Preparation method and application of self-cleaning membrane electrode

Abstract

The invention discloses a preparation method and application of a self-cleaning membrane electrode. Co(NO3)2·6H2O and a transition metal M salt are respectively dissolved in methanol, 2-methylimidazole is added to each solution, the two solutions are then mixed and stirred under ultrasound, centrifuged to obtain M-doped Co@MIM, washed with ethanol and then dried, the dried M-doped Co@MIM is annealed to obtain a catalyst, commercial carbon paper is cut into 2×2 cm pieces, the catalyst is added to isopropanol, a polytetrafluoroethylene dispersion is added dropwise, the mixture is heated and ultrasonically until it becomes a gel, the mixture is evenly coated on the carbon paper, and calcined to obtain a catalyst-modified self-cleaning membrane electrode. According to a degradation experiment of chlorophenol pollutants, the self-cleaning membrane electrode has an electrocatalytic degradation rate of 99% for chlorophenol within 2 to 3 hours, showing high electrocatalytic activity. Comparative degradation experiments and cycle experiments of the modified self-cleaning membrane electrode and a carbon paper membrane electrode show that the modified self-cleaning membrane electrode exhibits good conductivity and repeatability, providing a new green regeneration technology for wastewater treatment.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a catalyst-modified self-cleaning membrane electrode, and specifically relates to the preparation of a self-cleaning membrane electrode modified with a transition metal oxide catalyst and its application in the degradation of chlorophenols. The present invention belongs to water pollution treatment technology, and specifically belongs to the field of electrocatalytic degradation technology of chlorophenols. Background Art

[0002] 4-Chlorophenol (4-CP) is a widely used organic pollutant that poses a significant threat to the environment and health. Therefore, effective removal of chlorophenols is crucial to mitigating their adverse effects. Furthermore, disinfection byproducts generated during the removal of chlorophenols can easily cause secondary water pollution. Therefore, efficient self-cleaning membrane electrodes are key to achieving sustainable operation. Traditional membrane cleaning uses oxidizing chemicals, such as sodium hypochlorite (NaClO), with a typical dosage of 1-2 g Cl L -1 However, the high cost and high chemical consumption of these processes hinder their large-scale application. Repeated chemical consumption complicates the process, and the difficulty in regeneration hinders its large-scale application. Meanwhile, the membrane cleaning ability of chlorine-active species has received widespread attention. Numerous studies have found that chlorine-containing wastewater is more likely to generate chlorine radicals under electroactivation conditions. Anodic oxidation of chloride ions to generate reactive chlorine species (RCS) in situ is a viable method for membrane self-cleaning. Summary of the Invention

[0003] The present invention provides a method for preparing and applying a self-cleaning membrane electrode for the electrocatalytic dechlorination of chlorophenols. The method utilizes active metal oxide nanoparticles on the surface of the self-cleaning membrane to achieve efficient electrocatalytic degradation of chlorophenols. The method can be used to prepare a self-cleaning membrane electrode and electrocatalytically degrade chlorophenols through simple operations.

[0004] A method for preparing a self-cleaning membrane electrode comprises the following steps:

[0005] (1) First, 2.184 g to 40.68 g of Co(NO3)2·6H2O and 2.232 g to 44.64 g of transition metal M salt were dissolved in 50 to 1000 mL of methanol, and then 2.464 g to 49.28 g of 2-methylimidazole were added. The two solutions were then mixed and stirred under ultrasound for 7 to 10 minutes. After centrifugation and filtration, the mixture was washed with ethanol several times and dried to obtain Co@MIM doped with M.

[0006] (2) annealing the M-doped Co@MIM dried in step (1) to obtain a catalyst;

[0007] (3) Commercial carbon paper (CP) was cut into 2 × 2 cm pieces. To construct the electrode, 20–30 mg of the catalyst was added to 1–2 mL of isopropanol, and then 20–25 μL of concentrated polytetrafluoroethylene dispersion was added dropwise. The mixture was heated and ultrasonicated until it became a gel-like state and evenly coated on the carbon paper. After calcination, a catalyst-modified self-cleaning membrane electrode was obtained.

[0008] In step (1), the transition metal M salt is a soluble zinc salt, manganese salt, copper salt, iron salt, nickel salt, etc. with crystal water, where M represents a metal; the transition metal M salt is specifically one of zinc nitrate, manganese nitrate, copper nitrate, iron nitrate, nickel nitrate, zinc chloride, manganese chloride, copper chloride, iron chloride, nickel chloride, zinc sulfate, etc.

[0009] In step (2), the annealing step is to heat the temperature to 200-400°C at a heating rate of 2-5°C / min and keep the temperature for 2-3 hours.

