Synthesis of a yolk/shell Fe3O4@poly(ionic liquid)s-derived nitrogen doped graphitic porous carbon materials and its application as support for nickel catalysts

Article abstract of DOI:10.1039/c4ra10374b

The synthesis of yolk/shell spheres including a movable magnetic core, a poly(ionic liquid)s-derived porous carbon shell, and nickel nanoparticles confined within the porous shell is reported. The as-prepared carbon shell is graphitic and porous, as proven by X-ray diffraction, Brunauer-Emmett-Teller equation, and transmission electron microscopy characterizations. The ensuing catalyst has been employed for the tandem dehydrogenation of sodium borohydride and hydrogenation of several nitro/nitrile compounds in aqueous media, which resulted in high yields with a very low amount of the catalyst.

Full text of DOI:10.1039/c4ra10374b

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PAPER
Synthesis of a yolk/shell Fe O @poly(ionic liquid)s-
3
4
derived nitrogen doped graphitic porous carbon
materials and its application as support for nickel
catalysts†
Cite this: RSC Adv., 2015, 5, 2258
Mohammad Reza Nabid,* Yasamin Bide and Zahra Habibi
The synthesis of yolk/shell spheres including a movable magnetic core, a poly(ionic liquid)s-derived porous
carbon shell, and nickel nanoparticles confined within the porous shell is reported. The as-prepared carbon
shell is graphitic and porous, as proven by X-ray diffraction, Brunauer–Emmett–Teller equation, and
transmission electron microscopy characterizations. The ensuing catalyst has been employed for the
tandem dehydrogenation of sodium borohydride and hydrogenation of several nitro/nitrile compounds
in aqueous media, which resulted in high yields with a very low amount of the catalyst.
Received 13th September 2014
Accepted 17th November 2014
DOI: 10.1039/c4ra10374b
www.rsc.org/advances
carbon-containing sources are used as carbonaceous precursors
because of the total evaporation or decomposition of most
Introduction
Due to their unique properties, such as large surface area, carbon containing organic compounds to gaseous products
multi-functionality and excellent loading capacity, yolk/shell during high-temperature carbonization process. The synthesis
nanostructures (YSNs), consisting of a core encapsulated in a of N-doped carbon materials has been mainly accomplished
hollow capsule with a porous shell have attracted considerable under harsh reaction conditions, such as post treatment with
11
12
attention over the past few years in a variety of applications, amines, urea, ammonia, or direct methods employing poly-
1
–4
13
14
including catalysis, storage, and drug delivery. Among them, aniline or acetonitrile. In recent years, porous carbons have
YSNs with a magnetic core, due to improvements in the also been obtained via the hydrothermal carbonization of
1
5,16
stability, biocompatibility, and signicant magnetization biomass derivatives.
Employing suitable natural precursors
17
strength of iron oxides, are desirable in biomedical applica- has led to the synthesis of nitrogen-doped carbons. In 2010,
tions. Moreover, YSNs with a magnetic core and a functional Paraknowitsch and coworkers employed ionic liquids (ILs) for
shell are attractive because of their potential applications as the synthesis of mesoporous N-doped graphitic carbon at
5,6
ꢀ
18
catalyst supports and elimination of time-consuming separa- 1000 C in a SBA-15 template. Using ILs and poly(ionic liquid)s
tion procedures such as ltration or centrifugation. On the (PILs) as the precursors for the synthesis of carbon materials
other hand, the outer shells of yolk–shell composites usually leads to a feasible synthesis by controlling the structure on
need to have both high surface area and good dispersion different length scales, and also the incorporation of a certain
characteristics to act as catalyst supports. Among the supports, amount of heteroatoms. The biggest advantage of them
carbon materials are attractive choices due to their electronic compared with other carbon precursors is their charged nature,
and heat conductivity, chemical and physical stability, which causes a negligible vapor pressure, even at elevated
sustainable nature and the possibility of control of their temperatures at which typical carbonization occurs. Thus, high
7
chemical connectivity and nanostructures. In contrast to carbon yields with the control of process and morphology can
disordered or amorphous carbon, graphitized carbons with be obtained. Due to a clever choice of anion and cation and the
their well-developed crystalline structure, present high electric overall hydrophobicity, ILs and PIL molecules can wet most
19
8–10
conductivity and enhanced chemical stability.
