MOF-on-MOF loaded nanocomposite polyether sulfone self-cleaning membrane, and preparation method and application thereof

Abstract

The application relates to a kind of MOF-on-MOF load nano composite polyether sulfone self-cleaning membrane and its preparation method and application.The preparation method comprises the following steps: zirconium tetrachloride, 2-amino terephthalic acid, formic acid and solvent are mixed, and MOF nanoparticles are prepared by hydrothermal method;Tetrabutyl titanate, 2-amino terephthalic acid, methanol and solvent are mixed to prepare precursor solution;MOF nanoparticles are added to the precursor solution, and MOF-on-MOF particles are prepared by secondary hydrothermal method;MOF-on-MOF nanoparticles are placed in the thin layer function layer of polyether sulfone membrane by interfacial polymerization, and the nano composite polyether sulfone self-cleaning membrane is prepared.Compared with the prior art, the MOF-on-MOF modified PES membrane prepared by the application not only has high flux and high retention, but also has good self-cleaning performance, stability and anti-pollution performance.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a self-cleaning nanocomposite polyethersulfone membrane supported on MOF-on-MOF, its preparation method, and its application. Background Technology

[0002] Membrane technology, with its unique membrane materials and separation principles, can selectively separate pollutants in water, thereby retaining, to a certain extent, pollutants such as antibiotics, pesticides, and toxic metals, reducing their diffusion in the aquatic environment. Nanofiltration membranes are pressure-driven separation membranes, with separation precision between ultrafiltration and reverse osmosis membranes. Their molecular weight cutoff range is generally 200 Da to 1000 Da. They have excellent retention capabilities for divalent and multivalent ions, but their retention effect on monovalent ions is relatively weak. They have already achieved large-scale application in many fields such as water softening, industrial wastewater treatment, material concentration and separation, food processing, pharmaceutical refining, and seawater desalination pretreatment.

[0003] Currently, mainstream nanofiltration membrane preparation processes include interfacial polymerization, phase inversion, layer-by-layer self-assembly, chemical crosslinking, and surface grafting modification. Among these, interfacial polymerization is the most industrially mature and widely used. This process typically uses porous ultrafiltration substrates such as polyethersulfone (PES), polysulfone (PSf), or polyacrylonitrile (PAN) as the supporting membrane. Aqueous polyamines (monomers such as piperazine) and organic polyacrylamide chlorides (monomers such as trimesoyl chloride) undergo a polymerization reaction at the interface between the two phases, generating an ultrathin polyamide functional separation layer on the surface of the supporting membrane. Nanofiltration membranes prepared by this process exhibit excellent water permeability and easily controllable separation and retention performance.

[0004] Existing commercially available and laboratory-prepared nanofiltration membranes still suffer from several technical shortcomings in practical applications: First, membrane materials generally exhibit a trade-off between flux and retention performance, making it difficult to simultaneously achieve high water permeability while maintaining high retention rates. Second, membrane elements are susceptible to fouling by organic matter, colloids, and microorganisms in the water during long-term operation, leading to a continuous decline in membrane flux, increased system operating pressure, increased membrane cleaning frequency and maintenance costs, and a shortened service life of the membrane elements. To address these shortcomings, existing improvement schemes often employ inorganic nanofillers such as doping with graphene oxide, carbon nanotubes, and metal-organic frameworks (MOFs) or chemical modification of the membrane surface to optimize overall membrane performance. However, these modification methods generally suffer from cumbersome preparation processes and poor stability. Therefore, developing a modified nanofiltration membrane that balances high water flux, high separation selectivity, and excellent antifouling capabilities has practical engineering application value.

[0005] Metal-organic frameworks (MOFs) possess characteristics such as high specific surface area, tunable pore structure, and abundant surface active sites, demonstrating promising application potential in the photocatalytic degradation of pollutants. These materials exhibit excellent structural designability; by selecting different metal nodes and organic ligands, the chemical composition and physicochemical functions of the materials can be precisely controlled, achieving a synergistic construction of broad-spectrum light energy capture and highly efficient photocatalytic activity. The orderly pore structure within MOFs can accelerate reactant diffusion and product desorption, while the inherent semiconductor properties of some MOFs can generate photogenerated electron-hole pairs under light excitation, thereby triggering catalytic redox reactions. For example, CN112090297A discloses a composite film based on ultra-small MOFs, which uses a solvothermal method to synthesize ultra-small amino-functionalized MOF nanoparticles and combines them with a PES film through interfacial polymerization technology to prepare a self-assembled composite film based on ultra-small MOFs. However, this composite membrane has the following drawbacks: the catalyst preparation time is too long, requiring aging at room temperature for 30-50 h; it only focuses on the retention performance of macromolecular dyes and does not explore the retention capacity of the interfacial polymer membrane for inorganic salts; the single NH2-UiO-66 has a small visible light response range and does not have the ability to photocatalytically degrade dyes.

