A method for improving the separation performance of nanofiltration membranes by alkali regulation and its application

Abstract

The present invention discloses a method and application of alkali regulation to improve the separation performance of nanofiltration membranes, including immersing a PAN membrane in a NaOH solution, wiping off excess NaOH solution on the surface of the base membrane to obtain an alkali-treated PAN membrane; immersing the alkali-treated PAN membrane in a ferric chloride solution, removing the membrane after the reaction is completed, and thoroughly rinsing it with deionized water; adding a TA solution to form a selective layer, rinsing it with deionized water, and drying it. The present invention proposes a green and convenient method for preparing a high-retention nanofiltration membrane, using TA and FeCl3 as raw materials, using NaOH to pre-wet the base membrane, concentrating iron ions, and then releasing them during the coordination reaction process, and preparing a metal-polyphenol complexed nanofiltration membrane on the surface of the PAN base membrane to achieve efficient separation of inorganic salts and organic small molecules; the Fe-TA-10 membrane has a retention capacity of 96.37% for inorganic salts, and a retention rate of up to 98.96% for various drugs with relative molecular masses ranging from 365.4 (amoxicillin) to 822.94 (rifampicin).

Description

Technical Field

[0001] The present invention belongs to the technical field of nanofiltration membrane preparation, and specifically relates to a method for improving the separation performance of a nanofiltration membrane by alkali regulation and its application. Background Art

[0002] Nanofiltration membrane (MPNs) is a functional semipermeable membrane that allows certain low molecular weight solutes or ions to pass through. It is a new type of separation membrane. Most of them are composite membranes with a pore size of 1 to 2 nm and a molecular weight cutoff between reverse osmosis membranes and ultrafiltration membranes. It has a certain retention rate for small molecular substances such as dyes, organic matter, and inorganic salts.

[0003] The metal phenol network is a supramolecular network structure formed by the rapid coordination of natural polyphenols and metal ions. Metal ions can coordinate with functional groups such as hydroxyl, aldehyde, and ketone in polyphenol compounds to form stable complexes. Different metal ions (such as Cu 2+ 、Zn 2+ ) coordinates with polyphenols, and their ratio directly influences the pore size, hydrophilicity, and other properties of the MPN layer. Post-treatment of the initially formed MPN layer through physical or chemical methods, such as cross-linking, heat treatment, or surface modification, can improve the stability and fouling resistance of the membrane, enhance its long-term stability in practical applications, and improve its anti-fouling ability and separation efficiency.

[0004] Most traditional nanofiltration membranes are prepared by interfacial polymerization of amine monomers in the aqueous phase and acidic chlorides in the organic phase to form a thin polyamide (PA) selective layer on a porous substrate. However, this preparation method usually requires high temperature and high pressure conditions and takes a long time to complete, which consumes a lot of energy and increases costs. Most importantly, a large amount of organic solvent is usually required to dissolve the polymer during the interfacial polymerization process, which will cause environmental pollution and waste of resources. In addition, the interaction between the selective layer and the substrate is weak, and there is a risk of detachment from the PA film. In contrast, the preparation of non-polyamide nanofiltration membranes is simpler and more environmentally friendly. Among them, deposition method and layer-by-layer self-assembly method have always been the main methods for preparing non-polyamide nanofiltration membranes. However, one of the biggest disadvantages of non-polyamide nanofiltration membranes is that their desalination selectivity is not as good as that of polyamide nanofiltration membranes.

[0005] Currently, it is a major challenge to prepare nanofiltration membranes with excellent performance using simple processes. In nature, plant polyphenols have rich physical and chemical properties. Plant polyphenol tannic acid (TA) has been proposed for surface modification because it contains abundant catechol groups, which strongly bind to the surface through covalent or non-covalent bond structures. By utilizing the chelation effect of TA with metal ions, TA is used as an organic ligand and the transition metal ion Fe is selected. 3+As an inorganic cross-linking agent, a stable cross-linked network structure is formed on the surface of the ultrafiltration membrane in a very short time. Fan et al. directly deposited TA and Fe 3+ The Fe-TA selective layer was fabricated on an ultrafiltration membrane, but the density of the prepared selective layer was insufficient to achieve high-performance desalination. This study shows that the uniformity and density of the rapidly assembled Fe-TA film are not sufficient to achieve high-performance separation. Summary of the Invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for improving the separation performance of nanofiltration membranes by alkali regulation.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for improving the separation performance of nanofiltration membrane by alkali regulation, comprising:

[0010] The PAN film was immersed in a NaOH solution, and the excess NaOH solution on the surface of the base film was wiped off to prepare an alkali-treated PAN film;

[0011] Immerse the alkali-treated PAN membrane in the ferric chloride solution, remove the membrane after the reaction is complete, and rinse thoroughly with deionized water;

[0012] TA solution was added to form a selective layer, which was then rinsed with deionized water and dried.