Therefore, surfaces and form very homogeneous lms and coatings.
from the viewpoint of the catalytic application, graphitized Furthermore, ILs and PILs contain rmly incorporated conju-
mesoporous carbons with relatively large surface area and high gated nitrogen, sulfur, boron, or phosphorus atoms to provide a
crystallinity are more desired. Currently only a few conventional stable and delocalized charge. Many of these heteroatoms stay
incorporated within the carbonaceous scaffolds, consequently
creating heteroatom doped carbons. The doping with nitrogen
Faculty of Chemistry, Department of Polymer, Shahid Beheshti University, G.C., P.O. atoms enhances the electric conductivity and catalytic
2
0–22
Box 1983969411, Tehran, Iran. E-mail: m-nabid@sbu.ac.ir
activity.
Moreover, metal or metal oxide nanoparticles can
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra10374b
be stabilized in nitrogen doped carbon framework through the
1
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3 4
generation of topological defects and the activation of nitrogen- Finally, nickel nanoparticles immobilized on YS Fe O @
23,24
2+
neighboring carbon atoms.
Due to the additional backbone PIL-D-(N)GPC were synthesized by introducing Ni ions, which
immobilization, higher carbon yields have been observed in the interact well with the nitrogen groups of the support, and
2
5–28
case of PILs.
Recently, PILs have also gained considerable subsequently their reduction with sodium borohydride
18,26–30
attention as novel carbon precursors.
(Scheme 1).
Due to our interest in the development of catalysts for useful
The supported catalyst was employed for the tandem dehy-
31–36
new synthetic methodologies,
as well as the general drogenation of sodium borohydride and hydrogenation of
importance of this issue, herein, we report the synthesis and nitro/nitrile compounds. A plausible mechanism for this reac-
characterization of yolk/shell Fe @poly(ionic liquid)s-derived tion catalyzed by NiNPs@YS Fe @PIL-D-(N)GPC has been
3
O
4
3 4
O
nitrogen doped graphitic porous carbon material, and its shown in Scheme 2. The chemical modication of the adsor-
application as support for nickel catalysts. Recently, we reported bent surface with nitrogen based functional groups or other
a catalyst for the dehydrogenation of sodium borohydride and heteroatom and transition metal doping increases the binding
37
42
2
hydrogenation of nitriles. In this work, the as-prepared cata- energy states of H . On the other hand, in aqueous media the
lyst was employed for the tandem dehydrogenation of sodium organic substrates are concentrated on the hydrophobic pores
borohydride and hydrogenation of several nitro/nitrile of graphitic porous carbon. In our catalytic system, these three
compounds. We chose nickel nanoparticles because employ- issues are combined; substrates, H and catalyst, all of which
2
ing the rst row transition metals as catalysts in the reduction are in the hydrophobic pores of graphitic porous carbon. Thus,
reactions is considerable more desirable compared to the it is expected that an efficient catalytic reaction would be ach-
precious metals, owing to important advantages such as low- ieved. Fourier transform infrared (FTIR) spectra of Fe O4
3
38–41
cost and abundance.
magnetic particles, and Fe O @SiO are shown in Fig. S1.†
3 4 2
Fig. 1A–C show the FTIR spectra of Fe
Fe @SiO @PIL-D-(N)GPC, and YS Fe
respectively. The FTIR spectrum of Fe @SiO
3
O
4
@SiO
2
@PCMVImCl,
3
O
4
2
3 4
O @PIL-D-(N)GPC,
Results and discussion
3
O
4
2
@PCMVImCl
ꢁ
1
ꢁ1
3 4 2
Fe O @SiO
particles were synthesized with a modied sol- (Fig. 1A) shows absorption bands at 576 cm and 3431 cm
vothermal reaction, followed by a sol–gel process. Then, the ascribed to the Fe–O and O–H vibrations, respectively. More-
ꢁ
1
poly(3-cyanomethyl-1-vinylimidazolium chloride) (PCMVImCl) over, the band at 1091 cm
related to Si–O–Si stretching
layer was coated on the prepared particles via the polymeriza- vibrations of SiO shell can be seen. The adsorption peaks at
2
ꢁ
1
tion of the IL monomer in ethanol. Pyrolysis of Fe
SiO
magnetic nitrogen-doped graphitic porous carbon ((N)-GPC)
materials in general. Then, the SiO
by a selective etching process to obtain hollow structures. with the band at 1091 cm related to Si–O–Si. The peak at
3
O
4
@
3144 and 2926 cm can be assigned as the C–H stretching
@poly(imidazolium-based)ILs, allowed the preparation of vibrations of the imidazole ring and the alkyl chains.
