Rational Fabrication of Crystalline Smart Materials for Rapid Detection and Efficient Removal of Ozone

Article abstract of DOI:10.1002/anie.202015629

Traditional ozone sensing and removal materials still suffer from high energy consumption and low efficiency. Thus, seeking new ozone-responsive materials with high efficiency and broad working conditions is of great significance. Herein, we first develop

Full text of DOI:10.1002/anie.202015629

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Accepted Article
Title: Rational Fabrication of Crystalline Smart Materials for Rapid
Detection and Efficient Removal of Ozone
Authors: Dong Yan, Zhifang Wang, Peng Cheng, Yao Chen, and
Zhenjie Zhang
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RESEARCH ARTICLE
Rational Fabrication of Crystalline Smart Materials for Rapid
Detection and Efficient Removal of Ozone
Dong Yan,[a] [b] Zhifang Wang,[a] [b] Peng Cheng,[a] [b] Yao Chen, and Zhenjie Zhang*
[c]
[a] [b] [c]
Abstract: Traditional ozone sensing and removal materials still suffer
from high energy consumption and low efficiency. Thus, seeking new
ozone-responsive materials with high efficiency and broad working
conditions is of great significance. In this contribution, we first
developed covalent organic frameworks (COFs) for smart sensing
and efficient removal of ozone. Notably, imine-based COFs possess
dramatically fast optical responses (<1 s) to ozone as low as 0.1 ppm
under broad working conditions (e.g., in the presence or absence of
moisture, room temperature). Moreover, we found that imine-based
COFs can also be applied as excellent ozone removers that can
efficiently reduce the ozone concentration below the recommended
safety limit (<0.1 ppm) for humans. The mechanism for the
outstanding performance of imine-based COFs was in-depth unveiled
by various characterization techniques and analyses. This study not
only provides a new type of advanced materials for ozone sensing
and removal but also broadens the application scope of COFs.
some drawbacks, such as high-power consumption, low
selectivity, that limit their responsive efficiency and application
scenarios.[
10]
Moreover, water vapor (humidity) unavoidably
coexists with ozone in the surrounding atmosphere, which will
interfere with the response of the SMO-based sensors due to the
competitive adsorption of water.[11] For ozone removal application,
the dominating approaches are mostly based on traditional
activated carbon adsorption,[12] chemical absorption,[13] and
[
14]
catalytic decomposition methods. Currently, there is still lacking
advanced materials that can be applied for both ozone sensing
and removal. Seeking new type of ozone-responsive materials
which not only can remove ozone pollution with high efficiency,
but also can track the ozone with a fast optical response is a
campaign of the field.
Smart materials (also referred to intelligent or stimuli-
responsive materials) can undergo reversible changes by
external stimuli, such as temperature, light, pH, gases, chemical
compounds, or moisture, have attracted intense attention in many
fields as diverse as sensors,[ actuators, artificial muscles,
15]
[16]
[17]
Introduction
and information storage.[18] Covalent organic frameworks
COFs)[19-21] have emerged as a new class of smart materials and
(
Ozone is one of the primary air pollutants, well-recognized
based on its serious health effects, such as causing breathing
problems and respiratory diseases, damaging lung function, and
triggering asthma attacks.[1-3] The current Occupational Safety
[
22]
exhibited diverse, intelligent applications such as actuating,
[
23,24]
[25]
drug delivery,
and sensing due to their high crystallinity and
porosity,[
26]
defined pore environment,[27] high emission
efficiency,[ and extraordinary chemical stability.
28]
[29,30]
Moreover,
and Health Administration (OSHA) Air Quality Guidelines for
ambient ozone in the workplace has a recommended limit of 200
COFs can be readily predesigned and post-synthetically modified.
Thereby, active or functional groups can be feasibly customized
in COFs to meet the application demand.[31] For example, our
group installed photoresponsive groups (i.e., arylhydrazone) into
3
μg/m (~100 ppb). Working in an environment exceeding the limit
will cause potential health risks to humans. Thus, developing new
materials to detect ozone pollutants and reduce ozone pollution is
of considerable significance and in urgent demand. Until now,
COFs to construct smart materials, which possessed outstanding
reversible photomechanical performance.[
32]
Zhao and other
[
4]
ozone sensing methods mostly focus on semiconducting,
groups[33-35] used imine and triazine as the pH-responsive groups
to create smart COFs, which showed an optical response to acids.
