A Benzimidazole-Containing Covalent Organic Framework-Based

Subscriber access provided by University of Sussex Library

Article

A Benzimidazole-Containing Covalent Organic FrameworkBased QCM Sensor for Exceptional Detection of CEES Zi-Hao He, Shida Gong, Song-Liang Cai, Yi-Lun Yan, Gui Chen, Xin-Le Li, Sheng-Run Zheng, Jun Fan, and Wei-Guang Zhang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.9b00409 • Publication Date (Web): 01 May 2019 Downloaded from http://pubs.acs.org on May 8, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

A Benzimidazole-Containing Covalent Organic FrameworkBased QCM Sensor for Exceptional Detection of CEES Zi-Hao He,† Shi-Da Gong,§ Song-Liang Cai,*,†, ‡ Yi-Lun Yan,† Gui Chen,† Xin-Le Li,*‡ ShengRun Zheng,† Jun Fan,† and Wei-Guang Zhang*† †School ‡The

of Chemistry and Environment, South China Normal University, Guangzhou 510006, P. R. China

Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States

§School

of Chemistry and Chemical Engineering, Qingdao University, Qingdao 266071, P. R. China

KEYWORDS: Covalent Organic Frameworks, Mustard Gas Simulant, Quartz Crystal Microbalance; Volatile Organic Compounds.

ABSTRACT: Mustard gas poses a substantial concern for homeland security and the development of sensors for facile, rapid, highly sensitive and selective detection of mustard gas simulant is much desirable. Herein, a new benzimidazolecontaining covalent organic framework (COF), termed BABE-TFPy COF, was synthesized by the Schiff base condensation of 1(4,7-bis(4-aminophenyl)-1H-benzoimidazole-2-yl)ethan-1-ol (BABE) with 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPy). By virtue of its crystallinity, high porosity, excellent chemical stability, and abundant accessible benzimidazole sites, an unprecedented COF coated quartz crystal microbalance (QCM) sensor was judiciously fabricated for the detection of various volatile organic compounds (VOCs). Remarkably, the resultant BABE-TFPy COF coated QCM sensor exhibited significantly higher sensitivity to 2-chloroethyl ethyl sulfide (CEES), a typical hazardous mustard gas simulant, than those of the other common VOCs. Moreover, the frequency changes of the COF coated QCM sensor were linearly related to the concentrations of CEES vapor within the range of 5.6−19.7 ppm, and derived a strikingly low detection limit of 0.96 ppm (signal-to-noise ratio = 3), rendering it an extraordinary QCM sensor for the detection of CEES. The enthalpy change indicated by the temperaturevarying micro-gravimetric experiment, along with the Gaussian theoretical calculation, highly suggests a dual-hydrogen bonding formed between the BABE-TFPy COF and the CEES molecule account for such an exceptional recognition of CEES. Volatile organic compounds (VOCs), the major components of air pollution, can combine with inhaled air through evaporation or sublimation, endangering the ecological environment and health of human beings.1,2 Particularly, VOCs such as mustard gases that belong to chemical warfare agents are extremely toxic and deemed as mutagenic, antimitotic, carcinogenic, teratogenic, and cytotoxic agents, causing major casualties in military and terrorist attacks. Unfortunately, the major threat of mustard gas nowadays still exists in regional wars, landfills, sea, and certain storage facilities.3 To detect such mustard gas simulants, a plethora of analytical techniques such as infrared spectroscopy, liquid chromatography, gas chromatography, and gas chromatography-mass spectrometry have been developed to date.4-7 However, most of them are time-consuming, costly and unsuitable for real-time online detection. As such, the development of novel sensors for facile, rapid, highly sensitive and selective

detection of mustard gas simulant is highly desirable but remains a formidable challenge. Quartz crystal microbalance (QCM)8,9 sensors have recently garnered enormous interest owing to their fast response, high sensitivity, and selectivity, as well as facile use. During the operation, the QCM quartz crystal coated materials absorb the gas molecules, giving rise to minor mass change at the nano-gram level. Through piezoelectric effect, it can be converted into a frequency signal to realize sensing. The sensitivity and selectivity of the QCM sensors are primarily dictated by the physiochemical properties of coating materials. Up to now, a handful of functional materials such as polysiloxane,10 poly(vinylidene fluoride),11 and hybrid organic/inorganic polymers12 have been fabricated as QCM sensors. However, the research efforts of QCM sensors mainly concentrate on the detection of nerve agents (another class of chemical warfare agents)13,14, humidity,15,16 as well as common VOCs such as formaldehyde,17,18 benzene, toluene, ethylbenzene, and

ACS Paragon Plus Environment

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

xylenes (BTEX),19,20 relevant studies on sensing mustard gas simulants are still relatively rare. Therefore, it is imperative to develop a new QCM coating material that is rich in potential interaction sites for the rapid and selective recognition of mustard gas simulants. Covalent organic frameworks (COFs), periodically extended networks connected by strong covalent bonds, are an emerging class of crystalline porous organic polymers with two- or three-dimensional (2D or 3D) architectures.21-27 Owing to their appealing merits such as low mass density, large specific surface area, and adjustable pore size and structure, COFs have been widely used in various research fields spanning gas storage,28-30 chromatographic separation,31-33 asymmetric catalysis,34-36drug delivery,37-39 chemical sensor,40-42 and electronic devices.43-45 Nevertheless, the application of COFs as QCM coating materials for VOCs recognition has not yet been reported. In this work, we report on the designed synthesis of a benzimidazole-containing COF by the Schiff-base reaction of 1-(4,7-bis(4-aminophenyl)-1H-benzoimidazole-2yl)ethan-1-ol (BABE) with 1,3,6,8-tetrakis(4formylphenyl)pyrene (TFPy) (Scheme 1). The as-synthesized BABE-TFPy COF exhibited good crystallinity, high porosity, and excellent chemical stability. Importantly, the BABETFPy COF contains abundant and accessible -NH and -OH functionalities in the periodic channels, rendering potential hydrogen bonding sites to interact with guest molecules during the recognition process. Taking these considerations into account, we coated the BABE-TFPy COF on a QCM sensor through a drop-coating method for sensing various VOCs including a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES). Notably, the BABE-TFPy coated QCM sensor displayed significantly higher sensitivity to CEES vapor than the other common VOCs, even the concentration of the CEES vapor is much lower than the other vapors. Moreover, plausible recognition mechanism of the BABE-TFPy COF coated QCM sensor towards CEES was validated by experimental and theoretical calculation results. Scheme 1 Schematic representation for the synthesis of the BABE-TFPy COF and the model compound BPABE.

