Fe-NO / C type electro-Fenton catalyst, and preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a Fe-NO / C type electro-Fenton catalyst, a preparation method and application thereof. The Fe-NO / C type electro-Fenton catalyst is prepared by selecting polyacrylonitrile as a raw material to perform amidoximation, obtaining polyamidoxime; the polyamidoxime is mixed with Fe 3+ Chelation forms a Fe-N2O2 pre-coordination structure, and pyrolysis obtains the Fe-NO / C type electro-Fenton catalyst with a Fe-N2O2 single atom structure; the mass ratio of the polyamidoxime and Fe 3+ is 1:0.3-0.5; and the Fe-NO / C type electro-Fenton catalyst is used in antibiotic pharmaceutical wastewater degradation.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to an Fe-NO / C type electro-Fenton catalyst, its preparation method, and its application. Background Technology

[0002] While the development of antibiotic pharmaceuticals is rapid, many problems remain to be solved in the treatment of antibiotic-containing pharmaceutical wastewater. Common treatment methods for antibiotic-containing pharmaceutical wastewater include physical treatment, biological treatment, and advanced oxidation technologies. Physical treatment methods include adsorption and membrane separation; these methods focus on the separation and adsorption of pollutants, but their disadvantages include secondary pollution and high costs. Biological treatment methods include activated sludge processes, biofilm processes, and anaerobic digestion; these methods utilize the metabolic activities of microorganisms to degrade and transform pollutants in wastewater, but their disadvantages include poor treatment efficiency and low effectiveness for high-concentration, difficult-to-degrade pollutants. Traditional wastewater treatment methods often cannot completely degrade organic matter in wastewater; therefore, developing more efficient and environmentally friendly wastewater treatment technologies is currently a major challenge and a hot topic, possessing significant research value and broad application prospects.

[0003] Transition metal nanoparticle catalysts refer to a class of catalytic materials that use transition metal elements or alloys as the main active material, loaded onto the surface of a conductive support or encapsulated within the support, exhibiting two-electron oxygen reduction (2e-ORR) activity and H2O2 electroactivation performance. The transition metal is the source of the electro-Fenton activity. A common transition metal catalyst is the iron single-atom catalyst, with a structure of Fe-N4. Its strong adsorption of oxygen makes it prone to four-electron reduction, forming OH-. - Neither H2O nor H2O can generate H2O2 or hydroxyl radicals, thus lacking electro-Fenton catalytic ability. However, with further in-depth research on related materials, some metal-free carbon materials with special configurations, doped with heteroatoms and containing edge defects, have also been found to possess good electro-Fenton catalytic performance. Unlike transition metal carbon-based catalysts, whose transition metal / compound nanoparticles are supported on a carbon framework, the active sites of metal-free carbon-based catalysts are all integrated within the carbon framework, giving them superior stability. However, these special configurations of heteroatomation and edge defects have a certain degree of randomness, thus there are still many shortcomings in the distribution and regulation of active sites. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an Fe-NO / C type electro-Fenton catalyst, its preparation method, and its application. The specific technical solution is as follows.

[0005] The first aspect of this invention provides a Fe-NO / C type electro-Fenton catalyst, in which poly(gamma-amine oxime) and Fe... 3+After chelation, a Fe-N2O2 pre-coordinated structure is formed. Pyrolysis yields a Fe-NO / C type electro-Fenton catalyst with a Fe-N2O2 single-atom structure. Polyamine oxime and Fe 3+ The mass ratio is 1:0.3~0.5; The Fe-NO / C type electro-Fenton catalyst is used for the degradation of antibiotic pharmaceutical wastewater.

[0006] Traditional iron single-atom catalysts have a Fe-N4 structure, which exhibits excessive adsorption of oxygen, making them prone to four-electron reduction to form OH-. - Neither H2O nor H2O can generate H2O2 or hydroxyl radicals, thus lacking electro-Fenton catalytic activity. Therefore, this invention replaces the two N atoms in the Fe-N4 coordination structure with less electronegative O atoms, weakening the charge attraction to the central Fe atom, thereby reducing excessive adsorption of O2. This improves the selectivity of the two-electron pathway and the activity of in-situ electro-activation of H2O2. To form the Fe-N2O2 single-atom structure, this invention requires precisely customized pre-coordination structures to maintain the first shell configuration of the coordination center during pyrolysis. Polyamine oximes possess abundant amine oxime functional groups, exhibiting strong chelating effects on transition metals, and interact with Fe... 3+ The coordination forms a Fe-N2O2 pre-coordinated structure, enabling precise control over the distribution and regulation of active sites. Fe 3+ The dosage needs to be precisely controlled; too little Fe 3+ This results in sparse active sites, low two-electron oxygen reduction (2e-ORR) activity, and low H2O2 activation efficiency; excessive Fe... 3+ The addition of Fe leads to the formation of Fe particles and Fe oxide particles. Compared to single Fe atoms, Fe-based particles have lower atomic utilization and lower activity, thus reducing the efficiency of the catalyst.

[0007] In another preferred embodiment, the Fe 3+ It comes from soluble iron salts such as ferric nitrate or ferric chloride.

[0008] In another preferred embodiment, the poly(ammoxime) is obtained by ammoximation reaction of polyacrylonitrile as a raw material.

