A composite electrothermal film of graphitic carbon nitride and graphene and its preparation method

Abstract

This invention relates to the field of functional nanomaterial preparation, specifically to a graphitic carbon nitride / graphene composite electrothermal film and its preparation method. First, graphitic carbon nitride (g-C3N4) nanosheets are prepared by heating nitrogen-rich organic matter using high-energy microwaves. Next, the g-C3N4 nanosheets are subjected to a hydrothermal reaction to obtain soluble g-C3N4 nanosheets. Then, the soluble g-C3N4 nanosheets are dispersed in a graphene oxide (GO) solution, and after ultrasonic dispersion, the suspension is filtered to obtain a g-C3N4 / GO composite film. Finally, the film is reduced by microwave irradiation to obtain the graphitic carbon nitride / graphene (g-C3N4 / rGO) composite electrothermal film. Due to the addition of g-C3N4 nanosheets with good dispersibility and water solubility, its thermal conductivity is superior to that of existing pure graphene electrothermal films, making it suitable for use in insulation products. High-energy microwave irradiation heating has a faster rate and shorter processing time, and it boasts advantages such as simple process, convenient operation, low equipment requirements, low cost, high processing efficiency, and no secondary pollution, showing great application prospects.

Description

Technical Field

[0001] This invention patent relates to a graphitic carbon nitride and graphene composite electrothermal film and its preparation method, belonging to the field of functional nanomaterial preparation. Background Technology

[0002] Heating, hot water heating, and radiant heating are all essential sectors in Chinese people's lives. Since these methods typically use coal as a heat source, they produce polluting gases along with the heating process. As people's living standards improve and their environmental awareness increases, zero-emission and zero-pollution green energy is becoming increasingly popular. Therefore, electric heating is gradually becoming the mainstream method, and electric heating materials are increasingly being used in fields such as electrothermal therapy and electric heating.

[0003] Graphene, a novel two-dimensional nanomaterial, is currently the only known two-dimensional free-state atomic crystal. Graphene is composed of a single layer of carbon atoms separated by sp... 2 The two-dimensional honeycomb crystal structure formed by hybrid close-packing possesses extremely high thermal conductivity, excellent electrical and mechanical properties, and is considered one of the most ideal new thermal conductive materials. Graphene is known to be used in the field of electric heating, see patent CN 109152114 A (September 26, 2023) and patent US2014182063 A1 (July 3, 2014). However, the graphene electric heating films prepared by the above patents suffer from problems such as uneven heating and insignificant far-infrared heating, which prevent the full utilization of graphene's thermal properties.

[0004] Currently, methods for preparing graphene mainly include micromechanical exfoliation, chemical exfoliation, and chemical vapor deposition. Micromechanical exfoliation is the simplest and most direct method for preparing graphene. It utilizes the adhesive force of adhesive tape to peel off layers of graphite flakes through repeated application. The tape containing the graphite flakes is then adhered to a target substrate such as a silicon wafer. Finally, the tape is removed with solvents such as acetone, yielding graphene with a size greater than 100 μm. This method is simple to operate, but its yield is low and uncontrollable, making it difficult to meet the needs of large-area and large-scale graphene preparation. Chemical exfoliation uses redox reactions to introduce functional groups onto the carbon atoms of graphite layers, increasing the interlayer spacing and weakening the interlayer interactions. Then, the graphene oxide layers are separated layer by layer using ultrasound or rapid expansion to obtain graphene oxide. Finally, oxygen-containing functional groups are removed through chemical reduction or high-temperature reduction to obtain graphene. This method is currently an effective way to prepare graphene on a large scale, but the preparation cycle is long, and carbon atoms are often missing during oxidation, ultrasonication, and subsequent reduction processes, resulting in graphene with many defects and poor conductivity. Chemical vapor deposition uses carbon-containing compounds such as methane as a carbon source, growing graphene through high-temperature decomposition on the substrate surface. Although this method produces high-quality graphene and can achieve large-area growth, the reactant methane required for the reaction is expensive, and the experimental operation is relatively dangerous.

