A capillary force-induced ultra-low pressure separation membrane based on biomimetic technology and its preparation method and application

Abstract

The present invention discloses an ultra-low pressure separation membrane induced by capillary force constructed based on bionic technology, as well as a preparation method and application thereof. The ultra-low pressure separation membrane includes a relatively dense separation layer located on the upper layer of the ultra-low pressure separation membrane, a support layer located below the separation layer and having a finger-shaped pore structure, and a micro-nano structure located in the finger-shaped pore structure and having a capillary effect. The micro-nano structure is a large number of hydrophilic nanoparticles generated in the finger-shaped pore structure. The capillary channels formed between the large number of hydrophilic nanoparticles provide capillary force for the ultra-low pressure separation membrane. The ultra-low pressure separation membrane has a thickness of 50-400μm, achieves high-efficiency fine separation under ultra-low pressure conditions, and exhibits its advantages in energy conservation, membrane anti-fouling, and high-efficiency separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membranes, and specifically relates to an ultra-low pressure separation membrane induced by capillary force constructed based on bionic technology, and a preparation method and application thereof. Background Art

[0002] Advanced membrane technology is one of the most effective means of addressing resource scarcity, energy shortages, environmental pollution, and human health, and promoting the development of a circular economy and green industries. Compared to traditional separation technologies, membrane separation technology offers advantages such as no phase change, no secondary pollution, high separation efficiency, and a small footprint, leading to its widespread application in both industry and daily life. In membrane separation, a specially manufactured, selectively permeable membrane, driven by an external force, can separate, purify, and concentrate a mixture, making it a key material for separation. Pressure differential is the driving force for traditional membrane separations. During high-pressure osmotic processes, concentration polarization of the feed solution is inevitable. Furthermore, to achieve more precise separations, the pore size of the membranes being fabricated has become increasingly smaller. This increase in solute rejection is accompanied by a decrease in permeate flux and an increase in driving pressure, a phenomenon known as the "trade-off" effect in the membrane industry. Therefore, introducing a driving force into the membrane to achieve efficient separation at low or no pressure, thereby saving energy and mitigating this "trade-off" effect, is essential and a revolutionary innovation. Many researchers are committed to solving the "trade-off" effect in the membrane separation process, so as to achieve efficient separation while ensuring separation efficiency.

[0003] Patent document CN114570219 A discloses a high-flux, pollution-resistant separation membrane. This membrane is obtained by synchronously grafting cations and anions from ionic liquids onto the membrane surface, making the membrane surface electrically neutral. Under an operating pressure of 1.6 MPa, the pure water flux of the modified membrane reaches 225.1 L·m -2 ·h -1 , and the retention rate for bovine serum albumin is 98.5%.

[0004] Patent document CN104275059A discloses a high-flux composite nanofiltration membrane. This composite nanofiltration membrane is assembled into a fully carbon-selective separation layer by vacuum filtration on a porous polymer support layer. This membrane can achieve dye retention of over 99% and a membrane pure water flux of 80 L·m -2 ·h -1 bar -1 .

[0005] The document "Super-hydrophilic PVDF membrane modified by cross-linking plant polyphenols and hydrophilic polymers to construct a polymer network for oil-water separation" discloses the use of tannic acid (TA, natural plant polyphenols) and 3-aminopropyltriethoxysilane (APTES) to co-deposit on the surface of the PVDF microfiltration membrane to construct a base layer with a micro-nano rough structure, and the synthesized polyphenol-containing hydrophilic polymer is cross-linked with the base layer through hydrogen bonding, π-π, Michael addition and other reactions to construct a super-hydrophilic polymer network structure to obtain a modified separation membrane. The underwater oil droplet contact angle of the obtained modified separation membrane is greater than 140°, and the separation efficiency for various oil-water mixtures and surfactant-stabilized water-in-oil emulsions exceeds 99.9%.

