Ultrasensitive Detection of Formaldehyde in Gas and Solutions by a

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Ultrasensitive Detection Formaldehyde in Gas and Solutions by a Catalyst Pre-placed Sensor Based on Pillar[5]arene Derivative Qi Lin, Yan-Qing Fan, Guan-Fei Gong, Peng-Peng Mao, Jiao Wang, XiaoWen Guan, Juan Liu, You-Ming Zhang, Hong Yao, and Tai-Bao Wei ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01124 • Publication Date (Web): 25 May 2018 Downloaded from http://pubs.acs.org on May 26, 2018

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ACS Sustainable Chemistry & Engineering

Ultrasensitive Detection Formaldehyde in Gas and Solutions by a Catalyst Pre-placed Sensor Based on Pillar[5]arene Derivative Qi Lin*[a], Yan-Qing Fan[a], Guan-Fei Gong[a], Peng-Peng Mao[a], Jiao Wang[a], Xiao-Wen Guan[a], Juan Liu*[b], You-Ming Zhang[a], Hong Yao[a], Tai-Bao Wei*[a] [a]

Qi Lin, Yan-Qing Fan, Guan-Fei Gong, Peng-Peng Mao, Jiao Wang, Xiao-Wen Guan, You-

Ming Zhang, Hong Yao, Tai-Bao Wei. Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key Laboratory of Polymer Materials of Gansu Province, College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, 730070, China. E-mail: [email protected]; [email protected] [b]

Juan Liu. College of Chemical Engineering, Northwest University for Nationalities, Lanzhou,

730070, China. E-mail: [email protected].

ABSTRACT Abnormal formaldehyde (FA) degree is known to induce variety disease. Herein, we report a novel and efficient method for ultrasensitive detection formaldehyde in gas and solutions by a catalyst pre-placed sensor based on pillar[5]arene derivative (DP5J). By the catalyzation of (CF3SO3)2Bi, the DP5J could selectively and sensitively sense formaldehyde through an aggregation-induced emission (AIE) “turn-on” response within 7.5 seconds and the detection limits (LOD) for formaldehyde is 3.27×10-9 M. Moreover, a FA test kit was prepared

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by loading the catalyst (CF3SO3)2Bi pre-placed DP5J sensor (DP5J-Bi) on a silica gel plate. The test kit could conveniently and efficiently detect formaldehyde gas or solution with ultrasensitivity. Interestingly, the catalysts pre-placed method and FA reaction induced AIE fluorescence “turn-on” mechanism is a novel approach to achieve ultrasensitive detection of FA. Importantly, it’s also a novel approach for the efficient detection of other volatile organic compounds (VOCs).

KEYWORDS formaldehyde • ultrasensitive detection • pillar[n]arene • AIE fluorescence • preplaced catalyst (CF3SO3)2Bi

INTRODUCTION Formaldehyde (FA), a colorless, flammable, strong-smelling chemical gas, 1 is widely used in wood-processing, textiles, construction, carpeting, preserve tissues and the chemical industry 2. However, it is a major pollutant of indoor air due to its multiple sources (materials, combustion, painting, etc.) 3 and also is one of the most widespread volatile organic compounds (VOCs) 4. The World Health Organization (WHO) has set a very strict 30 min exposure limit of only 0.08 ppm 5. More important, FA is a carcinogen due to induce intra- and intermolecular cross-linkage between proteins and between proteins and DNA 6. FA is also naturally occurring in human cells and different organisms. The concentration of endogenous FA in human blood is about 2–3 mg/L; similar results were also found in the blood of monkeys and rats 5. But abnormal level of FA is associated with many types of diseases including Alzheimer’s disease, cognitive impairment, neurodegenerative diseases, atherosclerosis 7. For the above reasons, more and more chemists and environmentalists are concerned about detection of FA. In recent years, a serious of


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physical or chemical procedure were used to recognition and detection FA, such as HPLC 8, GC 9

, fluroimetry

10

, calorimetric methods

11

, laser-induced fluorescence spectroscopy (LIFS)

12

,

enzymatic methods 13, kinetic measurement 14, and so on, However, the instrument detection method is more expensive and requires a higher degree of professionalism. For chemical procedure of detection for FA almost is based on small molecule sensors, however, there were some limitations in these ways of detection for FA, such as low sensitivity, long response time, complicated operation, and so on. Therefore, it is very important to develop a simple and effective FA detection method. Aggregation-induced emission (AIE) was defined as another photophysical phenomenon associated with chromophore aggregation 15a. It is a luminescent phenomenon that a molecule or fragment exhibits enhanced luminescence property in the aggregated state, as a result of restriction of intramolecular rotations, vibrations or motions

15b

. Recently, chemosensors based

on aggregation-induced emission (AIE) have generated great interest due to their unique photophysical properties

15

. Moreover, pillar[n]arenes–based chemosensors also attracted

considerable attention since pillar[n]arenes were firstly reported by Ogoshi in 2008.

