Photocatalytic degradation of 2,4-dichlorophenol with V2O5-TiO2 catalysts: Effect of catalyst support and surfactant additives

Article abstract of DOI:10.1016/S1872-2067(15)61035-X

Binary oxide catalysts with various weight percentage V₂O₅ loadings were prepared by solid-state dispersion and the nanocomposites were modified with surfactants. The catalysts were analyzed using X-ray diffraction, diffuse-reflectance spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, and N₂ adsorption-desorption. The photocatalytic activities of the catalysts were evaluated in the degradation of 2,4-dichlorophenol under ultraviolet irradiation. The photocatalytic activity of 50 wt% V₂O₅-TiO₂ (50V₂O₅-TiO₂) was higher than those of pure V₂O₅, TiO₂, and P25. Interactions between V₂O₅ and TiO₂ affected the photocatalytic efficiencies of the binary oxide catalysts. Cetyltrimethylammonium bromide (CTAB) and hexadecyltrimethylammonium bromide (HTAB) significantly enhanced the efficiency of the 50V₂O₅-TiO₂ catalyst. The highest percentage of 2,4-dichlorophenol degradation (100%) and highest reaction rate (2.22 mg/(L·min)) were obtained in 30 min with the (50V₂O₅-TiO₂)-CTAB catalyst. It is concluded that the addition of a surfactant to the binary oxide significantly enhanced the photocatalytic activity by modifying the optical and electronic properties of V₂O₅ and TiO₂.

Full text of DOI:10.1016/S1872-2067(15)61035-X

Chinese Journal of Catalysis 37 (2016) 607–615
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
Photocatalytic degradation of 2,4‐dichlorophenol with V2O5‐TiO2
catalysts: Effect of catalyst support and surfactant additives
Eda Sinirtas, Meltem Isleyen, Gulin Selda Pozan Soylu*
Chemical Engineering Department, Faculty of Engineering, Istanbul University, Avcilar 34320, Istanbul, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history:
Binary oxide catalysts with various weight percentage V2O5 loadings were prepared by solid‐state
dispersion and the nanocomposites were modified with surfactants. The catalysts were analyzed
using X‐ray diffraction, diffuse‐reflectance spectroscopy, Fourier‐transform infrared spectroscopy,
scanning electron microscopy, and N2 adsorption‐desorption. The photocatalytic activities of the
catalysts were evaluated in the degradation of 2,4‐dichlorophenol under ultraviolet irradiation. The
photocatalytic activity of 50 wt% V2O5‐TiO2 (50V2O5‐TiO2) was higher than those of pure V2O5, TiO2,
and P25. Interactions between V2O5 and TiO2 affected the photocatalytic efficiencies of the binary
oxide catalysts. Cetyltrimethylammonium bromide (CTAB) and hexadecyltrimethylammonium
bromide (HTAB) significantly enhanced the efficiency of the 50V2O5‐TiO2 catalyst. The highest per‐
centage of 2,4‐dichlorophenol degradation (100%) and highest reaction rate (2.22 mg/(L·min))
were obtained in 30 min with the (50V2O5‐TiO2)‐CTAB catalyst. It is concluded that the addition of a
surfactant to the binary oxide significantly enhanced the photocatalytic activity by modifying the
optical and electronic properties of V2O5 and TiO2.
Received 6 October 2015
Accepted 22 December 2015
Published 5 April 2016
Keywords:
2,4‐Dichlorophenol
Degradation
Photocatalysis
Surfactant
Binary oxide
Characterization
© 2016, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
Heterogeneous photocatalytic oxidation has aroused con‐
siderable interest as a potential efficient method for degrading
Chlorophenols are toxic organic compounds and are listed
by the Environmental Protection Agency as priority water pol‐
lutants [1]. They have been used extensively in many industrial
products such as petrochemicals, pharmaceuticals, dyes, pulps,
pesticides, and paints [2–6]; therefore, chlorophenols are
common chloroaromatic pollutants [7]. Removing these con‐
taminants from water is a significant challenge because of ev‐
er‐increasing pollution and the shortage of high‐quality fresh
water [8]. The removal of these hazardous organic pollutants
has become necessary and important for environmental safety.
These organic compounds can be oxidized using chemical,
photochemical, and microbiological processes.
recalcitrant environmental contaminants. Semiconductors,
which have a filled valence band and an empty conduction
band, are important materials because of the electronic struc‐
tures of the metal atoms in chemical combinations [9]. A wide
range of chloroaromatics have been eliminated by this process,
mainly using TiO2 as a semiconductor photocatalyst. TiO2 is the
most widely used photocatalyst because of its low cost, abun‐
dance, high chemical stability, and low toxicity [10]. However, it
has two main defects. First, it is a relatively high energy band
gap material (Eg ≈ 3.2 eV), which can be excited under ultravio‐
let (UV) irradiation (λ < 387 nm). This practically rules out the
use of sunlight to induce photocatalytic reactions efficiently.
* Corresponding author. Tel: +90‐212‐4737070; Fax: +90‐212‐4737180; E‐mail: gpozan@istanbul.edu.tr
This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) within the research project 111M210
[2011‐2013].
DOI: 10.1016/S1872‐2067(15)61035‐X | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 37, No. 4, April 2016

