TiO2 Assisted Photocatalytic Decomposition of 2-Chloronaphthalene on Iron Nanoparticles in Aqueous Systems: Synergistic Effect and Intermediate Products

Article abstract of DOI:10.1134/S0036024419080119

Abstract: 2-Chloronaphthalene (2-CN), used as an intermediate for organic synthesis, is a new type of persistent organic pollutant. In this work, the decomposition efficiency and decomposition mechanism of 2-CN by zero-valent iron (ZVI) assisted TiO₂

Full text of DOI:10.1134/S0036024419080119

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2019, Vol. 93, No. 8, pp. 1620–1626. © Pleiades Publishing, Ltd., 2019.
PHOTOCHEMISTRY
AND MAGNETOCHEMISTRY
TiO Assisted Photocatalytic Decomposition of 2-Chloronaphthalene
2
on Iron Nanoparticles in Aqueous Systems: Synergistic Effect
and Intermediate Products
a,
a,
a
a
Jipeng Qi *, Chen Wang **, Jing Sun , and Shuping Li
a
School of Environmental Science and Engineering, Qilu University of Technology (Shandong Academy of Science),
Jinan, 250353 China
*
е-mail: hjqijipeng@163.com
**е-mail: shanqing123@126.com
Received July 9, 2018; revised September 19, 2018; accepted September 21, 2018
Abstract—2-Chloronaphthalene (2-CN), used as an intermediate for organic synthesis, is a new type of per-
sistent organic pollutant. In this work, the decomposition efficiency and decomposition mechanism of 2-CN
by zero-valent iron (ZVI) assisted TiO photodecomposition were studied in aqueous medium. Under UV
2
–2
light intensity of 38 mW cm , the optimal conditions for photodecomposition at an initial concentration of
–
1
–1
5
μmol L of 2-CN were pH 3 and 0.04 g L TiO and ZVI, as catalysts. Then, the decomposition efficiency
2
of 2-CN reached 66 and 100% in the UV/TiO and UV/ZVI/TiO systems, respectively. Based on analysis of
2
2
the primary intermediate products of 2-CN, the chlorine on 2-CN was first replaced by a hydroxyl group to
form 2-hydroxynaphthalene, and then the naphthalene ring was opened and gradually demethylated to pro-
duce small molecules, such as water and carbon dioxide.
Keywords: 2-chloronaphthalene, zero-valent iron, photodecomposition processes, intermediate products,
photodecomposition mechanism
DOI: 10.1134/S0036024419080119
INTRODUCTION
an attractive way to treat contaminated wastewater,
since it is cost-effective and non-toxic [18–20]. Vari-
ous catalysts have been applied during heterogeneous
In recent years, environmental pollution levels and
the distribution characteristics of polychlorinated
naphthalenes (PCNs) have attracted widespread
photocatalysis, such as TiO , ZnO, ZnS, Fe O , and
2
2
3
attention [1–3]. PCNs have been identified in air, MnO . Among them, TiO was the most effective, due
2
2
water, soil, sediment and biological matrices [4–8]. to long-term stability, controllable structure and eco-
Although environmental concentrations are typically
nomic excellence [21, 22]. However, TiO has poor
2
–1
–1
as low as ng L or μg L , PCNs may deteriorate the
health of humans and aquatic species, due to bioaccu-
mulation, toxicity, and lipophilic physico-chemical
properties [9–12]. Long-term exposure to PCNs can
damage organs, causing chloracene and liver disease
visible light absorption and relatively rapid recombi-
nation of charge carriers, limiting photocatalytic
activity [23]. Specifically, the photocatalytic elec-
tron–hole pairs of TiO have flash recombination on
2
–9
the order of 10 s, which is much shorter than the
chemical interaction time of TiO with adsorbed pol-
[
13]. 2-CN can be used as a model compound in
studying the processes involving more toxic PCNs.
The decomposition of 2-CN in water and wastewater
has not been evaluated in previous studies.
