Magnetic cation covalent organic framework material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of magnetic composite materials and analysis and detection, and particularly relates to a magnetic cation covalent organic framework material as well as a preparation method and application thereof, and the preparation method comprises the following steps: taking trialdehyde phloroglucinol and bromomethanthridine as monomers, and carrying out aldehyde amine condensation polymerization on the surfaces of Fe3O4 nanoparticles to obtain the magnetic cation covalent organic framework material. Based on the magnetic cation covalent organic framework material, a magnetic solid phase extraction-liquid chromatography-mass spectrometry detection method is established, and efficient enrichment and sensitive detection of phenoxy carboxylic acid herbicides can be realized. The magnetic cation covalent organic framework material has the advantages of simplicity and convenience in preparation, high enrichment efficiency, strong selectivity, good reusability and the like. The constructed detection method is rapid, sensitive and accurate, can meet the trace analysis requirements of phenoxy carboxylic acid herbicides in water, and has very strong practicability.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic composite materials and analysis and detection, and in particular relates to a magnetic cationic covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Phenoxycarboxylic acid herbicides are selective herbicides that mimic the effects of plant growth hormones, causing weeds to overgrow and die. They are used to control invasive aquatic plants in lakes, ponds, and natural waterways. Although phenoxycarboxylic acid herbicides have good weed control effects, long-term application may cause soil and water pollution. Acute exposure to phenoxycarboxylic acid herbicides has been reported to cause moderate toxicity in mammals, while chronic exposure to phenoxycarboxylic acid herbicides can lead to endocrine system disorders, soft tissue sarcomas, and fetal malformations. To ensure water quality safety, there is an urgent need to develop sensitive and accurate monitoring and analysis methods for phenoxycarboxylic acid herbicides.

[0003] Commonly used instruments for detecting phenoxycarboxylic acid herbicides include capillary electrophoresis, gas chromatography, gas chromatography-tandem mass spectrometry, liquid chromatography, and liquid chromatography-tandem mass spectrometry. Liquid chromatography-tandem mass spectrometry offers advantages such as high sensitivity, strong specificity, and the absence of complex derivatization procedures. However, the complex matrix of water samples and the relatively low levels of phenoxycarboxylic acid herbicides residues make effective sample pretreatment essential before instrumental analysis. Currently, solid-phase extraction (SPE) is the most commonly used pretreatment method for detecting phenoxycarboxylic acid herbicides in water samples due to its low cost and low solvent usage. However, this pretreatment method still has the following drawbacks: ① It requires multiple steps, including column activation, sample loading, washing, and elution, making the process cumbersome; ② If the water sample contains suspended matter or particulate matter, it may clog the column, requiring additional filtration; and ③ adsorbents (such as C18 and HLB) lack selectivity, and impurities such as humic acid and inorganic salts in the water sample may compete for adsorption sites, resulting in low recovery of the target phenoxycarboxylic acid herbicides.

[0004] Therefore, developing a new method for detecting phenoxycarboxylic acid herbicides has become a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of the present invention is to provide a magnetic cationic covalent organic framework material to meet the needs of enrichment and detection of trace phenoxycarboxylic acid herbicides in water bodies, and to construct a new magnetic solid-phase extraction pretreatment method suitable for the efficient enrichment of phenoxycarboxylic acid herbicides based on the magnetic cationic covalent organic framework material. Combined with liquid chromatography-tandem mass spectrometry, highly sensitive detection of trace phenoxycarboxylic acid herbicides in environmental water is achieved.

[0006] Based on this, the present invention discloses a method for preparing a magnetic cationic covalent organic framework material, which adopts the following technical means: A method for preparing a magnetic cationic covalent organic framework material comprises the following steps: It is prepared by aldehyde-amine condensation reaction on the surface of Fe3O4 nanoparticles using trialdehyde phloroglucinol and bromphenanthridine as monomers.

[0007] Furthermore, trialdehyde phloroglucinol and bromophenanthridine were used as monomers to carry out an aldehyde-amine polycondensation reaction on the surface of Fe3O4 nanoparticles, specifically: Fe3O4 nanoparticles were added to a mixed solvent of mesitylene and dioxane, ultrasonically dispersed evenly, and then methylphenanthridinium bromide and dilute acetic acid were added. After shaking for 2-12 hours, the particles were transferred to a pressure-resistant reaction tube, and trialdehyde phloroglucinol was added. After three freeze-pump-thaw cycles, a solvent thermal reaction was carried out. After the reaction, the product was collected by magnetic separation, washed with methanol, and dried to obtain a magnetic cationic covalent organic framework material.

