Materials Sciences and Applicatio ns, 2010, 1, 77-80
doi:10.4236/msa.2010.12014 Published Online June 2010 (http://www.SciRP.org/journal/msa)
Zinc Oxide Nanorods Prepared in Mixed Solvents
Mohammad Ashraf Shah1,2, Fahad M. Al-Marzouki1
1Department of Physics, King Abdul Aziz University, Jeddah, Kingdom of Saudi Arabia; 2Electron Microscopy Centre, Department
of Physics, Faculty of science, National Institute of Technology, Srinagar, India.
Received January 9th, 2010; revised February 27th, 2010; accepted March 2nd, 2010.
ABSTRACT
In this paper, we demonstrate a novel and direct synthesis of hexagonal-shaped zinc oxide (ZnO) nanorods at very low
temperature of ~ 80oC simply by using metallic zinc foil and de-ionized (DI) water with few drops of ethanol. The
formation of ZnO structures by the reaction of metals with DI water is suggested to occur due to the oxidation of metallic
zinc in presence of water. The synthesized ZnO products were characterized in terms of their structural and optical
properties. By the morphological investigations using FESEM, it was observed that the grown products are
hexagonal-shaped ZnO nanorods with the diameters in the range of 50-60 nm and length with ~ 1 micrometer. The EDS
and XRD pattern confirmed the composition and crystallinity of the grown nanorods and revealed that the grown
products are pure ZnO with the wurtzite hexagonal phase.
Keywords: ZnO, Nanorods, X-Ray Diffraction, Structural Properties
1. Introduction
Zinc oxide is rapidly gaining credibility as a material with
excellent possibilities for electronic and photonic devices.
It exhibits a wide band gap (3.37 eV), large excitation
binding energy (60 meV), biocompatibility, and high
melting temperature (2248K), presenting itself a promis-
ing material for wide range of well known technological
applications which are well documented [1-4]. Owing to
the semiconducting and piezoelectric dual properties of
ZnO crystals, novel applications are introduced which
have profound effect in many areas such as self-powdered
nanodevices and nanosystems [5]. The demonstration of
room temperature ultraviolet lasers, field effect transistors
and field emission arrays based on ZnO nanorods have
stimulated great interest in developing functional nan-
odevices. Moreover, the wide range of morphological
diversity in the nano-regime has made this material a
promising candidate in the field of nanotechnology and
opened up new possibilities for the fabrication of high
performance devices based on these nanostructures [6].
Among the various nanoforms, one dimensional (1D)
nanostructures have received considerable attention due to
their potential interests for understanding fundamental
physical concepts and for efficient field emission that has
enormous commercial applications such as field emission
flat panel displays, x-ray sources, parallel beam electron
microscopy and vacuum microwave amplifiers [7].
Apart from commercial methods, recently various new
methods have been developed for the synthesis of ZnO
nanostructures. Among the physical methods, chemical
and physical vapour deposition, metallorganic vapour
phase epitaxy, thermal reduction route, template based
method and pyrolysis methods have been used for the
successful synthesis of 1D ZnO nanostructures [8-12]. But
physical methods generally need expensive equipments,
high temperatures and complex producers which restrict
further development in actual applications. The chemical
methods reported in the literature include decomposition
routes of zinc precursor salt, sol-gel and solvothermal
process [13,14]. These approaches generally make use of
frequent amines or other additives that can produce un-
intentional defects. Therefore, it provides motivation and
is desirable for device application point of view to syn-
thesize zinc oxide nanostructures at low temperatures
without additives or organics.
In this paper, a versatile and expedient route to grow
zinc oxide nanorods by a simple reaction of zinc metal
with water at very low temperature of ~ 80oC using few
drops of ethanol has been presented. The grown nanorods
were characterized in detail in terms of their structural
properties. The morphological and structural investiga-
tions revealed that the as-grown ZnO nanorods are hex-
agonal and possessing well crystallinity with wurtzite
hexagonal phase. Finally a plausible growth mechanism
has been proposed for the growth of ZnO nanorods.

