Preparation of nanostructured zinc oxide from single source precursors

Article abstract of DOI:10.1080/15533171003629071

Nanostructured ZnO was prepared by pyrolysis of single source precursors, ZnCl2(benzsczH)2 and ZnCl2(cinnamsczH)2 (where, benzsczH = benzaldehyde semicarbazone and cinnamsczH = cinnamaldehyde semicarbazone). Powder X-ray diffraction pattern (PXRD) shows f

Full text of DOI:10.1080/15533171003629071

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Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry
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Preparation of Nanostructured Zinc Oxide from
Single Source Precursors
Anil M. Palve a & Shivram S. Garje a
a Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai,
India
Published online: 23 Mar 2010.
To cite this article: Anil M. Palve & Shivram S. Garje (2010) Preparation of Nanostructured Zinc Oxide from Single Source
Precursors, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:3, 153-156
To link to this article: http://dx.doi.org/10.1080/15533171003629071
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:153–156, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533171003629071
Preparation of Nanostructured Zinc Oxide from Single
Source Precursors
Anil M. Palve and Shivram S. Garje
Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E), Mumbai, India
cylinders,[17] and radial nanowire arrays[18] have been prepared
Nanostructured ZnO was prepared by pyrolysis of single source
precursors, ZnCl2(benzsczH)2 and ZnCl2(cinnamsczH)2 (where,
benzsczH = benzaldehyde semicarbazone and cinnamsczH = cin-
namaldehyde semicarbazone). Powder X-ray diffraction pattern
(PXRD) shows formation of hexagonal ZnO. The peak broadening
in PXRD and absorption towards blue region in absorption spectra
confirms the formation of nanoscale ZnO. The transmission elec-
tron microscopy images reveal formation of nanocrystals along
with nanorods. The optical band gaps of both the materials were
determined by using Tauc’s plots. They are found to be higher than
the band gap of bulk ZnO. Infrared spectra also showed formation
of ZnO.
by the various researchers.
Many preparation methods for ZnO have been reported.
Methods such as thermal evaporation, pyrolysis, hydrothermal
and capping agent assisted wet chemical methods, chemical va-
por deposition (CVD) have been used.[4] ZnO thin films have
been prepared by chemical bath deposition (CBD), spray pyroly-
sis, pulse laser deposition (PLD), electrodeposition, atomic layer
deposition (ALD), molecular beam epitaxy (MBE), and metal
organic chemical vapour deposition (MOCVD) techniques.[2]
Though plenty of methods for the preparation of ZnO have been
described, there are only few reports on the preparation using
single source precursors (SSPs).[19] Considering the advantages
of SSPs such as low toxicity, limited pre-reactions, clean de-
composition, etc., we thought it worthwhile to use them for
the preparation of ZnO. In the present investigation, we have
used zinc semicarbazone complexes, ZnCl2(benzsczH)2and
ZnCl2(cinnamsczH)2(where, benzsczH = benzaldehyde semi-
carbazone and cinnamsczH = cinnamaldehyde semicarbazone)
as SSPs, which on pyrolysis gave ZnO nanoparticles with some
nanorods.
Keywords nanostructures, semicarbazone complexes, zinc oxide
INTRODUCTION
ZnO is a wide band gap (3.4 eV) semiconductor with wurtzite
structure.[1] It has applications in short wavelength light emit-
ting devices, field emission devices and surface acoustic wave
devices as well as transparent conducting electrodes.[1] It has
useful physical properties suitable for optical and electronic
applications.[2] ZnO thin films can be used in organic light
emitting diodes and efficient UV lasers.[2,3] Its strong piezo-
electric and pyroelectric properties make it useful material in
actuators, nanogenerators and piezoelectric sensors.[3] It is bio-
safe and biocompatible material; hence it can be directly used
in biomedical applications without coating.[4]
Nanostructured materials can play important role in elec-
tronics, optics and photonics as their properties such as
electrical, mechanical, chemical and optical can be tuned
by preparing desired nanostructured materials.[3] A variety
of ZnO nanostructures such as nanowires,[5] nanobelts,[6]
nanosprings,[7] nanorings,[8] nanobows,[9] and nanohelices[10]
have been reported. Also nanorods,[11] nanosheets,[12] hollow
spheres,[13] tetrapods,[14] ellipsoids,[15] hexagonal pyramids,[16]
EXPERIMENTAL
Preparation of ZnCl2(benzsczH)2
To a round bottom flask containing 1.202 g (7.366 mmols)
of benzaldehydesemicarbazone dissolved in a ∼ 20 mL THF,
0.502 g (3.683 mmols) of ZnCl2dissolved in 10 mL THF was
added with continuous stirring and stirring was continued for
36 h. Then the solvent was evaporated in vacuo, when a yellow
solid was obtained. It was repeatedly washed with n-hexane
and cyclohexane (3 × 5 mL) to remove any impurities present
and then dried under vacuum to get free solid. (Yield, 0.892 g,
89.03 %) M.P.: 164◦C.
Elemental analysis, found (calcd): Zn: 14.00 (14.13), C:
41.35 (41.53), H: 3.45 (3.92), N: 17.92 (18.16), Cl: 15.12
(15.32). I.R.: 3460 cm−1, 3277 cm−1 (υNH2asym and sym),
3161cm−1 (υNH), 1599 cm−1 (υC=N), 1650 cm−1(υC=O). N.M.R.
(δ in ppm): 6.52 (s, NH2), 7.34–8.22 (m, C6H5-CH=), 10.27 (s,
NH). 13C (δ in ppm): 157.26 (C=O), 139.85 (C=N), 135.18,
129.48, 129.02, 126.98 (aromatic carbons).
Received 21 September 2009; accepted 17 January 2010.
Authors thank TIFR, Mumbai for providing PXRD. Thanks are also
due to SAIF, IIT-Mumbai for TEM images.
Address correspondence to Dr. Shivram S. Garje, Dept. of
Chemistry, Vidyanagari, Santacruz (East), Mumbai, 400098. E-mail:
ssgarje@chem.mu.ac.in
153