These works inspired us to explore the potential of using COFs
for ozone-related applications. To the best of our knowledge,
there has been no report using COFs for ozone sensing and
removal yet.
[
5]
absorbance,[6]
electrochemical,
UV
light
iodometric
[
7]
[8]
determination, and chemiluminescence methods. Among all
these techniques, semiconducting sensors based on
semiconducting metal oxides (SMO) such as SnO
2 2 3
, In O , and
ZnO are widely used.[9] However, these SMO materials still face
According to literature, unsaturated bonds such as imines and
alkenes can be cleaved with ozone.[36,37] Moreover, ozone
decomposition can be accelerated by initiators such as OH which
can be generated by the protonation of imine groups with water
molecules.[38-40] Usually, alteration of the chemical environment of
functional groups (e.g., imine) will affect the optical bandgaps of
[
a]
D. Yan, Z. Wang, Prof. P. Cheng, Prof. Z. Zhang
Key Laboratory of Advanced Energy Materials Chemistry
Ministry of Education, Nankai University
Tianjin 300071, China
E-mail: zhangzhenjie@nankai.edu.cn
D. Yan, Z. Wang, Prof. P. Cheng, Prof. Z. Zhang
Renewable Energy Conversion and Storage Center
College of Chemistry, Nankai University
Tianjin 300071, China
-
[b]
[c]
[§]
materials in the visible part of the spectrum, thus causing the color
change.[
35,41]
Therefore, imine can be an ideal responsive group
for ozone-related applications. To the best of our knowledge,
using imine-based materials for ozone sensing and removal
application has not been reported yet. A straightforward strategy
to design ozone responsive materials is to use imines as the
linkage of COFs (Scheme 1), [42-44] whose ordered structures and
high porosity can benefit their performance. In this contribution,
we for the first time expanded the application scope of COFs to
ozone-related applications: the selected COFs not only can serve
as smart ozone sensors with rapid, visible optical responses but
Prof. Y. Chen, Prof. Z. Zhang
State Key Laboratory of Medicine Chemistry Biology
College of Chemistry, Nankai University
Tianjin 300071, China
Dedicated to the 100th anniversary of Chemistry at Nankai
University
Supporting information for this article is given via a link at the end of the
document.
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
also can be applied for ozone removal with both high capacity and
efficiency.
Scheme 1. Schematic illustration of the construction approach of ozone
responsive imine-based COFs.
Figure 1. (a) Synthesis and chemical structure of TPB-DMTP-COF. (b)
Experimental, and predicted PXRD pattern of TPB-DMTP-COF. (c) HRTEM
image of TPB-DMTP-COF.
Results and Discussion
from yellow to orange-red was observed in 240 s for 0.2 ppm
ozone (Velocity: 80 mL/min) (Figure S4). With increasing the
ozone concentration, the response speed was dramatically
improved. Fourier transform infrared spectroscope (FT-IR)
spectra (Figure 2b) showed that the characteristic peak of C=N
The prominent properties of COFs, such as ordered structures,
high porosity, and extraordinary chemical stability, are usually
highly desirable for sensing and removal applications. Thereby,
we chose an imine-linked COF, TPB-DMTP-COF, as
representative in this study. TPB-DMTP-COF can be conveniently
synthesized with high yield via reaction of 2,5-
dimethoxyterephthalaldehyde (DMTA) and 1,3,5-tris-(4-
a
-
1
bond (1612 cm ) gradually disappeared, and new peaks
a
a
-
1
-1
-1 [45,46]
2
assigned to C=O (1683 cm ), NO (1518 cm , 1345 cm ),
-
1
and COOH (1730 cm ) groups appeared with the reaction time
extended. PXRD pattern displayed in Figure S5 also indicated
that TPB-DMTP-COF gradually lost its crystallinity with the
reaction time extended. A gradual structural decomposition was
aminophenyl) benzene (TAPB) (Figure 1a). Powder X-ray
diffraction (PXRD) (Figure 1b) and high-resolution transmission
electron microscopy (HRTEM) image (Figure 1c) revealed the
high crystallinity of TPB-DMTP-COF with a uniformed pore
