Graphite felt composite electrode and preparation method and application thereof

Abstract

The invention relates to the field of graphite felt electrodes, in particular to a graphite felt composite electrode and a preparation method and application thereof. The preparation method of the graphite felt composite electrode comprises the following steps: calcining a graphite felt in a mixed gas of ammonia gas and inert gas to obtain a nitrogen-graphite felt; performing electro-deposition in an electrolyte containing cobalt salt and stannous salt by taking the nitrogen-graphite felt as a working electrode and silver / silver chloride as a reference electrode to obtain an electro-deposited nitrogen-graphite felt; and carrying out annealing treatment on the nitrogen-graphite felt after electro-deposition to obtain the graphite felt composite electrode. The preparation method provided by the invention is low in cost, and the prepared electrode has a high degradation effect on antibiotics in wastewater.

Description

Technical Field

[0001] This invention relates to the field of graphite felt electrodes, and more particularly to a graphite felt composite electrode, its preparation method, and its application. Background Technology

[0002] Antibiotics, as a novel pollutant, produce wastewater characterized by poor biodegradability, high chemical oxygen demand (COD), high biotoxicity, and difficulty in degradation. Current treatment methods for antibiotic wastewater mainly include adsorption, biological methods, membrane bioreactors, and chemical methods. Compared to these methods, electrocatalytic oxidation technology offers advantages such as high oxidation efficiency, mild reaction conditions, and no secondary pollution.

[0003] As the core component of electrocatalytic reactions, the electrode's catalytic activity, stability, selectivity, and cost directly determine the degradation efficiency of antibiotics. However, currently commercially available catalytic electrodes are mainly composed of precious metals (ruthenium, iridium, platinum) and their oxides. Due to the high cost of precious metals, the application of electrocatalytic oxidation technology in antibiotic wastewater treatment is greatly limited. In recent years, graphite felt has been widely studied as a substrate for preparing antibiotic degradation electrodes because it has characteristics such as large specific surface area, high elasticity, and high conductivity, and can synergistically achieve efficient degradation of antibiotics with metals and metal oxides. However, preparing low-cost graphite felt electrodes with high catalytic degradation efficiency for antibiotics remains quite difficult. Summary of the Invention

[0004] This invention provides a graphite felt composite electrode, its preparation method, and its application. This electrode has a high degradation effect on antibiotics in wastewater and is low in cost.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for preparing a graphite felt composite electrode, comprising the following steps: Graphite felt was calcined under a mixture of ammonia and inert gas to obtain nitrogen-graphite felt. Using the nitrogen-graphite felt as the working electrode and silver / silver chloride as the reference electrode, electrodeposition was performed in an electrolyte containing cobalt salt and stannous salt to obtain the electrodeposited nitrogen-graphite felt. The electrodeposited nitrogen-graphite felt was annealed to obtain a graphite felt composite electrode.

[0006] In some specific embodiments, the flow rates of the ammonia and the inert gas are each independently 15~25 mL / min.

[0007] In some specific embodiments, the calcination temperature is 900~1000℃, and the calcination time is 20~40min.

[0008] In some specific embodiments, the molar ratio of cobalt in the cobalt salt to tin in the stannous salt is 6~8:1.

[0009] In some specific embodiments, the concentration of cobalt salt in the electrolyte is 0.025~0.045M.

[0010] In some specific embodiments, the electrolyte also includes citric acid.

[0011] In some specific embodiments, the concentration of citric acid in the electrolyte is 0.03~0.05M.

[0012] In some specific embodiments, the electrodeposition is performed under a constant current.

[0013] In some specific embodiments, the current density of the electrodeposition is 20~40 mA / cm². 2 The electrodeposition time is 3-5 minutes.

[0014] In some specific embodiments, the annealing conditions are: temperature of 400~600℃, time of 1~3h, and atmosphere of air.

[0015] A second aspect of the present invention also provides a graphite felt composite electrode prepared by the above-described method for preparing the graphite felt composite electrode.

