A fluorine-doped fe-n-c composite material, a preparation method and application and regeneration thereof

Abstract

The application provides a fluorine-doped Fe-N-C composite material and a preparation method and application and regeneration thereof, and belongs to the technical field of water pollution. In the application, an iron precursor, a zinc salt, an organic ligand and an organic solvent are mixed to synthesize Fe-doped metal organic framework Fe@ZIF-8 material, and then the Fe@ZIF-8 material is carbonized into Fe-N-C material; then the Fe-N-C material is mixed with a fluorine source and subjected to secondary carbonization to obtain the fluorine-doped Fe-N-C composite material. In the application, fluorine atoms are introduced into the Fe-N-C material to produce axial coordination with Fe of the FeN4 center, the fluorine element with high electronegativity can effectively improve the isoelectric point of the Fe-N-C material, the reaction activity of the material is enhanced, the Fe leaching of the material in the reaction process is inhibited, and the stability of the material is improved. In addition, the prepared fluorine-doped Fe-N-C composite material can be reused through fluorine-doping regeneration, and high reduction activity and stability can be maintained.

Description

Technical Field

[0001] This invention relates to the field of water pollution technology, and in particular to a fluorine-doped Fe-NC composite material, its preparation method, application, and regeneration. Background Technology

[0002] Fe-based materials have demonstrated significant advantages in addressing water pollution and environmental remediation, but their applications still have some limitations and drawbacks. Specifically, materials with low-valence Fe active species (such as zero-valent iron, Fe...) 2+ Fe-based materials (such as Fe ions) are easily affected by oxidation during storage and practical applications. The resulting iron oxide layer can obscure active sites, leading to a decrease in reducing activity. The performance of Fe-based materials is highly dependent on the pH value of the environment. In acidic environments, the materials exhibit strong reducing capabilities; however, under neutral or alkaline conditions, their reduction efficiency drops significantly, a characteristic that greatly limits the application range of the materials. Furthermore, highly reactive Fe-based materials often inevitably experience Fe ion leaching during use, resulting in the loss of active components and secondary water pollution. Another noteworthy issue is that, as chemical reducing agents, Fe-based materials often become deactivated after use due to surface oxidation and agglomeration of active component particles.

[0003] In recent years, researchers have employed numerous strategies to enhance the reduction performance of Fe-based reducing materials. For example, embedding or loading Fe species onto a support can generate metal-support interactions that improve metal dispersion and increase surface free energy. Carbon-based materials are a common support, possessing chemical and mechanical stability, and their structure and surface properties are easily tunable. In particular, heteroatom doping (N, P, B, S, etc.) of Fe-carbon composites can alter the electronic structure of the carbon matrix, improving the material's conductivity. Heteroatom doping can form a series of functional groups on the material surface, thereby changing the surface acid-base properties, hydrophilicity / hydrophobicity, adsorption sites, and active sites. Therefore, doping modification of Fe-C materials to enhance their reactivity and stability, as well as exploring effective methods for regenerating and recycling deactivated Fe-based reducing agents, are crucial for improving the sustainability and practicality of Fe-based materials. Summary of the Invention

[0004] The purpose of this invention is to provide a fluorine-doped Fe-NC composite material, its preparation method, application, and regeneration, which can improve the reduction activity and stability of Fe-based materials.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing fluorine-doped Fe-NC composite materials, comprising the following steps:

[0007] Iron precursor, zinc salt, organic ligand and organic solvent were mixed and polymerized to obtain Fe@ZIF-8;

[0008] The Fe@ZIF-8 was subjected to a first carbonization to obtain Fe-NC material;

[0009] The Fe-NC material was mixed with a fluorine source solution and subjected to a second carbonization process to obtain a fluorine-doped Fe-NC composite material.

[0010] Preferably, the iron precursor includes one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid; the zinc salt includes one or more of zinc nitrate, zinc chloride, and zinc sulfate; the organic ligand includes 2-methylimidazole; and the organic solvent includes methanol.