154
A. M. PALVE AND S. S. GARJE
Preparation of ZnCl2(cinnamsczH)2
1.027 g (5.428 mmols) of cinnamaldehydesemicarbazone
was dissolved in ∼ 20 mL THF in a round bottom flask. To
this 0.373 g (2.714 mmols) of ZnCl2 dissolved in 10 mL THF
was added with continuous stirring and stirring was continued
for 36 h. Then the solvent was removed using vacuum to get
a pale yellow solid. It was repeatedly washed with n-hexane
and cyclohexane (3 × 5 mL) to remove impurities present and
dried under vacuum to get free solid. (Yield, 1.200 g, 85.89 %)
M.P.:182◦C.
Elemental analysis, found (calcd): Zn: 12.73 (12.70), C:
45.99 (46.66), H: 4.18 (4.30), N: 16.43 (16.32), Cl: 13.42
(13.77). I.R.: 3454 cm−1, 3279 cm−1 (υNH2asym and sym), 3152
cm−1 (υNH), 1610 cm−1 (υC N), 1650 cm−1, (υC O). N.M.R.
(δ in ppm): 6.45 (s, NH2), 6.87–8.19 (m, C6H5-CH=CH-CH-),
10.23 (s NH). 13C (δ in ppm): 157.07 (C=O), 142.60, 136.84,
136.56 (CH=CH-CH=N), 129.26, 128.88, 127.13, 126.01 (aro-
matic carbons).
FIG. 1. Chemical structures of ZnCl2(benzsczH)2 (1) and ZnCl2
(cinnamsczH)2 (2).
mental analysis was found to match with 1:2 metal to ligand
stoichiometries. In the IR spectra of complexes the bands due to
asymmetric and symmetric stretchings of NH2 group as well as
N-H and C=O stretchings are observed. In the 1H NMR spectra
peak due to -NH proton is observed at about 10.2 ppm. These
observations are consistent with the ligand coordination through
oxygen and azomethine nitrogen atoms.[20,21]
Thermal decomposition of these complexes was carried out at
515◦C in furnace under nitrogen atmosphere. The black residue
obtained was characterized by microanalysis, powder XRD,
TEM, SAED, UV-VIS and IR spectroscopy. The black colors of
the materials obtained are due to carbon contamination coming
from the organic ligands. Thus, for ZnO obtained from pyrolysis
of precursor (1) microanalysis showed presence of 12.37% car-
bon whereas, for the material obtained by pyrolysis of precursor
(2) carbon present is found to be 13.52%.
Preparation of Nanostrucutred ZnO
Nanostructured ZnO was prepared by pyrolysis of above
precursors in furnace under nitrogen atmosphere. The precursor
was taken in quartz boat. The boat was kept at the center of
a horizontal wall furnace. The furnace was then heated at a
rate of 25◦C / min to 515◦C and held at this temperature for
one hour. After that the furnace was naturally cooled to room
temperature. The residue obtained in the boat was removed and
then characterized by microanalysis, XRD, TEM, SAED, UV-
VIS and IR spectroscopy.
INSTRUMENTATION
The absorption spectra were recorded on a UV-2401 PC
Shimadzu UV-vis spectrophotometer. XRD studies were car-
ried out using Cu Kα radiation on a X’pert PRO PANalyti-
cal X-ray diffractometer (Philips). TEM were recorded on a
PHILIPS, Model no-CM 200 with operating voltages 20–200
kV. IR spectra were taken on a Perkin Elmer FT-IR spectrome-
ter in 4000–400 cm−1 range. Microanalysis was carried out on
Thermo Finnigan, Italy Model FLASH EA 1112 Series elemen-
tal analyzer.
Figure 2 shows powder XRD patterns of the nanostruc-
tured ZnO obtained by pyrolysis of ZnCl2(benzsczH)2 and
ZnCl2(cinnamsczH)2 complexes. All the diffraction peaks could
be clearly indexed to hexagonal ZnO (JCPDS: 79-0205). In both
RESULTS AND DISCUSSION
In the present investigation, ZnCl2(benzsczH)2(1) and
ZnCl2(cinnamsczH)2 (2) were used as single source precursors
for the synthesis of ZnO nanocrystallites. The precursors were
prepared by simple addition reactions of ZnCl2 to correspond-
ing ligand (Eq. 1). Chemical structures of (1) and (2) are given
in Figure 1.
THF
ZnCl2 + 2 LH −−−−−−−→ ZnCl2(LH)2
[1]
R.T.
LH = semicarbazones of benzaldehyde and cinnamaldehyde
The complexes obtained were characterized by elemental
FIG. 2. XRD patterns of hexagonal ZnO (JCPDS: 79-0205) obtained by py-
rolysis of (a) ZnCl2(benzsczH)2 and (b) ZnCl2(cinnamsczH)2 at 515◦C.
1
analysis, IR, H and 13C NMR spectroscopic techniques. Ele-

