Preparation method and application of slow-release iron-carbon composite material

Abstract

The application relates to a preparation method and application of a slow-release iron-carbon composite material, relates to the fields of environment material preparation and water treatment technology, and comprises the following steps: preparing a slow-release iron-carbon composite material by liquid phase reduction method through the following steps: mixing biochar with strong electron transfer capacity, an iron salt solution A, cyclodextrin and a reducing agent B. The slow-release iron-carbon composite material prepared by the application has the advantages of simple preparation process, uniform distribution of nano zero-valent iron, good dispersity, good oxidation resistance and slow-release performance, can enrich chlorinated hydrocarbon pollutants on the material surface, and realizes efficient and persistent dechlorination of the material to chlorinated hydrocarbons.

Description

Technical Field

[0001] This invention relates to the fields of environmental material preparation and water treatment, specifically to a method for preparing and applying a slow-release iron-carbon composite material. Background Technology

[0002] Chlorinated aliphatic hydrocarbons (CAHs) are commonly used chemical raw materials and organic solvents worldwide. They were once widely used as industrial solvents for metal degreasing and as chemical intermediates in the manufacture of refrigerants and pesticides. Accidental leaks during CAH storage and improper disposal of CAH-containing wastewater have led to pollution in soil and groundwater. Furthermore, because CAHs often exist in non-aqueous liquid form and are tightly bound to soil particles and organic matter, they are difficult to utilize and degrade, posing a serious threat to human health and environmental safety. They have been listed as a priority pollutant for removal by many countries.

[0003] Nano-zero-valent iron (ZCE) is used for the reductive dechlorination of chlorinated hydrocarbons due to its strong reducing ability. However, the application of ZCE faces multiple challenges, including easy agglomeration, short lifespan, and low electron utilization efficiency. Firstly, due to its strong reducing properties, ZCE readily reacts with water and oxygen, resulting in significant electron waste. Secondly, a thick iron oxide passivation layer forms on the surface of ZCE during the reaction, hindering further reaction and leading to deactivation. Furthermore, the magnetic properties of ZCE cause particles to aggregate into large, chain-like particles, further reducing the reactive sites. These factors limit the practical application of ZCE in real-world scenarios.

[0004] Studies have shown that the introduction of carbon materials can form a galvanic cell effect with nano-zero-valent iron, enhancing the electron-losing ability of nano-zero-valent iron, thereby improving reactivity and extending its lifespan. Secondly, the large specific surface area of ​​carbon materials can immobilize nano-zero-valent iron, providing strong steric hindrance to prevent its aggregation and enhancing its strong adsorption capacity to adsorb chlorinated hydrocarbons onto the material surface, thus increasing the reactive sites of nano-zero-valent iron. However, in practical applications, iron-carbon composite materials often undergo side reactions with water and oxygen when treating wastewater containing chlorinated hydrocarbons, and these materials require continuous addition and are expensive. Therefore, developing novel, highly efficient, slow-release iron-carbon composite materials is particularly important. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for preparing and applying a slow-release iron-carbon composite material. This invention utilizes various biochars to prepare iron-carbon materials, selecting those with high selectivity for chlorinated hydrocarbons and strong electron transfer performance. These biochars are then combined with iron salt solution, cyclodextrin, and a reducing agent to prepare a slow-release iron-carbon composite material. This method helps reduce costs, minimizes side reactions, enhances electron release performance, and improves reactivity, enabling efficient and sustained dechlorination of chlorinated hydrocarbons. It effectively solves the problems of side reactions with water and oxygen, the need for continuous addition, and high cost associated with existing iron-carbon composite materials.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] The first objective of this invention is to provide a method for preparing a slow-release iron-carbon composite material, comprising the following steps:

[0008] A slow-release iron-carbon composite material was prepared by liquid-phase reduction of biochar with strong electron transfer capability, iron salt solution A, cyclodextrin, and reducing agent solution B.

[0009] Furthermore, the specific preparation steps of the liquid-phase reduction method are as follows:

[0010] Under an inert atmosphere, biochar with strong electron transfer capability and cyclodextrin are placed in iron salt solution A and mixed thoroughly. Reducing agent solution B is added dropwise to carry out the reaction. After separation and drying, a slow-release iron-carbon composite material can be obtained.

