Fabrication and application of highly ordered mesoporous Co3O4, NiO, and their metals

Article abstract of DOI:10.1016/j.jpcs.2009.12.049

Highly ordered mesoporous Co₃O₄, NiO, and their metals were synthesized by nanocasting method using there corresponding mesoporous SBA-15 silica as a template. The obtained porous metal oxides have high surface areas, large pore volume, and a narrow pore size distribution. The N₂-adsorption data for mesoporous metal oxides have provided the BET area of 257.7 m² g^-1 and the total pore volume of 0.46 cm³ g^-1. The mesoporous metals were employed as a catalyst in the synthesis of (S)-3-pyrrolidinol from chiral (S)-4-chloro-3-hydroxybutyronitrile, and a high yield to (S)-3-pyrrolidinol-salt was obtained on the mesoporous Co metal catalyst.

Full text of DOI:10.1016/j.jpcs.2009.12.049

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Journal of Physics and Chemistry of Solids 71 (2010) 612–615
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids
journal homepage: www.elsevier.com/locate/jpcs
Fabrication and application of highly ordered mesoporous Co3O4, NiO, and
their metals
Geon J. Kim, Xiao-Feng Guo n
Department of Chemical Engineering, Inha University, Incheon 402-751, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly ordered mesoporous Co3O4, NiO, and their metals were synthesized by nanocasting method
using there corresponding mesoporous SBA-15 silica as a template. The obtained porous metal oxides
have high surface areas, large pore volume, and a narrow pore size distribution. The N2-adsorption data
for mesoporous metal oxides have provided the BET area of 257.7 m2 gÀ1 and the total pore volume of
0.46 cm3 gÀ1. The mesoporous metals were employed as a catalyst in the synthesis of (S)-3-pyrrolidinol
Received 26 May 2009
Accepted 10 November 2009
Keywords:
A. Metals
from chiral (S)-4-chloro-3-hydroxybutyronitrile, and
obtained on the mesoporous Co metal catalyst.
a
high yield to (S)-3-pyrrolidinol-salt was
A. Nanostructures
A. Oxides
& 2009 Elsevier Ltd. All rights reserved.
D. Surface properties
1. Introduction
materials [4], and current research efforts are focused on the
preparation of nanomaterials with new morphologies [5]. Metals
with designed two-dimensional (2D) or three-dimensional (3D)
nanostructures, in particular, are expected to find useful applica-
tions in [6]. A variety of synthetic pathways has been proposed for
the development of nanostructure because of their numerous
potential applications. Though various metal and semiconductor
nanostructures have successfully been exploited, uniform mesos-
tructured crystallized metal patterns are rarely reported. In this
respect, a general synthetic strategy for mesostructured metal
guided by host–guest chemistry is much desired. We have
fabricated ordered mesoporous metal (OMM) replica with
hexagonally ordered mesopore channels (SBA-15), designated as
Co-SBA-15 and Ni-SBA-15, by using ordered mesoporous silica
(OMS) as a mold in this study (Scheme 1). Mesoporous metal
was employed as a catalyst for the synthesis of chiral (S)-3-
pyrrolidinol-HCl by the hydrogenation of (S)-4-chloro-3-hydroxy-
butyronitrile. In the catalytic reduction, the mesoporous metal
with one-dimensional mesopores showed a higher activity than
bulk metal.
For the preparation of ordered nanostructure arrays, a hard
template has some advantages when compared with a soft
template, especially in its specific topological stability, veracity,
predictability, and controllability. Supramolecular templated
mesoporous silica materials have drawn more and more attention
because of their uniform mesocavums (2–30 nm), large surface
areas, and large pore volumes, which make them perfect
candidates to serve as hard templates. Despite considerable
progress in the field of porous solids, major challenges remain
in the synthesis of ordered mesoporous materials with high metal
content from the coassembly of macromolecular surfactants and
inorganic species. Controlling the structure of metals at the
mesoscale (2–50 nm) is crucial for the development of improved
fuel cell electrodes and may also assist in the miniaturization of
optical and electronic materials for data transmission, storage,
and computation [1,2]. An early route to preparing mesoporous
metals involves the dealloying of a less noble metal from a
bimetallic alloy such as Raney nickel and other metals [3].
Dealloying processes provide limited control over structural
parameters such as pore geometry and order. In contrast, block
copolymer self-assembly or templating with metal species
provides access to highly ordered structures. The nanostructured
materials have received considerable attention because of their
novel size- and shape-dependent electronic, magnetic, optical,
and catalytic properties that differ drastically from those of bulk
2. Experimental
2.1. Synthesis of ordered mesoporous metal oxide and metal replica
using SBA-15 as template
A
high quality SBA-15 was prepared using the triblock
copolymer Pluronic P123 (Aldrich) as a surfactant and tetra-
ethylorthosilicate (TEOS, 98%, Aldrich) as a silica source, modify-
ing the synthetic procedure reported by Zhao et al. [7]. The
n Corresponding author. Tel.: +82 32 860 7472; fax: +82 32 872 4046.
E-mail address: guoxiaofeng1088@hotmail.com (X.-F. Guo).
0022-3697/$ - see front matter & 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2009.12.049

