One-step photocatalytic benzene hydroxylation over iron (II) phthalocyanine: A new application for an old catalyst

Article abstract of DOI:10.1016/j.jphotochem.2020.112412

In the present study, iron (II) phthalocyanine was introduced as an effective and recyclable photocatalyst for direct hydroxylation of benzene to phenol as a model reaction under photocatalytic conditions at ambient temperature. The effect of different parameters such as solvent, concentration of the oxidant, irradiation time, and amount of the catalyst was investigated. Acetonitrile was selected as the optimum solvent, where hydrogen peroxide plays the role of the oxidant which is considered as an eco-friendly process. The results not only showed a 15.2 % yield of phenol at a selectivity of higher than 99 % under optimized condition but also exhibited a highly stable and reusable behavior. The catalyst was thoroughly characterized by UV–vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field emission electron microscopy (FE-SEM), high-resolution transmittance electron microscopy (HR-TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm (BET), and X-ray photoelectron spectroscopy (XPS). Density-Functional Tight-Binding (DFTB+) calculation was used to study the catalyst transition energy on the Materials Studio software.

Full text of DOI:10.1016/j.jphotochem.2020.112412

Journal Pre-proof
One-step photocatalytic benzene hydroxylation over iron (II)
phthalocyanine: a new application for an old catalyst
Saeid Asghari, Shohreh Farahmand, Jalal. S. Razavizadeh, Mehran
Ghiaci
PII:
S1010-6030(19)31742-3
DOI:
https://doi.org/10.1016/j.jphotochem.2020.112412
JPC 112412
Reference:
To appear in:
Journal of Photochemistry & Photobiology, A: Chemistry
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Revised Date:
Accepted Date:
11 October 2019
22 January 2020
25 January 2020
Please cite this article as: Asghari S, Farahmand S, Razavizadeh JS, Ghiaci M, One-step
photocatalytic benzene hydroxylation over iron (II) phthalocyanine: a new application for an
old catalyst, Journal of Photochemistry and amp; Photobiology, A: Chemistry (2020),
doi: https://doi.org/10.1016/j.jphotochem.2020.112412
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One-step photocatalytic benzene hydroxylation over iron (II) phthalocyanine: a new
application for an old catalyst
a
a
a
a*
Saeid Asghari , Shohreh Farahmand , Jalal. S. Razavizadeh , Mehran Ghiaci
a
Department of Chemistry, Isfahan University of Technology, Isfahan 8415683111, Iran
*Corresponding author. Tel.; +98-31 3391 3254; FAX: +98-31 3391 2350.
E-mail address: mghiaci@cc.iut.ac.ir (M. Ghiaci).
Graphical Abstract
Highlights:


Visible-light accelerate the hydroxylation of benzene to phenol.
Phenol was achieved as the only product with high yield and practical TON and TOF.


High thermal and chemical stability of FePc led to its high reusability.
Abstract
In the present study, iron (II) phthalocyanine was introduced as an effective and
recyclable photocatalyst for direct hydroxylation of benzene to phenol as a model reaction
under photocatalytic conditions at ambient temperature. The effect of different parameters such
as solvent, concentration of the oxidant, irradiation time, and amount of the catalyst was
investigated. Acetonitrile was selected as the optimum solvent, where hydrogen peroxide plays
the role of the oxidant which is considered as an eco-friendly process. The results not only
showed a 15.2% yield of phenol at a selectivity of higher than 99% under optimized condition
but also exhibited a highly stable and reusable behavior. The catalyst was thoroughly
characterized by UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), field
emission electron microscopy (FE-SEM), high-resolution transmittance electron microscopy
(HR-TEM), X-ray diffraction (XRD), nitrogen adsorption-desorption isotherm (BET), and X-
ray photoelectron spectroscopy (XPS). Density-Functional Tight-Binding (DFTB+)
calculation was used to study the catalyst transition energy on the Materials Studio software.
Keywords: Benzene, Iron phthalocyanine, Photocatalytic hydroxylation, Phenol, Materials
studio 8.0
1
. Introduction
Phenol is regarded as one of the most important raw materials in the chemical industries
due to the key role in the synthesis of various useful compounds such as bisphenol A, epoxy
resins, polycarbonates, dyes and pigments, pharmaceuticals, and agrochemicals [1–5].

