Heavy metal-enriched block polymer nanofiltration membrane and preparation method thereof

Abstract

The application belongs to the technical field of membrane preparation, and discloses a heavy metal enrichment block polymer nanofiltration membrane and a preparation method, which comprises the following steps: constructing an ultrafiltration base film: by controlling the proportion of sulfonated polyether sulfone (SPES-F) oligomers and polyether sulfone (PES-OH) oligomers, a block structure polymer with different hydrophilic / hydrophobic segment ratios is synthesized, and finally the block structure polymer is constructed into a base film with uniform pore size, high flux and strong stability; interface polymerization modification: on the surface of the hydrophilic base film, a dense and ordered grid-shaped separation layer is generated by interface polymerization (IP). By adjusting the microstructure of the skin layer, an ultrathin skin layer is constructed, and the structural stability of the base film and the skin layer is cooperatively adjusted, so that the thin skin layer realizes short-range low-resistance and effective screening function.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane preparation, and particularly relates to a heavy metal enrichment block polymer nanofiltration membrane and a preparation method. BACKGROUND

[0002] With the acceleration of global industrialization, heavy metal pollution problems are becoming increasingly serious, and have become one of the core challenges of global water environment governance. Heavy metal ions such as Hg 2+ , Pb 2+ , Cd 2+ , Cu 2+ released in the process of industrial wastewater, mining waste liquid and electronic waste treatment pose a serious threat to the ecological system and human health due to their high toxicity, non-degradability and bioaccumulation. These heavy metal ions not only directly destroy the survival environment of aquatic organisms, leading to imbalance of the water ecosystem, but also may be transmitted through the food chain, eventually accumulating in the human body, causing various diseases and endangering human health.

[0003] Traditional heavy metal separation technologies such as chemical precipitation, ion exchange and adsorption have many problems in practical application. Although the chemical precipitation method is relatively simple to operate, it produces a large amount of sludge, which may cause secondary pollution if not properly treated, and the removal effect of low-concentration heavy metal ions is not good. The ion exchange method has 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, there are difficulties in the selection and regeneration of adsorbents, 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 of high efficiency, energy saving, no chemical addition, etc. Membrane separation technology can separate at room temperature, with low energy consumption, and without introducing new chemicals, avoiding secondary pollution. At the same time, membrane separation technology has high separation efficiency and can effectively remove heavy metal ions in water. However, the existing membrane materials still have significant bottlenecks in selectivity, stability and anti-pollution. 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 polluted, resulting in a decrease in flux and affecting the separation effect.

[0005] Therefore, a new type of composite nanofiltration membrane needs to be developed, which can realize heavy metal enrichment and separation at a relatively low cost, thereby meeting 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 can effectively separate and enrich heavy metal ions in complex water environments, providing an efficient, economical and sustainable solution to the problem of heavy metal pollution in global water environments. SUMMARY

[0006] In order to solve the above technical problems existing in the enrichment and separation of heavy metals, the present application provides a high-efficiency, stable and low-cost solution to prepare a heavy metal enrichment 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. The block structure can form uniform nanochannels by adjusting the hydrophilic / hydrophobic segment ratio, and has high flux and selectivity. The interfacial polymerization technology generates a dense functional layer on the surface of the base film by in-situ reaction of monomers, which can significantly improve the separation performance. In addition, the interpenetration of interfacial polymerization molecules and base film polymer chain segments can be achieved by the swelling of the base film to improve the compatibility of the interface, and the ion / covalent crosslinking between the active groups of the two interfacial polymers can further increase the stability of the interface

[0008] The present application proposes an innovative scheme of "block polymer base film + interfacial polymerization modification" to prepare a heavy metal enrichment block polymer nanofiltration membrane.

[0009] Constructing an ultrafiltration base film: by controlling the ratio of sulfonated polyether sulfone (SPES-F) oligomers and polyether sulfone (PES-OH) oligomers to synthesize block structure polymers with different hydrophilic / hydrophobic segment ratios, and finally construct a base film with uniform pore size, high flux and strong stability.

[0010] Interfacial polymerization modification: on the surface of the hydrophilic base film, a dense and ordered grid separation layer is generated by interfacial polymerization (IP). By adjusting the microstructure of the skin layer, an ultra-thin skin layer is constructed, and the structure stability of the base film and the skin layer is adjusted to realize the effective screening function of the thin skin layer with short-range low resistance.

