Preparation, characterization and photocatalytic properties of InVO 4 nanopowder and InVO4-TiO2 nanocomposite toward degradation of azo dyes and formaldehyde under visible light and ultrasonic irradiation

Article abstract of DOI:10.1007/s13738-012-0191-3

In this study, photocatalytic activity of InVO₄ and InVO ₄-TiO₂ nanoparticles in the degradation of aqueous solutions of industrial textile azo dyes such as Solophenyl Red 3BL, Coperoxon Nevy Blue RL and Black Nilusun 2BC (abbreviated as SR 3BL, CNB RL and BN 2BC, respectively) and also formaldehyde (abbreviated as FAD) under visible light and ultrasonic irradiations has been compared. The effect of various parameters such as pH, temperature, irradiation time, amounts of nanophotocatalyst and nanocomposite, and ultrasonic intensity on degradation rates was investigated. Then based on the Langmuir-Hinshelwood approach, reaction rates and adsorption equilibrium constants were calculated. The nanophotocatalyst and nanocomposite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectroscopic methods. It was observed that InVO ₄-TiO₂ nanopowder was more reactive than pure InVO ₄ in the degradation of azo dyes under both conditions of visible light and ultrasonic irradiations. It was noticeable that degradation percent was more under ultrasonic irradiation rather than under visible light irradiation.

Full text of DOI:10.1007/s13738-012-0191-3

J IRAN CHEM SOC (2013) 10:535–544
DOI 10.1007/s13738-012-0191-3
ORIGINAL PAPER
Preparation, characterization and photocatalytic properties
of InVO nanopowder and InVO –TiO nanocomposite toward
4
4
2
degradation of azo dyes and formaldehyde under visible light
and ultrasonic irradiation
Somayeh Dianat
Valiollah Mirkhani
Iraj Mohammadpoor-Baltork
•
Shahram Tangestaninejad
•
•
Majid Moghadam
•
Received: 5 May 2011 / Accepted: 9 November 2012 / Published online: 18 December 2012
Ó Iranian Chemical Society 2012
Abstract In this study, photocatalytic activity of InVO4
and InVO –TiO nanoparticles in the degradation of aque-
Introduction
4
2
ous solutions of industrial textile azo dyes such as Sol-
ophenyl Red 3BL, Coperoxon Nevy Blue RL and Black
Nilusun 2BC (abbreviated as SR 3BL, CNB RL and BN
Azo dyes constitute the largest class of dyes used in textile
industry. It is estimated that 10–15 % of these dyes is lost
during the dyeing process and released as effluent. One of
the problems associated with azo dyes is their resistance
towards aerobic degradation; however, under anaerobic
conditions, the azo bond is reduced and generates aromatic
amines that are colorless but can also be toxic and poten-
tially carcinogenic. New developments in advanced oxi-
dation processes (AOPs) are focused on providing a
promising and competitive solution for the abatement of
numerous hazardous compounds in wastewater. These
methods include Fenton or photo-assisted Fenton process,
ozone and/or peroxide photolysis, semiconductor photo-
catalysis process, and ultrasonic cavitation [1–7]. The ini-
tial step in the AOPs is the generation of high reactive
hydroxyl radicals which are suitable for the complete
elimination and full mineralization of various pollutants
such as phenols [8], chlorophenols [9], pesticides, [10] and
azo dyes [11].
2
BC, respectively) and also formaldehyde (abbreviated as
FAD) under visible light and ultrasonic irradiations has been
compared. The effect of various parameters such as pH,
temperature, irradiation time, amounts of nanophotocatalyst
and nanocomposite, and ultrasonic intensity on degradation
rates was investigated. Then based on the Langmuir–
Hinshelwood approach, reaction rates and adsorption equi-
librium constants were calculated. The nanophotocatalyst
and nanocomposite were characterized by X-ray diffraction
(
XRD), scanning electron microscopy (SEM) and UV-Vis
spectroscopic methods. It was observed that InVO –TiO
4
2
nanopowder was more reactive than pure InVO in the
4
degradation of azo dyes under both conditions of visible
light and ultrasonic irradiations. It was noticeable that
degradation percent was more under ultrasonic irradiation
rather than under visible light irradiation.
