Preparation of defective zirconium-based metal organic framework and application of defective zirconium-based metal organic framework in separation and purification of cyanidin anthocyanin

Abstract

The invention discloses preparation of a defective zirconium-based metal organic framework and application of the defective zirconium-based metal organic framework in separation and purification of cyanidin anthocyanin, and belongs to the technical field of efficient extraction, enrichment and separation of natural active molecules. The preparation method comprises the following steps: firstly, preparing a zirconium-based HP-UiO-66X material by taking zirconium tetrachloride and terephthalic acid as a metal center and an organic ligand raw material respectively under a solvothermal condition; in the synthesis process, a certain amount of benzoic acid is added as a regulator, and then the benzoic acid is etched by formic acid to form defects. The synthesized defective UiO-66X material has a hierarchical porous structure, and different groups modified by the ligand can form hydrogen bonds and other interactions on anthocyanin, so that the adsorption performance of the HP-UiO-66X material on the anthocyanin is improved.

Description

Technical Field

[0001] This invention discloses the preparation of a defective zirconium-based metal-organic framework and its application in the separation and purification of cyanidin-type anthocyanins, belonging to the field of efficient extraction and enrichment separation technology of natural active molecules. Background Technology

[0002] Anthocyanins are a class of natural, water-soluble polyphenolic pigments widely found in berries, fruits, vegetables, and grains. They possess multiple biological activities, including antioxidant, anti-inflammatory, cardiovascular protective, and metabolic regulation, making them valuable in functional foods, natural colorants, and pharmaceuticals. However, the anthocyanin content in plant matrices is typically low, and their structure is susceptible to degradation or structural transformation (e.g., tautomerism with flavanols and chalcones) depending on pH, temperature, and metal ion environments. Furthermore, natural samples often contain coexisting sugars, phenolic acids, polyphenol analogs, and various glycosidic isomers (e.g., cyanidin-3O-glucoside, cyanidin-3O-arabinoside, cyanidin-3O-galactoside, cyanidin-3O-rutinoside), making the efficient and selective enrichment and separation of anthocyanins a challenge. Therefore, developing enrichment and separation materials that simultaneously possess high selectivity, high stability, and scalability is of great importance.

[0003] Adsorption separation technology has attracted widespread attention in the extraction and purification of anthocyanins due to its advantages such as simple operation, environmental friendliness, and reusability. In recent years, metal-organic frameworks (MOFs) have become highly promising new adsorbents due to their high specific surface area, regular pore structure, and precisely tunable chemical environment. Among many MOFs, zirconium-based UiO-66 is considered very suitable as an adsorbent for natural products due to its excellent chemical stability, acid resistance, and the ease of functional group control of the Zr6O4(OH)4 metal cluster. However, the pore size of standard UiO-66 is about 6–8 Å, which is insufficient to accommodate larger anthocyanin molecules; in addition, the number of active sites in its pores that can form hydrogen bonds, π–π, or electrostatic interactions with anthocyanins is limited, resulting in insufficient adsorption capacity and insignificant selectivity. These structural limitations restrict the performance of traditional UiO-66 in distinguishing structurally similar anthocyanin isomers. Based on this, by introducing structural defects to construct hierarchical porous UiO-66, the micro / mesopore ratio of the material can be significantly improved, diffusion channels can be increased and more uncoordinated metal sites can be exposed, thereby enhancing the mass transfer and binding capacity of anthocyanin molecules in the pores, which is an important strategy for optimizing its adsorption performance.

[0004] However, existing methods for constructing defective UiO-66 mainly aim to increase the specific surface area or enhance the adsorption capacity for small molecule gases and organic solvent molecules. Their defect regulation usually focuses on changing the amount of regulator or the proportion of missing sites, rather than being specifically designed for anthocyanin molecules with complex structures, large molecular sizes and polyhydroxyl structural features.

[0005] In anthocyanin adsorption systems, the aforementioned defective construction methods have certain limitations: on the one hand, traditional defective UiO-66 is still mainly microporous, and the pore size is not well matched with the molecular scale of anthocyanins, resulting in limited molecular diffusion and low utilization of effective adsorption sites; on the other hand, the surface chemical environment of the UiO-66 framework in the existing technology is relatively simple, lacking functional sites that can form multiple interactions with structural units such as phenolic hydroxyl groups and glycosyl groups in anthocyanin molecules, thus limiting its selective adsorption capacity for anthocyanins.

[0006] Therefore, although the defective UiO-66 in the prior art shows good performance in some adsorption systems, it is difficult to meet the requirements of high adsorption capacity, high selectivity and controllable desorption when it is directly used for anthocyanin separation. Summary of the Invention

[0007] To address the aforementioned problems, this invention first prepares zirconium-based HP-UiO-66_X materials under solvothermal conditions, using zirconium tetrachloride and terephthalic acid as the metal center and organic ligand, respectively. A certain amount of benzoic acid is added as a regulator during the synthesis process, followed by etching the benzoic acid with formic acid to create defects. The synthesized defective UiO-66_X material possesses a hierarchical porous structure, and the different groups modified by the ligands can form hydrogen bonds and other interactions with anthocyanins, thereby improving the adsorption performance of HP-UiO-66_X materials for anthocyanins. Compared to traditional adsorbents such as activated carbon and silica gel, the method of this invention has advantages such as a regular pore structure, a large specific surface area, and an adjustable pore chemistry environment. Therefore, developing efficient and green new methods for the separation and purification of anthocyanins has significant theoretical and practical value.

