Facile Synthesis of Highly Porous Metal Oxides by Mechanochemical Nanocasting

Article abstract of DOI:10.1021/acs.chemmater.7b05405

Metal oxides with high porosity usually exhibit better performance in many applications, as compared with the corresponding bulk materials. Template-assisted method is generally employed to prepare porous metal oxides. However, the template-assisted method is commonly operated in wet conditions, which requires solvents, soluble metal oxide precursors, and a long time for drying. To overwhelm those drawbacks of the wet procedure, a mechanochemical nanocasting method is developed in the current work. Inspired by solid-state synthesis, this strategy proceeds without solvents, and the ball milling process can enable pores replicated in a shorter time (60 min). By this method, a series of highly porous metal oxides were obtained, with several cases approaching the corresponding surface area records (e.g., ZrO₂, 293 m² g^-1 Fe₂O₃, 163 m² g^-1 CeO₂, 211 m² g^-1 CuO_x-CeO_y catalyst, 237 m² g^-1 CuO_x-CoO_y-CeO_z catalyst, 203 m² g^-1). Abundant nanopores with clear lattice fringes in metal oxide products were witnessed by scanning transmission electron microscopy (STEM) in high angle annular dark field (HAADF). By combination of mechanochemical synthesis and nanocasting, current technology provides a general and simple pathway to porous metal oxides.

Full text of DOI:10.1021/acs.chemmater.7b05405

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Facile Synthesis of Highly Porous Metal
Oxides by Mechanochemical Nanocasting
Weiming Xiao, Shize Yang, Pengfei Zhang, Peipei Li, Peiwen Wu, Meijun
Li, Nanqing Chen, Kecheng Jie, Caili Huang, Ning Zhang, and Sheng Dai
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.7b05405 • Publication Date (Web): 13 Apr 2018
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Chemistry of Materials
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Facile Synthesis of Highly Porous Metal Oxides by Mechanochemical
Nanocasting
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Weiming Xiao,†,‡ Shize Yang,§,‡ Pengfei Zhang,+,ᴦ,* Peipei Li,+ Peiwen Wu,+ Meijun Li,# Nanqing
Chen,# Kecheng Jie,# Caili Huang,+ Ning Zhang,†,* Sheng Dai+,#,*
† Institute of Applied Chemistry, College of Chemistry, Nanchang University Nanchang, Jiangxi 330031, P. R. China
+ Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
§ Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
ᴦ School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China
# Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA
ABSTRACT: Metal oxides with high porosity usually exhibit better performance in many applications, as compared with the
corresponding bulk materials. Template-assisted method is generally employed to prepare porous metal oxides. However,
the template-assisted method is commonly operated in wet conditions, which requires solvents, soluble metal oxide precur-
sors and a long time for drying. To overwhelm those drawbacks of the wet procedure, a mechanochemical nanocasting
method is developed in current work. Inspired by solid-state synthesis, this strategy proceeds without solvents, and the ball
milling process can enable pore replicated in a shorter time (60 min). By this method, a series of highly porous metal oxides
were obtained, with several cases approach the corresponding surface area records (e.g., ZrO2: 293 m2 g-1, Fe2O3: 163 m2 g-1,
CeO2: 211 m2 g-1, CuOx-CeOy catalyst: 237 m2 g-1, CuOx-CoOy-CeOz catalyst: 202 m2 g-1). Abundant nanopores with clear lattice
fringes in metal oxide products were witnessed by scanning transmission electron Microscopy (STEM) in high angle annular
dark field (HAADF). By combination of mechanochemical synthesis and nanocasting, current technology provides a general
and simple pathway to porous metal oxides.
crystallize around the porous template. The final template
removal could release abundant pores within the crystalline
INTRODUCTION
metal oxides. This procedure is somewhat like the
Embedding porosity into metal oxides can significantly
macroscopic process termed “casting” except that it occurs in
advance their performance in many applications such as
nanoscale, so it is also called “nanocasting”.16-17 It is clear that
catalysis, sensors, microelectronics, photovoltaics and
the nanocasting pathway has several advantages to
biomedicines. It is understandable since larger active surfaces,
incorporate nanopores into metal oxides. However, to date,
faster mass transfer and higher storage volume can be
the nanocasting apporach is still a wet process, which requires
metal oxide precursors to be at liquid state or soluble in
solvents.16-18 It means that the refractory and insoluble metal
precursors cannot be used in the procedure, limiting the scope
of metal oxide precursors. Moreover, the pathway is a time-
expected in porous metal oxides.1-6 The porous metal oxides
are usually prepared by template-assisted processes, which
proceed via either soft- or hard-templating methods.7-11 For
the soft-templating method, self-assembly between metal
precursors and block copolymers results in ordered organic-
inorganic mesophases,11-13 followed by calcination to form
crystalline metal oxides at the same time removing organic
templates. The soft-templating approachwith membrane
intermediates aging from several days to one month, is time-
consuming, meanwhile this technology is limited to porous
metal oxides with low crystalline temperature (e.g., <400).
consuming procedure, which needs
a
slow solvent
evaporation and multi impregnation processes to well cast the
template.11,19 Thus, an alternative approach that can
overcome the drawbacks of wet nanocasting pathway is
highly desirable in the preparation of porous metal oxides.
