A nitrogen and phosphorus co-doped carbon-based confined iron phosphide composite material, a preparation method and application and regeneration thereof

Abstract

The application belongs to the technical field of chemical reducing materials, and specifically discloses a nitrogen and phosphorus co-doped carbon-based confined ferrophosphorus composite material, a preparation method and application thereof, and regeneration. First, iron precursor molecules, zinc salt, organic ligand and solvent are mixed to perform a polymerization reaction to obtain Fe@ZIF-8 material; then, the Fe@ZIF-8 material and a phosphorus source are sequentially subjected to phosphorization reaction and carbonization reaction to obtain the nitrogen and phosphorus co-doped carbon-based confined ferrophosphorus composite material. In the material, P doping can improve the specific surface area, electron transfer capacity and dispersibility of the material. Fe2P active sites formed by coordination of Fe and P significantly inhibit Fe leaching in the reaction process, and enhance the stability of the material; the material can efficiently reduce and remove bromate ions and other harmful substances in a wide pH value range; and the material can be regenerated by phosphorization, and a high reduction rate is maintained.

Description

Technical Field

[0001] This invention relates to the field of chemical reducing materials technology, and in particular to a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material, its preparation method, application, and regeneration. Background Technology

[0002] Iron-based materials, as ideal reducing agents with low cost, high reactivity, and environmental friendliness, are widely used in the reduction and removal of water pollution. However, iron-based materials are easily oxidized by air and water during storage and application, leading to reduced reduction efficiency. The size of the Fe active component is mainly distributed between tens of nanometers and hundreds of micrometers, resulting in low Fe atom utilization. During the reaction, Fe leaching from the material can also cause secondary pollution to the water. Furthermore, the pH value of the reaction system has a significant impact on the reducing activity of Fe-based materials.

[0003] Several methods have been proposed to improve the reduction activity and stability of iron-based materials. Existing research has found that reducing the particle size of the Fe active component and dispersing it uniformly on a support can increase the surface free energy. Immobilizing Fe nanoparticles on a support allows for effective regulation of the material's activity and stability through metal-support interaction. Carbon-based materials are a common type of support, exhibiting stable and controllable properties. Metal-organic frameworks (MOFs) are composed of organic ligands and metal ions that coordinate and polymerize. After carbonization in an inert atmosphere, they form unique three-dimensional porous carbon-based materials. The porous nature of MOF-derived materials makes it easier for active sites to contact contaminants. Because the metal atoms are uniformly dispersed in the MOF, the size of the metal nanoparticles in the carbonized material is well-limited, which is beneficial for improving atom utilization and stability. Furthermore, the structure and physicochemical properties of MOF-derived materials can be tuned by changing the synthesis conditions, such as altering the types and ratios of organic and metal ligands, or by doping heteroatoms during self-assembly. Heteroatom doping can alter the electronic structure of the carbon matrix, enhancing its conductivity and forming a series of surface functional groups. It can also effectively modulate the material's hydrophilicity, surface acid-base properties, and adsorption sites. In particular, heteroatoms can coordinate with metal atoms to form metal derivatives, such as metal oxides, metal phosphides, and metal sulfides. This coordination can improve the stability, atom utilization, and activity of the metal component. Iron phosphide (Fe...) has been reported... x P (Fe) materials have been successfully applied in rechargeable batteries and electrocatalytic water splitting. P doping optimizes the local environment of Fe atoms, significantly improving their conductivity and stability (Energy Storage Mater. 2022, 52, 685-735. J. Am. Chem. Soc. 2023, 145(6), 3647-3655). However, to date, Fe... xThe application of Fe materials in the reduction and removal of pollutants is rarely reported. Therefore, the research and preparation of Fe materials with high reducing activity and stability is crucial. x It is meaningful to use P materials and apply them to the reduction reaction of pollutants. Summary of the Invention

[0004] In view of this, the present invention provides a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material, its preparation method, application, and regeneration, to improve Fe... x The reducing activity and stability of P material.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material includes the following steps:

[0007] 1) Iron precursor molecules, zinc salt, organic ligands and solvent are mixed and polymerized to obtain Fe@ZIF-8 material;

[0008] 2) The Fe@ZIF-8 material obtained in step 1) is subjected to phosphating and carbonization reactions with a phosphorus source in sequence to obtain a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material.

[0009] Preferably, in step 1), the molar ratio of iron in the iron precursor molecule, zinc in the zinc salt, and organic ligand is 0.01–1.5:1:2–16, and the molar volume ratio of iron in the iron precursor molecule to solvent is 0.01–1.5:15–30 mL.

[0010] Preferably, the polymerization reaction temperature is 20–160°C, and the polymerization reaction time is 4–36 h.

[0011] Preferably, the iron precursor molecule includes one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid.

[0012] The zinc salt includes one or more of zinc nitrate, zinc chloride, and zinc sulfate;

[0013] The organic ligand is 2-methylimidazole;

[0014] The solvent includes methanol.

[0015] Preferably, in step 2), the mass ratio of Fe@ZIF-8 material to phosphorus source is 1:0.1-3.