[0011] Preferably, the molar ratio of iron in the iron precursor, zinc in the zinc salt, and organic ligand is 0.01–1.5:1:2–16.

[0012] Preferably, the polymerization reaction is carried out at a temperature of 20–160°C for a time of 4–36 hours.

[0013] Preferably, the temperature of the first carbonization is 850-1050°C and the time is 1-4 hours.

[0014] Preferably, the fluorine source in the fluorine source solution includes one or more of perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, and perfluoroundecanoic acid; the concentration of the fluorine source solution is 5-100 mg / L; and the concentration of the Fe-NC material in the fluorine source solution is 0.2-2 g / L.

[0015] Preferably, the second carbonization temperature is 600-800°C and the time is 1-4 hours.

[0016] The present invention provides a fluorine-doped Fe-NC composite material prepared by the preparation method described in the above technical solution.

[0017] This invention provides the application of the fluorine-doped Fe-NC composite material described in the above technical solution for reducing oxyacid pollutants in water.

[0018] This invention provides a method for regenerating the fluorine-doped Fe-NC composite material described above, comprising the following steps:

[0019] The fluorine-doped Fe-NC composite material, after being treated with pollutants in the reduced water, is mixed with fluorine compounds and subjected to a fluorination regeneration reaction.

[0020] This invention provides a method for preparing fluorine-doped Fe-NC composite materials. First, an iron precursor, zinc salt, organic ligand, and organic solvent are mixed to synthesize an Fe-doped metal-organic framework Fe@ZIF-8 material, which is then carbonized to form Fe-NC material. Using Fe-NC material, which has a strong adsorption capacity for anions, as a precursor, Fe-NC is mixed with a fluorine source and subjected to secondary carbonization to obtain the fluorine-doped Fe-NC composite material. This invention introduces fluorine atoms into the Fe-NC material, which axially coordinate with the Fe at the FeN4 center. The highly electronegative fluorine element effectively increases the isoelectric point of the Fe-NC material, enhances its reactivity, and inhibits Fe leaching during the reaction process, thus improving the material's stability. The results of the examples show that after fluorine doping, the material's activity increases by 2.35 times, and its stability increases significantly. Under pH conditions of 4.0–10, the material can achieve a 91–100% reduction and removal effect of bromate ions, and no Fe leaching phenomenon was detected during the reaction process.

[0021] The fluorine-doped Fe-NC composite material prepared by this invention can be reused through fluorine doping regeneration while maintaining high reduction activity and stability. During the regeneration process, the perfluorocarboxylic acid can act as a self-sacrificing carbon source, participating in the carbothermic reduction of the deactivated Fe-NC material. Through five consecutive cycles of fluorine doping carbonization regeneration-reuse, the material's bromate removal efficiency remains at 100%. This invention demonstrates the effectiveness of improving the performance of Fe-NC materials through fluorine doping technology and provides an environmentally friendly strategy for regenerating Fe-based materials.

[0022] Furthermore, this invention utilizes persistent pollutants, perfluorocarboxylic acids (PFCAs), as a fluorine source to dope Fe-NC materials. PFCAs belong to the perfluoroalkyl group (PFAS) family and are compounds composed of a perfluorocarbon chain and a carboxylic acid group. PFCAs possess certain water solubility due to the carboxylic acid group in their molecular structure and can be adsorbed by positively charged materials. This invention innovatively utilizes PFCAs as a fluorine doping source to prepare fluorine-doped Fe-NC composite materials, providing a promising solution for the resource recycling of perfluorinated pollutants and the mitigation of their environmental pollution problems. Attached Figure Description

[0023] Figure 1 The XRD patterns are of Fe(0.125)@NC and Fe(0.125)@FNC in Example 1, as well as Fe(0.125)@FNC' after reaction in Application Example 3 and Fe(0.125)@FNC-1, a material regenerated by fluorine doping.

