Composite self-cleaning fiber membrane based on triboelectric nanogenerator and preparation method thereof

Abstract

The application discloses a composite self-cleaning fiber membrane based on a friction nanogenerator and a preparation method thereof. The composite self-cleaning fiber membrane is composed of polyvinylidene fluoride nanofibers, single-walled carbon nanotubes and titanium dioxide nanoparticles. The single-walled carbon nanotubes are combined on the fiber filaments of the polyvinylidene fluoride nanofibers. The titanium dioxide nanoparticles are discretely attached to the surface of the fiber filaments of the polyvinylidene fluoride nanofibers. When serving as a friction layer of the friction nanogenerator, the composite self-cleaning fiber membrane can realize high electric output performance and ultraviolet light-driven self-cleaning function simultaneously, and effectively solves the performance attenuation problem caused by membrane pollution in an outdoor polluted environment.

Description

Technical Field

[0001] This invention relates to the field of triboelectric nanogenerator technology, and in particular to a composite self-cleaning fiber membrane based on a triboelectric nanogenerator and its preparation method. Background Technology

[0002] With the continuous growth of global energy demand and the increasing severity of environmental problems, the development of new clean energy technologies and environmentally friendly materials has become a cutting-edge focus in scientific research and engineering applications. Triboelectric nanogenerators (TENGs), as an emerging energy harvesting technology, can convert the mechanical energy widely present in the environment into electrical energy, opening up new avenues for distributed energy supply and self-powered systems. Electrospinning technology, due to its ability to prepare nanofiber membranes with high specific surface area, tunable pore structure, and excellent mechanical properties, shows great potential in filtration, sensing, biomedicine, and energy fields. In TENG devices, the material properties and surface structure of the friction layer have a decisive influence on the output performance; electrospun nanofiber membranes, due to their high specific surface area and porous structure, can significantly increase the frictional contact area and are therefore widely used as friction layer materials for TENGs. Against this backdrop, combining triboelectric nanogenerators with electrospinning technology to develop smart fiber materials with energy harvesting and self-cleaning functions has become an important research direction at the intersection of materials science and energy engineering.

[0003] Polyvinylidene fluoride (PVDF), a semi-crystalline polymer, is widely used in energy harvesting and sensing applications due to its outstanding piezoelectricity, chemical stability, and mechanical strength. The piezoelectric properties of PVDF mainly stem from its polar β-phase, which can be induced to form through a high-voltage electric field during electrospinning. However, the limited piezoelectric output and charge accumulation capacity of pure PVDF fiber membranes restricts their application in high-efficiency triboelectric nanogenerators. Furthermore, traditional PVDF membranes lack self-cleaning capabilities and are easily contaminated in outdoor or polluted environments, leading to performance degradation. Therefore, enhancing the energy harvesting efficiency and self-cleaning ability of PVDF fiber membranes through material composites and structural design has significant scientific and practical value.

[0004] Single-walled carbon nanotubes (SWCNTs) and titanium dioxide (TiO2) nanoparticles, as functional nanomaterials, offer innovative approaches to modifying PVDF fiber membranes. SWCNTs possess excellent electrical conductivity, mechanical strength, and a large specific surface area. Incorporating them into the PVDF matrix can form a conductive network, enhancing charge transport efficiency, reducing dielectric loss, and acting as a nanofiller to promote the formation of the β-phase in PVDF fibers. Studies have shown that the addition of appropriate amounts of SWCNTs can significantly improve the electrical output performance and mechanical durability of the composite fiber membrane. TiO2 nanoparticles are renowned for their photocatalytic activity and superhydrophilicity. Under ultraviolet light irradiation, they can decompose organic pollutants and impart self-cleaning properties to the material surface. Combining TiO2 with PVDF not only utilizes its photocatalytic function but also improves the morphology and surface properties of the fiber membrane through the interaction between nanoparticles and the polymer.

[0005] However, when incorporating the photocatalytic self-cleaning function of TiO2 into the triboelectric nanogenerator's friction layer, avoiding its negative impact on electrical output performance remains a key technical challenge in this field. Therefore, in outdoor or polluted environments, the performance of electrospun fiber membranes used as friction layers generally degrades due to contaminant adhesion, and current technologies lack effective means to balance high output with self-cleaning. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a composite self-cleaning fiber membrane based on a triboelectric nanogenerator and its preparation method. When used as the friction layer of a triboelectric nanogenerator, the composite self-cleaning fiber membrane of the present invention can simultaneously achieve high electrical output performance and ultraviolet light-driven self-cleaning function, effectively solving the performance degradation problem caused by membrane fouling in outdoor polluted environments.

[0007] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: In one aspect, the present invention provides a composite self-cleaning fiber membrane based on a triboelectric nanogenerator, which is composed of polyvinylidene fluoride nanofibers, single-walled carbon nanotubes and titanium dioxide nanoparticles. The single-walled carbon nanotubes are bonded to the filaments of the polyvinylidene fluoride nanofibers; the titanium dioxide nanoparticles are discretely attached to the surface of the filaments of the polyvinylidene fluoride nanofibers.

