Modified polyacrylonitrile fiber with heavy metal adsorption performance and preparation method thereof

Abstract

The invention provides a modified polyacrylonitrile fiber with heavy metal adsorption performance and a preparation method thereof, acrylonitrile, a carboxylic acid monomer, a third monomer, an initiator and a chain transfer agent are heated under an acidic condition, a polyacrylonitrile copolymer is prepared through water phase precipitation polymerization, and the polyacrylonitrile fiber is prepared through a spinning process; the method comprises the following steps: placing fibers in a carboxyl activation solution for activation reaction, and then placing the fibers in a polyamino compound reaction solution for grafting reaction. A multi-amino compound is introduced to the surface of the fiber, the heavy metal adsorption performance of the fiber is improved through the matching capacity of amino groups, and the polyacrylonitrile fiber with the excellent adsorption performance is successfully prepared. The carboxyl-containing polyacrylonitrile copolymer is prepared through direct polymerization, a base material is provided for subsequent modification, the fiber is endowed with the adsorption performance through grafting modification, meanwhile, excellent mechanical performance and weather resistance are reserved, the requirement of the market for the adsorption type functional fiber is met, and wide application prospects are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly materials, and in particular to a modified polyacrylonitrile fiber with heavy metal adsorption performance and a preparation method thereof. Background Art

[0002] Water is a precious resource essential for human survival. However, with the recent growth of industry, water pollution has become increasingly serious, becoming a global issue that cannot be ignored. With the rapid development of various industries, the generation of toxic and hazardous wastewater has increased year by year. Common water pollution sources include heavy metal and metalloid pollution, and organic compound pollution. However, due to a lack of environmental awareness and appropriate treatment methods, some hazardous wastewater is directly discharged into the natural environment, causing serious damage to the ecological environment and endangering human health. Therefore, how to efficiently, environmentally friendly, and economically treat water pollution is a hot topic of research.

[0003] Organic adsorbents are currently considered to be the most promising functional materials for industrial applications due to their fast heavy metal adsorption rate, cheap and readily available synthetic raw materials, and low preparation costs. Polyacrylonitrile fiber refers to fibers prepared by polymerizing more than 85% acrylonitrile and other monomers. It is also called acrylic fiber and has the reputation of "artificial wool". Because there are a large number of -CH2 groups, -CH groups, -CN groups and other groups on the polyacrylonitrile chain, this gives polyacrylonitrile fiber excellent tensile strength, flexibility and weather resistance. However, the presence of a large number of highly polar nitrile groups in polyacrylonitrile also leads to strong interactions between its molecular chains, poor water and moisture absorption properties, and strong electrostatic effects, which seriously limit its wide application. Therefore, the use of polyamino compounds for modification is of great significance for the functionalization of polyacrylonitrile fibers.

[0004] Polyamino compounds are water-soluble cationic compounds rich in amino groups. Amino groups are functional groups with chelating effects. The N atom of the amino group has unbonded lone pairs of electrons. Heavy metal ions, as metal cations, have empty orbitals in their molecular structure. The lone pairs of electrons combine with the empty orbitals to form stable coordination bonds, showing an excellent adsorption effect on heavy metal ions. Grafting polyamino compounds onto the surface of polyacrylonitrile fibers not only gives polyacrylonitrile fibers good adsorption properties, but also solves the problem of water solubility of polyamino compounds. CN 112900084 A discloses a chelated fiber, which uses polyacrylonitrile fibers as a supporting material, modifies the cyano groups therein, and uses 2,6-diaminopyridine as a ligand. CN114855451 A discloses a chelated fiber, which uses polyacrylonitrile fibers as a supporting material, modifies the cyano groups therein, and uses 2,6-diaminopyridine as a ligand. CN 109364891 A discloses a method for preparing modified polyacrylonitrile for treating antimony-containing wastewater. The method involves immersing a polyacrylonitrile substrate in an aqueous solution of hydroxylamine hydrochloride to effect in-situ amidoximation of the polyacrylonitrile substrate. Prior art polyacrylonitrile functionalization primarily targets the modification of cyano groups on its molecular chain, which can compromise the mechanical properties of polyacrylonitrile fibers, making them susceptible to damage during use and unsuitable for reuse. Therefore, improving the water absorption of polyacrylonitrile fibers without compromising their mechanical properties is crucial for expanding their applications, particularly in the environmentally friendly adsorption of heavy metals. Summary of the Invention

