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Intensification of sonochemical decolorization of anthraquinonic dye Acid Blue 25 using carbon tetrachloride

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Abstract

In this work, the influence of CCl(4) on the sonochemical decolorization of anthraquinonic dye Acid Blue 25 (AB25) in aqueous medium was investigated using high frequency ultrasound (1700 kHz). This frequency, reputed ineffective, was tested in order to introduce the ultrasound waves with high frequency in the field of degradation or removal of dyes from wastewater, due to its limited use in this field, and to increase the application of high frequency ultrasound wave in the field of environmental protection. The effects of various parameters such as the concentration of CCl(4), frequency (22.5 and 1700 kHz), solution pH, temperature and tert-butyl alcohol adding on the decolorization rate of AB25 was studied. The obtained results clearly demonstrated the significant intensification of AB25 decolorization in the presence of CCl(4). The enhancement effect of CCl(4) increased by decreasing temperature and by increasing the CCl(4) concentration. The pH has a significant influence on the bleaching of dye both in the absence and presence of CCl(4). The three investigated dosimeter methods (KI oxidation, Fricke reaction and H(2)O(2) production) well corroborate the improvement of the sonochemical effects in the presence of CCl(4). The best sonochemical decolorization rate of AB25 in aqueous solution both in the absence and presence of CCl(4) is observed to occur at 1700 kHz compared to 22.5 kHz. The sonochemical oxidation of CCl(4) generates oxidizing species in the liquid phase that are highly beneficial for oxidation of hydrophilic and non-volatile pollutant, such as dyes, because they are less susceptible to free radical attack due to lower stability of the generated free radicals.
Intensification of sonochemical decolorization of anthraquinonic dye Acid Blue
25 using carbon tetrachloride
Houria Ghodbane, Oualid Hamdaoui
*
Department of Process Engineering, Faculty of Engineering, University of Annaba, P.O. Box 12, 23000 Annaba, Algeria
article info
Article history:
Received 30 September 2008
Received in revised form 9 December 2008
Accepted 9 December 2008
Available online 24 December 2008
Keywords:
High frequency ultrasound
Decolorization
Acid Blue 25
Anthraquinonic dye
Carbon tetrachloride
abstract
In this work, the influence of CCl
4
on the sonochemical decolorization of anthraquinonic dye Acid Blue 25
(AB25) in aqueous medium was investigated using high frequency ultrasound (1700 kHz). This fre-
quency, reputed ineffective, was tested in order to introduce the ultrasound waves with high frequency
in the field of degradation or removal of dyes from wastewater, due to its limited use in this field, and to
increase the application of high frequency ultrasound wave in the field of environmental protection. The
effects of various parameters such as the concentration of CCl
4
, frequency (22.5 and 1700 kHz), solution
pH, temperature and tert-butyl alcohol adding on the decolorization rate of AB25 was studied. The
obtained results clearly demonstrated the significant intensification of AB25 decolorization in the pres-
ence of CCl
4
. The enhancement effect of CCl
4
increased by decreasing temperature and by increasing
the CCl
4
concentration. The pH has a significant influence on the bleaching of dye both in the absence
and presence of CCl
4
. The three investigated dosimeter methods (KI oxidation, Fricke reaction and
H
2
O
2
production) well corroborate the improvement of the sonochemical effects in the presence of
CCl
4
. The best sonochemical decolorization rate of AB25 in aqueous solution both in the absence and
presence of CCl
4
is observed to occur at 1700 kHz compared to 22.5 kHz. The sonochemical oxidation
of CCl
4
generates oxidizing species in the liquid phase that are highly beneficial for oxidation of hydro-
philic and non-volatile pollutant, such as dyes, because they are less susceptible to free radical attack
due to lower stability of the generated free radicals.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Synthetic dyes are an important class of recalcitrant organic
compounds and are often found in the environment as a result of
their wide industrial use. Dyes are used in many industries such
as food, paper, plastics, cosmetics and textile in order to color their
products. Among various industries, textile industry ranks first in
usage of dyes where the main sources of wastewater generated
originate from the washing and bleaching of natural fibers and
from the dyeing and finishing steps. There are more than 100,000
different commercial dyes and pigments exist with over 7 10
5
tones of dyestuff produced annually [1,2]. It is estimated that
10–15% of the overall production of dyes is released into the envi-
ronment, mainly via wastewater [3].
The discharge of very small amounts of dyes (less than 1 ppm
for some dyes) is aestheticaly displeasing, impedes light penetra-
tion, affects gas solubility damaging the quality of the receiving
streams and may be toxic to treatment processes, to food chain
organisms and to aquatic life. Azo, anthraquinone and indigo are
the major chromophores found in commercial dyes. Decolorization
of these dyes by physical or chemical methods is financially and of-
ten also methodologically demanding, time-consuming and mostly
not very effective. Recently, there has been increasing interest in
the application of advanced oxidation processes (AOPs) as attrac-
tive alternative treatments for the degradation of dyes in
wastewater.
Among the existing AOPs, sonochemical oxidation has received
considerable attention because of its particular efficacy toward
volatile and/or hydrophobic compounds [4,5]. The use of ultra-
sound in degradation of dyes and other pollutants has developed
in recent decades [6–11]. Sonochemical techniques involve the
use of ultrasonic waves to produce an oxidative environment via
cavitation bubbles generated during the rarefaction period of
sound waves. The formation, growth, and collapse of cavitation
bubbles, leading to high local temperatures and pressures, are con-
sidered the main mechanism through which chemical reactions oc-
cur in sonochemistry. In a homogeneous aqueous system, three
different reaction sites have been postulated: (i) the gaseous inte-
riors of collapsing cavities where both temperature and pressure
are extremely high (up to and above 5000 K and 1000 atm, respec-
tively), resulting in dissociation of chemical compounds including
water [4,5,12]; (ii) the interfacial liquid region between cavitation
1350-4177/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ultsonch.2008.12.005
* Corresponding author. Tel.: +213 771 598 509.
E-mail addresses: ohamdaoui@yahoo.fr, oualid.hamdaoui@univ-annaba.org
(O. Hamdaoui).
Ultrasonics Sonochemistry 16 (2009) 455–461
Contents lists available at ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultsonch
bubbles and the bulk solution where high temperature (ca. 1000–
2000 K) and high temperature gradients exist [4,5]; (iii) the bulk
solution region at ambient temperature where small amounts of
OH radicals diffusing from the interface may contribute to oxida-
tion and organic contaminant destruction reactions. Therefore,
OH and
OOH radicals can be generated from water and oxygen
dissociation through the reactions (1)–(5) [4,5].