Herein, we wish to show a versatile mechanochemical
nanocasting approach that enables a series of porous metal
oxides synthesized in a simple, rapid and sustainable manner.
Importantly, those metal oxides possess extremely porous
nano-architecture with high specific surface areas (e.g., ZrO2:
293 m2 g-1, Fe2O3: 163 m2 g-1, CeO2: 211 m2 g-1, CuOx-CeOy
catalyst: 237 m2 g-1 and CuOx-CoOy-CeOz catalyst: 202 m2 g-1).
Actually, mechanochemical synthesis, a solvent-free process,
has already manifested its talent in material community, in
which several porous materials such as: zeolite, co-crystal,
o
Note that block copolymers usually decompose below 200 C
in air, while the porous structure tends to collapse when
further treated at a higher temperature that is necessary for
the transformation of amorphous metal oxides to the
crystalline state.9,11,14
Toward this end, the hard-templating procedure is a
more general strategy to obtain crystalline porous metal
[9,11,15]
oxides.
Typically, a porous solid material such as silica
is chosen as the template, which is then filled by metal oxide
precursors via impregnation or coprecipitation processes,
followed by calcinating the hybrid to make metal oxides
metal-organic
frameworks,
polymers
of
intrinsic
microporosity and ordered mesoporous carbons have been
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prepared.20-26 In current contribution, we forward the scope
CO oxidation: Catalytic CO oxidation was carried out in a
fixed-bed reactor (straight quartz tube with inner diameter of
4 mm) at atmospheric pressure. For the measurement of CO
conversion as a function of reaction temperature, 20 mg cata-
lyst supported by quartz wool was loaded in the reactor. The
feed gas of 1 % CO balanced with dry air (< 4 ppm water)
passed though the catalyst bed at a flow rate of 10 mL min-1
corresponding to a gas hourly space velocity (GHSV) of 30,000
mL (h gcat)−1. The concentrations of CO and CO2 in the reactor
were analyzed by a Buck Scientific 910 gas chromatograph
equipped with a dual molecular sieve/porous polymer column
(Alltech CTR1) and a thermal conductivity detector. CO con-
version is the percentage of CO oxidized to CO2 after the reac-
tion.
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of mechanochemistry to the nanocasting pathway via ball
grinding, which promotes the mass transfer of metal
precursor from bulk into porous template by solid-state
process, certainly avioding those drawbacks of wet
nanocasting.
EXPERIMENTAL SECTION
Synthesis of porous metal oxides (ZrO2, Fe2O3, CeO2,
La2O3, CoOx, CuO) by ball milling: 2 g metal oxide precursors
(ZrCl4, Fe(OAc)2, Ce(OAc)3, La(NO3)3·6H2O, Co(OAc)2·4H2O or
commercial CuO) and 2 g of Com-SiO2 were added to a com-
mercially available 25 mL screw-capped stainless-steel reac-
tor along with two stainless steel ball bearings (diameter 1.2
cm, total mass 12.4 g). The reactor was placed in a high-speed
vibrating ball miller (Retsch MM400) and the mixtures were
ball milled for 60 min at a vibrational frequency of 30 Hz. The
resulting powders were calcinated at certain temperature (2
oC min-1). The calcinated products were stirred in 2.5 M NaOH
for 8 h at room temperature and then wash with deionized
H2O (repeating the process four times to remove the silica
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RESULTS and DISCUSSION
o
template), followed by drying at vacuum condition at 40 C
overnight. All the samples prepared by the mechanochemical
method are named as MO-MN-Y (MO is metal oxide, Y is calci-
nation temperature).
Synthesis of porous CuOx-CeOy: (0.1 g, 0.5 mmol)
Cu(OAc)2·H2O and (1.59 g, 5 mmol) Ce(OAc)3 were mixed by
ball milling for 10 min at a vibration frequency of 30 Hz. Then
1.69 g Com-SiO2 were added to the above mixture and ball
milling for another 60 min. The final mixture was calcinated at
o
o
500 C for 4 h in air (2 C min-1). The product was stirred in
2.5 M NaOH for 8 h at room temperature and then wash with
deionized H2O (repeating the process four times to remove
the Comm-SiO2), followed by drying at vacuum condition at 40
oC overnight.
