Cobalt-loaded ramie biochar fiber as well as preparation method and application thereof

Abstract

The invention provides a cobalt-loaded ramie biochar fiber and a preparation method and application thereof.The preparation method comprises the steps that ramie biochar fiber obtained through pyrolysis of raw ramie silk is added into a methanol aqueous solution of 2-methylimidazole, then a methanol aqueous solution of cobalt nitrate hexahydrate is added for a reaction, after the reaction is finished, the mixture is cooled to the room temperature, and the cobalt-loaded ramie biochar fiber is obtained. And centrifugally washing the solid, drying, and pyrolyzing again to obtain the cobalt-loaded ramie biochar fiber. The cobalt-loaded ramie biochar fiber has metal cobalt active sites, reaction conditions are mild, an oxidative degradation system formed by the cobalt-loaded ramie biochar fiber and persulfate in a water body and soil has a good degradation effect on unsymmetrical dimethylhydrazine, generation of N, N-dimethyl nitrosamine can be inhibited, and the biochar-loaded ramie biochar fiber has a good application prospect. A material which is simple to prepare, low in cost, convenient to apply and suitable for treating unsymmetrical dimethylhydrazine and a product thereof is provided for unsymmetrical dimethylhydrazine polluted site remediation in the technical field of environmental remediation, and large-scale popularization and application can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of persulfate activators, and particularly relates to a cobalt-loaded ramie biochar fiber and a preparation method thereof, and application of activated persulfate in synergistically degrading unsymmetrical dimethylhydrazine. Background Art

[0002] Unsymmetrical dimethylhydrazine (UDMH) is a high-performance liquid rocket propellant widely used in missiles and satellite launch vehicles. UDMH is flammable, explosive, highly toxic, corrosive, and carcinogenic. It easily enters the environment, causing serious pollution to water resources and harm to the human body. A single rocket launch produces up to 300 to 600 tons of UDMH wastewater, and the treatment of UDMH wastewater cannot be ignored. Common UDMH pollution remediation technologies include physical adsorption, chemical oxidation, and bioremediation. However, in actual applications, conventional treatment technologies such as ozone will produce a large amount of highly toxic conversion products during the treatment process, such as N-nitrosodimethylamine, which accumulate in the environment and cause greater harm.

[0003] In recent years, advanced oxidation technology (AOPs) based on a variety of reactive oxygen species (ROS) has become an environmental chemistry technology with broad prospects. Through this technology, persistent organic pollutants in water environments can be effectively mineralized or converted into biodegradable small-molecule organic substances, thereby achieving efficient removal of persistent organic matter. Among them, persulfate advanced oxidation technology (PS-AOPs) has attracted widespread attention from researchers due to its advantages such as diverse activation methods, wide pH adaptability, and strong oxidation ability of the generated ROS. Transition metal ions can effectively activate persulfate (PS) to produce a large amount of ROS, among which cobalt ions (Co) 2+ ) has the highest catalytic activity. However, due to the general toxicity of metal ions, this process is greatly limited in water treatment applications. At the same time, metal ions are difficult to recover in homogeneous reaction systems, resulting in unnecessary consumption of catalysts and increasing process operating costs. The use of heterogeneous cobalt-based catalysts to activate persulfate can effectively solve the above problems. Therefore, it is of great significance to develop a solid-phase cobalt-based material heterogeneous catalytic persulfate system to degrade UDMH in soil and water.

[0004] Loading cobalt-based catalysts onto a support material for PS activation is a common method. Depending on the support material, these can be broadly categorized as oxides, carbon materials, and metal-organic frameworks. Biochar, with its large surface area, rich pore structure, excellent chemical stability, strong anti-interference capabilities, and environmental friendliness, has the potential to activate PS. The synergistic effect between the cobalt species and the support not only effectively increases the surface area, thereby improving catalytic performance, but also effectively inhibits the leaching of cobalt ions, enhancing the catalyst's reusability and reducing the risk of secondary contamination. During catalyst preparation, the abundant functional groups and defect structures on the biochar surface can adsorb and immobilize metals. Metal salts can combine with nitrogen in organic compounds such as 2-methylimidazole to more effectively immobilize cobalt metal on the biochar. However, excessive cobalt metal can lead to aggregation, reduce material activity, and increase the risk of leaching. Therefore, the cobalt loading on the biochar needs to be controlled to enhance the material's catalytic performance.

