Gold nanoparticles confined in imidazolium-based porous organic polymers to assemble a microfluidic reactor: Controllable growth and enhanced catalytic activity

Article abstract of DOI:10.1039/c7ta08985f

A synthetic strategy is developed to grow Au nanoparticles supported by imidazolium-based porous organic polymers (Au/IM-POPs) along the inner surface of a fused-silica microfluidic capillary. The thickness of the hybrid Au/IM-POP material layers can be tuned by changing the precursor concentration. A variety of imidazolium-based porous organic polymers are developed from tetrakis[4-(1-imidazolyl)phenyl]methane and bromo-functionalized linker molecules and fully characterized, which may be used to support Au nanoparticles. Additionally the IM-POPs and Au/IM-POPs show porosity and the ability to take up guest molecules. The capillary coated with Au/IM-POPs is further assembled to obtain a catalytic microfluidic reactor. The catalytic activity of Au nanoparticles supported by the porous imidazolium polymer is probed by using the reduction of nitrobenzene derivatives flowing through the microfluidic reactor. The catalytic microfluidic reactor demonstrates significantly enhanced turnover frequency magnitudes in comparison with the corresponding reactions under batch conditions.

Full text of DOI:10.1039/c7ta08985f

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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
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DOI: 10.1039/C7TA08985F
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ARTICLE
Gold nanoparticles confined in imidazolium-based porous organic
polymers to assemble a microfluidic reactor: Controllable growth
and enhanced catalytic activity
Received 00th January 20xx,
Accepted 00th January 20xx
Haobin Fang, Shujian Sun, Peisen Liao, Ya Hu* and Jianyong Zhang*
DOI: 10.1039/x0xx00000x
A synthetic strategy is developed to grow Au nanoparticles supported by imidazolium-based porous organic polymer
(Au/IM-POP) along the inner surface of a fused-silica microfluidic capillary. The thickness of the hybrid Au/IM-POP material
layers is tunable by changing the precursor concentration. A variety of imidazolium-based porous organic polymers are
developed from tetrakis[4-(1-imidazolyl)phenyl]methane and bromo-functionalized linker molecules and fully
characterized, which may be used to support Au nanoparticles. Additionally the IM-POPs and Au/IM-POPs show porosity
and ability to uptake guest molecules. The capillary coated by Au/IM-POP is further assembled to obtain a catalytic
microfluidic reactor. The catalytic activity of Au nanoparticles supported in the porous imidazolium polymer is probed by
using the reduction of nitrobenzene derivatives flowing through the microfluidic reactor. The catalytic microfluidic reactor
demonstrates significantly enhanced turnover frequency magnitudes in comparison with the corresponding reactions
under batch conditions.
www.rsc.org/
for their high surface areas, well-defined pore structures and
chemical stability.21 When incorporating ionic building blocks
into POPs, the organic frameworks exhibit enhanced
Introduction
The application of microfluidic reactors in organic synthesis
has been explored extensively over recent years.1-5 In
microfluidic systems, reagent-containing fluid flows are
confined in volumes that have micrometer-scale internal
dimensions. This intrinsic confinement allows manipulation of
the flow movement and fine control over the reaction
conditions in a specific region. Additionally, the large surface
area to volume ratio of microfluidic reactors offers increasing
number of reaction sites exposed to reagents and rapid
thermal transfer across the reactor.6,7 Compared with bulk
systems, chemical processes performed in microfluidic
reactors possess many attractive advantages, such as low
consumption of reagents,8,9 precise selection of products,3,10,11
improved energy efficiency12 and applicability for explosive or
electrostatic attraction with guest species carrying opposite
charges.22 Notable examples include imidazolium-based POPs
(IM-POPs) for the in situ formation of Pd NPs reported by
Wang and co-workers.23 The resulting Pd NPs supported by the
ionic POPs exhibit excellent catalytic property and show no
obvious aggregation or leaching after mutiple runs. More
recently, Dai and co-workers developed nanoporous ionic
organic networks with an ionic density as high as three ion
pairs per unit.24 Au NPs supported by the ionic polymer
frameworks show exceptionally good catalytic activity for the
oxidation reaction of cyclohexanol to cyclohexanone. Most
studies of POP-supported metal nanoparticles have been
conducted in bulk state.25,26 To improve the catalytic
performance of these hybrid materials, research has focused
on improvements on the optimization of the chemical
composition and molecular arrangements.27,28 However, no
effort has been made to study the growth and catalytic
property of the supported hybrid materials in microfluidic
reactors.
