ISSN: 1847-9286
Open Access Journal
www.jese-online.org
Journal of
Electrochemical
Science and
Engineering
J. Electrochem. Sci. Eng. 3(4) 2013, 137-184
Volume 3 (2013)
No.
04
pp.
137-184
IAPC
J. Electrochem. Sci. Eng. 3(4) (2013) 137-184
Published: November 9, 2013
Open Access : : ISSN 1847-9286
www.jESE-online.org
Contents
VAISHAKA R. RAO, A. CHITHARANJAN HEGDE and K. UDAYA BHAT
Effect of heat treatment on structure and properties of multilayer Zn-Ni alloy coatings ........................ 137
JELENA GULICOVSKI, JELENA BAJAT, VESNA MIŠKOVIĆ-STANKOVIĆ, BOJAN JOKIĆ, VLADIMIR PANIĆ
and SLOBODAN MILONJIĆ
Cerium oxide as conversion coating for the corrosion protection of aluminum ...................................... 151
DEVESH KUMAR MAHLA, SUBHENDU BHANDARI, MOSTAFIZUR RAHAMAN and DIPAK KHASTGIR
Morphology and cyclic voltammetry analysis of in situ polymerized polyaniline/graphene
composites............................................................................................................................................ 157
ANANTHA N. SUBBA RAO and VENKATESHA T. VENKATARANGAIAH
Electrochemical treatment of trypan blue synthetic wastewater and its degradation pathway ............. 167
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149; doi: 10.5599/jese.2013.0036
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Effect of heat treatment on structure and properties of
multilayer Zn-Ni alloy coatings
VAISHAKA R. RAO, A. CHITHARANJAN HEGDE and K. UDAYA BHAT*
Electrochemistry Research Laboratory, Department of Chemistry, National Institute of Technology
Karnataka, Surathkal, Srinivasnagar-575025, India
*Department of Metallurgy and Materials Engineering, National Institute of Technology
Karnataka, Surathkal, Srinivasnagar-575025, India

Corresponding Author: E-mail: hegdeac@rediffmail.com, Tel.: +91-9980360242
Received: December 25, 2012; Revised: April 12, 2013; Published: Novembar 09, 2013
Abstract
Composition modulated multilayer alloy (CMMA) coatings of Zn-Ni were electrodeposited
galvanostatically on mild steel (MS) for enhanced corrosion protection using single bath
technique. Successive layers of Zn-Ni alloys, having alternately different composition were
obtained in nanometer scale by making the cathode current to cycle between two values,
called cyclic cathode current densities (CCCD’s). The coatings configuration, in terms of
compositions and thicknesses were optimized, and their corrosion performances were
evaluated in 5 % NaCl by electrochemical methods. The corrosion rates (CR)’s of multilayer
alloy coatings were found to decrease drastically (35 times) with increase in number of
layers (only up to 300 layers), compared to monolayer alloy deposited from the same bath.
Surface study was carried with SEM, while XRD was used to determine metal lattice
parameters, texture and phase composition of the coatings. The effect of heat treatment
on surface morphology, thickness, hardness and corrosion behaviour of multilayer Zn-Ni
alloy coatings were studied. The significant structural modification due to heat treatment
is not accompanied by any decrease in corrosion rate. This effect is related to the
formation of a less disordered lattice for multilayer Zn-Ni alloy coatings.
Keywords
Multilayer Zn-Ni alloy; Corrosion study; Heat treatment; SEM; XRD.
Introduction
An advanced coating technique, called composition modulated multilayer alloy (CMMA) coating is
gaining interest due to their improved properties, such as mechanical strength/hardness, enhanced
diffusivity, improved ductility/toughness, reduced density, reduced elastic modulus, increased
specific heat, higher thermal expansion coefficient, lower thermal conductivity, enhanced corrosion
doi: 10.5599/jese.2013.0036
137
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
and wear resistance, superior reflectance, soft magnetic properties, giant magnetoresistence and
corrosion resistance not attainable in any of the metallurgical alloys [1]. The CMMA materials
basically consists of alternating layers of metals/alloys on micro/nanometer scale, deposited electrolytically by making the cathode to cycle between two current densities at definite time intervals. The
coating with improved resistance to highly aggressive environmental condition is demanded for the
extended safe service life of industrial objects. Hence CMMA coating is well studied while finding its
wide spread industrial applications [2-4].
Blum first introduced the electrodeposition of multilayered alloy on Cu-Ni, demonstrating the
deposition of alternate Cu and Ni layers, tens of microns thick, from two different electrolytes [5].
The deposition using Single Bath Technique (SBT) for the fabrication of modulated alloys was
recorded by Brenner [6]. Tench and White proposed that the presence of Ni in the deposit was
responsible for improved corrosion resistance of fabricated Cu/Ni metal multilayers and also their
mechanical properties [7]. The Zn-Ni alloy electrodeposition has attracted interest of scientific
community because these alloys were found to be more corrosion resistant and thermally stable
than pure zinc [8]. Many authors have attempted to understand the characteristics of this
deposition process [9-12]. The abrupt change in the composition of the alloys and in the current
efficiency is observed during this complex codeposition at a given value of deposition potential/current density. Multilayer coating by electrolytic method is the most promising approach for
improving the corrosion resistance of Zn-Ni alloys, and is of distinct commercial interest [13-16].
The CMMA coating with Zn-Fe alloy as alternate layers was tested to exhibit better corrosion
protection than individual metals. The presence of high content of Fe in Zn-Fe alloy was reasoned
to be responsible for enhanced corrosion protection [17].
The thermal stability of the Zn-Ni alloy coatings is important for their general applications,
especially where they are expected to perform at elevated temperature conditions, such as in some
automotive applications. However, the conventional methods usually modify the physical properties
of the metal being protected with the limitations, such as susceptibility to damage by heat, cost, and
formation of oxide products. The real challenge to overcome these problem would be to develop a
novel protection coating with an exceptional thermal stability with minimum changes to the physical
properties of the protected metal. Though there are many reports with regard to the development
of CMMA Zn-Ni coatings using different baths and additives, no work has been reported with regard
to examine the thermal stability of those coatings [18-21]. Hence the present paper reports the
development of CMMA Zn-Ni alloy coatings on mild steel (MS) from acid chloride bath using gelatin
and glycerol as additives. The corrosion stability of CMMA Zn-Ni coatings on heat treatment have
been tested by subjecting the coated specimens to different temperatures. The CMMA Zn-Ni
coatings have been tested for their thickness, hardness, composition, surface morphology and
corrosion stability before and after heat treatment, and results are discussed.
Experimental
All electrodeposition were carried out from the same electrolytic bath prepared using analytical
grade reagents and double distilled water. Conventional Hull cell method was used to examine the
effect of current density (c.d.) and bath constituents [22]. The Zn-Ni alloy bath was prepared by
adding known amount of gelatin in hot distilled water (insoluble in cold water) and glycerol as
additives, to impart brightness to the coating. Electroplating process was carried out in a stirred
solution on a pre-cleaned MS panels, having 7.5 cm2 active surface area, at 30 °C and pH 4.0. The
Zn anode was used with the same exposed area. The electroplating of both monolayer (mono138
V. R. Rao et al.
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
lithic) and CMMA Zn-Ni coating was carried out using computer controlled DC power source,
having output speeds of up to 160 microseconds per step voltage/current change (N6705A,
Agilent Technologies) for 10 min (∼15 μm thickness), for comparison purpose. The coating thickness were determined by Faraday’s law and verified by measuring in Digital Thickness Meter
(Coatmeasure - M&C, AA Industries/Yuyutsu Instruments). The hardness of coatings was measured
using Digital Micro Hardness Tester (CLEMEX, Model: MMT-X7). The electrodeposited MS plates
were subjected to heat treatment by keeping in temperature controlled oven (Technico Ind. Ltd.,
3144) at temperature 100, 200, 300 and 400 °C for constant time duration of 60 minutes. The
modulation in the composition of alternate layer was affected by pulsing the current periodically.
The power pattern used for deposition of monolayer (direct Current) and multilayer (pulsed
current) coatings is shown in Figure 1. The optimal composition and operating parameters of the
bath is given in Table 1.
The corrosion behavior of the coatings were evaluated in 5 % NaCl solution at pH 4.0 using
Potentiostat/Galvanostat (ACM Instruments, Gill AC Series No-1480) at temperature 25 °C, using
saturated calomel electrode (SCE) as reference, and platinum as counter electrodes, respectively.
The corrosion rates (CR) were measured by Tafel extrapolation method at scan rate of 1 mV s-1 with
start potential +250 mV to reverse potential -500 mV. The electrochemical impedance spectroscopy
(EIS) measurements were made in frequency range of 100 kHz to 0.01 Hz at ±10 mV perturbing
voltage, to evaluate the barrier property of the coatings. The surface morphology and cross sectional
view of the CMMA coating were examined under Scanning Electron Microscopy (SEM, Model JSM6380 LA from JEOL, Japan). The variation in the phase structure of alloys in different layers were
confirmed by X-ray diffraction (XRD) study, using Cu Kα (λ = 0.15405 nm) radiation, in continuous
scan mode with a scan rate of 2°min-1 (XRD, JEOL JDX-8P). Conveniently, Zn-Ni CMMA coatings are
represented as: (Zn-Ni)1/2/n (where 1 and 2 indicate the first and second cathode current density
(CCCD’s) and ‘n’ represent the number of layers formed during total plating time. i.e. 10 min.
Direct current
Monolayer growth
Square current pulse
Multilayer growth
Figure 1. Power pattern used for deposition of monolayer (direct current) and multilayer
(square current pulse) coatings.
Results and Discussion
Monolayer Zn-Ni alloy coatings
The Hull cell study confirmed that 3.0 A dm-2 is the optimal c.d. for deposition of monolayer
Zn-Ni alloy from the bath (optimized) given in Table 1. The Zn-Ni alloy coating developed at
doi: 10.5599/jese.2013.0036
139
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
3.0 A dm-2 with ~8.0 wt.% Ni exhibited the least CR (14.46×10-2 mm y-1) compared to other
coatings at other c.d.’s as reported in Table 2.
Table 1. Bath composition and operating parameters of the optimized bath.
Bath ingredients
Concentration, g L-1
ZnCl2
27.2
NiCl2 x 6H2O
94.9
Boric acid
27.7
NH4Cl
100
Gelatin
5.0
Glycerol
2.5
Operating parameters
Anode: Pure Zinc
Cathode: Mild Steel
pH 4.0
Temperature: 30 °C
From the experimental data given in Table 2, it may be noted that the wt.% Ni in the
electrodeposited Zn-Ni alloy at all c.d. are less than that in the bath (64.5 % Ni). Hence it may be
inferred that the proposed bath follow anomalous type of codeposition, characteristic of all Zn-Fe
group metal alloys, explained by Brenner [6]. Hence, Zn-Ni alloy coating at 3.0 A dm-2, represented
as (Zn-Ni)3.0/mono has been taken as the optimal coating configuration for monolayer deposition
from the proposed bath.
Table 2. Corrosion data for monolayer Zn-Ni alloy coatings developed at different c.d.’s.
-E0
V vs. SCE
icorr
µA cm-2
CR × 10-2
mm y-1
1.0
Content of Ni
Wt. %
2.62
1.019
17.62
23.42
2.0
4.05
1.086
13.87
18.44
3.0
7.95
1.105
10.88
14.46
4.0
8.07
1.162
12.53
16.66
j
-2
A dm
Optimization of cyclic cathode current densities (CCCD’s) and number of layers in CMMA coatings
In the present work improving the corrosion resistance of monolayer Zn-Ni alloy by multilayer
technique is guided by the following principles [23-25]:
I. Periodic change in current density (c.d.) allows the growth of coatings having periodic change
in its chemical composition.
II. The corrosion resistance property of multilayer coatings or any functional property in general
reaches its maximum value when thickness of the individual layers reaches optimal nanoscale.
The amplitude of compositional modulation diminishes rapidly when layer thicknesses below
certain limit (about 50 nm).
Nanoscale multilayer coatings with alternate layers of alloys of different composition generally
show unique properties than bulk materials when each individual layer thickness is below ~100
nm. Different layered combinations offer unique mechanical, optical, magnetic and electronic
properties including improved good corrosion resistance. In all these cases, the properties of the
multilayer coatings depend on two factors, namely the composition and thickness of the individual
layers [26-28]. Hence by proper setting up of composition (by selection of cyclic current density,
CCCD’s) and thickness (by fixing the time for each layer deposition) of the individual layer it is
140
V. R. Rao et al.
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
possible to optimize the coating configuration [29,30]. Hence multilayer coatings have been
accomplished under different combination of CCCD’s and individual layer thickness. The
experimental procedure for optimization of coating configuration is explained below.
Multilayer coatings having 10 layers (arbitrarily chosen) have been developed at different
CCCD’s, namely at 1.0/3.0 and 2.0/4.0 A dm-2, using same binary alloy bath. The coatings at
different sets of CCCD’s were developed in order to try different possible modulations in
composition of individual layers, and their corrosion behaviours were studied, and corrosion data
are reported in Table 3.
