Nickel oxide thin film from electrodeposited nickel sulfide thin film: Peroxide sensing and photo-decomposition of phenol

Article abstract of DOI:10.1039/c4dt01658k

A novel non-enzymatic peroxide sensor has been constructed by using nickel oxide (NiO) thin films as sensing material, which were prepared by a two-step process: (i) electrodeposition of nickel sulfide (NiS) and (ii) thermal air oxidation of as-deposited NiS to NiO. The resultant material is highly porous and comprises interconnected nanofibers. UV-Vis spectroscopy, FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) were used for a complete characterization of nanostructured NiO thin films. Cyclic voltammetry study shows that NiO/ITO electrode facilitates the oxidation of hydrogen peroxide and exhibits excellent catalytic activity towards its sensing. The amperometric study of NiO/ITO was carried out to determine the sensitivity, linear range, detection limit of the proposed sensor. The sensor exhibits prominent electrocatalytic activity toward the oxidation of H₂O₂ with a wide linear range and a low detection limit. The possible use of the synthesized NiO thin films as an effective photocatalyst for the decomposition of phenol is also discussed. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4dt01658k

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Nickel oxide thin film from electrodeposited
nickel sulfide thin film: peroxide sensing and
photo-decomposition of phenol†
Cite this: Dalton Trans., 2014, 43,
13096
a
b
c
d
Sumanta Jana, Subhasis Samai, Bibhas C. Mitra, Pulakesh Bera and
Anup Mondal*
a
A novel non-enzymatic peroxide sensor has been constructed by using nickel oxide (NiO) thin films as
sensing material, which were prepared by a two-step process: (i) electrodeposition of nickel sulfide (NiS)
and (ii) thermal air oxidation of as-deposited NiS to NiO. The resultant material is highly porous and com-
prises interconnected nanofibers. UV-Vis spectroscopy, FTIR spectroscopy, X-ray photoelectron spec-
troscopy (XPS), X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) were
used for a complete characterization of nanostructured NiO thin films. Cyclic voltammetry study shows
that NiO/ITO electrode facilitates the oxidation of hydrogen peroxide and exhibits excellent catalytic
activity towards its sensing. The amperometric study of NiO/ITO was carried out to determine the sensi-
tivity, linear range, detection limit of the proposed sensor. The sensor exhibits prominent electrocatalytic
Received 5th June 2014,
Accepted 3rd July 2014
2 2
activity toward the oxidation of H O with a wide linear range and a low detection limit. The possible use
DOI: 10.1039/c4dt01658k
of the synthesized NiO thin films as an effective photocatalyst for the decomposition of phenol is
www.rsc.org/dalton
also discussed.
variable reflectance mirrors and non-emissive information dis-
Introduction
9
plays. Several deposition techniques, such as metal evapor-
1
0
11
12
13
Shape- and size-controlled synthesis of low-dimensional elec- ation, sputtering, sol gel, electrochemical and chemical
trochromic nanomaterials has become an advanced research techniques, are employed to synthesize NiO thin films.
topic due to its wide range of applications in different fields of However, the electrochemical technique is a facile and control-
1
,2
science and technology. The enormous use of electrochro- lable technique for tailoring crystallinity and morphology
1
3
mic material in devices is due to its efficient electron transport through several competing factors. The application of the
3
property. Nickel oxide (NiO), an electrochromic material material is strongly shape, size and morphology dependent.
(band gap energy from 3.6 to 4.0 eV) with high electron trans- Thus far, NiO nanostructures with different morphologies,
port property, has received a great deal of interest because of such as nanoplates, nanotubes and nanopowders, were syn-
1
4,15
its versatile application in modern science and technology. thesized and used extensively in different fields.
