Advanced catalytic oxidation process based on a Ti-permanganate (Mn/Ti-H+) reaction for the treatment of dye wastewater

Article abstract of DOI:10.1039/c9ra03045j

This article discusses the titanium (Ti)-based permanganate advanced catalytic oxidation process (ACOP) for the possible recovery of thousands of tons of dye wastewater. The heterogeneous catalyst TiO₂ in the solid state employed in the liquid phase reaction mixture with dye and potassium permanganate was recovered and reused several times for reproducible results. The kinetics were examined at various operational parameters like the effect of dyes, the effect of oxidants, the amount of catalysts, and the effect of acids, temperature, and various organic and inorganic additives used in the textile industry. The kinetics of advanced oxidation and the mechanism of dye de-coloration and degradation were monitored using the Congo red (CR) dye as a model in an aqueous medium and then applied to other dyes and real dye wastewater samples. The color removal was up to 98%, with the removal efficiency being linear with the dose at a particular time. This method could exhibit the complete color removal of the dye wastewater, leading to mineralization coupled with a change in the oxidation state of Mn from +7 to +2. The method also improved the BOD/COD ratio, followed by an increase in the salinity of the recycled water. This indicated that this method can be used not only for the highly efficient de-colorization of dye wastewater but also as a preliminary step for the utilization of the dye wastewater after its recycling. The newly developed system was proven to be very cost-effective and eco-friendly with low sludge quantity, which contained numerous nitrogenous compounds, and this was validated by FTIR and HPLC analyses; thus, the system may be used in treatment plants for the recovery of wastewater.

Full text of DOI:10.1039/c9ra03045j

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PAPER
Advanced catalytic oxidation process based on a Ti-
+
permanganate (Mn/Ti-H ) reaction for the
Cite this: RSC Adv., 2019, 9, 37562
treatment of dye wastewater
Rafia Azmat, * Anum Khursheed, Ailyan Saleem and Noshab Qamer
This article discusses the titanium (Ti)-based permanganate advanced catalytic oxidation process (ACOP)
2
for the possible recovery of thousands of tons of dye wastewater. The heterogeneous catalyst TiO in
the solid state employed in the liquid phase reaction mixture with dye and potassium permanganate was
recovered and reused several times for reproducible results. The kinetics were examined at various
operational parameters like the effect of dyes, the effect of oxidants, the amount of catalysts, and the
effect of acids, temperature, and various organic and inorganic additives used in the textile industry. The
kinetics of advanced oxidation and the mechanism of dye de-coloration and degradation were
monitored using the Congo red (CR) dye as a model in an aqueous medium and then applied to other
dyes and real dye wastewater samples. The color removal was up to 98%, with the removal efficiency
being linear with the dose at a particular time. This method could exhibit the complete color removal of
the dye wastewater, leading to mineralization coupled with a change in the oxidation state of Mn from
+7 to +2. The method also improved the BOD/COD ratio, followed by an increase in the salinity of the
recycled water. This indicated that this method can be used not only for the highly efficient de-
colorization of dye wastewater but also as a preliminary step for the utilization of the dye wastewater
after its recycling. The newly developed system was proven to be very cost-effective and eco-friendly
with low sludge quantity, which contained numerous nitrogenous compounds, and this was validated by
FTIR and HPLC analyses; thus, the system may be used in treatment plants for the recovery of wastewater.
Received 24th April 2019
Accepted 5th October 2019
DOI: 10.1039/c9ra03045j
rsc.li/rsc-advances
There are various methods available that are under practice for
Introduction
the treatment of industrial textile effluents aer biological
8,9
The textile industrial dyestuffs create one of the primary sets of treatments to make them safe. These processes include (i)
2
+
3+
organic compounds that characterize an accumulative envi- Fenton (H
2
O
2
/Fe ), (ii) Fenton-like (H
2
O
2
/Fe ), (iii) photo-
2
+
3+
3+
ronmental hazard, while 1–20% of the total world production of assisted Fenton (H
dyes is used in the dyeing process and discharged as the textile UV), and (iv) ozonation (Mn /oxalic acid/ozone and O
O /Fe (Fe )/UV and H O /Fe -oxalate/
2 2 2 2
2
+
/H O )
2 2
3
1
effluent in running streams. The extensive use of dyes is reactions as well as (v) advanced oxidation process (AOP) (O
/UV
3
problematic due to the consumption of a vast quantity of water; and H
only a small amount of the dyes is used in dye fabrication, while
The photo-Fenton process used for the degradation of Congo
2 2
a large quantity is discarded into the environment, which cau- red (CR) utilizes Fe /peroxy disulfate, Fe /H O /UV, and Fe /
2 2 2 2
O /UV) and photocatalysis (TiO /hy/O ).
3
+
0
0
ses pollution. The colored dye effluents are as such non-toxic, ammonium persulfate (APS)/UV, where 4-amino, 3-azo naph-
but they modify the ecosystem of the aquatic life in streams thalene sulphonic acid, quinol, dihydroxy-substituted naph-
and other water bodies via reducing the underwater photosyn- thalene, dihydroxy-substituted biphenyl, hydroquinone, and
3
+
2
thetic activity due to the unavailability of sunlight. Even the phenol are formed as reaction intermediates. In the Fe /peroxy
lowest amount of a dye produces a color that is extremely visible disulfate system, degradation decreases with an increase in the
in the effluent, thereby directly indicating that water has been concentration of the dye and pH. APS shows improved oxidation
polluted; also, removing the dye is challenging due to its than H
complex chemical structure. Different varieties of dyes such as dye.
