Materials Sciences and Application, 2011, 2, 977-980
doi:10.4236/msa.2011.28131 Published Online August 2011 (
Copyright © 2011 SciRes. MSA
Preparation of Copper (Cu) and Copper Oxide
(Cu2O) Nanoparticles under Supercritical
M. Asharf Shah*, M. S. Al-Ghamdi
Department of Physics, Faculty of Sciences, King Abdul Aziz University, Kingdom of Saudi Arabia, Saudi.
Email: *
Received May 19th, 2011; revised May 20th, 2011; accepted May 31st, 2011.
Temperature and pressure, both of which can affect the supersaturation and nucleation are responsible for solvents
properties. In this study, we use water as solvent under supercritical conditions and report copper (Cu) and (Cu2O)
nanoparticles of size ranging from 9 nm to 60 nms . This synthetic technique has the following advantages: Firstly, it is
one step synthesis approach, making it easy to control the growth kinetics. Secondly, the synthesis needs no sophisti-
cated equipments. Thirdly, the approach is non-toxic without producing hazardous waste as water is being used as sol-
vent as well as source of oxygen. Forth, it is a surfactant free synthesis and has bright prospects.
Keywords: Supercritical Water, Copper Powder, Synthesis, Characterization
1. Introduction
In chemical sciences, synthesis of transition metal and
metal oxide nanoparticles is a growing research field. As
the metal particles are reduced in size, bulk properties of
the particles disappear to be substituted to that of quan-
tum dot following quantum mechanical rules. It can thus
be easily understood that metal nanoparticles chemistry
differs from that of the bulk materials. Since with size
reduction the high surface area to volume ratio lead to
enhanced catalytic activity [1].
Among various metal nanoparticles, copper (Cu) and
copper oxide (Cu2O) nanoparticles have attracted con-
siderable attention because copper is one of the most
important in modern technologies and is readily available
[2]. Considerable interest has been focused on copper
nanoparticles due to their optical, catalytic, mechanical
and electrical properties [3,4]. It has been used as het-
erogeneous catalysts in many important chemical proc-
esses, such as degradation of nitrous oxide with ammonia
and oxidation of carbon monoxide, hydrocarbon and
phenol in supercritical water [5].
Cu and Cu2O nanoparticles have been synthesized
through different methods such as thermal decomposition,
metal salt reduction, microemulsion, laser ablation, DC arc
discharge, solvothermal and sonochemical reactions [6-10].
Among various techniques for synthesis, the hydrothermal
method of producing metal oxide nanomaterials is unique
and economical. Recently, we have reported the synthesis
of Cu2O nanoparticles of almost uniform size at 180˚C
without any surfactants and additives [11].
In the continuation of the development of simple syn-
thesis of nanoparticles, we herein report the synthesis of
copper and copper oxide nanoparticles from a simple,
green, low cost and reproducible process. The average
size of the nanoparticles is ~25 nms. Detailed and system-
atic studies would be necessary to optimize the conditions
for obtaining nanoparticles of desired dimensions. The aim
of the study is to provide the feasibility of the simple route
for the preparation of copper oxide nanostructures without
additives and organics. The reported method besides being
organics free is economical, fast and free of pollution,
which will make it suitable for large scale production.
2. Experimental
In a typical preparation process, 3 mg of copper powder
was added to 30 ml of distilled water in a glass vial and
was well sonicated for about 25 minutes in a sonicator.
The reaction mixture was transferred into a stainless steel
teflon lined metallic bomb of 100 ml capacity and sealed
under ordinary conditions. The autoclave was then
placed inside a preheated furnace and the mixture was
heated to 140˚C and maintained at this temperature for
Preparation of Copper (Cu) and Copper Oxide (Cu2O) Nanoparticles under Supercritical Conditions
Copyright © 2011 SciRes. MSA
15 hours. The furnace was allowed to cool after the de-
sired time and the resulting suspension was centrifuged
to retrieve the product, washed and then finally vacuum
dried for few hours.