Evans
4
16
Thin films of NiO are widely used as gas sensors, electroche- et al. reported that the nanofibres (a specific morphology of
mical display devices, p-type transparent conducting electro- NiO) are a very important nanostructure from the application
5
6
7
8
des, organic light emitting diodes (OLEDs), smart windows,
point of view. In the literature, it has also been found that
nickel or nickel-based chemically modified electrodes (e.g.
nickel-hexacyano ferrates, hydroxides and complex-modified
nickel electrodes) of a specific morphology were extensively
used for the electrooxidation and reduction processes.
this work, we have carefully investigated the synthesis of NiO
thin films from electrodeposited NiS thin films. The electro-
catalytic activity of synthesized films (NiO) has been tested for
peroxide sensing. The sensitivity, linear range and detection
limit are calculated by amperometric analysis. The effect of pH
and temperature (T) on the sensitivity was also investigated.
We have shown another important application of the syn-
a
Department of Chemistry, Indian Institute of Engineering Science and Technology,
Botanic Garden, Howrah 711103, WB, India. E-mail: anupmondal2000@yahoo.co.in,
sumantajana85@gmail.com; Fax: +91-33-2668-2916
17–19
In
b
Department of Chemistry, University of Calcutta, 92 APC Road, Kolkata-700009,
India
c
Department of Physics, Indian Institute of Engineering Science and Technology,
Botanic Garden, Howrah 711103, WB, India
d
Department of Chemistry, Panskura Banamali College, Vidyasagar University,
Purba Medinipur, 721152 WB, India
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4dt01658k
13096 | Dalton Trans., 2014, 43, 13096–13104
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thesized thin films, i.e. photocatalytic activity to decompose
toxic phenol at an ambient temperature. Photocatalysis is an
important technique for the treatment of pollutants and
removal of organic compounds, since it works at ambient
temperature and pressure. The photocatalytic activities of the
2
0,21
powder nanomaterials are common,
and there are very few
2
2
reports of thin films that can act as photocatalyst. Here, we
have used thin films directly to study the photocatalytic activity
of these materials to decompose phenol. This decomposition
of toxic substances by photocatalysis could be the basis of a
2
3,24
waste treatment application.
Experimental section
Chemicals and reagents
Fig. 1 Chronoamperometric (CA) deposition of NiS on ITO substrate at
Analytical grade nickel chloride (NiCl
acid (C
2
·6H
2
O) and D-tartaric −0.8 V, −0.9 V and −1.0 V in the presence of NiCl
H O ) were purchased from Merck (India). Thioaceta-
4 6 6
mide (TAA), hydrogen peroxide (H O ) and other reagents were
2 2
·6H O (50 ml 0.1 M),
D-tartaric acid (10 ml 0.2 M) and 25 ml of 0.1 M thioacetamide (TAA)
solution at pH 5.5.
2
2
purchased from Spectrochem (India), and they were used
without further purification. Phosphate buffer solutions −0.80 V is maximum, but the deposited material was not well-
0.1 M) of pH ranging from 2 to 12 were prepared by mixing adhered to the ITO substrate). The synthesized and well-
stock solutions of Na HPO –NaH PO . Deionized water was adhered black films were washed thoroughly with water and
(
2
4
2
4
used to prepare all the solutions and to rinse the electrodes.
methanol. Optical analysis and EDAX of as-deposited NiS have
been incorporated in the ESI.†
Deposition of NiS thin films
As-deposited NiS thin films were thermally oxidized at
Nickel sulfide (NiS) thin films were electrodeposited on ITO 300 °C, 400 °C and 450 °C for 20 minutes to generate oxide
−
2
coated glass substrate (resistance 10 ohm cm , surface area of films, and the black NiS was transferred to cloudy white NiO
2
2
× 1 cm ) at room temperature (25 °C) using a standard three- upon air oxidation.