16

In

addition, pillar[n]arenes have various supramolecular assembly driving forces including C-H···π, π···π, cation···π, hydrophobic/hydrophilic, etc.16,

17

These properties not only afforded

pillar[n]arenes outstanding abilities to selectively bind different kinds of guests,

18

but also

provided a novel platform for the construction of various interesting supramolecular systems 19-23

17,

as well as AIE-based chemosensors. However, to the best of our knowledge, there is no

report on pillar[n]arenes-based chemosensors for detection FA through AIE mechanism. In view of these and as a part of our research interests in molecular recognition,

24-29

herein,

we report a novel catalyst pre-placed FA sensor based on bis-thioacetylhydrazine functionalized


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pillar[5]arene. Our strategies are as follows: firstly, hydrazide groups were introduced as FA reaction recognition site as well as hydrogen bonding self-assembly site; secondly, pillar[5]arene group was employed as π···π stacking site and AIE fluorogen; finally, in order to improve recognition efficiency, after carefully screening, (CF3SO3)2Bi was used as a pre-placed catalyst. Interestingly, as we expected, the catalyst ((CF3SO3)2Bi, 0.01 equiv.) pre-placed DP5J sensor (DP5J-Bi) shows ultrasensitive recognition for FA through an AIE “turn-on” response within 7.5 second and the detection limits (LOD) for FA is 3.27×10-9 M. EXPERIMENTAL SECTION Materials. formaldehyde, 1,4-dimethoxybenzene, boron trifluoride ethyl ether and 1,4dibromobutane were reagent grade and used as received. Solvents were either employed as purchased or dried by CaCl2. Fresh double distilled water was used throughout the experiment. Nuclear magnetic resonance (NMR) spectra were recorded on Varian Mercury 400 and Varian Inova 600 instruments. Mass spectra were recorded on a Bruker Esquire 6000 MS instrument. The infrared spectra were performed on a Digilab FTS-3000 Fourier transform-infrared spectrophotometer. Melting points were measured on an X-4 digital melting-point apparatus (uncorrected).

Fluorescence

spectra

were

recorded

on

a

Shimadzu

RF-5301PC

spectrofluorophotometer.


4

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Scheme 1 Syntheses of DP5J. Synthesis of the DP5J. As shown in Scheme 1 and Scheme S1, the preparation of DP5J was presented in our previous papers.19a Hydrazine hydrate (0.1591 g, 3 mmol, 80 %) was added to a solution of the DPSE (0.5355 g, 0.5 mmol) in alcohol (30 mL). The mixture was heated in a round-bottomed flask at 80 °C for 18 h. The solvent was removed and the residue was recrystallized in acetone and petroleum ethers. The product DP5J was collected by filtration, and dried under vacuum (0.4915 g, 96.75 %). M.P.: 125 °C. 1H NMR (600 MHz, DCCl3, room temperature) δ (ppm): 7.63 (s, 2 H), 6.77 (m, 10 H), 3.71 (m, 42H), 3.05 (s, 4H), 2.42 (t, J=6.6Hz, 4H), 1.73 (m, 8H). ESI-MS m/z: [M]+ Calcd C55H70N4O12S2 1043.30, found 1043.28 (Figure S6 and S7). General Experimental Procedures: 1

H NMR titration. The DP5J (10 mg, 9.58×10-6 mol) was dissolved in the DMSO-d6 (0.5 ml),

then a series of different equivalents of formaldehyde (i.e. 0.5 equiv., 1.0 equiv., 1.5 equiv.) were added into the solution of DP5J and recorded their 1H NMR respectively.