[0009] A second aspect of this invention provides a method for preparing the Fe-NO / C type electro-Fenton catalyst, comprising the following steps: Hydroxylamine hydrochloride and N,N-dimethylformamide were mixed at a mass-to-volume ratio of 1 g: 10-20 mL. Under organic reagent conditions, an alkaline reagent was added to neutralize the HCl in the hydroxylamine hydrochloride. NH3OH was then added. +The hydroxylamine solution was obtained by converting it to free NH2OH and separating the precipitate. The alkaline reagent was a mixture of Na2CO3 and NaOH in a mass ratio of 5:1. The pH value after adding the alkaline reagent was 7.

[0010] Polyacrylonitrile powder and N,N-dimethylformamide were mixed at a mass-to-volume ratio of 1g:10~20mL and stirred continuously for 24~36h to dissolve them, thus obtaining a polyacrylonitrile solution.

[0011] A polyacrylonitrile solution and a hydroxylamine solution are mixed and subjected to a methine oxime reaction at 45℃~65℃ for 12h~24h, followed by purification to obtain polymetamine oxime; wherein the mass ratio of polyacrylonitrile to hydroxylamine hydrochloride is 1:1.3~1.5; preferably, during the mixing process of the polyacrylonitrile solution and the hydroxylamine solution, the mixture is first heated at 45℃ for 6h~12h, and then heated at 65℃ for 6h~12h; after purification, polymetamine oxime is obtained. The iron precursor solution was mixed with the poly(gamma-amino)oxime solution and reacted for 12-24 hours. The precipitate was collected by centrifugation. The precipitate was then kept at 850-950℃ for 60-120 minutes and acid-washed to obtain the Fe-NO / C type electro-Fenton catalyst. The acid washing was performed using a 0.5 mol / L sulfuric acid solution to remove non-single-atom impurities such as Fe-based nanoparticles or oxides generated during pyrolysis.

[0012] In another preferred embodiment, the purification refers to displacement purification using a mixture of ethanol and ethyl acetate in equal volume ratios.

[0013] In another preferred embodiment, the particle size of the poly(amine oxime) is 50 μm to 100 μm.

[0014] The application of the Fe-NO / C type electro-Fenton catalyst described in this invention in the degradation of antibiotic pharmaceutical wastewater.

[0015] In another preferred embodiment, the antibiotic in the antibiotic pharmaceutical wastewater is metronidazole, and the organic impurity is rhodamine B.

[0016] In another preferred embodiment, a three-electrode system is constructed using a substrate coated with a Fe-NO / C type electro-Fenton catalyst as the working electrode, Ag / AgCl as the reference electrode, and an inert material as the auxiliary electrode. This three-electrode system is used to degrade antibiotics in pharmaceutical wastewater. The loading of the Fe-NO / C type electro-Fenton catalyst in the working electrode is not less than 1 mg / cm³. 2 The inert material includes any one of platinum sheet, platinum wire, and graphite rod; the substrate is a glassy carbon electrode or a nickel foam substrate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In this invention, the strong chelation of iron ions by the amylopectin functional group of poly(amylopectin) oxime precisely forms a Fe-N₂O₂ pre-coordinated structure before pyrolysis. Compared with the traditional Fe-N₄ structure, replacing the two nitrogen atoms with oxygen atoms of lower electronegativity effectively weakens the charge attraction to the central iron atom and reduces the excessive adsorption capacity for oxygen, thereby significantly improving the selectivity of the two-electron oxygen reduction reaction. This lays the structural foundation for the efficient generation of hydrogen peroxide and hydroxyl radicals in the electro-Fenton process. The Fe-NO / C type electro-Fenton catalyst of this invention exhibits excellent two-electron selectivity and hydrogen peroxide yield in the oxygen reduction reaction, with a half-wave potential (E) of [missing value]. 1 / 2 The potential is as high as 0.688V. Further tests using rotating ring-disk electrodes show that at 0.6V, the hydrogen peroxide yield can reach 75%, with an electron transfer number of approximately 2.5, fully demonstrating the high selectivity of its two-electron oxygen reduction pathway and providing a sufficient source of hydrogen peroxide for efficient electro-Fenton degradation.

[0018] This invention effectively avoids problems such as sparse active sites and insufficient two-electron oxygen reduction activity caused by insufficient iron precursor addition (1:0.3~0.5) and reduced iron nanoparticle formation and atom utilization caused by excessive addition by precisely controlling the mass ratio of poly(ammonia oxime) to iron precursor (1:0.3~0.5). Simultaneously, by optimizing the pyrolysis temperature (850~950℃) and holding time (60~120 minutes), the stable formation of the Fe-N2O2 single-atom structure is ensured. The preparation method in this invention uses widely available raw materials, is simple and controllable, and has good reproducibility, providing a feasible technical path for the large-scale preparation of high-performance electro-Fenton catalysts.