electrode system (electrochemical analyzer CHI 620D). Initially,
Physical measurements
5
0
2
2 2
0 ml of 0.1 M NiCl ·6H O solution was mixed with 10 ml of
.1 M aqueous solution of D-tartaric acid and stirred for The structural properties of the thin films were studied by
0 minutes. Then, 25 ml of 0.1 M thioacetamide (TAA) solution X-ray diffraction (XRD) with a Seifert P3000 diffractometer
was added and stirred for an additional 10 minutes to make using Cu Kα (λ = 1.54 Å) radiation over an angle of 20°–80°.
the working solution. The final volume of the solution was The surface microstructure and morphology were analyzed
adjusted to 100 ml with deionized water. The pH of this with a Gemini Zeiss Supra 35VP (Carl Zeiss Microimaging
working solution was maintained at 5.5 by adding a diluted GmbH, Berlin, Germany) field-emission scanning electron
ammonia solution. A properly cleaned ITO glass substrate microscope (FESEM). The optical properties were recorded by
2
(
working area of 2 × 1 cm ), a Pt foil and a saturated Ag–AgCl UV-Vis (JASCO V-530) and FTIR (JASCO FTIR-460) spectropho-
electrode were considered as working, counter and reference tometers. X-ray photoelectron spectroscopy (XPS) measure-
electrodes respectively. Chronoamperometric (CA) analysis was ment was carried out on an ESCLAB KMII using Al as the
carried out to deposit NiS thin films. The CA analysis was exciting source and photoluminescence (PL) spectra were
carried out at three different potentials, namely, −0.80 V, recorded with Perkin-Elmer LS-55 Fluorimeter.
−
0.90 V and −1.00 V, respectively, for 300 s. The current-time
Electrocatalytic study
curves of NiS thin films in the working solution (as mentioned
above) at different potentials are displayed in Fig. 1. There is a The electrochemical oxidation and amperometric detection of
2
rapid current drop at the beginning, and then the current H O by NiO/ITO electrodes (with an active area of 2 × 1 cm )
2
2
density increases and becomes stationery after about 150 s. were monitored in a standard three-electrode system. In the
The rapid decay is due to double layer charging/discharging. electrochemical cell set up, NiO/ITO thin film was taken as the
Nevertheless, the current density for the thin films deposited working electrode, whereas a platinum wire and an Ag/AgCl
at −0.90 V is higher than at −1.0 V, which reveals better stabi- electrode were used as the auxiliary and reference electrodes,
lity of the films deposited at this potential (−0.90 V). The best respectively. Cyclic voltammograms (CVs) were recorded in a
stability of the material at −0.90 V was also confirmed from its cell containing 20 ml of 0.1 M phosphate buffer (pH 9.0,
physical appearance. Out of the three deposition potentials 50 °C) with a scan rate of 0.1 V s− . Same cell setup was used
studied, it was observed that uniform, stable and well-adhered at a constant potential 0.50 V (vs. Ag/AgCl) for amperometric
films were obtained only at −0.90 V (though current density at measurement.
1
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with JCPDS 04-0835 for cubic NiO. Here, the parent peaks of
NiS were not detected, which indicates a total conversion of
Results and discussion
Fig. 2(a) represents the X-ray diffraction pattern of electro- NiS to NiO at these temperatures. The observed d values along
deposited NiS thin film (deposited at −0.90 V) on ITO sub- with (h k l) indexed planes are in good agreement with stan-
strate. Comparing the observed diffraction pattern with dard d values. The peaks marked with ‘*’ in the XRD pattern
standard JCPDS, it was found that both the peak values (2θ) appears due to the In O present in the ITO substrate [JCPDS
2 3
and the intensity matched well with the JCPDS card no. ID 44-1087].
1
2-0041. The pattern shows three major diffractions from
Fig. 3(a) shows the FESEM image of as-deposited NiS.
(300), (021), and (131) planes, corresponding to a rhombo- Nearly spherical clusters were grown over the ITO substrate.
hedral NiS (a = 9.620 Å, c = 3.149 Å, Z = 9, C = 0.3273). Free Ni, Discrete surface coverage with randomly distributed spherical
NiO or other intermediate phases of NiS were not detected in nanoclusters is evident from the SEM image.
the XRD pattern.