[0011] Furthermore, the molar ratio of the reducing agent to the iron salt in the iron salt solution A is (3-5):1, and the mass ratio of the biochar with strong electron transfer capability, the iron ions in the iron salt solution A, and the cyclodextrin is (1-3):(1-3):(3-9).

[0012] Preferably, the mass ratio of the biochar with strong electron transfer capability, the iron ions in the iron salt solution A, and the cyclodextrin is 2.38:3:9.

[0013] Furthermore, the biochar with strong electron transfer capability is at least one of coconut shell-based biochar, lignin-based biochar, and coconut shell-based modified capacitor biochar; the iron salt is at least one of ferrous salt and ferric salt; the reducing agent in the reducing agent solution B is at least one of KBH4 and NaBH4; the cyclodextrin is at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and polymers produced using at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin as monomers.

[0014] Furthermore, the method for screening biochar with strong electron transfer capabilities includes the following specific steps:

[0015] (1) Under an inert atmosphere, a series of biochars were taken, and one type of biochar was added to an iron salt solution C and mixed thoroughly. Then, a reducing agent solution D was added. After the addition was complete, the mixture was stirred for 0.5-1.0 h. After separation and washing, the mixture was freeze-dried at -50 to -80°C for more than 12 hours to obtain a series of iron-carbon composite materials. The iron salt was at least one of divalent iron salt and trivalent iron salt, and the reducing agent in the reducing agent solution D was at least one of KBH4 and NaBH4.

[0016] (2) Each time, one of the iron-carbon composite materials was added to the wastewater containing chlorinated hydrocarbons and adsorption and degradation performance tests were conducted to obtain a series of adsorption and degradation performance test results. By comparing the series of adsorption and degradation performance test results, iron-carbon composite materials with good degradation effect on chlorinated hydrocarbons were screened out. Then, the electrochemical performance of the iron-carbon composite materials was characterized to screen out biochar with strong electron transfer ability.

[0017] Further, in step (1), the molar ratio of the reducing agent in the reducing agent solution D to the iron salt in the iron salt solution C is (3-5):1, and the mass ratio of the biochar with strong electron transfer capability to the iron ions in the iron salt solution C is (0.3-3):1.

[0018] Furthermore, in step (2), the amount of iron-carbon composite material added to the wastewater containing chlorinated hydrocarbons is 0.5-4 g / L, the concentration of chlorinated hydrocarbons in the wastewater is 5-50 mg / L, the reaction time is 7-20 days, and the reaction temperature is room temperature.

[0019] The slow-release iron-carbon composite material structure obtained by the present invention includes a coating layer with a thickness of 5-15 nm.

[0020] The second objective of this invention is to provide a slow-release iron-carbon composite material.

[0021] A third objective of this invention is to provide an application of a slow-release iron-carbon composite material for the treatment of wastewater contaminated with chlorinated hydrocarbons.

[0022] Specifically, chlorinated hydrocarbons can be pollutants such as trichloroethylene, tetrachloroethylene, and tetrachloroethane.

[0023] More specifically, in wastewater contaminated with chlorinated hydrocarbons, the chlorinated hydrocarbon is trichloroethylene.

[0024] Furthermore, the dosage of the slow-release iron-carbon composite material in wastewater containing chlorinated hydrocarbons is 0.5-5 g / L, the reaction time is 10-30 days, the reaction temperature is room temperature, the pH is 6-8, and the initial concentration of chlorinated hydrocarbons is 5-50 mg / L.

[0025] The present invention has the following beneficial effects:

[0026] 1. The slow-release iron-carbon composite material of the present invention utilizes biochar and modified biochar as the original carbon material to load nano-zero valent iron, thereby reducing the cost of iron-carbon composite materials and increasing the possibility of site application.

[0027] 2. In this invention, modified biochar with strong electron transfer properties is used to support nano-zero valent iron to prepare iron-carbon composite materials. By utilizing the high conductivity of modified biochar to form a galvanic cell with nano-zero valent iron, the electron loss ability of the iron-carbon composite material is enhanced, and the electron utilization rate of nano-zero valent iron is improved.

[0028] 3. In the preparation and use of the slow-release iron-carbon composite material of the present invention, cyclodextrin-like substances are used to modify the surface of nano-zero valent iron, inhibiting the occurrence of side reactions with oxygen and water, forming nanocracks on the surface of nano-zero valent iron, thereby enhancing the reactivity and long-lasting effect of nano-zero valent iron.

