Application of a cork activated carbon capacitive deionization electrode in brackish water desalination

Abstract

This invention discloses the application of a cork activated carbon capacitive deionization electrode in brackish water desalination, belonging to the field of brackish water desalination technology. Cork activated carbon or modified cork activated carbon is assembled into a CDI system as the electrode sheet for brackish water desalination. This electrode material features ultra-thin carbon nanosheet walls, high specific surface area, a well-defined hierarchical porous structure, and abundant oxygen-containing functional groups, providing a good pore structure and surface properties basis for the adsorption of sodium and chloride ions in brackish water. The desalination capacity of this capacitive deionization electrode material reaches 10.28 mg / g, demonstrating great application potential in the field of capacitive deionization.

Description

Technical Field

[0001] This invention belongs to the field of brackish water desalination technology, specifically relating to the application of a cork activated carbon capacitor deionization electrode in brackish water desalination. Background Technology

[0002] Freshwater resources are vital natural resources for sustainable socio-economic development and human survival. With increasing population and intensive industrial activity, freshwater shortages have intensified, making the development and utilization of unconventional water resources (brackish water, rainwater, etc.) a major strategy for alleviating the freshwater crisis. my country's per capita water resources are only one-quarter of the world average, and their distribution is uneven. Although my country faces a freshwater shortage, brackish water is widely distributed across approximately 1.6 million km². 2 The exploitable brackish water is 20 billion cubic meters. 3 In arid and water-scarce inland regions such as Northwest my country, brackish water is abundant and a major source of directly usable water. Because brackish water has a lower salinity than seawater, its desalination requires less energy. Therefore, brackish water treatment technology has become a preferred method for the comprehensive utilization of water resources and alleviating freshwater shortages, and it is of great significance for freshwater resource management and agricultural irrigation in Northwest my country.

[0003] Capacitive deionization (CDI) is an emerging desalination technology that is considered to have broad application prospects in the treatment of low-salinity waters such as brackish water due to its advantages of low energy consumption, high efficiency, and environmental friendliness. As a core component of the CDI system, excellent electrode materials are key to achieving efficient CDI desalination. Activated carbon, due to its low cost and abundant resources, has been widely used in energy storage and has also seen initial applications in capacitive deionization; however, its low desalination capacity limits its industrial application in CDI. During desalination, ions encounter migration resistance at the solution-electrode interface. When the electrode material has poor hydrophilicity, this resistance increases, reducing the ion migration rate and thus affecting the desalination capacity. Plasma is an emerging modification technology with advantages such as low excitation energy consumption, high energy density, and no pollution, and is widely used in the field of material modification. It utilizes high-voltage breakdown to ionize gas, generating active particle clusters that etch chemical bonds on the material surface, oxidizing or reducing raw materials and generating new functional groups on the material surface. Introducing oxygen-containing functional groups can improve the hydrophilicity of activated carbon, reduce ion diffusion resistance, increase active adsorption sites, and enhance adsorption performance. This is an effective strategy to improve the desalination performance of activated carbon electrodes in capacitive deionization technology.

[0004] Cork, the bark of the broad-leaved trees *Quercus variabilis* or *Quercus surber*, is an environmentally friendly, green, and renewable resource. my country's production accounts for about one-sixth of the world's total, with the Qinling-Bashan Mountains in Shaanxi Province and neighboring provinces accounting for over 65% of the national output. Cork is composed of tightly packed, closed, and hollow honeycomb-like cells (~25 μm), with cell walls (<1 μm) much thinner than wood cell walls (4-10 μm), making it more prone to producing abundant pores. The unique chemical component of cork, cork resin (40%), results in high volatile matter and carbon content and low ash content, making it suitable for preparing carbon materials with high adsorption capacity. Cork activated carbon retains a porous morphology and abundant surface oxygen content. After high-temperature activation, the cell walls become thinner and straighter, and open pores appear on the surface. This special porous structure and open ion diffusion channels are good precursors for promoting ion transport and active sites of battery electrode materials. However, there are no reports on the application of cork as a raw material for preparing capacitor deionization electrode materials in the field of brackish water desalination. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the technical problem to be solved by the present invention is to provide an application of a cork activated carbon capacitive deion electrode in brackish water desalination. By fully utilizing the unique honeycomb structure of cork, a cork activated carbon electrode material with a large specific surface area, reasonable pore size distribution, rich surface functional groups, and good desalination performance is prepared, which has the advantages of high desalination capacity and high average salt adsorption rate.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] The application of a cork activated carbon capacitive deionization electrode in brackish water desalination involves assembling cork activated carbon or modified cork activated carbon as electrode plates in a capacitive deionization reactor into a CDI system for brackish water desalination.

