Pd loaded and covalent-organic framework involved chitosan aerogels and their application for continuous flow-through aqueous CB decontamination

Article abstract of DOI:10.1039/c8ta03275k

We herein report a series of COF-based poroplastic chitosan aerogels via a facile templated freeze-drying approach. The obtained composite aerogels are hydrophilic, robust, uniform and processable, however, with COF crystallinity and functionalities. Specifically, by introducing Pd@COF species (up to 50 wt%), we fabricated Pd@COF@chitosan aerogels which can be used to build highly efficient continuous flow-through microreactors for chlorobenzene (CB) dechlorination in water at room temperature. Given the versatile structural, shaping, and functional features, this approach could hopefully bring COFs into practical applications, especially concerning the growing global environmental issues.

Full text of DOI:10.1039/c8ta03275k

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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/C8TA03275K
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Pd loaded and covalent-organic frameworks involved chitosan
aerogels and their application for continuous flow-through
aqueous CBs decontamination
Received 00th January 20xx,
Accepted 00th January 20xx
Fei Li,a† Luo-Gang Ding,a† Bing-Jian Yao,*a Ning Huang,b Jiang-Tao Li,a Qi-Juan Fu,a Yu-Bin Dong*a
DOI: 10.1039/x0xx00000x
www.rsc.org/
We report herein a series of COF-based poroplastic chitosan enormous potential in surpassing the traditional porous
aerogels via a facile templated freeze-drying approach. The materials in terms of improvement in performance. Aerogels
obtained composite aerogels are hydrophil, robust, uniform and are usually prepared in the form of self-supporting monoliths,
processable, however, with COFs crystallinity and functionalities. in which nanoscale building blocks are connected and
Specifically, by introducing Pd@COF species (up to 50 wt%), we stabilized without any apparent agglomeration. Therefore, the
fabricated Pd@COF@chitosan aerogel which can be used to build combination of the powdered COFs and the processable
highly efficient continuous flow-through microreactor for organic aerogels could be an alternative way to address COFs
chlorobenzenes (CBs) dechlorination in water at room shaping issue. On the other hand, the inherent intermiscibility
temperature. Given the versatile structural, shaping, and between COFs and organic aerogels would significantly
functional features, this approach could hopefully bring COFs into enhance their seamless fusion in the resulting composite
practical applications, especially the growing global environmental aerogel materials via hydrogel formation and following freeze-
issues.
drying processes.
Chitosan is one of the most abundant and low-cost natural
polysaccharides that obtained by deacetylation of chitin
wastes.5 The biocompatibility, biodegradability, hypotoxicity,
and antimicrobial make chitosan to be widely used in the
tissue engineering, separation membranes, wound dressing,
drug delivery and packing materials.6 In addition, chitosan
contains abundant amino and hydroxyl groups which can
stabilize organic species with H-bond donors or acceptors
through strong H-bonding interactions. Moreover, the amino
group on chitosan can interact with various organic groups for
3D network formation to improve the performance of
chitosan-based materials.7 Although chitosan showed great
promise in the fabrication of membranes, hydrogels, and
aerogels for its good flexibility and chemical stability, the
application of chitosan in preparation of the COF-based
aerogels has never been explored.
In this contribution, we report, first of its kind, a series of
COF-based chitosan aerogel monoliths by a facile templated
freeze-drying approach. The involved COF species are
stabilized and uniformly distributed in the covalently
crosslinked 3D aerogel networks with high COF loading (50
wt%). The shape of COF-involved aerogels could be easily
handled as demand by changing mould. The obtained highly
hydrophil composite aerogels possessed hierarchical pores and
remained intact in water. The entrapped COF species retained
their crystallinity, porosity, and accessibility in the aerogel
formats. Specifically, by introducing Pd NPs@COF composite
Covalent-organic frameworks (COFs), as an emerging class of
porous organic crystalline materials, have currently gained
considerable attention due to their variety of attractive
physical and chemical properties, such as gas separating,
catalysis, sensing, and heavy metal adsorption.1,2 However,
COFs are usually obtained as tiny micro or nano-sized fine
powders due to their crystalline nature, which caused their
handling and processability to be very difficult, consequently,
inevitably limited their practical applications in industry.
