A method for preparing zero-valent iron with a high Fe(II) content magnetite interface by regulating the redox intensity

Abstract

The application discloses a preparation method of zero-valent iron with a high Fe(II) content magnetite interface by regulating the redox intensity, and belongs to the field of water treatment. The method comprises the following steps: uniformly mixing zero-valent iron particles and ferrous ion solution at 20 DEG C-30 DEG C, regulating the initial pH value to 1-4 by using a sulfuric acid solution, adding a sulfur ion solution after 20 min of reaction and reacting for another 5 min, wherein the mass ratio of the added sulfur ion to the initial ferrous ion is 0.2-0.4:1; after the reaction is completed, the zero-valent iron particles are separated by magnetism, and are dried in a vacuum oven at 40 DEG C-60 DEG C for 4-12 h to obtain Fe3O4@mZVI materials. The zero-valent iron composite material with a high Fe(II) content magnetite interface prepared by the method can be prepared in an open system without controlling the anaerobic reaction atmosphere environment. Meanwhile, the ferrous ion is oxidized by using air, and no external oxidizing agent is needed, so that the method has the advantages of simple and rapid preparation and low cost. In the preparation process, the sulfur ion is added to regulate the redox reaction degree, the proportion of Fe(II) on the material surface is significantly improved, and the zero-valent iron composite material has better reaction activity and durability for pollutant removal.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically relating to a method for preparing zero-valent iron by controlling the redox intensity to prepare a high Fe(II) content iron(III) oxide interface. Background Technology

[0002] Zero-valent iron (ZVI) is a commonly used material in water treatment for pollutant removal. Due to its strong reducing properties, it can act as an electron donor, continuously releasing electrons to effectively reduce and remove recalcitrant pollutants such as nitro compounds and halogenated hydrocarbons. However, during use, a (hydro)oxide passivation film gradually forms on the surface of ZVI. This film hinders electron transfer, thereby reducing the catalytic activity and utilization efficiency of ZVI.

[0003] To alleviate the surface passivation problem of ZVI and improve its reactivity, surface modification has become an effective strategy. Among these methods, sulfidation modification is widely used due to its high efficiency, ease of operation, and low cost. This process generates a conductive iron sulfide layer (such as FeS and FeS2) on the ZVI surface. The newly formed interface does not affect electron transfer but can significantly suppress the side reactions between zero-valent iron and water, inhibit the accumulation of the passivation layer, and extend the lifespan of zero-valent iron. However, the sulfidation process of ZVI requires strict environmental conditions, necessitating an anaerobic environment and a long incubation time (usually greater than 6 hours). The long preparation cycle and complex process lead to increased costs, limiting the widespread application of sulfided zero-valent iron in actual production.

[0004] Fe3O4 also possesses good electrical conductivity (band gap of 0.11 eV), and can function similarly to sulfides to some extent. Fe3O4 can mediate the transfer of Fe... 0 The electron transfer process of contaminants can alleviate ZVI passivation caused by the accumulation of corrosion products. Currently, the synergistic effect of ZVI and Fe3O4 can be achieved through physical methods such as ball milling, but this method suffers from low solid-solid reaction efficiency, poor mass transfer, and long material preparation time. Alternatively, under certain conditions, oxidants (such as hydrogen peroxide and potassium permanganate) can directly react with ZVI to rapidly construct a Fe3O4 coating on the ZVI surface, thereby enhancing its reactivity. During this process, the reaction between ZVI and the oxidant also generates other reactive corrosion products, such as Fe(II) and Fe(OH)2, which also contribute to the reduction and removal of contaminants. However, although the vigorous reaction of oxidants with ZVI can shorten the preparation time and simplify the process to some extent, the high storage and usage costs of the added oxidant limit the widespread application of this method in actual production. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for rapidly preparing zero-valent iron composite materials with a high Fe(II) content and a Fe3O4 interface under mild conditions. In an open system, oxygen from the air is used to replace the externally added oxidant. This is achieved through in-situ production or external addition of Fe... 2+ , using Fe 2+ It oxidizes to Fe in the air. 3+ Fe 2+ and Fe 3+ The two substances were co-precipitated to prepare the Fe3O4 precursor Fe(OH)2·nFe(OH)3. Simultaneously, a reducing agent (S) was added during the preparation process. 2- The redox intensity was controlled to prevent Fe(OH)2 from being oxidized to Fe2O3 during the drying process, and to control the loading of more and faster Fe3O4 on the ZVI surface. Finally, after magnetic separation and drying of the solid particles, a zero-valent iron-supported magnetite composite material (Fe3O4@mZVI) was obtained.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing zero-valent iron at a high Fe(II) content ferric oxide interface by controlling redox intensity, the method comprising:

[0008] Step 1: Select micron-sized zero-valent iron (mZVI) as the substrate material, with a particle size between 1 and 200 microns;

[0009] Step 2: Zero-valent iron particles and ferrous ion solution are uniformly mixed at 20℃~30℃, with a mass ratio of zero-valent iron to ferrous ions of 1000~1500:1. The initial pH is adjusted to 1~4 using sulfuric acid solution. After reacting for 20 min, sulfide ion solution is added and reacted for another 5 min, with a mass ratio of added sulfide ions to initial ferrous ions of 0.2~0.4:1. After the reaction, the zero-valent iron particles are magnetically separated and dried in a vacuum oven at 40℃~60℃ for 4~12 h to obtain Fe3O4@mZVI material. Characterization results of the material (Fe3O4@mZVI) show that the surface of the zero-valent iron is loaded with magnetite crystals and has no reducing agent (S). 2- The residual and surface Fe(II) content is high and has a large proportion (Fe(II) / Fe(III)>3).

[0010] Furthermore, in step one, the particle size is between 58 and 75 micrometers.

[0011] Furthermore, in step two, the concentration of the sulfuric acid solution is 1 vol.

[0012] Furthermore, in step two, the solute in the sulfide ion solution is a substance with sulfide anion, such as sodium sulfide, and the cation should be a common cation that has no effect on the reaction system, such as potassium ion, ammonium ion, etc.

[0013] Furthermore, in step two, the sulfide ion concentration in the sulfide ion solution is 0.5 mM.

[0014] The advantages of this invention compared to existing technologies are as follows: The zero-valent iron composite material with a high Fe(II) content and a magnetite interface prepared by this method does not require a controlled anaerobic reaction atmosphere and can be carried out in an open system. Simultaneously, it utilizes air oxidation of ferrous ions, eliminating the need for external oxidants, and offers advantages such as simple, rapid, and low-cost preparation. The addition of sulfur ions during the preparation process can regulate the degree of redox reaction, significantly increasing the Fe(II) content on the material surface, resulting in better reactivity and durability for pollutant removal. Attached Figure Description

[0015] Figure 1 This is an X-ray diffraction (XRD) analysis diagram of the material;

[0016] Figure 2 This is an X-ray energy dispersive spectroscopy (XPS) analysis diagram of the material;

[0017] Figure 3 The diagram shows the removal efficiency of p-nitrophenol (PNP).

[0018] Figure 4 This is a diagram of the material's cyclic durability test. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0020] This invention utilizes a reducing agent (S) 2- This invention aims to prepare micron-sized zero-valent iron (mZVI)-supported Fe3O4 composite materials by controlling redox intensity, addressing the shortcomings of ZVI as a redox catalyst, such as easy surface passivation and high cost or complex processes of existing modification methods (e.g., sulfidation or oxidant treatment). This method can rapidly load Fe3O4 catalytic material (Fe3O4@mZVI) onto the ZVI surface under mild conditions, and Fe3O4@mZVI exhibits significantly enhanced activity and durability in the removal of p-nitrophenol (PNP). This invention offers advantages such as simple process, low cost, and mild conditions, making it suitable for the efficient removal of recalcitrant pollutants in water treatment.

