Polyurethane / cellulose acetate composite fiber membrane, preparation method and application

Abstract

The invention discloses a polyurethane / cellulose acetate composite fiber membrane, a preparation method and application, and belongs to the technical field of fiber membranes, the surface of the polyurethane / cellulose acetate composite fiber membrane is grafted with a polyethyleneimine chain segment; the raw materials for surface grafting comprise a polyurethane / cellulose acetate composite fiber membrane, polyethyleneimine and dopamine hydrochloride in a mass ratio of 1: (20-30): (0.4-0.8). The polyurethane / cellulose acetate composite fiber membrane has a bicontinuous structure and is high in mass transfer efficiency, and a regular fiber structure and a relatively high specific surface area provide a good physical basis for subsequent grafting of polyethyleneimine chain segments. The dopamine hydrochloride can be self-polymerized on the surface of the composite fiber membrane to form polydopamine, so that the surface activity and the adhesive force of the composite fiber membrane are enhanced, the grafting rate of polyethyleneimine is improved, and the polyethyleneimine can remarkably improve the adsorption capacity of the composite fiber membrane on heavy metal ions through coordination, ion exchange and physical adsorption.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber membranes, and particularly relates to a polyurethane / cellulose acetate composite fiber membrane, a preparation method and an application thereof. Background Art

[0002] With the rapid development of industrialization and urbanization, heavy metal ions such as Pb 2+ , Cd 2+ , Cu 2+ , Cr(VI), etc. are discharged into water bodies in large quantities through industries such as electroplating, mining, and metallurgy. Also, due to the non-degradability and bioaccumulation of heavy metal ions, they pose a serious threat to the ecological environment and human health.

[0003] In the industrial application field of heavy metal ions, the metal chromium element is widely used in industries such as steel, electroplating, leather tanning, printing and dyeing, and pigments. For example, in the steel industry, chromium is used to improve the hardness, wear resistance and corrosion resistance of steel. In the electroplating industry, chromium is used to give products a bright and durable surface coating. However, the pollution problem caused by metal chromium ions is also very serious. Metal chromium ions exist in two forms in the environment: trivalent chromium and hexavalent chromium. When the concentration of trivalent chromium exceeds the standard, it will accumulate in the human body and have an adverse effect on the biological system, such as interfering with the redox balance in cells and affecting mitochondrial function, etc.; hexavalent chromium is a strong oxidant and carcinogen. It can easily penetrate the biological membrane and enter the cell, and through a series of redox reactions, it generates highly reactive oxygen free radicals. These free radicals will cause serious damage to biological macromolecules such as DNA, proteins and lipids in the cell, and then trigger gene mutations, cell carcinogenesis and various organ dysfunctions. In the water bodies and soils in some industrial-intensive areas, the concentration of chromium ions far exceeds the environmental standard limit, posing a serious threat to the balance of the local ecological system and human health.

[0004] For the removal of heavy metal ions including chromium ions, the currently common methods are physical methods, chemical precipitation methods and biological methods. Among them, the physical method has low removal efficiency for low-concentration heavy metal ions, and high costs and maintenance expenses; the chemical precipitation method has high process requirements, and subsequent treatment is prone to cause secondary pollution; although the biological method is environmentally friendly, the adaptability and treatment efficiency of microorganisms are greatly affected by environmental factors, and the treatment cycle is long. Therefore, obtaining a material with high selectivity and high removal efficiency for heavy metal ions is of great significance for solving the heavy metal pollution problem, meeting the increasing demand for heavy metal pollution control and promoting the technological innovation and development in the field of environmental protection materials. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyurethane / cellulose acetate composite fiber membrane, a preparation method and an application thereof, which exhibit excellent properties such as high efficiency and high selectivity, so as to solve the pollution problem of heavy metal ions.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] In a first aspect, the present invention provides a polyurethane / cellulose acetate composite fiber membrane, and a polyethyleneimine chain segment is grafted on the surface of the polyurethane / cellulose acetate composite fiber membrane;

[0008] The raw materials for surface grafting include a polyurethane / cellulose acetate composite fiber membrane, polyethyleneimine, and dopamine hydrochloride in a mass ratio of 1:(20-30):(0.4-0.8).

[0009] Preferably, the molecular weight of the polyethyleneimine is 10,000-20,000.

