Conjugated microporous polymer material for detecting heavy metal iron in drinking water as well as synthesis method and application of conjugated microporous polymer material

Abstract

The invention discloses a conjugated microporous polymer material for detecting heavy metal iron in drinking water as well as a synthesis method and application thereof, the conjugated microporous polymer material for detecting heavy metal iron in drinking water is synthesized from terephthalic dihydrazide and 2, 5-dimethoxy terephthalaldehyde through a solvothermal reaction method, and during synthesis, the terephthalic dihydrazide and the 2, 5-dimethoxy terephthalaldehyde are subjected to a solvothermal reaction to obtain the conjugated microporous polymer material for detecting heavy metal iron in drinking water. The mass ratio of 2, 5-dimethoxy terephthalaldehyde is (2: 5) to (5: 2).

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food safety detection and new materials, and particularly relates to a conjugated microporous polymer (CMP) material for detecting heavy metal iron in drinking water and a synthesis method and application thereof. BACKGROUND

[0002] Fe 3+ is not only a trace element essential to the human body, but also can cause health problems such as liver damage and cardiovascular disease when taken in excess. As a common water pollutant, it may affect the safety of drinking water. Therefore, the detection of Fe 3+ in drinking water is of great significance in the field of environmental monitoring and public health. Currently, Fe 3+ in drinking water mainly comes from natural dissolution of iron-containing minerals (such as hematite and pyrite oxidation under acidic or low oxygen conditions) and soil infiltration, as well as industrial wastewater discharge, pipeline corrosion, iron-based coagulant residues, agricultural runoff, etc. According to the Standards for Drinking Water Health (GB 5749-2022) of China, the concentration of Fe 3+ in drinking water should not exceed 0.3 mg / L. Existing detection methods mostly use atomic fluorescence spectrometry, atomic absorption spectrometry and X-ray fluorescence spectrometry to determine metal content, but these methods are mostly time-consuming, costly and require skilled operators, which limits their application in routine analysis. In recent years, fluorescence sensing technology has become a research hotspot due to its high sensitivity, fast response and easy operation. Therefore, it is extremely important to explore new functional nanomaterials that can selectively and fluorescently detect Fe 3+ in drinking water.

[0003] Conjugated microporous polymers (CMPs) are a class of porous organic materials with extended π-conjugated networks and permanent microporous structures. Their high specific surface area, tunable pore size distribution and excellent optoelectronic properties make them have great potential in the fields of adsorption, catalysis and sensing. Compared with traditional fluorescent probes (such as small molecule dyes or metal-organic frameworks MOFs), CMPs have the advantages of molecular designability, signal amplification effect and good stability. Currently, Fe 3+ fluorescent sensors based on CMPs mainly achieve detection through electron transfer (ET) or energy competition absorption (ACQ) mechanisms. For example, triazine-based CMPs can enhance the fluorescence quenching efficiency through π-π stacking, while fluorescein-based CMPs can achieve specific recognition through the coordination of Fe 3+ with hydroxyl / carboxyl groups. Therefore, constructing Fe 3+ specific fluorescent probes based on CMPs has good application prospects.

[0004] According to GB 8538-2022, the iron detection methods are flame atomic absorption spectrometry and phenanthroline spectrophotometry. These methods have the advantages of high sensitivity, but have the disadvantages of high instrument cost and the need for professional operation. In view of the limitations of the above two detection methods, there is an urgent need in the market to develop a detection method that can be rapid, efficient, sensitive and easy to operate, so as to realize the rapid and accurate detection of Fe 3+ in water.

[0005] A new ultra-small hydra covalent organic polymer (UHCOP) was synthesized by the Schiff base reaction of 2,4,6-trihydroxy-1,3,5-benzene tricarboxaldehyde and 1,4-benzene dicarboxyhydrazine at room temperature. The UHCOP was used as a sensitive fluorescent sensor for rapid (<2 min) and selective detection of Fe 3+ in aqueous solution. The prepared UHCOP showed an ultra-small size with a diameter of 7.98±0.97 nm and emitted a stable fluorescence emission at 510 nm. The UHCOP showed good sensitivity and high selectivity to Fe 3+ . The coordination of UHCOP with Fe 3+ led to a significant aggregation-induced quenching reaction of UHCOP. The linear range was 5.0 μM~1.4 mM (R 2 =0.999) and the detection limit was 2.5 μM. Finally, UHCOP has been successfully applied to the detection of Fe 3+ in real water samples, proving that the prepared UHCOP as a sensitive fluorescent sensor is expected to be used for selective detection of Fe 3+ in aqueous solution. Although the UHCOP showed good selectivity to Fe 3+ , in real samples, other metal ions (such as Ni 2+ , Co 2+ , etc.) may coexist with Fe 3+ . These ions may have some impact on the detection results. At the same time, there is a lack of comprehensive verification of the anti-interference ability for practical applications. In addition, the detection limit of UHCOP is 2.5 μM, which is better than many existing methods, but in some practical applications, the concentration of Fe 3+ may be lower, especially in clean natural water bodies or treated drinking water. For example, the concentration of Fe 3+ in some environmental water samples may be lower than 1 μM.

