Electrode for capacitive deionization and preparation method thereof

Abstract

The invention relates to the technical field of capacitive deionization, in particular to an electrode for capacitive deionization and a preparation method thereof. The electrode for capacitive deionization comprises an electrode material, a carbon material and an adhesive, the electrode material is DHPZ, and a preparation method of the DHPZ comprises the following steps: S1, primary reaction: grinding and mixing 2, 5-dihydroxy-1, 4-benzoquinone and 2, 3-diaminophenazine, heating in inert gas, cooling, filtering, cleaning and performing vacuum drying to obtain a primary product; and S2, acidizing the primary product, namely mixing the primary product with 2mol / L nitric acid according to a mass-volume ratio of 1: 1, magnetically stirring for 5 hours, filtering, cleaning with deionized water, centrifuging for multiple times, and drying in vacuum at 60 DEG C for 15 hours to obtain the DHPZ. According to the electrode for capacitive deionization and the preparation method of the electrode, the problems that in the capacitive deionization related technology, the desalting capacity is low, and the adsorption capacity and the removal efficiency are not high are solved.

Description

Technical Field

[0001] The present application relates to the technical field of capacitive deionization, and in particular to an electrode for capacitive deionization and a preparation method thereof. Background Art

[0002] Ammonium ions can cause eutrophication of water bodies, promote the massive reproduction of aquatic plants such as algae, form algal blooms or red tides, consume a large amount of dissolved oxygen in the water, cause the death of aquatic organisms such as fish due to lack of oxygen, and destroy the aquatic ecological balance.

[0003] At present, the commonly used methods for removing ammonium ions in water include chemical precipitation, ion exchange and biological treatment. However, the chemical precipitation method requires the addition of a large amount of chemical agents to the water, which will produce a large amount of precipitated sludge, with high treatment costs and the introduction of new impurities. The ion exchange method uses ion exchange resins to exchange with ammonium ions in water, adsorbing ammonium ions on the resin to remove ammonium ions, but ion exchange resins need to be regenerated regularly, and a large amount of regenerated wastewater will be generated during the regeneration process, which is difficult to treat. The biological treatment method uses the metabolism of microorganisms to convert ammonium ions into harmless substances such as nitrogen, thereby removing ammonium ions, but this method requires a long reaction time and has high requirements on environmental conditions, such as temperature, pH value, etc.

[0004] Capacitive Deionization (CDI) is a new water treatment technology based on electrochemical principles. Compared with the above-mentioned traditional water treatment methods, CDI technology does not require the addition of chemical agents during the deionization process and only consumes a small amount of electrical energy during the electrode charging and discharging process. Therefore, it has lower energy consumption and does not produce secondary pollution. It is a green and environmentally friendly water treatment technology.

[0005] The electrodes in CDI technology usually use activated carbon or graphene, but in practical applications it is found that their desalination ability is low, and the adsorption capacity and removal efficiency are not high. Summary of the invention

[0006] The present application provides an electrode for capacitive deionization and a preparation method thereof, so as to solve the problems of low desalination capacity, low adsorption capacity and low removal efficiency in the related technologies of capacitive deionization.

[0007] In a first aspect, an electrode for capacitive deionization is provided, comprising an electrode material, a carbon material and a binder:

[0008] The electrode material is DHPZ, and its structural formula is shown below:

[0009]

[0010] The preparation method of DHPZ comprises the following steps:

[0011] S1. Preliminary reaction: grind and mix 2,5-dihydroxy-1,4-benzoquinone and 2,3-diaminophenazine in a molar ratio of 1:3 to 1:5, and heat them in an inert gas at 180 to 220° C. for 5 to 7 hours, filter them after cooling, wash them, and vacuum dry them to obtain a primary product;

[0012] S2. Acidification treatment of the primary product: mixing the primary product with 2 mol / L nitric acid at a mass volume ratio of 1:1, and magnetically stirring for 5 hours, filtering, washing with deionized water, centrifuging for multiple times, and vacuum drying at 60° C. for 15 hours to obtain the DHPZ.

[0013] Preferably, in S1, the cleaning includes cleaning with deionized water and cleaning with ethanol for 3 to 4 times respectively.

[0014] Preferably, the vacuum drying condition in S1 is vacuum drying at 60° C. for 15 to 20 hours.

[0015] Preferably, the carbon material is selected from carbon black and activated carbon.

