Electrode mat for capacitive deionization and method of making the same

Abstract

The application belongs to the technical field of capacitive deionization desalination, and relates to an electrode felt for capacitive deionization and a preparation method thereof. The preparation comprises the following steps: dissolving PAN and acetylated lignin into a homogeneous spinning solution by using DMF and DMSO double solvents, and then electrospinning to obtain a carbon fiber precursor; then, under a nitrogen atmosphere, the precursor is subjected to pre-oxidation, carbonization and CO2 activation treatment; finally, the obtained material is subjected to acidification treatment to obtain the electrode felt for capacitive deionization with a high specific surface area. The method has a wide raw material source and low cost. The specific pre-oxidation, carbonization and carbon dioxide etching process are combined with each other, so that the prepared electrode felt has a high specific surface and a high capacitive deionization effect.

Description

Technical Field

[0001] This invention belongs to the field of capacitive deionization technology, and particularly relates to an electrode felt for capacitive deionization and its preparation method. Background Technology

[0002] CDI technology not only has significant development potential in desalination and wastewater treatment, but also holds broad application prospects in the resource recovery of environmental waste. The development of CDI technology has gone through several stages, including proposing the CDI technology concept, explaining the CDI mechanism using Faraday reactions and ion exchange, and further explaining the MCDI mechanism. Traditional CDI reactors have low energy efficiency because when a voltage is applied across the electrodes, after the carbon electrode material adsorbs salt ions from the water to a certain extent, the increased ion concentration inside the electrode reduces the electrostatic force of the applied external electric field, posing a risk of desorption of ions stored in the electrode. This means that, especially in the later stages of electroadsorption, ion adsorption and desorption will occur simultaneously in the pores of the electrode material, reducing desalination efficiency. Membrane capacitive deionization (MCDI), a derivative technology of CDI, combines ion exchange membranes (IEMs) and carbon electrode materials into the CDI system. Under the action of an electrostatic field, the charged functional groups on the anion exchange membrane (AEM) and cation exchange membrane (CEM) can selectively permeate anions and cations respectively, allowing ions in the solution to migrate more regularly and directionally, thereby improving electroadsorption efficiency. The introduction of ion exchange membranes not only allows the microporous structure in the electrode material to maintain the same function as in CDI, but also enables the macroporous structure, which plays a smaller role in CDI, to store ions, significantly improving reactor performance. The limited adsorption capacity of electrode materials leading to insufficient desalination efficiency, and the high cost of electrodes resulting in a lack of market competitiveness compared to technologies like RO, are two major problems currently facing CDI technology applications. Therefore, the key to improving desalination efficiency lies in how to produce electrode materials with a larger specific surface area at a lower cost and fully utilize the pore structure of the electrode material. Summary of the Invention

[0003] The purpose of this invention is to provide a low-cost, environmentally friendly, and simple-to-operate porous electrode felt for capacitive deionization with high specific surface area and its preparation method. The method uses widely available raw materials and has low cost. The specific pre-oxidation, carbonization, and carbon dioxide etching processes are combined to give the prepared electrode felt a high specific surface area and a high capacitive deionization effect.

[0004] To achieve the objective of this invention, the technical solution adopted is as follows: a method for preparing an electrode felt for capacitor deionization, comprising the following steps:

[0005] (1) Polyacrylonitrile (PAN) is fully dissolved and uniformly dispersed in a mixed solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) to obtain solution A;

[0006] Specifically, using polyacrylonitrile (PAN), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) as raw materials, a homogeneous solution A is obtained by heating and stirring in an oil bath (generally stirring at a constant temperature of 90°C to obtain higher dissolution efficiency).

[0007] (2) Mix solution A from step (1) with acetylated lignin to obtain solution B; the mass ratio of polyacrylonitrile to acetylated lignin is at most 3:2.

[0008] Specifically, acetylated lignin is added to solution A at a certain mass ratio, and solution B is prepared by stirring thoroughly under heating conditions (stirring in an oil bath at 60-90°C). The acetylation of lignin is used to improve its solubility in organic solvents and increase the compatibility of polymers and lignin.

