J Nanopart Res
DOI 10.1007/s11051-010-0142-9
BRIEF COMMUNICATION
Low temperature synthesis of iron containing carbon
nanoparticles in critical carbon dioxide
Takashi Hasumura • Takahiro Fukuda •
Raymond L. D. Whitby • Ortrud Aschenbrenner
Toru Maekawa
•
Received: 13 August 2010 / Accepted: 4 November 2010
Ó Springer Science+Business Media B.V. 2010
Abstract We develop a low temperature, organic
solvent-free method of producing iron containing
carbon (Fe@C) nanoparticles. We show that Fe@C
nanoparticles are self-assembled by mixing ferrocene
with sub-critical (25.0 °C), near-critical (31.0 °C)
and super-critical (41.0 °C) carbon dioxide and
irradiating the solutions with UV laser of 266-nm
wavelength. The diameter of the iron particles varies
from 1 to 100 nm, whereas that of Fe@C particles
ranges from 200 nm to 1 lm. Bamboo-shaped
structures are also formed by iron particles and
carbon layers. There is no appreciable effect of the
temperature on the quantity and diameter distributions of the particles produced. The Fe@C nanoparticles show soft ferromagnetic characteristics. Iron
particles are crystallised, composed of bcc and fcc
lattice structures, and the carbon shells are graphitised after irradiation of electron beams.
Electronic supplementary material The online version of
this article (doi:10.1007/s11051-010-0142-9) contains
supplementary material, which is available to authorized users.
T. Hasumura T. Fukuda T. Maekawa (&)
Bio-Nano Electronics Research Centre, Toyo University,
2100 Kujirai, Kawagoe, Saitama 350-8585, Japan
e-mail: [email protected]
R. L. D. Whitby O. Aschenbrenner
School of Pharmacy and Biomolecular Sciences,
University of Brighton, Cockroft Building, Lewes Road,
Brighton BN2 4GJ, UK
Keywords Nanoparticles Carbon Iron Ferrocene Critical carbon dioxide UV laser Composite nanomaterials
Introduction
It has been demonstrated that nano materials such as
fullerenes, carbon nanotubes and magnetic nanoparticles can be effectively utilised for the development
of functional materials, nano or micro electro
mechanical systems (NEMS/MEMS), biochemical
sensors and biomedical devices (Li et al. 2008;
Bhushan 2007; Emerich and Thanos 2006). Magnetic
nanoparticles are, in particular, useful for biochemical and biomedical science and engineering research;
e.g., labelling, sorting and manipulation of target
molecules or cells (Harrison and Atala 2007; Gao
et al. 2006; Morimoto et al. 2008) and control of the
activities of biomolecules (Mizuki et al. 2010). A
number of different methodologies have been developed for the synthesis of nanoparticles (Heszler et al.
2000; Xu et al. 2003; Strobel and Pratsinis 2009),
amongst which thermal laser-assisted chemical
vapour deposition (thermal LCVD) (Buerki and
Leutwyler 1991; Wallenberger 1997) and the laser
pyrolysis method (Buerki and Leutwyler 1994;
Majima et al. 1994; Alexandrescu et al. 1998;
Alexandrescu et al. 1990) are commonly employed.
Since nanoparticles tend to agglomerate when the
process temperature is high, some innovative method
123
J Nanopart Res
of producing nanoparticles at low temperature is
required. The photolytic dissociation method using
UV photons is a non-thermal process performed at
room temperature. Metallocenes such as ferrocene
(Fe(cp)2), nickelocene (Ni(cp)2) and cobaltocene
(Co(cp)2) have been used as precursors for the
formation of metal-containing nanoparticles (Elihn
et al. 2001). UV lasers of wavelengths ranging from
193 to 355 nm have been used for the photolysis of
ferrocene and the deposition of iron containing
carbon nanoparticles (Ray et al. 1989; Ouchi et al.
2005; Park et al. 2008). Super-critical fluids are often
used in nanotechnology as well as chemical, electrical and environmental science and engineering.
Several anomalies such as critical opalescence,
divergence of the physical properties, critical fluctuations, the piston effect and so on appear as the fluid
systems approach the critical points (Stanley 1971;
Maekawa et al. 2004). It has also been demonstrated
that a variety of nanostructures are formed in fluids
under near-critical and super-critical conditions (Fukuda et al. 2007a, b, c; Rantonen et al. 2008; Park et al.
