A nitrogen-sulfur co-doped porous channel lignin-based carbon nanofiber and a preparation method thereof

Abstract

The present application provides a kind of nitrogen sulfur co-doped porous channel lignin-based carbon nanofiber and its preparation method, the preparation method is: the shell layer spinning solution and core layer spinning solution are prepared respectively, then the core layer spinning solution and shell layer spinning solution are prepared by coaxial electrospinning to obtain lignin-based nanofiber membrane;Lignin-based nanofiber membrane is pre-oxidized and carbonized, and nitrogen sulfur co-doped porous channel lignin-based carbon nanofiber is obtained by cooling;The lignin-based carbon fiber prepared by the present application does not need to add polyacrylonitrile and other petroleum-based raw materials, the preparation process is simple, the lignin-based carbon fiber prepared has porous channel structure, and the lignin-based carbon fiber co-doped with nitrogen and sulfur has excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lignin-based carbon nanofiber, and particularly relates to a nitrogen-sulfur co-doped porous lignin-based carbon nanofiber and a preparation method thereof. BACKGROUND

[0002] In the field of energy storage, due to the non-renewability of fossil raw materials and the potential environmental risks in the use process, the comprehensive application of fossil raw materials in special fields such as energy storage is restricted to a certain extent. It is a trend to develop green, renewable and environmentally friendly natural substances as raw materials for energy storage elements to replace fossil raw materials.

[0003] Carbon fibers have attracted widespread attention due to their high strength, small density and high temperature resistance. In the prior art, most lignin-based carbon fibers still need to add petroleum-based raw materials such as polyacrylonitrile, but the high cost and environmental problems of polyacrylonitrile limit its further application. Therefore, it is particularly important to find a low-cost, renewable and environmentally friendly lignin-based carbon fiber preparation method. SUMMARY

[0004] The present application aims to overcome the defects of the prior art and provides a nitrogen-sulfur co-doped porous lignin-based carbon nanofiber and a preparation method thereof.

[0005] The present application provides the following technical solutions:

[0006] The present application provides a preparation method of a nitrogen-sulfur co-doped porous lignin-based carbon nanofiber, comprising the following steps:

[0007] S1, dissolving polyethylene oxide and thiourea in an N, N-dimethylformamide solution to obtain a mixed solution, and adding alkali lignin to the mixed solution to obtain a shell spinning solution;

[0008] S2, dissolving polyvinylpyrrolidone in an N, N-dimethylformamide solution to obtain a core spinning solution;

[0009] S3, preparing a lignin-based nanofiber membrane by coaxial electrospinning of the core spinning solution and the shell spinning solution;

[0010] S4, pre-oxidizing and carbonizing the lignin-based nanofiber membrane, and cooling to obtain a nitrogen-sulfur co-doped porous lignin-based carbon nanofiber.

[0011] The polyethylene oxide (PEO) is added to the shell spinning solution as a spinning aid, which can greatly improve the spinnability of the lignin. In the coaxial electrospinning process, under the action of high voltage, the core spinning solution is stretched into a filament by the internal nozzle through the electric field, and the shell spinning solution is coated around the internal filament to form a shell, and finally a coaxial nanofiber structure is formed. The thiourea is used as a nitrogen source and a sulfur source, and after the pre-oxidation and carbonization processes, the nitrogen and sulfur are doped on the carbonized lignin. The polyvinylpyrrolidone in the interior is completely consumed in the subsequent carbonization process to become a gas, so that the coated carbon-based material forms a porous structure. The present application introduces new electronic energy levels or changes the distribution of the original electronic energy levels by doping nitrogen and sulfur, improves the mobility of the N, S co-doped lignin-based porous carbon nanofiber (NS-MCNFs), and thus enhances the electrochemical performance. Moreover, the porous structure increases the specific surface area of the material and exposes more active sites.

[0012] Further, the mass ratio of the polyethylene oxide, the thiourea and the lignin in the shell spinning solution is (0.15-0.5):1:(4.5-4.85), and the mass ratio of the thiourea and the N, N-dimethylformamide is 1:20.

