Continuous detection of HCl and NH3 gases with a high-performance fluorescent polymer sensor

Article abstract of DOI:10.1039/c8nj02344a

A novel fluorescent triazine-based covalent organic polymer (COP-1) sensor for HCl and NH₃ gases has been designed and synthesized. Both the COP-1 powders that were dispersed in solvents and the COP-1 film that was formed on the surface of quartz sheets exhibited stable fluorescence and a sensitive HCl/NH₃ response. Immersion in HCl-bubbled solvents weakens and red-shifts the fluorescence emission of the COP-1 powders, owing to a protonation-induced charge transfer (CT). Subsequent injection of NH₃ into the solvents recovers the fluorescence via deprotonation. Interestingly, the microporous COP-1 film also shows a similar fluorescence response to HCl/NH₃ gas, with high sensitivity and good reversibility, which suggests that it could serve as a solid-state optical probe for continuous and quantitative detection of HCl and NH₃ gases. The formation of the red-shifting hydrogen bonds is found to be the origin of the response.

Full text of DOI:10.1039/c8nj02344a

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January 2016 Pages 1–846
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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Continuous detection of HCl and NH gases with a high-
3
performance fluorescent polymer sensor
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
b
Ning Xu, Rui-Lei Wang, Dong-Peng Li, Zi-Yan Zhou, * Tian Zhang, * Yu-Zhong Xie, * Zhong-Min
c
Su
DOI: 10.1039/x0xx00000x
A novel fluorescent triazine-based covalent organic polymer (COP-1) sensor toward HCl and NH
and synthesized. Both the COP-1 powders dispersed in solvents and the COP-1 film formed on surface of quartz sheets
exhibit stable fluorescence and sensitive HCl/NH response. Immersed in HCl-bubbled solvents weakens and redshifts the
fluorescence emission of the COP-1 powders, owing to the protonation induced charge transfer (CT). Subsequent injection
of NH into the solvents recovers the fluorescence via deprotonation. Interestingly, the microporous COP-1 film also shows
similar fluorescence response to HCl/NH gas with high sensitivity and good reversibility, which could serve as a solid-state
optical probe for continuous and quantitative detection of HCl and NH gases. The formation of the red-shifting hydrogen
bonds is found to be the origin.
3
gases has been designed
www.rsc.org/
3
3
3
3
been reported, the solid-state ones with good reversibility and
2
4-27
Introduction
real-time efficiency are still appealing.
et al. has reported an optochemical gaseous HCl sensor with a
meso-tetramesitylporphyrin (MTMP) deposited glass
Recently, Kalimuthu
Irritating, volatile and colorless hydrogen chloride (HCl) and
-4
ammonia (NH ) gases have been widely applied in industry
3
1
.
substrate. The Soret band of the MTMP film was shifted from
434 nm to 452 nm upon exposure to HCl gas, whereas no shift
was observed when the film was subsequently treated with
The main sources of HCl and NH gases in air are fuel burning,
3
5
,6
chemical and biological metabolic processes. HCl gas is easily
dissolved in water to form hydrochloric acid, which is one
1
2
7
,8
NH
membrane for the detection of NH
at least 30 minutes completing the sensing process.
3
gas. Deshusses et al. reported a polyaniline composite
ingredient of the acid rain. Serious corrosion effect on
metals, facilities and buildings has also correlation with HCl
3
gas. However, it requires
1
3
9
and NH gases. HCl and NH gases could be inhaled into the
3
3
In this work, we synthesized a novel triazine-based
covalent organic polymer (COP-1) (Scheme 1). The
microporous COP-1 film was formed on surface of the quartz
sheets under solvent thermal conditions. The homogeneous
pores distributed on the COP-1 film are significant for gas
detection. To our delight, the COP-1 film shows strong
fluorescence, contrary to usual luminescent materials with
human body via the respiratory system, and long-term
exposure may cause laryngeal mucosal irritation, nasal erosion
1
0,11
ulcer and gastrointestinal diseases.
In order to mitigate the
hazard at utmost, on-site and real-time monitoring of the
1
2-16
pollutants is quite important.