[0006] While the separation membranes disclosed in the aforementioned literature can achieve effective separation and exhibit high flux and good contamination resistance, they still suffer from excessively high driving pressures during fine separation, leading to severe concentration polarization and membrane structural collapse, increased energy consumption, and shortened membrane life. Therefore, incorporating capillary forces into the membrane to achieve low-pressure or no-pressure drive while maintaining separation efficiency is a viable approach to addressing this "trade-off" effect, reducing energy consumption, and extending membrane life. Summary of the Invention

[0007] In view of the above-mentioned shortcomings, the first object of the present invention is to provide an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology;

[0008] The second object of the present invention is to provide a method for preparing an ultra-low pressure separation membrane induced by capillary force based on bionic technology;

[0009] The third object of the present invention is to provide an ultra-low pressure separation membrane induced by capillary force constructed based on bionic technology for use in dye desalination and anti-fouling.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A capillary force-induced ultra-low pressure separation membrane constructed based on bionic technology, the ultra-low pressure separation membrane includes a relatively dense separation layer located on the upper layer of the ultra-low pressure separation membrane, a support layer located below the separation layer and having a finger-like pore structure, and a micro-nano structure located in the finger-like pore structure and having a capillary effect. The micro-nano structure is a large number of hydrophilic nanoparticles generated in the finger-like pore structure. The capillary channels formed between the large number of hydrophilic nanoparticles provide capillary force for the ultra-low pressure separation membrane. The thickness of the ultra-low pressure separation membrane is 50-400μm.

[0012] Furthermore, the preparation method has the following specific steps:

[0013] 1) Preparation of a coagulation bath: Dissolve tannic acid in an HCl buffer solution containing tris(hydroxymethyl)aminomethane, then mix the solution with an ethanol solution containing 3-aminopropyltriethoxysilane, and allow to react for 1-8 hours to obtain a coagulation bath;

[0014] 2) Preparation of a casting solution: Dry base membrane material, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C to 80°C for 6-12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraping rod. The glass plate with the casting solution was then immersed in a coagulation bath to prepare a modified membrane via the NIPS phase inversion method.

[0015] 3) Cross-linking of the modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting solution is continued to be immersed in the coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 to obtain an ultra-low pressure separation membrane.

[0016] Furthermore, in step 1), the concentration of tannic acid is 0.5 g / L-2 g / L, and the concentration of 3-aminopropyltriethoxysilane is 0.5 g / L-2 g / L;

[0017] The base film material in step 2) is one or more of polyvinylidene fluoride PVDF, polyethersulfone PES, polysulfone PSF, and polyimide PEI, and the molecular weight of PEG is 600-10000;

[0018] The concentration of Fe2(SO4)3 in step 3) is 0.5g / L-10g / L.

[0019] Furthermore, in step 1), the concentration of tannic acid is 1 g / L, and the concentration of 3-aminopropyltriethoxysilane is 1 g / L;

[0020] The concentration of Fe2(SO4)3 in step 3) is 2 g / L.

[0021] Furthermore, the ultra-low pressure separation membrane is used in dye desalination treatment and anti-fouling research.

[0022] By adopting the above scheme, the present invention has the following advantages:

[0023] 1. The present invention proposes for the first time to drive the membrane for fine separation by constructing capillary force in the membrane. Inspired by the capillary phenomenon in nature, through a certain membrane making process and chemical reaction, the capillary force is successfully constructed in the membrane. The capillary force induces the membrane to achieve high-efficiency fine separation under ultra-low pressure conditions, showing its advantages in energy conservation, membrane anti-pollution and high-efficiency separation.

[0024] 2. In the present invention, tannic acid (TA) and 3-aminopropyltriethoxysilane (APTES) are reacted in a mixed solution of Tris-HCl buffer and ethanol for a certain period of time, and the reaction solution is used as a coagulation bath. The casting solution scraped on the glass plate is immersed in the coagulation bath for 12 hours. During the phase inversion process, the separation membrane is formed while the hydrophilic nanoparticles (HNPs) generated by the reaction of TA and APTES are fixed on the membrane pores and membrane surface. 3+ Further cross-linking of the membrane improves its stability. The large number of HNPs in the membrane pores resembles a gravel-like stacking structure, forming numerous capillary channels. During the separation process, water droplets quickly permeate the membrane under the induction of capillary forces, thus achieving fine separation of dyes and salts under low or no pressure.

[0025] 3. In the present invention, under ultra-low pressure separation conditions (0.02MPa), the ultra-low pressure separation membrane still maintains a high separation capacity of dye / salt (CR / NaCl) mixed solution up to 134L·m -2 ·h -1 The high flux can alleviate the "trade-off" effect to a certain extent. Due to the extremely low separation pressure, the concentration polarization phenomenon in the membrane separation process is weakened, and the membrane exhibits excellent anti-fouling performance.

