Investigation Of Photoelectrical Property Based On Semiconductors Decorated By Plasmons And Quantum Dots

Titanium dioxide （TiO₂） is a superb semiconductor which has been extensively used in photo-induced processes. However, its band gap is always located between 3.0 eV and 3.2 eV, which makes itself only responsive to light in UV-light section. Therefore, it is necessary to make some modification on titanium dioxide to narrow its wide band gap and make it possible to absorb light in visible light section. In this way, choosing suitable decorating materials and designing the morphology/structure of the system are of significance to the electrical property. Besides, due to its unique LSPR property, plasmonic materials have gained enormous interest in research and applications. Among them, Gold nanorods have the advantage of a wide range of absorption peaks which forms from their tunable aspect ratios. On this basis, it is vital to investigate the photocataytic property of Au nanorods, as well as its applications. The main content of this dissertation is as follows:1. Graphene quantum dots （GQDs） was designed and utilized to sensitize titanium dioxide nanofibers. The band gap of GQDs was measured to be 1.15 eV, which makes it possible to absorb photons in visible light section, generate electrons, transfer them to the conduction band of TiO₂ and finally form photocurrent. In this dissertation, the influence of various reaction conditions on the photoelectrical property was studied. It is found that TiO₂ nanofibers with mixed crystalline phases possess better photoelectrical activity than those with single phase. In addition, the photoelectrical property becomes better with more nitrogen in GQDs. The impact of the wavelength of incident light was also investigated and it is concluded that only photons with wavelength of 450-480 nm and above 550 nm could effectively enhance the photoelectrical property of the system, the mechanism of which is contributed to normal PL property and anti-stokes PL property of GQDs. The existence of GQDs tremendously reduces the band gap of the system and makes it responsive to photons with higher wavelength, which extensively broaden their application in photoelectric and photovoltaic fields.2. Gold nanorods decorated titanium dioxide rambutan-like microspheres were designed and synthesized. The photocatalytic property of the structure is characterized using degradation reaction of rhodamine B as model reaction. The role of gold nanorods is not limited in generating hot electrons to participate the reaction, but also to accelerate the reaction rate by their photothermal effect. The rambutan-like structure is proved to enormously enhance the photocatalytic activity, due to 3-dimensional distribution of TiO₂ branches on the surface of microspheres which prompts the muti-reflection of photons. The absorption rate of photons is thereby tremendously enhanced and the yield of hydroxyl radicals is improved. Compared to the structure of nanofibers, microspheres generates 2.5 times more hot electrons and the heating power of a single Au nanorods is 4.4 times higher. Besides, after loading Au nanorods, the degradation route changed to a N-deethylation process because of the change of absorption mode of rhodamine B on titanium dioxide. This strategy of structure design for improved photon absorption, which achieves high degradation rate and photothermal effect, is promising for the development of novel photocatalyst.3. Gold nanorods were prepared according to the traditional seed-mediated method, and various reaction conditions were tuned to investigate their influence on the aspect ratio of gold nanorods. On the basis of the normal gold nanorods, a second step of growth of the as-prepared gold nanorods was utilized to obtain dumbbell-like gold nanorods. A parameter of 6 is introduced in this dissertation to represent the extent of concave and convex of the rods. The value of θ increases with more gold ions added in the second step at first place, but decreases after it reaches to the maximum value. Dumbbell-like gold nanorods exhibit improved photocatalytic effect than straight rods and their activity is closely related to the vaule of θ. The photocatalytic activity of gold nanorods becomes better under the irradiation of visible light. This strategy of using surface-modified gold nanrods as photocatalyst provides a new way for the application and development of Au nano-catalyst.4. Dumbbell-like Au nanorods were used as photocatalyst to reduce GO sheets to RGO. Hot electrons generated by Au nanorods make them act as both catalyst and pore former in this process. GO sheets adhered by Au nanorods crack and react in the first place, and the large GO sheets are finally cut into small pieces. This method is convenient and highly efficient and the obtained RGO has more defects and disordered structure comparing with previous methods. On the basis of this method, Au/graphene/titanium dioxide composite materials were prepared and the catalytic property of these materials were investigated. This method of obtaining RGO and related composite materials offers an ideal, green and efficient method in this field.