Synthesis of benzimidazolones by immobilized gold nanoparticles on chitosan extracted from shrimp shells supported on fibrous phosphosilicate

Article abstract of DOI:10.1039/c9ra00481e

Here we demonstrate the synthesis of benzimidazolones from o-phenylenediamines and carbon dioxide in the presence of gold nanoparticles supported on a composite material based on microcrystalline chitosan from shrimp shells and fibrous phosphosilicate (CS-FPS/Au). The results showed that the gold nanoparticles were stable with the P, N and O atoms of CS-FPS. The morphology and structure of FPS leads to a higher catalytic activity. The CS-FPS/Au NPs were thoroughly characterized using TEM, FESEM, TGA, FTIR, and BET.

Full text of DOI:10.1039/c9ra00481e

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PAPER
Synthesis of benzimidazolones by immobilized
gold nanoparticles on chitosan extracted from
shrimp shells supported on fibrous phosphosilicate
Cite this: RSC Adv., 2019, 9, 6494
a
b
cd
Mahboobeh Zahedifar,
Ali Es-haghi, Rahele Zhiani*
cd
and Seyed Mohsen Sadeghzadeh
Here we demonstrate the synthesis of benzimidazolones from o-phenylenediamines and carbon dioxide in
the presence of gold nanoparticles supported on a composite material based on microcrystalline chitosan
from shrimp shells and fibrous phosphosilicate (CS–FPS/Au). The results showed that the gold nanoparticles
were stable with the P, N and O atoms of CS–FPS. The morphology and structure of FPS leads to a higher
catalytic activity. The CS–FPS/Au NPs were thoroughly characterized using TEM, FESEM, TGA, FTIR,
and BET.
Received 19th January 2019
Accepted 13th February 2019
DOI: 10.1039/c9ra00481e
rsc.li/rsc-advances
have been extensively studied because of their size related
properties, which can be leveraged for various applications.
1
. Introduction
28–31
The immobilization of precious metals and nanometals on Au NPs are also widely recognized as one of the most promising
several minerals and polymers for the preparation of hetero- catalysts for a number of reactions, including the reduction of
1
–9
32–34
35
geneous catalysts has been reported. For the expansion of nitrophenol,
green chemistry, chitosan (CS) as a natural polymer due to its oxidation of CO,
hydrodechlorination of 2,4-dichlorophenol,
36,37
aerobic selective oxidation of glucose to
38
39
high surface area, non-toxicity, biocompatibility, biodegrad- gluconate, and C–C cross coupling reactions. As smaller Au
ability and low cost can be used.
CS originates from chitin, NPs have a higher surface-to-volume ratio, the high catalytic
the second most abundant natural polymer aer cellulose, activity of Au NPs in these reactions strongly depends on the
which is present in crabs, fungi, shrimps and insects. Chito- active atoms at the NP surface. As particle sizes decrease,
sans are chemically stable, non-toxic and biodegradable poly- surface energies of the Au NPs increase, making them unstable,
saccharides. Chitosans are excellent ligands for the support of and resulting in a high tendency for inter-particle aggregation.
8,10,11
12
40
13
14
15
16
5,8
cerium, nickel, ruthenium, rhodium, copper and other This can reduce the catalytic efficiency of the catalysts. To
transition metal ions due to their insolubility in organic overcome this disadvantage, Au NPs are oen immobilized onto
44–46
41–43
solvents and the presence of functionalizable amino groups in solid supports with mesopores, including SBA-15,
Al
and SBA-16. When using one of these Au-
been successfully applied in catalytic hydrogenation, oxida- supported catalysts, the small Au NPs become dispersed
O ,
2 3
47,48
49
the morphology. Chitosan-supported metal complexes have MCM-41,
17
18
19
tion, Suzuki and Heck reactions. Moreover, to increase the mainly on the large, internal surfaces and pores of the support.
catalytic efficiency, hybrid materials of silica (CS–SiO ) have A consequence of this is that the active sites inside the pores are
2
been synthesized with different structures such as composite not readily available, which limits their application. Because of
20
21
membranes,
materials.
silica beads,
and hierarchical porous this, catalyst supports with good accessibility and high surface
areas (that is, not inside the pores), are highly desirable.
