Zero-valent iron packaged by carbon nano tube as well as preparation method and application of zero-valent iron

Abstract

The invention belongs to the technical field of catalytic materials, and particularly relates to carbon nano tube packaged zero-valent iron as well as a preparation method and application thereof. The preparation method of the carbon nanotube packaged zero-valent iron comprises the following steps: S1, mixing citric acid, ferric salt and water, and adjusting the pH value of the solution to 3.8-4.2 to obtain an iron precursor solution; s2, a biomass raw material and the iron precursor solution are mixed for a complex reaction, sol-gel is formed and dried, and a precursor is obtained; and S3, the precursor is heated to 700-800 DEG C in an inert atmosphere for pyrolysis, and the carbon nano tube packaged zero-valent iron is obtained. The carbon nanotube packaged zero-valent iron has excellent H2O2 catalysis performance and reductive dehalogenation capability, can realize efficient degradation of organic pollutants in water, especially halogenated organic pollutants, can be used for effective remediation of organic pollutants in wastewater, underground water and polluted soil, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of environmental catalytic materials, and more specifically, relates to a carbon nanotube-encapsulated zero-valent iron, its preparation method, and its application. Background Technology

[0002] Nano-zero-valent iron (NZFE) exhibits significant application potential in groundwater and soil remediation due to its strong reducing properties, high reactivity, and environmental friendliness. It can efficiently achieve the reductive dehalogenation reaction of halogenated organic pollutants (such as chloroalkanes and chlorophenols), converting them into intermediate products with lower toxicity or easier subsequent biological / chemical oxidation treatment; simultaneously, both the NZFE itself and the dissolved Fe... 2+ It can also be combined with hydrogen peroxide to form a Fenton-like or Fenton advanced oxidation system, which can rapidly oxidize or even mineralize recalcitrant organic pollutants, including intermediate products after reduction and dehalogenation, thereby significantly reducing the ecological risks to the environment and improving the overall remediation efficiency.

[0003] Currently, the preparation methods for nano-zero valent iron are mainly divided into chemical reduction methods (such as liquid-phase reduction) and carbothermal reduction methods. Chemical reduction methods typically involve reducing iron salts in a liquid phase using strong reducing agents (such as sodium borohydride). Although this method can be carried out at room temperature, it suffers from high preparation costs, stringent reaction condition control, easy agglomeration and deactivation of the prepared nano-zero valent iron, and potential introduction of secondary pollution. In contrast, the preparation of bio-carbon-supported nano-zero valent iron composites through a one-step carbothermal reduction of biomass and an iron source has attracted widespread attention due to its relatively simple preparation process, the availability of inexpensive and renewable biomass resources, and the fact that the bio-carbon carrier can effectively inhibit the agglomeration and oxidation of nano-zero valent iron, thereby improving its stability and dispersibility.

[0004] However, the traditional carbothermal reduction method for preparing biochar-supported nano-zero-valent iron faces two significant technical bottlenecks: (1) To achieve the reduction of iron oxides, a heat treatment temperature of up to 900 °C or even higher is usually required. For example, patent application CN115231680A discloses a biochar-supported nano-zero-valent iron material, in which iron powder and straw are ball-milled, heated to 900 °C in a tube furnace, and held at that temperature to obtain biochar-supported nano-zero-valent iron. This harsh high-temperature condition not only leads to huge energy consumption and significantly increases production costs, but also limits the large-scale industrial application and economic viability of this technology. In addition, excessively high temperatures can also cause the biochar pore structure to collapse, the specific surface area to decrease, and the sintering and growth of zero-valent iron nanoparticles, which will affect its final catalytic performance. (2) Although the biochar-supported nano-zero-valent iron material improves dispersibility and inhibits agglomeration through loading, the zero-valent iron is still exposed to the outside and is prone to react with oxygen to form an iron oxide passivation layer and react with water to undergo hydrogen evolution, leading to the deactivation of the nano-zero-valent iron.

