Molecularly imprinted adsorption material taking metal organic framework as carrier skeleton as well as preparation method and application of molecularly imprinted adsorption material

Abstract

The invention discloses a molecularly imprinted adsorption material taking a metal organic framework as a carrier skeleton as well as a preparation method and application of the molecularly imprinted adsorption material, and belongs to the technical field of adsorption materials. The preparation method comprises the following steps: carrying out hydrothermal reaction on transition metal salt and a phthalic acid ligand to obtain metal organic framework nanoparticles; the preparation method comprises the following steps: adsorbing flavonoid template molecules by metal organic framework nanoparticles, mixing with lysozyme and a disulfide bond reducing agent, performing phase change polymerization, and eluting to remove the flavonoid template molecules after the phase change polymerization is completed, thereby obtaining the molecularly imprinted adsorbing material with abundant imprinting sites and good stability. The adsorbent is good in flavonoid compound adsorption selectivity, high in rate, large in capacity, good in chemical stability, resistant to acid washing, capable of being recycled for multiple times and capable of being widely applied to extraction and separation of flavonoid compounds.

Description

Technical Field

[0001] The present invention relates to an adsorption material, in particular to a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton, a preparation method of the molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton, and an application of the molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton in the adsorption and separation of flavonoid compounds in a solution system, belonging to the technical field of adsorption materials. Background Art

[0002] Glycyrrhizic acid, also known as glycyrrhizin, is composed of a pentacyclic triterpene structure, uronic acid, and two glucuronic acid molecules. Glycyrrhizic acid is the primary active ingredient in the traditional Chinese medicine licorice root and the primary source of licorice sweeteners. In addition to its use as a natural sweetener in the food industry, glycyrrhizic acid exhibits numerous biological activities, including antioxidant, anti-tumor, antibacterial, anti-inflammatory, wound healing, free radical scavenging, and nervous system protection, demonstrating significant potential in the medical and nutritional health fields. Therefore, the extraction of chrysin from natural sources is of great significance.

[0003] Currently, glycyrrhizic acid extraction methods primarily include solvent extraction, macroporous resin adsorption, aqueous two-phase extraction, ionic liquid extraction, ultrasound / microwave-assisted extraction, supercritical fluid extraction, and superheated water extraction. While these extraction methods have achieved good results in extracting glycyrrhizic acid, they often require tedious and complex pretreatment procedures due to the complex composition of natural samples, which is time-consuming and labor-intensive. Furthermore, since natural products contain a variety of active ingredients with similar structures to glycyrrhizic acid, these methods lack selectivity for glycyrrhizic acid extraction, resulting in suboptimal purity of the extracted product.

