CN102765782B - Method for preparing hierarchical porous carbon capacitive deionization electrode - Google Patents

Abstract

The invention relates to a preparation method of a multi-level porous carbon capacitive desalination electrode, which belongs to the field of preparation of a capacitive desalination electrode. In the present invention, the silica template is impregnated into the precursor solution of the mesoporous carbon material, and a carbon material with a hierarchical porous structure is formed on the silica sphere through processes such as low-temperature volatilization, high-temperature curing, and carbonization in an inert atmosphere, and finally A porous carbon material with macropores, mesopores and micropores can be obtained by hydrofluoric acid etching. The porous carbon material, acetylene black and polytetrafluoroethylene emulsion were evenly mixed, spread on graphite paper, and dried overnight to prepare a hierarchical porous carbon capacitive desalination electrode. The invention has simple operation and easy control of conditions, and the obtained electrode has high specific surface area, good conductivity and high desalination performance, and has potential application prospects in low energy consumption, low cost and high efficiency capacitive desalination.

Description

Preparation method of hierarchical porous carbon capacitive desalination electrode

technical field

The invention relates to a preparation method of a multi-level porous carbon capacitive desalination electrode. The desalination electrode prepared by the invention has the desalination performance of high efficiency and low energy consumption. The technical field of the invention is applicable to the desalination of seawater and brackish water, and provides a new way for desalination with low energy consumption, low cost and high performance.

Background technique

The water resource crisis is one of the biggest resource crises facing the world in this century, and desalination of seawater and brackish water is an important way to solve this crisis. The existing desalination methods mainly include distillation (including multi-stage flash evaporation, multi-stage evaporation and compressed air distillation) and membrane method (including reverse osmosis and electrodialysis). However, the operation temperature of the distillation method is high, the danger of boiler scale is serious, and the corrosion is serious; the membrane method has strict requirements on membrane performance, high membrane damage rate and high cost. In addition, these desalination methods all have the disadvantages of high energy consumption and high cost. Therefore, adopting new technologies to reduce desalination costs has always been the most important development goal of seawater desalination technology. Therefore, the application prospect of desalination technology with low energy consumption and low cost is very bright. Capacitive Deionization (CDI) is a new desalination technology based on the principle of electric double layer capacitance. Compared with traditional desalination methods, this method has the advantages of low cost, high desalination efficiency, simple process equipment, easy implementation, no secondary pollution, and environmental friendliness. It provides a new high-efficiency, low-energy, and low-cost desalination technology. way. the

Based on the principle of CDI, it can be seen that the key to obtaining high CDI performance is the electrode material, which requires the electrode material to have the characteristics of large specific surface area, developed voids, and good conductivity. Porous carbon materials have the advantages of high specific surface area, good electrical conductivity, unique chemical stability, good formability, relatively low price, rich sources of raw materials, and relatively mature production processes, and are widely used in electrode materials. So far, porous carbon materials used as CDI electrodes mainly include activated carbon, carbon aerogel, carbon nanofibers, carbon nanotubes, graphene, and mesoporous carbon. Among them, activated carbon has become a widely used electrode material due to its large specific surface area, simple preparation, and low price, but its desalination efficiency is low, mainly because the existence of a large number of micropores is not conducive to ion penetration and adsorption, resulting in low specific surface area utilization. , disordered pore structure, and high internal resistance. In order to solve the above problems, mesoporous carbon materials with high specific surface area, highly uniform pore size distribution, large pore volume, and high mechanical stability have attracted great interest of researchers. Zou et al. found ordered mesoporous carbon with high specific surface area (Zou L, Li LX, Song HH, Morris G; Water Research, 2008, 42, 2340-2348) or mesoporous carbon materials with Ni surface modification ( Li LX, Zou L, Song HH, Morris G, Carbon 2009, 47, 775-781) have higher desalination capacity than traditional activated carbon electrodes. However, it should be pointed out that the specific capacitance value of the currently prepared mesoporous carbon materials used as desalination electrodes is far lower than the theoretical value of carbon materials, mainly due to some shortcomings of the materials such as relatively high internal resistance and low Surface area utilization. Therefore, in order to solve the above problems, a new type of multi-level porous (macropore, mesopore and microporous) carbon electrode material with higher surface area, high conductivity, well-developed voids, and high surface utilization rate is prepared. Efficient, low-energy desalination offers new avenues.