[0021] Example 1:

[0022] A zero-valent iron composite material with a high Fe(II) content iron(III) oxide interface, the specific steps are as follows:

[0023] Step 1: Select micron-sized zero-valent iron (mZVI) as the substrate material, with a particle size between 58 and 75 microns;

[0024] Step 2: Add 1.5g of mZVI particles and 1.0mM ferrous sulfate solution to 300ml of deionized water. The mass ratio of zero-valent iron to ferrous ions is 1300~1350:1. Adjust the pH to 3 with sulfuric acid solution (1 vol%). Control the reaction temperature at 25℃ using a water bath. Mix the materials evenly using mechanical stirring (400 rpm) and react for 20min. Then add 0.5mM sodium sulfide solution and react for another 25min. Magnetic separation of iron particles is then performed, and the mixture is dried in a vacuum oven at 60℃ for 4h to obtain Fe3O4@mZVI. The mass ratio of added sulfur ions to initial ferrous ions is 0.3:1. Simultaneously, t-Fe3O4@mZVI was prepared using the same steps, except that sodium sulfide solution was not added at the end.

[0025] The obtained Fe3O4@mZVI was characterized by... Figure 1 XRD analysis showed that Fe3O4@mZVI exhibited diffraction peaks of magnetite, indicating that magnetite was successfully loaded onto the material surface. Figure 2 XPS analysis showed that the sulfur on the surface of Fe3O4@mZVI material was in the form of sulfate (S(VI)), and no sulfur was present. 2- Residual; iron elements on the surface exist in two forms, Fe(II) and Fe(III), and the Fe(II) / Fe(III) ratio on the material surface is 3.27, indicating that Fe3O4@mZVI has a higher Fe(II) loading.

[0026] The prepared material was used to treat p-nitrophenol (PNP) with pristine zero-valent iron (mZVI) at 25°C, 400 rpm, pH 0 = 3, [PNP] = 500 mg / L, and ZVI = 5 g / L. From Figure 3 It can be seen that Fe3O4@mZVI is significantly more effective than mZVI and t-Fe3O4@mZVI in removing PNP. Fe3O4@mZVI can completely remove 500 mg / L of PNP within 20 min, indicating that a reducing agent (S) was added during the material preparation process. 2- It can regulate and accelerate the loading of magnetite on the surface of zero-valent iron and effectively improve the activity of zero-valent iron materials.

[0027] The prepared material was repeatedly treated with p-nitrophenol (PNP) under the same conditions as pristine zero-valent iron (mZVI). After each reaction, the supernatant was removed by magnetic separation, and fresh PNP solution (500 mg / L) was added to adjust the initial pH to 3 before the reaction was repeated. This process was used to assess the durability of the material. Figure 4 It can be seen that the Fe3O4@mZVI material exhibits the best durability, and the PNP removal efficiency is close to 80% in the third consecutive experiment (120~180 min). This indicates that the reducing agent (S) added during the material preparation process... 2- This allows Fe3O4@mZVI to retain more Fe(II), resulting in higher electron supply capacity and antioxidant capacity.

Claims

1. A method for preparing zero-valent iron at a high Fe(II) content iron(III) oxide interface by controlling redox intensity, characterized in that: The method is as follows: Step 1: Select micron-sized zero-valent iron (mZVI) as the substrate material, with a particle size between 1 and 200 microns; Step 2: Mix zero-valent iron particles and ferrous ion solution uniformly at 20℃~30℃, with a mass ratio of zero-valent iron to ferrous ions of 1000~1500:

1. Adjust the initial pH to 1~4 using sulfuric acid solution. After reacting for 20 min, add sulfide ion solution and react for another 5 min, with a mass ratio of added sulfide ions to initial ferrous ions of 0.2~0.4:

1. After the reaction, separate the zero-valent iron particles magnetically and dry them in a vacuum oven at 40℃~60℃ for 4~12 h to obtain Fe3O4@mZVI material. The sulfide ion concentration in the sulfide ion solution is 0.5 mM.

2. The method for preparing zero-valent iron at a high Fe(II) content ferric oxide interface by controlling redox intensity according to claim 1, characterized in that: In step one, the particle size is between 58 and 75 micrometers.

3. The method for preparing zero-valent iron at a high Fe(II) content ferric oxide interface by controlling redox intensity according to claim 1, characterized in that: In step two, the concentration of the sulfuric acid solution is 1 vol.

4. The method for preparing zero-valent iron at a high Fe(II) content ferric oxide interface by controlling redox intensity according to claim 1, characterized in that: In step two, the anion in the sulfide ion solution is a sulfide ion, and the cation has no effect on the reaction system.

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