Carbon nanofiber polymer cation-selective membrane, preparation method and application

Abstract

The application belongs to the field of selective membranes, and particularly relates to a carbon nanofiber polymer cation selective membrane, a preparation method and application. The carbon nanofiber polymer cation selective membrane has a dense three-dimensional porous structure and a high surface charge density. In the application of reverse electrodialysis salt gradient energy conversion, the carbon nanofiber polymer cation selective membrane has excellent ion flux and ion selectivity. The carbon nanofiber polymer cation selective membrane can be applied to a salt gradient power generation system, and high-performance salt gradient energy conversion can be obtained under different salt gradient and different pH value electrolyte solution environments.

Description

Technical Field

[0001] This invention belongs to the field of selective membranes, specifically relating to a carbon nanofiber polymer cation selective membrane, its preparation method, and its application. Background Technology

[0002] Many countries around the world are promoting the development of renewable energy harvesting technologies, among which reverse electrodialysis (RED) technology can directly convert the permeation energy present at the confluence of oceans and rivers into electrical energy. Ion-selective membranes are one of the most important components of RED systems; ideally, an ion-selective membrane should possess high power density, excellent stability, and sufficient mechanical strength. In recent years, a large number of novel membranes for converting permeation energy have been developed. However, some of these membranes are difficult to manufacture on a large scale, even if this can be achieved at a relatively low unit cost. Furthermore, issues such as high porosity, high mechanical strength, and high surface charge density need to be addressed. Finally, the stability of ion-selective membranes should be tested in practical applications of permeation energy.

[0003] Nanofluidic systems with different structures and properties are used for energy conversion. Nanofluidic channels are generally classified into one-dimensional (1D) nanopore channels, two-dimensional (2D) ion-selective membranes, three-dimensional (3D) fluid systems, and hybrid nanofluidic systems. Although the shape and size of one-dimensional nanopores (such as molybdenum disulfide channels) can be arbitrarily designed, their practical applications are limited by their high internal resistance, low porosity, and high fabrication cost. Furthermore, 2D ion-selective membranes (such as graphene oxide membranes) are typically formed by stacking 2D nanosheets to create continuous ion channels, and they have significant potential for applications in permeation energy harvesting. However, large-area fabrication of two-dimensional material membranes via vacuum filtration is challenging. In addition, hybrid nanofluidic systems generally exhibit high rectification effects and high energy harvesting potential, but suffer from weak interfacial bonding and poor stability. Due to their unique structure, 3D ion channels have attracted considerable interest in salinity gradient power generation. Their three-dimensional structure provides a richer array of ion channels and significantly shortens the ion transport path, resulting in higher ion conductivity.

[0004] Ion-selective membranes based on carbon nanomaterials have been shown to significantly improve permeability and energy conversion performance, with carbon nanofiber (CNF) membranes being an excellent choice due to their inherent three-dimensional porous structure and feasibility for large-scale fabrication. According to Debye's theory, the optimal channel size and high surface charge density formed by the dense three-dimensional network structure will more precisely regulate ion transport. However, CNF membranes prepared by conventional electrospinning suffer from drawbacks such as large pores, low surface charge density, and poor hydrophobicity. Therefore, there is an urgent need to develop an ion-selective membrane with high porosity, high surface charge density, high mechanical strength, and high salt gradient energy conversion efficiency.

[0005] This invention proposes a carbon nanofiber polymer cation-selective membrane to overcome the above-mentioned defects. Summary of the Invention

[0006] The purpose of this invention is to provide a carbon nanofiber polymer cation-selective membrane, its preparation method, and its application. Specifically, it provides a novel cation-selective membrane based on a three-dimensional porous structure of carbon nanofiber polymers. This membrane has excellent stability and is easy to convert salt gradient energy into electrical energy.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a carbon nanofiber polymer cation-selective membrane, comprising the following steps:

[0009] S1: Using Tris-HCl buffer as the base solution, add a solution containing DA, PSSNa, CuSO4, and H2O2 to form a mixed solution;

[0010] S2: The oxidized graphene@carbon nanofibers are vertically placed into the mixed solution for in-situ polymerization. PDA and PSSNa are uniformly filled into the three-dimensional voids of the graphene@carbon nanofibers to obtain the three-dimensional porous carbon nanofiber polymer cation-selective membrane.

[0011] As a preferred embodiment of the present invention, the Tris-HCl buffer solution has a pH of 8.5 and a concentration of 50 mmol / L.