[0006] The Department of Medical Research, Kaohsiung Medical University used cranberry bean-derived carbon dots (CB-CDs) as a potential fluorescent sensor for selective detection of Fe 3+The synthesis process of CB-CDs is non-toxic, convenient, and environmentally friendly. The obtained carbon dots exhibit stable fluorescence with a quantum yield of about 10.85%. By changing the excitation wavelength, the carbon dots emit a wide fluorescence emission range between 410 and 540 nm and are used to detect Fe 3+ . The results show that the fluorescence intensity of the carbon dots is quenched by Fe 3+ ions stronger than other heavy metals, and the detection of Fe 3+ can be achieved within 3 min. Spectral data show that the obtained carbon dots can detect Fe 3+ in a wide concentration range of 30-600 μM with a detection limit of 9.55 μM. However, the sample pretreatment is complex, although the synthesis process of CB-CDs is simple and green, the actual water sample may contain various impurities, which need to be pretreated to remove these impurities. For example, organic matter, suspended particles, etc. in water samples may affect the fluorescence performance of CB-CDs.

[0007] The existing University of Yanbian constructs a tetraphenylethylene covalent organic framework (TTPE-COF) with a rhombus skeleton through Schiff base reaction. TTPE-COF has a porous structure and a high surface area, and can selectively detect Fe 3+ . The detection limit of Fe 3+ is 3.07 μM. TTPE-COF has application potential in fluorescence sensors. However, this technology does not discuss the detection performance of TTPE-COF under different pH conditions. The existence form and chemical properties of Fe 3+ may be different under different pH values, which may affect the detection effect of COF. Moreover, TTPE-COF is not applied to the detection of Fe 3+ in real samples, which is insufficient in practical application.

[0008] The existing Jilin University four uses (p-aminophenyl) methane and chromogenic 2,5,8-trichloro-s-heptazine to synthesize the first example of a luminescent sensor based on a porous organic polymer POP-HT for selective detection of Fe 3+ . POP-HT shows obvious fluorescence quenching in the presence of Fe 3+ ions. In addition, a good linear relationship is established between the luminescence intensity and the corresponding Fe 3+ concentration. Experiments and theoretical calculations also study the luminescence quenching mechanism. The research results show that compared with other metal ions and organic solvents, POP-HT can be used as an effective luminescent indicator for qualitative and quantitative detection of Fe 3+ in aqueous solution. Although POP-HT can detect Fe 3+The detection sensitivity of ions is high, but the linear detection range is 5-600 ppm, and it may be necessary to dilute the sample for detection of higher concentration Fe³⁺ ions. In addition, the detection performance of POP-HT for Fe 3+ was mainly verified by laboratory simulation experiments, but there was a lack of detection verification of Fe 3+ ions in actual water samples or biological samples. SUMMARY

[0009] In view of the deficiencies of the prior art described above, the purpose of the present application is to synthesize a new type of CMP material (THDH-DMA), and to construct a Fe 3+ fluorescence detection method and a fluorescence test strip based on the material, so as to realize efficient and specific detection of Fe 3+ in drinking water, and to solve the problems of low sensitivity, complex operation and high cost in the existing heavy metal detection methods, and to provide a more convenient, accurate and economical means for food safety monitoring.

[0010] In order to achieve the above purpose, the technical scheme provided by the present application is as follows: The conjugated microporous polymer material for detecting heavy metal iron (Fe 3+ ) in drinking water is synthesized by a solvothermal reaction method of terephthalamidic hydrazide (THDH) and 2,5-dimethoxyterephthaldehyde (DMA), and the mass ratio of terephthalamidic hydrazide to 2,5-dimethoxyterephthaldehyde during synthesis is 2:5 to 5:2, preferably 1:1.

[0011] Preferably, the solvent during synthesis is o-dichlorobenzene and n-butanol, and the volume ratio of o-dichlorobenzene to n-butanol is 10:1 to 1:1, more preferably 17:3.

[0012] Preferably, acetic acid is also added during synthesis, and the mass-volume ratio of terephthalamidic hydrazide, 2,5-dimethoxyterephthaldehyde and acetic acid is (20-50) mg:(20-50) mg:(0.05-0.5) mL, more preferably 29.12 mg: 29.12 mg: 1 mL.

[0013] Preferably, the concentration of acetic acid is 6M.

[0014] The synthesis method of the conjugated microporous polymer material for detecting heavy metal iron in drinking water described above comprises the following steps: (1) terephthalamidic hydrazide and 2,5-dimethoxyterephthaldehyde are added to a mixed solution composed of o-dichlorobenzene and n-butanol, and ultrasonic treatment is performed for 10 min. Acetic acid is added to the mixed solution, and after ultrasonic treatment for 5 min, the obtained mixed solution is transferred to a 10 mL Schlenk reaction tube, 3 cycles of freeze-pump-thaw are performed, and heating is performed at 120℃ for 72 h; (2) After the reaction is completed, the solid is cooled to room temperature and washed with tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) for multiple times alternately. After washing, the product is dried at 100°C under vacuum to obtain a bright yellow powder.

