Janus structured negative friction layer material and preparation method, and triboelectric nanogenerator

Abstract

This application relates to the field of triboelectric nanogenerator technology, specifically to a negative friction layer material with a Janus structure and its preparation method, and a triboelectric nanogenerator. The process includes: S1, preparing MnCo-MOF nanoparticles; S2, calcining the MnCo-MOF nanoparticles to obtain hollow nanoparticles; S3, dispersing the hollow nanoparticles and PVDF powder in a first mixed solvent to obtain a first spinning solution, and simultaneously dispersing barium titanate particles and PVDF powder in a second mixed solvent to obtain a second spinning solution; S4, using electrospinning and a Janus needle with a dual-channel structure to spin the first and second spinning solutions to obtain a negative friction layer material with a Janus structure. This negative friction layer material has a large contact area at the friction interface, enabling it to generate more triboelectric charge during friction, significantly increasing its charge generation.

Description

Technical Field

[0001] This invention relates to the field of triboelectric nanogenerator technology, specifically to a negative friction layer material with a Janus structure and its preparation method, and a triboelectric nanogenerator. Background Technology

[0002] Among numerous polymer substrates, polyvinylidene fluoride (PVDF) and its copolymers have become the preferred substrates for the negative friction layer (P-NFM) of triboelectric nanogenerators (TENGs) due to their high electronegativity, excellent ferroelectric polarization characteristics, good flexibility, structural designability, and ease of processing and molding. Many studies have employed electrospinning technology to prepare nanofiber membranes (NFMs) with high specific surface area and high surface roughness from PVDF and its copolymers. This significantly increases the effective contact area and the number of contact sites at the triboelectric interface, thereby enhancing the amount of interfacial charge transfer during the contact electrification process and optimizing the electrical output performance of the TENG.

[0003] Metal-organic frameworks (MOFs) are a class of porous crystalline nanomaterials constructed from metal ions and organic ligands linked by strong coordination bonds. They possess excellent nanoscale pore structures, high internal specific surface areas, and tunable pore sizes, and have been extensively studied in sensing, catalysis, energy conversion, and storage. In recent years, some studies have used MOFs as active fillers to enhance the output performance of transurethral reductase (TENGs), demonstrating promising application potential. Compared to single-metal-organic frameworks, bimetallic-organic frameworks can leverage the synergistic effect of bimetals to inherit the inherent advantages of single-metal-organic frameworks while achieving structural and performance diversification. Bimetallic-organic frameworks can flexibly modulate the electronic structure to form a built-in electric field, enhancing charge separation and accumulation while suppressing charge recombination. They can also construct abundant hierarchical charge trapping sites, significantly improving the dielectric constant and interfacial polarization capability, reducing charge leakage and dissipation, and overcoming the limited charge accumulation capacity of single-metal-organic frameworks. Furthermore, nanoporous materials derived from organic frameworks possess narrow pore size distribution, ultra-high specific surface area, and excellent chemical stability, making them highly promising nanofillers that can be used to modify PVDF polymers to enhance their triboelectric properties. However, existing methods that introduce organic framework materials, such as bimetallic organic frameworks, into PVDF polymers, while improving their triboelectric properties, suffer from low environmental tolerance and short lifespan, significantly limiting their widespread application in the TENG (triboelectric encapsulation) field.

[0004] The Janus structure, characterized by its bifacial asymmetry, offers a new avenue for breakthroughs in TENG performance. Coupling the Janus structure with the TENG helps enhance interface charge trapping, improve output stability, and make it suitable for complex scenarios such as wearables, underwater applications, and high humidity environments. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a negative triboelectric layer material with a Janus structure. By using electrospinning technology, hollow nanoparticles with high surface activity, barium titanate particles, and PVDF materials are combined to form a negative triboelectric layer material with good triboelectric properties, thereby simultaneously improving TENG power generation efficiency and environmental tolerance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a negative friction layer material with a Janus structure, comprising the following steps: S1. ZIF-67 nanoparticles were synthesized using a room temperature solvent method. The synthesized ZIF-67 nanoparticles and manganese source were dispersed in a solvent, mixed evenly, and then centrifuged to collect MnCo-MOF nanoparticles. S2. The MnCo-MOF nanoparticles are calcined in air to obtain hollow nanoparticles. S3. Disperse the hollow nanoparticles and PVDF powder in a first mixed solvent, and stir continuously under water bath heating conditions until the mixture is homogeneous to obtain a first spinning solution. At the same time, disperse the barium titanate particles and the PVDF powder in a second mixed solvent, and stir continuously under the same conditions until the mixture is homogeneous to obtain a second spinning solution. S4. Using electrospinning and a Janus needle with a dual-channel structure, the first spinning solution and the second spinning solution are spun at a spinning solution flow rate of 1.5 mL / h-2.5 mL / h to obtain a negative friction layer material with a Janus structure.

[0007] Further, in step S3, the content of the hollow nanoparticles in the first mixed solvent is 0wt%-1wt%, and the content of the PVDF powder is 7wt%-15wt%. In the second mixed solvent, the content of barium titanate particles is 8wt%-12wt%, and the content of PVDF is 7wt%-15wt%. Further, the first mixed solvent is a mixture of N,N-dimethylformamide and acetone, and the mass ratio of N,N-dimethylformamide to acetone is (1-2):1; The second mixed solvent has the same components as the first mixed solvent.

[0008] Furthermore, in step S3, the water temperature of the hot water bath is 60℃-100℃.