[0012] As a preferred embodiment of the present invention, the concentrations of DA, PSSNa, CuSO4, and H2O2 are 2 mg / mL, 2 mg / mL, 5 mmol / mL, and 19.6 mmol / mL, respectively.

[0013] As a preferred embodiment of the present invention, the graphene@carbon nanofiber is prepared by traditional electrospinning process, and then carbonized in ammonia gas and treated by chemical vapor deposition for 30-480 min to grow vertical graphene sheets in situ, thus obtaining graphene@carbon nanofiber. The oxidation treatment is performed by plasma cleaning machine for 1-10 min.

[0014] As a preferred embodiment of the present invention, the in-situ polymerization temperature in step S2 is 25°C.

[0015] In a second aspect, the present invention provides a carbon nanofiber polymer cation-selective membrane obtained by the above preparation method, which has a dense three-dimensional porous structure of graphene oxide@carbon nanofibers, wherein PDA and PSSNa are uniformly filled in the pores of the graphene oxide@carbon nanofibers through in-situ polymerization.

[0016] A third aspect of the present invention provides an application of the above-described carbon nanofiber polymer cation-selective membrane.

[0017] As a preferred technical solution of the present invention, the application method is to place the carbon nanofiber polymer cation-selective membrane between a high-concentration salt solution and a low-concentration salt solution. Ag / AgCl electrodes are respectively set in the high-concentration salt solution and the low-concentration salt solution. Since the cation-selective membrane carries a negative charge, when the cations and anions in the high-concentration salt solution tend to migrate to the low-concentration salt solution under the drive of the salt difference, the cation-selective membrane allows the cations to pass through and blocks the migration of anions, thereby generating the directional movement of charges, that is, generating current, and realizing the conversion of salt difference energy into electrical energy.

[0018] As a preferred embodiment of the present invention, the molar concentration ratio of the low-concentration salt solution to the high-concentration salt solution is 0.000001:0.00001~1.

[0019] As a preferred embodiment of the present invention, the high-concentration salt solution and the low-concentration salt solution are any one of potassium chloride solution, sodium chloride solution, lithium chloride solution, calcium chloride solution, and magnesium chloride solution, and the salt types of the high-concentration salt solution and the low-concentration salt solution are the same.

[0020] The beneficial effects of this invention are:

[0021] The method for preparing the carbon nanofiber polymer cation-selective membrane provided by this invention is simple and easy to control. The resulting carbon nanofiber polymer cation-selective membrane exhibits high ion selectivity and high permeability conductivity, achieving high and stable output when applied to salinity gradient energy generation, and also demonstrates strong anti-fouling capabilities. The energy density of the carbon nanofiber polymer cation-selective membrane provided by this invention can reach 7.5 watts per square meter, far exceeding that of commercial ion exchange membranes under the same conditions. Attached Figure Description

[0022] Figure 1 The image shows a scanning electron microscope (SEM) image and elemental analysis diagram of the carbon nanofiber polymer cation-selective membrane in Example 1.

[0023] Figure 2 The graph shows the ionic conductivity of the carbon nanofiber polymer cation-selective membrane in Example 1 in electrolyte solutions of different concentrations.

[0024] Figure 3 The graph shows the transmittance curves of the cationic fluorescent dye Rhodamine 6G and the anionic fluorescent dye fluorescein sodium through the carbon nanofiber polymer cationic selective membrane in Example 1.

[0025] Figure 4This is a schematic diagram of the salt gradient energy conversion device of the carbon nanofiber polymer cation selective membrane in Example 2;

[0026] Figure 5 The graph shows the changes in current density and output power density of the carbon nanofiber polymer cation selective membrane in Example 2 under different external resistances.

[0027] Figure 6 This is a graph showing the change in output power density of the carbon nanofiber polymer cation-selective membrane in Example 2 over a period of 10 days.

[0028] Figure 7 The ultraviolet spectra of carbon nanofiber polymer cation-selective membrane, bovine serum albumin, carbon nanofibers, and graphene oxide@carbon nanofibers in Example 3 are shown below.

[0029] Figure 8 This is a graph showing the adsorption of bovine serum albumin by the carbon nanofiber polymer cation-selective membrane, carbon nanofibers, and graphene oxide@carbon nanofibers in Example 3.

[0030] Figure 9 The image shows the zeta potential diagrams of the carbon nanofiber polymer cation-selective membrane in Example 3 before and after it was contaminated with protein.