Traditional detection
methods for HCl and NH gases show deficiencies in sensitivity,
3
1
7-19
selectivity and operation.
2
8
aggregation-induced quenching (ACQ) traits.
experimental results show that the COP-1 film could serve as a
solid-state probe for HCl/NH gas, which features real-time
Moreover,
Optical detection technology shows great advantages in
high sensitivity, good selectivity, easy operation and low cost,
which has been extensively applied in environmental,
3
2
0-22
response, easy operation, high sensitivity and good
industrial and biological fields.
We devote ourselves to
develop well-behaved optical sensors for detection of HCl and
2
3
NH gas, particular for them operated in solid state.
3
Although several optical sensors for HCl and NH gases have
3
Scheme 1 The synthetic route of COP-1.
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reversibility. Quantum chemical calculations were also
performed to investigate the detection mechanism.
Acetic acid (3 mL, 0.063 mol) was slowly added into
acetimide ethyl ester (67.9 g, 0.78 mol) under stirring, and the
reaction temperature was maintained between 25°C-30°C.
Then the mixture was stirred for 24 h. After completion of the
reaction, the fractions below 80°C were removed by
distillation, and the residue was diluted with an appropriate
amount of methylene chloride. The white solid was removed
by pumping filtration. The filtrate was distilled at atmospheric
pressure, and the fractions between 149°C-155°C were
collected (15.7 g, 16 %).
Experimental
Materials and instruments
Powder X-ray diffraction (XRD) patterns were recorded on a
α
Siemens D5005 diffractometer with Cu K (λ = 1.5418 Å)
radiation in the range of 3-50°. Fourier transform infrared (FT-
IR) spectra were obtained with a Thermo Nicolet A370
spectrometer (KBr pellets). X-ray photoelectron spectroscopy
Synthesis of COP-1
2
,4,6-Trimethyl-1,3,5-triazine(0.24 g,
phthalaldehyde (0.40 g, 3 mmol), potassium hydroxide (0.33 g,
mmol) and methanol (75 mL) were put into a 100 mL Teflon
2
mmol),
1,4-
(
XPS) was obtained using an Escalab 250 instrument. The UV-
Vis diffuse reflectance spectra (DRS) were recorded on a
Shimadzu UV-3600 spectrometer. Scanning electron
microscope (SEM) images were obtained using Quanta FEG250
field emission environmental SEM (FEI, United States).
Nitrogen gas and carbondioxide gas porosimetry
measurements were performed on an automatic volumetric
adsorption equipment(ASIQM0G002-3) and porosity analyzer
after the samples were outgassed under vacuum at 70°C for 6
h. Thermogravimetric (TGA) curves were measured using
6
reactor. After the mixture was sonicated for 10 min, the
reactor was transferred to an oven, and then heated at 80°C
for 72 h. Yellow precipitate formed, which was collected by
filtration and washed with methanol for three times. The
collected sample was dried at 80°C under vacuum for 12 h to
give a yellow powder (78 % isolated yield).
Synthesis of the COP-1 film
Germany
STA449C-QMS403C
thermalanalyser.
The A quartz sheet (11.0 mm × 35.0 mm) was immersed into a
fluorescence spectra were measured by the Tianjin Gangdong chromic acid solution at 70°C for 60 min, which was washed
F-380 spectrophotometer. Different humidity environments thoroughly with acetone and ultrapure water then.
were created by a Constant Temperature and Humidity
Chamber (BPHS-060A, Shanghai Bluepard Experimental triazine (0.24 g, 2 mmol), 1,4-phthalaldehyde (0.40 g, 3 mmol),
Instruments Co., Ltd.).
potassium hydroxide (0.33 g, 6 mmol) and methanol (75 mL).
To a reactor (100 mL) was added 2,4,6-trimethyl-1,3,5-
All chemicals were obtained commercially and used as The mixture was sonicated for 10 min, to which the quartz
received unless otherwise stated. Potassium carbonate sheets were added. The reactor was heated at 80°C for 72 h
(
K
2
CO
3
), potassium hydroxide (KOH), methanol (CH
Cl ), ethanol (CH CH OH), acetonitrile sheet. The prepared COP-1 film was washed with methanol
), sodium chloride (NaCl), acetic acid and dried at room temperature.
