Carbon nanofiber, preparation method thereof and supercapacitor

Abstract

The invention provides a carbon nanofiber, a preparation method thereof and a supercapacitor, and belongs to the technical field of organic solid waste treatment or supercapacitors. The preparation method comprises the following steps: sequentially carrying out drying treatment, crushing treatment and screening treatment on kitchen garbage to obtain kitchen garbage powder; performing hot melting extraction on the kitchen garbage powder by using a non-polar organic solvent to obtain an extract; carrying out electrostatic spinning on the extract to obtain an extract precursor; carrying out pre-oxidation treatment on the extract precursor in air to obtain a pre-oxidation product; performing carbonization treatment on the pre-oxidized product in an inert atmosphere to obtain a carbonized product, so as to obtain the carbon nanofiber. According to the method, the kitchen garbage is taken as the raw material, the high-nitrogen-content and low-cost extract is obtained through hot melting extraction and serves as the carbon nanofiber precursor, the high-nitrogen-content carbon nanofiber is further prepared, and the excellent electrochemical performance effect is achieved at low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic solid waste treatment or supercapacitors, and particularly relates to a carbon nanofiber and a preparation method thereof, and a supercapacitor. Background Art

[0002] With the increasing demand for portable electronics and wearable devices, various ultra-high-performance energy storage systems (lithium-ion batteries, fuel cells, supercapacitors, etc.) have developed rapidly over the past decade. Supercapacitors, as a promising energy storage device, have been widely used in uninterruptible power supplies, rail transportation, and other fields due to their high power density, fast charge and discharge performance, and long cycle life.

[0003] Due to their excellent electrical conductivity and mechanical properties, carbon nanofibers have become an attractive electrode material for portable electronic products and wearable devices (such as curved screens, smart watches, smart clothing, and sensor systems). However, the production cost of polyacrylonitrile, the precursor for carbon nanofibers, is high, and carbon nanofibers prepared from polyacrylonitrile have a low heteroatom content, which significantly reduces their electrochemical performance as supercapacitor electrode materials.

[0004] The prior art reports on the use of hot-solution extraction of organic solid waste and the subsequent preparation of the extract into carbon nanofibers, which on the one hand reduces the production cost of carbon nanofibers and on the other hand realizes the high added value utilization of biomass waste. However, in the existing studies on the production of extracts from various raw materials through hot-solution extraction and the further preparation of carbon nanofibers, the main focus has been on the effects of extracts from different types of raw materials (such as low-rank coal, biomass, etc.) on the mechanical properties of carbon nanofibers, as well as the feasibility of applying extract-based carbon fibers in the field of energy storage. For example, patent application document CN108281298A proposes a method for preparing carbon nanofibers from coal / biomass-based extracts, demonstrating that coal / biomass-based extracts have good thermoplasticity and can be prepared into carbon nanofibers by electrospinning and further applied to supercapacitors.

[0005] In addition, heteroatom (especially nitrogen) doping of carbon nanofibers has been shown to be an effective strategy to improve their electrochemical performance. However, achieving high nitrogen doping usually requires the addition of costly dopants during the thermochemical conversion stage. This additional doping step further increases the conditions and complexity of the manufacturing process, greatly limiting the large-scale preparation of heteroatom-doped carbon nanofibers. Summary of the Invention

[0006] The present invention is based on the inventor's discovery and understanding of the following facts and problems: Patent application document CN108281298A uses hot-solvent extraction of coal / biomass-based extracts and then further prepares carbon nanofibers, but does not focus on the doping of specific heteroatom nitrogen. Although other reports on the preparation of carbon nanofibers in the prior art have found that the doping of heteroatom nitrogen can improve the electrochemical properties of carbon nanofibers, the cost of achieving nitrogen doping is relatively high. Without the addition of additional nitrogen-containing chemical reagents, there is still a lack of a method that can achieve low-cost self-nitrogen doping of carbon nanofibers and at the same time enable the carbon nanofibers to have excellent energy storage properties.