[0031] The technical solution of the present invention will be further described in detail below through specific implementation methods and embodiments. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below through specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This embodiment provides a method for preparing a carbon nanofiber polymer cation-selective membrane, including the following steps:

[0035] (1) Carbon nanofibers were prepared by traditional electrospinning process, and then carbonized in ammonia gas and treated by chemical vapor deposition for 30-480 min to grow vertical graphene sheets in situ, thus obtaining graphene@carbon nanofibers. Figure 1 The scanning electron microscope (SEM) image and elemental analysis diagram of the carbon nanofiber polymer cation-selective membrane are shown. Figure 1 a and Figure 1 c shows the scanning electron microscope (SEM) images of the thin film in its planar and cross-sectional areas, respectively. Figure 1b and 1d are their corresponding EDS mapping diagrams, which show that the polymer grows in large quantities on the surface of carbon nanofibers / graphene oxide.

[0036] (2) The graphene@carbon nanofibers were oxidized for 1 to 10 minutes using a plasma cleaner. In this embodiment, the treatment was 2 minutes. Through oxidation, oxygen-containing functional groups were obtained on the surface of graphene and carbon fibers, which prepared them for subsequent chemical modification.

[0037] (3) Prepare Tris-HCl buffer with a pH of 8.5 and a concentration of 50 mmol / L.

[0038] (4) Using the above Tris-HCl buffer as the base solution, add a solution containing DA (dopamine), PSSNa (sodium polystyrene sulfonate), CuSO4 and H2O2 to form a mixed solution, wherein the concentrations of DA, PSSNa, CuSO4 and H2O2 are 2 mg / mL, 2 mg / mL, 5 mmol / mL and 19.6 mmol / mL, respectively.

[0039] (5) The oxidized graphene@carbon nanofibers are vertically placed into the mixed solution, and in-situ polymerization is carried out at 25°C. PDA (polydopamine) and PSSNa are uniformly filled into the three-dimensional voids of the graphene@carbon nanofibers to obtain the three-dimensional porous carbon nanofiber polymer cation-selective membrane. In this step, copper sulfate and hydrogen peroxide generate reactive oxygen species (ROS) in an alkaline medium, including O2. ·- HO2 · and OH · These free radicals can increase the self-polymerization rate of dopamine. Small amounts of copper sulfate and hydrogen peroxide can improve the surface uniformity after in-situ polymerization. After in-situ polymerization, polydopamine contains a large number of phenolic hydroxyl groups, and sodium polystyrene sulfonate contains a large number of sulfonic acid groups, providing a large amount of surface charge for ion channels. Figure 2 The figure shows the ionic conductivity of the carbon nanofiber polymer cation-selective membrane in different concentration electrolyte solutions in this embodiment. It can be seen from the figure that the ion transport of the membrane is regulated by the surface charge of the ion channel. Figure 3 The transmittance curves of the cationic fluorescent dye Rhodamine 6G and the anionic fluorescent dye fluorescein sodium through the carbon nanofiber polymer cationic selective membrane in this embodiment are shown, demonstrating that the membrane has good cationic selectivity.

[0040] Example 2

[0041] This embodiment provides an application of the carbon nanofiber polymer cation-selective membrane of Example 1 in salinity gradient power generation. The application method involves placing the carbon nanofiber polymer cation-selective membrane between a high-concentration salt solution and a low-concentration salt solution. Ag / AgCl electrodes are respectively placed in the high-concentration and low-concentration salt solutions. Since the cation-selective membrane carries a negative charge, when cations and anions in the high-concentration salt solution tend to migrate to the low-concentration salt solution under the drive of the salinity gradient, the cation-selective membrane allows cations to pass through while blocking the migration of anions, thereby generating a directional movement of charge, i.e., generating current, realizing the conversion of salinity gradient energy into electrical energy. The molar concentration ratio of the low-concentration salt solution to the high-concentration salt solution is 0.000001:0.00001 to 1. The application range is wide, and the high-concentration and low-concentration salt solutions can be any one of potassium chloride solution, sodium chloride solution, lithium chloride solution, calcium chloride solution, and magnesium chloride solution. The requirement is that the salt types in the high-concentration and low-concentration salt solutions must be consistent. In this embodiment, the high-concentration salt solution was selected from the Yellow Sea near Qingdao, and the low-concentration salt solution was selected from Qingdao's tap water. The Ag / AgCl electrodes at both ends were electrically connected to a picoammeter and a variable resistance box, respectively. The specific device structure is shown in the attached figure. Figure 4 As shown in the attached figure, a salinity gradient power generation experiment was conducted using the above-mentioned device. The changes in current density and output power density measured under different external resistors are shown in the attached figure. Figure 5 As shown in the attached figure. To verify the continuity of this device, a 10-day power generation test was conducted, and the output power density variation is shown in the attached figure. Figure 6 As shown, this device can maintain a stable output.

