Graphene oxide-sodium alginate composite membrane for extracting marine osmotic energy and preparation method thereof

Abstract

The application discloses a preparation method of an oxidized graphene sodium alginate composite film for extracting marine osmotic energy, and specifically comprises the following steps: step 1, preparing a sodium alginate solution; step 2, preparing an oxidized graphene solution; step 3, placing the sodium alginate solution into the oxidized graphene solution, and obtaining a mixed dispersion liquid through electromagnetic stirring; step 4, taking a polycarbonate film, placing the polycarbonate film into a trace suction filter bottle with the polycarbonate film as a base, taking the mixed dispersion liquid into the trace suction filter bottle, and performing vacuum suction filtration to obtain a polycarbonate film covered with the oxidized graphene sodium alginate composite film; and step 5, stripping the polycarbonate film covered with the oxidized graphene sodium alginate composite film, and naturally drying to obtain the oxidized graphene sodium alginate composite film for extracting marine osmotic energy. The application further discloses the oxidized graphene sodium alginate composite film for extracting marine osmotic energy, and the prepared composite film has the characteristics of high power density, good stability and high economic value.

Description

Technical Field

[0001] This invention belongs to the field of marine salinity gradient energy development technology, and relates to a graphene oxide sodium alginate composite membrane for extracting marine permeation energy. This invention also relates to a method for preparing the graphene oxide sodium alginate composite membrane for extracting marine permeation energy. Background Technology

[0002] In recent years, with a growing global awareness of the urgency of mitigating the climate crisis caused by fossil fuel consumption, the exploration of sustainable and renewable energy has converged into an unprecedentedly powerful driving force. Among numerous emerging technological waves, reverse electrodialysis (RED) technology has stood out as a cutting-edge means of tapping the enormous potential of salinity gradient power generation in natural environments such as the ocean. The core of RED system performance lies in the development of high-power-density membranes, a field that continues to attract widespread attention and in-depth exploration from the scientific community, aiming to continuously optimize the ion selectivity, durability, and cost-effectiveness of membranes. Particularly noteworthy are two-dimensional (2D) materials such as graphene oxide (GO) and MXenes, which, with their unique structural characteristics and excellent chemical properties, have demonstrated extraordinary potential and superior performance in the field of salinity gradient energy conversion, injecting new vitality and hope into the development of RED technology.

[0003] Graphene oxide (GO) is an important derivative of graphene, obtained through the oxidation reaction of graphene. Its surface and edges contain numerous oxygen-containing groups, such as hydroxyl, epoxy, carboxyl, and carbonyl groups. These groups enable GO to provide extremely abundant surface charges when used as a nanochannel material, resulting in extremely high ion selectivity. Controlling the surface charge of nanochannels to achieve high OEC power has also proven to be an effective method. Huang's team discovered that re-stacking exfoliated GO sheets easily forms an unprecedented number of nanochannel arrays, also confirming GO as a two-dimensional material ideal for nanofluidic ion transport platforms. Jiang's team, through pre-assembly modification, effectively altered the surface charge polarity of GO nanochannels, producing GO membranes with strong cation or anion selectivity, achieving an OEC power density approximately 54% higher than that obtained using commercial ion exchange membranes. Lei's team utilized the self-exfoliation behavior of planar GO fragments on a GO substrate under alkaline conditions, encapsulating the separated GO fragments within nanochannels, increasing the OEC power density from 1.8 W / m². 2 Increased to 4.9 W / m 2Furthermore, the surface charge density of the membrane can be controlled by adjusting environmental conditions such as temperature, pH, and light, thereby improving the permeation energy conversion efficiency. However, the promoting effect of controlling the surface charge density is limited, and it is difficult to obtain extremely high surface charge densities, which necessitates the search for new methods. Cao's team achieved a high surface charge density of 10.6 W / m by truncating an ultra-thick graphene oxide membrane, using the cross-section as the permeation surface, and altering the ion transport pathway. 2 While this method achieves ultra-high power density, its limitations remain due to the difficulty in obtaining large-area cross-sections. To more effectively obtain high power density in osmotic energy conversion, researchers discovered through numerical simulations that the synergistic effect of surface charge and space charge within nanochannels can yield higher osmotic energy conversion power. This has been confirmed in numerous related experiments, providing a novel approach for the design of ion-selective membranes. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy. The composite membrane prepared by this method has the characteristics of high power density, good stability, and high economic value.

