Preparation of a Palygorskite-Supported Sensor and Its Application in Fluorescent Detection of Copper Ions, Iron Ions and Nitrite

Abstract

The present invention discloses the preparation of a palygorskite-supported sensor and its application in the fluorescence detection of copper ions, iron ions and nitrite. In the present invention, palygorskite and a fluorescent group are combined to form a supported fluorescence sensor. This palygorskite combines fluorescence and environmental protection for the detection of metal ions and nitrite. The palygorskite with fluorescence provides special applicability that cannot be achieved by traditional fluorescence sensors. The sensor causes fluorescence quenching after binding with Cu 2+ , Fe 3+ , which is manifested as "OFF" in the spectral change; after binding with the anion NO2 ‑ , it causes fluorescence quenching, which is manifested as "OFF" in the spectrum. It has high sensitivity and selectivity, can shorten the detection time and simplify the detection process. Therefore, the palygorskite-supported sensor PGS-APTES-TB has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion detection, and relates to a preparation method of a palygorskite-supported sensor capable of fluorescently detecting Cu 2+ , Fe 3+ and nitrite; the present invention also relates to the specific application of the sensor in fluorescently detecting Cu 2+ , Fe 3+ and nitrite. Background Art

[0002] As one of the inorganic pollutants, heavy metals have caused serious environmental pollution due to their non-degradable characteristics in organisms and potential carcinogenicity. Nowadays, with the rapid increase of global industrial activities, the heavy metal pollution in water bodies is becoming more and more serious. At present, researchers use instrument equipment to detect and remove pollutant ions in water, such as gas chromatographs and atomic absorption spectrophotometers. However, most of these instruments have disadvantages such as high equipment cost, cumbersome processes and high technical requirements. Therefore, at present, researchers are committed to developing an efficient and simple method for detecting ions.

[0003] Nitrite (NO2 − ) is a widely used color fixative and additive in meat products, and NO2 − is also produced by multi-leaf fruits and vegetables. However, excessive NO2 − is harmful to human health. Ingesting NO2 − above a certain concentration can cause leukemia, a disease in which the body's oxygen transport system is damaged, and is known to be particularly harmful to pregnant women and infants.

[0004] At present, optical detection has become an important research field because of its simple operation, simple technology, low cost, high selectivity, fast process, high sensitivity, intuitive and direct, and high application value in biochemical and chemical research. In this regard, with the development of nanotechnology, the application of fluorescent chemical sensors in biology, chemistry, environment, etc. is of great significance for the sensing of transition states and heavy metal ions. In addition, the use of chemical sensors and sensitive fluorophores to study trace heavy metal ions is of great significance for environmental and biological applications. However, most fluorescent chemical sensors are organic substances, which have certain pollution and limitations for the detection of ionic aqueous solutions.

[0005] Palygorskite (PGS) is a hydrated magnesium aluminum silicate with special fibrous morphology, large specific surface area and unique porous structure. Its 2:1 layered structure includes an octahedral layer and two silicon-oxygen tetrahedral layers. Due to the high specific surface area and micropore volume of palygorskite being conducive to the dispersion of metal oxide particles, palygorskite is considered a promising clay mineral loaded with metal oxides. However, natural palygorskite also has certain limitations, such as limited adsorption capacity, small metal binding constant, low selectivity, etc. Therefore, the present invention designs a kind of supported fluorescent sensor formed by combining palygorskite and fluorescent groups. This palygorskite combines fluorescence and environmental protection for the detection of metal ions and nitrite. The palygorskite with fluorescence provides special applicability that cannot be achieved by traditional fluorescent sensors. The palygorskite-supported sensor of the present invention has important application prospects for the fluorescent detection of metal ions and nitrite. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method of a sensor capable of fluorescently detecting Cu 2+ , Fe 3+ and nitrite;

[0007] Another object of the present invention is to provide the specific application of the above sensor for fluorescently detecting Cu 2+ , Fe 3+ and nitrite.

