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|Title: ||Fabrication of noble-metal nanostructures and applications to surface-enhanced Raman scattering|
|Other Titles: ||Gui jin shu na mi jie gou de zhi bei ji qi zai biao mian zeng qiang Laman guang pu zhong de ying yong|
|Authors: ||Chen, Limiao ( 陳立妙)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Nanostructured materials.|
Raman effect, Surface enhanced.
|Notes: ||CityU Call Number: TA418.9.N35 C545 2011|
xxii, 145 leaves : ill. (some col.) 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references.
|Abstract: ||Surface enhanced Raman scattering (SERS) can provide important information of
surface molecular structure and kinetic process directly. SERS technique is becoming a
strong hand in surface science and widely used in trace analysis and even single molecule
detecting, medical chemistry, environment sciences, biological and medical systems,
nanomaterials and sensors. SERS enhancement is related to the wavelength of the
exciting laser, the size and morphology of the substrate, the quantities of the absorbate
and so on. The evolution of SERS technique and the broadening the application are
depended on the development of SERS substrate. Thus, the preparation and properties of
SERS substrates become very important to develop SERS as a usual analytical tool. On
other hand, food safety issues caused by contamination of melamine have raised a great
deal of concern in China in last few years. Conventional chromatography-based methods
for detection of chemical contaminants are time-consuming and laborintensive. On the
basis of the above facts, we focus our study on the fabrication of SERS substrates (e.g. Pd
nanostructres, Ag-Pd alloy nanostructures, Au nanoparticles decorated ZnO (ZnO/AuNps)
nanoarrays, Ag nanoparticles modified carbon (C/AgNps) nanospheres and Ag
nanoparticles decorated Ag (Ag/AgNps) nanowires) and exploring the feasibility of using
SERS technique coupled with as-fabricated substrates for detection of melamine in food
such as egg white and raw milk solution. The main results are summaried as follows:
Firstly, Pd nanostructures with different shapes such as urchin-like, hemispherical,
flower-like and plate-like were successfully deposited on Si substrate in aqueous
hydrogen fluoride (HF) solution at room temperature. The morphology and size of the
nanostructures can be tuned by controlling the metal precursor concentration, reaction time and the organic additive concentration. This simple method was extended to
preparing other noble metal nanoparticles with various morphologies and sizes. The
morphology-dependent SERS activity of the as-synthesized nanostructures was
demonstrated. It was found that urchin-like nanoparticles had a higher SERS activity than
hemispherical and flower-like Pd nanostructures for Rhodamine 6G (R6G) probe
molecules due to its special morphology.
Secondly, dendritic and porous Ag-Pd alloy nanostructures were prepared through the
coreduction of AgNO3 and Pd(NO3)2 in aqueous HF solution and galvanic replacement
reaction using Ag nanoparticles as template, respectively. The morphology and
composition of Ag-Pd alloy nanostructures could be modulated by controlling the molar
ratios between metal precursors in the solutions or reaction time. In addition, the
morphology and composition-dependent activity of the as-synthesized Ag-Pd alloy
nanostructures was investigated. The enhancement factor was estimated to be on the
order of 106 using R6G as test probe molecules. For the Ag-Pd alloy nanoparticles with
similar morphology, the SERS signal intensity decreases with increasing the Pd content
in the Ag-Pd alloy. SERS mappings show that the porous Ag-Pd substrate exhibits better
reproducibility compared with the dendritic Ag-Pd substrate.
Thirdly, ZnO/AuNps nanoarrays were prepared by a simple solution method using
well-aligned ZnO nanoneedle arrays as templates. The coverage of Au nanoparticles on
the surface of ZnO nanoneedle can be tuned by varying the concentration of Au precursor.
High coverage leads to the formation of ZnO/AuNps nanoneedle bundles. The SERS
performances of ZnO/AuNps composite nanoarrays toward detection of R6G were
evaluated. The SERS enhancement factor is mainly influenced by Au coverage and morphologies of the ZnO/AuNps nanoarrays. Enhancement factor for the optimized
ZnO/AuNps nanoneedle arrays was estimated to be of the order of 107.
Fourthly, silver/carbon (Ag/C) core-shell nanospheres synthesized by a hydrothermal
method were used as templates for fabricating Ag/C/AgNps nanospheres. The particle
size of Ag nanoparticles increased with increasing the concentration of Ag precursor.
Detection of melamine molecules at concentrations as low as 1.0×10-8 M shows that the
Ag/C/AgNps nanosphere is an excellent SERS-active substrate. The effect of heavy metal
ions on the detection of melamine is also investigated. It was found that the SERS
spectrum profile of melamine is very sensitive to the presence of heavy metal ions: the
peak positions of the SERS bands exhibit some apparent change with the kind of metal
ion, showing a blue or red shift compared with those in the SERS spectrum of melamine;
the SERS signal intensity decrease with increasing the concentration of metal ion.
Fifthly, silver nanowires synthesized by a solvothermal method were used as
templates for fabricating Ag/AgNps nanowires. The number density and particle size of
Ag nanoparticles change with the concentration of AgNO3. Individual Ag/AgNps
nanowire exhibited strong SERS effect. Detecting of melamine molecule at
concentrations as low as 1.0×10-8 M was used as example to show the possible
applications of such Ag/AgNps nanowires.
Finally, the application of in rapid detections of melamine in egg white and raw milk
solution based on the SERS technique is demonstrated. It was found that melamine in
raw milk and egg white solution at low concentration (~10-8 M) can be easily detected
with little sample pretreatment.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086232|
|Appears in Collections:||AP - Doctor of Philosophy |
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