Comparative studies of various iron-mediated oxidative systems for the photochemical degradation of endosulfan in aqueous solution

Article abstract of DOI:10.1016/j.jphotochem.2015.03.014

This study investigated iron-mediated oxidative processes for the photochemical degradation of endosulfan, a chlorinated insecticide and central nervous system disruptor. At UV fluence of 360 mJ/cm², 52.4% and 32.0% removal of 2.45 μM initial endosulfan was observed by UV/Fe³⁺ and UV/Fe²⁺ processes, respectively, at an initial concentration of 17.8 μM iron. The degradation of endosulfan by UV/Fe³⁺ or UV/Fe²⁺ was dramatically enhanced by adding peroxide (i.e., H₂O₂, S₂O₈^2- or HSO₅^-). Among the UV/peroxide/Fe processes, the highest degradation efficiency of 99.0% at UV fluence of 360 mJ/cm² was observed by UV/HSO₅^-/Fe²⁺ with 2.45 μM [endosulfan]₀, 17.8 μM [Fe²⁺]₀, and 49.0 μM [HSO₅^-]₀. The observed degradation rate constant of endosulfan was promoted either by increasing [Fe²⁺]₀ and/or [peroxide]₀ or by decreasing [endosulfan]₀, while the initial degradation rate of endosulfan increased with increasing [Fe²⁺]₀, [peroxide]₀, or [endosulfan]₀. At UV fluence of 6000 mJ/cm², 45.0% mineralization as represented by the decrease in total organic carbon content was observed by UV/HSO₅^-/Fe²⁺ at 9.80 μM [endosulfan]₀, 980 μM [HSO₅^-]₀, and 17.8 μM [Fe²⁺]₀. The major by-product of endosulfan was observed in all cases to be endosulfan ether which was further degraded with an extended reaction time. The results suggest that iron-mediated advanced oxidation processes (AOPs) have a high potential for the removal of endosulfan and its by-product from contaminated water.

Full text of DOI:10.1016/j.jphotochem.2015.03.014

Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Comparative studies of various iron-mediated oxidative systems for
the photochemical degradation of endosulfan in aqueous solution
Noor S. Shah a,b,c, Xuexiang He b,d, Javed Ali Khan a,b, Hasan M. Khan a,
Dominic L. Boccelli b, Dionysios D. Dionysiou b,d,
*
a
Radiation Chemistry Laboratory, National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar 25120, Pakistan
Environmental Engineering and Science Program, University of Cincinnati, 705 Engineering Research Center, Cincinnati, OH 45221-0012, United States
Institute of Chemical Sciences, University of Swat, Swat 19130, Pakistan
Nireas-International Water Research Centre, University of Cyprus, Nicosia 1678, Cyprus
b
c
d
A R T I C L E I N F O
A B S T R A C T
Article history:
This study investigated iron-mediated oxidative processes for the photochemical degradation of
endosulfan, a chlorinated insecticide and central nervous system disruptor. At UV fluence of 360 mJ/cm2,
Received 6 October 2014
Received in revised form 8 March 2015
Accepted 16 March 2015
Available online 17 March 2015
52.4% and 32.0% removal of 2.45
respectively, at an initial concentration of 17.8
m
M initial endosulfan was observed by UV/Fe3+ and UV/Fe2+ processes,
m
M iron. The degradation of endosulfan by UV/Fe3+ or
2ꢀ
UV/Fe2+ was dramatically enhanced by adding peroxide (i.e., H2O2, S2O8
or HSO5ꢀ). Among the
UV/peroxide/Fe processes, the highest degradation efficiency of 99.0% at UV fluence of 360 mJ/cm2 was
observed by UV/HSO5ꢀ/Fe2+ with 2.45 M [Fe2+]0, and 49.0 M [HSO5ꢀ]0. The
M [endosulfan]0, 17.8
observed degradation rate constant of endosulfan was promoted either by increasing [Fe2+
and/or
Keywords:
Advanced oxidation processes (AOPs)
m
m
m
]
0
Endosulfan
Iron
Peroxides
UV-254nm
Water treatment
[peroxide]0 or by decreasing [endosulfan]0, while the initial degradation rate of endosulfan increased
with increasing [Fe2+]0, [peroxide]0, or [endosulfan]0. At UV fluence of 6000 mJ/cm2, 45.0% mineralization
as represented by the decrease in total organic carbon content was observed by UV/HSO5ꢀ/Fe2+ at
9.80 mM [endosulfan]0, 980 m m
M [HSO5ꢀ]0, and 17.8 M [Fe2+]0. The major by-product of endosulfan was
observed in all cases to be endosulfan ether which was further degraded with an extended reaction time.
The results suggest that iron-mediated advanced oxidation processes (AOPs) have a high potential for the
removal of endosulfan and its by-product from contaminated water.
ã 2015 Elsevier B.V. All rights reserved.
1. Introduction
preservative [6,7]. The acute and chronic toxicity of endosulfan is
widely recognized in a number of mammals including humans [8].
Organochlorine insecticides are an important class of pesti-
cides, commonly used on wood, crops and vegetables for the
control of mites, pests, and pest causing diseases [1]. However,
many of them have been reported to be highly toxic and can affect
the crop productivity [2], soil fertility [3], ecological balance [4],
and human health [5]. One of the most known organochlorine
insecticides is endosulfan (1,2,3,4,7,7-hexachlorobicyclo-2,2,1-
heptene-2,3-bishydroxymethane-5,6-sulfite). It is commonly used
on fruits, cotton, vegetables, tobacco, sugarcane, and tea for the
control of tsetse fly, mites, home garden pests, Colorado potato
beetles, and cabbage worms; it can also be used as a wood
Moreover, endosulfan is non-volatile and is highly persistent in the
environment, with a long half-life ranging from several months to
several years [9,10]. Residues of endosulfan have therefore been
detected in various environmental matrices such as water [11].
Considering its health risk, the US Environmental Protection
Agency has classified endosulfan as a “priority pollutant (category
Ib)” [12]. However, no control guidelines have been proposed for
this emerging organic pollutant [13]. It is thus highly important to
develop effective technologies for the detoxification of water
contaminated with endosulfan.