[0019] The Fe-NO / C type electro-Fenton catalyst of this invention achieves a degradation rate of over 98% for Rhodamine B within 1 hour. Within the first 20 minutes, the Rhodamine B concentration rapidly decreases to one-fifth of its initial concentration, exhibiting rapid degradation kinetics. Control experiments show that, without applied voltage, the Rhodamine B concentration only slightly decreases (<5%) within 5 minutes before stabilizing, proving that the observed degradation effect is mainly due to electro-Fenton catalysis, rather than physical adsorption. A simulated pharmaceutical wastewater degradation experiment using metronidazole as a model antibiotic further verifies the practical application value of this invention. Under a 5V DC voltage, the electro-Fenton system using the Fe-NO / C type electro-Fenton catalyst as the cathode achieves a degradation rate of 71.72% for metronidazole within 1 hour. Metronidazole, as a widely used antibiotic, is characterized by high water solubility, poor biodegradability, and potential toxicity, making it a typical example of pharmaceutical wastewater treatment. The highly efficient degradation of this type of pollutant by this invention fully demonstrates the enormous application potential of the prepared catalyst in the harmless treatment of antibiotic-containing pharmaceutical wastewater. Attached Figure Description

[0020] Figure 1The XRD diffraction pattern of the Fe-NO / C type electro-Fenton catalyst is shown.

[0021] Figure 2 SEM images of different catalysts: a is a metal-free NO / C type electro-Fenton catalyst, and b is a Fe-NO / C type electro-Fenton catalyst.

[0022] Figure 3 This is an EDS mapping diagram of the Fe-NO / C type electro-Fenton catalyst.

[0023] Figure 4 The figures show the N2 adsorption-desorption isotherms for different catalysts; a is the Fe-NO / C type electro-Fenton catalyst, and b is the metal-free NO / C type electro-Fenton catalyst.

[0024] Figure 5 The figures show pore size distribution curves; a represents the Fe-NO / C type electro-Fenton catalyst, and b represents the Fe-free NO / C type catalyst.

[0025] Figure 6 The figures show the LSV polarization curves of materials containing different metals; a is the Mn-NO / C type electro-Fenton catalyst, b is the Fe-NO / C type electro-Fenton catalyst, c is the Co-NO / C type electro-Fenton catalyst, and d is the Cu-NO / C type electro-Fenton catalyst.

[0026] Figure 7 The RRDE test curves for Fe-NO / C type electro-Fenton catalysts are shown.

[0027] Figure 8 The graph shows the electron transfer number and peroxide yield of Fe-NO / C type electro-Fenton catalysts at different potentials.

[0028] Figure 9 The images show the UV-vis spectra of RhB under different conditions; a) is the UV-vis spectrum of the RhB standard solution, b) is the concentration-maximum absorption intensity standard curve, c) is the UV-vis spectrum of the sampled solutions at different degradation times, and d) is the degradation efficiency of RhB by the Fe-NO / C type electro-Fenton catalyst and the comparison without bias voltage. RhB is Rhodamine B.

[0029] Figure 10 The images show the UV-vis spectra of MTZ under different conditions; a is the UV-vis spectrum of the MTZ standard solution, b is the concentration-maximum absorption intensity standard curve, c is the UV-vis spectrum of the sampled solutions at different degradation times, and d is the degradation efficiency of MTZ by the Fe-NO / C type electro-Fenton catalyst. MTZ is metronidazole. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise specified, all embodiments and preferred methods mentioned in this invention can be combined to form new technical solutions.

[0032] 1. Material preparation 1.1 Preparation of poly(amine oxime) (PAO) At room temperature, add 60 mL of N,N-dimethylformamide (DMF) to a beaker, then place a magnetic stirrer on it and set the temperature to 45°C and 500 rpm. Heat to 45°C and maintain the temperature. Then, slowly add 5.56 g of hydroxylamine hydrochloride. After the hydroxylamine hydrochloride has completely dissolved, slowly add a mixture of 3.056 g of Na₂CO₃ and 0.768 g of NaOH to the beaker. Seal the beaker and continue heating and stirring for 3 hours. The purpose of Na₂CO₃ and NaOH is to completely neutralize the HCl in the hydroxylamine hydrochloride according to the stoichiometric ratio, releasing hydroxylamine (NH₃OH) for the oxime reaction. Since the NaCl produced by the neutralization reaction is difficult to dissolve in DMF, a white precipitate will form. Therefore, after heating and stirring for 3 hours, remove the white precipitate by filtration or centrifugation, retaining the clear solution.

[0033] Add 60 mL of DMF to another beaker, place a magnetic stir bar inside, and put the beaker on a magnetic heating pan. Set the conditions to 45°C and 500 rpm. After heating to 45°C, slowly add 4.28 g of polyacrylonitrile (PAN) powder in batches to prevent clumping. After all the powder has been added, seal the pan and continue heating and stirring for 24 hours. Purpose of this operation: Since PAN is a polymer, it is soluble in DMF but the dissolution rate is slow and the solution viscosity is high. Therefore, before the oxime reaction, PAN should be completely dissolved in DMF to obtain a PAN DMF solution.

[0034] After both solutions have been pretreated, the DMF solution of hydroxylamine is added dropwise to the DMF solution of PAN, and the mixture is heated and stirred again for 12 hours. During this process, the heating temperature is adjusted to 55℃ for the first 6 hours and to 65℃ for the next 6 hours. The purpose of this operation is to convert the cyano functional group in PAN into a methylamine oxime functional group under the action of hydroxylamine. If a precipitate forms after the reaction, the supernatant is collected by centrifugation at 8000 rpm for 15 minutes, the precipitate is discarded, and the mixture is obtained.