[0008] The application of the cork activated carbon capacitive deion electrode in brackish water desalination involves placing cork activated carbon in a plasma reactor, evacuating it, and then introducing oxygen to modify it into modified cork activated carbon. During the reaction, the discharge power is 80-120W, the gas flow rate is 8-12cc / min, and the modification time is 5-10min.

[0009] The application of the cork activated carbon capacitive deion electrode in brackish water desalination, and the preparation method of the cork-based electrode material, include the following steps:

[0010] (1) Carbonization of cork: The cork sample was placed in a tube furnace and carbonized under a nitrogen atmosphere. After that, it was naturally cooled to room temperature to obtain carbonized cork charcoal.

[0011] (2) Activation of cork: Cork charcoal and KOH solid powder are thoroughly mixed and ground, activated under nitrogen atmosphere, and then naturally cooled to room temperature to obtain activated sample;

[0012] (3) Washing of the sample: After grinding the activated sample, wash it alternately with deionized water and hydrochloric acid solution until the pH is neutral, filter and dry to obtain cork activated carbon;

[0013] (4) Preparation of electrode material: After thoroughly mixing cork activated carbon, acetylene black (or carbon black) and polytetrafluoroethylene (60% PTFE) in anhydrous ethanol, the mixture is ultrasonically treated and then made into a thin sheet electrode material under an infrared lamp. After drying, the electrode material is cut to obtain the electrode material.

[0014] The application of the cork activated carbon capacitor deion electrode in brackish water desalination involves pretreatment of the cork before carbonization. Specifically, the cork waste is washed and dried with deionized water, crushed and sieved, and the cork particles are between 40-60 mesh.

[0015] The application of the cork activated carbon capacitor deion electrode in brackish water desalination, wherein the cork carbonization is carried out at 5-10℃ for min. -1 Heat to 550-600℃ at a rising rate and hold for 2 hours.

[0016] In the application of the cork activated carbon capacitor deion electrode in brackish water desalination, the mass ratio of cork charcoal to KOH solid powder is 1:3-1:6.

[0017] The application of the cork activated carbon capacitive deion electrode in brackish water desalination, wherein the cork is activated at 5-10℃ for min. -1 Heat to 750-800℃ at a rising rate and hold at that temperature for 1 hour.

[0018] The application of the cork activated carbon capacitor deion electrode in brackish water desalination involves preparing the electrode material with a mass ratio of modified cork activated carbon, acetylene black (or carbon black), and polytetrafluoroethylene (PTFE with a content of 60%) of 8:1:1; and drying it overnight at 80°C in an oven.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The raw material used is waste from cork processing, which is low-cost and abundant. The cork activated carbon and oxygen plasma-modified electrode material produced by the manufacturing method of this invention possesses a uniform honeycomb structure, ultrathin carbon nanosheets, high specific surface area, excellent hierarchical porous structure, and abundant oxygen-containing functional groups, providing a good pore structure and surface property basis for the adsorption of sodium and chloride ions in brackish water. The preparation method of this electrode material is simple, low-cost, and effective, exhibiting advantages such as high desalination capacity and high average salt adsorption rate, demonstrating great application potential in capacitive deionization. Attached Figure Description

[0021] Figure 1 SEM images of cork activated carbon at magnifications of 1.5k (a) and 30.0k (b);

[0022] Figure 2 The pore size distribution of cork activated carbon;

[0023] Figure 3 The figure shows the desalination capacity results of different cork activated carbon electrodes and modified electrodes. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments. Cork, also known as cork bark or cork oak, is the bark of the cork oak or cork oak tree. The scraps left over after industrial processing are cork industrial waste. The cork industrial waste used in the following embodiments can be the bark of the cork oak or cork oak tree, or a mixture of the two.

