Photon Factory Activity Report 2016 #34 (2017)

BL-27A/2015G700

Synthesis of Cu-Au nanoparticles by two-step gamma-ray irradiation reduction
methodMotoaki Tanaka1, Shintaro Toda1, Toshiyuki Matsui1, Akihiro Iwase1, Noboru Taguchi2, Shingo
Tanaka2, Qiu Xu3 and Fuminobu Hori1*
1) Osaka Prefecture University, Gakuen-cho1-1, Sakai, 599-8531 Osaka, Japan
2) National Institute of Advanced Industrial Science and Technology, Ikeda, Osaka 563-8577, Japan
3) Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan1 Introduction
Copper nanoparticles are key materials for various
industrial fields, because of its electrical and opticalproperties. Copper is rich in natural resources compare toother metals on earth; even so, it is important to control
the size and shape of copper particles for electric andphotonic devices. Generally, copper particles of microns
have been synthesized using chemical reduction methods.
However, they are easy to oxidize and re-dissolved since
their high surface activity, so that it is difficult tofabricate copper particles below nanometer size without
surface oxidation. Previously, we have successfully
synthesized pure copper particles with an average size of
about 20 nanometers diameter by gamma-ray irradiation
reduction method [1]. However, they are stable in argon
gas atmosphere. In this study, we attempted to synthesize
gold stabilized copper nanoparticles by one step reductionof gold and copper ions in aqueous solution undergamma-ray irradiation reduction field.
2 Experiment
Aqueous solutions of 1.0mM gold complex(NaAuCl4 2H2O) and 1.0mM Cu2+ ion of copper complex((CH3COO)2Cu H2O) with a cationic surfactant of sodium
dodecyl sulfate (SDS) and a radical scavenger of 8.5
vol% ethylene glycol (EG) were prepared. An aqueoussolution was poured into a polystyrene container and waspurged with argon gas for 10 minutes. After degassing,
they were irradiated with gamma-ray at Kyoto University
Research Reactor Institute. Total dose of gamma-rayirradiation was 20 kGy with the dose rate of 2.0 kGy/h.
All irradiated solutions were examined by using anUV/vis absorption spectrophotometer (Shimadzu UV2550) in the wavelength range of 200-800nm. The size
and the structure of the synthesized particles werecharacterized by transmission electron microscope (TEM)
on JEOL JEM-2000FX and energy dispersive X-ray
spectrometry (EDS). The samples for TEM were preparedby dispersing the all products on carbon films with amolybdenum mesh by dropping the solutions and weredried in vacuum.
In order to investigate stability of synthesized particles,
after samples exposed to air for 2months, samples werecharacterized by UV/vis absorption spectrophotometer,Fig.1 UV/vis spectra of solutions just irradiated by
gamma-ray irradiation and 2 months after.
TEM and X-ray Photoelectron Spectroscopy (XPS) at
KEK-PF BL-27A. The samples for XPS were prepared bydropping samples on germanium and dried in vacuum.
3 Results and Discussion
Figure 1 shows the UV/vis absorption spectra ofaqueous solutions after gamma-ray irradiation. In case of
the solid line, this graph has one peak around 520 nm.
The peak around 520 nm corresponds to the surface
plasmon resonance from pure Au nanoparticles. After 2
months, in case of the broken line, peak doesn’t change. Itshows that nanoparticles in samples didn’t change for 2months.
Figure 2 shows TEM images of nanoparticles just afterirradiation and 2months after irradiation. From left
figures, the shape of nanoparticles is spherical and its
mean diameter is about 11nm. Even after 2 months, fromright figure, the shape of nanoparticles kept spherical andnanoparticles didn’t form aggregation. The structure ofsynthesized nanoparticles can be estimated as a core shell(Au-core Cu-shell) type nanoparticle by EDS analysis(Fig. 3). We suppose the mechanism of this structural
nanoparticles is that Au ions are reduced faster than Cu
ions because of difference in redox potential. So first Au

Photon Factory Activity Report 2016 #34 (2017)

Fig.2. TEM images of nanoparticles just irradiated and 2months after irradiation.

Fig.3. EDS images of solutions just irradiated bygamma-ray irradiation.

Fig.4. EDS images of solutions 2months afterirradiation by gamma-ray irradiation.

Fig5. XPS of solutions exposed to air for 2months
cores are formed, next Cu are synthesized on surface ofAu core. Figure 4 shows EDS results of nanoparticles
exposed to air for 2 months. Nanoparticles kept Au-core
Cu-shell structure and were found to be stable in air.
Figure 5 shows XPS spectra of solutions exposed to airfor 2 months. From this figure, a peak was found around932.67 eV, which is originated from pure Cu metal. On
the other hand, other peaks correspond toCuO(933.5~934.0eV) were not observed. This resultmeans that Cu shell on Au core obtained resistance tooxidation. We found even if Cu shell are thin, Cu shell
are stable than pure Cu nanoparticle in air.
There is a possibility core-shell nanoparticles get
resistance to oxidation by interact of core-shell structure.
References[1] T. Hori et al., Jpn. J. Appl. Phys. 53, 05FC05 (2014)* horif@mtr.osakafu-u.ac.jp