Silver and copper nanoparticles stabilized on ionic liquids-functionalized polyhedral oligomeric silsesquioxane (POSS): Highly active and recyclable hybrid catalysts

Article abstract of DOI:10.1016/j.poly.2019.07.012

Two novel heterogeneous hybrid catalysts were successfully synthesized using octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) and ionic liquids, followed by immobilization of Cu and Ag nanoparticles. The obtained hybrid catalysts, Cu@POSS-ILs and Ag@POSS-ILs, were characterized using FT-IR, SEM, EDX, TEM, XRD and TGA. Catalytic studies demonstrated that Cu@POSS-ILs was an excellent catalyst for click reaction in aqueous medium. Furthermore, Ag@POSS-ILs was also exhibited to be an active catalyst for 4-nitrophenol (4-NP) reduction. Simple preparation and easy catalysts recovery and recyclability of Cu@POSS-ILs and Ag@POSS-ILs for at least 3 and 6 runs, respectively, without loss of catalytic activity could be considered as important advantageous from catalytic application point of view.

Full text of DOI:10.1016/j.poly.2019.07.012

Accepted Manuscript
Silver and copper nanoparticles stablized on ionic liquids-functionalized poly-
hedral oligomeric silsesquioxane (POSS): highly active and recyclable hybrid
catalysts
Ali Akbari, Aylar Naderahmadian, Bagher Eftekhari-Sis
PII:
S0277-5387(19)30482-6
https://doi.org/10.1016/j.poly.2019.07.012
POLY 14062
DOI:
Reference:
Polyhedron
To appear in:
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Accepted Date:
26 February 2019
8 July 2019
Please cite this article as: A. Akbari, A. Naderahmadian, B. Eftekhari-Sis, Silver and copper nanoparticles stablized
on ionic liquids-functionalized polyhedral oligomeric silsesquioxane (POSS): highly active and recyclable hybrid
catalysts, Polyhedron (2019), doi: https://doi.org/10.1016/j.poly.2019.07.012
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Silver and copper nanoparticles stablized on ionic liquids-
functionalized polyhedral oligomeric silsesquioxane (POSS): highly
active and recyclable hybrid catalysts
Ali Akbaria,b, Aylar Naderahmadiana and Bagher Eftekhari-Sis*,a,c
aDepartment of Chemistry, University of Maragheh, Maragheh 55181-83111, Iran.
b Cellular and Molecular Research Center, Cellular and Molecular Medicine Institute, Urmia University
of Medical Sciences, Urmia, Iran.
cDepartment of Chemistry, Sharif University of Technology, Tehran, Iran
eftekhari.sis@gmail.com; eftekharisis@maragheh.ac.ir
Abstract
Two novel heterogeneous hybrid catalysts were successfully synthesized using octa-aminopropyl
polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) and ionic liquids, followed
by immobilization of Cu and Ag nanoparticles. The obtained hybrid catalysts, Cu@POSS-ILs and
Ag@POSS-ILs, were characterized using FT-IR, SEM, EDX, TEM, XRD and TGA. Catalytic
studies demonstrated that Cu@POSS-ILs was an excellent catalyst for click reaction in aqueous
medium. Furthermore, Ag@POSS-ILs was also exhibited to be an active catalyst for 4-nitrophenol
(4-NP) reduction. Simple preparation and easy catalysts recovery and recyclability of Cu@POSS-
ILs and Ag@POSS-ILs for at least 3 and 6 runs, respectively, without loss of catalytic activity
could be considered as important advantageous from catalytic application point of view.
Keywords: polyhedral oligomeric silsesquioxane nanoparticles, ionic liquids, nanohybrid
materials, metal nanoparticles, click reaction, 4-nitrophenol reduction
1 Introduction