[0004] Molecularly imprinted polymers (MIPs) mimic the antibody-antigen interaction, enabling specific recognition of template molecules. They are ideal materials for efficient separations from complex systems. Currently, MIPs have been widely applied in fields such as chromatography, solid-phase extraction, biomimetic sensing, enzyme catalysis, and clinical drug analysis. In recent years, research has applied MIPs to the extraction of natural active ingredients. MIPs can selectively extract specific active ingredients with high extraction yields, significantly improving the purity of the extracts. References (“Molecularly imprinted polymers for the selective extraction of glycyrrhizic acid from liquorice roots”, C. Giuseppe, et al., Food Chemistry, 2011, 125, 1058-1063), references (“Synthesis of thermosensitive imprinted hydrogels and study of their separation properties for glycyrrhizic acid”, He Jiangchuan, et al., Chemical Research and Applications, 2005, 17(2), 216-219), and references (“Purification of glycyrrhizic acid by molecularly imprinted adsorption materials”, Xi Wanbao, et al., Fine Chemicals, 2018, 35(11), 1859-18650) disclose methods for preparing glycyrrhizic acid imprinted adsorption materials using acrylic acid as functional monomers and bulk polymerization, and achieve separation of glycyrrhizic acid from liquorice roots by solid phase extraction. Subsequently, the literature (“Molecularly Imprinted Solid Phase Extraction using Bismethacryloyl-β-cyclodextrin and Methacrylic Acid as Double Functional Monomers for Selective Analysis of Glycyrrhizic Acid in Aqueous Media”, W. Tang, et al, Journal of Chromatographic Science, 2017, 55(2), 166-173) disclosed a method for synthesizing glycyrrhizic acid imprinted adsorption materials in dimethyl sulfoxide using bismethacryloyl-β-cyclodextrin and methacrylic acid as double functional monomers. The prepared MIPs have good recognition ability for glycyrrhizic acid.The literature (“Preparation and Characterization of a Novel Molecularly Imprinted Polymer for the 2 Separation of Glycyrrhizic Acid”, J. Long, et al., Journal of Separation Science, 2017, 40(24), 4847-4856) discloses a method for preparing glycyrrhizic acid imprinted adsorption materials using N-vinylpyrrolidone as a functional monomer. The adsorption capacity of the prepared MIPs for glycyrrhizic acid is 15 mg / g. The paper (“Preparation and Application of Glycyrrhizic Acid Molecularly Imprinted Adsorption Materials on Multi-walled Carbon Nanotubes”, Resalaiti Yimin, et al., Chinese Journal of Experimental Traditional Chinese Medicine, 2016, 22(18), 45-50) discloses a method for synthesizing glycyrrhizic acid imprinted adsorption materials on the surface of multi-walled carbon nanotubes. The adsorption capacity of glycyrrhizic acid is 741.5 μg / g.

[0005] In summary, the equilibrium adsorption capacity of glycyrrhizic acid by the glycyrrhizic acid imprinted adsorption materials disclosed in the prior art is not high, and they are all imprinted layers generated by acrylic monomers. These imprinted layers will be damaged to a certain extent when eluted multiple times in acidic eluents, which limits their recycling and regeneration capabilities. Summary of the Invention

[0006] In response to the defects of the existing technology, the first purpose of the present invention is to develop a molecularly imprinted adsorption material with a metal-organic framework as the carrier skeleton, which has abundant imprinting sites, exhibits high adsorption capacity, good stability, resistance to acid washing, can be recycled multiple times, and can be widely used for the extraction of small molecule compounds corresponding to the template molecules.

[0007] The second object of the present invention is to provide a method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton. The preparation method is simple to operate, low in cost, mild in conditions, and is conducive to large-scale production.

[0008] A third object of the present invention is to provide a molecularly imprinted adsorption material with a metal-organic framework as a carrier skeleton for the adsorption and separation of flavonoids (e.g., glycyrrhizic acid) in solution systems. This material not only enables efficient and highly selective extraction of flavonoids from solution systems, but also exhibits excellent stability and resistance to acid washing, allowing for repeated reuse. It is highly practical and has great potential for application in the medical and food fields.

[0009] In order to achieve the above technical objectives, the present invention provides a method for preparing a molecularly imprinted adsorption material using a metal organic framework as a carrier skeleton, the method comprising the following steps:

[0010] 1) A transition metal salt and a phthalic acid ligand are hydrothermally reacted to obtain metal-organic framework nanoparticles;

[0011] 2) After the metal organic framework nanoparticles adsorb the flavonoid template molecules, they are mixed with lysozyme and a disulfide bond reducing agent to undergo phase change polymerization. After the phase change polymerization is completed, the flavonoid template molecules are eluted to obtain the product.