OH and
OOH rad-
icals combine to produce hydrogen peroxide that is released in the
medium (reactions (6) and (7)).
H
2
O ! H
þ
OH ð1Þ
O
2
! 2O ð2Þ
H
þ O
2
!
OOH ð3Þ
O þ H
2
O ! 2
OH ð4Þ
H
þ O
2
!
OH þ O ð5Þ
2
OH ! H
2
O
2
ð6Þ
2
OOH ! H
2
O
2
þ O
2
ð7Þ
Polar organic compounds are degraded by ultrasonic irradiation
to a much lower extent than volatile and hydrophobic substrates
[13]. It was reported that in the view point of practical application,
the present ultrasonic degradation rates need to be increased by at
least 10–100 times in order to be energy efficient, especially for the
non-volatile compounds, such as dyes [14]. Many studies have
demonstrated that the addition of chemicals, such as salt
[15–18], chloroalkanes [19] and carbon tetrachloride [20–30],in
the presence of ultrasonic waves increase the decomposition effi-
ciency and reduce the time required for removing the pollutants.
However, the use of CCl
4
for intensification of oxidation reactions
has been investigated using low frequency ultrasonic reactors.
Additionally, no work, to our knowledge, exists on the effect of
CCl
4
on the degradation of dyes using high frequency (1700 kHz)
ultrasonic waves. This frequency, reputed ineffective, was tested
in order to introduce the ultrasound waves with high frequency
in the field of degradation or removal of dyes from wastewater,
due to its limited use in this field, and to increase the application
of high frequency ultrasound wave in the field of environmental
protection.
In the present work, the effect of carbon tetrachloride adding on
the ultrasonic degradation in aqueous solution of the anthraqui-
nonic dye Acid Blue 25 (AB25) was investigated. Anthraquinonic
dyes represent the second most important class of commercial
dyes after azo-compounds and are mainly used for dyeing wool,
polyamide and leather. To optimize the kinetic of the degradation
process and to clarify the bleaching mechanism, several parame-
ters such as the concentration of CCl
4
, frequency, pH, temperature
and tert-butyl alcohol addition were investigated. Additionally, the
sonochemical efficiency in the presence of carbon tetrachloride
was evaluated using standard methods such as Fricke reaction, KI
oxidation and H
2
O
2
production.
2. Experimental
2.1. Reagents
Acid Blue 25 (abbreviation: AB25; C.I. number: 62055; chemical
class: anthraquinone; molecular formula: C
20
H
13
N
2
NaO
5
S) was
used as a model solute. Acid Blue 25 [1-amino-9,10-dihydro-
9,10-dioxo-4-(phenylamino)-2-anthracenesulfonic acid, monoso-
dium salt] (dye content 45%, molecular weight: 416.39 g mol
1
)
was purchased from Aldrich and was used as received. The molec-
ular structure of Acid Blue 25 (C.I. 62055) is shown in Fig. 1.
High purity carbon tetrachloride (99.9%) was purchased from
Sigma–Aldrich. Adequate amount of CCl
4
was added to dye solu-
tion in order to obtain the desired concentration and the mixture
was stirred vigorously using a magnetic stirring bar.
All reagents used in the present study were purchased among
the products of high purity (analytical grade).
Aqueous solutions of AB25 were prepared by dissolving the re-
quired amount in distilled water.
2.2. Reactor
Experiments were conducted in a 215 mL cylindrical water-
jacketed glass reactor (Fig. 2). Ultrasonic waves (1700 kHz) were
emitted from the bottom of the reactor through a piezo-electric
disc (diameter, 2 cm). Acoustic power dissipated in the reactor
(14 W) was measured using standard calorimetric method [31].
2.3. Procedure
Carbon tetrachloride is a compound with low solubility in water
(solubility 1200 mg L
1
at 25 °C [32]) and high vapor pressure
(114 mm Hg at 25 °C [32]). Consequently, an appropriate experi-
O
O
HN
NH
2
ONa
S
O
O
Fig. 1. Chemical structure of Acid blue 25 (AB25).
Coolant inlet
Transducer
Coolant outlet
Sampling port
Thermometer
XX °C
Geyser
Fig. 2. Scheme of the sonochemical reactor used for AB25 decolorization.
456 H. Ghodbane, O. Hamdaoui / Ultrasonics Sonochemistry 16 (2009) 455–461
mental procedure has been developed to ensure homogeneous
solution and to minimize evaporative losses.
Various solutions containing carbon tetrachloride was prepared
by adding the required amount of this agent and stirring overnight
using a magnetic stirring bar.
Ultrasonic decolorization of AB25 was carried out under iso-
thermal conditions using a constant solution volume of 100 mL.
Aqueous samples were taken from the solution and the concentra-
tions were analyzed. The concentrations of AB25 in the solution
before and after sonochemical bleaching were determined using
a UV–visible spectrophotometer (Jenway 6405) at 602 nm.
Sonochemical experiments involving oxidizing species genera-
tion were performed in the batch mode by sonicating 100 mL of
aqueous solution (distilled water, KI solution or Fricke solution)
in the absence and presence of CCl
4
using the same reactor used
for dye decolorization. The temperature was monitored continu-
ously and maintained at 20 °C.
Potassium iodide solution (0.1 M) was sonicated in the absence
and presence of CCl
4
. The absorbance of triiodide (I
3
) at 352 nm
(the molar absorptivity
e
= 26,000 L mol
1
cm
1
) was measured
with a UV–visible spectrophotometer.
Fricke solution was prepared by dissolving FeSO
4
(NH
4
)
2-
SO
4
6H
2
O (10
3
M), H
2
SO
4
(0.4 M) and NaCl (10
3
M) in water.
The obtained solution was sonicated in the absence and presence
of CCl
4
. The absorbance of Fe
3+
at 304 nm (the molar absorptivity
e
= 2197 L mol
1
cm
1
) was measured by using a UV–visible
spectrophotometer.
Hydrogen peroxide concentrations obtained in the absence and
presence of CCl
4
were determined using the iodometric method
[33]. The iodide ion (I
) reacts with H
2
O
2
to form the triiodide
ion (I
3
) that absorbs strongly at 352 nm (
e
= 26,000 L mol
1
cm
1
). Sample aliquots taken from the reactor were added in the
quartz cuvette of the spectrophotometer containing potassium io-
dide (0.1 M) and ammonium heptamolybdate (0.01 M). The mixed
solutions were allowed to stand for 5 min before absorbance was
measured.
