Carbon-coated nano-zero-valent iron composite materials, their preparation methods and applications

Abstract

This invention discloses a carbon-coated nano-zero-valent iron composite material, its preparation method, and its application. The preparation method includes the following steps: mixing lignin and tetrahydrofuran to obtain liquid B; adding an aqueous solution of nano-ferric oxide to liquid B to obtain liquid A; adding ZnCl2 to liquid A and stirring evenly at room temperature; heating at 80-90°C for 8-9 hours to obtain a dried composite; grinding the composite into powder; heating to 300°C and maintaining the temperature for 2-3 hours under nitrogen or inert gas conditions; cooling to room temperature to obtain a composite precursor; grinding the composite precursor into powder; calcining at 800-900°C for 2-3 hours under nitrogen or inert gas conditions to obtain the carbon-coated nano-zero-valent iron composite material. The carbon-coated nano-zero-valent iron composite material of this invention has a core-shell structure, inhibiting the aggregation of nano-zero-valent iron, and achieving antioxidant properties while ensuring the activity of nano-zero-valent iron, exhibiting efficient removal of 2,4-dichlorophenol.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional materials technology, specifically relating to a carbon-coated nano-zero-valent iron composite material, its preparation method, and its application. Background Technology

[0002] In recent years, based on sulfate radicals (SO4) ·- Persulfate advanced oxidation technology is considered an effective method for removing persistent organic pollutants from environmental media due to its advantages such as high efficiency and low cost. However, the high stability of persulfate (PDS) in the environment leads to its low conversion rate, and it usually needs to be activated during the pollutant removal process to promote the generation of reactive oxygen species (ROS).

[0003] Nano-zero valent iron (nZVI) is widely used for the oxidative degradation of persistent organic pollutants due to its advantages such as low toxicity, high efficiency, and environmental friendliness, and is considered an effective PDS activator. However, the high surface energy and reactivity of pure nZVI easily lead to rapid aggregation and surface passivation, hindering its large-scale application. To date, carbonaceous materials (such as biochar, carbon nanotubes, and redox graphene) have been used to load nZVI to improve its dispersibility and provide more reaction sites, but the problem of nZVI aggregation has been effectively solved. However, the passivation of nZVI leads to hindered electron transfer and reduced electron utilization, which still needs to be addressed. Although some studies have reported that the porous structure of carbonaceous materials can inhibit the passivation of nZVI to some extent, its protective effect on nZVI is very limited, and it is still difficult to obtain nano-zero valent iron composite materials with high oxidation resistance. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing carbon-coated nano-zero-valent iron composite materials. This method utilizes the amphiphilic properties of alkali lignin to synthesize stable carbon-coated nano-zero-valent iron composite materials through a combination of antisolvent method and carbothermal reduction method. The preparation method is simple and uses green and pollution-free raw materials.

[0005] Another objective of this invention is to provide a carbon-coated nano-zero-valent iron composite material (AL@nZVI) obtained by the above preparation method. This carbon-coated nano-zero-valent iron composite material not only maintains the reactivity of nano-zero-valent iron and is environmentally friendly without secondary pollution, but also can exist stably in the air environment for a long time without being oxidized, and has good antioxidant properties.

[0006] Another object of the present invention is to provide the application of the above-mentioned carbon-coated nano-zero-valent iron composite material in the removal of 2,4-dichlorophenol from liquids.

[0007] The objective of this invention is achieved through the following technical solution.

[0008] A method for preparing a carbon-coated nano-zero-valent iron composite material includes the following steps:

[0009] 1) Mix lignin and tetrahydrofuran to obtain liquid B, and add nano-iron oxide aqueous solution to liquid B dropwise (antisolvent method) to obtain liquid A. In this case, the ratio of nano-iron oxide in the nano-iron oxide aqueous solution to lignin in liquid B is 0.02:(0.4~0.6) by mass.

[0010] In step 1), the concentration of nano-ferric oxide in the nano-ferric oxide aqueous solution is 0.25 g / L.

[0011] In step 1), the concentration of lignin in liquid B is 20-30 g / L.

[0012] In step 1), the nano-iron oxide aqueous solution is a mixture of nano-iron oxide and water, and the nano-iron oxide has a particle size of 20-50 nm.

[0013] In step 1), the lignin is alkali lignin.

