An electro-Fenton cathode based on MOF-derived carbon and its preparation method and application

Abstract

An electro-Fenton cathode based on MOF-derived carbon and its preparation method and application, the electro-Fenton cathode comprises a penetrating electrode substrate and a MOF-derived carbon material located on the surface of the penetrating electrode substrate, the MOF-derived carbon material comprises a carbon shell and a composite component in the carbon shell, wherein the composite component comprises Fe3O4, Fe 0 The electro-Fenton cathode contains not only Fe3O4 but also Fe3C and Fe 0 The highly active ingredients not only promote the activation of H2O2 to generate ·OH, but also form a protective shell to prevent the leaching of iron ions inside the electrode, thereby increasing the stability of the entire catalyst.

Description

Technical Field

[0001] The present invention relates to the field of advanced oxidation technology, and in particular to a Fe3O4 / Fe 0 / Fe3C electro-Fenton cathode and its preparation method and application. Background Art

[0002] Since their discovery, antibiotics have been widely used to treat human and animal diseases. The increasing use of antibiotics inevitably leads to their entry into the environment, causing water pollution. Because antibiotic molecules are relatively stable, traditional methods struggle to completely degrade them. Therefore, the degradation of antibiotics in water has attracted widespread attention.

[0003] The electro-Fenton process is a type of advanced oxidation process characterized by strong controllability, fast reaction rates, and high degradation efficiency. Electro-Fenton primarily involves the in situ generation of H2O2 via a two-electron reduction reaction at the cathode. This H2O2 is then decomposed by a catalyst into ·OH, which oxidizes and degrades pollutants in water. In electro-Fenton systems, the properties of the electrode material are a major factor influencing the degradation efficiency of the process. In recent years, various electrode materials have been extensively studied, with iron-based catalysts being particularly popular due to their low cost and good environmental compatibility. However, traditional iron-based catalysts suffer from high leaching concentrations, low catalytic efficiency, and difficulty in recycling, hindering the practical application of electro-Fenton processes. Metal-organic frameworks (MOFs), composed of metal centers and organic ligands, possess excellent catalytic activity, tunable crystal structures, and high porosity, holding great promise for applications in catalysis. Upon further calcination, they transform into MOF-derived carbon structures composed of porous carbon embedded with metals, metal oxides, or metal carbides, enhancing conductivity, accelerating electron transfer, and improving stability. Iron-based MOFs have abundant unsaturated sites, which can serve as active sites for catalyzing the conversion of H₂O₂ to ·OH in Fenton systems. Further carbonization yields iron-based MOFs with improved electron transport and stability, leading to their widespread application in Fenton systems. However, the traditional preparation of iron-based MOF-derived carbons only yields less active iron oxides, making the preparation of highly active iron-based MOF-derived carbons challenging. Summary of the Invention

[0004] (1) Purpose of the invention

[0005] The purpose of the present invention is to provide an electro-Fenton cathode based on MOF-derived carbon and its preparation method and application, wherein the electro-Fenton cathode contains Fe3O4, Fe3C and Fe 0 The highly active ingredients not only promote the activation of H2O2 to generate ·OH, but also form a protective shell to prevent the leaching of iron ions inside the electrode, thereby increasing the stability of the entire catalyst.

[0006] (2) Technical solution

[0007] In order to solve the above problems, the first aspect of the present invention provides an electro-Fenton cathode based on MOF-derived carbon, comprising a penetrating electrode substrate and a MOF-derived carbon material located on the surface of the penetrating electrode substrate, wherein the MOF-derived carbon material comprises a carbon shell and a composite component in the carbon shell, wherein the composite component comprises Fe3O4, Fe 0 and Fe3C.

[0008] The penetrating electrode matrix refers to an electrode matrix through which liquid can pass while flowing during the reaction process.

[0009] The electro-Fenton cathode provided by the embodiment of the present invention contains not only Fe3O4 but also Fe3C and Fe 0 The highly active ingredients not only promote the activation of H2O2 to generate ·OH, but also form a protective shell to prevent the leaching of iron ions inside the electrode, thereby increasing the stability of the entire catalyst.