[0005] Therefore, there is an urgent need for a preparation method with advantages such as fast heating speed and easy process control, as well as a composite electrothermal film with uniform heating that can fully utilize the thermal properties of graphene. Summary of the Invention

[0006] Heterogeneous structures, which vertically stack two or more layers of two-dimensional crystals through interlayer van der Waals interactions, exhibit extraordinary performance exceeding that of individual components, attracting increasing attention from researchers in recent years. Due to the complementary physical properties of graphene and graphitic carbon nitride, they can be constructed into heterocomposite structures, fully utilizing the properties of each individual component to achieve optimal performance. For example, assembling graphene with graphitic carbon nitride can open the intrinsic bandgap of graphene, thus overcoming the zero bandgap barrier of graphene when constructing field-effect transistors. Furthermore, compared to graphitic carbon nitride, hybrid graphene / graphitic carbon nitride heterostructures exhibit enhanced light absorption in the visible light region, a promising feature for novel photovoltaic and electrothermal applications.

[0007] To address the shortcomings of existing technologies, this invention provides a method for preparing a composite electrothermal film of graphitic carbon nitride and graphene. The prepared material exhibits uniform heating, and compared with traditional heating methods, the preparation method is simple to operate, safe and effective, and highly repeatable.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a composite electrothermal film of graphitic carbon nitride and graphene and its preparation method, comprising the composite electrothermal film.

[0009] The composite electrothermal film, by mass parts, comprises the following components: soluble g-C3N4 nanosheets and graphene.

[0010] The mass ratio of the soluble g-C3N4 nanosheets to graphene is 0.1 to 5:1.

[0011] (1) The nitrogen-rich organic matter is added to a quartz crucible, and then the crucible is placed in the resonant cavity of a high-energy microwave oven for irradiation treatment to obtain a light yellow g-C3N4 powder.

[0012] (2) The powder is uniformly dispersed in deionized water, and the mixture is ultrasonically treated for 0.5 to 2 hours. After hydrothermal treatment, it is cooled to room temperature, washed with deionized water and freeze-dried overnight to obtain soluble g-C3N4 nanosheets.

[0013] (3) First, GO was prepared by the Hummers method: under ice bath conditions, graphite, sodium nitrate and potassium permanganate were weighed in a ratio of 1:1:3. Then, concentrated sulfuric acid was slowly added dropwise to a three-necked flask containing graphite and stirred. Then, the sample was mixed with sodium nitrate (NaNO3). Then, the weighed potassium permanganate (KMnO4) was added to the three-necked flask in batches and stirred. The mixture was then placed in a water bath and reacted. After adding deionized water to dilute the solution, hydrogen peroxide (H2O2) was gradually added to the three-necked flask while stirring until the liquid changed color and separated into layers. The lower layer of golden yellow viscous liquid was taken out, filtered, and washed with dilute HCl solution and deionized water until neutral to obtain graphene oxide (GO) solution.

[0014] (4) The soluble g-C3N4 nanosheets are dispersed in GO solution. The mixture is then placed in an ultrasonic instrument and ultrasonicated until homogeneous. The g-C3N4 / GO mixed dispersion is vacuum filtered using an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device. The composite membrane is placed in a vacuum drying oven and dried continuously at a temperature of 60°C for 12 hours.

[0015] (5) The composite film is placed in the resonant cavity of a high-energy microwave oven, and the vacuum degree, microwave power and microwave oven resonant cavity temperature are adjusted. The heat preservation reaction is carried out under microwave radiation heating to obtain the g-C3N4 / rGO composite electrothermal film.

[0016] Preferably, the nitrogen-rich organic compound is any one or at least two combinations of urea, dicyandiamide, and melamine, such as urea, urea and dicyandiamide, dicyandiamide, dicyandiamide and melamine, melamine, melamine and urea.

