Polymer amination-based ZIF modified TFN film as well as preparation method and application thereof

Abstract

The invention relates to a membrane material, in particular to a modified TFN membrane based on polymer amination ZIF and a preparation method and application of the modified TFN membrane. ZIF amination is realized by taking PEG as a reaction platform, so that the interface bonding force between the ZIF and a polyamide selection layer is enhanced; meanwhile, the agglomeration of the ZIF nanoparticles in the water-phase monomer is inhibited by utilizing the characteristics of the PEG surfactant. The polymer-mediated aminated ZIF can further induce a polyamide layer to form a Tailing structure with periodic nano stripes so as to realize accurate separation of salt and antibiotic molecules.

Description

Technical Field

[0001] This invention relates to a membrane material, specifically to a polymer-modified ZIF-based TFN membrane, its preparation method, and its application. Background Technology

[0002] Antibiotics, as core drugs in clinical treatment, are typically produced through fermentation or chemical synthesis. The products often contain large amounts of inorganic salts (such as sulfates and chlorides), residual culture medium components, and small molecule impurities. These impurities not only affect the purity and stability of antibiotics but may also interfere with subsequent formulation processes or cause adverse reactions in patients. Therefore, desalting is a crucial step in antibiotic purification, aiming to remove impurities, improve product purity, and meet pharmacopoeia standards.

[0003] In recent years, membrane separation technology has gradually become a research hotspot for antibiotic desalination due to its advantages such as simple operation, low energy consumption, and environmental friendliness. Among them, thin-film composite membranes (TFN membranes) have shown significant potential in multiple fields, including water treatment, due to their high selectivity, high throughput, and antifouling properties. However, when the separation target is further focused on the precise sieving of macromolecular solutes (antibiotics) and small molecule solutes (inorganic salts) (such as in the field of antibiotic desalination), the shortcomings of the structure and performance of traditional TFC membranes gradually become apparent. In the traditional interfacial polymerization process, the polymerization rate of aqueous monomers (such as PIP) is uncontrollable due to their high reactivity. The polyamide layer formed in this process has an uneven pore size distribution and is excessively dense, resulting in high retention of both salt ions and antibiotic molecules, making it impossible to achieve selective separation of the two.

[0004] Although introducing MOF nanofillers to construct a loose selective layer can improve salt permeability, poor interfacial compatibility and insufficient dispersibility between the filler and the polymer matrix can easily lead to interfacial defects, ultimately weakening the separation efficiency. While existing technologies involve amino modification before nanoparticle doping of the polymer membrane to improve compatibility, this method is complex and not suitable for industrial applications. Summary of the Invention

[0005] To address the aforementioned issues, this invention utilizes PEG as a reaction platform to achieve ZIF amination, thereby enhancing its interfacial bonding with the polyamide selective layer. Simultaneously, the surfactant properties of PEG are employed to inhibit the aggregation of ZIF nanoparticles in the aqueous monomer phase. Polymer-mediated amination of ZIF can further induce the formation of a Turing structure with periodic nanostripes in the polyamide layer, enabling precise separation of salt and antibiotic molecules.

[0006] Specifically, this invention provides a method for preparing a polymer-aminated ZIF-modified TFN film, which includes the following steps: (1) ZIF-8-NH2 was prepared using a precursor comprising a zinc source, an organic ligand and polyethylene glycol, wherein the organic ligand comprises an aminoimidazole; (2) The base membrane is successively immersed in an aqueous solution containing ZIF-8-NH2 and a polyamine, and an oil solution containing polyacryl chloride to achieve interfacial polymerization and form the polymer-modified ZIF-based TFN membrane.

[0007] In step (1), the zinc source is selected from one of zinc acetate, zinc nitrate, zinc chloride and zinc sulfate.

[0008] In step (1), the organic ligand comprises aminoimidazole and non-aminoimidazole. The aminoimidazole is one or more of 2-aminobenzimidazole, 2-aminoimidazole, 5-amino-1H-benzimidazole, and 2-amino-4-methylimidazole. The non-aminoimidazole is selected from one or more of 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 1-methylimidazole, and 1-ethylimidazole. The mass ratio of the aminoimidazole to the non-aminoimidazole is 1:5 to 5:1.

[0009] In step (1), the mass ratio of zinc source, organic ligand and polyethylene glycol in the precursor is 1:2-10:3-10.

[0010] In step (2), the base film is selected from one of polyimide, polysulfone, polyethersulfone, and polyolefin.

[0011] In step (2), the polyamine is selected from one or more of piperazine, ethylenediamine, and m-phenylenediamine; in the aqueous solution, the concentration of the polyamine is 0.5-5 wt%, and the concentration of ZIF-8-NH2 is 0.05-1 wt%.

[0012] In step (2), the polyacryl chloride is selected from one or more of pyromellitic chloride, terephthalic chloride, isophthalic chloride, and phthaloyl chloride; the concentration of the polyacryl chloride in the oil phase solution is 0.02-0.5wt%.

[0013] In step (2), the base membrane is immersed in the aqueous solution for 0.5-10 min and in the oil solution for 0.1-5 min.

[0014] The present invention also provides a polymer-modified ZIF-based TFN membrane prepared according to the above preparation method, which comprises a base membrane and a polyamide separation layer, wherein the polyamide separation layer contains ZIF-8-NH2.

[0015] The polymer-aminated ZIF-modified TFN membrane prepared by this invention can be used in antibiotic desalting.