structure, which was consistent with the simulated structure of
eclipsed-stacking mode. Notably, this COF possesses high
thermal stability, outstanding chemical stability in water, and
acid/base conditions and verified by PXRD patterns and
thermogravimetric analysis (TGA) (Figure S1) and showed high
confirmed by N
decrease of the surface area of TPB-DMTP-COF after treating
with dry O (Figure 2c). Further investigation revealed that the
2
adsorption measurement that showed the
3
decomposed COF could dissolve in Dimethylformamide (DMF) or
1
Dimethyl sulfoxide (DMSO) (Figure S6). H-NMR spectra (Figure
S7) showed that new peaks of carboxylate and aldehyde
appeared. X-ray photoelectron spectroscopy (XPS) revealed that
the peak assigned to C=N (398.6 eV) disappeared, the intensity
of the C-N (400.1 eV) dramatically increased. New peaks
assigned to C=O (288.5 eV) and N=O (405.8 eV) appeared
2
porosity (BET surface area of 2061 m /g) and meso-sized pores
(pore aperture of ~3.3 nm). These superior features would
guarantee the application of TPB-DMTP-COF under broad
working conditions.
According to literature, dry ozone can nucleophilically attack
imine groups in the Schiff base to form nitro, aldehyde, and
carboxylate moieties (Figure 2a).[36] Therefore, imine-based
COFs are potentially used for ozone sensing and removal in the
absence of humidity. To prove this hypothesis, TPB-DMTP-COF
was pre-loaded as a stationary phase in a glass tube (setup
details in Figure S2), and the whole system was then evacuated
in advance. Dry ozone was produced by an ozone generator that
connecting with a gas tank containing zero grade air (21% oxygen
and 79% nitrogen) provided by Air Liquide. The COF color rapidly
changed from yellow to orange-red upon purging dry ozone air
mixture in as short as 5 s (ozone concentration: 1225 ppm,
velocity: 500 mL/min) (Figure S3). Further studies also revealed
that TPB-DMTP-COF could be used as a rapid optical sensor for
dry ozone of different concentrations (e.g., 0.2 ppm, 5 ppm, 50
ppm). For example, the distinct color change of TPB-DMTP-COF
(
Figure 2d-e). Moreover, the XPS result also showed that the
content of the O element was dramatically increased (Figure S8,
Table S1). The above results indicate that TPB-DMTP-COF not
only can be used as a highly efficient ozone sensor in the absence
of the humidity but also potentially used for ozone removal with
high efficiency (the detailed study shown in the ozone removal
part).
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RESEARCH ARTICLE
concentration, the response speed was greatly improved (Figure
3b and Figure S11). Solid-state UV-Vis spectra were applied to
track the color change by comparing the absorption band shift.
Protonation of the imine groups in TPB-DMTP-COF caused a
significant red-shift of the absorption band in the solid-state UV-
Vis spectrum (Figure 3c).[34,35] PXRD measurement (Figure S14)
revealed that the crystalline structure was mostly maintained in
this fast sensing procedure. FT-IR spectra (Figure S15) also
-
showed that the characteristic peak of the C=N bond at 1612 cm
1
-1
+
[33]
shifted to 1644 cm , referred to C=NH bond vibration. These
results indicated that the color change was associated with the
protonation of imine groups. Further investigation revealed that
the TPB-DMTP-COF exhibited excellent reusability for wet ozone
sensing (>20 cycles) by simply using trimethylamine (TEA) to
recover the partially protonated COF. Moreover, we investigated
the effect of different RH on the sensing performance and found
TPB-DMTP-COF film can sense ozone with broad RHs ranging
from 15% to 90%, which covered the main RHs in ambient air.
TPB-DMTP-COF was also evaluated at a wide range of
temperatures (e.g., -20 ℃ and 85 ℃, 1225 ppm) and showed the
desirable real-time color changes (Figure S16). TPB-DMTP-COF
powders dispersed in common solvents such as tetrahydrofuran
(
THF) can also be used for ozone sensing. The color of the
suspension changed from yellow to red in ~3 min (Figure S17).