[0009] Furthermore, in step S4, during the spinning process, the spinning voltage is set to 15kV-25kV, the receiving distance is set to 16cm-20cm, the ambient temperature is set to the range of 20℃-30℃, and the ambient humidity is set to the range of 30%-45%.

[0010] Further, in step S1, the mass ratio of the ZIF-67 nanoparticles to the manganese source is (1.5-3):1.

[0011] Furthermore, the ZIF-67 nanoparticles and the synthesis method include slowly adding a 2-methylimidazole solution dropwise to a cobalt-containing solution, mixing and allowing it to stand, then centrifuging to collect the ZIF-67 nanoparticles.

[0012] Furthermore, in step S2, the calcination treatment temperature is 220℃-280℃, and the heating rate is 2℃ / min-8℃ / min.

[0013] This application also provides a negative friction layer material with a Janus structure, which is prepared by the above-described preparation method.

[0014] This application also provides a triboelectric nanogenerator, which includes a positive friction layer, a negative friction layer, a support structure, and electrodes. The positive friction layer and the negative friction layer are disposed opposite to each other and are respectively attached to the upper and lower surfaces of the support structure. The two ends of the electrodes are respectively connected to the upper and lower surfaces of the support structure to promote charge transfer. The negative friction layer is made of the aforementioned negative friction layer material.

[0015] The beneficial effects of this invention are as follows: The preparation method provided in this application involves calcining bimetallic MOF nanoparticles to form hollow nanoparticles, and then introducing these hollow nanoparticles together with tetragonal barium titanate nanoparticles into a PVDF matrix using electrospinning. A self-made Janus needle is used during the spinning process to obtain a negative friction layer material with a Janus structure. This results in a large friction interface contact area, enabling the generation of more triboelectric charge during friction and significantly increasing its charge generation. Simultaneously, the negative friction layer material possesses excellent mechanical and chemical stability, allowing it to maintain good performance under different environmental conditions, exhibiting both high power generation efficiency and excellent environmental tolerance. The negative friction layer material provided in this application has wide applications in flexible electronics, smart sensing and green energy, and can promote the development of triboelectric nanogenerators towards multifunctionality, high reliability and integration.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a preparation method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a triboelectric nanogenerator according to an embodiment of the present invention; Figure 3 The images show SEM images and particle size distribution diagrams of different nanoparticles shown in Example 1 of this invention. Figure 4 The XRD patterns of different nanoparticles shown in Example 1 of this invention are shown below. Figure 5 The figures show the dielectric constant and dielectric loss curves of the negative friction layer materials shown in Examples 1-4 and Comparative Example 1 of the present invention, as well as the polarization charge distribution and microcapacitor formation in pure PVDF negative friction layer materials (I), P-0.3HMC NFM (II), and P-0.7HMC NFM (III). Figure 6 The fiber diameter distribution and morphology of the negative friction layer material shown in Embodiments 3, 5-7 and Comparative Example 1 of the present invention are shown. Figure 7 The image shows the EDS diagram of the negative friction layer material in Embodiment 5 of the present invention. Figure 8 The curves showing the variation of dielectric constant and dielectric loss of the negative friction layer material in Examples 3, 5-7 and Comparative Example 1 of this invention are shown. Figure 9 This is a comparison chart of the output performance of the dual-electrode TENG devices corresponding to the negative friction layer materials shown in Embodiments 3, 5-7, and Comparative Example 1 of the present invention; Figure 10 The output voltage, instantaneous power, and power density variation curves of the dual-electrode TENG device corresponding to the negative friction layer material shown in Embodiment 5 of the present invention are shown in the range of 1MΩ-900MΩ external load. Figure 11 The results show the long-term cycling stability test results of the dual-electrode TENG device corresponding to the negative friction layer material shown in Embodiment 5 of the present invention.

[0018] Figure label: 1. Janus needle; 2. First spinning solution; 3. Second spinning solution; 4. Positive friction layer; 5. Negative friction layer; 6. Support structure; 7. Electrode. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] A preferred embodiment of this application illustrates a method for preparing a negative friction layer material with a Janus structure, comprising the following steps: S1. ZIF-67 nanoparticles were synthesized using a room-temperature solvent method, and the results are as follows: Figure 1 As shown in (a); the synthesized ZIF-67 nanoparticles and manganese source were dispersed in a solvent, mixed evenly, and then centrifuged to collect MnCo-MOF nanoparticles. The results are as follows. Figure 1 As shown in (b); S2. The MnCo-MOF nanoparticles are calcined in air, such as... Figure 1 As shown in (c), hollow nanoparticles (HMC) are obtained, namely MOF-derived hollow porous nanoparticles; S3. The hollow nanoparticles and PVDF powder are dispersed in a first mixed solvent and stirred continuously under water bath heating conditions until they are mixed evenly to obtain a first spinning solution 2. At the same time, barium titanate (BaTiO3) particles and PVDF powder are dispersed in a second mixed solvent and stirred continuously under water bath heating conditions until they are mixed evenly to obtain a second spinning solution 3. S4, such as Figure 1 As shown in (d), electrospinning is used, and Janus needle 1 with dual-channel structure is used to spin the first spinning solution 2 and the second spinning solution 3 at a spinning solution flow rate of 1.5 mL / h-2.5 mL / h to obtain a negative friction layer material with Janus structure.