Sonochemical degradation of organic pollutants has
been extensively studied in recent years [12–17]. The
chemical effects of high-intensity ultrasound primarily
result from cavitation phenomena (the formation, growth,
and collapse of bubbles in liquids) [18]. These phenomena
generate locally high temperatures and pressures for short
period of time, which in turn produce radical species
Keywords Photocatalyst ꢀ Degradation ꢀ Azo dye ꢀ
InVO ꢀ InVO –TiO ꢀ Ultrasonic irradiation
4
4
2
ꢀ ꢀ ꢀ
H , HO , HOO ) by sonolysis of H O. These radicals
2
(
directly destruct the solute [14, 19, 20].
Heterogeneous photocatalysis by visible light irradiation
on a semiconductor surface is an attractive advanced oxi-
dation process [7]. The adsorbed organic molecules in a
reaction are mineralized into carbon dioxide and water by
hydroxyl radicals or superoxide radical anions. These
S. Dianat ꢀ S. Tangestaninejad (&) ꢀ V. Mirkhani ꢀ
M. Moghadam ꢀ I. Mohammadpoor-Baltork
Catalysis Division, Department of Chemistry,
University of Isfahan, 81746-73441 Isfahan, Iran
e-mail: stanges@sci.ui.ac.ir
123

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J IRAN CHEM SOC (2013) 10:535–544
(
(
1)
2)
(
(
3)
4)
Scheme 1 Mechanism for decomposition of FAD under visible light and ultrasonic irradiation
active species are produced by the reaction of water with
valence band holes, and/or oxygen with conduction band
electrons when a photocatalyst absorbs light with greater
energy than its band gap. It is known that the photocatalytic
process occurs at the surface or within a few monolayers
around catalyst particles [21]. Oxides of transition metals
are widely applied as photocatalysts, but the activity
decline is frequently encountered because the electron–
hole charge recombination occurs on the oxide surface
within nanoseconds [22]. The efficiency of a photocatalytic
process can be influenced by many factors. For example,
the pH change in an aqueous solution can modify the
ionization state of the catalyst surface due to the estab-
lishment of acid–base equilibrium [11, 23]. The ionization
state change affects not only the adsorption mode of
reaction molecules, but also the selectivity of the reaction
Preparation of orthogonal InVO nanoparticles
4
A solution of NaVO
into a solution of InCl
(6.1 ml, 1 M) was added dropwise
(5.5 ml, 1 M) by vigorous stirring.
3
3
The pH of the solution was adjusted to about 7.9 using
NaOH solution (2 M). The solution was stirred for 80 min
and transferred into polytetrafluoroethylene reaction ves-
sels and kept at 150 °C for 4 h. After cooling to room
temperature, the powders were collected by filtration,
washed with deionized water several times and dried at
60 °C [28].
Preparation of InVO
–TiO nanocomposite
2
4
A typical method for the preparation of InVO
–TiO
2
4
nanocomposites is as follows: titanium tetraisopropoxide
(TTIP, 98 %, 20 mmol) was dissolved in isopropyl alcohol
[
24], since redox reactions in the photochemical process
are sensitive to variations in the surface potential [25].
Furthermore, addition of a proper electron-acceptor or
(392 mmol). A suspension of InVO (0.13 mmol) in water
4
(44 mmol), was added dropwise into the TTIP solution.
The pH of the resulting mixture was adjusted to 1–2 using
HCl solution (8 M) and stirred at room temperature for 1 h.
The mixture was heated to 45 °C until homogeneous
-
donor to the reaction solution inhibits the electron–hole
recombination and therefore increases the photocatalysis
efficiency [11].
The semiconductor InVO4 has narrow band gap of
InVO
–TiO hydrogel was formed. The hydrogel was
4 2
2
.0 eV [26, 27], which is able to induce hydrolysis of water
transferred into an autoclave, and heated up to 200 °C with
-
1
molecules under visible light. In this work, the photocata-
lytic activity of InVO4 nanoparticles and InVO –TiO
a rate of 2 °C min . Finally, the temperature was kept at
200 °C for 1 h. The hydrogel was cooled to room tem-
perature and dehydrated slowly at 50 °C in vacuum for
24 h. The dried gel was washed with hot water and dried at
room temperature.
4
2
nanocomposite in the degradation of azo dyes under visible
light and ultrasonic irradiation is compared.
