Preparation method of nitrogen-doped porous carbon fiber and its products and applications

Abstract

The present application relates to the technical field of carbon material preparation, and in particular to a method for preparing nitrogen-doped porous carbon fibers, and its products and applications. The above-mentioned preparation method comprises: subjecting phenolic resin fibers to a cross-linking reaction under the action of a cross-linking agent to prepare a fiber felt. The fiber felt, an activator and a nitrogen source are mixed, and then dried to prepare a precursor; in the precursor, the activator and the nitrogen source are uniformly distributed in the fiber felt. The precursor is carbonized to prepare an activated product doped with nitrogen atoms, and the activated product is washed to neutrality. The nitrogen-doped porous carbon fibers prepared by the above-mentioned method have good radioactive iodine adsorption properties.

Description

Technical Field

[0001] The present application relates to the technical field of carbon material preparation, and in particular to a preparation method of nitrogen-doped porous carbon fiber and its products and applications. Background Art

[0002] With the depletion of fossil fuels and the rapid growth of global energy demand, nuclear energy, as a safe, clean energy source that effectively reduces greenhouse gas emissions, is considered a viable alternative. However, while nuclear energy generates high economic value, it also produces some radioactive waste, posing a direct threat to human health and the environment. Among all radionuclides, radioactive iodine has attracted considerable attention due to its high volatility and specific effects on the human thyroid gland. 131 I is the most abundant radioactive iodine nuclide, usually existing in the form of simple substance or iodine-substituted hydrocarbon compounds (such as methyl iodide). 131 The effective adsorption and removal of I compounds has become an urgent problem to be solved in the field of nuclear protection.

[0003] Traditional iodine capture technology is mainly divided into wet processes (such as liquid absorption method) and dry processes. Among them, the dry process is widely used because of its advantages such as simple operation, high adsorption efficiency, and reusability. However, the adsorption capacity of the adsorption materials used in the dry process is limited and often cannot meet the needs of practical applications. In recent years, carbon materials have attracted much attention in the field of adsorption technology due to their high specific surface area and high porosity. However, in terms of radioactive iodine adsorption, studies have shown that the adsorption capacity of unmodified carbon materials for methyl iodide does not exceed 0.26g / g, which means that the adsorption performance of traditional carbon materials still has a lot of room for improvement. Therefore, the targeted development of a high-performance radioactive iodine adsorption material and its preparation method has high scientific research and industrial application value. Summary of the Invention

[0004] Based on this, the present application provides a preparation method of nitrogen-doped porous carbon fibers, and its products and applications. The nitrogen-doped porous carbon fibers prepared by the above method have good radioactive iodine adsorption performance.

[0005] In a first aspect, a method for preparing nitrogen-doped porous carbon fibers is provided, comprising the following steps:

[0006] The phenolic resin fibers are subjected to a cross-linking reaction under the action of a cross-linking agent to prepare a fiber felt;

[0007] The fiber mat, the activator and the nitrogen source are mixed and then dried to prepare a precursor, wherein the activator and the nitrogen source are uniformly distributed in the fiber mat;

[0008] The precursor is carbonized to prepare a nitrogen-doped activated product. During the carbonization process, the nitrogen source decomposes to form an active substance that can react with the carbon in the precursor. The activator chemically reacts with the carbon in the precursor to wash the activated product to neutrality.

[0009] In some embodiments, the preparation method further comprises the following steps:

[0010] The phenolic resin fiber is prepared by spinning a phenolic resin, wherein the phenolic resin comprises a thermoplastic novolac resin. Optionally, the thermoplastic novolac resin has a weight average molecular weight of 500 to 5000, and / or a melting point of the thermoplastic novolac resin at standard atmospheric pressure of 100 to 120° C. Further optionally, the thermoplastic novolac resin has a linear structure.

[0011] In some embodiments, the spinning method includes melt centrifugal spinning, electrospinning or wet spinning. Optionally, the temperature of the melt centrifugal spinning is 300-500° C., and the rotation speed is 2000-3000 r / min.

[0012] In some embodiments, the crosslinking agent is provided in the form of a solution comprising, by weight, the following components: 15-20 parts by weight of 36% hydrochloric acid, 15-20 parts by weight of the crosslinking agent, and 60-70 parts by weight of deionized water. Optionally, the crosslinking agent comprises at least one of urotropine, benzenesulfonyl chloride, and ethyl sulfate; further optionally, the crosslinking agent comprises urotropine.

[0013] In some embodiments, the cross-linking reaction temperature is 100-200°C.