[0015] The method for detecting iron in drinking water based on the conjugated microporous polymer material is as follows: the sample to be detected is added to the conjugated microporous polymer material solution and reacted for 0.5-10 min, preferably 1 min; the fluorescence intensity of the conjugated microporous polymer material is determined, and the concentration value of iron is calculated according to the function relationship formula: Y=0.278X+1.1363, R 2 =0.997, wherein Y is the fluorescence intensity of the conjugated microporous polymer material, X is the concentration value of iron, and the concentration unit is mg / L; the conjugated microporous polymer material solution is an acetonitrile, ethanol, DMF, methanol, water or dimethyl sulfoxide solution of the conjugated microporous polymer material, preferably DMF, wherein the concentration of the conjugated microporous polymer material is 10-1000 μg / L, the pH value of the conjugated microporous polymer material solution is 2.0-7.0, preferably 7, the fluorescence detection excitation wavelength is 350 nm, and the detection wavelength is 465 nm. The method can detect iron in the concentration range of 0.01-9 mg / L.

[0016] The conjugated microporous polymer material for detecting iron in drinking water described above can be used to prepare a test strip for detecting iron in drinking water. The blank test strip is soaked in the THDH-DMA suspension for 4 min, air-dried at room temperature, and repeatedly dried and soaked for 3 times to obtain a THDH-DMA fluorescence test strip.

[0017] The method for detecting iron in drinking water using the THDH-DMA fluorescence test strip described above is as follows: the prepared yellow THDH-DMA test strip is irradiated with a 365 nm ultraviolet lamp, and the THDH-DMA test strip appears blue. The THDH-DMA test strip is soaked in an iron ion solution for 1 min. After the test strip is dried, it is irradiated with a 365 nm ultraviolet lamp, and the fluorescence image is collected by using the built-in camera of a smart phone, and then the RGB (red-R, green-G and blue-B) signal values in the fluorescence image are automatically extracted by using the Color Picker APP. A linear function relationship between the G / B value and the Fe 3+ concentration is established, and the function relationship formula is: G / B=0.041X+1.738, R 20.995, wherein G / B is the RGB (red-R, green-G and blue-B) signal value in the fluorescence image, X is the concentration value of iron, the linear range of the method is 0-10 mg / L, the detection limit is 0.15 mg / L, which is lower than the limit standard of the World Health Organization. The angle of the ultraviolet lamp irradiation is 30-90°, preferably 45°, and the range of the ultraviolet lamp is 5-40 cm, preferably 20 cm.

[0018] The application is further described below: The application provides a novel conjugated microporous polymer (THDH-DMA) and a synthesis and application method thereof, which is used for rapid detection of Fe 3+ in drinking water. Not only does it solve the problems of low sensitivity, complex operation and high cost in the existing Fe 3+ detection methods, but also significantly improves the detection efficiency of Fe 3+ in water, providing a new way for efficient, convenient and economical heavy metal detection. By preparing the THDH-DMA material, a method for detecting Fe 3+ based on the THDH-DMA material is constructed, the linearity, specificity and anti-interference of the method are verified, and real water samples are detected. In addition, a visual detection platform based on a smart phone is established, realizing real-time monitoring of Fe 3+ on site. The method is as follows: the application synthesizes THDH-DMA by a solvothermal reaction method using terephthaldehyde hydrazide and 2,5-dimethoxyterephthaldehyde. The physicochemical properties and fluorescence characteristics of the THDH-DMA material are studied, and it is found that the THDH-DMA exhibits strong fluorescence emission under an excitation wavelength of 350 nm, and has high selectivity and anti-interference for Fe 3+ . Subsequently, a method for detecting Fe 3+ based on THDH-DMA fluorescence is established, and it is found that the method has the advantages of wide linear range and low detection limit. In order to optimize the detection method, we use the control variable method to systematically investigate the influence of factors such as the type of solvent, the pH value of the solution and the reaction time of THDH-DMA and Fe 3+ on the detection results, and finally determine the optimal reaction conditions as follows: the solvent is N,N-dimethylformamide (DMF), the pH value is 7, and the reaction time is 1 min. Finally, the THDH-DMA material is applied to the spiked recovery experiment of tap water and mineral water, and the results show that the recovery rate is high (97.99-104.55%) and the reproducibility is good (RSD≤2.88%), which indicates that the method for detecting Fe 3+ based on THDH-DMA has good practical application performance. Finally, a visual monitoring platform based on fluorescence test strips and a smart phone is established, realizing real-time monitoring of Fe 3+on-site real-time monitoring. The detection limit of THDH-DMA test strip in RGB analysis is 0.15 mg / L, which is lower than the maximum limit standard (0.3 mg / L) of China and WHO. 3+