O were obtained from Kermel Chemical Experimental procedures for detection of HCl and NH gases
3
OH), until a layer of COP-1 film formed on the surface of the quartz
dichloromethane (CH
2
2
3
2
(
CH
CH
3
CN), benzene (C
COOH ), NH ·H
6 6
H
(
3
3
2
3
Reagent Co., Ltd. (Tianjin, China). Concentrated sulfuric acid
SO ) and concentrated hydrochloric acid (HCl) were
obtained from Sinopharm Chemical Reagent Co., Ltd.
Shanghai, China). 1,4-Phthalaldehyde was obtained from Sun
23
A homemade device was constructed for the detection of HCl
(
H
2
4
and NH3 gas (Scheme 2). Gaseous HCl or NH3 of various
concentrations were obtained by injecting a certain volume
(
(
0.05 mL, 0.1 mL, 0.15 mL, 0.2 mL or 0.25 mL) of HCl or NH gas
3
Chemical Technology Co., Ltd. (Shanghai, China). Deionized
water was obtained from the Sartoriusarium 611DI water
purification system. 2,4,6-Trimethyl-1,3,5-triazine was
into a 4.3-mL sealed cuvette with an airtight syringe.
Fluorescence properties of the COP-1 film exposed to HCl gas
were monitored after remaining for 5 minutes. Afterwards,
2
9
prepared according to literatures.
Synthesis of 2,4,6-trimethyl-1,3,5-triazine
Anhydrous acetonitrile (53 mL, 1mol), absolute ethanol (58
mL, 1 mol), anhydrous benzene (82 mL, 1 mol) were put into a
500-mL round-bottom flask, then HCl gas (43.1g) was added
under stirring. The mixture was stirred at room temperature
for 48 h. The solid was collected by filtration and washed three
times (10 mL * 3) with dichloromethane (106.4 g, 86.1 %).
The solid (61.75 g, 0.5 mol, dissolved in 100 mL
2 3
dichloromethane) and K CO (86g, 0.6 mol, dissolved in 300 mL
distilled water) were rapidly mixed rapidly and stirred for 10
min. The organic phase was separated and the aqueous phase
was extracted twice (30 mL * 2) with dichloromethane. The
2 3
organic phase was dried over anhydrous K CO . The fractions
below 60°C were removed by distilling to get a pale yellow
liquid (acetimide ethyl ester, 36.7 g, 83.7%).
3
Scheme 2 Device for detection of HCl and NH gases.
2
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adopted. The electrostatic potential (ESP) and natural bond
orbital (NBO) analysis were also conducted at the same level.
1
Geometry and frequency calculations for excited S states of
COM-1-1P and COM-1-2P were done with the time-dependent
DFT (TD-DFT) approach at the B3LYP/6-31+G(d) level. The
excited-state transition properties at the optimized geometries
were obtained at the range-separated CAM-B3LYP level with 6-
3
2
3
1+G(d) basis set. All above calculations were carried out
3
with the Gaussian 09 package.
3
The vibrationally resolved fluorescence spectra, radiative
(
k
r
) and internal conversion (kic) rate constants for COM-1-1P
and COM-1-2P were computed by using the multimode
coupled thermal vibration correlation function (TVCF)
3
formalism implemented in the Molecular Materials Property
4
Scheme 3 Computational models for COM-1-1P (a), COM-1-2P (b), HCl (c),
COM-1 (d), COM-1-1HCl (e) and COM-1-2HCl (f).
3
5
Prediction Package (MOMAP), in which the photophysics
excess HCl gas was purged with nitrogen gas, and then we module shows superiority in predicting the optical properties
3
6
injected sufficient NH
its fluorescence. Until the fluorescence of the COP-1 film
recovered to the initial state, we purged excess NH gas and
3
gas into the sealed cuvette to recover of polymers and solid-state emitters.