[0035] Prepare 200 mL of a mixture of ethanol and ethyl acetate in an equal volume ratio, and pour it into a beaker. While stirring vigorously at 800 rpm, add the mixture dropwise to the ethanol and ethyl acetate mixture using a dropper. Due to solvent displacement, a white flocculent precipitate immediately forms. Collect the white flocculent precipitate by centrifugation or filtration, and wash it three times successively with ethanol and deionized water. Place it in a vacuum freeze dryer, freeze-dry it, and then remove the product. Grind it using a vibratory ball mill at 1200 rpm for 30 minutes. The milling bowl and grinding balls are made of stainless steel. The resulting white powder is PAO.

[0036] 1.2 Preparation of Fe-NO / C type electro-Fenton catalyst and comparative catalyst Weigh 0.4 g of ferric nitrate nonahydrate and dissolve it in 100 mL of deionized water. Disperse 1 g of PAO in 100 mL of deionized water. Then, add the iron precursor solution dropwise to the PAO dispersion and stir for 12 h. Filter the mixture, retaining the insoluble matter and discarding the solution. Wash the precipitate three times with deionized water and dry it in a vacuum oven at 60 °C to obtain the product, denoted as PAO-Fe.

[0037] To illustrate the effect of using iron ions, the above methods were used, but the reaction was carried out by replacing ferric nitrate nonahydrate with copper acetate, cobalt acetate, and manganese sulfate, respectively, to obtain PAO-Cu, PAO-Co, and PAO-Mn.

[0038] Take 0.5g of PAO-Fe, place it in a corundum ceramic boat, and then place it in a quartz tube, sealing it through a flange with a valve. Using a vacuum exchange device, first evacuate the quartz tube, then fill it with N2, repeating this process three times. On the last attempt, fill the quartz tube with excess N2 and open the valve to allow it to resonate with the outside atmosphere. After the pressure inside and outside the tube is balanced, adjust the N2 flow rate to 100 sccm, and use a robotic arm to move the quartz tube into the heating chamber of the multi-functional experimental furnace. Set the heating program as follows: heat to 900℃ at a rate of 5℃ / min, then hold at that temperature for 120 minutes. After the holding time, cut off the heating. After heating stops, the robotic arm automatically removes the quartz tube from the heating chamber and transfers it to the cooling chamber (cooled by a fan). After complete cooling, the black powder in the ceramic boat was removed and poured into a 250 mL glass flask. Then, 100 mL of 0.5 mol / L sulfuric acid solution was added, and a reflux device was connected. The flask and its contents were heated and stirred at 90 °C and 400 rpm for 12 h to obtain the Fe-NO / C type electro-Fenton catalyst.

[0039] After treating PAO-Cu, PAO-Co, and PAO-Mn using the above methods, Cu-NO / C type electro-Fenton catalysts, Co-NO / C type electro-Fenton catalysts, and Mn-NO / C type electro-Fenton catalysts were obtained. In addition, without adding any metal, PAO was directly pyrolyzed to obtain a metal-free NO / C type electro-Fenton catalyst, which served as a control.

[0040] 2. Performance Testing 2.1 Electrochemical performance testing Catalyst loading method: Weigh 5 mg of the above Fe-NO / C electro-Fenton catalyst and the Cu-NO / C, Co-NO / C, Mn-NO / C, and metal-free NO / C electro-Fenton catalysts used for comparison, place them in a sample vial, add 950 μL of ethanol, then add 50 μL of Nafion D-520 perfluorosulfonic acid resin solution, shake well, and sonicate for at least 30 min to promote dispersion, obtaining a catalyst ink with a concentration of 5 mg / mL. Take 10 μL of the catalyst ink and drop it onto a glassy carbon electrode, wait 10 minutes for it to dry naturally, and a uniform catalyst film will be formed on the electrode surface.

[0041] Electrochemical testing method: The ORR reaction activity was tested using a three-electrode system. The reference electrode was an Ag / AgCl electrode (filled with saturated KCl), the working electrode was a glassy carbon electrode coated with the catalyst and fixed on a rotating disk electrode assembly, and the auxiliary electrode was a platinum sheet. The electrolyte was a 0.1 mol / L KOH solution saturated with dissolved oxygen, and O2 was continuously introduced into the electrolyte at a flow rate of 40 sccm during the test. First, 20 cyclic voltammetric scans were performed at a scan rate of 0.1 V / s in the range of 0 to -1 V (relative to the Ag / AgCl electrode) to activate the electrode (remove surface contaminants and adsorbates, and stabilize the valence state of the metal elements in the catalyst). The ORR catalytic performance of the catalyst was evaluated by linear voltammetry (LSV) with the following parameters: scan rate 20 mV / s, sampling frequency 10 Hz, scan potential 0.2 to -1 V (relative to the Ag / AgCl electrode), and automatic IR compensation (80%). To accelerate the oxygen diffusion rate, the rotating disk electrode was rotated at speeds of 225, 400, 625, 900, 1225, 1600, and 2025 rpm. During data processing, the Ag / AgCl electrode potential was converted to the reversible hydrogen electrode (RHE) potential according to the Nernst equation. The half-wave potential (E1 / 2) corresponding to half the current density at 0.4V (relative to RHE) at 1600 rpm was used to measure the intrinsic ORR catalytic activity of the catalyst.

