A method for preparing a magnetic electrode based on improving electro-Fenton efficiency

Abstract

The present invention discloses a method for preparing a magnetic electrode based on improving the electro-Fenton efficiency. The present invention belongs to the field of environmental functional materials. By preparing a magnetic transition metal electrode, its electronic structure is regulated, thereby achieving the regulation of selectivity and reaction activity. At the same time, the inherent ferromagnetism of the transition metal electrode material itself and the paramagnetic properties of O2 are utilized to introduce an external magnetic field to magnetize the magnetic electrode, thereby improving mass transfer and reaction activity. It is possible to achieve coordinated regulation of 2-electron ORR selectivity, reaction activity and O2 mass transfer. By achieving efficient synthesis of H2O2, the reaction rate of the rate-limiting step is increased, thereby solving the problem of low overall efficiency of the electro-Fenton system, achieving the lowest cost, while improving sewage treatment efficiency and reducing process operation energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental functional materials, and in particular relates to a method for preparing a magnetic electrode based on improving electro-Fenton efficiency. Background Art

[0002] Electro-Fenton technology is a typical electrochemical advanced oxidation method, which is widely used in the field of refractory pollutant treatment. As it is expected to become an alternative process to traditional biochemical methods, it has gradually attracted widespread attention from researchers. The main principle of electro-Fenton technology is to use oxygen as an electron acceptor to generate a 2-electron oxygen reduction reaction (ORR) at the cathode, thereby generating H2O2 in situ (see formula 1-1). Subsequently, H2O2 reacts with Fe in the system. 2+ Ion combination (see formula 1-2) generates highly oxidizing OH free radicals, which are used to efficiently mineralize pollutants in sewage.

[0003] O2+2e - +2H + →H2O2 (k1≈5.9×10 -9 M -1 s -1 ) (1-1)

[0004] H2O2+Fe 2+ →Fe 3+ +·OH+OH - (k2≈70 M -1 s -1 ) (1-2)

[0005] Fe 3+ +e - →Fe 2+ (k3≈55 M -1 s -1 ) (1-3)

[0006] At present, the development of electro-Fenton technology is mainly limited by its low overall process efficiency, slow reaction rate, and serious rate limitation of key steps. Based on its process principle, considering the reaction rate of step 1 (Formula 1-1) (5.9×10 -9 M -1 s -1 ) is much lower than the rate of reaction step 2 (Formula 1-2) (70M -1 s -1 ) and the rate of reaction step three (1-3) (55M -1 s -1Therefore, the key issue in improving the overall low efficiency of electro-Fenton technology lies in increasing the reaction rate of reaction step 1 (Formula 1-1), that is, the 2-electron ORR reaction of O2 on the electrode surface to generate H2O2.

[0007] There are two main approaches to improving the reaction rate of the 2-electron ORR: (I) Exploiting the electronic structure characteristics to develop electrodes with different active sites to promote the faster reduction of O2 to H2O2 (2-electron reduction product) rather than to H2O (4-electron reduction product), thereby improving the selectivity of the 2-electron ORR. For example, iron-containing composite magnetic cathodes (patent number: CN115072839B, title: An iron-containing composite magnetic material, its preparation method and catalytic application), composite FeOCl / MoS2 / Cu2S particle electrodes (patent number: CN116589043A, title: Particle electrode and preparation method and electro-Fenton device), cobalt-doped carbon-based cathodes (patent number: CN116474808A, title: Preparation method of cobalt single-atom-doped carbon-based catalyst and its application in electro-Fenton system for degradation of phthalates), iron-tungsten composite electrodes (patent number: CN116282390A, title: An iron-tungsten composite electrode and its use, heterogeneous electro-Fenton reaction device and method for treating organic wastewater), etc. can be used. (II) Different strategies are used to alleviate the problem of low mass transfer efficiency caused by low O2 concentration. For example, a floating natural air diffusion device (patent number: CN116768328A, title: A floating natural air diffusion electro-Fenton electrode and a method for treating difficult-to-degrade sewage), a floating sandwich-type device (patent number: CN116282397A, title: A floating sandwich-type electro-Fenton food waste wastewater treatment device and method), etc. can be used.