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613
C
D
E
F
A
1
2
3
2 Theta
B
C
Scheme 1. Synthesis of mesoporous metal replica.
starting composition in molar ratio for the synthesis of high grade
SBA-15 was fixed as 1.72P123:0.1TEOS:0.6HCl:20H2O. Into the
calcined SBA-15, the solution of cobalt(II) acetylacetonate (Co(a-
cac)2, 97%, Aldrich) and nickel(II) acetylacetonate (Ni(acac)2, 97%,
Aldrich) dissolved in acetic acid and THF, respectively. As a typical
method, 1 g of SBA-15 was added to a solution obtained by
dissolving 0.6 g of Co(acac)2 or Ni(acac)2 in acetic acid (2.5 mL) or
THF (2.5 mL). The mixture was evaporated to remove the solvent
by heating at 393 K. The sample turned to a brown or yellow color
during the treatment. The silica composite sample was treated
thermally by following the same procedure as mentioned above at
373 and 433 K after additional impregnation of 0.6 g of Co(acac)2
or Ni(acac)2 in acetic acid (2.5 mL) or THF (2.5 mL). The sample
was calcined at 550 1C for 5 h (1 1C/min). The mesoporous metal
oxide was obtained by refluxing in 2 M NaOH for 2 h to remove
the silica template. The template-free mesoporous metal oxides
were designated as Co3O4-SBA-15 and NiO-SBA-15. Mesoporous
oxides were reduced to their corresponding metal with H2 flow
through the reactor while temperature was kept at 350 1C for 6 h.
The powder metal product was obtained and designated as Co-
SBA-15 and Ni-SBA-15, respectively.
D
E
F
0
20
40
2 Theta
60
80
Fig. 1. X-ray diffraction patterns of bulk Co (A); bulk Co3O4 (B); Co3O4-SBA-15 (C);
Co-SBA-15 (D); NiO-SBA-15 (E); and Ni-SBA-15 (F).
2.2. Characterization
X-ray powder diffraction (XRD) data of parent SBA-15 and its
corresponding replica (Co3O4 or NiO-SBA-15, and Co-SBA-15 or
Ni-SBA-15) were acquired on a D/MAX 2500V/PC diffractometer
using CuKa radiation. The morphology and microstructures of as-
prepared samples were characterized by field emission transmis-
sion electron microscopy (FE-TEM, S-4200) and field emission
scanning electron microscopy (FE-SEM, JEM-2100F). The nitrogen
adsorption/desorption analysis was performed at À196 1C by
using a surface area and porosity analyzer equipment (Micro-
meritics, ASAP 2010). The specific surface areas were calculated
according to the BET theory, and the mean pore size was
determined by BJH analysis.
2.3. Typical procedure for (S)-3-pyrrolidinol-salt
After dissolution of 4 g of (S)-4-chloro-3-hydroxybutyro-nitrile
in 40 mL of methanol, 0.5 mg of mesoporous metal was added to
that solution. The mixture was stirred under a hydrogen pressure
of 8 kg/cm2 at room temperature for 36 h in the autoclave reactor.
The solvent was evaporated finally to give a (S)-3-pyrrolidinol-
HCl salt. The yield of product was determined from the weight of
isolated salt.
Fig. 2. Scanning electron microscopy images of SBA-15 in low magnification (A);
Ni-SBA-15 in high magnification (B); and Co-SBA-15 in high magnification (C).
adsorption analysis. The wide-angle-X-ray diffraction (WAXRD)
results show characteristic peaks that can be indexed as Co3O4,
NiO, Co, and Ni crystalline phase and ordered mesophase (Fig. 1).
X-ray-diffraction (XRD) clearly shows characteristic peaks that
the ordered arrangement of mesopore in the synthesized replica
3. Results and discussion
The formation of mesopores in Co3O4-SBA-15, NiO-SBA-15,
Co-SBA-15, and Ni-SBA-15 was determined by XRD, TEM, and N2