[0026] 4. Compared with the separation membranes reported in existing patent literature, the ultra-low pressure separation membrane prepared by the present invention shows significant advantages in the separation of dye / salt mixtures, and has the advantages of ultra-low pressure drive, high flux and high retention.

[0027] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an enlarged view of the structure of the ultra-low pressure separation membrane of the present invention.

[0029] Figure 2 The SEM images and cross-sectional EDX images of the separation membranes described in Examples 1 and 3 of the present invention are shown;

[0030] Figure 3 These are SEM images of the separation membranes described in Examples 2, 4, and 5 of the present invention;

[0031] Figure 4 The XPS graphs of the separation membranes described in Examples 1 and 3 of the present invention are shown;

[0032] Figure 5The pure water flux and water contact angle test diagrams of the separation membranes described in Examples 1-4 of the present invention;

[0033] Figure 6 This is a performance diagram of the separation membrane described in Example 3 of the present invention for separating more than 80 dyes including Congo red, Victoria blue, methyl blue, Coomassie brilliant blue, direct black 38 and direct red;

[0034] Figure 7 This is a graph showing the separation performance of the separation membrane described in Example 3 of the present invention for dye / salt binary systems of different compositions;

[0035] Figure 8 This is a graph showing the long-term stable separation performance of the separation membrane described in Example 3 of the present invention for a dye / salt binary mixture system;

[0036] Figure 9 Graph showing the anti-pollution performance of the separation membrane against dyes and the separation performance of a dye / salt binary mixture system after 10 cycles according to Example 3 of the present invention;

[0037] Figure 10 This is a diagram of the molecular weight cut-off of the separation membranes described in Examples 1 and 3 of the present invention.

[0038] Figure 11 This is a diagram showing the separation performance of Example 11 for different dye and salt mixtures. DETAILED DESCRIPTION

[0039] The present invention will be described in detail below with reference to the accompanying drawings and examples. However, the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment involved in the present invention are conventional reagents, methods and equipment in the art.

[0040] Example 1: Preparation of an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology

[0041] The specific steps are as follows:

[0042] 1) Preparation of coagulation bath: A mixture of 1 L of tris(hydroxymethylaminomethane) (Tris)-HCl buffer and 100 mL of ethanol was used as the coagulation bath;

[0043] 2) Preparation of casting solution: Dry PVDF, PEG, LiCl, and NMP were added sequentially to a three-necked flask and mechanically stirred at 65°C for 12 h to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath to prepare a PVDF membrane (M-Pure) via the NIPS phase inversion method.

[0044] Example 2: Preparation of an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology

[0045] The specific steps are as follows:

[0046] 1) Preparation of a coagulation bath: Dissolve tannic acid (TA) at a concentration of 1 g / L in tris(hydroxymethyl)aminomethane (Tris)-HCl buffer, then mix with 3-aminopropyltriethoxysilane (APTES) in ethanol at a concentration of 1 g / L. The resulting solution, after reacting for 1 hour, serves as the coagulation bath.

[0047] 2) Preparation of the casting solution: Dry PVDF, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C for 12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath. The hydrophilic nanoparticles generated by the reaction in the coagulation bath were fixed in the membrane pores by the action of TA. After the NIPS phase transformation was complete, a modified membrane was obtained.

[0048] 3) Cross-linking of the modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting liquid is continued to be immersed in the coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 with a concentration of 2g / L. After the reaction is completed, it is repeatedly rinsed with deionized water to obtain an ultra-low pressure separation membrane (M-TA / AP1).

[0049] Example 3: Preparation of an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology

[0050] The specific steps are as follows:

[0051] 1) Preparation of a coagulation bath: Dissolve tannic acid (TA) at a concentration of 1 g / L in tris(hydroxymethyl)aminomethane (Tris)-HCl buffer, then mix with 3-aminopropyltriethoxysilane (APTES) in ethanol at a concentration of 1 g / L. The resulting solution, after reacting for 2 hours, serves as the coagulation bath.

[0052] 2) Preparation of the casting solution: Dry PVDF, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C for 12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath. The hydrophilic nanoparticles generated by the reaction in the coagulation bath were fixed in the membrane pores by the action of TA. After the NIPS phase transformation was complete, a modified membrane was obtained.

[0053] 3) Cross-linking of modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting solution is soaked in a coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 at a concentration of 2g / L. After the reaction is completed, it is repeatedly rinsed with deionized water to obtain an ultra-low pressure separation membrane (M-TA / AP2). Its structure is as follows Figure 1 shown.

