Fluorine functionalized covalent organic framework / graphene oxide material as well as preparation method and application thereof

Abstract

The invention provides a fluorine functionalized covalent organic framework / graphene oxide material as well as a preparation method and application thereof. The preparation method of the material comprises the following steps: carrying out a dehydration condensation reaction on an amino group on one side of 2, 4, 6-tri (4-aminophenyl)-1, 3, 5-triazine and a carboxyl group of graphene oxide, uniformly covalently grafting 2, 4, 6-tri (4-aminophenyl)-1, 3, 5-triazine on the surface of graphene oxide, adding 2, 3, 5, 6-tetrafluoroterephthalaldehyde, and carrying out a reaction to obtain the graphene oxide / 2, 4, 6-tri (4-aminophenyl)-1, 3, 5-triazine composite material. Finally, the fluorine-functionalized covalent organic framework is uniformly and covalently grafted on the surface of the graphene oxide, and the fluorine-functionalized covalent organic framework / graphene oxide material is obtained through washing and vacuum drying. The obtained material can be used as an adsorbent to be applied to sample pretreatment, and fluorine-containing pesticides can be extracted and detected. According to the method, one-pot synthesis is adopted, washing and drying of an intermediate material are not needed, and compared with other preparation methods, the synthesis time is short, and the process operation is simple.

Description

Technical Field

[0001] The invention relates to the technical field of composite materials, in particular to a fluorine-functionalized covalent organic framework / graphene oxide material, a preparation method and application thereof. Background Art

[0002] Fluorinated pesticides can improve the stability of pesticide molecules and enhance their lipophilic activity, thereby improving pesticide performance because they contain fluorine atoms. Fluorinated pesticides are usually more effective than traditional pesticides and can be used to control more pests and diseases, and are widely used in food and traditional Chinese medicine samples. As the proportion of fluorinated pesticides used increases, the problem of excessive fluorinated pesticide residues has gradually emerged, so it is particularly important to establish a detection method for fluorinated pesticides in complex matrix samples.

[0003] Covalent organic frameworks are widely used as adsorbent materials in complex matrix samples due to their structural adjustability and rich porosity. However, with the application, it is found that covalent organic frameworks still have some disadvantages: single adsorption mechanism, poor stability and selective recognition ability. Fluorine atoms can improve the stability of covalent organic frameworks and make their adsorption types richer. Therefore, the development of high-affinity fluorine-functionalized covalent organic framework materials is crucial to improve the selective recognition of target analytes.

[0004] Graphene oxide contains a large number of oxygen-containing functional groups, such as hydroxyl and carboxyl groups, which makes it easy to disperse in water and even polar solvents. Therefore, graphene oxide can improve the hydrophobicity of fluorine-functionalized covalent organic frameworks. At the same time, the large specific surface area and aromatic structure of graphene oxide are conducive to increasing the adsorption capacity of the composite material. However, the covalent organic framework / graphene oxide materials synthesized at present have problems such as long synthesis time, complex operation, few adsorption active sites and poor affinity for the target. For example, Gao et al. first prepared amino-functionalized graphene oxide, washed and dried it, and then reacted it with trialdehyde phloroglucinol monomer to prepare covalent organic framework / graphene oxide materials. In this process, the reaction time alone is as long as 90.5h, which is time-consuming and complicated. Therefore, the design and synthesis of a fluorine-functionalized covalent organic framework / graphene oxide composite material with simple preparation, high adsorption capacity, strong universality and high selectivity, and the realization of efficient extraction of multiple fluorine-containing pesticides in complex matrix samples is the current research direction. Summary of the invention

[0005] The purpose of the present invention is to provide a fluorine-functionalized covalent organic framework / graphene oxide material, a preparation method and application thereof, so as to solve the problems that the traditional covalent organic framework material has a long synthesis time, a single adsorption mechanism and the affinity needs to be further improved.