[0005] Another objective of this invention is to provide a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy.

[0006] The first technical solution adopted in this invention is a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, specifically including the following steps:

[0007] Step 1: Prepare sodium alginate solution;

[0008] Step 2: Prepare graphene oxide solution;

[0009] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0010] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0011] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0012] The first technical solution of this invention is further characterized by:

[0013] The specific process of step 1 is as follows:

[0014] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0015] Step 1.2: Dissolve sodium alginate in deionized water and stir it with electromagnetic stirring to obtain a sodium alginate solution.

[0016] In step 1, the concentration of sodium alginate solution is 1-20 mg / ml.

[0017] In step 2, the concentration of the graphene oxide solution is 0.1-5 mg / ml.

[0018] The specific process of step 2 is as follows:

[0019] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0020] Step 2.2: Add deionized water to the graphene oxide to dilute it and obtain a graphene oxide solution.

[0021] In step 3, the volume of sodium alginate solution added should not exceed the volume of graphene oxide solution.

[0022] In step 3, the electromagnetic stirring speed is 800-1200 r / min, and the electromagnetic stirring time is 6-24 h.

[0023] The vacuum filtration time in step 4 is 5-7 days.

[0024] The natural drying time in step 5 is 8-24 hours.

[0025] The second technical solution adopted in this invention is a graphene oxide sodium alginate composite membrane for extracting marine permeation energy, which is prepared by a method for preparing a graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention provides a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy and its preparation method. It ingeniously utilizes a two-dimensional layered framework formed by stacked graphene oxide nanosheets as a stable foundation, while sodium alginate, a widely found polysaccharide in nature, is rich in negatively charged functional groups that weave a dense cross-linked network between the nanosheets, endowing the membrane with excellent space charge distribution characteristics. This unique design concept not only greatly enhances the ion selectivity of the membrane but also achieves a significant increase in power density in RED applications. Under a 50-fold NaCl concentration gradient, the composite membrane exhibits an excellent power density of approximately 14.75 W / m²; and under a 50-fold KCl concentration gradient, its power density soars to 20.94 W / m², a figure far exceeding the industry-recognized benchmark of 5.0 W / m². Even more remarkably, the membrane's economic feasibility is also outstanding. Its raw materials are primarily sodium alginate, supplemented by graphene oxide, resulting in low cost and environmental friendliness. Combined with a simple manufacturing process, this forms a solid foundation for large-scale commercial application, indicating a broad market prospect. This invention is not only an innovative achievement in high-performance salinity gradient energy conversion membrane technology in the RED field, but also provides a completely new design concept and strategy for the development and utilization of marine salinity gradient energy. By empirically demonstrating the balance achieved between cost-effectiveness and power density, our work creates more possibilities for the practical application of marine salinity gradient energy, powerfully promoting the world's progress towards a greener and more sustainable energy future. Attached Figure Description

[0028] Figure 1 This is a schematic flowchart of the preparation method of the graphene oxide sodium alginate composite membrane for extracting marine permeation energy according to the present invention.

[0029] Figure 2 This is a scanning electron microscope image of the surface of the pure graphene oxide film in Example 6 of the present invention;

[0030] Figure 3 This is a scanning electron microscope image of the surface of the graphene oxide-sodium alginate composite film in Example 6 of the present invention;

[0031] Figure 4 This is a stress-strain curve of the pure graphene oxide film and the graphene oxide sodium alginate composite film in Example 6 of the present invention.

[0032] Figure 5 This is a Zeta potential diagram of pure graphene oxide dispersion, sodium alginate solution and mixed dispersion of graphene oxide and sodium alginate under different pH conditions in Example 6 of the present invention.

[0033] Figure 6 This is an X-ray diffraction pattern of the pure graphene oxide film and the graphene oxide sodium alginate composite film in Example 6 of the present invention.

[0034] Figure 7 This is the current-voltage characteristic curve of the composite membrane under a 1000-fold KCl concentration gradient in Example 6 of the present invention;

[0035] Figure 8 This is a schematic diagram showing the shift in transmembrane conductivity compared to bulk conductivity under different KCl concentrations in Example 6 of the present invention;

[0036] Figure 9 This is a current change curve of the composite membrane in 0.1M KCl solutions of different pH values ​​in Example 6 of the present invention under a periodic voltage of -0.1V to 0.1V.

[0037] Figure 10 This is a graph showing the change in current density of the graphene oxide-sodium alginate composite membrane with different parametric ratios as a function of external load in Example 6 of the present invention.

