Method for separating and purifying pomegranate peel polyphenol based on metal organic framework material

Abstract

The invention provides a method for separating and purifying pomegranate peel polyphenol based on a metal organic framework material, and belongs to the technical field of natural product extraction. The method comprises the following steps: (1) mixing a magnetic metal organic framework material with a pomegranate peel polyphenol crude extract, stirring for 50-70 minutes, and carrying out solid-liquid separation to obtain a magnetic metal organic framework material loaded with pomegranate peel polyphenol; (2) adding an elution solvent into the magnetic metal organic framework material loaded with pomegranate peel polyphenol, stirring, standing, and carrying out solid-liquid separation to obtain polyphenol eluent and precipitate; and (3) concentrating and drying the polyphenol eluent to obtain the high-purity pomegranate peel polyphenol. According to the invention, the inherent defects of the traditional resin in selectivity and dynamics are overcome by utilizing the specific regular pore system and metal active sites of the MOF material, and a better technical path is provided for deep development of pomegranate rind wastes.

Description

Technical Field

[0001] This invention belongs to the field of natural product extraction technology, and in particular relates to a method for separating and purifying pomegranate peel polyphenols based on metal-organic framework materials. Background Technology

[0002] Pomegranate (Punica granatum) has been valued since ancient times as an economically important plant, hailed as a "superfood" due to its immense health benefits. The increasing popularity and demand for pomegranates are primarily attributed to their versatility and health-promoting effects. The entire fruit possesses antibacterial, antioxidant, anticancer, antidiabetic, and anti-inflammatory activities. A pomegranate fruit consists of three parts: seeds, juice, and peel. The peel accounts for approximately 40%–50% of the total fruit weight. A significant amount of phenols, flavonoids, and tannins found in pomegranates are located in the peel; therefore, various biological characteristics and potential value of the pomegranate are related to the peel. However, in food processing, the peel and seeds are mostly considered byproducts of juice processing, often used as animal feed, and discarded in landfills or incinerated. Currently, value-added processing of byproducts from fruit and vegetable processing has become a global priority to promote sustainable, economically viable, and environmentally friendly waste management strategies. Extracting the abundant natural polyphenolic antioxidants from pomegranate peel is a core strategy for achieving high-value utilization of this agricultural byproduct. The recycling and development of these bioactive compounds not only provides a material basis for the innovation of functional foods and nutritional supplements to address the health challenges and nutritional needs of modern society, but also curbs the generation of environmental waste at its source. By building a circular economy model, this approach effectively promotes the transformation of the agricultural system towards sustainability, achieving efficient recycling and reuse of resources.

[0003] Purifying polyphenolic active compounds from crude extracts is crucial for research and production. Traditional polyphenol separation techniques mainly rely on solid-liquid extraction and liquid-liquid extraction. However, these methods suffer from drawbacks such as high organic solvent consumption, poor safety, and low production efficiency, making them unsuitable for large-scale industrial applications. In contrast, the most commonly used polyphenol separation method in industry and academia currently employs macroporous adsorption resins (MARs). This technology, a durable polymer with high adsorption capacity, encompasses various types including polar, non-polar, and slightly hydrophilic resins. Its significant advantages, such as high mechanical strength, diverse structures, low cost, and environmental friendliness, have led to its widespread application in the industrial recovery of plant bioactive substances. This technology primarily utilizes the high specific surface area and porous structure of the resin. Through van der Waals forces and weak interactions between the hydrophobic matrix of the resin and non-polar phenolic molecules, polyphenols in the extract are adsorbed onto the resin surface, achieving efficient enrichment and separation of polyphenols. Despite the unique advantages of the above methods, they have the following drawbacks: (1) Low utilization of adsorption sites and lack of molecular recognition ability, making it difficult to achieve both recovery efficiency and product purity. The pore size distribution of existing technologies (such as macroporous resin MAR) is extremely uneven, and its adsorption mechanism mainly relies on single, non-directional hydrophobic interactions (van der Waals forces). This adsorption method results in the material lacking precise size matching and chemical affinity for pomegranate peel polyphenols (such as punicalin with a large molecular weight), and a large number of internal micropores cannot be effectively utilized, and impurities (such as sugars and organic acids) are easily adsorbed at the same time. Ultimately, this leads to low saturated adsorption capacity per unit mass of adsorbent, and the purity of the target polyphenols in the elution product is not ideal. (2) Poor kinetic performance and long processing cycle: Macroporous resins are mostly micron-sized particles, with long internal diffusion paths and highly distorted pore structures. This results in a slow rate at which target molecules enter the adsorption sites, and a long time required to reach adsorption equilibrium.

