Electro-Fenton cathode and preparation method and application thereof

Abstract

The invention discloses an electro-Fenton cathode and a preparation method and application thereof. The electro-Fenton cathode comprises a substrate electrode and a ligand-iron oxide interface loaded on the surface of the substrate electrode. According to the method, a ligand-iron oxide interface is constructed by a method of simply adding a low-dose complex, so that the problem that Fe circulation is blocked in a Fenton reaction under a neutral / alkaline condition is solved, and high-added-value oxidation of glycerol is simply and conveniently realized through effective electro-Fenton production of OH and keeping of medium concentration of strong oxidation free radicals; the two bottlenecks of'uncontrollable free radicals' and'easy inactivation of the Fe catalyst 'in the electro-Fenton technology are broken through, and accurate regulation and control of a reaction path are realized through coordination engineering.

Description

Technical Field

[0001] The present application relates to the field of water treatment technology, and in particular to an electro-Fenton cathode and a preparation method and application thereof. Background Art

[0002] As the global energy structure shifts towards low-carbonization, the production of biodiesel, as a renewable alternative to fossil fuels, has shown a rapid growth trend in recent years. Every ton of biodiesel produced is accompanied by the production of about 10% of a by-product - crude glycerol. Glycerol as a by-product has become oversupplied and urgently needs high-value utilization. In the biodiesel production process, the crude product needs to go through a water washing process to remove impurities such as glycerol to improve product purity, thereby generating washing wastewater with a high glycerol content. Currently, the Electro-Fenton process is commonly used in the field of glycerol oxidation. It can efficiently convert biomass (such as glycerol) into high-value-added chemicals (such as glyceraldehyde, formic acid, etc.). Its most notable feature is the in-situ generation of hydrogen peroxide at the cathode, which is then converted by Fe 2+ It reacts with H2O2 to generate hydroxyl radicals (•OH), which can be oxidized into high value-added products. The electro-Fenton reaction depends on Fe 2 + / Fe 3+ The continuous catalytic cycle of H₂O₂ to produce •OH is achieved through the conversion of waste oils and fats to glycerol and biodiesel. Strong bases are often used as catalysts. High pH conditions can cause free iron in the electro-Fenton reaction to convert into iron precipitates, hindering the iron cycle and reducing glycerol conversion. To avoid the equipment and reagent losses associated with repeated pH adjustments, developing methods to enhance iron cycling at high pH is essential.

[0003] Ligand manipulation is widely used in homogeneous electro-Fenton water treatment processes. By introducing organic ligands (such as oxalic acid and citric acid) to form stable complexes with iron ions, the applicable pH range of electro-Fenton can be broadened (to neutral or even alkaline). However, due to the high reactivity and non-selectivity of •OH, it easily induces C—C bond cleavage, resulting in the degradation of glycerol molecules into low-value C1 products (small carboxylic acids, such as formic acid) rather than high-value C3 products (such as glyceraldehyde).

[0004] The type and concentration of free radicals play a key role in determining the type of glycerol oxidation products. Moderately strong free radicals effectively avoid C-C bond cleavage to produce C2 and C1 chemicals, thereby upgrading glycerol electrooxidation products to high-value C3 products. If a ligand-iron oxide interface could be constructed on the electro-Fenton cathode surface to enhance the iron cycle on the heterogeneous catalyst surface under high pH reaction conditions, achieving efficient electro-Fenton production of •OH while maintaining a moderate concentration of this strong oxidizing radical, avoiding C-C bond cleavage to produce low-value products, thereby improving the selectivity and yield of glyceraldehyde, this would have important environmental and economic significance.