Table 3. Corrosion rates of CMMA Zn-Ni coatings having 10 layers at different CCCD’s
in comparison with (Zn-Ni)3.0/mono developed from same bath.
CCCD’s
A dm-2
-E0
V vs. SCE
icorr.
µA cm-2
CR × 10-2
mm y-1
(Zn-Ni)1.0/3.0/10
1.085
8.416
11.18
(Zn-Ni)2.0/4.0/10
1.108
6.606
8.78
(Zn-Ni)3.0/mono
1.105
10.88
14.46
It may be noted that both (Zn-Ni)1.0/3.0/10 and (Zn-Ni)2.0/4.0/10 coatings exhibited less CR
compared to (Zn-Ni)3.0/mono coating. Hence, by choosing the above CCCD’s, multilayer coatings with
higher degree of layering, i.e. with 30, 60, 120, 300 and 600 layers have been developed by proper
setting up of the power source. It may be noted the CR’s decreased drastically with an increase in
number of layers in both sets of CCCD’s. It further indicates that improved corrosion property is
not the unique property of the layer composition; instead, the combined effect of composition
modulation and thickness of individual layers, or the number of layers. It should be noted that CR
decreased only up to 300 layers and then started increasing, i.e. 600 layers as shown in Table 4.
Table 4. Effect of layering on corrosion behavior of CMMA (Zn-Ni)1.0/3.0 and (Zn-Ni)2.0/4.0 coating
in comparison with monolayer (Zn-Ni)3.0/mono deposited from same bath at 303K
Coating
configuration
Number of
layers
Average thickness of
each layer, nm
E0
V vs. SCE
icorr
µA cm-2
CR × 10-2
mm y-1
10
30
60
120
300
600
10
30
60
120
300
600
1500
750
250
125
50
25
1500
750
250
125
50
25
1.085
1.037
1.056
1.067
1.041
1.050
1.108
1.085
1.050
1.007
1.135
1.036
8.416
7.125
4.531
2.357
1.319
3.577
6.606
4.989
2.125
1.056
0.31
1.975
11.18
9.47
6.02
3.13
1.75
4.75
8.78
6.63
2.82
1.40
0.41
2.61
Monolayer
15000
1.128
10.78
14.33
(Zn-Ni)1.0/3.0
(Zn-Ni)2.0/4.0
(Zn-Ni)3.0/mono
Further, though decrease of CR was found in both sets of CCCD’s, the CR corresponding to
(Zn-Ni)2.0/4.0 at 300 layers is the least, it has been taken as the optimal configuration for peak
doi: 10.5599/jese.2013.0036
141
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
performance against corrosion, and is represented as (Zn-Ni)2.0/4.0/300. The CR found to increase at
higher degree of layering, i.e. at 600 layers is due to shorter relaxation time for redistribution of
metal ions at the diffusion layer, during plating. It should be noted that under optimal condition,
the total thickness of CMMA (Zn-Ni)2/4/300 coating was found to be ~15 µm, calculated from
thickness Tester (Coatmeasure Model M&C), verified by Faraday law. Then from the total
thickness and number of layers allowed to form (300), it is predicted that the average thickness of
each layer is 50 nm.
Thermal stability of the monolayer and multilayer coatings
Thickness and Hardness of the coatings
The thickness and hardness of coatings were found to be decreased on heat treatment in both
(Zn-Ni)3.0/mono and (Zn-Ni)2.0/4.0/300 coatings. In the case of (Zn-Ni)2.0/4.0/300 coatings the decrease may
be attributed to the structural changes, evidenced by XRD study. The decrease is more
pronounced in case of monolayer when compared to the multilayer Zn-Ni alloy coatings. The
thickness of the coatings is directly related to the high tensile residual internal stresses, which
result from the presence of Ni in the alloy [31]. The drop in the coating thickness with the
temperature may be attributed to the iron enrichment caused by the formation of intermetallic
Zn/Fe compounds due to the inter-diffusion at the coating/substrate interface. It was predicted
that the iron enrichment in the interfacial region pushes nickel toward the surface [32]. The
decrease of thickness and hardness with increase in temperature observed in case of (ZnNi)2.0/4.0/300 is shown, in comparison with that of (Zn-Ni)3.0/mono coating in Table 5.
Table 5. Effect of temperature on thickness, hardness and corrosion behavior of CMMA
(Zn-Ni)2.0/4.0/300 coatings, in comparison with monolayer (Zn-Ni)3.0/mono deposited from same bath.
CCCD’s
A dm-2
(Zn-Ni)2.0/4.0/300
(Zn-Ni)3.0/mono
Treated temperature, °C
Thickness,
µm
Vicker hardness,
V100
-Ecorr
V vs. SCE
icorr
µA cm-2
CR×10-2
mm y-1
30
18.9
212
1.003
0.31
0.41
100
16.7
189
1.022
2.14
2.84
200
14.3
183
1.024
2.18
2.89
300
9.1
154
0.995
3.73
4.95
400
5.4
139
0.865
4.52
6.00
30
17.8
202
1.128
10.78
14.33
200
9.3
145
1.053
21.68
28.82
400
4.8
119
1.070
26.53
35.27
Further, in the case of monolayer Zn-Ni coating the decrease of hardness may be attributed to
the fact that the dislocation sources are active under the stress field (applied in the form of
heat) [33]. The decrease in the residual stress is also reasoned to be responsible for decrease in
hardness of the alloy coating with thermal treatment [34]. The CMMA coatings provide stress free
environment, because the attractive forces tend to bridge the gap between successive layers. However, with heat treatment the interaction with the substrate increased, and hence stress developed.
Corrosion study
Cyclic polarization study
The corrosion resistance exhibited by Zn-Ni coatings (both monolayer and multilayer) can be
better understood by Tafel polarization method as shown in Figure 2a, and corresponding
142
V. R. Rao et al.
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
corrosion parameters are reported in Table 5. Cyclic polarization study over a potential range
of -1.25V to -0.5V was studied and is shown in Figure 2b. The anodic current was made to move
from negative to positive, and then reversed. Cyclic polarization curves shows that there is no
much significance of the corrosion product formation with regard to the corrosion protection of
the alloy. The corrosion current value was found to be always higher than that of forward
scanning, indicating the dissolution of oxide film had occurred in the forward scanning and selfrepairing occurred during the process of backward scanning. CMMA Zn-Ni coating with optimal
configuration, (Zn-Ni)2.0/4.0/300 showing the least CR was opted for examining the thermal stability
of the coatings. The CR of the Zn-Ni CMMA coating in 5% NaCl solution, before and after heat
treatment of 100 °C represented as (Zn-Ni)2.0/4.0/300 and (Zn-Ni)2.0/4.0/300/100 °C), was found to be,
respectively about 35 times and 5 times, respectively, more corrosion resistive than conventional
(Zn-Ni)3.0/mono alloy coating as shown in Figure 2b.
a
b
Figure 2. Polarization behavior of CMMA (Zn-Ni)2.0/4.0/300 coatings:
a) after treatment at different temperature b), Cyclic polarization behavior of (Zn-Ni)3.0/mono,
CMMA (Zn-Ni)2.0/4.0/300 and CMMA (Zn-Ni)2.0/4.0/300/100°C.
Thus the corrosion resistance of multilayered Zn-Ni alloy coating has also decreased with heat
treatment. However, the decrease in CR’s were more significant in the case of multilayer Zn-Ni
alloy coating compared to monolayer coating after heat treatment. It is due to the fact that the
electroplated samples attained intrinsically different surfaces in terms of their electrochemical
properties. However, increase in the CR’s is not in proportion of the structural changes observed,
as will be discussed with XRD analysis.
Electrochemical impedance spectroscopy study
The electrode process involved in double layer capacitance and corrosion behaviors can be
better understood by electrochemical impedance spectroscopy (EIS) method. The small amplitude
signals from the test specimen are considered in EIS method. The Nyquist plot is the type of the
plot in which the data is plotted as imaginary impedance, Zimg vs. real impedance Zreal with the
provision to distinguish the contribution of polarization resistance (Rp) verses solution resistance
(Rs) [35]. EIS signals of Zn-Ni monolayer coating (at optimal c.d, i.e. 3.0 A dm-2) compared with the
(Zn-Ni)2.0/4.0/300 coating before and after heat treatment (at different temperatures) is shown on
doi: 10.5599/jese.2013.0036
143
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
Figure 3. Progressive decrease of polarization resistance of CMMA coatings with annealing
temperature supports the reduced corrosion resistance, may be due to diffusion of layers.
However, corrosion rate of monolayer coatings are more than multilayer coatings under all degree
of layering.
Figure 3. Electrochemical impedance response (Real vs. Imaginary reactance values) displayed
by CMMA (Zn-Ni)2.0/4.0/300 after heat treatment at 4 different set temperatures.
It may be noted that all the coatings exhibits one capacitive loop. However, at low frequency
limit the capacitive behaviour of the double layer tends to exhibit the inductive character,
indicated by decrease of both Zreal and Zimg. The gradual decrease in the diameter of semicircle
indicates that the polarization resistance, RP decreases with increase in temperature as shown in
Figure 3. The (Zn-Ni)2.0/4.0/300 coating showed maximum impedance, due to accumulation of
corrosion products at the electrode surface acting as barrier. The negative value of imaginary
impedance, Zimg at lower frequencies observed in coatings treated for higher temperatures are
attributed to the inductance behaviour caused by the change in corrosion potential at the
interface [36,37]. However, the radii of both capacitive loop and inductive character decreased
progressively with raise in temperature.
Surface morphology
Figure 4 displays the SEM image for surface morphology of (Zn-Ni)2.0/4.0/300 alloy coatings after
heat treatment at different temperatures. It may be noted that the surface non-homogeneity
increased with an increase of treatment temperature. However, Zn-Ni alloy coatings are found to
adhere onto the substrate as fine particles with compact arrangement. The increased
compactness with the heat treatment was also predicted to be main reason for good appearance
and high hardness [38].
The cross sectional view of CMMA (Zn-Ni)2.0/4.0/10 coating before and after heat treatment
(100 °C) is shown in Figure 5. It may be noted that distinctly visible alloy layers (Figure 5a) become
144
V. R. Rao et al.
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
fused (Figure 5b) due to diffusion of layers upon heat treatment. Thus thermal treatment of
electrodeposited multilayer Zn-Ni alloy coatings leads to both structural and behavioral changes.
(a)
(b)
(c)
(d)
Figure 4. SEM images of CMMA (Zn-Ni)2.0/4.0/300 coatings after treatment at different
temperatures: (a) 100°C (b) 200°C (c) 300°C and (d) 400°C.
Figure 5. SEM images across the cross section of CMMA (Zn-Ni)2.0/4.0/10 coatings before heat
treatment (a), and after heat treatment at 200°C (b).
XRD study
The XRD patterns of (Zn-Ni)3.0/mono and (Zn-Ni)2.0/4.0/300 alloy coating after heat treatment,
deposited from same bath is given in Figure 6 and 7 respectively. Variation in the surface
morphology of the monolayer coatings after heat treatment is supported by the variation in XRD
doi: 10.5599/jese.2013.0036
145
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
peaks. It has been reported that the phases obtained by the Zn-Ni coatings up to 13 % nickel do
not correspond to that reported on the thermodynamic phase diagram [39]. It may be noted that
the reflection corresponding to Zn(101), γ-phase (Ni5Zn21), Zn(103) phases and Ni3Zn22(335) as well
was observed in monolayer coating deposited at optimal c.d. i.e., 3.0 A dm-2. However, upon heat
treatment there was hardly any difference in the phases observed in the ((Zn-Ni)3.0/mono alloy
coatings before and after heat treatment up to 200 °C. However, at temperatures higher than
200 °C additional phases were observed corresponding to the intermetallic Zn/Fe compound
(Figure 6). The formation of this phase occurs due to inter diffusion in the interface region
between the Zn-Ni alloy and the steel substrate. ZnO phase formation at temperatures higher than
200 °C was attributed to the metal contact with the ambient oxygen. The X-ray diffraction line
broadening at temperatures higher than 200 °C may be related to the increase in the corrosion
current value, which is reported to be caused by the lattice strains [40].
Figure 6. XRD patterns of the (Zn-Ni)3.0/mono coatings after heat treatment at different
temperatures (200°C and 400°C) deposited from the same bath.