[0004] The approximate solution in the prior art usually includes the following steps (Yao Miaomiao, Li Wunian, Wu Wenjuan, et al. Research progress on separation and purification of plant polysaccharides by macroporous resin [J]. Yunnan Chemical Industry, 2026, 53(01): 1-5.): (1) Preparation of crude extract: Obtain crude extract of pomegranate peel by ethanol reflux or ultrasonic extraction. (2) Column adsorption: Pass the crude extract through a chromatographic column packed with macroporous resin (such as D101, AB-8, etc.) at a certain flow rate. (3) Dynamic washing: Wash the column bed with deionized water to remove strong polar impurities such as sugars, proteins, and pigments. (4) Solvent elution: Use 50%~80% ethanol solution as eluent to elute polyphenols from the resin. (5) Resin regeneration: Treat the resin with acid, alkali or hot ethanol for reuse. Limitations of existing methods: (1) Poor adsorption selectivity: The pore size distribution of macroporous resins is extremely wide and disordered, lacking the ability to selectively recognize specific molecules (such as punicalin), resulting in the final product purity being difficult to meet pharmaceutical grade standards. (2) Limited adsorption capacity: The specific surface area of ​​the resin is usually 500-800 m². 2 The effective active site density is low, which limits the amount that can be processed in a single cycle. (3) Slow mass transfer kinetics: Due to the twisted pores and large diffusion resistance inside the resin, it usually takes a long time to reach adsorption equilibrium, resulting in low production efficiency. (4) Stability issues: Polymer resins are prone to swelling or mechanical breakage after multiple cycles, which leads to a gradual decrease in adsorption performance. Therefore, it is extremely urgent to find efficient and rapid separation methods using novel adsorbents. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method for separating and purifying pomegranate peel polyphenols based on metal-organic framework (MOF) materials. This invention utilizes the unique regular pore system and metal active sites of MOF materials to overcome the inherent defects of traditional resins in terms of selectivity and kinetics, providing a superior technical path for the in-depth development of pomegranate peel waste.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for separating and purifying pomegranate peel polyphenols based on metal-organic framework materials, comprising the following steps: (1) Mix the magnetic metal-organic framework material with the crude extract of pomegranate peel polyphenols, stir for 50-70 min, and then perform solid-liquid separation to obtain the magnetic metal-organic framework material loaded with pomegranate peel polyphenols. (2) Add elution solvent to the magnetic metal-organic framework material carrying pomegranate peel polyphenols, stir, let stand, and perform solid-liquid separation to obtain polyphenol eluent and precipitate; (3) The polyphenol eluent was concentrated and dried to obtain high-purity pomegranate peel polyphenols.

[0007] Preferably, the magnetic metal-organic framework material is a composite adsorption medium with a magnetic core and an MOF shell structure, wherein the magnetic core is Fe3O4.

[0008] Preferably, the magnetic metal-organic framework material is Fe3O4@UiO-66-NH2.

[0009] Preferably, the mass-to-volume ratio of the magnetic metal-organic framework material to the crude extract of pomegranate peel polyphenols is 1 mg: 4-6 mL.

[0010] As a preferred embodiment, the preparation method of the crude extract of pomegranate peel polyphenols is as follows: pomegranate peel powder is mixed with 40%~60% ethanol solution, refluxed and extracted 2~4 times, the filtrates are combined, and concentrated by rotary evaporation until there is no alcohol odor, thus obtaining the crude extract of pomegranate peel polyphenols.

[0011] Preferably, the mass-to-volume ratio of the pomegranate peel powder to the ethanol solution is 1g:5~10mL.

[0012] Preferably, the solid-liquid separation method is as follows: using a magnet to gather magnetic metal-organic framework materials to achieve solid-liquid separation.

[0013] Preferably, the elution solvent is an ethanol solution with an initial concentration of 50% to 70%, and the volume-to-mass ratio of the elution solvent to the magnetic metal-organic framework material is 0.5 to 1.5 mL: 1 mg.

[0014] Preferably, the step also includes a step of recovering the precipitate obtained in step (2).