2
lutants [24].
ZVI, one of the most widely used zero-valent met-
als, is readily available, inexpensive, and non-toxic
In the past few decades, advanced oxidation pro-
cesses have been applied to the decomposition of
organic contaminants [14, 15]. Many of these methods
are based on the formation of highly reactive hydroxyl
radicals (OH). As a result of high oxidation potential,
OH can degradation organic contaminants into inter-
mediate compounds and even dissolve them in water,
carbon dioxide, and other inorganic compounds [16,
[
25]. Recently, ZVI was combined with photocatalytic
and considered to be a novel reactive method to
enhance the photoreaction efficiency of TiO [26].
2
ZVI can completely decompose and dissolve harmful
organic contaminants [27]. The major mechanisms
enhanced by ZVI include (a) inhibition of electron–
1
7]. Photocatalytic degradation has been suggested as hole pair recombination in TiO
and (b) production of
2
1620

TiO ASSISTED PHOTOCATALYTIC DECOMPOSITION
1621
2
–
1
ferrous ions in acidic conditions, which could form
Fenton-like system with hydroxyl radicals [28].
A 500 μmol L stock solution of 2-CN was prepared
in an amber bottle. To investigate the effect of the initial
-CN concentration, concentrations of 2-CN from 5 to
2
This study investigated the decomposition of 2-CN
–1
–1
using the UV/ZVI/TiO system. The effects of operat- 40 μmol L were used. Then, 5 μmol L of 2-CN was
2
used in other experiments, unless otherwise stated.
Different concentrations of TiO or ZVI were mixed
ing parameters, including light source, light intensity,
catalyst concentration, pH, and initial concentration
2
of 2-CN on the photocatalytic decomposition, were with 2-CN solution at pH 3 in the UV/TiO and
2
investigated. Finally, the optimal photodecomposition UV/ZVI/TiO systems, respectively. To study the
2
conditions and potential photodecomposition mecha- effect of pH on 2-CN decomposition, the required
nism of 2-CN were studied.
amounts of NaOH or H SO were added to the sam-
2 4
ples to obtain the desired solution pH. The suspen-
sions were stirred magnetically for the dark adsorption
experiment. Before irradiation, the photoreactor was
kept in the dark for 60 min to achieve adsorption equi-
librium. All samples were treated in triplicate.
MATERIALS AND METHODS
Chemical Regents
2
-CN (98.5%) was obtained from Bailingwei Com-
pany (Beijing, China). Acetonitrile, tert-butanol and
methanol (chromatographic grade) were obtained
RESULTS AND DISCUSSION
from Merck (Germany). TiO (Anatase P25, with
2
Effect of Light Source and Irradiation Intensity
The light source and irradiation intensity have been
average particle size of 30 nm, purity >99%) and ZVI
(
with average particle size of 30 μm, purity >99%)
were obtained from Sinopharm Chemical Reagent Co reported to be crucial parameters influencing the
(
Shanghai, China). All chemical reagents were of ana- direct photodecomposition of pollutants [29]. In this
lytical grade. All solutions were prepared using ultra- study, the decomposition of 2-CN was investigated
pure water from a Millipore water purification system. under various light sources (i.e., UV lamp, Xe lamp,
and sunlight) and at different intensities of UV lamps
–
2
(
i.e., 20, 32, and 38 mW cm ). The initial 2-CN con-
Analysis Procedures
–1
centration was 5 μmol L , and the initial pH value of
the solution was 7.0. Figure 1a demonstrates the
decomposition efficiency of 2-CN under irradiation
by different light sources. 2-CN was slightly decom-
posed by the sunlight irradiation process. The decom-
position efficiency of 2-CN was only 8.0% after
2
-CN was measured using a high-performance liq-
