A method for preparing an electrode material by regenerating lignin with a eutectic solvent

Abstract

The application belongs to the technical field of electrode materials, and particularly relates to a method for preparing an electrode material by regenerating lignin by using a eutectic solvent. The lignin is degraded by using a eutectic solvent to obtain a lignin derivative, and the degradation method is simple, efficient and environmentally friendly. After the lignin is degraded, phenolic aromatic monomers are generated, the lignin derivative is added into aniline, and then in-situ polymerization is carried out, the lignin derivative is used as a dopant, the obtained electrode material contains many nanofibers, has a large specific surface area and a stable structure, and is helpful to improve the conductivity, and the material exhibits excellent semiconductor behavior.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrode materials, and particularly relates to a method for preparing an electrode material from regenerated lignin by using a deep eutectic solvent. BACKGROUND

[0002] With the development of low-carbon economy, the demand for biomass is increasing all over the world. As a sustainable material to replace fossil resources, lignocellulosic biomass has broad development prospects. Unlike cellulose and hemicellulose, lignin is usually treated as waste or fuel, and only 5-10% of lignin is used for high-quality and high-value production. As the most widely available renewable aromatic biomass, lignin is the most promising renewable raw material for the preparation of alternative petrochemical products. Lignin is a polymer composed of phenylpropyl units connected by C-C, C-O-C and other chemical bonds. After depolymerization, various fuels and low molecular weight chemicals can be produced, such as alkylation of lignin degradation products, which can also replace fossil fuel resources. In recent years, deep eutectic solvents (DES) have been successfully used for the depolymerization and modification of lignin. Compared with other degradation methods, DES has mild reaction conditions and can achieve efficient degradation of lignin.

[0003] Polyaniline (PANI) is a representative p-type conductive polymer widely used as a solid electrode material for supercapacitors. Because it is easy to prepare and provides large pseudo-capacitance (> 800 F / g) and excellent rate performance. However, excessive oxidation and repeated volume changes during long-term charge / discharge cycles can lead to gradual performance degradation. As an electrochemically active additive, polyaniline needs to function in an acidic medium, which requires the resulting protonated polyaniline (emeraldine salt) to have high solubility characteristics in electrolyte solvents. In addition, the low utilization rate of PANI related to its electronic conductivity and the transport path of doped ions limits its high theoretical capacity. Therefore, people try to design and prepare PANI-based composites to improve the electrochemical defects of PANI as an electrode material. SUMMARY

[0004] In order to solve the above problems in the prior art, the application provides a method for preparing an electrode material from regenerated lignin by using a deep eutectic solvent.

[0005] A method for preparing an electrode material from regenerated lignin by using a deep eutectic solvent, which mixes deep eutectic solvent regenerated lignin, aniline and an oxidizing agent, and performs in-situ oxidative polymerization in an acidic medium to obtain the electrode material.

[0006] Preferably, the specific steps are as follows: dispersing the eutectic solvent regenerated lignin in an acidic medium to obtain a suspension; adding aniline to the suspension and stirring at 0-4 DEG C to obtain an aniline solution; dissolving an oxidizing agent in an amount of 1-2.5 times the mass of the aniline in an acidic medium, mixing the oxidizing agent with the aniline solution to perform in-situ oxidative polymerization, filtering after the reaction is completed, and washing and drying the filter residue to obtain the electrode material.

[0007] Preferably, the preparation method of the eutectic solvent regenerated lignin is as follows:

[0008] S1-1 mixing choline chloride and p-toluenesulfonic acid in a molar ratio of 1:1, stirring at 100-130 DEG C for about 30 minutes to obtain a eutectic solvent;

[0009] S1-2 adding lignin and the eutectic solvent in a mass ratio of 1:(10-25) into a reaction bottle, adding deionized water, heating at 100-140 DEG C for 3-13 hours to obtain a mixed solution; removing the reaction bottle and immersing it in a cold water bath to end the reaction;

[0010] S1-3 adding an acidic solution to the mixed solution to precipitate the lignin, then centrifuging and drying to obtain the eutectic solvent regenerated lignin.

