Facile preparation of a Ti/α-PbO2/β-PbO2 electrode for the electrochemical degradation of 2-chlorophenol

Article abstract of DOI:10.1016/S1872-2067(15)60851-8

A Ti/α-PbO₂/β-PbO₂ electrode with high stability was prepared and examined toward the electrochemical degradation of 2-chlorophenol. Scanning electron microscopy analysis revealed that Ti/α-PbO₂/β-PbO₂ had a cauliflower morphology comprising small β-PbO₂ crystals. The 2-chlorophenol removal rate using the Ti/α-PbO₂/β-PbO₂ electrode was 100% after 180 min of electrolysis under optimal conditions, which were selected based on the orthogonal test method, i.e., initial concentration of 2-cholorophenol = 50 mg/L, concentration of Na₂SO₄ = 0.1 mol/L, temperature = 35°C, and anode current density = 20 mA/cm². Kinetic analyses demonstrated that the electrochemical oxidation of 2-chlorophenol on the Ti/α-PbO₂/β-PbO₂ electrode followed pseudo-first order kinetics.

Full text of DOI:10.1016/S1872-2067(15)60851-8

Chinese Journal of Catalysis 36 (2015) 975–981
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c h n j c
Article
Facile preparation of a Ti/α-PbO2/β-PbO2 electrode for the
electrochemical degradation of 2-chlorophenol
Qianli Zhang, Xinyan Guo, Xiaodan Cao, Dongtian Wang, Jie Wei *
College of Chemistry and Material Engineering, Jiangsu Key Laboratory for Environment Functional Materials, Suzhou University of Science and
Technology, Suzhou 215009, Jiangsu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A Ti/α-PbO2/β-PbO2 electrode with high stability was prepared and examined toward the electro-
Received 8 January 2015
Accepted 27 March 2015
Published 20 July 2015
chemical degradation of 2-chlorophenol. Scanning electron microscopy analysis revealed that
Ti/α-PbO2/β-PbO2 had
a cauliflower morphology comprising small β-PbO2 crystals. The
2-chlorophenol removal rate using the Ti/α-PbO2/β-PbO2 electrode was 100% after 180 min of
electrolysis under optimal conditions, which were selected based on the orthogonal test method,
i.e., initial concentration of 2-cholorophenol = 50 mg/L, concentration of Na2SO4 = 0.1 mol/L, tem-
perature = 35 °C, and anode current density = 20 mA/cm2. Kinetic analyses demonstrated that the
electrochemical oxidation of 2-chlorophenol on the Ti/α-PbO2/β-PbO2 electrode followed pseu-
do-first order kinetics.
Keywords:
Electrochemical degradation
2-Chlorophenol
β-PbO2 electrode
α-PbO2 interlayer
Kinetic analysis
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
cy, cost effectiveness, and environmentally friendly attributes
[10,11]. The electrochemical degradation efficiency is largely
2-Chlorophenol is an environmental pollutant presenting in
water, soil, etc. It is widely used in industries and in our every-
day life as a fungicide, wood preservative, and intermediate in
the production of chlorinated pesticides or adhesives [1]. Ow-
ing to estrogenic, mutagenic and carcinogenic effects,
2-chlorophenol presents a threat to both the aquatic ecosystem
and human health. Accordingly, the decomposition of
2-chlorophenol in wastewater has been studied by many
methods such as photodegradation [2,3], chemical oxidation
[4–7], and electrochemical degradation [8,9].
dependent on the properties of the anodes. An ideal anode
must not only exhibit high efficiencies toward contaminant
degradation, but also be electrochemical stable and inexpensive
[12]. Recently, studies have mainly focused on “non-active”
anodes such as boron-doped diamond (BDD), SnO2, and PbO2,
which exhibit a high oxygen evolution overpotential and can
produce abundant hydroxyl radicals (•OH) [13]. Won’s group
[8] examined the electrochemical degradation of 2-chlorophe-
nol using a Pt/Ti electrode and a BDD electrode. The BDD elec-
trode displayed a significantly higher efficiency toward the
degradation of 2-chlorophenol than the Pt/Ti electrode. Ortiz’s
group [9] also reported the effective electrochemical degrada-
tion of 2-chlorophenol using a BDD anode. However, despite
the high chemical stability and outstanding efficiency of BDD
Among the above reported methods, electrochemical deg-
radation is an attractive option for the decomposition of
2-chlorophenol because of its high oxidation efficiency, fast
reaction rate, amenability to automation, high energy efficien-
* Corresponding author. Tel: +86-13776096178; Fax: +86-512-8056132; E-mail: ustsweijie@163.com, 1531041457@qq.com
This work was supported by the National Natural Science Foundation of China (251178283, 20905055), the Six-Field Talent Peak Program of Jiangsu
Province, and the Graduate Research and Innovation Plan of Jiangsu Province (SJLX_0580).
DOI: 10.1016/S1872-2067(15)60851-8 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 7, July 2015

