Preparation method and application of carbon cathode for electro-Fenton oxidation system

Abstract

The invention discloses a preparation method of a carbon cathode material for an electro-Fenton oxidation system. The preparation method comprises the following steps: S1, obtaining pretreated graphite powder and carbon nanotubes; s2, obtaining a perforated graphite plate; s3, mixing the pretreated graphite powder and carbon nanotubes with sodium sulfate to obtain a first mixture; absolute ethyl alcohol is added into the first mixture, then a polytetrafluoroethylene solution is added, and homogeneous paste is formed; s4, coating two sides of a perforated graphite plate with the homogeneous paste, covering two sides of the coated graphite plate with a metal wire mesh, and performing pressing treatment to obtain a primary cathode material; s5, the primary cathode material is subjected to thermocuring treatment and then soaked in deionized water, drying treatment is conducted after water is changed for multiple times, and an intermediate cathode material is obtained; and S6, soaking and drying the intermediate cathode material in acetone to obtain the cathode material. The cathode material is used in an electro-Fenton oxidation system, and the oxidative degradation effect on organic matters is improved by improving the efficiency of generating H2O2 by electrically reducing oxygen through a cathode.

Description

Technical Field

[0001] This invention relates to the fields of electrochemistry and water treatment technology, specifically to a method for preparing and applying a carbon cathode for an electro-Fenton oxidation system. Background Technology

[0002] Water pollution has become a major factor contributing to global ecological damage and hindering my country's economic development. However, traditional wastewater treatment methods are no longer sufficient to fully meet the requirements for improving water quality. Biological wastewater treatment methods are widely used for organic wastewater due to their low operating costs. However, when wastewater contains high salinity or substances that are toxic or strongly inhibitory to microorganisms (such as wastewater from various chemical and pharmaceutical industries), these methods often fail to achieve ideal treatment results or even become completely ineffective. In the past decade or so, research on various advanced oxidation technologies for treating recalcitrant organic matter has been extensive. These technologies mainly include Fenton oxidation, cathodic electro-Fenton oxidation, electrochemical anodic oxidation, photocatalytic oxidation, ultrasonic oxidation, and H2O2 / O3 oxidation. Their commonality lies in using active free radicals such as hydroxyl radicals (·OH) as the main oxidants to degrade organic matter. These technologies are non-selective in their degradation of organic matter and are environmentally friendly.

[0003] Among the aforementioned advanced oxidation technologies, the cathode electro-Fenton oxidation method (electro-Fenton oxidation) has become one of the research hotspots in the field of advanced oxidation technology. Its basic principle is that O2 is generated through a reduction reaction involving two electron transfers at the cathode; subsequently, it reacts with Fe... 2+ The Fenton reaction generates ·OH, which degrades organic matter. This method has many advantages over the traditional Fenton oxidation method: (1) because it can generate H2O2 in situ, it avoids the transportation and storage of H2O2, and has a high utilization rate; (2) because the cathode can not only reduce O2 to generate H2O2, but also reduce Fe. 3+ To regenerate Fe 2+ Function, therefore Fe 2+ The dosage and subsequent iron sludge production are both lower than those of the traditional Fenton oxidation method; (3) Under the electro-Fenton oxidation system, anodic oxidation also has a certain organic matter degradation effect. The efficiency of electro-Fenton oxidation in degrading organic matter mainly depends on the performance of the cathode material in generating H2O2.

[0004] Improving the accessibility of oxygen to the cathode material facilitates the reduction of O2 to H2O2 at the cathode, which in turn reacts with Fe. 2+The Fenton reaction occurs, generating highly oxidizing ·OH that degrades organic matter. Cathode electro-Fenton oxidation has the advantages of mild reaction conditions, no need for external H2O2, and good degradation effect of organic matter, thus having good application prospects. However, the cathode materials used in this oxidation technology still have important shortcomings: (1) The yield and current efficiency of H2O2 generation at the cathode still need to be further improved to reduce energy consumption and overcome the bottleneck of high processing cost; (2) The size of the cathode prepared by conventional methods cannot be controlled, and the mechanical properties are poor, which cannot meet the needs of industrialization; (3) In addition, some cathodes use metal as a skeleton, which has the problem of metal corrosion during use.