[0017] Preferably, the heating power of the high-energy microwave is 3 to 5 kW, for example, 3 kW, 3.5 kW, 4 kW, 4.5 kW, or 5 kW.

[0018] Preferably, the heating reaction time of the high-energy microwave is 1 to 10 min, for example, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min.

[0019] Preferably, the hydrothermal reaction temperature is 150-200℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, or 200℃.

[0020] Preferably, the hydrothermal reaction heat preservation time is 5 to 24 hours, for example, 6 hours, 8 hours, 12 hours, 16 hours, 20 hours, or 24 hours.

[0021] Preferably, the stirring time is 10 to 15 minutes, for example, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes.

[0022] Preferably, the reaction time is 2 to 3 hours, for example, 2 hours, 2.5 hours, or 3 hours.

[0023] Preferably, the reaction temperature is 35-40°C, for example, 35°C, 36°C, 37°C, 38°C, 39°C, or 40°C.

[0024] Preferably, the reaction time is 3 to 5 hours, for example, 3 hours, 4 hours, or 5 hours.

[0025] Preferably, the reaction temperature is 90-98℃, for example 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, or 98℃.

[0026] Preferably, the ultrasound time is 1 to 2 hours, for example, 1 hour, 1.5 hours, or 2 hours.

[0027] Preferably, in the g-C3N4 / rGO composite membrane, the mass ratio of soluble g-C3N4 to rGO is 0.2-3:1, for example, 0.2:1, 0.5:1, 1:1, 1.2:1, 1.5:1, 2:1, 2.2:1, 2.5:1.

[0028] Preferably, the heating power of the high-energy microwave is 3 to 5 kW, for example, 3 kW, 3.5 kW, 4 kW, 4.5 kW, or 5 kW.

[0029] Preferably, the heating reaction time of the high-energy microwave is 1 to 10 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, or 10 seconds.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. This invention provides a method for preparing a composite electrothermal film of graphitic carbon nitride and graphene. The surface of carbon nitride nanosheets is modified by a simple hydrothermal method, which improves the dispersibility of carbon nitride in aqueous solution and further enhances the uniform composite of carbon nitride and graphene.

[0032] 2. Carbon nitride exhibits excellent thermal stability and strong resistance to temperature decay, effectively suppressing thermal drift and maintaining structural stability. Furthermore, graphene possesses very high electrical conductivity. The two complement each other; graphene's superior electron mobility compensates for carbon nitride's low conductivity. The composite film of graphitic carbon nitride and graphene enhances the electrothermal performance of the graphene electrothermal film.

[0033] 3. This invention uses high-energy microwaves as a heating tool, which can simultaneously heat the material from the inside out without heat conduction and without thermal hysteresis. Compared with traditional muffle furnace heating for 2-6 hours, microwave heating can complete heating within 5-10 seconds, and has the advantages of fast heating rate, selective heating, energy saving and high efficiency, and easy control. Attached Figure Description

[0034] Figure 1 This diagram illustrates the preparation of the graphitic carbon nitride and graphene composite electrothermal film of the present invention.

[0035] Figure 2 This is a transmission electron microscope (TEM) image of graphitic carbon nitride of the present invention.

[0036] Figure 3 The present invention provides a Fourier transform infrared (FT-IR) test for graphitic carbon nitride and soluble carbon nitride.

[0037] Figure 4 This is a transmission electron microscope (TEM) image of the graphitic carbon nitride and graphene composite electrothermal film of the present invention. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are merely 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.

[0039] Reagents used in the examples: melamine, Shanghai Maclean Biochemical Technology Co., Ltd.; graphite powder, Shanghai Maclean Biochemical Technology Co., Ltd.; sulfuric acid, Shanghai Aladdin Reagent Co., Ltd.; nitric acid, Shanghai Aladdin Reagent Co., Ltd.; hydrochloric acid, Shanghai Aladdin Reagent Co., Ltd.; potassium permanganate, Sinopharm Chemical Reagent Co., Ltd.; hydrogen peroxide, Sinopharm Chemical Reagent Co., Ltd.

