A solid-phase microextraction fiber of a fluorine click multi-component covalent organic framework material and its preparation method

Abstract

The present invention discloses a solid-phase microextraction fiber of a fluorine-click multi-component covalent organic framework material and a preparation method thereof, belonging to the field of preparation of solid-phase microextraction materials. A COF material with an adjustable ratio of functional group methoxy to double bond is constructed by using a three-component unit, and then thiophenol is click-bonded to the fluorobenzene through a thiol-ene click chemical bond to construct a COF-V-X-F solid-phase microextraction material with an adjustable number of F functional groups. The material is coated on the surface of a stainless steel wire to prepare an SPME fiber, which can be applied to the efficient enrichment and extraction of persistent organic pollutants perfluorinated compounds. The room-temperature synthesis method makes the synthesis of COF mild and convenient. The prepared material has superhydrophobicity and F-F affinity. With the addition of methoxy groups, the coating maintains high stability after post-modification.

Description

Technical Field

[0001] The present invention mainly belongs to the field of preparation of solid-phase microextraction materials, and is a novel COF material-based SPME fiber and its preparation method, which can be applied to the enrichment and extraction of perfluoro- or polyfluoroalkyl substances (PFASs). Background Art

[0002] Solid-phase microextraction (SPME) is a technique based on the analyte distribution equilibrium between the sample matrix and the extraction phase. SPME is considered an environmentally friendly technique because it uses less solvent volume and, in some cases, no solvent. Due to its small geometry, simple operating procedure, and excellent integrated design, it is also an ideal technique for automation. The SPME process is also fast and sensitive because it integrates sampling, analyte separation, and enrichment into one step, thus simplifying sample preparation and reducing analyte loss during sample preparation.

[0003] As the core of SPME, the coating material of SPME is often the focus of attention. However, traditional coating materials are all broad-spectrum and have no selectivity for PFASs, and have disadvantages such as being prone to swelling in organic solvents and easily detaching from the substrate, and perform poorly in the trace and ultra-trace analysis of PFASs in complex sample matrices. Therefore, it is necessary to develop an adsorption coating material with certain selectivity for the target substance PFASs and high extraction efficiency.

[0004] Covalent organic frameworks (COFs) are a class of porous polymers that can precisely reticulate organic structural units into extended 2D and 3D open networks, form pre-designed topologies and adjustable pore structures through strong covalent bonds, and present a crystalline state. COFs have unique properties such as chemical modularity, large surface area, high stability, low density, and adjustable pore size and functionality, which make them widely used in many fields, such as adsorption and separation, optoelectronics, drug delivery, heterogeneous catalysis, sensing, and energy storage. However, there are still some defects in the synthesis of COFs at present. The synthesis conditions require relatively high, usually requiring high temperature and high pressure preparation, which limits the preparation and application of COFs. It is necessary to develop COF materials that can be post-modified with specific functions and their preparation methods under mild conditions.

[0005] Based on this, the present invention provides a preparation method of a modified COF-modified SPME fiber and its analytical application for PFASs. In the present invention, aniline is used as a regulator for COF synthesis, and a general multi-component imine COF is synthesized at room temperature, and then a novel COF is synthesized by click chemistry modification. This COF material is used as a coating material to prepare SPME fibers. The controllable SPME coating thickness and unique functionalized units further improve the trace extraction performance and reusability of SPME fibers for complex sample matrices. Summary of the Invention

[0006] The present invention provides a solid-phase microextraction fiber of a fluorine-click multi-component covalent organic framework material for the problem of low efficiency in extracting trace PFASs in complex sample matrices. The fiber uses a stainless steel wire as a carrier and is coated with COF-V-X-F powder. COF-V-X-F contains methoxy and F bifunctional groups. The methoxy group stabilizes the COF structure and expands the application range of the extraction fiber in complex samples. The F-F affinity of the F functional group provides the adsorption capacity and selectivity of the fiber for perfluorinated compounds. The ratio of methoxy group to F functional group in the prepared material is adjustable, and the ratio of the two can be further optimized for different samples. Aiming at the problem of harsh synthesis conditions for COF materials, a synthesis method of this COF-V-X-F material at normal pressure and room temperature has been developed. The solid-phase microextraction fiber coating prepared by the present invention has a uniform structure and stable morphology, and has the characteristics of good thermal stability, good chemical stability, long service life and high enrichment efficiency. It can be applied to the efficient enrichment and extraction of trace polyfluoro / perfluorinated compounds in complex samples, achieving high-sensitivity detection of PFASs.

