A metal-organic framework composite material modified with a natural polymer, its preparation method and application

Abstract

This invention relates to the field of water remediation materials technology, specifically to a metal-organic framework composite material modified with a natural polymer, its preparation method, and its application. The preparation method of the metal-organic framework composite material modified with the natural polymer includes the following steps: first, zinc acetate is reacted with imidazole to obtain Zn-MOFs; the pH is adjusted to 6.0-7.0; then, an aqueous solution of the natural polymer is added to react and form a gel dispersion; the solid-liquid mixture is separated and dried to obtain the final product. The metal-organic framework composite material modified with the natural polymer prepared by this invention has the advantages of good recyclability and effective removal of antibiotics.

Description

Technical Field

[0001] This invention relates to the field of water remediation materials technology, specifically to a metal-organic framework composite material modified with natural polymer materials, its preparation method, and its application. Background Technology

[0002] Tetracycline (TC) and erythromycin (ETM), as broad-spectrum antibiotics, primarily leave environmental residues from livestock and poultry excrement, medical wastewater, and pharmaceutical industry emissions. The polar structures of these two antibiotics (TC contains multiple hydroxyl and amide groups, while ETM contains macrolide structures) result in extremely slow natural degradation rates. Studies show that TC has a half-life greater than 100 days in soil, easily entering water bodies through surface runoff and accumulating in sediment; ETM has a hydrolysis half-life of up to 200 days in water bodies with pH=7, and its metabolites still possess antibacterial activity. Long-term antibiotic residues in water bodies pose multiple ecological risks; therefore, the degradation of antibiotics in water bodies urgently needs to be addressed.

[0003] Currently, while physical adsorption is widely used, activated carbon materials still face challenges such as difficult regeneration, high processing costs, and poor selectivity for polar antibiotics. Advanced oxidation technologies, such as the Fenton process and ozone oxidation, can effectively degrade antibiotic molecules, but they consume a lot of energy, have a narrow reaction pH range, and may produce more toxic intermediates. In terms of biological treatment technologies, the antibacterial activity of antibiotics significantly inhibits microbial metabolism, resulting in low degradation efficiency of TC and ETM by microorganisms. Furthermore, while membrane separation technology can achieve efficient retention of pollutants, it still faces bottlenecks such as severe membrane fouling and the difficulty of treating the concentrate.

[0004] Metal-organic frameworks (MOFs) are considered promising high-efficiency materials for antibiotic degradation due to their high specific surface area and structural tunability. However, their insufficient chemical stability under actual aquatic conditions limits their large-scale application in water treatment. Therefore, to improve their applicability for antibiotic degradation in water, it is necessary to enhance the stability and antibiotic degradation efficiency of MOFs.

[0005] The prior art (Bao Jiaxin, Wang Lianyan, Zhou Zhimao, et al. Research progress on adsorption of drug pollutants in water by chitosan complex microspheres [J]. Industrial Water and Wastewater, 2023, 54(1):1-5) discloses that the chitosan / MOF complex has the advantages of both: ① Modification of MOFs can increase the adsorption sites of chitosan and enhance chemical adsorption; ② The high porosity and variable pore size of MOFs solve the drawbacks of the linear structure of chitosan, which can enhance the specific surface area of ​​chitosan microspheres and improve the physical adsorption performance of chitosan.

[0006] Chinese Patent Publication No. CN119346081A discloses a bimetallic MOFs / chitosan composite gel, its preparation method, and its application. This gel modifies the MOFs adsorbent through metal doping (iron doping), optimizing its structure and increasing active adsorption sites. The doped iron ions bind through electrostatic attraction and coordination bonds, improving adsorption efficiency and selectivity. This allows the material to maintain excellent performance in complex aquatic environments, significantly enhancing its adsorption capacity for heavy metal ions and antibiotics in mine wastewater. However, this material requires the prior preparation of chitosan aerogel spheres, followed by mixing with soluble iron salts, soluble zinc sources, and methanol, and then reacting with 2-methylimidazole. Its reusability and antibiotic removal efficiency need further improvement.

[0007] Therefore, it is essential to develop a metal-organic framework composite material modified with natural polymers that can solve the above-mentioned technical problems, its preparation method, and its application in the removal of antibiotics from water. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a metal-organic framework composite material modified with natural polymer materials that has good recyclability and antibiotic removal effect, as well as its preparation method and application.

[0009] This invention is achieved through the following technical solutions:

[0010] The first aspect of this invention provides a method for preparing a metal-organic framework composite material modified with a natural polymer material, comprising the following steps: first, reacting zinc acetate with imidazole to obtain Zn-MOFs, adjusting the pH to 6.0-7.0, then adding an aqueous solution of a natural polymer material to react and form a gel dispersion, followed by solid-liquid separation and drying to obtain the final product.

[0011] The Zn-MOFs of this invention, combined with natural polymer materials through electrostatic interactions and hydrogen bonding networks, solves the core bottleneck problem of poor chemical stability and easy aggregation and deactivation of traditional MOF materials in water treatment. The natural polymer materials preferably contain abundant amino (-NH2) and hydroxyl (-OH) groups, providing a large number of additional adsorption sites, which strongly bind to antibiotic molecules (especially negatively charged groups) through electrostatic interactions and hydrogen bonds. The Zn-MOFs and natural polymer materials form a synergistic mechanism of "Zn-MOFs enrichment and catalysis - chitosan capture and immobilization," greatly improving the overall antibiotic removal efficiency.

