Palladium nanoparticles encapsulated in magnetically separable polymeric nanoreactors

Article abstract of DOI:10.1039/c3ta14992g

A method for immobilization of palladium nanoparticles in magnetically separable polymeric nanocapsules is presented. The method is based on co-encapsulation of palladium nanoparticles stabilized by hyperbranched polyamidoamine (H-PAMAM-C₁₅) modified with palmitoyl groups and hydrophobic magnetite nanoparticles within polyurea nanospheres. The synthesis of these polyurea nanospheres is based on nanoemulsification of chloroform, containing magnetic nanoparticles and palladium acetate, in water using suitable surfactants or dispersants. Then, the chloroform nano-droplets are confined in a polyurea shell formed by interfacial polycondensation between isocyanate and amine monomers. The palladium acetate was reduced with hydrogen to create palladium nanoparticles dispersed in the core of the polyurea nanocapsules. These catalytic polymeric nanoreactors were utilized in hydrogenation of alkenes and alkynes in water. The nanoreactors were easily separated from the reaction mixture via application of external magnetic field. The recyclability of these nanoreactors was examined in hydrogenation of styrene; no significant change was observed in their reactivity for up to four cycles.

Full text of DOI:10.1039/c3ta14992g

Journal of
Materials Chemistry A
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PAPER
Palladium nanoparticles encapsulated in
magnetically separable polymeric nanoreactors†
Cite this: J. Mater. Chem. A, 2014, 2,
3971
*
Ester Weiss, Bishnu Dutta, Yafit Schnell and Raed Abu-Reziq
A method for immobilization of palladium nanoparticles in magnetically separable polymeric nanocapsules
is presented. The method is based on co-encapsulation of palladium nanoparticles stabilized by
hyperbranched polyamidoamine (H-PAMAM-C15) modified with palmitoyl groups and hydrophobic
magnetite nanoparticles within polyurea nanospheres. The synthesis of these polyurea nanospheres is
based on nanoemulsification of chloroform, containing magnetic nanoparticles and palladium acetate, in
water using suitable surfactants or dispersants. Then, the chloroform nano-droplets are confined in a
polyurea shell formed by interfacial polycondensation between isocyanate and amine monomers. The
palladium acetate was reduced with hydrogen to create palladium nanoparticles dispersed in the core of
the polyurea nanocapsules. These catalytic polymeric nanoreactors were utilized in hydrogenation of
alkenes and alkynes in water. The nanoreactors were easily separated from the reaction mixture via
application of external magnetic field. The recyclability of these nanoreactors was examined in
hydrogenation of styrene; no significant change was observed in their reactivity for up to four cycles.
Received 2nd December 2013
Accepted 6th January 2014
DOI: 10.1039/c3ta14992g
www.rsc.org/MaterialsA
separation and the recyclability of these encapsulated catalysts
were easily enabled by centrifugation.
Introduction
Magnetic nanoparticles (MNPs) have been recently utilized
widely as supports for catalysts, by modication of the MNP
surface.11 The supported catalysts have proven to be effective
in numerous organic transformations and were easily sepa-
rated from the reaction media by applying an external
magnetic eld. Magnetic nanoparticles have also been utilized
recently in immobilization of metal nanoparticles.12 These
magnetically separable metal nanoparticles are prepared
mainly by adsorption of metal ions on the surface of the
magnetic nanoparticles. This can be done by using function-
alized MNPs with coordinating groups or using MNPs coated
with a silica layer, containing specic stabilizing groups.
Finally, the loaded ions are reduced with hydrogen, sodium
borohydride or hydrazine.
Here, we present a new method for the immobilization of
palladium nanoparticles that can be magnetically separable
as well. The method is based on encapsulation of palladium
nanoparticles and hydrophobic MNPs in the core of poly-
urea nanocapsules. These nanocapsules were prepared by
nanoemulsication and interfacial polymerization between
isocyanate and amine monomers.13 The resulted new
materials were characterized and their catalytic activity was
explored in hydrogenation of alkenes and alkynes in
aqueous medium. By applying an external magnetic eld,
they were easily separated from the reaction medium
and were recycled four times in hydrogenation of styrene in
water.