[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 solutions are as follows:

[0013] A preparation method of a heavy metal enrichment block polymer nanofiltration membrane, comprising the following steps:

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

[0015] The oligomer PES-OH with end group -OH as described in formula (I) and the oligomer SPES-F with end group -F and side chain containing amino group as described in formula (II) are added into a solution with NMP as solvent, toluene as water carrying agent and potassium carbonate as catalyst in a certain proportion, heated and reacted for a certain time under N2 atmosphere, then the obtained polymer solution is precipitated into deionized water, and finally dried to obtain polymer solid, which is the block polymer SPES-b-PES; by controlling the mass ratio of SPES-F and PES-OH, the block polymer X-a as described in formula (III) with different proportions of hydrophilic / hydrophobic segments is obtained, wherein a is the mole percentage of SPES-F in SPES-F and PES-OH;

[0016]

[0017] (2) Preparation of basic monomer

[0018] 1-BOC-4-methylpiperazine and potassium carbonate are dissolved in acetonitrile, heated and stirred for a certain time; then 1,6-dibromohexane is added to the solution, and the obtained mixture is heated and reacted and kept refluxing for a certain time, then the obtained light yellow solid is dissolved in hydrobromic acid and kept at constant temperature for a certain time, then it is precipitated in ethanol, filtered and washed with excess diethyl ether, and the obtained white solid is dried to obtain the BPIP6 monomer; 1,6-dibromohexane is replaced by different chain length linear dibromo-substituted or benzene ring bromo-substituted compounds to prepare basic monomers with different structures, and the structures of the prepared BPIPn and TPIPn monomers are shown in formula (IV) and (V), wherein n is the number of carbon atoms in the carbon chain of the monomer;

[0019]

[0020] (3) Preparation of block structure base film

[0021] Different block polymers X-a and DMSO are selected to prepare casting solution in a certain proportion, heated and stirred for several hours, and a uniform casting solution is obtained after sufficient dissolution, then it is placed in a desiccator at room temperature for a certain time to fully degas; the environmental temperature and humidity are controlled, the casting solution is uniformly poured on non-woven fabric, a stainless steel scraper is used to scrape it into a film and placed in air for a period of time, then the scraped film is transferred into a deionized water coagulation bath to be phase-inverted into a film, and the non-woven fabric is taken out after a period of time, and the corresponding block structure base film is obtained;

[0022] (4) Interfacial polymerization modification

[0023] 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, after maintaining for a certain time, the excess solution is discharged, a certain concentration of TMC n-hexane solution is poured, and after warming and solidification, a grid-shaped polyamide layer as shown in formula (VI) is formed on the surface of the base film;

[0024]

[0025]

[0026] As a preferred, the volume ratio of NMP: toluene in step (1) is 2:1.

[0027] As a preferred, the programmed temperature heating reaction condition in step (1) is first 140℃, 4h, and then changed to 160℃, 12h.

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

[0029] As a preferred, the stirring temperature in step (2) is 40-60℃, and the stirring time is 0.5h, and further preferably 50℃.

[0030] As a preferred, the reaction temperature in step (2) is 60-100℃, and the reaction time is 12-24h, and further preferably 80℃, 24h.

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

[0032] As a preferred, the stirring temperature of the casting solution in step (3) is 50-80℃, and the heating time is 4-6h, and further preferably 70℃, 6h.

[0033] As a preferred, the standing and defoaming time in step (3) is 6-24h, and further preferably 12h.

[0034] As a preferred, the ambient temperature and humidity in step (3) are 18-25℃, 20-50RH%, and further preferably 25℃, 40RH%.

[0035] As a preferred, the air bath time in step (3) is 0-60s, and further preferably 30s.

[0036] As a preferred, the gap of the film doctor blade in step (3) is 100-200μm, and further preferably 150μm.

[0037] As preferred, the temperature of the deionized water coagulation bath in step (3) is 15-25℃, and further preferably 25℃.

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

[0039] As preferred, the BPIP6 concentration in step (4) is 0.1wt.%-2wt.% and the soaking time is 10-30min, and further preferably 1.2wt.% and 30min.

[0040] As preferred, the TPIP3 concentration in step (4) is 0.1wt.%-2wt.% and the soaking time is 10-20min, and further preferably 1.0wt.% and 10min.

[0041] As preferred, the TMC concentration in step (4) is 0.1wt.%-2wt.% and the soaking time is 1-10min, and further preferably 0.5wt.% and 10min.

[0042] As preferred, the solidification temperature in step (4) is 50-80℃ and the time is 5-15min, and further preferably 70℃ and 10min.