[0007] The present invention aims to solve one of the technical problems in the related art to at least a certain extent. To this end, embodiments of the present invention provide a carbon nanofiber, a preparation method thereof, and a supercapacitor.

[0008] In a first aspect, an embodiment of the present invention provides a method for preparing carbon nanofibers, comprising the following steps: Step 1. Drying, crushing, and screening the kitchen waste in sequence to obtain kitchen waste powder; Step 2. performing hot solvent extraction on the kitchen waste powder using a non-polar organic solvent to obtain an extract; Step 3. electrospinning the extract to obtain extract raw fibers; Step 4. Pre-oxidizing the extract raw fibers in air to obtain a pre-oxidized product; carbonizing the pre-oxidized product under an inert atmosphere to obtain a carbonized product; and grinding the carbonized product to obtain carbon nanofibers.

[0009] The advantages and technical effects brought by the preparation method of the embodiment of the present invention are: (1) The preparation method of the embodiment of the present invention uses the extract obtained by hot-melt extraction of kitchen waste as the precursor for preparing carbon nanofibers. Compared with the process of preparing polyacrylonitrile by polymerization of acrylonitrile, the process is simple and easy, with low cost and easy to promote and apply.

[0010] (2) The preparation method of the embodiment of the present invention uses kitchen waste as raw material, which saves the cost of nitrogen-doping chemical reagents, and at the same time realizes the resource utilization of organic solid waste and reduces environmental pollution.

[0011] (3) Compared with other thermochemical conversion reactions, the preparation method of the embodiment of the present invention can promote the enrichment of nitrogen in kitchen waste into the extract through hot solvent extraction, thereby realizing the production of nitrogen-rich carbon nanofiber precursors and the application of organic solid waste in the field of energy storage.

[0012] In some embodiments, step 1 satisfies at least one of the following conditions: The kitchen waste is kitchen waste from a meat processing plant; The dry basis nitrogen content of the kitchen waste is greater than 12%; The holding temperature of the drying process is 60-100°C; The holding time of the drying process is 24 to 48 hours; The particle size of the kitchen waste powder is less than 200 μm.

[0013] In some embodiments, step 2 satisfies at least one of the following conditions: The non-polar organic solvent is kerosene, and the purity of the kerosene is ≥90%; The solid-liquid ratio of the kitchen waste powder to the non-polar organic solvent is 1:(8-12); The holding temperature of the hot-solution extraction is 350-375°C; The holding time of the hot-solution extraction is 1 to 2 hours.

[0014] In some embodiments, step 2 is specifically as follows: after uniformly mixing the kitchen waste powder and the non-polar organic solvent to obtain a mixture; transferring the mixture to a hot-solution extraction high-pressure reactor for hot-solution extraction, after the reaction is completed, opening the intermediate valve of the hot-solution extraction high-pressure reactor to transfer the high-temperature liquid phase to a receiving tank, and cooling to room temperature to obtain a liquid phase product; rotary evaporating the liquid phase product to obtain a solid phase product; and vacuum drying the solid phase product to obtain the extract.

[0015] In some embodiments, step 2 satisfies at least one of the following conditions: The holding temperature of the rotary evaporation is 130-140°C; The rotation speed of the rotary evaporation is 60-100 r / min; The time of the rotary evaporation is 0.5 to 2 hours; The vacuum drying temperature is 80-120°C. The vacuum drying temperature holding time is 12 to 24 hours.

[0016] In some embodiments, step 3 satisfies at least one of the following conditions: The amount of the extract used in a single electrospinning process is 1.5-2.5 mL; The positive electrode voltage used in the electrospinning is 18-22 kV; The cathode voltage used in the electrospinning process is -1.5 to -2.5 kV. The roller speed used in the electrospinning is 140-160 r / min; The propulsion speed adopted by the electrospinning is 1.1-1.3 mm / s.

