Preparation method and application of an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites.

Abstract

This invention discloses a method for preparing and applying an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites. The method includes: preparing Fe2O3 nanoparticles via a simple hydrothermal synthesis, followed by high-temperature calcination of the Fe2O3 nanoparticles with ammonium bicarbonate assistance. During this process, NH3 generated from ammonium bicarbonate is used as a reducing agent and a source of N dopant, successfully preparing the N-doped Fe3O4 composite material (Fe-xN-T). This preparation method is simple and low-cost, and the N element in the resulting product exists as interstitial N and is uniformly dispersed on the Fe3O4. The prepared N-doped Fe3O4 composite material can be used for the efficient catalytic ozone degradation of organic pollutants in tap water or municipal wastewater.

Description

Technical Field

[0001] This invention relates to the fields of nanomaterials and water purification technology, and particularly to an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites, its preparation method, and its application. Background Technology

[0002] To address the unpleasant odors and potential safety hazards caused by pyrazines in drinking water, there is an urgent need to develop efficient methods for their degradation. Currently, there are relatively few reported methods for degrading pyrazines, with biodegradation methods suffering from problems such as long cycles, harsh microbial survival conditions, and low degradation efficiency. Ozone oxidation has attracted much attention due to its high efficiency, rapid response, residue-free process, and environmental friendliness; however, ozone oxidation alone exhibits some selectivity in pollutant degradation. Introducing a catalyst can effectively promote ozone activation, generating reactive oxygen species such as hydroxyl radicals, which can effectively accelerate the degradation of recalcitrant organic compounds.

[0003] The long-term, high-efficiency, and stable processing capacity of ozone catalytic oxidation largely depends on the selected catalyst material. Metal oxides have attracted much attention as ozone oxidation catalysts. Iron oxide catalysts have multiple advantages, including being environmentally friendly, economical, low-toxicity, and sustainable. However, traditional metal oxide catalysts face many challenges, including easy agglomeration, secondary pollution caused by metal leaching, poor stability, and easy deactivation. In recent years, numerous studies have shown that heteroatom doping (e.g., nitrogen (N), sulfur (S), boron (B) elements) can modify the surface and electronic structure of metal oxides, enhance electron transport and activity, alleviate metal leaching and catalyst deactivation, and improve catalyst activity and stability.

[0004] In existing nitrogen doping of metal oxides, the doped nitrogen mainly exists in the form of nitrogen substitution. Nitrogen replaces some of the oxygen atoms in the metal oxide, allowing the metal to continue to exist in a saturated valence state. This not only fails to expose the metal sites to form new active centers, but also changes the molecular framework structure of the metal oxide, reducing its stability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing interstitial N-doped Fe3O4 composite materials with electron-rich Fe sites and their applications, aiming to alleviate the problems of iron ion dissolution and catalyst deactivation, thereby improving the activity and stability of the catalyst. Nitrogen (N) is widely available, and the preparation process of N-doped metal oxides is relatively simple and inexpensive. This method is expected to improve catalyst performance and provide a feasible solution for ozone catalytic oxidation processes.

[0006] In a first aspect, the present invention provides a method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites, the process of which is as follows:

[0007] Fe2O3 nanoparticles and ammonium bicarbonate powder were placed in different locations for calcination, and a protective gas atmosphere was provided during the calcination process, flowing from the location of the ammonium bicarbonate powder to the location of the Fe2O3 nanoparticles; the calcination temperature was 150℃~250℃; during the calcination process, ammonium bicarbonate pyrolyzes to produce NH3, and NH3 reduces Fe2O3 in the calcination environment and serves as the nitrogen source for nitrogen doping, reacting to generate interstitial N-doped Fe3O4 composite material.

[0008] This preparation method is simple, low-cost, and non-toxic. Nitrogen (N) exists as interstitial N and is uniformly distributed on Fe3O4, forming an Fe-N structure. This does not affect the original framework structure of Fe3O4, resulting in a composite material with higher stability. Simultaneously, the interstitial N forms additional chemical bonds with Fe, promoting the formation of electron-rich Fe sites. These electron-rich Fe sites contribute to ozone activation, generating hydroxyl radicals that effectively degrade organic pollutants in tap water or municipal wastewater.

[0009] Preferably, both Fe2O3 nanoparticles and ammonium bicarbonate powder are placed in a covered elongated crucible; the Fe2O3 nanoparticles are placed near the gas outlet of the crucible, and the ammonium bicarbonate powder is placed near the gas inlet of the crucible.