These results further confirmed that TPB-DMTP-COF could work
under broad conditions with superior selectivity, that can surpass
the traditional SMO materials.
Figure 2. (a) Mechanism for imine moieties reacting with ozone in the absence
of water. (b) FT-IR spectra of TPB-DMTP-COF after treating with dry ozone for
different times. (c) N sorption isotherms of TPB-DMTP-COF before and after
2
dry ozone treatment for different times. (d, e) XPS spectra of the C 1s and N 1s
spectra of TPB-DMTP-COF before and after dry ozone treatment.
In the real application scenarios, moisture usually coexists with
ozone. Thus, we further investigated if TPB-DMTP-COF can work
in the presence of moisture. TPB-DMTP-COF was firstly grown
on the etched silica substrate to form a thin film and then treated
with ozone (flow rate of 500 mL/min) under ambient conditions
(setup details shown in Figure S9). The ozone concentration in
ambient air can be conveniently adjusted from 0.1 ppm to 1225
ppm. Notably, TPB-DMTP-COF showed a fast and visible
response (~0.3 s, details in SI, Figure S10) with film color
changing from yellow to red upon purging wet ozone with different
concentrations. By contrast, a blank control directly purging air
under the same testing condition did not result in any color change
for TPB-DMTP-COF (Figure S11). Furthermore, the common
gases in the air, such as oxygen, nitrogen, and carbon dioxide,
were also tested as controls, and no distinct color changes for
TPB-DMTP-COF were observed under the same testing condition
as ozone (Figure S12). It should be noted that the color of TPB-
DMTP-COF after treating with wet ozone was slightly different
from that observed for TPB-DMTP-COF treated with dry ozone
Figure 3. (a) Illustration of the proposed reaction mechanism for the imine
groups in TPB-DMTP-COF with ozone in the presence of water. (b) Comparison
of the response time of TPB-DMTP-COF film for different ozone concentrations
at 40% RH (T = Trial). (c) Solid-state UV-Vis spectra of TPB-DMTP-COF and
after treating with 40% RH ozone. Insert: the color change of TPB-DMTP-COF
film after wet ozone treatment.
(
side by side comparison in Figure S13). Furthermore, TPB-
DMTP-COF was evaluated in different concentrations of ozone
e.g., 0.1 ppm, 1 ppm, 5 ppm, and 1000 ppm, RH = 40%).
Herein, we proposed a possible mechanism for the wet ozone
sensing by TPB-DMTP-COF. Imine groups in COFs can serve as
the primary adsorption site to bind with water molecules through
hydrogen bonds, which has been observed in previous
studies.[47,48] Imine groups are further protonated by the locked
(
Ascribed to the high sensitivity, the color change for TPB-DMTP-
COF could be readily distinguished by naked eyes (Video S1). For
example, film color changed from yellow to red in 195 s for 0.1
ppm (velocity of 80 mL/min). With increasing the ozone
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Angewandte Chemie International Edition
10.1002/anie.202015629
RESEARCH ARTICLE
-
water molecules to release OH , which can be captured by ozone
in materials were to be fully consumed as testing time extended.
The gradual loss of the crystallinity of TPB-DMTP-COF found
during the three parts (Figure S5 and S20) indicated the C=N
linkages were gradually consumed. Moreover, we also compared
the color change time of the amorphous and crystalline TPB-
DMTP-COF and found the crystalline sample showed a faster
to initiate ozone decomposition reaction.[38-40] Moreover, our
observation agreed well with literature results that the protonation
of the imines decreased the optical bandgaps in the visible part of
the spectrum, thus causing the color change (Figure 3a).[
Moreover, we observed that the excess ozone can further react
41]
with imine groups after the initial optical color change process (i.e., response than the amorphous one (Figure S30), again verifying
partial protonation) (Figure S18). FT-IR spectra (Figure S19)
the significance of the ordered structure of the COF for both
sensing and removal applications. We further used different
amounts of TPB-DMTP-COF to investigate the relationship
between sample amount and performance (Figure 4b). As
expected, the curves in Figure 4b possessed the same trend, and
the increased mass for COFs showed a higher capacity for ozone
removal. The ozone removal capacity of TPB-DMTP-COF (40
mg) can be up to approximately 0.9 mg/mg to reduce ozone
concentration from 1225 ppm to <10 ppm. Further study revealed
that connecting the end gas with additional pre-loaded COFs
tubes could further reduce the level of ozone from 10 ppm to 80
ppb, which met the recommended air quality limit by OSHA.