[0024] Figure 2(a) is a TEM image of Fe(0.125)@FNC prepared in Example 1; (b-e) are elemental mapping images of Fe(0.125)@FNC: (b) is C, (c) is F, (d) is N, and (e) is Fe.

[0025] Figure 3 XPS spectra of the N1s region of different materials prepared in Example 1: (a) Fe(0.125)@NC, (b) Fe(0.125)@FNC;

[0026] Figure 4 XPS spectra of different materials in the C1s region prepared in Example 1: (a) Fe(0.125)@NC, (b) Fe(0.125)@FNC;

[0027] Figure 5 (a) shows the effects of different materials on BrO3. - The reduction rate changes with reaction time, and (b) shows the reactivity of different materials;

[0028] Figure 6 The effect of different initial pH values ​​on the reduction reaction of different materials prepared in Example 1 is shown in (a) Fe(0.125)@NC and (b) Fe(0.125)@FNC.

[0029] Figure 7 The image shows the effect of fluorine doping regeneration and reuse of the Fe(0.125)@FNC material prepared in Example 1. Detailed Implementation

[0030] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0031] This invention provides a method for preparing fluorine-doped Fe-NC composite materials, comprising the following steps:

[0032] Iron precursor, zinc salt, organic ligand and organic solvent were mixed and polymerized to obtain Fe@ZIF-8;

[0033] The Fe@ZIF-8 was subjected to a first carbonization to obtain Fe-NC material;

[0034] The Fe-NC material was mixed with a fluorine source solution and subjected to a second carbonization process to obtain a fluorine-doped Fe-NC composite material.

[0035] In this invention, the iron precursor preferably includes one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid; the zinc salt preferably includes one or more of zinc nitrate, zinc chloride, and zinc sulfate; the organic ligand preferably includes 2-methylimidazole; and the organic solvent preferably includes methanol. When the iron precursor or zinc salt is two or more of the above, this invention does not have a special limitation on the ratio of different types of iron precursors or zinc salts, and any ratio is acceptable.

[0036] In this invention, the molar ratio of iron in the iron precursor, zinc in the zinc salt, and organic ligand is preferably 0.01–1.5:1:2–16, more preferably 0.0625–0.25:1:8.

[0037] In this invention, the organic ligand is preferably mixed with a first portion of organic solvent to obtain a first mixed solution, and the iron precursor and zinc salt are mixed with a second portion of organic solvent to obtain a second mixed solution (wherein the total amount of the first and second portions of organic solvent is the total amount of organic solvent added); the first and second mixed solutions are then mixed, stirred, and subjected to polymerization under static conditions; the stirring time is preferably 5-120 min, more preferably 60 min, and the stirring rate is preferably 200-800 rpm, more preferably 600 rpm; the ratio of the number of moles of iron in the iron precursor to the volume of the second portion of organic solvent is preferably 0.01-1.5 mmol:15-30 mL, more preferably 0.125-0.25:20 mL.

[0038] In this invention, the polymerization reaction temperature is preferably 20–160°C, more preferably 80–120°C, and the time is preferably 4–36 h, more preferably 12–24 h. During the polymerization process, the ZIF-8 framework separates and encapsulates the iron precursor molecules.

[0039] After the polymerization reaction was completed, the resulting mixture was repeatedly centrifuged and washed with methanol, and then vacuum dried to obtain Fe@ZIF-8 material.

[0040] In this invention, the first carbonization is preferably carried out under a protective atmosphere, preferably high-purity nitrogen or argon; the protective gas flow rate is preferably 25–150 mL / min. -1 .

[0041] In this invention, the temperature of the first carbonization is preferably 850–1050°C, more preferably 900–950°C; the time is preferably 1–4 hours, more preferably 2 hours; this invention does not have a particular limitation on the heating rate to the temperature of the first carbonization, and a heating rate well known in the art can be followed. During the first carbonization process, the Fe@ZIF-8 material is pyrolyzed and carbonized into Fe-NC material.