EXPERIMENTAL SECTION Materials and Instruments. Lactic acid, odichlorobenzene, dioxane, acetic acid, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, and ethanol were purchased from Macklin Chemistry (Shanghai, China). 3, 6dibromo benzene-1,2-diamine was purchased from Darui Chemicals Co. Ltd. (Shanghai, China). TFPPy and 4-(1pyrenyl) benzaldehyde were obtained from Aladdin Chemistry (Shanghai, China). All of these materials are of analytical grade and used without further purification. Powder X-ray diffraction (PXRD) measurements were conducted on an Ultima IV Multipurpose X-ray Diffractometer (Rigaku, Japan) equipped with a Cu-Kα radiation source. The Fourier transform infrared (FT-IR) spectra were recorded on a PerkinElmer Spectrum Two in the 4000-500 cm-1 region by using KBr pellets. Thermogravimetric analysis (TGA) was performed on a PerkinElmer TGA 8000 with a heating rate of 10 °C min-1 under an air atmosphere. Scanning electron microscope (SEM) images were obtained by ZEISS Gemini 500 (Carl Zeiss, Germany). Proton nuclear magnetic resonance (1H NMR) spectra were measured on Bruker AVANCE NEO 600 MHz with tetramethyl-silane (TMS) as an internal standard at ambient temperature. The solid-state carbon nuclear magnetic resonance (13C NMR) spectrum was collected on an Agilent 600M spectrometer. Nitrogen adsorptiondesorption measurement was conducted on a BELSORPMax gas adsorption instrument. Synthesis of 1-(4,7-dibromo-1H-benzoimidazole-2yl)ethan-1-ol (1). Lactic acid (338 mg) was dissolved in 6 M HCl (8 mL), in which 3, 6-dibromo benzene-1,2-diamine (665 mg) was added. The resulting mixture was heated at 115 °C for 24 h. After cooling to room temperature, the reaction mixture was neutralized to pH=8 with Na2CO3 and extracted with ethyl acetate. The combined organic phase was dried over anhydrous Na2SO4 and then concentrated under reduced pressure. Chromatographic purification on silica gel column by using ethyl acetate/petroleum ether = 1/1 as the eluent gave the compound 1 as a light red solid. 1H NMR (600 MHz, d6-DMSO) δ = 12.94 (s, 1H), 7.33 (s, 2H), 5.72 (s, 1H), 4.98 – 4.94 (m, 1H), 1.53 (d, J = 6.6 Hz, 3H). Synthesis of 1-(4,7-bis(4-aminophenyl)-1Hbenzoimidazole-2-yl)ethan-1-ol (BABE). A two-necked reaction flask was charged with compound 1 (320 mg) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline (520 mg), then 15 mL dioxane and 4 mL aqueous solution of K2CO3 (2 M) were added. The mixture was bubbled with argon for 20 min under stirring at room temperature, and then tetrakis(triphenylphosphine)palladium (95 mg) was added. The resulting reaction mixture was heated at 105 °C under an argon atmosphere for 72 h. The organic part was extracted with ethyl acetate three times, washed with brine, dried over anhydrous Na2SO4, and then concentrated under reduced pressure. The residue was purified by silica gel column chromatography using petroleum ethyl acetate/petroleum ether = 20:1 as the eluent to give the compound BABE as a yellow solid. 1H NMR (600 MHz, d6DMSO) δ = 11.76 (s, 1H), 7.85 (s, 2H), 7.21 (dd, J = 99.3, 26.6 Hz, 4H), 6.69 (s, 4H), 5.36 (d, J = 5.5 Hz, 1H), 5.23 (s, 4H), 4.99 – 4.94 (m, 1H), 1.52 (d, J = 6.6 Hz, 3H). Synthesis of the model compound BPABE. A twonecked flask was charged with BABE (480 mg, 0.15 mmol),