[0005] Therefore, there is an urgent need to study a high-performance cathode material that can improve the current efficiency of H2O2 generation by electro-reduction and reduce energy consumption when applied in the electro-Fenton system. This research is crucial for the electro-Fenton oxidation degradation of organic pollutants. Summary of the Invention

[0006] This invention discloses a method for preparing a carbon cathode for an electro-Fenton oxidation system and its application. The patented method allows for the preparation of a carbon cathode with a rough surface, strong hydrophobicity, and numerous micropores. This cathode material exhibits strong hydrophobicity while simultaneously displaying strong aerophilicity. When applied to an electro-Fenton system, it improves the efficiency of the cathode's electroreduction of oxygen to generate H₂O₂, thereby enhancing the degradation effect of organic pollutants in wastewater by electro-Fenton oxidation. Furthermore, this cathode material possesses excellent mechanical strength and stability, meeting the needs of industrial applications.

[0007] The first objective of this invention is to provide a method for preparing a carbon cathode for an electro-Fenton oxidation system, the method comprising: S1 involves heat-treating graphite powder and carbon nanotubes under a nitrogen protective atmosphere to obtain pretreated graphite powder and carbon nanotubes. S2 cuts the graphite plate and then punches holes in it to obtain a perforated graphite plate; S3 mixes the pretreated graphite powder and carbon nanotubes with sodium sulfate to obtain a first mixture; then adds anhydrous ethanol to the first mixture, stirs it evenly, and then adds polytetrafluoroethylene solution, and continues stirring until a homogeneous paste is formed. S4. The homogeneous paste is uniformly coated on both sides of the perforated graphite plate to obtain the coated graphite plate; a metal wire mesh is covered on both sides of the coated graphite plate and pressed to obtain the primary cathode material. S5 The primary cathode material is placed in a muffle furnace for thermosetting, then immersed in deionized water, with the water changed multiple times, and then dried to obtain the intermediate cathode material. S6 involves immersing the intermediate cathode material in acetone and then drying it under vacuum to obtain the carbon cathode material for the electro-Fenton oxidation system.

[0008] Specifically, the heat treatment in step S1 takes 30-90 minutes and is carried out at a temperature of 250-350°C.

[0009] Specifically, the thickness of the graphite plate being perforated in step S2 is 8-15 mm, the hole diameter is 5-10 mm, and the perforation area is 40%-80%.

[0010] Specifically, in step S3, the mass ratio of the pretreated graphite powder, carbon nanotubes, sodium sulfate, and polytetrafluoroethylene solution is 1:(0.01-0.1):(0.05-0.2):(0.5-2); and the solid content of the polytetrafluoroethylene solution is 60%.

[0011] Specifically, the pressing process in step S4 is performed at a pressure of 2-6 MPa for 5-10 minutes.

[0012] Specifically, the temperature of the thermosetting treatment in step S5 is 300-360℃, and the time is 40-120 min.

[0013] Specifically, the soaking treatment in step S6 takes 8-24 hours; the vacuum drying treatment takes 40-80°C for 40-120 minutes.

[0014] The second objective of this invention is to provide a carbon cathode material for an electro-Fenton oxidation system prepared by the preparation method described above.