2
The stretching vibrations belonging to the C–N of the imid-
ꢁ
1
middle layer was removed azole rings, which should appear at 1138 cm , was overlapped
2
ꢁ1
3 4
Scheme 1 Schematic diagram for the synthesis of NiNPs@YS Fe O @PIL-D-(N)GPC.
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Fig. 2 XRD patterns of Fe
O
3 4
3 4
@PIL-D-(N)GPC (A) and YS Fe O @PIL-D-
Scheme 2 A plausible mechanism for the tandem dehydrogenation of
sodium borohydride and reduction of 4-nitrotoluene catalyzed by
(N)GPC (B).
3 4
NiNPs@YS Fe O @PIL-D-(N)GPC.
ꢀ
(
N)GPC (Fig. 2B), the peak of silica at 20.12 is eliminated as
expected, due to the removing of silica intermediate shell.
ꢁ
1
Fig. 3A–C show the thermograms (TGs) of three samples:
about 1633 cm is related to the C]N stretching vibration of
the imidazole ring. FTIR spectrum of Fe @SiO @PIL-D-(N)
GPC is shown in Fig. 1B. The weak band at 3442 cm can be
Fe O , Fe O @SiO , and Fe O @SiO @PCMVImCl, respec-
3
O
4
2
3
4
3
4
2
3
4
2
ꢁ
1
3 4 2
tively. Compared to the TGA diagram of Fe O @SiO particles,
43
the considerably higher weight loss observed in the TGA
diagram of Fe O @SiO @PCMVImCl is from the organic
attributed to the N–H symmetric stretching vibration. The
band at 2925 cm corresponds to the C–H stretching vibration.
ꢁ
1
3
4
2
ꢁ1
decomposition of the composites. Before thermal decompo-
sition a slight weight loss of around 5.2% is observed, as
shown in Fig. 3C. This weight loss is probably due to the
evaporation of physically absorbed moisture, and its value is a
The broad peak around 1259 cm
C–N stretching vibration, which is overlapped with the peak of
Si–O–Si in the FTIR spectrum of Fe @SiO @PIL-D-(N)GPC,
but observable in the spectrum of YS Fe @PIL-D-(N)GPC.
Therefore, the FTIR analysis conrms the presence of N–H and
C–N species in the ensuing porous carbon. In the FTIR
spectrum of YS Fe O @PIL-D-(N)GPC (Fig. 1C), the adsorption
peak of Si–O–Si at 1099 cm
conrmed the successful elimination of the middle SiO layer.
The XRD patterns of Fe
PCMVImCl are presented in Fig. S2.† In the XRD pattern of
Fe @SiO @PIL-D-(N)GPC (Fig. 2A), in addition to the char-
is related to the
3
O
4
2
44
3 4
O
little higher in the Fe O @SiO @PCMVImCl composite parti-
3
4
2
cles compared to Fe
hydrophilicity of the PCMVImCl shell. Fe
shows two types of distinct weight loss events: successive rapid
3
O
4
@SiO
2
, which is caused by the high
3
O
4
@SiO clearly
2
3
4
ꢁ
1
was not observed, which
ꢀ
ꢀ
decompositions at 140 C and 260 C due to the decomposition
2
of the organic shell vs. the relatively slow weight loss region at
3 4 2 3 4 2
O @SiO , and Fe O @SiO @
ꢀ
around 520–700 C due to the intermolecular condensation of
the silica particles. The weight retention obtained for Fe -
3
O
4
2
3
ꢀ
ꢀ
ꢀ
O @SiO @PCMVImCl (Fig. 3C) at 780 C is 62.9%. Using the
acteristic diffraction peaks of Fe
3
O
4
at 2q ¼ 32.14 , 35.57 ,
4
2
ꢀ
ꢀ
ꢀ
weight retention at 780 C obtained for Fe O @SiO (91.2%) as
5
1.34 and a broad peak at around 2q ¼ 20.12 , which corre-
3 4 2
ꢀ
a reference, the PCMVImCl weight content is calculated to be
sponds to SiO , a wide diffraction peak at around 2q ¼ 25.63 is
2
2
8.3%. Two rapid thermal degradation events of Fe
3
O
4
@
also observed, which relates to the (002) plane of graphitic
mesoporous carbon. In the XRD pattern of the YS Fe O @PIL-D-
ꢀ
SiO
2
@PCMVImCl occur at 283, and 374 C under air
3
4
Fig. 1 FT-IR spectra of Fe
PIL-D-(N)GPC (B), and YS Fe
3
O
4
@SiO
2 3 4 2
@PCMVImCl (A), Fe O @SiO @
Fig. 3 TGA curves of Fe
B).
