Fabrication and characterization of dendrimer-encapsulated monometallic Co nanoparticles

Article abstract of DOI:10.1016/j.jallcom.2011.02.038

A series of cobalt (Co) nanoparticles were synthesized by employing PAMAM dendrimers with different generations (G 0.0-3.0) as templates and sodium borohydride as a reducing agent. Extensive characterizations of the products were done using TEM, FT-IR, VSM, TGA, and XPS. The magnetization curves have superparamagnetic non hysteric characteristic at lower fields and with nonsaturation characteristic at high fields. All XRD patterns indicate that amorphous structure of all products. The shake-up satellites are observed at higher energies of the XPS peaks.

Full text of DOI:10.1016/j.jallcom.2011.02.038

Journal of Alloys and Compounds 509 (2011) 5341–5348
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Fabrication and characterization of dendrimer-encapsulated monometallic
Co nanoparticles
H. Kavasa, Z. Durmusb, E. Tanrıverdib, M. S¸ enelb, H. Sozeric, A. Baykalb,∗
a Department of Physics, Fatih University, B. Cekmece, 34500 Istanbul, Turkey
b Department of Chemistry, Fatih University, B. Cekmece, 34500 Istanbul, Turkey
c TUBITAK-UME, National Metrology Institute, PO Box 54, 41470 Gebze-Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 January 2011
Received in revised form 4 February 2011
Accepted 7 February 2011
Available online 24 February 2011
A series of cobalt (Co) nanoparticles were synthesized by employing PAMAM dendrimers with different
generations (G 0.0–3.0) as templates and sodium borohydride as a reducing agent. Extensive characteri-
zations of the products were done using TEM, FT-IR, VSM, TGA, and XPS. The magnetization curves have
superparamagnetic non hysteric characteristic at lower fields and with nonsaturation characteristic at
high fields. All XRD patterns indicate that amorphous structure of all products. The shake-up satellites
are observed at higher energies of the XPS peaks.
Keywords:
Dendrimer
Cobalt
© 2011 Elsevier B.V. All rights reserved.
XPS
Chemical synthesis
Magnetic properties
1. Introduction
macromolecule that contains interior tertiary amine groups which
can effectively make coordination with metal ions. Such metal ions
Magnetic nanoparticles (MP) exhibit enhanced magnetic, opti-
cal, and electrical properties when compared with their bulk
counterparts rendering nanoparticles of interest for a variety of
applications information storage [1,2], color imaging [3], magnetic
refrigeration [4], ferro-fluids [5], cell sorting [6], medical diagno-
sis [7], and controlled drug delivery [8]. Most of these applications
require chemically stable, well-dispersed and uniform size parti-
cles. For this reason, new technologies in synthesis and methods of
analysis have been developed.
Dendrimers are very exiting cascade type three-dimensional
polymers that have well-defined molecular weight/size, uniform
dense terminal functional groups, and porosity. Generally, den-
drimers of low generation tend to exist in relatively open forms, at
higher generations (G ≥ 4.0) take intrinsically well-defined globular
structure. Dendrimers might provide reaction sites including their
interior or periphery. Accordingly, it is expected that the use of den-
drimers as templates/stabilizers for the synthesis of nanoparticles
are affected by the generation of dendrimers and show different
behavior from those prepared using conventional linear polymers
[9]. A poly-amidoamine (PAMAM) dendrimer is highly branched
may then be reduced to form encapsulated metal particles that can
be highly stable in solution. Since the same number of chelating
sites is present in all dendrimer molecules, this process can yield
mono-disperse metal particles [10–12].
Dendrimer-stabilized nanoparticles (DSN) may provide one
avenue toward controlled synthesis of supported metal catalysts.
