A method for preparing boron-doped porous graphene from lignin and products thereof

Abstract

The application belongs to the technical field of lignin application and graphene preparation, and particularly relates to a method for preparing boron-doped porous graphene from lignin and a product thereof. The method comprises the following steps: lignin and an alkaline metal additive are dissolved in deionized water, uniformly stirred, and then freeze-dried to obtain pretreated lignin powder; the pretreated lignin powder is pyrolyzed and carbonized under an inert atmosphere to obtain lignin pyrolysis carbon; the lignin pyrolysis carbon is stirred in a hydrochloric acid solution, and then washed, filtered and dried to obtain purified lignin pyrolysis carbon; the purified lignin pyrolysis carbon is mixed with a boron catalyst to perform a joule heat flash evaporation reaction, and boron-doped porous graphene is obtained. The application designs a novel process method, prepares boron-doped graphene with low density, high porosity and uniformity, and solves the problems of high preparation cost, complex process, uneven quality and narrow method applicability of graphene in the prior art.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lignin application and graphene preparation, and particularly relates to a method for preparing boron-doped porous graphene from lignin and a product. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the application and does not necessarily pertain to the prior art.

[0003] Graphene is a two-dimensional honeycomb hexagonal lattice structure composed of carbon atoms, which has excellent electrical conductivity, mechanical strength, thermal conductivity, transparency and chemical reactivity, and has many applications in electronic devices, sensors, energy storage technology, strength materials and optical devices. At present, the main methods for preparing graphene include mechanical exfoliation, chemical vapor deposition, oxidation-reduction and electron beam evaporation, but all have problems such as high raw material cost, complex process and high energy consumption. Therefore, it is urgent to develop a green, low-cost and rapid method for preparing high-quality graphene.

[0004] Lignin is the only renewable aromatic polymer in nature, with a carbon content of up to 60% and abundant industrial reserves, and is an ideal precursor for preparing graphene due to its low price. However, the functional groups and bond structures of lignin are complex, and the oxygen content is high, which makes it more difficult to graphitize than fossil raw materials or other biomass.

[0005] Patent application No. CN 105439135 A discloses a method for preparing graphene from lignin. The method first pretreats lignin with an alkaline solution, then adds a metal catalyst, uses a high-pressure homogenizer to homogenize and crack, and then puts the mixture into an autoclave for high-temperature and high-pressure treatment under an inert atmosphere to obtain graphene. This method is complicated and requires high equipment and catalyst costs.

[0006] Patent application No. CN 107235484 A discloses a method for preparing graphene from black liquor crude lignin. The method first pretreats black liquor crude lignin into alkali lignin, then adds a composite expansion catalyst composed of a metal salt and an expanding agent, and sintered at above 1000℃ for several hours under an inert atmosphere to obtain a graphene sample. This method has high energy consumption, high preparation cost of the composite catalyst and low preparation efficiency.

[0007] The patent application with the publication number CN112265983A discloses a lignin graphene and a preparation method thereof. The method first ball-mills the lignin and compresses it into a thin sheet, and then obtains a graphene powder by laser irradiation. The laser equipment used in the method has high purchase and maintenance cost, and the control parameters are complex, which is not suitable for large-scale high-temperature synthesis.

[0008] The patent application with the publication number CN115676811A discloses a method for preparing graphene from lignin. The method first pretreats the lignin with nitric acid to obtain a black solid phase, then hydrothermally treats it to obtain water-soluble graphene, and finally obtains graphene carbon quantum dots through dialysis and drying. The graphene product prepared by the method has a small size and a low yield, and the nitric acid environment is harmful.

[0009] Jiang et al. (Carbon 144 (2019) 241-248) reported a method for converting lignin / oxidized graphene composite (GO-Lignin) into graphitic carbon material by Joule heating. The method mixes lignin and oxidized graphene at a ratio of 1:1, compresses them into a thin film, and then heats the material by passing electricity to obtain a carbon film with a certain degree of graphitization. However, the product prepared by this method is not graphene, and graphene is needed as a raw material.

