Nitrogen-doped carbon nanofiber membrane anchored with ultrafine Fe-Mn bimetallic nanoparticles for flow-through electro-Fenton degradation of organic pollutants

Abstract

The present invention discloses a nitrogen-doped carbon nanofiber membrane anchored with ultrafine Fe-Mn bimetallic nanoparticles for flow-through electro-Fenton degradation of organic pollutants, belonging to the field of organic pollutant degradation. The nitrogen-doped carbon nanofiber membrane anchored with ultrafine Fe-Mn bimetallic nanoparticles is highly connected by nitrogen-doped carbon nanofibers, wherein the Fe-Mn bimetallic crystals are uniformly coated in the form of ultrafine particles in the fibers. Its preparation method comprises the following steps: using FeMn LDHs prepared by reacting a manganese source and an iron source as a metal source, mixing with polyacrylonitrile, and preparing a FeMn LDHs / PAN nanofiber membrane by electrospinning; performing carbonization treatment on the FeMn LDHs / PAN nanofiber membrane to obtain a FeMn / N-CNF nanofiber membrane. The present invention discloses a novel FeMn / N-CNF porous cathode membrane with strong metal-support interaction force, which can be combined with an IrO2 / RuO2-Ti electrode to construct a flow-through electro-Fenton membrane reactor with good anti-scaling ability. It can efficiently and stably purify organic wastewater in a wide pH range and meet the requirements of practical applications.

Description

Technical Field

[0001] The invention relates to the field of organic pollutant degradation, and in particular to a nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles for use in flow-through electro-Fenton degradation of organic pollutants. Background Art

[0002] With the rapid development of industry and agriculture, persistent pollutants have posed a huge challenge to water pollution control. Membrane filtration technology has the advantages of low energy consumption, simple operation, high interception efficiency, and environmental friendliness. It is an efficient water purification technology. However, pollutant clogging and membrane fouling are two inevitable problems that reduce membrane performance, which leads to the fact that the removal effect of persistent pollutants by traditional membrane filtration technology is always unsatisfactory. In order to solve the above problems, coupling membrane technology with electro-Fenton technology into membrane electro-Fenton is a feasible approach. On the one hand, pollutants in wastewater and foulants deposited on the membrane can be degraded by hydroxyl radicals (·OH) generated by electro-Fenton; on the other hand, compared with traditional batch electrochemistry, electro-Fenton membrane as a flow membrane electrode can significantly improve the kinetics and efficiency of the pollutant removal process. Despite these advantages, the high cost of catalysts, easy electrochemical corrosion, and unstable structure have limited the development of membrane electro-Fenton technology.

[0003] Carbonaceous materials have attracted the interest of researchers due to their low price, good conductivity and corrosion resistance. 3 The lack of hybrid carbon and the low efficiency of hydrogen peroxide generation greatly limit its application in membrane electro-Fenton systems. Current studies have shown that nitrogen doping can increase the Fermi level of carbon materials, enhance the adsorption of OOH· intermediates, and promote the generation of hydrogen peroxide. Among them, polyacrylonitrile (PAN) is an attractive precursor for N-doped carbon due to its high nitrogen content and good thermal stability. It is formed into a porous membrane composed of nitrogen-doped carbon nanofibers through electrospinning and carbonization processes. This membrane has a high specific surface area, high conductivity and excellent mechanical strength. However, such nitrogen-doped carbon electro-Fenton membranes still have problems such as poor hydrogen peroxide utilization and a narrow applicable pH range. Therefore, it is still a great challenge to explore new modification methods to improve its hydrogen peroxide activation rate and pH application range.

[0004] Transition metals (such as Fe and Mn) have excellent hydrogen peroxide activation ability due to the energy and spatial distribution characteristics of their d-orbital valence electrons. Considering the advantages of metal species and nitrogen-doped carbon nanofibers, the catalytic degradation ability of the electro-Fenton cathode film can be effectively improved by combining metal species with nitrogen-doped carbon materials through the synergistic effect between the carbon skeleton and the metal center. However, the intrinsic chemical inertness of the carbon surface often leads to weak interactions between the metal and the carbon carrier, which inevitably leads to problems such as low electron transfer efficiency and active metal leaching. In addition, during the high-temperature carbonization process, the weak interaction between the metal species and the carrier will lead to the migration and agglomeration of metal particles, thereby inhibiting the improvement of catalytic performance. Therefore, how to enhance the interaction between metal particles and nitrogen-doped carbon while inhibiting the occurrence of metal sintering during high-temperature carbonization is a research direction for improving the electro-Fenton performance. Summary of the invention

[0005] The purpose of the present invention is to provide a nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles for flow-through electro-Fenton degradation of organic pollutants to solve the above-mentioned problems in the background technology. The present invention discloses a novel FeMn / N-CNF porous cathode membrane with strong metal support interaction (SMSI), which is combined with IrO2 / RuO2-Ti electrodes to construct a flow-through reactor, which can perform efficient electro-Fenton degradation of various organic pollutants in a wide pH range.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide a nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles, which is formed by highly connected nitrogen-doped carbon nanofibers, wherein the Fe-Mn bimetallic crystals are in the form of ultrafine particles and are uniformly coated in the nitrogen-doped carbon nanofibers.

[0008] The pore size of the nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles is 100-2000nm, the diameter of the nitrogen-doped carbon nanofibers is 20-200nm, and the particle size of the Fe-Mn bimetallic nanoparticles is 3-5nm.

[0009] The second technical solution of the present invention is to provide a method for preparing the nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles, comprising the following steps:

[0010] Using a manganese source and an iron source as precursors, reacting to prepare an iron-manganese layered double hydroxide;

[0011] The FeMnLDHs / PAN nanofiber membrane is prepared by using the FeMnLDHs as a metal source and mixing it with polyacrylonitrile through electrospinning;

[0012] The FeMn LDHs / PAN nanofiber membrane is carbonized to obtain the nitrogen-doped carbon nanofiber membrane.

[0013] Preferably, the preparation method is as follows:

[0014] The manganese source and the iron source are dissolved in water, urea and NH4F are added to obtain a mixed solution, and the solution is heated to obtain an iron-manganese layered double hydroxide;

[0015] The iron-manganese layered double hydroxide and polyacrylonitrile are dissolved in DMF to obtain a spinning solution, and electrospinning is performed to obtain a FeMn LDHs / PAN nanofiber membrane;

[0016] The FeMn LDHs / PAN nanofiber membrane is subjected to a pre-oxidation treatment and then to a carbonization treatment to obtain the nitrogen-doped carbon nanofiber membrane.

[0017] After PAN and FeMn LDHs were mixed and electrospun, the mechanical strength was enhanced by pre-oxidation, and finally the FeMn / N-CNF porous membrane was obtained by carbonization under oxygen-free conditions.

[0018] Preferably, the manganese source is manganese chloride, and the iron source is ferric chloride; the molar ratio of the manganese source, the iron source, urea and NH4F is 10-20:40-50:20-30:10-20; and the heating is heating at 110-130°C for 10-15h.

[0019] Preferably, the mass ratio of the iron-manganese layered double hydroxide to polyacrylonitrile is 0.01-0.10:1-10.

[0020] Preferably, the voltage of the electrospinning is 10-15 kV, and the flow rate is 0.01-0.02 mL·min -1 , humidity is 10-20%, and temperature is 20-30℃.

