Mechanistic aspects for the oxidation of brilliant green dye by chloramine-T in the presence of perchloric acid: A spectrophotometric kinetic approach

Article abstract of DOI:10.1007/s11164-012-0986-y

The kinetics of a triarylmethane dye, brilliant green (BG), by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO₄ media at 303 K. Under identical experimental conditions, the rate law was -d [BG]/dt = k [BG] [H⁺]. Variations in ionic strength (μ) of the medium had no effect on the oxidation velocity. Addition of p-toluenesulfonamide, the reduction product of CAT and Cl^-, had no significant effect on the rate of reaction. The values of rate constants observed at five different temperatures (298, 303, 308, 313, and 318 K) were utilized to calculate the activation parameters. The observed results have been explained by a general mechanism and the related rate law has been obtained. The process demonstrated in this study is cost effective, which holds great promise in potential application for pollutant control.

Full text of DOI:10.1007/s11164-012-0986-y

Res Chem Intermed
DOI 10.1007/s11164-012-0986-y
Mechanistic aspects for the oxidation of brilliant green
dye by chloramine-T in the presence of perchloric acid:
a spectrophotometric kinetic approach
Ajaya Kumar Singh Shakila Bano
•
Received: 16 September 2012 / Accepted: 17 December 2012
Ó Springer Science+Business Media Dordrecht 2013
Abstract The kinetics of a triarylmethane dye, brilliant green (BG), by sodium N-
chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophoto-
metrically in HClO media at 303 K. Under identical experimental conditions, the
4
?
rate law was -d [BG]/dt = k [BG] [H ]. Variations in ionic strength (l) of the
medium had no effect on the oxidation velocity. Addition of p-toluenesulfonamide,
-
the reduction product of CAT and Cl , had no significant effect on the rate of
reaction. The values of rate constants observed at five different temperatures (298,
03, 308, 313, and 318 K) were utilized to calculate the activation parameters. The
3
observed results have been explained by a general mechanism and the related rate
law has been obtained. The process demonstrated in this study is cost effective,
which holds great promise in potential application for pollutant control.
Keywords Oxidation kinetics ꢀ Brilliant green ꢀ Chloramine-T ꢀ Perchloric acid
Introduction
Pollution of water by dyes by many industries to color their products is a serious
problem in the developed and developing countries. Brilliant green dye (BG—
C H N ꢀHO S), a triphenylmethane dye, is an odorless yellow-green to green
2
7
33
2
4
powder which is toxic and has mutagenic and carcinogenic effects that affect
aquatic biota and humans. It is also used extensively in textile dying and for the
production of cover paper in the paper industry. About 0.8–1.0 kg of BG dye is
consumed per ton of paper production [1, 2]. The removal of BG dye from
A. K. Singh (&)
Department of Chemistry, Govt. V.Y.T. PG. Autonomous College, Durg, Chhattisgarh, India
e-mail: ajayaksinghau@gmail.com
S. Bano
Department of Applied Chemistry, GD-Rungta College of Engineering & Technology, Bhilai, India
123

