Degradation of azo dye, acid red-14 by hexacyanoferrate(III) using iridium nanoclusters: A kinetic study

Article abstract of DOI:10.14233/ajchem.2016.19308

In the present work, a novel method for the treatment of wastewater containing an azo dye, acid red-14 by hexacyanoferrate [HCF(III)] in presence of iridium nanoclusters has been proposed. The effect of some important operational parameters such as pH, temperature and catalyst concentration (iridium nano) has been investigated by kinetic spectrophotometric method at λ_max 515 nm of the reaction mixture. The results reveal that degradation kinetics of acid red-14 follows first order kinetic model with respect to [HCF(III)], [acid red-14] and Ir nano concentration. Iridium nanoclusters were recovered with the help of centrifugation and reused for three consecutive cycles. Thermodynamic parameters E_a, ΔS^#, ΔF^#, ΔH^# and 'A' have been calculated by studying the reaction rate in the range of temperatures 40 to 55 °C. The formation of degradation products was characterized by chromatographic and spectroscopic techniques after the extraction with ethyl acetate. 1-Hydroxy-2-amino naphthalene and naphthalene sodium sulphate were identified as major degradation products. The results can provide fundamental knowledge for the treatment of wastewater containing acid red-14/other azo dyes.

Full text of DOI:10.14233/ajchem.2016.19308

Asian Journal of Chemistry; Vol. 28, No. 2 (2016), 335-338
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19308
Degradation of Azo Dye, Acid Red-14 by Hexacyanoferrate(III)
Using Iridium Nanoclusters: A Kinetic Study
*
RAJNI LASYAL and ANJALI GOEL
Department of Chemistry, Kanya Gurukul Campus, Gurukul Kangri Vishwavidyalaya, Haridwar-249 407, India
*Corresponding author: E-mail: lasyal.rajni@gmail.com
Received: 30 April 2015;
Accepted: 1 July 2015;
Published online: 3 November 2015;
AJC-17603
In the present work, a novel method for the treatment of wastewater containing an azo dye, acid red-14 by hexacyanoferrate [HCF(III)] in
presence of iridium nanoclusters has been proposed. The effect of some important operational parameters such as pH, temperature and
catalyst concentration (iridium nano) has been investigated by kinetic spectrophotometric method at λmax 515 nm of the reaction mixture.
The results reveal that degradation kinetics of acid red-14 follows first order kinetic model with respect to [HCF(III)], [acid red-14] and
Ir nano concentration. Iridium nanoclusters were recovered with the help of centrifugation and reused for three consecutive cycles.
Thermodynamic parameters Ea, ∆S#,∆F#,∆H# and ‘A’have been calculated by studying the reaction rate in the range of temperatures 40 to
55 °C. The formation of degradation products was characterized by chromatographic and spectroscopic techniques after the extraction
with ethyl acetate. 1-Hydroxy-2-amino naphthalene and naphthalene sodium sulphate were identified as major degradation products. The
results can provide fundamental knowledge for the treatment of wastewater containing acid red-14/other azo dyes.
Keywords: Kinetics, Degradation, Acid Red-14, HCF(III), Iridium nanoclusters.
nanoclusters) on the degradation of acid red-14. These are the
major variables governing the degradation process. Acid red-
14 is the common dye for fiber dyeing, especially for woolen
fibers [9]. Furthermore, the kinetics and mechanism of the
degradation of acid red-14 has also been elucidated based on
the experimental data.
INTRODUCTION
Fiber dyeing produces a great deal of wastewater [1]. The
effluent from the dyeing process is colourful and the release
of the associated wastewater to natural stream and rivers poses
severe problems to aquatic life and humans [2]. Considerable
efforts have been made by many researchers to find appropriate
treatment systems to remove pollutants and impurities of waste-
waters from the textile industries. The conventional treatment
techniques applied to textile wastewaters, such as chemical
coagulation/flocculation, membrane separation or elimination
by activated carbon adsorption, are costly and result in phase
transfer of pollutants [3-5]. Recently nanotechnology has been
extended to waste water treatments. Degradation of dye-stuffs
using nanoparticles has gained prominence due to their low
cost, easy availability and effectiveness [5-7]. Among the
different transition metals as catalyst the interest in iridium
based nanocatalyst is increasing due to their high activity,
stability and selectivity under different reaction conditions [8].
The aim of the present study is to develop a new method for
the treatment of wastewater containing, acid red-14 (AR-14)
by hexacyanoferrate(III) ions in presence of iridium nano-
cluster by kinetic spectrophotometric method in alkaline
medium and to investigate the effect of operational parameters
such as pH, temperature and catalyst concentration (iridium
EXPERIMENTAL
All the chemicals used in the study were of analytical
grade. Acid red-14 dye (chemical structure shown in Fig. 1.)
and IrCl3·3H2O were purchased from Loba Chemie Pvt. Ltd,
Mumbai, India and Sisco Research Laborateries Pvt. Ltd., India
respectively. pH of solution was kept constant by using KH2PO4
and NaOH solutions as buffer. Measurements of pH of solution
were carried out with a digital pH meter (Systronics µ pH
system 361). Iridium-nanoclusters (particle size 4.5 0.5 nm)
were synthesized by wet reduction method using polyvinyl-
pyrrolidone (PVP) as protecting agent after the reduction of
precursor salt, (IrCl3·3H2O), by methanol as reported earlier
by Goel et al. [10].
The kinetic experiments were carried out at pH (7.5) and
constant temperature (40 0.1 °C). The appropriate quantities
of all reactants except substrate were mixed in a 100 mL iodine
flask and kept at 40 1 °C. The reaction was initiated by

