Polyionic liquid modified self-supporting biochar electrode and application thereof in field of capacitive deionization

Abstract

The invention discloses a self-supporting biochar electrode modified by polyion liquid and application of the self-supporting biochar electrode in the field of capacitive deionization, and belongs to the field of water treatment. The preparation method comprises the following steps: depositing 1-vinyl-3-ethylimidazole bis (trifluoromethanesulfonyl) imide salt ([VEIM] [NTf2]) on the surface of a self-supporting biochar electrode BSC to obtain a polyion liquid modified self-supporting biochar electrode; then the self-supporting biochar electrode modified by the polyion liquid is used as an electrode for capacitive deionization desalination, and the salt adsorption capacity SACA per unit area can reach 0.921 mg / cm < 2 >; the strength is sufficient to withstand water flow impacts in CDI operation.

Description

Technical Field

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

[0002] Capacitive deionization (CDI), also known as electro - adsorption, works by applying an external voltage to form an electrostatic field between electrodes. Ions move towards the electrode plates with opposite charges under the action of electrostatic force and are adsorbed on the electrode surface, thereby achieving the purpose of desalination or purification. The properties of electrode materials are the essential factors determining the CDI efficiency.

[0003] Biochar is regarded as one of the most promising electrode materials due to its wide sources, renewability, low cost, and simple preparation. The traditional method for fabricating biochar electrodes is to grind carbon materials into powders, add conductive agents and binders, dissolve them together in organic solvents to form a slurry mixture, and then evenly coat the slurry on the surface of a metal current collector (such as nickel foam, aluminum foil, or copper foil). After drying, it is cut into electrodes. This not only has a complex preparation process, but also the added materials such as binders not only do not contribute to the electrochemical performance, but also block the pores of the active materials and reduce their performance. After being used for a period of time, the active materials will peel off from the current collector, affecting the service life of the electrodes.

[0004] Wood has excellent mechanical properties. The three - dimensional carbon material made from wood after high - temperature carbonization can maintain the integrity of the wood structure, so it can be directly used as an electrode without being crushed. After being made into a slurry and coated on the current collector, it not only simplifies the process, but also reduces the use of non - active substances, further reducing costs and improving environmental friendliness. At the same time, it effectively reduces the shedding of active substances caused by mechanical stress or electrochemical cycling, thereby extending the service life of the electrodes and reducing the maintenance costs and resource consumption caused by frequent electrode replacement. However, due to its high brittleness and low strength, massive biochar is difficult to withstand water flow impact during CDI operation, so it is urgent to improve its strength to meet the actual application requirements. Summary of the Invention

[0005] [Technical Problem]

[0006] The three - dimensional carbon material made from wood after high - temperature carbonization has high brittleness and low strength, and is difficult to withstand water flow impact during CDI operation. Therefore, it is urgent to improve its strength to meet the actual application requirements.

[0007] [Technical Solution]

[0008] To solve the above problems, the present invention polymerizes and deposits 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][NTf2]) ionic liquid on the surface of a self-supporting biochar electrode to obtain a self-supporting biochar electrode modified with polyionic liquid; then, using the self-supporting biochar electrode modified with polyionic liquid as the electrode, capacitive deionization desalination is carried out, and the salt adsorption capacity per unit area SAC A can be as high as 0.921 mg / cm 2 ; the strength is sufficient to withstand the water flow impact during CDI operation.

[0009] The first object of the present invention is to provide a method for preparing a self-supporting biochar electrode modified with polyionic liquid, including the following steps:

[0010] (1) Preparation of impregnation solution:

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

[0012] (2) Preparation of the electrode:

[0013] The self-supporting biochar electrode BSC is impregnated in the impregnation solution, kept at -0.04 to -0.06 MPa under vacuum for 15 to 25 min, then raised to -0.08 to 0.12 MPa and maintained for 20 to 30 min, taken out, and irradiated with ultraviolet light in a nitrogen atmosphere to form a crosslinked network, obtaining a self-supporting biochar electrode modified with polyionic liquid.

