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Health and the Environment Journal, 2012, Vol. 3, No. 1
Cyclic Voltammetric Study of Reactive Black 5 Dye at a Mercury Electrode
Nur Syamimi Z, Mohamad Hadzri Y, Zulkhairi O
School Of Health Sciences, Universiti Sains Malaysia, Health Campus, 16150 Kubang Kerian, Kelantan, Malaysia
Corresponding author email: [email protected]______________________________________________________________________________ ABSTRACT: A cyclic voltammetry (CV) study of Reactive Black 5 Dye (RB5) in Britton- Robinson buffer (BRB) using a hanging mercury drop electrode (HMDE) is described. CV was carried out by anodic and cathodic potential scan through within the range of + 200 to - 950 mV with no accumulation time. The effect of the different scan rates and pH of BRB on the peak height and peak potential of the analyte were also studied. The results show that in pH 2 to 5, reduction process on the hanging mercury electrode gave three cathodic peaks at + 75 to -151 mV for the first peak, - 98 to - 330 mV for the second peak and – 395 to -630 mV for the third peak. Only single reduction peak was obtained at -460 to -675 mV in pH 6 to 8 and two reduction peaks were obtained at - 530 to -640 mV for the first peak and -730 to -840 mV for the second peak in pH 9 to 12. All potentials were referred against Ag/AgCl as the reference electrode. The BRB pH 4.0 was noted as the best condition for the detection of RB5 in acidic medium and pH 9.0 in basic medium since both media gave maximum peak current. Effect of the scan rate and pH of BRB on both responses have proved that the reduction of RB5 is an irreversible reaction, pH dependent and the limiting current is adsorption controlled. Future work will cover study of cathodic stripping voltammetry of RB5 at the same type of electrode.
Keywords : Cyclic voltammetry, Britton-Robinson buffer, hanging mercury dropping electrode (HMDE) and Reactive Black 5 (RB5) Introduction
In the recent years, growing concern and
PeláezCid et al. (2008) dyes are
awareness about issues on environment have
brought together both analytical and material
science researchers to investigate appropriate
monitoring various pollutants worldwide.
pharmaceutical, printing inks, textile and
in waste aqueous effluents can contribute
[2, 7-naphthalenedisulfonic acid, 4-amino
-5-hydroxy-3,6-bis((4((2(sulfooxy) ethyl)
damage (Tonlé et al., 2007). Dyes are
sulfonyl) phenyl) azo)-tetrasodium salt]
substances which have the affinity to the
FIGURE 1, is categorized in vinyl
sulphonate azodye due to the presence of
Health and the Environment Journal, 2012, Vol. 3, No. 1
This paper describes the cyclic voltammetric
(Tunc et al., 2009). Textile, printing, and
mercury dropping electrode (HMDE) as the
widely used technique to acquire qualitative
information on electrochemical reactions
mg/L is toxic to fish, the concentration of
considerable information about the kinetic of
RB5 above 1000 mg/L leads to inhibition of
the system, number of electron transferred,
wastewater bacteria activity and it release
FIGURE 1: Chemical structure of RB5 dye Materials and methods Reagents
All solutions were prepared using double
distilled water and analytical grade reagents.