2
10,11
O
2
in treating the industrial effluent of the Congo red
3,4
acidic, basic, disperse, azo, diazo, anthraquinone-based, and
The biogenic materials prepared by oyster shells show
metal complex dyes are used; these dyes are highly resistant to excellent properties related to the surface area including
5–7
fading when exposed to light, water, and many chemicals.
porosity, sorption capacity, and high concentration of CaCO ,
3
which can be characterized by FTIR, SEM, and BET techniques.
The results show the excellent properties of AG25 in a dose-
dependent manner. Lin et al. (2018) reported 100%
Department of Chemistry, University of Karachi, 75270, Karachi, Pakistan. E-mail:
12
13
raasaeed200@yahoo.com
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removal of methylene green in 6 to 10 min using a hetero- inorganic additives and diluted according to the requirement of
junction photocatalyst, namely, Ag PO @MWCNTs@Cr:SrTiO
3
under natural solar radiation and visible light irradiation.
the experiment. During the experiment, the concentration of
dye in the aqueous solution was determined by comparing the
3
4
The current practices of textile dye wastewater remediation visible range spectrum with the standard solutions via a Shi-
and minimization are a severe threat due to the risk associated madzu 1800 UV-Vis spectrophotometer. The wavelength
with its color to the running water streams. The usual maximum (lmax) of CR was 497 nm.
management procedures involved in textile wastewaters are
elimination by activated carbon adsorption, coagulation/ following equation:
occulation, and membrane separation (ultraltration, reverse
The percent de-coloration of CR was determined by using the

A
o
ꢀ A
t
Percentage of Decoloration ¼
(1)
osmosis), but these processes are not the comprehensive solu-
tion of the removal of pollutants, while a biological treatment is
not an exact solution due to the biological resistance of some
A
t
14–18
HPLC analysis of the degraded dye product. The degraded
product of CR was subjected to HPLC analysis for the validation
of UV spectral analysis. The dye solution before and aer the
accomplishment of reaction was analyzed by the reversed-phase
HPLC technique, where each sample was ltered through a 0.45
mm lter and then, 20 mL of the volume was loaded to HPLC,
equipped with a C-18 column (250 mm ꢁ 4.6 mm). The mobile
phase was prepared by using acetonitrile and water (HPLC
grade) in a ratio of 65 : 35, followed by ltration through a 0.45
mm lter and degassed with the help of ultrasonic waves before
use. The elution time of the Congo red dye was reported to be
dyes.
Thus, the dye wastewater management requires ultra-
advanced processes for the recovery of colored water with the
elimination of all relative byproducts by using the developed
method. Therefore, for this purpose, the oxidizing agent KMnO
4
was used due to its preventive nature instead of any other
compound of a high oxidative potential for the preservation of
water bodies. Mn is an essential micronutrient for both plants
and animals and can be easily removed/consumed by a marine
organism. The aims and objectives of this innovation were to
develop an ultra-advanced oxidation method for the recovery of
thousands of tons of water discharged during dyeing and n-
ishing processes with a lot of chemical additives used during
dye fabrication. For this purpose, Congo red was selected, and
the kinetics were monitored at various operational parameters
for the establishment of the mechanism of dye degradation in
the presence of all the dye fabricated additives. The application
of current ACOP is discussed in the relative section of this
article using real dye water samples with several other dyes.
2
.9 min. The analysis was performed on the isocratic system,
where the mobile phase was set at the ow rate of 1 mL min
ꢀ1
and the absorbance was recorded at 495 and 278 nm through
19
a deuterium lamp.
Analytical analyses. The mineralization of CR was deter-
mined by chemical oxygen demand (COD) of the de-colorized
ltrate by using the standard method stated in (APHA, 2005)
and COD analyzer APHA 5220 C. The COD values of both acidic
ltrate and it's neutralized form were calculated and compared
with the literature value of CR wastewater. The degraded
product in the ltrate and residue aer mineralization was
identied by FTIR and compared with the dye and KMnO4
peaks before and aer oxidation. The salinity of the recovered
water was determined through a Benchtop Conductivity/TDS
meter, Model Jenway 4510, before and aer the reaction.
Results and discussion. CR is a synthetic dye in which the p
to p* and n to p transitions are responsible for its color. When
20


Experimental
Materials and methods
Chemicals, materials, instruments and removal methods.
The sodium salt of benzidinediazo-bis-1-naphthylamine-4-
sulfonic acid referred to as Congo red (CR) belongs to the
class azo and is used to dye cotton fabrics, as the acid-base
indicator dye, and as a synthetic medicine dye. CR dye was
purchased from the local dye dupatta center and used without
any additional purication. The structure and chemical formula
of CR are shown below in Fig. 1.
4
these transitions were affected by an oxidant (KMnO ), the color
of the dye disappeared. It was observed that the reaction was
valid in light as compared to that in dark, which was linked with
A stock solution of 0.001 M of CR was prepared using double
distilled water and diluted according to the requirement of the
experiment. A standard method was employed for the prepa-
the property of the oxidant (KMnO ) that it is light-sensitive.
4
The kinetics of the reaction
4
ration of aqueous solutions of KMnO , acids, organic and
The current investigation at various operational parameters
described the newly developed advanced catalytic oxidation
process (ACOP) for the oxidation of CR. The reaction was carried
4
out at various concentrations of the dye (CR), oxidant (KMnO ),
pH, and temperature, and diverse organic (naphthalene and
urea) and inorganic (NaCl and alum) additives. These additives
are commonly employed for dye xing for cellulose bers. The
rate of reaction at elevated concentrations of various additives
proved that it is cost-effective. The current ACOP covers the
following steps: (i) taking a dye solution and adding KMnO
activation of KMnO by adding H SO , (iii) adding TiO
4
, (ii)
as
Fig. 1 The chemical structure of Congo red.
