A dual-molecule modified graphene-based ion-selective membrane, and a preparation method and application thereof

Abstract

The application discloses a kind of amphiphilic molecule modified graphene-based ion selective membrane and its preparation method and application.The application is sequentially poured into alkaline graphene oxide aqueous solution with the cationic surfactant aqueous solution containing N(CH3)2 + And the aqueous solution containing-COO ‑ Of polymer, after being mixed uniformly, membrane is extracted into film, the film is dried and annealed, and the amphiphilic molecule modified graphene-based ion selective membrane is obtained.In the application, due to the electrostatic interaction between the N(CH3)2 + Region of the polar head of dioctadecyldimethylammonium bromide and-COO ‑ Of sodium polyacrylate, the ion selective membrane shows good ion selective performance.The ion selective membrane exhibits stable power generation performance by the synergistic effect of dioctadecyldimethylammonium bromide, sodium polyacrylate and graphene oxide.

Description

Technical Field

[0001] This invention relates to the field of ion-selective membrane technology, specifically to an amphiphilic molecule-modified graphene-based ion-selective membrane, its preparation method, and its application. Background Technology

[0002] Osmotic energy, also known as salinity gradient energy, is prominent due to its abundant reserves and ease of collection. Salinity gradients can be easily constructed from high-salinity water and diluted water, and can also be obtained from industrial production, seawater desalination plants, etc. Several membrane separation methods have been proposed to convert the Gibbs free energy during the mixing of different salt solutions into electrical energy, such as osmometry (PRO technology), capacitive mixing, and reverse electrodialysis (RED). RED is relatively easy to achieve by driving ions through a series of alternating cation- and anion-selective membranes. The core component of the RED reaction process is the ion-selective membrane. Therefore, efforts should be focused on developing ion-selective membranes with good ion selectivity and permeability. Polyelectrolytes, with their long-chain structure, strong hydrophilicity, and low resistivity, enable rapid ion transport and show great promise for collecting salinity gradient energy.

[0003] Generally, to improve ion selectivity, ionomers or functional group modifications are used to increase charge density. In a research paper published in Volume 6, pp. 24728-24739 of the journal *Journal of Materials Chemistry A* (Grapheneoxide–polybenzimidazolium nanocomposite anion exchange membranes for electrodialysis), a solution of polybenzimidazolium nanocomposite in dimethylacetamide was stirred and then added to a GO suspension dispersed in dimethylacetamide. The mixture was first stirred and then incubated in a shaker. The coating solution was then cast onto glass plates at room temperature and dried in an oven to obtain a mechanically robust anion exchange membrane with high selectivity. The research paper published in the journal *Advanced Functional Materials*, Volume 32, page 2108672 (Flexible Ionic Conjugated Microporous Polymer Membranes for Fast and Selective Ion Transport), describes the preparation of ion-selective membranes using a homogeneous electrolyte solution. This solution was prepared by dissolving 1,3,5-tris(N-carbazolyl)benzene, 6-(9H-carbazo-9-yl)-N,N,N-trimethylhexane-1-bromoamine or 9-(6-bromohexyl)-9H-carbazole and tetrabutylammonium hexafluorophosphate in a mixture of anhydrous dichloromethane (DCM) and acetonitrile (AcCN). This process enhanced the membrane's mechanical flexibility and improved its ion selectivity.

[0004] However, the ion channels of highly hydrophilic polyelectrolytes have great frictional forces with the transported hydrated ions, which leads to a decrease in the ion permeability of the ion-selective membrane and a decline in its performance. Therefore, it is necessary to improve the ion permeability of the ion-selective membrane and reduce the membrane resistance to better utilize it for salinity gradient power generation. Summary of the Invention

[0005] In view of the above-mentioned prior art, the purpose of this invention is to provide an amphiphilic molecule-modified graphene-based ion-selective membrane, its preparation method, and its application. In this invention, due to the polar head of bis(octadecyldimethylammonium bromide)2, N(CH3)2... + Region with sodium polyacrylate -COO - The electrostatic interaction between the components allows the ion-selective membrane to exhibit excellent ion-selective performance. The synergistic effect of dioctadecyldimethylammonium bromide, sodium polyacrylate, and graphene oxide contributes to the stable power generation performance of the ion-selective membrane.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing an amphiphilic molecule-modified graphene-based ion-selective membrane, wherein the preparation method comprises: using a graphene-containing membrane with N(CH3)2... + Aqueous solutions of cationic surfactants and those containing -COO - The polymer aqueous solution was poured into an alkaline graphene oxide aqueous solution, mixed evenly, filtered to form a membrane, and the membrane was dried and annealed to obtain an amphiphilic molecule-modified graphene-based ion-selective membrane.

