Download Report

Journal of Environmental Chemical Engineering 1 (2013) 975–980
Contents lists available at ScienceDirect
Journal of Environmental Chemical Engineering
journal homepage: www.elsevier.com/locate/jece
Degradation of textile dye C.I. Vat Black 27 by electrochemical method by using
carbon electrodes
Prakash Kariyajjanavar a,*, J. Narayana a, Y. Arthoba Nayaka b
a
b
Department of P.G. Studies & Research in Environmental Science, Kuvempu University, Jnana Sahyadri, Shankaraghatta, 577 451 Karnataka, India
Department of P.G. Studies & Research in Chemistry, Kuvempu University, Jnana Sahyadri, Shankaraghatta, 577 451 Karnataka, India
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 18 April 2013
Received in revised form 2 August 2013
Accepted 4 August 2013
The electrochemical degradation of industrial wastewater has become an attractive method in recent
years. In this work simulated dye wastewater containing vat dye C.I. Vat Black 27 is degraded from
electrochemical method using graphite carbon electrodes. The experimental results indicated that initial
pH, current density and supporting electrolytes were played an important role in the degradation of dye.
Electrochemical behavior of dye has been studied with cyclic voltammetry in basic medium using glassy
carbon as working electrode. The potentials selected for the dye was in the range 0.0 to 1.0 V. The UV–
vis and chemical oxygen demand (COD) studies were selected to evaluate the degradation efﬁciency. The
maximum color removal efﬁciency of 98% and chemical oxygen demand (COD) removal of 68% could be
achieved for dye, at 25 g/L of NaCl concentration. The LC–MS and FTIR studies revealed the degradation of
dye and conﬁrmed that aromatic rings were destroyed. The results revealed the suitability of the present
process for the effective degradation of dye C.I. Vat Black 27.
ß 2013 Elsevier Ltd. All rights reserved.
Keywords:
Carbon electrodes
Cyclic voltammetry
Electrochemical degradation
FTIR
LC–MS
UV–vis
Introduction
The discharge of textile wastewater to the environment
causes aesthetic problems due to the color and also damages the
quality of the receiving water [1]. Vat dyes account for about 15%
of total consumption of textile dyes [2,3]. Vat dyes cause
environmental concerns when released in industrial wastewaters due to their carcinogenic health effects [4]. Vat dyes are
practically insoluble in water, but can be reduced in the presence
of an alkali and a reducing agent to form a soluble dye known as
the leuco dye [5,6], which have a certain afﬁnity to cellulosic
ﬁbers. It needs to be reduced to its water soluble leuco-form
before dying.
The treatment of textile dye efﬂuent is difﬁcult and ineffective
with conventional biological processes [7] and several physicochemical methods because many synthetic dyes are very stable
to light, temperature and are non-biodegradable nature of most
dyes [8]. In this context, electrochemical technique is considered
to be a powerful means for the treatment of dyeing wastewater.
Indeed, electrochemical method has been successfully tested and
it has certain signiﬁcant advantages such as simple equipment,
easy operation and lower operating cost [9–12]. The process
requires signiﬁcantly less equipment than conventional
* Corresponding author. Tel.: +91 8282256251.
E-mail address: [email protected] (P. Kariyajjanavar).
2213-3437/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jece.2013.08.002
biological treatment processes [13,14]. Graphite electrodes were
used as anode and cathode by many researchers for the
application in organic oxidation [15,16]. Hence, there is an
interest in electrochemical methods to develop an efﬁcient, costeffective and eco-friendly alternative for the degradation of
dyestuffs [17]. In the past, graphite was frequently used as an
anode for the electrochemical degradation of textile dye as it is
relatively cheaper and gives satisfactory results [18]. The aim of
this work was to test the feasibility of electrochemical method
for the degradation of C.I. Vat Black 27 using graphite carbon
electrodes.
Experimental
Materials
The commercial vat dye, Indanthren Olive R Coll. (C.I. Vat
Black 27, CAS No. 2379-81-9) and was obtained from textile
industry Himatsingka Linens, Hassan, India. All other chemicals
used for the experiments were of analytical grade reagents and
obtained from s d ﬁne chem-limited, Mumbai, India. Cylindrical
carbon electrodes (chemical composition: graphite carbon + coke: 85% and ash 15%) were obtained from Power Cell Battery
India Limited. A digital DC power supply (AD 302S: 30 V, 2A) was
used as an electrical source. Double distilled water was used to
prepare the desired concentration of dye solutions and the
reagents.
