A polyacrylonitrile-based hydrogel and porous carbon material, and a preparation method and application thereof

Abstract

The present disclosure relates to a polyacrylonitrile-based hydrogel and porous carbon material, and a preparation method and application thereof, the method comprising the following steps: S1: mixing polyacrylonitrile raw material, biomass, graphene oxide and water to obtain a mixed solution; the mixed solution is subjected to hydrothermal treatment; the biomass comprises one or more of tannin compounds and lignin biomass. The polyacrylonitrile-based hydrogel is obtained by a one-step hydrothermal method, the preparation method is simple, the process is simple, it is green and non-toxic, the cost is low, and the problems of organic solvent pollution and difficult recovery are solved, and the product structure has good uniformity.

Description

Technical Field

[0001] This disclosure relates to the field of preparation of polyacrylonitrile-based hydrogels, specifically to a polyacrylonitrile-based hydrogel and a porous carbon material, as well as their preparation methods and applications. Background Technology

[0002] Supercapacitors are considered one of the most promising energy storage devices due to their ultra-high power density and long cycle life. However, the energy density of currently commercially available supercapacitors is still far lower than that of batteries, which greatly hinders their application. The electrode materials of supercapacitors determine their performance. Electrode materials are mostly carbon-based, and carbon-based materials containing heteroatoms enhance surface wettability and conductivity. Therefore, incorporating nitrogen into the carbon matrix is ​​crucial for enhancing capacitance performance. Polyacrylonitrile (PAC) has become a precursor material for preparing carbon materials, such as carbon fibers and carbon gels, due to its combined advantages of being nitrogen-rich, having tunable morphology, and relatively high carbon residue.

[0003] Currently, research and development trends using polyacrylonitrile (PA) as a precursor can be summarized in two aspects. Firstly, there is research on novel PA fiber forming processes, such as using plasticizers to synthesize PA copolymers to reduce the interaction between PA monomers and thus lower the polymer's melting point. This can be achieved by employing melt spinning processes or increasing the concentration of the spinning slurry in dry-jet wet spinning processes to improve the mechanical properties of the resulting fiber. Secondly, there is research on new varieties of PA fibers. Research on using PA materials as electrode materials in supercapacitors faces two main challenges. The first is obtaining PAN-based porous carbon fibers through electrospinning. The preparation of the spinning solution in electrospinning mainly involves dispersing PA in organic solvents (NN-dimethylacetamide, N-methylpyrrolidone, or N-dimethylformamide dimethyl sulfoxide) or inorganic solvents (sodium thiocyanate, zinc chloride). The first method uses large amounts of organic solvents, resulting in environmental pollution and time consumption. The second method uses inorganic solvents, which presents challenges such as difficult recovery, high requirements for spinning equipment materials, and complex operation. Another significant challenge is that polyacrylonitrile typically requires pre-oxidation in air at 250°C to prevent melting during subsequent high-temperature carbonization. Such approaches, methods, and techniques are not only time-consuming but also require stringent conditions, making it difficult to obtain a homogeneous mixture with the carbon precursor. This can lead to poor quality reproducibility of porous carbon prepared in different batches. Summary of the Invention

[0004] The purpose of this disclosure is to provide a polyacrylonitrile-based hydrogel and a porous carbon material, as well as their preparation method and application. The preparation method is green and non-toxic, the preparation process is simple, the product has a uniform structure and a high specific surface area, and it solves the problems of organic solvent pollution and difficult recycling.

[0005] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing polyacrylonitrile-based hydrogels, the method comprising the following steps:

[0006] S1: Polyacrylonitrile raw material, biomass, graphene oxide and water are mixed to obtain a mixed solution; the mixed solution is then subjected to hydrothermal treatment.

[0007] The biomass includes one or more of tannin compounds and lignin biomass.

[0008] Optionally, the tannin compounds are selected from one or more of condensed tannins, phenolic tannins, tannic acid, and gallic acid; the lignin biomass is selected from one or more of lignin, alkali lignin, lignin sulfate, lignin sulfonate, enzymatically hydrolyzed lignin, and organic solvent lignin; and the lignin sulfonate is selected from one or more of sodium lignin sulfonate and calcium lignin sulfonate.

