Dichloro (1,10-phenanthroline-5,6-dione) palladium (II) complex supported by mesoporous silica SBA-15 as a photocatalyst for degradation of 2,4-dichlorophenol

Article abstract of DOI:10.1016/j.molstruc.2014.08.024

A new photocatalyst, dichloro (1,10-phenanthroline-5,6-dione) palladium (II) complex supported on SBA-15 silica was synthesized by ship-in-a-bottle method. The products obtained were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), Ultraviolet-Visible spectroscopy (UV-Vis), ¹H NMR spectroscopy, N₂adsorption-desorption and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The band gap energy of the complex was determined by the diffuse reflectance spectroscopy (DRS) and density functional theory (DFT) calculation, indicating that it can be considered appropriate candidate for photocatalytic activity in the region of solar spectrum. The results indicated improved photocatalytic efficiency for the complex supported on SBA-15 silica compared to the pure complex. To improve photocatalytic activity, the effect of complex loading and optimal synthesis conditions were investigated.

Full text of DOI:10.1016/j.molstruc.2014.08.024

Journal of Molecular Structure 1076 (2014) 568–575
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Journal of Molecular Structure
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Dichloro (1,10-phenanthroline-5,6-dione) palladium (II)
complex supported by mesoporous silica SBA-15
as a photocatalyst for degradation of 2,4-dichlorophenol
b
a
A. Abolhosseini Sh. a, A.R. Mahjoub a, , M. Eslami-Moghadam , H. Fakhri
⇑
a Tarbiat Modares University, P. O. Box 14155-4383, Tehran, Iran
b Chemistry & Chemical Engineering Research Center of Iran, Tehran, Iran
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
A new photocatalyst, dichloro (1,10-phenanthroline 5,6-dione) palladium (II) complex was synthesized
and characterized. The band gap energy of the complex was determined by the experimental technique
and theoretical calculation, indicating that it can be considered as a good photocatalyst for photodegra-
dation of phenolic compound in the visible region of solar spectrum.
ꢀ
ꢀ
ꢀ
Dichloro (1,10-phenanthroline-5,6-
dione) palladium (II) complex has
been successfully synthesized in
various condition.
Complex/SBA-15 showed higher
efficiency than pure complex in the
degradation of 2,4-dichlorophenol
under visible light.
Complex/SBA-15 can be easily
separated from water and recycled.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2014
Received in revised form 11 August 2014
Accepted 13 August 2014
Available online 23 August 2014
A new photocatalyst, dichloro (1,10-phenanthroline-5,6-dione) palladium (II) complex supported on
SBA-15 silica was synthesized by ship-in-a-bottle method. The products obtained were characterized
by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron
microscopy (SEM), Ultraviolet–Visible spectroscopy (UV–Vis), 1H NMR spectroscopy, N2 adsorption–
desorption and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The band gap
energy of the complex was determined by the diffuse reflectance spectroscopy (DRS) and density func-
tional theory (DFT) calculation, indicating that it can be considered appropriate candidate for photocat-
alytic activity in the region of solar spectrum. The results indicated improved photocatalytic efficiency for
the complex supported on SBA-15 silica compared to the pure complex. To improve photocatalytic activ-
ity, the effect of complex loading and optimal synthesis conditions were investigated.
Keywords:
Dichloro (1,10-phenanthroline-5,6-dione)
palladium (II) complex
Photocatalytic activity
SBA-15
Ó 2014 Elsevier B.V. All rights reserved.
DFT calculation
Visible light
Introduction
⇑
Corresponding author. Tel.: +98 21 82883442; fax: +98 21 82883455.
E-mail addresses: a.abolhosseini@modares.ac.ir (A. Abolhosseini Sh.),
mahjouba@modares.ac.ir (A.R. Mahjoub).
