Cadmium oxide nanoplatelets: Synthesis, characterization and their electrochemical sensing property of catechol

Article abstract of DOI:10.1007/s13738-012-0211-3

Cadmium oxide (CdO) nanoplatelets were synthesized by thermal decomposition of cadmium malonate. The synthesized CdO nanoplatelets were characterized by X-ray diffraction (XRD); from the XRD analysis, it is clear that the phase structure of CdO nanoplatel

Full text of DOI:10.1007/s13738-012-0211-3

J IRAN CHEM SOC (2013) 10:771–776
DOI 10.1007/s13738-012-0211-3
ORIGINAL PAPER
Cadmium oxide nanoplatelets: synthesis, characterization
and their electrochemical sensing property of catechol
•
K. Giribabu R. Suresh R. Manigandan
•
•
•
A. Stephen V. Narayanan
Received: 6 August 2012 / Accepted: 27 December 2012 / Published online: 22 January 2013
Ó Iranian Chemical Society 2013
Abstract Cadmium oxide (CdO) nanoplatelets were
synthesized by thermal decomposition of cadmium mal-
onate. The synthesized CdO nanoplatelets were character-
ized by X-ray diffraction (XRD); from the XRD analysis, it
is clear that the phase structure of CdO nanoplatelets was
found to be face-centered cubic with the average crystalline
size of 40–50 nm. FT-IR analysis shows the presence of
surface carboxyl and hydroxyl groups on to the CdO
nanoplatelets. From DRS-UV–Vis analysis, both the direct
and indirect band gaps of the CdO nanoplatelets were
found to be 2.0 and 1.67 eV, respectively. From the
FE-SEM analysis, the morphology of the synthesized CdO
was found to be nanoplatelets, which were randomly
agglomerated. Further, HR-TEM was used to confirm the
formation of nanoplatelets. The electrochemical sensing
property of CdO nanoplatelets was carried out by cyclic
voltammetry (CV) by coating CdO nanoplatelets on Glassy
carbon electrode (GCE) and using it as working electrode
for sensing of catechol. The enhanced electrochemical
behaviour is mainly attributed to the nanometer dimensions
and surface hydroxyl groups on the CdO nanoplatelets.
Chronoamperometry (CA) was used to determine the sen-
sitivity and repeatability of the modified electrode. The
modified electrode shows linear range of catechol con-
centration between 7.5 9 10-6 and 1.5 9 10-4 M with
sensitivity of 9.8 nA lM-1
.
Keywords CdO nanoplatelets ꢀ Electrochemical sensing ꢀ
Catechol ꢀ Chronoamperometry
Introduction
Nanostructured metal oxides such as Fe2O3, TiO2, V2O5,
CuO and ZnO have received considerable attention over
the past decades, due to their unique electronic, optical,
thermal properties and their promising applications in
fabricating nanoscale devices [1–5]. In meticulous, the
nanostructured metal oxides are of great interest in the
fields of drug delivery, photocatalyst, electrocatalyst and
solid oxide fuel cells [6–8]. Among the various nano-
structured metal oxides, CdO is an important n-type
semiconductor metal oxide, which belongs to the II–VI
group with large band gap, low electrical resistivity and
high transmission in the visible region. Because of these
properties, it has been widely investigated in various fields
such as photovoltaic cells, transparent electrodes, etc. [9,
10]. Several synthetic routes such as hydrothermal method,
template assisted method, solvothermal methods, chemical
co-precipitation method, vapor phase transport, thermal
evaporation, microwave method and sonochemical method
were adopted to prepare CdO nanostructures. Depending
on the synthetic procedures, the morphology of the CdO
varies such as nanowires, nanotubes, nanofibers, nanorods,
nanoclusters, nanocubes, nanobelts and nanoparticles [11–
15]. The physical and chemical properties of CdO depend
on the size, shape and stoichiometry that further lies on the
synthetic procedures [16]. Nanostructured CdO has been
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-012-0211-3) contains supplementary
material, which is available to authorized users.