[0010] The mass fraction of the polytetrafluoroethylene concentrated dispersion in step (3) was 60%, which was purchased from Macklin.

[0011] In step (3), the ultrasonic temperature is 80-100°C and the time is 3-7 minutes.

[0012] Step (3) calcination is carried out in an air atmosphere at 350-370° C. for 20-30 minutes to remove polytetrafluoroethylene.

[0013] The application of the self-cleaning membrane electrode of the present invention is specifically to electrocatalytically degrade chlorophenol pollutants in wastewater, wherein the concentration of chlorophenol pollutants in the wastewater is 20-30 mg / L, the electrolyte solution during electrocatalytic degradation is a 0.05-0.07 mol / L NaCl solution, the pH value of the wastewater is 5-9, and the current value of the electrocatalytic degradation is 20-60 mA. The specific method is:

[0014] 120 mL of 4-chlorophenol solution (20 mg / L) was prepared in a 150 mL beaker and the pH of the solution was adjusted to 5-9 for 4-CP degradation experiments. The modified CP (2 × 2 cm) and CP were connected to the anode and cathode, respectively. The electrode holder was connected to a DC power supply (Longwei PS-302 DM (2A)). An air pump (Songbao SB-988) was used to pump air into the solution. At predetermined time intervals, the supernatant was extracted and filtered through a 0.22 µm mixed cellulose membrane before analysis. All experiments were performed at room temperature (25 °C).

[0015] The present invention proposes a simple and clean heat treatment method for preparing a self-cleaning membrane electrode. While degrading chlorophenol pollutants, it is concluded that metal defects and ultra-fast electron transfer are the essential reasons for the electrochemical oxidation of refractory substances in wastewater by the self-cleaning membrane electrode. The present invention creatively proposes a new method for preparing a modified self-cleaning membrane electrode. The electrocatalyst prepared by calcination has a high specific surface area, a uniform mesoporous structure, and a high degree of defects, which can significantly increase the electron transfer rate. At the same time, it has high electrocatalytic activity and can effectively degrade organic pollutants. The self-cleaning membrane electrode prepared by coating with a transition metal oxide catalyst is used for electrochemical oxidation dechlorination.

[0016] The present invention provides a method for preparing an electrocatalyst-modified self-cleaning membrane electrode and its application in promoting the electrocatalytic degradation of 4-CP, which can effectively remove organic pollutants and has the advantages of simple process, convenient operation, low cost, easy recycling and reuse, high treatment efficiency, and high degradation rate. It can effectively and quickly degrade organic pollutants and has good application prospects in the actual treatment of wastewater containing organic pollutants (such as chlorophenols).

[0017] The present invention is clean and efficient, has simple process operation, a feasible principle, and a green and environmentally friendly process, and at the same time achieves the reusability and corrosion resistance of the self-cleaning membrane electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the XRD pattern of the catalyst prepared in Example 1 of the present invention;

[0019] Figure 2 This is a graph showing the electrocatalytic degradation of 4-cp by the catalyst prepared in Example 1 of the present invention at different calcination temperatures;

[0020] Figure 3 This is a graph showing the electrocatalytic degradation of 4-cp by catalysts at different zinc-cobalt ratios prepared in Example 2 of the present invention;

[0021] Figure 4 The electron microscope images of the catalysts prepared in Example 2 of the present invention with different zinc and cobalt ratios (bf in the figure are CoO x 、Zn 0.5 CoO x 、Zn1CoO x 、Zn2CoO x 、Zn3CoO x SEM image of gh is Zn2CoO x TEM images and elemental mapping images);

[0022] Figure 5 Zn2CoO was prepared in Example 3 of the present invention.x Electrocatalytic degradation diagram of 4-cp by modified self-cleaning membrane electrode and carbon paper membrane electrode. DETAILED DESCRIPTION

[0023] The present invention is further described below with reference to specific examples. The simulated wastewater used in the examples was prepared by dissolving 4-chlorophenol in water, and its pH was adjusted using dilute hydrochloric acid and sodium hydroxide solution. The polytetrafluoroethylene concentrated dispersion used in the examples had a mass fraction of 60% and was purchased from Macklin.

[0024] Example 1

[0025] A preparation method and application of a self-cleaning membrane electrode for electrocatalytic dechlorination of chlorophenols, the specific steps are as follows:

[0026] First, Co(NO3)2·6H2O (2.184 g) and Zn(NO3)2·6H2O (2.232 g) were dissolved in 50 mL of methanol, and 2-methylimidazole (2.464 g) was added to each solution. After mixing, the two solutions were mixed and stirred under ultrasound for 7 minutes, and allowed to settle for 12 hours. The resulting precipitate was then centrifuged and filtered to obtain Zn-doped Co@MIM, which was washed three times with ethanol and dried in an oven at 60°C for 10 hours.