[0009] Optionally, the polyacrylonitrile raw material is selected from one or more of polyacrylonitrile, acrylonitrile binary copolymer, and acrylonitrile terpolymer; the weight-average molecular weight of the polyacrylonitrile raw material is 8,000 to 250,000.

[0010] The acrylonitrile binary copolymer is a copolymer of acrylonitrile monomer and a second monomer; the acrylonitrile terpolymer is a copolymer of acrylonitrile monomer, a second monomer, and a third monomer.

[0011] The second monomer is one or more of methyl acrylate and methyl methacrylate; the third monomer is one or more of itaconic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, sodium p-methacrylamide benzene sulfonate, and methylvinylpyridine.

[0012] Optionally, the mass ratio of biomass to polyacrylonitrile raw material in S1 is 1:(0.5-5), and the oxygen content of graphene oxide is 10%-40%; the mixing time in S1 is 3-10h; the hydrothermal treatment conditions in S1 include a hydrothermal temperature of 120℃-180℃ and a hydrothermal time of 20h-40h.

[0013] Optionally, step S1 includes the following steps:

[0014] S1-1. The polyacrylonitrile raw material is first mixed with water and then ultrasonically dispersed to obtain a polyacrylonitrile aqueous system.

[0015] S1-2, Biomass and water are mixed a second time, and then ultrasonically dispersed to obtain a biomass-water system;

[0016] S1-3. Graphene oxide and water are mixed for the third time and then ultrasonically dispersed to obtain the graphene oxide system.

[0017] S1-4. The polyacrylonitrile aqueous system, biomass aqueous system and graphene oxide system obtained above are mixed for the fourth time to obtain the mixed solution;

[0018] The concentration of the graphene oxide system is 1 mg / mL to 6 mg / mL.

[0019] The second aspect of this disclosure provides a polyacrylonitrile-based hydrogel prepared by the method described in the first aspect of this disclosure.

[0020] A third aspect of this disclosure provides a method for preparing porous carbon materials, the method comprising the following steps:

[0021] A polyacrylonitrile-based hydrogel was freeze-dried to obtain an aqueous graphene-polyacrylonitrile-based composite aerogel; the aqueous graphene-polyacrylonitrile-based composite aerogel was then subjected to carbonization treatment.

[0022] The polyacrylonitrile-based hydrogel is the polyacrylonitrile-based hydrogel described in the second aspect of this disclosure.

[0023] Optionally, the freeze-drying conditions include a freeze-drying temperature of -80 to -50°C and a time of 12 to 48 hours;

[0024] The carbonization treatment includes reacting the aqueous graphene-polyacrylonitrile-based composite aerogel with an inorganic alkaline solution under an inert atmosphere, with a carbonization temperature of 600–800°C and a carbonization time of 1–1.5 h.

[0025] The inorganic base is selected from one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate;

[0026] The mass ratio of the aqueous graphene-polyacrylonitrile-based composite aerogel to the inorganic alkaline solution is 1:(1-5).

[0027] This disclosure provides a fourth aspect of a porous carbon material prepared by the method described in the third aspect of this disclosure, wherein the porous carbon material has a BET specific surface area of ​​300–900 m². 2 / g; total porosity 45-70%; mesopore volume accounts for 10-63% of the total pore volume; macropore volume accounts for 10-38% of the total pore volume.

[0028] The fifth aspect of this disclosure provides an application of the porous carbon material described in the fourth aspect of this disclosure in a supercapacitor.

[0029] Through the above technical solution, this disclosure utilizes water as a solvent and biomass materials to modify polyacrylonitrile (PAC), while simultaneously adding a graphene oxide dispersion, to obtain a PAC-based hydrogel via a one-step hydrothermal method. The preparation method of this disclosure is simple, straightforward, green, non-toxic, and low-cost, while also solving the problems of organic solvent pollution and difficult recovery. The product structure exhibits good uniformity, and the porous carbon material prepared from this PAC-based hydrogel is more conducive to electrolyte transport in supercapacitors.