The reflection corresponding to Zn(101), γ-phase (Ni5Zn21) and Ni3Zn22(510) was highly
suppressed in the case of (Zn-Ni)2.0/4.0/300 coating on heat treatment at 4 different set temperatures. However at temperatures higher than 300 °C, the coating has shown weak signal
corresponding to Zn(100), Zn(102) and γ Zn-Ni phases, although Zn(103) phase completely
disappeared. The least CR exhibited by (Zn-Ni)2.0/4.0/300/100 was attributed to the ratio of the phase
structure corresponding to Zn(103) and weak signals corresponding to γ-phase of Zn (411, 330),
Zn(101) and Zn3Ni22(006) phase. The comparison between the XRD signals of the Zn-Ni monolayer
and CMMA coating on post-heat treatment reveals the fact that the exhibition of lesser CR of the
Zn-Ni CMMA coating upon heat treatment to that of the Zn-Ni monolayer coating deposited at
optimal c.d. i.e., 3.0 A dm-2, was attributed to the diffusion of the layered structure and formation
of different phase structure ratio as shown on Figure 6 and Figure 7.
146
V. R. Rao et al.
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
Figure 7. XRD patterns of the CMMA (Zn-Ni)2.0/4.0/300 coatings after heat treatment at
different temperature (100°C, 200°C, 300°C and 400°C), deposited from the same bath.
Conclusions
Based on the experimental investigation on development and characterization of CMMA Zn-Ni
alloy coatings on mild steel following observations were made as conclusions:
1. The coating configuration in terms CCCD’s and number of layers have been optimized for
deposition of the most corrosion resistant coatings from acid chloride bath using glycerol
and gelatin as additives.
2. The decrease in thickness and hardness of both monolayer and multilayer coatings due to
heat treatment were due to the active dislocation sources and decrease in the residual
stress.
3. Progressive decrease of polarization resistance of CMMA coatings with annealing
temperature supports the reduced corrosion resistance, may be due to diffusion of layers.
However, corrosion rate of monolayer coatings are more than multilayer coatings under all
degree of layering.
4. The corrosion resistance of multilayer coatings increased only up to certain number of
layers and then decreased due to interlayer diffusion.
5. Thermal treatment of electrodeposited (both monolayer and multilayer) Zn-Ni alloy
coatings led to significant structural change of the alloy, supported by SEM and XRD study.
6. A small increase of corrosion rates of Zn-Ni alloy due to annealing is related to the
formation of a more ordered lattice of the alloy.
7. However, the increase of corrosion rates, due to annealing is not in proportion of the
structural changes of the alloy occurred.
8. The corrosion resistance of both multilayered and monolayer coatings decreases with heat
treatment. However, it is more pronounced in case of monolayer coatings. It is due to the
fact that the electroplated samples attained intrinsically different interfacial structures.
doi: 10.5599/jese.2013.0036
147
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
HEAT TREATMENT OF MULTILAYER Zn-Ni ALLOY COATINGS
9. The structural changes due to heat treatment of monolayer Zn-Ni alloy coatings continue to
exist even in multilayer coatings. Further, the structural changes in alloy composition (both
monolayer and multilayer) are found to be a function of annealing temperatures.
Acknowledgement: Mr. Vaishaka R.Rao acknowledges National Institute of Technology Karnataka
(NITK), Surathkal for financial support in the form of Institute Fellowship.
References
[1] G. Injeti, B. Leo, Adv. Mater. 9 (2008) 1–11.
[2] P. Ganesan, S. P. Kumaraguru, B. N. Popov, Surf. Coat. Technol. 20 (2007) 7896– 7904.
[3] V. Thangaraj, N. Eliaz, A. C. Hegde, J. Appl. Electrochem. 39 (2009) 339–345.
[4] S. Yogesha, A. C. Hegde, J. Mater. Process. Technol. 211 (2011) 1409-1415.
[5] W. Blum, Trans. Am. Electrochem Soc. 40 (1921) 307-320.
[6] A. Brenner, Electrodeposition of Alloy, Academic Press., New York, p. 194.
[7] D. Tench, J. White, Tensile, J. Electrochem Soc. 138 (1991) 3757-58.
[8] Zhongda Wu, L. Fedrizzi, P.L. Bonora, Surf. Coat. Technol. 85 (1996) 170-174.
[9] R. Ramanauskas, I. Muleshkova, L. Maldonado, P. Dobrovolskis, Corros. Sci. 40 (1998) 401410.
[10] M. Gavrila, J.P. Millet, H. Mazille, D. Marchandise, J.M. Cuntz, Surf. Coat. Technol. 123
(2000) 164–172.
[11] J.B. Bajat, Z. Kacarevic-Popovic, V.B. Miskovic-Stankovic, M.D. Maksimovic, Prog. Org. Coat.
39 (2000) 127–135.
[12] R. Fratesi, G. Roventi, Surf. Coat. Technol. 82 (1996) 158-164.
[13] Jing-yin Fei, G.D. Wilcox, Surf. Coat. Technol. 200 (2006) 3533 – 3539.
[14] M. Rahsepar, M.E. Bahrololoom, Corros. Sci. 51 (2009) 2537–2543.
[15] K. Venkatakrishna, A. C. Hegde, J. Appl. Electrochem. 40 (2010) 2051–2059.
[16] A. Maciej, G. Nawrat, W. Simka, J. Piotrowski, Mater. Chem. Phys. 132 (2012) 1095–1102.
[17] Y. Liao, D.R. Gabe, G.D. Wilcox, Plat. Surf. Finish. 85 (1998) 88-91.
[18] J.-L. Chen, J.-H. Liu, S.-M. Li, M. Yu, Mater. Corros. 63 (2012) 607-613.
[19] S. Yogesha, R.S. Bhat, K. Venkatakrishna, G. P. Pavithra, Y. Ullal, A.C. Hegde, Synth. React.
Inorg. Met.-Org. Chem. 41 (2011) 65-71.
[20] R.S. Bhat, K.R. Udupa, A.C. Hegde, Trans. Inst. Met. Finish. 89 (2011) 268-274.
[21] V. Thangaraj, K. Ravishankar, A.C. Hegde, Chin. J. Chem. 26 (2008) 2285-2291.
[22] R. S. Bhat, K. U. Bhat, A. C. Hegde, Prot. Met. Phys. Chem. Surf. 47 (2011) 645-653.
[23] F. Jing-yin, L. Guo-zheng, X. Wen-li, W. Wei-kang, J. Iron. Steel Res. Int. 13 (2006) p. 61-67.
[24] R.S. Bhat, A.C. Hegde, Surf. Eng. Appl. Electrochem. 47 (2011) 112-119.
[25] B.N. Popova, S. Kumaragurua, P. Ganesana, J. Electrochem Soc. 1 (2006) 87-96.
[26] K.K. Chattopadhyay, A.N. Banerjee, Introduction to Nanoscience and Technology,
Connaught Circus, New Delhi, India, 2009, p. 155.
[27] V.K. Varadan, A.S. Pillai, D. Mukherji, M. Dwivedi, L. Chen, Nanoscience and Nanotechnology in Engineering, World Scientific Publishing Co. Pvt. Ltd. Singapore, 2010, p. 170.
[28] D.R. Baer, P.E. Burrows, A.A. El-Azab, Prog. Org. Coat. 47 (2003) 342-356.
[29] K. Venkatakrishna, A. C. Hegde, Mater. Manuf. Processes. 26 (2011) 29–36.
[30] S. Yogesha, K. Venkatakrishna, A. C. Hegde, Anti-Corros. Methods Mater. 58 (2011) 84-89.
[31] H.J.C. Voorwald, I.M. Miguel, M.P. Peres, M.O.H. Cioffi, J. Mater. Eng. Perform. 14 (2005),
249-257.
[32] J. Kondratiuk, P. Kuhn, E. Labrenz, C. Bischoff, Surf. Coat. Technol. 205 (2011) 4141-4153.
[33] L. P. Bicelli, B. Bozzini, C. Mele, L. D'Urzo, Int. J. Electrochem. Sci. 3 (2008) 356 – 408.
[34] B.K. Prasad, Mater. Sci. Eng. A277 (2000) 95-101.
148
V. R. Rao et al.
[35]
[36]
[37]
[38]
[39]
[40]
J. Electrochem. Sci. Eng. 3(4) (2013) 137-149
V. M. Huang, Shao-Ling Wu, M. E. Orazem, N. Pebere, B. Tribollet, V. Vivier, Electrochim.
Acta. 56 (2011) 8048-8057.
U.C. Nwaogu, C. Blawert, N. Scharnagl, W. Dietzel, K.U. Kainer, Corros. Sci. 52 (2010) 2143–
2154.
R. Ghosh, D.D.N. Singh, Surf. Coat. Technol. 201 (2007) 7346– 7359.
M. Pushpavanam, S.R. Natarajan, K. Balakrishan, L.R. Sharma, J. Appl. Electrochem. 21
(1991) 642-645.
C. Bories, J.P. Bonino, A. Rousset, J. Appl. Electrochem. 29 (1999) 1045-1051.
R. Ramanauskas, R. Juskenas, A. Kalinicenko, J. Solid State Electrochem. 8 (2004) 416-421.
© 2013 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
doi: 10.5599/jese.2013.0036
149
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156; doi: 10.5599/jese.2013.0037
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Cerium oxide as conversion coating for the corrosion protection
of aluminum
JELENA GULICOVSKI, JELENA BAJAT*, VESNA MIŠKOVIĆ-STANKOVIĆ*,
BOJAN JOKIĆ*, VLADIMIR PANIĆ**, SLOBODAN MILONJIĆ
Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11000 Belgrade, Serbia
*Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11120 Belgrade,
Serbia
**ICTM – Center of Electrochemistry, University of Belgrade, Njegoševa 12, 11000 Belgrade, Serbia

Corresponding Author: E-mail: rocenj@vinca.rs; Tel.: +381-11-3408-865; Fax: +381-11-3408-224
Received: August 9, 2013; Published: Novembar 09, 2013
Abstract
CeO2 coatings were formed on the aluminum after Al surface preparation, by dripping
the ceria sol, previously prepared by forced hydrolysis of Ce(NO3)4. The anticorrosive
properties of ceria coatings were investigated by the electrochemical impedance
spectroscopy (EIS) during the exposure to 0.03% NaCl. The morphology of the coatings
was examined by the scanning electron microscopy (SEM). EIS data indicated
considerably larger corrosion resistance of CeO2-coated aluminum than for bare Al. The
corrosion processes on Al below CeO2 coating are subjected to more pronounced
diffusion limitations in comparison to the processes below passive aluminum oxide film,
as the consequence of the formation of highly compact protective coating. The results
show that the deposition of ceria coatings is an effective way to improve corrosion
resistance for aluminum.
Keywords
Ceria, Coatings, Corrosion, Microstructure.
Introduction
It is well known that chromate-based chemical conversions were used for corrosion protection
of aluminum for decades. On the other hand, because of toxic and carcinogenic properties of
chromium, this kind of coatings should be soon withdrawn from all industrial processes [1,2].
doi: 10.5599/jese.2013.0037
151
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156
CERIUM OXIDE IN CORROSION PROTECTION OF Al
Many researchers tried to find alternative for chromate conversions; it is believed that rare
earth elements (cerium, lanthanum, neodymium and yttrium) could effectively inhibit the
corrosion of aluminum. Hinton et al. [3,4] introduced the application of lanthanide compounds for
this purpose. The reported results showed that these barrier coatings simply prevent contact
between aluminum surface and corrosive species. The best degree of corrosion inhibition is
achieved with cerium [5-8].
Based on these findings, the aim of this study was to examine efficacy of ceria based coating for
corrosion protection of aluminum, by means of the scanning electron microscopy (SEM) and the
electrochemical impedance spectroscopy (EIS).
Experimental
Materials
The aluminum panels, 20 mm18 mm1 mm in size, were used as substrates. The surface of
specimens was mechanically polished by 800, 1200, 2400 and 4000 grit emery papers. To remove
the surface contamination the panels were degreased in alkaline solution containing: NaOH,
Na3PO412H2O, Na2SiO3 and ethoxylate of nonylphenol with nine molecules of ethylene oxide,
during 1 min at 70 C. Finally, the panels were rinsed by distilled water and dried in air at room
temperature.
For the investigation in this study ceria sol which was obtained by forced hydrolysis of 1 N
Ce(NO3)4 aqueous solution was used. The ceria sol was synthesized by Gulicovski et al. [9]
according to the reported procedure. The main characteristics of the synthesized ceria sol are: pH
value of synthesized sol, 0.66, average particle size, 71 nm, and solid phase content, 0.51 mass%.
In order to obtain the stable and pure ceria dispersion, nitrates were removed from the prepared
sol by ultrafiltration. The final pH of the sol was around 4.
The CeO2 coatings were formed on the aluminum panels by dripping method. The ceria sol was
applied in the quantity of 230 μl. Between the two applications, dispersing medium was
evaporated at 35 C.
Methods
The corrosion behavior of the ceria-coated aluminum was determined by the electrochemical
impedance spectroscopy (EIS). EIS data were recorded at the open circuit potential using a Gamry,
Reference 600 potentiostatgalvanostatZRA.
To examine the surface morphology of the coatings, scanning electron microscope (SEM) JOEL,
model JSM-5800, at 20 kV was used.
