Improved membrane electrode and preparation and application method thereof

Abstract

The invention discloses an improved membrane electrode and a preparation and application method thereof. The improved membrane electrode comprises polyvinyl alcohol-activated carbon as a basic electrode, and a bimetallic doped carbon-based catalyst and a porous carbon-based catalyst which are respectively positioned on two sides of the basic electrode and are used as an anode and a cathode. Activated carbon is used as a catalytic membrane electrode base material, polyvinyl alcohol is used as a binder to prepare PVA-AC, a catalyst is loaded to the PVA-AC based on bimetallic blending, high-temperature pyrolysis and electrostatic spinning to prepare an electro-catalytic anode with excellent oxidation-reduction performance, and an electro-catalytic cathode is prepared based on high-temperature pyrolysis and electrostatic spinning. And an aeration device is further introduced to construct the CDI system.

Description

Improved membrane electrodes and their preparation and application methods Technical Field

[0001] This invention relates to a technology in the field of electrode preparation, specifically a membrane electrode suitable for organic degradation, a method for preparing the same, and a capacitive deionization system containing the membrane electrode. Background Technology

[0002] With the rapid development of the chemical industry, various chemical agents are widely used in industries such as papermaking, pharmaceuticals, and textiles. During production and use, a large amount of high-salt organic wastewater is generated. Currently, waste salt is generally treated by centralized storage in reservoirs, further realizing its resource utilization and recycling. However, the diverse types and complex composition of organic matter in waste salt are a key bottleneck restricting the harmless treatment of high-salt organic wastewater, and this bottleneck lies in the removal of organic matter. Summary of the Invention

[0003] This invention addresses the shortcomings of existing CDI technologies, such as poor desalination capacity, inability to achieve organic matter degradation and conversion, low wastewater resource utilization, and insufficient resistance to organic pollution. It proposes an improved membrane electrode and its preparation and application methods. Activated carbon is used as the base material for the catalytic membrane electrode, and polyvinyl alcohol is used as a binder to prepare PVA-AC. Based on bimetallic blending, high-temperature pyrolysis, and electrospinning, a catalyst is loaded onto PVA-AC to prepare an electrocatalytic anode with excellent redox performance. Simultaneously, an electrocatalytic cathode is prepared based on high-temperature pyrolysis and electrospinning, and an aeration device is further introduced to construct a CDI system.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a catalytic membrane electrode suitable for simultaneous salt ion removal and organic matter degradation, comprising: a polyvinyl alcohol-activated carbon as the base electrode, and a bimetallic doped carbon-based catalyst and a porous carbon-based catalyst located on both sides of the electrode as the anode and cathode, respectively.

[0006] The bimetallic doped carbon-based catalyst uses iron carbide-cobalt-zeolite imidazole ester as its framework.

[0007] The porous carbon-based catalyst uses carbonized carbon nanotubes-polyvinylpyrrolidone-zeolite imidazole ester as its framework.

[0008] This invention relates to a method for preparing the above-mentioned catalytic membrane electrode, by spraying a porous carbon-based catalyst and a bimetallic doped catalyst onto the cathode and anode, respectively.

[0009] The base electrode is prepared by dissolving polyvinyl alcohol in deionized water, stirring and allowing it to stand to remove bubbles, adding capacitor activated carbon powder, stirring at a constant temperature until uniform, obtaining an electrode slurry, and then coating it onto a flat plate surface. Specifically, polyvinyl alcohol is dissolved in deionized water and stirred continuously at 85°C for 5 hours until completely dissolved to prepare a polyvinyl alcohol solution with a concentration of 5-10 wt.%, and the capacitor activated carbon has a mass fraction of 10-30 wt.%.

[0010] The porous carbon-based catalyst is obtained by ultrasonically dispersing functionalized carbon nanotubes in a methanol solution, then sequentially adding zinc nitrate, 2-methylimidazole, and polyvinylpyrrolidone under continuous stirring, followed by high-speed centrifugation and high-temperature pyrolysis. Specifically, 0.1–0.3 g of functionalized carbon nanotubes are dissolved in 60 mL of methanol solution and ultrasonicated for 30 min, then 2.35 g of zinc nitrate, 5 g of 2-methylimidazole, and 1 g of polyvinylpyrrolidone are added; high-temperature pyrolysis is carried out under N2 atmosphere at a heating rate of 5 °C / min to 950 °C, and held at that temperature for 2 h.