4
2
4
2
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a catalyst for speeding up the oxidation reaction, (iv) additives concentration of the dye, which clearly indicated that nascent
and pH adjustment, (v) ltration and (vi) monitoring the optical oxygen (a reaction intermediate) was involved in dye degrada-
density. The mole ratio between the dye and KMnO was 1 : 1 tion. It was a fractional order of 2/5 kinetics concerning the dye,
4
without any difference in the concentration; this indicated that while the spectral scan at each elevated concentration of the dye
at a low concentration, the new ACOP was cost-efficient and eco- showed the formation of a complex of the dye with an oxidant,
friendly. Permanganate-based advanced catalytic oxidation and which later degraded into small fragments (Fig. 2).
2
the use of TiO as a catalyst have been widely investigated and
1,18,22,23,26
reported
in the literature, showing higher degradation
Effect of oxidant concentration on the oxidation of CR
efficiency; however, the current photocatalytic activity of
+
To make the current ACOP more effective and competitive with
permanganate-TiO /H -based oxidation that leads to complete
2
2
0–26
other existing processes of AOPs,
the effect of the incre-
mineralization has been found to be very effective in the pres-
ence of all dye additives and is thus used in dye fabrication in
the absence of UV irradiation.
ꢀ
4
mental concentration of the oxidant KMnO
10 ) on the decoloration of the dye was investigated. It was
fractional order kinetics, while de-coloration (Table 1)
4
(5 ꢁ 10 and 7.5
ꢀ4
ꢁ
decreased (27.10% and 38.56%) at elevated concentrations (5 ꢁ
Effect of dye concentration on the oxidation of CR
ꢀ4
ꢀ4
10
and 7.5 ꢁ 10 , respectively) as the excess of KMnO
4
le
The effect of the initial dye concentration of CR was monitored behind could be easily observed in the UV-Visible spectral scan
under new ACOP as a chief parameter in wastewater treatment through its peak in the visible region (Fig. 3). The objective of
with KMnO
4
. The maximum de-coloration of CR was 98.59% at this estimation was to select the best operational dosage of
in ACOP. The current ACOP is more advantageous over
any other reaction as [O] is released during the reaction, which
ꢀ4
1
ꢁ 10 M concentration of dye (Table 1), which was more than KMnO
4
14
the values previously reported by Agustina and Ang (2012),
who reported 94.5% to 81% of color removal under the Fenton is an important parameter; also, it is required as an electron
reaction for RB 4 and RR 2 at concentrations from 20 to scavenger to sustain the catalytic degradation reaction. The
2
00 ppm, respectively, within 60 min from 100% to 91.5%. results of the current investigation were similar to the results
15
17
Vaigan et al. (2009) reported that the de-coloration efficiency reported by Chakrabarti and Dutta (2004), who reported the
decreased from 57 to 31% in an SBR batch system for the requirement of a well-regulated air (oxygen) ow into the pho-
concentration of Reactive Blue B-16 dye (20 to 40 mg L
ꢀ1
,
tocatalytic system as the reduced movement of oxygen can bring
respectively). It was observed in the current investigation that % about an antagonistic effect on the photocatalytic reaction. The
de-coloration was unaffected by the increase in the current results were also in accordance with those reported by
Table 1 Effect of various concentrations of dye, oxidant, acid, and catalyst on the decoloration of Congo red
¼ dx/dt (10ꢀ ) mol dm min
3
ꢀ3
ꢀ1
k
(10 ) min
ꢀ3
ꢀ1
k
2
(10 ) mol dm min
ꢀ2
ꢀ1
3
ꢀ1
R
2
% De-coloration
[
Conc.]
k
0
1
ꢀ
4
ꢀ3
[
Dye] (10 ) mol dm
0
0
1
2
3
.8
.9
.0
.0
.0
3.7
4.4
4.9
6.6
13.1
28.9
30.1
44.2
15.7
25.3
36.68
36.9
97.63
6.47
0.329
0.303
0.395
0.180
0.193
93.55
95.01
98.59
91.45
95.75
11.6
ꢀ
4
ꢀ3
[
Oxidant] (10 ) mol dm
0
0
1
5
7
.5
.75
.0
.0
.5
3.1
3.6
4.9
2.3
5.4
12.6
22.3
44.2
4.4
7.79
0.163
0.213
0.395
0.712
0.77
91.28
93.77
98.59
27.10
38.56
27.64
97.63
0.85
6.5
0.79
ꢀ3
[
H
2
SO
4
] mol dm
0
0
0
0
0
.01
4.6
4.9
4.8
4.6
4.8
29.5
44.2
29.7
26.4
31.6
29.19
97.63
27.25
21.32
31.09
0.378
0.395
0.415
0.398
0.418
93.30
98.59
91.90
90.81
93.15
.02
.03
.04
.05
[
2
TiO ] g/50 mL
0
0
0
0
0
.05
.075
.1
.25
.5
4.5
4.6
4.9
4.8
4.9
28.9
27.7
44.2
35.9
35.8
29.37
24.64
97.63
45.1
0.355
0.378
0.395
0.387
0.403
92.06
87.54
98.59
95.16
94.55
42.55
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throughout the experiments, where zero-order kinetics was
observed (Table 1). Moreover, no reaction with HCl indicated
that not only protons but also sulfates were effective in the
discoloration reaction. Also, chloride ions reacted with
manganese to give MnCl
2
, which deactivated the manganese
ions according to the following equation:
2
KMnO
4
+ 16HCl / 2KCl + 2MnCl
MnCl + Dye / no reaction
in combination with KMnO
2
+ 8H
2
O + 5Cl
2
(2)
(3)
2
H
2
SO
4
4
releases [O], which was
found to be effective in de-coloration according to the following
reaction steps:
2
KMnO
4
+ 3H
2
SO
4
/ K
2
SO
4
+ 2MnSO
4
2
+ 3H O + 5[O] (4)
Dye + [O] / degraded product
(5)
Fig. 2 The UV-Visible spectral change at various concentrations of
Congo red after 5 min showing complex formation represented by (1)
degradation (2) observed within one hour simultaneously (a ¼ Dye, b ¼
The role of sulphates cannot be roled out in the presence of
a catalyst according to the following equation:
ꢀ5
ꢀ5
ꢀ4
ꢀ4
8
ꢁ 10 M, c ¼ 9 ꢁ 1 0 M, d ¼ 1.0 ꢁ 10 M, e ¼ 2.0 ꢁ 10 M, and f
ꢀ4
2ꢀ
CBꢀ
4ꢀ
/ SO c
SO
4
+ e
(6)
(7)
¼
3.0 ꢁ 10 M).