[0008] I. Preparation of Palygorskite-Supported Sensor

[0009] (1) Using water as a solvent, 4-bromobenzaldehyde and 4-methoxyphenylboronic acid as substrates, sodium bicarbonate as an acid-binding agent, and triphenylphosphine as a catalyst, react at 20°C - 30°C for 6 - 10 hours. After the reaction is completed, extract the reaction solution with ethyl acetate, evaporate the solvent, and elute with petroleum ether - ethyl acetate (the volume ratio of petroleum ether to ethyl acetate is 5:1 - 4:1) to obtain the product p-methoxybiphenylcarboxaldehyde (TB). (The mass spectrum of TB is shown in Figure 1 ).

[0010] Among them, the molar ratio of 4-bromobenzaldehyde to 4-methoxyphenylboronic acid is 1:1 - 1:2; the molar ratio of sodium bicarbonate to 4-bromobenzaldehyde is 1:1 - 1:2; the molar ratio of triphenylphosphine to 4-bromobenzaldehyde is 1:10 - 1:20.

[0011] (2) Add palygorskite (PGS) and the silane coupling agent 3-aminopropyltriethoxysilane (APTES) to toluene, reflux at 90°C - 100°C for 10 - 12 hours, cool, filter by suction, wash, and obtain the PGS-APTES solid. The infrared spectrum of PGS-APTES is shown in Figure 2 . Among them, the mass ratio of palygorskite to 3-aminopropyltriethoxysilane is 1:1 - 1:2.

[0012] (3) Using PGS-APTES and p-methoxybenzaldehyde as raw materials, p-toluenesulfonic acid as a catalyst, and ethanol as a solvent, reflux reaction was carried out at 70 °C - 80 °C for 20 - 24 hours. After the reaction, it was allowed to stand and cool to room temperature, filtered by suction, washed with dichloromethane and ethanol, and dried to obtain a pale yellow solid product, palygorskite-supported sensor (PGS-APTES-TB). The infrared spectrum of PGS-APTES-TB is shown in Figure 2 .

[0013] Among them, the mass ratio of PGS-APTES to p-methoxybenzaldehyde is 1:1 - 1:2; the mass ratio of p-toluenesulfonic acid to PGS-APTES is 1:3 - 1:4.

[0014] The structural formula of the palygorskite-supported sensor molecule PGS-APTES-TB is:

[0015]

[0016] II. Structure of the sensor molecule PGS-APTES-TB

[0017] Through the infrared spectrum (FT-IR), to explore whether small molecule organic compounds were successfully grafted onto palygorskite. First, from Figure 2 the infrared spectrum of PGS, it can be seen that the stretching vibration of the -OH group appears at 3623 cm -1 , 3551 cm -1 . The infrared absorption peaks of the stretching vibration and bending vibration of water adsorbed by PGS appear at 3419 cm -1 and 1647 cm -1 . The bending vibration absorption peak of Si-O and the stretching vibration absorption peak of Si-O-Si in PGS appear at 1025 cm -1 and 464 cm -1 respectively. Comparing PGS-APTES with PGS, the results show that PGS-APTES has a weak -N-H bending vibration absorption peak at 1557 cm -1 , and an asymmetric stretching vibration absorption peak of -C-H appears at 2936 cm -1 . The change in the absorption peak values of the above infrared spectra indicates that APTES was successfully grafted onto the surface of PGS. Comparing the infrared spectra of PGS-APTES and PGS-APTES-TB in the figure, the results show that the target product PGS-APTES-TB not only contains the absorption vibration peaks of the above PGS-APTES, but also a stretching vibration peak of -C-N appears at 1396 cm -1 . This indicates that the organic fluorescent group biphenylaldehyde was also successfully grafted onto PGS.