[0022] Tetragonal barium titanate nanoparticles possess advantages such as high voltage coefficient, high dielectric constant, low cost, and easy synthesis, making them ideal functional modification materials for optimizing the performance of triboelectric nanogenerators (TENGs). Introducing barium titanate nanoparticles into nanofiber-based negative friction layer materials can effectively enhance the electron gain and loss capacity of the negative friction layer material surface, increase the surface potential level, and thus increase the amount of triboelectric charge generated, ultimately achieving significant optimization of the output performance of barium titanate nanoparticles. This preparation method combines highly surface-active hollow nanoparticles, barium titanate particles, and PVDF materials using electrospinning technology to form a negative friction layer material with excellent triboelectric properties. This preparation method can effectively increase the contact area and charge generation at the triboelectric interface of the negative friction layer material, thereby improving the electrical output performance of the corresponding TENG. Simultaneously, the dual-channel Janus structure design optimizes the interfacial charge trapping ability, enhancing the stability and durability of the negative friction layer material.

[0023] In one embodiment, in step S3, the content of hollow nanoparticles in the first mixed solvent is 0wt%-1wt%, such as 0, 0.1wt%, 0.3wt%, 0.5wt%, and 0.7wt%. The content of PVDF powder is 7wt%-15wt%, preferably 10wt%. In this embodiment or other embodiments, in step S3, the content of barium titanate particles in the second mixed solvent is 8wt%-12wt%, and the content of PVDF is 7wt%-15wt%. By optimizing the content of each component in the first spinning solution 2 and the second spinning solution 3, it is helpful to precisely control the dispersion of hollow nanoparticles and barium titanate particles in the PVDF matrix, thereby improving the uniformity and stability of the negative friction layer material. At the same time, by optimizing the content of each component in the first spinning solution 2 and the second spinning solution 3, it is also helpful to improve the mechanical strength and electrical properties of the prepared negative friction layer material, providing a guarantee for the efficient operation of TENG.

[0024] In one embodiment, in step S3, the first mixed solvent is a mixture of N,N-dimethylformamide (DMF) and acetone (AC), and the mass ratio of N,N-dimethylformamide to acetone is (1-2):1. In this embodiment or other embodiments, it is preferable that the composition of the second mixed solvent is the same as that of the first mixed solvent. By selecting a mixture of N,N-dimethylformamide (DMF) and acetone (AC) as the first and second mixed solvents, PVDF and its copolymers, as well as added fillers (such as barium titanate particles), can be effectively dissolved, thereby helping to ensure that the first spinning solution 2 and the second spinning solution 3 have good flowability and stability during electrospinning. By optimizing the proportion of each component in the mixed solvent, the uniform dispersion of PVDF and added fillers in the solution can be further ensured, avoiding polymer precipitation and ensuring the quality of the final negative friction layer material.

[0025] In one embodiment, in step S3, the water bath temperature is 60℃-100℃. During the hot water bath process, proper temperature control effectively promotes the dissolution of each component and the cross-linking and reaction between hollow nanoparticles and PVDF powder, and between barium titanate particles and PVDF powder. Simultaneously, it avoids degradation of materials such as PVDF powder due to excessively high temperatures. This temperature range also helps improve the stability and uniformity of the spinning solution, thereby obtaining a high-performance nanofiber membrane.

[0026] In one embodiment, in step S4, during the spinning process, the spinning voltage is set to 15kV-25kV, the receiving distance is set to 16cm-20cm, the ambient temperature is controlled within the range of 20℃-30℃, and the ambient humidity is controlled within the range of 30%-45%. By optimizing the voltage, receiving distance, temperature, and humidity conditions during the electrospinning process, the diameter and surface morphology of the fibers can be precisely controlled, ensuring the uniformity of the fiber structure, which in turn helps to improve the triboelectric properties and stability of the Janus structure negative friction layer material.

[0027] In one embodiment, in step S1, the mass ratio of ZIF-67 nanoparticles to ZIF-67 nanoparticles is (1.5-3):1. By limiting the ratio of ZIF-67 nanoparticles to manganese source, the prepared MnCo-MOF nanoparticles have higher mass and specific surface area, thereby enhancing the charge trapping ability of the negative friction layer material and improving the electrical output performance of TENG. In this embodiment or other embodiments, the ZIF-67 nanoparticles and synthesis method include slowly adding a 2-methylimidazole solution dropwise to a cobalt-containing solution, mixing, allowing it to stand, and then centrifuging to collect the ZIF-67 nanoparticles. By using a slow dropwise addition method, the synthesis process of ZIF-67 nanoparticles can be effectively controlled, ensuring its uniformity and stability, thereby improving its composite effect with other materials such as manganese source, PVDF, etc., and thus helping to improve the overall performance of the finally prepared negative friction layer material. In some other embodiments, in step S2, the calcination treatment temperature is 220℃-280℃, and the heating rate is 2℃ / min-8℃ / min. This processing temperature range helps optimize the structure of MnCo-MOF nanoparticles, ensuring the formation of hollow nanoparticles with hollow porosity. The manganese source can be selected from potassium permanganate (KMnO4) or manganese oxide, etc. The cobalt in the cobalt-containing solution can be derived from cobalt salts such as cobalt nitrate.

[0028] One embodiment provides a negative triboelectric layer material with a Janus structure, which is prepared using the above-described method. This negative triboelectric layer material, by combining multiple functional materials, possesses excellent triboelectric properties and stability, balancing power generation efficiency and environmental tolerance, thereby significantly improving the output voltage and stability of the TENG (Transient Electron Generator).