[0008] This invention provides a method for preparing a defective zirconium-based metal-organic framework HP-UiO-66_X that adsorbs cyanidin anthocyanins, comprising the following steps: (1) Using ZrCl4, terephthalic acid or its derivatives, and benzoic acid as raw materials, zirconium-based HP-UiO-66_X materials were prepared by solvothermal method, followed by centrifugation, washing, and drying; (2) The dried zirconium-based HP-UiO-66_X was dissolved in N,N-dimethylformamide and formic acid was added. The reaction was carried out by solvothermal method. After the reaction was completed, the mixture was centrifuged, washed and dried to obtain the defective zirconium-based metal-organic framework HP-UiO-66_X.

[0009] In one embodiment of the present invention, in step (1), the terephthalic acid derivative is one of 2-aminoterephthalic acid, 2-hydroxyterephthalic acid, and 2-methylterephthalic acid.

[0010] In one embodiment of the present invention, in step (1), the terephthalic acid derivative is 2-hydroxyterephthalic acid or 2-aminoterephthalic acid.

[0011] In one embodiment of the present invention, in step (1), the molar ratio of ZrCl4 to benzoic acid is 0.67~0.70:2.93~3.00.

[0012] In one embodiment of the present invention, in step (1), the molar ratio of ZrCl4 to terephthalic acid or its derivative is 1:0.82~0.85.

[0013] In one embodiment of the present invention, in step (1), the conditions for the solvothermal method are: reaction at 120 °C for 10-12 h.

[0014] In one embodiment of the present invention, in step (2), the volume ratio of N,N-dimethylformamide and formic acid is 10:2.7~3.0.

[0015] In one embodiment of the present invention, in step (2), the conditions for the solvothermal method are: reaction at 120 °C for 10-12 h.

[0016] The present invention provides a defective zirconium-based metal-organic framework HP-UiO-66_X prepared by the method described above.

[0017] This invention provides the application of the aforementioned defective zirconium-based metal-organic framework HP-UiO-66_X in the enrichment and purification of cyanidin anthocyanins.

[0018] [Beneficial Effects] (1) Based on defect construction, this invention utilizes terephthalic acid and its derivatives (functional groups such as –NH2, –OH, –CH3, etc.) to design and synthesize a series of polarity-tunable HP-UiO-66_X materials. Different functional groups can generate differentiated hydrogen bonds, electrostatic interactions, or π–π interactions with the phenolic hydroxyl groups, glycosyl groups, or aromatic rings of anthocyanins, thereby regulating the adsorption strength and selectivity. Through dual regulation of defect structure and functional groups, the HP-UiO-66_X constructed in this invention not only significantly improves diffusion efficiency in terms of pore size, pore volume, and specific surface area, but also achieves highly selective adsorption of specific anthocyanins such as cyanidin series and mild and controllable desorption under low pH conditions, providing a novel material strategy for the efficient enrichment and separation of anthocyanins in complex natural systems.

[0019] (2) This invention adopts a design approach that combines functionalized ligands with defect construction. By introducing ligands with different functional groups and synergistically regulating the defect structure, HP-UiO-66_X materials with hierarchical pore structure and tunable surface polarity are constructed. The results show that different defect construction methods and functional group types have a significant impact on the adsorption kinetics, adsorption capacity and desorption behavior of anthocyanins. Their influence on the adsorption performance of anthocyanins has obvious structure dependence and unpredictability.

[0020] (3) This invention selects UiO-66 as the defect construction target, based on its excellent hydrothermal stability and acid stability, which can adapt to the acidic conditions required in the anthocyanin separation process. However, conventional UiO-66 is difficult to achieve efficient and selective adsorption of anthocyanins due to its limited pore size and insufficient active sites. This invention effectively improves the pore structure and interfacial chemical environment of UiO-66 by constructing defects and introducing functional groups, enabling it to simultaneously possess high adsorption capacity, high selectivity and controllable desorption performance for the first time, thereby solving the technical shortcomings of defective UiO-66 in the application of anthocyanin separation in the prior art.

[0021] (4) The present invention successfully prepared HP-UiO-66_X materials with different functional groups. HP-UiO-66_X materials with different functional groups were obtained by etching with formic acid, so that a hierarchical porous structure was formed inside the HP-UiO-66_X materials, and the adsorption capacity of anthocyanins reached 40 mg / g.

[0022] (5) The introduction of different side groups in this invention increases the interaction between the adsorbent material and anthocyanins, thereby increasing the adsorption amount of anthocyanins.

[0023] (6) The method of the present invention, through kinetic analysis, shows that the anthocyanin adsorption of HP-UiO-66_X material is mainly through chemical action.

[0024] (7) The HP-UiO-66_X materials obtained in this invention, namely HP-UiO-66_NH2 and HP-UiO-66_OH, have good selective enrichment and concentration performance for anthocyanins.