[0021] Preferably, the pre-oxidation treatment is carried out in an air atmosphere at 1-5°C·min -1 The temperature is raised to 200-250°C and then pre-oxidized for 30-60 minutes; the carbonization treatment is carried out under N2 atmosphere at 1-5°C·min -1 Heat to 600-1200℃ and carbonize for 30-120min.

[0022] The third technical solution of the present invention is to provide a flow-through electro-Fenton reactor, using the nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles as the cathode and the IrO2 / RuO2-Ti electrode as the anode; the applied voltage of the flow-through electro-Fenton reactor is -0.3 to -0.8V, and the pure water flux is 0.5 to 2mL cm-2 ·min -1 .

[0023] The fourth technical solution of the present invention is to provide an application of the above-mentioned flow-through electro-Fenton reactor in the field of degradation of organic pollutants.

[0024] The beneficial technical effects of the present invention are as follows:

[0025] The present invention provides a nitrogen-doped carbon nanofiber (FeMn / N-CNF) porous membrane anchored by ultrafine iron-manganese bimetallic nanoparticles. After research by the present invention, it was found that the alloy effect between the iron-manganese bimetallic significantly increased the number of metal-nitrogen bonds, and achieved a strong interaction between the iron-manganese bimetallic particles and the N-CNF. Such SMSI induces the coating of the iron-manganese metal particles by the carbon layer during the high-temperature carbonization process, thereby ensuring the ultrafine characteristics of the metal particles. In addition, the present invention designs a new gravity-driven flow-type membrane electro-Fenton system based on the FeMn / N-CNF porous membrane, which can stably and efficiently degrade rhodamine B in a wide pH range (3-9), and achieves a degradation efficiency of more than 90% within 60 minutes. The prepared FeMn / N-CNF porous membrane is composed of highly connected nanofibers, and the FeMn / N-CNF has a multi-pore feature, which provides a prerequisite for the gravity-driven operation of the flow-type membrane electro-Fenton system.

[0026] The present invention discloses a novel FeMn / N-CNF porous cathode membrane with SMSI effect, which can perform efficient electro-Fenton degradation of various organic pollutants in a wide pH range. During the high-temperature carbonization process, the SMSI-induced carbon encapsulation structure promotes the formation of ultrafine FeMn bimetallic nanoparticles in N-CNF, thereby increasing the number of active sites. At the same time, the presence of SMSI promotes the electron transfer between the FeMn bimetallic nanoparticles and the N-CNF carrier, and enhances the electro-Fenton reaction activity of the porous membrane. In addition, the carbon encapsulation structure prevents the active FeMn bimetallic nanoparticles from leaching into the aqueous solution environment, thereby ensuring good stability and reusability. Therefore, the membrane reactor designed based on the FeMn / N-CNF porous cathode membrane has a degradation rate of 96.8% of rhodamine B within 60 minutes, and has excellent degradation performance. After 5 cycles of stability experiments, FeMn / N-CNF maintains good degradation performance. The present invention not only promotes the research on the SMSI effect on carbon carriers, but also provides a new modification idea for the development of electro-Fenton membranes, which is helpful for designing stable and efficient membrane electro-Fenton reactors in a wide pH range. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 Schematic diagram of the synthesis of FeMn / N-CNF in Example 1.

[0029] Figure 2 This is the H2O2 standard curve in Part 1.2 of the effect verification.

[0030] Figure 3 This is the structural schematic diagram and actual picture of the flow membrane electro-Fenton degradation experimental device in Part 1.4 of the effect verification.

[0031] Among them, (a) is a structural diagram, and (b) is a physical picture.

[0032] Figure 4 2. The XRD patterns of FeMn / N-CNF in Example 1 and N-CNF in Comparative Example 1.

[0033] Figure 5 It is the morphology analysis diagram of FeMn / N-CNF in Example 1. Among them, (a) is a macroscopic photo, (b) and (c) are SEM images at different magnifications, (d) is a TEM image, (e), (f) and (g) are HR-TEM images at different magnifications, (h) and (i) are images after fast Fourier transformation of different parts, (j) is a HAADF-HRTEM image, (k) is a mapping diagram of N elements, (l) is a mapping diagram of C elements, (m) is a mapping diagram of Fe elements, and (n) is a mapping diagram of Mn elements.

[0034] Figure 6 It is the morphology analysis diagram of Fe / N-CNF in comparative example 1. Among them, (a) is a TEM image, and (b) is a HADDF-TEM image.

[0035] Figure 7XPS spectrum analysis of FeMn / N-CNF in Example 1 and Fe / N-CNF, Mn / N-CNF, and N-CNF in Comparative Example 1. Among them, (a) is the N1s XPS spectrum of FeMn / N-CNF, Fe / N-CNF, Mn / N-CNF, and N-CNF, (b) is the nitrogen species content diagram of FeMn / N-CNF, Fe / N-CNF, Mn / N-CNF, and N-CNF, (c) is the Mn 2p XPS spectrum of FeMn / N-CNF and Mn / N-CNF, and (d) is the Fe 2p XPS spectrum of FeMn / N-CNF and Fe / N-CNF.

[0036] Figure 8 The stress-deformation diagram and tensile-strain curve of FeMn / N-CNF in Example 1. Among them, (a) is the stress-deformation diagram, and (b) is the tensile-strain curve.

[0037] Fig. 9 Electrochemical characterization analysis of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, N-CNF in Comparative Example 1. (a) is the cyclic voltammetry curve, and (b) is the polarization curve at 1600 rpm and the H2O2 oxidation curve on the ring electrode.

[0038] Fig.10 The Rhb degradation and pseudo-first-order degradation kinetic constants of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, Fe+Mn / N-CNF, and N-CNF in Comparative Example 1 are shown. Among them, (a) is the Rhb degradation, and (b) is the pseudo-first-order degradation kinetic constant.

[0039] Fig.11 The degradation of Rhb and the pseudo-first-order degradation kinetic constant of FeMn / N-CNF at different reaction potentials in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant.

[0040] Fig.12 The degradation of Rhb and the pseudo-first-order degradation kinetic constant of FeMn / N-CNF at different pH values ​​in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant.

[0041] Fig.13 This is the degradation performance of FeMn / N-CNF in Example 1 in the cycle experiment.

[0042] Fig.14The product performance data of FeMn / N-CNF under humic acid interference in Example 1. Among them, (a) is the degradation of Rhb and the pseudo-first-order degradation kinetic constant, (b) is the pure water flux and tensile strength before and after degradation, and (c) is the SEM image before and after degradation.

[0043] Fig.15 The performance of generating hydrogen peroxide of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF and N-CNF in Comparative Example 1.

[0044] Fig.16 The performance of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, and N-CNF in Comparative Example 1 in terms of activated hydrogen peroxide.

[0045] Fig.17 The product performance data of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and N-CNF in Comparative Example 1 under different free radical scavengers. Among them, (a) is the Rhb degradation of FeMn / N-CNF, (b) is the pseudo-first-order degradation kinetic constant of FeMn / N-CNF, (c) is the pollution-free EPR spectrum of FeMn / N-CNF, FeMn / N-CNF-AF and N-CNF using DMPO spin trapping in the electric Fenton system, and (d) is the degradation mechanism diagram of the electric Fenton system of FeMn / N-CNF.

[0046] Fig.18 The product performance data of FeMn / N-CNF under different pollutant conditions in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant. DETAILED DESCRIPTION

[0047] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0048] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0049] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the invention pertains. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention.

[0050] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0051] The relevant parameters of the experimental reagents used in the following embodiments and comparative examples of the present invention are shown in Table 1.