[0005] Therefore, developing ligand regulation to achieve the construction of a ligand-iron oxide interface on the surface of the electro-Fenton cathode at high pH to strengthen the iron cycle on the surface of the heterogeneous catalyst to improve the selectivity and yield of glyceraldehyde is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present application provides an electro-Fenton cathode that introduces a ligand-iron oxide interface. Compared with the ordinary electro-Fenton reaction, the added complex introduces a ligand-iron oxide heterogeneous reaction active site on the electrode surface, which promotes the reduction of iron ions during the reaction, resulting in a change in the type and concentration of active substances in the oxidation system, thereby realizing the effective electro-Fenton production of •OH and maintaining a moderate concentration of this strong oxidizing free radical, significantly improving the yield and selectivity of high-value-added C3 product glyceraldehyde under medium / high pH conditions.

[0007] The present application provides an electro-Fenton cathode, comprising a substrate electrode and a ligand-iron oxide interface loaded on the surface of the substrate electrode.

[0008] The electro-Fenton cathode, whose surface is coated with a ligand-iron oxide interface, can simultaneously generate and activate hydrogen peroxide. In the reaction, hydrogen peroxide is produced by the two-electron reduction process of oxygen at the cathode, and no additional hydrogen peroxide needs to be added to the system. Hydrogen peroxide is decomposed by Fe (II) to produce hydroxyl radicals. The ligand-iron oxide performs cathode electron transfer to realize iron circulation, ensuring the continuous progress of the electro-Fenton reaction.

[0009] The type and concentration of free radicals play a key role in determining the type of glycerol oxidation products. Moderately strong free radicals effectively avoid C-C bond breakage to produce C2 and C1 chemicals, thereby upgrading glycerol electrooxidation products to high-value C3 products. The introduction of different ligands can shift the type and concentration of active species in the oxidation system. By constructing a ligand-iron oxide interface on the electro-Fenton cathode surface to enhance iron cycling on the heterogeneous catalyst surface, efficient electro-Fenton production of •OH is achieved while maintaining a moderate concentration of this strong oxidizing radical.

[0010] Ensure that Fe in solution is at high pH 3+ It can still circulate efficiently, achieve effective electro-Fenton production of •OH and maintain a moderate concentration of this strong oxidizing free radical, achieving high-value-added conversion of biomass products such as glycerol.

[0011] In some specific implementations, the substrate electrode includes, but is not limited to, one or more of a graphite plate, activated carbon fiber, carbon felt, or graphite felt electrode. The present application has no particular requirements for the selection of the substrate electrode. The ligand-iron oxide interface is formed by the deposition of a complex of iron and the ligand on the surface of the substrate electrode. The complex includes but is not limited to one or more of disodium ethylenediaminetetraacetic acid, N,N'-(1,2-ethanediyl)bisaspartic acid, citrate or oxalic acid. The present application has no special requirements for the selection of the complex.

[0012] At the same time, this application reveals the ternary regulatory effect of disodium ethylenediaminetetraacetic acid (EDTA) ligand concentration on the electro-Fenton system: by controlling the Fe species morphology / redox cycle / free radical generation to synergistically affect the reaction path, a balance between Fe precipitation inhibition and optimized catalytic activity is achieved at low doses of EDTA.

[0013] The present application also provides a method for preparing an electro-Fenton cathode, comprising: Mixing the iron salt, the complex and water to obtain an electrodeposition solution; the electrodeposition solution includes a complex of iron and the complex; The activated carbon felt is immersed in an electrodeposition solution and subjected to electrodeposition to obtain an electro-Fenton cathode.