[0008] Preferably, the substance contains N(CH3). 2+ The cationic surfactant aqueous solution contains N(CH3) 2+ The concentration of the obtained by mixing a cationic surfactant with deionized water is 0.01 mg / mL.

[0009] The one containing -COO - The polymer aqueous solution is composed of -COO - The polymer was obtained by mixing it with deionized water, and its concentration was 0.004 mg / mL.

[0010] Preferably, the substance contains N(CH3). 2+ The cationic surfactant is bis(octadecyldimethylammonium bromide), octadecyltrimethylammonium bromide, bis(decyldimethylammonium bromide), or decadecyltrimethylammonium bromide; the surfactant containing -COO - The polymer is sodium polyacrylate, polyacrylic acid, or sodium alginate.

[0011] Except for -COO - The polymers can also be selected from those containing sulfonate or quaternary ammonium groups, such as chitosan quaternary ammonium salt, polyacrylic acid, polycycloheximide, polylysine, polyethyleneamine, or polyphosphononitrile.

[0012] Preferably, the alkaline graphene oxide aqueous solution is obtained by dispersing graphene oxide in deionized water and then adding sodium hydroxide solution; the concentration of the sodium hydroxide solution is 0.2M.

[0013] Preferably, the concentration of the alkaline graphene oxide aqueous solution is 0.01 mg / mL; and the pH value of the alkaline graphene oxide aqueous solution is 10.

[0014] Preferably, the substance contains N(CH3). 2+ Cationic surfactants containing -COO - The mass ratio of the polymer to graphene oxide is 5:2:10.

[0015] Preferably, the drying temperature is 40°C and the drying time is 1 hour.

[0016] Preferably, the annealing temperature is 120°C and the annealing time is 3 hours.

[0017] In a second aspect, the present invention provides an amphiphilic molecule-modified graphene-based ion-selective membrane obtained by the above preparation method.

[0018] A third aspect of the present invention provides the application of an amphiphilic molecule-modified graphene-based ion-selective membrane in any of the following 1) to 3):

[0019] 1) Improve the permeability and ion selectivity of ion-selective membranes;

[0020] 2) Reduce the resistance of the ion-selective membrane;

[0021] 3) Prepare a salinity gradient power generation device.

[0022] The beneficial effects of this invention are:

[0023] Due to the polar head of dioctadecyl dimethylammonium bromide N(CH3)2 + The electrostatic interaction between the region and graphene oxide contributes to the good stability of the ion-selective membrane. The synergistic effect of bis(octadecyldimethylammonium bromide), sodium polyacrylate, and graphene oxide results in stable power generation performance. Based on this approach, not only bis(octadecyldimethylammonium bromide) but also other amphiphilic molecules with similar structures (such as polymers containing sulfonate or quaternary ammonium groups) can play a role in ion selectivity and permeability. This strategy can also be used to upgrade the performance of other polyelectrolyte ion-selective membranes. Attached Figure Description

[0024] Figure 1 a) XRD patterns of GP and GDP films in dry and wet conditions; b) FT-IR spectra of GO, GP, GD, and GDP films; c) TGA curves of GO, GP, and GDP films; d) High-resolution C1s spectrum of GP film, XPS C1s spectrum (dashed line) decomposed into 5 single Lorentz peaks (solid line), corresponding to 5 carbon bonds: C=C (282.9 eV), C−C (284.5 eV), C−O (286.17 eV), C=O (288.15 eV), O−C=O (289 eV); e) XPS spectrum of GDP film, XPS C1s spectrum (dashed line) decomposed into 5 single Lorentz peaks (solid line), corresponding to 5 carbon bonds: C=C (282.3 eV), C−C (284.6 eV), C−O (286.3 eV), C=O (288.15 ... f) XPS spectrum of GDP membrane;

