Aperture-adjustable hydrazide-based ultrafiltration membrane and preparation method thereof

Abstract

The invention relates to the technical field of ultrafiltration membranes, and discloses an aperture-adjustable hydrazide-based ultrafiltration membrane and a preparation method thereof.The preparation method comprises the following steps that S1, a hydrazino-containing halomethylated polymer and a long-chain dicarboxylic acid substance are placed in a first organic solvent, and a condensation reaction is conducted to obtain a modified polymer containing a hydrazide bond network structure; s2, dissolving the modified polymer containing the hydrazide bond network structure in a second organic solvent, adding a pore-forming agent to prepare a membrane casting solution, and treating the membrane casting solution by a non-solvent phase inversion method to form a cured membrane; and S3, soaking the cured membrane in an acid solution or an alkali solution, and hydrolyzing to obtain the hydrazide-based ultrafiltration membrane. The ultrafiltration membranes with different separation properties are prepared by constructing a polymer chain containing a hydrazide bond network structure in the membrane and utilizing hydrolysis of hydrazide groups in an acid-base environment and aperture adjustment, the preparation method is simple to operate and can be applied industrially, and the prepared ultrafiltration membranes are high in uniformity and good in separation property.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafiltration membranes, and particularly to a hydrazide-based ultrafiltration membrane with adjustable pore size and a preparation method thereof. Background Art

[0002] Ultrafiltration membranes have the characteristics of simple structure, convenient use, low cost, applicability to various complex and harsh environments, and great savings in space and energy. However, traditional ultrafiltration membranes have certain limitations when facing different separation requirements. Against this background, ultrafiltration membranes with adjustable pore sizes have emerged. They can accurately adapt to diverse substance separation scenarios, bringing a new development direction to the field of separation technology.

[0003] Chinese patent document with publication number CN112058091A discloses a preparation method of a salt-responsive silica membrane with adjustable pore size. This preparation method includes hydrolyzing tetraethyl orthosilicate to prepare monodisperse silica, then reacting it with a silane coupling agent and an initiator, followed by an ATRP reaction with a salt-responsive monomer, etc., and finally depositing it on the surface of the fiber membrane under pressure difference. However, the uniformity of the membrane prepared by this method cannot be guaranteed.

[0004] Chinese patent document with publication number CN106000105A discloses a high-flux nanofiber composite ultrafiltration membrane with adjustable pore size, which is a high-flux nanofiber composite ultrafiltration membrane composed of a polymer nanofiber layer prepared on non-woven fabric as a base layer and natural cellulose nanofibers as a gel layer. By combining electrospinning technology and spin coating method, heat-crosslinked polyacrylic acid / polyvinyl alcohol is used to increase the strength of the membrane, and by adjusting the coating amount of cellulose nanofibers and baking conditions, nanofiber composite ultrafiltration membranes with different pore sizes can be prepared according to actual application needs. However, the preparation process of this method is complex, and it is difficult to realize industrialization. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a hydrazide-based ultrafiltration membrane with adjustable pore size and a preparation method thereof. A polymer chain with a hydrazide bond network structure is constructed inside the membrane, and the pore size is adjusted by using the hydrolysis of hydrazide groups in acidic and alkaline environments, so as to prepare ultrafiltration membranes with different separation performances. The preparation method is simple to operate, can be applied industrially, and the prepared ultrafiltration membranes have high uniformity and good separation performance.

[0006] The specific technical solution of the present invention is as follows: A preparation method of a hydrazide-based ultrafiltration membrane with adjustable pore size includes the following steps: S1: A hydrazide-group-containing halomethylated polymer and a long-chain dicarboxylic acid substance are placed in a first organic solvent, and a condensation reaction is carried out to obtain a modified polymer with a hydrazide bond network structure; S2: Dissolve the modified polymer with a hydrazide bond network structure in a second organic solvent, add a pore-forming agent, and prepare a casting solution. The casting solution is treated by the nonsolvent phase inversion method to form a solidified film. S3: Immerse the solidified film in an acid solution or an alkali solution, and hydrolyze it to obtain a hydrazide-based ultrafiltration membrane.