[0014] In some embodiments, the activator is provided in the form of a solution, and the activator includes a chemical activator. Optionally, the chemical activator includes at least one of a KOH solution and a ZnCl2 solution. Further optionally, the activator is a KOH solution with a mass concentration of 5% to 20%, and the mass ratio of the KOH solution to the fiber mat is (0.1 to 4):1.

[0015] In some embodiments, the nitrogen source includes at least one of melamine, urea, and triethylenediamine. Alternatively, the nitrogen source includes urea. Further optionally, the mass ratio of urea to fiber felt is (0.1-2):1.

[0016] In some embodiments, the carbonization treatment temperature is 600-900° C., the time is 1.5-2.5 h, the heating rate is 3-8° C. / min, and the atmosphere is a protective atmosphere.

[0017] In a second aspect, a nitrogen-doped porous carbon fiber prepared according to the preparation method of the first aspect is provided.

[0018] In a third aspect, a method is provided for adsorbing radioactive iodine using nitrogen-doped porous carbon fibers prepared by the preparation method of the first aspect.

[0019] This application uses chemical activation of an activator to form a rich pore structure on the surface and / or within the nitrogen-doped porous carbon fibers, thereby increasing the specific surface area and porosity of the product and thereby enhancing the product's ability to adsorb radioactive iodine. Furthermore, because the activator is uniformly distributed in the precursor and pores are often formed at the location of the activator after the activation reaction, the pores in the carbon fibers are also evenly distributed, thereby improving the adsorption efficiency of the product.

[0020] Furthermore, the doped nitrogen atoms in the carbon fibers of the present invention can induce the activator to preferentially bind to the sp 2 The carbon atoms react, retaining the sp 3 Carbon atoms give the product a higher carbon retention rate and a more stable structure. In addition, nitrogen atoms can enhance the polarity of the product, allowing chemical adsorption between radioactive iodine and the product, thereby improving the adsorption effect.

[0021] Furthermore, the present invention prepares fiber mats from phenolic resin fibers through crosslinking reactions, which can increase the density of nitrogen-doped porous carbon fibers in the product and ensure the mechanical strength of the product. The phenolic resin fibers selected in the present invention are easy to synthesize and process and can be widely used in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a photo of nitrogen-doped porous carbon fibers according to an embodiment of the present application;

[0023] Figure 2 for Figure 1 SEM images of nitrogen-doped porous carbon fibers are shown;

[0024] Figure 3 For preparation Figure 1 Photo of the fiber mat intermediate obtained in the process of nitrogen-doped porous carbon fibers;

[0025] Figure 4 for Figure 3 SEM images of the fiber mat intermediate shown;

[0026] Figure 5 This is a comparison chart of the element contents of the samples of Example 1 and Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0027] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this application, "plurality" means at least two, such as two or three, unless otherwise specifically defined.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Traditional radioactive iodine capture technologies are mainly divided into two categories: wet processes (mainly including liquid absorption methods) and dry processes (mainly including solid adsorption methods). In comparison, dry processes have the advantages of high reliability, simple operation, and good economy. In the solid adsorption method, commonly used solid adsorbents include modified carbon materials, metal-modified ceramics, and aerogel materials. Among them, modified carbon materials have high specific surface area, high porosity, and good mechanical properties, making them one of the best choices for radioactive iodine adsorption materials. Modified carbon materials mainly include coconut shell activated carbon, coal-based activated carbon, walnut-based activated carbon, and activated carbon fiber. Activated carbon fiber is an activated carbon fiber. Specifically, a certain type of carbon fiber (such as phenolic-based fiber, viscose-based fiber, and asphalt-based fiber) is activated at high temperature to produce nano-scale pores on its surface, increasing the specific surface area. Therefore, compared with other types of modified carbon materials, activated carbon fiber generally has a richer pore structure and better physical adsorption effect on adsorbates. However, the currently used activated carbon fibers (such as viscose-based carbon fiber materials) have an adsorption capacity of no more than 0.26 g / g of methyl iodide without any modification, and such an adsorption capacity cannot meet the needs of practical applications.

[0031] Research has found that the low adsorption capacity of traditional activated carbon fibers for radioactive iodine may be due to the fact that activated carbon fibers capture radioactive iodine only through physical adsorption, resulting in a weak interaction between the adsorbent and the adsorbate. This means that radioactive iodine captured by the activated carbon fibers may be desorbed. Furthermore, the carbon skeleton of traditional activated carbon fibers has poor mechanical strength and often experiences structural collapse during use, which also reduces their adsorption capacity for radioactive iodine.

