High-stability salinity gradient power generation film, preparation method and application thereof

Abstract

The invention discloses a high-stability salinity gradient power generation film, a preparation method and application thereof, and a self-supporting film with an ordered layered structure is prepared by compounding montmorillonite MMT nanosheets and nanocellulose and combining vacuum filtration and gradient drying processes. The MMT nanosheet layered structure provides a directional ion channel, the negative charge surface enhances the cation selectivity, the nanocellulose flexible network inhibits MMT stacking, and the hydrogen-bond interaction improves the interface bonding force. The power density of the thin film reaches 4-6 W / m (50 times of salinity difference), the tensile strength is larger than or equal to 20 MPa, and the power attenuation rate is smaller than or equal to 5% after the thin film continuously operates for 100 hours. The preparation process is green and controllable, is suitable for seawater-river water and industrial wastewater salinity gradient power generation scenes, and has large-scale application potential.

Description

Technical Field

[0001] The present application relates to the field of membrane material technology, and in particular to a high-stability salt-difference power generation thin film, a preparation method and applications thereof. Background Art

[0002] With the continued growth of global energy demand and the urgent pursuit of sustainable energy, the development of new clean energy technologies has become increasingly important. Salinity-based energy, a renewable energy source with abundant reserves, is gaining widespread attention. As a key component in salinity-based energy conversion, the performance of salinity-based power generation thin films directly impacts the efficiency and feasibility of salinity-based power generation systems.

[0003] Existing salinity-based power generation thin films generally have a power density below 3 W / m², and due to the lack of a flexible substrate material, their tensile strength is less than 15 MPa. Furthermore, traditional clay-based films experience swelling and blockage of ion channels during long-term operation, resulting in a power attenuation rate exceeding 10%. This application aims to address these technical bottlenecks through a MMT-cellulose composite strategy. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-stability salt-difference power generation film and a preparation method thereof, and to produce a high-stability film material with a high permeability energy collection rate through simple design and single material modification.

[0005] The embodiments of the present application disclose a high-stability salt-difference power generation film, characterized in that the salt-difference power generation film is a self-supporting film formed by compounding montmorillonite MMT nanosheets and cellulose through a vacuum filtration process. The power density of the salt-difference power generation film is 4-6 W / m², and the power attenuation rate after 100 hours of continuous operation is ≤5%.

[0006] Preferably, the montmorillonite MMT nanosheet is an exfoliated layered structure with a thickness of 1-5 nm and a lateral size of 200-500 nm.

[0007] Preferably, the cellulose is nanocellulose fiber with a diameter of 10-50 nm and a length of 1-5 μm, and the mass of the cellulose accounts for 28.6% to 40% of the total mass of the salt difference power generation film.

[0008] The present invention also provides a method for preparing a high-stability salt-difference power generation thin film, comprising the following steps: S1 Preparation of montmorillonite (MMT) nanosheets: Pre-treat MMT powder, then ultrasonically disperse the pre-treated MMT powder in deionized water. After the ultrasonication, centrifuge the dispersion, filter the upper suspension, and obtain a MMT nanosheet dispersion. The concentration of the MMT nanosheet dispersion is 3-5 mg / mL. S2 Cellulose dispersion: The exfoliated nanocellulose was dispersed in a dimethyl sulfoxide (DMSO) solution at a 1:50 to 1:100 mass ratio of cellulose to DMSO. The suspension was magnetically stirred at room temperature for 48 h. The stirred suspension was centrifuged and the upper homogenous suspension was collected. The concentration of the suspension was measured and adjusted to 2 mg / mL by dilution or concentration to obtain a uniform cellulose suspension. S3 film preparation: MMT dispersion and cellulose suspension were mixed in a volume ratio of 1:1 and stirred for 24 hours to form a homogeneous mixture. A layer of the above mixture was formed on a polyvinylidene fluoride (PVDF) filter membrane substrate with a pore size of 0.22-0.45 μm by vacuum filtration. After drying, it was peeled off to obtain a self-supporting salt-difference power generation film.

[0009] Preferably, the drying method in step S3 is a three-stage gradient drying, in which the pre-drying is performed in a constant temperature of 25°C and a constant humidity of 50% to form a preliminary gel structure; in the second stage, the temperature is raised to 30°C, the humidity is reduced to ≤40%, and the air flow circulation at a wind speed of 1 m / s is turned on to continue drying for 18 hours; the third stage is to treat in a vacuum drying oven to completely remove moisture.