[0005] The purpose of the present invention is to prepare a polyacrylonitrile fiber with excellent heavy metal ion adsorption performance. First, a carboxyl-rich polyacrylonitrile copolymer is prepared by aqueous precipitation polymerization, which solves the problem that traditional polyacrylonitrile functional modification destroys the mechanical properties of the fiber. Then, the polyacrylonitrile fiber is obtained by wet spinning, and then the carboxyl groups on the polyacrylonitrile fiber are activated and modified by the EDC / NHS amidation method, and polyamino compounds are introduced on the fiber surface. The obtained fiber has the functions of good heavy metal ion adsorption performance, excellent mechanical properties and high hygroscopicity. It solves the problems of poor water absorption and single function of traditional polyacrylonitrile fiber, meets people's requirements for environmental protection of heavy metal adsorption, and has positive practical significance and good application prospects. The present invention has abundant raw material sources, simple process, green and environmental protection, simple and controllable fiber preparation process, and the obtained material has strong water absorption, good heavy metal ion adsorption performance and outstanding mechanical properties.

[0006] In order to achieve the above-mentioned purpose of the invention, the following technical solutions are adopted:

[0007] The present invention provides a method for preparing modified polyacrylonitrile fiber with heavy metal adsorption performance, comprising the following steps:

[0008] (1) Polyacrylonitrile fiber is prepared by one of the following methods:

[0009] (1.1) Acrylonitrile, a carboxylic acid monomer, an initiator, and a chain transfer agent are heated under acidic conditions to prepare a polyacrylonitrile copolymer by aqueous precipitation polymerization, the polyacrylonitrile copolymer is prepared into a spinning solution, and polyacrylonitrile fiber is prepared by a spinning process;

[0010] (1.2) heating acrylonitrile, a carboxylic acid monomer, a third monomer, an initiator, and a chain transfer agent under acidic conditions to prepare a polyacrylonitrile copolymer by aqueous precipitation polymerization, preparing the polyacrylonitrile copolymer into a spinning solution, and preparing polyacrylonitrile fiber by a spinning process; the third monomer is selected from at least one of methyl acrylate and sodium methacrylate;

[0011] (2) placing the polyacrylonitrile fiber in a carboxyl activation solution to perform an activation reaction to obtain the polyacrylonitrile fiber containing activated carboxyl groups;

[0012] (3) placing the polyacrylonitrile fiber containing activated carboxyl groups in a polyamino compound reaction solution to carry out a grafting reaction; after the reaction is completed, rinsing with deionized water several times to remove the unreacted polyamino compound, and drying to obtain a modified polyacrylonitrile fiber with heavy metal adsorption performance.

[0013] Preferably, in step (1), the carboxylic acid monomer is selected from at least one of acrylic acid, itaconic acid and maleic acid.

[0014] Preferably, in step (1), the initiator is a mixture of an oxidizing agent and a reducing agent, and is selected from any one of a potassium persulfate-sodium bisulfite initiation system, a sodium chlorate-sodium bisulfite initiation system, a sodium chlorate-sodium metabisulfite initiation system, and an ammonium persulfate-sodium metabisulfite initiation system.

[0015] Preferably, in step (1), the chain transfer agent is selected from at least one of N,N-diethylhydroxylamine, isopropyl alcohol and mercaptan.

[0016] Preferably, in step (1), the spinning process is an electrospinning process or a wet spinning process; when the wet spinning process is adopted, the polyacrylonitrile copolymer is placed in dimethylformamide, dimethylacetamide or sodium thiocyanate aqueous solution to prepare a spinning solution.