[0010] In a second aspect, the present invention provides a method for preparing an electro-Fenton cathode based on MOF-derived carbon, comprising:

[0011] Step 1: reacting a mixed reaction system containing a transmissive electrode substrate, an iron source, an organic ligand, sodium hydroxide, a regulator, and a solvent to form an iron-based MOF material on the surface of the transmissive electrode substrate, wherein the regulator is used to control the morphology and defects of the surface of the iron-based MOF material;

[0012] Step 2: calcining the penetrating electrode substrate with an iron-based MOFs material formed on the surface obtained in step 1 to obtain an electro-Fenton cathode based on MOF-derived carbon, wherein the specific conditions of the calcination include a calcination temperature of not less than 600°C.

[0013] In the embodiment of the present invention, the formation method of the iron-based MOFs material includes but is not limited to in-situ growth.

[0014] Specifically, the regulator is selected from at least one of formic acid, acetic acid, and hydrofluoric acid;

[0015] Based on the volume of the solvent as 100%, the added amount of the regulator is 0.1-30%.

[0016] In a preferred embodiment, the conditioning agent is acetic acid;

[0017] Preferably, the amount of the regulator added is 2-6%, which can ensure that the degradation rate of tetracycline in the prepared electro-Fenton cathode can reach more than 80%, can be recycled three times, and the removal rate remains above 60%;

[0018] More preferably, the addition amount of the regulator is 4-6%, which can ensure that the degradation rate of tetracycline in the prepared electro-Fenton cathode can reach more than 97%, and can be recycled 6 times with the removal rate still maintained at more than 80%.

[0019] Specifically: the penetrating electrode substrate is selected from at least one of stainless steel mesh, copper mesh, nickel mesh, cobalt mesh, and titanium mesh;

[0020] The iron source is selected from at least one of ferric nitrate, ferric chloride, and ferrous chloride;

[0021] The organic ligand is selected from at least one of terephthalic acid, fumaric acid, and trimesic acid;

[0022] The solvent is selected from at least one of methanol, N,N-dimethylformamide, and deionized water;

[0023] The mass ratio of the iron source to the organic ligand is 0.5-5:1, the mass of the sodium hydroxide is 0.1-5 times that of the iron source, and the mass of the solvent is 10-120 times that of the iron source.

[0024] Preferably, the mass ratio of the iron source to the organic ligand is 0.8-2:1, the mass of sodium hydroxide is 0.2-1 times that of the iron source, and the mass of the solvent is 50-100 times that of the iron source.

[0025] Specifically, the specific conditions of the reaction in step 1 include:

[0026] The reaction temperature is 20~200℃;

[0027] The reaction time is 2~200 h.

[0028] Specifically, the specific conditions for calcining in step 2 include:

[0029] The method is carried out under an inert atmosphere; the inert atmosphere is selected from at least one of carbon dioxide, nitrogen, and an inert gas;

[0030] Calcination temperature is 600~1000℃;

[0031] The calcination time is 0.5~10 h.

[0032] Calcination under these conditions ensures that the obtained electrode can achieve a degradation rate of tetracycline of more than 80% when used as an electro-Fenton cathode, and can be recycled three times with the removal rate still maintained at more than 60%.

[0033] Preferably, the calcination temperature of step 2 is 600-700° C., and the calcination time is 3-4 h. Calcination under these conditions can ensure that the degradation rate of tetracycline by the obtained electro-Fenton cathode can reach more than 97%, and it can be recycled 6 times with the removal rate still maintained at more than 80%.

[0034] In one embodiment, a method for preparing an electro-Fenton cathode based on MOF-derived carbon is provided, specifically comprising:

[0035] Step 1: Dissolve the iron source and the organic ligand in a solvent to form a suspension.

[0036] Step 2: Add a certain amount of regulator and sodium hydroxide solution to the suspension obtained in step 1.

[0037] Step 3: Place the pretreated stainless steel mesh into the suspension obtained in step 2 and transfer it to the reactor.