[0010] Preferably, the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder is 1:(1-5);

[0011] Preferably, the distance between the Fe2O3 nanoparticles and the ammonium bicarbonate powder placed in the covered elongated crucible should be between 3cm and 6cm.

[0012] Preferably, the amount of Fe2O3 nanoparticles remains constant, while the amount of ammonium bicarbonate powder varies with a specified molar ratio.

[0013] Preferably, the calcination conditions are to heat to the calcination temperature in a high-purity argon atmosphere, maintain the temperature for 20 to 50 minutes, and then allow it to cool naturally.

[0014] As a preferred method, the preparation process of Fe2O3 nanoparticles is as follows:

[0015] a. Dissolve ferric nitrate in deionized water and stir to obtain ferric nitrate solution.

[0016] b. Add an ammonia solution containing 25% to 28% ammonia dropwise to the ferric nitrate solution until the pH of the mixed solution is 9, then stop adding the ammonia solution and continue stirring.

[0017] c. The mixed solution obtained in step b is subjected to a hydrothermal synthesis reaction.

[0018] d. After the hydrothermal synthesis reaction is completed, the solid product obtained is washed and dried to obtain Fe2O3 nanoparticles.

[0019] Preferably, the magnetic stirring speed in step b is 200 r / min to 800 r / min.

[0020] Preferably, in step c, the hydrothermal synthesis reaction temperature is 40℃~160℃, and the reaction time is 8h~16h.

[0021] Preferably, the rinsing step d consists of rinsing with deionized water 0 to 5 times and rinsing with anhydrous ethanol 0 to 5 times.

[0022] Preferably, the drying process described in step d is drying in an oven at 40℃~120℃ for 8h~24h.

[0023] Secondly, the present invention provides a method for preparing interstitial N-doped Fe3O4 composite materials for ozone catalytic degradation of organic pollutants in tap water or municipal sewage.

[0024] Preferably, the organic pollutant is 2-ethyl-5-methylpyrazine.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. In the interstitial N-doped Fe3O4 composite material (Fe-xN-T) prepared by this invention, the N element exists as interstitial N and is uniformly distributed on Fe3O4, forming an Fe-N structure. This improves the stability of the catalyst, extends its service life, and reduces activity loss due to repeated use. Simultaneously, in this invention, ammonium bicarbonate powder and Fe2O3 nanoparticles are calcined in the same environment at 150℃ to 250℃. This temperature range allows ammonium bicarbonate to decompose and produce NH3 while preventing Fe2O3 from being reduced to zero-valent iron due to excessively high temperatures. This allows a series of reactions, including ammonium bicarbonate decomposition, Fe3O4 formation, and nitrogen doping, to be completed in a single calcination, simplifying the preparation process of the interstitial N-doped Fe3O4 composite material and reducing preparation costs.

[0027] 2. The interstitial N-doped Fe3O4 used in this invention to construct an electron-rich Fe-site composite material (Fe-xN-T) helps improve the electron transport capacity of the catalyst and enhance its electron transfer efficiency in catalytic reactions. This facilitates the effective utilization of electron transfer between ozone and organic matter to promote degradation reactions.

[0028] 3. In the interstitial N-doped Fe3O4 composite material (Fe-xN-T) prepared by this invention, the electron-rich Fe sites can react more effectively with ozone to generate hydroxyl radicals, thereby accelerating the degradation rate of pollutants.

[0029] 4. The interstitial N-doped Fe3O4-constructed electron-rich Fe site composite material (Fe-xN-T) prepared in this invention is expected to reduce the demand for rare elements and expensive metals, making the catalyst more environmentally friendly and sustainable.

[0030] 5. The interstitial N-doped Fe3O4 composite material (Fe-xN-T) prepared by this invention exhibits stable properties and good reproducibility in oxidative systems. Attached Figure Description

[0031] Figure 1 X-ray diffraction (XRD) pattern of Fe-2N-200 composite material provided by the present invention;

[0032] Figure 2 X-ray photoelectron spectroscopy (XPS) images of Fe-2N-200 composite material, Fe-2N-300 composite material and Fe3O4-2N(s) composite material provided for this invention;

[0033] Figure 3 The efficiency diagram of the series of composite materials provided by the present invention for degrading a pyrazine compound, 2-ethyl-5-methylpyrazine (EMP). Detailed Implementation

[0034] The following detailed embodiments further illustrate the present invention, but should not be construed as limiting the invention. Any simple modifications or substitutions made to the methods, steps, or conditions of the present invention without departing from its spirit and essence are within the scope of the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0035] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0036] Example 1:

[0037] A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites includes the following steps:

[0038] Step 1: Preparation of Fe2O3 nanoparticles.