Fig. 3(b) represents the SEM image of NiS thin film
Fig. 2(b) shows the XRD pattern of NiS film, annealed at annealed at 300 °C. An enormous morphological change is
3
00 °C, and a mixed phase of NiS–NiO was generated. The clearly visible in this SEM image. Clusters of NiS get fused and
observed and standard values along with (h k l) planes are in they form a flaky homogeneous morphology due to the air oxi-
good agreement with JCPDS # 04-0835. The pattern shows two dation. A good coverage of the ITO surface by the material is
major diffractions from (111) and (200) planes, corresponding also evident from the SEM image. Fig. 3(c) represents the SEM
to the cubic structure of NiO. Two additional diffraction peaks image of NiS thin film annealed at 400 °C. Here, the new gen-
with diminished intensity in the spectrum corresponding to erated morphology is very interesting. The entire ITO surface is
the planes (300) and (131) are due to the presence of parent fully covered with uniformly distributed NiO fibers. The mor-
NiS with the newly formed NiO. Hence, annealing at 300 °C phology of the deposited material is highly porous and com-
results in the incomplete conversion of NiS to NiO. It was con- posed of interconnected nanofibers. This uniform and highly
firmed that pure phase of NiO was detected at relatively higher ordered porous morphology is very important from the appli-
temperatures, e.g., 400 °C and 450 °C (Fig. 2(c) and (d)). Fig. 2c cation point of view. Fig. 3(d) shows the SEM image of a NiS
and 2d) represent the XRD patterns of NiS thin films annealed thin film annealed at 450 °C. A totally agglomerated cluster
at 400 °C and 450 °C, respectively. The observed patterns were type of morphology is evident from the SEM image. Hence,
compared with standard JCPDS data and found to match well from the SEM study it is clear that the annealing temperature
Fig. 2 XRD patterns of (a) as-deposited NiS, (b) NiS thin film annealed at 300 °C (horizontal planes (131), (300) are of NiS), (c) NiS thin film annealed
at 400 °C, (d) NiS thin film annealed at 450 °C.
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Fig. 3 FESEM images of (a) NiS thin film, (b) NiS thin film annealed at 300 °C, (c) NiS thin film annealed at 400 °C, (d) NiS thin film annealed
at 450 °C.
is the key factor for morphological changes, but higher temp- were unable to collect a minimum amount of powder material
erature does not necessarily ensure better morphology of the for BET and HRTEM analysis.
nanostructured films. From the morphological investigation it
The optical properties of the films were recorded using UV–
can be concluded that the material developed at 400 °C is Vis and FTIR spectrophotometry. As shown in Fig. 4(a), the
interesting and can be used in a potential application. There- absorption spectrum shows a sharp onset in absorbance at
fore, it was selected for the following characterizations and around 400 nm. The band gap energy was calculated using
1
/n
g
was used for the application purpose. We tried several times to Tauc’s relation: (αhν) = A(hν − E ), where hν is the incident
scrap off NiO powder from the ITO surface, but the syn- photon energy, ‘A’ is a constant and ‘n’ is the exponent, the
thesized material (NiO) was so strongly adhered to ITO that we value of which is determined by the type of electronic tran-
Fig. 4 (a) UV-Vis spectrum of NiO, inset is the Tauc plot. (b) FTIR spectrum of NiO thin film.