A. K. Singh, S. Bano
wastewater is, therefore, a challenge to us. Several photocatalytic degradation
procedures for the decolorization of triarylmethane dyes have been reported in the
literature [3–5]. In spite of the available procedures, there is still a need for a simple
method which is cost effective, non-toxic and environmentally benign. In the light
of the above considerations, only a kinetic method can be the most effective for
oxidative degradation of BG dye.
The diverse nature of the chemistry of N-metello N-arylhalosulfonamides (organic
haloamines) is attributed to their ability to act as sources of halonium cations,
hypohalite species and N-anions, which act as both bases and nucleophiles [6–10].
Sodium N-chloro p-toluenesulfonamide (p-CH C H SO NClNaꢀ3H O), well known
3
6
4
2
2
as chloramines-T (CAT), is an important member of this class of compounds.
Generally, CAT undergoes a two-electron change in redox reactions, resulting in the
formation of the reaction products p-toluenesulfonamide (PTS) and sodium chloride.
CAT is a source of positive halogen, and this reagent has been exploited as an oxidant
for a variety of substrates both in acidic and alkaline media [11, 12]. The species
responsible for the oxidizing character may be different depending on the pH of the
medium. The redox potential of the system is pH-dependent. CAT has been used as
oxidant in neutral, acidic and alkaline media [13, 14]. It is also used as an antiseptic
and antipyretic drug [15]. An extensive literature survey revealed that there are only a
few reports on the kinetics of oxidation of organic dyes by CAT [16–19].
Interestingly, no information is available on the oxidative behavior of CAT towards
BG dye from their kinetic and mechanistic aspects. The present study examines, in
detail, the kinetic and mechanistic aspects for the oxidation of BG dye by CAT in the
presence of HClO with the following objectives: (1) to determine the order of
4
reaction with respect to oxidant and dye, (2) to ascertain the reactive species, (3) to
?
-
study the effect of [H ], Cl ion, ionic strength, dielectric constant of the medium,
temperature, and one of the products of the oxidant on the reaction rate, (4) to study
the stoichiometry and analysis of the product, and (5) to propose the rate law and the
reaction mechanism in agreement with kinetic results.
Experimental
Materials
The stock solution of CAT (Loba Chem.) was prepared in water and standardized
iodometrically. BG dye (Sd. Fine) was used without further purification. Aqueous
solutions of desired strength were freshly prepared prior to use. Solvent studies were
made with acetonitrile (Loba Chem.). All the other chemicals were of analytical
reagent grade and were used as received. Double distilled water was used throughout
the studies.
Kinetic measurement
The detailed kinetic runs were performed under pseudo-first-order conditions with a
known excess of the [CAT] over [BG] using a visible spectrophotometer (Digital
0
0
1
23

A spectrophotometric kinetic approach
spectrophotometer 167; Systronics, India). In the present study, the kinetic
experiments were carried out between 293 and 318 K. A constant temperature
was maintained with an accuracy of ± 0.1 °C. Reactions were carried out in glass
stoppered Pyrex boiling tubes whose outer surfaces were coated black to eliminate
any photochemical effects. The oxidant as well as requisite amounts of BG, HClO4
and water were taken in separate tubes and thermostated for 30 min at 303 K. The
reaction was initiated by the rapid addition of a measured amount of CAT to the
stirred reaction mixture. Absorbance measurements were made at kmax = 622 nm
for BG dye for more than two half-lives. The absorbance readings at t = 0 and t = t
are D and D . Plots of log D /D versus time were made to evaluate the pseudo-first-
0
t
0
t
order rate constant kobs which were found reproducible within ± 4 %.
Stoichiometry
Stoichiometric experiments were conducted by mixing different amounts of BG dye
-3
-
and CAT at a molar ratio of 1:10 [BG]:[CAT] in the presence of 4 9 10 mol dm
3
HClO for 48 h at 303 K and the results are reported in Table 1. The results clearly
4
demonstrate the consumption of 1 mol of CAT per mole of BG, confirming the
following stoichiometry (Scheme 1).
Characterisation of products
The reaction mixture in the stoichiometric ratio in the presence of HClO under
4
stirred conditions was allowed to progress for 48 h at 303 K. After the completion
of the reaction, the mixture was neutralized with dilute NaOH and products were
extracted with ethyl acetate. The organic products were identified by using the TLC
technique and separated by column chromatography. The reduction product, PTS
(
TsNH ), was detected by TLC [20]. Further confirmation was determined by its
2
melting point, 139 °C, which was within close proximity to the reported
temperature of 137–140 °C in previous studies [21]. PTS was quantitatively
determined by its reaction with xanthydrol to yield the corresponding N-xanthyl-p-
toluenesulfonamide [16]. In a typical experiment, equal quantities of separated PTS
and xanthydol (0.20 g) were dissolved in 10 ml of glacial acetic acid. The reaction
mixture was stirred for 3 min at room temperature and allowed to stand for 90 min.
The derivative was filtered, recrystallized with dioxane/water (3:1), and dried at
room temperature. The mass of PTS was obtained with 80–85 % recovery in all the
cases. N,N-diethylamino benzophenone and p-N,N-diethylamino phenol were found
Table 1 Consumption of CAT in the oxidation of BG dye in acidic medium at 303 K
5
6
6
6
[
BG] 3 10
mol dm
[CAT] 3 10
-3
(mol dm ): initial
[CAT] 3 10
-3
(mol dm ): final
[CAT] 3 10
-3
(mol dm ): consumed
[CAT]:[BG]
-
3
(
)
1
3
5
.00
.00
.00
10.00
30.00
50.00
8.85
26.98
44.90
1.15
3.02
5.10
1.15
1.00
1.02
-
3
-3
4
Experimental conditions: [HClO ] = 4 9 10 mol dm
123