[0006] In summary, there is an urgent need to develop a novel composite separation membrane that can simultaneously achieve efficient retention of inorganic salts and in-situ catalytic degradation of organic pollutants. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane, its preparation method, and its application. The polyethersulfone modified composite membrane provided by this invention possesses high water flux permeability, excellent retention performance, superior antifouling ability, and photocatalytic self-cleaning properties.

[0008] The objective of this invention can be achieved through the following technical solutions: This invention first provides a method for preparing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane, the preparation method comprising the following steps: S1: MOF nanoparticles, denoted as NH2-UiO-66, were prepared by mixing zirconium tetrachloride, 2-aminoterephthalic acid, formic acid and solvent and then by hydrothermal method. S2: Tetrabutyl titanate, 2-aminoterephthalic acid, methanol and solvent are mixed to prepare a precursor solution; MOF nanoparticles obtained in S1 are added to the precursor solution, and MOF-on-MOF particles are obtained by a secondary hydrothermal method, denoted as NH2-MIL-125-on-NH2-UiO-66. S3: The MOF-on-MOF nanoparticles obtained in S2 are placed in the thin functional layer of the polyethersulfone membrane by interfacial polymerization to obtain the nanocomposite polyethersulfone self-cleaning membrane.

[0009] Further, in step S1, the mass ratio of zirconium tetrachloride, 2-aminoterephthalic acid, solvent, and formic acid is (0.1~3):(0.1~1):(10~50):(10~50), preferably (0.5~2):(0.3~0.8):(15~25):(15~25).

[0010] Furthermore, in step S1, the temperature of the hydrothermal method is 80~180 ℃, preferably 100-150 ℃.

[0011] Furthermore, in step S1, the hydrothermal method is performed for 12 to 48 hours, preferably 15 to 36 hours.

[0012] Further, in step S2, the mass ratio of tetrabutyl titanate, 2-aminoterephthalic acid, solvent and methanol in the precursor solution is (0.1~3):(0.1~1):(10~50):(10~50), preferably (0.5~2):(0.3~0.8):(15~25):(15~25).

[0013] Further, in step S2, the molar ratio of zirconium in the MOF nanoparticles to titanium in tetrabutyl titanate is 1:(0.5~5). The preparation method of MOF-on-MOF is similar to that of NH2-UiO-66, using a hydrothermal method. Typically, this method differs from the NH2-UiO-66 preparation method in that it uses mixed metal salts with different molar ratios. The molar mass of Ti is determined based on the 3.4284 mmol Zr contained in 1 g of NH2-UiO-66. For example, Ti-3.4284 mmol / Zr-3.4284 mmol, Ti-1.7142 mmol / Zr-3.4284 mmol, and Ti-6.8568 mmol / Zr-3.4284 mmol, thereby preparing the precursor solution of NH2-MIL-125.

[0014] Furthermore, in step S2, the temperature of the secondary hydrothermal method is 80~180 ℃, preferably 100~150 ℃.

[0015] Furthermore, in step S2, the duration of the secondary hydrothermal method is 12-48 hours, preferably 15-36 hours.

[0016] Furthermore, in step S3, the specific steps of interface aggregation are as follows: The polyethersulfone membrane was immersed in a piperazine aqueous solution, and then the excess piperazine aqueous solution on the membrane surface was removed. The polyethersulfone membrane was immersed in a hexane mixture containing MOF-on-MOF particles and 1,3,5-benzenetricarboxyl chloride, and interfacial polymerization occurred on the surface of the polyethersulfone membrane. The polyethersulfone membrane was then heat-treated to obtain a nanocomposite polyethersulfone self-cleaning membrane.

[0017] Furthermore, the mass ratio of the piperazine to 1,3,5-benzenetricarboxyl chloride is (0.1~10):(0.1~10), preferably (0.1~3):(0.1~3).

[0018] Furthermore, the mass ratio of the MOF-on-MOF particles to 1,3,5-benzenetricarboxylic acid chloride is (1~10):20, preferably (1~5):10.

[0019] Furthermore, the interface aggregation time is 0.5-5 min, preferably 1-2 min.

[0020] Furthermore, the temperature of the heat treatment is 50-120 °C.

[0021] Furthermore, the heat treatment time is 2-15 min.

[0022] The present invention also provides a self-cleaning membrane of nanocomposite polyethersulfone loaded with MOF-on-MOF, which is prepared by the above preparation method.

[0023] Furthermore, the nanocomposite polyethersulfone self-cleaning membrane includes a polyethersulfone support membrane and MOF-on-MOF particles loaded on and / or inside the polyethersulfone support membrane.

[0024] This invention also provides the application of a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane in photocatalytic degradation of dyes, antibiotic wastewater treatment, and seawater desalination.