[0016] Preferably, the mass ratio of the DHPZ, the carbon material and the adhesive is 7:2:1.

[0017] Preferably, it further comprises NMP, and the volume mass ratio of the NMP to the total amount of DHPZ, carbon material and binder is 1:5 to 1:10.

[0018] Preferably, the inert gas comprises nitrogen or argon.

[0019] Preferably, the binder is selected from one of carboxymethyl cellulose and polytetrafluoroethylene.

[0020] In a second aspect, a method for preparing an electrode for capacitive deionization is provided, which is used to prepare an electrode for capacitive deionization as claimed in any one of claims 1 to 8, characterized in that it comprises the following steps:

[0021] DHPZ, carbon material and binder are uniformly mixed in a ratio of 7:2:1 to obtain a mixture, NMP is added dropwise, and the mixture is ground for 1 to 5 minutes to obtain a slurry, wherein the mass volume ratio of the NMP to the mixture is 1:5 to 1:10;

[0022] The slurry is applied to an electrode sheet with a thickness of 80 to 300 μm to obtain an electrode.

[0023] The beneficial effects of the technical solution provided by this application include:

[0024] The present application provides an electrode for capacitive deionization and a preparation method thereof, wherein 2,5-dihydroxy-1,4-benzoquinone and 2,3-diaminophenazine are ground and mixed, and subjected to acid treatment to obtain DHPZ, and DHPZ is used as a part of the electrode to prepare the electrode together with a carbon material and a binder, so that the desalination capacity in the capacitive deionization application, especially the removal of ammonium ions, is improved, and the desalination amount and removal efficiency are high. Therefore, the problems of low desalination capacity, low adsorption capacity and low removal efficiency in the related technologies of capacitive deionization can be solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 Schematic diagram of the DHPZ preparation process provided for this application;

[0027] Figure 2 A Gaussian diagram of Example 1 provided in this application;

[0028] Figure 3 A schematic diagram of the electrochemical performance of Example 1 provided in this application;

[0029] Figure 4 A schematic diagram of the deionization capacity of Example 1 provided in this application;

[0030] Figure 5 Schematic diagram of the long deionization cycle capacity of Example 1 provided in this application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0032] See also Figure 1 As shown, the present application provides an electrode for capacitive deionization, which can solve the problems of low desalination capacity, low adsorption capacity and low removal efficiency in the related technologies of capacitive deionization.

[0033] The electrode for capacitive deionization comprises an electrode material, a carbon material and a binder, wherein the structural formula of the electrode material is as follows:

[0034]

[0035] The preparation method of DHPZ comprises the following steps:

[0036] S1. Preliminary reaction: 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and 2,3-diaminophenazine (TTFQ) are ground and mixed in a molar ratio of 1:3 to 1:5, and heated in an inert gas at 180 to 220° C. for 5 to 7 hours, and filtered after cooling, and then washed and dried to obtain a primary product;

[0037] The chemical formula of the initial product is:

[0038]

[0039] S2. Acidification treatment of the primary product: mixing the primary product with 2 mol / L nitric acid at a mass volume ratio of 1:1, and magnetically stirring for 5 hours, filtering, washing with deionized water, centrifuging for multiple times, and vacuum drying at 60° C. for 15 hours to obtain the DHPZ, specifically, the mass volume ratio is mg:mL. The “multiple times” in the “multiple times” of centrifuging is 3 to 6 times.

[0040] Furthermore, the reaction formula of the initial product is as follows:

[0041]

[0042] After acidification, the final product DHPZ was obtained:

[0043]

[0044] In some embodiments, in S1, the cleaning includes cleaning with deionized water and ethanol for 3 to 4 times respectively.

[0045] In some embodiments, the vacuum drying condition in S1 is vacuum drying at 60° C. for 15 to 20 hours.

[0046] In some embodiments, the carbon material is selected from carbon black and activated carbon.

[0047] In some embodiments, the ratio of DHPZ, carbon material, and binder is 7:2:1;

[0048] In some embodiments, the capacitive deionization electrode further comprises N-methylpyrrolidone (NMP), wherein the volume mass ratio of NMP to the total amount of DHPZ, carbon material and binder is 1:5 to 1:10. It should be noted that the NMP is pure, and the unit of volume mass ratio is mL to g.

[0049] In some embodiments, the inert gas includes nitrogen or argon.

[0050] In some embodiments, the binder is selected from one of carboxymethyl cellulose and polytetrafluoroethylene.