[0011] The bimetallic doped catalyst is obtained by ultrasonically dispersing 2-methylimidazole in a methanol solution, then adding a methanol solution of zinc nitrate, ferric nitrate, and cobalt nitrate dropwise under continuous stirring, followed by high-speed centrifugation, drying, and then high-temperature pyrolysis. Specifically, 5g of 2-methylimidazole is dissolved in 60mL of methanol and ultrasonically sonicated for 30min. Solution B is made by dissolving 0.35g of zinc nitrate, 0.36g of ferric nitrate, and 0.36g of cobalt nitrate in 60mL of methanol.

[0012] The spraying process involves electrospinning the coating onto the anode and cathode surfaces. Specifically, the following parameters are used: a positive high voltage of 18–21 kV, a negative high voltage of -3 kV, a needle inner diameter of 0.51 mm, an electrospray fluid injection rate of 0.5–1.0 mL / h, a distance of 10 cm between the receiving roller and the nozzle tip, a receiving roller rotation speed of 50–100 r / min, a nozzle lateral movement speed of 50–150 mm / min, an electrospinning ambient temperature of 10–70 °C, and a relative humidity of 10–80%. The spinning solutions used are 3 wt.% sulfosuccinic acid / 6–10 wt.% polyvinyl alcohol for the cathode and 3–5 wt.% polyethyleneimine / 6–10 wt.% polyvinyl alcohol for the anode.

[0013] The high-temperature pyrolysis is preferably carried out under a N2 atmosphere, with the temperature increased to 950°C at a heating rate of 5°C / min, and held at that temperature for 2 hours. Technical advantages

[0014] This invention simultaneously achieves the enrichment, conversion, and in-situ adsorption of organic phosphorus and inorganic phosphorus, replacing the traditional coagulation-sedimentation-adsorption-advanced oxidation coupling process. It does not produce secondary pollution such as sludge, and requires no addition of reagents or aeration, resulting in significant economic benefits. Compared to traditional electro-adsorption technology, which is only suitable for treating saline wastewater, this invention can simultaneously remove salt ions and degrade and convert organic matter, expanding the application scope of CDI. At the same time, it has a self-cleaning function, and the self-generated H2O2 can effectively sterilize, prevent electrode microbial contamination, and extend the system's operating life. Attached Figure Description

[0015] Figure 1 is a flowchart of the present invention;

[0016] Figure 2 is a scanning electron microscope (SEM) image of the catalytic composite membrane electrode prepared in this invention;

[0017] Figure 3 is a schematic diagram of the capacitor deionization unit;

[0018] In the figure: 1. Graphite current collector, 2. Three-layer composite film electrode, 3. Plastic separator, 4. Electrode. Detailed Implementation Example 1

[0019] This embodiment relates to a catalytic membrane electrode suitable for simultaneous salt ion removal and organic matter degradation, the preparation method of which includes:

[0020] Step 1: Clean the capacitor activated carbon powder with acetone, ethanol and deionized water by ultrasonic cleaning for 30 minutes and then dry it to remove surface moisture. The drying temperature is 80℃ and the time is 3 hours.

[0021] Step 2: Prepare a 10 wt.% polyvinyl alcohol solution, cool it to room temperature, add 30 wt.% of the capacitor activated carbon treated in Step 1, stir it evenly with mechanical stirring, and then prepare the basic electrode based on flat plate coating.

[0022] Step 3: After ultrasonically dispersing functionalized carbon nanotubes in methanol solution, zinc nitrate is added, and 2-methylimidazolium and polyvinylpyrrolidone are added under continuous stirring. After high-speed centrifugation, powder is obtained, and catalyst is obtained after high-temperature pyrolysis. The catalyst is then sprayed onto the base electrode obtained in step 2 to prepare the catalytic membrane cathode based on electrospinning.

[0023] The concentration of the carbon nanotubes in the methanol solution is 0.10 wt.%.

[0024] Step 4: Disperse 2-methylimidazole in methanol solution (solution A) using ultrasound, dissolve zinc nitrate, ferric nitrate and cobalt nitrate in methanol solution (solution B), add solution A dropwise to solution B and stir continuously for 24 hours, centrifuge at high speed and dry to obtain the precursor, and obtain the bimetallic doped catalyst after high temperature pyrolysis. Spray the bimetallic catalyst onto the catalytic membrane anode on the other side of the catalytic membrane cathode in step 3 based on electrospinning.

[0025] The zinc nitrate has a mass of 6.25g, the ferric nitrate has a mass of 0.20g, and the cobalt nitrate has a mass of 0.20g.

