Preparation method of asymmetric nanocellulose aerogel-based flexible friction nanogenerator

Abstract

The invention discloses a preparation method of an asymmetric nanocellulose aerogel-based flexible friction nanogenerator, and belongs to the technical field of friction nanogenerators. The invention aims to solve the problems of instability, poor mechanical property and low surface charge density of the existing nanocellulose and the problem that the output performance of the nanocellulose-based friction nanogenerator is easily influenced by the environment. The method comprises the following steps: 1, preparing a nanocellulose material; 2, preparation of an asymmetric nano cellulose aerogel; and 3, assembling the asymmetric nano cellulose aerogel based flexible friction nano generator. The preparation method is used for preparing the asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

Description

Technical Field

[0001] The invention belongs to the technical field of friction nanogenerators. Background Art

[0002] The operating principle of a triboelectric nanogenerator (TGN) is based on the coupling effect of contact electrification and electrostatic induction. The friction layer of a TGN is made of two different materials, which come into contact under the action of a driving force. Due to the different electron binding abilities of the two materials, electron transfer occurs, forming positive and negative charges upon contact. Mechanical action causes the friction materials to separate, generating an induced potential and generating a current in an external circuit. Therefore, TGNs can collect external signals and the mechanical energy generated by human movement, converting it into electrical energy, thus providing a sustainable power source for the long-term operation of wearable and portable smart electronic devices.

[0003] Cellulose, the most abundant natural polymer on Earth, is a key component of green and environmentally friendly industries due to its biodegradability, renewability, environmental friendliness, and non-toxicity. Currently, most piezoelectric and triboelectric materials are composed of polymers, but long-term use can lead to environmental problems such as white pollution. In applications such as wearable and implantable sensor devices, raw materials must meet specific criteria, including non-toxicity, good biocompatibility, and overall safety to the human body. Among these, nanocellulose materials, with their advantages of high specific surface area, high purity, and high adsorption capacity, have attracted extensive research attention in recent years. However, nanocellulose also suffers from low stability, low surface charge density, and poor mechanical properties, making it difficult to directly use as a friction material in triboelectric nanogenerators. Furthermore, the output performance of nanocellulose-based triboelectric nanogenerators is highly susceptible to environmental influences. Therefore, the research and development of multifunctional nanocellulose-based triboelectric nanogenerators has significant research value and application potential. Summary of the Invention

[0004] The present invention aims to solve the problems of instability, poor mechanical properties and low surface charge density of existing nanocellulose, as well as the problem that the output performance of nanocellulose-based friction nanogenerators is easily affected by the environment, and further provides a method for preparing an asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

[0005] A method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator is carried out according to the following steps:

[0006] 1. Preparation of nanocellulose materials:

[0007] ① Add nanocellulose to a mixed solution of 2,2,6,6-tetramethylpiperidin-1-oxide, sodium bromide, sodium hypochlorite and deionized water, stir evenly, and then vacuum filter and dry to obtain oxidized nanocellulose;

[0008] ② Add the oxidized nanocellulose to a mixed solution of ethylenediamine and deionized water for reaction, then add sodium cyanoborohydride for reaction, and finally vacuum filter and dry to obtain aminated nanocellulose; 2. Preparation of asymmetric nanocellulose aerogels:

[0009] ① Add the aminated nanocellulose, carbon nanotubes and titanium dioxide to the alkali / urea solution, stir evenly, and then freeze to obtain solution A;

[0010] ② Add the aminated nanocellulose and carbon nanotubes to the alkali / urea solution, stir evenly, and then freeze to obtain solution B;

[0011] ③ Add a crosslinker to solution A, stir at room temperature, freeze at low temperature for a short time, and then pour into a mold for gelation to obtain the lower layer hydrogel Janus A;

[0012] ④ Add a crosslinker to solution B, stir at room temperature, and then freeze at low temperature for a short time. Then pour it onto the lower hydrogel Janus A to gel, and obtain the upper hydrogel Janus B, that is, the asymmetric hydrogel.

[0013] ⑤ Soaking the asymmetric hydrogel in hot water and then freeze-drying it to obtain an asymmetric aerogel;

[0014] ⑥ Immersing the asymmetric aerogel in a fluorosilane hydrolysis solution and then freeze-drying it to obtain a fluorosilane-modified asymmetric nanocellulose aerogel;

[0015] 3. Assembly of asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator:

[0016] ① Using fluorosilane-modified asymmetric nanocellulose aerogel as the positive friction material, an electrode material is placed on the surface of the upper hydrogel Janus B of the positive friction material to obtain the positive electrode material of the triboelectric nanogenerator;

[0017] ② Using polytetrafluoroethylene film as the negative friction material, an electrode material is set on the surface of one side of the negative friction material to obtain the negative electrode material of the triboelectric nanogenerator;

[0018] ③ The lower layer hydrogel Janus A of the positive electrode material of the friction nanogenerator is brought into contact with the other side surface of the negative electrode material of the friction nanogenerator and assembled to obtain an asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention uses nanocellulose as raw material, which is low in cost, abundant in source, non-toxic and green;

[0021] 2、The application is used for chemical modification of nanocellulose by 2,2,6,6-tetramethylpiperidine-1-oxyl radical oxidation reaction and reductive amination reaction, grafting carboxyl groups and amino groups, which can significantly enhance the positive friction polarity and can be used as a positive friction material.

