Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

10B/2004G101

EXAFS study for the formation of noble metal nanoparticles prepared fromreverse micelles of metallosurfactants
Masayasu IIDA1 and Masafumi Harada*2
Department of Chemistry, Nara Women’s University, Nara 630-8506, Japan2
Department of Textile and Apparel Science, Faculty of Human Life and Environment,
Nara Women’s University, Nara 630-8506, Japan
1

Introduction
Microemulsion systems composed of noble
metallosurfactants can provide metal nanoparticles having
uniform shapes and sizes [1, 2]. In this study, we have
prepared silver and gold nanoparticles (Ag and Aunanoparticles) by the chemical reduction of theiralkylethylenediamine complexes in the microemulsion
systems using a reducing agent such as NaBH4, and haveestimated the average particle sizes of the Ag and Au
nanoparticles by means of EXAFS measurements. We
have tried to correlate the sizes of the nanoparticles withthe structures of the original microemulsions by changing
the alkyl-chain length of the original metal complexes andthe solvent composition.
Experimental
The amphiphilic bis(dodecylethylenediamine (= doden))silver nitrate, bis(hexadecylethylenediamine (= hexden))silver nitrate,and bis(dod-en)gold chloride
complexes were prepared by the reactions of dod-en andhexd-en ligands with the corresponding metal salts inmethanol. The microemulsion was prepared as the silver
complex/heptane/water (water/metal complex molar ratio
is in the range of 4-50) or gold complex/methanol/
diethylether ternary system. The reduction of themetallosurfactants was performed by adding NaBH4
aqueous solution to the microemulsion system and thenby shaking the water/heptane or water/diethylether phase.
EXAFS measurements of Ag-K or Au-L3 edges of these
metallosurfactant microemulsion systems were performed
using the 10 mm path length cell with polyimide film
windows at room temperature in a transmission mode at
BL-10B. The above obtained samples were poured into
cells for measurements, and the metal concentration of[Ag] in these microemulsion systems is in the range of
0.1-0.8 (mol/l). (3 mmol/l for [Au]) In order to extract
the backscattering amplitude and phase shift functions forthe curve-fitting, the reference compounds (Ag and Aufoils and Ag(NH3)2+ solid compound) were used in thisexperiment.

In all the samples, the peak around 1.8 nm assigned tothe bond of Ag-N appears with the same height. The peakassigned to the bond of Ag-Ag appears after the reduction,and their peak heights increase with increasing theduration of left under air. On the other hand, the sizes of
the Ag nanoparticles estimated by the EXAFS study weresignificantly larger than those by the TEM observationand the difference is larger for the silver(0) particles thanfor the gold(0) particles. Therefore, the following
characteristic features have been expected. 1) With
increasing the water content, the size of the metal
nanoparticles increases and the size distribution becomeslarger.
2) The longer alkyl-chain length of themetallosurfactant results in the smaller size and smaller
size-distribution of the metal nanoparticles. The detailed
analysis is in progress.

Results and Discussion
Figure 1 shows the Fourier transforms of Ag K-edge
EXAFS spectra for the metallosurfactant of Ag(dod-en)
microemulsion before and after the reduction withNaBH4.

References[1] A. Manna, T. Imae, M. Iida, and N. Hisamatsu,Langmuir, 17, 6000 (2001).
[2] M. Iida. S. Ohkawa, H. Er, N. Asaoka, and H.
Yoshikawa, Chem. Lett., 2002, 1050.
* harada@cc.nara-wu.ac.jp

Fig. 1 Fourier transforms of EXAFS spectra for Ag-K edge ofthe metallosurfactant of Ag(dod-en) microemulsion systems.

Users' Report183