uid chromatography (HPLC) (LC-20A, Shimadzu,
Japan) equipped with a C18 reverse phase column
(
dimensions: 250 × 4.6 mm, 5 μm) and a UV detector
set at 225 nm. The mobile phase was a mixture of water
and acetonitrile (vol/vol = 20 : 80) at a flow rate of
4
80 min of sunlight irradiation. This result revealed
–1
1
.0 mL min . The temperature of the column was that 2-CN persists in the environment, with limited
maintained at 30°C. The oxidation by-products were degradation. The decomposition efficiency of 2-CN
identified by liquid chromatography mass spectrome- was 24.0% after Xe lamp irradiation for 480 min. When
try (HPLC-MS/8040, Shimadzu, Japan), equipped 2-CN was exposed to UV irradiation alone, the
with Triple Quad MS, using ESI-ionization and oper- decomposition efficiency of 2-CN was promoted to
ating in full-scan mode. Separation was carried out 32.0% after 120 min. The photodecomposition reac-
using a C18 column (dimensions: 4.6 × 250 mm, tion under sunlight irradiation proceeded slowest. The
–1
5
μm) at a flow rate of 0.5 mL min . The mobile 2-CN photolysis efficiency was much higher under
phase was a mixture of acetonitrile and purified water UV light than under the Xe lamp. These results
vol/vol = 80 : 20). Chlorine ions produced from revealed that UV radiation was very effective for 2-CN
(
2
-CN decomposition were identified by ionic chro- photodecomposition.
matography (IC 90, Dionex, USA) equipped with a
column Dionex IonPac ASC14 (250 × 4.0 mm) and a
conductivity detector. The eluent was mixed with
The 2-CN spectrum was characterized by an ultra-
violet spectrophotometer, at 225 nm. In this study, UV
light irradiation was provided by a 300-W medium-
pressure mercury lamp (366 nm). 2-CN may not be
able to undergo direct photolysis, and water molecules
likely produce active radicals under UV light irradia-
tion. Therefore, 2-CN is oxidized by active species
under UV irradiation. As a typical radical quencher,
3
1
.5 mM NaCO and 1.0 mM NaHCO at a flow rate of
3 3
–
1
.0 mL min .
Experimental Procedures
All experiments were conducted in a 500-mL tertiary butanol (t-BuOH) can react with active spe-
capacity bath photoreactor (Xujiang, Nanjing, cies during UV irradiation [30]. Therefore t-BuOH
China). Three light sources were used: a UV lamp, a was used to investigate the effect of active species on
Xe lamp and sunlight. A cooling system was also 2-CN decomposition during direct UV irradiation
installed in the reactor to maintain the experimental processes. Specifically, with the injection of t-BuOH
temperature at 25 ± 1°C.
from 1.0 to 5.0 mL, the decomposition efficiency of
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 8 2019

1622
JIPENG QI et al.
2
-CN decreased from 32.0 to 12.0% after 120 min.
1
.00
.92
(
a)
This indicated that water molecules may produce
active species under UV irradiation.
0
Figure 1b shows the decomposition efficiency of
Sun light
Xe lamp
UV lamp
2
-CN under various irradiation intensities. The
decomposition efficiency of 2-CN slightly increased
with increasing irradiation intensity. The decomposi-
tion efficiency of 2-CN increased from 32.0 to 41.0%
when the irradiation intensity of UV lamp increased
0.84
0
.76
.68
–2
from 20 to 38 mW cm . Therefore, the decomposition
efficiency of 2-CN increased with the light intensity.
This phenomenon indicated that high photon flux
increased the probability of collision between photons
and activated sites on 2-CN, which enhanced the rate of
photolysis reaction [31]. To improve the decomposition
0
0
100 200 300 400 500
Time, min
1.00
0.90
0.80
0.70
0.60
(b)
–2
efficiency of 2-CN, light intensity of 38 mW cm was
applied to the following experiments.