[0019] In summary, a new conjugated microporous polymer THDH-DMA is synthesized in this application. Based on THDH-DMA material, a fluorescent detection method and fluorescent test strip are constructed, which have the advantages of wide linear range and low detection limit. The method realizes the specific fluorescent detection of Fe 3+ 3+ 3+ 3+ The THDH-DMA test strip prepared in this application has excellent stability and is easy to save. It does not need to rely on expensive laboratory professional equipment, and a portable visual method based on visual tracking is established to monitor Fe 3+ 3+ This application opens up a new path for the application of CMPs materials in the field of detection of heavy metal pollution in drinking water, not only provides valuable theoretical support and practical guidance for the progress of drinking water safety detection technology, but also provides inspiration for the detection of other metal ions and provides a new method for the development of subsequent fluorescent sensors. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 : SEM images of THDH-DMA (a, b) and TEM images of THDH-DMA (c, d); Figure 2 : (a) FT-IR spectra of THDH-DMA and monomers; (b) XPS spectra of THDH-DMA; (c) XPS spectra of C 1s region of THDH-DMA; (d) XPS spectra of N 1s region of THDH-DMA; (e) XPS spectra of O 1s region of THDH-DMA; Figure 3 : (a) XRD pattern of THDH-DMA; (b) TGA curve of THDH-DMA measured under N2; (c) N2 adsorption-desorption isotherm of THDH-DMA; Figure 4 : (a) Fluorescence spectrum of THDH-DMA (inset: picture of THDH-DMA under ultraviolet lamp); (b) CIE chromaticity diagram of THDH-DMA; (c) Fluorescence spectra of THDH-DMA, DMA and THDH; Figure 5 ​​​​​(a) The fluorescence intensity change of THDH-DMA in different solvents; (b) The fluorescence intensity change of THDH-DMA after adding Fe 3+ (a) The fluorescence intensity change of THDH-DMA in different solvents; (b) The fluorescence intensity change of THDH-DMA after adding Fe 3+ (a) The fluorescence intensity change of THDH-DMA in different solvents; (b) The fluorescence intensity change of THDH-DMA after adding Fe Figure 6 (a) The fluorescence emission spectra of THDH-DMA at different Fe 3+ (a) The fluorescence emission spectra of THDH-DMA at different Fe 3+ (a) The fluorescence emission spectra of THDH-DMA at different Fe 3+ (a) The fluorescence emission spectra of THDH-DMA at different Fe Figure 7 (a) The fluorescence emission spectra of THDH-DMA at different Fe 3+ (a) The fluorescence emission spectra of THDH-DMA at different Fe DETAILED DESCRIPTION

[0021] 1. Experimental method 1.1 Experimental reagents Terephthalic dihydrazide, 2,5-dimethoxyterephthaldehyde, acetic acid, o-dichlorobenzene, n-butanol, acetonitrile, ethanol, DMF, methanol, dimethyl sulfoxide, N,N-dimethylformamide, tetrahydrofuran were purchased from Shanghai McLean Biochemical Technology Co., Ltd. Sodium hydroxide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Hydrochloric acid was purchased from Xilong Scientific Co., Ltd. All metal ion standard solutions were purchased from Shanghai McLean Biochemical Technology Co., Ltd.

[0022] 1.2 Experimental equipment and instruments Schlenk tubes (10 mL) were purchased from Yongcheng Glass Instrument Co., Ltd., an analytical balance (BCE1241-1CCN) was purchased from Sartorius Instrument (Beijing) Co., Ltd., a micropipette was purchased from Thermo Fisher (Shanghai) Instrument Co., Ltd., a temperature-controlled ultrasonic cleaner (JP-040S) was purchased from Shenzhen Jielian Cleaning Equipment Co., Ltd., a vacuum oven (DZF-6050) was purchased from Shanghai Jinghong Experimental Equipment Co., Ltd., a pH meter (PHS-25-3C-3E-2F) was purchased from Shanghai Leici Technology Co., Ltd., a fluorescence spectrometer (F-7000) was purchased from Hitachi, Ltd., Japan, an X-ray powder diffractometer (Empyrean) was purchased from PANalytical, Netherlands, a field emission scanning electron microscope and energy spectrometer (JSM-7800F & TEAM) were purchased from JEOL Ltd., Japan, a transmission electron microscope and energy spectrometer (JEM-2100 & X-Max80) were purchased from JEOL Ltd., Japan, a specific surface, micropore and mesopore tester (BELSORP-max) was purchased from Micromeritics, an X-ray photoelectron spectrometer (K-Alpha+) was purchased from Thermo Fisher (Shanghai) Instrument Co., Ltd., a Fourier transform infrared spectrometer (IR Affinity-1) was purchased from Shimadzu Corporation, Japan, and a simultaneous thermal analyzer (STA449 F5) was purchased from NETZSCH Instruments Co., Ltd.

[0023] 1.3 Preparation of THDH-DMA The synthesis steps of THDH-DMA are as follows: THDH (29.12 mg, 0.15 mmol) and DMA (29.12 mg, 0.15 mmol) were added to a mixed solution consisting of 1.7 mL of o-dichlorobenzene and 0.3 mL of n-butanol, and ultrasonically treated for 10 min. 0.1 mL of 6 M acetic acid was added to the mixed solution, and after ultrasonic treatment for 5 min, the resulting mixture was transferred to a 10 mL Schlenk reaction tube, subjected to 3 cycles of freeze-pump-thaw, and heated at 120°C for 72 h. After the solid was cooled to room temperature, it was washed with THF and DMF alternately for several times. After washing, the product was dried at 100°C under vacuum to obtain a bright yellow powder.

[0024] 1.4 Experimental determination method 1.4.1 Characterization of THDH-DMA material (1) Field emission scanning electron microscopy A small amount of sample powder was sprinkled on a sample stage with conductive glue, and after purging with N2, gold spraying treatment was performed. Next, SEM measurement was performed, and the voltage of the electron microscope was 5.0 kv and 20.0 kv.