[0027] The dried Zn-doped Co@MIM was heated to 200, 300, 350, and 400 °C at a heating rate of 2 °C / min and annealed for 2 h to obtain ZnCoO catalysts. x -200, ZnCoO x -300, ZnCoO x -350, ZnCoO x -400;

[0028] Commercial carbon paper (CP) was cut into 2×2 cm. To construct the electrode, 25 mg of the multiple catalysts prepared above were added to 1.5 mL of isopropanol, and 20 μL of concentrated polytetrafluoroethylene dispersion was added dropwise. The mixture was heated and ultrasonically stirred at 80°C for 7 minutes until it became a gel. The obtained gel catalyst was evenly coated on the carbon paper and calcined in air at 350°C for 30 minutes to obtain multiple catalyst-modified self-cleaning membrane electrodes.

[0029] The modified self-cleaning membrane electrode was used for electrocatalytic reaction. The capacity of the reaction chamber was 150 mL. Then, 120 mL of 4-cp solution (20 mg / L) was added to a 150 mL beaker for 4-cp degradation experiment. The modified CP (2×2 cm) and CP were connected to the anode and cathode, respectively. The electrode holder was connected to a DC power supply (Longwei PS-302 DM (2A)) with a current value of 40 mA. An air pump (Songbao SB-988) pumped air into the solution. At predetermined time intervals, the supernatant was extracted and filtered through a 0.22 µm mixed cellulose membrane before analysis. All experiments were carried out at room temperature (25°C).

[0030] The concentration of 4-CP degraded during electrooxidation was monitored by HPLC (Water 2487) equipped with a C18 column and a UV detector. The mobile phase consisted of 70% (v / v) methanol and 30% ultrapure water at a flow rate of 1.0 mL / min. The detection wavelength was 270 nm, the injection volume was 10 μL, and the injection temperature was 25 °C.

[0031] Figure 1 The ZnCoO prepared at different annealing temperatures in Example 1 x -200, ZnCoO x -300, ZnCoO x -350, ZnCoO x -400 XRD patterns, XRD results further show that the diffraction peaks of the catalysts at different annealing temperatures have changed significantly, such as Figure 1 As shown, the characteristic diffraction peaks at angles of 7.2°, 10.2°, 12.5°, 14.5°, 16.2°, and 17.8° (JCPDS#43-0144) correspond to (100), (110), (111), (200), (210), and (211) of Zeolite 4A(Co), respectively, indicating that CoO x The structure of ZnCoO is similar to that of zeolite imidazole structure Co@MIM. With the gradual increase of calcination temperature, x The crystallinity of -200 (300℃, 350℃) shows a trend of slow decrease. In the area less than 20°, it can be observed that the main diffraction peaks at (100), (111) and (211) regularly shift to higher angles, which makes ZnCoO x -350 has a lattice stretching deformation and a smaller spacing, indicating that ZnCoO x -350 shows obvious lattice distortion. Figure 2 , The self-cleaning electrode at different annealing temperatures as anode electrocatalytic degradation of 4-cp reaction over time, it is found that the ZnCoO with the largest defect x-350 showed the best catalytic effect, with a degradation efficiency of 98% within 120 minutes, indicating that zinc doping and a high pyrolysis temperature caused defects to form on the crystal surface. The defects provided electron transmission channels for the electrochemical process, promoted the formation of highly active oxidants, and increased the electrochemical reaction rate.

[0032] Example 2

[0033] A preparation method and application of a self-cleaning membrane electrode for electrocatalytic dechlorination of chlorophenols, the specific steps are as follows:

[0034] First, Co(NO3)2·6H2O (4.364 g) and Zn(NO3)2·6H2O (2.232 g) were dissolved in 50 mL of methanol, and 2-methylimidazole (2.464 g) was added to each solution. After mixing, the two solutions were mixed and stirred under ultrasound for 3 minutes, and allowed to settle for 12 hours. The resulting precipitate was then centrifuged and filtered to obtain Zn-doped Co@MIM, which was washed three times with ethanol and dried in an oven at 60°C for 10 hours.