using an electrochemical workstation. All
0.10 g of RB5 dye was dissolved in 50.0 mL
double distilled water to produce 2000 ppm
RB5 dye stock solution. A stock of Britton-
with VA stand equipped with three electrode
Robinson-Buffer (BRB) solution (0.04 M) as
supporting electrolyte prepared as follows;
2.47 g boric acid (Fluka), 2.30 mL acetic
acid (Ashland Chemical) were diluted to 1 L
nitrogen for at least 20 mins. The RB5 dye
used to adjust the pH of the BRB solution to
solution was purged by gas for 5 mins and
allowed to stand for 3 s in order to obtain
cyclic voltammogrammes. Other parameters
used are medium drop size, stirrer speed
(2000rpm), initial potential, Ei (200 mV),
Health and the Environment Journal, 2012, Vol. 3, No. 1
respectively. Only single electroreduction
The concentration of RB5 dye in cell is 200
BRB of pH 6-8. Two electroreduction peaks
were observed (-530 to -640 mV and -730 to
-840 mV) in BRB pH 9-12. Cathodic cyclic
Results and Discussion
0.04 M BRB solution respectively at pH 4.0,
7.0 and 9.0 respectively with a scan rate of
25 mV/s were shown in FIGURE 2a, 2b
electroreduction peaks at +75 to -151 mV, -
FIGURE 2a : Cathodic cyclic voltammogram of 200 ppm RB5 dye in Health and the Environment Journal, 2012, Vol. 3, No. 1
FIGURE 2b: Cathodic cyclic voltammogram of 200 ppm RB5 dye in FIGURE 2c : Cathodic cyclic voltammogram of 200 ppm RB5 dye in Health and the Environment Journal, 2012, Vol. 3, No. 1
No peak was observed in anodic direction of
mechanism for the irreversible reduction of
the reverse scans in all pH of BRB solution
RB5 dye at the mercury electrode surface is
suggesting that the irreversible nature of an
electrode process (Gupta et al, 2010; Gupta
et al, 2010; Jain et al., 2007). A suggested
2e− + 2H+ + (R–N=N–R1) (R–NH–NH–R1) (1)
2e− + 2H+ + (R–NH–NH–R1) (R–NH2) + (R1–NH2) (2)
Equation 1: Suggested mechanism for the irreversible reduction of RB5 dye
A mechanism for azo reduction involves two
stages as given in reaction (1) and (2) above
(Karatas et al., 2009). An unstable colourless
The influence of pH of BRB on the cyclic
voltammetric behavior of RB5 dye has been
reaction (1) and the azo bond can reform
studied in the pH range of 2-12 with a scan
upon oxidation and regain the colour. R and
rate of 25mV/s. The results show that peak
potential, (Ep) of RB5 dye shifts to a more
play part as terminal electron acceptors are
(FIGURE 3) indicating that the reduction
utilized by carriers in the electron transport
chain. Hence, they regenerate themselves,
process involves the coupling of hydrogen
fortuitously reducing azo bond and finally
addition, the shifting of Ep is towards a more
negative value with increasing H+ in the
electrode reduction process (Jain et al.,
FIGURE 3: Effect of various pH of BRB on Ep of RB5 dye Health and the Environment Journal, 2012, Vol. 3, No. 1
In acidic medium, maximum peak current, Ip
maximum Ip of 180 nA is obtained at pH 9.0
(FIGURE 4b). Therefore, pH 4.0 and 9.0
(FIGURE 4a). In the basic medium, FIGURE 4a: Effects of pH 2-7 of BRB on Ip of RB5 dye FIGURE 4b: Effects of pH 8-12 of BRB on Ip of RB5 dye. Health and the Environment Journal, 2012, Vol. 3, No. 1
Effects of scan rate Effect of scan rate, (v) has been studied from
increase of Ip. Examination on the linear
relationship between Ip versus v (FIGURE
concentration of RB5 dye at 200 ppm. The v5) indicates that RB5 dye was adsorbed on
is found to affect on both Ip and Ep. When v,
is increased the Ep shifted towards more
negative direction and accompanied by an
FIGURE 5 : Plot of Ip versus v for 200 ppm RB5 dye in BRB pH 4.0 and 9.0
The linear plot of log Ip versus log v as
media is mainly controlled by diffusion with
shown in FIGURE 6 with a slope of 0.5088
(R2 = 0.9998, n = 10) for BRB pH 4.0 and
Yong, 2008; El-Sayed et al.,2010). It means
9.0. The slope of more than 0.5 indicates that
completely covered with the electroactive
the reduction process of RB5 dye in both
FIGURE 6 : Plot of log Ip versus log v for 200 ppm RB5 dye in BRB pH 4.0 and 9.0 Health and the Environment Journal, 2012, Vol. 3, No. 1
The linear relationship was found between Ip
diffusion controlled (Masek et al., 2011;
and the square root of v (FIGURE 7),
indicating that the reduction process is
FIGURE 7 : Plot of log Ip versus square root v for 200 ppm RB5 dye in BRB pH 4.0 and 9.0
A linear plot of Ep versus log v as shown in
irreversible nature of reduction process was
FIGURE 8a and FIGURE 8b confirmed
also done by observing the shift of Ep to a
that in BRB pH 4.0 and 9.0, the reduction of
more negative value with increasing of v
RB5 dye on the electrode surface is totally
FIGURE 8a : Plot of Ep versus log v for 200 ppm RB5 dye in BRB pH 4.0 Health and the Environment Journal, 2012, Vol. 3, No. 1
FIGURE 8b : Plot of Ep versus log v for 200 ppm RB5 dye in BRB pH 9.0 Conclusion
RB5 dye undergoes irreversible reduction at
the mercury electrode and was found to be
pH dependence. The limiting current is an
reduction peaks of RB5 dye were observed
5. Gupta, V.K., Jain, R. and Radhapyari, K.
References
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under batch anaerobic condition by mixed
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microbial culture. African Journal of
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and diesel by differential pulse voltammetry. Talanta 72: 1106-1113.