[0025] (2) Transmission electron microscopy A small amount of THDH-DMA was taken in a 2 mL centrifuge tube, and an appropriate amount of anhydrous ethanol was added. The resulting solution was dropped onto a precision copper mesh and dried under an infrared lamp for 20 min.

[0026] (3) Fourier infrared spectroscopy FT-IR was used to obtain the characteristic group information of the material. Potassium chloride was used for sample tabletting pretreatment, followed by FT-IR measurement, with a scanning range of 400-4000 nm and a resolution of 7.

[0027] (4) X-ray photoelectron spectroscopy A clean aluminum film was prepared, a double-sided adhesive tape was cut and pasted on the surface of the aluminum film, and an appropriate amount of material powder was evenly spread on the tape area. The aluminum film was folded and placed in a tablet press for pressing. The pressed sample was fixed on the XPS sample table for testing.

[0028] (5) BET specific surface area determination method THDH-DMA samples were ground into uniform powder, 60 mg of sample was weighed and loaded into a clean and dry sample tube, and the sample was subjected to heating and degassing treatment for 12 h under N2 gas environment. After degassing, the heating was turned off and the sample was naturally cooled to room temperature. The sample tube was removed from the degassing station, the total weight of the sample tube and sample was weighed, and the data was recorded. The sample tube was installed into the test port of the BET analyzer. N2 was introduced into the sample tube, and gas adsorption test was carried out at liquid nitrogen temperature (-196°C).

[0029] (6) Powder X-ray diffraction method Scanning was performed in the range of 2° to 40°, with a tube current of 100 mA and a tube voltage of 40 kV. The scanning rate was set to 10° per minute, the step angle was 0.01°, and Cu-Ka rays with a wavelength of 0.15406 nm were used as the radiation source.

[0030] (7) Thermogravimetric analysis method First, the weight of the empty crucible was measured, and then 2.0 mg of TAPA-BTT sample was accurately weighed and placed in the crucible. Before starting the test program, zeroing and temperature calibration operations were performed.

[0031] 1.5 Fluorescence characteristics of THDH-DMA material THDH-DMA 1 mg was weighed and added to 100 mL of DMF, and ultrasonic treatment was performed at room temperature for 30 min. 2.5 mL of THDH-DMA solution was taken into a quartz cuvette, and the fluorescence spectrum of THDH-DMA was measured to determine the excitation wavelength and emission wavelength.

[0032] 1.6 THDH-DMA fluorescence detection of Fe 3+Establishment of method (1) Establishment of standard curve The fluorescence intensity of the mixture was measured by adding a series of different concentrations of Fe 3+ (0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 mg / L) to the THDH-DMA suspension using a F-7000 fluorescence spectrometer. The linear range of detection was calculated using the Stern-Volmer formula I0 / I = 1 + Ksv[M] (I0is the fluorescence intensity of THDH-DMA before adding Fe 3+ ; I is the fluorescence intensity of THDH-DMA after adding Fe 3+ ; M represents the concentration (mg / L) of Fe 3+ ; and Ksv is the constant of the Stern-Volmer equation). The LOD was determined using the formula LOD = 3σ / k.

[0033] (2) Sensitivity The detection limit (Limit of Detection, LOD) of the method was determined using 3 times the signal-to-noise ratio. The LOD was the concentration of the sample being measured when the signal-to-noise ratio was 3 times and 10 times, and was determined using the formula LOD = 3σ / k.

[0034] (3) Selectivity and competition The selectivity of THDH-DMA for Fe 3+ was analyzed by measuring the degree of fluorescence quenching of the THDH-DMA suspension after adding Fe 3+ and other metal ions (10 mg / L). The degree of fluorescence quenching was expressed as I / I0, where I / I0=1 indicates constant fluorescence intensity, I / I0>1 indicates fluorescence enhancement, and I / I0<1 indicates fluorescence quenching. In addition, the anti-interference performance of Fe 3+ detection was tested by adding solutions of interfering ions at the same concentration when detecting Fe 3+ and measuring the fluorescence intensity of THDH-DMA in the mixed system.

[0035] (4) Optimization of experimental conditions for the method The material solvent, pH value, and reaction time of THDH-DMA and Fe 3+ for the method were optimized using the control variable method. The solvents selected were DMF, acetonitrile, ethanol, DMF, methanol, water, and dimethyl sulfoxide. The pH values were set to 2, 3, 4, 5, 6, and 7, respectively, and the reaction times were set to 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 min, respectively.

[0036] (5) Recovery rate and relative standard deviation Mineral water (Nongfushanquan Co. Ltd, Hangzhou, China) was purchased from a local supermarket in Shenzhen, and tap water was taken from the laboratory. After all water samples were filtered by 0.22 μm syringe filter, Fe 3+ ions were added at concentrations of 0.5, 2 and 5 mg / L, respectively. The fluorescence intensity was measured after the addition of THDH-DMA in solution, and the recovery rate and relative standard deviation were calculated.