[0017] Preferably, in step (1), the total monomer concentration in the raw material mixture for aqueous precipitation polymerization is 10-40% by mass, wherein acrylonitrile accounts for 85-98% of the total monomer mass, the carboxylic acid monomer accounts for 1-10% of the total monomer mass, the third monomer accounts for 0-0.5% of the total monomer mass, and the chain transfer agent accounts for 0.1-5% of the total monomer mass. For example, the total monomer concentration is one of 10%, 15%, 20%, 25%, 30%, 35%, and 40%; acrylonitrile accounts for one of 85%, 88%, 90%, 92%, 94%, 96%, and 98% of the total monomer mass; the carboxylic acid monomer accounts for one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10% of the total monomer mass; the third monomer accounts for one of 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% of the total monomer mass; and the chain transfer agent accounts for one of 0.1%, 0.5%, 1%, 2%, 3%, 4%, and 5% of the total monomer mass. More preferably, the total monomer concentration is 15-20%, of which acrylonitrile accounts for 90-92% of the total monomer mass, the carboxylic acid monomer accounts for 8-10% of the total monomer mass, the third monomer accounts for 0-0.5% of the total monomer mass, and the chain transfer agent accounts for 2-5% of the total monomer mass.

[0018] Preferably, in step (1), the mass ratio of the oxidant to the reducing agent in the initiator is 5:1 to 1:5, including but not limited to 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, and 1:5; wherein the amount of the oxidant is 0.1 to 5% by weight of the total monomers, including but not limited to 0.5%, 0.75%, 1%, 1.25%, 1.5%, 3%, and 5%. More preferably, the mass ratio of the oxidant to the reducing agent is 1:1 to 1:3; and the amount of the oxidant is 1 to 3% by weight of the total monomers.

[0019] Preferably, in step (1), the polymerization reaction temperature is 30-80°C, preferably 50-65°C, including but not limited to 30°C, 50°C, 55°C, 60°C, 65°C, 70°C, and 80°C.

[0020] Preferably, in the step (1), stirring is performed during the polymerization reaction, and the stirring speed is 30 to 300 r / min, preferably 200 to 300 r / min, including but not limited to 30 r / min, 80 r / min, 100 r / min, 120 r / min, 140 r / min, 160 r / min, 200 r / min, and 300 r / min.

[0021] Preferably, in step (1), the pH of the polymerization reaction solution is 1.5 to 4.5, preferably 2.5 to 3.5, including but not limited to 1.5, 2.5, 3.5, and 4.5. For example, the pH can be adjusted by dilute sulfuric acid and sodium hydroxide solution.

[0022] Preferably, in step (1), the polymerization reaction time is 0.5 to 6 hours, preferably 2 to 4 hours, including but not limited to 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours, 5 hours, and 6 hours.

[0023] Preferably, in step (1), when the wet spinning process is adopted, the solid content of the spinning solution is 10-30%, preferably 20-25%, including but not limited to 10%, 15%, 20%, 25%, and 30%.

[0024] Preferably, in step (2), the carboxyl activation solution is a mixed solution of EDC and NHS, wherein, calculated by mass fraction, the concentration of EDC is 0.1-10%, including but not limited to 0.1%, 0.25%, 0.3%, 0.5%, 0.7%, 0.75%, 1%, 1.5%, 2%, and 10%; the concentration of NHS is 0.5-10%, including but not limited to 0.5%, 0.75%, 1%, 2%, 3%, 4%, 5%, and 10%. More preferably, the concentration of EDC is 0.25-0.75%, and the concentration of NHS is 0.5-0.75%.

[0025] Preferably, in step (3), the polyamino compound is any one of diethylenetriamine, triethylenetetramine, and polyethyleneimine, and the concentration of the polyamino compound solution is 1-10%, preferably 1-5%, calculated by mass fraction. As an example, the concentration of the polyamino compound solution in step (3) is one of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. As an example, the polyethyleneimine is selected from polyethyleneimine with Mw=1000, 3000, 10000, and 70000.