[0014] The present application first mixes an iron salt, a complex and water to obtain an electrodeposition solution. In some specific implementations, the electrodeposition solution also includes sodium sulfate, and the sodium sulfate is anhydrous sodium sulfate. In some specific implementations, the mixing includes ultrasound and stirring, and the ultrasound time is 15 minutes to 30 minutes, which can be 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes, and 30 minutes; the stirring time is 20 minutes to 40 minutes, which can be 20 minutes, 22 minutes, 25 minutes, 28 minutes, 30 minutes, 32 minutes, 35 minutes, 38 minutes, and 40 minutes; the stirring temperature is 50°C to 70°C, which can be 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, and 70°C. The iron salt includes, but is not limited to, iron sulfate. This application has no specific requirements for the selection of the iron salt. The complex includes, but is not limited to, one or more of disodium ethylenediaminetetraacetic acid, N,N'-(1,2-ethanediyl)bisaspartic acid, citrate, or oxalic acid. This application has no specific requirements for the selection of the complex. In some specific implementations, the iron salt, complex, and sodium sulfate are mixed with water to produce an electrodeposition solution. The mass ratio of the iron salt, complex, sodium sulfate, and water is (0.03-0.3):(0.02-0.3):(7-29):(500-1000), preferably 0.139:0.0058:14.2;1000. In some specific implementations, the pH of the electrodeposition solution is 3 to 11, and can be 3, 4, 5, 6, 7, 8, 9, 10, or 11; the concentration of the complex in the electrodeposition solution is 0.1 mM to 1 mM, and can be 0.1 mM, 0.2 mM, 0.3 mM, 0.5 mM, 0.8 mM, 0.9 mM, or 1 mM; the concentration of iron in the electrodeposition solution is 0.1 mM to 2 mM, and can be 0.1 mM, 0.2 mM, 0.3 mM, 0.5 mM, 0.8 mM, 0.9 mM, 1 mM, 1.2 mM, 1.5 mM, 1.8 mM, or 2 mM.

[0015] The present application then immerses the activated carbon felt in an electrodeposition solution for electrodeposition to obtain an electro-Fenton cathode. In some specific implementations, the counter electrode in the electrodeposition is a ruthenium-iridium-titanium electrode sheet, the current of the electrodeposition is 10 mA to 50 mA, which can be 10 mA, 15 mA, 20 mA, 25 mA, 30 mA, 35 mA, 40 mA, 45 mA, 50 mA, and the time of the electrodeposition is 60 min to 90 min, which can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min. In some specific implementations, the preparation method of the activated carbon felt includes: The carbon felt is immersed in concentrated nitric acid, heated for surface activation, and ultrasonicated to obtain activated carbon felt; The ultrasonic treatment includes ultrasonic treatment in a solvent, including but not limited to water and / or ethanol. The present application has no particular requirements for the choice of solvent. The carbon felt is immersed in a concentrated nitric acid solution, heated in a water bath for surface activation, and ultrasonically removed from the surface by sequentially performing ultrapure water, ethanol, and ultrapure water to produce the activated carbon felt.

[0016] The introduction of a ligand-iron oxide heterogeneous reactive site promotes the reduction of iron ions during the reaction, leading to a shift in the type and concentration of active species in the oxidation system, thereby achieving efficient electro-Fenton production of •OH while maintaining a moderate concentration of this strong oxidizing radical. This scheme was applied to glycerol oxidation. Because hydroxyl radicals are non-selective, strong oxidizing radicals, excessive concentrations can lead to C-C bond cleavage, producing C2 and C1 chemicals. The ligand-iron oxide interface provides a moderate concentration of hydroxyl radicals, thereby improving the yield and selectivity of glyceraldehyde, a high-value-added C3 product, under medium / high pH conditions.

[0017] The present application also provides a method for oxidizing glycerol, comprising: forming a circuit with the above-mentioned electro-Fenton cathode or the electro-Fenton cathode prepared by the above-mentioned preparation method and an anode, adding glycerol, ferrous salt and electrolyte, and oxidizing glycerol.

[0018] Since there is a large amount of glycerol in the crude product of biodiesel, it needs to be washed with water to improve the quality of biodiesel, so a large amount of biodiesel washing wastewater containing high concentrations of glycerol is produced. In the process of converting waste oil into glycerol and biodiesel, a strong base is often used as a catalyst, which will cause the free iron in the electro-Fenton to be converted into iron precipitation, resulting in obstruction of the iron cycle and reduction of the glycerol conversion rate. To address this problem, the core is to solve the problem of obstructed reduction of electro-Fenton iron ions under medium / high pH and the problem of changes in the types and concentrations of active substances in the oxidation system. The method described in this application can oxidize biomass products such as glycerol under high pH conditions.