[0008] Furthermore, the single-walled carbon nanotubes are partially embedded inside the filaments of the polyvinylidene fluoride nanofibers and partially exposed on the surface of the filaments, forming a nanoscale protrusion structure on the surface of the filaments; a portion of the titanium dioxide nanoparticles are attached to the surface of the filaments of the polyvinylidene fluoride nanofibers through polyvinylidene fluoride microspheres; the particle size of the polyvinylidene fluoride microspheres is 1 to 2 μm.

[0009] Furthermore, the thickness of the composite self-cleaning fiber membrane is 80–120 μm; the diameter of the fiber filaments embedding single-walled carbon nanotubes is 1–2 μm; the single-walled carbon nanotubes form a cluster of single-walled carbon nanotubes with a diameter of 80–120 nm; and the particle size of the titanium dioxide nanoparticles is 20–50 nm.

[0010] Furthermore, the polyvinylidene fluoride microspheres are formed by electrostatic spraying, and the titanium dioxide nanoparticles are partially embedded in the surface of the polyvinylidene fluoride microspheres.

[0011] Another aspect of the present invention provides a method for preparing the composite self-cleaning fiber membrane, comprising the following steps: Step (1): Disperse single-walled carbon nanotubes in an organic solvent to obtain a single-walled carbon nanotube slurry; add polyvinylidene fluoride powder to the single-walled carbon nanotube slurry, heat and stir until dissolved to obtain an electrospinning solution; Step (2): Ultrasonically disperse titanium dioxide nanoparticles in an organic solvent to obtain a titanium dioxide nanoparticle dispersion; add polyvinylidene fluoride powder to the titanium dioxide nanoparticle dispersion, heat and stir until dissolved to obtain an electrostatic spray liquid; Step (3): Place the electrospinning solution and the electrospray solution in an electrospinning device, perform electrospinning and electrospraying simultaneously, and collect the electrospinning jet products; Step (4): The collected electrostatic jet products are dried to obtain the composite self-cleaning fiber membrane.

[0012] Preferably, the organic solvent is N,N-dimethylformamide.

[0013] Further, in step (1), the mass fraction of polyvinylidene fluoride in the electrospinning solution is 17-22 wt%, and the mass of single-walled carbon nanotubes is 0.01-0.05 wt% of the mass of polyvinylidene fluoride; in step (2), the mass fraction of polyvinylidene fluoride in the electrospinning solution is 7-12 wt%, and the mass of titanium dioxide nanoparticles is 0.2-1.0 wt% of the mass of polyvinylidene fluoride.

[0014] Further, in step (3), when electrospinning and electrospraying are performed simultaneously: the volume ratio of the electrospinning solution to the electrospraying solution is 2:1; the voltage of the high-voltage electrostatic field is 16-18kV; the propulsion rates of the electrospinning solution and the electrospraying solution are the same, both being 0.8-1.0mL·h-1.

[0015] Furthermore, in step (4), the drying conditions are: drying at 60-70℃ for 10-12 hours, and the thickness of the composite self-cleaning fiber membrane obtained after drying is 80-120 μm.

[0016] The present invention also provides a triboelectric nanogenerator, including a triboelectric layer, wherein the triboelectric layer is made of the composite self-cleaning fiber membrane described above.

[0017] The beneficial effects of this invention are as follows: (1) This invention constructs a three-dimensional conductive network by incorporating single-walled carbon nanotubes onto polyvinylidene fluoride nanofibers to efficiently transmit triboelectric charges. Furthermore, the single-walled carbon nanotubes and discretely attached titanium dioxide nanoparticles together impart a high specific surface area and multi-scale surface roughness to the fiber membrane, thereby significantly increasing the triboelectric contact area and enhancing the triboelectric charge density. Compared to pure polyvinylidene fluoride fiber membranes, the composite fiber membrane of this invention, when used as the triboelectric nanogenerator's triboelectric layer, exhibits a significant increase in both output voltage and current.

[0018] (2) This invention innovatively integrates the photocatalytic self-cleaning function of titanium dioxide nanoparticles into the triboelectric nanogenerator's triboelectric layer. Titanium dioxide is discretely attached to the fiber surface, fully exposing photocatalytic active sites. Under ultraviolet light irradiation, it can effectively decompose organic pollutants attached to the fiber membrane surface, restoring the fiber membrane to a clean state. This self-cleaning function effectively solves the problem of continuous degradation of electrical performance of fiber membranes caused by pollutant adhesion in outdoor or polluted environments, enabling the triboelectric nanogenerator to maintain stable high electrical output performance during long-term use, significantly extending the actual service life of the device.