3 4 2 3 4 2
O @SiO (A), and Fe O @SiO @PCMVImCl
3
O @PIL-D-(N)GPC (C).
4
(
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(Fig. 6). The oxygen mainly arises from Fe
3
O
4
and the thermally
stable groups in the carbon except for that of oxygen or water
absorbed on the carbon surface. The high-resolution XPS of N
1
s in the NiNPs@YS Fe O @PIL-D-(N)GPC shows two peaks for
3 4
N1s at 398.7 eV and 401.3 eV, which are attributed to pyridinic
and quaternary nitrogen in carbon structure, respectively
(Fig. 7A). These two different binding energies show that
nitrogen is embedded into the graphitic carbon structure
45
mainly in two forms. The spectrum of the Ni2p core level of
NiNPs@YS Fe O @PIL-D-(N)GPC is shown in Fig. 7B, which
3
4
demonstrates two bands at 855.9 and 873.5 eV assigned to
Fig. 4 TEM image of YS Fe
O
3 4
@PIL-D-(N)GPC.
0
0
Ni 2p3/2 and Ni 2p1/2, respectively. The two peaks with lower
2+
intensities at 861.7 and 879.5 eV correspond to Ni species that
could have been formed during the XPS sample preparation due to
the sensitivity of the stabilized Ni(0) nanoclusters to the aerobic
atmosphere. The Ni loading for the sample used for XPS
measurements was 9.8 wt%. Moreover, the absence of silicon band
at around 104 eV conrms the selective etching of silica shell.
Fig. 8 shows the nitrogen adsorption–desorption isotherms
recorded from YS Fe O @PIL-D-(N)GPC. The results showed
3
4
that the average pore sizes are 2.5 nm and by applying the BET
2
ꢁ1
model, the total surface area is calculated to be 138.63 m g
.
BET testing also showed a pore structure consisting of micro-
pores, and mesopores. The pore size distribution curve has
been shown in Fig. S3.†
3 4
Fig. 5 TEM images of NiNPs@YS Fe O @PIL-D-(N)GPC.
Catalytic hydrolysis of sodium borohydride can generate 4
atmosphere, which are due to the cleavage of the PCMVImCl mol of hydrogen per mol of sodium borohydride at room
polymer backbone (or carbonation).
The TEM image of YS Fe @PIL-D-(N)GPC is presented in
Fig. 4, which shows Fe magnetic particles coated with a
temperature, which in itself, is a useful approach for hydrogen
3 4
O
3 4
O
folded, lamellar-like morphology of stiff graphite plates with the
curved and wrapped structure. As clearly revealed, the lamellar-
like structures are, in fact, layered graphitic nanostructures.
Fig. 5 shows TEM images of NiNPs@YS Fe O @PIL-D-(N)GPC in
3
4
3 4
which three distinct components the black cores of Fe O , the
grey shells of graphite plates and the small black spheres of
nickel nanoparticles are observed.
The XPS spectrum of NiNPs@YS Fe O @PIL-D-(N)GPC
3 4
possesses four peaks centered at 284.7, 400.1, 530.9, and 711.4
eV, corresponding to C 1s, N 1s, O 1s, and Fe 2p, respectively
Fig. 7 XPS high-resolution spectra of the N 1s (A) and Ni 2p (B) of the
as-prepared NiNPs@YS Fe O @PIL-D-(N)GPC.
3 4
Fig. 6 XPS full spectrum of NiNPs@YS Fe
O
3 4
@PIL-D-(N)GPC.
3 4
Fig. 8 Nitrogen sorption isotherms of YS Fe O @PIL-D-(N)GPC.