[0037] 1.7 Construction of a smartphone integrated sensing platform based on fluorescent test strips Based on the installed Color Picker Version3.1 App smartphone (IOS Version18.3.1) and fluorescent THDH-DMA test strips, a smartphone integrated ratio sensing platform was developed for the smart visual detection of Fe 3+ . The test strips were immersed in the THDH-DMA suspension for 4 min, air-dried at room temperature, and repeated drying and immersion for 3 times to obtain THDH-DMA fluorescent test strips. Then the test strips were immersed in Fe 3+ (0-10 mg / L) solutions of different concentrations for 1 min, and after the test strips were dried, they were irradiated with a 365 nm ultraviolet lamp at an angle of 45° and a range of 20 cm. The focal length of the smartphone was fixed to capture the fluorescence image, improving the accuracy and reproducibility of the data. The linear regression relationship between the Fe 3+ concentration and the corresponding RGB value was established by Color Picker Version3.1 App, and the Fe 3+ concentration in the sample was calculated, realizing the smart detection of Fe 3+ .

[0038] 1.8 The method of the present application is as follows: The THDH-DMA was synthesized by a solvothermal reaction of benzene hydrazide and 2,5-dimethoxy-p-xylylene glycol. The fluorescence properties of THDH-DMA material were studied, and then a method for detecting Fe 3+ based on the fluorescence of THDH-DMA was established and optimized. The method was applied to the spiked recovery experiment of drinking water, and the results showed that the method had high recovery rate and good reproducibility. Finally, a smartphone sensing platform based on THDH-DMA test strips was established to realize the real-time detection of Fe 3+ on site.

[0039] 1.9 Characterization and evaluation of THDH-DMA material preparation 1.9.1 Field emission scanning electron microscopy and transmission electron microscopy First, the morphology of the synthesized THDH-DMA was analyzed. SEM images at different magnifications are shown in Figure 1 a and Figure 1THDH-DMA exhibited uniform chrysanthemum-like nanoflower structures with rod-like aggregates, as shown in Figure 1b. The TEM image (Figure 1c) shows that THDH-DMA has a uniform size and smooth surface. Figure 1 c) further confirmed the smooth rod-like structure of THDH-DMA. Figure 1 d shows that THDH-DMA exhibits a stacked porous structure.

[0040] The FT-IR spectra of THDH-DMA and monomers are shown in Figure 2. Figure 2 As shown in Figure 2a, after the reaction, the characteristic peaks (N-H) of THDH monomers at 3319 cm-1 and 3209 cm-1 disappeared and shifted to a lower waveband, and the stretching vibration (C=0) of DMA monomers at 1678 cm-1 weakened. -1 The FT-IR spectra of THDH-DMA and monomers are shown in Figure 2. -1 The FT-IR spectra of THDH-DMA and monomers are shown in Figure 2. -1 The FT-IR spectra of THDH-DMA and monomers are shown in Figure 2. -1 The FT-IR spectra of THDH-DMA and monomers are shown in Figure 2. Figure 2 b) shows that THDH-DMA is composed of C, N, and O. The high-resolution XPS spectrum of C 1s (c) shows four peaks at 290.68, 287.84, 286.08, and 284.77 eV, representing C=0, C-O, C=N, and C=C, respectively. C-O may come from C-OCH3 on THDH-DMA. Figure 2 b) shows that THDH-DMA is composed of C, N, and O. The high-resolution XPS spectrum of C 1s (c) shows four peaks at 290.68, 287.84, 286.08, and 284.77 eV, representing C=0, C-O, C=N, and C=C, respectively. C-O may come from C-OCH3 on THDH-DMA. Figure 2 b) shows that THDH-DMA is composed of C, N, and O. The high-resolution XPS spectrum of C 1s (c) shows four peaks at 290.68, 287.84, 286.08, and 284.77 eV, representing C=0, C-O, C=N, and C=C, respectively. C-O may come from C-OCH3 on THDH-DMA. Figure 2 b) shows that THDH-DMA is composed of C, N, and O. The high-resolution XPS spectrum of C 1s (c) shows four peaks at 290.68, 287.84, 286.08, and 284.77 eV, representing C=0, C-O, C=N, and C=C, respectively. C-O may come from C-OCH3 on THDH-DMA.

[0041] The structure of the obtained THDH-DMA polymer was also identified by XRD analysis using Cu-Ka radiation (a). The results showed that the broad diffraction peak at 23° confirmed the amorphous nature of THDH-DMA, which was mainly attributed to its amorphous organic component. Figure 3 The results showed that THDH-DMA exhibited excellent thermal stability, as even at a temperature of 320 °C, its mass remained at around 90% (Figure 1d). Figure 3b). In addition, the microporous properties of THDH-DMA were measured by N2 adsorption-desorption isotherms at 77 K. The isotherms of THDH-DMA showed typical type II adsorption isotherms. As shown in Fig. Figure 3 c, there was no saturation adsorption platform in the N2 adsorption-desorption isotherms, indicating that the porous structure of the material was irregular. The pore size distribution curve of THDH-DMA was calculated by the Horvath-Kawazoe method. As shown in the inset of Fig. Figure 3 c, the pore size was mainly distributed at 0.86 nm. According to the Brunauer-Emmet-Teller method, the surface area of THDH-DMA was calculated to be 61.62 m 2 g −1 .