Dendrimers are a special class of hyper branched polymers with
a specific molecular structure and controllable size. At higher
generation, they possess a very dense exterior, while containing
hollow pockets that can be ideal for use as nano-scale containers
[12]. This property finds widespread application in catalysis and
biomedical research. Dendrimers containing metal nanoparticles
also find applications in catalysis [13,14]. It is possible to pro-
duce dendrimer–metal nanocomposites by the following routes:
(1) forming of complexes by binding of metal ions to a template
of dendrimer molecules and (2) nanoclusture forming by immobi-
lization of the metal ions onto dendrimer templates. Composition,
size and structure of the system also strongly affect the properties
of dendrimer–metal nanocomposites [15–18].
In this study, the synthesis of Co nanoparticles via the template
of PAMAM dendrimers with different generation was presented.
Extensive characterizations of the fabricated nanocomposites have
been performed by using a variety of microscopy and spectroscopic
techniques.
∗
Corresponding author. Tel.: +90 212 866 33 00/2061; fax: +90 212 866 34 02.
E-mail address: hbaykal@fatih.edu.tr (A. Baykal).
0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2011.02.038

5342
H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
H2N
H2N
NH2
NH2
NH2
H2N
NH
HN
NH
NH
HN
O
O
O
O
H2N
HN
O
O
NH
H2N
NH2
NH
O
N
N
HN
NH2
N
O
O
HN
N
HN
N
OH
NH
O
O
NH
H
N
H2N
HN
O
O
O
H
N
N
NH2
H2N
N
O
O
N
HN
O
O
HN
NH
NH2
O
HN
H
N
O
O
NH
N
N
H
N
O
NH
NH
H
N
O
NH
H
N
N
O
N
H2N
O
O
N
N
O
O
O
NH2
NH
HN
N
N
G-0
HN
NH
H2N
O
O
O
O
N
HN
HN
O
N
O
NH2
O
N
O
N
N
H
N
N
H
O
HN
H
N
N
N
HN
O
H
NH
O
G-1
H2N
HN
NH
O
O
NH
N
O
O
NH2
N
N
H2N
N
H
N
O
O
O
N
H
NH
NH2
HN
HN
O
O
HN
G-2
O
NH
N
NH
O
O
N
H2N
N
NH
O
N
NH2
H2N
HN
HN
O
O
NH2
NH
O
O
G-3
O
O
NH
HN
HN
NH
NH2
H2N
H2N
NH2
NH2
H2N
Fig. 1. The structure of G0.0–G3.0 dendrimers.
2. Experimental
2.2. Characterization
2.1. Materials
X-ray powder diffraction (XRD) analysis was conducted on a Rigaku Smart Lab
Diffractometer operated at 40 kV and 35 mA using Cu K␣ radiation (ꢀ = 1.54178 A).
˚
Cobalt chloride (CoCl2·6H2O), sodium borohydride (NaBH4), were purchased
from Merck and used as received without further purification. All the chemicals are
of analytical grade.
Fourier transform infrared (FT-IR) spectra were recorded in transmission mode
with a Perkin Elmer BX FT-IR infrared spectrometer. The powder samples were
ground with KBr and compressed into a pellet (in the range 4000–400 cm−1).
Fig. 2. Schematic representation of the synthesis of dendrimer encapsulated Co nanoparticles.

H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
5343
Fig. 3. Changes in solution color of G220–Co2+ before (a) and after reduction (b) and the collection of Co nanoparticles by a magnet (c).
Transmission electron microscopy (TEM) analysis was performed using a JEOL
JEM 2100 microscope. A drop of diluted sample in alcohol was dripped on a TEM
grid.
XPS analysis using Phobus 150 Specs electron analyzer with conventional X-ray
source (AlKa).
The thermal stability was determined by thermogravimetric analysis (TGA,
Perkin Elmer Instruments model, STA 6000). The TGA thermograms were recorded
for 5 mg of powder sample at a heating rate of 10 ◦C min in the temperature range
of 30–800 ◦C under nitrogen atmosphere.
VSM measurements were performed by using a Quantum Design Vibrating sam-
ple magnetometer (QD-VSM). The sample was measured between 10 kOe at room
temperature and 10 K. ZFC (zero field cooling) and FC (field cooling) measurements
were carried out at 100 Oe and the blocking temperature was determined from the
measurements.