[0022] 3、The application loads carbon nanotubes and titanium dioxide in the three-dimensional network structure of nanocellulose aerogel through hydrogen bonds, which not only enhances the conductivity and surface roughness of nanocellulose aerogel, but also improves the mechanical properties of nanocellulose aerogel.

[0023] 4、The asymmetric nanocellulose aerogel-based flexible friction nanogenerator prepared by the application uses Janus A as the side in contact with the negative friction material, and due to the high roughness and large specific surface area of Janus A and the excellent conductivity of Janus B, the effective contact area of electric charge can be increased, the charge transfer speed between the electrode material can be accelerated, and the output performance of the friction nanogenerator can be significantly improved, and the open-circuit voltage can reach about 110V.

[0024] 5、The asymmetric structure designed by the application provides more stress conduction paths, which can improve the mechanical properties of the material.

[0025] 6、The asymmetric nanocellulose aerogel is hydrophobically modified by using heptadecafluorodecyltriethoxysilane, and the obtained asymmetric nanocellulose aerogel has high hydrophobicity, high stability and high charge transfer efficiency, which can significantly improve the output performance of the nanocellulose aerogel-based friction nanogenerator and increase the application range of the nanocellulose aerogel-based friction nanogenerator. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 The structure schematic diagram and working principle diagram of the asymmetric nanocellulose aerogel-based flexible friction nanogenerator prepared in Example 1 are shown in the figure.

[0027] Figure 2 The physical diagram of FACCTi-Janus prepared in Example Step 2 ⑥ is shown in the figure, a is the cross-sectional view of FACCTi-Janus, b is the mass of FACCTi-Janus, c is the physical diagram of FACCTi-Janus A, and d is the physical diagram of FACCTi-Janus B.

[0028] Figure 3These are SEM images of the FACCTi-Janus prepared in step 2 (6) of Example 1, wherein a is an SEM image of the FACCTi-Janus as a whole, b is a high-magnification SEM image of FACCTi-Janus B, c is a low-magnification SEM image of FACCTi-Janus B, and d is a high-magnification SEM image of FACCTi-Janus A and a low-magnification SEM image of FACCTi-Janus A;

[0029] Figure 4 Infrared spectra, XPS spectra and XRD spectra, a is the infrared spectra of TCNF, ACNF and CNF, b is the infrared spectra of ACC, ACCTi-Non-Janus and FACCTi-Janus A, c is the Ti 2p XPS spectra of FACCTi-Janus A, FACCTi-Janus B and ACCTi-Non-Janus, d is the XRD spectra of FACCTi-Janus A, FACCTi-Janus B, AC, ACC and ACCTi-Non-Janus;

[0030] Figure 5 This is a comparison of the output performance of the triboelectric nanogenerators prepared in Example 1 and Comparative Examples 1 to 6, where a is the short-circuit current and b is the open-circuit voltage;

[0031] Figure 6 The output performance diagram of the asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator prepared in Example 1 under different humidity environments, a is the short-circuit current, and b is the open-circuit voltage;

[0032] Figure 7 Mechanical performance diagrams of AC, ACC, ACCTi-Non-Janus, ACCTi-Janus and FACCTi-Janus. DETAILED DESCRIPTION

[0033] Specific embodiment 1: This embodiment is a method for preparing an asymmetric nanocellulose aerogel-based flexible friction nanogenerator, which is carried out according to the following steps:

[0034] 1. Preparation of nanocellulose materials:

[0035] ① Add nanocellulose to a mixed solution of 2,2,6,6-tetramethylpiperidin-1-oxide, sodium bromide, sodium hypochlorite and deionized water, stir evenly, and then vacuum filter and dry to obtain oxidized nanocellulose;

[0036] ② Add the oxidized nanocellulose to a mixed solution of ethylenediamine and deionized water for reaction, then add sodium cyanoborohydride for reaction, and finally vacuum filter and dry to obtain aminated nanocellulose; II. Preparation of asymmetric nanocellulose aerogel:

[0037] ① The aminated nanocellulose, carbon nanotubes and titanium dioxide are added to the alkali / urea solution and stirred uniformly, and then frozen to obtain solution A;

[0038] ② The aminated nanocellulose and carbon nanotubes are added to the alkali / urea solution and stirred uniformly, and then frozen to obtain solution B;

[0039] ③ The crosslinking agent is added to solution A, stirred at room temperature, then frozen for a short time at low temperature, and then poured into a mold to gel, to obtain lower layer hydrogel Janus A;

[0040] ④ The crosslinking agent is added to solution B, stirred at room temperature, then frozen for a short time at low temperature, and then poured on top of the lower layer hydrogel Janus A to gel, to obtain upper layer hydrogel Janus B, i.e. asymmetric hydrogel;

[0041] ⑤ The asymmetric hydrogel is immersed in hot water, then freeze-dried to obtain asymmetric aerogel;

[0042] ⑥ The asymmetric aerogel is immersed in a fluorosilane hydrolysis solution, then freeze-dried to obtain fluorosilane-modified asymmetric nanocellulose aerogel;

[0043] III. Assembly of asymmetric nanocellulose aerogel-based flexible friction nanogenerator:

[0044] ① The fluorosilane-modified asymmetric nanocellulose aerogel is used as the positive friction material, and an electrode material is arranged on the surface of the upper layer hydrogel Janus B of the positive friction material to obtain the positive material of the friction nanogenerator;