[0013] Further, the mass concentration of the polyvinylpyrrolidone in the core spinning solution is 20%-25%.

[0014] Further, in the step S1, the polyethylene oxide and the thiourea are dissolved in the N, N-dimethylformamide solution, and a mixed solution is obtained by water bath heating and stirring until complete dissolution. The lignin is added to the mixed solution, and then water bath heating and stirring are performed for 4h, followed by normal temperature stirring for 12h to obtain the shell spinning solution.

[0015] Further, in the step S2, the polyvinylpyrrolidone is dissolved in the N, N-dimethylformamide solution, and a core spinning solution is obtained by water bath heating and stirring until complete dissolution.

[0016] Further, the water bath heating temperature is 80℃.

[0017] Further, in the step S3, the push speed ratio of the shell spinning solution and the core spinning solution is 10:1, and the coaxial electrospinning conditions are as follows: static voltage: 22KV; receiving distance: 15cm; and the push speeds of the shell spinning solution and the core spinning solution are 0.6mL / h and 0.06mL / h, respectively.

[0018] Further, in the step S4, the pre-oxidation temperature is controlled at 250℃, the heating rate is 0.4℃ / min, and the pre-oxidation time is 1h.

[0019] Further, in the step S4, the carbonization temperature is 600℃, the control heating rate is 3℃ / min, and the carbonization time is 1h.

[0020] The application further provides the nitrogen-sulfur co-doped porous lignin-based carbon nanofiber prepared by the preparation method and application thereof in supercapacitor electrode materials.

[0021] The application has the following beneficial effects:

[0022] The lignin-based carbon fiber prepared by the application does not need to add petroleum-based raw materials such as polyacrylonitrile, the preparation process is simple, the cost is low, and the environment is friendly, the prepared lignin-based carbon fiber has a porous structure, and the lignin-based carbon fiber is co-doped with nitrogen and sulfur, and has excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0024] Figure 1 The specific surface capacitance curve of the NS-MCNF prepared in the embodiment 1 of the application and the MCNF prepared in the comparative example under different current densities;

[0025] Figure 2 The thermogravimetric test analysis diagram of the fiber obtained by electrospinning of the core spinning solution in the embodiment 1 of the application;

[0026] Figure 3 The SEM diagram of the cross section of the NS-MCNF prepared in the embodiment 1 of the application;

[0027] Figure 4 The SEM diagram and EDS diagram of the surface of the NS-MCNF prepared in the embodiment 1 of the application;

[0028] Figure 5 The electrochemical performance analysis result of the NS-MCNF prepared in the embodiment 1 of the application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some embodiments of the application, not all embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0030] The embodiment of the present application provides a preparation method of nitrogen-sulfur co-doped porous channel lignin-based carbon nanofiber, which comprises the following steps:

[0031] S1, polyethylene oxide and thiourea are dissolved in an N, N-dimethylformamide solution to obtain a mixed solution, and alkali lignin is added into the mixed solution to obtain a shell spinning solution;

[0032] S2, polyvinylpyrrolidone is dissolved in an N, N-dimethylformamide solution to obtain a core spinning solution;

[0033] S3, the core spinning solution and the shell spinning solution are prepared into a lignin-based nanofiber membrane through coaxial electrospinning;

[0034] S4, the lignin-based nanofiber membrane is pre-oxidized and carbonized, and then cooled to obtain nitrogen-sulfur co-doped porous channel lignin-based carbon nanofiber.

[0035] The present application is further described below through specific embodiments:

[0036] Embodiment 1

[0037] The embodiment prepares a nitrogen-sulfur co-doped porous channel lignin-based carbon nanofiber, and the specific process is as follows:

[0038] 1, 0.25g of polyethylene oxide (PEO) and 1g of thiourea are dissolved in 20g of an N, N-dimethylformamide (DMF) solution, and heated and stirred in a water bath at 80 DEG C until dissolved, to obtain a mixed solution; 4.75g of alkali lignin is added into the mixed solution, and heated and stirred in a water bath at 80 DEG C for 4h, and then stirred at room temperature for 12h, to obtain a lignin shell spinning solution;