[0010] An embodiment of the present application also provides an application of a high-stability salinity difference power generation film, wherein the high-stability salinity difference power generation film is used for osmotic energy power generation in a seawater-river water salinity gradient or industrial wastewater salinity gradient environment.

[0011] The advantages of the present invention are: 1. The present invention achieves precise control of material properties through a multi-scale composite design of MMT nanosheets and nanocellulose, combined with vacuum filtration and gradient drying processes. The layered structure of MMT nanosheets provides high-density directional ion channels, and its surface negative charge significantly enhances cation selectivity. Nanocellulose forms a three-dimensional flexible network, anchoring the MMT nanosheets through hydrogen bonds and van der Waals forces, inhibiting their stacking and reducing interface defects. The cellulose network gives the film high toughness. The MMT nanosheets serve as a rigid skeleton support, which is 100% higher than that of a single MMT membrane (strength ≤ 10 MPa). The composite interface inhibits swelling, and the power attenuation rate is ≤ 5% after 100 hours of continuous operation.

[0012] 2. The high-frequency ultrasound-assisted mixing of the present invention produces a cavitation effect, breaks the MMT-cellulose interface energy barrier, improves dispersion uniformity, shortens stirring time, and combines with magnetic stirring to form an interpenetrating network structure to prevent nanosheet sedimentation; staged moisture control avoids stress concentration and reduces film defects, reducing the film defect rate to <5%. Water molecules penetrate and soften the interface to achieve non-destructive peeling, and the yield rate is increased to 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 The figure shows the IV curve of the salt difference power generation film obtained in Example 1 of the present invention under a 50-fold NaCl concentration difference. DETAILED DESCRIPTION

[0015] The following is a detailed description of the technical solutions in the embodiments of the present invention, with reference to the accompanying drawings. Obviously, the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0016] Example 1 Preparation of S1 montmorillonite MMT nanosheets: 1.5 g of montmorillonite MMT powder was ground using an agate mortar for 10 minutes to eliminate lumps and ensure that the initial particle size of the powder was ≤50 μm. The pretreated MMT powder was added to 500 mL of deionized water and allowed to stand at room temperature for 30 minutes for pre-wetting. Ultrasonic dispersion was performed using a probe-type ultrasonic instrument with an ultrasonic frequency of 40-60 kHz and an ultrasonic time of 2-4 hours. During the ultrasonic process, a 5-minute pause was performed every 30 minutes to avoid overheating of the liquid (temperature control ≤40°C), and the container was gently shaken to ensure uniform dispersion. After the ultrasonication, the dispersion was centrifuged at 3000 rpm for 10 minutes to remove unpeeled MMT particles and impurities. The upper suspension was taken and filtered through a 0.45 μm nylon filter membrane to obtain a homogeneous MMT nanosheet dispersion. The dispersion concentration was determined by UV-visible spectrophotometry to confirm that the final concentration of the MMT nanosheet dispersion was 3 mg / mL. The single-sheet thickness of the MMT nanosheet was measured by atomic force microscopy to be 1-5 nm, and the lateral size was 200-500 nm as observed by transmission electron microscopy; S2 Cellulose dispersion: Take the cellulose raw material, treat it with a high-pressure homogenizer three times at a pressure of 1500 bar, and then purify and freeze-dry it to obtain nanocellulose powder with a diameter of 10-50 nm and a length of 1-5 μm.

[0017] 1.5 g of the above-mentioned nanocellulose powder was added to 500 mL of dimethyl sulfoxide (DMSO) solution and magnetically stirred at 200-400 rpm for 48 hours at room temperature (25±2°C) to ensure that the nanocellulose was fully dispersed. The stirred suspension was centrifuged at 3000 rpm for 10 minutes to remove undispersed aggregates and improve the homogeneity of the suspension. The upper homogeneous suspension was collected and the concentration was determined by ultraviolet-visible spectrophotometry (UV-Vis). The concentration was adjusted to 2 mg / mL by dilution or concentration to obtain a uniform 2 mg / mL cellulose suspension. S3 film preparation: 250 mL of MMT dispersion was mixed with 250 mL of cellulose suspension and stirred at 300 rpm using a magnetic stirrer at 25 ± 2 °C for 12 h. During the stirring, the mixture was paused for 10 min every 2 hours and the container was gently shaken to prevent sedimentation. Probe ultrasound at 40 kHz and 200 W was used to assist in dispersion for 10 min to ensure the formation of a homogeneous mixture. The homogeneous mixture was transferred to a vacuum filtration device and a hydrophilized PVDF filter membrane with a pore size of 0.22-0.45 μm was used. The vacuum pressure was adjusted to -0.09 MPa and the filtration time was controlled at 30-40 min until a uniform wet film with a thickness of about 100-150 μm was formed on the surface of the PVDF filter membrane. The membrane surface was rinsed with deionized water three times to remove residual DMSO solvent.