[0052] Table 1 Reagents used in the experiment

[0053]

[0054]

[0055] The relevant parameters of the experimental instruments used in the following embodiments and comparative examples of the present invention are shown in Table 2.

[0056] Table 2 Instruments used in the experiment

[0057] Instrument Name model Manufacturer Electrochemical workstation CHI660E Shanghai Chenhua Rotating Ring Disk Electrode HP-1A Jiangsu Jiangfen Tube Furnace OTF-1200X Hefei Kejing Electrospinning Machine DH-001 Tianjin Nayi Muffle furnace KSL-1000X-S Hefei Kejing UV-Vis Spectrophotometer UV-9000S Shanghai Yuanxi Electronic universal testing machine MTSE43.104 MTS Systems High performance liquid chromatography-mass spectrometry 2695-2996, ZQ2000 Waters Photochemical contact angle meter SDC-100 SINDIN Electron Spin Resonance Analyzer EMXPLUS Bruker X-ray diffractometer D8 ADVANCE Bruker X-ray Photoelectron Spectroscopy Axis Ultra DLD Kratos Field Emission Scanning Electron Microscope MIRA4 TESCAN Field Emission Transmission Electron Microscopy TF20 FEI Laser Confocal Raman Spectrometer LabRAM HR Evolution Horiba Scientific Inductively Coupled Plasma Optical Emission Spectrometer ICP-OES730 Agilent

[0058] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0059] Example 1

[0060] Preparation of FeMn / N-CNF materials

[0061] (1) Preparation of FeMn LDHs: Manganese chloride and ferric chloride were selected as precursors, and FeMnLDHs were synthesized by hydrothermal method. The specific preparation process is as follows: 0.2436g FeCl3·6H2O (15mM) and 0.5346g MnCl2·4H2O (45mM) were dissolved in 50mL deionized water (DI), and 1.5014g urea (25mM) and 0.37g NH4F (10mM) were added to obtain a mixed solution; after ultrasonicating the mixed solution for 30min, the obtained solution was transferred to a polytetrafluoroethylene high-temperature reactor, heated at 120℃ for 12h, taken out, filtered, and the obtained product was vacuum dried at 60℃ for 12h to obtain FeMn LDHs.

[0062] Meanwhile, Mn LDHs and FeLDHs were obtained by omitting only FeCl3·6H2O and only MnCl2·4H2O.

[0063] (2) Preparation of FeMn LDHs / PAN nanofiber membrane: FeMn LDHs was used as a metal source and mixed with PAN (polyacrylonitrile) to prepare FeMn LDHs / PAN nanofiber membrane by electrospinning. The specific preparation process is as follows: 0.03g FeMn LDHs and 1g PAN were mixed and added to 10mL DMF, and after stirring for 12h, a completely dissolved spinning solution was obtained, which was then electrospun; the electrospinning process was carried out on an electrospinning device (DH-001), and the mixed spinning solution was transferred to a 10mL syringe, and then electrospun on a drum collector covered with aluminum foil through an injection needle (23G) (the distance from the tip to the collector was 17.5cm, the applied voltage was 12kV, and the flow rate was 0.013mL min -1 , humidity 10-20%, temperature 25°C), the FeMn LDHs / PAN nanofiber membrane was collected and dried at 60°C for 12h to remove the residual solvent.

[0064] (3) Preparation of FeMn / N-CNF-AF membrane

[0065] FeMn / N-CNF membrane was prepared by two-step heating using FeMn LDHs / PAN nanofiber membrane as precursor. The specific preparation process was as follows: First, the dried FeMn LDHs / PAN nanofiber membrane was heated at 1°C min in air atmosphere. -1 After heating to 240℃, the product was pre-oxidized for 50min and then heated at 1℃·min in N2 atmosphere. -1 After heating to 900℃ and carbonizing for 60min, FeMn / N-CNF was obtained; then FeMn / N-CNF was pickled in 2M H2SO4 at 60℃ for 12h to remove all nanoparticles to obtain FeMn / N-CNF-AF.

[0066] Figure 1 Schematic diagram of the synthesis of FeMn / N-CNF in Example 1.

[0067] Comparative Example 1

[0068] The only difference from Example 1 is that the FeMn LDHs in step (2) are replaced by equal masses of Mn LDHs, FeLDHs and mixed LDHs (molar ratio, Mn LDHs:Fe LDHs=3:1) to prepare Fe / N-CNF, Mn / N-CNF and Fe+Mn / N-CNF; N-CNF is prepared by omitting only the metal source in step (2).

[0069] Effect verification

[0070] 1. Detection method

[0071] 1.1 Detection of pollutants

[0072] The absorbance A of the sample to be tested was detected by UV-9000S spectrophotometer, and the detection wavelength was 358nm (TC), 554nm (RhB), and 462nm (MO), and the absorbance of each sample was recorded. The sample concentration C was obtained by Lambert-Beer law (Formula 2-1):

[0073] A=abC#(2-1)

[0074] Among them, A is absorbance, a is absorption coefficient, b is optical path length, and C is sample concentration.

[0075] The pollutant removal rate is calculated by formula 2-2:

[0076]

[0077] Where C0 and C t represent the concentration of TC at the initial and reaction time (t), respectively.

[0078] Degradation kinetic constant (K app ) through ln(C0 / C t ) and time t (Formula 2-3) yields:

[0079]

[0080] Where C0 and C t represent the concentration of pollutants at the initial and reaction time (t), respectively.

[0081] 1.2 Determination of H2O2 content in solution

[0082] In this paper, potassium titanium oxalate spectrophotometry is used to determine the concentration of H2O2 generated in the reaction system. The specific steps are: use the gradient method to prepare the H2O2 standard solution, with 0mmol / L, 0.2mmol / L, 0.4mmol / L, 0.6mmol / L, 0.8mmol / L, and 1mmol / L as the gradient, and dilute the 10mmol / LH2O2 mother solution step by step to the target concentration. Use a pipette to accurately transfer the mother solution into the colorimetric tubes, mix it with 2mL of 2.4mol / L sulfuric acid solution to keep the reaction system at a certain acidity to eliminate the influence of impurity ions, add 1mL of 0.08mol / L potassium titanium oxalate solution as a color developer and make the volume to 5mL. After 10 minutes of color development, use an ultraviolet spectrophotometer to measure its absorbance at the maximum absorption wavelength of 400nm, and calculate it. Figure 2 The H2O2 standard curve is shown.

[0083] Figure 2This is the H2O2 standard curve in Part 1.2 of the effect verification.

[0084] 1.3 Electrochemical performance test

[0085] The membrane was analyzed by cyclic voltammetry (CV) using a CHI660E electrochemical workstation with 100mM Na2SO4 solution as the electrolyte. The test was conducted with 0.1M Na2SO4 solution as the electrolyte (pH=7), and a Pt sheet and a saturated calomel electrode were used as the counter electrode and reference electrode, respectively. The catalytic membrane was ground into powder, and 10mg of the catalyst was ultrasonically dispersed in a mixed solution of 0.48mL ultrapure water, 0.50mL isopropanol and 20μL Nafion solution as catalyst ink, and then 10μL of the catalyst ink was deposited on a glassy carbon electrode as the working electrode. The cyclic voltammetry (CV) test was performed in a saturated electrolyte solution of O2 or Ar at 50mV·s -1 The H2O2 selectivity of the catalysts was evaluated at a scanning rate of 1600 rpm based on a rotating disk electrode system. The ring potential was set at 1.45 V vs RHE, and the collection efficiency of the Pt ring was 0.37 after calibration.

