A polyionic liquid modified self-supporting biochar electrode and its application in the field of capacitive deionization

Abstract

The application discloses a kind of polyionic liquid modified self-supporting biochar electrode and its application in the field of capacitive deionization, belong to water treatment field.The application is deposited in self-supporting biochar electrode BSC surface by 1-vinyl-3-ethyl imidazole double trifluoromethanesulfonyl imidate salt ([VEIM][NTf2]), and polyionic liquid modified self-supporting biochar electrode is obtained;Afterwards, polyionic liquid modified self-supporting biochar electrode is used as electrode, and capacitive deionization desalination is carried out, and the salt adsorption capacity SAC of unit area A It can be as high as 0.921mg / cm 2 ; Strength is enough to withstand water flow impact in CDI operation.

Description

Technical Field

[0001] This invention relates to a self-supporting biochar electrode modified with polyionic liquid and its application in the field of capacitive deionization, belonging to the field of water treatment. Background Technology

[0002] Capacitive deionization (CDI), also known as electroadsorption, works by creating an electrostatic field between electrodes using an applied voltage. Ions move towards the oppositely charged electrode plates under the influence of electrostatic force and are adsorbed onto the electrode surface, thus achieving desalination or purification. The properties of the electrode material are the essential factor determining the efficiency of CDI.

[0003] Biochar is considered one of the most promising electrode materials due to its wide availability, renewable nature, low cost, and simple preparation. Traditional biochar electrode manufacturing methods involve grinding biochar into powder, adding conductive agents and binders, dissolving them together in an organic solvent to form a slurry mixture, and then uniformly coating the slurry onto the surface of a metal current collector (such as nickel foam, aluminum foil, or copper foil). After drying, the mixture is cut into electrodes. This process is not only complex, but the added binders and other materials not only do not contribute to electrochemical performance but also clog the pores of the active material, reducing its performance. After a period of use, the active material will peel off from the current collector, affecting the electrode's lifespan.

[0004] Wood possesses excellent mechanical properties. Three-dimensional carbon materials made from wood through high-temperature carbonization retain the integrity of the wood structure, allowing for direct use as electrodes without the need for pulverization. The resulting slurry is coated onto the current collector, simplifying the process, reducing the use of inactive substances, further lowering costs, and improving environmental friendliness. It also effectively reduces active material shedding caused by mechanical stress or electrochemical cycling, thus extending electrode lifespan and reducing maintenance costs and resource consumption associated with frequent electrode replacements. However, block biochar is brittle and has low strength, making it difficult to withstand water flow impacts during CDI operation. Therefore, there is an urgent need to improve its strength to meet practical application requirements. Summary of the Invention

[0005] [Technical Issues]

[0006] Three-dimensional carbon materials made from wood carbonized at high temperatures are brittle and have low strength, making them difficult to withstand the impact of water flow during CDI operation. Therefore, it is urgent to improve their strength to meet the needs of practical applications.

[0007] [Technical Solution]

[0008] To address the aforementioned issues, this invention polymerizes and deposits 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) ionic liquid onto the surface of a self-supporting biochar electrode, obtaining a polyionic liquid-modified self-supporting biochar electrode. Subsequently, using this polyionic liquid-modified self-supporting biochar electrode as the electrode, capacitive deionization and desalting are performed, achieving a salt adsorption capacity per unit area of ​​SAC. A It can reach up to 0.921 mg / cm³ 2 Its strength is sufficient to withstand the impact of water flow during CDI operation.

[0009] The first objective of this invention is to provide a method for preparing a polyionic liquid-modified self-supporting biochar electrode, comprising the following steps:

[0010] (1) Preparation of impregnation solution:

[0011] In a glove box, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) was dissolved in an acetone / water mixture to prepare a monomer solution; 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959) was added to the monomer solution and stirred until completely dissolved to obtain an impregnation solution;

[0012] (2) Electrode preparation:

[0013] The self-supporting biochar electrode (BSC) was immersed in an impregnation solution and maintained under vacuum at -0.04 to -0.06 MPa for 15 to 25 minutes. Then, the pressure was increased to -0.08 to 0.12 MPa and maintained for 20 to 30 minutes. After removal, it was irradiated with ultraviolet light under a nitrogen atmosphere to form a cross-linked network, thus obtaining a polyionic liquid-modified self-supporting biochar electrode.