Synthesis of porous CuOx-CoOy-CeOz: (0.1 g, 0.5 mmol)
Cu(OAc)2·H2O, (0.625 g, 2.5 mmol) Co(OAc)2·4H2O and
(0.793 g, 2.5 mmol) Ce(OAc)3 were mixed by ball milling for
10 min at a vibration frequency of 30 Hz. Then 1.52 g Com-
SiO2 were added to the above mixture and ball milling for an-
Scheme 1. A mechanochemical nanocasting route for the syn-
thesis of porous metal oxide.
o
other 60min. The final mixture was calcinated at 600 C for 1
o
h in air (1 C min-1). The calcinated product was stirred in 2.5
Scheme 1 shows a general route of mechanochemical
nanocasting process. The rigid scaffold used in this process
was commercial porous silica (Com-SiO2). The silica template
that is composed of nonuniform nanospheres, possesses a
high degree of interstitial porosity and a surface area of 184
m2/g (Table 1, Figure S1). The mechanochemical
nanocasting pathway was explored by XRD with ZrCl4 as a
model (Figure S2). Solid ZrCl4 was directly mixed with Com-
SiO2 by ball milling, and the ZrCl4 precursor well dispersed
within the interstitial pores of Com-SiO2, as evidenced by the
disappearance of XRD peaks of ZrCl4. The mixture was then
calcinated at 500 oC in air, and a group of peaks corresponding
to t-ZrO2 was observed. The ZrCl4 within Com-SiO2
decomposed into crystalline t-ZrO2 and the intermediate
product t-ZrO2/silica hybrid was formed. Finally, porous
crystalline metal oxides were obtained by the removal of
Com-SiO2 with NaOH. The Si residue is 1.09 atom%, as
suggested by the XPS result (Figure S3). Current
mechanochemical assembly was complete in 60 mins, much
shorter than 1-3 days required by wet nanocasting.19
Especially no solvents were needed. Hence, this technology in
M NaOH for 8 h at room temperature and then wash with de-
ionized H2O (repeating the process four times to remove the
o
Comm-SiO2), followed by drying at vacuum condition at 40 C
overnight.
Characterization: Powder X-rays diffraction (XRD) was
collected on a PANalytical Empyrean diffractometer operated
at 45 kV and 40 mA (scanning step: 0.02 ° per step). N2 ad-
sorption-desorption Isotherms were analyzed on a TriStar
3000 volumetric adsorption analyzer manufactured by Mi-
cromeritics Instrument Corp. Prior to analysis, all samples
were activated at 150 °C for 12 hours. Scanning Transmission
Electron Microscopy (STEM) were performed on a Nion mi-
croscope operated at 200 kV. The images are recorded using
high angle annular dark field (HAADF, inner angle 80 m rad)
and bright field (BF) imaging. Before observation, the sample
is baked at 160 °C for 8 h. Elemental analysis of the samples
was done by inductively coupled-plasma atomic emission
spectroscopy (ICP-AES) using Optima 2100 DV spectrometer
(PerkinElmer Corporation).
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principle can ignore the solubility issue of metal precursors,
and tolerate metal precursors with poor or even no solubility.
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The current study starts with ZrO2 and Fe2O3 by using
mechanochemical nanocasting method (Labeled as ZrO2-MN
and Fe2O3-MN). XRD patterns reveal the crystalline structures
of t-ZrO2 and γ-Fe2O3 (Figure 1). The broad diffraction peaks
suggest the small crystallite sizes of two metal oxides, which
in turn evidences that the metal oxide precursors can be well
dispersed around SiO2 template via ball milling. The porous
nature of metal oxide samples was then evaluated by N2
sorption measurement at 77 K. As presented in Figure 2, the
ZrO2-MN and Fe2O3-MN exhibit typical type IV curves with H3-
type hysteresis loops between relative pressure P/P0 = ~0.4-
1.0, indicating their mesoporous structures. The pore size
distributions (PSDs) by Barrett-Joyner-Halenda (BJH) model
are broad and centered around 12 nm. The PSDs roughly
follow the particle size of silica template. Moreover, both
metal oxides show high specific surface areas up to 276 and
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o
163 m2/g for ZrO2-MN and Fe2O3-MN calcinated at 500 C,
Figure 2. N2 adsorption-desorption isotherms (77 K) and the
pore size distributions of ZrO2 and Fe2O3 prepared by mecha-
nochemical nanocasting at different calcination temperatures.
For clarity, the isotherms of ZrO2-MN-400, ZrO2-MN-500,
Fe2O3-MN-400 and Fe2O3-MN-500 are offset along the y axis
by 200, 100, 150 and 75 cm3 g−1, respectively.
respectively (Table 1).