[0005] Therefore, developing a method for achieving efficient one-step carbothermal reduction at lower temperatures and simultaneously obtaining highly active and stable nano-zero-valent iron composite materials has become a critical issue that urgently needs to be addressed in this field. It is of great practical significance for promoting the practical application of nano-zero-valent iron technology in environmental remediation. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, the primary objective of this invention is to provide a method for preparing zero-valent iron encapsulated in carbon nanotubes.

[0007] A second objective of this invention is to provide zero-valent iron encapsulated in carbon nanotubes prepared by the aforementioned method.

[0008] A third objective of this invention is to provide the application of the carbon nanotube-encapsulated zero-valent iron in the degradation of organic pollutants.

[0009] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0010] This invention claims protection for a method for preparing zero-valent iron encapsulated in carbon nanotubes, comprising the following steps: S1. Mix citric acid, iron salt and water, adjust the pH of the solution to 3.8~4.2 to obtain an iron precursor solution; S2. The biomass raw material is mixed with the iron precursor solution to carry out a complexation reaction to form a sol-gel, which is then dried to obtain the precursor. S3. The precursor is pyrolyzed at 700~800 ℃ under an inert atmosphere to obtain carbon nanotube-encapsulated zero-valent iron.

[0011] This invention utilizes ferric citrate sol-gel, prepared in situ with citric acid and iron salts, as an iron precursor, and biomass raw materials as a carbon source. The iron is then prepared via a one-step carbothermal reduction method under an inert atmosphere. The carbon nanotube-encapsulated zero-valent iron prepared in situ using ferric citrate sol-gel prepared with citric acid and iron salts within a controlled pH range significantly reduces the carbothermal reduction temperature and forms carbon nanotube-encapsulated zero-valent iron in situ. This achieves excellent dispersion of zero-valent iron, giving the composite material abundant zero-valent iron reduction sites and enhancing its reductive dehalogenation ability. Furthermore, the hydrophobic surface of the in-situ generated carbon nanotubes improves the composite material's ability to adsorb and enrich organic pollutants. The zero-valent iron encapsulated in the hydrophobic carbon nanotubes can directionally transfer electrons to the organic pollutants adsorbed on the surface of the hydrophobic carbon nanotubes, thereby suppressing water matrix interference and inhibiting deactivation caused by the reaction of nano-zero-valent iron with oxygen or water. This improves the stability of zero-valent iron and the electron selectivity for reducing and degrading organic pollutants.

[0012] In addition, the zero-valent iron encapsulated in the carbon nanotubes and the Fe dissolved after reduction and dehalogenation 2+ This invention exhibits excellent catalytic performance against H2O2, achieving efficient degradation of organic pollutants through reduction-dehalogenation coupled with catalytic oxidation. Using water as the solvent for the iron precursor avoids the need for organic solvents in existing methods, making the overall approach more environmentally friendly and green.

[0013] Preferably, the iron salt is selected from at least one of ferric nitrate, ferric sulfate, and ferric chloride. More preferably, the iron salt is selected from ferric nitrate.

[0014] Preferably, pyrolysis is carried out at 700~730 °C; more preferably, pyrolysis is carried out at 700~710 °C. If the pyrolysis temperature is too low, the reduction rate decreases or even fails to form zero-valent iron, significantly reducing catalytic activity; while if the pyrolysis temperature is too high, the product is prone to sintering and agglomeration, increasing carbon loss and reducing catalytic activity; furthermore, energy consumption and economic costs increase dramatically.

[0015] Preferably, the molar ratio of citric acid to iron ions in the iron salt is 1:(0.8~1.2). Specifically, the molar ratio of citric acid to iron ions in the iron salt can be 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15, etc., or any range formed by the above ratios, such as 1:(0.9~0.95), 1:(0.9~1), 1:(0.95~1.1), etc., and the present invention is not limited thereto. Through extensive experimental research, the inventors have discovered that when the molar ratio of citric acid to iron ions in the iron salt is in the range of 1:(0.8~1.2), the zero-valent iron encapsulated in the prepared carbon nanotubes has abundant reduction sites and excellent dispersibility and stability due to being encapsulated in the in-situ generated carbon nanotubes. If the proportion of iron ions is too low, a highly active carbon nanotube-encapsulated zero-valent iron structure cannot be formed, resulting in a low loading of zero-valent iron and a decrease in the stability and activity of zero-valent iron. If the proportion of iron ions is too high, the reduction rate of iron decreases and metal agglomeration occurs, which also prevents the formation of this special carbon nanotube-encapsulated zero-valent iron, leading to a decrease in the stability and activity of zero-valent iron.

