the potential of gold nanoparticles embedded on...
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THE EVALUATION OF GOLD NANOPARTICLES EMBEDDED ON
POLYVINYL ALCOHOL MATRIX AS OXIDATION CATALYST
AND BIOSENSOR
SASHA MD. NASIR
UNIVERSITI TEKNOLOGI MALAYSIA
THE EVALUATION OF GOLD NANOPARTICLES EMBEDDED ON POLYVINYL
ALCOHOL MATRIX AS OXIDATION CATALYST AND BIOSENSOR
SASHA MD. NASIR
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Master of Science (Chemistry)
Faculty of Science
Universiti Teknologi Malaysia
MAY 2010
iii
For my family, but especially for my mom –
thank you for your unconditional love and continuous support
and to Ed and Debo
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ACKNOWLEDGEMENTS
First and foremost I would like to extend my thanks to my supervisor, Assoc.
Prof. Dr. Hadi Nur, whose help, stimulating suggestions and encouragement helped me
during the time of my research and writing of this thesis.
Additionally, I would like to express my gratitude and complements to all the
lecturers, laboratory officers and research officers from the Department of Chemistry
and Ibnu Sina Institute for Fundamental Science Studies, Universiti Teknologi Malaysia
for their assistance, supervision and wonderful cooperation.
I would also like to thank the Ministry of Science, Technology and Innovation
(MOSTI) for its financial support through Project No. 03-01-06-SF0326 (Vot. 79126).
My sincere appreciation is also extended to all my friends for their understanding
and continual support and also to my fellow lab mates for their valuable experience and
opinions along this study.
Last but not least, I would like to express my deepest gratitude to my beloved
parents, my sister and my brother for without their love, patience, understanding,
continuous motivation and support, this thesis would not have been possible
.
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PREFACE
This thesis is the result of my work carried out in the Department of Chemistry,
Universiti Teknologi Malaysia, between July 2007 to June 2009 under supervision of
Assoc. Prof. Dr. Hadi Nur. Parts of my work described in this thesis have been reported
in the following publications or presentations:
1. Nur, H., Nasir, S.M. (2008). Gold Nanoparticles Embedded on the Surface of
Polyvinyl Alcohol Layer. Journal of Fundamental Sciences. 4. 245-252.
2. Nur, H., Nasir, S.M. Gold Nanoparticles Embedded on the Surface of Polymeric
Layer as a Biological Sensor. Oral presentation in the Regional Annual
Fundamental Science Seminar 2008 (RAFSS’08). Ibnu Sina Institute for
Fundamental Science Studies, Universiti Teknologi Malaysia, Skudai, Johor.
27th - 29th
May, 2008.
3. Nur, H., Nasir, S.M. Gold Nanoparticles Embedded on the Surface of Polymeric
Layer as a Biological Sensor. Poster presentation in the Minggu Penyelidikan
Sains dan Matematik 2007. Fakulti Sains, Universiti Teknologi Malaysia, Skudai,
Johor. 31st December, 2007 – 3rd
January, 2008.
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ABSTRACT
In this study, a method for synthesizing polyvinyl alcohol (PVA) embedded gold film is presented. This approach takes advantage of the high affinity of thiol molecules towards gold. Gold particles, in the size range of 20 to 180 nm, were first prepared by the conventional Turkevitch method by the reduction of tetrachloroauric acid (HAuCl4
) with sodium citrate in water. The Ultraviolet-Visible (UV-Vis) absorption spectra and dark-field microscopy confirmed the presence of a surface plasmon resonance (SPR), attributed to the nanosized gold particles. The resultant gold particles of sizes as low as 27 nm with nearly spherical in shape were achieved as determined by Transmission Electron Microscopy (TEM) and Field Emission Scanning Electron Microscopy (FESEM). In the preparation of PVA embedded gold (PVA-Gold) film, PVA was functionalized with (3-mercaptopropyl) trimethoxysilane (MPTMS) which produced a thiol functionality on the surface. Then, gold particles were chemisorbed onto the surface of partially dried thiol functionalized PVA to produce PVA-Gold composite. The composite materials were characterized using Fourier transform infrared spectroscopy (FTIR), FESEM, TEM and UV-Vis diffuse reflectance (DRUV) spectroscopy. The TEM results showed that the gold particles embedded on the surface of PVA were polydispersed with the average particle size from 30 nm to 150 nm. The catalytic potential of PVA-Gold for oxidation reaction has been investigated in the liquid phase oxidation of styrene with aqueous tert-butyl hydroperoxide and the results were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). PVA-Gold were found to be highly active catalyst (95% conversion of styrene) and selective towards the oxidation of styrene to give benzaldehyde (73%) as the main product. Moreover, PVA-Gold also showed a very good regenerability in the repeated oxidation of styrene. The unique optical properties of PVA-Gold were also exploited in the interactions with several amino acids such as L-Arginine (Arg), L-Proline (Pro), L-Tryptophan (Trp) and L-Tyrosine (Tyr). The DRUV demonstrated that the surface plasmon resonance peaks for the amino acid – PVA-Gold conjugates were relatively shifted towards longer wavelength as evidence of a successful functionalization of gold with the amine groups of amino acid. The above findings suggest that PVA-Gold have potential application as heterogeneous oxidation catalyst and can be explored as probes for biosensing application.
