Facile fabrication of nickel oxide hollow spheres and amorphous carbon/nickel nanoparticles composites using colloidal carbonaceous microspheres as template

Article abstract of DOI:10.1246/cl.2005.1174

Core/shell structure with colloidal carbonaceous microspheres as core and nanowhisker-like Ni(OH)₂ as shell was synthesized by a facile precipitation method. NiO hollow spheres with hierarchical nanostructure and amorphous carbon/nickel nanoparticles composites were obtained by heat treatment in air and nitrogen, respectively. Nitrogen adsorption and desorption analysis indicated that these two novel products are both nanoporous materials with high specific surface area and large pore volume. Copyright

Full text of DOI:10.1246/cl.2005.1174

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Chemistry Letters Vol.34, No.8 (2005)
Facile Fabrication of Nickel Oxide Hollow Spheres and Amorphous Carbon/Nickel
Nanoparticles Composites Using Colloidal Carbonaceous Microspheres as Template
ꢀ
Mingbo Zheng, Jieming Cao, Yongping Chen, Xianjia Ma, Shaogao Deng, and Jie Tao
Nanomaterials Research Institute, College of Material Science and Technology,
Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P. R. China
(Received May 26, 2005; CL-050689)
Core/shell structure with colloidal carbonaceous micro-
D8 advance). The size and morphology of the samples were ex-
amined by transmission electron microscopy (TEM) (FEI, TEC-
NAI-20) and scanning electron microscopy (SEM) (LEO1530).
The N2 adsorption/desorption analyses were performed on a
Micromeritics ASAP 2010 instrument.
Figures 1a, 1b, and 1c show the XRD patterns of the sample
before calcinations, the sample calcined in air and the sample
calcined in nitrogen, respectively. The pattern of Figure 1a cor-
responds to the layered ꢀ-Ni(OH)2 structure (JCPDS code: 38-
spheres as core and nanowhisker-like Ni(OH)2 as shell was syn-
thesized by a facile precipitation method. NiO hollow spheres
with hierarchical nanostructure and amorphous carbon/nickel
nanoparticles composites were obtained by heat treatment in
air and nitrogen, respectively. Nitrogen adsorption and desorp-
tion analysis indicated that these two novel products are both
nanoporous materials with high specific surface area and large
pore volume.
0
715). The main peaks in Figures 1b and 1c can be indexed to
the (111), (200), (220) planes of cubic-phased NiO (JCPDS
code: 47-1049), and (111), (200), (220) planes of cubic-phased
metallic nickel (JCPDS code: 04-0850), respectively.
Figure 2a displays the TEM image of colloidal carbona-
ceous microspheres. From this image, it can be seen that they
NiO and Ni have attracted increasing attention because of
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–3
their extensive applications, especially in electrodes, cataly-
4
5
sis, and magnetic materials. As the current research is driving
towards nanoscale phenomena and technology, the exploration
of new synthesis methods for NiO and Ni with novel nanostruc-
ture will find new applications or improve their performance.
Therefore, many reports have concerned the synthesis of NiO
6
a
and Ni nanomaterials, including NiO nanosheets, NiO nanorib-
6d,6e
bons,6b NiO hollow spheres, porous NiO,
6c
nanoporous
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metallic nickel colloids, and nickel nanoparticles/carbon nano-
wall composites.5
Recently, colloidal carbonaceous microspheres as a novel
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,9
template have been reported. In comparison with polymer or
silica spheres, carbonaceous microspheres have two apparent
advantages: 1) they are green template; 2) surface modification
is unnecessary.
In this letter, a novel core/shell structure with colloidal
carbonaceous microspheres as a core and nanowhisker-like
Ni(OH)2 as a shell was successfully prepared. NiO hollow
spheres with hierarchical nanostructure and amorphous car-
bon/nickel nanoparticles composites were obtained by heat
treatment in air and nitrogen, respectively.
Figure 1. XRD patterns of the samples. (a) before calcination;
(b) calcined in air; (c) calcined in nitrogen.
The colloidal carbonaceous microspheres were fabricated
8
according to the method reported previously. The preparation
procedure of NiO hollow spheres and amorphous carbon/nickel
nanoparticles composites is described as follows: 0.001 mol of
nickel acetate was dissolved in 40 mL of distilled water to form
a clear solution. 100 mg of carbonaceous microspheres was add-
ed to the above solution. The mixture was ultrasonicated for