Results and Discussion
Surface morphology of bare Al and Al/CeO2
Figure 1 shows typical SEM images of the Al and Al/CeO2 specimens before and after prolonged
exposure to 0.03% NaCl solution. An uniform pattern of the Al surface can be seen after
mechanical polishing and degreasing (Figs. 1a and 1b). A highly porous film consisted of uniform
m-sized grains is observed at the Al surface after immersion in NaCl solution (Figs. 1c and 1d),
i.e., native homogeneous surface has been destroyed and a new layer of corrosion products was
produced.
152
J. Gulicovski at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156
Figure 1. Typical scanning electron micrographs of Al sample at two different magnifications:
before (a and b) and after exposure to 0.03% NaCl (c and d).
Typical surface morphology of a cerium oxide coating deposited onto Al panel is shown in Fig. 2.
Narrow cracks and sparing pits are visible (Figs. 2a and 2b); however, no signs of the peeling were
detected. The cracks are typical for rather thick conversion film and it is the result of the stress
induced in the film during the drying process. SEM micrographs of the film surface after immersion
in 0.03% NaCl solution (Figs. 2c and 2d) revealed presence of agglomerates of corrosion products
(Fig. 2c). The agglomerates appear to lay over compact granular structure (Fig. 2d), uniformly
consisted of m-sized fluffy grains.
Corrosion behavior
The corrosion behavior and stability of prepared Al/CeO2 sample were investigated by EIS after
different times of the exposure to 0.03 % NaCl. The data registered after 24 h of exposure are
shown in Fig. 3 as complex plane and Bode phase shift spectra and compared to the data of Al
reference sample. The complex plane spectra are consisted of at least three semicircles. The
semicircle at lowest frequencies (below 0.4 Hz) is more pronounced for Al/CeO2, whereas it is only
weakly indicated in the spectrum of Al (below 0.3 Hz). The peaks corresponding to two the high
frequency semicircles appear clearly in the phase shift spectra, whereas low frequency semicircle
can be observed only as a shoulder around 0.1 Hz for Al/CeO2. However, phase shifts at low
frequencies for both Al/CeO2 and Al are similar, around 20. The semicircles are larger for Al/CeO2,
especially two of them appearing at lower frequencies. This indicates good corrosion protection of
the applied ceria coating, since this kind of the spectra, usually observed for the corrosion of
aluminum, are assigned to the passive Al-oxide film (high frequency data) and corrosion-related
charge transfer processes beneath (low frequency data) [10-12].
doi: 10.5599/jese.2013.0036
153
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156
CERIUM OXIDE IN CORROSION PROTECTION OF Al
Figure 2. Typical scanning electron macrographs of Al/CeO2 sample at two different magnifications:
before (a and b) and after exposure to 0.03% NaCl (c and d).
Figure 3. Complex plane and Bode plots of Al and Al/CeO2 sample registered at open circuit
potential after 24 h exposure to 0.03 % NaCl. Inset: high frequency parts of the complex plane
spectra.
154
J. Gulicovski at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156
In order to examine the effect of exposure time on the characteristic features of the EIS
spectra, they were recorded at prolonged exposure times. Typical complex plain and Bode plots of
EIS data are presented in Fig. 4 by those registered after 312 h of exposure.
Figure 4. Complex plane and Bode plots of Al and Al/CeO2 sample registered at open circuit
potential after 312 h exposure to 0.03 % NaCl. Inset: high frequency parts of the complex plane
spectra.
As Fig. 4 shows, prolonged exposure to the corrosive environment does not considerably
change the characteristic features of the spectra. The comparison of Figs. 3 and 4 reveals that the
spectra for both Al and Al/CeO2 samples at high frequencies are poorly affected by the
prolongation of the exposure, which indicates that 24 h of exposure is sufficiently long to allow
complete formation of passive oxide layer. However, it appears that corrosion processes on bare
Al are not hindered since its spectra from Figs. 3 and 4 at lower frequencies, related to the charge
transfer, are similar. It follows that corrosion products formed after 24 h are not incorporated into
the passive film with impedance response at high frequencies.
These observations, except those related to the high frequency semicircles and passive
aluminum-oxide interlayer does not hold for Al/CeO2 sample. It is to be noted from Figs. 3 and 4
that the semicircles for Al/CeO2 sample in low frequency domain grow considerably upon the
increase in exposure time, which can be considered as a result of increased corrosion resistance
with respect to bare Al. At lowest frequencies (below 0.04 Hz), the semicircle in Fig. 4 is followed
by a straight line assignable to the diffusion controlled corrosion processes. Indeed, the
corresponding Bode plot reaches the values around 40, which is quite close to the theoretical
value of 45. Well pronounced diffusion limitations are due to the presence of a compact
protective film induced by CeO2.
doi: 10.5599/jese.2013.0036
155
J. Electrochem. Sci. Eng. 3(4) (2013) 151-156
CERIUM OXIDE IN CORROSION PROTECTION OF Al
Conclusions
With an appropriate surface pre-treatment, ceria was formed on the aluminum panels by
dripping method. These substrates were characterized by SEM and EIS methods in order to study
their possible applications as protective barriers in corrosive environment.
SEM analysis confirmed formation of the oxide film on Al and Al/CeO2 substrates after
immersion in 0.03 % NaCl solution. The film is consisted of Al2O3 agglomerates with compact
granular structure that improve corrosion resistance of the ceria coatings.
The results achieved by EIS measurements show that the semicircles obtained for Al/CeO2
sample in low frequency domain grow considerably upon the increase in exposure in NaCl, which
can be considered as a result of increased corrosion resistance with respect to bare Al.
It can be concluded that deposition of ceria coating is an effective way to improve corrosion
resistance for aluminum.
Acknowledgement: This work was financially supported by the Ministry of Education, Science and
Technological Development of the Republic of Serbia (Project number: 45012)
References
[1] S.H. Abdel, Surface Coatings Tech. 200 (2006) 3786-3792.
[2] J. Bieber, Mater. Lett. 105 (2007) 425-435.
[3] B.R.W. Hinton, D.R. Arnott, N.E. Ryan, Metals Forum 7 (1984) 211-217.
[4] B.R.W. Hinton, D.R. Arnott, N.E. Ryan, Metals Forum 9 (1986) 162-173.
[5] G.F. William, M.J. O’Keefe, H. Zhou, J.T. Grant, Surface Coatings Tech. 155 (2002) 208-213.
[6] A. Decroly, J.P. Petitjean, Surface Coatings Tech. 194 (2005) 1-9.
[7] P. Campestrini, H. Terryn, A. Hovestad, J.H.W. de Wit, Surface Coatings Tech. 176 (2004)
365-381.
[8] M.A. Dominguez-Crespo, A.M. Torres-Huerta, S.E., Rodil, E. Ramirez-Meneses, G.G. SuarezVelazquez, M.A. Hernandez-Perez, Electrochim. Acta 55 (2009) 498-503.
[9] J.J. Gulicovski, S.K., Milonjić, K. Meszaros Szecsenyi, K., Mater. Manufacturing Proc. 24
(2009) 1080-1085.
[10] M. Metikoš-Huković, R. Babić, Z. Grubač, J. Appl. Electrochem. 32 (2002) 35-41.
[11] C.M.A. Brett, J. Appl. Electrochem. 20 (1990)1000-1003.
[12] F.H. Cao, Z. Zhang, J.F. Li, Y.L. Cheng, J.Q. Zhang, C.N. Cao, Mater. Corros. 55 (2004) 18-23.
© 2013 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
156
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167; doi: 10.5599/jese.2013.0038
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Morphology and cyclic voltammetry analysis of in situ
polymerized polyaniline/graphene composites
DEVESH KUMAR MAHLA, SUBHENDU BHANDARI, MOSTAFIZUR RAHAMAN*,
DIPAK KHASTGIR
Rubber Technology Centre, Indian Institute of Technology Kharagpur, Kharagpur, India
*Presently at Chemical Engineering Department, College of Engineering Sciences, King Fahd
University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia

Corresponding Authors: E-mail: mrahaman1997@gmail.com; khasdi@rtc.iitkgp.ernet.in
Received: April 28, 2013; Revised: August 10, 2013; Published: Novembar 09, 2013
Abstract
Graphene (G) was synthesized from normal graphite powder via graphene oxide (GO).
Graphene was also produced from finer particles of graphite subjected to ball milling to
check the effect of particle size of graphene on the properties of composite.
PANI/graphene composites of different compositions were prepared by in situ
polymerization of aniline to polyaniline in the presence of graphene powder. Graphene,
graphene oxide and PANI/graphene composites were characterized by UV, IR, TEM, and
cyclic voltammetry. PANI/graphene composites exhibit higher current in cyclic
voltammetry study compared to either neat PANI or neat graphene. The value of
capacitance achieved for PANI/graphene composites is found to depend on the size of
graphene particles, finer the particle higher is the capacitance for the composites.
However, the effect of composition on CV characteristics of composite is relatively less
pronounced compared to the size of graphene sheets coated with PANI.
Keywords
Polyaniline; Graphene; Conductive composites; Cyclic voltammetry.
Introduction
Conductive polymer composites filled with different carbon fillers have been used in different
electrical and electronic applications [1–7]. Among the carboneous fillers, graphene based
polymer composites have attracted much attention in the recent years [8–10]. Graphene, oneatom-thick planar sheet of carbon atoms, is densely packed in a honeycomb crystal lattice of
doi: 10.5599/jese.2013.0038
157
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
IN SITU POLYMERIZED POLYANILINE/GRAPHENE COMPOSITES
graphite. Graphene, at large scale, is produced by reducing graphene oxide by some reducing
agent. Graphene is having large aspect ratio (ratio of surface area to thickness) [11], high
mechanical strength [12], high electrical conductivity [13], ability to disperse in polymers well [14],
high thermal conductivity and stability [15]. It can be effectively exploited for many applications
[16,17]. Graphene oxide derived from graphite through oxidation has many polar groups on its
surface like –C=O, –COOH, –OH, which give its properties like hydrophilicity, dispersibility, and
compatibility with many polymers.
Among conductive polymers, polyaniline (PANI) has attracted considerable attention because
of its ease of preparation, low cost of monomer, good environmental stability, good conductivity
control through doping as well as a good control of oxidation level. All these properties give PANI
the potential for wide applications [18–22]. It can effectively be used as opto-electronic sensors
[23–26], conductive paints and adhesive [27–29].
PANI has also good power and energy density, so it has been analyzed for the development of
new supercapacitor materials [30–32]. Generally, electrochemical super capacitors are of two
types; type-1 is electrical double layer capacitor (EDLC) due to charge separation at
electrode/electrolyte interface, and type-2 is pseudocapacitor, where capacitance is due to both
reversible faradic reaction and charge separation [33]. The latter category of capacitor materials
can be further divided in to two different types of material based on their origin, for example i)
metal oxide like RuO2 and ii) conducting polymer like PANI.
The energy and power density of power sources like batteries and capacitors can be shown by
Ragone plot. Batteries have good energy density and EDLC type capacitors have good power
density whereas pseudocapacitors work on the principle of both batteries and capacitors,
simultaneously. PANI can act as a pseudocapacitor and it has the power to store energy by
reversible chemical reactions, as observed in batteries, and also like EDLC. In polyaniline/graphene
composite, graphene not only increases the EDLC capacity of PANI but also helps in facilitating
charge transfer and consequently enhances the utilization of PANI as a capacitor material by
increasing available surface area.
The scrutiny of available literatures reveals that there exist some reports on PANI/graphene
composites. However, all these reports mainly deal with only one or at best two compositions of
PANI/graphene system. The effect of size of graphene particles on the properties of
PANI/graphene composites has not been extensively investigated. So the present study deals with
synthesis and characterization of PANI/graphene composites with different compositions. The
preparation of PANI/graphene composites with different size of graphene particles has also been
reported.
Experimental Details
Polyaniline was synthesized in aqueous medium as reported in the literature [34]. The graphite
oxide was prepared by modified Hummers method [35]. During the preparation of graphite oxide,
50 mg of graphite was mixed with 25 mg of NaNO3 and 2ml H2SO4. After stirring of the mixture for
10 minute in ice bath, 150 mg of KMnO4 was added to it with constant stirring for 15 minutes.
Then the resultant mixture was heated up to 98 °C and deionised water was added slowly with
constant stirring. H2O2 was added and then the suspension was filtered followed by washing of
filtrate with deionised water for 8 times to remove any water soluble residues. The filtrate so
prepared is graphite oxide which was used in further synthesis. During the preparation of
polyaniline/graphene composites the following steps have been adopted. In the first step, the
158
D. K. Mahla at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
graphite oxide was added (as per the ratio desired, explained below) to deionised water. The
mixture was ultrasonicated for one hour followed by addition of aniline to it, and the mixture was
again ultrasonicated for half an hour. While ultrasonicated, layers in graphite oxide were
delaminated to produce graphene oxide. This mixture of graphene oxide and aniline was then kept
as such for a day at room temperature. In this mixed mass the requisite amount of 0.2 M solution
of HCl was added at room temperature followed by requisite amount of 0.25 M solution of
ammonium persulfate was added. Continuous stirring was maintained during the reaction. After
addition of ammonium persulfate the stirring was continued for 10 minutes and the conical flask
was covered with lid and kept as such for 24 hours. The whole reaction was carried out between 5
- 10 °C with the help of ice bath. The polyaniline/graphene composite so prepared was filtered. To
remove the unreacted reactant from the mixture and to dope PANI adequately the filtrate was
repeatedly washed with 2 M HCl solution. The so prepared composite was dried in vacuum oven at
50 °C temperature until the final weight became constant.