[0006] The present invention is achieved in that:

[0007] The present invention prepares a chemically covalently modified fluorine-functionalized covalent organic framework / graphene oxide material by a one-pot method. The fluorine-functionalized covalent organic framework / graphene oxide material is synthesized by a Schiff base reaction and is used as an adsorbent for sample pretreatment to extract and detect fluorine-containing pesticides.

[0008] In the process of material preparation, the amino group on one side of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine undergoes a dehydration condensation reaction with the carboxyl group of graphene oxide, and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is uniformly covalently grafted onto the surface of graphene oxide; then 2,3,5,6-tetrafluoroterephthalaldehyde is added to the above system, and the amino group on the other side of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine undergoes a Schiff base condensation reaction with the aldehyde group of 2,3,5,6-tetrafluoroterephthalaldehyde, so that the fluorine-functionalized covalent organic framework is uniformly covalently grafted onto the surface of graphene oxide, thereby improving the adsorption performance of the traditional covalent organic framework. When the fluorine-functionalized covalent organic framework binds to graphene oxide, the adsorption active sites are increased. This adsorbent material has the advantages of fast mass transfer rate, high affinity, and high adsorption capacity. In the adsorption process, it mainly acts through F–F interactions, and synergistically uses strong hydrogen bonds, π–π stacking, and hydrophobic interactions to perform highly selective extraction of fluorine-containing pesticides in complex matrix samples.

[0009] The preparation method of the fluorine-functionalized covalent organic framework / graphene oxide material provided by the present invention specifically includes the following steps:

[0010] (1) Ultrasonically disperse graphene oxide and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in tetrahydrofuran and react at 65 °C to 80 °C;

[0011] (2) Dissolve 2,3,5,6-tetrafluoroterephthalaldehyde in a mixed solution of tetrahydrofuran and acetic acid;

[0012] (3) Add the solution obtained in step (2) to the reaction system of step (1) and react at 25 to 90 °C for 0.5 to 6 h;

[0013] (4) After the reaction in step (3) is completed, wash the material with acetonitrile and methanol and dry it under vacuum to obtain the fluorine-functionalized covalent organic framework / graphene oxide material.

[0014] Preferably, in step (1), the reaction temperature is 70 °C and the reaction time is 30 min.

[0015] Preferably, in step (1), the mass ratio of the amount of graphene oxide used to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is 1:(0.21 to 2.55).

[0016] Preferably, the molar ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to 2,3,5,6-tetrafluoroterephthalaldehyde in step (3) is 2:3.

[0017] Preferably, the reaction conditions in step (3) are: heating and stirring at a temperature of 50 °C to 70 °C for 2 h.

[0018] The fluorine-functionalized covalent organic framework / graphene oxide material prepared by the present invention is used as an adsorbent for the extraction and detection of fluorine-containing pesticides. The fluorine-containing pesticides include fluxapyroxad, flufenacet, bixafen, metconazole, and trifloxystrobin.

[0019] The present invention provides a fluorine-functionalized covalent organic framework / graphene oxide composite material based on graphene oxide, which is specifically synthesized by a one-pot method. The amino group on one side of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine undergoes a dehydration condensation reaction with the carboxyl group of graphene oxide, and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is uniformly covalently grafted onto the surface of graphene oxide. Then, 2,3,5,6-tetrafluoroterephthalaldehyde is added to the above system, and the amino group on the other side of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine undergoes a Schiff base condensation reaction with the aldehyde group of 2,3,5,6-tetrafluoroterephthalaldehyde, so that the fluorine-functionalized covalent organic framework is uniformly covalently grafted onto the surface of graphene oxide. There is no need to wash and dry the intermediate, which shortens the synthesis time. As an adsorbent material, it has a fast mass transfer rate and high affinity, and can be used for the rapid extraction and detection of fluorine-containing pesticides in complex matrix samples.