0.5 h and stirred for 1 h. Then the pH of the mixture was slowly
adjusted to 9 by addition of 5 wt % NH4OH dropwise. The result-
ing suspension was stirred for an additional 3 h. Then the solid
was centrifuged, washed, and redispersed in distilled water,
and this cycle was repeated five times. The solid was then
ꢁ
oven-dried at 100 C for 5 h, resulting in the Ni(OH)2/carbona-
ceous microspheres composites. The composites were heat-treat-
Figure 2. (a) TEM image of colloidal carbonaceous micro-
spheres; (b) TEM image of composites of Ni(OH)2 and carbona-
ceous microspheres; (c) TEM, and (d) SEM images of NiO
hollow spheres; (e) TEM, and (f) SEM images of amorphous
carbon/nickel nanoparticles composites.
ꢁ
ꢁ
ed under 450 C for 4 h in air and heat-treated under 600 C for
h in nitrogen, respectively. The crystal structures of the sam-
ples were characterized by X-ray diffraction (XRD) (Bruker
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Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.8 (2005)
1175
The polysaccharide-like surface of colloidal carbonaceous
microspheres is hydrophilic and has a distribution of –OH and
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–
C=O groups. When the carbonaceous microspheres were
2þ
dispersed in the solution of nickel acetate, the Ni ions could
be adsorbed on the surface of the microspheres, which led to
the high local supersaturation of Ni , thus provide potential
nucleation sites for the crystallization of the Ni(OH)2. With
the increasing pH by ammonia titration, Ni(OH)2 would firstly
heterogeneously nucleate on the surface of the carbonaceous
2
þ
2
þ
ꢂ
microspheres. As the reaction time increased, Ni and OH
diffuse continuously to the surface of the microspheres, and
Ni(OH)2 nuclei would grow and develop into Ni(OH)2 nano-
Figure 3. BET nitrogen adsorption and desorption isotherm
and pore size distribution plot (inset) for NiO hollow spheres.
ꢁ
whiskers. During the calcination at 450 C in air, the template
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3
may transform into CO2, which would escape effectively with-
out breaking the shell wall, and Ni(OH)2 would decompose into
have smooth surface. Figure 2b shows the typical TEM image of
the as-prepared sample. Nanowhiskers of Ni(OH)2 covered the
exterior of carbonaceous microspheres. It reveals a novel core/
shell structure with carbonaceous microspheres as the core and
nanowhisker-like Ni(OH)2 as the shell. Figures 2c and 2d pres-
ent the TEM and SEM images of the sample calcined in air, re-
spectively. One can see that the sample has hierarchical struc-
ture. The shell of the hollow spheres is composed of loosely
packed nanowhiskers and nanoparticles. Besides, the sample
underwent some shrinkage during the calcinations. The TEM
image (Figure 2e) and SEM image (Figure 2f) of the sample cal-
cined in nitrogen show the emergence of nickel nanoparticles.
Most of the particles in the products were found to be less than
ꢁ
NiO. When the composite was calcined at 600 C in nitrogen, the
template would be carbonized into amorphous carbon. Mean-
while, the NiO particles, which were prepared by thermal de-
composition of Ni(OH)2 on the surface of the template, would
be reduced to metallic Ni in the reductive atmosphere resulted
from the thermal decomposition of carbonaceous microspheres.7
In summary, NiO hollow spheres with hierarchical nano-
structures and amorphous carbon/nickel nanoparticles compo-
sites have been successfully prepared using carbonaceous micro-
spheres as template. N2 adsorption/desorption analysis indicated
that these two novel products are nanoporous materials with high
specific surface area and large pore volume. It is anticipated that
these novel materials will have potential applications in elec-
trode materials, catalysis and other fields.
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0
25 nm in dimension. According to Wang’s report, the template
transforms into amorphous carbon after calcination.
Figure 3 presents N2 adsorption/desorption analysis of NiO
hollow spheres. It exhibits a type IV isotherm with H3-type
hysteretic loop attributed to an interconnected mesoporous sys-
tem with a broad pore-size distribution. The inset of Figure 3
shows the pore-size distribution plot calculated by the BJH
This work was financially supported by the Scientific Re-
search Foundation for the Returned Overseas Chinese Scholars.
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1
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Published on the web (Advance View) July 23, 2005; DOI 10.1246/cl.2005.1174