[0016] A third aspect of the present invention also provides the application of the above-described graphite felt composite electrode in the electrocatalytic degradation of antibiotics.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The aforementioned graphite felt composite electrode possesses advantages such as high degradation efficiency, low dissolution, and high stability. Nitrogen doping modification of the graphite felt is achieved through ammonia treatment, regulating its electronic structure and improving its conductivity and specific surface area. Then, cobalt and tin active components are uniformly loaded via electrodeposition, followed by air annealing to form stable cobalt-tin oxides. This significantly improves the electrocatalytic degradation efficiency of antibiotics in wastewater, solving the problem of low catalytic activity in traditional graphite felt electrodes. The high oxygen evolution potential (~2.0V vs. SCE) of SnO2 effectively suppresses the oxygen evolution side reaction during water electrolysis; Co3O4, acting as a framework, significantly reduces the electrode's electron transport resistance, improving current efficiency. Air annealing at 500℃ ensures a strong bond between SnO2-Co3O4 and the graphite felt, preventing the active layer from detaching, while the chemical inertness of SnO2 effectively inhibits the dissolution of Co3O4. Attached Figure Description

[0018] The above and other objects, features, and advantages of the invention will be apparent from the following description of preferred embodiments illustrating the gist of the invention and its use, and the accompanying drawings, in which: Figure 1 This is a schematic diagram of the preparation process of the graphite felt composite electrode in this invention.

[0019] Figure 2 The images shown are characterization diagrams of the graphite felt composite electrode in Example 1, where (a) is a low-magnification scanning electron microscope image, (b) is a high-magnification scanning electron microscope image, (c) is a transmission electron microscope image, and (d) is a high-resolution transmission electron microscope image.

[0020] Figure 3 The image shows the elemental mapping of the graphite felt composite electrode in Example 1, where (a) is the graphite felt composite electrode, (b) is C, (c) is N, (d) is Co, (e) is Sn, and (f) is O.

[0021] Figure 4 The image shows the XPS spectrum of the graphite felt composite electrode in Example 1.

[0022] Figure 5 This is a high-resolution XPS spectrum of C1s of the graphite felt composite electrode in Example 1.

[0023] Figure 6 The image shows the high-resolution XPS spectrum of the N1s of the graphite felt composite electrode in Example 1.

[0024] Figure 7 This is a high-resolution XPS spectrum of Co2p in the graphite felt composite electrode of Example 1.

[0025] Figure 8 This is a high-resolution XPS spectrum of Sn3d in the graphite felt composite electrode of Example 1.

[0026] Figure 9 This is the high-resolution XPS spectrum of the O1s of the graphite felt composite electrode in Example 1.

[0027] Figure 10 The image shows the X-ray diffraction pattern of the graphite felt composite electrode in Example 1.

[0028] Figure 11 The electrocatalytic degradation efficiency of 30 mg / L levofloxacin was measured under the same conditions for the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1, the graphite felt in Comparative Example 1, the nitrogen-graphite felt in Comparative Example 2, the nitrogen-graphite felt / cobalt oxide in Comparative Example 3, and the nitrogen-graphite felt / tin oxide in Comparative Example 4.

[0029] Figure 12The degradation rate of levofloxacin by the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1 at different current densities is shown.

[0030] Figure 13 The degradation rate of levofloxacin by the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1 at different pH values.

[0031] Figure 14 The degradation rate of levofloxacin by the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1 at different sodium chloride concentrations is shown.

[0032] Figure 15 The degradation rate of levofloxacin at different initial concentrations was obtained from the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1.

[0033] Figure 16 The curve shows the degradation rate of levofloxacin over time.

[0034] Figure 17 According to Figure 16 The fitting curve of the first-order reaction kinetic equation obtained from the curve.

[0035] Figure 18 The degradation curve of levofloxacin under sacrificial agent and the electron paramagnetic resonance spectrum with 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) as the scavenger are shown in (a) and (b).

[0036] Figure 19 The curve shows the change in the degradation rate of levofloxacin with the number of degradation cycles.

[0037] Figure 20 Scanning electron microscope (SEM) image of a nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode after ten degradation cycles of levofloxacin.

[0038] Figure 21 The degradation rate of tetracycline, sulfamethazine, and metronidazole by the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode in Example 1.