22
The use of noble metal nanoparticles (NPs) in catalysis has
long been a topic of research because of their strong catalytic poor due to the typical tubular structure of the pore and pore
The accessibility of gold active sites on mesoporous silica is
23–27
activities.
catalysis, gold NPs (Au NPs) are the most stable metal NPs, and there is an urgent need for efficient and stable catalysts and
Among the reported noble metal NPs used in blocking, reducing the activity of the overall catalyst. Thus,
50–53
based on our previous work on nanocatalysis,
we felt that
use of dendritic brous phosphosilicate (FPS) was appropriate.
Department of Chemistry, Faculty of Science University of Jiro, Jiro, 7867161167, Our research team has presented brous phosphosilicate (FPS)
a
Iran
b
NPs, that have special morphology with their pore sizes grad-
Department of Biology, Islamic Azad University, Mashhad Branch, Mashhad, Iran
54
ually increasing from the center to the surface. FPS NPs
c
New Materials Technology and Processing Research Center, Department of Chemistry,
showed high specic surface areas due to the pores in the
structures, and the approachability of the active sites was
signicantly increased as a result of the special morphology and
Islamic Azad University, Neyshabur Branch, Neyshabur, Iran
d
Young Researchers and Elite Club, Islamic Azad University, Neyshabur Branch,
Neyshabur, Iran. E-mail: R_zhiani2006@yahoo.com
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2.2. General procedure for the preparation of FPS
TEOS (2.08 g) and TPP (3.67 g) were dissolved in a solution of
cyclohexane (30 mL) and 1-pentanol (1.5 mL). A stirred solution
of cetylpyridinium bromide (CPB 1 g) and urea (0.5 g) in water
Scheme 1 Carbonylation of o-phenylenediamine to benzimidazolone
with CO in the presence of CS–FPS/Au NPs.
2
(30 mL) was then added. The resulting mixture was continually
stirred for 45 min at room temperature and then placed in
ꢀ
a Teon-sealed hydrothermal reactor and heated at 120 C for
structure. Additionally, the 3D architecture generated hierar- 5 h. The FPS was then isolated by centrifugation, washed with
chical pore structure with macropores can also improve the deionized water and acetone, and dried in a drying oven.
mass transfer of reactants. FPS-based sorbents may have several
advantages over conventional silica-based sorbents, including 2.3. Extraction of chitosan from shrimp shells
(
i) high catalyst loading, (ii) minimum reduction in surface area
The following 3 steps, namely demineralization, deproteiniza-
tion and deacetylation were followed for the isolation of chito-
san. Demineralization of shrimp shells was carried out using
three different concentrations of HCI (4%, 3%, and 2%) at
aer functionalization and (iii) more accessibility of catalyst
sites to enhance the reaction, due to the brous structure and
highly accessible surface area of FPS.