Chlorinated phenolic compounds comprise a group of organic
pollutants that are resistant to degradation and have been used
http://dx.doi.org/10.1016/j.molstruc.2014.08.024
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
569
tion, and subsequently recycle the photocatalyst [13,14]. Palladium
can be placed on various supports such as carbon nanotubes [15],
graphene [16], metal–organic coordination polymer [17], fullerene
(C60) [18], functionalized mesoporous polymer [14], and mesopor-
ous silica materials [19]. However, as solid support in a typical cat-
alytic reaction silica is a proper choice, because of its wide
accessibility, excellent stability, porosity, and the fact that organic
groups can be robustly anchored to its surface to generate catalytic
sites [20]. SBA-15 is one of the most common ordered mesoporous
materials [21,22]. SBA-15 has better structural stability than MCM-
41, because of its considerably thicker pore walls [23]. This makes
SBA-15 as an appropriate support that can facilitate dispersion of
desired catalyst in a catalytic process. The dichloro (1,10-phenan-
throline) platinum (II) complex is considered as a suitable candi-
date for photocatalytic activity in the visible light irradiation
(sunlight) and tested as a photosensitizer for photodegradation of
4-chlorophenol [24]. In the current work, we investigated dichloro
(1,10-phenanthroline-5,6-dione) palladium (II) complex (Com)
supported onto mesoporous silica SBA-15 as a photocatalyst for
photodegradation of 2,4-dichlorophenol in the aqueous solution.
Fig. 1. FT-IR spectra of complex (a), parent SBA-15 (b), and Com/SBA-15 (c).
historically as wood preservatives, anti-rusting agents, herbicides,
and pesticides [1]. Among these, 2,4-dichlorophenol (2,4 DCP) has
been listed by the US Environmental Protection Agency (EPA) as a
priority environmental pollutant [2]. With direct irradiation, this
material produces organic compounds such as polychlorinated
dibenzo-p-dioxins that are more hazardous than the parent com-
pound [3]. Many efforts have been made to eliminate this toxic
chemical. Among various methods, photocatalytic technique has
become one of the main approaches in this field [4-7]. ZnO and
TiO2 are known as the best photocatalysts due to nontoxic nature,
chemical stability and high photosensitivity [8,9]. However, their
photocatalytic efficiencies decline because of fast recombination
of electron-hole pairs during their wide band gaps. Moreover, the
photocatalysts can be activated only by ultraviolet irradiation that
comprises less than 5% of the sunlight [10]. So, considerable
researches have been undertaken to use materials with a narrow
band gap adapted to the visible light that comprises more than
45% of the sunlight [11,12]. Supporting photocatalysts improve
photocatalytic efficiency because they can help increase the active
surface area of the photocatalyst, achieve more efficient separa-
Experimental
Chemicals
1,10-Phenanthroline-5,6-dione (phendione) was prepared
according to the method considered in the literature [25]. Pluronic
P123 (poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene
oxide) (EO20–PO70–EO20) was obtained from Sigma–Aldrich. Palla-
dium(II) chloride anhydrous, tetraethyl orthosilicate (TEOS 98%),
absolute ethanol (99.98%), sulfuric acid (H2SO4), nitric acid
(HNO3), hydrochloric acid (HCl 37%), 1,10-phenanthroline, and
sodium salt were obtained from Merck (Germany). Other chemi-
cals used were of analytical reagent or higher purity grade.
O
O
onto
KBr
Poured
ice
yellow
solution
H
cautiously
2SO4:HNO
3 (1:1)
130 0c
N
N
N
N
neutralized with
NaOH
at
heat
1,10-phenanthroline
1,10-phenanthroline-5,6-dione
(phendione)
NaCl
Cl
Cl
Cl
Cl
PdCl2
Na2
Pd
H
2O
Sodium
tetrachloropalladate(II)
(sln A)
1
mol
phendione
Com-1
A
1mol sln
1
mol
1mol sln
phendione
Com-2
Com-3
A
1
mol
phendione
A
1mol sln
Scheme 1. Schematic of synthesis ligand and complex.