Advanced oxidation processes (AOPs) are innovative treatment
technologies that rely on in situ generation of reactive hydroxyl
radical (ꢁOH) [14]. Various AOPs have been developed and studied
including Fenton (Fe2+/H2O2) and Fenton-like (e.g., Fe3+/H2O2)
reactions, photo-Fenton (UV/H2O2/Fe2+) and photo-Fenton-like
* Corresponding author at: Environmental Engineering and Science Program,
University of Cincinnati, 705 Engineering Research Center, Cincinnati, OH 45221-
0012, United States. Tel.: +1 513 556 0724; fax: +1 513 556 2599.
(e.g., UV/H2O2/Fe3+
)
reactions, UV/H2O2, UV/TiO2, microwave
decomposition and ionizing radiation treatment [15–18]. More
E-mail address: dionysios.d.dionysiou@uc.edu (D.D. Dionysiou).
http://dx.doi.org/10.1016/j.jphotochem.2015.03.014
1010-6030/ã 2015 Elsevier B.V. All rights reserved.

N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
81
recently, sulfate radical (SO4ꢁꢀ) based AOPs have also been gaining
researchers’ attention in degrading organic contaminants [19].
Both ꢁOH and SO4ꢁꢀ have high redox potentials of 2.72 V [20] and
2.5–3.1 V [21], respectively, depending on the measurement
conditions, and therefore, readily attack organic contaminants
including endosulfan having a comparable reported second-order
rate constant of 1.83 ꢂ109 Mꢀ1 sꢀ1 with ꢁOH and 1.50 ꢂ109 Mꢀ1 sꢀ1
operated at 70 eV with a scan mode ranging from m/z 50 to 450.
Other instrumentation conditions of the GC–MS method are
reported in our previous study [22]. The concentration of
endosulfan in the present study was the sum of endosulfan
stereoisomers, endosulfan I and endosulfan II. The determination
of by-products was performed based on comparison of the spectra
of the by-products with those of the standards in the NIST library
(USA) installed in the GC–MS [22].
A colorimetric method by UV–vis Spectrophotometer (Hewlett
Packard, 8452) was used for the quantification of PMS [28]. A
Shimadzu VCSH-ASI TOC analyzer was used for monitoring the
total organic carbon (TOC).
ꢁꢀ
with SO4 [22]. Hydrogen peroxide (H2O2), peroxymonosulfate
(PMS, HSO5ꢀ), and persulfate (PS, S2O82ꢀ) are capable of generating
ꢁꢀ
ꢁOH and/or SO4 after activation, such as by UV irradiation and
transition metals [19,23–25]. Iron (Fe), on the other hand, is
naturally abundant, cheap and non-toxic, and consequently has
been widely investigated for the catalytic decomposition of
peroxides and subsequently the enhancement in the degradation
of organic pollutants in water [25–27].
2.3. Experimental procedure
In this study, Fe3+ or Fe2+ was combined with germicidal
UV-254 nm and the dual activation of peroxide by iron and UV was
further investigated for the degradation of endosulfan. To
minimize the reagent cost while establishing environmentally
friendly and economical treatment methods, low concentrations of
iron and peroxide were used. A kinetic study on the degradation of
endosulfan was assessed by varying initial concentrations of the
oxidant, iron, or the target contaminant. Mineralization of
endosulfan was elucidated by the UV/peroxide/Fe2+ process. Major
transformation by-products were also investigated.
The photo-assisted experiment was conducted using a UV
photochemical apparatus housing two 15 W low-pressure Hg UV
lamps (Cole-Parmer) emitting light primarily at lmax = 254 nm,
with an average UV fluence rate of 0.1 mW/cm2 in the reaction
solution [22,29]. This study was conducted at pH 3.0 if not stated
otherwise and the pH was adjusted using 0.1 N HCl. Samples were
quenched with methanol prior to analysis by GC–MS. Due to the
limit of instrumental analysis, a higher initial concentration of
2.45 mM endosulfan was generally used. Other detailed experi-
mental parameters are shown in the figures and tables shown
below. For monitoring the TOC removal, an immediate analysis
after each treatment was performed without adding any quench-
ing agent. All the experiments were carried out in triplicate with
error bars representing the standard error of the mean.
2. Materials and methods
2.1. Chemicals and reagents
All the chemicals used in the present study were of high purity
and used as received. Standard endosulfan (C9H6Cl6O3S, 406.9 g/
mole, 99.5%) and endosulfan ether (C9H6Cl6O, 342.86 g/mole,
99.5%) were obtained from Supelco (Bellefonte, PA, USA). Sodium
persulfate and potassium peroxymonosulfate (active component
3. Results and discussion
3.1. Performance of UV/Fe and UV/peroxide/Fe
The degradation of endosulfan was evaluated by three different
sets of processes, namely, UV only, UV/Fe (i.e., UV/Fe3+ and
UV/Fe2+), and UV/peroxide/Fe (i.e., UV/peroxide/Fe3+ and
UV/peroxide/Fe2+, with the peroxide evaluated to be H2O2, PS,
or PMS). The UV fluence based pseudo first-order rate constant for
each reaction condition was determined and is shown in Table 1.
The presence of Fe and UV improved the degradation of endosulfan
compared to direct UV photolysis, with the degradation under
of
2KHSO5
a ,
potassium triple salt, commonly known as Oxone1
ꢃ
KHSO4 K2SO4) were obtained from Sigma–Aldrich (St.
ꢃ
Louis, MO, USA). Hydrogen peroxide (50%, v/v), ferrous sulfate,
ferric chloride, methanol, and hydrochloric acid (37.5%, w/w) were
purchased from Fischer Scientific (Pittsburgh, PA, USA).
2.2. Analytical methods
UV/Fe3+ being much faster than UV/Fe2+
.
An Agilent 7890 gas chromatography (GC) equipped with an
Agilent 5975 mass spectrometric detector (MS) and an HP-5MS
(5% phenyl methylsiloxane) capillary column (30 m, i.d., 0.25 mm)
was used for the detection of endosulfan and its by-products. Solid
phase microextraction (SPME) technique with the fiber made of
polydimethylsiloxane (PDMS) and fitted with a manual holder
(Supelco) was used for a direct injection of samples into the GC.