336 Lasyal et al.
Asian J. Chem.
O
S
3.8
3.6
3.4
3.2
3.0
2.8
2.6
2.4
2.2
2.0
1.8
1.6
O
OH
O-Na+
N
N
S
O-Na+
O
O
Fig. 1. Chemical structure of acid red-14
injecting the solution of acid red-14 into the aforementioned
reaction mixture which was also kept in thermostat at 40
1 °C. The progress of the reaction was measured spectrophoto-
metrically (Systronics -117) with a spectrometric quartz cell
(1 cm path length) at 515 nm corresponding to λmax of the
reaction mixture. It was verified that there is a negligible
interference from other species present in the reaction mixture
at this wavelength. The reaction rate was calculated by the
plot of absorbance vs. time using plane mirror method. For
product analysis the reaction mixture was kept at atmospheric
conditions for 24 h and the products were extracted with ethyl
acetate. The degradation products were characterized by UV-
visible spectroscopy and LC-MS (BRUKER, ELITE) methods
of analysis. The mobile phase consisted of methanol:water:
acetonitrile (25:50:25) at the flow rate of 300 µL/min.
5.8
6.2
6.4
6.6
6.8
pH
7.0
7.2
7.4
7.6
Fig. 2. Effect of pH on the degradation of acid red-14 by HCF(III).
Experimental conditions: [acid red-14] = 3.0 × 10-5 mol dm-3;
[HCF(III)] = 3.0 × 10-6 mol dm-3; [Ir nano] =1.004 × 10-7 mol dm-3;
Temperature = 40 0.1 °C
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
RESULTS AND DISCUSSION
Kinetic study: The catalyzed oxidation of acid red-14
has been studied at constant pH and temperature at different
concentrations of one reactant keeping the concentration of
others constant. The pH value is an important operational
parameter in actual wastewater treatment. To study the effect
of pH on the reaction rate, it varied from the value 6 to 7.5
only as above 7.5 the colour of dye changes. Fig. 2 showed
that the rate of degradation was maximum at pH 6.At high pH
values, the rate of degradation decreases which may be due to
columbic repulsion between anionic dye surface and hydroxyl
anion, hence they do not have opportunity to react with dye
molecules [11,12]. Fig. 3 suggested that the rate of degradation
of acid red-14 with respect to [HCF(III)] follows first order
kinetics at its lower concentrations tending towards zero order
at its higher concentrations. The effect of [HCF(III)] on the
rate of degradation has been studied by varying its concen-
tration from 1 × 10-6 to 9 × 10-6 mol dm-3 as shown in Fig. 3.
The effect of variation of dye concentrations has also been
studied by varying its concentration from 1 × 10-5 to 8 × 10-5
mol dm-3. Fig. 4 shows the first order dependence of rate on
the concentration of substrate. The effect of concentration of
Ir nano on the rate of degradation was also studied. A gradual
increase in rate with iridium nanoclusters concentration reveals
first order kinetics with respect to [Ir-nano]. The concentration
of iridium nanoparticles was varied about many times from
0.2 × 10-7 to 1.204 × 10-7 mol dm-3 (Fig. 5). The variation in
rate with the amount of catalyst shows that the rate of reaction
may have been controlled by the mass of catalyst. The effect
of precursor Ir was studied to compare its effect with Ir-nano
on the rate of degradation of acid red-14 by hexacyano-
ferrate(III) in aqueous alkaline medium.
0
2
4
6
8
10
[HCF(III)] × 106 mol dm–3
Fig. 3. Effect of [HCF(III)] on the degradation of acid red-14 by HCF(III).
Experimental conditions: [acid red-14] = 3.0 × 10-5 mol dm-3; [Ir
nano] = 1.004 × 10-7 mol dm-3; pH = 7.5; Temperature = 40 0.1 °C
7
6
5
4
3
2
1
0
0
1
2
3
4
6
5
7
8
9
[Acid red-14] × 105 mol dm–3
Fig. 4. Effect of [acid red-14] on the degradation of acid red-14 by HCF(III).
Experimental conditions: [HCF(III)] = 3.0 × 10-6 mol dm-3; [Ir nano]
=1.004 × 10-7 mol dm-3; pH = 7.5; Temperature = 40 0.1 °C