The graphite oxide in polyaniline/graphene composites was varied in different ratio with its
weight percent being 4, 8, 12 and 16 of combined weight of initially taken aniline and graphite
oxide. The nomenclature of the so varied weight has been given as PG4, PG8, PG12 and PG16.
PANI/graphene composites were also prepared in a little different way. In this preparation the
graphite powder as received was ball milled for 60 hours at 300 rpm to form finer particles of
graphite and used for preparation of graphene oxide followed by preparation of PANI/graphene
composites. This was done to check the effect of size of graphene sheet on composite properties.
The so prepared nano graphite powder was converted into graphite oxide by modified Hummers
method [19]. The procedure adopted for the preparation of polyaniline/nano-graphene composite
is the same as described earlier. The weight per cent of nano-graphite oxide has also been varied
in the same way as described above in the proportion of 4, 8, 12 and 16, and identified as PnG4,
PnG8, PnG12 and PnG16.
Different polyaniline/graphene composites were characterized by different techniques like
cyclic voltammetry (CV) and transmission electron microscopy (TEM). The CV study was performed
with different scan rates of 10 mV/s, 50 mV/s, 80 mV/s and 100 mV/s with electrolyte being 2 M
H2SO4 solution. The reference electrode used was Ag/AgCl and counter electrode being platinum
wire. The working electrode used in the experiment was modified glassy carbon electrode. The
polyaniline/graphene composite was mixed in the Nafion solution of chloroform. The mixture was
then put on the electrode with the help of glass rod. The CV was performed within the potential
range of -0.2 to 1.0 V at room temperature.
For TEM analysis, the samples were used after ultrasonication for one hour in deionised water.
IR and UV techniques were used for characterization, and sample of graphene and graphene oxide
were ultrasonicated in acetone for half an hour before testing. This solution was spread over KBr
pellet and IR was performed. For UV analysis the G and GO samples were ultrasonicated in
deionised water for 1 hour before test.
Results and Discussion
UV and FT-IR
Synthesized graphene oxide and graphene were characterized by UV and FT-IR spectroscopy.
From UV spectra (Figure 1), one can detect the π – π* transition at 260 nm (38461 cm-1) for the
graphene while graphene oxide shows n – π* transition at 305 nm (32786 cm-1) and π – π* at 240
nm (41667 cm-1). From IR spectra (Figure 2) for graphene a very few peaks can be detected as neat
doi: 10.5599/jese.2013.0038
159
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
IN SITU POLYMERIZED POLYANILINE/GRAPHENE COMPOSITES
graphene contains very few organic groups. FT-IR peak in between 3500 to 3100 cm-1 is due to the
absorbed moisture and the peak around 2200 cm-1 is due to atmospheric carbon dioxide often
seen if the experiment is not done in nitrogen environment. There is a little hump around 1500
cm-1 because of C=C stretching in benzene ring of graphene. In the case of GO, due to oxidation
there are several absorption bands corresponding to large number of chemical groups attached to
the graphene sheets.
Figure 1. UV spectra of graphene and graphene oxide.
Figure 2. FT-IR spectra of graphene and graphene oxide.
160
D. K. Mahla at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
TEM Analysis
In TEM images the presence of single layer graphene (Figure 3) and multi layer graphene sheets
stacked together (Figure 4) can be seen. From other TEM images (Figures 5 and 6) the formation of
polyaniline particles (Figure 5) and polyaniline coating on graphene sheets (Figure 6) can also be
detected. Graphite to graphene was routed through formation of graphene oxide followed by
ultrasonication when different degree of delamination of original graphite occured. If the extent of
delamination is very less, the original layered structure of graphite is almost retained. All these
studies reveal that successful preparation of graphene from graphite can be achieved by the
method described in experimental section.
Figure 3. TEM image of graphene
sheet
Figure 5. TEM image of polyaniline
particles
Figure 4. TEM image of few graphene
sheets stacked together
Figure 6. TEM image of polyaniline/graphene
composite.
Cyclic voltammetry analysis
The study of CV (current-voltage) for the polyaniline/graphene composite was carried out to
understand the electrochemical behavior of these composites. Figure 7 shows the CV of PANI, G,
GO and PG4. The shapes of CV curves show the reversible charge-discharge behavior of composite
electrode [36,37]. For PANI the first anodic peak appears around 0.29 V, which is associated with
the oxidation of leucoemeraldine to emeraldine [38–41]. The second anodic peak around 0.84 V is
attributed to the emeraldine to pernigraniline transition (Scheme 1). Figure 7 also shows that with
the addition of graphene the current flow increases and the peak also broadens as compared to
doi: 10.5599/jese.2013.0038
161
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
IN SITU POLYMERIZED POLYANILINE/GRAPHENE COMPOSITES
neat PANI and neat graphene as shown in the inset. The differences in qualitative and quantitative
shape of CV curve for PANI and polyaniline/graphene composites have been attributed to the
dispersion of PANI particles on graphene sheet which reduces the migration length of electrolyte
ions during the charge-discharge process where graphene sheets provide an excellent path for the
charge transfer [42]. Hence, the graphene increases the efficacy of PANI by providing a larger
surface area and reducing the resistance to current flow.
Scheme 1 Oxidation/reduction chemistry of polyaniline.
Figure 7. Cyclic voltammograms of PG8, polyaniline, graphite oxide and graphene
162
D. K. Mahla at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
The stability of the composite has been checked by repeating the CV plots under the same
condition for the same sample for several cycles [43]. Figure 8 shows the average particle size of
graphite as received and the nano sized graphite with cumulative contribution in the total number
of particles, %. The particle size analysis was done by Fritz particle size analyzer. The average
particle size of graphite is 800 µm while the particle size of nano graphite was beyond the range of
analyzer. Figure 9 shows that after 100, 200 and 300 CV cycles, at 0.08 V/s scan rate, the currentpotential graphs almost superimposes on each other. This reveals the good electrochemical
stability of the composite which is essential when it is used as a capacitor.
Figure 8. Particle size analysis of graphite and nano graphite
Figure 9. Cyclic voltammogram of PG8 at 100 mV/s scan rate after 100, 200 and 300 cycles
doi: 10.5599/jese.2013.0038
163
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
IN SITU POLYMERIZED POLYANILINE/GRAPHENE COMPOSITES
Both composition of PANI/graphene composite and size of graphene particles are expected to
influence current-voltage characteristics of composites. Figure 10 compares the current potential
behavior of polyaniline/graphene composite with variation in graphene weight percent and size of
graphene sheet. It shows that with the addition of graphene the peaks in current - potential plots
broaden in comparison to PANI. This is due to availability of alternate as well as low energy paths
for charge transfer in PANI/graphene system through graphene. The presence of graphene in
composite decreases the resistance of system hence there is an increase in the current and
broadening of the peak. As shown in Figure 10 the resistance in PnG4 is almost equal to that of PG8
composite. This shows that with smaller size of graphene sheet the available surface area is higher
and hence it leads to better utilization of PANI. Hence, this infers that with larger surface area the
small scale graphene better decreases the resistance of the system and increases the capacitance
of composite material by better utilization of PANI in composite. Figure 11 shows that with
increase in the graphene weight percent there is no much increase in the current flow relatively to
the neat PANI and in PANI/graphene composite as shown in Figure 7 [44]. It could also be seen
that at lower scan rates (for example 0.01 V/s) different oxidation and reduction peaks could be
distinguished but as the scan rate is increased, the peaks merged. This is due to the time constant
effect in CV, since I=E/Rs (e-t/CdRs), where E is the potential step, Rs being the solution resistance,
Cd, the double layer capacitance and t is time [45-46]. Here I decreases as the CdRs increases which
happens at a low scan rate. As the scan rate is increased CdRs doesn’t give enough time to the
current to decrease hence distinct peaks are not observed.
Figure 10. Cyclic voltammogram of PG4, PG8 and PnG4 at 10 mV/s scan rate
Conclusions
Different spectroscopic and morphological analysis show that chemical process used in this
experimentation leads to successful preparation of graphene sheet from graphite. From CV
analysis it has been found that the size of graphene sheet plays an important role in determining
164
D. K. Mahla at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
the capacitance of the composite. In fact, with the reduction of the size of graphene sheet there is
an increase in the capacitance value.
Acknowledgement: Authors would like to thank CSIR New Delhi for providing the fund to carry out
this research work.
References
[1] R. Ramasubramaniam, J. Chen, H. Liu, Appl. Phys. Lett., 83 (2003) 2928–2930.
[2] M. Rahaman, T. K. Chaki, D. Khastgir, J. Mater. Sci., 46 (2011) 3989–3999.
[3] W. J. Zou, S. S. Mo, S. L. Zhou, T. X. Zhou, N. N. Xia, D. S. Yuan, J. Electrochem. Sci. Eng. 1
(2011) 65–71.
[4] N. J. S. Sohi, M. Rahaman, D. Khastgir, Polym. Compos., 32 (2011) 1148–1154.
[5] V. Panwar, R. M. Mehra, Polym. Eng. Sci., 48 (2008) 2178–2187.
[6] N. Syarif, I. A. Tribidasari, W. Wibowo, J. Electrochem. Sci. Eng. 3 (2013) 37–45.
[7] X. Luo, D. D. L. Chung, Compos.: Part B, 30 (1999) 227–231.
[8] H. Kim, A.A. Abdala, C.W. Macosko, Macromolecules, 43 (2010) 6515–6530.
[9] T. Ramanathan, A.A. Abdala, S. Stankovich, D.A. Dikin, M. Herrera-Alonso, R.D. Piner, D.H.
Adamson, H.C. Schniepp, X. Chen, R.S. Ruoff, S.T. Nguyen, I. A. Aksay, R.K. Prud’homme,
L.C. Brinson, Nat. Nanotech., 3 (2008) 327–331.
[10] Y.W. Zhu, S. Murali, W.W. Cai, X.S. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Adv. Mater., 22 (2010)
3906–3924.
[11] M.D. Stoller, S.J. Park, Y.W. Zhu, J.H. An, R.S. Ruoff, Nano Lett., 8 (2008) 3498–3502.
[12] C. Lee, X. Wei, J.W. Kysar, J. Hone, Science, 321 (2008) 385–388.
[13] X. Du, I. Skachko, A. Barker, E.Y. Andrei, Nat. Nanotech., 3 (2008) 491– 495.
[14] H.B. Zhang, W.G. Zheng, Q. Yan, Y. Yang, J.W. Wang, Z.H. Lu, G.Y. Ji, Z.Z. Yu, Polymer, 51
(2010) 1191–1196.
[15] A. Yu, P. Ramesh, X. Sun, E.M. Bekyarova, E. Itkis, R.C. Haddon, Adv. Mater., 20 (2008)
4740–4744.
[16] A.K. Geim, Science, 324 (2009) 1530–1534.
[17] D. Li, R. B. Kaner, Science, 320 (2008) 1170–1168.
[18] A.G. Green, A.E. Woodhead, J. Chem. Soc., 1910 (1997) 2388‒2403.
[19] A. K. Sharma, Y. Sharma, J. Electrochem. Sci. Eng. 3 (2013) 47–56.
[20] M. Magioli, B. G. Soares, A. S. Sirqueira, M. Rahaman, D. Khastgir, J. Appl. Polym. Sci., 125
(2012) 1476–1485.
[21] M. Rahaman, L. Nayak, T. K. Chaki, D. Khastgir, Adv. Sci. Lett., 18 (2012) 54‒61.
[22] S. Bhadra, D. Khastgir, Polym. Test., 27 (2008) 851–857.
[23] S. Bhadra, S. Chattopadhyay, N.K. Singha, D. Khastgir, J. Appl. Polym. Sci., 108 (2008) 57–64.
[24] M. Rahaman, T. K. Chaki, D. Khastgir, J. Appl. Polym. Sci., 128 (2013) 161‒168.
[25] S. Bhadra, D. Khastgir, N.K. Singha, J.H. Lee, Prog. Polym. Sci., 34 (2009) 783–810.
[26] J.C. Chiang, A.G. MacDiarmid, Synth. Met., 13 (1986) 193–205.
[27] W. Hualan, H. Qingli, Y. Xujie, L. Lude, W. Xin, Electrochem. Commun., 11 (2009) 1158–
1161.