[0032] Based on the above analysis, the present application provides a method for preparing a nitrogen-doped porous carbon material. By adding a nitrogen source during the preparation of the material, a porous carbon fiber doped with nitrogen atoms is obtained, which increases the polarity of the porous carbon material so that the above material can undergo chemical adsorption with radioactive iodine, thereby improving the adsorption capacity for radioactive iodine. In addition, the introduction of nitrogen atoms can improve the structural stability and service life of the entire carbon fiber material. It should be noted that the porous structure of the material also ensures the physical adsorption capacity for radioactive iodine. In addition, the present application further improves the adsorption capacity and structural stability of the nitrogen-doped carbon fiber material by optimizing the process of the activation reaction so that the pores in the carbon fiber can be evenly distributed.

[0033] One embodiment of the present application provides a method for preparing nitrogen-doped porous carbon fibers, which comprises the following steps:

[0034] The phenolic resin fibers are subjected to a cross-linking reaction under the action of a cross-linking agent to prepare a fiber felt;

[0035] The fiber mat, the activator and the nitrogen source are mixed and then dried to prepare a precursor, wherein the activator and the nitrogen source are uniformly distributed in the fiber mat;

[0036] The precursor is carbonized to prepare a nitrogen-doped activated product. During the carbonization process, the nitrogen source decomposes to form an active substance that can react with the carbon in the precursor. The activator chemically reacts with the carbon in the precursor to wash the activated product to neutrality.

[0037] Fiber felt is a product made by non-directionally combining fiber strands through chemical crosslinking agents or mechanical action. The gaps between the fibers can increase the contact area with the adsorbate, which is beneficial to the adsorption of the adsorbate.

[0038] At least one of the activator and the nitrogen source is provided in the form of a solution. Exemplarily, the activator is provided in the form of a solution, and the fiber felt and the nitrogen source are dispersed in the activator solution. Compared to directly mixing the activator and nitrogen source with the fiber felt in solid form, the solution impregnation method adopted in this application enables the activator, nitrogen source, and fiber felt to be mixed more evenly. This application does not impose any restrictions on the drying temperature, which can optionally be 60°C. This application also does not impose any restrictions on the drying time.

[0039] Carbonization refers to the reaction process in which solids or organic matter are heated and decomposed in an airtight environment. The carbonization process includes heating, holding, and cooling steps. The heating step refers to the process of raising the temperature from room temperature to the target temperature. The holding step refers to maintaining the target temperature for a period of time to fully carbonize the precursor. After carbonization is completed, the precursor can be cooled naturally to room temperature or according to a pre-set cooling schedule, which is not limited in this application.

[0040] During the carbonization process, as the temperature rises, the non-carbon elements (such as oxygen elements) in the fiber felt volatilize out, and the resin fiber is converted into carbon fiber. The activator can react with some of the carbon atoms in the above-mentioned carbon fiber under high temperature conditions, that is, the activator can etch some of the carbon atoms in the carbon fiber, thereby obtaining an activated product. Compared with the unetched area, the structural stability of the etched area is worse. In the subsequent washing process, the unstable components in the etched area (such as soluble salts generated by the activation reaction) are removed, and then holes are formed at the position of the etched area. In addition, as the temperature rises, the nitrogen source undergoes a multi-step decomposition reaction to form nitrogen-containing free radicals with higher reactivity (such as NH2 free radicals, NH free radicals). These free radicals can react with the carbon atoms of the carbon fiber and are doped into the material in the form of nitrogen atoms (such as pyridine nitrogen atoms, pyrrole nitrogen atoms). It should be noted that due to the doping of nitrogen atoms, during the chemical activation process, the activator preferentially etches the sp in the carbon fiber skeleton. 2 Carbon atoms, making the sp 3 Carbon atoms are retained, thereby improving the carbon retention rate and structural stability of nitrogen-doped carbon fibers.

[0041] Deionized water or other acidic solutions may be used for washing, which is not limited in this application. After washing, the nitrogen-doped porous carbon fibers of this application are obtained through filtering, drying, and other steps.