[0040] Instruments used in the examples: hydrothermal reactor, Anhui Kemi Machinery Technology Co., Ltd.; microwave oven (NJZ10-3), Nanjing Jiequan Microwave Equipment Co., Ltd.; centrifuge (TG16-WS), Hunan Xiangyi Laboratory Instrument Development Co., Ltd.; vacuum oven (DZF-605), Shanghai Jinghong Experimental Equipment Co., Ltd.; transmission electron microscope (Tecnai G2), Thermo Fisher Scientific (FEI), USA; Fourier transform infrared spectrometer (Nicolet 5700), Thermo Fisher Scientific, USA.

[0041] Example 1

[0042] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 4kW microwave power for 10 minutes to obtain graphite phase carbon nitride nanosheets (g-C3N4 nanosheets).

[0043] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 10h to obtain soluble g-C3N4.

[0044] S3: Graphene oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous, the temperature was maintained at 0-4°C, 3g of potassium permanganate was added, the temperature was raised to 30-40°C, and stirred until a brown paste was formed. Water was added to dilute the paste, and the mixture was stirred for 0.5h. 1mL of H2O2 was added, the reaction was carried out, and the mixture was filtered. The product was washed with 20mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60-70°C for 24h to obtain GO.

[0045] S4: Weigh 20% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0046] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 4kW for 2-10s to obtain a graphitic carbon nitride / redox graphene (g-C3N4 / rGO) composite film.

[0047] Figure 1 A schematic diagram illustrating the preparation of a composite electrothermal film of graphitic carbon nitride and graphene.

[0048] The following section briefly explains its material characteristics:

[0049] Electrothermal performance test of g-C3N4 / rGO composite film: Copper foil was attached to both ends of the electrothermal film as electrodes, and a DC regulated power supply was used to provide external voltage. The circuit was formed by connecting the wires. The temperature change of the electrothermal film was recorded by thermocouple sensors and multi-channel temperature testers to characterize the electrothermal performance of the electrothermal film. The voltage was set to 10V and the heating time was 10min. The test was performed 3 times and the average value was taken.

[0050] Resistivity test of g-C3N4 / rGO composite film: First, the thickness of the electrothermal film is measured at at least 6 points using a digital micrometer (TESA digital micrometer, Switzerland), and the average value h is taken. Then, the sheet resistance at these 6 points is measured using a four-probe tester (FT-341 from Rico Instruments), and the average value Rs is taken. The volume resistivity of the electrothermal film is then Rv = Rs × h.

[0051] The flexibility test of the g-C3N4 / rGO composite film: First, the resistance Rv of the heating film is measured. Then, the heating film is bent on a circular shaft, and its resistance Rt is measured after every 10 bends. ΔR = |Rt - Rv|. The flexibility of the heating film is measured based on the value of ΔR / Rv.

[0052] g-C3N4 / rGO composite film heating uniformity test: Infrared thermal imager was used to measure the changes in temperature and distribution uniformity of the sample during the heating process. When the heating film was in a stable working state, the area within 30mm of the heating contour edge of the heating film was divided into 9 regions using the nine-square grid method (that is, the heating film was divided into 9 relatively uniform rectangular regions). The highest temperature of each region was measured, and the difference between the maximum and minimum values ​​among the 9 highest values ​​was taken as the temperature non-uniformity of the heating film.

[0053] Example 2

[0054] S1: Weigh out 10g of dicyandiamide and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 5kW microwave power for 5 minutes to obtain g-C3N4.

[0055] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 15h to obtain soluble g-C3N4.

