A method for preparing a carbon nanomaterial-PVA dual-channel membrane and its application

Abstract

This invention discloses a method for preparing a carbon nanomaterial-PVA dual-channel membrane. First, carbon nanomaterials are blended with PVA to form a coating solution. This solution is coated onto a glass plate and dried to form a flat membrane. The membrane is then cut into wide rectangular membranes and narrow rectangular strips. Two wide rectangular membranes are stacked together, and water is applied to bond one end. The narrow rectangular strips are then bonded to the middle of the double membrane, without contacting the bonded end. Finally, the long sides of the double membrane are bonded together to obtain the dual-channel membrane. The carbon nanomaterials used in this invention are single-layer graphene, graphene quantum dots, or carbon nanotubes, possessing two-dimensional water channels, resulting in high selectivity and salt rejection. Simultaneously, the dual-channel membrane features a large surface area, good mechanical properties, unobstructed flow channels, and good sealing performance, overcoming the shortcomings of existing tubular membranes such as small area, easy leakage, and low packing density. During diffusion dialysis, it eliminates the need for traditional flat-sheet membrane diffusion dialysis equipment such as septa, gaskets, meshes, and nuts.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically relating to a method for preparing a carbon nanomaterial-PVA dual-channel membrane and its application. Background Technology

[0002] Diffusion dialysis is a membrane process that uses the concentration difference between solutions on both sides of a membrane as the driving force to separate feed solutions. Besides the most common hemodialysis, scientists frequently use diffusion dialysis to purify drugs or recover acids or alkalis from feed solutions. Currently, flat sheet membranes made of various polymer materials are commonly used. However, conventional polymer flat sheet membranes have two limitations in diffusion dialysis: firstly, a single polymer flat sheet membrane cannot simultaneously achieve high flux and high ion rejection rate, as there is a displacement effect between flux and rejection rate; secondly, polymer flat sheet membranes need to be installed in specific diffusion dialysis units, which contain heavy plexiglass or steel plates, numerous gaskets, septa, nuts, and other accessories, making the equipment bulky and the installation process complex.

[0003] Carbon nanomaterials such as graphene and carbon nanotubes exhibit excellent selective mass transfer properties, capable of transferring smaller hydrated ions in solution under concentration gradients. Studies have shown that the permeation rate of hydrated protons through graphene films is higher than that of metal cations (such as Fe). 3+ The difference is almost two orders of magnitude; when the concentration of the iron-based electrolyte decreases to a certain level, Fe... 3+ Ions will be completely blocked by the graphene film, while H + It can still transmit at high speeds, so graphene membranes can be used to recover acid from large quantities of waste iron-based electrolytes in the steel industry through cyclic filtration, thereby reducing costs and emissions. For example, engineers at MIT have successfully fabricated a highly efficient dialysis membrane with a thickness of only 20 nanometers using a single-layer carbon atom material, graphene sheets. This membrane can rapidly filter nano-sized aqueous solution molecules, making it the most advanced dialysis membrane currently available (10⁻⁶ nanometers thick). -2 The filtration speed is 10 times that of m / s (Advanced Materials, 2017, 29, 33, 1700277).

[0004] Chinese patent CN109277003B discloses a graphene ultrafiltration membrane and its preparation method. The method involves ultrasonically dispersing graphene oxide in water to obtain a graphene oxide dispersion, then adding 50 wt% hydrazine hydrate and 28 wt% ammonia to react and obtain a partially reduced graphene oxide solution. Cadmium nitrate tetrahydrate aqueous solution and hexamethylenetetramine aqueous solution are reacted in a high-temperature reactor to obtain cadmium hydroxide nanowires. These nanowires are dispersed in water to obtain a cadmium hydroxide nanowire solution, which is then mixed evenly with the partially reduced graphene oxide solution to obtain a reaction mixture B. This reaction mixture B is then vacuum-filtered onto a polymer porous microfiltration membrane to obtain a graphene ultrafiltration membrane. This graphene ultrafiltration membrane forms linear water flow channels between its membrane layers, increasing the rejection rate and effectively retaining organic pollutants while achieving a high water flux. However, the preparation process of this graphene ultrafiltration membrane is cumbersome, and the graphene only covers the surface of the polymer porous microfiltration membrane without good bonding with it, resulting in a short service life.