[0025] Example 1

[0026] A method for preparing a cork activated carbon capacitor deion electrode includes the following steps:

[0027] (1) The cork industry waste was washed with deionized water, dried, further crushed and passed through a 40-60 mesh sieve to obtain the test sample;

[0028] (2) Place an appropriate amount of cork particles in a corundum boat, place it in a tube furnace with a nitrogen atmosphere, heat it to 550°C at a heating rate of 5°C / min, and carbonize it for 2 hours. After cooling, cork charcoal is obtained.

[0029] (3) Mix and grind cork charcoal and solid potassium hydroxide in a mortar at a mass ratio of 1:3 until the particle size is 0.3 mm to 0.45 mm. Then, load the mixture into a corundum boat and place it in a vacuum tube furnace. Under a nitrogen atmosphere, heat the mixture to 750°C at a heating rate of 5°C / min for 1 hour. After cooling, cork activated charcoal is obtained.

[0030] (4) Wash with deionized water and 1M hydrochloric acid alternately until the pH is neutral, and dry at 80°C to obtain cork activated carbon;

[0031] (5) Add 1 / 2 volume of anhydrous ethanol to the centrifuge tube, and add cork activated carbon, acetylene black and polytetrafluoroethylene (60% PTFE) in a mass ratio of 8:1:1. After sonicating for 2 hours, prepare the sample into a thin sheet under an infrared lamp, dry it overnight in an oven at 80°C, and cut the electrode material into 4cm×4cm electrode sheets, which are marked as CAC-3.

[0032] Through append Figure 1 A honeycomb structure and ultrathin carbon nanosheets (100-200 nm) can be observed. Through... Figure 2 It can be seen that the electrode sheet has a good hierarchical porous structure. Testing revealed that the prepared capacitive deionization electrode sheet has a high specific surface area (1960.02 m²). 2 / g), rich in oxygen-containing functional groups.

[0033] Example 2

[0034] The difference between this implementation method and Example 1 is that in step (3), the ratio of pre-carbonized sample to KOH is 1:4, and the prepared electrode sheet is marked as CAC-4.

[0035] Example 3

[0036] The difference between this implementation method and Example 1 is that in step (3), the ratio of pre-carbonized sample to KOH is 1:5, and the prepared electrode sheet is marked as CAC-5.

[0037] Example 4

[0038] The difference between this implementation method and Example 1 is that in step (3), the ratio of pre-carbonized sample to KOH is 1:6, and the prepared electrode sheet is marked as CAC-6.

[0039] Example 5

[0040] The preparation of the modified cork activated carbon capacitor deion electrode is as follows:

[0041] The CAC-3, CAC-4, CAC-5, and CAC-6 electrode sheets prepared in Examples 1-4 were placed in a plasma reactor. After evacuation using a vacuum pump, oxygen was introduced. The discharge power was set to 100W, the gas flow rate to 10cc / min, and the modification time to 5min. After the reaction, modified electrode sheets were obtained and labeled as CAC-3P, CAC-4P, CAC-5P, and CAC-6P, respectively.

[0042] Example 6

[0043] The desalination performance of the unmodified activated carbon electrode sheets and modified activated carbon electrode sheets prepared in Examples 1-5 was tested for brackish water.

[0044] (1) Unmodified activated carbon electrode sheets CAC-3, CAC-4, CAC-5 and CAC-6 were assembled into the CDI system as positive and negative electrode sheets of the capacitor deionization reactor, respectively. They were connected to the current collector in close contact with the electrodes through the positive and negative terminals of the electrochemical workstation to provide the operating voltage during the desalination test.

[0045] (2) Modified electrode sheets (CAC-3P, CAC-4P, CAC-5P and CAC-6P) were used as negative electrodes and assembled with unmodified activated carbon electrode sheets (CAC-3, CAC-4, CAC-5 and CAC-6) to form asymmetric electrodes for desalination testing.