A. K. Singh, S. Bano
Scheme 1 Stoichiometric equations for oxidation of BG dye by CAT in acidic medium
to be the oxidation products of BG dye. It was also observed that there was no
further oxidation of these products under the present reaction conditions.
Results and discussion
The detailed kinetic investigations were performed under pseudo-first-order
conditions of [CAT] ꢁ [BG] . The kinetics of oxidation of BG has been
0
0
investigated with several initial concentration of the reactant in the presence of
HClO at 303 K.
4
Effect of reactant concentrations on the reaction rate
With the oxidant in excess, at constant [CAT] , [HClO ] and temperature, plots of
0
4
log absorbance (Abs) versus time were linear, indicating a first-order dependence on
the rate of [BG] (Fig. 1). The values of pseudo-first order rate constants (kobs) were
0
listed (Table 2). Further, kobs did not change with the change in [BG] , confirming
0
the first-order dependence on [BG] . Under the same experimental conditions, an
0
increase in [CAT] , the value of k remains constant (Table 2), showing a zero-
0
obs
order reaction with respect to [CAT]. The rate constant was found to increase slightly
-3 -1
-
from 0.2 9 10 to 1.4 9 10
3
? -3
with an increasing [H ] from 0.5 9 10 to
s
.0 9 10 mol dm (Table 3; Fig. 2).
-
3
-3
4
Effect of PTS concentration on the reaction rate
The addition of PTS to the reaction mixture had no significant effect on the rate
(
Table 4).
1
23

A spectrophotometric kinetic approach
5
[
(
BG] x 10
-3
mol dm
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
)
1
2
2
3
4
5
.5
.0
.5
.0
.0
.0
6.0
.0
7
0
2
4
6
8
10
12
14
16
Time (min)
-
5
Fig. 1 First-order plots of the oxidation of BG by CAT in acidic medium. [BG] = 1.5 9 10
,
mol dm , [HClO ] = 4 9 10 mol dm
4
,
-6
-
5
-5
-5
-5
-5
6 9 10
-5
-3
mol dm , [CAT] = 4 9 10
2
9 10
,
3 9 10
,
4 9 10
,
5 9 10
,
7 9 10
-
3
-3
-3
Table 2 Effect of BG dye and CAT concentrations on the rate of reaction at 303 K
6
CAT] 3 10 (mol dm
-3
5
[BG] 3 10 (mol dm
-3
3
-1
[
)
)
k
obs 3 10 (s
)
0
1
1
2
3
4
5
6
4
4
4
4
4
4
4
4
.50
.00
.50
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
1.50
2.00
2.50
3.00
4.00
5.00
6.00
7.00
1.40
1.41
1.40
1.39
1.40
1.40
1.41
1.40
1.40
1.41
1.40
1.39
1.40
1.40
1.41
1.40
-
3
-3
4
Experimental conditions: [HClO ] = 4 9 10 mol dm
Effect of ionic strength on the reaction rate
The effect of ionic strength (l) of the medium was studied by adding requisite
amounts of KNO , with all other experimental conditions held constant. The rate of
reaction remains constant with the increase in ionic strength of the medium. The rate
3
123