[0016] Compared to existing technologies, this invention achieves the synthesis and dispersion of MOFs based on a "polymer-mediated MOFs" strategy. Using PEG as the reaction medium, a mixed ligand strategy is employed to functionalize ZIF-8 with amino groups. The polymer-mediated amino grouping of ZIF significantly improves the dispersion stability of ZIF-8-NH2 in aqueous phase. Simultaneously, the amino groups of ZIF-8-NH2 competitively participate in the interfacial polymerization process, inducing the formation of a periodic nano-stripe Turing structure in the polyamide layer. This structure reduces the selective layer thickness to 160 nm (5 nm at its thinnest point), providing a low-resistance mass transfer pathway for molecular transport. The PA-ZIF-NH2 membrane achieves a pure water flux of 22.8 L·m⁻²·h⁻¹·bar⁻¹, while simultaneously narrowing the membrane pore size distribution (geometric deviation reduced from 1.30 to 1.20). In tests with a mixture of antibiotics and salts, the membrane exhibits a TC / NaCl selectivity of 49.6 and a TC / Na₂SO₄ selectivity of 28.2, while also demonstrating excellent cycling stability. Its performance advantages stem from: (1) the microporous structure (~1.1 nm) in ZIF-8-NH2 provides a mass transfer channel for the precise sieving of antibiotics and salts; (2) the presence of aminated ZIF reduces the surface charge of the membrane and regulates the degree of crosslinking, weakens the electrostatic repulsion effect of ions, and reduces the salt rejection rate; (3) the nano-striped Turing structure increases the mass transfer area. Attached Figure Description

[0018] Figure 1 (a) XRD pattern, (b) UV-vis pattern, (c) FTIR pattern, (d) thermogravimetric pattern, (e) micro-thermogravimetric analysis image, (f) pore size distribution of ZIF-8 and ZIF-8-NH2; Figure 2 1H NMR spectra of ZIF-8 and ZIF-8-NH2; Figure 3 XPS spectral analysis of ZIF-8 and ZIF-8-NH2: (a) full spectrum scan, (b) Zn 2p high resolution spectrum, (c) N 1s peak fitting of ZIF-8, (d) N 1s peak fitting of ZIF-8-NH2. Figure 4 (ab) SEM images and (c) electron paramagnetic resonance spectra of ZIF-8 and ZIF-8-NH2; Figure 5 (a) Particle size distribution of nanoparticles in ZIF-8-NH2 powder and PEG-ZIF-NH2 suspension in aqueous solution; (b) Transmittance curve of ZIF-8-NH2 powder and PEG-ZIF-NH2 suspension over time; (c) Digital photograph of ZIF-8-NH2 powder and PEG-ZIF-NH2 suspension; (d) Zeta potential of ZIF-8 and ZIF-8-NH2. Figure 6 (a) 1H NMR of PIP, (b) PEG, (c) mixture of PIP and PEG, (d) schematic diagram of hydrogen bond interactions between PEG and PIP; Figure 7 The effect of ZIF-8 and ZIF-8-NH2 suspensions on the diffusion rate of PIP; Figure 8 Characterization of the interaction between ZIF-8-NH2 and TMC: (a) Infrared spectra of ZIF-8 and ZIF-8-NH2 after reacting with TMC, (b) full spectrum of XPS spectra of ZIF-8-NH2 before and after reacting with TMC, (c) narrow scan spectrum of Cl element, (d) narrow scan spectrum of N element; Figure 9 Morphology of TFC and TFN membranes formed by different aqueous monomers: (a) PA membrane, (b) PA-ZIF membrane, (c) PA-ZIF-NH2 membrane; Figure 10 (a) FTIR spectra of the membrane before and after the interfacial polymerization reaction; (b) C1s narrow scan spectra of PA, PA-ZIF, and PA-ZIF-NH2 membranes; (c) relative content distribution of each chemical state in the C1s spectrum; (d) O1s narrow scan spectra. Figure 11 Dynamic water contact angle variation curves of PA, PA-ZIF and PA-ZIF-NH2; Figure 12 Pure water permeability of PA, PA-ZIF and PA-ZIF-NH2 membranes; Figure 13 Performance of PA membranes in single solute systems (antibiotics or salts); Figure 14 Performance of PA-ZIF membranes in single solute systems (antibiotics or salts); Figure 15 Performance of PA-ZIF-NH2 membranes in single solute systems (antibiotics or salts); Figure 16 (a) Molecular weight cutoff and (b) pore size distribution of PA, PA-ZIF and PA-ZIF-NH2 membranes; Figure 17 Zeta potential of PA, PA-ZIF and PA-ZIF-NH2 membranes; Figure 18Separation performance and cycling stability of PA-ZIF-NH2 membrane in salt / antibiotic mixed system: (a) Separation performance in TC / Na2SO4 mixed system, (b) Separation performance in TC / NaCl mixed system, (c) Changes in TC and NaCl concentrations during the cycling feed, (d) Changes in TC and Na2SO4 concentrations during the cycling feed. Detailed Implementation Example 1

[0019] Preparation of ZIF-8-NH2 crystals 1 g Zn(OAc)₂, 2.5 g 2-Hmim, 2.5 g 2-aminobenzimidazole, and 6 g PEG 200 were ground in a mortar for 10 minutes. The mixture was then transferred to an oven and heated (80°C, 10 minutes) to form a ZIF suspension (named PEG-ZIF-NH₂). After heating, PEG-ZIF was washed by centrifugation with deionized water and methanol, repeated three times each. After washing, the resulting solid was dried in an oven.