[0025] Figure 2a) AFM image of the GO membrane, with the inset showing the height of the area marked by the blue line; b) AFM image of the GP membrane, with the inset showing the height of the area marked by the blue line; c) AFM image of the GDP membrane, with the inset showing the height of the area marked by the blue line; d) Stress-strain curves of the GP and GDP membranes, with the insets being photographs of the GP and GDP membranes after immersion and compression in the permeation energy harvesting experiment; e) Photographs of the GP membrane (top) and GDP membrane (bottom) and water contact angle; f) SEM image of the GDP membrane cross-section; g) EDX mapping elements on the GDP membrane cross-section; h) XRD images of the GO, GP, GD (GO / DODAB) and GDP membranes; i) Flocculation process after mixing graphene oxide and DODAB.

[0026] Figure 3 a) Zeta potential of GDP solutions under different pH conditions, with insets showing photographs of solutions at pH 7 and 10; b) Schematic diagram of GDP membrane preparation; c) Photographs of GDP solutions at different pH values; d) IV curves of GDP membranes with different DODAB amounts; e) IV curves of GDP membranes with different PAAS amounts; f) Zeta potential of a mixed solution of GO, GP, and GDP at pH 10.

[0027] Figure 4 a) Current density-voltage curves of GO, GP, GD, and GDP membranes, with the concentration gradient fixed at 0.5 M / 0.01 M; b) Ionic conductivity of GO, GP, and GDP membranes at different NaCl concentrations; c) Current density-voltage curves of GDP membranes under a 50-fold NaCl concentration gradient in both forward and reverse diffusion directions; d) Current density-voltage curves under different concentration gradients; e) The current density-voltage curves represent the open-circuit voltage and short-circuit current of the GDP membrane under a 50-fold NaCl concentration gradient. The osmotic potential and current are obtained by subtracting the unbalanced electrode potential using a pair of salt bridges. The attached figure shows the equivalent circuit of the osmotic energy harvesting system; f) Cation transfer number and energy conversion efficiency of the GDP membrane under different concentration gradients; g) Maximum output power density of the GDP membrane under different electrolytes; h) Maximum output power density of the GDP membrane at different pH values; i) Osmotic energy harvesting of the GDP membrane by mixing real river water (Xiaoqing River in Jinan) and seawater (Yellow Sea). Detailed Implementation

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0029] As described in the background section, graphene oxide films are ideal for controlling ion transport due to their layered structure. However, graphene oxide films are prone to swelling in water. Annealing is typically used to improve the stability of graphene oxide films in water. However, annealing reduces the carboxyl content, thereby decreasing ion selectivity.

[0030] Based on this, the purpose of this invention is to provide an amphiphilic molecule-modified graphene-based ion-selective membrane, its preparation method, and its applications. This invention uses PAAS (Polyhydrophobic Alginate Assay) to ensure the spatial electrification of the graphene oxide annealed membrane. However, when ions transport within the pores, pore-ion interactions (viscous effects) hinder ion transport. Therefore, this invention selects amphiphilic molecules to hydrophobically modify the nanochannels, thereby reducing the frictional force of ion transport and counteracting the viscosity effect. DODAB is a typical amphiphilic molecule; its structure can be divided into two parts: the nonpolar tail regions of two long-chain alkanes and N(CH3). 2+ The polar head region (see) Figure 1 Long-chain alkanes form hydrophobic interfaces within the nanochannels, reducing ion transport friction and improving permeability. Due to electrostatic interactions, DODAB's N(CH3)... 2+ The region will absorb more PAAS molecules, thereby further increasing the surface charge density of the nanochannels. On the other hand, graphene oxide nanosheets can be absorbed by N... + -O - The interactions, including cation-π interactions, are tightly bound to the polar head. Therefore, DODAB acts as a binder between adjacent graphene oxide nanosheets, giving the GDP membrane excellent mechanical strength and solution stability. Consequently, the membrane exhibits excellent ion selectivity, high ion flux, and stability, which are crucial for efficient permeation energy harvesting.

