Preparation method and application of zirconium-based MOF enzyme-mimic catalytic membrane

Abstract

This invention discloses a method for preparing a zirconium-based MOF enzyme-mimicking catalytic membrane, mainly comprising: using a hydrolyzed polyacrylonitrile ultrafiltration membrane as a base membrane, and pre-modifying the base membrane with a polydopamine coating; loading UiO-66-NH2 with phosphotriesterase-like catalytic function onto the pre-treated hydrolyzed polyacrylonitrile ultrafiltration membrane via pressure-assisted self-assembly, resulting in a UiO-66-NH2 loading of 0.71-1.42 mg / cm³. 2 A zirconium-based MOF enzyme-mimicking catalytic membrane was prepared. Compared with powdered UiO-66-NH2, the catalytic membrane prepared in this invention solves the problems of easy agglomeration and difficult separation of nanocatalysts in heterogeneous reactions, and improves the dispersibility, stability and reusability of the catalyst. The inherent pores of UiO-66-NH2 nanoparticles and the interstitial pores formed by stacking ensure that it has excellent water flux and catalytic effect while maintaining high loading, thus achieving effective removal of MPO.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology, specifically relating to the preparation of a zirconium-based MOF enzyme-mimicking catalytic membrane and its method for removing organophosphorus pesticides from water. Background Technology

[0002] Pesticide residues in the soil enter environmental water bodies through rainwater or surface runoff and accumulate persistently, seriously endangering ecological security and human health. These pesticide residues are harmful to the human nervous system, irreversibly inhibiting the enzyme (acetylcholinesterase, AChE) that hydrolyzes the neurotransmitter acetylcholine in neuronal synapses, thus damaging the structure and function of the brain.

[0003] Enzymatic degradation technology is an effective treatment method for removing micro-pollutants from water. Natural enzymes have superior catalytic efficiency and regional and stereospecificity, which is conducive to the efficient removal of micro-pollutants. However, they have drawbacks such as poor stability, long purification time, and high cost. Enzyme mimics with enzyme-like activity can carry out the catalytic reaction of natural enzymes. They have high stability, are easy to mass-produce, have diverse structures, and good adaptability, making them an ideal substitute for natural enzymes.

[0004] Metal-organic frameworks (MOFs) possess characteristics such as high porosity, large specific surface area, cage-like structure, abundant functional sites, and good stability, making them widely used in adsorption, separation, gas storage, sensing, and catalysis. Among them, zirconium-based MOFs (taking UiO-66-NH2 as an example) have Lewis acid-like active sites similar to phosphotriesterases, enabling them to catalyze the hydrolysis of phosphate ester bonds in nerve agents. They can replace PTEs, and UiO-66-NH2 can effectively overcome the disadvantages of PTEs, such as easy inactivation, high production costs, and difficult storage. Combining separation membranes with MOFs is beneficial for improving removal and recovery performance. Although zirconium-based MOFs can effectively hydrolyze organophosphates, N-ethylmorpholine is required as a buffer solution. The buffer solution eliminates acidic byproducts and deprotonates water molecules to promote the reaction. Due to the limitations of homogeneous buffer solutions, zirconium-based MOFs are difficult to use on a large scale. Therefore, it is necessary to introduce heterogeneous basic polymer buffers. PEI (polyethyleneimine) contains multiple amine groups and aliphatic carbons and is composed of many secondary amines, making it an excellent candidate material for basic isomeric buffers required for MOF catalysis. Summary of the Invention

[0005] To address the aforementioned limitations of existing technologies, this invention provides a method for preparing a zirconium-based MOF enzyme-mimicking catalytic membrane and removing organophosphorus pesticides from water. UiO-66-NH2, possessing phosphotriesterase-like catalytic function, is loaded onto a base membrane using pressure-assisted self-assembly technology. The binding stability between the UiO-66-NH2 catalytic layer and the base membrane is enhanced by pre-modifying the base membrane with a polydopamine coating. This method is the first to apply an enzyme-mimicking catalytic membrane to the removal of organophosphorus pesticides, thus providing a novel strategy for the application of enzyme-mimicking catalytic membranes.

[0006] The UiO-66-NH2 enzyme-mimicking catalytic membrane prepared by this invention effectively solves the problems of high cost, easy inactivation, and strict storage conditions of biological enzymes. Compared with powdered UiO-66-NH2, the catalytic membrane prepared by loading UiO-66-NH2 with phosphotriesterase-like catalytic function onto a base membrane solves the problems of easy agglomeration, difficult separation, and high energy consumption of nanocatalysts in heterogeneous reactions, and improves the dispersibility, stability, and reusability of the catalyst. The inherent pores of UiO-66-NH2 nanoparticles and the interstitial pores formed by stacking ensure that UiO-66-NH2 has excellent water flux and catalytic effect while having high loading capacity, achieving effective removal of MPO (methyl paraoxon).