[0016] Preferably, the phosphating reaction temperature is 300–400°C and the phosphating reaction time is 0.5–4 h; the carbonization reaction temperature is 850–1050°C and the carbonization reaction time is 1–4 h.

[0017] Preferably, the phosphorus source in step 2) includes sodium hypophosphite and / or potassium hypophosphite.

[0018] Another object of the present invention is to provide a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material prepared by the above preparation method.

[0019] Another object of the present invention is to provide an application of a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material in reducing pollutants in water.

[0020] Another object of the present invention is to provide a method for regenerating nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite materials, the regeneration method comprising the following steps:

[0021] The used nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material was subjected to a phosphating regeneration reaction with a phosphorus source to complete the regeneration of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material.

[0022] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention uses ZIF-8 material, which can confine iron precursor molecules, as a precursor to prepare a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material through phosphating and carbonization processes. The N, P, and Fe elements in the material are highly dispersed within a dodecahedral carbon matrix structure. The Fe active component in the material exhibits good dispersion and high atomic utilization. P doping modulates the electronic structure of Fe atoms and the carbon matrix, resulting in a larger specific surface area, better electron transport capability, and improved dispersibility in the reaction solution. Furthermore, this invention allows for the adjustment of the material's structural characteristics and surface physicochemical properties by varying the Fe loading, P doping amount, and carbonization temperature. The Fe2P active sites formed by Fe and P coordination significantly inhibit Fe leaching during the reaction process, enhancing the material's stability. The material can reduce and remove 80-100% of bromate ions within a pH range of 4.0-10.0, and the Fe leaching range is 22.98-4.53 μg / L. -1 The material can be reused through phosphating regeneration and retains a reduction rate of over 85% after five cycles. Furthermore, the material maintains high reduction activity in simulated real-world polluted water samples. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 X-ray diffraction pattern of Fe(x)@ZIF-8 prepared in Example 1;

[0026] Figure 2 FESEM images of Fe(x)@ZIF-8 prepared in ZIF-8 and Example 1, wherein, Figure 2 In this context, 'a' represents ZIF-8. Figure 2 In this context, b represents Fe(0.0625)@ZIF-8. Figure 2 In this context, c represents Fe(0.125)@ZIF-8. Figure 2 In this context, d represents Fe(0.25)@ZIF-8;

[0027] Figure 3 The XRD patterns of Fe2P(x)@P(y)NC-z prepared in Examples 1-3 are shown.

[0028] Figure 4 The TEM characterization results are for Fe2P(0.125)@P(1.0)NC-950 prepared in Example 1. Figure 4 In the image, 'a' represents the TEM image of the material. Figure 4 In the image, b is a high-magnification TEM image of the material. Figure 4 In the diagram, 'c' represents the selected area electron diffraction pattern of the material. Figure 4 In the image, d represents the TEM image of the material. Figure 4 In the diagram, 'e' represents the carbon element distribution of the material. Figure 4 f in the figure represents the distribution of O element in the material. Figure 4 In the figure, g represents the N element distribution map of the material. Figure 4 In the diagram, h represents the P element distribution of the material. Figure 4 In the diagram, 'i' represents the Fe element distribution of the material. Figure 4 The scale bar for d to i in the figure is 50 nm.

[0029] Figure 5 The results show the reduction performance of the materials prepared in Examples 1 and Comparative Examples 1-3 for bromate ions. Figure 5 In the figure, 'a' represents the reduction / removal curve. Figure 5 In the equation, b represents the Fe leaching result during the reaction process;

[0030] Figure 6 The concentration-time distribution and mass balance curves of bromate ions and reduction products (bromine ions) in the reaction solution containing the Fe2P(0.125)@P(1.0)NC-950 material synthesized in Example 1 are shown.

[0031] Figure 7The results show the reduction performance of Fe2P(0.125)@P(1.0)NC-950 prepared in Example 1 in reaction systems at different pH values. Figure 7 In the figure, 'a' represents the reduction / removal curve. Figure 7 In the figure, b represents the result of Fe leaching in the reaction;

[0032] Figure 8 Reduction removal curves of bromate ions by Fe2P(0.125)@P(1.0)NC-950 prepared in Example 1 for different water samples;

[0033] Figure 9 The curves show the reduction and removal of bromate ions by the regenerated Fe2P(0.125)@P(1.0)NC-950. Detailed Implementation

[0034] This invention provides a method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material, comprising the following steps:

[0035] 1) Iron precursor molecules, zinc salt, organic ligands and solvent are mixed and polymerized to obtain Fe@ZIF-8 material;

[0036] 2) The Fe@ZIF-8 material obtained in step 1) is subjected to phosphating and carbonization reactions with a phosphorus source in sequence to obtain a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material.

[0037] In this invention, the molar ratio of iron in the iron precursor molecule, zinc in the zinc salt, and organic ligand in step 1) is 0.1-1.5:1:2-16, preferably 0.15-1:1:4-15, further preferably 0.25-0.75:1:5-12, and even more preferably 0.5:1:10.