[0012] The preparation method of the molecularly imprinted adsorption material using a metal organic framework as a carrier skeleton of the present invention first synthesizes metal organic framework nanoparticles by a hydrothermal method. For example, the metal organic framework MIL-101 formed by transition metal salts (iron salts, copper salts, chromium salts, etc.) and phthalic acid ligands has a porous structure with intramolecular voids, a large specific surface area, and exhibits good adsorption properties. It can serve as an excellent carrier for molecularly imprinted adsorption materials. Its porous structure and high specific surface area provide more space and opportunities for the recognition and binding of flavonoid template molecules, which is more conducive to the formation of more flavonoid compound imprinting sites. On this basis, lysozyme is used as the functional monomer and is polymerized on the surface of metal-organic framework nanoparticles under the action of a disulfide bond reducing agent. Lysozyme contains multiple functional groups such as carboxyl, amino, hydroxyl and thiol. On the one hand, it can form multiple interactions with flavonoid template molecules, which can effectively enhance the imprinting effect. On the other hand, after the disulfide bonds of lysozyme are reduced by a reducing agent, the amphiphilic unfolded lysozyme oligomers form a stable nanofilm at the interface driven by the decrease in interfacial free energy. It can still maintain good functionality and stability under acidic conditions, so that the imprinted layer can maintain a good morphology during acid elution, giving the imprinted adsorption material the ability to be recycled repeatedly, with strong practicality and huge application potential in the medical and food fields.

[0013] As a preferred embodiment, the transition metal salt includes iron ( ),chromium( ) and copper ( ) at least one of the soluble salts of iron ( ). Soluble salts include nitrates, chlorides, etc., specifically FeCl3, Cr(NO3)3, Fe(NO3)3, Cu(NO3)2, etc. ),chromium( ) and copper ( ) and phthalic acid ligands mainly form the metal-organic framework MIL-101.

[0014] As a preferred solution, the phthalic acid ligand includes at least one of terephthalic acid, 2-aminoterephthalic acid, 2-amino-1,4-phthalic acid, 2-hydroxy-1,4-phthalic acid, and 1,4-phthalic acid.

[0015] As a preferred solution, the molar ratio of the transition metal salt to the phthalic acid ligand is 1:0.5~3.

[0016] As a preferred embodiment, the hydrothermal reaction conditions are: temperature of 120-220°C and time of 8-36 hours. Under the preferred hydrothermal conditions, the formed metal-organic framework has a nanoparticle size, with uniform and regular truncated octahedral particles and a particle size of 300-400 nm.

[0017] As a preferred embodiment, the mass ratio of the metal organic framework nanoparticles to the flavonoid template molecule, lysozyme and disulfide bond reducing agent is 1: 0.2~1.2: 1.0~5: 0.4~3.0.

[0018] As a preferred embodiment, the disulfide bond reducing agent includes at least one of tris(2-carboxyethyl)phosphine (TCEP), 2-mercaptoethanol, 2-mercaptoethylamine hydrochloride, dithiothreitol, and hydroxylamine hydrochloride. The preferred reducing agent is capable of effectively reducing disulfide bonds in lysozyme at room temperature, thereby achieving phase change polymerization of lysozyme.

[0019] As a preferred solution, the phase change polymerization conditions are: o C temperature, and react for 4 to 36 hours.

[0020] As a preferred embodiment, the elution employs a mixed solution of glacial acetic acid and methanol in a volume ratio of 8 / 92 to 15 / 85 as the eluent. This preferred eluent enables efficient elution of flavonoid template molecules from the imprinted adsorption material, thereby obtaining more imprinted sites. Furthermore, while glacial acetic acid is a good eluent for flavonoid compounds, conventional imprinted adsorption materials (such as acrylic acid or dopamine) are easily structurally destroyed by glacial acetic acid. The chrysin imprinted membrane layer formed by lysozyme phase change polymerization in the present invention exhibits excellent stability and resistance to acid washing, allowing the introduction of an appropriate proportion of glacial acetic acid to enhance the elution efficiency of glycyrrhizic acid.

[0021] The present invention also provides a molecular imprinting adsorption material with a metal organic framework as a carrier skeleton, which is obtained by the preparation method.