[0008] In electro-Fenton technology, improving the low process efficiency requires balancing the reactivity, selectivity, and O2 mass transfer of the cathode's two-electron ORR. While existing technologies address selectivity and O2 mass transfer separately, these two issues are synergistic. Failure to couple the two-electron ORR selectivity and O2 mass transfer effectively prevents maximizing the electro-Fenton system's cathode two-electron ORR reaction rate. Summary of the Invention

[0009] The present invention proposes a method for preparing a magnetic electrode based on improving the electro-Fenton efficiency to solve the technical problems existing in the above-mentioned prior art.

[0010] To achieve the above objectives, the present invention provides a method for preparing a magnetic electrode based on improving the electro-Fenton efficiency, comprising:

[0011] S1, cutting the nickel foam into electrode sheets of uniform size, ultrasonically cleaning the electrode sheets with hydrochloric acid to remove surface metal oxides, rinsing them with deionized water, then soaking the electrode sheets with an organic solvent to remove surface organic matter, rinsing them, and drying them to obtain a clean nickel foam electrode substrate;

[0012] S2, dissolving cobalt nitrate hexahydrate and 2-methylimidazole in a reaction solvent to obtain solution A and solution B;

[0013] S3, mixing the solution A and the solution B to obtain a mixed solution, adding the nickel foam electrode substrate to the mixed solution, soaking and allowing to stand, and washing the sample to obtain a precursor;

[0014] S4, placing the precursor in a porcelain boat, heating it in a heating furnace under air atmosphere, raising the temperature to the target temperature at a fixed heating rate, and maintaining it for 2 hours. After the calcination process is completed, the temperature is naturally cooled to obtain a magnetic cathode for the Fenton system;

[0015] S5, the magnetic cathode and anode are combined to form an electrode pair, forming an electro-Fenton system in an electrolyte solution, and a magnetic field is applied to the cathode and anode of the electro-Fenton system respectively, with the S pole and N pole corresponding to the magnetic field, thereby strengthening the polarity of the magnetic electrode through the magnetic field.

[0016] Preferably, the nickel foam substrate in S1 is rectangular, with a length of 2 to 10 cm and a width of 1 to 5 cm.

[0017] Preferably, the organic solvent in S1 is acetone or ethanol.

[0018] Preferably, the reaction solvent in S2 is deionized water or methanol.

[0019] Preferably, the mass ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole in S2 determines the size of the magnetic electrode.

[0020] Preferably, the heating furnace in S4 is a tubular furnace or a muffle furnace.

[0021] Preferably, the magnetic field in S5 is an electromagnet with controllable magnetic field size.

[0022] Preferably, the magnetic field strength is 50-500 mT.

[0023] Preferably, if the magnetic field in S5 is a permanent magnet, the magnetic field strength is 250 mT.

[0024] Preferably, the anode in S5 is any one of a platinum anode, a graphite anode and a titanium anode.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The present invention provides a method for preparing a magnetic electrode based on improving electro-Fenton efficiency. The method utilizes in-situ growth-evaporation induced self-assembly to prepare a highly selective ferromagnetic cathode. The ferromagnetism of the material itself is utilized through a magnetic field to achieve coordinated regulation of the two-electron ORR selectivity and O2 mass transfer. Under magnetic conditions, the ferromagnetic cathode improves the O2 mass transfer in the two-electron ORR process. This, for the first time, achieves the efficient synthesis of H2O2 under the coordinated regulation of the two-electron ORR selectivity and O2 mass transfer in an electro-Fenton system.

[0027] The present invention achieves the goal of maximizing the efficiency of the electro-Fenton system by realizing the efficient synthesis of H2O2 and increasing the reaction rate of the rate-limiting step, thereby solving the problem of overall low efficiency of the electro-Fenton system and achieving the lowest cost while improving the sewage treatment efficiency and reducing the energy consumption of the process operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0029] Figure 1 This is a comparison diagram of the nickel foam electrode before and after modification according to Example 1 of the present invention;

[0030] Figure 2 This is a scanning electron microscope image of the nickel foam loaded with ZIF67 according to Example 1 of the present invention;

[0031] Figure 3 This is a scanning electron microscope image of ZIF67 prepared using deionized water as a solvent in Example 1 of the present invention;

[0032] Figure 4 This is the elemental energy spectrum of ZIF67 prepared using deionized water as solvent in Example 1 of the present invention;

[0033] Figure 5 This is the X-ray diffraction pattern of the ZIF67 material loaded on the nickel foam substrate according to Example 1 of the present invention;

[0034] Figure 6 This is an X-ray photoelectron spectrum of the magnetic electrode according to Example 1 of the present invention;