In this study, we investigate the in situ growth and catalytic
activity of Au NPs supported by IM-POPs on the inner surface
of a microfluidic capillary. The insertion of imidazolium
moieties has been demonstrated as an effective approach to
creating cationic frameworks.29-31 Through a finely designed
surface functionalization process, the inner surface of the
fused-silica capillary was coated with dangling bromo groups
as anchors for the IM-POPs. Subsequent in situ growth of IM-
POPs supported Au NPs along the surface was characterized
toxic reactions.13-15 As
a
versatile technological tool,
microfluidics are a promising method to extend the utilization
of supported catalysts from conventional flasks into
continuous-flow synthesis.16,17
Supported metal nanoparticles on porous materials are a class
of heterogeneous catalysts with potentially extremely high
efficiency.18-20 Among various porous materials, porous organic
polymers (POPs) have attracted significant research interest
Sun Yat-Sen University, MOE Laboratory of Polymeric Composite and Functional
Materials, MOE Laboratory of Bioinorganic and Synthetic Chemistry, School of
Materials Science and Engineering, Guangzhou 510275, China. *Email:
huya3@mail.sysu.edu.cn; zhjyong@mail.sysu.edu.cn
Electronic Supplementary Information (ESI) available: experimental details,
characterization and sorption data of IM-POPs and Au/IM-POPs, and catalysis data.
See DOI: 10.1039/x0xx00000x
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using scanning electron microscopy (SEM) and transmission process,
Journal Name
and
is
then
brominated ViewbAryticle On(li3ne-
DOI: 10.1039/C7TA08985F
electron microscopy (TEM). Control over the thickness of the bromopropyl)triethoxysilane treatment. Multiple bromination
POPs layers could be achieved by facile adjustment of the processes are required to ensure the homogeneity of bromo-
precursor concentration. As a model system, nitroarene functionalized coatings. Subsequently, reactants for the
reduction was used to test the catalytic activity of Au NPs formation of POPs containing imidazolium cations are injected
grown in the capillary.32 The IM-POP-supported Au NPs into the capillary using a syringe pump. The reactants include
constrained in the capillary exhibit excellent conversion and tetrakis[4-(1-imidazolyl)phenyl]methane (TIM) and 1,4-bis-
selectivity for the reduction of nitrobenzene derivatives into bromomethyl-benzene (2BrB) (see below).30 The imidazolium
corresponding anilines. A significant increase in the TOF moieties of TIM can react with the bromo groups of 1,4-bis-
magnitude of the Au NPs grown in the capillary was measured bromomethyl-benzene to produce extended networks IM-
presenting their enhanced catalytic efficiency.
POP-2BrB. Meanwhile, the coupling reaction of TIM with the
dangling –Br groups on the surface leads to an improved
connection between the IM-POPs and capillary. Due to the
cationic nature of IM-POPs grown along the capillary surface,
subsequently injected AuCl4- anions are readily exchanged with
Br-. Following an in situ reduction induced by NaBH4 solution,
Au NPs are formed and stabilized within the porous channels
of the IM-POP-2BrB layer.