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Fig. 5 XPS spectra of NiO thin film.
sition causing the absorption. The exponent can take values of for NiO/ITO electrode were determined using the Michaelis–
2
7
1
/2 or 2 depending upon whether the transition is direct or Menten equation:
indirect, respectively. Since NiO is a direct band gap semicon-
app
2
I ¼ ðImax ꢀ ½SꢁÞ=ðKM þ ½SꢁÞ
ðiÞ
ductor, we can evaluate E from the plot of (αhν) vs. hν. The
g
2
inset of Fig. 4(a) shows the (αhν) vs. hν plot, corresponding to
where I is the steady-state current, Imax is the maximum
current measured under enzyme saturation and [S] is the con-
centration of substrate. A rearrangement of Michaelis–Menten
equation yields the electrochemical version of the Lineweaver–
Burk equation, which also enables the analysis of the enzyme
kinetics.
band gap 3.65 eV. This band energy was calculated considering
the thickness of NiO thin film to be 280 nm, which has been
confirmed from a surface Profilometer (Bruker Contour GT).
−
1
FTIR (400 to 3000 cm ) spectrum of NiO thin film
−1
(
Fig. 4(b)) shows only one sharp band at 553 cm . This band
represents the stretching of Ni–O, which is in agreement with
app
2
5
1
=I ¼ 1=Imax þ KM =ðImax ꢀ ½SꢁÞ
ðiiÞ
similar observations by Korosec et al. The absence of other
peaks in the spectrum clearly indicates the absence of water
molecules and/or hydroxide ions. Optical analysis and other
characterizations of NiS have been incorporated in the ESI.†
Performance of NiO thin film towards oxidation of H O
2
2
The XPS measurement reveals the chemical states of Fig. 6 represents the CV’s of NiO/ITO electrode in PBS buffer at
bonded atoms. Fig. 5(a) and 5(b) are the XPS spectra of de- pH 9.0 at a scan rate of 0.1 V s− . The first CV scan was taken
1
2
+
posited NiO for the Ni 2p and O 1s. XPS spectrum of Ni
2 2
without adding H O into the buffer solution and an oxidation
(
Fig. 5(a)) shows two peaks at binding energies 852.3 eV and peak was detected at 0.50 V. Then, H O was gradually (mM
2 2
8
72.01 eV corresponding to Ni 2p3/2 and Ni2p1/2 states. The range) added to this PBS buffer, and the oxidation peak
spectrum suggests only the presence of +2 state of Ni, whereas
the peak centered at 530.8 eV corresponds to the O 1s
2
−
(Fig. 5b), which indicates a normal state of O
in the
compound.
Electrocatalytic activity of NiO
The electrocatalytic activities of NiO/ITO thin films were
explored by a cyclic voltammetry (CV) study. Being a frequent
product of many enzymatic reactions catalyzed by a large
2 2
number of oxidases, H O was taken as a model molecule in
2
6
the field of biosensors. Cyclic voltammograms (CVs) were
recorded in a cell containing 20 ml of 0.1 M phosphate buffer
(
PBS) at pH 9.0 with gradual addition of H
cell setup was used at a constant applied potential of 0.50 V
vs. Ag/AgCl) for the chronoamperometric (CA) measurement.
The amperometric responses were recorded with successive
addition (µM range) into the PBS buffer. The apparent
2 2
O (mM). The same
(
2 2
H O
Fig. 6 CV’s of NiO/ITO electrode in phosphate buffer solution (PBS,
Michaelis–Menten constant, KM , and the maximum current pH 9) with different amounts of H addition.
app
2
O
2
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(at 0.50 V) increases with gradual addition of H
2
O
2
. This bration curve, the linear region was estimated and found to be
increase in current height (in anodic sweep) with gradual 10 µM–1000 µM. The calibration curve was also used to calcu-
addition of H indicates an obvious electrocatalytic oxi- late the sensitivity of the proposed sensor, which was found to
dation of H
around 0.50 V, compared to 0.60 V for CPE (carbon paste elec- tion limit was also estimated to be 1.28 mM (signal-to-noise
2 2
O
2 2
O
. The oxidation potential was found to be be ∼2.3 mA mM− (correlation coefficient 0.9318). The detec-
1
2
8
trode)-modified nickel oxide electrode.
