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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 v 5) 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
studies by stripping voltammetry. Journal 1. Ambrosi, A., Antiochia, R., Campanella, of Colloid and Interface Science 350: L., Dragone, R. and Lavagnini, I. (2005). Journal of Hazardous Materials 122: 219- 2. Badawy, W.A., El-Reis, M.A. and Mahdi, determination of some antidiabetic drugs Electroanalytical Chemistry 648: 20-27. for type 2 diabetic patients. Talanta 82: 7. Hadzri, M., Rahim, A. and Ahmad, R. ( Malaysian Journal of Chemistry 12: 009- and applications, Wiley, New York, 190- Health and the Environment Journal, 2012, Vol. 3, No. 1 8. Jain, R., Radhapyari, K. & Jadon, N. 14. Peláez-Cid, A.A., Blasco-Sancho, S. and chloride on a mercury electrode. Journal electrochemical detection. Talanta 75: of Colloid and Interface Science 314: 9. Jain, R., Radhapyari, K. and Jadon, N. Chinese Chemical Letters 19: 1337- antiretroviral drug. Journal of Colloid and 16. Sarıgul, T. and Inam, R. (2009). Study 10. Karatas, M., Dursun, S. and Argun, M.E. under batch anaerobic condition by mixed stripping voltammetry. Electrochimica microbial culture. African Journal of 17. Tonlé, K.I., Ngameni, E., Tcheumi, H.L. characterization, catalase-like activity, Dyes and Pigments. Available online. Hazardous Materials 163: 187-198. voltammetry. Food Chemistry. Article investigations of reactive dyes; cathodic Analytica Chimica Acta 349: 101-109. and diesel by differential pulse voltammetry. Talanta 72: 1106-1113.

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