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

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

[0045] Compared with the prior art, the present application has the following advantages:

[0046] 1. By adjusting the hydrophilic-hydrophobic block ratio, the phase inversion method induces microphase separation to form an ultrafiltration membrane base film with uniform pore size and high porosity, effectively reduces the mass transfer resistance, realizes high flux, anti-pollution and long service life of the ultrafiltration level, at the same time provides effective support for the separation layer, and improves the overall stability of the composite membrane.

[0047] 2. By the molecular chain interpenetration mechanism induced by the swelling of the base film, the monomers and the base film molecular chains form a physical entanglement network during the interfacial polymerization, and the crosslinking reaction constructs the valence bond anchoring point at the interface, forming a "interpenetration-crosslinking" double locking structure. This design can effectively inhibit the problem of interlayer peeling off of the traditional composite membrane, and the bonding strength of the skin layer and the base film is significantly improved, and the complete interface is still maintained under high pressure and alternating acid and alkali environment.

[0048] 3. By fine-tuning the hydrophilic / hydrophobic segment ratio of the block polymer base film, combined with the ultra-thin and dense skin layer generated by interfacial polymerization, the synergistic effect of "large size base film ion channel + short range screening skin layer" is realized. The sulfonic acid group (-SO3H) and amino group (-NH) of the base film provide heavy metal adsorption sites, while the mesh structure of the separation layer enhances selective screening, breaking through the contradiction between selectivity and flux of traditional membrane materials. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is an interfacial polymerization modification schematic diagram. DETAILED DESCRIPTION

[0050] In order to further illustrate the technical solutions of the present application, the preferred embodiments of the present application are described below in combination with some specific examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present application, and are not a limitation on the claims of the present application.

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

[0052] The oligomer PES-OH with -OH end group as shown in formula (I) and the oligomer SPES-F with -F end group and amino-containing side chain as shown in formula (II) are added in a certain proportion into a solution with NMP as solvent, toluene as water carrying agent, and potassium carbonate as catalyst, heated under N2 atmosphere for a certain time by programmed temperature rise, then the obtained polymer solution is precipitated into deionized water, and finally dried to obtain polymer solid, which is the block polymer SPES-b-PES; by controlling the mass ratio of SPES-F and PES-OH, the block polymer X-a as shown in formula (III) with different hydrophilic / hydrophobic segment ratios is obtained, wherein a is the mole percentage of SPES-F in SPES-F and PES-OH;

[0053]

[0054] Preparation of basic monomer

[0055] 1-BOC-4-methylpiperazine and potassium carbonate are dissolved in acetonitrile and heated and stirred for a certain time; then 1,6-dibromohexane is added to the solution, and the obtained mixture is heated and kept at reflux for a certain time; then the obtained light yellow solid is dissolved in hydrobromic acid and kept at constant temperature for a certain time, and then precipitated in ethanol, filtered and washed with excess diethyl ether; the obtained white solid is dried to obtain the BPIP6 monomer; 1,6-dibromohexane is replaced by different chain length linear dibromo-substituted compounds or benzene ring bromide to prepare basic monomers with different structures, such as (IV) and (V), which are schematic structural formula of BPIPn and TPIPn monomers prepared by replacing different bromides, wherein n is the number of carbon atoms in the carbon chain of the monomer;

[0056]

[0057] Example 1

[0058] The casting solution was prepared by mixing X-40 and DMSO in a mass ratio of 12:88. The casting solution was stirred at 70°C for 6h, then deaerated at room temperature for 12h in a desiccator to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C and 40 RH%. The casting solution was uniformly poured onto the non-woven fabric, and the gap of the doctor blade was controlled to be 150 pm to scrape it into a film and placed in the air for 10s. Then the scraped film was placed in a 10°C deionized water coagulation bath to phase inversion into a film, and the film was taken out after 5min. Subsequently, the prepared base film was clamped into a jacket, 2.0wt.% TPIP3 aqueous solution was poured in, the surface TPIP3 aqueous solution was removed after 10min, 2.0wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10min, the excess solution on the surface was removed, and the finished product film was obtained after 15min of solidification at 50°C, as shown in FIG. 1. Figure 1

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

[0060] Example 2

[0061] The casting solution was prepared by mixing X-40 and DMSO in a mass ratio of 10:90. The casting solution was stirred at 70°C for 6h, then deaerated at room temperature for 12h in a desiccator to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C and 40 RH%. The casting solution was uniformly poured onto the non-woven fabric, and the gap of the doctor blade was controlled to be 150 pm to scrape it into a film and placed in the air for 30s. Then the scraped film was placed in a 15°C deionized water coagulation bath to phase inversion into a film, and the film was taken out after 8min. Subsequently, the prepared base film was clamped into a jacket, 1.5wt.% BPIP6 aqueous solution was poured in, the surface BPIP6 aqueous solution was removed after 10min, 1.0wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10min, the excess solution on the surface was removed, and the finished product film was obtained after 10min of solidification at 60°C.