Integrating COFs onto or within various substrates to obtain a
shapable, cost-efficient and feasible, and easily popularized
devices is an imperative approach to expand the potential
applications of COF-based materials.3
As known, aerogels, especially organic aerogels, are an
extreme case of hierarchically porous materials, with more
than ca. 80% of porosity and an ultimate low mass density
ranging from 0.8-0.001 g/cm3. 4 Therefore, aerogels can be of
a.College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Center of Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of Education,
Shandong Normal University, Jinan 250014, P. R. China. *E-mail:
yaobingjian1986@163.com, yubindong@sdnu.edu.cn
b.Department of Chemistry, Texas A&M University, College Station, Texas 77843-
3255, United States
† These authors contributed equally to this work.
Electronic
Supplementary
Information
(ESI)
available.
See
DOI: 10.1039/x0xx00000x
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Scheme 1. Schematic representation of TpPa-1
,
TpPa-NO2
,
NUS-2 and TpTe-1. Their sample photographs and SEM images were inserted.
species into chitosan aerogel, we have achieved catalytically 32.94 (± 0.002) Å and c = 3.50 (± 0.002) Å. Rwp and Rp values
active chitosan aerogel monolith which can be used to build converged to 3.12 and 2.72%, respectively. PXRD pattern of
highly efficient continuous flow-through microreactor for this unit cell well matched with the experimental profile.8d The
chlorobenzenes (CBs) dechlorination in water at room experimental PXRD pattern displayed a strong peak at 3.3o
temperature.
together with some relatively weaker signals at 5.9o, 6.9o, 9.1o,
The COFs (Scheme 1), which were used for the fabrication of 14.9o, 18.4o, 22.6o, which were assigned to (100), (110), (200),
COF-chitosan aerogels, were prepared according to the (210), (220), (320), (330) reflections, respectively. The slightly
modified reported methods.8 TpPa-1 NUS-2, and broad peak at higher 2θ (26.8o) is mainly due to π-π stacking
, TpPa-NO2,
TpTe-1 were respectively synthesized by the reaction of 1,3,5- between the COF layers and corresponds to the (001) plane
triformylphloroglucinol (TFP) with 1,4-phenelynediamine, 2- (Fig. 1a).10
nitro-1,4-phenelynediamine,
terephthalohydrazide with the aid of HOAc under solvothermal
conditions (120oC, 72 h, ESI). The as-synthesized TpPa-1
TpPa-
hydrazine,
and
,
NO2 and NUS-2 were characterized by Fourier transform
infrared (FT-IR) and solid-state 13C cross-polarization magic
angle spinning (CP-MAS) spectroscopies (Fig. S1-S17, ESI). As
revealed by the measured powder X-ray diffraction (PXRD)
patterns (Fig. S1-S17, ESI), they all featured a 2D eclipsed
layered sheets, which were well consistent with the reported
results. The morphology of the obtained COFs was also
examined by SEM measurement. As shown in Scheme 1
, TpPa-
1
,
TpPa-NO2 and TpTe-1 were obtained as uniform micro-
meter nanofibers, while NUS-2 was obtained with flower-like
morphology, implying their phase purity.
Besides IR and CP-MAS (ESI), the structural modelling of
TpTe-1 was performed by the Materials Studio (ver. 7.0) suite
of programs for more precise structural information (Table S1,
ESI).9 Molecular geometry optimization was conducted with
MS DMol3 module. Finally, Pawley refinement was applied for
profile fitting, producing the refined PXRD profile using the
space group of P6/m with the lattice parameters of a = b =
Fig. 1 a) The simulated and measured PXRD patterns for TpTe-1 and Pd@TpTe-1
b) Crystal structure of TpTe-1 based on the PXRD data by Materials Studio. c)
Synthesis of Pd@-TpTe-1. The sample photograph and TEM image of Pd@-TpTe-
were inserted.
.
1
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Fig. 2 a) Fabrication of COF-chitosan hybrid aerogel monoliths. b) COF-chitosan aerogels (COF, 50 wt%) based on TpPa-1
,
TpPa-NO2
,
NUS-2 and TpTe-1. c) Vertical-
(
TpTe-1@chitosan) and side-directions (TpPa-NO2@chitosan and TpTe-1@chitosan) pressing tests conducted with a 250 g balance weights, and the exhibition of
TpTe-1@chitosan aerogel propped on the grassy leaves of the spider plant. d) Photographs of four obtained COF-chitosan aerogels with various shapes based on
different moulds.