Over the past decades, a massive attention has been devoted to the preparation and utilization of
metal nanoparticles (NPs) due to their exceptional physical and chemical properties that make
them as ideal candidates for a broad range of applications such as sensing, electronics, drug
delivery and antibacterial activities [1-5]. Apart from these applications, metal NPs have attracted
an extensive interest in catalysis. It is worth mentioning that from practical catalytic application
point of view, metal NPs aggregations could be considered as important shortcomings, resulting
in a remarkable decrease in their initial catalytic activities. Therefore, utilization of supporting
materials for the immobilization of metal NPs is quite substantial. This strategy not only be able
to solve the problem of catalysts recycling, but also improve the activity and stability of the
catalysts by synergestic interaction between metal NPs and supporting materials [6, 7]. Among
various solid supports for metal NPs dispersion [3, 8-10], there is less attention on the use of
polyhedral oligomeric silsesquioxane-ionic liquids (POSS-ILs) as a new type of nanohybrid
materials [11, 12]. Polyhedral oligomeric silsesquioxanes (POSS) is a new class of organic-
inorganic hybrid materials with the molar ratio of 1.5 for O/Si. POSS structure could be expressed
by the typical formula TnRm, where T shows the number of Si atoms and R the organic functional
groups [13-15]. Among various types of POSS structures [14, 16, 17], the cubic structure (T8R8)
with a rigid cage-like core has attracted a considrable attention due to its unique properties, such
as good biocompatibility, high mechanical stability and easy surface functionalization, which
make POSS as an ideal nano-building for fabricating multi-functional materials with various
applications [18-21]. As a novel promising materials, ionic-liquids (ILs), i.e. pure organic salts
with low melting temprature, have been vigorously explored by both academic and industrial
communities owing to their unique fundamental properties [22, 23]. It is worth to noting that the
preparation of new ILs-based materials with higher performences are still desirable. Recently,
POSS hybrid nanostructure was used in order to modulate of ILs properties for utilization in
different fields. For example, as a pioneer research group, Chujo et al. synthesized a series of
imidazolium based ILs metrials containing POSS nanoparticles with high thermal stability and
low melting temprature [24-28]. Articles survey showed that there are little reports on the use of
polyhedral oligomeric silsesquioxane-ionic liquids (POSS-ILs) as catalysts. For instance, Leng et
al. proposed new strategies to prepare amphiphilic polyoxometalate hybrid catalysts using POSS
and ionic liquids for epoxidation reaction [12, 29, 30]. In another interesting report, POSS was
functionalized with methyl imidazole and used as a novel catalyst for the efficient conversion of

CO2 and epoxides into cyclic carbonates [31]. Taking into account that the embedding of POSS
into ILs could create high-tech materials, and in the course of our studies on POSS chemistry [13,
14, 32] herein for the first time, we developed an innovative exploitation of octa-aminopropyl
polyhedral oligomeric silsesquioxane hydrochloride salt (OA-POSS) [33, 34] as a nano-building
block for constructing new POSS-ILs nanohybrid material. A topic of interest in this context is the
use of synthesized POSS-ILs as an appropriate solid support in the preparation of well-dispersed
Cu and Ag nanoparticles. The resulting catalysts, Cu@POSS-ILs and Ag@POSS-ILs NPs, were
fully characterized by FT-IR, EDX, SEM, TEM, XRD and TGA analysis. Moreover, catalytic
experiments have shown that Cu@POSS-ILsand Ag@POSS-ILsNPs exhibited remarkable
catalytic activities and recyclability in click reaction and 4-NP reduction, respectively.
2 Materials and methods
2.1 Materials
Copper acetate monohydrate, hydrazine hydrate (80 %), all benzyl halides (Benzyl chloride,
benzyl bromide, 2-nitrobenzyl chloride, 4-nitrobenzyl chloride and 2-methylbenzyl chloride) and
alkynes (phenyl acetylene, propargyl alcohol and 2-Methylbut-3-yn-2-ol), sodium azide, 3-
Aminopropyltriethoxysilane (APTES), 2‐(chloromethyl)oxirane and 1-methylimidazole were
purchased from Sigma-Aldrich (Germany). All solvents were supplied from Merck (Germany).
Sodium borohydride (NaBH4), Silver nitrate (AgNO3) and 4-Nitrophenol (4-NP) were obtained
from Sigma-Aldrich (Germany).
2.2. Synthesis of Octa-aminopropyl polyhedral oligomeric silsesquioxane hydrochloride salt
(OA-POSS)
OA-POSS was synthesized according to the previous procedure with hydrolytic condensation of
APTES in acidic medium [33]. Briefly, in a 500 ml two-neck round bottom flask equipped with a
condenser and a magnetic stirrer, 180 mL methanol and concentrated HCl (15 mL, 35–37%) were
added, followed by addition of APTES (7.5 ml, 30 mmol) in drops at 60 °C. Successively, the
reaction temperature was increased and refluxed at 90 °C for 16 h with vigorous stirring. After
cooling the reaction mixture to room temperature, in order to obtain white precipitate, 300 ml THF
was added. The obtained OA-POSS was filtrated and washed several times with THF, then
collected, and dried at 40 °C under vacuum for 24 h. finally OA-POSS as a white powder was