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Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
electrode, its large-scale practical application is limited by its
high cost and difficulty in selecting a suitable substrate for the
thin diamond layer [14,15].
pared with twice-distilled water.
2.2. Electrode preparation
Alternatively, PbO2 electrodes have been used as anodes in
the chlor-alkali industry for over 70 years because of their high
electrical conductivity, which is similar to that of metals, good
stability, high overpotential for oxygen evolution, low cost, ease
of fabrication, and long service life. In recent decades, PbO2
anodes have been applied to oxidize organic pollutants
[10,16–19]. An SnO2–Sb layer between the Ti substrate and
PbO2 has been commonly introduced to enhance the adhesion
of the PbO2 layer [20]. Niu’s group has reported several suc-
cessful studies on the electrochemical mineralization of envi-
ronment contaminants such as perfluorooctanoic acid, per-
fluorocarboxylic acid [21,22], and sulfamethoxazole [13] using
PbO2 electrodes.
PbO2 displays two allotropic forms, orthorhombic and te-
tragonal (α and β). Compared with α-PbO2 that features a com-
pact structure, β-PbO2 is widely used in electrochemical degra-
dation owing to its porous structure that leads to high electro-
chemical efficiency and large surface area [23,24]. However,
direct electrodeposition of β-PbO2 on a Ti substrate lessens the
anode stability and activity because the porous β-PbO2 struc-
ture can easily detach from the Ti substrate.
A Ti metal net (2.0 cm  2.0 cm  0.1 cm) was used as the
substrate. Before deposition, the Ti substrate underwent sand-
blasting, ultrasonic cleaning in acetone for 10 min, ultrasonic
cleaning in deionized water for 10 min, immersion in 40%
NaOH at 80 °C for 2 h, etching in boiling 15% oxalic acid for 2 h,
and rinsing with deionized water [29]. After pretreatment, in-
terlayer α-PbO2 was prepared using the pretreated Ti substrate
as an anode and a Cu plate as a cathode in alkaline solution (0.1
mol/L PbO, 3.5 mol/L NaOH) at 40 °C and 10 mA/cm2 for 2 h.
Finally, top layer β-PbO2 was electrodeposited on the above
prepared substrate in acidic solution at 60 °C using a current
density of 20 mA/cm2 for 2 h. The acid solution consisted of 50
g/L Cu(NO3)2, 0.5 g/L NaF, and 150 g/L Pb(NO3)2 [23].
2.3. Electrode characterization
Scanning electron microscopy (SEM; HITACHI-4700, Japan)
was used to characterize the morphology of the electrode sur-
face. X-ray diffraction (XRD) patterns of the samples were rec-
orded on a D/max-RB X-ray diffractometer (Rigaku, Japan)
using Cu Kα radiation (40 kV, 100 mA).
Some methods have been reported to improve the adhesion
of β-PbO2 on the substrate. For instance, the electrodeposited
β-PbO2 on a platinized Ti (Ti-Pt) substrate was reported to be