[0019] (3) The preparation method of the present invention adopts a one-step forming process of simultaneous electrospinning and electrospraying. The electrospinning solution containing single-walled carbon nanotubes and the electrospray solution containing titanium dioxide nanoparticles are simultaneously electrospinned and electrosprayed to form a composite fiber membrane with an embedded conductive network and a surface photocatalytic layer in one step. This process does not require post-treatment or additional cross-linking, and the composition and process parameters of the spinning solution and the spray solution can be independently controlled. The conductivity of the fiber skeleton and the photocatalytic activity of the surface particles can be flexibly optimized. The structure is highly controllable and suitable for continuous and large-scale production, with good prospects for industrial application. Attached Figure Description

[0020] Figure 1 Comparative diagrams of the electrospun fiber membranes of Comparative Example 1, Comparative Example 2, and the Examples.

[0021] Figure 2 This is an EDS analysis diagram of the PVDF / SWCNTs / TiO2 composite self-cleaning fiber membrane according to an embodiment of the present invention.

[0022] Figure 3 This is an EDS spot scan analysis diagram of the fiber membranes of the embodiments and Comparative Example 3 of the present invention.

[0023] Figure 4FTIR analysis results for PVDF nanofiber membranes, PVDF / TiO2 composite fiber membranes, and PVDF / SWCNTs / TiO2 composite fiber membranes.

[0024] Figure 5 Figure 1 shows the triboelectric properties of PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane.

[0025] Figure 6 A comparison of the dielectric properties of PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane.

[0026] Figure 7 A comparison of the charging rates of PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane.

[0027] Figure 8 Figure 1 shows the mechanical tensile test results for three thicknesses of PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane.

[0028] Figure 9 The diagram shows the voltage output results of three different fiber membranes after cyclic collision, as shown in Comparative Example 1, Comparative Example 2, and the embodiment of the present invention. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention provides a composite self-cleaning fiber membrane based on a triboelectric nanogenerator. The membrane is composed of polyvinylidene fluoride (PVDF) nanofibers, single-walled carbon nanotubes (SWCNTs), and titanium dioxide (TiO2) nanoparticles. The SWCNTs are attached to the PVDF nanofiber filaments, partially embedded within the fibers and partially exposed on the fiber surface, forming nanoscale protrusions on the fiber surface. The SWCNTs embedded within the fibers form a three-dimensional network framework, supporting the PVDF nanofibers, preventing fiber collapse, maintaining the uniform filamentary structure of the fibers, and providing an efficient channel for triboelectric charge transport. The SWCNTs exposed on the fiber surface, together with the TiO2 nanoparticles, constitute the nanoscale protrusion structure, increasing the surface roughness of the fibers. The TiO2 nanoparticles are discretely attached to the surface of the PVDF nanofiber filaments. For example, some TiO2 nanoparticles can be attached to the surface of the fiber filaments by electrostatically spraying PVDF microspheres (preferably with a particle size of 1–2 μm). These microspheres act as carriers, allowing the TiO2 particles to partially embed into the surface of the microspheres, thereby enhancing their adhesion. The remaining TiO2 particles are directly attached to the surface of the fiber filaments. This structure enables the fiber membrane to possess a conductive network (provided by SWCNTs), surface nanoscale roughness (contributed by both SWCNTs and TiO2 particles), and photocatalytic active sites (provided by surface TiO2).

[0031] In some preferred embodiments, the overall thickness of the composite self-cleaning fiber membrane is controlled between 80 and 120 μm. If the thickness is less than 80 μm, the mechanical strength of the fiber membrane is insufficient to meet the requirements of practical applications; if the thickness exceeds 120 μm, the charge transfer distance within the friction layer increases, which is detrimental to electrical output performance. The diameter of SWCNTs is preferably 1–2 nm, which can form single-walled carbon nanotube clusters with a diameter of 80–120 nm; the particle size of TiO2 nanoparticles is preferably 20–50 nm. The diameter of the fiber filaments embedding the single-walled carbon nanotubes is 1–2 μm. Controlling the size of SWCNTs and TiO2 within the above range can effectively prevent adhesion between fiber filaments, maintain a uniform filamentary structure of the fiber filaments, and form a stable skeletal support, which is conducive to charge transfer between fiber filaments, thereby improving the electrical performance of the triboelectric nanogenerator (TENG).

[0032] This invention also provides a method for preparing the above-mentioned composite self-cleaning fiber membrane. This method employs a one-step forming process combining simultaneous electrospinning and electrospraying, and includes the following steps: Step (1) Preparation of electrospinning solution: Disperse SWCNTs in an organic solvent (e.g., N,N-dimethylformamide, DMF) and process it using a dispersion device (e.g., high-pressure homogenizer or ball mill) to obtain an SWCNTs slurry. Add PVDF powder (preferably with an average relative molecular mass of 600,000 to 800,000) to the slurry and heat and stir at 300 to 500 rpm for 2 to 4 hours at 60 to 80°C to completely dissolve the PVDF and obtain the electrospinning solution. In this electrospinning solution, the mass fraction of PVDF is preferably 17 to 22 wt%, and the mass of SWCNTs is 0.01 to 0.05 wt% (more preferably 0.02 to 0.04 wt%) of the mass of PVDF. Controlling the particle size and amount of SWCNTs within the above range can avoid fiber unevenness caused by insufficient electric field force or precipitation during spinning, and at the same time prevent excessive SWCNTs from causing fiber adhesion or uneven force on the spinning solution. Higher molecular weight and higher concentration of PVDF solution are beneficial for electrospinning to form nanofibers with uniform thickness and stable structure, and to uniformly embed SWCNTs inside the fiber.