[0086] 1.4 Electro-Fenton degradation experiment

[0087] The electro-Fenton performance of the catalytic membrane was evaluated by the degradation and mineralization of RhB. The universality of the catalytic membrane was demonstrated by the degradation of tetracycline hydrochloride and methyl orange, respectively. The filtration, adsorption and electrocatalytic performance of the catalytic membrane on pollutants (replacing O2 in EF with Ar) were used as control experiments. All degradation experiments were carried out in a homemade circulating electro-Fenton reactor with a reaction area of ​​3cm*3cm, with dead-end filtration under applied voltage. The experimental device (flowing membrane electro-Fenton degradation experimental device) is as follows: Figure 3 As shown in the figure, IrO2 / RuO2-Ti electrode was used as the counter electrode, FeMn / N-CNF catalytic membrane was used as the working electrode, and the pollutants were continuously fed into the quartz column using a peristaltic pump. The hollow quartz column with controllable flow rate was used to maintain 10 mL min -1 The flow rate flows into the reactor. In order to maintain a relatively stable pressure, a peristaltic pump is used to ensure that the pure water flux of the system is kept stable at 1 mL cm -2 ·min -1 . The target pollutant is 10mg·L -1 , pH was adjusted by 0.1M H2SO4 and NaOH solution. Unless otherwise specified, degradation was performed at pH = 7, with a working potential of -0.6 V vs SCE. Before degradation, the electrolyte containing pollutants was purged with O2 for 30 min to achieve oxygen saturation, and during the degradation process, the electrolyte was purged with O2 at 0.03 L min in the quartz column. -1O2 was introduced at a constant flow rate of . At given time intervals, 1.5 mL of sample was taken and immediately filtered through a 0.22 μm organic filter membrane, and 50 μL of methanol was added to quench the possible residual ·OH before analysis. The stability of the catalyst was tested by five consecutive degradation experiments of rhodamine B.

[0088] The contribution of each catalyst component to the two main steps of the electro-Fenton reaction was analyzed using a pollutant-free electro-Fenton system to speculate on the possible catalytic mechanism. The H2O2 generation and activation reactions were carried out in an H-type double-cell electrolytic cell, each containing 50mL of 0.05M Na2SO4 electrolyte. The concentration of H2O2 in the electrolyte was detected by potassium oxalate titanium spectrophotometry. DMPO was used as a spin trap, and the generated hydroxyl radicals were detected by electron spin resonance spectroscopy (EPR, Bruker EMXPLUS).

[0089] Figure 3 The schematic diagram and the actual picture of the flow membrane electro-Fenton degradation experimental device in Part 1.4 of the effect verification are shown in Figure 1. Among them, (a) is the schematic diagram and (b) is the actual picture.

[0090] 2. Characterization Methods

[0091] 2.1 X-ray diffraction (XRD)

[0092] The crystal structure of the sample was analyzed by D8 ADVANCE X-ray diffractometer, with Cu Kα ray (λ = 0.15418 nm) as the ray source and a scanning speed of 4° min -1 , the operating current and voltage were 40mA and 40kV, respectively, and all materials were scanned in the range of 10° to 80°.

[0093] 2.2 X-ray Photoelectron Spectroscopy (XPS)

[0094] The catalyst was analyzed by XPS using an Axis Ultra DLD X-ray photoelectron spectrometer to obtain the elemental and valence compositions of the sample.

[0095] 2.3 Field emission scanning electron microscopy (SEM)

[0096] The microstructure and morphology of the catalysts were characterized by MIRA4 field emission scanning electron microscope.

[0097] 2.4 High-resolution field emission transmission electron microscopy (HRTEM)

[0098] The samples were characterized using a TF20 high-resolution field emission transmission electron microscope equipped with an energy dispersive X-ray spectrometer (EDS) at an accelerating voltage of 200 kV, and the elemental distribution state of the catalyst was observed using a high-angle annular dark field scanning transmission electron microscope (HAADF-STEM).

[0099] 2.5 Laser Confocal Raman Spectroscopy (Raman)

[0100] The carbon defect content of the catalyst was analyzed using a HORIBA Scientific high-resolution Raman spectrometer with a wavelength of 532 nm.

[0101] 2.6 Inductively coupled plasma optical emission spectroscopy (ICP-OES)

[0102] ICPOES 730 inductively coupled plasma emission spectrometer was used to detect the content of metal Fe and Mn in the catalyst and the amount of metal ions leached during the electro-Fenton reaction.

[0103] 2.7 Electron paramagnetic resonance spectroscopy (EPR)

[0104] Using DMPO and TEMP as spin trapping agents, the active free radicals generated by the catalyst during the reaction were detected on an EMXPLUS electron spin resonance spectrometer.

[0105] 2.8 Photochemical Contact Angle Meter (WCA)

[0106] The SDC-100 photochemical contact angle meter was used to measure the change in water contact angle of the catalytic film to effectively evaluate the wettability of the catalytic film.

[0107] 3. Results Analysis

[0108] 3.1 Inductively coupled plasma optical emission spectroscopy (ICP-OES)

[0109] The content of metal elements in the product was determined by ICP-OES (Table 3). The test results showed that the Mn content in the catalytic film FeMn / N-CNF was 1.19wt%, which was significantly higher than the Fe content (0.5wt%), which may be due to the higher content of metal Mn in the metal source FeMn LDHs than the metal Fe. By adjusting the metal source, the contents of the prepared Mn / N-CNF and Fe / N-CNF were 2.69wt% (Mn) and 3.08wt% (Fe), respectively. The increase in metal content may be due to the lack of the addition of a second metal. The metal content of FeMn / N-CNF-AF after acid washing accounts for very little of the catalyst, indicating that the acid washing step successfully removed the metal from the catalytic film. At the same time, the test results of FeMn LDHs showed that the ratio of Fe element to Mn element was about 1:3, which was consistent with the ratio of the doped amount, indicating that FeMn LDHs was successfully synthesized.

[0110] Table 3 Metal content in the obtained products measured by ICP-OES

[0111]

[0112] 3.2 X-ray diffraction (XRD) crystal structure analysis

[0113] Figure 4 2. The XRD patterns of FeMn / N-CNF in Example 1 and N-CNF in Comparative Example 1.

[0114] Depend on Figure 4 It can be seen that both catalysts have characteristic peaks belonging to the (002) crystal plane of carbon (PDF#97-061-7290) at 20°~30°, indicating that the catalytic film was successfully carbonized when the temperature was raised to 900°C. Secondly, compared with N-CNF, FeMn / N-CNF has characteristic peaks belonging to the 031 crystal plane of FeMn2C (PDF#97-067-0828) at 40°~50°, indicating that FeMn2C nanoparticles are formed with the addition of FeMnLDHs.

[0115] 3.3 Material morphology analysis

[0116] Figure 5It is the morphology analysis diagram of FeMn / N-CNF in Example 1. Among them, (a) is a macroscopic photo, (b) and (c) are SEM images at different magnifications, (d) is a HAADF-STEM image, (e), (f) and (g) are HR-TEM images at different magnifications, (h) and (i) are images after fast Fourier transformation of different parts, (j) is a HAADF-STEM image, (k) is a mapping diagram of N elements, (l) is a mapping diagram of C elements, (m) is a mapping diagram of Fe elements, and (n) is a mapping diagram of Mn elements.

[0117] Among them, (f) and (g) are the enlarged images of the box area in (e), and (h) and (i) are the images after fast Fourier transformation of (f) and (g), respectively.