[0025] (8) The method of the present invention is simple and easy to implement, low in cost, and the product process is simple, suitable for industrial production, and has good market prospects. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation of HP-UiO-66_X and HP-UiO-66_X using the solvothermal method in this invention; Figure 2 This is a model diagram of Example 1; Figure 3 The XRD spectra of HP-UiO-66_X and simulated UiO-66 in Examples 1-4 are shown below; Figure 4 The FT-IR spectra of HP-UiO-66_X in Examples 1-4 are shown. Figure 5 Transmission electron microscope images of HP-UiO-66_X in Examples 1-4; Figure 6 Images showing the BET specific surface area of ​​HP-UiO-66_X in Examples 1-4; Figure 7 These are scanning electron microscope images of HP-UiO-66_X in Examples 1-4; Figure 8 Thermogravimetric analysis was performed on Examples 1-4 HP-UiO-66_X and Comparative Examples 1-4 UiO-66_X; Figure 9 1H-NMR analysis of HP-UiO-66_X in Examples 1-4; Figure 10 The pore size distribution of HP-UiO-66_X in Examples 1-4; Figure 11 The N2 adsorption-desorption isotherms for HP-UiO-66_X in Examples 1-4 are shown. Figure 12 The standard curve of the ultraviolet-visible absorption spectrum of anthocyanins; Figure 13 The pore size distribution of Example 1 HP-UiO-66_X is shown to show the adsorption performance of anthocyanins. Figure 14 This is the adsorption performance of anthocyanins by the pore size distribution of HP-UiO-66_X in Example 2; Figure 15This is the adsorption performance of anthocyanins by the pore size distribution of Example 3 HP-UiO-66_X; Figure 16 This is the pore size distribution of Example 4 HP-UiO-66_X and its adsorption performance on anthocyanins; Figure 17 These are internal diffusion models of anthocyanin adsorption by HP-UiO-66_X in Examples 1-4; Figure 18 This is a pseudo-first-order kinetic model for the adsorption of anthocyanins by HP-UiO-66_X in Examples 1-4; Figure 19 These are pseudo-second-order kinetic models for the adsorption of anthocyanins by HP-UiO-66_X in Examples 1-4; Figure 20 These are BET surface area images of HP-UiO-66_X before and after anthocyanin adsorption in Examples 1-4; Figure 21 Example 3 shows the desorption performance of anthocyanins by HP-UiO-66_OH at different pH values; Figure 22 Example 3 shows the desorption performance of anthocyanins by HP-UiO-66_OH at different temperatures; Figure 23 Example 3 shows the desorption performance of HP-UiO-66_OH on anthocyanins at different ethanol volume fractions; Figure 24 Example 3 shows the desorption performance of anthocyanins by HP-UiO-66_OH at different desorption times; Figure 25 Example 3 shows the desorption performance of anthocyanins by HP-UiO-66_OH under different desorption cycles; Figure 26 This is the zeta potential of HP-UiO-66_OH and anthocyanins in pure water in Example 3; Figure 27 It refers to the zeta potential of anthocyanins at different pH values; Figure 28 The zeta potential of HP-UiO-66_OH in Example 3 at different pH values; Figure 29 These are mass spectra after desorption of HP-UiO-66_X in Examples 1-4; Figure 30 Example 3 shows the adsorption and desorption of different anthocyanins by HP-UiO-66_OH; Figure 31 This is the dynamic adsorption-desorption curve of anthocyanins by HP-UiO-66_OH in Example 3; Figure 32It is the high performance liquid chromatography standard curve of cyanidin-3O-glucoside. Detailed Implementation

[0027] Example 1 A method for preparing a defective zirconium-based metal-organic framework material includes the following steps: 150 mg of ZrCl4 and 100 mg of 2-aminoterephthalic acid (the molar ratio of metal center to ligand is 1:0.82) were added to 2.98 g of benzoic acid, dissolved in 10 mL of N,N-dimethylformamide, and then 50 μL of deionized water were added. The mixed solution was sealed in a Schott vial and sonicated for 5–10 min until the precipitate was completely dissolved. The Schott vial containing the mixed solution was then placed in an oven at 120 °C for 12 h using a solvothermal method. After the reaction was complete, the solution was centrifuged at 8000 rpm for 8 min, and the precipitate was immersed in 10 mL of DMF for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of DMF was added again for washing, and this process was repeated three times. The precipitate obtained after centrifugation was then immersed in 10 mL of methanol for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of methanol was added again for washing, and this process was repeated three times. Finally, the precipitate was vacuum dried at 70 °C for 12 h. The dried solid was dissolved in 10 mL of N,N-dimethylformamide and 2.7 mL of formic acid was added. The mixed solution was sealed in a Schott vial and sonicated for 5-10 min until the precipitate was completely dissolved. The Schott vial containing the mixed solution was then placed in an oven at 120 °C for 12 h using a solvothermal method. After the reaction, the precipitate was centrifuged at 8000 rpm for 8 min, immersed in 10 mL of DMF, and soaked for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of DMF was added again for washing, and this process was repeated three times. The precipitate obtained after centrifugation was then immersed in 10 mL of methanol for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of methanol was added again for washing, and this process was repeated three times. Finally, the precipitate was vacuum dried at 70 °C for 12 h. This yielded a method for preparing a defective zirconium-based metal-organic framework material, named HP-UiO-66_NH2.

[0028] Example 2 The preparation method of a defective zirconium-based metal-organic framework material is the same as that in Example 1, except that 2-aminoterephthalic acid is replaced with 100 mg of 2-hydroxyterephthalic acid (the molar ratio of metal center to ligand is 1:0.82). The preparation method of the defective zirconium-based metal-organic framework material is named HP-UiO-66_OH.

[0029] Example 3 The preparation method of a defective zirconium-based metal-organic framework material is the same as that in Example 1, except that 2-aminoterephthalic acid is replaced with 92 mg of terephthalic acid (the molar ratio of metal center to ligand is 1:0.82). The preparation method of the defective zirconium-based metal-organic framework material is named HP-UiO-66.

[0030] Example 4 The preparation method of a defective zirconium-based metal-organic framework material is the same as that in Example 1, except that 2-aminoterephthalic acid is replaced with 100 mg of 2-methylterephthalic acid (the molar ratio of metal center to ligand is 1:0.82). The preparation method of the defective zirconium-based metal-organic framework material is named HP-UiO-66_CH3.

[0031] Comparative Example 1 150 mg of ZrCl4 and 100 mg of 2-aminoterephthalic acid (the molar ratio of metal center to ligand is 1:0.82) were added to 2.98 g of benzoic acid, dissolved in 10 mL of N,N-dimethylformamide, and then 50 μL of deionized water were added. The mixed solution was sealed in a Schott vial and sonicated for 5–10 min until the precipitate was completely dissolved. The Schott vial containing the mixed solution was then placed in an oven at 120 °C for 12 h using a solvothermal method. After the reaction was complete, the precipitate was centrifuged at 8000 rpm for 8 min, immersed in 10 mL of DMF, and soaked for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of DMF was added again for washing, and this process was repeated three times. The precipitate obtained after centrifugation was then immersed in 10 mL of methanol for 8 h. After centrifugation at 8000 rpm for 8 min, 10 mL of methanol was added again for washing, and this process was repeated three times. Finally, the precipitate was vacuum dried at 70 °C for 12 h in a vacuum drying oven. The zirconium-based metal-organic framework material UiO-66_NH2 was obtained.