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

[0063] Example 3

[0064] X-40 and DMSO were configured into a casting solution at a mass ratio of 7:93, the casting solution was stirred and reacted at 60°C for 5h, then deaerated in a desiccator at room temperature for 12h to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C and 40RH%, the casting solution was uniformly poured on the non-woven fabric, and the gap of the doctor blade was controlled to 150μm to be scraped into a film and placed in the air for 50s, then the scraped membrane was put into a 20°C deionized water coagulation bath to be phase-inverted into a film, and the membrane was taken out after 8min. Subsequently, the prepared base film was taken out and clamped in a jacket, 1.5wt.% TPIP6 aqueous solution was poured in, the surface TPIP6 aqueous solution was removed after 10min, 1.0wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10min, the excess solution on the surface was removed, and the finished membrane was obtained after 10min of 60°C solidification.

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

[0066] Example 4

[0067] A casting solution was prepared with X-40 and DMSO in a mass ratio of 5:95. The casting solution was stirred at 60 °C for 5 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process was strictly controlled at an ambient temperature and humidity of 25 °C, 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the casting knife gap was controlled at 150 pm to form a film and placed in the air for 60 s. Then the prepared film was placed in a 25 °C deionized water coagulation bath to phase inversion into a film, and the film was taken out after 10 min. Subsequently, the prepared base film was clamped into a jacket, 0.5 wt.% BPIP6 aqueous solution was poured in, the surface BPIP6 aqueous solution was removed after 10 min, 0.1 wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10 min, the excess solution on the surface was removed, and the finished film was obtained after 5 min of 80 °C curing.

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

[0069] Example 5

[0070] A casting solution was prepared with X-50 and DMSO in a mass ratio of 12:88. The casting solution was stirred at 70 °C for 6 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process was strictly controlled at an ambient temperature and humidity of 25 °C, 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the casting knife gap was controlled at 150 pm to form a film and placed in the air for 10 s. Then the prepared film was placed in a 10 °C deionized water coagulation bath to phase inversion into a film, and the film was taken out after 5 min. Subsequently, the prepared base film was clamped into a jacket, 2.0 wt.% TPIP3 aqueous solution was poured in, the surface TPIP3 aqueous solution was removed after 10 min, 2.0 wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10 min, the excess solution on the surface was removed, and the finished film was obtained after 15 min of 50 °C curing.

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

[0072] Example 6

[0073] X-50 and DMSO were configured into a casting solution at a mass ratio of 10:90, the casting solution was stirred and reacted at 70°C for 6h, and then deaerated in a desiccator at room temperature for 12h to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C and 40RH%, the casting solution was uniformly poured on the non-woven fabric, and the casting knife gap was controlled to 150μm to be scraped into a film and placed in the air for 30s, then the scraped film was put into a 15°C deionized water coagulation bath to be phase-inverted into a film, and the film was taken out after 8min. Subsequently, the prepared base film was taken out and clamped in a jacket, 1.5wt.% BPIP6 aqueous solution was poured in, the surface of the BPIP6 aqueous solution was removed after 10min, 1.0wt.% TMC n-hexane solution was added to the surface, the IP reaction was removed after 10min, and the excess solution was removed, and the finished membrane was obtained after 10min of 60°C solidification.

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

[0075] Example 7

[0076] A casting solution was prepared by mixing X-50 and DMSO in a mass ratio of 7:93. The casting solution was stirred at 60 °C for 5 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process was strictly controlled at an ambient temperature and humidity of 25 °C and 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the gap of the doctor blade was controlled at 150 pm to form a film. The film was placed in air for 50 s, then transferred into a 20 °C deionized water bath for phase inversion to form a film. The film was removed after 8 min. Subsequently, the prepared base film was clamped into a jacket, and 1.2 wt.% TPIP6 aqueous solution was poured into the jacket. After 10 min, the surface TPIP6 aqueous solution was removed, and 0.5 wt.% TMC in n-hexane was added to the surface. After 10 min of IP reaction, the excess solution on the surface was removed. The product film was obtained after 10 min of solidification at 70 °C.

