# Recent Advances and Applications of Semiconductor Photocatalytic Technology
## 4 Common Preparation Methods
### Electrospinning  
Electrospinning technology is a method of directly producing polymer nanofibers [161; 162; 163; 164; 165; 166; 167]. Electrospinning techniques have the advantages of simple manufacturing equipment, low spinning \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Semiconductor**} & \multirow{2}{*}{**Crystal Structure**} & \multicolumn{3}{c}{**Band Gap Structure (PH = 7)**} & \multirow{2}{*}{**Reference**} \\ \cline{3-6}  & & **CB** & **VB** & **E\({}_{\text{g}}\)/eV** \\ \hline TiO\({}_{2}\) & Anatase & \(-0.50\) & 2.70 & 3.20 & [149] \\ ZnO & & \(-0.31\) & 2.89 & 3.20 & [150] \\ CuO & & \(-1.16\) & 0.85 & 2.00 & [151] \\ CdS & & \(-0.90\) & 1.50 & 2.40 & [152] \\ ZnS & & \(-1.04\) & 2.56 & 3.60 & [101] \\ g-C\({}_{3}\)N\({}_{4}\) & & \(-1.30\) & 1.40 & 2.70 & [139; 153] \\ g-C\({}_{3}\)N\({}_{4}\) & & \(-1.53\) & 1.16 & 2.70 & [154] a \\ Ta\({}_{3}\)N\({}_{5}\) & & \(-0.75\) & 1.35 & 2.10 & [155] \\ TaON & & \(-0.75\) & 1.75 & 2.50 & [156] \\ Fe\({}_{2}\)O\({}_{3}\) & & 0.28 & 2.48 & 2.20 & [157] \\ Bi\({}_{2}\)O\({}_{3}\) & & 0.33 & 3.13 & 2.80 & [158] \\ BiVO\({}_{4}\) & & \(-0.30\) & 2.10 & 2.40 & [159] \\ WO\({}_{3}\) & & \(-0.10\) & 2.70 & 2.80 & [160] \\ Ag\({}_{3}\)PO\({}_{4}\) & Cubic & 0.04 & 2.49 & 2.45 & [161] \\ \hline \hline \end{tabular}  
* Measurement by the valence band X-ray photoelectron spectroscopy (VB XPS) spectrum.  
\end{table} 
Table 2: Band gaps of common photocatalysts. Figure 3: Photocatalyst preparation method. cost, a wide variety of spinnable materials, and a controllable process. Electrospinning technology is one of the major methods for effectively preparing nanofiber materials. Electrospinning technology has been used to produce various nanofibers including organic, organic/inorganic composites, and inorganic nanofibers. Electrospinning device mainly consists of a high-voltage power supply, a nozzle and liquid supply device, and a fiber receiving device, as shown in Figure 4A. High voltage power supplies typically use a DC power supply that can generate thousands to tens of thousands of volts. The function of the high voltage power supply is to generate a high voltage electric field so that the liquid becomes charged and polarized, eventually forming a jet. The liquid supply device is a container (such as a syringe) having a capillary at one end, and the container is filled with a polymer solution or melt. In addition, as experimental requirements have increased, many experiments have gradually adopted liquid flow control systems that allow for a more accurate control of liquid flow. The fiber receiving device is a metal receiving plate at the opposite end of the nozzle and may be a rotating roller or an aluminum foil layer on the plane of the metal plate. The receiving device is grounded with a wire and connected to the negative electrode of the high voltage power source. During electrospinningning, the high voltage electric field melts and deforms the polymer solution, which then forms conical droplets that protrude at the end of the showerhead. When the repulsive force of the surface of the droplet exceeds the surface tension, a minute jet ejects from the surface of the droplet. These jets undergo a high-speed stretching of electric field force at short distances, the solvent volatilizes and solidifies, and, finally, it deposits on the receiving plate to form polymer fibers. Figure 4B shows an SEM image of a polyvinylidene fluoride (PVDF) /TiO\({}_{2}\) fiber film prepared by an electrospinning method. We can observe that the nanofiber membrane prepared by electrospinning has a porous structure. The conventional fiber has a specific surface area of 0.4 m\({}^{2}\)g\({}^{-1}\), as compared with a conventional fiber membrane, and the electrospinning fiber has a specific surface area of about 40 m\({}^{2}\)g\({}^{-1}\)[163]. The electrospinningning fiber membrane has a large specific surface area, which can effectively solve the disadvantage that the specific surface area of the photocatalyst is small.