Given our continued interest in nanocatalysis and catalyst
development for organic reactions, a novel strategy was re-
ported for preparation of the desired nanocomposites by
modication of chitosan as a natural resource along with
extraction from shrimp shells, for the development of the
industrial applications of chitosan. Herein, chitosan was
extracted from shrimp shells and novel immobilized gold NPs
on natural chitosan supported on brous FPS as a catalyst
ꢀ
ambient temperature (28 ꢂ 2 C) with a solid to solvent ratio
1
: 5 (w/v) for 16 hours. The residue was washed and soaked in
tap water until neutral pH was obtained. Deproteinization of
shrimp shells was done using 4% NaOH at ambient tempera-
ꢀ
ture (28 ꢂ 2 C) with a solid to solvent ratio 1 : 5 (w/v) for 20
hours. The residue was washed and soaked in tap water until
neutral pH was obtained. Then the puried chitin was dried
until it became crispy. Chitin akes were ground into small
particles to facilitate deacetylation. The removal of acetyl groups
from chitin was performed using four different concentrations
2
catalyzing the carbonylation of o-phenylenediamine with CO is
reported. The unique cone shaped channels of the FPS can
mimic the chitosan pocket and the open brous structure will
provide better accessibility for the active Au sites and efficient
diffusion of the substrates and products, which is known to play
a crucial role in gold NP catalysis. Therefore, we hypothesized
that the gold nanoparticles supported on FPS could show
signicant improvements in the carbonylation of o-phenyl-
ꢀ
of NaOH (30%, 40%, 50%, and 60%) at 650 C with a solid to
solvent ratio 1 : 10 (w/v) for 20 hours. The residue was washed
with tap water until neutral pH was obtained. The resulting
chitosan was then dried in a cabinet dryer for 4 hours at 65 ꢂ
ꢀ
5
0 C and prepared for characterization.
2
enediamine with CO under solvent-free conditions (Scheme 1).
2.4. General procedure for the preparation of CS–FPS NPs
FPS (2 mmol) and water (20 mL) were mixed together in
a beaker, and then acetic acid (0.75 mL) was dispersed into the
mixture by ultrasonication. Chitosan (250 mg) was added at
2
. Experimental
2.1. Materials and methods
ꢀ
room temperature and stirred for another 16 h at 60 C. The
High purity chemical materials were purchased from Fluka and
Merck. Melting points were determined in open capillaries
using an Electrothermal 9100 apparatus and are uncorrected.
FTIR spectra were recorded using a VERTEX 70 spectrometer
resultant products were collected and washed with ethanol and
deionized water sequentially, and then dried under vacuum at
ꢀ
6
0 C for 2 h for further use.
(Bruker) in transmission mode using spectroscopic grade KBr
2.5. General procedure for the preparation of CS–FPS/Au
pellets for all of the powders. The particle size and structure of
nanoparticles were observed using a Philips CM10 transmission
electron microscope operated at 100 kV. Powder X-ray diffrac-
tion data were obtained using Bruker D8 Advance model with
Cu Ka radiation. Thermogravimetric analysis (TGA) was carried
NPs
A 100 mL round-bottom ask was charged with 0.5 g FPS
nanocomposite, 0.1 g HAuCl
were ultrasonically dispersed for 30 min. Subsequently, fresh
NaBH solution (0.2 M, 10 mL) was added dropwise into the
above suspension. The product was isolated by centrifugation,
washed repeatedly with deionized water and ethanol, and dried
under vacuum.
4
and 50 mL acetonitrile, which
ꢀ
ꢁ1
4
out using a NETZSCH STA449F3 at a heating rate of 10 C min
1
13
under nitrogen. H and C NMR spectra were recorded using
a BRUKER DRX-300 AVANCE spectrometer at 300.13 and 75.46
MHz and a BRUKER DRX-400 AVANCE spectrometer at 400.22
and 100.63 MHz, respectively. Elemental analyses for C, H,
and N were performed using a Heraeus CHN-O-Rapid analyzer.
2.6. General procedure for synthesis of benzimidazolones
Purity determination of the products and reaction monitoring CS–FPS/Au NPs (50 mg) and o-phenylenediamine derivatives
were accomplished using TLC on silica gel polygram SILG/UV (1 mmol) were charged into a reactor vessel without using any
2
54 plates. Mass spectra were recorded using a Shimadzu co-solvent. The reactor vessel was placed under a constant
ꢀ
GCMS-QP5050 Mass Spectrometer.
pressure of CO
2
and then heated to 110 C for 3 h and then
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the reactor was cooled to ambient temperature. The progress
of the reaction was monitored using TLC, upon completion
of the reaction EtOH was added to the reaction mixture and the
CS–FPS/Au NPs were separated by distillation under vacuum. The
solvent was removed from the solution and the resulting product
was puried by recrystallization using n-hexane/ethyl acetate.