In the past decades catalysis by metal nanoparticles (NPs) has
been intensively investigated due to their large surface area
and unique properties.1 The nanoparticles have two major
drawbacks; they tend to aggregate and their recovery using
trivial procedures is difficult. Employing an electrostatic, steric
or electrostatic–steric stabilizer can prevent aggregation of
metal nanoparticles. Common stabilizers are organic poly-
mers,2 dendrimers,3 surfactants4 and organic ligands.5 Recov-
erability is achieved by immobilization of NPs that also can
prevent their aggregation. Immobilization on solid supports,6
such as inorganic materials and organic polymers, is used
extensively. Other immobilization techniques are based on
encapsulation of metallic NPs in sol–gel matrices7 and in
metal organic frameworks.8 In addition, encapsulation of
metal NPs in the shell of polymeric microcapsules has attrac-
ted a great deal of attention in the past years, because it
provides immobilization and protection of NPs from the
reaction media.9 For example, encapsulation of palladium
nanoparticles and their application in catalytic hydro-
dechlorination of chlorophenols were demonstrated.10 The
Institute of Chemistry, Casali Center of Applied Chemistry and the Center for
Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Jerusalem
91904, Israel. E-mail: Raed.Abu-Reziq@mail.huji.ac.il; Fax: +972-4-6585469; Tel:
+972-2-6586097
† Electronic supplementary information (ESI) available: SEM images and DLS
measurements of polyurea nanocapsules formed from different amine and
isocyanate monomers, EDS analysis of MNPs@PU capsules, and the TGA curve
of Pdnano/MNPs@PU. See DOI: 10.1039/c3ta14992g
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Table 1 Average size distribution of capsules formed using different
surfactants or dispersants
Results and discussion
Synthesis and characterization of polyurea nanocapsules
Entry
Surfactant
Average size distribution (nm)
Generally, the polyurea nanocapsules were prepared in two
steps. The rst step included nanoemulsication of chloroform,
containing the isocyanate monomer, in water. Stabilization of
the chloroform nano-droplets in water was performed using 4%
of surfactant. In the second step, interfacial polycondensation
reaction occurred when an amine monomer was added slowly
to the chloroform–water nanoemulsion. Polymeric nanospheres
were formed aer stirring for 16 hours at room temperature.
The preparation process is illustrated in Scheme 1. To optimize
the synthesis process of the polyurea nanocapsules, different
parameters such as the type of the surfactant, the isocyanate
and the amine monomers, were examined and their effect on
the polymeric nanocapsule structure was studied.
1
2
3
4
5
Bu-PVP
SDS
CTAC
Tween 80
Reax 88
1755
245
114
Polyurea chunks
105
Initially, different surfactants were employed in the prepa-
ration of nanocapsules. The monomers polymethylene poly-
phenyl isocyanate (PAPI 27) and 1,6-hexamethylenediamine
(HMDA) were selected to create the polyurea shells. In partic-
ular, the polyoxyethylene (20) sorbitan monooleate (Tween 80),
polyoxyethylene (20) stearyl ether (Brij 78), butylated poly-
vinylpyrrolidone (Bu-PVP), sodium dodecyl sulfate (SDS), cetyl-
trimethylammonium chloride (CTAC) and the dispersant
lignosulfonic acid (Reax 88A) were tested. Phase separation was
observed during the interfacial polymerization when Brij 78
was utilized to stabilize the nanoemulsion. When Tween 80 was
used, only polyurea chunks were produced. All other surfactants
enabled formation of polyurea capsules. However, the desired
small-sized polyurea nanocapsules could be obtained only
when the surfactant CTAC or the dispersant Reax 88A was
utilized. This was indicated by dynamic light scattering (DLS)
measurements (Table 1) and scanning electron microscopy
(SEM) images (Fig. 1). In addition, transmission electron
microscopy (TEM) analysis (Fig. 2) showed a core–shell struc-
ture indicating the formation of hollow nanocapsules.
Fig. 1 SEM images of polyurea nanocapsules obtained using the
following surfactants and dispersants: (a) Bu-PVP, (b) SDS, (c) CTAC (d)
Tween 80 and (e) Reax 88A.