[0025] To address the issues of rapid photogenerated carrier recombination rates and poor cycle stability in single MOF materials, existing technologies have developed MOF-on-MOF composite structures. This structure involves the directional epitaxial growth of one MOF crystal onto the surface of another. Leveraging the lattice matching and coordination bonds between the two MOFs, this composite structure can construct a heterogeneous interface with fewer defects and tighter atomic bonding. This reduces charge trapping losses at the interface and creates low-impedance charge transport pathways, thereby improving photogenerated charge separation efficiency. Furthermore, the band positions, photoresponse ranges, and catalytic properties of the two MOF components can be screened and synergistically configured. For example, one type of MOF can be selected for broad-spectrum solar light absorption, while the other type enables targeted catalytic conversion of pollutants. This cascaded approach completes the entire process of light absorption, carrier separation, and interfacial catalytic reaction, effectively improving pollutant degradation efficiency. Meanwhile, the MOF-on-MOF composite structure fully inherits the advantages of high specific surface area and porous structure of monomeric MOFs, which is conducive to the full exposure of catalytic active sites and efficient mass transfer in the reaction medium, avoiding the drawbacks of increased mass transfer resistance caused by the introduction of non-porous supports in conventional composite schemes. Compared with single-component MOFs and composite systems of MOFs with heterogeneous inorganic / polymer supports, the MOF-on-MOF heterostructure exhibits superior comprehensive performance in suppressing photogenerated charge recombination, optimizing catalytic activity, and improving the cycling stability of materials, making it a preferred technical route for preparing high-performance pollutant photocatalytic materials.

[0026] This invention successfully prepared NH2-MIL-125-on-NH2-UiO-66 particles using a secondary hydrothermal method. The process is simple, controllable, and highly reproducible. MOF-on-MOF particles were prepared through in-situ growth using a secondary hydrothermal process. The two MOF crystals exhibit excellent lattice matching characteristics, achieving atomic-level tight bonding through strong coordination bonds. Compared to conventional single NH2-UiO-66, the MOF-on-MOF particles with added NH2-MIL-125 have abundant and fully exposed active sites, exhibiting both excellent visible light response and photocatalytic activity. They can efficiently degrade organic dyes (methylene blue, Congo red, rhodamine B, methyl orange) in water under visible light conditions. The MOF-on-MOF functional particles, possessing both high stability and high photocatalytic activity, are loaded onto the surface of a polyethersulfone-based membrane via interfacial polymerization. This allows the modified composite membrane to simultaneously exhibit excellent water flux and pollutant retention performance, significantly enhancing the membrane surface hydrophilicity and endowing it with superior antifouling properties and visible light-driven self-cleaning capability. This effectively alleviates problems such as pollutant adhesion and flux decay on the membrane surface, greatly improving the long-term operational stability and overall separation performance of nanofiltration membranes. Therefore, this invention provides a composite membrane based on a MOF-on-MOF structure, which improves permeability, antifouling performance, and self-cleaning performance through the synergistic pore and interface design of the two MOFs.

[0027] Compared with the prior art, the present invention has the following technical advantages: (1) This invention first prepares NH2-UiO-66 particles using a hydrothermal method, and then successfully prepares NH2-MIL-125-on-NH2-UiO-66 with a MOF-on-MOF composite structure using a secondary hydrothermal method, in order to improve the problems of fast photogenerated carrier recombination rate and poor stability during recycling of single MOF materials. The MOF-on-MOF prepared by this invention can achieve efficient photocatalytic degradation of organic dye pollutants under visible light conditions.

[0028] (2) The MOF-on-MOF composite particles prepared in this invention are composited with NH2-MIL-125, which has better visible light response performance, on an NH2-UiO-66 matrix. The two MOFs have similar coordination topologies and lattice constants, which can construct atomically close heterojunction interfaces and reduce interface defect density; by matching their band structures, the photoresponse performance can be effectively optimized. The composite structure has a large specific surface area and excellent pore structure, which can fully expose catalytic active sites, improve carrier migration and electron transport efficiency, effectively suppress photogenerated electron-hole recombination, enhance the redox ability of the system, and make up for the shortcomings of fast carrier recombination and low catalytic efficiency of single MOF. Under visible light irradiation, the MOF-on-MOF composite particles can generate highly oxidizing reactive oxygen free radicals, which can efficiently degrade organic pollutants in water and mineralize them into CO2 and H2O.

[0029] (3) This invention employs an interfacial polymerization process to immobilize MOF-on-MOF nanoparticles onto a polyethersulfone (PES)-based membrane, thereby preparing a modified PES self-cleaning composite membrane loaded with NH2-UiO-66 and NH2-MIL-125 particles. This constructs a multifunctional composite membrane integrating sieving and photocatalytic degradation functions with self-cleaning properties. The modified PES membrane obtained by this invention possesses both high water flux and retention capacity, and its anti-fouling and self-cleaning abilities are significantly improved.