[0010] Chen et al. (ACS nano, 2022, 16 (4): 6646-6656.) reported a method for converting plastic into boron-doped graphene. The method mixes plastic with carbon black and boric acid, and converts it into vortex graphene by millisecond high-temperature flash evaporation. However, the raw material used in this method is plastic, which needs to add carbon black as a conductive agent, and boric acid is used as a dopant. Compared with the ordered structure of plastic, lignin is difficult to graphitize, and carbon particles are easy to aggregate. Using this method, even if graphitic carbon is prepared, it is also difficult to obtain a graphene thin layer by exfoliation.

[0011] In summary, it is difficult to efficiently and low-costly prepare graphene from lignin as the only carbon source in the prior art, which cannot meet the high-value utilization of lignin and the green, low-cost and rapid preparation of graphene. SUMMARY

[0012] In order to solve the problems of the prior art, the purpose of the present application is to provide a method for preparing boron-doped porous graphene from lignin and a product. The present application designs a new process to prepare boron-doped graphene with low density, high porosity and uniformity, which solves the problems of high cost, complex process and uneven quality of graphene in the prior art, and the narrow applicability of the method.

[0013] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0014] In a first aspect, the present application provides a method for preparing boron-doped porous graphene from lignin, comprising the following steps:

[0015] S1, dissolving lignin and alkaline metal additives in deionized water, stirring uniformly, and freeze-drying to obtain pretreated lignin powder;

[0016] S2, pyrolyzing and carbonizing the pretreated lignin powder under an inert atmosphere to obtain lignin pyrolysis carbon;

[0017] S3, stirring the lignin pyrolysis carbon in a hydrochloric acid solution, and then washing, filtering, and drying to obtain purified lignin pyrolysis carbon;

[0018] S4, mixing the purified lignin pyrolysis carbon with a boron catalyst, and performing a joule heat flash evaporation reaction to obtain boron-doped porous graphene.

[0019] In a second aspect, the present application provides boron-doped porous graphene obtained by the method of the first aspect.

[0020] The beneficial effects achieved by one or more technical solutions of the present application are as follows:

[0021] 1. The present application uses alkaline metal additives to thin the lignin precursor, and obtains carbon nanosheets after preliminary carbonization. The carbon nanosheets have a two-dimensional morphology, a porous structure, and strong electrical conductivity. Joule heating can instantly heat the carbon nanosheets to an ultra-high temperature (above 2000℃), so that the carbon skeleton is fully broken and rearranged. The boron catalyst reacts with carbon at such an extremely high temperature to form boron carbide, which further separates carbon atoms and rearranges to form a graphene layer, while boron atoms are embedded in the graphite lattice. Finally, the boron-doped porous graphene product is obtained. The above principle makes the preparation method suitable for various industrial lignins, and can flexibly control the graphitization degree, pore structure, and doping site of the carbon product.

[0022] 2. The boron-doped porous graphene prepared by the present application has a high degree of graphitization, rich pore structure, and boron doping sites. Compared with existing lignin-based graphene products, the preparation efficiency is higher, the cost is lower, the ductility is better, and the graphene structure characteristics are more in line with the graphene structure characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0023] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the description of the exemplary embodiments of the present application and their description serve to explain the present application, and do not constitute an improper limitation of the present application.