[0013] As a preferred embodiment of the method of the present invention, the pH of the NaOH solution is 8-12.

[0014] As a preferred embodiment of the method of the present invention, the pH of the NaOH solution is 10.

[0015] As a preferred embodiment of the method of the present invention, the PAN membrane is immersed in the NaOH solution for 60 seconds.

[0016] As a preferred embodiment of the method of the present invention, the alkali-treated PAN membrane is immersed in a ferric chloride solution, wherein the concentration of the ferric chloride solution is 1 to 20 g / L.

[0017] As a preferred embodiment of the method of the present invention, the alkali-treated PAN membrane is immersed in the ferric chloride solution for 60 seconds.

[0018] As a preferred embodiment of the method of the present invention, the concentration of the TA solution is 4 g / L.

[0019] As a preferred embodiment of the method of the present invention, the addition time of the TA solution is 60 seconds.

[0020] Another object of the present invention is to overcome the deficiencies in the prior art and provide the use of the nanofiltration membrane prepared by the method described above in separating antibiotic drugs.

[0021] As a preferred embodiment of the application of the present invention, the antibiotic drugs include amoxicillin, tetracycline, rifampicin, and puerarin.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention proposes a green and convenient method for preparing a high-retention nanofiltration membrane, which uses TA and FeCl3 as raw materials, uses NaOH to pre-wet the base membrane, concentrates iron ions, and then releases them during the coordination reaction. A metal-polyphenol complex nanofiltration membrane is prepared on the surface of the PAN base membrane to achieve efficient separation of inorganic salts and organic small molecules; the Fe-TA-10 membrane has a retention capacity of 96.37% for inorganic salts and a maximum retention rate of 98.96% for various drugs with relative molecular masses ranging from 365.4 (amoxicillin) to 822.94 (rifampicin).

[0024] (2) The modified nanofiltration membrane prepared by the method of the present invention does not require any toxic chemical reagents for pretreatment, and the required raw materials are cheap and easy to operate. Therefore, it has high environmental friendliness and applicability, and has demonstrated the great potential of nanofiltration membranes in the separation of drugs such as antibiotics. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0026] Figure 1 This is a preparation route map of the Fe-TA-10 film in Example 1 of the present invention;

[0027] Figure 2The scanning electron micrographs of the surfaces of PAN-based films prepared in the examples of the present invention and the comparative examples are shown, wherein (a) is a Fe-TA film, (b) is a Fe-TA-8 film, (c) is a Fe-TA-10 film, and (d) is a Fe-TA-12 film;

[0028] Figure 3 The infrared analysis diagrams of the PAN-based film, Fe-TA film and Fe-TA-n film of the present invention are shown below;

[0029] Figure 4 The pore size distribution diagrams of the Fe-TA membrane, Fe-TA-8 membrane, Fe-TA-10 membrane, and Fe-TA-12 membrane of the present invention are shown;

[0030] Figure 5 The figure shows the retention and flux results of four salts by the modified nanofiltration membranes with different pH values ​​of the present invention;

[0031] Figure 6 XPS analysis charts of PAN-based film, Fe-TA film, Fe-TA-8 film, Fe-TA-10 film, and Fe-TA-12 film of the present invention;

[0032] Figure 7 Graph showing the flux and retention of different drugs using different membranes of the present invention. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0036] Experimental materials and reagents involved in the embodiments of the present invention:

[0037] Polyacrylonitrile (PAN) membrane was purchased from Taian Lanjing Trading Co., Ltd.

[0038] Tannic acid (TA, AR) and anhydrous ferric chloride (FeCl3, AR) were purchased from MacLean Chemical Reagent Company and used to prepare the metal polyphenol network layer (MPN);

[0039] Sodium hydroxide (NaOH), sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), sodium chloride (NaCl), and magnesium chloride (MgCl2) were all purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. NaOH was used to create alkaline conditions to promote the precipitation of iron and facilitate the deprotonation of hydroxyl groups, thereby promoting the binding with metal ions.