[0042] In this invention, the Fe loading in the Fe-NC material is preferably 0.15 to 21.1 wt%, preferably 0.96 to 4.21 wt%, and more preferably 1.97 wt%.

[0043] In this invention, the fluorine source in the fluorine source solution preferably includes one or more of perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid and perfluoroundecanoic acid; when the fluorine source is two or more of the above, this invention does not have a special limitation on the ratio of different types of fluorine sources, and any ratio is acceptable.

[0044] In this invention, the fluorine source solution is preferably an aqueous solution of a fluorine source; the concentration of the fluorine source solution is preferably 5-100 mg / L; the concentration of the Fe-NC material in the fluorine source solution is preferably 0.2-2 g / L, more preferably 1.0-1.5 g / L, and even more preferably 1 g / L.

[0045] In this invention, the preferred method for mixing the Fe-NC material with the fluorine source is as follows: the Fe-NC material is placed in a fluorine source solution, and the mixing time is 6 to 24 hours, more preferably 16 hours. After filtration and separation, the material is vacuum dried at a temperature of 60 to 100°C (more preferably 80°C) and then subjected to a second carbonization.

[0046] In this invention, the second carbonization is preferably carried out under a protective atmosphere, preferably high-purity nitrogen or argon; the protective gas flow rate is preferably 25–150 mL / min. -1 .

[0047] In this invention, the temperature for the second carbonization is preferably 600–800°C, more preferably 650–700°C, and the time is preferably 1–4 hours, more preferably 2–3 hours. During the second carbonization process, a fluorine source in the mixture dops the Fe-NC material with fluorine.

[0048] In this invention, the Fe loading in the fluorine-doped Fe-NC composite material is preferably 0.97 to 4.35 wt%, more preferably 1.99 to 3.5 wt%.

[0049] The present invention provides a fluorine-doped Fe-NC composite material prepared by the preparation method described in the above technical solution.

[0050] This invention provides the application of the fluorine-doped Fe-NC composite material described in the above technical solution for reducing oxyacid pollutants in water.

[0051] The present invention does not specifically limit the types of oxyacid acid pollutants, and any corresponding oxyacid acid pollutant well known in the art can be used. In the embodiments of the present invention, bromate ion aqueous solution is specifically used as simulated oxyacid acid wastewater.

[0052] In this invention, the preferred method of application is to mix the fluorine-doped Fe-NC composite material with oxyacid acid wastewater for reduction.

[0053] In this invention, the reduction reaction is preferably carried out under normal temperature and pressure conditions, and the pH of the reduction reaction is 4.0 to 10.0, preferably 6.0; the concentration of the fluorine-doped Fe-NC composite material in the oxyacid wastewater is preferably 0.15 to 0.30 g / L, more preferably 0.25 g / L; the initial concentration of the oxyacid in the oxyacid wastewater is preferably 0.04 to 0.10 mmol / L, more preferably 0.08 mmol / L; the reduction reaction time is preferably 1 to 4 h, more preferably 2 h; and the stirring rate is preferably 200 to 2000 rpm, more preferably 400 to 1000 rpm.

[0054] The present invention does not impose any special limitations on the method of application described herein; it may be applied in accordance with methods known in the art.

[0055] This invention provides a method for regenerating the fluorine-doped Fe-NC composite material described above, comprising the following steps:

[0056] The fluorine-doped Fe-NC composite material, after being treated with pollutants in the reduced water, is mixed with fluorine compounds and subjected to a fluorination regeneration reaction.

[0057] The conditions for the fluorination regeneration reaction described in this invention are the same as those for the second carbonization; the types of fluorine compounds are the same as those for the fluorine sources described above.