[0012] This invention develops an in-situ composite technology under pH control. By pre-adjusting Zn-MOFs to a weakly acidic environment (pH 6.0-7.0) and then composited with an aqueous solution of natural polymer materials, a gel is ultimately formed. This ensures that the natural polymer materials can efficiently and uniformly coat the surface of Zn-MOFs, forming a stable three-dimensional network structure, rather than a simple physical mixture. This technology is suitable for water bodies with complex pH levels, especially acidic polluted water bodies.

[0013] In one embodiment of the present invention, the mass fraction of natural polymer materials in the metal-organic framework composite material is 0.5-1.0%.

[0014] In one embodiment of the present invention, the pH is adjusted to 6.0-7.0 after the reaction of the aqueous solution containing the added natural polymer material is completed.

[0015] In one embodiment of the present invention, the metal-organic framework composite material has a positive zeta potential in the pH range of 6.0-7.0.

[0016] In one embodiment of the present invention, the natural polymer material is selected from at least one of chitosan and polydopamine.

[0017] The metal-organic framework composite material modified with natural polymers of this invention ultimately forms a gel-like product, which, after freeze-drying, becomes a porous solid material with good mechanical strength and is not easily fragmented. In practical water treatment operations (such as packed column or stirred and then allowed to stand), it facilitates solid-liquid separation and material recovery through sedimentation, filtration, or centrifugation, solving the engineering problem of difficult recovery of nanopowder materials. This effect is attributed to the key step of "pH-induced gelation." At the end of the preparation process, NaOH is added dropwise to adjust the pH to near neutral, which enhances the hydrogen bonding between positively charged chitosan chains, causing cross-linking of the molecular chains and forming a three-dimensional network structure that firmly encapsulates and fixes the Zn-MOF particles within it, ultimately forming an easily handled solid material.

[0018] In one embodiment of the present invention, zinc acetate reacts with imidazole in an alcohol-water system.

[0019] Preferably, the zinc acetate is first dissolved in water and the imidazole is dissolved in ethanol before the reaction is carried out.

[0020] More preferably, the concentration of zinc acetate dissolved in water is 0.1-0.2 mol / L, and the concentration of imidazole dissolved in ethanol is 0.4-0.5 mol / L.

[0021] In one embodiment of the present invention, the mass ratio of zinc acetate to imidazole is 0.7-1.4:1.

[0022] In one embodiment of the present invention, the reaction temperature of zinc acetate with imidazole is 20-25°C and the reaction time is 3-5 hours.

[0023] In one embodiment of the present invention, the concentration of natural polymer in the aqueous solution of the natural polymer material is 0.5-1 g / 100 mL.

[0024] In one embodiment of the present invention, the aqueous solution of the natural polymer material contains acetic acid with a volume concentration of 0.5-1.0%.

[0025] In one embodiment of the present invention, the ratio of the amount of Zn-MOFs to the aqueous solution of the natural polymer material is 1-2 g: 100 mL.

[0026] In one embodiment of the present invention, after the reaction of zinc acetate with imidazole is completed, solid-liquid separation is performed, and the product is dried to obtain Zn-MOFs, which are then added to water to adjust the pH to 6.0-7.0.

[0027] Preferably, the drying method used in obtaining Zn-MOFs is vacuum drying; after the gel dispersion is formed, the drying method is to first pre-freeze and then perform vacuum freeze-drying.

[0028] As one embodiment of the present invention, the preparation method specifically includes the following steps:

[0029] (1) Imidazole and zinc acetate must be dispersed before reaction and stirred continuously at room temperature;

[0030] (2) Synthesize Zn-MOFs, add water to obtain Zn-MOFs dispersion, and adjust the pH of Zn-MOFs dispersion to 6.0-7.0;

[0031] (3) Prepare aqueous solutions of natural polymer materials;

[0032] (4) Mix the Zn-MOFs obtained in step (2) with the aqueous solution of the natural polymer material obtained in step (3) and stir to react;

[0033] (5) Adjust the pH value of the mixture obtained in step (4) with alkaline solution to form a gel dispersion;

[0034] (6) The gel dispersion was washed, centrifuged and freeze-dried to obtain a metal-organic framework composite material modified with natural polymer materials.

[0035] Preferably, the stirring in step (1) is magnetic stirring, with a speed of 500-600 rpm and a time of 3-5 hours.

[0036] Preferably, the pH adjustment in step (2) uses a 1 M NaOH solution.

[0037] Preferably, the stirring in step (4) is magnetic stirring, with a speed of 500-600 rpm and a time of 1-2 hours.

[0038] Preferably, in step (5), the pH value of the mixture obtained in step (4) is slowly adjusted to 6.0-7.0 with an alkaline solution to form a gel dispersion.

[0039] Preferably, the freeze-drying conditions in step (6) are: pre-freezing at -80°C and then freeze-drying under vacuum for 12-24 hours.

[0040] A second aspect of the present invention provides a metal-organic framework composite material modified with natural polymer materials prepared by the above-described preparation method.

[0041] A third aspect of this invention provides the application of the aforementioned metal-organic framework composite material modified with natural polymers in the preparation of wastewater treatment agents. The wastewater treatment agent is used for treating livestock and poultry breeding wastewater, pharmaceutical industrial wastewater, or secondary effluent from urban wastewater treatment plants.