[0022] The molecularly imprinted adsorption material of the present invention uses a metal organic framework as a carrier skeleton and metal organic framework nanoparticles as the carrier skeleton. The material has a porous structure with internal voids, a large specific surface area, and good adsorption performance. It can adsorb more flavonoids, thereby facilitating the subsequent formation of more flavonoid imprinting sites. The imprinted active sites of the imprinted layer on the surface of the organic framework nanoparticle carrier skeleton are fully exposed, which can greatly improve its selectivity and adsorption capacity. The entire adsorption material has a large specific surface area, many active sites, a large adsorption capacity, and selective recognition and strong adsorption capabilities for target molecules. In particular, the nanofilm formed by lysozyme through phase change has good acid resistance and can withstand multiple repeated acid elution processes while maintaining good morphology and adsorption performance, providing a favorable guarantee for achieving the repeated recycling regeneration capability of the imprinted adsorption.

[0023] The present invention also provides an application of a molecularly imprinted adsorption material with a metal-organic framework as a carrier skeleton, which is used for adsorbing and separating flavonoids from a solution system. The molecularly imprinted adsorption material with a metal-organic framework as a carrier skeleton of the present invention exhibits good adsorption selectivity for flavonoids in a solution system, a large adsorption capacity, good stability, resistance to acid washing, and repeatable recycling, thus having strong practicality. For flavonoids such as glycyrrhizic acid, a molecularly imprinted adsorption material prepared using glycyrrhizic acid as a template molecule exhibits high selective recognition and binding capabilities for glycyrrhizic acid and can be used for the selective adsorption and separation of glycyrrhizic acid from licorice roots, demonstrating excellent specific separation capabilities.

[0024] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0025] 1) The molecularly imprinted adsorption material with a metal organic framework as the carrier skeleton of the present invention uses porous MOF nanocrystal particles with a high specific surface area as the carrier skeleton, which can effectively solve the defects of easy agglomeration and easy embedding of imprinted sites in traditional imprinting methods.

[0026] 2) The molecularly imprinted adsorption material with a metal organic framework as the carrier skeleton of the present invention has excellent recognition and binding capabilities for flavonoids. Taking Example 1 as an example, MIL101-MIPs prepared with glycyrrhizic acid as the template molecule has a high equilibrium adsorption capacity for glycyrrhizic acid (85.5 mg / g), good selectivity (imprinting factor of 3.92), and fast adsorption rate (equilibrium time: 70 min). It can efficiently and selectively identify and enrich glycyrrhizic acid. In the adsorption and separation experiment of glycyrrhizic acid in licorice roots, it showed good selectivity and enrichment ability.

[0027] 3) The preparation method of the molecularly imprinted adsorption material with a metal organic framework as the carrier skeleton of the present invention uses porous MOF nanocrystal particles with a high specific surface area as the carrier skeleton, which can induce the imprinting sites to be evenly distributed on its surface, thereby avoiding the problem of easy embedding of imprinting sites in traditional imprinting methods, increasing the content of effective imprinting sites, and the imprinting sites located on the surface are more easily exposed to the adsorbed molecules, and the imprinting effect is significantly enhanced.

[0028] 4) The present invention provides a method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton. Lysozyme is selected as the functional monomer, and a disulfide bond reducing agent is used to induce a phase change of lysozyme to form an imprinted layer that is resistant to acid washing. The imprinted sites can be evenly distributed on the surface of the imprinted layer, which is conducive to the effective arrival of the adsorbed molecules. The formed imprinted layer has good acid resistance and can maintain an intact morphology and a high adsorption capacity during multiple adsorption-desorption cycles. The excellent regeneration ability brought about by the acid washing resistance effectively expands the application potential and value of the prepared imprinted material.

[0029] 5) The preparation method of the molecularly imprinted adsorption material with a metal organic framework as the carrier skeleton of the present invention is easy to operate, has a short synthesis process, mild synthesis conditions, and has good acid washing resistance. The imprinted material has a strong recycling ability, which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be derived from these drawings without inventive effort.

