Electronic Supplementary Material
Synthesis and Optical Properties of Gold/Silver
Nanocomposites on Multi-walled Carbon Nanotubes
Prepared via Galvanic Replacement
of Silver Nanoparticles
Judy M. Obliosca,a,c Yi-Shuan Wu,a Hsin-Yi Hsieh,b Chia-Jung Chang,a Pen-Cheng Wang,*,a and
Fan-Gang Tseng*,a,b
a
Department of Engineering and System Science and bInstitute of NanoEngineering and
MicroSystems, National Tsing Hua University, 101 Section 2, Kuang-Fu Road, Hsinchu 30013,
Taiwan
c
Nano Science and Technology, Taiwan International Graduate Program, Institute of Physics,
Academia Sinica, 128 Section 2, Academia Road, Nankang, Taipei 11529, Taiwan
*To whom correspondence should be addressed. Telephone: +886-3-5715131 ext. 34270, Fax:
+886-3-5733054, E-mail: fangang@ess.nthu.edu.tw (FGT); Telephone: +886-3-5742372, Fax:
+886-3-5720724, E-mail: wangpc@ess.nthu.edu.tw (PCW)
Submitted to
Journal of Nanoparticle Research
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This file includes:
Experimental details
Materials and Instrumentation
Synthesis of Multi-walled Carbon Nanotube (MWCNT)
Synthesis of Silver Nanoparticles on MWCNT (Ag-CNT)
Synthesis of Ag/Au core-shell on MWCNT (Au-Ag-CNT)
Preparation of CNT, Au-CNT and Au-Ag-CNT Samples for Raman Spectroscopy
Separation of Au Nanobowls (Au NBs) from MWCNT Surfaces
Supporting Figures
Fig. S1 SEM and HR-TEM (inset) images of MWCNT
Fig. S2 Histogram of the size distribution of Ag/Au core-shell grown on MWCNT
surfaces
Fig. S3 Au-Ag-CNT hybrids (i. e., Ag/Au core-shell on MWCNT) produced at different
[HAuCl4], replacement reaction times and temperatures
Fig. S4 HAADF-STEM image of Ag/Au on MWCNT produced after 10-min
replacement reaction of Ag with Au.
Fig. S5 TEM image of Au-Ag-CNT hybrids at 10-min replacement time and TEM-EDX
percent elemental Au and Ag in Au-Ag-CNT products
Fig. S6 Histogram of the diameter size distribution of Au nanobowls (Au NBs) and Au
NB tip
References
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Experimental details
Materials and Instrumentation: Reagents, H2SO4, polyvinylpyrrolidone (PVP), and AgNO3,
were purchased from Sigma-Aldrich while ethylene glycol was acquired from Shimakyu’s Pure
Chemicals. Deionized water (DI) was used for all solution preparations. Gold/silver
nanocomposites on MWCNT (Au-Ag-CNT) products were filtered (Millipore, MWCO 10,000)
and concentrated using a Hitachi-Himac CR 22GII centrifuge (Rotor # 47, 15A). UV–vis
absorption spectra were recorded on a Jasco V-670 spectrophotometer. TEM and high resolution
TEM (including the high angle annular dark field, HAADF-STEM) micrographs were taken
from a JOEL 2010F and a JEOL JEM 3000F transmission electron microscopes operated at 200
kV and 300 kV, respectively. SEM images were taken from a JEOL 6380 scanning electron
microscope. Raman spectra were recorded using a confocal Raman microscope consisting of a
He-Ne laser, a microscope, an imaging spectrometer, and a liquid-N2 cooled CCD detector.
Synthesis of Multi-walled Carbon Nanotube (MWCNT): The synthesis of MWCNT was carried
out by a two-step process consisting of a catalyst preparation followed by the thermal chemical
vapor deposition (CVD) process. First, catalyst metal layers consisting of Ti, Al, and Ni, with
thickness of 1750, 525, and 175 Å, respectively, were consecutively deposited via sputtering on a
Si substrate. Next, MWCNT growth was carried out using a thermal CVD system described in
the literature (Zhang et al. 2003). CVD was performed in a 5-cm diameter quartz tube. Gas flow
rates were controlled using mass flow controllers. After loading the substrate into the furnace,
the tube was evacuated to a base pressure of 2 x 10-2 Torr. Argon (Ar) gas with a flow rate of 400
sccm was introduced while the quartz tube was gradually heated to the growth temperature of
800 °C. Then, the growth was initiated by adding a mixture of ammonia (NH3) and ethane
3
(C2H4) with flow rates of 90 sccm and 30 sccm, respectively. The growth step usually lasts for
30 min under a reaction pressure of 1 atm. Structural properties of the samples were
characterized using SEM.
Synthesis of Silver Nanoparticles on MWCNT (Ag-CNT): The as-grown MWCNT on a 1.2 cm
x 2 cm silicon wafer was placed in a three-necked round bottom flask, added with 30 mL of 96
% H2SO4 and heated at 90 oC under reflux for 100 min. The resulting product, oxidized CNT on
Si substrate (Si-CNT-COOH), was then washed with running DI water for 2 min and air dried.