[0058] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] (1) Preparation of metal-organic framework ZIF-8 material (Fe(x)@ZIF-8) for confined iron precursor molecules:

[0061] 16 mmol of 2-methylimidazole was dissolved in 20 mL of methanol solution and mixed thoroughly to obtain solution A; 2 mmol of zinc nitrate hexahydrate and 0.25 mmol of ferric acetylacetone (Fe(acac)3) were dissolved in 20 mL of methanol solution and mixed thoroughly to obtain solution B; solution A was added to solution B, and the mixture was stirred at 600 rpm for 1 h and then allowed to stand in a reactor for polymerization for 4 h at a polymerization temperature of 120 °C. The resulting mixture was repeatedly centrifuged and washed with methanol, and then dried in a vacuum oven at 120 °C to obtain Fe(x)@ZIF-8 material, where x is the molar ratio of Fe and Zn elements, i.e., Fe(0.125)@ZIF-8 material was obtained.

[0062] (2) Carbonization preparation of Fe-NC materials (Fe(0.125)@NC) and fluorine-doped Fe-NC composite materials (Fe(0.125)@FNC):

[0063] Fe(0.125)@ZIF-8 was placed in the middle of the isothermal zone of the tube furnace and heated at 25 mL / min. -1 In a high-purity nitrogen atmosphere (purity ≥ 99.999%), the temperature was increased at a rate of 5℃·min. -1 The tube furnace was heated to 950℃ and held for 2 hours for carbonization treatment to obtain Fe(0.125)@NC material; the Fe loading was 1.97wt%.

[0064] Fe(0.125)@NC was mixed with 1000 mL of a 100 mg / L perfluorooctanoic acid (PFOA) aqueous solution to achieve a Fe(0.125)@NC concentration of 1.0 g / L in the PFOA solution. The mixing time was 16 h. After filtration and separation, the material was dried in a vacuum oven at 80 °C and then placed in the middle of the constant temperature zone of a tube furnace for 25 min. -1 In a high-purity nitrogen atmosphere (purity ≥ 99.999%), the temperature was increased at a rate of 5℃·min. -1 The tubular furnace was heated to 700℃ and held for 2 hours to perform fluorine doping and carbonization treatment, resulting in material Fe(0.125)@FNC; wherein the Fe loading was 1.99 wt%.

[0065] Example 2

[0066] The only difference from Example 1 is that the amount of iron acetylacetone (Fe(acac)3) is 0.125 mmol, resulting in material Fe(0.0625)@NC; wherein the loading of Fe is 0.96 wt%.

[0067] The final material Fe(0.0625)@FNC was prepared, with an Fe loading of 0.97 wt%.

[0068] Example 3

[0069] The only difference from Example 1 is that the amount of iron acetylacetone (Fe(acac)3) used is 0.5 mmol, resulting in material Fe(0.25)@NC; wherein the loading of Fe is 4.21 wt%.

[0070] The final material Fe(0.25)@FNC was prepared, with an Fe loading of 4.35 wt%.

[0071] Test Example 1

[0072] 1) The X-ray diffraction (XRD) results of the Fe-NC material (Fe(0.125)@NC) and the fluorine-doped Fe-NC composite material (Fe(0.125)@FNC) prepared in Example 1 are as follows: Figure 1 As shown, the materials exhibit only two relatively broad diffraction peaks at 24.3° and 43.7°, which are attributed to the (0,0,2) and (1,0,1) crystal planes of graphitic carbon, respectively. The intensity and position of the peaks did not change due to the deactivation or regeneration carbonization process of the materials, indicating that the Fe active component in the materials is still in a highly dispersed state.

[0073] 2) The fluorine-doped Fe-NC composite material (Fe(0.125)@FNC) prepared in Example 1 was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown, where, Figure 2 In the image, (a) is the TEM image of the material, (b) is the elemental distribution map of C, (c) is the elemental distribution map of F, (d) is the elemental distribution map of N, and (e) is the elemental distribution map of Fe. Figure 2 The scale bars for (b~e) are all 50 nm. Figure 2 The results show that after the fluorine-doped carbonization reaction, the material retains its regular dodecahedral shape. The elemental distribution image shows that C, N, F, and Fe elements are uniformly distributed in the material, with the uniform distribution of F indicating that fluorine has been successfully doped into the structure of the Fe-NC composite.

