Choline derivative-modified tight ultrafiltration membrane, preparation method and application thereof

Abstract

The present application relates to the technical field of tight ultrafiltration membrane, and particularly relates to a tight ultrafiltration membrane based on choline derivative modification, a preparation method and application thereof. The preparation method selects a choline derivative with a hydroxyl group and a quaternary ammonium salt group as a bifunctional water phase monomer, selects an ionic strong polar monomer, and utilizes the electrostatic interaction between anions and cations to slow down the interface polymerization reaction to form a polyester modifier, so as to constrain the polymerization reaction position, accurately limit the polymerization reaction in the inside of the base membrane channel and the channel interface, promote the uniform and narrow membrane hole, and greatly improve the uniformity of the membrane pore size distribution. The tight ultrafiltration membrane can realize a high Congo red retention rate and a moderate sodium chloride retention rate, and exhibits excellent membrane separation performance in high-precision dye separation.

Description

Technical Field

[0001] This invention relates to the field of compact ultrafiltration membrane technology, and more particularly to compact ultrafiltration membranes based on choline derivative modification, their preparation methods, and applications. Background Technology

[0002] Ultrafiltration membrane separation technology boasts advantages such as low energy consumption, high efficiency, and environmental friendliness, and is widely used in wastewater treatment, biopharmaceuticals, food processing, and drinking water purification. Currently, the industry primarily employs the solvent-induced phase inversion method to prepare ultrafiltration membranes, a mature process with strong mass production adaptability. This process uses a membrane-forming substrate and core solvents such as N-methylpyrrolidone to prepare a homogeneous casting solution. After coating, solvent-induced phase separation, and curing, an ultrafiltration membrane with an asymmetric microporous structure is formed, simultaneously achieving good water flux and mechanical structural stability. The ultrafiltration membrane surface is relatively dense, with pore sizes typically ranging from 5 to 100 nm, effectively removing suspended solids, organic matter, bacteria, viruses, and other macromolecular pollutants from water through size sieving. However, ultrafiltration membranes prepared by the traditional phase inversion method still face many challenges in practical applications. On the one hand, the ultrafiltration membrane substrate itself is highly hydrophobic, easily adsorbing organic matter and protein pollutants during operation, which can easily lead to severe membrane fouling and flux decline, significantly shortening the service life of the membrane module. On the other hand, the uneven diffusion rates of solvent and non-solvent during phase transformation can easily lead to uneven pore size and wide pore size distribution in the prepared ultrafiltration membrane. This structural defect directly results in insufficient separation precision and selectivity of the membrane, making it difficult to achieve efficient separation of small molecule organics (such as dyes) and inorganic salts.

[0003] Interfacial polymerization is currently the main technique for preparing nanofiltration membranes. It involves using an ultrafiltration membrane as a substrate, impregnating its surface with an aqueous phase containing amine monomers and an organic phase containing acyl chloride monomers, respectively. Polymerization at the aqueous-organic phase interface forms a dense separation layer, thereby achieving the removal of inorganic salts and small-molecule organic compounds and improving the membrane's separation precision. However, amine monomers (such as m-phenylenediamine and piperazine) have rapid diffusion rates, high reactivity, and fast polymerization rates. Therefore, the reaction process is intense, the control window is narrow, and the separation layer formed on the membrane surface has a very dense structure, with pore sizes typically only around 1 nm. This dense separation layer tends to have high rejection rates for both small-molecule organic compounds and inorganic salts, making it difficult to separate small-molecule organic compounds (such as dyes) from inorganic salts.

[0004] Therefore, how to provide a preparation scheme for a separation membrane with a uniform and fine porous structure on its surface, so as to achieve the effect of retaining and removing small molecule organic matter and allowing inorganic salts to pass through, thereby achieving the separation of organic matter and inorganic salts, has become a technical problem that urgently needs to be solved in the membrane field. Summary of the Invention

[0005] In polymerization reactions, alcohol monomers (such as polyols and sugar alcohols) can also serve as aqueous phase monomers. Compared to amine monomers, they exhibit milder reactions and better biocompatibility, potentially reducing the rate of interfacial polymerization and preventing the formation of overly dense separation layers. However, these monomers have relatively simple structures and functions, lacking charged groups, and cannot utilize strong forces to constrain the interfacial polymerization reaction sites, thus failing to improve the pore size distribution of ultrafiltration membranes. This invention, through molecular structure design, provides an aqueous phase monomer that combines reactivity with dynamic regulation of membrane pore microstructure, thereby achieving precise, controllable, and multi-dimensional modification of the ultrafiltration membrane pore structure. This design approach, aiming to reduce the pore size of ultrafiltration membranes and avoid the formation of dense separation layers, is expected to solve the aforementioned technical problems. Therefore, the first objective of this invention is to provide a method for preparing a compact ultrafiltration membrane modified with choline derivatives; the second objective is to provide a compact ultrafiltration membrane modified with choline derivatives; and the third objective is to provide applications of the compact ultrafiltration membrane modified with choline derivatives.