[0033] Step (2) Preparation of electrostatic spray solution: TiO2 nanoparticles (particle size 20-50 nm) are ultrasonically dispersed in an organic solvent (e.g., DMF). The ultrasonic conditions are exemplarily: ultrasonic dispersion at a frequency of 40-60 kHz at room temperature for 90-120 min to obtain a TiO2 dispersion. PVDF powder (preferably with an average relative molecular mass of 600,000-800,000) is added to this dispersion, and the mixture is heated and stirred at 60-80°C and 300-500 rpm for 2-4 h until completely dissolved to obtain the electrostatic spray solution. In this electrostatic spray solution, the mass fraction of PVDF is preferably 7-12 wt%, and the mass of TiO2 nanoparticles is 0.2-1.0 wt% (more preferably 0.4-0.6 wt%) of the mass of PVDF. Lower concentrations and lower molecular weight PVDF solutions readily form micron-sized PVDF microspheres (particle size approximately 1-2 μm) in electrostatic spraying, while the TiO2 particles are uniformly dispersed in the electrostatic spray solution, with most ultimately adhering to the surface of the microspheres and a small portion directly adhering to the fiber filaments. If the TiO2 particle size is too large or the amount used is too much, the particles will be difficult to adhere or cause fiber adhesion; if the particle size is too small or the amount used is too little, it will be difficult to form an effective self-cleaning structure.

[0034] Step (3) Synchronous electrospinning and electrospraying: The electrospinning solution and electrospraying solution are respectively loaded into two independent nozzles of the electrospinning equipment, and electrospinning and electrospraying are performed simultaneously. For example, the volume ratio of the spinning solution to the spraying solution is controlled at 2:1. If the proportion of the spinning solution is too large, the self-cleaning structure (TiO2 / PVDF microspheres) will be relatively small, affecting the self-cleaning performance; if the proportion of the spraying solution is too large, the TiO2 distribution will be too dense, which will easily lead to fiber adhesion and reduce the electro-output performance. The voltage of the high-voltage electrostatic field is preferably 16-18kV. If the voltage of the high-voltage electrostatic field is too large, it will cause the fiber filaments to be uneven due to the excessive electric field force. If the voltage of the high-voltage electrostatic field is too small, the fiber filaments will also be uneven due to insufficient electric field force to pull the fiber filaments. The propulsion rate of the electrospinning solution and the electrospraying solution is the same, which is 0.8-1.0 mL·h. -1 The distance between the nozzle tip and the receiving device (such as an aluminum foil collector) is preferably 17–20 cm. If the distance is too short, the solvent in the electrospinning solution and electrostatic spray will not evaporate completely, leading to fiber adhesion. If the distance is too long, the fiber collection will be uneven. The ambient temperature during the process is controlled at 30–40°C, and the relative humidity is controlled at 30–45%. Too low a temperature or too high a humidity will cause incomplete solvent evaporation and fiber adhesion. Too high a temperature or too low a humidity will cause the fiber to become brittle and affect its mechanical properties. Therefore, within the above parameter range, during the simultaneous electrospinning and electrostatic spraying process, the solvent can fully evaporate, avoiding fiber adhesion. At the same time, the electric field force is sufficient to pull and form uniform fiber filaments and microspheres, and the PVDF microspheres formed by spraying are uniformly attached to the electrospun fiber filaments. Most of the TiO2 particles are loaded on the surface of the microspheres, and a small portion is directly attached to the fiber surface. The SWCNTs in the electrospinning solution can be partially and uniformly embedded inside the fiber.

[0035] Step (4) Drying treatment: The electrostatic jet product on the collector is dried at 60-70℃ for 10-12 hours to obtain a composite self-cleaning fiber membrane. Excessive drying temperature or time will cause the fiber membrane to become brittle and hard, resulting in decreased mechanical properties; insufficient drying may leave residual solvent, affecting electrical properties. The thickness of the dried fiber membrane is controlled at 80-120 μm, preferably 90-100 μm, to balance mechanical strength and charge transfer efficiency.

[0036] This invention also provides a triboelectric nanogenerator (TENG) comprising a triboelectric layer using the aforementioned composite self-cleaning fiber membrane. Exemplarily, this fiber membrane can be attached to a conductive electrode as a negative electrode triboelectric layer, and paired with a positive electrode triboelectric layer (such as a nylon membrane or other positive materials) to form a contact-separation TENG. Because the fiber membrane possesses both high electrical output and self-cleaning capability, this TENG can maintain stable energy harvesting performance even during long-term operation outdoors or in polluted environments.