[0017] In some embodiments, step 4 satisfies at least one of the following conditions: The heating rate of the pre-oxidation treatment is 0.8-1.2°C / min; The holding temperature of the pre-oxidation treatment is 200-300°C; The holding time of the pre-oxidation treatment is 1 to 2 hours; The heating rate of the carbonization treatment is 4-6°C / min; The holding temperature of the carbonization treatment is 700-900°C; The heat preservation time of the carbonization treatment is 1 to 2 hours.

[0018] In a second aspect, an embodiment of the present invention provides a carbon nanofiber obtained by the preparation method described in the first aspect.

[0019] The advantages and technical effects brought by the carbon nanofibers of the embodiments of the present invention are as follows: Since the carbon nanofibers are prepared by the preparation method of the first aspect, the production cost of the carbon nanofibers in the embodiment of the present invention is low, and since the carbon nanofibers are rich in nitrogen, they have good electrochemical properties.

[0020] In some embodiments, the nitrogen content in the carbon nanofibers is greater than 3%.

[0021] In a third aspect, an embodiment of the present invention provides a supercapacitor, wherein the electrodes of the supercapacitor include the carbon nanofibers described in the second aspect.

[0022] The advantages and technical effects brought by the supercapacitor of the embodiment of the present invention are as follows: Since the carbon nanofibers described in the second aspect are used as the supercapacitor electrode material, the supercapacitor of the embodiment of the present invention has low production cost and good electrochemical performance. DETAILED DESCRIPTION The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0023] In a first aspect, an embodiment of the present invention provides a method for preparing carbon nanofibers, comprising the following steps: Step 1. Drying, crushing, and screening the kitchen waste in sequence to obtain kitchen waste powder; Step 2. performing hot solvent extraction on the kitchen waste powder using a non-polar organic solvent to obtain an extract; Step 3. electrospinning the extract to obtain extract raw fibers; Step 4. Pre-oxidizing the extract raw fibers in air to obtain a pre-oxidized product; carbonizing the pre-oxidized product under an inert atmosphere to obtain a carbonized product; and grinding the carbonized product to obtain carbon nanofibers.

[0024] In step 1, according to the precursor characteristics required for carbon nanofibers, the extract prepared by hot-solution extraction of kitchen waste can be used as a more suitable carbon nanofiber precursor. Kitchen waste can provide sufficient nitrogen atoms for the extract obtained by hot-solution extraction, and hot-solution extraction can convert the original kitchen waste into a carbon nanofiber precursor with high carbon content, low ash content and hot-solubility properties.

[0025] In step 2, hot-solution extraction is used as a thermochemical conversion and disposal method for organic solid waste. The organic solid waste is hot-solution treated in a highly dispersed and thermally stable non-polar organic solvent. In this process, deoxidation and aromatization reactions mainly occur, converting the organic solid waste into a high-carbon, low-ash extract. Since the non-polar solvent does not participate in the chemical reaction, it can not only retain the heteroatoms in the organic solid waste in the extract as much as possible, but also the solvent can be easily recycled and reused, greatly reducing the production cost of the extract. In addition, the softening point of the extract produced by hot-solution is 150~250℃, which is similar to asphalt. The carbon content, ash content and softening point of the extract obtained in step 2 are all key parameters in the process of preparing carbon nanofibers. In addition, the hot-solution extraction of the kitchen waste powder in this step, rather than directly hot-solution extraction of the kitchen waste, is to improve the extraction yield.

[0026] In step 3, the extract is electrospun to prepare extract raw fibers in order to obtain nanofiber morphology.

[0027] In step 4, the extract raw fibers are subjected to pre-oxidation treatment and carbonization treatment to finally obtain carbon nanofibers.

[0028] The preparation method of the embodiment of the present invention improves the overall design of the process flow, uses kitchen waste as raw material, and uses a non-polar organic solvent as a hot-melt medium to perform hot-melt extraction on kitchen waste powder to obtain a high-carbon, low-ash, nitrogen-rich extract with hot-melt properties. The extract is further prepared into high-nitrogen carbon nanofibers through electrospinning, pre-oxidation treatment and carbonization treatment, achieving excellent electrochemical performance at a relatively low cost. It can not only solve the problem of efficient and clean disposal of kitchen waste, but also provide a new preparation method for supercapacitor electrode materials, realizing practical applications in the field of energy storage and conversion, and has high economic value and practical value.