[0016] Preferably, the mass ratio of the biomass raw material to the iron salt is 3:(0.1~0.15). More preferably, the mass ratio of the biomass raw material to the iron salt is 3:(0.12~1.4). Most preferably, the mass ratio of the biomass raw material to the iron salt is 3:0.1386. In this invention, when the mass ratio of the biomass raw material to the iron is within the above range, it is easier to obtain zero-valent iron encapsulated in carbon nanotubes, and the resulting composite material has a better ability to adsorb and enrich organic pollutants and superior catalytic activity.

[0017] Preferably, the biomass raw material is at least one selected from walnut shells, peanut shells, coconut shells, rice husks, straw, and sawdust. More preferably, the biomass raw material is walnut shell powder.

[0018] Preferably, the concentration of biomass raw material in the sol-gel is 0.075~0.1 g / mL.

[0019] Preferably, the heating rate is 3~8 °C / min. More preferably, the heating rate is 5~6 °C / min. Within the above preferred ranges, carbon nanotubes can grow more gradually and form carbon nanotube-encapsulated zero-valent iron more effectively.

[0020] Preferably, the pyrolysis time is 1.5 to 3 hours. More preferably, the pyrolysis time is 1.9 to 2.1 hours. Within the above preferred ranges, the carbon nanotube-encapsulated zero-valent iron obtained by pyrolysis exhibits superior catalytic performance.

[0021] Preferably, the inert atmosphere is nitrogen or argon. More preferably, the inert atmosphere is argon.

[0022] Preferably, in step S1, ammonia is used to adjust the pH to 3.8-4.2.

[0023] Preferably, in step S2, the complexation reaction is carried out by heating in a water bath at 60~80 °C.

[0024] Preferably, in step S3, the pyrolysis is followed by cooling to room temperature.

[0025] More specifically, the zero-valent iron encapsulated in carbon nanotubes prepared by this invention can be stored in a vacuum dryer for later use.

[0026] Furthermore, this invention seeks protection for zero-valent iron encapsulated in carbon nanotubes prepared by the above-described method.

[0027] Preferably, the diameter of the zero-valent iron encapsulated in the carbon nanotubes is 100-200 nm. Within this preferred diameter range, the catalytic performance is better.

[0028] Furthermore, this invention seeks protection for the application of the carbon nanotube-encapsulated zero-valent iron in the degradation of organic pollutants.

[0029] The carbon nanotube-encapsulated zero-valent iron provided by this invention exhibits good Fenton-like catalytic activity, enabling the catalytic degradation of organic pollutants. Furthermore, the zero-valent iron possesses reductive dehalogenation properties, demonstrating excellent removal capabilities for recalcitrant halogenated organic pollutants. The hydrophobic carbon nanotubes can also adsorb and enrich halogenated organic pollutants, triggering electron transfer from the zero-valent iron to the captured halogenated organic pollutants, thus achieving reductive dehalogenation. Simultaneously, the carbon nanotube-encapsulated zero-valent iron also exhibits excellent catalytic performance for H₂O₂. Combining reductive dehalogenation and catalytic oxidation functions, this ultimately enables the efficient degradation of halogenated organic pollutants in water.

[0030] Preferably, the organic pollutant is a recalcitrant organic pollutant, including but not limited to recalcitrant halogenated and non-halogenated organic pollutants. Preferably, the organic pollutant is a chlorinated organic pollutant or a brominated organic pollutant. Preferably, the organic pollutant is 2,4,6-trichlorophenol.

