Photoinduced topotactic growth of bismuth nanoparticles from bulk srbi 2ta2o9

Article abstract of DOI:10.1021/cm400065x

In situ growth of bismuth (Bi) nanoparticles on bulk SrBi ₂Ta₂O₉ (SBT) platelet is achieved by UV light illumination of SBT in aqueous glucose solutions. Interestingly, the as-produced Bi nanoparticles (NPs) are uniformly oriented with the epitaxial relationship of [001]_Bi//[110]_SBT, appearing as meso-single-crystal phase despite spatial separation between the NPs. Systematic investigations indicate that Bi(III) at the (110)_SBT plane is topotactically reduced by photogenerated electrons, producing Bi atoms serving as nucleation seeds oriented from the (003) plane. Further growth of these oriented nuclei leads to formation of Bi NPs arranged laterally in mesocrystalline superstructure. The reported finding presents a simple, environmentally friendly approach toward preparation of highly organized, surface supported metal NPs through direct photoreduction of bulk metal oxides.

Full text of DOI:10.1021/cm400065x

Article
pubs.acs.org/cm
Photoinduced Topotactic Growth of Bismuth Nanoparticles from
Bulk SrBi2Ta2O9
Yingxuan Li,† Ling Zang,§ Yan Li,† Yun Liu,⊥ Chunyan Liu,⊥ Ying Zhang,†,‡ Hongquan He,†,‡
and Chuanyi Wang*,†
†Laboratory of Eco-Materials and Sustainable Technology (LEMST), Xinjiang Technical Institute of Physics and Chemistry; Key
Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi, Xinjiang 830011,
China
‡University of Chinese Academy of Sciences, Beijing 100049, P.R. China
§Department of Materials Science and Engineering, The University of Utah, Salt Lake City, Utah 84108, United States
⊥Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
S
* Supporting Information
ABSTRACT: In situ growth of bismuth (Bi) nanoparticles on
bulk SrBi2Ta2O9 (SBT) platelet is achieved by UV light
illumination of SBT in aqueous glucose solutions. Interest-
ingly, the as-produced Bi nanoparticles (NPs) are uniformly
oriented with the epitaxial relationship of [001]Bi//[110]SBT
,
appearing as meso-single-crystal phase despite spatial separa-
tion between the NPs. Systematic investigations indicate that
Bi(III) at the (110)SBT plane is topotactically reduced by
photogenerated electrons, producing Bi atoms serving as nucleation seeds oriented from the (003) plane. Further growth of these
oriented nuclei leads to formation of Bi NPs arranged laterally in mesocrystalline superstructure. The reported finding presents a
simple, environmentally friendly approach toward preparation of highly organized, surface supported metal NPs through direct
photoreduction of bulk metal oxides.
KEYWORDS: Bi nanoparticles, SrBi2Ta2O9, photoreduction, oriented growth
photocatalysis to control the crystallographic orientation of
metal NPs thus produced, which in turn determines the
properties of metal NPs in many cases. In comparison to
transition metals, the synthesis of main group metal NPs is less
studied. Particularly, the synthesis of main group metal NPs by
photochemical approach has not yet been reported.
Bismuth (Bi) is one of the most studied elements in solid-
state physics because of its unusually rich electronic properties
due to its complex and highly anisotropic Fermic surface.7 A
number of recent results, such as exotic electronic phenomena,8
thermoelectricity,9 and superconductivity,10 are making Bi an
interesting object of experimental and theoretical studies.