Spectral measurement of the samples was done using an ion trap
After the excitation of organic molecule by light, both the
collision between the excited organic molecule and Fe3+ [30] and
the transfer of an electron from organic molecule to the center of
Fe3+ in its complex [31] were reported to be responsible for the
destruction of organic compounds. A different mechanism was
proposed by De Laat et al. [27] who observed that Fe(OH)2+ in
acidic aqueous solution of Fe3+ is highly photosensitive with a
molar extinction coefficient at 254 nm of 1500–3500 Mꢀ1 cmꢀ1
.
Table 1
Comparison of different processes in the removal of endosulfan in terms of degradation efficiency (%) (calculated at UV fluence of 360 mJ/cm2), UV fluence based pseudo first-
order degradation rate constant (kobs), and EE/O value. Experimental conditions: [endosulfan]0 = 2.45
mM, [peroxide]0 = 49.0 m ] ]0 = 17.8 mM, pH 3.0.
M, [Fe2+ 0 = [Fe3+
Percent degradation (%)
kobs (cm2/mJ)
UV fluence for one-order
EE/O value
removal of endosulfan (mJ/cm2)
(k Wh mꢀ3/order)
UV only
19.8
32.0
52.4
69.4
76.8
86.0
91.3
93.1
99.0
6.18 ꢂ 10ꢀ4
1.11 ꢂ10ꢀ3
2.09 ꢂ 10ꢀ3
3.45 ꢂ10ꢀ3
4.19 ꢂ 10ꢀ3
5.83 ꢂ 10ꢀ3
6.82 ꢂ10ꢀ3
7.62 ꢂ10ꢀ3
12.1 ꢂ10ꢀ3
3.72 ꢂ103
2.07 ꢂ103
1.10 ꢂ103
6.67ꢂ102
5.50 ꢂ102
3.95 ꢂ102
3.38 ꢂ 102
3.02 ꢂ102
1.90 ꢂ102
20.2 ꢂ10ꢀ1
11.5 ꢂ10ꢀ1
6.24 ꢂ10ꢀ1
3.62 ꢂ10ꢀ1
3.01 ꢂ10ꢀ1
2.11 ꢂ10ꢀ1
1.82 ꢂ10ꢀ1
1.64 ꢂ10ꢀ1
1.03 ꢂ10ꢀ1
UV/Fe2+
UV/Fe3+
UV/H2O2/Fe3+
UV/PS/Fe3+
UV/PMS/Fe3+
UV/H2O2/Fe2+
UV/PS/Fe2+
UV/PMS/Fe2+

82
N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
Table 2
Rate constants for the potential elementary reactions in the AOPs under different conditions.
No
1
Reaction
Rate constants (Mꢀ1 sꢀ1
= 0.07
)
Ref.
[51]
Fe(HO)2+ + hv ! Fe2+ + ꢁOH
K
Fe2+ + H2O2 ! Fe3+ + OHꢀ + ꢁOH
Fe3+ + H2O2 ! HO2ꢁ + Fe2+ + H+
Fe2+ + HSO5ꢀ ! Fe3+ + SO4ꢁꢀ + OHꢀ
Fe2+ + HSO5ꢀ ! Fe3+ + SO42ꢀ + ꢁOH
2
70
[52]
[33]
[36]
[53]
[54]
[36]
[55]
[56]
[57]
[14]
[26]
[49]
[58]
[26]
[26]
3
0.01–0.02
3.0 ꢂ l04
4
5
Fe2+ + S2O82ꢀ ! Fe3+ + SO4ꢁꢀ + SO4
Fe3+ + HSO5ꢀ ! Fe2+ + SO5ꢁꢀ + H+
2ꢀ
6
27
7
ꢁ
H2O2/HO2ꢀ + hv ! 2 OH
8
K
K
K
= 1.0
= 1.04
= 1.8
! ꢁOH + SO4
ꢀ
ꢁꢀ
9
HSO5 + h
S2O82ꢀ + h
n
ꢁꢀ
10
11
12
13
14
15
16
n
! 2 SO4
5.5 ꢂ109
4.0 ꢂ108
1.9 ꢂ1010
4.6 ꢂ109
2.7 ꢂ107
1 ꢂ105
ꢁOH + ꢁOH ! H2O2
2ꢀ
SO4ꢁꢀ + SO4ꢀ ! S2O8
Fe2+ + ꢁOH ! Fe3+ + OHꢀ
Fe2+ + SO4ꢁꢀ ! Fe3+ + SO4
2ꢀ
ꢁOH + H2O2 ! H2O + HO2
ꢁ
HSO5ꢀ + SO4ꢁꢀ ! SO5ꢁꢀ + SO42ꢀ + H+
Fe(OH)2+ could therefore be easily photo-reduced by UV-254 nm to
Fe2+ and generate subsequently reactive ꢁOH as shown by Reaction
(1) in Table 2 [17,20,32]. As a result, Xu [17] attributed the
decolorization of dye X-3B in Fe3+ system under UV or visible light
irradiation to the attack of ꢁOH. On the other hand, according to
Balzani and Carassiti [31], Fe2+ can be oxidized in acidic aqueous
solution by UV-254 nm to Fe3+ which subsequently generates ꢁOH
for the degradation of contaminants [32]. The UV/Fe2+ was,
however, less effective in producing hydroxyl radical [31], which is
in agreement with the higher degradation of endosulfan by
UV/Fe3+ than by UV/Fe2+ as observed in the present study.
concentration, i.e., 49.0 m
M, UV/PMS/Fe (UV/PMS/Fe3+ or UV/PMS/
Fe2+) was found to be more effective in the removal of endosulfan
than with the other two oxidants (H2O2 and PS), consistent with
previous data obtained by Khan et al. [26] and Rastogi et al. [36].
According to Antoniou et al. [24], the oxidizing property of an
oxidant depends upon the energy of the lower unoccupied
molecular orbital of the central atom to accommodate an electron.
A lower energy allows the oxidant to accept an electron more easily
and the oxidizing property can subsequently be greater [24].