1
Effect of Catalyst Concentration
TiO is a widely used photocatalyst because of high
2
2
3
catalytic activity, and the concentration of TiO
2
affected the generation of hydroxyl radicals during
photodecomposition process. ZVI is oxidized to fer-
rous ions in aqueous solution under acidic conditions,
which can generate a Fenton-like system with
hydroxyl radicals [28]. This study determined the opti-
0
40
80
120
160
Time, min
mal concentration of TiO , and then added different
2
concentrations of ZVI. Finally, the optimal concen-
tration of ZVI was determined to generate the
Fig. 1. Effect of light source (a) and irradiation intensity
b) on decomposition of 2-CN; 5 μmol L of 2-CN, pH 7,
without TiO or ZVI; 1—20, 2—32, 3—38 mW cm
–1
(
UV/ZVI/TiO system. Before irradiation, the reaction
–2
2
.
2
mixture of the catalyst and 2-CN was stirred in dark-
ness to achieve adsorption equilibrium. The adsorp-
tion capacity was gradually increased and stabilized
absorption of some photons. A higher concentration
with time. The maximum adsorption of TiO and ZVI
2
of TiO further produced a screening effect for UV
2
was 8.0, 6.0, and 13.0%, respectively (Fig. 2a). The
light irradiation [32, 33], reducing the decomposition
–1
effects of the concentration of TiO (0–0.08 g L ) efficiency of 2-CN. Therefore, the optimal concentra-
2
–1
(
Fig. 2b) and ZVI (0–0.06 g L ) (Fig. 2c) on the tion of TiO for the decomposition of 2-CN was
2
–1
decomposition of 2-CN was investigated with an ini- 0.04 g L .
–1
tial 2-CN concentration of 5 μmol L at pH 3.0, with
a medium-pressure mercury lamp and an irradiation
time of 60 min.
Figures 2c, 2d demonstrate the effect of ZVI con-
centration on the decomposition of 2-CN at pH 3.0 in
the UV/ZVI and UV/ZVI/TiO systems, respectively.
2
In the UV/TiO system, the decomposition effi-
2
As shown in Fig. 2c, the decomposition efficiency
increased slowly from 41.0 to 47.0% as the addition of
ciency of 2-CN increased from 41.0 to 66.0% with
increasing TiO concentration from 0 to 0.04 g L
–1
–1
2
ZVI changed from 0 to 0.06 g L in the UV/ZVI sys-
after 60 min UV irradiation (Fig. 2b), respectively.
This was because the water molecule and hydroxyl
ions were oxidized to hydroxyl radicals by the surface
tem. As shown in Fig. 2d, the decomposition effi-
ciency increased rapidly from 66.0 to 100% as the
–1
addition of ZVI changed from 0 to 0.04 g L in the
hole of TiO . The concentration of hydroxyl radicals
2
UV/ZVI/TiO system. The major mechanisms
2
gradually increased with increasing TiO , thus
2
enhanced by ZVI include (a) inhibition of electron–
enhancing the decomposition efficiency of 2-CN.
hole pair recombination in TiO and (b) production of
2
However, the decomposition efficiency of 2-CN
ferrous ions in acidic conditions, which could form
Fenton-like system with hydroxyl radicals. However,
higher concentrations of ZVI did not improve the
decreased from 66.0 to 56.0% with increasing TiO
2
–1
concentration from 0.04 to 0.08 g L after 60 min UV
irradiation. Above 0.04 g L–1 of TiO , the decomposi- decomposition efficiency of 2-CN: with increased
2
–
1
tion efficiency of 2-CN gradually decreased. concentration of ZVI from 0.04 to 0.06 g L , the effi-
Increased TiO concentration likely resulted in the ciency of 2-CN was decreased. Decreased decomposi-
2
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TiO ASSISTED PHOTOCATALYTIC DECOMPOSITION
1623
2
(
b)
1
.0
6
0
0
(
a)
0.9
.8
UV/TiO
2
TiO
2
ZVI
TiO + ZVI
2
4
0
0
10 20 30 40 50 60
Time, min
0
0.02 0.04 0.06 0.08
1
Concentration of TiO
, g Lꢁ
2
1
00
(
c)
(d)
0
6
0
0
0
0
5
80
60
4
UV/ZVI
UV/ZVI/TiO
2
3
0
0.02
0.04
0.06
0.02
0.04
0.06
ꢁ1
ꢁ
1
Concentration of ZVI, g L
Concentration of ZVI, g L
Fig. 2. Effect of TiO and ZVI concentration on the photodecomposition efficiency(η) of 2-CN; concentration of 2-CN was
2
μmol L–1, pH 3.0; concentration of TiO : (a) 0.08, (b, c) from 0 to 0.08, (d) 0.04 g L ; concentration of ZVI: (a) 0.06, (b) 0,
–1
5
(
2
c) from 0 to 0.06, (d) 0.04 g L–1
.