[0007] Hydrazine is a class of compounds containing -NHNH 2 group. In a specific environment, a carboxylic acid or its derivative can react with a polymer containing a hydrazide group, and then form a hydrazide bond (-CONHNH 2 ). The hydrazide bond can undergo hydrolysis under acidic or alkaline conditions. Based on this property, after constructing polymer chains connected by hydrazide bonds inside the membrane, by precisely controlling the hydrolysis degree of the hydrazide bond under different conditions, ultrafiltration membranes with different pore sizes can be prepared. In the present invention, first, a halomethylated polymer containing a hydrazide group is placed in a specific environment, and a long-chain dicarboxylic acid substance is introduced to generate a modified polymer with a hydrazide bond network structure. Subsequently, using the nonsolvent phase inversion method, the modified polymer is prepared into a relatively dense solidified film. The solidified film is placed in an acid-base solution, and through the hydrolysis process of the hydrazide bond, uniform pores are formed inside the ultrafiltration membrane. By regulating the hydrolysis process and degree of the hydrazide bond, the pore size inside the membrane can be adjusted to prepare ultrafiltration membranes with different separation performances. This preparation method is simple in operation, can be applied industrially, and the hydrolysis process is simple and reliable, efficiently realizing the pore size adjustment of the ultrafiltration membrane. Introducing hydrazide bonds onto the polymer chain finally forms a polymer with an interpenetrating network structure. The solidified film formed in this way has high overall stability and good uniformity. Hydrolysis makes the pores inside the ultrafiltration membrane form uniformly and abundantly, thereby improving the flux and retention performance.

[0008] Optionally, in step S3, the acid solution is selected from hydrochloric acid solution or sulfuric acid solution with a pH value of 4 - 6; the alkali solution is selected from sodium hydroxide solution or potassium hydroxide solution with a pH value of 8 - 10.

[0009] Optionally, in step S3, the soaking time is 2 - 24 h.

[0010] Optionally, in step S1, the molar ratio of the halomethylated polymer containing a hydrazide group to the long-chain dicarboxylic acid substance is 2:1 - 4:1.

[0011] Optionally, in step S1, the long-chain dicarboxylic acid substance is selected from one or more of sebacic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid, and azelaic acid.

[0012] Optionally, the first organic solvent is ethanol.

[0013] Optionally, in step S1, the reaction temperature of the condensation reaction is 50 - 80 °C, and the reaction time is 6 - 24 h.

[0014] Optionally, the condensation reaction uses a polar solvent such as DMSO (dimethyl sulfoxide) or DMF (N,N-dimethylformamide) as a catalyst, and the molar ratio of the long-chain dicarboxylic acid substance to the catalyst is 1:1 - 1:3.

[0015] Optionally, in step S1, the hydrazine-containing halomethylated polymer is obtained by a quaternization reaction of a halomethylated polymer with hydrazine hydrate.

[0016] Optionally, the molar ratio of the halomethylated polymer to hydrazine hydrate is 1:2 - 1:5, the reaction temperature of the quaternization reaction is 40 - 80 °C, and the reaction time is 5 - 60 min.

[0017] Preferably, the molar ratio of the halomethylated polymer to hydrazine hydrate is 1:2 - 1:3, and the reaction time is 5 - 20 min.

[0018] Optionally, the halomethylated polymer is selected from one or more of chloromethylated polyethersulfone, chloromethylated polysulfone, chloromethylated polyether ketone, bromomethylated polyphenylene ether, chloromethylated polyether ether ketone, and chloromethylated polyether ketone ketone.

[0019] Optionally, the halomethylated polymer is obtained by halomethylating a polymer.

[0020] Optionally, the degree of halogen methylation of the halomethylated polymer is 10 - 100%.

[0021] Optionally, in step S2, the pore-forming agent is selected from one or more of ethanol, PEG300, PEG600, and PEG800.

[0022] Optionally, the second organic solvent is DMSO, DMF, or NMP (N-methylpyrrolidone).

[0023] Another specific technical solution of the present invention is: a hydrazide-based ultrafiltration membrane with adjustable pore size, prepared by the above preparation method.

