Heavy metal enriched block polymer nanofiltration membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane preparation, and discloses a heavy metal enriched block polymer nanofiltration membrane and a preparation method thereof, and the preparation method comprises the following steps: constructing an ultrafiltration base membrane: synthesizing block structure polymers with different hydrophilic / hydrophobic chain segment proportions by controlling the proportion of sulfonated polyether sulfone (SPES-F) oligomer and polyether sulfone (PES-OH) oligomer; finally, the base membrane with uniform pore diameter, high flux and strong stability is constructed; and interface polymerization modification: generating a compact and ordered latticed separation layer on the surface of the hydrophilic base membrane by adopting interface polymerization (IP). The ultrathin skin layer is constructed by regulating and controlling the microstructure of the skin layer, and the structural stability of the base membrane and the skin layer is cooperatively regulated and controlled, so that the short-distance low-resistance and effective screening function of the thin skin layer is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane preparation, and in particular relates to a heavy metal-enriched block polymer nanofiltration membrane and a preparation method thereof. Background Art

[0002] With the acceleration of the global industrialization process, the problem of heavy metal pollution has become increasingly severe and has become one of the core challenges in global water environment governance. Heavy metal ions such as Hg 2+ , Pb 2+ , Cd 2+ , Cu 2+ released during the treatment of industrial wastewater, mining waste liquid and electronic waste pose a serious threat to the ecosystem and human health due to their high toxicity, non-degradability and bioaccumulation. These heavy metal ions not only directly damage the living environment of aquatic organisms, leading to the imbalance of the water ecosystem, but may also accumulate in the human body through the food chain, ultimately causing various diseases and endangering life and health.

[0003] Traditional heavy metal separation technologies such as chemical precipitation, ion exchange and adsorption have many problems in practical applications. Although the chemical precipitation method is relatively simple to operate, it will produce a large amount of sludge, which may cause secondary pollution if not properly treated, and the removal effect on low-concentration heavy metal ions is not good. The ion exchange method has a high selectivity for heavy metal ions, but the regeneration process of ion exchange resin is complex, the cost is high, and the service life of the resin is limited. Although the adsorption method has a certain removal effect, the selection and regeneration of adsorbents are also difficult, and the adsorption capacity is limited and the efficiency is low.

[0004] In contrast, membrane separation technology has gradually become the mainstream solution for heavy metal treatment due to its advantages such as high efficiency, energy saving and no chemical addition. Membrane separation technology can be carried out at room temperature, with low energy consumption, and will not introduce new chemical substances, avoiding secondary pollution. At the same time, membrane separation technology has a high separation efficiency and can effectively remove heavy metal ions in water. However, the existing membrane materials still have significant bottlenecks in terms of selectivity, stability and anti-pollution performance. For example, some membrane materials have low selectivity for different heavy metal ions and cannot achieve effective separation; some membrane materials are prone to performance degradation during long-term use and have poor stability; some membrane materials are easily contaminated, resulting in a decrease in flux and affecting the separation effect.

[0005] Therefore, it is necessary to develop a new type of composite nanofiltration membrane that can achieve heavy metal enrichment and separation at a relatively low cost to meet the huge demand in practical applications. This new type of composite nanofiltration membrane should have high selectivity, high stability and good anti-pollution performance, and be able to effectively separate and enrich heavy metal ions in a complex water environment, providing an efficient, economical and sustainable solution for solving the problem of heavy metal pollution in the global water environment. Summary of the Invention

[0006] In order to solve the above-mentioned technical problems existing in the current heavy metal enrichment and separation, the present invention provides an efficient, stable and low-cost solution to prepare a heavy metal-enriched block polymer nanofiltration membrane.

[0007] Block polymer membranes have become a research hotspot in recent years due to their designable microphase separation structure, high porosity and surface functionalization potential. Their block structure can form uniform nanopores by regulating the ratio of hydrophilic / hydrophobic segments, and have both high flux and selectivity. The interfacial polymerization technology generates a dense functional layer by in-situ reaction of monomers on the surface of the substrate membrane, which can significantly improve the separation performance. In addition, the interfacial compatibility can be improved by swelling the substrate membrane to interpenetrate the interfacial polymerization molecules and the polymer segments of the substrate membrane, and the interfacial compatibility stability can be further increased by using ionic / covalent crosslinking between the active groups of the two interfacial polymers.

