Magnetic dispersive solid-phase extraction adsorbent with ZIF-67 loaded on magnetic carbon nanotubes as well as preparation method and application of magnetic dispersive solid-phase extraction adsorbent

Abstract

The invention discloses a magnetic dispersive solid-phase extraction adsorbent with a magnetic carbon nanotube loaded with ZIF-67, and relates to application of the magnetic dispersive solid-phase extraction adsorbent in water extraction. According to the composite material, a carboxylated multi-walled carbon nanotube and dimethyl imidazole cobalt (ZIF-67) composite material MMWCNT and ZIF-67 is adopted as an adsorbent, and efficient enrichment and detection of diazepam and metabolites thereof in a water body are achieved through a magnetic dispersive solid-phase extraction (m-dSPE) technology. The composite material has high specific surface area, excellent magnetism and good adsorption performance, target pollutants can be efficiently enriched under the condition that the pH is 9-10, and the extraction efficiency exceeds 70%. Experiments show that the method is simple and convenient to operate and high in recovery rate, and can be widely applied to the fields of environmental pollutant analysis, water quality monitoring and drug residue detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocomposites, and particularly relates to a magnetic dispersive solid-phase extraction adsorbent of magnetic carbon nanotubes loaded with ZIF-67, and a preparation method and application thereof. Background Art

[0002] In recent years, diazepam and its metabolites (nordiazepam, oxazepam, and temazepam) have been frequently detected in surface water environments worldwide. These drug residues not only affect the metabolic functions and behavioral characteristics of fish, but may also weaken their stress response capabilities. More notably, the drug residue levels detected in some edible fish have exceeded the safety limits, which is mainly attributed to water pollution rather than illegal addition, indicating that the bioaccumulation of drugs caused by aquaculture water pollution may pose potential residual risks. These findings highlight the urgent need to establish rapid, accurate, and reliable analytical methods for detecting diazepam and its metabolites in water environments.

[0003] Metal-organic frameworks (MOFs) are crystalline porous materials formed by the self-assembly of metal ions or clusters with organic ligands through coordination bonds, possessing both the rigidity of inorganic materials and the flexibility of organic materials. Their core advantage lies in their ultra-high specific surface area and adjustable pore structure. They are ideal candidates for applications such as gas storage, separation, catalysis, and environmental remediation, and their structures and functions can be customized by selecting specific metal ions and organic linkers.

[0004] Magnetic dispersive solid-phase extraction (m-SPE) is a sample pretreatment technique based on magnetic nanomaterials, which realizes the efficient enrichment and separation of target substances by dispersing functionalized magnetic adsorbents in sample solutions. Its core principle is to use magnetic or magnetizable materials as the adsorbent matrix, and rapidly separate the target substances from the sample matrix under the action of an external magnetic field, avoiding the cumbersome steps such as centrifugation and filtration in traditional solid-phase extraction. Summary of the Invention

[0005] The purpose of the present invention is to synthesize a magnetic solid-phase extraction adsorbent with magnetic carboxylated multi-walled carbon nanotubes as the substrate and ZIF-67 loaded on its surface. The MOFs are loaded on the surface of the magnetic multi-walled carbon nanotubes and are used for the trace analysis of diazepam in water. This adsorbent is simple to prepare, has high adsorption performance, is easy to separate, has good method reproducibility, and the samples after pretreatment can be rapidly analyzed, showing great potential application value in the field of analytical detection.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A preparation method of a magnetic dispersive solid-phase extraction adsorbent of magnetic carbon nanotubes loaded with ZIF-67, comprising the following steps:

[0008] S1. Add carboxylated multi-walled carbon nanotubes to water for dispersion to prepare a suspension; then add iron salts, mix and heat; then add ammonia water for reaction; after the reaction is completed, separate the magnetic carbon nanotubes;

[0009] S2. Disperse the magnetic carbon nanotubes obtained in step S1 in a solvent, and then add 2-methylimidazole to obtain a mixture;

[0010] S3. Add cobalt nitrate solution to the solvent, and then dropwise add the mixture obtained in step S2 while shaking. After the mixture turns dark purple during the reaction, continue stirring to ensure complete reaction; after the reaction is completed, wash and dry to obtain the magnetic dispersive solid-phase extraction adsorbent.