[0026] Step 5: Place the anode and cathode in a crosslinking solution prepared by 5 wt.% glutaraldehyde, 1 mL of 12 mol / L concentrated hydrochloric acid, 90 mL of isopropanol and 10 mL of deionized water for thermal crosslinking. The temperature is controlled at 60℃ for 1 hour and then vacuum dried at 80℃ for 2 hours.

[0027] As shown in Figures 1 and 2, the catalytic membrane electrode prepared in this embodiment is based on polyvinyl alcohol-activated carbon as the base electrode, and bimetallic doped carbon-based catalyst and porous carbon-based catalyst are sprayed onto the surface of the base electrode, respectively.

[0028] As shown in Figures 2 and 3, the capacitive deionization (CDI) unit based on the catalytic membrane electrode prepared above includes a plastic separator 3, a catalytic membrane electrode 2, a graphite current collector 1, and a glass plate shell arranged sequentially on one side, and an electrode 4, a graphite current collector 1, and a glass plate shell arranged sequentially on the other side. The two shells are closed and have a circulating cooling water channel inside. The water inlet and outlet adopt a bottom-inlet and top-outlet mode to prevent short-circuiting.

[0029] As shown in Figure 3, a solution of 10 mmol / L NaCl and 0.1 mmol / L HEDP was prepared using a circulating influent / outfluent mode. The solution flow rate was set at 10 mL / min, and the voltage was 1.3 V. A complete operating cycle included adsorption and desorption, with times of 70 minutes and 30 minutes, respectively. During the adsorption phase, the solution conductivity decreased from 1090 to 925 μS / cm, and the adsorption capacity was 40.2 mg / g. The maximum concentration of self-produced hydrogen peroxide was 114 μmol / L, and the maximum conversion efficiency of organophosphorus compounds was 71.5%. During the desorption phase, the solution conductivity rapidly returned to its initial value, and the desorption rate was 98.1%. Compared with traditional advanced oxidation technologies, this technology can achieve a cost reduction of over 80%, resulting in significant economic benefits. Example 2

[0030] The difference between the preparation method in this embodiment and the previous embodiment is that:

[0031] The concentration of the nanotubes is 0.2 wt.%.

[0032] The mass of the ferric nitrate is 0.36g, and the mass of the cobalt nitrate is 0.36g.

[0033] The catalytic membrane electrode described above was placed in an electrocatalytic capacitor deionization system, as shown in Figure 3. A solution of 10 mmol / L NaCl and 0.1 mmol / L HEDP was used, employing a circulating influent / outfluent water mode. The solution flow rate was set at 10 mL / min, and the voltage was 1.3 V. A complete operating cycle included adsorption and desorption, with times of 70 minutes and 30 minutes, respectively. During the adsorption phase, the solution conductivity decreased from 1090 μS / cm to 881 μS / cm, with an adsorption capacity of 47.5 mg / g. The maximum concentration of self-produced hydrogen peroxide was 158 μmol / L, and the maximum conversion efficiency of organophosphorus compounds was 89.9%. During the desorption phase, the solution conductivity rapidly increased to its initial value, with a desorption rate of 99.1%. Increasing the carbon nanotube concentration enhances the electrode's conductivity and introduces considerable adsorption sites to promote ion adsorption. Increasing the quality of bimetallic doping enhances hydrogen peroxide activation, increases free radical content, and promotes organophosphorus degradation. Example 3

[0034] The difference between the preparation method in this embodiment and the previous embodiment is that:

[0035] The concentration of the carbon nanotubes is 0.30 wt.%.

[0036] The mass of the ferric nitrate is 0.50g, and the mass of the cobalt nitrate is 0.50g.

[0037] The aforementioned catalytic membrane electrode was placed in an electrocatalytic capacitor deionization system, as shown in Figure 3. A concentration of 10 mmol / L NaCl and 0.1 mmol / L HEDP was configured, using a circulating influent / outfluent water mode. The solution flow rate was set at 10 mL / min, and the voltage was 1.3 V. A complete operating cycle included adsorption and desorption, with times of 70 minutes and 30 minutes, respectively. During the adsorption phase, the solution conductivity decreased from 1090 μS / cm to 911 μS / cm, with an adsorption capacity of 42.2 mg / g. The maximum self-produced hydrogen peroxide concentration was 98 μmol / L, and the maximum organophosphorus conversion efficiency was 76.8%. During the desorption phase, the solution conductivity rapidly increased to its initial value, with a desorption rate of 96.8%. When the carbon nanotube concentration was too high, the intermediate layer became too dense, completely covering the underlying activated carbon electrode. This damaged the activated carbon electrode's structure, such as reducing its specific surface area, which was detrimental to enhancing adsorption performance and inhibiting hydrogen peroxide production, thus suppressing the degradation and transformation of organic matter.