stored in a sealed vial for further usage (with a yield of 33%). Spectroscopic data are as follows:
1H NMR (300 MHz, D2O): δ 2.91(t, CH2NH3, 16 H), 1.68 (m, SiCH2CH2, 16 H), 0.68 (t, SiCH2,
16 H) ppm.13C NMR (100 MHz, D2O): δ 41.04 (s, CH2NH3), 20.01 (s, SiCH2CH2), 8.55 (s, SiCH2)
ppm. FT-IR (KBr, cm−1): 3224, 3025, 2920, 1604, 1494, 1125, 1107, 935, 705 cm−1.
2.3. Synthesis of 1‐methyl‐3‐(oxiran‐2‐ylmethyl)‐1H–imidazol‐3‐ium chloride (ILs)
To a 100 ml round bottom flask equipped with a reflux condenser, 3.9 ml (50 mmol) 2-
(chloromethyl)oxirane and 4.0 ml (50 mmol) 1-methylimidazole were added. The reaction mixture
was stirred at 70 °C for 48 h in order to form a two-phase mixture. The upper layer was decanted
and the lower phase was washed with ethyl acetate for three times. Finally, the product was
obtained as a brown liquid [35] .
2.4. Synthesis of ionic liquid-functionalized polyhedral oligomeric silsesquioxane (POSS-ILs)
ILs (51 mg), OA-POSS (50 mg) and triethyl amine (0.5 ml) were charged in a 10 ml round bottom
flask containing 2 ml DMSO and equipped with a reflux condenser and a magnetic stirrer. The
reaction mixture was stirred vigorously at 90 °C for 24 h in an oil bath. After cooling to room
temperature, the reaction mixture was poured into excess acetonitrile (CH3CN) under vigorous
stirring to precipitate POSS-ILs as a brown solid compound, then washed with DMSO and dried
in a vacuum oven at 70 °C for 24 h.
2.5. Preparation of Cu@POSS-ILs and Ag@POSS-ILs hybrid materials
25 mg of POSS-ILs was dispersed in 5 ml DMF ultrasonically for 1 h, then 4 mg of copper acetate
was added and the mixture was stirred for another 1 h, followed by adding 10 µl hydrazine hydrate
(80 %). The reaction was kept at room temperature under vigorous stirring for a further 1 h. the
product was separated, washed with ethanol and dried under vacuum at 60 °C for 6 h to afford
Cu@POSS-ILs. In the case of Ag@POSS-ILs, 70 mg of POSS-ILs was dissolved in 5 ml distilled
water, followed by adding 50 mg AgNO3 and stirring for 1 h in order to get a milky solution. To
reduce the Ag ions to Ag NPs, 5 ml of NaBH4 aqueous solution (20 mmol/L) was added dropwise.