All experiments were conducted in triplicate and the mean val-
ues were reported.
3. Results and discussion
3.1. Effect of CCl
4
adding on AB25 decolorization
Sonochemical decolorization of AB25 (50 mg L
1
) without and
with the addition of various concentrations of CCl
4
was shown in
Fig. 3. It was observed that the bleaching of AB25 solutions was sig-
nificantly improved by the addition of CCl
4
. Increasing of CCl
4
con-
centration will result in increase of ultrasonic decolorization. This
enhancement is due to the degradation of CCl
4
by pyrolytic cleav-
age in cavitation bubbles, which conducts to the release of oxidiz-
ing agents that can react with AB25 molecules. The sonolytic
degradation of CCl
4
has been studied by several research groups
[34–37]. The overall reaction mechanism can be written as [34–
37].
CCl
4
!
CCl
3
þ
Cl ð8Þ
CCl
4
!: CCl
2
þ Cl
2
ð9Þ
CCl
3
!: CCl
2
þ
Cl ð10Þ
CCl
3
þ
CCl
3
! CCl
4
þ : CCl
2
ð11Þ
CCl
3
þ
CCl
3
! C
2
Cl
6
ð12Þ
: CCl
2
þ : CCl
2
! C
2
Cl
4
ð13Þ
Cl þ
Cl ! Cl
2
ð14Þ
Cl
2
þ H
2
O ! HClO þ HCl ð15Þ
Pyrolysis reactions of CCl
4
and H
2
O (reaction (1)) proceed in the
hot cavitation bubbles. The carbon–chloride bond in CCl
4
was pref-
erentially broken at high temperature to produce large amount of
Cl radicals compared to the hydrogen–oxygen bond in H
2
O due to
the fact that the carbon–chloride bond strength in CCl
4
is 73
kcal mol
1
and the hydrogen–oxygen bond energy in H
2
Ois
119 kcal mol
1
[36]. The formation of
Cl radicals will lead to a ser-
ies of recombination reactions conducting to the formation of addi-
tional active species, such as HClO, Cl
2
and chlorine-containing
radicals (
Cl,
CCl
3
and :CCl
2
), having strong oxidizing property,
which will markedly accelerate the decolorization of AB25 in aque-
ous solution.
In this study, the pH of AB25 solution (50 mg L
1
) dropped from
the initial value of 5.7 to a final of 2.8 after 40 min of ultrasonic
irradiation in the presence of 399 mg L
1
of CCl
4
. This was partially
attributed to the formation of HClO and HCl during the bleaching
process. The same phenomenon in the initial pH decrease during
sonolytic decolorization experiment was observed for all the used
CCl
4
concentrations. Additionally, the drop in solution pH is signif-
icant as the CCl
4
concentration increased due to the enhancement
of HClO and HCl production.
During this study, different runs were compared using the ini-
tial decolorization rate (mg L
1
min
1
), rather than the pseudo-
first-order kinetic constant. For an initial dye concentration of
50 mg L
1
, the initial rate of decolorization increased significantly
from 0.1467 without CCl
4
to 15.609 and 17.325 mg L
1
min
1
in
the presence of 399 and 798 mg L
1
of CCl
4
, respectively. That is,
the addition of 798 mg L
1
of CCl
4
results in a 118-fold increase
of the rate of AB25 bleaching. The decolorization rate in the pres-
ence of 399 mg L
1
of CC1
4
was 106 times greater than that calcu-
lated in the absence of CCl
4
.
CCl
4
concentrations ranging from 100 to 798 mg L
1
were used
because the objective of this work is to study the effect of CCl
4
add-
ing on the sonochemical decolorization of AB25 using 1700 kHz
ultrasonic irradiation which is reputed as ineffective. Further stud-
ies are needed to optimize the concentration of CCl
4
and in order to
prevent residual amount of CCl
4
in the final discharge effluent
stream. Additionally, the losses of CCl
4
by evaporation will be in-
creased with the increase of its concentration, which is also against
the use of an over-high concentration.
In the present work, the decolorization rate for an initial AB25
concentration of 50 mg L
1
was enhanced 18 times by the addition
0
0.2
0.4
0.6
0.8
1
010203040506070
Time (min)
C/C
0
Without 100 mg/L 160 mg/L
239 mg/L 399 mg/L 798 mg/L
Fig. 3. Sonochemical decolorization of AB25 (C
0
= 50 mg/L) without and with the
addition of different concentrations of CCl
4
(conditions: volume: 100 mL; natural
pH (5.7); temperature: 20 ± 1 °C; frequency: 1700 kHz; power: 14 W).
H. Ghodbane, O. Hamdaoui / Ultrasonics Sonochemistry 16 (2009) 455–461
457
of 100 mg L
1
of CCl
4
, 36 times in the presence of 160 mg L
1
of
CCl
4
and 48 times by the addition of 239 mg L
1
of CCl
4
. This
finding is similar to that made in previous work on methyl orange
decolorization using horn type 20 kHz sonicator [25], which re-
ported that the rate of sonochemical decomposition of methyl or-
ange was enhanced more than 100 times by adding CCl
4
into the
dye solution. Okitsu et al. [23] have indicated that the decomposi-
tion ratio became 4.8 times larger by the addition of 100 ppm of
CCl
4
and 8.9 times larger by the addition of 150 ppm of CCl
4
and
11 times larger by the addition of 200 ppm of CCl
4
and 14 times
larger by the addition of 250 ppm of CCl
4
, respectively. The low
enhancement effect in the work of Okitsu et al. [23] may be attrib-
uted to different geometric and experimental conditions. Using a
high intensity ultrasonic irradiation (frequency: 200 kHz, calori-
metric power: 80 W), Okitsu et al. [23] reported that the decompo-
sition ratio became 41 times larger by the addition of 100 ppm of
CCl
4
and 100 times larger by the addition of 150 ppm of CCl
4
,
respectively. A direct comparison of literature data obtained using
CCl
4
for the enhancement of sonochemical decomposition is not
possible since experimental conditions are not the same.