[0054] Example 4: Preparation of an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology

[0055] The specific steps are as follows:

[0056] 1) Preparation of a coagulation bath: Dissolve tannic acid (TA) at a concentration of 1 g / L in tris(hydroxymethyl)aminomethane (Tris)-HCl buffer, then mix with 3-aminopropyltriethoxysilane (APTES) in ethanol at a concentration of 1 g / L. The resulting solution, after reacting for 4 hours, serves as the coagulation bath.

[0057] 2) Preparation of the casting solution: Dry PVDF, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C for 12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath. The hydrophilic nanoparticles generated by the reaction in the coagulation bath were fixed in the membrane pores by the action of TA. After the NIPS phase transformation was complete, a modified membrane was obtained.

[0058] 3) Cross-linking of the modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting liquid is continued to be immersed in the coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 with a concentration of 2g / L. After the reaction is completed, it is repeatedly rinsed with deionized water to obtain an ultra-low pressure separation membrane (M-TA / AP4).

[0059] Example 5: Preparation of an ultra-low pressure separation membrane induced by capillary force based on biomimetic technology

[0060] The specific steps are as follows:

[0061] 1) Preparation of a coagulation bath: Dissolve tannic acid (TA) at a concentration of 1 g / L in tris(hydroxymethyl)aminomethane (Tris)-HCl buffer, then mix with 3-aminopropyltriethoxysilane (APTES) in ethanol at a concentration of 1 g / L. The resulting solution, after reacting for 8 hours, serves as the coagulation bath.

[0062] 2) Preparation of the casting solution: Dry PVDF, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C for 12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath. The hydrophilic nanoparticles generated by the reaction in the coagulation bath were fixed in the membrane pores by the action of TA. After the NIPS phase transformation was complete, a modified membrane was obtained.

[0063] 3) Cross-linking of the modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting liquid is continued to be immersed in the coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 with a concentration of 2g / L. After the reaction is completed, it is repeatedly rinsed with deionized water to obtain an ultra-low pressure separation membrane (M-TA / AP8).

[0064] Example 6: SEM scanning test of ultra-low pressure separation membrane

[0065] 1. Experimental Materials

[0066] The PVDF membrane (M-Pure), ultra-low pressure separation membrane (M-TA / AP1), ultra-low pressure separation membrane (M-TA / AP2), ultra-low pressure separation membrane (M-TA / AP4), and ultra-low pressure separation membrane (M-TA / AP8) obtained in Examples 1-5.

[0067] 2. Experimental methods

[0068] The surface of the membranes prepared in Examples 1-5 was characterized using a field emission scanning electron microscope (SEM). The freeze-dried membrane samples were cut into 2×4 mm 2 The sample strip was glued to the sample stage with the front side facing up using conductive glue. After gold spraying, the surface morphology of the film was observed using SEM.

[0069] 3. Experimental results

[0070] The microstructure of the fabricated membranes was characterized in detail:

[0071] like Figure 2 As shown, Figure 2 a shows an optical photograph showing that the M-Pure membrane is white, and the SEM characterization results show that the surface of the M-Pure membrane is smooth and the uniformly distributed membrane pores can be clearly observed. Figure 2 b shows the cross-sectional morphology and EDX characterization results of the M-Pure membrane, where finger-like sublayers and large voids are observed on the membrane cross-section. Further zooming in on the bottom layer of the membrane reveals a nodular structure formed by PVDF polymer chains, and EDX results indicate the presence of oxygen in the cross-section.

[0072] Figure 2The color of the M-TA / AP2 film in c turned dark blue, which is due to its 3+ After treatment, a complexation reaction occurred with TA in the membrane. Meanwhile, a large number of HNPs were observed on the membrane surface, which was due to the physical cross-linking of TA and APTES hydrolysis products in the coagulation bath and binding to the membrane surface through covalent bonds, hydrogen bonds and π-π interactions. Figure 2 d shows that the large cavity of the membrane has disappeared from the cross section, and a large number of HNPs have filled into the membrane pores. The local magnification of the bottom of the membrane shows a different morphology from that of the M-Pure membrane, with a large number of HNPs existing in the pores of the M-TA / AP2 membrane. 3+ Upon treatment, it chelates with the hydroxyl groups on the HNPs, forming a rough, sand-like structure that facilitates water transport. Simultaneously, the capillary forces formed between the numerous HNPs accelerate the transport of water molecules. EDX characterization results further reveal a significant increase in the Si content and the presence of Fe in the M-TA / AP2 membrane, indicating the successful incorporation of the NPs into the membrane.