[0030] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0031] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0032] Figure 1 These are photographs (a) of the polyacrylonitrile-based hydrogel and (b) of the porous carbon material in Example 1 of this disclosure.

[0033] Figure 2 These are scanning electron microscope (SEM) images (a and b) and transmission electron microscope (TEM) images (c) of the porous carbon material in Embodiment 1 of this disclosure. Detailed Implementation

[0034] The specific embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this disclosure.

[0035] The first aspect of this disclosure provides a method for preparing a polyacrylonitrile-based hydrogel, the method comprising the following steps:

[0036] S1: Polyacrylonitrile raw material, biomass, graphene oxide and water are mixed to obtain a mixed solution; the mixed solution is then subjected to hydrothermal treatment.

[0037] The biomass includes one or more of tannin compounds and lignin biomass.

[0038] This disclosure describes the preparation of polyacrylonitrile-based hydrogels using water as a solvent for polyacrylonitrile raw materials, overcoming the problems of organic solvent pollution and difficult recycling. The preparation method is simple, easy to implement, and green and non-toxic. At the same time, the polyacrylonitrile-based hydrogel is more conducive to electrolyte transport in supercapacitors.

[0039] According to one embodiment of this disclosure, the tannin compound is selected from one or more of condensed tannins, phenolic tannins, tannic acid, and gallic acid; the lignin biomass is selected from one or more of lignin, alkali lignin, lignin sulfate, lignin sulfonate, enzymatically hydrolyzed lignin, and organic solvent lignin; the lignin sulfonate is selected from one or more of sodium lignin sulfonate and calcium lignin sulfonate. The above-described embodiments are advantageous for obtaining porous carbon materials from polyacrylonitrile-based hydrogels with high carbon yield and good atom economy, further enabling supercapacitors to have higher specific capacitance and energy density.

[0040] According to one embodiment of this disclosure, the polyacrylonitrile raw material is selected from one or more of polyacrylonitrile, acrylonitrile binary copolymer, and acrylonitrile terpolymer; the weight-average molecular weight of the polyacrylonitrile raw material is 8000-250000; the acrylonitrile binary copolymer is a copolymer of acrylonitrile monomer and a second monomer; the acrylonitrile terpolymer is a copolymer of acrylonitrile monomer, a second monomer, and a third monomer; the second monomer is one or more of methyl acrylate and methyl methacrylate; the third monomer is one or more of itaconic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, sodium p-methacrylamide benzenesulfonate, and methylvinylpyridine. The above-described embodiments are advantageous for producing porous carbon materials with high carbon yield and good atom economy from polyacrylonitrile-based hydrogels, further enabling supercapacitors to have higher specific capacitance and energy density.

[0041] According to one embodiment of this disclosure, the mass ratio of biomass to polyacrylonitrile raw material in S1 is 1:(0.5-5), preferably 1:(2-5); the oxygen content of the graphene oxide is 10%-40%, preferably 15%-30%. In this disclosure, the oxygen content of the graphene oxide refers to the mass fraction of oxygen element in the graphene oxide. The above-described embodiments are beneficial for obtaining porous carbon materials with larger BET specific surface area and higher porosity, avoiding the collapse of porous carbon materials, and further enabling supercapacitors to have higher specific capacitance and energy density.

[0042] According to one embodiment of this disclosure, the mixing time in S1 is 3–10 hours, preferably 6–8 hours; the hydrothermal treatment conditions in S1 include a hydrothermal temperature of 120°C–180°C, preferably 140°C–160°C, and a hydrothermal time of 20–40 hours, preferably 28–30 hours. The above embodiments are beneficial for obtaining porous carbon materials with larger BET specific surface area and higher porosity, further enabling supercapacitors to have higher specific capacitance and energy density.

[0043] According to one embodiment of this disclosure, step S1 includes the following steps:

[0044] S1-1. The polyacrylonitrile raw material is first mixed with water and then ultrasonically dispersed to obtain a polyacrylonitrile aqueous system.