[0018] The wet film was pre-dried in a constant temperature and humidity chamber (25°C, 50% humidity) for 6 hours to form a preliminary gel structure. The temperature was then raised to 30°C, the humidity was reduced to ≤40%, and air circulation was activated at a speed of 1 m / s. Drying continued for 18 hours. Finally, the film was treated in a vacuum drying oven (30°C, -0.05 MPa) for 2 hours to completely remove moisture and enhance film density. The dried film, along with the PVDF substrate, was immersed in deionized water for 5 minutes. The osmotic pressure difference in the water allowed the film to naturally peel off. The film was gently grasped by the edge with tweezers and spread flat on a polytetrafluoroethylene plate. The film was then treated in a UV-ozone cleaner (wavelength 254 nm) for 10 minutes to remove surface organic matter and enhance hydrophilicity. After post-treatment, the salinity-grade power generation film was obtained.

[0019] The salinity difference power generation film was tested using conventional testing methods. The thickness was measured to be 30±2μm using a micrometer. The tensile strength was measured to be ≥20 MPa using a universal material testing machine. The elongation at break was 6%-8%. The power density at 50 times the NaCl concentration difference was 5.0±0.3 W / m 2 , the power density attenuation rate is ≤5% after 100 hours of continuous operation. Example 2

[0020] The concentration of MMT in step S1 of Example 1 was adjusted to 4 mg / mL (originally 3 mg / mL). The remaining steps (cellulose dispersion, mixing ratio, vacuum filtration, drying conditions, etc.) were exactly the same as in Example 1, and a uniformly distributed MMT-cellulose composite nanofilm was finally obtained.

[0021] A digital micrometer (accuracy ±1 μm) was used to measure the MMT-cellulose composite nanofilm at five different locations and the average thickness was 35 ± 3 μm, a slight increase from 30 ± 2 μm in Example 1. This is due to the enhanced film density resulting from the increased MMT concentration. A universal testing machine (ASTM D882 standard) measured a tensile strength of 28 ± 2 MPa and an elongation at break of 6 ± 0.5%, indicating that the increased MMT content improved film rigidity. Using an Ag / AgCl electrode at a 50-fold NaCl concentration difference, the power density was 5.8 ± 0.3 W / m². Increasing MMT concentration increases ion channel density. After 100 hours of continuous operation, the power density decayed by 3.4%, indicating that the high MMT content inhibits cellulose swelling in salt solutions. Example 3

[0022] The concentration of MMT in step S1 of Example 1 was adjusted to 5 mg / mL (originally 3 mg / mL). The remaining steps (cellulose dispersion, mixing ratio, vacuum filtration, drying conditions, etc.) were exactly the same as in Example 1, and a uniformly distributed MMT-cellulose composite nanofilm was finally obtained.

[0023] The MMT-cellulose composite nanofilm was measured at five different locations using a digital micrometer (accuracy ±1 μm) and the average thickness was 40 ± 4 μm, a significant increase from the 30 ± 2 μm in Example 1. This increase was attributed to the deposition of more nanosheets due to the increased MMT concentration. Using a universal testing machine (ASTM D882), the tensile strength was 31 ± 2 MPa, and the elongation at break was 5.5 ± 0.5%, indicating that the MMT nanosheets restricted cellulose chain slip. Using an Ag / AgCl electrode at a 50-fold NaCl concentration gradient, the power density was 6.2 ± 0.3 W / m², indicating that the high MMT concentration enhanced ion selectivity. After 100 hours of continuous operation, the power density decayed by ≤ 3.0%, indicating that the high MMT content inhibited cellulose swelling in saline solutions.