[0029] One embodiment provides a triboelectric nanogenerator, such as Figure 2 As shown, the triboelectric nanogenerator includes a positive friction layer 4, a negative friction layer 5, a support structure 6, and electrodes 7. The negative friction layer 5 is made of the aforementioned negative friction layer material. The positive friction layer 4 and negative friction layer 5 are positioned opposite each other and are respectively adhered to the upper and lower surfaces of the support structure 6. The two ends of the electrodes 7 are connected to the upper and lower surfaces of the support structure 6 to promote efficient charge transport. In this embodiment or other embodiments, MSS-C1 NFM is used as the positive friction layer 4 of the triboelectric nanogenerator, the support structure 6 is a PET elastic support structure, and double-sided conductive cloth is used as the electrodes 7. The positive friction layer 4 and negative friction layer 5 are respectively adhered to the upper and lower acrylic plate surfaces of the PET elastic support structure, and the two ends of the double-sided conductive cloth are respectively connected to the upper and lower acrylic plate surfaces of the PET elastic support structure, assembling a complete dual-electrode triboelectric nanogenerator device. This triboelectric nanogenerator uses the aforementioned Janus-structured negative friction layer material as the negative friction layer 5, which significantly improves its power generation efficiency and enhances output stability. It can also adapt to complex application scenarios such as wearable devices, underwater environments, and high humidity conditions, thus broadening the application range of this triboelectric nanogenerator. The preparation of the MSS-C1 NFM includes: adding 4 wt% PLA to a 9:1 mixture of CF and DMF; stirring at room temperature for 8 hours; adding 1 wt% CS to the mixture; and continuing to stir at room temperature for another 12 hours until homogeneous. Subsequently, under conditions of 50 kV voltage, 18 cm receiving distance, 100 rpm drum rotation speed, and 25℃ ± 3℃, the required MSS-C1 NFM was efficiently prepared using SSFSE.

[0030] Example 1

[0031] A method for preparing a negative friction layer material with a Janus structure includes the following steps: S1. Weigh 3.493 g of cobalt nitrate hexahydrate and dissolve it in 200 mL of methanol, mixing thoroughly to form a cobalt-containing solution. Weigh 6.489 g of 2-methylimidazole and dissolve it in 200 mL of methanol, mixing thoroughly to form a 2-methylimidazole solution. Under continuous stirring, slowly add the 2-methylimidazole solution dropwise to the cobalt-containing solution to form a mixture. After the addition of the 2-methylimidazole solution is complete, continue stirring at room temperature for 30 min, then let it stand at room temperature for 24 h. Then, centrifuge the mixture at 8000 rpm for 10 min, collect the solid product, and wash the solid product with methanol several times. After washing, transfer it to a vacuum environment at 60 °C for drying to obtain ZIF-67 nanoparticles, such as... Figure 3As shown in (a-1) and (a-2).

[0032] 50 mg of ZIF-67 nanoparticles were weighed and added to 30 mL of anhydrous ethanol. The mixture was sonicated for 1 hour to ensure uniform dispersion of the ZIF-67 nanoparticles in the ethanol. Subsequently, 25 mg of KMnO4 powder was added to the dispersion, and sonication was continued for another hour to ensure uniform dispersion of the KMnO4 powder. The dispersion was then stirred using a magnetic stirrer to promote the reaction between the ZIF-67 nanoparticles and KMnO4 powder, forming a mixture. After continuous stirring for 10 hours, the mixture was centrifuged at 8000 rpm for 10 minutes. MnCo-MOF nanoparticles were then collected. Figure 3 As shown in (b-1) and (b-2), the MnCo-MOF nanoparticles were washed with ethanol several times, and then transferred to a vacuum environment at 60°C for drying.

[0033] S2. MnCo-MOF nanoparticles were placed in a ceramic boat and then placed in a tube furnace. Under air atmosphere, the temperature was increased from room temperature to 250°C at a rate of 5°C / min, and then held at this temperature for calcination. After calcination for 2 hours, crude hollow nanoparticles were obtained. The hollow nanoparticles were then washed with anhydrous ethanol three times and dried to obtain purified hollow nanoparticles, which were labeled as HMC. Figure 3 (c-1) and (c-2) and Figure 4 As shown. Afterwards, store it at room temperature for later use.

[0034] S3. Hollow nanoparticles were added to a mixed solvent of DMF and AC in a mass ratio of 6:4. After ultrasonic dispersion for 1 hour, PVDF powder was added to the mixed solvent, and the mass fraction of hollow nanoparticles in the mixed solvent was 0.1 wt%, and the mass fraction of PVDF powder was 10 wt%. Then, the mixture was heated and stirred in a water bath at 80°C for 1 hour to obtain the first spinning solution 2.

[0035] S4. The first spinning solution 2 is transferred to a syringe equipped with an 18G needle. Electrospinning is performed on the first spinning solution 2 at a spinning voltage of 18kV, a receiving distance of 18cm, a receiving roller speed of 400rpm, an ambient temperature of 25℃±5℃, and an ambient humidity of 40%±5%, with a spinning solution flow rate of 2mL / h to obtain an HMC-based negative friction layer material, labeled as P-0.1HMC NFM.