3
Results and discussions
repeated the above procedures for the measurement of
another concentration. The COP-1 film used to investigate its
Synthesis conditions
3
fluorescent response to NH gas was pretreated with abundant
The influence of raw material ratios or reaction temperature
on the yields has been studied. We employed three different
raw material ratios to conduct the experiments at three
different temperatures. The yields of the obtained products
are shown in Table S1. The optimal ratio of raw materials was
determined to be 2 : 3 (2, 4, 6-trimethyl-1, 3, 5-triazine : 1, 4-
Phthalaldehyde) and the optimal reaction temperature was
HCl gas. The aim is to determine an original state with
completely quenched fluorescence intensity. Similarly,
fluorescence properties of the COP-1 film exposed to NH
were monitored after remaining for 5 minutes. Afterwards,
excess NH gas was purged with nitrogen gas, and then we
3
gas
3
injected sufficient HCl gas to recover its fluorescence. Until the
fluorescence of the COP-1 film recovered to the original state,
determined to be 80
Structure characterizations
, and the relative humidity is 38% when The structure of COP-1 was firstly characterized by powder
℃.
we purged excess NH
for the measurement of another concentration. The
temperature is 28
3
gas and repeated the above procedures
℃
detecting HCl and NH gases.
3
XRD and FT-IR (Fig. S1). The powder XRD pattern shows two
7,38
3
Quantum chemical calculations
strong peaks, suggesting a semi-crystalline nature.
The
diffraction peaks at 8.5° and 26.3° can be assigned to the (110)
and (001) planes, respectively. The FT-IR spectrum of COP-1
The monomer model we used as the effective fragment in
calculations for COP-1 was named as COM-1. The geometry
optimizations and frequency calculations were performed
using the density functional theory (DFT) for ground states of
COM-1-1P, COM-1-2P, HCl, COM-1, COM-1-1HCl and COM-1-
-1
shows a characteristic vibrating band at 1631 cm , indicating
-1
existence of the olefin group. Moreover, the band at 1373 cm
can be assigned to the triazine ring.
3
0,31
2HCl (Scheme 3) at the B3LYP
level with 6-31+G(d) basis
set. The local energy minima were ensured by the absence of
imaginary frequencies and no symmetry constraint was
Fig. 1 XPS survey spectra for COP-1 (a) and the high-resolution parts for C 1s (b) and N 1s (c).
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microcellular polymeric framework (Fig. 2). The aperture size
determined by the pore-size distribution curve was 1.4 nm.
The Brunauer-Emmett-Teller (BET) surface area was
2
-1
determined to be 29.1 cm g , and the pore volume was 0.037
3
-1
cm g . All above results indicate the perfect pore
distributions.
Thermal and fluorescence stability
As can be seen from the TGA curve, COP-1 shows good
thermal stability with the decomposition temperature as high
as 450 °C and a total weight loss of 50% after decomposition
(Fig. S4), indicating that COP-1 is thermally stable. The
fluorescence stability of the solid-state optical material shows
great importance in sensing applications. The fluorescence
spectra were examined under room temperature as shown in
Fig. S5. Even after a month, no obvious changes in band shape
and fluorescence intensity were observed for both COP-1
2 2
Fig. 2 (a) N adsorption curve at 77 K; (b) Pore-size distribution (N ) curve at 77 powders and COP-1 film, indicating excellent fluorescence
K; (c) CO
curve at 273 K.
2 2
adsorption curves at 273 K and 298 K; (d) Pore-size distribution (CO )
stability.
Detection of HCl and NH in liquid medium
3
As a powerful tool to evaluate the chemical composition The abundant electron-donating nitrogen (N) atoms of COP-1
3
9
of macromolecules, XPS analysis of COP-1 was performed as
shown in Fig. 1, with the total (a) and deconvoluted high-
resolution C 1s (b) and N1s (c) spectra. The peaks at 284.4 and
tend to accept protons, which offer the opportunity for its
application as a pH monitor. Therefore, we studied the
fluorescent responses of the COP-1 powders dispersed in
aqueous solutions to various pH values (Fig. 3). Results show
that the fluorescence intensity declines with the gradually
decreased pH values. Particularly, in strong acid medium (pH <
284.9 eV on the high-resolution XPS spectrum of C 1s can be
assigned to the C-C bond of benzene ring and C=C bond,
respectively. The peaks at 286.6 and 288.7 eV can be ascribed
to the carbon of the triazine ring. For N 1s, the peaks at 398.7
eV and 399.1 eV correspond respectively to the C-N and C=N in
3
), significant weakened and red-shifted emission were
4
0-42
observed. It was found the thermodynamic pK value of the
a
the triazine ring.