[0042] In one embodiment of the present invention, the wastewater treatment agent is used to adsorb and / or degrade antibiotics.

[0043] Preferably, the antibiotic is at least one of tetracycline antibiotics and macrolide antibiotics.

[0044] More preferably, the tetracycline antibiotic is tetracycline, and the macrolide antibiotic is erythromycin.

[0045] The metal-organic framework composite material modified with natural polymer materials described in this invention has a saturated adsorption capacity of not less than 520 mg / g for tetracycline and 590 mg / g for erythromycin.

[0046] This invention can be reused at least 5 times with a degradation performance decrease of no more than 15%.

[0047] The beneficial effects of this invention are:

[0048] The metal-organic framework (MOF) composite material modified with natural polymers of this invention maintains excellent structural integrity during long-term use in aqueous solutions, effectively overcoming the problems of metal ion dissolution, framework collapse, or loss of activity that traditional MOF materials are prone to in complex aqueous chemical environments. Simultaneously, the material is not prone to aggregation, maintaining high dispersibility and ensuring full exposure of all active sites. This effect is attributed to the coating and stabilizing effect of the natural polymers. The natural polymers bind tightly to the Zn-MOF surface through electrostatic interactions and hydrogen bonds, forming an organic protective layer that shields the Zn-O coordination bonds from direct attack by water molecules, thereby enhancing chemical stability. The long-chain structure of the natural polymers generates a steric hindrance effect, effectively preventing the MOF nanoparticles from approaching each other and agglomerating, allowing them to be stably and uniformly dispersed in water, ensuring excellent mass transfer efficiency and operability.

[0049] The metal-organic framework composite material modified with natural polymer materials of this invention has a broad spectrum of antibiotic resistance and exhibits excellent adsorption and degradation effects on a variety of antibiotics.

[0050] This invention achieves superior performance across a wider range of pH conditions (especially weakly acidic to neutral) by precisely controlling the pH value (6.0-7.0) during the composite process, thus adapting to the complex pH environment of real wastewater. This effect is attributed to the precise pH-controlled preparation process, which ensures that the natural polymer materials bind to Zn-MOFs in an optimal state (partially protonated), giving the composite material a tunable and stable Zeta potential. This allows the material to optimize its surface charge by adjusting the pH when treating wastewater with varying pH levels, thereby maintaining highly efficient interaction with the target pollutants (whose charge also varies with pH).

[0051] This invention screened the raw materials used in the preparation and found that the reaction of zinc acetate and imidazole can significantly improve the recycling performance and antibiotic removal effect of metal-organic framework composites modified with natural polymer materials. Furthermore, the order in which the raw materials are added during the preparation process also has a significant impact on the recycling performance and antibiotic removal effect.

[0052] This invention compared the effects of LED light source irradiation with and without LED light source irradiation, and found that the adsorption and degradation performance of metal-organic framework composite materials for tetracycline and erythromycin was further improved after LED simulated natural light irradiation. Attached Figure Description

[0053] Figure 1 Transmission electron microscopy images of Zn-MOFs and CS@Zn-MOFs (scale bar: 200 nm).

[0054] Figure 2Scanning electron microscope image of CS@Zn-MOFs (scale bar: 200 nm).

[0055] Figure 3 Elemental analysis for CS@Zn-MOFs.

[0056] Figure 4 The particle size distribution diagrams are shown for Zn-MOFs and CS@Zn-MOFs.

[0057] Figure 5 The infrared spectra of zinc acetate and Zn-MOFs are shown.

[0058] Figure 6 The image shows the XRD pattern of CS@Zn-MOFs, with the vertical axis representing the intensity in count.

[0059] Figure 7 The image shows the XRD pattern of CS@Zn-MOFs, with the vertical axis representing the logarithm of the count.

[0060] Figure 8 High-resolution XPS full spectrum of CS@Zn-MOFs.

[0061] Figure 9 XPS spectra of CC, CN, and C=O in CS@Zn-MOFs.

[0062] Figure 10 XPS spectra of Zn2p1 and Zn2p3 in CS@Zn-MOFs.

[0063] Figure 11 Comparison images of nano-ZnO, CS@Zn-MOFs, and CS@Zn-MOFs + LED reacting with methylene blue solution before and after 2 h.

[0064] Figure 12 The UV spectra of nano-ZnO, CS@Zn-MOFs, and CS@Zn-MOFs + LED reacting with methylene blue solution at different times.

[0065] Figure 13 The UV spectra of nano-ZnO, CS@Zn-MOFs, and CS@Zn-MOFs + LED mixed with TC solution at different times within 2 h.

[0066] Figure 14 The degradation effects of nano-ZnO, CS@Zn-MOFs, and CS@Zn-MOFs + LED on TC within 2 h were evaluated, with ***p<0.001.

[0067] Figure 15The degradation effects of nano-ZnO, CS@Zn-MOFs, and CS@Zn-MOFs + LED on ETM within 2 h were evaluated, with ***p<0.001.

[0068] Figure 16 Tyndall effect diagrams for CS@Zn-MOFs + LED degradation before, during, and 2 h after the first recovery and redispersion.

[0069] Figure 17 The degradation efficiency of TC after four recycling and reuse of the CS@Zn-MOFs + LED composite material in Example 1 is shown.