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ABSTRAK
Dalam kajian ini, suatu kaedah bagi mensintesis filem polivinil alkohol (PVA) terpahat emas dilaporkan. Kaedah ini, mempergunakan sifat saling tarik molekul tiol yang kuat terhadap emas. Partikel emas, bersaiz dalam julat 20 nm – 180 nm, pertamanya disediakan menurut kaedah konvensional Turkevitch secara penurunan asid tetrakloroaurik (HAuCl4
) dengan natrium sitrat di dalam air. Spektrum serapan ultralembayung-nampak (UV-Vis) dan mikroskopi medan gelap menunjukkan terdapat bukti plasmon resonans permukaan (SPR) yang disebabkan oleh partikel emas bersaiz nano. Partikel emas yang diperolehi bersaiz paling kecil 27 nm dan hampir berbentuk sfera seperti yang diperlihatkan oleh mikroskopi elektron pancaran (TEM) dan mikroskopi elektron pengimbasan pancaran medan (FESEM). Dalam penyediaan filem PVA bertatahkan emas (PVA-Emas), PVA telah difungsikan dengan (3-merkaptopropil) trimetoksisilana (MPTMS) bagi melekatkan kumpulan berfungsi tiol pada permukaannya. Kemudian, partikel emas dijerap kimia pada permukaan separa kering PVA berfungsikan tiol untuk seterusnya menghasilkan komposit PVA-Emas. Bahan komposit tersebut telah dicirikan dengan spektroskopi inframerah transformasi Fourier (FTIR), FESEM, TEM dan spektroskopi pemantulan difusi ultralembayung-nampak (DRUV). Keputusan daripada TEM menunjukkan partikel emas terpahat pada permukaan PVA secara berserakan dengan purata saiz partikel di antara 30 nm hingga 150 nm. Keupayaan emas sebagai mangkin bagi tindak balas pengoksidaan dikaji dalam pengoksidaan stirena dengan tert-butil hidroperoksida (TBHP) dalam fasa cecair dan hasil tindak balas tersebut telah dianalisis menggunakan kromatografi gas (GC) dan kromatografi gas-spektrometri jisim (GC-MS). PVA-Emas didapati mangkin yang sangat aktif (95% penukaran stirena) dan selektif terhadap pengoksidaan stirena kepada benzaldehid (73%), sebagai hasil utama. Tambahan lagi, PVA-Emas memperlihatkan kebolehulangan yang sangat baik bagi pengoksidaan stirena. Sifat optik emas yang unik telah dieksploitasikan dalam interaksinya dengan beberapa amino asid seperti L-Arginine (Arg), L-Proline (Pro), L-Tryptophan (Trp) dan L-Tyrosine (Tyr). Spektrum DRUV menunjukkan puncak plasmon resonans permukaan bagi konjugat amino asid-PVA Emas telah beranjak kepada nombor gelombang yang lebih tinggi secara relatif menjadi bukti bahawa emas telah difungsikan dengan kumpulan amina dalam amino asid dengan jayanya. Keputusan kajian menunjukkan bahawa PVA-Emas berpotensi diaplikasikan sebagai mangkin pengoksidaan heterogen dan berguna sebagai prob dalam aplikasi biosensor.