[0005] Chinese patent CN106492654A discloses a multifunctional graphene / polymer composite permeable membrane, its preparation method, and its applications. This method combines a moisture-wicking polymer with a graphene-based composite material, forming effective chemical bonds such as hydrogen bonds, ionic bonds, and covalent bonds through polar functional groups. This creates permeable channels with reinforced hydrophilic and hydrophobic groups on the basis of the moisture-wicking polymer, significantly improving the membrane's mechanical strength, abrasion resistance, acid and alkali resistance, antibacterial and antifouling capabilities, thermal conductivity, and heat resistance during water permeation. It is a long-life, self-cleaning, multifunctional composite permeable membrane that requires no replacement during operation. However, this composite membrane is a conventional flat sheet membrane with a small effective utilization area and a simple membrane structure, failing to fundamentally change the flux during separation.

[0006] A study published in *Separation and Purification Technology* (298, 2022, 121586) describes the preparation of a reduced graphene / CHZ nanofiltration composite membrane with ultrafast water permeability using carbazide (CHZ) as both a reducing agent and a crosslinking agent via a self-assembly vacuum filtration method. The obtained reduced graphene / CHZ nanofiltration membrane exhibits a water flux greater than 1600 Lm. -2 h - 1 bar -1The membrane exhibits excellent separation efficiency, with removal rates of up to 99% for Congo Red (CR), Malachite Green (MG), and Crystal Violet (CV). More importantly, this composite membrane demonstrates highly efficient and selective separation of various mixed dyes. Furthermore, the membrane maintains good stability after long-term immersion in solutions with varying pH values. Its separation performance, combining complete repulsion of single dyes with selective filtration of mixed dyes, makes it an ideal material for dye separation, purification, and reuse. However, the separation and filtration device was tested using a vacuum filtration system at a pressure of 0.9 bar, and only one type of recovered liquid could be obtained within a given timeframe. Although varying the flow rates of the feed solution and water can adjust the composition of the recovered liquid, the membrane's simple structure, being a flat sheet membrane, cannot fundamentally alter the flux and selectivity during separation.

[0007] The paper "Separation and Purification Technology" (235, 2020, 116147) describes a method using viscous PVA adhesive (15 wt%) to bond the two sides of a flat sheet membrane, forming a single-tube membrane with a length of 30-60 cm. This membrane can separate glyphosate acidified solutions containing HCl during diffusion dialysis. However, due to the high viscosity of the adhesive, it is difficult to coat evenly, resulting in slow coating speed and large usage. Consequently, the adhesive layer is uneven and prone to wrinkling, increasing its thickness. Furthermore, when the tubular membrane is filled with liquid, excessive bending can cause it to form a "V" shape, hindering liquid flow. Finally, during diffusion dialysis, because one side of the membrane is the feed solution and the other is water, when the feed concentration is high, water permeation is often very severe due to the osmotic pressure on both sides of the membrane. This manifests as less recovered liquid from the water-passing side and a large volume of residual liquid from the feed-passing side. At low water flow rates, no recovered liquid may even flow out, significantly reducing the recovery rate and increasing the volume of residual liquid. Summary of the Invention

[0008] To overcome the shortcomings of the prior art, this invention provides a method for preparing a carbon nanomaterial-PVA dual-channel membrane. This invention effectively combines carbon nanomaterials and PVA polymers, with the carbon nanomaterials uniformly dispersed within the PVA polymer matrix. Furthermore, a dual-channel structure is designed, effectively increasing the membrane area. The dual-channel membrane structure is equivalent to connecting two tubular membranes end-to-end to form a dual-channel structure, replacing the previous single-channel tubular membrane and avoiding the "V"-shaped bending phenomenon.