[0074] 3) The elemental composition of the material surface and bulk phase was characterized using X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma emission spectroscopy (ICP-OES), and the results are shown in Table 1.

[0075] Table 1 Elemental composition of material surface

[0076]

[0077] a Measurement by XPS

[0078] b Measured by ICP-OES

[0079] As shown in Table 1, the nitrogen (N) content on the material surface remained essentially unchanged after fluorine doping. The measured nitrogen (F) content on the Fe(0.125)@FNC surface was 1.19 at%.

[0080] Figure 3 XPS spectra of the N1s region of Fe(0.125)@NC and Fe(0.125)@FNC materials prepared in Example 1, where (a) is Fe(0.125)@NC and (b) is Fe(0.125)@FNC; Figure 4 XPS spectra of the C1s region of the Fe(0.125)@NC and Fe(0.125)@FNC materials prepared in Example 1, where (a) is Fe(0.125)@NC and (b) is Fe(0.125)@FNC; Figures 3-4 It can be seen that after F doping, the proportions of pyridine N, N-Fe, pyrrole N, graphite N and N oxide in the material remain basically unchanged; the appearance of CF bonds at 292.3 eV proves that F was successfully introduced into the carbon matrix during the carbonization process.

[0081] 4) The surface charge density of the material in solutions at different pH values ​​was measured and analyzed using a Zeta potentiometer. The pH value corresponding to a Zeta potential of 0 is the isoelectric point (IEP) of the material. The results are shown in Table 1. Due to the high nitrogen content (9.22 at%) on the surface of the Fe(0.125)@NC material, it exhibits a high IEP value, indicating that it has a certain ability to adsorb anions in aqueous solution. Compared with the Fe(0.125)@NC material, the isoelectric point of Fe(0.125)@FNC is improved, which is presumably due to the doping of the highly electronegative F element into the carbon matrix.

[0082] 5) The water contact angle of different materials was tested using an optical static contact angle meter. The results are shown in Table 1. The results show that all materials exhibit excellent hydrophilicity due to the abundance of N-containing functional groups on the material surface, while the hydrophilicity of the materials decreased slightly after fluorine doping.

[0083] Application Example 1

[0084] The Fe-NC material (Fe(0.125)@NC) prepared in Example 1 and the fluorine-doped Fe-NC composite material (Fe(0.125)@FNC) were applied to the reaction of reducing bromate ions in an aqueous phase.

[0085] A potassium bromate aqueous solution was prepared with an initial concentration of 0.08 mmol / L and an initial pH of 6.0. The reaction conditions were ambient temperature and pressure. The concentration of the material in the potassium bromate aqueous solution was 0.25 g / L. The reaction time was 2 h, and the stirring rate was 400 rpm. To evaluate the leaching of iron ions during the reduction and removal of bromate ions by the reducing material, the reaction solution after 2 h was collected, filtered, and the concentration of Fe ions in the solution was determined by the o-phenanthroline spectrophotometric method.