[0038] In this invention, the molar volume ratio of iron in the iron precursor molecule to the solvent is 0.01-1.5:15-30 mL, preferably 0.065-1:18-26 mL, more preferably 0.125-0.375:20-25 mL, and even more preferably 0.25:22 mL.

[0039] In this invention, the polymerization reaction temperature is 50–160°C, specifically 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 120°C, 140°C, and 150°C; the polymerization reaction time is 4–36 hours, specifically 5 hours, 8 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, and 35 hours.

[0040] In this invention, the mixing in step 1) is preferably performed by first mixing the organic ligand with the first part of the solvent to obtain mixed solution A, and then mixing the iron precursor molecule and zinc salt with the second part of the solvent to obtain mixed solution B; and then mixing mixed solution A and mixed solution B.

[0041] In this invention, the total amount of the first part solvent and the second part solvent is the amount of solvent added.

[0042] In this invention, before the polymerization reaction in step 1), a stirring step is also included. The stirring time is 5 to 120 min, specifically 10 min, 20 min, 40 min, 50 min, 60 min, 80 min, or 100 min; the stirring speed is 200 rpm to 800 rpm, specifically 300 rpm, 400 rpm, 500 rpm, 600 rpm, or 700 rpm.

[0043] In this invention, the iron precursor molecules include one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid, and the particle size of the iron precursor molecules is within the pore size of the ZIF-8 framework. and cavity diameter During the polymerization reaction, the ZIF-8 framework can separate and encapsulate iron precursor molecules.

[0044] In this invention, the zinc salt includes one or more of zinc nitrate, zinc nitrate hexahydrate, zinc chloride, and zinc sulfate; the organic ligand includes 2-methylimidazole; and the solvent includes methanol.

[0045] In this invention, the mass ratio of Fe@ZIF-8 material to phosphorus source in step 2) is 1:0.1 to 3, preferably 1:0.5 to 2.5, further preferably 1:1 to 2, and even more preferably 1:1.5.

[0046] In this invention, the temperature of the phosphating reaction is 300-400℃, specifically 320℃, 340℃, 350℃, 360℃, or 380℃; the time of the phosphating reaction is 0.5-4h, specifically 1h, 1.5h, 2h, 2.5h, 3h, or 3.5h.

[0047] In this invention, the temperature of the carbonization reaction is 850-1050℃, specifically 880℃, 900℃, 920℃, 950℃, 980℃, 1000℃, 1200℃, or 1400℃; the time of the carbonization reaction is 1-4 hours, specifically 1.5 hours, 2 hours, 2.5 hours, 3 hours, or 3.5 hours.

[0048] In this invention, the phosphorus source in step 2) includes sodium hypophosphite and / or potassium hypophosphite.

[0049] In this invention, the phosphating and carbonization reactions in step 2) are preferably carried out independently in a tube furnace.

[0050] In this invention, the Fe@ZIF-8 material and the phosphorus source in step 2) are preferably not in contact during the reaction.

[0051] In this invention, the Fe@ZIF-8 material and the phosphorus source in step 2) are preferably spaced 0.5 to 2 cm apart during the reaction, specifically 0.8 cm, 0.9 cm, 1 cm, 1.2 cm, 1.5 cm, or 1.8 cm.

[0052] In this invention, during the reaction of the Fe@ZIF-8 material and the phosphorus source in step 2), the phosphorus source is preferably located upstream of the tubular furnace containing the Fe@ZIF-8 material.

[0053] In this invention, the phosphating and carbonization reactions in step 2) are preferably carried out independently under an inert atmosphere, more preferably under high-purity nitrogen and high-purity argon; the gas flow rate is preferably 25–100 mL / min. -1 Specifically, it can be 30mL min -1 50mL min -1 75mL min -1 80mL min -1 .

[0054] The present invention also provides a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material prepared by the above preparation method.

[0055] In this invention, the Fe loading is preferably 0.92 to 4.14 wt%, specifically 1 wt%, 2 wt%, 3 wt%, or 4 wt%.

[0056] The present invention also provides an application of nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material in reducing pollutants in water.

[0057] In this invention, the amount of nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material is preferably 0.15-0.3 g / L, specifically 0.18 g / L, 0.2 g / L, 0.22 g / L, 0.25 g / L, or 0.28 g / L.

[0058] In this invention, the reaction time of the reduction process is 1 to 4 hours, specifically 1.5 hours, 2 hours, 2.5 hours, 3 hours, and 3.5 hours.

[0059] In this invention, the reaction temperature and pressure of the reduction process are preferably at room temperature and pressure.

[0060] In this invention, the reduction process is preferably carried out under stirring conditions, and the stirring rate is preferably 200 to 2000 rpm, specifically 400 rpm, 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, or 1800 rpm.

[0061] In this invention, the concentration of pollutants in the water is preferably 0.04 to 0.1 mmol / L, specifically 0.05 mmol / L, 0.06 mmol / L, or 0.08 mmol / L.

[0062] In this invention, the pollutants in the water include, but are not limited to, bromate.

[0063] This invention also provides a method for regenerating nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite materials, the regeneration method comprising the following steps:

[0064] The used nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material was subjected to a phosphating regeneration reaction with a phosphorus source to complete the regeneration of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material.