Page 2 of 16

Page 3 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design 4-(1-pyrenyl)benzaldehyde (798 mg, 0.30 mmol) and 6 mL ethanol. The mixture was bubbled with argon for 20 min, and then 0.5 mL acetic acid was added. After that, the resulting mixture was heated at 85 °C under argon atmosphere for 48 h. The formed solid was filtered, washed with ethanol and purified by recrystallization using a mixed solution of DMSO/H2O = 10/1 to give the model compound as a yellow solid. 1H NMR (600 MHz, d6-DMSO) δ = 12.29 (s, 1H), 8.92 (d, J = 3.9 Hz, 2H), 8.43 (d, J = 6.7 Hz, 2H), 8.37 (d, J = 7.6 Hz, 2H), 8.32 (dd, J = 14.5, 7.9 Hz, 4H), 8.27 (s, 4H), 8.26 – 8.22 (m, 6H), 8.18 (d, J = 9.3 Hz, 2H), 8.13 (dd, J = 15.2, 7.6 Hz, 4H), 7.86 – 7.83 (m, 4H), 7.81 (d, J = 8.0 Hz, 2H), 7.58 (dd, J = 13.1, 7.9 Hz, 3H), 7.52 (d, J = 8.2 Hz, 2H), 7.40 (d, J = 7.6 Hz, 1H), 5.52 (d, J = 5.3 Hz, 1H), 5.09 – 5.04 (m, 1H), 1.60 (d, J = 6.6 Hz, 3H). Synthesis of the BABE-TFPy COF. An odichlorobenzene/EtOH (0.8 mL/0.2 mL) mixture of BABE (6.9 mg, 0.02 mmol) and TFPy (6.2 mg, 0.01 mmol) in a 10 mL vial was stirred for 10 min under argon. Then a 0.1 mL portion of 9 M acetic acid was added, and the resulting mixture continued to be bubbled with argon for 15 min. The vial was sealed quickly and heated at 110 °C for 96 h. The precipitate was collected by centrifugation and washed with EtOH several times. The powder was dried at 90 °C under vacuum for 12 h to give the light green BABE-TFPy COF in an isolated yield of 80%. Preparation of the BABE-TFPy coated QCM sensor. The BABE-TFPy COF was used as a coating material and deposited onto the surface of QCM quartz crystal by a dropcoating method. The blank QCM electrode was soaked into a piranha solution (30% H2O2: 98% H2SO4, 1:3 v/v) for 20 min and washed thoroughly with ultrapure water and ethanol in sequence. Then the QCM electrode was dried with nitrogen gas and loaded into the QCM device. Stabilized under nitrogen gas flow of 400 mL/min, the frequency was recorded and named F0. The finely ground BABE-TFPy COF（2 mg）was suspended in ethanol (2 mL) and sonicated for several hours. The obtained suspension was dropped carefully onto the center of QCM electrode surface using a microsyringe and allowed it to be naturally volatilized. The resulting QCM electrode was finally placed at 90 °C for 1 h under vacuum. Gas phase QCM System and testing process. The ATcut quartz crystals (gold-coated, 6 MHz resonant frequency) were employed throughout the experiments. They were installed in a homemade gas phase pulsemeasuring QCM system, which contains a test chamber (685 mL), an oscillator detector, a temperature-control device, a frequency counter and a computer, as described in Scheme S1. The QCM system was conditioned under a nitrogen flow (400 mL/min) at a testing temperature before the measurement to obtain a stable frequency. The nitrogen gas was then turned off for a while and the frequency was recorded. Different kinds of volatile samples were respectively injected into the test chamber using a microsyringe. The corresponding frequency was recorded when the adsorption equilibrium of the QCM system was observed. After each measurement, the nitrogen gas was turned on to allow the QCM system to be conditioned again and the frequency would finally return to a value that was close to the starting frequency.

Gaussian calculations. The geometries of the molecules studied were fully optimized using the Gaussian 16 software46 with the dual level of theoretical method B3LYPD3/Def2-TZVP//B3LYP/Def2-SVP.47-51 This dual level method uses a lower level (LL), B3LYP/Def2-SVP, to do the optimization and frequency analysis and a higher level (HL), B3LYP-D3/Def2-TZVP, to get the accurate single point energy. The optimized structures were confirmed to be minima on the potential energy surface via vibration frequency analysis. The interaction enthalpy (Hint) between BPABE and CEES was calculated according to the following equation. Hint = (Ecomplex, HL+ Ecomplex corr, LL) – [(EBPABE,HL + E BPABE corr, LL) + (ECEES, HL + ECEES corr, LL)] EX corr, LL means the thermal correction to enthalpy from the single point energy of the molecule X obtained at the lower level of theory, B3LYP/Def2-SVP.

RESULTS AND DISCUSSION Characterization of the BABE-TFPy COF The crystalline structure of the BABE-TFPy COF was resolved by powder X-ray diffraction (PXRD) analysis in conjugation with structural simulation. The PXRD pattern of the BABE-TFPy COF exhibited an intense peak at 2.7°, corresponding to (100) facet. Minor four peaks at 5.5°, 8.2°, 11.0°, and 23.5° are assignable to the (220), (330), (440) and (001) facets, respectively. In order to elucidate the stacking configuration of the obtained COF, two possible stacking modes, eclipsed AA packing (space group: P1, Figure 1b and Table S1) and staggered AB packing (space group: P1, Figure 1c and Table S2), were constructed by Materials Studio software.52 The experimental PXRD pattern of the BABETFPy COF did not reproduce the simulated one using AB stacking mode, especially the appearance of the peaks at 2−5°. In contrast, the AA stacking mode well reproduced the experimental PXRD pattern of the BABE-TFPy COF with corresponding peak positions and relative intensities. Pawley refinement was conducted to verify a great agreement between suggested mode and experimental one (Figure 1a). Moreover, the refinement deduced unit-cell parameters of a = 46.49 Å, b = 46.82 Å, c = 3.96 Å, α =70.2°, β = 89.8°, and γ = 89.7°, with Rwp = 7.87% and Rp = 6.04 %.

Figure 1. (a) PXRD patterns of the BABE-TFPy COF: experimental (black) and Pawley refined (red), the difference between the experimental and the refined patterns (green),



simulated PXRD pattern for the eclipsed AA mode (blue), simulated for the staggered AB mode (orange). Space-filling models of the BABE-TFPy COF in (b) eclipsed AA and (c) staggered AB stacking modes.