[0086] Figure 5 (a) shows the effects of different materials on BrO3. - The reduction rate changes with reaction time. Figure 5 (b) shows the reduction activity results of different materials during the reaction process: the materials' reaction with BrO3 - The reduction curve can be fitted using pseudo-first-order reaction kinetics (Ri). 2 >0.95), the observed pseudo-first-order rate constants (k) obtained by fitting are used. obs ,min –1 Using the mass concentration of active sites and initial BrO3 - Concentration versus apparent constant k obs After normalization, the intrinsic pseudo-first-order rate constants (k) are obtained. int ,mmol h –1 g Fe –1 To evaluate the reducing activity of materials. For example... Figure 5 As shown in (b), fluorine doping increased the reducing activity of the material by 2.35 times. This is likely due to the increased isoelectric point of the material surface (as shown in Table 1). A higher isoelectric point makes the material more prone to surface protonation in aqueous solutions, which in turn makes it easier for the material surface to attract anions from the aqueous solution. Since the solid-liquid heterogeneous reaction mainly occurs at the material surface, the adsorption of bromate ions on the material surface is a crucial step in the reaction, and the material's activity is influenced by the adsorption of bromate ions on the material surface.

[0087] In addition, the stability of the material during the reaction process was evaluated by the Fe leaching level in the solution after the reaction. After the reaction, the Fe leaching concentration of Fe(0.125)@NC in the reaction solution was measured to be 55.69 μg / L, while no Fe leaching was detected in the Fe(0.125)@FNC material in the solution, indicating that the stability of the material was significantly enhanced after fluorine doping.

[0088] Application Example 2

[0089] The initial pH of the potassium bromate aqueous solution in Application Example 1 was adjusted to 4.0, 6.0, 8.0, and 10.0. The Fe-NC material (Fe(0.125)@NC) and the fluorine-doped Fe-NC composite material (Fe(0.125)@FNC) from Example 1 were applied to the reduction reaction to investigate the effect of different reaction pH values ​​on the reduction and removal of bromate by the materials. The results are as follows: Figure 6 As shown, (a) represents Fe(0.125)@NC, and (b) represents Fe(0.125)@FNC. Figure 6 As shown, the material's reduction effect on bromate ions decreases with increasing pH in the reaction system. This pH dependence may be due to the presence of H+ in the solution. + The reduction potential of bromate ions directly participates in the reduction reaction and changes with pH. As the pH of the reaction solution increases, the surface charge of Fe(0.125)@NC and Fe(0.125)@FNC gradually changes from positive to negative. Therefore, with increasing pH, the electrostatic adsorption of negatively charged bromate ions on the material surface decreases, leading to a decrease in the reduction efficiency at higher pH values. When the pH increases from 4.0 to 10.0, the reduction efficiency of Fe(0.125)@NC for bromate ions decreases from 100% to 84%, while the reduction efficiency of Fe(0.125)@FNC can remain between 100% and 90%.

[0090] In addition, calculations during the experiment revealed that the leaching level of Fe(0.125)@NC during the reaction process ranged from 71.21 to 23.73 μg / L. After fluorine doping, no Fe ion leaching was observed in Fe(0.125)@FNC under conditions ranging from pH 4.0 to 10.0, indicating that the material exhibits excellent stability.

[0091] Application Example 3

[0092] The reduction and removal effect of the Fe(0.125)@FNC material prepared in Example 1 on bromate ions was tested using the method in Application Example 1.

[0093] The testing steps were repeated again with the used Fe(0.125)@FNC material (named Fe(0.125)@FNC');

[0094] Then, Fe(0.125)@FNC' was regenerated by fluorine doping, and the resulting material was Fe(0.125)@FNC-y, where y represents the number of times the material was regenerated by fluorine doping. The regeneration method is as follows:

[0095] (1) Collect the used materials:

[0096] After the reaction was completed, the used material was washed with ultrapure water several times and collected by filtration. The collected material was then placed in a vacuum oven and dried at 60°C for 12 hours to obtain Fe(0.125)@FNC' material.