[0011] In the present invention, carboxylated multi-walled carbon nanotubes are first used as a template, and with the assistance of magnetic nanoparticles, ZIF-67 is coated on its surface by an in-situ growth method to obtain an MMWCNT@ZIF-67 composite material; then the crystal growth conditions are optimized by a solvothermal method to make the composite material have a uniform microporous structure and stable magnetic properties; finally, the obtained composite material is washed, dried and ground to prepare a uniform magnetic adsorbent.

[0012] Preferably, the concentration of the suspension prepared from carboxylated multi-walled carbon nanotubes is 0.01 - 0.02 g / ml.

[0013] Preferably, in step S1, the mass of carboxylated multi-walled carbon nanotubes is 1 - 2 g; the mixing mass ratio of carboxylated multi-walled carbon nanotubes to ferric chloride is 20:47; the dosage of ammonia water added in step S1 is 10 - 15 mL.

[0014] Preferably, in step S2, the reaction mass ratio of magnetic carbon nanotubes to 2-methylimidazole is 125:41; in step S3, the molar ratio of cobalt nitrate to 2-methylimidazole is 1:2.

[0015] More preferably, in step S1, the iron salts are ferric chloride hexahydrate and ferrous chloride tetrahydrate. Further, the ratio of carboxylated multi-walled carbon nanotubes, ferric chloride hexahydrate, ferrous chloride tetrahydrate and ammonia water in step S1 is 2 g, 17.3 mmol, 8.7 mmol and 10 mL.

[0016] Preferably, in step S2, the cobalt nitrate is cobalt nitrate hexahydrate, and the ratio of magnetic carbon nanotubes, 2-methylimidazole and cobalt nitrate hexahydrate is 0.5 g, 20 mmol and 10 mmol.

[0017] Preferably, the solvent used in step S2 is water or methanol; the solvent used in step S3 is methanol.

[0018] The present invention also provides the use of the magnetic carbon nanotube supported ZIF-67 composite as a magnetic dispersive solid phase extraction adsorbent for the simultaneous extraction and enrichment of diazepam and its metabolites in water; the specific application includes the following steps:

[0019] (1) Extraction: The water sample to be tested is left standing for 24 h to precipitate insoluble impurities. Then the sample is transferred to a centrifuge tube, centrifuged, and the supernatant is concentrated in a glass beaker, and the pH value of the liquid is adjusted. Take the water sample in a conical flask, add an appropriate amount of standard working solution and internal standard, and mix well by shaking for extraction.

[0020] (2) Extraction: Add the MMWCNT@ZIF-67 composite to step (1), continuously shake at room temperature, use a rubidium magnet to touch the bottle wall to magnetically attract all the composite, discard the supernatant, then shake and elute, collect the eluate, concentrate and redissolve it, and filter it through a 0.22 μm needle filter to obtain the sample to be tested.

[0021] (3) Detection: Quantitatively detect the sample to be tested in (2) by a high performance liquid chromatography-mass spectrometry (HPLC-MS).

[0022] Preferably, in step (1), the water sample is centrifuged at 10,000 rpm for 10 min.

[0023] Preferably, in step (1), the pH value of the water sample is adjusted to 9-10 with formic acid and ammonia water.

[0024] Preferably, in step (2), 100 mg of the magnetic carbon nanotube supported ZIF-67 composite is added to the sample to be tested.

[0025] Preferably, in step (2), the enrichment volume of the water sample is 50-100 mL.

[0026] Preferably, in step (2), the shaking speed at room temperature is 190-220 rpm, and the adsorption time is 20 min-40 min.

[0027] Preferably, in step (2), the desorbing solution is acetonitrile, and the volume of the desorbing solution is 10-15 mL.

[0028] Preferably, in step (2), the concentration method is nitrogen blowing concentration with an automatic nitrogen blowing instrument, and the nitrogen blowing temperature is 45 °C.