[0038] Figure 11 This is a graph showing the power density of the graphene oxide-sodium alginate composite membrane as a function of external load under different parameter ratios in Example 6 of the present invention.

[0039] Figure 12 This is a graph showing the power density of the graphene oxide sodium alginate composite membrane in artificial and natural seawater as a function of external load in Embodiment 6 of the present invention.

[0040] Figure 13 This is a statistical result of the maximum power density of the graphene oxide-sodium alginate composite film of different thicknesses in Example 6 of the present invention;

[0041] Figure 14 This is a bar chart showing the maximum power density of the graphene oxide film and the graphene oxide sodium alginate composite film in different concentration gradient NaCl solutions in Example 6 of the present invention.

[0042] Figure 15 This is a bar chart showing the power density of the graphene oxide-sodium alginate composite membrane in Example 6 of the present invention in different electrolyte solutions with a concentration gradient of 50 times.

[0043] Figure 16 This is a bar chart showing the maximum power density of the graphene oxide-sodium alginate composite film under different test areas under a 1000-fold NaCl solution concentration gradient in Example 6 of the present invention.

[0044] Figure 17 This is a comparison diagram of the power density of this application and existing technologies in Embodiment 6 of the present invention;

[0045] Figure 18 This is a bar chart showing the maximum power density variation of the graphene oxide-sodium alginate composite membrane in Example 6 of the present invention under different pH values ​​and pH gradients.

[0046] Figure 19 This is a bar chart showing the change in current density when the graphene oxide-sodium alginate composite membrane in Example 6 of the present invention reaches its maximum power density.

[0047] Figure 20 This is a bar chart showing the maximum power density variation of the graphene oxide film in Example 6 of the present invention under different pH and pH gradients;

[0048] Figure 21 This is a bar chart showing the change in current density when the graphene oxide film in Example 6 of this invention reaches its maximum power density.

[0049] Figure 22 This is a schematic diagram of the axial cation concentration of the nanochannel model under different space charge densities in Embodiment 6 of the present invention;

[0050] Figure 23 This is a diagram showing the axial anion concentration distribution of the nanochannel model under different space charge densities in Example 6 of this invention.

[0051] Figure 24 This is a bar chart of cation and anion fluxes in a nanochannel model under different space charge densities in Example 6 of this invention;

[0052] Figure 25 This is a radial cation concentration distribution diagram of the nanochannel model under different channel radii in Example 6 of the present invention;

[0053] Figure 26 This is a radial anion concentration distribution diagram of the nanochannel model under different channel radii in Embodiment 6 of the present invention;

[0054] Figure 27 This is a bar chart showing the flux of anions and cations in a nanochannel model under different channel radii in Example 6 of the present invention. Detailed Implementation

[0055] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0056] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0057] Step 1: Prepare sodium alginate solution;

[0058] The specific process is as follows:

[0059] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0060] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, obtaining a sodium alginate solution; the solution is pale yellow and has a certain viscosity;

[0061] The concentration of sodium alginate solution is 1-20 mg / ml;

[0062] Step 2: Prepare a graphene oxide solution; the concentration of the graphene oxide solution is 0.1-5 mg / ml;

[0063] The specific process is as follows:

[0064] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0065] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0066] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it, so that the graphene oxide nanosheets and sodium alginate molecular chains are fully cross-linked to obtain a mixed dispersion; the mixed dispersion has a certain viscosity, and the viscosity gradually increases as the sodium alginate solution content increases.

[0067] The electromagnetic stirring speed is 800-1200 r / min, and the electromagnetic stirring time is 6-24 h;

[0068] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane. The vacuum filtration time is 5-7 days.

[0069] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and allow it to dry naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy; the natural drying time is 8-24 hours.

[0070] Since the main component of the composite membrane is sodium alginate, and sodium alginate cannot form a membrane on its own, the stable structure of the composite membrane benefits from the stacking of graphene oxide. When the sodium alginate content in the mixed dispersion is too high, it will lead to unstable membrane structure. Moreover, a high sodium alginate content will greatly increase the viscosity of the mixed dispersion, which will lengthen the membrane formation cycle of vacuum filtration, reduce the efficiency of the membrane formation cycle, and even cause blockage, making vacuum filtration impossible. Therefore, the volume of sodium alginate solution added in step 3 should not be greater than the volume of graphene oxide solution.