[0020] Preparation of TFN membranes containing ZIF-8-NH2 0.1 g of the above ZIF-8-NH2 suspension (PEG-ZIF-NH2) was weighed and added to 100 mL of 1 wt% PIP aqueous solution. The solution was ultrasonically stirred until uniformly dispersed to form the aqueous phase solution for interfacial polymerization. Simultaneously, a 0.1 wt% TMC / n-hexane solution was prepared as the oil phase solution. TFN membranes containing ZIF-8-NH2 particles were prepared using interfacial polymerization. The specific steps are as follows: First, the polyimide (P84®) base membrane was immersed in the aqueous phase solution for 2 minutes, then the aqueous phase solution was poured out, and the surface of the base membrane was gently wiped dry using a rubber roller. Next, the surface of the base membrane was immersed in the oil phase solution for 1 minute. The resulting membranes were named PA-ZIF, and the effective test area of ​​the membrane was 12.56 cm². 2 .

[0021] Comparative Example 1 The membrane was prepared using the same interfacial polymerization conditions, the difference being that the aqueous solution did not contain nanoparticles, and the prepared membrane was named PA.

[0022] Comparative Example 2 Preparation of ZIF-8 crystals 1 g Zn(OAc)₂, 5 g 2-Hmim, and 6 g PEG 200 were ground in a mortar for 10 minutes. The mixture was then transferred to an oven and heated (80°C, 10 minutes) to form a ZIF suspension (named PEG-ZIF). After heating, PEG-ZIF was washed by centrifugation with deionized water and methanol, repeating each process three times. After washing, the resulting solid was dried in an oven.

[0023] Preparation of TFN membranes containing ZIF-8 0.1 g of the above ZIF-8 (PEG-ZIF) was weighed and added to 100 mL of 1 wt% PIP aqueous solution, and ultrasonically stirred until uniformly dispersed to form the aqueous phase solution for interfacial polymerization. Simultaneously, a 0.1 wt% TMC / n-hexane solution was prepared as the oil phase solution. TFN membranes containing ZIF-8 particles were prepared using the classic interfacial polymerization method. The specific steps are as follows: First, the PI-based membrane was immersed in the aqueous phase solution for 2 minutes, then the aqueous phase solution was poured out, and the surface of the membrane was gently wiped dry using a rubber roller. Next, the surface of the membrane was immersed in the oil phase solution for 1 minute. The resulting membranes were named PA-ZIF.

[0024] Characterization (1) Physical test The crystal structures of ZIF-8 and ZIF-8-NH2 were characterized by XRD, with a test range of 5. o -40 o The scan rate is 10 o / min. The chemical binding states and elemental information of ZIF crystals, TFC and TFN films were obtained by XPS analysis. The morphology of ZIF crystals and the prepared films was observed by SEM, and FTIR and solid-state UV-Vis spectroscopy were used to detect the functional group information of crystals and films.

[0025] In addition, using nuclear magnetic resonance hydrogen spectroscopy (NMR) 1 The ratio of the two ligands (2-Hmim and 2-aminobenzimidazole) in the ZIF-8-NH2 structure was analyzed by 1H NMR. Deuterated acetic acid was used as the solvent for ZIF-8 and ZIF-8-NH2 to avoid interference with the solvent. 1 Interference from the 1H NMR signal. Deuterated water was used as the solvent when analyzing the hydrogen bonding interactions between PEG and PIP. Thermogravimetric analysis was used to measure the thermal stability of the prepared ZIF crystals in an air atmosphere, with a test range of 25°C. o C to 900 o C, heating rate is 10 o / min. The microporous structure of the ZIF material was characterized by the N2 adsorption-desorption isotherm (BET method). Before testing, the sample needed to be heated to 120°C. oDegassing was performed at C for 12 hours to thoroughly remove adsorbed moisture, gas, or other impurities from the material surface and pores. The wettability of the membrane surface was measured at room temperature using a contact angle goniometer. During the test, 0.2 μL of test liquid was dropped onto the membrane surface through a syringe needle, and the contact angle between the liquid and the membrane surface was recorded. The dynamic contact angle was measured for 65 seconds to comprehensively evaluate the dynamic changes in membrane surface wettability. The Zeta potential of the ZIF nanoparticles was measured. Vacancies in the ZIF crystals were analyzed using electron paramagnetic resonance spectroscopy.

[0026] (2) Determination of diffusion coefficient The diffusion coefficient of polypropylene (PIP) from the aqueous phase to the oil phase was determined using ultraviolet (UV) absorption spectroscopy. The specific experimental steps are as follows: First, 1.9 mL of an aqueous PIP solution (with or without nanoparticles) was injected into the bottom of a quartz cuvette, followed by the addition of 0.2 mL of pure n-hexane solution to form a diffusion interface. The concentration of PIP in the n-hexane phase was quantitatively analyzed over time by continuously monitoring the UV absorption spectrum in the 200-400 nm wavelength range. Determining the location of the diffusion interface is crucial in this process. The specific operating steps are as follows: First, an aqueous solution was added to the quartz cuvette until the characteristic absorption peak of PIP was detected in the UV spectrum. Then, the volume of the aqueous solution was gradually reduced until the characteristic PIP peak disappeared, at which point the PIP layer height was lower than the optical path height. Finally, 0.2 mL of n-hexane solution was added for subsequent measurements.