[0073] like Figure 3 As shown, aggregated TA particles appeared on the surface of the M-TA / AP1 membrane. This is due to the short coagulation bath reaction time, which prevented the formation of HNPs and resulted in the appearance of TA aggregates on the membrane surface. Furthermore, a decrease in large voids and the formation of a small amount of HNPs were observed in cross-sections. When the coagulation bath reaction time was extended to 4 hours, nanoparticle aggregation was also observed on the surface of the M-TA / AP4 membrane. Cross-sectional images revealed significant changes in the membrane base, with a significant decrease in HNPs and the development of a lamellar structure at the membrane bottom. This is presumably due to the high HNP concentration in the coagulation bath, which slowed the exchange rate between solvent and nonsolvent during phase separation, leading to the formation of a lamellar structure at the membrane bottom. When the coagulation bath reaction time was extended to 8 hours, HNP aggregation on the M-TA / AP8 membrane surface became more pronounced, and cross-sectional images revealed a thicker lamellar structure at the membrane bottom.

[0074] Example 7: Chemical composition test of ultra-low pressure separation membrane

[0075] 1. Experimental Materials

[0076] The PVDF membrane (M-Pure) in Example 1 and the ultra-low pressure separation membrane (M-TA / AP2) in Example 3.

[0077] 2. Experimental methods

[0078] Fourier transform infrared spectroscopy (FTIR, Nicolet iS50, GER) was used to characterize the chemical composition of the membranes prepared in Example 1 and Example 3. Before testing, the prepared membranes were freeze-dried to a constant weight using a freeze dryer.

[0079] 3. Experimental results

[0080] like Figure 4 a) The appearance of some new absorption signals of the modified membrane M-TA / AP2 compared with the M-Pure membrane. -1 The peak at 1630 cm is the C=O stretching vibration in TA. -1 The peak at 1568 cm is the C=C stretching vibration band of the benzene main chain. -1 These results indicate that during the modification process, TA and APTES underwent Michael addition reaction and Schiff base reaction, and the adhesion effect caused by TA oxidation anchored the generated hydrophilic nanoparticles HNPs in the membrane pores and membrane surface.

[0081] Example 8: Element Content Test of Ultra-Low Pressure Separation Membrane

[0082] 1. Experimental Materials

[0083] The PVDF membrane (M-Pure) in Example 1 and the ultra-low pressure separation membrane (M-TA / AP2) in Example 3.

[0084] 2. Experimental methods

[0085] XPS was used to further characterize the changes in the chemical composition and element content of the membrane surface before and after modification. The specific test steps are as follows: The cut area is 1×1cm 2 The membrane was used as a test sample and was attached to a sample stage using conductive adhesive. The membrane surfaces in Examples 1 and 3 were scanned and analyzed using XPS, and the binding energy was calibrated using carbon (284.8 eV) as an internal standard.

[0086] 3. Experimental results

[0087] from Figure 4 b It can be seen that the prepared film has characteristic peaks of C1s, N1s, F1s and O1s at 285.6eV, 400.5eV, 531.1eV and 688.6eV respectively. The modification of the film by TA and APTES leads to a decrease in the F element peak intensity of the M-TA / AP2 film and an increase in the O element peak intensity. Figure 4 The C1s nuclear energy spectrum of the M-TA / AP2 film in c shows that the characteristic peaks of C=O, CO and C=C appear at the binding energies of 288.1eV, 286.6eV and 284.8eV. Figure 4 d and Figure 4 The characteristic peak of O-Fe(III) appears in figure f, indicating that the TA and APTES functional layers were successfully constructed on the membrane surface, and Fe was successfully introduced. 3+ , further improving the stability of the coating.

[0088] Example 9: Contact angle test of ultra-low pressure separation membrane

[0089] 1. Experimental Materials

[0090] The PVDF membrane (M-Pure), ultra-low pressure separation membrane (M-TA / AP1), ultra-low pressure separation membrane (M-TA / AP2), ultra-low pressure separation membrane (M-TA / AP4), and ultra-low pressure separation membrane (M-TA / AP8) obtained in Examples 1-5.