Contents of the invention

The object of the present invention is to solve the above problems and provide a method for preparing a multi-level porous carbon capacitive desalination electrode for seawater desalination treatment using an electric double layer capacitive desalination method. Hierarchical carbon materials that effectively combine macropores, mesopores and micropores can choose to combine the advantages of various porous materials. Diffusion, mass transfer and other aspects show characteristics superior to those of single pore structure materials. The interconnected macropores and mesopores are conducive to the penetration of ions into the deep pores, improving the effective utilization of the specific surface; at the same time, the shorter ion diffusion path also reduces the internal resistance of the electrode material. In addition, the simultaneous presence of micropores and mesopores endows the desalination electrode with a higher specific surface area, which is beneficial to obtain higher CDI performance. A hierarchical porous carbon capacitive desalination electrode prepared by effectively combining macropores, mesopores and micropores has higher specific surface area, good conductivity and better desalination performance.

The purpose of the present invention is achieved by the following technical means and measures.

The present invention provides a method for preparing a hierarchical porous carbon capacitive desalination electrode, which is characterized by the following preparation process and steps:

(1) Preparation of electrode materials:

Monodisperse silica (SiO ₂ ) microspheres were ultrasonically dispersed in a certain amount of ethanol solution, naturally deposited at 15 ~ 35 ^o C, and then sintered at high temperature to obtain a SiO ₂ template; adding hydrogen at a concentration of 20 wt% to phenol Sodium oxide solution, after stirring evenly, slowly add formaldehyde solution with a concentration of 37 wt%, raise the temperature to 65~75 ^o C and react for 1~2.5 h, after cooling to room temperature, use 0.6 M hydrochloric acid to adjust the pH to neutral, and vacuum distillation at low temperature to reduce Then add ethanol and stir for 10-12 h, then centrifuge to remove inorganic salts to obtain a phenolic resin precursor solution with a concentration of 20 wt%; stir and mix the ethanol solution of the structure directing agent (concentration: 4.76 wt%) with the phenolic resin precursor solution uniform. Then the _SiO2 template is impregnated into the mixed solution, and the excess solution is removed by suction filtration after the low-temperature volatilization reaction, further low-temperature volatilization and high-temperature curing, and then carbonized in an inert atmosphere and then added with a concentration of 10 wt% hydrofluoric acid solution to stir the reaction to remove the _SiO2 template After fully washing and drying, the hierarchical porous carbon material can be obtained; the preparation of the hierarchical porous carbon capacitive desalination electrode:

The hierarchical porous carbon material prepared in step (1), acetylene black and polytetrafluoroethylene emulsion are stirred and mixed according to the mass ratio of 80:10:10~90:5:5, and then applied to the conductive base graphite paper, and then placed on the Dry overnight at 100-120 ^o C; finally a multi-level porous carbon capacitive desalination electrode is produced.

The diameter of the above-mentioned monodisperse SiO ₂ microspheres is 100-400 nm; the solid content of the microspheres in the ethanol dispersion of the above-mentioned SiO ₂ microspheres is 1%-10%. A dispersion of silica microspheres with a certain particle size and density can form a better quality template structure; when the size is too small or the density is too low, the deposition rate is too slow, and the dispersion will exist in a balanced dispersion system, which will lead to It is difficult to form a template or the formation time is too long; when the size of the microspheres is too large or the density of the dispersion is too high, the deposition rate is too fast, and the colloidal microspheres concentrated at the bottom of the container have no time to undergo the phase transition from disorder to order, resulting in the Template quality is poor.

The aforementioned structure directing agent is F127 (PEO ₁₀₆ -PPO ₇₀ -PEO ₁₀₆ ), P123 (PEO ₂₀ -PPO ₇₀ -PEO ₂₀ ) or a mixture of both. In addition, the molar ratio of phenol, formaldehyde, sodium hydroxide and structure directing agent is 1: 2: 0.1: 0.005~0.025. The hydrophilic ends of the three-block copolymer PEO-PPO-PEO have strong hydrogen bonding with the phenolic resin precursor, which ensures good dispersion and provides the possibility for further polymerization and pyrolysis reactions; secondly, PEO-PPO - The PEO template has a large number of oxygen atoms and a low decomposition temperature, which is easy to remove and is a good template for the preparation of porous carbon materials.

