Magnetically recoverable, nanoscale-supported heteropoly acid catalyst for green synthesis of biologically active compounds in water

Article abstract of DOI:10.1016/S1872-2067(12)60645-7

12-Tungstophosphoric acid supported on aerosil silica and silica-coated γ-Fe₂O₃ nanoparticles was prepared and characterized using transmission electron microscopy, scanning electron microscopy, and inductively coupled plasma atomic emission spectroscopy. The catalytic activity of the two prepared catalysts was compared in the synthesis of 1,8-dioxo-9,10- diaryldecahydroacridines in water. 12-Tungstophosphoric acid was highly dispersed on the silica-coated γ-Fe₂O₃ nanoparticles and showed higher activity and a higher reuse number compared with the acid supported on aerosil silica. The catalyst could be recovered simply by using an external magnetic field and could be reused several times without appreciable loss of its catalytic activity.

Full text of DOI:10.1016/S1872-2067(12)60645-7

Chinese Journal of Catalysis 34 (2013) 1513–1518
ava i l a b l e a t w w w. s c i e n c ed 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
Magnetically recoverable, nanoscale‐supported heteropoly acid
catalyst for green synthesis of biologically active compounds
in water
Ezzat Rafiee*, Sara Eavani, Maryam Khodayari
Faculty of Chemistry, Razi University, Kermanshah, 67149, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
12‐Tungstophosphoric acid supported on aerosil silica and silica‐coated γ‐Fe2O3 nanoparticles was
prepared and characterized using transmission electron microscopy, scanning electron microscopy,
and inductively coupled plasma atomic emission spectroscopy. The catalytic activity of the two
prepared catalysts was compared in the synthesis of 1,8‐dioxo‐9,10‐diaryldecahydroacridines in
water. 12‐Tungstophosphoric acid was highly dispersed on the silica‐coated γ‐Fe2O3 nanoparticles
and showed higher activity and a higher reuse number compared with the acid supported on aerosil
silica. The catalyst could be recovered simply by using an external magnetic field and could be re‐
used several times without appreciable loss of its catalytic activity.
Received 20 December 2012
Accepted 25 March 2013
Published 20 August 2013
Keywords:
Core‐shell particle
Magnetically recoverable catalyst
Heteropoly acid
Xanthene
© 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Hydroacridine
1. Introduction
portance because the catalytic activity is determined by the
catalyst surface area for some HPA‐catalyzed reactions
The heterogenization of homogeneous catalytic materials is
an attractive strategy for overcoming the difficulties involved in
the separation and reusability of homogeneous catalysts. Het‐
eropoly acids (HPAs) are suitable choices as catalysts because
of their strong Brönsted acidities, high thermal stabilities, and
structural flexibilities, and also because their low volatilities
and low corrosive properties make them suitable for green
technology applications [1–3]. Heterogenization or immobiliza‐
tion of such catalysts is usually required for ease of recycling
and ease of separation of the catalysts from the reaction prod‐
ucts [4–6]. The nature of the support affects the acidity, activity,
and leaching of the catalyst. An increased interest in the het‐
erogenization of supported HPAs has arisen because of the
superior activities of these systems compared with those of
bulk HPAs [7–9]. Supported systems are also of practical im‐
[10–13].
In this study, two different kinds of materials, namely aero‐
sil silica and silica‐coated γ‐Fe2O3 nanoparticles, were used as
supports for the immobilization of HPAs. The effects of these
supports on the catalyst acidity, activity, leaching, and recycla‐
bility were investigated. Based on the obtained results, a spe‐
cific heterogeneous HPA catalyst was used for the syntheses of
biologically useful building blocks, namely 1,8‐dioxo‐9,10‐dia‐
ryldecahydroacridines, 1,8‐dioxooctahydroxanthenes, and
14‐aryl‐14H‐dibenzo[a,j]xanthenes (Scheme 1) [14–16]. Alt‐
hough many methods are available for the syntheses of these
compounds [17–24], there is still a scope for further research
on the development of one‐pot, facile, and efficient processes
using green heterogeneous solid acid catalysts in water. It is
expected that these catalysts will provide a model for preparing
*Corresponding author. Tel/Fax: +98‐831‐4274559; E‐mail: e.rafiei@razi.ac.ir, ezzat_rafiee@yahoo.com
This work was supported by Razi University Research Council and Iran National Science Foundation.