[0071] Example 1

[0072] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0073] Step 1: Prepare sodium alginate solution;

[0074] Step 2: Prepare graphene oxide solution;

[0075] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0076] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0077] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0078] Example 2

[0079] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0080] Step 1: Prepare sodium alginate solution;

[0081] The specific process of step 1 is as follows:

[0082] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0083] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, thereby obtaining a sodium alginate solution.

[0084] In step 1, the concentration of sodium alginate solution is 1-20 mg / ml;

[0085] Step 2: Prepare graphene oxide solution; the concentration of graphene oxide solution in step 2 is 0.1-5 mg / ml;

[0086] The specific process of step 2 is as follows:

[0087] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0088] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0089] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0090] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0091] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0092] Example 3

[0093] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0094] Step 1: Prepare sodium alginate solution;

[0095] The specific process of step 1 is as follows:

[0096] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0097] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, thereby obtaining a sodium alginate solution.

[0098] In step 1, the concentration of sodium alginate solution is 1-20 mg / ml;

[0099] Step 2: Prepare graphene oxide solution; the concentration of graphene oxide solution in step 2 is 0.1-5 mg / ml;

[0100] The specific process of step 2 is as follows:

[0101] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0102] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0103] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0104] In step 3, the volume of sodium alginate solution added should not exceed the volume of graphene oxide solution;

[0105] In step 3, the electromagnetic stirring speed is 800-1200 r / min, and the electromagnetic stirring time is 6-24 h;

[0106] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0107] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0108] Example 4

[0109] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0110] Step 1: Prepare sodium alginate solution;

[0111] The specific process of step 1 is as follows:

[0112] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0113] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, thereby obtaining a sodium alginate solution.

[0114] In step 1, the concentration of sodium alginate solution is 1-20 mg / ml;

[0115] Step 2: Prepare graphene oxide solution; the concentration of graphene oxide solution in step 2 is 0.1-5 mg / ml;

[0116] The specific process of step 2 is as follows:

[0117] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0118] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0119] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0120] In step 3, the volume of sodium alginate solution added should not exceed the volume of graphene oxide solution;

[0121] In step 3, the electromagnetic stirring speed is 800-1200 r / min, and the electromagnetic stirring time is 6-24 h;

[0122] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0123] The vacuum filtration time in step 4 is 5-7 days;

[0124] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0125] Example 5

[0126] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0127] Step 1: Prepare sodium alginate solution;

[0128] The specific process of step 1 is as follows:

[0129] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0130] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, thereby obtaining a sodium alginate solution.

[0131] In step 1, the concentration of sodium alginate solution is 1-20 mg / ml;

[0132] Step 2: Prepare graphene oxide solution; the concentration of graphene oxide solution in step 2 is 0.1-5 mg / ml;

[0133] The specific process of step 2 is as follows:

[0134] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0135] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0136] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and use electromagnetic stirring to fully dissolve it to obtain a mixed dispersion.

[0137] In step 3, the volume of sodium alginate solution added should not exceed the volume of graphene oxide solution;

[0138] In step 3, the electromagnetic stirring speed is 800-1200 r / min, and the electromagnetic stirring time is 6-24 h;

[0139] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0140] The vacuum filtration time in step 4 is 5-7 days;

[0141] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and dry it naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy.

[0142] The natural drying time in step 5 is 8-24 hours.

[0143] Example 6

[0144] The present invention relates to a method for preparing a graphene oxide-sodium alginate composite membrane for extracting marine permeation energy, as follows: Figure 1 As shown, the specific steps include the following:

[0145] Step 1: Prepare sodium alginate solution;

[0146] The specific process of step 1 is as follows:

[0147] Step 1.1: Take deionized water into the reactor and take a certain amount of sodium alginate;

[0148] Step 1.2: Dissolve sodium alginate in deionized water and stir it magnetically to ensure complete dissolution, thereby obtaining a sodium alginate solution.

[0149] In step 1, the concentration of sodium alginate solution is 10 mg / ml;

[0150] Step 2: Prepare graphene oxide solution; the concentration of graphene oxide solution in step 2 is 0.1-5 mg / ml;

[0151] The specific process of step 2 is as follows:

[0152] Step 2.1: Take a certain amount of graphene oxide into another reactor and take deionized water;

[0153] Step 2.2: Dilute the graphene oxide with deionized water to obtain a graphene oxide solution;

[0154] Step 3: Add the sodium alginate solution prepared in Step 1 to the graphene oxide solution prepared in Step 2, and mix them at a ratio of 40 ml : x ml. Stir the mixture with electromagnetic stirring to ensure complete dissolution, thereby fully crosslinking the graphene oxide nanosheets with the sodium alginate molecular chains to obtain a mixed dispersion. The mixed dispersion has a certain viscosity, and the viscosity gradually increases as the sodium alginate solution content increases.