[0007] The present invention adopts the following technical solutions:

[0008] A preparation method of a solid-phase microextraction fiber of a fluorine-click multi-component covalent organic framework material, comprising the following steps:

[0009] S1: Preparation of SPME fiber: First, soak and treat the stainless steel wire with aqua regia. Immerse one end of the treated steel wire into the glue and rotate it slowly, then immerse the glued steel wire fiber into the COF-V-X-F powder and rotate it. Take out the stainless steel wire, dry it, and wash away the residual powder material on the surface to obtain the SPME fiber.

[0010] Preferably, the length of the steel wire is 10 cm and the cross-sectional diameter is 300 μm.

[0011] S2: Preparation of COF-V-X: Dissolve 1,4-dialdehyde-2,5-divinylbenzene and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde in 1,4-dioxane to form solution A. Mix aniline and 1,4-dioxane to form solution B. Add solution B to solution A, add an acetic acid catalyst, and react fully to form solution C. Then add 1,3,5-tris(4-aminophenyl)benzene to 1,4-dioxane to form solution D. Mix solution C and solution D again, ultrasonically mix evenly, and react at room temperature to obtain COF-V-X.

[0012] S3: Preparation of COF-V-X-F: Mix COF-V-X and 2,2'-azobis(isobutyronitrile), then add trifluorotoluene to form a solid-liquid mixture reaction system. Under nitrogen protection, add p-fluorothiophenol to the reaction system and react at 80 °C. After filtering the reaction product, centrifuge, wash with methanol and dry in vacuum to obtain COF-V-X-F powder.

[0013] Preferably, aqua regia is prepared according to the volume ratio of concentrated nitric acid to concentrated hydrochloric acid of 1:3.

[0014] Preferably, the aqua regia treatment process refers to vertically immersing the steel wire in aqua regia and corroding for 5 min. The aqua regia needs to be freshly prepared.

[0015] Preferably, the glue refers to epoxy resin glue or polyimide, and slowly rotate clockwise for 3 circles.

[0016] Preferably, the drying refers to drying in an oven at 60 °C for 12 h.

[0017] Preferably, the molar ratio of 1,4-dialdehyde-2,5-divinylbenzene to 2,5-dimethoxybenzene-1,4-dicarboxaldehyde is 1:(0.5 - 2).

[0018] Preferably, the total concentration range of solution A is 22 - 25 mg / mL.

[0019] Preferably, the concentration of solution B is 0.036 - 0.050 mmol / mL.

[0020] Preferably, the concentration of solution D is 28 - 30 mg / mL.

[0021] Preferably, the amount of acetic acid catalyst is 70 - 100 μL.

[0022] Preferably, to ensure the uniformity of the solution, it is necessary to ultrasonicate for 5 min and vortex for 1 min after mixing the solution in each step.

[0023] Preferably, the reaction time at room temperature is 1 - 3 days.

[0024] Preferably, the reaction in S3 is carried out in a stirring mode.

[0025] Preferably, the ratio of COF-V-X to trifluorotoluene is 10 mg / mL, the mass ratio of the catalyst 2,2'-azobis(isobutyronitrile) to COF-V-X is 1:(8 - 10), and the volume ratio of p-fluorothiophenol to trifluorotoluene is 1:20.

[0026] Application: The prepared SPME fiber is applied to the high-efficiency solid-phase microextraction of persistent organic pollutant perfluorinated compounds.

[0027] The solid-phase microextraction fiber of the fluorine click multi-component covalent organic framework material described in the present invention has the characteristics of adjustable three components, and at the same time has high stability, super hydrophobic characteristics and F-F affinity. The multi-component COF is synthesized by the room-temperature method. The reaction conditions are mild. The fluorine-functionalized COF is constructed by post-modification and bonding of fluorine-containing monomers. The SPME fiber is prepared by coating glue on the surface of a stainless steel wire. The multi-components are 1,4-dialdehyde-2,5-divinylbenzene, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 1,3,5-tris(4-aminophenyl)benzene. The ratio of the functional group methoxy group to the double bond is adjustable. The methoxy group improves the stability of COF, and the double bond provides a post-modification site. The room-temperature method uses a mixed solution of aniline regulator and 1,4-dioxane as the synthesis solvent. The fluorine functional group is bonded with polyfluorobenzenethiol on the double bond of the multi-component COF through thiol-ene click chemistry. The fluorine content can be adjusted by the number of constructed double bonds to form COF-V-X-F. The click part has F-F affinity and has a high extraction efficiency for fluorine-containing organic pollutants.