DOI: 10.1016/S1872‐2067(12)60645‐7 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 34, No. 8, August 2013

Ezzat Rafiee et al. / Chinese Journal of Catalysis 34 (2013) 1513–1518
R
R
O
O
O
O
Ar
N
O
O
R'
14-aryl-14H-dibenzo[a,j]xanthenes
1,8-dioxo-octahydroxanthenes
1,8-dioxo-9,10-diaryl-decahydroacridines
Scheme 1. Structures of biologically active compounds synthesized in this study.
supported HPA catalysts for use in the syntheses of other bio‐
logically active compounds in water.
coupled plasma atomic emission spectroscopy (ICP‐AES) using
a Spectro Ciros CCD spectrometer. The potential variations
were measured with a Hanna 302 pH meter and a dou‐
ble‐junction electrode.
2. Experimental
2.1. Catalyst preparation
2.3. Synthesis of three biologically active compounds
The reagents and solvents used in this work were obtained
from Fluka, Aldrich, or Merck and were used without further
purification. The catalyst samples were prepared by immobili‐
zation of 40 wt% of H3PW12O40 (PW) on the surfaces of aerosil
silica (SBET = 311 m2/g) [9] and silica‐coated γ‐Fe2O3 nanoparti‐
cles (Fe2O3@SiO2 NPs) [25]. These samples were designated
PW/SiO2 and Fe2O3@SiO2‐PW, respectively. The W content
determined using ICP‐AES was slightly lower than that ex‐
pected from the preparation stoichiometry. Typically, PW
loadings of ca. 29.2 wt% for the PW/SiO2 sample and ca. 33.4
wt% for the Fe2O3@SiO2‐PW sample were obtained.
For synthesis of 1,8‐dioxo‐9,10‐diaryldecahydroacridines, a
mixture of an aldehyde (1.0 mmol), 5,5‐dimethyl‐1,3‐cyclo‐
hexanedione (dimedone, 2.0 mmol), an amine (1.0 mmol), and
Fe2O3@SiO2‐PW catalyst (0.02 g) in water (5 ml) was stirred
under reflux conditions. After completion of the reaction, indi‐
cated by thin‐layer chromatography (TLC), the mixture was
cooled to room temperature and the solid (containing catalyst
and product) was filtered off and washed with water (10 ml).
The product was dissolved in acetonitrile, and the catalyst was
separated from the product using an external magnet. The sol‐
vent was evaporated in a vacuum to give the crude product,
which was purified by recrystallization from ethanol.
2.2. Catalyst characterization
For synthesis of 1,8‐dioxooctahydroxanthenes, a mixture of
an aldehyde (1.0 mmol), dimedone (2.0 mmol), and
Fe2O3@SiO2‐PW catalyst (0.02 g) in water (5 ml) was refluxed,
and the reaction was monitored by TLC. After completion of the
reaction, the catalyst was separated and the product was puri‐
fied according to the above procedure.
Transmission electron microscopy (TEM) was performed
using a TEM microscope (Philips CM 120 kV, the Netherlands).
The morphologies of the supported catalysts were observed by
scanning electron microscopy (SEM) using a model XL30
Philips SEM. The W contents were determined by inductively
For synthesis of 14‐aryl‐14H‐dibenzo[a,j]xanthenes, a mix‐
(b)
)
(a)
)
(c)
)
35
30
25
20
15
10
5
(d)
0
25-30 30-40 40-50 50-60 60-70 70-80 80-90
Particle diameter (nm)
Fig. 1. SEM images of Fe2O3@SiO2‐PW (a) and PW/SiO2 (b) catalysts, and TEM image (c) and diameter histogram (d) of Fe2O3@SiO2‐PW catalyst.

Ezzat Rafiee et al. / Chinese Journal of Catalysis 34 (2013) 1513–1518
ture of 2‐naphthol (2.0 mmol), an aldehyde (1.0 mmol), and
pacities. In the case of PW/SiO2, the predominant formation of
multilayers resulted in lower dispersion of intact PW anions on
the silica support, leading to low accessibility of protons for
participation in the reaction. However, in Fe2O3@SiO2‐PW, PW
formed a monolayer of isolated Keggin anions on the exterior
surface of the support, so a large number of active sites were
exposed to the surface, and therefore this catalyst exhibited
excellent activity in the reaction.