[0011] Preferably, the acidic medium is a hydrochloric acid solution.

[0012] Preferably, the mass ratio of lignin to the eutectic solvent in S1-2 is 1:19.

[0013] Preferably, the mass ratio of the amount of distilled water to lignin in S1-2 is 1:4.

[0014] Preferably, the pH of the acidic solution in S1-3 is 2, and the amount of the acidic solution added is in a mass ratio of (40-60):1 to lignin.

[0015] Preferably, the amount ratio of the eutectic solvent regenerated lignin to aniline is (0.5-3 g):0.91 mL.

[0016] Preferably, the oxidizing agent is ammonium persulfate.

[0017] Preferably, the reaction time of the in-situ oxidative polymerization is 20-24 hours, and the reaction temperature of the in-situ oxidative polymerization is 0-4 DEG C.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The lignin degradation product is prepared by using a low eutectic solvent in one step, and the low eutectic solvent regenerated lignin is obtained, the degradation method is simple, efficient and environmentally friendly; the lignin after degradation produces phenolic aromatic monomers, and the acetate and phenolic hydroxyl signal is enhanced; the low eutectic solvent regenerated lignin is used as a dopant and is doped into polyaniline, and the obtained composite material contains many nanofibers, has a large specific surface area and a stable structure, and is helpful to improve the conductivity, and the composite material exhibits excellent semiconductor behavior. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 FTIR spectra of the electrode materials in Examples 1-3 and Comparative Example 1 1 H NMR spectra;

[0021] Figure 2 FTIR spectra of the electrode materials in Examples 1-3 and Comparative Example 1

[0022] Figure 3 SEM images of the electrode materials in Examples 1-3 and Comparative Example 1: (a) PANI, (b) LDP 0.5 / PANI, (c) LDP 1.0 / PANI and (d) LDP 3.0 / PANI. DETAILED DESCRIPTION

[0023] The application will be further described below in conjunction with specific examples.

[0024] Source of raw materials

[0025] Alkaline lignin (AL, Mw = 6483) was purchased from Aladdin Reagent Co., Ltd.

[0026] Example 1

[0027] Choline chloride and p-toluenesulfonic acid were mixed in a molar ratio of 1:1, stirred at 130°C and a rotation speed of 300 rpm for about 30 minutes to obtain a low eutectic solvent, which was stored in a desiccator. 1 gram of alkaline lignin and 19 grams of low eutectic solvent were added to the reaction bottle, 250 microliters of distilled water was added, and heated at 130°C for 5 hours. At the end of the reaction, the reaction bottle was taken out and quickly immersed in a cold water bath to end the reaction. 50 mL of hydrochloric acid solution with pH = 2 was added to the reaction bottle, lignin was precipitated, and solid was obtained by centrifugation, and freeze-dried to obtain low eutectic solvent regenerated lignin, which was marked as LDP.

[0028] Take 1.0 g of LDP and disperse it in 50 mL of 1.0 M HC1 solution to obtain a suspension; add 0.91 mL of aniline to the suspension and magnetically stir at 0°C for 2 hours to obtain an aniline solution. Take 2.30 g of ammonium persulfate (APS) and dissolve it in 50 mL of 1.0 M HC1 solution. Mix the above solutions in a 1:1 molar ratio of aniline to APS and perform in-situ chemical oxidative polymerization at 0°C for 24 hours. Filter the reaction product, repeatedly rinse the filtrate with distilled water until the pH value is 7, and dry under vacuum to a constant mass to obtain an electrode material, labeled as LDP / PANI. 1.0 / PANI.

