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ELECTROCHEMICAL DEGRADATION OF NAPHTHOL AS-BO BATIK DYES

Muji Harsini1, Suyanto1, Yhosep Gita Y. Y.2, Lilik Rhodifasari1, Handoko Darmokoesomo1

ABSTRACT

Nahptol AS-BO is one of the synthetic dyes often used in the dyeing process of batik fabric. The treatment of the wastewater released is a serious problem from an environmental point of view. The present investigation is focused at constant potential electrochemical degradation of naphthol AS-BO using a nanoporous carbon paste electrode in a solu-tion containing NaCl as a supporting electrolyte. The effect of the potential applied, the solution pH and the degradation time is followed. It is found that the optimum values of the potential and pH refer to 12 V and 1, correspondingly. It is experimentally verified that the degradation process is of ECE mechanism, while the rate-determining chemical step is of a second order. The method studied provides COD value decrease to 90.84 %, while naphthol AS-BO presence decreases to 88.74 %.

Keywords: naphthol AS-BO, nanoporous carbon, electrode, electrochemical degradation, batik.

Received 05 January 2017Accepted 20 July 2017

Journal of Chemical Technology and Metallurgy, 52, 6, 2017, 1116-1122

1 Department of Chemistry, Faculty of Science and Technology Universitas Airlangga2 Department of Physics, Faculty of Science and Technology Universitas Airlangga, Kampus C Mulyoejo Surabaya 60115, Indonesia E-mail: muji-h@fst.unair.ac.id

INTRODUCTION

Naphthol is frequently used to dye batik, a traditional dress of Indonesia. AS-BO Naphthol refers to the aromatic azo group dyes which are potentially carcinogenic and mutagenic [1]. 18 azo dyes are studied [2] and it is found that 11 of them pass practically unchanged through the activated sludge system, 4 are adsorbed by the activated sludge, while only 3 biodegrade.

The aromatic azo group dyes are widely (60 % - 70 %) used in textile industry including batik production [3]. Some physical, chemical, and biological processes are applied to these dyes treatment as water pollutants but they produce a new form of sewage sludge in large quantities [4]. Thus reprocessing is required.

Electrochemical degradation is a new method of organic compounds treatment leading to products like CO2, H2O and NH3 [5]. This technique is simple, easy to operate and is cost effective. Electrodes are important components of an electrochemical reaction. Dyes wastes

are successfully treated electrochemically using metal plate electrodes [6], electrodes modified by SnO2 [7], PT-Bi/C nanostructured electrodes [8] and TiO2-ZnO nanocomposite electrodes [9].

Nanoporous carbon electrode are widely used saving because of their wide surface area and good conductivity [5]. They have been also used in degradation of textile dyes like malachite green [10], remazol black B [11] and indigo blue [12]. It is reported that more than 99 % of the dyes present in the wastewaters are degraded. This electrode material is chosen for the study presented.

EXPERIMENTAL

0.5690 g of naphthol AS-BO were dissolved in an aqueous solution containing 0.9311 g of NaOH. The solution obtained was mixed with 0.4346 g fast blue B salt.

0.7 g of a nanoporous carbon powder and 0.3 g paraffin pastilles were mixed in a ratio of 7 to 3. The mixture was heated at about 80oC and then deposited on

Muji Harsini, Suyanto, Yhosep Gita Y. Y., Lilik Rhodifasari, Handoko Darmokoesomo

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Both electrodes were connected [13] to a DC source as illustrated in Fig. 1. 50.0 mL of 50 ppm sample solution containing 0.1 M NaCl as a supporting electrolyte were introduced to the electrolysis cell. A magnetic stirrer was used throughout the whole period.

The degradation of 50.0 mL of 50 ppm of naphthol AS-BO containing 0.1 M NaCl was followed varying the degradation time at optimal conditions. The values of naphthol AS-BO concentration after degradation were treated in correspondence with first, second and third order kinetic equations aiming to obtained the linear relationship expected. COD determination was carried out spectrophotometrically (SNI 6989.2: 2009) using a closed reflux method.

RESULTS AND DISCUSSION

The reaction taking place with the addition of fast blue B salt (C14H12Cl4N4O2Zn) is presented in Fig. 2.

Fig. 1. Scheme of electrochemical degradation control set. (1) DC source, (2) electrodes, (3) electrolysis cells and (4) magnetic stirrer.