Fe2O3@SiO2‐PW catalyst (0.02 g) in water (5 ml) was stirred
under reflux conditions for an appropriate time. Purification of
the products and recycling of the catalyst were similar to the
procedures described above.
3. Results and discussion
The morphological features of the catalysts were observed
using SEM. The Fe2O3@SiO2‐PW catalyst had a uniform and
spherical morphology (Fig. 1(a)), but the PW/SiO2 catalyst con‐
sisted of a PW layer composed of several aggregates of PW
particles rather than a continuous film (Fig. 1(b)). TEM obser‐
vations indicated that Fe2O3@SiO2‐PW had a well‐defined
core‐shell structure, almost spherical in shape, and of diameter
60–70 nm (Fig. 1(c) and (d)). The surface area of the nanoscale
Fe2O3@SiO2 support was higher than that of commercial SiO2,
leading to higher dispersion of PW and a higher PW loading
capacity.
The catalytic activities of the samples were compared using
the reaction of benzaldehyde, dimedone, and 4‐ethylaniline in
water. The reaction was carried out at 70 °C because of the low
solubility of dimedone in the reaction mixture at lower tem‐
peratures. The results are summarized in Table 1. A blank ex‐
periment in the absence of a catalyst showed that a catalyst is
essential in this reaction (Table 1, entry 1). The effects of aero‐
sil silica and Fe2O3@SiO2 NPs on the product yield were poor
(Table 1, entries 2 and 3). The catalytic activities of SiO2 and
Fe2O3@SiO2 are attributed to the presence of Si–OH groups on
the outer surfaces of these supports. Fe2O3@SiO2 NPs have
large surface‐to‐volume ratios and therefore have highly dis‐
persed surface functional groups compared with SiO2, and this
may lead to improved catalytic activity. PW/SiO2 gave a mod‐
erate yield (Table 1, entry 4). When Fe2O3@SiO2‐PW was used
as the catalyst, a significant improvement in the yield was ob‐
served (Table 1, entry 5). Although the Fe2O3@SiO2‐PW and
PW/SiO2 catalysts had similar PW loadings (according to
ICP‐AES analysis), they had different monolayer coverage ca‐
In order to compare the reusabilities of the Fe2O3@SiO2‐PW
and PW/SiO2 catalysts, model reactions were carried out using
0.10 g of each catalyst, and the experiments were appropriately
scaled up. At the end of the reaction, the mixture was centri‐
fuged and water was removed from the mixture to leave a res‐
idue (containing the product and catalyst). The product was
dissolved in acetonitrile and the catalyst was separated from
the product by filtration (for PW/SiO2) or by attaching an ex‐
ternal magnet to the reaction vessel, followed by decantation of
the product solution (for Fe2O3@SiO2‐PW). The catalyst was
then dried and used in the next run. The PW/SiO2 catalyst had
poor reusability, and significant loss of catalytic activity was
observed after the first run (Fig. 2(a)). This was caused by
leaching of PW from the support into the reaction mixture, and
was measured using ICP‐AES (Fig. 2(b)). The acid strengths and
quantities of acid sites of the catalysts were examined by po‐
100
(a)
80
60
40
20
0
(b)
80
PW/SiO2
Fe2O3@SiO2-PW
60
40
20
0
(c)
Table 1
600
Catalytic activity of various solid acids in model reaction.
400
200
O
O
O
CHO
NH2
Catalyst, 70 o
C
2
+
+
Water, 30 min
N
O
50
(d)
40
30
Catalyst
amount (g)
—
Isolated
yield (%)
—
Entry
Catalyst
1
2
3
4
5
6
7
8
—
SiO2
20
1
0.01
0.01
0.01
0.01
0.005
0.02
0.03
—
14
35
86
49
95
94
Fe2O3@SiO2
PW/SiO2
Fe2O3@SiO2‐PW
Fe2O3@SiO2‐PW
Fe2O3@SiO2‐PW
Fe2O3@SiO2‐PW
0
1
2
3
4
Run
Fig. 2. Catalyst reusability. (a) Catalyst activity; (b) Leaching of PW
measured by ICP‐AES; (c) Catalyst acid strength indicated by initial
electrode potential (Ei); (d) Quantities of acid sites of the catalysts.