[0155] In step 3, the volume of sodium alginate solution added should not exceed the volume of graphene oxide solution; in step 3, the electromagnetic stirring speed is 900 r / min, and the electromagnetic stirring time is 24 h.

[0156] Step 4: Take a polycarbonate membrane and place it in a microfiltration flask. Take the mixed dispersion in the microfiltration flask and perform vacuum filtration to obtain a polycarbonate membrane covered with a graphene oxide sodium alginate composite membrane.

[0157] The vacuum filtration time in step 4 is 7 days;

[0158] Step 5: Peel the graphene oxide sodium alginate composite membrane from the polycarbonate membrane covered with the graphene oxide sodium alginate composite membrane, and allow it to dry naturally to obtain the graphene oxide sodium alginate composite membrane for extracting marine permeation energy; the natural drying time in step 5 is 24 hours.

[0159] Since the main component of the composite membrane is sodium alginate, and sodium alginate cannot form a membrane on its own, the stable structure of the composite membrane benefits from the stacking of graphene oxide. When the sodium alginate content in the mixed dispersion is too high, it will lead to membrane instability. Furthermore, a high sodium alginate content will significantly increase the viscosity of the mixed dispersion, lengthening the membrane formation cycle of vacuum filtration, reducing membrane efficiency, and even causing blockage, making vacuum filtration impossible. Therefore, in this application, the mixing ratio of the mixed dispersion (40 ml : xml) is x ≤ 40.

[0160] like Figure 4 As shown, the graphene oxide-sodium alginate composite membrane for extracting marine permeability exhibits certain light transmittance and good mechanical properties. When the composite membrane is immersed in real seawater, its volume expands while maintaining its shape. Figure 2 As shown, under SEM (scanning electron microscopy), the surface of the pure graphene oxide membrane is relatively smooth, and the cross-section reveals a typical stacked structure of two-dimensional layered membranes. In contrast, the surface of the graphene oxide-sodium alginate composite membrane for extracting marine permeation energy exhibits many spherical substances, such as... Figure 3As shown, significant material doping between the layered structures can also be observed at the cross-section. EDS analysis reveals uniform elemental distribution on both the surface and cross-section of the composite membrane, indicating thorough mixing of sodium alginate (SA) and graphene oxide (GO), resulting in a homogeneous composite membrane structure. Further analysis using XPS images reveals a significant increase in the intensity of CC=O within the composite membrane compared to the pure GO membrane, further demonstrating the effective integration of sodium alginate and graphene oxide nanosheets. The composite membrane exhibits excellent performance in the permeation energy conversion process, which is directly related to the surface charge density and pore size of the ion transport nanochannels within the composite membrane. Figure 5 As shown, measurements of the Zeta potential of the mixed dispersion reveal that it exhibits the highest Zeta potential under alkaline conditions. The Zeta potential initially increases and then decreases with increasing sodium alginate content, reaching its maximum at x=25. This indicates that the surface charge density of the composite film reaches its maximum near the parametric ratio of x=25. Simultaneously, as... Figure 6 As shown, XRD analysis of composite membranes with different parametric ratios reveals that the peak of the XRD pattern gradually shifts to the left with increasing sodium alginate content, indicating a gradual increase in interlayer spacing. Analysis of the conductivity values ​​of the composite membranes with different parametric ratios shows that at x=30, the composite membrane exhibits a larger surface charge density, a larger interlayer spacing, and the highest conductivity. We believe this is the fundamental reason why this parametric ratio composite membrane has the best permeate energy conversion performance. The increased hydrophobicity of the composite membrane surface with increasing sodium alginate content may also be one of the reasons for the increased power density of the composite membrane.