[0005] Therefore, it is necessary to design and prepare a cobalt-loaded biochar catalytic material with low metal cobalt loading and the ability to maintain high activity during the reaction process to ensure efficient catalytic activation of persulfate to degrade unsymmetrical dimethylhydrazine. Summary of the Invention

[0006] (1) Technical issues to be solved

[0007] The present invention provides a cobalt-loaded ramie biochar fiber and a preparation method and application thereof, in order to solve the technical problem of how to efficiently catalyze and activate persulfate to degrade unsymmetrical dimethylhydrazine.

[0008] (2) Technical solution

[0009] In order to solve the above technical problems, the present invention provides a method for preparing cobalt-loaded ramie biochar fiber, which comprises the following steps:

[0010] S1. Ramie raw silk was placed in a crucible and placed in a tubular furnace, and pyrolyzed under nitrogen to obtain ramie biochar fibers;

[0011] S2. dissolving 2-methylimidazole in a methanol-water solution, adding ramie biochar fibers, and ultrasonically mixing to obtain a homogeneous 2-methylimidazole solution;

[0012] S3. Dissolving cobalt nitrate hexahydrate in aqueous methanol and ultrasonicating at room temperature to obtain a homogeneous solution of cobalt nitrate hexahydrate;

[0013] S4. The homogeneous solutions prepared in steps S2 and S3 were mixed, stirred, and the mixed solution was poured into a stainless steel autoclave containing a polytetrafluoroethylene liner for reaction, and the reaction was cooled to room temperature after completion;

[0014] S5. The cooled mixed solution was poured out, and the solid was centrifuged and washed and dried;

[0015] S6. The dried solid was placed in a crucible and placed in a tube furnace, and pyrolyzed under nitrogen conditions to obtain cobalt-loaded ramie biochar fibers.

[0016] Furthermore, in step S1, the nitrogen flow rate is 120 mL / min, the pyrolysis temperature is 550° C., and the pyrolysis time is 2 h.

[0017] Furthermore, in step S2, the concentration of 2-methylimidazole is 0.05-0.20 mol / L, and the mass ratio of 2-methylimidazole to biochar fiber is (1.5-0.5):1.

[0018] Furthermore, in step S3, the concentration of cobalt nitrate hexahydrate is 0.10-0.25 mol / L.

[0019] Furthermore, in step S4, when the solutions are mixed, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is (4-8):1; and the mixed solution is reacted in a high-pressure reactor at 150° C. for 4 hours.

[0020] Furthermore, in step S5, the solution is poured out, and the solid is washed three times by centrifugation with methanol and water respectively, with chromatographic grade methanol being used; and dried at 60°C.

[0021] Furthermore, in step S6, the nitrogen flow rate is 120 mL / min, the pyrolysis temperature is 700° C., and the pyrolysis time is 2 h.

[0022] In addition, the present invention also provides a cobalt-loaded ramie biochar fiber, which is prepared by the above method.

[0023] In addition, the present invention also proposes an application of cobalt-loaded ramie biochar fiber, using the above-mentioned cobalt-loaded biochar fiber as a catalyst to activate the persulfate oxidation degradation system of the pollutant unsymmetrical dimethylhydrazine. The method is to add cobalt-loaded ramie biochar fiber and potassium persulfate to the unsymmetrical dimethylhydrazine water body or contaminated soil, stir or shake, and then react to achieve the degradation of unsymmetrical dimethylhydrazine.