Recently, considerable attention has been directed to nano-
structured Bi because it may exhibit performance superior to its
bulk counterpart.9−11 It has been found that Bi NPs could act
as the best catalysts for the growth of dimension-controlled
semiconductor quantum wires and rods by the solution−
liquid−solid mechanism.12 A variety of methods, such as
inverse micelles,13 radiolytic reduction in aqueous solution,14
the thermolysis of a bismuth-thiolate precursor,15 and solution-
INTRODUCTION
■
Metal nanoparticles (NPs) have attracted enormous attention
due to their unique properties and broad applications. Various
methods, via solution-phase or vapor-phase, have been
developed to prepare metal NPs.1 However, preparation of
metal NPs by direct reduction of bulk metal oxides at ambient
temperature remains a challenge, due to the homogeneity of
bulk oxides2 and the intrinsically slow mass transfer between
the solid reactants and products in most solid-state reactions.3
Although Cu NPs were fabricated by electroreduction of CuO
at room temperature, the starting material CuO was also
particulate in the same nanometer size, rather than bulk phase.4
Among all the methods, preparing metal NPs via photo-
reduction is particularly promising because it can be operated
under ambient condition, and the only energy consumed is
light. Although metal oxide-based photochemistry has been a
topic of intensive research since 1972,5 the direct photo-
reduction of bulk oxides to nanoparticulate metals is rarely
reported. By means of photocatalytic reduction, surface
supported transition metal NPs, such as Au, Ag, and Pt, can
be produced onto the semiconductor catalysts,6 though metal
salts must be provided as the source reagent, and it is usually
difficult to achieve a dense and uniform dispersion of metal
NPs in these cases. Moreover, it is difficult for the conventional
Received: January 8, 2013
Revised: April 23, 2013
Published: April 25, 2013
© 2013 American Chemical Society
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based reduction,16 have been thereby developed for the
synthesis of Bi NPs. However, in situ reducing Bi-based oxide
to achieve oriented growth of Bi NPs on a substrate has not yet
been reported.17 Controlling materials at the nanometer scale is
of great challenge, particularly when long-range ordering is
pursued.18
RESULTS AND DISCUSSION
Light-Induced Color and XRD Changes of SBT.
SrBi2Ta2O9 (SBT) has proven to be a highly active photo-
catalyst under UV irradiation,20 consistent with its band gap of
3.6 eV as estimated from the optical absorption onset (Figure
S1, Supporting Information). Figure 1 shows the color change
■
In the present work, we demonstrate a light-induced
approach that couples the synthesis and oriented arrangement
of Bi NPs without using organic agents via an in situ topotactic
transformation process, in which SrBi2Ta2O9 acts as a physical
substrate, chemical source, and crystallization ‘catalyst’. Our
findings not only enrich the growth mechanisms for hybrid
metal-semiconductor nanostructures but also prove that bulk
metal oxide can be topotactically reduced to metal NPs with
unique structures by a photochemical approach at ambient
temperature.
Figure 1. Photographs showing color change of SBT powders
dispersed in aqueous glucose solution before and after photoreaction
under UV light irradiation. The insets show the appearance of dried
powders isolated from the Pyrex reaction cell.
EXPERIMENTAL SECTION
■
Sample Preparation. In this study, SrBi2Ta2O9 (SBT) has been
synthesized by a molten salt route.19 In a typical synthesis, carbonates
(Sr(NO3)2, 99%) and oxides (Bi2O3, and Ta2O5, 99.9%) were used as
starting materials in a desired molar ratio, and NaCl and KCl were
weighted by molar ratio of 1:1 as a mixed solvent. The raw materials
and mixed solvent (in weight ratio 1:1) were ground for 0.5 h in an
agate mortar. The mixture was first placed in an alumina crucible and
heated in a tube furnace at 850 °C for 3 h and, subsequently, cooled
naturally to room temperature. Pure SrBi2Ta2O9 powder was obtained
after removing the salt flux with deionized water and drying at 50 °C
for 3 h.
of the SrBi2Ta2O9 powder after 20 h of UV light irradiation.
Surprisingly, the color of the powder changed from light yellow
to distinct black, characteristic of significant chemical change of
the materials.
Figure 2 shows the X-ray diffraction (XRD) patterns of SBT
powers before and after the photocatalytic reaction. The main
Characterization. Powder X-ray diffraction (XRD) patterns were
acquired using a Bruker D8 powder diffractometer with Cu Kα
radiation, 0.02 step size, and 0.2 s step time. Thermogravimetry (TG)
was performed on a NETZSCH STA 449F3 instrument. The sample
was heated in an alumina crucible under air flow with a heating rate of
10 °C/min. Field emission scanning electron microscopy (FESEM)
images were obtained on a ZEISS SUPRA55VP microscope.
Transmission electron microscopy (TEM) was performed on JEOL
model JEM-1210 and FEI Tecnai F30 electron microscopes at the
accelerating voltage of 200 kV. The FEI Tecnai F30 was equipped for
energy-dispersive X-ray spectroscopy. Optical properties were analyzed
with a spectrophotometer (Shimadzu SolidSpec-3700DUV) and
converted from reflection to absorbance by the standard Kubelka−
Munk method. The nitrogen adsorption/desorption isotherms were
acquired by a Micromeritics ASAP2020 sorptometer at −196 °C.