3.2. Effect of CCl
4
on KI oxidation, Fricke reaction and H
2
O
2
production
The effect of different CCl
4
concentrations raging from 100 to
798 mg L
1
on the oxidation of 0.1 M KI solution is shown in
Fig. 4 in terms of the amount of I
3
formed. The rate of I
3
pro-
duced without addition of CCl
4
is 1.04
l
M min
1
, whereas those
in the presence of 100, 160, 239, 399 and 798 mg L
1
of CCl
4
are
respectively 12.96, 18.42, 27.68, 35.76 and 38.64
l
M min
1
. The
rates of I
3
produced in the presence of CCl
4
are approximately
12.4 to 37.1 times larger when compared with that formed in the
absence of CCl
4
. This behavior is analogous to that made in previ-
ous works on the production of I
3
in the presence of CCl
4
[23]. Re-
cently, Zhou et al. [29] have investigated the ultrasonic oxidation of
iodide in the presence of CCl
4
. They indicated that the ultrasonic
oxidation of iodide was found to be significantly promoted by
the addition of CCl
4
. Sonochemical reactions taking place in the
presence of CCl
4
and KI have been detailed by Rajan et al. [38].
Fig. 5 shows the results of Fricke dosimeter obtained in the ab-
sence and presence of 399 mg L
1
of CCl
4
. The production of Fe
3+
was significantly enhanced with the addition of CCl
4
. The rate of
Fe
3+
formed is 2.64 and 50.15
l
M min
1
in the absence and pres-
ence of CCl
4
respectively. In the presence of CCl
4
, the rate of Fe
3+
formed was calculated for the first 7 min (linear portion of the
curve). The formation rate of Fe
3+
becomes 19 times larger by the
addition of 399 mg L
1
of CCl
4
. After 30 min of sonication,
the yields of Fe
3+
in Fricke reaction are 83.7 and 744.2
l
M in the
absence and presence of 399 mg L
1
of CCl
4
, respectively.
The concentration of H
2
O
2
generated in water during sonication
was measured in the absence and presence of 399 mg L
1
of CCl
4
by using the potassium iodide method [33]. In this method, the tri-
iodide concentration is equivalent to the H
2
O
2
concentration. Fig. 6
shows the concentration of triiodide ion as a function of sonication
time. More triiodide ion was formed in the presence of CCl
4
than in
its absence. However, the increase of triiodide concentration may
be a combined result of the increase of both the formation of
H
2
O
2
and other oxidizing species produced during degradation of
CCl
4
. The same finding has been reported by Wang et al. [25].
The rate of triiodide formation in the absence of CCl
4
was
0.7789
l
M min
1
and in the presence of 399 mg L
1
of CCl
4
was
26.9810
l
M min
1
. It means that the triiodide concentration be-
came 35 times larger by the addition of 399 mg L
1
of CCl
4
. Using
the p-hydroxyphenyl acetic acid dimerization method, Zheng
et al. [27] have indicated that more hydrogen peroxide was pro-
duced during the early stages in the presence of 150
l
M of CCl
4
,
but at later times sonication with and without CCl
4
showed similar
hydrogen peroxide concentrations. These results confirmed that
the enhancement of triiodide concentration is due to a combined
contribution of H
2
O
2
and oxidizing species formed during CCl
4
sonolysis.
The three investigated methods (KI oxidation, Fricke reaction
and H
2
O
2
production) well corroborate the improvement of the
sonochemical effects in the presence of CCl
4
. Additional oxidizing
0
20
40
60
80
100
0 5 10 15 20 25 30
Time (min)
Triiodide concentration (µM)
Without
100 mg/L
160 mg/L
239 mg/L
399 mg/L
798 mg/L
Fig. 4. Iodide dosimeter in the absence and presence of different concentrations of
CCl
4
(conditions: volume: 100 mL; KI concentration: 0.1 M; natural pH; tempera-
ture: 20 ± 1 °C; frequency: 1700 kHz; power: 14 W).
0
100
200
300
400
500
600
700
800
0 5 10 15 20 25 30 35
Time (min)
Fe
3+
concentration (µM)
Without
399 mg/L
Fig. 5. Fricke dosimeter in the absence and presence of 399 mg L
1
of CCl
4
(conditions: volume: 100 mL; temperature: 20 ± 1 °C; frequency: 1700 kHz; power:
14 W).
0
50
100
150
200
250
300
350
400
450
500
0 5 10 15 20 25 30 35
Time (min)
Triiodide concentration (µM)
Without
399 mg/L
Fig. 6. Amount of triiodide ions formed in the absence and presence of 399 mg L
1
of CCl
4
using the iodometric method (conditions: volume: 100 mL; temperature:
20 ± 1 °C; frequency: 1700 kHz; power: 14 W).
458 H. Ghodbane, O. Hamdaoui / Ultrasonics Sonochemistry 16 (2009) 455–461
species in the liquid phase produced during CCl
4
sonolysis are
highly beneficial for oxidation of non-volatile solute species which
are less susceptible to free radical attack.
3.3. Comparison of AB25 decolorization at two frequencies: 22.5 and
1700 kHz
Most of the previous works carried out using CCl
4
for intensifi-
cation of oxidation reactions have been investigated using low fre-
quency ultrasonic reactors [19–22,24–27]. The decolorization of
50 mg L
1
AB25 solution in the absence and presence of 399 mg
L
1
of CCl
4
was investigated at two different frequencies: 22.5
and 1700 kHz. The 22.5 kHz ultrasonic irradiation was carried out
with a commercial supply Microson XL 2000 equipped with a tita-
nium horn (6 mm diameter) mounted at the top of the cylindrical
glass vessel.
Frequency is an important parameter in sonochemical oxida-
tion. It can affect cavitation in several ways: by modifying bubble
number, bubble size, cavitation threshold and the temperatures
reached during the collapse. The sonochemical decolorization of
AB25 both in the absence and presence of CCl
4
is shown in Fig. 7.
From this figure, it is clearly shown that the best decolorization
is obtained at 1700 kHz both without and with the addition of
CCl
4
. For both frequencies (22.5 and 1700 kHz), a significant
enhancement of the bleaching of AB25 solutions was obtained in
the presence of 399 mg L
1
of CCl
4
. At 22.5 kHz, the initial decolor-
ization rate increased significantly from 0.0418 mg L
1
min
1
in
the absence of CCl
4
to 3.6555 mg L
1
min
1
in the presence of
399 mg L
1
of CCl
4
. Thus, the addition of CCl
4
(399 mg L
1
) results
in a 87-fold increase of the initial decolorization rate. The best
sonochemical decolorization rate of AB25 in aqueous solution is
observed to occur at 1700 kHz. This is because the number of
acoustic cycles and the number of cavitation collapses increases
at high frequency leading to the increase of CCl
4
degradation and
therefore to the formation of more oxidizing species, which en-
hance AB25 decolorization. This result is consistent with the work
of Pétrier and Francony [37] focusing on elimination of CCl
4
that
reports a better degradation yield at high frequency (800 kHz).