After separation by centrifuge, the product was washed with ethanol and dried under vacuum at
60 °C for 6 h.
2.6. General procedure for click reaction by Cu@POSS-ILs hybrid catalyst
To a mixture of alkyne (1 mmol), the organic halide (1.1 mmol) and NaN3 (1 mmol), 7 mg of
Cu@POSS-ILs catalyst was added in water. Then the reaction was stirred at 50 °C for 12 h, and
the conversion of the starting materials was monitored by TLC. Finally, Cu@POSS-ILs catalyst
was separated and the product was extracted with EtOAc (3 × 5 ml) with no further purification.
To optimize, click reaction was carried out in various time (2, 6 and 12 h), different solvents (water,
toluene, acetonitrile, acetone and ethanol) with various amount of catalysts (0, 1, 3, 5, 7 and 9 mg).
2.7. General procedure for reduction of 4-NP using Ag@POSS-ILs hybrid catalyst
In a typical experiment, aqueous solution of 4-NP (4 mg, 10 ml) and NaBH4 (100 mg) were mixed
in a 25 ml round bottom flask, followed by adding 7 mg as-prepared hybrid catalyst. The reaction
progress i.e. the conversion of 4-NP to 4-AP was monitored by the UV-Vis spectroscopy in a
scanning range of 200-700 nm at room temperature.
2.2 Instrumentation
Fourier transform infrared (FT-IR) spectra were carried out on a Win-Bomem spectrometer,
version 3.04 Galactic Industries Corporation over the range of 400–4000 cm−1. The scanning
electron microscopy (SEM) analyses were done by a VWGA3 TESCAN (20.0 KV) microscope
field emission scanning electron microscope (FE-SEM) at an accelerating voltage of 20 keV with
an energy-dispersive X-ray (EDX) spectroscopy. The XRD diffraction patterns of samples were
collected with a Bruker D8 Advance diffractometer using a Cu Kα radiation source (λ= 0.154059
nm) at 30 keV in the scan range (2θ) from 4 to 70°. Thermogravimetric (TGA) analyses were
performed using a Linseis L81A1750 (Germany) at a heating rate of 10 °C/min under high purity
nitrogen atmosphere from 50 to 800 °C. UV–Vis absorption spectra were recorded on a Shimadzu
UV-1800 model spectrophotometer.
3 Results and discussion
3.1. Synthesis and characterization of hybrid catalysts

The aim of this work was to exploit a simple and facile method in order to synthesize a novel
POSS-ILs hybrid solid support for immobilization of Cu and Ag NPs. Scheme 1 showed the
synthesis routes of POSS-ILs based catalysts in which octa-aminopropyl polyhedral oligomeric
silsesquioxane hydrochloride salt (OA-POSS) functionalized with imidazolium moiety, followed
by immobilization of Cu and Ag NPs.

R
O
Si
R
O
POSS
Si
Si
R
N
O
R
O
Si
O
N
O
O
Cl
O
O
R
Si
R=
Si
O
NH
. HCl
Si
O
O
2
O
Si
ILs
8
R
DMSO
Et3N
R
R
N
N
N
N
OH
N
N
n
N
O
n
N
N
OH
O
O
N
N
O
N
N
N
NH
N
O
O
NH
n
N
N
H
O
Si
O
N
HO
N
N
OH
O
Si
n
O
N
O
Si
O
N
N
Si
N
O
O
Si
O
H
N
O
HN
O
Si
N
O
N
O
O
Si
O
N
N
N
Si
O
n
N
N
NH
OHn
N
HO
O
N
N
O
N
HN
NH
N
N
N
N
N
O
N
O
N
n
n
O
HO
O
HO
N
N
N
N
N
N
N
POSS-ILs
Cu(OAC)2.H2O
N2H4
AgNO3
NaBH4
Cu NPs
Ag NPs
POSS-ILs@Cu
POSS-ILs@Ag
POSS

Scheme 1. Synthetic approach to prepare of POSS-ILs, Cu@POSS-ILs and Ag@POSS-ILs NPs
Obtained hybrid catalysts, Cu@POSS-ILs and Ag@POSS-ILs, were used in click reaction and 4-
NP reduction, respectively. Excellent catalytic activity of these hybrid catalysts could be explained
that the synthesized POSS-ILs solid support not only facilitated the well dispersion of metal
nanoparticles but also the hydrophobicity of inorganic core in POSS has been proved to be helpful
in the organic transformations.
Figure 1 depicts the FT-IR spectra of synthesized POSS based samples. A band at around 1120-
1125 cm-1 could be seen in all spectra, which is related to the asymmetric vibration of Si-O-Si on
the POSS nanoparticles [34, 36]. Furthermore, the bands at 2865 and 2920 cm-1 in the FT-IR
spectra proved the existence of propyl chains in OA-POSS [33]. POSS-ILs and hybrid catalysts
show characteristic bands at 1425-1630 cm-1 and 2850-2930 cm-1 regions that are corresponded to
imidazolium groups and CH2 stretching vibrations, respectively, suggesting the coexistence of
POSS nanoparticles and ILs moiety [35]. After immobilization of Ag and Cu nanoparticles on the
POSS-ILs solid support, the peaks related to Si-O-Si and organic moiety in POSS-ILs are
consistent. However, small shifts could be seen in the bands of imidazolium regions, confirming
the formation of hybrid catalysts by coordination of Ag and Cu NPs with poly ionic liquid on OA-
POSS.