[0037] The present invention will be further described below through specific embodiments.

[0038] Example 1. Preparation of electrospinning solution Single-walled carbon nanotubes (SWCNTs, 1–2 nm in diameter) were dispersed in N,N-dimethylformamide (DMF) and homogenized using a high-pressure homogenizer to obtain an SWCNT slurry with an average particle size of 1.2 μm. Polyvinylidene fluoride (PVDF) powder (average relative molecular mass 600,000) was added to this slurry, and the mixture was magnetically stirred at 400 rpm for 3 hours at 60 °C until the PVDF was completely dissolved, yielding an electrospinning solution. In this spinning solution, the mass fraction of PVDF was 22 wt%, and the mass of SWCNTs was 0.03 wt% of the PVDF mass.

[0039] 2. Preparation of electrostatic spray fluid Titanium dioxide (TiO2) nanoparticles (particle size 20–50 nm) were ultrasonically dispersed in DMF at 50 kHz for 90 min at room temperature to obtain a TiO2 dispersion. PVDF powder (average relative molecular mass 600,000) was added to this dispersion, and the mixture was magnetically stirred at 400 rpm for 3 h at 60 °C until the PVDF was completely dissolved, yielding an electrostatic spray solution. In this electrostatic spray solution, the mass fraction of PVDF was 10 wt%, and the mass of the TiO2 nanoparticles was 0.6 wt% of the PVDF mass.

[0040] 3. Synchronous electrospinning and electrostatic spraying A dual-nozzle electrospinning apparatus was used, with the electrospinning solution loaded into one nozzle and the electrospinning liquid loaded into the other. The propulsion rate of both nozzles was set to 1.0 mL·h. -1 The volume ratio of electrospinning solution to electrospray solution was 2:1. A high-voltage power supply was connected at 18kV to both nozzles and at the negative terminal to an aluminum foil collector. The distance between the nozzle tip and the collector was 20cm. The ambient temperature was controlled at 40℃ and the relative humidity at 35%. Both nozzles were started simultaneously; electrospinning formed nanofibers, and electrospraying formed microspheres. These two materials were then deposited together on the collector to obtain the fiber membrane precursor.

[0041] 4. Drying treatment The fiber membrane precursor on the collector was dried at 60°C for 12 hours to obtain a composite self-cleaning fiber membrane with a thickness of 95 μm.

[0042] Comparative Example 1: Pure PVDF nanofiber membrane PVDF powder (average relative molecular mass 600,000) was dissolved in DMF and magnetically stirred at 400 rpm for 3 hours at 60°C to obtain a PVDF spinning solution with a mass fraction of 22 wt%. A single-nozzle electrospinning apparatus was used with a feed rate of 1.0 mL. -1 The voltage was 18kV, the distance between the nozzle tip and the aluminum foil collector was 20cm, the ambient temperature was 40℃, and the relative humidity was 35%. Collection time was 2 hours to obtain a PVDF nanofiber membrane. The collected fiber membrane was dried at 60℃ for 12 hours to obtain a pure PVDF nanofiber membrane with a thickness of 95μm.

[0043] Comparative Example 2: PVDF / TiO2 Composite Fiber Membrane The same synchronous electrospinning-electrospraying process as in the previous example was used, the only difference being that SWCNTs were not added to the electrospinning solution. The specific steps are as follows: (1) Electrospinning solution: Dissolve PVDF powder (average relative molecular mass 600,000) in DMF and stir at 60℃ and 400rpm for 3h to obtain a spinning solution with PVDF mass fraction of 22wt% (excluding SWCNTs).

[0044] (2) Electrostatic spray solution: Same as in Example 1. TiO2 nanoparticles (particle size 20-50 nm) were ultrasonically dispersed in DMF (50 kHz, 90 min), and PVDF powder (average relative molecular mass 600,000) was added. The mixture was stirred at 60 °C and 400 rpm for 3 h to obtain the electrostatic spray solution. The mass fraction of PVDF in the electrostatic spray solution was 10 wt%, and the mass of TiO2 was 0.6 wt% of the mass of PVDF.

[0045] (3) Synchronous spinning-spraying: A dual-nozzle device was used, with a volume ratio of electrospinning solution to electrospraying solution of 2:1, a propulsion rate of 1.0 mL·h-1, a voltage of 18 kV, a distance of 20 cm between the nozzle and the collector, an ambient temperature of 40℃, a relative humidity of 35%, and a collection time of 2 h.

[0046] (4) Drying: Dry at 60℃ for 12 hours to obtain a fiber membrane with a thickness of about 95μm.

[0047] Comparative Example 3: PVDF / SWCNTs Composite Fiber Membrane According to the electrospinning solution formulation of the example (PVDF 22wt%, SWCNTs 0.03wt%), single-nozzle electrospinning (parameters same as Comparative Example 1) was used to obtain a PVDF / SWCNTs composite fiber membrane with a thickness of 95μm.