[0006] To achieve the first objective, the technical solution adopted by this invention is as follows: The preparation method of compact ultrafiltration membranes modified with choline derivatives includes: Prepare aqueous solutions containing choline derivatives and organic solutions containing acyl chloride lipophilic monomers, respectively; The choline derivative comprises hydroxyl and quaternary ammonium salt groups; The aqueous solution containing choline derivatives is coated on the surface of an ultrafiltration membrane. The membrane is allowed to stand for the first time to impregnate it with the aqueous solution containing choline derivatives. After impregnation, the residual aqueous solution containing choline derivatives on the surface of the ultrafiltration membrane is removed to obtain a pretreated membrane. The organic phase solution containing acyl chloride hydrophilic monomers is coated on the surface of the pretreated membrane. After a second standing period, the choline derivative and the acyl chloride hydrophilic monomers undergo interfacial polymerization to form a polyester modifier. After the reaction is completed, the residual organic phase solution containing acyl chloride hydrophilic monomers on the surface is removed to obtain the nascent membrane. After heat treatment and rinsing, the nascent membrane is subjected to heat treatment and rinsing to obtain a compact ultrafiltration membrane modified with choline derivatives.

[0007] Preferably, the choline derivative is tartrate choline, and the mass percentage concentration of tartrate choline in the aqueous solution containing the choline derivative is 0.05wt% to 2.0wt%.

[0008] Choline tartrate is a zwitterionic bifunctional monomer that dissociates to generate choline cations and hydrogen tartrate anions. Unlike traditional interfacial polymerization techniques that create a separate membrane on the ultrafiltration membrane surface, this invention utilizes the strong polarity of the ionic monomer and the electrostatic interaction between the cations and anions to precisely confine the polymerization reaction within the pores of the base membrane. This allows the polymer to grow in situ within the membrane pores, achieving uniform narrowing of the pore interior. Specifically, the anionic polyhydroxy structure provides multiple reaction sites for crosslinking with acyl chloride-containing lipophilic monomers, resulting in pore narrowing within the pores. The larger molecular size and dissociated cations end-cap the acyl chloride-containing lipophilic monomers, slowing down the interfacial polymerization reaction and inducing pore widening. By adjusting the monomer addition amount to balance the pore narrowing and widening effects, bidirectional continuous adjustment of the ultrafiltration membrane pore size can be achieved in a single interfacial polymerization step, overcoming the shortcomings of uneven pore size distribution and the limitation of only unidirectional pore size control in ultrafiltration membranes.

[0009] Preferably, the mass percentage concentration of choline tartrate in the aqueous solution containing the choline derivative is 0.2wt% to 0.4wt%.

[0010] Preferably, the aqueous solution containing choline derivatives contains sodium hydroxide, and the mass percentage concentration of sodium hydroxide is 0.3wt% to 0.5wt%.

[0011] Preferably, the acyl chloride-containing lipophilic monomer is trimesoyl chloride (TMC), and the mass percentage concentration of trimesoyl chloride in the organic phase solution of the acyl chloride-containing lipophilic monomer is 0.05wt% to 0.15wt%.

[0012] Preferably, the ultrafiltration membrane is selected from polysulfone membranes.

[0013] Preferably, the first settling time is 2 to 4 minutes, and the second settling time is 8 to 12 minutes.

[0014] Preferably, the heat treatment temperature is 55℃~65℃ and the time is 4min~6min.

[0015] To achieve the second objective, the technical solution adopted by this invention is as follows: The compact ultrafiltration membrane based on choline derivative modification is prepared by any of the above-described methods for preparing a compact ultrafiltration membrane based on choline derivative modification, comprising an ultrafiltration base membrane and a polyester modifier filling the pores of the ultrafiltration base membrane, wherein the polyester modifier is polymerized by the choline derivative and the acyl chloride lipophilic monomer at the interface inside the membrane pores.