[0031] Figure 1 The roadmap for synthesizing the glycyrrhizic acid imprinted polymer MIL-101@MIPs in Example 1

[0032] Figure 2 Scanning electron microscope images of MIL-101 (a) and MIL-101@MIPs (b) prepared in Example 1.

[0033] Figure 3 Infrared spectrum analysis diagrams of MIL-101 (a) and MIL-101@MIPs (b) prepared in Example 1.

[0034] Figure 4 This is a comparison chart of the adsorption capacity of glycyrrhizic acid and its structural analogs by the glycyrrhizic acid imprinted adsorption material MIL-101@MIPs prepared in Example 1.

[0035] Figure 5 This is a graph showing the morphology of the glycyrrhizic acid imprinted adsorption material MIL-101@MIPs prepared in Example 1 after multiple acid washing cycles and the changes in the adsorption capacity of glycyrrhizic acid. DETAILED DESCRIPTION

[0036] The following examples are intended to further illustrate the present invention, but are not intended to limit the scope of protection of the claims of the present invention.

[0037] Example 1

[0038] Preparation of MOF nanocrystal particles MIL-101:

[0039] 1) Cr(NO3)3 (0.541 g, 2.0 mmol), 2-aminoterephthalic acid (0.362 g, 2.0 mmol) and deionized water (10.0 mL) were added to a round-bottom flask at once and magnetically stirred at room temperature for 10 min to dissolve. After mixing well, the mixture was transferred to a tetrafluoroethylene-lined reactor and heated at 200 °C. o C for 10 h, and after cooling to room temperature, the product was washed alternately with N'N'-dimethylformamide and ethanol, and dried in vacuo at 60 °C for 12 h to obtain MIL-101.

[0040] 2) MIL-101 (0.2 g) and glycyrrhizic acid (0.2 g) were sequentially added to a round-bottom flask. 100.0 mL of deionized water was added and stirred for 2.0 h. Then, 0.3 g of lysozyme and 0.107 g of tris(2-carboxyethyl)phosphine hydrochloride were quickly added at room temperature and stirred for 12.0 h. After the reaction, the template molecule was washed with a mixture of ethanol and acetic acid (9:1 by volume) until no UV-Vis absorption peak at 254 nm was detected. The product was washed with deionized water to a neutral pH and dried overnight at 80°C in a vacuum oven. As a control, a non-imprinted polymer, MIL-101@NIPs, was also prepared. The preparation method of MIL-101@NIPs was identical to that of MIL-101@MIPs, except that the template molecule, glycyrrhizic acid, was omitted.

[0041] The preparation process of MIL-101@MIPs and the selective extraction and enrichment process of glycyrrhizic acid from licorice roots of the present invention are shown in Figure 1 .

[0042] To study the adsorption performance of the synthesized MIL-101@MIPs for glycyrrhizic acid, batch adsorption experiments (isotherm adsorption, kinetic adsorption, selective adsorption and regeneration cycle performance experiments) were carried out.

[0043] First, an isotherm adsorption experiment was conducted to study the effect of initial glycyrrhizic acid concentration on the adsorption capacity of MIL-101@MIPs. 15.0 mg of MIL-101@MIPs or MIL-101@NIPs were dispersed into 15.0 mL of different concentrations (50-500 mg L -1 ) in a glycyrrhizic acid solution and shaken for 30 o The mixture was shaken at 400 °C for 70 min. The supernatant and polymer were separated by centrifugation (8000 rpm, 5 min). The concentration of glycyrrhizic acid in the supernatant was measured by UV-visible spectrometry at 254 nm. The equilibrium adsorption capacity of glycyrrhizic acid by MIL-101@MIPs or MIL-101@NIPs was calculated using the following formula:

[0044] Formula 1

[0045] Among them, C o and C e are the initial concentration and equilibrium concentration of glycyrrhizic acid (mg L -1 ). V is the volume of glycyrrhizic acid solution (15.0 mL), and m is the mass of adsorbent MIL-101@MIPs or MIL-101@NIPs (15.0 mg).