[0029] 4. The cyclodextrin-like substances used in the slow-release iron-carbon composite material of the present invention have a special external hydrophilic and internal hydrophobic structure, which can enrich chlorinated hydrocarbons adsorbed on the surface of the iron-carbon composite material onto the nano-zero-valent iron surface. The material has good selectivity for chlorinated hydrocarbon pollutants and can be used in sewage or groundwater with complex water composition and high concentration of coexisting components, and has good application potential.

[0030] 5. The reaction conditions of this invention are mild and easy to operate. The products after the reaction can be separated by magnetic separation. The material cost is low. It can remove chlorinated hydrocarbon pollutants in a green and long-lasting manner and has certain application prospects in complex groundwater pollution. Attached Figure Description

[0031] Figure 1 SEM image of the iron-carbon composite material prepared in Example 3;

[0032] Figure 2 TEM image of the iron-carbon composite material prepared in Example 3;

[0033] Figure 3 This is a diagram showing the adsorption effect of the material in Example 4;

[0034] Figure 4 The image shows the degradation effect of the material in Example 4;

[0035] Figure 5 The electrochemical impedance spectroscopy of the material in Example 4 is shown.

[0036] Figure 6 SEM image of the sustained-release iron-carbon composite material prepared in Example 5;

[0037] Figure 7TEM image of the sustained-release iron-carbon composite material prepared in Example 5;

[0038] Figure 8 The image shows the adsorption effect of the sustained-release iron-carbon composite material prepared in Example 5.

[0039] Figure 9 The degradation effect diagram of the slow-release iron-carbon composite material prepared in Example 5 is shown.

[0040] Figure 10 SEM image of the degraded material of the slow-release iron-carbon composite material prepared in Example 5;

[0041] Figure 11 SEM image of the degraded iron-carbon composite material prepared in Comparative Example 1. Detailed Implementation

[0042] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0043] Before preparing the slow-release iron-carbon composite material, the present invention requires screening of biochar, as shown in Examples 1-3:

[0044] Example 1: Iron-carbon composite material supported on coconut shell biochar with nano-zero valent iron

[0045] (1) Under N2 atmosphere, 0.5g of coconut shell biochar was added to 2.482g of 0.045mol / L FeSO4·7H2O solution and thoroughly shaken and mixed for 2h. Then, 1.013g of 0.268mol / L NaBH4 solution was added dropwise and stirred for 1h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80℃ for 12h to obtain an iron-carbon composite material of coconut shell biochar loaded with nano-zero valent iron.

[0046] Example 2: Iron-carbon composite material with lignin-based biochar supporting nano-zero-valent iron

[0047] (1) Under N2 atmosphere, 0.5g of lignin-based biochar was added to 2.482g of 0.045mol / L FeSO4·7H2O solution and thoroughly shaken and mixed for 2h. Then, 1.013g of 0.268mol / L NaBH4 solution was added dropwise and stirred for 1h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80℃ for 12h to obtain lignin-based biochar-supported nano-zero-valent iron iron composite material.

[0048] Example 3: Iron-carbon composite material of coconut shell-based capacitor modified biochar supported on nano-zero valent iron

[0049] (1) Under N2 atmosphere, 0.5g of coconut shell-based capacitor modified biochar was added to 2.482g of 0.045mol / L FeSO4·7H2O solution and thoroughly shaken and mixed for 2h. Then, 1.013g of 0.268mol / L NaBH4 solution was added dropwise and stirred for 1h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80℃ for 12h to obtain lignin-based biochar-supported nano-zero-valent iron iron composite material.

[0050] Figure 1 SEM image of an iron-carbon composite material of biochar-supported nano-zero-valent iron for coconut shell-based capacitors. Figure 2 The image shows a TEM image of an iron-carbon composite material of coconut shell-based capacitor modified biochar loaded with nano-zero valent iron. It can be seen that after loading nano-zero valent iron onto the biochar of coconut shell-based capacitor modified biochar, the nano-zero valent iron is well dispersed on the surface of the biochar.