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

[0015] In an 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 an embodiment of the present invention, the mass ratio of 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][NTf2]) to 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) is 1:0.01 to 0.03.

[0017] In an embodiment of the present invention, the preparation method of the self-supporting biochar electrode BSC is as follows:

[0018] The balsa wood slices are hydrothermally treated at 170 - 190 °C for 4 - 10 h to obtain the pretreated balsa wood slices; under a nitrogen atmosphere, the pretreated balsa wood slices are heated to 700 - 900 °C and held for 110 - 130 min; then cooled to room temperature, washed, and dried to obtain the self-supporting biochar electrode BSC;

[0019] Among them, the size of the balsa wood slices is (1 - 2)×(1 - 2)×(0.2 - 0.5) cm 3 ; the heating rate is 3 - 5 °C / min; the cooling rate is 3 - 5 °C / min; the washing is with a hydrochloric acid solution with a concentration of 0.5 - 1.5 mol / L and deionized water until neutral; the drying is at 100 - 110 °C for 10 - 15 h.

[0020] In an embodiment of the present invention, the ultraviolet irradiation is at 365 nm, 8 - 15 mW / cm 2 UV lamp irradiation for 5 - 15 min.

[0021] The second object of the present invention is the self-supporting biochar electrode modified with polyionic liquid prepared by the method of the present invention.

[0022] The third object of the present invention is to provide a method for capacitive deionization desalination based on a self-supporting biochar electrode modified with polyionic liquid, including the following steps:

[0023] Using the self-supporting biochar electrode modified with polyionic liquid as the cathode and anode, and performing electrochemical treatment in a salt-containing solution.

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

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

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

[0027] [Beneficial effects]

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

[0029] Compared with traditional electrodes, the self-supporting biochar electrode modified with polyionic liquid used in the present invention does not need to prepare slurry, coat or add current collector and binder, avoiding the use of organic solvents; not only is the process more environmentally friendly, but also the proportion of inactive ingredients is reduced, thereby significantly improving the salt adsorption capacity of the electrode. Moreover, the self-supporting biochar electrode modified with polyionic liquid has no risk of slurry shedding during use and has excellent long-term stability.

[0030] (2) Hierarchical porous structure and high conductivity enable efficient desalination:

[0031] Thanks to the inherent high porosity of balsa wood, the hierarchical porous structure formed after carbonization can still maintain sufficient ion transmission 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 better than other self-supporting electrode materials.

[0032] (3) Polyionic liquids enhance mechanical strength:

[0033] The three-dimensional network structure formed by the highly conductive polyionic liquid on the surface of the biochar skeleton not only provides a conductive pathway, but also effectively inhibits the brittle fracture of the carbon material through interfacial bonding enhancement and stress dispersion, making the compressive strength of the electrode reach 5.1 MPa (the original BSC is 1.9 MPa), which can withstand the 50 kPa water flow impact in the CDI device.

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

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

[0036] In addition, conventional conductive polymers are mostly rigid linear structures with weak interfacial bonding with carbon substrates, which are prone to brittle cracking. However, ionic liquids, with their flexible molecular structure, can fit tightly to carbon substrates through van der Waals forces, hydrogen bonds and other forces, significantly enhancing interfacial compatibility and structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a physical picture 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. Specific embodiments

[0039] The following are descriptions of the preferred embodiments of the present invention. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0040] Testing method:

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

[0042] Place the sample between two parallel indenter heads of a universal material testing machine, apply a vertical pressure at a constant rate (0.5 mm / min), and record the maximum load (N) when the sample breaks.

[0043] Compressive strength (MPa) = maximum load (N) / sample compression area (mm 2 )

[0044] (2) Calculation method for salt adsorption capacity per unit mass of the electrode (SAC A , mg / cm 2 )

[0045]

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

[0047] Raw materials used in the examples:

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

[0049] Birch wood: purchased from Guo's Outdoor Garden, Linyi, Shandong.