[0039] 1-1.9 g of Fe(NO3)3·9H2O powder was dissolved in 100 mL of deionized water to obtain a ferric nitrate solution. Ammonia solution was added dropwise to the ferric nitrate solution until the pH of the mixed solution reached 9. After stirring for 30 minutes, the mixed solution was transferred to a polytetrafluoroethylene (PTFE) vessel for hydrothermal synthesis. The ammonia solution was an aqueous solution containing 25%-28% ammonia. The ferric nitrate solution was prepared by dissolving 9 g of Fe(NO3)3·9H2O powder in 100 mL of deionized water. The PTFE vessel was a 200 mL volume vessel equipped with a corresponding high-pressure reactor. The hydrothermal synthesis reaction was carried out in an oven at 80°C for 10 hours.

[0040] 1-2. After the hydrothermal synthesis reaction, the obtained solid was rinsed three times each with deionized water and anhydrous ethanol to remove residual chemicals from the solid surface. The rinsed solid component, free of chemical residue, was then dried to obtain Fe2O3 nanoparticles. The drying procedure was to dry in an oven at 60℃ for 12 hours.

[0041] Step 2: Prepare Fe3O4 nanoparticles and complete nitrogen doping.

[0042] 2-1. Place ammonium bicarbonate and Fe2O3 nanoparticles at opposite ends of a covered alumina square crucible; maintain a distance of 4 cm between the ammonium bicarbonate and Fe2O3 nanoparticles; place the end with ammonium bicarbonate near the gas inlet of the alumina square crucible, and place the end with Fe2O3 nanoparticles near the gas outlet of the alumina square crucible.

[0043] 2-2. A square alumina crucible is calcined at high temperature, causing ammonium bicarbonate to pyrolyze and generate NH3. The NH3 is then carried by the gas flow past the Fe2O3 nanoparticles. NH3 acts as a reducing agent and a source of nitrogen dopant, reacting with the Fe2O3 nanoparticles to generate interstitial N-doped Fe3O4 composite material (Fe-xN-T). The high-temperature calcination procedure is as follows: under the protection of high-purity argon, the temperature is increased to 200℃ at a rate of 5℃ per minute and held for 30 minutes, followed by natural cooling. The resulting material is then milled to obtain the Fe-xN-T composite material.

[0044] In this step, the mass of Fe2O3 nanoparticles used for high-temperature calcination is 0.5g, and the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder is 1:2. Therefore, the mass of ammonium bicarbonate powder used for high-temperature calcination is 0.494g.

[0045] In this embodiment, a Fe-xN-T composite material was prepared, where x represents the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder used in the preparation process, and T represents the calcination temperature (in °C). Within the specified molar ratio and calcination temperature range, Fe in Fe-xN-T exists entirely as Fe3O4, and N exists entirely as interstitial N. The X-ray diffraction (XRD) pattern of Fe-2N-200 is shown below. Figure 1 As shown, this indicates that Fe exists in Fe-2N-200 as Fe3O4. The X-ray photoelectron spectroscopy (XPS) spectrum of N1s in Fe-2N-200 is shown below. Figure 2 As shown, N exists in Fe-2N-200 in an interstitial form.

[0046] Example 2

[0047] A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites. The difference between this embodiment and Example 1 is that the calcination temperature in steps 2-2 is different; in this embodiment, the calcination temperature is 150℃, and the resulting material is named Fe-2N-150.

[0048] Example 3

[0049] A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites is disclosed. The difference between this embodiment and Example 1 is that the calcination temperature in steps 2-2 is different; in this embodiment, the calcination temperature is 250℃, and the resulting material is named Fe-2N-250.

[0050] Example 4

[0051] A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites is disclosed. The difference between this embodiment and Example 1 lies in the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder; in this embodiment, the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder is 1:1. The amount of Fe2O3 nanoparticles remains constant at 0.5 g, while the amount of ammonium bicarbonate powder is adjusted accordingly based on the specified molar ratio. The resulting material is named Fe-1N-200.