Results and discussion
The synthetic scheme to grow Au NPs supported by IM-POP on
the inner surface of a fused-silica capillary is presented in
Figure 1. Prior to initiating the synthesis of IM-POP, the
capillary surface undergoes a NaOH-induced hydroxylation
Fig. 1 Schematic illustration showing bromination and subsequent growth of IM-POP-supported Au NPs on the inner surface of a microfluidic capillary.
a
b
c
d
Fig. 2 Morphology studies of the IM-POP-2BrB-based Au NPs grown within the microfluidic capillary. a) SEM image of a thick Au/IM-POP-2BrB layer (Au/IM-
POP-2BrB growth parameters: cTIM = 0.046 mol L-1 and c2BrB = 0.091 mol L-1 in CHCl3 in a 1:1 volume ratio; injection speed 0.2 mL/min). b) SEM image of a thin
Au/IM-POP-2BrB layer grown by diluting the CHCl3 solutions of TIM and 2BrB by 5 times. c,d) SEM and high-resolution TEM images of Au/IM-POP-2BrB from
the material presented in a).
The morphology of the resulting Au NPs supported by IM-POP- 42.9 ± 5.8 µm (Figure 2a). The precursor concentration for the
2BrB within the microfluidic capillary (denoted as c-Au/IM- formation of IM-POP-2BrB, plays a key role in determining the
POP-2BrB) is characterized using SEM and TEM (Figure 2). The thickness of the c-Au/IM-POP-2BrB layers. Figure 2b presents
SEM image of the capillary cross section confirms the growth the SEM image of the cross section of a sample prepared by
of a homogeneous c-Au/IM-POP-2BrB layer with a thickness of using a five-fold dilution of TIM and 2BrB dissolved in CHCl3.
2 | J. Name., 2012, 00, 1-3
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The thickness of the close-packed c-Au/IM-POP-2BrB layers is The simultaneous presence of Br- counterion isVireewvAertaiclleedOnlbinye
decreased to be 16.5 ± 2.9 µm due to this lowering energy-dispersive X-ray (EDX) analysisDO(FI:ig10u.r10e39S/C37).TA0C8r9o8s5sF-
concentration of reactants. SEM shows that c-Au/IM-POP-2BrB polarization magic-angle-spinning (CP/MAS) 13C NMR supports
is macroscopically composed of interconnected polymer the formation of imidazolium corresponding to the signal at
spheres with a diameter of 4.4 ± 0.9 µm (Figure 2c). This 54.1 ppm (Figure S4). Fourier-transform infrared spectroscopy
spherical particulate morphology is in agreement with those (FT-IR) of Au/IM-POP-2BrB and IM-POP-2BrB are nearly
observed in other cationic POP systems.24,33,34 The Au NPs identical confirming the presence of organic imidazolium
supported by IM-POP-2BrB was characterized using high polymer backbone (Figure S5). Thermalgravimetric analysis
resolution TEM, and the TEM image determines nanoparticles (TGA) reveals that both IM-POP-2BrB and Au/IM-POP-2BrB are
o
of 3.8 ± 1.5 nm for c-Au/IM-POP-2BrB (Figure 2d).
thermally stable at temperatures below 300 C (Figure S6). At
To further understand the behaviours of Au/IM-POP in temperatures above 300 oC, the decompositions of the
capillary, IM-POP and Au/IM-POP were prepared under batch materials are activated.
conditions (denoted as b-IM-POP and b-Au/IM-POP,
respectively) to measure the intrinsic properties of the
materials. b-IM-POP-2BrB and b-Au/IM-POP-2BrB were
prepared under batch conditions following the same POP
synthesis and Au NPs growth procedures as presented in
Figure 1 (see SI for experimental details). SEM measurements
show that the b-Au/IM-POP-2BrB exhibit the same spherical
morphology as compared with c-Au/IM-POP-2BrB (Figure S1).
The sizes of the Au NPs supported by b-IM-POP are found to
be closely correlated with the concentration of HAuCl4/EtOH
b)
8
7
6
5
4
3
2
1
0
solutions used for Au NPs growth (Figure 3a,S2). The sizes of
Au NPs decrease when increasing the concentrations of HAuCl4
in the range of 0.0626 to 0.50 mmol L-1 (Figure 3b, Table S1).