[0097] (2) Regenerated and restored materials:

[0098] Fe(0.125)@FNC' was mixed with 1000 mL of a 100 mg / L perfluorooctanoic acid (PFOA) solution, where the mass concentration of Fe(0.125)@FNC' in the PFOA solution was 1.0 g / L. The mixing time was 16 h. After filtration and separation, the material was dried in a vacuum oven at 80 °C and then placed in the middle of the constant temperature zone of a tube furnace for 25 min. -1 Under a high-purity nitrogen atmosphere, the temperature was increased at a rate of 5℃ / min. -1 The material was subjected to fluorine doping and carbonization treatment by heating the tubular furnace to 700℃ and holding it for 2 hours, resulting in material Fe(0.125)@FNC-1. This process is recorded as cycle-1, and the contaminant reduction test was performed again. The above regeneration-test steps were repeated to obtain the test results for cycles-2,-3,-4, and-5.

[0099] The reacted Fe(0.125)@FNC' and the fluorine-doped regenerated material Fe(0.125)@FNC-1 were used in the reduction reaction, and the test results are as follows. Figure 5 and Figure 7 As shown; meanwhile, the XPS characterization results are shown in Table 1. From Table 1, Figure 5 and Figure 7 It can be seen that Fe(0.125)@FNC' has poor reduction activity, achieving only 43% reduction of bromate ions within a 2-hour reaction time. Compared to Fe(0.125)@FNC material, the O content in Fe(0.125)@FNC' material increases, presumably due to oxidation during the reduction reaction. After fluorine doping and regeneration, the O content on the surface of Fe(0.125)@FNC-1 material significantly decreases. Notably, the surface Fe content in the fluorine-doped carbonized Fe(0.125)@FNC-1 material is basically consistent with that before regeneration, suggesting that perfluorinated compounds act as a self-sacrificing carbon source during carbonization and regeneration, protecting the stability of the material structure. After five consecutive cycles of fluorine-doped carbonization regeneration and reuse, Fe(0.125)@FNC-5 material exhibits a near 100% bromate ion removal rate within 60 minutes.

[0100] The results above demonstrate that the fluorine-doped carbonization regeneration method can effectively restore the activity of deactivated Fe-NC materials, and is an environmentally friendly strategy for regenerating Fe-NC materials.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a fluorine-doped Fe-NC composite material for reducing oxyacid acid pollutants in water, characterized in that, Includes the following steps: Iron precursor, zinc salt, organic ligand and organic solvent were mixed and polymerized to obtain Fe@ZIF-8; The Fe@ZIF-8 was subjected to a first carbonization to obtain Fe-NC material; Fe-NC material was mixed with a fluorine source solution and subjected to a second carbonization to obtain a fluorine-doped Fe-NC composite material. The fluorine source in the fluorine source solution includes one or more of perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, and perfluoroundecanoic acid.

2. The preparation method according to claim 1, characterized in that, The iron precursor includes one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid; the zinc salt includes one or more of zinc nitrate, zinc chloride, and zinc sulfate; the organic ligand includes 2-methylimidazole; and the organic solvent includes methanol.

3. The preparation method according to claim 2, characterized in that, The molar ratio of iron in the iron precursor, zinc in the zinc salt, and organic ligand is 0.01–1.5:1:2–16.

4. The preparation method according to claim 3, characterized in that, The polymerization reaction is carried out at a temperature of 20–160°C for a duration of 4–36 hours.

5. The preparation method according to claim 1 or 4, characterized in that, The first carbonization temperature is 850–1050℃, and the time is 1–4 hours.

6. The preparation method according to claim 1, characterized in that, The concentration of the fluorine source solution is 5–100 mg / L; the concentration of the Fe-NC material in the fluorine source solution is 0.2–2 g / L.

7. The preparation method according to claim 1 or 6, characterized in that, The second carbonization temperature is 600–800℃, and the time is 1–4 hours.

8. The fluorine-doped Fe-NC composite material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the fluorine-doped Fe-NC composite material according to claim 8 in reducing oxyacid salt pollutants in water.

10. The method for regenerating the fluorine-doped Fe-NC composite material according to claim 8, characterized in that, Includes the following steps: The fluorine-doped Fe-NC composite material, after being treated with pollutants in the reduced water, is mixed with fluorine compounds and subjected to a fluorination regeneration reaction.

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