Synthesis, Resonance Absorption Properties And Photocatalystic Application Of Metal-Semiconductor Composite Nanostructures

Recently, composite nanostructures that integrate two or more nanoscale components have attracted much attention, owing to the intriguing behaviors and functionalities far beyond those of their individual counterparts induced by synergistic effect between these objects, and the promising examples of such structures are metal-semiconductor composite nanomaterials. For example, the noble metal surface plasmon resonance can be tailored with different semiconductor shell thicknesses, and the appropriate surface plasmon resonance band can enhance the light absorption of semiconductors. In addition, the introduction of metal nanoparticles provides more reaction hot-spots for the photocatalysis processes, which can improve the catalytic activity of semiconductor photocatalysts. Therefore, metal-semiconductor composite nanomaterials have great prospect in various application fields, such as biosensing, medical imaging, photo-electron, photocatalysis, energy conversion and the like. In this paper, the metal-semiconductor nanostructures with different morphology, components, and spatial distributions have been prepared through two strategies, and their optical resonance absorption characteristics were also further investigated. The followings are the details:Firstly, we have proposed a facile aqueous-phase method to synthesize symmetric and asymmetric Au-AgCdSe hybrid nanorods with controlled morphologies and spatial distributions based on Au nanorods. By controlling the growth kinetics with pH value of the system, AgCdSe could selectively grow at one end, at both the ends or on the side surface of a Au nanorod, generating a mike-like, dumbbell-like, or toothbrush-like hybrid nanorod, respectively. These three types of Au-AgCdSe hybrid nanorods displayed distinct localized surface plasmon resonance. In addition, photoluminescence properties of the hybrid nanorods were also further studied. The obvious luminescent quenching were observed in all three types of Au-AgCdSe nanorods, but only the milk-like hybrid nanorod exhibited a very weak photoluminescence peak at704nm. For explaining these phenomena, a competitive mechanism was introduced between exciton emission enhanced by near field coupling and photoluminescence quenching of semiconductor by the metal portion, and the hypothesis was further verified by the mike-like hybrid nanorods with different rod length.Secondly, we have further prepared Au-Ag2S core-shell hetero-nanorods by the similar method. In this method, the sulfidation mechanism of Ag nanolayer could be controlled by simply adjusting the pH value of the system, resulting in the form of three types of Au/Ag2S core/shell nanorods with completed, corner-opened, or end-opened shells. In addition, Au-CdS core-shell hetero-nanorods with different thickness shells have been also prepared using an improved method. The surface plasmon resonance band of core-shell hetero-nanorods could be tunable ranged from visible to near-infrared wavelength by using different shell shapes and thicknesses.Thirdly, the thickness-controlled CdS/SiO2core-shell nanowires have been also abtained by using an improved Stober method. The influences of silica shell coating and annealing processes on their optical properties have been further investigated. The results showed that silica coating could passivate the surface of semiconductor nanowires, and reduce the number of nonradiative energy channels; In addition, silica shell could improve the thermochemical stability of CdS NWs, and benefit high-temperature annealing recrystallization to reduce the defect state density and restrain the interaction between exciton and defect state, which induced the enhancement of semiconductor band-gap emission with the slowed photoluminescence lifetime. Based on CdS/SiO2core-shell nanowire, we further synthesized CdS/SiO2-Ag composite nanostructure, and observed surface plasmon resonance enhanced the band-edge absorption of CdS nanowires.Finally, we take the photodegradation experiments of RhB with Au-CdS core-shell nanorods to demonstrate the application of metal-semiconductor nanocomposites in photocatalysis field. During the process of photodegradation, as a bi-functional photocatalyst, Au-CdS hetero-nanorods not only exhibited high photocatalytic activity, but also displayed a good real-time monitoring feature, which predicted they have bright prospects in application of photo-electron, photocatalysis and energy conversion fields.