[0029] In the preparation methods of the embodiments of the present invention, any food waste can be used as raw material, generally with a dry-basis nitrogen content of 4% or more. Examples include discarded fruits and vegetables (e.g., with a dry-basis nitrogen content of approximately 4%), household food waste (e.g., with a dry-basis nitrogen content of approximately 8%), and food waste from meat processing plants (e.g., with a dry-basis nitrogen content of approximately 14%). In some embodiments, in step 1, the food waste is food waste from meat processing plants. Food waste contains varying amounts of nitrogen, primarily derived from the lignocellulose and protein components (such as vegetable leaves and meat) in the food waste. The nitrogen content depends on the content of these components in the food waste. Food waste from specific scenarios, such as food waste from meat processing plants, has a higher dry-basis nitrogen content, making it nitrogen-rich, which helps increase the nitrogen content in carbon nanofibers.

[0030] In some embodiments, in step 1, the dry basis nitrogen content of the kitchen waste is greater than 8%, for example, 8%, 10%, 12%, 13%, 14%, etc. This nitrogen content indicates that the waste is nitrogen-rich kitchen waste, which is beneficial to increasing the nitrogen content in the carbon nanofibers.

[0031] In some embodiments, in step 1, the drying process is maintained at a temperature of 60°C to 100°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, etc. If the drying process is maintained at a temperature that is too low, it is not conducive to reducing the moisture content of the food waste, thereby hindering subsequent hot solvent extraction. If the drying process is maintained at a temperature that is too high, it is not conducive to reducing costs and increasing efficiency.

[0032] In some embodiments, in step 1, the drying treatment is carried out for a holding time of 24 to 48 hours, for example, 24 hours, 30 hours, 35 hours, 40 hours, 45 hours, 48 ​​hours, etc. If the drying treatment holding time is too short, it is not conducive to reducing the moisture content of the food waste, thereby hindering subsequent hot solvent extraction. If the drying treatment holding time is too long, it is not conducive to reducing costs and increasing efficiency.

[0033] In some embodiments, in step 1, the particle size of the food waste powder is 200 μm or less, for example, 50 μm, 100 μm, 150 μm, 200 μm, etc. If the particle size of the food waste powder is too small, it tends to agglomerate, which is not conducive to subsequent hot-solvent extraction. If the particle size of the food waste powder is too large, the contact area between the non-polar organic solvent and the food waste powder during subsequent hot-solvent extraction is too small, which is also not conducive to improving extraction efficiency.

[0034] In some embodiments, in step 2, the non-polar organic solvent is kerosene, and the purity of the kerosene is ≥90%. Kerosene is relatively inexpensive compared to other non-polar solvents and is therefore preferred as the hot melt medium. Using high-purity kerosene as the hot melt medium can reduce the impurity content in the extract.

[0035] In some embodiments, in step 2, the solid-to-liquid ratio of the kitchen waste powder to the non-polar organic solvent is 1:(8-12), such as 1:8, 1:9, 1:10, 1:11, 1:12, etc. When this solid-to-liquid ratio is too low, the amount of non-polar organic solvent is excessive, resulting in excessive solvent recovery. When this solid-to-liquid ratio is too high, the amount of non-polar organic solvent is insufficient, which is not conducive to improving the yield of the extract.

[0036] In some embodiments, in step 2, the holding temperature of the hot-solution extraction is 350°C to 375°C, for example, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C, etc. If the holding temperature of the hot-solution extraction is too low, it is not conducive to improving the extraction efficiency. If the holding temperature of the hot-solution extraction is too high, it is not conducive to reducing costs and increasing efficiency.