Figure 1. FT-IR spectra of OA-POSS, POSS-ILs, Ag@POSS-ILs and Cu@POSS-ILs
XRD patterns of Ag@POSS-ILs and Cu@POSS-ILs samples were investigated to study the
crystalline nature of Ag and Cu NPs present inside the hybrid catalysts. As it could be seen from
figure 2, the XRD pattern of Ag@POSS-ILs included some sharp peaks at 2Ө = 38.2°, 44.5° and
65.1° corresponding to (111), (200) and (220) sets of lattice plane, respectively, suggesting the
presence of crystalline Ag NPs [37]. In the case of Cu@POSS-ILs, two peaks at 2Ө = 26.8° (111)
and 34.5° (200) were characteristic of the face-centered cubic (fcc) structure of Cu NPs. Two weak
XRD peaks at around 2Ө = 43.7° and 52.5° were also observed. [38, 39].

Figure 2. XRD patterns of Ag@POSS-ILs and Cu@POSS-ILs
The cross-section fracture surfaces and the elemental composition of the synthesized hybrid
catalysts were investigated by SEM and EDX analysis, respectively. Figure 3A shows the SEM
image of Cu@POSS-ILs with irregular blocks and smooth surfaces. In the case of Ag@POSS-ILs
hybrid catalyst, Figure 3C, the SEM image depicts a fluffy rough surface composed of aggregated
nanoparticles. Moreover, the EDX results is illustrated in Figure 3B and 3D, which confirms the
existence of Si, Cu and Ag elements in the structure of hybrid catalysts. The content of Ag and Cu
was 17.60 % and 10.19 wt %, respectively.

Figure 3. SEM images (with the magnification of 3.00 kx) of A) Cu@POSS-ILs, C) Ag@POSS-ILs and EDX
patters of B) Cu@POSS-ILs, D) Ag@POSS-ILs
TEM images were recorded in order to investigate the size and shape of Cu and Ag NPs fabricated
on the surface of hybrid catalysts. Figure 4 shows TEM images of Cu@POSS-ILs and Ag@POSS-
ILs with two different magnifications. In the TEM images of both hybrid catalysts, black
aggregated micelles with spherical shapes and size of 50-60 nm are obviously seen, confirming
the presence of POSS units (Figure 4A and 4C). The same observations were reported by Leng et
al. [30] and Bivona et al. [31]. In the high-resolution TEM images, uniformly dispersed dark
nanoparticles with small size of 5-10 nm could be seen clearly in Figure 4B and 4D, indicating the
existence of Cu and Ag NPs in the hybrid catalysts, respectively.
Figure 4. TEM images of A and B) Cu@POSS-ILs, C and D) Ag@POSS-ILs with two different magnifications (60
and 20 nm)
TGA profiles in Figure 5 demonstrates that the prepared hybrid catalysts have excellent thermal
stability with decomposition starting at about 300 °C. The weight loss of 10 % before 300 °C could
be related to the loss of adsorbed water. The weight loss in 300-500 °C is attributed to the
destruction of organic groups.

Figure 5. TGA thermograms of POSS-ILs, Cu@POSS-ILs and Ag@POSS-ILs
3.2. Catalytic experiments
Referring to TEM images and scheme 1, the synthesized POSS-ILs solid support enabled us in
situ preparation and immobilization of Cu and Ag NPs with small size and high dispersion in
which are favorable and critical from catalytic application point of view. In addition, obtained
catalysts possessed both POSS and ILs in their structures, it was considered that the catalysts could
facilitate organic transformations [40]. In this regard, we decided to study the catalytic activity of
the Cu@POSS-ILs and Ag@POSS-ILs in click reaction and 4-NP reduction, respectively. In the
case of Cu@POSS-ILs, to optimize the reaction conditions, the effects of some parameters such
as catalyst amount, temperature, reaction time and various solvents were investigated for model
reaction of phenyl acetylene, benzyl chloride and sodium azide to synthesize 1-benzyl-4-phenyl-
1,2,3-triazole with Cu@POSS-ILs as hybrid catalyst (Table 1).
Table 1. Selection of click reaction in the presence of Cu@POSS-ILs hybrid catalyst