[0045] S1-2, Biomass and water are mixed a second time, and then ultrasonically dispersed to obtain a biomass-water system;

[0046] S1-3. Graphene oxide and water are mixed for the third time and then ultrasonically dispersed to obtain the graphene oxide system.

[0047] S1-4. The polyacrylonitrile aqueous system, biomass aqueous system and graphene oxide system obtained above are mixed for the fourth time to obtain the mixed solution;

[0048] The concentration of the graphene oxide system is 1 mg / mL to 6 mg / mL.

[0049] The second aspect of this disclosure provides a polyacrylonitrile-based hydrogel prepared by the method described in the first aspect of this disclosure.

[0050] A third aspect of this disclosure provides a method for preparing porous carbon materials, the method comprising the following steps:

[0051] A polyacrylonitrile-based hydrogel was freeze-dried to obtain an aqueous graphene-polyacrylonitrile-based composite aerogel; the aqueous graphene-polyacrylonitrile-based composite aerogel was then subjected to carbonization treatment.

[0052] The polyacrylonitrile-based hydrogel is the polyacrylonitrile-based hydrogel described in the second aspect of this disclosure.

[0053] According to one embodiment of this disclosure, the freeze-drying conditions include a freeze-drying temperature of -80 to -50°C, preferably -45°C to -60°C, and a freeze-drying time of 12 to 48 hours, preferably 24 to 38 hours.

[0054] According to one embodiment of this disclosure, the carbonization treatment includes reacting the aqueous graphene-polyacrylonitrile-based composite aerogel with an inorganic alkaline solution under an inert atmosphere, with a carbonization temperature of 600–800°C and a carbonization time of 1–1.5 h; preferably, the carbonization temperature is 700–800°C. In a further embodiment, the carbonization treatment includes reacting the aqueous graphene-polyacrylonitrile-based composite aerogel with an inorganic alkaline solution in a molten state under an inert atmosphere. The above embodiments do not require soft or hard templates to obtain porous carbon materials, simplifying the method and facilitating the production of porous carbon materials with larger BET specific surface areas and higher porosity, further enabling supercapacitors to have higher specific capacitance and energy density.

[0055] According to one embodiment of this disclosure, the inorganic alkali is selected from one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate; the mass ratio of the aqueous graphene-polyacrylonitrile-based composite aerogel to the inorganic alkali solution is 1:(1-5), preferably 1:(2-4); the inert atmosphere includes one or more of nitrogen, helium, and argon. The above embodiments are advantageous for obtaining porous carbon materials with larger BET specific surface area and higher porosity, further enabling supercapacitors to have higher specific capacitance and energy density.

[0056] This disclosure provides a fourth aspect of a porous carbon material prepared by the method described in the third aspect of this disclosure, wherein the porous carbon material has a BET specific surface area of ​​300–900 m². 2 / g; total porosity 45-70%; mesopore volume accounting for 10-63% of total pore volume; macropore volume accounting for 10-38% of total pore volume; preferably, the BET specific surface area of ​​the porous carbon material is 500-900 m² / g. 2 / g; total porosity 60-70%; mesopore volume accounts for 23-63% of total pore volume; macropore volume accounts for 10-30% of total pore volume.

[0057] The fifth aspect of this disclosure provides an application of the porous carbon material described in the fourth aspect of this disclosure in a supercapacitor.

[0058] The present invention will be further illustrated by the following examples, but the present invention is not limited thereto.

[0059] The polyacrylonitrile raw material used in the examples was purchased from Shanghai Petrochemical Co., Ltd.; tannic acid was purchased from Maclean's Reagent Company; and calcium lignosulfonate and sodium lignosulfonate were purchased from BASF Biotechnology Co., Ltd. in Hefei. Unless otherwise specified, all other reagents were commercially available products.

[0060] The BET test was performed on an instrument of model JW-BK200C.

[0061] SEM was performed using a JSK-6480A scanning electron microscope.

[0062] TEM was performed on a transmission electron microscope instrument of model number Bioscope system.

[0063] The electrochemical workstation was used on an instrument of model CHI600E.