[0027] (3) Membrane pore size distribution and molecular weight cutoff (MWCO) test The pore size distribution characteristics of the membrane were systematically evaluated using four groups of neutral solutes with different molecular weights (diethylene glycol, glucose, sucrose, and raffinose, all at a concentration of 100 mg / L). The experiments were conducted in a self-built cross-flow filtration system under constant pressure of 6 bar. Changes in the concentration of each model compound were monitored using a total organic carbon analyzer. The Stokes radius (r) of the aforementioned neutral solutes was determined. s Its molecular weight can be calculated using the following formula: ; The pore size distribution of the membrane can be calculated using the following function: ; (4) Separation performance test To investigate the separation performance of different composite membranes, their permeate flux and rejection rate were tested in a cross-flow testing apparatus. During the testing process, the membrane was first pre-pressurized at 8 bar for 0.5 hours to ensure it reached a stable state. For the formal testing, the pressure was adjusted to 6 bar. The effective test area of ​​the membrane was 3.14 cm². 2The permeation flux and rejection rate are calculated using the following formulas: ; Wherein, Permeance is the permeation flux, measured in Lm. -2 h -1 bar -1 p represents the test pressure, in bar. A The effective test area is in meters (m²). 2 , where is the permeate volumetric flow rate, in L / h. -1 The retention rates of the membrane for both salt and antibiotics were calculated using the following formula: ; Where R is the rejection rate, Cp is the solute concentration in the permeate, and Cf is the solute concentration in the feed solution. The test solutions were salt (1000 mg / L) and antibiotic (50 mg / L). The concentration of antibiotic before and after filtration was quantitatively analyzed by the intensity of characteristic peaks in UV-Vis spectroscopy.

[0028] Characterization results Preparation of Aminated ZIF Based on Polymers Figure 1 XRD characterization showed that the introduction of amino groups did not change the crystal structure of ZIF-8. Figure 1 a). The solid UV-Vis absorption spectrum of the modified crystalline powder changed significantly: the absorption edge of ZIF-8 at 230 nm corresponds to the π→π electronic transition of the imidazole ligand, while the new absorption edge of ZIF-8-NH2 at 300 nm is attributed to the n→π transition of the amino group ( Figure 1 b). The presence of amino groups was also confirmed by infrared spectroscopy, with the infrared spectrum at 3400 cm⁻¹. -1 New stretching vibration peaks belonging to amino groups appeared on both sides. Figure 1 c). Thermogravimetric analysis was then performed on both, and the thermal stability of ZIF-8-NH2 was slightly lower than that of ZIF-8. Figure 1 d). Among them, 200 o The weight loss stage below C corresponds to the removal of residual solvent within the pores, 400-500 o The mass loss within region C originates from the pyrolysis of organic ligands and skeletal collapse. The thermogravimetric analysis (TGA) curves show that the temperature corresponding to the maximum weight loss rate of ZIF-8-NH2 is approximately 20°C lower than the temperature corresponding to the maximum weight loss rate of ZIF-8. Figure 1 e), further confirming the slight decrease in its thermal stability. Nitrogen adsorption-desorption tests showed that amination did not significantly alter the pore size distribution of ZIF, and ZIF-8-NH2 still maintained a microporous structure of approximately 1 nm. Figure 1f), this pore size characteristic can achieve efficient separation of antibiotic molecules and ions through size sieving effect.

[0029] To further verify the Zn in the ZIF structure 2+ The coordination mechanism with organic ligands was investigated, and the chemical structure of the organic ligands was characterized using NMR technology. 1 In the 1H NMR spectrum, the characteristic peak at 7.37 ppm is attributed to the proton of the methyl group in 2-Hmim; after amination modification, new characteristic peaks at δ=7.24 and 7.41 are added to the spectrum, corresponding to the characteristic peaks of the benzene ring proton in 2-aminobenzimidazole, respectively. Figure 2 By analyzing the area of ​​each characteristic peak in the integrated 1H NMR spectrum, the ligand composition of ZIF-8-NH2 was calculated to be 46.8% 2-Hmim and 53.2% 2-aminobenzimidazole. This result indicates that PEG can serve not only as a reaction medium for ZIF synthesis but also as a functionalizing medium for amination modification. This phenomenon may be related to the binding interaction between the active functional groups in the PEG molecular chain and the amino ligands.

[0030] The chemical binding state and binding energy of ZIF-8 and its aminated product ZIF-8-NH2 were characterized by XPS. XPS full-spectrum analysis showed that all samples exhibited typical characteristic peaks for Zn, C, N, and O elements. Figure 4 a) The Zn 2p high-resolution XPS spectrum shows a significant chemical shift in the characteristic peak of ZIF-8-NH2 compared to ZIF-8, which may be due to the interaction between the 2-aminobenzimidazole ligand and Zn. 2+ The coordination effect altered its original coordination environment with 2-Hmim. Figure 4 b). Furthermore, compared to the single characteristic peak in the N 1s spectrum of ZIF-8, the N 1s spectrum of ZIF-8-NH2, after peak fitting, exhibits a bimodal structure, indicating the successful introduction of the amino functional group (b). Figure 4 cd).