[0020] The present invention adopts a mutually promoting strategy, and a fluorine-functionalized covalent organic framework is uniformly covalently grown on the surface of graphene oxide through an amide bond, so that the composite material reaches a stable state. At the same time, the aromatic structure of graphene oxide, as well as the large specific surface area, uniform pore structure and rich types of adsorption forces (F–F interaction, strong hydrogen bond, hydrophobic interaction and π–π stacking interaction) of the fluorine-functionalized covalent organic framework, are beneficial to increasing the mass transfer rate and adsorption capacity of the material. The fluorine-functionalized covalent organic framework / graphene oxide material prepared by the present invention has a unique porous, fluffy and cross-linked network structure different from the uniform and smooth appearance structure of the three-dimensional fluorine-functionalized covalent organic framework, and has more adsorption active sites, thus showing higher affinity and larger adsorption capacity, and is suitable for use as an adsorbent material in the field of sample pretreatment. Description of the Drawings

[0021] Figure 1 It is a scanning electron microscope image of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 at 15,000 times magnification.

[0022] Figure 2 The infrared spectrogram of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 in the wavenumber range of 500 - 4000 cm -1 Wave number range.

[0023] Figure 3 The N2 adsorption-desorption isotherm and pore size distribution diagram of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1.

[0024] Figure 4 The X-ray diffraction pattern of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1.

[0025] Figure 5 The X-ray photoelectron spectroscopy pattern of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1.

[0026] Figure 6 The scanning electron microscope image of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 2.

[0027] Figure 7 The adsorption capacity diagram of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 2.

[0028] Figure 8 The adsorption kinetic curve of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1.

[0029] Figure 9 The comparison diagram of the adsorption amounts of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 and a commercial adsorbent for fluorine-containing pesticides.

[0030] Figure 10 The adsorption amount diagram of the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 for compounds with different structures.

[0031] Figure 11 The scanning electron microscope image at 5000 times of the phenyl-fluorine-functionalized covalent organic framework / graphene oxide material prepared in Comparative Example 1.

[0032] Figure 12 The N2 adsorption-desorption isotherm and pore size distribution diagram of the phenyl-fluorine-functionalized covalent organic framework / graphene oxide material prepared in Comparative Example 1.

[0033] Figure 13 The adsorption capacity diagram of the fluorine-functionalized covalent organic framework / graphene oxide materials prepared in Example 1 and Comparative Example 1.

[0034] Figure 14Recovery comparison chart of the fluorine-functionalized covalent organic framework / graphene oxide materials prepared in Example 1 and Comparative Example 1 for the extraction and detection of fluorine-containing pesticides. Detailed implementation manners

[0035] The present invention will be further described below with reference to the accompanying drawings. The specific embodiments described are only used to explain the present invention and are not used to limit the present invention. In the following embodiments, the processes and methods not described in detail are all conventional methods well known in the art, and the reagents used are all commercially available analytical pure or chemical pure.

[0036] Example 1

[0037] Add graphene oxide (GO, 100 mg) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT, 0.48 mmol, 170.1 mg) to a 100 mL single-necked flask, and then add tetrahydrofuran (22 mL). Ultrasonically treat for 2.0 h to uniformly disperse the GO and TAPT mixed solution, and heat and stir this system at 70 °C for 30 min. Dissolve 2,3,5,6-tetrafluoroterephthalaldehyde (TFA, 0.72 mmol, 148.3 mg) in tetrahydrofuran (8.0 mL) and acetic acid (1.0 mL) and mix evenly. Slowly add this solution dropwise to the above reaction system, and heat and stir at 70 °C for 2.0 h. Wash the material with acetonitrile and methanol respectively to remove unreacted substances and impurities, and then perform vacuum drying at 45 °C to obtain the fluorine-functionalized covalent organic framework / graphene oxide material (FCOF / GO).

