D362130

Dr. F F.M. AL-K et al Int. Journal of Engineering Research and Application
ISSN : 2248-9622, Vol. 3, Issue 6, Nov-Dec 2013, pp.21-30

RESEARCH ARTICLE

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OPEN ACCESS

A Simple Method for Synthesis, Purification and concentration
Stabilized Goldnanoparticles
Dr. Fatin F.M. AL-Kazazz1, Kifah A. F. AL-Imarah2, Ikteffam.Abed ALHasnawi3, Agelmashotjafar L4, Dr.Ban Abbas Abdul-Majeed5
1

Assistant Professor /University of Al-Mustansiryiah/College of Science /Department of Chemistry/E.mail:
Head of Chemists/ Ministry Of Science and Technology
3
Ph.D Student / University of Al-Mustansiryiah/College of Science /Department of Chemistry
4
Ministry of Science and technology, Iraq
5
Professor/ University of Baghdad/College of Medicine
2

ABSTRACT:
The greatest barriers to biological nanoparticles in use are issues of particle stability in shape and size control.
Simple process is desirable for several reasons likewide range of sample volumes, gentle conditions and
inexpensive equipment.
Gold nanoparticles(GNPs) which are produced by reducing gold chloride with TSC have very limited time
storage. In order to get highly stable nanoparticles, purification has been performed for industrial applications.
Removal of the side product of the reaction between HAuCl4 with Tri-Sodium Citrate (TSC)is considered to
make GNPs more stable. The result demonstrates that GNPs are more stable after the purification process.
Low degree of polydispersity can be achieved during gold nanoparticles synthesis, however, the particles need
to be purified post-synthesis. The present research relates to single process for the removal of small-molecule
impurities and the isolation of small nanoparticles from larger nanostructures through dialysis and
microfiltration then concentration these small nanoparticles through polymer adsorbent materials by a factor of
100 or more to storage in the room temperature prolongs the stability of the purified gold nanoparticles
suspension up to one year.The size and shape of the GNps is measured by atomic force microscopy (AFM), and
the optical properties by UV-Vis spectrometer.
Keywords: Gold nanoparticles (GNPs), thermal decomposition, dialysis, microfiltration, polymer absorbent

I.

The claimes

The purification of water-soluble gold
nanoparticles is particularly difficult because the
nanoparticles and the impurities have similar
solubility, often making standard purification
techniques
(i.e.
precipitation,
extraction,
chromatography, centrifugation or dialysis) inadequate
or inefficient. Although reasonable purity is afforded
via these methods, the nanoparticles remain
contaminated with precursor molecules, e.g., salts and
free ligand.
1. A method for producing a population of gold
nanoparticles having a narrow size distribution
comprising pure GNPs which indicated through
the decreasing in their particle size and stable for
one year.
2. The possibility to prepare monodisperse inorganic
nanoparticles of pure materials in the sub-20 nm
size regime has opened an effective ﬁeld of
research. This ﬁeld is needed to go to the next
step and develop methods of scaling up the
synthesis of these materials.
3. A simple method for stabilized, water-soluble
nanoparticles based upon the size of the
nanoparticles was found out comprises:

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The invention didn’t mix metal salts with a
solution of an organic surface that had a
functional group such as a thiol, disulfide,
amine, oxide, or amide to prepare a stabilized
nanoparticles only mixed a reducing agent
was added to reduce the metal salt to the free
metal.
b) The thermal decomposition method for
producing gold nanoparticles in the less or
20 nm size regime from a mixture of gold
salts ( HAuCl4) and reducing agents such as
(TSC, NaBH4 or both) and refluxing said
homogenous mixture to a temperature above
the melting point of gold salts and water not
exceed 90 oC, but usually obtain product
with high dispersity and low nanoparticle
concentration which limit its application.
c) A “broad size distribution” in reference to a
population of nanoparticles will refer to
nanoparticles ranging in size from about 1
nm to about 100 nm, wherein the majority of
nanoparticles are spread over a large range of
particle sizes. For desirable size and
monodispersity stabilized gold nanoparticles ,
the method comprises the using of dialysis
membrane to an aqueous nanoparticle
a)

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solution in the presence of buffer to purify
from soluble impurities and remove
particles having a broad size distribution
without adding a substantially water-miscible
organic solvent.
d) Moreover, the concentration of as-produced
gold colloidal through polymer absorbent by
a factor of 100 or more without aggregating
the material give stable nanoparticles for
more than one year at room temperature.