+
-1
showed that the C=NH at the position of 1644 cm was retained,
while the characteristic peaks assigned to -NO and -COOH
2
groups gradually appeared. PXRD, SEM, and porosity
measurement indicated that TPB-DMTP-COF could decompose
with the reaction time extended (Figure S20-23). Thus, we
proposed a mechanism for the reaction process of TPB-DMTP-
COF in the presence of humidity. Water and ozone molecules will
competitively bond with the imine groups in COFs. Imine groups
prefer to bind with water molecules due to the hydrogen bonds,
hence facilitating the protonation of C=N to C=NH+ groups.
Meanwhile, the unprotonated C=N groups can also undergo the
same decomposition reaction as that occurred in the absence of
humidity. It should be noted that once C=N groups are protonated
to form C=NH+ groups, they cannot further react with ozone,
proved by FT-IR spectra (Figure S24, control experiment detailed
in SI).
Based on the above results, TPB-DMTP-COF not only can be
used for sensing applications but also shows great potential for
ozone removal. In order to emphasize the significance and
advantage of the high porosity and crystallinity of COFs, an
amorphous phase of TPB-DMTP-COF was synthesized for
comparison (details in SI). PXRD pattern and FT-IR spectra
confirmed the formation of an amorphous polymer (Figure S25-
S26). N
2
adsorption data collected at 77 K (Figure S27) showed
2
a relatively low BET surface area of 234 m /g compared with TPB-
DMTP-COF (2061 m /g). The same amount of amorphous and
2
crystalline TPB-DMTP-COF was independently put into the
hollow glass tube connected to the ozone system by using the
4
0% RH air as the inlet gas (Figure S28). An ozone monitor was
used to detect the concentration of ozone residue. The ozone
outlet concentration was kept to 2.45 mg/L (~1225 ppm) at a
velocity of 500 mL/min. Interestingly, as showed in Figure 4a, the
amorphous and crystalline TPB-DMTP-COF showed quite
different performances (Figure 4 and Figure S29). The ozone
residue curve of the amorphous polymer increased straight to 50
ppm (the upper detection limit of the ozone detecting instrument)
in 250 s. By contrast, the ozone residue concentration curve of
TPB-DMTP-COF firstly increased to ~35 ppm, then decreased to
Figure 4. (a) Ozone concentration detected for amorphous and crystalline TPB-
DMTP-COF (40% RH). (b) Ozone concentration was detected for different
amounts of TPB-DMTP-COF (40% RH). (c) Ozone concentration was detected
for different amounts of TPB-DMTP-COF (dry ozone). (d) Ozone concentration
was detected for different materials at the same amount (20 mg, 40% RH). The
Blue dashed line represented the upper limit of the ozone concentration monitor.
Besides, dry ozone was also tested to evaluate the
performance of TPB-DMTP-COF. TPB-DMTP-COF (dry ozone)
also showed the same trend as that for 40% RH (Figure 4c). It
should be noted that the removal performance for dry ozone was
more efficient than that for wet ozone (Figure S31). For instance,
the ozone removal capacity for dry ozone was nearly one time
higher than that for wet ozone (40% RH) (Figure 4b-c). Moreover,
the COF could also work under broad humidity levels. As
predicted, FT-IR spectra (Figure S32) showed that the imine
moieties in TPB-DMTP-COF indeed reacted with ozone at broad
RHs (15-90%). Herein, we propose a possible explanation.
According to the reaction mechanisms (Figure 2a and Figure S33),
each imine group in TPB-DMTP-COF could consume one ozone
~
15 ppm in 310 s, and finally increased to 50 ppm in 600 s. Since
the testing condition was consistent, the performance of the
ozone removal by crystalline TPB-DMTP-COF was nearly 2.4
times higher than that of the amorphous polymer.