ꢀ
+
SO4 c + H O / SO + H + O
2
4
18
Saquib et al. (2008); they observed the decoloration of Patent
Blue VF (2) and Fast Green FCF (1) in the presence of hydrogen
Usually, an advanced oxidation process, including the Fen-
peroxide (H
potassium bromate using Hombikat UV 100 and found that it is production, which is formed in acidic conditions. Therefore,
O ), ammonium persulphate ((NH ) S O
2 2 4 2 2 8
), and ton reaction, is a highly pH-reliant process due to the role of OH
4,6
useful in the degradation of both dyes.
the current ACOP was investigated for the maximum degrada-
tion at various pH values in the range of 2–9 using either H SO
2
4
Effect of acid concentration on the oxidation of CR
or NaOH. It was found that lower pH was more effective and [O]
was the main oxidant in the acidic medium. Lachheb et al.
The rate of oxidation monitored in the presence of hydrochloric
21
(
2002) reported that a pH value below 6 was found to be
suitable for the degradation of CR or azo dyes in the presence of
TiO , where strong adsorption of azo dyes was observed as
a consequence of the electrostatic attraction of the positively
charged TiO with the dye; this was similar to the results re-
acid (HCl) and sulphuric acid (H
in the presence of HCl. Therefore, H
2
SO
4
) showed no de-coloration
SO was used as a medium
2
4
2
2
22
ported by Rupa et al. in 2007. The current results showed that
the alkaline medium was not effective as the dye molecules were
negatively charged, which decreased the adsorption capability,
while they were adsorbed more readily on the TiO
2
particles in
the acidic medium. At elevated concentrations of KMnO
4
,
excess oxidant was le behind, which can be easily observed by
its peak in the visible region of the UV-Visible spectral scan
(Fig. 4). The nal pH at the end of the reaction was found
through a pH meter; it was acidic but was maintained neutral by
the addition of a small amount of alkali.
Effect of catalyst concentration on the oxidation of CR
TiO
2
, having an essential damaging nature, which may lead to
, was
the complete mineralization of organic carbon into CO
2
used here to accelerate the reaction as a catalyst because the
reaction was prolonged and required almost 48 h for comple-
Fig. 3 The UV-Visible spectral change at various concentrations of
KMnO after 5 min showing complex formation represented by (1)
degradation (2) observed within one hour simultaneously (a ¼ dye, b ¼
tion. The addition of TiO reduced the time interval and 98%
2
4
de-coloration was achieved in 1 h (Table 1, Fig. 5). The mech-
anism involved in the Ti-mediated AOP suggested that the dye
ꢀ
5
ꢀ5
ꢀ4
ꢀ4
5
ꢁ 10 M, c ¼ 7.5 ꢁ 10 M, d ¼ 1 ꢁ 10 M, e ¼ 5 ꢁ 10 M, and f ¼
ꢀ4
ꢀ
7.5 ꢁ 10 M).
adsorbed on the catalyst surface, where e from Mn and the
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1
3
Dye + hy (Vis) / Dye* or Dye*
(9)
1
1
3
Dye* or Dye* + 5[O] / degradation product
(10)
(11)
(12)
3
+
CBꢀ
(e )
Dye* or Dye* + TiO
2
/ Dye + TiO
2
+
Dye / degradation product
The effect of a change in temperature
The effect of a change in temperature showed that the reaction
was independent of temperature. In contrast, a detailed litera-
ture search showed that temperature plays a vital role. Xu et al.
23
(
2005) reported that in the batch experiment, potassium
permanganate was effective for the decolorization of 10 types of
dyes at various concentrations and elevated temperatures, while
Benetoli et al. (2011) showed that the effect of temperature on
Fig. 4 The UV-Visible spectral change at various concentrations of
24
H
2
SO
degradation (2) observed within one hour simultaneously (a ¼ dye, b ¼
.01 M, c ¼ 0.02 M, d ¼ 0.03 M, e ¼ 0.04 M, and f ¼ 0.05 M).