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

[0078] Example 8

[0079] A casting solution was prepared by mixing X-50 and DMSO in a mass ratio of 5:95. The casting solution was stirred at 60 °C for 5 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process was strictly controlled at an ambient temperature and humidity of 25 °C and 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the gap of the doctor blade was controlled at 150 pm to form a film. The film was placed in air for 60 s, then transferred into a 25 °C deionized water bath for phase inversion to form a film. The film was removed after 10 min. Subsequently, the prepared base film was clamped into a jacket, and 0.5 wt.% BPIP6 aqueous solution was poured into the jacket. After 10 min, the surface BPIP6 aqueous solution was removed, and 0.1 wt.% TMC in n-hexane was added to the surface. After 10 min of IP reaction, the excess solution on the surface was removed. The product film was obtained after 5 min of solidification at 80 °C.

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

[0081] Example 9

[0082] X-60 and DMSO were configured into a casting solution at a mass ratio of 12:88, the casting solution was stirred at 70°C for 6h, then deaerated in a desiccator at room temperature for 12h to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C, 40RH%, the casting solution was uniformly poured on the non-woven fabric, and the gap of the doctor blade was controlled to be 150μm to be scraped into a film and placed in the air for 10s, then the scraped film was put into a 10°C deionized water coagulation bath to be phase-inverted into a film, and the film was taken out after 5min. Subsequently, the prepared base film was taken out and clamped in a jacket, 2.0wt.% TPIP3 aqueous solution was poured in, the surface TPIP3 aqueous solution was removed after 10min, 2.0wt.% TMC n-hexane solution was added on the surface, the IP reaction was carried out for 10min, then the excess solution on the surface was removed, and the finished membrane was obtained after 15min of 50°C solidification.

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

[0084] Example 10

[0085] A casting solution was prepared with X-60 and DMSO in a mass ratio of 10:90. The casting solution was stirred at 70 °C for 6 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25 °C and 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the gap of the doctor blade was controlled to 150 pm to be scraped into a film and placed in the air for 30 s. Then the scraped film was placed in a 15 °C deionized water coagulation bath to be phase-inverted into a film. The film was taken out after 8 min. Subsequently, the prepared base film was clamped into a jacket, 1.5 wt.% BPIP6 aqueous solution was poured in, the surface BPIP6 aqueous solution was removed after 10 min, 1.0 wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10 min, the excess solution on the surface was removed, and the finished film was obtained after 10 min of 60 °C curing.

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

[0087] Example 11

[0088] A casting solution was prepared with X-60 and DMSO in a mass ratio of 7:93. The casting solution was stirred at 60 °C for 5 h, then degassed at room temperature for 12 h in a desiccator to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25 °C and 40 RH%. The casting solution was uniformly poured onto a non-woven fabric, and the gap of the doctor blade was controlled to 150 pm to be scraped into a film and placed in the air for 50 s. Then the scraped film was placed in a 20 °C deionized water coagulation bath to be phase-inverted into a film. The film was taken out after 8 min. Subsequently, the prepared base film was clamped into a jacket, 1.5 wt.% TPIP6 aqueous solution was poured in, the surface TPIP6 aqueous solution was removed after 10 min, 1.0 wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10 min, the excess solution on the surface was removed, and the finished film was obtained after 10 min of 60 °C curing.

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

[0090] Example 12

[0091] X-60 and DMSO were configured into a casting solution at a mass ratio of 5:95, the casting solution was stirred at 60°C for 5h, then deaerated in a desiccator at room temperature for 12h to obtain a uniform casting solution. The preparation process strictly controlled the environmental temperature and humidity to be 25°C, 40RH%, the casting solution was uniformly poured on the non-woven fabric, and the gap of the doctor blade was controlled to be 150μm to be scraped into a film and placed in the air for 60s, then the scraped film was put into a 25°C deionized water coagulation bath to be phase-inverted into a film, and the film was taken out after 10min. Subsequently, the prepared base film was clamped in a jacket, 0.5wt.% BPIP6 aqueous solution was poured, the surface BPIP6 aqueous solution was removed after 10min, 0.1wt.% TMC n-hexane solution was added to the surface, the IP reaction was carried out for 10min, the excess solution on the surface was removed, and the finished membrane was obtained after 5min of 80°C curing.