Average pore diameters were determined using the Barrett−Joyner−
Halenda (BJH) method.
Photochemical Reactions. Photoreaction was performed at 25
°C under atmospheric pressure in a closed circulation system using a
high-pressure Hg lamp (500 W). A water filter was used to remove
infrared light. SBT powder (0.2 g) was dispersed and magnetically
stirred in a Pyrex top-irradiation reaction cell containing 90 mL H2O
and 15g C6H12O6·H2O. The suspension was evacuated prior to
irradiation and was maintained at about 25 °C by immersing the
reaction cell in a water bath with a constantly controlled temperature.
The produced H2 and CO2 were quantitatively measured by online gas
chromatography (Agilent 7890A) with a thermal conductivity detector
(TCD) and 5 Å molecular sieve column, using N2 as carrier gas.
Apparent quantum yield (A.Q.Y.) was calculated by the following
equation: A.Q.Y. (%) = Ne/Np = 3NBi/Np, where Np, Ne, and NBi
represent the number of incident photons, the number of reacted
electrons, and the number of reduced Bi atoms, respectively. The
amount of the elemental Bi was determined by the weight loss on TG
curve between 445 and 700 °C. The intensity of incident light was
measured by a light flux meter (1930-C, Newport) with a light sensor.
The average illumination intensity of the incident light at 365 nm (λ =
365 nm, half width = 15 nm) was 35 mW/cm2.
Figure 2. XRD patterns of SBT sample before and after photoreaction.
The inset is the zoom-in of the XRD patterns from 21° to 26°.
diffraction peaks of both samples can be assigned to the
structure of SBT. However, a new peak (marked by the arrows)
at 2θ ≈ 22.7° appears after UV irradiation, which matches the
(003) peak of rhombohedral Bi (JCPDS card no. 05-0519).
Consequently, it is speculated that elemental Bi is formed from
the photoreduction of SBT, and formation of this metal phase
causes the color of SBT change from pale yellow to black as
shown in Figure 1.
Morphological and Microstructural Features of Bi on
SBT. Comparing parts a and b of Figure 3, the representative
field emission scanning electron microscopy (FESEM) images
of the samples before and after photoreaction, the original
platelet shape of SBT retains even after 20 h photoreaction.
The remarkable difference between the two samples is that the
photogenerated Bi NPs are densely dispersed on the surface of
the platelet, forming an adlayer-like pattern. In contrast, as
shown in Figure 3a, the outer surface of SBT platelet before
photoreaction appears smooth and no NPs. The FESEM result
agrees with the transmission electron microscopy (TEM)
analysis (Figure 3c and d and Figure S2, Supporting
Information). The TEM image in Figure 3d shows that the
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significantly increased with irradiation time, indicating the time-
dependent growth of the particles with the photoreaction.
Figure 5a shows the high-resolution TEM (HRTEM) image
of a single NP anchored to the edge of the SBT platelet (after
Figure 3. FESEM images and TEM images of SBT sample before (a,
c) and after photoreaction (b, d). The inset in part d shows the
histogram of particle size distribution.
diameter of the NPs located at the surface of the platelet is in
the range of 6−10 nm. Corresponding particle size distribution
histogram is shown in the inset. Therefore, it is concluded that
the formation of this granular layer was due to the
photoreaction at the surface of SBT in the presence of aqueous
glucose.
Time-dependent evolution of the NP growth was also
studied by TEM (Figure 4). At the initial stage (10 h), NPs
Figure 5. (a) HRTEM images of a single NP anchored to the SBT
edge. The insets of part a are the corresponding FFT of the region as
marked by the red square and a schematic atomic structure of NP. (b)
EDX spectrum of a single NP anchored to the SBT edge acquired
from the red circled region in HAADF-STEM image of Bi-SBT (inset
of part b).
20 h of photoreaction). The fast Fourier transformation (FFT)
of the TEM image shows a pattern of 5 spots corresponding to
the crystallographic planes of rhombohedral Bi. Additional
representative HRTEM images are presented in Figure S3,
Supporting Information. Figure 5b gives the high angle annular
dark field scanning TEM (HAADF-STEM) image and a
representative EDX spectrum recorded from the individual NPs
anchored to the edge of the platelet, further confirming the
formation of elemental Bi product. The carbon and copper
signals originate from the carbon-coated copper grid. More
EDX investigation on other NPs anchored to the edge also
proves that bismuth is the only detectable element (Figure S4,
Supporting Information).