[0039] Figure 22 This study aims to identify a possible pathway for the electrocatalytic degradation of levofloxacin (LEVO) based on the results of liquid chromatography-mass spectrometry (LC-MS). Detailed Implementation

[0040] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0041] This invention provides a method for preparing a graphite felt composite electrode, the preparation process of which is illustrated in the schematic diagram below. Figure 1 As shown, it includes the following steps: Graphite felt was calcined under a mixture of ammonia and inert gas to obtain nitrogen-graphite felt. Using the nitrogen-graphite felt as the working electrode and silver / silver chloride as the reference electrode, electrodeposition was performed in an electrolyte containing cobalt salt and stannous salt to obtain the electrodeposited nitrogen-graphite felt. The electrodeposited nitrogen-graphite felt was annealed to obtain a graphite felt composite electrode.

[0042] The method for preparing the graphite felt composite electrode of the present invention involves first calcining the graphite felt in ammonia to achieve nitrogen doping of the graphite felt, obtaining nitrogen-graphite felt, and then electrodepositing cobalt salt and stannous salt on its surface. After annealing, the cobalt salt and stannous salt form SnO2 and Co3O4 on the surface of the graphite felt, thereby obtaining the graphite felt composite electrode.

[0043] In some embodiments, the flow rates of the ammonia and the inert gas are each independently 15 to 25 mL / min. As examples, the flow rates of the ammonia and the inert gas can be independently 15 mL / min, 18 mL / min, 20 mL / min, 22 mL / min, and 25 mL / min, etc.

[0044] In this invention, the specific type of inert gas is not specifically limited, and conventional inert gases in the art can be selected. In some embodiments, the inert gas may be nitrogen, argon, etc.

[0045] In some embodiments, the calcination temperature is 900~1000℃, and the calcination time is 20~40min. As examples, the calcination temperature can be 900℃, 920℃, 950℃, 980℃, and 1000℃, etc., and the calcination time can be 20min, 25min, 30min, 35min, and 40min, etc.

[0046] In this invention, by controlling the calcination temperature and time within the above-mentioned range, it is helpful to achieve uniform and deep doping of nitrogen species, while avoiding the cumulative etching caused by high temperature.

[0047] In some embodiments, the molar ratio of cobalt in the cobalt salt to tin in the stannous salt is 6 to 8:1. For example, the molar ratio of cobalt in the cobalt salt to tin in the stannous salt can be 6:1, 6.2:1, 6.5:1, 6.8:1, 7:1, 7.2:1, 7.5:1, 7.7:1, and 8:1, etc.

[0048] In this invention, by controlling the molar ratio of Co in the cobalt salt and Sn in the stannous salt within the aforementioned range, the Co3O4 formed in situ after annealing can effectively disperse SnO2 grains, promoting their uniform distribution at the nanoscale on the graphite felt surface and achieving high-density exposure of active sites. Simultaneously, using Co3O4 as a conductive framework to construct continuous electron transport channels effectively compensates for the inherent defect of low intrinsic conductivity in SnO2. If the molar ratio of Co is too high, SnO2 will be completely coated by Co3O4, resulting in extremely low effective exposure of the core mineralization sites. The dominant phase on the electrode surface will be Co3O4 with a low oxygen evolution potential, leading to severe oxygen evolution side reactions during water electrolysis. If the molar ratio of Sn is too high, SnO2 is prone to agglomeration, forming loose, blocky large grains, resulting in a significant increase in the electrode's electron transport resistance.

[0049] In some embodiments, the concentration of cobalt salt in the electrolyte is 0.025~0.045M. As an example, the concentration of cobalt salt in the electrolyte can be 0.025M, 0.03M, 0.035M, 0.04M, and 0.045M, etc.

[0050] In some embodiments, the electrolyte further includes citric acid.

[0051] In this invention, citric acid is added to the electrolyte, which can form a stable complex with tin-cobalt cations, inhibiting the hydrolysis of metal ions and achieving synchronous and uniform co-deposition. Simultaneously, it slows down the ion release rate and regulates the nucleation and growth kinetics.