[0014] In one embodiment of the present invention, the concentration of the monomer solution is 0.015 to 0.045 g / mL.

[0015] In one embodiment of the present invention, the volume ratio of acetone to water in the acetone / water mixed solution is 3 to 5:1.

[0016] In one embodiment of the present invention, the mass ratio of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) to 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959) is 1:0.01 to 0.03.

[0017] In one embodiment of the present invention, the method for preparing a self-supporting biochar electrode (BSC) is as follows:

[0018] Balsa wood chips were hydrothermally treated at 170–190℃ for 4–10 h to obtain pretreated balsa wood chips; under a nitrogen atmosphere, the pretreated balsa wood chips were heated to 700–900℃ and held for 110–130 min; then cooled to room temperature, washed, and dried to obtain self-supporting biochar electrode (BSC).

[0019] The dimensions of the balsa wood chips are (1~2)×(1~2)×(0.2~0.5)cm. 3 The heating rate is 3-5℃ / min; the cooling rate is 3-5℃ / min; the washing is done with 0.5-1.5 mol / L hydrochloric acid solution and deionized water until neutral; the drying is done at 100-110℃ for 10-15 h.

[0020] In one embodiment of the present invention, the ultraviolet irradiation is 365 nm, 8–15 mW / cm². 2 Irradiate with UV lamp for 5–15 minutes.

[0021] The second objective of this invention is to prepare a self-supporting biochar electrode modified with a polyionic liquid using the method described herein.

[0022] A third objective of this invention is to provide a method for capacitive deionization and desalting using a self-supporting biochar electrode modified with a polyionic liquid, comprising the following steps:

[0023] A self-supporting biochar electrode modified with a polyionic liquid was used as the cathode and anode for electrochemical treatment in a salt solution.

[0024] In one embodiment of the present invention, the concentration of sodium chloride in the salt solution is 100–500 mg / L.

[0025] In one embodiment of the present invention, the voltage during electrochemical treatment is 0.9–1.5 V, and the distance between the cathode and the anode is 0.5–1.5 cm.

[0026] The fourth objective of this invention is the application of the self-supporting biochar electrode modified with polyionic liquid as described in this invention in the field of capacitive deionization (CDI) desalination.

[0027] [Beneficial Effects]

[0028] (1) Simplify the preparation process and improve environmental friendliness and adsorption performance:

[0029] Compared to traditional electrodes, the self-supporting biochar electrode modified with polyionic liquid in this invention eliminates the need for slurry preparation, coating, or the addition of current collectors and binders, thus avoiding the use of organic solvents. This not only makes the process more environmentally friendly but also reduces the proportion of inactive components, thereby significantly improving the electrode's salt adsorption capacity. Furthermore, the self-supporting biochar electrode modified with polyionic liquid has no risk of slurry shedding during use and exhibits excellent long-term stability.

[0030] (2) The hierarchical porous structure works synergistically with high conductivity to achieve efficient desalination:

[0031] Thanks to the inherent high porosity of balsa wood, the hierarchical porous structure formed after carbonization can still maintain sufficient ion transport channels after modification with polyionic liquid. At the same time, the introduction of highly conductive polyionic liquid significantly improves the conductivity of the electrode. This conductive-porous synergistic effect makes the salt adsorption capacity of the electrode superior to other self-supporting electrode materials.

[0032] (3) Polyionic liquid enhances mechanical strength:

[0033] The three-dimensional network structure formed by the highly conductive polyionic liquid on the surface of the biochar framework not only provides a conductive path, but also effectively suppresses the brittle fracture of the carbon material through enhanced interfacial bonding and stress dispersion, enabling the electrode to achieve a compressive strength of 5.1 MPa (the original BSC was 1.9 MPa) and withstand the impact of 50 kPa water flow in the CDI device.