The AA stacking model in TpTe-1 was determined by the detected in Pd@TpTe-1 after Pd loading, which were well
force-field-based molecular mechanics calculations. Compared demonstrated by the PXRD pattern (Fig. 1a).14
to AB-type staggered structure, the eclipsed model is more
Next, we demonstrated that chitosan, together with cross-
energetic preferential (Tables S1-S2, Fig. S18, ESI). The eclipsed linker, was able to incorporate with the as-synthesized COFs
2D structure contains a hexagonal structural unit, in which the into aerogels. As shown in Fig. 2a, composite COF-chitosan
opposite Ocarbonyl···Ocarbonyl distance is ca. 3.4 nm (Fig. 1b). The aerogels were prepared by mixing crystalline COF powders
close-packed 2D layers with an interlayer distance of 3.6 Å with acidic chitosan in water, followed by the addition of
indicated that adjacent layers in TpTe-1 are in a weak π-π cross-linker of 1,4-butanediol diglycidyl ether. It has been
contact (Fig. 1b). The broad PXRD peak observed at 26.8° proven that the primary amino group on chitosan can interact
might result from the defect in π-π stacking between with epoxy moiety through amino-epoxy reaction.15 The
successive COF layers. 11
formation of -NH-CH2-CH(OH)- linkage was fruther confirmed
As indicated in Fig. 1c, Pd NPs embedded Pd@TpTe-1 was by IR spectra (Fig. S22, ESI). The characteristic peaks at 856 and
simply prepared by the reduction (NaBH4, H2O, 5 h, r.t.) of 913 cm-1 attributed to epoxy group basically disappeared in
Pd(II)@TpTe-1 that was obtained by impregnating of TpTe-1 in the spectrum of chitosan-aerogel. However, the peaks at 2924
a solution of Pd(NO3)2 in MeOH at room temperature for 1 h. and 2868 cm-1 for methylene bands and the peak at 1108 cm-1
The formation of Pd@TpTe-1 was accompanied by a distinct for C-O-C band were still present. In addition, the band at 1593
visual colour change from yellow to dark brown (Fig. 1c). The cm-1 that corresponds to the primary amine group on chitosan
loading amount of Pd, as determined by inductively coupled was shifted to 1566 cm-1, and the peak area was significantly
plasma (ICP) measurement, is up to 6.8 wt %. The oxidation decreased in the spectrum for chitosan-aerogel. Thus, the FTIR
state of the encapsulated Pd species before and after analysis confirmed the successful conjugation of 1,4-
reduction was determined by X-ray photoelectron butanediol diglycidyl ether to the amine group of chitosan.
spectroscopy (XPS, Fig. S19, ESI). The observation of Pd d5/2
After that, the sticky composite dispersion was immediately
and d3/2 peaks at 335.8 and 340.9 eV in the XPS spectrum of transferred into suitable mould, which was allowed to stand at
Pd@TpTe-1 demonstrated the successful reduction from room temperature for several hours until a robust hydrogel
Pd((II) to Pd (0),12 and the atomic lattice fringes had an was formed. Then, the obtained hydrogel was transferred into
interplanar spacing of 0.24 nm corresponding to the 1/3 (422) a cooler for several hours to generate the ice crystals. After
fringes of face-centred cubic (fcc) Pd NPs (Fig. 1c).13 TEM and freeze-drying at -50oC for 24 h to remove the ice crystals, ice-
EDS mapping (Fig. S20, ESI) images indicated that the Pd NPs templated macroporous and COF-chitosan aerogel was
(3-5 nm) homogeneously distributed in the COF matrix. obtained and finally peeled off from the mould.