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release from sodium borohydride (hydrogen content of 10.7 hydrophobic nature of porous carbon, the reactants tend to
46
wt%).
collect at those sites rather than water solvent. On the other
On the other hand, theoretical and also experimental studies hand, nickel nanoparticles as catalyst and hydrogen also exist in
have established that substitutional doping of carbon materials the pores. Thus, an efficient catalytic reaction probably occurs
can be employed to modify their physical and/or chemical as the reagents and catalyst concentrate in an area. Moreover, to
properties and also affect the hydrogen adsorption and optimize the amount of the catalyst, different amounts of the
47
desorption process. A modication approach of base activa- catalyst, including 0.8, 1, and 1.2 mol% Ni were used for model
4
8,49
46,50
tion,
NiNPs), and nanoscaffolds
GPC allows sodium borohydride to release 4 mol of H2 in In addition, the model reaction was carried out without catalyst
aqueous solution at room temperatures. in which no product was obtained over 24 h. According to these
Our investigation on the catalyst loading showed a high results, the optimum reaction condition is water as solvent and
atom efficiency of title NiNPs@YS Fe @PIL-D-(N)GPC. We 1 mol% Ni for the NiNPs@YS Fe @PIL-D-(N)GPC to catalyze
rst used 4-nitrotoluene as a model compound to demonstrate the tandem reaction. The summary of these results are given in
NiNPs@YS Fe @PIL-D-(N)GPC catalysis for the tandem Table S1.†
dehydrogenation of sodium borohydride, the hydrogenation of We also studied the support effect on nickel nanoparticles
(N-doped structure), transition-metal catalysts,
reaction in water at room temperature. The optimum amount of
46,51
(
by NiNPs@YS Fe O @PIL-D-(N) the catalyst considering the reaction time and yield was 1 mol%.
3 4
3
O
4
3 4
O

3 4
O
nitro compounds and to obtain the optimum reaction condi- catalysis. Nickel nanoparticles were used as active catalysts
tions. We examined the catalytic reactions at room temperature without a support in a model reaction for the catalytic reduction
in different solvents including DMSO, methanol, ethanol, of 4-nitrotoluene, but the conversion yield was low (33%). It
water, and determined water to be the best solvent to convert 4- could be due to the aggregation of nickel nanoparticles without
nitrotoluene to p-toluidine. Actually, because of the
a
support, resulting in reduced catalytic activity. The
a
3 4
Table 1 The reduction reaction of nitro/nitrile compounds with NiNPs@YS Fe O @PIL-D-(N)GPC as catalyst
Isolated yield
(%)
Entry
Compound
Product
Time (min)
1
2
30
30
90
91
3
30
87
4
5
25
30
92
90
6
7
30
30
90
88
8
9
60
60
89
80
1
0
45
87
a
ꢀ
4
Reaction conditions: 5 mL of deionized water, 1 mmol nitro/nitrile, 0.5 mmol NaBH , and 0.006 g catalyst at 25 C.
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improvement of the results with the support could be due to p–
p interactions of the aromatic groups in reactants with the
Conclusion
support preferring the close proximity of the reagents to the In this work, we have achieved several important aims: (i)
catalytic sites.
having a heterogeneous catalyst with the advantage of being
To evaluate the general applicability of the catalyst, different efficient, reusable, cost-effective and also removing the need for
nitro compounds were tested for reduction reaction using the catalyst ltration with magnetic separation; (ii) having a
sodium borohydride and 0.006 g catalyst containing 1 mol% Ni yolk–shell structure with unique properties such as large
ꢀ
1
at 25 C in water (Table 1). The H NMR spectra of the products surface area, multi-functionality and excellent loading capacity;
have been presented in Fig. S4–10.† As can be seen, various (iii) employing porous carbon as stabilizer for nanoparticles,
nitro compounds can generate the related amine in excellent which has several important advantages such as large surface
yields. The catalytic reaction could be extended to 1-methoxy-4- area, stability, and straightforward synthesis; (iv) using poly-
nitrobenzene, 1-nitronaphthalene, 1-uoro-4-nitrobenzene, 1- (ionic liquid)s as precursor for the synthesis of nitrogen doped
iodo-3-nitrobenzene, 1-bromo-4-nitrobenzene, and also nitro- porous carbon; (v) carrying out the tandem reaction in an
ethane compounds, which were all transformed to the respec- environmentally friendly and safe method; (vi) having the
tive amine derivatives with high yields (Table 1, entries 2ꢁ7). catalytic activity for reduction of nitro and nitrile compounds
Moreover, with respect to general applicability of the catalyst with high yields.