[0016] To achieve the third objective, the technical solution adopted by this invention is as follows: Applications of choline derivative-modified compact ultrafiltration membranes include the application of the choline derivative-modified compact ultrafiltration membranes to any one or more of the following: separation of mixed systems containing dyes and inorganic salts, decolorization treatment of dyeing and printing industrial wastewater, and desalination and purification of water-soluble dyes.

[0017] Preferably, the dye includes one or more of Congo Red, Direct Red, and Direct Blue, and the inorganic salt includes one or more of sodium salt, potassium salt, and lithium salt.

[0018] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: This invention provides a compact ultrafiltration membrane based on choline derivative modification and its preparation method. The method uses a choline derivative possessing both hydroxyl and quaternary ammonium groups as a bifunctional aqueous monomer. This ionic monomer not only possesses strong polarity, anchoring the monomer to the polar aqueous phase, but its dissociated choline cations also inhibit the diffusion of polyhydroxy anions and end-cap the organic phase monomer. These synergistic effects effectively slow down the interfacial polymerization reaction, precisely confining the reaction within the membrane pores, allowing the generated polymer to grow in situ within the pores, thus achieving uniform narrowing of the ultrafiltration membrane pore size. Unlike traditional interfacial polymerization techniques that construct a separation layer on the membrane surface, this invention utilizes the unique configuration of the choline derivative to actively control the interfacial reaction site and polymer growth site in situ, achieving precise and controllable construction of the internal structure of the ultrafiltration membrane pores. This invention achieves uniform internal shrinkage of membrane pores without forming an additional surface separation layer, significantly improving the uniformity of pore size distribution and thus enabling efficient separation of small-molecule organic matter and inorganic salts. Simultaneously, the capping effect of cations at high concentrations allows for a moderate recovery of pore size, achieving bidirectional regulation of membrane pore size and overcoming the limitation of traditional non-ionic monomers in providing only one dimension of membrane pore size control. The preparation method provided by this invention is simple to operate, has mild reaction conditions, and exhibits good process reproducibility and potential for large-scale production.

[0019] The compact ultrafiltration membrane based on choline derivative modification provided by this invention has at least the following performance characteristics: I. Convenient and precise bidirectional control of the pore size inside the ultrafiltration membrane: This invention uses choline derivatives as bifunctional monomers. These monomers have both polymerization reactivity and pore size control functions. The bidirectional adjustment of the ultrafiltration membrane pore size can be achieved through a single interfacial polymerization process, overcoming the technical problems of traditional monomers having single functions and limited pore size control dimensions.

[0020] 2. Significantly improves the uniformity of ultrafiltration membrane pore size: The anions and cations generated by the dissociation of choline derivatives can constrain the location of the polymerization reaction through electrostatic interaction, so that the polymerization reaction is precisely limited to the inside of the base membrane pores, which promotes the uniform narrowing of ultrafiltration membrane pores and effectively improves the problem of excessively wide pore size distribution of ultrafiltration membranes.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] Figure 1 This is a SEM image of the compact ultrafiltration membrane based on choline derivative modification provided in Embodiment 2 of the present invention.

[0023] Figure 2 This is a SEM image of the compact ultrafiltration membrane based on choline derivative modification provided in Embodiment 3 of the present invention.

[0024] Figure 3 This is a SEM image of the compact ultrafiltration membrane based on choline derivative modification provided in Example 5 of the present invention.

[0025] Figure 4 These are Zeta potential histograms of the choline derivative-modified compact ultrafiltration membranes provided in Examples 1 to 6 of this invention.

[0026] Figure 5 In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Example 2 of this invention, the tartrate anion (Jss) - ) and choline cations (Jss + Radial distribution function (RDF) plot of water molecules (H2O) and water molecules (H2O).

[0027] Figure 6 In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Example 5 of this invention, the tartrate anion (Jss) - ) and choline cations (Jss + Radial distribution function (RDF) plot of water molecules (H2O) and water molecules (H2O).

[0028] Figure 7 In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Examples 2 and 5 of this invention, the tartrate anion (Jss) dissociated from tartrate choline is... - The mean square displacement (MSD) curve of the graph.

[0029] Figure 8 In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Examples 2 and 5 of this invention, the choline cations (Jss) dissociated from tartrate choline are... + The mean square displacement (MSD) curve of the graph.

[0030] Figure 9In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Example 3 of this invention, the tartrate anion (Jss) dissociated from tartrate choline is... - The mean square displacement (MSD) curve of the graph.

