Three-dimensional nanofiber composite aerogel and preparation method and application thereof

Abstract

The application discloses a kind of three-dimensional nanofiber composite aerogel and its preparation method and application, it is related to nanofiber composite aerogel material technical field, the first nanofiber is prepared by electrospinning technology in the present application, then electrospinning nanofiber, cellulose nanocrystal, chemical crosslinking agent end-capped isocyanate and water are mixed homogeneously, and stable dispersion liquid is prepared, then sequentially freeze-drying and heat crosslinking treatment are carried out, finally, the surface of above-mentioned product is loaded with polymer nanoparticles, and three-dimensional nanofiber composite aerogel with porous three-dimensional network structure, good mechanical stability and excellent adsorption performance is obtained.The present application solves the technical problems of poor mechanical stability and low adsorption capacity of existing nanofiber aerogel adsorption material.The preparation method of three-dimensional nanofiber composite aerogel described in the present application is simple, and the operability is strong, and anion and cation dye can be simultaneously and efficiently adsorbed and separated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanofiber composite aerogel materials, and particularly relates to a three-dimensional nanofiber composite aerogel and a preparation method and application thereof. BACKGROUND

[0002] Water bodies are the main carriers of pollutants in the environment. With the circulation of aquatic ecosystems, pollutants enter surface water and groundwater through various pathways such as runoff, diffusion, and infiltration, causing contamination of drinking water sources and food, and posing a serious threat to the ecological environment and human health. Among them, organic dyes are widely used in food, leather, papermaking and textile industries, and are one of the most common and typical pollutants in water bodies. Organic dyes in wastewater can cause dysfunction of multiple organs, reproductive system and central nervous system of human body, and most of them are stable in nature and difficult to degrade. Therefore, it is necessary to develop a method for efficiently removing organic dyes from wastewater. Among the many methods, water purification technology based on adsorbents is considered one of the most promising methods due to its simple process, strong operability and high efficiency.

[0003] Electrospinning is one of the most effective methods for preparing nanofibers, and has the characteristics of simple device, wide range of raw material sources, and good controllability of fiber structure. The high specific surface area and high aspect ratio of electrospun nanofibers make them exhibit excellent mass transfer performance. Three-dimensional nanofiber aerogels constructed by electrospun nanofibers not only have high specific surface area and high porosity, but also have a unique multi-level interconnected pore structure. The micro-nano network transport channels formed thereby can realize more efficient mass transfer, effectively improving the application performance of nanofiber materials in the field of adsorption and separation, and are an ideal pollutant removal material. However, traditional three-dimensional nanofiber aerogels have poor mechanical stability and low adsorption capacity, which limits their practical application. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a three-dimensional nanofiber composite aerogel and a preparation method and application thereof, so as to solve the technical problems of poor mechanical stability and low adsorption capacity of existing nanofiber aerogel adsorption materials.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] The preparation method of the three-dimensional nanofiber composite aerogel disclosed by the present application comprises the following steps:

[0007] Step one: uniformly mixing electrospun nanofibers, cellulose nanocrystals, blocked isocyanate and water to obtain a uniform dispersion liquid;

[0008] Step two: the dispersion liquid is subjected to freezing molding, freeze drying and heat crosslinking treatment in sequence to obtain the crosslinked product, electrospun nanofiber-cellulose nanocrystal composite aerogel;

[0009] Step three: the polymer nanoparticles are loaded on the surface of the electrospun nanofiber-cellulose nanocrystal composite aerogel to obtain a three-dimensional nanofiber composite aerogel.

[0010] Preferably, the electrospun nanofiber in step one is prepared by mixing one or more of polyacrylonitrile, nylon, cellulose acetate and polyethylene imine.

[0011] Further preferably, the mass ratio of the electrospun nanofiber to the cellulose nanocrystal in step one is 1:0.25-0.67; and the total mass of the electrospun nanofiber and the cellulose nanocrystal in step one accounts for 0.6-2.4wt% of the dispersion liquid.

