American Journal of Anal yt ical Chemistry, 2011, 2, 814-819
doi:10.4236/ajac.2011.27093 Published Online November 2011 (http://www.SciRP.org/journal/ajac)
Multiwall Carbon Nanotube Modified Electrochemical
Sensor for Reactive Black 5
Velliangiri Sreeja1, Raman Sasikumar2, Marimuthu Alagarsamy2, Paramasivam Manisankar2*
1Vellalar College for Wo men (Autonomous), Tamil Nadu, India
2Department of Industrial Chemistry, Alagappa University, Tamil Nadu, India
Received July 18, 2011; revised August 19, 2011; accepted August 29, 2011
Abstract
Cyclic voltammograms of reactive black5 (RB5) at different pHs in the range 1.0 - 13.0 on multiwall carbon
nanotube modified glassy carbon electrode revealed the presence of one well-defined irreversible anodic
peak around 975 mV in acidic and neutral pHs. Adsorption controlled oxidation observed at acidic pH 1.0
resulted in the maximum peak current response in cyclic voltammograms. A systematic differential pulse
stripping voltammetric studies were carried out using the modified electrode at pH 1.0. The accumulation
parameters, accumulation potential and time were optimized for maximum adsorption of the dye which was
ascertained from the SEM photographs and XRD results. The stripping parameters were optimized and cali-
bration was made under optimum conditions. The range of study was from 0.5 ppm to 100 ppm and the
lower limit of determination was 100 ppm. Five identical experiments were carried out and the RSD value
obtained was 2.5% suggesting good reproducibility. The proposed method was successfully applied to de-
termine the concentration of dye in the fabric and wastewater after dyeing.
Keywords: Cyclic Voltammetry, Reactive Black 5, Stripping Voltammetry, Multiwall Carbon Nanotubes
1. Introduction
An important milestone in the history of carbon materials
is the discovery of carbon nanotubes (CNTs) [1] having
two distinct types of structures namely single walled and
multiwalled. As a consequence of the excellent electro-
nic and conducting properties of CNTs, electrodes modi-
fied with CNTs have demonstrated to improve the elec-
troanalytical performance of different species. Due to
their uniqueness, CNTs have received enormous atten-
tion for the preparation of electrochemical sensors as it
was extensively reviewed [2-5]. The subtle electronic
behavior of CNTs reveals that they have the ability to
promote electron-transfer reaction when used as electro-
de materials. Recently CNT film coated electrodes have
received increasing attention in analytical studies [7-9].
However a major barrier for developing the CNT modi-
fied electrode is the insolubility of CNTs in usual media
[10] and many efforts have been made to disperse CNTs
into suitable solvents such as DMF [11], acetone [12]
and concentrated sulphuric acid [13]. Yuan-hai Zhu et al.
[14] functionalized MWCNTs using nitrating mixture
and neutralized with dil. NaOH. The modified MW-
CNTs were water soluble and used for the determination
of phenylephrine. In recent days, a noncovalent method
[15] has been developed and ported for solubilizing
MWCNTs functionalized with Congo red. Surfactants
are a special kind of amphiphilic molecules, which can
spontaneously adsorb at the interfaces or assemble into
micelles in solutions, forming various regulated struc-
tures at electrode surfaces or in solutions. This resulted
in extensive applications in electroanalysis [16]. MWC-
NTs modified electrodes fabricated in the presence of
surfactants resulted in high sensitivity and selectivity.
MWCNT/GCE modified electrode fabricated in the pre
sence of SDS exhibited enhanced sensing of organic po-
llutants [17,18]. Hence the present work, we used anionic
surfactant, sodium dodecyl sulphate (SDS) to disperse
MWCNTs.
Reactive dyes are the main group of dyes used in the
textile industry [19]. They are very effective in fabric
dyeing due to the reactive groups capable of forming co-
valent bonds with a hydroxyl or amino group on the fiber.
Inefficiency in the dyeing process resulted in 10% - 15%
of all dyestuff being lost directly to wastewater [20].
Billions of kilograms of dyes are produced per annum

815 V. SREEJA ET AL.
and are used in diverse applications including textile
dyes, paints, pigments, printing inks and food colouring.
In general about 20% of dye loses would have entered
the environment via the wastewater treatment facilities
[21,22]. In that water body dyes have been shown poten-
tially to have a long half-life in the environment. Ana-
lytical chemistry in pollution control is playing an ever-
increasing vital role in international trade and industry.
The confidence and reliability of analytical results must
play a major part in world trade and industrial pollution
control. The methods used for monitoring these dyes
during dyeing and washing are generally based on chro-
matography and spectrophotometry [23]. The determina-
tion of dyes by spectrophotometry has presented special
problems owing to lack of selectivity and sensitivity.