[0024] The salt difference power generation film obtained in Example 1 was subjected to current-voltage curve characteristic analysis under a 50-fold NaCl concentration difference. The results are as follows: Figure 1As shown: It can be seen that the current increases linearly with increasing voltage, indicating that the salinity-difference power generation film exhibits approximately ohmic characteristics within the test voltage range. That is, the film resistance value is relatively stable, and the ion transport process is not significantly hindered, reflecting the uniformity of the ion conduction channels within the material. When the voltage is positive, the current continues to increase with increasing voltage, indicating that the film has a strong response ability to ion migration in the salinity-difference power generation scenario and can effectively use the salt concentration difference to drive the directional movement of ions to generate current. This process achieves the preparation of a highly stable salinity-difference power generation film through the MMT-cellulose composite strategy. Its layered structure design effectively balances ion selectivity and mechanical stability.

[0025] According to Examples 1-3, it can be seen that a 3 mg / mL MMT concentration prioritizes flexibility and is suitable for scenarios with low mechanical strength requirements. A 4 mg / mL MMT concentration offers balanced performance and is recommended for standardized applications. A 5 mg / mL MMT concentration can significantly improve the power generation efficiency and durability of the film at the expense of slight flexibility, providing an optimized solution for scenarios with high power requirements (such as industrial wastewater power generation).

[0026] This implementation mode is only an illustrative description of this patent and does not limit its scope of protection. People skilled in the art may also make partial changes to it. As long as it does not exceed the spirit of this patent, it will be regarded as an equivalent replacement of this patent and will be within the scope of protection of this patent.

Claims

1. A high-stability salt difference power generation film, characterized in that: The salt difference power generation film is a self-supporting film formed by combining montmorillonite MMT nanosheets and cellulose through a vacuum filtration process. The power density of the salt difference power generation film is 4-6 W / m 2 , and the power attenuation rate after 100 hours of continuous operation is ≤5%.

2. The high-stability salt difference power generation thin film according to claim 1, characterized in that: The montmorillonite MMT nanosheet is an exfoliated layered structure with a thickness of 1-5 nm and a lateral size of 200-500 nm.

3. The high-stability salt difference power generation thin film according to claim 1, characterized in that: The cellulose is a nanocellulose fiber with a diameter of 10-50 nm and a length of 1-5 μm. The mass of the cellulose accounts for 28.6% to 40% of the total mass of the salt difference power generation film.

4. A method for preparing a high-stability salt difference power generation film, characterized in that: The following steps are involved: S1 Preparation of montmorillonite (MMT) nanosheets: Pre-treat MMT powder, then ultrasonically disperse the pre-treated MMT powder in deionized water. After the ultrasonication, centrifuge the dispersion, filter the upper suspension, and obtain a MMT nanosheet dispersion. The concentration of the MMT nanosheet dispersion is 3-5 mg / mL. S2 Cellulose dispersion: The exfoliated nanocellulose was dispersed in a dimethyl sulfoxide (DMSO) solution at a 1:50 to 1:100 mass ratio of cellulose to DMSO. The suspension was magnetically stirred at room temperature for 48 h. The stirred suspension was centrifuged and the upper homogenous suspension was collected. The concentration of the suspension was measured and adjusted to 2 mg / mL by dilution or concentration to obtain a uniform cellulose suspension. S3 film preparation: MMT dispersion and cellulose suspension were mixed in a volume ratio of 1:1 and stirred for 24 hours to form a homogeneous mixture. A layer of the above mixture was formed on a polyvinylidene fluoride (PVDF) filter membrane substrate with a pore size of 0.22-0.45 μm by vacuum filtration. After drying, it was peeled off to obtain a self-supporting salt-difference power generation film.

5. The method for preparing a high-stability salt difference power generation thin film according to claim 4, characterized in that: The drying method in step S3 is a three-stage gradient drying method. In the first stage, pre-drying is performed in a constant temperature and humidity box at 25°C and 50% to form a preliminary gel structure; in the second stage, the temperature is raised to 30°C, the humidity is reduced to ≤40%, and an air flow circulation with a wind speed of 1 m / s is started to continue drying for 18 hours; in the third stage, treatment is performed in a vacuum drying box to completely remove moisture.

6. An application of a high-stability salt difference power generation film, characterized in that: The high-stability salt difference power generation film is used in osmotic energy power generation in a seawater-river water salinity gradient or industrial wastewater salinity gradient environment.

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