[0024] Figure 1 Flowchart of the method for preparing boron-doped porous graphene from lignin of the present application;

[0025] Figure 2This is a microscopic morphology of boron-doped porous graphene prepared from lignin prepared in Example 1 of the present invention;

[0026] Figure 3 This is a microscopic morphology of boron-doped porous graphene prepared from lignin obtained in Example 2 of the present invention;

[0027] Figure 4 This is a microscopic morphology of boron-doped porous graphene prepared from lignin obtained in Example 3 of the present invention;

[0028] Figure 5 This is a microscopic morphology of the carbon product prepared in Comparative Example 1 of the present invention;

[0029] Figure 6 This is a microscopic morphology of the carbon product prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0030] A first typical embodiment of the present invention is as follows Figure 1 As shown, a method for preparing boron-doped porous graphene from lignin comprises the following steps:

[0031] S1, dissolving lignin and alkaline metal additives in deionized water, stirring evenly and freeze-drying to obtain pretreated lignin powder;

[0032] S2, pyrolyzing and carbonizing the pretreated lignin powder under an inert atmosphere to obtain lignin pyrolysis charcoal;

[0033] S3, stirring the lignin pyrolytic carbon in a hydrochloric acid solution, and then washing, filtering, and drying to obtain purified lignin pyrolytic carbon;

[0034] S4. Mixing the purified lignin pyrolysis carbon with a boron catalyst, performing a Joule heat flash reaction, and obtaining boron-doped porous graphene.

[0035] In the present invention, the alkaline metal additive can promote the dissolution and dispersion of lignin in the aqueous solution, making the freeze-dried lignin sample flaky, achieving the thinning treatment of the precursor, and serving as a carbonization template; the pretreated lignin is pre-carbonized in a tubular furnace to remove volatiles, enhance conductivity, stabilize the morphology of the carbon material, and preliminarily produce carbon nanosheets; the Joule heat flash reaction can heat the carbon nanosheets to above 2000°C in a very short time, and the boron catalyst can catalyze the graphitization of the carbon nanosheets within this temperature range, ultimately breaking the C-C bond of the benzene ring and reorganizing it into sp 2 Hybrid graphene sheets.

[0036] In one or more embodiments of the embodiment, the lignin comprises at least one of alkali lignin, Kraft lignin, organic solvent lignin, lignin sulfonate and hydrolysis lignin. The lignin used in the application is an industrial by-product, which is cheap and easy to obtain.

[0037] In one or more embodiments of the embodiment, the alkaline metal additive comprises at least one of potassium acetate, potassium hydroxide, potassium carbonate and sodium hydroxide. The alkaline metal additive used in the application is cheap and easy to obtain, has high solubility, is easy to operate and has a wide range of applications.

[0038] In one or more embodiments of the embodiment, the concentration of lignin dissolved in deionized water is 5-20 mg / mL; the mass ratio of lignin to alkaline metal additive is 20:1-1:2, preferably 5:1-1:1. The application has researched and designed the ratio of lignin and alkaline metal additive, and obtained a better mixing ratio, so as to ensure that the lignin is fully dispersed in the solution. The above-mentioned lignin concentration can ensure the full dispersion and mixing of the material, and reduce the drying time. The above-mentioned ratio of lignin to alkaline metal additive can ensure that the lignin is fully dissolved and dispersed in the aqueous solution, and porous carbon nanosheets are prepared, which reduces the processing energy consumption and equipment corrosion. When the lignin is higher than the above-mentioned range, or when the alkaline metal additive is lower than the above-mentioned range, the lignin cannot be fully dispersed in the aqueous solution.

[0039] In one or more embodiments of the embodiment, in step S1, the vacuum degree of freeze-drying is 1.0x10 -5 -2.0x10 -5 bar, the freezing temperature is -60 to -70℃, the freezing time is 1h, and the drying temperature is 15-25℃, and the drying time is 24-48h. By controlling the parameters of freeze-drying, the pretreated lignin powder is fully dried.

[0040] In one or more embodiments of the embodiment, in step S2, the pyrolysis temperature is 700-900℃, the heating rate is 5-20℃ / min, and the holding time is 30-120min. The application has researched and designed the lignin pre-carbonization process, and obtained better process parameters, so as to ensure that the volatile matter is fully released, and the electrical conductivity of lignin pyrolysis carbon meets the requirements of Joule heat flash evaporation reaction. When the pyrolysis temperature and holding time are lower than the above-mentioned range, or the heating rate is higher than the above-mentioned range, lignin pyrolysis carbon with good electrical conductivity cannot be obtained.