570
A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
1 mmol phendione in 3 ml ethanol was added and the reaction
continued at 40 °C for 1 h. The precipitate formed was centrifuged
and washed with water and then acetone. The resulting product
was dried in a vacuum oven.
Synthesis of complex in SBA-15 through the ‘‘ship in a bottle’’ method
Synthesis of SBA-15 was conducted according to the literature
[26]. Complex supported on SBA-15 (Com/SBA-15) was done as
follows: (1 g) of SBA-15 was dispersed in 25 ml clear solution con-
taining 0.65 mmol of sodium tetrachloropalladate (II) and stirred
for 2 h, subsequently 0.65 mmol of phendione in ethanol was
added dropwise with constant stirring for 1 h at the room temper-
ature and then stirred for 48 h. The pale olive green precipitate
formed was filtered out and dried in a vacuum oven. The ICP anal-
ysis of this Com/SBA-15 showed that 22.26% of the complex was
placed on the silica support.
Fig. 2. Low angel XRD pattern of SBA-15 (a), and C/S-4 (b).
Characterization
The products were characterized by X-ray powder diffraction
Solvents used were of reagent grade and purified before use by
standard methods.
(XRD) on Holland Philips X-pert diffractometer (Cu
Ka =
1.5418 Å). The FT-IR spectra were recorded on a Thermo Scientific
NICOLET IR100 FT-IR spectrometer. The pellets made with KBr
and the catalysts were prepared before the analyses. UV–Vis
absorption spectra were obtained using Shimadzu UV-2550-
8030 spectrophotometer in the range of 190–800 nm with slit
width of 5.0 nm and light source with the wavelength of
360.0 nm at the room temperature. Inductively coupled plasma
(ICP) data are provided by Varian vista-PRO. The textural surface
properties of the samples were determined by physical adsorp-
tion–desorption of N2 at ꢂ196 °C using a BELSORP-mini II (Bel
Japan). Before the measurements, the samples were degassed at
150 °C for 1 h. The specific surface area and the pore size distribu-
tion were calculated by the Brunauer–Emmett–Teller (BET) and
Brunauer–Joyner–Hallenda (BJH) methods, respectively. The field
emission scanning electron microscopy (FESEM) analysis was car-
ried out using a Philips XL-300. The diffuse reflectance spectros-
Synthesis method
Synthesis of dichloro (phendione) palladium (II): (M.W = 387/51 g/mol)
Simple synthesis of complex (Com-1). Palladium chloride (177 mg,
1 mmol) and sodium chloride (586 mg, 10 mmol) were added to
100 ml double distilled water. The reaction mixture was stirred
at ꢁ50 °C to clear the solution (sln A), it was then cooled and fil-
tered. Then, 1 mmol of phendione in ethanol was added dropwise
to the filtrate containing sodium tetrachloropalladate (II). The olive
green precipitate formed was centrifuged and washed with water
and then acetone. The resulting product was dried in the vacuum.
Microwave assisted synthesis of complex (Com-2). The mixture of
1 mmol phendione and 1 mmol sln A was exposed to microwave
irradiation (power 75%) for 3 min. An 800 W microwave oven
was used for irradiation. The mixture was then centrifuged and
the dark green product was washed several times with double dis-
tilled water and dried in a vacuum oven.
copy (DRS) of the catalysts was tested in
a Perkin Elmer
Lambda 35 UV–Vis spectrometer. The spectra were recorded
timely in the range of 300–800 nm using BaSO4 as the reference
standard. 1H NMR spectra were recorded on a Brucker Avance
DPX-250 spectrometer at 250 MHz in DMSO-d6 using tetramethyl
silane as internal reference. Chromatographic analysis was per-
formed with a HPLC system including a Varian 9012 HPLC pump
Ultrasonic assisted synthesis of complex (Com-3). The sln A poured in
an Erlenmeyer and placed in the ultrasonic bath. Then, a solution of
Fig. 3. N2 adsorption–desorption isotherms (A) and the BJH pore size distribution calculated from the desorption branch of the isotherms (B) of SBA-15 (a) and C/S-4 (b) .