[0037] In some embodiments, in step 2, the holding time of the hot-solution extraction is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, 2 hours, etc. When the holding time of the hot-solution extraction is too short, it is not conducive to improving the yield of the extract. When the holding time of the hot-solution extraction is too long, it is not conducive to reducing costs and increasing efficiency.

[0038] In some embodiments, step 2 specifically comprises: uniformly mixing the kitchen waste powder with the non-polar organic solvent to obtain a mixture; transferring the mixture to a hot-solution extraction autoclave for hot-solution extraction; after the reaction is completed, opening the intermediate valve of the hot-solution extraction autoclave to transfer the high-temperature liquid phase to a receiving tank, and cooling to room temperature to obtain a liquid phase product; rotary evaporating the liquid phase product to obtain a solid phase product; and vacuum drying the solid phase product to obtain the extract. During the hot-solution extraction process, a filter is provided at the upper end of the intermediate valve. When the intermediate valve is opened, in-situ separation of the solid and liquid phase products is achieved, and the extract in the liquid phase product can have low ash and high carbon characteristics.

[0039] In some embodiments, in step 2, the rotary evaporation temperature is 130-140°C, for example, 130°C, 132°C, 134°C, 136°C, 138°C, 140°C, etc. If the rotary evaporation temperature is too low, it is not conducive to improving the extraction efficiency of the extract. If the rotary evaporation temperature is too high, it is not conducive to reducing costs and increasing efficiency.

[0040] In some embodiments, in step 2, the rotary evaporation speed is 60-100 r / min, for example, 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, etc. If the rotary evaporation speed is too slow, it is not conducive to improving the extraction efficiency of the extract. If the rotary evaporation speed is too high, it is not conducive to reducing costs and increasing efficiency.

[0041] In some embodiments, in step 2, the rotary evaporation time is 0.5 to 2 hours, for example, 0.5 hours, 0.8 hours, 1 hour, 1.5 hours, 2 hours, etc. When the rotary evaporation time is too short, it is not conducive to improving the yield of the extract. When the rotary evaporation time is too long, it is not conducive to improving production efficiency.

[0042] In some embodiments, in step 2, the vacuum drying is performed at a holding temperature of 80°C to 120°C, such as 80°C, 90°C, 100°C, 110°C, 120°C, etc. If the vacuum drying holding temperature is too low, it is not conducive to improving drying efficiency. If the vacuum drying holding temperature is too high, it is not conducive to reducing costs and increasing efficiency.

[0043] In some embodiments, in step 2, the vacuum drying holding time is 12 to 24 hours, for example, 12 hours, 15 hours, 20 hours, 24 hours, etc.

[0044] In some embodiments, step 3 satisfies at least one of the following conditions: The amount of the extract used in a single electrospinning process is 1.5-2.5 mL; The positive electrode voltage used in the electrospinning is 18-22 kV; The cathode voltage used in the electrospinning process is -1.5 to -2.5 kV. The roller speed used in the electrospinning is 140-160 r / min; The propulsion speed adopted by the electrospinning is 1.1-1.3 mm / s.

[0045] In some embodiments, step 4 satisfies at least one of the following conditions: The heating rate of the pre-oxidation treatment is 0.8-1.2°C / min; The holding temperature of the pre-oxidation treatment is 200-300°C; The holding time of the pre-oxidation treatment is 1 to 2 hours; The heating rate of the carbonization treatment is 4-6°C / min; The holding temperature of the carbonization treatment is 700-900°C; The heat preservation time of the carbonization treatment is 1 to 2 hours.

[0046] In a second aspect, an embodiment of the present invention provides a carbon nanofiber obtained by the preparation method described in the first aspect.

[0047] Since the carbon nanofibers are prepared by the preparation method of the first aspect, the production cost of the carbon nanofibers in the embodiment of the present invention is low, and since the carbon nanofibers are rich in nitrogen, they have good electrochemical properties.

[0048] In some embodiments, the nitrogen content in the carbon nanofibers is greater than 3%, indicating that the carbon nanofibers have sufficient electrochemical active sites, thereby improving the storage capacity of electrolyte ions and pseudocapacitance.