[0009] (3) Transfer solution B from step (2) to an electrospinning machine to prepare carbon fiber precursor.

[0010] (4) After the carbon fiber precursor in step (3) is cut, it is first pre-oxidized in an air atmosphere. After the pre-oxidation is completed, it is immediately carbonized and activated by CO2 in a nitrogen atmosphere to obtain a porous felt made of polyacrylonitrile / lignin.

[0011] Specifically, the pre-oxidation process includes the following steps: after the carbon fiber precursor is placed in a tube furnace, it is first heated to 180°C at a rate of 0.5–1°C / min, and then heated to 250–280°C at a rate of 0.5–1°C / min, and held at that temperature for 120–180 min.

[0012] Because when the linear macromolecule of PAN is heated above 180℃, the nitrile groups on the side chains undergo cyclization and cross-linking, thus achieving thermal stabilization, it can be said that the structure of polyacrylonitrile only undergoes significant changes above 180℃. Therefore, pre-oxidation is performed at a heating rate of 0.5–1℃ / min before this (1℃ / min is optimal from a cost perspective). Furthermore, excessively rapid heating will cause the electrode felt to curl and increase its brittleness. Since electrochemical testing uses a three-electrode system in an electrolytic cell, the electrode felt is best when it is flat, compressible, and cuttable; similarly, the electrode felt should be soft and flat during use. After reaching 180℃, pre-oxidation continues at a heating rate of 0.5–1℃ / min. The reduced rate ensures complete pre-oxidation, forming a heat-resistant trapezoidal structure.

[0013] Specifically, the carbonization and CO2 activation treatment steps include: heating to 900-1000℃ at a rate of 0.5℃ / min under a nitrogen atmosphere, then introducing CO2 into the N2 stream (controlling the flow rate of the two gases at 0.2-0.4 NL / min), holding at this temperature for 120-180 min, and then naturally cooling under the protection of the surrounding atmosphere (a mixture of carbon dioxide and nitrogen).

[0014] Although pre-oxidation forms a heat-resistant trapezoidal structure, excessively rapid carbonization can still cause the fibers to bend, making them unsuitable for placement into the electro-adsorption module.

[0015] (5) The porous felt prepared by polyacrylonitrile / lignin in step (4) is acidified by soaking in mixed acid, and after washing and drying, the porous electrode felt for capacitor deionization is obtained. The mixed acid is a mixture of nitric acid and sulfuric acid. Acidification with mixed acid introduces hydroxyl groups, which will lead to a decrease in conductivity and thus a decrease in specific capacitance. Therefore, a mixed acid of sulfuric acid and nitric acid of appropriate concentration should be selected for acidification. The concentration of sulfuric acid in the mixed acid is 0.5-1 mol / L, the concentration of HCl is 0.5-1 mol / L, and the soaking time is 20-40 minutes. Compared with the unacidified solution, the specific capacitance only decreases by about 0.5, while the hydrophilicity is improved and the adsorption capacity is greatly increased. The optimal concentration of sulfuric acid in the mixed acid is 0.5 mol / L, the concentration of HCl is 0.5 mol / L, and the soaking time is 30 minutes. At this time, the maximum adsorption capacity can be obtained.

[0016] Preferably, in step (1), the volume ratio of N,N-dimethylformamide (DMF) to dimethyl sulfoxide (DMSO) is 1:1, the total solids content of acetylated lignin and polyacrylonitrile is 30%, and the mass ratio of polyacrylonitrile to acetylated lignin is 1 to 1.5: 1 to 4 (e.g., 2:3, 1:1 and 3:2, preferably 1:1 to 4).

[0017] And / or, in step (2), the lignin acetylation treatment method includes: dissolving lignin in a mixed solution of pyridine and acetic anhydride (generally, about 1g of lignin is used in 30ml of mixed solution), wherein the volume ratio of pyridine to acetic anhydride is 1:1, stirring at room temperature to carry out the acetylation reaction (the reaction time is generally 36-48h), filtering and collecting the precipitate after the reaction is completed, and freeze-drying to obtain acetylated lignin.