[0038] In this example, the fluorine-functionalized covalent organic framework (FCOF) was prepared as a control. The specific preparation method is as follows: Add TAPT (0.48 mmol, 170.1 mg) to a 100 mL single-necked flask, and then add tetrahydrofuran (22 mL) to dissolve it, and heat at 70 °C. Dissolve TFA (0.72 mmol, 148.3 mg) in tetrahydrofuran (8.0 mL) and acetic acid (1.0 mL) and mix evenly. Slowly add this solution dropwise to the TAPT solution, and heat and stir at 70 °C for 2.0 h. Wash the material with acetonitrile and methanol respectively to remove unreacted substances and impurities, and then perform vacuum drying at 45 °C to obtain the fluorine-functionalized covalent organic framework (FCOF).

[0039] The FCOF / GO, FCOF, and GO prepared in this example were respectively subjected to scanning electron microscopy tests, and the results are as Figure 1 shown. From Figure 1It can be seen that graphene oxide exhibits a wrinkled sheet structure, and the three-dimensional fluorinated covalent organic framework exhibits a uniform and smooth spherical structure. As the fluorinated covalent organic framework grows uniformly on the surface of graphene oxide, the obtained FCOF / GO presents a unique porous, fluffy, cross-linked network sheet structure, resulting in an increase in adsorption sites and facilitating an increase in the adsorption capacity.

[0040] Figure 2 This is the Fourier transform infrared spectrum of the FCOF / GO prepared in this example. Figure 2 It can be seen that the peak at 1175 cm –1 of FCOF / GO is attributed to the C–F of 2,3,5,6-tetrafluoroterephthalaldehyde; the peak at 1622 cm –1 is attributed to the C=N generated by the Schiff base condensation reaction between 2,3,5,6-tetrafluoroterephthalaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine; the peak at 3477 cm –1 is attributed to the O–H of graphene oxide and the N–H in the amide bond formed by the dehydration condensation of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and graphene oxide, indicating the successful synthesis of FCOF / GO.

[0041] The N2 adsorption-desorption isotherm and pore size distribution of the FCOF / GO prepared in this example are as Figure 3 shown. The specific surface area of FCOF / GO is 469.8 m 2 / g, and the average pore size is 2.6 nm, indicating that it is a mesoporous material.

[0042] The X-ray diffraction results of the FCOF / GO prepared in this example are as Figure 4 shown. It can be seen from Figure 4 that strong diffraction peaks appear at 2θ = 2.83°, 4.91°, 5.72° and 7.55° for FCOF / GO, and the characteristic diffraction peak of graphene oxide (2θ = 11.88°) weakens, indicating the successful grafting of the fluorinated covalent organic framework on the surface of graphene oxide.

[0043] The X-ray photoelectron spectroscopy of the FCOF / GO prepared in this example is as Figure 5 shown. F1s belongs to 2,3,5,6-tetrafluoroterephthalaldehyde, N1s belongs to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, and O1s belongs to GO, indicating the presence of C, N, O, and F elements in the fluorinated covalent organic framework / graphene oxide composite material, indicating its successful synthesis.

[0044] Example 2

[0045] Add graphene oxide (GO, 100 mg) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT, 0.24 mmol, 85.06 mg) into a 100 mL single-necked flask. Subsequently, add tetrahydrofuran (22 mL), and ultrasonically treat for 2.0 h to uniformly disperse the GO and TAPT mixed solution. Then heat and stir this system at 70 °C for 30 min. Dissolve 2,3,5,6-tetrafluoroterephthalaldehyde (TFA, 0.36 mmol, 74.16 mg) in tetrahydrofuran (8.0 mL) and acetic acid (1.0 mL) and mix well. Slowly add this solution dropwise to the above reaction system, heat and stir at 50 °C for 2.0 h. Wash the material with acetonitrile and methanol respectively to remove unreacted substances and impurities, and then perform vacuum drying at 45 °C to obtain the fluorine-functionalized covalent organic framework / graphene oxide material (FCOF / GO).

