Selected-control synthesis of metal phosphonate nanoparticles and nanorods

Article abstract of DOI:10.1021/ic048436t

By surfactant-assisted methods, nanoscale Co(O₃PC ₆H₅)·H₂O species of different morphologies, namely, nanoparticles and nanorods, have been successfully synthesized and characterized. Upon removal of the organic

Full text of DOI:10.1021/ic048436t

Inorg. Chem. 2005, 44, 2140−2142
Selected-Control Synthesis of Metal Phosphonate Nanoparticles and
Nanorods
Shu-Yan Song, Jian-Fang Ma,* Jin Yang, Min-Hua Cao, and Ke-Chun Li
Department of Chemistry, Northeast Normal UniVersity, Changchun 130024, P. R. China
Received November 7, 2004
By surfactant-assisted methods, nanoscale Co(O3PC6H5)
‚
H2O
methods for the synthesis of nanoscale metal phosphonate
proves to be intriguing and valuable.
species of different morphologies, namely, nanoparticles and
nanorods, have been successfully synthesized and characterized.
Upon removal of the organic part of the compound, peculiar
Co2P2O7 porous nanorods formed.
Surfactant-assisted methods have been widely used in the
preparation and morphology control of materials such as
silica particles, silica nanotubes, carbon nanotubes, and CdS
and CdSe nanorods.8 The surfactant plays an important role
in determining the morphology of the products, as surfactant
mesophases have proved to be useful and versatile soft
templates that can form different conformations by self-
assembly and lead to the formation of different nanostruc-
tures.9 Herein, we report a successful method using surfac-
tants, namely, cetyltrimethylammonium bromide (CTAB)
and sodium dodecyl benzene sulfonate (SDBS), for the
preparation of Co(O3PC6H5)‚H2O nanoparticles and nanorods
under different conditions.
Nanometer-scale materials have attracted intensive atten-
tion in the past decades because of their unique physical and
chemical properties and potential applications in nanodevices
and functional materials.1 Great progress has been made in
the fabrication of inorganic and organic nanosize materials,
such as carbon nanotubes, metal nanorods, metal oxides
nanowires, and polyaniline nanoparticles.2-5 However, to the
best of our knowledge, few reports on the synthesis of
nanoscale metal phosphonates have been published to date.6
Owing to their specific characteristics and potential applica-
tions as sorbents, sensors, catalysts, ion exchangers, ionic
conductors, and nonlinear optical materials,7 exploring proper
Co(O3PC6H5)‚H2O, which exhibits peculiar and fascinating
magnetic properties including magnetic ordering, canted
antiferromagnetism, and antiferromagnetic resonance, has
been studied as a model for two-dimensional (2D) magne-
tism.10 The properties of inorganic and organic hybrid
materials, such as catalytic activity, sensitivity, conductivity,
and photonic efficiency, are often closely related to their
chemical composition, size, crystal structure, surface chem-
istry, and shape.11 Nanorods and nanoparticles often offer
larger surface areas than the corresponding solid films or
bulk materials. The ability to synthetically tune these material
parameters, especially their size and morphology, then proves
* To whom correspondence should be addressed. E-mail:
jfma@public.cc.jl.cn.
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2140 Inorganic Chemistry, Vol. 44, No. 7, 2005
10.1021/ic048436t CCC: $30.25
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Chart 1. Effect of Surfactant on the Growth Process of
Co(O3PC6H5)‚H2O Nanorods
shapes (Figure 1c, 1d, and 1f). A high-resolution TEM
(HRTEM) image and selected area electron diffraction
(SAED) pattern of the sample 2 (inset in Figure 1e), taken
from a single rod, show that the nanorod is structurally