[0015] Preferably, the recovery method involves alternately rinsing the precipitate with anhydrous ethanol and deionized water to restore the adsorption activity of the magnetic metal-organic framework material.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention utilizes the superparamagnetism, high specific surface area, and multiple chemical interactions of a composite adsorption medium with a magnetic core (Fe3O4) and a metal-organic framework (MOF) shell structure to achieve precise capture of polyphenolic compounds, mainly pungent glycosides, from pomegranate peel extract. The method of this invention does not require a complex adsorption column packing process; rapid separation of the adsorbent from the liquid phase can be achieved by applying an external magnetic field.

[0017] (2) The method of the present invention can significantly improve efficiency: Due to the extremely high specific surface area of ​​MOF (3 to 10 times that of traditional resin) and highly ordered straight channels, the saturation capacity of adsorbent per unit mass is greatly increased, and the molecular diffusion resistance is extremely small.

[0018] (3) High purity and high activity retention of the product are achieved: strong chemical affinity sites (coordination bonds, π-π interactions) can accurately anchor the target polyphenols, and mild desorption conditions avoid long-term oxidation. The purity of the target component in the final product is higher than that of the traditional resin method, and the biological activity is retained to the maximum extent, which enhances the market added value of the product.

[0019] (4) Flexible operation and fast separation speed: Traditional adsorption columns are prone to problems such as "column clogging" or "excessive pressure", especially when processing high-viscosity fluids such as pomegranate peel extract containing a small amount of pectin or macromolecular impurities. The method of this invention can complete solid-liquid separation within seconds by relying on an external magnetic field. Compared with traditional gravity sedimentation or filtration, it greatly shortens the production auxiliary time and avoids the problems of "column clogging" or "excessive pressure", making it particularly suitable for processing high-viscosity fluids such as pomegranate peel extract containing a small amount of pectin or macromolecular impurities. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention; Figure 2 The graph shows the polyphenol content of pomegranate peel extract before and after separation and purification using the method of this invention. Figure 3 The fitting curve is a quasi-first-order dynamic. Figure 4 The curve is a quasi-second-order dynamic fitting curve; Figure 5 Fit curves to the Langmuir model; Figure 6 Fit curves for the Freundlich model. Detailed Implementation

[0021] This invention provides a method for separating and purifying pomegranate peel polyphenols based on metal-organic framework materials, comprising the following steps: (1) Mix the magnetic metal-organic framework material with the crude extract of pomegranate peel polyphenols, stir for 50-70 min, and then perform solid-liquid separation to obtain the magnetic metal-organic framework material loaded with pomegranate peel polyphenols. (2) Add elution solvent to the magnetic metal-organic framework material carrying pomegranate peel polyphenols, stir, let stand, and perform solid-liquid separation to obtain polyphenol eluent and precipitate; (3) The polyphenol eluent was concentrated and dried to obtain high-purity pomegranate peel polyphenols.

[0022] In this invention, the magnetic metal-organic framework material is a composite adsorption medium with a magnetic core and a MOF shell structure, wherein the magnetic core is Fe3O4; and the magnetic metal-organic framework material is Fe3O4@UiO-66-NH2.

[0023] In this invention, the preparation method of Fe3O4@UiO-66-NH2 is as follows: Fe3O4@PDA is dissolved in anhydrous DMF and sonicated to obtain solution 1; 1-1.5 times the amount of anhydrous DMF in solution 1 is taken, and aminoterephthalic acid, ZrCl4, and benzoic acid are added sequentially to the additional DMF, and sonicated until completely dissolved to obtain solution 2; solution 1 and solution 2 are rapidly mixed, transferred to a three-necked flask, and stirred in an oil bath at 80-100℃ for 2-4 hours; the mixture is then naturally cooled to 20-30℃ and centrifuged at 10000-15000 rpm for 3-1 hour. The precipitate was collected at 0 min; the sample was washed alternately with DMF and ethanol 3-5 times, and dried for 10-14 h to obtain a black powder Fe3O4@UiO-66-NH2; the mass-to-volume ratio of Fe3O4@PDA to anhydrous DMF was 2-3 mg:1 mL, preferably 2.2-2.8 mg:1 mL, more preferably 2.5 mg:1 mL; the sonication time was 5-15 min, preferably 7-12 min, more preferably 10 min; the amount of additional DMF was preferably 1.1-1.3 times the amount of anhydrous DMF in solution 1. The preferred step is 1.25 times the amount of DMF. The mass-to-volume ratio of the aminoterephthalic acid to the separately taken DMF is 1 mL: 4-5 mg, preferably 1 mL: 4.25-4.75 mg, more preferably 1 mL: 4.5 mg. The mass-to-volume ratio of the ZrCl4 to the separately taken DMF is 1 mL: 5-7 mg, preferably 1 mL: 5.5-6.5 mg, more preferably 1 mL: 6 mg. The mass-to-volume ratio of the benzoic acid to the separately taken DMF is 1 mL: 18-22 mg, preferably 1 mL: 19-21 mg. mg, more preferably 1 mL: 20 mg; the oil bath temperature is preferably 85~95℃, more preferably 90℃, the oil bath stirring time is preferably 2.5~3.5h, more preferably 3h, the cooling temperature is preferably 22~28℃, more preferably 25℃, the centrifugation speed is preferably 11000~13000rpm, more preferably 12000rpm, the centrifugation time is preferably 4~6min, more preferably 5min; the drying time is preferably 11~13h, more preferably 12h.