[0032] Comparative Example 2 A method for preparing a zirconium-based metal-organic framework material is the same as that for Comparative Example 1, except that the ligand is changed to 100 mg of 2-hydroxyterephthalic acid (the molar ratio of the metal center to the ligand is 1:0.82). This method is named UiO-66_OH.

[0033] Comparative Example 3 A method for preparing a zirconium-based metal-organic framework material is the same as that for Comparative Example 1, except that the ligand is changed to 92 mg of terephthalic acid (the molar ratio of the metal center to the ligand is 1:0.82). This method is named UiO-66.

[0034] Comparative Example 4 A method for preparing a zirconium-based metal-organic framework material is the same as that for Comparative Example 1, except that the ligand is changed to 100 mg of 2-methylterephthalic acid (the molar ratio of the metal center to the ligand is 1:0.82). This method is named UiO-66_CH3.

[0035] Characterization of the defective zirconium-based metal-organic framework material HP-UiO-66_X of this invention: The crystal structure of HP-UiO-66_X was determined using an X-ray diffractometer (Shimadzu XRD-7000S, Shimadzu, Japan) at a scan rate of 8° / min within the 2θ range of 5–50°. Figure 3 As shown, all diffraction peaks conform to the XRD pattern of the standard sample, indicating that a modified material with the same topological structure as the original UiO-66 has been successfully synthesized.

[0036] The structure of HP-UiO-66_X was analyzed by Fourier transform infrared spectroscopy (FTIR) (Spectrum Two, Platinum Elmer Instruments Ltd., Japan). HP-UiO-66_X was mixed with KBr and then compressed into thin sheets. The structures were then analyzed at 4000-400 cm⁻¹. -1 The analysis is performed within the wavenumber range. For example... Figure 4 As shown, at approximately 1570 cm -1 The absorption peak at that point is attributed to the -COOH group and Zr. 4+ The coordination effect, and 478 cm -1 The nearby spectral bands correspond to the stretching vibrations of the Zr-O bond. In HP-UiO-66_OH, the bands are located at 3200-3600 cm⁻¹. -1The broad bands within the range reflect the stretching vibration of -OH. The original HP-UiO-66 exhibits typical doublets at ~1590 and ~1390 cm⁻¹, corresponding to the asymmetric and symmetric stretching vibrations of the carboxylate, respectively, confirming the integrity of the framework structure.

[0037] Transmission electron microscopy (TEM) image acquisition was performed using a JEM-2100 (UHR) instrument, such as... Figure 5 As shown, HP-UiO-66_X has a clear octahedral crystal particle morphology, while HP-UiO-66_NH2 and HP-UiO-66_OH have a clear porous structure inside.

[0038] The specific surface area of ​​the sample was determined using a porous BET analyzer (Micromeritics ASAP 2460). For example... Figure 6 As shown, the specific surface area of ​​HP-UiO-66_NH2 is 1253 m². 2 The specific surface area of ​​HP-UiO-66_OH is 1248 m² / g. 2 / g, the specific surface area of ​​HP-UiO-66 is 1482 m² 2 The specific surface area of ​​HP-UiO-66_CH3 is 1309 m² / g. 2 / g.

[0039] Scanning electron microscopy (SEM) images were acquired using a JSM-7800F instrument. For example... Figure 7 As shown, after etching, uneven voids were observed on the surface of HP-UiO-66_NH2 and HP-UiO-66_OH defects, while textures were observed on the surface of HP-UiO-66 and HP-UiO-66_CH3 after etching.

[0040] Thermogravimetric analysis (TGA) was performed using a TGA-550 thermogravimetric analyzer with a temperature range of 30-800 ℃ and a heating rate of 10 ℃ min under nitrogen atmosphere. -1 .like Figure 8 As shown, HP-UiO-66_X exhibits a smaller decomposition weight loss (37.65%) compared to UiO-66_X. The decomposition weight loss rates for HP-UiO-66_NH2, HP-UiO-66_OH, HP-UiO-66, and HP-UiO-66_CH3 are 40.3%, 25.6%, 32.7%, and 33.8%, respectively. This indicates that the absence of benzoic acid linker increases after defect etching.

[0041] 1¹H-NMR spectra were determined using a Bruker AVANCE III (400 MHz) spectrometer. The optimized sample digestion procedure was as follows: 10 mg of sample and 25 mg of NaOH were added, followed by 0.55 mL of D₂O, and the solution was sonicated repeatedly until clear. Figure 9 As shown, all HP-UiO-66_X showed no benzoic acid signal in the 1H NMR spectrum (δ = 7.76-7.66, 7.44-7.34 and 7.34-7.24 ppm, respectively), indicating that the modifier was successfully etched in the structure.

[0042] The pore size distribution of the sample was determined using a multi-pore BET analyzer (Micromeritics ASAP 2460). For example... Figure 10 As shown, the pore size distribution of HP-UiO-66_X shows a maximum pore size of 3.8 nm, while the pore size of HP-UiO-66_OH is ~3.68 nm.

[0043] The Brunauer–Emmett–Teller surface area of ​​the samples was determined using a porous BET analyzer (Micromeritics ASAP 2460). For example... Figure 11 As shown, the nitrogen adsorption isotherms of HP-UiO-66_X all exhibit typical mixed characteristics of type I and type IV, indicating that micropores and mesopores coexist.