[0008] The present invention proposes an innovative solution of "block polymer substrate membrane + interfacial polymerization modification" to prepare a heavy metal-enriched block polymer nanofiltration membrane.

[0009] Construct an ultrafiltration substrate membrane: By controlling the ratio of sulfonated polyethersulfone (SPES-F) oligomers and polyethersulfone (PES-OH) oligomers, a block-structured polymer with different hydrophilic / hydrophobic segment ratios is synthesized, and finally a substrate membrane with uniform pore size, high flux and strong stability is constructed.

[0010] Interfacial polymerization modification: On the surface of the hydrophilic substrate membrane, interfacial polymerization (IP) is used to generate a dense and ordered grid-like separation layer. By regulating the microstructure of the skin layer, an ultra-thin skin layer is constructed, and the structural stability of the substrate membrane and the skin layer is synergistically regulated to achieve the functions of short-range low resistance and effective screening of the thin skin layer.

[0011] This method can break through the functional limitations of traditional membrane materials and provide an efficient, stable and low-cost separation membrane for heavy metal separation.

[0012] The specific technical solution is as follows:

[0013] A method for preparing a heavy metal-enriched block polymer nanofiltration membrane, comprising the following steps:

[0014] (1) Preparation of block polymer SPES-b-PES

[0015] The oligomer PES-OH with -OH end groups as described in formula (I) and the oligomer SPES-F with -F end groups and amino groups in the side chain as described in formula (II) are added to a solution with NMP as the solvent, toluene as the water-carrying agent and potassium carbonate as the catalyst in a certain proportion, and in N 2The reaction was heated with a programmed temperature increase in an atmosphere for a certain period of time, and then the obtained polymer solution was precipitated into deionized water. Finally, it was dried to obtain a polymer solid, which was the block polymer SPES-b-PES. By controlling the mass ratio of SPES-F and PES-OH, block polymers X-a as described in formula (III) with different hydrophilic / hydrophobic segment ratios were obtained, where a was the molar percentage of SPES-F in SPES-F and PES-OH.

[0016]

[0017] (2) Preparation of basic monomers

[0018] 1-BOC-4-methylpiperazine and potassium carbonate were dissolved in acetonitrile and heated with stirring for a certain period of time. Then, 1,6-dibromohexane was added to the solution, and the resulting mixture was heated for reaction and maintained under reflux. After a certain period of time, the obtained pale yellow solid was dissolved in hydrobromic acid and allowed to stand under constant temperature for a certain period of time. Subsequently, it was precipitated in ethanol, filtered, and washed with an excess of diethyl ether. The obtained white solid was dried to obtain the BPIP6 monomer. 1,6-Dibromohexane was replaced with straight-chain dibromo substituents or brominated benzene rings with different chain lengths to prepare basic monomers with different structures. The structural formulas of the prepared BPIPn and TPIPn monomers were as shown in formula (IV) and (V), where n was the number of carbon atoms in the carbon chain of the monomer.

[0019]

[0020] (3) Preparation of block-structured base membranes

[0021] Different block polymers X-a and DMSO were selected to prepare a casting solution in a certain proportion, heated and stirred for several hours, and a homogeneous casting solution was obtained after complete dissolution. Then, it was placed in a dryer at room temperature to defoam for a certain period of time. Controlling the environmental temperature and humidity, the casting solution was evenly poured onto the non-woven fabric, and a stainless steel scraper was used to scrape it into a film and placed in the air for a certain period of time. Subsequently, the scraped film was transferred to a deionized water coagulation bath for phase inversion to form a film. After a certain period of time, the non-woven fabric was removed to obtain the corresponding block-structured base membrane.

[0022] (4) Interfacial polymerization modification

[0023] The prepared base membrane was placed in a jacket, and an aqueous solution of a certain concentration of BPIPn or TPIPn was evenly poured on the top of the prepared base membrane. After maintaining for a certain period of time, the excess solution was drained, and a n-hexane solution of a certain concentration of TMC was poured in. After heating and curing, a grid-like polyamide layer as shown in formula (VI) was formed on the surface of the base membrane.