[0048] A FEI Apreo 2S multifunctional high-resolution field emission scanning electron microscope, equipped with an Oxford Instruments Ultim Max 4.0 energy dispersive spectroscopy (EDS) system, was used to characterize the nanofiber surface morphology of the fiber membrane and the doping of TiO2 powder and single-walled carbon nanotubes. Figure 1 As can be seen, the surface of the PVDF nanofiber membrane without any doping in Comparative Example 1 is smooth; in Comparative Example 2, after the addition of nano-TiO2 particles, there are obvious protrusions on the surface of the fiber; in the embodiment, single-walled carbon nanotubes and TiO2 particles are doped at the same time, and a nanoscale protrusion structure is formed on the surface of the fiber, and the fiber is supported by a single-walled carbon nanotube network, presenting a unique non-smooth surface morphology.

[0049] like Figure 2 As shown, (a) is a scanning electron microscope (SEM) image of the composite fiber membrane; (bd) are the corresponding EDS (Electron Scanning) elemental distribution maps, showing the signal distributions of fluorine (F Kα1,2, green), carbon (C Kα1,2, red), and titanium (Ti Kα1, blue-green), respectively. The results indicate that F, C, and Ti exhibit continuous and uniform spatial distribution in the fiber membrane, which directly confirms the successful composite of PVDF, single-walled carbon nanotubes (SWCNTs), and titanium dioxide (TiO2). Furthermore, the dopants achieve uniform nanoscale dispersion within the fiber matrix without significant agglomeration. This uniform composite structure is a crucial foundation for the material's excellent self-cleaning properties.

[0050] EDS spot scan analysis images of the PVDF / SWCNTs composite fiber membrane doped only with single-walled carbon nanotubes in Comparative Example 3 and the PVDF / SWCNTs / TiO2 composite fiber membrane co-doped with single-walled carbon and nano-TiO2 particles in the Examples are shown below. Figure 3 As shown, this further confirms that the dopant was successfully dispersed in the PVDF fiber filaments.

[0051] A Nicolet IS10 Fourier transform infrared spectrometer was used, with a scanning range of 400 cm⁻¹. -1 ~4000cm -1 , is used to characterize the percentage of β phase in the fiber membrane. Figure 4FTIR spectra of the prepared PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane are shown. The figures show that the β-phase to α-phase ratio in the TiO2-doped fiber membrane is slightly lower than that in the undoped pure PVDF fiber membrane. The β-phase to α-phase ratio in the fiber membrane co-doped with single-walled carbon nanotubes and titanium dioxide is higher than that in the undoped pure PVDF fiber membrane. The FT-IR absorption follows the Lambert-Beer law, and the relative fraction of the β-phase in the fiber membrane can be calculated using the following formula: ; Among them: A β and K β They are 837cm respectively -1 The absorption peak intensity and absorption coefficient at that point are shown; the absorption coefficient is 6.1 × 10⁻⁶. 4 cm 2 / mol, A α and K α They are 763cm respectively -1 The absorption peak intensity and absorption coefficient at the specified location are shown, with the absorption coefficient being 7.7 × 10⁻⁶. 4 cm 2 / mol. Based on Fourier transform infrared spectroscopy analysis, the β-phase content in the PVDF nanofiber membrane, PVDF / TiO2 composite fiber membrane, and PVDF / SWCNTs / TiO2 composite fiber membrane were calculated to be 80.1%, 76.1%, and 91.4%, respectively. FTIR analysis showed that the β-phase content of the pure PVDF fiber membrane was 80.1%, which decreased to 76.1% after TiO2 doping alone, indicating that TiO2 inhibits β-phase formation. In contrast, the composite fiber membrane of this invention, simultaneously doped with SWCNTs and TiO2, had a β-phase content as high as 91.4%, significantly higher than that of pure PVDF. This indicates that SWCNTs can effectively overcome the negative effects of TiO2 and synergistically induce the orientation and crystallization of PVDF molecular chains. The high β-phase content provides the molecular structural basis for the high electrical output performance of the fiber membrane of this invention.

[0052] The triboelectric properties of the electrospun composite fiber film were tested using a linear motor and an electrometer (a simple triboelectric nanogenerator (TENG) with a contact area of ​​30*30mm was fabricated by linear reciprocating impact with a force of 5N). The power generation principle of the contact-separation TENG is based on charge transfer caused by contact electrification and electrostatic induction coupling. Under the action of external force, the copper electrode comes into contact with the surface of the fiber film, triggering the triboelectric effect. Due to the different electron-gaining and losing abilities of the two materials, the copper electrode surface becomes positively charged and the fiber film surface becomes negatively charged. Currently, the two equal and opposite charges are on the same plane, so there is no potential difference between the two electrodes. When the force applied to the TENG is unloaded, a potential difference is formed between the two electrodes due to the separation of the two charged surfaces. During the gradual separation of the two electrodes, the potential difference drives electrons from one end of the fiber film electrode to the other end of the copper electrode, generating a transient current until electrostatic equilibrium is reached. When pressure is applied again to one end of the electrode, reducing the distance between the two ends, a potential difference reappears between the electrodes. This causes electrons to flow from the copper electrode back to the fiber membrane electrode, reducing the induced charge on the electrodes. This periodic contact and separation process allows electrons to transfer back and forth in the external circuit, forming a current.