[0012] Further preferably, the addition amount of the capped isocyanate in step one accounts for 10-30% of the total mass of the electrospun nanofiber and the cellulose nanocrystal.

[0013] Further preferably, in step one, the homogenization speed is 8000-15000rpm, and the homogenization time is 5-20min.

[0014] Preferably, in step two, the freezing molding temperature is-80--40℃, and the freezing molding time is 30-60min; the freeze drying temperature is-80--60℃, and the freeze drying time is 20-30h; the heat crosslinking treatment temperature is 120-130℃, and the heat crosslinking treatment time is 1-2h.

[0015] Further preferably, in step two, the dispersion liquid needs to be first divided into the mold, and then subjected to subsequent freezing molding, freeze drying and heat treatment.

[0016] Preferably, in step three, the loaded nanoparticles include at least one of polyaniline and polypyrrole.

[0017] The application discloses a three-dimensional nanofiber composite aerogel prepared by the preparation method of the three-dimensional nanofiber composite aerogel.

[0018] The application discloses an application of the three-dimensional nanofiber composite aerogel as an organic dye adsorbent.

[0019] The application discloses an application of the three-dimensional nanofiber composite aerogel as an anionic and cationic organic dye adsorbent.

[0020] Compared with the prior art, the application has the beneficial effects that:

[0021] The preparation method of the three-dimensional nanofiber composite aerogel disclosed in the application uses electrospun nanofiber as a skeleton, cellulose nanocrystal as a reinforcing phase, and a blocked isocyanate as a chemical crosslinking agent to prepare a nanofiber composite aerogel with stable structure, and then loads polymer nanoparticles on the fiber surface of the aerogel. The three-dimensional nanofiber composite aerogel provided by the application has a simple preparation process, strong operability, no secondary pollution, belongs to an environmentally friendly material, and is suitable for industrialized production and application. Compared with traditional aerogels, the three-dimensional nanofiber composite aerogel proposed in the application shows better flexibility and good mechanical stability. The advantages mainly include:

[0022] 1. The electrospun nanofiber has strong flexibility, good uniformity, high specific surface area, and excellent mass transfer performance.

[0023] 2. The cellulose nanocrystal, as a natural nanoscale rod-shaped cellulose material, has high crystallinity and high strength, and is a green reinforcing phase that can improve the mechanical properties of the composite material.

[0024] 3. The nanofiber and the cellulose nanocrystal both have rich chemical groups on the surface. Experimental data show that the two are irregularly interpenetrated together to form a hierarchical porous three-dimensional network structure with interconnected pores, which is beneficial to improving the adsorption efficiency as an adsorbent. By combining the electrospun nanofiber and the cellulose nanocrystal, the pore structure inside the aerogel can be more robust. Experimental results show that the three-dimensional nanofiber composite aerogel composed of the electrospun nanofiber and the cellulose nanocrystal has a larger specific surface area and total pore volume, and improves the adsorption capacity of the composite aerogel.

[0025] 4. The blocked isocyanate is unblocked under heating conditions to generate active -NCO groups, which can chemically crosslink with the hydroxyl groups on the cellulose nanocrystal to produce firm adhesion between the fibers.

[0026] 5. Loading the polymer nanoparticles on the surface of the aerogel fiber can further improve the adsorption performance and increase the adsorption capacity.

[0027] The three-dimensional nanofiber composite aerogel prepared by the method of the application shows smaller deformation and better mechanical stability according to experimental data, effectively solving the problem of poor mechanical stability of the nanofiber aerogel in the prior art.