[0050] Linden wood: purchased from Research Wood Workshop, Hefei, Anhui.

[0051] The preparation method of the wood chips is as follows: Cut balsa wood, linden wood or birch wood into wood chips with dimensions of 1.5 cm × 1.5 cm × 0.2 cm, wash them 4 times with deionized water, then wash them 3 times with absolute ethanol, and dry them for standby.

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

[0053] For the solutions involved in the examples and comparative examples, if the solvent is not specifically specified, water is used as the solvent.

[0054] Example 1

[0055] A method for preparing a self - supported biochar electrode modified with polyionic liquid, comprising the following steps:

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

[0057] Hydrothermally pretreat the balsa wood chips at 180 °C for 6 h to enhance carbonization stability; then, under a nitrogen atmosphere, heat up to 800 °C at a rate of 5 °C / min and hold for 120 min; then cool down to room temperature at a rate of 5 °C / min; wash with 1 mol / L hydrochloric acid solution and deionized water until neutral, and finally dry at 105 °C for 12 h to obtain the self - supported biochar electrode BSC;

[0058] (2) Preparation of impregnation solution:

[0059] In a glove box, dissolve 0.3 g of 1 - vinyl - 3 - ethylimidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][NTf2]) in 10 mL of acetone / water mixed solution (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 - methylpropiophenone (Irgacure 2959) to the above monomer solution and stir until completely dissolved to obtain the impregnation solution;

[0061] (3) Modification of the electrode with polyionic liquid:

[0062] Immerse the self - supported biochar electrode BSC in the impregnation solution, keep it under vacuum at - 0.05 MPa for 20 min, then raise the pressure to - 0.1 MPa and maintain for 25 min, and then take it out;

[0063] Irradiate with a 365 nm UV lamp (10 mW / cm 2 ) for 10 min under a nitrogen atmosphere to form a cross - linked network, and obtain a self - supported biochar electrode modified with polyionic liquid (BSC - 1).

[0064] Example 2

[0065] Adjust the concentration of the monomer solution in step (2) of Example 1 to 0.03 g / mL, and keep the others the same as in Example 1 to obtain a self - supported biochar electrode modified with polyionic liquid (BSC - 2).

[0066] Example 3

[0067] Adjust the concentration of the monomer solution in step (2) of Example 1 to 0.045 g / mL, and keep the others the same as in Example 1 to obtain a self-supporting biochar electrode modified with poly(ionic liquid) (BSC-3).

[0068] Comparative Example 1

[0069] Do not adopt steps (2) and (3) of Example 2 to obtain a self-supporting biochar electrode BSC.

[0070] Comparative Example 2

[0071] Adjust the balsa wood chips in step (1) of Example 2 to birch wood chips, and keep the others the same as in Example 2 to obtain an electrode.

[0072] Comparative Example 3

[0073] Adjust the balsa wood chips in step (1) of Example 2 to basswood chips, and keep the others the same as in Example 2 to obtain an electrode.

[0074] Comparative Example 4

[0075] Adjust step (1) of Example 2 to be:[[]]

[0076] Soak the balsa wood chips in 0.7 mol / L phosphoric acid solution for 12 h; then, under a nitrogen atmosphere, heat them to 800 °C at a rate of 5 °C / min and keep them at this temperature for 120 min; then cool them to room temperature at a rate of 5 °C / min; wash them with 1 mol / L hydrochloric acid solution and deionized water until neutral, and finally dry them at 105 °C for 12 h to obtain a self-supporting biochar electrode BSC;

[0077] Keep the others the same as in Example 2 to obtain an electrode (BSC-P).