[0029] Example 2

[0030] Mix choline chloride and p-toluenesulfonic acid in a 1:1 molar ratio, stir at 130°C and a rotation speed of 300 rpm for about 30 minutes to obtain a deep eutectic solvent, which is stored in a desiccator. Add 1 g of alkali lignin and 19 g of the deep eutectic solvent to a reaction bottle, add 250 microliters of distilled water, and heat at 130°C for 5 hours. At the end of the reaction, remove the reaction bottle and quickly immerse it in a cold water bath to end the reaction. Add 50 mL of a hydrochloric acid solution with a pH of 2 to the reaction bottle to precipitate the lignin, centrifuge to obtain a solid, and freeze-dry to obtain a deep eutectic solvent regenerated lignin, labeled as LDP.

[0031] Take 1.0 g of LDP and disperse it in 50 mL of 1.0 M HC1 solution to obtain a suspension; add 0.91 mL of aniline to the suspension and magnetically stir at 0°C for 2 hours to obtain an aniline solution. Take 2.30 g of ammonium persulfate (APS) and dissolve it in 50 mL of 1.0 M HC1 solution. Mix the above solutions in a 1:1 molar ratio of aniline to APS and perform in-situ chemical oxidative polymerization at 0°C for 24 hours. Filter the reaction product, repeatedly rinse the filtrate with distilled water until the pH value is 7, and dry under vacuum to a constant mass to obtain an electrode material, labeled as LDP 0.5 / PANI.

[0032] Example 3

[0033] Mix choline chloride and p-toluenesulfonic acid in a 1:1 molar ratio, stir at 130°C and a rotation speed of 300 rpm for about 30 minutes to obtain a deep eutectic solvent, which is stored in a desiccator. Add 1 g of alkali lignin and 19 g of the deep eutectic solvent to a reaction bottle, add 250 microliters of distilled water, and heat at 130°C for 5 hours. At the end of the reaction, remove the reaction bottle and quickly immerse it in a cold water bath to end the reaction. Add 50 mL of a hydrochloric acid solution with a pH of 2 to the reaction bottle to precipitate the lignin, centrifuge to obtain a solid, and freeze-dry to obtain a deep eutectic solvent regenerated lignin, labeled as LDP.

[0034] Take 3.0 grams of LDP and disperse in 50 milliliters of 1.0M HCl solution to obtain a suspension; add 0.91 mL of aniline to the suspension and magnetically stir at 0°C for 2 hours to obtain an aniline solution. Take 2.30g of ammonium persulfate (APS) and dissolve in 50 mL of 1.0M HCl solution. Mix the above solutions in a 1:1 molar ratio of aniline to APS and perform in-situ chemical oxidative polymerization at 0°C for 24 hours. Filter the reaction product, repeatedly rinse the filtrate with distilled water to pH 7, and dry to constant mass under vacuum to obtain an electrode material, labeled LDP 3.0 / PANI.

[0035] Example 4

[0036] Mix choline chloride and p-toluenesulfonic acid in a 1:1 molar ratio, stir at 100°C and a rotation speed of 400 rpm for about 30 minutes to obtain a deep eutectic solvent, which is stored in a desiccator. Add 1 gram of alkali lignin and 10 grams of deep eutectic solvent to a reaction bottle, add 250 microliters of distilled water, and heat at 100°C for 13 hours. At the end of the reaction, remove the reaction bottle and quickly immerse it in a cold water bath to end the reaction. Add 40 mL of hydrochloric acid solution with pH = 2 to the reaction bottle to precipitate the lignin, centrifuge to obtain a solid, and freeze-dry to obtain deep eutectic solvent regenerated lignin, labeled LDP.

[0037] Take 1.0 grams of LDP and disperse in 50 milliliters of 1.0M HCl solution to obtain a suspension; add 0.91 mL of aniline to the suspension and magnetically stir at 4°C for 2 hours to obtain an aniline solution. Take 1.80g of ammonium persulfate (APS) and dissolve in 50 mL of 1.0M HCl solution. Mix the above solutions in a 1:1 molar ratio of aniline to APS and perform in-situ chemical oxidative polymerization at 4°C for 22 hours. Filter the reaction product, repeatedly rinse the filtrate with distilled water to pH 7, and dry to constant mass under vacuum to obtain an electrode material.