[0031] Figure 10 In the molecular dynamics simulation of the choline-derived modified compact ultrafiltration membrane provided in Example 3 of this invention, the choline cations (Jss) dissociated from tartrate choline are... + The mean square displacement (MSD) curve of the graph. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention, but cannot be used to limit the scope of this invention.

[0033] In the following embodiments, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available, unless otherwise specified, and are carried out in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0034] The main raw materials used in the following examples and comparative examples are as follows: Polysulfone-based membrane, purchased from Jiangsu Qicheng Purification Technology Co., Ltd., with a molecular weight cutoff (MWCO) of 20,000 Da and a pure water flux of 230–260 L·m⁻¹. -2 ·h -1 The bovine serum albumin retention rate was 98.6%–99.2%. L-(+)-Choline tartrate, 98% purity, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Tartaric acid, purity ≥95%, purchased from China Maclean Biochemical Co., Ltd.; Choline chloride, 99% pure, was purchased from China Maclean Biochemical Co., Ltd. Sodium hydroxide, purity ≥96%, purchased from Tianjin Fengchuan Chemical Reagent Technology Co., Ltd. Trimethylbenzene chloride, 99% purity, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. n-Hexane, 98% purity, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Congo red, analytical grade, purchased from Tianjin Guangfu Fine Chemical Research Institute; Sodium chloride, analytical grade, purchased from China Maclean Biochemical Co., Ltd.

[0035] Example 1 The preparation of a compact ultrafiltration membrane based on choline derivative modification includes the following steps: Step 1: Prepare the aqueous phase solution and the organic phase solution separately.

[0036] Preparation of the aqueous solution: Dissolve choline tartrate in an aqueous sodium hydroxide solution to obtain the aqueous solution; wherein the mass percentage concentration of choline tartrate is 0.05 wt% and the mass percentage concentration of sodium hydroxide is 0.4 wt%. Preparation of organic phase solution: Dissolve trimesoyl chloride in n-hexane to obtain organic phase solution; wherein the mass percentage concentration of trimesoyl chloride (TMC) is 0.1 wt%.

[0037] Step 2: Aqueous phase pretreatment of the base membrane.

[0038] The aforementioned aqueous solution was coated onto the surface of the polysulfone-based ultrafiltration membrane. After standing for 3 minutes, the aqueous solution was allowed to impregnate the polysulfone-based ultrafiltration membrane. After impregnation, the residual aqueous solution on the surface was removed to obtain the pretreated membrane.

[0039] Step 3: Prepare the primary membrane using interfacial polymerization reaction.

[0040] The prepared organic phase solution was poured onto the surface of the pretreated membrane to coat it evenly. After coating, the membrane was allowed to stand for 10 minutes to allow the choline tartrate and trimesoyl chloride to undergo interfacial polymerization. After the reaction was completed, the residual organic phase solution on the surface of the pretreated membrane was removed to obtain the nascent membrane.

[0041] Step 4: Prepare a compact ultrafiltration membrane based on choline derivative modification.

[0042] The nascent membrane prepared above was placed in a forced-air drying oven and heat-treated at 60°C for 5 minutes to promote full cross-linking of interfacial polymerization, shape and regulate the pore structure, and remove residual solvent from the membrane. After heat treatment, the surface was rinsed with deionized water to remove free monomers, salts and by-products and to unclog the membrane pores. After rinsing, a compact ultrafiltration membrane based on choline derivative modification was obtained.

[0043] Example 2 The only difference from Example 1 is that the mass percentage concentration of choline tartrate in step one is adjusted to 0.1 wt%, while the rest of the process is the same as in Example 1. The SEM image of the choline derivative-modified compact ultrafiltration membrane prepared in this example is shown below. Figure 1 As shown.

[0044] Example 3 The only difference from Example 1 is that the mass percentage concentration of choline tartrate in step one is adjusted to 0.3 wt%, while the rest of the process is the same as in Example 1. The SEM image of the choline derivative-modified compact ultrafiltration membrane prepared in this example is shown below. Figure 2 As shown in the figure, the film is dense and flat with no obvious cracks, and the film uniformity is good.

[0045] Example 4 The only difference from Example 1 is that the mass percentage concentration of tartrate choline in step one is adjusted to 0.5 wt%, and the rest of the process is the same as in Example 1.

[0046] Example 5 The only difference from Example 1 is that the mass percentage concentration of choline tartrate in step one is adjusted to 1.0 wt%, while the rest of the process is the same as in Example 1. The SEM image of the choline derivative-modified compact ultrafiltration membrane prepared in this example is shown below. Figure 3 As shown.