[0007] To address the aforementioned technical problems, this invention proposes a method for preparing a zirconium-based MOF enzyme-mimicking catalytic membrane, mainly comprising: Step 1, using a hydrolyzed polyacrylonitrile ultrafiltration membrane as the base membrane, and pre-modifying the base membrane with a polydopamine coating; Step 2, loading a zirconium-based MOF (UiO-66-NH2) with phosphotriesterase-like catalytic function onto the pre-treated hydrolyzed polyacrylonitrile ultrafiltration membrane via pressure-assisted self-assembly, resulting in a UiO-66-NH2 loading of 0.71-1.42 mg / cm³. 2 Zirconium-based MOF enzyme-mimicking membrane.

[0008] Furthermore, in the preparation method described in this invention:

[0009] The specific process of step one is as follows: Dissolve an appropriate amount of dopamine hydrochloride and NaIO4 in 50mM Tris-HCl with pH=8.5 to obtain solution A. In solution A, the mass ratio of dopamine hydrochloride to NaIO4 is 4:9, and the concentration of dopamine hydrochloride is 2mg / mL. Fix the hydrolyzed polyacrylonitrile ultrafiltration membrane in a container, and then pour in solution A. Solution A covers the hydrolyzed polyacrylonitrile ultrafiltration membrane. Shake at 37℃ for 20-60 minutes, remove the mixed solution, rinse 3 times with ultrapure water, and store in ultrapure water for later use.

[0010] Preferably, the oscillation time is 30 minutes.

[0011] In step two, the zirconium-based MOF (UiO-66-NH2) is prepared using an amino-containing ligand and a zirconium metal salt via a hot solvent method. The specific process is as follows: First, a certain mass of NH2-BDC (terephthalic acid) and ZrCl4 are dissolved in DMF. Then, formic acid and H2O are added. The molar ratio of NH2-BDC to ZrCl4 is 4:5, the final concentration of NH2-BDC is 16 mmol / L, and the volume ratio of DMF, formic acid, and H2O is 80:2:1. Finally, the reaction is carried out at 100℃ for 12 h, followed by separation and purification to obtain the zirconium-based MOF (UiO-66-NH2) solution.

[0012] The specific process of step two is as follows: The base membrane pre-modified with a polydopamine coating is fixed in an ultrafiltration cup. A certain volume of zirconium-based MOF (UiO-66-NH2) solution is poured into the ultrafiltration cup, wherein the dry mass ratio of UiO-66-NH2 of the zirconium-based MOF to the base membrane area is (0.71~1.42) mg / cm³. 2 At room temperature, the membrane was filtered three times under pressure at 0.1–0.3 MPa and washed with pure water to obtain a zirconium-based MOF enzyme-mimicking membrane, which was then stored in ultrapure water.

[0013] Preferably, the dry mass ratio of zirconium-based MOF (UiO-66-NH2) to substrate film area is 0.71 mg / cm². 2 .

[0014] When the zirconium-based MOF enzyme-mimetic membrane prepared by the method of this invention is used to remove methyl paraoxon, a certain concentration of PEI is added to the solution, and the removal rate of methyl paraoxon is above 80%.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) Metal-organic frameworks can not only remove micro pollutants by adsorption, but also provide various acid and base sites through their high-density metal centers and organic frameworks, thereby efficiently catalyzing the degradation of micro pollutants.

[0017] (2) The enzyme-like catalytic membrane prepared by using phosphoesterase-like UiO-66-NH2 can effectively overcome the disadvantages of PTE such as easy inactivation, high production cost and difficult storage.

[0018] (3) The HPAN membrane was pre-modified by PDA (Polydopamine) coating, which enhanced the bonding stability between the UiO-66-NH2 catalyst layer and the matrix membrane.

[0019] (4) The prepared enzyme-like catalytic membrane can remove more than 95% of MPO and can be reused. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the invention's preparation method and the process of removing methyl parathion from water;

[0021] Figure 2 This is the X-ray diffraction pattern of the UiO-66-NH2 film obtained during the preparation process in Example 1;

[0022] Figure 3 These are surface cross-sectional views of the materials used in the preparation process of Example 1, where (a), (b), and (c) are surface views, and (d), (e), and (f) are cross-sectional views.