[0091] 2. Experimental methods

[0092] The contact angle changes of the films prepared in Examples 1-5 were characterized at room temperature using a DSA100 contact angle meter. The hydrophilicity of the membrane surfaces was evaluated by measuring the contact angle changes of the membranes. The test steps were as follows: a 10×30 mm cut area was obtained. 2 The membrane was used as the test sample, which was attached to a glass slide and flattened. A 2 μL droplet was dropped on the membrane surface, and the contact angle change within 0 to 40 seconds after the water droplet contacted the membrane surface was measured. Each sample was measured 3 times and the average value was taken.

[0093] 3. Experimental results

[0094] like Figure 5 As shown in Figure 2, the initial water contact angle of the M-Pure membrane is 87.5°. Due to the inherent hydrophobicity of the membrane, the water contact angle does not change significantly after 40s, and its value is 85.1° ( Figure 5 b) The initial contact angle of the modified membrane decreases. This is because the presence of hydrophilic NPs on the membrane surface and in the membrane pores increases the binding force for water molecules, while the capillary forces provided by the capillary channels formed between the nanoparticles in the pores accelerate the penetration of water droplets. Among the modified membranes with different coagulation bath reaction times, the M-TA / AP2 membrane exhibits the highest hydrophilicity, with an initial contact angle of 47.2°, which decreases to 35° after 40 seconds.

[0095] Example 10: Performance test of ultra-low pressure separation membrane

[0096] 1. Experimental Materials

[0097] The PVDF membrane (M-Pure), ultra-low pressure separation membrane (M-TA / AP1), ultra-low pressure separation membrane (M-TA / AP2), ultra-low pressure separation membrane (M-TA / AP4), and ultra-low pressure separation membrane (M-TA / AP8) obtained in Examples 1-5.

[0098] 2. Experimental methods

[0099] Water flux test: Place the membrane in the membrane tank, use deionized water as feed liquid, and test its water flux after stabilization for 1 hour without applying pressure (the minimum pressure of the pressure gauge is 0.02MPa), which is recorded as J (L·m -2 ·h -1 ), the water flux is calculated by formula (1);

[0100] Separation performance test of different dyes: The dye concentration used was 0.1 g / L, no pressure was applied, and after stabilization, the membrane was tested for dye flux. The feed liquid and filtrate were collected, and the membrane retention rate R (%) for different dyes was calculated according to formula (2). The separation performance of the dye / salt binary system (Congo red and NaCl mixed solution, Congo red and Na2SO4 mixed solution) was tested. The concentrations of dye and salt in the feed liquid were 0.1 g / L and 1 g / L, respectively. The membrane retention rate for different dyes and salts was calculated according to formula (2). The anti-fouling performance of the membrane was characterized by a cyclic test of Congo red dye solution. The model pollutant was 0.1 g / L Congo red solution. Under no pressure, dye separation was first performed. After 90 minutes of operation, the dye solution was replaced with deionized water and washed for 10 minutes under no pressure. The dye solution was then separated again. The entire anti-fouling test was divided into three pollution stages and two pure water washing stages.

[0101]

[0102]

[0103] In formula (1), V is the volume of permeate in a certain period of time (L), A is the effective filtration area of the membrane pool (m 2 ), Δt is the filtrate collection time (h); in formula (2), R is the solute retention rate (%); C f is the solute concentration in the original solution (g·L -1 );C p is the solute concentration in the permeate (g·L -1 );

[0104] The conductivity of the inorganic salt solution was measured using a conductivity meter, and the concentrations of the solutes in the NaCl and Na2SO4 solutions in the permeate and feed solution were calculated based on the standard curves. The absorbance was measured at the maximum absorption wavelength of the dye using an ultraviolet spectrophotometer, and the concentrations of the solutes in the different dye solutions in the permeate and feed solution were calculated based on the standard curves. Finally, the retention rate of each separation system was calculated according to formula (2).

[0105] Neutral polyethylene glycol was used to test the molecular weight cutoff of the membranes in Examples 1 and 3 to investigate whether the increase in flux of the M-TA / AP2 modified membrane in Example 3, compared to the M-Pure membrane in Example 1, was due to capillary forces, not pore size or porosity. When filtering a PEG solution of a certain concentration, the molecular weight of PEG at a retention rate of 90% is called the molecular weight cutoff. The specific steps are: 1 g·L -1 The PEG solution was used as the test stock solution of the membrane. After the filtration test, the retention rate of the membrane for PEG with different molecular weights (1000, 2000, 4000, 6000, 8000, 10000, 20000 and 40000) was calculated. The molecular weight-retention rate curve of PEG was made and fitted. The molecular weight of PEG corresponding to the intersection of the fitting curve and the position of 90% retention rate was the retention rate molecular weight of the nanofiltration membrane.