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Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
Secondly, the low rate of electron transfer to reducible species
(e.g., oxygen in oxidation reactions, protons in hydrogen pro‐
duction from water) and high recombination rate of the photo‐
produced electron‐hole pairs limit the rates of photocatalytic
reactions [11]. Research to find alternative high‐performance,
low‐cost photocatalysts is therefore important [12–14]. Among
the strategies adopted to minimize the effects of these draw‐
backs of TiO2 photocatalysts, coupling TiO2 with another metal
oxide is a promising route.
thylammonium bromide (CTAB; Merck), hexadecyltrime‐
thylammonium bromide (HTAB; Merck), and poly(vinyl alco‐
hol) (PVA; Merck). The organic compounds used in the photo‐
catalytic experiments were 2,4‐dichlorophenol, phenol,
4‐chlorophenol, 2‐chlorophenol, hydroquinone, catechol, and
methanol (for high‐performance liquid chromatography
(HPLC), ≥ 99%)); they were purchased from the Fluka Compa‐
ny and used without further purification. Deionized water was
used for the preparation of all the catalysts and to dilute the
2,4‐dichlorophenol solution.
Improvement of the photocatalytic activity of TiO2 by dop‐
ing with transition metals such as Pt, Fe, Mo, Ru, and V or non‐
metals, and mixing with other metal oxides to form composite
semiconductors has been investigated. The combination of a
semiconductor substrate and metal cluster improves the pho‐
tocatalytic activity by trapping the photoinduced charge carri‐
ers, thereby improving the charge‐transfer processes, as a re‐
sult of the recombination of electrons and holes prior to the
superoxide activation process [15]. Additionally, surfactants
have often been used to increase the photodegradation
efficiencies of UV‐TiO2 systems [16,17]. Several attempts have
been made to enhance the efficiencies of TiO2 catalysts using
visible light [18–20]. For example, V‐doped TiO2, which has a
band gap of 3.0–3.2, compared with 2.5–2.7 eV for TiO2, is a
promising visible‐light‐driven photocatalyst [21,22]. Catalytic
systems based on vanadium oxides are highly active and selec‐
tive for a number of industrially relevant chemical transfor‐
mations. It has already been established that the catalyst sup‐
port plays an important role in both the activity and selectivity
[23–26]. ZrO2‐TiO2 and Fe3O4‐TiO2 composite photocatalysts
are examples of mixed metal oxides used in the degradation of
chlorophenols [27,28]. This type of catalyst has been thor‐
oughly investigated in the treatment of organic wastewater.
Catalysts are usually prepared using sol‐gel and hydrothermal
methods. There are no reports of photocatalysts for
2,4‐dichlorophenol removal prepared by solid‐state dispersion.
The synthesis of inexpensive, active, and nanosized photocata‐
lysts using simple methods therefore needs to be investigated.
In the present work, binary metal oxide catalysts
(V2O5‐TiO2) were prepared by solid‐state dispersion. 2,4‐Di‐
chlorophenol was used as a model pollutant to evaluate the
photocatalytic activities of the catalysts under UV irradiation.
The effects of the metal oxide ratio and surfactant additives on
the photocatalytic efficiency were examined. The catalysts were
analyzed using X‐ray diffraction (XRD), diffuse‐reflectance
spectroscopy (DRS), scanning electron microscopy (SEM), Fou‐
rier‐transform infrared (FT‐IR) spectroscopy, and N2 adsorp‐
tion‐desorption, and the relationship between the catalyst
structure and photocatalytic activity was examined.
2.2. Catalyst preparation
Pure TiO2 was prepared using a sol‐gel method [29]. TiCl4
(1.5 mL) was slowly added dropwise to ethanol (15 mL) at
room temperature. A large amount of HCl gas was exhausted
during the mixing process. The obtained light‐yellow solution
was gelatinized for several days to form a sol‐gel. The gel was
dried in an oven at 105 °C for 1 d, ground to a fine powder, and
calcined at 600 °C for 4 h.
V2O5‐doped TiO2 catalysts were prepared using a solid‐state
dispersion method. V2O5 and TiO2 samples were mixed in spe‐
cific weight percentage proportions, namely 10:90, 50:50,
70:30, 90:10; for example, 10V2O5‐TiO2 denotes the catalyst
nominally containing 10 wt% V2O5. The binary oxide catalysts
were dried at 110 °C for 1.5 h, calcined in air at 450 °C for 6 h,
and ball milled.
V2O5‐TiO2 binary oxides and surfactants (CTAB, HTAB, or
PVA) were mixed in weight ratios of 1:1 using a solid‐state dis‐
persion method. The resultant catalyst was dried at 110 °C for
1.5 h, heated at 150 °C in air for 5 h at a heating rate of 10
°C/min, and ball milled.
2.3. Catalyst characterization
The BET surface areas of the samples were determined from
N2 adsorption‐desorption isotherm measurements at −196 °C.
The samples were degassed at 200 °C prior to the actual meas‐
urements.
Powder XRD patterns of the samples were obtained using a
Rigaku D/Max‐2200 diffractometer with Cu Kα ( = 1.540 Å)
radiation. Samples were scanned from 10° to 80° (2θ) at a rate
of 2°/min. The sizes of the crystalline domains were calculated
using the Scherrer equation, t = C/Bcosθ, where  is the X‐ray
wavelength (Å), B is the full width at half maximum, θ is the
Bragg angle, C is a factor that depends on the crystallite shape
(taken to be 1), and t is the crystallite size (Å).
The morphologies and size distributions of the photocata‐
lysts were determined using SEM (JEOL/JSM‐6335F).
Samples for FT‐IR spectroscopy were prepared as KBr pel‐
lets. All spectra were recorded at a 4 cm−1 resolution and 100
scans were performed. The surface OH groups of the photo‐
catalysts were detected by FT‐IR spectroscopy (Perkin Elmer
Precisely Spectrum One).
UV‐visible (UV‐vis) DRS was performed using a UV‐vis
spectrophotometer (Shimadzu UV‐3600), with BaSO4 as the
reference.
2. Experimental
2.1. Materials
The starting materials for catalyst preparation were V2O5
(Merck), TiO2 P25 (Degussa), ammonium vanadium oxide (Alfa
Aesar, 99%), ethanol (absolute), titanium tetrachloride (≥
99%), TiCl4 (carbon tetrachloride; Merck), cetyltrime‐

Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
609
Photoluminescence (PL) spectra were recorded at room





(50V2O5-TiO2)-PVA
temperature using a fluorescence spectrophotometer (Agilent
Technologies‐Cary Eclipse), with a xenon lamp as the excitation
source. The sample was dispersed in ethanol using an ultra‐
sonic bath and the excitation wavelength used in the PL meas‐
urements was 530 nm.








 









(50V2O5-TiO2)-HTAB















(50V2O5-TiO2)-CTAB







2.4. Evaluation of photocatalytic activity



50V2O5-TiO2








Photoactivity studies were performed at atmospheric pres‐
sure and room temperature (25 °C). In a typical experiment, the
catalyst (100 mg) was dispersed in 2,4‐dichlorophenol solution
(50 mL) of initial concentration 25 mg/L and neutral pH (pH 5)
under magnetic stirring. Phenol photooxidation runs were
performed using a cylindrical quartz batch photoreactor. A
Luzchem LZC‐5 photoreactor system was used in all experi‐
ments. The light source was a 64‐W UV‐B lamp (Luzchem
LZC‐UVB), with a maximum light intensity at 312 nm and illu‐
mination distance 18 cm from the target. The light intensity of
the UV lamp used for degradation experiments was recorded
using a UV/vis power meter (Smart Sensor‐AR823). The pho‐
toreactor system had a magnetic stirrer, which was used to
achieve uniform conditions in the reaction mixture. Before the
UV light was turned on, the solution was stirred for 1 h to en‐
sure good adsorption equilibrium between the catalyst and the
solution. After irradiation for 5 h, the 2,4‐dichlorophenol solu‐
tion was filtered through a membrane filter (pore size 0.45
mm) and the filtrate was used for total organic content (TOC)
measurements (TOC‐V, Shimadzu).





