A method for preparing a bulk carbon electrode with controllable microchannel size and morphology

Abstract

The present invention belongs to the technical field of the preparation of electrode materials, and discloses a method for preparing a large-sized carbon electrode with controllable microchannel size and morphology. The steps are as follows: First, the biomass powder is subjected to delignification treatment; then, a mixed suspension of the biomass powder, a crosslinking agent, and a solvent is prepared, and a low-temperature treatment is carried out at different temperature gradients by using a temperature-controlled refrigeration device to control the microchannel size; at the same time, a unidirectional, bidirectional, or non-directional low-temperature treatment method is used by the temperature-controlled refrigeration device to adjust the morphology of the microchannel; finally, a carbonization treatment is carried out. The method of the present invention can prepare a through-type microchannel carbon electrode with different pore sizes and microchannel morphologies by adjusting the preparation process parameters, and is expected to be applied to various fields such as chemical production and environmental protection, so it has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon electrodes, and particularly relates to a method for preparing a large-sized carbon electrode with controllable microchannel size and morphology. Background Art

[0002] Carbon materials are widely used in the fields of electrochemistry, adsorption, catalysis, etc. Common carbon materials include graphite, carbon felt, carbon nanotubes, activated carbon, biomass carbon, graphene, etc. Carbon materials have the advantages of stable chemical properties, low cost, and controllable morphology. In electrochemical water treatment, mainly powder carbon and binder are mixed and then coated on a carrier to be used as a carbon electrode. However, problems such as the shedding of carbon materials may occur during long-term operation, and the addition of the binder may affect the conductivity of the electrode material. There is a related patent (CN 108910859A) reporting a method for preparing porous carbon materials by using a polymer material as a precursor through freeze-drying and high-temperature carbonization. However, the pore channels of the carbon materials prepared by this method are disorderly, and the pore size and pore channel morphology cannot be controlled. In addition, existing pore-forming methods such as the ice template method are mostly used for the preparation of porous ceramics and high-thermal-conductivity composite materials, but there is no application in the field of large-sized carbon electrodes, mainly because the problems of poor conductivity and the inability to form large-area electrodes are difficult to solve. Therefore, it is difficult for carbon materials to be mass-produced industrially and utilized practically. Summary of the Invention

[0003] The present invention uses biomass powder materials as raw materials and prepares a large-sized carbon electrode material with micron-scale through channels by means of low-temperature freezing and high-temperature carbonization. By adjusting the solid powder content, low-temperature treatment temperature, low-temperature treatment method, crosslinking agent content, and solvent composition, carbon electrode materials with different pore sizes and pore morphologies can be prepared. In actual production, biomass is a renewable resource that is inexhaustible in the natural environment. Preparing it into a carbon electrode material is the development and reuse of waste resources. Therefore, the large-sized microchannel carbon electrode prepared by the present invention has great potential in large-scale applications.

[0004] The technical solution of the present invention:

[0005] A method for preparing a large-sized carbon electrode with controllable microchannel size and morphology, comprising the following steps:

[0006] (1) Adjustment of microchannel size and morphology: After the biomass powder is subjected to delignification treatment, it is formulated into a suspension with a crosslinking agent and a solvent in a certain proportion. The treated suspension is placed in a mold and subjected to unidirectional, bidirectional, or non-directional low-temperature treatment at different temperature gradients by using a temperature-controlled refrigeration device, and then dried and formed;

[0007] (2) Carbonization of the material: The dried and formed material is placed in a high-temperature resistance furnace for carbonization treatment to obtain a microchannel carbon electrode material with controllable size.

[0008] In step (1), the biomass powder after delignification treatment is formulated into a suspension with a crosslinking agent and a solvent, and the mass ratio of the three is 8-35%: 1-9%: 60-100%. Too much solid powder will cause the channels not to form, and too little will cause the mechanical strength of the material to be too low to be formed.

[0009] In step (1), the particle size of the biomass powder is 2-30 μm. If the particle size of the biomass powder is too large, the diameter and morphology of the microchannels cannot be controlled. If it is too small, carbonization is difficult to form.

[0010] The crosslinking agent in step (1) includes but is not limited to polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and glycerol.

[0011] The solvent in step (1) includes but is not limited to camphor, camphene, dimethyl sulfoxide, tert-butanol, water, formamide, and butyraldehyde stearate.