[0106] The porosity of the membrane is defined as the ratio of the volume of the pores to the volume of the membrane. The specific experimental method is to soak the dry membrane in isopropyl alcohol for 24 hours, record the mass of the membrane before and after soaking, and calculate the porosity of the membrane according to formula (3).

[0107]

[0108] Where W w is the mass of the wet film, W d is the mass of the dry film, ρ i is the density of isopropyl alcohol (0.78 g·cm -3 ), ρ p is the density of PVDF (1.77 g·cm -3 ).

[0109] 3. Experimental results

[0110] Table 1

[0111]

[0112] Combined from Table 1 Figure 5 It can be seen that the membrane prepared in Example 3 has the best overall performance. This is because when the coagulation bath reaction time is 1 hour, the reaction is incomplete and fewer nanoparticles are formed. As the reaction time increases, the number of nanoparticles produced gradually increases. When the reaction time is 4 hours and 8 hours, the concentration of nanoparticles in the coagulation bath is too high, which slows down the phase separation process. From the cross-sectional view, it can be seen that the bottom layer of the formed membrane becomes a layered structure, resulting in a decrease in flux.

[0113] Figure 5 It can be seen that the membrane prepared in Example 3 (M-TA / AP2) has the highest water flux of 179.6 L·m -2 ·h -1 .at the same time, Figure 6 The results show that the flux of M-TA / AP2 membrane for Congo red (CR), Victoria blue B (VBB), methylene blue (MB), Coomassie brilliant blue (CBB), direct black 38 (DB 38), and direct red 80 (DR 80) dye solutions are 160.5 L·m -2 ·h -1 、149.0L·m -2 ·h -1 、168.2L·m -2 ·h -1 、160.5L·m -2 ·h -1 、183.4L·m -2 ·h -1 、198.7L·m -2 ·h -1 The retention rates were 99.3%, 99.7%, 99.6%, 99.7%, 99.8% and 99.7% respectively. Figure 7 It shows that the membrane prepared in Example 3 still maintains high flux and high retention for dyes and high permeability for salts when treating dye / salt mixed systems with different components. Figure 8 It shows that the membrane prepared in Example 3 exhibits long-term stable separation performance when treating a dye / salt binary mixed system. Figure 9 The membrane prepared in Example 3 was tested for Congo red dye solution after three cycles. The membrane maintained a high and stable dye flux after three cycles, demonstrating good anti-fouling performance. After 10 cycles of separation of a binary dye / salt mixture, the membrane still exhibited good separation performance for the dye / salt mixture.

[0114] from Figure 10 It can be seen that the molecular weight cut-off of the M-Pure membrane is 20396Da, and its porosity is 84.3±0.2%. After the capillary force is introduced, the molecular weight cut-off of the M-TA / AP2 membrane is reduced to 17170Da, and its porosity is 82.9±0.8%. The pore size of the modified membrane is basically unchanged compared with the original membrane. Figure 9 b shows that the pore size distribution of the M-TA / AP2 membrane is σ = 1.48, which is comparable to the pore size distribution of the M-Pure membrane, σ = 1.53. The reduced molecular weight cut-off of the modified membrane, while the porosity and pore size distribution remain essentially unchanged, suggests that the increase in flux of the modified membrane is due to capillary forces.

[0115] Example 11: Comparative Experiment

[0116] 1. Experimental methods

[0117] 1) Preparation of the control group: According to the method in the prior art, the membrane was surface modified with TA and APTES, and then Fe3+ The membrane prepared after cross-linking was used as a control. The specific steps were as follows:

[0118] Preparation of base film: Dry PVDF, PEG, LiCl, and NMP were added to a three-necked flask in sequence and mechanically stirred at 65°C for 12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraping rod, dried, and demolded to obtain a base film.

[0119] The prepared basement membrane was modified by immersing it in a Tris-HCl buffer containing TA and APTES for 12 hours. After surface modification, the membrane was rinsed with deionized water. The modified membrane obtained in the previous step was then immersed in an Fe2(SO4)3 solution for crosslinking for 2 hours. After the crosslinking reaction was complete, it was rinsed with deionized water to obtain the modified membrane M-TA / AP / D. During the membrane modification process, the concentration of TA was 1g / L, the concentration of APTES was 1g / L, and the concentration of Fe2(SO4)3 solution was 2g / L.