Anatase TiO2
 Orthorhombic V2O5


TiO2
V2O5


















10
20
30
40
2
50
60
70
80
Fig. 1. XRD patterns of V2O5, TiO2, 50V2O5‐TiO2, CTAB‐assisted
V2O5‐TiO2, HTAB‐assisted V2O5‐TiO2 and PVA‐assisted V2O5‐TiO2 cata‐
lysts.
entry of nitrogen probe molecules. In addition, when CTAB is
added to 50V2O5‐TiO2, the surface area decreases 17 to 10
m2/g. However, the photocatalytic activity does not only de‐
pend on the BET surface area. This point was clarified by a se‐
ries of detailed experiments.
Fig. 1 shows the XRD patterns of the V2O5‐TiO2 catalysts, and
pure V2O5 and TiO2. The diffraction peaks can be indexed to
orthorhombic V2O5 (JCPDS 41‐1426) and anatase TiO2 (JCPDS
89‐4921). No peaks for other phases were detected. The pat‐
terns show that the pure V2O5 catalyst consists of an ortho‐
rhombic phase and pure TiO2 has significant peaks from the
anatase crystal phase. Orthorhombic V2O5 is the dominant
phase in the catalysts prepared using solid‐state dispersion,
whereas anatase TiO2 prevails in the catalysts prepared by
coprecipitation. XRD confirms the presence of V2O5 and TiO2 in
the composites, confirming the successful introduction of V2O5
onto TiO2. Many studies have confirmed that the photocatalytic
activity of anatase‐phase TiO2 is higher than those of the
brookite or rutile phases [30]. For 50V2O5‐TiO2, the dominant
V2O5 phase is orthorhombic, with some TiO2 embedded on the
V2O5 particles. The phase structure, crystallite size, and crystal‐
linity of V2O5 play important roles in the photocatalytic activity.
Figure 1 shows that the XRD patterns of all the surfac‐
The concentrations of 2,4‐dichlorophenol and products
were determined using an HPLC (Thermo Finnigan) system
equipped with a C‐18 column. The mobile phase was a metha‐
nol/water (70/30, v/v) mixture at a flow rate of 1 mL/min.
3. Results and discussion
3.1. Structures and textural properties of V2O5‐TiO2 binary ox‐
ides
The BET surface areas of the catalysts are shown in Table 1.
The surface areas of the prepared V2O5 and TiO2 are 25 and 40
m2/g, respectively. For the V2O5‐TiO2 series, the surface areas
decrease with increasing V2O5 content. This is because surface
coverage by the V2O5 particles increases, and this prevents the
Table 1
The crystallite sizes, specific surface areas, band gap, morphology of materials and 2,4‐dichlorophenol degradation efficiencies over 30 min.
Catalyst
V2O5 crystallite size (nm)
SBET (m2/g) Band gap (eV) 2,4‐Dichlorophenol degradation (%)
kr (mg/(L·min))
0.87
10V2O5‐TiO2
50V2O5‐TiO2
70V2O5‐TiO2
90V2O5‐TiO2
(50V2O5‐TiO2)‐CTAB
(50V2O5‐TiO2)‐HTAB
(50V2O5‐TiO2)‐PVA
V2O5
27
30
33
37
35
38
42
40
43
32
22
17
12
8
2.31
2.26
2.24
2.21
2.21
2.24
2.26
2.35
3.12
3.12
60
85
79
75
100
93
18
72
66
59
1.49
1.19
1.13
2.22
1.84
0.12
10
6
4
25
40
50
1.09
0.95
0.77
TiO2 (synthesis)
TiO2 (P25)