Notably, the framework of TpTe-1 remained intact (Fig. S21,
ESI) and the diffraction (2θ value at 40o) of Pd species was
Fig. 2b shows that COF-chitosan aerogels with regular
shapes at high COF loading (50 wt%) could be readily achieved
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base on presented approach. The obtained aerogels are robust
and lightweight (density in the range of 0.056-0.069 g/cm3). As
shown in Fig. 2c, they can withstand pressing, indicating their
high mechanical stability. Notably, the COF-chitosan aerogels
could easily meet the different morphologic requirements and
were readily to process into useful forms. By changing the
mould, the shapes of hybrid COF-chitosan aerogels could be
expediently varied as desired. Fig. 2d exhibited some heart-,
bear-, elephant- and fish-shaped aerogel monoliths by
different cast moulding based on the presented approach. In
addition, the structural integrity and uniform dispersion of COF
species in aerogels were further demonstrated by PXRD and
SEM measurements (Fig. S23-S27, ESI). It is different from pure
chitosan aerogel, all the cross-linked hybrid COF-aerogels are
very stable in water and common organic solvents such as
acetone and ethanol (Fig. S28, ESI), furthermore, showed
significant water uptake but with low swelling ratio (Table S3,
ESI). For example, the water uptake amount of TpTe-
1@chitosan was up to ca. 1876 wt% (immersing in H2O for 24
h, r.t.). However, both vertical and in-plane dimensional
changes only slightly increased with the largest value of 3.1 %
over the process. The sponge-like hydrophil nature and highly
interconnected porosity of the aerogels not only enhanced the
water adsorption and mass transport, but also endowed such
COF-based aerogels an application prospect in water.
It is noteworthy that the Pd@TpTe-1@chitosan aerogel (50
wt % of Pd@TpTe-1 loading) could also be was readily
prepared by the same freeze-drying way using Pd@TpTe-1 as
the initial materials. The Pd-loaded amount was determined to
be 3.5 wt % (calcd. 3.4 wt %) based on ICP analysis, indicating
no Pd loss during the aerogel fabrication process. The PXRD
pattern of Pd@TpTe-1@chitosan showed that the Pd@TpTe-1
structural integrity and crystallinity were well-maintained
during the processing process. In addition, the Pd (2θ value at
40o) and chitosan species (2θ value at 20.3o) were also
detected (Fig. S29, ESI). The uniform texture of the Pd NPs
loaded hybrid aerogel was further supported by the evenly
distributed Pd, C, N, and O elements based on the EDS
measurement (Fig. S30, ESI). Similarity, the obtained
Pd@TpTe-1@chitosan aerogel is lightweight, robust,
hydrophilic and stable in water and common organic solvents
such as acetone and ethanol (Fig. S31-S33, ESI), moreover, it
can also be easily tuned by changing mould. For example, it
could be shaped into “U-shaped casting” by U-shaped glass
tube (Fig. 3a). As shown in Fig. 3b-3c, the chitosan aerogel
exhibited highly developed interconnected 3D macroporous
structure, in which a large quantity of COF nanocrystals was
densely packed in the texture of aerogel matrix, implying its
phase purity. On the other hand, Pd@COF species were well
“dissolved” in the chitosan-aerogel phase without any
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DOI: 10.1039/C8TA03275K
Fig. 3 a) “U-shaped” Pd@TpTe-1@chitosan casting. b) and c) SEM cross-section
images of Pd@TpTe-1@chitosan. d) N2 sorption isotherms of pure chitosan
aerogel, TpTe-1, Pd@TpTe-1, TpTe-1@chitosan and Pd@TpTe-1@chitosan. e)
The sponge-like water absorption behavior of Pd@TpTe-1@chitosan (Video S1,
ESI). The stress–strain curve of Pd@TpTe-1@chitosan aerogel in the wet state
was inserted.
In addition, the porosities of these COF-chitosan aerogels
were investigated based on their N2 sorption at 77 K (Fig. S34-
S36 and Table S4, ESI). For example, the pure chitosan aerogels
exhibited an improved gas capacity and pore accessibility upon
incorporation of TpTe-1 and Pd@TpTe-1 (Fig. 3d). Its surface
area was enhanced from 5.6 m2/g to 83.4 m2/g in TpTe-
1@chitosan aerogel and 55.7 m2/g in Pd@TpTe-1@chitosan
aerogel, respectively, but they were less than those of pristine
TpTe-1 (359.6 m2/g) and Pd@TpTe-1 (107.3 m2/g), because
the ice-templating generated macropores that did not
significantly contribute to the surface area.16
Compared to TpTe-1@chitosan, the low swelling ratio
(2.9 %) and high-water absorption (1319 wt%) features in
Pd@TpTe-1@chitosan were well-maintained after Pd loading
(Table S3, ESI). Its sponge-like water uptake behaviour was
shown in Fig. 3e. The photographs showed that the wet hybrid
aerogel was highly elastic, and it could be easily and fully
compressed by hand meanwhile the adsorption water was
forced out. The compressed aerogel could immediately and
completely recover its original shape once it was immersed in
water again (Video S1, ESI). The stress–strain measurement
indicated that Pd@TpTe-1@chitosan column in the wet-state
allowed to be readily pressed into thin slice with the highest
stress rate of 90 % (Fig. 3e).