[0040] Four inorganic salts were used to test the separation performance of the nanofiltration membrane. Amoxicillin (McLean Chemical Reagent Company, >99%, AR), rifampicin (McLean Chemical Reagent Company, >97%, CR), tetracycline (Shanghai Aladdin Biochemical Technology Co., Ltd., 98%, AR), and puerarin (McLean Chemical Reagent Company, 98%, AR) were used to test the separation performance of the nanofiltration membrane for antibiotics.

[0041] Characterization of the membrane in the embodiment of the present invention:

[0042] The chemical composition of the coordination nanofiltration membrane was analyzed using total reflection Fourier transform infrared spectroscopy (ATR-FTIR, Thermo Fisher Scientific, IS 50);

[0043] Scanning electron microscopy (FESEM, Zeiss, Germany SUPRA 55) was used to characterize the micromorphology of the nanofiltration membrane. A contact angle tester (OSA100, Ningbo NB Scientific Instrument Co., Ltd., China) was used to characterize the hydrophilicity of the membrane by measuring the water contact angle (WCA). X-ray photoelectron spectroscopy (XPS, ThermoFisher Nexsa, USA) was used to detect the atomic content of membrane elements and calculate the cross-linking degree of the membrane.

[0044] At different wavelengths, an ultraviolet-visible spectrophotometer (UV-1900) was used to detect the absorbance of the filtrate and the original solution to test the separation performance of different drugs.

[0045] Membrane filtration performance test in the embodiment of the present invention:

[0046] (1) Filtration performance of membrane

[0047] The flux and retention of the membrane were measured using a cross-flow filtration device. The effective area of ​​the membrane in the test device was 9.616 cm 2 Before each test, the membrane was pre-pressed at a pressure of 0.5 MPa for 20 minutes, and then measured. The flux P of the membrane can be calculated by the following formula:

[0048]

[0049] Where P is the filtration flux (Lm -2 h -1bar -1 ), V is the volume of the filtrate increased in △t time (L), A is the filtration area (m 2 ), Δt is the filtration time (h), and Δp is the transmembrane pressure (bar).

[0050] The retention performance of nanofiltration membranes for different inorganic salts is calculated by the following equation:

[0051]

[0052] Among them C p and C f are the concentrations of the filtrate and the original solution, respectively. The salt concentration was measured by a conductivity meter (Raymag DDS-307).

[0053] (2) Drug retention performance test

[0054] In this embodiment of the present invention, 200 ppm solutions of amoxicillin, tetracycline, rifampicin, and puerarin were selected as test drugs. The ultraviolet absorbance of the original solution and the filtrate before and after filtration was tested to calculate the drug retention performance of the Fe-TA membrane and the Fe-TA-n membrane. The calculation method is the same as the formula for calculating the retention performance of nanofiltration membranes for different inorganic salts.

[0055] (3) Pore size distribution

[0056] The molecular weight cutoffs of Fe-TA membranes and Fe-TA-n membranes were measured using neutral PEG solutions of different molecular weights (PEG200, PEG400, PEG600, and PEG1000) at a concentration of 200 ppm to calculate the pore size distribution of the membrane surface. Characterization was performed using a total organic carbon analyzer (C / N 3100, Jena, Germany).

[0057] r s (m) = 16.74 × 10 -12 ×MW0.557

[0058] Wherein, MW (g / mol) is the relative molecular mass of PEG; r s (nm) is the Stokes radius of PEG;

[0059] According to the relative molecular weight of the tested neutral solute molecules and the corresponding retention rate, a log-constant probability (neutral solute vs. hydrodynamic radius) fitting curve or linear equation is drawn;

[0060] where μ p is the point where the retention rate is 50% in the fitting curve, σ g (Geometric standard deviation) is the ratio of molecular weights when the rejection rate is 84.13% and 50%;

[0061] Finally, neglecting the spatial and dynamic interactions between the solute and the pore, μ p and σ g μ s and σ p replace.