Table 1. Summary of pore parameters for metal oxides,
calculated by N2 adsorption-desorption isotherms at 77 K.
a)
SBET
Pore Volume b)
(cm3 g-1)
Average
Pore Size
(nm)
c)
Sample
(m2 g-1)
Figure 1. XRD patterns of ZrO2 and Fe2O3 prepared by
mechanochemical nanocasting at different calcination
temperature.
Com-SiO2
184
293
276
231
134
163
143
82
0.40
0.60
0.63
0.51
0.26
0.31
0.30
0.07
0.06
0.06
0.17
0.03
0.01
0.24
0.57
0.20
-
9.1
7.3
8.2
7.8
6.7
6.9
7.6
3.0
6.0
10.2
16.7
6.7
5.5
4.9
9.0
11.8
-
ZrO2-MN-400
ZrO2-MN-500
ZrO2-MN-600
Fe2O3-MN-400
Fe2O3-MN-500
Fe2O3-MN-600
ZrO2-400
In general, a higher calcination temperature is necessary
toward the synthesis of metal oxides with a better crystallini-
ty. But, it usually causes crystal growth together with pore
collapsing. We then studied the porous structures of ZrO2-MN
and Fe2O3-MN prepared under different calcination tempera-
tures. When the calcination temperature was increased from
o
o
400 C to 600 C, the N2 sorption isotherms kept similar pro-
files (Figure 2 and Table 1). In contrast, control ZrO2 and
Fe2O3 samples, obtained by directly calcinating the ZrCl4 and
Fe(OAc)2 yet without SiO2, show much lower specific surface
areas (Table 1 and Figure S4), in turn arguing for the pore
directing role of mechanochemical nanocasting method.
ZrO2 -500
40
ZrO2 -600
23
To inquire the scope of mechanochemical nanocasting
method, several rare-earth metal oxides and transition metal
oxides were also prepared at 500 oC. The CeO2, La2O3 and CoOx
(Figure S5) possess high specific surface areas of 211, 219
and 68 m2 g-1, respectively (Table 1, Figure S6), which are
comparable to the record values.27-31 It is noteworthy that
even bulk CuOx (SBET = ~0.3 m2 g-1) can be used as precursors,
and they can be embed with some porosity (SBET = 25 m2 g-1)
via mechanochemical nanocasting method (Table 1, Figure
S7). It seems like that the migration of CuO on silica surface by
solid grinding is possible.
Fe2O3 -400
Fe2O3 -500
Fe2O3 -600
CeO2-MN
36
16
8
211
219
68
La2O3-MN
CoOx-MN
Bulk-CuOx
CuO-MN
0.3
25
0.13
-
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CuOx-CeOy-MN
237
203
0.19
0.22
3.6
4.6
Considering the mechanochemical nanocasting procedure
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was operated in the steel stainless reactor with stainless-steel
ball, the Fe contents in the model metal oxides were analyzed.
In this work, the Fe contents in the ZrO2-MN-600, La2O3-MN
and CuOx-CeOy-MN were examined, and their weight percents
were 0.028%, 0.0067% and 0.22%, respectively. It suggests
that the abrasion of steel can be neglected in this procedure.
In addition, the CO oxidation performance of CuOx-CeOy-MN
and CuOx-CoOy-CeOz-MN was investigated. As illustrated in
Figure 3d, the two hybrids are active for CO oxidation. The
T100 values (Temperature for 100% CO conversion) are 200
CuOx-CoOy-CeOz-MN
a) Specific Surface Area calculated using the BET equation;
Single Point Pore Volume at relative pressure of 0.95;
Average pore diameter between 1.7-30 nm from the
b)
c)
adsorption branch by BJH model.
Metal oxide hybrids often exhibit better catalytic perfor-
mance than each metal counterpart.32-35 For example, transi-
tion-metal-doped ceria is a typical system in which transition
metal additives significantly enhance the catalytic activity of
ceria in CO oxidation.36-38 Certainly, creating abundant porosi-
ty into transition-metal-doped ceria could further benefit
their catalytic performance. Then, we would like to try the
mechanochemical synthesis of porous CuOx-CeOy and CuOx-
CoOy-CeOz, two classes of active hybrids for CO oxidation.36-41
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and 160 C, respectively, which are comparable to many of
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copper-ceria catalysts. 42-45 Due to the facile synthesis proce-
dure, CuOx-CeOy-MN and CuOx-CoOy-CeOz-MN may have the
potential applications in the removal of toxic CO.
o
The XRD pattern of CuOx-CeOy-MN even calcinated at 500 C
shows no diffraction peaks that can be attributed to the cop-
per species, evidencing the highly dispersed copper species
within ceria (Figure 3a). The Cu content determined by the
ICP-AES is 3.5 wt.%. The broad peaks corresponding to cubic
ceria indicate its small crystallite size. The XRD pattern of
CuOx-CoOy-CeOz-MN offers typical peaks for CuO, Co3O4 and
cubic CeO2 (Figure 3a). The Cu and Co contents determined
by the ICP-AES are 4.2 wt.% and 23.5 wt.%, respectively.