stable in the electrochemical degradation of real textile
wastewater [25,26]. A fluoride-doped Ti/β-PbO2 anode showed
good performance in the electrochemical degradation of the
dimethyl phthalate ester [27]. β-PbO2 electrode modified by
either TiO2 or Co3O4 effectively electrochemically oxidized acid
orange 7 [28] and bisphenol A [12], respectively. Additionally,
to improve the activity and stability of β-PbO2 electrode, sever-
al layers of SnO2-Sb2O5-RuO2 and α-PbO2 were introduced be-
tween β-PbO2 and the substrate. Zheng et al. [10] investigated
the electrochemical degradation of 4-chlorophenol on
Ti/SnO2-Sb2O5-RuO2/α-PbO2/β-PbO2, and Chen et al. [23] in-
vestigated the influence of doped nano-CeO2 on Al/α-PbO2/
β-PbO2 electrode for enhancing electro-catalytic activity.
In this study, a Ti/α-PbO2/β-PbO2 electrode was prepared
simply by electrodeposition. The layer of α-PbO2 enhanced the
adhesion between the β-PbO2 layer and Ti substrate. The pre-
pared Ti/α-PbO2/β-PbO2 electrode displayed high catalytic
activity and long lifetime toward the degradation of 2-chloro-
phenol. The degradation of complex compounds, i.e., 2,4-di-
chlorophenol and bisphenol A, was also investigated to further
evaluate the efficiency of the Ti/α-PbO2/β-PbO2 electrode.
Polarization curves were obtained on the CHI 660C electro-
chemical workstation (Shanghai ChenHua Instrument Co., Ltd.)
using a conventional three-electrode system. A Ti/α-PbO2/
β-PbO2 electrode with an effective surface area of 1 cm2 was
used as the working electrode, a saturated calomel electrode
(SCE) was used as the reference electrode, and a platinum elec-
trode was used as the counter electrode. The measurements
were conducted at room temperature.
2.4. Procedure of electrochemical degradation
Electrochemical oxidation of 2-chlorophenol was performed
in a 150 mL beaker using a Cu plate (8 cm2) as the cathode and
Ti/α-PbO2/β-PbO2 (8 cm2) as the anode. The anode and cath-
ode were positioned vertically and parallel to each other with a
distance of 1 cm. Na2SO4 was chosen as the supporting electro-
lyte.
During electrochemical degradation, a portion of the reac-
tion solution was withdrawn from the reactor at certain time
intervals to determine the concentration of residual 2-chloro-
phenol in the test solution using a UV spectrophotometer
(TU-1901). The removal rate () was calculated according to
Eq. (1):
η = (A0 – A)/A0  100%
(1)
where A0 and Aare the absorbance values of the organic pollu-
tant at time zero and t (s), respectively.
2. Experimental
2.1. Materials
3. Results and discussion
2-Chlorophenol, 2,4-dichlorophenol, and bisphenol A were
obtained from Sigma-Aldrich. All other chemicals were pur-
chased from Shanghai Sinopharm Chemical Reagent Co., Ltd. All
chemicals were of analytical grade. The solutions were pre-
3.1. Electrode characterization
SEM was used to characterize the morphology and surface

Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
977
structure of the etched Ti substrate, Ti/α-PbO2, Ti/β-PbO2, and
Ti/α-PbO2/β-PbO2 (Fig. 1). As observed in Fig. 1(a), the etching
process in oxalic acid solution generated a Ti surface with a
rough texture, which is expected to increase the surface area of
the Ti substrate and strengthen the interaction between the
deposition layers and Ti substrate [29]. As expected, interlayer
α-PbO2 (Fig. 1(b) and (c)) consisted of uniformly shaped parti-
cles in close proximity, i.e., rod-like and fiber-like particles that
were smaller than those of the β-PbO2 layer. Such a structure is
expected to facilitate the deposition of β-PbO2 layer in the sub-
sequent electrode fabrication step. As observed in Fig. 1(d),
Ti/β-PbO2 comprised typical pyramid-shaped crystals, as con-
sistent with the findings of reported studies [27,28,30]. In con-
trast, the Ti/α-PbO2/β-PbO2 electrode (Fig. 1(e)) featured a
completely different structure from that of Ti/β-PbO2. Specifi-
cally, the Ti/α-PbO2/β-PbO2 electrode featured a cauliflow-
er-type structure comprising clusters of PbO2 crystals. Fur-
thermore, some pores were visible between the PbO2 crystals.
Such a cauliflower structure is expected to lead to high surface
areas for enhancing the adsorption and degradation of pollu-
tants, as demonstrated in these literature studies that reported
the synthesis of comparable β-PbO2 cauliflower-like structures
using other methods [31,32]. Accordingly, Ti/α-PbO2/β-PbO2 is
expected to exhibit high activity toward the electrochemical
degradation of 2-chlorophenol.
α-PbO2 and top layer β-PbO2 that agree with those of standard
references (PDF 01-075-2415, 01-073-0851), thereby indicat-
ing the formation of α-PbO2 and β-PbO2 crystals in the prepared
samples. The α-PbO2 grains were small as deduced from the
relatively weak and wide α-PbO2 characteristic diffraction
peaks. The small α-PbO2 grains are expected to promote the
crystallization of β-PbO2 as indicated by the strong and sharp
β-PbO2 characteristic diffraction peaks.
3.2. Electrode electrochemical behavior
Polarization curves are typically measured to determine the
oxygen evolution overpotential of anode electrodes. More spe-
cifically, the onset of oxygen evolution is indicated by a sudden
current increase in the linear polarization curve. Anodic oxygen
evolution causes a power loss in organic wastewater treatment
because oxygen evolution is a side reaction that reduces the
current efficiency of organic oxidation [33]. Thus, the use of
anodes with a high oxygen evolution overpotential favors the
electrochemical oxidation of organics. The mechanism is as
follows [34]:
PbO2[] + H2Oads → PbO2[·OH]ads + H+ + e
R + PbO2[·OH]ads → PbO2[] + RO + H+ + e
(2)
(3)
where PbO2[] represents the electroactive sites of the electrode
and RO represents the organic oxidation products. The oxida-
•
tion of organics is influenced by the amount of adsorbed OH.
Fig. 1(f) shows the XRD patterns of the intermediate layer
Oxygen evolution is an undesirable concomitant reaction.
PbO2[·OH]ads + H2O → PbO2[] + O2 + 3H+ + 3e
(4)
Furthermore, ozone generates easily when PbO2 electrodes
with high overpotentials are employed, as reported [35]. Ozone
is an ideal strong oxidizer for the degradation of organic pollu-
tants with zero toxic residues generation. Ozone can either
directly react with organic pollutants or react with H2O to gen-
erate •OH radicals as follows:
(a)
(c)
(e)
(b)
O3– + H2O →·OH + OH– + O2
(5)
Fig. 2 shows the linear polarization curves obtained in 0.1
mol/L H2SO4 using Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 elec-
trodes. As observed, the oxygen evolution potential of the
Ti/α-PbO2/β-PbO2 electrode was 3.1 V, which is much higher
than that of Ti/β-PbO2 (1.6 V) and some reported electrodes
such as β-PbO2 (1.8 V) [30], Ti/β-PbO2 doped with F− (2.0 V)
(d)
8
6
Ti/-PbO2
(f)
4
-PbO
2
Ti/-PbO2/-PbO2
2
0
-PbO
2
1.5
2.0
2.5
3.0
3.5
10 20 30 40 50 60 70 80
2/(o)
Potential (V)
Fig. 1. SEM images of Ti substrate (a), Ti/α-PbO2 (b, c), Ti/β-PbO2 (d),
and Ti/α-PbO2/β-PbO2 (e). (f) XRD patterns of α-PbO2 and β-PbO2.
Fig. 2. Anodic linear sweep voltammograms of the Ti/β-PbO2 and
Ti/α-PbO2/β-PbO2 electrodes in 0.1 mol/L H2SO4. Scan rate = 100 mV/s.