[0024]

[0026] Preferably, in step (1), the volume ratio of the solvent NMP to toluene is 2:1.

[0027] Preferably, in step (1), the programmed temperature heating reaction conditions are first 140 °C for 4 h, and then changed to 160 °C for 12 h.

[0028] Preferably, in step (2), the molar ratio of 1-BOC-4-methylpiperazine: potassium carbonate: 1,6-dibromohexane is = 5:5:2.

[0029] Preferably, in step (2), the stirring temperature is 40 - 60 °C, the stirring time is 0.5 h, and more preferably 50 °C.

[0030] Preferably, in step (2), the reaction temperature is 60 - 100 °C, the reaction time is 12 - 24 h, and more preferably 80 °C for 24 h.

[0031] Preferably, in step (3), the mass ratio of the block polymer X-a to DMSO in the casting solution is 7:93.

[0032] Preferably, in step (3), the stirring temperature of the casting solution is 50 - 80 °C, the heating time is 4 - 6 h, and more preferably 70 °C for 6 h.

[0033] Preferably, in step (3), the static defoaming time is 6 - 24 h, and more preferably 12 h.

[0034] Preferably, in step (3), the environmental temperature and humidity are 18 - 25 °C and 20 - 50 RH% respectively, and more preferably 25 °C and 40 RH%.

[0035] Preferably, in step (3), the air bath time is 0 - 60 s, and more preferably 30 s.

[0036] Preferably, in step (3), the gap of the doctor blade is 100 - 200 μm, and more preferably 150 μm.

[0037] Preferably, in step (3), the temperature of the deionized water coagulation bath is 15 - 25 °C, and more preferably 25 °C.

[0038] Preferably, in step (3), the phase inversion time is 5 - 10 min, and more preferably 8 min.

[0039] Preferably, in step (4), the concentration of BPIP6 is 0.1 wt.% - 2 wt.%, the soaking time is 10 - 30 min, and more preferably 1.2 wt.% for 30 min.

[0040] Preferably, the concentration of TPIP3 in step (4) is 0.1 wt.% to 2 wt.%, and the soaking time is 10 to 20 min, more preferably 1.0 wt.% and 10 min.

[0041] Preferably, the concentration of TMC in step (4) is 0.1 wt.% to 2 wt.%, and the soaking time is 1 to 10 min, more preferably 0.5 wt.% and 10 min.

[0042] Preferably, the curing temperature in step (4) is 50 to 80 °C, and the time is 5 to 15 min, more preferably 70 °C and 10 min.

[0043] A heavy metal-enriched block polymer nanofiltration membrane is prepared by the above preparation method.

[0044] The composite nanofiltration membrane prepared by the present invention has the advantages of excellent heavy metal ion selectivity and stability, good hydrophilicity and antifouling property, and low cost, and has broad application prospects in practical applications involving the treatment of various heavy metal components such as industrial wastewater.

[0045] Compared with the prior art, the advantages of the present invention are as follows:

[0046] 1. By regulating the hydrophilic-hydrophobic block ratio, the phase inversion method induces microphase separation to form an ultrafiltration membrane substrate with uniform pore size and high porosity, effectively reducing the mass transfer resistance, achieving ultrafiltration-level high flux, antifouling and long life, and at the same time providing effective support for the separation layer to improve the overall stability of the composite membrane.

[0047] 2. Through the molecular chain interpenetration mechanism induced by the swelling of the substrate membrane, physical entanglement networks are formed between the monomers and the polymer chains of the substrate membrane during the interfacial polymerization process. At the same time, crosslinking reactions construct valence bond bonding anchor points at the interface to form an "interpenetrating-crosslinking" double-locking structure. This design can effectively inhibit the problem of interlayer peeling and falling off of traditional composite membranes, significantly improving the bonding strength between the skin layer and the substrate membrane, and maintaining a complete interface under high pressure and alternating acid-base environments.