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Fluorescence titration. A serious of the DP5J-Bi with different equivalents (from 0 equiv. to 39 equiv.) of formaldehyde were prepared by dissolve DP5J-Bi (5 mg) and proper equivalent of formaldehyde in DMF (2 mL). Then record their fluorescence intensity at 450 nm. Calculation formula of LOD. Linear Equation: y=Ax + B =

N = 20 ,

S=A106, LOD = K K = 3

State, Fi: the fluorescence intensity of DP5J-Bi with different concentration formaldehyde at λex= 450 nm; F0: the average of 20 times fluorescence intensity of DP5J-Bi with different concentration formaldehyde at λex= 450 nm; A: Slope of linear fitting of fluorescence titration; B: intercept of linear fitting of fluorescence titration. Preparation of the Catalyst (CF3SO3)2Bi Pre-placed DP5J Sensor (DP5J-Bi). A solution of (CF3SO3)2Bi (2 µL, 0.1 M) was added into the solution of DP5J (2mL, 1×10-2 M) in DMF, the mixture was stirred about 2 min at room temperature to give the catalyst (CF3SO3)2Bi preplaced DP5J sensor (DP5J-Bi) as a colorless liquid. Preparation of the FA Test Kits. The FA test kits were prepared by loading the catalyst (CF3SO3)2Bi pre-placed DP5J sensor (DP5J-Bi) on a silica gel plate (i.e. the silica gel plate was


6

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soaked in the solution of the catalyst (CF3SO3)2Bi pre-placed DP5J sensor (DP5J-Bi) about 1 min), then, drying in the air and obtained the FA test kits. Procedure for the DP5J-Bi sensing of formaldehyde solution. With the addition of the solution of formaldehyde (30 equiv.) into the solution of DP5J-Bi (1×10-2 M, 2 mL) in DMF, a strong blue fluorescence was observed for FA test kit under the radiation of a UV light at 365 nm. This fluorescence changing could be distinguished by naked-eyes through UV lamp. Procedure for the DP5J-Bi sensing of formaldehyde gas. When the FA test kit was put into the container which contained saturated formaldehyde vapor about 2 min, a strong blue fluorescence was observed for FA test kit under the radiation of a UV light at 365 nm. This fluorescence changing also could be distinguished by naked-eyes through UV lamp. RESULTS AND DISCUSSION A bis-thioacetylhydrazine functionalized pillar[5]arene derivative (DP5J) was synthesized by rationally connecting a pillar[5]arene moiety and the thioacetylhydrazine groups (Scheme 1). The recognition properties of compound DP5J was investigated by adding various aldehydes including benzaldehyde, salicylaldehyde, p-fluorobenzaldehyde, m-bromobenzaldehyde, pchlorobenzaldehyde,

p-bromobenzaldehyde,

n-caprylaldehyde,

p-tolualdehyde,

m-chloro-

benzaldehyde, o-bromobenzaldehyde, m-fluorobenzaldehyde, glutaraldehyde and FA into the DMF solution of DP5J, respectively and measuring the fluorescence emission spectrum. As shown in the Figure 1a and Figure S8, when 30 equiv. of FA was added into the solution of DP5J in DMF, dramatic fluorescence enhance was observed at λem = 450 nm, the apparent fluorescence emission color change from indiscernible to blue could be distinguished by nakedeyes under the irradiation of UV lamp at 365 nm. Meanwhile, other aldehydes couldn’t induce


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similar response. Therefore, DP5J can selectively recognize FA, however, the recognition reaction time of DP5J for FA exceeds 30 s (Figure S9).

Figure 1. (a) Fluorescence spectrum of DP5J-Bi in DMF with various aldehydes (30 equiv.) (1. Free DP5J, 2. benzaldehyde, 3. salicylaldehyde, 4. p-fluorobenzaldehyde, 5. m-bromobenzaldehyde, 6. p-chlorobenzaldehyde, 7. p-bromobenzaldehyde, 8. n-caprylaldehyde, 9. ptolualdehyde, 10. m-chlorobenzaldehyde, 11. o-bromobenzaldehyde, 12. m-fluoro-benzaldehyde, 13. glutaraldehyde, 14. FA). (b) Fluorescence photos of DP5J-Bi and DP5J-Bi+FA in DMF; (c) The Photos showing the Tyndall effect of DP5J-Bi and DP5J-Bi+FA. (d) Fluorescence color change (under the UV lamp, at λex = 365 nm) of silica gel plate treated by DP5J-Bi after addition different concentration FA (from 0 M to 1×10-9 M). In order to overcome the problem of long response time of DP5J for FA, we rationally introduce catalysts into the recognition system of DP5J for FA. As we all known, metal triflates are superior catalysts for imine-linked compound formation 31, therefore, we screened a series of metal triflates including ((CF3SO3)2Fe, (CF3SO3)3Sc, (CF3SO3)2Bi, (CF3SO3)2Cu and (CF3SO3)3Y) as catalysts (0.01 equiv.) to improve FA recognition efficiency. As a result, as


8

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shown in Figure 2 and Figure S10, the (CF3SO3)2Bi shows the best catalyzing effect for the FA recognition process not only in solution but also in gas (Figure S11). Meanwhile, as shown in Figure S9b, by the catalyzing of (CF3SO3)2Bi, the FA sensing process only need 7.5 s, which is faster than most reported FA sensors (Table 1).