[0052] Example 5

[0053] A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites is disclosed. The difference between this embodiment and Example 1 lies in the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder; in this embodiment, the molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder is 1:5. The amount of Fe2O3 nanoparticles remains constant at 0.5g, while the amount of ammonium bicarbonate powder is adjusted accordingly based on the specified molar ratio. The resulting material is named Fe-5N-200.

[0054] Comparative Example 1

[0055] A method for preparing a N-substituted doped Fe3O4 composite material is disclosed. The difference between this comparative example and Example 1 lies in the calcination temperature in steps 2-2; in this example, the calcination temperature is 300℃, and the resulting material is named Fe-2N-300, where N exists in the form of substituted N. The X-ray photoelectron spectroscopy (XPS) spectrum of N1s of Fe-2N-300 is shown below. Figure 2 As shown.

[0056] Comparative Example 2

[0057] A method for preparing a N-doped Fe3O4 composite material includes the following steps:

[0058] Step 1: Preparation of Fe2O3 nanoparticles.

[0059] 1-1.9 g of Fe(NO3)3·9H2O powder was dissolved in 100 mL of deionized water to obtain a ferric nitrate solution. Ammonia solution was added dropwise to the ferric nitrate solution until the pH of the mixed solution reached 9. After stirring for 30 minutes, the mixed solution was transferred to a polytetrafluoroethylene (PTFE) vessel for hydrothermal synthesis. The ammonia solution was an aqueous solution containing 25%-28% ammonia. The ferric nitrate solution was prepared by dissolving 9 g of Fe(NO3)3·9H2O powder in 100 mL of deionized water. The PTFE vessel was a 200 mL volume vessel equipped with a corresponding high-pressure reactor. The hydrothermal synthesis reaction was carried out in an oven at 80°C for 10 hours.

[0060] 1-2. After the hydrothermal synthesis reaction, the obtained solid was rinsed three times each with deionized water and anhydrous ethanol to remove residual chemicals from the solid surface. The rinsed solid component, free of chemical residue, was then dried to obtain Fe2O3 nanoparticles. The drying procedure was to dry in an oven at 60℃ for 12 hours.

[0061] Step 2: Prepare Fe3O4 nanoparticles and complete nitrogen doping.

[0062] 2-1. Mix 0.494g of ammonium bicarbonate powder and 0.5g of Fe2O3 nanoparticles in a mortar and pestle for 30 minutes until fully mixed, and then place them in a covered alumina square crucible.

[0063] 2-2. The alumina square crucible was calcined at high temperature, causing ammonium bicarbonate to pyrolyze and generate NH3. NH3 served as a reducing agent and a source of doped nitrogen, reacting with Fe2O3 nanoparticles. The high-temperature calcination procedure was as follows: under the protection of high-purity argon, the temperature was increased to 200℃ at a rate of 5℃ per minute and held for 30 minutes, followed by natural cooling. The resulting material was then milled to obtain a substituted nitrogen-doped Fe3O4 composite material, named Fe3O4-2N(s).

[0064] The N-substituted Fe3O4 composite material (Fe3O4-2N(s)) prepared in this comparative example has N present in the form of substituted N. The X-ray photoelectron spectroscopy (XPS) spectrum of N1s of Fe3O4-2N(s) is shown in the figure below. Figure 2 As shown.

[0065] Example 6

[0066] Application of N-doped Fe3O4 composite materials provided in Examples 1-5 and Comparative Examples 1-2, which are used for the degradation of EMP and its odor removal.

[0067] The effectiveness of this embodiment was verified using the following experiments:

[0068] This experiment simulates the application of various prepared composite materials in the efficient degradation of odorous organic pollutants, specifically 2-ethyl-5-methylpyrazine (EMP), using ozone catalysis. EMP was dissolved in 1 L of deionized water to a concentration of 5 μm / L and then added to an ozone catalytic reactor. The materials prepared in Examples 1-5 and Comparative Examples 1-2 were then added to the solution in the ozone catalytic reactor, with a catalyst dosage of 0.03 g / L and a total dosage of 30 mg. Ozone was continuously aerated into the reactor, and the ozone concentration was measured at the reactor outlet. Samples of the simulated wastewater were taken at regular intervals to monitor the EMP concentration.