Experimental
Estimation of the point of zero charge (PZC) of InVO
and InVO –TiO
4
4
2
Materials
PZC of prepared catalyses was estimated according to the
pervious literature [29].
Indium chloride (InCl /Aldrich), sodium metavanadate
3
(
NaVO /Merck), sodium hydroxide (NaOH/Merck), tita-
3
nium tetraisopropoxide (TTIP, 98 %, Merck), isopropyl
alcohol (Merck), SR 3BL (Ciba-Geigy), CNB RL (Merck),
and BN 2BC (Merck) were used as received without fur-
ther purifications. The pH value of solutions was adjusted
Instrumentation
The crystal structures of the catalysts (InVO
and InVO –
4
4
TiO ) were investigated by X-ray diffraction (X-ray dif-
2
-
1
-1
with 0.05 mol L HCl and 0.2 mol L NaOH solutions
and doubly distilled water was used for dye solution
preparation.
fractometer, Bruker, D8ADVANCE, Germany) with Cu
Ka radiation. Scanning electron micrographs (SEM) were
carried out with a Philips XL30 field emission microscope
1
23

J IRAN CHEM SOC (2013) 10:535–544
537
using an acceleration voltage of 20 kV. The specific sur-
face area of catalysts were determined by BET (Brunauer–
Emmett–Teller) measurement were carried out at low
the amount of photocatalyst used for degradation of dyes
(5 mg), no adsorption and/or degradation were observed in
the dark. Based on these results, we concluded that the
presence of visible light has a significant role in the deg-
radation of dyes. Besides, control experiments involving a
solution of azo dyes under visible light or ultrasonicate
irradiation in the absence of each photocatalyst were car-
ried out. The results showed that in the absence of photo-
catalyst, no degradation was observed. The lamp was
inserted around the suspension after its intensity became
stable. Photodegradation of dye was carried out in an open
vessel in the batch photoreactor. After the reaction was
over, the photocatalyst was filtered, and the photolyte was
temperature by adsorption of N gas with an ASAP 2000
2
micromeritics instrument.
The diffuse reflectance UV–Vis experiments were per-
formed on a Varian Lary 5E diode array spectrometer
equipped with a 60-mm Hitachi integrating sphere acces-
sory. The pH values of the solutions were measured using a
digital pH-meter (Metrohm 827). The pH-meter was cali-
brated with standard buffers at 25 °C (pH 4.0 and 7.0). The
UV–Vis spectra of the solutions were recorded by a
UV–Vis spectrophotometer (160 Shimadzu, Japan). The
mineralization percent of azo dyes was estimated by total
organic carbon (TOC) analysis. In this regard, TOC curves
were obtained with a Beckman 915A analyzer.
analyzed by UV–Vis spectrophotometer at its kmax
.
In the case of FAD, 100 mg of catalyst was added to
10 ml of 1,000 ppm solution in a photochemical cell. The
mixture then was exposed to visible light for 120 min.
Photodegradation experiments
General procedure for degradation of azo dyes
under ultrasonic irradiation
The SR 3BL, CNB RL and NB 2BC dyes solutions were
prepared by dissolving 0.02, 0.05 and 0.10 g of dyes in 1 L
of deionized water, respectively. A photoreactor was
designed with a cylindrical quartz cell configuration and an
internal light source surrounded by a quartz jacket, where
the suspension of the catalyst and aqueous dyes completely
surrounded the light source. The temperature of the sus-
pension was maintained at 25 ± 1 °C by water circulation
through an external cooling coil. The optical pathlength
was ca. 2 cm. The light source was a 400 W Na lamp
A UP 400S ultrasonic processor equipped with a 3 mm
wide and 140 mm long probe, immersed directly into the
reaction mixture, was used for sonication. The operating
frequency was 24 kHz and the output power was 0–400 W
through manual adjustment. The total volume of the solu-
tion was 10 ml.
InVO or InVO –TiO (5 mg) was suspended in fresh
4
4
2
aqueous dye solution (10 mL). Then, the solution was
sonicated by ultrasonic waves. Photodegradation of dye
was carried out at atmospheric pressure in a batch photo-
reactor. The temperature of the suspension was maintained
at 25 ± 1 °C by water circulation through an external
cooling coil. After the reaction was done, the photocatalyst
was filtered, and the photolyte was analyzed by UV–Vis
spectrophotometer at kmax for each dye.