[0014] 2) Add ZnCl2 to liquid A obtained in step 1) and stir evenly at room temperature. Heat at 80-90°C for 8-9 hours to obtain a dry composite.

[0015] In step 2), the ZnCl2 is 4-6 wt% of liquid A.

[0016] In step 2), the mixing is performed by magnetic stirring for at least 1 hour.

[0017] 3) Grind the composite into powder, heat it to 300°C at a heating rate of 5-10°C / min under nitrogen or inert gas atmosphere and hold for 2-3 hours, then cool it to room temperature to obtain the composite precursor;

[0018] 4) Grind the composite precursor into powder and calcine it at 800-900℃ for 2-3 hours in a nitrogen or inert gas environment to obtain carbon-coated nano-zero-valent iron composite material.

[0019] The carbon-coated nano-zero-valent iron composite material obtained by the above preparation method.

[0020] In the above technical solution, the carbon-coated nano-zero-valent iron composite material has a rich porous carbon skeleton and zero-valent iron nanoparticles uniformly loaded on the carbon skeleton and wrapped in a carbon shell formed by lignin.

[0021] The above-mentioned carbon-coated nano-zero-valent iron composite material is used for the removal of 2,4-dichlorophenol from liquids.

[0022] In the above technical solution, the catalytic activation target of the carbon-coated nano-zero-valent iron composite material is persulfate.

[0023] In the above technical solution, the carbon-coated nano-zero-valent iron composite material is added to a solution containing 2,4-dichlorophenol to be degraded, and then persulfate is added and shaken.

[0024] In the above technical solution, the removal rate of 2,4-dichlorophenol is as high as 100% within 60 minutes of adding persulfate.

[0025] The above-mentioned carbon-coated nano-zero-valent iron composite material is used to improve the stability of materials placed in an air environment.

[0026] In the above technical solution, after being placed in an air environment for 60 days, the removal rate of 2,4-dichlorophenol is more than 90% within 60 minutes.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The preparation method of this invention combines the antisolvent method with the carbothermic reduction method in steps 3) and 4). In the preparation process, lignin is selected as the carbon source. Taking advantage of the amphiphilic properties of lignin, the lignin molecules are coated with nano-Fe3O4 under the action of the antisolvent method. After immobilization at 300°C, it is carbothermally reduced at 800-900°C. After cooling, carbon-coated nano-zero-valent iron composite material can be obtained.

[0029] The carbon source selected in this invention is lignin, a byproduct of the chemical industry, and the precursor of zero-valent iron is nano-iron oxide. A carbon-coated nano-zero-valent iron composite material is synthesized by combining antisolvent method and carbothermal reduction. This preparation method can avoid the aggregation of zero-valent iron and is carried out in a non-liquid phase environment, thus avoiding the generation of wastewater in the production process.

[0030] The carbon-coated nano-zero-valent iron composite material of the present invention has a core-shell structure, and the shell structure can effectively inhibit the aggregation of nano-zero-valent iron. In addition, while ensuring the activity of nano-zero-valent iron, it can also achieve antioxidant properties and has the ability to efficiently activate persulfate to remove 2,4-dichlorophenol. Attached Figure Description

[0031] Figure 1 The removal rates of 2,4-dichlorophenol by the carbon-coated nano-zero-valent iron composite materials prepared in Examples 1 to 4 and by the commercial nano-zero-valent iron in Comparative Example 1 are shown.

[0032] Figure 2 Fourier transform infrared (FTIR) scan of carbon-coated nano-zero-valent iron composite material;

[0033] Figure 3 X-ray diffraction (XRD) pattern of carbon-coated nano-zero-valent iron composite material;

[0034] Figure 4 The removal rate of 2,4-dichlorophenol by the carbon-coated nano-zero-valent iron composite material prepared in Example 3 (under different initial pH values);

[0035] Figure 5 The removal rates of 2,4-dichlorophenol were compared between the samples placed in air for 60 days and the samples from freshly prepared carbon-coated nano-zero-valent iron composite materials.

[0036] Figure 6 The image shows a scanning electron microscope (SEM) image of the carbon-coated nano-zero-valent iron composite material prepared in Example 3. In (a), the inset is a 10,000x magnified SEM image within the box in (a), and (b) is the energy dispersive spectroscopy (EDS) map of the carbon-coated nano-zero-valent iron composite material.