[0064] The Blue Electric system was tested on an instrument of model CT2001A, and the specific test method was cyclic stability testing.

[0065] The graphene oxide used in the examples was prepared according to the method in the doctoral dissertation "Preparation and Performance Study of Graphene-based Cobalt Oxide (Hydrogen Hydroxide) Composite Materials" by Bao Lin, and graphene oxide with oxygen contents of 5%, 15% and 30% was obtained.

[0066] Example 1

[0067] (1) Add 2g of polyacrylonitrile (molecular weight 80000) to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a polyacrylonitrile water system.

[0068] (2) Add 4g of calcium lignosulfonate to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a biomass water system.

[0069] (3) Add 10 mL of graphene oxide with an oxygen content of 15% and a concentration of 4 mg / mL to 10 mL of deionized water, stir, and ultrasonically disperse for 3 h to obtain the graphene oxide system.

[0070] (4) The above polyacrylonitrile water system, biomass water system and graphene oxide system are mixed and stirred for 5 hours to obtain a homogeneous mixed solution; the mass ratio of added biomass to polyacrylonitrile raw material is 1:2.

[0071] (5) The above mixed solution was transferred to a high-pressure reactor for hydrothermal treatment at a temperature of 150°C for 30 hours to obtain a polyacrylonitrile-based hydrogel.

[0072] (6) The obtained polyacrylonitrile-based hydrogel was freeze-dried at a temperature of -60℃ for 36 hours to obtain an aqueous graphene polyacrylonitrile-based composite aerogel.

[0073] (7) The above-mentioned aqueous graphene polyacrylonitrile-based composite aerogel was mixed with 6 mol / L KOH solution at a mass ratio of 1:1, dried at 80°C for 8 hours, and then transferred to a tube furnace and carbonized at 700°C for 1 hour under the protection of inert nitrogen gas to obtain porous carbon material.

[0074] Example 2

[0075] (1) Add 2g of polyacrylonitrile (molecular weight 250000) to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a polyacrylonitrile water system.

[0076] (2) Add 6g of tannic acid to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a biomass water system;

[0077] (3) Add 10 mL of graphene oxide with an oxygen content of 30% and a concentration of 5 mg / mL to 10 mL of deionized water, stir, and ultrasonically disperse for 3 h to obtain the graphene oxide system.

[0078] (4) The above polyacrylonitrile water system, biomass water system and graphene oxide system are mixed and stirred for 7 hours to obtain a homogeneous mixed solution; the mass ratio of added biomass to polyacrylonitrile raw material and graphene oxide is 1:3.

[0079] (5) The above mixed solution was transferred to a high-pressure reactor for hydrothermal treatment at a temperature of 120°C for 25 hours to obtain a polyacrylonitrile-based hydrogel.

[0080] (6) The obtained polyacrylonitrile-based hydrogel was freeze-dried at a temperature of -80℃ for 24 hours to obtain an aqueous graphene polyacrylonitrile-based composite aerogel.

[0081] (7) The above-mentioned aqueous graphene polyacrylonitrile-based composite aerogel was mixed with 5 mol / L KOH solution at a mass ratio of 1:3, dried at 80°C for 8 hours, and then transferred to a tube furnace and carbonized at 800°C for 1.2 hours under the protection of inert nitrogen gas to obtain porous carbon material.

[0082] Example 3

[0083] The method in this embodiment is the same as in embodiment 1, except that the polyacrylonitrile weighed in (1) is 4g, the biomass weighed in (2) is 1g, and the mass ratio of biomass to polyacrylonitrile raw material in (4) is 1:0.25.

[0084] Comparative Example 1

[0085] (1) Add 2g of polyacrylonitrile (molecular weight 80000) to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a polyacrylonitrile water system.

[0086] (2) Add 4g of sodium lignosulfonate to 5ml of deionized water, stir, and ultrasonically disperse for 3h to obtain a biomass water system.

[0087] (3) The above polyacrylonitrile aqueous system and biomass aqueous system are mixed and stirred for 5 hours to obtain a homogeneous mixed solution; the mass ratio of added biomass to polyacrylonitrile raw material is 1:2.