[0010] By adopting the above technical solutions, the composite fiber membrane prepared from polyurethane and cellulose acetate by electrospinning technology has a bicontinuous structure, and a fiber membrane with larger pores and higher specific surface area can be formed. The addition of polyurethane can significantly improve the mechanical properties of the fiber membrane, and the high-strength hard segment structure can ensure the structural stability of the fiber membrane in dynamic water flow. The formed fiber membrane with a porous structure can also provide rich adsorption sites and diffusion channels for heavy metal ions. Polyurethane and cellulose acetate interact through hydrogen bonds between hydroxyl groups and amide groups, and the binding force between molecular chains also increases during the composite process, further optimizing the pore distribution of the fiber. The composite fiber membrane itself can also directly participate in the adsorption of heavy metal ions. Specifically:

[0011] The amide bond in polyurethane can enhance the affinity for metal ions through coordination, which is beneficial to complexation reactions. The oxygen-containing functional groups of cellulose acetate can, on the one hand, directly form stable chelates with metal ions, and on the other hand, the oxygen-containing functional groups carry negative charges in solution, and can strengthen the adsorption ability of the composite fiber membrane for heavy metal ions through electrostatic adsorption. By compounding cellulose acetate, the hydrophilicity of the composite fiber membrane is also enhanced, which is beneficial to the diffusion and mass transfer of heavy metal ions in the aqueous phase.

[0012] Furthermore, a polyethyleneimine chain segment is also grafted on the surface of the polyurethane / cellulose acetate composite fiber membrane. A large number of amine groups are contained in the polyethyleneimine chain segment. These amine groups can form stable coordination bonds with heavy metal ions through coordination, and can also release protons to adsorb metal ions through ion exchange. The branched structure of polyethyleneimine can also form a three-dimensional network on the surface of the composite fiber membrane, increasing the adsorption site density and greatly enhancing the adsorption ability and adsorption strength of the composite fiber membrane for heavy metal ions.

[0013] The polyethyleneimine segments, carried by a polyurethane / cellulose acetate composite fiber membrane, not only possess a strong adsorption capacity for heavy metal ions but also complement the negative charge of the composite fiber membrane, broadening its application in heavy metal ion treatment. The hydrophilicity of polyethyleneimine improves the surface wettability of the composite fiber membrane, reducing the diffusion resistance of heavy metal ions and increasing their mass transfer rate. The fiber structure of the composite fiber membrane also collaborates with the microporous network of the polyethyleneimine segments to form multi-stage mass transfer channels, enhancing adsorption capacity. The composite fiber membrane also provides excellent mechanical support, preventing the polyethyleneimine from becoming water-soluble. The high strength and anti-swelling properties of the polyurethane segments effectively prevent the polyethyleneimine segments from being washed away by water during wastewater treatment, thereby extending the service life of the composite fiber membrane.

[0014] However, since the polyurethane / cellulose acetate composite fiber membrane itself has general hydrophilicity and weak binding force with polyethyleneimine, dopamine hydrochloride is also added in the process of grafting polyethyleneimine segments. The composite fiber membrane is first treated with dopamine hydrochloride impregnation and a layer of polydopamine coating can be composited on the surface. Polydopamine contains a large number of catechol groups and amino groups, which can be tightly combined with the composite fiber membrane to form a stable intermediate layer. It can not only significantly increase the reaction site density on the surface of the composite fiber membrane, provide more anchor points for the subsequent grafting of polyethyleneimine segments, but its adhesion can also reduce the dissolution rate of polyethyleneimine during dynamic adsorption.

[0015] After the composite fiber membrane is compounded with polydopamine, the amino groups in it can react with the primary amine groups in the polyethyleneimine molecular chain segments to form covalent bonds, greatly improving the grafting rate of the polyethyleneimine chain segments. It can also adsorb the polyethyleneimine molecular chains through the π-π stacking structure to form a multi-layer load, thereby forming a multi-level adsorption site. Trace heavy metal ions in wastewater can be removed through multi-level adsorption.