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gives rise to the well-resolved XRD peaks as shown in Fig. 1,
which can be assigned to (1 0 0), (1 1 0), and (2 0 0) diffractions of
the 2D hexagonal space group (p6mm). The XRD results showed
that the OMM replicas fabricated from ordered mesoporous SBA-
15 in this work exhibited well-developed regular mesoporous
channels.
wall was successfully performed in the whole range of mesopores
of starting SBA-15 silica.
To analyze the pore geometry and structure of ordered
mesoporous oxides, BJH analyses were performed to measure
the N2 adsorption branch corresponding to the equilibrium
(Fig. 3). N2 adsorption/desorption isotherm of calcined original
SBA-15 (Fig. 3A) was the H1-type hysteresis loop that is typical for
mesoporous materials with ordered cylindrical channels.
However, the mesoporous metal oxide showed a hysteresis curve
corresponding to the cylinder-like mesopore channels (Fig. 3B and
3C). The N2-adsorption data for Co3O4-SBA-15 have provided a BET
area of 257.8 m2 gÀ1 and a pore volume of 0.46 cm3 gÀ1. The latter
can be related to the volume of the ordered mesopores primarily,
with minor contribution of micropores. The NiO-SBA-15 also
exhibited a very high adsorption amount of nitrogen. The NiO-
SBA-15 sample gave a BET area of 256.7 m2 gÀ1 and a pore volume
of 0.50 cm3 gÀ1. The N2 adsorption result also indicates that Co3O4-
SBA-15 had a quite narrow pore-size distribution of 7.1 nm, while
the pore size distribution for SBA-15 silica was centered at 7.2 nm.
The mean pore size of NiO-SBA-15 was 6.3 nm.
Fig. 4 shows the two types of FE-TEM images for Co-SBA-15
and Ni-SBA-15 viewed along or perpendicular to the direction of
hexagonal pore arrangement. As can be seen in those TEM images,
the mesopore structures of Co-SBA-15 and Ni-SBA-15 are exactly
the inverse replica of SBA-15 silica. The TEM image at high
magnifications showed the well-defined mesopore structures in
ordered mesoporous metals. The metal nanorods are
interconnected by spacers, which are constituted by the metal
that filled the channel-interconnecting micropores within the
SBA-15 wall.
FE-SEM images revealed that the as-synthesized mesoporous
metal consists of many rope-like domains with relatively uniform
sizes of ꢀ2
mm, which are aggregated into wheat-like macro-
structures. Both Co-SBA-15 and Ni-SBA-15 replica have exhibited
the same morphological feature as compared to the correspond-
ing parent SBA-15 silica mold (Fig. 2). This result indicates that
the introduction of Co(acac)2 or Ni(acac)2 to form the metal oxide
500
450
400
350
A
300
250
200
B
150
100
C
50
0
In the catalytic reduction of the 4-chloro-3-hydroxy butyroni-
trile, metal catalysts such as Raney metal, palladium, and
platinum can be used preferably to convert the cyano group into
the primary amine. In this work, OMM were tested as a catalyst
for the synthesis of (S)-3-pyrrolidinol-HCl salt (S-PD-salt) from
the optically active (S)-4-chloro-3-hydroxybutyronitrile (S-CHB),
and the results for the catalytic activity are listed in Fig. 5.
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
Fig. 3. N2 adsorption/desorption isotherms for SBA-15 silica (A); Co3O4-SBA-15
(B); NiO-SBA-15 (C).
Fig. 4. TEM photographs of SBA-15 (pore entrance) (A); SBA-15 (view of side wall) (B); Ni-SBA-15 (pore entrance) (C); Ni-SBA-15 (view of side wall) (D); Co-SBA-15 (pore
entrance) (E); and Co-SBA-15 (view of side wall) (F).