[0048] 3. Through precise regulation of the hydrophilic / hydrophobic chain segment ratio of the block polymer substrate membrane, combined with the ultrathin dense skin layer generated by interfacial polymerization, the synergistic effect of "large-size substrate membrane ion channels + short-range sieving skin layer" is achieved. The sulfonic acid groups (-SO 3 H) and amino groups (-NH) of the substrate membrane provide heavy metal adsorption sites, while the grid structure of the separation layer enhances selective sieving, breaking through the contradiction between selectivity and flux of traditional membrane materials. Description of the Drawings

[0049] Figure 1 It is a schematic diagram of interfacial polymerization modification. Detailed Embodiments

[0050] To further illustrate the technical solution of the present invention, the preferred implementation of the present invention will be described below in conjunction with some specific embodiments. However, it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than a limitation on the claims of the present invention.

[0051] Preparation of block polymer SPES-b-PES

[0052] The oligomer PES-OH with -OH end groups as described in formula (I) and the oligomer SPES-F with -F end groups and amino groups in the side chain as described in formula (II) are added to a solution with NMP as the solvent, toluene as the water-carrying agent, and potassium carbonate as the catalyst in a certain proportion. Under a nitrogen 2 atmosphere, the temperature is raised stepwise and heated for a certain time. Then, the obtained polymer solution is precipitated into deionized water and finally dried to obtain a polymer solid, which is the block polymer SPES-b-PES. By controlling the mass ratio of SPES-F and PES-OH, block polymers X-a as described in formula (III) with different hydrophilic / hydrophobic segment ratios are obtained, where a is the molar percentage of SPES-F in SPES-F and PES-OH.

[0053]

[0054] Preparation of basic monomers

[0055] 1-BOC-4-methylpiperazine and potassium carbonate are dissolved in acetonitrile and heated with stirring for a certain time. Then, 1,6-dibromohexane is added to the solution, and the obtained mixture is heated to react and kept under reflux. After a certain time, the obtained pale yellow solid is dissolved in hydrobromic acid and allowed to stand for a certain time under constant temperature conditions. Subsequently, it is precipitated in ethanol, filtered, and washed with an excess of diethyl ether. The obtained white solid is dried to obtain the BPIP6 monomer. By replacing 1,6-dibromohexane with straight-chain dibromo substituents or benzene ring bromo substituents with different chain lengths, basic monomers with different structures are prepared. The structural schematic diagrams of the BPIPn and TPIPn monomers prepared by replacing different bromo compounds are shown in (IV) and (V), where n is the number of carbon atoms in the carbon chain of the monomer.

[0056]

[0057] Example 1

[0058] Prepare a casting solution by mixing X-40 and DMSO at a mass ratio of 12:88. Stir the casting solution at 70 °C for 6 h, then place it in a dryer at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 10 s. Then, put the scraped film into a 10 °C deionized water coagulation bath for phase inversion to form a film, and take out the film after 5 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 2.0 wt.% aqueous solution of TPIP3, remove the surface TPIP3 aqueous solution after 10 min, add a 2.0 wt.% hexane solution of TMC to the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 50 °C for 15 min to obtain the finished film, as Figure 1 shown.

[0059] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0060] Example 2

[0061] Prepare a casting solution by mixing X-40 and DMSO at a mass ratio of 10:90. Stir the casting solution at 70 °C for 6 h, then place it in a dryer at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 30 s. Then, put the scraped film into a 15 °C deionized water coagulation bath for phase inversion to form a film, and take out the film after 8 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 1.5 wt.% aqueous solution of BPIP6, remove the surface BPIP6 aqueous solution after 10 min, add a 1.0 wt.% hexane solution of TMC to the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 60 °C for 10 min to obtain the finished film.

[0062] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0063] Example 3

[0064] The casting solution was prepared by mixing X-40 and DMSO in a mass ratio of 7:93. The casting solution was stirred and reacted at 60 °C for 5 h, and then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. The preparation process strictly controlled the environmental temperature and humidity at 25 °C and 40 RH%. The casting solution was evenly poured onto the non-woven fabric, and the gap of the doctor blade was controlled at 150 μm to scrape it into a film and placed in the air for 50 s. Then, the scraped film was put into a 20 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 8 min. Subsequently, the prepared bottom film was taken out and clamped into the jacket, and 1.5 wt.% aqueous solution of TPIP6 was poured in. After 10 min, the surface TPIP6 aqueous solution was removed, and a n-hexane solution of 1.0 wt.% TMC was added to the surface. After the IP reaction for 10 min, the excess solution on the surface was removed, and the film was cured at 60 °C for 10 min to obtain the finished film.