It is reasonable to speculate that the NPs formed on the top
of platelet are also metallic Bi because no other new peaks are
observed in the XRD patterns (Figure 2) except that of Bi
(003). Measuring the NPs on the surface of SBT by EDX, four
elements, Sr, Bi, Ta, and O are detected (Figure S5, Supporting
Information). Due to the interference by the SBT substrate, the
composition of the NPs cannot be exclusively identified in this
way. To further prove that the surface NPs are only composed
of elemental Bi, the sample after photoreaction was quickly
heated from room temperature up to 500 °C with a heating rate
of 25 °C min−1 and annealed at 500 °C for 1 h in air. After such
thermal treatment, the sample color turns back to light yellow
(almost identical to the original color of pristine SBT, Figure
6a), indicating disappearance of metallic Bi, which has proven
Figure 4. TEM images of SBT samples for (a) 10 h and (b) 30 h
photoreaction. The inset of part a shows size distribution histogram.
with diameter of 3−7 nm and relatively low density were
formed. The corresponding histogram inset in Figure 4a shows
that the average particle diameter is 4.1 nm. As the
phtotoreaction proceeded for 30 h, NPs with multiple sizes
and shapes were formed on the top surface of SBT platelet
because of the contacting among the NPs (Figure 4b). The
coalescence of the NPs resulted in the large increase in particle
sizes compared to the NPs obtained in 20 h. Therefore, it is
concluded that the size of the NPs formed on the SBT platelet
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To further investigate the role of glucose in the growth of Bi
NPs, the control experiment without glucose was also carried
out under identical conditions, in which hydrogen evolution
was hardly observed. The XRD pattern and FESEM image of
SBT powers after photoreaction for 20 h in the absence of
glucose are provided in the Supporting Information (Figure
S10). The XRD pattern of the catalyst after the reaction is not
affected by photoreaction and the (003) peak of rhombohedral
Bi is hardly visible. Additionally, no NPs were found on the
SBT platelet after photoreaction. These results indicate that the
presence of glucose indeed plays a key role in the process of Bi
NP growth.
HRTEM image taken from the top surface of SBT platelet
after 20 h photoreaction is shown in Figure 7a1, where distinct
Figure 7. (a) HRTEM image taken from the top surface of SBT
platelet after 20 h photoreaction. FFT patterns (a2, a3) corresponding
to the areas marked by red square. (a4) Schematic illustration of the
́
Moire fringes in (a1). The lines in this figure represent the lattice
planes in the crystals. (b) SAED pattern measured over the atop Bi
NPs along the [0001]Bi and [001]SBT zone axis. Two sets of SAED
spots corresponding to the rhombohedral Bi are marked by red and
green dashed lines.
Moire
́
fringes are observed, which are formed from the
interference of two relaxed crystal lattices. The spacing (d) of
the Moire
1:22
́
fringes is determined to be 1.68 nm according to eq
Figure 6. (a) Color and (c) XRD changes of the irradiated sample
before and after calcination. (b) TEM image of SBT after calcination.
The inset of part b is the corresponding SAED pattern.
d1 × d2
|d1 − d2|
d =
(1)
to be easily vaporized at 500 °C.21 The vaporization of Bi is also
supported by the selected area electron diffraction (SAED)
pattern (Figure 6b) and the disappearance of the XRD peak at
2θ ≈ 22.7° (Figure 6c) of the sample after thermal treatment.
The vaporization of Bi NPs leaves mesopores on the top of
the platelet as clearly proved by black spots in FESEM images
(Figure S6, Supporting Information) and N2 adsorption (giving
a narrow distribution of the pores at ∼3.8 nm, Figure S7,
Supporting Information). These observations are consistent
with the results of thermogravimetry (TG) (Figure S8,
Supporting Information), which shows a relatively high-
temperature weight loss by about 2% of its initial weight
between 445 and 700 °C. Considering the fact that the metal
oxides within SBT are not evaporable at 500 °C (because the
SBT can be synthesized at 850 °C), the above observed
morphology change and weight loss at elevated temperature is
solely due to the vaporization of metallic Bi. This means that
the NPs formed on the top of SBT platelet are composed of
elemental Bi. Without light irradiation, no NPs were ever
observed on the surface of SBT (Figure S9, Supporting
Information), even after placing it in a glucose solution for long
time (20 h), indicating that the reduction of Bi(III) in SBT is
due to photochemical process.
where d1 (0.24 nm) and d2 (0.21 nm) are the interplanar
spacings for the Bi {104} and SBT {220} planes, respectively.