[0041] In one or more embodiments of the embodiment, in step S3, the molar concentration of the hydrochloric acid solution is 0.05-0.2 mol / L, the mass ratio of the lignin pyrolytic carbon to the hydrochloric acid solution is 1:50-1:200, the stirring speed is 300-800 rad, and the stirring time is 2-4 h; the washing is performed with 1-2 L of deionized water; and the drying temperature is 45-65°C, and the drying time is 24-48 h. The purification and drying process of the carbon nanosheets is researched and designed in the present application, and a better process is obtained to ensure that the inorganic components in the carbon nanosheets are completely removed. Otherwise, the inorganic impurities remain in the carbon nanosheets, which is not conducive to the graphitization of the subsequent carbon nanosheets.

[0042] In one or more embodiments of the embodiment, in step S4, the mass ratio of the purified lignin pyrolytic carbon to the boron catalyst, which is at least one of boric acid, sodium tetraborate, potassium tetraborate, ammonium borate, and boron oxide, is 20:1-2:1, and preferably 10:1-5:1. The proportion of the boron catalyst is researched and designed in the present application, and a better mixing ratio is obtained to ensure the graphitization effect of the carbon product. Otherwise, when the boron catalyst is lower than the above range, the graphitization degree of the carbon product is poor, and the content of the doped boron atoms is small.

[0043] In one or more embodiments of the embodiment, in step S4, the Joule heat flash evaporation reaction is performed by an electric flash evaporation reactor, the load of the electric flash evaporation reactor is 50-200 mg, the resistance range is 1-25Ω, the applied voltage range is 20-100 V, and the power-on time is 0.1-8 s. The Joule heat flash evaporation process is researched and designed in the present application, and better process parameters are obtained to ensure that the carbon material is heated to the required temperature for boron catalytic graphitization. Otherwise, when the mixture load, resistance is higher than the range, or the voltage, power-on time is lower than the range, the temperature or the heating rate will be low, and the graphene product cannot be obtained.

[0044] In a second typical embodiment of the present application, a boron-doped porous graphene is obtained by the method as described in the first typical embodiment. The boron-doped porous graphene has a high graphitization degree, ductility, and porosity.

[0045] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples and comparative examples.

[0046] Example 1

[0047] S1: Dissolve Kraft lignin and potassium carbonate in deionized water according to a preset mass ratio, stir uniformly, and obtain a mixed solution. Specifically, the mass of lignin added in each milliliter of water ranges from 5 mg. The mass ratio of lignin to potassium carbonate is 1:1. Place the mixed solution in a vacuum freeze-drying box for freeze-drying to obtain pretreated lignin powder. Specifically, the vacuum degree of the freeze-drying machine is 2.0 x 10 -5 bar, the freezing temperature is -70℃, the freezing time is 1 h, the drying temperature is 25℃, and the drying time is 48 h.

[0048] S2: Pyrolyze and carbonize the pretreated lignin powder in S1 under an inert atmosphere, and cool to obtain lignin pyrolysis carbon; specifically, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, and the holding time is 120 min.

[0049] S3: Stir, wash, filter, and dry the lignin pyrolysis carbon in S2 in a hydrochloric acid solution to obtain purified lignin pyrolysis carbon; specifically, the molar concentration of the hydrochloric acid solution is 0.2 mol / L, the mass ratio of the pyrolysis carbon to the hydrochloric acid solution is 1:200, the stirring speed is 800 rad, the stirring time is 4 h, the washing is performed with 2 L of deionized water, the drying temperature is 65℃, and the drying time is 48 h.

[0050] S4: Mix the purified lignin pyrolysis carbon in S3 with ammonium borate according to a certain proportion, place in an electric flash evaporation reactor, and obtain a boron-doped porous graphene product after heating. Specifically, the mass ratio of the purified lignin pyrolysis carbon to the ammonium borate is 10:1, the loading of the carbon / boron mixture in the electric flash evaporation reactor is 100 mg, the resistance range is 10Ω, the applied voltage range is 60 V, and the electrification time is 2 s.