[0042] Based on a four-electron system, the selectivity of the catalyst for the two-electron / four-electron pathway in the ORR reaction and the H₂O₂ yield were evaluated. The electrode preparation method was largely the same as the electrolytic cell system, but the catalyst was coated on a glassy carbon disk of a ring-disk electrode (RRDE). The platinum ring of the RRDE was connected individually to one channel of a dual potentiostat. During the test, the rotation speed was 1600 rpm, and the same LSV scan was performed on the catalyst-loaded glassy carbon disk, while the platinum ring of the RRDE was kept at a fixed potential of 0.5 V (compared to Ag / AgCl), and current changes were recorded. During this process, the peroxides generated by the catalyst on the glassy carbon disk were ejected and rapidly electro-oxidized again upon contact with the platinum ring, generating significant current perturbations. Therefore, based on the glassy carbon disk current and the platinum ring current, the hydrogen peroxide yield and the selectivity of the two-electron ORR could be calculated to evaluate the catalyst's potential in the electro-Fenton reaction.

[0043] 2.2 Degradation performance test Using nickel foam as a substrate, the concentration of the catalyst ink was increased to 20 mg / mL, and the solvent was changed to a mixture of ethanol / N-methylpyrrolidone / water. A 10*50*0.1 mm piece of nickel foam was cut, precisely weighed, then immersed in the catalyst ink, removed, dried under an infrared lamp, and precisely weighed again to obtain the catalyst loading. This process was repeated several times until the catalyst surface area ratio reached 1 mg / cm². 2 .

[0044] A three-electrode system was employed. The working electrode was a nickel foam loaded with catalyst, held by a titanium electrode clip; the reference electrode was an Ag / AgCl electrode; and the auxiliary electrode was a platinum sheet of similar size to the nickel foam. The electrolyte was a Na₂SO₄ solution containing 50 mg / L of the organic pollutant Rhodamine B (supporting electrolyte, 1 mol / L), with the pH adjusted to 3 using KOH and H₂SO₄. A fixed potential (-0.8 V vs Ag / AgCl) was applied to the working electrode using a chronoamperometry method, and O₂ was continuously introduced into the electrolyte during the reaction. At 5 min and 10 min after the start of the reaction, 2 mL of the solution was pipetted into clean centrifuge tubes for sampling. The concentration of the organic pollutant was quantitatively analyzed by UV-Vis spectroscopy to evaluate the degradation efficiency.

[0045] For the degradation experiment of simulated pharmaceutical wastewater containing metronidazole, catalyst powder and binder polytetrafluoroethylene powder were mixed at a mass ratio of 9:1, and ground with ethanol in an agate mortar until a viscous mud-like substance was formed. The mud was spread onto a 10*50*0.15mm stainless steel mesh (316L material, 200 mesh), and the catalyst was uniformly loaded onto the entire stainless steel mesh using a roller pressing method, followed by drying. The catalyst loading was calculated by the mass change of the stainless steel mesh before and after loading (note: deducting the mass of the binder). Based on experience from multiple trials, the loading was adjusted to 2 mg / cm³. 2 A two-electrode system was employed. A stainless steel mesh loaded with catalyst, held by stainless steel electrode clamps, served as the cathode, while a platinum mesh of similar size served as the anode. The electrolyte was a 1 mol / L Na₂SO₄ solution containing 80 mg / L metronidazole, with the pH adjusted to 3 and pre-saturated with dissolved oxygen. The system was directly driven by a 5V DC regulated power supply, with continuous O₂ flow during the degradation process. Solution samples were taken at different time points after the reaction began, and the removal rate of metronidazole was quantitatively analyzed using UV-Vis spectroscopy to evaluate the degradation potential of the prepared material and related electrochemical methods for antibiotic-containing pharmaceutical wastewater.

[0046] 3. Results 3.1 Material Structure Characterization The crystal structure information of the material was analyzed using X-ray diffraction (XRD). The XRD pattern of the Fe-NO / C type electro-Fenton catalyst is shown below. Figure 1 As shown, the XRD diffraction pattern of the Fe-NO / C type electro-Fenton catalyst shows only one broad diffraction peak around 25°, corresponding to the (002) plane of graphitic carbon. This is a common characteristic of pyrolysis-derived carbon materials, indicating that the material has a certain degree of graphitization. Notably, no sharp diffraction peaks belonging to face-centered cubic metal elemental crystals were found, which to some extent proves that the metal elements in the catalyst are dispersed on the carbon support in the form of individual atoms, without agglomeration to form nanoparticle crystal structures. This is consistent with the expected design of single-atom active sites.

[0047] Furthermore, the metal-free NO / C type electro-Fenton catalyst and the Fe-NO / C type electro-Fenton catalyst were characterized by scanning electron microscopy (SEM). Figure 2As shown, the metal-free NO / C electro-Fenton catalyst exhibits a distinct macroporous network carbon structure with carbon particles measuring 100 μm. In contrast, the morphology of the Fe-NO / C electro-Fenton catalyst differs significantly from that of the metal-free NO / C electro-Fenton catalyst, with dense carbon nanospheres stacked in a relatively loose manner to form a porous nanostructure. The addition of metal alters the material morphology because transition metals enhance the stability of carbon at high temperatures. Without Fe, most of the carbon evaporates upon heating, resulting in a macroporous network carbon structure similar to that of the metal-free NO / C electro-Fenton catalyst; while the Fe-stabilized carbon only partially volatilizes at high temperatures, forming a loose, porous structure of stacked nanospheres similar to that of the Fe-NO / C electro-Fenton catalyst. This porous structure facilitates the formation of a large specific surface area, enhancing mass diffusion during the ORR reaction.