[0052] In some embodiments, the concentration of citric acid in the electrolyte is 0.03~0.05M. As an example, the concentration of citric acid in the electrolyte can be 0.03M, 0.035M, 0.04M, 0.045M, and 0.05M, etc.

[0053] In this invention, by controlling the concentration of citric acid in the electrolyte within the above-mentioned range, citric acid can form a stable chelate complex with tin and cobalt cations. This can effectively inhibit the hydrolysis and precipitation of metal ions, level the reduction potential of tin and cobalt ions, and achieve synchronous and uniform co-deposition of the two. It can also delay the interfacial release rate of metal ions, thus preparing a nano-porous tin-cobalt composite deposition layer on the graphite felt surface.

[0054] In some embodiments, the electrodeposition is performed under a constant current.

[0055] In some embodiments, the current density of the electrodeposition is 20~40 mA / cm². 2 The electrodeposition time is 3-5 minutes. As an example, the electrodeposition current density can be 20 mA / cm². 2 25mA / cm 2 30mA / cm 2 35mA / cm 2 and 40mA / cm 2 The electrodeposition time can be 3 min, 3.5 min, 4 min, 4.5 min, and 5 min, etc.

[0056] In this invention, by controlling the current and time of electrodeposition within the above-mentioned range, it is helpful to form a deposition layer with high porosity and uniform thickness.

[0057] In some embodiments, the annealing conditions are: a temperature of 400~600°C, a time of 1~3 hours, and an atmosphere of air. For example, the annealing temperature can be 400°C, 450°C, 500°C, 550°C, and 600°C, etc., and the time can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours, etc.

[0058] In this invention, by controlling the annealing temperature and time within the above range, it is helpful for the complete conversion of tin cobalt metal / low-valence oxides into SnO2 and Co3O4, and to prevent severe oxidation of graphite felt.

[0059] A second aspect of the present invention also provides a graphite felt composite electrode prepared by the above-described method for preparing the graphite felt composite electrode.

[0060] A third aspect of the present invention also provides the application of the above-described graphite felt composite electrode in the electrocatalytic degradation of antibiotics.

[0061] In some embodiments, the application includes the following steps: Antibiotics, sodium chloride, and water were mixed to obtain an electrolyte containing antibiotics. The electrolyte containing antibiotics was electrocatalytically degraded using a graphite felt composite electrode as the anode and a platinum sheet electrode as the cathode in a constant current mode using an electrochemical workstation.

[0062] In this invention, the specific types of antibiotics are not specifically limited. In some embodiments, antibiotics include, but are not limited to, levofloxacin.

[0063] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0064] Example 1 The graphite felt was placed in the quartz tube of a tube furnace. Under the protection of argon, the furnace temperature was first raised to 950℃, and then a mixture of ammonia and argon was introduced (the flow rates of argon and ammonia were both 20 mL / min). The furnace was calcined at 950℃ for 30 min to obtain nitrogen-graphite felt. Using the nitrogen-graphite felt as the working electrode and silver / silver chloride as the reference electrode, in an electrolyte composed of citric acid, cobalt nitrate, and stannous chloride, wherein the concentration of citric acid is 0.04 M, the concentration of cobalt nitrate is 0.035 M, and the concentration of stannous chloride is 0.005 M, at a voltage of 30 mA / cm². 2 Electrodeposition at current density for 4 min; The electrodeposited nitrogen-graphite felt was then placed in a quartz tube of a tube furnace and annealed at 500°C for 2 hours in an air atmosphere to obtain a graphite felt composite electrode, denoted as nitrogen-graphite felt / cobalt oxide-tin oxide electrode.

[0065] Example 2 The graphite felt was placed in the quartz tube of a tube furnace. Under the protection of argon, the furnace temperature was first raised to 900℃, and then a mixture of ammonia and argon was introduced (the flow rates of argon and ammonia were both 15 mL / min). The furnace was calcined at 900℃ for 20 min to obtain nitrogen-graphite felt. Using the nitrogen-graphite felt as the working electrode and silver / silver chloride as the reference electrode, in an electrolyte composed of citric acid, cobalt nitrate, and stannous chloride, wherein the concentration of citric acid is 0.03 M, the concentration of cobalt nitrate is 0.025 M, and the concentration of stannous chloride is 0.004 M, at a voltage of 20 mA / cm²... 2 Electrodeposition at current density for 3 min; The electrodeposited nitrogen-graphite felt was then placed in a quartz tube of a tube furnace and annealed at 450°C for 2 hours in an air atmosphere to obtain a graphite felt composite electrode, denoted as nitrogen-graphite felt / cobalt oxide-tin oxide electrode.