Therefore, the energy of the three oxidants in the order of
PMS < H2O2 < PS [24] suggests an easier electron accepting
property of the nonsymmetrical PMS and consequently easier
activation by transition metals to generate radicals for water
decontamination [23,36,37]. The degradation of endosulfan by
UV/peroxide/Fe was more in PS than H2O2 which was probably due
to the lower OꢀꢀO bond energy in PS leading to a higher radical
quantum yield [22,26,38].
Addition of peroxides in UV/Fe2+ and UV/Fe3+ systems
significantly increased the removal of endosulfan with
UV/peroxide/Fe2+ to be more efficient than UV/peroxide/Fe3+
regardless of the peroxide type (Table 1). The peroxides can be
dissociated into radical species under the dual activation by Fe and
UV as shown by Reactions (2)–(10) (Table 2). The reaction between
H2O2 and Fe2+ is faster and can generate ꢁOH (Reaction (2) in
To compare the economic efficiency of these processes, the
electrical energy per order of degradation (EE/O, k Wh mꢀ3/order
of degradation) as recommended by the International Union of
Pure and Applied Chemistry (IUPAC) was used [39]. The EE/O value
was calculated following an expression in Eq. (1) [26,40].
ꢁ
Table 2) as compared to relatively less reactive HO2 that is
generated by H2O2/Fe3+ (Reaction (3) in Table 2) [33,34],
contributing to the faster degradation of endosulfan. Similarly,
the ꢁaꢀctivatiꢁon of PS and PMS by Fe2+ has been reported to generate
SO4 and OH (Reactions (4)–(6) in Table 2) as compared to less
EE Pt
reactive radical species, such as SO5 by Fe3+ (Reaction (7) in
¼
(1)
ꢁꢀ
O
V
Table 2) [35]. Besides, the oxidation of peroxide by Fe has been
reported to take place via electron transfer mechanism involving
the transfer of an electron from Fe2+ to peroxide in UV/peroxide/
Fe2+ which is a faster process than the electron transfer from
peroxide to Fe3+ due to the favorable redox conditions [23,36]. The
regeneration of Fe2+ by the photo-reduction of Fe3+ under UV
irradiation catalyzes the UV/peroxide/Fe2+ reaction, as shown by
Reaction (1) in Table 2, making it a promising AOP for effective
water decontamination.
where P is the power in kW; t is the exposure time in h and V is the
volume of the reaction solution in m3.
The EE/O results (as shown in Table 1) were found to be in the
order:
UV/PMS/Fe2+ < UV/PS/Fe2+ < UV/H2O2/Fe2+ < UV/PMS/
Fe3+ < UV/PS/Fe3+ < UV/H2O2/Fe3+ < UV/Fe3+ < UV/Fe2+ < UV only,
which was in agreement with the above discussion on the
degradation efficiency of these iron-mediated AOPs. The most
efficient UV/peroxide/Fe2+ (i.e., UV/H2O2/Fe2+, UV/PS/Fe2+ and
UV/PMS/Fe2+) processes were further studied and discussed in
the following sections.
The removal of endosulfan by UV/peroxide/Fe was affected by
the type of peroxide as well. At the same initial peroxide molar

N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
83
Fig. 3. Variation in kobs and initial degradation rate (
m
M cm2/mJ, calculated from
the change in concentration of endosulfan with UV fluence for the initial 120 mJ/
cm2 UV fluence) as a function of different initial concentrations of endosulfan by
UV/PMS/Fe2+ process. Experimental conditions: [endosulfan]0 = 0.61, 1.22, 2.45, and
Fig. 1. Variation in UV fluence based pseudo first-order degradation rate constant of
endosulfan, kobs (cm2/mJ), at different initial concentrations of peroxide in UV/
3.70 mM, [PMS]0 = 49.0 m ]0 = 17.8 mM, pH 3.0.
M, [Fe2+
peroxide/Fe2+ processes. Experimental conditions: [endosulfan]0 = 2.45
mM, [per-
oxide]0 = 12.25, 24.5, and 49.0 m ]0 = 17.8 mM, pH 3.0.
M, [Fe2+
of radical species (Reactions (11)–(16) in Table 2) at high initial
3.2. Effect of different initial concentrations of peroxide
peroxide concentrations [34].
The peroxide dissociates into reactive radicals (i.e., ꢁOH and/or
SO4ꢁꢀ) under the dual activation by UV-254 nm and Fe2+ as shown
by Reactions (2), (4)–(6), (8)–(10) in Table 2. Elevation of initial
concentrations of the peroxide can thus probably result in an
increase in the rate of radical formation. As shown in Fig. 1, the
degradation of endosulfan was investigated in the present study at
different initial peroxide concentrations, i.e., 12.25, 24.5 and
3.3. Effect of different initial concentrations of Fe2+
At a high concentration, there can be a problem with Fe2+
precipitation, resulting in a complementary secondary treatment
and thus higher operational cost for a large-scale water treatment
[34]. Lower concentrations of Fe2+ were therefore applied in this
study. Unlike the effect of [peroxides]0, the kobs of endosulfan
49.0
m
M while keeping [Fe2+
molar ratio of 0.70, 1.40 and 2.75, respectively.
]
0 to be 17.8
m
M corresponding to an
degradation was steadily increased with increasing [Fe2+
] at the
0
[oxidant]0/[Fe2+
]
current studied reaction conditions as shown in Fig. 2. The rate of
radical formation is expected to increase with increasing [Fe2+]0 as
shown by Reactions (2), (4)–(6) in Table 2 which in turn, could lead
to a faster degradation of endosulfan. The formation of Fe3+ as a
result of oxidative reactions of Fe2+ with ꢁOH and SO4ꢁꢀ (Reactions
(13) and (14) in Table 2) may also contribute to the improved
0
Though not including the previously proposed optimum ratio of
1:1 [26], current [oxidant]0/[Fe2+
]
range can still provide useful
0
information on the influence of oxidant dosage on the treatment
efficiency. The increased initial concentrations of peroxide led to
faster degradation of endosulfan as suggested by the increase in UV
fluence based pseudo first-order rate constant (kobs, cm2/mJ).