[0024] Compared with the prior art, the present invention has at least the following advantages: In the present invention, a polymer is first introduced into the halo-methyl active sites, and then a quaternization reaction occurs with hydrazine hydrate as an intermediate. Under specific conditions, a long-chain dicarboxylic acid substance is introduced to generate a modified polymer with a hydrazide bond network structure. The network structure is beneficial to forming a relatively dense ultrafiltration membrane structure after curing and shaping. After the hydrolysis of the hydrazide bond, the pores inside the ultrafiltration membrane become more uniform and abundant. By regulating the hydrolysis process and degree of the hydrazide bond, the pore size inside the membrane can be adjusted to prepare ultrafiltration membranes with different separation performances. The preparation method is simple to operate and can be applied industrially. The hydrolysis process is simple and reliable, and the pore size adjustment of the ultrafiltration membrane is efficiently achieved. The cured membrane formed thereby has high overall stability and good uniformity. Hydrolysis makes the pores inside the ultrafiltration membrane uniform and abundant, thereby improving the flux and rejection performance. Description of the Drawings

[0025] Figure 1 It is a scanning electron microscope comparison diagram of the chloromethylated polysulfone membrane of Comparative Example 1 and the hydrazide group ultrafiltration membrane M1-1:2 of Example 1. Detailed Embodiments

[0026] The present invention will be described below through specific examples. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. Without departing from the spirit and scope of the inventive concept, the changes and advantages that can be conceived by those skilled in the art are included in the present invention, and the scope of protection of the present invention is defined by the appended claims and any equivalents thereof.

[0027] Unless otherwise defined, all technical terms and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present disclosure belongs. The raw materials and equipment used in the present invention are conventional raw materials and equipment in the art and can be obtained from conventional commercial channels unless otherwise specified; the methods used in the present invention are conventional methods in the art unless otherwise specified.

[0028] The explanations of the reagents PEG300, PEG600, PEG800, and PEG20000 mentioned below are as follows: PEG is the abbreviation of Polyethylene Glycol, and the following numbers represent their average molecular weights. The above reagents are all commercially available.

[0029] Aqueous solution separation tests were conducted on each example. The test method was as follows: The hydrazide group ultrafiltration membrane was used to conduct separation tests on a 1 g / L PEG20000 aqueous solution at 25 °C and a pressure of 2 bar. The test duration was set to 6 hours of continuous operation. During this period, the flow rate of the permeate was recorded every 30 minutes to calculate the flux of the ultrafiltration membrane. At the same time, before and after the test, feed liquid and permeate samples were collected respectively, and the ultraviolet spectrophotometry was used to measure the concentration of PEG20000, so as to calculate the rejection rate of the ultrafiltration membrane for PEG20000. To ensure the accuracy and reliability of the test data, the tests for each example were repeated 3 times, and the average value was taken as the final test result.