The SiO ₂ template impregnated with the above-mentioned precursor needs to undergo two-step reaction of low-temperature volatilization and high-temperature curing, wherein the temperature of low-temperature volatilization is 30-60 ^o C; the temperature of high-temperature curing is 100-140 ^o C. Low temperature volatilization and high temperature curing make the phenolic resin further volatilize and polymerize to form a rigid polymer skeleton. If the temperature is too low, the polycondensation reaction of phenolic resin is slow, which is not conducive to the complete formation of rigid polymer skeleton. Due to curing under aerobic conditions, when the temperature is too high, the phenolic resin is oxidized and blackened.

The above-mentioned carbonization process needs to be realized by segmented temperature- ^controlled calcination in an inert atmosphere. The temperature increase rate is controlled at 1 ^o C/min. ~1100 ^o C, hold at this temperature for 1-6 hours. Inert protective gases include nitrogen and argon, and the gas flow rate is 80-140 mL/min. The carbonization process is carried out under the protection of inert gas, which is conducive to maintaining the carbon skeleton structure. If it is roasted under oxygen-containing conditions, it will lead to the collapse of the carbon skeleton. In addition, the carbonization process is roasted in two stages, because the low temperature for a period of time is conducive to the complete degradation of the triblock copolymer; followed by high temperature carbonization to form a stable carbon skeleton structure with a certain degree of graphitization.

The novel porous carbon capacitive desalination electrode with hierarchical structure prepared by the method of the invention has higher specific surface area, good conductivity and better desalination performance, simple preparation process and easy operation. It has potential application prospects in capacitive desalination.

Detailed ways

Specific embodiments of the present invention are described below.

Example 1

Monodisperse silica microspheres with a diameter of 150 nm were ultrasonically dispersed in an ethanol solution (1 wt%), and then sintered at 600 ^° C for 1.5 h after deposition at 20 ^° C for 1-2 weeks to obtain SiO ₂ template. Add 0.13 g of 20 wt% sodium hydroxide solution to 0.61 g of molten phenol, stir well, then slowly add 1.05 g of 37 wt% formaldehyde solution, heat up to 65 ^o C for 2 h, cool to room temperature and use 0.6 M hydrochloric acid was used to adjust the pH to neutral, and vacuum dehydration at low temperature until viscous, then adding ethanol solution and stirring for 10 h, and finally centrifuged to remove inorganic salts to obtain a phenolic resin precursor solution with a concentration of 20 wt%. Add 1 g of F127 (PEO ₁₀₆ PPO ₇₀ PEO ₁₀₆ ) into 20 g of ethanol and stir to dissolve, then add the precursor solution and stir to mix well. Wherein the molar ratio of phenol, formaldehyde, sodium hydroxide and the structure directing agent is 1: 2: 0.1: 0.012. Then add 0.5 g SiO ₂ template into the above mixed solution, volatilize at 30 ^o C until the solution is viscous, remove the excess solution by suction filtration, further volatilize at 30 ^o C for 8 h, and then place it in a tube for 8 h after curing at 100 ^o C for 24 h. In the furnace, under the protection of nitrogen with a gas flow rate of 100 mL/min, the heating rate was controlled to be 1 ^o C/min. First, the temperature was raised to 350 ^o C, and kept at 350 ^o C for 2 hours, then the temperature was raised to 800 ^o C, and at 800 ^o C C for 4 h. After cooling to room temperature, 10 wt% hydrofluoric acid solution was added and stirred overnight to remove the SiO ₂ template, and the hierarchically porous carbon material was obtained after thorough washing and drying. The obtained hierarchical porous carbon material, acetylene black and polytetrafluoroethylene emulsion were mixed uniformly according to the mass ratio of 80:10:10, then spread on graphite paper, and then dried overnight at 100 ^o C ~ 120 ^o C. Finally, a hierarchical porous carbon desalination electrode is prepared.

The specific capacitance of the above-mentioned hierarchical porous carbon desalination electrode was tested. CHI 660D electrochemical workstation was used, the electrolyte was 1 M sodium chloride solution, the scan rate was 10 mV/s, and the voltage range was -0.5 V~0.5 V; the specific capacitance of the electrode was measured to be greater than 120 F/g. The electrode prepared above was tested for its desalination performance, and its desalination efficiency was greater than 90% in 600 ppm brine.