3. Results and discussion
3.1. Synthesis and characterization of CS–FPS/Au catalyst
The rst step in accomplishing this catalyst design was the
functionalization of FPS with chitosan groups, which could
then act as pseudo chelators or ligands to control metal leach-
ing during the reaction. Functionalization was achieved by post-
synthetic modication of FPS bers by reaction with chitosan to
produce CS–FPS. This material was then treated with HAuCl
4
followed by hydrogen reduction, to produce Au nanoparticles
supported on FPS (Scheme 2). It is important to note that we
were unable to load a detectable amount of Au on the FPS
surface without chitosan functionalization, as we lost most of
4
the HAuCl during the washing step. When we avoided the
washing step, Au nanoparticles with bigger particle sizes and
broad particle size distribution were obtained. However, aer
chitosan functionalization, smaller and monodispersed Au
nanoparticles were obtained, indicating the role of chitosan,
which acts as a pseudo ligand and binds with HAuCl4.
Fig. 1 TEM images of FPS NPs (a); CS–FPS NPs (b); CS–FPS/Au NPs (c);
and FESEM images of FPS NPs (d); CS–FPS NPs (e); and CS–FPS/Au
NPs (f).
3.2. Catalytic properties of CS–FPS/Au catalyst
TEM and FESEM images of FPS are shown in Fig. 1. It can be
seen that the FPS sample consists of wall-like domains (Fig. 1a)
and the wall sizes are xed (Fig. 1d). Close inspection of these
images reveals that the material possesses dendrimeric bers
about 30–50 nm, and the morphology of the NPs is near-wall
(Fig. 1c and f).
The XRD patterns of FPS and CS–FPS/Au NPs are shown in
Fig. 2. The XRD pattern of FPS NPs displays a number of crys-
(thicknesses of 8–10 nm) arranged in three dimensions to form
walls, which can allow easy access to the available high surface
area. To study the effect of silica and phosphate concentration
on the morphology, we conducted a series of experiments in
which the TPP to TEOS molar ratio was varied. When equal
amounts of TEOS and TPP were used, the FPSs were mono-
dispersed thin bers with a single-handed wall. The FESEM and
TEM images of CS–FPS NPs showed that aer modication the
morphology of FPS did not change (Fig. 1b and e). The bers
of FPS have many Si–OH and P–OH groups on the surfaces. The
Si–OH and P–OH groups on the surface could serve as aggre-
gation centers for the growth of Au NPs on the surface of FPS.
Fig. 1c and f show FESEM and TEM images of the Au NPs. As we
can see, the as-prepared metal nanoparticles are spherical
without obvious aggregation. The diameter of the Au NPs was
55
talline peaks, consistent with a similar reports (Fig. 2a).
ꢀ
ꢀ
ꢀ
ꢀ
Moreover, new peaks at 2q ¼ 38.1 , 44.3 , 64.5 and 77.7
reective of Au (JCPDS 04-0784) (Fig. 2b) crystals were observed
for CS–FPS/Au NPs further conrming the successful growth
of Au particles on the surface of FPS. The broad peak between
ꢀ
2
0–30 corresponds to amorphous silica. XRD patterns can be
Scheme 2 Schematic illustration of the synthesis of CS–FPS/Au NPs. Fig. 2 XRD analysis of (a) FPS NPs and (b) CS–FPS/Au NPs.
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easily indexed to the cubic phase of Au NPs. Fig. 2b reveals that
Au NPs exhibit sharp peaks of Au (111), Au (200), Au (220), Au
(
311), and Au (222). The thermal behavior of CS–FPS/Au NPs is
ꢀ
shown in Fig. 3. The weight loss below 150 C was ascribed to
the elimination of physisorbed and chemisorbed solvent on the
surface of the CS–FPS/Au NPs material. In the second stage
ꢀ
(
180–350 C), weight loss is about 24 wt% for all catalysts, which
can be attributed to the organic group derivatives.
The FTIR spectra in Fig. 4 demonstrate the presence of
surface silanols, hydroxyl and phosphate groups, anchored
complex, and [HAuCl ] in (a) FPS, and (b) CS–FPS/Au NPs. The
4
FT-IR analysis of FPS represents the following functional
groups. Pure FPS showed a typical broad peak around
ꢁ
1
3
399 cm associated with the presence of hydroxyl groups and
the intensity of this peak increased which could be due to the Fig. 4 FTIR spectra of (a) FPS NPs and (b) CS–FPS/Au NPs.
presence of immobilized phosphate groups on the framework
of the FPS. The FPS materials also showed an additional peak
ꢁ
1
around 1483 cm which is ascribed to the phosphate moiety
and uniform mesostructure with a decrease in surface area,
pore diameter and pore volume parameters in comparison with
those of pristine FPS. With the functionalization by CS, the
corresponding pore volumes were drastically reduced. This
could be ascribed to increased loading with the sensing probe,
which occupies a large volume inside the phosphosilicate walls.