uniform with a clearly resolved interplanar spacing of about
14.5 Å, which corresponds to (010) planes, and that the axis
of the nanorod is along the [001] direction.
The hydrothermal synthesis method and the temperature
have significant effects on the size and morphology of Co-
(O3PC6H5)‚H2O. When the reaction was carried out by
stirring the mixture at 60 °C for 3 days, only bulk Co(O3-
PC6H5)‚H2O was observed. When CTAB or SDBS was used
in the reaction, Co(O3PC6H5)‚H2O nanorods were obtained
instead of nanoparticles. Clearly, the interaction between the
surfactant and the reactant has a great effect on the result.
Chart 1 illustrates the effect of surfactant on the growth
process of Co(O3PC6H5)‚H2O nanorods. Co(O3PC6H5)‚H2O
exhibits a lamellar structure with alternating Co-O3P and
phenyl layers. The hydrophobic groups of CTAB connect
to the top and bottom phenyl layers of Co(O3PC6H5)‚H2O
with van der Waals forces, which can efficiently prevent the
particle from growing along the direction perpendicular to
the layers. However, in the side of the lamellar structure,
the hydrophilic Co-O3P layer and hydrophobic phenyl layer
stack alternately, so no stable protecting shell of CTAB can
be formed. The growth of Co(O3PC6H5)‚H2O nanorods along
the c axis rather than the a axis can be determined by its
highly anisotropic character along the c axis. The structure
of the inorganic polymeric Co-O3P layer is shown in Figure
2.12 Each cobalt ion is coordinated to five phosphonate
oxygen atoms and one water molecule. Each phosphonate
group is coordinated to four cobalt ions. The two-dimensional
polymeric structure can be described as columns built up of
alternating cobalt and phosphonate ions, extending along the
c axis, with each column is linked to two neighboring
columns. Thus, the anisotropic character along the c axis is
apparently different from that along the a axis. From a kinetic
perspective, the activation energy for the [001] direction of
growth of Co(O3PC6H5)‚H2O is lower than that for growth
Figure 1. (a) XRD patterns of samples 1-3. (b) TEM image of sample
1. (c,d) TEM images of sample 2, (e) HRTEM image of sample 2 and
(inset) SAED image. (f) TEM image of sample 3.
to be significant. In this work, we intended to prepare Co-
(O3PC6H5)‚H2O nanoparticles and nanorods by the use of
hydrothermal method. The reaction of Co(NO3)2‚6H2O with
sodium phenylphosphonate (SPP) in a 1:1 stoichiometry in
water was carried out in a Teflon-lined autoclave at 100 °C
for 2 days, and Co(O3PC6H5)‚H2O nanoparticles were
obtained. When the surfactants CTAB or SDBS were added
into the reaction mixture, Co(O3PC6H5)‚H2O nanorods
formed.
X-ray powder diffraction (XRD) patterns of the samples
were collected on a Rigaku Dmax 2000 X-ray diffractometer
with Cu KR radiation (λ ) 0.154178 nm), with 2θ ranging
from 2° to 40°. Sample 1 (nanoparticles) was prepared
without use of surfactant, whereas samples 2 and 3 (nano-
rods) were prepared using CTAB and SDBS, respectively.
The details of the syntheses are given in the Supporting
Information. Figure 1a shows the XRD patterns of the three
samples. All of the peaks of the three samples are to be the
same and can be indexed to the simulated XRD powder
pattern of Co(O3PC6H5)‚H2O (Figure S10 in the Supporting
Information), indicating that they are the same compound
[Co(O3PC6H5)‚H2O]. The morphology of the prepared Co-
(O3PC6H5)‚H2O was further investigated with transmission
electron microscopy (TEM). Typical TEM images show that
sample 1 is a particlelike shape with a diameter of 40-60
nm (Figure 1b) and samples 2 and 3 display straight, rodlike
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Inorganic Chemistry, Vol. 44, No. 7, 2005 2141