[0035] The dried Zn-doped Co@MIM was heated to 350°C at a heating rate of 2°C / min and annealed for 2 hours to obtain the catalyst Zn 0.5 CoO x ;

[0036] Commercial carbon paper (CP) was cut into 2×2 cm. To construct the electrode, 25 mg of catalyst was added to 1.5 mL of isopropanol, and 20 μL of concentrated polytetrafluoroethylene dispersion was added dropwise. The mixture was heated and ultrasonicated at 80°C and stirred for 7 minutes until it became gel-like. The obtained gel-like catalyst was evenly coated on the carbon paper and calcined in air at 350°C for 30 minutes to obtain a catalyst-modified self-cleaning membrane electrode.

[0037] The ratio of raw materials was adjusted, and other conditions were the same as in Example 2 to prepare different catalysts, as shown in Table 1:

[0038] Table 1

[0039] <![CDATA[Co(NO3)2·6H2O]]> <![CDATA[Zn(NO3)2·6H2O]]> catalyst 2.184g 2.232g <![CDATA[Zn1CoO x ]]> 2.184g 4.464g <![CDATA[Zn2CoO x ]]> 2.184g 6.696g <![CDATA[Zn3CoO x ]]>

[0040] The prepared modified self-cleaning membrane electrode was used for electrocatalytic reaction, and the experiment was carried out in the same manner as in Example 1. The results are as follows: Figure 3 As shown in the figure, it was found that with the increase of zinc content, the degradation efficiency of 4-cp gradually increased, indicating that zinc doping is beneficial to the generation of active species in the electrocatalytic process, accelerating electron transfer and improving electrocatalytic efficiency. Figure 4 , Figure 4 The electron microscope images of the catalysts prepared in Example 2 with different zinc-cobalt ratios (bf in the figure are CoO x、Zn 0.5 CoO x 、Zn1CoO x 、Zn2CoO x 、Zn3CoO x SEM image of gh is Zn2CoO x TEM images and elemental mapping images), it was found that Zn2CoO x The catalyst structure on the surface of the modified self-cleaning membrane electrode underwent obvious morphological distortion, indicating that vacancy defects can promote the generation of active chlorine radicals and improve the electrocatalytic efficiency.

[0041] Example 3

[0042] A preparation method and application of a self-cleaning membrane electrode for electrocatalytic dechlorination of chlorophenols, the specific steps are as follows:

[0043] First, Co(NO3)2·6H2O (2.184 g) and Zn(NO3)2·6H2O (4.464 g) were dissolved in 50 mL of methanol, and 2-methylimidazole (2.464 g) was added to each solution. After mixing, the two solutions were mixed and stirred under ultrasound for 7 minutes, and allowed to settle for 12 hours. The resulting precipitate was then centrifuged and filtered to obtain Zn-doped Co@MIM, which was washed three times with ethanol and dried in an oven at 60°C for 10 hours.

[0044] The dried Zn-doped Co@MIM was heated to 350°C at a heating rate of 2°C / min and annealed for 2 hours to obtain the catalyst Zn2CoO x ;

[0045] Commercial carbon paper (CP) was cut into 2×2 cm. To construct the electrode, 20 mg of catalyst was added to 2 mL of isopropanol, and 25 μL of concentrated polytetrafluoroethylene dispersion was added dropwise. The mixture was heated and ultrasonicated at 90 °C and stirred for 5 min until it became gel-like. The obtained gel-like catalyst was evenly coated on the carbon paper and calcined in air at 360 °C for 25 min to obtain a catalyst-modified self-cleaning membrane electrode.

[0046] According to the application method of Example 1, the pH value of the 4-chlorophenol solution (20 mg / L) was adjusted from the natural pH value (6.5) to 5-9 by adjusting the amount of hydrochloric acid (0.1 M) or NaOH solution (0.1 M) added to study the effect of pH on the electrocatalytic degradation of 4-CP. The degradation rate results for 120 min are shown in Table 2.

[0047] Table 2

[0048] pH Degradation rate / % 5.0 87.5 7.0 98.6 9.0 75.2

[0049] It can be seen from Table 2 that the degradation effect is best under neutral conditions.

[0050] The reusability and stability of the self-cleaning membrane electrode were investigated. After the degradation process was completed, the self-cleaning membrane electrode was recovered and rinsed with deionized water to conduct a recycling test under the same conditions. The stability of the membrane electrode was evaluated by repeating the 4-CP degradation experiment three times, with each catalytic degradation for 120 minutes. The results of the cyclic degradation experiment are shown in Table 3. Zn2CoO x The modified self-cleaning membrane electrode has good cycling performance, and the degradation rate remains above 90% after three repeated cycle tests.

