Photocatalytic Activity of TiO₂ Nanofibers: The Surface Crystalline Phase Matters.

The crystal phases and surface states of TiO₂ can intrinsically determine its performance in the applications of photocatalysis. Here, we prepared TiO₂ nanofibers with different crystal phase contents by electrospinning followed via calcination at different temperatures. The TiO₂ nanofibers were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrometry, transmission electron microscopy (TEM), and photocatalytic performance testing. The results showed that the phases of TiO₂ nanofibers were layered, that surface crystal phase transition rate was faster than that of internal layers contributed the difference in the ratio of anatase and rutile in the outer and inner layer of TiO₂ nanofibers. The TiO₂ nanofibers obtained at 575 °C had the best photocatalytic activity, taking only 25 min to degrade Rhodamine B. At 575 °C, the rutile content of the sample surface was about 80 wt.%, while the internal rutile content was only about 40 wt.%. Subsequently, we prepared two different structures of anatase-rutile core-shell TiO₂ nanofibers. The core-shell structure can be clearly seen by TEM characterization. The photocatalytic activity of two kinds of core-shell TiO₂ nanofibers was tested. The results showed that the photocatalytic activity was close to that of the pure phase TiO₂ nanofibers, which corresponded with the surface phase. This further proves that the photocatalytic activity of the material is mainly affected by its surface structure.