[0030] (4) The MOF-on-MOF modified PES composite membrane prepared by this invention can simultaneously achieve high retention and high water flux, while also possessing good self-cleaning performance, antifouling performance, and structural stability. Performance test results show that the modified membrane can achieve a retention rate of over 95% for antibiotic pollutants, and the retention rate for small molecule inorganic salt sodium sulfate (Na2SO4) is also higher than 95%.

[0031] (5) The preparation process of the MOF-on-MOF modified PES composite membrane of the present invention is simple and easy to implement, with a short production cycle and low production cost. The overall preparation process has excellent stability and does not require additional aging treatment. Compared with traditional membrane modification processes, the interfacial polymerization modification method adopted in the present invention has mild reaction conditions, fast reaction rate, and high film formation efficiency. It does not require complicated and cumbersome post-processing operations, and can achieve precise and controllable construction of membrane functional layer structure. The overall film formation performance is excellent and has good prospects for industrial application. The modified PES composite membrane prepared by the present invention can effectively achieve efficient separation of antibiotics and inorganic salts, and has excellent application potential in the fields of antibiotic industrial wastewater treatment and seawater desalination pretreatment. It provides a new technical solution for the efficient and stable separation of antibiotics and inorganic salt systems. Attached Figure Description

[0032] Figure 1 The graph shows the photocatalytic degradation data of methylene blue for the composite catalysts with different Zr and Ti ratios of NH2-UiO-66, NH2-MIL-125 and NH2-MIL-125-on-NH2-UiO-66 prepared in Example 1 of this invention.

[0033] Figure 2 The image shows the photocatalytic degradation data of NH2-MIL-125 prepared in Example 1 of this invention for four different dyes (methylene blue, rhodamine B, Congo red, and methyl orange).

[0034] Figure 3 The image shows the photocatalytic degradation data of NH2-MIL-125-on-NH2-UiO-66 prepared in Example 1 of this invention for four different dyes (methylene blue, rhodamine B, Congo red, and methyl orange).

[0035] Figure 4 This is a SEM image of NH2-MIL-125-on-NH2-UiO-66 obtained in Example 1 of the present invention.

[0036] Figure 5 The graph shows the antibiotic retention and flux data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4 of the present invention.

[0037] Figure 6 The graph shows the inorganic salt rejection and flux data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4 of the present invention.

[0038] Figure 7 The graph shows the antifouling data of bovine serum albumin for the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-2 of this invention.

[0039] Figure 8This is a graph showing the antifouling flux recovery data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-2 of the present invention.

[0040] Figure 9 The graph shows the contact angle data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4 of the present invention.

[0041] Figure 10 This is a graph showing the photocatalytic self-cleaning and methylene blue retention cycle stability test data of the modified PES membrane in Example 2 of the present invention. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0043] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0044] Example 1: This embodiment provides a method for preparing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane, the specific preparation method is as follows: Particles of S1 and NH2-UiO-66: 5 mmol ZrCl4 and 5 mmol 2-aminoterephthalic acid (NH2-H2BDC) were dissolved in a mixed solution of 55 mL N,N-dimethylformamide and 6.8 mL formic acid. The solution was then transferred to a 100 mL polytetrafluoroethylene (PTFE) liner, which was then transferred to a reaction vessel and tightened. The reaction vessel was then placed in an oven at 120 °C for 24 h. After the solution cooled naturally to room temperature, it was washed three times with DMF and methanol by centrifugation at 8000 rpm for 5 min. The supernatant was discarded, and the precipitate was collected. The washed solid was dried overnight in an oven at 80 °C to obtain a brownish-pink MOF particle solid NH2-UiO-66.

[0045] Preparation of S2 and MOF-on-MOF: 2-Aminoterephthalic acid (9 mmol) was dissolved in a solution of N,N-dimethylformamide and methanol (v / v = 9:1, 20 mL). Tetrabutyl titanate (4 mmol) was then added dropwise to the solution, and the mixture was stirred until well combined. The resulting solution was then poured into a beaker containing 1 g of NH₂-UiO-66, sonicated, and allowed to stand in an oven at 150 °C. Finally, the precipitate was thoroughly washed several times with methanol, and the washed solid was dried in an oven at 80 °C to obtain a brown composite powder, namely NH₂-MIL-125-on-NH₂-UiO-66.

[0046] S3. Preparation of nanocomposite polyethersulfone self-cleaning membrane: A 100 mm diameter PES membrane was placed in a frame membrane holder. In the next step, a 1 wt% piperazine aqueous solution was transferred onto the membrane and allowed to stand for 5 min. After this, excess solution was discarded, and air bubbles were removed using a rubber roller.