[0034] (4) Functional integration of ionic liquids: wide pH stability, high conductivity and strong interfacial compatibility with carbon substrates

[0035] Ionic liquids, as ionic compounds, possess intrinsically high conductivity and remain stable in a wide pH range. In contrast, conventional conductive polymers (such as polypyrrole (PPy), polyaniline (PANI), and polythiophene (PT)) rely on acidic dopants to maintain their conductivity. In neutral or alkaline environments, their conductivity decreases, and they may even lose their function due to hydrolysis or oxidation.

[0036] In addition, conventional conductive polymers are mostly rigid linear structures with weak interfacial bonding with carbon substrates, making them prone to brittleness. Ionic liquids, on the other hand, with their flexible molecular structure, can adhere tightly to carbon substrates through van der Waals forces, hydrogen bonds, and other forces, significantly enhancing interfacial compatibility and structural stability. Attached Figure Description

[0037] Figure 1 This is a photograph of the self-supporting biochar electrode modified with polyionic liquid prepared in Example 1.

[0038] Figure 2XRD patterns (a) and Raman spectra (b) of BSC, BSC-1, BSC-2 and BSC-3. Detailed Implementation

[0039] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0040] Test method:

[0041] (1) Test method for compressive strength:

[0042] The sample was placed between two parallel indenters of a universal testing machine, and a vertical pressure was applied at a constant rate (0.5 mm / min). The maximum load (N) at which the sample broke was recorded.

[0043] Compressive strength (MPa) = Maximum load (N) / Sample pressure area (mm²) 2 )

[0044] (2) Salt adsorption capacity per unit mass of electrode (SAC) A mg / cm 2 Calculation method:

[0045]

[0046] Where: C0—initial concentration of salt solution (mg / L); Ct—concentration of salt solution after desalination (mg / L); V—volume of treated salt solution (L); A—area of ​​biochar electrode (cm²) 2 ).

[0047] Raw materials used in the examples:

[0048] Balsa wood: Purchased from Guangzhou Qigao Light Wood Trading Company.

[0049] Birch wood: Purchased from Guoji Outdoor Garden, Linyi, Shandong.

[0050] Linden wood: Purchased from Yanmu Workshop, Hefei, Anhui.

[0051] The preparation method of wood chips is as follows: cut balsa wood, linden wood or birch wood into wood chips with a size of 1.5 cm × 1.5 cm × 0.2 cm, wash with deionized water 4 times, then wash with anhydrous ethanol 3 times, and dry for later use.

[0052] 1-Vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]): purchased from Shanghai Chengjie Chemical Co., Ltd.

[0053] Unless otherwise specified, the solvents used in the solutions mentioned in the examples and comparative examples are water.

[0054] Example 1

[0055] A method for preparing a polyionic liquid-modified self-supporting biochar electrode includes the following steps:

[0056] (1) Preparation of self-supporting biochar electrode (BSC):

[0057] Balsa wood chips were hydrothermally pretreated at 180℃ for 6 h to enhance carbonization stability; then, under a nitrogen atmosphere, the temperature was increased to 800℃ at a rate of 5℃ / min and held for 120 min; then, the temperature was reduced to room temperature at a rate of 5℃ / min; then, the chips were washed with 1 mol / L hydrochloric acid solution and deionized water until neutral; and finally, the chips were dried at 105℃ for 12 h to obtain a self-supporting biochar electrode (BSC).

[0058] (2) Preparation of impregnation solution:

[0059] In a glove box, 0.3 g of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) was dissolved in 10 mL of acetone / water mixture (4:1, v / v) to prepare a monomer solution with a concentration of 0.015 g / mL.

[0060] Add 0.006 g of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959) to the above monomer solution and stir until completely dissolved to obtain the impregnation solution;

[0061] (3) Polyionic liquid modified electrode:

[0062] The self-supporting biochar electrode (BSC) was immersed in the immersion solution, and then kept under vacuum at -0.05 MPa for 20 min, followed by raising the pressure to -0.1 MPa and maintaining it for 25 min before being removed.

[0063] Under a nitrogen atmosphere, a 365 nm UV lamp (10 mW / cm²) was used. 2 Irradiation for 10 min resulted in the formation of a cross-linked network, yielding a polyionic liquid-modified self-supporting biochar electrode (BSC-1).