This d value is identical within experimental error to the
observed value of 1.65 nm (Figure 7a1). The FFT pattern of
two domains marked in Figure 7a1 corresponds to the pure
SBT substrate (yellow circles, Figure 7a2) and a combination of
SBT substrate and Bi NPs (white circle, Figure 7a3),
respectively. For the substrate SBT, single-crystalline character-
istic is confirmed by the SAED pattern (Figure 7b and Figure
S2c, Suporting Information). On the other hand, the SAED
pattern measured over the atop Bi NPs along the [0001]Bi zone
axis (Figure 7b) shows that, in addition to the spots due to
SBT, two sets of extra diffraction spots (marked by red and
green lines) indexed well to the rhombohedral Bi are
simultaneously observed, suggesting that the primary Bi crystals
have two sets of in-plane orientations. This observation
indicates that the overall crystalline aggregates are long-range
ordered although the positioning of individual NPs within a
local area seems to be random.23 This highly organized
arrangement of Bi NPs is analogous to the previously observed
NP assembly in mesocrystals, in which the elemental units are
nanocrystals that all grow in the same crystallographic
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orientation in a manner of single crystal.23 Mesocrystals are of
strong interest, mainly due to their new chemical and physical
properties compared to the individual nanocrystals.24 Consid-
ering the unique features of Bi metal, the surface supported
mesocrystal-like Bi assemblies will be of great interest for
fundamental physics and chemistry studies, where some
unprecedented properties are expected to emerge from the
anisotropic nature.
Mechanism of the Photochemical Topology Process.
The formation mechanism of the Bi NPs is schematically
illustrated in Figure 8, which is closely related to the crystal
Figure 9. CO2 and H2 evolutions from photochemical decomposition
of C6H12O6 over SBT under UV light irradiation.
transferred from bulk to surface by diffusion (step 2 in Figure
8). The oriented nuclei are developed preferentially along the
two perpendicular [110] and [110] directions within the SBT
̅
platelet plane, resulting in two sets of in-plane orientations of
the Bi NPs, as indeed evidenced in the SAED spots in Figure
7b. The driving force for the diffusion process might result from
the concentration gradient of the reduced Bi atoms constrained
in the SBT particles. Similar behavior has also been reported in
the literature for Bi NPs growth.28 With this diffusion process,
the chemical potential and interface energy of entire system will
be decreased. The outward diffusions of both Bi and O2−lead to
the formation of voids within the SBT domains as is proved by
the FESEM images (Figure S6, Supporting Information) and
pore size distributions (Figure S7, Supporting Information) of
the annealed Bi-SBT, which is similar to the electroreduction
procedure.29 A similar crystal growth process has previously
been observed in galvanic replacement reactions.30 The
formation of Bi NPs on the edge of SBT platelet is likely
caused by a defect growth mechanism.
Along with the crystal structure, the band positions of SBT
with respect to the electrode potential of (Bi2O2)2+/Bi are
equally important. For the growth of Bi NPs, the conduction
band level of SBT should be more negative than the reduction
potential of (Bi2O2)2+ to form Bi. First principal calculations
reveal that the conduction band minimum (CBM) of SBT is
mainly determined by Ta 5d state, which has higher reduction
potential than most other d0 elements.20,31 Under UV light
irradiation, the excited electrons in the CB of SBT possess a
high enough reduction potential to reduce (Bi2O2)2+ in SBT.
Therefore, the reduction potential of SBT might be one of the
factors for the Bi NPs growth. Theoretically, for semi-
conductors in aqueous solution, the photogenerated electrons
in the conduction band can reduce the cations therein
depending on thermodynamic and kinetic conditions.32
According to the work by Chen and coauthors,32 all the
semiconductors that satisfies the conditions are likely
susceptible to be reduced. Except for the photoinduced growth
of Bi NPs from SBT, Ag+ ions in Ag2CO3 were also found to be
reduced to form metallic Ag as reported by Yu et al.33
Figure 8. Schematic crystal structure and stacking models of SBT. Top
(a) and side (b) views of surface structures of the SBT platelet,
respectively. (c) Schematic illustration of the crystal orientation of the
SBT platelet. (d, e) Formation mechanism of the oriented Bi NPs
from SBT via a topotactic photochemical transformation reaction
under light irradiation.
