A PDA@MIL-101 functionalized ultrafiltration membrane and its application in treating high-algae water

Abstract

The present invention discloses a PDA@MIL-101 functionalized ultrafiltration membrane and its application in treating high-algae water, belonging to the field of ultrafiltration membrane and water treatment technology. The present invention uses PDA@MIL-101 nanomaterials and polyethersulfone as raw materials. The PDA@MIL-101 nanomaterials are rich in hydroxyl functional groups, which help to improve the hydrophilicity and electronegativity of the ultrafiltration membrane. The improvement of hydrophilicity is conducive to the formation of a hydration layer on the membrane surface, reducing the pollution layer formed by the contact between pollutants and the membrane. The increase in electronegativity increases the repulsion between pollutants and the membrane surface, thereby improving the anti-pollution ability of the membrane. The pure water flux of the PDA@MIL-101 functionalized ultrafiltration membrane provided by the present invention can reach 440L / (m 2 h), UV 254 The interception rate can reach 45%, and the irreversible pollution after three cycles is 16%.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafiltration membranes and water treatment, and in particular relates to a PDA@MIL-101 functionalized ultrafiltration membrane and application thereof in treating high-algae water. Background Art

[0002] In recent years, with the frequent occurrence of algal blooms in surface water, it has posed a huge challenge to drinking water safety. Suspended pollutants in high-algae water bodies, such as algal cells and their secreted extracellular organic matter, are the main cause of the deterioration of effluent water quality due to their easy solubility, easy dispersion, and complex composition, affecting the operation of conventional water treatment processes. Ultrafiltration has been proven to be an efficient, reliable, and feasible technology for treating high-algae water. Ultrafiltration technology can maintain the integrity of algal cells and avoid the problem of deterioration of effluent water quality due to algal cell fragmentation. However, there are still problems such as low organic matter retention rate and severe membrane fouling. In order to solve the above problems, many scholars have conducted extensive research on pre-membrane pretreatment, such as pre-coagulation and pre-oxidation. However, pretreatment inevitably leads to process complexity, and even excessive addition of reagents can cause algal cell rupture, resulting in deterioration of water quality and aggravated membrane fouling.

[0003] Studies have shown that hydrophilic modification of ultrafiltration membranes can effectively alleviate irreversible fouling of ultrafiltration membranes. Mixed matrix membranes are usually prepared by methods such as hydrophilic polymer blending, hydrophilic monomer grafting, coating, and blending of hydrophilic nanoparticles, including metal oxide nanoparticles, carbon nanomaterials, and metal-organic frameworks. Recently, the application of metal-organic frameworks in the membrane field has become increasingly extensive. Metal-organic frameworks are highly porous nanomaterials formed by the coordination between metal ions and organic ligands. They have great advantages such as large specific surface area, adjustable structure, and easy functionalization. They can effectively improve the hydrophilicity and filtration capacity of ultrafiltration membranes. Wang et al. (“Metal organic framework UiO-66 incorporated ultrafiltration membranes for simultaneous organic matter and heavy metal ion removal”) modified ultrafiltration membranes by blending UIO-66, improving the humic acid removal rate while alleviating membrane fouling of the ultrafiltration membrane. Shaeli et al. ("Long-term stable metal organic framework (MOF)-based mixed matrix membranes for ultrafiltration") significantly improved the membrane's pure water flux and flux recovery rate by adding metal organic frameworks (UiO-66 and UiO-66-NH2) to polyethersulfone and sulfonated polyethersulfone, demonstrating enhanced anti-fouling effects. However, in the field of high-algae water treatment, research on improving organic matter removal efficiency while mitigating irreversible fouling of ultrafiltration membranes is rare.

[0004] Therefore, how to provide an ultrafiltration membrane that can improve the removal efficiency of organic matter in high-algae water while alleviating irreversible membrane fouling has become a technical problem that technicians in this field urgently need to solve. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a PDA@MIL-101 functionalized ultrafiltration membrane and its application in treating high-algae water.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The invention provides a PDA@MIL-101 functionalized ultrafiltration membrane. Raw materials for preparing the PDA@MIL-101 functionalized ultrafiltration membrane include PDA@MIL-101 nanomaterial and polyethersulfone.

[0008] Preferably, the mass ratio of the PDA@MIL-101 nanomaterial to polyethersulfone is (0.1-0.2):16.

[0009] Preferably, the structure of the PDA@MIL-101 functionalized ultrafiltration membrane includes a bottom layer void structure, a middle layer finger-like pore structure and a top layer sponge-like pore structure.