4
after 5 min showing complex formation represented by (1)
the decolorization of methylene blue (MB) increased with a rise
ꢂ
0
in temperature in the range from 4 to 28 C; no effect of
ꢂ
temperature in the range from 28 to 37 C was observed with the
ꢀ1
activation energy being 13.09 kJ mol , which was found to be
catalyst coupled with oxygen, played an effective part in degra- higher than the energy of activation of current ACOP (E
a
¼
ꢀ
1
25
dation. The % degradation of CR was found to be approximately 0.9495 kJ mol ). Medien and Khalil (2010) reported that the
the same, with an increase in the concentration of the catalyst rise in temperature increases the rate of oxidation of crystal
(
0.05 to 2.5 g/50 mL); this was comparable with the results by violet (CV), Malachite green (MG), Rhodamine B (RB), and
22
Rupa et al. (2007) , who reported 80% de-coloration at the methylene blue (MB) under Fenton oxidation. Moreover, the
ꢀ1
concentrations from 1.5 to 3.00 g L . The % de-coloration with energy of activation showed the high efficiency of the reaction.
time suggests that an increase in the catalyst quantity does not The thermodynamic activation parameters (Table 2) showed
affect the % de-coloration with time (Fig. 5). The possible that E
decreased with an increase in the temperature, which
a
1
acceleration in the reaction in the presence of the catalyst
occurred according to the following reaction pathway:
was effective for the activation of the oxidant in the acidic
medium. The values of enthalpy of activation (DH), free energy
of activation (DG), and entropy of activation (DS) showed that no
26–29
2
KMnO
4
+ 3H
2
SO
4
/ K
2
SO
4
+ 2MnSO
4
2
+ 3H O + 5[O] (8) solvated states were present in the reaction mixture,
and CR
degradation occurred through the complex formation with the
oxidant KMnO . The current investigation proves that new
4
ACOP is cost-effective as no extra energy is required for the
acceleration of the rate of reaction.
Effect of dye additives
Urea and naphthalene are famous in the dye industry as dye
xers on fabrics and are released as additives in water bodies
with dye wastewater, which makes the dye wastewater more
complex and challenging to treat. Therefore, these two additives
were considered in the current new AOP system. The effects of
Table
2 Thermodynamic activation parameters for Congo red
oxidation
Temperature
K
DS
kJ K mol
ꢀ1
ꢀ1
ꢀ1
ꢀ1
E
a
kJ mol
DG kJ
DH kJ mol
2
88
after 298
min showing complex formation represented by (1) the degradation 308
0.9495
12.786
12.933
13.623
13.907
14.344
ꢀ1.445
ꢀ1.528
ꢀ1.611
ꢀ1.694
ꢀ1.778
ꢀ0.049
ꢀ0.049
ꢀ0.05
Fig. 5 The UV-Visible spectral change at various amounts of TiO
5
(
2
2) observed within one hour simultaneously (a ¼ dye, b ¼ 0.05 g/50 318
ꢀ0.049
ꢀ0.049
mL, c ¼ 0.075 g/50 mL, d ¼ 0.1 g/50 mL, e ¼ 0.25 g/50 mL, and f ¼ 0.5 328
g/50 mL).
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4
Table 3 Effect of concentration of organic and inorganic additives on de-coloration of dye with KMnO
4
(Congo red ¼ 1 ꢁ 10ꢀ M, KMnO
¼ 1 ꢁ
4
ꢀ4
1
0
M, H
Conc.] mol dm
Urea
2
SO
4
¼ 0.02 M, TiO ¼ 0.1 g/50 mL, temperature ¼ 298 K)
2
ꢀ3
¼ dx/dt (10ꢀ3) mol dm min
ꢀ3
ꢀ1
ꢀ3
ꢀ1
ꢀ1
3
ꢀ1
2
[
k
0
k
1
(10 ) min
k
2
mol dm min
R
% De-coloration
0
0
0
0
0
.001
.005
.01
.05
.1
4.9
5.1
5
5.1
4.7
56.2
41.6
38.5
40.9
28.2
1.7073
0.6075
0.507
0.5758
0.2492
0.362
0.417
0.409
0.409
0.386
98.29
96.26
95.33
95.48
91.12
Naphthalene
0
0
0
0
0
.001
.005
.01
.05
.1
4.9
4.9
5
4.9
4.7
31.6
36.6
36.4
30.4
29.8
0.3146
0.444
0.4265
0.2781
0.2781
0.403
0.407
0.416
0.427
0.397
93.15
94.24
93.93
92.99
92.37
Potash alum
0
0
0
0
0
.001
.005
.01
.05
.1
3.8
3.5
3.7
4
31.7
26.4
68.8
47.2
42.9
0.6474
0.4916
10.043
1.9751
1.4465
0.217
0.194
0.198
0.24
96.73
96.42
100
99.22
98.44
3.9
0.230
Sodium chloride
0
0
0
0
0
.001
.005
.01
.05
.1
5
48.6
86.8
83.9
98.2
86.1
0.9919
3.6748
5.829
6.511
6.1992
0.387
0.396
0.406
0.383
0.396
97.35
100
100
100
100
5.2
5.2
5.2
5.2
the added organic additives, i.e., urea and naphthalene were degraded product of CR. Therefore, the reaction mixture was
investigated, and it was found that the rate of reaction was prepared in a round bottom ask, and we tried to collect the gas
independent of the added organic additives (Table 3). Moreover, in a water-lled gas jar placed in a water bath. No displacement
it was established that present AOP was advantageous in the of water into the gas jar showed that oxygen was not released,
degradation of dye wastewater in the presence of these critical thereby suggesting that oxygen was used in the degradation of
28
dye additives. Similarly, we added inorganic additives, such as
NaCl and alum, which are also used in various dye processes, and
they were also investigated under developed AOP. It was found
that new AOP was also valuable in the treatment of the complex
nature of the dye wastewater (Fig. 6) and the dye wastewater could
be restored completely in the presence of dye additives.