structure of SBT, and can be described as an intergrowth
between (Bi2O2)2+ sheets and (SrTa2O7)2− perovskite like
layers (Figure 8a, b). According to the results in Figure 7 and
the symmetries of SBT, the bottom and top surfaces of the SBT
platelet are terminated {001} facets, while the side surfaces are
{110} facets. The atomic structures of the {001} and {110}
facets are shown in Figure 8a and b, respectively. Under
photochemical conditions, some photogenerated electrons in
{110}-oriented SBT platelets are trapped by the (Bi2O2)2+
terminated {001} surface because these planes have a net of
positive charges,25 resulting in the formation of Bi atoms via a
topotactic reduction process (step 1 in Figure 8) similar to the
topotactic electroreduction procedure.26 The photogenerated
electrons also act as reducing agents to convert protons to H2,
whereas the photogenerated holes are simultaneously con-
sumed by glucose to eventually convert to CO2. This unique
process results in much higher ratio of CO2/H2 than that of the
stoichiometric photoreforming reaction of glucose,27 in agree-
ment with the experimental observations. As shown in Figure 9,
in the present system, the evolved gas analysis indicates the
production of CO2 and H2 during photoreaction, and their ratio
is ∼1.1/1 after 20 h of photoreaction, respectively. This CO2/
H2 ratio is significantly higher than that of the stoichiometry of
the photoreforming reaction of glucose.27 The apparent
quantum yield of SBT sample at 365 nm is calculated to be
0.066%.
Substrate supported metal NPs offer an important class of
nanomaterials due to their tunable size and interfacial
interaction. However, most of metal NPs are synthesized in
liquid phase and must be coated with organic capping ligands
to prevent aggregation and phase transformation into bulk
phase. These capping ligands often significantly interfere the
interfacial interaction between the NPs and substrate.34 The in
situ photoreduction method developed in this study enables
Because of the cryalline lattice match between (110)SBT and
(003)Bi planes (both having d spacing ≈0.4 nm), the in situ
photoreduction of Bi(III) results in oriented nucleation of Bi
from the (003)Bi plane via in situ topotactic transformation.
These nuclei serve as seeds for continuous NPs growth with the
epitaxial relationship of [001]Bi//[110]SBT as more Bi atoms are
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stabilized by the strong epitaxial interaction between the metal
and metal oxide phase (as shown in Figure 7). Such clean
nanostructures may offer new material systems for systematic
investigation and improvement of the catalytic performance.
Further study exploring the application of the supported Bi
NPs is currently underway.
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■
In summary, this work presents a novel approach to fabricate
surface supported Bi NPs by in situ topotactic photoreduction
of SBT. Our findings prove that bulk metal oxide can be
photoreduced under ambient condition to produce well-defined
nanocrystals. This newly developed method has several features
regarding nanomaterials fabrication and potential application in
surface science and catalysis: (i) producing Bi NPs homoge-
neously distributed onto the entire surface of SBT platelet; (ii)
achieving large area crystallographic alignment of Bi NPs, which
is otherwise very difficult to achieve by other methods; (iii)
producing epitaxial interface between Bi and SBT phase, which
enables strong electronic communicatin between the two
phases when used in catalysis; and (iv) being simple and
environmentally friendly in view of the direct photoreduction of
metal oxide to metal under ambient condition.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details, UV−vis spectrum, additional TEM and
SEM images, EDX spectrum, N2 adsorption−desorption
isotherms and pore size distributions, and TG analysis. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: yxli@ms.xjb.ac.cn (Y.L.); cywang@ms.xjb.ac.cn
(C.W.).
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(23) Xu, A.-W.; Antonietti, M.; Yu, S.-H.; Colfen, H. Adv. Mater.
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Notes
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
(26) He, Z.; Gudavarthy, R. V.; Koza, A. J.; Switzer, J. A. J. Am. Chem.
Soc. 2011, 133, 12358.
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This work was supported by the National Nature Science
Foundation of China (Grant Nos. 21001113, 21173261), the
“One Hundred Talents Project Foundation Program” of
Chinese Academy of Sciences, International Science and
Technology Cooperation Program of Xinjiang Uygur Auton-
omous Region (20116010), the “Cross-Cooperation Program
for Creative Research Teams” of Chinese Academy of Sciences,
and the “Western Light” Program of Chinese Academy of
Sciences (XBBS200916).
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