[0030] Example 1: (1) Preparation of halomethylated polymer 1) 18.00 g of polysulfone and 700 mL of chloroform solvent were added to a three-necked flask and stirred until completely dissolved under a constant temperature oil bath at 50 °C; 2) 12.00 g of paraformaldehyde was added to the above solution and stirred continuously for 30 min; 3) Then, 45 mL of trimethylchlorosilane was slowly added dropwise to the above solution and mixed thoroughly; 4) 2.0 mL of stannic chloride catalyst was pre-dissolved in 80 mL of anhydrous chloroform and added to the above reaction for continuous reaction. 5) The reaction time of the above reaction was controlled to be 3 h to obtain a product with a chloromethylation degree of 10%. After the reaction was terminated, the solid was precipitated and purified with absolute ethanol, and then dried at a constant temperature of 60 °C to constant weight to obtain chloromethylated polysulfone for standby; (2) Quaternization process of halomethylated polymer and hydrazine hydrate 1) The prepared chloromethylated polysulfone was immersed in an aqueous solution, and the aqueous solution covered the chloromethylated polysulfone; 2) Four groups of specimens were set according to the molar ratio of chloromethylated polysulfone to hydrazine hydrate of (1:2, 1:3, 1:4, 1:5). For each group of specimens, the corresponding ratio of hydrazine hydrate and chloromethylated polysulfone immersed in the aqueous solution were added to a three-necked flask for reaction. The reaction temperature was 60 °C and the reaction time was 20 min to obtain chloromethylated polysulfone containing hydrazide groups. The chemical general formula of this reaction was: R-CH 2 Cl + N 2 H 4 ·H 2 O → R-CH 2 NHNH 2 + HCl + H 2 O; 3) After the chloromethylated polysulfone containing hydrazide groups was washed repeatedly with deionized water, it was dried at a constant temperature of 50 °C in a vacuum drying oven to constant weight; (3) Condensation reaction process of amino group and long-chain dicarboxylic acid 1) Immerse the hydrazine-group-containing chloromethylated polysulfone in the first organic solvent ethanol solution, and the ethanol solution submerges the hydrazine-group-containing chloromethylated polysulfone. 2) Add it to a three-necked flask according to the molar ratio of hydrazine-group-containing chloromethylated polysulfone to sebacic acid of 2:1. The reaction temperature is 60 °C, and the reaction time is 12 h. DMSO is used as a catalyst during the reaction. The molar ratio of sebacic acid to the catalyst is 1:1.5 to obtain a modified polymer with a hydrazide bond network structure. The chemical general formula of this reaction is: R-(COOH) 2 +2R'-NHNH 2 →R'-NHNHCO-R-CONHNH-R'+2H 2 O; 3) After washing the modified polymer with a hydrazide bond network structure with ethanol multiple times, dry it at a constant temperature of 50 °C in a vacuum drying oven until it reaches a constant weight. (4) Phase inversion membrane preparation process 1) Thoroughly mix the modified polymer with a hydrazide bond network structure, the pore-forming agent ethanol, and the second organic solvent DMSO with a weight ratio of 22:5:73, and react for 8 hours to form a casting solution. 2) Carry out the phase inversion process of the prepared casting solution in deionized water by the non-solvent phase inversion method to form a solidified membrane; (5) Post-hydrolysis process of the ultrafiltration membrane Immerse the solidified membrane in a hydrochloric acid solution with a pH value of 5 for 12 hours, then rinse it with deionized water and dry it to obtain a hydrazide group ultrafiltration membrane.

[0031] Finally, a hydrazide group ultrafiltration membrane M1-a is prepared, where a represents the molar ratio of chloromethylated polysulfone to hydrazine hydrate. The aqueous solution separation test results are shown in Table 1 below: Table 1 Performance comparison of the hydrazide group ultrafiltration membrane prepared in Example 1. Sample Molar ratio of chloromethylated polysulfone to hydrazine hydrate <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 1-1:2 1:2 49.1 92.9 Example 1-1:3 1:3 51.6 88.4 Example 1-1:4 1:4 54.5 79.5 Example 1-1:5 1:5 59.5 75.5

[0032] It should be noted that the selection of chloromethylated polysulfone as the halomethylated polymer in this embodiment is only an example. In other embodiments, chloromethylated polyethersulfone, chloromethylated polyether ketone, bromomethylated polyphenylene ether, chloromethylated polyether ether ketone, chloromethylated polyether ketone ketone, etc. can also be used. Like chloromethylated polysulfone, they all contain halomethylation reaction active sites, and the molecular backbone structures have certain similarities. In the subsequent reaction for preparing the ultrafiltration membrane, they can react with hydrazine hydrate to introduce nitrogen-containing active groups, and then react with long-chain dicarboxylic acid substances to form hydrazide bonds, and finally form a modified polymer with an interpenetrating network structure. In this embodiment, DMSO is selected as the catalyst for the condensation reaction. It can be understood that in other embodiments, polar solvents such as DMF can also be used as the catalyst for the condensation reaction. Since the hydrazide bond can be hydrolyzed under acidic or alkaline conditions, the selection of hydrochloric acid solution in this embodiment is only an example. It can be understood that in other embodiments, sulfuric acid solution, sodium hydroxide solution or potassium hydroxide solution can also be used. In this embodiment, the chloromethylation degree of chloromethylated polysulfone is 10%. When the halomethylation degree is higher, it means that the number of halomethyl groups carried on the molecular chain of the halomethylated polymer is more abundant. In the subsequent quaternization reaction, halomethyl as the active site, the increase in the number can significantly improve the probability of its effective collision and reaction with hydrazine hydrate, which is beneficial to the promotion of the quaternization reaction. Therefore, the halogenomethylation degree range of the halomethylated polymer of the present invention is 10-100%. In this embodiment, DMSO is used as the second organic solvent. It can be understood that in other embodiments, DMF and NMP can also be used.