[0010] Preferably, the preparation method of the PDA@MIL-101 nanomaterial comprises: mixing a suspension of MIL-101 and dopamine hydrochloride, then adding Tris-HCl buffer, stirring, centrifuging and drying to obtain the PDA@MIL-101 nanomaterial.

[0011] Preferably, the preparation method of the MIL-101 comprises: mixing a CrCl3·6H2O solution and a terephthalic acid solution, heating the mixture, centrifuging, washing and drying to obtain the MIL-101.

[0012] The present invention provides a method for preparing the PDA@MIL-101 functionalized ultrafiltration membrane described in the above technical solution, using PDA@MIL-101 nanomaterial and polyethersulfone as raw materials, and preparing the PDA@MIL-101 functionalized ultrafiltration membrane through non-solvent-induced phase separation.

[0013] Preferably, the preparation method of the PDA@MIL-101 functionalized ultrafiltration membrane comprises the following steps: adding polyethersulfone to an N-methylpyrrolidone solution of PDA@MIL-101 nanomaterial and polyvinylpyrrolidone, stirring evenly, and degassing to obtain an ultrafiltration membrane casting liquid; coating the ultrafiltration membrane casting liquid on a substrate, then performing scraping, and then immersing the substrate in water to obtain the PDA@MIL-101 functionalized ultrafiltration membrane.

[0014] Preferably, the mass ratio of the polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone is 16:(0.1-0.2):1:(82.8-82.9).

[0015] Preferably, the soaking time is 10 minutes.

[0016] The present invention also provides the use of the PDA@MIL-101 functionalized ultrafiltration membrane described in the above technical solution in treating high-algae water.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] The present invention uses PDA@MIL-101 nanomaterial and polyethersulfone as raw materials. The PDA@MIL-101 nanomaterial is rich in hydroxyl functional groups, which helps to improve the hydrophilicity and electronegativity of the ultrafiltration membrane. The improved hydrophilicity is conducive to the formation of a hydration layer on the membrane surface, reducing the contamination layer formed by the contact between pollutants and the membrane. The improved electronegativity increases the repulsion between the pollutants and the membrane surface, thereby improving the anti-pollution ability of the membrane.

[0019] The pure water flux of the PDA@MIL-101 functionalized ultrafiltration membrane provided by the present invention can reach 440L / (m 2 h), UV 254 The rejection rate can reach 45%, and the irreversible pollution in three cycles is 16%. Compared with the unmodified membrane, the pure water flux is increased by 1.53 times, and UV 254 The rejection rate increased by 17% and the flux recovery rate increased by 15%, providing a solid foundation for the wide application of ultrafiltration membranes in high-algae water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0021] Figure 1 TEM and digital images of MIL-101 (a) and PDA@MIL-101 nanomaterial (b) in Example 1;

[0022] Figure 2 The XPS graphs (a) of the MIL-101 and PDA@MIL-101 nanomaterials in Example 1 and the FTIR spectra (b) of the PDA, MIL-101 and PDA@MIL-101 nanomaterials in Example 1 are shown;

[0023] Figure 3 The SEM images of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 are shown;

[0024] Figure 4 The cross-sectional SEM images of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 at different magnifications are shown;

[0025] Figure 5 FTIR spectra of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2;

[0026] Figure 6 The water contact angles (a) of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 and the zeta potential diagram (b) of the ultrafiltration membranes in Example 1 and Comparative Example 1 are shown;

[0027] Figure 7The pure water flux and UV of the ultrafiltration membrane in Examples 1-3 and Comparative Examples 1-2 are 254 Retention rate graph;

[0028] Figure 8 Diagram of the experimental setup for testing the anti-fouling performance of ultrafiltration membranes;

[0029] Figure 9 The three circulation flow total graphs (a), membrane fouling resistance graph (b), water flux recovery graph after cleaning (c) of the ultrafiltration membrane in Examples 1-3 and Comparative Examples 1-2, and the surface SEM graph (d) of the ultrafiltration membrane before and after fouling in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] An embodiment of the present invention provides a PDA@MIL-101 functionalized ultrafiltration membrane. Raw materials for preparing the PDA@MIL-101 functionalized ultrafiltration membrane include PDA@MIL-101 nanomaterial and polyethersulfone.

[0033] The present invention uses PDA@MIL-101 nanomaterial and polyethersulfone as raw materials. The PDA@MIL-101 nanomaterial is rich in hydroxyl functional groups, which helps to improve the hydrophilicity and electronegativity of the ultrafiltration membrane. The improved hydrophilicity is conducive to the formation of a hydration layer on the membrane surface, reducing the contamination layer formed by the contact between pollutants and the membrane. The improved electronegativity increases the repulsion between the pollutants and the membrane surface, thereby improving the anti-pollution ability of the membrane.