2009). In this letter, we show that iron containing
carbon (Fe@C) nanoparticles are produced by mixing
Fe(cp)2 with sub-critical (25.0 °C), near-critical
(31.0 °C) and super-critical (41.0 °C) carbon dioxide
(CO2) and irradiating the solutions with pulsed laser
beams of 266-nm wavelength.
Experimental details
A schematic diagram of the experimental system is
shown in Fig. 1. The inner volume of the critical fluid
chamber made of aluminium was 12 ml. 10 mg of
Fe(cp)2 (Tokyo Chemical Industry Co. Ltd) was placed
in the chamber, and residual gases in the chamber were
purged by flowing CO2 gas at 70 °C for 10 min. Then,
liquid CO2 of its critical density (4.68 9 102 kg m-3)
(Somayajulu 1989) was injected into the chamber, and
the fluid temperature was set at 25.0 °C (sub-critical),
31.0 °C (near-critical) or 41.0 °C (super-critical) by a
heater installed around the chamber, which was regulated by a PID-controller (C541, Technol Seven Co.
Ltd). Note that the critical temperature and pressure
are, respectively, 31.0 °C and 7.38 MPa (Somayajulu
1989). The temperature was monitored by a thermistor
(SZL-64, Takara Thermistor Co. Ltd) embedded
inside the chamber wall. We confirmed that critical
123
Fig. 1 Schematic diagram of the experimental system. The
critical fluid chamber, the volume of which is 12 ml, is made of
aluminium. Sub-critical, near-critical or super-critical carbon
dioxide, with which Fe(cp)2 is mixed, is confined in the
chamber. The fluid temperature, which is monitored by a
thermistor embedded inside the chamber wall, is set at 25.0,
31.0 or 41.0 °C by a heater installed around the chamber and
PID-controller. The Fe(cp)2/CO2 solution is irradiated with
laser beams of 193 and 266-nm wavelength. The structures of
the materials produced in the chamber are observed by a
transmission electron microscope. The internal structures and
elements of the materials are also analysed by the selected area
electron diffraction method and energy-dispersive X-ray
spectroscopy
opalescence occurred at 31.0 °C even after Fe(cp)2 had
been mixed with CO2. We measured the absorption
spectrum of deuterium/tungsten/halogen light (DH20
00-DUV, Ocean Optics Inc) passing through the
Fe(cp)2/CO2 solutions by an ultraviolet–visible spectrometer (DH2000-DUV, USB2000, Ocean Optics Inc).
The light source provided a 190–1700 nm range and the
detectable spectrum range was 200–1100 nm. The
above Fe(cp)2/CO2 solutions were irradiated with
pulsed beams from a neodymium-doped yttrium/aluminium/garnet (Nd: YAG) laser (Brilliant Quantel Ltd
Co) or ArF excimer laser (COMPex Pro 50, Coherent
Inc) through a synthetic quartz glass installed at the top
of the chamber. The diameter and thickness of the
synthetic quartz glass were 20 and 5 mm. The irradiation conditions in the case of Nd: YAG laser were as
follows: the wavelength = 266 nm, the beam diameter = 10 mm, the pulse generation frequency =
10 Hz, the mean pulse duration = 4.3 ns, the total
number of pulses = 105 and the energy of each
J Nanopart Res
pulse = 50 mJ, whereas those in the case of ArF
excimer laser, the wavelength = 193 nm, the beam
diameter = 10 mm, the pulse generation frequency = 50 Hz, the mean pulse duration = 30 ns,
the total number of pulses = 1.8 9 105 and the energy
of each pulse = 20 mJ. After each experiment, the fluid
was gradually released controlled by a valve switch. The
structures formed in the chamber were observed by a
transmission electron microscope (TEM) (JEM2200FS, JEOL). We also analysed the internal structures
and elements of the materials produced in the chamber
by the selected area electron diffraction method (SAED)
(JEM-2200FS, JEOL) and energy-dispersive X-ray
spectroscopy (EDS) (JED-2300T, JEOL). We estimated
the distributions of the diameters of materials produced
in the chamber directly from TEM images and by the
dynamic scattering method (Zetasizer nano-zs, Malvern
Instruments Ltd). Finally, we obtained the magnetisation-magnetic field curve of the materials produced in
the chamber by a vibrating sample magnetometer
(VSM) (7407, Lake Shore Crytronics Inc).
