# Graphene Quantum Dots Doped PVDF(TBT)/PVP(TBT) Fiber Film with Enhanced Photocatalytic Performance
## 3 Results and Discussion
### Synthesis of PVDF(TBT)/PVP(TBT)-GQDs  
We hydrothermally processed the PVDF(TBT)/PVP(TBT) film to form the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst. The surface morphology of the prepared photocatalyst was observed by SEM. Figure 3A shows an SEM image of the pure PVDF(TBT) fiber created by electrospinning. As can be seen, the PVDF(TBT) fiber diameter was a few micrometers and the fiber surface was relatively smooth. Furthermore, the orientation of the PVDF(TBT) fibers was random and the fibers were interwoven to form a non-woven fiber film. Figure 3B,C are SEM images of the PVDF(TBT)/PVP(TBT) photocatalyst at different magnifications. From Figure 3B, we can clearly see that some fibers were intertwined. The higher magnification SEM image demonstrates the entanglement between the fibers (Figure 3C). As shown in Figure 3A, there was no entanglement when electrospinningning the PVDF(TBT) film. Therefore, when performing electrospinningning to produce the PVDF(TBT)/PVP(TBT) nanofiber (Scheme 1B), the two intertwined fibers produced must be PVDF(TBT) and PVP(TBT) fibers. Therefore, in the PVDF(TBT) and PVDF(TBT)/PVP(TBT) films, dissolving PVP fibers creates a gap at the original positions of PVP, thereby increasing the specific surface area of the film. Among them, PVDF(TBT)-H\({}_{2}\)O and PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O achieved the effect of dissolving PVP by immersing the film in deionized water. PVDF(TBT)-GQDs and PVDF(TBT)/PVP(TBT)-GQDs dissolve PVP during the hydrothermal preparation of quantum dots. Comparing Figures 3D and 3A, we found that there were some small particles on the surface of the PVDF(TBT) fiber in Figure 3D. Since the PVDF(TBT)-GQDs films were hydrothermally prepared based on PVDF(TBT) films, it can be concluded that the small particles in Figure 3D are GQDs. Figure 3E,F are SEM images of the PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O and PVDF(TBT)/PVP(TBT)-GQDs,  
Figure 2: (**A**) Photograph of the GQDs under 365 nm ultraviolet light; (**B**,**C**) are TEM images of GQDs at low and high magnifications; and (**D**) the size distribution chart of the GQDs. respectively. PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O was prepared by immersing the PVDF(TBT)/PVP(TBT) film in deionized water for 12 h and dried in air. As can be seen from Figure 3E, the PVP fibers in the PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O film dissolved because the PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O film had been soaked in deionized water. Dissolved PVP can increase the specific surface area of the fiber film and thereby improve its photocatalytic performance. Similarly, as shown in Figure 3F, PVP fibers in PVDF(TBT)/PVP(TBT)-GQDs were also dissolved. In the hydrothermal preparation of GQDs, PVP in the PVDF(TBT)/PVP(TBT)-GQDs fiber film is in contact with water, resulting in partial PVP dissolution. Figure 4 shows the x-ray diffraction (XRD) pattern of the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst. The XRD pattern shows that the peaks of the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst we prepared are in agreement with the TiO\({}_{2}\) standard cards (PDF#21-1272 is a standard card of TiO\({}_{2}\)[54]. The characteristic diffraction peaks at 25.198, 36.867, 37.756, 38.467, 48.057, 53.857, 55.047, 62.448, 62.626, 68.782, 70.314, 74.815, 75.061, and 76.005 correspond to the (101), (103), (004), (112), (200), (105), (211), (213), (204), (116), (220), (107), (215), and (301) planes of TiO\({}_{2}\), indicating the existence of anatase TiO\({}_{2}\). Figure 4 shows that the TiO\({}_{2}\) was successfully attached to the PVDF(TBT)/PVP(TBT)-GQDs photocatalysts, which can significantly improve the photocatalytic performance of the PVDF(TBT)/PVP(TBT)-GQDs photocatalyst. Figure 3: SEM images of (**A**) single electrospinningnning PVDF(TBT) nanofiber; (**B**) PVDF(TBT)/PVP(TBT) nanofiber; (**C**) PVDF(TBT)/PVP(TBT) nanofiber; (**D**) PVDF (TBT)-GQDs nanofiber; (**E**) PVDF(TBT)/PVP(TBT)-H\({}_{2}\)O nanofiber, and (**F**) PVDF(TBT)/PVP(TBT)-GQDs nanofiber. The photocatalyst was also examined with x-ray photoelectron spectroscopy (XPS).