[0161] The ion transport area of ​​the composite film is controlled by using an open-cell silicon wafer, with an open-cell area of ​​3x10⁻⁶. -8 m 2 The ion transport characteristics of the hybrid membrane were studied by monitoring the transmembrane ion current. Figure 7 As shown, 0.5M and 0.01M NaCl solutions were used as artificial seawater and river water for the experiment. A composite membrane with a parametric ratio (x=20) was used as the experimental subject. KCl solution with a concentration gradient of 1000 times was added to both ends of the composite membrane, and the IV curve of the composite membrane was tested. After reversing the concentration gradient, the test was repeated. The two IV curves of the composite membrane were approximately parallel, indicating that the composite membrane has good symmetry. Furthermore, as... Figure 8 As shown, the experiment tested the changes in transmembrane conductivity of the composite membrane under different concentrations of KCl solution. When the electrolyte concentration was <0.01 M, the transmembrane conductivity deviated significantly from the bulk value (red dashed line), indicating that ion transport across the composite membrane was mainly controlled by the membrane surface charge at this point. Figure 9As shown, 0.1M KCl solutions with different pH values ​​were selected as background solutions in the experiment. The current change curves under the action of periodic voltage from -0.1V to 0.1V were tested. The transmembrane current and voltage change showed consistency, and the current magnitude did not change significantly, indicating that the composite membrane has a certain degree of stability under the three pH environments.

[0162] like Figure 10 As shown in the figure, the salt gradient current density and power density of the GO / SA composite membrane were tested with respect to the external load under different parameter ratios. When x = 30, the GO / SA composite membrane exhibited the highest current density under different loads, as shown in the figure. Figure 11 As shown, the power density of the GO-SA composite membrane reaches its maximum value of approximately 14.75 W / m² when the external load is approximately 7000 Ω. 2 ,like Figure 17 As shown, this is the currently recognized industry benchmark (5W / m). 2 This is 295% of the power density reported for most existing materials. For example... Figure 12 As shown, under the influence of natural seawater and artificial river water, the power density of this composite membrane even reaches as high as 19.39 W / m³. 2 By observing the power density curves of the composite membrane under different parametric ratios as a function of external load, we can easily find that the composite membrane with a higher power density reaches its maximum value under a lower external load. This indicates that the crosslinking of sodium alginate and graphene oxide nanosheets significantly alters the resistance of the GO-SA composite membrane. By measuring the IV curve of the composite membrane under an external voltage of -0.2V to 0.2V and calculating the conductivity of the composite membrane, the composite membrane exhibits maximum conductivity at x=30. Simultaneously, by analyzing the Zeta potential of the mixed dispersions with different parametric ratios, we found that the crosslinking of sodium alginate and graphene oxide nanosheets greatly increases the Zeta potential of the mixed dispersion. This results in a larger surface charge in the nanochannels of the GO-SA composite membrane, thereby increasing the ion selectivity of the composite membrane. Therefore, at x=30, the composite membrane has a larger surface charge density and higher ion selectivity. Simultaneously, the composite membrane has a larger interlayer spacing, leading to a larger conductivity and thus a larger ion flux, resulting in a higher power density. In addition, we conducted continuous measurements of composite membranes with different parametric ratios under an external load of 13000Ω for 90 minutes, taking experimental data every 5 minutes for result analysis. We found that the power density and current density of the composite membrane were relatively stable, indicating that the composite membrane has a certain degree of stability.

[0163] The experiment also tested the relationship between the power density of the optimal parametric ratio composite membrane and membrane thickness at different membrane thicknesses. We obtained composite membranes of different thicknesses by vacuum filtration of mixed dispersions of different volumes, and then cut the obtained composite membranes to a size of approximately 0.25 cm².2 Small films were used to measure the thickness of each film using a thickness gauge, roughly dividing them into five groups: 30µm, 40µm, 50µm, 60µm, and 70µm. Each group was tested, and nine sets of data were obtained for each group for statistical analysis. Experimental results show that, as... Figure 13 As shown, the maximum power density can be obtained when the film thickness is about 50 μm, and the average power density is as high as 15.82 W / m² under a 50-fold NaCl solution concentration gradient. 2 This is significantly higher than most reported materials. Furthermore, using the parametric ratio composite membrane (x=30) exhibiting the highest power density under a 50-fold NaCl concentration gradient as the experimental subject, such as... Figure 14 As shown, the power density and current density of the composite membrane as a function of external load were tested under different NaCl concentration gradients. The composite membrane exhibited a high power density of 50.59 W / m³ under a 500-fold concentration gradient. 2 Furthermore, the experiment also tested the composite membrane under a 50-fold concentration gradient, such as... Figure 15 The figure shows the variation of power density and current density with external load in different electrolyte solutions. The composite membrane exhibits the highest power density in KCl solution, at 20.94 W / m³. 2 The values ​​of LiCl, MgCl2, and CaCl2 are 13.17 W / m. 2 9.19W / m2, 6.75W / m 2 The power density and various data demonstrate superior performance. For example... Figure 16 As shown, regrettably, the power generation performance of the composite membrane drops sharply under large-area testing. At a NaCl solution concentration gradient of 1000 times, the test area increased to 0.25 mm. 2 At that time, the power density was only 7.85 W / m. 2 .