[0019] In some specific implementations, the pH of the glycerol oxidation is neutral or alkaline; the amount of glycerol added is 50mM to 200mM; the current of the glycerol oxidation is 100mA to 500mA; the concentration of the ferrous salt is 0.2mmol / L to 0.5mmol / L; the ferrous salt includes ferrous sulfate and / or ferrous chloride; the concentration of the electrolyte is 40mmol / L to 50mmol / L; the electrolyte includes sodium sulfate and / or potassium sulfate. The neutral to alkaline conditions are adjusted by adding hydrochloric acid and sodium hydroxide after adding EDTA, and the concentration of hydrochloric acid and sodium hydroxide is controlled in the range of 0.5-2mM. An efficient, green and mild biomass conversion path is provided to convert glycerol, a by-product of biodiesel production, into a higher-value chemical glyceraldehyde.

[0020] This application constructs a ligand-iron oxide interface by simply adding a low-dose complex, thereby solving the problem of Fe cycling being blocked in the Fenton reaction under neutral / alkaline conditions. By effectively electro-Fenton-generating •OH and maintaining a moderate concentration of this strong oxidizing free radical, the high-value-added oxidation of glycerol is simply achieved. It has broken through the two major bottlenecks of "uncontrollable free radicals" and "easy deactivation of Fe catalysts" in electro-Fenton technology, and achieved precise control of the reaction path through coordination engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 1 of the present application; Figure 2 This is an SEM image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 2 of the present application; Figure 3 This is a SEM image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 3 of the present application; Figure 4 This is an SEM image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Comparative Example 1 of the present application; Figure 5 This is an EDS image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 1 of the present application; Figure 6 This is an EDS image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 2 of the present application; Figure 7 This is an EDS image of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Example 3 of the present application; Figure 8 The EDS graph of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Comparative Example 1 of the present application; Figure 9Raman spectra of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Examples 1-3 and Comparative Example 1 of the present application; Figure 10 X-ray diffraction patterns of the electro-Fenton cathode based on ligand-regulated iron cycling provided in Examples 1-3 of the present application; Figure 11 Synchrotron radiation soft X-ray images of the electric Fenton cathode based on ligand-regulated iron cycle provided in Example 1 and Comparative Example 1 of the present application; Figure 12 Hydroxyl radical monitoring diagram of the system solutions of Examples 1-3 and Comparative Example 1 of the present application by adding terephthalic acid through fluorescence spectroscopy; Figure 13 This is a graph showing the yield of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1-3 and Comparative Example 1 of the present application; Figure 14 This is a graph showing the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1-3 and Comparative Example 1 of the present application; Figure 15 This is a graph showing the yield of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 4, 5, 6, and 7 of the present application; Figure 16 This is a graph showing the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 4, 5, 6, and 7 of the present application; Figure 17 This is a graph showing the yield of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 8, 9, 10, and 11 of the present application; Figure 18 This is a graph showing the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 8, 9, 10, and 11 of the present application; Figure 19 This is a graph showing the results of liquid chromatography detection of glyceraldehyde production, a glycerol oxidation product, in the system solutions of Examples 1, 12, 13, and 14 of the present application; Figure 20 This is a diagram showing the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 12, 13, and 14 of the present application. DETAILED DESCRIPTION

[0022] It should be understood that the expression "one or more of" includes individually each of the items recited after the expression and various combinations of two or more of the recited items, unless otherwise apparent from the context and usage. The expression "and / or" in conjunction with three or more recited items should be understood to have the same meaning, unless otherwise apparent from the context.

[0023] The terms "comprising", "having" or "containing", including their grammatical synonyms, should generally be understood as open and non-restrictive, e.g., not excluding other unrecited elements or steps, unless otherwise specifically stated or understood from the context.

[0024] It should be understood that the order of steps or the order in which certain actions are performed is not important as long as the application remains operable. Additionally, two or more steps or actions may be performed simultaneously.

[0025] The use of any and all examples or exemplary language such as "for example" or "including" herein is intended only to better illustrate the present application and does not limit the scope of the present application. No language in this specification should be construed as indicating any non-claimed element is essential to the practice of the present application.