tion efficiency of 2-CN at high ZVI concentrations cals promoted the formation of hydrogen peroxide by
may result from particle screening, as the generated following reactions [35]:
hydroxyl radical is scavenged by the iron surface.
−
•−
2
e + O → O ,
(1)
(2)
(3)
2
Miller reported that the hydroxyl radical was very
reactive with iron oxide [34]. High reactivity between
the iron and hydroxyl radical may reduce the decom-
position of 2-CN. Therefore, the most effective con-
centration of ZVI for the decomposition of 2-CN was
•−
+
•
O + H → HO ,
2
2
•
2
+
−
HO + H + e → H O ,
2
2
which had stronger oxidation susceptibility. At pH val-
ues greater than 5.0 and 7.0, the decomposition effi-
ciency of 2-CN was decreased due to the following
–1
0.04 g L .
•
+
processes: (a) the scavenging of OH by H ions and
Effect of pH
The effect of pH on the photodecomposition of 2-
2+
(
b) more Fe formed precipitates and lost catalytic
ability. These results demonstrated that the
UV/ZVI/TiO system was more effective for the oxi-
2
CN was investigated over the pH range of 3.0–9.0 with
dation decomposition of 2-CN under acidic condi-
–
1
–1
an initial concentration of 5 μmol L 2-CN, 0.04 g L
tions. Therefore, the optimal pH value for the decom-
–1
–2
TiO , 0.04 g L ZVI, light intensity of 38 mW cm , position of 2-CN in the UV/ZVI/TiO
system was 3.0.
2
2
and irradiation time of 60 min.
Effect of Radical Scavengers
Figure 3 shows that the decomposition efficiency
of 2-CN decreased from 100 to 25.0% with increased
To better understand the properties of active radi-
pH from 3.0 to 9.0 in the UV/ZVI/TiO system after cals in the decomposition of 2-CN, radical scavenger
2
experiments were carried out in the UV/ZVI/TiO
2
6
0 min UV irradiation. Apparently, the decomposition
system. Isopropanol was used as a scavenger, because
it can react with hydroxyl radicals. EDTA-2Na was
also used as a scavenger, because it could react with
efficiency of 2-CN was faster in acidic solutions than
in alkaline solutions in the UV/ZVI/TiO system.
2
Because the point of zero charge (PZC) of TiO was
2
+
H . Finally, since p-benzoquinone could react with
superoxide radicals, it was also used as a scavenger
6
.3, when the initial solution pH was below the PZC of
TiO , the surface of TiO was positively charged. This
2
2
[
36].
enabled it to absorb negatively charged 2-CN mole-
cules, enhancing the decomposition efficiency of
As shown in Fig. 4, the decomposition efficiency of
2
-CN decreased from 100 to 62.0, 75.0, and 80.0%
2
-CN. Conversely, when the pH was above PZC, the
with the addition of isopropanol, p-benzoquinone and
surfaces of both TiO and 2-CN were negatively
2
EDTA-2Na, respectively. These results indicated that
charged, resulting in electrostatic repulsion and
reducing the decomposition efficiency of 2-CN.