[28] J.P. Zheng, P.J. Cygan, T.R. Jow, J. Electrochem. Soc., 142 (1995) 2699.
[29] A.J. Burke, J. Power Sources, 91 (2000) 37.
[30] B.E. Conway, Electrochemical Supercapacitors, Kluwer-Plenum, New York (1999).
[31] S. Sopčić, M. Kraljić Roković, Z Mandić, J. Electrochem. Sci. Eng. 2 (2012) 41–52.
[32] S. Chandra, et al., Chem. Phys. Lett., 519–520 (2012) 59–63.
[33] T. Nakajima, A. Mabuchi, R. Hagiwara, Carbon, 26 (1988) 357–361.
[34] L. Anton, H. Heyong, F. Michael, K. Jacek, J. Phys. Chem. B, 102 (1998) 4477–4482.
doi: 10.5599/jese.2013.0038
165
J. Electrochem. Sci. Eng. 3(4) (2013) 157-167
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
IN SITU POLYMERIZED POLYANILINE/GRAPHENE COMPOSITES
H. Dongxue, C. Ying, Colloid. Surf., 259 (2005) 179–187.
V. Khomenko, E. Frackowiak, F. Beguin, Electrochimica Acta, 50 (2005) 2499–2506.
Z. Hao, C. Gaoping, W. Weikun, Y. Keguo, X. Bin, Z. Wenfeng, C. Jie, Y. Yusheng,
Electrochimica Acta, 54 (2009) 1153–1159.
H. Chi-Chang, L. Jeng-Yan, Electrochimica Acta, 47 (2002) 4055–4067.
R. Prakash, J. Appl. Polym. Sci., 83 (2002) 378–385.
E.I. Santiago, E.C. Pereira, L.O.S. Bulhões, Synth. Met., 98 (1998) 87–93.
E. Smela, W. Lu, B.R. Mattes, Synth. Met., 151 (2005) 25–42.
Y. Jun, W. Tong, S. Bo, F. Zhuangjun, Q. Weizhong, Z. Milin, W. Fei, Carbon, 48 (2010) 487–
493.
Z. Lu, Z. Liang, X. Yuxi, Q. Tengfei, Z. Linjie, S. Gaoquan, Electrochimica Acta, 55 (2009) 491–
497.
Y. Li, H. Peng, G. Li, Kezheng Chen, Eur. Polym. J., 48 (2012) 1406–1412.
Y.G. Wang, H.Q. Li, Y.Y. Xia, Adv. Mater., 18 (2006) 2619–2623.
J. B. Allen, R.F. Larry, 2nd addition, Electrochemical Methods: Fundamentals and
Applications, John Wiley (2001).
© 2013 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
166
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184; doi: 10.5599/jese.0039
Open Access : : ISSN 1847-9286
www.jESE-online.org
Original scientific paper
Electrochemical treatment of trypan blue synthetic wastewater
and its degradation pathway
ANANTHA N. SUBBA RAO and VENKATESHA T. VENKATARANGAIAH
Department of P.G. Studies and Research in Chemistry, School of Chemical Sciences, Kuvempu
University, Shankaraghatta-577451, Shimoga, Karnataka, India

Corresponding Authors: E-mail: drtvvenkatesha@yahoo.co.uk, Tel.: +91-9448855079; fax: +91-08282256255.
Received: October 17, 2013; Revised: October 28, 2013; Published Novembar 09, 2013
Abstract
The trypan blue (TB) dye synthetic wastewater was treated in presence of chloride ions by
electrochemical method. The effect of current density, pH, initial concentration of dye and
supporting electrolyte on color and COD removal were investigated. The UV-Vis absorption
intensity, chemical oxygen demand (COD), cyclic voltammetry (CV), Fourier transforminfrared spectroscopy (FT-IR), gas chromatography – mass spectrometry (GC-MS) analysis
were conducted to investigate the kinetics and degradation pathway of TB dye.
Keywords
Cataract, Teratogenic, Carcinogenic, Niagara blue, Diamine blue, Decolorization, COD
removal, Active anode, Oxidants, Indirect oxidation.
Introduction
Dyes find extensive applications in industries like textile, leather, pulp and paper, printing,
photographs [1]. The wastewater from these industries is therefore loaded with the dyes. It is
aesthetically unbearable and can turn out to be fatal if this wastewater is allowed to combine with
the natural water resources. The presence of dyes or organic molecules increases the biological
oxygen demand (BOD), chemical oxygen demand (COD) and total organic carbon (TOC) content of
natural water, which especially poses challenges to the survival of aquatic life besides causing
serious health hazards leading to the imbalance in ecology [2-4].
Chemical, physical, biological, and advanced oxidation processes are in practice to treat the
wastewater. The electrochemical method is efficient, less time consuming and it does not require
the addition of any chemical reagent. In this method, the organic pollutant is oxidized either by
doi: 10.5599/jese.2013.0039
167
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
direct electron exchange with the anode (direct oxidation) or by the electrochemically generated
oxidants (indirect oxidation). Direct oxidation is possible if the organic pollutant is oxidizable
within the overpotential of oxygen (OER) and hydrogen evolution reactions. Indirect oxidation is
brought about by the oxidants generated during electrolysis, such as hydroxyl radical (•OH).
Hydroxyl radical (•OH, H+/H2O) is a powerful oxidizing agent with standard reduction potential of
2.7 V vs. standard hydrogen electrode. Active chlorine species (oxidants) like Cl2, Cl3-, ClO2-, ClO3-,
HOCl, ClO- are generated in presence of chloride electrolyte and these species can oxidize the
organics into simple biodegradable molecules [5,6].
The electrochemical degradation of methyl violet 2B, acridine, eosin yellow [7], alphazurine dye
[8], reactive blue 81, reactive red 2 [9], reactive blue-4, reactive orange-16 [10], reactive red 120
[11], reactive brilliant red K-2BP [12], methyl green [13], methyl red [14] and other dyes has been
successfully achieved in presence of suitable electrolyte and operating conditions. Furthermore,
the results from these works infer that the extent of degradation of an organic pollutant not only
depends on the operating conditions employed, but also on the structural, chemical and
electrochemical properties of the pollutant itself [7]. The nature of the electrolyte and its
concentration, electrode material, pH, current density, wastewater flow rate (stirring rate) and the
mechanism of oxidation also significantly influence the extent of degradation of organics.
Complete incineration of organics with high efficiency can be achieved by electrochemical method
under optimum conditions.
The molecules o-tolidine, benzidine and o-dianisidine are carcinogenic in nature [16,17]. Trypan
blue (TB) (Congo blue 3B / Niagara blue 3B / Diamine blue 14) is an o-tolidine based diazo dye, well
known for its ability to selectively color the dead cells blue. It is also used in the dyeing of textiles,
leather and paper [18].
Table 1: Properties and structure of Trapan blue
Properties
Chemical structure
Molecular formula: C34H24N6Na4O14S4
Molecular weight: 960.8
Color Index number: 23850
λmax / nm = 590 [19]
TB dye (Table I) emerged as one of the most frequently used staining agent in cataract, as well
as other anterior segment surgeries in the late 1990s [20]. However, there are reports which unveil
the complications in cataract surgery with the usage of TB. C Lüke et al. [21] reported the toxic
effects of TB after a short duration of retinal exposure and recommended minimizing the usage of
TB in intraocular applications [20,22]. TB carries associated risk at higher concentrations and
longer duration of exposure [20-22]. Long term presence of 0.2 % TB can cause considerable
damage to the retina [23]. International Agency for Research on Cancer provides sufficient evidences for the carcinogenic and teratogenic effects of TB in animals and possibly in humans [24,25].
168
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
The photocatalytic degradation of TB is reported in the literature [15,26] but there are no work
solely focused on the degradation of TB by electrochemical method [15]. In the present work, the
electrochemical oxidation of TB with Pt as anode material has been investigated and probable
degradation pathway of TB has been proposed.
Materials and Chemicals
Chemicals
Commercially available trypan blue (TB) dye was (purchased from HiMedia, Mumbai, India)
used for the studies. Analytical grade NaCl, Na2SO4, Na2CO3 and NaNO3 and their aqueous
solutions were (HiMedia Laboratories Pvt. Ltd, Bangalore, India) used as electrolytes. pH of each
electrolyte was adjusted by H2SO4 and NaOH. The dil. HNO3 was used for the pretreatment of
electrodes (HiMedia Laboratories Pvt. Ltd, Bangalore, India).
Experimental
A single compartment glass container was used as electrolytic cell (6.5 cm diameter x 10 cm
height, covered with Teflon® lid provided with gaps to insert the electrodes). Two Pt foils
(dimension 0.5 cm × 0.5 cm, thickness 0.018 cm, supplied by Systronics India Ltd. Bangalore, India)
of surface area, 0.54 cm2 were used as anode and cathode which were separated by 0.5 cm in the
electrolytic cell. The potentials of working electrode (anode) were recorded relative to saturated
calomel electrode (SCE). A DC source with galvanostatic mode (Model PS-618 chemilink systems,
Navi Mumbai, India) was used for power supply. The synthetic wastewater of TB dye was prepared
with ultrapure water obtained from Elix 3 Milli-pore system (resistivity, > 18 MΩ cm at 25 °C). A
magnetic stirrer (550 rotations per minute) was used for the agitation of wastewater during
electrolysis.
Electrolysis
The solution with the composition of 50 mg L-1 TB dye solution and NaCl, 0.2 % was prepared in
Millipore water and was subjected to electrolysis under galvanostatic condition for 60 minutes.
The Pt electrodes were dipped in dilute HNO3, sonicated for 1 minute and thoroughly washed with
Millipore water. All experiments were carried out at ambient temperature. To monitor the
progress of the degradation process, electrolyzed samples were collected at appropriate time
intervals and subjected to analysis. The effect of current density, pH, nature of electrolyte and its
concentration on COD and color removal efficiency was examined. The optimum condition for the
maximum color and COD removal efficiency was determined.
Analysis
Cyclic voltammetry (CV)
The cyclic voltammetric measurements were performed at room temperature with
conventional three electrode system connected to software controlled electrochemical work
station (CH Instruments 660C, USA). The working electrode was a Pt disk and counter electrode
was a Pt foil. The working electrode surface was polished with 0.05 μm alumina, washed with
methanol, dipped in 10 % HNO3, sonicated for 2 min and then washed thoroughly with Millipore
water before use. The open circuit potential was recorded in 0.2 % NaCl solution and the potential
window from +1.1 V to -1.1 V was selected for CV scans. CV for blank solution (0.2 % NaCl) and TB
dye solution (50 mg L-1 + NaCl 0.2 %) were recorded at the scan rate of 100 mV s-1.
doi: 10.5599/jese.2013.0039
169
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
Spectroscopic and chemical analysis
The extent of degradation was monitored by evaluating color and COD removal. UV-Vis
absorbance spectra of samples were recorded by Ocean Optics UV-Vis HR 4000 spectrophotometer (UV-Vis-NIR light source, DT-MINI-2-GS and Jaz detector). The percentage color
removal was calculated by using the relation (1) with reference to the absorption intensity at λmax
of 590 nm.
[
]
( )
Where Abs0 and Abst are the absorbance at 590 nm at time 0 and t minutes of electrolysis
respectively.
The COD (g(O2) L-1) estimation was carried out by open reflux method and its values used to
monitor the progress in degradation. The percentage COD removal was calculated using the
relation (2).
[
]
( )
Where COD0 and CODt are the COD at time 0 and t minutes of electrolysis respectively.
The percentage average current efficiency (ACE) was calculated using the following relation (3)
[6].
[
]
( )
Where F is the Faraday’s constant (96,485 C mol-1), COD in (g O2 L-1), I is the current (A), V is the
volume (L) of electrolyte, t – time (s), 8 – gram equivalent mass of oxygen (g equiv-1).
To determine the degradation pathway, the test samples at selected time intervals (15 and
40 min) were subjected to freeze drying using Lyophilizer (Delvac, India) at -50 ± 5 °C under
reduced pressure of 0.12 mbar. Freeze drying eliminates the chances of decomposition of
intermediates and only the volatile compounds are removed. The solid residue thus obtained was
subjected to UV-Vis spectroscopy, Fourier Transform Infrared Spectroscopy FT-IR (Alpha, Brucker)
and gas chromatography mass spectrometry (GC-MS) analyses. The solid residue was finely mixed
with KBr, pressed into a disk and subjected to FT-IR analysis. The FT-IR spectrums recorded are the
average 16 scans from wave number 4000 cm-1 to 500 cm-1. GC-MS analysis was carried out in
order to detect the end products of TB degradation. The samples were analyzed using GC-MS
system (Trace GC Ultra and Trace DSQ THERMO-Electron Corporation, Austin, TX, USA) with a HP5MS, 5 % phenyl methyl silox column (30 m × 0.25 mm, film thickness 0.25 µm). A temperature
gradient program at 10° C min-1 was applied between 40 °C and 250 °C.