Therefore, demand for phenol production is rising dramatically [6]. Although the Fenton
2
+
reagent (Fe -H
2
2
O ) traditionally used for benzene hydroxylation, highly acidic conditions and
producing a great quantity of corrosive wastes has limited its application. In spite of the fact
that the well-known cumene process is extensively used to produce phenol [7–9], it suffers
from notable drawbacks such as high energy consumption, low yield and selectivity of phenol
(~5-6%) [10], harsh reaction conditions, and formation of the considerable amount of acetone
as a by-product [11]. To meet the elimination of crucial bottlenecks of the cumene process and
to consider environmental issues, many attempts have been developed to find an appropriate
alternative method for synthesis of phenol. Recently, one-step hydroxylation of benzene to
phenol as an appealing route has received considerable attention. In this regard, direct
hydroxylation of benzene has been widely studied using several kinds of oxidizing agents such
as H
the best choices due to its natural abundance, low cost, and environmentally friendly properties
18,19], however, harsh reaction conditions [20,21] and the need for reducing agents (hydrogen
2
O
2
[12,13], N
2
O [14,15], and O
2
[16,17]. Molecular oxygen can be considered as one of
[
gas, ascorbic acid, nicotinamide adenine dinucleotide (NADH), etc.) has restricted its
practicality [16]. Consequently, one-step hydroxylation of benzene using hydrogen peroxide
has attracted extensive attention due to the prominent properties such as being an eco-friendly
and affordable oxidant, cleaner reaction conditions and producing water as the only by-product.
[
22]. However, many reported catalysts suffer from the low yield or poor selectivity of the
desired product because of the poor reactivity of the aromatic C-H bond [23]. Thus, the effort
to design and synthesis of effective catalysts is still a never-ending challenge.
Photocatalytic hydroxylation of benzene to phenol have brought into focus in recent
studies. Against this background, employing inexpensive visible light seems to be more
efficient and promising. In contrast to conventional methods, photocatalytic reactions carried
out under mild conditions. As the aromatic C-H bond activation has been becoming a holy grail

particularly in oxidation reactions, driving the hydroxylation of benzene in the presence of
visible light as a green source of energy can be considered as a prosperous route. Up to now,
several homogeneous systems [24] are introduced such as 2,3-dichloro-5,6-dicyano‑p‑
benzoquinone (DDQ) [25] for photocatalytic hydroxylation, however, their utilization is
restricted due to the problem of catalyst separation [24,25].
Transition metal complexes are regarded as the high-performance catalysts in the
oxidation of different organic substrates. Recently, the increasing application of iron complexes
predicts a renaissance in the non-noble metal catalysis [26]. Metallophthalocyanines (MPCs)
are a class of metal complexes with remarkable features such as high chemical and thermal
stability and facile preparation using cheap raw materials. Moreover, they were used as
effective oxidation catalysts for a wide range of organic substrates such as toluene [27], benzyl
alcohol [28], olefins [29], and mercaptans [30]. MPCs with the extended π-conjugated
structures are regarded as versatile photocatalysts capable of the production of highly reactive
intermediates via radical routes [31]. These macrocycles are naturally found in most active sites
of oxygenase enzymes [32,33] and can activate a variety of inactive bonds even C-H bond in
methane [34,35]. Presumably, like other Fe(II) containing materials, Iron (II) phthalocyanine
(
FePc) can turn hydrogen peroxide into the hydroxyl radicals via the Fenton-like route, which
provides a successful pathway to hydroxylation of benzene under the photocatalytic conditions
36]. It is worth noting that, MPCs are normally insoluble in common organic solvents such as
[
acetonitrile which endows them the possibility of recovery. The highlight features above
promote the motivation of utilization of MPCs as the heterogeneous photocatalysts in the
various oxidation reactions [37,38].
Herein, FePc was successfully synthesized using microwave irradiation known as a
green approach, and its photocatalytic behavior was assessed in the liquid-phase hydroxylation
of benzene as a model reaction. A proper yield of phenol was achieved by controlling reaction