(
k [ 450 nm).
A general photocatalytic method was carried out as the
following: InVO or InVO –TiO (5 mg) was suspended in
4
4
2
fresh aqueous dye solution (10 ml). The suspension was
stirred in the dark for 30 min to investigate the amount of
dispersion and adsorption in the absence of light. Due to
The degradation efficiency (%) was calculated by
following formula:
Efficiencyð%Þ ¼ ðC0 ꢁ C=C0Þ ꢂ 100
ð1Þ
where C is the initial dyes concentration and C is the
0
concentration of dyes after irradiation.
Kinetic measurements for degradation of azo dyes
The degradation rate of SR 3BL, CNB RL and NB 2BC at
any specified condition was followed by spectrophoto-
metric measurements with the time profile of the absor-
bance being at their kmax (according to Table 2). All of the
measurements were done three times and the mean values
of data were reported.
The observed pseudo-first order degradation rate con-
stants, kobs, can be calculated from the slopes of the
4 2 2
Fig. 1 XRD patterns of a InVO , b InVO4–TiO and c TiO
123

5
38
J IRAN CHEM SOC (2013) 10:535–544
for calculation of the mean crystallites size. In Fig. 1b, five
distinctive TiO peaks are found at 25.3°, 37.9°, 48.0°,
2
5
4.6° and 62.8°, which correspond to anatase (101), (103,
004 and 112), (200), (105 and 211), (204) crystal planes,
respectively. This XRD pattern is the same as XRD pattern
of pure TiO (Fig. 1c), which indicates that the TiO has
2
2
retained its crystallinity upon mixing with InVO and no
4
change in its crystallinity was observed during the prepa-
ration of nanocomposite. According to XRF results, the
amount of InVO is low (\5 %) and obviously it does not
4
present in the XRD pattern of InVO –TiO .
4
2
The crystal size of the InVO and InVO –TiO species
4
4
2
were calculated by Scherer equation. The particle sizes
were about 39–45 nm and 12–15 nm for InVO4 and
InVO –TiO , respectively, which demonstrate that these
4
2
compounds are nanoparticles. The BET specific surface
2
area (92 m /g) of the InVO –TiO is larger than those of
4
2
2
the pure TiO (64 m /g) and pure InVO (18.3 m /g).
2
2
4
Figure 2 presents the SEM images of both pristine
InVO and InVO coated with TiO . As shown in Fig. 2a,
4
4
2
b, both photocatalysts have the sizes in nanometer range.
The size of the InVO particles treated with TiO is similar
4
2
to that of the pristine InVO . However, the surface of the
4
TiO -coated InVO was smoother compared with that of
2
4
pristine InVO4.
Figure 3 shows the UV–Vis diffusion reflectance spectra
of InVO and InVO –TiO photocatalysts. In comparison
4
4
2
with InVO –TiO whose absorption edge is about 520 nm,
4
2
the InVO showed an obvious absorption in visible light
4
region at 650 nm. The band gap of the compound, which
was estimated from the absorption edge, is about 2.0 eV.
This value is much narrower than observed values for the
4 4 2
Fig. 2 SEM images of a InVO , b InVO –TiO
natural-logarithmic plots of the drug fraction remained
versus time in accordance with Eq. (2):
4d (4th row transition metals) compounds such as InNbO
2.5 eV) and 5d (5th row transition metals) compounds
such as InTaO (2.6 eV) [30]. In addition, the absorption
4
(
lnðCt=C0Þ ¼ ꢁkobst
where C is the initial concentration and C is the remaining
ð2Þ
4
0
t
concentration of azo dye at time t. According to the Beer-
Lambert law, the absorption (A) of a dissolved substance is
a linear function of its concentration. Therefore, the
pseudo-first order rate constants, kobs, were calculated from
the slopes of the natural-logarithmic plots of absorption
versus time.