[0042] THDH-DMA was dissolved in a DMF solution, and the obtained THDH-DMA solution had a stable emission at 465 nm with a maximum excitation wavelength of 350 nm (Fig. Figure 4 a). The CIE chromaticity diagram of THDH-DMA showed that THDH-DMA had blue fluorescent properties (Fig. Figure 4 c), which was consistent with its color under ultraviolet light irradiation in Fig. Figure 4 a. Compared with THDH-DMA, the emission spectra of DMA and THDH had no obvious emission peak at 465 nm (Fig. Figure 4 b).

[0043] 1.11 Fe 3+ fluorescence detection method

[0044] The fluorescence properties of THDH-DMA in several common solvents were tested under an excitation wavelength of 350 nm. As shown in Fig. Figure 5 a, the fluorescence spectra of THDH-DMA were different with different solvents. THDH-DMA showed the strongest fluorescence intensity in DMF, and had excellent dispersibility in DMF, so DMF was selected as the solvent for subsequent fluorescence measurement. The alkaline pH might seriously interfere with the detection of Fe 3+ , so only the fluorescence intensity changes of THDH-DMA under acidic and neutral conditions were tested. As shown in Fig. Figure 5 b, the acidic environment would cause a slight decrease in the fluorescence intensity of THDH-DMA. After the addition of Fe 3+ , the fluorescence of THDH-DMA was quenched to some extent, and the quenching degree was the largest at pH=7, so pH=7 was selected as the best detection condition. In addition, the reaction time of THDH-DMA with Fe 3+ was tested. As shown in Fig. Figure 5 c, the fluorescence of THDH-DMA was quenched to some extent after the addition of Fe 3+It was significantly quenched after addition and remained basically unchanged after 1 min, indicating that THDH-DMA and Fe 3+ The reaction is rapid. At the same time, Fe 3+ Afterwards, under 365 nm ultraviolet light, the fluorescence of THDH-DMA changed from blue to green.

[0045] 1.11.2 Fe 3+ Establishment of fluorescence detection method Figure 6 a shows that under the optimal detection conditions, the fluorescence intensity of THDH-DMA increases with the addition of Fe 3+ At the same time, with the addition of Fe 3+ As the concentration of THDH-DMA gradually increased, the fluorescence of THDH-DMA changed from blue to green under UV light, and the intensity gradually decreased ( Figure 6 a). Fit the data to the Stern-Volmer equation, and the linear fitting curve is as follows Figure 6 As shown in b. I0 / I and Fe 3+ There is a linear relationship between the concentrations, and the linear fitting equation is y=0.278x+1.1363, R 2 =0.9970, the linear range was 0.01-9 mg / L, and the LOD was 0.0038 mg / L. The above results showed that the prepared THDH-DMA had a strong affinity for Fe 3+ It has excellent fluorescence detection performance with high correlation and low detection limit in a wide linear range.

[0046] By comparing the addition of Fe 3+ and other metal ions (K + 、Na + 、As 3+ 、Mn 2+ 、Hg 2+ 、Co 2+ 、Ag + 、Cu 2+ 、Zn 2+ and Ni 2+ The fluorescence spectrum and quenching degree of THDH-DMA were used to analyze the effect of THDH-DMA on Fe 3+ Selectivity. Figure 6 As shown in c, K + and Na + After the addition of As 2+ After adding Fe 3+After the addition of ions, the fluorescence intensity of THDH-DMA is significantly quenched. Other ions will reduce the fluorescence intensity of THDH-DMA, but the effect is small. Under the irradiation of ultraviolet light, the fluorescence images of different metal ions ( Figure 6 c) also further confirmed the above conclusion. All these results show that THDH-DMA has a great influence on Fe 3+ It has good selectivity. The anti-interference test results are as follows Sample As shown in d, when Fe 3+ After the solution of Fe ions and other metal ions was mixed, the fluorescence of THDH-DMA was significantly quenched, which also showed that THDH-DMA could achieve the fluorescence of Fe ions even in the presence of other metal ions. 3+ Selective sensing with minimal interference.

[0047] 1.11.3 Fe in real samples 3+ Detection Successfully tested Fe in tap water and mineral water 3+ , further confirming the potential of the synthesized THDH-DMA fluorescence sensor in practical applications. In order to ensure the accuracy and reliability of the experiment, considering that there may be no Fe in the real sample, 3+ ions, so they need to be added. As shown in Table 1, Fe 3+ The recoveries in real water samples ranged from 97.99% to 104.55%, demonstrating high accuracy. Furthermore, the RSDs for all samples were ≤2.88%, demonstrating the excellent precision and reproducibility of the assay.