II.

INTRODUCTION

The physical and chemical properties of
nanoparticles are critically dependent on their size.
Many
applications
require
monodispersed
nanoparticles, i.e., particles of uniform size, with a
defined particle size. However, chemical synthesis
usually results in nanoparticles with a broad particle
size distribution, i.e., polydispersed nanoparticles.
Methods are known in the art for determining the size
of nanoparticles and for separating nanoparticles
based on their size.
The ability to tailor low-polydispersity
particles is important, in several cases (e.g., using
polymeric stabilizers, reverse micelles, or thermal
decomposition methods.
The report paper
byIrshadHussain et al based on a simple one-step
protocol for the preparation of near-monodisperse
gold hydrosols in the small size regime (<5 nm). The
particle size can be controlled by varying the
concentration of the stabilizing polymer, which can be
readily displaced by thiol ligands to yield monolayer
protected clusters of the usual type [1].
NatalliaShalkevich and coworkers [2], they
have developed a simple method for the preparation of
nearly mono-dispersed stable gold colloids with a
fairly high concentration using two-steps procedure.
First they synthesized citrate capped (GNPs) and then
exchange the citrate ions with Triethyleneglycolmonomercaptoundecylether (EGMUDE). This leads to the
immediate precipitation and formation of composite
assemblies.
Samuel et al. have demonstrated millifluidicbenchtop
reactor system for the gram-scale synthesis and
purification
of
monodisperse,
hydrophilically
functionalized gold nanoparticles with different sizes
and shapes [3].
The paper by Steinigeweg summarized the
results of the separation and purification of Gold
Nanoparticles in the 20–250 nm Size Range by
continuous density gradient centrifugation and
glycerol/water mixtures as separation media to obtain
highly purified metal colloids [4].
Balasubramanianet al work demonstrates
how impurities are identified and removed, and the
optimal purification of 20-nm GNPs was achieved by
centrifugation operating at 7000 rpm for 20 min which
satisfactorily recovers ∼80% of GNPs without
detectable impurities. Storage in the dark at 4 °C
prolongs the stability of the purified GNP suspensions
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up to 20 days. Purified GNPs can be a reference
material to evaluate toxicity or reactivity of other
engineered nanomaterials [5].
Sweeney etal.have reported studies aimed at assessing
the suitability of diafiltration for (i) the purification of
water-soluble thiol-stabilized 3-nm gold nanoparticles,
(ii) the separation of a bimodal distribution of
nanoparticles into the corresponding fractions, and
(iii) the separation of a polydisperse sample into
fractions of differing mean core diameter. They
demonstrate that diafiltration produces nanoparticles
with a much higher degree of purity than is possible
by dialysis or a combination of solvent washes,
chromatography,
and
ultracentrifugation
[6].
Therefore, purification and size-based separation of
nanoparticles remain significant challenges in the
preparation of well-defined materials for fundamental
studies and applications [7-9].
We find out a simple protocol for converting
the thermal decomposition method to produce gold
nanoparticles from a mixture of gold salts and
reducing agents (TSC or both TSC and NaBH4) at
room temperature or by refluxing said homogenous
mixture to a temperature above the melting point of
gold salts and water as a solvent which produced low
nanoparticle concentration and highdispersity to
produce as- nanoparticles of a desirable size, and
monodispersity which have a great potential in largescale manufacturing for industrial demand and other
applications.
The water - based GNPs be purified from
soluble impurities and removed side product using a
dialysis membrane combined with microfiltration and
increased the concentration of as-produced colloidal
material through polymer absorbent by a factor of 100
or more without aggregating the material and
remained stable for more than one year at room
temperature. The size and shape of the GNPs is
measured by atomic force microscopy (AFM), and
the optical properties by UV-Vis spectrometer.
III.
EXPERIMENTAL DETAILS
This work deals with thermal decomposition
methods used for producing stable GNPs of various
diameters in size. The success of the below procedure
depends upon several factors including the use of
clean glassware and stirrers. Most methods avoid use
of chromic acid because of the toxicity and
carcinogenicity of Cr (VI) compounds and reported
cleaning with aqua regia that dissolves almost all
inorganic materials including gold particles from
previous preparations, followed by detergent and
rinsing many times with water (the last rinses are
always done with the purest water available) then with
organic solvent such as acetone or ethanol to remove
organic impurities. The resistivity of water used was
18 M ohm cm, which is the theoretical limit at which
conductivity is due only to the dissociation of water
into [H+ and OH- ] ions. However immediately upon
contact with air water absorbs CO2. The CO2 reacts
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with water to produce carbonic acid, which ionizes to
make the actual resistivity of the “pure” water about 1
M ohm cm and reduces the pH from 7 to 6 or less
[10]. We use containers with narrow necks and tight
fitting caps rather than beakers to reduce possible
entry of contaminants from air and to keep air out and
sample in during storage.