[0056] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0057] S4: Weigh 20% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0058] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 4kW for 2-10s to obtain the g-C3N4 / rGO composite film.

[0059] Example 3

[0060] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 5kW microwave power for 10 minutes to obtain g-C3N4.

[0061] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 10h to obtain soluble g-C3N4.

[0062] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0063] S4: Weigh 20% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0064] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 4kW for 10s to obtain the g-C3N4 / rGO composite film.

[0065] Example 4

[0066] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 5kW microwave power for 5 minutes to obtain g-C3N4.

[0067] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 24h to obtain soluble g-C3N4.

[0068] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0069] S4: Weigh 20% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0070] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 5kW for 10s to obtain the g-C3N4 / rGO composite film.

[0071] Figure 2 The image shown is a transmission electron microscope (TEM) image of the graphitic carbon nitride obtained in step 1, which exhibits typical two-dimensional ultrathin nanosheet morphology characteristics similar to graphene. Figure 2 The data shows that although multiple nanosheets are stacked together, they are still relatively transparent, indicating that the resulting product is extremely thin.

[0072] Example 5

[0073] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 5kW microwave power for 10 minutes to obtain g-C3N4.

[0074] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 24h to obtain soluble g-C3N4.

[0075] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0076] S4: Weigh 50% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0077] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 3kW for 5s to obtain the g-C3N4 / rGO composite film.

[0078] Example 6

[0079] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 3kW microwave power for 10 minutes to obtain g-C3N4.

[0080] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 18h to obtain soluble g-C3N4.

[0081] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0082] S4: Weigh 30% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at a temperature of 60℃ for 12 hours.

[0083] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 3kW for 10s to obtain the g-C3N4 / rGO composite film.

[0084] Example 7

[0085] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 4kW microwave power for 10 minutes to obtain g-C3N4.

[0086] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 24h to obtain soluble g-C3N4.

[0087] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0088] S4: Weigh 20% of the mass of GO g-C3N4 and place it in a beaker. Add water and ultrasonically disperse for 0.5 h. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 h.

[0089] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 4kW for 5s to obtain the g-C3N4 / rGO composite film.

[0090] Figure 3 The images show infrared spectroscopy results for graphitic carbon nitride and soluble graphitic carbon nitride. As can be seen from the images, compared with graphitic carbon nitride, soluble carbon nitride has many hydrophilic groups (-NH2, -OH and -C=O) on its surface, which gives it excellent dispersibility and solubility.

[0091] Example 8

[0092] S1: Weigh out 10g of melamine and 0.15g of carbon fiber, mix them evenly, and add them to a quartz crucible. Then place the crucible into the resonant cavity of a high-energy microwave oven. Use a water ring pump to evacuate the resonant cavity to 1×10⁻⁶. 4 Below Pa, the circulating water cooling device was turned on, and melamine was irradiated at 4kW microwave power for 10 minutes to obtain g-C3N4.

[0093] S2: Weigh 1g of g-C3N4 and disperse it in 50mL of deionized water. Then transfer the mixed solution to a reaction vessel and keep it at 180℃ for 24h to obtain soluble g-C3N4.

[0094] S3: Graphite oxide (GO) was prepared using the Hummers oxidation method. Specifically, 1g of graphite powder was placed in a three-necked flask, heated to 0°C in an ice bath, sulfuric acid and sodium nitrate were added and stirred until homogeneous. The temperature was maintained at 0–4°C, 3g of potassium permanganate was added, the temperature was raised to 30–40°C, and the mixture was stirred until a brown paste was formed. The paste was diluted with water and stirred for 0.5 h. 1 mL of H2O2 was added, the reaction was initiated, and the mixture was filtered. The product was washed with 20 mL of hydrochloric acid to remove chloride ions, centrifuged, and dried at 60–70°C for 24 h to obtain GO.