[0065] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0066] Example 4

[0067] Prepare a casting solution by mixing X-40 and DMSO at a mass ratio of 5:95. Stir the casting solution at 60 °C for 5 h, then place it in a desiccator at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 60 s. Then, put the scraped film into a 25 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 10 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 0.5 wt.% aqueous solution of BPIP6, remove the surface BPIP6 aqueous solution after 10 min, add a n-hexane solution of 0.1 wt.% TMC on the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 80 °C for 5 min to obtain the finished film.

[0068] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0069] Example 5

[0070] Prepare a casting solution by mixing X-50 and DMSO at a mass ratio of 12:88. Stir the casting solution at 70 °C for 6 h, then place it in a desiccator at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 10 s. Then, put the scraped film into a 10 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 5 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 2.0 wt.% aqueous solution of TPIP3, remove the surface TPIP3 aqueous solution after 10 min, add a n-hexane solution of 2.0 wt.% TMC on the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 50 °C for 15 min to obtain the finished film.

[0071] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0072] Example 6

[0073] The casting solution was prepared by mixing X-50 and DMSO at a mass ratio of 10:90. The casting solution was stirred and reacted at 70 °C for 6 h, and then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%. The casting solution was evenly poured onto the non-woven fabric, and the gap of the doctor blade was controlled at 150 μm to scrape it into a film and placed in the air for 30 s. Then, the scraped film was put into a 15 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 8 min. Subsequently, the prepared bottom film was taken out and clamped into the jacket, and 1.5 wt.% BPIP6 aqueous solution was poured in. After 10 min, the surface BPIP6 aqueous solution was removed, and a n-hexane solution containing 1.0 wt.% TMC was added to the surface. After 10 min of IP reaction, the excess solution on the surface was removed, and the film was cured at 60 °C for 10 min to obtain the finished film.

[0074] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0075] Example 7

[0076] The casting solution was prepared by mixing X-50 and DMSO at a mass ratio of 7:93. The casting solution was stirred and reacted at 60 °C for 5 h, then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%, the casting solution was evenly poured onto the non-woven fabric, and the gap of the film scraping knife was controlled at 150 μm to scrape it into a film and placed in the air for 50 s. Then, the scraped film was put into a 20 °C deionized water coagulation bath for phase inversion film formation, and the film was taken out after 8 min. Subsequently, the prepared bottom film was clamped into the jacket, 1.2 wt.% aqueous solution of TPIP6 was poured in, the surface TPIP6 aqueous solution was removed after 10 min, a n-hexane solution containing 0.5 wt.% TMC was added to the surface, the excess solution on the surface was removed after 10 min of IP reaction, and the finished film was obtained after curing at 70 °C for 10 min.

[0077] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0078] Example 8

[0079] The casting solution was prepared by mixing X-50 and DMSO at a mass ratio of 5:95. The casting solution was stirred and reacted at 60 °C for 5 h, then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. During the preparation process, the environmental temperature and humidity were strictly controlled at 25 °C and 40RH%, the casting solution was evenly poured onto the non-woven fabric, and the gap of the film scraping knife was controlled at 150 μm to scrape it into a film and placed in the air for 60 s. Then, the scraped film was put into a 25 °C deionized water coagulation bath for phase inversion film formation, and the film was taken out after 10 min. Subsequently, the prepared bottom film was clamped into the jacket, 0.5 wt.% aqueous solution of BPIP6 was poured in, the surface BPIP6 aqueous solution was removed after 10 min, a n-hexane solution containing 0.1 wt.% TMC was added to the surface, the excess solution on the surface was removed after 10 min of IP reaction, and the finished film was obtained after curing at 80 °C for 5 min.