[0065] In this invention, the mass ratio of nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material to phosphorus source in the regeneration reaction is preferably 1:0.5 to 1.5, more preferably 1:0.8 to 1.2, and even more preferably 1:1.

[0066] In this invention, the phosphorus source is preferably placed 0.5 to 2 cm upstream of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material at a distance of 1 cm, specifically at 0.8 cm, 0.9 cm, 1 cm, 1.2 cm, 1.5 cm, or 1.8 cm.

[0067] In this invention, the temperature of the phosphating regeneration reaction is preferably 300-400°C, specifically 320°C, 340°C, 350°C, 360°C, or 380°C; the regeneration reaction time is preferably 0.5-1 h, specifically 0.6 h, 0.7 h, 0.8 h, or 0.9 h.

[0068] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0069] Example 1

[0070] (1) Preparation of ZIF-8 metal-organic framework materials (Fe(x)@ZIF-8) with confined iron precursor molecules:

[0071] 16 mmol of 2-methylimidazole was dissolved in 20 mL of methanol and mixed thoroughly to obtain solution A. 2 mmol of zinc nitrate hexahydrate and iron acetylacetone (Fe(acac)3) (0.125, 0.25, or 0.5 mmol respectively) were dissolved in 20 mL of methanol and mixed thoroughly to obtain solution B. An equal volume of solution A was added to solution B, and the mixture was stirred at 600 rpm for 1 h, then allowed to stand in a reactor for polymerization for 4 h at a polymerization temperature of 120 °C. During polymerization, the ZIF-8 framework separated and encapsulated the iron precursor molecules. The resulting mixture was repeatedly washed by centrifugation with methanol and dried under vacuum to obtain Fe(x)@ZIF-8 material, where x is the molar ratio of Fe to Zn.

[0072] (2) Phosphating and carbothermal treatment yielded nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material (Fe2P(x)@P(y)NC-z):

[0073] 0.5 g of Fe(x)@ZIF-8 was placed in the middle of the isothermal zone of the tube furnace, and 0.5 g of sodium hypophosphite was placed 1 cm upstream of Fe(x)@ZIF-8 as a phosphorus source. The solution was heated to 25 mL / min. -1 In a high-purity nitrogen atmosphere, the material was phosphated by heating to 350℃ and holding for 2 hours in a tube furnace, followed by carbonization by heating to 950℃ and holding for 2 hours; the heating rate was 5℃ / min. -1 Finally, the material Fe2P(x)@P(y)NC-z was obtained, where y is the mass ratio of sodium hypophosphite to Fe(x)@ZIF-8, and z is the carbonization temperature.

[0074] The Fe2P(x)@P(1.0)NC-950 materials with different loadings prepared according to the above synthesis steps are: Fe2P(0.0625)@P(1.0)NC-950(Fe(0.0625)@ZIF-8), Fe2P(0.125)@P(1.0)NC-950(Fe(0.125)@ZIF-8), and Fe2P(0.25)@P(1.0)NC-950(Fe(0.25)@ZIF-8); the Fe loadings in the materials are 0.92, 1.88, and 4.14 wt%, respectively.

[0075] Example 2

[0076] The amount of Fe(acac)3 in step (1) of Example 1 was adjusted to 0.25 mmol, the carbonization temperature of the material in step (2) was adjusted to 850 or 1050 °C, and other experimental conditions were the same as in Example 1.

[0077] The Fe2P(0.125)@P(1.0)NC-z materials prepared according to the above synthesis steps and treated at different carbonization temperatures are: Fe2P(0.125)@P(1.0)NC-850 and Fe2P(0.125)@P(1.0)NC-1050; the Fe loading in the materials are 1.39 wt% and 2.35 wt%, respectively.

[0078] Example 3

[0079] The amount of Fe(acac)3 in step (1) of Example 1 was adjusted to 0.25 mmol, and the amount of sodium hypophosphite in step (2) was adjusted to 1.0 g. Other experimental conditions were the same as in Example 1.

[0080] The material prepared according to the above synthesis steps is Fe2P(0.125)@P(2.0)NC-950, wherein the Fe loading is 1.79 wt%.

[0081] Example 4

[0082] (1) Preparation of ZIF-8 metal-organic framework materials (Fe(x)@ZIF-8) with confined iron precursor molecules:

[0083] 4 mmol of 2-methylimidazole was dissolved in 15 mL of methanol and mixed thoroughly to obtain solution A. 2 mmol of zinc nitrate hexahydrate and 0.1 mmol of phthalic anhydride were dissolved in 15 mL of methanol and mixed thoroughly to obtain solution B. An equal volume of solution A was added to solution B, and the mixture was stirred at 200 rpm for 1 h, then allowed to stand in a reactor for polymerization for 24 h at 20 °C. During polymerization, the ZIF-8 framework separated and encapsulated the iron precursor molecules. The resulting mixture was repeatedly washed by centrifugation with methanol and dried under vacuum to obtain Fe(x)@ZIF-8 material, where x is the molar ratio of Fe to Zn.