[0036] Depend on Figure 3It can be seen that the ZIF-67 nanoparticles obtained in step S1 have a dodecahedral structure with an average particle size of 287.9 ​​± 45.82 nm. After introducing Mn, the morphology and crystal structure of the ZIF-67 nanoparticles did not change significantly, and the resulting MnCo-MOF nanoparticles still maintained a regular dodecahedral morphology. The hollow nanoparticles obtained after calcination underwent some surface shrinkage due to the pyrolysis of organic components during carbonization, but their overall framework structure was well maintained, still exhibiting a polyhedral morphology, specifically a dodecahedral structure. Compared with ZIF-67 and MnCo-MOF, the particle size of the calcined hollow nanoparticles was slightly reduced, with an average particle size of 270.95 ± 37.01 nm. Figure 4 As shown in (a), the XRD characteristic diffraction peaks of the prepared ZIF-67 completely match the simulated characteristic peak spectrum of ZIF-67, with no obvious impurity peaks, indicating that the product has high crystallinity and good phase purity. The intensity of the characteristic diffraction peaks of the MnCo-MOF nanoparticles obtained after Mn doping decreased significantly, and some peak shapes even disappeared. This may be because the introduction of Mn element reduced the crystallinity of ZIF-67. Furthermore, no manganese-based characteristic diffraction peaks were observed in the prepared MnCo-MOF nanoparticles, indicating that most of the manganese element has been successfully incorporated into the MOF framework structure. Figure 4 As shown in (b), the XRD pattern of the prepared hollow nanoparticles shows only the characteristic diffraction peaks of MnCo2O4. Six distinct diffraction peaks appear at 2θ = 18.4°, 31.1°, 36.5°, 44.4°, 58.9°, and 64.5°, corresponding to the (111), (220), (311), (400), (511), and (440) crystal planes of the MnCo2O4 standard card (JCPDS#00-0231237), respectively. This indicates that the MnCo2O4 crystalline phase has been successfully generated.

[0037] Example 2

[0038] The difference between this embodiment and Embodiment 1 is that in step 3, the mass fraction of hollow nanoparticles is 0.3 wt%. Finally, an HMC-based negative friction layer material is obtained, labeled as P-0.3HMC NFM.

[0039] Example 3

[0040] The difference between this embodiment and Embodiment 1 is that in step 3, the mass fraction of hollow nanoparticles is 0.5 wt%. Finally, an HMC-based negative friction layer material is obtained, labeled as P-0.5HMC NFM.

[0041] Example 4

[0042] The difference between this embodiment and Embodiment 1 is that in step 3, the mass fraction of hollow nanoparticles is 0.7 wt%. Finally, an HMC-based negative friction layer material is obtained, labeled as P-0.7HMC NFM.

[0043] Example 5

[0044] S1. Weigh 3.493 g of cobalt nitrate hexahydrate and dissolve it in 200 mL of methanol, mixing thoroughly to form a cobalt-containing solution. Weigh 6.489 g of 2-methylimidazole and dissolve it in 200 mL of methanol, mixing thoroughly to form a 2-methylimidazole solution. Under continuous stirring, slowly add the 2-methylimidazole solution dropwise to the cobalt-containing solution to form a mixture. After the addition of the 2-methylimidazole solution is complete, continue stirring at room temperature for 30 min, then let it stand at room temperature for 24 h. Then, centrifuge the mixture at 8000 rpm for 10 min, collect the solid product, and wash the solid product with methanol several times. After washing, transfer it to a vacuum environment at 60 °C for drying to obtain ZIF-67 nanoparticles.

[0045] 50 mg of ZIF-67 nanoparticles were weighed and added to 30 mL of anhydrous ethanol. The mixture was sonicated for 1 h to ensure uniform dispersion of the ZIF-67 nanoparticles in the anhydrous ethanol. Subsequently, 25 mg of KMnO4 powder was added to the dispersion, and sonication was continued for another 1 h to ensure uniform dispersion of the KMnO4 powder. The dispersion was then stirred using a magnetic stirrer to promote the reaction between the ZIF-67 nanoparticles and KMnO4 powder, forming a mixture. After stirring continuously for 10 h, the mixture was centrifuged at 8000 rpm for 10 min to obtain MnCo-MOF nanoparticles. The MnCo-MOF nanoparticles were washed several times with ethanol and then dried under vacuum at 60 °C.

[0046] S2. MnCo-MOF nanoparticles were placed in a ceramic boat and then placed in a tube furnace. Under air atmosphere, the temperature was increased from room temperature to 250°C at a rate of 5°C / min and held at this temperature for calcination. After calcination for 2 hours, crude hollow nanoparticles were obtained. The hollow nanoparticles were then washed with anhydrous ethanol three times and dried to obtain purified hollow nanoparticles, which were labeled HMC. They were then stored at room temperature for later use.

[0047] S3. Hollow nanoparticles were added to a mixed solvent of DMF and AC in a mass ratio of 6:4. After ultrasonic dispersion for 1 hour, PVDF powder was added to the mixed solvent, and the mass fraction of hollow nanoparticles in the mixed solvent was 0.1 wt%, and the mass fraction of PVDF powder was 10 wt%. Then, the mixture was heated and stirred in a water bath at 80°C for 1 hour to obtain the first spinning solution 2.

[0048] Simultaneously, barium titanate particles were added to a mixed solvent of DMF and AC at a mass ratio of 6:4. After ultrasonic dispersion for 1 hour, PVDF powder was added to the mixed solvent, ensuring that the mass fraction of barium titanate particles and PVDF powder in the mixed solvent was 10 wt%. Subsequently, the solution was heated and stirred in a water bath at 80°C for 1 hour to obtain the second spinning solution 3.

[0049] S4. The first spinning solution 2 and the second spinning solution 3 are transferred to a 10 mL syringe equipped with a self-made Janus needle 1. Electrospinning is performed on the first spinning solution 2 at a spinning voltage of 21 kV, a receiving distance of 18 cm, a receiving roller speed of 400 rpm, an ambient temperature of 25℃±5℃, and an ambient humidity of 40%±5%, with a spinning solution flow rate of 2 mL / h to obtain a negative friction layer material with a Janus structure, labeled as JF NFM.