[0008] Furthermore, the mass ratio of the Fe3O4 nanoparticles to bromophenanthridine is 1:2-5. If too few Fe3O4 nanoparticles are added, the magnetic response is poor, and if too many Fe3O4 nanoparticles are added, the surface-coated cationic covalent organic framework material is less, and the enrichment effect is affected. The molar feed ratio of the trialdehyde phloroglucinol to bromphenanthridine is 1:1.5-3; The volume ratio of mesitylene, dioxane and dilute acetic acid is 5:4.5~5.5:0.5~2; The concentration of the dilute acetic acid is 5-7 mol·L -1 ; The molar concentration of the trialdehyde phloroglucinol in the reaction system is 0.01-0.1 mmol / mL; Furthermore, the reaction temperature of the solvent thermal reaction is 100-120° C., and the reaction time is 48-120 h.

[0009] The present invention also discloses a magnetic cationic covalent organic framework material, which is prepared by any of the above-mentioned preparation methods and has a simplified structural formula of Fe3O4@DB-iCOF.

[0010] The present invention also discloses the application of the magnetic cationic covalent organic framework material as a magnetic solid phase extraction adsorbent for detecting the content of phenoxycarboxylic acid herbicides in water.

[0011] Furthermore, the specific detection method for the content of phenoxycarboxylic acid herbicides in the water body is: ultrasonically mixing the water sample with the magnetic cationic covalent organic framework material, oscillating adsorption, magnetic separation, removing impurities with a cleaning agent, then ultrasonically desorbing with a desorbent, blowing with nitrogen, re-dissolving, filtering, and transferring to an injection bottle, and detecting by liquid chromatography tandem mass spectrometry.

[0012] Furthermore, the pH of the water sample is 3-7, the amount of magnetic cationic covalent organic framework material in every 25 mL of water sample is 5-20 mg, and the oscillation adsorption time is 10-60 min.

[0013] Furthermore, the cleaning agent is acetonitrile.

[0014] Furthermore, the desorbent is 5% ammonia-methanol, and the amount of the desorbent used in every 25 mL of water sample is more than 2.5 mL.

[0015] Furthermore, the phenoxycarboxylic acid herbicide is one or more of 2-methyl-4-chlorophenoxyacetic acid (MCPA), 2-(4-chloro-2-methylphenoxy) propionic acid (MCPP), 2-methyl-4-chlorophenoxybutyric acid (MCPB), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP), 2,4-dichlorophenoxybutyric acid (2,4-DB), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4,5-trichlorophenoxypropionic acid (2,4,5-TP).

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a magnetic cationic covalent organic framework material, which contains rich pyridinium quaternary ammonium cations and a high specific surface area, and has the advantages of a simple preparation method and low cost.

[0017] (2) The present invention confirms that the magnetic cationic covalent organic framework material can be used for magnetic solid phase extraction of phenoxycarboxylic acid herbicides and exhibits good selectivity and reusability.

[0018] (3) The phenoxycarboxylic acid herbicide detection method constructed based on the magnetic cationic covalent organic framework material of the present invention has a wide linear range, high sensitivity and good reproducibility.

[0019] (4) The detection method provided by the present invention is stable, reliable, simple and economical, and is suitable for routine detection of trace amounts of phenoxycarboxylic acid herbicides in complex samples such as environmental water, and has strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a comparison diagram of the X-ray diffraction of the magnetic cationic covalent organic framework material in Example 1; Figure 2 : This is the hysteresis loop diagram of the Fe3O4 and magnetic cation covalent organic framework material in Example 1; FIG3(A) is a graph showing the test results at different pH values ​​in Example 2; FIG3(B) is a graph showing the detection results at different ionic strengths in Example 2; FIG3(C) is a graph showing the test results at different adsorbent dosages in Example 2; FIG3(D) is a graph showing the detection results at different oscillation adsorption times in Example 2; FIG3(E) is a graph showing the test results under different desorbent types in Example 2; FIG3(F) is a graph showing the test results at different desorbent volumes in Example 2; Figure 4 This is a graph showing the adsorption selectivity of the magnetic cationic covalent organic framework material of Example 3; Figure 5 This is a flow chart for the preparation of the magnetic cationic covalent organic framework material and the detection of phenoxycarboxylic acid herbicides of the present invention. DETAILED DESCRIPTION

[0021] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are generally performed under conventional conditions or as recommended by the manufacturer.