[0026] Preferably, in the step (2), the temperature of the activation reaction is 4 to 30° C., preferably 5 to 25° C., the reaction pH is 4.0 to 8.0, preferably 4.5 to 5.5, and the reaction time is 0.5 to 4 h, preferably 1 to 2 h. As an example, the temperature of the activation reaction in the step (2) includes but is not limited to 4° C., 5° C., 10° C., 15° C., 20° C., 25° C., and 30° C.; the reaction pH is one of 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, and 8.0; and the reaction time is one of 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, and 4.0 h.

[0027] Preferably, in step (2), stirring is performed during the activation reaction at a stirring speed of 100 r / min.

[0028] Preferably, in step (3), the temperature of the grafting reaction is 20-50°C, preferably 25°C, the reaction pH is 5.0-10.0, preferably 7.0-8.0, and the reaction time is 2-12h, preferably 2-4h. As an example, the temperature of the grafting reaction in step (3) includes but is not limited to 20°C, 25°C, 30°C, 35°C, 40°C, and 50°C; the reaction pH is one of 5.0, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, and 10.0; and the reaction time is one of 2h, 3h, 4h, 5h, 6h, 7h, 8h, and 10h.

[0029] Preferably, in step (3), stirring is performed during the grafting reaction at a stirring speed of 100 r / min.

[0030] Preferably, in step (3), the drying temperature is 40°C to 100°C, preferably 50°C to 60°C, and the drying time is 1 hour to 24 hours, preferably 8 hours to 12 hours. For example, in step (2), the drying temperature includes but is not limited to 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, and 100°C; the drying time includes but is not limited to 1 hour, 2 hours, 5 hours, 10 hours, 15 hours, 20 hours, and 24 hours.

[0031] On the other hand, the present invention provides a modified polyacrylonitrile fiber with heavy metal adsorption performance, wherein the modified polyacrylonitrile fiber is formed by grafting carboxylated polyacrylonitrile with a polyamino compound, wherein the carboxylated polyacrylonitrile is a copolymer of acrylonitrile and a carboxylic acid monomer or a copolymer of acrylonitrile, a carboxylic acid monomer and a third monomer, wherein the third monomer is selected from at least one of methyl acrylate and sodium methacrylate.

[0032] Preferably, the polyamino compound is any one of diethylenetriamine, triethylenetetramine and polyethyleneimine.

[0033] The present invention also provides a modified polyacrylonitrile fiber with heavy metal adsorption performance, which is prepared by the above method.

[0034] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0035] 1. This invention utilizes aqueous precipitation polymerization, using acrylonitrile and carboxylic acid monomers as primary monomers, to prepare polyacrylonitrile copolymers. Carboxyl groups are directly introduced into the copolymer, providing a matrix material for subsequent polyamino modification. Furthermore, carboxyl groups are hydrophilic, improving the hydrophilic properties of polyacrylonitrile fibers. Compared to previous modification methods, this invention directly polymerizes carboxyl-rich polyacrylonitrile copolymers, effectively resolving the problem of poor mechanical properties and the resulting disadvantages of reuse.

[0036] 2. The present invention has abundant raw material sources, simple synthesis process, mature and controllable fiber membrane preparation process, and is suitable for large-scale production; after the introduction of carboxyl and polyamino compounds, the obtained fiber has strong water absorption and excellent heavy metal adsorption capacity, which solves the problems of poor water absorption and single function of traditional polyacrylonitrile fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, some of the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0038] Figure 1 This is a schematic diagram of the preparation process of polyacrylonitrile fiber with heavy metal adsorption performance in Example 1 of the present invention.

[0039] Figure 2 Schematic diagram comparing the heavy metal adsorption capacity of polyacrylonitrile fibers of Examples 1 to 3 of the present invention and the comparative example. DETAILED DESCRIPTION

[0040] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0041] Unless otherwise specified, % in the present invention refers to percentage by weight.