[0051] The micro-morphology of the boron-doped porous graphene prepared in Example 1 is shown in FIG. 1. Figure 2 As can be seen, the boron-doped porous graphene presents a regular layered graphene folding morphology, and the honeycomb structure indicates that the graphene has abundant mesoporous structures.

[0052] Example 2

[0053] S1: Dissolve Kraft lignin and potassium carbonate in deionized water according to a preset mass ratio, stir uniformly, and obtain a mixed solution. Specifically, the mass of lignin added in each milliliter of water ranges from 5 mg. The mass ratio of lignin to potassium carbonate is 1:1. Place the mixed solution in a vacuum freeze-drying box for freeze-drying to obtain pretreated lignin powder. Specifically, the vacuum degree of the freeze-drying machine is 2.0 x 10 -5 bar, the freezing temperature is -70℃, the freezing time is 1 h, the drying temperature is 25℃, and the drying time is 48 h.

[0054] S2: pyrolyzing and carbonizing the pretreated lignin powder under inert atmosphere to obtain lignin pyrolysis carbon, and cooling to obtain lignin pyrolysis carbon; specifically, the pyrolysis temperature is 800 DEG C, the heating rate is 10 DEG C / min, and the holding time is 60 min.

[0055] S3: stirring, washing, filtering and drying the lignin pyrolysis carbon in the hydrochloric acid solution to obtain purified lignin pyrolysis carbon; specifically, the molar concentration of the hydrochloric acid solution is 0.1 mol / L, the mass ratio of the pyrolysis carbon to the hydrochloric acid solution is 1:100, the stirring speed is 800 rad, the stirring time is 4 h, the washing is performed with 2 L of deionized water, the drying temperature is 65 DEG C, and the drying time is 24 h.

[0056] S4: mixing the purified lignin pyrolysis carbon with sodium tetraborate according to a certain proportion, placing in an electric flash evaporation reactor, and heating after electrification to prepare a boron-doped porous graphene product; specifically, the mass ratio of the purified lignin pyrolysis carbon to sodium tetraborate is 5:1, the loading of the carbon / boron mixture in the electric flash evaporation reactor is 200 mg, the resistance range is 20 Ω, the applied voltage range is 80 V, and the electrification time is 1 s.

[0057] The micro-morphology of the boron-doped porous graphene prepared in Example 2 is shown in FIG. 2. Figure 3 As can be seen, the boron-doped porous graphene presents a turbo-banded graphene staggered morphology and has a rich pore structure.

[0058] Example 3

[0059] S1: dissolving hydrolysis lignin and sodium hydroxide in deionized water according to a preset mass ratio, stirring uniformly to obtain a mixed solution; specifically, the mass of lignin added in each milliliter of water ranges from 20 mg, and the mass ratio of lignin to sodium hydroxide is 5:1. The mixed solution is placed in a vacuum freeze-drying box for freeze-drying to obtain pretreated lignin powder; specifically, the vacuum degree of the freeze-drying machine is 2.0 x 10 -5 bar, the freezing temperature is -70 DEG C, the freezing time is 1 h, the drying temperature is 25 DEG C, and the drying time is 48 h.

[0060] S2: pyrolyzing and carbonizing the pretreated lignin powder under inert atmosphere to obtain lignin pyrolysis carbon, and cooling to obtain lignin pyrolysis carbon; specifically, the pyrolysis temperature is 700 DEG C, the heating rate is 5 DEG C / min, and the holding time is 60 min.

[0061] S3: stirring, washing, filtering and drying the lignin pyrolysis carbon in the hydrochloric acid solution to obtain purified lignin pyrolysis carbon; specifically, the molar concentration of the hydrochloric acid solution is 0.1 mol / L, the mass ratio of the pyrolysis carbon to the hydrochloric acid solution is 1:100, the stirring speed is 800 rad, the stirring time is 4 h, the washing is performed with 2 L of deionized water, the drying temperature is 65 DEG C, and the drying time is 24 h.