[0046] The scanning electron micrograph of the FCOF / GO prepared in this example is as Figure 6 shown, and it can be observed that the fluorine-functionalized covalent organic framework / graphene oxide material has a cross-linked, loose, and porous network structure.

[0047] Figure 7 The adsorption amounts of fluxapyroxad, flufenacet, bixafen, trifloxystrobin, and triticonazole by the fluorine-functionalized covalent organic framework / graphene oxide material prepared in this example are shown, indicating that under these synthesis conditions, the fluorine-functionalized covalent organic framework / graphene oxide material can adsorb fluorine-containing pesticides.

[0048] Example 3

[0049] Use the fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 of the present invention as an adsorbent to investigate its adsorption kinetics.

[0050] Weigh FCOF / GO (2.0 mg), and add 2.0 mL of a 50 μg / mL mixed standard solution (fluxapyroxad, flufenacet, bixafen, trifloxystrobin, and triticonazole) to it. Shake on a shaker at 25 °C for different times (0.08, 0.33, 0.66, 1.0, 5.0, 10, 30, 60, 240 min). After the shaker stops, take the supernatant and filter it through a 0.22 μm PTFE filter membrane, and then perform liquid phase analysis and detection. The detector is an ultraviolet detector (detection wavelength is 210 nm). The results are as Figure 8 shown. Within 10 min on the shaker, the adsorption amounts of fluxapyroxad, flufenacet, bixafen, trifloxystrobin, and triticonazole by FCOF / GO show a rapid upward trend and basically tend to the adsorption equilibrium state after 10 min. The reason is that the uniform pore size distribution of FCOF / GO makes it have the advantage of fast mass transfer rate.

[0051] Example 4

[0052] The fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 of the present invention was used as an adsorbent to investigate the differences from commercial adsorbent materials.

[0053] Weigh 2.0 mg of the materials (SCX, C18, HLB, Al2O3, GO, SAX, silica gel, and FCOF / GO), add 2.0 mL of a 50 μg / mL mixed standard solution (fluxapyroxad, flufenacet, bixafen, trifloxystrobin, and triticonazole) thereto, shake in a shaker for 720 min, filter through a 0.22 μm PTFE membrane, collect the effluent for liquid phase analysis and detection, and use an ultraviolet detector (detection wavelength: 210 nm). The results are as Figure 9 shown. FCOF / GO has a higher adsorption capacity than other commercial adsorbents (SCX, C18, HLB, Al2O3, GO, SAX, silica gel). It is speculated that this is because the adsorption force of commercial adsorbents is single, while the adsorption of fluorine-containing pesticides by FCOF / GO is mainly based on F–F interactions, supplemented by strong hydrogen bonds, π–π stacking, and hydrophobic interactions, which synergistically adsorb fluorine-containing pesticides.

[0054] Example 5

[0055] The fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 of the present invention was used as an adsorbent, and compounds with different structures were used to further investigate its adsorption selectivity and anti-matrix interference ability.

[0056] Weigh FCOF / GO (2.0 mg), add 2.0 mL of a 50 μg / mL mixed standard solution (fluxapyroxad, flufenacet, bixafen, trifloxystrobin, triticonazole, catechin, rutin, and syringic acid) thereto, shake in a shaker for 720 min, filter through a 0.22 μm PTFE membrane, collect the effluent for liquid phase analysis and detection, and use an ultraviolet detector (detection wavelength: 210 nm). The results are as Figure 10 shown. The adsorption amount of other interfering components in the sample is significantly less than that of fluorine-containing pesticides. This is because a large number of F atoms provide F–F interaction active sites, which have a high affinity for fluorine-containing pesticides, and synergistically improve the adsorption ability with strong hydrogen bonds, π–π stacking, and hydrophobic interactions, proving that FCOF / GO has high selectivity and good anti-matrix interference ability for fluorine-containing pesticides.