[0084] (2) Phosphating and carbothermal treatment yielded nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material (Fe2P(x)@P(y)NC-z):

[0085] 0.5 g of Fe(x)@ZIF-8 was placed in the middle of the isothermal zone of the tube furnace, and 1.5 g of potassium hypophosphite was placed 1 cm upstream of Fe(x)@ZIF-8 as a phosphorus source. The solution was heated to 25 mL / min. -1 In a high-purity nitrogen atmosphere, the material was phosphated by heating to 300℃ and holding for 1 hour in a tube furnace, and then carbonized by heating to 1000℃ and holding for 1 hour; the heating rate was 5℃ / min. -1Finally, the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material was obtained: Fe2P(x)@P(y)NC-z, where y is the mass ratio of sodium hypophosphite to Fe(x)@ZIF-8, and z is the carbonization temperature.

[0086] Example 5

[0087] (1) Preparation of ZIF-8 metal-organic framework materials (Fe(x)@ZIF-8) with confined iron precursor molecules:

[0088] 10 mmol of 2-methylimidazole was dissolved in 30 mL of methanol and mixed thoroughly to obtain solution A. 2 mmol of zinc nitrate hexahydrate and 3 mmol of ferrocene were dissolved in 30 mL of methanol and mixed thoroughly to obtain solution B. An equal volume of solution A was added to solution B, and the mixture was stirred at 400 rpm for 1 h, then allowed to stand in a reactor for polymerization for 4 h at a polymerization temperature of 160 °C. During polymerization, the ZIF-8 framework separated and encapsulated the iron precursor molecules. The resulting mixture was repeatedly centrifuged and washed with methanol, and then vacuum dried to obtain Fe(x)@ZIF-8 material, where x is the molar ratio of Fe to Zn.

[0089] (2) Phosphating and carbothermal treatment yielded nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material (Fe2P(x)@P(y)NC-z):

[0090] 0.5 g of Fe(x)@ZIF-8 was placed in the middle of the isothermal zone of the tube furnace, and 1.5 g of sodium hypophosphite was placed 1 cm upstream of Fe(x)@ZIF-8 as a phosphorus source. The solution was heated to 25 mL / min. -1 In a high-purity nitrogen atmosphere, the material was phosphated by heating to 400℃ and holding for 0.5 hours in a tube furnace, and then carbonized by heating to 850℃ and holding for 4 hours; the heating rate was 5℃ / min. -1 Finally, the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material was obtained: Fe2P(x)@P(y)NC-z, where y is the mass ratio of sodium hypophosphite to Fe(x)@ZIF-8, and z is the carbonization temperature.

[0091] Experimental Example 1

[0092] The Fe(x)@ZIF-8 and ZIF-8 prepared in Example 1 were subjected to X-ray diffraction (XRD), and the results are as follows: Figure 1 As shown, through Figure 1 It can be seen that the diffraction peaks of the synthesized material are consistent with the diffraction peak positions and intensities of the ZIF-8 standard XRD pattern, indicating the successful synthesis of ZIF-8 crystals and that the loading of Fe does not destroy the crystal structure of ZIF-8.

[0093] The scanning electron microscopy (FESEM) results of ZIF-8 and Fe(x)@ZIF-8 obtained in Example 1 are as follows: Figure 2 As shown, where, Figure 2 In this context, 'a' represents ZIF-8. Figure 2 In this context, b represents Fe(0.0625)@ZIF-8. Figure 2 In this context, c represents Fe(0.125)@ZIF-8. Figure 2 In this context, d represents Fe(0.25)@ZIF-8. The synthesized materials all exhibit a similar rhombic dodecahedral structure, and the loading of Fe did not alter the microstructure of ZIF-8, but only resulted in an increase in the size of the synthesized ZIF-8 framework.

[0094] The XRD patterns of Fe2P(x)@P(y)NC-z prepared in Examples 1-3 are as follows: Figure 3 As shown, through Figure 3 It can be seen that all materials exhibit two broad diffraction peaks near 2θ = 24.3 and 43.7°, which are attributed to the (0,0,2) and (1,0,1) crystal planes of graphite carbon, respectively. Compared with the materials with lower Fe loading (i.e., Fe2P(0.0625)@P(1.0)NC-950), the materials with higher Fe loading (i.e., Fe2P(0.125)@P(1.0)NC-950, Fe2P(0.125)@P(1.0)NC-1050, Fe2P(0.125)@P(2.0)NC-950 and Fe2P(0.25)@P(1.0)NC-950) exhibit two weak diffraction peaks near 40.3 and 44.2°, which are attributed to the (1,1,1) and (2,0,1) crystal planes of Fe2P, respectively. Furthermore, the XRD pattern reveals that increasing the carbonization temperature, Fe loading, and P doping concentration are beneficial to the formation of Fe2P crystals.