Then, N2 sorption measurement at 77 K was used to examine
the porosity of CuOx-CeOy-MN and CuOx-CoOy-CeOz-MN hy-
brids. Both isotherm curves illustrate increasing N2 uptakes
(P/P0 > 0.1) together with clear hysteresis loops (Figure 3b
and 3c), typical features of mesoporous materials. What’s
attractive is the high specific surface areas achieved by CuOx-
CeOy-MN and CuOx-CoOy-CeOz-MN (237 and 203 m2 g-1, re-
spectively) (Table 1). Current work also tried to prepare po-
rous perovskite LaMnO3. Although only amorphous phase was
o
obtained, the sample even after calcinated at 700 C offered a
high surface area of 162 m2 g-1 (Figure S8).
Figure 4. STEM-HAADF and STEM-BF images of Fe2O3 (a-d)
and CeO2 (e-f).
The porous morphologies of metal oxide materials were
observed by scanning transmission electron Microscopy
(STEM) in high angle annular dark field (HAADF) or bright
field (BF). As shown in Figure 4, Fe2O3-MN is composed of
irregular particle aggregates in the range of several hundred
nanometers (Figure 4a). Rich porosity created by the removal
of silica sphere is observed in amplified images (Figure 4c-
4d). The apparent pores locate in ~4-20 nm, which match
well with the PSD by N2 adsorption isotherm. Moreover, the
Fe2O3-MN sample has a well crystalline structure with clear
lattice fringes (012), as shown in the high-resolution images
(Figure 4b). Moreover, interstitial porosity from both bumps
Figure 3. (a) XRD patterns of CuOx-CeOy-MN and CuOx-CoOy-
CeOz-MN, (b) and (c) N2 adsorption-desorption isotherms (77
K) and the pore size distributions of CuOx-CeOy-MN and CuOx-
CoOy-CeOz-MN (the isotherm of CuOx-CeOy-MN is offset along
the y axis by 30 cm3 g-1 for clarity), (d) CO conversion over
CuOx-CeOy-MN and CuOx-CoOy-CeOz-MN at different tempera-
ture (reaction condition: catalyst 20 mg, space velocity 30,000
mL (h g cat)−1, 1 vol% CO balance in dry air).
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Chemistry of Materials
and nanoparticles are seen in CeO2-MN, with the formation of
hierarchical pores (Figure 4e-4f).
ly prepared. Importantly, a well dispersion of active metal
species in the hybrids even at sub-nano scale can be guaran-
teed by this strategy, thus offering an exceptional catalytic
performance in CO oxidation. It is expected that a number of
advanced porous materials will be prepared by this mechano-
chemical nanocasting method in the near future.
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Meanwhile, structural details of the hybrid metal oxide
CuOx-CoOy-CeOz-MN were studied by STEM-HAADF images
(Figure 5). A sponge-like nanoarchitecture with a number of
accessible pores was observed in the sample (Figure 5a).
Previous literatures already confirmed the synergetic interac-
tion of copper, cobalt and cerium species in CuOx-CoOy-CeOz
catalyst, while the dispersion or structure of those elements in
atomic scale has not been clarified yet.40 High-resolution
STEM-HAADF images illustrate many aggregated nanoparti-
cles with clear crystalline structures (Figure 5b-5d). Two
classes of sub-10 nm particles are carefully recognized by
their lattice fringes, which could be attributed to CeO2 and Cu-
doped Co3O4. Subsequent element mapping in a 48*48 nm
zone also supports this observation, because cerium and co-
balt species locate in different domains (Figure 5e-5h). Cur-
rent STEM and XRD results suggest that the CuOx-CoOy-CeOz-
MN catalyst is primarily composed of sub-10 nm CeO2 and Cu-
doped Co3O4 particle aggregates.
ASSOCIATED CONTENT
Supporting Information. The N2 adsorption-desorption iso-
therms of Com-SiO2, ZrO2-MN, Fe2O3-MN, CeO2, La2O3, CoOx,
bulk-CuOx, CuO-MN and LaOx-MnOx; SEM image of Com-SiO2;
XRD patterns of CeO2, La2O3, CoOx, bulk-CuOx, CuO-MN, LaOx-
MnOx and ZrO2/Com-SiO2 hybrid; STEM-HAADF images of
LaOx-MnOx; XPS spectra of ZrO2-MN-500 are available free of
charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*
nzhang.ncu@163.com (N. Zhang); chemistryzpf@sjtu.edu.cn
(P. Zhang); dais@ornl.gov (S. Dai).
Author Contributions
‡ These authors contributed equally to this work.