[0057] Example 6

[0058] The fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 of the present invention was used as an adsorbent, and a miniaturized tip solid-phase extraction-high performance liquid chromatography method was used for the extraction of fluorine-containing pesticides.

[0059] The Astragalus membranaceus sample was crushed into a uniform powder. 1.0 g of the sample powder was weighed and placed in a 50 mL centrifuge tube, and 10 mL of acetonitrile was added. The mixture was vortexed for 1.0 min, ultrasonically extracted for 10 min, and then centrifuged at 8000 rpm for 6.0 min. The supernatant was collected, and the operation was repeated twice. The collected supernatant was rotary evaporated to dryness and then redissolved in 20 mL of acetonitrile-water (5:95, v / v) to obtain a sample solution.

[0060] A miniaturized device composed of a 5 mL syringe and a 200 μL disposable pipette tip was selected. First, the bottom of the disposable pipette tip was filled with absorbent cotton, and then, 10.0 mg of the adsorbent weighed precisely was added, and the upper layer of the adsorbent was sealed with absorbent cotton again. Finally, the disposable pipette tip with the adsorbent added was assembled with the syringe. Subsequently, the whole pretreatment procedure was completed through four steps: activation (1.0 mL of methanol and 1.0 mL of water), loading (5.0 mL of a 2.0 μg / mL spiked sample mixed solution (fluxapyroxad, flufenacet, bixafen, metconazole, and trifloxystrobin), 500 rpm), elution (1.0 mL of methanol-water (1:9, v / v)), and elution (1.0 mL of methanol, 500 rpm). After the elution solution was blown to dryness with nitrogen, 200 μL of methanol-water (78:22, v / v) was selected for reconstitution, and it was vortexed to dissolve it fully. The obtained reconstituted solution was filtered through a disposable syringe filter membrane (polytetrafluoroethylene, 0.22 μm) and then subjected to liquid phase detection and analysis. The results showed that this method had a high recovery rate (96.1–99.0%), and it was considered that the fluorine-functionalized covalent organic framework / graphene oxide material had universality and could be used as an adsorbent in different sample pretreatment methods.

[0061] Example 7

[0062] The fluorine-functionalized covalent organic framework / graphene oxide material prepared in Example 1 of the present invention was used as an adsorbent, and the shaker-assisted dispersive filter head solid-phase extraction-high performance liquid chromatography method was adopted for the extraction and detection of fluorine-containing pesticides.

[0063] The Astragalus membranaceus, honeysuckle, and tea samples were ground into uniform powders. Weighed 1.0 g of each sample powder and placed it in a 50 mL centrifuge tube, then added 10 mL of acetonitrile. The mixture was vortexed for 1.0 min, subjected to ultrasonic extraction for 10 min, and then centrifuged at 8000 rpm for 6.0 min. The supernatant was collected, and the operation was repeated twice. The collected supernatant was rotary evaporated to dryness and then redissolved in 20 mL of acetonitrile-water (5:95, v / v) as the sample solution. Accurately weighed 10 mg of FCOF / GO in a 10 mL centrifuge tube, added 5.0 mL of the sample solution, and oscillated on a shaker for 3.0 min. At this time, connect a 5 mL syringe barrel to a disposable syringe filter membrane filter (polytetrafluoroethylene, 0.22 μm), then pour the sample solution in the centrifuge tube into the syringe barrel and pass through the filter head once from top to bottom, which is considered as one sample loading. 1.0 mL of acetonitrile-water (1:9, v / v) was used as the eluent, and 1.0 mL of methanol was used as the eluant. The syringe was repeatedly pulled and pushed for 1.0 min, and the eluate was collected and blown with nitrogen. Subsequently, 200 μL of methanol-water (78:22, v / v) was selected for reconstitution, and vortexed to dissolve it thoroughly. The obtained reconstituted solution was filtered through a 0.22 μm PTFE filter membrane and then subjected to liquid phase detection and analysis. The results showed that: cyflufenamid (1.746 μg / g) was detected in Astragalus membranaceus from Shanxi, boscalid (0.496 μg / g) was detected in Astragalus membranaceus from Anhui, boscalid (0.369 μg / g) was detected in honeysuckle from Shandong, and boscalid (0.319 μg / g) was detected in the tea sample, proving that this method can be successfully applied to the detection of fluorine-containing pesticides in different complex matrix samples.