[0034] In a preferred embodiment, the mass ratio of the PDA@MIL-101 nanomaterial to polyethersulfone is (0.1-0.2):16, more preferably (0.1-0.15):16. Controlling the amount of the PDA@MIL-101 nanomaterial within the aforementioned range facilitates obtaining an ultrafiltration membrane with excellent water permeability and anti-fouling capabilities. Excessive use of the PDA@MIL-101 nanomaterial can cause aggregation on the membrane surface, reducing membrane porosity and inhibiting the formation of straight pore structures, thus affecting the membrane's water permeability and anti-fouling capabilities.

[0035] In a preferred embodiment, the structure of the PDA@MIL-101 functionalized ultrafiltration membrane includes a bottom layer void structure, a middle layer finger-like pore structure and a top layer sponge-like pore structure.

[0036] In a preferred embodiment, the preparation method of the PDA@MIL-101 nanomaterial comprises: mixing a suspension of MIL-101 and dopamine hydrochloride, then adding Tris-HCl buffer, stirring, centrifuging and drying to obtain the PDA@MIL-101 nanomaterial.

[0037] In a preferred embodiment, the usage ratio of MIL-101, dopamine hydrochloride and Tris-HCl buffer is 0.1 g:0.1 g:20 mL.

[0038] In a preferred embodiment, the preparation process of the MIL-101 suspension includes: dispersing MIL-101 in a mixture of water and ethanol, and obtaining the MIL-101 suspension by ultrasonication; the amount ratio of MIL-101 to the mixture of water and ethanol is 0.1 g:60 mL; the volume ratio of water to ethanol in the mixture of water and ethanol is 1:1; and the ultrasonication time is 10 min.

[0039] In a preferred embodiment, the concentration of the Tris-HCl buffer is 0.01 mol / L, and the pH is 8.5.

[0040] In a preferred embodiment, the preparation method of the MIL-101 comprises: mixing a CrCl3·6H2O solution and a terephthalic acid solution, heating the mixture, centrifuging, washing and drying to obtain the MIL-101.

[0041] In a preferred embodiment, the solvent of the CrCl3·6H2O solution and the terephthalic acid solution is water; the amount ratio of CrCl3·6H2O to water in the CrCl3·6H2O solution is 2.66g:45mL; the amount ratio of terephthalic acid to water in the terephthalic acid solution is 1.66g:45mL.

[0042] In a preferred embodiment, the volume ratio of the CrCl 3 ·6H 2 O solution to the terephthalic acid solution is 1:1.

[0043] In a preferred embodiment, the heating temperature is 210° C. and the heating time is 12 hours.

[0044] In a preferred embodiment, the cleaning is specifically cleaning with water and ethanol alternately.

[0045] The present invention provides a method for preparing the PDA@MIL-101 functionalized ultrafiltration membrane described in the above technical solution, using PDA@MIL-101 nanomaterial and polyethersulfone as raw materials, and preparing the PDA@MIL-101 functionalized ultrafiltration membrane through non-solvent-induced phase separation.

[0046] In a preferred embodiment, the preparation method of the PDA@MIL-101 functionalized ultrafiltration membrane includes the following steps: adding polyethersulfone to an N-methylpyrrolidone solution of PDA@MIL-101 nanomaterial and polyvinylpyrrolidone, stirring evenly, and degassing to obtain an ultrafiltration membrane casting liquid; coating the ultrafiltration membrane casting liquid on a substrate, then scraping the membrane, and then immersing the substrate in water to obtain the PDA@MIL-101 functionalized ultrafiltration membrane.

[0047] In a preferred embodiment, the mass ratio of the polyethersulfone, PDA@MIL-101 nanomaterial, polyvinyl pyrrolidone and N-methyl pyrrolidone is 16:(0.1-0.2):1:(82.8-82.9).

[0048] In a preferred embodiment, the polyethersulfone is pre-treated by vacuum drying the polyethersulfone powder at 80° C. for 24 hours.

[0049] In a preferred embodiment, the degassing method is static degassing for 12 hours.

[0050] In a preferred embodiment, the substrate is a glass plate; and the scraper used for the scraping film is a 150 μm scraper.

[0051] In a preferred embodiment, the soaking time is 10 minutes.

[0052] The present invention also provides the use of the PDA@MIL-101 functionalized ultrafiltration membrane described in the above technical solution in treating high-algae water.