[0038] Step 4: Place the reactor in step 3 in an oven and heat it.

[0039] Step 5: After cooling, open the reactor in step 4, take out the obtained stainless steel mesh electrode grown with the iron-based MOF, rinse it with a solvent, and then put it in an oven to dry.

[0040] Step 6: Place the stainless steel mesh electrode dried in step 5 into a tube furnace and calcine it. After cooling, the target electrode is obtained.

[0041] In this embodiment, sodium hydroxide is added in the form of a solution, and the concentration of the sodium hydroxide solution is preferably 0.1 to 10 M.

[0042] Based on the volume of the solvent used in step 1 being 100%, the amount of the hydroxide solution added is 0.1% to 30%.

[0043] The third aspect of the present invention provides the use of the above-mentioned electrode and the electrode prepared by the above-mentioned preparation method in catalytic degradation of antibiotics.

[0044] Specifically, the antibiotic is preferably tetracycline.

[0045] In one embodiment, antibiotics are dissolved in water to prepare a sewage concentration of 0.01 to 15 mg / L. The sewage is then poured into a reactor, a DC power supply is turned on, and the current density of the gas diffusion electrode and the composite electrode cathode is controlled. The current density of the gas diffusion electrode is in the range of 0.1 to 100 mA / cm 2 The current density of the catalytic cathode ranges from 0.1 to 20 mA / cm 2 Finally, the degradation time is controlled to be 10~180 min to achieve the degradation of pollutants.

[0046] (3) Beneficial effects

[0047] The above technical solution of the present invention has the following beneficial technical effects:

[0048] The preparation method provided by the present invention uses a regulator to induce defects in the in-situ grown MOF, and then further calcines the MOF precursor at a temperature of not less than 600°C to obtain a composite structure electric Fenton cathode, wherein the electric Fenton cathode contains Fe3O4, Fe3C and Fe 0 , where Fe3O4 / Fe 0 It can effectively provide catalytic active sites for H2O2 and promote the activation of H2O2 to generate ·OH. When the electro-Fenton cathode is used to remove tetracycline, the removal efficiency is greatly improved. At the same time, the Fe3C in the electrode can form a protective shell to prevent the leaching of internal iron ions and increase the stability of the entire catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The Fe3O4 / Fe 0 / Fe3C electro-Fenton cathode. a and b are scanning electron microscope images at different magnifications.

[0050] Figure 2 X-ray diffraction patterns of the electro-Fenton cathodes provided in Example 1 and Comparative Example 1 of the present invention;

[0051] Figure 3 X-ray diffraction patterns of the electro-Fenton cathodes provided in Examples 1-3 of the present invention and Comparative Example 2;

[0052] Figure 4 X-ray diffraction patterns of the electro-Fenton cathodes provided in Examples 1 and 4 of the present invention and Comparative Example 3;

[0053] Figure 5 The Fe3O4 / Fe 0 High-resolution transmission electron microscopy image of a / Fe3C electro-Fenton cathode;

[0054] Figure 6 Schematic diagram of the device used in the application of the present invention;

[0055] Figure 7 Graphs showing the degradation effects of tetracycline by the electro-Fenton cathodes provided in Examples 1-3 and Comparative Example 2 of the present invention, wherein a is a graph showing the tetracycline removal efficiency, and b is a graph showing the kinetic fitting curve of the degradation process;

[0056] Figure 8 Graphs showing the degradation effects of tetracycline by the electro-Fenton cathode provided in Examples 1 and 4 and Comparative Example 3 of the present invention, wherein a is a graph showing the tetracycline removal efficiency, and b is a graph showing the kinetic fitting curve of the degradation process;

[0057] Figure 9 The Fe3O4 / Fe 0 / Fe3C electro-Fenton cathode recycling test results. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0059] The raw materials and reagents used in the embodiments of the present invention are all conventional commercially available products.

[0060] Among them, the stainless steel mesh has an aperture of 100 meshes.