(MBDI), 2,4-toluene diisocyanate (TDI), 1,6-hexamethylene dii-
socyanate (HDI) and PAPI 27, as the isocyanate monomers. SEM
images (ESI, Fig. S1†) and DLS measurements (ESI, Table S1†)
indicate that nanocapsules were produced when the combina-
tions of PAPI 27 and DETA or HMDA, as well as the combination
of MBDI and DETA or HMDA, were used. In the presence of
PAPI 27 the capsules formed were smaller; therefore, the
isocyanate PAPI 27 was chosen as the optimized isocyanate
monomer. The monomers PAPI 27 and DETA are trifunctional
monomers, and in their presence highly cross-linked shells can
be formed. The degree of cross-linking affects the diffusion of
the substrate into the capsule core. Thus, in order to form
strong shells that enable diffusion of the reactants into the
nanocapsules, HMDA and PAPI 27 were chosen as the mono-
mers for building the polymeric shells.
The effect of the amine and isocyanate monomers on the
construction of polyurea nanocapsules was examined with Reax
88A as the stabilizer of the nanoemulsions. The monomers used
were HMDA and diethylenetriamine (DETA), as the amine
monomers,
and
4,40-metyhlene-bis(cyclohexylisocyanate)
The effect of the PAPI 27 : HMDA molar ratios on the forma-
tion of polyurea nanocapsules was examined using seven different
molar ratios: 1 : 0.4, 1 : 0.7, 1 : 0.9, 1 : 1.1, 1 : 1.25, 1 : 1.5 and
1 : 1.73, using Reax 88A as the emulsion stabilizer. SEM images
(ESI, Fig. S2†) and DLS measurement (ESI, Table S2†) showed no
signicant change in the nanocapsule size. Furthermore, Bru-
nauer–Emmett–Teller (BET) measurements were performed for
both PAPI 27 : HMDA molar ratios, 1 : 1 and 1 : 1.73; the pore
˚
˚
Scheme 1 Preparation of polyurea nanocapsules.
3972 | J. Mater. Chem. A, 2014, 2, 3971–3977
radius observed was 24.636 A and 33.028 A, respectively.
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although most of the capsules observed by TEM were empty
(Fig. 4a). Furthermore, a small fraction of non-encapsulated
MNPs was observed (Fig. 4b). On the other hand, the encapsu-
lation process of MNPs at 1 : 1.73 isocyanate : amine ratio was
successful, and no MNPs were seen outside the nanocapsules
(Fig. 4c). Energy dispersive X-ray spectroscopy (EDX) measure-
ment (ESI, Fig. S3†) was performed and coincided with TEM
analysis, which demonstrated encapsulation of MNPs, within the
polymeric nanocapsules. In addition, X-ray diffraction (XRD)
measurements were performed (ESI, Fig. S4†). The XRD pattern
shows characteristic peaks of magnetite, Fe3O4.
Fig. 2 TEM images of polyurea nanocapsules obtained using Reax
The encapsulation of MNPs within the core enables facile
separation of the nanocapsules from the aqueous medium, by
applying an external magnetic eld. In order to ensure fast and
easy separation different loading percentages of MNPs were
examined. In all loading percentages polyurea nanocapsules
were formed. Though, at low loading percentages, 1.5%, TEM
analysis (Fig. 5a) revealed that the nanocapsules formed are
mostly empty capsules. With loading percentages of 2.5% and
above, TEM images (Fig. 5) indicate that the nanocapsules
formed contain the required MNPs. In order to facilitate fast
separation of the polyurea nanocapsules, the loading
percentage was chosen to be 9%.
88A, with an isocyanate amine molar ratio of 1 : 1.73.