[0016] At the same time, the compounding of polydopamine can also form a flexible cross-linked network on the surface of the composite fiber membrane, optimizing the hydrophilicity of the composite fiber membrane and promoting the diffusion and mass transfer of heavy metal ions. After compounding with polydopamine, the polydopamine and polyethyleneimine chain segments can construct nanoscale pores on the surface of the composite fiber membrane. Combined with the pore structure of the composite fiber membrane itself, a hierarchical pore structure can be formed, which can significantly improve the permeation flux and retention rate of the fiber composite membrane and increase the adsorption capacity of the composite fiber membrane for heavy metal ions.

[0017] Preferably, the mass ratio of cellulose acetate to polyurethane in the polyurethane / cellulose acetate composite fiber membrane is (0.8-1):1.

[0018] By adopting the above technical solution, in the present invention, polyurethane and cellulose acetate are compounded to obtain a composite fiber membrane. The molecular chain of cellulose acetate contains a rich hydrogen bond network, and an interpenetrating structure can be formed with the amide group of polyurethane through hydrogen bond interaction, enhancing the mechanical stability and anti-swelling performance of the composite fiber membrane, and providing a stable substrate for the subsequent compounding of polydopamine and the graft modification of polyethyleneimine. In addition, the addition of cellulose acetate can also regulate the porosity of the polyurethane fiber membrane, and the formed bicontinuous structure can make the fiber distribution wider and the porosity higher, providing a high specific surface area for the adsorption of heavy metal ions.

[0019] Meanwhile, the oxygen-containing functional groups contained in cellulose acetate itself can directly participate in heavy metal adsorption through electrostatic and coordination interactions, thereby increasing the adsorption capacity of the composite fiber membrane.

[0020] Preferably, the polyurethane / cellulose acetate composite fiber membrane is treated by alkali activation.

[0021] By adopting the above technical solution, a large number of acetyl groups are contained in the molecular chain of the polyurethane / cellulose acetate composite fiber membrane, which will hinder the exposure of hydroxyl groups in the composite fiber membrane. Therefore, before the surface graft modification treatment of the composite fiber membrane, the composite fiber is first treated by alkali activation. Under the action of alkali, part of the acetyl groups can be hydrolyzed to generate free hydroxyl groups, thereby providing corresponding covalent grafting sites for the catechol groups and amino groups in polydopamine. At the same time, the content of surface polar groups of cellulose acetate after alkali treatment increases, showing stronger polarity, which is beneficial to the compounding of polydopamine and the grafting of polyethyleneimine, and improving the binding force of the grafted product.

[0022] Moreover, the prior alkali activation treatment can cause the fiber structure in cellulose acetate to swell, destroy its crystalline structure, form more amorphous regions and microporous structures, increase the specific surface area of the composite fiber membrane, provide a large amount of space for the uniform loading of polyethyleneimine chain segments, and can also remove low-molecular-weight impurities in the composite fiber membrane after alkali treatment, strengthen the binding force between fibers, and improve the mechanical strength of the composite fiber membrane.

[0023] In the second aspect, the present invention provides a preparation method of a polyurethane / cellulose acetate composite fiber membrane, comprising the following technological steps:

[0024] S1. Add polyurethane and cellulose acetate to a solvent, stir and dissolve at 40 - 45 °C to obtain an electrospinning solution; then prepare polyurethane / cellulose acetate composite nanofibers through electrospinning and drying treatments;

[0025] S2. Immerse the polyurethane / cellulose acetate composite nanofibers in an alkali solution for activation for 20 - 24 h, and obtain a polyurethane / cellulose acetate composite fiber membrane after washing, drying and deposition;

[0026] S3. Add dopamine hydrochloride to the buffer solution, adjust the pH value of the solution to 8 - 9, stir evenly to obtain a dopamine solution, add the polyurethane / cellulose acetate composite fiber membrane, stir and react for 15 - 30 min, and obtain the pretreated polyurethane / cellulose acetate composite fiber membrane after washing and drying;

[0027] S4. Dissolve polyethyleneimine in water to obtain an aqueous polyethyleneimine solution, add the pretreated polyurethane / cellulose acetate composite fiber membrane, stir and react for 12 - 15 h, and finally obtain the product after drying.

[0028] Preferably, the lye includes one or a combination of more of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous sodium carbonate solution, and aqueous calcium hydroxide solution.

[0029] Preferably, the concentration of the dopamine solution is 2 - 4 g / L.

[0030] Preferably, the concentration of the aqueous polyethyleneimine solution is 10 - 30 g / L.