[0053] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0054] Polyethersulfone (PES) (Mn = 100,000) was purchased from BASF AG, Germany, analytical grade; N-methylpyrrolidone (NMP) was purchased from Shanghai Aladdin Reagent, analytical grade; polyvinylpyrrolidone (PVP) K30 was purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd., analytical grade; dopamine hydrochloride was purchased from Shanghai MacLean Reagent, 98% purity; Tris-HCl buffer was purchased from Xiamen Aimimanni Biotechnology Co., Ltd., analytical grade. CrCl₃·6H₂O was purchased from Shanghai Aladdin Reagent, 98% purity; and terephthalic acid (PTA) was purchased from Shanghai Aladdin Reagent, 99% purity.

[0055] Example 1

[0056] A preparation method of PDA@MIL-101 functionalized ultrafiltration membrane:

[0057] (1) Dissolve 2.66 g of CrCl3·6H2O in 45 mL of deionized water and stir on a magnetic stirrer for 20 min to completely dissolve to obtain a CrCl3·6H2O solution; dissolve 1.66 g of terephthalic acid (PTA) in 45 mL of deionized water and stir on a magnetic stirrer for 20 min to completely dissolve to obtain a PTA solution; mix the above CrCl3·6H2O solution and PTA solution in a volume ratio of 1:1, place them in an oven at 210°C and dry them for 12 h, then cool them to room temperature and centrifuge them. The resulting precipitate is washed alternately with deionized water and ethanol, and then dried in an oven at 80°C overnight. The resulting green powder is MIL-101.

[0058] (2) 0.1 g of the MIL-101 obtained in step (1) was dispersed in 60 mL of a mixture of deionized water and ethanol in a volume ratio of 1:1, and ultrasonicated for 10 min to obtain a suspension of MIL-101; 0.1 g of dopamine hydrochloride was added to the above-mentioned MIL-101 suspension, magnetically stirred for 2 min, and then 20 mL of Tris-HCl buffer (0.01 mol / L, pH = 8.5) was injected. After stirring for 24 h, the mixture was centrifuged and vacuum dried to obtain PDA@MIL-101 nanomaterial.

[0059] (3) The polyethersulfone (PES) powder was vacuum-dried at 80°C for 24 hours to obtain dry PES; polyvinylpyrrolidone (PVP) and the PDA@MIL-101 obtained in step (2) were dissolved in N-methylpyrrolidone, and after ultrasonication for 30 minutes, the above-mentioned dry PES was added, magnetic stirring was performed for 12 hours, and the mixture was allowed to stand for 12 hours for degassing to obtain an ultrafiltration membrane casting solution; the above-mentioned ultrafiltration membrane casting solution was coated on a clean glass plate, and then the film was scraped on the clean glass plate with a 150 μm scraping knife, and then it was placed in deionized water and soaked for 10 minutes to remove excess reagents in the membrane, thereby obtaining a PDA@MIL-101 functionalized ultrafiltration membrane; wherein the mass ratio of polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone was 16:0.1:1:82.9.

[0060] Example 2

[0061] The difference from Example 1 is that in step (3), the mass ratio of polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone is 16:0.15:1:82.85.

[0062] Example 3

[0063] The difference from Example 1 is that in step (3), the mass ratio of polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone is 16:0.2:1:82.8.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that in step (3), the mass ratio of polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone is 16:0:1:83.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that in step (3), the mass ratio of polyethersulfone, PDA@MIL-101 nanomaterial, polyvinylpyrrolidone and N-methylpyrrolidone is 16:0.05:1:82.95.

[0068] The components of the ultrafiltration membrane casting solution in Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0069] Table 1 Compositions of ultrafiltration membrane casting solutions in Examples 1-3 and Comparative Examples 1-2

[0070] Membrane number PES (wt%) PVP (wt%) NMP (wt%) PDA@MIL-101 (wt%) Comparative Example 1 M0 16 1 83 -- Comparative Example 2 M1 16 1 82.95 0.05 Example 1 M2 16 1 82.90 0.1 Example 2 M3 16 1 82.85 0.15 Example 3 M4 16 1 82.80 0.2

[0071] The morphology and structure of the MIL-101 and PDA@MIL-101 nanomaterials in Example 1 were characterized by field emission transmission electron microscopy (TEM, Talos-F200X, USA). Figure 1 .