[0053] Figure 5 From left to right, the figures show the triboelectric properties of the PVDF nanofiber membrane prepared in Comparative Example 1, the PVDF / TiO2 composite fiber membrane in Comparative Example 2, and the PVDF / SWCNTs / TiO2 composite fiber membrane from the examples. As can be seen from the figures, the highest short-circuit current of the undoped PVDF fiber membrane is 4.03 μA, the transferred charge is 46.4 nC, and the open-circuit voltage is 157.8 V. The highest short-circuit current of the spray-doped titanium dioxide membrane is 2.71 μA, the transferred charge is 38.8 nC, and the open-circuit voltage is 125.8 V. The highest short-circuit current of the simultaneously doped single-walled carbon nanotube and titanium dioxide membrane is 7.37 μA, the transferred charge is 119.4 nC, and the open-circuit voltage is 262.7 V. This indicates that the electrical properties of the fiber membrane simultaneously doped with single-walled carbon nanotubes and titanium dioxide are significantly improved.

[0054] Figure 6 This is a comparison chart of the dielectric properties of the PVDF nanofiber membrane in Comparative Example 1, the PVDF / TiO2 composite fiber membrane in Comparative Example 2, and the PVDF / SWCNTs / TiO2 composite fiber membrane in the examples. From... Figure 6 As can be seen, the dielectric constant of the fiber film spray-doped with titanium dioxide is slightly improved, while the dielectric constant of the fiber film co-doped with single-walled carbon nanotubes and titanium dioxide is significantly improved. At high frequencies, the dielectric loss of the fiber film co-doped with single-walled carbon nanotubes and titanium dioxide is significantly reduced.

[0055] use Figure 7The circuit diagram shown in the middle left figure demonstrates the charging rates of different fiber membranes used in Comparative Example 1, Comparative Example 2, and the Example, charging a 100μF capacitor to 3.5V. As can be seen from the figure, the fiber membrane co-doped with single-walled carbon nanotubes and titanium dioxide exhibits a significantly improved charging rate.

[0056] Following the aforementioned preparation method, PVDF nanofiber membranes, PVDF / TiO2 composite fiber membranes, and PVDF / SWCNTs / TiO2 composite fiber membranes with three thicknesses (60 μm, 100 μm, and 140 μm) were prepared respectively. Their tensile strengths were then tested, and the results are as follows: Figure 8 As shown. Figure 8 The data shows that the tensile strength of the fiber membrane co-doped with single-walled carbon nanotubes and titanium dioxide is about 4-5 times higher than that of the PVDF fiber membrane without any dopants.

[0057] Three different fiber membranes, namely Comparative Example 1, Comparative Example 2, and the embodiment of the present invention, were subjected to continuous cyclic collision tests for 12 hours (collision force 5N, collision speed 2m / s), and their voltage output results were measured. Figure 9 As shown in the figure. The test results show that the voltage of the PVDF nanofiber membrane and the PVDF / TiO2 composite fiber membrane decreased significantly during cyclic collision, while the voltage output of the PVDF / SWCNTs / TiO2 composite fiber membrane remained stable with almost no significant decrease.

[0058] Comparison of photocatalytic self-cleaning performance of fiber membranes: Four types of fiber membranes from Example 1 and Comparative Examples 1-3 were cut into 2cm × 2cm samples. Rhodamine B ethanol solution (0.1 mg / mL) was uniformly sprayed onto the surface, and after natural drying, they were irradiated with a xenon lamp (500W, 5cm distance) for 0.5h, 1.0h, 1.5h, and 2h, respectively. During irradiation, circulating cooling water was introduced to maintain the reactor temperature at 25±2℃. After irradiation, the color change of the fiber membrane surface was observed, and the absorbance of residual Rhodamine B was measured using a spectrophotometer to calculate the residual rate. The fiber membranes after contamination-light irradiation treatment were assembled into a TENG, and their open-circuit voltage was tested and compared with the initial value. The results are shown in Table 1.