Magnetically separable polyurea nanocapsules (MNPs@PU
nanocapsules)
Encapsulation of MNPs in polyurea nanocapsules was per-
formed using a similar procedure utilized in the preparation of
polyurea nanospheres. Therefore, chloroform containing
magnetite nanoparticles coated with oleate groups and PAPI 27
was nanoemulsied in water. HMDA was added in order to start
interfacial polymerization, thus yielding magnetically separable
polyurea nanocapsules. This process was studied using two
different PAPI 27 : HMDA molar ratios, 1 : 1 and 1 : 1.73, in the
presence of CTAC or Reax 88A as the stabilizer. Both molar
ratios enabled the formation of nanocapsules. According to DLS
measurements, when 1 : 1 molar ratio was applied the average
size of the nanocapsules was 106 nm and 110 nm in the pres-
ence of CTAC and Reax 88A, respectively. At 1 : 1.73 ratio,
capsules were formed with an average size of 113 nm and
224 nm using CTAC and Reax 88A, respectively. Although when
CTAC was used with 1 : 1 molar ratio, TEM analysis indicated
that the MNPs were not encapsulated (Fig. 3a and b). A shell–
core structure was observed, indicating that polyurea nano-
capsules were formed though no MNPs were found within the
core (Fig. 3a). MNPs were only seen outside the capsule (Fig. 3b).
At 1 : 1.73 ratio, encapsulation of MNPs was partially achieved
and MNPs were seen outside the capsules as well as within; as
observed in TEM images (Fig. 3c). It seems that the MNPs were
extracted from the oil droplets during the formation process of
the nanocapsules. This may be explained by the ability of CTAC
to form micelles in water, which can extract the MNPs and
stabilize them in the aqueous medium.
Palladium nanoparticles encapsulated in polyurea
nanoreactors (Pdnano@PU nanocapsules)
Aer establishing a method for the formation of magnetically
separable nanocapsules, their ability to act as nanoreactors was
Fig. 4 TEM images of MNPs@PU nanocapsules prepared in the
presence of Reax 88A with different amine : isocyanate molar ratios. (a
and b) Ratio of 1 : 1; (c), ratio of 1 : 1.73.
In the presence of the dispersant Reax 88A at 1 : 1 iso-
cyanate : amine ratio, the MNP encapsulation was accomplished,
Fig. 3 TEM images of MNPs@PU nanocapsules prepared in the
presence of CTAC with different amine : isocyanate molar ratios. Fig. 5 TEM images representing different MNP loading percentages.
(a and b) Ratio of 1 : 1; (c) ratio of 1 : 1.73.
(a) 1.5%, (b) 2.5%, (c) 5%, (d) 7.5% and (e) 9%.
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examined. Thus, palladium acetate and hyperbranched poly- palladium acetate, H-PAMAM-C15 and PAPI 27 were dissolved in
amidoamine modied with palmitoyl groups (H-PAMAM-C15 chloroform and nanoemulsied in water. This was followed by
)
(Scheme 2) were dissolved in chloroform and nanoemulsied in the addition of HMDA, to form a polyurea nanocapsule by
water. This was followed by polycondensation to form polyurea interfacial polymerization. The resulting nanocapsules were
nanocapsules. The resulting nanocapsules were treated with treated with hydrogen, in order to form the desired heteroge-
hydrogen in order to reduce Pd(II) to Pd(0), and the Pdnano@PU neous catalyst Pdnano/MNPs@PU. The preparation process is
catalyst was obtained. In order to prevent aggregation of the illustrated in Scheme 3.
formed Pd nanoparticles, H-PAMAM-C15 was added. H-PAMAM-
SEM and TEM analyses (Fig. 7) reveal formation of polyurea
C15 can stabilize Pd particles via coordinative interaction nanocapsules, with an average size of 220 nm correlating with
between the amine groups of the H-PAMAM-C15 and Pd data obtained using DLS (ESI, Table S3,† Entry 3). EDX
nanoparticles.
measurements show the presence of Pd and Fe, demonstrating
SEM analysis (Fig. 6a) of the resultant heterogeneous catalyst that simultaneous encapsulation of Pd and MNPs was achieved
revealed aggregates with apparent border lines between each (Fig. 8). Further indication for the presence of Pd in the nano-
nanocapsule, indicating that the aggregation is due to the high capsules was obtained using inductively coupled plasma (ICP)
vacuum required for imaging. This correlates with the average mass spectrometry measurements, in which the Pd concentra-
size distribution obtained in DLS measurements. DLS tion was 0.013 mmol gꢀ1. In addition, thermal gravimetric
measurements showed an average size of 220 nm, an increase of analysis (TGA) measurements (ESI, Fig. S6†) show that the
100 nm in the capsules size (ESI, Table S3,† Entry 1 and Entry 2), nanocapsules are composed of 9% non-decomposable mate-
aer encapsulation of the palladium nanoparticles. Apparently, rials attributed to the MNPs and the Pd nanoparticles.