[0047] A hexane solution containing 0.01 wt% NH2-MIL-125-on-NH2-UiO-66 and 0.10 wt% 1,3,5-benzenetricarboxylic acid chloride was prepared and sonicated for 5 min to completely dissolve TMC in hexane. This mixed solution was slowly added to the surface of the PES membrane as the organic phase to induce interfacial polymerization. After interfacial polymerization for 1 min, the prepared membrane was transferred to an 80 ℃ oven and heated for 10 min to complete the reaction between TMC and PIP, yielding a modified PES self-cleaning membrane containing NH2-MIL-125-on-NH2-UiO-66, denoted as membrane M1.

[0048] Example 2: This embodiment provides a method for preparing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane. The difference from Example 1 is that, in step S3, the mass concentration of NH2-MIL-125-on-NH2-UiO-66 is 0.03 wt%, while other steps are the same as in Example 1.

[0049] The nanocomposite polyethersulfone self-cleaning membrane prepared in this embodiment is designated as the M2 membrane.

[0050] Example 3: This embodiment provides a method for preparing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane. The difference from Example 1 is that in step S3, the mass concentration of NH2-MIL-125-on-NH2-UiO-66 is 0.05 wt%, while other steps are the same as in Example 1.

[0051] The nanocomposite polyethersulfone self-cleaning membrane prepared in this embodiment is designated as the M3 membrane.

[0052] Example 4: This embodiment provides a method for preparing a MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane. The difference from Example 1 is that in step S3, the mass concentration of the piperazine aqueous solution is 2 wt%, the mass concentration of NH2-MIL-125-on-NH2-UiO-66 is 0.03 wt%, and the other steps are the same as in Example 1.

[0053] The nanocomposite polyethersulfone self-cleaning membrane prepared in this embodiment is designated as M4 membrane.

[0054] Comparative Example 1: This comparative example is used to prepare a polyethersulfone membrane that does not contain MOF-on-MOF particles. The specific preparation method is as follows: S1. Place a 100 mm diameter PES membrane in the frame membrane holder. In the next step, transfer an aqueous solution containing 1 wt% piperazine onto the membrane and let it stand for 5 min. After this, discard the excess solution and remove air bubbles using a rubber roller.

[0055] A 0.10 wt% solution of 1,3,5-benzenetricarboxylic acid chloride / n-hexane was prepared and slowly added to the membrane surface as the organic phase. To completely dissolve TMC in hexane, the solution was sonicated for 5 min. After interfacial polymerization for 1 min, the prepared membrane was transferred to an oven at 80 °C for 10 min to complete the reaction between TMC and PIP, yielding a polyethersulfone membrane without MOF-on-MOF particles, denoted as the M0-1 membrane.

[0056] Comparative Example 2: This comparative example was used to prepare a polyethersulfone membrane without MOF-on-MOF particles. The difference from Comparative Example 1 is that this comparative example used a 2 wt% piperazine aqueous solution; other steps were the same as in Comparative Example 1. A polyethersulfone membrane without MOF-on-MOF particles was obtained, denoted as M0-2 membrane.

[0057] Comparative Example 3: This comparative example was used to prepare a polyethersulfone membrane with a single MOF particle. The difference from Comparative Example 1 is that 0.03 wt% of NH₂-UiO-66 was added when preparing the 0.10 wt% 1,3,5-benzenetricarboxylic acid chloride / n-hexane solution; other steps were the same as in Comparative Example 1. A polyethersulfone membrane containing a single MOF particle was obtained, denoted as M0-3 membrane.

[0058] Comparative Example 4: This comparative example was used to prepare a polyethersulfone membrane with a single MOF particle. The difference from Comparative Example 1 is that 0.03 wt% NH₂-MIL-125 was added when preparing the 0.10 wt% 1,3,5-benzenetriacyl chloride / n-hexane solution; other steps were the same as in Comparative Example 1. A polyethersulfone membrane containing a single MOF particle was obtained, denoted as M0-4 membrane.

[0059] Based on the successful preparation of the modified polyethersulfone self-cleaning membrane and the unmodified polyethersulfone membrane, this invention further investigated the permeation and retention properties of the PES membrane and the modified membrane using pressure membrane separation technology. Under a certain pressure, small-molecule solutes and solvents pass through the membrane with a certain pore size, while large-molecule solutes are retained and do not pass through. Specific tests included the following: (1) The separation performance of the membrane was tested by cross-flow filtration. The membrane was pre-pressurized at 25 °C and 0.5 MPa for 30 min using a filtration device, and then the permeate was collected at fixed time intervals. Finally, the permeate flux J (L·m) was calculated using equation (1). -2 ·h -1 ),as follows: (1); Where V is the volume of infiltrated water, T is the time consumed by the infiltrated water, and A is the effective filtration area (taken as 0.0038m²). 2 P represents the filtration pressure.

[0060] In the antibiotic retention test, the volume of deionized water permeating through the membrane at 0.5 MPa over 1 hour was first measured using a cross-flow device. The pure water flux of the ultrafiltration membrane was then calculated, with the effective area of ​​the ultrafiltration membrane being 0.0038 m². 2 Simultaneously, 500 mL of antibiotic (ciprofloxacin CIP, norfloxacin NOR, tetracycline TC) solution (20 ppm) was permeated using a cross-flow filtration device, and the retention rate of the PES membrane was tested.