30
Furthermore, literature search showed the oxidative degra-
dation of Blue 2B (B54) and Red 12B (R31) by the Fenton's reagent
ꢀ
in an aqueous medium with two added inorganic ions like Cl
ꢀ
2
30
and SO
dyes like azo dyes, Procion Red MX-5B (MX-5B), and Cationic
Blue X-GRL (CBX) in the presence of UV-illuminated TiO and
4
. Hu et al. (2003) reported the effect of various ions on
2
showed that the rate of decolorization was enhanced due to
irradiation. They also reported that the reaction was useful for
the treatment of dye wastewater. The plot of % de-coloration with
respect to time in the treatment of dye wastewater showed that it
was found operational in the treatment of CR in the presence of
various kinds of additives (Fig. 7).
Fig. 6 The UV-Visible spectral change at various concentrations of
urea after 5 min showing complex formation represented by (1) the
degradation (2) observed within one hour simultaneously (a ¼ dye, b ¼
Mineralization of CR
The mineralization of the dye was studied in relation to the
released oxygen as the main oxidant and CO
as the main 0.001 M, c ¼ 0.005 M, d ¼ 0.01 M, e ¼ 0.05 M, and f ¼ 0.1 M).
2
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Fig. 7 A plot of % de-coloration and time in the presence of diverse ions.
the dye. The mineralization of the dye into CO2 was tested FTIR studies of ACOP
through limewater, where the formation of a white precipitate
The FTIR spectra of the dye before de-coloration in an aqueous
medium are presented in Fig. 8a and compared with the FTIR
spectrum of the reaction mixture of the dye and KMnO aer de-
4
of CaCO showed that the dye nally degraded into CO and
3
2
H
2
O. This test showed that CO
2
gas was produced during the
reaction, but no traces of the O
2
gas in the reaction proved that
coloration (Fig. 8b and c). The observed FTIR spectral peak of
it was utilized in oxidation. The reaction was also carried out in
the absence of O by seal packing the reaction vessel, and it was
the CR dye (Fig. 8a) showed stretching of N–H at 34 622.22 and
2
ꢀ1
ꢀ1
2
1
370.51 cm as in charged amines (C]NH–), and the peak at
found that the oxidation of the dye occurred due to the evolu-
tion of an [O] radical, which oxidized the double bond of C]C
and converted it into CO2 through the degradation of the
organic compound CR. The test for COD showed that it
decreased from 3000 ppm to 71.2 ppm by this method, whereas
649.14 cm corresponded to the double bond stretching of
–
N]N– as in an azo compound (Table 4). The specic peaks at
390.68, 1193.94, and 1112.93 cm were attributed to the C]C
ꢀ1
1
stretching of an aromatic compound, S]O stretching, and C–N
vibration of aliphatic amines, respectively. The peaks at 746.45
31
by neutralizing the ltrate, it was reduced to 53.6 ppm. The
OH radical formation was also tested via benzoic acid. No
effervescence on the addition of benzoic acid showed that OH
radicals were not the part of current ACOP and degradation
occurred via the released oxygen according to the following
ꢀ1
and 617.22 cm
were due to the CH deformation of the
31
benzene ring. The spectrum of the decolorized ltrate (Fig. 8b)
indicates that the three peaks ascribed to water at 3406.29,
ꢀ1
1
637.56, and 2083.12 cm are due to the O–H stretching of H-
bonding, scissor bending of O–H–O, and coupled peak of
26
equation:
scissor bending and broadband, respectively (Table 4). Also, the
ꢀ1
peaks at 597.93, 1107.14, 1384.89, and 2362.8 cm
were
2
4 2 4 2 4 4 2
KMnO + 3H SO / K SO + 2MnSO + 3H O + 5[O] (13)
attributed to the ]C–H bending of an alkene, C–N stretching of
32
amine, S]O bending, and –C]C– stretching, respectively.
This indicated that the decolorization of CR was linked to the
breaking of azo bonds, which was related to the breaking of
The complete color removal of the dye (Fig. 3) initiated the
change in the oxidation state of Mn from Mn to Mn :
7
+
2+
chromophores, i.e., unsaturated conjugated bonds, namely,
7
þ
ꢀ
2þ
Colorless
Mn þ 5e /Mn
32
–
N]N– in the dye, where the entire de-aromatization of the
Colored
dye was related to the current ACOP process.
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Fig. 8 (a) The infrared spectrum of Congo red; (b) the FTIR spectrum of the decolorized form of dye; (c) the FTIR spectrum of sludge formed
after dye mineralization.
HPLC analysis of the nal product
Table 4 Dye peaks in the de-colorized filtrate and sludge
The HPLC analysis of the nal degraded product of the CR dye
solution was performed, which proved the complete minerali-
zation of the dye. Initially, the chromatograms of both the
samples were established at 495 nm based on the reports of
Choi and co-workers (2013). The absorbance at the retention
time of 1.749 min was recorded for the CR dye, where 100%
De-colorized
ltrate
Dye peaks
Sludge
N–H
N]N
C]C
S]O
C–N
Absent
Absent
Present
Present
Present
Present
Present
Present
Absent
Absent
19
concentration of the dye was eluted; however, the solution aer
Present treatment showed no absorbance at the same retention time
Present
]C–H
(Fig. 9a and b). Furthermore, the dye solution before and aer
the reaction was scanned once again at a new absorbance of
78 nm. This wavelength was selected in the ultraviolet region
2
because of the resultant solution, which became colorless aer
the treatment (Fig. 10a and b). The chromatograms recorded at
Also, the sludge formed at the end of the reaction was sub-
jected to FTIR, and the resulting spectrum (Fig. 8c) showed
278 nm for the Congo red dye show two peaks at the elution
ꢀ
1
multiple peaks. The peaks at 3404.36 and 3747.69 cm were
times of 1.680 and 3.078 min (Fig. 10a), whereas the sample of
Congo red aer the treatment showed four disintegrated
products at 1.448, 2.306, 3.360, and 3.760 min rather than at
ꢀ
1
due to the N–H stretching, while the peak at 1585.49 cm was
due to the bending of the N–H bond (Table 4). Furthermore, the
ꢀ
1
specic peak at 2926.01 cm was due to the stretching of the ]
C–H bond, while there was another peak at a lower wavelength
3
(
.077 min (Fig. 10b). It is clearly indicated in the chromatogram
Fig. 10b) that the characteristic peak of the Congo red dye at
a retention time of 1.680 min in the ultraviolet region shis to
.306 min. In contrast, the ve different eluted peaks shown in
ꢀ
1
of 628.79 cm , which appeared because of the bending of ]C–
ꢀ
1
H of the alkene. The peaks at 1649.14 and 1739.79 cm were
2
attributed to –N]N– double bond stretching; the two bands at
Fig. 10b indicate that the Congo red dye fragmented into other
components.
