precursor and has partially converted into anatase. In our previous study [13][14][15], we found that the aggregation of anatase and TiO 2 (B) phases in T(AB)_T and T(AB)_H samples are not random, but rather the materials are annealed together with a well-matched phase interface. The phase interface allows photogenerated electrons and holes to readily migrate across the interfaces, which can reduce the recombination of the photogenerated charges and thus improve the photoactivity in reactions [13,14].…”

“…The bandgaps of anatase and TiO 2 (B) phase obtained are ~3.19 and ~3.05 eV, respectively. In our previous study, the conduction band (CB) and valence band (VB) edge potentials of TiO 2 (B) nanofibers were located at -0.33 and 2.72 eV [15]. The corresponding edge potentials of anatase nanofibers were located at -0.38 and 2.80 eV, respectively.…”

“…On the other hand, the diffraction peaks from both anatase and TiO 2 (B) phases were also observed in the patterns of samples T(AB)_T and T(AB)_H, which reveal the mixed crystal phase in these two fibers. The crystal phase ratio between TiO 2 (B) and anatase was calculated from the intensity ratio (I 33.4°/ I 37.8°) of the peak at 33.4° and the peak at 37.8° [13][14][15], which are characteristic reflections from the (3 -11) plane of TiO 2 (B) and the (004) plane of anatase, respectively. The anatase fractions in T(AB)_T and T(AB)_H were 33% and 35%.…”

“…For instance, commercial P25 (Degussa), which is composed of 20% rutile and 80% anatase, has been proven to be an exceptionally good photocatalyst for degradation of organic pollutants. Similarly, the mixed phase anatase/TiO 2 (B) nanofibers have shown much better photoactivity for organic pollutant degradation than pure anatase or TiO 2 (B) phases [13][14][15]. The principal reason for the high photoactivity of the mixed phase TiO 2 is ascribed to the efficient interfacial charge transfer between the different phases, which can reduce the recombination of the photogenerated electrons and holes and thus produce more ROS.…”

Atomic Mechanism of Predictable Phase Transition in Dual‐Phase H2Ti3O7/TiO2 (B) Nanofiber: An In Situ Heating TEM Investigation

“…Cerium ions were easily and selectively doped into the TiO 2 (B) (110) plane in fiber-shaped TiO 2 (B)/anatase core-shell nanostructures in order to enhance the photoactivity. [7] Additionally, the (010) plane is a stable plane that exhibits the largest area in TiO 2 (B) structure, shows favorable bidentate adsorption of ethylene glycol, and plays an important role in nanosheet-shaped TiO 2 (B). [8] Clearly, the two planesplay key roles in various applications of nanoscale TiO 2 (B).…”