A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
571
Table 1
Textural properties of SBA-15 and Com/SBA-15 samples with various among of complex.
No.
Sample
Complex (wt%)
BET surface area (m2 gꢂ1
)
Pore volume (cm3 gꢂ1
)
1
2
3
4
5
6
7
SBA-15
(C/S-1)
(C/S-2)
(C/S-3)
(C/S-4)
(C/S-5)
(C/S-6)
–
5.65
843.69
770.35
683.91
551.44
481.10
411.78
352.4
0.97
0.89
0.81
0.68
0.63
0.56
0.42
10.94
18.19
22.26
27.21
36.88
Fig. 4. SEM image of Com 1 (a and b), Com 2 (c), Com 3 (d and e) and parent SBA-15 (f and g).

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A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
2
Fig. 5. (A) Shows (
a
h
m)
Vs photon energy plots of the complex. The inset is the absorption spectra of complex, and (B) molecular orbital surfaces and energy levels.
Result and discussion
Characterization of sample
Syntheses of ligand and metal complex are summarized in
Scheme 1. The FT-IR spectra of parent SBA-15 is shown in Fig. 1b.
Parent SBA-15 gives band around 3000–3600 cmꢂ1 and a sharp
band at 1643 cmꢂ1 that can be assigned to the symmetrical
stretching vibration mode of O–H and deformation of the adsorbed
water molecules, respectively. The bands corresponding to Si–O–Si
and Si–O are detected at 1110 and 856 cmꢂ1, respectively [26].
Spectrum of the palladium (II) complex is shown in Fig. 1a. The five
IR bands characteristic of the complex appear at 3072 cmꢂ1 (@CAH
band), 1701 cmꢂ1 (C@O band), 1571 cmꢂ1 (C@C band), 1426 cmꢂ1
(C@N band) and 718 cmꢂ1 (bending CAH band) show that the
Fig. 6. UV–Vis spectra of photodegradation of 2,4-DCP in the presence of Com-2
under visible light.
desired complex was formed [28]. The wavenumbers of Pd–N
vibrations are usually difficult to identify since the M–N stretching
modes, where M is a heavy atom, are usually of low intensity [29].
The characteristic bands of the complex were also observed in
Com/SBA-15 spectra (Fig. 1c).
(CA, USA), a six-port Cheminert HPLC valve from Valco (Houston,
USA) with a 20-lL sample loop and equipped with a Varian 9050
UV–Vis detector. Chromatographic data were recorded and ana-
lyzed using Chromana software (version 3.6.4). An ODS-Zorbax
As expected, the 1H NMR spectrum showed three distinct pro-
ton environments for [Pd(phendione)Cl2], a doublet of doublet
(dd) at d 9.003 (3J = 3 Hz, 4J = 1.5 Hz), a dd at d 8.413 (3J = 7.87 Hz,
4J = 1.37 Hz), and a dd at d 7.701 (3J = 7.75 Hz, 3J = 4.75 Hz). These
three proton signals integrated to 1:1:1.
column (250 mm ꢃ 4.6 mm, with 3
lm particle size) was applied
to separate the chlorophenols under gradient elution conditions.
A mixture of 20 mmol Lꢂ1 phosphate buffer (pH 4) and acetoni-
trile (60:40) for 15 min and 100% acetonitrile for 15 min at the
flow rate of 1 mL minꢂ1 was used as the mobile phase and the
analyses were detected at 280 nm. The retention time of the dif-
ferent photoproducts was the following ones: hydroquinone (HQ),
4.13 min, pyrocatechol (PC), 5.81 min, 2-chlorophenol (2-CP),
7.13 min, 4-chlorophenol (4-CP), 7.33 min and 2,4-dichlorophenol
(2,4-DCP), 9.8 min.