However, the increase in kobs was not linear with increasing
[peroxide]0, which was probably due to significant radical
scavenging effect of the peroxide as well as the recombination
degradation performance, since Fe3+
, under UV irradiation
(i.e., UV/Fe3+), was highly efficient in the removal of endosulfan
as discussed above. Liou et al. [41] reported that the Fe2+ promoted
efficiency on the degradation rate constant of TNT by photo-Fenton
Fig. 2. Variation in kobs at different initial concentrations of Fe2+ in UV/peroxide/Fe2
Fig. 4. Removal of TOC and change in PMS residuals in UV/PMS/Fe2+ process.
Experimental conditions: [endosulfan]0 = 9.80 mM, [PMS]0 = 980 m
M, [Fe2
+
processes. Experimental conditions: [endosulfan]0 = 2.45
m
M, [peroxide]0 = 49.0
M, [Fe2+
]
0 = 1.78, 8.90, and 17.8 M, pH 3.0.
m
]0 = 17.8 mM, pH 3.0.
+
m

84
N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
Table 3
List of by-products formed during the degradation of endosulfan by the UV/Fe and UV/peroxide/Fe AOPs.
Compound
RT (min)
MW
Structural formula
Detected in process
UV/peroxide/Fe
UV only, UV/Fe
Endosulfan I
14.1
406.9
Cl
Cl
O
O
Cl
Cl
Cl
Cl
S
S
O
O
Cl
Endosulfan II
15.8
406.9
Cl
Cl
Cl
O
O
Cl
Cl
p
p
(1) Endosulfan Alcohol
(2) Endosulfan Ether
11.3
11.2
360.0
342.0
Cl
Cl
Cl
OH
OH
Cl
Cl
Cl
p
Cl
Cl
Cl
Cl
O
O
Cl
Cl
p
(3) Endosulfan Lactone
15.7
356.0
Cl
Cl
Cl
O
Cl
Cl
Cl
reaction increased with the increase in Fe2+ concentration upto
2.88 mM. This value is much higher than the highest concentration
target contaminant [42]. Besides, the high molar absorption
coefficient for endosulfan at 254 nm,
254 = 40,877 Mꢀ1 cmꢀ1 [22],
e
of Fe2+, i.e., 17.8
m
M(in the present study), and therefore no
probably contributed to the strong decrease in the permeability of
solution for light absorptionwhen increasing initial concentrations
of endosulfan, which affected not only its direct photolysis, but also
the activation of PMS for radical generation [44]. Moreover,
competition between endosulfan and its by-products for reactive
radicals became stronger and thus the apparent degradation rate
constant decreased with the elevated initial concentrations of
endosulfan [45].
inhibition effect of Fe2+ was observed herein. Further study is
needed to investigate the positive impact of the increase in initial
concentration of Fe2+ on the kobs of endosulfan degradation.
3.4. Effect of different initial concentrations of endosulfan
The impact of initial concentration of endosulfan was assessed
on its degradation by UV/PMS/Fe2+ (the most efficient process
currently studied) while keeping the initial molar concentrations
of Fe2+ and PMS constant. At each studied concentration, the initial
3.5. Mineralization
degradation rate of endosulfan (
the initial 120 mJ/cm2 UV fluence. Fig. 3 shows that the initial
degradation rate increased from 0.0036 to 0.0099
cm2/mJ
when the initial concentration of endosulfan increased from
0.61 to 3.70 M. Most likely, a larger number of target molecules
m
Mꢃ
cm2/mJ) was calculated for
The study on mineralization indicates a potential decrease in
mass concentration of organic pollutant in water bodies and is
useful to compare the efficiency of the tested technologies for the
removal of target organic contaminants [26,46]. The mineraliza-
tion of endosulfan was monitored in terms of TOC by UV/PMS/Fe2+
process. An [endosulfan]0/[PMS]0 stoichiometric molar ratio of
1:18 for a complete oxidation of endosulfan was estimated by the
following stoichiometric reaction (Eq. (2)).
m
M
ꢃ
m
were exposed to radicals at a higher analyte concentration and
consequently resulted in a high degradation rate [26]. However,
the increase in [endosulfan]0 decreased the observed degradation
rate constant of endosulfan as suggested by kobs. This observation
was consistent with the trend observed in previous studies by Devi
et al. [42] and Samet et al. [43]. Such decrease in kobs has been
attributed to the decrease in the ratio of reactive radicals to the
C9H6Cl6O3S + 18HSO5ꢀ + H2O ! 9CO2 + 6Clꢀ + 26H+ + 19SO4 (2)
2ꢀ
Using UV fluence of 480 mJ/cm2, at a given [endosulfan]0/
[PMS]0 molar ratio, endosulfan was efficiently removed as

N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
85
attack of radical species may therefore lead to the detection of
aforementioned three by-products with only one isomeric form. In
fact, the study by Forman et al. [48] also showed that isomerism in
endosulfan arose due to pyramidal stereochemistry of sulfite group
and both endosulfan isomers yielded identical endosulfan alcohol,
endosulfan ether, and endosulfan lactone.
Fig. 5 illustrates variation in endosulfan ether treated by
UV/Fe3+, UV/Fe2+, UV/H2O2/Fe3+ and UV/PS/Fe3+. It was also
observed in UV/PMS/Fe3+ and UV/peroxide/Fe2+ processes, but
the concentration was not high enough to be quantified possibly
due to their high treatment efficiency. The formation and further
destruction of endosulfan ether by different processes was
consistent with the effectiveness of these processes in degrading
parent endosulfan as discussed above. It shows again the
effectiveness of iron-mediated AOPs for water decontamination.
The presented by-product identification, elucidation of degra-
dation pathways and mineralization provide important funda-
mental literature information on the removal and potentially
toxicity reduction of endosulfan. The formed main by-products
(alcohol, ether and lactone) have been reported to be non-toxic
suggesting a successful detoxification of endosulfan [12]. It has
been interpreted by Shah et al. [49] and Khan et al. [50] that the
chlorine group was mainly responsible for the toxicity of
organochlorine compounds and their by-products. The minerali-
zation of endosulfan as estimated by stoichiometric reaction
(Eq. (2)) indicated a significant loss of chloride ion by the tested
technologies, suggesting the decrease in the toxicity of the target
contaminant. Nevertheless, more studies are required to evaluate
the toxicity of the by-products of endosulfan.