Combination with the measurements
+
from the room-temperature UV-Vis DRS, we also obtained the NH moiety at the N atom of the triazine ring falls in the range
band energies and band gap results of COP-1 (Fig. S2). The of 2.82~3.30. Thus, at least one N atom of the triazine core
4
3
valence band (VB) energy and band gap are assessed to be has been protonated when pH < pKa.
1.14 eV and 2.50 eV, respectively. By simple addition, the
conduction band (CB) energy is 3.64 eV.
To gain deeper insight into the pH-dependent
luminescent behavior of the COP-1 powders dispersed in acid
The morphologies of the COP-1 film were characterized
by SEM (Fig. S3). The COP-1 film possesses pores with various
sizes, indicating its potential applications for adsorption and
catalysis. On the surface of the COP-1 film, there distributes
homogeneous pores, revealing its sheet-like structure. The N2
2
and CO adsorption assays at low temperatures show sufficient
porosity of the COP-1 powders, which further suggests its
Fig. 4 Calculated vibrationally resolved fluorescence spectra of COM-1-1P and
COM-1-2P (T = 298 K).
Table 1 Calculated k
r
, kic and Φ
F
(T = 298 K) for COM-1-1P and COM-1-2P
ꢀ
1
ꢀ1
kr (s )
kic (s )
ΦF
8
7
8
8
COMꢀ1ꢀ1P
COMꢀ1ꢀ2P
2.00×10
1.12×10
1.85×10
0.46×10
0.52
0.20
Fig. 3 Fluorescent responses of the COP-1 powders dispersed in aqueous
solutions to various pH values (λmax = 453 nm).
4
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3
Fig. 5 Images showing the COP-1 film under visible light (a) and UV lamp (excited at 365 nm) (b) before and after exposed to HCl gas, and recovery by NH gas.
medium (pH < 3), we performed theoretical calculations on fluorescence changes from green to orange take place in all
COM-1-1P and COM-1-2P (see Scheme 3). We propose more N solvents. Subsequent injecting into the solvents with NH gas
3
atoms of triazine moiety are protonated as pH decreases. The recovers the fluorescence (Fig. S7). The reason can be ascribed
calculated vibrationally resolved fluorescence spectra at room to the protonation via dissociation of HCl and deprotonation
temperature are shown in Fig. 4. The fluorescence spectrum of upon further contact with NH
3
in liquid, similar to the above-
COM-1-2P exhibits a drastic red-shift compared to COM-1-1P, stated pH-dependent luminescent mechanism. As HCl or NH
3
whereas the fluorescence intensity declines remarkably, in gas cannot be dissolved in organic solvents efficiently, only
good agreement with the experimental observations. qualitative results were given to show its sensing ability to
F r r 3
Moreover, the fluorescence quantum yield [Φ = k / (k + kic)] HCl/NH .
predicted by computation also shows a decrease from 0.52 for
COM-1-1P to 0.20 for COM-1-2P. The weakened emission
arises from the reduced k
magnitude, overwhelming the reduced kic by merely four fold
see Table 1).