[0039] 2, 5g of polyvinylpyrrolidone (PVP) is dissolved in 15g of an N, N-dimethylformamide (DMF) solution, and heated and stirred in a water bath at 80 DEG C until dissolved, to obtain a core spinning solution;

[0040] 3, 1mL of the core spinning solution and 5mL of the shell spinning solution are respectively taken into 5mL syringes, and a lignin-based nanofiber membrane is prepared through coaxial electrospinning, and the specific electrospinning conditions are as follows: electrostatic voltage: 22KV; receiving distance: 15cm, and the pushing speeds of the shell spinning solution and the core spinning solution are 0.6mL / h and 0.06mL / h respectively;

[0041] 4, the lignin-based nanofiber membrane is placed in a tube furnace for pre-oxidation and carbonization, the pre-oxidation temperature is controlled at 250 DEG C, the heating rate is 0.4 DEG C / min, the pre-oxidation time is 1h, and then the carbonization is carried out, the heating rate is controlled at 3 DEG C / min, the carbonization temperature is 600 DEG C, the carbonization time is 1h, and then the nitrogen-sulfur co-doped lignin-based porous channel carbon nanofiber (NS-MCNFs) is obtained after cooling.

[0042] Example 2

[0043] This embodiment prepares a nitrogen and sulfur co-doped porous channel lignin-based carbon nanofiber, and the specific process is as follows:

[0044] 1. Take 0.5 g of polyethylene oxide (PEO) and 1 g of thiourea and dissolve them in 20 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a mixed solution; take 4.5 g of alkali lignin and add it to the mixed solution, heat and stir in a water bath at 80°C for 4 h, and then stir at room temperature for 12 h to obtain a lignin shell spinning solution;

[0045] 2. Take 5 g of polyvinylpyrrolidone (PVP) and dissolve it in 15 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a core layer spinning solution;

[0046] 3. Take 1 mL of the core layer spinning solution and 5 mL of the shell layer spinning solution in a 5 mL syringe, and prepare a lignin-based nanofiber membrane by coaxial electrospinning, and the specific electrospinning conditions are as follows: electrostatic voltage: 22 KV; receiving distance: 15 cm; and the pushing speeds of the shell layer spinning solution and the core layer spinning solution are 0.6 mL / h and 0.06 mL / h, respectively.

[0047] 4. Place the lignin-based nanofiber membrane in a tube furnace for pre-oxidation and carbonization, control the pre-oxidation temperature at 250°C, the heating rate is 0.4°C / min, the pre-oxidation time is 1 h, then carbonize it, control the heating rate at 3°C / min, the carbonization temperature is 600°C, the carbonization time is 1 h, and cool to obtain nitrogen and sulfur co-doped lignin-based porous channel carbon nanofiber (NS-MCNFs).

[0048] Example 3

[0049] This embodiment prepares a nitrogen and sulfur co-doped porous channel lignin-based carbon nanofiber, and the specific process is as follows:

[0050] 1. Take 0.15 g of polyethylene oxide (PEO) and 1 g of thiourea and dissolve them in 20 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a mixed solution; take 4.85 g of alkali lignin and add it to the mixed solution, heat and stir in a water bath at 80°C for 4 h, and then stir at room temperature for 12 h to obtain a N,S co-doped lignin shell spinning solution;

[0051] 2. Take 5 g of polyvinylpyrrolidone (PVP) and dissolve it in 15 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a core layer spinning solution;

[0052] 3. Take 1 mL of core layer spinning solution and 5 mL of shell layer spinning solution in 5 mL syringes, respectively, to prepare lignin-based nanofiber membranes by coaxial electrospinning. The specific electrospinning conditions are: electrostatic voltage: 22 KV; receiving distance: 15 cm, and the pushing speeds of the shell layer spinning solution and the core layer spinning solution are 0.6 mL / h and 0.06 mL / h, respectively.