[0070] Figure 18 The degradation efficiency of ETM after four recycling cycles of the CS@Zn-MOFs + LED composite material in Example 1 is shown.

[0071] Figure 19 The degradation efficiency of TC after four recycling cycles of the CS@Zn-MOFs + LED composite material in Example 2 is shown.

[0072] Figure 20 The degradation efficiency of ETM after four recycling cycles of the CS@Zn-MOFs + LED composite material in Example 2 is shown.

[0073] Figure 21 The effect of Zn-MOFs synthesized using imidazole and dimethylimidazolium on chitosan encapsulation efficiency is compared. *p<0.05.

[0074] Figure 22 The graph shows the comparison of the residual rates of tetracycline after degradation by Zn-MOFs synthesized using imidazole and dimethylimidazolium under LED irradiation. ***p<0.001.

[0075] Figure 23 The graph shows the comparison of the residual rates of erythromycin after degradation by Zn-MOFs synthesized using imidazole and dimethylimidazol under LED irradiation. **p<0.01.

[0076] Figure 24 To compare the effect of different chitosan concentrations on the encapsulation efficiency of CS@Zn-MOFs materials in Example 2.

[0077] Figure 25 For the degradation effect of CS@Zn-MOFs + LED on TC and ETM in Comparative Example 3, ***p<0.001.

[0078] Figure 26 For the degradation effect of CS@Zn-MOFs + LED on TC and ETM in Comparative Example 4, ***p<0.001. Detailed Implementation

[0079] The present invention will be further described below with reference to specific embodiments, and the advantages and features of the present invention will become clearer as a result. However, these embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0080] Example 1: Preparation of CS@Zn-MOFs composite material

[0081] 1. Raw materials:

[0082] Zinc acetate dihydrate (C4H6O4Zn·2H2O), analytical grade;

[0083] Imidazole (C3H4N2), analytical grade;

[0084] Chitosan (degree of deacetylation ≥ 95%, CS), biochemical reagents;

[0085] Glacial acetic acid (C2H4O2), analytical grade;

[0086] Sodium hydroxide (NaOH), analytical grade;

[0087] Methylene blue (MB), analytical grade;

[0088] Anhydrous ethanol, deionized water.

[0089] 2. Preparation process:

[0090] (a) Synthesis of Zn-MOFs:

[0091] 2.2 g of zinc acetate dihydrate was dissolved in 100 mL of deionized water and sonicated to prepare a 0.1 mol / L solution. 2.7 g of imidazole was dissolved in 100 mL of anhydrous ethanol and sonicated to prepare a 0.4 mol / L solution. The zinc acetate aqueous solution was slowly added dropwise to the imidazole ethanol solution at room temperature (25℃) and with mechanical stirring at 600 rpm. After the addition was complete, the reaction was continued for 5 hours. After the reaction was complete, 10 mL of the reaction solution was retained. The remaining suspension was centrifuged (10000 g, 10 min), washed three times with deionized water, and then dried in a vacuum oven at 60℃ for 15 hours to obtain a white Zn-MOFs solid powder.

[0092] (b) Preparation of CS@Zn-MOFs composite materials:

[0093] Prepare a 0.5% (w / v) chitosan solution: Weigh 0.05 g of chitosan powder and dissolve it in 10 mL of 0.5% (v / v) acetic acid aqueous solution, stirring magnetically until completely dissolved. Weigh 0.1 g of the Zn-MOFs powder prepared in step (a) and dissolve it in 1 mL of deionized water to obtain a Zn-MOFs dispersion. Adjust the pH of the Zn-MOFs dispersion to 6.5 with 1 mol / L NaOH solution, and then add it to the above 10 mL chitosan solution. Stir at 600 rpm for 1 hour at room temperature. Subsequently, slowly adjust the pH of the above mixture to 6.5 with 1 mol / L NaOH solution, and observe that the system gradually becomes gel-like. Collect the gel product by centrifugation, wash it three times with deionized water, then freeze it in an ultra-low temperature freezer at -80℃ for 12 hours, and then transfer it to a freeze dryer for lyophilization to finally obtain CS@Zn-MOFs composite material solid powder.

[0094] Conclusion 1-1: A white solid powder was successfully obtained using the above method.

[0095] Example 2: Preparation of CS@Zn-MOFs composite material

[0096] (a) Synthesis of Zn-MOFs:

[0097] 4.4 g of zinc acetate dihydrate was dissolved in 100 mL of deionized water and sonicated to prepare a 0.2 mol / L solution. 3.4 g of imidazole was dissolved in 100 mL of anhydrous ethanol and sonicated to prepare a 0.5 mol / L solution. The zinc acetate aqueous solution was slowly added dropwise to the imidazole ethanol solution at room temperature (25℃) and with mechanical stirring at 600 rpm. After the addition was complete, the reaction was continued for 3 hours. After the reaction was complete, 10 mL of the reaction solution was retained. The remaining suspension was centrifuged (10000 g, 10 min), washed three times with deionized water, and then dried in a vacuum oven at 60℃ for 15 hours to obtain a white Zn-MOFs solid powder.