[0026] In addition, the numerical ranges and parameters used to define this application are approximate values. The relevant numerical values in the specific examples have been presented as accurately as possible. However, any numerical value inherently inevitably contains standard deviations due to individual testing methods. Therefore, unless otherwise expressly stated, it should be understood that all ranges, amounts, values, and percentages used in this disclosure are modified by the word "about." As used herein, "about" generally means that the actual value is within plus or minus 10%, 5%, 1%, or 0.5% of a particular value or range.

[0027] The present application provides an electro-Fenton cathode, comprising a substrate electrode and a ligand-iron oxide interface loaded on the surface of the substrate electrode.

[0028] This application constructs a ligand-iron oxide interface by simply adding a low-dose complex, thereby solving the problem of Fe cycling being blocked in the Fenton reaction under neutral / alkaline conditions. By effectively electro-Fenton-generating •OH and maintaining a moderate concentration of this strong oxidizing free radical, the high-value-added oxidation of glycerol is simply achieved. It has broken through the two major bottlenecks of "uncontrollable free radicals" and "easy deactivation of Fe catalysts" in electro-Fenton technology, and achieved precise control of the reaction path through coordination engineering.

[0029] The present application is further described below with reference to the following examples. The scope of protection of the present application is not limited by the following examples. Example 1

[0030] This embodiment provides an electro-Fenton cathode, and a method for preparing the electro-Fenton cathode includes: S1. Surface activation of carbon felt: immersing the carbon felt in a concentrated nitric acid solution and heating it in a water bath for surface activation. Surface grease and impurities are then removed by ultrasonic treatment in ultrapure water, ethanol, and ultrapure water, respectively, to obtain surface-activated carbon felt. S2. Carbon felt surface ligand-iron oxide structure: 0.5 mM Fe salt and 0.1 mM disodium ethylenediaminetetraacetic acid (EDTA) complex were mixed and added to distilled water along with anhydrous sodium sulfate. After ultrasonication, heating and stirring were performed to prepare a carbon felt electroplating solution. After complete dissolution, the pH was adjusted to 7 using appropriate concentrations of hydrochloric acid and sodium hydroxide. The surface-activated carbon felt obtained in step S1 was immersed in the electroplating solution and loaded with Fe and the complex via cathodic electrodeposition at a current of 30 mA. After the reaction, the solution was washed to remove unreacted impurities, thereby producing the electro-Fenton cathode with the ligand-iron oxide interface.

[0031] Using a conductive substrate (such as carbon felt) as the working electrode, a constant current of 30 mA is applied to drive the metal ions in the electrolyte to undergo a reduction reaction on the electrode surface for 60 minutes to form Fe metal or alloy nanostructures.

[0032] The surface morphology of the electro-Fenton cathode after the reaction in Example 1 was characterized, and the SEM image was as follows: Figure 1 As shown, from Figure 1 It can be clearly seen that a large amount of Fe is introduced into the electrode surface, proving that the Fe salt of Example 1 is deposited on the surface of the carbon felt.

[0033] The surface morphology of the electro-Fenton cathode after the reaction in Example 1 was characterized, and the EDS image was as follows: Figure 5 As shown, from Figure 5 It can be clearly seen that Fe is evenly distributed on the electrode surface, proving that the Fe salt in Example 1 is evenly distributed on the carbon felt surface.

[0034] The electro-Fenton cathode after the reaction in Example 1 was characterized by X-ray diffraction. The X-ray diffraction pattern is as follows: Figure 10 As shown, from Figure 10 It can be seen that the peak intensity of Fe oxide is weakened, and EDTA partially complexes Fe 2+ / Fe 3+ .

[0035] The electro-Fenton cathode after the reaction in Example 1 was characterized by Raman spectroscopy. The Raman spectrum is shown in FIG. Figure 9 As shown, from Figure 9 It can be seen that A 1g The red shift causes stretching vibration, and the internal Fe-O vibration is weakened; the Eg blue shifts, and the Fe-O outward bending vibration is enhanced. This is because the N coordination of a small amount of EDTA system causes Fe-O to stretch. The synchrotron radiation soft X-ray image of the electric Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is as follows Figure 11 shown.