[0037] Figure 7 The images shown are transmission electron microscope (TEM) images of the carbon-coated nano-zero-valent iron composite material prepared in Example 3, where (a, b) are 3000x TEM images, (c) is 10000x EDS TEM image, and (d) is 50000x TEM image.

[0038] Figure 8 The X-ray photoelectron spectroscopy (XPS) analysis of the carbon-coated nano-zero-valent iron composite material prepared in Example 3 before and after activation with persulfate is shown in the figures. (a) is the C 1s spectrum of the carbon-coated nano-zero-valent iron composite material before activation with persulfate; (b) is the C 1s spectrum of the carbon-coated nano-zero-valent iron composite material after activation with persulfate; (c) is the O 1s spectrum of the carbon-coated nano-zero-valent iron composite material before activation with persulfate; (d) is the O 1s spectrum of the carbon-coated nano-zero-valent iron composite material after activation with persulfate; (e) is the Fe 2p spectrum of the carbon-coated nano-zero-valent iron composite material before activation with persulfate; and (f) is the Fe 2p spectrum of the carbon-coated nano-zero-valent iron composite material after activation with persulfate. Detailed Implementation

[0039] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0040] The sources of the medicines involved in the following examples are as follows:

[0041]

[0042] The models of the instruments involved in the following embodiments are as follows:

[0043]

[0044]

[0045] The concentration of 2,4-DCP was determined using a high-performance liquid chromatograph (HPLC) equipped with an Agilent C18 column (250 mm × 4.6 mm, 5 μm). HPLC involved measuring the absorbance of 2,4-DCP at a specific ultraviolet wavelength, preparing aqueous solutions of 2,4-DCP standards at different concentrations, and obtaining a standard curve of 2,4-DCP concentration versus absorbance. The absorbance of the test solution was then substituted into the equation of the standard curve to obtain the concentration of 2,4-DCP in the test solution. Filtration was performed using a 0.22 μm PTFE membrane.

[0046] Removal rate (degradation rate) = C t / C0, where C t C0 represents the concentration of 2,4-DCP at a specific time point; C0 represents the initial concentration of 2,4-DCP before degradation.

[0047] Examples 1-4

[0048] A method for preparing a carbon-coated nano-zero-valent iron composite material includes the following steps:

[0049] 1) Lignin and tetrahydrofuran are mixed to obtain liquid B. A nano-iron oxide aqueous solution is added dropwise to liquid B (antisolvent method) to obtain liquid A. The mass ratio of nano-iron oxide in the nano-iron oxide aqueous solution to lignin in liquid B is X, and the value of X is shown in Table 1. The nano-iron oxide aqueous solution is a mixture of nano-iron oxide and water. The particle size of nano-iron oxide is 20-50 nm. The concentration of nano-iron oxide in the nano-iron oxide aqueous solution is 0.25 g / L. The concentration of lignin in liquid B is 20 g / L. The lignin is alkali lignin.

[0050] Liquid A contains spheres of nano-iron oxide particles coated with lignin molecules. The antisolvent method utilizes the amphiphilicity of lignin, which includes hydrophobic groups (phenylpropane units) and hydrophilic parts (hydroxyl and carboxyl groups). With the addition of the nano-iron oxide aqueous solution, the hydrophobic groups of lignin can self-assemble into a core through π-π interactions, while the hydrophilic parts turn to their surface, thereby forming spherical nanoparticles.

[0051] 2) Add ZnCl2 to liquid A obtained in step 1) and stir magnetically for 1 hour at room temperature until homogeneous. Heat in a water bath at 80°C for 8 hours to obtain a dry composite, wherein ZnCl2 is 4 wt% of liquid A.

[0052] 3) Grind the composite into powder using an agate mortar and pestle, heat it to 300°C in a tube furnace under nitrogen atmosphere at a heating rate of 5°C / min, and hold it at that temperature for 2 hours. Then cool it to room temperature of 20-25°C to obtain the composite precursor (AL@Fe-300).

[0053] 4) Grind the composite precursor into powder, heat it to 800℃ in a tube furnace under nitrogen atmosphere at a heating rate of 10℃ / min, calcine it at 800℃ for 2 hours, and cool it to room temperature of 20-25℃ to obtain carbon-coated nano-zero-valent iron composite material.