Vol. 28, No. 2 (2016)
Degradation of Azo Dye, Acid Red-14 by Hexacyanoferrate(III) Using Iridium Nanoclusters 337
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
TABLE-2
RATE OF DEGRADATION OF REACTION MIXTURE
FOR THREE CONSECUTIVE CYCLES
Ir precursor
Ir nano
No. of cycles
Before recovery
After I cycle
After II cycle
After III cycle
-dA/dt × 103 (min-1) Particle size (nm) by XRD
2.0
1.4
0.8
0.6
4.50
17.03
49.34
56.50
0.888
250 nnm
0.687
0.486
0.286
0.085
-0.116
515 nm
Product
268 nm
Acid red-14
(a)
(b)
0.2
0.4
0.6
0.8
1.0
1.2
220.0 288.6 357.1 425.7 494.3 562.9 631.4 700.0
Wavelength (nm)
[Ir nano]/[Ir precursor] × 107 mol dm–3
Fig. 6. UV-visible spectra of (a) acid red-14 and (b) extracted product
Fig. 5. Effect of [Ir nano/Ir precursor] on the degradation of acid red-14
by HCF(III). Experimental conditions: [acid red-14] = 3.0 × 10-5
mol dm-3; [HCF(III)] = 3.0 × 10-6 mol dm-3; pH = 7.5; Temperature
= 40 0.1 °C
of the dye molecule in the solution [13]. The disappearance of
this band and formation of new bands at 250 and 268 nm
supports the degradation by hexacyanoferrate(III) ions. In
order to provide supported evidences for degradation, identi-
fication of degradation products was carried out by LC-MS
(Fig. 7). 1-Hydroxy-2-amino naphthalene and naphthalene
sodium sulphate have been confirmed as the major degradation
products. Proposed chemical structures of the expected degra-
dation products are given in Table-3.
Thermodynamic parameters: To evaluate the thermody-
namic parameters for the oxidation of acid red-14, the reaction
has been studied at four different temperatures i.e. 40, 45, 50
and 55 °C. The calculated values of energy of activation (Ea),
entropy of activation (∆S#), energy of formation (∆F#),enthalpy
of activation (∆H# ) and Arrhenius factor (A) are presented in
Table-1. Low value of energy of activation reveals good
catalytic activity of Ir nano while large entropy of activation
shows the formation of polar species during the reaction.
157.0
4.128e+7
100%
TABLE-1
THERMODYNAMIC PARAMETERS
Parameters
Values
8.08
7.44
-34.38
18.72
5.55 × 105
75%
Ea (kcal mol-1)
∆H# (kcal mol-1)
∆S# (e.u.)
∆F# (kcal mol-1)
A (L mol-1 s-1)
50%
223.0
1.197e+7
305.2
1.011e+7
Efficiency of recycled catalyst: In order to investigate
the economy of the present method, iridium nanoparticles were
recovered and reused for three consecutive cycles.After the first
degradation cycle the treated reaction mixture was centrifuged.
The obtained nanoparticles were washed thoroughly with
double distilled water five to six times and were further reused
as catalyst in the kinetic study. The same method was used
further for two successive cycles at fixed experimental condi-
tions. The results are presented in Table-2. It was found that
the rate of reaction decreased with each successive cycle.
This may be due to increase in size of nanoparticles because
of agglomeration.
25%
0%
419.2
6.851e+6
159.0
4.696e+6
224.8
353.1
2.542e+6
2.562e+6
Fig. 7. LC-MS spectra of degraded products of acid red-14
Mechanism: Though it is difficult to propose a mechanism
for such complex reaction, however, based on the above experi-
mental results and previously reported work, the following
tentative mechanism reaction for the oxidation of acid red-14
can be proposed:
Identification of degradation products: Degradation
of acid red-14 was monitored by UV-visible spectroscopy
(Fig. 6). Acid red-14 is characterized by maximum absorption
at 515 nm attributed to the chromophore containing azo linkage
k1
D– + Irn
Complex (C)
(1)
k
–
1