[0009] Technical solution

[0010] A method for preparing a carbon nanomaterial-PVA dual-channel membrane includes the following steps:

[0011] (1) Preparation of coating solution: Dissolve polyvinyl alcohol (PVA) in water to prepare a PVA aqueous solution with a mass concentration of 5-7%, then add carbon nanomaterial solution dropwise into the PVA aqueous solution and stir for 12-36 hours to obtain coating solution;

[0012] (2) Preparation of the film: The coating solution from step (1) is uniformly coated on a glass plate and then dried to obtain a flat film. After removing it from the glass plate, it is cut into a wide rectangular film and a narrow rectangular strip. The wide rectangular film has a length of 24-32cm and a width of 6-8cm, and the narrow rectangular strip has a length of 22-30cm and a width of 0.6-0.8cm.

[0013] (3) Preparation of double-channel membrane: Take two rectangular membranes with wide dimensions prepared in step (2), stack them together, and then apply water to one end of the two membranes to bond them together. The width of the bonding area is 0.5-1.5cm, resulting in a double-layer membrane bonded at one end. Peel off the non-bonded end of the double-layer membrane, and bond the lower surface of the narrow rectangular strip to the middle of the membrane below the double-layer membrane. Align one end of the rectangular strip with the top of the non-bonded end of the membrane below the double-layer membrane, and the other end is 2-4cm away from the bottom of the bonded end of the membrane below the double-layer membrane. Cover the non-bonded end of the double-layer membrane, bond the upper surface of the rectangular strip to the membrane above the double-layer membrane, and then bond the long sides of both sides of the double-layer membrane to obtain a double-channel membrane with two openings at one end and bonded at the other end.

[0014] Furthermore, in step (1), the carbon nanomaterial is one of single-layer graphene, graphene quantum dots, or carbon nanotubes.

[0015] Furthermore, in step (1), when the carbon nanomaterial solution is dropped into the PVA aqueous solution, the PVA aqueous solution is preheated to 50-70℃.

[0016] Furthermore, in step (1), the mass ratio of the carbon nanomaterial to PVA is (1-4):6000.

[0017] Furthermore, in step (2), the thickness of the flat sheet membrane is 0.08-0.14 mm.

[0018] Furthermore, in step (3), the amount of water applied is controlled such that 1 mL of water covers an area of ​​15-25 cm². 2 The temperature of the water used for coating should be controlled between 15-60℃.

[0019] The carbon nanomaterial-PVA dual-channel membrane prepared by the above method is applied in diffusion dialysis. The application method is as follows: the carbon nanomaterial-PVA dual-channel membrane is vertically suspended in a container filled with mother liquor, with the opening facing upwards. The opening of the carbon nanomaterial-PVA dual-channel membrane is higher than the height of the mother liquor in the container. During use, the feed solution to be treated is continuously fed into one opening of the carbon nanomaterial-PVA dual-channel membrane for diffusion dialysis, while the residual liquid is continuously discharged from the other opening.

[0020] Compared with existing technologies, the present invention has the following beneficial effects:

[0021] (1) This invention incorporates carbon nanomaterials into the PVA matrix, fully utilizing the two-dimensional water channels and high salt rejection rate of carbon nanomaterials. This results in a carbon nanomaterial / PVA composite membrane exhibiting high selectivity and retention rate during the recovery of acidic solutions. Simultaneously, the permeation rate of hydrated protons within the carbon nanomaterial film far exceeds that of metal cations (such as Fe). 3+ The rate of separation is such that carbon nanomaterials / PVA membranes can be used to separate acidic liquids via semi-dynamic diffusion dialysis.