[0031] The morphology and structure of the synthesized ZIF-8 and ZIF-8-NH2 nanoparticles were further characterized. SEM characterization results showed that amination did not significantly alter the surface morphology of the ZIF crystals; both exhibited regular cubic structures with particle sizes ranging from 90 to 110 nm. Figure 4 ab). Electron paramagnetic resonance (EPR) spectral analysis revealed no significant paramagnetic signal in ZIF-8-NH2. Figure 4c) indicates that the amination modification did not introduce lattice defects or uncoordinated metal sites into the ZIF framework. Combined with the XRD and EPR analysis results, the amination modification did not significantly change its coordination environment or structural stability while maintaining the integrity of the crystal structure.

[0032] Polymer regulation of ZIF particle dispersibility and monomer diffusion rate To verify the effect of polymer on improving the dispersibility of nanoparticles, a laser particle size analyzer was used to analyze the particle size of two dispersion systems: (1) ZIF-8-NH2 solid powder directly dispersed in an aqueous solution; (2) ZIF-8-NH2 suspension containing PEG. The results showed that due to the good compatibility of PEG with the aqueous phase, ZIF-8-NH2 exhibited nanoscale dispersion in the PEG-modified system, while the directly dispersed ZIF-8-NH2 powder agglomerated to form micron-sized aggregates. Figure 5 a). The transmittance of the solution at 650 nm was further measured using a UV-Vis spectrophotometer to assess the dispersion stability. The initial transmittance of the PEG-ZIF-NH2 suspension was 22.4%, significantly higher than the 1.0% of the directly dispersed ZIF-8-NH2 powder solution. Figure 5 b). Low transmittance indicates severe light scattering in the directly dispersed system, which is also evidence of the formation of large-sized aggregates. With prolonged storage time, the transmittance of the directly dispersed system increases sharply within 24 hours, reflecting the decrease in nanoparticle concentration due to sedimentation; while the transmittance of the PEG-ZIF-NH2 system shows only slight changes, demonstrating its excellent dispersion stability. Figure 5 c). Furthermore, Zeta potential analysis showed that the surface potential of ZIF-8 nanoparticles was 4.6 mV, while the potential of the amination-modified ZIF-8-NH2 increased to 8.6 mV ( Figure 5 d). This may be because the increased surface charge density enhances the electrostatic repulsion between particles, thereby inhibiting aggregation and improving dispersibility. Combined with the above results, it can be confirmed that the introduction of PEG effectively improves the stability of ZIF-8-NH2 nanoparticles through steric hindrance and electrostatic synergistic effects.

[0033] Polymer PEG not only affects the dispersibility of nanoparticles in solution, but also synergistically influences the interfacial polymerization process with the aqueous monomer PIP through hydrogen bonding. To further investigate the interaction mechanism between PEG and PIP, a... 1 Characterized by 1H NMR. For example... Figure 6As shown in Figure ac, neither the NH nor OH signals of PIP nor PEG showed peaks in deuterated water; the peak at 4.70 ppm was the peak for the deuterated aqueous solvent. The proton characteristic peak of PIP was located at 2.66 ppm, while the proton characteristic peaks of PEG appeared at 3.59 ppm and 3.66 ppm. When the two were mixed, the proton signal peak of PIP shifted to 2.58 ppm, and the proton signal peaks of PEG shifted to 3.57 ppm and 3.63 ppm, respectively. These chemical shift changes indicate that the electron cloud density of the NH atom bonded to CH2 in PIP and the O atom bonded to CH2 in PEG both changed, indicating a hydrogen bonding interaction between the oxygen-containing functional groups of NH and PEG. Figure 6 d).

[0034] As mentioned earlier, the polymer PEG not only promotes the uniform dispersion of nanoparticles in solution but also forms hydrogen bonds with the aqueous monomer PIP, thereby limiting the diffusion behavior of PIP. The effects of PEG and nanoparticles on the diffusion kinetics of PIP were investigated using ultraviolet spectroscopy. Figure 7 As shown, with the addition of PEG and nanoparticles, the concentration of PIP in the organic phase gradually decreased, indicating that the synergistic effect of nanoparticles and polymers significantly slowed down the diffusion rate of PIP. These results demonstrate that the introduction of PEG not only improved the dispersibility of nanoparticles but also effectively regulated the diffusion behavior of PIP through hydrogen bonding interactions, thereby making the interfacial polymerization process more controllable.

[0035] Polymer-aminated ZIF-mediated TFN film interface enhancement To further verify the chemical bonding between the -NH2 group in ZIF-8-NH2 and TMC, ZIF-8 and ZIF-8-NH2 powders were dispersed separately in a hexane solution containing TMC, and the resulting nanoparticles were characterized by FTIR and XPS. FTIR analysis showed that after the reaction of ZIF-8-NH2 with TMC, the nanoparticles exhibited a bonding activity at 1540 cm⁻¹. -1 and 1680 cm -1 The presence of significant characteristic peaks at these locations corresponds to the C=O stretching vibration and NH bending vibration of the amide bond, respectively, confirming that the amino group can undergo an amidation reaction with TMC. Figure 8 a). XPS further verified the chemical bonding state between -NH2 and the acyl chloride group. After the reaction of ZIF-8-NH2 with TMC, a new Cl 2p characteristic peak was added to the full spectrum scan, which originated from the acyl chloride group of TMC ( Figure 8 bc). Furthermore, the N 1s narrow-spectrum scan showed a significant broadening of the peak shape and a marked leftward shift in the peak center position (bc). Figure 8d), This phenomenon can be attributed to the significant changes in the chemical environment, bond strength and electron density of nitrogen caused by the O=CN bond generated by the reaction of ZIF-8-NH2 with TMC.