Salinity of the recovered water. The salinity of the recovered
water related to the mineralization of the dye wastewater
through current new ACOP was tested for its possible reuse and
ꢀ
1
1
500.62 and 1384.89 cm corresponded to the stretching of the
nitro compound. Moreover, the peaks at 2370.51, 1465.90, and
ꢀ
1
1
047.35 cm were due to C]N stretching, bending of alkane,
32
and C–N stretching of amine, respectively.
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Fig. 9 (a) The HPLC chromatogram of Congo red dye and the absorbance spectrum recorded at 495 nm. (b) The HPLC chromatogram of
solution resulting after the treatment and the absorbance spectrum recorded at 495 nm.
appropriate management. For this purpose, two commonly water. The salinity and TDS of the recovered water were
used methods, namely, the measurements of electrical comparable with the salinity levels tolerable for livestock and
ꢀ1
conductivity (EC) and total dissolved solids (TDS) were other purposes (5970–7460 mS cm or 5.9–7.5 dS m; 4000–5000
ꢀ1
33
employed. EC and TDS were monitored at the optimized (mg L or ppm)), which proved that the new ACOP is eco-
concentrations of the dye, KMnO , H SO , and TiO
, i.e., 1 ꢁ friendly, cost-effective, and easily manageable.
M, 1 ꢁ 10 M, 0.02 M, and 0.1 g/50 mL, respectively. The Application of current ACOP in real and several dye waste-
4
2
4
2
ꢀ4
ꢀ4
10
values of electrical conductivity and total dissolved solids water samples. Aer the successful development of current
increased (Table 5); this conrmed the mineralization of the dye ACOP on CR dye wastewater restoration at the laboratory scale,
into smaller fragments, due to which the electrical conductivity it was applied to several dyes, including Reactive blue, Reactive
of the solution increased, followed by an increase in TDS yellow, acridine orange, methylene blue, and thionine, followed
coupled with an improvement in BOD/COD of the recovered by real red dye wastewater, which was collected from a dye shop
Fig. 10 (a) The HPLC chromatogram of Congo red dye and the absorbance spectrum recorded at 278 nm. (b) The HPLC chromatogram of
solution resulting after treatment and the absorbance spectrum recorded at 278 nm.
a
Table 5 EC and TDS of the reaction
Conductivity
mS
ꢀ1
33
Dye solution
TDS mg L
Literature value
ꢀ1
ꢀ1
ꢀ1
Original dye solution
106.6
63.6
75.3
75.9
5970–7460 (mS cm ) or 5.9–7.5 (dS m ) 4000–5000 (mg L or ppm)
Aer adding KMnO
Aer adding H SO
Aer adding TiO
4
125.4
126.3
127.3
2
4
2
76.4
Aer complete de-coloration
With all additives
5660
5780
3390
4000
a
Congo red ¼ 1 ꢁ 10ꢀ4 M, KMnO
¼ 1 ꢁ 10ꢀ4 M, H
4
2
SO
4
¼ 0.02 M, TiO
2
¼ 0.1 g/50 mL, temperature ¼ 298 K, and distilled water conductivity ¼ 18.31
mS.
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Fig. 11 The UV-Visible spectra showing the absorption peaks of different dyes: (A) dye wastewater, (B) Reactive red, (C) Reactive blue, (D)
thionine, (E) Reactive yellow, (F) acridine orange, and (G) methylene blue. In contrast, the degradated product observed within one hour is
represented by (2).
aer its prime use of fabric dyeing. The observed spectral
change aer the application of ACOP on several dyes showed
Acknowledgements
the complete mineralization of the colored wastewater with all The author is very thankful to HEC Pakistan for providing
the dye additives being used in dye xing (Fig. 11). This showed nancial support through Research Project No. 20-2282/NRPU/
that thousands of tons of dye wastewater could be restored for R&D/HEC/12/5014.
its reuse in the dye fabrication industry.
References
Conclusion
1
I. K. Konstantinou and T. A. Albanis, Appl. Catal., B, 2004, 49,
1–4.
The new advanced catalytic oxidation process indicates its
promising result for the decoloration and treatment of dye
wastewater in the presence of organic and inorganic additives,
which help the dye to x onto the fabric and make the nature of
the wastewater complex and challenging to treat. The decolor-
2 G. E. Walsh, L. H. Bahner and W. B. Horning, Environ. Pollut.
Ecol. Biol., 1980, 21, 169–179.
3 P. Nigam, G. Armour, I. M. Banat, D. Singh and R. Marchant,
Bioresour. Technol., 2000, 72, 219–226.
ation of the dye with an oxidant (KMnO
4
) was found to go
4 K. C. Chen, J. Y. Wu, D. J. Liou and S. C. Hwang, J. Biotechnol.,
2003, 101, 57–68.