[0038] Example 5

[0039] Mix choline chloride and p-toluenesulfonic acid in a 1:1 molar ratio, stir at 120°C and a rotation speed of 200 rpm for about 30 minutes to obtain a deep eutectic solvent, which is stored in a desiccator. Add 1 gram of alkali lignin and 25 grams of deep eutectic solvent to a reaction bottle, add 250 microliters of distilled water, and heat at 140°C for 3 hours. At the end of the reaction, remove the reaction bottle and quickly immerse it in a cold water bath to end the reaction. Add 60 mL of hydrochloric acid solution with pH = 2 to the reaction bottle to precipitate the lignin, centrifuge to obtain a solid, and freeze-dry to obtain deep eutectic solvent regenerated lignin, labeled LDP.

[0040] Take 1.0 g of LDP and disperse in 50 mL of 1.0 M HCl solution to obtain a suspension; add 0.91 mL of aniline to the suspension and stir magnetically at 2°C for 2 hours to obtain an aniline solution. Take 1.0 g of ammonium persulfate (APS) and dissolve in 50 mL of 1.0 M HCl solution. Mix the above solutions in a 1:1 molar ratio of aniline to APS and perform in-situ chemical oxidative polymerization at 2°C for 20 hours. Filter the reaction product, wash the filtrate repeatedly with distilled water until the pH value is 7, and dry under vacuum to a constant mass to obtain an electrode material.

[0041] Comparative Example 1

[0042] This comparative example differs from Example 1 in that the amount of LDP is changed from 1.0 g to 0 g, denoted as PANI.

[0043] The lignin, LDP in Example 1, and electrode materials obtained in Examples 1-3 and Comparative Example 1 are subjected to hydrogen nuclear magnetic resonance spectroscopy testing. The results of the nuclear magnetic resonance testing of the electrode materials obtained in Examples 1-3 and Comparative Example 1 are shown in Figure 1 , the SEM results are shown in Figure 2 , and the conductivity test results are shown in Table 1.

[0044] Table 1. Conductivity of samples before and after incorporation of lignin derivatives

[0045]

[0046] Figure 1 The H NMR spectra of lignin, LDP in Example 1, i.e., lignin before and after degradation 1 , are shown. The two peaks at 7.5-7.0 ppm correspond to the ortho, para, and meta positions on the benzene ring, respectively. The broad peak at 7.0-6.3 ppm is due to the aromatic protons in the guaiacol unit, 4.0-3.5 ppm is the methoxy proton signal, the sharp peak at 3.5-3.3 ppm is the proton signal of water in the solvent, and the peak at 3.4 ppm is the proton signal in choline chloride. The appearance of this peak may be due to a slight reaction between lignin and the solvent choline chloride during processing, or there may be a small amount of eutectic solvent residue. The sharp peak at 2.5 ppm should be the proton signal that is not deuterated in deuterated dimethyl sulfoxide. 2.5-2.2 ppm is attributed to the proton signal of the aromatic ring acetate, and it can be seen that the intensity of the acetate signal of the degraded lignin increases significantly. In addition, 4.3-4.0 ppm is the phenolic hydroxyl proton signal, and it can be seen that a stronger phenolic hydroxyl proton signal appears after degradation, which may be due to the breaking of the β-O-4 bond.

[0047] Figure 2The infrared spectra of the electrode materials obtained in Examples 1-3 and Comparative Example 1 are shown. It can be seen that the composite of lignin derivative and polyaniline also exhibits the characteristic peak of PANI. -1 The peak at 1487 cm is due to the quinone structure of PANI. -1 The sharp peak at 1301 cm is due to the benzene structure of PANI. -1 and 1113cm -1 The peaks at 3420 cm are assigned to the CN deformation of the benzene ring unit and the CH bending vibration of the N=Q=N segment. -1 The broad band at 1728 cm is due to the NH stretching of aromatic amine, and the weak peak intensity of the composite can be attributed to the connection between NH and OH and the interaction between LDP and PANI. -1 The intensity of the peak at 528 cm-1 increased significantly with the increase of the percentage of LDP in the composites of lignin derivatives and polyaniline. -1 The intensity of the aromatic ring deformation peak at α-H decreased significantly, indicating that the aromatic ring in the polymer structure became more stable.