[0069] The test results are as follows Figure 3 As shown, in Figure 3 In the diagram, the ● line represents the remaining concentration of EMP without a catalyst. The line represents the remaining EMP concentration when the Fe-2N-200 composite material prepared in Example 1 is added. The line represents the remaining EMP concentration when the Fe-2N-150 composite material prepared in Example 2 is added. The line represents the remaining EMP concentration when the Fe-2N-250 composite material prepared in Example 3 is added. The line represents the remaining EMP concentration when the Fe-1N-200 composite material prepared in Example 4 is added. The line represents the remaining EMP concentration when the Fe-5N-200 composite material prepared in Example 5 is added; the line with a '■' represents the remaining EMP concentration when the Fe-2N-300 composite material prepared in Comparative Example 1 is added; and the line with a '□' represents the remaining EMP concentration when the Fe3O4-2N(s) composite material prepared in Comparative Example 2 is added. Figure 3 The results showed that after 30 minutes of reaction, ozone oxidized 37.6% of EMP without a catalyst. However, with the catalysts Fe-2N-200, Fe-2N-150, Fe-2N-250, Fe-1N-200, Fe-5N-200, Fe-2N-300, and Fe3O4-2N(s), the EMP degradation efficiencies after 30 minutes were 100.0%, 86.4%, 94.6%, 90.8%, 90.1%, 48.7%, and 50.2%, respectively. The interstitial N-doped Fe3O4 composite materials prepared according to this invention all exhibited highly efficient ozone-catalyzed EMP degradation performance, while the performance of the substituted N-doped Fe3O4 composite materials prepared in the comparative proportions was poor. The Fe-2N-200 composite catalyst exhibited the best performance in catalyzing the degradation of EMP by ozone. Furthermore, ICP-OES testing showed that in simulated wastewater at pH 3, pH 5, pH 7, and pH 9, the iron ion dissolution after 30 minutes of reaction was only 0.046, 0.032, 0.027, and 0.015 mg / L, respectively, indicating extremely low dissolution rates. This demonstrates the high stability of the interstitial N-doped Fe3O4 composite catalyst.

Claims

1. A method for preparing an interstitial N-doped Fe3O4 composite material with electron-rich Fe sites, characterized in that: The process is as follows: Fe2O3 nanoparticles and ammonium bicarbonate powder were placed in different locations for calcination, and a protective gas atmosphere was provided during the calcination process, flowing from the location of the ammonium bicarbonate powder to the location of the Fe2O3 nanoparticles; the calcination temperature was 150℃~250℃; during the calcination process, ammonium bicarbonate pyrolyzes to produce NH3, and NH3 reduces Fe2O3 in the calcination environment and serves as a nitrogen source for nitrogen doping, reacting to generate interstitial N-doped Fe3O4 composite material. The molar ratio of Fe2O3 nanoparticles to ammonium bicarbonate powder is 1:(1~5); during calcination, the distance between ammonium bicarbonate powder and Fe2O3 nanoparticles is 3cm~6cm.

2. The preparation method according to claim 1, characterized in that: The calcination conditions are to heat to the calcination temperature under a high-purity argon atmosphere, maintain the temperature for 20 to 50 minutes, and then allow it to cool naturally.

3. The preparation method according to claim 1, characterized in that: The preparation process of Fe2O3 nanoparticles is as follows: a. Dissolve ferric nitrate in deionized water and stir to obtain a ferric nitrate solution; b. Add an ammonia solution containing 25%–28% ammonia dropwise to the ferric nitrate solution until the pH of the mixed solution is 9, then stop adding the ammonia solution and continue stirring; c. The mixed solution obtained in step b is subjected to a hydrothermal synthesis reaction; d. The solid product obtained after the hydrothermal synthesis reaction is completed is washed and dried to obtain Fe2O3 nanoparticles.

4. The preparation method according to claim 3, characterized in that: In step b, the stirring rate is 200 r / min to 800 r / min.

5. The preparation method according to claim 3, characterized in that: In step c, the hydrothermal synthesis reaction temperature is 40℃~160℃, and the reaction time is 8 h~16 h.

6. The preparation method according to claim 3, characterized in that: The drying process described in step d involves drying in an oven at 40 ℃ to 120 ℃ for 8 h to 24 h.

7. The application of the interstitial N-doped Fe3O4 composite material prepared by the preparation method described in claim 1 in the ozone catalytic degradation of organic pollutants in tap water or municipal sewage.

8. The application according to claim 7, characterized in that: The organic pollutant is 2-ethyl-5-methylpyrazine.

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