[0066] Example 3 The graphite felt was placed in the quartz tube of a tube furnace. Under the protection of argon, the furnace temperature was first raised to 1000℃, and then a mixture of ammonia and argon was introduced (the flow rates of argon and ammonia were both 25 mL / min). The mixture was calcined at 1000℃ for 40 min to obtain nitrogen-graphite felt. Using the nitrogen-graphite felt as the working electrode and silver / silver chloride as the reference electrode, in an electrolyte composed of citric acid, cobalt nitrate, and stannous chloride, wherein the concentration of citric acid is 0.05 M, the concentration of cobalt nitrate is 0.045 M, and the concentration of stannous chloride is 0.006 M, at a current of 40 mA / cm². 2 Electrodeposition at current density for 5 min; The electrodeposited nitrogen-graphite felt was then placed in a quartz tube of a tube furnace and annealed at 550°C for 2 hours in an air atmosphere to obtain a graphite felt composite electrode, denoted as nitrogen-graphite felt / cobalt oxide-tin oxide electrode.

[0067] Comparative Example 1 Untreated graphite felt.

[0068] Comparative Example 2 The graphite felt was placed in the quartz tube of a tube furnace. Under argon protection, the furnace temperature was first raised to 950℃, and then a mixture of ammonia and argon was introduced (the flow rates of argon and ammonia were both 20 mL / min). The mixture was calcined at 950℃ for 30 min to obtain nitrogen-graphite felt.

[0069] Comparative Example 3 The preparation of the graphite felt composite electrode differs from that in Example 1 in that stannous chloride is not present in the electrolyte, and it is referred to as nitrogen-graphite felt / cobalt oxide.

[0070] Everything else is the same as in Example 1.

[0071] Comparative Example 4 The preparation of the graphite felt composite electrode differs from that in Example 1 in that cobalt nitrate is not present in the electrolyte, and it is referred to as nitrogen-graphite felt / tin oxide.

[0072] Everything else is the same as in Example 1.

[0073] Characterization and performance testing (1) Characterization Figure 2 These are characterization images of the graphite felt composite electrode in Example 1, where (a) is a low-magnification scanning electron microscope (SEM) image, (b) is a high-magnification SEM image, (c) is a transmission electron microscope (TEM) image, and (d) is a high-resolution TEM image. Figure 2 It can be seen that the surface of the graphite felt is loaded with a large number of particles or flakes composed of SnO2 and Co3O4, and the lattice stripes of the SnO2 (110) crystal plane and the Co3O4 (311) crystal plane can be clearly seen.

[0074] Figure 3 These are elemental mapping images of the graphite felt composite electrode in Example 1, where (a) is the graphite felt composite electrode, (b) is C, (c) is N, (d) is Co, (e) is Sn, and (f) is O. Figure 3 It can be seen that nitrogen, cobalt, tin and oxygen elements are distributed on the surface of graphite felt in graphite felt composite electrodes.

[0075] Figure 4The XPS spectrum of the graphite felt composite electrode in Example 1 shows that the graphite felt composite electrode contains carbon, nitrogen, cobalt, tin, and oxygen elements. Figure 5 The image shows a high-resolution XPS spectrum of C1s. It can be seen that C=C, CH, CO, and C=O bonds exist on the surface of the graphite felt composite electrode. Figure 6 The image shows a high-resolution XPS spectrum of N1s. It can be seen that the nitrogen doped in the graphite felt is mainly pyrrole nitrogen. Figure 7 This is a high-resolution XPS spectrum of Co2p. It can be seen that cobalt has two valence states: +3 and +2. Figure 8 This is a high-resolution XPS spectrum of Sn3d. It can be seen that tin has two valence states: +2 and +4. Figure 9 This is a high-resolution XPS spectrum of O1s. It can be seen that oxygen exists in CO bonds, C=O bonds, and lattice oxygen.