[0098] (b) Preparation of CS@Zn-MOFs composite materials:

[0099] To prepare a 0.5% (w / v) chitosan solution: Weigh 0.1 g of chitosan powder and dissolve it in 10 mL of 1% (v / v) acetic acid aqueous solution. Stir magnetically until completely dissolved. Weigh 0.2 g of the Zn-MOFs powder prepared in step (a) and dissolve it in 1 mL of deionized water to obtain a Zn-MOFs dispersion. Adjust the pH of the Zn-MOFs dispersion to 7.0 with 1 mol / L NaOH solution, and then add it to the above 10 mL chitosan solution. Stir at 600 rpm for 1 hour at room temperature. Subsequently, slowly adjust the pH of the above mixture to 7.0 with 1 mol / L NaOH solution, and observe that the system gradually becomes gel-like. Collect the gel product by centrifugation, wash it three times with deionized water, then freeze it in an ultra-low temperature freezer at -80℃ for 12 hours, and then transfer it to a freeze dryer for lyophilization to finally obtain CS@Zn-MOFs composite material solid powder.

[0100] Conclusions 1-2: A white solid powder was successfully obtained using the above method. Furthermore, compared to Example 1, the degradation effect of TC and ETM after 5 cycles of degradation for 2 hours remained almost unchanged, specifically as follows: Figure 19 and Figure 20 As shown.

[0101] Example 3: Characterization of the CS@Zn-MOFs composite material prepared in Example 1

[0102] The morphology of Zn-MOFs and CS@Zn-MOFs in Example 1 was characterized using transmission electron microscopy (TEM, JEM-1400 PLUS, NEC Corporation, Japan). The surface morphology and elemental composition of CS@Zn-MOFs were observed using scanning electron microscopy (SEM, Zeiss, Germany). Particle size and zeta potential were determined using a Malvern Zeta potential and particle size analyzer (Nano-ZS90, Malvern Instruments, UK). Characteristic spectra were obtained using a UV-Vis spectrophotometer (UV-2600, Shimadzu Corporation, Japan) and a Fourier transform infrared spectrometer (FTIR, Nicolet iS5, Thermo Fisher Scientific, USA), respectively. The phase structure and surface elemental composition of CS@Zn-MOFs composite materials were analyzed using X-ray powder diffraction (XRD, D8 ADVANCE, Bruker GmbH, Germany) and X-ray photoelectron spectroscopy (XPS, Escalab 250Xi, Thermo Fisher Scientific, USA).

[0103] Conclusion 2: The above method was used to prepare the following... Figure 1 The nanoparticles shown by TEM are uniform in morphology and of moderate size. The CS@Zn-MOFs composite material has a particle size between 200 and 800 nm.

[0104] Conclusion 3: Figure 2 SEM surface morphology analysis revealed that there are voids between the nanoparticles.

[0105] Conclusion 4: Figure 3 Elemental analysis results showed that the normalized mass ratio of Zn reached 40.24%, indicating that Zn was successfully doped into MOFs.

[0106] Conclusion 5: Figure 4 The particle size results showed that the particle size of MOFs increased after CS coating, with an average particle size of about 500 nm.

[0107] The pH of the Zn-MOFs dispersion was adjusted during the preparation process of Example 1, and the potential of Zn-MOFs under different pH conditions was tested. The specific results are shown in Table 1. The surface potential of Zn-MOFs changed with the pH value of the water body, and finally 6.0-7.0 was determined as the reaction pH.

[0108] Table 1 Potential (mV) of Zn-MOFs in different pH environments

[0109]

[0110] Conclusion 6: Figure 5 The image shows the infrared spectra of zinc acetate and Zn-MOFs samples. The characteristic peak of the zinc acetate spectrum is located at 3056 cm⁻¹. -1 1543 cm -1 1419 cm -1 and 688 cm -1 Location: 3056 cm -1 The absorption peak at 1543 cm⁻¹ likely corresponds to the stretching and antisymmetric stretching vibrations of the methyl group in acetate, but is slightly shifted compared to the common spectral regions for methyl stretching and antisymmetric stretching vibrations; -1 The peak at 1419 cm⁻¹ corresponds to the asymmetric stretching vibration of the acetate group; -1 The peak corresponds to the symmetric stretching vibration of the acetate ion; 688 cm⁻¹ -1 The peak at 2702 cm⁻¹ corresponds to the stretching vibration of the Zn-O bond. Zn-MOFs show a peak at 2702 cm⁻¹. -1 2469 cm -1 1641 cm -1 1511 cm -1 980 cm -1 and 842 cm -1 Characteristic peak at 2702 cm⁻¹ -1 With 2469 cm -1 The peak at 1641 cm⁻¹ likely corresponds to the vibration of the CH bond on the imidazole ring, but its position is slightly shifted compared to the common spectral region;-1 The peak at 980 cm⁻¹ is attributed to the stretching vibration of the C=N bond; -1 The peak at 3260 cm⁻¹ corresponds to the stretching vibration of the CN bond. Among the characteristic peaks of the imidazole infrared spectrum, the peak at 3260 cm⁻¹ is... -1 The nearby absorption peaks typically correspond to the stretching vibrations of the NH bond. This characteristic peak did not appear in the infrared spectrum of the MOF, indicating that zinc had successfully coordinated with imidazole.