The excited-state properties play important roles in
determining the excited-state dynamics. The natural transition
orbital (NTO) analyses for S states were performed and the
corresponding landscapes are shown in Fig. S6. It can be seen
that the S state of COM-1-1P exhibits a hybridized local and
r
by more than one order of
(
1
1
4
4
charge-transfer (HLCT) feature, with local excitation (LE) on
the upper styryl branch and charge transfer (CT) from the
bottom styryl branch to the central triazine ring. Instead,
almost pure CT character was found for COM-1-2P, with
obvious CT from the left two styryl branches to the triazine
core and the right styryl branch. The HLCT state in COM-1-1P
offers an effective pathway to obtain efficient luminescence as
not only LE contributes significant orbital overlap to
strengthen k
However, the relative pure CT state in COM-1-2P shows orbital
separation, which induces a lower k and red-shifted emission
r
but also CT provides full exciton utilization.
r
compared to COM-1-1P. The calculation result implies
protonation could promote the intramolecular charge transfer,
thus gives rise to the weak and red-shifted emission.
Fig. 6 Electrostatic potential at 0.002 a.u. isosurface of electron density.
With the aim to investigate the response of solvent-
3
dispersed COP-1 powders to HCl/NH , the HCl gas was bubbled
through different organic solvents. Fortunately, observable
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film changes from greenish yellow to dark orange at first and
recovers afterwards under UV lamp. The structures of the
COP-1 powders before and after exposed to HCl gas then to
3
NH gas were also characterized by powder XRD and FT-IR. The
major peaks on both the powder XRD patterns and IR spectra
experience slight changes (Fig. S8), indicating that the skeleton
3
of COP-1 was hardly damaged upon exposure to HCl/NH gas.
Theoretical calculations were also conducted on HCl,
COM-1, COM-1-1HCl and COM-1-2HCl (Scheme 3) to
understand the fluorescent response of the COP-1 film to HCl
gas. According to the electrostatic potential (ESP) diagram, the
adsorption of HCl molecules (Fig. 6a) to the N atoms of the
triazine ring of COM-1 (Fig. 6b) could form red-shifting
4
5
hydrogen bonds with H−Cl bond lengthening since negative
N pulls positive H closer to it, leading to the polarization of the
H−Cl bond (Fig. 6c and 6d). The natural population analysis
Fig. 7 (a) Fluorescent responses of the original COP-1 film to HCl gas with various
concentrations (λmax = 453 nm); (b) Linear relationship between the fluorescence
intensities and gaseous HCl concentrations; (c) Fluorescent responses of the (NPA) charges of significant atoms (Scheme 3) obtained by
pretreated COP-1 film to NH
fluorescence intensities and gaseous NH
3
gas; (d) Linear relationship between the
concentrations.
NBO analysis were listed in Table 2. The NPA charges of the
hydrogen (H) atoms in HCl molecules of COM-1-1HCl and
COM-1-2HCl are nearly equal to the bonded protons of COM-
3
1
-1P and COM-1-2P. Moreover, the bond lengths of the
N…H−Cl hydrogen bonds in COM-1-1HCl and COM-1-2HCl are
also similar to the N-proton bonds (see Scheme 3). Thus, the
adsorption of HCl molecules to the COP-1 film could also
enhance the charge transfer during the excited-state transition,
which weakens and redshifts the fluorescence intensity.
Subsequent exposure to NH3 gas removes HCl molecules
adsorbed on the COP-1 film and recovers the fluorescence.
Next we quantitatively investigated the fluorescent
responses of the original COP-1 film to HCl gas with various
concentrations (0.0116, 0.0232, 0.0348, 0.0464, 0.0580,
HCl/N , v/v). The HCl gas was gradually injected into a 4.3-mL
2
cuvette containing the COP-1 film with the increasing gaseous
HCl concentration, and the procedures are detailed in the
experimental section. Weakened and red-shifted fluorescence
were found (Fig. 7a), and the fluorescence intensities of the
COP-1 film decreases linearly with the increased gaseous HCl
concentrations (Fig. 7b). The detection limit for HCl gas was
Fig. 8 Fluorescence of the COP-1 film upon alternative treatment with HCl and
NH gases.