[0050] Example 6

[0051] The difference between this embodiment and embodiment 6 is that in step S4, the first spinning solution 2 and the second spinning solution 3 are respectively transferred to a 10 mL syringe equipped with an 18G needle. Electrospinning is used, and under the conditions of spinning voltage of 18kV, receiving distance of 18cm, receiving roller speed of 400rpm, ambient temperature of 25℃±5℃, and ambient humidity of 40%±5%, the second spinning solution 3 and the first spinning solution 2 are spun sequentially at a spinning solution flow rate of 2mL / h to obtain a double-layered negative friction layer material with a Janus structure, labeled as JM NFM.

[0052] Example 7

[0053] The difference between this embodiment and Embodiment 6 is that in step S3, only barium titanate particles are added to a mixed solvent of DMF and AC with a mass ratio of 6:4. After ultrasonic dispersion for 1 hour, PVDF powder is added to the mixed solvent, and the mass fraction of barium titanate particles and PVDF powder in the mixed solvent is 10 wt%. Subsequently, it is heated and stirred in a water bath at 80°C for 1 hour to obtain the second spinning solution 3.

[0054] In step S5, the second spinning solution 3 is transferred to a syringe equipped with an 18G needle. Electrospinning is performed on the first spinning solution 2 at a spinning solution flow rate of 2 mL / h under the conditions of a spinning voltage of 21 kV, a receiving distance of 18 cm, a receiving roller speed of 400 rpm, an ambient temperature of 25℃±5℃, and an ambient humidity of 40%±5%, to obtain a barium titanate-doped negative friction layer material, labeled as BT NFM.

[0055] Comparative Example 1 PVDF powder was added to a mixed solvent of DMF and AC at a mass ratio of 6:4, and ultrasonically dispersed for 1 hour, with the mass fraction of PVDF powder in the mixed solvent being 10 wt%. Subsequently, the solution was heated and stirred in a water bath at 80°C for 1 hour to obtain a spinning solution.

[0056] The spinning solution was transferred into a syringe equipped with an 18G needle, and electrospinning was performed on the first spinning solution 2 at a spinning voltage of 18kV, a receiving distance of 18cm, a receiving roller speed of 400rpm, an ambient temperature of 25℃±5℃, and an ambient humidity of 40%±5%, with a spinning solution flow rate of 2mL / h to obtain a pure PVDF-based negative friction layer material, labeled as PVDF NFM.

[0057] Square samples with an effective area of ​​3.5cm × 3.5cm were cut from the HMC-based negative friction layer materials prepared in Examples 1-4 and the pure PVDF-based negative friction layer material prepared in Comparative Example 1, respectively, as samples for this test. After clamping and fixing each test sample using electrode 7, the dielectric constant and dielectric loss of each test sample were tested and analyzed under different frequency conditions using a Keysight E4980AL LCR meter. The analysis results are as follows: Figure 5 As shown.

[0058] Depend on Figure 5As shown in Figures (a) and (b), the dielectric loss of the HMC-based negative friction layer materials prepared in Examples 1-4 and the pure PVDF-based negative friction layer material prepared in Comparative Example 1 both exhibit a monotonically increasing trend with increasing test frequency. This change can be explained by the synergistic effect of dipole relaxation and conductivity loss. Compared to the pure PVDF-based negative friction layer material prepared in Comparative Example 1, the HMC-based negative friction layer materials prepared in Examples 1-4 exhibit significantly better dielectric properties, with a dielectric constant significantly higher than that of the pure PVDF-based negative friction layer material (11.58). Furthermore, when the amount of hollow nanoparticles added does not exceed 0.5 wt%, the relative dielectric constant of the HMC-based negative friction layer material increases with the increase of the amount of hollow nanoparticles added. This is because the introduction of hollow nanoparticles constructs a microcapacitor network inside the nanofibers, significantly increasing the dipole density of the system. Specifically, as shown... Figure 5 As shown in (c), when hollow nanoparticles are uniformly dispersed in the PVDF matrix, the thin dielectric layer between adjacent nanofillers forms a large number of microcapacitors, effectively improving the capacitance characteristics of the fiber, thus enabling the HMC-based negative friction layer material to capture more space charge. Simultaneously, the nanoporous structure of the hollow nanoparticles has a high specific surface area, providing abundant trapping sites for induced charges during triboelectric charging, further enhancing the system's charge storage capacity. However, when the amount of hollow nanoparticles added further increases, the excess hollow nanoparticles agglomerate in the PVDF matrix, forming local conductive pathways. This change is consistent with the percolation threshold theory. Therefore, it can be concluded that the optimal addition amount of hollow nanoparticles in the HMC-based negative friction layer material is no more than 0.5 wt%, at which the HMC-based negative friction layer material can achieve efficient capture and stable storage of triboelectric charges.

[0059] The fiber diameter, morphology, etc., of the HMC-based negative friction layer material prepared in Example 3, the Janus-structured negative friction layer material prepared in Example 5, the Janus-structured bilayer negative friction layer material prepared in Example 6, the barium titanate-doped negative friction layer material prepared in Example 7, and the pure PVDF-based negative friction layer material prepared in Comparative Example 1 were tested. The test structures are as follows: Figure 6 As shown.