detectable interface boundary, displaying
connected morphological feature.
a
seamless-
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readily recovered by centrifugation, washed withVeietwhAarnticolel,Oannlinde
DOI: 10.1039/C8TA03275K
dried in air for the next run under the same conditions. The
PXRD analysis indicated that the crystallinity and structural
feature of Pd@TpTe-1 were well maintained, and the HRTEM
image revealed that no Pd NPs aggregation occurred, while
XPS analysis indicated that no valence change for Pd species
was detected (Fig. S37-38, ESI). ICP analysis showed that no Pd
leaching occurred even after five catalytic runs (Table S5, ESI).
These features make Pd@TpTe-1 an ideal candidate to
fabricate Pd@COF-involved chitosan aerogel (Fig. S39-S42).
More importantly, the Pd@TpTe-1 still showed excellent
activity and the dehalogenation yield was up to 96% even after
five catalytic runs (Fig. S43-S47, ESI). Thus, the porous TpTe-1
herein is an ideal platform to load and support Pd NPs for CBs
dechlorination in water. The TpTe-1 itself, however, showed
no activity to the dehalogenation (Fig. S48, ESI).
Fig. 4 Dehalogenation of p-chlorophenol catalysed by Pd@TpTe-1 nanocrystals in
water. a) Reaction time examination (black line) and the leaching test (red line).
The solid catalyst of Pd@TpTe-1 was filtrated from the reaction solution after 15
min, whereas the filtrate was transferred to a new vial and the reaction was
carried out under the same conditions for an additional 75 min. b) Catalytic
cycles. After each run, the catalyst was collected by centrifugation, washed with
ethanol and air dried for next catalytic run under the same conditions. Reaction
conditions: p-chlorophenol (0.5 mmol), HCO2NH4 (5.0 mmol), Pd@TpTe-1 (25
mg, 3.0 mol % Pd), H2O (5 mL), r.t., in air. Yield was determined by GC analysis.
With above results in hand, we next explored the scope of
the dehalogenation reactions with a variety of substituted CBs
performed in the batch experiments under the optimized
conditions. Interestingly, Pd@TpTe-1 is tolerant to wide range
of functional groups such as -OH, -OCH3, -NH2, -CHO, -CN, -
COC2H5, -CO2H, and -COCH3 at different substituted positions
on the CBs, and the dehalogenation reactions proceed
extraordinarily well with different CBs substrates, giving the
corresponding dechlorinated products with high yields (93 -
≥99 %, Fig. S49-S64, ESI). As shown in Table 1, the electronic
effect of substituents appeared to be crucial for the
dehalogenation. For example, the CBs with electron-donating
groups were more active for the aqueous dehalogenation
under the given conditions (Table 1, entries 1-7), the target
dechlorinated products were isolated in excellent yields (96 -
99%) within 1.5-3 h. Meanwhile, the CBs with electron-
withdrawing groups showed less reactivity under the reaction
conditions (Table 1, entries 8-15), and the excellent yields (93 -
>99%) were also observed but after a prolonged reaction time
(3-6 h). Besides, larger sized CBs such as 1-chloronaphthalene
and 4-chlorobiphenyl could also be completely dechlorinated
with excellent yields within 6 h (99 % and 93 %, respectively,
entries 16-17) under the reaction conditions.
Chlorobenzenes (CBs), as an important class of hazardous
persistent pollutants, exist objectively and widely in various
water sources such as wastewater, groundwater, river, and
estuaries. 17 On the other hand, the C-Cl bond has been found
to be comparatively inert,18 so the development of new
strategy for highly efficient aqueous CBs degradation is a very
imperative but challenging task. Compared to traditional
detoxification methods such as catalytic oxidation, photo-
chemical treatment, and transition metal-assisted catalytic
hydrogenation,19 Pd NPs catalysed hydrodechlorination is a
more attractive approach. Because it can be employed to treat
the CBs in water under mild conditions,20 furthermore,
facilitates the dechlorinated product recycling with lower net
impact on the environment.