[0015] The third objective of this invention is to provide an application of the carbon cathode material described above for use in an electro-Fenton oxidation system for the oxidation and degradation of organic pollutants in wastewater.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: (1) A perforated graphite plate was used as a substrate to support the preparation of the cathode for electrocatalytic materials. A protruding structure was pressed out on the surface using a metal wire mesh to increase the roughness of the cathode surface and improve the hydrophobicity and aerophilicity of the material surface. Graphite powder and carbon nanotubes were mixed and used to prepare the cathode material. The ORR of the graphite powder with oxygen-containing groups removed provided an electron transfer path and improved the cathode reaction rate. Its micron-sized particle structure maintained the overall strength of the electrode and prevented the structure from collapsing during the reaction. The nano-sized pores of carbon nanotubes provided a fast diffusion channel for oxygen and organic pollutants. "Nanobridges" were built between graphite particles to reduce the interfacial resistance and improve the electron transfer rate. Sodium sulfate was used as a pore-forming agent to expand the specific surface area of ​​graphite / carbon nanotubes, increase the O2 diffusion channel, and further improve the H2O2 yield. (2) The cathode material prepared by the preparation method of the present invention has high surface roughness and abundant micropores. The cathode surface has strong hydrophobicity and strong gas affinity. When applied to the electro-Fenton oxidation degradation of organic pollutants in wastewater, it is beneficial to the process of gas adsorption at the water-gas-solid three-phase interface, which improves the accessibility of oxygen to the cathode. In addition, the abundant micropores inside the cathode material increase the effective electrochemical reaction area, which helps to improve the efficiency of cathode electroreduction of oxygen to generate H2O2, and generate a strong oxidizing active free radical oxidant to degrade organic pollutants in wastewater. (3) The sodium sulfate used in the preparation of the cathode material in this invention mainly serves as a pore-forming agent. During the soaking process, it dissolves into the aqueous phase. The deionized water used to soak the cathode material can be evaporated using the residual heat of thermal curing, and sodium sulfate can be recrystallized, thus enabling its repeated use as a pore-forming agent. In addition, the cathode prepared by the scheme provided by this invention does not use any metal materials or metal compounds, but still has excellent mechanical strength and good corrosion resistance, which can meet the requirements of large-scale industrial applications. Attached Figure Description

[0017] Figure 1 A physical image of carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 of the present invention; Figure 2 SEM image of carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 of this invention; Figure 3 This is an analysis diagram of the water contact angle of carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 of the present invention; Figure 4 The image shows the adsorption of bubbles in the electro-Fenton oxidation system by the carbon cathode material prepared in Example 1 of this invention. Figure 5 The graph shows the effect of the carbon cathode material prepared in Example 1 of the present invention on the electroreduction to generate H2O2 and the corresponding apparent current efficiency. Figure 6 (a) is a graph showing the effect of the carbon cathode material prepared in Example 1 of the present invention on the degradation of tetracycline solution, an organic pollutant in wastewater, in the electro-Fenton oxidation system. Figure 6 (b) is a graph showing the effect of the carbon cathode material prepared in Example 1 of the present invention on the degradation of organic pollutants in wastewater - landfill leachate in the electro-Fenton oxidation system. Detailed Implementation Plan To facilitate understanding of the invention, a more comprehensive description is provided below. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0018] Example 1 S1 heat-treated 10g of graphite powder and 0.1g of carbon nanotubes at 350℃ for 80min under a nitrogen protective atmosphere to obtain pretreated graphite powder a and carbon nanotube a. S2 cuts an 8mm thick graphite plate and drills holes in it to obtain a graphite plate a with a hole diameter of 5mm and a drilling area of ​​80%. S3 mixes 10g of pretreated graphite powder a, 0.1g of carbon nanotubes a, and 0.5g of sodium sulfate evenly to obtain the first mixture a; then add 4g of anhydrous ethanol to the first mixture a, stir evenly, and then add 5g of polytetrafluoroethylene solution with a solid content of 60%, and continue stirring until a homogeneous paste a is formed. S4. A homogeneous paste a is uniformly coated on both sides of a perforated graphite plate to obtain a coated graphite plate a; a 400-mesh metal wire mesh is covered on both sides of the coated graphite plate a and pressed at 2MPa for 10min to obtain a primary cathode material a. S5 The primary cathode material a is placed in a muffle furnace at 360℃ for heat curing treatment for 120 min, and then immersed in deionized water for 5 water changes and drying treatments to obtain intermediate cathode material a. S6 immersed intermediate cathode material a in acetone for 8 hours, and then dried it under vacuum at 80°C for 120 minutes to obtain carbon cathode material a for the electro-Fenton oxidation system.