[0060] Depend on Figure 6As shown in (a), (b), (c), and (e), the Janus-structured negative friction layer material prepared in Example 5 has a fiber diameter of 600.05 ± 11.74 nm, which is significantly larger than the HMC-based negative friction layer material prepared in Example 3 and the barium titanate-doped negative friction layer material prepared in Example 7. This is because the hollow nanoparticles and barium titanate particles undergo a recombination effect at the tip of the self-made Janus needle 1, leading to an increase in the flow resistance of the spinning jet. Consequently, the jet cannot be sufficiently refined during electric field stretching, ultimately resulting in an increase in fiber diameter. Figure 6 As can be seen from (d), the negative friction layer material with Janus structure and double layer prepared in Example 6 has a large thickness and a rough surface. Figure 6 Image (f) is a TEM image of a single fiber in the negative friction layer material with a Janus structure prepared in Example 5. Figure 6 From (f) in the middle, we can see that, by Figure 6 (f) As can be seen, the hollow nanoparticles and barium titanate particles are arranged in parallel within the PVDF matrix, forming a typical Janus structure within each fiber. The barium titanate particles significantly promote charge generation and trapping within the PVDF matrix, while the hollow nanoparticles not only enhance the charge generation efficiency of the PVDF matrix but also, due to their hollow structure, act as charge traps, further capturing and storing a large amount of charge. Therefore, it can be concluded that the negative friction layer material with a Janus structure can effectively promote the generation, transfer, and storage of interfacial charges.

[0061] To further confirm that hollow nanoparticles and barium titanate particles have been successfully introduced into the PVDF matrix and to clarify their elemental distribution characteristics within the fiber, EDS was used to characterize the negative friction layer material with a Janus structure prepared in Example 5. The results are as follows: Figure 7 As shown.

[0062] Depend on Figure 7 It can be seen that C, O, Mn, Co, Ti, and Ba elements are uniformly distributed throughout the negative friction layer material with the Janus structure. Among them, Mn and Co are characteristic elements of hollow nanoparticles, while Ti and Ba are characteristic elements of barium titanate particles. This result proves that hollow nanoparticles and barium titanate particles have been successfully introduced into the PVDF matrix, further confirming that hollow nanoparticles and barium titanate particles have excellent dispersion in composite nanofibers and exhibit no obvious agglomeration.

[0063] Square samples with an effective area of ​​3.5 cm × 3.5 cm were cut from the HMC-based negative friction layer material prepared in Example 3, the Janus-structured negative friction layer material prepared in Example 5, the Janus-structured double-layered negative friction layer material prepared in Example 6, the barium titanate-doped negative friction layer material prepared in Example 7, and the pure PVDF-based negative friction layer material prepared in Comparative Example 1, respectively, and used as samples for this test. After clamping and fixing each test sample with electrodes, the dielectric constant and dielectric loss of each test sample were tested and analyzed with frequency under different frequency conditions using a Keysight E4980AL LCR meter. The analysis results are as follows: Figure 8 As shown.

[0064] Depend on Figure 8 As shown in (a), the negative friction layer material with a Janus structure prepared in Example 5 has the highest dielectric constant, indicating that the introduction of hollow nanoparticles and barium titanate particles as fillers can significantly improve the dielectric properties of the PVDF-based composite friction layer. Figure 8 As shown in (b), the dielectric loss of all samples exhibits a monotonically increasing trend with increasing test frequency. This is because, with increasing frequency, the dipole turning and chain segment movement hysteresis of the PVDF matrix intensify, the interfacial polarization relaxation hysteresis between the hollow nanoparticles and barium titanate fillers and the polymer becomes significantly delayed, and the conductivity loss caused by carrier migration is significantly enhanced. Ultimately, the macroscopic manifestation is that the dielectric loss continuously increases with increasing test frequency. However, the dielectric loss values ​​of all samples remain at an extremely low level (<0.16), which can be considered negligible in practical applications.

[0065] Square samples with an effective area of ​​3.5cm × 3.5cm were precisely cut from the negative friction layer materials prepared in Comparative Example 1, Example 3, and Examples 5-7, respectively, and used as negative friction layer samples for testing. Simultaneously, MSS-C1 NFM was selected as the positive friction layer 4 material; two pieces of stable and highly conductive double-sided conductive cloth were selected as electrodes 7; and a PET resilient device was used as the support structure 6 for the entire TENG device, assembled together with the negative friction layer samples to form a dual-electrode TENG device. The positive friction layer 4 and negative friction layer were respectively adhered to the upper and lower acrylic plates of the prepared PET resilient device, and the two ends of the double-sided conductive cloth were connected to the upper and lower acrylic plates of the PET resilient device, respectively. Subsequently, the dual-electrode TENG device was placed on a pressure sensor, and the two electrodes 7 of the dual-electrode TENG device were connected to the red / black alligator clips of a Keithley 6514 electrometer (Tektronix, USA), ensuring stable electrical connection and good contact. A linear electric cylinder is driven to reciprocate continuously according to set parameters, thereby applying an external force with a fixed frequency to the dual-electrode TENG device, simulating the force conditions in a real-world working scenario. During the test, the output performance parameters of the dual-electrode TENG device were measured in real-time and accurately at a sampling rate of 1000 points / second, including key indicators such as open-circuit voltage, short-circuit current, transferred charge, and power. The results are as follows: Figure 9 As shown.