[0048] Figure 3 The SEM images of the electrode materials obtained in Examples 1-3 and Comparative Example 1 are shown. Figure 3 The fibrous structure of PANI and the LDP particles bonded to it can be clearly seen. The surface morphology changes significantly with increasing LDP content in the composite. In the absence of LDP, the particles are thicker and smoother. The composite of a lignin derivative and polyaniline shows a mixture of nanofibers and particles, with LDP imparting a stable cylindrical shape. The nanofiber morphology provides a high surface contact area, a preferred factor for preparing conductive polymer composites. Figure 3 The LDP / PANI composites are described to form a tightly integrated nanocomposite matrix in the polymer matrix.

[0049] Table 1 shows the changes in the conductivity of the resulting electrode materials when varying the amount of LDP added to PANI. Compared to PANI, the conductivity of LDP / PANI ranges from 0.57 S / cm to 1.36 S / cm. As the LDP doping level in PANI increases, the conductivity continues to increase further, but at a slower rate. LDP acts as the primary dopant during the polymerization process, maximizing the number of charge carriers. Using LDP as a dopant can produce polymers with excellent semiconducting properties.

[0050] The above specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the present embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for preparing an electrode material by regenerating lignin using a deep eutectic solvent, characterized in that: The electrode material is obtained by mixing the regenerated lignin of the deep eutectic solvent, aniline and an oxidant, and performing an in-situ oxidative polymerization reaction in an acidic medium; The preparation method of the deep eutectic solvent regenerated lignin is: S1-1. Mix choline chloride and p-toluenesulfonic acid in a molar ratio of 1:1, and stir at 100-130° C. for about 30 minutes to obtain a deep eutectic solvent; S1-2: adding lignin and a deep eutectic solvent to a reaction flask at a mass ratio of 1:(10-25), adding deionized water, and heating at 100-140°C for 3-13 hours to obtain a mixed solution; removing the reaction flask and immersing it in a cold water bath to terminate the reaction; S1-3: adding an acidic solution to the mixed solution to precipitate the lignin, and then centrifuging and drying to obtain the deep eutectic solvent-regenerated lignin.

2. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1, characterized in that: The specific steps are as follows: dispersing the regenerated lignin of the low eutectic solvent in an acidic medium to obtain a suspension; adding aniline to the suspension and stirring at 0-4°C to obtain an aniline solution; dissolving an oxidant with a mass 1-2.5 times that of the aniline in the acidic medium, mixing with the aniline solution, and performing an in-situ oxidative polymerization reaction; filtering after the reaction is completed, and washing and drying the filter residue to obtain the electrode material.

3. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 2, characterized in that: The acidic medium is a hydrochloric acid solution.

4. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1, characterized in that: The mass ratio of lignin to deep eutectic solvent in S1-2 is 1:

19.

5. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1, characterized in that: The mass ratio of the amount of deionized water added to lignin in S1-2 is 1:

4.

6. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1, characterized in that: The acidic solution in S1-3 has a pH of 2, and the added amount is in a mass ratio of (40-60) to lignin:

1.

7. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1 or 2, characterized in that: The dosage ratio of the deep eutectic solvent regenerated lignin to aniline was (0.5-3 g) : 0.91 mL.

8. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1 or 2, characterized in that: The oxidant is ammonium persulfate.

9. The method for preparing an electrode material by regenerating lignin using a deep eutectic solvent according to claim 1 or 2, characterized in that: The reaction time of the in-situ oxidative polymerization is 20-24 h, and the reaction temperature of the in-situ oxidative polymerization is 0-4°C.

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