[0042] The present application forms a rich pore structure on the surface and / or inside of the carbon fiber through the chemical activation of the activator, thereby increasing the specific surface area and porosity of the product, and further enhancing the adsorption capacity of the product for radioactive iodine. Furthermore, since the activator is evenly distributed in the precursor, and pores are often formed at the position of the activator after the activation reaction, the pores in the carbon fiber can also be evenly distributed, thereby improving the adsorption efficiency of the product. In addition, the present application prepares phenolic resin fibers into fiber felts through a spinning method, which can increase the density of nitrogen-doped carbon fibers in the product and ensure the mechanical strength of the product. The phenolic resin fibers selected in the present application are easy to synthesize and process, can be widely used in industrial production, and the phenolic resin fibers have a high carbon residue rate after carbonization, which is conducive to providing structural stability of the product.

[0043] In a specific embodiment, the preparation method further comprises the following steps:

[0044] The phenolic resin fiber is prepared by a spinning method using a phenolic resin, wherein the phenolic resin includes a thermoplastic phenolic resin, and the phenolic resin includes a thermoplastic phenolic resin. Optionally, the weight average molecular weight of the thermoplastic phenolic resin is 500 to 5000; and / or, the melting point of the thermoplastic phenolic resin at standard atmospheric pressure is 100 to 120°C; further optionally, the thermoplastic phenolic resin has a linear structure. Specifically, the weight average molecular weight of the thermoplastic phenolic resin can be 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500 or 5000. When the weight average molecular weight is greater than 5000, the difficulty of processing increases, while when the weight average molecular weight is less than 500, the phenolic resin is not easy to form. The melting point of the thermoplastic phenolic resin at standard atmospheric pressure can be 100°C, 105°C, 110°C, 115°C or 120°C. Thermoplastic novolac resins with a linear structure are soluble in organic solvents, melt upon heating, and do not solidify even after prolonged heating. They only solidify after the addition of a curing agent, forming an insoluble and infusible solid. Typically, linear novolac resins are transparent solids ranging from colorless to yellow.

[0045] In a specific embodiment, the spinning method includes melt centrifugal spinning, electrospinning or wet spinning. Optionally, the spinning method is melt centrifugal spinning, the temperature of the melt centrifugal spinning is 300-500°C, and the rotation speed is 2000-3000 r / min. Specifically, the temperature of the melt centrifugal spinning can be 300°C, 350°C, 400°C, 450°C or 500°C, and the rotation speed can be 2000 r / min, 2200 r / min, 2400 r / min, 2600 r / min, 2800 r / min or 3000 r / min.

[0046] In a specific embodiment, the crosslinking agent is provided in the form of a solution, which comprises the following components, calculated by weight: 15-20 parts of 36% hydrochloric acid, 15-20 parts of a crosslinking agent, and 60-70 parts of deionized water. Optionally, the crosslinking agent comprises at least one of urotropine, benzenesulfonyl chloride, and ethyl sulfate; further optionally, the crosslinking agent comprises urotropine. Specifically, the solution, calculated by weight, may comprise 15, 16, 17, 18, 19, or 20 parts of 36% hydrochloric acid, 15, 16, 17, 18, 19, or 20 parts of the crosslinking agent, and 60, 62, 64, 66, 68, or 70 parts of the deionized water. A more compact fiber mat is obtained through the crosslinking method, and the nitrogen-doped carbon fiber material prepared thereby also has higher structural stability.

[0047] In a specific embodiment, the temperature of the cross-linking reaction is 100-200° C. Specifically, the temperature of the cross-linking reaction can be 100° C., 120° C., 140° C., 160° C., 180° C. or 200° C.

[0048] In a specific embodiment, the activator is provided in the form of a solution, and the activator includes a chemical activator. The chemical activator includes at least one of a KOH solution and a ZnCl2 solution. Optionally, the activator is a KOH solution with a mass concentration of 5% to 20%, preferably a 10% KOH solution. Further optionally, the mass ratio of the KOH solution to the fiber mat is (0.1-4):1. Specifically, the mass concentration of the KOH solution can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. The mass ratio of the KOH solution to the fiber mat can be 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. When the above ratio is less than 0.1:1, the resulting product has no or a small number of pores. When the above ratio is greater than 4:1, the carbon skeleton of the product may collapse due to the pores being too dense or the number of pores being too large.

[0049] In a specific embodiment, the nitrogen source includes at least one of melamine, urea and triethylenediamine. Optionally, the nitrogen source includes urea. Further optionally, the mass ratio of urea to fiber felt is (0.1-2):1. Specifically, the mass ratio of urea to fiber felt can be 0.1:1, 0.5:1, 1:1, 1.5:1 or 2:1. When the above ratio is less than 0.1:1, the doped nitrogen atoms are too few, and the improvement in the polarity of the product is small. When the above ratio is greater than 2:1, when the doped nitrogen atoms are too many, the carbon content in the product is relatively reduced, which will have an adverse effect on the structural strength of the product.