ACKNOWLEDGMENT
P. F. Zhang and S. Dai was supported by the Division of Chemi-
cal Sciences, Geosciences, and Biosciences, Office of Basic En-
ergy Sciences, US Department of Energy. W.M.X. and N.Z.
thank the National Natural Science Foundation of China (No.
21062013 and 21663016) and the China Scholarship Council.
The electron microscopy (S.Z.Y.) was supported by the U.S.
Department of Energy (DOE), Office of Science, Basic Energy
Sciences, Materials Science and Engineering Division
and through
a
user proposal at Oak Ridge National
Laboratory’s Center for Nanophase Materials Sciences, which
is a U.S. Department of Energy Office of Science User Facility.
P. F. Zhang acknowledges Shanghai Pujiang Program (Grant
No. 17PJ1403500), Thousand Talent Program and National
Natural Science Foundation of China (Grant No. 21776174)
for the partial support.
REFERENCES
(1) Wang, Y.; Arandiyan, H.; Scott, J.; Bagheri, A.; Da, H.; Amala,
R. Recent advances in ordered meso/microporous metal oxides
for heterogeneous catalysis: a review. J. Mater. Chem. A 2017, 5,
8825–8846.
(2) Yang, X. Y.; Chen, L. H.; Li, Y.; Rooke, J. C.; Sanchez, C.; Su, B.
L. Hierarchically porous materials: synthesis strategies and struc-
ture design. Chem. Soc. Rev. 2017, 46, 481–558.
(3) Thomas, A. Functional Materials: From Hard to Soft Porous
Frameworks. Angew. Chem. Int. Ed. 2010, 49, 8328–8344.
(4) Taguchi, A.; Schüth, F. Ordered mesoporous materials in ca-
talysis. Microporous Mesoporous Mater. 2005, 77, 1–45.
(5) Zhang, P.; Lu, H.; Zhou, Y.; Zhang, L.; Wu, Z.; Yang, S.; Shi, H.;
Zhu, Q.; Chen, Y.; Dai, S. Mesoporous MnCeOx solid solutions for
low temperature and selective oxidation of hydrocarbons. Nat.
Commun. 2015, 6, 8446.
(6) Poyraz, A. S.; Kuo, C. H.; Biswas, S.; King’ondu, C. K.; Suib, S.
L. A general approach to crystalline and monomodal pore size
mesoporous materials. Nat. Commun. 2013, 4, 2952.
(7) Feinle, A.; Elsaesser, M. S.; Hüsing, N. Sol–gel synthesis of
monolithic materials with hierarchical porosity. Chem. Soc. Rev.
2016, 45, 3377−3399.
Figure 5. STEM-HAADF images of CuOx-CoOy-CeOz-MN (a-d),
and the element mapping signals: f) Ce_M, g) Co_L, h) O_K.
CONCLUSIONS
In summary, an efficient, general and simple route to di-
recting high porosity into metal oxide has been explored
based on the mechanochemical nanocasting. The method does
not need solvents and can shorten the pore filling process
from 1-3 days to 60 min. Especially, current strategy inherent-
ly ignores the solubility issue of metal precursors, which sig-
nificantly expands the library of resources available for po-
rous metal oxides. By this method, many metal oxides and
their hybrid catalysts with high surface areas were successful-
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 7
(8) Ren, Y.; Ma, Z.; Bruce, P. G. Ordered mesoporous metal ox-
ides: synthesis and applications. Chem. Soc. Rev. 2012, 41, 4909–
4927.
use as a potential adsorbent for carbon dioxide capture. J. Colloid
Interface Sci. 2014, 436, 52–62.
(29) Yadav, A. A.; Lokhande, A. C.; Pujari, R. B.; Kim, J. H.; Lo-
khande, C. D. The synthesis of multifunctional porous honey
comb-like La2O3 thin film for supercapacitor and gas sensor appli-
cations. J. Colloid Interface Sci. 2016, 484, 51–59.
(30) Smått, J. H.; Weidenthaler, C.; Rosenholm, J. B.; Lindén, M.
Hierarchically Porous Metal Oxide Monoliths Prepared by the
Nanocasting Route. Chem. Mater. 2006, 18, 1443-1450.
(31) Sun, X.; You, R.; Hu, X.; Mo, J.; Xiong, R.; Ji, H.; Li, X.; Cai, S.;
Zheng, C.; Meng, M. Calcination system-induced nanocasting syn-
thesis of uniform Co3O4 nanoparticles with high surface area and
enhanced catalytic performance. RSC Adv. 2015, 5, 35524–35534.
(32) Yuan, C.; Wu, H. B.; Xie, Y.; Lou, X. W. Mixed Transition-
Metal Oxides: Design, Synthesis, and Energy-Related Applications.