[0076] Figure 10 The image shows the X-ray diffraction pattern of the graphite felt composite electrode in Example 1. Figure 10 It can be seen that the main components loaded on the surface of the graphite felt are Co3O4 and SnO2.

[0077] (2) Performance testing Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. Using an electrochemical workstation, the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1, the graphite felt from Comparative Example 1, the nitrogen-graphite felt from Comparative Example 2, the nitrogen-graphite felt / cobalt oxide from Comparative Example 3, and the nitrogen-graphite felt / tin oxide from Comparative Example 4 were used as anodes, and a platinum sheet electrode was used as the cathode. An A / cm² voltage was applied. 2 Electrocatalytic degradation of an electrolyte containing levofloxacin was performed for 30 min using a constant current mode at current density. The results of the electrocatalytic degradation are as follows: Figure 11 As shown. By Figure 11 It is known that ammonia treatment, loaded cobalt oxide, and loaded tin oxide can all improve the degradation rate of levofloxacin on graphite felt, and cobalt oxide and tin oxide can also have a synergistic effect to promote the degradation of levofloxacin.

[0078] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. Using an electrochemical workstation with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, voltages of 5, 10, 20, and 30 mA / cm were applied. 2 Electrocatalytic degradation of levofloxacin in an electrolyte solution containing 30 mg / L was performed in constant current mode for 30 min. The electrocatalytic degradation results are as follows: Figure 12 As shown. By Figure 12 It can be seen that the degradation rate of levofloxacin increases with increasing current density. When the current density increases from 5 mA / cm², the degradation rate increases further. 2 Increased to 30 mA / cm 2 At that time, the degradation rate of levofloxacin increased from 61.8% to 100%. This is because as the current density increases, the rate of hydroxyl group generation accelerates, resulting in more hydroxyl groups coming into contact with levofloxacin, thereby increasing the degradation efficiency of levofloxacin.

[0079] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. The pH of the levofloxacin-containing electrolyte was adjusted to 3, 5, 7, 9, and 11, respectively. An electrochemical workstation was used with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, at a current of 30 mA / cm². 2 Electrocatalytic degradation of levofloxacin-containing electrolytes at different pH values ​​was performed for 30 min using a constant current mode. The electrocatalytic degradation results are as follows: Figure 13 As shown. By Figure 13 It was found that as the pH value increased from 3 to 5, the degradation rate of levofloxacin increased from 98.6% to 100%. Then, as the pH value continued to increase to 10, the degradation rate of levofloxacin gradually decreased to 79.6%. This indicates that low pH conditions can suppress the oxygen evolution side reaction, improve current efficiency, and allow more free radicals to participate in the degradation reaction. At the same time, under low pH conditions, active chlorine species in the solution mainly exist in the form of highly reactive HClO, thus enabling more effective degradation of levofloxacin.

[0080] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentrations of sodium chloride in the electrolyte were 1, 2, 3, 4, and 5 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. An electrochemical workstation was used with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, at a current of 30 mA / cm². 2 Electrocatalytic degradation of levofloxacin-containing electrolytes with different sodium chloride concentrations was performed for 30 min using a constant current mode at different current densities. The electrocatalytic degradation results are as follows: Figure 14 As shown. By Figure 14 It can be seen that as the NaCl concentration increased from 1 g / L to 2 g / L, the degradation rate of levofloxacin increased from 88.9% to 100%, and then as the NaCl concentration gradually increased to 5 g / L, the degradation rate of levofloxacin gradually decreased to 92.0%. This is because an appropriate amount of Cl... - Highly oxidizing and active chlorine species (such as Cl2, HClO, ClO) can be generated by anodic electrolysis.- This allows for the rapid oxidation and degradation of LEVO molecules. However, when the NaCl concentration is too high, excess Cl... - This may cause the active sites on the electrode surface to be shielded, hindering the ·OH generation process, and at the same time triggering the further conversion of active chlorine species into chlorates with weaker oxidizing power.