Further increase in the HAuCl4 concentration ranging from
0.50 to 1.0 mmol L-1 results in increasing sizes of Au NPs. This
concentration dependency can be explained by the two-step
growth mechanism of Au NPs formation proposed by Polte
0.0
0.2
0.4
0.6
0.8
1.0
-
and co-workers.35 In the first step, the Au precursor, AuCl4 , is
c(HAuCl4) / mmol L-1
covered into metallic gold nuclei. Subsequently, Au NPs are
formed from the nuclei via coalescence. At the high
concentrations (0.50 to 1.0 mmol L-1), a large number of nuclei
exist and the coalescence is a size-determining step for the
formation of Au NPs. Thus, an increasing concentration of
Au0 4f7/2 83.5 eV
c)
Au0 4f5/2
87.2 eV
-
Au+ 4f5/2
88.5 eV
AuCl4 leads to a higher possibility for several adjacent nuclei to
Au+ 4f7/2
85.0 eV
coalesce, and consequently an increasing NP size. In contrast,
nucleation plays a decisive role in determining Au NP size at
the low concentrations (0.0626 to 0.50 mmol L-1). When
94 92 90 88 86 84 82 80 78 76
Binding Energy/eV
-
increasing the concentration of AuCl4 in this range, the
number of nuclei is increased, thus the number of Au atoms in
each of the nuclei is decreased.
d)
IM-POP-2BrB
Au/IM-POP-2BrB
The chemical structure of Au NPs grown within IM-POP-2BrB
was probed using X-ray photoelectron spectroscopy (XPS).
Figure 3c shows the Au 4f spectrum for b-Au/IM-POP-2BrB.
The Au 4f7/2 core level was modeled with two components
including two peaks at 83.5 and 85.0 eV corresponding to
Au(0) and Au(I), respectively.36-38 The small amount of Au(I) is
suggested to be present on the surface of Au NPs and help
stabilize them against electrostatic aggregation.37,39 As shown
in Figure 3d, PXRD patterns further prove the existence of
crystalline Au NPs encapsulated in the IM-POP networks. For
IM-POP-2BrB, the broad peak at around 22.5° indicates
formation of an amorphous phase for IM-POP-2BrB.30,40 After
loading Au NPs, the amorphous nature of the host IM-POP
matrix remains unchanged while the Au (111) lattice plane is
detected as indicated by the strong peak at around 38.0°.41,42
10
20
30
40
50
2o
60
70
80
Fig. 3 Characterization of Au/IM-POP-2BrB synthesized under batch
conditions, a) TEM image of Au/IM-POP-2BrB when using a HAuCl4/EtOH
solution at 0.5 mmol L-1, b) diagram showing the sizes of Au NPs synthesized
at various concentrations of HAuCl4 (all the error bars in the inset represent
standard deviations), c) XPS spectrum for Au/IM-POP-2BrB in the binding
energy range of Au species, d) PXRD patterns of IM-POP-2BrB and Au/IM-
POP-2BrB.
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MeOH sorption isotherms of both IM-POP-2BrBVieawnAdrticAleuO/nIMline-
POP-2BrB are type II, the uptake capacities of IM-POP-2BrB
Au
Br-
N
Br-
N
N
DOI: 10.1039/C7TA08985F
N
N
N
and Au/IM-POP-2BrB reach 351 cm3 g-1 (50.1 wt%) and 234
cm3 g-1 (33.4 wt%), respectively, at P/P0 = 0.85 at 298 K (Figure
S10). As compared to N2, the remarkably increased MeOH
uptake capacity is suggested to result from the higher
temperature and the enhanced interaction between polar
MeOH vapour and the charged network of IM-POP-2BrB and
Au/IM-POP-2BrB.44,45 Other IM-POP materials with various
bromo-functionalized linker molecules show similar sorption
behaviours. These results show that Au/IM-POPs have charged
pore surfaces and are ready to capture guests.