[0120] 2) The performance of the modified membrane M-TA / AP / D obtained in the control group was compared with that of the ultra-low pressure separation membrane (M-TA / AP2) obtained in Example 3.

[0121] 2. Experimental results

[0122] Table 2

[0123]

[0124] From Table 2 and Figure 11 It can be seen that under no pressure (the minimum pressure of the pressure gauge is 0.02 MPa), the pure water flux of the M-TA / AP / D membrane is 49.6 L·m -2 ·h -1 In the present invention, the pure water flux of the optimal membrane M-TA / AP2 membrane is as high as 179.6 L·m -2 ·h -1 , which is 3.6 times the water flux of the M-TA / AP / D membrane, indicating that the nanoparticles prepared by TA and APTES are constructed into the membrane pores, and the capillary channels formed between the nanoparticles effectively provide capillary force, accelerating the rapid transmission of water molecules. At the same time, the flux of the M-TA / AP / D membrane for different types of dyes is 45.8 L·m -2 ·h -1 The retention rate of different dyes is above 91.2%, and the retention rate of salt is less than 10%. The M-TA / AP2 membrane maintains a high retention rate of more than 99.6% for different dyes and less than 10% for salt, while the flux of different dyes is as high as 149.0L·m -2 ·h -1The above is more than three times that of M-TA / AP / D membranes. The comparative results demonstrate the innovation of the patented invention. By introducing capillary force into the membrane, an ultra-low pressure, high-flux dye / salt separation membrane was prepared while maintaining high separation efficiency.

[0125] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalent features for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An ultra-low pressure separation membrane induced by capillary force based on biomimetic technology, characterized in that: The ultra-low pressure separation membrane includes a relatively dense separation layer located on the upper layer of the ultra-low pressure separation membrane, a support layer located below the separation layer and having a finger-shaped pore structure, and a micro-nano structure located in the finger-shaped pore structure and having a capillary effect. The micro-nano structure is a large number of hydrophilic nanoparticles generated in the finger-shaped pore structure. The capillary channels formed between the large number of hydrophilic nanoparticles provide capillary force for the ultra-low pressure separation membrane. The thickness of the ultra-low pressure separation membrane is 50-400 μm. The specific steps of the preparation method of the capillary force-induced ultra-low pressure separation membrane constructed based on biomimetic technology are as follows: 1) Preparation of a coagulation bath: Dissolve tannic acid in an HCl buffer solution containing tris(hydroxymethylaminomethane), then mix the solution with 3-aminopropyltriethoxysilane in ethanol, and allow to react for 1-8 hours to obtain a coagulation bath. 2) Preparation of the casting solution: Dry base membrane material, PEG, LiCl, and NMP were sequentially added to a three-necked flask and mechanically stirred at 65°C to 80°C for 6-12 hours to obtain a uniform casting solution. After standing to degas, the uniform casting solution was scraped onto a glass plate using a scraper. The glass plate with the casting solution was then immersed in a coagulation bath to prepare a modified membrane via the NIPS phase inversion method. 3) Cross-linking of the modified membrane: After the NIPS phase transformation is complete, the glass plate with the casting solution is continued to be immersed in the coagulation bath for 12 hours and then cross-linked with Fe2(SO4)3 to obtain an ultra-low pressure separation membrane; In step 1), the concentration of tannic acid is 0.5 g / L-2 g / L, and the concentration of 3-aminopropyltriethoxysilane is 0.5 g / L-2 g / L; The base film material in step 2) is one or more of polyvinylidene fluoride (PVDF), polyethersulfone (PES), polysulfone (PSF), and polyimide (PEI), and the molecular weight of PEG is 600-10,000; The concentration of Fe2(SO4)3 in step 3) is 0.5 g / L-10 g / L.

2. The ultra-low pressure separation membrane constructed by capillary force induction based on biomimetic technology according to claim 1, characterized in that: In step 1), the concentration of tannic acid is 1 g / L, and the concentration of 3-aminopropyltriethoxysilane is 1 g / L; The concentration of Fe2(SO4)3 in step 3) is 2 g / L.

3. Application of the ultra-low pressure separation membrane according to any one of claims 1 to 2 in dye desalination treatment and anti-fouling research.

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