The content of palladium in the samples is confirmed finally
by the ICP analysis. The final products of the complex supported
by SBA-15 mesoporous silica are denoted as C/S-1 (5.65%), C/S-2
(10.94%), C/S-3 (18.19%), C/S-4 (22.26%), C/S-5 (27.21%), and
C/S-6 (36.88%), according to the complex loading determined by
the ICP.
The XRD patterns at small angles for the initial mesoporous
silica SBA-15 show three Bragg peaks below 2.5 (2h) (Fig. 2), indi-
cating its well-ordered two-dimensional mesostructure [21]. These
three strong peaks at 1.1287, 1.8225 and 2.1291 with d-spacings of
90.88, 56.28 and 48.18 Å, respectively, were indexed as 100, 110
and 200 reflections associated with the hexagonal structure. The
decrease in the peak intensity after supporting of the complex
can be ascribed to an overall decrease in the electron density con-
trast between the silica wall and the complex due to the complex
location inside the silica support [30].
Theoretical calculations
Theoretical studies were performed using the Gaussian 03 pro-
gram package [27] on a Windows-XP operating PC. Full optimiza-
tion of the complex structure was carried out by the density
functional theory (DFT-B3LYP) level in conjunction with effective
core potential basis set (LANL2DZ) for Pd atom, and 6-
311++G(d,p) basis set for Cl, N, O, C, and H atoms.
Nitrogen adsorption–desorption measurements were used to
examine the textural properties of the samples. Typical isotherms
and pore size distributions are depicted in Fig. 3. All the materials

A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
573
Fig. 7. HPLC-UV chromatograms of photodegradation of 2,4-DCP by C/S-4at various times: (a) 0 min, (b) 25 min, (c) 50 min, (d) 75 min, and (e) standard samples of
intermediate.
n
exhibited type IV isotherms and H1 hysteresis loops characteristic
of mesoporous solids and SBA architectures. A steep capillary con-
densation step appearing at the relative pressure of P/P0 = 0.6–0.8
(Fig. 3(A)) indicate the presence of regular mesopores in the sam-
ples, which was confirmed by a narrow pore size distribution in the
mesopore range (Fig. 3(B)) [31]. The results obtained for analysis of
textural characteristics (BET surface area, average pore size and
pore volume) of the samples are given in Table 1. As shown in
Table 1, the surface area and the pore volume decreased after sup-
porting of the complex pores of SBA-15.
ð
a
hv
Þ ¼ Bðh
v
ꢂ EgÞ
ð1Þ
where h
t
is the photon energy,
a
is the absorption coefficient, B is a
constant value, Eg is the band gap energy and n is assigned to trans-
mittance, which is 1/2 and 2 for indirect and direct band gap ener-
gies, respectively. The absorption coefficient (
the following equation:
a
) is determined by
1
a
¼ ꢂ LnT
ð2Þ
t
In this equation, T is the transmittance value and t is the thickness
of the substance used that is exposed to the UV–Vis irradiation. As it
To examine the photocatalytic activity of the complex, influence
of experimental conditions on the morphology of the product was
investigated. Fig. 4a–e exhibits the complex morphologies under
different conditions. The FE-SEM image revealed the needle-like
morphology obtained for all synthesized products. It was observed
that the change in reaction condition from ultrasonic to microwave
led to a decrease in the particle size and more homogeneous mor-
phology. Fig. 4f and g correspond to SBA-15. These micrographs
confirmed the formation of SBA-15 consisting of particles with
rope-like shape.
is shown in Fig. 5(A), the value of optical band gap gained by extrap-
2
olating the linear region of a plot of (
a
ht
)
Vs ht
. Using Eq. (1), the
measured band gap energies of the complex was about 2.10 eV.
The structure and energy levels of the highest occupied molec-
ular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) of the complex is shown in Fig. 5(B) and the energy gap
between them is about 2.00 eV. The result shows good agreement
with the experimental data.