[0031] The zero-valent iron encapsulated in carbon nanotubes provided by this invention can be used as a hydrogen peroxide catalyst to catalyze the degradation of recalcitrant organic pollutants in industrial wastewater, groundwater, or soil using H2O2 (a Fenton-like oxidation reaction). The zero-valent iron encapsulated in carbon nanotubes prepared by this invention can catalyze a Fenton-like reaction.

[0032] Preferably, the present invention seeks protection for the application of citric acid in reducing the pyrolysis reaction temperature in the one-step carbothermal reduction method for preparing carbon nanotubes encapsulated with zero-valent iron.

[0033] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for preparing carbon nanotube-encapsulated zero-valent iron (ZVFe) via a simple one-step carbothermal reduction method. Citric acid-iron sol-gel, prepared in situ from citric acid and iron salts, serves as the iron precursor, lowering the carbothermal reduction temperature of ZVFe and generating nano-ZVFe encapsulated within carbon nanotubes with abundant in-situ active sites. This structure achieves excellent dispersibility and stability while enhancing the material's ability to adsorb and enrich organic pollutants and improve catalytic efficacy. The carbon nanotube-encapsulated ZVFe prepared by this invention exhibits excellent catalytic performance against H₂O₂ and reductive dehalogenation capabilities, enabling it to effectively degrade recalcitrant organic pollutants, especially halogenated organic pollutants. Attached Figure Description

[0034] Figure 1 The images show the XRD patterns of zero-valent iron encapsulated in carbon nanotubes prepared in Example 1 and Comparative Example 1; where Fe / WS-C represents zero-valent iron encapsulated in carbon nanotubes prepared in Example 1, and Fe / WS-NC represents zero-valent iron encapsulated in carbon nanotubes prepared in Comparative Example 1.

[0035] Figure 2The image shows a scanning electron microscope (SEM) image of zero-valent iron encapsulated in carbon nanotubes prepared in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to the specification and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0037] Example 1 A carbon nanotube-encapsulated zero-valent iron (Fe / WS-C) is prepared as follows: S1. Dissolve 1.67 g of ferric nitrate (Fe(NO3)3·9H2O) completely in 40 mL of pure water, add 0.87 g of citric acid (C6H8O7·H2O, with a molar ratio of citric acid to iron ions of 1:1), stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the iron precursor solution. S2. Add 3.0 g of walnut shell powder to the iron precursor solution in step S1, and carry out a complexation reaction at a water bath temperature of 70 ℃ until a green sol-gel is formed. Then transfer it to an oven at 80 ℃ for further drying to obtain the precursor. S2. Place the precursor from step S2 in a tube furnace and heat it to 700 ℃ at a heating rate of 5 ℃ / min under argon protection. Pyrolyze it at 700 ℃ for 2 h and then cool it to room temperature to obtain carbon nanotube-encapsulated zero-valent iron.

[0038] Example 2 A zero-valent iron encapsulated in carbon nanotubes is prepared as follows: S1. Dissolve 1.67 g of ferric nitrate (Fe(NO3)3·9H2O) completely in 40 mL of pure water, add 0.72 g of citric acid (C6H8O7·H2O, with a molar ratio of citric acid to iron ions of 1:1.2), stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the iron precursor solution. S2. Add 3.0 g of walnut shell powder to the iron precursor solution in step S1, and carry out a complexation reaction at a water bath temperature of 70 ℃ until a green sol-gel is formed. Then transfer it to an oven at 80 ℃ for further drying to obtain the precursor. S2. Place the precursor from step S2 in a tube furnace and heat it to 700 ℃ at a heating rate of 5 ℃ / min under argon protection. Pyrolyze it at 700 ℃ for 2 h and then cool it to room temperature to obtain carbon nanotube-encapsulated zero-valent iron.