Fig. 5. Change in the concentration of endosulfan ether (
fluence by UV/Fe and UV/peroxide/Fe. Experimental conditions: [endosulfan]0
2.45 M, [peroxide]0 = 49.0 0 = 17.8 M, pH 3.0.
M, [Fe2+ 0 = [Fe3+
mM) as a function of UV
=
m
m
]
]
m
discussed earlier in Section 3.1, however, no mineralization of
endosulfan in terms of TOC removal was observed. This is possibly
due to the fact that mineralization is a complex and multistep
process and requires high UV fluence [26,47]. At molar concen-
trations of 980 mM PMS, 17.8 m mM endosulfan,
M Fe2+ and 9.80
only 45% of TOC removal was observed at UV fluence as high as
6000 mJ/cm2 (Fig. 4). The concentration of PMS was also monitored
and a rapid decay was shown during the reaction. At UV fluence of
6000 mJ/cm2, 98% of the PMS was decomposed (Fig. 4). Therefore,
the mineralization was relatively fast at the beginning of reaction
and slowed down after UV fluence of 4000 mJ/cm2, which was
consistent with the trend observed in previous studies by Khan
et al. [26] and Wang and Chu [35].
4. Conclusions
Three different UV based processes were investigated for the
degradation of endosulfan, i.e., UV only, UV/Fe and UV/peroxide/Fe.
The main pathway of endosulfan degradation was most likely from
the reaction of ꢁOH and/or SO4ꢁꢀ generated. Iron can be activated
by UV, promoting the removal of endosulfan as compared to UV
only process. Dual activation of peroxide by UV and iron was found
to be more efficient. The observed degradation rate constant of
endosulfan increased significantly with increasing initial concen-
trations of peroxide or Fe2+ at the present studied conditions. The
TOC reduction was a slow process by UV/PMS/Fe2+ especially at the
later stage of irradiation treatment when most of PMS was
decomposed. The formation and further disappearance of endo-
sulfan ether as a function of different UV fluence suggested that
iron-mediated AOPs are good alternative technologies for the
removal of endosulfan and its by-products from contaminated
water. This study is useful for the potential practical applications of
AOPs in the presence of natural transition metals for environmen-
tal remediation.
3.6. Identification of by-products and degradation pathways of
endosulfan
The degradation of endosulfan by UV only, UV/Fe and
UV/peroxide/Fe resulted in the formation of several by-products.
Total of three by-products, i.e., endosulfan alcohol, endosulfan
ether and endosulfan lactone, were identified and are shown in
Table 3. In UV only and UV/Fe processes, only endosulfan ether was
identified; while in UV/peroxide/Fe systems regardless of the
peroxide or catalyst type, all the mentioned by-products were
detected. The conversion of endosulfan into its corresponding
alcohol, ether, and lactone by-products by the attack of hydroxyl
and/or sulfate radicals in UV/peroxide/Fe processes was probably
through hydrogen abstraction and/or electron transfer mecha-
nisms, which have been explained in detail in our previous
publication [22].
Acknowledgments
D.D. Dionysiou and X. He are grateful to the Cyprus Research
Promotion Foundation for providing partial financial support for
this project through Desmi 2009–2010 which was co-funded by
the European Regional Development Fund and the Republic of
Cyprus through the Research Promotion Foundation (Strategic
Endosulfan ether was the most significant by-product. The
GC–MS analysis showed two isomeric forms of endosulfan,
identified by the mass spectral search program (NIST, USA)
installed in the GC–MS as endosulfan I (retention time (RT) = 14.1
min) and endosulfan II (RT = 15.8 min). However, the by-products
were detected at only one single RT. The seven membered
dioxathiepine-3-oxide ring in endosulfan contains a sulfite group,
this sulfite group undergoes conformational and configurational
changes due to attractive interaction between the lone pair of
electrons on sulfur and the axial hydrogen on the adjacent
methylene groups [48]. As a result, two conformational isomers of
endosulfan are formed. The loss of the sulfur moiety due to the
Infrastructure Project NEA FAODOMH/STPATH/0308/09). The
authors would like to acknowledge the Higher Education
Commission (HEC), Islamabad, Pakistan for partially funding this
project through an International Research Support Initiative
Program (IRSIP). D.D. Dionysiou also acknowledges support from
the University of Cincinnati through a UNESCO co-Chair Professor
position on “Water Access and Sustainability”.

86
N.S. Shah et al. / Journal of Photochemistry and Photobiology A: Chemistry 306 (2015) 80–86
[30] K. Wu, Photo-Fenton degradation of a dye under visible light irradiation, J. Mol.
References
Catal. A: Chem. 144 (1999) 77–85.
[31] V. Balzani, V. Carassiti, Photochemistry of Coordination Compounds, Academic
[1] A.H. Arias, T.P. Marcelo, E.M. Jorge, Multi-year monitoring of estuarine
sediments as ultimate sink for DDT, HCH and other organochlorinated
pesticides in Argentina, Environ. Monit. Assess. 172 (2011) 17–32.
[2] S.A. Tiyagi, S. Ajaz, M.F. Azam, Effect of some pesticides on plant growth root
nodulation and chlorophyll content of chickpea, Arch. Agron. Soil Sci. 50
(2004) 529–533.
[3] X.-M. Xie, M. Liao, C.-Y. Huang, W.-P. Liu, S. Abid, Effects of pesticides on soil
biochemical characteristics of a paddy soil, J. Environ. Sci. 16 (2004) 252–255.
[4] H.S. Sandhu, R.S. Brar, Pesticides, Textbook of Veterinary Toxicology, Kalyani
Publishers, Ludhiana, New Delhi, India, 2009.
[5] U. Tiemann, In vivo and in vitro effects of the organochlorine pesticides DDT,
TCPM, methoxychlor and lindane on the female reproductive tract of
mammals: a review, Reprod. Toxicol. 25 (2008) 316–326.
[6] C.P. Rice, S.M. Chernyak, C.J. Hapeman, S. Bilboulian, Air–water distribution of
the endosulfan isomers, J. Environ. Qual. 26 (1997) 1101–1107.
Press, New York, USA, 1970, pp. 159.
[32] I.P. Pozdnyakov, E.M. Glebov, V.F. Plyusnin, V.P. Grivin, Y.V. Ivanov, D.Y.