[0051] Example 1

[0052] In this embodiment, the electrode for capacitive deionization includes electrode material, activated carbon and carboxymethyl cellulose, and the preparation method of the electrode material includes the following steps:

[0053] S1. Grind and mix 1 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4 mmol of 2,3-diaminophenazine, and heat them at 200° C. in nitrogen for 6 h. Filter them after cooling. Wash the product three times with deionized water and three times with ethanol. Dry them under vacuum at 60° C. for 16 h to obtain a primary product.

[0054] S2. Acidification treatment of the primary product: 50 mg of the primary product was mixed with 50 mL of 2 mol / L nitric acid, and magnetically stirred for 5 h. After filtering, the mixture was washed with deionized water, centrifuged three times, and vacuum dried at 60° C. for 15 h to obtain an electrode material, which was recorded as DHPZ.

[0055] The mass ratio of DHPZ: activated carbon: carboxymethyl cellulose is 7:2:1. In this embodiment, 7 mg of DHPZ, 2 mg of activated carbon, and 1 mg of carboxymethyl cellulose are taken;

[0056] After mixing DHPZ, activated carbon and carboxymethyl cellulose, 1 mL of NMP was added, and the mixture was ground and then applied to the electrode sheet with a coating thickness of 150 μm. The electrode sheet was made of a 1 cm diameter 2 Round carbon paper.

[0057] Example 2

[0058] In this embodiment, the electrode for capacitive deionization includes electrode material, carbon black and carboxymethyl cellulose, and the preparation method of the electrode material includes the following steps:

[0059] S1. Grind and mix 1 mmol of 2,5-dihydroxy-1,4-benzoquinone and 3 mmol of 2,3-diaminophenazine, and heat them at 180°C in nitrogen for 5 h. Filter after cooling, wash the product with deionized water 4 times, and then wash it with ethanol 4 times. Dry it in vacuum at 60°C for 15 h to obtain a primary product.

[0060] S2. Acidification treatment of the primary product: 50 mg of the primary product was mixed with 50 mL of 2 mol / L nitric acid, and magnetically stirred for 5 h. After filtering, the mixture was washed with deionized water, centrifuged 5 times, and vacuum dried at 60° C. for 15 h to obtain an electrode material, which was recorded as DHPZ.

[0061] The mass ratio of DHPZ to carbon black and carboxymethyl cellulose is 7:2:1. In this embodiment, 7 mg of DHPZ, 2 mg of carbon black and 1 mg of carboxymethyl cellulose are used;

[0062] After DHPZ, carbon black and carboxymethyl cellulose were mixed, 0.5 mL of NMP was added, and the mixture was ground and then applied to the electrode sheet with a coating thickness of 80 μm. The electrode sheet was made of a 1 cm diameter 2 Round carbon paper.

[0063] Example 3

[0064] In this embodiment, the electrode for capacitive deionization includes electrode material, carbon black and polytetrafluoroethylene, and the preparation method of the electrode material includes the following steps:

[0065] S1. Grind and mix 1 mmol of 2,5-dihydroxy-1,4-benzoquinone and 5 mmol of 2,3-diaminophenazine, and heat them at 220° C. in an inert gas for 7 h. After cooling, filter the mixture, wash the product with deionized water 4 times, wash it with ethanol 3 times, and dry it in vacuum at 60° C. for 20 h to obtain a primary product.

[0066] S2. Acidification treatment of the primary product: 50 mg of the primary product was mixed with 50 mL of 2 mol / L nitric acid, and magnetically stirred for 5 h. After filtering, the mixture was washed with deionized water, centrifuged 6 times, and vacuum dried at 60° C. for 15 h to obtain an electrode material, which was recorded as DHPZ.

[0067] The mass ratio of DHPZ, carbon black and polytetrafluoroethylene is 7:2:1. In this embodiment, 7 mg of DHPZ, 2 mg of activated carbon and 1 mg of polytetrafluoroethylene are taken;

[0068] After mixing DHPZ, activated carbon and polytetrafluoroethylene, 0.8 mL of NMP was added, and the mixture was ground and then applied to the electrode sheet with a coating thickness of 300 μm. The electrode sheet was made of a 1 cm diameter 2 Round carbon paper.