[0164] Sodium alginate exhibits significant pH sensitivity; under acidic conditions, —COO - The sodium alginate transforms into -COOH, decreasing its ionization degree and hydrophilicity. The molecular chain contracts, and as pH increases, the -COOH groups continuously dissociate, increasing the hydrophilicity of sodium alginate and extending its molecular chain. At pH 3, the surface charge density of the GO / SA composite membrane remains low. Furthermore, due to the contraction of the sodium alginate molecular chain, the space charge density within the composite membrane is also low, resulting in low ion selectivity and power density. When the high concentration end (pH 3) and the low concentration end (pH 11) are both at the same time, the surface charge density within the composite membrane increases, and the sodium alginate molecular chain extends, increasing the space charge density. This improves the ion selectivity of the composite membrane and increases the power density. Additionally, due to the H+ at both ends... +With significant concentration differences, the power density further increases under the drive of chemical potential. In an environment of pH=11, both the surface charge density and space charge density of the composite membrane reach their maximum values, which also results in the highest power density. Therefore, the composite membrane exhibits different power generation performance under different pH conditions. Experimental results show that, as... Figure 18 As shown, the composite membrane exhibits the highest power density under alkaline conditions, representing a 19.7% increase compared to the neutral environment, while the composite membrane shows the lowest power density under acidic conditions, decreasing by 35.1% compared to the neutral environment. Figure 19 As shown, when the composite membrane reaches its maximum power density, its current density changes according to the same pattern (Figue 4B). Figure 20 , 21 As shown, the experiment simultaneously tested the power density and current density changes of pure graphene oxide membranes under different pH conditions as a control. Although the power generation performance of the composite membrane under acidic conditions is far inferior to that under alkaline conditions, it still exhibits a high power density of 8.14 W / m. 2 The power density experiment was supplemented with tests on pure graphene oxide membranes under different pH conditions as a control. In summary, this composite membrane also has great application potential in extracting permeation energy from acidic or alkaline wastewater.

[0165] The GO-SA composite membrane uses a two-dimensional layered structure of graphene oxide membrane as a framework and sodium alginate as a filler. The two are cross-linked through hydrogen bonds to form a stable nanochannel structure. We simplified the nanochannel structure and conducted research based on a cylindrical nanochannel model.

[0166] When the crosslinking amount of sodium alginate and graphene oxide is low, the space charge density within the nanochannels is low. As the sodium alginate content increases, the space charge content within the nanochannels increases. Through numerical model analysis, we found that, for the same surface charge density, an increase in the space charge density within the nanochannels can increase the diffusion current and diffusion voltage, thereby increasing the power generation of the nanopores. Furthermore, as... Figure 22 As shown, a higher space charge density along the axial direction of the nanochannel leads to the enrichment of cations within the nanochannel, such as... Figure 23 As shown, anions dissipate, thus giving the nanochannels greater ion selectivity. Furthermore, as the solution pH increases, the surface charge density of the nanochannels increases, and this increase in surface charge density, in conjunction with space charge, further enhances the ion selectivity of the nanochannels, resulting in greater salinity gradient power generation. This is one of the reasons why the composite membrane exhibits extremely high power density in alkaline environments.

[0167] When sodium alginate is crosslinked with graphene oxide, the space charge within the nanochannels increases, accompanied by an expansion of the interlayer spacing of the composite film. This study first set the nanochannel radius to 2-6 nm. Through numerical model analysis, when the surface charge density remains constant, the salinity gradient power generation of the nanochannels initially increases and then decreases with increasing nanochannel radius, reaching a maximum at a channel radius of approximately 3-4 nm. Further analysis revealed that with increasing channel radius, the diffusion current within the nanochannels increases, but the ion selectivity gradually decreases, leading to a significant drop in diffusion voltage within the nanochannels, thus causing the power generation to initially increase and then decrease. Combined with experimental results related to the composite film, with increasing sodium alginate content, the interlayer spacing of the composite film increases, and the power density gradually increases, reaching a maximum at x=30. Therefore, when studying the mechanism of increased power density in the composite film, the channel radius in the numerical model should be controlled below 3 nm. It is worth noting that when the nanochannel radius is within the range of 2.0-2.4 nm, such as... Figure 25 , 26 As shown, the concentrations of cations and anions within the nanochannels change relatively little, and are mainly observed at the low concentration end. This is related to the variation in the thickness of the double layer within the nanochannels, which is also the main reason for the change in ion selectivity of the nanochannels.