As known, the most of reported Pd-catalysed dechlorination
used hydrogen as the reducing agent, which is not convenient
and safe to use.21 Therefore, the aid of stable nongaseous
hydrogen source should be an alternative to the catalytic CBs
dechlorination by hydrogen gas. On the other hand, the most
reported dechlorinating reactions were performed in organic
solvents, which would not facilitate the removal of chlorinated
waste in practical water treatment. For this reason, we initially
used p-chlorophenol dechlorination as the model reaction to
examine the catalytic activity and stability of Pd@TpTe-1 in
water, in which the solid HCO2NH4 was used as the hydrogen
source instead of molecular hydrogen. After optimization, we
were pleased to find that p-chlorophenol was almost
completely transferred to phenol (99 %) in water at room
temperature within 1.5 h in the presence of Pd@TpTe-1 (3.0
mol % of Pd) (Fig. 4a). The high activity of Pd@TpTe-1 was
certainly ascribed to the highly dispersed and small sized Pd
NPs in COF matrix, the greater surface area, and accessible
mesoporous pores of the COF. The hot leaching test was
performed indicated that no further reaction occurred without
Pd@TpTe-1 after ignition of the reaction at 15 min, suggesting
that it exhibits a typical heterogeneous catalyst nature. In
addition, the recyclability of Pd@TpTe-1 was also examined
(Fig. 4b). After each catalytic run, the solid catalyst could be
Fig. 5 Continuous-flow setup (graphic and photographic representations) for the
continuous catalytic dehalogenation operation.
After that, we designed a continuous flow-through setup for
aqueous dehalogenation based on Pd@TpTe-1@chitosan
aerogel monolith. The use of flow-through microreactor model
for aqueous dechlorination is more ascendant as it would
allow to overcome the issues associated with batch operation
in practical water treatment. As shown in Fig. 5, an aqueous
solution (10 mL) of p-chlorophenol (1 mmol) and HCO2NH4 (10
5
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mmol) was pumped through a piece of Pd@TpTe-1@chitosan presented approach to be viable for the construcVtiieownAroticflemOanlninye
DOI: 10.1039/C8TA03275K
aerogel monolith (91 mg, 3 mol % Pd) using a peristaltic pump more new and interesting COF-based materials and shaped
at a flow rate of 1.0 mL/min. The reaction was finished within devices for various applications, especially the growing global
ca. 2 h with a 98 % yield (Table 1, entry 18, and S65, ESI). By environmental issues.
contrast, the TpTe-1@chitosan without Pd NPs exhibited no
Table 1. Catalytic results for the aqueous CBs dechlorination in batch and continuous-
activity to the dehalogenation under the reaction conditions
flow microreactor experiments a
(Fig. S66, ESI).
entry
1
substrate
product
t (h) yield (%)b
It was noteworthy that the Pd@TpTe-1@chitosan aerogel
monolith was stable and robust, and it could be reused at least
five times without obvious loss of its catalytic activity. The
dechlorination yield for p-chlorophenol at the fifth run was still
up to 93% (Fig. S39, ESI). In addition, PXRD pattern showed
that the crystallinity of Pd@TpTe-1 was well kept during the
multiple catalytic cycles (Fig. S40, ESI). HRTEM image revealed
that no significant Pd aggregation occurred after recycle (Fig.
S41, ESI). ICP analysis indicated that no Pd leaching was
observed after this reusable continuous flow-through process
(Table S6, ESI). Thus, Pd@TpTe-1@chitosan aerogel herein
could be considered as a long-life catalytic material for the
aqueous CBs dechlorination under the given conditions.
In contrast, the no COF-involved Pd@chitosan aerogel (Pd,
3.0mol%) showed a much worse catalytic performance for this
aqueous CBs dechlorination. For example, the p-chlorophenol
dechlorination yield was down to 76% under the same
conditions. Moreover, the corresponding yield went through a
dramatic decreasing process during catalytic cycle, and only
3.5 % yield for the fifth catalytic run was obtained (Fig. S39,
S71-S75, ESI). This clearly resulted from the serious Pd NPs
aggregation and leaching without the assistance of COF
platform (Fig. S42, and Table S6, ESI).