[0062] The pore size distribution calculation formula is as follows:

[0063]

[0064] Example 1

[0065] This embodiment provides a method for improving the separation performance of nanofiltration membranes by alkali control, the main steps of which are:

[0066] (1) Immerse the upper surface of the PAN base film with 5 mL of NaOH solution, and keep in contact with the membrane surface for 60 s. Use a wipe to wipe away the excess NaOH solution on the surface of the base film to prepare an alkali-treated PAN base film; wherein the pH of the NaOH solution is 10.

[0067] (2) Place the alkali-treated PAN-based membrane in a container with the membrane facing upward, pour in a 4 g / L ferric chloride solution, keep it in contact with the membrane surface for 60 seconds, remove the membrane, and rinse it with deionized water five times;

[0068] 5 mL of TA solution with a concentration of 4 g / L was added to the container with a contact time of 60 s to form an MPN layer;

[0069] (3) After rinsing with deionized water, the mixture was placed in an oven at 60° C. for 120 seconds to obtain the nanofiltration membrane, which was named Fe-TA-10 membrane.

[0070] The preparation route of Fe-TA-10 membrane can be found in Figure 1 .

[0071] Example 2

[0072] This embodiment provides a method for improving the separation performance of nanofiltration membranes by alkali control, the main steps of which are:

[0073] (1) Immerse the upper surface of the PAN base film with 5 mL of NaOH solution, and keep it in contact with the membrane surface for 60 seconds. Use a wipe to wipe away the excess NaOH solution on the surface of the base film to prepare an alkali-treated PAN base film; wherein the pH of the NaOH solution is 8.

[0074] (2) Place the alkali-treated PAN-based membrane in a container with the membrane facing upward, pour in a 4 g / L ferric chloride solution, keep it in contact with the membrane surface for 60 seconds, remove the membrane, and rinse it with deionized water five times;

[0075] 5 mL of TA solution with a concentration of 4 g / L was added to the container with a contact time of 60 s to form an MPN layer;

[0076] (3) After rinsing with deionized water, the mixture was placed in an oven at 60° C. for 120 seconds to obtain the nanofiltration membrane, which was named Fe-TA-8 membrane.

[0077] Example 3

[0078] This embodiment provides a method for improving the separation performance of nanofiltration membranes by alkali control, the main steps of which are:

[0079] (1) Immerse the upper surface of the PAN base membrane with 5 mL of NaOH solution, and keep in contact with the membrane surface for 60 s. Use a wipe to wipe away the excess NaOH solution on the surface of the base membrane to prepare an alkali-treated PAN base membrane; wherein the pH of the NaOH solution is 12.

[0080] (2) Place the alkali-treated PAN-based membrane in a container with the membrane facing upward, pour in a 4 g / L ferric chloride solution, keep it in contact with the membrane surface for 60 seconds, remove the membrane, and rinse it with deionized water five times;

[0081] 5 mL of TA solution with a concentration of 4 g / L was added to the container with a contact time of 60 s to form an MPN layer;

[0082] (3) After rinsing with deionized water, the mixture was placed in an oven at 60° C. for 120 seconds to obtain the nanofiltration membrane, which was named Fe-TA-12 membrane.

[0083] Comparative Example 1

[0084] (1) Place the PAN-based membrane in a container with the membrane facing upward, pour in a 4 g / L ferric chloride solution, leave it in contact with the membrane surface for 60 seconds, remove the membrane, and rinse it with deionized water five times;

[0085] 5 mL of TA solution with a concentration of 4 g / L was added to the container with a contact time of 60 s to form an MPN layer;

[0086] (2) After rinsing with deionized water, the mixture was placed in an oven at 60° C. for 120 seconds to obtain the nanofiltration membrane, which was named Fe-TA membrane.

[0087] The surface scanning electron microscope images of the PAN base film prepared in Examples 1 to 3 and Comparative Example 1 are shown in FIG. Figure 2 , it can be seen that compared with PAN-based membranes, tannic acid coordinates with iron ions to form a dense MPN layer attached to the membrane surface (e.g. Figure 2 a), the membrane pores on the membrane surface are significantly reduced. In addition, unlike the relatively smooth surface of PAN-based membrane (prepared with an electron microscope image in the supporting literature), the Fe-TA membrane ( Figure 2 a) and a small amount of polymer appears;

[0088] Figure 2b and 2c are the morphological microstructures of the modified membrane after adding sodium hydroxide solution with pH values ​​of 8 and 10, respectively. Under alkaline conditions, iron ions will precipitate and combine with hydroxide to form iron hydroxide particles. Figure 2 (bd) It can be seen that when the pH value increases, the amount of polymer on the membrane surface increases significantly and the particle size increases.

