The average fiber diameter of the composite nanofibers is 290 ± 90 nm which decreases to 210 ± 60 nm, 180 ± 70 nm, and 140 ± 80 nm after sintering at 500°C, 550°C, and 600°C, respectively. It is known that crystalline grains of anatase TiO2 are spherical, while selleckchem rutile ones are of rod structure. With the increase of the sintering temperature, some anatase TiO2 grains will transform to rutile ones, which may result in the thinning of the fibers. Moreover, transformation

of anatase TiO2 grains to rutile ones will introduce stress in the fibers, which will cause the fibers to become brittle and even fracture. The insets in Figure  1b, c, d are high-magnification photos of nanofibers, which indicate that the surfaces of TiO2 nanofibers sintered at 500°C and 550°C are rather smooth, while become a little rough when sintering

temperature increases to 600°C. Figure  2 shows the XRD patterns of TiO2 nanofibers. All the peaks of the TiO2 nanofibers sintered at 500°C are indexed for anatase TiO2 with dominant (101) peaks. The mean grain size determined from the XRD pattern using the Scherrer formula is around 16 nm. The nanofibers sintered at 550°C, 600°C, and 700°C are observed to contain both anatase and rutile phases. The phase composition can be determined from XRD results according to the following equation [29]: (2) where click here W R, A A, and A R represent rutile weight percentage, integrated intensity of anatase (101) peak, and rutile (110) peak, respectively [29]. The calculated rutile contents in the above three mixed-phase nanofiber samples are approximately 15.6, 87.8, and 90.5 wt.%, and the mean grain sizes are 22, 30, and 42 nm, respectively. The XRD results indicate that with the increase of sintering temperature, the grain size is gradually increased; however, rutile content is sharply increased in the temperature range of 550°C to 600°C. Figure 1 SEM images of electrospun nanofibers. As-spun TiO2-PVP nanofibers (a), TiO2 nanofibers after calcination at 500°C (b), 550°C (c), and 600°C (d). The insets in b, c, and d are high-magnification photos of single nanofibers. Figure 2 XRD patterns

of TiO 2 nanofibers sintered at 500°C, 550°C, 600°C, and 700°C. The diffractions of anatase and rutile phase are labeled in the figure as ‘A’ and ‘R’, respectively. Characterization Acetophenone of ultrathin ZnO layers deposited by ALD method To detect the crystallographic structure and thickness of ZnO layers, except FTO substrates, glass substrates were also used to deposit ZnO layers. XRD patterns for ZnO layers deposited on glass substrate are shown in Figure  3a. A 4-nm-thick ZnO layer does not show any diffraction peak, whereas peaks corresponding to hexagonal phase ZnO are observed for the thickness of 10 or 20 nm, which indicates that the deposited ZnO layers by ALD method are polycrystalline. Figure  3b shows the UV–vis transmission spectra for the FTO substrates without ZnO layers and with ZnO layers of different thicknesses.