[0048] Elemental distribution and mapping of Fe-NO / C type electro-Fenton catalysts under scanning electron microscopy X-ray energy scattering (EDS) spectra, as shown in the figure. Figure 3 As shown, the carbon layer at the selected scanning location is relatively densely packed. Carbon (red) is uniformly distributed throughout the field of view, presenting a three-dimensional image similar to the SEM image, indicating that the material is predominantly C. Nitrogen (green) and oxygen (dark blue) are sparser than C in the field of view, indicating that N and O mainly exist as dopants within the carbon framework. Iron (light blue) is basically distributed as single dots, which may indicate two possibilities: either the iron content in the material is extremely low, and the image shows noise; or iron exists in the material as single atoms.

[0049] To further investigate this issue, EDS spectral scanning was performed. The total elemental distribution of the product is shown in Table 1: Carbon had the highest content, at 91%, consistent with previous mapping conclusions. Nitrogen and oxygen had lower contents, at 4.5% and 3.2% respectively, consistent with elemental doping characteristics. Iron had a content of 1.2%, indicating that the Fe signal in the mapping diagram was not noise, but rather an effective signal generated by Fe active sites existing in single-atom form, consistent with the expected designed structure of the material.

[0050] Table 1. Distribution of total elements in the products The porous structure of the material significantly affects the utilization rate of active sites and the mass transfer rate during the electrocatalytic reaction. To investigate the pore structure of the prepared material, N2 physical adsorption analysis experiments were conducted. The measured adsorption-desorption isotherms are shown below. Figure 4As shown, the Fe-NO / C electro-Fenton catalyst exhibits a significant increase in gas adsorption in the low-pressure region, indicating the presence of numerous microporous structures; a distinct adsorption-desorption hysteresis loop appears in the intermediate region, indicating the presence of mesoporous structures; while a sharp increase in adsorption occurs in the high-pressure region, indicating the presence of some macroporous structures. In summary, the Fe-NO / C electro-Fenton catalyst exhibits a hierarchical porous structure of micropores-mesopores-macropores, which is beneficial for the stepwise diffusion of substances during the electrochemical reaction process. The specific surface area of ​​the Fe-NO / C electro-Fenton catalyst, calculated using the multi-point BET method, is 423.44 m². 2 The concentration of 1 / g indicates that the prepared material has a large specific surface area. In contrast, the metal-free NO / C type electro-Fenton catalyst, due to the lack of metal stability, loses its microporous structure and only exhibits mesoporous and macroporous structures, resulting in a significant loss of specific surface area, only 117.63 m². 2 / g. Based on the N2 adsorption-desorption curves of the two samples, a QSDFT model was used for fitting (this model mainly reflects the micropore distribution), and the resulting pore size distribution curve (e.g.) was obtained. Figure 5 (As shown) This also illustrates that Fe-NO / C type electro-Fenton catalysts have a large number of microporous structures, while metal-free NO / C type electro-Fenton catalysts do not.

[0051] 3.2 Evaluation of Electrochemical Performance The material exhibits excellent ORR activity, which is a prerequisite for ensuring efficient electro-Fenton degradation. Therefore, to evaluate the ORR electrocatalytic activity of the synthesized catalysts, a three-electrode working system was used. The prepared catalysts containing different metals were loaded onto a rotating disk electrode, and LSV measurements were performed in an oxygen-saturated 0.1 mol / L KOH solution. Figure 6 It can be seen that the LSV of all samples exhibits the following characteristics: a low current stable state in the 0.8~1.0V region, at which no reaction occurs; a rapidly increasing current density (absolute value) in the 0.6~0.8V region, combined with the presence of saturated oxygen in the solution, indicates that the ORR reaction begins to occur in this potential range; in the low potential range <0.6V, the trend of increasing absolute current slows down, but still shows a negative increasing trend, which is related to the continuous production of peroxides by the ORR reaction.

[0052] Using E1 / 2 as a direct standard for evaluating the ORR activity of the materials, the E1 / 2 values ​​for the Mn-NO / C, Fe-NO / C, Co-NO / C, and Cu-NO / C electro-Fenton catalysts were 0.576 V, 0.688 V, 0.623 V, and 0.622 V, respectively. The results show that the Fe-NO / C electro-Fenton catalyst has the highest E1 / 2 among the samples, indicating its superior performance in the electrocatalytic generation of peroxides for ORR. Furthermore, it is noteworthy that in the low potential range, the Fe-NO / C electro-Fenton catalyst achieves a higher absolute current density at the same potential compared to other comparative samples, indicating that the ORR reaction kinetics are significantly enhanced under the catalysis of the Fe-NO / C electro-Fenton catalyst.