parameters, selecting an appropriate solvent, and optimizing the amount of oxidant and
catalyst. By controlling the reaction conditions, the maximum yield of phenol and TON reached
1
5.2% and 84.7, respectively, which rival those of noble-metal catalysts. Also, the reusability
of the catalyst investigated, and the catalytic reactivity maintained during four successive runs.
2
2
. Experimental
.1. Materials
Ammonium heptamolybdate tetrahydrate and dimethylformamide (DMF) were
prepared from Sigma-Aldrich Co. Phthalic anhydride, urea, iron (II) sulfate tetrahydrate,
benzene, ethanol, and hydrogen peroxide (30 wt%) were purchased from Merck Chemical Co.
All the chemicals were used without any further purification.
2
.2. Characterization techniques
The catalyst was fully characterized using ICP-OES, UV-Vis, FT-IR, DRS, XPS, XRD,
FE-SEM, HR-TEM, BET, GC, and GC-MS techniques which are described in the supporting
information.
2
.3. Preparation of FePc
The procedure for the synthesis of FePc is described in detail in the supporting
information. The structure of FePc confirmed by FT-IR, NMR, XRD, FE-SEM, HR-TEM, and
sorption-desorption studies (Fig. S1-S6).
N
2
2
.4. General procedure for photocatalytic hydroxylation
Photocatalytic reactivity of the synthesized catalyst was studied for benzene
hydroxylation as a benchmark for the oxidation reaction. In this regard, a suspension containing
-
2
FePc (5.25×10 mmol, 30 mg), benzene (11.25 mmol, 1 mL), hydrogen peroxide (32.65 mmol,
3
mL), and acetonitrile (5 mL) was prepared. The resulting mixture was then transferred into
the sealed reaction tubes and allowed to stirrer under light irradiation using a 100 W mercury
lamp at room temperature conditions. The reaction tube was placed in a 15 cm distance to the

2
lamp (light intensity =383.68 (W/m )). After sufficient time, the catalyst was separated using
centrifuging (10 min, 6000 rpm). The mixture of reaction was analyzed by GC-MS techniques
using acetophenone as the internal standard. Finally, the yield and selectivity of the phenol
were calculated by using the following equations:
푚푚표푙 표푓 푝ℎ푒푛표푙
푃ℎ푒푛표푙 푦ꢀ푒푙푑 =
× 100
(1)
(2)
푚푚표푙 표푓 ꢀ푛ꢀ푡ꢀ푎푙 푏푒푛푧푒푛푒
푚푚표푙 표푓 푝ℎ푒푛표푙
푃ℎ푒푛표푙 푠푒푙푒푐푡ꢀ푣ꢀ푡푦 =
× 100
푚푚표푙 표푓 푡표푡푎푙 푝푟표푑푢푐푡푠
3
3
. Results and discussion
.1 synthesis of FePc and photocatalytic test
The synthesis of FePc was illustrated in Scheme 1a, where phthalic anhydride has
involved in a cyclotetramerization by urea in the presence of iron (II) sulfate tetrahydrate under
microwave irradiation. FePc was purified as described in the experimental section and its
structure was characterized by FE-SEM, HR-TEM, XPS, XRD, UV-Vis, DRS, and IR.
Furthermore, photocatalytic benzene hydroxylation reaction was performed at room
temperature using hydrogen peroxide as the oxidant (Scheme 1b). To achieve the highest yield
and selectivity of the phenol, several experiments were carried out to optimize conditions.
Scheme 1. Preparation of FePc (a) and benzene hydroxylation over FePc (b)

3
.2. UV-Vis studies
Fig. 1 shows the UV-Vis spectrum of FePc in DMF with a considerable extinction
5
-1
-1
coefficient (approximately 10 L. mol .cm ) due to the 18 π-electron conjugated system [39].
The electron transition of a1u leads to the Q-band at 662 nm [40]. Fig. 2a shows the DRS of
e
g
FePc which is measured and transformed into the Kubelka-Munk (Fig. 2b) function to calculate
the experimental transition energy (ETr) of FePc and the obtained result is 2.25 eV which is in
a good agreement with theoretical data (Table 6).
Fig. 1. UV-Vis spectrum of FePc
Fig. 2. Diffuse reflectance of FePc (a) and Kubelka-Munk fitted spectrum (b)
3
.6. XPS analysis
The XPS spectrum of FePc is shown in Fig.3(a-d). XPS results at the region of Fe 2p
Fig. 3d) displays two main peaks at 712.1 eV and 721.7 eV which are correlated to 2p3/2 and
1/2, respectively [41]. Splitting of these peaks (Fe 2p1/2 –Fe 2p3/2) is about 9.2 eV which
(
2
p
indicates a normal state of paramagnetic high spin Fe (II) in FePc [41,42]. Deconvoluted N 1s
spectrum (Fig. 3b) consists mainly of four peaks which are related to pyridinic-N of the FePc
rings (398.8 eV), pyrrolic-N and imine bonds in the FePc structure (400.4 eV), and shake-up