Band gap determination
Photocatalytic degradation of 2,4-DCP
To investigate the optical properties the band gap energy calcu-
lated using UV–Vis absorption spectroscopy. To this end, tauc
relation was used [32]:
Photocatalytic activity of the complexes and Com/SBA-15 prod-
ucts were evaluated by degradation of 2,4-DCP in water. The
experiment was as follows: 25 mg photocatalyst was placed into

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A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
Fig. 9. Recycled testing of the photoactivity of C/S-4 under visible light.
2,4-DCP. So, the peak at 283.5 nm is defined as the characteristic
peak of 2,4-DCP. Intensity of the characteristic peak decreases with
the irradiation time and tends to disappear after 180 min illumina-
tion, which indicates that 2,4-DCP can be photodegraded effec-
tively by the photocatalyst.
The HPLC profiles during photodegradation of 2,4-DCP over the
C/S-4 are shown in Fig. 7. The 2,4-DCP showed a characteristic peak
at retention time (RT) 9.7 min; it gradually decreased by increasing
the reaction time, indicating the excellent photocatalytic activity of
the C/S-4. Fig. 7(e) shows the chromatograms of standard samples
of intermediate that help to assign their peak in during
photodegradation.
Effect of complex loading
The complex quantity affects degradation rate of 2,4-DCP. To
obtain optimal complex loading level, the degradation tests of tar-
get pollutant were carried out using different Com/SBA-15 with
varied loading levels of the complex (5.65, 10.94, 18.19, 22.26,
27.21 and 36.88 wt%) and the results are presented in Fig. 8. The
degradation rate of 2,4-DCP (by adsorption and photodegradation)
increased by increasing the loaded complex. The photodegradation
efficiency and activity of Com/SBA-15 increased when complex
loading increased from 5.65 to 22.26 wt%, reaching a maximum
at 22.26 wt% complex and then decreased with a further increase
in the complex loading (>22.26 wt%).
It is also seen that all the Com/SBA-15 tested had activities
higher than that obtained by using the complex was solely. The
results of the comparative study on the behavior of Com-1, Com-
2, Com-3, and C/S-4 in the photodegradation of 2,4-DCP are shown
in Fig. 8(C). In this figure, compared with the results obtained with
the complex at the same conditions and an unexpected increase in
degradation of the 2,4-DCP molecule was observed when mesopor-
ous silica SBA-15 was employed as the support.
Fig. 8. Photodegradation of 2,4-DCP using different samples under visible light
irradiation for 180 min: (A) C/C0 ꢁ t and (B and C) ln(C0/C) ꢁ t.
50 mL of 10.0 mg Lꢂ1 2,4-DCP aqueous solution in a beaker. Before
photocatalytic reaction, the suspension was sonicated for 5 min
and then stirred in the dark for 30–45 min (depending on the type
of samples and their darkness times found based on the absorption
experiment), to ensure the establishment of an adsorption–desorp-
tion equilibrium between the catalyst and 2,4-DCP. The visible
illumination was provided by a 400 W lamp (high-pressure mer-
cury-vapor lamp and k = 546.8 nm and air diffuser (air pump, flow:
3.5 L minꢂ1) was located at the bottom of the reactor to uniformly
disperse air into the solution. The photocatalytic reaction temper-
ature was kept at the room temperature using cooling fans to pre-
vent any thermal catalytic effect.
Reusability
One of the advantages of Com/SBA-15 is stability of photocata-
lyst during photocatalytic reaction. The results of 4 recycles with
each recycle containing 75 min of irradiation shown in Fig. 9. As
seen, the repetitive use of C/S-4 shows almost no change in its pho-
tocatalytic activity. So, this can be considered as a good photocat-
alyst for photodegradation of 2,4-dichlorophenol.