[0078] Comparative Example 5

[0079] Adjust 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][NTf2]) in step (2) of Example 2 to 1-vinyl-3-ethylimidazolium bromide ([VEIM][Br]); keep the others the same as in Example 2 to obtain an electrode.

[0080] Comparative Example 6

[0081] Adjust step (3) of Example 2 to be:[[]]

[0082] Immerse the self-supporting biochar electrode BSC in the impregnation solution, keep it under vacuum at -0.05 MPa for 45 min, and then take it out; irradiate it with a 365 nm UV lamp (10 mW / cm 2 ) for 10 min in a nitrogen atmosphere to form a crosslinked network;

[0083] The rest is the same as in Example 2 to obtain the electrode.

[0084] Comparative Example 7

[0085] Traditional electrode 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] Self-supporting electrode made of basswood (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] An electrode was prepared by electrodepositing polypyrrole on the BSC electrode; this process was carried out in a three - electrode system;

[0090] Among them, it 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 (enhancing ion permeability) dissolved in 1 M hydrochloric acid aqueous solution.

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

[0092] Example 4

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

[0094] The electrodes prepared in Examples 1 - 3 and Comparative Examples 1 - 7 were used as the cathode and anode respectively, and were electrochemically treated in an aqueous sodium chloride solution; among them, the concentration of sodium chloride was 300 mg / L; the voltage in the electrochemical treatment was 1.2 V; the distance between the cathode and the 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 Not measured in the literature Comparative Example 8 0.3 Not measured in the literature Comparative Example 9 0.648 3.5

[0098] Example 5

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

[0100] Using the electrodes prepared in Example 1 as the cathode and anode respectively, and conducting electrochemical treatment in an aqueous sodium chloride solution;

[0101] Wherein, the concentration of sodium chloride is 300 mg / L;

[0102] In the electrochemical treatment, the distance between the cathode and the anode is 1 cm, and the voltages are 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 desalination using a self-supporting biochar electrode modified with polyionic liquid, comprising the following steps:

[0108] Using the electrodes prepared in Example 1 as the cathode and anode respectively, and conducting electrochemical treatment;

[0109] Wherein, the concentrations of sodium chloride are 150, 300, and 500 mg / L;

[0110] In the electrochemical treatment, the distance between the cathode and the 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 preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for preparing a self-supporting biochar electrode modified with polyionic liquid, characterized in that, It includes the following steps: (1) Preparation of the impregnation solution: In a glove box, 1-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide ([VEIM][NTf2]) is dissolved in an acetone / water mixed solution to prepare a monomer solution. 2-Hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959) is added to the above monomer solution and stirred until completely dissolved to obtain the impregnation solution. (2) Preparation of the electrode: The self-supporting biochar electrode is impregnated in the impregnation solution, kept under vacuum at -0.04 to -0.06 MPa for 15 to 25 min, then raised to -0.08 to 0.12 MPa and maintained for 20 to 30 min, taken out, and irradiated with ultraviolet light in a nitrogen atmosphere to form a cross-linked network, obtaining a self-supporting biochar electrode modified with poly(ionic liquid).

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

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

1.

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

03.

5. The method according to claim 1, wherein The ultraviolet irradiation is at 365 nm, 8 - 15 mW / cm 2 The UV lamp is irradiated for 5 - 15 min.

9. The self-supporting biochar electrode modified with poly(ionic liquid) prepared by the method according to any one of claims 1 to 5.

7. A method for capacitive deionization desalination using a self-supporting biochar electrode modified with polyionic liquid, characterized in that, It includes the following steps: The self-supporting biochar electrode modified with poly(ionic liquid) according to claim 6 is used as the cathode and anode for electrochemical treatment in a salt-containing solution.

8. The method according to claim 7, wherein The concentration of sodium chloride in the salt-containing solution is 100 to 500 mg / L.

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

10. The application of the self-supporting biochar electrode modified with poly(ionic liquid) according to claim 6 in the field of capacitive deionization (CDI) desalination.

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