3 4
NiNPs@YS Fe O @PIL-D-(N)GPC, we also tested the reduction
reaction of nitrile compounds to the corresponding amines and
the results are shown in Table 1, entries 8–10. The reduction of
Experimental
benzonitriles is an important issue because it allows the easy Materials
preparation of a variety of biologically active benzyl amines
compounds. Moreover, the reduction reaction of picolinonitrile
1
-Vinylimidazole, and chloroacetonitrile were obtained from
0
Sigma-Aldrich and used without further purication. 2,2 -
Azobis(2-methylpropionitrile) (AIBN) (Aldrich) was recrystal-
lized from methanol. CMVImCl as IL monomer was prepared
according to the literature, and its H NMR spectrum is
presented in Fig. S14.† Nickel(II) acetate tetrahydrate was
purchased from Alfa Aesar. Ferric chloride hexahydrate
was examined, which resulted in the related amine in high yield
1
(
Table 1, entry 9). The H NMR spectra of the products are
shown in Fig. S11–13.†
53
1
As catalysis is a kinetic phenomenon, to investigate the
recyclability and deactivation of the catalyst, the initial rates
obtained from kinetic plots should be considered. If a single
data point aer long reaction time in each run was taken, one
might incorrectly conclude that the catalyst is completely stable
(
FeCl $6H O), trisodium citrate dehydrate (Na Cit$2H O),
3 2 3 2
sodium acetate (NaAc), ethylene glycol (EG), tetraethyl ortho-
silicate (TEOS), and sodium hydroxide (NaOH) were purchased
from Merck Chem. Toluene was dried from sodium.
Dichloromethane and methanol were dried from calcium
hydride and magnesium, respectively. All other solvents and
reagents were purchased from Aldrich or Merck and used
without further purication unless otherwise stated.
52
and recyclable. Therefore, the conversion yields for every run
aer 10 min for the reduction reaction of 4-nitrotoluene were
measured (Fig. 9A). As the conversion yields aer 10 min for
seven runs did not reduce considerably, we concluded that the
synthesized catalyst had good stability and recyclability. To
examine the productivity of the as-prepared catalyst, we inves-
tigated the reduction reaction of 4-nitrotoluene as a model
reaction up to seven cycles aer the completion of the reaction.
Instruments and characterization
By design, the magnetic extraction excludes the need for ltra- IR spectra were recorded on a Bomem MB-Series FTIR spec-
tion, centrifugation or the workup of the nal reaction mixture trophotometer. Transmission electron microscopy (TEM) anal-
to recover the catalyst, and consequently allows the easy recy- yses were performed using a LEO 912AB electron microscope.
cling of the catalyst. The results have been presented in Fig. 9B, Ultrasonic bath (EUROSONIC® 4D ultrasound cleaner with a
which indicates that the yield of product aer every run does frequency of 50 kHz and an output power of 350 W) was used to
not change signicantly.
disperse materials in solvents. Thermogravimetric analysis
TGA) was carried out using STA 1500 instrument at a heating
(
ꢀ
ꢁ1
rate of 10 C min in air. The specic surface area was calcu-
lated using the Brunauer–Emmett–Teller (BET) equation. Pore
size distribution was determined by the Barrett–Joyner–
ꢀ
Halenda (BJH) method. The samples were degassed at 150 C
for 20 h before measurements. X-ray powder diffraction (XRD)
data were collected on an XD-3A diffractometer using Cu Ka
radiation. XPS analysis was performed using a VG multilab 2000
spectrometer (ThermoVG scientic) in an ultrahigh vacuum.
Catalysis products were analyzed using a Varian 3900 gas
chromatograph (GC) (conversions were obtained using n-
decane as an internal standard). AA-680 Shimadzu (Kyoto,
Japan) ame atomic absorption spectrometer (AAS) with a
Fig. 9 Effect of recycling on the catalytic activity and productivity of
NiNPs@YS Fe O @PIL-D-(N)GPC after 10 (A) and after 30 min (B).
3 4
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deuterium background corrector was used for the determina- washing several times with deionized water and ethanol, the
1
tion of the metal. H NMR spectra were recorded with a black product was dried overnight in oven.
BRUKER DRX-300 AVANCE spectrometer, and DMSO or CDCl3
were used as solvents.