3.4. Effect of pH
The influence of solution pH on the sonochemical decoloriza-
tion of 50 mg L
1
AB25 aqueous solution was investigated in the
presence of 399 mg L
1
of CCl
4
. Fig. 8 illustrates the initial decolor-
ization rate as a function of initial pH. The decolorization rates
were nearly unchangeable (15.614 and 15.609 mg L
1
min
1
)in
the pH range 3.2–5.7 and decrease in the pH range 7–10.5. The ini-
tial decolorization rates were decreased significantly at pH values
of 1 (11.964 mg L
1
min
1
) and 11.8 (3.2358 mg L
1
min
1
).
The absorbance data of dye solution determined spectrophoto-
metrically indicated that change of the initial pH of dye solution
has no effect on the k
max
of AB25 (pH 1–11.8). Based on this obser-
vation and in order to explain the obtained results in the presence
of CCl
4
, the influence of pH on the sonochemical decolorization of
AB25 in the absence of CCl
4
was shown in Fig. 9. It was found that
the rate of AB25 decolorization in the absence of CCl
4
was strongly
pH dependent. The initial bleaching rates in acidic solutions (1–3)
are higher, especially at pH 1, and decrease from pH 1 to 5, and
there is almost no change in the pH range of 5–8. Higher decolor-
ization rates are observed in basic media (9.3–11.8). AB25 is a non-
volatile compound and the region of decolorization would be at the
exterior of the cavitation bubbles. It is possible that the change in
the solution pH results in the change of hydrophobic property of
the dye, which affects the ultrasonic decolorization. The accelera-
tion of decolorization in acidic conditions is probably associated
with the effect of protonation of negatively charged SO
3
group in
acidic medium and, obviously, the hydrophobic character of the
resulting molecule enhances its reactivity under ultrasound treat-
ment because AB25 is accumulated in the interface of the cavita-
tion bubbles. Moreover, in acidic conditions (pH 1–3), the
recombination of
OH radicals (reaction (6)) is less effective before
react against AB25 concentrated in the interface. In the pH range
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30 35 40 45
Time (min)
C/C
0
1700 kHz (without)
1700 kHz (399 mg/L)
22.5 kHz (without)
22.5 kHz (399 mg/L)
Fig. 7. Sonochemical decolorization of AB25 (C
0
=50mgL
1
) in the absence and
presence of 399 mg L
1
of CCl
4
at two frequencies: 22.5 and 1700 kHz (conditions:
volume: 100 mL; natural pH (5.7); temperature: 20 ± 1 °C; power: 14 W).
0
2
4
6
8
10
12
14
16
1 3.2 5.7 7 9.3 10.5 11.8
pH
Initial decolorization rate (mg/L min)
Fig. 8. Initial decolorization rate at various pHs in the presence of 399 mg L
1
of
CCl
4
(conditions: volume: 100 mL; initial dye concentration: 50 mg L
1
; tempera-
ture: 20 ± 1 °C; frequency: 1700 kHz; power: 14 W).
0
0.05
0.1
0.15
0.2
0.25
0.3
1 3 5 7 8 9.3 10.6 11.8
pH
Initial decolorization rate (mg/L min)
Fig. 9. Initial decolorization rate at various pHs in the absence of CCl
4
(conditions:
volume: 100 mL; temperature: 20 ± 1 °C; initial dye concentration: 50 mg L
1
;
frequency: 1700 kHz; power: 14 W).
H. Ghodbane, O. Hamdaoui / Ultrasonics Sonochemistry 16 (2009) 455–461
459
5–8, AB25 reaches the ionized state, and its hydrophilicity and sol-
ubility are enhanced, and thus the decolorization is carried out in
the bulk of the solution where there is a lower concentration of
OH
because only about 10% of the
OH generated in the bubble can dif-
fuse into the bulk solution [14]. Additionally, the bleaching rate de-
crease at pH 5 and 8 due to the fact that a higher number of
OH
species recombine to H
2
O
2
. The enhancement of decolorization
rate at basic conditions may be caused by the change of hydropho-
bic property of the dye. The same results were obtained for the
decolorization of reactive brilliant red by 20 kHz ultrasonic irradi-
ation [39].
In the presence of CCl
4
, the initial decolorization rates in the pH
range 3.2–9 are higher than that obtained at pH 1. At pH 1, AB25 is
accumulated in the interfacial region of the cavitating bubbles and
decreases the degradation of CCl
4
, which reduces the amount of
the oxidizing agents produced by the oxidation of CCl
4
and there-
fore the AB25 decolorization. At pH 3.2–9.3, the hydrophilicity of
AB25 is improved and the bleaching is carried out in the bulk solu-
tion. Another reason may be that at acidic pH, the chlorine is pres-
ent in the solution in the form of hypochlorous acid, which has a
higher oxidation potential (1.49 V) than hypochlorite (0.94 V)
[40–42]. The lower decolorization rates in basic conditions, espe-
cially at pH 11.8, seem to be due to the enhancement of AB25
hydrophobicity as well as to the decreased production of chlo-
rine/hypochlorite at higher pH conditions, because of the forma-
tion of chlorate or perchlorate [40–42], which react more slowly
with dye molecules. The hypochlorite is prevalent in alkaline con-
dition [40–42]. It seems that hypochlorous acid (HClO) is the key
reactive intermediate in the sonochemical decolorization of AB25
in the presence of CCl
4
.
3.5. Effect of temperature
The effects of aqueous temperature on the sonochemical decol-
orization rate were investigated in the presence of 399 mg L
1
of
CCl
4
. The initial rates of AB25 decolorization obtained for sonolysis
of a 50 mg L
1
solution at temperatures of 20, 30, 40 and 50 °C are
15.609, 14.087, 13.979 and 11.348 mg L
1
min
1
, respectively. The
rate of AB25 sonochemical decolorization in the presence of CCl
4
decreases with increasing temperature between 20 and 50 °C. This
is due to the increased solvent vapor pressure inside the bubble;
increasing solvent vapor pressure attenuates the efficacy of cavita-
tional collapse, the maximum temperature reached during such
collapse, and, consequently, the rates of cavitational reactions.
3.6. Effect of tert-butyl alcohol
The influence of tert-butyl alcohol on the sonochemical decolor-
ization of dye in the presence of 399 mg L
1
of CCl
4
was investi-
gated (Fig. 10). In our experiments, varying concentrations of
tert-butyl alcohol (399, 798 and 1570 mg L
1
) were added to
50 mg L
1
AB25 solutions. The obtained results indicated that the
addition of 399, 798 and 1570 mg L
1
of tert-butyl alcohol de-
creased the initial decolorization rate from 15.609 mg L
1
min
1
in the absence of tert-butanol to 6.5236, 1.7794 and 1.2742
mg L
1
min
1
, respectively. The degradation was effectively
quenched, but not completely, by the addition of tert-butyl alcohol.