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE
STATEMENT
DEDICATION
ACKNOWLEDGEMENTS
PREFACE
ASTRACT
ABSTRAK
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
LIST OF ABBREVIATIONS
LIST OF APPENDICES
i
ii
iii
iv
v
vi
vii
viii
xi
xii
xiv
xvi
1 INTRODUCTION
1.1 Research Background 1
1.2 Problem Statement 4
1.3 Research Objectives 7
1.4 Scope of Study 8
2 LITERATURE REVIEW
2.1 Historic Introduction of Gold Nanoparticles 9
2.2 Wet Chemical Synthesis of Gold Nanoparticles 11
2.2.1 Turkevitch Method 12
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2.2.2 Brust-Schiffrin Method 13
2.2.3 Seed Mediated Growth Method 14
2.3 Important Properties of Gold Nanoparticles 14
2.3.1 Absorption Properties 14
2.3.2 Scattering Properties 16
2.4 Polymers as Support 18
2.4.1 PVA Composite using Sol-Gel Process 18
2.4.2 Polymers as Support for Gold 20
2.5 Gold Catalysis 22
2.6 Gold Nanoparticles in Biosensors 23
3 EXPERIMENTAL
3.1 Chemicals 25
3.2 Synthesis of Gold Nanoparticles in Different 25
Sizes and Shapes
3.2.1 Synthesis of 20 nm Gold Nanoparticles 26
3.2.2 Synthesis of 30 nm to 180 nm 27
Gold Nanoparticles
3.3 Preparation of PVA Embedded Gold Film 28
(PVA-Gold)
3.4 Catalytic Oxidation Reactions 29
3.4.1 Catalytic Activity of PVA-Gold Film 29
3.4.2 Reusability of the Catalyst 29
3.5 Interactions of PVA-Gold Film with Amino Acids 30
3.6 Characterization Techniques 30
3.6.1 Ultraviolet-Visible Spectroscopy (UV-Vis) 31
3.6.2 Optical Imaging of Gold Nanoparticles 32
3.6.3 Field Emission Scanning 33
Electron Microscopy (FESEM)
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3.6.4 Transmission Electron Microscopy (TEM) 34
3.6.5 Fourier Transform Infrared - Attenuated Total 35
Reflectance (FTIR-ATR)
3.6.6 Ultraviolet-Visible Diffuse Reflectance 36
Spectroscopy (DRUV)
3.6.7 Gas Chromatography (GC) 37
3.6.8 Gas Chromatography-Mass Spectrometry 38
(GC-MS)
4 RESULTS AND DISCUSSION
4.1 Optical Properties of Gold Nanoparticles 39
4.2 Surface Morphology of Gold Nanoparticles 44
4.3 PVA-Gold Film Characterization 46
4.3.1 FTIR Spectra of PVA-Gold Film 46
4.3.2 DRUV of PVA-Gold Film 49
4.3.3 FESEM of PVA-Gold Film 50
4.3.4 TEM of PVA-Gold Film 52
4.4 Catalytic Activity of PVA-Gold Film 53
4.5 Interaction of PVA-Gold Film with 56
Amino Acids
5 CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions 59
5.2 Future Work 61
REFERENCES 62
APPENDICES 74
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LIST OF TABLES
TABLE NO. TITLE PAGE
3.1 Approximate amount of citrate and the corresponding sizes of nanoparticles for samples S2 – S6.
28
4.1 The catalytic activity of PVA-Gold film during the catalyst reuse in the oxidation of styrene.
55
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 Schematic representation of the proposed gold nanoparticles embedded in the surface of polymer: (a) gold nanoparticles attached on the surface of the polymer layer by chemisorption, (b) gold nanoparticles embedded in the polymer layer by attachment of nanoparticles on the surface of partially dried functionalized polymeric layer.
6
2.1 The Lycurgus Cup (4th 10 Century B.C.) is ruby red in transmitted light and green in reflected light, due to the presence of gold colloids.
2.2 Chemical structure of sodium citrate.
12
2.3 Formation of gold nanoparticles coated with organic shells by reduction of Au(III) compounds in the presence of thiols.
13
2.4 Formation of surface charges on a metal particle by the electric field of light.
15
2.5 Strong absorption band around 520 nm in the spectrum is the origin of the observed colour of the nanoparticle solution.