[0053] The ORR pathway selectivity and peroxide yield of the Fe-NO / C type electro-Fenton catalyst were tested using RRDE. Figure 7 As shown in the figure, the black line represents the current response of the Fe-NO / C type electro-Fenton catalyst supported on the glassy carbon disk as the potential changes. It is worth noting that due to changes in the thickness, area, and internal resistance of the coated electrode, the current response curve under RRDE does not completely coincide with the LSV curve measured under RDE, which is normal. The red line represents the current response sensed by the outer platinum ring as the potential applied to the Fe-NO / C type electro-Fenton catalyst changes (a bias voltage of 0.5V vs Ag / AgCl is fixedly applied to the platinum ring to detect the peroxides generated and diffused in the disk). The results show that as the absolute value of the current of the Fe-NO / C type electro-Fenton catalyst increases, the current response generated by the platinum ring also increases. The current density of both reaches a peak at around 0.5V, and then decreases slightly. This may be because the large electrode thickness affects mass transfer, leading to a temporary insufficiency in oxygen supply or the inability of products to diffuse out in time. As the potential continues to decrease, the absolute values ​​of the current density collected by the glassy carbon disk and the platinum ring both increase again. This could be because the ORR reaction can proceed faster at a lower potential, producing more peroxides that diffuse out; or it could be that the hydrogen evolution reaction (HER) begins to occur, creating some competition for the ORR reaction.

[0054] To further analyze the RRDE test data, based on the calculation methods for peroxide yield and electron transfer number, the RRDE test curves were transformed into curves showing the changes in peroxide yield and electron transfer number at different potentials (e.g., Figure 8(As shown). Unlike the previous intuitive analysis of RRDE, the Fe-NO / C type electro-Fenton catalyst can achieve a peroxide yield of 75% and an electron transfer number of 2.5 at around 0.6V. However, as the potential decreases further, the peroxide yield decreases slightly, reaching a relatively stable state when it approaches 50%, while the electron transfer number approaches 3. Therefore, the continuous increase in current density in the low potential range of the RRDE test curve should be attributed to HER rather than ORR. Although some HER reaction competes with ORR, the Fe-NO / C type electro-Fenton catalyst still exhibits excellent ORR activity for peroxide generation via a two-electron transfer step, which provides a good performance foundation for the subsequent use of the material in electro-Fenton degradation.

[0055] 3.3 Electro-Fenton Degradation Test of Pollutants Because the prepared catalyst exhibited excellent two-electron ORR performance in electrochemical tests, electro-Fenton degradation experiments of organic compounds, using 50 mg / L Rhodamine B (RhB) as a representative, were conducted to further evaluate its application potential. For convenient quantitative analysis, RhB standard solutions of different concentrations from 50 mg / L to 1 mg / L were prepared in sequence, and a standard curve was plotted based on the maximum absorption intensity in the UV-vis spectrum. Figure 9 As shown in Figure a, the RhB solution exhibits significant absorption of visible light at 500 nm; therefore, this peak is used as the basis for quantification. UV-Vis spectra of standard solutions at different concentrations were measured, and a standard curve was plotted with solution concentration on the x-axis and the absorption intensity at 500 nm on the y-axis, as shown in Figure a. Figure 9 As shown in b in the figure. The R-squared value of the standard curve after linear fitting. 2 The value of 0.995 indicates that within the selected concentration range, there is a good linear relationship between absorbance and concentration, which can be used as a reliable quantitative reference.

[0056] A 1 mol / L Na₂SO₄ electrolyte was prepared, and the pH was adjusted to 3 using KOH and H₂SO₄. RhB was added to achieve a concentration of 50 mg / L for use in electro-Fenton degradation experiments. Considering the geometric area of ​​the electrode (0.2 cm²) in conventional electrochemical tests... 2 ) and catalyst loading (~0.25 mg / cm³) 2 The loading capacity of Fe-NO / C electro-Fenton catalyst was significantly low, making it difficult to show a noticeable degradation effect on RhB at a concentration of 50 mg / L. Therefore, in order to increase the catalyst loading and loading area, a 5 cm long and 1 cm wide nickel foam was used as a substrate, and Fe-NO / C type electro-Fenton catalyst was loaded by slurry coating to achieve a loading of 1 mg / cm². 2 Similarly, a three-electrode system was constructed, with the working electrode biased at -0.8V (vsAg / AgCl).

[0057] The solution was sampled at 5 min, 10 min, 20 min, 40 min and 60 min after the start of degradation (approximately 2 mL, 1% of the total electrolyte volume), and the intensity change of the maximum absorption peak at 500 nm was monitored using UV-Vis. Figure 9 (c) The degradation effect of Fe-NO / C type electro-Fenton catalyst on RhB at different times is as follows: Figure 9 As shown in d, the results indicate that the Fe-NO / C electro-Fenton catalyst has a significant effect on the electro-Fenton degradation of RhB. Within the first 20 minutes, the concentration of RhB decreased rapidly. By the 5th minute, the Fe-NO / C electro-Fenton catalyst had degraded 31.6% of the RhB, while by the 20th minute, the RhB concentration was less than 10 mg / L, only one-fifth of its original value. Due to the significant decrease in RhB concentration, the degradation of RhB by the Fe-NO / C electro-Fenton catalyst gradually slowed down. When degradation continued for 1 hour, although the RhB solution still had a visible purple-red color, its actual concentration decreased from the initial 50 mg / L to 0.89 mg / L, demonstrating the excellent degradation effect of the Fe-NO / C electro-Fenton catalyst on RhB. Considering the large specific surface area of ​​the Fe-NO / C electro-Fenton catalyst and the high catalyst loading in the degradation experiment, a control experiment was conducted under the same experimental conditions but without the applied voltage to avoid the illusion of efficient RhB degradation caused by physical adsorption. The results showed that, without current or voltage, the concentration of RhB decreased only slightly (<5%) in the first 5 minutes, and then tended to stabilize. Since RhB is a relatively stable and difficult-to-degrade organic dye, the effective degradation of RhB by the Fe-NO / C type electro-Fenton catalyst reflects the potential of this electrocatalytic material in the electro-Fenton degradation of organic pollutants.