[0048] Table 1 Detection of Fe in real water samples using THDH-DMA 3+ Performance (mean ± SD) (n = 3) Amount added (mg / L) Concentration (mg / L) RSDs (%) Recovery (%) Tap water ND*0.49 ± 0.142.01 ± 0.225.11 ± 1.36 00.525 Mineral water -2.881.082.67 -97.99100.73102.17 ND0.52 ± 0.111.98 ± 0.545.16 ± 0.63 00.525 Figure 7 -2.152.721.21 -104.5599.20103.21 * ND: Not detectable

[0049] Design of a smartphone-integrated ratiometric sensing platform for Fe 3+ Perform visual tracking detection ( Figure 7 First, the yellow THDH-DMA test strips were irradiated with a 365 nm UV lamp, and the THDH-DMA test strips turned blue ( Figure 7 a). Figure 7As shown in Fig. b, the fluorescence image of the prepared THDH-DMA test strip at 21 days was consistent with that at the initial time, indicating that the prepared test strip had excellent stability and could maintain its original properties for 21 days, which was conducive to preservation. Next, the test strip treated with THDH-DMA was immersed in different concentrations (0, 0.5, 2, 4, 6, 8, 10 mg / L) of Fe 3+ solution. After the test strip was dried, it was irradiated with a 365 nm ultraviolet lamp, and the fluorescence image was collected using the built-in camera of a smartphone. Next, RGB analysis was performed. Since RGB analysis can effectively reduce human perception errors of color, the free Color Picker APP was used to automatically extract the RGB (red-R, green-G, and blue-B) signal values in the fluorescence image. Then, the linear relationship was calculated according to the obtained signal values. As shown in Fig. ​ c, after immersion in different concentrations of Fe 3+ solution, the color change of the THDH-DMA test strip under ultraviolet light was obvious. After collecting the fluorescence image using the App, the linear relationship between the G / B value and the concentration of Fe 3+ was established. Within the concentration range of 0-10 mg / L, the G / B value and the concentration of Fe 3+ presented an excellent linear relationship (R 2 = 0.995), and the fitted linear equation was G / B = 0.041x + 1.738. According to the calculated LOD = 3σ / k , the detection limit was 0.15 mg / L, which was lower than the limit standard of China and the World Health Organization. Therefore, without relying on expensive laboratory professional equipment, a portable visual method based on visual tracking could be developed for Fe 3+ detection.

Claims

1. A conjugated microporous polymer material for detecting heavy metal iron in drinking water, characterized in that: The conjugated microporous polymer material for detecting heavy metal iron in drinking water is synthesized by a solvent thermal reaction method using terephthaloyl dihydrazide and 2,5-dimethoxyterephthalaldehyde. During the synthesis, the mass ratio of terephthaloyl dihydrazide to 2,5-dimethoxyterephthalaldehyde is 2:5 to 5:

2.

2. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 1, characterized in that: During the synthesis, the mass ratio of terephthaloyl hydrazide to 2,5-dimethoxyterephthalaldehyde is 1:

1.

3. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 1, characterized in that: The solvents used in the synthesis are o-dichlorobenzene and n-butanol, and the volume ratio of the o-dichlorobenzene to n-butanol is 10:1 to 1:

1.

4. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 3, characterized in that: The solvents used in the synthesis are o-dichlorobenzene and n-butanol, and the volume ratio of o-dichlorobenzene to n-butanol is 17:

3.

5. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 1, characterized in that: Acetic acid is also added during the synthesis, and the mass volume ratio of terephthalhydrazide, 2,5-dimethoxyterephthalaldehyde, and acetic acid is (20-50) mg: (20-50) mg: (0.05-0.5) mL.

6. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 5, characterized in that: Acetic acid was also added during the synthesis, and the mass volume ratio of terephthalhydrazide, 2,5-dimethoxyterephthalaldehyde, and acetic acid was 29.12 mg:29.12 mg:1 mL.

7. The conjugated microporous polymer material for detecting heavy metal iron in drinking water according to claim 5, characterized in that: The acetic acid concentration was 6M.

8. The method for synthesizing a conjugated microporous polymer material for detecting heavy metal iron in drinking water according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: (1) Add terephthaloylhydrazide and 2,5-dimethoxyterephthalaldehyde to a mixed solution of o-dichlorobenzene and n-butanol and sonicate for 10 min. Add acetic acid to the mixed solution, sonicate for 5 min, and transfer the resulting mixture to a 10 mL Schlenk reaction tube. Perform three freeze-pump-thaw cycles and heat at 120°C for 72 h. (2) After the reaction is completed, the solid is cooled to room temperature and then washed alternately with tetrahydrofuran and N,N-dimethylformamide several times. After washing, the product is vacuum-dried at 100°C to obtain a bright yellow powder.

9. The method for detecting iron in drinking water using a conjugated microporous polymer material according to claim 8, characterized in that: The method comprises adding a sample to be tested into a conjugated microporous polymer material solution and reacting for 0.5 to 10 minutes, measuring the fluorescence intensity of the conjugated microporous polymer material, and then calculating the iron concentration value according to a functional relationship. The functional relationship is: Y=0.278X+1.1363, R 2 is 0.997, wherein Y is the fluorescence intensity of the conjugated microporous polymer material, X is the concentration of iron, and the concentration unit is mg / L; the conjugated microporous polymer material solution is an acetonitrile, ethanol, DMF, methanol, water or dimethyl sulfoxide solution of the conjugated microporous polymer material, wherein the concentration of the conjugated microporous polymer material is 10-1000 μg / L, the pH value of the conjugated microporous polymer material solution is 2.0-7.0, the fluorescence detection excitation wavelength is 350 nm, and the detection wavelength is 465 nm.

10. Use of the conjugated microporous polymer material for detecting heavy metal iron in drinking water according to any one of claims 1 to 7 in preparing a test strip for detecting heavy metal iron in drinking water.

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