[0022] (2) This invention features a dual-channel structure, overcoming the "V"-shaped bending phenomenon of existing tubular membranes. The dual-channel membrane can be vertically placed into small volumes of mother liquor, increasing the membrane packing density and facilitating diffusion dialysis. In contrast, existing tubular membranes, when placed in mother liquor, exhibit a "V"-shaped bend due to the limited volume of the container, making them prone to breakage and hindering liquid flow. The dual-channel membrane boasts a larger surface area, unobstructed flow channels, and leak-proof design, overcoming the limitations of previously reported tubular membranes such as small surface area, easy leakage, and insufficient packing density. During diffusion dialysis, it eliminates the need for traditional flat-sheet membrane diffusion dialysis equipment such as diaphragms, gaskets, mesh screens, and nuts.

[0023] (3) The dual-channel membrane prepared in this invention has unique advantages in the field of diffusion dialysis, unlike the membranes reported in current literature and patents:

[0024] ① Compared with the BPPO / PVA flat sheet membrane applied to diffusion dialysis reported in Chinese Patent ZL201210206572.6, the present invention does not require accessories such as plexiglass tank, gasket, nut and stirrer. The dual-channel membrane has the advantages of large effective area, high membrane weight ratio and fast separation speed.

[0025] ② Compared with Chinese Patent ZL201710256743.9 and Journal of Membrane Science (563, 2018, 142–148), the dual-channel membrane of the present invention does not require accessories such as outer plate, gasket, separator, and nut during diffusion dialysis. The dual-channel membrane has the advantages of low cost, high membrane weight ratio, and smooth flow channel.

[0026] ③ Compared to graphene dialysis membranes (Advanced Materials, 2017, 29, 33, 1700277), although carbon materials possess excellent mechanical, thermal, and chemical stability, their poor dispersibility limits their further application. This invention effectively links PVA and carbon nanomaterials through polar functional groups to form hydrogen bonds, ionic bonds, and covalent bonds, thereby improving the mechanical strength, abrasion resistance, and acid and alkali resistance of the composite membrane during dialysis. Therefore, the carbon nanomaterials used in this invention are selected from single-layer oily graphene dispersions, oily graphene quantum dot solutions, or carbon nanotube powders, which are doped with PVA to prepare carbon nanomaterial / PVA composite membranes. These composite membranes are then used for diffusion dialysis separation of the feed solution.

[0027] ④ Compared with the tubular membrane reported in *Separation and Purification Technology* (235, 2020, 116147), this invention introduces carbon nanomaterials into the PVA mother liquor. Carbon nanomaterials possess excellent selective mass transfer characteristics, capable of transferring smaller hydrated ions in the solution under concentration gradient conditions, thereby giving the membrane high selectivity and salt rejection rate. Secondly, the dual-channel structure overcomes the problem of fluid resistance caused by the "V"-shaped bend in the dialyzer of the reported tubular membrane, allowing for natural and smooth flow of the feed solution in the channels. Finally, during the bonding process, the dual-channel membrane overcomes the problems of large adhesive layer thickness, wrinkling, and leakage inherent in the reported tubular membrane. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the single-layer graphene-PVA dual-channel membrane prepared in Example 1; wherein, 1-wide rectangular membrane 1; 2-narrow rectangular strip; 3-adhesive end; 4-opening.

[0029] Figure 2 This is a schematic diagram of the apparatus for diffusion dialysis using the single-layer graphene-PVA dual-channel membrane prepared in Example 1. Detailed Implementation

[0030] To further understand the present invention, the technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. In the following embodiments, the single-layer graphene, graphene quantum dots, and carbon nanotubes used were all purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd., but are not limited thereto.

[0031] Example 1: Preparation of a single-layer graphene-PVA dual-channel membrane

[0032] A method for preparing a single-layer graphene-PVA dual-channel membrane includes the following steps:

[0033] (1) Preparation of coating solution: Polyvinyl alcohol (PVA) was dissolved in water to prepare 600 mL of PVA aqueous solution with a mass concentration of 5%; 10 mL of monolayer graphene aqueous solution with a mass concentration of 1 mg / mL was sonicated for 30 min and then dissolved in 50 mL of DMF to obtain monolayer graphene organic solution, which was then added dropwise to the above PVA aqueous solution preheated to 60℃ and stirred for 24 h to obtain coating solution;

[0034] (2) Preparation of the film: The coating liquid from step (1) is uniformly coated on a glass plate and then dried in a ventilated environment to obtain a flat film with a thickness of 0.09 mm. After removing it from the glass plate, it is cut into two wide rectangular films and one narrow rectangular strip. The wide rectangular films are 28 cm long and 6 cm wide, and the narrow rectangular strip is 24 cm long and 0.6 cm wide.