[0028] The electrostatic spinning nanofiber and cellulose nanocrystal used in the application have rich chemical groups on the surface, which is beneficial to improve the adsorption efficiency as an adsorbent; the polymer nanoparticles are carried on the surface of the aerogel fiber, which can further improve the adsorption performance and increase the adsorption capacity. Therefore, the three-dimensional nanofiber composite aerogel prepared by the application can simultaneously and efficiently adsorb and remove anionic and cationic dyes by the synergistic effect of the electrostatic spinning nanofiber, cellulose nanocrystal and polypyrrole. The experimental results show that the composite aerogel has better comprehensive adsorption effect on acid orange 7, acid red 14 and rhodamine B dyes; and the adsorption effect on anionic and cationic dyes is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The scanning electron microscope image of the polyacrylonitrile nanofiber membrane synthesized in the application;

[0030] Figure 2 The scanning electron microscope image of the three-dimensional nanofiber composite aerogel prepared in Example 6 of the application;

[0031] Figure 3 The digital photos of the three-dimensional nanofiber composite aerogel prepared in the application and the three-dimensional nanofiber composite aerogel with a weight of 20g of a weight, wherein A1 is the digital photo of the crosslinked aerogel of Example 6, A2 is the digital photo of the aerogel of Example 6 after carrying polypyrrole, A3 is the digital photo of the aerogel of Example 6 with a weight of 20g of a weight; B1 is the digital photo of the crosslinked aerogel of Comparative Example 2, B2 is the digital photo of the aerogel of Comparative Example 2 after carrying polypyrrole, and B3 is the digital photo of the aerogel of Comparative Example 2 with a weight of 20g of a weight;

[0032] Figure 4 The N2 adsorption-desorption curve and pore size distribution graph of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel prepared in Example 6 of the application, wherein A is the N2 adsorption-desorption curve of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel; and B is the pore size distribution graph of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel;

[0033] Figure 5 The Fourier infrared spectrograms of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel prepared in the application before crosslinking, after crosslinking and after carrying polypyrrole;

[0034] Figure 6 The flow chart of the preparation method of the three-dimensional nanofiber composite aerogel in the application. DETAILED DESCRIPTION

[0035] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort should fall within the protection scope of the present application.

[0036] It should be noted that the terms "first", "second" and the like in the description and claims of the present application and the above drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units need not be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0037] The present application will be described in further detail below with reference to the drawings:

[0038] Reference is made to Figure 6 The flow chart of the preparation method of the three-dimensional nanofiber composite aerogel disclosed in the present application is shown in the following table:

[0039] (1) Homogenize the electrospun nanofiber, cellulose nanocrystal, blocked isocyanate and water to obtain a uniform dispersion liquid;

[0040] (2) Dispense the above dispersion liquid into a mold, and sequentially perform freeze forming, freeze drying and heat treatment;

[0041] (3) Load polymer nanoparticles on the above product to obtain a three-dimensional nanofiber composite aerogel.

[0042] Preferably, the electrospun nanofiber in step (1) is prepared by mixing one or more of polyacrylonitrile, nylon, cellulose acetate and polyethylene imine.

[0043] Preferably, the mass ratio of the electrospun nanofiber and the cellulose nanocrystal in step (1) is 1:0.25-0.67; the total mass of the electrospun nanofiber and the cellulose nanocrystal accounts for 0.6-2.4wt% of the dispersion liquid; and the addition amount of the blocked isocyanate is 10-30% of the total mass of the electrospun nanofiber and the cellulose nanocrystal.

[0044] Preferably, the homogenization speed in step (1) is 8000-15000 rpm, and the homogenization time is 5-20 min.

[0045] Preferably, the freeze-forming temperature in step (2) is -80 to -40℃, and the freeze-forming time is 30-60 min; the freeze-drying temperature is -80 to -60℃, and the freeze-drying time is 20-30 h; the heat treatment temperature is 120-130℃, and the heat treatment time is 1-2 h.

[0046] Preferably, the polymer nanoparticles in step (3) are at least one of polyaniline and polypyrrole.