[0023] Figure 4 The Fourier transform infrared spectra of the relevant materials and zirconium-based MOF enzyme-mimicking membranes used in the preparation process of Example 1 are shown.

[0024] Figure 5 This is the water contact angle of the membrane prepared in Example 1;

[0025] Figure 6 The MPO removal rate of the membrane prepared in Example 1;

[0026] Figure 7 Example 3 shows the MPO removal rate of the catalytic membrane obtained with different PDA deposition times;

[0027] Figure 8 This refers to the MPO removal rate of the catalytic membranes obtained in Example 4 with different UiO-66-NH2 loadings;

[0028] Figure 9 Example 5 shows the MPO removal rate of MPO solutions with different PEI concentrations;

[0029] Figure 10 The MPO removal rate of the UiO-66-NH2 membrane stored for different times; Detailed Implementation

[0030] The design concept of the zirconium-based MOF (Metal-organic framework) enzyme-mimicking catalytic membrane proposed in this invention is as follows: UiO-66-NH2 with phosphotriesterase-like catalytic function is loaded onto a base membrane using pressure-assisted self-assembly technology; furthermore, the binding stability between the UiO-66-NH2 catalytic layer and the base membrane is enhanced by pre-modifying the base membrane with a PDA (Polydopamine) coating. Compared with powdered UiO-66-NH2, the catalytic membrane prepared by loading UiO-66-NH2 with phosphotriesterase-like catalytic function onto the base membrane solves the problems of easy agglomeration, difficult separation, and difficult energy consumption for recovery of nanocatalysts in heterogeneous reactions, and improves the dispersibility, stability, and reusability of the catalyst. Due to the inherent pores of UiO-66-NH2 nanoparticles and the interstitial pores formed by stacking, it is possible to ensure a high loading of UiO-66-NH2 on the base film while maintaining excellent water flux and catalytic effect. When this catalytic film is used to remove MPO (methyl paraoxon), it has a high removal rate, achieving effective removal of MPO.

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are not intended to limit the present invention in any way.

[0032] Example 1: Preparation and application of a zirconium-based MOF enzyme-mimicking catalytic membrane

[0033] like Figure 1 As shown, it includes the following steps:

[0034] Step 1: The zirconium-based MOF UiO-66-NH2 is prepared using an amino-containing ligand and a zirconium metal salt via a hot solvent method. The specific process is as follows:

[0035] 0.1242 g (0.686 mmol) NH2-BDC and 0.2023 g (0.868 mmol) ZrCl4 were dissolved in 40 mL of DMF, 1 mL of formic acid and 500 μL of H2O were added, and the solution was ultrasonically treated for 20 min to make it homogeneous. The system was reacted at 100 °C for 12 h. The product was separated and purified by washing it three times with DMF and then three times with ultrapure water. The resulting zirconium-containing MOF UiO-66-NH2 powder was ultrasonically dispersed into 500 mL of ultrapure water for later use.

[0036] A certain volume of the above UiO-66-NH2 aqueous solution was taken, centrifuged, and vacuum dried overnight. The mass was weighed to obtain its concentration. The concentration of the zirconium-containing MOF UiO-66-NH2 prepared in Example 1 was 0.4624 mg / mL.

[0037] like Figure 2 As shown, the prepared zirconium-containing MOF (UiO-66-NH2) was characterized by X-ray diffraction. The peak positions of UiO-66-NH2 were basically consistent with those of its standard card, indicating good crystallinity. This proves that the above preparation process successfully synthesized a zirconium-containing MOF (UiO-66-NH2).

[0038] Step 2: Using a hydrolyzed polyacrylonitrile ultrafiltration membrane as the base membrane, pre-modify the base membrane with a polydopamine coating, as follows:

[0039] 2-1) First, the area is 27.2 cm² 2 Commercial PAN ultrafiltration membranes were soaked in 50℃ NaOH (1M) solution for 1 hour, and then washed three times with ultrapure water to obtain hydrolyzed PAN (HPAN) membranes, which were then stored in ultrapure water for later use.

[0040] 2-2) Fix the above HPAN membrane in an ultrafiltration cup with the active side facing up. Quickly pour the mixed solution prepared by dissolving 40 mg of dopamine hydrochloride and 90 mg of NaIO4 in 20 mL of Tris-HCl (50 mM, pH = 8.5) buffer into the ultrafiltration cup. In a constant temperature shaking incubator, shake and soak the HPAN membrane at 37°C for 20 minutes to allow dopamine to deposit on the base membrane. Remove the mixed solution and rinse 3 times with ultrapure water.