[0012] In step (1), a temperature-controlled refrigeration device is used for unidirectional, bidirectional, or non-directional low-temperature treatment at different temperature gradients. The temperature gradient and treatment time program are as follows: for a through-type microchannel with a diameter of 70-200 μm, first perform low-temperature treatment at -10 to -15 °C for 5-60 min, and then perform low-temperature treatment at -30 to -35 °C for 5-60 min; for a through-type microchannel with a diameter of 20-80 μm, first perform low-temperature treatment at -35 to -40 °C for 5-60 min, and then perform low-temperature treatment at -60 to -65 °C for 5-60 min; for a through-type microchannel with a diameter of 4-30 μm, first perform low-temperature treatment at -65 to -70 °C for 5-60 min, and then perform low-temperature treatment at -90 to -95 °C for 5-60 min. The temperature gradient is the key factor leading to channel penetration. Changing the gradient cooling sequence will cause the channel to close and not allow water to pass through.

[0013] In step (1), a temperature-controlled refrigeration device is used for unidirectional, bidirectional, or non-directional low-temperature treatment at different temperature gradients. The low-temperature treatment method process is as follows: when the low-temperature treatment method is unidirectional, the microchannel morphology is a trumpet-shaped channel with an aperture ratio of 1.5:1 to 6:1 at both ends, and the electrode height range is 5-35 mm; when the low-temperature treatment method is bidirectional, the microchannel morphology is a layered channel with a length of 0.1-70 mm, and the electrode height range is 5-70 mm; when the low-temperature treatment method is non-directional, the microchannel morphology is staggered.

[0014] In step (2), the carbonization process is as follows: under a vacuum condition with a vacuum degree of 1 - 100 Pa, the temperature is increased at a heating rate of 8 - 10 °C / min, and kept at 200 - 400 °C for 0.5 - 2 h; then under a vacuum condition of 0.001 - 1 Pa, the temperature is increased at a heating rate of 4 - 5 °C / min, and kept at 400 - 600 °C for 0.5 - 2 h; finally under a vacuum condition of 0.001 - 1 Pa, the temperature is increased at a heating rate of 1 - 2 °C / min, and kept at 600 - 900 °C for 1 - 3 h.

[0015] The beneficial effects of the present invention are as follows: using biomass powder materials as raw materials, a large - scale carbon electrode material with micron - level through - channels is prepared by means of low - temperature freezing and high - temperature carbonization. By adjusting the solid powder content, low - temperature treatment temperature, low - temperature treatment method, cross - linker content, and solvent composition, carbon electrode materials with different micro - channel diameters and morphologies can be prepared. The micro - channel structure confines the reaction process within the grid of the electrode, overcomes the mutual repulsion between ions and the electrode under the action of the electric field force, shortens the mass transfer distance, improves the reaction efficiency of the electrode and the utilization rate of active free radicals, and increases the effective reaction area of the electrode. The preparation process of the low - temperature freezing method is simple, requires low equipment, has low production costs, is easy to operate and control, and is easy to achieve large - scale preparation and batch production. Moreover, biomass is a renewable resource that is inexhaustible in the natural environment, and preparing it into a carbon electrode material is the development and reuse of waste resources. Description of the Drawings

[0016] Figure 1 It is a scanning electron microscope image of the micro - channel carbon electrode prepared by the unidirectional low - temperature treatment method of the present invention.

[0017] Figure 2 It is a scanning electron microscope image of the micro - channel carbon electrode prepared by the bidirectional low - temperature treatment method of the present invention.

[0018] Figure 3 It is a scanning electron microscope image of the micro - channel carbon electrode prepared by the non - directional low - temperature treatment method of the present invention.

[0019] Figure 4 It is a scanning electron microscope image of a porous carbon electrode without micro - channels.

[0020] Figure 5 It is the preparation flow chart of the present invention. Detailed Embodiments

[0021] To further illustrate the present invention, the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0022] Example 1

[0023] (1) Weigh 60 g of bamboo powder, place it in an aqueous NaOH solution with a concentration of 3 mol / L, heat it to boiling and maintain for 5 h. After treatment, rinse it repeatedly with high-purity water until the bamboo powder is neutral. Then add the washed bamboo powder and 5 g of polyvinyl butyral to 200 mL of dimethyl sulfoxide, and mix evenly to prepare a suspension.

[0024] (2) Pour the treated suspension into a mold with dimensions of 170 mm * 170 mm * 30 mm, and perform unidirectional low-temperature treatment using a temperature-controlled refrigeration device. First, perform low-temperature treatment at -35 to -40 °C for 50 min, then at -60 to -65 °C for 50 min, and then dry and form.