[0035] (3) Preparation of the double-channel membrane: Take the two rectangular membranes with wide dimensions prepared in step (2), stack them together, and then apply water to one wide end of the two membranes to bond them together. The bonding area is 1 cm wide, resulting in a double-layer membrane bonded at one end. The amount of water applied is controlled to be 1 mL, and the coating area is 20 cm². 2 The water temperature is controlled at 35℃. The non-adhesive end of the double-layer membrane is peeled off. The lower surface of a narrow rectangular strip is adhered to the middle of the membrane sheet below the double-layer membrane. One end of the rectangular strip is aligned with the top of the non-adhesive end of the membrane sheet below the double-layer membrane, and the other end is 3cm away from the bottom of the adhesive end of the membrane sheet below the double-layer membrane. Water is dripped onto the part of the rectangular strip near the bottom of the adhesive end of the double-layer membrane. Then, pressure is applied along the length of the rectangular strip, and the water adheres along the direction of pressure until the entire rectangular strip is adhered to the membrane sheet below. The non-adhesive end of the double-layer membrane is covered, and the upper surface of the rectangular strip is adhered to the membrane sheet above the double-layer membrane. Water is then applied to the long sides of both sides of the double-layer membrane to adhere them, resulting in a double-channel membrane with two openings at one end and an adhesive end at the other. This is the carbon nanomaterial-PVA double-channel membrane.

[0036] The structure of the carbon nanomaterial-PVA dual-channel membrane prepared in this embodiment is as follows: Figure 1As shown, the dual-channel membrane of the present invention contains two wide rectangular membranes 1 and a narrow rectangular strip 2. The long sides of the two wide rectangular membranes 1 are bonded together, and one end of the two wide rectangular membranes 1 is bonded together to form a bonding end 3. The other end is divided into two openings 4 by the narrow rectangular strip 2.

[0037] The physical dimensions, water content, and linear expansion coefficient of the monolayer graphene-PVA dual-channel membrane prepared in Example 1 were tested. The test methods are referenced in (Separation and Purification Technology, 184, 2017, 1–11). The test results show that the effective area of ​​the dual-channel membrane is 214 cm². 2 The tube volume is 100±5mL, the water content of the double-tube membrane is 145.6%, and the linear expansion coefficient is 10.5%. The weight percentage of the wet membrane in the diffusion dialysis tank is 3.3%, which is much higher than the membrane weight ratio of traditional flat sheet membrane diffusion dialysis equipment (0.4-1.7%, see Separation and Purification Technology, 235, 2020, 116-147).

[0038] The graphene-PVA dual-channel membrane prepared in Example 1 was used for diffusion dialysis to separate acid. A schematic diagram of the apparatus is shown below. Figure 2 As shown, the method is as follows: using a 1L large volume cylinder as a container, add 500mL of water as the mother liquor, and prepare 0.5L of H2SO4 / FeSO4 acid solution as the feed solution. The acid solution contains H... + The ion concentration is 3.1 mol L. -1 (M), Fe 2+ The ion concentration was 0.26 M. A graphene-PVA dual-channel membrane was vertically suspended in a container filled with mother liquor, with the opening of the membrane facing upwards and higher than the height of the mother liquor in the container. Feed solution was introduced into one opening of the membrane at a rate of 61.8 mL / h, with the liquid level 12 cm above the mother liquor level. Diffusion dialysis was performed. Residual liquid was discharged from the other opening of the membrane. The residual liquid was collected every 1 hour, and the H+ in the recovered solution (mother liquor) and the residual liquid was tested. + Ion concentration and Fe 2+ Ion concentration was determined, and recovery and rejection rates were calculated. The entire semi-dynamic diffusion dialysis process ran for 6 hours.