[0061] Example 1

[0062] Fe3O4 / Fe 0 Preparation of Fe3C electro-Fenton cathode:

[0063] Step a: Pretreat the stainless steel mesh by cutting the mesh into 3×3 cm pieces and placing it in 10% dilute hydrochloric acid, ultrasonically treating it for 2 minutes, and rinsing it three times with ultrapure water. Then, place it in 10% sodium hydroxide solution, ultrasonically treating it for 2 minutes, and rinsing it three times with ultrapure water. Finally, place it in a 60°C oven to dry.

[0064] Step b: Dissolve 0.56 g of FeCl3·6H2O and 0.33 g of terephthalic acid in 50 mL of N,N-dimethylformamide to obtain a mixed solution;

[0065] Step c: Place the stainless steel mesh pretreated in step a into the mixed solution obtained in step b, and add 4 mL of sodium hydroxide solution (2 M) and 2 mL of acetic acid to obtain a reaction system, and place the obtained reaction system in a reactor and heat it to 110°C and maintain it for 24 hours to obtain the Fe-MOF stainless steel mesh.

[0066] Step d: The Fe-MOF stainless steel mesh obtained in step c was dried in an oven at 60°C, and then placed in a tube furnace filled with argon, and calcined at 600°C at a rate of 5°C / min for 3 h. After the tube furnace was cooled naturally, Fe3O4 / Fe 0 / Fe3C electro-Fenton cathode.

[0067] Examples 2-4

[0068] Examples 2 to 4 respectively provide an electro-Fenton cathode, and the preparation method thereof is basically the same as that of Example 1. The differences are shown in Table 1.

[0069] Table 1 Experimental conditions of Examples 1 to 4

[0070] Example Example 1 Example 2 Example 3 Example 4 Amount of acetic acid added (v / v) 4% 2% 6% 4% Calcination temperature (℃) 600 600 600 700 Degradation rate of tetracycline 97.7% 84.7% 97.2% 97.0%

[0071] Comparative Example 1

[0072] The process is basically the same as Example 1, except that step d is not performed and only the Fe-MOF stainless steel mesh is obtained.

[0073] Comparative Example 2

[0074] The process is basically the same as Example 1, except that acetic acid as a regulator is not added in step c.

[0075] Comparative Example 3

[0076] The process is basically the same as that of Example 1, except that the calcination temperature in step d is 400°C.

[0077] Characterization of the electrodes provided in each embodiment and comparative example

[0078] The scanning electron microscope image of the electro-Fenton cathode provided in Example 1 is as follows: Figure 1 As shown. Figure 1 a It can be seen that Fe3O4 / Fe 0 / Fe3C is grown in situ on a stainless steel mesh by Figure 1 b It can be seen that after calcination at 600℃, Fe3O4 / Fe 0 / Fe3C has a uniform crystal structure and retains the original crystal form of Fe-MOF, indicating that the pore structure of the material is still retained during the calcination process.

[0079] Figure 2 The Fe3O4 / Fe 0 The X-ray diffraction patterns of the Fe3O4 / Fe3C electro-Fenton cathode and the Fe-MOF cathode provided in Comparative Example 1 show that the derivative peaks of Fe-MOF at 2θ=9.12, 10.72, 20.02, and 21.56° correspond to the (002), (101), (202), and (211) crystal planes, indicating that the prepared Fe-MOF is MIL-88B (Fe). 0 The X-ray diffraction pattern of the MIL-88B / Fe3C electrode has diffraction peaks at 2θ=18.3, 30.2, 35.5, 57.1 and 62.7°, which correspond to the (111), (220), (311), (511) and (440) planes of Fe3O4 crystals, indicating that after calcination, part of MIL-88B (Fe) is converted into Fe3O4. The diffraction peaks at 2θ=44.6 and 65.0° correspond to the (111), (220), (311), (511) and (440) planes of Fe3O4 crystals. 0The (110) and (200) crystal planes of the crystal correspond to each other, indicating that after the regulation of acetic acid, the Fe in the MOF precursor has higher activity and can react with carbon under calcination conditions. Therefore, a part of Fe is reduced to zero-valent iron, Fe 0 The generation of Fe 3+ Fe 2+ The conversion of H2O2 to ·OH can be further promoted. The diffraction peaks at 2θ = 26.4°, 42.9°, 43.7°, 59.7° and 69.5° correspond to the (020)(211)(102)(311) and (042) crystal planes of Fe3C, which proves that the organic ligand is carbonized during the calcination process and reacts with part of the highly active Fe to form Fe3C crystal form. The appearance of Fe3C crystal form can prevent the active sites inside the catalyst from directly contacting the reaction solution, thereby enhancing the stability of the catalyst.