[0045] ② A polytetrafluoroethylene film is used as the negative friction material, and an electrode material is arranged on the surface of the negative friction material to obtain the negative material of the friction nanogenerator;

[0046] ③ The lower layer hydrogel Janus A of the positive material of the friction nanogenerator is contacted with the other surface of the negative material of the friction nanogenerator and assembled to obtain the asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

[0047] Compared with traditional nanocellulose aerogels, the asymmetric nanocellulose aerogels similar to Janus structure constructed in the embodiment can significantly improve the comprehensive performance. The designed aerogel presents different pore size distribution and titanium dioxide content on both sides. The side with higher titanium dioxide content is named Janus A, and the pore size of this side is small. The side with lower titanium dioxide content is named Janus B (since a small amount of titanium dioxide in Janus A in step 2③ may not be loaded on nanocellulose, it may be separated out during the hot water soaking process in step 2⑤, and part of it reaches the Janus B side along with the water flow), and the pore size of this side is large. With Janus A as the side in contact with the negative friction material, an asymmetric nanocellulose aerogel-based flexible friction nanogenerator with high electrical output performance is prepared. The high roughness and large specific surface area of Janus A and the excellent electrical conductivity of Janus B can increase the effective contact area of the electric charge and accelerate the charge transfer speed between the electrode material, thereby significantly improving the output performance of the friction nanogenerator. In addition, the design of the asymmetric structure provides more stress conduction paths, which can improve the mechanical properties of the material.

[0048] The beneficial effects of the embodiment are:

[0049] 1. The embodiment selects nanocellulose as the raw material, which is low in cost, abundant in source, non-toxic, and a green and environmentally friendly material.

[0050] 2. The embodiment chemically modifies nanocellulose through 2,2,6,6-tetramethylpiperidine-1-oxyl radical oxidation reaction and reductive amination reaction, grafts carboxyl groups and amino groups, significantly enhances the positive friction polarity, and can be used as a positive friction material.

[0051] 3. The embodiment loads carbon nanotubes and titanium dioxide in the three-dimensional network structure of nanocellulose aerogel through hydrogen bonds, which not only enhances the electrical conductivity and surface roughness of nanocellulose aerogel, but also improves the mechanical properties of nanocellulose aerogel.

[0052] 4. The asymmetric nanocellulose aerogel-based flexible friction nanogenerator prepared in the embodiment uses Janus A as the side in contact with the negative friction material. Due to the high roughness and large specific surface area of Janus A and the excellent electrical conductivity of Janus B, the effective contact area of the electric charge can be increased, and the charge transfer speed between the electrode material can be accelerated, thereby significantly improving the output performance of the friction nanogenerator, and the open-circuit voltage can reach about 110V.

[0053] 5. The asymmetric structure designed in the embodiment provides more stress conduction paths, which can improve the mechanical properties of the material.

[0054] 6、The embodiment uses heptadecafluorodecyltriethoxysilane to modify the asymmetric nanocellulose aerogel, and the obtained asymmetric nanocellulose aerogel has high hydrophobicity, high stability and high charge transfer efficiency, which can significantly improve the output performance of the nanocellulose aerogel-based friction nanogenerator, and increase the application range of the nanocellulose aerogel-based friction nanogenerator.

[0055] Specific embodiment two: the difference between this embodiment and specific embodiment one is that: the mass ratio of nanocellulose to 2,2,6,6-tetramethylpiperidine-1-oxyl radical in step one ① is 1:(0.01~0.02); the mass ratio of nanocellulose to sodium bromide in step one ① is 1:(0.1~0.2); the molar ratio of the mass of nanocellulose to sodium hypochlorite in step one ① is 1g:(0.45~1.05)mmol; the mass ratio of nanocellulose to deionized water in step one ① is 1:(50~100). The others are the same as specific embodiment one.

[0056] Specific embodiment three: the difference between this embodiment and one of specific embodiments one or two is: the mass ratio of oxidized nanocellulose to ethylenediamine in step one ② is 1:(1.02~3.57); the mass ratio of oxidized nanocellulose to sodium cyanoborohydride in step one ② is 1:(0.25~0.3); the mass ratio of oxidized nanocellulose to deionized water in step one ② is 1:(40~60). The others are the same as specific embodiment one or two.

[0057] Specific embodiment four: the difference between this embodiment and one of specific embodiments one to three is: in step one ②, the oxidized nanocellulose is added to the mixed solution of ethylenediamine and deionized water, and the reaction is carried out at a temperature of 25℃~35℃ for 5h~7h, then sodium cyanoborohydride is added, and the reaction is carried out at a temperature of 20℃~30℃ for 2h~4h. The others are the same as specific embodiment three.

[0058] Embodiment five: the difference between this embodiment and one of the embodiments one to four is that: the alkali / urea solution in steps two ① and ② is a mixed solution of sodium hydroxide, urea and deionized water, the mass ratio of sodium hydroxide to urea is 1:(1.5-2), and the mass ratio of sodium hydroxide to deionized water is 1:(10-15); the carbon nanotubes in steps two ① and ② are multi-walled carbon nanotubes; the crystal form of titanium dioxide in step two ① is anatase; the cross-linking agent in steps two ③ and ④ is epichlorohydrin; the fluoro-silane hydrolysis solution in step two ⑥ is specifically prepared by the following steps: under the conditions of room temperature and stirring speed of 300 rpm-500 rpm, heptadecafluorodecyltriethoxysilane, ethanol and acetic acid are stirred for 1 h-3 h, the volume ratio of heptadecafluorodecyltriethoxysilane to ethanol is 1:(80-120), and the volume ratio of heptadecafluorodecyltriethoxysilane to acetic acid is 1:(3-4). The others are the same as embodiments one to four.