16
2.6 Under a microscope with white light illumination, (a) 58 and (b) 78 nm gold particles have the appearance of highly fluorescent green and yellowish particles, respectively.
17
2.7 Chemical structure of PVA.
22
3.1 Synthesis of 20 nm gold nanoparticles.
26
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3.2 Synthesis of gold nanoparticles of different sizes.
27
4.1 Reaction scheme for the synthesis of gold nanoparticles by Turkevitch method.
40
4.2(a) Absorption spectra of gold nanoparticle solutions for samples S1-S6.
41
4.2(b) Photographs of colloidal dispersions of gold nanoparticles with increasing size for samples S1-S6.
42
4.3 Representative photograph of gold nanoparticles viewed under optical microscope. The different colours corresponds to different shape of the particles.
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4.4 FESEM images of gold nanoparticles prepared from different concentration of citrate. Images (a) – (f) correspond to samples S1 – S6. The inset in images (a) – (f) shows the TEM images of gold nanoparticles.
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4.5 FTIR spectra of (a) control PVA film, (b) PVA-MPTMS film prepared under acid condition and (c) PVA-Gold film.
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4.6 DRUV spectra of (a) PVA-MPTMS film prepared under acid condition and (b) PVA-Gold film.
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4.7 FESEM micrograph of (a) PVA film, (b) PVA-MPTMS film, and (c) PVA-Gold film.
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4.8 TEM micrograph of PVA-Gold film.
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4.9 Schematic representation of the oxidation of styrene.
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4.10 The conversion and product selectivity of the oxidation of styrene with tert-butyl hydroperoxide using PVA-MPTMS and PVA-Gold as catalyst.
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4.11 Chemical structure of various amino acids.
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4.12 DRUV spectra of PVA-Gold film before (a) and after interaction with amino acids; (b) Pro, (c) Trp (d) Tyr and (e) Arg.
58
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LIST OF ABBREVIATIONS
% - Percentage
wt %. - Percentage of weight
° - Degree
°C - Degree Celsius
λmax wavelength of maximum
atm - atmospheric pressure
absorbance
Au - Aurum (gold)
CCD -
cm - centimeter
Charge coupled device
cm2
DNA - Deoxyribonucleic acid
- centimeter squared
E° Electrode potential
FESEM - Field emission scanning electron microscopy
FTIR - Fourier transform infrared
FTIR-ATR - Fourier transform infrared – attenuated total reflectance
g - Gram
GC - Gas chromatography
GC-MS - Gas chromatography with mass spectrometry
HAuCl4 -
HCl - Hydrochloric acid
Hydrogen tetrachloroaurate
HNO3 -
L - Liter
Nitric Acid
M - Molar
mL - milliliter
xv
μL - microliter
μm - micrometer
mm - millimeter
MPTMS - (3-mercaptopropyl) trimethoxysilane
nm - Nanometer
NA -
SO
Numerical Aperture
2
SPR - Surface plasmon resonance
- Sulfur dioxide
TBHP - tert-butyl hydroperoxide
UV - Ultraviolet
UV-Vis - Ultraviolet-visible
UV-Vis DR - Ultraviolet-visible diffuse reflectance spectroscopy
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LIST OF APPENDICES
APPENDIX TITLE PAGE
A Chemical reagents for synthesis of gold nanoparticles and chemical reagents for synthesis of PVA-Gold.
74
B Chemical reagents for catalytic testing and chemical reagents for interactions with amino acids.
75
C Calculation of % Conversion and % Selectivity. 76
D GC chromatogram of oxidation of styrene with TBHP at 70º C for 3 hours.
77
E GC chromatogram of oxidation of styrene with TBHP at 70º C for more than 24 hours.
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CHAPTER 1
INTRODUCTION
1.1 Research Background
Nanoparticles can be defined as particles with at least one of their three-
dimensional sizes in the range of 1 – 100 nm. Recent intense interest in nanoparticles
stems from the fact that nanoparticles exhibit unique properties compared to their bulk
counterparts. Many of these properties including physical, chemical, optical, electrical
and magnetic can be controlled by relatively simple tuning of their sizes, shapes,
compositions, protecting ligands and interparticle distance. To date, the most widely
studied nanoparticles have been those of metals, semiconductors and magnetic materials
due to the potential applications of these materials in optoelectronics, catalysis,
reprography, and other areas [1]. However, among these metallic particles, gold
nanoparticles stand out in particular due to their associated strong surface plasmon
resonance (SPR). Surface plasmon was found to be dependent not only on the size of the
gold nanoparticles but on their shape as well [2]. The SPR absorption and other unique
properties resulting from the small gold particle size can be exploited in a wide range of
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sensing applications such as bioimaging [3-5], chemical and biological sensing [6, 7]
and colorimetric assays for DNA detection [8, 9].
