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. 2019 Apr 3;9(4):535.
doi: 10.3390/nano9040535.

Photocatalytic Activity of TiO₂ Nanofibers: The Surface Crystalline Phase Matters

Hongnan Zhang  1 , Ming Yu  2 , Xiaohong Qin  3
Affiliations

Photocatalytic Activity of TiO₂ Nanofibers: The Surface Crystalline Phase Matters

Hongnan Zhang et al. Nanomaterials (Basel). .

Abstract

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.

Keywords: TiO2 nanofibers; core-shell structure; crystal phase transition; mixed phases; photocatalytic activity.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
SEM images of electrospun nanofibers: (A) electrospun PVP/Ti(OBu)4 composite nanofibers; (B) TiO2 nanofibers calcined in air at 500 °C for 5 h.
Figure 2
Figure 2
(A) XRD pattern, (B) visible Raman spectra, and (C) UV Raman spectra of the TiO2 nanofibers calcined in air at different temperatures.
Figure 3
Figure 3
Weight percentage of the rutile phase in the TiO2 nanofibers calcined at different temperatures estimated by (A) XRD, (B) visible Raman (the inset shows the area ratio of the anatase phase to the rutile phase [32]), and (C) UV Raman spectroscopy (the inset shows the area ratio of the rutile phase to the anatase phase [32]).
Figure 4
Figure 4
Schematic diagram of the phase transition of TiO2 nanofibers calcined at different temperatures.
Figure 5
Figure 5
Photodegradation curves of Rhodamine B on TiO2 nanofibers calcined at different temperatures.
Figure 6
Figure 6
Conceptual model of mixed phases TiO2 catalysts: (1) the rutile lattice, (2) the anatase lattice, and (3) interfacial and surface sites.
Figure 7
Figure 7
TEM images of (A) anatase core@rutile shell TiO2 nanofibers; (B) rutile core@anatase shell TiO2 nanofibers, respectively.
Figure 8
Figure 8
(A) XRD pattern, (B) visible Raman spectra, and (C) UV Raman spectra of anatase core@rutile shell TiO2 nanofibers and rutile core@anatase shell TiO2 nanofibers as well as pure anatase and rutile TiO2 nanofibers.
Figure 9
Figure 9
Photodegradation curves of Rhodamine B on anatase core@rutile shell TiO2 nanofibers and rutile core@anatase shell TiO2 nanofibers as well as pure anatase and rutile TiO2 nanofibers.
See this image and copyright information in PMC

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