[0050] In a specific embodiment, the carbonization temperature is 600-900°C, the time is 1.5-2.5 hours, the heating rate is 3-8°C / min, and the atmosphere is a protective atmosphere. Specifically, the carbonization temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, the time can be 1.5 hours, 2 hours or 2.5 hours, and the heating rate can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min or 8°C / min. The protective atmosphere can be a gas that does not react with the system, such as nitrogen or argon.

[0051] In another embodiment of the present application, a nitrogen-doped porous carbon fiber prepared according to the above preparation method is provided.

[0052] Furthermore, the present application also provides an application of the nitrogen-doped porous carbon fiber prepared by the above preparation method in adsorbing radioactive iodine.

[0053] In order to make it easier to understand and implement the present application, the following relatively easy-to-implement, more specific and detailed embodiments and comparative examples are provided as references. Through the description and performance results of the following specific embodiments and comparative examples, the various embodiments of the present application and their advantages will also be apparent.

[0054] Unless otherwise specified, the raw materials used in the following experimental examples can be purchased from the market.

[0055] Example 1

[0056] (1) Preparation of phenolic resin fiber

[0057] 10 g of thermoplastic phenolic resin was weighed and melt-centrifugal spun in a melt spinning machine to obtain phenolic resin fibers.

[0058] (2) Preparation of fiber felt

[0059] Prepare a crosslinker solution containing 67% water, 36% HCl, and 15% hexamine by weight. Immerse phenolic resin fibers in the crosslinker solution and heat to 120°C at a rate of 15°C / hour for two hours. Then, react at 200°C under vacuum for two hours. After cooling, obtain a fiber mat.

[0060] (3) Preparation of precursor

[0061] Weigh 1g of fiber mat and place it in a square porcelain boat. Add 3g of a 10% KOH solution to the boat, immersing the fiber mat in the KOH solution. Then, add 1g of urea to the boat. Dry the boat at 60°C to obtain the precursor.

[0062] (4) Carbonization of the precursor

[0063] The precursor was placed in a tube furnace and heated from room temperature to 800°C at a heating rate of 5°C / min under nitrogen, then maintained for 2 hours. After cooling to room temperature, the activated product was obtained.

[0064] (5) Post-treatment of activated products

[0065] The activated product was washed with distilled water until neutral, and then dried to obtain nitrogen-doped porous carbon fibers.

[0066] Example 2

[0067] Example 2 is basically the same as Example 1, except that: the KOH solution with a mass concentration of 10% weighed in (3) is 4 g.

[0068] Example 3

[0069] Example 3 is basically the same as Example 1, except that the urea weighed in (3) is 2 g.

[0070] Comparative Example 1

[0071] Commercial viscose-based activated carbon fiber is used.

[0072] Comparative Example 2

[0073] Comparative Example 2 is substantially the same as Example 1, except that urea is not added in (3).

[0074] Comparative Example 3

[0075] Comparative Example 3 is substantially the same as Example 1, except that: the KOH solution with a mass concentration of 10% is not added in (3).

[0076] Performance Testing

[0077] (1) Test of specific surface area, pore volume and average pore diameter

[0078] Nitrogen isothermal adsorption and desorption tests were performed using a surface area analyzer (ASPS 2020). The specific surface area was calculated using the BET method, and the pore volume and average pore diameter of each sample were calculated using the DR volume filling method. The test results are shown in Table 1.

[0079] (2) Macroscopic morphology observation

[0080] The samples of Example 1 and the phenolic resin fiber intermediate were photographed. Figure 1 This is a photo of Example 1. Figure 3 This is a photograph of the fiber mat intermediate obtained during the preparation of Example 1.

[0081] (3) Microscopic morphology observation

[0082] The surface micromorphology of the sample of Example 1 and the phenolic resin fiber intermediate was observed using a scanning electron microscope (model: TESCAN VEGA3 LMH), and corresponding electron microscope photos were taken. Figure 2 is an electron microscope photograph of Example 1, Figure 4 This is an electron microscope photograph of the fiber mat intermediate obtained during the preparation of Example 1. Figure 2 The sample surface in is relatively rough, and obvious pores can be observed on the surface of the sample; Figure 4 The surface of the sample is relatively smooth and no obvious pores are observed. This indicates that the sample treated with the activator can produce certain pores.