338 Lasyal et al.
Asian J. Chem.
products are simple and less hazardous. Iridium nanoparticles
proved as an efficient catalyst for the oxidation of acid red-14
as they demonstrated the enhanced degradation rate compared
to iridium precursor which may be due to large surface area to
volume ratio. Moreover, these nanoparticles can be recovered
and reused making them potential candidates for dye degra-
dation technologies. The work provides an economical solution
to aquatic environment in terms of time saving, use of very
small concentration of catalyst and is equally useful in the
degradation of several other dyes.
TABLE-3
PROPOSED STRUCTURES OF ACID RED-14
DEGRADATION PRODUCTS
m.w.
Proposed structure
OH
159
NH2
1-Hydroxy-2-amino naphthalene
REFERENCES
353
SO3Na
1. Z. Shen, W. Wang, J. Jia, J.Ye, X. Feng and A. Peng, J. Hazard. Mater.,
84, 107 (2001).
Naphthalene sodium sulphate
2. N.M. Mahmoodi and M. Arami, J. Photochem. Photobiol. Chem., 182,
60 (2006).
k2
3. M.R. Samarghandi, M. Zarrabi, A. Amrane, M.N. Sepehr, M. Noroozi,
S. Namdari and A. Zarei, Desalination Water Treat., 40, 137 (2012).
4. H. Ghodbane, A.Y. Nikiforov, O. Hamdaoui, P. Surmont, F. Lynen, G.
Willems and C. Leys, J. Adv. Oxid. Technol., 17, 372 (2014).
5. A.D. Bokare, R.C. Chikate, C.V. Rode and K.M. Paknikar, Appl. Catal.
B, 79, 270 (2008).
6. W.X. Zhang, J. Nanopart. Res., 5, 323 (2003).
7. T. Poursaberi, M. Hassanisadi and F. Nourmohammadian, Prog. Color
Colorants Coat., 5, 35 (2012).
C + Fe(CN)63–
Irn + Fe(CN)64– + Products (2)
slow
From the above reaction mechanism, it is assumed that in
alkaline medium mono azo dye acid red-14 (D) exist as anion
(D-) [14] which forms a loosely bonded complex with iridium
nanoparticles (Irn). This complex (C) slowly reacts with HCF(III)
ion resulting into products along with Irn and Fe(CN)64-.
Conclusion
8. A. Goel and R. Sharma, J. Indian Chem. Soc., 89, 1191 (2012).
9. S. Kundu and H. Liang, J. Colloid Interf. Sci., 354, 597 (2011).
10. A. Goel and N. Rani, Open J. Inorg. Chem., 2, 67 (2012).
11. A.P. Davis and C.P. Huang, Water Sci. Technol., 21, 455 (1989).
12. A.V. Rupa, D. Manikandan, D. Divakar and T. Sivakumar, J. Hazard.
Mater., 147, 906 (2007).
13. J. Lin, X. Zhao, D. Liu, Z. Yu, Y. Zhang and H. Xu, J. Hazard. Mater.,
157, 541 (2008).
14. V. Vatanpour, N. Daneshvar and M.H. Rasoulifard, J. Environ. Eng.
Manage., 19, 277 (2009).
The present work shows that acid red-14 can be easily
degraded by hexacyanoferrate(III) in presence of iridium
nanoparticles. The reaction follows first order kinetics with
respect to acid red-14 at pH of 7.5 and constant temperature
of 40 0.1 °C while the order of reaction with respect to
[HCF(III)] has been found to be one at its lower concentration
tending towards zero at its higher concentration. Degradation