[0080] Figure 3 The X-ray diffraction patterns provided for the electro-Fenton cathodes provided in Examples 1-3 and Comparative Example 2 show that at the same calcination temperature, when the addition amount of acetic acid is 0%, the main crystal form of the material is Fe3O4, and a small amount of Fe3C crystal form exists. When the addition amount of acetic acid is 2%, the diffraction peak of Fe3C gradually strengthens, and Fe3C appears at 2θ=44.6°. 0 The diffraction peaks indicate that after the regulation of the crystal form, the Fe in the catalyst is more likely to combine with carbon at high temperature to form a stable Fe3C structure, and in the presence of high-temperature carbon, the Fe in the material is more likely to be reduced to Fe 0 As the addition of acetic acid increases to 4% and 6%, the Fe3C and Fe 0 The diffraction intensity is significantly enhanced, indicating that after being regulated by the regulator, Fe is more likely to react with carbon to form low-valent iron or iron carbide. Therefore, the results of X-ray diffraction prove that by adding acetic acid as a regulator, Fe that promotes the generation of ·OH can be generated under calcination conditions. 0 and Fe3C which increases the stability of the catalyst.

[0081] Figure 4 The X-ray diffraction patterns of the electric Fenton cathodes provided in Examples 1 and 4 and the electric Fenton cathode provided in Comparative Example 3 show that when the calcination temperature is 600-700°C, the crystal form of the electrode contains Fe3O4, Fe 0 , Fe3C three components.

[0082] Figure 5 The Fe3O4 / Fe 0 / Fe3C electro-Fenton cathode. As can be seen from the figure, the outermost layer of the material is wrapped by an amorphous carbon shell, and the part close to the carbon shell is a Fe3C structure. The lattice fringe spacing of Fe3C in the R1 region is 0.210 nm, corresponding to the (211) crystal plane of Fe3C, and the lattice fringe spacing of Fe3O4 is 0.296 nm, corresponding to the (211) crystal plane of Fe3O4. The lattice fringe spacing of Fe3C in the R2 region is 0.206 nm, corresponding to the (102) crystal plane of Fe3C, and the lattice fringe spacing of Fe3O4 in the R2 region is 0.206 nm, corresponding to the (102) crystal plane of Fe3C. 0 The lattice fringe spacing is 0.143 nm and 0.202 nm, corresponding to Fe 0 The (220) and (110) crystal planes of Fe3O4 are further extended into the material, and the lattice fringes of Fe3O4 appear with a spacing of 0.483 nm, which corresponds to the (111) crystal plane of Fe3O4. Therefore, the results of high-resolution transmission electron microscopy are consistent with the results of X-ray diffraction, further proving that the material is composed of Fe3O4, Fe 0 and Fe3C, and in a certain area, Fe3C acts as the outer layer of the catalyst, Fe 0 It is the middle layer and Fe3O4 is the core of the catalyst.

[0083] Application Examples

[0084] Dissolve tetracycline in water to obtain a wastewater concentration of 10 mg / L, and then pour the wastewater into Figure 6 In the reactor shown, the reactor uses a gas diffusion electrode as an auxiliary cathode to produce H2O2, and the electrodes provided in Examples 1-4 and Comparative Examples 1-3 are used as catalytic cathodes to produce OH. Air is used as an oxygen source, a DC power supply is turned on, and the current density of the gas diffusion electrode is controlled to be 2.5 mA / cm 2 and the current density at the catalytic cathode was 3.5 mA / cm 2 , the degradation time is 12 min.