Possible degradation mechanism
Combining our experiment results with related studies [32-34],
a postulated mechanism for degradation of 2,4-DCP is proposed in
Scheme 2. Under the irradiation, the electrons (eꢂ) are excited from
the HOMO to the LUMO of the complex leaving behind h+. The elec-
trons are very active; so, can be easily trapped and transferred to
Fig. 6 shows the UV–Vis spectra of 2,4-DCP water sample with
the initial pH 4.0 in the presence of Com-2 under visible light. As
shown in the curves, peaks at 230 and 283.5 nm are assigned to

A. Abolhosseini Sh. et al. / Journal of Molecular Structure 1076 (2014) 568–575
575
HQ
=
R.T 4.13 min
OH
OH
O2
4-CP
=
OH
R.T 7.33 min
OH
OH
Cl
OH
OH
Cl
v
h
-
+
-
Com
OH
Com
Com
Cl
(e )
(h )
Cl
-
H2O
OH
OH
OH
Com
(e )
-
Cl
OH
Cl
Cl
-
OH
Cl
O
H
C
O
O
H
-
Com
(e )
OH
acids
R.T 2.88 min
Organic
=
Cl
OH
OH
Cl
OH
Cl
OH
2,4-DCP
Cl
Cl
=
R.T 9.8 min
-
H2O
-
Com
OH
OH
(e )
+
Cl
Com
(h )
H+
OH
H2O
OH
OH
2-CP
O2
=
R.T 7.13 min
OH
PC
=
R.T 5.81 min
Scheme 2. Producing pathway of the intermediate degradation products of 2,4-DCP.
the 2,4-DCP molecules promoting the [2, 4 – DCP]Åꢂ formation. In
the oxidative reaction, the positive holes (h+) react with the mois-
ture present on the surface and produce hydroxyl radicals (ÅOH).
It is observed that the dechlorination reaction produced the form
of2-CP, 4-CP, HQand PC. Additionally, theattack ofhydroxylradicals
occurs most favorably to the aromatic compound [35]. When the
benzene rings are broken, the major products are maleic, fumaric,
oxalic, formic, and acetic acids, eventually all these acids are com-
pletely degraded into CO2 and H2O [36-38].
[4] R. Asahi, T. Morikawa, et al., Science 293 (2001) 269–271.
[5] E.I. Seck, J.M. Doña-Rodríguez, et al., Appl. Catal. B: Environ. 125 (2012) 28–34.
[6] K.H. Leong, P. Monash, et al., Solar Energy 101 (2014) 321–332.
[7] J. Zhou, K. Wu, et al., Appl. Catal. A: Gen. 470 (2014) 336–343.
[8] Y.L. Pang, A.Z. Abdullah, et al., Appl. Catal. B: Environ. 100 (2010) 393–402.
[9] C.-L. Kuo, T.-J. Kuo, et al., J. Phys. Chem. B 109 (2005) 20115–20121.
[10] C. Burda, Y. Lou, et al., Nano Letters 3 (2003) 1049–1051.
[11] D. Huang, C. Persson, Chem. Phys. Lett. 591 (2014) 189–192.
[12] W. Liu, M. Ji, et al., J. Hazard. Mater. 186 (2011) 2001–2008.
[13] C. Tang, J. Sun, et al., Appl. Catal. B: Environ. 146 (2014) 201–212.
[14] R. Xing, L. Wu, et al., J. Mol. Catal. A: Chem. 371 (2013) 15–20.
[15] T.B. Ogunbayo, T. Nyokong, J. Mol. Catal. A: Chem. 337 (2011) 68–76.
[16] J. Xu, R. Meng, et al., J. Alloys Compd. 564 (2013) 84–90.
[17] M. Bagherzadeh, F. Ashouri, et al., Inorg. Chem. Commun. 44 (2014) 10–14.
[18] H. Veisi, R. Masti, et al., J. Mol. Catal. A: Chem. 385 (2014) 61–67.
[19] N. Batail, A. Bendjeriou, et al., Appl. Catal. A: Gen. 388 (2010) 179–187.