[0036] Effect of polymer-aminated ZIF on the surface properties of TFN films The introduction of different nanoparticles into an aqueous solution has a significant regulatory effect on the surface morphology of the film. For example... Figure 9 As shown in Figure a, the polyamide film prepared using PIP as a single aqueous monomer exhibits a typical nodular structure, with a PA layer thickness of approximately 195 nm. When ZIF-8 particles are introduced into the aqueous solution, the nodular structure on the film surface decreases, replaced by a non-uniform protruding morphology. This is attributed to the random distribution of ZIF-8 particles in the polyamide network and their aggregation during polymerization. Figure 9 b). In contrast, after the introduction of ZIF-8-NH2 particles, the PA-ZIF-NH2 film surface exhibited a unique nano-striped structure, and its distribution was more uniform and ordered than the protrusion morphology in the ZIF-8 film. Figure 9 c). Furthermore, the cross-section selective layer also exhibits a gradient-modified, uniform, and dense structure with an average thickness of approximately 160 nm and a minimum thickness of only 5 nm. Although the presence of PEG promotes the uniform dispersion of ZIF-8 particles in the aqueous solution, during interfacial polymerization, unmodified ZIF-8 particles, lacking chemical interaction with TMC, are prone to random movement during diffusion from the aqueous to the oil phase, leading to particle aggregation. In contrast, the amino groups in ZIF-8-NH2 particles can chemically react with TMC, fixing them within the polyamide network and achieving uniform particle distribution. Moreover, the introduction of ZIF-8-NH2 induces the formation of striped structures on the membrane surface, which is related to the formation mechanism of Turing structures. A Turing structure refers to a periodic striped pattern on the membrane surface caused by the periodic changes in chemical concentration due to system instability in a reaction-diffusion system. Interfacial polymerization is a typical reaction-diffusion system, but the similar diffusion coefficients between PIP and TMC are usually insufficient to induce the formation of Turing structures. The introduction of PEG and nanoparticles into the aqueous monomer significantly reduced the diffusion rate of PIP, providing conditions for the formation of Turing structures. Furthermore, ZIF-8-NH2 and PIP competitively react with TMC, inducing a "local activation and lateral inhibition" phenomenon, thereby forming a periodic stripe structure on the film surface.

[0037] Infrared spectroscopy was used to analyze the functional groups on the membrane surface. When the membrane surface contains only aqueous monomers, the functional groups at 2927 cm⁻¹ are... -1 755 cm -1 690 cm -1Characteristic functional groups belonging to ZIF-8 appear at this location, corresponding to the stretching vibrations of C–H, Zn–O, and Zn–N respectively. Figure 10 a) The aforementioned characteristic peaks confirm the stable existence of ZIF-8 particles in the aqueous phase. However, when an oil phase is introduced for interfacial polymerization, the peak value at 1623 cm⁻¹... -1 The presence of significant characteristic peaks at C1s corresponds to the stretching vibrations of CO and CN, indicating the successful preparation of the polyamide selective layer. Furthermore, XPS analysis was used to analyze the influence of nanoparticles on the chemical composition of the polyamide selective layer. PA, PA-ZIF, and PA-ZIF-NH2 all showed distinct characteristic peaks of C1s, CO / CN, and CO in their high-resolution C1s spectra, further verifying the successful crosslinking of the polyamide selective layer. Figure 10 b). Furthermore, the peak shape of PA-ZIF-NH2 is significantly different from the previous two, with its area at the CN peak being significantly larger than the previous two. Figure 10 c). The added CN bonds originate from the abundant -NH2 in the ZIF-8-NH2 nanomaterial, which facilitates reaction with more acyl chloride molecules. In the O 1s spectrum, the O=CN binding energy positions of PA-ZIF and PA-ZIF-NH2 show significant shifts compared to the original PA film. This may be due to the coordination reaction between O and ZIF in the polyamide structure, leading to a change in the electron cloud density around the O atom. Figure 10 d).

[0038] The surface wetting properties of the composite membrane were evaluated using dynamic water contact angle testing. The initial contact angle of the pure PA membrane was 58.7°, indicating moderate hydrophilicity. After introducing ZIF-8 and ZIF-8-NH2 nanoparticles, the contact angles of the PA-ZIF and PA-ZIF-NH2 membranes decreased to 39.4° and 32.0°, respectively, showing a significant improvement in hydrophilicity. Figure 11 This phenomenon can be attributed to the following synergistic mechanisms: (1) the inherent porous structure of the ZIF material enhances the interaction between the membrane surface and water molecules; (2) the introduction of nanoparticles interferes with the crosslinking reaction between PIP and TMC, leading to an increase in the proportion of unreacted acyl chloride groups, which further hydrolyze in the aqueous phase to generate hydrophilic carboxylic acid groups. Notably, the dynamic contact angle decrease rate of the PA-ZIF-NH2 membrane is significantly higher than that of the PA-ZIF membrane. This is because the unique raised stripe-like topology formed on the surface of the PA-ZIF-NH2 membrane increases surface roughness and capillary effect, further promoting the rapid spread of water.