[0024] Furthermore, when the cobalt-loaded biochar fiber was used as a catalyst to activate the oxidation degradation system of unsymmetrical dimethylhydrazine by potassium persulfate in unsymmetrical dimethylhydrazine water, the initial concentration of unsymmetrical dimethylhydrazine was 50-100 mg / L, the ratio of cobalt-loaded ramie biochar fiber to unsymmetrical dimethylhydrazine solution was (0.01-0.05 g):100 mL, the ratio of potassium persulfate to unsymmetrical dimethylhydrazine water was (0.02-0.05 g):100 mL, the magnetic stirring rate was 220 rpm, and the reaction time was 0. 6h; Cobalt-loaded biochar fiber was used as a catalyst to activate the oxidative degradation system of potassium peroxydisulfate to degrade UDMH in contaminated soil. The initial concentration of UDMH was 100-200 mg / kg, the mass ratio of cobalt-loaded ramie biochar fiber to UDMH-contaminated soil was (0.125-0.25):5, the mass ratio of potassium peroxydisulfate to UDMH-contaminated soil was (0.125-0.25):0.5, the tumbling oscillation rate was 70 rpm, and the reaction time was 3.0h.

[0025] (3) Beneficial effects

[0026] The present invention provides a cobalt-loaded ramie biochar fiber, a preparation method, and an application thereof. The preparation method comprises adding ramie biochar fibers obtained by pyrolyzing ramie raw silk to a methanol solution of 2-methylimidazole, then adding a methanol solution of cobalt nitrate hexahydrate to react, cooling to room temperature after the reaction, centrifuging and washing the solid, drying it, and then pyrolyzing it again to obtain the cobalt-loaded ramie biochar fiber. The cobalt-loaded ramie biochar fiber has metallic cobalt active sites and mild reaction conditions. It can form an oxidative degradation system with persulfate in both water and soil, has a good degradation effect on unsymmetrical dimethylhydrazine, and can inhibit the formation of N,N-nitrosodimethylamine. This provides a simple, low-cost, and easy-to-use material suitable for the treatment of unsymmetrical dimethylhydrazine and its products in the field of environmental remediation technology for the remediation of unsymmetrical dimethylhydrazine-contaminated sites, and is suitable for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM morphology of the cobalt-loaded biochar fiber material prepared in Example 1;

[0028] Figure 2 The degradation and activation effects of UDMH in aqueous solution at different oxidant concentrations when the cobalt-loaded biochar fiber material prepared in Example 1 was used at a dosage of 0.1 g / L.

[0029] Figure 3 Co in Example 1 4％ -Degradation and activation effect of UDMH in soil when the dosage of BC is 0.5% and the dosage of oxidant is 0.5%. DETAILED DESCRIPTION

[0030] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings and examples.

[0031] Example 1

[0032] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550 ° C for 2 h under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 0.5:1. Ultrasonic treatment was performed at room temperature for 1.5 h to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; 2-methylimidazole was homogeneously dissolved in methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution. The solution was mixed with a homogeneous solution of cobalt nitrate hexahydrate, with the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole controlled at 4:1. After stirring for 20-30 minutes, the mixture was poured into a stainless steel autoclave containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction, the mixture was cooled to room temperature and centrifuged. The solution was decanted, and the solid was washed three times with water and methanol, respectively, and dried at 60°C. The solid was placed in a crucible in a tube furnace and pyrolyzed for 2 hours at a nitrogen flow rate of 120 mL / min to obtain cobalt-loaded ramie biochar fibers. The cobalt-loaded ramie biochar fibers were characterized using scanning electron microscopy.

[0033] Prepare 100 mg / L UDMH solution, add 100 mL into a conical flask, add cobalt-loaded ramie biochar fiber (0.1 g / L) and potassium persulfate (0.15, 0.25, 0.35, 0.45, 0.55, 0.65 g / L), stir at 220 rpm for 30 min, then take samples at 0, 5, 10, 20, 30, and 40 min after adding cobalt-loaded ramie biochar fiber, and perform quantitative analysis using a high performance liquid chromatograph with a UV detector, and the degradation rate is 90%.

