*2.4. Fiber Morphology*

The nanofiber morphology of the films was observed by FE-SEM (GeminiSEM 300, ZEISS, Oberkochen, Germany). The average diameters of nanofiber and their distributions were obtained through randomly measuring 100 fibers with Nano Measurer 1.2 (Fudan University, Shanghai, China).

#### *2.5. Fourier Transform Infrared (FTIR) Analysis*

FTIR analysis was carried out by method of KBr pellet to determine interactions among the components. The FTIR spectrum was obtained by using a Nicolet 170-SX instrument (Thermo Nicolet Ltd., Waltham, MA, USA). The wavenumber range was 4000–400 cm<sup>−</sup><sup>1</sup> and an average of 32 scans at 4 cm<sup>−</sup><sup>1</sup> were performed for each measurement.

## *2.6. X-ray Diffraction (XRD) Analysis*

The crystal structure of the nanofiber films can be examined through XRD. XRD analysis was performed through an X'Pert Pro diffractometer (PA Analytical B.V., Eindhoven, The Netherlands) with the conditions at 40 kV, 35 mA. The diffraction range was 5–90◦ (2θ) and the rate of scanning was 2◦ min−1.