electron transitions of pyrrole rings (402.3 eV and 404.8 eV), respectively [43]. It is worth
noting that the nitrogen atoms are mainly coordinated to Fe through the pyridinic-N atoms
(85.3 %), whereas the other peaks represent about 6.2%, 4.2%, and 4.2%, respectively [44].
Deconvoluted C 1s spectrum (Fig. 3c) also consists of four peaks. Two main peaks which are
found at 284.8 eV and 285.9 eV are related to 24 carbon atoms in the benzene rings and 8
carbon atoms in the pyrrole rings, respectively. Also, the peaks which are observable at 287.5
eV and 289.0 eV are related to shake-up satellites of pyrrole carbon atoms in the FePc structure
[
45]. The peak at 200.19 eV is attributed to Cl 2p as a result of the residual amount of chlorine
from the purification step.
Fig. 3. Full survey XPS spectra (a), at the region of N 1S (b), C 1s (c), Fe 2p (d)
.8. Photocatalytic reactions
The photocatalytic reactivity of FePc was studied in the hydroxylation of benzene to
3
phenol using hydrogen peroxide as an eco-friendly oxidant. Various parameters such as the
effect of the solvent, time, concentration of the oxidant, and amount of the catalyst were
investigated and all results are collected in Tables 1-5.
3
.8.1 Effect of solvent on the yield of phenol

Various organic solvents tested for the hydroxylation of benzene using hydrogen
peroxide (Table 1). The reaction was not performed in solvent-free conditions as well as in
non-polar solvents such as hexane, carbon tetrachloride, and chloroform due to insoluble raw
material and oxidant. Also, a mixture of H O:butanol did not provide the desired medium for
2
this reaction, might be due to the oxidation capability of the solvent. The moderate yield of
phenol was achieved using acetone while acetonitrile shows the highest yield of the desired
product. Acetonitrile as an aprotic polar solvent leads to the considerable miscibility of the
organic and aqueous reactants as two distinct phases [46,47]. Moreover, one of the intriguing
features of nitrile solvents is the ability of formation of peroxycarboximidic acid in the presence
of hydrogen peroxide, which can act as a co-catalyst to facilitate the hydroxylation of benzene
[
48].
Table 1. Effect of the solvent on the phenol yield
a
Yield (%)
Entry
Solvent
Selectivity (%)
±
SD
1
2
Solvent-Free
1.3 ± 0.1
1.8 ± 0.1
>99
>99
H
2
O:Butanol (2:1)
3
4
5
6
7
Acetonitrile
Acetone
15.2 ± 0.1
7.4 ± 0.1
<1
>99
>99
>99
>99
>99
Hexane
Carbon tetrachloride
Chloroform
<1
1.2 ± 0.1
2 2
Reaction conditions: Benzene (11.25 mmol), H O (32.65 mmol), FePc (30
mg), solvent (5 mL), r.t., 6 h.
a
Phenol yield = mmol phenol/mmol initial benzene
3
.8.2 Effect of time on the yield of phenol
The reaction did not progress in the first hour, but phenol was formed as time increased.
Table 2). After 2 h, the phenol efficiency did not improve, and therefore the 6 h time was
chosen as the optimum time.
Table 2. Effect of time on the phenol yield
(