The formation of Au nanoparticles upon reduction led to
further, but less pronounced, reduction of the porosity prop-
erties (Table 1, entry 3). The formation of Au nanoparticles upon
reduction led to a further, but less pronounced, reduction in the
porosity properties. Interestingly, in the case of CS–FPS/Au the
reduction in pore volume upon the formation of particles was
5
6
coming from TPP. The main peak in the spectrum of FPS is the
ꢁ
1
additional peak which appears at 1232 cm , which could be
assigned to the –P]O stretching vibration indicating the
presence of phosphate groups.
the shoulder at 1108 cm are due to the TO and LO modes of
asymmetric stretching of Si–O–P bonds, respectively.
bands at about 724 and 795 cm were assigned to the asym-
metric stretching of the bridging oxygen atoms bonded to
a phosphorus atom. These peaks suggest the successful reac-
tion between the TEOS and the TPP (Fig. 4a). These clearly
indicate the graing of CS on the surface of FPS. The CS–FPS
composite shows bands at around 1091, 793 and 462 cm . The
strong and broad absorption band at 3000–3550 cm is related
to the –OH and –NH stretching vibrations and the two narrow
peaks at around 2930 and 2895 cm are assigned to –CH and
CH fragments (Fig. 4b).
57,58
ꢁ1
The band at 963 cm and
ꢁ
1
59,60
The
ꢁ
1
61
ꢁ
1
3
ꢁ1
3
ꢁ1
particularly marked (from 0.24 cm g for FPS to 0.13 cm g
for CS–FPS/Au). This nding suggests the formation of Au
nanoparticles directly within the pores of the CS–FPS derivative
ꢁ
1
ꢁ1
(Table 1).
–
2
3.2.1. Effect of experimental conditions. The temperature
The N adsorption–desorption isotherms of CS–FPS/Au NPs
2
effects on the reaction revealed that temperature signicantly
showed a characteristic type IV curve (Fig. 5), which is consis-
tent with literature reports on standard brous silica spheres.
As for FPS, the BET surface area, total pore volume, and BJH
promoted the reaction. From the viewpoint of practical appli-
cation, as the reaction of o-phenylenediamine with CO is
2
highly exothermic, effective heat removal is fundamental to save
2
ꢁ1
3
ꢁ1
pore diameter were determined as 34 m g , 0.24 cm g , and
.43 nm, whereas the corresponding parameters for CS–FPS
2
2
ꢁ1
3
ꢁ1
have decreased to 29 m g , 0.21 cm g , and 2.05 nm. The
nitrogen sorption analysis of CS–FPS also conrms a regular
Fig. 3 TGA diagram of CS–FPS/Au NPs.
Fig. 5 Adsorption–desorption isotherms of CS–FPS/Au NPs.