[0035] Figure 7 1 is a hysteresis loop diagram of the magnetic electrode according to the first embodiment of the present invention;

[0036] Figure 8 1 is a linear sweep voltammetry curve of the magnetic electrode of Example 1 of the present invention under normal conditions (N) and under magnetic field enhancement conditions (M);

[0037] Figure 9Comparison of cathode H2O2 production of the electrode of Example 1 of the present invention under normal conditions (N) and under magnetic field enhancement conditions (M);

[0038] Figure 10 The figure shows the comparison of the degradation rate of the antibiotic sulfadiazine (SMR) by the electrode of Example 1 of the present invention under normal conditions (N) and under magnetic field enhancement conditions (M). DETAILED DESCRIPTION

[0039] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0041] Example 1

[0042] This embodiment provides a method for preparing a magnetic electrode based on improving electro-Fenton efficiency, comprising:

[0043] 1. Cut the nickel foam into electrode sheets of (1-5) x (2-10) cm in size, ultrasonically clean them with 10-30% hydrochloric acid to remove surface metal oxides, rinse them with deionized water, and then soak them in acetone or ethanol for 8-24 hours to remove surface organic matter. After rinsing, dry them at 60-80°C to obtain a clean nickel foam electrode substrate.

[0044] 2. Dissolve 0.2-0.6 g of cobalt nitrate hexahydrate and 0.7-2.3 g of 2-methylimidazole in 20-25 ml of deionized water to obtain solutions A and B, respectively;

[0045] 3. After mixing solutions A and B obtained in step 2 at room temperature for 5 to 15 minutes, add the clean nickel foam substrate obtained in step 1, soak and let stand for 8 hours, and wash the sample to obtain the precursor;

[0046] 4. Place the precursor in a porcelain boat and heat it in a tube furnace or muffle furnace under air atmosphere at 5℃min -1 The heating rate is increased to 300-450°C and maintained for 2 hours. After the calcination process is completed, the temperature is naturally cooled to obtain a magnetic cathode for the Fenton system, which is represented by ZIF67-NF.

[0047] 5. The prepared magnetic cathode and anode are combined to form an electrode pair to form an electro-Fenton system in an electrolyte solution. A magnetic field is applied to the S pole and N pole corresponding to the cathode and anode of the electro-Fenton system respectively. The magnetic field strength in the system is 250 mT. The polarity of the ferromagnetic electrode is strengthened by applying the magnetic field.

[0048] Figure 1 3 is a comparison diagram of the cathode before and after modification in this embodiment.

[0049] Figure 2 This is a scanning electron microscope photo of the nickel foam substrate after loading ZIF67. It can be seen that the surface of the three-dimensional porous structure nickel foam substrate has been loaded with sheet-like ZIF67 material, covering the surface of the nickel foam substrate.

[0050] Figure 3 This is a scanning electron microscope image of the monolithic structure of the ZIF67 material prepared in this embodiment. It can be seen that the material is a nanospindle with pointed ends and a wide middle. The size of the material prepared in this embodiment is 1.5 to 2 μm. Compared with the conventional rhombic hexadecahedron ZIF67, its aspect ratio is increased. Nanomaterials with a large aspect ratio are believed to have better electron transmission capabilities.

[0051] Figure 4 is the energy spectrum distribution diagram of the magnetic ZIF67 material prepared in this embodiment, from Figure 4 As can be seen from the figure, the distribution of C, Co, and N that make up ZIF67 indicates the successful synthesis of ZIF67 material.

[0052] Figure 5 This is the X-ray diffraction pattern of the magnetic electrode prepared in this embodiment. It can be seen that sharp diffraction peaks can be seen on the main diffraction crystal planes (211), (222), (200), and (411), which coincide with the standard ZIF67 card. It can be shown that the magnetic electrode material prepared in this embodiment is a NF sheet loaded with ZIF67.

[0053] Figure 6 is the X-ray photoelectron spectrum of the ferromagnetic electrode of the electro-Fenton system prepared in Example 1. Figure 6 The full spectrum analysis shows that the C1s orbital, O1s orbital, Co2p orbital, and Ni2p orbital on the electrode surface are all detected. The C1s, representing the C element, comes from the C element in the metal organic framework, Co comes from the magnetic metal core in the metal organic framework, Ni comes from the metal NF substrate, and O is the oxygen contained in the air atmosphere during the calcination process. By combining with metal Ni and Co to form metal oxides, this test result can also well illustrate that the prepared magnetic ZIF67 material has been successfully loaded on the substrate. As shown in Table 1, the elemental analysis of the precursor NF and the prepared ferromagnetic electrode ZIF67-NF of this example.