[0095] S4: Weigh 5% of g-C3N4 by mass of GO and place it in a beaker. Add water and ultrasonically disperse for 1 hour. Then, use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the g-C3N4 / GO mixed dispersion. Place the composite membrane in a vacuum drying oven and dry it continuously at 60℃ for 12 hours.

[0096] S5: Place the g-C3N4 / GO composite film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the g-C3N4 / GO composite film at a microwave power of 4kW for 2-10s to obtain the g-C3N4 / rGO composite film.

[0097] Figure 4 This is a transmission image of a graphitic carbon nitride and graphene composite electrothermal film. As can be seen from the image, g-C3N4 nanosheets and graphene are stacked layer by layer to form a two-dimensional layered structure.

[0098] Comparative Example 1: Preparation of Graphitic Carbon Nitride by Conventional Thermal Polycondensation

[0099] Currently, thermal polycondensation is a common method for preparing graphitic carbon nitride. For example, the Liang Shijing research group at Fuzhou University first calcined melamine in a muffle furnace at 500℃ for 4 hours, synthesizing a graphitic carbon nitride precursor via thermal polycondensation. Then, they dispersed the graphitic carbon nitride in an ethanol-water solution, ultrasonically treated it, stirred it for a period of time, and then continued ultrasonic exfoliation. Finally, they centrifuged it to obtain graphene-like carbon nitride (Liang Shijing, Lin Qiuyan, Bi Jinhong, Liu Minghua, A Nanosheet with Molecular-Level Thickness and Its Preparation Method and Application, Publication No.: CN103254200A). Although this method can obtain graphitic carbon nitride, the thermal polycondensation reaction, ultrasonic treatment, stirring, and centrifugation processes make the preparation cycle very lengthy and complex.

[0100] Comparative Example 2: Preparation of Graphene-like Carbon Nitride by Microwave Method

[0101] Given the advantages of microwave synthesis in terms of high efficiency and environmental friendliness, research institutions such as South China Normal University, Nanjing University, and Anhui University have gradually begun to use microwave heating of melamine to synthesize graphitic carbon nitride. For example, Wang Xin et al. of South China Normal University (Wang Xin, Yang Liqin, Chen Zhihong, Preparation and application of graphitic carbon nitride under microwave conditions, application number: CN202110045000.3, application publication number: CN112875660A) used urea as a synthesis raw material and copper oxide as a microwave absorber. They rapidly prepared graphitic carbon nitride by heating it under microwave (100-500W) conditions for 15-25 minutes. However, the separate placement of the microwave absorber and the raw material significantly reduced the thermal efficiency, making it difficult to take advantage of the rapid heating of the bulk phase by microwave irradiation, which seriously affected the preparation efficiency.

[0102] Comparative Example 3: Preparation of Graphene-like Carbon Nitride by Microwave Method

[0103] Professor Yuan Yupeng's team at Anhui University (Yuan Yupeng, Zhao Gege, Du Haiwei, Jiang Daochuan, Zhu Chuhong, A carbon nitride material with n-π* transition and its preparation method, application number: CN202210537783.1. Publication number: CN115159477A) rapidly prepared graphitic carbon nitride by microwave irradiation with a heating frequency of up to 900MHz for 20 minutes. However, the separate placement of the microwave absorber and the raw materials makes it difficult to take full advantage of the rapid heating of the bulk phase by microwave irradiation.

[0104] Comparative Example 4: Preparation of Graphene-like Carbon Nitride Nanosheets by Microwave Method

[0105] In addition, the research group of Academician Zou Zhigang of Nanjing University first synthesized the precursor by irradiation at 800W microwave power for 25 minutes, and then carried out high-temperature calcination and etching for 25 hours to finally obtain ultrathin carbon nitride nanosheets with a thickness of 3nm (Gao Jun, Preparation and performance study of micro-nano structure g-C3N4, Master's thesis of Nanjing University, 2012). Its stacking thickness is close to 10 layers, reaching the critical standard of two-dimensional ultrathin nanosheets with graphene-like structure. However, this method has complicated steps and is time-consuming.

