Exploring the Length of Gold Nanorods M. Varón-Izquierdo1, S. Lim1, I. Ojea1, J. Arbiol2, V. Puntes1 Català de Nanotecnologia, Campus UAB, 08193 Bellaterra, Spain. 2GAEN-CeMARC, Group of Advanced Electron Nanoscopy - Centre de Microscòpia d’Alta Resolució de Catalunya, Universitat de Barcelona, Lluís Solé i Sabaris 1-3, E-08028 Barcelona, Catalonia, Spain Miriam.varon.icn@uab.es 1Institut
EXPERIMENTAL
INTRODUCTION
Synthetic Procedure: The seed-mediated growth method
The seed-mediated growth formation mechanism of gold nanorods (Au NRs) in CTAB (Cetyl Trimethyl Ammonium Bromide) micellar solution remains a subject of
Study of the effect of synthetic parameters: presence of different ions and use of different seeds
seeds
debate [1], but all mechanism for the growth of Au NRs are based on the crystal
Mandatory for obtain rods
growth inhibition, which is closely related to the crystalline structure and thermodynamic stability of the face-centered cubic (fcc) structure of the metallic
Ascorbic Acid
CTAB
Cations + HAuCl4 + CTAB + Ascorbic Acid + Seeds
Seeding
gold. The use of cationic surfactant CTAB is a crucial parameter in the synthesis Gold Nanorods
HAuCl4 (+ cations)
of Au NRs following a seed-mediated method. However, the trimethylammonium
Ag + Pt +
headgroup alone does not efficiently direct NP growth into rods and silver nitrate plays a crucial role in obtaining Au NRs in high yield. In fact, the kinetics of reduction of gold ions to atomic gold showed that the reduction was slower in the
UV-Vis Spectroscopy
Au Pt
Constant
variable
variable
presence of silver nitrate. In this work, we present the synthesis of bimodal metallic systems including Au
SAMPLE
and Pt. The influence of different parameters that have crucial influence in the final
A
morphology of Au NRs will be discussed. In detail, the control of the length of Au
B
Effect of Silver Ions
Pt (4-5 nm)
x x
x
x x
x
Effect of Platinum Ions
Synthesis with Pt
B: with AgNO3
Au (2-3 nm) x
E1 , E2 , E3
seeds
K2PtCl4
x
D
different seeds in the growth solution.
A: no AgNO3
AgNO3
SEEDS
C
NRs will be studied by systematically varying both presence of different ions and
Synthesis with Au
CATIONS
Synthesis with Au
seeds
C: no AgNO3
D: with AgNO3
seeds
More K2PtCl4
-
+ E2
E1
E3
Introduction
In the absence of silver ions, low yield of Au NRs were produced.
In the presence of silver ions, the morphology of Au NRs can be controlled.
In the absence of silver ions, long Au NRs were produced.
In the presence of silver ions, no Au NRs were formed.
2.0
E2 E1 E2 E1 E3 E3
1.8 1.4
1.2 1.1
AgNo3 improves shape control
2.0
1.5
1.0
Absorvance (a.u.)
2.5
Absorvance (a.u.)
1.6
C D
1.3
Absorvance (a.u.)
B A
3.0
1.0 0.9 0.8 0.7
Platinum ions spoils rods synthesis
1.4 1.2
It can be observed that increasing the amount of platinum
1.0 0.8
0.6
0.6
0.5
0.4
salt avoids the formation of the rods. The majority product obtained are gold nanoparticles (Au NPs).
0.4 0.5
0.3
0.2
0.2
0.0
0.1
0.0
300
400
500
0.0 300
400
500
600
700
800
900
300
1000
400
500
600
700
800
900
600
700
800
900
1000
W avelength (nm)
1000
Wavelength (nm)
Wavelength (nm)
Effect of Different Seeds (without ions) Synthesis with Au
seeds
Synthesis with Pt
A
A
A
seeds
C
C
C
2.0
In the absence of silver ions, low yield of Au NRs were obtained.
Absorvance (a.u.)
1.6 1.4
2.0
C
1.2
[1-10]
1.0
The HRTEM shows that Au NR can be single crystal or twined crystal.
0.8 0.6 0.4
PLATINUM SEEDS FAVORS THE GROWTH OF EXTREMELY LONG Au NRs
1.5
Absorvance (a.u.)
A
1.8
(1-11) (002) (1-1-1)
1.0
0.5
0.2
Twinned Au NW
[110] Au 0.0 300
400
500
600
700
800
900
1000
0.0 300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
800
900
1000
The EELS spectra shows that both particles and long NRs are formed by gold.
CONCLUSIONS 1. The seed-mediated growth method allows the synthesis of high yield Au NRs (low aspect ratio (AR)). 2. The growth mechanism of Au NRs depends on the presence or absence of silver and platinum salts. 3. The size and the shape of Au NRs can be controlled by adjusting two synthetic parameters: presence of different salts and seeds. Platinum salt spoils rods synthesis and platinum seeds favors the growth of extremely long rods. 4. Au rods of 10 µm can be synthesized in the presence of Pt NPs in aqueous solution. Au NRs with AR up to 200 were obtained. This is a noteworthy achievement, since in the bibliography Au NRs with AR from 2.9 to 4.5 have been previously reported by standard routes. 5. By changing the Au NRs AR, the longitudinal surface plasmon resonance band can be tuned from the visible to near infrared (NIR) wavelength [2-4], for this reason we can not observe it in the UV-vis spectra.
REFERENCES [1] Jana, N.R., L. Gearheart, and C.J. Murphy, Journal of Physical Chemistry B, 105:19 (2001) p. 4065-4067.
ACKNOWLEDGEMENTS
[2] El-Sayed, M.A., Accounts of Chemical Research, 34:4 (2001) p.257-264.
Inorganic Nanoparticles Group
[3] Kelly, K.L., et al., Journal of Physical Chemistry B, 107:3 (2003) p.668-677.
Ministerio de Educación y ciencia. MAT2006-13572-C02-02
[4] Mohamed, M.B., et al., Journal of Physical Chemistry B, 102:47 (1998) p.9370-9374.