[0018] To further confirm the above conclusion, scanning electron microscopy was also used to observe the morphological changes. Figure 9 In, a represents the scanning electron micrograph of PGS; b represents the scanning electron micrograph of PGS-APTES; c is the scanning electron micrograph of PGS-APTES-TB. By comparison, it can be clearly found that PGS is a smooth rod-like structure. After grafting APTES, the surface becomes slightly rough. Finally, on the surface of the product PGS-APTES-TB, certain granular objects can be clearly observed on the surface of PGS. This further verifies the successful grafting of the organic fluorescent group TB onto PGS.

[0019] III. Fluorescent Detection of Cu 2+ ,Fe 3+ by Palygorskite-Supported Sensors

[0020] Dissolve the PGS-APTES-TB sensor molecule in ethanol to form a homogeneous suspension with a mass-volume ratio of 50 - 100 mg / mL; Transfer the suspension to a series of quartz cuvettes, and add aqueous solutions of various metal ions (Ca 2+ ,Cu 2 + ,Fe 3+ ,Cr 3+ ,Sr 2+ ,Ba 2+ ,Co 2+ ,Hg 2+ ,Bi 2+ ,Zn 2+ ,Mg 2+ ,Al 3+ ,La 3+ ,Pb 2+ ) with a concentration of 1 M. It was observed that only the addition of Cu 2 + ,Fe 3+ could cause quenching of the fluorescence emission performance of the sensor PGS-APTES-TB (selective detection of Cu 2+ ,Fe 3+ fluorescence diagram is shown in Figure 3 ), while other cations could not produce similar fluorescence performance quenching changes. Therefore, the sensor PGS-APTES-TB can achieve selective response to Cu 2+ ,Fe 3+ .

[0021] IV. Application of Palygorskite-Supported Sensors in Fluorescent Detection of Nitrite

[0022] Transfer the PGS-APTES-TB suspension to a series of quartz cuvettes, and add various anions (H2PO4 -, NO2 - , HCO3 - , ClO3 - , F - , SCN - , CO3 2- , S2O3 2- ) aqueous solution. It was observed that only the addition of NO2 - could cause quenching of the fluorescence emission performance of the sensor PGS - APTES - TB (selective detection of NO2 - Fluorescence diagram is shown in Figure 4 ), while other anions could not produce similar quenching changes in fluorescence performance. Therefore, the sensor PGS - APTES - TB can achieve selective response to NO2 - .

[0023] V. Determination of the lowest detection limit

[0024] To study the lowest detection limit (LOD) of the multi - channel palygorskite - supported sensor PGS - APTES - TB for Cu 2+ , Fe 3+ and NO2 - , fluorescence titration experiments of PGS - APTES - TB for Cu 2+ , Fe 3+ and NO2 - were carried out. First, the lowest detection limit (LOD) of the ethanol suspension of PGS - APTES - TB for the aqueous solution of Cu 2+ (1 M) was determined and the data were linearly fitted (The diagram of the lowest detection limit determination of Cu 2+ is shown in Figure 5 , and the linear fitting of the lowest detection limit of Cu 2+ is shown in Figure 6 ). It was calculated that the LOD of PGS - APTES - TB for Cu 2+ was 1.9×10 -8 M. By the same method, the LOD of Fe 3+ was 2.1×10 -8 M (The diagram of the lowest detection limit determination of Fe 3+ is shown in Figure 5 , and the linear fitting of the lowest detection limit of Fe 3+ is shown in Figure 6 ). By the same method, the LOD of NO2 - was 3.2×10 -8 M. (The diagram of the lowest detection limit determination of NO2 - is shown in Figure 7 , and the linear fitting of the lowest detection limit of NO2 - is shown in Figure 8 ).