[0054] Table 1

[0055] Example X serial number Example 1 (for comparison) 0.02:0.2 AL@Fe-10 Example 2 (for comparison) 0.02:0.3 AL@Fe-15 Example 3 0.02:0.4 <![CDATA[AL@Fe 0 -20]]> Example 4 0.02:0.6 <![CDATA[AL@Fe 0 -30]]>

[0056] The carbon-coated nano-zero-valent iron composite material prepared in Example 3 was subjected to SEM (… Figure 6 Tests revealed that the carbon-coated nano-zero-valent iron composite material possesses a rich porous carbon skeleton and uniformly loaded zero-valent iron nanoparticles encapsulated in a carbon shell formed by lignin on this carbon skeleton.

[0057] The carbon-coated nano-zero-valent iron composite material prepared in Example 3 was subjected to TEM (… Figure 7 Tests revealed that AL@Fe 0 -20 carbon shell encapsulates nano-Fe 0 Spherical particles are uniformly dispersed in a porous carbon matrix. Figure 7 ).like Figure 7 As shown in bc, AL@Fe 0 The -20 EDS elemental map further confirms that the iron nanoparticles are coated with lignin molecules, forming spherical nanoparticles through self-assembly, and that a thin carbon shell is formed by lignin during carbonization, encapsulating the zero-valent iron nanoparticles. Furthermore, HR-TEM images reveal AL@Fe 0 -20 contains Fe 0 The nucleus is encased in a carbon shell, forming a core-shell structure.

[0058] Example 5

[0059] The carbon-coated nano-zero-valent iron composite materials prepared in Examples 1-4 were used to activate persulfate in the degradation of 2,4-DCP in aqueous solution. Specifically, 15 mg of the carbon-coated nano-zero-valent iron composite material was added to 50 mL of the degradation solution, which was a mixture of deionized water and 2,4-DCP. The concentration of 2,4-DCP in the degradation solution was 20 mg / L (CO). Then, 20 mg of sodium persulfate was added, and the mixture was shaken at 150 rpm for 1 hour in a constant-temperature shaker (room temperature). The concentration of the remaining 2,4-DCP was determined by high-performance liquid chromatography (HPLC) (CO). t .

[0060] Comparative Example 1

[0061] Commercial nano-zero-valent iron (Beijing Innocare Technology Co., Ltd.) was used as a persulfate activator in the degradation of 2,4-DCP. The specific method was as follows: 2.5 mg of commercial nano-zero-valent iron was added to 50 mL of the solution to be degraded. The solution was a mixture of water and 2,4-DCP, with a 20 mg / L concentration of 2,4-DCP (CO). Then, 20 mg of sodium persulfate was added. The mixture was incubated at 150 rpm for 1 hour in a constant-temperature shaker (room temperature). The concentration of the remaining 2,4-DCP was determined by high-performance liquid chromatography (HPLC) (CO). t .

[0062] Figure 1 The degradation rates of 2,4-DCP by the carbon-coated nano-zero-valent iron composite materials prepared in Examples 1-4 and by the commercial nano-zero-valent iron in Comparative Example 1 are given by... Figure 1 It can be seen that the degradation efficiency (removal rate) of 2,4-DCP in Comparative Example 1 can reach 67.68% after 1 hour of reaction. The degradation rates of 2,4-DCP by the carbon-coated nano-zero-valent iron composite materials prepared in Examples 1-4 are 47.98%, 65.7%, 100%, and 92.8%, respectively. This indicates that compared with commercial nano-zero-valent iron, the carbon-coated nano-zero-valent iron composite materials prepared in Examples 3 and 4 have a better activation effect on persulfate.

[0063] The carbon-coated nano-zero-valent iron composite materials obtained in Examples 1-4 were subjected to FTIR (…). Figure 2 Analysis revealed that the carbon-coated nano-zero-valent iron composite materials synthesized in different embodiments contained relatively few functional groups, and the functional groups decreased with the decreasing mass ratio of the carbon source lignin. (575cm) -1 The Fe-O bond strength at the site continuously increases, indicating that the carbon source content is one of the important factors affecting the coating of iron oxides and the degree of reduction of iron oxides.