K. Giribabu ꢀ R. Suresh ꢀ R. Manigandan ꢀ V. Narayanan (&)
Department of Inorganic Chemistry, University of Madras,
Guindy Maraimalai Campus, Chennai 600025,
Tamil Nadu, India
e-mail: vnnara@yahoo.co.in
A. Stephen
Department of Nuclear Physics, University of Madras,
Guindy Maraimalai Campus, Chennai, India
123

772
J IRAN CHEM SOC (2013) 10:771–776
employed in processes such as energy storage system, elec-
trochromic thin films [17], magnetoresistive devices [18],
heterogeneous catalysis and gas sensors [19]. Furthermore,
CdO and other cadmium-based oxides were demonstrated to
have excellent electrocatalytic activity toward various com-
pounds, ozone and oxygen evolution [20]. Nanostructured
CdO-modified electrodes have been used to detect diverse
organic molecules such as glucose, dopamine, cysteine,
propylamine, hydroquinone and methanol [21–25] as model
compounds. Large amounts of phenolic compounds were
released in the environment by various industries, such as
coal mining, oil refinery, paint, polymer and pharmaceutical
preparation. These compounds are harmful to human beings.
Hence, it becomes more important to monitor the levels of the
phenolic compounds in the environment. Though, chemically
modified electrodes and enzyme-modified electrodes were
reported to analyse the levels of catechol [26, 27], the enzyme
modification process was tedious and the modified electrodes
were unstable under room temperature conditions due to the
poor stability of the immobilized enzymes.
electrode, platinum as the counter electrode and saturated
calomel electrode (SCE) as the reference electrode. Cyclic
voltammetric measurements were carried out using 0.1 M
phosphate buffer solution (PBS) as the background electrolyte.
Synthesis of cadmium malonate
Cadmium malonate [CdC3H2O4ꢀ2H2O] was prepared by
stirring cadmium acetate and malonic acid in 1:1 ratio in
50 mL of distilled water at 60 °C for 2 h. Cadmium mal-
onate was obtained by evaporating the above solution in
water bath at 80 °C for 3 h.
Synthesis of CdO nanoplatelets
Cadmium malonate was heated in muffle furnace at 550 °C
for 6 h; the temperature of the muffle furnace was raised at
the rate of 5 °C min-1. After that, the temperature of the
muffle furnace was reduced to room temperature and the
obtained CdO nanoplatelets were used for characterization.
In this work, we report the synthesis of CdO nanopar-
ticles using cadmium malonate as single precursor via
facile thermal decomposition route. The synthesized CdO
nanoparticles were used to modify the glassy carbon
electrode and employed for the electrochemical sensing
towards catechol.
Results and discussions
X-ray diffraction studies
XRD pattern of CdO was shown in Fig. 1. The diffraction
peaks of CdO reveal that it has a face-centered cubic structure,
which exactly matches with JCPDS No. 75–0592 along with
space group of Fm3m (225) and no impurity phases such as
CdO2 and Cd(OH)2 were observed. The observed diffraction
peaks at 2h = 33.020°, 38.34°, 55.32°, 65.95° and 69.30° are
associated with [111], [200], [220], [311] and [222] plane,
respectively, with the d-spacing values of 0.46, 0.40, 0.27,
0.23 and 0.22 nm, respectively. The sharp diffraction peaks
clearly indicate the high crystalline nature of the prepared
CdO. Using Scherrerequation, the average crystallite sizewas
calculated and found to be 40–50 nm.
Experimental
Materials
Cadmium acetate, malonic acid, sodium hydrogen phos-
phate and sodium dihydrogen phosphate were purchased
from Qualigens (Mumbai, India) and were used without
further purification. Catechol was purchased from Sigma
(USA) and was used as received. Doubly distilled water
was used as the solvent.