[0019] Example 2 S1 heat-treated 10g of graphite powder and 1g of carbon nanotubes at 250℃ for 30min under a nitrogen protective atmosphere to obtain pretreated graphite powder b and carbon nanotube b. S2 cuts a graphite plate with a thickness of 15mm and then drills holes in it to obtain a graphite plate b with a hole diameter of 10mm and a drilling area of ​​60%. S3 mixes 10g of pretreated graphite powder b and 1g of carbon nanotubes b with 2g of sodium sulfate to obtain a first mixture b; then adds the first mixture b to 4g of anhydrous ethanol, stirs it evenly, and then adds 10g of polytetrafluoroethylene solution with a solid content of 60%, and continues to stir until a homogeneous paste b is formed. S4. The homogeneous paste b is uniformly coated on both sides of the perforated graphite plate to obtain the coated graphite plate b; a 200-mesh metal wire mesh is covered on both sides of the coated graphite plate b and pressed at 5MPa for 5min to obtain the primary cathode material b. S5 The primary cathode material b is placed in a muffle furnace at 300℃ for heat curing treatment for 40 minutes, and then soaked in deionized water for 3 water changes and drying treatments to obtain the intermediate cathode material b. S6 immersed the intermediate cathode material b in acetone for 16 hours, and then dried it under vacuum at 40°C for 100 minutes to obtain the carbon cathode material b for the electro-Fenton oxidation system.

[0020] Example 3 S1 heat-treated 10g of graphite powder and 0.5g of carbon nanotubes at 300℃ for 90min under a nitrogen protective atmosphere to obtain pretreated graphite powder c and carbon nanotube c. S2 cuts a 10mm thick graphite plate and drills holes in it to obtain a graphite plate c with a hole diameter of 8mm and a drilling area of ​​40%. S3 mixes 10g of pretreated graphite powder c and 0.5g of carbon nanotubes c with 1g of sodium sulfate to obtain a first mixture c; then the first mixture c is added to 2g of anhydrous ethanol, stirred evenly, and then 20g of polytetrafluoroethylene solution with a solid content of 60% is added, and stirred continuously until a homogeneous paste c is formed. S4. A homogeneous paste c is uniformly coated on both sides of a perforated graphite plate to obtain a coated graphite plate c. A 300-mesh metal wire mesh is covered on both sides of the coated graphite plate c and pressed at 3MPa for 8 minutes to obtain a primary cathode material c. S5 The primary cathode material c is placed in a muffle furnace at 320℃ for heat curing treatment for 60 minutes, and then soaked in deionized water for 4 water changes and drying treatments to obtain the intermediate cathode material c. S6 immersed the intermediate cathode material c in acetone for 24 hours, and then dried it under vacuum at 60°C for 80 minutes to obtain the carbon cathode material c for the electro-Fenton oxidation system.

[0021] Performance testing Please see Figure 1 , Figure 1 Here is a physical image of the carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 of this invention; from Figure 1 It can be observed that the cathode surface has a protruding structure, which increases its surface roughness and thus improves the hydrophobicity and aerophilicity of the material surface; Figure 2 The image shows a SEM image of the carbon cathode material a used in the electro-Fenton oxidation system prepared in Example 1 of this invention. The SEM image visually demonstrates that the cathode has abundant micropores and mesopores, which facilitates the contact between the catalytic active material and the electrolyte, increases the effective electrochemical reaction area, and helps to improve the efficiency of the cathode electroreduction of oxygen to generate H2O2. Figure 3 This is an analysis diagram of the water contact angle of carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 of the present invention; (The diagram is from...) Figure 3 It can be seen that the water contact angle θ of the carbon cathode material a for the electro-Fenton oxidation system prepared in Example 1 is... w The contact angle (θ) of the bubble in the aqueous phase on the solid surface is 143°, exhibiting strong hydrophobicity; based on Young's equation, the contact angle (θ) of the bubble in the aqueous phase on the solid surface can be derived. b The contact angle θw between water in the gas phase and the solid surface satisfies the following relationship: θ b =180-θ w θ w The larger θ is w The smaller the value, the stronger the surface hydrophobicity, and the stronger the aerophilicity, the more complementary the two properties become. Therefore, when the carbon cathode material a prepared in Example 1 for the electro-Fenton oxidation system acquires superhydrophobic properties, it exhibits strong aerophilicity when immersed in water. Figure 4 This image shows the adsorption of bubbles in the electro-Fenton oxidation system by the carbon cathode material prepared in Example 1 of this invention; Figure 4 It can be seen that at the water-gas-solid three-phase interface, a large number of bubbles are adsorbed on the surface of the cathode material prepared in Example 1, which intuitively shows the strong gas affinity of the cathode surface.