[(Fig._1)TD$IG]
P. Kariyajjanavar et al. / Journal of Environmental Chemical Engineering 1 (2013) 975–980
976
Instrumentation
1.4
Electrochemical degradation studies
Graphite carbon electrodes of 4.5 cm length and 0.8 cm
diameter were used as anode and cathode for electrochemical
degradation studies [19]. The effective electrode area was
11.82 cm2. The supporting electrolytes such as NaCl and Na2SO4
were added to the electrolytic solution, which increases the
conductivity of the solution and reduces the electrolysis time. The
solution was kept under agitation using magnetic stirrer.
1.2
Current 10-5 (A)
UV–vis studies
A UV–vis spectrophotometer (Systronics-119) was employed to
measure the optical density of dye solution (lmax = 590) before and
after electrolysis. The degradation efﬁciency was calculated using
the relation:
%E ¼
Ai A f
100
Ai
1.0
0.8
Ipc
0.6
0.4
0.2
Vat Black 27
Blank
0.0
-0.2
0.0
-0.2
-0.4
(1)
-0.6
-0.8
-1.0
Potential (V)
where, Ai and Af are absorbance values of dyes solutions before and
after treatment with respect to their lmax, respectively or Ai and Af
are initial and ﬁnal COD values of the dyes solutions, respectively.
Fig. 1. Cyclic voltammograms of dye C.I. Vat Black 27 on glassy carbon: scan rate.
100 mV s1; pH: 9; concentration of dye: 50 mg/L. Inset plot: DPV: scan rate
100 mV s1.
pH and conductivity measurement
A water analyser (Systronics, Model-371) was used to measure
the pH and conductivity of the dye solution before and after
electrolysis under different electrolysis conditions.
was no anodic peak found, indicating the irreversible nature of the
dye (Fig. 1). The cathodic peak currents observed for C.I. Vat Black 27
attributed to the reduction of ketones to alcohols. These data are
very much important to assess the feasibility of the electrochemical
process for the degradation of the dye C.I. Vat Black 27.
Liquid chromatography–mass spectrometry studies (LC–MS)
The extent of degradation of dye samples were analyzed by LC–
MS studies (LCMS-2010A, Shimadzu, Japan). The LC–MS was ﬁtted
with column C18. The mobile phase was methanol:water (90:10).
The ﬂow rate was 0.2 mL min1 and the injection volume of dye was
5 mL. The dye solutions were injected into LC column before and after
electrolysis. Analyses using ESI (electron spray ionization) interface
were done under the same chromatographic conditions as described
for the APCI (atmospheric pressure chemical ionization) analysis,
except the guard column, which was not used in the ESI analysis.
FTIR studies
To study the structural changes of dye before and after
electrolysis the dye samples were characterized by using Fourier
transform Infrared Spectrometry (FTIR) spectrometer (model 3010
Jasco, Japan). The scan range of the wave number was set from 400
to 4600 cm1. The dye samples (freeze dried) were kept in the
sample holder and scanned to obtain the FTIR spectra.
Inﬂuence of electrolysis conditions on dye degradation
Effect of supporting electrolytes
From the experimental observation, it could be concluded that,
the degradation efﬁciency of dye solutions were found to be
enhanced in the presence of NaCl than that of Na2SO4. Since, may
be attributed to the generation of more powerful oxidizing agents
such as Cl2, HOCl and OCl [19]. The degradation in the presence of
Na2SO4 is attributed to the generation of persulfate ions that can
oxidize organic dyes [21].
The S2O82 ions are formed the oxidation of SO42 species:
2Na2 SO4 ! S2 O8 2 þ 2Naþ þ 2e
(2)
Moreover, the increased concentration of supporting electro[(Fig._2)TD$IG]
lytes
results in a decrease in the operating voltage at the given
6.0
The C.I. Vat Black 27 is a commercial textile dye, best known to
polycyclic aromatic carbonyl dyes cover the entire color range of
black [20].