Fig. 2. Reaction of AS-BO Naphthol and fast blue B salt.

O

NH

OH

O

N

ONaH

O

N2+

ON2

+

CH3

CH3

Cl-

Cl-

ZnCl2

O

NH

ONa

NN

OCH3

OCH3

NN

ONa

HN

O

+ 2 NaOH2 2

Naphtol AS-BO(cream)

Fast blue B salt(light green)

+ 2 H2O

Blue

+

the body of the electrode consisting of 3 mm of carbon rode and paraffin. After drying the electrode surface was smoothed using HVS paper until a glossy appearance was obtained. The active carbon electrode prepared was used as an anode, while a Ag wire acted as a cathode.

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Fig. 3 illustrates the potential applied and the percentage of AS-BO naphthol degradation. It is evident that the potential increase to 12 V brings about decrease of the dye present to 80.47 %.

Fig. 4 shows that the solution pH affects the degradation. The latter increases with pH decrease. The percentage of degradation amounts to 84 % at pH of 1. In an acidic solution the structure of AS-BO naphthol corresponds to that shown by Fig. 5. It is worth adding that the dye solubility in water as well as its stability is decreased. Thus its degradation is facilitated. That pH of 1 is chosen for the further experiments.

Fig. 6 shows that the degradation increases with the treatment time increase. Degradation of 88.74 % is reached within 2 h. The spectrum patterns obtained subsequently show that longer time is required to obtain greater degradation. This can most probably be attributed to the large area of naphthol AS-BO molecule which in turn is connected with the electrode surface area used.

The UV-Vis spectra obtained are illustrated in Fig. 7. That recorded prior to the degradation shows two maxima at 315 nm and 604.5 nm. The latter peak decreases with the treatment time increase. This is probably due to N=N bond breaking. This process is

Fig. 5. Acid-base equilibrium reaction of AS-BO naphthol compound.

Fig. 3. Relation curve of degradation potential to 50 mL naphthol 50 ppm in 20 minutes.

Fig. 4. Relationship between pH of solution and AS-BO naphthol 50 ppm that degraded at 12 V for 20 minutes.

O

NH

OH

NN

OCH3

OCH3N

N

OH

HN

O

O

NH

O-

NN

OCH3

OCH3

NN

O-

HN

O

+ H+

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Fig. 6. Relationship between time of degradation and degraded Naphthol AS-BO.

most probably facilitated through the oxidation of the hipochlorite ion (OCl-) formed at the anode. The peak at 315 nm referring to the benzene ring of naphthol AS-BO is also affected by the time of the degradation procedure.

The kinetic study data is listed in Table 1. It is evident that naphthol AS-BO degradation proceeds as a second order reaction (the correlation coefficient is 0.858). This implies that in case the initial concentration of naphthol AS-BO is increased twice, the rate of reaction decreases exponentially. The profile referring to the relation of ln 1/C in respect to the degradation time presented in Fig. 8 shows that the rate constant is equal to 0.001 ppm/min. This in turn indicates that 18.29 min are required to degrade half of 50 mL Naphthol AS-BO, i.e. 55.9 ppm.

The electrochemical investigation is carried out

Table 1. Kinetic study data.

Time (minute)

C (ppm)

√C (ppm1/2)

ln C (ppm) 1/√C (ppm-1/2) 1/C (ppm-1)

½ order 1st order

1 ½ order

2nd order

0 55.90 7.477 40.234 0.134 0.018 10 26.37 5.135 3.272 0.195 0.038 20 13.30 3.647 2.588 0.274 0.075 25 12.14 3.484 2.496 0.287 0.082 30 11.198 3.346 2.416 0.299 0.089 35 10.54 3.246 2.355 0.308 0.095 40 9.59 3.097 2.261 0.323 0.104 45 9.22 3.036 2.221 0.329 0.108 50 8.84 2.973 2.179 0.336 0.113 60 8.08 2.842 2.089 0.352 0.124

120 6.29 2.508 1.839 0.399 0.159 R2 0.530 0.644 0.7604 0.858

Fig. 8. Second order reaction kinetics of naphthol AS-BO.

Fig. 7. UV-Vis spectrum of electrochemical degradation of naphthol AS-BO solution at variations of degradation time.