[0039] Example 3 A zero-valent iron encapsulated in carbon nanotubes is prepared as follows: S1. Dissolve 1.67 g of ferric nitrate (Fe(NO3)3·9H2O) completely in 40 mL of pure water, add 1.09 g of citric acid (C6H8O7·H2O, with a molar ratio of citric acid to iron ions of 1:0.8), stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the iron precursor solution. S2. Add 3.0 g of walnut shell powder to the iron precursor solution in step S1, and carry out a complexation reaction at a water bath temperature of 70 ℃ until a green sol-gel is formed. Then transfer it to an oven at 80 ℃ for further drying to obtain the precursor. S2. The precursor from step S2 is placed in a tube furnace and heated to 700 ℃ at a heating rate of 5 ℃ / min under argon protection. It is then pyrolyzed at 700 ℃ for 2 h and cooled to room temperature to obtain carbon nanotube-encapsulated zero-valent iron.

[0040] Comparative Example 1 This comparative example provides carbon nanotube-encapsulated zero-valent iron (Fe / WS-NC), which differs from Example 1 only in that citric acid is not added. The specific preparation method is as follows: S1. Dissolve 1.67g of ferric nitrate (Fe(NO3)3·9H2O) completely in 40 mL of pure water, stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the iron precursor solution. S2. Add 3.0 g of walnut shell powder to the iron precursor solution in step S1, stir and evaporate at a water bath temperature of 70 ℃, and then transfer to an 80 ℃ oven for further drying to obtain the precursor; S2. Place the precursor from step S2 in a tube furnace and heat it to 700 ℃ at a heating rate of 5 ℃ / min under argon protection. Pyrolyze it at 700 ℃ for 2 h and then cool it to room temperature to obtain carbon nanotube-encapsulated zero-valent iron.

[0041] Comparative Example 2 This comparative example provides a type of biochar (WS-C), which differs from Example 1 only in that it does not contain ferric nitrate. The specific preparation method is as follows: S1. Dissolve 0.87g of citric acid (C6H8O7·H2O) completely in 40 mL of pure water, stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the citric acid solution. S2. Add 3.0 g of walnut shell powder to the citric acid solution in step S1, stir and evaporate at a water bath temperature of 70 ℃, and then transfer to an 80 ℃ oven for further drying to obtain the precursor; S2. Place the precursor from step S2 in a tube furnace and heat it to 700 ℃ at a heating rate of 5 ℃ / min under argon protection. Pyrolyze it at 700 ℃ for 2 h and then cool it to room temperature to obtain biochar.

[0042] Comparative Example 3 A carbon nanotube-encapsulated zero-valent iron (Fe / WS-C) is presented in this comparative example, differing from Example 1 only in that the carbothermic reduction temperature is reduced to 660 °C. The preparation process is as follows: S1. Dissolve 1.67 g of ferric nitrate (Fe(NO3)3·9H2O) completely in 40 mL of pure water, add 0.87 g of citric acid (C6H8O7·H2O), stir thoroughly to dissolve, and adjust the pH of the solution to 4.0 with ammonia water to obtain the iron precursor solution. S2. Add 3.0 g of walnut shell powder to the iron precursor solution in step S1, and carry out a complexation reaction at a water bath temperature of 80 ℃ until a green sol gel is formed. Then transfer it to an 80 ℃ oven for further drying to obtain the precursor. S2. Place the precursor from step S2 in a tube furnace and heat it to 660 ℃ at a heating rate of 5 ℃ / min under argon protection. Pyrolyze it at 660 ℃ for 2 h and then cool it to room temperature to obtain carbon nanotube-encapsulated zero-valent iron.

[0043] Test Example 1 Structural Characterization The products prepared in Example 1 and Comparative Example 1 were subjected to XRD tests.

[0044] Figure 1 The images show the XRD patterns of zero-valent iron encapsulated in carbon nanotubes prepared in Example 1 and Comparative Example 1. Figure 1 As shown, graphitic carbon peaks appeared in the Fe / WS-C prepared in Example 1, and characteristic peaks of high-intensity zero-valent Fe were also detected simultaneously. When only an iron precursor was added during the preparation process without citric acid (corresponding to the material prepared in Example 1, labeled Fe / WS-NC in the figure), no characteristic peaks of zero-valent Fe were observed, and the graphitic carbon peaks were not obvious. This indicates that after the addition of citric acid, zero-valent iron can be successfully generated at a carbothermal reduction temperature of 700 °C, and because iron has the function of catalyzing graphitization, graphitic carbon is generated at this temperature.