2.3. Synthesis
2.3.1. The synthesis of dendrimers
PAMAM dendrimers were synthesized according to the literature [14]. Ethylene-
diamine (10.0 g, 0.166 mol) was dissolved in 100 mL methanol. Methyl acrylate
(0.751 mol (94.6 g) was added to above solution at 40 ◦C and the system stirred
for 24 h under nitrogen. Excess methyl acrylate was removed under vacuum at
room temperature. A Michael addition between the amine and the acrylate yielded
a product bearing four terminal methyl ester groups. Subsequently, ethylenedi-
b
a
C110
C120
C130
C140
G1
C010
C020
C030
C040
G0
4000
3500
3000
2500
2000
1500
1000
500
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Wavenumber (cm-1)
c
d
1642
1538
C210
C310
C220
C230
C240
G2
C320
C330
C340
G3
1649
1545
4000
3500
3000
2500
2000
1500
1000
500
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Wavenumber (cm-1)
Fig. 4. FT-IR spectra of (a) Co–G0.0, (b) Co–G1.0, (c) Co–G2.0, (d) Co–G3.0 (the feed molar ratio of Co2+ to dendrimers is 10:1, 20:1, 30:1 and 40:1).

5344
H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
Table 1
Some chemical and physical characteristic of dendrimers.
Generation
Molecular formula
Molecular
weight
Number of
terminal
amino
Number of
total amino
groups
(g mol−1
)
groups
G0
G1
G2
G3
C
C
C
C
22H48O4N10
516
1429
3254
6905
4
8
16
32
10
26
58
62H128O12N26
142H288O28N58
302H609O60N132
122
Table 2
Denotation of dendrimer-encapsulated monometallic Co-nanoparticles.
C020
C120
C220
C320
Generation
Metal/Dendrimer molar ratio
10:1
20:1
30:1
40:1
G0
G1
G2
G3
C010
C110
C210
C310
C020
C120
C220
C320
C030
C130
C230
C330
C040
C140
C240
C340
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber (cm
)
Fig. 5. FT-IR spectra of Co–G0–G3 (the feed molar ratio of Co2+ to dendrimers is
20:1).
followed by further stirring for 2 h in order to drive the coordination reaction to
completion (Fig. 2). The feed molar ratio of Co2+ to dendrimers is 10:1, 20:1, 30:1
and 40:1, respectively (Table 2). Afterwards, 10 mL of 0.3 M NaBH4 solution (freshly
prepared) was introduced into the above solution quickly, and then the mixture
was stirred vigorously for 1 h. The solid was filtered, rinsed three times with Milli-Q
water, and then dried under vacuum at 50 ◦C (Fig. 3).
amine (120 g, 2.00 mol) was dissolved in methanol and added to the four terminal
methyl ester containing dendrimer, stirred for 48 h under nitrogen and excess reac-
tants were removed by vacuum distillation. Then, product bearing four terminal
amino groups were obtained, defined as the G0 PAMAM. By repeating the above
cycle, higher generation PAMAM dendrimers (up to G3) were synthesized. Purity of
the amine-terminated PAMAM dendrimers was characterized via FT-IR, 1H and 13
C
As presented in Fig. 3, the Co NP’s were prepared via a two-step sequence. The
coordination of Co2+ ions with dendrimers and subsequent chemical reduction to
produce Co NP’s. After the coordination of Co2+ to the dendrimer, solution turns into
green (Fig. 3a). When Co2+ ions were reduced into Co NP’s, solution color becomes
dark gray (Fig. 3b). This is an important indication of reduction of Co2+ ions into Co
[20,21]. After the dispersion of solid product in an aqueous solution, they could be
easily collected by magnet (Fig. 3c).
NMR. The results agreed well with that reported in the literature [19]. The struc-
tures of dendrimers are given in Fig. 1. The characteristics and abbreviations are
presented in Table 1.