[0047] Example 1:

[0048] S1. Preparation of polyacrylonitrile nanofiber membrane: polyacrylonitrile powder was dissolved in N,N-dimethylformamide, and magnetic stirring was performed at room temperature for 8 h to obtain a spinning sol with a concentration of 10 wt%. Then, the polyacrylonitrile sol was placed in an electrospinning jet, the pore size of the nozzle was 0.4 mm, the sol injection speed was 1 mL / h, the distance from the nozzle to the aluminum foil receiving plate was 15 cm, the voltage was 12 kV, and electrospinning was performed for 3 h. The collected product was dried to obtain a polyacrylonitrile nanofiber membrane. The scanning electron microscope image is shown in FIG. 1. Figure 1 As can be seen, the prepared polyacrylonitrile nanofiber has a smooth surface and uniform thickness, and the fiber diameter is about 315 nm.

[0049] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water, and homogenized at 12000 rpm for 10 min. Then, the mass ratio of cellulose nanocrystal to polyacrylonitrile nanofiber was 1:0.67, and the addition amount of blocked isocyanate was 10% of the total mass of polyacrylonitrile nanofiber and cellulose nanocrystal, and the homogenization was continued for 10 min to prepare a dispersion liquid with a total mass of polyacrylonitrile nanofiber and cellulose nanocrystal of 0.6 wt%.

[0050] S3. The above dispersion liquid was placed in a mold, frozen at -80℃ for 30 min, and then freeze-dried at -80℃ for 20 h. After the freeze-drying was completed, an uncrosslinked aerogel was obtained, which was then placed in a 125℃ reaction for 90 min for heat crosslinking treatment to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0051] S4. 10 mg of the above aerogel was soaked in 4 mL of an ethanol solution containing 0.1 mmol of pyrrole monomer and shaken for 2 h to ensure that the pyrrole monomer was fully infiltrated into the polyacrylonitrile-cellulose nanocrystal composite aerogel, then 1 mL of an ethanol solution containing 0.1 mmol of FeCl3·6H2O was added, wherein ethanol was used as a solvent and FeCl3·6H2O was used as an initiator for the polymerization of the pyrrole monomer to initiate the polymerization reaction of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h to allow the pyrrole monomer to polymerize under the catalysis of FeCl3·6H2O and form polypyrrole and adhere to the polyacrylonitrile-cellulose nanocrystal composite aerogel. The aforementioned composite aerogel was taken out and washed with deionized water to remove unreacted pyrrole monomer, initiator and other impurities, and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-1.

[0052] Example 2:

[0053] S1. The same as Example 1.

[0054] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 12000 rpm for 10 min. Then, cellulose nanocrystals, polyacrylonitrile nanofibers and cellulose nanocrystals were added in a mass ratio of 1:0.67, and the amount of blocked isocyanate added was 30% of the total mass of polyacrylonitrile nanofibers and cellulose nanocrystals. The homogenization was continued for 10 min to prepare a dispersion liquid with a total mass of 1.2 wt% of polyacrylonitrile nanofibers and cellulose nanocrystals.

[0055] S3. The above dispersion liquid was placed in a mold and frozen at -70°C for 40 min, then freeze-dried at -70°C for 24 h. After freeze-drying, an uncrosslinked aerogel was obtained, which was then placed in a 130°C reaction for 60 min for thermal crosslinking treatment to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0056] S4. 20 mg of the above aerogel was soaked in 4 mL of an ethanol solution containing 0.2 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of an ethanol solution containing 0.2 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h. After taking out, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-2.

[0057] Example 3:

[0058] S1. The same as Example 1.

[0059] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square pieces and placed in deionized water, and homogenized at 12000 rpm for 10 min; then the mass ratio of cellulose nanocrystal to polyacrylonitrile nanofiber was 1:0.67, and the blocked isocyanate was added in an amount of 10% of the total mass of polyacrylonitrile nanofiber and cellulose nanocrystal, and homogenized for another 10 min, to prepare a dispersion liquid with a total mass of 2.4 wt% of polyacrylonitrile nanofiber and cellulose nanocrystal.

[0060] S3. The above dispersion liquid was placed in a mold, frozen at -70°C for 40 min, and then freeze-dried at -70°C for 30 h. After freeze-drying, an uncrosslinked aerogel was obtained, which was then placed in a hot crosslinking treatment at 120°C for 120 min to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0061] S4. 40 mg of the above aerogel was soaked in 4 mL of an ethanol solution containing 0.4 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of an ethanol solution containing 0.4 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h. After removal, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-3.