[0044] The separation and purification performance of the defective zirconium-based metal-organic framework material of this invention for anthocyanins: (1) Adsorption performance of anthocyanins by HP-UiO-66_NH2, HP-UiO-66_OH, HP-UiO-66 and HP-UiO-66_CH3 Blueberry anthocyanins were dissolved in water to prepare anthocyanin-water solutions of 40, 60, 80, 100, and 120 mg / L, respectively. The absorbance of the anthocyanins was measured using an SP-2500 UV-Vis spectrophotometer in the range of 200–800 nm. Water was used as a blank. Figure 12 As shown, a concentration of 40-120 mg / L was established. -1 The standard curve of anthocyanin solution.

[0045] Blueberry anthocyanins were dissolved in water to prepare a 120 mg / L anthocyanin-water solution. Using a typical adsorption experiment, 10 mg of each of HP-UiO-66_NH2, HP-UiO-66_OH, HP-UiO-66, and HP-UiO-66_CH3 were added to 5 mL of the anthocyanin-water solution and allowed to stand for adsorption. After a certain adsorption time, the supernatant was collected, and the UV-Vis absorption spectrum was measured and compared with the UV-Vis absorption spectrum before anthocyanin adsorption. The supernatant was then poured back to continue adsorption. The adsorption amount q at a certain time t was... t Determined by the following formula:

[0046]

[0047] In the formula, C0, C t and C e (mg L -1 The initial, time t, and adsorption end concentrations of anthocyanins in the solution are respectively: V (L) is the solution volume, and m (g) is the mass of adsorbent added.

[0048] The absorbance of anthocyanins was measured in the range of 200–800 nm using an SP-2500 UV-Vis spectrophotometer, with water as a blank. Figure 13-16 As shown, the adsorption and absorption rate of anthocyanins by HP-UiO-66_NH2 was 38.1 mg g. -1 The adsorption and absorption rate of anthocyanins by HP-UiO-66_OH was 39.5 mg / g. -1 It is higher than HP-UiO-66 (32.5 mg g). -1 ) and HP-UiO-66_CH3 (30.6 mg g) -1 Therefore, compared with the other three HP-UiO-66_X materials, HP-UiO-66_OH exhibits the best adsorption performance in terms of adsorption rate and adsorption capacity.

[0049] (2) Internal diffusion model of anthocyanins by HP-UiO-66_X Blueberry anthocyanins were dissolved in water to prepare a 120 mg / L anthocyanin-water solution. Using a typical adsorption experiment, 10 mg of adsorbent was added to 5 mL of the anthocyanin-water solution. The sample was allowed to stand in the anthocyanin solution for adsorption. After a certain adsorption time, the supernatant was taken, and the UV-Vis absorption spectrum was measured and compared with the UV-Vis absorption spectrum before anthocyanin adsorption. The supernatant was then poured back to continue adsorption.

[0050] The intraparticle diffusion dynamics model uses the following equation:

[0051] In the formula k i The adsorption constant of intraparticle diffusion kinetics (nmol g) -1 min 0.5 ), C i It is the intercept of the linear curve.

[0052] like Figure 17 As shown, the adsorption process of all HP-UiO-66_X can be divided into three stages: the first stage is rapid adsorption at surface active sites, followed by a decrease in the internal diffusion rate, and the third stage is saturation equilibrium of pore adsorption.

[0053] (3) Adsorption kinetics of anthocyanins by HP-UiO-66_X Blueberry anthocyanins were dissolved in water to prepare a 120 mg / L anthocyanin-water solution. Using a typical adsorption experiment, 10 mg of adsorbent was added to 5 mL of the anthocyanin-water solution. The sample was allowed to stand in the anthocyanin solution for adsorption. After a certain adsorption time, the supernatant was taken, and the UV-Vis absorption spectrum was measured and compared with the UV-Vis absorption spectrum before anthocyanin adsorption. The supernatant was then poured back to continue adsorption.

[0054] The adsorption kinetics of anthocyanins were evaluated using pseudo-first-order and pseudo-second-order models:

[0055]

[0056] Where q t and q e (mg g 1 ) represent the amount of anthocyanins adsorbed at a certain time t and equilibrium time, respectively, k1 (min) 1 ) and k2 (g mg 1 min 1 ) are the rate constants of the pseudo-first-order and pseudo-second-order models, respectively.

[0057] The absorbance of anthocyanins was measured in the range of 200–800 nm using an SP-2500 UV-Vis spectrophotometer, with water as a blank.

[0058] like Figure 18-19 As shown, compared with the pseudo-first-order model, the R-values ​​of the HP-UiO-66_X pseudo-second-order model fitting data for anthocyanins are significantly higher. 2 The coefficient is higher. This indicates that the adsorption process of anthocyanins by HP-UiO-66_X is mainly controlled by chemisorption.

[0059] The specific surface area of ​​the sample after adsorption was determined using a porous BET analyzer (Micromeritics ASAP 2460). For example... Figure 20 As shown, the specific surface area of ​​HP-UiO-66_X decreased significantly after adsorbing anthocyanins, with HP-UiO-66_NH2 and HP-UiO-66_OH showing better adsorption effects, and the reduction exceeded 97%.

[0060] (4) Desorption performance of anthocyanins by HP-UiO-66_OH 10 mg of HP-UiO-66_OH was weighed and added to 5 mL of anthocyanin solution with a concentration of 120 mg / L. After the adsorbent reached adsorption equilibrium, it was dried under vacuum. Then, it was desorbed with 5 mL of 50% ethanol aqueous solution, and the pH was adjusted with hydrochloric acid at 50℃ for 2 h. After centrifugation, the supernatant was collected and the desorbed anthocyanin content was determined by high performance liquid chromatography (Agilent 1260 Infinity II). The equilibrium experiment was repeated three times, and the desorption rate at five different pH values ​​was calculated.