IV.

Materials

All materials were of analytical grade from
Sigma Aldrich and used without any
further
purification; ultra- pure water was provided from
deionize ultra filtered system. Polymer absorbent
made of polyacrylate -polyalcohol has molecular
weight 20k Daltons. Dialysis tubular form membrane
for sample volume 20-50 ml were used.

V.

Synthesis of gold nanoparticles

Method No.1:
In this work, solutions of citrate reduced
GNPs were preparedaccording to the Turkevich and
Frens method [9,10]. The reaction (100 mL final
volume) was performed in a 3-neck 250 mL round
bottom flask with the center neck attached to a reflux
condenser. The flask was set in a hot plate with a
magnetic stirrer to provide continuous mixing. The
temperature was precisely maintained by circulating
thermostated water within the uncertainties of ± 0.1
o
C. During the thermal decomposition, water is passed
through condensing jacket. Vapors rising from the
solvent are cooled as they pass through tube, leading
to condensation of the solvent vapors. The condensed
solvent then falls back into the reaction vessel. This
re-condensation prevents any significant loss of
volume of the solvent during the thermal
decomposition reaction. Thus, the relative ratio of
metal to solvent stays substantially constant
throughout the reaction. As long as the temperature of
the homogeneous mixture is raised to above the
melting point of the metal salt, the desired thermal
decomposition reaction will take place and lead to
formation of metal nanoparticles.
50 mL sample of aqueous(2.5 ×10-4M)
HAuCl4.3H2O( Hydrogen tetrachloroaurate (III)
trihydrate)was prepared in a flask. The solution was
brought to boil at (65-70 0C) while stirring, and 1.0
mL of 5%(0.17M) aqueous Tri-sodium citrate (TSC)
was added. The boiling and stirring was continued for
25 min after the final color change. After cooling to
room temperature, the GNPs solution was diluted
using DIH2O to replace the water evaporated during
boiling.
Method No. 2:
GNPs were prepared by the reduction of
hydrogen tetrachloroaurate (III) trihydrate with
reducing agent and Sodium borohydride(NaBH4) . In
brief, 1.0 mM HAuCl4 (10 mL) was prepared and then
0.5 ml aliquots of freshly prepared 0.5mM NaBH 4
were added at 10 °C to the slowly mixing solution
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of gold salt until a stable orangered/purplecolored
colloid was observed (≅0.8-1.2 mL NaBH4). The
reaction was left for 18 hours at 20 °C and finally,
solutions were purified and filtered as described later
and stored at 4° C. This reaction does not need high
temperature to proceed. The changes of color are very
fastto ruby red.
Method No. 3:
According toBrown et al. [11], we prepared
GNPs using a seeding method to give a small
nanoparticles with a diameter of ~5.0 nm. A brief
description is as follows; 1.0 ml of 1% HAuCl4 was
added to 90.0 ml of water at room temperature (2023ºC). After 1 minute of stirring, 2.0 ml of 38.8 mM
TSC was added. One minute later, 1.0 ml of fresh
0.075% NaBH4 was added. The colloidal solution was
stirred for an additional 5 minutes and stored in a dark
bottle at 4ºC.

VI.