1
.2
1.0
0.8
0
0
0
.6
.4
.2
Results and discussion
Catalysts characterization
The XRD technique was used to investigate the phase
structures of the samples. The XRD pattern of the as-pre-
pared InVO , InVO –TiO and TiO samples are shown in
0.0
2
00
300
400
500
600
700
800
Wavelength (nm)
4
4
2
2
Fig. 1. The XRD peaks in Fig. 1a correspond to the
Fig. 3 UV-vis diffusion reflectance spectra of InVO
InVO –TiO (dash line)
4
(solid line) and
orthorhombic phase of InVO . The peak at 32.9° was used
4
4
2
1
23

J IRAN CHEM SOC (2013) 10:535–544
539
Table 1 Structure and characteristics of azo dyes
-
1
)
Name
Structure
MW (g mol
1,373
k
max(nm)
Dye concentration
-
1
)
(
mg L
SR 3BL
530
570
20
SO Na
O
H
3
NCOH
NaSO3
N
N
N
N
NaSO3
2
CNB RL
1,110
50
MeO
N
NH2 OH
N
2N
H
SO Na
3
N
N
N
N
N
COONa
2
NB 2BC
731.26
570
100
N
N
N
N
N
H
SO Na
3
NaSO3
edge of InVO –TiO is more than pristine TiO (absorption
4
Table 2 The optimum values of different factors for degradation of
SR 3BL, CNB RL and BN 2BC at different conditions
2
2
edge *400 nm), that demonstrates coating InVO4 with
TiO cause to improve TiO band gap.
2
2
Conditions
Azo dye Visible light
Ultrasonic
irradiation
Degradation of azo dyes
InVO
4
InVO
TiO
4
–
InVO
4
InVO
TiO
4
–
2
2
Table 1 summarized the structure, characteristics and
concentration of the azo dyes.
pH
SR 3BL
3.0
7.2
7.4
7.4
15
15
15
25
25
25
5
3.1
3.8
3.3
1
7.2
7.4
7.4
1
CNB RL 3.5
BN 2BC 3.1
First, the reaction parameters (i.e., pH, irradiation time,
temperature, amount of catalyst, and ultrasonic intensity)
were optimized and their optimum values are presented in
Table 2.
Irradiation
time (min)
SR 3BL
15
CNB RL 15
BN 2BC 15
1
1
1
1
Temperature
(
SR 3BL
25
25
25
25
5
25
Effect of pH
°C)
CNB RL 25
BN 2BC 25
25
25
5
In Fig. 4, the degradation efficiency of CNB RL in the
presence of InVO and InVO –TiO under visible light and
Catalyst amount SR 3BL
5
5
5
–
–
–
4
4
2
(
mg)
CNB RL
BN 2BC
SR 3BL
CNB RL
BN 2BC
5
5
5
ultrasonic irradiation at different pH values is shown.
Similar patterns were obtained for other azo dyes that due
to brevity are not shown here. It was found that the deg-
radation of these dyes by InVO and InVO –TiO are pH
5
5
5
Ultrasonic
intensity (%)
–
100
100
100
100
100
100
–
4
4
2
–
dependent and increased by decreasing pH. This can be
explained by the point of zero charge (PZC) of InVO and
4
InVO –TiO nanopowders and a difference in the adsorp-
4
2
tion ability of InVO and InVO –TiO nanoparticles. In
2
charged, below these, it is positively charged. The ionic
compounds like SR 3BL, CNB RL and BN 2BC bearing
negative charge can easily be adsorbed on the surface
4
4
general, the PZC of InVO and InVO –TiO nanopowders
4
4
2
are almost at pH 4.9 and 7.8, respectively. While above
these pH values, the surface of these catalysts is negatively
of InVO
and InVO –TiO below pH 4.9 and 7.8,
4 4 2
123

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J IRAN CHEM SOC (2013) 10:535–544
100
8
0
0
0
0
6
4
2
Vis, InVO4
US, InVO4
Vis, InVO - TiO2
4
US, InVO - TiO2
4
0
2
4
6
8
10
pH
Fig. 4 Influence of the initial pH on the degradation percent of CNB
-
RL (50 mg L ) solution in various conditions
1
respectively. Moreover, the degradation of SR 3BL, CNB
RL and BN 2BC in acidic medium is favorable and due to
the electrostatic repulsion, the adsorption ability of InVO4
and InVO –TiO nanoparticles rapidly decreases in basic
4
2
medium.
Effect of the time
-
1
The degradation percent of 50 mg L CNB at optimum pH
values by InVO and InVO –TiO under visible light and
4
4
2
ultrasonic irradiations is shown in Fig. 5a, b, respectively.