Results and discussion
It was recently shown that Ni(cp)2 was decomposed
without laser irradiation by mixing oxygen molecules
with Ni(cp)2/super-critical CO2 solution (Hasumura
et al. 2010). Therefore, we checked the effect of
oxygen molecules on the decomposition of Fe(cp)2 and
confirmed that Fe(cp)2 was not decomposed by oxygen
molecules dissolved in CO2 unlike Ni(cp)2. We found
that the black soot was formed on the inner surface of
the quartz glass after irradiation of the UV laser of
266 nm wavelength into sub-, near- and super-critical
CO2, in which Fe(cp)2 was dissolved. TEM images of
particles, the electron diffraction pattern and EDS
mappings of carbon and iron atoms obtained in the case
of super-critical CO2 (41.0 °C) are shown in Fig. 2.
X-ray diffraction (XRD) data are also shown in Fig. S1
in the Electronic Supplementary Material. As is clearly
shown, iron nanoparticles, which were covered with
carbon shells, were produced. It is supposed that iron
particles were composed of several domains of bcc and
Fig. 2 TEM images,
electron diffraction pattern
and EDS mappings of
selected areas of a material
formed on the surface of the
quartz glass in super-critical
carbon dioxide (41.0 °C).
a TEM image of a selected
area of the material. b TEM
image and electron
diffraction pattern. c EDS
mapping of carbon
corresponding to image a.
d EDS mapping of iron
corresponding to image a.
The material is formed by
partially crystallised iron
particles composed of
several domains of bcc and
fcc lattice structures, which
were captured by partially
graphitised carbon shells
(see also the Electronic
Supplementary Material for
the x-ray diffraction
spectrum)
123
J Nanopart Res
fcc lattice structures (Jarlborg and Peter 1984; Li et al.
1995), whilst carbon shells were formed by domains of
graphitised carbon layers (Ruoff et al. 1993). Note that
ferromagnetism of iron is caused by bcc lattice
structures, whereas paramagnetism by fcc structures
(Williamson et al. 1972). The diameter of iron particles
captured by carbon shells varied from 1 to 100 nm
from the TEM images. We found that Fe@C particles
dispersed in acetone and therefore we measured the
diameter of the Fe@C particles dispersed in acetone by
the dynamic scattering method. The diameter of the
Fe@C particles varied from 200 nm to 1 lm. Fe@C
nanoparticles produced in sub-critical (25.0 °C) and
near-critical CO2 (31.0 °C) are shown in Figs. S2 and
S3 in the Electronic Supplementary Material. The
quantity of Fe@C particles produced in sub- and nearcritical CO2 was almost the same as that produced in
super-critical CO2 (41.0 °C). The distribution of the
diameter of the particles produced in sub- and nearcritical CO2 was also more or less the same as that
produced in super-critical CO2. In other words, there
was no appreciable effect of the temperature on the
production of iron containing carbon particles. Interestingly, bamboo-shaped structures, made of carbon
and iron, were also created (see Fig. S4 in the
Electronic Supplementary Material) (Lu et al. 2005).
We will be investigating the bamboo structures and
discussing the details on another occasion.
It is known that the decomposition energies
corresponding to Fe(cp)2 ? Fecp ? cp and Fecp ?
Fe ? cp are, respectively, 3.9 and 2.9 eV (Ray et al.
1989), and therefore it is supposed that two-photon
absorption was constantly occurring and ferrocene
was decomposed into iron and two cp-rings during
the irradiation of photons of 266-nm wavelength,
which corresponds to 4.7 eV. It is also supposed that
during the interval between two pulses, dissociated
high-energy iron atoms were cooled and coagulated
each other to form particles, during which the excess
energy was transferred to cp-rings and as a result, the
rings were decomposed (Ray et al. 1989). Dissociated
carbon atoms formed layers around the iron particles
(Heszler et al. 2000; Ouchi et al. 2005; Park et al.
