Electronic Supplementary Material
Fabrication and Characterization of Copper Nanoparticles using Thermal Reduction: The
Effect of Nonionic Surfactants on size and yields on nanoparticles
Mohammad Hossein Habibi*, Reza Kamrani and Reza Mokhtari
Nanotechnology Laboratory, Department of Chemistry, University of Isfahan, Isfahan, 8174673441 I.R. Iran
Characterization methods
Thermal gravimetric differential thermal analysis (TG-DTA) measurements were carried out to
examine the temperature dependent changes using a Mettler TA4000 system (About 7.0 mg of
copper complex precursor was heated from room temperature to 700 °C at a constant heating rate
of 10 °C.min-1). Cyclic voltammograms were recorded by using a SAMA Research Analyzer M500 for copper complex precursor. Three electrodes were utilized in this system, a glassy carbon
working electrode, a platinum disk auxiliary electrode and Ag wire as reference electrode. The
glassy carbon working electrode (Metrohm 6.1204.110) with 2.0 ± 0.1 mm diameter was
manually cleaned with 1  m alumina polish prior to each scan. Tetrabutylammonium perchlorate
(TBAP) was used as supporting electrolyte. The solutions were deoxygenated by purging with Ar
for 5 min. All electrochemical potentials were calibrated vs. internal Fc+/o (Eº = 0.38 V vs. SCE)
couple under the same conditions. The UV–vis absorption spectra of the copper nanoparticles
were recorded with a UV–vis spectrophotometer (Cary 100 Scan Spectrophotometers, Varian).
The crystalline phase of colloids was studied by X-ray diffraction (XRD) technique with a bruker
D8 advance X-Ray diffractometer in the diffraction angle range 2θ=20-60°, using Cu Kα
radiation. Philips XL-30 scanning electron microscopy (SEM) was used to image the size and
morphology of these copper powders. An elemental composition analysis of the films was
performed using energy dispersive X-ray spectroscope (EDX) connected to the SEM. FT-IR
spectra of nano-particles of copper were recorded as KBr disc on a bruker FT-IR (Tensor 27)
spectrophotometer. The microstructure, particle size and morphologies were investigated by a
Leo 912 AB transmission electron microscopy (TEM). TEM samples were prepared by
suspending sample powder in solvent then dropping solution on a copper-mesh holder. Sample
was allowed to dry before TEM analysis.
Preparation of copper precursor
Preparation of Bis-(oxalato)-copper (II) precursor
Bis-(oxalato)-copper(II) precursor was prepared using aqueous solution (25mL) of copper
acetate, Cu(OOCCH3)2.H2O (2 mmol, 0.4 g), and potassium oxalate, K2C2O4.H2O (2 mmol, 0.37
g). The solution was stirred for about 15 min and a blue precipitate was centrifuged and washed
with ethanol several times. The product was dried at 50 oC. The copper oxalate was characterized
by cyclic voltametry (CV), powder X-ray diffraction (XRD) and thermogravimetry–differential
thermal analyses (TG-DTA).
Preparation of copper nanoparticles
Preparation of copper nanoparticles using Bis-(oxalato)-copper(II)
as precursor and
dodecylamine as surfactant
Bis-(oxalato)-copper(II) (0.4 g) was added to 4 mL dodecyl amine to create a homogenous
solution, then refluxed for 1 h at 140 °C. Then triphenyl phosphine (3.9 g) (a reducing agent) was
added to the solution. The solution was heated to a temperature of 180 °C with stirring for 1 h.
The solution was then cooled to room temperature. Finally, the reacted solution was mixed with
10 mL ethanol, and the particles were allowed to precipitate overnight. The supernatant was
removed, and the nanoparticle sediment was washed, dried (49% yield based on Cu-NPs). The
nanoparticles were suspended in hexane and were ready for analysis (Scheme S1).
Preparation of copper nanoparticles using Bis-(oxalato)-copper(II) as precursor and Tween-80 as
surfactant
The same procedure as above except bis-(oxalato)-copper (II) (0.16 g) was added to 2 mL
Tween-80 and 1.28 g triphenyl phosphine with 97% yield based on isolated copper nanoparticles
(Table 1).
Preparation of copper nanoparticles using Bis-(oxalato)-copper(II) as precursor and Triton X-100
as surfactant
The same procedure as above except bis-(oxalato)-copper(II) (0.24 g) was added to 2 mL
Tween-80 and 1.93 g triphenyl phosphine with 99% yield based on isolated copper nanoparticles
(Table S1).
Results and Discussions
Thermo gravimetric analysis of the Cu-NPs revealed about 4% weight loss when heated between
room temperature to 700 °C. A three-phase decomposition profile showed an initial weight loss
due to evaporation of trapped solvent in the sample followed by decomposition of dodecylamine.
Low weight loss could be due to deposition of layers of carbon around the copper particles and
this might hinder further effective decomposition during the analysis thus leading to small
amount of weight loss only. FTIR spectroscopy is applied to find out whether there are any peaks
due to the surfactant in the final Cu-NPs for that would confirm the surface capping of the CuNPs (Fig. S1). In our measurement, the OH stretching vibration of the terminal OH group in
TX100 leads to a broad and weak band centered at 3429 cm−1. The weak and sharp bands at
1623, 1485, 1439, 1314, 1104, 749, 703 and 519 cm-1 arise from the normal vibrations having the
character of C–C stretching vibration of a benzene ring and symmetric and asymmetric stretching
of the CH2 groups, terminal CH3 and of CH of TX100. The elemental identity of the
nanoparticles was determined by means of EDX analyses for the copper using analytical scanning
electron microscopy (SEM). Growth of nanoparticles is influenced by the strength of adsorption
of the encapsulating ligands and the competition between the interparticle aggregation for the
growth of particles and the molecular encapsulation for the stabilization of nanoparticles (Fig.
S2).
Scheme S1 Synthesis route of copper nanoparticles using copper precursor and nonionic
surfactants
Fig. S1 FT-IR spectra of the copper nanoparticles synthesized using bis-(oxalato)-copper(II) as
precursor and Triton X-100 as capping agent
Fig. S2 Suggested mechanism for the synthesis of copper nanoparticles using copper oxalate as
precursor and Triton X100 as nonionic surfactants