The degradation percent under visible light in the presence
of InVO powder increased by increasing the irradiation
4
time and after 5 min, the degradation yield of CNB RL was
about 42 %. While due to the synergistic effect between the
two phases, the degradation percent in the presence of
InVO –TiO powder was 98 % at the same time. In addi-
Fig. 5 Influence of irradiation time on degradation percent of CNB
-
RL (50 mg L ) solution under a visible light and b ultrasonic
1
irradiation
4
2
tion, there was an increase in the photocatalytic activity of
InVO and InVO –TiO under ultrasonic irradiation than
4
4
2
5
4
3
2
visible light irradiation. The chemical effect of high inten-
sity ultrasound primarily results from acoustic cavitation:
the formation, growth, and impulsive collapse of bubbles in
liquids. Ultrasound affected the degradation rate of organic
dyes from three different phenomena. First of all, ultrasound
may induce the deaggregation of the photocatalyst, leading
to an increase in its surface and thus in its catalytic perfor-
mance. Then, it induces mass transport acceleration of
chemical species between the solution phase and the pho-
tocatalyst surface and vice versa. The main effect of ultra-
sound is to contribute through cavitation to scissor the H O
1
Vis, InVO4
2
2
Vis, InVO -TiO2
4
produced by this method. Thus, ultrasonic irradiation pro-
motes the generation of radicals in the reaction media. On
the other hand, collapse of the produced bubbles results in
generation of high temperature and pressure. Therefore, the
reaction can be accelerated under ultrasonic irradiation [31].
0
0
2
4
6
8
10
12
14
16
Time (min)
-1
Fig. 6 Initial degradation of CNB RL (50 mg L ) solution at 25 °C
in the presence of InVO and InVO –TiO at kmax (570 nm)
4
4
2
1
23

J IRAN CHEM SOC (2013) 10:535–544
541
Table 3 Pseudo-first order degradation rate constants (k) for the
photodegradation of different azo dyes under visible light and ultra-
sonic irradiation in presence of InVO and InVO –TiO
1
00
4
4
2
8
6
4
0
0
0
Azo dye
Visible light
Ultrasonic
irradiation
InVO4
InVO4-TiO2
InVO
k (min
4
InVO
k (min
4
–TiO
-1
2
InVO
-1
k (s
4
4 2
InVO –TiO
-1
k (s )
-1
)
)
)
SR 3BL
(
0.0969
0.0582
0.0506
0.164
0.035
0.011
0.006
0.011
0.002
0.002
-
-
1
1
20
0
20 mg L
)
CNB RL
(
0.055
0.067
50 mg L
)
2
0
50
80
100
BN 2BC
(
-3
Ultrasonic density (W Cm )
-
1
100 mg L )
Fig. 8 Influence of ultrasonic power on degradation percent of CNB
-
RL (50 mg L ) solution
1
Kinetics study Figure 6 shows the variations of ln(C /C )
0
was investigated in the range of 25–80 °C. The results
showed that temperature effect on degradation yield is
negligible. Thus, the 25 °C was introduced as optimum
temperature. The influence of temperature on degradation
percent of CNB RL under different conditions is shown in
Fig. 7.
t
-
1
at kmax versus time for CNB RL (50 mg L ) solution at
5 °C in the presence InVO and InVO –TiO under vis-
2
4
4
2
ible light. The high correlation coefficient of lines can be
taken as pronounced evidence for pseudo-first order deg-
radation kinetics. Similar plots have been obtained for SR
-
1
-1
3
BL (20 mg L ), and BN 2BC (100 mg L ). The values
of observed pseudo-first order rate constants, kobs, for these
azo dyes under visible light and ultrasonic irradiations were
collected in Table 3.