[0061] The desorption rate is calculated by the following formula:

[0062] In the formula, C0 and C d (mg L 1 The values ​​represent the initial anthocyanin concentration and the anthocyanin concentration after desorption, respectively.

[0063] like Figure 21 As shown, different pH values ​​of the elution solvent significantly affected the release rate of anthocyanins from HP-UiO-66_OH. When using a mixture of 50% ethanol and water at pH=1, the release rate of anthocyanins was the highest (83%) compared to other elution solvents. This may be because the addition of hydrochloric acid effectively disrupted the intermolecular interaction between HP-UiO-66_OH and anthocyanins, thereby enabling the release of anthocyanins.

[0064] 10 mg of HP-UiO-66_OH was weighed and added to 5 mL of anthocyanin solution with a concentration of 120 mg / L. After the adsorbent reached adsorption equilibrium, it was dried under vacuum. Then, it was desorbed with 5 mL of pH=1 50% ethanol aqueous solution at 20 ℃, 30 ℃, 40 ℃, 50 ℃, and 60 ℃ for 2 h each. After centrifugation, the supernatant was collected and the desorbed anthocyanin content was determined by high performance liquid chromatography. The desorption rate was calculated at five temperatures by repeating the equilibrium experiment three times.

[0065] The desorption rate is calculated by the following formula:

[0066] In the formula, C0 and C d (mg L 1 The values ​​represent the initial anthocyanin concentration and the anthocyanin concentration after desorption, respectively.

[0067] like Figure 22 As shown, different elution solvent temperatures have a certain impact on the release rate of anthocyanins from HP-UiO-66_OH. The highest anthocyanin release rate (73%) was observed at a desorption temperature of 50 °C compared to other temperatures. The enhanced desorption process with increasing temperature can be attributed to the weakening of hydrogen bonds and π-π interactions between anthocyanins and the MOF backbone, as well as the accelerated molecular diffusion at higher temperatures. However, excessive heating may lead to partial degradation of anthocyanins, thereby reducing the overall desorption efficiency.

[0068] 10 mg of HP-UiO-66_OH was weighed and added to 5 mL of anthocyanin solution with a concentration of 120 mg / L. After the adsorbent reached adsorption equilibrium, it was dried under vacuum. Then, it was desorbed with 5 mL of 30%, 40%, 50%, 60%, and 70% ethanol aqueous solutions at pH=1, respectively, at 50 °C for 2 h. After centrifugation, the supernatant was collected and the desorbed anthocyanin content was determined by high-performance liquid chromatography. The desorption rate was calculated for the five volume fractions of ethanol solution by repeating the equilibrium experiment three times.

[0069] The desorption rate is calculated by the following formula:

[0070] In the formula, C0 and C d (mg L 1 The values ​​represent the initial anthocyanin concentration and the anthocyanin concentration after desorption, respectively.

[0071] like Figure 23 As shown, the elution solvent of different volume fractions of ethanol solution has a certain influence on the release rate of anthocyanins in HP-UiO-66_OH. When the volume fraction of ethanol solution is 50%, the release rate of anthocyanins is the highest (79%) compared with other volume fractions.

[0072] 10 mg of HP-UiO-66_OH was weighed and added to 5 mL of anthocyanin solution with a concentration of 120 mg / L. After the adsorbent reached adsorption equilibrium, it was dried under vacuum. Then, it was desorbed with 5 mL of pH=1 50% ethanol aqueous solution at 50 °C for 30 min, 1 h, 2 h, 3 h, and 4 h, respectively. After centrifugation, the supernatant was collected and the desorbed anthocyanin content was determined by high-performance liquid chromatography. The desorption rate was calculated at five different time points after three repeated equilibrium experiments.

[0073] The desorption rate is calculated by the following formula:

[0074] In the formula, C0 and C d (mg L 1 The values ​​represent the initial anthocyanin concentration and the anthocyanin concentration after desorption, respectively.

[0075] like Figure 24 As shown, different desorption times have a certain impact on the release rate of anthocyanins from HP-UiO-66_OH. Desorption time experiments show that the desorption rate increases rapidly within the first 2 hours and then tends to plateau after 2 hours. Taking HP-UiO-66_OH as an example, the desorption rate is approximately 61% at 30 min, increases to 69% at 1 hour, and reaches 78% at 2 hours. Further extending the time to 3-4 hours does not significantly increase the desorption rate. Therefore, setting 2 hours as the equilibrium desorption time ensures both efficiency and consideration of experimental cycle and energy consumption.

[0076] 10 mg of HP-UiO-66_OH was weighed and added to 5 mL of anthocyanin solution with a concentration of 120 mg / L. After the adsorbent reached adsorption equilibrium, it was dried under vacuum. Then, it was desorbed with 5 mL of pH=1 50% ethanol aqueous solution, and desorbed 1, 2, 3, 4, and 5 times at 50 °C for 2 h. After centrifugation, the supernatant was collected and the desorbed anthocyanin content was determined by high performance liquid chromatography. The desorption rate was calculated for each of the five desorption cycles after three repeated equilibrium experiments.

[0077] The desorption rate is calculated by the following formula:

[0078] In the formula, C0 and C d (mg L 1 The values ​​represent the initial anthocyanin concentration and the anthocyanin concentration after desorption, respectively.

[0079] like Figure 25 As shown, different desorption cycles have a certain impact on the release rate of anthocyanins in HP-UiO-66_OH. The desorption rate increased from 63% in the first cycle to 83% in the second cycle and 92% in the third cycle, further increasing to 98% and 99% in the fourth and fifth cycles, respectively. These results indicate that most anthocyanins are released within two cycles, while additional cycles primarily target the strongly retained fractions. From a practical standpoint, two to three cycles are sufficient to achieve over 90% desorption with minimal solvent and energy consumption.