[0029] Preferably, for the chromatographic conditions of the HPLC-MS / MS in step (3): the filler of the chromatographic column is C18, and the mobile phase is acetonitrile and 0.1% formic acid solution; for the mass spectrometry conditions: the ionization mode is electrospray ionization positive ion mode, and the scanning mode is multiple reaction monitoring.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) After the magnetic carbon nanotubes are combined with ZIF-67, they not only provide rich adsorption active sites through functional groups such as carboxyl and hydroxyl groups on the surface of the carbon nanotubes, but also significantly enhance the mechanical stability and chemical tolerance of the composite material, thereby synergistically improving the overall adsorption performance.

[0032] (2) The synthetic material is inexpensive and easily available.

[0033] (3) The composite material has strong magnetism and can be easily enriched by a rubidium magnet, omitting the time-consuming centrifugation operation.

[0034] (4) The adsorbent for magnetic dispersive solid-phase extraction synergistically adsorbs diazepam through various interactions such as π-π interaction, hydrophobic effect, and hydrogen bond interaction.

[0035] (5) As an adsorbent for magnetic dispersive solid-phase extraction, only simple addition of water samples for enrichment is required, followed by separation with a magnet, which can save a large amount of pretreatment time. Description of the Drawings

[0036] Figure 1 It is a process diagram of the preparation and detection analysis of MMWCNT@ZIF-67 in the examples of the present invention.

[0037] Figure 2 It is an infrared spectrum diagram of the MMWCNT@ZIF-67 composite material in the examples of the present invention.

[0038] Figure 3 It is an X-ray diffraction diagram of the MMWCNT@ZIF-67 composite material in the examples of the present invention.

[0039] Figure 4 It is an X-ray photoelectron spectroscopy diagram of the MMWCNT@ZIF-67 composite material in the examples of the present invention.

[0040] Figure 5 It is a hysteresis regression line diagram of the MMWCNT@ZIF-67 composite material in the examples of the present invention.

[0041] Figure 6 It is a morphology diagram of the MMWCNT@ZIF-67 composite material in the examples of the present invention.

[0042] Figure 7 It is a pseudo-first-order kinetic curve of MMWCNT@ZIF-67 adsorbing diazepam.

[0043] Figure 8 It is a pseudo-second-order kinetic curve of MMWCNT@ZIF-67 adsorbing diazepam.

[0044] Figure 9Isotherm adsorption model (Langmuir model) for the adsorption of diazepam by MMWCNT@ZIF-67.

[0045] Figure 10 Isotherm adsorption model (Freundlich model) for the adsorption of diazepam by MMWCNT@ZIF-67.

[0046] Figure 11 Is the relationship diagram between adsorption conditions and extraction efficiency; (a) is the relationship diagram between the methanol ratio of the adsorption working solution and extraction efficiency; (b) is the relationship diagram between adsorption pH and extraction efficiency; (c) is the relationship diagram between adsorption time and extraction efficiency; (d) is the relationship diagram between the desorbing solution type and extraction efficiency. Specific implementation manners

[0047] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0048] In the embodiments of the present invention, the test methods used are all conventional methods without special instructions; the materials, reagents, etc. used are, without special instructions, reagents and materials that can be obtained from commercial channels. Depending on the treatment scenario, the reagents used are of analytical purity or chromatographic purity.

[0049] Example 1 Preparation and characterization of magnetic carbon nanotube supported ZIF-67 composite

[0050] As Figure 1 shown, the synthesis steps are as follows:

[0051] (1) Suspend 2 g of commercially available carboxylated multi-walled carbon nanotubes (purchased from Aladdin, purity 95%, outer diameter 8 - 15 nm, length 50 μm) in 100 mL of ultrapure water, and ultrasonically treat for 10 min to ensure sufficient dispersion. Subsequently, add 17.3 mmol of ferric chloride hexahydrate and 8.7 mmol of ferrous chloride tetrahydrate to the suspension in sequence, and stir until completely dissolved. Heat the mixed solution to 80 °C, and slowly add 10 mL of ammonia water under continuous stirring, and the reaction lasts for 60 min. After the reaction is completed, use a magnet to separate the magnetic carbon nanotubes, and wash them repeatedly with ultrapure water until neutral (pH = 7). Finally, wash once with ethanol to remove residual impurities, and dry at 80 °C to obtain magnetic carbon nanotubes.