Detecting the nanoparticle formation
process

In the synthesis process of GNPs, a portion of
the reaction mixture (0.5 to 1 mL) was taken out from
the flask at different reaction time and immediately
poured into 9 mL ice-cooled water at 0°C. Such an
operation can basically cease the formation process of
GNPs due to the low temperature surrounding and the
dilution effect, so it was called here as a “samplefrozen” operation. Then, the AFM samples were
prepared at the earliest time and the ultraviolet visible
(UV-Vis) spectra were recorded.
Glass microscope slides (25×75×1 mm,) were cut into
smaller pieces (25×10 mm) and carefully cleaned by
soaking in a solution of nitric acid/water
(50/50%) for 20 min. Rinsed slides were immersed in
Piranha solution (70% concentrated sulfuric acid: 30%
hydrogen peroxide, 7:3) for 20 min and extensively
rinsed with water. Cleaned glass slides were dried
under a nitrogen stream and kept in closed desiccator.
UV-Vis spectra were recorded on a UV-visible
spectrophotometer to collect the surface Plasmon
resonance (SPR) information of GNPs, in which the
highly concentrated samples were diluted by DIH2O to
adapt the measurement limitation. AFM samples were
prepared by dropping the diluted gold colloids on
glass microscope slides.
Purification Method ofGold Nanoparticles Solution
Can GNPs be purified from soluble impurities by
extensively washing the nanoparticles with clean
buffer solutions?
The membrane pores permit ions (or small molecules)
to pass through but not the large colloidal particles
(Figure 1). When a sol containing dissolved ions
(electrolyte) or molecules is placed in a bag of
semipermeable membrane dipping in pure water, the
ions diffuse through the membrane. By using a
continuous flow of fresh water, the concentration of
the electrolyte outside the membrane tends to be zero.

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Thus diffusion of the ions into pure water remains
brisk all the time.
Figure 1: Rigid particles smaller than the pore size

will go through the dialysis membrane (Left).
Operation of microfiltration to remove more
impurities and sample
The dialysis tubing cellulose membrane was
used in this dialysis process, the outside and inside of
the dialysis tubing was rinsed with 20ml of DIH2O for
15 to 30 minutes to remove sodium azide preservative.
The water was poured out and the step repeated with
another 20ml of deionized water. The dialysis is done
in three days by immersing the dialysis tube
containing GNPs in deionized water. The water is
changed every 24 hour. In general, dialysis will be
most effective when the buffer is replaced a few times
over the course of a day and then left overnight at
room temperature on a stir plate. A standard protocol
for dialysis is 16 to 24 hours. Many factors affect the
rate dialysis, including: diffusion coefficients, pH,
temperature, time, concentration of species, sample
volume, dialysate (buffer) volume, number of
dialysate changes, membrane surface area, membrane
thickness, molecular charges and dialysate agitation
(stirring).
The dialysates (buffers) are commonly used
in dialysis must be maintained under strict pH control
to stabilize their molecular properties. The typical pH
range for dialysis buffers is 6 to 8. The larger the
dialysate volume, the greater the driving force for
diffusion of small molecules. We generally
recommend a 100:1 buffer to sample volume ratio. By
replacing the buffer just as the rate of diffusion slows
down and the solutions are approaching equilibrium,
you can maintain the driving force and the rate of
dialysis. We generally recommend two or three buffer
changes over the period of 12 - 24 hrs as follows: First
buffer change, after 2-3 hours; Second buffer change,
after 4-5 hours and Last buffer change, prior to
leaving overnight.

VII.

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dilute material in other solvents or buffers. Typically,
the concentration of GNPs is limited by the synthesis
method and ranges from ( 0.01 - 0.2 ) mg of gold per
mL of solution. We have used polymer absorbent to
increase the concentration of as-produced gold
colloidal material by a factor of 100 without
aggregating the material and keep the particle size to
smaller value.
In order to concentrate the GNPs that have
been prepared using Turkevich process, we tried to
concentrate them down because we need to fit about
5mg into 20-50ml of space, perhaps even dry them
out. Boiling reaction solution down will turn it from
red to gray with black powder and gold flake like
layers floating on top turn the particle size to larger
value.
Polymer absorbent is a solution for easy
concentration, high water absorbent capacity, made of
polyacrylate-polyalcohol it has the property of
expanding as it absorbs water. The high molecular
weight polymer can be used with dialysis membranes
of molecular weight 20k Daltons without
contaminating the sample (figure 2). After dialysis
process, simply remove the dialysis tubing containing
the sample and coat it with absorbent. Water and
smaller molecules diffuse through the membrane and
are absorbed by absorbent. Concentration continues
unattended until a certain volume of water is removed
from the sample. The insoluble characteristic makes
absorbent easy to remove after absorbency.
Table (1) and Figure (3)show the data for the
"rinsing" of the gold colloid has ( λmax 520, OD
1.817, as in Figure 2)with dialysate buffer solutions
and microfiltration to remove all residual reactants
resulting in a high purity solution that contains only
nanoparticles (λmax 525.5 , OD 2.672). Further
concentration with polymer absorbent results in the
removal of excess water to yield an increase in its (OD
4.560).
Table 1: GNPs peak absorbance due to purification
and concentration
GNPs
synthesis
by λ (nm)
OD
method No.1
Without [Dialysis,
520.0
1.817
Filtration & Absorbent]
With
[Dialysis
+
525.5
2.672
Filtration]
With
[Dialysis
+
527 .5
4.560
Filtration + Absorbent]
The length of time needed for concentration
will depend on the final volume, the surface to volume
ratio of the membrane tubing and the amount of
absorbent.