[0034] Figure 1 This is the SEM morphology of the cobalt-loaded biochar fiber material prepared in Example 1. Figure 2 The degradation and activation effects of aqueous UDMH under different oxidant concentrations when the cobalt-loaded biochar fiber material prepared in Example 1 was used at a dosage of 0.1 g / L. Figure 3 Co in Example 1 4％ -Degradation and activation effect of UDMH in soil when the dosage of BC is 0.5% and the dosage of oxidant is 0.5%.

[0035] Example 2

[0036] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550 ° C for 2 h under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 1:1. Ultrasonic treatment was performed at room temperature for 1.5 h to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; the 2-methylimidazole homogeneous solution was mixed with the hexahydrate A homogeneous cobalt nitrate solution was mixed, with a molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole of 4:1. After stirring for 20-30 minutes, the mixture was poured into a stainless steel autoclave containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction was completed, the mixture was cooled to room temperature and the solution was poured out. The solid was washed three times by centrifugation with water and methanol, respectively, and dried at 60°C. The solid was placed in a crucible in a tube furnace and pyrolyzed for 2 hours at a nitrogen flow rate of 120 mL / min to obtain cobalt-loaded ramie biochar fibers. The cobalt-loaded ramie biochar fibers were characterized using scanning electron microscopy.

[0037] Prepare 100 mg / L UDMH solution, add 100 mL into a conical flask, add cobalt-loaded ramie biochar fiber (0.1 g / L) and potassium persulfate (0.15, 0.25, 0.35, 0.45, 0.55, 0.65 g / L), stir at 220 rpm for 30 min, then take samples at 0, 5, 10, 20, 30, and 40 min after adding cobalt-loaded ramie biochar fiber, and perform quantitative analysis using a high performance liquid chromatograph with a UV detector, and the degradation rate is 90%.

[0038] Example 3

[0039] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550 ° C for 2 h under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 1.6:1. Ultrasonic treatment was performed at room temperature for 1.5 h to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; the 2-methylimidazole homogeneous solution was mixed with hexahydrate to obtain a cobalt nitrate hexahydrate homogeneous solution. A homogeneous aqueous cobalt nitrate solution was mixed, with the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole controlled at 4:1. After stirring for 20-30 minutes, the mixture was poured into a stainless steel autoclave containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction was completed, the mixture was cooled to room temperature and the solution was poured out. The solid was washed three times by centrifugation with water and methanol, respectively, and dried at 60°C. The solid was placed in a crucible and placed in a tube furnace. It was pyrolyzed for 2 hours under a nitrogen flow rate of 120 mL / min to obtain cobalt-loaded ramie biochar fibers. The cobalt-loaded ramie biochar fibers were characterized using scanning electron microscopy.

[0040] Prepare 100 mg / L UDMH solution, add 100 mL into a conical flask, add cobalt-loaded ramie biochar fiber (0.1 g / L) and potassium persulfate (0.15, 0.25, 0.35, 0.45, 0.55, 0.65 g / L), stir at 220 rpm for 30 min, then take samples at 0, 5, 10, 20, 30, and 40 min after adding cobalt-loaded ramie biochar fiber, and perform quantitative analysis using a high performance liquid chromatograph with a UV detector, and the degradation rate is 90%.

[0041] Comparative Example 1

[0042] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550°C for 2 hours under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in a methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 0.5:1. The solution was ultrasonicated at room temperature for 1.5 hours to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in a methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; the 2-methylimidazole homogeneous solution was mixed with the cobalt nitrate hexahydrate homogeneous solution, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole was controlled to be 4:1. After stirring for 20 to 30 minutes, the mixture was poured into a stainless steel high-pressure reactor containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the solution was poured out, the solid was centrifuged and washed three times with water and methanol respectively, and dried at 60°C to obtain cobalt-loaded ramie biochar fiber. The cobalt-loaded ramie biochar fibers were characterized by scanning electron microscopy.