encapsulation of H-PAMAM-C15 and palladium acetate, which Furthermore, the TGA curve demonstrates a total weight loss of
was converted to palladium nanoparticles, within the nano- 5% at 50 ꢁC, ascribed to the removal of volatile compounds,
ꢁ
capsules, led to the increase in their size. TEM analysis (Fig. 6b) such as chloroform. The sharp mass reduction step at 220 C
indicates that palladium nanoparticles are formed and encap- (86%) corresponds to the decomposition of the polyurea shell
sulated within the polyurea nanocapsule. The average size of and H-PAMAM-C15
.
the palladium nanoparticles was 10.3 nm (ESI, Fig. S5†).
Catalytic application of Pdnano/MNPs@PU nanocapsules
Palladium nanoparticles encapsulated in magnetically
separable nano-reactors (Pdnano/MNPs@PU nanocapsules)
The catalytic ability of the magnetically separable catalyst
Pdnano/MNPs@PU was examined in hydrogenation reaction of
Aer achieving the ability of polyurea nanocapsules to be easily
separated, by encapsulation of MPNs, as well as to perform as
heterogeneous catalysts, by encapsulation of palladium acetate
and their reduction, our goal was to combine both abilities and
form recyclable catalytic nanoreactors. Therefore, MNPs,
Scheme 2 Structure of hyperbranched polyamidoamine modified
with palmitoyl groups (H-PAMAM-C15).
Scheme 3 Preparation of Pdnano/MNPs@PU nanocapsules.
Fig. 6 (a) SEM image of Pdnano@PU nanocapsules after treatment with
hydrogen. (b)TEM image of Pdnano@U nanocapsules after treatment Fig. 7 (a) SEM image of Pdnano/MNPs@PU nanoreactors. (b)TEM
with hydrogen.
image of Pdnano/MNPs@PU nanoreactors.
3974 | J. Mater. Chem. A, 2014, 2, 3971–3977
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Fig. 8 EDX measurement of Pdnano/MNPs@PU nanoreactors.
various alkenes and alkynes, in aqueous media. The reactions
were performed under 200 psi of hydrogen for 6.5 hours. Aer
the reactions complete, the catalyst was easily separated from
the reaction medium via an external magnetic eld. These
results are summarized in Table 2.
The reduction of aromatic alkenes was successful, and
saturated products were obtained in excellent yields (Table 2,
Entry 1–6). No effect of withdrawing and donor groups was
observed. The selectivity of Pdnano/MNPs@PU nanoreactors in
reduction of cinnamic aldehyde was examined (Table 2, Entry
Fig. 9 SEM image of the recycled catalyst Pdnano/MNPs@PU.
7); only C]C could be reduced, and 3-phenylpropanal was
obtained in a yield of 66%. In addition, the hydrogenation
reaction of aromatic alkynes was effective, and fully saturated
products were achieved in high yields (Table 2, Entry 8–10). The
recyclability of the catalyst was tested in hydrogenation of
styrene. The catalyst did not lose its reactivity, and full conver-
sion of styrene to ethylbenzene was obtained in four consecu-
tive cycles. Importantly, no signicant change could be
observed in the capsule's morphology and size, as conrmed by
SEM analysis of the recycled catalyst (Fig. 9). The reaction
medium aer the separation of the nanoreactors was analyzed
using ICP, in which no palladium was detected.
Table 2 Hydrogenation of alkenes and alkynes by Pdnano/MNPs@PU
nanoreactorsa
Entry
Substrate
Product
Yield (%)b
100
Conclusion
1
2
The design and immobilization of Pd nanoparticles together
with MNPs in polyurea nanocapsules was described. These
nanoreactors can be easily separated from the reaction medium
by applying an external magnetic eld, and act as catalysts in
hydrogenation of alkenes and alkynes at room temperature, in
aqueous medium. The ability to separate these nanoreactors
from the reaction media enables the recyclability of the catalyst.
We anticipate that the method for catalyst immobilization in
magnetically separable nanocapsules, developed in this work,
can be applied in different elds and may lead to new oppor-
tunities in the area of green chemistry.