Cl
N
N
POSS-ILs@Cu NPs
Solvent, heat
N
Ph
NaN3
Ph
Catalyst
Entry
Solvent
T (°C)
Time (h)
Yield (%)a
amount (mg)
1
0
1
3
5
7
9
7
7
7
7
7
7
7
7
7
7
H2O
H2O
70
70
70
70
70
70
r.t
12
12
12
12
12
12
12
12
12
12
2
0
54
62
67
72
73
0
2
3
H2O
4
H2O
5
H2O
6
H2O
7
H2O
8
H2O
40
50
60
50
50
50
50
50
50
48
82
77
35
66
5
9
H2O
10
H2O
11
H2O
12
H2O
6
13
C2H5OH
CH3CN
toluene
acetone
12
12
12
12
14
15
N.Rb
N.R
N.R
16
a Isolated yield.
b No Reaction.
As it can be seen from Table 1 (entry 1), no product was obtained when the reaction was carried
out in the absence of catalyst, demonstrating the need of Cu@POSS-ILs hybrid catalyst to achieve
desired product. Entries 2-6 showed the effect of Cu@POSS-ILs amount in the model reaction.
By increasing the amount of hybrid catalyst from 1 to 7 mg, the product yield increased from 54
to 72 % at 70 °C, respectively. As the reaction temperature has a significant effect on the product
yield, we found that no product was obtained at room temperature (entry 7). In contrary, by
increasing the reaction temperature (e.g. 40-70 °C), a remarkable increase in the product yield was
obtained (entries 9 and 10). According to Table 1 and entry 9, desired product, 1-benzyl-4-phenyl-

1,2,3-triazole, was isolated in highest yield (82%) at 50 °C after 12 h. Therefore, in all remaining
experiments, 50 °C was selected as the optimum reaction temperature. Also, the time dependence
of click reaction was illustrated in Table 1. On the other hand, when the reaction time was less
than 12 h, the low amount of product was isolated (entries 11 and 12). Additionally, the catalytic
performance of Cu@POSS-ILs was explored in various solvents. As illustrated in Table 1 (entries
14-16), the model reaction was not promoted in acetonitrile, toluene and acetone. In the case of
ethanol as a solvent (entry 13), only 5% product yield was achieved. Compared to other solvents,
experimental results showed that the click reaction with high yield was carried out in water as a
green solvent. Finally, the best optimized conditions were achieved by conducting the model
reaction in the presence of 7 mg of Cu@POSS-ILs in water at 50 °C for 12 h (entry 9). Using this
optimized condition, to evaluate the scope of general applicability of Cu@POSS-ILs hybrid
catalyst, the reaction of different alkynes and substituted benzyl halides was examined. As shown
in Table 2, compared to aliphatic alkynes, the click reaction of phenyl acetylene occurred with
higher yield (entries 1-5). Benzyl chlorides with electron-withdrawing group are less reactive than
those with electron-donating group (entries 3-5). Additionally, due to lack of steric hindrance,
benzyl chloride with nitro group at para position was more reactive to the click reaction than the
ortho derivative.
Table 2. Click reaction of various starting materials in the presence of Cu@POSS-ILs hybrid
catalyst.
Entry
1
Benzyl halide
Alkyne
Product
Yield (%)
82
Cl
N
N
Ph
N
Ph
Ph
Br
N
N
2
75
Ph
N

O2N
Cl
NO2
N
3
4
52
69
Ph
Ph
N
N
Ph
H3C
Cl
N
CH3
N
N
Ph
Cl
NO2
N
N
5
6
67
6
Ph
N
Ph
N
NO2
Cl
HO
N
N
OH
Cl
Br
Br
H3C
N
HO
H3C
7
8
9
6
N
N
CH3
OH
H3C
N
HO
N
10
22
N
OH
H3C
HO
H3C
N
N
N
CH3
OH
H3C