[0080] To investigate the pH sensitivity of anthocyanin desorption behavior, 10 mg of HP-UiO-66_OH and anthocyanin solution with a concentration of 120 mg / L were adjusted to different pH values ​​with hydrochloric acid, and the zeta potential was measured at different pH values ​​and in pure water. Three parallel experiments were repeated.

[0081] like Figure 26 As shown, the zeta potential of anthocyanins and HP-UiO-66_OH in pure water is as follows: Figure 27 As shown, anthocyanin aqueous solutions at different pH values, such as Figure 28 As shown, the potential of the HP-UiO-66_OH aqueous solution at different pH values ​​changes from a weak negative charge to a significant positive charge at pH = 1, highlighting the decisive role of electrostatic interaction in controlling the desorption process.

[0082] Mass spectra of the desorbed solutions of four types of HP-UiO-66_X were tested after standing for 2 h at 50℃ with 50% ethanol (pH=1, HCl). Figure 29 As shown, no ligands were detected in any of the four MOFs in the desorption solution. The structure of the HP-UiO-66_X metal-organic framework remained stable during the desorption process, and no structural collapse occurred.

[0083] (5) Adsorption and desorption selectivity of anthocyanins by HP-UiO-66_OH Cyanide- 3O - Glucoside (C3G), Cyanidin- 3O -Arabanoside (C3A), cyanidin- 3O -Galactoside (C3Ga), Cyanidin- 3O -Rutin (C3Ru), Delphinidin- 3O - Glucoside (D3G), Malvaceain - 3O - Glucoside (Mv3G), Petunidin- 3O - Glucosides (Pt3G) were dissolved separately to prepare 120 mg / L solutions. Using a typical adsorption experiment, 10 mg of HP-UiO-66_OH was added to 5 mL of each solution. The samples were allowed to stand in the solution for adsorption. After a certain adsorption time, the supernatant was measured by high-performance liquid chromatography (HPLC) and compared with the HPLC chromatogram before adsorption. Once the adsorbent reached adsorption equilibrium, it was vacuum dried. Then, desorption was performed using 5 mL of pH=1 50% ethanol aqueous solution at 50 °C for 2 h. After centrifugation, the supernatant was used to determine the desorbed anthocyanin content by HPLC. Three parallel experiments were repeated, and the desorption rate was calculated.

[0084]

[0085] In the formula, C0, C1 and Cd (mg L 1 These represent the initial anthocyanin concentration, the anthocyanin concentration after adsorption, and the anthocyanin concentration after desorption, respectively. Figure 30 As shown, the adsorption rate of C3G was 93%, and the desorption rate was 95%. The cyanidin series exhibited higher adsorption rates (C3A (90%), C3Ga (84%), and C3Ru (80%), and also higher desorption rates (C3A (94%), C3Ga (95%), and C3Ru (94%). Delphinidin- 3O - Glucoside (D3G) adsorption rate 65%, adsorption rate 45%, mallow pigment- 3O - Glucoside (Mv3G) adsorption rate 89%, adsorption rate 46%, petunia extract- 3O - The adsorption rate of glucoside (Pt3G) was 83%, and the adsorption efficiency was 58%. The adsorbent exhibited ideal selectivity of high adsorption-high desorption for cyanidin series anthocyanins, making it very suitable for separation and purification. However, it showed moderate adsorption-low desorption for delphinidin, malvidin, and petuniain, indicating that these molecules are more likely to bind in the pores or interact too strongly with functional groups, which is not conducive to recovery.

[0086] (6) Dynamic adsorption-desorption curves of anthocyanins by HP-UiO-66_OH Column chromatography experiments were performed using an EZ-type gravity column (d = 9.56 mm and l = 55 mm), packed with 80 mg of the selected adsorbent. First, the adsorbent was rinsed with 20 mL of deionized water using a peristaltic pump (LHZW005XT) until the effluent was colorless. Then, a 120 mg / L crude blueberry anthocyanin solution was pumped into the column using a peristaltic pump at flow rates of 0.2 mL / min, 0.4 mL / min, and 0.6 mL / min. During adsorption, 1.5 mL of the effluent was collected periodically, and the absorbance of residual anthocyanins in the water was detected at 520 nm using UV-Vis spectroscopy. This process continued until the absorbance of anthocyanins in the effluent equaled that of the initial solution. A dynamic adsorption curve was plotted with adsorption time on the x-axis and the ratio of the absorbance of anthocyanins in the effluent to that in the initial solution on the y-axis.

[0087] When adsorption equilibrium was reached, the injection was stopped. 20 mL of deionized water and 20 mL of ethanol were then passed through for washing. Next, a 50% ethanol aqueous solution (pH=1) was passed through for desorption at flow rates of 0.2 mL / min, 0.4 mL / min, and 0.6 mL / min. One tube of effluent was collected every 1.5 mL, and the absorbance of residual anthocyanins in the water was detected at 520 nm using UV-Vis spectroscopy until the peak representing anthocyanins in the effluent disappeared. A dynamic desorption curve was plotted with adsorption time on the x-axis and the absorbance of anthocyanins in the effluent on the y-axis.

[0088] like Figure 31 As shown, the breakthrough adsorption curves of A / A0 versus adsorption time are plotted. Breakthrough time (t) b ) and exhaustion time (t) e The values ​​indicate the time required for the anthocyanin concentration in the eluent to reach 10% and 90% of the initial anthocyanin concentration. HP-UiO-66_OH showed the shortest breakthrough time (approximately 2 min) and exhaustion time (approximately 33 min) at 0.2 mL / min. The dynamic desorption curves show that the absorbance of anthocyanins in the eluent increases rapidly at the beginning, and the amount of desorbed anthocyanins gradually decreases with increasing desorption time.