[0095] The Fe2P(0.125)@P(1.0)NC-950 prepared in Example 1 was characterized by transmission electron microscopy (TEM), and the results are as follows: Figure 4 As shown, where, Figure 4 In the image, 'a' represents the TEM image of the material. Figure 4 In the image, b is a high-magnification TEM image of the material. Figure 4 In the diagram, 'c' represents the selected area electron diffraction pattern of the material. Figure 4 In the image, d represents the TEM image of the material. Figure 4 In the diagram, 'e' represents the carbon element distribution of the material. Figure 4 f in the figure represents the distribution of O element in the material. Figure 4 In the figure, g represents the N element distribution map of the material. Figure 4 In the diagram, h represents the P element distribution of the material. Figure 4 In the diagram, 'i' represents the Fe element distribution of the material. Figure 4 The scale bar for d to i in the figure is 50 nm. Figure 4 The results show that the Fe(x)@ZIF-8 framework retains a certain rhombic dodecahedral structure after phosphating and high-temperature carbonization, without causing the collapse of the ZIF-8 framework. Elemental distribution images show that C, O, N, P, and Fe elements are uniformly distributed in the material structure, with the uniform distribution of N and P elements indicating the successful synthesis of a nitrogen-phosphorus co-doped carbon matrix.

[0096] The elemental composition of the material surface and bulk phase was characterized using X-ray photoelectron spectroscopy (XPS), elemental analysis, and inductively coupled plasma-enhanced optical emission spectroscopy (ICP-OES). The results are shown in Tables 1 and 2. The characteristic peaks in the P 2p region of P can be deconvolved and fitted into four peaks: the 2p peaks of P-Fe. 3 / 2 2p of P-Fe 1 / 2 The presence of PC and P-Fe bonds indicates that P atoms were successfully doped into the carbon matrix and formed Fe-P coordination after phosphating and carbonization. The characteristic peaks of the N1s region of N can be deconvolved and fitted into five peaks: pyridine N, N-Fe, pyrrole N, graphitic N, and N oxide. The content of peaks formed by deconvolution fitting of the P 2p and N1s spectra is summarized in Table 2. The N-Fe bonds present in the N 1s region and the P-Fe bonds present in the P 2p region demonstrate the coexistence of Fe-N and Fe-P coordination in the P-doped material.

[0097] Table 1. Elemental composition of the material surface and bulk phase.

[0098]

[0099]

[0100] Table 2 Fitting results of the P 2p and N1s regions in XPS spectra

[0101]

[0102] The surface impedance, specific surface area, and water contact angle of the measured materials are shown in Table 3. Materials with higher carbonization temperatures and phosphorus doping levels exhibited lower surface impedance, indicating that increasing the carbonization temperature and phosphorus doping level can improve the conductivity and specific surface area of ​​the materials. All materials exhibited excellent hydrophilicity. This is mainly due to the introduction of many hydrophilic surface functional groups during N-doping and P-doping. Increasing the carbonization temperature led to a decrease in hydrophilicity because high-temperature carbonization causes the decomposition of some functional groups on the material surface. Phosphating treatment improved the hydrophilicity of the materials, which is beneficial for improving the dispersion of the materials in water and reducing the mass transfer resistance during material reactions.

[0103] Table 3 Results of surface impedance, specific surface area, and water contact angle of the materials.

[0104]

[0105]

[0106] Comparative Example 1

[0107] The only difference between this comparative example and Example 1 is that no phosphorus source is added during the reaction process in step 2) (the heating step is performed as in Example 1). Finally, the material Fe(x)@NC-z is obtained.

[0108] The Fe(x)@NC-950 materials with different loadings prepared according to the above synthesis steps are: Fe(0.0625)@NC-950, Fe(0.125)@NC-950 and Fe(0.25)@NC-950; the Fe loadings in the materials are 0.96, 1.97 and 4.21 wt%, respectively.

[0109] Comparative Example 2

[0110] The only difference between this comparative example and Example 1 is that the amount of iron precursor molecules added to solution B in step 1) is zero, and no phosphorus source is added during the reaction process in step 2). The final material obtained is NC-z.

[0111] The material prepared according to the above synthesis steps is NC-950, wherein the Fe loading is 0 wt%.

[0112] Comparative Example 3

[0113] The only difference between this comparative example and Example 1 is that the amount of iron precursor molecules added to solution B in step 1) is zero, and the final material P(y)NC-z is obtained.

[0114] The material prepared according to the above synthesis steps is P(1.0)NC-950, wherein the Fe loading is 0 wt%.

[0115] Application Example 1

[0116] The materials prepared in Example 1 and Comparative Examples 1-3 were applied to the reaction of reducing bromate ions in an aqueous phase.

[0117] The reaction conditions used were: ambient temperature and pressure; initial solution pH: 6.0; material dosage: 0.25 g / L; initial bromate (potassium bromate) concentration: 0.08 mmol / L; reaction time: 2 h; stirring speed: 400 rpm. To evaluate the leaching of iron ions during the reduction and removal of bromate ions by the reducing agent, the reaction solution after 2 h was filtered, and the concentration of Fe ions in the solution was determined by the o-phenanthroline spectrophotometric method.