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potentiodynamically in presence of 10 ppm of naphthol AS-BO dissolved in a supporting electrolyte solution of 0.1 M NaCl. The effect of the scan rate, v, is followed. Naphthol AS-BO voltammogram is illustrated in Fig. 9, while the values of the anodic and cathodic currents are summarized in Table 2. It is evident that they increase with scan rate increase. It is concluded [14] that the reaction studied follows

an electrochemical-chemical-electrochemical (ECE) mechanism. This is verified by the linear relationships of Ipc/Ipa vs. v, Ipa/Ipc vs. v, Ipc vs. ν and Ipc vs. log v (Table 3).

The data obtained provide to assume that the degradation initiates the formation of chlorine gas at the anode surface, which then reacts with water to give hypochloric acid. The latter interacts with naphthol

Fig. 9. Cyclic voltammogram of naphthol AS-BO with supporting electrolyte of NaCl solution at variations of swept potential rate.

Fig. 10. Voltammogram of naphthol AS-BO solution at variations of degradation time. Comparison of voltammogram at t=10 and t=120 minutes.

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Table 4. Values of the anodic peak currents and the relative current decrease obtained.

Time (minute) Ipa (mA) Ipa (mA) Relative current decrease (%)

10 10.14 24.45 58.53 20 9.43 24.45 61.43 30 8.23 24.45 66.34 40 0 24.45 100 50 0 24.45 100

AS-BO to produce simpler products, i.e. CO2 and H2O.This chemical step is followed by an irreversible electrochemical reaction evidenced by the separation of the cathodic and the anodic peaks p( E )∆ . The latter is found equal to 1.89 V in case of a scan rate of 30 mV/s, i.e. the requirement of an irreversible electron transfer step p( E )∆ > 0.059/n V [15] is fulfilled.

Cyclic voltammetry analysis is also carried out in naphthol AS-BO solution after degradation proceeding within different time intervals. The voltammogram shown in Fig. 10 shows that the the anodic and cathodic peaks decrease with degradation time increase. It is evident that the time affects the amount of degraded molecules. This is illustrated by the values presented

in Table 4. They refer to the relative current decrease observed with degradation time increase. It is seen it amounts to 100 % at t = 40 min. The UV-Vis analysis shows that the corresponding degradation percentage refers to 83 %.

COD (chemical oxygen demand) of naphthol AS-BO solution is determined to find the amount of oxygen required for wastes degradation in water throughout the chemical process studied. This analysis is done prior to and after degradation. COD analysis of the supporting electrolyte of 0.1 M NaCl (treated as a blank solution) is also carried out. The results in Table 5 show that the degradation amounts to 71.23 % at t = 60 min, while it is 90.84 % at t = 120 min.

Table 5. COD analysis of naphthol AS-BO solution prior to and after degradation.

Solution COD COD Reduce (%)

Naphthol AS-BO 50 ppm 282.646 -

60 minute of degradation 81.321 71.23

120 minute of degradation 25.889 90.84

Table 2. Cathodic and anodic currents as a function of the scan rate applied in case of naphthol AS-BO degradation.

v(V/second) Ipa(mA) Ipc(mA) 0,01 2,89 -4,04 0,02 3,68 -4,81 0,03 4,89 -5,34

Table 3. Regression equations obtained in course of the electrochemical investigation carried out.Curve The regression equation Linearity (R2) ν vs Ipc/Ipa y = 15.500x - 1.573 0.959 ν vs Ipa/Ipc y = -10.500x - 0.587 0.916 √ν vs Ipc y = -18.608x - 2.187 0.999 Log ν vs Ipc y = 0.242x + 1.086 0.994

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CONCLUSIONS

Electrochemical degradation of naphthol AS-BO dye is carried out under optimum conditions referring to 12 V and pH=1. The cyclic voltammetry investigation shows that the overall process is of electrochemical-chemical-electrochemical (ECE) mechanism. The rate-determining chemical step proceeds as a second order reaction. COD percentage prior to and after degradation amounts to 90.84 %.

Acknowledgements

Thanks and high appreciation to the Ministry of Research, Technology and Higher Education through the Institute of Research and Innovation, Universitas Airlangga for the financial support of this research. Thanks are also extended to Prof. Ris. Gustan Pari (Forest Products Research Center, Bogor) as a provider of nanoporous carbon.

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