In order to check the amperometric H
the current response with concentration of H O at working Fig. 8(b), the apparent Michaelis–Menten constant (KM ) was
ratio = 3).
2 2
O sensor activity,
Then, applying the Lineweaver–Burk model (eqn (ii)) on
app
2
2
potential i.e. 0.5 V was studied and is shown in Fig. 7. When calculated from the plot of 1/Icat vs. 1/S (Fig. 8(b)). The
app
M
app
M
an aliquot of H
2
O
2
(in the μM range) was added to the PBS
K
was found to be around 0.65 mM. This K
is smaller
buffer, the oxidation current rose sharply, and then reached a than that of some other electrodes like horseradish peroxidase
2
9
30
app
steady value within 10 s. The response time of the sensor was (HRP), Fe
0 s, and the attainment of steady state current was an suggests that the electrode has a higher affinity to oxidized
additional 4 s; however, for NiS/ITO electrode no catalytic H O . A comparative study of H O sensing with other reported
2
O
3
/GC and PB-Fe
2
O
3
/GC. The smaller K
M
value
1
2
2
2 2
3
5–45
response was observed.
sensors
reveals that our NiO/ITO electrode is quite
To obtain the calibration curve, the steady state current effective as a peroxide sensor (ESI, Table 1†).
values were plotted against the concentration of H O , as
2
2
shown in Fig. 8(a). The calibration curve shows that the pH and temperature (T) dependent stability and sensitivity
2 2
current increases linearly with addition of H O , and it reaches
a steady state after a certain period of time. From the cali-
The stability and the performances of the modified electrodes
were tested over a wide range of pH (2–11) and temperature
(
10–80 °C). It was determined that the maximum electrocataly-
tic decomposition of H O took place at pH 9 (Fig. 9(a)) and
2
2
the maximum catalytic activity (Fig. 9(b)) was detected at
0 °C.
The reproducibility and stability of this NiO/ITO-based new
2 2
sensor were also studied by adding a fixed amount of H O
5
(
(
1 mM) to the buffer solution. The relative standard deviation
RSD) of the sensor response was 4.7% for five successive
measurements using the same electrode. The NiO/ITO elec-
trode activity was restored up to 90% by storing the electrode
at 20 °C for 20 days, which suggests long-term stability of the
electrode.
Photodegradation of phenol
To demonstrate the potential applicability of the synthesized
nanoporous NiO thin films, we investigated its activity with
phenol degradation. Phenol is a major pollutant of surfaces
and groundwater and according to World Health Organization
(WHO)’s recommendations in 1994, the exposure limit of
Fig. 7 Amperometric responses of NiS/ITO and NiO/ITO electrodes
with successive addition of H
.50 V (vs. Ag/AgCl).
2 2
O to PBS at an applied potential of
0
Fig. 8 (a) Calibration curve (b) corresponding Lineweaver–Burk plot of NiO/ITO electrode.
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2 2
Fig. 9 Effect of (a) pH and (b) temperature (T) on the catalytic response of NiO/ITO electrode for H O sensing.
Fig. 10 (a) Photoluminescence spectra of residual phenol in presence of NiO thin films at an excitation wavelength at 280 nm. (b) Intensity of
residual phenol as a function of irradiation time.
phenol in inland water should not be higher than 0.02 mg catalytic reactivity in the decomposition of phenol. The essen-
−
1 31
L
.