[0052] (2) Weigh 0.5 g of the magnetic carbon nanotubes prepared in step (1) and disperse them in 100 mL of methanol. Then add 20 mmol of 2-methylimidazole and mix well. Separately, dissolve 10 mmol of cobalt nitrate hexahydrate in 100 mL of methanol to form a pink solution. Dropwise add this solution to the magnetic carbon nanotube mixture containing 2-methylimidazole while oscillating. During the dropping process, the mixture gradually turns dark purple, and the entire dropping process lasts for 15 - 30 min. After the dropping is completed, continue stirring for 24 h to ensure complete reaction. After the reaction ends, wash the product repeatedly with ultrapure water until the waste liquid is colorless, and dry it in an oven at 80 °C to obtain MMWCNT@ZIF-67.

[0053] Characterization of MMWCNT@ZIF-67:

[0054] Characterize MMWCNT@ZIF-67 by Fourier transform infrared spectroscopy, and the results are as Figure 2 shown. MMWCNT@ZIF-67 shows a characteristic stretching peak of O-H at 3428 cm-1, indicating the presence of -COOH. At 571 cm -1 a characteristic absorption peak of Fe3O4 appears, successfully loading Fe3O4 particles. The adsorption peaks in the range of 500 - 1500 cm -1 come from the stretching ligands of 2-methylimidazole, and the peaks at 1571 cm -1 and 2911 cm -1 are attributed to the stretching vibrations of C=N and C-H bonds in 2-methylimidazole respectively, and many ZIF-67 structures are formed on the relatively large number of MMWCNT-COOH. By performing powder X-ray diffraction on the material, the results are as Figure 3 shown. Compared with MMWCNT-COOH, MMWCNT@ZIF-67 jointly has the characteristic peaks of Fe3O4. In the range of 5 - 15 degrees, MMWCNT@ZIF-67 simultaneously has the characteristic peaks of ZIF-67. Characterize MMWCNT@ZIF-67 by X-ray photoelectron spectroscopy, and the results are as Figure 4 shown. The energy regions of C1s (284.68 eV), N1s (399.13 eV) and O1s (531.13 eV) in the composite material are shown in the figure. Figure 4 b, 4c and 4d respectively show the binding energies of C1s, N1s, O1s. See Figure 4 c. The photoelectron binding energy of N1s is 397.08 eV, indicating that this peak is the pyridine N peak. Figure 4 e shows two main peaks, and their binding energies are 797.18 eV and 781.33 eV respectively, which are the characteristics of Co2p 1 / 2 and Co2p 3 / 2 respectively. Moreover, Co2p3 / 2 The XPS spectrum of Co 2+ species is characteristic of ZIF-67. The binding energies of Fe2p3 / 2 and Fe2p1 / 2 are 710.73 eV and 723.83 eV respectively, which are consistent with the characteristic peaks of Fe3O4. The vibrating sample magnetometer was used to analyze the magnetism of MMWCNT@ZIF-67, and the results are as Figure 5 shown. In the range of -20000 - 20000 Oe, the saturation magnetization rates of MMWCNT-COOH and MMWCNT@ZIF-67 are 29.31 emu / g and 22.24 emu / g respectively. The magnetism of MMWCNT-COOH is stronger than that of MMWCNT@ZIF-67. Although the magnetism decreases slightly, the material can still be separated from the liquid by a magnet within 3 minutes. MMWCNT@ZIF-67 was characterized by scanning electron microscopy, and the results are as Figure 6 shown. The polygon-structured ZIF-67 was clearly observed in MMWCNT@ZIF-67. The morphology of MMWCNT@ZIF-67 is like a bunch of grapes, with MMWCNT as the chain connecting the ZIF-67 structures.

[0055] Example 2

[0056] Characterization of the adsorption performance of MMWCNT@ZIF-67

[0057] Adsorption steps:

[0058] (1) Adsorption kinetics: Place it in a 10 mL centrifuge tube, add 5 mL of the prepared diazepam aqueous solution at 100 mg / L, mix well, and oscillate horizontally in the dark at room temperature at a constant speed. Samples are taken at time points of 10, 20, 60, 100, 140, 180, 240, and 360 min to evaluate the dynamic adsorption performance.