Characterization
FT-IR spectroscopy
FT-IR spectrum of CdO was recorded on Schimadzu FT-IR
8300 series instrument using potassium bromide pellets.
The DRS-UV–Visible spectrum of the sample was recor-
ded on UV-1601OC, Shimadzu instrument. Powder X-ray
diffraction (XRD) analysis was carried out using Brucker
D8 ADVANCE with monochromatic CuKa1 radiation
FT-IR spectrum of CdO is shown in Fig. 2. The spectrum
exhibits a broad band near 3,400 cm-1 due to the OH-
stretching vibrations of free and hydrogen-bonded hydroxyl
groups. The peak at 1,380 cm-1 corresponds to the C=O/C–O
vibrations. The other bands at 852 and 723 cm-l may be related
to the water molecules combined with the hydroxide [28]. A
peak at 520 cm-1 corresponds to the formation of Cd–O [29].
˚
(k = 1.5406 A). The morphology of the sample was ana-
lysed by FE-SEM using a HITACHI SU6600 field emis-
sion-scanning electron microscopy and HR-TEM using a
FEI TECNAI G2 model T-30 at accelerating voltage of
250 kV. Cyclic voltammetry was performed using CHI
600A instrument with bare and modified GCE as working
Thermogravimetric analysis
The thermal decomposition of cadmium malonate was
investigated by thermogravimetric analysis (TGA) under
123

J IRAN CHEM SOC (2013) 10:771–776
773
Fig. 1 X-ray diffraction pattern of CdO nanoplatelets
Fig. 3 TGA curve of cadmium malonate
relation between the absorption coefficient (A) and the
incident photon energy (hm) can be given as
À
Á
1=n
ðahmÞ ¼ A hm ꢁ Eg
where a is a constant and Eg is the band gap of the material
and exponent n depends on the type of transition. For direct
allowed transition, n = 1/2; indirect allowed transition,
n = 2; and for direct forbidden, n = 3/2. To determine the
possible transitions, (ahm)1/n versus hm were plotted, and
corresponding band gap were obtained from extrapolating
the straight portion of the graph on hm axis. The direct band
gap calculated from (ahm)2 versus hm plot is found to be
2.00 eV and the indirect band gap is 1.67 eV calculated
‘
from (ahm) versus hm plot as shown in Figs. S2 and S3,
respectively. However, the obtained band gap of the CdO
nanoplatelets is smaller than the reported value [30]. This
difference in band gap of CdO originates from non-stoi-
chiometric composition and strongly influenced by the
synthetic procedures [31]. In fact, the presence of cadmium
interstitials, i.e., Cd2? ions, or oxygen vacancies gives rise
to defect states and there may be some finite transition
probabilities from these states, which leads to the indirect
transitions in CdO.
Fig. 2 FT-IR spectrum of CdO nanoplatelets
nitrogen atmosphere. Figure 3 shows a small weight loss at
about 150 °C, which might be due to the hydrated water
molecules. The compound undergoes decomposition above
310 °C, with a weight loss of approximately 67.0 %. From
the first weight loss, it is evident that the decomposed
product contains surface hydroxyl groups. These surface
hydroxyl groups were lost on further heating in the tem-
perature range of 600–700 °C. The remaining mass was
found to be 33.0 %.
FE-SEM analysis
Figure 4a and b shows the FE-SEM image of the synthe-
sized CdO; it can be seen that diameter of CdO nanopar-
ticles annealed at 550 °C is in the range of 90–220 nm.