[0025] (3) Place the dried green body in a carbonization furnace. The carbonization furnace needs to first reach a vacuum condition with a vacuum degree of 10 Pa, start heating at a heating rate of 10 °C / min, and hold at 300 °C for 0.5 h; then under a vacuum condition of 0.001 Pa, start heating at a heating rate of 5 °C / min, and hold at 600 °C for 2 h; finally, under a vacuum condition of 0.001 Pa, start heating at a heating rate of 2 °C / min, and hold at 900 °C for 3 h, so that the green body is completely carbonized to obtain a carbon electrode material with a microchannel diameter of 20 - 80 μm and a trumpet-shaped morphology, as Figure 1 shown.

[0026] Example 2

[0027] (1) Weigh 60 g of natural pine powder, place it in an aqueous NaOH solution with a concentration of 5 mol / L, heat it to boiling and maintain for 8 h. After treatment, rinse it repeatedly with high-purity water until the pine powder is neutral. Then add the washed pine powder and 1 g of polyvinyl alcohol to 200 mL of water, and mix evenly to prepare a suspension.

[0028] (2) Pour the treated suspension into a mold with dimensions of 170 mm * 170 mm * 30 mm, and perform bidirectional low-temperature treatment using a temperature-controlled refrigeration device. First, perform low-temperature treatment at -35 to -40 °C for 30 min, then at -60 to -65 °C for 30 min, and then dry and form.

[0029] (3) Place the dried green body in a carbonization furnace. The carbonization furnace needs to first reach a vacuum condition with a vacuum degree of 10 Pa, start heating at a heating rate of 10 °C / min, and hold at 300 °C for 0.5 h; then under a vacuum condition of 0.001 Pa, start heating at a heating rate of 5 °C / min, and hold at 600 °C for 2 h; finally, under a vacuum condition of 0.001 Pa, start heating at a heating rate of 2 °C / min, and hold at 900 °C for 3 h, so that the green body is completely carbonized to obtain a carbon electrode material with a microchannel diameter of 20 - 80 μm and a layered morphology, asFigure 2 as shown

[0030] Example 3

[0031] (1) Weigh 60 g of straw powder, place it in a 1.5 mol / L NaOH aqueous solution, heat it to boiling and keep it for 3 h. After treatment, repeatedly rinse it with high-purity water until the straw powder is neutral. Then add the washed straw powder and 2 g of polyvinylpyrrolidone to 200 mL of tert-butanol, and mix evenly to prepare a suspension.

[0032] (2) Pour the treated suspension into a mold of 170 mm * 170 mm * 30 mm, and use a temperature-controlled refrigeration device for non-directional low-temperature treatment. First, perform low-temperature treatment at -35 to -40 °C for 20 min, then perform low-temperature treatment at -60 to -65 °C for 20 min, and then dry and form.

[0033] (3) Place the dried green body in a carbonization furnace. The carbonization furnace needs to first reach a vacuum condition with a vacuum degree of 10 Pa, start heating at a heating rate of 10 °C / min, and keep it at 300 °C for 0.5 h; then under a vacuum condition of 0.001 Pa, start heating at a heating rate of 5 °C / min, and keep it at 600 °C for 2 h; finally, under a vacuum condition of 0.001 Pa, start heating at a heating rate of 2 °C / min, and keep it at 900 °C for 3 h, so that the green body can be completely carbonized to obtain a carbon electrode material with a microchannel diameter of 20 - 80 μm and an interlaced morphology, as Figure 3 as shown

[0034] Comparative Example 1

[0035] (1) Weigh 80 g of natural pine powder, place it in a 5 mol / L NaOH aqueous solution, heat it to boiling and keep it for 8 h. After treatment, repeatedly rinse it with high-purity water until the pine powder is neutral. Then add the washed pine powder and 1 g of polyvinyl acid to 100 mL of water, and mix evenly to prepare a suspension.

[0036] (2) Pour the treated suspension into a mold of 170 mm * 170 mm * 30 mm, and use a temperature-controlled refrigeration device for unidirectional low-temperature treatment. First, perform low-temperature treatment at -35 to -40 °C for 20 min, then perform low-temperature treatment at -60 to -65 °C for 20 min, and then dry and form.