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Table
1
Structural parameters of FPS, CS–FPS, and CS–FPS/Au phenylenediamine, and the general form of the rate equation
materials determined from nitrogen sorption experiments
for this process is depicted in eqn (1):
2
ꢁ1
3
ꢁ1
Catalyst
S
BET (m g
)
V
t
(cm g
)
D
BJH (nm)
a
b
] [CS–FPS/Au]
c
r ¼ k[o-phenylenediamine] [CO
2
(1)
FPS
CS–FPS
CS–FPS/Au
34
29
16
0.24
0.21
0.13
2.43
2.05
1.68
in which k represents the rate constant, and [o-phenylenedi-
amine], [CO ] and [CS–FPS/Au] represent the o-phenylenedi-
2
amine, CO and catalyst concentrations respectively; a, b and c
2
represent the orders of reactants. For the synthesis of 2-benzi-
midazolones, pioneering works have shown that the reaction is
rst order with respect to CO . In the present catalytic system,
2
energy. Reaction yields were dramatically enhanced from 61%
ꢀ
ꢀ
to 94% with the increase in temperature from 90 C to 110 C for
ꢀ
assuming that the reaction is also rst order for CO and the
3
h. When the temperature increased to 110–120 C, there was
2
concentration of the catalyst does not change signicantly
no obvious enhancement in the yield for the reaction of o-
during the reaction, eqn (1) can be rewritten as eqn (2) or (3):
phenylenediamine with CO
2
. From the perspective of energy
ꢀ
conservation, 110 C was used as the optimum reaction
temperature (Fig. 6a). Fig. 6b displays the effect of carbon
dioxide pressure. The yield of 2-benzimidazolones gradually
improved when carbon dioxide pressure increased from
a
c
r ¼ kobs[o-phenylenediamine] k ¼ k[CO ][CS–FPS/Au] (2)
obs
2
r ¼ ꢁd[o-phenylenediamine]/dt ¼ kobs[o-phenylenediamine] (3)
0
.5 MPa to 1.5 MPa because the enhanced carbon dioxide
where, kobs is the observed pseudo-rst-order rate constant for
o-phenylenediamine conversion. Integrating eqn (3) yields
eqn (4):
concentration in the reaction phase resulted in the improve-
ment of product yield. With a further increase of carbon dioxide
pressure to 2.5 MPa, the concentration of o-phenylenediamine
was diluted which reduced the reaction activity. Fig. 6c illus-
trates the dependence of o-phenylenediamine yield on reaction
time. The yield of 2-benzimidazolones increased remarkably
ln[o-phenylenediamine] ¼ ꢁkobs
t
(4)
To determine the reaction order of o-phenylenediamine,
between 1–3 h, and there was no signicant change with further experiments were carried out at three different o-phenylenedi-
prolonging the reaction time, the reaction was almost amine concentrations as shown in Fig. 7. All the kinetic exper-
completed within 3 h. As shown in Fig. 6d, the yield of 2-ben- iments showed good t to rst order kinetics, implying that the
zimidazolones enhanced with increasing amounts of CS–FPS/ reaction is rst order for o-phenylenediamine (eqn (5)).
Au NPs catalyst. No product was obtained in the absence of
r ¼ kobs[o-phenylenediamine]
(5)
the catalyst. Moderate yields of product were observed following
the addition of 30–40 mg of catalyst into the sample reaction;
when the model reaction was carried out in the presence of
3
.2.3. Efficiency of CS–FPS/Au catalysts. To probe the scope
5
0 mg of catalyst, the best result was obtained. The model
reaction was not enhanced by increasing the amount of catalyst.
.2.2. Kinetic reaction. In order to provide useful evidence
and limitations of the CS–FPS/Au NPs, we further examined the
catalytic activity to other o-phenylenediamines under the opti-
mized reaction conditions as listed in Table 2. o-Phenylenedi-
amines bearing an electron-donating substituent (Table 2, entries
3
for the progress of the reaction mechanism, a study of the
reaction kinetics catalyzed by CS–FPS/Au NPs was undertaken
for the model reaction of CO
2
cycloaddition to o-
Fig. 6 The effect of reaction temperature (a); the effect of CO
2
Fig. 7 Pseudo-first order kinetic plots for the natural logarithm of
pressure (b); the effect of reaction time (c); the effect of catalyst different o-phenylenediamine concentrations versus time catalyzed
ꢀ
amount (d) on yield.
by CS–FPS/Au NPs (50 mg) at 110 C and 1.5 MPa CO
2
.
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Table 2 Synthesis of 2-benzimidazolone derivatives in the presence
a
of CS–FPS/Au NPs
b
Entry
1
o-Phenylenediamine
Product
Yield (%)
94
2
3
4
5
90
92
91
95
Fig. 9 TEM images of CS–FPS/Au nano-catalysts before reaction (a)
and after reaction (b). Particle size distribution before reaction (c) and
after reaction (d).
catalyzing reactions. However, these nanoparticles generally lose
their activity slowly during every reaction cycle. This loss in
activity is a result of the nanoparticles growing larger in size
through the Ostwald ripening process, in which small nano-
particles merge together to form larger nanoparticles. In the
case of the CS–FPS/Au catalyst system, we observed no appre-
ciable Ostwald ripening, and the particle size and distribution
remained the same even aer the reaction, which in turn main-
tained the catalytic activity. Ostwald ripening may be absent
because most of the Au nanoparticles are present between two
6
97
62
a
Reaction conditions: o-phenylenediamine derivatives (1 mmol), CS–
b
2
FPS/Au NPs (50 mg), CO 1.5 MPa, 3 h. Isolated yield.