Example 2

Monodisperse silica microspheres with a diameter of 250 nm were ultrasonically dispersed in an ethanol solution (3 wt%), and then sintered at 600 ^° C for 1.5 h after deposition at 25 ^° C for 1-2 weeks to obtain SiO ₂ template. Add 0.26 g of 20 wt% sodium hydroxide solution to 1.22 g of molten phenol, stir well, then slowly add 2.1 g of 37 wt% formaldehyde solution, heat up to 70 ^o C for 1.5 h, cool to room temperature and use 0.6 M hydrochloric acid was used to adjust the pH to neutral, dehydrated under vacuum at low temperature until viscous, then added ethanol and stirred for 12 h, and finally centrifuged to remove inorganic salts to obtain a phenolic resin precursor solution with a concentration of 20 wt%. Add 1.5 g of P123 (PEO ₂₀ -PPO ₇₀ -PEO ₂₀ ) into 30 g of ethanol and stir to dissolve, then add the precursor solution and stir to mix evenly. Wherein the molar ratio of phenol, formaldehyde, sodium hydroxide and the structure directing agent is 1: 2: 0.1: 0.02. Then 2 g of SiO ₂ template was added to the above mixed solution, volatilized at 45 ^o C until the solution was viscous, and the excess solution was removed by suction filtration, then volatilized at 45 ^o C for 5 h for self-assembly, cured at 120 ^o C for 20 h and placed in a tube furnace In the process, under the protection of ^nitrogen with a gas ^flow rate of 80 mL/min, the heating rate ^was controlled to be 1 ^o C/min. ^o C for 4 h. After cooling to room temperature, 10 wt% hydrofluoric acid solution was added and stirred overnight to remove the SiO ₂ template, and the hierarchically porous carbon material was obtained after thorough washing and drying. The obtained hierarchical porous carbon material, acetylene black and polytetrafluoroethylene emulsion were mixed uniformly according to the mass ratio of 85:10:5, then spread on graphite paper, and then dried overnight at 100 ^o C ~ 120 ^o C. Finally, a hierarchical porous carbon desalination electrode is prepared.

The specific capacitance of the above-mentioned hierarchical porous carbon desalination electrode was tested. CHI 660D electrochemical workstation was used, the electrolyte was 1 M sodium chloride solution, the scan rate was 10 mV/s, and the voltage range was -0.5V~0.5V; the specific capacitance of the electrode was measured to be greater than 95 F/g. The electrode prepared above was tested for its desalination performance, and its desalination efficiency was greater than 85% in 800 ppm brine.

Example 3

Monodisperse silica microspheres with a diameter of 400 nm were ultrasonically dispersed in an ethanol solution (6 wt%), and then sintered at 600 ^° C for 1.5 h after deposition at 28 ^° C for 1-2 weeks to obtain SiO ₂ template. Add 0.13 g of 20 wt% sodium hydroxide solution to 0.61 g of molten phenol, stir well, then slowly add 1.05 g of 37 wt% formaldehyde solution, heat up to 75 ^o C for 1.5 h, cool to room temperature and use 0.6 M hydrochloric acid to adjust the pH to neutral, vacuum dehydration at low temperature to viscous, then add ethanol and stir for 10 h, and finally centrifuge to remove inorganic salts to obtain a phenolic resin precursor solution with a concentration of 20 wt%. Add 0.5 g F127 (PEO ₁₀₆ PPO ₇₀ PEO ₁₀₆ ) and 0.5 g P123 (PEO ₂₀ -PPO ₇₀ -PEO ₂₀ ) into 20 g of ethanol and stir to dissolve, then add the precursor solution and stir to mix evenly. Wherein the molar ratio of phenol, formaldehyde, sodium hydroxide and the structure directing agent is 1: 2: 0.1: 0.017. Then 4 g of SiO ₂ template was added to the above mixed solution, volatilized at 55 ^o C until the solution was viscous, the excess solution was removed by suction filtration, and then volatilized at 55 ^o C for 5 h for self-assembly, cured at 100 ^o C for 24 h and placed in a tube furnace In the process, under the protection of nitrogen with a gas flow rate of 130 mL/min, the heating rate was controlled to be 1 ^o C/min. First, the temperature was raised to 500 ^o C, and kept at 500 ^o C for 3 h, then the temperature was raised to 1000 ^o C, and at 1000 ^o C C for 2 h. After cooling to room temperature, 10 wt% hydrofluoric acid solution was added and stirred overnight to remove the SiO ₂ template, and the hierarchically porous carbon material was obtained after thorough washing and drying. The obtained hierarchical porous carbon material, acetylene black and polytetrafluoroethylene emulsion were mixed uniformly according to the mass ratio of 90:5:5, then spread on graphite paper, and then dried overnight at 100 ^o C ~ 120 ^o C. Finally, a hierarchical porous carbon desalination electrode is prepared.