[20] V. Polshettiwar, C. Len, et al., Coord. Chem. Rev. 253 (2009) 2599–2626.
[21] D. Zhao, J. Feng, et al., Science 279 (1998) 548–552.
[22] D. Zhao, Q. Huo, et al., J. Am. Chem. Soc. 120 (1998) 6024–6036.
[23] M. Kruk, M. Jaroniec, et al., J. Phys. Chem. B 104 (1999) 292–301.
[24] A.K. Aboul-Gheit, S.M. Ahmed, et al., Eur. J. Chem. 2 (2011) 104–108.
[25] Y. Yamada, H. Sakurai, Y. Miyashita, K. Fujisawa, K. Okamoto, Polyhedron 21
(2002) 2143.
[26] M. Kruk, M. Jaroniec, et al., Chem. Mater. 12 (2000) 1961–1968.
[27] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
V.G. Zakrzewski, J.A. Montgomery Jr, R.E. Stratmann, J.C. Burant, S. Dapprich,
J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelti, C. Adamo, S. Clifford, J.
Ochterski, G.A. Petersson, P. Y. Ayala, Q. Cui, K. MoroKuma, D.K. Malick, A.D.
Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, B.B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Martin, D.J. Fox,
T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez, M.
Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, M.
Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN 98 (Revision A. 3), Gaussian
Inc., Pittsburgh, PA, USA, 1998.
Conclusion
The Com/SBA-15 was successfully prepared via a facile method
at room temperature and its application for photodegradation of
2,4-dichlorophenol was investigated under visible light irradiation.
The experimental observations show that: (i) the diffuse reflec-
tance spectroscopy (DRS) for complex revealed that this product
can be used as an active photocatalyst in the visible region of solar
spectrum that this is in agreement with the results obtained using
the theoretical studies, (ii) maximum removal efficiency can be
achieved by C/S-4 (22.26 wt%) under 75 min visible light irradia-
tion, (iii) data collected from HPLC confirmed that 2-CP, 4-CP,
HQ and PC are intermediates during photodegradation of
2,4-dichlorophenol, (iv) introduction of SBA-15 into complex is
companied with high surface area and easy separation that this
result is a better photocatalytic activity for photodegradation of
2,4-dichlorophenol.
[28] C.A. Goss, H.D. Abruna, Inorg. Chem. 24 (1985) 4263–4267.
[29] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds: Theory and Applications in Inorganic Chemistry, John Wiley,
1997.
Acknowledgment
[30] H. Aliyan, R. Fazaeli, et al., Appl. Surface Sci. 276 (2013) 147–153.
[31] A.V. Neimark, P.I. Ravikovitch, Microporous Mesoporous Mater. 44-45 (2001)
697–707.
[32] E.A. Davis, N.F. Mott, Philos. Mag. 22 (1970) 0903–0922.
[33] S.-M. Lam, J.-C. Sin, et al., Desalinat. Water Treatment. 41 (2012) 131–169.
[34] J.-C. Sin, S.-M. Lam, A.R. Mohamed, K.-T. Lee, Int. J. Photoenergy 2012 (2012)
185159.
[35] A. Di Paola, M. Bellardita, et al., Catal. Today 161 (2011) 35–40.
[36] F.J. Benitez, J. Beltran-Heredia, et al., Chemosphere 41 (2000) 1271–1277.
[37] B. Boye, M.M. Dieng, et al., Environ. Sci. Technol. 36 (2002) 3030–3035.
[38] C.Y. Kwan, W. Chu, Water Res. 38 (2004) 4213–4221.
Support of this investigation by Tarbiat Modares University and
Iranian nanotechnology initiative council is gratefully
acknowledged.
References
[1] M. Czaplicka, Sci. Total Environ. 322 (2004) 21–39.
[2] USEPA, Priority pollutant list, Appendix A. US environmental protection
agency, Washington, DC. 40 CFR 423, 1981.
[3] A.M. Volodin, Catalysis Today. 58 (2000) 103–114.