[0054] Table 1

[0055]

[0056] Figure 7 This is the hysteresis loop test curve of the electric Fenton system electrode prepared in Example 1. The curve is a standard ferromagnetic curve symmetrical about the origin 0. From the shape of the curve, the residual magnetic induction intensity Br and the coercive force H c By comparing the ratio of the two materials, we can confirm that the material belongs to the hard magnetic category, a group of ferromagnetic materials represented by Fe, Co, and Ni. Its main characteristics are characterized by two aspects: first, it can be strongly magnetized under the influence of an external magnetic field; second, it has hysteresis, which means that the hard magnetic material retains its magnetization state after the external field is removed. Therefore, the hysteresis loop test proves that the cathode material we prepared has excellent ferromagnetism and its inherent ferromagnetism is not affected by multiple cycles of magnetization and demagnetization.

[0057] Figure 8 The linear voltammetric curves of the electro-Fenton system magnetic electrode and carrier NF prepared in Example 1 under enhanced external magnetic field conditions (M) and without magnetic field conditions (N). At the ORR reaction potential of -0.6 V, it can be observed that after loading the NF, the ORR response current of the entire electrode is improved to a certain extent. After applying a magnetic field to the magnetic electrode, the current density is increased by 0.283 mA cm -2 , which means that after magnetic field strengthening, the reaction activity of the material has been improved twice. In this observation, we can find that due to the limited oxygen mass transfer, the local oxygen concentration at the cathode is insufficient, resulting in a significant decrease in the reduction current of the system without an external magnetic field (ZIF67-NF-N) at about -0.5V. For the system with an external magnetic field (ZIF67-NF-M), a platform of reduction current appears at around -0.5V, which lasts until the potential drops to -0.6V, when the reduction current begins to decline. This shows that the introduction of a magnetic field has alleviated the problem of insufficient local oxygen concentration to a certain extent, that is, it has alleviated the limitation of oxygen mass transfer. This is mainly due to the continuous enrichment of paramagnetic oxygen to the electrode surface interface under the action of a magnetic field and external force.

[0058] In order to test the improvement of H2O2 accumulation under magnetic field, the H2O2 accumulation test was carried out as follows: ZIF67-NF magnetic electro-Fenton cathode and BDD anode were assembled into an electrode pair, connected to the positive and negative poles of a DC power supply, and inserted into a 100 mL, pH=3, 50 mM Na2SO4 electrolyte solution. Air was pumped in at a rate of 100 mL min-1. -1 The electrolyte solution was passed through at a flow rate of 10 mA cm -2, the test was carried out under the conditions of magnetic field and no magnetic field respectively, and the test results are as follows Figure 9 As shown in the experimental results, it can be seen that after the magnetic field is applied, at the reaction end point 120 minutes, the H2O2 is significantly increased by more than 50% compared with the condition without a magnetic field.

[0059] The magnetic electro-Fenton cathode prepared in this example and the BDD anode were assembled into an electrode pair electro-Fenton system. The degradation rate of pollutants in sewage was used as the evaluation standard of the system efficiency. In this experiment, the initial concentration of SMR was 50 mg L -1 The concentration of FeSO4 was 50 μmol L -1 , current density 10 mA cm -2 , the degradation rate curve is drawn with the SMR concentration C and the initial concentration C0 in the sample at the sampling time as the Y axis and the time T as the X axis, as shown in Figure 10 As shown, it can be found that after superimposing the magnetic field under the electro-Fenton system, the degradation rate of the samples has been improved. From the experimental results, it can be known that the pollutant degradation effect of ZIF67-NF after being magnetized by the magnetic field is most significantly improved, with an efficiency increase of about 50.1%. The mineralization time can reach 92.4% in 120 minutes. This shows that the electro-Fenton system of the magnetic electro-Fenton composite cathode ZIF67-NF has an ideal removal effect on sulfathiazole antibiotic treatment, and the application of the magnetic field has a secondary strengthening effect on the utilization of the electrode ferromagnetism without changing the electrode material. The present invention provides a new idea and reference for electrode loading magnetic materials, and on the basis of not changing the material of the electrode itself, provides a new method and technical support for improving the efficiency of the electrode and reaction system, opening up a direction for the development of the performance potential of transition metal magnetic materials themselves.