[0031] Ion-polymers (PAAS) provide surface charge to the channels, ensuring their selectivity, but the viscous effect hinders ion transport. Therefore, amphiphilic molecules with hydrophobic tails (DODAB) are used to reduce friction during ion transport in nanochannels and improve their permeability. Simultaneously, due to the N(CH3) content of DODAB... 2+ Due to the electrostatic interaction between the region and the negatively charged groups on the PAAS chain (Ⅰ), DODAB will also absorb more PAAS molecules. On the other hand, DODAB absorbs more PAAS molecules through N... + -O -The interaction between ions and cation-π interactions acts as a binder between adjacent GO nanosheets, giving the GDP membrane excellent solution stability (II), thus enabling long-term, stable, and efficient osmotic energy collection. Furthermore, PAAS can reduce the flocculation capacity of the mixed solution, preventing the final membrane from agglomerating into large clumps that could affect the ion permeation capacity of subsequent membranes. PAAS-regulated flocculation also improves the mechanical properties of the GDP membrane, enhancing its practical application capabilities.

[0032] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0033] Note: The graphene oxide used in this invention was prepared using a modified Hummer method. The specific method is as follows:

[0034] I. Low Temperature Stage (Ice Water Bath)

[0035] Add 70 mL of 98 wt% concentrated sulfuric acid to a three-necked flask, add 1.5 g of sodium nitrate, stir until dissolved, add 3 g of graphite powder, and stir for 30 min. Slowly add 9 g of potassium permanganate, maintain the ice bath temperature at 0°C, and stir for one hour. The solution changes from black to dark green.

[0036] II. Medium Temperature Stage

[0037] Pour in hot water and heat quickly to 40°C. React for one hour.

[0038] III. Cancellation of the high-temperature phase

[0039] Add 3% hydrogen peroxide to 500mL of ice water, adding it slowly and continuously while ensuring the temperature remains below 60°C. Cool to room temperature. At this point, the slurry concentration is approximately 6 mg / mL.

[0040] IV. Washing

[0041] Let stand overnight, separate into layers, and discard the supernatant. Prepare 5% dilute hydrochloric acid (60 mL concentrated hydrochloric acid + 360 mL water); add to the slurry and stir, then filter to remove sulfate and permanganate ions. Filter once or twice with an equal volume of deionized water. Wash once by centrifugation at 8000 rpm, dispersing the bottom slurry into a concentrated solution, and store in the upper part of the refrigerator. Dialyze for two weeks. Sonicate at 30% power for half an hour, then centrifuge at 3000 rpm for 30 minutes to remove the precipitate; centrifuge at 10000 rpm for 30 minutes, discard the supernatant, and the remainder is the target product.

[0042] Dioctadecyl dimethyl ammonium bromide (DODAB, 99%), sodium hydroxide (NaOH, AR), sodium chloride (NaCl, AR), potassium chloride (KCl, 99.5%), and lithium chloride (LiCl, AR) were purchased from Ron's reagents.

[0043] Sodium polyacrylate (PAAS, Mw 5-7 million, 80 mesh) was purchased from Macklin. All chemicals were used as received.

[0044] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0045] Example 1: Preparation of amphiphilic molecule-modified graphene-based ion-selective membranes

[0046] (1) Dissolve 0.5 mg of dioctadecyl dimethyl ammonium bromide (DODAB, 99%) in 50 mL of deionized water and mix well to obtain an aqueous solution of dioctadecyl dimethyl ammonium bromide.

[0047] Dissolve 0.2 mg of sodium polyacrylate in 50 mL of deionized water and mix well to obtain an aqueous solution of sodium polyacrylate.

[0048] 1 mg of graphene oxide was dispersed in 100 mL of deionized water, and then 0.2 M sodium hydroxide solution was added to adjust the pH to 10 to obtain an aqueous solution of graphene oxide.

[0049] (2) Pour the bis(octadecyldimethylammonium bromide) solution obtained in step (1) into an aqueous solution of graphene oxide with a pH of 10 and stir for 1 minute. Then pour the sodium polyacrylate solution into the mixed solution and stir for 1 minute to obtain a mixed solution with small and uniform flocculation. Pour the mixed solution onto cellulose ester membrane filter paper (pore size 200 nm) for vacuum filtration to form a membrane. Place the filtered membrane along with the filter paper into a glass petri dish and place it in an oven at 40°C for 1 hour to ensure that the water in the membrane slowly escapes. Then anneal it in an oven at 120°C for 3 hours to ensure the stability of the membrane and obtain an amphiphilic molecule-modified graphene-based ion-selective membrane (GDP membrane).