100
3
96
4
5
100
100
6
7
8
99
66
87
Experimental section
Materials
Lignosulfonic acid, polymethylene polyphenyl isocyanate and
butylated polyvinylpyrrolidone were contributed by FMC
Corporation. All other reagents were purchased from either
Acros or Sigma-Aldrich, and were used without further puri-
cation, with the exception of methyl acrylate, which was puried
under reduced pressure.
9
100
100
Instrumentation
NMR measurements were preformed on 400 MHz and 500 MHz
Bruker spectrometers. Images were acquired using a high
resolution scanning electron microscope (HR SEM), Sirion (FEI
Company), using a Schottky type eld emission source and a
secondary electron (SE) detector. The images were scanned at
10
a
4 mmol of substrate, 2.6 ꢂ 10ꢀ2 mmol Pd, 2 mL H2O, 200 psi H2, room
temperature, 6.5 hours. b Determined by 1H NMR and GC.
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5 kV acceleration voltage. Transmission electron microscopy [COCH2CH2NH, NH (CH2)2NH, NH (CH2)2NH2], 3.20–3.50
and electron diffraction spectroscopy were performed with a (S) (NCH2), 3.50–4.0 (CH3O). 13C NMR (D2O, 125 MHz) d: 31–59
Tecnai F20 G2 (FEI company), operated at 200 kV. Inductively (CH2, CH3), 171–178 (C]O). MALDI-TOF: m/z ¼ 5798.90.
coupled plasma mass spectrometry measurements were per-
formed on a 7500cx system (Agilent company), using an external
standard calibration. Dynamic light scattering measurements
were performed using a Nano-zeta sizer (Malvern instruments),
model ZEN3600. Gas chromatography (GC) was used to analyze
hydrogenation products. GC was performed using an Agilent-
GC-7890A with a capillary column (HP-5, 30 meters) and a
thermal conductivity detector (TCD). Emulsication was per-
formed using a Kinematica Polytron homogenizer PT-6100,
equipped with dispersing aggregates 3030/4EC. Thermogravi-
metric analysis was performed on a Mettler Toledo TG
50 analyzer. Measurements were carried out at a temperature
range that extended from 25–950 C, at a heating rate of 10 C
minꢀ1, under an air atmosphere. Sonication was performed
using a Sonics Vibra Cell, model VCX-130 (130 watt). The
average molecular mass of H-PAMAM was determined by matrix
assisted laser desorption ionization-time of ight (MALDI-TOF)
using a Voyager DE PRO MALDI-TOF mass spectrometer
(Applied Biosystems). The mass spectra were acquired using a
matrix of a-cyano-4-hydroxycinnamic acid, in the linear positive
ion mode by using an accelerating voltage of 25 000 V, a grid
voltage of 94%, a guide wire of 0.05%, and an extraction delay
General procedure for the synthesis of hyperbranched
polyamidoamine (H-PAMAM-C15
)
Palmitoyl chloride (6 g, 0.0218 mol) was dissolved in 15 mL
CHCl3, and added to a solution of H-PAMAM (2 g, 0.083 mol)
and triethylamine (6.1 g, 0.044 mol) in 30 mL CHCl3. The
ꢁ
reaction mixture was stirred for 24 h at 35 C under nitrogen.
Then, the mixture was cooled to room temperature and washed
with 50 mL water three times. The organic layer was collected
and dried over anhydrous magnesium sulfate, ltered and
concentrated under reduced pressure. The material was poured
in 100 mL methanol and the precipitate was collected, washed
with methanol and dried under vacuum. 3.5 g (40%) of yellow
wax were obtained. Elementary anal.: C, 72.19; H, 12.93; N,
10.97. FTIR (KBr, cmꢀ1) 3311, 2924, 2852, 1644, 1376, 1219, 722,
586. 1H NMR (CDCl3, 500 MHz) d: 0.87–0.89 (t, 3H, CH3), 1.24–
1.26 (22H, –CH2), 1.52–1.58 (2H, –CH2), 2.29–2.40 (2H, –NCH2),
3.34–3.67 (2H, –NCH2, –OCH3). 13C NMR (CDCl3, 125 MHz) d:
14.1, 22.68, 23.90, 29.27–29.72, 31.92–31.93, 42.82, 211.