Angew. Chem. Int. Ed. 2014, 53, 1488–1504.
1
2
3
4
5
6
7
8
(9) Yang, H.; Zhao, D. Synthesis of replica mesostructures by
the nanocasting strategy. J. Mater. Chem. 2005, 15, 1217–1231.
(10) Schüth, F. Endo- and Exotemplating to Create High-
Surface-Area Inorganic Materials. Angew. Chem. Int. Ed. 2003, 42,
3604–3622.
(11) Lee, J.; Orilall, M. C.; Warren, S. C.; Kamperman, M.; Disalvo,
F. J.; Wiesner, U. Direct access to thermally stable and highly crys-
talline mesoporous transition-metal oxides with uniform pores.
Nat. Mater. 2008, 7, 222−228.
(12) Yang, P.; Zhao, D.; Margolese, D. I.; Chmelka, B. F.; Stucky,
G. D. Block Copolymer Templating Syntheses of Mesoporous Metal
Oxides with Large Ordering Lengths and Semicrystalline Frame-
work. Chem. Mater. 1999, 11, 2813–2826.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(13) Antonelli, M.; Ying, J. Y. Synthesis of Hexagonally Packed
Mesoporous TiO2 by a Modified Sol-Gel Method. Angew. Chem. Int.
Ed. 1995, 34, 2014–2017.
(14) Soler-Illia, G. J. d. A. A.; Sanchez, C.; Lebeau, B.; Patarin, J.
Chemical Strategies to Design Textured Materials: from Mi-
croporous and Mesoporous Oxides to Nanonetworks and Hierar-
chical Structures. Chem. Rev. 2002, 102, 4093-4138.
(15) Yue, W.; Zhou, W. Crystalline mesoporous metal oxide.
Prog. Nat. Sci. 2008, 18, 1329–1338.
(33) Wolf, D.; Buyevskaya, O. V.; Baerns, M. An evolutionary
approach in the combinatorial selection and optimization of cata-
lytic materials. Appl. Catal. A-Gen. 2000, 200, 63–77.
(34) Park, J. B.; Graciani, J.; Evans, J.; Stacchiola, D.; Senanayake,
S. D.; Barrio, L.; Liu, P.; Sanz, J. F.; Hrbek, J.; Rodriguez, J. A. Gold,
Copper, and Platinum Nanoparticles Dispersed on Ce-
Ox/TiO2(110) Surfaces: High Water-Gas Shift Activity and the
Nature of the Mixed-Metal Oxide at the Nanometer Level. J. Am.
Chem. Soc. 2010, 132, 356–363.
(35) Graciani, J.; Mudiyanselage, K.; Xu, F.; Baber, A. E.; Evans, J.;
Senanayake, S. D.; Stacchiola, D. J.; Liu, P.; Hrbek, J.; Sanz, J. F.; J. A.
Rodriguez, Highly active copper-ceria and copper-ceria-titania
catalysts for methanol synthesis from CO2. Science 2014, 345,
546–550.
(36) Konsolakis, M. The role of Copper–Ceria interactions in ca-
talysis science: Recent theoretical and experimental advances.
Appl. Catal. B-Environ. 2016, 198, 49–66.
(37) Gamarra, D.; Munuera, G.; Hungría, A. B.; Fernández-
García, M.; Conesa, J. C.; Midgley, P. A.; Wang, X. Q.; Hanson, J. C.;
Rodríguez, J. A.; Martínez-Arias, A. Structure-Activity Relationship
in Nanostructured Copper-Ceria-Based Preferential CO Oxidation
Catalysts. J. Phys. Chem. C, 2007, 111, 11026–11038.
(38) Larsson, P. O.; Andersson, A. Oxides of copper, ceria pro-
moted copper, manganese and copper manganese on Al2O3 for the
combustion of CO, ethyl acetate and ethanol. Appl. Catal. B-
Environ. 2000, 24, 175–192.
(39) Liu, Z. G.; Chai, S. H.; Binder, A.; Li, Y. Y.; Ji, L. T.; Dai, S. In-
fluence of calcination temperature on the structure and catalytic
performance of CuOx-CoOy-CeO2 ternary mixed oxide for CO oxi-
dation. Appl. Catal. A-Gen. 2013, 451, 282–288.
(40) Binder, A. J.; Toops, T. J.; Unocic, R. R.; Parks II, J. E.; Dai, S.
Low-Temperature CO Oxidation over a Ternary Oxide Catalyst
with High Resistance to Hydrocarbon Inhibition. Angew. Chem.
Int. Ed. 2015, 54, 13263–13267.
(41) Chen, S.; Zhao, S.; Xu, Z.; Liu, Z.; Zhu, R. Influence of pH on
the catalytic performance of CuO–CoOx–CeO2 for CO oxidation.