Ezzat Rafiee et al. / Chinese Journal of Catalysis 34 (2013) 1513–1518
tentiometric titration with n‐butylamine [10,11]. This method
cling and reuse compared with PW/SiO2 are other advantages
that favor the use of Fe2O3@SiO2 NPs for immobilization of
HPAs.
To investigate the effect of the catalyst loading, the model
reaction was carried out in the presence of different amounts of
Fe2O3@SiO2‐PW catalyst. The best result was obtained in the
presence of 0.02 g of Fe2O3@SiO2‐PW; the use of higher
amounts of catalyst had no effect on the product yield (Table 1,
entries 5–8).
The catalytic system was used to synthesize structurally di‐
verse 1,8‐dioxo‐9,10‐diaryldecahydroacridine derivatives; the
results are summarized in Table 2. Benzylamine, aniline, and
aromatic amines with electron‐donating group gave the ex‐
pected product a (Table 2, entries 1–6), whereas amines sub‐
stituted with electron‐withdrawing groups gave 1,8‐dioxooc‐
tahydroxanthene derivatives (Table 2, entries 7 and 8). Ben‐
zaldehyde and other aromatic aldehydes were used and were
found to react well to give the corresponding 1,8‐dioxo‐9,10‐
diaryldecahydroacridines in excellent yields (Table 2, entries
1–6). However, because solid aldehydes are insoluble in aque‐
ous media, it was necessary to use a surfactant to solubilize
these compounds in water (Table 2, entries 5 and 6).
Encouraged by these results, we used the Fe2O3@SiO2‐PW
catalyst in the reaction of dimedone or 2‐naphthol with various
aromatic aldehydes, affording a series of xanthene derivatives
in excellent yields, in short reaction times (Table 3)
The proposed mechanism for the synthesis of 1,8‐dioxo‐
9,10‐diaryldecahydroacridines a is shown in Scheme 2. First,
the acid catalyst converts the aldehyde into a convenient elec‐
trophile via protonation of the carbonyl group, and then one
molecule of dimedone condenses with the aromatic aldehyde
to produce intermediate I. Then, a second activated dimedone
enables the determination of the total number of acid sites and
their distribution. As a criterion for interpreting the obtained
results, the initial electrode potential (Ei) was taken to indicate
the maximum acid strength of the sites. The number of milli‐
moles of amine per gram of solid needed to reach the plateau
indicated the total number of acid sites. The PW/SiO2 sample
had strong acid sites, which might indicate a low interaction
level and the predominant formation of less dispersed intact
PW anions on the silica support. This supported catalyst there‐
fore showed significant leaching of PW in water, and its acid
strength and the total number of acid sites decreased signifi‐
cantly after the first run (Fig. 2(c) and (d)). The potentiometric
results for the Fe2O3@SiO2‐PW sample showed a lower Ei value
compared with that of the PW/SiO2 sample for the first run,
which may be a consequence of strong interactions with the
support in Fe2O3@SiO2‐PW. The interacting species were well
dispersed on the support surface and did not leach during the
reaction. So, the Fe2O3@SiO2‐PW catalyst could be recovered
and reused several times (Fig. 2); only 27.3% of the initial PW
content totally leached into the reaction mixture during four
successive runs. The yield of the product was not substantially
changed (10% difference) after the fourth run. The potentiom‐
etric titration results showed that most of the acid sites were
preserved during four cycles (Fig. 2(d)).
The above results show that the use of nanoscale
Fe2O3@SiO2 as a support leads to excellent PW distribution and
a higher number of surface active sites, compared with an aer‐
osil silica support. Complete recovery of the Fe2O3@SiO2‐PW
catalyst using an external magnetic field and improved recy‐
Table 2
Fe2O3@SiO2‐PW‐catalyzed synthesis of 1,8‐dioxo‐9,10‐diaryl‐decahy‐
droacridine derivatives.
Table 3
Fe2O3@SiO2‐PW‐catalyzed synthesis of xanthene derivatives.