[0018] Generally, after the reaction is complete, the reaction solution is stirred and then added dropwise to ice water.

[0019] And / or, in step (3), the electrostatic voltage is 15-20KV, the spinning solution push speed is 45-35μL / min, the receiving distance is 10-20cm, and the receiving roller speed is 100-300r / min.

[0020] And / or, in step (5), wash until neutral, and dry by vacuum drying at 40-80°C for 12-24 hours.

[0021] Compared with the prior art, the present invention achieves the following beneficial effects:

[0022] (1) Lignin has a wide range of sources and high chemical stability. It is an organic fiber obtained by chemical treatment of natural wood and is environmentally friendly. In this invention, lignin is used to partially replace polyacrylonitrile as a carbon source to prepare porous electrode felt. The preparation method is simple, environmentally friendly, and can effectively reduce costs.

[0023] (2) The specific pre-oxidation, carbonization and carbon dioxide etching processes are combined to make the prepared electrode felt have a high specific surface area. In particular, when CO2 is activated, the etching rate of acetylated lignin is faster than that of PAN. It can be used as a partial sacrificial polymer, which will greatly improve the porosity and pore structure of the electrode material. On this basis, further synergistic mixed acid acidification treatment is used to further optimize the pore structure and increase the specific surface area. At the same time, hydroxyl groups are introduced to improve hydrophilicity. The prepared electrode felt has excellent desalination effect in capacitive deionization desalination applications. Especially when used in MCDI technology, the electrode felt plays a more complete role and improves the salt adsorption efficiency more effectively. Attached Figure Description

[0024] Figure 1 These are scanning electron microscope images of the composite porous carbon electrode materials in Examples 1-4;

[0025] Figure 2 These are nitrogen adsorption-desorption isotherm curves of the composite porous carbon electrode materials in Examples 1-4;

[0026] Figure 3 These are constant current charge-discharge diagrams of the composite porous carbon electrode materials of Examples 1-4 in a current density of 1 A / g, a voltage range of -1 to 0 V, and an electrolyte of 6 M KOH.

[0027] Figure 4 These are the cyclic voltammetry curves of the composite porous carbon electrode materials in Examples 1-4 with a voltage window of -1 to 0V and an electrolyte of 6M KOH.

[0028] Figure 5 The AC impedance diagrams of the composite porous carbon electrode materials in Examples 1-4 are shown.

[0029] Figure 6 The graphs show the adsorption-desorption curves of the composite porous carbon electrode materials in Examples 1-4 in a 100 mL / g NaF solution.

[0030] Figure 7 This is the electro-adsorption device used for desalination performance testing in the embodiments.

[0031] Figure 8 This is the MCDI module in the embodiment. Detailed Implementation

[0032] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or variations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0033] The present invention will be further described in detail below with reference to the embodiments:

[0034] Example 1

[0035] Step 1: Weigh 8.77g of polyacrylonitrile and add it to 50mL of DMF and DMSO mixture. Seal the mixture in a blue-capped bottle and heat it in an oil bath at 90℃ while stirring until it is completely dissolved to obtain a mixed solution.

[0036] Step 2: Weigh 13.15g of lignin and add it to the mixed solution from Step 1. Seal the solution in a blue-capped bottle and heat it in an oil bath at 90°C with stirring until it is completely dissolved to obtain solution A.

[0037] Step 3: Transfer solution A to a 10mL syringe and perform electrospinning. The electrostatic voltage is 18KV, the spinning solution push rate is 35μL / min, the receiving distance is 10cm, and the receiving roller speed is 150r / min. A successfully spun carbon fiber precursor is obtained.