[0049] In a third aspect, an embodiment of the present invention provides a supercapacitor, wherein the electrodes of the supercapacitor include the carbon nanofibers described in the second aspect.

[0050] Since the carbon nanofibers described in the second aspect are used as the supercapacitor electrode material, the supercapacitor of the embodiment of the present invention has low production cost and good electrochemical performance.

[0051] The present invention is described in detail below with reference to the embodiments.

[0052] Example 1 Kitchen waste from a meat processing plant (dry basis nitrogen content of 13.9 wt%) was collected and dried in an oven at 80°C for 24 h. To achieve better reaction uniformity, the dried nitrogen-rich kitchen waste was crushed using a crusher, and then samples with a particle size of <200 μm were screened out for use.

[0053] The nitrogen-rich food waste powder was mixed with 90% pure kerosene at a solid-to-liquid ratio of 1:10. The mixture was then hot-melt extracted in a stainless steel autoclave, heated to a predetermined temperature of 350°C for 1.5 hours. After the reaction, the intermediate valve was opened and the hot liquid product was transferred to a receiving tank and cooled to room temperature. The liquid product was then rotary evaporated at 140°C and 80 rpm for 1 hour. The resulting extract was transferred to a Petri dish and dried in a vacuum drying oven at 80°C for 12 hours.

[0054] 2 mL of the extract was then drawn into a syringe as the spinning solution. This solution was then fed into an electrospinning device at a speed of 1.2 mm / s. The positive and negative electrodes of the electrospinning device were set at 20 kV and -2 kV, respectively, and the roller speed was 150 rpm. During spinning, elliptical cone droplets were continuously formed, and mist-like filaments were ejected from the cone surface. Simultaneously, filaments were continuously collected by the roller. Spinning ended when the spinning solution was exhausted, resulting in carbon nanofiber precursors.

[0055] The electrospun carbon nanofiber precursors were then placed in a horizontal tube furnace and pre-oxidized in air. The temperature was increased from room temperature to 200°C at a rate of 1°C / min and maintained at this temperature for 1.5 hours. Immediately after the pre-oxidation reaction, the atmosphere was switched to an inert atmosphere for carbonization. The temperature was increased to 700°C at a rate of 5°C / min and maintained at this temperature for 2 hours. After the carbonization reaction, the solid product was cooled to room temperature to obtain carbon nanofibers, which are suitable electrode materials for supercapacitors.

[0056] The electrochemical properties of the supercapacitor electrode material prepared in this example are as follows: When nitrogen-doped (with a nitrogen content of 3.26 wt%), the material exhibits excellent specific capacitance and conductivity. After assembly, it has a specific capacitance of 270 F / g and an impedance of 0.92 Ω.

[0057] Example 2 Waste fruits and vegetables (dry basis nitrogen content of 4.3 wt%) were collected and dried in an oven at 80 °C for 24 h. The dried nitrogen-rich kitchen waste was crushed using a crusher, and then samples with a particle size of <200 μm were screened for use.

[0058] The nitrogen-rich food waste powder was mixed with 90% pure kerosene at a solid-to-liquid ratio of 1:10. The mixture was then hot-melt extracted in a stainless steel autoclave, heated to a predetermined temperature of 375°C for 2 hours. After the reaction, the intermediate valve was opened and the hot liquid product was transferred to a receiving tank and cooled to room temperature. The liquid product was then rotary evaporated at 140°C and 80 rpm for 1 hour. The resulting extract was transferred to a Petri dish and dried in a vacuum drying oven at 80°C for 12 hours.

[0059] 2.5 mL of the extract was then drawn into a syringe as the spinning solution. This solution was then pushed into an electrospinning device at a speed of 1.2 mm / s. The positive and negative electrodes of the electrospinning device were set at 20 kV and -2 kV, respectively, and the roller rotated at 150 rpm. During spinning, elliptical cone droplets were continuously formed, and mist-like filaments were ejected from the cone surface. Simultaneously, filaments were continuously collected by the roller. Spinning ended when the spinning solution was exhausted, resulting in carbon nanofiber precursors.