[0022] Application examples First, 200 mL of 0.05 M sodium sulfate electrolyte solution (pH=3.0) was added to a beaker reactor. The graphite plate anode and the electro-Fenton carbon cathode material prepared in Example 1 of this invention were placed parallel to each other, with an electrode spacing of 2.0 cm and an immersion area of ​​24 cm² in the solution for both the cathode and anode. 2An air pump is started to introduce air into the solution to provide oxygen and to stir the solution. The cathode and anode are connected to the negative and positive terminals of a DC power supply, respectively. An optimized electrolysis voltage of 4.0V is controlled to initiate the electrochemical reaction. Samples are taken at different reaction times to analyze the H2O2 concentration, and the apparent current efficiency generated by H2O2 is calculated. Figure 5 The diagram shows the effect of the carbon cathode material prepared in Example 1 of this invention on the electroreduction of H2O2 and the corresponding apparent current efficiency. Figure 5 It was found that after 60 min of electrolysis, the H2O2 concentration in the solution reached 246 mg / L, with a corresponding apparent current efficiency of 55.4%. Considering that some of the generated H2O2 undergoes decomposition at the anode, the actual amount of H2O2 produced by the cathode is higher than the measured value, and the actual current efficiency is also higher than the calculated apparent current efficiency. Compared with most cathodes reported in the literature, this cathode exhibits relatively better H2O2 generation performance.

[0023] Secondly, the carbon cathode material prepared in Example 1 of this invention was used to construct an electro-Fenton oxidation system for degrading tetracycline aqueous solution and leachate from landfills after biological pretreatment at landfill transfer stations, both of which achieved good results. The specific experimental method and results for constructing the electro-Fenton oxidation system for degrading tetracycline aqueous solution are as follows: In a beaker reactor, 200 mL of a mixed solution of tetracycline and sodium sulfate (pH=3.0) was added, followed by the addition of ferrous sulfate to make the solution contain 56 mg / L Fe. 2+ The graphite plate anode and the cathode using the carbon cathode material a prepared in Example 1 of this invention are placed parallel to each other, with an electrode spacing of 2.0 cm and an immersion area of ​​24 cm² in the solution for both the cathode and anode. 2 The air pump is started to introduce air into the solution to provide oxygen and to stir the solution. The cathode and anode are connected to the negative and positive terminals of the DC power supply, respectively. The electrochemical reaction is controlled at an electrolysis voltage of 4.0V. Samples are taken at different reaction times to analyze the concentration of tetracycline. Figure 6 (a) This image shows the effect of the carbon cathode material prepared in Example 1 of the present invention on the degradation of tetracycline solution, an organic pollutant in wastewater, in the electro-Fenton oxidation system. Figure 6 (a) It can be seen that the carbon cathode material prepared in Example 1 of the present invention for use in the electro-Fenton oxidation system can completely remove 200 mg / L of tetracycline in the electro-Fenton oxidation system within a reaction time of 60 min.