[0050] Example 2

[0051] (1) Dissolve 0.5 mg of octadecyltrimethylammonium bromide in 50 mL of deionized water and mix well to obtain an aqueous solution of bis(octadecyldimethylammonium bromide).

[0052] Dissolve 0.2 mg of polyacrylic acid in 50 mL of deionized water and mix well to obtain an aqueous solution of sodium polyacrylate.

[0053] 1 mg of graphene oxide was dispersed in 100 mL of deionized water, and then 0.2 M sodium hydroxide solution was added to adjust the pH to 10 to obtain an aqueous solution of graphene oxide.

[0054] (2) Pour the octadecyltrimethylammonium bromide solution obtained in step (1) into an aqueous solution of graphene oxide with a pH of 10 and stir for 1 minute. Then pour the polyacrylic acid solution into the mixed solution and stir for 1 minute to obtain a mixed solution with small and uniform flocculation. Pour the mixed solution onto cellulose ester membrane filter paper (pore size 200 nm) for vacuum filtration to form a membrane. Place the filtered membrane along with the filter paper into a glass petri dish and place it in an oven at 40°C for 1 hour to ensure that the water in the membrane slowly escapes. Then anneal it in an oven at 120°C for 3 hours to ensure the stability of the membrane and obtain an amphiphilic molecule-modified graphene-based ion-selective membrane (GDP membrane).

[0055] Example 3

[0056] (1) Dissolve 0.5 mg of didecyl dimethyl ammonium bromide in 50 mL of deionized water and mix well to obtain an aqueous solution of dioctadecyl dimethyl ammonium bromide.

[0057] Dissolve 0.2 mg of sodium alginate in 50 mL of deionized water and mix well to obtain an aqueous solution of sodium polyacrylate.

[0058] 1 mg of graphene oxide was dispersed in 100 mL of deionized water, and then 0.2 M sodium hydroxide solution was added to adjust the pH to 10 to obtain an aqueous solution of graphene oxide.

[0059] (2) The didecyldimethylammonium bromide solution obtained in step (1) was poured into an aqueous solution of graphene oxide with a pH of 10 and stirred for 1 minute. Then, sodium alginate solution was poured into the mixed solution and stirred for 1 minute to obtain a mixed solution with small and uniform flocculation. The mixed solution was poured onto cellulose ester membrane filter paper (pore size 200 nm) for vacuum filtration to form a membrane. The filtered membrane, along with the filter paper, was placed in a glass petri dish and dried in an oven at 40°C for 1 hour to ensure that the water in the membrane slowly escaped. Then, it was annealed in an oven at 120°C for 3 hours to ensure the stability of the membrane, thus obtaining an amphiphilic molecule-modified graphene-based ion-selective membrane (GDP membrane).

[0060] Comparative Example 1

[0061] The difference from the example is that no aqueous solution of dioctadecyldimethylammonium bromide and aqueous solution of sodium polyacrylate are added to obtain the GO membrane.

[0062] Comparative Example 2

[0063] The difference from the example is that no aqueous solution of dioctadecyldimethylammonium bromide is added to obtain the GD membrane.

[0064] Comparative Example 3

[0065] The difference from the example is that no aqueous sodium polyacrylate solution is added, resulting in a GP membrane.

[0066] Characterization:

[0067] The interlayer spacing of GP and GDP films under wet conditions was characterized by XRD. Figure 1 a). After soaking in 0.1 M NaCl solution for 6 h, the interlayer spacing of GP increased from 0.8034 nm to 1.4466 nm. In contrast, the interlayer spacing of GDP did not increase significantly, increasing from 0.8336 nm to 0.9032 nm. This indicates that GDP is more stable than GP films in aqueous solution, which can also be attributed to the strong interaction between DODAB and GO. FT-IR spectroscopy analysis was then performed ( Figure 1 b). In the spectrum of the GDP membrane, 3451 cm⁻¹ −1 There is a distinct absorption peak at 1627 cm⁻¹, which is attributed to O−H stretching. −1 The nearby absorption peak is the characteristic C=O absorption peak of carboxylate. (Compared to GO and GP films at 3480 cm⁻¹) −1 Compared to the nearby O−H absorption peaks, the GD and GDP films show a significant red shift, which is likely due to the formation of hydrogen bonds between GO and DODAB. TGA was also used to demonstrate that the GDP film exhibits good thermal stability, withstanding temperatures up to 200°C. Figure 1 c). The weight variation of the GDP membrane is significant, especially at temperatures exceeding 200°C, which may be due to the decomposition of DODAB and the membrane network. Overall, the thermal stability meets the requirements for most RED processes operating below 200°C. The functional groups of the GP and GDP membranes, such as hydroxyl (-OH), carbonyl (-C=O), and carboxyl (-C-O=O), were characterized using XPS. Figure 1 d and Figure 1 e). The mass ratio of each element on the surface of the GDP membrane was determined to be C: N: O: Na = 61.33: 0.79: 26.34: 9.43. Figure 1 f). The proportion of oxygen functional groups in GDP is greater than that in GP, ​​which may be due to the higher load of PAAS in GDP.

[0068] like Figure 2 As shown in c, the GDP nanosheets obtained in Example 1 are significantly thicker than the GP nanosheets prepared in Comparative Example 3. Figure 2 b). The thickness of the monolayer graphene oxide is 0.8 nm ( Figure 2 a) The thickness of the GDP nanosheets is approximately 12 nm. Figure 2 c). The additional thickness proves the connection between GO and DODAB via N. + -O − Strong interactions, including cation-π interactions. For example... Figure 2As shown in Figure d, the highest tensile stresses of the GP membrane and GDP membrane are 25.16 MPa and 39.58 MPa, respectively. Compared with the GP membrane, the GDP membrane exhibits better mechanical properties and stronger tensile strength. The attached figures show photographs of the GP and GDP membranes after long-term permeation energy collection tests and pressure filtration. It is evident that the morphology of the GDP membrane remains unchanged when the GP membrane is damaged. The enhanced mechanical strength can also be attributed to the strong interaction between DODAB and GO. DODAB acts as a bonding agent between adjacent graphene oxide nanosheets. On the other hand, DODAB reduces the hydrophilicity of the composite membrane. The GP membrane surface is hydrophilic with a water contact angle of 40.69°, while the GDP membrane is more hydrophobic with a water contact angle of 78.57°. Figure 2 e). As can be seen from the cross-sectional view, the film thickness is approximately 500 nm, exhibiting a distinct laminar flow structure. Figure 2 f). EDX images of the GDP membrane show that N and Na elements are uniformly distributed between the graphene oxide nanosheets, indicating that DODAB and PAAS are well intercalated into the graphene oxide nanosheets. Figure 2 g). Then, the interlayer spacing was characterized using XRD. Figure 2 h). The original graphene oxide film and the GP film have similar interlayer spacing, indicating that the introduction of PAAS does not cause expansion of the graphene oxide film. The interlayer spacing of the GD film is significantly increased because the structural units become larger and thicker during the self-assembly process (h). Figure 2 The interlayer spacing of the GDP membrane was 0.8336 nm, which was significantly smaller than that of the GD membrane, indicating that PAAS played an important regulatory role in flocculation and ensured the appropriate structural units for constructing nanochannels in the GDP membrane.