Vorobyev, N.M. Bazhin, Mechanism of Fe(OH)2+
photolysis in aqueous
(aq)
solution, Pure Appl. Chem. 72 (2000) 2187–2197.
[33] A. Mehrdad, B. Massoumi, R. Hashemzadeh, Kinetic study of degradation of
Rhodamine B in the presence of hydrogen peroxide and some metal oxide,
Chem. Eng. J. 168 (2011) 1073–1078.
[34] E. Evgenidou, I. Konstantinou, K. Fytianos, I. Poulios, Oxidation of two
organophosphorous insecticides by the photo-assisted Fenton reaction, Water
Res. 41 (2007) 2015–2027.
[35] Y.R. Wang, W. Chu, Degradation of
a xanthene dye by Fe(II)-mediated
activation of Oxone process, J. Hazard. Mater. 186 (2011) 1455–1461.
[36] A. Rastogi, S.R. Al-Abed, D.D. Dionysiou, Sulfate radical-based ferrous
peroxymonosulfate oxidative system for PCBs degradation in aqueous and
sediment systems, Appl. Catal. B: Environ. 85 (2009) 171–179.
[7] G.F. Antonius, M.E. Byers, J.C. Snyder, Residues and fate of endosulfan on field-
grown pepper and tomato, Pest. Sci. 54 (1998) 61–67.
[8] Y. Lu, K. Morimoto, T. Takeshita, T. Takeuchi, T. Saito, Genotoxic effects of
[37] B. Meunier, Potassium monopersulfate – just another primary oxidant or a
highly versatile oxygen atom donor in metalloporphyrin-mediated
oxygenation and oxidation reactions, New J. Chem. 16 (1992) 203–211.
[38] J.A. Khan, X. He, N.S. Shah, H.M. Khan, E. Hapeshi, D. Fatta-Kassinos, D.D.
Dionysiou, Kinetic and mechanism investigation on the photochemical
a-endosulfan and b-endosulfan on human HepG2 cells, Environ. Health
Perspect. 108 (2000) 559–561.
[9] S.B. Chattopadhyay, Principles and Procedures of Plant Protection, Oxford and
IBH publishing Co. Pvt. Ltd., New Delhi, India, 1993, pp. 85–86.
[10] USEPA, office of prevention pesticides, Endosulfan Red Facts, US
Environmental Protection Agency, Washington DC, USA, 2002.
[11] A. Kaushik, H.R. Sharma, S. Jain, S. Dawra, C.P. Kaushik, Pesticide pollution of
river Ghaggar in Haryana, India, Environ. Monit. Assess. 160 (2010) 61–69.
[12] N.S. Shah, J.A. Khan, S. Nawaz, H.M. Khan, Role of aqueous electron and
hydroxyl radical in the removal of endosulfan from aqueous solution using
gamma irradiation, J. Hazard. Mater. 278 (2014) 40–48.
[13] D.J. Hamilton, A. Ambrus, R.M. Dieterle, A.S. Felsot, C.A. Harris, P.T. Holland, A.
Katayama, N. Kurihara, J. Linders, J. Unsworth, S.S. Wong, Regulatory limits for
pesticide residues in water (IUPAC Technical report), Pure Appl. Chem. 75
(2003) 1123–1155.
[14] G.V. Buxton, C.L. Greenstock, W.P. Helman, A.B. Rose, Critical review of rate
constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl
radicals (ꢁOH/Oꢁꢀ) in aqueous solution, J. Phys. Chem. Ref. Data 17 (1988)
513–780.
[15] S. Chiron, A. Fernandez-Alba, A. Rodriquez, E. Garcia-Calvo, Pesticide chemical
oxidation: state-of-the-art, Water Res. 34 (2000) 366–377.
2ꢀ
degradation of atrazine with activated H2O2, S2O8 and HSO5ꢀ, Chem. Eng.
J. 252 (2014) 393–403.
[39] J.R. Bolton, Ultraviolet Applications Handbook, 2nd ed., Bolton Photosciences
Inc., 2001, pp. 27.
[40] J.R. Bolton, K.G. Bircher, W. Tumas, C.A. Tolman, Figures-of-merit for the
technical development and application of advanced oxidation processes, J.
Adv. Oxid. Technol. 1 (1996) 13–17.
[41] M.-J. Liou, M.-C. Lu, J.-N. Chen, Oxidation of TNT by photo-Fenton process,
Chemosphere 57 (2004) 1107–1114.
[42] L.G. Devi, K.S.A. Raju, S.G. Kumar, K.E. Rajashekhar, Photo-degradation of di azo
dye Bismarck Brown by advanced photo-Fenton process: influence of
inorganic anions and evaluation of recycling efficiency of iron powder, J.
Taiwan Inst. Chem. Eng. 42 (2011) 341–349.
[43] Y. Samet, I. Wali, R. Abdelhédi, Kinetic degradation of the pollutant guaiacol by
dark Fenton and solar photo-Fenton processes, Environ. Sci. Pollut. Res. 18
(2011) 1497–1507.
[44] K. Dutta, S. Mukhopadhyay, S. Bhattacharjee, B. Chaudhuri, Chemical oxidation
of methylene blue using a Fenton-like reaction, J. Hazard. Mater. 84 (2001)
57–71.
[45] H. Ghodbane, O. Hamdaoui, Decolorization of antraquinonic dye, C.I. Acid Blue
25, in aqueous solution by direct UV irradiation, UV/H2O2 and UV/Fe(II)
processes, Chem. Eng J 160 (2010) 226–231.
[16] J.A. Herrera-Melian, E. Tello Rendon, J.M. Dona Rodriguez, A. Viera Suarez, C.
Valdes Do Campo, J. Perez Pena, J. Arana Mesa, Incidence of pretreatment by
potassium permanganate on hazardous laboratory wastes photodegradability,
Water Res. 34 (2000) 3967–3976.
[17] Y. Xu, Comparative studies of the Fe3+ 2+-UV, H2O2-UV TiO2-UV/vis systems for
/
[46] Y. Shi, L. Xu, D. Gong, J. Lu, Effects of sterilization treatments on the analysis of
TOC in water samples, J. Environ. Sci. 22 (2010) 789–795.
the decolorization of a textile dye X-3B in water, Chemosphere 43 (2001)
1103–1107.
