ChemCatChem
10.1002/cctc.201702011
FULL PAPER
have been reported about their use in various reaction systems,
2-
B
12
H
12] -capped AuNPs can be immobilized completely on the surface of
-CD@Fe . The Fe @-CD@AuNPs were separated via an external
3
O
4
3 4
O
such as the coupling reactions, CO
2
conversion, selective
Due to the generality of the -CD-
closo-B12H12] -based host-guest assembled strategy, further
[29-31]
magnet and the residual solution was colorless, indicating that there was
no monodispersed AuNPs. The obtained products were washed and dried
under vacuum at 60 ℃.
oxidation reactions, etc.
2
-
[
studies are ongoing in the fabrication of Pt, Pd and Ag composites,
which are able to catalyse other chemical reactions in our
anticipation.
Structural characterization
The morphology and size of specimens were characterized by
transmission electron microscopy (TEM) using a Hitachi H-7000FA TEM
at an accelerating voltage of 100 kV. High-resolution TEM (HRTEM)
images were captured on a JEM-2100 microscope operated at 200 kV.
Scanning electron microscopy (SEM) images were taken on a field-
emission microscope (Zeiss Sigma) operated at an accelerating voltage of
20 kV. X-ray powder diffraction (XRD) was performed using a Rigaku
SmartLab diffractometer with a Cu-K radiation source (λ = 1.54184 Å).
The energy-dispersive X-ray (EDX) analysis was performed using a
KEVEX X-ray energy detector. The X-ray photoelectron spectroscopy
Conclusions
In summary, we have developed a hierarchical and rapid route
to fabricate metal composites based on the host-guest self-
assembly of CDs and boron clusters. Key to this approach is the
2
-
12
usage of the dual-functional [closo-B12H ] (intrinsic reducibility
and host-guest complexation), which plays an essential role of
reductant and stabilizer in the AuNPs preparation as well as a
supramolecular anchor for the tight immobilization of AuNPs on
(XPS) experiments were carried out using an electron spectroscope
(Escalab 250Xi; Thermo Fisher Scientific) with an Al-K source (15 kV and
10 mA). FTIR spectra for the different samples were recorded on a Thermo
3 4
the magnetic substrates. Moreover, the obtained Fe O @-
Nexus 670 FTIR spectrometer. The magnetic measurements were carried
out using a vibrating sample magnetometer (VSM, EV7, ADE, USA) with
an applied field between -9000 and 9000 Oe at room temperature. The Au
loading amount was determined by inductively couple plasma mass
spectrometry (ICP-MS, IRIS Intrepid Ⅱ; Thermo Elemental, Franklin,
CD@Au composites showed high catalytic activity and
remarkable recyclability in the selective reduction of nitro
aromatics. This self-assembled fabrication strategy can also
extend out to design other fascinating metal composites, such as
Pt, Pd and Ag, which would show great potential for various
catalytic reactions.
USA). The UV-vis spectra were recorded on
a Persee TU-1901
spectrophotometer.
Selective reduction of the nitro-aromatics
4
Aromatic nitro compounds (1.5 mmol, 1 equiv), NaBH (15 mmol, 10 equiv)
Experimental Section
3 4
and magnetic Au nanocomposites Fe O @-CD@10 nm AuNPs (0.2 g)
were loaded into a 100-mL glass vial. Unless otherwise noted, absolute
ethanol (50 mL) was then added as the solvent and the mixtures were
incubated for 2-4 h under stirring at 298 K with agitation speed of 180 rpm.
After the reaction was completed (monitored via TLC), the catalysts were
facilely separated from solution via an external magnet, and washed with
absolute ethanol (10 mL 3), the filtrate was collected and the solvent was
evaporated under reduced pressure. The residue was purified by column
chromatography on a silica gel to give the pure product. Yields were those
of the isolated products.
Materials
Cesium closo-dodecaborate (Cs
from Strem Chemicals (Newburyport, USA). Other starting reagents
analytical reagent grade) were purchased from Sinopharm Chemical
Reagent Co., Ltd (Shanghai, China) and used as received unless stated
2
[closo-B12H12], 98%) were purchased
(
-
1
otherwise. Milli-Q ultra-pure water (18 MΩ cm ) was used to prepare all
solutions.
2
-
Formation of the [closo-B12
H12] -capped AuNPs
3
mL of HAuCl ·4H O (0.05 M) and 6 mL of Cs
4
2
2
[closo-B12H12] (0.05 M)
were added to a 100mL round-bottom flask with 50 mL H
mixture turned faint red immediately and then stirred for 30 min
continuously. The free Cs [closo-B12 12] in solution was removed by
centrifugation at 12000 rpm for 15 min. The collected nanoparticle samples
with an average diameter of 10 nm were washed and dispersed in H O.
The size of AuNPs could be controlled by changing the feed ratio of
precursors. AuNPs with an average diameter of 19 nm and 41 nm were
2
O at 298 K. The
Acknowledgements
2
H
This work was financially supported by the Fundamental
Research Funds for the Central Universities (no.
2042016HF1054) and Wuhan University Experiment Technology
Project Funding (no. WHU-2016-SYJS-06). And we are grateful
to Bi-Chao Xu and Pei Zhang of the Core Facility and Technical
Support, Wuhan Institute of Virology for her technical support in
transmission electron microscopy. Bin Qi and Chenchen Wu
contributed equally to this work.
2
successfully prepared by adjusting the feed ratio of HAuCl
4 2
and Cs [closo-
12
B H12] to 1:0.7 and 1:04.
3 4
Formation of the -CD@Fe O magnetic substrate
1
g purchased nano-Fe (4.32 mmol, with an average diameter of 200
3 4
O
nm) and 5.6 g -CD (4.32 mmol) were added to a 250mL round-bottom
flask with 100 mL H O. The mixtures were incubated for 48 h under stirring
at 298 K with agitation speed of 180 rpm. After completed, the products
2
Conflict of interest
were washed 3 times with H O to remove uncombined -CD and then dried
2
under vacuum at 60 ℃.
The authors declare no conflict of interest.
Formation of the Fe
3
O
4
@-CD@AuNPs nanocomposite
Keywords: dodecaborate clusters • host-guest assembly •
magnetism • gold nanoparticles • nitro-aromatics reduction
The obtained -CD@Fe
3
O
4
substrates (0.25 g) were added to the 50 mL
2-
[
closo-B12H12] -capped AuNPs solution (mAu = 0.03 g) with three different
sizes (10 nm, 19 nm and 41 nm), respectively. The mixtures were then
shaken by hand for 1 minute and let stand for 15 minutes so that the [closo-
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