ꢁ
ꢁ
General procedure for preparation of polyurea nanocapsules
time of 340 ms. Surface areas were determined by the N2 Bru- The isocyanate monomer (0.7–1.1 g) was dissolved in 8.9 g of
nauer–Emmett–Teller method (NOVA-1200e). The pore volume CHCl3 and later emulsied with 33.5 g of water, containing a
and radius were measured using the BJH model. Powder X-ray suitable surfactant (2.0 g), by milling at 14 000 rpm for 1 min.
diffraction analysis was performed using an X-ray Diffractom- Then 5 drops of 1 M HCl were added, the emulsion was soni-
eter D8 Advance.
cated for 17 min and the amine monomer (0.9–1.3 g) was
dropped slowly. The resultant mixture was stirred for 16 h at
room temperature.
Synthesis of hydrophobic magnetite nanoparticles
Magnetite nanoparticles were prepared according to Massart's
method.14 Briey, 400 mL of H2O was degassed for 15 min under
General procedure for preparation of Pd@PU nanoreactors
nitrogen. Then, 11.6 g (42.9 mmol) of FeCl3$6H2O and 4.3 g 2.0 g of Reax 88A were dissolved in 33.5 g of water and
(21.6 mmol) of FeCl2$4H2O were added and heated at 85 ꢁC. homogenized for 1 min at 14 000 rpm. Then, 1.1 g of PAPI 27,
15 mL of concentrated ammonium (28%) was added and the 0.3 g of H-PAMAM-C15, and 0.15 g of palladium acetate were
mixture was heated for additional 30 min. Aer that, 18 mL dissolved in 8.9 g of chloroform and emulsied with the water
(57 mmol) of oleic acid was added, resulting in the formation of phase for 1 min. Aer that, 5 drops of 1 M HCl were added, the
a black precipitant. The mixture was stirred for an additional emulsion was sonicated for 17 min, and 0.9 g of HMDA (70% in
5 min, and then cooled to room temperature. The black water) was slowly added. Then the solution was stirred for 16 h
precipitant was collected and washed ve times with water, ve at room temperature. The next step was to reduce the palladium
times with acetone, and then dispersed in 50 mL of chloroform. acetate to Pd nanoparticles, using a glass-lined autoclave. Aer
sealing, the autoclave was purged 3 times with hydrogen and
pressurized to 500 psi. The autoclave was stirred at room
temperature for 24 h.
General procedure for the synthesis of hyperbranched
polyamidoamine (H-PAMAM)15
Ethylenediamine (18.03 g, 0.3 mol) was dissolved in 28 mL of
methanol, and added into a 100 mL single neck ask. Then,
methyl acrylate (25.83 g, 0.3 mol) was slowly added, with
General procedure for preparation of Pd/MNPs@PU
nanoreactors
constant stirring, over a period of 20 minutes. Aer 48 h of room The oil phase contains 1.1 g PAPI 27, 1.0 g of MNPs dispersed in
temperature stirring, methanol was removed under reduced 8.9 g of chloroform, 0.3 g H-PAMAM-C15 and 0.15 g palladium
pressure, and the resultant material was heated at 60 ꢁC for 1 h, acetate. Later it was emulsied with the water phase, 2.0 g Reax
100 ꢁC for 2 h, 120 ꢁC for 2 h and 140 ꢁC for 2 h, under vacuum. 88A in 33.5 g water, at 14 000 rpm for 1 min. Then, 5 drops of
34.26 g (95%) of a light yellow viscous dope was obtained. 1 M HCl were added, the emulsion was sonicated for 17 min and
1
Elementary anal.: C, 51.75; H, 8.56; N, 23.32. H NMR (CDCl3): 0.9 g HMDA (70% in water) was slowly added. The solution was
1.80–2.32
(NH2–NH),
2.30–2.52
(COCH2),
2.51–3.02 stirred for 16 h at room temperature. The formed capsules were
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separated using a magnetic eld, washed three times each with
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nanoparticles using a glass-lined autoclave. Aer sealing, the
autoclave was purged 3 times with hydrogen and pressurized to
500 psi. The autoclave was stirred at room temperature for 24 h.
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