[0060] The electrospun carbon nanofiber precursors were then placed in a horizontal tube furnace and pre-oxidized in air. The temperature was increased from room temperature to 300°C at a rate of 1°C / min and maintained at this temperature for 2 hours. Immediately after the pre-oxidation reaction, the atmosphere was switched to an inert atmosphere for carbonization. The temperature was increased to 900°C at a rate of 5°C / min and maintained at this temperature for 2 hours. After the carbonization reaction, the solid product was cooled to room temperature to obtain carbon nanofibers, which are suitable electrode materials for supercapacitors.

[0061] The electrochemical properties of the supercapacitor electrode material prepared in this example are as follows: When nitrogen-doped (with a nitrogen content of 1.92 wt%), the material exhibits excellent specific capacitance and conductivity. After assembly, it has a specific capacitance of 249 F / g and an impedance of 0.82 Ω.

[0062] Example 3 Domestic waste kitchen waste (dry basis nitrogen content of 8.0 wt%) was dried in an oven at 80°C for 24 h. The dried nitrogen-rich kitchen waste was crushed using a crusher, and then samples with a particle size of <200 μm were screened out for use.

[0063] The nitrogen-rich food waste powder was mixed with 90% pure kerosene at a solid-to-liquid ratio of 1:10. The mixture was then hot-melt extracted in a stainless steel autoclave, heated to a predetermined temperature of 375°C for 1.5 hours. After the reaction, the intermediate valve was opened and the hot liquid product was transferred to a receiving tank, where it was cooled to room temperature. The liquid product was then rotary evaporated at 140°C and 80 rpm for 1 hour. The resulting extract was transferred to a Petri dish and dried in a vacuum drying oven at 80°C for 12 hours.

[0064] 2.5 mL of the extract was then drawn into a syringe as the spinning solution. This solution was then pushed into an electrospinning device at a speed of 1.2 mm / s. The positive and negative electrodes of the electrospinning device were set at 20 kV and -2 kV, respectively, and the roller rotated at 150 rpm. During spinning, elliptical cone droplets were continuously formed, and mist-like filaments were ejected from the cone surface. Simultaneously, filaments were continuously collected by the roller. Spinning ended when the spinning solution was exhausted, resulting in carbon nanofiber precursors.

[0065] The electrospun carbon nanofiber precursors were then placed in a horizontal tube furnace and pre-oxidized in air. The temperature was increased from room temperature to 250°C at a rate of 1°C / min and maintained at this temperature for 1.5 hours. Immediately after the pre-oxidation reaction, the atmosphere was switched to an inert atmosphere for carbonization. The temperature was increased to 800°C at a rate of 5°C / min and maintained at this temperature for 1.5 hours. After the carbonization reaction, the solid product was cooled to room temperature to obtain carbon nanofibers, which are suitable electrode materials for supercapacitors.

[0066] The electrochemical properties of the supercapacitor electrode material prepared in this example are as follows: When nitrogen-doped (with a nitrogen content of 2.44 wt%), the material exhibits excellent specific capacitance and conductivity. After assembly, it has a specific capacitance of 256 F / g and an impedance of 0.85 Ω.

[0067] Comparative Example 1 The preparation method of this comparative example is the same as that of Example 1, except that coal is used instead of the kitchen waste from the meat processing plant in Example 1.

[0068] Comparative Example 2 The preparation method of this comparative example is the same as that of Example 1, except that a mixture of sawdust and rice husks in a mass ratio of 1:1 is used instead of the kitchen waste from the meat processing plant in Example 1.

[0069] Comparative Example 3 0.7 g of polyacrylonitrile and 9.3 g of dimethylformamide were mixed, incubated in a 60°C water bath for 3 hours, and then slowly stirred to obtain a polyacrylonitrile spinning solution. The polyacrylonitrile spinning solution was then electrospun using the same electrospinning parameters as in Example 1 to produce carbon nanofibers for use as supercapacitor electrode materials.