Because tert-butyl alchol molecules pass in the cavitation bubbles,
they are able to scavenge oxidizing species in the bubble and re-
duce significantly the decolorization rate of dye. Another factor
that also affects the rate of AB25 bleaching is the formation of vol-
atile products from the tert-butyl alcohol degradation that accu-
mulate inside the bubble and react with oxidizing species,
conducting to the deceleration of the decolorization of dye. Addi-
tionally, Pétrier and Francony [37] have demonstrated that addi-
tion of an excess of 1-butanol (10-fold CCl
4
initial concentration)
does not affect rates of carbon tetrachloride destruction. It seems
that tert-butyl alcohol and its degradation products inhibited the
bleaching of AB25 by scavenging active species, such as HClO, Cl
2
and chlorine-containing radicals (
Cl,
CCl
3
and :CCl
2
), having strong
oxidizing properties which will markedly inhibit the decolorization
of AB25 in aqueous solution. The increase of the tert-butyl alcohol
concentration leads to the decrease of the decolorization rate. The
bleaching rate with respect to that obtained in the absence of tert-
butyl alcohol was decreased 58% in the presence of 399 mg L
1
of
tert-butanol, 89% in the presence of 798 mg L
1
of tert-butanol
and 92% in the presence of 1570 mg L
1
of tert-butanol. The ob-
served differences can be due to the increase of the accumulation
of tert-butyl alcohol and its degradation products in the cavitation
bubbles with increasing alcohol concentration, conducting to more
scavenging effect. Regardless of the absence and presence of tert-
butyl alcohol, the pH of the reaction matrix decreased from the ini-
tial value of 5.7 to a final of 2.9 after 30 min of ultrasonic irradia-
tion, which was attributed to the formation of HClO and HCl.
From these results, we can infer that AB25 sonochemical decolor-
ization in the presence of CCl
4
is mainly due to the reaction with
chlorine-containing radicals and other oxidizing species such as
HClO and Cl
2
.
4. Conclusion
The sonochemical decolorization of AB25 in aqueous phase
using 1700 kHz ultrasound was significantly enhanced and im-
proved in the presence of CCl
4
. The effects of some operational
parameters on the bleaching of AB25 were discussed and found
that the decolorization rate is strongly dependent on the concen-
tration of CCl
4
, the temperature and the solution pH. It seems that
hypochlorous acid (HClO) is the key reactive intermediate in the
sonochemical decolorization of AB25 in the presence of CCl
4
. The
used sonochemistry dosimeters well corroborate the enhancement
of the sonochemical effects in the presence of CCl
4
. The best sono-
chemical decolorization rate of AB25 in aqueous solution is
observed to occur at 1700 kHz compared to 22.5 kHz. The degrada-
tion of dye in the presence of CCl
4
was effectively quenched, but
not completely, by the addition of tert-butyl alcohol.
High frequency ultrasonic waves (1700 kHz) used in the pres-
ence of CCl
4
was shown to be of interest for the treatment of
wastewaters contaminated with anthraquinonic dyes. The sono-
chemical process in the presence of CCl
4
may be utilized for the
decomposition of hydrophilic and non-volatile pollutants in water
because they are less susceptible to free radical attack due to lower
stability of the generated free radicals.
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 35 40
Time (min)
C/C
0
Without tert-butanol
399 mg/L tert-butanol
798 mg/L tert-butanol
1570 mg/L tert-butanol
Fig. 10. Effect of tert-butyl alcohol on the sonochemical decolorization of AB25
(C
0
=50mgL
1
) in the presence of 399 mg L
1
of CCl
4
(conditions: volume: 100 mL;
natural pH (5.7); temperature: 20 ± 1 °C; power: 14 W).
460 H. Ghodbane, O. Hamdaoui / Ultrasonics Sonochemistry 16 (2009) 455–461
This work has discussed the sonolytic degradation of only one
acid anthraquinone dye (Acid Blue 25) but this method could be
used for the degradation of other acid anthraquinone dyes such
as Acid Blue 40, 41, 51, 53, 129 and 230 that have very similar
chemical structures with Acid Blue 25.
Further studies are needed to optimize the concentration of
CCl
4
and in order to prevent residual amount of CCl
4
in the final
discharge effluent stream.
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... However, it has been found that the sonochemical degradation rate of nonvolatile contaminants is rather slow due to the limited amount of free radicals reaching the bulk zone (solution) (Goel et al. 2004;Torres et al. 2007;Merouani et al. 2010;Ferkous et al. 2017 Many efforts have been devoted to ameliorate the energy efficiency of this method (US), specifically toward the degradation of nonvolatile contaminants. Consequently, several additives have been tested in order to evaluate their effects on the rate of pollutants decomposition, e.g., salts (Mahamuni and Pandit 2006;Guo et al. 2008;Merouani et al. 2010;Ferkous et al. 2016), S 2 O 8 2− (Ferkous et al. 2017), IO 4 − , O 3 (Mahamuni and Pandit 2006;Guo et al. 2008;Merouani and Hamdaoui 2019), CCl 4 (Mahamuni and Pandit 2006;Bejarano-Pérez and Suarez-Herrera 2008;Guo et al. 2008;Ghodbane and Hamdaoui 2009;Merouani et al. 2010;Park et al. 2011;Uddin and Okitsu 2016), catalysts (Torres et al. 2007;Bejarano-Pérez and Suarez-Herrera 2008;Guo et al. 2008;Merouani et al. 2010;Boutamine et al. 2017), H 2 O 2 (Merouani et al. 2010), C 6 F 14 (Uddin and Okitsu 2016), etc. Of all these additives, CCl 4 has shown the most attractive attention due to the huge intensification observed in the removal rate of several nonvolatile organic pollutants (e.g., phenol, Bisphenol A, 2,4-dinitrophenol, methyl orange, C.I. acid orange 8, etc.) in the presence of CCl 4 (Wang et al. 2007;Guo et al. 2008;Gültekin et al. 2009;Merouani et al. 2010). ...