[0033] Example 2: (1) Preparation of the halomethylated polymer: The same as in Example 1; (2) Quaternization process of the halomethylated polymer and hydrazine hydrate 1) Place the prepared chloromethylated polysulfone in an aqueous solution, and the aqueous solution covers the chloromethylated polysulfone; 2) According to the molar ratio of chloromethylated polysulfone to hydrazine hydrate of 1:2, add hydrazine hydrate and the chloromethylated polysulfone soaked in the aqueous solution to a three-necked flask. The reaction temperature is 60 °C. Set four groups of samples, and the reaction time for each group of samples is (5, 20, 45, 60) min to obtain chloromethylated polysulfone containing hydrazide groups; 3) Wash the chloromethylated polysulfone containing hydrazide groups with deionized water multiple times, and then dry it at a constant temperature of 50 °C in a vacuum drying oven until it reaches a constant weight; (3) Condensation reaction process of the amino group and the long-chain dicarboxylic acid: The same as in Example 1; (4) Phase inversion membrane preparation process: The same as in Example 1; (5) Post-hydrolysis process of the ultrafiltration membrane: The same as in Example 1.

[0034] Finally, the hydrazide - based ultrafiltration membrane M2 - b was obtained, where b represents the reaction time of chloromethylated polysulfone and hydrazine hydrate. The separation test results are shown in Table 2 below: Table 2 Performance comparison of the hydrazide - based ultrafiltration membrane prepared in Example 2.

[0035] Example 3: (1) Preparation of the halomethylated polymer: The same as in Example 1; (2) Quaternization process of the halomethylated polymer and hydrazine hydrate 1) Place the prepared chloromethylated polysulfone in an aqueous solution, and the aqueous solution covers the chloromethylated polysulfone; 2) According to the molar ratio of chloromethylated polysulfone to hydrazine hydrate of 1:2, add the mixture of chloromethylated polysulfone and water and hydrazine hydrate to a three - necked flask. The reaction temperature is 60 °C and the reaction time is 30 min to obtain chloromethylated polysulfone containing hydrazide groups; 3) Wash the chloromethylated polysulfone containing hydrazide groups with deionized water multiple times, and then dry it at a constant temperature of 50 °C in a vacuum drying oven until it reaches a constant weight; (3) Condensation reaction process of amino groups and long - chain dicarboxylic acids 1) Immerse the chloromethylated polysulfone containing hydrazide groups in an ethanol solution of the first organic solvent, and the ethanol solution covers the chloromethylated polysulfone containing hydrazide groups; 2) Set three groups of samples according to the molar ratio of chloromethylated polysulfone containing hydrazide groups to sebacic acid of (2:1, 3:1, 4:1). For each group of samples, add the corresponding ratio of chloromethylated polysulfone containing hydrazide groups and sebacic acid to a three - necked flask. The reaction temperature is 60 °C and the reaction time is 12 h. DMSO is used as a catalyst during the reaction, and the molar ratio of sebacic acid to the catalyst is 1:1.5 to obtain a modified polymer with a hydrazide - bond network structure; 3) Wash the modified polymer with a hydrazide - bond network structure with ethanol multiple times, and then dry it at a constant temperature of 50 °C in a vacuum drying oven until it reaches a constant weight; (4) Phase - inversion membrane - forming process: The same as in Example 1; (5) Post - hydrolysis process of the ultrafiltration membrane: The same as in Example 1.

[0036] Finally, the hydrazide - based ultrafiltration membrane M3 - c was obtained, where c represents the molar ratio of the polymer to sebacic acid. The separation test results are shown in Table 3 below: Table 3 Performance comparison of the hydrazide - based ultrafiltration membrane prepared in Example 3.