[0038] Step 4: After cutting the carbon fiber precursor from Step 3, place it in a tube furnace. First, in an air atmosphere, heat it to 180℃ at a rate of 1℃ / min, then heat it to 250℃ at a rate of 0.5℃ / min, and hold it for 120 min to obtain pre-oxidized fiber. Carbonize the pre-oxidized fiber in a nitrogen atmosphere, heat it to 1000℃ at a rate of 0.5℃ / min, introduce CO2 into the N2 stream, and control the flow rates of the two gases to be between 0.2 and 0.4 NL / min (fluctuations within this range have little impact on the treatment effect). Hold it for 120 to 180 min (fluctuations within this range have little impact on the effect), and allow it to cool naturally under the protection of the mixed gas to obtain a porous felt made of polyacrylonitrile / lignin.

[0039] Step 5: Place the porous electrode felt from Step 4 into a mixed acid for acidification. The optimal concentration of sulfuric acid and HCl in the mixed acid is 0.5 mol / L, which will result in the maximum adsorption capacity. After soaking for 30 minutes, wash until neutral and dry in a vacuum oven at 60°C for 16 hours to obtain the final porous electrode felt, named RP-1.

[0040] This can be seen through SEM testing (see...) Figure 1 In (a) of the sample, the fiber thickness is relatively uniform, but there are a few beads, mainly due to the strong interaction between lignin and polyacrylonitrile. The fiber diameter is approximately 0.3-0.4 μm. In nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve, and the specific surface area of ​​the electrode material is 79.6 m². 2 / g; its electrochemical performance was further studied. In the galvanostatic charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the charge-discharge curve was a symmetrical triangular shape, with a specific capacitance of 65.0F / g. In the cyclic voltammetry (CV) test, the scan rate was 10mV / s, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the curve showed a similar rectangular shape. In the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) of the electrode material was 1.98Ω. In the desalination performance test, the voltage applied across the electrode was 1.6V, the electrolyte was 50ml of 100mg / L NaF aqueous solution, and the electroadsorption capacity of the electrode material was 8.29mg / g.

[0041] Example 2

[0042] Step 1: Weigh 8.77g of polyacrylonitrile and add it to 50mL of DMF and DMSO mixture. Seal the mixture in a blue-capped bottle and heat it in an oil bath at 90℃ while stirring until it is completely dissolved to obtain a mixed solution.

[0043] Step 2: Weigh 13.15g of lignin and dissolve it in 360mL of a mixed solution of pyridine and acetic anhydride, where the volume ratio of pyridine to acetic anhydride is 1:1. Stir at room temperature for 48h to carry out the acetylation reaction. Then, after stirring the reaction solution, add it dropwise to ice water, filter to collect the precipitate, and freeze-dry it using a freeze dryer to obtain acetylated lignin. Weigh 13.15g of the obtained acetylated lignin and add it to the mixed solution from Step 1. Seal the solution in a blue-capped bottle and heat it in an oil bath at 90℃ with stirring until completely dissolved to obtain solution A.

[0044] Step 3: Transfer solution A to a 10mL syringe and perform electrospinning. The electrostatic voltage is 18KV, the spinning solution push rate is 35μL / min, the receiving distance is 10cm, and the receiving roller speed is 150r / min. A successfully spun carbon fiber precursor is obtained.

[0045] Step 4: After cutting the carbon fiber precursor from Step 3, place it in a tube furnace. First, in an air atmosphere, heat it to 180℃ at a rate of 1℃ / min, then heat it to 250℃ at a rate of 0.5℃ / min, and hold it for 120 min to obtain pre-oxidized fiber. Carbonize the pre-oxidized fiber in a nitrogen atmosphere, heat it to 1000℃ at a rate of 0.5℃ / min, introduce CO2 into the N2 stream, and control the flow rates of the two gases to be between 0.2 and 0.4 NL / min (fluctuations within this range have little impact on the treatment effect). Hold it for 120 to 180 min (fluctuations within this range have little impact on the effect), and allow it to cool naturally under the protection of the mixed gas to obtain a porous felt made of polyacrylonitrile / lignin.

[0046] Step 5: The porous electrode felt from Step 4 is placed in a mixed acid solution with a sulfuric acid concentration of 0.5 mol / L and an HCl concentration of 0.5 mol / L. After soaking for 30 minutes, it is washed until neutral and dried in a vacuum oven at 60°C for 16 hours to obtain the final porous electrode felt, named RP-2.