2008). We also irradiated laser beams of 193-nm
wavelength, which corresponds to 6.4 eV, into supercritical CO2, in which Fe(cp)2 was dissolved, supposing that the quantity of nanoparticles would
increase thanks to higher energy of photons. However, the quantity of Fe@C nanoparticles produced in
123
the case of 193 nm was much less than that in the
case of 266 nm. The absorption spectrum of the
Fe(cp)2/super-critical CO2 solution at 41.0 °C is
shown in Fig. 3. The absorption of 266 nm photons
was higher than that of 193 nm, which explains why
irradiation of 266 nm photons was much more
effective than that of 193 nm photons for the
production of Fe@C nanoparticles.
The magnetisation-magnetic field curve of Fe@C
nanoparticles is shown in Fig. 4. The magnetic
features are summarised as follows: the saturation
magnetisation = 3.7 9 10-5 Wb m kg-1, the remnant magnetisation = 3.9 9 10-6 Wb m kg-1 and
the coercivity = 7.7 A m-1. The present Fe@C
nanoparticles showed soft ferromagnetic characteristics. The saturation magnetisation of the present
Fig. 3 Absorption spectrum of Fe(cp)2/super-critical CO2 solution at 41.0 °C. The absorption of photons of 266-nm wavelength
is higher than that of 193 nm, which explains why the quantity of
iron containing carbon nanoparticles produced by irradiation of
266 nm photons is larger than that of 193 nm photons
Fig. 4 Magnetic moment-magnetic field curve of iron containing
carbon particles at 25 °C. The saturation magnetisation, remnant
magnetisation and coercivity being 3.7 9 10-5 Wb m kg-1,
3.9 9 10-6 Wb m kg-1 and 7.7 A m-1, the particles show soft
ferromagnetic characteristics
J Nanopart Res
Fig. 5 TEM image and electron diffraction pattern of iron
containing carbon nanoparticles after irradiation of electron
beams. Iron particles are composed of bcc and fcc lattice
structures and carbon shells are graphitised
Fe@C nanoparticles is higher than that of the
previously produced magnetic nanoparticles (Pol
et al. 2003; 2008; Fuertes et al. 2008), but lower
than that of Fe@C nanoparticles, which were produced by arc discharge (Borysiuk et al. 2008).
As we mentioned above, iron particles were
partially crystallised, and carbon layers were partially
graphitised. We irradiated the Fe@C nanoparticles
with electron beams under an acceleration voltage of
200 kV for 10 s in the TEM. The power flux of the
electron beams was 19.2 lW lm-2, which was
determined by the current and diameter of the
electron beams; 17 nA and 15 lm. A TEM image
of iron particles captured by carbon shells and the
electron diffraction pattern after irradiation of the
electron beams are shown in Fig. 5. The iron particles
were crystallised showing clear bcc and fcc lattice
structures (Jarlborg and Peter 1984; Li et al. 1995),
and the carbon layers were graphitised, the gap
between which was 0.34 nm (Ruoff et al. 1993).
Conclusions
We developed a low temperature, organic solventfree method of producing iron containing carbon
nanoparticles. We synthesised Fe@C nanoparticles
by mixing Fe(cp)2 with sub-, near- and super-critical
CO2 and irradiating UV laser of 266-nm wavelength
into the solutions. The present result suggests that
nanoparticles composed of iron/nickel or iron/cobalt
alloys, which are covered with carbon shells, may be
produced by mixing ferrocene and nickelocene or
ferrocene and cobaltocene with critical carbon dioxide and irradiating UV lasers into the solutions, in
which case the magnetisation of particles will
increase (Kim et al. 2007; Kozhuharova et al.
2005). Since iron particles and carbon shells were
crystallised after irradiation of electron beams, a large
number of Fe@C nanoparticles may be crystallised
by annealing them at an appropriate temperature and
time. Since core magnetic particles are not oxidised
thanks to carbon shells covering them, the magnetisation will not deteriorate, which makes the present
magnetic nanoparticles more practical considering
their application to the studies in the fields of
nanoelectronics, nanomagnetism, biochemistry and
biomedical science and engineering (Gao et al. 2006;
Morimoto et al. 2008; Mizuki et al. 2010).
Acknowledgments Part of this study has been supported by a
Grant for the High-Tech Research Centres organised by the
Ministry of Education, Culture, Sports, Science and Technology
(MEXT), Japan, since 2006. T. Fukuda would like to thank
MEXT for their financial support.