78 Design of a Photo-voltaic System to Enhance Network Dynamic Stability
2. Experimental
2.1 Materials
All the reagents and solvents were of analytical grade and
were used without any further purification. Zinc powder
was used as a source of Zinc and was cleaned by ul-
tra-sonication in acetone and water for 20 minutes in each
solvent.
2.2 Preparation of the Samples
In a typical synthesis, appropriate amount of zinc metal
foil was taken with 50 ml of distilled water in a Tef-
lon-lined stainless steel chamber with 110 ml capacity.
Few drops of ethanol were added to avoid the agglom-
eration. The prepared reaction mixture was kept at 80oC in
an oven for 24 hours. After the desired time, the system
was allowed to cool down naturally and the resulting
mixture was centrifuged. The zinc foils, collected from the
reactions vessels, were washed with de-ionized water
several times and finally dried in air.
2.3 Characterization
The morphology and the size of the products were ex-
amined by using field emission scanning electron micro-
scope (FESEM; FEI NOVA NANOSEM-600) coupled
with energy dispersive x-ray (EDX) spectrometer. The
crystallinity and crystal phases of the grown nanorods
were observed by using X-ray diffraction patterns meas-
ured with Cu-Kα (λ = 0.15141 nm) radiation (Siemens D
5005 diffractometer).
3. Results
3.1 Morphology of Samples
The general morphologies of the as-grown structures,
obtained after the reaction of zinc foil with water at 80oC
for 24h, was observed by FESEM and demonstrated in
Figure 1 which confirms that the grown products are
hexagonal nanorod shaped. Figure 1(a) and (b) show the
low and high magnification FESEM images of the nano-
rods and confirms that the nanorods are grown in a very
high density over the whole foil substrate. The typical
lengths of the grown nanorods are 1 μm. The typical di-
ameters of the as-grown nanorods are ~ 60 ± 10 nm. The
nanorods are exhibiting hexagonal surfaces and facets
throughout their lengths which confirm that the nanorods
are well-crystalline.
3.2 X-Ray Dispersive Analysis
To check the composition of the as-grown nanorods, EDX
analysis was performed. Figure 2 demonstrates the typi-
cal EDX analysis of the as-grown ZnO nanorods. It is
confirmed from the EDX analysis that the grown nano-
rods are composed of zinc and oxygen only. The mo-
lecular ratio of Zn:O of the grown nanorods, calculated
from EDX and quantitative analysis data, is close to that
of 1:1. Except Zn and O, no other peak for any other
element has been found in the spectrum which again
confirmed that the grown nanorods are pure ZnO.
3.3 X-Ray Diffraction Analysis
To identify the crystallinity and crystal phases of the
as-grown structures, X-ray diffraction (XRD) analysis
was performed and shown in Figure 1. Figure 1 shows
the typical XRD pattern of the as-grown nanostructures on
zinc foil. All the peaks in the pattern can be indexed to
hexagonal wurtzite structure with space group P63mc and
lattice constants a = 0.3249 nm, c = 0.5206 nm, (JCPDS
card no. 36-1451). No diffraction peaks arising from any
impurity can be detected in the pattern confirms that the
grown products are pure ZnO.
Figure 1. Typical (a) low and (b) high-resolution FESEM
images of nanorods obtained by the reaction of zinc metal
powder with water at 80˚C for 24 h

Zinc Oxide Nanorods Prepared in Mixed Solvents 79
Figure 2. The corresponding EDX analysis confirming the existence of all elements involved in sample preparation
Figure 3. XRD pattern of zinc oxide nanorods
4. Discussion
The formation of ZnO nanorods on zinc foil in the pres-
ence of water can be explained by various chemical reac-
tions. As initially, zinc does not react with water mole-
cules but at 80°C and under pressure in Teflon-lined
stainless chamber, the zinc reacted with water and forms a
protective zinc hydroxide (Zn(OH)2) layer with dissolved
hydroxide ions onto the surfaces of the zinc foil according
to the following reaction mechanism.
Zn2+ + 2OH- → Zn(OH)2 (s)
Moreover, as the concentration of the Zn2+ and OH⎯ ions
exceeds a critical value, the precipitation of ZnO nuclei
starts. The Zn(OH)2 can be transformed into the ZnO
crystals via the simple chemical reactions mentioned
below:
Zn(OH)2
ZnO + H2O
The precipitates of Zn(OH)2
are more soluble as com-
pared to the ZnO precipitates, therefore, the formed
Zn(OH)2 precipitates tend to continuously produce Zn2+
and OH⎯ ions which form the ZnO nuclei. The formed
ZnO nuclei are the building blocks for the formation of the
final products. With increasing the reaction time, the
deposition over the ZnO nuclei increases in uni-direction
and finally ZnO nanorods were deposited over the Zn-foil
substrates. Even though a plausible growth process for the
formation of ZnO hexagonal-shaped ZnO nanorods are
described here but more studies are needed to clearly
explain the growth process for the formation of these
nanorods.
5. Conclusions
An efficient and expedient route has been explored for the
synthesis of ZnO nanorods at low temperature without
additives and surfactants. The proposed single source and
catalyst free method is simple, economic and environ-
mentally benign which will make it suitable for various
ZnO nanorods based applications.
6. Acknowledgements
We are also pleased to acknowledge World Bank for their
financial support in procuring Scanning Electron Mi-
croscopy.

80 Design of a Photo-voltaic System to Enhance Network Dynamic Stability
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