Figure 2. Change in the emission spectrum of catalysts pre-placed DP5J (1×10-2 M) upon the addition of FA (30 equiv.) in DMF. As we all know that the selectivity and sensitivity are important features for chemosensors. Therefore, we carefully investigated the FA specific selectivity of catalyst ((CF3SO3)2Bi, 0.01 equiv.) pre-placed DP5J sensor (DP5J-Bi) over other competitive species by competitive experiments (Figure 3a and 3b). The results showed that the miscellaneous competitive aldehydes

including

bromobenzaldehyde, tolualdehyde,

benzaldehyde,

salicylaldehyde,

p-chlorobenzaldehyde,

m-chloro-benzaldehyde,

p-fluorobenzaldehyde,

p-bromobenzaldehyde,

o-bromobenzaldehyde,

n-caprylaldehyde,

m-fluorobenzaldehyde

mpand

glutaraldehyde did not lead to any significant interference in the FA sensing process. The selectivity of DP5J-Bi for FA should be attributed to the difference between FA and substituted aldehydes. For substituted aldehydes, due to the coulombic or conjugation interactions of formyl


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group with substituent group, the reactivity of substituted aldehydes with amine is lower than the reactivity of FA, thereby the DP5J shows special selectivity for FA (Figure 3a and 3b).

Figure 3. (a) The photographs of fluorescence changes for DB5J-Bi with FA and co-existing various other aldehydes (39 equiv.) in DMF; (b) Change in the emission spectrum of DP5J-Bi (1×10-2 M) in the presence of FA and co-existing various other aldehydes (39 equiv.) in DMF. (1. Free DP5J-Bi; other co-existing aldehydes: 2. benzaldehyde, 3. salicylaldehyde, 4. pfluorobenzaldehyde,

5.

m-bromobenzaldehyde,

6.

p-chlorobenzaldehyde,

7.

p-bromo-

benzaldehyde, 8. n-caprylaldehyde, 9. p-tolualdehyde, 10. m-chlorobenzaldehyde, 11. obromobenzaldehyde, 12. m-fluoro-benzaldehyde, 13. glutaraldehyde, 14. FA). In addition, in order to evaluate the FA detection sensitivity of the DP5J-Bi, a fluorescence titration experiment was carried out at room temperature. As shown in Figure S12, the increasing concentrations of FA resulted in a gradual increase of the emission intensity at 450 nm (Figure S12). Strikingly, an excellent linear dependence (R2 = 0.98921) the concentrations of FA was observed. Meanwhile, the lowest fluorescent response concentration (LOD) of the DP5J-Bi for FA was determined by fluorescent titrations and calculated on the basis of 3σ/m method

32

was

3.27×10-9 M (Figure S12 and S13), which indicated the DP5J-Bi has ultrasensitivity for FA and


10

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more sensitive than most reported sensors (Table 1). Table 1. Comparison of the LOD and response time of sensor for FA with previously reported FA sensors.

Refs.

Journal and Year. Volume. Page

Response Time

LOD (M)

[4b]

Angew. Chem. Int. Ed. 2016, 55, 3356.

30 min

7.1×10-7

[30]

Anal. Chem. 2017, 89, 9360

-

1×10-4

[29]

Sens. Actuators B. 2013, 177, 370.

39 s

5×10-6

[4a]

Sens. Actuators B. 2018, 256, 1011.

46 s

6.67×10-7

[10b]

Chem. Commun. 2016, 52, 9582.

-

7.7×10-7

[33]

Anal. Chim. Acta. 2011, 683, 212

20 min

(0.17-1)×10-8

[10c]

Chem. Commun. 2017, 53, 6520.

-

3×10-6

[34]

J. Mater. Sci. Technol. 2015, 31, 913.

24 s

3.3×10-8

[4c]

Chem. Commun. 2016, 52, 11247.

-

7.8×10-7

[35]

Analyst, 2016,141, 3395.

-

2×10-7

[37]

ACS Appl. Mater. Interfaces. 2016, 8, 14318

-

1.2×10-6

[38]

ACS Appl. Mater. Interfaces. 2016, 8, 31764

Ultrasensitive Detection of Formaldehyde in Gas and Solutions by a

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