O
CHO
R
Catalyst (0.02 g)
+
R2NH2
+ 2
O
70 oC, Water
R1
O
O
O
R1
O
R1
Catalyst (0.02 g)
70 oC, Water
O
O
O
b
CHO
O
O
R
OH
or
R
N
R2
O
Catalyst (0.02 g)
70 oC, Water
O
c
b
a
Time
(min)
30
Isolated
yield (%)
74
Entry
R1
R2
Product a
Time
(min)
25
30
55
60
30
30
45
Isolated
yield (%)
94
Entry
R
Producta
1
2
3
4
5 b
6 b
7
H
H
H
4‐CH3
4‐Cl
3‐NO2
H
C6H5
C6H5CH2
1a
2a
3a
4a
5a
6a
7b
8b
1
2
3
4
5
6
7
8
H
1b
2b
3b
4b
5c
6c
7c
8c
45
30
30
30
25
40
40
81
95
93
94
96
61
90
4‐CH3
4‐OCH3
2‐Cl
95
84
96
93
94
72
90
4‐CH3CH2‐C6H5
4‐CH3CH2‐C6H5
4‐CH3CH2‐C6H5
4‐CH3CH2‐C6H5
4‐Cl‐C6H5
H
4‐CH3
4‐OCH3
2‐Cl
8
H
4‐NO2‐C6H5
a All products were identified by comparing their spectral data with
those of the authentic samples [23,26].
30
a All products were identified by comparing their spectral data with
those of the authentic samples [20,27].
b 0.05 g of SDS was used in these reactions.

Ezzat Rafiee et al. / Chinese Journal of Catalysis 34 (2013) 1513–1518
R1
OH
H
O
H
Catalyst
OH
R1
H
OH
OH
O
OH
OH
H
O
O
Catalyst
Catalyst
O
O
O
R1
R1
R1
R1
O
O
O
O
R2NH2
H
O
O
H
H
H
OH2
H
OH NR2
(III)
O
O
OH OH
(I)
(II)
R1
R1
R1
O
O
O
O
O
O
-H2O
H
N
R2
N
O
NHR2
R2
OH
Scheme 2. The proposed mechanism for the synthesis of 1,8‐dioxo‐9,10‐diaryl‐decahydroacridines.
R
R
O
O
O
O
O
O
Catalyst
Catalyst
H
H
+
+
-H2O
O
O
O
O
R
O
OH
OH
OH
R
R
Catalyst
H
Catalyst
+
OH
-H2O
R
OH
R
OH
OH
R
-H2O
O
Catalyst
Scheme 3. The proposed mechanism for the synthesis of xanthene derivatives.
reacts with I to give intermediate II. Nucleophilic attack of an
amine group on a carbonyl group creates intermediate III. In
the next step, cyclization occurs by nucleophilic attack of an
amine group on a carbonyl group. Finally, by the removal of
one water molecule, the acridine derivatives are generated.
Similar to the mechanism in Scheme 2, the interaction of an
aldehyde with the catalyst surface generates an electrophilic
carbon center, followed by nucleophilic attack of the activated
dimedone or 2‐naphthol to generate the xanthene derivatives
(Scheme 3).
ventional support matrices, leading to improved catalytic activ‐
ities of HPA‐supported catalysts. Moreover, the magnetic prop‐
erties of Fe2O3 enable complete recovery of the
Fe2O3@SiO2‐PW catalyst using an external magnetic field; this
is an important advantage of the use of a magnetically separa‐
ble catalyst. The Fe2O3@SiO2‐PW catalyst was used in a novel
methodology for the aqueous syntheses of 1,8‐dioxo‐9,10‐dia‐
ryldecahydroacridines, 1,8‐dioxooctahydroxanthenes, and
14‐aryl‐14H‐dibenzo[a,j] xanthenes, which are biologically
interesting compounds. The use of water as the solvent, low
catalyst loading, simple work‐up for the isolation of high‐purity
products in excellent yields, mild reaction conditions, and cata‐
lyst recyclability are features of this new procedure. These
characteristics of our protocol make the reaction suitable for
scale‐up and commercialization.