[0118] Depend on Figure 5 As shown in (b), the prepared FeMn / N-CNF porous membrane is composed of highly connected nanofibers, and FeMn / N-CNF has multi-pore characteristics, which provides a prerequisite for the gravity-driven operation of the flow membrane electro-Fenton system. Figure 5 As shown in (c) and (d), the nanofiber diameter is about 150nm and the membrane pore size is about 940nm. Although the XRD spectrum of FeMn / N-CNF ( Figure 4 ) has obvious characteristic peaks of FeMn2C, but Figure 5 No obvious large particles were observed in (d). The internal morphology of FeMn / N-CNF was further examined by high-resolution transmission electron microscopy (HR-TEM). In (d) and (e), a large number of ultrafine metal nanoparticles with a diameter of 3-5nm (shown in the red area) were uniformly anchored on the carbon nanofibers. Figure 5 (f) and (h) show that the ultrafine metal nanoparticles show obvious lattice stripes, but the presence of the carbon coating structure leads to low crystallinity of the metal nanoparticles. (g) and (i) show that the lattice spacing of the ultrafine metal nanoparticles is 0.2602nm, which matches the (031) crystal plane of FeMn2C shown by XRD, further indicating that the FeMn / N-CNF synthesis is successful. The mapping image of the high-angle annular dark field scanning transmission electron microscope (HADDF-STEM) shows that C, Fe, Mn and N elements exist on the nanofibers, further indicating that the ultrafine FeMn nanoparticles are uniformly coated in the nitrogen-doped carbon nanofibers.

[0119] Figure 6 It is the morphology analysis diagram of Fe / N-CNF in comparative example 1. Among them, (a) is a TEM image, and (b) is a HADDF-TEM image.

[0120] Depend on Figure 6 It can be seen that the Fe / N-CNF prepared with Fe LDHs as the single metal source exhibits morphological characteristics different from those of FeMn / N-CNF. Large nanoparticles with a particle size of about 20 nm can be clearly observed, which also explains the obvious Fe3C characteristic peak in the XRD spectrum of Fe / N-CNF.

[0121] 3.4 X-ray Photoelectron Spectroscopy (XPS)

[0122] Figure 7 XPS spectrum analysis of FeMn / N-CNF in Example 1 and Fe / N-CNF, Mn / N-CNF, and N-CNF in Comparative Example 1. Among them, (a) is the N1s XPS spectrum of FeMn / N-CNF, Fe / N-CNF, Mn / N-CNF, and N-CNF, (b) is the nitrogen species content diagram of FeMn / N-CNF, Fe / N-CNF, Mn / N-CNF, and N-CNF, (c) is the Mn 2p XPS spectrum of FeMn / N-CNF and Mn / N-CNF, and (d) is the Fe 2p XPS spectrum of FeMn / N-CNF and Fe / N-CNF.

[0123] In order to explore this coordination relationship, the types and contents of nitrogen species in different materials were analyzed. Figure 7 (a) shows that there are four nitrogen species, namely pyridinic-N (398.20 eV), pyrrolic-N (399.15 eV), graphitic-N (400.89 eV) and oxidized-N (403.51 eV); among them, pyridinic-N and pyrrolic-N are more inclined to combine with metals to form metal-nitrogen (MN) bonds. Figure 7 (b) shows that the content of pyridinic N and pyrrolic N in FeMn / N-CNF (52%) is higher than that in Fe / N-CNF (42%) and Mn / N-CNF (46%), indicating that the alloying effect between FeMn bimetallics can significantly increase the number of MN bonds. The enhanced chemical interaction between metal and nitrogen atoms improves the adhesion strength at the metal / support interface and realizes SMSI between FeMn metal and N-CNF. During the high-temperature carbonization process, such SMSI induces the formation of a carbon encapsulation structure ( Figure 5 (e)), inhibiting the migration and agglomeration of metal particles and promoting the formation of ultrafine particles. High-resolution Fe 2p spectrum ( Figure 7 (c)) deconvolutes into three peaks at about 710.00eV, 711.80eV, and 714.56eV, which are respectively attributed to Fe 2+ , Fe 3+ , sat.. Similarly, the Mn 2p spectrum ( Figure 7 (d)) is also deconvoluted into two manganese species, namely Mn2+ (641.20eV and 652.92eV) and Mn 3+ (643.18 eV and 655.12 eV). After the addition of the second metal, the peaks corresponding to Fe 2p and Mn 2p shifted to higher binding energies, indicating the increase of high-valent metal species. The change in valence state may be due to SMSI-induced electron transfer from metal to N-CNF.

[0124] 3.5 Material mechanical properties analysis

[0125] Excellent mechanical properties can ensure the excellent stability and durability of the catalytic membrane, so that it can work for a long time under actual working conditions. Therefore, the FeMn / N-CNF was subjected to a tensile test using an electronic universal testing machine, and the deformation degree of the membrane was observed after artificial stress was applied to jointly evaluate the mechanical properties of the membrane.

[0126] Figure 8 The stress-deformation diagram and tensile-strain curve of FeMn / N-CNF in Example 1. Among them, (a) is the stress-deformation diagram, and (b) is the tensile-strain curve.

[0127] pass Figure 8 As shown in (a), the catalytic membrane can still maintain its original structure and has good flexibility under a certain pressure, and (b) shows that the prepared FeMn / N-CNF membrane can withstand a tensile strength of ~2.02Mpa. The above results show that the prepared catalytic membrane has good mechanical strength, laying the foundation for good durability and stability.

[0128] 3.6 Electrochemical characterization analysis

[0129] In order to explore the electrochemical performance of the catalyst, the cyclic voltammetry curves of FeMn / N-CNF, FeMn / N-CNF-AF, N-CNF, Mn / N-CNF, and Fe / N-CNF were measured by cyclic voltammetry in an electrolyte solution (pH = 7) containing 0.1M Na2SO4 saturated with O2 or Ar to determine the ORR activity of the corresponding catalyst. To further explore the selectivity of the catalyst for oxygen reduction reaction, the two-electron ORR selectivity of the catalyst was evaluated using a rotating disk electrode.

[0130] Fig. 9 Electrochemical characterization analysis of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, N-CNF in Comparative Example 1. (a) is the cyclic voltammetry curve, and (b) is the polarization curve at 1600 rpm and the H2O2 oxidation curve on the ring electrode.

[0131] Among them, the solid line and dotted line in (a) represent the cyclic voltammetry curves in 0.1M Na2SO4 solution (pH=7) saturated with O2 and N2, respectively.

[0132] Fig. 9 (a) shows that the CV curves of FeMn / N-CNF, Mn / N-CNF, Fe / N-CNF, N-CNF and FeMn / N-CNF-AF have higher reaction currents in O2 saturated solution than in N2, indicating that all catalysts have considerable ORR activity. Among them, FeMn / N-CNF has a more positive peak potential than N-CNF and has better ORR activity, which can be attributed to the increase in the ratio of pyridinic-N to pyrrolic-N, which is positively correlated with ORR activity, due to the addition of metals ( Figure 7 (b)), further promoting the improvement of ORR activity. Fig. 9 (b) shows that the disk current and ring current of FeMn / N-CNF, Mn / N-CNF, Fe / N-CNF, N-CNF and FeMn / N-CNF-AF correspond to the two-electron oxygen reduction reaction and the activation of H2O2, respectively. The results show that N-CNF has the highest two-electron selectivity, so the addition of metals improves the ORR activity of carbon nanofibers, but reduces their two-electron selectivity.