[0046] In the kinetic adsorption experiment, different adsorption times (5–90 min) were set, and the initial concentration of glycyrrhizic acid was set at 300 mg L -1 , other operations are the same as isotherm adsorption, and the adsorption amount Q at adsorption time t is calculated using formula 1 t (mgg -1 ) (The concentration of glycyrrhizic acid solution at time t is used instead of C e ).

[0047] To verify the selectivity of MIL-101@MIPs in recognizing glycyrrhizic acid, glycyrrhetinic acid, hesperidin, quercetin and sinapinic acid were selected as their structural analogs for selective adsorption experiments. Except for replacing the above-mentioned glycyrrhizic acid solution with the solution of its structural analogs, other operations were exactly the same.

[0048] To examine the recyclability of MIL-101@MIPs, seven adsorption-desorption cycles were performed using the same batch of MIL-101@MIPs. Following glycyrrhizic acid adsorption, the MIL-101@MIPs were shaken in a mixture of ethanol and acetic acid (9:1 by volume) to remove the adsorbed glycyrrhizic acid. The eluent was then washed with deionized water until neutrality was achieved, followed by a single wash with ethanol. The polymer was then dried under vacuum at 60°C for 8 h to obtain the regenerated imprinted adsorbent. The regenerated MIL-101@MIPs were used for the next adsorption cycle, and the adsorption capacity of glycyrrhizic acid by the regenerated MIL-101@MIPs was calculated using the adsorption isotherm method. The reusability of the material was evaluated by analyzing the change in adsorption capacity with the number of regenerations. All adsorption experiments were repeated three times, and the average value was calculated.

[0049] Extraction and isolation of glycyrrhizic acid from licorice root: Licorice root was purchased from a local Chinese medicine pharmacy. A crude extract of licorice root was prepared using an ethanol-water mixture (1:1 volume ratio). The purchased licorice root was dried and ground into a powder. A 0.5 g sample was added to a 100 mL round-bottom flask, and 50 mL of the extractant was added. The mixture was magnetically stirred at 60°C for 1.0 h and then centrifuged (6000 rpm for 5 min) to separate the supernatant. The supernatant was filtered through filter paper and diluted with mobile phase. After filtration through a 0.45 μm microporous fiber membrane, the extract was analyzed by HPLC.

[0050] Figure 2 Scanning electron micrographs of MIL-101 (a) and MIL-101@MIPs (b) prepared in Example 1 show that MIL-101 exhibits a uniform, regular truncated octahedral shape, with a particle size of approximately 300-400 nm and a smooth surface. The surface of MIL-101@MIPs coated with the imprinted layer becomes rough. MIL-101, as a carrier, evenly distributes imprinted sites on its surface, facilitating increased adsorption of glycyrrhizic acid and improving mass transfer efficiency in adsorption experiments.

[0051] Figure 3 This is the infrared spectrum analysis of the MOF nanocrystals MIL-101 and molecularly imprinted adsorption material MIL-101@MIPs prepared in Example 1. 3464 cm -1 The characteristic absorption peak at 1412 cm-1 is due to the superposition of the broad peaks of the amino group NH on the ligand and the OH in the adsorbed water in MIL-101, while the absorption peak at 1674 cm-1 is due to the asymmetric stretching vibration of the carboxyl group. -1 and 540cm -1The absorption peaks at 1594 cm-1 and 1595 cm-2 correspond to the stretching vibrations of CN and Zr-O bonds, respectively, which indicates the successful synthesis of MIL-101. -1 and 1628 cm -1 C=O stretching vibrations, combined NH and CN bending vibrations, and CN stretching vibrations in the amide I region are observed. These results indicate that the formed lysozyme nanofilm adopts an antiparallel β-sheet structure. Compared with MIL-101(Cr), MIL-101@MIPs better inherit the characteristic absorption peaks of MIL-101, indicating that the structure and properties of MIL-101 remain unchanged during the synthesis of MIL-101@MIP, demonstrating remarkable stability.