[0106] In addition, Wang Jigang and others from the Dongda Industrial Technology Research Institute in Zhangjiagang City directly prepared graphite-like carbon nitride (CN201610065411.8, CN201610908265.0, and CN201710331913.5) using high-energy microwave irradiation. However, the above-mentioned invention patents only obtained graphite-like carbon nitride and applied it to functional fields such as photocatalysis or lubrication, but did not achieve its composite with graphene or its application in fields such as electrothermal.

[0107] Comparative Example 5: Preparation of graphene and carbon nitride composite materials by conventional thermal polycondensation method

[0108] Currently, thermal polycondensation is also a common method for preparing graphitic carbon nitride composites. For example, Professor Zhao Huijun's team at Griffith University, Australia (Li Y, Zhang H, Liu P, et al. Cross-linked g-C3N4 / rGO nanocomposites with tunable band structure and enhanced visible light photocatalytic activity[J]. Small, 2013, 9(19): 3336-3344.) first uniformly mixed graphene oxide (GO) with cyanamide, and then heated it to about 550℃ in a tube muffle furnace with argon gas. The former was reduced to rGO by heating, and the latter was thermally polycondensed to generate g-C3N4, finally generating rGO / g-C3N4 composite. However, this method requires a pre-treatment time of up to 4 hours, resulting in low preparation efficiency. Furthermore, this method cannot synthesize large-sized ultrathin carbon nitride nanosheets, which means that carbon nitride and graphene cannot be completely composited. In addition, the rGO / g-C3N4 composite prepared by this method is a powder sample, which cannot be applied to the field of electrothermal film heating.

[0109] Comparative Example 6: Preparation of a composite of graphene and graphitic carbon nitride by direct microwave heating of melamine and graphene oxide.

[0110] The research group of Professors Gu Yongpan and Wang Jigang at Southeast University used a mixture of melamine and GO as a precursor to synthesize a rGO / g-C3N4 composite via microwave heating (Gu Y, Yu Y, Zou J, et al. The ultra-rapid synthesis of rGO / g-C3N4 composite via microwave heating with enhanced photocatalytic performance[J]. Materials Letters, 2018, 232: 107-109.). However, the presence of GO during the preparation process inhibited the growth of g-C3N4, ultimately reducing the size of the rGO / g-C3N4 composite. Furthermore, the resulting product was not uniformly distributed. Due to the intense and complex reaction process after mixing melamine and GO, other intermediate products such as melamine were also present in the synthesized product. Additionally, the product prepared by this method is a powder sample, which cannot be directly applied to the field of electrothermal film heating.

[0111] Comparative Example 7: Graphene Electrothermal Film

[0112] S1: Measure the GO solution, and then use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the GO dispersion. Place the GO membrane in a vacuum drying oven and dry it continuously at a temperature of 60℃ for 12 h.

[0113] S2: Place the GO film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the GO film with 5kW microwave power for 10s to obtain the rGO film.

[0114] Comparative Example 8: Graphene Electrothermal Film

[0115] S1: Measure the GO solution, and then use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the GO dispersion. Place the GO membrane in a vacuum drying oven and dry it continuously at a temperature of 60℃ for 12 h.

[0116] S2: Place the GO film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the GO film with 5kW microwave power for 5s to obtain the rGO film.

[0117] Comparative Example 9: Graphene Electrothermal Film

[0118] S1: Measure the GO solution, and then use an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device to vacuum filter the GO dispersion. Place the GO membrane in a vacuum drying oven and dry it continuously at a temperature of 60℃ for 12 h.

[0119] S2: Place the GO film in a microwave resonant cavity, evacuate the microwave resonant cavity, and irradiate the GO film with a microwave power of 4kW for 10s to obtain the rGO film.