[0061] (2) Four inorganic salt solutions (Na2SO4, MgSO4, MgCl2 and NaCl) with a concentration of 1000 ppm were prepared as simulated seawater. The membrane's rejection rate of inorganic salts was tested by measuring the conductivity of the permeate. The rejection rate of the substance was calculated using equation (2): (2); Where R represents the inorganic salt rejection rate (%), C p and C f The values ​​are the salt concentrations (μs / cm) of the permeate and feed solution, respectively.

[0062] (3) In this experiment, bovine serum albumin (BSA) was used as a contaminant to test the antifouling ability of the membrane material. To ensure that the pH value of the BSA solution was constant (pH≥7.4), a PBS buffer was prepared, and then the buffer was used to prepare a 1 g / L BSA solution to evaluate the antifouling performance of the membrane.

[0063] First, pure water was pre-pressurized at 0.5 MPa for 30 minutes, then continuously supplied for 60 minutes (J1), followed by a 60-minute contamination test using BSA (J). p Then, the membrane surface was cleaned for 10 minutes. The water flux (J2) was measured again over 60 minutes. The flux was recorded every 10 minutes during this period.

[0064] The membrane antifouling performance is obtained by Equation 3-6, including flux recovery rate (FRR, %), total fouling ratio (Rt, %), reversible fouling ratio (Rr, %), and irreversible fouling ratio (Rir, %).

[0065] (3); (4); (5); (6); (4) This experiment tested the self-cleaning performance of the membrane surface by measuring the flux recovery of pure water after filtration with methylene blue (MB) aqueous solution. The entire operation process consisted of four steps: (1) Measuring the pure water permeation flux (J) w1 (2) MB filtration and permeation flux measurement (J MB (3) Measure the pure water flux (J) after simple water rinsing. rw (4) Measure the pure water flux (J) again after 30 minutes of visible light irradiation. w2 The flux recovery rate (FRR,%) of the polyethersulfone self-cleaning membrane was calculated using equation (8): (7).

[0066] Figure 1The figures show the photocatalytic degradation data of methylene blue for the composite catalysts with different Zr / Ti ratios, namely NH2-UiO-66, NH2-MIL-125, and NH2-MIL-125-on-NH2-UiO-66, prepared in Example 1 of this invention. As can be seen from the figures, compared to NH2-UiO-66 and NH2-MIL-125 alone, NH2-MIL-125-on-NH2-UiO-66 (Ti / Zr 1:1) showed the best degradation effect on methylene blue, reaching a degradation rate of 96.8% at 105 min. The degradation rates for NH2-MIL-125@UiO-66 (Ti / Zr 2:1) and NH2-MIL-125-on-NH2-UiO-66 (Ti / Zr 1:2) were 79.5% and 63.6%, respectively. This is attributed to the synergistic effect of the bimetallic compounds, where the Ti and Zr ratios are equal, which modulates the electron cloud distribution and optimizes the band structure to enhance visible light response. This avoids the excessively narrow bandgap of pure Ti-based MOFs while retaining a wider visible light absorption capacity than pure Zr-based MOFs. Therefore, the MOF-on-MOF catalyst constructed in this invention exhibits significantly superior photocatalytic degradation performance of methylene blue dye compared to single MOFs, thanks to its efficient charge separation and broad spectral response characteristics.

[0067] Figure 2 The figure shows the photocatalytic degradation data of NH2-MIL-125 prepared in Example 1 of this invention for four different dyes (methylene blue, rhodamine B, Congo red, and methyl orange). As can be seen from the figure, the degradation rates of NH2-MIL-125 for methylene blue, rhodamine B, Congo red, and methyl orange at 105 min were 79.5%, 76.5%, 25.9%, and 26.4%, respectively. This may be attributed to the high polarity of methyl orange, and according to the principle of "like dissolves like" and adsorption rules, the hydrogen bonds and van der Waals forces on the surface of NH2-MIL-125 are relatively weak, resulting in a less effective adsorption of methyl orange compared to methylene blue, which is also a cationic and nonpolar dye. The degradation of rhodamine B may be due to the enhanced visible light response of the amino functional groups of NH2-MIL-125. Congo red is an anionic dye. NH2-MIL-125 has limitations in adsorbing anionic dyes because its surface lacks strong polar groups that can form electrostatic attraction or hydrogen bonds with the anions of Congo red.