[0069] Experimental Example 1: Selection of Raw Material Ratio

[0070] Positively charged DODAB has a strong electrostatic interaction with graphene oxide, and the mixture of the two solutions easily produces a large flocculation effect. Figure 3 a). Therefore, the pH of the graphene oxide solution was first adjusted to regulate the surface charge of the graphene oxide colloidal particles, and then DODAB and PAAS were added. Figure 3 b). Figure 3 a shows the Zeta potentials of GDP solutions with pH values ​​from 1 to 14. It can be seen that the Zeta potential of the solution changes from −2.74 mV to −54.2 mV with varying pH. The solution is most stable at pH 10 because the Zeta potential is the highest. Figure 3c). After controlling the size of the flocculation, the proportions of each component used to prepare the GDP membrane were determined using the controlled variable method. The amounts of each raw material were adjusted according to the method in Example 1: GO:PAAS=10:1, GO:DODAB:PAAS=10:1:1, GO:DODAB:PAAS=10:2:1, GO:DODAB:PAAS=10:5:1, GO:DODAB:PAAS=10:10:1. The mass ratio of GO to PAAS was controlled at 10:1, and the effect of DODAB content on the ion-selective membrane was studied. Figure 3 d) The amount of DODAB monomer affected the selectivity of the GDP membrane. Excessive DODAB monomer would clog the nanochannels and reduce membrane performance. The amounts of each raw material were adjusted according to the method in Example 1: GO:DODAB:PAAS = 10:5:1, GO:DODAB:PAAS = 10:5:2, GO:DODAB:PAAS = 10:5:5, GO:DODAB:PAAS = 10:5:10. The selectivity was highest when the mass ratio of GO to DODAB was 10:5. Then, with the mass ratio of GO to DODAB fixed, the optimal amount of PAAS added was determined, such as... Figure 3 As shown in e, the zeta potential of the GDP mixed solution (-54.2 mV) is more negative compared to the graphene oxide solution (-43.7 mV) and the GP solution (-46.8 mV). Figure 3 f) indicates that the GDP membrane possesses abundant negative functional groups. This may be attributed to the N(CH3) group of DODAB. 2+ This region, due to electrostatic interactions, facilitates the absorption of PAAS molecules. DODAB molecules contain only one positive charge, while PAAS molecules contain multiple negative charges.

[0071] Experimental Example 2: Transmembrane ion transport characteristics.

[0072] 1) The membrane radius was 7.5 cm. A 0.5 M sodium chloride solution was prepared by dissolving 29.22 g of NaCl in 1000 ml of deionized water to simulate seawater. A 0.01 M sodium chloride solution was prepared by dissolving 0.5844 g of NaCl in 1000 ml of deionized water to simulate river water.

[0073] The ion transport performance and energy conversion were determined using an electrochemical workstation (CHI760E B18569). During the testing, the GDP membrane prepared in Example 1 and the GO, GD, and GP membranes prepared in Comparative Examples 1-3 were combined with a PI membrane. The test area was controlled by perforation of the PI membrane, and the perforation area was adjusted to the required test area; the size of the perforation was the actual test area. The above membranes (membranes prepared in the examples or comparative examples + PI membranes) were sandwiched between two chambers of a test electrolytic cell (a CH2010H type frosted-mouth electrolytic cell with replaceable membranes). The two chambers contained 0.5M and 0.01M salt solutions, respectively. The apparatus was connected to the electrochemical workstation, and cyclic voltammetry was used to record the IV curves. The scanning voltage range was −0.3V to +0.3V, with a step voltage of 0.001V. A saturated potassium chloride salt bridge was used to eliminate the unbalanced redox potential at the electrolyte interface. The measured voltage was the diffusion potential (…). Figure 4 e).

[0074] Figure 4 The IV curve obtained from the GDP membrane in section a shows that the area enclosed by the X and Y axes is the largest, indicating that the GDP membrane has the highest output power density. The X-axis represents the voltage, which indirectly reflects the selectivity of the ion-exchange membrane; the higher the voltage, the higher the selectivity and the better the permeability. The Y-axis represents the current density; the higher the current density, the lower the resistance of the ion-exchange membrane, and the greater the permeation flux. It can be seen that, compared to the CO membrane, although the GD membrane contains dioctadecyldimethylammonium bromide aqueous solution, dioctadecyldimethylammonium bromide increases the membrane resistance and reduces the permeability. However, when combined with sodium polyacrylate aqueous solution, it significantly improves the membrane permeability and reduces the membrane resistance. This indicates a significant synergistic effect between sodium polyacrylate and dioctadecyldimethylammonium bromide, which can both improve membrane permeability and reduce membrane resistance. Figure 4 As can be seen from b to f, the GDP ion exchange membrane prepared in Example 1 has higher selectivity.

[0075] Separately prepare 5 M and 0.05 M sodium chloride solutions, replacing the 0.5 M sodium chloride solution, and place them in the chamber of the test electrolytic cell, according to... Figure 4 As can be seen from d, the greater the concentration gradient between sodium chloride salt solutions, the stronger the permeation capacity of the GDP ion exchange membrane prepared in Example 1.