[0046] The test conditions for the above two tests were as follows: a 10 mM NaCl solution was used to simulate brackish water, and a peristaltic pump was used to control the influent flow rate at 1 mL / min. -1 In constant pressure mode, a voltage of 1V was applied with a plate spacing of 1mm. The water concentration was measured using a conductivity meter, and data was recorded every 1 second. Each electrode pair underwent three cycles, with each cycle consisting of 20 minutes of charging at 1V and 20 minutes of discharging at 0V. Desalination-related indicators were calculated using data from the third cycle. To improve the conductivity between the electrode plates and the current collector, gold foil was placed between them. After assembling the CDI system, the peristaltic pump was turned on. Small air bubbles appeared at the water outlet. To ensure the accuracy of the conductivity test, the CDI system was run for 30 minutes without voltage before the test to purge the air bubbles from the water flow channel.

[0047] Depend on Figure 3 It can be seen that the desalination capacities of CAC-3 and CAC-3P electrodes are 9.44 mg / g and 10.28 mg / g, respectively, while the adsorption capacities per unit mass of CAC-4, CAC-5, and CAC-6 electrodes are 6.68 mg / g, 7.45 mg / g, and 8.08 mg / g, respectively. Currently, the desalination capacity of activated carbon prepared from biomass is generally between 5-7 mg / g. Activated carbon prepared from cork, due to its unique natural honeycomb structure, possesses a hierarchical porous structure and exhibits a relatively high desalination capacity when used as a capacitive deionization electrode.

Claims

1. The application of a cork activated carbon capacitive deionization electrode in brackish water desalination, characterized in that, (1) The cork industry waste was washed with deionized water, dried, further crushed and passed through a 40-60 mesh sieve to obtain the test sample; (2) Place an appropriate amount of cork particles in a corundum boat, place it in a tube furnace with a nitrogen atmosphere, heat it to 550°C at a heating rate of 5°C / min, and carbonize it for 2 hours. After cooling, cork charcoal is obtained. (3) Mix and grind cork charcoal and solid potassium hydroxide in a mortar at a mass ratio of 1:3 until the particle size is 0.3 mm ~ 0.45 mm. Then, load it into a corundum boat and place it in a vacuum tube furnace. Under a nitrogen atmosphere, heat it to 750°C at a heating rate of 5°C / min for 1 hour. After cooling, cork activated carbon is obtained. (4) Wash with deionized water and 1M hydrochloric acid alternately until the pH is neutral, and dry at 80°C to obtain cork activated carbon; (5) Add 1 / 2 volume of anhydrous ethanol to the centrifuge tube, add cork activated carbon, acetylene black and polytetrafluoroethylene in a mass ratio of 8:1:1, sonicate for 2 hours, make the sample into a thin sheet under infrared lamp, dry it overnight in an oven at 80 ℃, cut the electrode material into 4cm × 4cm electrode sheets, and mark them as CAC-3. (6) The prepared CAC-3 electrode sheet was placed in the plasma reactor, and oxygen was introduced after evacuation by a vacuum pump. The discharge power was set to 100W, the gas flow rate was 10cc / min, and the modification time was 5min. After the reaction, the modified electrode sheet was obtained and labeled as CAC-3P. (7) The modified electrode CAC-3P was used as the negative electrode and assembled with the electrode CAC-3 to form an asymmetric electrode; a 10 mM NaCl solution was used to simulate brackish water, and the influent flow rate was controlled by a peristaltic pump at 1 mL / min. In constant pressure mode, a voltage of 1 V was applied and the plate spacing was 1 mm. The concentration of the effluent was detected by a conductivity meter, and data was recorded every 1 second. Each pair of electrodes was run for three cycles. Each cycle included charging at 1 V for 20 min and discharging at 0 V for 20 min. The desalination index was calculated using the data obtained from the third cycle. Gold foil was placed between the electrode and the current collector. The results showed that the desalination capacities of the CAC-3 electrode and the CAC-3P electrode were 9.44 mg / g and 10.28 mg / g, respectively.

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