It was demonstrated that gold nanoparticles could readily bind thiol, amine,
cyanide and diphenylphosphine functional groups [10-13]. Amino acids, which is a
constituent of proteins, are considered as suitable agents in the biofunctionalization of
gold nanoparticles due to the presence of different functional groups, such as –SH and
–NH2
, with affinity for gold. Generally, amino acids can be adsorbed on the gold
particle surface during the formation of particles, using amino acid itself as a reducing
agent [14-16], or in the latter stage, by ligand exchange reactions or binding on the
former adsorbed stabilizing molecules [17]. Most applications of gold nanoparticles as
sensors are based on detecting the shifts in the SPR peak, due to either the change in the
local dielectric constant of the nanoparticles resulting from adsorbed biomolecules or
due to biomolecule induced agglomeration of the nanoparticles [18].
Gold in the bulk is chemically inert and has often been regarded to be poorly
active as a catalyst. However, when the dimension of gold is reduced below ~10 nm, it
turns out to be surprisingly active for many reactions such as CO oxidation, especially at
low temperatures as first discovered by Haruta [19]. The catalytic activity of both
heterogeneous and homogeneous gold based catalyst is now well established in different
processes: selective or complete oxidation, hydrochlorination, and hydrogenation
reactions [20]. All of these applications show the special reactivity of gold compared
with platinum group metals and this may be explained in terms of the electronic states
(+1, +3) and the high electrode potential of gold (Eº = +1.69 V).
Nanoparticles have a tendency to aggregate and are difficult to recover from
reactions due to their small size. Therefore, in order to overcome these difficulties, it is
necessary to immobilize the gold nanoparticles onto a matrix material such as polymers
because the immobilized nanoparticles are more stable. The principle advantages of the
method are that the resulting materials are easily prepared in a single-step procedure and
the possibility to control the thickness of the polymeric layer. These materials also
3
possess the processing and handling advantages of bulk materials. Other benefits of
immobilizing nanoparticles in polymeric matrices include increased stability, improved
processability, recyclability, and solubility in a variety of organic solvents. Among
polymers, polyvinyl alcohol (PVA) is a commercially important water soluble polymer
which is known to be a good stabilizer of noble metal particles. PVA is also the most
important material for the dehydration of organic mixtures owing to its good chemical
stability, film forming ability and high hydrophilicity [21]. Other polymers commonly
used for the stabilization of gold nanoparticles are poly(1-vinylpyrrolidone) and
poly(ethylene glycol) [22]. In the case of heterogeneous catalysis, the catalytic
properties of gold were shown to depend strongly on the support, the preparation
method, and particularly the size of the gold particles [23, 24].
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1.2 Problem Statement
Gold nanoparticles hold a particular interest to those in the biological sciences
because they are on the same size scale as biological macromolecules, proteins and
nucleic acids. The interactions between biomolecules and nanomaterials have formed the
basis for a number of applications including detection, biosensing, cellular and in-situ
hybridisation labelling, cell tagging and sorting, point-of-care diagnostics, kinetic and
binding studies, imaging enhancers, and even as potential therapeutic agents.
Recently, it has been reported that the scattering property of gold nanoparticle
could be harnessed in a living cell to make cancer detection easier [25, 26]. What makes
the approach so promising is that the method was simple, employing only inexpensive
microscope and white light. However, the method used was not practical because in the
above method, the gold nanoparticles were in solution form such that it could not be
recovered and reused. In this research, we investigated the feasibility of immobilizing
gold nanoparticles (and also their conjugates) in polymer film without degradation of
their SPR properties.