Results and Discussion
Cyclic Voltammetry Studies
The cyclic voltammograms are shown in Fig. 1. A peak at -0.23 V was observed during cathodic
sweep of blank solution. The hydrogen evolution begins approximately at -0.80 V. The
voltammogram obtained for the dye solution showed the same pattern as the blank and no new
peak was observed during the anodic sweep. This indicates that the TB dye does not undergo
direct electrochemical reaction on Pt in the potential range from -1.1 to +1.1 V. The decrease in
anodic peak (at -0.80 V vs. SCE) current can be attributed to the adsorption of dye on the surface
of working electrode.
170
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
Figure 1. CV of 0.2 % NaCl and 50 mg L-1 TB + 0.2 % NaCl solutions; scan rate 100 mV s-1
Effect of Supporting Electrolyte
To determine the effect of different supporting electrolytes, preliminary investigations on TB
degradation were carried out separately in presence of chloride (Cl-), sulfate (SO42-), nitrate (NO3-)
and carbonate (CO32-) ions. In all the cases 34.2 mM solution of electrolyte was was used. On
electrolysis of the solution for 60 min, showed a 100 %, 42 %, 27 %, 15 % color removal in
presence of Cl-, CO32-, NO3-, SO42- ions respectively. Similar trend was observed by Fornazari et al.
[27] in the electrochemical degradation of phenol-formaldehyde mixture [27,28]. The presence of
Cl- ions is not only essential for the color removal but also its in situ generated oxidants cleave the
TB bonds. Therefore, NaCl was selected as the supporting electrolyte for the present studies. Fig.
2A and Fig. 2B depict the effect of different electrolytes on absorption intensity and color removal
of dye.
The Pt is an active anode and during electrolysis the generation of hydroxyl radical is limited [6].
In presence of CO32-, NO3-, SO42- ions, the oxidation of TB is possible only either by the hydroxyl
radicals generated on Pt anode or by direct electron transfer with the anode. But Pt anode does
not show any electrochemical activity for the oxidation of TB (Fig. 1). On Pt, in presence of oxygen
and above 0.8 V there exists Pt and PtO mixture [29]. Slight decolorization of TB in presence CO32-,
NO3-, SO42- ions is perhaps due to oxidation by the hydroxyl radicals generated on Pt and by PtO/Pt
couple. Below are the possible reactions (4) – (7) on the surface of the Pt anode [19,30].
Pt + H2O  Pt-OHads + H+ + e-
(4)
Pt-OHads  PtO + H+ + e-
(5)
xPtO + Raq  ROx + xPt
(6)
2PtO  2Pt + O2
(7)
doi: 10.5599/jese.2013.0039
171
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
Decoloration is the clear evidence for the cleavage of the chromophoric (–N=N-) group of TB
dye. Since decolorization was very slow in presence of CO32-, NO3-, SO42- electrolytes, hence the
COD removal cannot be more than color removal and is very small. Therefore COD was not
measured in these cases.
Figure 2A. The variation of absorption with electrolysis time. Conditions; 0.2% NaCl + 50 mg L-1
TB, current density – 93 mA cm-2, λmax = 590 nm
Figure 2B. Effect of supporting electrolytes on color removal
Decoloration is the clear evidence for the cleavage of the chromophoric (–N=N-) group of TB
dye. Since decolorization was very slow in presence of CO32-, NO3-, SO42- electrolytes, hence the
172
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
COD removal cannot be more than color removal and is very small. Therefore COD was not
measured in these cases.
Effect of NaCl Concentration
The effect of NaCl concentration on the rate of color and COD removal was investigated with
NaCl concentration ranging from 0.05 % to 3.0 %. Fig. 3A and 3B, show the effect of NaCl on color
and COD removal respectively.
Figure 3A. Effect of NaCl concentration on color removal
Figure 3B. Effect of NaCl concentration on COD removal (electrolysis time 60 min)
doi: 10.5599/jese.2013.0039
173
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
The amount of oxidants on the anode surface increases with the applied current density. But, at
the given current density, the amount of Cl- ions is the limiting factor. If Cl- ion concentration in the
solution is less, the current supplied would be lost in oxygen evolution, which is otherwise could
be used to generate active chlorine species. The optimum Cl- ion concentration can facilitate high
current efficiency and thus less energy consumption. At higher concentrations of Cl- ions, the
applied current density is efficiently utilized to generate more oxidants [6]. At the same time, the
concentration of Cl- ions should not exceed the concentration level commonly found in any real
wastewater sample. So, the effect of Cl- ion concentration was tested within 0.3 % NaCl.
Complete decolorization of TB solution occurred in 30 min of electrolysis with all concentrations
of NaCl from 0.1 % to 0.3 %, except with 0.05 % NaCl, in which 98 % color removal was achieved.
The rate of decoloration increased with increase in Cl- ion concentration. Concomitant COD
removal was observed with decolorization. The COD removal after 60 min electrolysis increased
largely with NaCl concentration from 0.05 % to 0.2 %. After this concentration, only slight
improvement in the COD removal was noticed. Therefore, 0.2 % NaCl was chosen as the optimum
concentration for further studies.
Effect of Current Density
The efficiency and energy consumption for the degradation process is dependent on the
applied current density and electrolysis time. Higher current density always leads to high energy
consumption and low current efficiency. The degradation of TB in the present case takes place by
indirect oxidation brought about by the oxidants generated during electrolysis. Higher current
density enhances the rate of electrode reactions and hence rate of generation of oxidants also
elevates. A range of current density from 37 to 111 mA cm-2 was applied to determine its effect on
color and COD removal. The rate of color and COD removal increased with applied current density
(Fig. 4A and 4B). The COD removal increased as current density increased from 37 to 55 mA cm-2,
beyond which slow and steady raise in COD was noticed. In contrast, the current efficiency
decreased with increse in applied current density.
Figure 4A. Effect of current density on color removal
174
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
Figure 4B. Effect of current density on COD removal; conditions - 0.2 % NaCl,
current density- 93 mA cm-2, dye – 50 mg L-1; electrolysis time – 60 min
The color removal was 100 % in all cases and the COD removal was 70 % to 95 % with 25 % to
11 % current efficiency. This implies that with increase in current density, though the production
of oxidants increased, the undesired hydrogen and oxygen evolution reactions also increased
alongside and consumed major part of the supplied current. A charge consumption of 3.60 kC L-1
was recorded for 92 % of COD removal under the current density of 93 mA cm-2 (60 min) whereas,
2.88 kC L-1 charge was consumed for the same COD removal under the current density of
37 mA cm-2 (120 min). This indicates that higher COD removal can be achieved with less charge
(and hence energy) consumption, but requires longer time duration.
Effect of pH
pH influences the chemical form of the oxidant present in the electrolyte. The electrolysis was
carried out at four different pH. The electrochemical reaction in presence of chloride ions can be
represented as in reactions (8) – (11);
2Cl- → Cl2(aq) + 2e- (Standard potential of Cl2 (Eo = 1.40 V vs. SHE)
(8)
Cl2(aq) + H2O → HOCl + H+ + Cl- (Eo of HOCl = 1.49 V vs. SHE)
(9)
HOCl ↔ H+ + OCl- (Eo of ClO- = 0.89 V vs. SHE)
(10)
TB + OCl- → Intermediates → CO2 + H2O + Cl-
(11)
The pH variation influences the equilibrium in reaction (10) and the HOCl predominates in the
pH range 3-8 but above pH 8, ClO- is the major candidate [26,31]. The oxidation by HOCl and
Cl2(aq) [5,6] is therefore expected to be more favorable and faster at near neutral pH. Furthermore,
reactions in reaction (12) and (13) are expected to take place on the active anode such as Pt. The
MOx(HOCl) mediates the oxidation unselectively and hence higher COD removal efficiency was
noticed [26].
doi: 10.5599/jese.2013.0039
175
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
MOx(•OH) + Cl- → MOx(HOCl) + e-
(12)
-
MOx(HOCl) + TB → Intermediates → MOx + CO2 + H2O + Cl + H
+
(13)
The effect of pH on color and COD removal with electrolysis time is shown in Figs. 5A and 5C,
respectively. Fig. 5B illustrates the slow decrease in the absorption intensity of the peak in the
visible region with increase in pH (11.8). It is evident that color and COD removal is above 90 % in
pH 3.1 and 6.2. As the pH increased to 9.0, the rate of color and COD removal reduced to 82 % and
became 67 % in pH 11.8.
Figure 5A. Effect of pH on color removal
Figure 5B. Variation in the intensity of peak at 590 nm in pH 11.8
176
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
Figure 5C. Effect of pH on COD removal; conditions cNaCl, 0.2 % (w/v),
current density – 93 mA cm-2, [TB] – 50 mg L-1, electrolysis time – 60 min
Complete decoloration was achieved in all pH except with pH 11.8, for which 88 % color
removal was achieved. The difference in COD removal in pH 3.1 and pH 6.2 was only 3 % and in
both the cases it was above 90 %. But COD removal decreased above pH 9.0. Hence, for further
studies, pH 6.2 was selected.
Effect of Initial Dye Concentration
At the optimized operating conditions of electrolysis process, only fixed amount of oxidants are
generated at the anode. The energy would be simply lost if the generation of oxidants is more
than that required to oxidize the available organics in the wastewater. Sufficient concentration of
organics should be available for the efficient utilization of generated oxidants. The TB solutions of
different concentrations ranging from 25 to 100 mg L-1 were prepared and electrolysed under
optimized operating conditions (93 mA cm-2, pH 6.3 and 0.2 % NaCl concentration). The color and
COD removal decreased gradually with increase in initial concentration of TB. Fig. 6 shows the
trend of color and COD removal with time for different initial concentrations of TB dye. A 100 %
decolorization was achieved within 30 min for all initial concentrations of TB. But 100, 91, 75 and
67 % COD removal was attained with 25, 50, 75 and 100 mg L-1 initial TB concentrations
respectively after 60 min electrolysis.
At initial concentration of 25 mg L-1, the in situ generated oxidants were efficienty oxidized the
TB completely. But, the dye concentration was less than the amount of oxidants available in the
electrolysis cell (dye concentration is the limiting factor). When the TB dye concentration was
increased to 100 mg L-1, the amount of oxidants was less than the equivalent value, not sufficient
to degrade the entire amount of TB (oxidant concentration is the limiting factor). Under the
currrent density - 93 mA cm-2 and 60 min of electrolysis, the COD removal was 92 % for the initial
concentraiton of 50 mg L-1 chosen as the optimum condition.
doi: 10.5599/jese.2013.0039
177
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
Figure 6. Effect of initial concentration of TB on COD and color removal.
Kinetics of TB Degradation
During the electrolysis, the concentration of TB in synthetic wastewater decreased
exponentially for all applied current densities but the rate of oxidation increased with increase in
current density, indicating that the degradation of TB followed the first order kinetics [32]. If we
consider that the oxidants generated on electrolysis spontaneously react with TB, then from the
steady state approximation, the concentration of oxidants (Ox) can be estimated [32] and the rate
of oxidation of TB can be expressed as in Eq. (13) and (14);
Table 2. Degradation kinetics data
Parameters
j / mA cm-2*
Initial concentration of TB, mg L-1 #
37
55
74
93
111
25
50
75
100
kapp / min-1
0.022
0.032
0.037
0.044
0.053
0.058
0.043
0.026
0.021
Regression
0.867
0.978
0.967
0.974
0.993
0.974
0.986
0.92
0.841
-1
-2
* TB concentration - 50 mgL ; # Current density - 93 mA cm
[
]
[
]
][
[
]
(13)
(14)
On integrating the above equation;
[
]
[
]
(15)
where [Ox] is the concentration of oxidants, kapp is the apparent pseudo first-order rate constant
([Ox] is considered as very high), COD0 and CODt are the COD at time 0 and t minutes of
electrolysis respectively.
The slope gives kapp which are tabulated in Table II. The first order rate constant steadily
increased with increase in applied current density and decreases with increase in initial
178
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
concentration of TB dye (Fig. 7A and 7B). The regression value indicates the deviation from the
first order reaction rate equation for current density 37 mA cm-2 and TB concentration 100 mg L-1
can be attributed to the fact that at lower applied current density and high initial concentration of
TB, the active concentration of oxidants is the limiting factor. Moreover, the area of the anode
used in all these experiments was only 0.57 cm2.
Figure 7A. Plot of ln (C0/Ct) vs. time for different applied current densities
Figure 7B. Plot of ln(C0/Ct) vs time for different initial dye concentrations
The oxidants generated on the surface of such a small area of Pt anode under the current
density of 37 mA cm-2 might not be so high to satisfy the steady state approximation for first order
doi: 10.5599/jese.2013.0039
179
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
kinetics. Similarly, oxidants generated under the current density of 93 mA cm-2 and 100 mg L-1
initial concentration of TB dye, a similar deviation was observed.