[0047] Example 6 The only difference from Example 1 is that the mass percentage concentration of choline tartrate in step one is adjusted to 2.0 wt%, and the rest of the process is the same as in Example 1.

[0048] Zeta potential histograms of the choline derivative-modified compact ultrafiltration membranes prepared in Examples 1 to 6 are shown below. Figure 4 As shown.

[0049] Comparative Example 1 The only difference from Example 3 is that in step one, no tartrate choline is added (i.e., the mass percentage concentration of tartrate choline is 0 wt%), and the rest of the process is the same as in Example 3.

[0050] Comparative Example 2 The only difference from Example 3 is that in step one, tartrate choline is replaced with tartrate acid; the rest of the process is the same as in Example 3.

[0051] Comparative Example 3 The only difference from Example 3 is that in step one, choline tartrate is replaced with choline chloride, and the rest of the process is the same as in Example 3.

[0052] Detection example The testing process for pure water flux is as follows: Different membrane samples (effective filtration area 2.206 × 10⁻⁶) were compared. -3 m 2The membrane was loaded into the test unit, using deionized water as the feed solution, and pre-pressurized at an operating pressure of 0.5 MPa for 30 minutes to stabilize the membrane performance. Subsequently, the pressure was maintained at 0.5 MPa, and the volume of permeate was collected over a certain period of time. The pure water flux was calculated using the following formula: ; In the formula, Water permeation flux, in L·m -2 ·h -1 ; S Effective membrane area, in m² 2 ; Infiltration time, in hours; Is The volume of infiltrated water collected internally, in liters (L). The test was conducted at a constant temperature of (25±1)℃.

[0053] The retention rate test process is as follows: After completing the pure water flux test, the feed solution was replaced with a mixed aqueous solution of 100 mg / L Congo red and 1000 mg / L sodium chloride. The system was operated under the same pressure and temperature (0.5 MPa, 25 ± 1 °C). Once the system flux stabilized, both the feed solution and permeate samples were collected. The concentration of Congo red was determined using a UV-Vis spectrophotometer, and the concentration of sodium chloride was determined using a conductivity meter. The rejection rate was calculated using the following formula: ; In the formula, R For retention rate, The concentration of NaCl (or Congo Red) in the permeate is expressed in mg / L. This represents the concentration of NaCl (or Congo Red) in the feed solution, expressed in mg / L.

[0054] Test results.

[0055] The test results of the properties of different membrane surfaces and their separation performance are shown in Table 1.

[0056] Table 1

[0057] The data in Table 1 show that the membrane separation performance of Comparative Example 1, without the addition of tartrate choline, was poor, with a rejection rate of only 16.40% for Congo red and only 0.67% for sodium chloride. This indicates that the unmodified ultrafiltration membrane, due to its large pore size, could not achieve effective separation. In contrast, all examples with the addition of tartrate choline successfully prepared compact ultrafiltration membranes with practical separation performance. As the mass concentration of tartrate choline increased from 0.05 wt% to 2.0 wt%, the membrane performance showed a regular change: the continuous introduction of hydroxyl groups gradually increased the hydrophilicity of the membrane; the negative charge on the membrane surface and the dye rejection rate both showed a trend of first increasing and then decreasing; while the pore size and pure water flux of the ultrafiltration membrane showed a trend of first decreasing and then increasing. Example 3 represents the turning point in performance change. Under the conditions of this example, the membrane surface exhibits the strongest negative charge (-44.35mV), the smallest pore size (3.053nm), the Congo red rejection rate reaches a peak of 99.42%, and the pure water flux decreases to 20.57 L·m⁻². -2 ·h -1 Upon further increasing the concentration of tartrate choline, the negative charge on the membrane surface decreased to -30.82 mV, the membrane pore size rebounded to 3.412 nm, the membrane cross-linking structure became looser, and the pure water flux significantly increased. The membrane sample provided in Example 6 achieved a flux of 62.31 L·m⁻¹. -2 ·h -1 .

[0058] The above results indicate that the pore size of ultrafiltration membranes can be bidirectionally adjusted by regulating the concentration of added choline tartrate. The essence of this is to precisely confine the polymerization reaction within the pores of the base membrane, allowing the polymer to grow in situ within the channels, thereby achieving uniform narrowing and controllable adjustment of the pore size.