Under acidic conditions, oxygen molecules were
−
2
HO/O radicals played an important role in 2-CN
+
decomposition in the UV/ZVI/TiO system. H also
2
could promote the decomposition of 2-CN in the
–
reduced by electrons (e ) on the surface of TiO to
2
UV/ZVI/TiO system. This phenomenon could be
2
•
−
produce superoxide radicals (O ). Superoxide radi- associated with efficient photogenerated electron
2
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JIPENG QI et al.
1.0
0.8
0.6
0.4
0.2
0
1.0
0.8
0.6
0.4
0.2
0
pH 3
pH 5
pH 7
pH 9
None
Isopropanol
p-Benzoquinone
EDTA-2Na
−0.2
−0.2
0
10
20
30
40
50
60
0
10
20
30
40
50
Time, min
Time, min
Fig. 3. Effect of pH on decomposition of 2-CN in
Fig. 4. Effect of isopropanol, p-benzoquinone, and
UV/ZVI/TiO system (concentration of 2-CN was
EDTA-2Na on the decomposition of 2-CN (concentra-
2
μmol L–1, concentration of TiO was 0.04 g L , and
–1
–1
5
tion of 2-CN was 5.0 μmol L , pH 3, concentration of
2
–
–1
1
TiO2 was 0.04 g L , and concentration of ZVI was
concentration of ZVI was 0.04 g L , with pH from 3.0
to 9.0).
0.04 g L– ).
1
transfer in the UV/ZVI/TiO system, which facilitated pseudo-first-order reaction kinetics model (Fig. 5b).
2
+
–1
greater participation by H in the photocatalytic pro- The decomposition rate constants, (k, min ), of
cesses and greatly promoted oxygen molecules to yield 2-CN decreased with increased initial concentration,
superoxide radicals [37, 38]. These superoxide radicals and the pseudo-first-order rate constant k decreased
–
1
further induced the formation of H O and then par- from 0.050 to 0.023 min . The results demonstrated
2
2
ticipated in the photocatalytic processes. Therefore, that the initial concentration greatly affected the
−
2
decomposition rate of 2-CN.
HO/O radicals contributed more to the decomposi-
tion of 2-CN.
Identification of Intermediate Products
Effect of 2-CN Initial Concentration
and Kinetics Analysis
In this study, the intermediate products of 2-CN
were detected by HPLC-MS under the optimal photo-
decomposition conditions for 2-CN. The decomposi-
The effect of the initial concentration of 2-CN on
the photodecomposition efficiency was investigated
tion solutions of 2-CN were collected in the UV/TiO
2
–
1
and UV/ZVI/TiO system at the irradiation times of
2
over a concentration range from 5.0 to 40.0 μmol L .
Figure 5a demonstrates the decomposition of 2-CN
under various initial concentrations. The decomposi-
tion efficiency of 2-CN was decreased from 100 to
1
0, 20, 30, 40, and 50 min. Then, 10 μL of each sample
solution was injected into the HPLC-MS system.
Four intermediate products were detected in both the
UV/TiO and UV/ZVI/TiO systems, which indicated
7
5
9.0% as the concentration of 2-CN increased from
2
2
–1
that the photodecomposition of 2-CN had a similar
pathway in both systems. When the irradiation time
reached 10 min, the most abundant fragment, ion
.0 to 40.0 μmol L after 60 min in the UV/ZVI/TiO
2
system. The decreased decomposition efficiency in
the UV/ZVI/TiO system was mainly caused by the
2
following processes: (a) some hydroxyl radicals could
be captured by the intermediate products of 2-CN,
and (b) the same concentration of catalyst generated
stable amounts of hydroxyl radicals, which were not
sufficient for the oxidation of the 2-CN at higher
Table 1. Pseudo-first-order kinetics for 2-CN decomposi-
2
tion at different initial concentrations (C ), R is correlation
0
coefficient
C , μmol L– Decomposition, % k, min-1
1
R2
2-CN concentrations.