[0062] Example 4:

[0063] S1. The same as Example 1.

[0064] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square pieces and placed in deionized water, and homogenized at 15000 rpm for 5 min; then the mass ratio of cellulose nanocrystal to polyacrylonitrile nanofiber was 1:0.43, and the blocked isocyanate was added in an amount of 20% of the total mass of polyacrylonitrile nanofiber and cellulose nanocrystal, and homogenized for another 10 min, to prepare a dispersion liquid with a total mass of 0.6 wt% of polyacrylonitrile nanofiber and cellulose nanocrystal.

[0065] S3. The above dispersion liquid was placed in a mold, frozen at -40°C for 60 min, and then freeze-dried at -60°C for 24 h. After freeze-drying, an uncrosslinked aerogel was obtained, which was then placed in a hot crosslinking treatment at 125°C for 90 min to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0066] S4. 10 mg of the above aerogel was soaked in 4 mL of an ethanol solution containing 0.1 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of an ethanol solution containing 0.1 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h. After removal, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-4.

[0067] Example 5:

[0068] S1. The same as Example 1.

[0069] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 10000 rpm for 20 min. Then, cellulose nanocrystals were added in a mass ratio of 1:0.25 to the polyacrylonitrile nanofiber and cellulose nanocrystals, and a blocked isocyanate was added in an amount of 10% of the total mass of the polyacrylonitrile nanofiber and cellulose nanocrystals. Homogenization was continued for 10 min to obtain a dispersion liquid with a total mass of polyacrylonitrile nanofiber and cellulose nanocrystals of 0.6 wt%.

[0070] S3. The above dispersion liquid was placed in a mold and frozen at -40°C for 60 min, then freeze-dried at -60°C for 24 h. After freeze-drying was completed, an uncrosslinked aerogel was obtained, which was then placed in a hot crosslinking treatment at 125°C for 90 min to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0071] S4. 10 mg of the above aerogel was soaked in 4 mL of an ethanol solution containing 0.1 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of an ethanol solution containing 0.1 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h. After removal, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-4.

[0072] Example 6:

[0073] S1. The same as Example 1.

[0074] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 12000 rpm for 10 min. Then, cellulose nanocrystals were added in a mass ratio of 1:0.25 to the polyacrylonitrile nanofiber and cellulose nanocrystals, and a blocked isocyanate was added in an amount of 10% of the total mass of the polyacrylonitrile nanofiber and cellulose nanocrystals. Homogenization was continued for 10 min to obtain a dispersion liquid with a total mass of polyacrylonitrile nanofiber and cellulose nanocrystals of 1.2 wt%.

[0075] S3. The dispersion liquid above was placed in a mold, frozen at -80°C for 40 min, and then freeze-dried at -70°C for 24 h. After the freeze-drying was completed, the uncrosslinked aerogel was obtained, which was then placed in a heat crosslinking treatment at 125°C for 90 min to obtain the crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel. The digital photograph is shown in FIG. 1A1. Figure 3 A1 in FIG. 1A1.

[0076] S4. 10 mg of the aerogel above was soaked in 4 mL of an ethanol solution containing 0.3 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of an ethanol solution containing 0.3 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and the mixture was reacted at room temperature for 12 h. After being taken out, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, which was denoted as PPCA-6. The digital photograph is shown in FIG. 1A2. The scanning electron microscope image is shown in FIG. 1A3. Figure 3 A2 in FIG. 1A2. The scanning electron microscope image is shown in FIG. 1A3. Figure 2 As shown in the figure, the prepared three-dimensional nanofiber composite aerogel is composed of polyacrylonitrile nanofibers and cellulose nanocrystals randomly interpenetrated together to form a hierarchical porous three-dimensional network structure with interconnected pores.