Methodof Concentrating GNPs

For many applications it is desirable to have
a high concentration solution available from which to
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Figure2: UV-VIS spectrum for the formation of ruby red GNPs from the reaction (5%)TSC and (2.5×10-4M)
HAuCl4 solution at ( 65-70)0C before dialysis.

Figure 3: The influence of dialysis and polymer adsorbance on the stability of gold nanoparticles through UV-Vis
spectrum and AFM images : curve (1)before dialysis , curve (2) after dialysis and absorbent {2-fold dilution with
H2O} and curve (3) without dilution.

VIII.

Determination the Stability of
Colloidal Gold

There are several important factors that can
influence the stability of colloidal GNPs. Among the
most important factors are the particle sizes,
concentration, reducing agent, and local environment.
Different reducing agents provide differing levels of
stability to salt, light, heat and pH value.
Stability of gold NPs was investigated by
measuring the absorption spectra of the gold colloidal
sol prepared at various times. The sample was stored
at room temperature in a transparent vial and UVVisible spectra of the sample were taken after the
formation of final ruby redgold colloid sol (Plasmon
absorbance at 527.7 nm) then after one week, two
weeks, one month, and two months. The results
indicate that there is small obvious difference in
position and symmetry of absorption peak during the
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initial two weeks (Table 1and Figure 3) from Plasmon
absorbance at 527.7 nm to 523nm. After six months,
the position of the peak has a slight blue shift (from
523 to 517 nm)suggesting the formation of smaller
particles without any aggregation. Even after one year
the Plasmon absorbance remained at 517 nm and no
aggregation was observed as in (Table 2 and Figure
4). Thus, colloidal gold can remain stable at room
temperature for as long as several months. The reason
for the stability of the colloid gold sol is described in
the discussion section.
Table 2: The stability of gold nanoparticles synthesis
with method No.3.
GNPs synthesis by ( TSC
λ
OD
+ HAuCl4)
(nm)
[Withdialysis, filtration
5 17
1.608
and polymer absorbent]
( 2.5 -fold
After one year
dilution)
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Figure 4: UV-VIS spectrum for the stability of GNPs synthesis with method No.3 and AFM image which indicate
decreasing in their particle size and stable for one year after dialysis, 0.25µm filtration and polymer absorbent.
IX.
RESULTS
Decreasing reaction rate by lowering temperature:
Basically, the chemical reaction rate depends
on temperature; the high rate of nanoparticle
formation can be decreased at a low temperature. In
this work, the nanoparticle synthesis was therefore
performed at 80°C and 60°C.It was found that the
formation rate of GNPs slowed at lower temperatures.
The color of the colloids obtained at 75°C (Table 3
and Figure 6) did not differ from that of those
produced under boiling state (Table 4).

Chunfang Li et al have been reported, that the reaction
rate was greatly enhanced at high reactant
concentration by the citrate method[12].
The first effort in our work was heated
(2.5×10-4M) aqueous chloroauric acid solution to
boiling at 60 0C and the 3.3 times molar amount of
sodium citrate was added, followed by continuously
heating for a certain period to get the ruby red
colloids.In Table3, We could find that GNPs
synthesized in presence of (2.5×10-4M) HAuCl4have
an average size of 15-20 nm with large size
distribution,
while
at
a
high
HAuCl4
concentration,1.0mM, the particle size was decreased
8-10
nm
with
a
narrow
distribution.