Voltammetry
The cyclic voltammetric measurements were carried out using
CHI660D electrochemical workstation (CH Instruments Austin,
USA) controlled by electrochemical software. A three electrodes
system was used for the cyclic voltammetric experiments. The
working electrode was highly polished, glassy carbon disk with an
effective surface area of 0.06 cm2. A platinum wire and saturated
calomel were used as counter and reference electrodes, respectively. The cyclic voltammagrams of C.I. Vat Black 27 (50 mg/L,)
was recorded in pH 9 using glassy carbon as working electrode. The
potential range selected was 0.0 to–1.0 V. The voltammetric curve of
C.I. Vat Black 27 shows a cathodic peak at 0.692 V (Ipc), and there
(a)
5.0
4.5
4.0
NaCl
Na2SO4
3.5
Decolourisation (%)
Results and discussion
Voltage (V)
5.5
3.0
100
80
60
40
(b)
20
0
5
10
15
20
25
30
35
-1
Electrolyte concentration (g L)
Fig. 2. Effect of supporting electrolytes on (a) voltage variation and (b) degradation
efﬁciency. Electrolysis condition: concentration of the dye solution: 50 mg/L;
electrodes: graphite carbon; current density: 170 A m2; time: 240 min.
[(Fig._3)TD$IG]
P. Kariyajjanavar et al. / Journal of Environmental Chemical Engineering 1 (2013) 975–980
current density (Fig. 2a). An increase in the concentration of NaCl
up to 25 g/L accelerated the degradation rate, enabling the
degradation efﬁciency of C.I. Vat Black 27 of 98% (Fig. 2b).
977
Removal of Colour & COD (%)
100
Effect of initial pH
A signiﬁcant difference in the extent of degradation was
noted when the concentration of NaCl was at 25 g/L. The initial
pH of the solution (3–11) was adjusted using 1 M H2SO4 or
NaOH [22,23]. The electrolysis was carried out at the current
density of 170 A m2 for 240 min with a dye concentration of
50 mg/L at room temperature. From the absorption spectral
studies it was conﬁrmed that, the larger dye molecules were
degraded into simple substituted aromatic compounds [24].
However, the hypochlorite can lead to partial mineralization of
dyes [21] and the degradation efﬁciency of C.I. Vat Black 27 was
found higher in both neutral and basic pH and slightly lower in
acidic pH. After electrolysis the ﬁnal pH was found to be slightly
basic.
90
80
70
60
Colour
COD
50
40
85
170
255
340
425
2
Current Density (A/m )
Fig. 3. Effect of current densities on degradation and COD removal efﬁciencies of
dye C.I. Vat Black 27. Electrolysis condition: concentration of the dye solution:
50 mg/L; pH: 9; NaCl: 25 g/L; current density 170 A m2; time: 240 min.
Effect of current density
The electrolysis of dye solution was carried out at different
current densities (85, 170, 255, 340 and 425 A m2) at graphite
carbon electrodes to investigate the inﬂuence of current density
on the degradation efﬁciency of C.I. Vat Black 27 keeping NaCl
concentration at 25 g/L, dye concentration at 50 mg/L, pH at 9
and temperature at 300 K. It can be found that, the degradation
and COD removal efﬁciencies increased (Fig. 3) with increasing
the applied current density [25]. This is because of the increased
rate of generation of oxidants, such as chlorine/hypochlorite at
higher current densities [26]. It was also reported that current
density only slightly affects current efﬁciency or enhances
chlorine/hypochlorite production when increased along with
the chloride concentration [27]. Up to a current density of
170 A m2, the degradation efﬁciency of the dye was increased
almost linearly. pH is another parameter that plays an important
role in indirect electrochemical processes because it inﬂuences
the form of the electrogenerated active chlorine and its
oxidation potential; thus, depending on the pH, the electrogenerated molecular chlorine can disproportionate to form
hypochloric acid (Eq. (3)) which is deprotonate to hypochlorite
ions (Eq. (4))
Cl2 þ H2 O ! HOCl þ HCl
(3)
HOCl ! Hþ þ OCl
(4)
At higher current densities accumulation of OCl in the
electrolyte causes the increase in pH after which the concentration
of OCl reaches to a certain level at which point the oxidation
process is initiated [28]. The degradation efﬁciency was attained
almost constant and energy consumption was found to be more at
higher current densities (>170 A m2) with a subsequent stripping
of electrodes [29]. Therefore, the optimal current density for the
successive electrochemical degradation was ﬁxed at 170 A m2.