[0028] Advantages of the present invention:

[0029] (1) The present invention designs an SPME fiber with a COF coating. This coating exhibits a high specific surface area (731.05 m 2 ·g -1 ), and an ordered microporous structure. Due to its high hydrophobicity and F-F, it exhibits efficient analysis characteristics for hydrophobic analytes. For perfluoroalkyl acids and polyfluoroalkyl acid type compounds, its unique F-F affinity characteristics also show specific and efficient extraction effects for PFASs.

[0030] (2) The COF coating designed in the present invention has a multi-component structure. The methoxy groups therein will further improve the stability of COF. Therefore, the COF coating has high efficiency and stability, which provides an important guarantee for the extraction of complex sample matrices;

[0031] (3) In addition to using traditional acetic acid as a catalyst, the present invention also adds aniline as a regulator, making the synthesis conditions of COF more mild and reliable.

[0032] (4) The immobilized coating method of epoxy resin glue or polyimide ensures the stability of the coating and the controllability of the coating thickness, which determines the stability and good reproducibility of the analysis process. Description of the drawings

[0033] Figure 1 It is the PXRD powder diffraction pattern of the multi-component COF, indicating the high crystallinity of COF;

[0034] Figure 2It is the thermogravimetric diagram of the COF coating material. The coated COF can have a stable structure below 200 °C;

[0035] Figure 3 It is the PXRD powder diffraction diagram of the COF coating material treated with different organic solvents for 3 days. The COF coating can stably exist in a variety of solvents;

[0036] Figure 4 It is the nitrogen adsorption - desorption isotherm curve diagram of the COF coating material, used to characterize the specific surface area of the COF material;

[0037] Figure 5 It is the electron microscope image of the SPME fiber. The COF material is stably attached to the SPME steel wire fiber;

[0038] Figure 6 It is the synthesis steps and applications of the SPME fiber of COF - V - 0.33 - F;

[0039] Figure 7 It is the total ion chromatogram of the liquid chromatography - mass spectrometry (LC - MS) for the trace extraction of 7 PFASs at 1 pg / L in water by the SPME fiber. Detailed implementation mode

[0040] To make the above - mentioned features and advantages of the present invention more obvious and understandable, specific examples are given below for detailed description. Unless otherwise specified, the methods of the present invention are all conventional methods in the art.

[0041] Example 1

[0042] A preparation method of an SPME fiber of a fluorine - click multi - component COF mainly includes the following steps:

[0043] (1) Dissolve 0.02 mmol of 1,4 - dialdehyde - 2,5 - divinylbenzene and 0.04 mmol of 2,5 - dimethoxybenzene - 1,4 - dialdehyde in 0.5 mL of 1,4 - dioxane to form solution A. Mix 110 μL of aniline in 5 mL of 1,4 - dioxane to form solution B. Mix solutions A and B, add 70 μL of acetic acid catalyst, and react fully for 5 min to form solution C. Dissolve 0.04 mmol of 1,3,5 - tris(4 - aminophenyl)benzene in 0.5 mL of 1,4 - dioxane by ultrasonic treatment to form solution D. Then mix solutions C and D, ultrasonic for 5 min, and react at room temperature of 25 °C for 2 days. It is observed that the solution gradually becomes turbid and an orange precipitate is formed. After filtering the reaction product, centrifuge separation is carried out, and it is washed by centrifugal separation with tetrahydrofuran (2×10 mL) and methanol (3×10 mL) respectively. The yellow solid COF - V - 0.33 is collected by vacuum drying at 60 °C for 12 h.

[0044] (2) Add 100 mg of COF-V-0.33 and 10 mg of 2,2'-azobisisobutyronitrile into a 20 mL Schlenk tube, then add 10 mL of trifluorotoluene. Under nitrogen protection, add 0.5 mL of p-fluorothiophenol to the reaction system, stir at 80 °C for 48 h. After filtering the reaction product, wash it by centrifugation with methanol (6×10 mL). Finally, dry it in vacuo at 60 °C for 12 h to obtain COF-V-0.33-F, and perform electron microscopy characterization as Figure 5 .