Since the decomposition temperature is around 550 °C, the
size of the CdO nanoparticles increases due to the phe-
nomenon called high degree of supersaturation of the
decomposed products of cadmium malonate complex. This
high degree of supersaturation accelerates the crystal
growth formation reaction within a short time. At this
DRS-UV–Visible spectroscopy
The diffused reflectance spectrum was carried out for CdO
in room temperature. The variation of optical absorbance
with wavelength (k) of CdO is shown in Fig. S1. The
nature and value of the optical band gap can be determined
by the fundamental absorption, which is due to the electron
excitation from the valance band to conduction band. The
123

774
J IRAN CHEM SOC (2013) 10:771–776
stage, the controlling step of the reaction takes place by the
transformation from grain growth to crystal nucleus for-
mation. The rate of particle aggregation is a predominant
factor, which controls both the morphology and structure of
the CdO nanoparticles [32]. At the temperature of 550 °C,
the crystal nucleus continue to grow and nucleus aggre-
gation would be predominant which was caused by the
rapid formation of crystal nucleus due to high temperature
which results in aggregation among the crystal nucleus [33,
34].
HR-TEM analysis
The formation of CdO nanoplatelets were confirmed by
HR-TEM analysis (Fig. 4c). The size of the nanoplatelets
was found to be *200 nm, which is consistent with the
FE-SEM analysis. The edges of the nanoplatelets were thin
and irregular in nature.
Electrochemical sensing property
Figure 5 shows the cyclic voltammograms (CV) of bare
and CdO/GCE in the absence of 0.1 mM catechol in 0.1 M
PBS. It can be seen that no oxidation–reduction peak was
observed at the CdO/GCE in 0.1 M PBS in the potential
range of -0.4 to ?1.0 V. Curve b of Fig. 5 clearly indi-
cates that the CdO/GCE is not electroactive in the selected
potential range which pointed out that the CdO/GCE can be
utilized for the sensing of catechol. Though the CdO/GCE
is not active in the selected potential range, it shows higher
current response when compared with that of bare GCE
(Fig. 6). In Fig. 6, the CdO/GCE (curve b) shows shift in
potential with enhanced peak current in presence of
0.1 mM catechol than the bare GCE (Fig. 6a) indicates the
electrocatalytic ability of the modified electrode. This
electrocatalytic effect was attributed to the larger available
surface area of the modifying layer due to the nanometer
size of the sample [1], as evident by the FE-SEM analysis.
Further, the surface –OH group of CdO shown in FT-IR
forms the hydrogen bonding with the hydroxyl group of
catechol. This hydrogen bonding effectively contributes to
the weakening of hydroxyl bond to facilitate the electron
transfer through the hydroxyl group of catechol O–H–O to
surface hydroxyl group of CdO. The mechanism of elct-
rooxidation of catechol at CdO/GCE is shown in
Scheme 1. Figure 7 shows the effect of scan rate on the
electrochemical response of 0.1 mM catechol at the CdO/
GCE. As can be seen in Fig. 7, the oxidation peak current
shifted positively and the reduction peak current moved
negatively, and the value of DE was less than 300 mV.
Figure 7 shows that both the oxidation and reduction peak
currents were almost linearly proportional to the square
root of scan rate in the range of 10–100 mV s-1. It
Fig. 4 a, b FE-SEM images of CdO nanoplatelets with a magnifi-
cation of 500 nm. c HR-TEM images of CdO nanoplatelets
suggests that the CdO layer has good electrochemical
activity and fast electron transfer at pH 7.4. It is reported
that the redox process of catechol proceeds through
123

J IRAN CHEM SOC (2013) 10:771–776
775
Fig. 5 Cyclic voltammograms of (a) bare GCE and (b) CdO/GCE in