[0022] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in this application can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in this application are used in a conventional manner in this area or in accordance with the product instructions. In addition, any methods and materials similar to or equivalent to those described herein can be applied to the present method. The preferred embodiments and materials described herein are for demonstration purposes only.

[0023] Example 1 This embodiment discloses a method for preparing a magnetic cationic covalent organic framework material: Ferric chloride hexahydrate, trisodium citrate and urea were dissolved in 30 mL of water at a molar ratio of 1:2:3, and 300 mg of polyacrylamide was added with stirring. After 1 h, the mixture was transferred to a reactor and reacted at 200 °C for 12 h. The product was collected by magnetic separation, washed repeatedly with water and ethanol, and dried at 60 °C to obtain Fe3O4 nanoparticles.

[0024] 60 mg of Fe3O4 nanoparticles were ultrasonically dispersed in a mixed solvent of 2.4 ml of mesitylene and 2.4 ml of dioxane, and 0.36 mmol (136.9 mg of phenanthroline bromide) and 0.48 mL of 6 mol·L -1The reaction mixture was stirred at room temperature for 4 hours in dilute acetic acid and then transferred to a pressure-resistant reaction tube. 0.24 mmol (50.4 mg) of trialdehyde phloroglucinol was added. Three freeze-pump-thaw cycles were performed and the reaction was continued at 120°C for 72 hours. After the reaction, the product was collected by magnetic separation, washed with methanol, and dried at 60°C to produce the magnetic cationic covalent organic framework (Fe3O4@DB-iCOF).

[0025] Figure 1 The X-ray diffraction comparison diagram of the magnetic cationic covalent organic framework material prepared in this example (compared with Fe3O4 and DB-iCOF) is shown in Figure 2. Figure 1 It can be seen that the XRD spectrum of the magnetic cationic covalent organic framework material prepared in this example contains typical diffraction peaks of Fe3O4 nanoparticles and cationic covalent organic framework material (DB-iCOF).

[0026] Figure 2 This is the hysteresis loop diagram of the magnetic cationic covalent organic framework material prepared in this embodiment. Figure 2 It can be seen that the saturation magnetic intensities of Fe3O4 nanoparticles and magnetic cationic covalent organic framework materials (Fe3O4@DB-iCOF) are 78.2 and 17.9 emu·g, respectively. -1 The magnetic cationic covalent organic framework material has good magnetic properties. Under the action of an external magnetic field, it can be quickly and thoroughly separated from the solution, which can meet the subsequent magnetic separation requirements.

[0027] Example 2 This example discloses a method for detecting phenoxycarboxylic acid herbicides based on a magnetic cationic covalent organic framework material, and studies the influence of key parameters in the pretreatment process on the final detection results, thereby determining the optimal pretreatment conditions for the detection method.

[0028] The pretreatment conditions were optimized by a single-factor experimental method. 5 mg of the magnetic cationic covalent organic framework material prepared in Example 1 was weighed into a 50 mL glass bottle, and 25 mL of water was added for ultrasonic dispersion. 0.5 mL of a phenoxycarboxylic acid herbicide standard solution was added, the pH of the solution was adjusted to 7, oscillation adsorption was performed for 30 min, magnetic separation was performed, and the supernatant was discarded. After washing with an appropriate amount of acetonitrile, 5 mL of a 5% ammonia-methanol desorbent was added, ultrasonic desorption was performed for 10 min, magnetic separation was performed, and the eluate was collected. Finally, the solution was dried and redissolved with nitrogen, filtered with a filter membrane, and analyzed by liquid chromatography tandem mass spectrometry.

[0029] Liquid chromatography (AB SCIEX ExionLC AC) was performed on a C18 column (100 mm × 2.1 mm, 2.6 μm) with a mobile phase consisting of 5 mmol / L ammonium acetate (A) and methanol (B) at a flow rate of 0.3 mL / min. The gradient elution program was: 0–5 min, 40–65% B; 5–5.01 min, 65–40% B; and 5.01–7 min, 40% B. Tandem mass spectrometry (AB SCIEX QTRAP 4500) was performed using an electrospray ionization source in negative ionization mode and multiple reaction monitoring (MRM) mode. Phenoxycarboxylic acid herbicides were quantified using an external standard. MRM mode parameters are shown in Table 1.