[0133] 3.7 Effects of adsorption and electrocatalysis on the degradation performance of FeMn / N-CNF

[0134] Electrochemically assisted advanced oxidation technology has multiple catalytic reactions, so it is necessary to reveal the dominant catalytic reaction in the FeMn / N-CNF membrane electro-Fenton system. Therefore, the present invention investigates the degradation performance of FeMn / N-CNF for RhB in the membrane electro-Fenton mode and compares it with simple filtration adsorption and electrocatalytic performance. All experiments were carried out in a 0.1M Na2SO4 electrolyte solution with a pH of 7, and the catalytic membrane area was kept at 9 cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was continuously introduced during the reaction. For comparison, no additional voltage was applied to the filtration adsorption system. Ar was continuously introduced into the solution during the reaction, and the flow rate was maintained at 0.3 L min -1 The electrocatalytic system applied a reaction voltage of -0.6 V vs SCE, and Ar was introduced for 30 min before the reaction to reach argon saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0135] 3.8 Effect of Precursors on Electro-Fenton Degradation of RhB by Catalytic Membrane

[0136] In the previous characterization test, it was found that the introduction of the second metal would lead to an increase in the proportion of MN, which further led to a strong metal-support interaction, reflected in the formation of a carbon-coated ultrafine FeMn nanoparticle structure. In order to explore the effect of metal addition on the electro-Fenton degradation performance of the catalytic membrane and the effect of the ultrafine structure induced by SMSI on the electro-Fenton degradation of RhB, the degradation performance of the catalytic membrane prepared from precursors of different metal sources was tested by electro-Fenton. All experiments were carried out in a 0.1M Na2SO4 electrolyte solution with a pH of 7, and the catalytic membrane area was kept at 9cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min. -1 The flow rate was maintained during the reaction.

[0137] Fig.10 The Rhb degradation and pseudo-first-order degradation kinetic constants of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, Fe+Mn / N-CNF, and N-CNF in Comparative Example 1 are shown. Among them, (a) is the Rhb degradation, and (b) is the pseudo-first-order degradation kinetic constant.

[0138] Table 4 Comparison of FeMn / N-CNF and related literature

[0139]

[0140]

[0141] Fig.10 The results show that the degradation rate of pollutants in FeMn / N-CNF within 60 minutes is 96.8%, which is higher than that of Mn / N-CNF (86.2%), Fe / N-CNF (71.2%), NCNF (74.7%) and Fe+Mn / N-CNF (87.5%), indicating that FeMn / N-CNF has the best degradation activity for rhodamine b. Such excellent degradation performance is better than the degradation performance of various electro-Fenton membranes recently reported in the prior art (as shown in Table 4). The electro-Fenton degradation of RhB by catalytic membranes follows pseudo-first-order kinetics, and the kinetic constants are ranked as follows: FeMn / N-CNF (0.526min -1 )>Fe+Mn / N-CNF(0.0328min -1 )>Mn / N-CNF(0.0308min-1 )>N-CNF(0.0225min -1 )>Fe / N-CNF(0.019min -1 ), indicating that the degradation reaction of rhodamine B undergoes faster kinetics on the FeMn / N-CNF surface. To further explore the effect of ultrafine FeMn bimetallic nanoparticles, FeMn / N-CNF-AF obtained by acid washing of FeMn / N-CNF was subjected to electro-Fenton test. Compared with FeMn / N-CNF, FeMn / N-CNF-AF exhibited significantly lower rhodamine b degradation rate (69.3%) and degradation kinetics (0.0168 min -1 ). The above data results and analysis show that the synergistic effect between ultrafine FeMn nanoparticles and N-CNF can effectively improve the degradation efficiency of RhB.

[0142] 3.9 Effect of different reaction potentials on membrane electro-Fenton degradation of RhB

[0143] In actual degradation, reaction potential is a key factor in the membrane electro-Fenton system. Since it can directly affect the H2O2 generation capacity of the catalytic membrane, the ability to achieve efficient degradation in a wide potential range is the key to whether FeMn / N-CNF can be applied in practical scenarios. To this end, the present invention applies different reaction potentials to FeMn / N-CNF in the potential range of -0.3 to -0.8 V vs SCE to determine its degradation performance. All experiments were carried out in a solution of 0.1 M Na2SO4 electrolyte at a pH of 7, and the catalytic membrane area was kept at 9 cm- 2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0144] Fig.11 The degradation of Rhb and the pseudo-first-order degradation kinetic constant of FeMn / N-CNF at different reaction potentials in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant.

[0145] like Fig.11 At lower potentials, the degradation rate of FeMn / N-CNF gradually increases with the increase of applied potential, and the highest degradation performance is shown at an applied potential of -0.6 V vs SCE, with a pseudo-first-order degradation kinetic constant of 0.0526 min -1. This is attributed to more H2O2 generation and stronger oxidation. However, when the potential is further increased to -0.8V vs SCE, the degradation performance continues to decline. This is because the excessively high potential can easily further reduce the locally generated H2O2 molecules to H2O (Formula 2-4, 2-5, 2-6), resulting in a slowdown in the degradation rate. However, FeMn / N-CNF exhibits good rhodamine b degradation reaction kinetics in the entire potential range.

[0146] H2O2+·OH→H2O+·OOH#(2-4)

[0147] 2H2O2→2H2O+O2#(2-5)

[0148] 2H2O2→2H2O+O2#(2-6)

[0149] 3.10 Effect of different pH values ​​on membrane electro-Fenton degradation of RhB

[0150] The narrow pH range is a defect of the previous electro-Fenton system. A wide pH range of degradation can further demonstrate the universality of FeMn / N-CNF, especially the ability to maintain good electro-Fenton degradation performance under alkaline conditions.

[19] Therefore, the present invention tests the degradation of RhB by membrane electro-Fenton at a pH range of 3-9. All experiments were conducted in a 0.1 M Na2SO4 electrolyte solution, and the catalytic membrane area was kept at 9 cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0151] Fig.12 The degradation of Rhb and the pseudo-first-order degradation kinetic constant of FeMn / N-CNF at different pH values ​​in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant.

[0152] like Fig.12As shown. Under the conditions of pH = 3, 5, 7, and 9, FeMn / N-CNF achieved a degradation performance of more than 90% of pollutants within 60 minutes, and the degradation rates were close, revealing its adaptability to pH. Thanks to the SMSI-induced carbon encapsulation structure, the metal leaching amount of FeMn / N-CNF in the range of pH = 3-9 is negligible (Table 5), achieving efficient degradation of FeMn / N-CNF in a wide pH range. Overall, FeMnC / NCNF-900 achieved efficient degradation in a wide pH range, which has certain practical significance.

[0153] Table 5 Metal element contents in metal leaching tests measured by ICP-OES

[0154] pH <![CDATA[Fe(mg L -1 )]]> <![CDATA[Mn(mg L -1 )]]> 3 0.0048 0.0147 5 0.0043 0.0038 7 0.0025 0.0012 9 0.0037 0.0020

[0155] 3.11 Study on the Cyclic Stability of FeMn / N-CNF

[0156] Because the catalyst exists in the form of a membrane, the catalytic membrane can be easily recovered for reuse. However, being able to be used repeatedly and maintain good performance is another key indicator of whether the catalytic membrane has practical application value. At the same time, in actual water treatment, membrane fouling and scaling problems limit the application of the membrane. Being able to achieve long-term stable and efficient degradation while achieving efficient anti-fouling ability is a prerequisite for the practical application of the membrane electro-Fenton system. Therefore, the present invention evaluates the sustainable electro-Fenton performance of the catalytic membrane through 5 cycles of degradation, and evaluates the anti-fouling and anti-scaling ability of the catalytic membrane by characterizing the morphology and internal structure of the catalytic membrane after five reactions. The five degradation experiments were all carried out in a 0.1M Na2SO4 electrolyte solution with a pH of 7, and the catalytic membrane area was maintained at 9cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0157] Fig.13 This is the degradation performance of FeMn / N-CNF in Example 1 in the cycle experiment.