[0064] The carbon-coated nano-zero-valent iron composite materials obtained in Examples 1-4, and the carbon-coated nano-zero-valent iron composite material obtained in Example 3 after being placed in air for 60 days, were subjected to XRD (…). Figure 3 Analysis, by Figure 3 It can be seen that as the carbon source content increases, the reduction degree of iron oxide also increases, eventually reducing it to nano-zero valent iron (Fe). 0 Furthermore, XRD analysis of the carbon-coated nano-zero-valent iron composite material after it had been exposed to air for 60 days revealed that... Figure 3 The carbon-coated nano-zero-valent iron composite material prepared in Example 3 still retains the state of zero-valent iron, indicating that it can achieve the antioxidant properties of nano-zero-valent iron.

[0065] Example 6

[0066] Carbon-coated nano-zero-valent iron composite material was used as a persulfate activator in the degradation of 2,4-DCP. Specifically, 15 mg of the carbon-coated nano-zero-valent iron composite material prepared in Example 3 was added to 50 mL of the degradation solution. The degradation solution had different initial pH values ​​(pH = 3, 5, 7, 9, 11, and naturally left unadjusted). The degradation solution was a mixture of water and 2,4-DCP, with a 20 mg / L concentration (denoted as CO). Then, 20 mg of sodium persulfate was added, and the mixture was shaken at 150 rpm for 1 hour in a constant-temperature shaker. The remaining 2,4-DCP concentration (denoted as C) was determined by high-performance liquid chromatography. t .

[0067] Figure 4 The carbon-coated nano-zero-valent iron composite material prepared in Example 3 was processed according to Example 6 (pH was set to 6.71 without adjustment). Figure 4 The removal rate of 2,4-DCP by the method shown in the figure (without pH adjustment) is determined by... Figure 4 It is evident that the carbon-coated nano-zero-valent iron composite material prepared in Example 3 exhibits broad pH adaptability for activating persulfate in the removal of 2,4-DCP. Under both acidic and neutral conditions, 2,4-dichlorophenol can be completely removed within 30 minutes. Furthermore, although the removal rate of 2,4-DCP gradually decreases with increasing pH, it still reaches 53.2% at pH = 11.

[0068] Example 7

[0069] 15 mg of the carbon-coated nano-zero-valent iron composite material prepared in Example 3 (which has been left in air for 60 days) was added to 50 mL of a solution to be degraded. The solution was a mixture of water and 2,4-DCP, with a concentration of 20 mg / L (denoted as CO). Then, 20 mg of sodium persulfate was added, and the mixture was shaken at 150 rpm for 1 hour in a constant-temperature incubator. The concentration of the remaining 2,4-DCP was determined by high-performance liquid chromatography (HPLC) and denoted as C. t Degradation rate such as Figure 5 As shown, by Figure 5 It can be seen that the carbon-coated nano-zero-valent iron composite material prepared in Example 3 can still efficiently remove 2,4-DCP after being placed in the air for 60 days. Its removal efficiency of 2,4-DCP is basically the same as that of the newly prepared carbon-coated nano-zero-valent iron composite material. This indicates that the carbon-coated nano-zero-valent iron composite material has good antioxidant properties and stability.

[0070] The carbon-coated nano-zero-valent iron composite material prepared in Example 3 was subjected to XPS testing, such as... Figure 8 As shown in (a, c, e), the sp peak of the C1s of the newly prepared carbon-coated nano-zero-valent iron composite material was found to be... 2 and sp 3 The characteristic peaks of hybrid carbon correspond to approximately 284.5 eV and 285.1 eV, respectively, and are considered to represent the structures of graphitized carbon and amorphous carbon. Meanwhile, characteristic peaks corresponding to CO and C=O oxygen-containing structures were observed at 531.92 eV and 533.745 eV, respectively. Furthermore, characteristic peaks corresponding to Fe were observed at 706.86 eV, 710.08 eV, and 711.91 eV, respectively. 0 Fe 2+ and Fe 3+ Characteristic peaks of Fe. 3+ and Fe 2+ The appearance of the peak indicates that the surface of zero-valent iron may be partially oxidized during the preparation, storage and use of the material.