PREPARATION OF NANOSTRUCTURED ZINC OXIDE
155
FIG. 4. Absorption spectra of nanostructured ZnO obtained by pyrolysis of
(a) ZnCl2(benzsczH)2 and (b) ZnCl2(cinnamsczH)2at 515◦C.
ogy along with few nanorods is observed. The average grain size
of nanoparticles is 27 nm for material obtained from precursor
(1) whereas for precursor (2) it is about 10 nm. These values
are consistent with those calculated from XRD. The width of
nanorods obtained from precursor (1) is between 100 to 130 nm
(Figure 3b). For nanorods obtained from precursor (2) width is
about 80 nm. SAED patterns of ZnO obtained from precursor (1)
and (2) show the presence of well defined rings indicating that
the materials obtained are crystalline in nature. It also confirms
the formation of hexagonal ZnO.
The absorption spectra of nanostructured ZnO were recorded
by dispersing particles in methanol. In spectra of materials ob-
tained from both the precursors a blue shift is observed com-
pared to bulk ZnO (305 nm). The absorption bands are ob-
served at 280 nm and 272 nm for materials obtained from
precursor (1) and (2), respectively (Figure 4). The optical band
FIG. 3. (a) TEM image and SAED pattern (inset) of ZnO nanoparticles ob-
tained by pyrolysis of ZnCl2(benzsczH)2at 515◦C.
(b) TEM image of ZnO nanorods obtained by pyrolysis of ZnCl2(benzsczH)2at
515◦C.
the cases ZnO particles are found to have preferred growth along
(101) plane. The peak broadening in XRD patterns suggest pres-
ence of nanosize ZnO. The average grain size (D) was calculated
using Scherrer’s formula.[22] For the material obtained from pre-
cursor (1), average particle size calculated was found to be 32.51
nm whereas for material obtained from precursor (2) it is found
to be 14.64 nm. It can be seen that the peaks for ZnO obtained
from precursor (2) are broader compared to those from precursor
(1). This suggests smaller particle size for ZnO obtained from
precursor (2) compared with the material obtained from precur-
sor (1). This is also evident from the particle sizes calculated
using Scherrer’s formula.
FIG. 5. A plot of (αhν)2versus hν of nanosructured ZnO obtained by pyrolysis
of (a) ZnCl2(benzsczH)2 and (b) ZnCl2(cinnamsczH)2 at 515◦C.
Figure 3a and 3b show representative TEM images and
SAED pattern of the nanostructured ZnO. Plate-like morphol-

156
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CONCLUSION
Nanostructured ZnO was successfully obtained by py-
rolysis of single source precursors, ZnCl2(benzsczH)2 and
ZnCl2(cinnamsczH)2. The PXRD showed formation of hexag-
onal ZnO. The morphology of the materials was found to be
mainly nanoparticles with presence of some nanorods. This
suggests that the single source precursors could be promising
molecules for convenient synthesis of nanostructured materials
as they have inherent advantages over conventional dual source
precursors.
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