[0025] VI. Detection mechanism analysis

[0026] To explore the recognition mechanism of the fluorescent chemical sensor PGS-APTES-TB for various metal ions, detailed electronic configuration analysis of PGS-APTES-TB and PGS-APTES-TB after adding cations was carried out by X-ray photoelectron spectroscopy (XPS), as Figure 10 shown: After adding Cu 2+ to the EtOH solution of PGS-APTES-TB, a new Cu 2+ peak appeared in the full spectrum ( Figure 10 a), and in Figure 10 b and Figure 10 d, it was shown that the binding energy of -NH-NH- in PGS-APTES-TB shifted from 399.76 eV to 400.06 eV, and the binding energy of -C-O in PGS-APTES-TB shifted from 399.04 eV to 399.29 eV. This indicates that the addition of Cu 2+ changed the coordination relationship between N atoms. Figure 10 There are two strong binding energy peaks in 2p3 / 2 c, which are 935.3 eV and 955.0 eV respectively. These are the characteristic signal peaks of Cu 2p1 / 2 and Cu Figure 11 Figure 11 3+ 3+ 3+ 2p3 / 2 Figure 11 a), and in Figure 11 b and Figure 11 d, it was shown that the binding energy of -NH-NH- in PGS-APTES-TB shifted from 399.76 eV to 400.48 eV, and the binding energy of -C-O in PGS-APTES-TB shifted from 532.04 eV to 532.39 eV. This indicates that the addition of Fe 3+ may lead to a shift of electrons due to the coordination relationship with N atoms. Figure 11 There are two strong binding energy peaks in 2p3 / 2 c, which are 711.9 eV and 725 eV respectively. These are the characteristic signal peaks of Fe 2p1 / 2 and Fe

[0027] Figure 12 Figure 12 ), it can be seen that at 2θ = 26.7 °There is a diffraction peak at this position, which indicates that there are π-π stacking interaction forces between PGS-APTES-TB molecules. When Cu 2+ and Fe 3+ are added to PGS-APTES-TB, the position of the diffraction peak of PGS-APTES-TB does not change, which indicates that the addition of Cu 2+ and Fe 3+ does not destroy the π-π stacking interaction forces between molecules.

[0028] Transmission electron microscopy was also used to observe the changes after adding Cu 2+ and Fe 3+ to PGS-APTES-TB ( Figure 13 ). Among them, Figure 13 (a) is PGS-APTES-TB, Figure 13 (b) is PGS-APTES-TB with Cu 2+ and Figure 13 (c) is PGS-APTES-TB with Fe 3+ . After the addition of metal cations, they will adhere to the surface of PGS-APTES-TB, changing the transmission electron microscopy image of PGS-APTES-TB. Because after the addition of metal cations, the cations will coordinate with the fluorescent groups on the surface of PGS, causing the metal ions to adhere to the surface of PGS-APTES-TB. To sum up, the addition of Cu 2+ and Fe 3+ causes fluorescence quenching of the fluorescent chemical sensor PGS-APTES-TB. This is because Cu 2+ and Fe 3+ coordinate with the fluorescent luminescent group TB on PGS, destroying the hydrogen bond forces on TB.

[0029] To sum up, the present invention designs and synthesizes a palygorskite-supported sensor capable of fluorescently detecting Cu 2+ and Fe 3+ and nitrite. In this sensor, biphenyl acts as a rigid structure, causing the host to emit strong fluorescence. The combination of this sensor with Cu 2+ and Fe 3+ causes fluorescence quenching, which is manifested as "OFF" in the spectral change; with the anion NO2 -Combination causes fluorescence quenching, which is manifested as "OFF" in the spectrum. It has high sensitivity and selectivity, can shorten the detection time and simplify the detection process. Therefore, the palygorskite-supported sensor PGS-APTES-TB has good application prospects and makes a certain contribution to the research and development of environmentally friendly materials. The raw materials of the present invention are cheap and easily available, with low cost; the process is simple, the reaction conditions are mild, and the energy consumption is low; the product has a high yield and good detection performance; it has high sensitivity, good selectivity, and is easy to recycle multiple times, being green and environmentally friendly. Brief Description of the Drawings

[0030] Figure 1 is the mass spectrum of the fluorophore of the sensor PGS-APTES-TB of the present invention;

[0031] Figure 2 is the infrared spectrum of the sensor PGS-APTES-TB of the present invention;

[0032] Figure 3 is the fluorescence performance graph of the sensor PGS-APTES-TB of the present invention for selectively detecting cations;