The morphology and the size of the products was car-
ried out using high resolution FE-SEM (FEI NOVA
NANOSEM-600) coupled with energy dispersive X-ray
spectrometer (EDX). The features and shapes of the par-
ticles were also imaged by Transmission Electron Mi-
croscope (TEM) operated at 200kV. The obtained pow-
ders were characterized by X-ray powder diffraction
(XRD) using Siemens D 5005 diffractometer using Cu
Kα radiation (λ = 0.15141 nm) in the 2 theta range from
25-65˚C with 0.02˚C/min.
3. Results and Discussion
3.1. Morphology
For the micro-structural analysis, the as synthesized
samples were directly transferred to the FESEM chamber
without disturbing the original nature of the products.
Figure 1 (a,b) and (c,d) show the low and high magnifi-
cation FESEM images of the nanoparticles and confirms
that the nanoparticles are grown with well defined mor-
phology. The nanoparticles are almost spherical in shape
and have diameters varying between 9 to 60 nm, with an
average diameter of 25 nm.
In some regions, we notice the big nanoparticles (hav-
ing average diameter of 100 nm) which are surrounded
by smaller nanoparticles. The particle size was also ex-
amined using TEM. Figure 2 displays TEM micrographs
of samples revealing the particle size approximately
ranges from 25 nms. From the TEM micrographs it is
clear that the particles are not agglomerated and can be
readily seen as spherical.
3.2. Structural Characterization
To identify the crystallinity and crystal phases of the
as-grown structures, X-ray diffraction (XRD) analysis
was performed and shown in Figure 3. All the peaks
could be clearly indexed to cubic phase with lattice con-
stants a = 3.61, b = 3.61 and c = 3.61 and with a space
group of Pm-3m, which is consistent with the literature
(JCPDS-47-2416). There are also traces of Cu2O having
almost same peaks but different lattice parameters. The
XRD diffraction peaks indicate small size of crystalline
nanoparticles. No diffraction peaks arising from any im-
purity can be detected in the pattern confirms that the
grown products are pure. It is confirmed from the EDX
analysis that the grown nanoparticles are composed of
copper and oxygen only as shown in Figure 4. The mo-
lecular ratio of Cu:O of the grown nanoparticles, calcu-
lated from EDX and quantitative analysis data is men-
tioned as inset in Figure 4.
Figure 1. Typical (a and b) low and (c and d) high-resolution FESEM image s of sample s.
(a) (b)
Preparation of Copper (Cu) and Copper Oxide (Cu2O) Nanoparticles under Supercritical Conditions
Copyright © 2011 SciRes. MSA
Figure 2. The TEM micrograph of samples
3.3. Formation Mechanism
The current synthesis method is slightly modified version
of our method reported earlier [11] for the synthesis of
Cu2O nanoparticles. In this technique, copper and copper
oxide nanoparticles by the reaction of copper with water
can be explained according to the simple reaction at
140˚C. As the concentration of the Cu2+ and OH ions
exceeds a critical value, the precipitation of hydroxide
nuclei starts. The Cu(OH)2 can be transformed into the
Cu2O crystals via the simple chemical reactions
 
CuOHs2CuOs+2H Ol
Figure 3. XRD pattern of Cu and Cu2O nanoparticles.
Figure 4. the EDX pattern of CuO nanoparticles.
Preparation of Copper (Cu) and Copper Oxide (Cu2O) Nanoparticles under Supercritical Conditions
Copyright © 2011 SciRes. MSA
The Cu metal on reaction with water slowly gives out
hydrogen (g) and the liberated oxygen reacts with metal to
give oxides as shown in the above reaction. The similar
study has been reported earlier, where evolution of
hydrogen has been documented [12-14]. The Cu reacts
with oxygen and forms nuclei, which further serve as seed
for Cu2O nanoparticles growth. The growth of nanopart-
icles could be occurring at the small oxide nuclei that may
be present on the metal surfaces.
4. Conclusions
We have presented a very versatile, non toxic and envi-
ronmental friendly approach for the synthesis of Cu and
Cu2O nanoparticles at 140˚C without using any organics.
This facile, reproducible and low cost approach should
promise us a future large scale synthesis of nanostruc-
tures for many applications in nanotechnology. The tech-
nique could be extended and expanded to provide a con-
venient strategy for the synthesis of oxide nanostructures.
5. Acknowledgements
One of the authors (Shah M.A) is pleased to acknowledge
the KACST, Riyadh and Bei Zhang for characterization
of samples.
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