[0111] Conclusion 7: Data processed after baseline correction using software, Figure 6 and Figure 7 The characteristic diffraction peaks of this sample are mainly at 15.205°, 18.687°, and 20.884°. The diffraction peaks of conventional ZIF-8 (MOFs synthesized from zinc-based imidazole frameworks) are located at 12.7°, 14.8°, and 16.4°. The higher diffraction angles measured in this study are believed to be related to the constraint effect of the coating layer. Specifically, the chitosan polymer chains are bound to the Zn-MOFs surface through coordination or hydrogen bonding, causing the Zn-MOFs unit cells to shrink, resulting in a slight shift of the characteristic peaks towards the higher 2θ direction. The peak area of ​​the 15.205° diffraction peak is 8342, significantly higher than the peak areas of the other two peaks (1044 and 1199 respectively), indicating a higher crystallinity and larger grain size in the synthesized MOFs product. Furthermore, a significant broadening background was observed in the original data within the 10°-30° range, which is believed to be caused by amorphous scattering due to the chitosan added during sample preparation.

[0112] Conclusion 8: The results of high-resolution XPS are as follows Figure 8 , Figure 9 , Figure 10 As shown, the results demonstrate that a pure metal-organic framework with a well-defined coordination structure was successfully synthesized in this experiment. Zinc (Zn) was used as the catalyst. 2+ The carbon (C) and nitrogen (N) atoms in the imidazole ligands exist in a stable coordinate bond with the nitrogen atom in the imidazole ligand. The carbon (C) and nitrogen (N) atoms mainly originate from the imidazole organic framework, while the oxygen (O) atoms originate from residual acetate ions and surface-adsorbed water. The narrow half-maximum width (FWHM) of the binding energies of each element indicates a homogeneous chemical environment, further demonstrating the high structural regularity of the synthesized zinc-imidazole MOFs (Zn-MOFs).

[0113] Example 4: Performance evaluation of the CS@Zn-MOFs composite material prepared in Example 1

[0114] 1. Determination of the redox power of CS@Zn-MOFs

[0115] The oxidation capacity of CS@Zn-MOFs was evaluated using methylene blue solution, with nano-ZnO as a control. Three aliquots of methylene blue solution of the same concentration (50 μM, 5 mL, source leaf CAS: 7220-79-3) were prepared and labeled as codes 1, 2, and 3. Nano-ZnO (0.25 mg), CS@Zn-MOFs (0.4 mL, 5 mg / mL), and CS@Zn-MOFs (0.4 mL, 5 mg / mL) were added to the methylene blue solution, respectively. The third aliquot was tested under simulated sunlight from an LED lamp (585–620 nm, 75 mW / cm²). 2 Irradiation (denoted as CS@Zn-MOFs + LED) was performed, and the color change of methylene blue was observed. The absorbance was measured by a UV-Vis spectrophotometer at 0 min, 30 min, 60 min, 90 min, and 120 min.

[0116] 2. Degradation performance test of CS@Zn-MOFs on tetracycline (TC)

[0117] Before testing the degradation performance of TC by CS@Zn-MOFs, 50 g of commercially available TC (≥96%, Aladdin) was dissolved in 10 mL of deionized water. The preparation process required protection from light to obtain a TC stock solution (5 mg / mL). 0.26 mL of this TC stock solution was diluted in 9.74 mL of deionized water to obtain a TC test solution (130 μg / mL). Three aliquots of this test solution were prepared (labeled 1, 2, and 3). Nano-ZnO (2.0 mg), CS@Zn-MOFs (0.4 mL, 5 mg / mL), and CS@Zn-MOFs (0.4 mL, 5 mg / mL) were added to the three aliquots, respectively. The third aliquot was tested under a simulated sunlight LED lamp (585–620 nm, 75 mW / cm²). 2 Irradiation was performed using CS@Zn-MOFs + LED. The absorbance was measured using a UV-Vis spectrophotometer at 0 min, 20 min, 40 min, 60 min, 90 min, and 120 min.

[0118] 3. Degradation performance test of CS@Zn-MOFs on erythromycin (ETM)

[0119] Before testing the degradation performance of ETM by CS@Zn-MOFs, 60 mg of commercially available ETM (potency ≥850 μg / mg, Aladdin) was dissolved in 10 mL of deionized water. The preparation process required protection from light to obtain a TC stock solution (6 mg / mL). 0.25 mL of this TC stock solution was diluted in 9.75 mL of deionized water to obtain a TC test solution (150 μg / mL). Three aliquots of this test solution were prepared (denoted as 1, 2, and 3). Nano-ZnO (2.0 mg), CS@Zn-MOFs (0.4 mL, 5 mg / mL), and CS@Zn-MOFs (0.4 mL, 5 mg / mL) were added to the three test solutions, respectively. The third test solution was exposed to simulated sunlight using an LED lamp (585–620 nm, 75 mW / cm²). 2 Irradiation (denoted as CS@Zn-MOFs + LED) was performed. The degradation efficiency of ETM by nano-ZnO (2.0 mg), CS@Zn-MOFs (0.4 mL, 5 mg / mL), and CS@Zn-MOFs + LED (0.4 mL, 5 mg / mL) was determined by erythromycin enzyme-linked immunosorbent assay (ELISA) kit at 0, 0.5 h, 1 h, 1.5 h, and 2 h.

[0120] Stability testing was conducted using a laser pointer to perform Tyndall effect tests on the CS@Zn-MOFs samples or the mixture of the sample and antibiotic before, during, and after the degradation of TC for 2 hours.