[0062] S4: The purified lignin pyrolysis carbon of S3 is mixed with boron oxide in a certain proportion, and is put into an electric flash evaporation reactor to prepare a boron-doped porous graphene product after heating. Specifically, the mass ratio of the purified lignin pyrolysis carbon to the boron oxide is 5:1, the loading of the carbon / boron mixture in the electric flash evaporation reactor is 50 mg, the resistance range is 5Ω, the applied voltage range is 30V, and the electrification time is 4s.

[0063] The micro-morphology of the boron-doped porous graphene prepared in Example 3 is shown in FIG. 3. As can be seen, the boron-doped porous graphene presents a folded and stacked morphology of graphene sheets, and has high ductility. Figure 4

[0064] Comparative Example 1

[0065] No boron catalyst is added in the present comparative example.

[0066] S1: Alkaline lignin and potassium carbonate are dissolved in deionized water in a predetermined mass ratio, and are stirred uniformly to obtain a mixed solution. Specifically, the mass of lignin added in each milliliter of water ranges from 5 mg. The mass ratio of lignin to potassium carbonate is 1:1. The mixed solution is put into a vacuum freeze-drying box to obtain a pretreated lignin powder. Specifically, the vacuum degree of the freeze-drying machine is 2.0×10 -5 bar, the freezing temperature is -70℃, the freezing time is 1h, the drying temperature is 25℃, and the drying time is 48h.

[0067] S2: The pretreated lignin powder of S1 is pyrolyzed and carbonized under an inert atmosphere to obtain lignin pyrolysis carbon; specifically, the pyrolysis temperature is 900℃, the heating rate is 5℃ / min, and the holding time is 120min.

[0068] S3: The lignin pyrolysis carbon of S2 is stirred, washed, filtered and dried in a hydrochloric acid solution to obtain purified lignin pyrolysis carbon; specifically, the molar concentration of the hydrochloric acid solution is 0.2mol / L, the mass ratio of the lignin pyrolysis carbon to the hydrochloric acid solution is 1:200, the stirring speed is 800rad, the stirring time is 4h, the washing is performed with 2L of deionized water, the drying temperature is 65℃, and the drying time is 48h.

[0069] S4: The purified lignin pyrolysis carbon of S3 is put into an electric flash evaporation reactor to prepare a graphite carbon product after heating. Specifically, the loading of the purified lignin pyrolysis carbon in the electric flash evaporation reactor is 100mg, the resistance range is 10Ω, the applied voltage range is 60V, and the electrification time is 4s.

[0070] The micro-morphology of the carbon product prepared is shown in FIG. 4. Figure 5 ​As shown, it can be seen that when no boron catalyst is added, the carbon product obtained by electro-flash evaporation has a tendency to graphitize, but it is mainly composed of disordered microcrystalline graphite and turbostratic graphite structure, with a low degree of graphitization and no graphene is formed.

[0071] Comparative Example 2

[0072] No basic metal additive was added in this comparative example.

[0073] S1: Add Kraft lignin to deionized water and stir evenly to obtain a lignin suspension solution. Specifically, the mass range of lignin added per milliliter of water is 5 mg. The lignin solution is placed in a vacuum freeze drying box and freeze-dried to obtain pretreated lignin powder. Specifically, the vacuum degree of the freeze drying box is 2.0×10 -5 bar, freezing temperature is -70℃, freezing time is 1h, drying temperature is 25℃, drying time is 48h.

[0074] S2: Pyrolysis and carbonization of the pretreated lignin powder in S1 under an inert atmosphere, and cooling to obtain lignin pyrolysis charcoal; specifically, the pyrolysis temperature is 900° C., the heating rate is 5° C. / min, and the holding time is 120 min.