Spectroscopic Analysis
UV-vis spectroscopic analysis
UV-Vis spectrum of TB dye showed three major peaks at 235, 318 and 590 nm. The peak at 590
nm corresponds to the chromophoric azo group. On electrolysis (50 mgL-1 dye, 93 mAcm-2), the
intense blue color of the solution turned in to wine red in the first 10 min, then transformed slowly
into pale yellow color, which persisted till the end. The intensity of the peak at 590 nm rapidly
decreased to zero absorbance on electrolysis, which can be ascribed to the cleavage of azo group.
Figure 8A. UV-Visible absorbance of TB at different time intervals of electrolysis
Figure 8B. Absorbance of residue obtained by the evaporation of electrolyzed TB solution
180
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
For the first 10 min of electrolysis, the peak at 585 nm showed blue shift and gradually reached
zero absorbance. The blue shift can be attributed to the detachment of auxochromes from the
parent dye structure during electrolysis. A new peak at 407 nm was observed, which can be
ascribed to the formation of a fragment from the parent dye. This peak diminishes very slowly. The
pale yellow color is due to the absorption at 412 nm, (absorption color – violet (412 nm),
perceived color – yellow) which reduced slowly with time (Fig. 8A). Peak at 318 nm reduced with
time, reached minimum value and again increased with a blue shift at 288 nm. This peak can be
assigned to the low molecular weight oxidized fragments with conjugated π bonds in which nπ*
and ππ* transitions are allowed (-C=O, -C=C-, -C=N-, -(CO)NH-). Similar effect was observed by
Hanene et al. [34] in the degradation of Amido black (AB) on boron doped diamond electrode.
The electrolyzed dye solution was evaporated at lower temperature with reduced pressure.
UV-Vis spectrum of the solid thus obtained was taken by dissolving it in water. Interestingly, the
peak at 288 nm was absent. This observation validates our suspicion that compounds leading to
this peak were low molecular volatile compounds (Fig. 8B). After 40 min electrolysis, the UV-Vis
spectrum of the residue obtained by evaporation does not show any peak, except a peak in 200 to
220 nm range. This is due to the small amount of aromatic compounds resistant to indirect
oxidation remained in the solution, which also accounts for the residual COD after 60 min.
FT-IR analysis
The FT-IR spectrum of TB dye (Fig. 9A) exhibits a characteristic band at 1579 cm-1 corresponding
to azo group [34, 35]. The bands at 1492 cm-1 and 1423 cm-1 correspond to C=C aromatic ring
stretching in combination with C=N [34] and methyl bending respectively. The keto form of the TB
is dominant (Table I) [36]. The peak at 1617 cm-1 is due to α,β-unsaturated C=O stretch. The peaks
at 1339, 1188 and 1128 cm-1 are due to aromatic amine C-N and -SO3- (S=O) stretch [35]. The peak
obtained at 1042 cm-1 is due to C-O. The broad doublet peak at 674 cm-1 and 644 cm-1 indicates
the aromaticity. In Fig. 9B and 9C, the peaks at 1579, 1492, 1423 cm-1 and 1339, 1128, 1042,
674 cm-1 disappeared completely indicating the breakage of corresponding groups.
Figure 9. FT-IR spectra of A) TB dye B) residue obtained by evaporation of sample electrolyzed
for 15 min C) electrolyzed for 40 min
doi: 10.5599/jese.2013.0039
181
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
The peak at 1229 cm-1 disappeared in Fig. 9C, indicating that group corresponding to this frequency is susceptible to oxidation by the electrochemically generated oxidants [37]. The peak at
1119 cm-1 shifted to 1108 cm-1. While peak 674 cm-1 disappeared completely, 644 cm-1 shifted to
621 cm-1. In Fig. 9C the peak at 1637 cm-1 is due to the carbonyl stretch of carboxylate salts,
1380 cm-1 is due to C-N of aliphatic amines. This suggests the formation of carboxylic acids and
amines. 1008 cm-1 is devoted to C-O stretch and peak at 966 cm-1 is due to the formation of ClO3and OCl- during electrolysis [34,35]. These changes in the FT-IR spectrum are the clear evidence for
the degradation of TB into simpler molecules, like aromatic and aliphatic amines and carboxylic
acids.
Identification of intermediate products and degradation pathway
The intermediates of TB degradation were identified by gas chromatography mass spectrometry (GC-MS). On the basis of the intermediates and end products as depicted by GC-MS, a
possible degradation pathway is proposed in Fig. 10. GC-MS revealed that the parent TB molecule
was completely disintegrated into simpler molecules.
Figure 10. A possible degradation pathway of TB
182
A. N. Subba Rao at al.
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
Decomposition of TB was initiated with the cleavage of azo bonds resulting in the formation of
three different intermediates 1 (3,3'-dimethyl-1,1'-bi(cyclohexa-2,5-dien-1-ylidene)-4,4'-diimine), 2
(5-amino-3,4-dihydroxynaphthalene-2,7-disulfonic acid) and 3 (2,5,7-trihydroxy-3-[(4-hydroxy-2methylphenyl)diazenyl]naphthalene-1,4-dione). Intermediate 3 resulted from the cleavage of one
of the azo bonds in the parent molecule was found in very small concentration. The absorption at
412 nm in UV-Vis spectroscopy can be attributed to this intermediate. The sulfonic group in
intermediate 2 renders it water soluble. A foamy layer was formed on the surface of the
electrolytic bath solution during electrolysis gradually disappeared with time. This can be
attributed to the formation of intermediates 1 and 3 at the beginning of electrolysis. Further
oxidation of intermediates 2 and 3 produced aromatic acids and phenols, 5 (naphthalene1,2,3,6,8-pentol), 6 (3,5-dihydroxybenzene-1,2-dicarboxylic acid), 9 (benzene-1,2,4-triol). Aliphatic
acids were generated on the oxidative ring opening of 4, 6 and 9, which decomposed into CO2 to
accomplish the degradation process.
Conclusion
The TB dye synthetic wastewater was successfully treated in presence of Cl- with Pt foil as
anode material. The removal of TB was dependent on the applied current density, pH, type of
supporting electrolyte and concentration of TB dye and NaCl. The degradation of TB was achieved
only in presence of NaCl as supporting electrolyte suggesting that the active chlorine species (Cl2,
ClO-, HOCl) generated during the electrolysis played crucial role in the oxidation of TB. The rate of
removal of TB increased with increase in current density and NaCl concentration and decreased
with rise in initial concentration of TB and pH. Under the optimum conditions (current density –
93 mA cm-2, pH - 6.2, NaCl concentration - 0.2 %, initial TB concentration – 50 mgL-1) maximum
COD and color removal achieved after 60 min electrolysis was 92 % and 100 % respectively. The
first order rate constant for COD removal at these conditions was 0.044 min-1. The UV-Vis
spectroscopy, FT-IR and GC-MS analysis confirmed the complete degradation of TB into simple
aliphatic carboxylic acid and CO2 suggesting that the treatment of wastewater containing TB dye as
pollutant can be successfully accomplished by electrochemical method.
Acknowledgement: We thank department of chemistry, Kuvempu University, Shankaraghatta and
UGC, New Delhi for their financial support.
References
[1] H. Zollinger, Synthesis, Properties of Organic Dyes and Pigments. In: Color Chemistry. New
York, USA: VCH Publishers; (1987) pp-92-102
[2] M. B. Ibrahim, N. Poonam, S. Datel, M. Roger, Bioresour Technol. 58 (1996) 217-227
[3] E. Forgacs, T. Cserháti, G. Oros, Environ Inter. 30 (2004) 953971
[4] W. Przystaś, E. Zabłocka-Godlewska, E. Grabińska-Sota, Water, Air, Soil Pollut. 223 (2012)
1581-1592
[5] S. Song, J. Fan, Z. He, L. Zhan, Z. Liu, J. Chen, X. Xu, Electrochim. Acta 55 (2010) 3606-3613
[6] C. A. Martinez-Huitle, E. Brillas, Appl Catal B: Environ 87 (2009) 105-145
[7] F. Zaviska, P. Drogui, J. F. Blais, G. Mercier, J. Appl. Electrochem. 39 (2009) 2397-2408
[8] J. L. Nava, M. A. Quiroz, C. A. Martínez-Huitle, J. Mex. Chem. Soc. 52 (2008) 249-255
[9] E. Kusmierek, E. Chrzescijanska, M. Szadkowska-Nicze, J. Kaluzna-Czaplinska, J. Appl.
Electrochem. 41 (2011) 51–62.
[10] R. G. da Silva, S. A. Neto, A. R. de Andrade, J. Braz. Chem. Soc. 22 (2011) 126-133
doi: 10.5599/jese.2013.0039
183
J. Electrochem. Sci. Eng. 3(4) (2013) 167-184
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
TRYPAN BLUE ELECTROCHEMICAL OXIDATION
T. Panakoulias, P. Kalatzis, D. Kalderis, A. Katsaounis, J. Appl. Electrochem. 40 (2010)
1759-1765
L. Jiancheng, Y. Jie, L. Weishan, H. Qiming, X. Hongkang, J. Electrochem. Sci. Eng. 2 (2012)
171-183
D. A. Carvalho, J. H. B. Rocha, N. S. Fernandes, D. S. da Silva, C. A. Martínez-Huitle, Latin
Am. Appl. Res. 41 (2011) 127-133
M. Panizza, G. Cerisola, Ind. Eng. Chem. Res. 47 (2008) 6816-6820
J. Marugán, M. J. López-Muñoz, R. van Grieken, J. Aguado, Ind. Eng. Chem. Res. 46 (2007)
7605-7610
Health Hazard Alert - Benzidine-, o-Tolidine-, and o-Dianisidine- Based Dyes. NIOSH Report
DHEW (NIOSH) Publication No. 81-106, December 1980.
H. B. Mansour, D. Corroler, D. Barillier, K. Ghedira, L. Chekir, R. Mosrati, Food Chem.
Toxicol. 45 (2007) 1670-1677
Toxicology data network, National Library of Medicine, Hazardous Substance Data Bank
(HSDB), U.S department of Health and Human services. http://toxnet.nlm.nih.gov/cgibin/sis/search/f?./temp/~s8y7RI:1, August, 2013
P. Jiang, J. Zhou, A. Zhang, Y. Zhong, J. Environ. Sci. 4 (2010) 500-506
V. Jhanji, E. Chan, S. Das, H. Zhang, R. B. Vajpayee, Eye 25 (2011) 1113-1120
C. Lüke, M. Lüke, T. S. Dietlein, A. Hueber, J. Jordan, W. Sickel, B. Kirchhof, Br. J.
Ophthalmol. 89 (2005) 1188-1191
B. T. van Dooren, W. H. Beekhuis, E. Pels, Arch. Ophthalmol. 122 (2004) 736-742
M. Veckeneer, K. van Overdam, J. Monzer, K. Kobuch, W. van Marle, H. Spekreijse, J. van
Meurs, Graefe’s Arch. Clin. Exp. Ophthalmol. 239 (2001) 698-704
M. M. Turbow, Nature, 206 (1965) 637.
C. H. Waddington, M. M. Perry, J. Embryol. Exp. Morph. 4 (1956) 110-119
S. A. Elfeky, A. S. A. Al-Sherbini, Kinet and Catal. 52 (2011) 391-396
A. L. T. Fornazari, G. R. P. Malpass, D. W. Miwa, A. J. Motheo, Water, Air, Soil Pollut. 223
(2012) 4895-4904
M. Gaber, N. A. Ghalwa, A. M. Khedr, M. F. Salem, J. Chem. 2013 (2013) 1-9
C. Song, J. Zhang, PEM fuel cell electrocatalysts and catalyst layers, fundamentals and
applications, Spinger-Verlag London Limited, Vancouver, Canada, 2008, p. 89-134
http://www.springer.com/978-1-84800-935-6
R. B. Moghaddam, P. G. Pickup, Electrochim. Acta 97 (2013) 326-332
G. R. P. Malpass, D. W. Miwa, R. L. Santos, E. M. Vieira, A. J. Motheo, Environ. Chem. Lett.
10 (2012) 177-182
M. Panizza, G. Cerisola, Chemosphere 77 (2009) 1060-1064
H. Akrout, L. Bousselmi, Arab. J. Geosci. (2012) 5033-5041
H. Z. Zhao, Y. Sun, L. N. Xu, J. R. Ni, Chemosphere 78 (2010) 46-51
S. Raghu, C. W. Lee, S. Chellammal, S. Palanichamy, C. A. Basha, J. Hazard. Mater. 171
(2009) 748-754
J. P. Graham, M. A. Rauf, S.Hisaindee, M. Nawaz, J. Molecul. Struc. 1040 (2013) 1-8
S. S. Vaghela, A. D. Jethva, B. B. Mehta, S. P. Dave, S. Adimurthy, G. Ramachandraiah,
Environ. Sci. Technol, 39 (2005) 2848-2855
© 2013 by the authors; licensee IAPC, Zagreb, Croatia. This article is an open-access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/)
184