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Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
[27], and TiO2-NTs/SnO2-Sb/PbO2 (2.0 V) [34]. As observed in
Fig. 1, Ti/α-PbO2/β-PbO2 featured a cauliflower-like structure
with few pores, whereas Ti/β-PbO2 consisted of typical compact
pyramid-shaped crystals. Thus, Ti/α-PbO2/β-PbO2 has a larger
electroactive surface than Ti/β-PbO2. Accordingly, the genera-
tion of OH radicals on Ti/α-PbO2/β-PbO2 is easier and higher
than that on Ti/β-PbO2, and the oxygen evolution potential is
considerably higher on the Ti/α-PbO2/β-PbO2 electrode.
Table 1
Factors and levels of orthogonal test.
Variable
Level 1
5
50
0.05
30
Level 2
10
100
0.1
Level 3
20
200
0.2
Current density (mA/cm2)
Initial concentration (mg/L)
Electrolyte concentration (mol/L)
Reaction temperature (°C)
•
40
35
Table 2
Electrode stability is an important property in practical ap-
plication. The stability of PbO2 electrodes is usually influenced
by superficial ruptures and detachment of the PbO2 film owing
to the permeation of solution. Under normal conditions (such
as a current density of 20 mA/cm2), a PbO2 electrode can re-
main highly functional for several years. To reduce the testing
time, an accelerated life test was used to evaluate the service
life of the Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes in 1.0
mol/L H2SO4 at 60 °C at a current density of 4 A/cm2. The elec-
trolysis time when the potential reached 10 V was regarded as
the service life of the electrode [14]. As determined herein, the
service lives of the Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes
were 10 and 15 h, respectively. Though the electrode lifetime is
strongly dependent on several conditions such as current den-
sity, pH, and temperature, the lifetimes of the Ti/β-PbO2 and
Ti/α-PbO2/β-PbO2 electrodes are estimated to be 45.6 and 68.4
years, respectively, at a current density of 20 mA/cm2 accord-
ing to Eq. (6) proposed by Hine et al. [12] as follows:
Analysis of the L9 (34) test result.
Current
Initial
Electrolyte
Reaction Removal
Test
No.
density concentration concentration temperature rate
(mA/cm2)
5
(mg/L)
50
100
200
50
100
200
50
100
200
92.99
92.18
91.56
1.43
(mol/L)
0.05
0.1
0.2
0.1
0.2
0.05
0.2
0.05
0.1
91.40
93.50
91.56
1.94
(°C)
30
40
35
35
30
40
40
35
(%)
1
85.61
89.31
88.62
95.65
88.35
91.68
97.72
96.90
95.53
2
3
4
5
6
7
8
9
K1
K2
K3
R
5
5
10
10
10
20
20
20
87.84
91.89
96.72
8.88
30
89.83
92.80
93.72
3.89
sen according to the results in Table 2 as follows: anode current
density 20 mA/cm2, reaction temperature 35 °C, electrolyte
concentration 0.1 mol/L, and 2-chlorophenol initial concentra-
tion 50 mg/L. For instance, the average removal rates of
2-chlorophenol at 5, 10, and 20 mA/cm2 were 87.84%, 91.89%,
and 96.72%, respectively. Hence a current density of 20
mA/cm2 was chosen as the optimal current density.
The variations in the 2-chlorophenol removal rate on the
Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes under the selected
experimental conditions are shown in Fig. 3(a). As observed,
both the Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes were
effective toward the electrochemical degradation of 2-chloro-
phenol. After 180 min of reaction, the removal rate of
2-chlorophenol on the respective electrodes Ti/β-PbO2 and
Ti/α-PbO2/β-PbO2 were 78.4% and 100%, respectively. The
higher removal rate of the Ti/α-PbO2/β-PbO2 electrode when
compared with that of the Ti/β-PbO2 electrode at the same
degradation time supports the fact that using interlayer α-PbO2
can increase the electrode oxidation activity for 2-chlorophe-
nol.
The calculated voltage of cell U(t) is based on the potential
at nil current, the overpotentials of the anode and cathode, and
the ohmic drop through the solution of resistance R. The cell
voltage can be directly measured during electrolysis reaction.
As observed, the cell voltage was mostly stable on both the
Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes (Fig. 3(b)) during
an electrochemical degradation period of 300 min, thus indi-
cating that the prepared electrodes are very stable. The average
values of the cell voltage were 4.62 and 4.34 V for the
Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes, respectively. This
finding indicates the onset of a low energy consumption on
both electrodes; energy consumption is proportional to the cell
t = (A1/A)2t1
(6)
where A1 is the current density in the accelerated test (4
A/cm2), A is the current density in practical applications (0.02
A/cm2), t1 is the lifetime of the electrode in the accelerated test
(h), and t is the electrode lifetime in practical applications (h).
The longer lifetime of the Ti/α-PbO2/β-PbO2 electrode (com-
pared with that of the Ti/β-PbO2 electrode) indicates that the
α-PbO2 interlayer greatly enhances the electrochemical stabil-
ity of top layer β-PbO2 because of the slow formation of an in-
sulating TiO2 layer owing to the hindered diffusion of O2− ions
in water to the Ti substrate in the presence of the compact
α-PbO2 interlayer [34].
3.3. Electrochemical degradation of 2-chlorophenol
The one-factor-at-a-time is a classical methodology adopted
for investigating the influence of several factors on a particular
parameter. However, such a methodology involves numerous
experiments, and some important conclusions on the interac-
tion among factors can be missed. In the present study, an or-
thogonal test was designed to circumvent the above disad-
vantages [36]. Four parameters were considered: current den-
sity, initial concentration, electrolyte concentration, and reac-
tion temperature. Table 1 lists the experimental conditions, and
an orthogonal L9 (34) was considered for the optimization of
the experimental conditions. Table 2 shows the orthogonal test
results. The K and R values are listed in Table 2. Based on the R
values, the influence of the various studied parameters on elec-
trochemical oxidation decreased in the order of current density
> reaction temperature > electrolyte concentration > initial
concentration. The optimal experimental conditions were cho-

Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
979
degradation under the optimum conditions established above.
Fig. 4 shows the removal rates of 2,4-dichlorophenol and bi-
Ti/ -PbO2/-PbO2
Ti/ -PbO2
100
80
60
40
20
0
sphenol
A as a function of degradation time using the
(a)
Ti/α-PbO2/β-PbO2 anode. As observed, the Ti/α-PbO2/β-PbO2
anode also displayed high activity toward the electrochemical
degradation of these two complex organic pollutants. As ob-
served from Fig. 3(a) and Fig. 4, the removal rates of
2-chlorophenol and 2,4-dichlorophenol could reach 100% in
180 and 240 min of electrolysis, respectively, whereas the re-
moval rate of bisphenol A could reach 78% after 240 min of
electrolysis.

0
50
100
150
200
250
300
3.4. Kinetic and UV–visible spectroscopy studies
Time (min)
5.0
4.8
4.6
4.4
4.2
4.0
Determining the electrochemical degradation mechanism is
of importance for the control of pollutants. Many research
studies have focused on the electrochemical oxidation mecha-
nism of chlorophenol. However, the mechanism is not very
clear because detection of the transient intermediate is very
difficult. To date, the electrochemical degradation mechanism
of chlorophenol has been based on the presence of some state
intermediates, as identified by high-performance liquid chro-
matography. Based on resonance Raman spectroscopy,
high-performance liquid chromatography, UV–visible spec-
troscopy, and theoretical calculations, Cong et al. [38] reported
that some of the chlorophenols were oxidized to benzoquinone,
while others directly degraded into organic acids. However,
oxidation to benzoquinone proceeded primarily at the early
stages of the degradation process. Other possible intermediates
were catechol, phenol, resorcin, hydroquinone, fumaric acid,
maleic acid, and oxalic acid. The UV–visible spectrum of
2-chlorophenol shows two absorbance peaks at 217 and 274
nm, which are due to the phenol structure. As observed in Fig.
5, the absorbance peaks changed slightly within 30 min of reac-
tion, which may be due to the influence of intermediates fea-
turing benzene rings such as benzoquinone, catechol, resorcin,
phenol, and hydroquinone. The absorbance peaks decreased
after 60 min of degradation owing to the degradation of
2-chlorophenol into organic acids such as fumaric acid, maleic
acid, and oxalic acid.
(b)
Ti/-PbO2
Ti/-PbO2/-PbO2
0
50
100
150
200
250
300
Time (min)
Fig. 3. Removal rate of 2-chlorophenol (a) and variations in cell voltage
during electrolysis (b) in the presence of the Ti/β-PbO2 and Ti/α-PbO2/
β-PbO2 anodes. Anode current density 20 mA/cm2, reaction tempera-
ture 35 °C, concentration of Na2SO4 0.1 mol/L, and initial concentration
of 2-chlorophenol 50 mg/L.
voltage [37]. The cost associated with electrical power usage
for 1000 kg of wastewater was calculated as 22 and 20 kWh
using the Ti/β-PbO2 and Ti/α-PbO2/β-PbO2 electrodes, respec-
tively.
More complex compounds, 2,4-dichlorophenol and bi-
sphenol A, were selected to further investigate the performance
of the Ti/α-PbO2/β-PbO2 electrode toward electrochemical
0.10
100
80
0 min
30 min
60 min
90 min
0.08
0.06
0.04
0.02
0.00
60

