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.