A. K. Singh, S. Bano
?
Table 3 Effect of H concentration on the reaction rate at 303 K
?
3
H ] 3 10 (mol dm
-3
3
-1
3
-1
)
3
-1
[
)
k
obs 3 10 (s
)
k
cal 3 10 (s
k
expected 3 10 (s )
0
1
2
3
4
.50
.00
.00
.00
.00
0.20
0.40
0.78
1.10
1.40
0.20
0.40
0.80
1.20
1.70
0.20
0.40
0.78
1.10
1.40
-3
-5
-3
-6
Experimental conditions: [BG] = 4 9 10 mol dm , [CAT] = 4 9 10 mol dm
-
constant was found to be 1.4 3 10 (s ) by using KNO from 5 9 10 to
3
-1
-3
3
-
3
-3
0 9 10 mol dm .
2
Effect of chloride ion on the reaction rate
-
The addition of Cl ions in the form of NaCl had a negligible effect on the rate,
indicating that no free chlorine is formed in the reaction.
Effect of dielectric constant and temperature on the reaction rate
Rate constant values decreased with the increase in the acetonitrile %, that is, with
decreasing dielectric constant or polarity of the medium (Table 4; Fig. 3). The
reaction was carried out at different temperatures (298, 303, 308, 313, and 318 K),
keeping other experimental conditions constant. The rate of reaction increased with
an increase in the temperature. From the linear Arrhenius plots of log kobs versus 1/T
-
1
(
activation
Fig. 4), the activation energy (E ) was calculated as 41.31 kJ mol . Other
a
parameters
determined
-1
were
enthalpy
of
activation
#
(DS = -
#
(
DH = 38.80 ± 0.02 kJ mol ),
entropy
of
activation
-
1
#
-1
1
and the Arrhenius factor (log A = 4.27) (Table 5).
63.64 ± 0.23 JK ), free energy of activation (DG = 96.45 ± 0.12 kJ mol ),
Polymerization study
In order to ascertain the presence of free radicals in the reaction, the reaction
mixture containing acrylamide was kept for 24 h in an inert atmosphere. When the
reaction mixture was diluted with methanol, no precipitate was found. On the basis
of this, it can very easily be inferred that there is no possibility of the formation of
free radicals in the reaction [22].
Reactive species of CAT
CAT acts as a mild oxidant both in acidic and alkaline media. In general, CAT
undergoes a two-electron change in its reactions forming the reduction products,
PTS and sodium chloride. The oxidation potential of the CAT-TsNH redox couple
2
1
23

A spectrophotometric kinetic approach
2
R = 0.996
0
0
0
0
.0015
.0010
.0005
.0000
0
.000
0.001
0.002
0.003
0.004
+
[H ]
?
?
-3
-3
-3
Fig. 2 Effect of [H ] on the rate constant (kobs) at 303 K. [H ] = 0.5 9 10 , 1 9 10 , 2 9 10
3
,
-3
-3
-5
-3
-6
9 10 , 4 9 10 , [BG] = 4 9 10 mol dm , [CAT] = 4 9 10 mol dm
-3
Table 4 Effect of PTS and acetonitrile concentrations on the rate of reaction at 303 K
6
PTS] 3 10 (mol dm
-3
3
-1
[
)
[CH3CN] (%)
D
k
obs 3 10 (s
)
1
2
3
4
5
.00
.00
.00
.00
.00
1.40
1.40
1.40
1.40
1.40
1.40
1.00
0.60
0.35
0.19
0
5
.00
.00
73.60
71.80
70.00
68.20
66.50
1
2
3
0.00
0.00
0.00
-
5
-3
mol dm , [CAT] = 4 9 10
-6
-3
4
mol dm , [HClO ] =
Experimental conditions: [BG] = 4 9 10
-3
-
3
4
9 10 mol dm
varies with pH of the medium (E is 1.14 V at pH 0.65, 0.778 V at pH 7.0, 0.614 V
0
at pH 9.7, and 0.50 V at pH 12). Depending on the pH, CAT furnishes different
types of reactive species in solutions. The suggested oxidizing species in acidified
?
CAT solutions are TsNHCl, TsNCl , HOCl, and H OCl [23, 24].
2
2
ꢂ
þ
TsNClNa ꢀ TsNCl þ Na
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ꢂ
þ
TsNCl þ H ꢀ TsNHCl
TsNHCl ꢀ TsNCl þ TsNH
TsNHCl þ H O ꢀ TsNH þ HOCl
2
2
2
2
2
123

A. K. Singh, S. Bano
1
1
0
0
0
0
.2
.0
.8
.6
.4
.2
2
R
= 0.993
0.0136
0.0140
0.0144
0.0148
0.0152
1
/D
Fig. 3 Effect of dielectric constant on the observed rate constants in the oxidation of BG by CAT in acidic
-3
-
5
-3
-6
-3
-3
4
medium. [BG] = 4 9 10 mol dm , [CAT] = 4 9 10 mol dm , [HClO ] = 4 9 10 mol dm
1
1
1
1
1
1
.5
.4
.3
.2
.1
.0
2
R
= 0.993
0.00315
0.00320
0.00325
0.00330
0.00335
1/T
Fig. 4 Effect of temperature on the pseudo-first-order rate constant for the oxidation of BG by CAT in acidic
-
5
-3
-6
-3
-3
-3
4
medium. [BG] = 4 9 10 mol dm , [CAT] = 4 9 10 mol dm , [HClO ] = 4 9 10 mol dm
TsNCl þ H O ꢀ TsNHCl þ HOCl
ð5Þ
ð6Þ
2
2
þ
ꢂ
HOCl ꢀ H þ ClO
Spectral changes of brilliant green during oxidation by CAT in acidic medium
The color of the BG dye is due to the structure, in which a central carbon is bonded
to three aromatic rings, one of which is in the quinoid form (the chromophore) and
the oxochrome is -NR . The changes in the absorption spectra of BG dye
2
-
5
-3
-6
(4 9 10 mol dm ) solution during the oxidation process in CAT (4 9 10
-
mol dm ) in acidic media HClO (4 9 10 mol dm ) at 303 K at different times
3
-3
-3
4
1
23