... On the other hand, it is well known that the size of active bubbles in sonocavitating medium is an interval rather than a single value, as demonstrated experimentally and theoretically (Burdin et al. 1999;Tsochatzidis et al. 2001;Labouret and Frohly 2002;Avvaru and Pandit 2009;Brotchie et al. 2009;Iida et al. 2010). After a depth research in the literature reports focusing on the use of CCl 4 as intensification technique, it was observed that either RCS generation or H • scavenging (or both) induced by CCl 4 during sonolysis is the main mechanism reported for justifying the intensifying role of CCl 4 vis-à-vis the sonolytic degradation of nonvolatile organics (Wang et al. 2007;Guo et al. 2008;Ghodbane and Hamdaoui 2009;Gültekin et al. 2009;Merouani et al. 2010). However, since CCl 4 can act as an oxidants-generator (RCS) from the endothermal dissociation of CCl 4 within the bubble, this means that the bubbles population (active bubbles) in the sonochemical reactor may be greatly modified due to the change of the sonoactivity of individual cavities. ...
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... Yet, relative to the US power, the effect of degassing plays a minor role here since a continuous rise in the solution temperature is observed within the entire range of US power. According to Ghodbane and Hamdaoui (2009), an increase in the solution temperature enhances the solvent vapor pressure inside the cavities. This increases the stability of cavities against the vibrant implosion due to the cushioning effect of an increased amount of solvent vapor inside the former. ...
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In the dye removal application, regeneration of hydrogen titanate nanotubes (HTN, H2Ti3O7) has been achieved via thermal activation of persulfate anion (PS, S2O8²⁻) by using the conventional hot plate technique which has limitations from the commercial perspective since it does not provide any precise control over the thermal generation process typically during the scale-up operation. To overcome this drawback, HTN have been synthesized via hydrothermal process which exhibit the methylene blue (MB) adsorption of 93% at the initial dye concentration and solution pH of 90 µM and 10 respectively. HTN have been regenerated via the thermal activation of PS by varying its initial concentration and regeneration temperature, within the range of 0.27–1 wt% and 40–80 °C, under the thermal conditions set by the autoclave and pulsed ultrasound (US) cavitation process. The results of recycling experiments suggest that the optimum values of initial PS concentration and temperature, for the regeneration of HTN under the autoclave conditions, are 1 wt% and 70 °C with the maximum MB adsorption of 92%, while, the corresponding values for the pulsed US cavitation process are 1 wt%, 80 °C, and 91% respectively. Thus, the regeneration and recycling of HTN have been successfully demonstrated by using the autoclave and pulsed US cavitation process. Under the optimum conditions, MB degradation involves the generation and attack of SO4•− for both the thermal generation techniques. The regeneration techniques developed here may be utilized in future during the scale-up operation and also for the regeneration of adsorbents besides HTN.
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An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe²⁺ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80 mM, the Fe²⁺ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20-25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15%, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore ·OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21mg/L, and the COD value decreased to 80.83mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.
Chapter
Throughout the last two decades, there has been a lot of interest in using ultrasonic as an alternate advanced oxidation method for the degradation of textile dyes in wastewater. This technique effectively destroys pollutants by reactive ∙OH radical and/or pyrolysis in various reaction zones. The addition of CCl4 increased dye sonolytic degradation by tens to hundreds of times (intensification viewpoint). Despite several investigations on the issue, the mechanism by which CCl4 enhanced the sonolytic removal of textile dyes has not been clearly determined. This chapter will address this topic. To begin, works done on the CCl4-induced intensification of organic dyes were reviewed, together with their experimental conditions and noteworthy results. Second, all elements that influence the intensifying aspect of CCl4 were shown. Thirdly, using a newly constructed model of single bubble sonochemistry, the different reactive species generated through CCl4 pyrolysis were identified. The model’s results were then utilized to explain the intensifying action of CCl4 in the breakdown of aqueous organic pollutants by ultrasound. Finally, several prospects for large-scale use of this new intensification approach were highlighted, as well as some emphasizing innovation requirements. To the best of our knowledge, this is the first review focuses on ultrasound/CCl4 technique for fast dye removal from wastewater.KeywordsTextile dyesSonochemical treatmentProcess intensificationCarbon tetrachloride (CCl4)Computational Analysis
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The present study combines, for the first time, experimental degradation findings and numerical simulation results of CCl4 sonochemistry for (i) understanding the right mechanism by which CCl4 improves Safranin O (SO) sono-bleaching (1.7 MHz, 15 W) and (ii) stating the impact of operational conditions on reactive species dis- tribution toward the degradation process. The hydrophilicity/hydrophobicity of SO are the main keys controlling its elimination as function of the solution pH in the absence of CCl4. In the presence of CCl4, a drastic enhancement in the SO degradation rate was observed. The quantity of reactive chlorine species (RCS) and reactive oxygen species (ROS) produced through CCl4 and H2O sono-pyrolysis within hot bubbles are the key parameters responsible for SO rapid degradation. Theoretical results indicated the increase of RCS and • OH production proportionally with the rise of CCl4 concentration from 0 to 5 mM, conversely to the bubble tem- perature and CCl4 conversion yield which were reduced. In addition, it was observed that the degradation of SO is more promoted at the liquid temperature of 25 ◦C, because of the synergy between RCS and • OH radicals at this liquid temperature. However, the competition between RCS and • OH radicals at 45 ◦C negatively affects the degradation rate.
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This paper aims to investigate the uses of leonardite powder (LP) as an effective adsorbent for the removal of basic red 18 (BR18) and reactive red 180 (RR180) dyes. LP was characterized using scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), Zeta potential, Brunauer Emmett‐Teller (BET) analysis, Fourier transform infrared spectroscopy (FTIR), and X‐ray fluorescence (XRF). The adsorption process was assessed based on pH, size and the amount of the adsorbent, BR18 and RR180 concentration, and the contact time. BR18 dye was completely adsorbed onto the LP (the removal efficiency equals 100%) after 45 min at the optimum condition (original pH (6.5), the particle size of 45 μm, the adsorbent dose of 0.25 g/L, and the initial concentration of 10 mg/L). For RR180, the maximum removal efficiency (74%) was obtained when one gram per liter (1 g/L) LP with 45um size was added to an RR180 solution of 10 mg/L concentration. Langmuir isotherm was used to explain the adsorption of BR18. In contrast, RR180 adsorption was described by the Freundlich model. The adsorptions of both dyes followed the pseudo‐second‐order kinetics. The reusability of the LP was assessed. For BR18, the efficiency decreased to 96% in the 2nd cycle and reached 42% in the 5th cycle. In RR180, LP was not able to be reused efficiently. As a result, the LP ability for BR18 removal is higher than the RR180 in terms of uptake and reusability.