[0042] Example 1

[0043] A method for preparing polyacrylonitrile fiber with heavy metal adsorption performance, the preparation process diagram is shown in the attached Figure 1 , the specific steps are as follows:

[0044] 9.2g acrylonitrile, 0.8g acrylic acid, and 0.2g isopropyl alcohol were added to a flask, followed by 40g deionized water, 0.1g potassium persulfate as an initiator, and 0.2g sodium bisulfite. The mass ratio of oxidant to reducing agent was 1:2. The reaction temperature was controlled at 50°C, the pH at 3.0, and the solution was mechanically stirred at 200 rpm / min for 2 hours. After termination, desaturation, and dehydration, a polymer filter cake was obtained. Dimethylformamide and the polymer filter cake were dissolved in a weight ratio of 100:22. After degassing, polyacrylonitrile fibers were spun via a wet spinning process.

[0045] 0.25 wt% 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and 0.5 wt% N-hydroxysuccinimide (NHS) were dissolved in deionized water to prepare an EDC / NHS carboxyl activation solution. A 3 wt% diethylenetriamine solution was then prepared. Polyacrylonitrile fiber was immersed in the EDC / NHS carboxyl activation solution, and the solution pH was adjusted to 5.0. The reaction temperature was controlled at 5°C, the stirring rate was 100 rpm / min, and the reaction time was 1 hour. After the activation reaction, the activated polyacrylonitrile fiber was immersed in the diethylenetriamine solution, and the solution pH was adjusted to 7.5. The reaction temperature was controlled at 25°C, the stirring rate was 100 rpm / min, and the reaction time was 4 hours. After the reaction, the fiber was rinsed several times with deionized water to remove unreacted polyamino compounds. The fiber was then vacuum dried at 60°C for 8 hours to obtain diethylenetriamine-grafted polyacrylonitrile fiber.

[0046] Example 2

[0047] 9.1g acrylonitrile, 0.89g itaconic acid, 0.01g methyl acrylate, and 0.5g thiol were added to a flask. Then, 50g deionized water, 0.1g sodium chlorate as an initiator, and 0.3g sodium metabisulfite were added. The mass ratio of oxidant to reducing agent was 1:3. The reaction temperature was controlled at 60°C and the pH was controlled at 2.5. The solution was mechanically stirred at 300 rpm / min for 3 hours. After termination, desaturation, and dehydration, a polymer filter cake was obtained. Dimethylacetamide and the polymer filter cake were dissolved in a weight ratio of 100:25. After degassing, polyacrylonitrile fibers were spun via a wet spinning process.

[0048] Dissolve 0.5wt% EDC and 0.5wt% NHS in deionized water to prepare an EDC / NHS carboxyl activation solution, and prepare a 5wt% triethylenetetramine solution. Immerse the polyacrylonitrile fiber in the EDC / NHS carboxyl activation solution, adjust the solution pH to 4.5, control the reaction temperature to 20°C, stir at a rate of 100rpm / min, and react for 2h. After the activation reaction is completed, immerse the activated polyacrylonitrile fiber in the triethylenetetramine solution, adjust the solution pH to 7.0, control the reaction temperature to 25°C, stir at a rate of 100rpm / min, and react for 4h. After the reaction is completed, rinse with deionized water several times to remove unreacted polyamino compounds, and vacuum dry the polyacrylonitrile fiber at 60°C for 8h to obtain triethylenetetramine-grafted polyacrylonitrile fiber.

[0049] Example 3

[0050] 9.0g acrylonitrile, 0.95g acrylic acid, 0.05g sodium methacrylate, and 0.3g N,N-diethylhydroxylamine were added to a flask. Then, 45g deionized water, 0.3g ammonium persulfate as initiator, and 0.3g sodium metabisulfite were added. The mass ratio of oxidant to reducing agent was 1:1. The reaction temperature was controlled at 65°C, the pH was controlled at 3.5, and the solution was mechanically stirred at 300rpm / min for 4h. After termination, desing, and dehydration, a polymer filter cake was obtained. A sodium thiocyanate aqueous solution and the polymer filter cake were dissolved in a weight ratio of 100:20. After degassing, polyacrylonitrile fiber was spun via a wet spinning process.