[0068] Figure 3This figure shows the photocatalytic degradation data of four different dyes (methylene blue, rhodamine B, Congo red, and methyl orange) using NH2-MIL-125-on-NH2-UiO-66 prepared in Example 1 of this invention. As can be seen from the figure, after 105 min of photocatalysis, the degradation rates of methylene blue, rhodamine B, Congo red, and methyl orange reached 96.8%, 79.3%, 82.9%, and 39.5%, respectively. Compared to the NH2-MIL-125 photocatalyst alone, the dark adsorption of NH2-MIL-125-on-NH2-UiO-66 decreased more significantly. The stronger dark adsorption degradation ability compared to the single NH2-MIL-125 photocatalyst is due to the significant selectivity of NH2-UiO-66 for anionic dyes.

[0069] Figure 4 The image shows a SEM image of NH2-MIL-125-on-NH2-UiO-66 prepared in Example 1. As can be seen from the image, NH2-MIL-125-on-NH2-UiO-66 are regular and uniform octahedral particles with a size of approximately 500-800 nm.

[0070] Figure 5 The figures show the antibiotic rejection and flux data for the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4. As can be seen from the figures, compared to the unmodified PES membrane and the single MOF-modified control membrane, the MOF-on-MOF modified PES membrane prepared in this invention can significantly improve the permeate flux while maintaining excellent rejection performance, achieving simultaneous optimization of rejection performance and water flux, resulting in superior overall separation performance. Specifically, the optimal membrane M2, while maintaining high rejection, increased its pure water flux from 13.84 L·m⁻¹ compared to the pure membrane M0-1. -2 ·h -1 ·bar -1 Increased to 23.76 L·m for modified membrane M2. -2 ·h -1 ·bar -1 The flux increased by as much as 41.75%, as detailed in Table 1. Therefore, this invention significantly improved the water flux of the PES membrane while maintaining the antibiotic solution separation ability through MOF-on-MOF nanoparticle modification. This modified PES membrane has good application prospects in the treatment of antibiotic-containing wastewater. The increase in PES membrane permeability may be due to the synergistic effect of the following two factors: (1) the additive nanoparticles endow the membrane with hydrophilicity, thereby increasing the rate at which water passes through the membrane; (2) compared with the PES matrix membrane, the pore size and porosity of the additive membrane are enlarged, which is beneficial to permeability. Therefore, the modification scheme of this invention significantly improves the hydrophilicity and degradation ability of the membrane, providing certain reference value for the development of new membranes.

[0071] Figure 6The figures show the inorganic salt rejection data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4. As can be seen from the figures, compared to the unmodified PES membrane and the single MOF-modified control membrane, the MOF-on-MOF-modified PES membrane prepared in this invention significantly improves the permeate flux while maintaining excellent rejection performance, achieving simultaneous optimization of rejection performance and salt flux, resulting in superior overall separation performance. Detailed data are shown in Table 1. Therefore, this invention significantly improves the water flux of the PES membrane while maintaining its inorganic salt solution separation ability through MOF-on-MOF nanoparticle modification. This modified PES membrane has good application prospects in seawater desalination.

[0072] Table 1. Antibiotic, inorganic salt rejection, and water flux data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4. Figure 7 The figures show the antifouling data of bovine serum albumin (BSA) on the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-2. As can be seen from the figures, the modified PES membrane exhibits good antifouling performance; after BSA contamination, the optimal membrane M2 flux can still recover to 95.6%. Therefore, this modification significantly improves the antifouling ability of the PES membrane.

[0073] Figure 8 The figures show the antifouling flux recovery data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-2. As can be seen from the figures, the flux recovery rate of the modified PES membrane after three cycles of bovine serum albumin-water alternating circulation can reach over 90%, while the rejection rate remains above 95%.

[0074] Figure 9The figures show the contact angle data of the modified PES membranes in Examples 1-4 and the control membranes in Examples 1-4 of this invention. As can be seen from the figures, the contact angles of M1, M2, M3, and M4 are 19.94°, 13.07°, 20.97°, and 23.47°, respectively, while the contact angles of the control membranes M0-1, M0-2, M0-3, and M0-4 are 31.65°, 40.30°, 23.58°, and 23.11°, respectively. The introduction of MOF-on-MOF particles can enhance the surface hydrophilicity of the membrane, but its effect is affected by the concentration and dispersion uniformity. An appropriate concentration of NH2-MIL-125-on-NH2-UiO-66 particles not only ensures high hydrophilicity of the membrane surface but also reduces water molecule transport resistance by forming a uniform nanochannel network, providing a foundation for improving membrane flux. This is attributed to the fact that the amino (-NH2) and hydroxyl (-OH) functional groups on the surface of NH2-MIL-125-on-NH2-UiO-66 particles can partially embed into the polyamide network during interfacial polymerization and form hydrogen bonds with water molecules, thereby increasing the hydrophilicity of the membrane surface.

