Investigation of Plasmon Enhanced Optical Properties and Photocatalytic Applications of Composite Nanostructures

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Addis Ababa University


In this dissertation, we investigated plasmon enhanced optical properties and photocatalytic applications of composite nanostructures by using noble materials from theoretical and experimental perspectives. The theoretical investigation mainly focused on the optical and plasmonic properties of spherical and spheroidal ZnO@Ag core-shell nanocomposite embedded in nonabsorptive medium. The e_ective dielectrics function, polarizability, refractive index and optical absorbance for spherical as well as absorption cross-section and radiation e_ciency for spheroidal nanocomposite are studied. These optical and plasmonic properties are tuned when size of core and/or composite, shell thickness, shape of core and/or shell, and refractive index of the host-medium is changed. In spherical nanocomposite, there are two resonances associated with interfaces while in spheroidal nanocomposite four plasmonic resonances are appeared that correspond to interfaces and the bonding/antibonding pairs. The tunable of plasmonic resonances from UV to infrared spectral regions of such composite enables it to exhibit very interesting material properties in a variety of applications. Experimentally, we emphasized the optical properties and photocatalytic applications of ZnO nanoparticles, triple layered ZnO@SiO2@Ag core-shell composite nanostructures and Bi doped/undoped TiO2 nanostructures. In particular, we synthesized ZnO nanoparticles using three di_erent methods as presented in the experimental section of the study. Due to di_erent synthesis methods and procedures as well as di_erent surfactant/stablizing agent, the synthesized ZnO nanoparticles have di_erent morphology, band gap energy, varying quantum size e_ect and photocatalytic responses. The photocatalytic performance of ZnO nanoparticles were evaluated by using methyl orange dye as a pollutant under UV-light irradiation. Triple layered ZnO@SiO2@Ag core-shell nanocomposites are also fabricated at 400 oC for di_erent calcination time. The photocatalytic activity and stability of the as-synthesized samples were evaluated by photo-degradation of organic methylene blue under ultraviolet light irradiation. When ZnO@SiO2 is coated with Ag, the stability and photocatalytic performance of the composite ZnO@SiO2@Ag photocatalysts were highly enhanced. In addition, Bi- doped/undoped TiO2 nanoparticles are synthesized by green synthesis method using zingiber o_cinale extract solution. After doping Bi, the band gap energy is decreased from 3:00 eV to 2:76 eV , absorption region is shifted to visible range of solar spectrum, and surface function is modi_ed. The photocatalytic activity of the sample is analyzed by UV-Vis spectroscopy using trypan blue dye. The photo-degradation e_ciency of chemical synthesis TiO2 nanoparticles is enhanced to 98:34 % by doping basic metal Bi and using ginger extraction solution. The synthesized samples were analyzed using a characterization techniques such as X-ray di_raction (XRD) spectroscopy, scanning electron microscope (SEM), Transmission electron microscope (TEM), Ultraviolet visible (UV-Vis) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS).



Investigation, Plasmon, Enhanced Optical Properties, Photocatalytic, Applications of Composite, Nanostructures