# Recent Advances and Applications of Semiconductor Photocatalytic Technology
## 5 Methods for Improving Photocatalytic Efficiency
### Precious Metal Depositing  
Precious metal deposition on semiconductor surfaces considered to be an effective way of capturing excited electrons. The basic principle of precious metal deposition on a semiconductor surface is as follows. When the noble metal and the semiconductor are in contact, the work function of the metal is larger than the work function of the semiconductor, so the electron continuously moves from the semiconductor to the metal until the energy levels of both are equal. Thus, the metal surface and the semiconductor surface each obtain excessive negative and positive charges, causing band bending near the interface where the semiconductor is in contact with the metal, thereby forming a Schottky barrier. The Schottky barrier can capture photogenerated electrons at the surface of the semiconductor and suppress the recombination of electron-hole pairs [224], thereby improving photocatalytic efficiency. Among the surface precious metal deposits, the most commonly used metal is the Pt of Group VIII [225; 226; 227; 228; 229; 230; 231; 232]. In addition to Pt, noble metals such as Ag [233; 234; 235; 236; 237; 238], Ru [239; 240], Pd [241; 242; 243; 244; 245], and Au [246; 247; 248; 249; 250] are also used to improve the photocatalytic performance of semiconductors. However, the major disadvantage of precious metals such as Ag, Ru, Pd, and Au is that the price is relatively high and not suitable for large scale applications [251; 252; 253; 254; 255; 256; 257]. Take TiO\({}_{2}\) as an example. Due to the large ionic radius of the noble metal, it is impossible to enter the TiO\({}_{2}\) lattice. Therefore, in order to improve the photocatalytic performance of TiO\({}_{2}\), it is possible to change the surface characteristics of TiO\({}_{2}\) by depositing a noble metal on the surface of TiO\({}_{2}\) photocatalyst [258; 259; 260; 261]. The surface modification of a noble metal to TiO\({}_{2}\) photocatalyst is achieved by changing the electron distribution [261]. When TiO\({}_{2}\) contacts the noble metal, carriers are redistributed, and a space charge layer is formed on the surface of the TiO\({}_{2}\) close to the metal particle interface. The space charge layer facilitates the transfer of photogenerated electrons to the interface between the noble metal and TiO\({}_{2}\)[258; 259; 262], thereby suppressing the recombination of photogenerated electrons and holes, improving photocatalytic efficiency. [PERSON] et al. [263] deposited single atom and diatomic clusters (Pd, Pt, Ag/Pd, Ag/Pt, and Pd/Pt) on the surface of TiO\({}_{2}\) (P25) using a high energy radiation reduction method. By the photocatalytic decomposition of toluene, it was found that palladium/platinum-titanium dioxide (Pd/Pt-TiO\({}_{2}\)) has the strongest decomposing ability for toluene in the ultraviolet and visible range. Two methods in [PERSON]'s experiment are shown in Figure 6. In the comparison of different preparation methods, it was found that the sample prepared by the one-step method had the highest degradation ability to phenol in the visible range. [PERSON] et al. [264] deposited Au nanoparticles on the surface of sulfated TiO\({}_{2}\). Au nanoparticles have excellent electron trapping ability and can effectively prolong the lifetime of electron-hole pairs. In the photocatalyst experiment, under the condition of pH = 6.5, the decomposition rate of the photocatalyst to Congo red dye can reach 97.6%. [PERSON] et al. [265] used an innovative sonic degradation deposition method to deposit a series of noble metals on the surface of TiO\({}_{2}\) within 10-20 s. These precious metals include single or complex noble metals such as Au, Cu, Pd, Pt, Au-Pd, Au-Cu, Au-Fe, Au-Co, Au-Pt-Au-Rh, and Au-Ru. In photocatalytic experiments under room temperature and visible light conditions, the decomposition rate of methyl orange dye was highest with the AuPd/TiO\({}_{2}\) (mass ratio of Au: Pd is 3:1) catalyst. Most precious metals are toxic, expensive, and not suitable for a wide range of applications.