References
Alexandrescu R, Cojocaru S, Crunteanu A, Morjan I, Voicu I,
Diamandescu L, Vasiliu F, Huisken F, Kohn B (1990)
Preparation of iron carbide and iron nanoparticles by laser
induced gas phase pyrolysis. J Phys IV France 90:Pr8537–Pr8-544
Alexandrescu R, Morjan I, Crunteanu A, Cojocaru S, Petcu S,
Teodorescu V, Huisken F, Kohn B, Ehbrecht M (1998)
Iron-oxide-based nanoparticles produced by pulsed laser
pyrolysis of Fe(CO)5. Mater Chem Phys 55:115–121
Bhushan B (2007) Nanotribology and nanomechanics of
MEMS/NEMS and BioMEMS/BioNEMS materials and
devices. Microelectron Eng 84:387–412
Borysiuk J, Grabias A, Szczytko J, Bystrzejewski M, Twardowski A, Lange H (2008) Structure and magnetic properties of carbon encapsulated Fe nanoparticles obtained
by arc plasma and combustion synthesis. Carbon 46:
1693–1701
Buerki PR, Leutwyler S (1991) Homogeneous nucleation of
diamond powder by CO2 laser driven gas-phase reactions.
J Appl Phys 69:3739–3744
123
J Nanopart Res
Buerki PR, Leutwyler S (1994) CO2-laser-induced vapor-phase
synthesis of HN-diamond nanoparticles at 0.6–2 bar.
Nanostruct Mater 4:577–582
Elihn K, Otten F, Boman M, Heszler P, Kruis FE, Fissan H,
Carlsson J-O (2001) Size distributions and synthesis of
nanoparticles by photolytic dissociation of ferrocene.
Appl Phys A 72:29–34
Emerich DF, Thanos CG (2006) The pinpoint promise of
nanoparticle-based drug delivery and molecular diagnosis.
Biomol Eng 23:171–184
Fuertes AB, Valdés-Solı́s T, Sevilla M (2008) Fabrication of
monodisperse mesoporous carbon capsules decorated with
ferrite nanoparticles. J Phys Chem C 112:3648–3654
Fukuda T, Ishii K, Kurosu S, Whitby R, Maekawa T (2007a)
Formation of clusters composed of C60 molecules via selfassembly in critical fluids. Nanotechnology 18:145611
Fukuda T, Maekata T, Hasumura T, Rantonen N, Ishii K,
Nakajima Y, Hanajiri T, Yoshida Y, Whitby R, Mikhalovsky S (2007b) Dissociation of carbon dioxide and
creation of carbon particles and films at room temperature.
New J Phys 9:321
Fukuda T, Watabe N, Whitby R, Maekawa T (2007c) Creation
of carbon onions and coils at low temperature in nearcritical benzene irradiated with an ultraviolet laser.
Nanotechnology 18:415604
Gao C, Li W, Morimoto H, Nagaoka Y, Maekawa T (2006)
Magnetic carbon nanotubes: synthesis by electrostatic
self-assembly approach and application in the biomanipulations. J Phys Chem B 110:7213–7220
Harrison BS, Atala A (2007) Carbon nanotube applications for
tissue engineering. Biomaterials 28:344–353
Hasumura T, Fukuda T, Whitby RLD, Aschenbrenner O,
Maekawa T (2010) Low temperature synthesis of fibres
composed of carbon–nickel nanoparticles in super-critical
carbon dioxide. Chem Phys Lett 493:304–308
Heszler P, Elihn K, Boman M, Carlson J-O (2000) Optical
characterisation of the photolytic decomposition of ferrocene into nanoparticles. Appl Phys A 70:613–616
Jarlborg T, Peter M (1984) Electronic structure, magnetism and
curie temperatures in Fe, Co and Ni. J Magn Magn Mater
42:89–99
Kim JH, Kim J, Lim SK, Kim CK, Yoon CS (2007) Synthesis
of monolayered Ni–Fe alloy nanoparticles based on
nanotemplate approach. J Magn Magn Mater 310:2402–
2404
Kozhuharova R, Ritschel M, Elefant D, Graff A, Mönch I,
Mühl T, Schneider CM, Leonhardt A (2005) (FexCo1-x)alloy filled vertically aligned carbon nanotubes grown by
thermal chemical vapor deposition. J Magn Magn Mater
290–291:250–253
Li F, Yang J, Xue D, Zhou R (1995) X-ray diffraction and
Mossbauer studies of the (Fe1-xNix)4N compounds
(0 B x B 0.5). J Magn Magn Mater 151:221–224
Li C, Thostenson ET, Chou TW (2008) Sensors and actuators
based on carbon nanotubes and their composites: a
review. Compos Sci Technol 68:1227–1249
Lu Y, Zhu Z, Liu Z (2005) Carbon-encapsulated Fe nanoparticles from detonation-induced pyrolysis of ferrocene.