[0058] To verify the potential of the prepared catalytic material in the degradation of antibiotic-containing pharmaceutical wastewater, a Fe-NO / C type electro-Fenton catalyst was used as the cathode, and electro-Fenton degradation of metronidazole (MTZ) solution was directly carried out under the drive of a DC regulated power supply. MTZ is a widely used antibiotic, mainly for treating anaerobic bacterial and protozoal infections. It is highly soluble in water, difficult to biodegrade, and has side effects including neurotoxicity and genotoxicity. Its release into the environment easily leads to drug resistance. Therefore, using MTZ as a model to study the degradation performance of antibiotic-containing pharmaceutical wastewater is representative. Figure 10 In the figure, 'a' represents the UV absorption spectra of MTZ solutions at different concentrations. A significant absorption is observed at 320 nm, which is taken as the wavelength of maximum absorption. A plot of concentration versus absorption intensity at the maximum absorption wavelength is then performed. After linear fitting, R0... 2 The value is 0.999, which meets the requirements of the standard curve. Figure 10(b) Furthermore, samples were taken at different times during the electro-Fenton degradation process, and the sample solutions had the same maximum absorption wavelength as the standard solutions ( Figure 10 (c) Using the absorbance at the maximum absorption wavelength as a quantitative standard, it was found that the MTZ degradation rate reached approximately 15% after 5 minutes of degradation, demonstrating that the prepared catalytic material (electrode) has a significant MTZ degradation capacity. After 1 hour of continuous degradation, the MTZ degradation rate was 71.72%, indicating that the Fe-NO / C type electro-Fenton catalyst has high MTZ degradation efficiency. Based on the MTZ degradation experiment, it can be demonstrated that the electro-Fenton degradation method using the Fe-NO / C type electro-Fenton catalyst as the electrode material has good potential for the harmless treatment of pharmaceutical wastewater containing antibiotics, and is expected to be further developed and applied.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Fe-NO / C type electro-Fenton catalyst, characterized in that, Polyamine oxime and Fe 3+ After chelation, a Fe-N2O2 pre-coordinated structure is formed. Pyrolysis yields a Fe-NO / C type electro-Fenton catalyst with a Fe-N2O2 single-atom structure. Polyamine oxime and Fe 3+ The mass ratio is 1:0.3~0.5; The Fe-NO / C type electro-Fenton catalyst is used for the degradation of antibiotic pharmaceutical wastewater.

2. The Fe-NO / C type electro-Fenton catalyst according to claim 1, characterized in that, The Fe 3+ It comes from soluble iron salts such as ferric nitrate or ferric chloride.

3. The Fe-NO / C type electro-Fenton catalyst according to claim 1, characterized in that, The poly(ammoxime) is obtained by ammoximation reaction of polyacrylonitrile as a raw material.

4. A method for preparing the Fe-NO / C type electro-Fenton catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: Hydroxylamine hydrochloride and N,N-dimethylformamide were mixed at a mass-to-volume ratio of 1 g: 10 mL to 20 mL. Under an organic cyclic environment, an alkali was added to neutralize the HCl in the hydroxylamine hydrochloride. NH3OH was then added. + The hydroxylamine solution is obtained by converting it into free NH2OH. Polyacrylonitrile powder and N,N-dimethylformamide are mixed at a mass-volume ratio of 1g:10~20mL to obtain a polyacrylonitrile solution. A polyacrylonitrile solution and a hydroxylamine solution were mixed and subjected to a methine oxime reaction at 45℃~65℃ for 12h~24h, followed by purification to obtain polymethine oxime; wherein the mass ratio of polyacrylonitrile to hydroxylamine hydrochloride was 1:1.3~1.

5. Ferric nitrate or ferric chloride is mixed with poly(amine oxime) in water and reacted for 12-24 hours. The precipitate is then collected by centrifugation. The precipitate is kept at 850-950℃ for 60-120 minutes and then acid-washed to obtain the Fe-NO / C type electro-Fenton catalyst.

5. The preparation method according to claim 4, characterized in that, The purification refers to displacement purification using a mixture of ethanol and ethyl acetate in equal volume ratios.

6. The preparation method according to claim 4, characterized in that, The particle size of the poly(amine oxime) is 50 μm to 100 μm.

7. The application of the Fe-NO / C type electro-Fenton catalyst according to any one of claims 1 to 3 in the degradation of antibiotic pharmaceutical wastewater.

8. The application according to claim 7, characterized in that, The antibiotic in the antibiotic pharmaceutical wastewater is metronidazole, and the organic impurity is rhodamine B.

9. The application of the Fe-NO / C type electro-Fenton catalyst according to claim 7 in the degradation of antibiotic pharmaceutical wastewater, wherein a substrate coated with the Fe-NO / C type electro-Fenton catalyst is used as the working electrode, Ag / AgCl is used as the reference electrode, and an inert material is used as the auxiliary electrode to form a three-electrode system; Antibiotics in pharmaceutical wastewater were degraded using a three-electrode system; among which... The loading of Fe-NO / C type electro-Fenton catalyst in the working electrode is not less than 1 mg / cm³. 2 .

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