[0077] Example 7:

[0078] S1. Preparation of nylon 6 nanofiber membrane: nylon 6 particles were dissolved in a mixed solution of m-cresol and formic acid 4:6, v / v, and stirred magnetically at room temperature for 12 h to obtain a spinning sol with a concentration of 32 wt%. Then, the spinning sol was placed in an electrospinning sprayer, the pore size of the nozzle was 0.7 mm, the sol injection speed was 0.5 mL / h, the distance from the nozzle to the aluminum foil receiving plate was 15 cm, and the voltage was 15 kV. After electrospinning for 2 h, the collected product was dried to obtain a nylon 6 nanofiber membrane.

[0079] S2. The prepared nylon 6 nanofiber membrane was cut into square fragments of 0.5 cm x 0.5 cm and placed in deionized water for homogenization at 12000 rpm for 30 min. Then, the mass ratio of cellulose nanocrystal nylon 6 nanofiber and cellulose nanocrystal was 1:0.67, and the addition amount of blocked isocyanate was 10% of the total mass of nylon 6 nanofiber and cellulose nanocrystal. Continue to homogenize for 15 min to prepare a dispersion liquid with a total content of nylon 6 nanofiber and cellulose nanocrystal of 0.6 wt%.

[0080] S3. The dispersion liquid above was placed in a mold, frozen at -80°C for 30 min, and then freeze-dried at -80°C for 20 h. After the freeze-drying was completed, the uncrosslinked aerogel was obtained, which was then placed in a heat crosslinking treatment at 125°C for 90 min to obtain the crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel.

[0081] S4. 10 mg of the above aerogel was soaked in 4 mL of 0.2 mol / L hydrochloric acid solution containing 0.2 mmol of aniline monomer and shaken for 2 h to ensure that the aniline monomer was fully penetrated into the nylon 6-cellulose nanocrystal composite aerogel, then 1 mL of 0.2 mol / L hydrochloric acid solution containing 0.1 mmol of ammonium persulfate was added, wherein 0.2 mol / L hydrochloric acid was used as the solvent and ammonium persulfate was used as the initiator for the polymerization of aniline monomer to initiate the polymerization reaction of aniline monomer, and the mixture was reacted at room temperature for 12 h to allow the aniline monomer to polymerize under the catalysis of ammonium persulfate and form polyaniline attached to the polypropylene-cellulose nanocrystal composite aerogel. After the above composite aerogel was taken out, it was repeatedly washed with 0.002 mol / L hydrochloric acid solution to remove unreacted aniline monomer, initiator and other impurities, and after drying, the obtained three-dimensional nanofiber composite aerogel was denoted as PPCA-7.

[0082] Example 8:

[0083] S1. Preparation of polyacrylonitrile / polyethyleneimine composite nanofiber membrane: Polyacrylonitrile powder and polyethyleneimine powder were dissolved in N,N-dimethylformamide at a ratio of 1:1 and stirred magnetically at room temperature for 10 h to obtain a spinning sol with a concentration of 10 wt%. Then, the spinning sol was placed in an electrospinning injector, the pore size of the nozzle was 0.5 mm, the sol injection speed was 1 mL / h, the distance from the nozzle to the aluminum foil receiving plate was 15 cm, and the voltage was 11 kV. After electrospinning for 2.5 h, the collected product was dried to obtain a polyacrylonitrile / polyethyleneimine nanofiber membrane.

[0084] S2. The prepared polyacrylonitrile / polyethyleneimine nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 12000 rpm for 10 min. Then, cellulose nanocrystals, polyacrylonitrile / polyethyleneimine nanofiber and cellulose nanocrystals were added in a mass ratio of 1:0.67, and the amount of blocked isocyanate added was 10% of the total mass of polyacrylonitrile / polyethyleneimine nanofiber and cellulose nanocrystals. Continue to homogenize for 10 min to prepare a dispersion liquid with a total mass of 0.6 wt% of polyacrylonitrile / polyethyleneimine nanofiber and cellulose nanocrystals.