As shown in Figure 4a, the reaction process of TPB-DMTP-
COF could be divided into three parts. The first part of the reaction
curve with a steep increase was possibly due to the reaction of
ozone with imines on the material’s surface. This hypothesis was
verified by the reaction curve of the amorphous polymer with a
relatively low surface area (porosity mostly attributed to particle
packing) that showed a similar trend. The second part was mostly
attributed to the reaction inside the pores of the framework. The
third part of the reaction curve indicated that the reactive groups
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
molecule in the presence of humidity,[38-40] while each imine group
will consume two ozone molecules in the absence of water.[36] All
these results prove that TPB-DMTP-COF is an outstanding
material used for ozone removal with both high efficiency and
capacity in the presence or absence of humidity.
In order to investigate the generality of the imine-based COFs
for ozone sensing and removal, various common COFs with
different linkages, including boroxine-linked COF-1 (Figure S34a)
and polyimide-linked PI-COF-2 (Figure S34b) were also
investigated (See SI for more details). As predicted, COF-1 and
PI-COF-2 did not display any optical response through dry or wet
ozone treatment due to the absence of reactive groups for ozone
color change. Moreover, imine-based COFs can serve as capable
and efficient agents to remove trace or high concentration of
ozone to meet the recommended air quality limit by OSHA.
Attributed to the ordered structure and high porosity of COFs,
imine-based COFs showed much better performance than other
materials (e.g., activated carbon, amorphous polymer, monomer,
MOFs) for ozone removal application. These results further
validate the crucial role of the imines in COFs for ozone sensing
and removal applications. The findings of this study not only pave
a new avenue for ozone sensing and removal but also provide
solid evidence for understanding the excellent performance of the
imine-based COFs.
(
Figure S35-S36). PXRD pattern and FT-IR spectra (Figure S37-
S40) confirmed no structural changes occurred after ozone
treatment. To prove the generality of imine-based COFs for ozone
sensing, another imine-based COF, Py-DMTA-COF (Figure
S34c) was designed and synthesized. As expected, Py-DMTA-
COF exhibited fast optical responses through treatment with both
wet and dry ozone (Figure S41). PXRD pattern and FT-IR spectra
Acknowledgments
The authors acknowledge the National Natural Science
Foundation of China (21971126) and 111 Project (B12015).
(
Figure S42-S43) revealed the same results as those for TPB-
DMTP-COF, further proved the generality of imine groups for Conflict of interest
ozone sensing applications. Besides, the ozone removal
performance of TPB-DMTP-COF with other materials was also
The authors declare no conflict of interest.
applied for further investigation. Traditional activated carbon, MIL-
00 (Fe), a small model compound of imine COFs (Figure S44),
1
and amorphous phase of TPB-DMTP-COF were chosen as
representatives for comparison. We used the same amount of
these materials under the same testing conditions to compare the
ozone removal performance with TPB-DMTP-COF. As displayed
in Figure 4d, the curves of the model compound and MIL-100 (Fe)
rose to 50 ppm in ~20 s, while the curve of activated carbon
reached 50 ppm in ~390 s. By contrast, the curve of TPB-DMTP-
COF reached 50 ppm in ~600 s, again verifying the advantages
of the high porosity and ordered structures of COFs. We also
tested the ozone removal performance of Py-DMTA-COF (Figure
S45) and found that this COF possessed both rapid optical
responses and good removal performances to ozone. These
results further validated the generality of the imine-based COFs
and showed their superiority to other materials.
Keywords: Smart materials • Covalent organic framework •
Ozone detection • Ozone removal • Generality
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Angewandte Chemie International Edition
10.1002/anie.202015629
RESEARCH ARTICLE
We demonstrated the first
example to use imine-based
covalent organic frameworks
Dong Yan, Zhifang Wang, Peng
Cheng, Yao Chen, and Zhenjie
Zhang*
(COFs) for smart sensing and
efficient removal of ozone, and
showed that the COFs’
performance could surpass
traditional materials.
Page No. 1– Page No. 6
Rational
Fabrication
of
Crystalline Smart Materials
for Rapid Detection and
Efficient Removal of Ozone
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