[0072] Figure 1 TEM and digital photos of MIL-101 (a) and PDA@MIL-101 nanomaterial (b) in Example 1. Figure 1 From the TEM image (a), it can be observed that MIL-101 exhibits an octahedral morphology, with a particle size between 200-400 nm, and a smooth lattice plane with sharp corners, which are typical characteristics of MIL-101 crystals. Figure 1 In the TEM image (b), it can be observed that PDA@MIL-101 exhibits a similar octahedral morphology, with little change in particle size, but the lattice plane is slightly rough, and is clearly wrapped in a shell by polydopamine. Figure 1 As can be seen from the digital photo (inset), MIL-101 has a green powdery appearance, which is also the typical color of the metal organic framework MIL-101. The PDA@MIL-101 obtained after polydopamine modification has a brown powdery appearance, indicating that polydopamine has been successfully loaded.

[0073] The elemental composition of the MIL-101 and PDA@MIL-101 nanomaterials in Example 1 was analyzed using an X-ray photoelectron spectrometer (XPS, EscaLabXi+, USA). The functional group composition of the MIL-101 and PDA@MIL-101 nanomaterials in Example 1 was analyzed using a Fourier transform infrared spectrometer (FTIR, BrukerInvenioS, Germany) with a scanning range of 4000–500 cm -1 , the results are shown in Figure 2 .

[0074] Figure 2 The XPS graph (a) of the MIL-101 and PDA@MIL-101 nanomaterials in Example 1 and the FTIR spectra (b) of the PDA, MIL-101 and PDA@MIL-101 nanomaterials in Example 1 are shown. Figure 2 (a) It can be seen that MIL-101 contains Cr, O, and C elements. The presence of N element in the spectrum after dopamine oxidation self-healing further indicates that the PDA coating is successfully coated on MIL-101. The C1s spectrum of MIL-101 shows characteristic peaks at binding energies of 284eV and 288eV, representing CC and OC=O, respectively. The binding energies of 577eV and 587eV show Cr 2p3 / 2 and Cr 2p1 / 2 (Cr 3+ ), and the peak becomes weaker after modification. The O1s spectrum peaks with binding energies of 531.7eV and 533.4eV correspond to the oxygen molecules and HOH of the organic ligands, respectively. Figure 2 (b) It can be seen that the OC=O symmetry leads to the -1 A high-intensity absorption peak appeared at 1622 cm -1 The absorption peaks at 1018 and 748 cm are caused by the vibrational stretching of the carbonyl group of the ligand terephthalic acid. -1 The characteristic peak appears due to the vibration of the benzene ring inside the nanoparticles. -1 The absorption peak at 1265cm is due to the stretching vibration of Cr-O. -1 The weak absorption peak at 3400cm is caused by the vibration of the amide bond. -1 The broad absorption peak is caused by the vibration of the hydroxyl -OH or -NH functional groups in dopamine. The above results show that the modification of nanoparticles is successful.

[0075] The microstructure morphology of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 was analyzed by scanning electron microscopy (SEM, TESCAN MIRALMS, Czech Republic). Figure 3-4 .

[0076] Figure 3 1-3 and Comparative Example 1-2 are SEM images of the ultrafiltration membranes. Figure 3 It can be seen that when a small amount of PDA@MIL-101 nanomaterial is added, such as M1 and M2, the membrane surface shows a smooth and flat morphology; with the further addition of nanomaterials, nanoparticles gradually appear on the surface of M3 and M4 membranes, which further proves the successful addition of nanoparticles. Figure 3 In M2, the nanoparticles are evenly dispersed and the surface is smooth. This is because polydopamine increases the compatibility between the membrane matrix and the nanoparticles. However, when the addition amount exceeds 0.1wt%, the nanoparticles agglomerate on the surface. This is due to the uneven dispersion of nanoparticles in the casting solution and the increased viscosity of the casting solution caused by excessive addition, which leads to nanoparticle agglomeration.

[0077] Figure 4 The cross-sectional SEM images of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 at different magnifications are shown. Figure 4 As can be seen in the figure, all ultrafiltration membranes are composed of three components: a bottom void structure, a middle finger-like pore structure, and a dense sponge-like pore structure at the membrane top. From M0 to M2, with the addition of nanoparticles, the pore structure shifts from an inclined to a straight morphology. The straight pore structure is more conducive to the passage of water molecules, thereby improving the water permeability of the ultrafiltration membrane. From M2 to M4, with the continued addition of nanoparticles, the pore structure continues to shift toward an inclined state, and the voids at the bottom of the ultrafiltration membrane are improved. This enhanced structure can improve the mechanical properties of the ultrafiltration membrane and enhance its practical application. The pore structure of the M0 membrane varies in size, while the modified membrane pores are more uniform. The above improvements in membrane pore structure can be analyzed from both thermodynamic and kinetic perspectives during the phase transition process. When a small amount of PDA@MIL-101 nanomaterial is added, the increased hydrophilicity leads to a thermodynamically dominant effect, accelerating the phase separation process. However, excessive addition increases the viscosity of the casting solution, shifting the phase separation process from kinetically dominated to delayed separation, inhibiting the formation of straight finger-like pores.