[0053] 4. Place the lignin-based nanofiber membrane in a tube furnace for pre-oxidation and carbonization. The pre-oxidation temperature is controlled at 250°C, the heating rate is 0.4°C / min, and the pre-oxidation time is 1 h. Then, carbonization is performed with a controlled heating rate of 3°C / min and a carbonization temperature of 600°C for 1 h. Cooling obtains nitrogen and sulfur co-doped lignin-based porous carbon nanofibers (NS-MCNFs).

[0054] Example 4

[0055] This example prepares a nitrogen and sulfur co-doped porous lignin-based carbon nanofiber. The specific process is as follows:

[0056] 1. Weigh 0.25 g of polyethylene oxide (PEO) and 1 g of thiourea into 20 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a mixed solution. Weigh 4.75 g of alkali lignin and add it to the mixed solution. Stir in a water bath at 80°C for 4 h, and then stir at room temperature for 12 h to obtain an N, S co-doped lignin shell layer spinning solution.

[0057] 2. Weigh 5 g of polyvinylpyrrolidone (PVP) into 20 g of N,N-dimethylformamide (DMF), and heat and stir in a water bath at 80°C until dissolved to obtain a core layer spinning solution.

[0058] 3. Take 1 mL of core layer spinning solution and 5 mL of shell layer spinning solution in 5 mL syringes, respectively, to prepare lignin-based nanofiber membranes by coaxial electrospinning. The specific electrospinning conditions are: electrostatic voltage: 22 KV; receiving distance: 15 cm, and the pushing speeds of the shell layer spinning solution and the core layer spinning solution are 0.6 mL / h and 0.06 mL / h, respectively.

[0059] 4. Place the lignin-based nanofiber membrane in a tube furnace for pre-oxidation and carbonization. The pre-oxidation temperature is controlled at 250°C, the heating rate is 0.4°C / min, and the pre-oxidation time is 1 h. Then, carbonization is performed with a controlled heating rate of 3°C / min and a carbonization temperature of 600°C for 1 h. Cooling obtains nitrogen and sulfur co-doped lignin-based porous carbon nanofibers (NS-MCNFs).

[0060] Comparative Example

[0061] Compared with Example 1, the shell spinning solution is different, but the rest of the steps are the same as in Example 1. Finally, lignin-based porous carbon nanofibers (MCNFs) are prepared.

[0062] Preparation process of shell spinning solution in comparative example: 0.25g of polyethylene oxide (PEO) was weighed and dissolved in 20g of DMF solution. The mixture was heated and stirred in a water bath at 80℃ until dissolved to obtain a mixed solution. 4.75g of alkali lignin was weighed and added to the mixed solution. The mixture was heated and stirred in a water bath at 80℃ for 4h, and then stirred at room temperature for 12h to obtain lignin shell spinning solution.

[0063] Test Analysis Example

[0064] Electrochemical tests were performed on the two lignin-based carbon nanofibers prepared in Example 1 and the comparative example. (See...) Figure 1 At current densities of 0.2, 0.5, 1, and 2 Ag... -1 The specific capacitances of NS-MCNFs were 80.5, 71.3, 67.3, and 62.2 F g, respectively. -1 The specific capacitances of MCNFs were 40.7, 32.37, 27.1, and 21.1 F g, respectively. -1 It can be seen that the N,S co-doped NS-MCNFs exhibit superior electrochemical performance, proving their suitability as electrode materials for supercapacitors.

[0065] The core spinning solution was electrospun separately, and thermogravimetric analysis was performed on it. The results are as follows: Figure 2 As shown, it can be observed that PVP is basically consumed at around 475℃, proving the feasibility of the multi-channel structure.

[0066] The cross-section of the NS-MCNFs prepared in Example 1 was tested by SEM, and the results are as follows: Figure 3 As shown, carbon nanofibers can be observed to be porous.

[0067] The surface of the NS-MCNFs prepared in Example 1 was tested by SEM and EDS, and the results are as follows: Figure 4 As shown, the distribution of N and S elements in the carbon nanofibers can be observed, indicating that nitrogen and sulfur are co-doped on the carbon nanofibers through the preparation method of the present invention.