[0037] Example 4: (1) Preparation of the halomethylated polymer: The same as in Example 1; (2) Quaternization process of halomethylated polymer and hydrazine hydrate: same as Example 3; (3) Condensation reaction process of amino group and long-chain dicarboxylic acid 1) Immerse the hydrazine group-containing chloromethylated polysulfone in the first organic solvent ethanol solution, and the ethanol solution covers the hydrazine group-containing chloromethylated polysulfone; 2) Take three groups of hydrazine group-containing chloromethylated polysulfone and add them to a three-necked flask. According to the molar ratio of hydrazine group-containing chloromethylated polysulfone to long-chain dicarboxylic acid of 2:1, add long-chain dicarboxylic acid for reaction. The reaction temperature is 60 °C, the reaction time is 12 h, and DMSO is used as a catalyst during the reaction. The molar ratio of long-chain dicarboxylic acid to the catalyst is 1:1.5 to obtain a modified polymer with a hydrazide bond network structure, where each group of long-chain dicarboxylic acids is sebacic acid, dodecanedioic acid, and tetradecanedioic acid respectively; 3) Wash the modified polymer with a hydrazide bond network structure with ethanol multiple times, and then dry it at a constant temperature of 50 °C in a vacuum drying oven until it reaches a constant weight; (4) Phase inversion membrane preparation process: same as Example 1; (5) Post-hydrolysis process of ultrafiltration membrane: same as Example 1.

[0038] Finally, a hydrazide group ultrafiltration membrane M4-d is prepared, where d represents the type of long-chain dicarboxylic acid. The separation test results are shown in Table 4 below: Table 4 Performance comparison of the hydrazide group ultrafiltration membrane prepared in Example 4. Sample Type of long-chain dicarboxylic acid <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 4 - Sebacic acid Sebacic acid 49.1 92.9 Example 4 - Dodecanedioic acid Dodecanedioic acid 54.8 86.5 Example 4 - Tetradecanedioic acid Tetradecanedioic acid 58.5 81.3

[0039] It should be noted that this example verifies that when sebacic acid, dodecanedioic acid, and tetradecanedioic acid participate in the reaction as long-chain dicarboxylic acids, a hydrazide group ultrafiltration membrane with excellent separation performance can be successfully prepared. This is because during the reaction of these long-chain dicarboxylic acids with polymers containing nitrogen active groups to form hydrazide bonds, their molecular structures and chemical properties can promote the reasonable construction of the interpenetrating network structure, thereby endowing the ultrafiltration membrane with good separation performance. It can be understood that hexadecanedioic acid, octadecanedioic acid, and azelaic acid with similar structural characteristics can also produce similar chemical reaction processes and results.

[0040] Example 5: (1) Preparation of halomethylated polymer: same as Example 1; (2) Quaternization process of halomethylated polymer and hydrazine hydrate: same as Example 3; (3) Condensation reaction process of amino group and long-chain dicarboxylic acid 1) Immerse the hydrazine group-containing chloromethylated polysulfone in the first organic solvent ethanol solution, and the ethanol solution covers the hydrazine group-containing chloromethylated polysulfone; (2) Add the chloromethylated polysulfone containing hydrazino groups and sebacic acid into a three-necked flask according to the molar ratio of 2:1. The reaction temperature is 60 °C and the reaction time is 12 h. DMSO is used as the catalyst during the reaction. The molar ratio of sebacic acid to the catalyst is 1:1.5 to obtain a modified polymer with a hydrazide bond network structure; (3) Wash the obtained modified polymer with a hydrazide bond network structure multiple times with ethanol and then dry it at a constant temperature of 50 °C in a vacuum drying oven until a constant weight is achieved; (4) Phase inversion membrane formation process (1) Divide the modified polymer with a hydrazide bond network structure into four groups. Add a pore former and an organic solvent DMSO to each group and mix them thoroughly for 8 hours to form a casting solution. The weight ratio of the modified polymer with a hydrazide bond network structure, the pore former, and the organic solvent DMSO in each group is 22:5:73. The pore formers are ethanol, PEG300, PEG600, and PEG800 respectively; (2) Carry out the phase inversion process of the prepared casting solution in deionized water by the non-solvent phase inversion method to form a solidified membrane; (5) Post-hydrolysis process of the ultrafiltration membrane: the same as in Example 1.

[0041] Finally, a hydrazide group ultrafiltration membrane M5-e is prepared, where e represents the type of pore former. The separation test results are shown in Table 5 below: Table 5 Performance comparison of the hydrazide group ultrafiltration membranes prepared in Example 5. Sample Type of pore-forming agent <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 5 - Ethanol Ethanol 49.1 92.9 Example 5 - PEG300 PEG300 51.8 90.3 Example 5 - PEG600 PEG600 52.6 88.6 Example 5 - PEG800 PEG800 52.9 88.0

[0042] Example 6: (1) Preparation of the halomethylated polymer: the same as in Example 1; (2) Quaternization process of the halomethylated polymer and hydrazine hydrate: the same as in Example 3; (3) Condensation reaction process of the amino group and the long-chain dicarboxylic acid: the same as in Example 1; (4) Phase inversion membrane formation process: the same as in Example 1; (5) Post-hydrolysis process of the ultrafiltration membrane: Divide the solidified membrane into three groups and soak them in hydrochloric acid solutions with pH values of (4, 5, 6) for 12 hours respectively, then rinse them with deionized water and dry them to obtain hydrazide group ultrafiltration membranes.