5 V. J. Poots, G. McKay and J. J. Healy, Water Res., 1976, 10,
1061–1066.
through a complex formation step in the beginning, the
complex later on undergo to the degradation with an increase in
the salinity of the recovered water. This led to the conclusion
that TiO
2
reduced the time interval, thereby providing 98.59%
6 V. J. Poots, G. McKay and J. J. Healy, Water Res., 1976, 10,
1067–1070.
7 G. McKay, Am. Dyest. Rep., 1979, 68, 29.
8 A. Altaf, S. Noor, Q. M. Sharif and M. Najeebullah, J. Chem.
Soc. Pak., 2010, 32, 115–116.
de-coloration within 1 h. It was also concluded that new ACOP
was effective due to the generation of nascent oxygen [O] and e
from the oxidant (KMnO ) and catalyst (TiO ). The dye peak
4 2
shied toward the region of shorter wavelength and higher
region, indicating the formation of smaller dye fragments
consisting of compounds having C]C, C–N, S]O, or ]C–C
ꢀ
9 R. Andreozzi, V. Caprio, A. Insola and R. Marotta, Catal.
Today, 1999, 53, 51–59.
bonds, which was conrmed through FTIR and HPLC; these 10 L. G. Devi, S. G. Kumar and K. M. Reddy, Cent. Eur. J. Chem.,
compounds were later converted to CO . The sludge formed at
2009, 7, 468–477.
the end of the degradation reaction was subjected to FTIR, 11 L. Gomathi Devi, S. Girish Kumar, K. Mohan Reddy and
2
which showed the formation of the smaller degraded products
of functional groups N–H, ]C–H, C]N, and N]N.
C. Munikrishnappa, Desalin. Water Treat., 2009, 4, 294–305.
12 X. Inthapanya, S. Wu, Z. Han, G. Zeng, M. Wu and C. Yang,
Environ. Sci. Pollut. Res., 2019, 26, 5944–5954.
13 Y. Lin, S. Wu, X. Li, X. Wu, C. Yang, G. Zeng, Y. Peng, Q. Zhou
and L. Lu, Appl. Catal., B, 2018, 227, 557–570.
Conflicts of interest
14 T. Agustina and H. Ang, Int. J., 2012, 3, 141–148.
It conrmed that there is no conict of interest in between 15 A. Vaigan, M. A. Moghaddam and H. Hashemi, J. Environ.
authors.
Health Sci. Eng., 2009, 6, 11–16.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 37562–37572 | 37571

View Article Online
RSC Advances
Paper
1
1
1
1
6 R. Azmat, N. Qamar, R. Naz and A. Khursheed, Pak. J. Pharm. 25 H. A. Medien and S. M. Khalil, J. King Saud Univ., Sci., 2010,
Sci., 2016, 29. 22, 147–153.
7 S. Chakrabarti and B. K. Dutta, J. Hazard. Mater., 2004, 112, 26 R. Azmat, F. V. Mohammed and T. Ahmed, Front. Chem.
69–278. China, 2011, 6, 84.
8 M. Saquib, M. A. Tariq, M. Faisal and M. Muneer, 27 R. P. Sontakke, A. K. Mishra and K. S. Muralidhara, Study on
2
Desalination, 2008, 219, 301–311.
physiochemical analysis of textile industry effluent and in vitro
9 Y. S. Choi, Y. Long, M. J. Kim, J. J. Kim and G. H. Kim, J.
Environ. Sci. Health, Part A: Toxic/Hazard. Subst. Environ.
Eng., 2013, 48, 501–508.
study of decolourization of the Congo Red acidic dye by bacterial
species,
Textile
Value
Chain,
2016,
https://
textilevaluechain.in/2019/05/27/2326/.
2
0 American Public Health Association, APHA, Standard 28 R. Azmat, B. Yasmeen and F. Uddin, Asian J. Chem., 2007, 19,
Methods for the Examination of Water and Wastewater, 1115.
American Public Health Association, Washington DC, 21st 29 P. K. Malik and S. K. Saha, Sep. Purif. Technol., 2003, 31, 241–
edn, 2005, p. 1220. 250.
1 H. Lachheb, E. Puzenat, A. Houas, M. Ksibi, E. Elaloui, 30 C. Hu, C. Y. Jimmy, Z. Hao and P. K. Wong, Appl. Catal., B,
2
C. Guillard and J. M. Herrmann, Appl. Catal., B, 2002, 39,
5–90.
2 A. V. Rupa, D. Manikandan, D. Divakar, S. Revathi,
2003, 46, 35–47.
31 H. Lade, S. Govindwar and D. Paul, Int. J. Environ. Res. Public
Health, 2015, 12, 6894–6918.
7
2
M. E. Preethi, K. Shanthi and T. Sivakumar, Indian J. Chem. 32 B. L. Mojet, S. D. Ebbesen and L. Lefferts, Chem. Soc. Rev.,
Technol., 2007, 14, 71. 2010, 39, 4643–4655.
3 X. R. Xu, H. B. Li, W. H. Wang and J. D. Gu, Chemosphere, 33 Australian soil fertility manual, ed. G. Price, CSIRO
005, 59, 893–898. PUBLISHING, 2006.
2
2
2
4 L. O. Benetoli, B. M. Cadorin, C. D. Postiglione, I. G. Souza
and N. A. Debacher, J. Braz. Chem. Soc., 2011, 22, 1669–1678.
37572 | RSC Adv., 2019, 9, 37562–37572
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