[0039] H + The ion concentration was titrated with a standard Na₂CO₃ solution (0.05 M), Fe 2+ The concentration of the ions was titrated with KMnO4 solution (0.002 M). Recovery rate R H and retention rate (η) Fe The calculation formula for ) is as follows:

[0040] R H (%) = (C) d-H ×V d )×100 / (C f-H ×V feed (1)

[0041] η Fe (%) = (1-C) d-Fe ×V d / (C f-Fe ×V feed ))×100 (2)

[0042] In the formula, C d-H For the H in the recovery liquid + Ion concentration, V d C represents the volume of the recovered liquid. f-H For H in the raw material liquid + concentration, V feed C represents the volume of the raw material liquid. d-Fe Fe in the recovery liquid 2+ Ion concentration, C f-Fe Fe in the raw material solution 2+ Ion concentration.

[0043] The test results are shown in Table 1:

[0044] Table 1. Separation of H2SO4 / FeSO4 acid solution in semi-dynamic diffusion dialysis using a single-layer graphene-PVA dual-channel membrane in Example 1.

[0045]

[0046] As shown in Table 1, after 6 hours of semi-dynamic diffusion dialysis, the H in the recovered solution... + The ion concentration is 1.283 M, H + The ion recovery rate reached 49.9%, Fe 2+ The ion rejection rate was 89.2%, indicating a good separation effect.

[0047] Example 2: Preparation of graphene quantum dot-PVA dual-channel membrane

[0048] Replace the 10 mL monolayer graphene aqueous solution with a mass concentration of 1 mg / mL in step (1) with a 10 mL graphene quantum dot aqueous solution with a mass concentration of 1 mg / mL, and the rest is the same as in Example 1.

[0049] The effective area of ​​the graphene quantum dot-PVA dual-channel membrane was measured to be 295.7 cm². 2The tube contains 105±5 mL of water with a water content of 103.3% and a linear expansion coefficient of 19.8%. The wet membrane accounts for 3.6% of the total weight in the dialysis tank.

[0050] To compare the effect of graphene quantum dot doping, a reference sample was prepared using the same steps, but the reference sample did not contain graphene quantum dots and was simply PVA.

[0051] The dual-channel membrane prepared in Example 2 was used for diffusion dialysis to separate acid, following the same test protocol as in Example 1. The test results are shown in Table 2.

[0052] Table 2. Separation of H2SO4 / FeSO4 acid solution in semi-dynamic diffusion dialysis using the graphene quantum dot-PVA dual-channel membrane in Example 2.

[0053]

[0054] As shown in Table 2, after 6 hours of semi-dynamic diffusion dialysis, H + The ion recovery rate reached 51.0%, Fe 2+ The ion rejection rate was 88.3%; while the reference sample H + The ion recovery rate was only 26.7%. During the semi-dynamic diffusion dialysis process, as time progressed, the H+ ions in the residual liquid flowing out of the tube increased. + The ion concentration initially decreased rapidly, then gradually stabilized, while Fe... 2+ The ion concentration decreases slowly. As the flow rate increases, the acid concentration in the residual liquid increases.

[0055] Example 3: Preparation of carbon nanotube-PVA dual-channel membrane

[0056] The 10 mL monolayer graphene aqueous solution with a mass concentration of 1 mg / mL in step (1) was replaced with 10 mg of carbon nanotube powder to prepare a carbon nanotube-PVA dual-channel membrane.

[0057] The effective area of ​​the carbon nanotube-PVA bipolar membrane was measured to be 215 cm². 2 The tube has a volume of 80±5 mL, a water content of 115.1%, a linear expansion coefficient of 14.7%, and a wet membrane weight percentage of 3.5% in the dialysis tank.