[0051] Example 4: Material Performance Testing

[0052] In this embodiment, trichloroethylene was selected as the characteristic pollutant. The adsorption, degradation performance and electrochemical tests of the materials were conducted on the materials. The materials included the coconut shell biochar-supported nano-zero valent iron iron composite material prepared in Example 1, the lignin-based biochar-supported nano-zero valent iron iron composite material prepared in Example 2, the coconut shell-based capacitor-modified biochar-supported nano-zero valent iron iron composite material prepared in Example 3, and unsupported nano-zero valent iron. In addition, 25 mg / L of trichloroethylene wastewater (CK group) without any added materials was set up as a blank control.

[0053] The adsorption performance and electrochemical tests of the iron-carbon composite materials in Examples 1-3 for chlorinated hydrocarbon pollutants are as follows:

[0054] (1) Adsorption and degradation performance test: First, a 25 mg / L trichloroethylene solution was prepared and placed in a 100 mL headspace vial containing a tetrafluorosilicone pad; then, 200 mg of the material was added, and the solution was shaken in a constant temperature shaking incubator at 20 °C and 180 rpm. At regular intervals (0 h, 2 h, 4 h, 8 h, 12 h, 24 h, 2 d, 3 d, 4 d, 5 d, 6 d), 320 μL to 40 mL of ultrapure water were taken and placed in brown sample vials. The concentration of trichloroethylene in the solution at different time points was measured using a purge-and-trap gas chromatography-mass spectrometry (GC-MS). The adsorption results are shown below. Figure 3As shown in the figure. Furthermore, the concentration of chloride ions in the solution was measured using an anion chromatography instrument to obtain the actual degradation rate of trichloroethylene. The degradation results are shown in the figure. Figure 4 As shown;

[0055] (2) Electrochemical testing: The electron transfer capability of biochar was characterized by electrochemical impedance spectroscopy, cyclic voltammetry, polarization curves, and linear voltammetry scans. The results are as follows: Figure 5 As shown.

[0056] Depend on Figures 3-5 Results:

[0057] Figure 3 , Figure 4 , Figure 5 As can be seen, the coconut shell-based biochar-supported nano-zero-valent iron iron composite material prepared in Example 1, the lignin-based biochar-supported nano-zero-valent iron iron composite material prepared in Example 2, and the coconut shell-based capacitor-modified biochar-supported nano-zero-valent iron iron composite material prepared in Example 3 all have good adsorption performance, degradation performance, and electron transfer ability for trichloroethylene. Among them, the coconut shell-based capacitor-modified biochar-supported nano-zero-valent iron iron composite material in Example 3 has the best performance in all aspects.

[0058] Coconut shell-based capacitor-modified biochar material was obtained through material optimization, and slow-release iron-carbon composite materials were prepared as shown in Examples 5-9. In Examples 5-9, the iron salt solution was FeSO4·7H2O solution, the biochar was coconut shell-based capacitor-modified biochar, the cyclodextrin polymer was β-cyclodextrin (mw = 1134), and the reducing agent was NaBH4. The specific preparation process of Examples 5-9 is as follows:

[0059] Example 5: Preparation of slow-release iron-carbon composite material

[0060] Under a nitrogen atmosphere, 1.5 g of coconut shell-based capacitor-modified biochar and 4.5 g of β-cyclodextrin were added to 5.907 g of 0.106 mol / L FeSO4·7H2O solution. After shaking and mixing for 2 h, 2.411 g of 0.637 mol / L NaBH4 was added dropwise. After the addition was complete, stirring was continued for 1 h. After magnetic separation, the mixture was washed three times with deionized water and ethanol, and then freeze-dried at -80 °C for 12 h to obtain a slow-release iron-carbon composite material with a mass ratio of iron ions: carbon: cyclodextrin of 2.38:3:9.

[0061] Figure 6 SEM image of a slow-release iron-carbon composite material with biochar-supported nano-zero-valent iron modified for coconut shell-based capacitors. Figure 7TEM image of a slow-release iron-carbon composite material of coconut shell-based capacitor modified biochar loaded with nano-zero valent iron; it can be seen that after being coated with β-cyclodextrin, the particle size of the nano-zero valent iron on the surface increases and the surface has an uneven granular texture. This proves that β-cyclodextrin is attached to the surface of the nano-zero valent iron and forms nanocracks on the surface. These nanocracks help electrons break through the confinement of the oxide layer and transport electrons outward.