[0064] Comparative Example 1

[0065] Add graphene oxide (GO, 100 mg) and 1,3,5-tris(4-aminophenyl)benzene (TAPB, 0.48 mmol, 168.7 mg) to a 100 mL single-necked flask, then add tetrahydrofuran (22 mL), and ultrasonically treat for 2.0 h to disperse GO and TAPB evenly. Heat and stir this system at 70 °C for 30 min. Dissolve 2,3,5,6-tetrafluorobenzaldehyde (TFA, 0.72 mmol, 148.3 mg) in tetrahydrofuran (8.0 mL) and acetic acid (1.0 mL) and mix evenly. Slowly add this solution dropwise to the above reaction system, heat and stir the reaction at 70 °C for 2.0 h, wash the material with acetonitrile and methanol respectively to remove unreacted substances and impurities, and then carry out vacuum drying at 45 °C to obtain phenyl fluoride-functionalized covalent organic framework / graphene oxide material (B-FCOF / GO).

[0066] This comparative example prepared phenyl fluoride-functionalized covalent organic framework (B-FCOF) without adding graphene oxide as a control, as follows: Add TAPB (0.48 mmol, 168.7 mg) to a 100 mL single-necked flask, then add tetrahydrofuran (22 mL) to dissolve it, and heat at 70 °C. Dissolve TFA (0.72 mmol, 148.3 mg) in tetrahydrofuran (8.0 mL) and acetic acid (1.0 mL) and mix well. Slowly add this solution dropwise to the above TAPB solution, heat and stir the reaction at 70 °C for 2.0 h. Wash the material with acetonitrile and methanol respectively to remove unreacted substances and impurities, and then perform vacuum drying at 45 °C to obtain phenyl fluoride-functionalized covalent organic framework (B-FCOF).

[0067] Scanning electron microscopy tests were performed on B-FCOF / GO, GO, and B-FCOF prepared in this comparative example, and the results are as Figure 11 shown. Figure 11 Among them, the morphology of graphene oxide is a wrinkled sheet, and the phenyl fluoride-functionalized covalent organic framework has a spherical cluster structure. The morphology of the synthesized phenyl fluoride-functionalized covalent organic framework / graphene oxide composite material is that clusters of spheres grow on the wrinkled sheets. Compared with FCOF / GO, the different monomer types affect the morphology and structure of the composite material.

[0068] Figure 12 is the N2 adsorption-desorption isotherm and pore size distribution diagram of B-FCOF / GO. The BET specific surface area is 230.5 m 2 / g, and the average pore size is 3.7 nm, indicating that it is a mesoporous material and its specific surface area is smaller than that of FCOF / GO.

[0069] The materials prepared in Example 1 and Comparative Example 1 of the present invention were used as adsorbents to investigate the adsorption performance and compare their adsorption capacities for fluorine-containing pesticides.

[0070] Weigh 2.0 mg of materials B-FCOF / GO and FCOF / GO into different centrifuge tubes respectively, add 2.0 mL of 50 μg / mL mixed standard solution (fluxapyroxad, flufenacet, bixafen, trifloxystrobin, and triticonazole) to them, shake in a shaker for 720 min, filter through a 0.22 μm PTFE filter membrane, and collect the effluent for liquid phase analysis and detection. The detector is an ultraviolet detector (detection wavelength is 210 nm). The results are as Figure 13As shown, FCOF / GO has a higher adsorption capacity for five fluorinated pesticides than B-COF / GO. It is speculated that this is because 2,4,6-tris(4-aminophenyl)-1,3,5-triazine and 2,3,5,6-tetrafluoroterephthalaldehyde were selected as COF monomers to prepare the fluorine-functionalized covalent organic framework graphene oxide material, which has a more fluffy porous structure, a larger specific surface area, and more adsorption sites.