[0037] (3) Place the dried green body in a carbonization furnace. The carbonization furnace needs to first reach a vacuum condition with a vacuum degree of 10 Pa, start heating at a heating rate of 10 °C / min, and hold the temperature at 300 °C for 0.5 h; then, under a vacuum condition of 0.001 Pa, start heating at a heating rate of 5 °C / min, and hold the temperature at 600 °C for 2 h; finally, under a vacuum condition of 0.001 Pa, start heating at a heating rate of 2 °C / min, and hold the temperature at 900 °C for 3 h, so that the green body can be completely carbonized to obtain a porous carbon electrode material without microchannels, as Figure 4 shown. Since the mass fraction of the biomass powder in it is 80%, which is much greater than the proportion in the embodiment, the microchannels of the carbon electrode material cannot be formed.

Claims

1. A method for preparing a bulk carbon electrode with controllable microchannel size and morphology, characterized by the following steps: (1) Adjustment of microchannel size and morphology: After delignification treatment, biomass powder is mixed with a cross-linking agent and a solvent in a certain proportion to form a suspension. The suspension is placed in a mold and a temperature-controlled refrigeration device is used to perform unidirectional, bidirectional or non-directional low-temperature treatment on the mold under different temperature gradients, and then dried and formed. The mass ratio of the biomass powder after delignification treatment, the cross-linking agent and the solvent is 8-35%: 1-9%: 60-100%. A controllable temperature refrigeration device is used to perform unidirectional, bidirectional or non-directional low-temperature treatment on the mold under different temperature gradients. The temperature gradient and treatment time program are as follows: for a through-type microchannel with a diameter of 70 to 200 μm, the mold is first subjected to low-temperature treatment at -10 to -15°C for 5 to 60 minutes, and then to low-temperature treatment at -30 to -35°C for 5 to 60 minutes; for a through-type microchannel with a diameter of 20 to 80 μm, the mold is first subjected to low-temperature treatment at -35 to -40°C for 5 to 60 minutes, and then to low-temperature treatment at -60 to -65°C for 5 to 60 minutes; for a through-type microchannel with a diameter of 4 to 30 μm, the mold is first subjected to low-temperature treatment at -65 to -70°C for 5 to 60 minutes, and then to low-temperature treatment at -90 to -95°C for 5 to 60 minutes; A controllable temperature refrigeration device is used to perform unidirectional, bidirectional or non-directional low-temperature treatment on the mold under different temperature gradients. The low-temperature treatment process is as follows: when the low-temperature treatment method is unidirectional, the microchannel morphology is a trumpet-shaped channel with an aperture ratio of 1.5:1 to 6:1 at both ends, and the height range of the microchannel carbon electrode is 5-35 mm; when the low-temperature treatment method is bidirectional, the microchannel morphology of the microchannel carbon electrode is a layered channel with a length of 0.1 to 70 mm, and the height range of the microchannel carbon electrode is 5-70 mm; when the low-temperature treatment method is non-directional, the microchannel morphology in the microchannel carbon electrode is staggered; (2) Material carbonization: The dried and formed material is placed in a high-temperature resistance furnace for carbonization treatment to obtain a microchannel carbon electrode material with controllable size.

2. The method for preparing a bulk carbon electrode according to claim 1, characterized in that in step (1), the particle size of the biomass powder is 2 to 30 μm.

3. The method for preparing a bulk carbon electrode according to claim 1, wherein in step (1), the crosslinking agent comprises polyvinyl butyrate, polyvinyl pyrrolidone, polyvinyl acid, and glycerol.

4. The method for preparing a bulk carbon electrode according to claim 1, wherein in step (1), the solvent comprises camphor, camphene, dimethyl sulfoxide, tert-butanol, water, formamide, and stearic acid butyraldehyde.

5. The method for preparing a bulk carbon electrode according to claim 1 is characterized in that in step (2), the procedure of the carbonization treatment is as follows: under a vacuum condition of a vacuum degree of 1 to 100 Pa, the temperature is increased at a heating rate of 8 to 10°C / min, and the temperature is kept at 200 to 400°C for 0.5 to 2 hours; then under a vacuum condition of 0.001 to 1 Pa, the temperature is increased at a heating rate of 4 to 5°C / min, and the temperature is kept at 400 to 600°C for 0.5 to 2 hours; finally, under a vacuum condition of 0.001 to 1 Pa, the temperature is increased at a heating rate of 1 to 2°C / min, and the temperature is kept at 600 to 900°C for 1 to 3 hours.

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