The reusability and recoverability of the catalyst are substantial issues from an economic point of
view. In this regard, the reusability of Cu@POSS-ILs hybrid catalyst in the click reaction of phenyl
acetylene, benzyl chloride and sodium azide to synthesize 1-benzyl-4-phenyl-1,2,3-triazole was
tested. For each run, the catalyst was separated from the reaction mixture by centrifugation, washed
with distilled water and ethyl acetate, dried and reused in the next run. Figure 6 showed that after
three times recycling the catalyst, the reaction yields slightly decreased due to the loss of catalyst
activity.
Figure 6. Reusability of Cu@POSS-ILs hybrid catalyst in click reaction
In addition, leaching experiment demonstrated that the reaction process was heterogeneously
catalyzed by Cu@POSS-ILs and the hybrid catalyst was stable during the reaction process.
In the present work, the catalytic activity of Ag nanoparticles stabilized on the surface of POSS-
ILs solid support, Ag@POSS-ILs, was evaluated in the reduction of 4-NP into 4-amino phenol (4-
AP) using sodium borohydride (NaBH4) as a reducing agent in aqueous medium. Upon addition
of Ag@POSS-ILs, the reaction color changed gradually from yellow to colorless in a period of 0-
16 minutes, demonstrating the successful conversion of 4-NP to 4-AP. This conversion could be
easily monitored by UV-Vis spectroscopy. As it could be seen from Figure 7, the absorbance band
at 400 nm relating to nitrophenolate anion remarkably decreased with time and new absorbance
peak at 300 nm corresponding to 4-AP gradually observed. In the absence of catalyst, the
absorbance band kept unchanged and the reduction reaction would not carry out over the time.

Figure 7. Time-dependent UV-Vis spectral changes in 4-NP reduction by Ag@POSS-ILs
The catalytic conversion of 4-NP into 4-AP could be expressed using the equation 1.
퐶0 ‒ 퐶푡
(4-NP)% =
× 100
퐶0
Whereby, Ct and C0 showed the concentration of 4-NP at time t and 0, respectively.
Moreover, a linear correlation between Ln (Ct/C0) and the reaction time at room temperature was
depicted in Figure 8, suggesting that the reduction of 4-NP was expected to be a pseudo-first-order
process. The kinetic rate constant (k) of the reaction was possible to determine from Figure 8 and
equation 2,
퐶푡
퐿푛 =‒ 퐾푡
퐶0

Figure 8. Linear relationship of Ln (Ct/C0) as a function of time
For Ag@POSS-ILs hybrid catalyst, the kinetic rate constant (k) was obtained about 0.2631 s-1 with
the error of ±0.0096. The high catalytic performance could be attributed to the unique structure of
as-prepared POSS-ILs solid support, which acted as a platform for well-dispersion of fabricated
Ag NPs with very small sizes. The reusability of the hybrid catalyst was also tested. In this regard,
at the end of the reaction, the catalyst was washed repeatedly with ethanol and water in order to
remove any reaction byproducts from the previous run. Then the washed catalyst was used in the
reaction to confirm the stability of its catalytic activity. As it could be seen from Figure 9, by
increasing the number of reactions runs, the reaction time increased.
Figure 9. Reusability of Ag@POSS-ILshybrid catalyst in 4-NP reduction

4 Conclusion
New hybrid organic-inorganic materials of imidazolium ionic liquids-functionalized polyhedral
oligomeric silsesquioxane (POSS) were successfully fabricated and considered as a solid support
for in-situ immobilization of Cu and Ag metal nanoparticles (Cu@POSS-ILs and Ag@POSS-ILs).
The combination of POSS and ionic liquid not only led to well-dispersion of metal nanoparticles
but also facilitated the organic transformation. As-prepared hybrid materials, Cu@POSS-ILs and
Ag@POSS-ILs, were used as efficient catalysts in click reaction and 4-NP reduction, respectively.
Easy preparation, simple catalyst separation and reusability made the synthesized catalysts
(Cu@POSS-ILs and Ag@POSS-ILs) promising catalytic hybrid catalysts for click reaction and 4-
NP reduction.
Acknowledgements We are grateful to the University of Maragheh for financial support.
Corresponding author thanks the Iran Science Elites Federation (ISEF).
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 New supporting material based on POSS-ionic liquid was synthesized.
 Ag and Cu metal nanoparticles were immobolized on POSS-ionic liquid.
 Catalytic performances of the as prepared hybrid materials were investigated in click
reaction and 4-NP reduction