[0052] Figure 4 This figure compares the adsorption capacities of glycyrrhizic acid and its structural analogs by the glycyrrhizic acid-imprinted adsorbent material MIL-101@MIPs prepared in Example 1. When the initial concentration of glycyrrhizic acid and its structural analogs was 300 mg / L and the adsorption time was 70 minutes, MIL-101@MIPs adsorbed 85.5, 57.9, 37.8, 42.6, and 39.5 mg / g of glycyrrhizic acid, glycyrrhetinic acid, hesperidin, quercetin, and sinapinic acid, respectively. However, MIL-101@NIPs lacks imprinting sites compatible with glycyrrhizic acid, resulting in similar adsorption capacities for glycyrrhizic acid and the other reference substances, with the adsorption capacities remaining relatively low.

[0053] Figure 5 Figure 1 shows the morphology and glycyrrhizic acid adsorption capacity of the glycyrrhizic acid-imprinted adsorbent material MIL-101@MIPs prepared in Example 1 after multiple acidic washing cycles. After seven cycles, the microscopic morphology of the MIL-101@MIPs remained virtually unchanged, and the glycyrrhizic acid adsorption capacity showed little loss. This demonstrates that the MIL-101@MIPs prepared with lysozyme as the functional monomer possess excellent acid resistance.

[0054] Example 2

[0055] Preparation of MOF nanocrystal particles MIL-101:

[0056] 1) Cr(NO3) 2· 9H2O (0.8 g, 2.0 mmol) and terephthalic acid (0.332 g, 2.0 mmol) were dissolved in DMF (40.0 mL) in sequence, and the mixture was transferred to a reactor with a tetrafluoroethylene liner at 150 o C for 12 h, and after cooling to room temperature, the product was washed alternately with acetone and ethanol and dried in vacuo at 60 °C for 12 h to obtain MIL-101.

[0057] 2) MIL-101 (0.15 g) and glycyrrhizic acid were sequentially added to a round-bottom flask. 100 mL of deionized water was added and stirred for 2 h. Then, 0.25 g of lysozyme and 0.98 g of tris(2-carboxyethyl)phosphine hydrochloride were quickly added at room temperature and stirred for 10 h. After the reaction, the template molecule was washed with eluent until no UV-Vis absorbance peak at 254 nm was detected. The product was washed with deionized water to a neutral state and dried in a vacuum oven at 80°C overnight. As a control, a non-imprinted polymer, MIL-101@NIPs, was also prepared. The preparation method of MIL-101@NIPs was identical to that of MIL-101@MIPs, except that the template molecule, glycyrrhizic acid, was omitted.

[0058] The equilibrium adsorption capacities of glycyrrhizic acid for the imprinted adsorbent MIL-101@MIPs and the non-imprinted adsorbent MIL-101@NIPs prepared in Example 2 were 67.7 mg g -1 and 25.7 mg g -1 , the imprinting factor is 2.63, and the imprinting effect is significant.

[0059] Comparative Example 1

[0060] Preparation of MOF nanocrystal particles MIL-101:

[0061] 1) Fe(NO3)3·9H2O (1.13 g, 2.8 mmol), Cu(NO3)2·3H2O (0.68 g, 2.8 mmol), and terephthalic acid (0.928 g, 5.6 mmol) were sequentially added to a mixture of DMF (21 mL), ethanol (4 mL), and deionized water (3 mL). The mixture was magnetically stirred at room temperature for 15 min to dissolve the mixture. After mixing well, the mixture was transferred to a microwave reaction chamber and heated at 150°C. o C (900 W) for 4 h, cooled to room temperature, washed with methanol, and dried in vacuo at 60 °C for 12 h to obtain MIL-101.