[0033] Figure 4 is the fluorescence performance graph of the sensor PGS-APTES-TB of the present invention for selectively detecting anions;

[0034] Figure 5 is for the sensor PGS-APTES-TB of the present invention to detect Cu 2+ , Fe 3+ fluorescence titration graph;

[0035] Figure 6 is for the sensor PGS-APTES-TB of the present invention to detect Cu 2+ , Fe 3+ linear fitting graph

[0036] Figure 7 is for the sensor PGS-APTES-TB of the present invention to detect NO2 − fluorescence titration graph;

[0037] Figure 8 is for the sensor PGS-APTES-TB of the present invention to detect NO2 − linear fitting graph;

[0038] Figure 9 is the scanning electron microscope comparison graph of the sensor PGS-APTES-TB of the present invention;

[0039] Figure 10 is for the sensor PGS-APTES-TB of the present invention to detect Cu 2+ X-ray photoelectron spectroscopy graph;

[0040] Figure 11 is for the sensor PGS-APTES-TB of the present invention to detect Fe 3+X-ray photoelectron spectroscopy diagram;

[0041] Figure 12 shows the X-ray diffraction spectrum of the Cu 2+ , Fe 3+ detected by the sensor PGS-APTES-TB of the present invention;

[0042] Figure 13 is a transmission electron microscope comparison diagram of the sensor PGS-APTES-TB of the present invention. Detailed implementation manners

[0043] The preparation of the palygorskite-supported sensor and the application of fluorescence detection of Cu 2+ , Fe 3+ and nitrite of the present invention will be further described below through specific examples.

[0044] Example 1. Preparation of the palygorskite-supported sensor molecule PGS-APTES-TB

[0045] (1) 4-bromobenzaldehyde (0.15 mmol), 4-methoxyphenylboronic acid (0.15 mmol), NaHCO3 (0.15 mmol), H2O (3 mL) and a catalytic amount of triphenylphosphine (0.015 mmol) were respectively added into a reaction tube. After stirring the mixture at room temperature for 6 hours, the reaction solution was extracted with ethyl acetate, and finally the product TB was separated by a chromatographic column (petroleum ether:ethyl acetate = 5:1) (the mass spectrum is shown in Figure 1).

[0046] (2) PGS (2 g), APTES (2 g) and toluene (150 mL) were added into a 250 mL round-bottom flask and refluxed at 100 °C for 12 h. Then, it was slightly cooled and filtered by suction, and then washed with water 3 times to obtain the PGS-APTES solid.

[0047] (3) PGS-APTES (1 g), TB (1 g), p-toluenesulfonic acid (0.3 g) and 50 mL of ethanol were respectively added into a 100 mL round-bottom flask, and the mixture was refluxed at 80 °C for 24 h. After the reaction was completed, it was allowed to stand and cool to room temperature, then filtered by suction, and washed with dichloromethane and ethanol 3 times. Finally, it was dried to obtain a pale yellow solid PGS-APTES-TB (the infrared spectrum is shown in Figure 2), and the yield was 80%.

[0048] Example 2. Application of the palygorskite-supported sensor for fluorescence detection of Cu 2+ , Fe 3+ application

[0049] Add the compound PGS-APTES-TB into small reagent bottles in units of 10 mg, then add 0.2 mL of EtOH into the small reagent bottles, stir to form a stable and uniform suspension, transfer the suspension into a series of quartz cuvettes, and add aqueous solutions of various metal ions (Ca 2+ , Cu 2+ , Fe 3+ , Cr 3+ , Sr 2+ , Ba 2+ , Co 2+ , Hg 2+ , Bi 2+ , Zn 2+ , Mg 2+ , Al 3+ , La 3+ , Pb 2+ ) with a concentration of 1 M, and observe the fluorescence under a 365 nm ultraviolet lamp. If the fluorescence of the suspension is quenched, it indicates that the added one is Cu 2+ , Fe 3+ . If the fluorescence of the suspension is not quenched, it indicates that the added one is not Cu 2+ , Fe 3+ .