[0089] The separation performance test further shows that the retention rate increases and the pore size becomes smaller after adding alkaline solution.

[0090] Comparative Example 2

[0091] (1) PAN-based films, Fe-TA films and Fe-TA-n films were characterized by ATR-FTIR. Figure 2 As shown, the 1450, 2240 and 2930 cm-1 -1 The peaks at correspond to the bending vibration of CH2, the stretching vibration of C≡N and the stretching vibration of CH2, respectively.

[0092] Fe-TA membrane at 3100-3600 cm -1 There is a broadband peak at the center, which is mainly due to the fact that a large number of phenolic hydroxyl groups in TA have not yet reacted with Fe 3+ Complete coordination, and under alkaline conditions, the metal ions can more completely coordinate with the hydroxyl groups in tannic acid, and thus this peak is weakened; at 1650cm -1 The peaks at 1710 cm -1 The new peaks at 1650 cm-1 and 1660 cm-2 can be attributed to the C=O stretching vibrations of the carboxyl group and ester group of the TA substrate, respectively. -1 The characteristic peak shift occurred at 1560cm, which may be due to the influence of hydrogen bonds, which can affect the vibration frequency of chemical bonds in molecules, thereby causing the absorption peak in the infrared spectrum to shift. -1 The peak at is attributed to the C-C stretching vibration of the aromatic ring in TA.

[0093] (2) The retention and pore size distribution (MWCO) of the membrane were characterized by retaining PEG molecules of different molecular weights. The results are shown in Figure 4.

[0094] The MWCO values ​​of the Fe-TA, Fe-TA-8, Fe-TA-10, and Fe-TA-12 membranes were 894, 749, 712, and 864 Da, respectively. Among them, the Fe-TA-10 membrane had the smallest pore size and demonstrated the best performance in inorganic salt and small molecule separation tests. However, excessively alkaline conditions can have the opposite effect. Sodium hydroxide with excessively high pH values ​​can enhance the inorganic nature of the membrane, affecting its structure and hindering pore size adjustment.

[0095] (3) Performance test and analysis of modified nanofiltration membrane

[0096] In order to study the effect of different concentrations of sodium hydroxide on the separation performance of nanofiltration membranes, the flux and retention of nanofiltration membranes with different alkalinity were tested by separating 1000ppm sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride aqueous solutions. The results are shown in Figure 5 ;

[0097] pass Figure 5 It can be observed that with the addition of NaOH solution, the retention performance of the membrane for different salts increases. As the pH value gradually increases, the retention of sodium sulfate gradually increases, but when the pH value is too high (pH 12), the retention decreases slightly, among which the retention of sodium sulfate is as high as 97.37%.

[0098] In addition, the order of the rejection rates of magnesium chloride and sodium chloride changed after the addition of sodium hydroxide solution.

[0099] The surface of the MPN layer produced by the coordination of Fe and TA has a negative charge. Since the surface of the nanofiltration membrane has a negative charge, the rejection rate of divalent anions is higher than that of monovalent anions, and the rejection rate of monovalent cations is higher than that of divalent cations, so the rejection rate of SO4 2- The retention rate is higher than Cl - , to Na + The retention rate is higher than Mg 2+ ;

[0100] Among them, for magnesium sulfate, the retention of Fe-TA-12 membrane is higher than that of Fe-TA-10 membrane, but the pore size of the former is larger than that of the latter. This may be because under alkaline conditions, the number of aggregated iron ions is greater and the positive charge is stronger, which improves the retention of magnesium sulfate.

[0101] The addition of sodium hydroxide reduces the membrane pore size, increasing the steric hindrance of the nanofiltration membrane for divalent cations and leading to a slightly higher rejection rate. Therefore, after the addition of sodium hydroxide, the Fe-TA-n membrane has a slightly higher rejection rate for magnesium chloride than for sodium chloride.

[0102] In addition, the rejection rate of the nanofiltration membrane for the four salts has been improved. On the one hand, it is due to the reduction of the pore size. On the other hand, the alkaline solution can control the precipitation of iron ions and deprotonate the hydroxyl group of TA, which is beneficial to Fe 3+ With O - So it is easier for TA to coordinate better.