Au/IM-POP-2BrB
IM-POP-2BrB
Br-
N
N
N
N
Au
Br-
N
N
N
N
N
N
1) HAuCl4
2) NaBH4
Au/IM-POP-2BrAn
IM-POP-2BrAn
Br-
+
Br Br
Br
Au
Br-
Br
N
N
N
N
Br
Br
Br
Br
IM-POP-2BrTMB
Br-
Au/IM-POP-2BrTMB
Br
Au
Br-
N
N
N
N
IM-POP-3BrTMB
Au/IM-POP-3BrTMB
Scheme 1 Synthetic route to IM-POPs and Au/IM-POPs.
The synthesis of present imidazolium-based porous organic
polymers can be extended from 1,4-bis-bromomethyl-benzene
to a range of bromo-functionalized linker molecules by
performing
imidazolyl)phenyl]methane under identical conditions (Scheme
1). These linker molecules include 9,10-
bis(bromomethyl)anthracene (2BrAn), 2,4-bis-bromomethyl-
1,3,5-trimethyl-benzene (2BrTMB) and 2,4,6-
reactions
with
tetrakis[4-(1-
a
b
c
tris(bromomethyl)mesitylene (3BrTMB). Following the
synthesis of IM-POPs, Au NPs were grown using HAuCl4
solutions all at a concentration of 0.25 mmol L-1. The resulting
IM-POPs and Au/IM-POPs are characterized by various
techniques including SEM, TEM, EDX, XPS, PXRD, CP/MAS
NMR, FT-IR and TGA (See SI, Figure S1-S8 for synthesis and
detailed characterization). As can be seen from the TEM
images in Figure 4, spherical Au NPs are embedded within the
matrix of IM-POPs formed by three linkers. The average sizes
of Au NPs were measured to be 3.7 ± 0.8 nm, 4.2 ± 0.8 nm and
3.6 ± 0.9 nm for Au/IM-POP-2BrAn, Au/IM-POP-2BrTMB and
Au/IM-POP-3BrTMB, respectively. These are similar to that
measured from IM-POP-2BrB under similar conditions (3.7 ±
1.1 nm). It suggests that various imidazolium-based porous
organic polymers may be used to support gold nanoparticles
to assemble a microfluidic reactor. Since the Au NP sizes are
not strongly correlated with the species of linker molecules, 1,4-
bis-bromomethyl-benzene (2BrB) was chosen in the
subsequent catalytic studies.
The porosity and sorption properties of IM-POPs and Au/IM-
POPs were studied using gas and vapour sorption analysis. N2
adsorption-desorption isotherms at 77 K demonstrate that IM-
POP-2BrB has low adsorption capacity of 19.0 cm2 g-1 with
calculated Brunauer-Emmett-Teller (BET) surface area of 8.6
m2 g-1 and total pore volume of 0.034 cm3 g-1 (Figure S9). After
loading Au NPs, the BET surface area and the total pore
volume of Au/IM-POP-2BrB increases to 88.1 m2 g-1 and 0.10
cm3 g-1, respectively. The low N2 uptake of both the materials
may be attributed to their flexible frameworks and charged
pore channels which result in weak interaction between
nitrogen and framework.43 The slightly higher surface and pore
volume of Au/IM-POP-2BrB may be attributed to the pillar
effect of Au NPs to enlarge the pore channels. In contrast,
Fig. 4 TEM images showing the growth of Au NPs within IM-POPs
synthesized with a range of bromo-functionalized linker molecules, (a)
Au/IM-POP-2BrAn, (b) Au/IM-POP-2BrTMB and (c) Au/IM-POP-3BrTMB.