The FT-IR spectrum of the BABE-TFPy COF indicated an obvious consumption of starting materials evidenced by the disappearance of stretching bands of aldehyde and amino (Figure 2a). Moreover, the FT-IR spectrum showed a characteristic peak at 1618 cm-1 arising from the C=N linkage, indicating the occurrence of imine condensation. A strong peak at ~3449 cm-1 was assignable to the -OH stretching in an aliphatic hydroxyl group. These characteristic peaks matched well with the FT-IR spectrum of the model compound BPABE . 13C cross-polarization magic angle spinning (CP-MAS) solid-state NMR spectroscopy further corroborated the formation of imine linkage in the COF. The 13C CP-MAS NMR spectrum of the BABE-TFPy COF showed a peak at 158.6 ppm corresponding to the imine carbons (Figure 2b) and a signal at 22.0 ppm was assigned to the methyl group in the COF. The permanent porosity of the BABE-TFPy COF was assessed by the Brunauer–Emmett–Teller (BET) surface area. As shown in Figure 2c, the BABE-TFPy COF possesses a type I adsorption isotherm, indicating its micro-porosity. The BET surface area and total pore volume were found to be 462 m2g-1 and 0.34 cm3g−1, respectively. The pore size distributions of the BABE-TFPy COF was estimated using nonlocal density functional theory (NLDFT), yielding a pore size at 1.97 nm (Figure 2d), which is in good agreement with the predicted values for an eclipsed AA stacking mode.

stability without significant weight loss up to 330 °C under a nitrogen atmosphere (Figure 3c). To investigate the chemical stability of the BABE-TFPy COF, we dispersed the COF powder in different solvents such as DMSO, EtOH, DMF, THF and aqueous HCl (2 M) for 48 hours at room temperature. Surprisingly, the BABE-TFPy COF still retained its crystallinity as evident by PXRD analyses (Figure 3d), indicating the chemically robust nature of the BABE-TFPy COF.

Figure 3. (a) SEM image of the BABE-TFPy COF showing a flake-like structure. (b) TEM image of the BABE-TFPy COF showing stacking sheet. (c) TGA curve of the BABE-TFPy COF. (d) PXRD patterns of the BABE-TFPy COF upon a 48 h treatment in different conditions.

Sensitivity to CEES vapor

Figure 2. (a) FT-IR spectra of the BABE-TFPy COF, model compound BPABE, and starting materials of BABE and TFPy. (b) The solid-state 13C NMR spectrum of the BABE-TFPy COF. Asterisks denote the spinning sidebands. (c) N2 adsorption (●) and desorption (○) isotherm curves of the BABE-TFPy COF. (d) Pore size distribution profile of the BABE-TFPy COF.

The scanning electron microscopy (SEM) revealed that the BABE-TFPy COF adopted an irregular morphology (Figure 3a) while the transmission electronic microscopy (TEM) images presented the sheet-like morphology, supporting the formation of π−π stacking of the 2D COF layers (Figure 3b). Thermogravimetric analysis (TGA) revealed that the BABE-TFPy COF displayed high thermal

We investigated the response frequency of COF coated QCM sensor to CEES vapor at different temperatures. It was found that the response frequency increased with heating up at 30-40 °C and decreased significantly starting at 45 °C (Figure S1). Therefore, we selected 40 °C as the testing temperature. To probe the relationship between the response frequency of the QCM sensor and the concentration of CEES, we tested the BABE-TFPy coated QCM sensor with the optimum coating amount at 40 °C. The real-time measurement of the BABE-TFPy coated QCM sensor for different concentrations of CEES vapor within the range of 5.6−39.5 ppm is illustrated in Figure 4a. The frequency shifts increased progressively with the increasing concentration of the CEES vapor. The BABE-TFPy coated QCM sensor displayed rapid response and excellent reversibility toward CEES vapor. Moreover, the responses described in Figure 4b represents the frequency shifts (∆f) of the BABE-TFPy coated QCM sensor against the different concentrations of CEES vapor varied from 5.6 to 39.5 ppm. The data points refer to frequency shifts from the equilibrium state in response to the injection amounts of CEES vapor. A linear relationship between the frequency shifts of the QCM sensor and the CEES vapor concentrations were observed in the range of 5.6−19.7 ppm and an equation y = −8.21+3.11x could be derived by linear fitting, giving rise to a regression coefficient (R2) value of 0.993. The sensitivity of such a COF coated QCM sensor was calculated to be as high as 3.11 Hz/ppm. Moreover, the


Page 4 of 16

Page 5 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design detection performance of the model compound was evaluated under similar conditions (Figure S2). The result revealed that the model compound BPABE was significantly less sensitive to CEES than the BABE-TFPy COF, indicating the importance of the periodical 1D channel of the resulting BABE-TFPy COF. To assess the reproducibility of the BABE-TFPy coated QCM sensor, we repeatedly conducted injections of CEES vapor (5.6 ppm and 8.4 ppm) three times and the timedependent frequency shifts were recorded. The COF coated QCM sensor exhibited a similar response frequency towards CEES vapor for each cycle (Figure 4c), indicating an excellent reproducibility of the BABE-TFPy coated QCM sensor. The subtle deviations were presumably due to the errors in quantitative injection and concentration differences stemming from the dilution process. The limit of detection (LOD) of the BABE-TFPy coated QCM sensor was estimated by the measured sensor sensitivity (Hz/ppm). Considering that the noise level of the resulting COF coated QCM sensor was 1 Hz, and the signal-to-noise ratio was 3:1, the LOD thus is calculated to be as low as 0.96 ppm. Selectivity to CEES vapor Selectivity is another key factor for evaluating the performance of COF coated QCM sensor. Figure 4d and Figure S3 showed the response of the BABE-TFPy coated QCM sensor to a large number of vapors including water, hexane, acetonitrile, ethanol, tetrahydrofuran, ethyl acetate, dioxane, dichloromethane, chloroform, ether, petroleum ether, acetone, benzene, toluene, isooctane, carbon tetrachloride, methane acid, dichloroethane, pyridine, and