[0059] Embodiment six: the difference between this embodiment and one of the embodiments one to five is that: the mass ratio of the aminated nanocellulose to the carbon nanotubes in step two ① is 1:(0.15-0.35); the mass ratio of the aminated nanocellulose to the titanium dioxide in step two ① is 1:(0.0625-0.25); the mass ratio of the aminated nanocellulose to the alkali / urea solution in step two ① is 1:(20-30); the mass ratio of the aminated nanocellulose to the carbon nanotubes in step two ② is 1:(0.15-0.35); the mass ratio of the aminated nanocellulose to the alkali / urea solution in step two ② is 1:(20-30); the mass ratio of solution A to the cross-linking agent in step two ③ is 1:(1.5-2); the mass ratio of solution B to the cross-linking agent in step two ④ is 1:(1.5-2). The others are the same as embodiments one to five.

[0060] Embodiment seven: the difference between this embodiment and one of the embodiments one to six is that: the freezing in steps two ① and ② is specifically freezing for 2 h-4 h under the condition of temperature of-10℃ to-30℃; the stirring at room temperature in steps two ③ and ④ is specifically stirring for 5 min-8 min under the condition of room temperature and rotation speed of 1200 rpm-1500 rpm; the short-time freezing at low temperature in steps two ③ and ④ is specifically freezing for 15 min-30 min under the condition of temperature of-10℃ to-30℃; the gelation in steps two ③ and ④ is specifically gelation for 1 h-2 h under the condition of temperature of 50℃-70℃. The others are the same as embodiments one to six.

[0061] Embodiment eight: different from any one of embodiments one to seven, the thickness ratio of the lower asymmetric hydrogel Janus A to the upper asymmetric hydrogel Janus B in step two ④ is 1:(0.9~1.1). The rest is the same as embodiments one to seven.

[0062] Embodiment nine: different from any one of embodiments one to eight, the soaking in hot water in step two ⑤ is specifically soaking in deionized water at a temperature of 70℃~90℃ for 8h~10h; the soaking in the fluorosilane hydrolysis solution in step two ⑥ is specifically soaking at a temperature of 40℃~60℃ for 12h~36h; the freeze-drying in steps two ⑤ and ⑥ is specifically freeze-drying at a temperature of -30℃~ -50℃ for 12h~36h. The rest is the same as embodiments one to eight.

[0063] Embodiment ten: different from any one of embodiments one to nine, the electrode material in steps three ① and ② is copper foil. The rest is the same as embodiments one to nine.

[0064] The beneficial effects of the present application are verified by the following examples:

[0065] Example one:

[0066] A preparation method of an asymmetric nanocellulose aerogel-based flexible friction nanogenerator, which is carried out according to the following steps:

[0067] I. Preparation of nanocellulose material:

[0068] ① The nanocellulose is added into a mixed solution of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium bromide, sodium hypochlorite and deionized water, stirred uniformly, and then vacuum filtered and dried to obtain oxidized nanocellulose;

[0069] The mass ratio of the nanocellulose to 2,2,6,6-tetramethylpiperidine-1-oxyl radical is 1:0.016; the mass ratio of the nanocellulose to sodium bromide is 1:0.16; the mass of the nanocellulose to the molar of sodium hypochlorite is 1g:0.9mmol; the mass ratio of the nanocellulose to deionized water is 1:75;

[0070] ② The oxidized nanocellulose is added into a mixed solution of ethylenediamine and deionized water, reacted at a temperature of 30℃ for 6h, then sodium cyanoborohydride is added, reacted at a temperature of 25℃ for 3h, and finally vacuum filtered and dried to obtain aminated nanocellulose;

[0071] The mass ratio of the oxidized nanocellulose to ethylenediamine is 1:2.55; the mass ratio of the oxidized nanocellulose to sodium cyanoborohydride is 1:0.29; and the mass ratio of the oxidized nanocellulose to deionized water is 1:50; II. Preparation of asymmetric nanocellulose aerogel

[0072] ①The aminated nanocellulose, carbon nanotubes and titanium dioxide were added into the alkali / urea solution and stirred uniformly, and then frozen at a temperature of -20℃ for 2h to obtain solution A;

[0073] The mass ratio of the aminated nanocellulose to carbon nanotubes is 1:0.25; the mass ratio of the aminated nanocellulose to titanium dioxide is 1:0.125; and the mass ratio of the aminated nanocellulose to the alkali / urea solution is 1:25;

[0074] ②The aminated nanocellulose and carbon nanotubes were added into the alkali / urea solution and stirred uniformly, and then frozen at a temperature of -20℃ for 2h to obtain solution B;

[0075] The mass ratio of the aminated nanocellulose to carbon nanotubes is 1:0.25; and the mass ratio of the aminated nanocellulose to the alkali / urea solution is 1:25;