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One of the most important issues in the world in recent years is water pollution, which is brought about by rapid industrialization. Peroxymonosulfate (PMS) oxidation is an effective technique for wastewater treatment. Transition metals such as cobalt, manganese, iron are used to activate PMS. Therefore, in this study, a novel activated carbon and cobalt phthalocyanine catalyst (Co-AC) was synthesized by the solvothermal method.Rhodamine B (RhB) and 2,4,6-Trichlorophenol (2,4,6-TCP) were used as model pollutants in the catalytic tests. The effective catalytic activity was observed at a low concentration of Co-AC and PMS compared to the literature. XRD, TEM, Raman, SEM and XPS techniques were used for the characterization of the as-synthesized catalyst. In addition, the surface area of Co-AC was calculated by BET and QS-DFT analysis. As a result, the degradation of RhB was found to be 97.07% after 16 minutes, and 100% for 2,4,6-TCP after 6 minutes. Experimental parameters such as temperature, pH, the concentration of the catalyst and PMS were studied and optimum conditions were determined In addition, TOC removal values were found to be 46% for RhB and 66% for 2,4,6-TCP, respectively. The ICP-OES technique was used for the cobalt leaching and the results were found to be 1.35 mgL ⁻¹ for the RhB solution and 1.38 mgL ⁻¹ for 2,4,6-TCP. These results are in good agreement with previously published works. The synthesized activated carbon-supported cobalt-based catalyst in line with these results acts as an effective catalyst especially in the treatment of wastewater containing pollutants such as RhB and 2,4,6-TCP.
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Dyes and dyestuffs find use in a wide range of industries but are of primary importance to textile manufacturing. Wastewater from the textile industry can contain a variety of polluting substances including dyes. Increasingly, environmental legislation is being imposed to control the release of dyes, in particular azo-based compounds, into the environment. The ability of microorganisms to decolourise and metabolise dyes has long been known, and the use of bioremediation based technologies for treating textile wastewater has attracted interest. Within this review, we investigate the mechanisms by which diverse categories of microorganisms, such as the white-rot fungi and anaerobic bacterial consortia, bring about the degradation of dyestuffs.
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A new treatment process was employed to treat wastewater generated from a factory manufacturing syntan (synthetic tannin). In this treatment process, in-situ production of hypochlorous acid was achieved by the use of an aqueous sodium chloride solution for chlorine production. As the graphite anode and stainless steel cathode zones were kept unseparated, the hypochlorous acid was produced by electrolysis. The hypochlorous acid was utilized for the oxidation of organic matter present in the wastewater. The results showed that for an initial COD concentration of 10,000 mg/l, a turbidity of 277 NTU, a tannin concentration of 4000 mg/l, a temperature of 27±1°C, a current density of 42.5 mA/cm2, a sodium chloride content of 3% and an electrolysis period of 210 min showed an effluent COD concentration of 230 mg/l, a turbidity of 9 NTU, a tannin concentration below the detection limit and a temperature of 37±2°C.
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The sonolytic degradation of aqueous carbon tetrachloride is investigated at a sound frequency of 20 kHz and 135 W (112.5 W cm-2) of power. The observed first-order degradation rate constant in an Ar-saturated solution is 3.3 × 10-3 s-1 when the initial CCl4 concentration, [CCl4]i, is 1.95 × 10-4 mol L-1 and increases slightly to 3.9 × 10-3 s-1 when [CCl4]i = 1.95 × 10-5 mol L-1. Low concentrations (10-8−10-7 mol L-1) of the organic byproducts, hexachloroethane and tetrachloroethylene, are detected, as well as the inorganic products chloride ion and hypochlorous acid. The chlorine mass balance after sonolysis is determined to be >70%. The reactive intermediate, dichlorocarbene, is identified and quantified by means of trapping with 2,3-dimethyl-2-butene. The presence of ozone in the sonicated solution does not significantly effect the rate of degradation of carbon tetrachloride; however, O3 inhibits the accumulation of hexachloroethane and tetrachloroethylene. Ultrasonic irradiation of an aqueous mixture of p-nitrophenol (p-NP) and carbon tetrachloride results in the acceleration of the sonochemical degradation of p-NP. The sonolytic rate of degradation of p-NP appears to be enhanced by the presence of hypochlorous acid, which results from the sonolysis of CCl4.
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Methylene blue (MB) is one of typical textile dyestuffs that cannot be degraded by a conventional method such as biological treatment. In this study, degradation of MB in aqueous solution under ultrasonic field at the multibubble sonoluminescence (MBSL) condition was tried for the first time. At the optimum condition of MBSL, 0.1mM MB solution was degraded completely within 30min, which is quite faster than the reaction rate for the photocatalytic degradation of MB in aqueous TiO2 dispersions under UV-irradiation. The sonochemical degradation of MB at the MBSL condition was found to be first-order with respect to MB concentration. Also, it has been found that MB was degraded by the oxidation process by OH radicals.
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The sonochemical reactions of CCl4-H2O mixtures in an argon atmosphere have been investigated and compared with those of HCCl3-H2O mixtures. The observed products from the CCl4 reaction were CO2, O2, Cl2, HCl, C2Cl6 and C2Cl4. After an initiation period, the rates of formation of certain products were found to be constant: d(Cl)/dt = 9.6 μequiv./min.; d(C2Cl6)/dt = 4.2 μmoles/min. (20°); the rate of production of C2Cl4 was an order of magnitude slower; the elemental Cl2 concentration remained essentially constant after the first half hour of reaction. After the initial period, the rate of production of inorganic chlorine was insensitive to a 15° temperature change. The products identified from the HCCl3 reaction were HCl, C2Cl6 and C2Cl4: d(Cl)/dt = 4.1 μequiv./min. (20°). Some interrelationships between cavitation and chemical reaction are discussed. A free radical mechanism is proposed to account for the rate data and observed products.
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2,4-dichlorophenoxyacetic acid (2,4-D) undergoes efficient degradation when an O2- or Ar-saturated aqueous solution is subjected to high-frequency (640 kHz) sonolysis. 2,4-dichlorophenol, hydroquinone, and catechol are major reaction intermediates common to various experimental conditions. The similarities between the reaction intermediates of sonolytic and radiolytic reactions indicate •OH radical as the primary reactive species responsible for 2,4-D degradation. Very little 2,4-D degradation occurs if the sonolysis is carried out in the presence of the •OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. Most of the 2,4-D eventually forms oxalic acid, which, unlike other •OH-mediated oxidation methods, is not easily mineralized with high-frequency ultrasound.