5
and 6) were converted to the corresponding 2-benzimidazolones
in high yields. Whereas, o-phenylenediamines with an electron-
withdrawing group (Table 2, entries 2–4) gave the product in
good yields, which is probably due to the reduced electron density
of the o-phenylenediamine nitrogen atom.
bers of FPS, which implies that the nanoparticles cannot grow
larger than 50 nm in size because such a growth would be
restricted by the bers of FPS. Therefore, even aer several
reaction cycles, the size and distribution of Au nanoparticles
remains nearly the same (Fig. 9), and thus, the system maintains
nearly the same catalytic activity. These results clearly indicate
the advantage of the brous nature of FPS. Also, the loading
amount of the organic compounds in the fresh CS–FPS/Au NPs
were determined by TGA aer ten reuses. These amounts were
about equal to the fresh nanocomposites (Fig. 10).
3
.2.4. Stability of CS–FPS/Au catalyst. Furthermore, we
checked the recycling ability of the recovered catalyst. The
results of the recycling experiments are summarized in Fig. 8.
The recovered catalyst exhibited almost similar activity under
identical conditions at least for ten runs. The catalytic activity of
nano-Au depends on the size of the particles, and we observed
that Au-nanoparticles with varying sizes are effective in
Fig. 10 TGA diagram of CS–FPS/Au NPs. New catalyst (blue), recov-
Fig. 8 Recyclability of the catalyst.
ered catalyst (red).
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. Conclusions
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2 M. S. Funk, Anim. Cogn., 2002, 5, 167–176.
3 M. L. Wang, T. T. Jiang, Y. Lu, H. J. Liu and Y. Chen, J. Mater.
Chem. A, 2013, 1, 5923–5933.
In the present study CS–FPS/Au NPs was synthesized and
characterized as an environmentally-friendly nanocatalyst for
the synthesis of benzimidazolones from o-phenylenediamines
and CO with various electronically diverse substrates. More-
2
over, this procedure is an environmentally safe alternative for
producing benzimidazolones, and it demonstrates the chemical
2
2
4 X. Zhang and Z. Su, Adv. Mater., 2012, 24, 4574–4577.
5 Z. M. de Pedro, E. Diaz, A. F. Mohedano, J. A. Casas and
J. J. Rodriguez, Appl. Catal., B, 2011, 103, 128–135.
6 Y. M. Liu, H. Tsunoyama, T. Akita, S. H. Xie and T. Tsukuda,
ACS Catal., 2011, 1, 2–6.
7 X. Yang, C. Huang, Z. Y. Fu, H. Y. Song, S. J. Liao, Y. L. Su,
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8 Z. Y. Zhong, J. Y. Lin, S. P. Teh, J. Teo and F. M. Dautzenberg,
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2
2
2
2
2
utilization potential of CO in the preparation of industrially
signicant benzimidazolone intermediates. The chemistry and
further synthetic applications of this green methodology are
under active research for their extended applications in our
laboratory.
9 F. Wang, X. Liu, C.-H. Lu and I. Willner, ACS Nano, 2013, 7,
7278–7286.
Conflicts of interest
30 H. Miyamura, R. Matsubara, Y. Miyazaki and S. Kobayashi,
Angew. Chem., Int. Ed., 2007, 46, 4151–4154.
There are no conicts to declare.
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1 H. Gu, J. Wang, Y. Ji, Z. Wang, W. Chen and G. Xue, J. Mater.
Chem. A, 2013, 1, 12471–12477.
2 X. Wang, H. Liu, D. Chen, X. Meng, T. Liu, C. Fu, N. Hao,
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