[0080] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0081] Example 9

[0082] The casting solution was prepared by mixing X-60 and DMSO at a mass ratio of 12:88. The casting solution was stirred and reacted at 70 °C for 6 h, and then degassed in a dryer at room temperature for 12 h to obtain a homogeneous casting solution. The preparation process strictly controlled the environmental temperature and humidity at 25 °C and 40 RH%. The casting solution was evenly poured onto the non-woven fabric, and the gap of the doctor blade was controlled at 150 μm to scrape it into a film and placed in the air for 10 s. Then, the scraped film was put into a 10 °C deionized water coagulation bath for phase inversion to form a film, and the film was taken out after 5 min. Subsequently, the prepared bottom film was taken out and clamped into the jacket, and 2.0 wt.% of the TPIP3 aqueous solution was poured in. After 10 min, the surface TPIP3 aqueous solution was removed, and a 2.0 wt.% TMC n-hexane solution was added to the surface. After the IP reaction for 10 min, the excess solution on the surface was removed, and the film was cured at 50 °C for 15 min to obtain the finished film.

[0083] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0084] Example 10

[0085] Prepare a casting solution by mixing X-60 and DMSO at a mass ratio of 10:90. Stir the casting solution at 70 °C for 6 h, then place it in a dryer at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 30 s. Then, put the scraped film into a 15 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 8 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 1.5 wt.% aqueous solution of BPIP6, remove the surface BPIP6 aqueous solution after 10 min, add a 1.0 wt.% n-hexane solution of TMC on the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 60 °C for 10 min to obtain the finished film.

[0086] Performance test: Perform relevant performance tests on the prepared finished film, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0087] Example 11

[0088] Prepare a casting solution by mixing X-60 and DMSO at a mass ratio of 7:93. Stir the casting solution at 60 °C for 5 h, then place it in a dryer at room temperature for 12 h to remove air bubbles and obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40% RH. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film, and place it in the air for 50 s. Then, put the scraped film into a 20 °C deionized water coagulation bath for phase inversion film formation, and take out the film after 8 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 1.5 wt.% aqueous solution of TPIP6, remove the surface TPIP6 aqueous solution after 10 min, add a 1.0 wt.% n-hexane solution of TMC on the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure at 60 °C for 10 min to obtain the finished film.

[0089] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0090] Example 12

[0091] Prepare a casting solution by mixing X-60 and DMSO at a mass ratio of 5:95. Stir the casting solution at 60 °C for 5 h, then place it in a dryer at room temperature for 12 h to remove air bubbles to obtain a homogeneous casting solution. During the preparation process, strictly control the environmental temperature and humidity at 25 °C and 40 RH%. Pour the casting solution evenly onto the non-woven fabric, control the gap of the doctor blade at 150 μm, scrape it into a film and place it in the air for 60 s, then put the scraped film into a 25 °C deionized water coagulation bath for phase inversion to form a film, and take out the film sheet after 10 min. Subsequently, take out the prepared bottom film and clamp it into the jacket, pour in a 0.5 wt.% aqueous solution of BPIP6, remove the surface BPIP6 aqueous solution after 10 min, add a n-hexane solution of 0.1 wt.% TMC on the surface, remove the excess solution on the surface after 10 min of IP reaction, and cure it at 80 °C for 5 min to obtain the finished film.

[0092] Performance test: The prepared finished film was subjected to relevant performance tests, and the test results are shown in Table 2. (For the specific test method, see the reference Charge-Sign-Independent Separation of Mono-and Divalent Ions With Nanofiltration Membranes; Adv. Funct. Mater. 2024, 2416458.)

[0093] The reaction parameters of the preparation methods of each example are shown in Table 1:

[0094]

[0095] Table 1 Parameter table of membrane preparation method.

[0096]

[0097] Table 2 Test result table.

