Investigation of Plasmon Enhanced Optical Properties and Photocatalytic Applications of Composite Nanostructures
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Date
2021-03-07
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Addis Ababa University
Abstract
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).
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Keywords
Investigation, Plasmon, Enhanced Optical Properties, Photocatalytic, Applications of Composite, Nanostructures