[0158] like Fig.13 As shown, the degradation performance of the FeMn / N-CNF membrane reactor only decreased slightly after five cycles, indicating its good catalytic stability.

[0159] 3.12 Study on the interference of humic acid on the degradation performance of FeMn / N-CNF

[0160] Humic acid present in actual wastewater may interfere with the degradation of pollutants by contaminating the membrane surface, thus negatively affecting the degradation process. -1 The pH of Humic Acid (HA) was 7, and the electrolyte solution was 0.1M Na2SO4. The catalytic membrane area was kept at 9 cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 Electro-Fenton experiments were conducted to evaluate the application prospects of FeMn / N-CNF in complex water matrices. The experiments were all conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min. -1 The flow rate was kept constant during the reaction. To further evaluate the effect of HA, permeability and tensile strength measurements were performed.

[0161] Fig.14 The product performance data of FeMn / N-CNF under humic acid interference in Example 1. Among them, (a) is the degradation of Rhb and the pseudo-first-order degradation kinetic constant, (b) is the pure water flux and tensile strength before and after degradation, and (c) is the SEM image before and after degradation.

[0162] result( Fig.14 (a) shows that the degradation efficiency of pollutants in FeMn / N-CNF is not significantly affected by HA, indicating that the FeMn / N-CNF system has good tolerance to NOM interference in water treatment. It shows that FeMn / N-CNF has great potential for wastewater purification as an electro-Fenton cathode membrane under complex conditions.

[0163] Fig.14 The results shown in (b) show that the pure water flux and tensile strength of FeMn / N-CNF containing HA before and after degradation of RhB did not change significantly, indicating its excellent mechanical stability. The FeMn / N-CNF samples after reaction were characterized by scanning electron microscopy to further evaluate their self-cleaning ability. No fiber breakage or pore blockage was observed on the surface of the porous membrane after degradation ( Fig.14 (c)), indicating that the FeMn / N-CNF cathode has excellent morphological and structural stability. In summary, the FeMn / N-CNF membrane filter has significant antifouling ability and sustainable degradation stability, and has broad application prospects in actual wastewater treatment.

[0164] 3.13 Study on the performance of FeMn / N-CNF in generating H2O2

[0165] The generation of H2O2 is the rate-limiting step of the electro-Fenton reaction, which has a huge impact on the performance of electro-Fenton in degrading organic pollutants. Therefore, effectively evaluating the performance of the catalytic membrane in generating H2O2 by two-electron ORR is one of the keys to explaining the internal mechanism of the efficient degradation performance of the catalytic membrane. The present invention conducts experiments in a single-chamber electrolytic cell without pollutants to detect the amount of H2O2 generated, and determines the effect of the catalytic membrane prepared by different metal sources on the accumulation of H2O2 under the conditions of the presence or absence of metals and the strength of the interaction between metal carriers. All experiments were conducted in a 0.1M Na2SO4 electrolyte solution maintained at a pH of 7, and the catalytic membrane area was maintained at 9 cm -2 All experiments were conducted in a flow reactor. The voltage applied to the reaction system was -0.6 V vs SCE, and Ar was introduced for 30 min before the reaction to reach argon saturation and then maintained at 0.3 L min. -1 The flow rate was maintained during the reaction.

[0166] Fig.15 The performance of generating hydrogen peroxide of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF and N-CNF in Comparative Example 1.

[0167] like Fig.15 As shown in the figure, N-CNF has the highest H2O2 generation, followed by FeMn / N-CNF, Mn / N-CNF, Fe / N-CNF, and FeMn / N-CNF-AF. Combined with the electrochemical characterization described above, the present invention found that although FeMn / N-CNF has the strongest ORR activity ( Fig. 9 (a)), but the addition of metals leads to a decrease in the adsorption and desorption capacity of ·OOH, which ultimately leads to a decrease in its two-electron selectivity ( Fig. 9 (b)). It is worth noting that FeMn / N-CNF exhibits higher ORR activity and two-electron selectivity than Mn / N-CNF and Fe / N-CNF due to SMSI ( Fig. 9 ), and then reached a higher hydrogen peroxide production within 60 min (36.23 mmol L -1 )( Fig.15 ).

[0168] 3.14 Study on the performance of FeMn / N-CNF activated with H2O2

[0169] The H2O2 activation step is often the rate-determining step in the membrane electro-Fenton reaction and has a huge impact on the entire catalytic reaction. Therefore, the present invention effectively evaluates the H2O2 activation ability of each catalytic membrane under the condition of adding H2O2. In this regard, experiments were conducted in a single-chamber electrolytic cell without pollutants to detect the activation ability of H2O2. All experiments were conducted in a 0.1M Na2SO4 electrolyte solution maintained at a pH of 7, and the concentration of H2O2 was 50mmol L -1 , the catalytic membrane area is maintained at 9 cm -2 All experiments were conducted in a flow reactor. The voltage applied to the reaction system was -0.6 V vs SCE, and Ar was introduced for 30 min before the reaction to reach argon saturation and then maintained at 0.3 L min. -1 The flow rate was maintained during the reaction.

[0170] Fig.16 The performance of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and Fe / N-CNF, Mn / N-CNF, and N-CNF in Comparative Example 1 in terms of activated hydrogen peroxide.

[0171] like Fig.16 As shown in Figure 2, N-CNF has almost no ability to activate hydrogen peroxide, with an activation rate of only 0.0015 min L -1 After the introduction of Fe / Mn catalyst, the hydrogen peroxide activity rate of different catalytic membranes follows the FeMn / N-CNF (0.1024min L -1 )>Mn / N-CNF(0.0889min L -1 )>Fe / N-CNF(0.0331min L -1 )>N-CNF(0.0015min L -1 ). The results show that FeMn bimetallic nanoparticles are the key catalytic sites for H2O2 activation. At the same time, the ultrafine characteristics of FeMn bimetallic nanoparticles increase the surface active area of ​​FeMn / N-CNF. In addition, the presence of SMSI can enhance the ability of the carrier to stabilize metal particles and promote electron transfer, which is beneficial to the stability of FeMn / N-CNF and the electro-Fenton reaction kinetics. These synergistic effects, coupled with the advantageous characteristics of the porous structure, enable FeMn / N-CNF to efficiently generate and activate hydrogen peroxide.