[0062] Example 6: Preparation of slow-release iron-carbon composite material

[0063] The only difference between this embodiment and Embodiment 5 is the change in the raw material synthesis ratio of the slow-release iron-carbon composite material:

[0064] Under a nitrogen atmosphere, 1 g of coconut shell-based capacitor-modified biochar and 4.5 g of β-cyclodextrin were added to 2.482 g of 0.045 mol / L FeSO4·7H2O solution. After shaking and mixing for 2 h, 1.013 g of 0.268 mol / L NaBH4 solution was added dropwise. After the addition was complete, stirring was continued for 1 h. After magnetic separation, the mixture was washed three times with deionized water and ethanol, and then freeze-dried at -80 °C for 12 h to obtain a slow-release iron-carbon composite material with a mass ratio of iron ions: carbon: cyclodextrin of 1:2:9.

[0065] Example 7: Preparation of slow-release iron-carbon composite material

[0066] The only difference between this embodiment and Embodiment 5 is the change in the raw material synthesis ratio of the slow-release iron-carbon composite material.

[0067] Under a nitrogen atmosphere, 0.5 g of coconut shell-based capacitor-modified biochar and 3 g of β-cyclodextrin were added to 2.482 g of 0.045 mol / L FeSO4·7H2O solution. After shaking and mixing for 2 h, 1.013 g of 0.268 mol / L NaBH4 solution was added dropwise. After the addition was complete, stirring was continued for 1 h. After magnetic separation, the mixture was washed three times with deionized water and ethanol, and then freeze-dried at -80 °C for 12 h to obtain a slow-release iron-carbon composite material with a mass ratio of iron ions: carbon: cyclodextrin of 1:1:6.

[0068] Example 8: Preparation of slow-release iron-carbon composite material

[0069] The only difference between this embodiment and Embodiment 5 is the change in the raw material synthesis ratio of the slow-release iron-carbon composite material.

[0070] Under a nitrogen atmosphere, 1g of coconut shell-based capacitor-modified biochar and 3g of β-cyclodextrin were added to 4.964g of 0.089mol / L FeSO4·7H2O solution. After shaking and mixing for 2h, 2.026g of 0.536mol / L NaBH4 solution was added dropwise. After the addition was complete, stirring was continued for 1.0h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80℃ for 12h to obtain a slow-release iron-carbon composite material with a mass ratio of iron ions: carbon: cyclodextrin of 2:2:6.

[0071] Example 9: Preparation of slow-release iron-carbon composite material

[0072] The only difference between this embodiment and Embodiment 5 is the change in the raw material synthesis ratio of the slow-release iron-carbon composite material.

[0073] Under a nitrogen atmosphere, 1g of coconut shell-based capacitor-modified biochar and 1.5g of β-cyclodextrin were added to 2.482g of 0.045mol / L FeSO4·7H2O solution. After shaking and mixing for 2h, 2.026g of 0.536mol / L NaBH4 solution was added dropwise. After the addition was complete, stirring was continued for 1.0h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80℃ for 12h to obtain a slow-release iron-carbon composite material with a mass ratio of iron ions: carbon: cyclodextrin of 1:2:3.

[0074] Comparative Example 1:

[0075] Compared with Example 5, Comparative Example 1 did not add cyclodextrin during the preparation of the material, and its specific preparation steps are as follows:

[0076] Under a nitrogen atmosphere, 1.5 g of coconut shell-based capacitor-modified biochar was added to 5.907 g of 0.106 mol / L FeSO4·7H2O solution. After shaking and mixing for 2 h, 2.411 g of 0.637 mol / L NaBH4 was added dropwise. After the addition was complete, stirring was continued for 1 h. After magnetic separation, the mixture was washed three times with deionized water and ethanol respectively, and then freeze-dried at -80 °C for 12 h to obtain an iron-carbon composite material with a mass ratio of iron ions to carbon of 2.38:3.

[0077] Example 10: Application of slow-release iron-carbon composite materials

[0078] Trichloroethylene was selected as the characteristic pollutant, and adsorption and degradation tests of chlorinated hydrocarbons by slow-release iron-carbon composite materials were conducted. The test materials included the slow-release iron-carbon composite materials prepared in Examples 5, 6, 7, 8, 9 and Comparative Example 1.