[0043] A 200 g / kg UDMH-contaminated soil sample was prepared and added to a 50 mL centrifuge tube. Cobalt-loaded ramie biochar fiber (0.125 g) and potassium peroxydisulfate (0.125 g) were added. The tube was placed on an inversion shaker and stirred at 70 rpm for 3.0 h. 1 mL of methanol was then added to quench the reaction. The reaction solution was pre-treated with alkaline distillation and then derivatized with salicylic aldehyde. The UDMH content was analyzed using gas chromatography (ECD detector), and the degradation rate reached 98%.

[0044] Comparative Example 2

[0045] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550°C for 2 hours under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in a methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 0.5:1. The solution was ultrasonicated at room temperature for 1.5 hours to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in a methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; the 2-methylimidazole homogeneous solution was mixed with the cobalt nitrate hexahydrate homogeneous solution, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole was controlled to be 4:1. After stirring for 20 to 30 minutes, the mixture was poured into a stainless steel high-pressure reactor containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the solution was poured out, the solid was centrifuged and washed three times with water and methanol respectively, and dried at 60°C to obtain cobalt-loaded ramie biochar fiber. The cobalt-loaded ramie biochar fibers were characterized by scanning electron microscopy.

[0046] A 200 g / kg UDMH-contaminated soil sample was prepared and added to a 50 mL centrifuge tube. Cobalt-loaded ramie biochar fiber (0.125 g) and potassium peroxydisulfate (0.125 g) were added. The tube was placed on an inversion shaker and stirred at 70 rpm for 3.0 h. 1 mL of methanol was then added to quench the reaction. The reaction solution was pre-treated with alkaline distillation and then derivatized with salicylic aldehyde. The UDMH content was analyzed using gas chromatography (ECD detector), and the degradation rate reached 98%.

[0047] Comparative Example 3

[0048] Ramie raw silk was placed in a corundum crucible and put into a tube furnace, and pyrolyzed at 550°C for 2 hours under a nitrogen flow rate of 120 mL / min to obtain ramie biochar fiber; 2-methylimidazole was dissolved in a methanol aqueous solution, and ramie biochar fiber was added, and the mass ratio of ramie biochar fiber to 2-methylimidazole was controlled to be 0.5:1. The solution was ultrasonicated at room temperature for 1.5 hours to obtain a 2-methylimidazole homogeneous solution, and cobalt nitrate hexahydrate was dissolved in a methanol aqueous solution and stirred at room temperature to obtain a cobalt nitrate hexahydrate homogeneous solution; the 2-methylimidazole homogeneous solution was mixed with the cobalt nitrate hexahydrate homogeneous solution, and the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole was controlled to be 4:1. After stirring for 20 to 30 minutes, the mixture was poured into a stainless steel high-pressure reactor containing a polytetrafluoroethylene liner and reacted at 150°C for 4 hours. After the reaction was completed, the mixture was cooled to room temperature, the solution was poured out, the solid was centrifuged and washed three times with water and methanol respectively, and dried at 60°C to obtain cobalt-loaded ramie biochar fiber. The cobalt-loaded ramie biochar fibers were characterized by scanning electron microscopy.