CEES. Notably, the COF coated QCM sensor exhibited a significant response frequency to CEES vapor, while very low-frequency shifts to water and other common VOCs. Such response frequencies remained much lower than that of the CEES vapor, even the vapor concentrations of these VOCs are dozens or hundreds of times higher than that of CEES (Table S3, injection of 0.8 μL pure volatile samples). These results unambiguously indicate that the BABE-TFPy coated QCM sensor displays a high selectivity towards CEES vapor in comparison to other VOCs. To further investigate whether other VOCs are prone to interfere with the recognition of CEES, several samples such as water, hexane, tetrahydrofuran, acetonitrile, dichloromethane, chloroform, carbon tetrachloride, ethanol, benzene were mixed with CEES (9:1, v/v) respectively to conduct selective tests. As shown in Figure S4, the mixed samples with CEES exhibited remarkable higher response frequencies than those with the pure ones, suggesting these samples did not interfere with the recognition process of CEES. In addition, we also investigated the real-time dynamic response of the BABE-TFPy coated QCM sensor to two wellknown chemical warfare agent simulants, dimethyl methyl phosphonate (DMMP) and diethoxyphosphoryl formonitrile (DCNP). As shown in Figure S5, the BABETFPy coated QCM sensor showed much longer response time (>40 min) to DMMP and DCNP than that of the CEES vapor. Moreover, their frequency changes were also significantly lower than that of CEES. Therefore, the BABETFPy coated QCM sensor exhibits a much better sensing capacity to CEES than DMMP and DCNP vapors.

Figure 4. (a) Real-time dynamic response curve of the BABE-TFPy coated QCM sensor exposed to CEES vapor with increasing concentration at 40 °C. (b) Responses of the BABE-TFPy coated QCM sensor to different CEES concentrations in the range of 5.6– 39.5 ppm. The inset shows the fitting curve in the range of 5.6−19.7 ppm. (c) Reproducibility of the BABE-TFPy coated QCM sensor exposed to 5.6 ppm and 8.4 ppm of CEES. (d) Frequency change of BABE-TFPy coated QCM sensor in response to various vapors at 40 °C. ACS Paragon Plus Environment


Plausible recognition mechanism of the BABE-TFPy coated QCM sensor to CEES To investigate the underlying recognition mechanism of the COF coated QCM sensor to CEES molecule, we tested the response frequencies of the BABE-TFPy coated QCM sensor to three particular VOCs, i.e., diethyl sulfide, 1chlorobutane, and n-pentane that mimic the structures of CEES. As shown in Figure S6, the response frequencies of these three compounds are much lower than that of the CEES vapor. We surmised that the thioether group and chlorine atom in CEES molecule can simultaneously form a unique dual-hydrogen bonding with the backbones of the BABE-TFPy COF, whereas the VOCs of n-pentane, diethyl sulfide and 1-chlorobutane containing zero or one receptor atom preclude the formation of such dual-hydrogen bonding, leading to their low response frequencies. Therefore, the stronger dual-hydrogen bonding interactions between the CEES molecule and the COF may account for the exceptional response of the BABE-TFPy coated QCM sensor to CEES vapor than other VOCs.13

temperatures are shown in Figure 5c. The –△H is calculated to be -44.9 kJ·mol-1 on the basis of the Clausius–Clapeyron equation, indicating that hydrogen bonding can be formed between the CEES molecule and the skeletons of the BABETFPy COF. To verify the above-mentioned measured △H value and study the direct interactions between the model compound PBABE and the CEES molecule, we conducted a simulation using Gaussian 16 software. Electrostatic potential on the 0.001 au molecular surface of the model compound BPABE is presented in Figure 6a. The simulation reveals that the two most positive (blue) areas with the surface maxima (Vs, max) are present around the –NH and –OH groups, indicating that the model compound, PBABE can electrostatically interact with the CEES molecule in an effective fashion. Consequently, structural optimization and the binding energy calculation for the PBABE–CEES complex were further conducted. As depicted in Figure 6b, a short O-H…S hydrogen bonding is formed between –OH of the model compound, PBABE and the thioether of CEES. Aside from this, an N-H…Cl hydrogen bonding between – NH of PBABE and chlorine of CEES is also present. For the PBABE–CEES complex, the computed enthalpy change is calculated to be -45.9 kJ·mol-1, further supporting the energetically favorable formation of a dual-hydrogen bonding between the CEES molecule and the model PBABE compound. This theoretical interaction enthalpy matches well with the experimental one using the temperaturevarying micro-gravimetric method (-44.9 kJ·mol-1).54 The foregoing results highly suggest that the plausible dualhydrogen bonding interactions formed between the BABETFPy COF containing benzimidazole and hydroxyl units and the CEES molecule, presumably account for the exceptional detection of CEES molecule.

Figure 5. Gravimetric curves of the BABE-TFPy coated QCM sensor at (a) 313 K and (b) 318 K to CEES with different concentrations of 14.1, 16.9, and 19.7 ppm, respectively. (c) Based on the experimental results in (a) and (b), two isotherms are plotted to calculate the enthalpy change (△H).

Adsorption thermodynamics of the BABE-TFPy COF to CEES molecule For mass-type sensors, it has been proved that thermodynamics are decisive in the adsorption. Based on the classical physical-chemistry adsorption theories, lower adsorption heat (-△H) leads to weak reversible physical adsorption with poor selectivity, and higher -△H might result in irreversible chemical adsorption with inferior repeatability. However, the moderate value of -△H, which is typically in the range of -80 ～ -40 kJ·mol-1, could meet the requirement of the gas sensor with good selectivity and reversibility.18, 53,54 According to Clausius - Clapeyron equation, at least two isotherms are needed to calculate △H. The response frequencies of the BABE-TFPy coated QCM sensor to different concentrations of CEES at 313 K and 318 K are illustrated in Figures 5a and 5b, respectively. While the corresponding linear plots obtained from various

Figure 6. (a) Electrostatic potential on the 0.001 au molecular surface of the model compound BPABE, computed at the B3LYP-D3/Def2-TZVP//B3LYP/Def2-SVP level. The colour bar (kcal mol-1) is given in the bottom left. The two most positive (blue) areas, which are indicated by pink balls (A and B), have the surface maxima (Vs, max) of 33.65 and 45.29 kcal mol-1, respectively. (b) Optimized geometries and the dual-hydrogen bonding between the model compound BPABE and CEES molecule.