[0024] In this invention, the preparation method of Fe3O4@PDA is as follows: Fe3O4 nanoparticles are dispersed in Tris-HCl buffer, sonicated, dopamine hydrochloride is added, mechanically stirred, and the product is separated by magnetic separation. The supernatant is discarded, and the product is resuspended and washed with deionized water and anhydrous ethanol sequentially until the supernatant is colorless. The product is dried to obtain black powder Fe3O4@PDA. The mass-to-volume ratio of Fe3O4 nanoparticles to Tris-HCl buffer is 7 mg:4~8 mL, preferably 7 mg:5~7 mL, more preferably 7 mg:6 mL. The concentration of the Tris-HCl buffer is 8~12 mM, preferably 9~11 mM, more preferably 10 mM. The pH of the Tris-HCl buffer is 7~10, preferably 8~9, more preferably 8.5. The sonication time is 5~15 min, preferably 8~12 min, more preferably 10 min. The ratio of dopamine hydrochloride to Fe3O4 nanoparticles is 7:7~9, preferably 7:7.5~8.5, and more preferably 7:8. The temperature of the mechanical stirring is 20~30℃, preferably 22~28℃, and more preferably 25℃. The time of the mechanical stirring is 10~14h, preferably 11~13h, and more preferably 12h. The speed of the mechanical stirring is 300~700rpm, preferably 400~600rpm, and more preferably 500rpm. The drying time is 10~14h, preferably 11~13h, and more preferably 12h.

[0025] In this invention, the preparation method of the crude extract of pomegranate peel polyphenols is as follows: pomegranate peel powder is mixed with a 40%~60% ethanol solution, refluxed and extracted 2~4 times, the filtrates are combined, and concentrated by rotary evaporation until no alcohol odor is detected, thereby obtaining the crude extract of pomegranate peel polyphenols; the pomegranate peel powder is preferably obtained by pulverizing and passing it through a 40-mesh sieve; the concentration of the ethanol solution is preferably 45%~55%, more preferably 50%; the number of reflux extractions is preferably 3 times, wherein the volume-to-mass ratio of the ethanol solution to the pomegranate peel powder used in the 3 reflux extractions is 1g:10mL, 1g:5mL, and 1g:5mL respectively; the mass-to-volume ratio of the magnetic metal-organic framework material to the crude extract of pomegranate peel polyphenols is 1mg:4~6mL, preferably 1mg:4.5~5.5mL, more preferably 1mg:5mL; the stirring time is preferably 55~65min, more preferably 60min.

[0026] In this invention, the solid-liquid separation method is as follows: using a magnet to gather magnetic metal-organic framework materials to achieve solid-liquid separation.

[0027] In this invention, the elution solvent is an ethanol solution with an initial concentration of 50% to 70%, preferably 55% to 65%, and more preferably 60%; the volume-to-mass ratio of the elution solvent to the magnetic metal-organic framework material is 0.5 to 1.5 mL: 1 mg, preferably 0.7 to 1.2 mL: 1 mg, and more preferably 1 mL: 1 mg; the standing time is 5 to 15 min, preferably 8 to 12 min, and more preferably 10 min.