[0070] Table 1. Physical parameters and electrochemical properties of supercapacitor electrode materials in various embodiments and comparative examples

[0071] *: The specific capacitance test condition in all embodiments and comparative examples is a current density of 1 A / g.

[0072] In the present invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless they are mutually inconsistent.

[0073] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing carbon nanofibers, characterized in that: The following steps are involved: Step 1. Drying, crushing, and screening the kitchen waste in sequence to obtain kitchen waste powder; Step 2. performing hot solvent extraction on the kitchen waste powder using a non-polar organic solvent to obtain an extract; Step 3. electrospinning the extract to obtain extract raw fibers; Step 4. pre-oxidizing the extract raw silk in air to obtain a pre-oxidized product; The pre-oxidation product is carbonized under an inert atmosphere to obtain a carbonized product and carbon nanofibers.

2. The preparation method according to claim 1, wherein Step 1: At least one of the following conditions must be met: The kitchen waste is kitchen waste from a meat processing plant; The dry basis nitrogen content of the kitchen waste is greater than 12%; The holding temperature of the drying process is 60-100°C; The holding time of the drying process is 24 to 48 hours; The particle size of the kitchen waste powder is less than 200 μm.

3. The preparation method according to claim 1, wherein Step 2: At least one of the following conditions must be met: The non-polar organic solvent is kerosene, and the purity of the kerosene is ≥90%; The solid-liquid ratio of the kitchen waste powder to the non-polar organic solvent is 1:(8-12); The holding temperature of the hot-solution extraction is 350-375°C; The holding time of the hot-solution extraction is 1 to 2 hours.

4. The preparation method according to claim 1, wherein Step 2 is specifically as follows: after uniformly mixing the kitchen waste powder and the non-polar organic solvent, a mixture is obtained; the mixture is transferred to a hot-solution extraction high-pressure reactor for hot-solution extraction. After the reaction is completed, the intermediate valve of the hot-solution extraction high-pressure reactor is opened to transfer the high-temperature liquid phase to a receiving tank, and cooled to room temperature to obtain a liquid phase product; the liquid phase product is rotary evaporated to obtain a solid phase product; and the solid phase product is vacuum dried to obtain the extract.

5. The preparation method according to claim 4, wherein: Step 2: At least one of the following conditions must be met: The holding temperature of the rotary evaporation is 130-140°C; The rotation speed of the rotary evaporation is 60-100 r / min; The time of the rotary evaporation is 0.5 to 2 hours; The vacuum drying temperature is 80-120°C. The vacuum drying temperature holding time is 12 to 24 hours.

6. The preparation method according to claim 1, wherein Step 3: At least one of the following conditions must be met: The amount of the extract used in a single electrospinning process is 1.5-2.5 mL; The positive electrode voltage used in the electrospinning is 18-22 kV; The cathode voltage used in the electrospinning process is -1.5 to -2.5 kV. The roller speed used in the electrospinning is 140-160 r / min; The propulsion speed adopted by the electrospinning is 1.1-1.3 mm / s.

7. The preparation method according to claim 1, wherein Step 4: At least one of the following conditions must be met: The heating rate of the pre-oxidation treatment is 0.8-1.2°C / min; The holding temperature of the pre-oxidation treatment is 200-300°C; The holding time of the pre-oxidation treatment is 1 to 2 hours; The heating rate of the carbonization treatment is 4-6°C / min; The holding temperature of the carbonization treatment is 700-900°C; The heat preservation time of the carbonization treatment is 1 to 2 hours.

8. A carbon nanofiber, characterized in that Obtained by the preparation method according to any one of claims 1 to 7.

9. The carbon nanofiber according to claim 8, wherein The nitrogen content in the carbon nanofibers is greater than 3%.

10. A supercapacitor, characterized in that: The electrode of the supercapacitor comprises the carbon nanofiber according to claim 8 or 9.

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