[0078] The ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 were analyzed using a Fourier transform infrared spectrometer (FTIR, Bruker InvenioS, Germany) with a scanning range of 4000-500 cm -1 , the results are shown in Figure 5 .

[0079] Figure 5 FTIR spectra of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2. Figure 5 It can be seen that all membranes have the highest peaks at 1244, 1152 and 1105 cm -1The three characteristic peaks at 3400 cm-1 are attributed to the ether bond and sulfone bond of PES, and the peaks show a weakening trend, which may be due to the reduction of the proportion of relevant surface functional groups. -1 The enhanced characteristic peak at the hydroxyl-rich (OH) peak provided by polydopamine. The less pronounced characteristic peak of M4 may be due to nanoparticle agglomeration, resulting in a less pronounced increase in surface functional groups. FTIR spectra demonstrate successful nanoparticle incorporation, and the hydroxyl-rich nanomaterial contributes to increased hydrophilicity and electronegativity of the ultrafiltration membrane.

[0080] The porosity and average pore size of the ultrafiltration membrane were measured by dry and wet weight method. The results are shown in Table 2.

[0081] Wet film (4cm 2 ) was first weighed, and then dried at 100°C for 12 hours to obtain the weight of the dry film. The porosity (ε) was calculated as follows:

[0082]

[0083] Where W1 and W2 are the weights of wet and dry films, respectively, in g; ρ is the density of water, in g / cm 3 ; A is the membrane area, cm 2 ; l is the thickness of the film, cm.

[0084] The calculation formula for the average pore size r of the ultrafiltration membrane is:

[0085]

[0086] Where η is the viscosity of water, pa·s; Q is the volume of permeated water, m 3 / s; ΔP is the working pressure, Pa.

[0087] Table 2 Porosity and average pore size of ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2

[0088] Membrane number Porosity (%) Pore ​​diameter (nm) Comparative Example 1 M0 45 43.87 Comparative Example 2 M1 50 42.96 Example 1 M2 62 42.82 Example 2 M3 55 42.49 Example 3 M4 52 42.84

[0089] As shown in Table 2, with increasing PDA@MIL-101 nanomaterial content, the porosity increased from 45% in the original membrane M0 to 62% in M2. The average pore size of all membranes ranged from 42 to 44 nm. Compared to the original membrane, the average pore size of the modified membranes decreased slightly, which is associated with a faster phase separation process. Table 2 shows that the PDA@MIL-101 nanoparticle blend significantly increased the porosity of the PES ultrafiltration membrane. However, due to the high hydrophilicity of the nanoparticles, excessive addition increased the viscosity of the casting solution, impairing phase separation and thus reducing the porosity. This trend is consistent with the changes in the cross-sectional SEM images.

[0090] The water contact angle of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 was analyzed using a contact angle / surface tension meter (Lauda Scientific LSA100, Germany). The surface Zeta potential of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 was analyzed using a solid surface Zeta potential tester (Anton Paarsurpass, Austria). The results are shown in Table 1. Figure 6 .

[0091] Figure 6 The water contact angle (a) of the ultrafiltration membranes in Examples 1-3 and Comparative Examples 1-2 and the Zeta potential (b) of the ultrafiltration membranes in Example 1 and Comparative Example 1 are shown. Figure 6 As can be seen in (a), the water contact angle of the M0 membrane is 71°. After adding different amounts of PDA@MIL-101 nanomaterials, the membrane contact angle shows a trend of first decreasing and then increasing, among which the M2 membrane has the lowest contact angle of 57.8°. Since the polydopamine-modified MIL-101 has good hydrophilicity, the addition of nanoparticles can improve the hydrophilicity of the membrane surface. The rich hydroxyl functional groups of the composite material are conducive to forming hydrogen bonds with water molecules, thereby forming a hydration layer, reducing the direct contact between the hydrophobic components of high algae water and the membrane, and improving the anti-fouling ability of the ultrafiltration membrane. Due to the characteristics of the composite material, the trend of hydrophilicity change is consistent with the trend of change in the porosity membrane pore structure. From Figure 6 As can be seen in (b), the membrane surface has a negative charge at pH = 7. This is due to the increase in hydroxyl groups in the modified membrane (e.g. Figure 5 ), the hydroxyl functional groups increase the electronegativity of the membrane surface. As the pH increases from 5 to 9, the zeta potential of the original membrane decreases from -19mV to -41mV, while that of the M2 membrane decreases from -20mV to -53mV. Compared to the unmodified membrane, the zeta potential electronegativity of the modified membrane increases by 1.5 times. This is related to the abundant hydroxyl groups provided by polydopamine. The increased electronegativity can better repel negatively charged pollutants, providing better anti-fouling capabilities.