Analysis of COD
The electrolysis was carried out at a current density of
170 A m2. At this current density, hypochlorite (OCl) generated
[(Fig._4)TD$IG]
70
70
(a)
(b)
60
COD removal (%)
COD removal (%)
60
50
40
50
40
30
20
30
10
20
0
2
4
6
8
pH
10
12
5
10
15
20
25
30
35
-1
NaCl (g L )
Fig. 4. Effect of pH and NaCl concentrations on COD removal efﬁciencies of the dye C.I. Vat Black 27. Electrolysis condition: concentration of the dye solution: 50 mg/L;
electrodes: graphite carbon; current density: 170 A m2; time: 240 min.
978
P. Kariyajjanavar et al. / Journal of Environmental Chemical Engineering 1 (2013) 975–980
in the solution drives the oxidation process at basic pH. The
maximum COD removal efﬁciency of 68% was observed at pH 8
(Fig. 4a). The percent removal of COD increased with increase in
the concentration of NaCl (Fig. 4b). This conﬁrmed that the
electrogenerated chlorine/hypochlorite will play an important role
in the electrochemical degradation process of the dyestuffs.
Liquid chromatography–mass spectrometry studies (LC–MS).
LC–MS studies were employed to monitor the diminution in
mass of the fragments of C.I. Vat Black 27 dye before and after
electrolysis. MS spectrum of the dye C.I. Vat Black 27 recorded
before electrolysis shows more number of peaks at higher m/z
values due to the presence of dye and other impurities (Fig. 5a). The
MS spectrum of the ﬁltrate solution after complete electrolysis
shows the absence of majority of the peaks (Fig. 5b). This clearly
indicated that almost all dye was coagulated and removed in the
form of sludge. The remaining peaks at low m/z values in the mass
spectra may be due to the presence of substituted simple aromatic
compounds.
shows a broad and intense band at 3476 cm1 could be attributed
to stretching vibrations of –N–H groups. The sharp bands at
1639 cm1 could be attributed to stretching vibrations of C5
5O
group. The medium band at 2934, 1587, 1514, 1456 cm1 could be
attributed to stretching vibrations of 5
5C–H, –C–H, –C5
5C–, –C–C–
groups respectively. The weak bands at 1342, 1265, 1024, 690 and
418 cm1 could be due to bending of frequencies of 5
5C–H, –C5
5C–,
–N–H and –C–H groups. After the treatment of dye C.I Vat Black 27
the spectrum conﬁrms that, almost stretching and bending
frequencies of different groups were gradually disappeared
(Fig. 6b). In addition, the broad peak around 3400 cm1, which
is assigns to –OH vibration [30].
Electrical energy consumption
The major operating cost is associated with the electrical energy
consumption during electrochemical degradation process. The
electrical energy consumption (E) is required to decompose 50 mg/
L C.I Vat Black 27 dye solution at various current densities was
calculated using the relation:
VIt E
103
Vs
FT-IR
E¼
FT-IR spectroscopic technique employed to follow up the
electrochemical degradation process of C.I. Vat Black 27 during
240 min of electrochemical process. The spectrum of dye (Fig. 6a)
where, E is the electrical energy consumption (kWh m3), V is the
applied voltage (V), I is the applied current (A), tE is the electrolysis
time (h) and Vs is the volume of dye solution (m3). As per the
[(Fig._5)TD$IG]
(5)
Fig. 5. Mass spectrum of C.I. Vat Black 27: (a) before electrolysis and (b) clear ﬁltrate after complete electrolysis. Electrolysis condition: concentration of the dye solution:
50 mg/L; electrodes: graphite carbon; pH: 9; current density 170 A m2; time: 240 min.
[(Fig._6)TD$IG]
P. Kariyajjanavar et al. / Journal of Environmental Chemical Engineering 1 (2013) 975–980
979
Fig. 6. FT-IR spectrum of C.I. Vat Black 27 (a) before electrolysis and (b) after electrolysis, Electrolysis condition: concentration of the dye solution: 50 mg/L; electrodes:
graphite carbon; pH: 9; current density: 170 A m2; time: 240 min.
Table 1
The electrical energy consumed during electrochemical degradation of C.I. Vat Black 27 dye solution (50 mg/L); Electrolysis time 240 min.