[0069] Comparative Example 1

[0070] In this comparative example, the electrode for capacitive deionization includes an electrode material, carbon black and carboxymethyl cellulose, and the preparation method of the electrode material DHPZ includes the following steps:

[0071] 1 mmol of 2,5-dihydroxy-1,4-benzoquinone and 4 mmol of 2,3-diaminophenazine were ground and mixed, and heated at 180°C in nitrogen for 5 h. After cooling, the product was filtered, washed three times with deionized water and three times with ethanol, and dried in vacuum at 60°C for 16 h to obtain DHPZ.

[0072] The mass ratio of DHPZ, carbon black and carboxymethyl cellulose is 7:2:1. In this embodiment, 7 mg of DHPZ, 2 mg of carbon black and 1 mg of carboxymethyl cellulose are used;

[0073] After DHPZ, carbon black and carboxymethyl cellulose were mixed, 1 mL of NMP was added dropwise, and the mixture was ground and then applied to an electrode sheet to obtain an electrode. The electrode sheet was a 1 cm diameter 2 Round carbon paper.

[0074] Comparative Example 2

[0075] In this comparative example, the electrodes used for capacitive deionization are activated carbon, carbon black and carboxymethyl cellulose, and the mass ratio of activated carbon: carbon black: carboxymethyl cellulose is 7:2:1, specifically 7 mg activated carbon, 2 mg carbon black and 1 mg carboxymethyl cellulose.

[0076] Comparative Example 3

[0077] In this comparative example, the electrode used for capacitive deionization is activated carbon.

[0078] The electrodes for capacitive deionization manufactured in the above embodiments and comparative examples were tested for their deionization performance.

[0079] Gaussian graph:

[0080] See also Figure 2 Shown is a Gaussian diagram of the electrode prepared in Example 1.

[0081] It can be seen that the energy level difference of the prepared product DHPZ is lower than that of 2,5-dihydroxy-1,4-benzoquinone (DHBQ) and 2,3-diaminophenazine (TTFQ), the reaction can occur, and the electronic structure is relatively more stable, that is, it can have a longer service life and higher stability as an electrode material.

[0082] Electrochemical performance test:

[0083] The electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were connected to an electrochemical workstation, and cyclic voltammetry tests were performed at different scan rates (1 mV / s, 2 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 50 mV / s), and the current-potential curves were recorded. Figure 3 The figure is a schematic diagram of the electrochemical performance of the electrode prepared in Example 1. As the scan rate increases, the adsorption and desorption rates of ammonium ions on the electrode surface accelerate; and the electrode can still maintain a good rectangular shape at a higher scan rate, indicating that it has high capacitance stability and fast response capability.

[0084] Deionization performance test:

[0085] Prepare two electrodes prepared in Example 1 and test them separately. Taking Example 1 as an example, the two prepared electrodes are connected to the positive and negative electrodes of the power supply respectively, separated by an ion exchange membrane, placed in a sealed container, and then injected with a certain volume of 0.01 mol / L NH4Cl solution to ensure that the solution completely immerses the electrodes.

[0086] Use a conductivity meter to measure the conductivity of the 0.01 mol / L NH4Cl solution in the initial state, and record the volume V0 of the NH4Cl solution (unit: L);

[0087] Apply voltage (0.8V, 1V, 1.2V) to start the capacitive deionization process, and start timing at the same time, recording the time t (unit: min);

[0088] Every 5 minutes, measure the conductivity of the solution t , and record the time at this time. According to the relationship between conductivity and concentration, the ion concentration c at different time points is calculated. t , calculated as follows:

[0089] κ=kc

[0090] Where κ is the conductivity of the solution, k is the proportionality coefficient, and c is the concentration of ions in the NH4Cl solution (unit: mol / L).

[0091] Knowing that the conductivity of the NH4Cl solution in the initial state is κ0 and the initial concentration c0 is 0.01 mol / L, the proportionality coefficient can be obtained

[0092] During the deionization process, the conductivity of the solution was measured every 5 minutes. t , and according to the formula κ t =k t c t Get the concentration c of ions in the solution at the corresponding time t .

[0093] According to the change in ion concentration, calculate the desalination amount q t :

[0094]

[0095] Where c0 is the initial concentration of NH4Cl solution 0.01 mol / L, c t is the ion concentration in the NH4Cl solution at a certain time, V0 is the volume of the NH4Cl solution, M is the molar mass of NH4Cl, and m0 is the mass of the electrode.

[0096] The deionization performance curve is drawn with time as the horizontal axis and desalination amount (mg / g) as the vertical axis.