[0045] (3) Immerse one end of a stainless steel wire with a diameter (φ = 300 μm) and a length of 10 cm into aqua regia, corrode it at room temperature for 5 min, then alternately wash it several times with ultrapure water and ethanol under the action of ultrasound, and air dry it for later use. Immerse the treated end of the steel wire into epoxy resin sealant to obtain a thin layer of glue, then immerse the prepared glue-coated steel wire fiber into COF-V-0.33-F powder, rotate it clockwise for 3 circles, carefully take out the stainless steel wire, control the length of the coating to be 1.5 cm, scrape off the excess part with a glass slide, and then dry it at room temperature for 24 h. Finally, wash off the residual COF powder on the surface with methanol to obtain the required SPME fiber.

[0046] Example 2

[0047] Perform solid-phase microextraction analysis experiments on seven PFASs in Minjiang River water with the obtained SPME fiber:

[0048] For the solid-phase microextraction operation, use the self-made SPME fiber, take 10 mL of Minjiang River water sample, insert the solid-phase microextraction fiber into a 1.0 ng / mL solution of seven PFASs, see Figure 7 . Enrich it in the stirring mode, set the pH of the extraction solution to 4, elute it with 100 μL of 1% ammonia methanol, pass the elution solvent through a 0.22 μm filter membrane, and the injection volume is 10 μL for LC-MS analysis. The analysis results are quantified by the external standard method. Table 1 shows the investigation of the SPME method. The detection limits of the method established by the SPME fiber of the novel COF material are between 0.17 - 1.43 ng / L, and the quantification limits are also between 0.89 - 4.75 ng / L. In addition, the detection linear range of this method is relatively wide, up to 0.5 - 20000 ng / L. Through the intuitive display of the enrichment factor, we can see the extraction performance of the SPME fiber, and the highest enrichment factor of the COF-coated fiber can reach 31 times.

[0049] Table 1 shows the performance investigation of the SPME-LC-MS method established by the SPME fiber

[0050]

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a solid-phase microextraction fiber of a fluorine click multi-component covalent organic framework material, characterized in that, It has three adjustable components, high stability, super hydrophobic properties and FF affinity, and includes the following preparation steps: First, the stainless steel wire is treated by soaking it in aqua regia, one end of the treated steel wire is immersed in glue and rotated slowly, then the glue-coated steel wire is immersed in COF-VXF powder and rotated, the stainless steel wire is taken out, dried, and the powder material remaining on the surface is washed off to obtain the SPME fiber; The preparation method of the COF-VXF powder comprises the following steps: (1) Preparation of COF-VX: 1,4-dialdehyde-2,5-divinylbenzene and 2,5-dimethoxybenzene-1,4-diformaldehyde were dissolved in 1,4-dioxane to form solution A. Aniline and 1,4-dioxane were mixed to form solution B. Solution B was added to solution A. Acetic acid was added as a catalyst to react fully to form solution C. 1,3,5-tri(4-aminophenyl)benzene was then added to 1,4-dioxane to form solution D. Solution C and solution D were mixed and mixed evenly by ultrasonication. The mixture was reacted at room temperature to obtain COF-VX. (2) Preparation of COF-VXF: COF-VX and 2,2-azobisisobutyronitrile were mixed, and trifluorotoluene was added to form a solid-liquid mixture reaction system. Under nitrogen protection, p-fluorobenzenethiol was added to the reaction system and reacted at 80°C. The reaction product was filtered, washed by methanol centrifugation and vacuum dried to obtain COF-VXF powder.

2. The preparation method according to claim 1, characterized in that, The length of the stainless steel wire was 10 cm and the cross-sectional diameter was 300 μm.

3. The preparation method according to claim 1, characterized in that The molar ratio of 1,4-dialdehyde-2,5-divinylbenzene to 2,5-dimethoxybenzene-1,4-dicarboxaldehyde is 1:(0.5-2), the total concentration of solution A is 22-25 mg / mL; the concentration of solution B is 0.036-0.050 mmol / mL; the concentration of solution D is 28-30 mg / mL; and the amount of acetic acid catalyst used is 70-100 μL.

4. The preparation method according to claim 1, wherein The reaction time at room temperature in step (1) is 1-3 days.

5. The preparation method according to claim 1, characterized in that, The dosage ratio of COF-VX and trifluorotoluene is 10 mg / mL, the volume ratio of p-fluorothiophenol and trifluorotoluene is 1:20, and the mass ratio of catalyst 2,2-azobisisobutyronitrile and COF-VX is 1:8-1:

10.

6. The solid phase microextraction fiber obtained according to the preparation method according to any one of claims 1 to 5.

7. Use of the solid-phase microextraction fiber according to claim 6, characterized in that: The prepared SPME fiber was applied to efficient solid phase microextraction of persistent organic pollutants (POPs) and perfluorinated compounds.

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