Current (A)
Current density (A m2)
Energy consumption (kWh m3)
Degradation (%)
0.10
0.20
0.30
0.40
0.50
085
170
255
340
425
7.40
15.20
31.20
44.00
59.00
87
99
99
99
99
results, the minimum electrical energy consumption was
15.20 kWh m3 at 170 A m2 current density. At higher current
densities, the energy consumption was found to be increased and it
may be attributed to the increased hydrogen and oxygen evolution
reaction (Table 1).
Conclusions
In the present work the electrochemical degradation of C.I Vat
Black 27 was carried out using graphite carbon as anode and
cathode, in the optimal operating conditions (current density
170 A m2, NaCl concentration 25 g/L and at room temperature).
Increasing the initial pH will lead to corresponding decrease in the
degradation efﬁciency of C.I. Vat Black 27 dye. The effect of the
hypochlorite at pH 9 can lead the degradation efﬁciency of the dye.
Cyclic voltammograms of C.I. Vat Black 27 shows irreversible
electrochemical natures. UV–vis, MS spectral studies and FT-IR
studies conﬁrmed that the proposed electrochemical degradation
process is an effective method for the degradation of C.I. Vat Black
27 dye.
Acknowledgements
The Authors are grateful to DBT, DST and UGC, New Delhi for the
ﬁnancial support extended. Also grateful to Kuvempu University,
Power Cell Battery India Limited, DyStar Textilfarben GmbH & Co.
Deutschland KG for their support to carry out this work.
References
[1] D. Georgiou, C. Metallinou, A. Aivasidis, E. Voudrias, K. Gimouhopoulos, Decolorization of azo-reactive dyes and cotton-textile wastewater using anaerobic digestion and acetate-consuming bacteria, Biochem. Eng. 19 (2004) 75–79.
[2] I. Chaari, M. Feki, M. Medhioub, J. Bouzid, E. Fakhfakh, F. Jamoussi, Adsorption of a
textile dye indanthrene blue RS (C.I. Vat Blue 4) from aqueous solutions onto
smectite-rich clayey rock, J. Hazard. Mater. 172 (2009) 1623–1628.
[3] I. Chaari, F. Jamoussi, Application of activated carbon for vat dye removal from
aqueous solution, J. Appl. Sci. Environ. Sanit. 6 (2011) 247–256.
[4] D.S.L. Balan, R.T.R. Monteiro, Decolorization of textile Indigo dye by ligninolytic
fungi, J. Biotechnol. 89 (2001) 141–145.
[5] P. Santhi, J.J. Moses, Study on different reducing agents for effective vat dyeing on
cotton fabric, Indian J. Fibre Text. Res. 35 (2010) 349–352.
[6] P. Kariyajjanavar, J. Narayana, Y.A. Nayaka, Degradation of simulated dye wastewater by electrochemical method on carbon electrodes, Indian J. Nat. Sci. 1 (2012)
809–821.
[7] G. Guven, A. Perendeci, A. Tanyolac, Electrochemical treatment of simulated beet
sugar factory wastewater, Chem. Eng. J. 151 (2009) 149–159.
[8] A. Anouzla, Y. Abrouki, S. Souabi, M. Saﬁ, H. Rhbal, Colour and COD removal of
disperse dye solution by a novel coagulant: application of statistical design
for the optimization and regression analysis, J. Hazard. Mater. 166 (2009)
1302–1306.
[9] A. Dirany, I. Sires, N. Oturan, A. Ozcan, M.A. Oturan, Electrochemical treatment of
the antibiotic sulfachloropyridazine: kinetics reaction pathways and toxicity
evolution, Environ. Sci. Technol. 46 (2012) 4074–4082.
[10] F. Akbal, A. Kuleyin, Decolorization of levaﬁx brilliant blue E-B by electrocoagulation method, Environ. Prog. Sustainable Energy 30 (2011) 29–36.
980
P. Kariyajjanavar et al. / Journal of Environmental Chemical Engineering 1 (2013) 975–980
[11] Y. Chu, D. Zhang, L. Liu, Y. Qian, L. Li, Electrochemical degradation of m-cresol using
porous carbon-nanotube-containing cathode and Ti/SnO2–Sb2O5–IrO2 anode: kinetics, byproducts and biodegradability, J. Hazard. Mater. 252 (2013) 306–312.
[12] M. Hongzu, W. Bo, L. Xiaoyan, Studies on degradation of methyl orange wastewater
by combined electrochemical process, J. Hazard. Mater. 149 (2007) 492–498.