[0049] A 200 g / kg UDMH-contaminated soil sample was prepared and added to a 50 mL centrifuge tube. Cobalt-loaded ramie biochar fiber (0.125 g) and potassium peroxydisulfate (0.125 g) were added. The tube was placed on an inversion shaker and stirred at 70 rpm for 3.0 h. 1 mL of methanol was then added to quench the reaction. The reaction solution was pre-treated with alkaline distillation and then derivatized with salicylic aldehyde. The UDMH content was analyzed using gas chromatography (ECD detector), and the degradation rate reached 98%.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing cobalt-loaded ramie biochar fiber, characterized in that: The preparation method comprises the following steps: S1. Ramie raw silk was placed in a crucible and placed in a tubular furnace, and pyrolyzed under nitrogen to obtain ramie biochar fibers; S2. dissolving 2-methylimidazole in a methanol-water solution, adding ramie biochar fibers, and ultrasonically mixing to obtain a homogeneous 2-methylimidazole solution; S3. Dissolving cobalt nitrate hexahydrate in aqueous methanol and ultrasonicating at room temperature to obtain a homogeneous solution of cobalt nitrate hexahydrate; S4. The homogeneous solutions prepared in steps S2 and S3 were mixed, stirred, and the mixed solution was poured into a stainless steel autoclave containing a polytetrafluoroethylene liner for reaction, and the reaction was cooled to room temperature after completion; S5. The cooled mixed solution was poured out, and the solid was centrifuged and washed and dried; S6. The dried solid was placed in a crucible and placed in a tube furnace, and pyrolyzed under nitrogen conditions to obtain cobalt-loaded ramie biochar fibers.

2. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S1, the nitrogen flow rate is 120 mL / min, the pyrolysis temperature is 550° C., and the pyrolysis time is 2 h.

3. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S2, the concentration of 2-methylimidazole is 0.05-0.20 mol / L, and the mass ratio of 2-methylimidazole to biochar fiber is (1.5-0.5):

1.

4. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S3, the concentration of cobalt nitrate hexahydrate is 0.10-0.25 mol / L.

5. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S4, when the solutions are mixed, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is (4-8):1; and the mixed solution is reacted in a high-pressure reactor at 150° C. for 4 hours.

6. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S5, the solution is poured out, and the solid is washed three times by centrifugation with methanol and water respectively, using chromatographic grade methanol; and dried at 60°C.

7. The method for preparing cobalt-loaded ramie biochar fiber according to claim 1, wherein: In step S6, the nitrogen flow rate is 120 mL / min, the pyrolysis temperature is 700° C., and the pyrolysis time is 2 h.

8. A cobalt-loaded ramie biochar fiber, characterized in that: The cobalt-loaded ramie biochar fiber is prepared by the method according to any one of claims 1 to 7.

9. An application of cobalt-loaded ramie biochar fiber, characterized in that: The cobalt-loaded biochar fiber described in claim 8 is used as a catalyst to activate persulfate to oxidatively degrade the pollutant unsymmetrical dimethylhydrazine. The method is to add cobalt-loaded ramie biochar fiber and potassium peroxydisulfate to unsymmetrical dimethylhydrazine water or contaminated soil, stir or shake, and then react to achieve the degradation of unsymmetrical dimethylhydrazine.

10. The use of cobalt-loaded ramie biochar fiber according to claim 9, characterized in that: When cobalt-loaded biochar fiber was used as a catalyst to activate potassium persulfate in UDMH water to degrade UDMH, the initial concentration of UDMH was 50-100 mg / L, the ratio of cobalt-loaded ramie biochar fiber to UDMH solution was (0.01-0.05 g):100 mL, the ratio of potassium persulfate to UDMH water was (0.02-0.05 g):100 mL, the magnetic stirring rate was 220 rpm, and the reaction time was 0.6 h. Cobalt-loaded biochar fiber was used as a catalyst to activate the oxidative degradation system of potassium peroxydisulfate in contaminated soil to degrade unsymmetrical dimethylhydrazine. The initial concentration of unsymmetrical dimethylhydrazine was 100-200 mg / kg, the mass ratio of cobalt-loaded ramie biochar fiber to unsymmetrical dimethylhydrazine-contaminated soil was (0.125-0.25):5, the mass ratio of potassium peroxydisulfate to unsymmetrical dimethylhydrazine-contaminated soil was (0.125-0.25):0.5, the tumbling oscillation rate was 70 rpm, and the reaction time was 3.0 h.

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