To achieve the safe level within this range is really tial requirement for phenol decomposition is separation of
−
+
difficult due to its stability and solubility in water. In the electrons (e ) and holes (h ) by absorbing light. The photo-
present work, we have investigated the photocatalytic activity generated electrons and holes react with adsorbed surface sub-
of the synthesized materials (NiO), taking directly the thin stances like O2 and OH− and form reactive species like O2
films (as the scrapping off NiO powder material from ITO sub- and OH* (hydroxyl radicals). These are the major oxidative
strate is not possible due to the strong adherence of NiO to the
−
ITO substrate). Five thin films with an active surface area of
2
2
× 1 cm each were vertically placed into a 100 ml (100 ppm)
aqueous solution of phenol. At specific time intervals
15 minutes), an aliquot of phenol was withdrawn from the
(
reaction bath, and the changes in concentration were moni-
tored with PL spectroscopy at an excitation of 280 nm. It is
clear from Fig. 10(a) that the maximum emission occurs at
∼307 nm, which is the characteristic fluorescence emission of
phenol (λmax value of pure phenol was determined by UV-Vis
spectroscopy and was found to be 258 nm). It has been
observed that the intensity decreases gradually with increasing
exposure time. Fig. 10(b) represents the relative conc. vs. time,
and it shows that the emission peak intensity decreases up to
6
6% within 100 minutes. The decrease of the emission peak
intensity at 307 nm is attributed to the degradation of phenol.
Hence, our synthesized NiO thin films show effective photo- Fig. 11 Schematic representation of possible photodegradation path.
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species for the decomposition of organic pollutants. Degra-
dation of phenol corresponds to hydroxylation of the phenyl
9 J. S. E. M. Svensson and C. G. Granqvist, Sol. Energy Mater.,
1985, 12, 391–402.
•
32
ring as promoted by hydroxyl radicals ( OH), where excited 10 J. S. E. M. Svensson and C. G. Granqvist, Sol. Energy Mater.,
NiO nanoparticles get the necessary activation energy to react 1987, 16, 19–26.
with OH radicals and produce CO and H O. The common 11 A. E. Jiménez-González,
A. A. R. Gutiérrez, Surf. Eng., 2000, 16, 77–79.
quinone, and benzoquinone, are also expected to form during 12 W. Brückner, R. Kaltofen, J. Thomas, M. Hecker,
•
33
J.
G.
Cambray
and
2
2
intermediates, such as catechol, hydroxyhydroquinone, hydro-
3
4
the decomposition. A possible photodegradation mechanism
of phenol is illustrated in Fig. 11.
M. Uhlemann, S. Oswald, D. Elefant and C. M. Schneider,
J. Appl. Phys., 2003, 94, 4853–4858.
13 L. Berkat, L. Cattin, A. Reguig, M. Regragui and
J. C. Bernede, Mater. Chem. Phys., 2005, 89, 11–20.
Conclusion
14 Y. G. Wang and Y. Y. Xia, Electrochim. Acta., 2006, 51,
223–3227.
3
Nano-sized NiO thin films were successfully synthesized by the
oxidation of electrodeposited NiS thin films at 400 °C. Electro-
deposition of nickel sulphide and their conversion to nickel
oxide thin films by air annealing was found to be a convenient
and cost-effective method. The synthesized NiO thin films
1
5 G. Malandrino, L. M. S. Perdicaro, I. L. Fragal, R. L. Nigro,
M. Losurdo and G. Bruno, J. Phys. Chem. C, 2007, 111,
3211–3215.
16 S. A. G. Evans, J. M. Elliott, L. M. Andrews, P. N. Bartlett,
P. J. Doyle and G. Denuault, Anal. Chem., 2002, 74,
were found to be effective towards H O2 oxidation. Its high
2
1322–1326.
sensitivity and wide linear range features make it an effective
sensor. The pH and temperature dependency study suggests
that the catalytic activity is strongly dependent on these para-
meters. The reproducibility and stability study also reveals long-
term stability of the sensor. The synthesized NiO thin films
show high photocatalytic activity towards decomposition of
phenol. The result indicates a great potential for the application
of NiO as a pollutant cleanup for environmental interest.
1
1
7 A. Kicela and S. Daniele, Talanta, 2006, 68, 1632–1639.
8 S. Majdi, A. Jabbari and H. Heli, J. Solid State Electrochem.,
2007, 11, 601–607.
1
2
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