[0050] Example 3 Application of Palygorskite-Supported Sensor for Fluorescent Detection of NO2 -

[0051] Transfer the suspension into a series of quartz cuvettes, and add aqueous solutions of various anions (H2PO4 - , NO2 - , HCO3 - , ClO3 - , F - , SCN - , CO3 2- , S2O3 2- ) with a concentration of 1 M, and observe the fluorescence under a 365 nm ultraviolet lamp. If the fluorescence of the suspension is quenched, it indicates that the added one is NO2 - . If the fluorescence of the suspension is not quenched, it indicates that the added one is not NO2 - .

Claims

1. A preparation method of a palygorskite-supported sensor, comprising the following steps: (1) Using water as a solvent, 4-bromobenzaldehyde and 4-methoxyphenylboronic acid as substrates, sodium bicarbonate as an acid-binding agent, and triphenylphosphine as a catalyst, reacting at 20°C - 30°C for 6 - 10 hours. After the reaction, extract the reaction solution with ethyl acetate, evaporate the solvent, and elute with petroleum ether - ethyl acetate to obtain the product p-methoxybiphenylcarboxaldehyde; (2) Add palygorskite and 3-aminopropyltriethoxysilane to toluene, reflux and react at 90°C - 100°C for 10 - 12 hours, cool, filter by suction, wash to obtain the PGS-APTES solid; (3) Using PGS-APTES and p-methoxybiphenylcarboxaldehyde as raw materials, p-toluenesulfonic acid as a catalyst, and ethanol as a solvent, reflux and react at 70°C - 80°C for 20 - 24 hours. After the reaction, let it stand and cool to room temperature, filter by suction, wash with dichloromethane and ethanol, and dry to obtain the pale yellow solid product palygorskite-supported sensor PGS-APTES-TB.

2. The preparation method of the palygorskite-supported sensor according to claim 1, characterized in that: In step (1), the molar ratio of 4-bromobenzaldehyde to 4-methoxyphenylboronic acid is 1:1 - 1:

2.

3. The preparation method of the palygorskite-supported sensor according to claim 1, characterized in that: In step (1), the molar ratio of sodium bicarbonate to 4-bromobenzaldehyde is 1:1 - 1:2; the molar ratio of triphenylphosphine to 4-bromobenzaldehyde is 1:10 - 1:

20.

4. The preparation method of the palygorskite-supported sensor according to claim 1, characterized in that: In step (2), the mass ratio of palygorskite to 3-aminopropyltriethoxysilane is 1:1 - 1:

2.

5. The preparation method of the palygorskite-supported sensor according to claim 1, wherein: In step (3), the mass ratio of PGS-APTES to p-methoxybiphenylcarboxaldehyde is 1:1 - 1:

2.

6. The preparation method of the palygorskite-supported sensor according to claim 1, wherein: In step (3), the mass ratio of p-toluenesulfonic acid to PGS-APTES is 1:3 - 1:

4.

7. Application of the palygorskite-supported sensor prepared by the method according to claim 1 in fluorescence detection of Cu 2+ , Fe 3+ .

8. The application according to claim 7, wherein: Ca was added to the ethanol suspension of the palygorskite-supported sensor 2+ , Cu 2+ , Fe 3+ , Cr 3+ , Sr 2+ , Ba 2+ , Co 2+ , Hg 2+ , Bi 2+ , Zn 2+ , Mg 2+ , Al 3+ , La 3+ , Pb 2+ . Only Cu 2+ , Fe 3+ can quench the fluorescence of the suspension.

9. The application of the palygorskite-supported sensor prepared by the method according to claim 1 in the fluorescence detection of nitrite.

10. The application according to claim 9, wherein: Add H2PO4 to the ethanol suspension of the palygorskite-supported sensor - , NO2 - , HCO3 - , ClO3 - , F - , SCN - , CO3 2- , S2O3 2- aqueous solutions. Only NO2 - can quench the fluorescence of the suspension.

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