[18] M. Trapido, I. Epold, J. Bolobajev, N. Dulova, Emerging micropollutants in
water/wastewater: growing demand on removal technologies, Environ. Sci.
Pollut. Res. (2014) 1–6.
[19] S. Yang, P. Wang, X. Yang, L. Shan, W. Zhang, X. Shao, R. Niu, Degradation
efficiencies of azo dye Acid Orange 7 by the interaction of heat, UV and anions
with common oxidants: persulfate, peroxymonosulfate and hydrogen
peroxide, J. Hazard. Mater. 179 (2010) 552–558.
[47] A. Riga, K. Soutsas, K. Ntanpegliotis, V. Karyannis, G. Papapolymerou, Effect of
system parameters and of iorganic salts on the decolorization and degradation
of Procion H-exl dyes. Comparison of H2O2/UV, Fenton, UV/Fenton, TiO2/UV
and TiO2/UV/H2O2 processes, Desalination 211 (2007) 72–86.
[48] S.E. Forman, A.J. Durbetaki, M.V. Cohen, R.A. Olofson, Conformational
equilibria in cyclic sulfites and sulfates. The configurations and
conformations of the two isomeric thiodans1, J. Org. Chem. 30 (1965) 169–175.
[49] N.S. Shah, J.A. Khan, S. Nawaz, M. Ismail, K. Khan, H.M. Khan, Kinetic and
mechanism investigation on the gamma irradiation induced degradation of
endosulfan sulfate, Chemosphere 121 (2015) 18–25.
[20] D.M. Stanbury, A.G. Sykes, Advances in Inorganic Chemistry, 33, Academic
Press, New York, 1989, pp. 69.
[50] J.A. Khan, N.S. Shah, S. Nawaz, M. Ismail, F. Rehman, H.M. Khan, Role of eꢀ
,
aq
[21] P. Neta, R.E. Huie, A.B. Ross, Rate constants for reactions of inorganic radicals in
aqueous solution, J. Phys. Chem. Ref. Data 17 (1988) 1027–1284.
[22] N.S. Shah, X. He, H.M. Khan, J.A. Khan, K.E. O’Shea, D.L. Boccelli, D.D. Dionysiou,
Efficient removal of endosulfan from aqueous solution by UV-C/peroxides: a
comparative study, J. Hazard. Mater. 263 (2013) 584–592.
[23] G.P. Anipsitakis, D.D. Dionysiou, Radical generation by the interaction of
transition metals with common oxidants, Environ. Sci. Technol. 38 (2004)
3705–3712.
ꢁOH and Hꢁ in radiolytic degradation of atrazine: a kinetic and mechanistic
approach, J. Hazard. Mater. 288 (2015) 147–157.
[51] R. Chen, J.J. Pignatello, Role of quinone intermediates as electron shuttles in
Fenton and photoassisted Fenton oxidations of aromatic compounds, Environ.
Sci. Technol. 31 (1997) 2399–2406.
[52] E. Neyens, J. Baeyens, A review of classic Fenton’s peroxidation as an advanced
oxidation technique, J. Hazard. Mater. 98 (2003) 33–50.
[53] P. Neta, R.E. Huie, Free-radical chemistry of sulfite, Environ. Health Perspect. 64
[24] M.G. Antoniou, A.A. de la Cruz, D.D. Dionysiou, Degradation of microcystin-LR
using sulfate radicals generated through photolysis, thermolysis and eꢀ
transfer mechanisms, Appl. Catal. B: Environ. 96 (2010) 290–298.
[25] P. Nfodzo, H. Choi, Triclosan decomposition by sulfate radicals: effects of
oxidants and metal dose, Chem. Eng. J. 174 (2011) 629–634.
[26] J.A. Khan, X. He, H.M. Khan, N.S. Shah, D.D. Dionysiou, Oxidative degradation ꢀof
(1985) 209–217.
[54] L.R. Bennedsen, J. Muff, E.G. Søgaardet, Influence of chloride and carbonates on
the reactivity of activated persulfate, Chemosphere 86 (2012) 1092–1097.
[55] J.H. Baxendale, J.A. Wilson, The photolysis of hydrogen peroxide at high light
intensities, Trans. Faraday Soc. 53 (1957) 344–356.
[56] G. Mark, M.N. Schuchmann, H.-P. Schuchmann, C. von Sonntag, The photolysis
of potassium peroxodisulphate in aqueous solution in the presence of
atrazine in aqueous solution by UV/H2O2/Fe2+, UV/S2O82ꢀ/Fe2+ and UV/HSO5
/
Fe2+ processes: a comparative study, Chem. Eng. J. 218 (2013) 376–383.
tertbutanol:
a simple actinometer for 254 nm radiation, J. Photochem.
[27] J. De Laat, H. Gallard, S. Ancelin, B. Legube, Comparative study of the oxidation
of atrazine and acetone by H2O2/UV, Fe(III)/UV Fe(III)/H2O2/UV and Fe(II) or Fe
(III)/H2O2, Chemosphere 39 (1999) 2693–2706.
[28] C. Liang, C.-F. Huang, N. Mohanty, R.M. Kurakalva, A rapid spectrophotometric
determination of persulfate anion in ISCO, Chemosphere 73 (2008) 1540–1543.
[29] X. He, A.A. de la Cruz, D.D. Dionysiou, Destruction of cyanobacterial toxin
cylindrospermopsin by hydroxyl radicals and sulfate radicals using UV-
254 nm activation of hydrogen peroxide, persulfate and peroxymonosulfate, J.
Photochem. Photobiol. A Chem. 251 (2013) 160–166.
Photobiol. A: Chem. 55 (1990) 157–168.
[57] Y. Guan, J. Ma, X. Li, J. Fang, L. Chen, Influence of pH on the formation of sulfate
and hydroxyl radicals in the UV/peroxymonosulfate system, Environ. Sci.
Technol. 45 (2011) 9308–9314.
[58] G.V. Buxton, T.N. Malone, G. Arthur Salmon, Reaction of SO4ꢀ with Fe2+, Mn2+
and Cu2+ in aqueous solution, J. Chem. Soc. Faraday Trans. 93 (1997)
2893–2897.