Additional complications are noticed in chromatography
as this group of compounds is usually ionic and of high
polarity, as well as nonvolatile and thermally unstable.
HPLC, at its current stage of development, is clearly not
a method for analytical problems with a high repetition
rate because the receptive condition of the system re-
quires 24 to 36 hours. On the other hand, electroanalysis
is a manageable method, which is suitable for various
problems [24]. Reactive Black5 (RB5) is a commonly
and widely used reactive dye and hence development of
sensitive stripping voltammetric method for its determina-
tion using MWCNT modified GCE is undertaken.
2. Experimental
2.1. Reagents and Apparatus
Multi-Walled CNTs (I.D.x length (2 - 15) nm × (1 - 10)
µm, produced by arc method) purchased from the Sigma
Aldrich and AR sodium dodecyl sulphate (SDS) from
Merck. The reactive black 5 was obtained from Astick
Dyestuff pvt. Ltd, Mumbai, India. The stock solution
was prepared by dissolving the substance in double dis-
tilled water purified from TKA purification system. For
studies aqueous media, 0.1 M H2SO4 (for pH 1.0), Brit-
ton Robinson Buffers (for pH 4.0, 7.0, 9.2) and 0.1 M
NaOH (for pH 13.0) were used. The electrochemical
studies were performed with a CHI 760 C electrochemi-
cal workstation (CH Instruments, USA). The MWCNT
/GCE was working electrode. Platinum wire and Ag/
AgCl were employed as an auxiliary and reference elec-
trode respectively. To get reproducible results, great care
was taken in the electrode pretreatment.
2.2. Fabrication of MWCNT/GCE
1 mg MWCNT was dispersed in 1 ml of 0.1 M sodium
dodecyl sulphate using an ultrasonicator to give black
suspensions. Cast films were prepared by placing 5 L of
the MWCNT/surfactant suspension on GCE and then
evaporating it in an oven at 50˚C.
3. Results and Discussion
3.1. Cyclic Voltammetric Studies of RB5
Cyclic voltammogram of RB5 using GCE and MWCNT/
GCE were recorded and presented Figure 1. Only one
oxidation peak was observed in both cyclic voltammo-
grams. The oxidation peak appeared at lower potential
with higher current when MWCNT/GCE was employed.
This indicates facile oxidation at this modified electrode
and hence develop voltammetric studies of RB5 passed
using MWCNT/GCE. The oxidation peak was found to
shift anodically with increase in scan rate. The plot of
peak current versus scan rate resulted in straight line with
good correlation whereas lesser correlation was observed
between Peak current and square root of scan rate. Sug-
gesting adsorption-controlled oxidation. Log of peak cu-
rrents were correlated with the log of scan rate and it re-
sulted in straight line with slope 0.6004, conforming ad-
sorption-controlled oxidation of RB5 in this acidic pH.
Absence of peak in the reverse scan and fractional αn
value determined from slope of the plot Ep vs. log re-
vealed irreversible oxidation. The dye concentration was
varied from 300 ppm to 1000 ppm at constant scan rate
of 100 mV/s. The peak potential of the anodic peak in-
creased with increase in concentration. The peak current
also showed increasing trend with increase in concentra-
tion. Adsorption and higher current response in the cv
studies suggested the development of adsorptive strip-
ping procedure for the determination of RB5.
Figure 1. Cyclic voltammogram of 500 ppm RB5 on (a)
GCE; (b) MWCNTs/GCE at pH-1.0 scan rate 100 mV/s.

V. SREEJA ET AL.
816
3.2. Adsorption of RB5 on MWCNT/GCE tential, accumulation time was varied between 5 s and 40
s and maximum peak current in the DPSV was observed
at 30 s under the optimum accumulation conditions, RB5
was accumulated and the adsorption of RB5 was con-
firmed by many preconcentration and stripping voltam-
metric were investigations were performed for accumu-
lation potentials (Eacc) varying from –1000 mV to 1000
mV at an accumulation time of 15 s. Differential pulse
stripping voltammograms (DPSV) were recorded and
maximum Peak current was observed. Which was fixed
as the optimum accumulation potential. Since the dye
molecule is anionic due to the presence of sulphonate ion
in the dye RB5, the effective adsorptive accumulation is
in the positive potential. Differential pulse stripping volt-
ammograms were recorded for the adsorbed RB5 under
optimized accumulation conditions by varying pulse am-
plitude maximum peak current conditions were found out
and the results are presented in Table 1.