[0068] The electrochemical performance of the NS-MCNFs prepared in Example 1 was tested, and the results are as follows: Figure 5 As shown. Figure 5 a shows the CV curves of NS-MCNFs at different scan rates. As the scan rate increases, the CV curves undergo some distortion. When the scan rate is below 20 mV / s... -1At this time, the CV curve still remains rectangular, but it is greatly distorted at high scan rates. Figure 5 b is the GCD curve at different current densities, and the GCD curve still remains triangular as the current density increases. Figure 5 c is the specific capacitance at different current densities, and it can be seen that the specific capacitance decreases as the current density increases. Therefore, the NS-MCNFs can be used as supercapacitor electrode materials.

[0069] The present application does not need to add petroleum-based raw materials such as polyacrylonitrile, has a simple preparation process, low cost and is environment-friendly, and the prepared NS-MCNFs have excellent performance and can be used as supercapacitor electrode materials.

[0070] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing nitrogen and sulfur co-doped porous channel lignin-based carbon nanofibers, characterized in that, The method comprises the following steps: S1, dissolving polyethylene oxide and thiourea in N, N-dimethylformamide solution to obtain a mixed solution, and adding alkali lignin into the mixed solution to obtain a shell spinning solution; S2, dissolving polyvinylpyrrolidone in N, N-dimethylformamide solution to obtain a core spinning solution; S3, preparing a lignin-based nanofiber by coaxial electrospinning of the core spinning solution and the shell spinning solution; S4, pre-oxidizing and carbonizing the lignin-based nanofiber, and cooling to obtain a nitrogen-sulfur co-doped porous lignin-based carbon nanofiber.

2. The method for preparing nitrogen-sulfur co-doped porous lignin-based carbon nanofibers as described in claim 1, characterized in that: The mass ratio of polyethylene oxide, thiourea and alkali lignin in the shell spinning solution is (0.15-0.5):1:(4.5-4.85), and the mass ratio of thiourea and N, N-dimethylformamide is 1:

20.

3. The method for preparing nitrogen-sulfur co-doped porous lignin-based carbon nanofibers as described in claim 1, characterized in that: The mass concentration of polyvinylpyrrolidone in the core spinning solution is 20%-25%.

4. The method for preparing nitrogen-sulfur co-doped porous lignin-based carbon nanofibers as described in claim 2, characterized in that: In step S1, polyethylene oxide and thiourea are dissolved in N, N-dimethylformamide solution, heated and stirred in a water bath until completely dissolved to obtain a mixed solution, alkali lignin is added into the mixed solution, heated and stirred in a water bath for 4h, and then stirred at room temperature for 12h to obtain a shell spinning solution.

5. The method for preparing nitrogen-sulfur co-doped porous lignin-based carbon nanofibers as described in claim 3, characterized in that: In step S2, polyvinylpyrrolidone is dissolved in N, N-dimethylformamide solution, heated and stirred in a water bath until completely dissolved to obtain a core spinning solution.

6. The method of producing nitrogen and sulfur co-doped porous lignin-based carbon nanofibers according to claim 1, wherein: In step S3, the push speed ratio of the shell spinning solution and the core spinning solution is 10:1, the coaxial electrospinning conditions are: static voltage: 22KV; receiving distance: 15cm, and the push speed of the shell spinning solution and the core spinning solution is 0.6mL / h and 0.06mL / h, respectively.

7. The method of producing nitrogen and sulfur co-doped porous lignin-based carbon nanofibers according to claim 1, wherein: In step S4, the pre-oxidation temperature is controlled at 250℃, the heating rate is 0.4℃ / min, and the pre-oxidation time is 1h.

8. The method of producing nitrogen and sulfur co-doped porous lignin-based carbon nanofibers according to claim 1, wherein: In step S4, the carbonization temperature is 600℃, the control heating rate is 3℃ / min, and the carbonization time is 1h.

9. A nitrogen-sulfur co-doped porous channel lignin-based carbon nanofiber, characterized in that: The method is prepared by any one of claims 1-8.

10. The nitrogen-sulfur co-doped porous lignin-based carbon nanofiber of claim 9 is used as an electrode material for supercapacitors.

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