[0062] 2) MIL-101 (0.3 g) and glycyrrhizic acid were sequentially added to a round-bottom flask. 100.0 mL of deionized water was added and stirred for 2.0 h. Then, 0.4 g of lysozyme and 0.182 g of dithiothreitol were quickly added at room temperature and stirred for 8.0 h. After the reaction, the template molecule was washed with an ethanol-acetic acid mixture until no UV-Vis absorption peak at 254 nm was detected. The product was washed with deionized water to a neutral state and dried in a vacuum oven at 80°C overnight. As a control, a non-imprinted polymer, MIL-101@NIPs, was also prepared. The preparation method of MIL-101@NIPs was identical to that of MIL-101@MIPs, except that the template molecule, glycyrrhizic acid, was omitted.

[0063] The MIL-101 nanocrystal particles prepared in Example 3 were aggregated and had a diameter of approximately 100-150 nm. They were coated with a lysozyme imprinting layer to obtain MIL-101@MIPs. The surface of MIL-101@MIPs was slightly rough, and the imprinting effect was significant. The maximum equilibrium adsorption capacity of glycyrrhizic acid for MIL-101@MIPs and MIL-101@NIPs was 74.4 mg g, respectively. -1 and 17.3 mg g -1 , which are lower than those of MIL-101@MIPs in Example 1 (85.5 mg g -1 ), this is because the MIL-101 prepared in Example 3 has a small particle size and exhibits obvious agglomeration, which results in a reduced specific surface area of the prepared MIL-101@MIPs, a slightly lower content of imprinted sites, and some imprinted sites are difficult to effectively reach.

[0064] The above is only a preferred specific implementation scheme of the present invention, but the protection scope of the present invention is not limited thereto. Any equivalent exchange or change of the technical solution and inventive concept of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a molecularly imprinted adsorption material using a metal organic framework as a carrier skeleton, characterized by: The following steps are involved: 1) A transition metal salt and a phthalic acid ligand are hydrothermally reacted to obtain metal-organic framework nanoparticles; 2) After the metal organic framework nanoparticles adsorb the flavonoid template molecules, they are mixed with lysozyme and a disulfide bond reducing agent to undergo phase change polymerization. After the phase change polymerization is completed, the flavonoid template molecules are eluted to obtain the product.

2. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1, characterized in that: The transition metal salt includes iron ( ),chromium( ) and copper ( ) at least one of the soluble salts of The phthalic acid ligand includes at least one of terephthalic acid, 2-aminoterephthalic acid, 2-amino-1,4-phthalic acid, 2-hydroxy-1,4-phthalic acid, and 1,4-phthalic acid.

3. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1 or 2, characterized in that: The molar ratio of the transition metal salt to the phthalic acid ligand is 1:0.5-3.

4. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1, characterized in that: The conditions of the hydrothermal reaction are: temperature of 120-220° C. and time of 8-36 hours.

5. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1, characterized in that: The mass ratio of the metal organic framework nanoparticles to the flavonoid template molecules, lysozyme and disulfide bond reducing agent is 1: 0.2~1.2: 1.0~5: 0.4~3.

0.

6. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 5, characterized in that: The disulfide bond reducing agent includes at least one of tris(2-carboxyethyl)phosphine, 2-mercaptoethanol, 2-mercaptoethylamine hydrochloride, dithiothreitol, and hydroxylamine hydrochloride.

7. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1, characterized in that: The phase change polymerization conditions are: o C temperature, and react for 4 to 36 hours.

8. The method for preparing a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 1, characterized in that: The elution adopts a mixed solution of glacial acetic acid and methanol with a volume ratio of 8 / 92 to 15 / 85 as an eluent.

9. A molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton, characterized by: The method is obtained by any one of claims 1 to 8.

10. The use of a molecularly imprinted adsorption material with a metal organic framework as a carrier skeleton according to claim 9, characterized in that: Used for adsorption and separation of flavonoids in solution systems.

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