[0103] (4) XPS analysis charts of PAN-based film, Fe-TA film, Fe-TA-8 film, Fe-TA-10 film, and Fe-TA-12 film are shown in Figure 6, it can be seen that all films have three main peaks, corresponding to C1s (294.8eV), N 1s (410.3eV) and O1s (540.8eV). In addition, in the Fe-TA film with complete coordination, iron (Fe 2p) appears a new peak around 711eV, confirming the presence of Fe in the film. 3 + .

[0104] Analysis of the O1s peak reveals the binding forms of O with other elements. As shown in the figure, three O bonds are observed on Fe-TA: CO (532.7 eV), C=O (531.9 eV), and Fe-O (530.9 eV) [reference]. The figure clearly shows that the Fe-O peak is enhanced after the introduction of sodium hydroxide, demonstrating that the degree of deprotonation of the hydroxyl group can be effectively controlled under alkaline conditions, changing the coordination state of the complex. The CO and C=O peaks are weakened, and the weakening of the CO peak is more significant than that of the C=O peak, indicating that the role of the phenolic hydroxyl group (C-OH) in coordination is significantly greater than that of the ester group (OCO) of TA.

[0105] All these results demonstrate that the MPN layer was successfully coated on the membrane surface and the modified MPN membrane was successfully prepared.

[0106] Comparative Example 3

[0107] The retention performance and permeation flux of Fe-TA-8 / 10 / 12 membrane for four drugs, amoxicillin (M = 365.4), tetracycline (M = 444.44), rifampicin (M = 822.94) and puerarin (M = 416.38), are shown in Table 2. Figure 7 .

[0108] It can be seen that with the increase of the relative molecular weight of amoxicillin, tetracycline, and rifampicin, the corresponding retention increases in turn. It is worth noting that puerarin has a higher retention than tetracycline with a larger relative molecular weight. This may be because tetracycline contains amino groups with positive charge in its structure. Due to the Donnan effect, the retention will be slightly reduced.

[0109] Among them, the Fe-TA-10 membrane has a retention rate of 98.96% for rifampicin, the drug with the largest molecular weight. This high retention rate provides a strong guarantee for the application of nanofiltration membranes in membrane separation of drugs.

[0110] The present invention provides a rapid and low-cost method, which achieves the effect of separating inorganic salts from organic small molecules by forming a metal phenolic network (MPN) layer through a coordination reaction between tannic acid and iron. During the formation of the MPN layer, sodium hydroxide on the surface of the basement membrane can enrich iron ions on the surface of the basement membrane to fix the iron ions. In addition, alkaline solutions with different pH values ​​can effectively control the aggregation degree of the iron ions. During the coordination reaction, the iron ions are gradually released. Under the acidic condition of tannic acid, the iron hydroxide is released into iron ions and hydroxide. The iron ions are coordinated with the tannic acid, and the hydroxide can adjust the pH of the solution so that the pH of the solution is greater than 7, forming a more stable MPN network structure. Therefore, the aggregation degree of the iron ions can be controlled, thereby preparing a high-density MPN layer, and greatly improving the rejection rate of the nanofiltration membrane for inorganic salts.

[0111] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, and all of these should be included in the scope of the present invention.

Claims

1. A method for improving the separation performance of a nanofiltration membrane by alkali regulation, characterized in that: include, Immersing the PAN film in a NaOH solution and wiping off excess NaOH solution on the surface of the base film to prepare an alkali-treated PAN film, wherein the pH of the NaOH solution is 8-12 and the PAN film is immersed in the NaOH solution for 60 seconds; The alkali-treated PAN membrane was immersed in a ferric chloride solution. After the reaction was completed, the membrane was removed and thoroughly rinsed with deionized water. The concentration of the ferric chloride solution was 4 g / L, and the alkali-treated PAN membrane was immersed in the ferric chloride solution for 60 seconds. TA solution was added to form a selective layer, which was then rinsed with deionized water and dried. The concentration of the TA solution was 4 g / L, and the duration of adding the TA solution was 60 s.

2. The method according to claim 1, wherein: The pH of the NaOH solution is 10.

3. Use of the nanofiltration membrane prepared by the method according to claim 1 or 2 in separating antibiotic drugs.

4. The use according to claim 3, characterized in that: The antibiotic drugs include amoxicillin, tetracycline, and rifampicin.

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