2.3.2. The synthesis of Co nanoparticles via the template of dendrimers
Briefly, certain amount of CoCl2·6H2O dissolved in 10 mL of in Milli-Q water was
added drop-wise into a 10 mL of 1 mM dendrimer (G0.0, 1.0, 2.0 and 3.0) solution,
b
a
C010
C020
C030
C040
C110
C120
C130
C140
20
30
40
50
60
70
80
20
30
40
50
60
70
80
c
C210
C220
C230
C240
20
30
40
50
60
70
Fig. 6. XRD powder pattern of (a) Co–G0, (b) Co–G1, (c) Co–G2 (the feed molar ratio of Co2+ to dendrimers is 10:1, 20:1, 30:1 and 40:1).

H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
5345
100
90
80
70
60
15
C020
C120
C220
C320
10
5
C020
0
C120
C220
-5
-10
-15
C320
700
100
200
300
400
500
600
Temperature (°C)
-15000
-10000
-5000
0
5000
10000
15000
Magnetic Field (kOe)
Fig. 7. TGA curves of Co–G0–G3 (the feed molar ratio of Co2+ to dendrimers is 20:1).
Fig. 9. M–H hysteresis curves of curves of Co–G0–G3 (the feed molar ratio of Co2+
to dendrimers is 20:1).
3. Results and discussion
corresponding to amide (–CO–NH–) I and II of G1–G3 dendrimers
appear at 1642 cm−1 and 1538 cm−1, respectively. These results
strongly indicate that dendrimers still exist in the nanocomposite
(coordination reaction between the cobalt ions and the nitrogen or
oxygen atoms from amide groups when cobalt ions are introduced
into the solution of the dendrimers) [24–26].
3.1. FT-IR analysis
Fig. 4 shows the FT-IR spectra from the water solution of the den-
drimers (G0–G3), the mixture of dendrimers and the cobalt ions; (a)
G0–Co2+, (b) G1–Co2+, (c) G2–Co2+, (d) G3–Co2+. As it can be seen,
the G0 to G3 dendrimers (Fig. 5) spectra exhibit two broad peaks
centered at 1649 and 1545 cm−1, assigned to the C O stretching
(amide I) and N–H bending/C–N stretching (amide II) vibrations of
the dendrimers [22–25], respectively. The C–H stretch modes can
be observed at 2945 cm−1 and 2842 cm−1. When the cobalt ions are
added into the solution of the dendrimers (G1–G3), the new bands
3.2. XRD analysis
The XRD powder patterns of Co–G1–G2 (the feed molar ratio of
Co2+ to dendrimers is 10:1, 20:1, 30:1 and 40:1) were presented
8000
C020
C120
7000
6000
5000
4000
83000
C320
C220
7000
6000
5000
4000
3000
820
810
800
790
780 820
810
800
790
780
Binding Energy (eV)
Fig. 8. XPS curves of Co–G0–G3 (the feed molar ratio of Co2+ to dendrimers is 20:1).

5346
H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
Fig. 10. TEM images of (a) Co–G0, (b) Co–G1, (c) Co–G2, (d) Co–G3 (the feed molar ratio of Co2+ to dendrimers is 20:1).

H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
5347
Table 3
values of binding energies; it may be caused by different surface
chemistry (hydroxide, oxide, boride or nitride of cobalt) of Co nano
metals in C220 samples. The Co–O bonding vibration (in FTIR spec-
trum) peak is stronger in this sample when it is compared with that
in others, so it can be inferred that Co has more oxidized surface
in C220 than others. The binding energy value difference may be
explained in the light of this fact.
Binding energies of Co 2p3/2 and Co 2p1/2 peaks for the samples.
Samples
Co 2p3/2 (eV)
Co 2p1/2 (eV)
C020
C120
C220
C320
784.3
784.6
782.3
784,2
799.5
800.1
797.4
799.5
3.5. Magnetic measurements
in Fig. 6. All XRD patterns indicate that amorphous structure of all
products. In any XRD powder patterns given in Fig. 6, there is no
Bragg peak which indicate the crystalline structure of the products
[21,27,28].