Table 3: Color and peak absorbance change for the reaction(5%) TSC and (2.5×10-4M) HAuCl4 and increase
boiling with time to synthesis (AuNPs) solution at 60 0C.
Time, min.
λ, nm
OD
Color change
10.0
20.0
25.0
32.0
36.0
42.0
52.0
79.0

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549.50
531.00
528.00
526.00
524.50
523.50
523.00
523.00

0.090
0.121
0.130
0.221
0.307
0.557
0.815
0.914

Faint violet
Faint violet
Pink
Pink
Bright pink violet
Red
Ruby red
Ruby red

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Figure 6:UV-VIS spectrumfor the reaction (5%) TSC and (2.5×10-4M) HAuCl4 and increase boiling with time to
synthesis GNPs solution at 60 0C.
The SPR peaks of the gold colloids taken-out
from the reaction mixture at different time were also
studied by UV-Vis spectroscopy. We found that the
colloidal samples prepared at (2.5×10-4M) show SPR
peaks around 523 nm, and the reaction time should be
controlled at 30 to 40 min, although longer reaction
time (~70 min) did not cause aggregation.
The color and the SPR peaks of these
colloids do not show obvious differences, and no
obvious difference is found in the full width at half
maximum of these peak profiles. GNPs show that the
size polydispersity varies with the reactant
concentration increase although the particle average
sizes are all located in a range of 10 to 20 nm. The
large size distribution of GNPs at high reactant
concentration will limit further applications such as
size-related bioassays. Moreover, the as obtained gold
colloids from high gold salt concentration and low
TSC concentration (1%) give gold sols with double
OD value (1.82) when compare with (0.91) value for
higher TSC concentration (5%).
Table 3 : Color and peak absorbance change due to
the reaction (1%) TSC and (1 ×10-3 M) HAuCl4 and
increase boiling with time to synthesis GNPs
solution at 750C.
Time, min
λ nm
Abs.
Color
(OD)
change
10.0
530.0
1.208
Violet
20.0

530.0

1.382

25.0
32.0

528.0
520.0

1.659
1.817

deep
violet
Red
ruby red

Aggregation mechanism of gold nanoparticles:
UV-Visible spectroscopy can be used as a
simple and reliable method for monitoring the stability
of nanoparticle solutions. In second method, solution
of 18 ml DIH2O, 0.5ml (0.01M) TSC and 0.5ml
(0.1M) NaBH4 was shaken and them added dropwise
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to 0.5 ml of HAuCl4t the color change to ruby
red.When
added
(1.0ml
or
2.0ml)
from
HAuCl4(0.01M)the color change to deep violet and
then precipitate black particles.
The optical properties of GNPs change when
particles aggregate and the conduction electrons near
each particle surface become delocalized and are
shared amongst neighboring particles. When this
occurs, the surface Plasmon resonance shifts to lower
energies, causing the absorption and scattering peaks
to red-shift to longer wavelengths. This is agree with
the determination of an optimal set of conditions for
the synthesis of GNPs is described in the work of Yuri
et al. [ 13].They found Submicrometer “dense” liquid
domains and aggregates (in the gray and blue
solutions) of globules about 30–50 nm in diameter as
intermediates in the citrate synthesis of GNPs. With
decreasing nanoparticle diameter, the λ
max shifts to a
shorter wavelength.
As shown in Table 3 and Figure 5, the
particles destabilize, the original extinction peak will
decrease in intensity (due to the depletion of stable
nanoparticles), and often the peak will broaden or a
secondary peak will form at longer wavelengths (due
to the formation of aggregates). The rapid change in
the extinction spectrum as HAuCl4 concentration is
increased and clearly demonstrates that the
nanoparticles are agglomerating.
UV-Visible spectroscopy can be used as a
characterization technique that provides information
on whether the nanoparticle solution has destabilized
over time. Un aggregated GNPs will have a red color
in solution, If the particles aggregate, the solution will
appear blue/purple and can progress to a clear solution
with black precipitates.

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Table 3: Color and peak absorbance for the reaction (0.01M) TSC, ( 0.1M) NaBH 4 with different volumes of
(0.01M) HAuCl4 in order to study the nanoparticles aggregation process
Volume of HAuCl4
λ max
OD
Color change
0.5 ml
520 nm ( sharp peak)
0.775
Ruby red
0.75ml
520 nm
0.2915
Blue - Purple
971 nm (broaden peak)
0.493
1.0 ml
~ 551 nm ( broaden peak)
~ 1.076
Deep violet
1.5 ml
~ 563 nm (broaden peak)
~ 0.447
Black pptn.
2.0ml
No peak
No peak
Black pptn.