[0059] (2) Isothermal adsorption: Weigh 10 mg of the prepared MMWCNT@ZIF-67 composite material and place it in a 10 mL centrifuge tube. Add 5 mL of diazepam aqueous solutions with a series of concentrations, mix well, and oscillate horizontally in the dark at room temperature at a constant speed for 24 h. Enrich the complex with a magnet, and after the supernatant is filtered through a microporous filter membrane, it is measured on a machine to evaluate the static adsorption performance.

[0060] Performance test of MMWCNT@ZIF-67 for adsorbing diazepam:

[0061] The experimental data were fitted by the pseudo-first-order adsorption kinetics model and the pseudo-second-order adsorption kinetics model, and the results are as Figure 7 、 Figure 8As shown in Table 1. The results show that the adsorption process of MMWCNT@ZIF-67 was fitted by pseudo-first-order (diffusion-dominated) and pseudo-second-order (chemisorption-dominated) kinetic models. The higher goodness of fit of the pseudo-second-order model (R 2 > 0.99) indicates that the adsorption process is mainly chemisorption, accompanied by a synergistic mechanism of physical adsorption (π-π interaction, hydrophobic effect, hydrogen bonding).

[0062] Table 1 Fitting parameter table of adsorption kinetic model of MMWCNT@ZIF-67 for diazepam

[0063]

[0064]

[0065] The adsorption mechanism of MMWCNT@ZIF-67 was investigated by the isothermal adsorption model. The results are as Figure 9 and Figure 10 shown. The Freundlich model (R 2 = 0.987) fits the experimental data better than the Langmuir model (R 2 = 0.973), indicating that its adsorption process follows the heterogeneous surface multi-molecular layer mechanism. The measured adsorption capacity reached 447 mg / g, and the theoretical maximum adsorption capacity was 607.1 mg / g.

[0066] Example 3 Effects of different adsorption conditions and desorption conditions on the extraction efficiency of the prepared adsorbent

[0067] (1) Adsorption solvent

[0068] In this example, the extraction efficiency of diazepam and its metabolites was investigated when the commonly used loading solution was methanol mixed with a certain proportion of pure water as the loading solution. The working solution environments were set as methanol aqueous solutions with methanol-to-water ratios of 9:1, 1:1, 1:9, and 0:1. The results are as Figure 11 (a) shown. The extraction efficiency of diazepam and its metabolites is the highest in a 100% water environment.

[0069] (2) Adsorption pH

[0070] In this example, the extraction efficiency of diazepam and its metabolites with different pH loading solutions was investigated. The results are shown in Figure 11 (b). When the pH is in the range of 2 - 8, the recovery shows an upward trend. Under the condition of pH = 8, the recovery range of the target compounds is 47.3% - 100%, and the recovery of oxazepam and temazepam is around 50%; when pH > 8, the recovery range of the target compounds is 73.6% - 94.3%, and the recovery of oxazepam and temazepam exceeds 70%.

[0071] (3) Adsorption time

[0072] The extraction efficiency of the target substance by the oscillation adsorption time of the sample solution. The results are shown in Figure 11 (c). When the oscillation adsorption time is 5 min, the recovery rate ranges from 79% to 93.6%; within the time range of 5 - 60 min, the recovery rate of the target substance varies within the range of 80% - 96%.

[0073] (4) Selection of desorption solvent

[0074] Investigate the screening of desorption and elution solutions for diazepam, nordiazepam, temazepam, and oxazepam from MMWCNT@ZIF-67. The results are as Figure 11 (d). The recovery rate of choosing methanol as the elution solvent is 81.3% - 105.5%; the recovery rate of choosing acetonitrile as the elution solvent is 82% - 102%; the recovery rate of choosing acetonitrile solution containing 1% formic acid is 62.4% - 92.4%. The results show that appropriate amounts of methanol and acetonitrile can be selected as the elution solutions for desorption from MMWCNT@ZIF-67.