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615
2
NiO-SBA-15
1
0
Bulk NiO
-1
-2
-2
-1
0
1
2
+
Potential [V vs. Ag/Ag
]
Fig. 7. Cyclic voltammograms of NiO in 0.5 M Et4NBF4/Propylene carbonate (PC) at
70 mV/s scan rate; loading amount of the working electrode: 5 mg/cm2.
of reaction. The catalyst could be recycled efficiently, as
summarized in Fig. 6. After three times reuse, catalysts retained
the high activity, but a low decrease in yield was found by
repeated use, indicating the slight loss.
Fig. 5. Catalytic activities of mesoporous metals in the hydrogenation of chiral
(S)-4-chloro-3-hydroxybutyronitrile to obtain the (S)-3-pyrrolidinol-HCl salt
(H2: 8 kg/cm2; Temp.: 80 1C).
Mesoporous nickel oxide electrodes were used in the electro-
chemical capacitor and their performance was tested using cyclic
voltammetry (CV) as indicated in Fig. 7. The high porosity and
large pore size of films allow for easy access of the redox process
and results in high packing density of the active material. Such
type of porous materials leads to a high surface specific area and
porous volume, which provide the structural foundation for the
high specific capacitance.
100
90
80
70
60
50
40
30
20
4. Conclusions
The OMM such as Ni-SBA-15 and Co-SBA-15 have been
synthesized by nanocasting method using their corresponding
mesoporous silicas as a mold. The obtained NiO-SBA-15 and
Co3O4-SBA-15 have the high surface area with a narrow pore size
distribution, exhibiting BET area of 257.8 m2 gÀ1 and a total pore
1st Recycle
2nd Recycle
Bulk Recycle
10
0
volume of 0.46 cm2 gÀ1
. The OMM were employed in the
synthesis of (S)-3-pyrrolidinol-salt from chiral (S)-4-chloro-3-
hydroxybutyronitrile. It was investigated that the OMM are
efficient for the hydrogenation of cyano groups to amine, and
higher activity was obtained by nanocasting method than bulk
metal.
0
4
8
12
16
Time (h)
20
24 28 32
Fig. 6. The recyclability of Ni-SBA-15 in the hydrogenation of chiral (S)-4-chloro-
3-hydroxybutyronitrile to obtain the (S)-3-pyrrolidinol-HCl salt (H2: 8 atm;
Temp.: 80 1C).
References
Accordingly the effect of support type on the product yield was
determined, and the obtained results are shown in Fig. 5. The Ni-
SBA-15 and Co-SBA-15 gave much higher yield to S-PD-salt than
the bulk Co in the reduction of S-CHB. It was attributed to OMM
with a large volume and big pore size. Mesoporous Ni showed
slightly higher activity than mesoporous Co metal.
Recyclability of Ni-SBA-15 was investigated in the same
reactions as mentioned above. The catalyst was collected by
simple washing with MC, THF solvent for reuse after completion
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