[0059] Comparative Example 2 (tartaric acid, providing a single anion) and Comparative Example 3 (choline chloride, providing a single cation) verified the indispensability of the bifunctional molecular structure of tartrate choline, as shown in Table 1: The pure water flux of Comparative Example 2 was 18.27 L·m. -2 ·h -1 The Congo red rejection rate was 99.54%, while the sodium chloride rejection rate was as high as 55.8%, and the membrane surface charge was -46.76 mV. Compared with Example 3, the Congo red rejection rate remained basically the same after tartaric acid substitution, but the sodium chloride rejection rate surged from 21.37% to 55.8%. This result indicates that the absence of choline cations leads to the loss of the buffering and end-capping regulation effect of the quaternary ammonium salt groups on the reaction process, resulting in uncontrolled reaction, a shift of the interfacial polymerization reaction site towards the membrane surface, and a significant increase in the negative charge density on the membrane surface. This results in a stronger electrostatic repulsion of negatively charged chloride ions, leading to an abnormally high sodium chloride rejection rate. This demonstrates that choline cations are a key factor in anchoring the polymerization reaction within the membrane pores and preventing excessive surface cross-linking.

[0060] The pure water flux of Comparative Example 3 was 40.20 L·m -2 ·h -1 The Congo red rejection rate was only 96.93%, the sodium chloride rejection rate was only 8.8%, and the membrane surface charge was -36.53 mV. Compared with Example 3, the pure water flux increased from 20.57 L·m⁻¹. -2 ·h -1 Increased to 40.20 L·m -2 ·h -1 The Congo red rejection rate decreased from 99.42% to 96.93%. This result indicates that although choline chloride contains one hydroxyl group and one quaternary ammonium salt group, it has only one hydroxyl group, extremely low reactivity, and lacks a hydroxyl reaction site provided by the hydrogen tartrate anion. Therefore, it cannot form a highly cross-linked polyester layer with trimesoyl chloride, making it difficult to form sufficient polymer inside the membrane pores to achieve uniform narrowing. The membrane structure is loose, resulting in a significant decrease in Congo red rejection rate and a substantial increase in pure water flux.

[0061] Comparative Examples 2 and 3 together demonstrate that the bifunctional synergistic mechanism of the tartrate anion providing polyhydroxy reaction sites and the choline cation providing quaternary ammonium salt regulatory groups in tartrate choline is indispensable. Only when the two work together in the interfacial polymerization process can the interfacial polymerization reaction be precisely confined to the inside of the membrane pores, so that the polymer grows uniformly in the membrane pores, and the pore size can be precisely controlled in both directions, such as low-concentration densification and high-concentration moderate pore expansion.

[0062] To elucidate the mechanism of the above-mentioned performance changes at the molecular scale, molecular dynamics simulations were used to analyze the diffusion behavior and interaction of tartrate anions and cations at low concentrations (Example 2: tartrate choline mass percentage concentration of 0.1 wt%) and high concentrations (Example 5: tartrate choline mass percentage concentration of 1.0 wt%).

[0063] First, the interaction energies (i.e., hydration energies) between anions and cations and water molecules are calculated using the following formula to assess their hydration strength and diffusion capacity in the aqueous phase: E int = E A+B - E A - E B ; In the formula, E int Intermolecular interaction energy, expressed in kcal / mol; E A+B The total energy of the ion-water molecule binding system is expressed in kcal / mol. E AThe total energy of ions (anions or cations) is expressed in kcal / mol. E B This represents the total energy of a water molecule, expressed in kcal / mol.

[0064] The interaction energies between the tartrate anion and tartrate choline cation and water molecules at low and high concentrations are shown in Tables 2 and 3, respectively.

[0065] Table 2. Interaction energy between ions and water molecules at low concentrations (Example 2)

[0066] Table 3 Interaction energy between ions and water molecules at high concentrations (Example 5)

[0067] The data provided in Tables 2 and 3 show that, regardless of whether the concentration is low (Example 2) or high (Example 5), the interaction energy between anions and water molecules is significantly higher than that between cations, indicating that anions bind more tightly to water molecules and have a stronger hydration effect.

[0068] In addition, such as Figure 5 and Figure 6 As shown, in the molecular dynamics simulations of the choline derivative-modified ultrafiltration membranes provided in Examples 2 and 5, respectively, the tartrate anion (Jss) - ) and choline cations (Jss + The radial distribution function (RDF) plot of anions and water molecules (H2O) further confirms that the density of water molecules is higher around anions.

[0069] Then, the electrostatic interaction energy between anions and cations was calculated, as shown in Table 4.