[0075] Application Example 1

[0076] Methodological investigation of MMWCNT@ZIF-67 as an adsorbent for magnetic dispersive solid-phase extraction in the detection of aquaculture water

[0077] Sample pretreatment: After collecting the water sample, let it stand for 24 h to precipitate insoluble impurities. Then transfer the sample to a centrifuge tube and centrifuge at 10,000 rpm for 10 min. Concentrate the supernatant in a 1 L glass beaker and adjust the pH value of the liquid to about 10 with ammonia water and formic acid. Take 100 mL of the water sample in a 250 mL conical flask, add an appropriate amount of standard working solution and internal standard, shake well and wait for purification. Add 100 mg of MMWCNT@ZIF-67 composite adsorbent to the above sample, continuously shake at room temperature for 5 - 20 min, touch the bottle wall with a rubidium magnet to magnetically attract all the composite, discard the supernatant, add 10 mL of acetonitrile and shake for 3 min for elution, collect the eluate, then add 5 mL of acetonitrile and shake for 3 min for elution, concentrate the eluate, blow to near dryness with nitrogen at 45 °C, redissolve with 1 mL of 0.1% formic acid acetonitrile (v / v) solution, and determine by HPLC-MS / MS after filtration through a microporous filter membrane.

[0078] HPLC-MS / MS method: Use a YMC-Triart C18 column (100 mm × 2.1 mm, 3.0 μm; YMC, Kyoto, Japan); select an LC-30AD 220V liquid chromatograph from Shimadzu Corporation, Japan; a triple quadrupole mass spectrometer, model API5500, with a software workstation Analyst 1.6.3; set the flow rate at 250 μL / min; column temperature at 30 °C; injection volume at 5 μL; select 0.1% formic acid solution (A) and chromatographic grade acetonitrile (B) as the mobile phase; the gradient elution program is shown in Table 2.

[0079] Table 2 Gradient Elution Schedule

[0080]

[0081]

[0082] Adopt the positive ion detection mode of the electrospray ionization source; the mass spectrometry scanning method is multiple reaction monitoring; the ion source temperature is 550 °C; the collision cell pressure is 8 psi; the curtain gas pressure is 20 psi; the nebulizing gas pressure is 35 psi; the spray voltage is 5500 V; the sheath gas flow rate is 25 arbitrary units; the intake voltage is 10 V; the collision cell ejection voltage is 18 V; the auxiliary gas pressure is 55 psi; the dwell time is 100 ms. The collision energy (CE), de-clustering potential (DP), precursor ion Q1 and product ion Q3 masses of the drug for mass spectrometry scanning are shown in Table 3.

[0083] Table 3 Main Mass Spectrometry Parameters

[0084]

[0085] Note: The ones marked with "*" are quantitative ions.

[0086] Standard curve drawing: Prepare a series of standard mixed solutions with concentrations of diazepam and its metabolite standard solutions ranging from 0.1 to 50 ng / mL.

[0087] Linearity, LOD and LOQ of the method: As shown in Table 3, diazepam, nordiazepam, temazepam and oxazepam have good linearity in the concentration range of 0.1 - 50 ng / ml, with LOD between 0.0009 - 0.004 ng / ml and LOQ between 0.001 - 0.005 ng / ml.

[0088] Table 3 Linearity, LOD and LOQ of the Method

[0089]

[0090] Recovery and precision: The results are shown in Table 4. At three spiked concentration levels, the within-batch average recovery of the target analytes was 73%-112%, and the relative standard deviation was 0.8%-15.2%; the between-batch average recovery was 87.5%-101.3%, and the relative standard deviation was 3.8%-14.6%.

[0091] Table 4 Recovery and precision of diazepam and its metabolites (n = 6)

[0092]

[0093]

[0094] Application Example 2

[0095] Actual detection of aquaculture water using MMWCNT@ZIF-67 as an adsorbent for magnetic dispersive solid-phase extraction: Water samples were collected from aquaculture farms in Zhuhai, Yangjiang, Jiangmen, Zhanjiang, Shantou, and Zhongshan for the analysis of diazepam and its metabolites. Qualitative and quantitative analyses were performed using the established HPLC-MS / MS method, and the results showed that diazepam and its metabolites were not detected in all samples.