SEM and XRD analysis. The SEM micrographs were re-
corded for the MWCNT/GCE surface and adsorbed RB5
and presented in Figures 2(a)-(b) respectively. The SEM
figure of MWCNT/GCE is entirely different from that of
dye adsorbed. Figure 2(b) shows well developed rod like
structure for the dye with approximately 100 nm dia.
Comparison of the two SEMs confirms the strong ad-
sorption of the dye on MWCNT/GCE. The X-ray dif-
fractograms of the MWCNT/GCE and RB5 adsorbed on
MWCNT/GCE are presented in Figures 3(a)-(b) respec-
tively. The XRD results reveal different semi-cry- stal-
line nature of both.
3.3. Differential Pulse Stripping Voltammetry
The Differential pulse stripping voltammetric behaviour
of RB5 is shown in Figure 4. At this accumulation po-
Figure 2. SEM photographs of (a) MWCNTs deposited on GCE; (b) RB5 deposited on MWCNTs/GCE.
Figure 3. XRD behaviour of (a) MWCNTs deposited on
GCE; (b) RB5 deposited on MWCNTs deposited on GCE. Figure 4. DPSV of 0.3 ppm RB5 standard sample at pH 1.0 under optimum condition.

817 V. SREEJA ET AL.
Table 1. Optimum experimental conditions of RB5 for dif-
ferential pulse stripping voltammetry .
Variables Range examined Optimum value
Deposition potential (mV) –1000 to 1000 0
Deposition time (Sec) 5 to 40 30
Amplitude (mV) 25 to 150 100
Pulse width (mSec) 25 to 150 100
Scan increment (mV) 4 to 10 10
3.4. Analytical Characteristics
Differential pulse stripping voltammograms at different
concentrations of RB5 were recorded under maximum
peak current conditions. From the results, a linear cali-
bration graph was obtained (Figure 5) indicating linear
dependence between the two. The range of determination
was found between 0.5 ppm to 100 ppm. The limit of de-
tection was 100 ppb. The reproducibility of stripping
signal was realized in terms of relative standard devia-
tion for 5 identical measurements carried out and found
to be 2.5%.
3.5. Determination of RB5 in the Wastewater
To validate the proposed method for the determination of
RB5 on real samples, the dye content in the wastewater
obtained from the lab scale dying process was deter-
mined by employing the calibration plot. A cotton fabric
was dyed with RB5 in the laboratory as per the proce-
dure described here. For the dyeing process, the dye bath
was set with 0.5 g of the fabric at 40˚C for 15 minutes.
Additions of 0.5 ml of 5% sodium carbonate solution, 1
ml of 5% dye solution, 0.5 ml of 3% sodium chloride
solution, 0.5 ml of wetting agent were added. The mate-
rial to liquor (MLR) ratio was kept at 1:25 and the total
volume was kept at 50 ml. After the dyeing, the dyed
cotton fabric was taken out, cooled, washed with cold
water and dried. The spent dye liquor or wastewater of
the dye bath after dying was collected from the labora-
tory scale dying unit.
The spent dye liquor was subjected to stripping analy-
sis under optimized conditions proposed from the DPSV
studies. The spent dye liquor containing the unspent dye
was made acidic by adding 0.1 M H2SO4 and the total
volume was kept at 50 ml. The pH of the solution was
ascertained and kept at 1.0. 10 ml of this solution was
taken in the cell and the DPSV experiment was carried
out under optimum conditions using MWCNT modified
glassy carbon electrode. The differential pulse stripping
voltammogram is presented in Figure 6. The stripping
peak current was measured and substituted in the calibra-
tion equation. Thus the amount of RB5 present in the
spent dye liquor was determined. The same DPSV deter-
mination was repeated for 6 times and the amount of
RB5 was determined in each experiment. With the RSD
value of 2.9%, the concentration of the dye in the spent
dye liquor was determined to be 9.2 ± 0.2 ppm with the
help of the calibration plot.
4. Conclusions
Based on this study, it is concluded that the adsorptive
stripping voltammetric measurements of RB5 on MWC-
NT/GCE has resulted in an efficient method for the de-
termination of RB5. The range of determination was
found in between 0.5 ppm to 100 ppm. The limit of de-
tection was 100 ppb. High sensitivity, good reproducibility
Figure 5. Calibration plot of DPSV of RB5 at pH 1.0 under
optimum condition.
Figure 6. DPSV of 0.3 ppm RB5 real sample at pH 1.0 un-
der optimum condition.

V. SREEJA ET AL.
818
and simple instrumentation are the added advantages.
This method can be easily applied for the determination
dye in the waste water.
5. Acknowledgements
Mr. R. Sasikumar acknowledges UGC, New Delhi for
providing Research Fellowship in Science for Meritori-
ous Students.
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