The magnetization curves and their lognormal Langevien fits
of all samples are shown in Fig. 9. The magnetization curves
have superparamagnetic non hysteric characteristic at lower fields
and with nonsaturation characteristic at high fields. The Co
nanoparticles without dendrimer frame (C020) have saturation
magnetization of 15.5 emu/g. The diamagnetic effect of surface
spins to bulk spins, magnetically dead layers caused by oxidation of
surface of Co may cause the decline of Ms with respect to the bulk
Ms value of Co. The additional mass of dendrimers can be seen as
a decrease of compound mass accordance with remaining mass of
them at higher temperatures in TGA. By increasing the generation
number dendrimer frame, the magnetization is generally decreas-
ing except for C220. The obtained Ms values by extrapolation of Ms
curves with 1/H are found as 13.7, 5 and 9.2 emu/g for C120, C220
and C320, respectively. Both XPS and FTIR analysis show that the
different surface nature of Co for C220 sample. The surface includ-
ing more oxides of Co cause the antiferromagnetic alignment of
surface spins around the Co ferromagnetic core. The more oxidized
surface may contribute the total magnetization with reducing effect
for C220 sample.
3.3. TG analysis
Thermal analysis was used to estimate the thermal stabil-
ity of Co–G0–G3 (the feed molar ratio of Co2+ to dendrimers is
20:1) nanocomposite, and the obtained TGA curves (Fig. 7). About
14%, 16%, 19% and 22% weight gain in the temperature range of
100–400 ◦C can be observed in the TGA curve. The number of sur-
face amines increased from dendrimer generations one to three. Gu
et al. [29] stated that % weight loss is increasing, when dendrimer
generation number is increased. And also similar behavior was also
observed in Fig. 7.
3.4. XPS analysis
XPS measurements were carried out to gain more insight into
the chemical covalent linkages on the surface of Co nanoparti-
cles. The experimental XPS spectra of the samples have peaks with
shoulder and the deconvoluted peaks were fitted by Gaussian func-
tions (Fig. 8). The binding energies of Co 2p3/2 peaks are ascribed
as 784.3, 784.6, 782.3 and 784,2 eV and that of Co 2p1/2 peaks are
ascribed as 799.5, 800.1, 797.4 and 799.5 eV for C020, C120, C220
and C320, respectively (Table 3). The spin-orbital energies were
calculated as 15.6, 15.7, 15.1 and 15.3 eV. The shake-up satellites
are observed at higher energies of these peaks and found as 790.6,
790.7, 785.7 and 789.6 eV for 2p3/2, and 806.7, 807.1, 801.5 and
3.6. TEM analysis
The successful formation of Co nanoparticles via the reduction
of Co2+ under the template of dendrimers was first confirmed by
TEM studies. Fig. 10 shows the TEM micrographs of Co nanoparti-
cles obtained using different generation of dendrimers (G0.0–G3.0)
as templates with the same feed molar ratio (20:1) of Co2+ to den-
drimers. The Co particles aggregated easily, probably because of the
high mobility of the particles as well as the magnetic interaction
between the particles [42].
803.5 eV for 2p1/2
.
In the literature the binding energies for Co 2p for different
oxides, nitrides, chlorides, hydroxide and other complex of Co are
reported as in Table 4. Also the shifting of binding energy toward
the high energy values were observed with changing pH values
of precursor solution [30–41]. All samples except C220 have close
4. Conclusions
The cobalt nanoparticles are obtained and characterized using
PAMAM dendrimers as templates. XRD analysis showed that the
amorphous structure of the all products and FT-IR analysis proved
the presence of between dendrimer and Co nanoparticles. The dia-
magnetic effect of surface spins to bulk spins, magnetically dead
layers caused by oxidation of Co surface may cause the decline of
Ms with respect to the bulk Ms value of Co.