[0045] Figure 2 This is a scanning electron microscope (SEM) image of zero-valent iron encapsulated in carbon nanotubes prepared in Example 1. Figure 2 As shown, from Figure 2 The electron microscope image on the left shows a typical metal composite material encapsulated by carbon nanotubes formed through a top-growth model. Here, it is zero-valent iron encapsulated by carbon nanotubes, with a diameter of about 100~200 nm.

[0046] Test Example 2 (1) Experimental materials: zero-valent iron (Fe / WS-C) encapsulated in carbon nanotubes prepared in Example 1; zero-valent iron (Fe / WS-NC) encapsulated in carbon nanotubes prepared in Comparative Example 1; bio-carbon (WS-C) prepared in Comparative Example 2; zero-valent iron encapsulated in carbon nanotubes prepared in Comparative Example 3.

[0047] (2) Evaluation of Fenton-like catalytic degradation effect: Experimental Method: The simulated pollutant was 2,4,6-trichlorophenol. 50.0 mL of wastewater (containing 30.0 mg / L of 2,4,6-trichlorophenol, with a natural pH of 5.0) and 0.02 g of the products prepared in Examples 1, 1 to 3 were added to a cylindrical glass reaction vessel without adjusting the pH. 2.0 mL of 6% H₂O₂ solution was added to initiate the reaction. After 2 h of reaction, a sample was taken, filtered through a 0.22 μm filter, and the concentration of 2,4,6-trichlorophenol in the filtrate was immediately determined by HPLC.

[0048] (3) Experimental results: After adding the carbon nanotube-encapsulated zero-valent iron (Fe / WS-C) prepared in Example 1 as a catalyst, the removal rate of 2,4,6-trichlorophenol reached 81.1%; after adding the carbon nanotube-encapsulated zero-valent iron (Fe / WS-NC) prepared in Comparative Example 1 as a catalyst, the removal rate of 2,4,6-trichlorophenol was only 53.3%; after adding the biochar (WS-C) prepared in Comparative Example 2 as a catalyst, the removal rate of 2,4,6-trichlorophenol was only 33.4%. Compared with the carbon nanotube-encapsulated zero-valent iron prepared in Example 1, the pollutant removal capacity of the products prepared in Comparative Example 1 and Comparative Example 2 was significantly reduced.

[0049] The carbon nanotube-encapsulated zero-valent iron obtained in Example 1 achieves excellent dispersion of zero-valent iron, giving the composite material abundant zero-valent iron reduction sites and enhancing its reductive dehalogenation ability. Furthermore, the hydrophobic surface of the in-situ generated carbon nanotubes improves the composite material's ability to adsorb and enrich organic pollutants. The zero-valent iron encapsulated in the hydrophobic carbon nanotubes can directionally transfer electrons to the organic pollutants adsorbed on the surface of the hydrophobic carbon nanotubes, thereby suppressing interference from the aqueous matrix and inhibiting deactivation caused by the reaction of nano-zero-valent iron with oxygen or water, thus improving the stability of zero-valent iron and the electron selectivity for reductive degradation of organic pollutants. In addition, the zero-valent iron encapsulated in the carbon nanotubes and the Fe dissolved after reductive dehalogenation... 2+ It leverages its excellent catalytic performance for H2O2, combined with reductive dehalogenation and catalytic oxidation functions, to achieve a removal efficiency of 81.1% for chlorophenol compounds.

[0050] In Comparative Example 1, without the addition of citric acid precursor, zero-valent Fe and graphite carbon could not be obtained through carbothermal reduction at the experimental pyrolysis temperature (700 °C). In Comparative Example 2, the gas released during the pyrolysis of citric acid had a pore-forming effect, and the resulting biochar could enrich and adsorb organic pollutants; however, due to the absence of zero-valent iron or other Fenton-like catalysts, its reductive dehalogenation ability and Fenton catalytic activity were low. In Comparative Example 3, the pyrolysis temperature was reduced to 660 °C; due to the excessively low temperature, zero-valent iron and graphite carbon could not be obtained through carbothermal reduction.