Figure 5: UV-VIS spectrum for the reaction (0.01M) TSC, ( 0.1M) NaBH 4 with different volumes of (0.01M)
HAuCl4 in order to study the nanoparticles aggregation process.
Figure (6) shows the third method data, ruby red colloidal gold has been obtained upon reaction gold salt with
freshly prepared ice-cold sodium borohydride without using TSC. The gold particle sizes are 12 ± 2 nm due to the
Plasmon absorbance near 519 nm with 0.820 OD.

Figure 6: UV-VIS spectrum for the reaction of 0.5ml (0.5 mM) NaBH 4 with 10ml (1.0 mM) HAuCl4 to
produce gold nanoparticles .
An excess of NaBHn4 is needed both to reduce the
ionic gold and to stabilize the (GNPs) that form. The
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chemical reaction is the NaBH4 reduction of gold salt
as follow:
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HAuCl4 + 3e– = Au0 + H+ +4Cl(8)
HAuCl4+ 4 NaBH4λ Au0+ 5/2 H2+ 2B2 H6+ 4NCl
(9)
* Where the core of Au0 nucleates when reducing
agents provide eAdsorption of borohydride plays a key role in
stabilizing growing GNPs by providing a particle
surface charge as shown in Jennifer and
Mozhganworks [14,15]. There must be enough
borohydride to stabilize the particles as the reaction
proceeds. However, later in the reaction too much
NaBH4 increases the overall ionic strength and

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aggregation will occur.
The aggregation can also be brought about by
addition of electrolytes such as NaCl. Nanoparticles
are kept in suspension by repulsive electrostatic forces
between the particles owing to adsorbed borohydride
(Figure 7). Salt shields the charges allowing the
particles to clump together to form aggregates. The
colloidal gold solution turns blue. A Red shift peak
around 530-550 nm appears along with a decrease in
the intensity of the Plasmon absorbance which
indicates onset of aggregation.

Figure 7: The aggregation of GNPs due to the addition of electrolyte
Therefore, reaction conditions, including
stirring time and relative quantities of reagents (both
the absolute number of moles of each reactant as well
as their relative molarities), must be carefully
controlled to obtain stable colloidal gold. It was also
found that the initial concentration of NaBH4 must be
twice that of gold salt: [NaBH4] / [HAuCl4] = 2.0.
When concentration of borohydride was varied from
2.0 mM while using 1.0 mM gold salt, breakdown of
the product took place in less than an hour. Small
GNPs were prepared by the procedure in (No.2) due to
the reaction of gold salt with sodium borohydride.
Synthesis GNPs using NaBH4 is found difficult to be
stopped. However once the reaction is started, the
GNPs grow along the time. After red color has been
achieved which shows the formation GNPs, the
solution becomes dark, and continues growing and
growing, and finally the particles settle down in the
bottom of the flask. This method is not suitable for
industrial preparation purpose which need fast and
stable product for a long periods.

X.

CONCLUSION

A thermal decomposition method for
producing GNPs from a mixture of gold salts and
reducing agents (TSC, NaBH4 or both) at room
temperature and refluxing said homogenous mixture
to a temperature above the melting point of gold salts
and solvent (Boiling range: 100°C for solvent (water)
), wherein the concentration of the gold salts and
reducing agent is selected according to the chemical
reaction equation.
GNPs dialysis rate protocol is affected by
diffusion coefficients, pH, temperature, time,
www.ijera.com

concentration of species, sample volume, dialysate
(buffer) volume, number of dialysate changes,
membrane surface area, membrane thickness,
molecular charges and dialysate agitation (stirring).
We have used a simple method to synthesize pure
GNPs of a desirable size, and monodispersity which
have a great potential in large-scale manufacturing for
industrial demand and other applications. The GNPs
be purified from soluble impurities and removed side
product using a dialysis membrane.
Increased the concentration of as-produced
colloidal material through polymer absorbent by a
factor of 100 or more without aggregating the material
and remained stable for more than one year at room
temperature.
The size and shape of the GNPs is measured
by atomic force microscopy (AFM), and the optical
properties by UV-Vis spectrometer.

XI.

Acknowledgements

The authors thank Dr.SamirChadaat general
manager
of
material
researchdepartment
;Dr.ZarhaAzat
manager of advance material
department/Ministry of Science and technology ,
Baghdad, Iraq) for their helpful in atomic force
microscopy (AFM) measurement and assistantin UVVisible spectrometer .

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