[0172] 3.15 Study on the degradation mechanism of RhB by FeMn / N-CNF membrane electro-Fenton system

[0173] In the EF reaction, reactive oxygen species (ROS) are considered to be the main active free radicals for the degradation of organic matter. In order to explore the existence of free radical species and the intrinsic reaction mechanism during the degradation of FeMn / N-CNF, a series of free radical capture experiments were carried out using tert-butyl alcohol (TBA, ·OH capture agent) and p-benzoquinone (p-BQ, ·O2- capture agent). All quenching experiments were carried out in a 0.1M Na2SO4 electrolyte solution with a pH of 7, and the catalytic membrane area was kept at 9 cm -2 The pollutant was modeled with RhB at a concentration of 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0174] Fig.17 The product performance data of FeMn / N-CNF, FeMn / N-CNF-AF in Example 1 and N-CNF in Comparative Example 1 under different free radical scavengers. Among them, (a) is the Rhb degradation of FeMn / N-CNF, (b) is the pseudo-first-order degradation kinetic constant of FeMn / N-CNF, (c) is the pollution-free EPR spectrum of FeMn / N-CNF, FeMn / N-CNF-AF and N-CNF using DMPO spin trapping in the electric Fenton system, and (d) is the degradation mechanism diagram of the electric Fenton system of FeMn / N-CNF.

[0175] like Fig.17 As shown in Figure 2, the degradation rate of FeMn / N-CNF dropped sharply to 0.0204 min L after adding tert-butyl alcohol. -1 , while the addition of benzoquinone did not lead to significant changes in catalytic performance. When the concentration of tert-butyl alcohol was increased to 1 M, the degradation rate slowed down to 0.0069 min L -1 The strongest quenching effect of tert-butyl alcohol indicates that ·OH is the main active oxygen species in the FeMn / N-CNF electro-Fenton reaction system. In order to explore the effect of FeMn bimetallic on ·OH generation, DMPO was used as a spin trapping agent for EPR experiments. Fig.17 As shown in (c), FeMn / N-CNF shows a four-fold characteristic peak belonging to the DMPO-OH intensity ratio of 1:2:2:1, which verifies the results of the quenching experiment. After acid washing, the characteristic peak intensity is significantly weakened, indicating that the amount of ·OH generated is reduced, which indicates that the presence of FeMn bimetallic nanoparticles promotes the generation of ·OH. Based on the above experiments, the possible reaction mechanism ( Fig.17(d) ), hydrogen peroxide is generated in situ on nitrogen-doped carbon nanofibers and then captured by metal nanoparticles anchored on the fibers and immediately converted into ·OH. The generated hydrogen peroxide also participates in the M 3+ In addition, applying a negative voltage to the cathode provides additional electrons, accelerating the M 3+ / M 2+ The redox cycle is conducive to the continuous and stable progress of the reaction. The electro-Fenton reaction is explained by the following equations (Formulas 2-7 to 2-14).

[0176] O2+2e - +H2O→H2O2#(2-7)

[0177] ≡Mn 3+ +e - →≡Mn 2+ #(2-8)

[0178] ≡Fe 3+ +e - →≡Fe 2+ #(2-9)

[0179] ≡Mn 2+ +H2O2→≡Mn 3+ + OH#(2-10)

[0180] ≡Fe 2+ +H2O2→≡Fe 3+ + OH#(2-11)

[0181] ≡Mn 3+ +H2O2→≡Mn 2+ +·OOH+H + #(2-12)

[0182] ≡Fe 3+ +H2O2→≡Fe 2+ +·OOH+H + #(2-13)

[0183] ≡Mn 3+ +≡Fe 2+ →≡Mn 2+ +≡Fe 3+ #(2-14)

[0184] 3.16 Study on the degradation performance of FeMn / N-CNF on different pollutants

[0185] Considering the complex water quality environment in the actual degradation reaction, the catalytic membrane is required to be able to cope with the challenges from different pollutants. To this end, the present invention compares the performance of FeMn / N-CNF in degrading different pollutants to evaluate the universality of FeMn / N-CNF. All experiments were carried out in a 0.1M Na2SO4 electrolyte solution with a pH of 7, and the catalytic membrane area was kept at 9 cm -2 The pollutants are TC, MO and RhB, and the concentration is 10 mg L -1 All experiments were conducted in a flow-through reactor. The voltage applied in the electro-Fenton system was -0.6 V vs SCE, and O2 was introduced for 30 min before the reaction to reach oxygen saturation and then maintained at 0.3 L min -1 The flow rate was maintained during the reaction.

[0186] Fig.18 The product performance data of FeMn / N-CNF under different pollutant conditions in Example 1. Among them, (a) is the degradation of Rhb, and (b) is the pseudo-first-order degradation kinetic constant.

[0187] Fig.18 As shown, when dealing with other difficult-to-degrade pollutants (MO, TC), FeMn / N-CNF achieved a degradation rate of more than 90% in 60 minutes, further demonstrating excellent universality. The above results indicate that FeMn / N-CNF is a promising electro-Fenton cathode membrane that can cope with high-intensity complex water treatment.

[0188] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles, characterized in that: The nitrogen-doped carbon nanofibers have highly connected porous structures, and the Fe-Mn bimetallic crystals are in the form of ultrafine particles uniformly coated in the nitrogen-doped carbon nanofibers; The method for preparing the nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles comprises the following steps: Using a manganese source and an iron source as precursors, reacting to prepare an iron-manganese layered double hydroxide; The FeMnLDHs / PAN nanofiber membrane is prepared by using the FeMnLDHs as a metal source and mixing it with polyacrylonitrile through electrospinning; The FeMn LDHs / PAN nanofiber membrane is carbonized to obtain the nitrogen-doped carbon nanofiber membrane.

2. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 1, characterized in that: The membrane pore size is 100-2000nm, the diameter of the nitrogen-doped carbon nanofiber is 20-200nm, and the particle size of the Fe-Mn bimetallic nanoparticle is 3-5nm.

3. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 1, characterized in that: The preparation method is as follows: The manganese source and the iron source are dissolved in water, urea and NH4F are added to obtain a mixed solution, and the solution is heated to obtain an iron-manganese layered double hydroxide; The iron-manganese layered double hydroxide and polyacrylonitrile are dissolved in DMF to obtain a spinning solution, and electrospinning is performed to obtain a FeMn LDHs / PAN nanofiber membrane; The FeMn LDHs / PAN nanofiber membrane is subjected to a pre-oxidation treatment and then to a carbonization treatment to obtain the nitrogen-doped carbon nanofiber membrane.

4. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 3, characterized in that: The manganese source is manganese chloride, and the iron source is ferric chloride; the molar ratio of the manganese source, the iron source, urea and NH4F is 10-20:40-50:20-30:10-20; and the heating is heating at 110-130°C for 10-15h.

5. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 1, characterized in that: The mass ratio of the iron-manganese layered double hydroxide to polyacrylonitrile is 0.01-0.10:1-10.

6. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 3, characterized in that: The voltage of the electrospinning is 10-15 kV, and the flow rate is 0.01-0.02 mL·min -1 , humidity is 10-20%, and temperature is 20-30℃.

7. The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to claim 3, characterized in that: The pre-oxidation treatment is carried out in an air atmosphere at 1-5°C·min -1 The temperature is raised to 200-250°C and then pre-oxidized for 30-60 minutes; the carbonization treatment is carried out under N2 atmosphere at 1-5°C·min -1 Heat to 600-1200℃ and carbonize for 30-120min.

8. A flow-through electro-Fenton reactor, characterized in that: The nitrogen-doped carbon nanofiber membrane anchoring ultrafine Fe-Mn bimetallic nanoparticles according to any one of claims 1 to 7 is used as the cathode, and the IrO2 / RuO2-Ti electrode is used as the anode; the applied voltage of the flow-through electro-Fenton reactor is -0.3 to -0.8 V, and the pure water flux is 0.5 to 2 mL cm -2 ·min -1 .

9. Use of the flow-through electro-Fenton reactor according to claim 8 in the field of degradation of organic pollutants.

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