[13] P. Kariyajjanavar, J. Narayana, Y.A. Nayaka, Degradation of textile wastewater by
electrochemical method, Hydrol. Curr. Res. 2 (2011) 110, http://dx.doi.org/
10.4172/2157-7587.1000110.
[14] F. Li, Z. Yanwei, Y. Weishen, C. Guohua, Y. Fenglin, Electrochemical degradation of
aqueous solution of Amaranth azo dye on ACF under potentiostatic model, Dyes
Pigments 76 (2008) 440–446.
[15] C. Cameselle, M. Pazos, M.A. Sanroman, Selection of an electrolyte to enhance the
electrochemical decolourisation of indigo optimisation and scale-up, Chemosphere 60 (2005) 1080–1086.
[16] M.A. Sanroman, M. Pazos, M.T. Ricart, C. Cameselle, Decolourisation of textile
indigo dye by DC electric current, Eng. Geol. 77 (2005) 253–261.
[17] C.A. Martinez-Huitle, E. Brillas, Decontamination of wastewaters containing
synthetic organic dyes by electrochemical methods: a general review, Appl. Catal.
B Environ. 87 (2009) 105–145.
[18] P. Kariyajjanavar, J. Narayana, Y.A. Nayaka, Electrochemical degradation of C.I. Vat
Brown1 dye on carbon electrode, Adv. Chem. Lett. 1 (2013) 32–39.
[19] P. Kariyajjanavar, J. Narayana, Y.A. Nayaka, Studies on degradation of reactive
textile dyes solution by electrochemical method, J. Hazard. Mater. 190 (2011)
952–961.
[20] K. Hunger, Industrial Dyes, Chemistry, Properties, Applications, Wiley-VCH,
Germany, 2003.
[21] F. Yi, S. Chen, C. Yuan, Effect of activated carbon ﬁber anode structure and
electrolysis conditions on electrochemical degradation of dye wastewater, J.
Hazard. Mater. 157 (2008) 79–87.
[22] I.M. Hasnain, L.S. Lang, F.A.H. Asaari, H.A. Aziz, N.A. Ramli, J.P.A. Dhas, Low cost
removal of disperse dyes from aqueous solution using palm ash, Dyes Pigments
74 (2007) 446–453.
[23] J. Basiri Parsa, M. Rezaei, A.R. Soleymani, Electrochemical oxidation of an azo dye
in aqueous media investigation of operational parameters and kinetics, J. Hazard.
Mater. 168 (2009) 997–1003.
[24] A. Fatiha, R.G. Mouffok, M. Belhadj, A. Addou, J. Brisset, Bleaching and degradation
of textile dyes by nonthermal plasma process at atmospheric pressure, Ind. Eng.
Chem. Res. 45 (2006) 23–29.
[25] N.M. Abu Ghalwa, L.M.S Abdel, Electro-chemical degradation of acid green dye in
aqueous wastewater dyestuff solutions using a lead oxide coated titanium
electrode, J. Iran. Chem. Soc. 2 (2005) 238–243.
[26] H. Ma, B. Wang, X. Luo, Studies on degradation of methyl orange wastewater
by combined electrochemical process, J. Hazard. Mater. 149 (2007)
492–498.
[27] M. Li, Q. Xue, Z. Zhang, C. Feng, N. Chen, X. Lei, Z. Shen, N. Sugiura, Removal
of geosmin (trans-1,10-dimethyl-trans-9-decalol) from aqueous solution
using an indirect electrochemical method, Electrochim. Acta 55 (2010)
6979–6982.
[28] J.B. Parsa, M. Rezaei, A.R. Soleymani, Electrochemical oxidation of an azo dye in
aqueous media investigation of operational parameters and kinetics, J. Hazard.
Mater. 168 (2009) 997–1003.
[29] D. Rajkumar, B.J. Song, J.G. Kim, Electrochemical degradation of Reactive
Blue 19 in chloride medium for the treatment of textile dyeing wastewater
with identiﬁcation of intermediate compounds, Dyes Pigments 72 (2007)
1–7.
[30] Z. Seferoglu, N. Ertan, T. Hokelek, E. Sahin, The synthesis spectroscopic properties
and crystal structure of novel, bis-hetarylazo disperse dyes, Dyes Pigments 77
(2008) 614–625.