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Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
tant‐assisted 50V2O5‐TiO2 nanoparticles have similar profiles
and all the diffraction peaks can be indexed to orthorhombic
V2O5 and anatase TiO2. Although all the samples show the same
morphologies, the crystallite sizes and relative peak intensities
change on addition of a surfactant. The crystallite sizes are 42,
38, and 35 nm for (50V2O5‐TiO2)‐PVA, (50V2O5‐TiO2)‐HTAB,
and (50V2O5‐TiO2)‐CTAB, respectively. The size differences
may lead to morphological and structural differences [31].
The nanostructural morphology has an important effect on
the photocatalytic activity. The SEM images of 50V2O5‐TiO2 and
surfactant‐assisted V2O5‐TiO2 catalysts are shown in Fig. 2. Fig.
2(a) shows a SEM‐energy dispersive X‐ray spectroscopy (EDS)
image of the 50V2O5‐TiO2 catalyst. The figure shows that the
sample has a mixed morphology consisting of micro‐ and mac‐
ro‐clusters. EDS analysis indicates the presence of Ti, V, and O
on the 50V2O5‐TiO2 surface. The SEM‐EDS results clearly show
that the synthesized 50V2O5‐TiO2 consists of particles. Fig. 2(b)
shows that on CTAB addition the particle morphology changes
to rod‐like and significant particle interactions occur. However,
agglomeration is seen in the SEM photograph of the
(50V2O5‐TiO2)‐PVA and (50V2O5‐TiO2)‐HTAB catalysts. There
are irregular and coarse grains in addition to agglomeration in
the morphology of (50V2O5‐TiO2)‐HTAB. These nanoparticles
gradually self‐assemble into aggregates with a specific mor‐
phology as a result of van der Waals interactions with surfac‐
tant molecules adsorbed on the nanocrystal surfaces and the
tendency to minimize the interfacial energy [32,33].
mining its photocatalytic activity [35]. The UV‐vis DRS spectra
of various samples are shown in Fig. 3. The band gaps of the
samples were calculated from the onset of the absorption edges
to be 2.26, 2.21, 2.24, and 2.26 eV for 50V2O5‐TiO2, (50V2O5‐
TiO2)‐CTAB, (50V2O5‐TiO2)‐HTAB, and (50V2O5‐TiO2)‐PVA,
respectively (Table 1). The band gaps are close to each other.
The absorption of visible light by V2O5‐TiO2 catalysts is bet‐
ter than that by TiO2. V2O5 loading therefore significantly im‐
proves visible‐light absorption by TiO2 photocatalysts. Surfac‐
tant addition has a minor impact on the catalyst band gap en‐
ergy. However, doping of the pure catalyst with a surfactant
such as CTAB decreases the absorption wavelength into the
visible region. In solution, CTAB, which is a cationic surfactant,
ionizes and is selectively adsorbed on the crystal surfaces. This
changes the growth rates of different crystal surfaces, and dif‐
ferent morphologies are formed [36]. This change in the band
gap energy positively affects the photocatalytic activity.
(50V2O5‐TiO2)‐CTAB therefore shows strong absorption in the
UV region, indicating that this material would show photocata‐
lytic activity under UV irradiation.
Fig. 4 shows the FT‐IR spectra in the range 450–4000 cm−1
for various samples. The samples all have similar FT‐IR spectra,
indicating that the structures of V2O5 and TiO2 did not change
after surfactant loading. The Ti–O–Ti bending vibration at
420–650 cm−1 confirms the formation of anatase TiO2. This is in
agreement with the XRD results. The band at 1016 cm−1 from
the V–O (vanadyl oxygen) stretching vibration and the bands at
844 and 580 cm−1 from O–V–O stretching modes are observed
for pure V2O5. The bands at 1000–1030 cm−1 represent the
O–V–O stretching vibration and the bands at 800–830 cm−1 due
to Ti–O–V linkage [37] was observed for V2O5‐TiO2 and surfac‐
tant doped V2O5‐TiO2 nanocomposites. Furthermore, the sharp
bands at about 2850, 2918 and 1474 cm−1 are assigned to the
C–H and C=C stretches. The absorption bands at 2918 and
2850 cm−1 are due to the C–H asymmetric and symmetric
stretching vibrations of CTAB and HTAB, respectively [38]. The
IR spectra show two intense bands, assigned to asymmetric
(2918 cm−1) and symmetric (2850 cm−1) stretching vibrations
of C–CH2 in methylene chains. The sharp bands in the region
1450–1500 cm−1 are attributed to deformation of –CH2– and
–CH3 [39] of the incorporated surfactants. These results indi‐
The surfactants act as structure‐directing agents and can
reduce the particle size; therefore, they influence the particle
morphology [34]. Surfactants greatly affect the morphology of
V2O5‐TiO2, and the crystal structure, as shown by the XRD re‐
sults.
3.2. Optical properties of V2O5‐TiO2 binary oxides
The optical absorption properties of a semiconductor, which
are related to the electronic structure, are key factors in deter‐
(a)
(b)
50V2O5-TiO2
(50V2O5-TiO2)-HTAB
(50V2O5-TiO2)-CTAB
(50V2O5-TiO2)-PVA
(d)
200
300
400
500
600
700
800
(c)
Wavelength (nm)
Fig. 2. SEM images of (a) 50V2O5‐TiO2, (b) (50V2O5‐TiO2)‐CTAB, (c)
(50V2O5‐TiO2)‐HTAB, and (d) (50V2O5‐TiO2)‐PVA catalysts.
Fig. 3. UV‐vis DRS spectra of 50V2O5‐TiO2 and surfactant loaded
50V2O5‐TiO2 catalysts.

Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
611
gated based on degradation of 2,4‐dichlorophenol in aqueous
solution in the presence of a small amount of H2O2 under UV‐B
irradiation. The reactions follow pseudo‐first‐order kinetics.
The rate constants are listed in Table 1.
(50V2O5-TiO2)-PVA
(50V2O5-TiO2)-HTAB
In general, the diffusion rate of adsorbed reactive species on
the surface is faster than the photocatalytic reaction rate. The
photocatalytic reaction is therefore the rate‐controlling step.
Photocatalytic degradation can be described using the Lang‐
muir‐Hinshelwood equation [44]:
(50V2O5-TiO2)-CTAB
r = –dC/dt = krKadsC/(1+KadsC)
50V2O5-TiO2
where r is the initial reaction rate (mg/(L·min)), kr is the
Langmuir‐Hinshelwood reaction rate constant (mg/(L·min))
and K is the Langmuir adsorption constant (L/mg).
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm1)
Heterogeneous photocatalytic processes involve many steps
such as diffusion, adsorption, and reaction. An appropriate pore
distribution promotes diffusion of reactants and products, and
this favors the photocatalytic reaction [45]. Before the photo‐
catalytic reaction, dark reactions were performed, i.e., in the
presence of a catalyst without irradiation, to ensure adsorp‐
tion‐desorption equilibrium. The effects of strongly oxidizing
additives such as H2O2 are controversial and depend on the
substrate type and various experimental parameters [46]; their
usefulness should be carefully checked under the operating
conditions. In our case, the highest degradation rate was
achieved with addition of 0.15 mL of H2O2. The improved cata‐
lytic activity of V2O5‐TiO2 in the presence of H2O2 is attributed
to the reactive radical intermediates (•OH) formed from the
oxidants by reaction with photogenerated electrons; these in‐
termediates can themselves act as strong oxidants and as elec‐
tron scavengers, inhibiting electron‐hole recombination at the
semiconductor surface. The activities were calculated and are
given in Table 1.
Fig. 4. FT‐IR spectra of 50V2O5‐TiO2 and surfactant loaded 50V2O5‐TiO2
catalysts.
cate that the higher catalytic activities of CTAB‐ and
HTAB‐doped V2O5‐TiO2 can be attributed to higher concentra‐
tions of methylene chains compared with that in pure
V2O5‐TiO2.
Fig. 5 shows the PL spectra of V2O5‐TiO2, (50V2O5‐TiO2)‐
CTAB, (50V2O5‐TiO2)‐HTAB, and (50V2O5‐TiO2)‐PVA. The PL
emission is the result of separation and recombination of ex‐
cited electrons and holes [40]. A lower PL intensity implies
decreased recombination, and possibly higher photocatalytic
activity [41]. This is reasonable because CTAB and HTAB addi‐
tion can improve the separation of photogenerated elec‐
tron‐hole pairs and provide faster transport of charge carriers,
thereby enhancing the photocatalytic performance [42,43]. As
shown in Fig. 5, all the samples exhibited a strong emission
peak at around 530 nm. The intensities varied, and those for
(50V2O5‐TiO2)‐CTAB and (50V2O5‐TiO2)‐HTAB were much
lower than those for the other catalysts. This suggests that the
addition of CTAB or HTAB inhibits electron‐hole recombination
and improves the photocatalytic activity. These results are in
good agreement with the activity results.
The photocatalytic degradation performances of V2O5, TiO2,
and V2O5‐TiO2 binary oxide catalysts in the oxidative degrada‐
tion of 2,4‐dichlorophenol were monitored; the results are
shown in Fig. 6. The data in Table 1 show that 72% degradation
of 2,4‐dichlorophenol was achieved with the pure V2O5 catalyst
under UV‐B irradiation for 30 min. Under the same conditions,
the photodegradation rate was only 66% for the synthesized
3.3. Photocatalytic activity
The photocatalytic activities of the samples were investi‐
1.0
V2O5
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
TiO2 (synthesis)
TiO2 (P25)
10V2O5-TiO2
(50V2O5-TiO2)-PVA
(50V2O5-TiO2)-HTAB
(50V2O5-TiO2)-CTAB
50V2O5-TiO2
50V2O5-TiO2
70V2O5-TiO2
90V2O5-TiO2
0
5
10
15
20
25
30
510
520
530
540
550
Time (min)
Wavenlength (nm)
Fig. 5. PL spectra of 50V2O5‐TiO2 and surfactant loaded 50V2O5‐TiO2
Fig. 6. Degradation activities of V2O5, TiO2 (synthesis), TiO2 (P25) and
catalysts.
V2O5‐TiO2 catalysts.