Concentration of oxidized CNT product (0.14 mg/mL) was determined by subtracting its weight
before and after removal from Si substrate. A typical polyol process (Jiang et al. 2007) was
conducted to afford the formation of silver nanoparticles (Ag NPs) on the oxidized CNT. This
was carried out by immersing the previously prepared Si-CNT-COOH into the mixture
consisting of 0.24 g PVP, 36 mL of the reducing agent, ethylene glycol and 2.0 mL of 50 mM
AgNO3. The resulting mixture was sonicated for 2 hrs in a cold water bath. During the sonication
process, complete removal of Ag-CNT products from Si wafer was observed. The wafer was
taken out while the mixture was collected in another tube and centrifuged at 8000 rpm for 45 min
at 4 oC. Repeated washing of Ag-CNT product with DI water via centrifugation at 8000 rpm for
10 min at 4oC was done to ensure complete removal of excess PVP and ethylene glycol. Samples
were examined under TEM.
Synthesis of Ag/Au core-shell on MWCNT (Au-Ag-CNT): A galvanic replacement reaction
(Sun et al. 2002; Sun et al. 2002) was carried out to prepare Ag/Au core-shell on CNT. 200 L
of Ag-CNT product was diluted to 3 mL with DI water and stirred for 25 min at low temperature
4
(4 oC). Thereafter, 0.3 mL of 1mM HAuCl4 was added dropwise and the mixture was vigorously
stirred for another 3 min. The product was purified by centrifugation at 7000 rpm for 10 min at 4
o
C. Products were examined under TEM. Size distributions of Ag/Au core-shell produced at
different conditions on CNT surfaces were determined using an Image Pro Plus 4.5 software.
Preparation of MWCNT, Ag-CNT and Au-Ag-CNT Samples for Raman Spectroscopy: A
sample well was made by using a 5 mm x 5 mm PDMS (thickness = 225 m) substrate that has a
3-mm diameter hole at the center. This substrate was then stacked on a Si wafer of the same area.
10 L of concentrated sample was spotted onto this well and was analyzed under Raman
spectroscopy to reveal the crystallinity of the nanotubes. Raman spectra were recorded using a
LabRAM HR, HORIBA Jobin Yvon spectrometer with an excitation wavelength of 632.8 nm
from a He-Ne laser of spot size 2.86 m in diameter using 50 x objective lens. Data were
obtained under a 5-s exposure time over 3 collection cycles.
Separation of Au Nanobowls (Au NBs) from MWCNT Surfaces: 100 L of Au-Ag-CNT was
added with 2 mL of 1% OT (1-octanethiol) in ethanol at pH 10 and the resulting mixture was
sonicated for 90 s. Sample purification and collection were done by repeated centrifugation at
12000 rpm for 45 min at 4 oC.
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Fig. S1 SEM and HR-TEM (inset) images of MWCNT
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Fig. S2 Histograms of the size distribution of a Ag NPs and b-d Ag/Au core-shell grown on
MWCNT surfaces. Ag-Au core-shell produced at different [HAuCl4], replacement reaction times
and temperatures: b 1 mM, 1 min, 4 oC, c 1mM, 3 min, 4 oC and d 1mM, 10 min, 4 oC. There
were 133, 354, 194 and 151 nanostructures measured in histograms a, b, c and d, respectively.
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b
a
c
d
e
Fig. S3 Ag/Au core-shell on MWCNT produced at different [HAuCl4], replacement reaction
times and temperatures: a 50 mM, 10 min, 4oC; b 1mM, 10 min, 100 oC; c 1mM, 10 min, 4 oC
and d 1mM, 3 min, 4 oC. e High magnification of (d). Scale bars for a, b and d = 50 nm
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a
Spectrum
1
Spectrum
b
Cu
Fig. S4 a HAADF-STEM image of Ag/Au on MWCNT produced after 10-min replacement
reaction of Ag with Au. The yellow arrow points the location of a nanohybrid analyzed under
point-EDX and displays the corresponding spectrum (b) showing the co-existence of Ag and Au
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a
b
70
Ag
Au
% Element
60
Time (min) % Ag % Au
1
57
42
2
45
54
10
29
70
50
40
30
0
2
4
6
8
10
Replacement Reaction Time (min)
Fig. S5 a TEM image of Au-Ag-CNT at 10-min replacement time. b TEM-EDX percent
elemental Au and Ag in Au-Ag-CNT products prepared at different Au replacement times
10
Fig. S6 a Histogram of the diameter size distribution of Au nanobowls (Au NBs) (n = 182) and b
histogram of Au nanobowl tip diameter distribution (n = 256) after separation of Ag/Au coreshell from MWCNT surfaces via 1-octanethiol treatment.
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References
Jiang HJ, Zhu LB, Moon KS, Wong CP (2007) The preparation of stable metal nanoparticles
on carbon nanotubes whose surfaces were modified during production. Carbon 45:655-661
Sun YG, Mayers BT, Xia YN (2002) Template-engaged replacement reaction: A one-step
approach to the large-scale synthesis of metal nanostructures with hollow interiors. Nano
Lett 2:481-485
Sun YG, Xia YN (2002) Shape-controlled synthesis of gold and silver nanoparticles. Science
298:2176-2179
Zhang RY, Amlani L, Baker J, Tresek J, Tsui RK (2003) Chemical vapor deposition of singlewalled carbon nanotubes using ultrathin Ni/Al film as catalyst. Nano Lett 3:731-735
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