[0079] The specific steps are as follows:

[0080] First, a 25 mg / L trichloroethylene solution was prepared and placed in a 100 mL headspace vial containing a tetrafluorosilicone pad. Then, 200 mg of a slow-release iron-carbon composite material was added, and the solution was shaken in a constant-temperature shaking incubator at 20 °C and 180 rpm. At regular intervals (0 days, 1 day, 2 days, 4 days, 8 days, 12 days, 16 days, and 20 days), 6 mL samples were taken and added to a sample vial. The concentration of chloride ions in the solution was measured using an anion chromatography instrument to obtain the actual degradation rate of trichloroethylene. The degradation results are shown in Table 1.

[0081] Table 1

[0082] Example 5 Example 6 Example 7 Example 8 Example 9 Comparative Example 1 Degradation rate 100％ 80％ 86.5％ 94.7％ 89％ 83.3％

[0083] From Table 1, Figure 8 , Figure 9 It can be seen that the slow-release iron-carbon composite material prepared in Example 5 with a mass ratio of iron salt:carbon:cyclodextrin of 2.38:3:9 showed the best degradation effect, achieving a 100% degradation rate of trichloroethylene in the solution. The slow-release iron-carbon composite material prepared in Example 8 with a mass ratio of iron salt:carbon:cyclodextrin of 2:2:6 was the next best, with a degradation effect of 94.7%. The slow-release iron-carbon composite material prepared in Example 6 with a mass ratio of iron salt:carbon:cyclodextrin of 1:2:9 showed the worst relative degradation effect.

[0084] Figure 10 This is a SEM image of the slow-release iron-carbon material prepared in Example 5 after degradation. Figure 11 The image shows a SEM image of the iron-carbon composite material prepared in Comparative Example 1 after degradation. Figure 10 , Figure 11 It can be seen that the slow-release iron-carbon composite material still maintains a high degree of integrity after the reaction, and a large amount of flaky iron oxide is generated on the surface of the material after the reaction, which further proves that the slow-release iron-carbon composite material of the present invention has excellent slow-release degradation performance and provides a new solution for chlorinated hydrocarbon pollution in groundwater.

[0085] Material aging test:

[0086] (1) Experimental conditions: Trichloroethylene was selected as the characteristic pollutant, and Example 5 was used as the optimal ratio for degradation performance testing. The experiment was divided into 8 groups: Experimental groups 1-8. Under the premise of controlling single-factor variables, the degradation of trichloroethylene in solution by iron-carbon composite material and slow-release iron-carbon composite material in air and water for 15 days and 30 days respectively was tested.

[0087] (2) Grouping:

[0088] Experimental Group 1: The iron-carbon composite material prepared in Comparative Example 1 was aged in air for 15 days;

[0089] Experimental Group 2: The slow-release iron-carbon composite material prepared in Example 5 was aged in air for 15 days;

[0090] Experimental Group 3: The iron-carbon composite material prepared in Comparative Example 1 was aged in air for 30 days;

[0091] Experimental group 4: The slow-release iron-carbon composite material prepared in Example 5 was aged in air for 30 days;

[0092] Experimental Group 5: The iron-carbon composite material prepared in Comparative Example 1 was aged in water for 15 days;

[0093] Experimental group 6: The slow-release iron-carbon composite material prepared in Example 5 was aged in water for 15 days;

[0094] Experimental Group 7: The iron-carbon composite material prepared in Comparative Example 1 was aged in water for 30 days;

[0095] Experimental Group 8: The slow-release iron-carbon composite material prepared in Example 5 was aged in water for 30 days.

[0096] (3) Test methods:

[0097] First, eight 25 mg / L trichloroethylene solutions were prepared and placed in eight 100 mL headspace vials containing PTFE silicone pads. Then, 200 mg of the test material from experimental groups 1-8 was added to each vial, and the vials were shaken in a constant-temperature shaking incubator at 20 °C and 180 rpm. At regular intervals (0 days, 1 day, 2 days, 4 days, 8 days, 12 days, 16 days, and 20 days), 320 μL to 40 mL of ultrapure water were collected in brown sample vials. The concentration of trichloroethylene in the solution was measured using purge-trap gas chromatography-mass spectrometry (GC-MS), and 6 mL of the solution was taken to measure the chloride ion content. The actual degradation rate of trichloroethylene was obtained, and the results are shown in Table 2.