612
Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
TiO2 catalyst. The 50V2O5‐TiO2 catalyst gave the highest per‐
centage of 2,4‐dichlorophenol degradation (85%); however,
higher weight percentages (70–90 wt%) did not noticeably
change the reactivity and the value decreased slightly with
further loadings of V2O5. 2,4‐Dichlorophenol degradation de‐
creased to 60% for 10 wt% V2O5 mixed with TiO2.
These results confirm that the optimum V2O5‐TiO2 weight
ratio is 1:1. This is because few V2O5‐TiO2 heterostructures can
be formed on the surface when the V2O5 content is too low;
when it is too high, excess V2O5 can cover active sites on the
TiO2 surface and few V2O5‐TiO2 heterostructures are formed.
V2O5‐TiO2 nano‐heterostructures with a V2O5‐TiO2 weight ratio
of 1:1 show the highest photocatalytic activity.
The activity of the photocatalyst is influenced by its crystal‐
linity and other factors such as surface area, crystal size, syn‐
thetic method, band gap, crystal phase, and surface OH groups.
The activity results show that the surface area, particle size,
and surface OH groups are not the only factors that contribute
to high reactivity in 2,4‐dichlorophenol degradation. The inter‐
actions in binary oxide catalysts are more important than the
surface area, particle size, and surface OH groups. The optimum
photodegradation activity was achieved with 50V2O5‐TiO2. Our
XRD observations clearly show that V interacts with Ti.
The specific surface area decreases with increasing V2O5
content (70% to 90%) in the binary oxide catalysts because of
TiO2 pore blockage. In addition, a high V2O5 content (70% or
90%) prevents TiO2 crystallization. The results show that the
photocatalytic activity of V2O5‐TiO2 was significantly decreased
by high loading with V2O5 clusters (70% and 90%). These re‐
sults are in agreement with those in the Refs. [47,48].
Neppolian et al. [49] reported that electron injection was the
major factor in the activities of binary oxide catalysts, along
with other physicochemical characteristics. The transfer of
electrons from ZrO2 to TiO2 through chemical interactions be‐
tween ZrO2 and TiO2 to form TiOZr bonds was the main
process observed in binary oxide catalysts. Wu et al. [50] de‐
scribed mutual chemical interactions between pure oxides
when they were coprecipitated (TiOZr), and this pro‐
foundly affected the photocatalytic properties.
In this study, the photocatalytic activity of 50V2O5‐TiO2 was
higher than those of nano‐TiO2 (synthesized) and Aeroxide
P25. Although the surface area of the 50V2O5‐TiO2 catalyst was
comparable to or even lower than those of TiO2 and P25, it
showed high activity. However, the changes in surface areas
were not as great as these in the catalytic activities; therefore,
differences among the activities were associated with the active
species on the surfaces. 2,4‐Dichlorophenol removal of 59%
was achieved with Degussa P25. Various synthesized novel
catalysts with higher photocatalytic activities than that of De‐
gussa P25 have been reported. Xu et al. [51–53] investigated
the photocatalytic activity of TiO2 supported on ZSM‐5, zeolite
A, silica, and alumina in the photooxidations of 4‐chlorophenol
and acetophenone. The photocatalytic activity of TiO2/ZSM5
was higher than those of prepared TiO2 powder and Degussa
P25.
The data in Table 1 show that CTAB and HTAB loading im‐
proved the degradation activity of 50V2O5‐TiO2. The photo‐
catalytic performance in 30 min over the prepared catalysts
decreased in the order (50V2O5‐TiO2)‐CTAB (ca. 100%) >
(50V2O5‐TiO2)‐ HTAB (ca. 93%) > (50V2O5‐TiO2) (ca. 85%) >
(50V2O5‐TiO2)‐ PVA (ca. 18%). The (50V2O5‐TiO2)‐CTAB sam‐
ple achieved complete degradation in 30 min (Table 1) and
gave the highest reaction rate (2.22 mg/(L·min)). One explana‐
tion of the results is strong interactions between V2O5‐TiO2 and
HTAB. Only 18% degradation of 2,4‐dichlorophenol was
achieved in 30 min with the (50V2O5‐TiO2)‐PVA catalyst. The
decrease in the activity can probably be explained by partial
blocking of the active species of the V2O5‐TiO2 binary oxide by
large PVA particles. The SEM photograph of V2O5‐TiO2 loaded
with PVA shows particle agglomeration, which would cause a
drop in the photocatalytic activity. These results show that
surfactant loading changed the surface areas and particle sizes
of the samples.
These observations indicate that the local structure, crystal‐
linity, surface morphology, and particle shape of the V2O5‐TiO2
powder affect the photocatalytic performance. The crystal
structure, crystallinity, morphology, and surface area of a ma‐
terial are important factors in its photocatalytic performance
[54–56]. The photocatalytic activity results suggest that the
enhanced photocatalytic activity of (50V2O5‐TiO2)‐CTAB can be
attributed to an appropriate pore distribution and high separa‐
tion rate of photoinduced charge carriers. The addition of CTAB
to the synthesis system not only alters the surface parameters,
especially the pore distribution, but also enhances the pho‐
toinduced charge separation rate of V2O5‐TiO2. These results
show that the pore distribution and photoinduced charge sep‐
aration rate both play important roles in promotion of the
(a)
1.0
0.8
0.6
0.4
0.2
0.0
(50V2O5-TiO2)-HTAB
(50V2O5-TiO2)-CTAB
(50V2O5-TiO2)-PVA
50V2O5-TiO2
0
5
10
15
20
25
30
(b)
Time (min)
100
80
60
40
20
0
Fig. 7. (a) Degradation activities of 50V2O5‐TiO2 and surfactant‐loaded
50V2O5‐TiO2 catalysts. (b) TOC removal for photocatalytic degradation
of 2,4‐dichlorophenol.
The performance data of modified V2O5‐TiO2 catalysts with
various HTAB, CTAB, and PVA loadings are shown in Fig. 7(a).

Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
613
id‐state dispersion method were used in the photocatalytic
degradation of 2,4‐dichlorophenol under UV‐B irradiation. The
photocatalysts showed high photocatalytic activities in
2,4‐dichlorophenol degradation. The chemical interactions
between V2O5 and TiO2 to form VOTi bonds affect the pho‐
toefficiencies of binary oxide catalysts. The effects of various
surfactants (CTAB, HTAB, and PVA) on the photocatalytic deg‐
radation of 2,4‐dichlorophenol were also investigated.
(50V2O5‐TiO2)‐CTAB gave the highest percentage of
2,4‐dichlorophenol degradation (100%) and the highest reac‐
tion rate (2.22 mg/(L·min)) in 30 min. The catalytic activity of
(50V2O5‐TiO2)‐CTAB was higher than those of nano TiO2 and
P25 photocatalysts. The structural, morphological, optical, and
photocatalytic properties of the catalyst play a significant role
during photocatalysis. In summary, the effectiveness of using a
surfactant such as CTAB to construct an efficient visi‐
ble‐light‐driven 50V2O5‐TiO2 photocatalyst was shown. The
local structure and crystallinity significantly affected the pho‐
tocatalytic performance. The results indicate that the photo‐
catalytic degradation of wastewater containing chlorophenols
can be achieved using (50V2O5‐TiO2)‐CTAB. Such heterostruc‐
tured nanocomposites may help in the design of highly efficient
photocatalysts for organic compounds, and have potential
technological applications.
25
20
15
10
5
(a)
2.4-Dichlorophenol
2-Chlorophenol
Phenol
Others
Catechol
0
25
(b)
20
15
10
5
2.4-Dichlorophenol
2-Chlorophenol
Phenol
Others
Catechol
0
0
5
10
15
20
25
30
Time (min)
Fig. 8. Concentration profiles for intermediates obtained during the
photocatalytic oxidation reaction using (a) 50V2O5‐TiO2 (b)
(50V2O5‐TiO2)‐CTAB.
photocatalytic activity of (50V2O5‐TiO2)‐CTAB.
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614
Eda Sinirtas et al. / Chinese Journal of Catalysis 37 (2016) 607–615
Graphical Abstract
Chin. J. Catal., 2016, 37: 607–615 doi: 10.1016/S1872‐2067(15)61035‐X
Photocatalytic degradation of 2,4‐dichlorophenol with V2O5‐TiO2 catalysts: Effect of catalyst support and surfactant additives
Eda Sinirtas, Meltem Isleyen, Gulin Selda Pozan Soylu*
Istanbul University, Turkey
hν
1.0
(50V2O5-TiO2)-PVA
0.8
e‐
h+
VB
(V2O5‐TiO2)‐CTAB
0.6
0.4
0.2
0.0
CB
+
(50V2O5-TiO2)-HTAB
e‐
h+
50V2O5-TiO2
‐
O2
(50V2O5-TiO2)-CTAB
OH
0
5
10
15
20
25
30
O2
Time (min)
H2O
(V2O5‐TiO2)‐cetyltrimethylammonium bromide (CTAB) was prepared using a solid‐state dispersion method. The dispersion of modified
(V2O5‐TiO2)‐CTAB were successfully enhanced. CTAB was innovatively introduced into the system of V2O5‐TiO2. This catalyst efficiently
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