[0076] ③The crosslinking agent was added into solution A, and stirred at room temperature and a rotation speed of 1500rpm for 5min, and then frozen at a temperature of -20℃ for 30min, and then poured into a mold (30mm×30mm×2mm), and gelled at a temperature of 60℃ for 1h to obtain lower-layer hydrogel Janus A;

[0077] The mass ratio of solution A to the crosslinking agent is 1:1.77; and the thickness of the lower-layer hydrogel Janus A is 1mm;

[0078] ④The crosslinking agent was added into solution B, and stirred at room temperature and a rotation speed of 1500rpm for 5min, and then frozen at a temperature of -20℃ for 30min, and then poured above the lower-layer hydrogel Janus A, and gelled at a temperature of 60℃ for 1h to obtain upper-layer hydrogel Janus B, i.e. asymmetric hydrogel;

[0079] The mass ratio of solution B to the crosslinking agent is 1:1.77; and the thickness of the upper-layer hydrogel Janus B is 1mm;

[0080] ⑤The asymmetric hydrogel was placed in deionized water at a temperature of 80℃ and soaked for 8h, and then freeze-dried at a temperature of -40℃ for 24h to obtain asymmetric aerogel.

[0081] ⑥ Immersing the asymmetric aerogel in a fluorosilane hydrolysis solution at 50°C for 24 hours, and then freeze-drying it at -40°C for 24 hours to obtain a fluorosilane-modified asymmetric nanocellulose aerogel;

[0082] 3. Assembly of asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator:

[0083] ① Using fluorosilane-modified asymmetric nanocellulose aerogel as the positive friction material, an electrode material is set on the surface of the upper hydrogel Janus B of the positive friction material to obtain the positive electrode material of the triboelectric nanogenerator;

[0084] The thickness of the fluorosilane-modified asymmetric nanocellulose aerogel is 2 mm;

[0085] ② Using polytetrafluoroethylene film as the negative friction material, an electrode material is set on the surface of one side of the negative friction material to obtain the negative electrode material of the triboelectric nanogenerator;

[0086] The thickness of the polytetrafluoroethylene film is 0.03 mm;

[0087] ③ The lower layer hydrogel Janus A of the positive electrode material of the friction nanogenerator is brought into contact with the other side surface of the negative electrode material of the friction nanogenerator and assembled to obtain an asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

[0088] The alkali / urea solution described in step 2 ① and ② is a mixed solution of sodium hydroxide, urea and deionized water; the mass ratio of the sodium hydroxide to urea is 7:12; the mass ratio of the sodium hydroxide to deionized water is 7:81;

[0089] The carbon nanotubes described in step 1 and 2 are multi-walled carbon nanotubes;

[0090] The crystal form of titanium dioxide in step 2① is anatase;

[0091] The cross-linking agent in step 2 (3) and (4) is epichlorohydrin;

[0092] The fluorosilane hydrolysis solution described in step 2 (6) is specifically prepared according to the following steps: at room temperature and a stirring speed of 400 rpm, stirring 17 heptadecafluorodecyltriethoxysilane, ethanol and acetic acid for 2 h, the volume ratio of the 17 heptadecafluorodecyltriethoxysilane to ethanol is 1:100, and the volume ratio of the 17 heptadecafluorodecyltriethoxysilane to acetic acid is 1:3.33;

[0093] The electrode material described in step 3 ① and ② is copper foil.

[0094] Comparative Example 1: This embodiment differs from Example 1 in that: Step 3 ① uses aerogel prepared from natural nanocellulose as a positive friction material; the aerogel prepared from natural nanocellulose is specifically prepared according to the following steps:

[0095] ① Add natural nanocellulose to the alkali / urea solution and stir evenly, then freeze at -20°C for 2 hours to obtain solution C;

[0096] The mass ratio of the natural nanocellulose to the alkali / urea solution is 1:25; the alkali / urea solution is a mixed solution of sodium hydroxide, urea and deionized water; the mass ratio of the sodium hydroxide to urea is 7:12; the mass ratio of the sodium hydroxide to deionized water is 7:81;

[0097] ② Add a crosslinker to solution C, stir at room temperature and 1500 rpm for 5 minutes, then freeze at -20°C for 30 minutes, pour into a mold (30 mm × 30 mm × 2 mm), and gel at 60°C for 1 hour to obtain a natural nanocellulose hydrogel;

[0098] The mass ratio of the solution C to the cross-linking agent is 1:1.77; the thickness of the natural nanocellulose hydrogel is 2 mm;

[0099] ③ The natural nanocellulose hydrogel was placed in deionized water at 80° C. and soaked for 8 hours, and then freeze-dried at -40° C. for 24 hours to obtain the natural nanocellulose aerogel. Other steps were the same as those in Example 1.

[0100] Comparative Example 2: This embodiment differs from the first embodiment in that in step 3①, the oxidized nanocellulose prepared in step 1① is used as the positive friction material. Other aspects are the same as those of the first embodiment.

[0101] Comparative Example 3: This embodiment differs from Example 1 in that in step 3 ①, the aminated nanocellulose prepared in step 1 ② is used as the positive friction material. Other aspects are the same as in Example 1.

[0102] Comparative Example 4: This embodiment differs from Example 1 in that in step 3 ①, the hydrogel prepared from solution B in step 2 ② is used as the positive friction material, that is, the upper layer of hydrogel is used as the positive friction material. Other aspects are the same as Example 1.