[0031] Preferably, the mass fractions of polyurethane and cellulose acetate in the electrospinning solution are 12 - 16 wt%; the electrospinning process is an electrostatic high voltage of 14 - 18 kV, a spinning solution flow rate of 0.4 - 0.8 mL / h, and a receiving distance of 12 - 15 cm.

[0032] Preferably, the solvent is N,N - dimethylformamide.

[0033] Preferably, the buffer solution is an aqueous mixed solution of potassium dihydrogen phosphate, disodium hydrogen phosphate, and ammonium persulfate with a mass ratio of 1:(0.9 - 1.1):(3 - 3.2); this buffer solution is prepared by the following method: mix potassium dihydrogen phosphate, disodium hydrogen phosphate, and ammonium persulfate and add them to deionized water, and stir and dissolve to obtain the buffer solution.

[0034] By adopting the above technical solutions, first mix polyurethane and cellulose acetate and obtain polyurethane / cellulose acetate composite nanofibers by electrospinning; then through alkali activation treatment, more active groups are exposed and the pore structure of the formed composite fiber membrane is optimized, which is beneficial to the composite of polydopamine and the grafting of polyethyleneimine, and improves the adsorption amount of heavy metal ions; then immerse the obtained composite fiber membrane after deposition in the dopamine solution, and dopamine hydrochloride gradually polymerizes on the surface of the composite fiber membrane, and a layer of polydopamine is composited; then add it to the aqueous polyethyleneimine solution, and the polyethyleneimine chain segments can react with the active groups in the polydopamine, thereby realizing the grafting of the polyethyleneimine chain segments, which can improve the adsorption ability of heavy metal ions and can also well adsorb and remove trace heavy metal ions.

[0035] In a third aspect, the present invention provides an application of a polyurethane / cellulose acetate composite fiber membrane, which can be applied to the adsorption and removal of heavy metal ions in any one of industrial wastewater treatment, drinking water purification, seawater desalination pretreatment, and environmental remediation.

[0036] By adopting the above technical solution, the polyurethane / cellulose acetate composite fiber membrane obtained by the present invention has extremely strong adsorption capacity and large adsorption capacity for heavy metal ions, and has great inclusiveness for the adsorption environment, can adapt to various environments, and meets the requirements for the adsorption and removal of heavy metal ions in various fields.

[0037] Advantages of the present invention:

[0038] 1. The present invention obtains a fiber membrane of polyurethane / cellulose acetate with complete fiber morphology, uniform diameter, and a bicontinuous structure through electrospinning technology. This regular fiber structure and high specific surface area provide a good physical basis for the subsequent grafting of polyethyleneimine segments, and can more effectively contact and interact with the target substance. The composite of cellulose acetate can provide more active sites on the one hand, and can directly participate in the adsorption and removal of heavy metal ions on the other hand, improving the adsorption capacity of the composite fiber membrane.

[0039] 2. The polyurethane / cellulose acetate composite fiber membrane of the present invention is first compounded with a layer of polydopamine, and then polyethyleneimine segments are grafted. The polydopamine layer formed by the self-polymerization of hydrochloric acid dopamine can enhance the surface activity and adhesion of the composite fiber membrane, improve the grafting rate of polyethyleneimine segments, and fix the polyethyleneimine segments on the surface of the composite fiber membrane by chemical bonding and physical adsorption methods, avoiding the water solubility of polyethyleneimine, and also improving the adsorption effect on heavy metal ions. The finally obtained composite fiber membrane not only retains the characteristics of the polyurethane / cellulose acetate fiber membrane itself and has good mechanical properties, but also greatly improves the ability to heavy metal ions after grafting modification, can adapt to different requirements and scenarios, and has strong functional compositeness. Description of the drawings

[0040] The present invention will be further described below with reference to the accompanying drawings.