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Figure 3. XRD pattern and TEM image of sample 2 after heating.
Figure 2. Structure of an inorganic polymeric layer of Co(O3PC6H5)‚
H2O.
to 600 °C under N2, which is consistent with the calculated
value of 37.4% considering the loss of the organic portion.
The holes in crystalline Co2P2O7 are formed by removing
the organic part of the Co(O3PC6H5)‚H2O. All of the
diffraction peaks in the XRD pattern of the sample after
heating (Figure 3a) can be indexed to pure monoclinic
Co2P2O7 [space group P21/c] with lattice constants a ) 7.008
Å, b ) 8.345 Å, and c ) 9.004 Å (JCPDS 79-0825). Element
analysis obtained via inductively coupled plasma-atomic
emission spectrometry (ICP-AES) (Labtest Equipment Co.
model 710) further confirms the elemental composition of
the compounds in the expected stoichiometric proportions,
obsd (%) Co, 41.02; P, 20.84; calcd (%) Co, 40.39, P, 21.23.
In summary, a surfactant-directed synthetic route was
developed for the synthesis of metal phosphonate nanostruc-
tures. The unique properties combined with the simple and
controllable synthetic approach can provide useful informa-
tion for the study in related fields.
along the a axis. This means a higher growth rate along the
c axis and a lower one along the a axis to form Co(O3PC6H5)‚
H2O nanorods that grow preferentially along the [001]
directon.13 Different concentration ratios of [CTAB]/[SPP]
gave nanorods with different diameters: 30-40 nm ([SPP]
) 5 mM, [CTAB] ) 40 mM), 50-60 nm ([SPP] ) 20 mM,
[CTAB] ) 40 mM), and 70-80 nm ([SPP] ) 40 mM,
[CTAB] ) 40 mM). With a high concentration ratio of
[CTAB] to [SPP], the surfactant can envelop the crystal seeds
of Co(O3PC6H5)‚H2O well, which leads to the formation of
nanorods with small diameters.
Divalent metal phenlyphosphonates M(O3PC6H5)‚H2O (M
) Mn, Ni, Cu, Zn, Cd) also have lamellar structures.12 When
Ni(NO3)2‚6H2O was used instead of Co(NO3)2‚6H2O, nano-
particles and nanorods of Ni(O3PC6H5)‚H2O could be
prepared analogously. However when M(NO3)2‚6H2O (M )
Mn, Cu, Zn, Cd) was used, only nanoparticles of M(O3-
PC6H5)‚H2O (M ) Mn, Cu, Zn, Cd) were obtained even if
surfactant (CTAB or SDBS) was used. The probable reason
is that the van der Waals force between the adjacent phenyl
layers is much stronger than those between the phenyl layer
and the hydrophobic groups of CTAB so that the surfactant
cannot change the morphology of the metal phenylphospho-
nate.
Acknowledgment. We thank the National Natural Sci-
ence Foundation of China (No. 20471014) and the Fok Ying
Tung Education Foundation for support. TEM work was
performed by Doctor L.-H. Ge at the Changchun Institute
of Applied Chemistry, Chinese Academy of Sciences,
Changchun, China.
Supporting Information Available: Experiment section. Ther-
mal gravimetric curve for sample 2 (Figure S1). Images of the
samples obtained using different concentration ratios of [CTAB]
to [SPP] (Figures S2 and S3). TEM images of other transition metal
phosphonates (Figures S4-S9). Simulated XRD powder pattern
of Co(O3PC6H5)‚H2O (Figure S10). This material is available free
of charge via the Internet at http://pubs.acs.org.
Heating the nanorods at 600 °C in air for 2 h yielded
bluish-violet nanoporous crystalline Co2P2O7 without altering
the 1D morphology, and many holes formed in the nanorods
(Figure 3b). From TGA analysis (see Supporting Informa-
tion), a total of 37.4% weight loss was observed from 200
(13) Fang, Y.-P.; Xu, A.-W.; Song, R.-Q.; Zhang, H.-X.; You, L.-P.; Yu,
J. C.; Liu, H.-Q. J. Am. Chem. Soc. 2003, 51, 16025.
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