[0051] Test Example 3 (1) Experimental materials: zero-valent iron encapsulated in carbon nanotubes prepared in Example 2.

[0052] (2) Evaluation of Fenton-like catalytic degradation effect: Experimental Method: The simulated pollutant was 2,4,6-trichlorophenol. 50.0 mL of wastewater (containing 30.0 mg / L of 2,4,6-trichlorophenol, with a natural pH of 5.0) and 0.02 g of carbon nanotube-encapsulated zero-valent iron prepared in Example 2 were added to a cylindrical glass reaction vessel. Without adjusting the pH, 2.0 mL of 6% H₂O₂ solution was added to initiate the reaction. After 2 h of reaction, a sample was taken, filtered through a 0.22 μm filter, and the concentration of 2,4,6-trichlorophenol in the filtrate was immediately determined by HPLC.

[0053] (3) Experimental results: After adding the carbon nanotube-encapsulated zero-valent iron prepared in Example 2 as a catalyst, the removal rate of 2,4,6-trichlorophenol reached 80.6%, showing high catalytic activity.

[0054] Test Example 4 (1) Experimental materials: zero-valent iron encapsulated in carbon nanotubes prepared in Example 3.

[0055] (2) Evaluation of Fenton-like catalytic degradation effect: Experimental Method: The simulated pollutant was 2,4,6-trichlorophenol, but not limited to 2,4,6-trichlorophenol. 50.0 mL of wastewater (containing 30.0 mg / L of 2,4,6-trichlorophenol, with a natural pH of 5.0) and 0.02 g of the material prepared in Example 3 were added to a cylindrical glass reaction vessel. Without adjusting the pH, 2.0 mL of 6% H2O2 solution was added to initiate the reaction. After 2 h of reaction, a sample was taken, filtered through a 0.22 μm filter, and the concentration of 2,4,6-trichlorophenol in the filtrate was immediately determined by HPLC.

[0056] (3) Experimental results: After adding the carbon nanotube-encapsulated zero-valent iron prepared in Example 3 as a catalyst, the removal rate of 2,4,6-trichlorophenol reached 78.1%, showing high catalytic activity.

[0057] The foregoing examples are merely illustrative, used to explain some features of the method described in this invention. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are demonstrated by the applicant's actual experimental results. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of the invention. Some numerical ranges used in the claims also include sub-ranges within them, and variations within these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing zero-valent iron encapsulated in carbon nanotubes, characterized in that, Includes the following steps: S1. Mix citric acid, iron salt and water, adjust the pH of the solution to 3.8~4.2 to obtain an iron precursor solution; S2. The biomass raw material is mixed with the iron precursor solution to carry out a complexation reaction to form a sol-gel, which is then dried to obtain the precursor. S3. The precursor is pyrolyzed at 700~800 ℃ under an inert atmosphere to obtain carbon nanotube-encapsulated zero-valent iron.

2. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, The iron salt is selected from at least one of ferric nitrate, ferric sulfate, and ferric chloride.

3. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, The molar ratio of citric acid to iron ions in the iron salt is 1:(0.8~1.2).

4. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, The mass ratio of the biomass raw material to the iron in the iron salt is 3:(0.1~0.15).

5. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, The biomass raw material is at least one of walnut shells, peanut shells, coconut shells, rice husks, straw, and sawdust.

6. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, The heating rate is 3~8 °C / min.

7. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1 or 6, characterized in that, The pyrolysis time is 1.5 to 3 hours.

8. The method for preparing zero-valent iron encapsulated in carbon nanotubes according to claim 1, characterized in that, Heat to 700~730 ℃ for pyrolysis.

9. Zero-valent iron encapsulated in carbon nanotubes prepared by the preparation method according to any one of claims 1-8.

10. The application of zero-valent iron encapsulated in carbon nanotubes as described in claim 9 in the degradation of organic pollutants.

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