[0075] Figure 10 The figures show the photocatalytic self-cleaning and methylene blue retention cycle stability test data of the modified PES membrane in Example 2 of this invention. As can be seen from the figures, the antifouling stability and photocatalytic self-cleaning ability of the M2 membrane were evaluated through seven consecutive cycles of methylene blue retention experiments, followed by visible light irradiation (retention test-irradiation-flux test-retention test). As the number of cycles increased from 1 to 7, the pure water flux decreased significantly, from the initial 413.10 L·m⁻¹. -2 ·h -1 Reduced to 296.34 L·m -2 ·h -1 The low flux indicates that the membrane may be affected by fouling accumulation or pore blockage, leading to flux reduction. In contrast, although the dye rejection rate decreased slightly, it remained at a high level, indicating that the membrane's dye rejection was relatively stable and that the accumulation of pollutants had little impact on the rejection effect. This is mainly due to the membrane's photocatalytic self-cleaning ability.

[0076] In summary, this invention provides a MOF-on-MOF supported thin-film nanocomposite polyethersulfone self-cleaning membrane. First, NH2-MIL-125-on-NH2-UiO-66 composite particles are prepared via a hydrothermal method, and then the MOF-on-MOF nanoparticles are firmly loaded onto the surface of a polyethersulfone-based membrane using an interfacial polymerization process. This invention innovatively introduces MOF-on-MOF particles and combines them with an interfacial polymerization modification strategy, resulting in a composite membrane that balances good water flux and pollutant retention performance while effectively improving the membrane's surface hydrophilicity, thus endowing the membrane with excellent antifouling properties and photocatalytic self-cleaning characteristics. This modified composite membrane has broad application prospects and practical engineering value in the fields of antibiotic wastewater purification and seawater desalination pretreatment.

[0077] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane, characterized in that, The preparation method includes the following steps: S1: MOF nanoparticles, denoted as NH2-UiO-66, were prepared by mixing zirconium tetrachloride, 2-aminoterephthalic acid, formic acid and solvent and then by hydrothermal method. S2: Tetrabutyl titanate, 2-aminoterephthalic acid, formic acid and solvent are mixed to prepare a precursor solution; MOF nanoparticles obtained in S1 are added to the precursor solution, and MOF-on-MOF particles are obtained by a secondary hydrothermal method, denoted as NH2-MIL-125-on-NH2-UiO-66. S3: The MOF-on-MOF nanoparticles obtained in S2 are placed in the thin functional layer of the polyethersulfone membrane by interfacial polymerization to obtain the nanocomposite polyethersulfone self-cleaning membrane.

2. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 1, characterized in that, In step S1, the mass ratio of zirconium tetrachloride, 2-aminoterephthalic acid, solvent, and formic acid is (0.1~3):(0.1~1):(10~50):(10~50). The temperature of the hydrothermal method is 80~180℃; The hydrothermal method takes 12 to 48 hours.

3. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 1, characterized in that, In step S2, the mass ratio of tetrabutyl titanate, 2-aminoterephthalic acid, solvent and methanol in the precursor solution is (0.1~3):(0.1~1):(10~50):(10~50). The molar ratio of zirconium in the MOF nanoparticles to titanium in tetrabutyl titanate is 1:(0.5~5).

4. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 1, characterized in that, In step S2, the temperature of the secondary hydrothermal method is 80~180 ℃; The duration of the secondary hydrothermal method is 12-48 hours.

5. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 1, characterized in that, In step S3, the specific steps of interface aggregation are as follows: The polyethersulfone membrane was immersed in a piperazine aqueous solution, and then the excess piperazine aqueous solution on the membrane surface was removed. The polyethersulfone membrane was immersed in a hexane mixture containing MOF-on-MOF particles and 1,3,5-benzenetricarboxyl chloride, and interfacial polymerization occurred on the surface of the polyethersulfone membrane. The polyethersulfone membrane was then heat-treated to obtain a nanocomposite polyethersulfone self-cleaning membrane.

6. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 5, characterized in that, The mass ratio of piperazine to 1,3,5-benzenetricarboxylic acid chloride is (0.1~10):(0.1~10). The mass ratio of the MOF-on-MOF particles to 1,3,5-benzenetricarboxylic acid chloride is (1~10):

20.

7. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 5, characterized in that, The interface aggregation time is 0.5-5 min.

8. The method for preparing a MOF-on-MOF supported nanocomposite polyethersulfone self-cleaning membrane according to claim 5, characterized in that, The heat treatment temperature is 50-120 ℃; The heat treatment time is 2-15 min.

9. A self-cleaning membrane of nanocomposite polyethersulfone loaded with MOF-on-MOF, characterized in that, Prepared by the preparation method according to any one of claims 1-8; The nanocomposite polyethersulfone self-cleaning membrane includes a polyethersulfone support membrane and MOF-on-MOF particles loaded on the surface and / or inside the polyethersulfone support membrane.

10. The application of the MOF-on-MOF loaded nanocomposite polyethersulfone self-cleaning membrane as described in claim 9 in photocatalytic degradation of dyes, antibiotic wastewater treatment, and seawater desalination.

Images