[0071] XPS tests were performed on the carbon-coated nano-zero-valent iron composite material from Example 3, which was used in Example 5. Figure 8 As shown in (b, d, f), compared to before use, the amount of sp in the carbon-coated nano-zero-valent iron composite material after use... 2 The characteristic peak of -C corresponds to an increase in graphitic carbon from 56.28% to 62.35%, while sp 3 The percentage of disordered amorphous carbon corresponding to the characteristic peak of -C decreased from 36.9% to 23.41%. This indicates that defects or disordered structures are involved in the degradation process of 2,4-DCP, and that graphitization increases during this process, enhancing electron transfer as an electron shuttle and promoting the degradation of 2,4-DCP. Furthermore, the CO content on the surface of the used carbon-coated nano-zero-valent iron composite material increased significantly, from 41.58% to 47.47%. However, compared with the newly prepared carbon-coated nano-zero-valent iron composite material, the content of oxygen-containing C=O groups on the used carbon-coated nano-zero-valent iron composite material decreased significantly, from 58.42% to 44.95%. The decrease in C=O content on the material surface directly indicates its participation in the activation of PDS. PDS can attack C=O to generate peroxides and dioxane adducts, generating singlet oxygen through the mutual attack of intermediate products, thus achieving the degradation and removal of 2,4-DCP via a non-radical pathway. Furthermore, after activation of persulfate, the carbon-coated nano-zero-valent iron composite material showed a decrease in the content of ferric iron (Fe(III)) from 48.24% to 44.38% compared to the newly prepared carbon-coated nano-zero-valent iron composite material, while the content of ferrous iron (Fe(II)) significantly increased from 41.99% to 55.61%, indicating that besides Fe... 0 Besides being continuously oxidized to Fe(II), the redox cycle reaction between Fe(II) and Fe(III) at the solid / liquid interface is achieved by increasing the Fe... 0The increased utilization rate further promoted the continuous generation of Fe(II) and enhanced the interfacial electron transfer efficiency between persulfate and pollutants, thereby greatly promoting the generation of reactive oxygen species and improving the degradation efficiency of 2,4-DCP.

[0072] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a carbon-coated nano-zero-valent iron composite material, characterized in that, Includes the following steps: 1) Mix lignin and tetrahydrofuran to obtain liquid B, and add nano-iron oxide aqueous solution to liquid B to obtain liquid A. The ratio of nano-iron oxide in the nano-iron oxide aqueous solution to lignin in liquid B is 0.02:(0.4~0.6) by mass. 2) Add ZnCl2 to liquid A obtained in step 1) and stir evenly at room temperature. Heat at 80-90°C for 8-9 hours to obtain a dry composite. 3) Grind the composite into powder, heat it to 300°C at a heating rate of 5-10°C / min under nitrogen or inert gas atmosphere and hold for 2-3 hours, then cool it to room temperature to obtain the composite precursor; 4) Grind the composite precursor into powder and calcine it at 800-900℃ for 2-3 hours in a nitrogen or inert gas environment to obtain carbon-coated nano-zero-valent iron composite material.

2. The preparation method according to claim 1, characterized in that, In step 1), the nano-ferric oxide aqueous solution is a mixture of nano-ferric oxide and water, and the concentration of nano-ferric oxide in the nano-ferric oxide aqueous solution is 0.25 g / L; the concentration of lignin in liquid B is 20-30 g / L.

3. The preparation method according to claim 2, characterized in that, In step 1), the particle size of the nano-iron oxide is 20-50 nm, and the lignin is alkali lignin.

4. The preparation method according to claim 1, characterized in that, In step 2), the ZnCl2 is 4-6 wt% of liquid A; in step 2), the stirring is performed by magnetic stirring for at least 1 hour.

5. The carbon-coated nano-zero-valent iron composite material obtained by the preparation method according to any one of claims 1 to 4.

6. The carbon-coated nano-zero-valent iron composite material according to claim 5, characterized in that, This carbon-coated nano-zero-valent iron composite material has a rich porous carbon skeleton and zero-valent iron nanoparticles uniformly loaded on the carbon skeleton and encapsulated by a carbon shell formed by lignin.

7. The application of the carbon-coated nano-zero-valent iron composite material as described in claim 5 in the removal of 2,4-dichlorophenol from liquids.

8. The application according to claim 7, characterized in that, The catalytic activation target of carbon-coated nano-zero-valent iron composite material is persulfate.

9. The application according to claim 7, characterized in that, The carbon-coated nano-zero-valent iron composite material was added to a solution containing 2,4-dichlorophenol to be degraded, and then persulfate was added and shaken. Within 60 minutes of adding persulfate, the removal rate of 2,4-dichlorophenol reached 100%.

10. The application of the carbon-coated nano-zero-valent iron composite material as described in claim 5 in improving the stability of materials placed in an air environment.

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