[0058] The dual-channel membrane prepared in Example 3 was used for diffusion dialysis to separate acid, following the same test scheme as in Example 1. The test results are shown in Table 3.

[0059] Table 3. Separation of H2SO4 / FeSO4 acid solution in semi-dynamic diffusion dialysis using carbon nanotube-PVA dual-channel membrane in Example 3.

[0060]

[0061] As shown in Table 3, after 6 hours of semi-dynamic diffusion dialysis, H + The ion recovery rate reached 35.4%, Fe 2+ The ion rejection rate was 97.1%.

Claims

1. A method for preparing a carbon nanomaterial-PVA dual-channel membrane, characterized in that, Includes the following steps: (1) Preparation of coating solution: PVA is dissolved in water to prepare a PVA aqueous solution with a mass concentration of 5-7%. Then, carbon nanomaterial solution is added dropwise to the PVA aqueous solution and stirred for 12-36 hours to obtain the coating solution. (2) Preparation of the film: The coating solution from step (1) is uniformly coated on a glass plate and then dried to obtain a flat film. After removing it from the glass plate, it is cut into a wide rectangular film and a narrow rectangular strip. The wide rectangular film has a length of 24-32cm and a width of 6-8cm, and the narrow rectangular strip has a length of 22-30cm and a width of 0.6-0.8cm. (3) Preparation of double-channel membrane: Take two rectangular membranes with wide dimensions prepared in step (2), stack them together, and then apply water to one end of the two membranes to bond them together. The width of the bonding area is 0.5-1.5cm, resulting in a double-layer membrane bonded at one end. Peel off the non-bonded end of the double-layer membrane, and bond the lower surface of the narrow rectangular strip to the middle of the membrane below the double-layer membrane. Align one end of the rectangular strip with the top of the non-bonded end of the membrane below the double-layer membrane, and the other end is 2-4cm away from the bottom of the bonded end of the membrane below the double-layer membrane. Cover the non-bonded end of the double-layer membrane, bond the upper surface of the rectangular strip to the membrane above the double-layer membrane, and then bond the long sides of both sides of the double-layer membrane to obtain a double-channel membrane with two openings at one end and bonded at the other end.

2. The method for preparing the carbon nanomaterial-PVA dual-channel membrane as described in claim 1, characterized in that, In step (1), the carbon nanomaterial is one of single-layer graphene, graphene quantum dots or carbon nanotubes.

3. The method for preparing the carbon nanomaterial-PVA dual-channel membrane as described in claim 1, characterized in that, In step (1), when the carbon nanomaterial solution is dropped into the PVA aqueous solution, the PVA aqueous solution is preheated to 50-70℃.

4. The method for preparing the carbon nanomaterial-PVA dual-channel membrane as described in claim 1, characterized in that, In step (1), the mass ratio of carbon nanomaterial to PVA is (1-4):6000.

5. The method for preparing the carbon nanomaterial-PVA dual-channel membrane as described in claim 1, characterized in that, In step (2), the thickness of the flat diaphragm is 0.08-0.14 mm.

6. The method for preparing the carbon nanomaterial-PVA dual-channel membrane according to any one of claims 1-5, characterized in that, In step (3), the amount of water applied is controlled such that 1 mL of water covers an area of ​​15-25 cm². 2 The temperature of the water used for coating should be controlled between 15-60℃.

7. The application of the carbon nanomaterial-PVA dual-channel membrane prepared by the method according to any one of claims 1-6 in diffusion dialysis.

8. The application as described in claim 7, characterized in that, The application method is as follows: The carbon nanomaterial-PVA dual-channel membrane is suspended vertically in a container containing mother liquor with the opening facing upwards. The opening of the carbon nanomaterial-PVA dual-channel membrane is higher than the height of the mother liquor in the container. When in use, the liquid to be treated is continuously input into one opening of the carbon nanomaterial-PVA dual-channel membrane for diffusion dialysis, and the residual liquid is continuously output from the other opening of the carbon nanomaterial-PVA dual-channel membrane.

Images