[0041] Step 3: Prepare zirconium-based MOF enzyme-mimicking membranes via pressure-assisted self-assembly:

[0042] Take 40 mL of the zirconium-based MOF (UiO-66-NH2) aqueous solution obtained in step one and pour it into the ultrafiltration cup. Filter it three times under pressure at 0.2 MPa to obtain a membrane, which is called a zirconium-based MOF enzyme-mimetic catalytic membrane. Wash it with pure water to remove the loose UiO-66-NH2. Store the obtained membrane in ultrapure water for later use.

[0043] Step 4: Use the zirconium-based MOF enzyme-mimicking membrane obtained above to remove methyl paraoxon from water.

[0044] A 1 mM aqueous solution of methyl parathion (MPO) containing 3 mg / mL PEI was prepared and added to the ultrafiltration vessel. The permeate was collected within 3 hours at room temperature (25°C). The absorbance of the filtrate was measured using a UV-Vis spectrophotometer, and the permeate concentration and removal rate were calculated based on the MPO standard curve. Figure 6 As shown.

[0045] Example 2: Properties of the zirconium-based MOF enzyme-mimicking membrane prepared by the method of the present invention

[0046] 1) Observe the surface and section morphology. Use a scanning electron microscope to observe the surface section morphology of the prepared film and related materials, such as... Figure 3 As shown in the figures, (a), (b), and (c) are surface views, and (d), (e), and (f) are cross-sectional views. The surface morphology of the HPAN membrane in step 2-1) above is smooth and relatively loose, as shown in Figures (a) and (d), while the base film after pre-modification with polydopamine coating forms a more compact surface morphology and dispersed small aggregates, as shown in Figures (b) and (c). This confirms the successful deposition of a PDA layer on the HPAN membrane. After loading UiO-66-NH2, it can be observed that the distribution of UiO-66-NH2 on the membrane surface is relatively uniform and orderly, without obvious visible cracks or defects. As shown in Figures (c) and (f), the UiO-66-NH2 catalyst layer is thick and dense on the base membrane surface, and the loading of UiO-66-NH2 is as high as 0.71 mg / cm³. 2 The film thickness is approximately 10.41 μm.

[0047] 2) Surface chemical characterization. The surface chemical properties of zirconium-containing MOFs UiO-66-NH2 and HPAN, NaIO4 / PDA, and zirconium-based MOF enzyme-mimicking films were characterized using Fourier transform infrared spectroscopy (FT-IR), such as... Figure 4 As shown in the figure. The FT-IR results show that after PDA coating, the original HPAN base film exhibits high optical density at 1455, 2242, and 2934 cm⁻¹. -1 The corresponding CH, C≡N, and -OH functional groups are still retained at approximately 3200–3600 cm⁻¹. -1 A broad peak associated with the -NH- group appeared, confirming that the PDA layer was successfully coated on the HPAN membrane surface. The membrane loaded with UiO-66-NH2 showed Zr-O bonds at 767 cm⁻¹, attributable to metal nodes in the framework. -1 The absorption peaks are located at 1256, 1500, and 1570 cm⁻¹. -1 The presence of stretching vibration peaks at the location is attributed to CN, C=C and CO in aminoterephthalic acid (NH2-BDC), respectively, which proves the existence of the UiO-66-NH2 catalyst layer on the membrane.

[0048] 3) Surface hydrophilicity / hydrophobicity. Surface hydrophilicity / hydrophobicity is one of the key properties of membranes. Hydrophilic membrane surfaces have a strong affinity for water molecules, which is beneficial for improving the water flux of the membrane. Changes in membrane surface hydrophilicity were clarified by testing the water contact angle. Figure 5The results show that after PDA coating modification of the base membrane, the water contact angle decreased from 42° to 27.45°. After loading the UiO-66-NH2 catalyst layer, the surface roughness of the membrane was slightly improved, and the presence of hydrophilic amino groups in the MOF further enhanced the hydrophilicity of the membrane surface, resulting in a water contact angle of 12.5°. This further demonstrates that the abundant hydroxyl and amino functional groups on the PDA surface enhance the hydrophilicity of the membrane surface.

[0049] Example 3: Optimization of deposition time in the preparation method of the present invention

[0050] Six zirconium-based MOF enzyme-mimicking membranes were prepared. The preparation process was basically the same as in Example 1, except that the deposition time in the polydopamine coating pre-modification process in step 2 was 10 min, 20 min, 30 min, 40 min, 50 min, and 60 min, respectively, and finally six zirconium-based MOF enzyme-mimicking membrane samples were obtained.