Carbon 43:369–374
Maekawa T, Ishii K, Shiroishi Y, Azuma H (2004) Onset of
buoyancy convection in a horizontal layer of a
123
supercritical fluid heated from below. J Phys A Math Gen
37:7955–7969 (and references cited therein)
Majima T, Miyahara T, Haneda K, Ishii T, Takami M (1994)
Preparation of iron ultrafine particles by the dielectric
breakdown of Fe(CO)5 using a transversely excited
atmospheric CO2 laser and their characteristics. Jpn J
Appl Phys 33:4759–4763
Mizuki T, Watanabe N, Nagaoka Y, Fukushima T, Morimoto H,
Usami R, Maekawa T (2010) Activity of an enzyme
immobilized on superparamagnetic particles in a rotational
magnetic field. Biochem Biophys Res Commun
393:779–782
Morimoto H, Ukai T, Nagaoka Y, Grobert N, Maekawa T
(2008) Tumbling motion of magnetic particles on a
magnetic substrate induced by a rotational magnetic field.
Phys Rev E 78:021403
Ouchi A, Tsunoda T, Bastl Z, Marysko M, Vorlicek V, Bohacek J, Vacek K, Pola J (2005) Solution photolysis of
ferrocene into Fe-based nanoparticles. J Photochem Photobiol A Chem 171:251–256
Park JB, Jeong SH, Jeong MS, Kim JY, Cho BK (2008) Synthesis of carbon-encapsulated magnetic nanoparticles by
pulsed laser irradiation of solution. Carbon 46:1369–1377
Park KC, Wang F, Morimoto S, Fujishige M, Morisako A, Liu
X, Kim YJ, Jung YC, Jang IY, Endo M (2009) One-pot
synthesis of iron oxide–carbon core–shell particles in
supercritical water. Mater Res Bull 44:1443–1450
Pol VG, Motiei M, Gedanken A, Calderon-Moreno J, Mastai Y
(2003) Sonochemical deposition of air-stable iron nanoparticles on monodispersed carbon spherules. Chem Mater
15:1378–1384
Rantonen NJK, Toyabe T, Maekawa T (2008) Catalyst-free
growth of needle-shaped carbon filaments at low temperature in a near-critical binary fluid. Carbon 46:1225–
1231
Ray U, Hou HQ, Zhang Z, Schwarz W, Vernon M (1989) A
crossed laser-molecular beam study of the one and two
photon dissociation dynamics of ferrocene at 193 and
248 nm. J Chem Phys 90:4248–4257
Ruoff RS, Lorents DC, Chan B, Malhotra R, Subramoney S
(1993) Single crystal metals encapsulated in carbon
nanoparticles. Science 29:346–348
Somayajulu GR (1989) Estimation procedures for critical
constants. J Chem Eng Data 34:106–120
Stanley HE (1971) Introduction to phase transition and critical
phenomena. Oxford University Press, Oxford
Strobel R, Pratsinis SE (2009) Direct synthesis of maghemite,
magnetite and wustite nanoparticles by flame spray
pyrolysis. Adv Powder Technol 20:190–194
Wallenberger FT (1997) Inorganic fibres and microfabricated
parts by laser assisted chemical vapour deposition
(LCVD): structures and properties. Ceram Int 23:119–126
Williamson DL, Bukshpan S, Ingalls R (1972) Search for
magnetic ordering in hcp. Iron Phys Rev B 6:4194–4206
Xu ZF, Xie Y, Feng WL, Schaefer HF (2003) Systematic
investigation of electronic and molecular structures for the
first transition metal series metallocenes M(C5H5)2
(M = V, Cr, Mn, Fe, Co, and Ni). J Phys Chem A 107:
2716–2729