0
The initial concentration crucially affected the
5
100 (50 min)
99 (60 min)
95 (60 min)
79 (60 min)
0.050
0.048
0.036
0.023
0.993
0.920
0.913
0.975
decomposition kinetics. The pseudo-first-order
kinetic rate constants for 2-CN decomposition at dif-
ferent initial concentrations are listed in Table 1. In
this study, the removal of 2-CN was fit with the
1
0
0
0
2
4
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TiO ASSISTED PHOTOCATALYTIC DECOMPOSITION
1625
2
m/z = 144, was obtained. The ion at m/z = 144 was
identified as naphthol. When the irradiation time
reached 20 min, the most abundant fragment was ion
m/z = 129, identified as naphthalene. When the irradi-
ation time reached 30 min, the most abundant frag-
ment, m/z = 105, was obtained, which was identified
as ethylbenzene. When the irradiation time reached
40 min, the most abundant fragment was m/z = 69,
pentyne. When the irradiation time reached 50 min,
the primary intermediate products of 2-CN remained
unchanged, and the decomposition efficiency of
(
a)
1
0
0
0
0
.0
.8
.6
.4
.2
0
ꢂM Lꢁ1
0 ꢂM L
0 ꢂM Lꢁ
0 ꢂM Lꢁ
5
1
2
4
ꢁ
1
1
1
2-CN reached 100%. These results indicated that the
ꢁ
0.2
primary intermediate products of 2-CN were naph-
thol, naphthalene, ethylbenzene, and pentyne. These
results also support the efficiency of the
0
10
20
30
5
40
50
60
Time, min
UV/ZVI/TiO system for the photodecomposition of
ꢁ
1
2
2
(b)
ꢂM L , R = 0.993
4
3
2
1
0
0
0
0
0
2-CN.
ꢁ1
2
1
2
4
0 ꢂM L , R = 0.920
0 ꢂM L , R = 0.913
0 ꢂM L , R = 0.975
ꢁ1
2
Combining an understanding of the generated ions
with the identification results of the intermediate
products, a possible decomposition pathway of 2-CN
was proposed, as shown in Fig. 6: 2-CN was first
attacked by OH to release chloride and form naphthol.
Then, the naphthalene ring was broken by OH oxida-
tion to form alkyne and ethyl. Finally, the intermedi-
ate products of 2-CN were further decomposed into
H O and CO .
ꢁ1
2
2
2
0
10
20
30
40
50
60
CONCLUSIONS
Time, min
Fig. 5. Effect of initial concentration on decomposition of
In this study, the optimal photodecomposition
–1
conditions and photodecomposition mechanism of
2-CN were determined. ZVI enhanced the oxidation
2
-CN (concentration of 2-CN was 5.0 to 40 μmol L ,
–1
pH 3, concentration of TiO was 0.04 g L , and concen-
tration of ZVI was 0.04 g L ; (a) decomposition effi-
ciency of 2-CN; (b) kinetic model decomposition of
2
–1
susceptibility of the UV/TiO system. The decomposi-
2
tion of 2-CN followed the pseudo-first-order kinetic
model. The intermediate products of 2-CN were pri-
2-CN.
Cl
OH
+
Cl−
+ H O
2
m/z = 162
m/z = 144
m/z = 129
m/z = 105
+
CH CH OH
+ CH CH −
3 2
3
2
m/z = 83
m/z = 64
m/z = 46
CH −+
CO , H O, CH CH OH
2 2 3 2
3
m/z = 69
Fig. 6. Decomposition pathway for photodecomposition of 2-CN (concentration of 2-CN was 5.0 μmol L–1, pH 3.0, concentra-
–1
–1
tion of TiO was 0.04 g L , and concentration of ZVI was 0.04 g L ).
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 93 No. 8 2019

1626
JIPENG QI et al.
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