[0036] The shortened t2g and e2g distances of Fe confirm the coordination between Fe and N. This indicates that the ligand-iron oxide interface was successfully constructed by adding low-dose EDTA.

[0037] This embodiment also provides a method for glycerol oxidation, the method comprising: The above-mentioned electro-Fenton cathode and the titanium-based ruthenium-iridium coated electrode were used as anodes to form a circuit, 0.5 mmol / L of ferrous salt and 50 mmol / L of sodium sulfate as electrolyte were added, the pH was 7, and the current was 30 mA to oxidize glycerol. Example 2

[0038] This embodiment provides an electro-Fenton cathode. The difference between the preparation method of the electro-Fenton cathode and that of Example 1 is that the concentration of EDTA is changed to 0.5 mM. The method for glycerol oxidation is the same as that of Example 1. The SEM image of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is as follows: Figure 2 As shown, the EDS diagram of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is as follows Figure 6 The X-ray diffraction pattern of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is shown in FIG. Figure 10 shown. Example 3

[0039] This embodiment provides an electro-Fenton cathode. The difference between the preparation method of the electro-Fenton cathode and that of Example 1 is that the concentration of EDTA is changed to 1 mM. The method for glycerol oxidation is the same as that of Example 1. The SEM image of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is as follows: Figure 3 As shown, the EDS diagram of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is as follows Figure 7 The X-ray diffraction pattern of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this embodiment is shown in FIG. Figure 10 shown. Example 4

[0040] This embodiment provides an electro-Fenton cathode, the preparation method of which differs from that of Example 1 in that the current is changed to 10 mA. The method for glycerol oxidation is the same as that of Example 1. Example 5

[0041] This embodiment provides an electro-Fenton cathode, the preparation method of which differs from that of Example 1 in that the current is changed to 20 mA. The method for glycerol oxidation is the same as that of Example 1. Example 6

[0042] This embodiment provides an electro-Fenton cathode, the preparation method of which differs from that of Example 1 in that the current is changed to 40 mA. The method for glycerol oxidation is the same as that of Example 1. Example 7

[0043] This embodiment provides an electro-Fenton cathode, the preparation method of which differs from that of Example 1 in that the current is changed to 50 mA. The method for glycerol oxidation is the same as that of Example 1. Example 8

[0044] This embodiment provides an electro-Fenton cathode. The preparation method of the electro-Fenton cathode differs from that of Example 1 in that the pH is changed to 3. The method for glycerol oxidation is the same as that of Example 1. Example 9

[0045] This embodiment provides an electro-Fenton cathode. The preparation method of the electro-Fenton cathode differs from that of Example 1 in that the pH is changed to 5. The method for glycerol oxidation is the same as that of Example 1. Example 10

[0046] This embodiment provides an electro-Fenton cathode. The preparation method of the electro-Fenton cathode differs from that of Example 1 in that the pH is changed to 9. The method for glycerol oxidation is the same as that of Example 1. Example 11

[0047] This embodiment provides an electro-Fenton cathode, and the preparation method of the electro-Fenton cathode differs from that of Example 1 in that the pH is changed to 11. The method for glycerol oxidation is the same as that of Example 1. Example 12

[0048] This embodiment provides an electro-Fenton cathode. The preparation method of the electro-Fenton cathode differs from that of Example 1 in that the concentration of Fe in the solution system is changed to 0.5 mM. The method for glycerol oxidation is the same as that of Example 1. Example 13

[0049] This embodiment provides an electro-Fenton cathode. The difference between the preparation method of the electro-Fenton cathode and that of Example 1 is that the concentration of Fe in the solution system is changed to 1 mM. The method for glycerol oxidation is the same as that of Example 1. Example 14