[0071] The fluorine-functionalized covalent organic framework / graphene oxide materials prepared in Example 1 and Comparative Example 1 of the present invention were used as adsorbents, and the extraction and detection effects on fluorinated pesticides were compared by shake-flask assisted dispersive filter head solid-phase extraction-high performance liquid chromatography.

[0072] Precisely weigh 10 mg of FCOF / GO and B-FCOF / GO into 10 mL centrifuge tubes, respectively, add 5.0 mL of the sample solution, and shake on a shaker for 3.0 min. At this time, connect a 5 mL syringe barrel to a disposable syringe filter membrane filter (polytetrafluoroethylene, 0.22 μm), then pour the sample solution in the centrifuge tube into the syringe barrel and pass it through the filter head once from top to bottom, which is considered as one sample loading. 1.0 mL of acetonitrile-water (1:9, v / v) was used as the eluent, and 1.0 mL of methanol was used as the eluent. Pull and push the syringe repeatedly for 1.0 min, collect the eluate, and blow it with nitrogen. Subsequently, 200 μL of methanol-water (78:22, v / v) was selected for reconstitution, and vortexed to dissolve it completely. The reconstituted solution obtained was filtered through a 0.22 μm PTFE filter membrane and subjected to liquid phase detection and analysis. The results are as Figure 14 shown, indicating that the recovery rate of B-FCOF / GO prepared in Comparative Example 1 for fluorinated pesticides was 51.5–74.8%, which was significantly lower than the recovery rate of FCOF / GO for fluorinated pesticides in Example 1 (86.4–90.0%).

Claims

1. A method for preparing a fluorine-functionalized covalent organic framework / graphene oxide material, characterized in that: The steps include: (1) ultrasonically dispersing graphene oxide and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in tetrahydrofuran and reacting at 65° C. to 80° C.; (2) dissolving 2,3,5,6-tetrafluorobenzaldehyde in a mixed solution of tetrahydrofuran and acetic acid; (3) adding the solution obtained in step (2) to the reaction system in step (1) and reacting at 25 to 90° C. for 0.5 to 6 hours; (4) After the reaction in step (3) is completed, the material is washed with acetonitrile and methanol and dried in vacuo to obtain a fluorine-functionalized covalent organic framework / graphene oxide material.

2. The method for preparing the fluorine-functionalized covalent organic framework / graphene oxide material according to claim 1, characterized in that: In step (1), the reaction temperature is 70° C. and the reaction time is 30 min.

3. The method for preparing the fluorine-functionalized covalent organic framework / graphene oxide material according to claim 1, characterized in that: The mass ratio of graphene oxide to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in step (1) is 1:(0.21-2.55).

4. The method for preparing the fluorine-functionalized covalent organic framework / graphene oxide material according to claim 1, characterized in that: The molar ratio of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to 2,3,5,6-tetrafluorobenzaldehyde in step (3) is 2:

3.

5. The method for preparing the fluorine-functionalized covalent organic framework / graphene oxide material according to claim 1, characterized in that: The reaction conditions in step (3) are: heating and stirring the reaction at 50°C to 70°C for 2h.

6. Fluorine-functionalized covalent organic framework / graphene oxide material prepared by the method according to any one of claims 1 to 5.

7. The fluorine-functionalized covalent organic framework / graphene oxide material according to claim 6 is used as an adsorbent in the extraction and detection of fluorine-containing pesticides.

8. The use according to claim 7, characterized in that: The fluorine-containing pesticides include fluopyram, flufenacet, bixafen, clofothiazolin and trifloxystrobin.

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