Photon Factory Activity Report 2017 #35 (2018)

BL-27A/2017G545

Characterization of Ni-Au nanoparticles synthesized by gamma-ray irradiation
reduction method
Shintaro Toda1, Motoaki Tanaka1, 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) Institute for Integrated Radiation and Nuclear Science, Kyoto University, Kumatori, Osaka 5900494, Japan
1 Introduction
Metal nanoparticles are of interest from the viewpointof various kinds of functional materials such as catalysts,
electronic conductivity and light absorption. These
properties, which are not necessarily observed in bulk
materials, strongly depend on their size, shape, structure
and alloy component. In general, nano-structured metallic
materials can be fabricated by the reduction of metal ionsin solution including a reduction agent. The reduction rateof metal ions in solution strongly depends on their redox
potential. In the case of nickel, which is useful forcatalytic material, the fabrication of nano-sized material
by the reduction reaction is difficult because of highredox potential. Moreover, the metal ions in water
solution can not be reduced without adding of a reduction
agent. In our previous work [1-3], we have successfully
synthesized various kinds of nanoparticles such as Au, Ag,Pt, Pd, Cu and their complexes in aqueous solutions by
ultrasonic, gamma-ray, high energetic ion and electron
irradiation reduction methods. Especially in cases ofgamma-ray and electron irradiation, hydrated electrons(eaq-) in water, which a radiolysis product, act as strong
reduction agent. The purpose of this study is to synthesize
the multicomponent nanoparticles including Ni inaqueous solution by using gamma-ray irradiation
reduction method.
2 ExperimentThree aqueous solutions Ni, Au and Au+Ni wereprepared. They contained metal ions (Ni: NiCl2 2.5mM,Au: Na[AuCl4]・2H2O 1mM, Au+Ni: NiCl2 2.5mM andNa[AuCl4]・2H2O 1mM) and Polyvinylpyrrolidone-K25
0.1mM, Ascorbic acid 1mM and ion exchanged water
20.0 ml. All solutions were bubbled by 5mL/min Ar gas
flow in 5min. They were irradiated with 1.17 and 1.33
MeV gamma-ray from 60Co source at Institute forIntegrated Radiation and Nuclear Science, Kyoto
University at room temperature. The total dose was 20.0
kGy with the dose rate of 10.0 kGy/h. For all theirradiated solutions, ultra violet and visible light (UV-vis)
absorptions were measured in the wavelength range of
200–800 nm. The products were dispersed on an
amorphous carbon film with a copper mesh by droppingand were dried in vacuum for the transmission electronmicroscopy (TEM). After drying, samples were observedby using a conventional TEM and STEM equipped withenergy dispersive. The samples for X-ray photoelectron
spectroscopy (XPS) at KEK-PF BL-27A were preparedby dropping samples on Ge substrates and dried invacuum. Powder X-ray diffraction (PXRD) of products
supported on carbon black was also measured.
3 Results and Discussion
Although any NP in Ni solution was not observed,
nanoparticles were observed in Au+Ni solution as shownin figure 1. Ni is easy to oxidize in water during gamma
ray irradiation so that it is difficult to growth the Ni
particle in water solution. Fig.2 shows XPS spectrum ofnanoparticles salvaged from Au+Ni colloidal solution
indicating existence of metallic Ni. Fig.3 shows UV-vis
absorption spectra for Au and Au+Ni colloidal solutions.
The absorption peak of 520nm corresponds to the surface
plasmon resonance (SPR) of pure Au nanoparticles.
However, comparing Au+Ni with Au solution, theposition of SPR peak in Au+Ni is slightly lower than thatof pure Au. The mean particle size of nanoparticles ineach Au+Ni and Au solution is almost same. Then, thisdifference is the characteristic change of light absorption
for these nanoparticles essentially. On the other hand,
PXRD patterns of products in Au and Au+Ni solutions
clearly different (Fig.5). Namely, the diffraction peak ofAu+Ni shifted to higher angle compared to that of Au. In
thermally equilibrium, it is known that Ni-Au alloy issolid-solution in whole concentration. Taking intoFig. 1 TEM image and particle size distribution ofnanoparticles produced in Au+Ni solution.

Au+NiNi 2p 3/2

Ni 2p 1/2875

870

865860855

850

Au+NiAu

Intensity(arb. unit)

Intensity(arb. unit)

Photon Factory Activity Report 2017 #35 (2018)845

76788082

84

Biding energy(eV)

2/(deg)

Fig. 2 XPS spectra of nanoparticles produced in Au+Ni
solution by gamma ray irradiation.

Fig. 5 PXRD patterns for nanoparticles produced inAu+Ni and Au solutions.

Absorbance(arb. unit)

Au+Ni
Au

300

400

500

600

700

consideration of Vegard’s law, Ni concentration in Au
nanoparticles is calculated as 4.3%.From these results, itis thought that the reduction of Au ions affects thereduction of Ni ions and inhibit the oxidation duringirradiation. Consequently, Au nanoparticles including Ni
were fabricated in Au+Ni ions solution.

800

Wavelength(nm)Fig. 3 UV-vis absorption spectra for colloidal solutions ofnanoparticles produced in Au+Ni and Au solutions.

Fig. 4 TEM image and particle size distribution for
nanoparticles produced in Au solution.

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Taniguchi, S. Okuda, T. Akita, T. Abe, T. Kambara,
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[2]. A. Okamoto, K. Nagata, N. Taguchi, A. Iwase, andF. Hori, Jpn. J. Appl. Phys. 51 (2012) 11PH01.
[3]. T. Hori, K. Nagata, A. Iwase, and F. Hori, Jpn. J.
Appl. Phys. 53, (2014) 05FC05* horif@mtr.osakafu-u.ac.jp