[0097] Figure 4 This is the deionization performance curve of the electrode prepared in Example 1.

[0098] It can be seen that the slope is larger in the initial stage, indicating that the desalination rate is faster; as time goes by, the slope gradually decreases and the desalination rate decreases. Within 30 minutes, it can reach 80-90 mg / g, and the desalination rate is faster.

[0099] Deionization long cycle capability test:

[0100] Two electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were prepared and tested respectively. Taking Example 1 as an example, the two prepared electrodes were connected to the positive and negative electrodes of the power supply respectively, separated by an ion exchange membrane, placed in a sealed container, and then injected with a certain volume of 0.01 mol / L NH4Cl solution to ensure that the solution completely submerged the electrodes.

[0101] The conductivity σ0 of the 0.01 mol / L NH4Cl solution in the initial state was measured using a conductivity meter.

[0102] Repeat the above deionization performance test, the duration of the deionization process is 30min, the voltage is 1.2V, and the conductivity of the solution is measured after each test. n (n represents the number of cycles), 50 cycles were performed, and the ion removal rate after each cycle was calculated based on the change in conductivity:

[0103]

[0104] Figure 5 Schematic diagram of the long deionization cycle capacity of the electrode prepared in Example 1.

[0105] In 50 cycles, the removal capacity of ammonium ions fluctuated slightly with the increase in the number of cycles, and the performance was relatively stable; SEC (specific energy consumption) was also stable at an average value. During long-term use, the energy consumed to remove each mole of ammonium ions was relatively stable and could adapt to long-term use.

[0106] It can be seen that with the increase of the number of cycles, the fluctuation range of the performance indicators is not large, indicating that the electrode has good long-cycle ability.

[0107] The present application also provides a method for preparing an electrode for capacitive deionization, and the preparation method thereof is described in the above-mentioned embodiment.

[0108] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features applied for herein.

Claims

1. An electrode for capacitive deionization, characterized in that: It includes electrode materials, carbon materials and binders: The electrode material is DHPZ, and its structural formula is shown below: The preparation method of DHPZ comprises the following steps: S1. Preliminary reaction: grind and mix 2,5-dihydroxy-1,4-benzoquinone and 2,3-diaminophenazine in a molar ratio of 1:3 to 1:5, and heat them in an inert gas at 180 to 220° C. for 5 to 7 hours, filter them after cooling, wash them, and vacuum dry them to obtain a primary product; S2. Acidification treatment of the primary product: mixing the primary product with 2 mol / L nitric acid at a mass volume ratio of 1:1, and magnetically stirring for 5 hours, filtering, washing with deionized water, centrifuging for multiple times, and vacuum drying at 60° C. for 15 hours to obtain the DHPZ.

2. The electrode for capacitive deionization according to claim 1, characterized in that: In S1, the cleaning includes cleaning with deionized water and ethanol 3 to 4 times in sequence.

3. The electrode for capacitive deionization according to claim 1, characterized in that: The vacuum drying condition in S1 is vacuum drying at 60° C. for 15 to 20 hours.

4. The electrode for capacitive deionization according to claim 1, characterized in that: The carbon material is selected from carbon black and activated carbon.

5. The electrode for capacitive deionization according to claim 1, characterized in that: The mass ratio of the DHPZ, the carbon material and the adhesive is 7:2:

1.

6. The electrode for capacitive deionization according to claim 1, characterized in that: It also includes NMP, and the volume mass ratio of the NMP to the total amount of DHPZ, carbon material and binder is 1:5-1:

10.

7. The electrode for capacitive deionization according to claim 1, characterized in that: The inert gas includes nitrogen or argon.

8. The electrode for capacitive deionization according to claim 1, characterized in that: The binder is selected from one of carboxymethyl cellulose and polytetrafluoroethylene.

9. A method for preparing an electrode for capacitive deionization, which is used to prepare an electrode for capacitive deionization as claimed in any one of claims 1 to 8, characterized in that: It includes the following steps: DHPZ, carbon material and binder are uniformly mixed in a ratio of 7:2:1 to obtain a mixture, NMP is added dropwise, and the mixture is ground for 1 to 5 minutes to obtain a slurry, wherein the mass volume ratio of the NMP to the mixture is 1:5 to 1:10; The slurry is applied to an electrode sheet with a thickness of 80 to 300 μm to obtain an electrode.

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