[0059] Table 1 Comparative Examples 1 and 3, lacking TiO2, exhibited almost no photocatalytic degradation ability, with Rhodamine B residue exceeding 95% after 2 hours of irradiation. The TENG voltage dropped significantly after contamination and could not be recovered. Comparative Example 2, while containing TiO2 and possessing some photocatalytic degradation ability (25% residue), lacked a SWCNTs conductive network. Under illumination, photogenerated carriers from TiO2 could not be effectively discharged, resulting in severe recombination with triboelectric charges. Consequently, the voltage retention rate after contamination-irradiation was only 48%, even lower than that of pure PVDF. In this embodiment, SWCNTs form a conductive network, and TiO2 is discretely attached to the fiber surface. The two work synergistically: as irradiation time increases, the Rhodamine B residue gradually decreases, falling below 5% after 2 hours of irradiation. Simultaneously, the SWCNTs conductive network rapidly discharges triboelectric charges, inhibiting photogenerated carrier recombination. Therefore, the voltage retention rate after contamination-irradiation remains as high as 92%. Thus, the composite self-cleaning fiber membrane of this invention combines highly efficient photocatalytic self-cleaning ability with excellent electrical output stability, maintaining high electrical output performance for extended periods in polluted outdoor environments.

[0060] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0061] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite self-cleaning fiber membrane based on a triboelectric nanogenerator, characterized in that, The composite self-cleaning fiber membrane is composed of polyvinylidene fluoride nanofibers, single-walled carbon nanotubes, and titanium dioxide nanoparticles. The single-walled carbon nanotubes are bonded to the filaments of the polyvinylidene fluoride nanofibers; the titanium dioxide nanoparticles are discretely attached to the surface of the filaments of the polyvinylidene fluoride nanofibers.

2. The composite self-cleaning fiber membrane according to claim 1, characterized in that, The single-walled carbon nanotubes are partially embedded inside the filaments of the polyvinylidene fluoride nanofibers and partially exposed on the surface of the filaments, forming a nanoscale protrusion structure on the surface of the filaments; a portion of the titanium dioxide nanoparticles are attached to the surface of the filaments of the polyvinylidene fluoride nanofibers through polyvinylidene fluoride microspheres; the particle size of the polyvinylidene fluoride microspheres is 1 to 2 μm.

3. The composite self-cleaning fiber membrane according to claim 1, characterized in that, The composite self-cleaning fiber membrane has a thickness of 80–120 μm; the fiber filaments embedding single-walled carbon nanotubes have a diameter of 1–2 μm; the single-walled carbon nanotubes form a cluster of single-walled carbon nanotubes with a diameter of 80–120 nm; and the titanium dioxide nanoparticles have a particle size of 20–50 nm.

4. The composite self-cleaning fiber membrane according to claim 2, characterized in that, The polyvinylidene fluoride microspheres are formed by electrostatic spraying, and the titanium dioxide nanoparticles are partially embedded in the surface of the polyvinylidene fluoride microspheres.

5. A method for preparing the composite self-cleaning fiber membrane according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step (1): Disperse single-walled carbon nanotubes in an organic solvent to obtain a single-walled carbon nanotube slurry; add polyvinylidene fluoride powder to the single-walled carbon nanotube slurry, heat and stir until dissolved to obtain an electrospinning solution; Step (2): Ultrasonically disperse titanium dioxide nanoparticles in an organic solvent to obtain a titanium dioxide nanoparticle dispersion; add polyvinylidene fluoride powder to the titanium dioxide nanoparticle dispersion, heat and stir until dissolved to obtain an electrostatic spray liquid; Step (3): Place the electrospinning solution and the electrospray solution in an electrospinning device, perform electrospinning and electrospraying simultaneously, and collect the electrospinning jet products; Step (4): The collected electrostatic jet products are dried to obtain the composite self-cleaning fiber membrane.

6. The method for preparing the composite self-cleaning fiber membrane according to claim 5, characterized in that, The organic solvent is N,N-dimethylformamide.

7. The method for preparing the composite self-cleaning fiber membrane according to claim 5, characterized in that, In step (1), the mass fraction of polyvinylidene fluoride in the electrospinning solution is 17-22 wt%, and the mass of single-walled carbon nanotubes is 0.01-0.05 wt% of the mass of polyvinylidene fluoride; in step (2), the mass fraction of polyvinylidene fluoride in the electrospinning solution is 7-12 wt%, and the mass of titanium dioxide nanoparticles is 0.2-1.0 wt% of the mass of polyvinylidene fluoride.

8. The method for preparing the composite self-cleaning fiber membrane according to claim 5, characterized in that, In step (3), the electrospinning and electroblowing are performed synchronously: the volume ratio of the electrospinning liquid to the electroblowing liquid is 2:1; the voltage of the high-voltage electrostatic field is 16-18 kV; the propelling speed of the electrospinning liquid and the electroblowing liquid is the same, both being 0.8-1.0 mL·h -1 .

9. The method for preparing the composite self-cleaning fiber membrane according to claim 5, characterized in that, In step (4), the drying conditions are: drying at 60-70℃ for 10-12 hours, and the thickness of the composite self-cleaning fiber membrane obtained after drying is 80-120 μm.

10. A triboelectric nanogenerator, comprising a triboelectric layer, characterized in that, The friction layer is a composite self-cleaning fiber membrane as described in any one of claims 1 to 4.

Images