CONCLUSIONS


Page 6 of 16

Page 7 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design In summary, we have prepared a new benzimidazolecontaining BABE-TFPy COF possessing good crystallinity, moderate porosity, and remarkable chemical stability. A BABE-TFPy coated QCM sensor was firstly fabricated for the detection of hazardous VOCs including CEES. Remarkably, the COF coated QCM sensor exhibited high sensitivity and selectivity to CEES vapor, rendering it an exceptional QCM sensor for the detection of CEES. The recognition process is ascribed to the formation of dualhydrogen bonding interactions between the CEES molecule and the backbone of the BABE-TFPy COF, as evident by a series of QCM measurements and Gaussian simulations. This work uncovers the vast potential of designed COFs as high-performance QCM sensors, and opens up new perspectives toward the rational design of tailor-made COFs bearing specific functional sites for the targeted detection of hazardous VOCs.

ASSOCIATED CONTENT Supporting Information. Additional information such as the gas phase pulse-measuring QCM system, the NMR spectra, and tables for the fractional atomic coordinates of the simulated COFs. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author [email protected]; [email protected]; [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We gratefully acknowledge the financial support from the National Natural Science Foundation of P. R. China (Grant Nos. 21603076 and 21571070) and the Natural Science Foundation of Guangdong Province (Grant Nos. 2016A030310437 and 2018A030313193).

REFERENCES (1) Baek, S. O.; Suvarapu, L. N.; Seo, Y. K. Occurrence and concentrations of toxic VOCs in the ambient air of Gumi, an electronics-industrial city in Korea. Sensors 2015, 15, 19102-19123. (2) Yi, W. Y.; Lo, K. M.; Mak, T.; Leung, K. S.; Leung, Y.; Meng, M. L. A Survey ofWireless Sensor Network Based Air Pollution Monitoring Systems. Sensors 2015, 15, 31392-31427. (3) Gerac, M. J. Mustard gas: imminent danger or eminent threat? Ann. Pharmacother. 2008, 42, 237-246. (4) Carrick, W. A.; Cooper, D. B.; Muir, B. Retrospective identification of chemical warfare agents by high-temperature automatic thermal desorption–gas chromatography–mass spectrometry. J. Chromatogr. A 2001, 92, 241-249. (5) Schans, G.P.; Groenendijk, R. M.; deJong, L.P.A.; Noort, H.P. B.D. Standard operating procedure for immunuslotblot assay for analysis of DNA/sulfur mustard adducts in human blood and skin. J. Anal. Toxicol. 2004, 28, 316-319. (6) Kimm, G. L.; Hook, G. L.; Smith, P. A. Application of headspace solid-phase microextraction and gas chromatography–mass spectrometry for detection of the

chemical warfare agent bis(2-chloroethyl) sulfide in soil. J. Chromatogr. A 2002, 971, 185-191. (7) Rao, M. K.; Bhadury, P. S.; Sharma, M.; Dangi, R. S.; Bhaskar, A. S.; Raza, S. K.; Jaiswal, D. K. A facile methodology for the synthesis and detection of N7-guanine adduct of sulfur mustard as a biomarker. Can. J. Chem. 2002, 80, 504-509. (8) Marx, K. A. Quartz crystal microbalance: a useful tool for studying thin polymer films and complex biomolecular systems at the solution− surface interface. Biomacromolecules 2003, 4, 1099-1120. (9) Su, W. C.; Zhang, W. G.; Zhang, S.; Fan, J.; Yin, X.; Luo, M. L.; Ng, S. C. A novel strategy for rapid real-time chiral discrimination of enantiomers using serum albumin functionalized QCM biosensor. Biosens. Bioelectron. 2009, 25, 488-492. (10) He, W.; Liu, Z. X.; Du, X. S.; Jiang, Y. D.; Xiao, D. Analytical application of poly {methyl [3-(2-hydroxy-3, 4-difluoro) phenyl] propyl siloxane} as a QCM coating for DMMP detection. Talanta 2008, 76, 698-702. (11) Ying, Z. H.; Jiang, Y. D.; Du, X. S.; Xie, G. Z; Yu, J. S.; Wang, H. PVDF coated quartz crystal microbalance sensor for DMMP vapor detection. Sens. Actuators, B 2007, 125, 167-172. (12) Zhao, Y. Q.; Du, X.; Wang, X. Y.; He, J. H.; Yu, Y. B.; He, H. Effects of F doping on TiO2 acidic sites and their application in QCM based gas sensors. Sens. Actuators, B 2010, 151, 205-211. (13) Bunkar, R.; Vyas, K. D.; Rao, V. K.; Kumar, S.; Singh B.; Kaushik, M. P.; Epoxy Resin Modified Quartz Crystal Microbalance Sensor for Chemical Warfare Agent Sulfur Mustard Vapor Detection. Sensors Transducers J. 2010, 113, 4147. (14) Zhang, Z.; Fan, J.; Yu, J. M.; Zheng, S. R.; Chen, W. J.; Li, H. G.; Wang, Z. J.; Zhang, W. G. New Poly(N,NDimethylaminoethyl Methacrylate)/Polyvinyl Alcohol Copolymer Coated QCM Sensor for Interaction with CWA Simulants. ACS Appl. Mater. Interfaces 2012, 4, 944−949. (15) Yuan, Z.; Tai, H. L.; Ye, Z. B.; Liu, C. H.; Xie, G. Z.; Du, X. S.; Jiang, Y. D. Novel highly sensitive QCM humidity sensor with low hysteresis based on graphene oxide (GO)/poly(ethyleneimine) layered film. Sens. Actuators, B 2016, 234, 145-154. (16) Chappanda, K. N.; Shekhah, O.; Yassine, O.; Patole, S. P.; Eddaoudi, M.; Salama, K. N. The quest for highly sensitive QCM humidity sensors: The coating of CNT/MOF composite sensing films as case study. Sens. Actuators, B 2018, 257, 609619. (17) Huang, W.; Wang, X. Q.; Jia, Y. T.; Li, X. Q.; Zhu, Z. G.; Li, Y.; Si, Y.; Ding, B.; Wang, X. L.; Yu, J. Y. Highly sensitive formaldehyde sensors based on polyvinylamine modified polyacrylonitrile nanofibers. RSC Adv. 2013, 3, 22994-23000. (18) Wang, L. Y.; Wang, Z. X.; Xiang, Q.; Chen, Y.; Duan, Z. M.; Xu, J. Q. High performance formaldehyde detection based on a novel copper (II) complex functionalized QCM gas sensor. Sens. Actuators, B 2017, 248, 820-828. (19) Wang, L. Y.; Cha, X. L.; Wu, Y. L.; Xu, J.; Cheng, Z. X.; Xiang, Q.; Xu, J. Q. Superhydrophobic Polymerized nOctadecylsilane Surface for BTEX Sensing and Stable Toluene/Water Selective Detection Based on QCM Sensor. ACS Omega 2018, 3, 2437-2443. (20) Kumar, A.; Brunet, J.; Varenne, C.; Ndiaye, A.; Pauly, A.; Penza, M.; Alvisi, M. Tetra-tert-butyl copper phthalocyaninebased QCM sensor for toluene detection in air at room temperature. Sens. Actuators, B 2015, 210, 398-407. (21) Ding, S. Y.; Wang, W. Covalent organic frameworks (COFs): from design to applications. Chem. Soc. Rev. 2013, 42, 548-568. (22) Cai, S. L.; Zhang, W. G.; Zuckermann, R. N.; Li, Z. T.; Zhao, X.; Liu, Y. The organic flatland—recent advances in synthetic 2D organic layers. Adv. Mater. 2015, 27, 5762-5770.