[0121] 5. Evaluation of the recyclability performance of CS@Zn-MOFs

[0122] To investigate the reusability of CS@Zn-MOFs materials, the CS@Zn-MOFs + LED material group was recycled and cleaned using an ultrafiltration tube. Under the same conditions, its catalytic degradation efficiency for tetracycline (TC) and erythromycin (ETM) was re-evaluated, with four recycling cycles and five repeatability tests. The reusability of the material was comprehensively evaluated by calculating the recovery rate of CS@Zn-MOFs and its degradation efficiency for TC and ETM after 2 hours.

[0123] Conclusion 9: Figure 11 The results show that the CS@Zn-MOFs composite material prepared in Example 1 has redox properties, especially exhibiting superior redox properties under light conditions, and has advantages in antibiotic degradation.

[0124] Conclusion 10: Figure 12 , Figure 13 , Figure 14 , Figure 15The results showed that the CS@Zn-MOFs composite material had good degradation effects on both TC and EMT, with degradation efficiencies exceeding 85% after 2 hours.

[0125] Conclusion 11: Figure 16 The results showed that the CS@Zn-MOFs recovered before the degradation reaction, during the degradation of antibiotics, and during the first recovery after the degradation reaction all exhibited a significant Tyndall effect, indicating that the CS@Zn-MOFs composite material has good colloidal stability.

[0126] Conclusion 12: Table 2 shows that after TC and EMT treatment, the recovery rates of the two groups of CS@Zn-MOFs composite materials were all greater than 80% in three trials, indicating high recovery efficiency.

[0127] Table 2 Recovery rate (%) of CS@Zn-MOFs

[0128]

[0129] Conclusion 13: Figure 17 and Figure 18 The results showed that the degradation efficiency of CS@Zn-MOFs composite material after four recycling cycles was greater than 80% for TC and EMT, and the degradation performance decreased by no more than 15% after five cycles, indicating that it has good reusability.

[0130] Comparative Example 1: Study on the binding and degradation effects of Zn-MOFs synthesized from dimethylimidazole and zinc acetate with CS.

[0131] Based on Example 1, imidazole was replaced with the same molar amount of dimethylimidazolium to investigate the binding performance of Zn-MOFs synthesized by this method with CS.

[0132] (a) Preparation of Zn-MOFs:

[0133] 2.2 g of zinc acetate dihydrate was dissolved in 100 mL of deionized water and sonicated to prepare a 0.1 mol / L solution. 3.3 g of dimethylimidazole was dissolved in 100 mL of anhydrous ethanol and sonicated to prepare a 0.4 mol / L solution. The zinc acetate aqueous solution was slowly added dropwise to the dimethylimidazole ethanol solution at room temperature (25℃) and with mechanical stirring at 600 rpm. After the addition was complete, the reaction was continued for 5 hours. After the reaction was complete, 10 mL of the reaction solution was retained. The remaining suspension was centrifuged (10000 g, 10 min), washed three times with deionized water, and then dried in a vacuum oven at 60℃ for 15 hours to obtain a white Zn-MOFs solid powder.

[0134] (b) Preparation of CS@Zn-MOFs composite materials:

[0135] Prepare a 0.5% (w / v) chitosan solution: Weigh 0.05 g of chitosan powder and dissolve it in 10 mL of 0.5% (v / v) acetic acid aqueous solution, stirring magnetically until completely dissolved. Weigh 0.1 g of the Zn-MOFs powder prepared in step (a) and dissolve it in 1 mL of deionized water to obtain a Zn-MOFs dispersion. Adjust the pH of the Zn-MOFs dispersion to 6.5 with 1 mol / L NaOH solution, and then add it to the above 10 mL chitosan solution. Stir at 600 rpm for 1 hour at room temperature. Subsequently, slowly adjust the pH of the above mixture to 6.5 with 1 mol / L NaOH solution, and observe that the system gradually becomes gel-like. Collect the gel product by centrifugation, wash it three times with deionized water, then freeze it in an ultra-low temperature freezer at -80℃ for 12 hours, and then transfer it to a freeze dryer for lyophilization to finally obtain CS@Zn-MOFs composite material solid powder.

[0136] The encapsulation efficiency of chitosan by the CS@Zn-MOFs composite solid powders prepared in Example 1 and Comparative Example 1 was determined, and the test was conducted under the aforementioned conditions using an LED lamp (585–620 nm, 75 mW / cm²). 2 The degradation effect of chitosan on tetracycline (TC) and erythromycin (ETM) within 2 hours of irradiation is expressed as residual rate (%). The chitosan encapsulation efficiency is as follows: Figure 21 As shown, the residual rates of TC and ETM are respectively as follows: Figure 22 and Figure 23 As shown.

[0137] Note: The binding ability of Zn-MOFs prepared in Comparative Example 1 to chitosan was lower than that in Example 1, indicating that the effect of dimethylimidazole in synthesizing composite nanomaterials is not as good as that of imidazole. After treatment with CS@Zn-MOFs synthesized by imidazole and dimethylimidazole, respectively, for 2 h, the residual rate of tetracycline and erythromycin using the imidazole synthesis method was lower.

[0138] Comparative Example 2: Effect of different chitosan concentrations on CS@Zn-MOFs materials

[0139] Based on Example 1, the effect of different chitosan concentrations on CS@Zn-MOFs materials was investigated. Zn-MOFs dispersions of the same concentration as in Example 1 were coated with chitosan (CS) solutions of 0.5%, 1%, and 1.5% (w / v), respectively, and the encapsulation efficiency (%) was measured. Specifically, as shown below... Figure 24 As shown.