[0120] Table 1 Preparation Time Schedule

[0121]

[0122] Table 2 Comparison of thermal conductivity and resistivity

[0123]

Claims

1. A method for preparing a composite electrothermal film of graphitic carbon nitride and graphene, characterized in that: The composite electrothermal film is a two-dimensional layered structure formed by stacking soluble g-C3N4 nanosheets and graphene layers, with a thermal conductivity of 30–60 W / m. -1 K -1 The soluble g-C3N4 nanosheets are two-dimensional g-C3N4 nanosheets prepared by hydrothermal treatment. The mass ratio of the soluble g-C3N4 nanosheets to graphene is 0.1–5:1; The preparation method of the graphitic carbon nitride and graphene composite electrothermal film is as follows: (1) Preparation of g-C3N4; Nitrogen-rich organic matter was added to a quartz crucible, and then the crucible was placed in a high-energy microwave oven resonant cavity for irradiation treatment to obtain pale yellow g-C3N4 powder. (2) Preparation of soluble g-C3N4; The powder is uniformly dispersed in deionized water to obtain a mixture, which is then ultrasonically treated for 0.5 to 2 hours. After hydrothermal treatment, the mixture is cooled to room temperature, washed with deionized water, and freeze-dried overnight to obtain soluble g-C3N4 nanosheets. (3) Preparation of GO dispersion; First, GO was prepared using the Hummers method: Under ice bath conditions, graphite, sodium nitrate, and potassium permanganate were weighed in a ratio of 1:1:

3. Then, concentrated sulfuric acid was slowly added dropwise to a three-necked flask containing graphite while stirring. The sample was then mixed with sodium nitrate, and the weighed potassium permanganate was added in batches to the three-necked flask while stirring and reacting in a water bath. After adding deionized water to dilute the solution, hydrogen peroxide was gradually added to the three-necked flask while stirring until the liquid changed color and separated into layers. The lower layer of golden yellow viscous liquid was taken, filtered, and washed with dilute hydrochloric acid solution and deionized water until neutral to obtain a graphene oxide solution. (4) Preparation of g-C3N4 / GO composite membrane The soluble g-C3N4 nanosheets were dispersed in a GO solution to obtain a mixture. The mixture was then sonicated in an ultrasonic instrument until homogenized. The g-C3N4 / GO mixed dispersion was vacuum filtered using an organic filter membrane with a pore size of 0.22 μm and a vacuum filtration device. The composite membrane was placed in a vacuum drying oven and dried continuously at 60°C for 12 hours to obtain the first composite membrane. (5) Preparation of g-C3N4 / rGO composite electrothermal film; The first composite film is placed in the resonant cavity of a high-energy microwave oven, the microwave power is adjusted to 3-5W, and it is kept warm for 3-10s under microwave radiation heating to obtain the g-C3N4 / rGO composite electrothermal film.

2. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (1), the nitrogen-rich organic compound is any one or a combination of at least two of urea, dicyandiamide, and melamine.

3. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (1), the heating power of the high-energy microwave is 3 to 5 kW.

4. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (1), the heating reaction time of the high-energy microwave is 1 to 10 minutes.

5. The method for preparing a composite electrothermal film of graphitic carbon nitride and graphene according to claim 1, characterized in that: In step (2), the hydrothermal reaction temperature is 150-200℃.

6. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (2), the hydrothermal reaction is kept at a temperature of 5 to 24 hours.

7. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (4), the conditions for ultrasonic dispersion are: ultrasonic machine operating frequency 80kHz, power 100W, and ultrasonic treatment at room temperature for 1-2 hours.

8. The method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to claim 1, characterized in that: In step (5), the mass ratio of soluble g-C3N4 to rGO in the g-C3N4 / rGO composite membrane is 0.2-3:

1.

9. The composite electrothermal film prepared by the method for preparing a graphitic carbon nitride and graphene composite electrothermal film according to any one of claims 1 to 8.

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