[0088] (4) The above mixed solution was transferred to a high-pressure reactor for hydrothermal treatment at a temperature of 150°C for 30 hours to obtain a polyacrylonitrile-based hydrogel.

[0089] (5) The obtained polyacrylonitrile-based hydrogel was freeze-dried at -60℃ for 36 hours to obtain an aqueous polyacrylonitrile-based composite aerogel.

[0090] (6) The above-mentioned waterborne polyacrylonitrile-based composite aerogel was mixed with 6 mol / L KOH solution at a mass ratio of 1:1, dried at 80°C for 8 hours, and then transferred to a tube furnace and carbonized at 700°C for 1 hour under inert nitrogen protection to obtain porous carbon material.

[0091] Test Example 1

[0092] The porous carbon materials obtained in Examples 1-3 and Comparative Example 1 were subjected to BET tests, and the test results are shown in Table 1.

[0093] Table 1

[0094]

[0095]

[0096] According to the data in Table 1, the porous carbon material prepared by the method of this disclosure has a large BET specific surface area, high total porosity, and a relatively high proportion of mesopore volume in the total pore volume, indicating that the porous carbon material obtained by the method of this disclosure has more mesopores.

[0097] Test Example 2

[0098] The porous carbon materials obtained in Examples 1-3 and Comparative Example 1 were subjected to electrochemical performance testing. Specifically, the porous carbon materials obtained in Examples 1-3 and Comparative Example 1 were mixed with conductive agent acetylene black and binder PVDF (PVDF in NMP suspension at 60 wt.%) at a mass ratio of 8:1:1, and coated onto a 1 cm thick substrate. 2 Electrodes, serving as current collectors, are pressed onto square nickel foam. They are then dried at 80°C for 12 hours, with each working electrode having an area of ​​0.5 cm². 2 The mass loading ranged from 1.5 to 4 mg. Both three-electrode and two-electrode tests were performed on a CHI 660E electrochemical workstation. CV tests were conducted within a potential window of -1.2 V to 0.6 V by varying the scan rate. GCD tests were performed with current densities ranging from 0.5 to 20 Ag. -1 Between. Place the electrodes in the blue electric system for testing.

[0099] In the three-electrode test, the platinum electrode is used as the counter electrode, and the Hg / HgO electrode is used as the reference electrode. The specific capacitance is calculated using the formula C = IΔt / (m*ΔV); where C is the specific capacitance of the electrode (Fg). -1), Δt is the discharge time (s) of the GCD curve; ΔV is the voltage window range obtained by the test (V); I is the response current (A); ν is the scan rate used during the test (Vs). -1 ), where m is the mass (g) of the active material loaded on the working electrode.

[0100] The battery employs a two-symmetric electrode system, using carbon material coated on nickel foam as the positive and negative electrodes, separated by a water-based separator specifically designed for supercapacitors. The battery casing utilizes both 2016 and 2023 type button cell housings. After assembly at room temperature, the battery is compacted and tested using a press. Cycle stability testing is conducted in a blue battery testing system. Power density P is calculated using the formula P = E * 3600 / Δt, and energy density E is calculated using the formula E = C * ΔV. 2 / (2*3.6) calculation: where P is the power density (Wkg) -1 E is the energy density (Wh / kg) -1 ΔV(V) and Δt(s) represent the voltage window and discharge time for the two-electrode GCD test. The test results are shown in Table 2.

[0101] Table 2

[0102]

[0103] As shown in Table 2, the porous carbon material prepared by the method of this disclosure exhibits higher specific capacitance and energy density when used to make supercapacitors. A comparison between Example 3 and Example 1 shows that, within the mass ratio range of biomass to polyacrylonitrile raw materials disclosed in this disclosure, the porous carbon material used to make supercapacitors exhibits higher specific capacitance and energy density.