Cow’s milk allergy (1 of 2) Some reactions to cows’ milk involve themedicine, the term cow’s milk allergy isonly used to describe reactions involvingfood labels every time you shop – even ifreactions are normally called cow’s milk Mild to moderate milk allergy can be found in some unlikely foods. Cow’s milk allergy is common in infantsreaction. Lactose (milk sugar) is u
Differentiation of Emboli Background: The difficulty of distinguishing solid from air emboli using transcranial Doppler has limited its use in situations where both types of emboli can occur, such as in mechanical heart valve patients. Particulate microemboli are thought to be the most damaging. Literature: Analysis of index modulation in microembolic Doppler signals par
Health and the Environment Journal, 2012, Vol. 3, No. 1
This paper describes the cyclic voltammetric
(Tunc et al., 2009). Textile, printing, and
mercury dropping electrode (HMDE) as the
widely used technique to acquire qualitative
information on electrochemical reactions
mg/L is toxic to fish, the concentration of
considerable information about the kinetic of
RB5 above 1000 mg/L leads to inhibition of
the system, number of electron transferred,
wastewater bacteria activity and it release
FIGURE 1: Chemical structure of RB5 dye 
Health and the Environment Journal, 2012, Vol. 3, No. 1
respectively. Only single electroreduction
The concentration of RB5 dye in cell is 200
BRB of pH 6-8. Two electroreduction peaks
were observed (-530 to -640 mV and -730 to
-840 mV) in BRB pH 9-12. Cathodic cyclic
Results and Discussion 
Health and the Environment Journal, 2012, Vol. 3, No. 1
FIGURE 2b: Cathodic cyclic voltammogram of 200 ppm RB5 dye in 
Health and the Environment Journal, 2012, Vol. 3, No. 1
No peak was observed in anodic direction of
mechanism for the irreversible reduction of
the reverse scans in all pH of BRB solution
RB5 dye at the mercury electrode surface is
suggesting that the irreversible nature of an
electrode process (Gupta et al, 2010; Gupta
et al, 2010; Jain et al., 2007). A suggested
2e− + 2H+ + (R–N=N–R1) (R–NH–NH–R1) (1)
2e− + 2H+ + (R–NH–NH–R1) (R–NH2) + (R1–NH2) (2)
Equation 1: Suggested mechanism for the irreversible reduction of RB5 dye
A mechanism for azo reduction involves two
stages as given in reaction (1) and (2) above
(Karatas et al., 2009). An unstable colourless
The influence of pH of BRB on the cyclic
voltammetric behavior of RB5 dye has been
reaction (1) and the azo bond can reform
studied in the pH range of 2-12 with a scan
upon oxidation and regain the colour. R and
rate of 25mV/s. The results show that peak
potential, (Ep) of RB5 dye shifts to a more
play part as terminal electron acceptors are
(FIGURE 3) indicating that the reduction 
Health and the Environment Journal, 2012, Vol. 3, No. 1
In acidic medium, maximum peak current, Ip
maximum Ip of 180 nA is obtained at pH 9.0
(FIGURE 4b). Therefore, pH 4.0 and 9.0 
Health and the Environment Journal, 2012, Vol. 3, No. 1
Effects of scan rate Effect of scan rate, (v) has been studied from
increase of Ip. Examination on the linear
relationship between Ip versus v (FIGURE 
Health and the Environment Journal, 2012, Vol. 3, No. 1
The linear relationship was found between Ip
diffusion controlled (Masek et al., 2011;
and the square root of v (FIGURE 7), 
Health and the Environment Journal, 2012, Vol. 3, No. 1
FIGURE 8b : Plot of Ep versus log v for 200 ppm RB5 dye in BRB pH 9.0