[0066] Depend on Figure 9 It can be seen that the dual-electrode TENG device assembled from the pure PVDF-based negative friction layer material prepared in Comparative Example 1 has the lowest output performance, with an open-circuit voltage of only 436.32V, a short-circuit current of only 11.16μA, and a transferred charge of only 118.75nC. When barium titanate particles are introduced, such as the dual-electrode TENG device assembled from the barium titanate-doped negative friction layer material prepared in Example 7, the output performance is significantly improved, with the open-circuit voltage increasing to 705.91V, the short-circuit current increasing to 14.24μA, and the transferred charge increasing to 131.86nC. This is mainly attributed to the fact that BT nanoparticles can effectively enhance the interfacial polarization and space charge polarization of the composite material, inducing more surface triboelectric charge generation during frictional contact, while reducing the charge recombination rate inside the friction layer and suppressing charge leakage. Furthermore, BT can induce PVDF to generate more β-phase, enhancing the ferroelectric and piezoelectric responses of the matrix itself, forming a synergistic enhancement with the triboelectric effect, thereby achieving an improvement in electrical output. When hollow nanoparticles are further introduced, such as the dual-electrode TENG device assembled from the negative friction layer material with Janus structure prepared in Example 5 and the double-layer negative friction layer material with Janus structure prepared in Example 6, its output performance is further significantly improved.

[0067] The output performance of the dual-electrode TENG device assembled from the negative friction layer material with Janus structure prepared in Example 5 under different external loads was tested, and the results are as follows: Figure 10 As shown.

[0068] Depend on Figure 10 As shown in (a), the dual-electrode TENG device assembled from the negative friction layer material with a Janus structure prepared in Example 5 exhibits an increasing output voltage with increasing external load, and tends to saturate when the load becomes sufficiently large. Meanwhile, from Figure 10 As shown in (b), both instantaneous power and power density exhibit a pattern of first increasing and then decreasing. When the external load is 40MΩ, both reach their peak values, with instantaneous power of 8.058mW and power density of 6.578W / m2, corresponding to an output voltage of 576.73V.

[0069] The long-term cycling stability of the dual-electrode TENG device assembled from the negative friction layer material with the Janus structure prepared in Example 5 was tested. Specifically, the dual-electrode TENG device was subjected to a continuous operating cycle test for nearly 3 hours under test conditions of 25N external force, 4Hz frequency, and 1GΩ external load resistance. The results are as follows: Figure 11 As shown.

[0070] Depend on Figure 11 It can be seen that the output performance of the dual-electrode TENG device remained stable for the first 2 hours without significant attenuation; after 2 hours, its output performance only showed a slight decrease. This further verifies that the negative friction layer material with Janus structure prepared in Example 5 has excellent long-term output stability. At the same time, it also shows that the negative friction layer material with Janus structure prepared in Example 5 has excellent structural reliability, providing core performance assurance for the practical application of the negative friction layer material with Janus structure prepared in Example 5 in fields such as low-frequency micromechanical energy harvesting and self-powered sensing systems.

[0071] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0072] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a negative friction layer material having a Janus structure, characterized by, The method comprises the following steps: S1, synthesizing ZIF-67 nanoparticles by a room temperature solvent method, dispersing the synthesized ZIF-67 nanoparticles and a manganese source in a solvent, uniformly mixing, and then performing centrifugal treatment to collect MnCo-MOF nanoparticles; S2, placing the MnCo-MOF nanoparticles in an air atmosphere for calcination treatment to obtain hollow nanoparticles; S3, dispersing the hollow nanoparticles and PVDF powder in a first mixed solvent, continuously stirring under water bath heating conditions, uniformly mixing to obtain a first spinning solution, and dispersing barium titanate particles and the PVDF powder in a second mixed solvent, continuously stirring under the same conditions, and uniformly mixing to obtain a second spinning solution; S4, performing spinning treatment on the first spinning solution and the second spinning solution by an electrospinning method and using a Janus needle head with a double-channel structure at a spinning solution flow rate of 1.5 mL / h-2.5 mL / h to obtain a negative friction layer material with a Janus structure.

2. The production method according to claim 1, wherein In step S3, the content of the hollow nanoparticles in the first mixed solvent is 0wt%-1wt%, and the content of the PVDF powder is 7wt%-15wt%. The content of the barium titanate particles in the second mixed solvent is 8wt%-12wt%, and the content of the PVDF is 7wt%-15wt%.

3. The production method according to claim 2, wherein The first mixed solvent is a mixed solvent of N,N-dimethylformamide and acetone, and the mass ratio of the N,N-dimethylformamide to the acetone is (1-2):

1. The second mixed solvent has the same components as the first mixed solvent.

4. The production method according to claim 2, wherein In step S3, the water bath temperature of the hot water bath is 60℃-100℃.

5. The production method according to claim 1, wherein In step S4, during the spinning treatment, the spinning voltage is set to 15kV-25kV, the receiving distance is set to 16cm-20cm, the environmental temperature is set to be within the range of 20℃-30℃, and the environmental humidity is set to be within the range of 30%-45%.

6. The production method according to claim 1, wherein In step S1, the mass ratio of the ZIF-67 nanoparticles to the manganese source is (1.5-3):

1.

7. The production method according to claim 6, wherein The synthesis method of the ZIF-67 nanoparticles comprises slowly adding a 2-methylimidazole solution to a cobalt-containing solution, uniformly mixing, standing, and then performing centrifugal treatment to collect ZIF-67 nanoparticles.

8. The production method according to claim 1, wherein In step S2, the treatment temperature of the calcination treatment is 220℃-280℃, and the heating rate is 2℃ / min-8℃ / min.

9. A negative friction layer material having a Janus structure, characterized by, The preparation method is prepared by any one of claims 1-8.

10. A friction nanogenerator, characterized in that, The friction nanogenerator comprises a positive friction layer, a negative friction layer, a support structure, and an electrode, the positive friction layer and the negative friction layer are oppositely arranged and are respectively pasted on the upper surface and the lower surface of the support structure, the two ends of the electrode are respectively connected with the upper surface and the lower surface of the support structure to facilitate charge transmission, and the material of the negative friction layer is the negative friction layer material of claim 9.

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