[0118] Figure 5 The results show the reduction performance of different materials for bromate ions. Figure 5 In the figure, 'a' represents the reduction / removal curve. Figure 5 In the figure, b represents the Fe leaching result during the reaction process. NC-950 and P(1.0)NC-950, as control materials without Fe loading, showed bromate ion reduction rates of only 9.8% and 16.3%, respectively, within 120 min. This reduction effect may be due to the presence of some active sites in the carbon-based materials doped with heteroelements. After Fe loading, the removal rate of bromate ions reached over 85.5%. Figure 6 The concentration-time distribution and mass balance curves of bromate ions and reduction products (bromine ions) in the reaction solution containing the Fe2P(0.125)@P(1.0)NC-950 material synthesized in Example 1 were obtained. The results showed that the material could completely reduce bromate ions to bromide ions within 90 minutes, with a mass balance greater than 95%. This indicates that bromate ions are reduced and removed rather than adsorbed on the iron-containing material. Furthermore, the reduction effect of the material was greatly enhanced after Fe loading, indicating that Fe is the main active component in the bromate ion reduction reaction. Figure 5 Figure a shows that the reduction effect of the material increases with increasing Fe loading, and P doping also increases the reduction and removal rate of bromate ions. Iron leaching during the reaction process is commonly used as a standard for evaluating the stability of iron-based materials. Figure 5 In the figure, b represents the Fe leaching results of different materials during the reaction process. P doping significantly inhibits iron leaching during the reaction process. The high activity and high stability of P-doped Fe-based materials are largely attributed to the formation of Fe-P species, as evidenced by the presence of Fe2P species in the XPS and XRD spectra of Fe 2p and P 2p.

[0119] Highly dispersed Fe components are embedded in a conductive carbonaceous matrix, forming a metal-carbon heterojunction. This heterojunction induces the Mott-Schottky effect through spontaneous electron transfer from the Fermi level to the carbonaceous matrix. Therefore, bromate ions can be readily reduced to bromide ions by active electrons enriched on the carbon-based surface. Since bromate ion reduction involves electron transfer between the metal and the carbon support, the conductivity of the support strongly influences the reaction efficiency. Table 3 shows that P doping reduces the surface impedance of the material from 381.5 Ω (Fe(0.125)@NC-950) to 170.1 Ω (Fe2P(0.125)@P(1.0)NC-950) because P doping increases the carrier concentration, thereby improving the conductivity of the carbon matrix. Furthermore, Table 3 shows that P doping causes a more significant change in the ZIF-8 framework. Compared with Fe(0.125)@NC-950, Fe2P(0.125)@P(1.0)NC-950 has a larger specific surface area and better dispersibility in water, which is also the reason for the enhanced reduction activity of P-doped materials.

[0120] Application Example 2

[0121] The initial pH of the solution in Application Example 1 was adjusted to 4, 6, 8, and 10. The material Fe2P(0.125)@P(1.0)NC-950 from Example 1 was then applied to the reduction reaction to investigate the effect of different reaction pH values ​​on the reduction and removal of bromate. The results are as follows: Figure 7 As shown, where Figure 7 In the figure, 'a' represents the reduction / removal curve. Figure 7 In the figure, b represents the Fe leaching result in the reaction. As shown, the reduction rate of bromate ions by the material decreases with increasing pH in the reaction system. This pH dependence may be due to the presence of H+ in the solution. + It directly participates in the reduction reaction and the change in the reduction potential of bromate ions with pH. As the reduction reaction proceeds, the H+ in the solution... + The concentration of bromate gradually decreased, leading to a corresponding increase in the pH of the reaction system. Since the reduction reaction potential increases with increasing pH, acidic conditions favor the reduction of bromate ions. Furthermore, because the conversion rate of bromate ions is directly proportional to the rate of bromate ion adsorption on the material surface, and increasing the pH inhibits bromate ion adsorption, increasing the reaction pH leads to a decrease in the bromate ion reduction rate. After reacting for 120 min at pH = 10.0, the bromate ion conversion rate of Fe2P(0.125)@P(1.0)NC-950 remained around 80%. Notably, the Fe leaching amount of Fe2P(0.125)@P(1.0)NC-950 material during the reaction process ranged from 22.98 to 4.53 μg / L, indicating that the material exhibits outstanding stability.

[0122] Application Example 3

[0123] To explore the possibilities and prospects of the material in practical environmental applications, the dosage of Fe2P(0.125)@P(1.0)NC-950 in Example 1 was adjusted to 0.25 g / L, and the initial concentration of bromate pollution was adjusted to 0.08 mmol / L. The reaction water samples were ultrapure water, ultrapure water (with added inorganic salts), ultrapure water (with added organic matter), tap water, and water samples from the Yangtze River and Jiuxiang River. The water quality parameters of the water samples are shown in Table 4. The remaining conditions were the same as in Application Example 1.