[0047] This can be seen through SEM testing (see...) Figure 1 In (b) of the sample, the fiber thickness is relatively uniform, but there are a few beads, mainly due to the strong interaction between lignin and polyacrylonitrile. The fiber diameter is approximately 0.3-0.5 μm. In the nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve, and the specific surface area of ​​the electrode material is 1123 m². 2 / g; its electrochemical performance was further studied. In the galvanostatic charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to 0V, the electrolyte was 6M KOH, the charge-discharge curve was symmetrical triangular, and the specific capacitance was 288.8F / g; in the cyclic voltammetry (CV) test, the scan rate was 10mV / s, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the curve showed a similar rectangular shape; in the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) of the electrode material was 0.96Ω; in the desalination performance test, the voltage applied across the electrode was 1.6V, the electrolyte was 50ml of 100mg / L NaF aqueous solution, and the electroadsorption capacity of the electrode material was 51.37mg / g.

[0048] Example 3

[0049] Step 1: Weigh 10.97g of polyacrylonitrile and add it to 50mL of a mixture of DMF and DMSO. Seal the mixture in a blue-capped bottle and heat it in an oil bath at 90℃ while stirring until it is completely dissolved to obtain a mixed solution.

[0050] Step 2: Weigh 10.97g of lignin and dissolve it in 300mL of a mixed solution of pyridine and acetic anhydride, where the volume ratio of pyridine to acetic anhydride is 1:1. Stir at room temperature for 48h to carry out the acetylation reaction. Then, after stirring the reaction solution, add it dropwise to ice water, filter to collect the precipitate, and freeze-dry it using a freeze dryer to obtain acetylated lignin. Weigh 10.97g of the obtained acetylated lignin and add it to the mixed solution from Step 1. Seal the solution in a blue-capped bottle and heat it in an oil bath at 90℃ with stirring until completely dissolved to obtain solution A.

[0051] Step 3: Transfer solution A to a 10mL syringe and perform electrospinning. The electrostatic voltage is 18KV, the spinning solution push rate is 35μL / min, the receiving distance is 10cm, and the receiving roller speed is 150r / min. A successfully spun carbon fiber precursor is obtained.

[0052] Step 4: After cutting the carbon fiber precursor from Step 3, place it in a tube furnace. First, in an air atmosphere, heat it to 180℃ at a rate of 1℃ / min, then heat it to 250℃ at a rate of 0.5℃ / min, and hold it for 120 min to obtain pre-oxidized fiber. Carbonize the pre-oxidized fiber in a nitrogen atmosphere, heating it to 1000℃ at a rate of 0.5℃ / min. Introduce CO2 into the N2 stream, controlling the flow rates of both gases within 0.2–0.4 NL / min (fluctuations within this range have little impact on the treatment effect), and hold it for 120–180 min (fluctuations within this range have little impact on the effect). Allow it to cool naturally under the protection of the mixed gas. This yields a porous felt made of polyacrylonitrile / lignin.

[0053] Step 5: The porous electrode felt from Step 4 is placed in a mixed acid solution with a sulfuric acid concentration of 0.5 mol / L and an HCl concentration of 0.5 mol / L. After soaking for 30 minutes, it is washed until neutral and dried in a vacuum oven at 60°C for 16 hours to obtain the final porous electrode felt, named RP-3.

[0054] This can be seen through SEM testing (see...) Figure 1 In (c) of the sample, the fibers are relatively uniform in thickness, with a diameter of approximately 0.5-0.8 μm. In nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve, and the specific surface area of ​​this electrode material is 556.3 m². 2 / g; its electrochemical performance was further studied. In the galvanostatic charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to 0V, the electrolyte was 6M KOH, the charge-discharge curve was symmetrical triangular, and the specific capacitance was 176.8F / g; in the cyclic voltammetry (CV) test, the scan rate was 10mV / s, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the curve showed a similar rectangular shape; in the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) of the electrode material was 1.54Ω; in the desalination performance test, the voltage applied across the electrode was 1.6V, the electrolyte was 50ml of 100mg / L NaF aqueous solution, and the electroadsorption capacity of the electrode material was 31.13mg / g.