(23) Diercks, C. S.; Yaghi, O. M. The atom, the molecule, and the covalent organic framework. Science 2017, 355, 1585. (24) Li, X. L.; Zhang, C. L.; Cai, S. L.; Lei, X. H.; Altoe, V.; Hong, F.; Urban, J. J.; Ciston, J.; Chan E. M.; Liu, Y. Facile transformation of imine covalent organic frameworks into ultrastable crystalline porous aromatic frameworks. Nat. Commun. 2018, 9, 2998. (25) Zhou, T. Y., Xu, S. Q.; Wen, Q.; Pang, Z. F.; Zhao, X. OneStep Construction of Two Different Kinds of Pores in a 2D Covalent Organic Framework. J. Am. Chem. Soc. 2014, 136, 15885-15888. (26) Lin, G. Q.; Ding, H. M.; Chen, R. F.; Peng, Z. K.; Wang, B. S.; Wang, C. 3D Porphyrin-Based Covalent Organic Frameworks. J. Am. Chem. Soc. 2017, 139, 8705-8709. (27) Ding, H. M.; Li, j.; Xie, G. H.; Lin, G. Q.; Chen, R. F.; Peng, Z. K.; Yang, C. L.; Wang, B. S.; Sun, J. L.; Wang, C. An AIEgenBased 3D Covalent Organic Framework for White LightEmitting Diodes. Nat. Commun. 2018, 9, 5234. (28) Furukawa, H.; Yaghi, O. M. Storage of hydrogen, methane, and carbon dioxide in highly porous covalent organic frameworks for clean energy applications. J. Am. Chem. Soc. 2009, 131, 8875-8883. (29) Rabbani, M. G.; Sekizkardes, A. K.; Kahveci, Z.; Reich, T. E.; Ding, R.; El-Kaderi, H. M.; A 2D Mesoporous Imine-Linked Covalent Organic Framework for High Pressure Gas Storage Applications. Chem.-Eur. J. 2013, 19, 3324-3328. (30) Li, Z. P.; Feng, X.; Zou, Y. C.; Zhang, Y. W.; Xia, H.; Liu, X. M.; Mu, Y. A 2D azine-linked covalent organic framework for gas storage applications. Chem. Commun. 2014, 50, 13825-13828. (31) Yang, C. X.; Liu, C.; Cao, Y. M.; Yan, X. P.Facile roomtemperature solution-phase synthesis of a spherical covalent organic framework for high-resolution chromatographic separation. Chem. Commun. 2015, 51, 12254-12257. (32) Long, Q. H.; Yang, C. X.; Yan, X. P.; Bottom-up synthesis of chiral covalent organic frameworks and their bound capillaries for chiral separation. Nat. Commun. 2016, 7, 12104. (33) Zhang, K.; Cai, S. L; Yan, Y. L.; He, Z. H.; Lin, H. M.; Huang, X. L.; Zheng, S. R.; Fan, J. Zhang, W. G. Construction of a hydrazone-linked chiral covalent organic framework–silica composite as the stationary phase for high performance liquid chromatography. J. Chromatogr. A 2017, 1519, 100–109. (34) Xu, H.; Jiang, D. L. Stable, crystalline, porous, covalent organic frameworks as a platform for chiral organocatalysts. Nat. Commun. 2015, 7, 905. (35) Xu, H. S.; Ding, S.Y.; An, Wu, H. Wang, W. Constructing crystalline covalent organic frameworks from chiral building blocks. J. Am. Chem. Soc. 2016, 138, 11489(36) Han, X.; Huang, J. J.; Yuan, C.; Liu, Y. Cui, Y. Chiral 3D Covalent Organic Frameworks for High Performance Liquid Chromatographic Enantioseparation. J. Am. Chem. Soc. 2018, 140, 892–895. (37) Fang, Q. R.; Wang, J. H.; Gu, S.; Kaspar, R. B.; Zhuang, Z. B. Zheng, J.; Guo, H. X.; Qiu, S. L.; Yan, Y. S. 3D porous crystalline polyimide covalent organic frameworks for drug delivery. J. Am. Chem. Soc. 2015, 137, 8352-8355. (38) Vyas, V. S.; Vishwakarma, M.; Moudrakovski, I.; Haase, F.; Savasci, G.; Ochsenfeld, C.; Spatz, J. P.; Lotsch, B. V. Exploiting noncovalent interactions in an imine-based covalent organic framework for quercetin delivery. Adv. Mater. 2016, 28, 87498754. (39) Bai, L.; Phua, S. Z. F.; Lim, W. Q.; Jana, A.; Luo, Z.; Tham, H. J. P.; Zhao, L. Z.; Gao Q.; Zhao, Y. L. Nanoscale covalent organic frameworks as smart carriers for drug delivery. Chem. Commun. 2016, 52, 4128-4131. (40) Kaleeswaran, D.; Vishnoia P.; Murugavel, R. Correction:[3+ 3] Imine and β-ketoenamine tethered