[0103] Comparative Example 5: This embodiment differs from the embodiment 1 in that in step 3 ①, the lower layer hydrogel prepared in step 2 ③ is used as the positive friction material, that is, the lower layer hydrogel alone is used as the positive friction material. Other aspects are the same as those of the embodiment 1.

[0104] Comparative Example 6: This embodiment differs from the first embodiment in that the asymmetric hydrogel prepared in the second embodiment (5) is used as the positive friction material in step 3 (1). The rest is the same as the first embodiment.

[0105] The oxidized nanocellulose prepared in step 1① of Example 1 was named TCNF (TC); the aminated nanocellulose prepared in step 1② was named ACNF (AC); the asymmetric hydrogel prepared in step 2⑤ was named ACNF-CNT & TiO2-Janus (ACCTi-Janus); the fluorosilane-modified asymmetric nanocellulose aerogel prepared in step 2⑥ was named PFDTES & ACNF-CNT & TiO2-Janus (FACCTi-Janus), with the two asymmetric sides named FACCTi-JanusA and FACCTi-Janus B, respectively. The aerogel prepared in comparative example 1, prepared from natural nanocellulose, was named CNF; the upper hydrogel alone in comparative example 4 was named ACNF-CNT (ACC); and the lower hydrogel alone in comparative example 5 was named ACNF-CNT & TiO2-Non-Janus (ACCTi-Non-Janus).

[0106] Figure 1 This is a schematic diagram of the structure and operating principle of the asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator prepared in Example 1. As can be seen from the figure, when the two friction layer materials come into contact, equal amounts of opposite charges are generated on the surfaces of the positive friction layer material and the polytetrafluoroethylene film, without any external circuit flow. Due to differences in electron affinity, the polytetrafluoroethylene film is negatively charged. When the two friction layers begin to separate, the electrostatic induction effect drives electrons through an external circuit from the top electrode to the bottom electrode, generating an electrical signal. When the two friction layers completely separate, the transmitted electrons reach saturation. When the two friction layers come into contact again, electrons flow from the bottom electrode to the top electrode, generating opposite electrical signals. This contact-separation process is repeated, generating a continuous electrical signal.

[0107] Figure 2 This is a photo of the FACCTi-Janus prepared in step 2 (6) of Example 1. (a) shows a cross-section of the FACCTi-Janus, (b) shows the mass of the FACCTi-Janus, (c) shows a FACCTi-Janus A, and (d) shows a FACCTi-Janus B. The asymmetric nanocellulose aerogel (30 mm x 30 mm x 2 mm in length, width, and thickness) is flexible, lightweight, and has a low density. Due to the different titanium dioxide content on each side of the aerogel, the surface color also varies. The side with higher titanium dioxide content, Janus A, has a gray surface color; the side with lower titanium dioxide content, Janus B, has a black surface color. Overall, the asymmetry of the titanium dioxide content between the two sides is apparent.

[0108] Figure 3 These are SEM images of the FACCTi-Janus prepared in step 2 (6) of Example 1. a is an SEM image of the FACCTi-Janus as a whole, b is a high-magnification SEM image of FACCTi-Janus B, c is a low-magnification SEM image of FACCTi-Janus B, and d is a high-magnification SEM image of FACCTi-Janus A and a low-magnification SEM image of FACCTi-Janus A. As can be seen from the figures, the pore sizes of Janus A and Janus B in the asymmetric nanocellulose aerogel are significantly different: Janus A has a small pore size and a large specific surface area, while Janus B has a large pore size and a small specific surface area. The overall pore size distribution is asymmetric.

[0109] Figure 4 Figures 1 and 2 are infrared spectra, XPS spectra and XRD spectra. a is the infrared spectra of TCNF, ACNF and CNF, b is the infrared spectra of ACC, ACCTi-Non-Janus and FACCTi-Janus A, c is the Ti 2p XPS spectra of FACCTi-Janus A, FACCTi-Janus B and ACCTi-Non-Janus, d is the XRD spectra of FACCTi-Janus A, FACCTi-Janus B, AC, ACC and ACCTi-Non-Janus. As shown in Figures 1 and 2, compared with the CNF curve, the 810 cm -1 and 1732cm -1 The characteristic peaks at 1654 cm-1 on the ACNF curve correspond to the C=O bending vibration peak and stretching vibration peak in the carboxyl group, indicating that the oxidation reaction of cellulose occurs on the hydroxyl group. -1 The characteristic peak at 1420 cm corresponds to the NH bending vibration peak; -1 The characteristic peak at 1200 cm corresponds to the CN bending vibration peak, which proves that the carboxyl group and amino group are successfully grafted on the nanocellulose. -1 The characteristic peaks at 1143 cm -1 The characteristic peaks at 1100 cm correspond to the characteristic peaks of -CF2 stretching vibration and -CF3 stretching vibration; -1 ~1000cm -1The absorption peaks of Si-O-Si and Si-O-C correspond to the typical peaks of Si-O-Si and Si-O-C, indicating that the fluorosilane is successfully grafted onto the nanocellulose aerogel. As can be seen from Figures c and d, the broad peak at 20.3° of the AC curve corresponds to the (110) crystal face inherent to the cellulose II crystal structure; the diffraction peak at 25.8° of the ACC curve corresponds to the (002) crystal face of the carbon nanotube; the diffraction peaks at 20.3°, 36.9°, 37.7°, 38.4°, 48.0°, 53.8°, 55.0°, 62.5°, 68.7°, 70.2°, 75.0° of the FACCTi-Janus B curve correspond to the (101), (103), (004), (112), (201), (105), (211), (204), (116), (220), (215) crystal faces of titanium dioxide, respectively, indicating that the carbon nanotube and titanium dioxide are successfully loaded in the nanocellulose aerogel. The Ti 2p peak intensity of the FACCTi-Janus A curve in Figure c is higher than that of the FACCTi-Janus B curve, and the titanium dioxide diffraction peak intensity of the FACCTi-Janus A curve in Figure d is higher than that of the FACCTi-Janus B curve, further proving the asymmetry of the titanium dioxide concentration.