The catalytic performance of Au/IM-POP was evaluated as a
representative in the reduction of nitroarene derivatives to
corresponding anilines, which is an important transformation
in organic chemistry and chemical industry, and also a model
reaction to test the catalytic activity of Au NPs.32,42,46,47 The
reduction of 1-chloro-4-nitrobenzene to 4-chloroaniline was
initially chosen as a probe reaction. The reaction was
performed in both microfluidic reactors and flasks in order to
compare the catalytic activity (see ESI for details and product
characterization). Figure 5 shows the microfluidic reaction
system containing the capillary functionalized with a layer of
Au/IM-POP-2BrB material as heterogeneous catalyst. For a
capillary with a length of 1.0 m, the reactant, 1-chloro-4-
nitrobenzene (1 mmol), was dissolved in THF (4 mL). The
reduction agent, NaBH4 (3 mmol), was dissolved in water (2
mL). After mixing the solutions, 2 mL of the resulting mixture
was taken to be introduced into the capillary using a syringe.
The mixture (2 mL) passed through the capillary during 1.5 h
controlled by the syringe pump. At room temperature, 1-
chloro-4-nitrobenzene was catalytically reduced to product
4 | J. Name., 2012, 00, 1-3
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that could be collected at the end of the capillary and tested catalytic performance for the reduction ofView1-Acrthiclloe rOon-li4ne-
using gas chromatography (GC). For measurements under nitrobenzene into 4-chloroaniline in THDF-OHI:21O0.1(023:91/,C7vT/Av0).89T8h5eF
batch conditions, Au/IM-POP-2BrB was added into the mixed effect of coating thickness was investigated, and c-Au/IM-POP
reactants directly and the reaction was performed under Ar with a coating thickness of 42.9 ± 5.8 µm shows more
atmosphere.
complete conversion (97%), and higher selectivity (98%) and
TOF (6115 h-1) when compared with those with thin coating
(16.5 ± 2.9 µm with TOF 5827 h-1) (Table 1, entry 1,6). The
amount of Au in Au/IM-POP-2BrB was determined using either
inductively coupled plasma (ICP) or atomic absorption
spectroscopy (AAS) technique. The apparent turnover
frequency (TOF) of the Au NPs supported by IM-POP was
calculated as the amount of nitrobenzene that a mole of Au
can concert per unit time.48 In contrast, among b-Au/IM-POP
prepared from various HAuCl4 concentrations (0.25, 0.50 and
0.75 mmol L-1), Au/IM-POP of 0.25 mmol L-1 shows higher
conversion (98%), selectivity (> 99%) and TOF (647 h-1) for the
reduction of 1-chloro-4-nitrobenzene under batch conditions
(Table 1, entry 7-9). The TOF values of b-Au/IM-POP-2BrB are
measured to range from 607 h-1 to 647 h-1. By confining Au/IM-
POP hybrid materials within the capillary, a significant increase
(up to 10 times) in the TOF of Au NPs is demonstrated. This
improved TOF was possibly caused by the increasing
proportion of Au NPs that could be exposed to the
nitrobenzene derivatives when Au/IM-POP was transformed to
the confined layer. This is suggested to result from the
improved contact between substrate materials and the
catalytic active sites of Au NPs by confining within the
surface.49
Fig. 5 Schematic representation of the microfluidic reactor assembled from
an Au/IM-POP-functionalized capillary, and the reduction of nitrobenzene
derivatives catalyzed by Au NPs on the inner capillary surface.
The catalytic reduction results are summarized in Table 1.
Au/IM-POP-2BrB in the microfluidic reactor exhibits excellent
Table 1 Reduction of nitrobenzene derivatives to anilines catalyzed by Au/IM-POP-2BrB at RT.