[0051] 0.75wt% EDC and 0.75wt% NHS were dissolved in deionized water to prepare an EDC / NHS carboxyl activation solution, and a 1wt% polyethyleneimine (Mw=10000) solution was prepared. The polyacrylonitrile fiber was immersed in the EDC / NHS carboxyl activation solution, the pH of the solution was adjusted to 5.5, the reaction temperature was controlled to 25°C, the stirring rate was 100rpm / min, and the reaction time was 1h. After the activation reaction was completed, the activated polyacrylonitrile fiber was immersed in the polyethyleneimine solution, the pH of the solution was adjusted to 8.0, the reaction temperature was controlled to 25°C, the stirring rate was 100rpm / min, and the reaction time was 2h. After the reaction was completed, it was rinsed with deionized water several times to remove the unreacted polyamino compound, and the polyacrylonitrile fiber was vacuum dried at 50°C for 12h to obtain polyethyleneimine-grafted polyacrylonitrile fiber.

[0052] Comparative Example

[0053] Dimethylformamide and polyacrylonitrile with a weight average molecular weight of 10w were dissolved in a weight ratio of 100:20, and PAN fibers were obtained under the same wet spinning conditions as in Example 1 after degassing.

[0054] During the adsorption experiment, 100 mL of simulated wastewater containing Cu(Ⅱ) heavy metals with an initial concentration of 200 mg / L was prepared and placed in four sample bottles. 0.1 g of polyacrylonitrile fiber was then added to each sample bottle. The sample was placed on a shaker at 25°C for constant temperature shaking. After 24 hours, the sample was taken out and the copper ion concentration in the adsorbed solution was measured. The heavy metal adsorption capacity of the polyacrylonitrile fiber was calculated. Figure 2 Schematic diagram comparing the heavy metal adsorption capacity of the fibers of Examples 1 to 3 and the PAN fibers of the comparative example. It is obvious from the figure that the adsorption performance of the fiber membranes prepared in Examples 1 to 3 is significantly better than that of the PAN nanofiber membrane of the comparative example.

[0055] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a modified polyacrylonitrile fiber having heavy metal adsorption performance, comprising the following steps: (1) preparing polyacrylonitrile fiber by one of the following methods: (1.1) Acrylonitrile, a carboxylic acid monomer, an initiator, and a chain transfer agent are heated under acidic conditions to prepare a polyacrylonitrile copolymer by aqueous precipitation polymerization, the polyacrylonitrile copolymer is prepared into a spinning solution, and polyacrylonitrile fiber is prepared by a spinning process; (1.2) heating acrylonitrile, a carboxylic acid monomer, a third monomer, an initiator, and a chain transfer agent under acidic conditions to prepare a polyacrylonitrile copolymer by aqueous precipitation polymerization, preparing the polyacrylonitrile copolymer into a spinning solution, and preparing polyacrylonitrile fiber by a spinning process; the third monomer is selected from at least one of methyl acrylate and sodium methacrylate; (2) placing the polyacrylonitrile fiber in a carboxyl activation solution to perform an activation reaction to obtain the polyacrylonitrile fiber containing activated carboxyl groups; (3) placing the polyacrylonitrile fiber containing activated carboxyl groups in a polyamino compound reaction solution to carry out a grafting reaction; after the reaction is completed, rinsing with deionized water several times to remove the unreacted polyamino compound, and drying to obtain a modified polyacrylonitrile fiber with heavy metal adsorption performance.

2. The method according to claim 1, wherein The carboxylic acid monomer is selected from at least one of acrylic acid, itaconic acid, and maleic acid; the initiator is a mixture of an oxidant and a reducing agent, and is selected from any one of a potassium persulfate-sodium bisulfite initiation system, a sodium chlorate-sodium bisulfite initiation system, a sodium chlorate-sodium metabisulfite initiation system, and an ammonium persulfate-sodium metabisulfite initiation system; the chain transfer agent is selected from at least one of N,N-diethylhydroxylamine, isopropyl alcohol, and mercaptan; in the raw material mixture for aqueous precipitation polymerization, the total monomer concentration is 10-40%, wherein acrylonitrile accounts for 85-98% of the total monomer mass, the carboxylic acid monomer accounts for 1-10% of the total monomer mass, the third monomer accounts for 0-0.5% of the total monomer mass, and the chain transfer agent accounts for 0.1-5% of the total monomer mass; in the step (1), the mass ratio of the oxidant to the reducing agent in the initiator is 5:1-1:5, wherein the amount of the oxidant is 0.1-5% relative to the total monomer mass.