[0041] Figure 1 is the SEM image of the polyurethane / cellulose acetate composite fiber membrane before alkali treatment in Example 1 of the present invention;

[0042] Figure 2 is the SEM image of the polyurethane / cellulose acetate composite fiber membrane after alkali treatment in Example 1 of the present invention. Detailed implementation manners

[0043] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0044] Embodiment

[0045] Embodiment 1. A polyurethane / cellulose acetate composite fiber membrane is prepared by the following method:

[0046] S1. Polyurethane and cellulose acetate are added to N,N-dimethylformamide, wherein the mass ratio of polyurethane to cellulose acetate is 1:1, and they are stirred and dissolved at 40 °C to obtain an electrospinning solution with a mass fraction of 14%. Then, polyurethane / cellulose acetate composite nanofibers are prepared by electrospinning and drying treatment. The electrospinning process is as follows: an electrostatic high voltage of 16 kV, a spinning solution flow rate of 0.6 mL / h, and a receiving distance of 15 cm.

[0047] S2. The polyurethane / cellulose acetate composite nanofibers are impregnated in a 0.2 mol / L aqueous sodium hydroxide solution and activated for 24 h, and a polyurethane / cellulose acetate composite fiber membrane is obtained after washing, drying, and deposition.

[0048] S3. 600 mg of hydrochloric acid dopamine is added to 200 mL of buffer solution, and the pH value of the solution is adjusted to 8.5. After stirring evenly, a dopamine solution with a concentration of 3 g / L is obtained. The buffer solution is prepared by the following method: 1 g of potassium dihydrogen phosphate, 1 g of disodium hydrogen phosphate, and 3 g of ammonium persulfate are added to 200 mL of deionized water and stirred and dissolved to obtain the buffer solution.

[0049] Subsequently, 1 g of the polyurethane / cellulose acetate composite fiber membrane is added, and the reaction is stirred for 20 min. After washing and drying, a pretreated polyurethane / cellulose acetate composite fiber membrane is obtained.

[0050] S4. 25 g of polyethyleneimine (average molecular weight of 15,000) is dissolved in water to obtain an aqueous polyethyleneimine solution with a concentration of 20 g / L. The pretreated polyurethane / cellulose acetate composite fiber membrane obtained in step S3 is added, and the reaction is stirred for 14 h. Finally, it is obtained after drying.

[0051] Embodiment 2. A polyurethane / cellulose acetate composite fiber membrane, the difference from Embodiment 1 is only that the mass ratio of polyurethane to cellulose acetate in step S1 is 1:0.8.

[0052] Example 3. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that the addition amount of dopamine hydrochloride is 400 mg; the addition amount of polyethyleneimine is 20 g.

[0053] Example 4. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that the addition amount of dopamine hydrochloride is 800 mg; the addition amount of polyethyleneimine is 30 g.

[0054] Example 5. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that in step S1, the mass fraction of the electrospinning solution is 12%; the concentration of the dopamine solution is 2 g / L; the concentration of the polyethyleneimine aqueous solution is 30 g / L.

[0055] Example 6. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that in step S1, the mass fraction of the electrospinning solution is 16%; the concentration of the dopamine solution is 4 g / L; the concentration of the polyethyleneimine aqueous solution is 10 g / L.

[0056] Example 7. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that in step S1, the mass ratio of polyurethane to cellulose acetate is 1:0.6.

[0057] Example 8. A polyurethane / cellulose acetate composite fiber membrane, the difference from Example 1 is only that in step S1, the mass ratio of polyurethane to cellulose acetate is 1:1.2.

[0058] Example 9. A polyurethane / cellulose acetate composite fiber membrane is prepared by the following method:

[0059] S1. Add polyurethane and cellulose acetate to N,N-dimethylformamide, where the mass ratio of polyurethane to cellulose acetate is 1:1, stir and dissolve at 40 °C to obtain an electrospinning solution with a mass fraction of 14%; then prepare polyurethane / cellulose acetate composite nanofibers by electrospinning and drying, where the electrospinning process is: electrospinning voltage 16 kV, spinning solution flow rate 0.6 mL / h, receiving distance 15 cm;

[0060] S2. Deposit the polyurethane / cellulose acetate composite nanofibers to obtain a polyurethane / cellulose acetate composite fiber membrane;

[0061] S3. Add 600 mg of dopamine hydrochloride to 200 mL of buffer solution, adjust the pH value of the solution to 8.5, and stir evenly to obtain a dopamine solution with a concentration of 3 g / L, where the buffer solution is prepared by the following method: Add 1 g of potassium dihydrogen phosphate, 1 g of disodium hydrogen phosphate and 3 g of ammonium persulfate to 200 mL of deionized water and stir to dissolve to obtain the buffer solution;

[0062] Subsequently, 1 g of polyurethane / cellulose acetate composite fiber membrane was added, and the mixture was stirred and reacted for 20 min. After washing and drying, a pretreated polyurethane / cellulose acetate composite fiber membrane was obtained;

[0063] S4. Dissolve 25 g of polyethyleneimine (average molecular weight of 15,000) in water to obtain an aqueous polyethyleneimine solution with a concentration of 20 g / L. Add the pretreated polyurethane / cellulose acetate composite fiber membrane obtained in step S3, stir and react for 14 h, and finally obtain the product after drying.