NaBH4, THF/H2O
NO2
NH2
R1
R2
Au/IM-POP-2BrB
Entry
R
Catalysta
Au content
/mmol g-1
0.024
t/h
Conv./%b Sel./%b
TOF/h-1
1c
2d
3e
4f
R1 = R2 = 4-Cl
c-Au/IM-POP-2BrB thick
1.5
1.5
1.5
1.5
1.5
1.5
3.0
97
96
98
97
91
92
98
98
92
98
99
>99
95
6115
5724
6037
6037
5720
5827
647
5g
6h
7i
R1 = R2 = 4-Cl
R1 = R2 = 4-Cl
c-Au/IM-POP-2BrB thin
b-Au/IM-POP-2BrB-1
(cHAuCl4 0.25 mmol L-1)
b-Au/IM-POP-2BrB-2
(cHAuCl4 0.50 mmol L-1)
b-Au/IM-POP-2BrB-3
(cHAuCl4 0.75 mmol L-1)
c-Au/IM-POP-2BrB thick
c-Au/IM-POP-2BrB thick
c-Au/IM-POP-2BrB thick
c-Au/IM-POP-2BrB thick
c-Au/IM-POP-2BrB thick
0.030
0.062
>99
8i
9i
R1 = R2 = 4-Cl
R1 = R2 = 4-Cl
0.23
0.14
1.5
1.5
96
91
92
640
607
>99
10c
11c
12c
13c
14c
R1 = R2 = 4-H
R1 = R2 = 4-Me
0.024
0.024
0.024
0.024
0.024
1.5
1.5
1.5
1.5
1.5
99
98
92
94
92
99
97
95
98
94
6161
5905
5650
5841
5460
R1 = R2 = 3-Me
R1 = R2 =2-Me
R1 = 4-CHO, R2 = 4-CH2OH
a c-Au/IM-POP-2BrB thick has a coating thickness of 42.9 ± 5.8 µm, and c-Au/IM-POP-2BrB thin has a coating thickness of 16.5 ± 2.9 µm.b Conv.: (conversion)
and Sel. (selectivity) were determined by GC. c Conditions for c-Au/IM-POP-2BrB thick: capillary length, 1.0 m; injection speed, 3 µL min-1; nitrobenzene
derivatives, 0.33 mmol; NaBH4, 1.0 mmol; Au/substrate, 0.01 mol%; THF-H2O (2:1, v/v), 2.0 mL. d-g The first-fourth recycling runs of entry 1. h Conditions for
c-Au/IM-POP-2BrB thin: capillary length, 2.0 m; injection speed, 3 µL min-1; nitrobenzene derivatives, 0.15 mmol; NaBH4, 0.45 mmol; Au/substrate, 0.01
mol%; THF-H2O (2:1, v/v), 2.0 mL. I Conditions for b-Au/IM-POP-2BrB: nitrobenzene derivatives, 1.0 mmol; NaBH4, 3.0 mmol; Au/substrate, 0.1 mol%; THF-
H2O (2:1, v/v), 6.0 mL.
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The capillary of c-Au/IM-POP could be reused as shown in the
reduction of 1-chloro-4-nitrobenzene. The catalytic activity of
c-Au/IM-POP was maintained for over another four recycling
runs (Table 1, entry 2-5). The Au content within the catalyst
after four runs was experimentally measured to be 0.025
mmol g-1, which is nearly identical to the value prior to
initiating the reduction, showing the catalysis was
heterogeneous.
Acknowledgements
We gratefully acknowledge the NSFC (51573216), the NSF of
Guangdong Province (S2013030013474) and the FRF for the
Central Universities (16lgjc66, 17lgpy03) for financial support.
View Article Online
DOI: 10.1039/C7TA08985F
Notes and references
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5
the reduction of
a range of nitrobenzene derivatives.
Nitrobenzene, 4-nitrotoluene, 3-nitrotoluene and 2-nitroluene
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Conclusions
9
In summary, we have successfully developed a strategy for
fabricating a catalytic microfluidic reactor via coating Au/IM-
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Journal of Materials Chemistry A
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DOI: 10.1039/C7TA08985F
Table of Contents
Gold nanoparticles confined in imidazolium-based porous organic polymers show
high activity in a microfluidic reactor.