4. Conclusions
Nanoscale supports such as Fe2O3@SiO2 have higher cata‐
lyst loading capacities and higher dispersions than many con‐

Ezzat Rafiee et al. / Chinese Journal of Catalysis 34 (2013) 1513–1518
Graphical Abstract
Chin. J. Catal., 2013, 34: 1513–1518 doi: 10.1016/S1872‐2067(12)60645‐7
Magnetically recoverable, nanoscale‐supported heteropoly acid catalyst for green synthesis of biologically active compounds in
water
Ezzat Rafiee*, Sara Eavani, Maryam Khodayari
Razi University, Iran
12‐Tungstophosphoric acid (PW) catalysts supported on aerosil silica and silica‐coated γ‐Fe2O3 nanoparticles (Fe2O3@SiO2‐PW) were
prepared and characterized. These catalysts were used for the aqueous syntheses of 1,8‐dioxo‐9,10‐diaryldecahydroacridines and xan‐
thene derivatives, which are biologically interesting compounds.
[12] Miyaji A, Ohnishi R, Okuhara T. Appl Catal A, 2004, 262: 143
[13] Dias J A, Caliman E, Dias S C L, Paulo M, de Souza A T C P. Catal
Acknowledgments
Today, 2003, 85: 39
[14] Hernandez‐Gallegos Z, Lehman‐F P A, Hong E, Posadas F, Hernan‐
dez‐Gallegos E. Eur J Med Chem, 1995, 30: 355
[15] Girault S, Grellier P, Berecibar A, Maes L, Mouray E, Lemiere P,
We thank the Razi University Research Council and Iran Na‐
tional Science Foundation (INSF) for support of this work.
Debreu M A, Davioud‐Charvet E, Sergheraet C. J Med Chem, 2000,
43: 2646
References
[16] Ion R M, Planner A, Wiktorowicz K, Frackowiak D. Acta Biochim
[1] Misono M. Chem Commun, 2001: 1141
Pol, 1998, 45: 833
[2] Min J S, Mizuno N. Catal Today, 2001, 71: 89
[17] Shakibaei G I, Mirzaei P, Bazgir A. Appl Catal A, 2007, 325: 188
[3] Kozhevnikov I V. Catal Rev‐Sci Eng, 1995, 37: 311
[18] Bhattacharya A K, Rana K C, Mujahid M, Sehar I, Saxena A K. Bioorg
[4] Wu Y, Ye X K, Yang X G, Wang X P, Chu W L, Hu Y C. Ind Eng Chem
Med Chem Lett, 2009, 19: 5590
Res, 1996, 35: 2546
[19] Naik M A, Sachdev D, Dubey A. Catal Commun, 2010, 11: 1148
[5] Dias A S, Pillinger M, Valente A A. Microporous Mesoporous Mater,
[20] Gong K, Fang D, Wang H L, Zhou X L, Liu Z L. Dyes Pigments, 2009,
2006, 94: 214
80: 30
[6] Zhang Z X, Zhang F W, Zhu Q Q, Zhao W, Ma B C, Ding Y. J Colloid
[21] Shen W, Wang L M, Tian H, Tang J, Yu J J. J Fluorine Chem, 2009,
Interface Sci, 2011, 360: 189
130: 522
[7] Baker L C W, Glick D C. Chem Rev, 1998, 98: 3
[22] Hong M, Cai C. J Fluorine Chem, 2009, 130: 989
[8] Okuhara T. Chem Rev, 2002, 102: 3641
[23] Ko S K, Yao C F. Tetrahedron Lett, 2006, 47: 8827
[9] Rafiee E, Joshaghani M, Eavani S, Rashidzadeh S. Green Chem,
[24] Kidwai M, Bhatnagar D. Tetrahedron Lett, 2010, 51: 2700
2008, 10: 982
[25] Rafiee E, Eavani S. Green Chem, 2011, 13: 2116
[10] Rafiee E, Eavani S, Rashidzadeh S, Joshaghani M. Inorg Chim Acta,
[26] Piao Y, Burns A, Kim J, Wiesner U, Hyeon T. Adv Funct Mater, 2008,
2009, 362: 3555
18: 3745
[11] Rafiee E, Paknezhad F, Shahebrahimi Sh, Joshaghani M, Eavani S,
[27] Seyyedhamzeh M, Mirzaei P, Bazgir A. Dyes Pigments, 2008, 76:
Rashidzadeh S. J Mol Catal A, 2008, 282: 92
836