[0089] (7) Purification of anthocyanins in the actual system by HP-UiO-66_OH To verify the enrichment and purification performance of HP-UiO-66_OH in a real crude blueberry sample, the following procedure was used to perform adsorption-desorption treatment on the crude sample, and the experimental results and calculations are presented accordingly. The crude blueberry sample was prepared at a mass concentration of 120 mg·L⁻¹. -1 (In water, 12 mg crude product / 100 mL), adsorption and desorption were performed using HP-UiO-66_OH as the adsorbent. Desorption was performed using a 50% (v / v) ethanol-water solution at pH = 1, at a temperature of 50 °C, for 2 h. The desorbed solutions were combined and lyophilized to obtain the desorbed product powder for subsequent analysis. To ensure the accuracy of the quantitative results of anthocyanin content in the crude and purified products, two calibration methods were established and adopted: one was UV-Vis spectroscopy (used for pH differential quantification of total anthocyanins), and the other was high-performance liquid chromatography (HPLC, used for standard curve testing and quantification of cyanidin-3-O-glucoside C3G). The standard curve is shown below. Figure 32 As shown.

[0090] HPLC determination of C3G (cyanidin-3-O-glucoside) in the crude product:

[0091]

[0092] Therefore, the content of C3G in the crude product relative to the total mass of the crude product is 4.55%.

[0093] Where A is the HPLC peak area of ​​C3G; d is the intercept of the HPLC standard curve of cyanidin-3O-glucoside; V is the volume of the crude product solution (L); k is the slope of the HPLC standard curve of cyanidin-3O-glucoside; and M is the total mass of the crude product (mg).

[0094] HPLC determination of purified C3G from HP-UiO-66_OH:

[0095]

[0096] Therefore, the C3G content after purification is 20%, which is about 4.4 times higher than the 4.55% in the crude product.

[0097] Where A is the HPLC peak area of ​​C3G; d is the intercept of the HPLC standard curve of cyanidin-3O-glucoside; v is the volume of the desorption solution (L); k is the slope of the HPLC standard curve of cyanidin-3O-glucoside; and m is the total mass of the purified sample (mg).

[0098] Determination of total anthocyanins (TAC) in crude product by pH differential method:

[0099]

[0100] Therefore, the total anthocyanin content in the crude product relative to the total mass of the crude product is 18.5%.

[0101] Where A is the absorbance difference of the sample (A530 nm - A700 nm) pH 1.0 - (A530 nm - A700 nm) pH 4.5; MW is the molecular weight of cyanidin-3O-glucoside (449.2 g / mol); DF represents the dilution factor; V is the volume of the crude solution (L); M is the total mass of the crude product (mg); and ε is the molar extinction coefficient of cyanidin-3O-glucoside (26900 L mol-1 cm-1).

[0102] pH differential method for determining total anthocyanin TAC after purification of HP-UiO-66_OH:

[0103]

[0104] Therefore, the content of total anthocyanins after purification was 97.3% of the total mass of the purified sample.

[0105] Where A is the absorbance difference of the sample (A530 nm - A700 nm) pH 1.0 - (A530 nm - A700 nm) pH 4.5; MW is the molecular weight of cyanidin-3O-glucoside (449.2 g / mol); DF represents the dilution factor; v is the volume of the purified solution (L); m is the total mass of the purified sample (mg); and ε is the molar extinction coefficient of cyanidin-3O-glucoside (26900 Lmol-1cm-1).

[0106] HP-UiO-66_OH significantly enriched the total anthocyanin content in the crude product from 18.5% to approximately 97.3% in the desorption products, achieving highly selective enrichment (TAC benchmark). Simultaneously, the relative content of the target monomer C3G increased from 4.55% to 20.0%, demonstrating a significant enrichment ability for the target monomer (monomer selectivity or component enrichment).

[0107] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for the preparation of a defective zirconium metal-organic framework HP-UiO-66_X adsorbing the defectanin series of anthocyanins, characterized in that, Comprising the following steps: (1) ZrCl4, terephthalic acid or its derivatives, benzoic acid as raw material, by solvothermal method to prepare zirconium-based HP-UiO-66_X material, centrifugation, washing, drying; the terephthalic acid derivatives are one of 2-amino terephthalic acid, 2-hydroxy terephthalic acid, 2-methyl terephthalic acid; (2) the dried zirconium-based HP-UiO-66_X is dissolved in N, N-dimethylformamide and formic acid is added, and the reaction is carried out by solvothermal method, and after the reaction is completed, centrifugation, washing, drying, to obtain a defective zirconium-based metal organic framework HP-UiO-66_X.

2. The method of claim 1, wherein, In step (1), the terephthalic acid derivative is 2-hydroxy terephthalic acid.

3. The method of claim 1, wherein, In step (1), the terephthalic acid derivative is 2-amino terephthalic acid.

4. The method of claim 1, wherein, In step (1), the molar ratio of ZrCl4 to benzoic acid is 0.67-0.70:2.93-3.

00.

5. The method of claim 1, wherein, In step (1), the molar ratio of ZrCl4 to terephthalic acid or its derivatives is 1:0.82-0.

85.

6. The method of claim 1, wherein, In step (1), the solvothermal method is carried out at 120℃ for 10-12 h.

7. The method of claim 1, wherein, In step (2), the volume ratio of N, N-dimethylformamide to formic acid is 10:2.7-3.

0.

8. The method of claim 1, wherein, In step (2), the solvothermal method is carried out at 120℃ for 10-12 h.

9. The defective zirconium-based metal organic framework HP-UiO-66_X prepared by the method of any one of claims 1-8.

10. The use of the defective zirconium-based metal organic framework HP-UiO-66_X of claim 9 in enriching and purifying cyanidin-based anthocyanins.

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