A spectrophotometric kinetic approach
Table 5 Effect of temperature and values of activation parameters for the oxidation of BG dye by CAT
in acidic medium at 303 K
3
#
#
-1
#
Temp.
K)
k
(s
obs 9 10
E
mol
a
(KJ
-1
DH (KJ
DS (JK
DG (KJ
mol )
logA
4.27
-
1
-1
mol
-1
-1
(
)
)
)
mol
)
298
303
308
313
318
0.98
1.40
1.70
2.20
2.90
41.31
38.80 ± 0.02
-163.64 ± 0.23 96.45 ± 0.12
-5
-3
mol dm
-6
-3
mol dm ,
Experimental
[
conditions:
[BG] = 4 9 10
-3
,
[CAT] = 4 9 10
-
HClO ] = 4 9 10 mol dm
3
4
are shown in Fig. 5. The decrease of the absorption peak of the dye at
kmax = 622 nm indicates a rapid degradation of the BG dye. The decrease is also
meaningful with respect to the bond, i.e. central carbon attached to the aromatic ring
(
quinoid form) as the most active site for oxidative attack. The decrease in the
absorption intensity of the band at kmax during the oxidation also expresses the loss
of conjugation.
Reaction mechanism and rate law
A general mechanism Scheme (2) was proposed to substantiate the observed
kinetics during the oxidation of BG dye by CAT in acidic medium.
K
þ
BG þ H ꢀ C ðfast stepÞ
ð7Þ
ð8Þ
k
C þ H Oꢂ! products ðslow stepÞ
In Scheme (2), the BG dye reacts with acid to form a BG-H (C) intermediate in
2
?
a fast equilibrium step. In the next slow rate-determining step, intermediate species
(
C) reacts with H O to form products.
2
According to the reaction, Scheme (2), and considering the fact that 1 mol of BG
dye is oxidized by 1 mol of CAT, the rate of reaction can be expressed as:
Rate ¼ ꢂdc=dt ¼ k K ½BGꢃ ½Hþꢃ
By reversing and rearranging Eq. 9, Eq. 10 becomes:
ð9Þ
1
½BGꢃ
1
¼
¼
ð10Þ
kobs
rate
kK½Hþꢃ
?
Equation (10) indicates that, if we plot a graph between 1/kobs versus 1/[H ], we
get a straight line with positive intercepts at the y-axis (Fig. 6). This proves the
validity of the rate law (Eq. 9) and the proposed reaction Scheme (2), on the basis of
which the rate law (Eq. 9) has been derived. From the value of the intercept and
-
1
slope of the plot, kK was found to be 0.407 s
.
123

A. K. Singh, S. Bano
Fig. 5 Spectral changes during oxidative degradation of BG by CAT in acidic medium. [BG] =
4
-
5
-3
-6
-3
-3
-3
4
9 10 mol dm , [CAT] = 4 9 10 mol dm , [HClO ] = 4 9 10 mol dm
Effect of dielectric constant on the reaction rate
The effect of change of the solvent composition on the reaction rate was studied by
varying the concentrations of acetonitrile from 0 to 30 % by volume, and the rate
constants are listed in Table 4. The rate constant of the reaction decreased with
increasing acetonitrile % from 0 to 30 %. The rate of oxidation was found to depend
on the polarity of medium. When the polarity of solvent was increased, the rate of
reaction decreased. In order to determine the effect of the dielectric constant
(
polarity) of the medium on the rate of reaction, the oxidative degradation of BG
dye by CAT was studied for various concentrations of acetonitrile. The data clearly
revealed that the rate constant values decreased with the increase in the acetonitrile
%
, that is, with decreasing dielectric constant or polarity of the medium.
The effect of the dielectric constant of the medium on the rate constant of a
reaction between two ions has been described by the well known equation given
below:
2
Z Z e N
A
1
B
logkobs ¼ logk0
ꢄ
ð11Þ
2
:303ð4pe ÞdABRT
D
0
Where k is the rate constant in a medium of infinite dielectric constant, Z and Z
B
0
A
are the charges of the reacting ions, dAB refers to the size of activated complex, T is
absolute temperature, and D is the dielectric constant of the medium. A plot is made
1
23