Entry
Time (h) Phenol yield (%) Selectivity (%)
1
2
3
4
2
4
2.4 ± 0.1
8.4 ± 0.1
15.2 ± 0.1
15.8 ± 0.1
>99
>99
>99
6
10
>99
Reaction conditions: Benzene (11.25 mmol), H
30 mg), Solvent (5 mL), r.t.
2
O
2
(32.65 mmol), FePc
(
The kinetics of the reaction was studied by plotting the ln (C
t
/C ) versus time (Fig. 4).
0
C
0
and C are due to the initial benzene concentration and benzene concentration at time t,
t
-1
-4 -1
respectively. Thus, the rate constant of the reaction calculated to be 0.025 h (4.15 ˟10 S ).
Fig. 4. Kinetics studies for the benzene hydroxylation reaction.
3
.8.3 Effect of the oxidant/benzene ratio on the yield of phenol
The effect of the concentration of hydrogen peroxide on the yield of phenol investigated
using different molar ratios of oxidant to benzene, and all results collected in Table 3. The yield
of phenol reached the maximum when the oxidant/benzene ratio increased from 1 to 3. More
increase in this ratio led to over-oxidation products such as hydroquinone. Consumption of the
hydrogen peroxide in the oxidation reaction and its self-decomposition made the lower
effectiveness of this oxidant. Therefore, the molar ratio of the oxidant to benzene should be
more than stoichiometric ratios. Based on the previous studies, the amount of oxidant in the
present work is more affordable [13,22].

Table 3. Effect of oxidant to benzene ratio on the phenol yield
Entry Oxidant/benzene
Phenol yield (%)
0.7 ± 0.1
Selectivity (%)
1
2
3
4
5
1
2
3
4
5
>99
>99
>99
>99
4.0 ± 0.1
15.2 ± 0.1
15.5 ± 0.1
5.4 ± 0.1
a
62
Reaction conditions: Benzene (11.25 mmol), FePc (30 mg), acetonitrile (5 mL), r.t., 6
a
h. Hydroquinone identified as the by-product of the reaction.
3
.8.4 Effect of the amount of the catalyst on the yield of phenol
For investigating the effect of the amount of catalyst, the amount of FePc was varied
from 10 to 40 mg. while the other parameters were kept constant. The results summarized in
Table 4, showing the conversion of reaction increased rapidly from 2% for 10 mg of the catalyst
to 7.6% for 20 mg of the catalyst, and the maximum conversion achieved using 30 mg of the
catalyst. Further increase in the amount of the catalyst had no noticeable effect on the yield of
the phenol. Moreover, the catalyst is not active enough in the absence of light, and the yield of
phenol was miserable (Table 4, entry 5).
Table 4. Effect of the amount of catalyst on the phenol yield
Entry Amount of Cat. (mg) Phenol yield (%) Selectivity (%)
1
2
3
4
5
6
Catalyst-free
Trace
Trace
>99
>99
>99
>99
>99
10
20
30
2.0 ± 0.1
7.6 ± 0.1
15.2 ± 0.1
1.8 ± 0.1
15.8 ± 0.1
a
30
40
Reaction conditions: Benzene (11.25 mmol), H
mL), r.t., 6 h. In the absence of light.
2
O
2
(32.65 mmol), acetonitrile (5
a
3
.9 Catalyst recovery
The recycle-ability of FePc investigated using a reaction under the optimized
conditions. By completion of the reaction, the catalyst separated using centrifugation (10 min,

6
000 rpm), washed with acetonitrile and ethanol several times, and then dried at 60 ˚C. The
catalyst was subjected to further photocatalytic reactions under optimized conditions. The
results depicted in Fig. 5 showed that the synthesized catalyst had no diminution in the
reactivity after four cycles that clarifying the catalyst has notable stability in the structure. Also,
ICP results showed the iron content of the catalyst is nearly constant during the four runs of
reaction (Table. 5).
Fig. 5 Reusability of FePc
Table. 5. The results of ICP for Iron content in the FePc during
four runs of reactions
a
b
Entry
Run
1st
Iron Content in the catalyst (% wt.)
1
2
3
4
0.3756
0.3586
0.3402
0.3422
2nd
3rd
4th
a
2 2
Reaction conditions: Benzene (11.25 mmol), H O (32.65 mmol), FePc (30
b
mg), acetonitrile (5 mL), r.t., 6 h. Iron content of the FePc in 50 mg catalyst
which was measured using ICP-OES
3
.10. Molecular Simulation Calculation
Molecular simulation calculation was applied to explore the Capability of FePc as a
3
photocatalyst. Accordingly, the Dmol module of materials studio 8.0 was used to optimize the
FePc structure with density mixing (charge 0.2, spin 0.5) by the PWC local density