Synthesis of nickel nanoparticles immobilized on YS
Fe @PIL-D-(N)GPC (NiNPs@YS Fe @PIL-D-(N)GPC)
Aqueous solutions of nickel(II) acetate tetrahydrate (0.01 mL,
.15 M) and YS Fe @PIL-D-(N)GPC (0.1 g in 10 mL) were mixed
and placed in an ultrasonic bath (50 kHz) for 10 min to well
disperse metal ions in the hybrid material. Mixture was stirred
at room temperature for 8 h, and then reduction was carried out
3
O
4
3 4
O
3 4 3 4 2
Synthesis and coating of Fe O with silica (Fe O @SiO )
0
3 4
O
Fe
ture. Typically, FeCl
0.20 g, 0.68 mmol) were rst dissolved in ethylene glycol (20
3 4
O nanoclusters were synthesized according to the litera-
54
3
(0.65 g, 4.0 mmol) and trisodium citrate
(
mL). Next, NaAc (1.20 g) was added with stirring. The mixture
was vigorously stirred for 30 min, and then sealed in a Teon-
4
with the addition of 0.5 mL aqueous solution of NaBH (0.01 M)
to the mixture and stirring at room temperature for 1 h. It was
lined stainless-steel autoclave. The autoclave was heated to
ꢀ
ltered under vacuum, washed well with ethanol and water (2 ꢂ
2
00 C, maintained for 10 h, and then allowed to cool to room
ꢀ
2
0 mL) and dried under vacuum at 50 C for 4 h to obtain
temperature. The obtained Fe O particle suspension was
3
4
3 4
NiNPs@YS Fe O @PIL-D-(N)GPC. The AAS and TGA were used to
determine the amount of nickel in the synthesized catalyst.
successively washed three times with H
dried in a vacuum oven for 12 h at room temperature. For the
coating of Fe with silica, 50.0 mL of the as-prepared Fe
nanocluster solution (containing 0.4 g Fe ) was dispersed
2
O and EtOH, and then
3
O
4
3 4
O
General procedure for the tandem dehydrogenation of
sodium borohydride and hydrogenation of nitro/nitrile
3 4
O
into the mixture of deionized water (10.0 mL), ethanol (100.0
compounds with NiNPs@YS Fe O @PIL-d-(N)GPC as catalyst
mL) and NH $H O (50.0 mL). Aer ultrasound treatment for 10
3 4
3
2
min, a certain amount of TEOS was quickly added into the
system. The reaction was allowed to proceed with stirring for 8 h
at room temperature. Finally the products were separated by
magnet and washed using deionized water for the next-step.
To 2 mL distilled water, 1 mmol nitro/nitrile was added and
into this solution 0.006 g ultrasonically dispersed NiNPs@YS
Fe O @PIL-d-(N)GPC catalyst (1 mol% Ni) in water (3.0 mL) was
3
4
introduced. Finally, 0.5 mmol NaBH (0.038 g) was introduced.
4
The mixture was stirred. Aer the completion of the reaction,
the catalyst was removed via an external magnetic eld and
washed twice with CH Cl (6.0 mL). Then, the organic phase
2 2
was combined and the solvent was removed under vacuum to
obtain the pure product. The conversions were determined by
the gas chromatography (GC) analysis.
Preparation of Fe
Fe @SiO @PCMVImCl)
The PIL layer on silica particles was synthesized via polymeri-
zation of IL monomer in the presence of Fe @SiO particles
in ethanol. In a general polymerization procedure, 3 g of
CMVImCl monomer, 200 mg of AIBN and 5 mL of deionized
water were added to 70 mL of ethanol containing 3 g of
3 4 2
O /SiO /PILs composite particles
(
3
O
4
2
3
O
4
2
Acknowledgements
3 4 2
dispersed Fe O @SiO particles. The dispersion was degassed
by purging with nitrogen for 30 min prior to polymerization.
The nancial support provided by the Iran National Science
Foundation (INSF) is gratefully acknowledged.
The polymerization was conducted with vigorous stirring over-
ꢀ
night at 80 C. Aer cooling down, the obtained Fe
3
O
4
@
Notes and references
SiO @PCMVImCl composite particles were washed by four
2
centrifugation/redispersion cycles with deionized water, and
1
2
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ꢀ
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6
Carbonization process
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3
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2
1597.
sample was put into an aluminum oxide crucible in an oven and
ꢀ
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ꢀ
ꢁ1
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Preparation of the yolk/shell Fe O @poly(ionic liquid)s-
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derived nitrogen-doped graphitic porous carbon materials (YS
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Fe O @poly(ionic liquid)s-derived nitrogen-doped graphitic
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3 4
O
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