[0055] Example 4

[0056] Step 1: Weigh 13.15g of polyacrylonitrile and add it to 50mL of a mixed solution of DMF and DMSO. Seal the solution in a blue-capped bottle and heat it in an oil bath at 90℃ while stirring until completely dissolved.

[0057] Step 2: Weigh 8.77g of lignin and dissolve it in 240mL of a mixed solution of pyridine and acetic anhydride, where the volume ratio of pyridine to acetic anhydride is 1:1. Stir at room temperature for 48h to carry out the acetylation reaction. Then, after stirring the reaction solution, add it dropwise to ice water, filter to collect the precipitate, and freeze-dry it using a freeze dryer to obtain acetylated lignin. Weigh 8.77g of the obtained acetylated lignin and add it to the mixed solution from Step 1. Seal the solution in a blue-capped bottle and heat it in an oil bath at 90℃ with stirring until completely dissolved to obtain solution A.

[0058] Step 3: Transfer solution A to a 10mL syringe and perform electrospinning. The electrostatic voltage is 18KV, the spinning solution push rate is 35μL / min, the receiving distance is 10cm, and the receiving roller speed is 150r / min. A successfully spun carbon fiber precursor is obtained.

[0059] Step 4: After cutting the carbon fiber precursor from Step 3, place it in a tube furnace. First, in an air atmosphere, heat it to 180℃ at a rate of 1℃ / min, then heat it to 250℃ at a rate of 0.5℃ / min, and hold it for 120 min to obtain pre-oxidized fiber. Carbonize the pre-oxidized fiber in a nitrogen atmosphere, heating it to 1000℃ at a rate of 0.5℃ / min. Introduce CO2 into the N2 stream, controlling the flow rates of both gases within 0.2–0.4 NL / min (fluctuations within this range have little impact on the treatment effect), and hold it for 120–180 min (fluctuations within this range have little impact on the effect). Allow it to cool naturally under the protection of the mixed gas. A porous felt made of polyacrylonitrile / lignin is obtained.

[0060] Step 5: The porous electrode felt from Step 4 is placed in a mixed acid solution with a sulfuric acid concentration of 0.5 mol / L and an HCl concentration of 0.5 mol / L. After soaking for 30 minutes, it is washed until neutral and dried in a vacuum oven at 60°C for 16 hours to obtain the final porous electrode felt, named RP-4.

[0061] This can be seen through SEM testing (see...) Figure 1 In (d) of the sample, the fiber thickness is relatively uniform, with a fiber diameter of approximately 0.9-1.1 μm; in nitrogen adsorption-desorption (BET) analysis, the nitrogen adsorption-desorption curve of the electrode material is a type IV curve, and the specific surface area of ​​the electrode material is 263.5 m². 2 / g; its electrochemical performance was further investigated. In the galvanostatic charge-discharge (GCD) test, the current density was 1A / g, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the charge-discharge curve was a symmetrical triangular shape, with a measured specific capacitance of 98.1F / g; in the cyclic voltammetry (CV) test, the scan rate was 10mV / s, the voltage window was -1 to 0V, the electrolyte was 6M KOH, and the curve showed a similar rectangular shape; in the electrochemical impedance spectroscopy (EIS) test of the electrode material, the equivalent series resistance (Rs) of the electrode material was 1.79Ω; in the desalination performance test, the voltage applied across the electrode was 1.6V, the electrolyte was 50ml of 100mg / L NaF aqueous solution, and the electroadsorption capacity of the electrode material was 18.32mg / g.

[0062] In the above embodiments and comparative examples, the desalination performance test was conducted using a system consisting of a DC power supply, a water storage tank, a peristaltic pump, an MCDI module, and a conductivity meter. Figure 7 The electroadsorption device shown was tested. The water tank stores the salt solution; the peristaltic pump provides power to allow the salt solution to pass through the MCDI module and controls the flow rate; the conductivity meter is used to test the conductivity of the salt solution; and the DC power supply provides external voltage to the MCDI module.