[0104] The preferred embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0105] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0106] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing polyacrylonitrile-based hydrogels, characterized in that, The method includes the following steps: S1: Polyacrylonitrile raw material, biomass, graphene oxide and water are mixed to obtain a mixed solution; the mixed solution is then subjected to hydrothermal treatment. The biomass includes one or more of tannin compounds and lignin biomass; The mass ratio of biomass to polyacrylonitrile raw material in S1 is 1:(0.5~5).

2. The method according to claim 1, wherein, The tannin compounds are selected from one or more of condensed tannins, phenolic tannins, tannic acid, and gallic acid; the lignin biomass is selected from one or more of lignin, alkali lignin, lignin sulfate, lignin sulfonate, enzymatically hydrolyzed lignin, and organic solvent lignin; the lignin sulfonate is selected from one or more of sodium lignin sulfonate and calcium lignin sulfonate.

3. The method according to claim 1, wherein, The polyacrylonitrile raw material is selected from one or more of polyacrylonitrile, acrylonitrile binary copolymer, and acrylonitrile terpolymer; the weight average molecular weight of the polyacrylonitrile raw material is 8,000 to 250,000. The acrylonitrile binary copolymer is a copolymer of acrylonitrile monomer and a second monomer; the acrylonitrile terpolymer is a copolymer of acrylonitrile monomer, a second monomer, and a third monomer. The second monomer is one or more of methyl acrylate and methyl methacrylate; the third monomer is one or more of itaconic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, sodium p-methacrylamide benzene sulfonate, and methylvinylpyridine.

4. The method according to claim 1, wherein, The mass ratio of biomass to polyacrylonitrile raw material and graphene oxide in S1 is 1:(0.5~5), and the oxygen content of the graphene oxide is 10%~40%. The mixing time described in S1 is 3 to 10 hours; the hydrothermal treatment conditions described in S1 include a hydrothermal temperature of 120°C to 180°C and a hydrothermal time of 20 to 40 hours.

5. The method according to claim 1, wherein, Step S1 includes the following steps: S1-1. The polyacrylonitrile raw material is first mixed with water and then ultrasonically dispersed to obtain a polyacrylonitrile aqueous system. S1-2, Biomass and water are mixed a second time, and then ultrasonically dispersed to obtain a biomass-water system; S1-3. Graphene oxide and water are mixed for the third time and then ultrasonically dispersed to obtain the graphene oxide system. S1-4. The polyacrylonitrile aqueous system, biomass aqueous system and graphene oxide system obtained above are mixed for the fourth time to obtain the mixed solution; The concentration of the graphene oxide system is 1 mg / mL to 6 mg / mL.

6. A polyacrylonitrile-based hydrogel prepared by the method according to any one of claims 1 to 5.

7. A method for preparing porous carbon materials, characterized in that, The method includes the following steps: A polyacrylonitrile-based hydrogel was freeze-dried to obtain an aqueous graphene-polyacrylonitrile-based composite aerogel; the aqueous graphene-polyacrylonitrile-based composite aerogel was then subjected to carbonization treatment. The polyacrylonitrile-based hydrogel is the polyacrylonitrile-based hydrogel as described in claim 6.

8. The method according to claim 7, wherein, The freeze-drying conditions include a freeze-drying temperature of -80 to -50°C and a time of 12 to 48 hours; The carbonization treatment includes reacting the aqueous graphene-polyacrylonitrile-based composite aerogel with an inorganic alkaline solution under an inert atmosphere, with a carbonization temperature of 600–800°C and a carbonization time of 1–1.5 h. The inorganic base is selected from one or more of potassium hydroxide, sodium hydroxide, potassium carbonate, and sodium carbonate; The mass ratio of the aqueous graphene-polyacrylonitrile-based composite aerogel to the inorganic alkaline solution is 1:(1~5); the concentration of the inorganic alkaline solution is 1~6 mol / L.

9. The porous carbon material prepared by the method according to any one of claims 7 or 8, characterized in that, The porous carbon material has a BET specific surface area of ​​300~900 m². 2 / g; total porosity 45~70%; mesopore volume accounts for 10~63% of total pore volume; macropore volume accounts for 10~38% of total pore volume.

10. The application of the porous carbon material according to claim 9 in supercapacitors.

Images