absence of 0.1 mM catechol in 0.1 M PBS
Fig. 7 Cyclic voltammograms at CdO/GCE for 0.1 mM catechol at
different scan rates: (a) 10, (b) 20, (c) 30, (d) 40, (e) 50, (f) 60, (g) 70,
(h) 80,(i) 90 and (j) 100 mV s-1
Fig. 6 Cyclic voltammograms of a bare GCE and b CdO/GCE in
presence of 0.1 mM catechol in 0.1 M PBS
Fig. 8 Typical amperometric i–t responses of CdO/GCE for the
detection of catechol at an applied potential of 0.4 V versus SCE in
pH 7.4 PBS under stirring condition. Inset figure shows the plot of
current response versus concentration of catechol
IPa ¼ nFQv=4RT
n ¼ IPa4RT=FQv
where n is the number of electrons involved in the reaction,
ð2Þ
I
Pa is the anodic peak current, R is the gas constant, T is the
temperature (K), F is the Faraday constant, Q is the charge
and v corresponds to the scan rate. The total number of
electrons involved in the redox process of catechol is 1.73
(*2). To determine the sensitivity and repeatability,
response of CdO/GCE chronoamperometric measurements
was carried out in 0.1 M PBS at stirring condition and the
optimum electrode potential was selected as ?0.4 V versus
SCE. Figure 8 displays the chronoamperometric current–
time response of the CdO/GCE upon the addition of
Scheme 1 Mechanism of electrooxidation of catechol at CdO/GCE
2e-, 2H? process [35]. In order to calculate, the number of
electrons involved in the overall reaction can be obtained
by the following equation,
123

776
J IRAN CHEM SOC (2013) 10:771–776
2. P.C. Lansaker, J. Backholm, G.A. Niklasson, C.G. Granqvist,
Thin Solid Films 518, 1225–1229 (2009)
3. A. Dhayal Raj, T. Pazhanivel, P. Suresh Kumar, D. Mangalaraj,
D. Nataraj, N. Ponpandian, Curr. Appl. Phys. 10, 531–537 (2010)
4. D. Kalpana, K.S. Omkumar, S. Suresh Kumar, N.G. Rengana-
than, Electrochim. Acta 52, 1309–1315 (2006)
5. T. Miwa, S. Kaneco, H. Katsumata, T. Suzuki, K. Ohta, S.C.
Verma, K. Sugihara, Int. J. Hydrogen Energy 35, 6554–6560
(2010)
6. P. Suresh, S. Rodrigues, A.K. Shukla, H.N. Vasan, N. Munich-
andraiah, Solid State Ionics 176, 281–290 (2005)
7. R. Suresh, R. Prabu, A. Vijayaraj, K. Giribabu, A. Stephen, V.
Narayanan, Synth. React. Inorg. Met. Org. Nano Met. Chem. 42,
303–307 (2012)
8. C.S.S.R. Kumar, F. Mohammad, Adv. Drug Deliv. Rev. 63,
789–808 (2011)
9. R.K. Gupta, K. Ghosh, R. Patel, S.R. Mishra, P.K. Kahol, Curr.
Appl. Phys. 9, 673–677 (2009)
10. F. Yakuphanoglu, Sol. Energy 85, 2704–2709 (2011)
11. F. Zhang, F.L. Bei, J.M. Cao, X. Wang, J. Solid State Chem. 181,
143–149 (2008)
12. D.H. Fan, J. Cryst. Growth 311, 2300–2304 (2009)
13. R.R. Salunkhe, D.S. Dhawale, U.M. Patil, C.D. Lokhande, Sens.
Actuators B 136, 39–44 (2009)
0.2 mL of 0.1 mM catechol. A successive addition of
catechol to continuously stirred 0.1 M PBS produces a
significant increase in the current. The almost equal current
steps for each addition of catechol illustrate that the CdO/
GCE is stable and has an efficient electrocatalytic activity
towards the catechol. The prompt response was attributed
to the heterogeneous electron transfer of CdO/GCE. The
calibration graph for the determination of catechol by the
CdO/GCE is shown as the inset in Fig. 8. The linear range
was almost found between 7.5 9 10-6 and 1.5 9 10-4
M
with a correlation coefficient of 0.9952 corresponding with
a sensitivity of 9.8 nA lM-1, shows that the CdO/GCE is
highly sensitive towards catechol. The results clearly
indicate that the electrocatalytic reaction takes place
between the CdO/GCE and catechol, which is due to the
electron transfer between catechol and the modified elec-
trode; as a result, the electrochemical oxidation of catechol
becomes easier. In addition, it is clear that CdO/GCE can
be effectively used for the electrochemical sensing of
catechol.