[0030] Table 1. Structural information of phenoxycarboxylic acid herbicides and relevant parameters for MRM mode detection

[0031] ① Study the influence of pH value on the test results: The pH values ​​of the loading solutions were adjusted to 1, 3, 5, 7, 9, and 11, respectively. Other experimental conditions were exactly the same as above. The recoveries of the phenoxycarboxylic acid herbicides detected in the six groups of experiments are shown in Figure 3 (A).

[0032] ② Ionic strength: The ionic strength was studied by adjusting the NaCl concentration in the loading solution to 0, 0.001, 0.01, 0.1, 0.5, and 1 M. Other experimental conditions were exactly the same as above. The recoveries of the phenoxycarboxylic acid herbicides detected in the six experiments are shown in Figure 3 (B).

[0033] ③ Study the effect of adsorbent dosage on test results: The dosage of magnetic cationic covalent organic framework material was adjusted to 2.5 mg, 5 mg, 10 mg, and 20 mg, respectively. The other experimental conditions were exactly the same as above. The recovery rates of phenoxycarboxylic acid herbicides detected in the four groups of experiments are shown in Figure 3 (C).

[0034] ④ Study the effect of oscillation adsorption time on the test results: The oscillation adsorption time was adjusted to 10 min, 20 min, 30 min, 45 min, and 60 min, respectively. Other experimental conditions were exactly the same as above. The recovery rates of phenoxycarboxylic acid herbicides detected in the five groups of experiments are shown in Figure 3 (D).

[0035] ⑤ Study the effect of desorbent types on test results: The desorbent types were adjusted to MA, 5% HAc-MA, 5% NH3·H2O-MA, ACN, 5% HAc-ACN, and 5% NH3·H2O-ACN, respectively. Other experimental conditions were exactly the same as above. The recoveries of the phenoxycarboxylic acid herbicides detected in the six groups of experiments are shown in Figure 3 (E).

[0036] ⑥ Study the effect of desorbent volume on test results: The desorbent volumes were adjusted to 2.5 mL, 5 mL, 7.5 mL, and 10 mL, respectively. Other experimental conditions were exactly the same as above. The recoveries of the phenoxycarboxylic acid herbicides detected in the four groups of experiments are shown in Figure 3 (F).

[0037] The above results show that when using magnetic cationic covalent organic framework materials as adsorbents for the detection of phenoxycarboxylic acid herbicides, in the pretreatment step, the water sample pH should be set between 3 and 7, the ion concentration should be 0 M, the adsorbent dosage should be between 5 and 20 mg, the oscillation adsorption time should be longer than 10 min, the desorbent should preferably be 5% NH3·H2O-MA, and the desorbent volume should be set above 2.5 mL to achieve better treatment results.

[0038] Example 3 Investigation on the enrichment selectivity of phenoxycarboxylic acid herbicides by magnetic cationic covalent organic framework materials: 5 mg of magnetic cationic covalent organic framework material was ultrasonically dispersed in 25 mL of water containing 10 μg / L phenoxycarboxylic acid herbicides, hexabromocyclododecane, perfluorooctanoic acid, amantadine and rimantadine. After oscillation adsorption for 60 min, magnetic separation was performed and the supernatant was collected.

[0039] Add 5 mL of 5% ammonia-methanol desorbent, perform ultrasonic desorption for 10 min, perform magnetic separation, and collect the eluate.

[0040] The additional cleaning process was performed by adding 2.5 mL of acetonitrile after the adsorption was completed and before adding the desorbent, and ultrasonic cleaning was performed for 3 min.

[0041] The concentrations of oxycarboxylic acid herbicides, hexabromocyclododecane, perfluorooctanoic acid, amantadine, and rimantadine in the supernatant, washing solution, and eluent were determined by liquid chromatography-tandem mass spectrometry, and the recoveries were calculated.

[0042] The results show that: Figure 4As shown in A, when the desorption is performed directly without a washing step, the recovery rate of phenoxycarboxylic acid herbicides remains between 88.5% and 94.1%, which is less affected. The recovery rates of perfluorooctanoic acid, hexabromocyclododecane, adamantane and rimantadine are 90.2%, 68.3%, 0.7% and 1.4%, respectively. The supernatant after adsorption was tested, and it was found that the contents of adamantane and adamantane in the supernatant accounted for 97.3% and 99.3%, respectively. This shows that when loading the sample, the magnetic cationic covalent organic framework material can shield the interference of alkaline compounds. From Figure 4 As shown in Figure B, when 2.5 mL of ACN was used as the cleaning agent before desorption, the loss of phenoxycarboxylic acid herbicides in the desorption solution due to the cleaning step was less than 8%, while the recoveries of perfluorooctanoic acid and hexabromocyclododecane in the desorption solution dropped to 66.8% and 9.4%, respectively. This demonstrates that the cleaning step can assist in the removal of neutral interferences and that the magnetic cationic covalent organic framework material has good adsorption selectivity for phenoxycarboxylic acid herbicides.