[0085] S3. The above dispersion liquid was placed in a mold, frozen at -80°C for 30 min, and then freeze-dried at -80°C for 20 h. After freeze-drying was completed, an uncrosslinked aerogel was obtained, which was then placed in a 125°C reaction for 90 min for thermal crosslinking treatment to obtain a crosslinked polyacrylonitrile / polyethyleneimine-cellulose nanocrystal composite aerogel.

[0086] S4. 10 mg of the above aerogel was soaked in 4 mL of 0.2 mol / L hydrochloric acid solution containing 0.1 mmol of pyrrole monomer and 0.1 mmol of aniline monomer and shaken for 2 h to ensure that the pyrrole monomer and the aniline monomer were fully infiltrated into the polyacrylonitrile / cellulose nanocrystal composite aerogel, then 1 mL of 0.2 mol / L hydrochloric acid solution containing 0.4 mmol of FeCl3·6H2O was added, wherein the 0.2 mol / L hydrochloric acid solution was used as a solvent and the FeCl3·6H2O was used as an initiator for copolymerization of the pyrrole and the aniline monomers, to initiate the polymerization reaction of the pyrrole and the aniline monomers, and the mixture was reacted at room temperature for 12 h, allowing the pyrrole monomer and the aniline monomer to copolymerize under the catalysis of the FeCl3·6H2O to form a pyrrole and aniline copolymer and adhere to the polyacrylonitrile-polyethyleneimine-cellulose nanocrystal composite aerogel. After the above composite aerogel was taken out, it was repeatedly washed with 0.002 mol / L hydrochloric acid solution to remove unreacted monomers, initiators and other impurities. After drying, a three-dimensional nanofiber composite aerogel was obtained, which was denoted as PPCA-8.

[0087] Comparative Example 1

[0088] S1. The same as Example 1.

[0089] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 12000 rpm for 10 min. Then, the mass ratio of cellulose nanocrystal to polyacrylonitrile nanofiber membrane was 1:0.67, and the amount of blocked isocyanate added was 10% of the total mass of electrospun nanofiber and cellulose nanocrystal. The homogenization was continued for 10 min to prepare a dispersion liquid with a total content of electrospun nanofiber and cellulose nanocrystal of 0.6 wt%.

[0090] S3. The above dispersion liquid was placed in a mold and frozen at -80°C for 30 min, and then freeze-dried at -80°C for 20 h. After the freeze-drying was completed, it was subjected to thermal crosslinking treatment at 125°C for 90 min to obtain a crosslinked polyacrylonitrile-cellulose nanocrystal composite aerogel, which was denoted as PCA-1.

[0091] Comparative Example 2

[0092] S1. The same as Example 1.

[0093] S2. The prepared polyacrylonitrile nanofiber membrane was cut into 1 cm x 1 cm square fragments and placed in deionized water and homogenized at 12000 rpm for 10 min. Then, the amount of blocked isocyanate added was 10% of the mass of electrospun nanofiber. The homogenization was continued for 10 min to prepare a dispersion liquid with a content of electrospun nanofiber of 0.6 wt%.

[0094] S3. The dispersion was placed in a mold, frozen at -80℃ for 30 min, and then freeze-dried at -80℃ for 20 h to obtain uncrosslinked aerogel, which was then heat-crosslinked at 125℃ for 90 min to obtain polyacrylonitrile nanofiber aerogel, denoted as PA-1, the digital photo is shown in Figure 3 B1 of FIG. 1.

[0095] S4. 10 mg of the above aerogel was soaked in 4 mL of ethanol solution containing 0.1 mmol of pyrrole monomer and shaken for 2 h, then 1 mL of ethanol solution containing 0.1 mmol of FeCl3·6H2O was added to initiate the polymerization of the pyrrole monomer, and mixed at room temperature for 12 h. After taking out, it was washed with deionized water and dried to obtain a three-dimensional nanofiber composite aerogel, denoted as PPCA-1, the digital photo is shown in Figure 3 B2 of FIG. 1.