[0064] Example 2

[0065] The concentration of the monomer solution in step (2) of Example 1 was adjusted to 0.03 g / mL, while other parameters remained the same as in Example 1, to obtain a polyionic liquid modified self-supporting biochar electrode (BSC-2).

[0066] Example 3

[0067] The concentration of the monomer solution in step (2) of Example 1 was adjusted to 0.045 g / mL, while other steps remained the same as in Example 1, to obtain a polyionic liquid modified self-supporting biochar electrode (BSC-3).

[0068] Comparative Example 1

[0069] Without using steps (2) and (3) of Example 2, a self-supporting biochar electrode (BSC) was obtained.

[0070] Comparative Example 2

[0071] The balsa wood chips in step (1) of Example 2 were changed to birch wood chips, while the rest remained the same as in Example 2, and the electrode was obtained.

[0072] Comparative Example 3

[0073] The balsa wood chips in step (1) of Example 2 were changed to linden wood chips, while the rest remained the same as in Example 2, to obtain the electrode.

[0074] Comparative Example 4

[0075] Adjust step (1) of Example 2 as follows:

[0076] Balsa wood chips were soaked in 0.7 mol / L phosphoric acid solution for 12 h; then, under a nitrogen atmosphere, the temperature was increased to 800℃ at a rate of 5℃ / min and held for 120 min; then, the temperature was decreased to room temperature at a rate of 5℃ / min; then, the chips were washed with 1 mol / L hydrochloric acid solution and deionized water until neutral; and finally, the chips were dried at 105℃ for 12 h to obtain a self-supporting biochar electrode (BSC).

[0077] Everything else remained the same as in Example 2, resulting in electrode (BSC-P).

[0078] Comparative Example 5

[0079] In step (2) of Example 2, the 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) was changed to 1-vinyl-3-ethylimidazolium bromide salt ([VEIM][Br]); all other steps remained the same as in Example 2, and the electrode was obtained.

[0080] Comparative Example 6

[0081] Adjust step (3) of Example 2 as follows:

[0082] The self-supporting biochar electrode (BSC) was immersed in the impregnation solution and maintained under vacuum at -0.05 MPa for 45 min, then removed and subjected to a 365 nm UV lamp (10 mW / cm²) under a nitrogen atmosphere. 2 Irradiation for 10 minutes forms a cross-linked network;

[0083] Everything else remains the same as in Example 2, and the electrode is obtained.

[0084] Comparative Example 7

[0085] Traditional electrodes made of balsa wood (Promising honeycombed cork activated carbon for high desalination performance brackish water treatment. Industrial Crops and Products, 2024, 222:119887).

[0086] Comparative Example 8

[0087] Efficient capacitive deionization using natural basswood-derived, freestanding, hierarchically porous carbon electrodes. ACS Applied Materials & Interfaces, 2018, 10(37):31260-31270.

[0088] Comparative Example 9

[0089] Polypyrrole is electrodeposited onto the BSC electrode to form the electrode; this process is carried out in a three-electrode system.

[0090] The system includes a BSC working electrode, a Pt counter electrode, and an Ag / AgCl reference electrode. The electrolyte is 0.1 M pyrrole monomer, 0.1 M sodium p-toluenesulfonate (dopant), and 0.1 M LiClO4 (to enhance ion permeability) dissolved in 1 M hydrochloric acid aqueous solution.

[0091] The electrolyte was placed in an ice bath at 10°C, and pulse electrodeposition was performed by periodically switching the on time (0.8 V, 5 s) and the off time (10 s) for a total duration of 30 min. The electrolyte was then washed with water and dried.

[0092] Example 4

[0093] A method for capacitive deionization and desalination using a self-supporting biochar electrode modified with polyionic liquid includes the following steps:

[0094] The electrodes prepared in Examples 1-3 and Comparative Examples 1-7 were used as cathodes and anodes, respectively, and were subjected to electrochemical treatment in an aqueous sodium chloride solution. The concentration of sodium chloride was 300 mg / L; the voltage during the electrochemical treatment was 1.2 V; and the distance between the cathode and anode was 1 cm.