[0050] This embodiment provides an electro-Fenton cathode. The difference between the preparation method of the electro-Fenton cathode and that of Example 1 is that the concentration of Fe in the solution system is changed to 2 mM. The method for glycerol oxidation is the same as that of Example 1. Comparative Example 1

[0051] This comparative example provides a method for improving the high-value conversion of glycerol. The difference between the preparation method of the electro-Fenton cathode and that of Example 1 is that EDTA is not added. The SEM image of the electro-Fenton cathode based on ligand-regulated iron circulation provided in this comparative example is as follows: Figure 4 As shown, the EDS diagram of the electro-Fenton cathode based on ligand-regulated iron cycle provided in this comparative example is as follows Figure 8 The synchrotron radiation soft X-ray image of the electric Fenton cathode based on ligand-regulated iron cycle provided in this comparative example is shown as follows: Figure 11 The Raman spectra of the electro-Fenton cathode based on ligand-regulated iron cycle provided in Examples 1-3 and Comparative Example 1 are shown in FIG. Figure 9 shown.

[0052] The system solutions of Examples 1-3 and Comparative Example 1 of the present application were tested by liquid chromatography for the yield of glyceraldehyde, a product of glycerol oxidation. Figure 13 As shown in the figure, the selectivity results of glyceraldehyde, a glycerol oxidation product, were detected by liquid chromatography in the system solutions of Examples 1-3 and Comparative Example 1 of the present application. Figure 14 As shown, after 12 hours, under neutral conditions with only Fe addition, the yield of glyceraldehyde, a high-value-added C3 product, was only 0.79 mmol / L, with a selectivity of 43.97%. However, the addition of a low dose of EDTA significantly increased glyceraldehyde yield to 4.41 mmol / L, a 5.58-fold increase compared to the EDTA-free condition, while maintaining selectivity at 41.02%. This demonstrates that the low-dose EDTA system significantly increases glyceraldehyde yield while maintaining selectivity.

[0053] The solution after the reaction in Example 1 was filtered and the product was detected by liquid chromatography. In addition, to directly demonstrate the regulatory effect of the addition of EDTA ligand on the electro-Fenton reaction, terephthalic acid (TPA) was added to the original reaction system as a ·OH probe for fluorescence analysis to quantify the hydroxyl radical production in the system at different reaction time points.

[0054] The system solutions of Examples 1-3 and Comparative Example 1 of the present application were added with terephthalic acid and the hydroxyl radicals were monitored by fluorescence spectroscopy. Figure 12 As shown in the figure, compared with the EDTA-free system and the high-dose EDTA system, the low-dose EDTA system maintains a moderate concentration of strong oxidative free radicals, avoiding the possibility that the strong oxidative system may cause the cleavage of the glycerol CC bond and form low-value-added products.

[0055] The system solutions of Examples 1, 4, 5, 6, and 7 of the present application were tested by liquid chromatography for the yield of glyceraldehyde, a product of glycerol oxidation. Figure 15 As shown, the results of the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 4, 5, 6, and 7 of the present application are shown in FIG. Figure 16As shown, the rate of H2O2 generation at the cathode with medium current density is similar to that of Fe 2+ The regeneration rate is matched, and the rapid circulation of Fe promotes continuous ·OH generation and maintains a stable ·OH concentration.

[0056] After the reaction of Examples 1, 8, 9, 10, and 11, the solution was filtered and its product was quantitatively detected by liquid chromatography. The pH adjustment process was adjusted by hydrochloric acid and sodium hydroxide after adding EDTA. The concentration control range of hydrochloric acid and sodium hydroxide was 0.5-2 mM. The system solutions of Examples 1, 8, 9, 10, and 11 of the present application were detected by liquid chromatography. The yield of glyceraldehyde, a glycerol oxidation product, was as shown in the figure. Figure 17 As shown, the results of the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 8, 9, 10, and 11 of the present application are shown in FIG. Figure 18 As shown, under neutral conditions, a stable complex is formed, which inhibits precipitation and promotes Fe 2+ / Fe 3+ cycle.