[0063] MCDI module such as Figure 8 As shown, the module consists of an acrylic plate, a silicone pad to prevent water leakage, a titanium current collector to improve conductivity and make the current distribution more uniform, graphite paper (current collector), electrodes, anion and cation membranes, and a mesh to separate the two electrodes to prevent short circuits.

[0064] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A method for preparing an electrode felt for capacitive deionization, characterized in that: Includes the following steps: (1) Dissolve and uniformly disperse polyacrylonitrile in a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide to obtain solution A; (2) Mix solution A from step (1) thoroughly with acetylated lignin to obtain solution B. The mass ratio of polyacrylonitrile to acetylated lignin is at most 3:

2. (3) Transfer solution B from step (2) to an electrospinning machine to prepare carbon fiber precursor; (4) After cutting the carbon fiber precursor in step (3), it is first pre-oxidized in an air atmosphere. After the pre-oxidation is completed, it is immediately carbonized and activated by CO2 in a nitrogen atmosphere to obtain a porous felt made of polyacrylonitrile / lignin. The pre-oxidation includes the following steps: under an air atmosphere, first heat to 180°C at a rate of 0.5–1°C / min, then increase the temperature to 250–280°C at a rate of 0.5–1°C / min, and hold for 120–180 min; The carbonization and CO2 activation treatment includes the following steps: under a nitrogen atmosphere, the temperature is increased to 900-1000℃ at a rate of 0.5-1℃ / min, then CO2 is introduced into the N2 stream, and the temperature is maintained for 120-180min, and then the temperature is naturally cooled under the protection of the atmosphere; the flow rate of the two gases is controlled at 0.2-0.4NL / min. (5) The porous felt prepared by polyacrylonitrile / lignin in step (4) is acidified by soaking in mixed acid, and then washed and dried to obtain a porous electrode felt for capacitor deionization; the mixed acid is a mixture of nitric acid and sulfuric acid, the sulfuric acid concentration in the mixed acid is 0.5-1 mol / L, the HCl concentration is 0.5-1 mol / L, and the soaking time is 20-40 minutes.

2. The method for preparing the electrode felt for capacitor deionization according to claim 1, characterized in that: In step (1), the volume ratio of N,N-dimethylformamide and dimethyl sulfoxide is 1:1, and the total solids content of acetylated lignin and polyacrylonitrile is 30%. And / or, in step (1), the mass ratio of polyacrylonitrile to acetylated lignin is 1-1.5:1-4.

3. The method for preparing the electrode felt for capacitor deionization according to claim 1, characterized in that: In step (1), the mass ratio of polyacrylonitrile to acetylated lignin is 1:1 to 4.

4. The method for preparing the electrode felt for capacitor deionization according to claim 1, characterized in that: In step (2), the lignin acetylation treatment method includes: dissolving lignin in a mixed solution of pyridine and acetic anhydride, wherein the volume ratio of pyridine to acetic anhydride is 1:1, stirring at room temperature to carry out the acetylation reaction, filtering and collecting the precipitate after the reaction is completed, and freeze-drying to obtain acetylated lignin.

5. The method for preparing the electrode felt for capacitor deionization according to claim 1, characterized in that: In step (3), the electrostatic voltage is 15-20KV, the spinning solution push speed is 45-35μL / min, the receiving distance is 10-20cm, and the receiving roller speed is 100-300r / min.

6. The method for preparing the electrode felt for capacitor deionization according to claim 1, characterized in that: In step (5), the concentration of sulfuric acid in the mixed acid is 0.5 mol / L, the concentration of HCl is 0.5 mol / L, and the soaking time is 30 minutes.

7. An electrode felt for capacitive deionization, characterized in that: The electrode felt is prepared by the method according to any one of claims 1 to 6.

8. The application of the electrode felt for capacitive deionization as described in claim 7, characterized in that: The electrode felt is used as an electrode in a CDI or MCDI.

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