[0070] The electrostatic interaction energy between anions and cations is calculated using the following formula: E int'= E A1+B1 -E A1 - E B1 ; in, E int' It represents the electrostatic interaction energy between anions and cations, expressed in kcal / mol. E A1+B1 The total energy of a single ion (anion or cation) is expressed in kcal / mol. E A1The energy of a single anion is expressed in kcal / mol. E B1 This represents the energy of a single cation, expressed in kcal / mol.

[0071] Table 4

[0072] As shown in Table 4, with the increase of tartrate choline concentration, the electrostatic interaction energy between anions and cations increased from -74.92 kcal / mol in Example 2 to -76.05 kcal / mol in Example 5. This indicates that the electrostatic interaction is enhanced, the diffusion of anions in the aqueous phase is somewhat restricted, and the anion diffusion rate decreases, with the diffusion coefficient value decreasing from 0.155 Å. 2 / ps decreased to 0.115Å 2 / ps, such as Figure 7 As shown; however, cations, due to their hydrophobic quaternary ammonium salt structure, exhibit relatively weak hydration, and their diffusion rate is less affected by concentration. Therefore, they diffuse faster in the aqueous phase, with diffusion coefficients ranging from 0.147 Å. 2 / ps increased to 0.163Å 2 / ps, such as Figure 8 As shown.

[0073] Furthermore, to reveal the competition mechanism during the reaction, the binding energies of the anions and cations to the organic phase monomer TMC at high concentrations (Example 5) were calculated as follows: E bind = E a+b - E a - E b ; In the formula, E bind The binding energy between anion / cation and TMC is expressed in kcal / mol. E a+b The total energy of the system after the anion / cation-TMC combination is expressed in kcal / mol. E a The energy of a single ion (anion or cation) before binding, expressed in kcal / mol; E b The energy of a single TMC molecule before binding is expressed in kcal / mol.

[0074] The interaction energies between anions, cations and TMC of the choline derivative-modified ultrafiltration membrane prepared in Example 5 are shown in Table 5.

[0075] Table 5

[0076] As shown in Table 5, in Example 5, the binding energy between the cation and TMC is stronger (-78.70 kcal / mol) than that between the anion and TMC (-76.91 kcal / mol), indicating that at high concentrations, the cation preferentially dominates the interfacial polymerization reaction.

[0077] The differences in diffusion and reaction behaviors between anions and cations revealed by the above molecular simulations correspond to the changes in membrane performance with concentration in Table 1, constituting microscopic evidence for the integrated mechanism of confined polymerization and pore size regulation within the ultrafiltration membrane pores. Specifically: at low concentrations, the hydrogen tartrate anion diffuses faster, and its hydroxyl functional groups preferentially react with trimesoyl chloride, resulting in... Figure 1 It can be seen that the membrane surface of Example 2 still exhibits a porous structure at low concentrations, but the pore size is smaller, indicating that the polymerization reaction is effectively confined within the ultrafiltration membrane channels, achieving internal narrowing. As the concentration increases, the cation capping effect strengthens, and the degree of reaction moderately decreases, such as... Figure 3 As shown, the pore size on the membrane surface increases relatively, and the structure becomes more porous, achieving moderate pore expansion. This structural transformation is consistent with the pattern of pore size first decreasing and then increasing in Table 1. In addition, the strong polarity of the anions and cations causes them to accumulate on the aqueous phase side (i.e., inside the membrane pores), effectively inhibiting the excessive diffusion of monomers into the organic phase, successfully anchoring the polymerization reaction inside the membrane pores, and achieving in-situ modification of the membrane pores.

[0078] In summary, Examples 1-6 achieved bidirectional controllable preparation of ultrafiltration membranes with synergistic regulation of anion and cation concentrations by adjusting the concentration of tartrate choline. In the low concentration range (e.g., Examples 1-3), the anion-dominated interfacial polymerization reaction promotes the compaction and narrowing of membrane pores, improving separation selectivity; in the medium-to-high concentration range (e.g., Examples 4-6), the cation-dominated interfacial polymerization reaction induces the loosening and expansion of membrane pores, increasing water flux.

[0079] Example 3 is a typical manifestation of the dominant role of anions: In the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Example 3, the tartrate anion (Jss) dissociated from tartrate choline... - The mean square displacement (MSD) curve of ) is shown below. Figure 9 As shown; in the molecular dynamics simulation of the choline derivative-modified compact ultrafiltration membrane provided in Example 3, the choline cations (Jss) dissociated from tartrate choline... + The mean square displacement (MSD) curve of ) is shown below. Figure 10 As shown.