[0168] We compared and analyzed the effects of changes in space charge and channel radius from the perspective of ion flux. We found that, for example... Figure 24 As shown, with increasing space charge density, the cation flux within the nanochannel increases while the anion flux decreases, such as... Figure 27 As shown, with the increase of the channel radius, both the cation flux and anion flux within the nanochannel gradually increase. Therefore, when sodium alginate and graphene oxide crosslink, simultaneously increasing both the space charge and interlayer spacing, the effect of the space charge will reduce the increase in anion flux caused by the increased interlayer spacing. This will maintain the ion selectivity of the nanochannel at a high level. Simultaneously, the nanochannel possesses a large ion flux. Under the combined influence, the nanochannel exhibits a very large diffusion current, thereby achieving extremely high salinity gradient power generation.

[0169] In summary, the functional groups on the surface of graphene oxide provide a large amount of surface charge, while sodium alginate provides a large amount of space charge between the layers. The synergistic effect of surface and space charges gives the composite membrane excellent ion selectivity. Simultaneously, the cross-linking of sodium alginate with graphene oxide increases the interlayer spacing of the two-dimensional membrane and expands the ion transport channels, resulting in a greater ion flux. The combined effect of superior ion selectivity and greater ion flux allows the composite membrane to generate a larger osmotic current under a given salinity gradient, thus achieving a power density far exceeding that of pure graphene oxide membranes. Furthermore, the composite membrane, with graphene oxide nanosheets as its basic framework and sodium alginate as its main filler, and using sodium alginate as the primary raw material, possesses high economic value, thus providing a feasible solution for the commercialization of RED salinity gradient power generation.

Claims

1. A method for preparing an oxidized graphene sodium alginate composite film for extracting marine osmotic energy, characterized by, Specifically comprising the following steps: Step 1, preparing a sodium alginate solution; Step 2, preparing a graphene oxide solution; Step 3, placing the sodium alginate solution prepared in step 1 into the graphene oxide solution prepared in step 2, and fully dissolving it by electromagnetic stirring to obtain a mixed dispersion liquid; Step 4, taking a polycarbonate film, placing the polycarbonate film as a substrate into a micro-filtration bottle, and taking the mixed dispersion liquid into the micro-filtration bottle to perform vacuum filtration to obtain a polycarbonate film covered with a graphene oxide-sodium alginate composite film; Step 5, stripping the graphene oxide-sodium alginate composite film from the polycarbonate film, naturally drying, and obtaining the graphene oxide-sodium alginate composite film for extracting marine osmotic energy.

2. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The specific process of step 1 is as follows: Step 1.1, taking deionized water in a reactor, and taking a certain amount of sodium alginate; Step 1.2, dissolving the sodium alginate in the deionized water, fully dissolving it by electromagnetic stirring, and obtaining a sodium alginate solution.

3. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The concentration of the sodium alginate solution in step 1 is 1-20 mg / ml.

4. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The concentration of the graphene oxide solution in step 2 is 0.1-5 mg / ml.

5. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The specific process of step 2 is as follows: Step 2.1, taking a certain amount of graphene oxide in another reactor, and taking deionized water; Step 2.2, adding the deionized water to the graphene oxide to dilute it to obtain a graphene oxide solution.

6. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The volume of the sodium alginate solution added in step 3 is not greater than the volume of the graphene oxide solution.

7. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The speed of the electromagnetic stirring in step 3 is 800-1200 r / min, and the time of the electromagnetic stirring is 6-24 h.

8. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The time of the vacuum filtration in step 4 is 5-7 days.

9. The method of claim 1, wherein the preparation of the graphene oxide sodium alginate composite film for extracting marine osmotic energy is characterized by, The time of the natural drying in step 5 is 8-24 h.

10. An oxidized graphene sodium alginate composite film for extracting marine osmotic energy, characterized by: The graphene oxide-sodium alginate composite film for extracting marine osmotic energy is prepared by the method of any one of claims 1-9.

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