[0038] In summary, the catalytic membrane electrode prepared by this invention possesses a loose mesoporous structure, high specific surface area, excellent conductivity, and hydrophilicity. These characteristics promote ion migration and diffusion, enhance ion mass transfer through aeration, suppress double-layer overlap effects, are unaffected by coexisting ions, and strengthen desalination capabilities. The loading of the cathode catalyst and the stable dissolved oxygen in the influent enhance the in-situ self-production of hydrogen peroxide by the CDI, and further generate free radicals through anodic activation to achieve organic matter degradation. The capacitive deionization unit (CDI) of the catalytic membrane electrode prepared by this invention can be used for simultaneous inorganic salt removal and organic matter degradation and transformation, and is suitable for the treatment of organic saline wastewater and the removal of trace organic pollutants from electronic-grade ultrapure water.

[0039] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A catalytic membrane electrode suitable for simultaneous salt ion removal and organic matter degradation, characterized in that, include: The basic electrode consists of polyvinyl alcohol-activated carbon and bimetallic doped carbon-based catalyst and porous carbon-based catalyst located on both sides as anode and cathode, respectively; the bimetallic doped carbon-based catalyst uses iron carbide-cobalt-zeolite imidazole ester as a framework; the porous carbon-based catalyst uses carbon carbon nanotube-polyvinylpyrrolidone-zeolite imidazole ester as a framework.

2. A method for preparing a catalytic membrane electrode according to claim 1, characterized in that, A porous carbon-based catalyst and a bimetallic doped catalyst are respectively sprayed onto both sides of a base electrode. The porous carbon-based catalyst is obtained by ultrasonically dispersing functionalized carbon nanotubes in a methanol solution, then sequentially adding zinc nitrate, 2-methylimidazole, and polyvinylpyrrolidone under continuous stirring, followed by high-speed centrifugation and high-temperature pyrolysis. The bimetallic doped catalyst is obtained by ultrasonically dispersing 2-methylimidazole in a methanol solution, then dropwise adding a methanol solution of zinc nitrate, ferric nitrate, and cobalt nitrate under continuous stirring, followed by high-speed centrifugation, drying, and then high-temperature pyrolysis.

3. The preparation method according to claim 2, characterized in that, The base electrode is prepared by dissolving polyvinyl alcohol in deionized water, stirring and allowing it to stand to remove bubbles, adding activated carbon powder, stirring at a constant temperature until uniform, obtaining an electrode slurry, and then coating it onto the surface of a flat plate.

4. The preparation method according to claim 2, characterized in that, The aforementioned spraying is performed by electrospinning onto both sides of the base electrode. Specifically, the following conditions are met: a positive high voltage of 18–21 kV and a negative high voltage of -3 kV are used; the needle inner diameter is 0.51 mm; the electrospinning fluid injection speed is 0.5–1.0 mL / h; the distance between the receiving roller and the nozzle tip is 10 cm; the receiving roller rotation speed is 50–100 r / min; the nozzle lateral movement speed is 50–150 mm / min; the electrospinning ambient temperature is 10–70 °C; the relative humidity is 10–80%; and the spinning solution used is 3 wt.% sulfosuccinic acid / 6–10 wt.% polyvinyl alcohol for the cathode and 3–5 wt.% polyethyleneimine / 6–10 wt.% polyvinyl alcohol for the anode.

5. The preparation method according to claim 2, characterized in that, The high-temperature pyrolysis is carried out under N2 atmosphere, with the temperature increased to 950°C at a rate of 5°C / min and held at that temperature for 2 hours.

6. A capacitive deionization unit based on the catalytic membrane electrode of any of the preceding claims, characterized in that, include: The enclosure consists of a plastic partition, a catalytic membrane electrode, a graphite current collector, and a glass plate shell arranged sequentially on one side, and an electrode, a graphite current collector, and a glass plate shell arranged sequentially on the other side. The two shells are closed and have a circulating cooling water channel inside. The water inlet and outlet adopt a bottom-inlet and top-outlet mode to prevent short-circuiting.

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