[0092] Pure water flux and UV of ultrafiltration membrane 254 Retention rate test, the results are shown in Figure 7 .

[0093] Pure water flux test: Use Shanghai Mosu ultrafiltration cup for dead-end filtration. First, pre-press the membrane sample at 0.15MPa for 30 minutes. After the test system stabilizes, measure the pure water flux at 0.1MPa. The calculation formula for pure water flux is:

[0094]

[0095] Where JW is the pure water flux, L / (m 2 ·h); V is the volume of the filtrate during the measurement time, L; A is the effective filtration area of ​​the ultrafiltration membrane, m 2; t is the ultrafiltration membrane filtration time, h.

[0096] High algae solution retention rate test: The laboratory cultured Microcystis aeruginosa solution was used as a simulated natural water body, where the concentration of Microcystis aeruginosa was OD 680 =0.100~0.130,UV 254 =0.030~0.035. Use UV-visible spectrophotometer at wavelength 254nm to measure the absorbance of the permeate, and obtain the concentration of the permeate and the original solution through the standard curve; 254 The calculation formula for the retention rate is:

[0097]

[0098] Where R is UV 254 Retention rate, %; Cp is the mass concentration of the original solution, μg / L; Cf is the mass concentration of the permeate, μg / L.

[0099] Figure 7 The pure water flux and UV of the ultrafiltration membrane in Examples 1-3 and Comparative Examples 1-2 are 254 Retention rate graph, in which the bar graph represents pure water flux and the line graph represents UV 254 Retention rate. Figure 7 It can be seen that with the addition of nanoparticles, the water flux of the modified membrane is 254 The retention rate is higher than that of the unmodified membrane. The water flux of M2 reaches 440L / (m 2 ·h), equivalent to the original membrane 287L / (m 2 ·h) is 1.53 times. The water flux of ultrafiltration membrane is often affected by many factors. M2 membrane has a straight pore structure, increased porosity, increased hydrophilicity, etc. In addition, metal organic framework is a porous material. MIL-101 has Pore ​​diameter, much larger than the diameter of water molecules This structure is conducive to the transport of water molecules. The decrease in pure water flux of M3 and M4 can be attributed to the tilted membrane pore structure and reduced hydrophilicity. 254 The rejection rate is only 28%, while the M2 membrane can reach up to 45%. There are a lot of small molecular organic matter in high algae water, which can easily pass through the membrane, resulting in the unmodified PES membrane being sensitive to UV. 254 The size repulsion effect of the extracellular organic matter and the surface of the nanocomposite membrane are both negatively charged. Compared with pure PES membrane, the nanocomposite membrane has a stronger charge repulsion between the extracellular organic matter and the membrane surface. Figure 6 (b), thereby enhancing the repulsion of extracellular organic matter. In addition, the slightly reduced average pore size (Table 2) and increased hydrophilicity ( Figure 6 (a)) is also UV 254 Factors that increase removal rate.

[0100] In order to test the anti-pollution performance of the ultrafiltration membrane, the test was carried out by alternating filtration of deionized water and high algae solution. The experimental device is as follows: Figure 8 As shown, 200 mL of pure water was first filtered at 0.1 MPa, and then the solution was replaced with 300 mL of high algae water solution. The flux change was recorded by an electronic balance; 200 mL of deionized water was then used for in-situ backwashing; the solution was converted to pure water again, and the membrane was filtered alternately for 3 times. The flux recovery rate (FRR) after three cycles of the membrane was calculated. The results are shown in Figure 9 .

[0101]

[0102] R r =R t -R ir ×100%

[0103] Where FRR is the flux recovery rate, R ir is the irreversible pollution in the nth cycle, R t For reversible pollution, R r is the total pollution, J e(n) is the terminal flux at the end of the nth cycle, J s(n+1) is the initial flux of the n+1th cycle, J0 is the initial flux, J s4 is the initial flux of the 4th cycle.