[0043] Finally, a hydrazide group ultrafiltration membrane M6-f is prepared, where f represents the pH value of the hydrochloric acid solution. The separation test results are shown in Table 6 below: Table 6 Performance comparison of the hydrazide group ultrafiltration membranes prepared in Example 6. Sample pH value of hydrochloric acid solution <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 6-4 4 52.3 87.2 Example 6-5 5 49.1 92.9 Example 6-6 6 47.6 93.6

[0044] Example 7: (1) Preparation of the halomethylated polymer: the same as in Example 1; (2) Quaternization process of halomethylated polymer and hydrazine hydrate: same as Example 3; (3) Condensation reaction process of amino group and long-chain dicarboxylic acid: same as Example 1; (4) Membrane formation process by phase inversion: same as Example 1; (5) Post-hydrolysis process of ultrafiltration membrane: The cured membranes were divided into three groups and immersed in sodium hydroxide solutions with pH values of (8, 9, 10) for 12 hours respectively, then rinsed with deionized water and dried to obtain hydrazide group ultrafiltration membranes.

[0045] Finally, the hydrazide group ultrafiltration membrane M7-g was prepared, where g represents the pH value of the sodium hydroxide solution. The separation test results are shown in Table 7 below: Table 7 Performance comparison of the hydrazide group ultrafiltration membranes prepared in Example 7. Sample pH value of sodium hydroxide solution <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 7-8 8 46.1 93.8 Example 7-9 9 50.9 91.6 Example 7-10 10 52.5 90.3

[0046] Example 8: (1) Preparation of halomethylated polymer: same as Example 1; (2) Quaternization process of halomethylated polymer and hydrazine hydrate: same as Example 3; (3) Condensation reaction process of amino group and long-chain dicarboxylic acid: same as Example 1; (4) Membrane formation process by phase inversion: same as Example 1; (5) Post-hydrolysis process of ultrafiltration membrane: The cured membranes were divided into five groups and immersed in hydrochloric acid solution with a pH value of 5. The immersion time for each group was (2, 6, 12, 18, 24) hours respectively. After immersion, they were rinsed with deionized water and dried to obtain hydrazide group ultrafiltration membranes.

[0047] Finally, the hydrazide group ultrafiltration membrane M8-h was prepared, where h represents the immersion time in hydrochloric acid solution. The separation test results are shown in Table 8 below: Table 8 Performance comparison of the hydrazide group ultrafiltration membranes prepared in Example 8. Sample Immersion time in hydrochloric acid solution <![CDATA[Flux (L·m -2 ·h -1 ·bar -1 )]]> Rejection rate (%) Example 8-2 2 44.9 94.6 Example 8-6 6 47.6 93.2 Example 8-12 12 49.1 92.9 Example 8-18 18 54.3 87.6 Example 8-24 24 59.6 84.6

[0048] As can be seen from Tables 1 to 8: The present invention designs and prepares a hydrazide group ultrafiltration membrane with acid-base triggered adjustable pore size, which can flexibly adjust the pore size inside the membrane by controlling the hydrolysis process and degree of hydrazide bonds, forming ultrafiltration membranes with different separation performances to meet diverse actual application requirements. After testing, the hydrazide group ultrafiltration membrane has a high rejection rate and flux.