[0140] Note: When the chitosan mass volume concentration is 0.5%, its encapsulation efficiency reaches 92%, while the encapsulation efficiency is less than 90% when the chitosan mass volume concentration is 1% and 1.5%. From the perspective of saving materials, 0.5% is the best choice.

[0141] Comparative Example 3: Study on the Influence of Different Zinc Salt Types on CS@Zn-MOFs Materials

[0142] Based on Example 1, zinc acetate dihydrate was replaced with the same amount of zinc nitrate. CS@Zn-MOFs materials were synthesized using an aqueous solution of zinc nitrate. The degradation effects of these materials on tetracycline (TC) and erythromycin (ETM) under LED irradiation were investigated under the aforementioned test conditions. Specifically, as follows... Figure 25 As shown.

[0143] Note: The degradation effect of Comparative Example 3 was significantly worse than that of Example 1, indicating that the effect of zinc nitrate preparation was not as good as that of zinc acetate. The reason for this is that the introduction of acetate ions generates many MOFs in the form of stacked sheets, which achieves good spatial isolation and increases the space for attachment and adsorption.

[0144] Comparative Example 4: Study on the Influence of Different Feeding Sequences on CS@Zn-MOFs Materials

[0145] A one-pot method was used. 2.2 g of zinc acetate dihydrate was dissolved in 100 mL of deionized water and sonicated to prepare a 0.1 mol / L solution. 2.7 g of imidazole was weighed and dissolved in 100 mL of anhydrous ethanol and sonicated to prepare a 0.4 mol / L solution. The zinc acetate aqueous solution was slowly added dropwise to the imidazole ethanol solution under mechanical stirring at 600 rpm at room temperature (25℃). Then, 10 mL of 0.5% (w / v) chitosan was added dropwise. The reaction was allowed to proceed for 5 h, followed by centrifugation (10000 g, 10 min), washing three times with deionized water, and drying in a vacuum oven at 60℃ for 15 hours to obtain a white solid powder. The degradation effects on tetracycline (TC) and erythromycin (ETM) under LED irradiation were investigated under the aforementioned test conditions, as detailed below. Figure 26 As shown.

[0146] Overall conclusion:

[0147] The comparison of experimental data from the above embodiments and comparative examples fully demonstrates the effectiveness of the CS@Zn-MOFs composite material provided by this invention:

[0148] 1. It exhibits remarkable photocatalytic degradation performance, showing high adsorption capacity and fast adsorption rate for tetracycline and erythromycin.

[0149] 2. The inherent defect of poor stability of MOF materials is effectively solved by chitosan coating. The structure is stable in acidic environment, not easy to be etched, and excellent recycling performance is achieved, thus reducing the cost of use.

[0150] 3. The preparation process of this invention is simple, the conditions are mild, and the raw materials used are environmentally friendly and low in toxicity, which has the potential for large-scale industrial application.

[0151] The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. The application of a metal-organic framework composite material modified with a natural polymer in the preparation of wastewater treatment agents, characterized in that, The wastewater treatment agent is used to adsorb and degrade antibiotics, wherein the antibiotic is at least one of tetracycline and erythromycin; The preparation method of the metal-organic framework composite material modified by the natural polymer material includes the following steps: first, zinc acetate is reacted with imidazole to obtain Zn-MOFs, the pH is adjusted to 6.0-7.0, then an aqueous solution of the natural polymer material is added to react and form a gel dispersion, followed by solid-liquid separation and drying to obtain the final product. The natural polymer material is selected from at least one of chitosan and polydopamine.

2. The application according to claim 1, characterized in that, The mass fraction of natural polymer materials in the metal-organic framework composite material is 0.5-1.0%; and / or the pH is adjusted to 6.0-7.0 after the reaction of the aqueous solution containing natural polymer materials is completed; and / or the zeta potential of the metal-organic framework composite material is positive in the pH range of 6.0-7.

0.

3. The application according to claim 1, characterized in that, The zinc acetate reacts with imidazole in an alcohol-water system.

4. The application according to claim 3, characterized in that, First, dissolve the zinc acetate in water and the imidazole in ethanol, and then proceed with the reaction.

5. The application according to claim 4, characterized in that, The concentration of zinc acetate dissolved in water is 0.1-0.2 mol / L, and the concentration of imidazole dissolved in ethanol is 0.4-0.5 mol / L.

6. The application according to claim 1, characterized in that, The mass ratio of zinc acetate to imidazole is 0.7-1.4:1; and / or the reaction temperature of zinc acetate and imidazole is 20-25℃, and the reaction time is 3-5 h; and / or the concentration of natural polymer in the aqueous solution of the natural polymer is 0.5-1 g / 100 mL, and the aqueous solution of the natural polymer contains acetic acid with a volume concentration of 0.5-1.0%; and / or the volume ratio of Zn-MOFs to the aqueous solution of the natural polymer is 1-2 g:100 mL.

7. The application according to claim 1, characterized in that, After the reaction between zinc acetate and imidazole is completed, solid-liquid separation is performed, followed by drying to obtain Zn-MOFs, which are then added to water to adjust the pH to 6.0-7.0.

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