[0098] Table 2

[0099]

[0100] As shown in Table 2, overall, under the same aging time and aging conditions, the material with a shorter aging time has a higher degradation rate for trichloroethylene. Among them, the degradation rate of air aging is higher than that of water aging. However, when comparing the two materials, the final degradation rate of the slow-release iron-carbon composite material is much higher than that of the iron-carbon composite material.

[0101] In summary, this invention improves the reactivity of biochar by reacting it with iron salt solution, cyclodextrin, and reducing agent, thereby accelerating the enrichment of chlorinated hydrocarbons on the material surface, increasing the reaction rate of nano-zero valent iron with chlorinated hydrocarbons, reducing side reactions, enhancing electron slow-release performance, and improving reactivity, thus achieving efficient and sustained dechlorination of chlorinated hydrocarbons by the material.

[0102] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. An application of a slow-release iron-carbon composite material, characterized in that, The slow-release iron-carbon composite material is used in the treatment of wastewater containing chlorinated hydrocarbons. The preparation method of the sustained-release iron-carbon composite material includes the following steps: A slow-release iron-carbon composite material was prepared by liquid-phase reduction of biochar with strong electron transfer capability, iron salt solution A, cyclodextrin, and reducing agent solution B. The specific preparation steps of the liquid-phase reduction method are as follows: Under an inert atmosphere, biochar with strong electron transfer capability and cyclodextrin are placed in iron salt solution A and mixed thoroughly. Reducing agent solution B is added dropwise to carry out the reaction. After separation and drying, a slow-release iron-carbon composite material can be obtained. The biochar with strong electron transfer capability is at least one of lignin-based biochar and coconut shell-based modified capacitor biochar; the iron salt is at least one of ferrous salt and ferric salt; the reducing agent in the reducing agent solution B is at least one of KBH4 and NaBH4; the cyclodextrin is at least one of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and a polymer produced using at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin as a monomer. The molar ratio of the reducing agent to the iron salt in the iron salt solution A is (3-5):1, and the mass ratio of the biochar with strong electron transfer capability, the iron ions in the iron salt solution A, and the cyclodextrin is 2.38:3:

9.

2. The application of the slow-release iron-carbon composite material according to claim 1, characterized in that, The method for screening biochar with strong electron transfer capabilities includes the following specific steps: (1) Under an inert atmosphere, a series of biochars were taken, and each biochar was added to an iron salt solution C and mixed thoroughly. Then, a reducing agent solution D was added. After the addition was complete, the mixture was stirred for 0.5-1.0 h. After separation and washing, the mixture was freeze-dried at -50 to -80°C for more than 12 hours to obtain a series of iron-carbon composite materials. (2) Each time, one of the iron-carbon composite materials was added to the wastewater containing chlorinated hydrocarbons and adsorption and degradation performance tests were conducted to obtain a series of adsorption and degradation performance test results. By comparing the series of adsorption and degradation performance test results, the iron-carbon composite material with good degradation effect on chlorinated hydrocarbons was selected. The electrochemical properties of the iron-carbon composite material were then characterized to screen out biochar with strong electron transfer capabilities.

3. The application of the slow-release iron-carbon composite material according to claim 2, characterized in that, In step (1), the molar ratio of the reducing agent in the reducing agent solution D to the iron salt in the iron salt solution C is (3-5):1, and the mass ratio of the biochar with strong electron transfer capability to the iron ions in the iron salt solution C is (0.3-3):

1.

4. The application of the slow-release iron-carbon composite material according to claim 2, characterized in that, In step (2), the amount of iron-carbon composite material added to the wastewater containing chlorinated hydrocarbons is 0.5-4 g / L, the concentration of chlorinated hydrocarbons in the wastewater is 5-50 mg / L, the reaction time is 7-20 days, and the reaction temperature is room temperature.

5. The application of the slow-release iron-carbon composite material according to claim 1, characterized in that, The slow-release iron-carbon composite material is added to wastewater containing chlorinated hydrocarbons at a mass of 0.5-5 g / L, the reaction time is 10-30 days, the reaction temperature is room temperature, the pH of the wastewater is 6-8, and the initial concentration of chlorinated hydrocarbons in the wastewater is 5-50 mg / L.

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