Claims

1. A method for preparing a heavy metal-enriched block polymer nanofiltration membrane, characterized in that The steps include: (1) Preparation of block polymer SPES-b-PES The oligomer PES-OH with the terminal group -OH as described in formula (I) and the oligomer SPES-F with the terminal group -F and amino group in the side chain as described in formula (II) are added in a certain proportion to a solution with NMP as solvent, toluene as water carrier and potassium carbonate as catalyst, and the temperature is programmed to react for a certain time in N2 atmosphere, and then the obtained polymer solution is precipitated into deionized water, and finally dried to obtain a polymer solid, i.e., a block polymer SPES-b-PES; by controlling the mass ratio of SPES-F and PES-OH, a block polymer Xa with different ratios of hydrophilic / hydrophobic segments as described in formula (III) is obtained, wherein a is the molar percentage of SPES-F in SPES-F and PES-OH; (2) Preparation of basic monomers 1-BOC-4-methylpiperazine and potassium carbonate are dissolved in acetonitrile, heated and stirred for a certain period of time; then 1,6-dibromohexane is added to the solution, and the resulting mixture is heated to react and kept under reflux. After a certain period of time, the obtained light yellow solid is dissolved in hydrobromic acid, and allowed to stand for a certain period of time under constant temperature conditions, and then precipitated in ethanol, filtered and washed with excess diethyl ether, and the obtained white solid is dried to obtain BPIP6 monomer; 1,6-dibromohexane is replaced with straight-chain dibromo substituents or benzene ring bromides of different chain lengths to prepare basic monomers of different structures. The structural formulas of the prepared BPIPn and TPIPn monomers are shown in (IV) and (V), wherein n is the number of carbon atoms in the carbon chain of the monomer; (3) Preparation of block structure base membrane Select different block polymers Xa and DMSO to prepare a casting solution in a certain ratio, heat and stir for several hours, obtain a uniform casting solution after full dissolution, and then place it in a dryer at room temperature for full degassing for a period of time; control the ambient temperature and humidity, pour the casting solution evenly on the non-woven fabric, use a stainless steel scraper to scrape it until it forms a film and place it in the air for a period of time, then transfer the scraped film into a deionized water coagulation bath for phase transformation into a film, and take out the non-woven fabric after a period of time to obtain the corresponding block structure base film; (4) Interfacial polymerization modification The prepared base film is placed in a jacket, a certain concentration of BPIPn or TPIPn aqueous solution is uniformly poured on the top of the prepared base film, and after a certain period of time, the excess solution is discharged, and a certain concentration of TMC n-hexane solution is poured, and after heating and curing, a grid-like polyamide layer as shown in formula (VI) is formed on the surface of the base film; 2. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: In step (1), the volume ratio of solvent NMP: toluene is 2:1; the programmed temperature heating reaction conditions are first 140° C. for 4 h, and then changed to 160° C. for 12 h.

3. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The molar ratio of 1-BOC-4-methylpiperazine: potassium carbonate: 1,6-dibromohexane in step (2) is 5:5:2; the stirring temperature is 40-60°C, more preferably 50°C, and the stirring time is 0.5h; the reaction temperature in step (2) is 60-100°C, and the reaction time is 12-24h, more preferably 80°C, 24h.

4. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The mass ratio of block polymer Xa:DMSO in the casting solution described in step (3) is 7:93; the stirring temperature of the casting solution is 50-80°C, the heating time is 4-6h, and more preferably 70°C, 6h; the standing degassing time described in step (3) is 6-24h, and more preferably 12h.

5. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The ambient temperature and humidity described in step (3) are 18-25°C and 20-50RH%, respectively, and more preferably 25°C and 40RH%, respectively; the air bath time is 0-60s, and more preferably 30s; the stainless steel scraper gap is 100-200μm, and more preferably 150μm; the deionized water coagulation bath temperature is 15-25°C, and more preferably 25°C; the phase inversion time is 5-10min, and more preferably 8min.

6. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The BPIP6 concentration in step (4) is 0.1wt.% to 2wt.%, and the soaking time is 10 to 30 min, more preferably 1.2wt.% and 30 min.

7. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The concentration of TPIP3 in step (4) is 0.1wt.% to 2wt.%, and the soaking time is 10 to 20 minutes, more preferably 1.0wt.%, 10 minutes.

8. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The concentration of the TMC n-hexane solution in step (4) is 0.1wt.% to 2wt.%, and the soaking time is 1 to 10 min, more preferably 0.5wt.% to 10 min.

9. The method for preparing a heavy metal-enriched block polymer nanofiltration membrane according to claim 1, characterized in that: The curing temperature in step (4) is 50-80°C, and the curing time is 5-15 minutes, more preferably 70°C, 10 minutes.

10. A heavy metal-enriched block polymer nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 9.

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