40
bisphenol A
2,4-dichlorophenol
2-chlorophenol
20
0
0
50
100
150
200
250
300
200
250
300
350
400
Time (min)
 (nm)
Fig. 4. Removal rates of 2,4-dichlorophenol and bisphenol A using a
Ti/α-PbO2/β-PbO2 anode. The reaction conditions are the same as those
stated in Fig. 3.
Fig. 5. Variations in the UV–visible spectrum of 2-chlorophenol as a
function of electrochemical degradation time using a Ti/α-PbO2/β-PbO2
electrode. The reaction conditions are the same as those stated in Fig. 3.

980
Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
respectively. Kinetics analysis revealed that the degradation of
5
4
3
2
1
0
2-chlorophenol followed a pseudo-first order reaction assessed
over a short electrolysis time of 150 min, with a regression
coefficient of 0.9829 and a pseudo rate constant of 0.013 min−1
.
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A Ti/α-PbO2/β-PbO2 electrode with cauliflower-like struc-
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Graphical Abstract
Chin. J. Catal., 2015, 36: 975–981 doi: 10.1016/S1872-2067(15)60851-8
Facile preparation of a Ti/α-PbO2/β-PbO2 electrode for the electrochemical degradation of 2-chlorophenol
Qianli Zhang, Xinyan Guo, Xiaodan Cao, Dongtian Wang, Jie Wei *
Suzhou University of Science and Technology
100
80
60

40
20
0
Ti/-PbO2/-PbO2
Ti/-PbO2
0
50
100
150
200
250
300
Time (min)
A cauliflower-structured Ti/α-PbO2/-PbO2 anode displays high activity toward the degradation of 2-chlorophenol, with a long active
service life of 68.4 years at a current density of 20 mA/cm2.

Qianli Zhang et al. / Chinese Journal of Catalysis 36 (2015) 975–981
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