3. The method according to claim 2, wherein In the step (1), the polymerization reaction temperature is 30 to 80° C.; stirring is performed during the polymerization reaction at a stirring speed of 30 to 300 r / min; the pH of the polymerization reaction solution is 1.5 to 4.5; and the polymerization reaction time is 0.5 to 6 h.

4. The method according to claim 2, wherein The total monomer concentration is 15-20%, wherein acrylonitrile accounts for 90-92% of the total monomer mass, the carboxylic acid monomer accounts for 8-10% of the total monomer mass, the third monomer accounts for 0-0.5% of the total monomer mass, and the chain transfer agent accounts for 2-5% of the total monomer mass; in the step (1), the mass ratio of the oxidant to the reducing agent in the initiator is 1:1-1:3; the amount of the oxidant is 1-3% of the total monomer mass; in the step (1), the polymerization reaction temperature is 50-65°C; stirring is performed during the polymerization reaction at a stirring speed of 200-300 r / min; the pH of the polymerization reaction solution is 2.5-3.5; and the polymerization reaction time is 2-4 hours.

5. The method according to claim 2, wherein In the step (1), the spinning process is an electrospinning process or a wet spinning process; when the wet spinning process is adopted, the polyacrylonitrile copolymer is placed in dimethylformamide, dimethylacetamide or sodium thiocyanate aqueous solution to prepare a spinning solution; when the wet spinning process is adopted, the solid content of the spinning solution is 10 to 30%; In the step (2), the carboxyl activation solution is a mixed solution of EDC and NHS, wherein the concentration of EDC is 0.1-10% by mass; the concentration of NHS is 0.5-10% by mass; in the step (3), the polyamino compound is any one of diethylenetriamine, triethylenetetramine and polyethyleneimine, and the concentration of the polyamino compound solution is 1-10% by mass.

6. The method according to claim 5, wherein In the step (2), the activation reaction temperature is 4-30°C, the reaction pH is 4.0-8.0, and the reaction time is 0.5-4h; in the step (3), the grafting reaction temperature is 20-50°C, the reaction pH is 5.0-10.0, the reaction time is 2-12h, the drying temperature is 40-100°C, and the drying time is 1h-24h.

7. The method according to claim 5, wherein In the step (2), the carboxyl activation solution is a mixed solution of EDC and NHS, wherein the concentration of EDC is 0.25-0.75% and the concentration of NHS is 0.5-0.75% calculated by mass fraction; the temperature of the activation reaction is 5-25°C, the reaction pH is 4.5-5.5, and the reaction time is 1-2 hours; stirring is performed during the activation reaction at a stirring speed of 100 r / min; in the step (3), the concentration of the polyamino compound solution is 1-5%; the temperature of the grafting reaction is 25°C, the reaction pH is 7.0-8.0, and the reaction time is 2-4 hours; stirring is performed during the grafting reaction at a stirring speed of 100 r / min; the drying temperature is 50-60°C, and the drying time is 8-12 hours.

8. A modified polyacrylonitrile fiber having heavy metal adsorption performance, characterized in that: The modified polyacrylonitrile fiber is formed by grafting carboxylated polyacrylonitrile with a polyamino compound. The carboxylated polyacrylonitrile is a copolymer of acrylonitrile and a carboxylic acid monomer or a copolymer of acrylonitrile, a carboxylic acid monomer and a third monomer, wherein the third monomer is selected from at least one of methyl acrylate and sodium methacrylate.

9. The modified polyacrylonitrile fiber according to claim 8, wherein The polyamino compound is any one of diethylenetriamine, triethylenetetramine and polyethyleneimine.

10. The modified polyacrylonitrile fiber according to claim 8 or 9, characterized in that It is characterized in that The method is prepared by the method according to any one of claims 1 to 7.

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