[0064] Comparative Example

[0065] Comparative Example 1, a polyurethane / cellulose acetate composite fiber membrane, which is only different from Example 1 in that the addition amount of dopamine hydrochloride is 200 mg.

[0066] Comparative Example 2, a polyurethane / cellulose acetate composite fiber membrane, which is only different from Example 1 in that the addition amount of dopamine hydrochloride is 1 g.

[0067] Comparative Example 3, a polyurethane / cellulose acetate composite fiber membrane, was prepared by the following method:

[0068] S1. Add polyurethane and cellulose acetate to N,N-dimethylformamide, where the mass ratio of polyurethane to cellulose acetate is 1:1, stir and dissolve at 40 °C to obtain an electrospinning solution with a mass fraction of 14%; then prepare polyurethane / cellulose acetate composite nanofibers by electrospinning and drying treatment, where the electrospinning process is: electrospinning voltage 16 kV, spinning solution flow rate 0.6 mL / h, and receiving distance 15 cm;

[0069] S2. Immerse the polyurethane / cellulose acetate composite nanofibers in a 0.2 mol / L aqueous sodium hydroxide solution for activation for 24 h, and obtain a polyurethane / cellulose acetate composite fiber membrane after washing, drying and deposition;

[0070] S3. Dissolve 25 g of polyethyleneimine (average molecular weight of 15,000) in water to obtain an aqueous polyethyleneimine solution with a concentration of 20 g / L. Add 1 g of polyurethane / cellulose acetate composite fiber membrane, stir and react for 14 h, and finally obtain the product after drying.

[0071] Comparative Example 4, a polyurethane / cellulose acetate composite fiber membrane, which is only different from Example 1 in that the addition amount of polyethyleneimine is 10 g.

[0072] Comparative Example 5, a polyurethane / cellulose acetate composite fiber membrane, which is only different from Example 1 in that the addition amount of polyethyleneimine is 40 g.

[0073] Comparative Example 6. A polyurethane / cellulose acetate composite fiber membrane was prepared by the following method:

[0074] S1. Polyurethane and cellulose acetate were added to N,N-dimethylformamide, where the mass ratio of polyurethane to cellulose acetate was 1:1, and stirred and dissolved at 40 °C to obtain an electrospinning solution with a mass fraction of 14%; then polyurethane / cellulose acetate composite nanofibers were prepared by electrospinning and drying treatment, and the electrospinning process was: an electrostatic high voltage of 16 kV, a spinning solution flow rate of 0.6 mL / h, and a receiving distance of 15 cm;

[0075] S2. The polyurethane / cellulose acetate composite nanofibers were impregnated in a 0.2 mol / L aqueous sodium hydroxide solution and activated for 24 h, and a polyurethane / cellulose acetate composite fiber membrane was obtained after washing, drying and deposition;

[0076] S3. 600 mg of hydrochloric acid dopamine was added to 200 mL of buffer solution, and the pH value of the solution was adjusted to 8.5. After stirring evenly, a dopamine solution with a concentration of 3 g / L was obtained. The buffer solution was prepared by the following method: 1 g of potassium dihydrogen phosphate, 1 g of disodium hydrogen phosphate and 3 g of ammonium persulfate were added to 200 mL of deionized water and stirred and dissolved to obtain the buffer solution;

[0077] Subsequently, 1 g of the polyurethane / cellulose acetate composite fiber membrane was added, and the reaction was stirred for 20 min, and the product was obtained after washing and drying.

[0078] Comparative Example 7. A polyurethane fiber membrane, the difference from Example 1 is only that cellulose acetate is not added in step S1.