[0075] S3: The lignin pyrolytic charcoal described in S2 is stirred, washed, filtered, and dried in a hydrochloric acid solution to obtain purified lignin pyrolytic charcoal; specifically, the molar concentration of the hydrochloric acid solution is 0.2 mol / L, the mass ratio of pyrolytic charcoal to hydrochloric acid solution is 1:200, the stirring speed is 800 rad, the stirring time is 4 h, 2 L of deionized water is used for washing, the drying temperature is 65 ° C, and the drying time is 48 h.

[0076] S4: The purified lignin pyrolytic carbon described in S3 is mixed with boric acid in a certain proportion, placed in an electroflash reactor, and heated by electrical current to produce a boron-doped porous graphene product. Specifically, the mass ratio of the purified lignin pyrolytic carbon to boric acid is 10:1, the loading of the carbon / boron mixture in the electroflash reactor is 100 mg, the resistance range is 10 Ω, the applied voltage range is 60 V, and the power-on time is 2 seconds.

[0077] The microstructure of the obtained carbon product is as follows Figure 6 As shown in Figure 2, the carbon product exhibits a long-range ordered graphite lattice structure, and the degree of graphitization reaches 85%, but no two-dimensional graphene structure is formed.

[0078] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing boron-doped porous graphene from lignin, characterized in that: The following steps are involved: S1, dissolving lignin and alkaline metal additives in deionized water, stirring evenly and freeze-drying to obtain pretreated lignin powder; S2. Pyrolyzing and carbonizing the pretreated lignin powder under an inert atmosphere to obtain lignin pyrolysis charcoal; the pyrolysis temperature is 700-900 °C, the heating rate is 5-20 °C / min, and the holding time is 30-120 min; S3, stirring the lignin pyrolytic carbon in a hydrochloric acid solution, and then washing, filtering, and drying to obtain purified lignin pyrolytic carbon; S4. Mixing the purified lignin pyrolysis carbon with a boron catalyst and performing a Joule heating flash reaction to obtain boron-doped porous graphene; the Joule heating flash reaction is performed in an electric flash reactor with a loading capacity of 50-200 mg, a resistance range of 1-25 Ω, an applied voltage range of 20-100 V, and a power-on time of 0.1-8 s; The alkaline metal additive includes at least one of potassium acetate, potassium hydroxide, potassium carbonate and sodium hydroxide; The boron catalyst is at least one of boric acid, sodium tetraborate, potassium tetraborate, ammonium borate and boron oxide, and the mass ratio of purified lignin pyrolysis carbon to the boron catalyst is 20:1 to 2:

1.

2. The method according to claim 1, wherein The lignin includes at least one of alkali lignin, Kraft lignin, organosolv lignin, lignin sulfonate and hydrolyzed lignin.

3. The method according to claim 1, wherein The concentration of lignin dissolved in deionized water is 5-20 mg / mL; the mass ratio of lignin to the alkaline metal additive is 20:1-1:

2.

4. The method according to claim 1, wherein The mass ratio of lignin to alkaline metal additive is 5:1~1:

1.

5. The method according to claim 1, wherein In step S1, the vacuum degree of freeze drying is 1.0×10 -5 ~2.0×10 -5 bar, freezing temperature is -60~-70 ℃, freezing time is 1 h, drying temperature is 15~25 ℃, and drying time is 24~48 h.

6. The method according to claim 1, wherein In step S3, the molar concentration of the hydrochloric acid solution is 0.05-0.2 mol / L, the mass ratio of lignin pyrolysis carbon to the hydrochloric acid solution is 1:50-1:200, and the stirring time is 2-4 h; 1-2 L of deionized water is used for washing; the drying temperature is 45-65 °C, and the drying time is 24-48 h.

7. The method according to claim 1, wherein In step S4, the mass ratio of the purified lignin pyrolysis charcoal to the boron catalyst is 10:1 to 5:

1.

8. A boron-doped porous graphene, characterized in that: Obtained by the method according to any one of claims 1 to 7.

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