[0051] Table 3

[0052] Number of cycles Degradation rate of pollutants / % 1 99.1 2 96.5 3 91.8

[0053] from Figure 5 , through Zn2CoO x Comparison of the electrocatalytic 4-cp degradation of the modified self-cleaning membrane electrode and the carbon paper membrane electrode without catalyst coating shows that Zn2CoO x The modified self-cleaning membrane electrode has good electrical conductivity and electrocatalytic performance.

[0054] Example 4

[0055] A preparation method and application of a self-cleaning membrane electrode for electrocatalytic dechlorination of chlorophenols, using other transition metals (such as: M = Mn, Cu, Fe, Ni) to replace the metal zinc in the above embodiment, the specific steps are as follows:

[0056] Co(NO3)2·6H2O (21.184 g) and M(NO3)2·6H2O (respectively Mn(NO3)2·6H2O (41.791 g), Cu(NO3)2·6H2O (43.096 g), Fe(NO3)2·6H2O (35.234 g), Ni(NO3)2·6H2O (42.337 g)) were dissolved in 150 mL of methanol, and 2-methylimidazole (24.64 g) was added. Then, the two solutions were mixed and stirred under ultrasound for 10 minutes, and allowed to settle for 12 hours. The resulting precipitate was then centrifuged and filtered to obtain Co@MIM doped with metal M, which was washed three times with ethanol and dried in an oven at 60°C for 10 hours.

[0057] The dried Co@MIM doped with metal M was heated to 400℃ at a heating rate of 5℃ / min and annealed for 3 hours to obtain the catalysts Mn2CoO x 、Cu2CoO x 、Fe2CoO x 、Ni2CoO x ;

[0058] Commercial carbon paper (CP) was cut into 2×2 cm. To construct the electrode, 30 mg of catalyst was added to 2 mL of isopropanol, and 22 μL of concentrated polytetrafluoroethylene dispersion was added dropwise. The mixture was heated and ultrasonically stirred at 100 °C for 3 min until it became gel-like. The obtained gel-like catalyst was evenly coated on the carbon paper and calcined in air at 370 °C for 20 min to obtain a catalyst-modified self-cleaning membrane electrode.

[0059] According to the application method of Example 1, the experiment was carried out. The self-cleaning membrane electrode prepared by using other transition metals in Example 4 can still achieve the degradation effect of the metal zinc-doped self-cleaning membrane electrode in Example 1 on 4-cp.

Claims

1. A method for preparing a self-cleaning membrane electrode, characterized in that: The specific steps include: (1) 2.184 g to 40.68 g of Co(NO3)2·6H2O and 2.232 g to 44.64 g of transition metal M salt were dissolved in 50 to 1000 mL of methanol, and 2.464 g to 49.28 g of 2-methylimidazole were added. The two solutions were then mixed and stirred under ultrasound for 7 to 10 minutes. After centrifugation and filtration, the mixture was washed with ethanol and dried to obtain Co@MIM doped with M. (2) annealing the M-doped Co@MIM dried in step (1) to obtain a catalyst; (3) Cut commercial carbon paper into 2 × 2 cm pieces, add 20–30 mg of the catalyst into 1–2 mL of isopropanol, and then dropwise add 20–25 μL of concentrated polytetrafluoroethylene dispersion. Heat and ultrasonicate the mixture, and evenly coat the resulting gel-like substance on the carbon paper. After calcination, a catalyst-modified self-cleaning membrane electrode is obtained.

2. The method for preparing the self-cleaning membrane electrode according to claim 1, characterized in that: Step (1) The transition metal M salt is a zinc salt, manganese salt, copper salt, iron salt, or nickel salt with crystal water, where M represents a metal; specifically, it is one of zinc nitrate, manganese nitrate, copper nitrate, iron nitrate, nickel nitrate, zinc chloride, manganese chloride, copper chloride, iron chloride, nickel chloride, and zinc sulfate.

3. The method for preparing the self-cleaning membrane electrode according to claim 1, characterized in that: In step (2), the annealing step is to heat the temperature to 200-400°C at a heating rate of 2-5°C / min and keep the temperature for 2-3 hours.

4. The method for preparing the self-cleaning membrane electrode according to claim 1, characterized in that: The mass fraction of the polytetrafluoroethylene concentrated dispersion in step (3) is 60%.

5. The method for preparing the self-cleaning membrane electrode according to claim 1, characterized in that: In step (3), the ultrasonic temperature is 80-100°C and the time is 3-7 minutes.

6. The method for preparing the self-cleaning membrane electrode according to claim 1, characterized in that: Step (3) calcination is carried out in an air atmosphere at 350-370° C. for 20-30 minutes.

7. Application of the self-cleaning membrane electrode prepared by the method of claim 1 to electrocatalytically degrade chlorophenol pollutants in wastewater.

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