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New Journal of Chemistry
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ARTICLE
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In the present study, DPSNs@Cu–BTC nanocomposites were 2.3 Synthesis of the DPSNs
DOI: 10.1039/D0NJ02672G
prepared by first growing Cu2O NPs in the center-radial porous
Monodispersed DPSNs were prepared by using CTA·Tos as a
surfactant, [BMIM] OTF as a co-surfactant, TEA as a mineralizing
agent, water as a solvent and TEOS as a silica precursor. A
typical synthesis of DPSNs with a size of ca. 245±26 nm was
performed as follows: a mixture of CTA·Tos (0.96 g), [BMIM]
OTF(0.30 g), TEA (0.105 g) and water (50 mL) was stirred at 80 °C
for 1 h, and then TEOS (7.8 mL) was quickly added into the
surfactant solution. The mixture was stirred at a speed of 1000
rpm at 80 °C for another 2 h. The DPSNs thus formed were
filtered, washed, and dried in an oven at 60 °C. The CTA·Tos was
removed from particles by template extraction. The as-
prepared DPSNs (1.0 g) were added into ethanolic HCl
(concentrated HCl (15 mL) in ethanol (100 mL), and sonicated
for 2 h. The suspension was stirred at 70 °C for 24 h. The
extraction procedure was repeated three times to efficiently
remove the surfactant. Finally, the precipitates were
centrifuged, washed with ethanol, and dried in air at 60 °C.
channels of DPSNs and then creating a reaction between
DPSNs@Cu2O and 1,3,5-benzenetricarboxylic acid (H3BTC) by
dissolution in acid, oxidation and self-assembly. Additionally,
Cu2O was chosen instead of CuO because the chemical stability
of Cu2O is relatively poor and it can be dissolved by the acidity
of the H3BTC ligand without producing residual Cu2O.
Introducing Cu2O NPs into DPSNs pores by indirect fabrication
not only solves the problem that Cu–BTC cannot be directly
grown in the pores of DPSNs, but also makes full use of the
effect of confining the center-radial porous channels to reduce
the sizes of the Cu–BTC NPs thus formed. It is expected that the
homogeneous distribution of small-sized Cu-BTC in the pores of
the DPSNs can construct DPSNs@Cu–BTC nanocomposites with
good catalytic performance and cycle stability in the
epoxidation of olefins.
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2. Experimental section
2.1 Materials
2.4 Synthesis of the DPSNs@Cu2O
DPSNs@Cu2O nanocomposites were synthesized following the
reported procedure with some modifications.25 In a typical
synthesis, PVP (1.0 g) was fully dissolved in Cu(NO3)2 aqueous
solution (0.01 M, 50 mL) under vigorous magnetic stirring.
DPSNs (50 mg) and L-Ascorbic acid (70 mg) were mixed in water
(2.0 mL), which was then quickly injected into the Cu(NO3)2
aqueous solution, followed by the immediate introduction of
NH3·H2O aqueous solution (60 μL). Typically, the color changed
to dark red-yellow within 5 s, indicating the formation of Cu2O.
The reaction mixture was kept stirring for 2 min, and the
product was collected by centrifugation at 8000 rpm for 10 min.
Subsequently, the NPs were washed with ethanol and deionized
water (volume ratio 1:1) three times to remove excess PVP, and
were redispersed in benzyl alcohol (BnOH, 2.5 mL), and stored
in a refrigerator at 4.0 °C. DPSNs@Cu2O with theoretical load
percentages of 10, 20 and 30 wt.% were fabricated by adjusting
the amount of L-Ascorbic acid from 17.5 mg to 70 mg, the
volume of Cu(NO3)2 solution (12.5, 25, 50 mL) and different
amounts of NH3·H2O (15, 30, 60 μL), respectively (Table S1).
Tetraethyl orthosilicate (TEOS, 99%), cetyltrimethylammonium
tosylate (CTA Tos, 98%), triethanolamine (TEA, 99%), 3-
aminopropyltriethoxysilane (APTES, 98%), L-Ascorbic acid
(Sigma-Aldrich, 99%), benzyl alcohol (Aldrich, 99%), and cis-
Cyclooctene (C8H14, 99%) were purchased from Sigma Aldrich.
Aqueous ammonia (NH3·H2O, 25%), concentrated hydrochloric
acid (HCl, 37%), toluene (99%), absolute ethanol (99%), copper
nitrate trihydrate (Cu(NO3)2·3H2O, 99%), poly-(vinylpyrrolidone)
(PVP, K-30), and acetonitrile (CH3CN, 99%) were purchased from
Beihua Fine Chemicals. 1,3,5-benzenetricarboxylic acid (H3BTC,
95%) was purchased from Alfa Aesar. Ultrapure water with a
resistivity higher than 18.2 MΩ·cm, which was obtained from a
three-stage Millipore Mill-Q Plus 185 purification system
(Academic), was used in all experiments. All reagents with
analytical grade were used as received.
2.2 Characterization
For transmission electron microscopy (TEM) observations,
powder samples were added on carbon-coated copper grids
and observed on a JEOL JEM-2100F transmission electron
microscope equipped with an energy dispersive X-ray
spectrometer (EDX) at an acceleration voltage of 200 kV. The
phase composition of the samples was analyzed by powder X-
ray diffraction (XRD, M21X) with Cu Kα radiation (40 kV, 150 mA,
λ=1.5406 Å). The copper content of the samples was measured
with inductively coupled plasma-atomic emission spectrometry
(ICP-AES). Chemical compositions were obtained using X-ray
photoelectron spectroscopy (XPS, Shimadzu ESCA-3200).
Fourier transform infrared spectra (FTIR) were obtained using a
Nicolet 6700 Fourier spectrometer. The specific surface areas of
the catalysts were calculated by the BET (Brunauer-Emmett-
Teller) method, and the pore-size distributions of the catalysts
were derived from the adsorption branches of isotherms by
Barrett−Joyner−Halenda (BJH) method.
2.5 Synthesis of the DPSNs@Cu-BTC
DPSNs@Cu-BTC nanocomposites were synthesized by
increasing the dosage and providing additional oxygen,
following the partial procedure of Au NPs@Cu-BTC.26 H3BTC
(0.275 mmol) was added into a mixture of BnOH (7.5 mL) and
ethanol (0.5 mL), and then sonicated for 30 min to achieve a
homogeneous solution. Subsequently, 2.5 mL of DPSNs@Cu2O
NPs in BnOH was added, followed immediately by an O2 balloon,
and then reacted at 80 °C overnight unless otherwise noted. The
product was collected by centrifuging at 5000 rpm for 5 min,
washed with methanol several times, and finally dried at room
temperature. In addition, the loading capacity of Cu-BTC on the
DPSNs was controlled by adjusting different Cu2O amounts
(Table S2). The percentages of copper species being introduced
into the DPSNs were determined to be 1.4, 4.0 and 9.2 wt.% for
2 | J. Name., 2012, 00, 1-3
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Zhou, Zihao