[0085] See also Figure 7-9 The degradation effects of each embodiment and comparative example are as follows:

[0086] like Figure 7 As shown, the tetracycline removal rates of the electrodes provided in Examples 1-3 and Comparative Example 2 (differentiated by the amount of acetic acid used) were 97.7%, 84.7%, 97.2%, and 67.8%, respectively. The degradation process was fitted using a first-order reaction kinetic equation, and the reaction rates obtained were 0.277, 0.147, 0.283, and 0.092 min, respectively. -1 It can be seen that the reaction kinetic constant of the electrode obtained in Example 1 is increased by 3.0 times compared with that of Comparative Example 2.

[0087] Figure 8 The degradation effect of the electrodes provided in Examples 1, 4, and Comparative Example 3 on tetracycline was 97.7%, 97.0%, and 35.1%, respectively. The degradation process was fitted with a first-order reaction kinetic equation, and the obtained reaction rates were 0.277, 0.276, and 0.033 min, respectively. -1 It can be seen that the reaction kinetic constant of the electrode provided in Example 1 is increased by 8.4 times compared with that of Comparative Example 3.

[0088] Figure 9 The results of the cyclic use test of the electro-Fenton cathode provided in Example 1 of the present invention are shown in FIG. Figure 9 After six cycles, the degradation efficiency of tetracycline still remained above 80%, indicating that the electrode has high stability.

[0089] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. An electro-Fenton cathode based on MOF-derived carbon, comprising a penetrating electrode substrate and a MOF-derived carbon material located on the surface of the penetrating electrode substrate, wherein the MOF-derived carbon material comprises a carbon shell and a composite component within the carbon shell, characterized in that: The composite components include Fe3O4, Fe 0 and Fe3C.

2. A method for preparing an electro-Fenton cathode based on MOF-derived carbon, characterized in that: include: Step 1: reacting a mixed system containing a transmissive electrode substrate, an iron source, an organic ligand, sodium hydroxide, a regulator, and a solvent to form an iron-based MOF material on the surface of the transmissive electrode substrate, wherein the regulator is used to regulate the surface morphology and defects of the iron-based MOF material; Step 2: calcining the penetrating electrode substrate with an iron-based MOF material formed on the surface obtained in step 1 to obtain an electro-Fenton cathode based on MOF-derived carbon, wherein the specific conditions of the calcination include a calcination temperature of not less than 600°C.

3. The preparation method according to claim 2, wherein: The regulator is selected from at least one of formic acid, acetic acid, and hydrofluoric acid; Based on the volume of the solvent as 100%, the added amount of the regulator is 0.1-30%.

4. The preparation method according to claim 3, wherein: The regulator is acetic acid, and the added amount of the regulator is 2-6%.

5. The preparation method according to claim 2, characterized in that In step 1: The penetrating electrode substrate is selected from at least one of stainless steel mesh, copper mesh, nickel mesh, cobalt mesh, and titanium mesh; The iron source is selected from at least one of ferric nitrate, ferric chloride, and ferrous chloride; The organic ligand is selected from at least one of terephthalic acid, fumaric acid, and trimesic acid; The solvent is selected from at least one of methanol, N,N-dimethylformamide, and deionized water.

6. The preparation method according to claim 5, characterized in that In step 1: The mass ratio of the iron source to the organic ligand is 0.5-5:1; The mass of the sodium hydroxide is 0.1 to 5 times that of the iron source; The mass of the solvent is 10 to 120 times that of the iron source.

7. The preparation method according to claim 2, characterized in that The specific conditions of the reaction in step 1 include: The reaction temperature is 20~200℃; The reaction time is 2~200 h.

8. The preparation method according to claim 2, characterized in that The specific conditions for calcining in step 2 include: Carry out under inert atmosphere; Calcination temperature is 600~1000℃; The calcination time is 0.5~10 h.

9. Use of the electro-Fenton cathode according to claim 1 or the electro-Fenton cathode prepared by the preparation method according to any one of claims 2 to 8 in catalytic degradation of antibiotics.

10. The use according to claim 9, characterized in that The antibiotic is tetracycline.

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