[0083] (4) Analysis of sample element content

[0084] The samples of Example 1 and Comparative Example 2 were tested for their C, O, and N content using elemental analysis. Figure 5 As shown, compared with Comparative Example 2, the sample of Example 1 not only contains about 3% nitrogen, but also has a higher carbon content.

[0085] (5) Iodine adsorption test

[0086] The static methyl iodide adsorption method was used to test the adsorption properties of the prepared materials. Take a 1cm*1cm square sample and place it in a crucible, and record the mass m1 at this time. Add 1ml of CH3I to the crucible, seal it, and place it in a closed hydrothermal reactor at 50°C for 4h. After cooling to room temperature, record the mass m2. The methyl iodide adsorption capacity is (m2-m1) / m1. Repeat the experiment 3 times and take the average value. It should be noted that since radioactive iodine is harmful to the human body, this application uses non-radioactive methyl iodide for adsorption testing. The test results are shown in Table 1.

[0087] Table 1

[0088]

[0089] As shown in Table 6, the specific surface area of ​​Example 1 can reach 1544.0473 m 2 / g, pore volume and pore size are also larger, and the adsorption performance of methyl iodide can reach 0.38g / g. Compared with Example 1, Example 2 increases the consumption of KOH solution, and Example 3 increases the consumption of urea. The specific surface area, pore volume and average pore size of the sample are all improved, and the adsorption capacity of iodine is also improved. The above results show that the activator can promote the formation of pore structure in the product. The nitrogen source can not only induce the activator to etch the sample, and then produce a more abundant pore structure, but also can be doped with nitrogen atoms formed in the product, improve the polarity of the product, and further improve the adsorption capacity of the product to iodine.

[0090] Although the specific surface area of ​​comparative example 1 can reach 1453.8016m 2 / g, but the average pore diameter is only 1.7025nm and the pore volume is only 0.5145cm 3 / g, so Comparative Example 1 has a poor adsorption capacity for methyl iodide. Comparative Example 2, in which only KOH solution was added, showed a significant decrease in specific surface area, pore volume, and pore diameter, further demonstrating that the nitrogen source can induce the activator to etch the sample. Comparative Example 3, in which only nitrogen source was added, showed the smallest specific surface area, pore volume, and pore diameter, and the worst adsorption performance, indicating that the activator has a significant impact on the formation of the product's pore structure.

[0091] In summary, the nitrogen-doped porous carbon material obtained by the preparation method of the present application has a better adsorption effect on methyl iodide.

[0092] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] The above-described embodiments merely represent several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make a number of variations and improvements without departing from the concept of the present application, and these variations and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the patent application shall be based on the appended claims, and the description and drawings may be used to interpret the content of the claims.

Claims

1. Application of nitrogen-doped porous carbon fibers in adsorbing radioactive iodine, characterized in that: The method for preparing the nitrogen-doped porous carbon fiber comprises the following steps: (1) Preparation of phenolic resin fiber Weigh 10 g of thermoplastic phenolic resin and perform melt centrifugal spinning in a melt spinning machine to obtain phenolic resin fibers; (2) Preparation of fiber felt A crosslinking agent solution containing water, 36% HCL, and urotropine in proportions of 67%, 18%, and 15% by weight, respectively, was prepared; phenolic resin fibers were immersed in the crosslinking agent solution, and the temperature was raised to 120°C at a rate of 15°C / h, kept at this temperature for two hours, and then reacted at 200°C under vacuum conditions for two hours. After cooling, a fiber mat was obtained; (3) Preparation of precursor 1 g of fiber felt was weighed and placed in a square porcelain boat. 3 g of a 10% KOH solution was weighed and added to the porcelain boat so that the fiber felt was immersed in the KOH solution. 1 g of urea was then added to the porcelain boat, and the porcelain boat was dried at 60°C to obtain a precursor. (4) Carbonization of the precursor The precursor was placed in a tube furnace and heated from room temperature to 800°C at a heating rate of 5°C / min under nitrogen protection, then maintained for 2 h and cooled to room temperature to obtain an activated product; (5) Post-treatment of activated products The activated product was washed with distilled water until neutral, and then dried to obtain nitrogen-doped porous carbon fibers.

2. The use according to claim 1, characterized in that The weight average molecular weight of the thermoplastic phenolic resin is 500 to 5000; and / or the melting point of the thermoplastic phenolic resin at standard atmospheric pressure is 100 to 120° C.; The thermoplastic novolac resin has a linear structure.

3. The use according to claim 2, characterized in that The temperature of the melt centrifugal spinning is 300-500° C., and the rotation speed is 2000-3000 r / min.

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