Effect of catalyst amount
The effect of InVO
and InVO –TiO nanopowders amounts
4 2
4
-1
on the photocatalytic degradation of SR 3BL (20 mg L ),
-1
-1
Effect of temperature
CNB RL (50 mg L ), BN 2BC (100 mg L ) at optimum
pH values and using different amounts of photocatalysts
(3–30 mg) was also studied. The results showed that the
-1
-1
The prepared SR 3BL (20 mg L ), CNB RL (50 mg L ),
-1
and BN 2BC (100 mg L ) at optimum pH values were
treated with InVO and InVO –TiO (5 mg) nanopowders
optimum amount of InVO and InVO –TiO catalysts for
4 4 2
the degradation of these azo dyes under visible and ultra-
sonic irradiations was 5 mg. Indeed, the number of
absorbed photons and the number of dye molecules
adsorbed increased by an increase in the amount of catalyst
4
4
2
and exposed to visible light and ultrasonic irradiations for
5 and 1 min, respectively. The effect of temperature on
1
the degradation percent of SR 3BL, CNB RL and BN 2BC
Fig. 7 Influence of temperature
on degradation percent of CNB
1
00
-
RL (50 mg L ) solution
1
8
6
4
2
0
0
0
0
0
Vis, InVO4
US, InVO4
Vis, InVO4-TiO2
US, InVO4-TiO2
2
5
45
65
80
Temp (°C)
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J IRAN CHEM SOC (2013) 10:535–544
-
1
Table 5 Degradation percent of FAD (1,000 mg L ) by InVO
InVO –TiO nanopowders under visible light for 120 min
4
and
4
3
2
1
0
0
0
0
0
4
2
Catalyst
Degradation (%)
InVO
InVO
4
4
64.25
83.17
–TiO
2
increased by increasing the irradiation time (Fig. 9 and
Table 4). The absorbance and TOC measurements indi-
cated that degradation of the dye molecule is a relatively
fast process but overall degradation is not.
Degradation of FAD
0
50
100
150
200
250
Time (min)
-
1
To a solution of FAD (1,000 mg L ) with the acidic pH,
catalyst (100 mg of InVO or InVO –TiO ) was added and
Fig. 9 TOC reduction during the degradation of BN 2BC at pH 3.3
mediated by combined heterogeneous photocatalysis under visible
light, induced by InVO
4
4
2
exposed to visible light for 120 min. The data are listed in
Table 5. It was observed that InVO –TiO was more efficient
4
4
2
in comparison with InVO nanopowder. The higher photo-
4
Table 4 Degradation and mineralization efficiency of BN 2BC
under visible light after prolonged
-
1
catalytic activity of InVO –TiO can be illustrated by syn-
4
2
(100 mg L , pH 3.3) by InVO
time of irradiation
4
ergistic effect. Scheme 1 has been proposed for FAD
degradationunder visiblelightandultrasonicirradiation[32].
Time of
irradiation
Absorbance TOC
(mg L
Degradation Mineralization
(%)
-
1
)
(%)
HCHO þ ꢀOH ! ꢀCHO þ H2O
ð1Þ
ð2Þ
(
min)
ꢀ
ꢀ
CHO þ ꢀOH ! HCOOH
0
0.525
0.016
0.015
0.010
0.005
39.1
17.3
13.1
9.2
–
–
ꢁ
þ
CHO þ ꢀO ꢁ! þ H HCOOOH ꢁ! þ HCHOHCOOH
2
3
6
0
0
96.9
97.1
98.1
99.0
55.7
66.5
76.5
87.0
ð3Þ
ð4Þ
ꢁ
1
2
20
40
HCOOH ꢁ! ꢀ OH or O H2 þ CO2:
2
5.1
Relation between phase composition and photocatalytic
activity
which in turn enhanced the degradation percent. In addi-
tion, the degradation percent increased slightly under
Considering the consistency of photocatalytic activities and
phase compositions, higher photocatalytic activities of
ultrasonic irradiation and in the presence of InVO –TiO2
4
nanopowder by increasing the amount of catalyst.
Effect of ultrasonic intensity
mixed-phase TiO can be ascribed to the synergistic effect.
2
On one hand, as confirmed in Fig. 2, the stronger photo-
absorption of InVO in the range of wavelengths 650 nm
4
provides more probabilities to promote electrons from
valence band into conductive band, which is favorable to
produce more electron–hole pairs and hence to form more
active hydroxyl and oxygen anion free radicals. On the
other hand, in InVO –TiO , the electron transfer from
An ultrasonic horn (24 kHz) with different power from 20
-
3
to 100 Wcm were used to study the effect of US inten-
-
sity on the degradation of SR 3BL (20 mg L ), CNB RL
1
-
50 mg L ), and BN 2BC (100 mg L ) at optimum pH
1
-1
(
4
2
values by InVO and InVO –TiO . As shown in Fig. 8, the
4
InVO to TiO phase can reduce the recombination of
4
4
2
2
effect of US intensity on the degradation of CNB RL is
negligible. For two other azo dyes similar results were
obtained.