approximation (LDA) in conjunction with double numerical basis set [49,50]. The optimized
structure used to calculate the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energies of FePc by density-functional tight-binding
(DFTB+). The theoretical ETr of FePc is consistent with the experimental ETr obtained from the
Kubelka-Munk function described earlier. The results have summarized in Table 6.
Table 6. Orbital distribution structures and energies for FePc
Structure
HOMO
Orbital distribution structure
Energy (eV) ETr (eV)
3.76
2.42
LUMO
6.18
3
.11. A proposed mechanism
Concerning the results attained in this study and reported literature [36], the mechanism
of photocatalytic hydroxylation of benzene during a Fenton-like process is shown in Scheme
. It is clear that the catalytic reactivity of MPCs is strongly dependent on their metal centers
51]. The first step of the photocatalytic hydroxylation of benzene begins with a single electron
2
[

transition from the valance band to the conduction band. Arguably, the excited state of the FePc
FePc*) can activate the hydrogen peroxide by a single electron transfer process to produce
(
hydroxyl radicals. In the next step, the hydroxyl radical addition to the benzene moiety creates
a cyclohexadienyl radical as an intermediate of benzene hydroxylation. Furthermore, a
hydrogen abstraction from the intermediate produces phenol and regenerate the catalyst [52].
Scheme 2. A proposed mechanism for photocatalytic hydroxylation of benzene using FePc.
3
.12 Comparison of FePc with other reported catalysts
In Table 7 the results obtained from previously reported catalysts for direct
hydroxylation of benzene to phenol using hydrogen peroxide are compared to the present study.
Composites of iron (II) based on zeolites and mesoporous silica (entries 1-3), graphene, other
carbon-based catalysts (entries 4-6), and metal-organic frameworks (entry 7) are examples of
catalysts which have been used in liquid-phase hydroxylation of benzene to phenol. In the
present study iron (II) phthalocyanine was successfully synthesized using a more beneficial
microwave method which represented the desired photocatalytic reactivity.
Table 7. Photocatalytic activity of FePc and some previously reported catalysts for benzene hydroxylation.
a
b
TOF(h-1) c reference
Entry
Catalyst
hν Time (h) Temp. (˚C) Phenol yield (%)
Phenol sel. (%) TON
1
2
Fe-CN/TS-1
+
+
4
4
60
60
10
12
96
10.04
59.4
2.51
[53]
[54]
3 4
Fe-g-C N /SBA-15
94.3
14.84

3
4
5
6
7
VO
x
/SBA-16
-
-
4
6
6
8
8
60
60
13.8
5.8
97.5
91.5
89.1
97
32.4
8.1
[55]
[12]
[12]
[56]
[22]
this
CNT7000
FG7-10
-
-
-
60
1.4
-
-
-
-
CCG
-
60
17.5
20
MIL-100(Fe)
+
r. t.
98
0.083
0.010
d
8
FePc
+
6
r. t.
15.2
100
508.17
84.7
work
a
d
b
c
Phenol yield = mmol phenol / mmol initial benzene. Turnover number (TON)= (mmol phenol / mmol Fe). Turnover frequency (TOF)= (TON / time)
2 2
Reaction conditions: Benzene (11.25 mmol), H O (32.65 mmol), FePc (30 mg), Solvent (5 mL), r.t., 6 h.
5
. Conclusion
In summary, FePc was prepared by microwave irradiation during a cyclotetramerization
of phthalic anhydride, in the presence of iron (II) sulfate and urea. The uniform spherical
structure with a narrow size distribution of catalyst was demonstrated by electron microscopy
images. The theoretical and experimental results obtained from DFTB+ calculation and
Kubelka-Munk function confirmed the capability of the synthesized structure as a visible-light
photocatalyst. In this regard, the FePc* promotes the formation of hydroxyl radicals via a SET
mechanism to initiate the one-step hydroxylation of phenol. Controlling the reaction
parameters and selection of a proper solvent allowed us to achieve 15.2% yield of phenol.
Therefore, this investigation expressed FePc as a stable and reusable photocatalyst which
effectively produces phenol from benzene. Moreover, it can compete for the well-known
cumene process which involves time- and energy-consuming processes.
Author Statement
The present work is funded by the Isfahan University of Technology, and I as the
advisor of the project have submitted the manuscript for publication in the Journal of
Photochemistry and Photobiology A: Chemistry.
Conflict of Interest
The authors declare no competing financial interest.

Acknowledgments
This work was partially supported by the research council of the Isfahan University of
Technology (IUT), Iran.
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