[0081] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentrations of levofloxacin (LEVO) were 30, 40, 50, and 60 mg / L, respectively. Using an electrochemical workstation with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, an A / cm... 2 Electrocatalytic degradation of levofloxacin was performed in a constant-current mode at current density using electrolytes containing different initial concentrations. The electrocatalytic degradation results are as follows: Figure 15 As shown. By Figure 15 It can be seen that as the initial concentration of levofloxacin increased from 30 mg / L to 60 mg / L, the degradation rate of levofloxacin gradually decreased from 100% to 63.3%. This is because at a lower initial concentration, the active species are sufficient to efficiently degrade levofloxacin. However, as the initial concentration increases, the number of active species available for distribution per unit levofloxacin molecule decreases, leading to a decline in degradation efficiency.

[0082] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. An electrochemical workstation was used with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, at a current of 30 mA / cm². 2 Electrocatalytic degradation of an electrolyte containing levofloxacin was performed for 30 min using a constant current mode at current density, yielding... Figure 16 The curve showing the degradation rate of levofloxacin over time is shown. Figure 17 This is a fitting curve for the first-order reaction kinetic equation obtained from this curve. Figure 17 It can be seen that the degradation of levofloxacin follows a first-order kinetic process.

[0083] Levofloxacin, sodium chloride, and water were mixed to obtain electrolyte A containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. Levofloxacin, sodium chloride, tert-butanol (TBA), and water were mixed to obtain electrolyte B containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. The concentration was 0.5 M. Levofloxacin, sodium chloride, ammonium acetate (NH4OAc), and water were mixed to obtain electrolyte C containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, the concentration of levofloxacin (LEVO) was 30 mg / L, and the concentration of ammonium acetate was 0.5 M. Using an electrochemical workstation with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, an A / cm² voltage was applied. 2 Electrocatalytic degradation of electrolytes A, B, and C was performed in constant current mode at current density for 5, 10, 15, and 20 min, respectively. The electrocatalytic degradation rate curves are shown below. Figure 18 As shown in (a). By Figure 18 As shown in (a), after 20 minutes, the degradation rate of levofloxacin was 95.1% without the addition of sacrificial agents (tert-butanol and ammonium acetate). After the addition of tert-butanol and ammonium acetate, the degradation rates of levofloxacin decreased to 49.9% and 78.2%, respectively. Since tert-butanol can inhibit hydroxyl groups and ammonium acetate can inhibit hypochlorite free radicals, both hydroxyl and hypochlorite are active free radicals. However, hydroxyl groups contribute more to the degradation process of levofloxacin. Figure 18 (b) shows the electron paramagnetic resonance spectrum of electrolyte A during the electrocatalytic degradation process using 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) as the scavenger. It can be seen that hydroxyl and hypochlorite reactive free radicals are present in the solution during the degradation of levofloxacin.

[0084] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. An electrochemical workstation was used with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, at a current of 30 mA / cm². 2 Electrocatalytic degradation of an electrolyte containing levofloxacin was performed in a constant current mode at current density for 30 min, and the degradation process was repeated 10 times to obtain... Figure 19 The curve showing the degradation rate of levofloxacin with the number of degradation cycles is shown. It can be seen that after ten degradation cycles, the degradation rate of levofloxacin is still as high as 93.8%, indicating that the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode has good reusability. Figure 20This is a scanning electron microscope (SEM) image of the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode after ten degradation cycles. It can be seen that cobalt oxide and tin oxide are still loaded on the graphite felt surface, demonstrating that the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode possesses excellent structural and compositional stability.

[0085] The antibiotics tetracycline, sulfamethazine, and metronidazole were mixed with sodium chloride and water, respectively, to obtain an electrolyte containing antibiotics. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of antibiotics was 30 mg / L. An electrochemical workstation was used with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, at a current of 30 mA / cm². 2 Electrocatalytic degradation of electrolytes containing different antibiotics was performed using a constant current mode with varying current density. Figure 21 The degradation rates of tetracycline, sulfamethazine, and metronidazole by the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode are shown. As can be seen, the degradation rates of tetracycline, sulfamethazine, and metronidazole by the composite electrode are 92.3%, 87.6%, and 89.8%, respectively. This demonstrates the versatility of the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode for the degradation of various antibiotics.