[0051] Figure 7 Example 3 illustrates the variation in MPO removal rate with different PDA deposition times. In this example, the MPO removal experiment was conducted using the same method as step 4 of Example 1. As the PDA deposition time increased, the catalytic membrane separation performance improved. Considering the influence of deposition time on membrane water flux and MPO removal rate, the deposition time was ultimately determined to be 20–60 minutes, with an MPO removal rate of over 80%. It can be seen that the removal rate was highest at 87.09% when the deposition time was 30 minutes.

[0052] Example 4: Optimization of UiO-66-NH2 loading in the preparation method of the present invention

[0053] A comparative example (UiO-66-NH2 loading of 0) and five zirconium-based MOF enzyme-mimicking membranes were prepared. The preparation process was basically the same as in Example 1, except that the deposition time for the polydopamine coating pre-modification in step 2 was changed from 20 minutes to 30 minutes. In step 3, during the pressure-assisted self-assembly preparation of the zirconium-based MOF enzyme-mimicking membrane, the volume of the zirconium-containing UiO-66-NH2 aqueous solution prepared in step 1 poured into the ultrafiltration vessel was 0 (comparative example) and 0.17 mg / cm³, respectively, based on the ratio of the dry mass of zirconium-containing UiO-66-NH2 to the base membrane area. 2 0.35 mg / cm 2 0.71 mg / cm 2 1.06 mg / cm 2 and 1.42 mg / cm 2 The methyl parathion (MPO) aqueous solution with a concentration of 1 mM and containing 3 mg / mL PEI prepared in Example 1 was placed into the catalytic membranes prepared above with different UiO-66-NH2 loadings. Figure 8The effect of loading on MPO removal was shown. With increasing UiO-66-NH2 loading, the MPO removal rate of the catalytic membrane initially increased and then slightly decreased. Ultimately, the loading was determined to be 0.71–1.42 mg / cm³ in this invention. 2 The MPO removal rate is over 80%, from Figure 8 It can be seen from this that when the UiO-66-NH2 loading is 0.71 mg / cm³, 2 At that time, the MPO removal rate was the highest at 87.09%.

[0054] Example 5: Optimization of PEI concentration in the preparation method of the present invention

[0055] Six aqueous solutions of methyl parathion (MPO) containing different concentrations of PEI were prepared to optimize the PEI concentration. The PEI concentrations were (0, 1 mg / mL, 2 mg / mL, 3 mg / mL, 4 mg / mL, and 5 mg / mL), resulting in six MPO aqueous solutions.

[0056] In this embodiment, the MPO removal experiment was performed using the same method as step 4 of Example 1, wherein the MPO concentration was 1.5 mM. Figure 9 The changes in MPO removal rate with different PEI concentrations are shown. The MPO removal rate reached its highest level of 95.12% when the PEI concentration was 2 mg / mL. Subsequently, the removal rate decreased with further increases in PEI concentration. This may be because the PEI content in the feed solution was too high, and the larger PEI molecules surrounded UiO-66-NH2, which hindered the interaction between the substrate MPO and the active sites of UiO-66-NH2 Zr.

[0057] Example 6: Reusability of the zirconium-based MOF enzyme-mimicking membrane prepared in this invention

[0058] The UiO-66-NH2 composite catalytic membrane was stored in ultrapure water at room temperature, and the results were as follows: Figure 10 As shown, the removal rate remained at 95% during the 10-day test, further demonstrating that the catalyst UiO-66-NH2 was effectively immobilized on the membrane and that the enzyme activity did not decrease over time.

[0059] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. An application of a zirconium-based MOF enzyme-mimicking membrane, wherein the zirconium-based MOF enzyme-mimicking membrane is prepared according to the following steps: First, a hydrolyzed polyacrylonitrile ultrafiltration membrane is used as a base membrane, and the base membrane is pre-modified with a polydopamine coating; then, UiO-66-NH2 with phosphotriesterase-like catalytic function is loaded onto the above-treated hydrolyzed polyacrylonitrile ultrafiltration membrane by pressure-assisted self-assembly, resulting in a UiO-66-NH2 loading of 0.71-1.42 mg / cm³. 2 A zirconium-based MOF enzyme-mimicking membrane; characterized in that, When the zirconium-based MOF enzyme-mimetic membrane was used to remove methyl paraoxon, a certain concentration of PEI was added to the solution, and the removal rate of methyl paraoxon was over 80%.

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