A spectrophotometric kinetic approach
Scheme 2 Mechanistic pathway for oxidative degradation of BG dye by CAT in acidic medium
between logkobs and 1/D, and a straight line having a negative slope was obtained
(Fig. 3), indicating an interaction between a charged ion and a dipolar molecule.
From the slope of the straight line, the dAB value has been calculated and found to
˚
be 0.4 A.
In Scheme (2), the negligible effect of the variation of ionic strength of the
medium on the rate oxidation of BG dye is well explained. Entropy of activation
plays an important role in the case of the reaction between ions or between an ion
123

A. K. Singh, S. Bano
5
4
3
2
1
000
000
000
000
000
0
2
R = 0.999
0
400
800
1200
1600
2000
+
1
/[H ]
?
-3
-3
4
Fig. 6 Graphical representation of 1/kobs and 1/H concentration. [HClO ] = 0.5 9 10 , 1 9 10 ,
2
-3
-3
-3
-5
-3
9 10 , 3 9 10 , = 4 9 10 , [BG] = 4 9 10 mol dm , [CAT] = 4 9 10 mol dm
-6
-3
and a neutral molecule, or a neutral molecule forming ions. When the reaction takes
place between two similarly charged species, the transition state will be a more
highly charged ion, and, due to this, more solvent molecules will be required than
for the separate ions, leading to a decrease in entropy. On the other hand, when the
reaction takes place between two ions of opposite charges, their union will result in
a lowering of the net charge and due to this some frozen solvent molecules will be
released with an increase of entropy [25]. On the basis of this information, the
observed negative entropy of activation supports the rate limiting step of the
proposed scheme. The proposed mechanism is also supported by the moderate value
#
of energy of activation and other parameters. The high positive values of DH and
#
DG indicate that the transition state is highly solvated.
Multiple regression analysis
To discover the relationship between dependent, that is, pseudo-first-order variable
?
rate constant kobs, and one independent variable [H ] in order to arrive at a
conclusion whether or not the proposed mechanism is well in accordance with our
experimental kinetic data, we have been helped by a multivariate regression analysis
using the computer package STAT GRAPHICS. With the aid of a multivariate
regression analysis, a relationship between the observed pseudo-first-order rate
?
constant kobs and the concentration of H , except BG dye, was determined.
kobs ¼ k ½Hþꢃ
where kobs is 8.88 9 10 . The R-squared statistic indicated that the model as fitted
ð12Þ
-
16
?
explains 100 % of the variability in [H ]. The adjusted R-squared statistic, which is
more suitable for comparing models with different numbers of independent vari-
ables, is 0.0 %. The standard error of the estimate shows the standard deviation of
the residuals to be 0.0. This supports the validity of the rate law given in Eq. 9. The
1
23

A spectrophotometric kinetic approach
proposed reactions in Scheme 2 are also valid because these equations were used to
calculate the rate based on the multiple regression analysis (Eq. 12). The similarity
among the three rates, that is, the observed (experimentally), calculated (from rate
law), and predicted (from regression analysis) results, clearly support the validity of
the rate law expressed in Eq. 9, and hence, the proposed reaction mechanism.
Conclusion
In this study, BG dye was successfully degraded in acidic medium by the CAT
oxidant, and it was found that the reaction of BG dye follows kinetics with the rate
?
law:rate = k [BG] [H ]. The addition of PTS had no significant effect on the rate.
Activation parameters for the overall reaction have been computed. A possible
reaction mechanism and the related rate law have been deduced. The present redox
system can be adopted for treating the chosen BG dye present in industrial effluents
to reduce toxicity caused by BG dye. This novel approach could be used as a highly
efficient and green technology for BG dye degradation.
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