[0086] Levofloxacin, sodium chloride, and water were mixed to obtain an electrolyte containing levofloxacin. The concentration of sodium chloride in the electrolyte was 2 g / L, and the concentration of levofloxacin (LEVO) was 30 mg / L. Using an electrochemical workstation with the nitrogen-graphite felt / cobalt oxide-tin oxide composite electrode from Example 1 as the anode and a platinum sheet electrode as the cathode, the electrolyte containing levofloxacin was electrocatalytically degraded for 30 min in a constant current mode with a current density of 30 mA / cm2. The resulting test solution was then used for liquid chromatography-mass spectrometry (LC-MS) analysis. Figure 22This study describes the possible pathways for the electrocatalytic degradation of levofloxacin (LEVO) based on liquid chromatography-mass spectrometry (LC-MS) results. In pathway I, the benzoxazine ring of levofloxacin is opened, generating compound P1. Then, the piperazine ring of P1 opens, generating an amino group, yielding compound P2. Next, P2 loses a carboxyl group to generate compound P3. Finally, P3 loses both a methyl and an amino group to generate compound P4. In pathway II, the piperazine ring of levofloxacin opens, generating a nitro group, yielding compound P5. P5 then undergoes defluorination and further carboxyl removal, generating compound P6. Finally, the benzoxazine ring of P6 is opened, generating compound P7. In pathway III, the piperazine ring of levofloxacin is opened, generating compound P8. Subsequently, the piperazine ring of P8 is removed, generating compound P9. Next, P9 loses a carboxyl group, generating compound P10. Finally, the benzoxazine ring of P10 opens with the pyridine ring in the quinoline ring, generating P11. In pathway IV, P8 completely loses its piperazine ring, yielding compound P12. Subsequently, P12 loses its carboxyl group, yielding compound P13. As the quinoline and benzoxazine rings in P13 are opened, compound P14 is formed. Then, P14 loses two more carboxyl groups, yielding compound P15. Finally, intermediates P4, P7, P11, and P15 continue to cleave and separate, mineralizing into CO2 and H2O.

[0087] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A method for preparing a graphite felt composite electrode, characterized by, The method comprises the following steps: calcining the graphite felt under a mixed gas of ammonia and inert gas to obtain nitrogen-graphite felt; electrodepositing the nitrogen-graphite felt as a working electrode and silver / silver chloride as a reference electrode in an electrolyte containing cobalt salt and stannous salt to obtain nitrogen-graphite felt after electrodepositing; annealing the nitrogen-graphite felt after electrodepositing to obtain graphite felt composite electrode.

2. The method of claim 1, wherein the graphite felt composite electrode is prepared by the steps of: The flow rate of the ammonia and the inert gas is independently 15-25 mL / min.

3. The method of claim 1, wherein the graphite felt composite electrode is prepared by the steps of: The calcination temperature is 900-1000 ℃, and the calcination time is 20-40 min. ​ 4. The method for preparing the graphite felt composite electrode according to claim 1, characterized in that, The molar ratio of cobalt element in the cobalt salt to tin element in the stannous salt is 6-8:

1.

5. The method for preparing the graphite felt composite electrode according to claim 1, characterized in that, The concentration of the cobalt salt in the electrolyte is 0.025-0.045 M.

6. The method of claim 1, wherein the graphite felt composite electrode is prepared by the steps of: The electrolyte further comprises citric acid. The concentration of the citric acid in the electrolyte is 0.03-0.05 M.

7. The method for preparing the graphite felt composite electrode according to claim 1, characterized in that, The electrodepositing is performed under constant current. The current density of the electrodeposition is 20-40 mA / cm 2 The time of the electrodeposition is 3-5 min.

8. The method for preparing the graphite felt composite electrode according to claim 1, characterized in that, The annealing condition is: temperature 400-600 ℃, time 1-3 h, and atmosphere air.

9. The graphite felt composite electrode prepared by the method of any one of claims 1-8.

10. The graphite felt composite electrode of claim 9 for use in electrocatalytic degradation of antibiotics.

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