14. F. Yakuphanoglu, Appl. Surf. Sci. 257, 1413–1419 (2010)
15. C.C. Vidyasagar, Y. Arthoba Naik, T.G. Venkatesh, R. Viswa-
natha, Powder Technol. 214, 337–343 (2011)
16. M. Ghosh, C.N.R. Rao, Chem. Phys. Lett. 393, 493 (2004)
17. V. Srinivasan, J.W. Weidner, J. Power Sour. 108, 15–20 (2002)
18. L.D. Kadam, S.H. Pawar, P.S. Patil, Mater. Chem. Phys. 68,
280–282 (2001)
19. H. Okabe, J. Akimitsu, T. Kubodera, M. Matoba, T. Kyomen, M.
Itoh, Phys. B (Amsterdam, Neth.) 378-380, 863 (2006)
20. M. Longhi, L. Formaro, J. Electroanal. Chem. 464, 149–157 (1999)
21. F. Svegl, B. Orel, I.G. Svegl, C.V. Kaucic, Electrochim. Acta 45,
4359–4371 (2000)
22. I.G. Casella, M.R. Guascito, J. Electroanal. Chem. 476, 54–63
(1999)
23. I.G. Casella, M. Gatta, J. Electroanal. Chem. 534, 31–38 (2002)
24. I.G. Casella, J. Electroanal. Chem. 520, 119–125 (2002)
25. L.F. Fan, X.Q. Wu, M.D. Guo, Y.T. Gao, Electrochim. Acta 52,
3654–3659 (2007)
26. D. Quan, W. Shin, Electroanalysis 16, 1576–1582 (2004)
27. S. Mu, Biosens. Bioelectron. 21, 1237–1243 (2006)
28. R.B. Fahim, G.A. Kolta, J. Phys. Chem. 74, 2502–2506 (1970)
29. A. Moses Ezhil Raj, D. Deva Jayanthi, V. Bena Jothy, Solid State
Sci. 10, 557–562 (2008)
30. B.S. Zou, V.V. Volkov, Chem. Mater. 11, 3037–3043 (1999)
31. A. Gulino, G. Tabbi, A.A. Scalisi, Chem. Mater. 15, 3332–3336
(2003)
Conclusion
CdO nanoplatelets were synthesized by simple thermal
decomposition of cadmium malonate at 550 °C. The XRD,
FT-IR and DRS-UV–Vis analyses were used to study the
synthesized sample spectrally and FE-SEM analysis was
used to study the morphology of the sample. CdO nano-
platelets were successfully fabricated onto the GCE for
sensing of catechol. From the electrochemical measurements,
it is clearly understood that the CdO nanoplatelet-modified
electrode shows a wide linear range of concentration for
catechol sensing.
Acknowledgments One of the authors (K.Giribabu) wish to thank
Department of Science and Technology (DST), Government of India
for the financial assistance in the form of INSPIRE fellowship (Inspire
Fellow no.10226) under the AORC scheme. In addition, authors thank
National Centre for Nanoscience and Nanotechnology (NCNSNT),
University of Madras for recording FE-SEM.
32. Z.C. Michael Hu, T. Michael Harris, H. Charles Byers, J. Colloid
Interface Sci. 198, 87–99 (1998)
33. S. Zhaorigetu, H. Yao, Garidi. Front. Chem. Chin. 3, 277–280
(2006)
34. F. Zhang, J. Yang, Int. J. Chem. 1, 18–22 (2009)
35. R.M. Wightman, E. Strope, P.M. Plotsky, R.N. Adams, Nature
262, 145–146 (1976)
References
1. R. Suresh, R. Prabu, A. Vijayaraj, K. Giribabu, A. Stephen, V.
Narayanan, Mater. Chem. Phys. 134, 590–596 (2012)
123