[0060] Example 2

[0061] The difference between this embodiment and Example 1 is that the organic solvent for removing organic matter in step 1 is ethanol, and the soaking time is 24 hours; the rest is the same as the specific embodiment 1.

[0062] Example 3

[0063] The difference between this embodiment and embodiment 1 is that the solvent required for the reaction in step 2 is methanol, and the amount used is 15-25 ml.

[0064] Example 4

[0065] The difference between this embodiment and Example 1 is that the mass of cobalt nitrate hexahydrate required for the reaction in step 2 is 0.2-0.6 g, and the mass of 2-methylimidazole is 0.7-2.3 g. In this embodiment, the mass ratio of cobalt nitrate hexahydrate to 2-methylimidazole is 1:3.53, and the ratio is related to the size of the prepared ZIF67 material.

[0066] Example 5

[0067] The difference between this embodiment and the first embodiment is that the stirring time of solutions A and B in step 3 is 15 minutes, and the rest is the same as any one of the specific embodiments 1 to 5.

[0068] Example 6

[0069] The difference between this embodiment and the first embodiment is that the entire heating process in step 4 is carried out in a muffle furnace under an air atmosphere, and the rest is the same as any one of the specific embodiments 1 to 5.

[0070] Example 7

[0071] The difference between this embodiment and the first embodiment is that the application of the entire magnetic field in step 5 is performed by an electromagnet with controllable magnetic field magnitude. The rest is the same as the first embodiment from the first to the fifth embodiment.

[0072] Example 8

[0073] The difference between this embodiment and the first embodiment is that the intensity of the magnetic field applied in step five is 50-500 mT, and the rest is the same as any one of the first to fifth specific embodiments.

[0074] Embodiment 9

[0075] The difference between this embodiment and the first embodiment is step five, in which the anode forming an electrode pair with the magnetic cathode can be a platinum anode, a graphite anode, a titanium anode, etc.

[0076] The above description is merely a preferred embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a magnetic electrode based on improving electro-Fenton efficiency, characterized in that: include: S1, cutting the nickel foam into electrode sheets of uniform size, ultrasonically cleaning the electrode sheets with hydrochloric acid to remove surface metal oxides, rinsing them with deionized water, then soaking the electrode sheets with an organic solvent to remove surface organic matter, rinsing them, and drying them to obtain a clean nickel foam electrode substrate; S2, dissolving cobalt nitrate hexahydrate and 2-methylimidazole in a reaction solvent to obtain solution A and solution B; S3, mixing the solution A and the solution B to obtain a mixed solution, adding the nickel foam electrode substrate to the mixed solution, soaking and allowing to stand, and washing the sample to obtain a precursor; S4, placing the precursor in a porcelain boat, heating it in a heating furnace under air atmosphere at 5 ° C min -1 The heating rate was increased to 300-450°C and maintained for 2 hours. After the calcination process was completed, the temperature was naturally cooled to obtain a magnetic cathode for the Fenton system. S5, the magnetic cathode and anode are combined to form an electrode pair, forming an electro-Fenton system in an electrolyte solution, and a magnetic field is applied to the cathode and anode of the electro-Fenton system respectively, with the S pole and N pole corresponding to the magnetic field, thereby strengthening the polarity of the magnetic electrode through the magnetic field.

2. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The nickel foam electrode substrate in S1 is rectangular, with a length of 2 to 10 cm and a width of 1 to 5 cm.

3. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The organic solvent in S1 is acetone or ethanol.

4. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The reaction solvent in S2 is deionized water or methanol.

5. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The mass ratio of the cobalt nitrate hexahydrate to the 2-methylimidazole in S2 determines the size of the magnetic electrode.

6. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The heating furnace in S4 is a tubular furnace or a muffle furnace.

7. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The magnetic field described in S5 is an electromagnet with controllable magnetic field size.

8. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 7, characterized in that: The magnetic field strength is 50-500 mT.

9. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: In S5, if the magnetic field is a permanent magnet, the magnetic field strength is 250 mT.

10. The method for preparing a magnetic electrode based on improving electro-Fenton efficiency according to claim 1, characterized in that: The anode in S5 is any one of a platinum anode, a graphite anode and a titanium anode.

Images