Table 4
Binding energies (B.E.) for Co 2p of various oxides, nitrides, chlorides, hydroxides
and other complexes of Co.
B.E. (eV)
Complex
Ref.
[31]
778.0
778.2
778.4
780.4
781.2
781.6
781.9
782.0
782.1
782.6
783.2
783.3
783.6
783.6
787.6
796.8
798.0
798.2
804.1
Co2N
CoN
Co2N3
[31]
[31]
[32]
[33]
[34]
Acknowledgements
Co(OH)2
CoO, Co(OH)2, Co2O3
Co(OH)2
Co(OH)2
Co(OH)2
Co(II) Chloride
Co3O4
Co(OH)2
Co(OH)2
Co3O4
The authors are thankful to the Fatih University, Research
Project Foundation (Contract no: P50020902-2) and Turkish Min-
istry of Industry and TUBITAK (Contract no: 110T487) for financial
support of this study, to Dr. Özgür DUYGULU for TEM measure-
ments.
[33–36]
[40]
[30]
[33]
[33]
[34–39]
[40]
References
CoSiF6
[41]
[40]
[33]
[40]
[33]
[40]
Co(OH)2
CoO, Co2O3
Co3O4, Co(OH)2
Co(OH)2
Co2O3
[1] J. Heidmann, A.M. Taratorin, Handbook of Magnetic Materials, vol. 19, 2011, 1.
[2] C.W.
Thiel,
T.
Böttger,
R.L.
Cone,
J.
Lumin.
(2011),
doi:10.1016/j.jlumin.2010.12.015.
[3] B. Zhang, J. Cheng, X. Gong, X. Dong, X. Liu, G. Ma, J. Chang, J. Colloid Interface
Sci. 322 (2008) 485.

5348
H. Kavas et al. / Journal of Alloys and Compounds 509 (2011) 5341–5348
[4] S. Othmani, R. Blel, M. Bejar, M. Sajieddine, E. Dhahri, E.K. Hlil, Solid State
Commun. 149 (2009) 969.
[23] G. Socrates, Infrared and Raman Characteristic Group Frequencies: Tables and
Charts, 3rd ed., Wiley, Chichester, 2001.
[5] M.F. Casula, A. Corrias, P. Arosio, A. Lascialfari, T. Sen, P. Floris, I.J. Bruce, J. Colloid
Interface Sci. (2011), doi:10.1016/j.jcis.2011.01.088.
[6] H. Ito, R. Kato, K. Ino, H. Honda, J. Biosci. Bioeng. 109 (2010) 182.
[7] B. Fenga, R.Y. Honga, Y.J. Wua, G.H. Liuc, L.H. Zhongb, Y. Zhengd, J.M. Dinge, D.G.
Wei, J. Alloys Compd. 473 (2009) 356.
[24] L. Jin, S. Yang, Q.W. Tiana, H.X. Wua, Y.J. Cai, Mat. Chem. Phys. 112 (2008) 977.
[25] T. Endo, T. Yoshimura, K. Esumi, J. Colloid Interface Sci. 286 (2005) 602.
[26] D.X. Liu, J.X. Gao, J.C. Murphy, T.C. Williams, J. Phys. Chem. B 108 (2004) 12911.
[27] K. Yasui, T. Morikawa, K. Nishio, H. Masuda, Jpn. J. Appl. Phys. 44 (2005) L469.
[28] J.X. Xu, Y. Xu, Mater. Lett. 60 (2006) 2069.
[8] S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L.V. Elst, R.N. Muller, Chem. Rev.
108 (2008) 2064.
[29] B.F. Pan, F. Gao, H.C. Gu, J. Colloid Interface Sci. 284 (2005) 1.
[30] J.G. Dillard, M.H. Koppelman, J. Colloid Interface Sci. 87 (1982) 56.
[31] W. De La Cruz, O. Contreras, G. Soto, E.P. Tijerina, Revista Mexicana De Fisica
52 (5) (2006) 409.
