**5. Some other recent photosynthesis applications of metal/semiconductor hybrid nanocrystals**

Beside hydrogen evolution and photoreduction of CO2 form photocatalysis, metal/semicon‐ ductor hybrid nanocrystals recently are used for photosynthesis applications. Metal or noble metal is usually employed as catalysts in organic synthesis [139]. Moreover, noble metal has plasmonic effect and induces the organic reaction under visible light and enhances the conversion efficiency [140]. Combining with semiconductor nanocrystals, metal/semiconduc‐ tor hybrid nanocrystals have potential advantages in organic photosynthesis: higher conver‐ sion efficiency, higher selectivity, and lower by-products [141–143].

For instance, Au/CeO2 is employed for oxidation of Alcohol forming aldehyde or ketone under irradiation of visible light [144]. The reaction rate depends on the surface area of Au nanopar‐ ticles, the power of irradiation and the function group of organic compound (Figure 28A–C), and a high selectivity of oxidation is also showed in such hybrid nanocrystals (Figure 28D–F). Beside, metal/semiconductor hybrid nanocrystals, such as Au/ZrO2, can be used for other organic reaction: reduction of nitroaromatic compound, Suzuki reaction, ester reaction. and so on [140, 142–143].

Metal/Semiconductor Hybrid Nanocrystals and Synergistic Photocatalysis Applications http://dx.doi.org/10.5772/61888 329

**Figure 28.** Reaction rate depending on surface area of Au nanoparticles (A), light intensity (B), and substituted func‐ tional groups. Copyright: America Chemistry Society, 2012.

In summary, metal/semiconductor photocatalysts have shown their potential application on hydrogen evolution, photoreduction for conversing CO2 into fuel and organic photosynthesis. Although there is a long way before the metal/semiconductor hybrid nanocrystals being implemented in real-life application, more photocatalysts with different components, special architectures, or structures would be designed for the real-life application.

## **6. Summary and outlook**

**Figure 27.** SEM images and schematic of CeO2 modified with HPO4 ions (A–D) and CH4 evolution from photoreduc‐

**5. Some other recent photosynthesis applications of metal/semiconductor**

Beside hydrogen evolution and photoreduction of CO2 form photocatalysis, metal/semicon‐ ductor hybrid nanocrystals recently are used for photosynthesis applications. Metal or noble metal is usually employed as catalysts in organic synthesis [139]. Moreover, noble metal has plasmonic effect and induces the organic reaction under visible light and enhances the conversion efficiency [140]. Combining with semiconductor nanocrystals, metal/semiconduc‐ tor hybrid nanocrystals have potential advantages in organic photosynthesis: higher conver‐

For instance, Au/CeO2 is employed for oxidation of Alcohol forming aldehyde or ketone under irradiation of visible light [144]. The reaction rate depends on the surface area of Au nanopar‐ ticles, the power of irradiation and the function group of organic compound (Figure 28A–C), and a high selectivity of oxidation is also showed in such hybrid nanocrystals (Figure 28D–F). Beside, metal/semiconductor hybrid nanocrystals, such as Au/ZrO2, can be used for other organic reaction: reduction of nitroaromatic compound, Suzuki reaction, ester reaction. and

tion of CO2 (E and F). Copyright: America Chemistry Society, 2015.

328 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

sion efficiency, higher selectivity, and lower by-products [141–143].

**hybrid nanocrystals**

so on [140, 142–143].

Metal/semiconductor hybrid NCs did have advantages on integration of functionalities of noble metal and semiconductors based on well-controlled morphologies and heterointer‐ face control. Then they could have potential applications to improve the quantum yield of photoinduced electrons or holes for photoreduction and photooxidation. This review has demonstrated the recent research efforts to synthesize metal/semiconductor hybrid NCs and to understand and control the photocatalytic applications, such as photocatalytic water splitting, CO2 photoreduction, and photoinduced organic synthesis. First, on the long term, it can be expected that innovative design and improved synthetic capabilities in the development of elaborate metal/semiconductor NCs with defined topologies and interface control will deliver exciting opportunities in both fundamental understanding and practical

exploitation of unconventional properties and functionalities stemming from properly engineered heterostructures with tailored interfaces and structural features. It can also be expected that some recent new synthesis strategy, such as the reaction between coordinat‐ ed cation ions and semiconductor nanostructures (core/shell, heterodimers, doped NCs), nonepitaxial growth of metal/semiconductor core/shell, and heterodimers will speed up the precise photocatalysts synthesis and design. The new mechanism of photocatalysis, such as plasmon-enhanced photocatalysis, the synergistic cooperation of plasmonic metals, and cocatalysts based on well-defined interface will also boost each of them to an unprecedent‐ ed level of catalytic performance.