[0042] Example 3

[0043] This embodiment tests the anti-protein contamination of the carbon nanofiber polymer cation-selective membrane of Example 1. Bovine serum albumin (BSA) was used as the protein contaminant in this embodiment, with a protein concentration of 1000 mg / L. The specific experimental method is as follows: a 5 cm × 5 cm carbon nanofiber polymer cation-selective membrane was completely rinsed with phosphate-buffered saline (PBS, pH = 7.4), and then contacted with 20 mL of PBS solution containing 1000 mg / L BSA for 12 h at room temperature. The BSA solution was drained, and all loose BSA molecules were rinsed with deionized water. The wash water and used BSA solution were collected together, and the amount of BSA adsorbed was measured. The amount adsorbed was confirmed by comparing it with 1000 mg / L BSA. The same testing method was used for carbon nanofibers and graphene oxide@carbon nanofibers, compared with this embodiment. The BSA content was detected at 280 nm using a UV spectrophotometer. The results are attached. Figures 7 to 9 As shown in the figure, the cation-selective membrane has excellent resistance to protein fouling. Figure 9 As can be seen, the potential value did not change significantly before and after contamination, indicating that the carbon nanofiber polymer cation-selective membrane of Example 1 has excellent anti-protein contamination properties.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. The order of description in the above preparation method does not represent the order of operations in actual implementation. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanofiber polymer cation-selective membrane, characterized in that, Includes the following steps: S1: Using Tris-HCl buffer as the base solution, add DA, PSSNa, and CuSO4. 4、 The solution of H2O2 forms a mixed solution; S2: The oxidized graphene@carbon nanofibers are vertically placed into the mixed solution for in-situ polymerization. PDA and PSSNa are uniformly filled into the three-dimensional voids of the oxidized graphene@carbon nanofibers to obtain the carbon nanofiber polymer cation-selective membrane.

2. The preparation method according to claim 1, characterized in that, The Tris-HCl buffer solution has a pH of 8.5 and a concentration of 50 mmol / L.

3. The preparation method according to claim 2, characterized in that, The DA, PSSNa, CuSO 4、 The H2O2 concentrations were prepared at 2 mg / mL, 2 mg / mL, 5 mmol / mL, and 19.6 mmol / mL.

4. The preparation method according to claim 2, characterized in that, The graphene@carbon nanofibers are prepared by traditional electrospinning process, carbon nanofibers are then carbonized in ammonia gas and treated by chemical vapor deposition for 30-480 min to grow vertical graphene sheets in situ, thus obtaining graphene@carbon nanofibers. The oxidation treatment is performed by plasma cleaning machine for 1-10 min.

5. The preparation method according to claim 2, characterized in that, The in-situ polymerization temperature in step S2 is 25°C.

6. The carbon nanofiber polymer cation-selective membrane obtained by the preparation method according to any one of claims 1 to 5, characterized in that, It has a dense three-dimensional porous structure of graphene oxide@carbon nanofibers, in which PDA and PSSNa are uniformly filled in the voids by in-situ polymerization.

7. The application of the carbon nanofiber polymer cation selective membrane as described in claim 6 in salinity gradient power generation.

8. The application according to claim 7, characterized in that, The application method involves placing the carbon nanofiber polymer cation-selective membrane between a high-concentration salt solution and a low-concentration salt solution. Ag / AgCl electrodes are respectively placed in the high-concentration and low-concentration salt solutions. Since the cation-selective membrane carries a negative charge, when the cations and anions in the high-concentration salt solution tend to migrate to the low-concentration salt solution under the drive of the salt gradient, the cation-selective membrane allows the cations to pass through and blocks the migration of anions, thereby generating a directional movement of charge, i.e., generating current, and realizing the conversion of salt gradient energy into electrical energy.

9. The application according to claim 8, characterized in that, The molar concentration ratio of the low-concentration salt solution to the high-concentration salt solution is 0.000001:0.00001~1.

10. The application according to claim 8, characterized in that, The high-concentration salt solution and the low-concentration salt solution are any one of potassium chloride solution, sodium chloride solution, lithium chloride solution, calcium chloride solution, and magnesium chloride solution, and the salt types of the high-concentration salt solution and the low-concentration salt solution are the same.

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