Photon Factory Activity Report 2014 #32 (2015) B

9C/2013G005

Microwave-Assisted Synthesis of Transition-metal Oxide Nanoparticles
Masafumi HARADA*, Asumi NAKAGAWA, and Mayuu KOGAI
Department of Clothing Environmental Science, Faculty of Human Life and Environment,
Nara Women’s University, Nara 630-8506, Japan
1 Introduction
Transition-metal oxides, such as manganese, cobalt,
nickel and iron, have attracted increasing attention owing
to their potential applications in high-performanceelectrodes, catalysts, magnetic materials and battery
devices. Over the past years great efforts have been paidfor the microwave (MW)-assisted synthesis of transitionmetal oxide nanoparticles [1,2], because the MW heating
can provide generation of homogeneous nucleation sites
as compared to the conventional heating. In this study wehave demonstrated the MW-assisted rapid synthesis ofmagnetite (Fe3O4) and manganese oxide (MnO andMn3O4) nanoparticles and characterized their structuresusing EXAFS measurements.
2 Experimental
In a typical experiment for the preparation of Fe3O4
nanoparticles, Fe(CH3COO)2 (or Fe(acac)3) (1 mmol) andoleylamine (10 mmol) were mixed and heated in oil bathat 393 K for 30 min. After cooling to room temperature,
1-dodecanol (50 ml) dissolving oleic acid (3 mmol) andtrioctylphosphine oxide (TOPO, 1 mmol) was added tothe solution. The solution was heated to 533 K, and kept
at this temperature for 20 min (or 60 min) under MW
irradiation. The MW reactor was a focused single-mode
MW synthesis system (CEM Discover SP). The
temperature and pressure was controlled by regulation ofMW power output. After naturally cooling down to room
temperature, the colloidal solutions were collected for theEXAFS measurements. For the preparation of manganeseoxide nanoparticles, similar procedures were applied
except the use of various manganese precursors such asMn(CH3COO)2·4H2O and Mn(COOH)2·xH2O. The
EXAFS measurements were carried out in a transmission
mode at BL-9C. Data analysis was performed by
REX2000 (Rigaku Co.).
3 Results and Discussion
Figure 1 shows the Fourier transforms (FTs) of thecolloidal Fe3O4 nanoparticles and their referencecompounds. Even after the shorter irradiation time of 20min, FT spectra of the colloidal samples show the firstpeak assigned to Fe-O bond (around 1.5 Å) and thesecond peak assigned to Fe-Fe bond (around 2.6 Å and3.1 Å), which are similar to those of Fe3O4 referencecompound. This obviously indicates the formation of
Fe3O4 nanoparticles coordinated by oleylamine, oleic acid,and TOPO molecules in 1-dodecanol. Furthermore, asshown in Fig. 2, the dependence of reaction condition(irradiation time, kinds of precursors, additives andsolvents, and so on) on the structure of the manganeseFig. 1. Fourier transforms of Fe K-edge EXAFS spectra for (a) FeOpowder, (b) Fe2O3 powder, (c) Fe3O4 powder, and those of thecolloidal Fe3O4 nanoparticles prepared from Fe(CH3COO)2 by MW
irradiation of (d) 0 min, (e) 20 min, and (f) 60 min, and those of thecolloidal Fe3O4 nanoparticles prepared from Fe(acac)3 by MW
irradiation of (g) 0 min, (h) 20 min, and (i) 60 min.

Fig. 2. Fourier transforms of Mn K-edge EXAFS spectra for (a)Mn2O3 powder, (b) MnO powder, (c) Mn3O4 powder, and those ofthe colloidal MnO nanoparticles prepared from Mn(CH3COO)2 byMW irradiation of (d) 20 min and (e) 60 min, and those preparedfrom Mn(COOH)2 by MW irradiation of (f) 20 min and (g) 60 min.

oxide nanoparticles is also examined. The detailed
analysis is in progress.
References[1] M. Baghbanzadeh et al., Angew. Chem. Int. Ed. 2011,
50, 11312-11359.
[2] Y. -J. Zhu et al., Chem. Rev. 2014, 114, 6462-6555.
*harada@cc.nara-wu.ac.jp