[0095] The test results are as follows:

[0096] Table 1

[0097] example <![CDATA[SAC A (mg / cm 2 )]]> Compressive strength (MPa) Comparative Example 1 0.533 1.9 Example 1 0.751 3.7 Example 2 0.921 5.1 Example 3 0.727 3.2 Comparative Example 2 0.258 7.1 Comparative Example 3 0.352 5.9 Comparative Example 4 0.621 1.5 Comparative Example 5 0.698 5.3 Comparative Example 6 0.602 2.2 Comparative Example 7 0.0354 Untested literature Comparative Example 8 0.3 Untested literature Comparative Example 9 0.648 3.5

[0098] Example 5

[0099] A method for capacitive deionization and desalination using a self-supporting biochar electrode modified with polyionic liquid includes the following steps:

[0100] The electrodes prepared in Example 1 were used as cathode and anode, respectively, and were subjected to electrochemical treatment in an aqueous sodium chloride solution.

[0101] The concentration of sodium chloride is 300 mg / L;

[0102] In the electrochemical treatment, the distance between the cathode and anode is 1 cm, and the voltage is 0.9, 1.2, and 1.5 V.

[0103] The test results are as follows:

[0104] Table 2

[0105] Voltage (V) <![CDATA[SAC A (mg / cm 2 )]]> 0.9 0.751 1.2 0.921 1.5 0.872

[0106] Example 6

[0107] A method for capacitive deionization and desalination using a self-supporting biochar electrode modified with polyionic liquid includes the following steps:

[0108] The electrodes prepared in Example 1 were used as cathodes and anodes, respectively, and subjected to electrochemical treatment.

[0109] The concentrations of sodium chloride were 150, 300, and 500 mg / L.

[0110] In the electrochemical treatment, the distance between the cathode and anode is 1 cm, and the voltage is 1.2 V.

[0111] The test results are as follows:

[0112] Table 3

[0113] Concentration (mg / L) <![CDATA[SAC A (mg / cm 2 )]]> 150 0.558 300 0.921 500 1.188

[0114] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a self-supporting biochar electrode modified with a polyionic liquid, characterized in that, Includes the following steps: (1) Preparation of impregnation solution: In a glove box, 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide salt ([VEIM][NTf2]) was dissolved in an acetone / water mixture to prepare a monomer solution; Add 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959) to the above monomer solution and stir until completely dissolved to obtain the impregnation solution; (2) Electrode preparation: The self-supporting biochar electrode was immersed in an impregnation solution and maintained under vacuum at -0.04 to -0.06 MPa for 15 to 25 minutes, then raised to -0.08 to 0.12 MPa and maintained for 20 to 30 minutes. After removal, it was irradiated with ultraviolet light under a nitrogen atmosphere to form a cross-linked network, thus obtaining a polyionic liquid modified self-supporting biochar electrode.

2. The method according to claim 1, characterized in that, The concentration of the monomer solution is 0.015–0.045 g / mL.

3. The method according to claim 1, characterized in that, The volume ratio of acetone to water in an acetone / water mixed solution is 3 to 5:

1.

4. The method according to claim 1, characterized in that, The mass ratio of 1-vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide ([VEIM][NTf2]) to 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (Irgacure 2959) is 1:0.01 to 0.

03.

5. The method according to claim 1, characterized in that, Ultraviolet irradiation is at 365nm, 8–15mW / cm². 2 Irradiate with UV lamp for 5–15 minutes.

6. The polyionic liquid-modified self-supporting biochar electrode prepared by the method according to any one of claims 1 to 5.

7. A method for capacitive deionization and desalination using a self-supporting biochar electrode modified with polyionic liquid, characterized in that, Includes the following steps: The self-supporting biochar electrode modified with the polyionic liquid as described in claim 6 is used as the cathode and anode, and electrochemical treatment is performed in a salt solution.

8. The method according to claim 7, characterized in that, The concentration of sodium chloride in the salt solution is 100–500 mg / L.

9. The method according to claim 7, characterized in that, The voltage in the electrochemical treatment is 0.9–1.5V, and the distance between the cathode and anode is 0.5–1.5cm.

10. The application of the polyionic liquid-modified self-supporting biochar electrode of claim 6 in the field of capacitive deionization (CDI) desalination.

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