[0043] Example 4 Investigation on the reusability of magnetic cationic covalent organic framework materials: The recovery of phenoxycarboxylic acid herbicides was evaluated by comparing the recovery of these compounds over six extraction-desorption cycles. After each cycle, the Fe3O4@DB-iCOF was re-equilibrated by sequentially flushing with methanol and water for 5 minutes. The recoveries of the eight phenoxycarboxylic acid herbicides remained excellent (89.7%-96.6%) over the six cycles, demonstrating the excellent reusability of the Fe3O4@DB-iCOF.

[0044] Example 5 The linear range, correlation coefficient, detection limit, quantification limit and precision of the detection method of the present invention for phenoxycarboxylic acid herbicides were measured. The results are shown in Table 2.

[0045] Table 2

Claims

1. A method for preparing a magnetic cationic covalent organic framework material, characterized in that: The method comprises the following steps: using trialdehyde phloroglucinol and bromophenanthridine as monomers, and carrying out aldehyde-amine polycondensation reaction on the surface of Fe3O4 nanoparticles to prepare the product.

2. The preparation method according to claim 1, characterized in that Using trialdehyde phloroglucinol and bromophenanthridine as monomers, an aldehyde-amine polycondensation reaction was carried out on the surface of Fe3O4 nanoparticles, specifically: Fe3O4 nanoparticles were added to a mixed solvent of mesitylene and dioxane, ultrasonically dispersed evenly, and then bromophenanthridine and dilute acetic acid were added. The mixture was shaken and transferred to a pressure-resistant reaction tube. Trialdehyde phloroglucinol was added. After three freeze-pump-thaw cycles, a solvent thermal reaction was carried out. After the reaction, the product was collected by magnetic separation, washed with methanol, and dried to obtain a magnetic cationic covalent organic framework material.

3. The preparation method according to claim 2, characterized in that The mass ratio of the Fe3O4 nanoparticles to the bromphenanthridine is 1:2-5; The molar feed ratio of the trialdehyde phloroglucinol to bromphenanthridine is 1:1.5-3; The volume ratio of mesitylene, dioxane and dilute acetic acid is 5:4.5-5.5:0.5~2; The concentration of the dilute acetic acid is 5~7 mol·L -1 ; The molar concentration of the trialdehyde phloroglucinol in the reaction system is 0.01-0.1 mmol / mL; The reaction temperature of the solvent thermal reaction is 100-120° C., and the reaction time is 48-120 h.

4. A magnetic cationic covalent organic framework material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 3, and its structural formula is Fe3O4@DB-iCOF.

5. The use of the magnetic cationic covalent organic framework material according to claim 4, characterized in that: As a magnetic solid phase extraction adsorbent, it is used to detect the content of phenoxycarboxylic acid herbicides in water.

6. The use according to claim 5, characterized in that The specific detection method of the phenoxycarboxylic acid herbicide content in the water body is: The water sample is ultrasonically mixed with the magnetic cationic covalent organic framework material, subjected to oscillation adsorption, magnetic separation, impurities are removed with a cleaning agent, and then ultrasonically desorbed with a desorbent. After nitrogen blowing and redissolution, the sample is filtered and transferred to an injection bottle for detection by liquid chromatography tandem mass spectrometry.

7. The use according to claim 6, characterized in that The pH of the water sample is 3-7, the amount of the magnetic cationic covalent organic framework material in each 25 ml water sample is 5-20 mg, and the oscillation adsorption time is 10-60 min.

8. The use according to claim 6, characterized in that The desorbent is 5% ammonia-methanol.

9. The use according to claim 6, characterized in that For every 25 ml of water sample, the amount of desorbent used is more than 2.5 mL.

10. The use according to claim 6, characterized in that The phenoxycarboxylic acid herbicide is one or more of 2-methyl-4-chlorophenoxyacetic acid, 2-(4-chloro-2-methylphenoxy) propionic acid, 2-methyl-4-chlorophenoxybutyric acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy) propionic acid, 2,4-dichlorophenoxybutyric acid, 2,4,5-trichlorophenoxyacetic acid and 2,4,5-trichlorophenoxypropionic acid.

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