[0024] The specific experimental methods and results for constructing an electro-Fenton oxidation system to degrade landfill leachate after biological pretreatment at a landfill transfer station are as follows: In a beaker reactor, the leachate from the biological pretreatment process at the landfill transfer station and ferrous sulfate were added to make the solution contain 56 mg / L Fe. 2+The graphite plate anode and the cathode prepared using the carbon cathode material of Example 1 of this invention were placed parallel to each other, with an electrode spacing of 2.0 cm and an immersion area of ​​24 cm² in the solution for both the cathode and anode. 2 The air pump is started to introduce air into the solution to provide oxygen and to stir the solution. The cathode and anode are connected to the negative and positive terminals of the DC power supply, respectively. The electrochemical reaction is controlled at an electrolysis voltage of 4.0V, and samples are taken at different reaction times to analyze the COD concentration. Figure 6 (b) is a graph showing the effect of the carbon cathode material prepared in Example 1 of the present invention on the degradation of organic pollutants in wastewater—landfill leachate—in the electro-Fenton oxidation system. Figure 6 (b) It is evident that the carbon cathode material prepared in Example 1 of this invention for use in the electro-Fenton oxidation system can reduce the COD in the leachate of a biologically pretreated landfill transfer station from 684 mg / L to 102 mg / L after 6 hours of reaction in the electro-Fenton oxidation system, achieving a removal rate of 85%. These results demonstrate that the cathode material exhibits excellent degradation capabilities for organic pollutants in wastewater when applied in the electro-Fenton system.

[0025] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a carbon cathode material for an electro-Fenton oxidation system, characterized in that, The preparation method includes: S1 involves heat-treating graphite powder and carbon nanotubes under a nitrogen protective atmosphere to obtain pretreated graphite powder and carbon nanotubes. S2 cuts the graphite plate and then punches holes in it to obtain a perforated graphite plate; S3 mixes the pretreated graphite powder and carbon nanotubes with sodium sulfate to obtain a first mixture; then adds anhydrous ethanol to the first mixture, stirs it evenly, and then adds polytetrafluoroethylene solution, and continues stirring until a homogeneous paste is formed. S4. The homogeneous paste is uniformly coated on both sides of the perforated graphite plate to obtain the coated graphite plate; a metal wire mesh is covered on both sides of the coated graphite plate and pressed to obtain the primary cathode material. S5 The primary cathode material is placed in a muffle furnace for thermosetting, then immersed in deionized water, with the water changed multiple times, and then dried to obtain the intermediate cathode material. S6 involves immersing the intermediate cathode material in acetone and then drying it under vacuum to obtain the carbon cathode material for the electro-Fenton oxidation system.

2. The preparation method according to claim 1, characterized in that, The heat treatment in step S1 lasts for 30-90 minutes and at a temperature of 250-350°C.

3. The preparation method according to claim 1, characterized in that, The thickness of the graphite plate with holes in step S2 is 8-15 mm, the hole diameter is 5-10 mm, and the drilling area is 40%-80%.

4. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of the pretreated graphite powder, carbon nanotubes, sodium sulfate, and polytetrafluoroethylene solution is 1:(0.01-0.1):(0.05-0.2):(0.5-2); the solid content of the polytetrafluoroethylene solution is 60%.

5. The preparation method according to claim 1, characterized in that, The pressure for the pressing process in step S4 is 2-6 MPa, and the time is 5-10 min.

6. The preparation method according to claim 1, characterized in that, The temperature for the thermosetting treatment in step S5 is 300-360℃, and the time is 40-120 min.

7. The preparation method according to claim 1, characterized in that, The soaking treatment in step S6 lasts for 8-24 hours; the vacuum drying treatment temperature is 40-80℃ and the time is 40-120 minutes.

8. A carbon cathode material for an electro-Fenton oxidation system prepared by the preparation method according to any one of claims 1-7.

9. The application of the carbon cathode material for an electro-Fenton oxidation system as described in claim 8 in the oxidation and degradation of organic pollutants in wastewater in an electro-Fenton oxidation system.

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