RSC Adv. 2015, 5, 61735–61741.
(42) Desyatykh, I. V.; Vedyagin, A. A.; Mishakov, I. V.; Shubin, Y.
V. CO oxidation over fiberglasses with doped Cu-Ce-O catalytic
layer prepared by surface combustion synthesis. Appl. Surf. Sci.
2015, 349, 21–26.
(43) Zheng, X.; Wang, S.; Wang, X.; Wang, S.; Wang, X.; Wu, S.
Synthesis, characterization and catalytic property of ceria spheri-
cal nanocrystals. Mater. Lett. 2005, 59, 2769–2773.
(44) Zheng, X. C.; Wu, S. H.; Wang, S. P.; Wang, S. R.; Zhang, S. M.;
Huang, W. P. The preparation and catalytic behavior of copper–
cerium oxide catalysts for low-temperature carbon monoxide
oxidation. Appl. Catal. A-Gen. 2005, 283, 217–223.
(16) Deng, X.; Chen, K.; Tu
̈
ysu
̈
z, H. Protocol for the Nanocasting
Method: Preparation of Ordered Mesoporous Metal Oxides. Chem.
Mater. 2017, 29, 40−52.
(17) Lu, A. H.; Schüth, F. Nanocasting: A Versatile Strategy for
Creating Nanostructured Porous Materials. Adv. Mater. 2006, 18,
1793–1805.
(18) Jongh, P. E. d.; Eggenhuisen, T. M. Melt Infiltration: an
Emerging Technique for the Preparation of Novel Functional
Nanostructured Materials. Adv. Mater. 2013, 25, 6672–6690.
(19) Wang, Y.; Ren, J.; Wang, Y.; Zhang, F.; Liu, X.; Guo, Y.; Lu, G.
Nanocasted Synthesis of Mesoporous LaCoO3 Perovskite with
Extremely High Surface Area and Excellent Activity in Methane
Combustion. J. Phys. Chem. C 2008, 112, 15293–15298.
(20) Stolle, A.; Szuppa, T.; Leonhardt, S. E. S.; Ondruschka, B.
Ball milling in organic synthesis: solutions and challenges. Chem.
Soc. Rev. 2011, 40, 2317–2329.
(21) Meng, X.; Xiao, F. S. Green Routes for Synthesis of Zeolites.
Chem. Rev. 2014, 114, 1521−1543.
(22) James, S. L.; Adams, C. J.; Bolm, C.; Braga, D.; Collier, P.;
Friščić, T.; Grepioni, F.; Harris, K. D. M.; Hyett, G.; Jones, W.; Krebs,
A.; Mack, J.; Maini, L.; Orpen, A. G.; Parkin, I. P.; Shearouse, W. C.;
Steedk, J. W.; Waddelli, D. C. Mechanochemistry: opportunities for
new and cleaner synthesis. Chem. Soc. Rev. 2012, 41, 413–447.
(23) Friščić, T. Supramolecular concepts and new techniques in
mechanochemistry: cocrystals, cages, rotaxanes, open metal–
organic frameworks. Chem. Soc. Rev. 2012, 41, 3493–3510.
(24) Zhang, P.; Li, H.; Veith, G. M.; Dai, S. Soluble Porous Coordi-
nation Polymers by Mechanochemistry: From Metal-Containing
Films/Membranes to Active Catalysts for Aerobic Oxidation. Adv.
Mater. 2015, 27, 234–239.
(25) Biswal, B. P.; Chandra, S.; Kandambeth, S.; Lukose, B.; Hei-
ne, T.; Banerjee, R. Mechanochemical Synthesis of Chemically
Stable Isoreticular Covalent Organic Frameworks. J. Am. Chem.
Soc. 2013, 135, 5328−5331.
(26) Zhang, P.; Wang, L.; Yang, S.; Schott, J. A.; Liu, X.; Mahurin,
S. M.; Huang, C.; Zhang, Y.; Fulvio, P. F.; Chisholm, M. F.; Dai, S.
Solid-state synthesis of ordered mesoporous carbon catalysts via
a mechanochemical assembly through coordination cross-linking.
Nat. Commun. 2017, 8, 15020.
(27) Liang, X.; Xiao, J.; Chen, B.; Li, Y. Catalytically Stable and Ac-
tive CeO2 Mesoporous Spheres. Inorg. Chem. 2010, 49, 8188–
8190.
(28) Kamimura, Y.; Shimomura, M.; Endo, A. Simple template-
free synthesis of high surface area mesoporous ceria and its new
(45) Mock, S. A.; Zell, E. T.; Hossain, S. T.; Wang, R. Effect of Re-
duction Treatment on CO Oxidation with CeO2 Nanorod-
Supported CuOx Catalysts. ChemCatChem 2018, 10, 311–319.
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