[0057] After the reaction of Examples 1, 12, 13, and 14 was completed, the solution was filtered and its product was quantitatively detected by liquid chromatography. The results of the glyceraldehyde yield of the glycerol oxidation product of the system solution of Examples 1, 12, 13, and 14 of the present application were detected by liquid chromatography as shown in the figure. Figure 19 As shown, the results of the selectivity of glyceraldehyde, a glycerol oxidation product, detected by liquid chromatography in the system solutions of Examples 1, 12, 13, and 14 of the present application are shown in FIG. Figure 20 As shown, at low Fe concentrations, the Fe-EDTA complex stabilizes the catalysis, the ·OH generation rate matches the glycerol oxidation pathway, and the glyceraldehyde selectivity and yield are higher.

[0058] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and application concept of the present application within the technical scope disclosed in the present application, and they should be covered by the scope of protection of the present application.

Claims

1. An electro-Fenton cathode, characterized in that The invention comprises a substrate electrode and a ligand-iron oxide interface loaded on the surface of the substrate electrode.

2. The electro-Fenton cathode according to claim 1, characterized in that The base electrode comprises one or more of a graphite plate, an activated carbon fiber, a carbon felt or a graphite felt electrode; The ligand-iron oxide interface is formed by the complex of iron and the ligand being deposited on the surface of the substrate electrode; The complex comprises one or more of disodium ethylenediaminetetraacetate, N,N'-(1,2-ethanediyl)bisaspartic acid, citrate or oxalic acid.

3. A method for preparing an electro-Fenton cathode, characterized in that: include: mixing the iron salt, the complex and water to obtain an electrodeposition solution; The electrodeposition solution includes a complex of iron and a coordination compound; The activated carbon felt is immersed in an electrodeposition solution and subjected to electrodeposition to obtain an electro-Fenton cathode.

4. The preparation method according to claim 3, characterized in that The counter electrode in the electroplating is a ruthenium-iridium-titanium electrode sheet, the electroplating current is 10 mA to 50 mA, and the electroplating time is 60 min to 90 min.

5. The preparation method according to claim 3, characterized in that The pH of the electrodeposition solution is 3 to 11; the concentration of the complex in the electrodeposition solution is 0.1 mM to 1 mM; and the concentration of iron in the electrodeposition solution is 0.1 mM to 2 mM.

6. The preparation method according to claim 3, characterized in that The mixing includes ultrasound and stirring, the ultrasound time is 15 minutes to 30 minutes; the stirring time is 20 minutes to 40 minutes; the stirring temperature is 50° C. to 70° C.; the iron salt includes ferric sulfate.

7. The preparation method according to claim 3, characterized in that The iron salt, the complex, sodium sulfate and water are mixed to obtain an electrodeposition solution; the mass ratio of the iron salt, the complex, sodium sulfate and water is (0.03-0.3): (0.02-0.3): (7-29): (500-1000).

8. The preparation method according to claim 3, characterized in that The preparation method of the activated carbon felt comprises: The carbon felt is immersed in concentrated nitric acid, heated for surface activation, and ultrasonicated to obtain activated carbon felt; The ultrasonication includes performing ultrasonication in a solvent, and the solvent includes water and / or ethanol.

9. A method for glycerol oxidation, characterized in that: include: The electro-Fenton cathode according to claim 1 or 2 or the electro-Fenton cathode prepared by the preparation method according to any one of claims 3 to 8 is connected to an anode to form a circuit, and glycerol, ferrous salt and electrolyte are added to oxidize glycerol.

10. The method according to claim 9, characterized in that The pH of the glycerol oxidation is neutral or alkaline; the amount of glycerol added is 50mM to 200mM; the current of the glycerol oxidation is 100mA to 500mA; the concentration of the ferrous salt is 0.2mmol / L to 0.5mmol / L; the ferrous salt includes ferrous sulfate and / or ferrous chloride; the concentration of the electrolyte is 40mmol / L to 50mmol / L; the electrolyte includes sodium sulfate and / or potassium sulfate.

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