[0028] In this invention, there is also a step of restoring the precipitate obtained in step (2). The method of restoration is to alternately rinse the precipitate with anhydrous ethanol and deionized water to restore the adsorption activity of the magnetic metal-organic framework material. The number of alternating rinses is 3 to 5 times, preferably 4 times.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1: Synthesis of Fe3O4@UiO-66-NH2

[0031] Preparation of Fe3O4@PDA: 0.35 g of Fe3O4 nanoparticles were dispersed in 300 mL of Tris-HCl buffer (10 mM, pH 8.5) and sonicated for 10 min (40 kHz, 25 °C). 0.40 g of dopamine hydrochloride was added in a single addition, and the mixture was mechanically stirred at 25 °C for 12 h (500 rpm). The product was separated by magnetic separation, and the supernatant was discarded. The product was resuspended in deionized water and then washed with anhydrous ethanol followed by magnetic separation until the supernatant was colorless. The product was dried for 12 h to obtain black Fe3O4@PDA powder.

[0032] Preparation of Fe3O4@PDA@UiO-66: Dissolve 10 mg Fe3O4@PDA in 4 mL of anhydrous DMF and sonicate for 10 min to obtain solution 1. Separately, take 5 mL of DMF and add 22.5 mg aminoterephthalic acid, 30 mg ZrCl4, and 100 mg benzoic acid sequentially, sonicating until completely dissolved to obtain solution 2. Quickly mix solution 1 and solution 2, transfer to a three-necked flask, and stir in an oil bath at 90 °C for 3 h. Allow to cool naturally to 25 °C, centrifuge at 12000 rpm for 5 min to collect the precipitate. Wash alternately with DMF and ethanol 3–5 times, and dry for 12 h to obtain a black powder Fe3O4@UiO-66-NH2.

[0033] Example 2

[0034] Pomegranate peel was dried to constant weight and pulverized through a 40-mesh sieve using a high-speed pulverizer to obtain pomegranate peel powder. The powder was then sealed and stored at 4°C in a light-proof container. 100g of the pomegranate peel powder was weighed and extracted three times by reflux with 50% ethanol. The amounts of 50% ethanol solution used in the three reflux extractions were 1000mL, 500mL, and 500mL respectively, with each extraction lasting 1 hour. The filtrates were combined and concentrated by rotary evaporation until no alcohol odor remained, yielding a crude extract of pomegranate peel polyphenols.

[0035] 20 mg of Fe3O4@UiO-66-NH2 (magnetic MOF material) obtained in Example 1 was added to 100 mL of crude pomegranate peel polyphenol extract. The mixture was thoroughly mixed and shaken for 60 min (to achieve adsorption equilibrium), ensuring the magnetic adsorbent (magnetic MOF material) was fully suspended in the extract. At this point, the ordered channels of the magnetic MOF intercepted polyphenol molecules through size exclusion effect and anchored them within the framework through hydrogen bonding, π-π stacking, and metal coordination. After adsorption equilibrium was achieved, a magnet was placed outside the container. Under the influence of the magnetic field, the magnetic adsorbent rapidly converged to the sidewall or bottom of the container, achieving rapid separation from the liquid phase.

[0036] Add 20 mL of 60% ethanol solution to the polyphenol-loaded magnetic adsorbent (magnetic MOF material), stir well, and let stand for 10 min. The elution solvent enters the MOF channels and disrupts the interaction between the adsorbent and the polyphenols. Apply an external magnetic field again to cause the magnetic adsorbent to settle, and collect the polyphenol-rich eluent.

[0037] The eluent was concentrated under reduced pressure and freeze-dried to obtain high-purity pomegranate peel polyphenol powder. The results are shown in the table below. Figure 2 The magnetic adsorbent was rinsed four times alternately with anhydrous ethanol and deionized water to restore the adsorption activity of the MOF material for recycling. See the detailed procedure below. Figure 1 .

[0038] Depend on Figure 2 It can be seen that the polyphenol content in the crude pomegranate peel polyphenol extract changed significantly after adsorption treatment. The polyphenol content was approximately 21% before adsorption, and increased significantly to approximately 53% after adsorption. The results indicate that the method of this invention has a good adsorption and enrichment effect on polyphenols and can effectively increase the polyphenol concentration in the sample.

[0039] Experimental example: Adsorption kinetics of Fe3O4@Uio-66-NH2

[0040] The Fe3O4@UiO-66-NH2 obtained in Example 1 was administered at a dose of 0.5 mg·mL. -1 The amount added was 0.5 mg·mL⁻¹. -1 In gallic acid solution, at pH 4.0, 25℃, and 300 r·min -1The mixture was then subjected to magnetic separation and UV-Vis for 120 min. The adsorption performance of gallic acid was experimentally investigated, and the results are shown below. Figure 3 and Figure 4 .