fluorescent covalent-organic frameworks for CO2 uptake and nitroaromatic sensing. J. Mater. Chem. C 2015, 3, 10040-10040. (41) Ding, S. Y.; Dong, M.; Wang, Y. W.; Chen, Y. T.; Wang, H. Z.; Su C. Y.; Wang, W. Thioether-based fluorescent covalent organic framework for selective detection and facile removal of mercury (II). J. Am. Chem. Soc. 2016, 138, 3031–3037. (42) Zhang, C. L.; Zhang, S.M.; Yan, Y. H.; Xia, F.; Huang, A.; Xian, Y. Z. Highly Fluorescent Polyimide Covalent Organic Nanosheets as Sensing Probes for the Detection of 2,4,6Trinitrophenol. ACS Appl. Mater. Interfaces 2017, 9, 13415-13421. (43) Wan, S.; andara, F. G.; Asano, A.; Furukawa, H.; Saeki, A.; Dey, S. K.; Liao, L.; Ambrogio, M. W.; Botros, Y. Y.; Duan, X. F.; Seki, S.; Stoddart, J. F.; Yaghi, O. M. Covalent Organic Frameworks with High Charge Carrier Mobility. Chem. Mat. 2011, 23, 4094–4097. (44) Cai, S. L.; Zhang, Y. B.; Pun, A. B.; He, B.; Yang, J. H.; Tom, F. M.; Sharp, I. D.; Yaghi, O. M.; Fan, J.; Zheng, S. R.; Zhang, W. G.; Liu, Y. Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework. Chem. Sci. 2014, 5, 4693-4700. (45) Hao, Q.; Zhao, C. Q.; Sun, B.; Lu, C.; Liu, J.; Liu, M. J.; Wan L. J.; Wang, D. Confined synthesis of two-dimensional covalent organic framework thin films within superspreading water layer. J. Am. Chem. Soc. 2018, 140, 12152–12158. (46) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Barone, V.; Petersson, G. A.; Nakatsuji, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K. Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A.; Peralta, Jr., J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; . Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 16, Revision B.01, Gaussian, Inc., Wallingford CT, 2016. (47) Becke, A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098-3100. (48) Lee, C.; Yang, W.; Parr, R. G. Development of the ColleSalvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37,785-789. (49) Becke, A. D. Density-functional thermochemistry. III. The role of exact exchange. J. Chem. Phys. 1993, 98, 5648-5652. (50) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104. (51) Weigend, F.; Ahlrichs, R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297-3305. (52) Accelrys Software Inc. Materials Studio 5.0: Modeling Simulation for Chemical and Material, San Diego, CA, 2009. (53) Xu, P. C.; Yu, H. T.; Guo, S.B.; Li, X. X. Microgravimetric thermodynamic modeling for optimization of chemical sensing nanomaterials. Anal. Chem. 2014, 86, 4178-4187. (54) Yan, D.; Xu, P. C.; Xiang, Q.; Mou, H. R.; Xu, J. Q.; Wen, W. J.; Li, X. X.; Zhang, Y. Polydopamine nanotubes: bioinspired synthesis, formaldehyde sensing properties and thermodynamic investigation. J. Mater. Chem. A 2016, 4, 34873493.


Page 8 of 16

Page 9 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


SYNOPSIS TOC (For Table of Contents Use Only)

A Benzimidazole-Containing Covalent Organic FrameworkBased QCM Sensor for Exceptional Detection of CEES Zi-Hao He,† Shi-Da Gong,§ Song-Liang Cai,*,†, ‡ Yi-Lun Yan,† Gui Chen,† Xin-Le Li,*‡ ShengRun Zheng,† Jun Fan,† and Wei-Guang Zhang*† A benzimidazole-containing COF coated QCM sensor was fabricated for the first time for the exceptional detection of CEES, a typical hazardous mustard gas simulant, showing a strikingly low detection limit of 0.96 ppm. The recognition process was ascribed to the dual-hydrogen bonding between the CEES molecule and the COF backbone, as evident by QCM measurements and Gaussian simulations.


9


Scheme 1 253x190mm (300 x 300 DPI)


Page 10 of 16

Page 11 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1 253x190mm (300 x 300 DPI)



Figure 2 253x190mm (300 x 300 DPI)


Page 12 of 16

Page 13 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3 253x190mm (300 x 300 DPI)



Figure 4 253x190mm (300 x 300 DPI)


Page 14 of 16

Page 15 of 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5 253x190mm (300 x 300 DPI)



Figure 6 253x190mm (300 x 300 DPI)


Page 16 of 16

A Benzimidazole-Containing Covalent Organic Framework-Based

Recommend Documents