[0092] Performance test: The prepared finished membrane was subjected to relevant performance test, and the test results are shown in Table 2. (For specific test method, see 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 method of each example are shown in Table 1:

[0094]

[0095] Table 1: Membrane preparation method parameter table.

[0096]

[0097] Table 2: Test results table.

Claims

1. A method for preparing a heavy metal enrichment block polymer nanofiltration membrane, characterized in that... Includes the following steps: (1) Preparation of block polymer SPES-b-PES The oligomer PES-OH with -OH end groups as described in formula (I) and the oligomer SPES-F with -F end groups and amino side chains as described in formula (II) are added in a certain proportion to a solution with NMP as solvent, toluene as dehydrating agent and potassium carbonate as catalyst. The mixture is heated in a N2 atmosphere for a certain time by programmed temperature increase. The resulting polymer solution is then precipitated in 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, the block polymer Xa as described in formula (III) with different proportions of hydrophilic / hydrophobic segments is obtained, where 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 were dissolved in acetonitrile and heated and stirred for a certain time. Then, 1,6-dibromohexane was added to the solution, and the resulting mixture was heated and refluxed. After a certain time, the resulting pale yellow solid was dissolved in hydrobromic acid and allowed to stand at a constant temperature for a certain time. Subsequently, it was precipitated in ethanol, filtered, and washed with excess diethyl ether. The resulting white solid was dried to obtain the BPIP6 monomer. 1,6-dibromohexane was replaced with straight-chain dibromo-substituted products or benzene ring brominated products of different chain lengths to prepare basic monomers with different structures. The structural formulas of the prepared BPIPn and TPIPn monomers are shown in (IV) and (V), respectively, where n is the number of carbon atoms in the monomer carbon chain. (3) Preparation of block structure base film Different block polymers Xa and DMSO were selected and prepared into a casting solution in a certain proportion. The solution was heated and stirred for several hours to fully dissolve and obtain a homogeneous casting solution. Then, the solution was placed in a desiccator at room temperature for a period of time to fully degas. The ambient temperature and humidity were controlled, and the casting solution was poured evenly onto a nonwoven fabric. A stainless steel scraper was used to scrape the solution into a film and placed it in the air for a period of time. The scraped film was then transferred into a deionized water coagulation bath for phase inversion to form a film. After a period of time, the nonwoven fabric was removed to obtain the corresponding block structure base film. (4) Interface aggregation modification The prepared base film is placed in a jacket, and a certain concentration of BPIPn or TPIPn aqueous solution is poured evenly onto the top of the prepared base film. After maintaining it for a certain time, the excess solution is drained, and a certain concentration of TMC n-hexane solution is poured in. 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 enrichment block polymer nanofiltration membrane as described in claim 1, characterized in that: In step (1), the volume ratio of solvent NMP to toluene is 2:1; the programmed temperature heating reaction conditions are first 140℃ for 4h, and then changed to 160℃ for 12h.

3. The method for preparing a heavy metal enrichment block polymer nanofiltration membrane as described in 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℃ and the stirring time is 0.5h; the reaction temperature in step (2) is 60-100℃ and the reaction time is 12-24h.

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

5. The method for preparing a heavy metal enrichment block polymer nanofiltration membrane as described in claim 1, characterized in that: The ambient temperature and humidity in step (3) are 18-25℃ and 20-50RH%, respectively; the air bath time is 0-60s; the gap between the stainless steel scrapers is 100-200μm; the temperature of the deionized water coagulation bath is 15-25℃; and the phase transformation time is 5-10min.

6. The method for preparing a heavy metal enrichment block polymer nanofiltration membrane as described in claim 1, characterized in that: Step (4) When the BPIPn aqueous solution is a BPIP6 aqueous solution, the concentration of BPIP6 is 0.1 wt.% to 2 wt.%, and the soaking time is 10 to 30 min.

7. The method for preparing a heavy metal enrichment block polymer nanofiltration membrane as described in claim 1, characterized in that: In step (4), when the TPPn aqueous solution is a TPP3 aqueous solution, the concentration of TPP3 is 0.1 wt.% to 2 wt.%, and the soaking time is 10 to 20 min.

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

9. The method for preparing a heavy metal enrichment block polymer nanofiltration membrane as described in claim 1, characterized in that: The curing temperature in step (4) is 50-80℃ and the time is 5-15 min.

10. A heavy metal enrichment block polymer nanofiltration membrane, prepared by the preparation method described in any one of claims 1-9.

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