[0076] 2) Prepare 0.5 M and 0.01 M lithium chloride, sodium chloride, and potassium chloride solutions respectively. Following the test method in 1), place the 0.5 M and 0.01 M lithium chloride solutions in two chambers of the test electrolyzer, the 0.5 M and 0.01 M sodium chloride solutions in two chambers of the test electrolyzer, and the 0.5 M and 0.01 M potassium chloride solutions in two chambers of the test electrolyzer. Test the permeability of the GDP ion-exchange membrane prepared in Example 1. Figure 4 As can be seen from g, the GDP ion exchange membrane prepared in Example 1 has the highest permeation capacity for potassium chloride.

[0077] 3) Prepare 0.5M and 0.01M sodium chloride solutions with pH values ​​of 3, 7, 9, and 11 respectively. Place the sodium chloride solutions of the same pH value into two chambers of the test electrolytic cell, and test the permeability of the GDP ion exchange membrane prepared in Example 1 according to the test method in 1). Figure 4 As can be seen from h, the GDP ion exchange membrane has the highest permeability when the sodium chloride solution is at pH 11.

[0078] 4) Take 100 mL of Xiaoqing River water (from Banqiao Wharf, Xiaoqing River, Jinan City) and Yellow Sea seawater (from Wanpingkou Seaside Scenic Area, Rizhao City), filter them separately using a Buchner funnel to remove sediment, place the filtered seawater in the high-concentration chamber of the test electrolyzer, and place the filtered river water in the low-concentration chamber of the test electrolyzer, and test the permeability of the GDP ion exchange membrane prepared in Example 1 according to the test method in 1). Figure 4 As can be seen, the GDP ion exchange membrane prepared in Example 1 exhibits excellent permeation performance. By connecting several of the above-mentioned test electrolyzers in series, it can replace batteries commonly used in LCD displays and be used as a salinity gradient power generation device to power devices such as LCD displays.

[0079] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing an amphiphilic molecule-modified graphene-based ion-selective membrane, characterized in that, The preparation method is as follows: [The following text appears to be a separate, unrelated section:] [Contains N(CH3)2] + Aqueous solutions of cationic surfactants and those containing -COO - The polymer aqueous solution was poured into the alkaline graphene oxide aqueous solution in sequence, mixed evenly, filtered to form a membrane, and the membrane was dried and annealed to obtain an amphiphilic molecule-modified graphene-based ion-selective membrane. The one containing N(CH3) 2+ The cationic surfactant is bis(octadecyldimethylammonium bromide), octadecyltrimethylammonium bromide, bis(decyldimethylammonium bromide), or decadecyltrimethylammonium bromide; the surfactant containing -COO - The polymer is sodium polyacrylate, polyacrylic acid, or sodium alginate; The alkaline graphene oxide aqueous solution is obtained by dispersing graphene oxide in deionized water and then adding sodium hydroxide solution; the concentration of the sodium hydroxide solution is 0.2M; the concentration of the alkaline graphene oxide aqueous solution is 0.01 mg / mL; and the pH value of the alkaline graphene oxide aqueous solution is 10. The N(CH3)2 + Cationic surfactants containing -COO - The mass ratio of the polymer to graphene oxide is 5:2:

10.

2. The preparation method according to claim 1, characterized in that, The N(CH3)2 + The cationic surfactant aqueous solution is composed of N(CH3)2 + The concentration of the obtained by mixing a cationic surfactant with deionized water is 0.01 mg / mL. The one containing -COO - The polymer aqueous solution is composed of -COO - The polymer was obtained by mixing it with deionized water, and its concentration was 0.004 mg / mL.

3. The preparation method according to claim 1, characterized in that, The drying temperature is 40℃ and the drying time is 1 hour.

4. The preparation method according to claim 1, characterized in that, The annealing temperature is 120°C and the annealing time is 3 hours.

5. An amphiphilic molecule-modified graphene-based ion-selective membrane obtained by the preparation method according to any one of claims 1 to 4.

6. The use of the amphiphilic molecule-modified graphene-based ion-selective membrane according to claim 5 in any one of the following 1) to 3): 1) Improve the permeability and ion selectivity of ion-selective membranes; 2) Reduce the resistance of the ion-selective membrane; 3) Prepare a salinity gradient power generation device.

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