[0039] Antibiotic desalting properties like Figure 12First, the pure water flux of the PA membrane, PA-ZIF membrane, and PA-ZIF-NH2 membrane was tested. The pure water flux of the TFC membrane (PA membrane) without added nanoparticles was 7.3 Lm. -2 h -1 bar -1 ( Figure 12 The lower flux may be due to the highly cross-linked structure of the PA layer, which limits its free volume, and the chain effect between the PA layer and the membrane substrate further restricts water molecule transport. After introducing ZIF and aminated ZIF particles, the water flux increased to 3 times. Possible reasons for the flux increase include: (1) the porosity and hydrophilicity of ZIF can provide additional channels for water transport; (2) the aggregation of ZIF particles in the PA layer may lead to the formation of interfacial voids and a relatively loose PA layer. When ZIF-8-NH2 nanoparticles are added, the water flux of the TFN membrane is further improved. This may be because: (1) the amino modification significantly enhances the hydrophilicity of ZIF, forming a more hydrophilic membrane surface and promoting water molecule transport; (2) the amino-induced striped structure makes the polyamide layer have a more wrinkled morphology, which further increases the specific surface area of ​​the polyamide layer, thereby expanding the water transport pathway; (3) the selective layer thickness of the PA-ZIF-NH2 membrane is thinner than that of the PA-ZIF membrane, and the thinner selective layer is beneficial to improving the water flux.

[0040] Furthermore, three antibiotic molecules (tetracycline hydrochloride (TC), ciprofloxacin hydrochloride (CIP), and chlortetracycline hydrochloride (CTC)) and three inorganic salts (Na₂SO₄, NaCl, and KCl) were selected as model compounds for antibiotic desalting experiments. The PA membrane without nanoparticles exhibited high retention rates for antibiotics (>98.2%), as well as high retention rates for inorganic salts (>98.7% for Na₂SO₄). This high retention rate is attributed to the dense and relatively thick selective layer structure. Figure 13 ).

[0041] After incorporating ZIF material into the PA layer, the water flux of the PA-ZIF membrane significantly increased, but the Na₂SO₄ rejection rate decreased to 41.5%. Furthermore, the antibiotic rejection rate of the membrane also decreased synchronously to approximately 85.2%. This may be because the aggregation and disordered distribution of ZIF particles formed interfacial defects, leading to a simultaneous decrease in both salt and antibiotic rejection rates. Figure 14 ).

[0042] When using PA-ZIF-NH2 membranes for separation testing, selective separation of salts and antibiotics can be achieved. The rejection rate of Na2SO4 by PA-ZIF-NH2 is reduced to 14.6%, and the rejection rates of NaCl and KCl are further reduced to 8.0%. Figure 15 Meanwhile, PA-ZIF-NH2 maintained high retention of antibiotics, with a retention rate of 98.3% for TC, and 96.1% and 93.2% for CTC and CIP, respectively. To investigate this selective separation phenomenon, the retention of neutral solute molecules of different molecular weights by the three membranes was measured to calculate their MWCO and pore size distribution.

[0043] The MWCO of the PA membrane is 390 Da, while that of the PA-ZIF-NH2 membrane is similar. In contrast, the MWCO of the PA-ZIF membrane increases to 562 Da. Pore size distribution shows that the average effective pore sizes of the PA, PA-ZIF, and PA-ZIF-NH2 membranes are 0.6, 0.68, and 0.76 nm, respectively, with corresponding geometric deviations of 1.26, 1.30, and 1.20 nm. Figure 16 The abnormal increase in MWCO of PA-ZIF membrane may be due to interfacial defects caused by the disordered distribution of ZIF-8 nanoparticles in the polyamide selective layer. These defects not only lead to an increase in effective pore size, but also cause a decrease in pore size distribution uniformity (increased geometric deviation). Thanks to the directional regulation effect of amino functionalization, ZIF-8-NH2 particles in PA-ZIF-NH2 membrane exhibit a highly ordered arrangement, and their pore size distribution shows a rightward shift trend with the lowest geometric deviation value. This structural optimization can be attributed to: (1) the molecular sieving effect of the inherent micropores (about 1.1 nm) of ZIF-8-NH2 causes the overall pore size of the membrane to shift to the right; (2) under polymer-mediated conditions, amino groups inhibit the reactivity of PIP and TMC through synergistic competition, thereby delaying the interfacial polymerization process and promoting the formation of a looser polyamide network structure.

[0044] Besides pore size distribution, the surface charge characteristics of nanofiltration membranes also significantly influence solute transport behavior. All membranes prepared in this experiment exhibited negative charge, primarily due to the inherent characteristic of residual acyl chloride groups hydrolyzing to form -COOH groups after interfacial polymerization. However, the surface charge of the TFN membranes (PA-ZIF and PA-ZIF-NH2) with added nanoparticles was lower than that of the PA membranes overall. This can be attributed to the neutralizing effect of the positive charge of the ZIF and ZIF-NH2 nanoparticles on the membrane surface charge. The reduced surface charge leads to decreased solute transport behavior with SO4. 2- and Cl - The electrostatic repulsion between them decreases, which is one of the reasons for the decrease in salt rejection rate of TFN membrane.