[0080] from Figure 9 and Figure 10This indicates that both ions can diffuse freely within the system, with the hydrogen tartrate anion having a diffusion coefficient of 0.141 Å. 2 / ps, the diffusion coefficient of tartrate choline cations is 0.153 Å. 2 The results indicate that cations have slightly stronger diffusion and migration capabilities than anions. Both types of ions can be uniformly distributed in the reaction zone. Anions can continuously impart a negative charge to the membrane surface, and their polyhydroxy structures can continuously crosslink with trimesoyl chloride. Cations, on the other hand, confine the interfacial polymerization reaction within the pores through electrostatic constraint and end-capping, avoiding excessive crosslinking. The synergistic effect of both allows the polymer to grow uniformly in situ inside the membrane pores, resulting in highly dense pores and enhanced negative charge on the membrane surface. This leads to a high Congo red rejection rate (99.42%) and a moderate sodium chloride rejection rate (21.37%), demonstrating excellent membrane separation performance for high-precision dye separation.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a compact ultrafiltration membrane modified with choline derivatives, characterized in that, include: Prepare aqueous solutions containing choline derivatives and organic solutions containing acyl chloride lipophilic monomers, respectively; The choline derivative comprises hydroxyl and quaternary ammonium salt groups; The aqueous solution containing choline derivatives is coated on the surface of an ultrafiltration membrane. The membrane is allowed to stand for the first time to impregnate it with the aqueous solution containing choline derivatives. After impregnation, the residual aqueous solution containing choline derivatives on the surface of the ultrafiltration membrane is removed to obtain a pretreated membrane. The choline derivative is tartrate choline, which is dissolved in an aqueous sodium hydroxide solution to obtain an aqueous solution. The organic phase solution containing acyl chloride hydrophilic monomers is coated on the surface of the pretreated membrane. After a second standing period, the choline derivative and the acyl chloride hydrophilic monomers undergo interfacial polymerization to form a polyester modifier. After the reaction is completed, the residual organic phase solution containing acyl chloride hydrophilic monomers on the surface is removed to obtain the nascent membrane. After heat treatment and rinsing, the nascent membrane is subjected to heat treatment and rinsing to obtain a compact ultrafiltration membrane modified with choline derivatives.

2. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 1, characterized in that, The mass percentage concentration of choline tartrate in the aqueous solution containing choline derivatives is 0.05wt% to 2.0wt%.

3. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 2, characterized in that, The mass percentage concentration of choline tartrate in the aqueous solution containing the choline derivative is 0.2wt% to 0.4wt%.

4. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 1, characterized in that, The aqueous solution containing choline derivatives contains sodium hydroxide, with a mass percentage concentration of 0.3 wt% to 0.5 wt%. The acyl chloride-containing lipophilic monomer is pyromellitic trimethylolpropionate (PMT), and the mass percentage concentration of PMT in the organic phase solution of the acyl chloride-containing lipophilic monomer is 0.05 wt% to 0.15 wt%.

5. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 1, characterized in that, The ultrafiltration membrane is selected from any one of polysulfone-based ultrafiltration membranes, polyethersulfone-based ultrafiltration membranes, polyvinylidene fluoride ultrafiltration membranes, polyacrylonitrile-based ultrafiltration membranes, and polyvinyl chloride ultrafiltration membranes.

6. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 1, characterized in that, The first settling time is 2 to 4 minutes, and the second settling time is 8 to 12 minutes.

7. The method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in claim 1, characterized in that, The heat treatment temperature is 55℃~65℃, and the time is 4min~6min.

8. A compact ultrafiltration membrane based on choline derivative modification, characterized in that, The membrane is prepared using the method for preparing a compact ultrafiltration membrane based on choline derivative modification as described in any one of claims 1 to 7, comprising an ultrafiltration base membrane and a polyester modifier filling the pores of the ultrafiltration base membrane, wherein the polyester modifier is formed by polymerization of the choline derivative and the acyl chloride lipophilic monomer at the interface within the membrane pores.

9. The application of compact ultrafiltration membranes modified with choline derivatives, characterized in that, The compact ultrafiltration membrane based on choline derivative modification as described in claim 8 is applied to the separation of dyes and inorganic salts in a mixed system containing dyes and inorganic salts.

10. The application of the choline derivative-modified compact ultrafiltration membrane as described in claim 9, characterized in that, The dye includes one or more of Congo Red, Direct Red, and Direct Blue, and the inorganic salt includes one or more of sodium salt, potassium salt, and lithium salt.

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