[0049] Comparative Example 1 (1) Preparation of halomethylated polymer 1) 18.00 g of polysulfone and 700 mL of chloroform solvent were added to a three-necked flask and stirred at 50 °C in a constant-temperature oil bath until completely dissolved; 2) 12.00 g of paraformaldehyde was added to the above solution and continuously stirred for 30 min; 3) Then 45 mL of trimethylchlorosilane was slowly added dropwise to the above solution and thoroughly mixed; 4) 2.0 mL of stannic chloride catalyst was pre-dissolved in 80 mL of anhydrous chloroform and added to the above reaction for continuous reaction; 5) The reaction time of the above reaction was controlled to be 3 h to obtain a product with a chloromethylation degree of 10%. After the reaction was terminated, the solid was precipitated and purified with absolute ethanol, and then dried at 60 °C in a constant temperature until constant weight to obtain chloromethylated polysulfone; (2) Phase inversion membrane preparation process 1) Chloromethylated polysulfone, pore-forming agent ethanol, and organic solvent DMSO with a weight ratio of 22:5:73 were thoroughly mixed and reacted for 8 hours to form a casting solution; 2) The prepared casting solution was subjected to a phase inversion process in deionized water by the non-solvent phase inversion method. After the phase inversion was completed, the obtained membrane was taken out of the deionized water and dried to obtain a chloromethylated polysulfone membrane.

[0050] Comparing the chloromethylated polysulfone membrane and the hydrazide group ultrafiltration membrane M1-1:2 prepared in Example 1, the microscopic structure was observed by scanning electron microscopy (SEM) technology, and the results were as Figure 1 shown. The membrane prepared in Comparative Example 1 had finger-like pores, a relatively large porosity, and a non-uniform pore size distribution. The hydrazide group ultrafiltration membrane M1-1:2 prepared in Example 1 hardly showed obvious large pore structures, and the overall structure was denser, showing a stronger interception ability.

[0051] In the present invention, the raw materials and equipment used, unless otherwise specified, are common raw materials and equipment in the art; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0052] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size, characterized in that: The following steps are involved: S1: placing a hydrazine-containing halomethyl polymer and a long-chain dicarboxylic acid substance in a first organic solvent to undergo a condensation reaction to obtain a modified polymer containing a hydrazide bond network structure; S2: dissolving the modified polymer containing a hydrazide bond network structure in a second organic solvent, adding a pore-forming agent to prepare a casting solution, and treating the casting solution by a non-solvent phase conversion method to form a solidified film; S3: Soaking the solidified membrane in an acid solution or an alkaline solution, and obtaining a hydrazide-based ultrafiltration membrane through hydrolysis.

2. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S3, the acid solution is selected from a hydrochloric acid solution or a sulfuric acid solution with a pH value of 4-6; the alkaline solution is selected from a sodium hydroxide solution or a potassium hydroxide solution with a pH value of 8-10.

3. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S3, the soaking time is 2-24 hours.

4. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S1, the molar ratio of the hydrazine-containing halomethyl polymer to the long-chain dicarboxylic acid is 2:1-4:

1.

5. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S1, the long-chain dicarboxylic acid substance is selected from one or more of sebacic acid, dodecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, octadecanedioic acid and azelaic acid; and the first organic solvent is ethanol.

6. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S1, the reaction temperature of the condensation reaction is 50-80°C, and the reaction time is 6-24h; the condensation reaction uses DMSO or DMF polar solvent as a catalyst, and the molar ratio of the long-chain dicarboxylic acid substance to the catalyst is 1:1-1:

3.

7. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 1, characterized in that: In step S1, the hydrazine group-containing halomethylated polymer is obtained by quaternization reaction of the halomethylated polymer and hydrazine hydrate, wherein the molar ratio of the halomethylated polymer to the hydrazine hydrate is 1:2-1:5, the reaction temperature of the quaternization reaction is 40-80°C, and the reaction time is 5-60min.

8. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to claim 7, characterized in that: The halomethylated polymer is selected from one or more of chloromethylated polyethersulfone, chloromethylated polysulfone, chloromethylated polyetherketone, bromomethylated polyphenylene ether, chloromethylated polyetheretherketone and chloromethylated polyetherketoneketone; the halomethylation degree of the halomethylated polymer is 10-100%.

9. The method for preparing a hydrazide-based ultrafiltration membrane with adjustable pore size according to any one of claims 1 to 8, characterized in that: In step S2, the pore-forming agent is selected from one or more of ethanol, PEG300, PEG600 and PEG800; and the second organic solvent is DMSO, DMF or NMP.

10. A hydrazide-based ultrafiltration membrane with adjustable pore size, characterized in that: The method is described in any one of claims 1 to 9.

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