photogenerated charges. As shown in Fig. 10a, this is
because the conductive band of TiO locates at a higher
2
energy position than that of InVO . Since InVO has a
4
4
stronger photoabsorption than TiO , there will be more
2
Mineralization
photogenerated carriers in it. For the photocatalysis fol-
lowing free radical mechanism, hydroxyl free radicals are
formed by oxidating hydroxyl groups with photogenerated
holes. According to the mechanism of photodecomposing
FAD and azo dyes (in Fig. 10b, c), more hydroxyl free
The total organic carbon (TOC) of BN 2BC solution was
monitored during 4 h irradiation with visible light with
InVO . It was observed that the total mineralization
4
1
23

J IRAN CHEM SOC (2013) 10:535–544
543
Fig. 10 Representation of the
drive electron transfer and
relative photocatalysis
reactions. a Bands positions of
InVO
bands bending of InVO
TiO during degradation of azo
4
and TiO
2
, b the surface
4
and
2
dyes and FAD, c mineralization
of azo dyes and FAD by oxygen
anion free radicals on the
surface of TiO
2
radicals are consumed during the formation of formic acid
and dyeOX, suggesting that more photogenerated holes are
consumed. Combined with its faster rate of forming formic
acid than TiO , more photogenerated electrons will tem-
2
porarily accumulate in InVO . As presented in Fig. 8b, this
4
accumulation of electrons leads to a bigger bending
123

5
44
J IRAN CHEM SOC (2013) 10:535–544
(
upward shift) of conductive band in InVO than that in
4
2. R. Andreozzi, V. Caprio, A. Insola, R. Marotta, Catal. Today 53,
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1 (1999)
TiO and makes the electron transfer from InVO to TiO
2
2
4
3
. J.-M. Herrmann, Catal. Today 53, 115 (1999)
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37, 1 (2002)
feasible as expected. After the electron transfer from InVO4
4
to TiO , oxygen anion free radicals are formed on the sur-
2
face of TiO phase (Fig. 10c). Due to their strong Lewis
2
5. K. Pirkanniemi, M. Sillanp a¨ a¨ , Chemosphere 48, 1047 (2002)
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. P.R. Gogate, A.B. Pandit, Adv. Environ. Res. 8, 501 (2004)
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base characteristics, formic acid molecule and dyeOX can be
adsorbed more easily on TiO phase. The electron transfer
2
not only inhibits the recombination of photogenerated
charges, but is also favorable for adsorbed compounds to be
further oxidized. This can be considered as the activation
9. M. Pera-Titus, V. Garcı
´a-Molina, M.A. Ba n˜ os, J. Gim e´ nez,
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1
effect by TiO . Therefore, the relation between phase
2
(
composition and photocatalytic activity can be ascribed to
maximizing the synergistic effect in InVO –TiO .
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4
2
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Conclusion
1
1
1
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Heterogeneous photocatalytic oxidation process using vis-
ible light and ultrasonic irradiations can be efficiently
applied for the degradation of non-biodegradable azo dyes
(
2007)
19. C. Petrier, M.-F. Lamy, A. Francony, A. Benahcene, B. David,
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-
1
-1
such as SR 3BL (20 mg L ), CNB RL (50 mg L ) and
-
1
BN 2BC (100 mg L ). The results clearly delineate the
important role of the reaction conditions in achieving the
highest degradation efficiency. Photodegradation rate was
found to reach maximum value at acidic and neutral med-
ium with 5 mg amount of InVO and InVO –TiO . The
D.K. Sharma, J. Am. Chem. Soc. 107, 8054 (1985)
2
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4
4
2
comparison of photocatalytic activity of InVO and InVO –
4
4
2
TiO clearly indicated that InVO –TiO is more efficient for
2
2
4
degradation of these azo dyes. Moreover, the photocatalytic
activity of InVO –TiO is greater in the presence of ultra-
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4
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sonic irradiation compared to visible light irradiation. The
photocatalytic degradation shows pseudo-first order kinet-
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3
2
3
3
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Acknowledgments The authors gratefully acknowledge the finan-
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(2008)
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