[0124] Table 4 Water quality parameters of water samples

[0125]

[0126] Test results are as follows Figure 8 As shown, compared with the ultrapure water control sample, the reduction rate of bromate ions by the material in tap water, the Yangtze River, and the Jiuxiang River samples decreased to 97%, 91%, and 83%, respectively. The higher pH value in the actual water samples is one of the reasons for the decreased reduction efficiency of bromate ions. Meanwhile, the salinity and total organic carbon value of tap water, the Yangtze River, and the Jiuxiang River are much higher than those of ultrapure water, indicating that the inorganic ions and dissolved organic matter in the actual water samples are much higher than those in ultrapure water. To further verify the influence of inorganic ions and dissolved organic matter on the reduction reaction of the material, we studied the reduction rate of the material in ultrapure water with the addition of inorganic salts and humic acid, respectively. The reduction rate of bromate ions in ultrapure water (with added inorganic salts) was slightly slower, but bromate ions could still be completely reduced within 120 min. The reduction rate of the material in ultrapure water (with added organic matter) only reached 94%. The above experimental results regarding different bromate ion concentrations indicate that the reduction process is affected by the adsorption of bromate ions on the surface of the material. Inorganic ions and dissolved organic matter may compete with bromate ions for adsorption on the material surface, thereby inhibiting the reduction of ultrapure water (with added inorganic salts) and ultrapure water (with added organic matter). In summary, when this material is used to reduce bromate ion contaminants in actual water samples, its reduction efficiency is not only inhibited by the high pH value of the actual water body, but also adversely affected by the presence of inorganic ions and dissolved organic compounds in the water. Nevertheless, the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material obtained in this invention still shows considerable potential for practical environmental applications.

[0127] Application Example 4

[0128] The Fe2P(0.125)@P(1.0)NC-950 prepared in Example 1 was tested for its reduction and removal effect on bromate ions using the detection method described in Example 1.

[0129] Repeat the detection steps again with the used Fe2P(0.125)@P(1.0)NC-950;

[0130] Then, the used Fe2P(0.125)@P(1.0)NC-950 is regenerated. The regeneration method is as follows:

[0131] (1) Collect the used materials:

[0132] 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 to dry for 12 hours.

[0133] (2) Regenerated and restored materials:

[0134] The used material was placed in the middle of the constant temperature zone of a tube furnace. Sodium hypophosphite was placed 1 cm upstream of the material as the phosphorus source, with a sodium hypophosphite to material ratio of 0.5:1. Under a high-purity nitrogen atmosphere of 25 mL / min, the tube furnace was heated to 350℃ and held for 0.5 h to perform phosphating regeneration treatment on the material. The phosphating regenerated material was obtained and designated as Cycle-1, and wastewater reduction tests were performed again. The above regeneration-test steps were repeated to obtain the test results for Cycle-2, Cycle-3, Cycle-4, and Cycle-5. The test results are as follows: Figure 9 As shown, through Figure 9 It can be seen that the reduction rate of bromate ions in the used material is significantly reduced, reaching only about 50% of the initial value. XPS analysis of the used material, as shown in Table 5, reveals a significant increase in oxygen content on the material surface after the reaction, indicating a certain degree of oxidative deactivation on the material surface after the reduction reaction. In contrast, XPS results show that the oxygen content in the regenerated material is close to that of the initial Fe2P(0.125)@P(1.0)NC-950 material. The material after phosphating regeneration treatment exhibits a 100% bromate ion removal rate within 90 minutes, completely restoring its original activity, and the material can maintain a bromate ion removal rate of over 85% after 5 regeneration cycles.

[0135] Table 5. Elemental composition of the surface and bulk phase of the material after reaction and after phosphating regeneration.

[0136]

[0137] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0138] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material, characterized in that, Includes the following steps: 1) Iron precursor molecules, zinc salt, organic ligands and solvent are mixed and polymerized to obtain Fe@ZIF-8 material; 2) The Fe@ZIF-8 material obtained in step 1) is subjected to phosphating and carbonization reactions with a phosphorus source in sequence to obtain a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material. The iron precursor molecule includes one or more of ferric acetylacetone, ferrous acetylacetone, ferrocene, and ferrophthalic acid. In step 2), the mass ratio of Fe@ZIF-8 material to phosphorus source is 1:0.1~3; The phosphorus source in step 2) includes sodium hypophosphite and / or potassium hypophosphite.

2. The method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 1, characterized in that, In step 1), the molar ratio of iron in the iron precursor molecule, zinc in the zinc salt, and organic ligand is 0.01~1.5:1:2~16, and the molar volume ratio of iron in the iron precursor molecule to solvent is 0.01~1.5:15~30mL.

3. The method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 1, wherein the polymerization reaction temperature is 20~160℃ and the polymerization reaction time is 4~36h.

4. The method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 1, wherein the zinc salt comprises one or more of zinc nitrate, zinc chloride, and zinc sulfate; The organic ligand is 2-methylimidazole; The solvent includes methanol.

5. The method for preparing a nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 1, wherein the phosphating reaction temperature is 300~400℃ and the phosphating reaction time is 0.5~4h; the carbonization reaction temperature is 850~1050℃ and the carbonization reaction time is 1~4h.

6. The nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 6 in the reduction of pollutants in water.

8. The regeneration of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material according to claim 6, characterized in that, The regeneration method includes the following steps: The used nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material was subjected to a phosphating regeneration reaction with a phosphorus source to complete the regeneration of the nitrogen-phosphorus co-doped carbon-based confined iron phosphide composite material.

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