[0079] Comparative Example 8. A polyurethane / cellulose acetate composite fiber membrane was prepared by the following method:

[0080] S1. Polyurethane and cellulose acetate were added to N,N-dimethylformamide, where the mass ratio of polyurethane to cellulose acetate was 1:1, and stirred and dissolved at 40 °C to obtain an electrospinning solution with a mass fraction of 14%; then polyurethane / cellulose acetate composite nanofibers were prepared by electrospinning and drying treatment, and the electrospinning process was: an electrostatic high voltage of 16 kV, a spinning solution flow rate of 0.6 mL / h, and a receiving distance of 15 cm;

[0081] S2. The polyurethane / cellulose acetate composite nanofibers were impregnated in a 0.2 mol / L aqueous sodium hydroxide solution and activated for 24 h, and the product was obtained after washing, drying and deposition.

[0082] Performance detection test

[0083] Prepare a 200 mg / L hexavalent chromium solution. Add 20 mg of the polyurethane / cellulose acetate composite fiber membranes obtained in the examples and comparative examples to 20 mL of the 200 mg / L hexavalent chromium solution, and oscillate at a constant temperature of 303 K for 6 h, with an oscillation speed of 120 rpm.

[0084] After the oscillation is completed, use an ultraviolet spectrophotometer to detect the residual concentration of hexavalent chromium ions after equilibrium adsorption, and calculate the adsorption capacity of the sample.

[0085] The test results are shown in Table 1:

[0086] Table 1 Test results of performance detection

[0087]

[0088] According to Table 1, in combination with Example 1, Example 7, Example 8 and Comparative Example 7, it can be seen that the adsorption capacities of Example 7, Example 8 and Comparative Example 7 are lower than that of Example 1, indicating that the adsorption capacities of Example 7, Example 8 and Comparative Example 7 have decreased. The reason is that in Example 7, Example 8 and Comparative Example 7, the content of cellulose acetate in the polyurethane / cellulose acetate composite fiber membrane was adjusted. Specifically, in Example 7, the addition amount of cellulose acetate was reduced, the structural stability of the composite fiber membrane decreased, the binding rate between the composite fiber membrane and polydopamine decreased, the grafting rate of the polyethyleneimine segment decreased, and the adsorption capacity for heavy metal ions decreased. In Comparative Example 7, no cellulose acetate was added, and the performance degradation was particularly obvious. In Example 8, the proportion of cellulose acetate was increased, which would lead to a decrease in the tensile strength and hardness of the composite fiber membrane, a decrease in structural stability, uneven pore distribution, and was not conducive to the adsorption of heavy metal ions.

[0089] In combination with Example 1 and Comparative Examples 1 to 3, it can be seen that the adsorption capacities of Comparative Examples 1 to 3 are significantly lower than that of Example 1. The reason is that the only difference between Comparative Examples 1 to 3 and Example 1 is the adjustment of the addition amount of dopamine hydrochloride. In Comparative Example 1, the addition amount of dopamine hydrochloride was reduced, which would lead to a decrease in the grafting rate of the polyethyleneimine segment, and correspondingly a decrease in the adsorption capacity for heavy metal ions. In Comparative Example 3, no dopamine hydrochloride was added, and it was difficult for the polyethyleneimine segment to graft onto the composite fiber membrane, or some were grafted onto the composite fiber membrane but would also fall off with the water flow scouring during the adsorption treatment process, and the polyethyleneimine dissolved in water, resulting in a decrease in the adsorption effect on heavy metal ions. In Comparative Example 2, the addition amount of dopamine hydrochloride was increased. Although the content of polydopamine increased, it was difficult for the polyethyleneimine segment to fully utilize the active sites of polydopamine, and the increase in the content of polydopamine would affect the pore structure of the composite fiber membrane and the mass transfer process of heavy metal ions, resulting in a decrease in the adsorption capacity.