[0041] Depend on Figure 3 and Figure 4 The results show that the quasi-secondary model is dominant: R 2 =0.98, significantly higher than the pseudo-first-order R. 2 =0.94, predicted Qe=15.09mg·g -1 The value seamlessly overlaps with the experimental platform value, k2 = 2.91 × 10⁻⁶. -4 g·mg -1 ·min -1 The results fall within the characteristic range of chemisorption, and the linear curve shows no systematic bias, confirming that the rate-limiting step for gallic acid by Fe3O4@UiO-66-NH2 is surface coordination chemisorption, which can be directly used for mechanism and capacity design.

[0042] At 25℃, Fe3O4@UiO-66-NH2 was added at a concentration of 0.10 mg·mL. -1 The amounts were added to solutions with initial concentrations ranging from 0.5 to 40 mg / L. -1 The isothermal adsorption of polyphenols in gallic acid solutions within a certain range was investigated, and the results are shown in [Figure number missing]. Figure 5 and Figure 6 .

[0043] Depend on Figure 5 and Figure 6 It can be seen that at 25℃, Fe3O4@UiO-66-NH2 at a concentration of 0.10 mg·mL -1 The amounts were added to solutions with initial concentrations ranging from 0.5 to 40 mg / L. -1 Within a range of gallic acid solutions, the adsorption isotherms exhibit typical Langmuir characteristics (R0). 2 =0.980), the uniform single-layer model significantly outperforms Freundlich (R² = 0.980). 2 =0.057). Linear fitting gives the theoretical maximum capacity qmax = 400 ± 8 mg·g. -1 With an affinity constant KL = 0.25 ± 0.01 L·mg -1 The product of the two is qmax·KL=100L·g -1 This confirms that Fe3O4@UiO-66-NH2 has both high capacity and strong affinity for the target polyphenols, with no signs of multilayer adsorption, meeting the design requirements for quantitative recovery by magnetic solid-phase extraction.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for separating and purifying pomegranate peel polyphenols based on metal-organic framework materials, characterized in that, Includes the following steps: (1) Mix the magnetic metal-organic framework material with the crude extract of pomegranate peel polyphenols, stir for 50-70 min, and then perform solid-liquid separation to obtain the magnetic metal-organic framework material loaded with pomegranate peel polyphenols. (2) Add elution solvent to the magnetic metal-organic framework material carrying pomegranate peel polyphenols, stir, let stand, and perform solid-liquid separation to obtain polyphenol eluent and precipitate; (3) The polyphenol eluent was concentrated and dried to obtain high-purity pomegranate peel polyphenols.

2. The method according to claim 1, characterized in that, The magnetic metal-organic framework material is a composite adsorption medium with a magnetic core and a MOF shell structure, wherein the magnetic core is Fe3O4.

3. The method according to claim 2, characterized in that, The magnetic metal-organic framework material is Fe3O4@UiO-66-NH2.

4. The method according to claim 1, characterized in that, The mass-to-volume ratio of the magnetic metal-organic framework material to the crude extract of pomegranate peel polyphenols is 1 mg: 4-6 mL.

5. The method according to claim 1, characterized in that, The preparation method of the crude extract of pomegranate peel polyphenols is as follows: mix pomegranate peel powder with 40%~60% ethanol solution, reflux extract 2~4 times, combine the filtrates, and concentrate by rotary evaporation until there is no alcohol odor to obtain the crude extract of pomegranate peel polyphenols.

6. The method according to claim 5, characterized in that, The mass-to-volume ratio of the pomegranate peel powder to the ethanol solution is 1g:5~10mL.

7. The method according to claim 1, characterized in that, The solid-liquid separation method is as follows: using a magnet to gather magnetic metal-organic framework materials to achieve solid-liquid separation.

8. The method according to claim 1, characterized in that, The elution solvent is an ethanol solution with an initial concentration of 50% to 70%, and the volume-to-mass ratio of the elution solvent to the magnetic metal-organic framework material is 0.5 to 1.5 mL: 1 mg.

9. The method according to claim 1, characterized in that, It also includes a step of restoring the precipitate obtained in step (2).

10. The method according to claim 9, characterized in that, The recovery method involves alternately rinsing the precipitate with anhydrous ethanol and deionized water to restore the adsorption activity of the magnetic metal-organic framework material.

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