3
Detection of gaseous HCl and NH
Encouraged by its sensing ability in liquid, we endeavor to
develop a gaseous HCl/NH sensor with COP-1. As the COP-1
3
with the COP-1 film
-4
calculated to be 1.0967 × 10 . Similar procedures were applied
3
to study the quantitative fluorescent responses of the pre-
powders are limited in convenient and practical applications,
we finally attached them onto the quartz sheets to form a
polymer film. Sensor experiments were done with first
treated COP-1 film to NH gas with given concentrations. As
3
expected, enhanced and blue-shifted emission were observed
(Fig. 7c), and the emission intensities increase proportionally
3
exposure of the COP-1 film to HCl gas and then to NH gas.
to the rising gaseous NH concentrations (Fig. 7d).
3
Images are shown in Fig. 5. The color of the COP-1 film
changes from yellow to orange firstly and recovers to original
subsequently under visible light. The fluorescence of the COP-1
Table 2 NPA charges (in e) on selected atoms for HCl, COM-1 and four complexes obtained by NBO analysis
N1
N2
N3
H1
H2
Cl1
Cl2
HCl
0.282
−0.282
COMꢀ1
−0.515
−0.569
−0.573
−0.570
−0.570
−0.516
−0.513
−0.572
−0.495
−0.567
−0.515
−0.516
−0.510
−0.501
−0.491
COMꢀ1ꢀ1HCl
COMꢀ1ꢀ2HCl
COMꢀ1ꢀ1P
COMꢀ1ꢀ2P
0.440
0.435
0.450
0.463
−0.773
−0.747
0.432
0.463
−0.743
6
| J. Name., 2012, 00, 1-3
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Pl Ne ae swe Jd oo u nr no at l ao dfj Cu sh te mm ai sr tgr iyn s
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microporous COP-1 film exhibit stable fluorescence and
sensitive HCl/NH response. The COP-1 powders were used to
successively detect HCl and NH in liquid medium. The as-
prepared COP-1 film was applied for reversible detection of
HCl and NH gases. Quantum chemical calculations show that
3
3
3
the weak and red-shifted fluorescence response of the COP-1
powders/film to HCl originates from the adsorption of
proton/HCl to the N atoms of triazine rings. The interaction
between negative N of the triazine ring and positive H of
proton/HCl could lead to a charge-transfer (CT) state.
Subsequent exposure of the HCl-pretreated COP-1
Fig. 9 Responses of the COP-1 film toward other potential co-existing
interference gases: (a) acid gases; (b) volatile organic compounds.
The detection limit for NH
3
gas was determined to be 5.8925 ×
0 . The above results show that the COP-1 film could be
applied to the continuous and quantitative detection of HCl
and NH gases with high sensitivity. The reversibility is one
-4
3
powders/film to NH cause deprotonation/desorption and
1
recovers the fluorescence. As a visible and easy-operating
detection strategy, it paves a new way for continuous
detection of acidic and alkaline gases.
3
important factor for fluorescent chemosensors in practical
applications. The reversibility of the COP-1 film was
investigated by cycling the reaction of the probe with HCl and
Conflicts of interest
3 3
NH gases (Fig. 8), due to the high affinity of NH toward HCl.
There are no conflicts to declare.
These reversible cycles, fluorescence bright green and weak
orange, could be repeated for five or more times under the
same condition, demonstrating the good reversibility of the
Acknowledgements
3
COP-1 film toward HCl and NH gases. In addition, we also
studied the fluorescence sensor stability of the COP-1 film (Fig. This work is supported by the Natural Science Foundation of
S9). The experimental results show that there was no Shandong Province (Grant Nos. ZR2017BB034 and
significant change in the fluorescence intensity of COP-1 film ZR2018LB019) and the National Natural Science Foundation of
after three hours, indicating its good detection stability.
China (Grant Nos. 21703122 and 21463026). Thanks to the
Moreover, we created different humidity environments supporting of the Scientific Research Foundation of Shandong
40%, 50%, 60%, 70% and 80%) by a Constant Temperature University of Technology.
(
and Humidity Chamber, to study the effect of humidity on the
detection of HCl gas by COP-1 (Fig. S10). The cuvette
containing COP-1 film was placed in the Constant Temperature
and Humidity Chamber under a specific humidity for 15
minutes. After that, 0.3 ml of dry HCl gas was injected into the
Notes and references
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6,
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J. Name., 2013, 00, 1-3 | 7
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