The specific capacitance of the above-mentioned hierarchical porous carbon desalination electrode was tested. CHI 660D electrochemical workstation was used, the electrolyte was 1 M sodium chloride solution, the scan rate was 10 mV/s, and the voltage range was -0.5 V~0.5 V; the specific capacitance of the electrode was measured to be greater than 80 F/g. The electrode prepared above was tested for its desalination performance, and its desalination efficiency was greater than 80% in 300 ppm brine.

Claims (7)

1. The preparation method of multi-level porous carbon capacitive desalination electrode is characterized in that comprising the following steps: (1) Preparation of electrode materials: ultrasonically disperse monodisperse silica (SiO ₂ ) microspheres in a certain amount of ethanol solution, deposit naturally at 15 ~ 35 ^o C, and then sinter at high temperature to obtain SiO ₂ template; Add a sodium hydroxide solution with a concentration of 20 wt% to the mixture, stir evenly, slowly add a formaldehyde solution with a concentration of 37 wt%, raise the temperature to 65~75 ^o C and react for 1~2.5 h, and adjust the pH to neutral with 0.6 M hydrochloric acid after cooling to room temperature low-temperature vacuum distillation to reduce the water content, then add ethanol and stir for 10-12 h, then centrifuge to remove inorganic salts to obtain a phenolic resin precursor solution with a concentration of 20 wt%; mix the ethanol solution with a concentration of 4.76 wt% The resin precursor solution was stirred and mixed evenly; then the _SiO2 template was impregnated into the mixed solution, and the excess solution was removed by suction filtration after low-temperature volatilization reaction, further low-temperature volatilization and high-temperature curing, and then carbonized in an inert atmosphere and then added with a concentration of 10 wt% Hydrogen Fluorine The acid solution is stirred and reacted to remove the _SiO2 template, and the hierarchical porous carbon material can be obtained after sufficient washing and drying; (2) Preparation of capacitive desalination electrode: Stir and mix the hierarchically porous carbon material prepared in step (1), acetylene black and polytetrafluoroethylene emulsion according to the mass ratio of 80:10:10~90:5:5 Spread it on the conductive substrate graphite paper, and then dry it overnight at 100-120 ^o C; finally, a multi-level porous carbon capacitive desalination electrode is produced. 2. The preparation method of the hierarchical porous carbon capacitive desalination electrode according to claim 1, characterized in that the diameter of the monodisperse _SiO2 microspheres is 100-400 nm. 3. The preparation method of the hierarchical porous carbon capacitive desalination electrode according to claim 1, characterized in that the mass fraction of the microspheres in the ethanol solution of the _SiO2 microspheres is 1-10%. 4. The preparation method of the hierarchical porous carbon capacitive desalination electrode according to claim 1, characterized in that the structure directing agent includes F127 (PEO ₁₀₆ -PPO ₇₀ -PEO ₁₀₆ ) and P123 (PEO ₂₀ -PPO ₇₀ -PEO ₂₀ ) or a mixture of both. 5. the preparation method of hierarchical porous carbon capacitance type desalination electrode according to claim 1 is characterized in that in the described preparation process, the mol ratio of phenol, formaldehyde, sodium hydroxide and structure directing agent is 1: 2: 0.1: 0.005~0.025. 6. The preparation method of the hierarchical porous carbon capacitive desalination electrode according to claim 1, characterized in that the _SiO2 template impregnated with the precursor needs to undergo two-step reactions of low-temperature volatilization and high-temperature curing, wherein the temperature of low-temperature volatilization 30~60 ^o C; high temperature curing temperature is 100~140 ^o C. 7. The preparation method of the hierarchical porous carbon capacitive desalination electrode according to claim 1, characterized in that the carbonization process in the inert atmosphere needs to be realized by segmented temperature-controlled calcination, and the controlled heating rate is 1 ^o C/ Min, first raise the temperature to 300~500 ^o C, keep it at this temperature for 1-4 hours, then raise the temperature to 500~1100 ^o C, and keep it at this temperature for 1-6 hours; inert protective gas includes nitrogen and argon, gas The flow rate is 80-140 mL/min.