[0110] The contact separation power generation test was carried out on the friction nanogenerators prepared in Example 1 and Comparative Examples 1 to 6 under the condition of 30% RH of the environmental humidity, the pressure was 100 N, and the frequency was 1 Hz. Figure 5The output performance comparison diagram of the friction nanogenerator prepared in Example 1 and Comparative Examples 1 to 6, a is the short-circuit current, b is the open-circuit voltage; it can be seen from the figure that after grafting carboxyl groups and amino groups and loading carbon nanotubes and titanium dioxide, the output performance of the sample is significantly improved, the open-circuit voltage is increased from 26V (CNF) to 85V (ACCTi-Non-Janus), and the short-circuit current is increased from 0.18μA (CNF) to 1.24μA (ACCTi-Non-Janus); after the asymmetric structure design, the open-circuit voltage is increased from 85V After modification with fluorosilane, the open circuit voltage increased from 108 V (ACCTi-Non-Janus) to 113 V (FACCTi-Janus), and the short-circuit current increased from 1.63 μA (ACCTi-Janus) to 1.78 μA (FACCTi-Janus). This phenomenon is attributed to the following points: first, the amino groups in ethylenediamine are grafted onto nanocellulose through carboxyl groups, and the amino groups have strong electron-donating ability; second, Janus A is used as the side in contact with the negative friction material. Due to the high roughness and large specific surface area of ​​Janus A and the excellent conductivity of Janus B, the effective contact area of ​​the charge can be increased, and the charge transfer speed between the electrode material can be accelerated, thereby significantly improving the output performance of the friction nanogenerator; finally, after fluorosilane modification, the added functional groups provide more transfer charges, thereby significantly improving the output performance.

[0111] Under conditions of different ambient humidity, the asymmetric nanocellulose aerogel-based flexible friction nanogenerator prepared in Example 1 was subjected to a contact-separation power generation test with a pressure of 100 N and a frequency of 1 Hz. Figure 6 This is the output performance diagram of the asymmetric nanocellulose aerogel-based flexible friction nanogenerator prepared in Example 1 under different humidity environments, where a is the short-circuit current and b is the open-circuit voltage. It can be seen from the figure that due to the successful grafting of fluorosilane, the aerogel can operate in a high-humidity environment. As the ambient humidity increases from 30% to 80%, the open-circuit voltage decreases from 113V to 92V, and the short-circuit current decreases from 1.78μA to 1.54μA, a decrease of only 18.58% and 13.48% respectively.

[0112] Figure 7The mechanical property graph of AC, ACC, ACCTi-Non-Janus, ACCTi-Janus and FACCTi-Janus. With the addition of nanomaterials (carbon nanotubes and titanium dioxide), the tensile strength of nanocellulose aerogel is continuously improved. The tensile strength increases from 0.16 MPa (AC) to 0.44 MPa (ACC), then to 0.54 MPa (ACCTi-Non-Janus), and finally to 1.38 MPa (ACCTi-Janus). Among them, the tensile strength of ACCTi-Janus aerogel (1.38 MPa) is significantly higher than that of ACCTi-Non-Janus gel (0.54 MPa), which is 2.56 times that of ACCTi-Non-Janus aerogel, which is due to the design of the asymmetric structure in the asymmetric nanocellulose aerogel provides more stress conduction paths, which can improve the mechanical properties of the material. Then, the asymmetric nanocellulose aerogel is modified by fluorosilane, forming a fluorosilane network on the surface and inside of the aerogel, further strengthening the mechanical properties of the asymmetric nanocellulose aerogel, and the tensile strength of FACCTi-Janus aerogel is 2.63 MPa.

Claims

1. A method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator, characterized in that It is carried out in the following steps:

1. Preparation of nanocellulose materials: ① Add nanocellulose to a mixed solution of 2,2,6,6-tetramethylpiperidin-1-oxide, sodium bromide, sodium hypochlorite and deionized water, stir evenly, and then vacuum filter and dry to obtain oxidized nanocellulose; ② Add the oxidized nanocellulose to a mixed solution of ethylenediamine and deionized water for reaction, then add sodium cyanoborohydride for reaction, and finally vacuum filter and dry to obtain aminated nanocellulose; 2. Preparation of asymmetric nanocellulose aerogels: ① Add the aminated nanocellulose, carbon nanotubes and titanium dioxide to the alkali / urea solution, stir evenly, and then freeze to obtain solution A; ② Add the aminated nanocellulose and carbon nanotubes to the alkali / urea solution, stir evenly, and then freeze to obtain solution B; ③ Add a crosslinker to solution A, stir at room temperature, freeze at low temperature for a short time, and then pour into a mold for gelation to obtain the lower layer hydrogel Janus A; ④ Add a crosslinker to solution B, stir at room temperature, and then freeze at low temperature for a short time. Then pour it onto the lower hydrogel Janus A to gel, obtaining the upper hydrogel Janus B, that is, obtaining an asymmetric hydrogel; ⑤ Soaking the asymmetric hydrogel in hot water and then freeze-drying it to obtain an asymmetric aerogel; ⑥ Immersing the asymmetric aerogel in a fluorosilane hydrolysis solution and then freeze-drying it to obtain a fluorosilane-modified asymmetric nanocellulose aerogel; 3. Assembly of asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator: ① Using fluorosilane-modified asymmetric nanocellulose aerogel as the positive friction material, an electrode material is set on the surface of the upper hydrogel Janus B of the positive friction material to obtain the positive electrode material of the triboelectric nanogenerator; ② Using polytetrafluoroethylene film as the negative friction material, an electrode material is set on the surface of one side of the negative friction material to obtain the negative electrode material of the triboelectric nanogenerator; ③ The lower layer hydrogel Janus A of the positive electrode material of the friction nanogenerator is brought into contact with the other side surface of the negative electrode material of the friction nanogenerator and assembled to obtain an asymmetric nanocellulose aerogel-based flexible friction nanogenerator.

2. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The mass ratio of the nanocellulose described in step 1① to 2,2,6,6-tetramethylpiperidin-1-oxyl free radical is 1:(0.01~0.02); the mass ratio of the nanocellulose described in step 1① to sodium bromide is 1:(0.1~0.2); the molar ratio of the mass of the nanocellulose described in step 1① to sodium hypochlorite is 1g:(0.45~1.05)mmol; the mass ratio of the nanocellulose described in step 1① to deionized water is 1:(50~100).

3. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The mass ratio of the oxidized nanocellulose described in step 1 ② to ethylenediamine is 1:(1.02~3.57); the mass ratio of the oxidized nanocellulose described in step 1 ② to sodium cyanoborohydride is 1:(0.25~0.3); the mass ratio of the oxidized nanocellulose described in step 1 ② to deionized water is 1:(40~60).

4. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that Step 1②: Add the oxidized nanocellulose to a mixed solution of ethylenediamine and deionized water, react at a temperature of 25°C to 35°C for 5h to 7h, then add sodium cyanoborohydride, and react at a temperature of 20°C to 30°C for 2h to 4h.

5. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The alkali / urea solution described in steps ① and ② is a mixed solution of sodium hydroxide, urea and deionized water, the mass ratio of the sodium hydroxide to urea is 1: (1.5~2), and the mass ratio of the sodium hydroxide to deionized water is 1: (10~15); the carbon nanotubes described in steps ① and ② are multi-walled carbon nanotubes; the crystal form of titanium dioxide described in step ① is anatase; the cross-linking agent described in steps ③ and ④ is epichlorohydrin; the fluorosilane hydrolysis solution described in step 2 ⑥ is specifically prepared according to the following steps: at room temperature and a stirring speed of 300rpm~500rpm, stirring heptafluorodecyltriethoxysilane, ethanol and acetic acid for 1h~3h, the volume ratio of the heptafluorodecyltriethoxysilane to ethanol is 1: (80~120), and the volume ratio of the heptafluorodecyltriethoxysilane to acetic acid is 1: (3~4).

6. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The mass ratio of the aminated nanocellulose described in step 2① to the carbon nanotubes is 1:(0.15~0.35); the mass ratio of the aminated nanocellulose described in step 2① to titanium dioxide is 1:(0.0625~0.25); the mass ratio of the aminated nanocellulose described in step 2① to the alkali / urea solution is 1:(20~30); the mass ratio of the aminated nanocellulose described in step 2② to the carbon nanotubes is 1:(0.15~0.35); the mass ratio of the aminated nanocellulose described in step 2② to the alkali / urea solution is 1:(20~30); the mass ratio of solution A described in step 2③ to the cross-linking agent is 1:(1.5~2); the mass ratio of solution B described in step 2④ to the cross-linking agent is 1:(1.5~2).

7. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The freezing described in steps 1 and 2 is specifically freezing at a temperature of -10°C to -30°C for 2h to 4h; the stirring at room temperature described in steps 3 and 4 is specifically stirring at room temperature and a rotation speed of 1200rpm to 1500rpm for 5min to 8min; the short-term freezing at low temperature described in steps 3 and 4 is specifically freezing at a temperature of -10°C to -30°C for 15min to 30min; the gelation described in steps 3 and 4 is specifically gelation at a temperature of 50°C to 70°C for 1h to 2h.

8. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The thickness ratio of the lower hydrogel Janus A to the upper hydrogel Janus B in the asymmetric hydrogel described in step 2 (4) is 1:(0.9~1.1).

9. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The soaking in hot water in step 2 (5) is specifically soaking in deionized water at a temperature of 70°C to 90°C for 8h to 10h; in step 2 (6), the asymmetric aerogel is immersed in a fluorosilane hydrolysis solution at a temperature of 40°C to 60°C for 12h to 36h; the freeze-drying in steps 2 (5) and (6) is specifically freeze-drying at a temperature of -30°C to -50°C for 12h to 36h.

10. The method for preparing an asymmetric nanocellulose aerogel-based flexible triboelectric nanogenerator according to claim 1, characterized in that The electrode material described in step 3 ① and ② is copper foil.

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