For practical application, more complicated and larger scale
CBs aqueous system was elected to study the dechlorination
on the above setup. Representative result was shown in Table
1 (entry 19). We were pleased to find that the dechlorinating
reaction proceeded smoothly on the device and was
completed within 10 h to give the quantitative yields of the
desired dechlorinating products. Thus, an aqueous solution (25
mL) of p-chlorophenol (1 mmol), p-chlorbenzoic acid (1 mmol)
and p-chloroacetophenone (1 mmol) was pumped through the
Pd@TpTe-1@chitosan aerogel monolith (91 mg, 3 mol % Pd)
at flow rate of 1 mL/min. The corresponding dechlorinating
yields for p-chlorophenol, p-chlorbenzoic acid, and p-
chloroacetophenone were 100, 99, and 100 %, respectively
(Fig. S76, ESI). Hopefully, this COF-aerogel-based microreactor
model has a promising potential for its application in practical
water treatment.
Cl
OH
OH
1.5
99
Cl
OH
OH
2
3
4
1.5
98
Cl
OH
OH
1.5
1.5
98
98
OH
Cl
Cl
OH
OH
Cl
Cl
OH
5
1.5
97
Cl
Cl
Cl
NH2
O
NH2
O
6
7
1.5
3
96
98
8c
9
3
6
6
6
6
≥99
98
Cl
NO2
NH2
CHO
Cl
CHO
Cl
CN
CN
O
10
11
12
≥99
≥99
94
O
Cl
Cl
O
O
Cl
CO2H
CO2H
13
14
15
1.5
6
98
93
O
O
O
O
Cl
Cl
Cl
3
≥99
N
N
16
6
≥99
Cl
17
6
2
93
98
18d
Cl
OH
OH
OH
OH
Cl
19e
10
≥99
CO2H
O
Cl
CO2H
O
Cl
Conclusions
a Reaction condition for batch experiment: aryl chloride (0.5 mmol), HCO2NH4 (5
In summary, we developed a facile and powerful approach for
the fabrication of COF-involved 3D hybrid aerogels with high
COF loading. The generated lightweight and robust aerogels
can be easily moulded into different shapes as desired.
Specially, by introducing the Pd NPs, the generated
Pd@COF@chitosan aerogel can be used to build highly
efficient continuous flow-through microreactor for aqueous
CBs dechlorination at room temperature. We expect the
b
mmol), Pd@TpTe-1 (25 mg, 3 mol% Pd), H2O (5 mL), r.t., in air. Yields were
c
determined by GC (Fig. S49-S64, ESI). The attached -NO2 was also reduced
during dechlorination. d p-Chlorophenol dechlorination via Pd@TpTe-1@chitosan
aerogel flow-through microreactor: p-chlorophenol (1 mmol), HCO2NH4 (10
mmol), aerogel (91 mg, 3 mol % Pd), H2O (10 mL), r.t. (Fig. S65, and S67-S70, ESI).
e The three-component CBs dechlorination on the microreactor: p-chlorophenol
(1 mmol), p-chlorbenzoic acid (1 mmol), p-chloroacetophenone (1 mmol) ,
HCO2NH4 (30 mmol), aerogel (91 mg, 3 mol % Pd), H2O (25 mL), r.t. (Fig. S76, ESI).
6 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry A
Journal Name
COMMUNICATION
2018, 30, 1704171. (c) S. Y. Ding, J. Gao, Q. Wang, Y. Zhang,
W. G. Song, C. Y. Su, W. Wang, J. Am. CDhOeI:m10. .S10o3Vc9i.e,/wC2A80rTt1iAc1l0e,3O12n73li5n3Ke
19816-19822. (d) S. B. Kalidindi, H. Oh, M. Hirscher, D. Esken,
C. Wiktor, S. Turner, G. V. Tendeloo, R. A. Fischer, Chem. Eur.
J., 2012, 18, 10848-10856.
Conflicts of interest
There are no conflicts to declare.
,
Acknowledgements
13 Y.-A. Li, S. Yang, Q.-K. Liu, G.-J. Chen, J.-P. Ma, Y.-B. Dong,
Chem. Commun., 2016, 52, 6517-6520.
We are grateful for financial support from NSFC (Grant Nos.
21671122, 21604049 and 21475078), Shandong Provincial
Natural Science Foundation (BS2015CL015), China, A Project of
Shandong Province Higher Educational Science and Technology
Program (J15LC05) and the Taishan Scholar’s Construction
Project. We thank Dr. J. Cui (Institute of Chemistry Chinese
Academy of Sciences) for very helpful discussion.
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Journal of Materials Chemistry A
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DOI: 10.1039/C8TA03275K
Pd NPs loaded COF-chitosan aerogel with desired shapes can be used to build highly efficient continuous flow-
through microreactor to catalyse CBs dechlorination in water at room temperature.