[0090] Combined with Example 1 and Comparative Examples 4 to 5, it can be seen that the adsorption amounts of Comparative Examples 4 to 6 are significantly decreased compared with Example 1. The reason is that the only difference between Comparative Examples 4 to 6 and Example 1 lies in the adjustment of the addition amount of polyethyleneimine. In Comparative Example 4, the addition amount of polyethyleneimine is reduced, lacking the chelation and coordination effect between the polyethyleneimine chain segments and heavy metal ions, and the adsorption ability of the composite fiber membrane for heavy metal ions will obviously decrease. In Comparative Example 6, no polyethyleneimine is added, and the adsorption ability decreases more significantly. In Comparative Example 5, the addition amount of polyethyleneimine is increased. On the one hand, the active sites on the surface of the composite fiber membrane are already saturated and fully utilized, and increasing polyethyleneimine further has no obvious effect on improving the adsorption ability. On the other hand, when the content of polyethyleneimine is too high, the molecular chains of its branched structure will entangle with each other, which is instead unfavorable for the mass transfer of heavy metal ions and reduces the adsorption amount of the composite fiber membrane.

[0091] Combined with Example 1 and Comparative Example 8, it can be seen that the adsorption amount of Example 1 is significantly increased compared with Comparative Example 8, indicating that grafting polyethyleneimine chain segments can well improve the adsorption ability of the composite fiber membrane for heavy metal ions.

[0092] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0093] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyurethane / cellulose acetate composite fiber membrane, characterized in that, The surface of the polyurethane / cellulose acetate composite fiber membrane is grafted with polyethyleneimine segments; The raw materials for the surface grafting include a polyurethane / cellulose acetate composite fiber membrane, polyethyleneimine, and dopamine hydrochloride in a mass ratio of 1:(20-30):(0.4-0.8).

2. The polyurethane / cellulose acetate composite fiber membrane according to claim 1, wherein In the polyurethane / cellulose acetate composite fiber membrane, the mass ratio of cellulose acetate to polyurethane is (0.8-1):

1.

3. The polyurethane / cellulose acetate composite fiber membrane according to claim 1, characterized in that, The polyurethane / cellulose acetate composite fiber membrane is treated by activation with an alkali solution.

4. The polyurethane / cellulose acetate composite fiber membrane according to claim 1, characterized in that, The molecular weight of the polyethyleneimine is 10,000-20,000.

5. A method for preparing the polyurethane / cellulose acetate composite fiber membrane according to any one of claims 1 to 4, characterized in that, It includes the following technological steps: S1. Add polyurethane and cellulose acetate to a solvent, stir and dissolve at 40-45 °C to obtain an electrospinning solution; then prepare polyurethane / cellulose acetate composite nanofibers through electrospinning and drying. S2. Immerse the polyurethane / cellulose acetate composite nanofibers in an alkali solution for activation for 20-24 h, and obtain a polyurethane / cellulose acetate composite fiber membrane after washing, drying, and deposition. S3. Add dopamine hydrochloride to a buffer solution, adjust the pH value of the solution to 8-9, stir evenly to obtain a dopamine solution, add the polyurethane / cellulose acetate composite fiber membrane, stir and react for 15-30 min, and obtain a pretreated polyurethane / cellulose acetate composite fiber membrane after washing and drying. S4. Dissolve polyethyleneimine in water to obtain an aqueous polyethyleneimine solution, add the pretreated polyurethane / cellulose acetate composite fiber membrane, stir and react for 12-15 h, and finally obtain the product after drying.

6. The preparation method of the polyurethane / cellulose acetate composite fiber membrane according to claim 5, characterized in that, The alkali solution includes one or a combination of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, sodium carbonate aqueous solution, and calcium hydroxide aqueous solution.

7. The preparation method of the polyurethane / cellulose acetate composite fiber membrane according to claim 5, characterized in that, The concentration of the dopamine solution is 2-4 g / L.

8. The preparation method of the polyurethane / cellulose acetate composite fiber membrane according to claim 5, characterized in that, The concentration of the aqueous polyethyleneimine solution is 10-30 g / L.

9. The preparation method of the polyurethane / cellulose acetate composite fiber membrane according to claim 5, characterized in that, In the electrospinning solution, the mass fractions of polyurethane and cellulose acetate are 12-16 wt%; the electrospinning process is an electrostatic high voltage of 14-18 kV, a spinning solution flow rate of 0.4-0.8 mL / h, and a receiving distance of 12-15 cm.

10. Use of the polyurethane / cellulose acetate composite fiber membrane according to any one of claims 1 to 4, characterized in that, The polyurethane / cellulose acetate composite fiber membrane can be applied to the adsorption and removal of heavy metal ions in any one of industrial wastewater treatment, drinking water purification, seawater desalination pretreatment, and environmental remediation.

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