[0096] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solutions of the present invention, rather than limitations on the specific implementation manners of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the claims of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a magnetic solid-phase extraction adsorbent loaded with ZIF-67 on magnetic carbon nanotubes, characterized in that, It includes the following steps: S1. Add carboxylated multi-walled carbon nanotubes into water for dispersion to prepare a suspension; then add iron salt, mix and heat; then add ammonia water for reaction; after the reaction is completed, separate the magnetic carbon nanotubes; S2. Disperse the magnetic carbon nanotubes obtained in step S1 into a solvent, and then add 2-methylimidazole to obtain a mixture; S3. Add cobalt nitrate solution into a solvent, and then dropwise add the mixture obtained in step S2 while oscillating. After the mixture turns dark purple during the reaction, continue stirring to ensure complete reaction; after the reaction is completed, wash and dry to obtain the magnetic dispersive solid-phase extraction adsorbent.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass of the carboxylated multi-walled carbon nanotubes is 1 - 2 g; the mixing mass ratio of the carboxylated multi-walled carbon nanotubes to the iron salt is 20:47; the dosage of the ammonia water added in step S1 is 10 - 15 mL.

3. The preparation method according to claim 1, characterized in that, In step S2, the reaction mass ratio of the magnetic carbon nanotubes to 2-methylimidazole is 125:41; in step S3, the molar ratio of cobalt nitrate to 2-methylimidazole is 1:

2.

4. The preparation method according to claim 1, wherein The solvent used in step S2 is water or methanol; the solvent used in step S3 is methanol.

5. The magnetic dispersive solid-phase extraction adsorbent obtained by the preparation method described in claim 1.

6. Use of the magnetic dispersive solid-phase extraction adsorbent according to claim 5 in the enrichment and purification of diazepam and its metabolites in water, characterized in that, The metabolite is one or more of nordazepam, temazepam or oxazepam.

7. The application according to claim 6, wherein The magnetic dispersive solid-phase extraction adsorbent is used for the extraction and enrichment of diazepam and its metabolites in water, and is applied to the analysis and detection of diazepam and its metabolites.

8. The application according to claim 7, characterized in that, The extraction and enrichment include the following steps: (1) Extraction: Let the sample to be tested stand for 24 h to precipitate insoluble impurities; then centrifuge the sample to be tested, collect the supernatant and adjust the pH value of the supernatant; (2) Extraction: Add the MMWCNT@ZIF-67 complex of the magnetic dispersive solid-phase extraction adsorbent into the supernatant in step (1), continuously oscillate at room temperature, and magnetically attract all the complexes, discard the supernatant, elute, collect the eluate, concentrate and then redissolve, and filter to obtain the sample to be tested; (3) Detection: Quantitatively detect the sample to be tested in step (2) by high performance liquid chromatography - mass spectrometry.

9. The application according to claim 8, wherein In step (1), adjust the pH value of the sample to be tested to 9 - 10; the sample to be tested is the water sample to be tested.

10. The application according to claim 8, characterized in that The high performance liquid chromatography - mass spectrometry conditions are as follows: Chromatographic conditions: Use a C18 chromatographic column with a specification of 100 mm × 2.1 mm, 3.0 μm; the flow rate is 250 μL / min; the column temperature is 30 °C; the injection volume is 5 μL; the mobile phase is 0.1% formic acid solution A and acetonitrile B; the gradient elution program is as follows: at 0 min, the volume fraction of mobile phase A in the mobile phase is 85%, and the volume fraction of mobile phase B in the mobile phase is 15%; at 2 min, the volume fraction of mobile phase A in the mobile phase is 5%, and the volume fraction of mobile phase B in the mobile phase is 85%; at 2.5 min, the volume fraction of mobile phase A in the mobile phase is 5%, and the volume fraction of mobile phase B in the mobile phase is 85%; at 3 min, the volume fraction of mobile phase A in the mobile phase is 85%, and the volume fraction of mobile phase B in the mobile phase is 15%; at 7 min, the volume fraction of mobile phase A in the mobile phase is 85%, and the volume fraction of mobile phase B in the mobile phase is 15%; Mass spectrometry conditions: Electrospray ionization source positive ion detection mode was adopted; the mass spectrometry scanning method was multiple reaction monitoring.

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