The catalysis by metal nanoparticles is one of the most important and attractive
research owing to an increase in exposed surface area and to a possibility of finding
novel properties generated by quantum size effect [27]. The use of homogeneous gold
catalyst could be unfavourable in practical applications as the separation and reuse of the
catalyst after reaction would be problematic. Most studies on gold catalysts have been
focused on gold oxide supports as these catalytic systems are mostly used for gas-phase
oxidation. However, as recently reported, gold catalysts also represent a useful
alternative to platinum group metals systems for liquid phase oxidation [28]. In this case,
the presence of a solvent such as water dramatically affects the interaction between the
reagent and the catalytically active materials. In particular, gold on polymer shows
superior selectivity and is much less affected by poisoning, when compared with
classical palladium and platinum catalysts. As poisoning represents one of the major
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drawbacks limiting industrial application in liquid phase oxidation involving oxygen as
the oxidant, the advantage of using a gold catalyst may not be of only academic interest
but could also have industrial potential. As a consequence, there is a growing need for a
general procedure to prepare gold catalysts with high dispersion, regardless of the
polymer support used.
Despite a large number of methods reported to immobilize gold nanoparticle in
polymer film, it is still desirous to develop a simple and effective synthesis of such
nanoparticles with better size control and uniform particle distribution. Nevertheless, the
difficult handling of these extremely fine particles has posed a strong limitation to their
use. Most metal nanoparticles are very unstable. They can aggregate because of the high
surface free energy and readily oxidized-contaminated by air, moisture, sulfur dioxide
(SO2
) and so on. Therefore, the embedding of gold nanoparticles in a polymer surface
represents a valid solution to the manipulation and stabilization problems. Furthermore,
polymer embedding represents a straightforward but effective way to use the mesoscopic
properties of metal nanoparticles.
Previous studies reported that the immobilization of gold nanoparticles on
polymeric surfaces or substrates involved the immersion of the functionalized surface
such as thiol functionalized polymer in gold solutions [20] followed by drying.
However, this method is not practical as the gold nanoparticles attached to the surface
may be easily detached since they are only linked to the functionalized polymeric
surface via chemisorption so that the particle-to-surface contact area is too small to
allow a strong attachment. Our approach is different compared to the previous study as
the gold nanoparticles are annealed on the surface of partially dried functionalized
(3-mercaptopropyl) trimethoxysilane (MPTMS) polymeric layer. Thus, the gold
nanoparticles are not only linked to the functional groups on the polymer surface but are
actually embedded in the polymer layer which enhanced the particle-to-surface contact
area between gold nanoparticles and PVA film, making it more difficult for the
detachment of the gold nanoparticles as presented schematically in Figure 1.1.
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Figure 1.1: Schematic representation of the proposed gold nanoparticles embedded in
the surface of polymer: (a) gold nanoparticles attached on the surface of the polymer layer by chemisorption, (b) gold nanoparticles embedded in the polymer layer by attachment of nanoparticles on the surface of partially dried functionalized polymeric layer.
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1.3 Research Objectives
The objectives of the study are:
(1) To synthesize gold nanoparticles using the Turkevitch method via the reduction
of HAuCl4
with sodium citrate in water.
(2) To incorporate gold nanoparticles on the surface of functionalized PVA.
(3) To investigate the catalytic activity of the gold nanoparticles embedded on PVA
for liquid phase oxidation of styrene.
(4) To investigate the structural and morphological properties of the gold
nanoparticles embedded on PVA in the interactions with amino acids.
8
1.4 Scope of Study
In this research, the gold nanoparticles will be synthesized by the reduction of Au
(III) ions with citrate in water, a process pioneered by Turkevitch [30] in 1951 and later
refined by Frens [31]. In this method, citrate serves as both reducing agent and an
anionic stabilizer. It yields uniform and almost spherical particles with diameters
ranging from a few to approximately 150 nm. The size of the resulting colloidal gold
nanoparticles, whose surfaces are negatively charged with citrate, is controlled by the
molar ratio of HAuCl4
/ sodium citrate (the lower the ratio, the smaller the particle size).
The produced gold nanoparticles will be studied on its surface morphology and physical
properties especially related to its SPR absorption and scattering properties.
Then, the stable incorporation of gold nanoparticles on the surface of polymeric
layer, such as PVA, will be achieved by using MPTMS as a linker molecule which has
the ability to react with the functional groups of the polymeric layer [32]. The catalytic
activity of gold nanoparticles embedded on PVA (PVA-Gold) was investigated for the
oxidation of styrene and the biosensing capability of PVA-Gold were studied on the
interactions with various amino acids.