[0045] The separation performance of the PA-ZIF-NH2 membrane in TC / Na2SO4 and TC / NaCl mixed systems was further tested. The results showed that the PA-ZIF-NH2 membrane exhibited a TC rejection rate higher than 97.1% in both separation systems, while its rejection rates for Na2SO4 and NaCl were lower than 18.7% and 8.3%, respectively. Figure 18 ab). Although the flux of PA-ZIF-NH2 decreased to some extent due to fouling of the membrane pores by antibiotics and salts, its retention performance remained stable during 40 hours of continuous operation. The antibiotic desalination capacity of the PA-ZIF-NH2 membrane was verified through a circulating feed experiment. Figure 18 (cd). In the TC / Na2SO4 system, the concentrations of both TC and Na2SO4 in the feed solution increased slightly within a 6-h filtration cycle; while in the TC / NaCl system, the TC concentration increased continuously, while the NaCl concentration increased more slowly, demonstrating good antibiotic desalting performance. The difference in separation performance between the two systems may be attributed to the higher Na2SO4 rejection rate of the PA-ZIF-NH2 membrane compared to NaCl, thus confirming the membrane's high-efficiency antibiotic desalting performance. The calculated NaCl / TC and Na2SO4 / TC selectivity coefficients of the PA-ZIF-NH2 membrane were 49.6 and 28.2, respectively, showing advantages in flux and selectivity compared to those reported in the literature. These results indicate that PA-ZIF-NH2 exhibits significant application potential in the field of antibiotic separation and purification.

[0046] Table 1. Comparison of the desalination performance of antibiotics by the TFN membranes prepared in this study and those in the literature.

[0047] References: 1. Wang Z, Xia D, Wang B, Liu H, Zhu L. Highly permeable polyamidenanofiltration membrane incorporated with phosphorylated nanocellulose forenhanced desalination. J Membr Sci 647, 120339 (2022). 2. Luo X, Liang J, Han W, Wang J, Zhou Z. Fe-and-N co-doped Fe-ZIF-8-NH2(1 / 10) prepared by molecular-scale cages effect for highly efficientphotocatalytic degradation of organic dyes. J Mol Struct 1291, 135910 (2023). 3. Wu B, Wang NX, Lei JH, Shen Y, An QF. Intensification of masstransfer for zwitterionic amine monomers in interfacial polymerization tofabricate monovalent salt / antibiotics separation membrane. J Membr Sci 643,120050 (2022). 4. Guo YS, et al. High-flux zwitterionic nanofiltration membraneconstructed by in-situ introduction method for monovalent salt / antibioticsseparation. J Membr Sci 593, 117441 (2020). 5. Jun BM, Lee HK, Kwon YN. Acid-catalyzed hydrolysis of semi-aromatic polyamide NF membrane and its application to water softening andantibiotics enrichment. Chem Eng J 332, 419-430 (2018). 6. Shen YJ, Kong QR, Fang LF, Qiu ZL, Zhu BK. Construction ofcovalently-bonded tannic acid / polyhedral oligomeric silsesquioxanesnanochannel layer for antibiotics / salt separation. J Membr Sci 623, 119044(2021). 7. Bai Y, et al. Microstructure optimization of bioderived polyesternanofilms for antibiotic desalination via nanofiltration. Sci Adv 9, adg6134(2023).

Claims

1. A method for preparing a polymer-aminoated ZIF modified TFN membrane, characterized in that, Comprising the following steps: (1) preparing ZIF-8-NH2 with a precursor containing a zinc source, an organic ligand containing an amino imidazole and polyethylene glycol; (2) immersing the base film in an aqueous solution containing ZIF-8-NH2 and a polyamine, and an oil phase solution containing a polyacyl chloride to achieve interfacial polymerization to form the polyamine ZIF-modified TFN membrane.

2. The method of claim 1, wherein, In step (1), the zinc source is selected from one of zinc acetate, zinc nitrate, zinc chloride and zinc sulfate.

3. The method of claim 1, wherein, In step (1), the organic ligand contains an amino imidazole and a non-amino imidazole, the amino imidazole is one or more of 2-amino benzimidazole, 2-aminoimidazole, 5-amino-1H-benzimidazole, 2-amino-4-methylimidazole, and the non-amino imidazole is selected from one or more of 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-isopropylimidazole, 2-butylimidazole, 1-methylimidazole, 1-ethylimidazole, and the mass ratio of the amino imidazole and the non-amino imidazole is 1:5-5:

1.

4. The method of claim 1, wherein, In step (1), the mass ratio of the zinc source, the organic ligand and the polyethylene glycol in the precursor is 1:2-10:3-10.

5. The method of claim 1, wherein, In step (2), the base film is selected from one of polyimide, polysulfone, polyethersulfone, polyolefin.

6. The method of claim 1, wherein, In step (2), the polyamine is selected from one or more of piperazine, ethylenediamine, m-phenylenediamine; in the aqueous solution, the concentration of the polyamine is 0.5-5wt%, and the concentration of ZIF-8-NH2 is 0.05-1wt%.

7. The method of claim 1, wherein, In step (2), the polyacyl chloride is selected from one or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, m-phenyldicarboxylic acid chloride; in the oil phase solution, the concentration of the polyacyl chloride is 0.02-0.5wt%.

8. The method of claim 1, wherein, In step (2), the base film is immersed in the aqueous solution for 0.5-10min, and in the oil phase solution for 0.1-5min.

9. A polymer aminoated ZIF modified TFN membrane prepared according to the method of claim 1, wherein, comprising a base film and a polyamide separation layer containing ZIF-8-NH 2。 10. The application of the polyamine ZIF-modified TFN membrane in the desalination of antibiotics according to claim 9.

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