[32] Y.P. Wang, Y.J. Wang, Q.L. Ren, L. Li, L.F. Jiao, D.W. Song, G. Liu, Y. Han, H.T. Yuan,
Fuel Cells 10 (2010) 510.
[9] L. Jin, S. Yang, Q. Tian, H. Wu, Y. Cai, Mater. Chem. Phys. 112 (2008) 977.
[10] R.C. Hedden, B.J. Bauer, A.P. Smith, F. Grohn, E. Amis, Polymer 43 (2002) 5473.
[11] Y. Niu, H. Lu, D. Wang, Y. Yue, S. Feng, J. Organomet. Chem. 696 (2011) 544.
[12] O. Ozturk, T.J. Black, K. Perrine, K. Pizzolato, C.T. Williams, F.W. Parsons, J.S.
Ratliff, J. Gao, C.J. Murphy, H. Xie, H.J. Ploehn, D.A. Chen, Langmuir 21 (2005)
3998.
[33] C.H. Liu, B.H. Chen, C.L. Hsueh, J.R. Ku, F. Tsau, K.J. Hwang, Appl. Catal. B 91
(2009) 368.
[13] B. Natarajan, N. Jayaraman, J. Organomet. Chem. 696 (2011) 722.
[14] Y. Niu, R.M. Crooks, C. R. Chim. 6 (2003) 1049.
[34] N. Patel, G. Guella, A. Kale, A. Miotello, B. Patton, C. Zanchetta, L. Mirenghi, P.
Rotolo, Appl. Catal. A 323 (2007) 18.
[15] Y.J. Jin, Y.J. Luo, G.P. Li, J. Li, Y.F. Wang, R.Q. Yang, W.T. Lu, Forensic Sci. Int. 179
(2008) 34.
[35] N. Patel, R. Fernandes, G. Guella, A. Kale, A. Miotello, B. Patton, C. Zanchetta, J.
Phys. Chem. 112 (2008) 6968.
[16] L. Balogh, R. Valluzzi, G.L. Hagnauer, K.S. Laverdure, S.P. Gido, D.A. Tomalia, J.
Nanopart. Res. 1 (1999) 353.
[36] N. Patel, R. Fernandes, A. Miotello, J. Power Sources 188 (2009) 411.
[37] R. Fernandes, N. Patel, A. Miotello, M. Filippi, J. Mol. Catal. A: Chem. 298 (2009)
1.
[38] R. Fernandes, N. Patel, A. Miotello, Appl. Catal. B 92 (2009) 68.
[39] R. Fernandes, N. Patel, A. Miotello, Int. J. Hydrogen Energy 34 (2009) 2893.
[40] C.H. Liu, Y.C. Kuo, B.H. Chen, C.L. Hsueh, K.J. Hwang, J.R. Ku, F. Tsau, M.S. Jeng,
Int. J. Hydrogen Energy 35 (2010) 4027.
[17] M.F. Ottaviani, R. Valluzzi, L. Balogh, Macromolecules 35 (2002) 5105.
[18] Y.Y. Cheng, D.Z. Chen, R.Q. Fu, Polym. Int. 54 (2005) 495.
[19] D.A. Tomalia, A.M. Naylor, W.A. Goddard, Angew. Chem. 29 (1990) 138.
[20] Y. Chen, K.Y. Liev, J.L. Li, Appl. Surf. Sci. 255 (2009) 4039.
[21] H.X. Wu, C.X. Zhang, L. Jin, H. Yang, S.P. Yang, Mater. Chem. Phys. 121 (2010)
342.
[41] T. Sekine, N. Ikeo, Y. Nagasawa, Appl. Surf. Sci. 100/101 (1996) 30.
[42] Y. Chen, K.Y. Liew, J.L. Li, Appl. Surf. Sci. 255 (2009) 4039.
[22] H.M. Tan, Y.J. Luo, Dendritic Polymer, Chemical Industry Press, Beijing, 2002.