[0104] Figure 9 The three circulation flow total graphs (a), membrane fouling resistance graph (b), water flux recovery graph after cleaning (c) of the ultrafiltration membrane in Examples 1-3 and Comparative Examples 1-2, and the surface SEM graph (d) of the ultrafiltration membrane before and after fouling in Example 1 and Comparative Example 1. Figure 9 (a) is the result of five membrane circulation filtration tests. Due to the interaction between algae cells and their secretions and the membrane surface during the filtration process, the flux of high algae water is lower than that of pure water, and it shows a typical two-stage decline trend. First, the filter cake layer formed rapidly by algae cells causes a rapid decline in flux. Then, extracellular organic matter continues to compress the filter cake layer, causing the flux to decline further. Due to the increased hydrophilicity and electronegativity, such as Figure 9 (c) The water flux recovery rate of the modified membranes is better than that of the unmodified M0 membrane. The flux recovery rate of the M2 membrane reached 84% after three cycles. The flux recovery rate trend also showed a trend of first increasing and then decreasing. The flux recovery rate change trend is consistent with the membrane hydrophilicity trend. The irreversible fouling of the membrane accounts for Figure 9(b) After three cycles, the irreversible pollution of the modified membrane was significantly reduced, with M0 irreversible pollution being 31% and M2 irreversible pollution being 16%, a decrease of 15%. The effective mitigation of the modified membrane is mainly attributed to the increase in membrane hydrophilicity and electronegativity. The hydration layer formed on the membrane surface reduces the pollution layer formed by the contact between the pollutants and the membrane. The negative charge on the membrane surface increases the repulsion between the pollutants and the membrane surface, thereby improving the membrane's anti-pollution ability. Figure 9 As can be seen in (d), uneven and significant contaminant deposition forms on the surface of the M0 membrane after backwashing, while the M2 membrane shows no significant difference. In summary, the modified membranes exhibit improved anti-fouling capabilities in filtering high-algae-containing aqueous solutions. The M2 membrane exhibits the best performance in filtering high-algae-containing water and pure water.

[0105] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. Application of a PDA@MIL-101 functionalized ultrafiltration membrane in treating high algae-rich water, characterized in that: The raw materials for preparing the PDA@MIL-101 functionalized ultrafiltration membrane include PDA@MIL-101 nanomaterial and polyethersulfone; the mass ratio of the PDA@MIL-101 nanomaterial to polyethersulfone is 0.1:16; The structure of the PDA@MIL-101 functionalized ultrafiltration membrane includes a bottom void structure, a middle finger-like pore structure and a top sponge-like pore structure; The preparation method of the PDA@MIL-101 nanomaterial comprises: mixing a suspension of MIL-101 and dopamine hydrochloride, then adding a Tris-HCl buffer, stirring, centrifuging and drying to obtain the PDA@MIL-101 nanomaterial; The preparation method of the MIL-101 comprises: mixing a CrCl3·6H2O solution and a terephthalic acid solution, heating the mixture, centrifuging, washing and drying to obtain the MIL-101.

2. The use of the PDA@MIL-101 functionalized ultrafiltration membrane according to claim 1 in treating high algae water, characterized in that: The preparation method of the PDA@MIL-101 functionalized ultrafiltration membrane comprises the following steps: using PDA@MIL-101 nanomaterial and polyethersulfone as raw materials, and preparing the PDA@MIL-101 functionalized ultrafiltration membrane through non-solvent induced phase separation.

3. The use of the PDA@MIL-101 functionalized ultrafiltration membrane in treating high algae-rich water according to claim 2, characterized in that: The preparation method of the PDA@MIL-101 functionalized ultrafiltration membrane is specifically as follows: polyethersulfone is added to an N-methylpyrrolidone solution of PDA@MIL-101 nanomaterial and polyvinylpyrrolidone, stirred evenly, and degassed to obtain an ultrafiltration membrane casting liquid; the ultrafiltration membrane casting liquid is coated on a substrate, and then scraped, and then the substrate is immersed in water to obtain the PDA@MIL-101 functionalized ultrafiltration membrane.

4. The use of the PDA@MIL-101 functionalized ultrafiltration membrane in treating high-algae water according to claim 3, characterized in that: The mass ratio of the polyethersulfone, PDA@MIL-101 nanomaterial, polyvinyl pyrrolidone and N-methyl pyrrolidone is 16:(0.1-0.2):1:(82.8-82.9).

5. The use of the PDA@MIL-101 functionalized ultrafiltration membrane in treating high-algae water according to claim 3, characterized in that: The soaking time is 10 minutes.

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