[0096] Test Example 1:

[0097] The BET specific surface area and pore size distribution of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel (PPCA-6) prepared in Example 6 were measured by a full-automatic specific surface area and porosity analyzer.

[0098] As shown in Figure 4 , compared with the polyacrylonitrile nanofiber membrane, the three-dimensional nanofiber composite aerogel composed of polyacrylonitrile nanofibers and cellulose nanocrystals showed a larger specific surface area and total pore volume.

[0099] Test Example 2:

[0100] The functional group composition of the polyacrylonitrile nanofiber membrane and the three-dimensional nanofiber composite aerogel was analyzed by a Fourier transform infrared spectrometer.

[0101] As shown in Figure 5 , compared with the polyacrylonitrile nanofiber membrane, the vibration peaks of the uncrosslinked three-dimensional nanofiber composite aerogel at 3343 cm -1 -OH, -NH, 1022 cm -1 C=C were stronger, indicating the successful introduction of cellulose nanocrystals and blocked isocyanate; in comparison, the vibration peaks of the crosslinked three-dimensional nanofiber composite aerogel at 3343 cm -1 , 1022 cm -1 were weakened, indicating that the blocked isocyanate reacted with the cellulose nanocrystals; and the vibration peaks of the three-dimensional nanofiber composite aerogel coated with polypyrrole at these two places were enhanced again, which was related to the successful introduction of polypyrrole.

[0102] Test Example 3:

[0103] The mechanical strength of the three-dimensional nanofiber composite aerogels prepared in Comparative Example 2 and Example 6 was compared by loading a 20 g weight.

[0104] As shown in A3 and B3 in FIGS. Figure 3 As shown in A3 and B3 in FIGS. The three-dimensional composite nanofiber aerogel (A3) with cellulose nanocrystals showed less deformation after loading a 20 g weight, indicating that the introduction of cellulose nanocrystals significantly improved the mechanical properties of the nanofiber aerogel. Therefore, the preparation scheme of the nanofiber composite aerogel proposed in the present application is beneficial to improving the mechanical strength of the material.

[0105] Test Example 4:

[0106] 10 mg of three-dimensional nanofiber composite aerogel was added to 5 mL of a mixed solution of 5 μg / mL dyes acid orange 7, acid red 14 and rhodamine B, and after shaking at room temperature for 6 h, the aerogel was removed with tweezers; then, HPLC-DAD was used to detect the acid orange 7, acid red 14 and rhodamine B in the solution before and after adsorption, and the adsorption efficiency of each aerogel for the three dyes was calculated.

[0107] Table 1 shows the test results of the aerogels in Examples 1-6, Comparative Example 1 and Comparative Example 2 on the adsorption performance of organic dyes. As shown in Table 1, compared with the aerogels without polypyrrole coating PCA-1 and PA-1 and without cellulose nanocrystals PPA-1 and PA-1, the composite aerogels PPCA-1-PPCA-6 have better comprehensive adsorption effect on the three dyes. The aerogels PCA-1 and PA-1 without polypyrrole coating have almost no adsorption effect on anionic dyes acid orange 7 and acid red 14, while after coating with polypyrrole, the adsorption effect of the aerogel on anionic dyes is significantly improved. In addition, the adsorption effect of the composite aerogel on cationic dyes is better than that of the aerogel without cellulose nanocrystals PPA-1 and without polypyrrole coating PCA-1. In summary, the three-dimensional nanofiber composite aerogel described in the examples of the present application can simultaneously achieve efficient removal of anionic dyes and cationic dyes by utilizing the synergistic effect of electrospun nanofibers, cellulose nanocrystals and polypyrrole.

[0108] Table 1 Adsorption efficiency of three-dimensional nanofiber composite aerogel on organic dyes

[0109]

[0110] In summary, the application discloses a preparation of nanofiber by electrospinning technology; the electrospinning nanofiber, cellulose nanocrystal, blocked isocyanate and water are mixed and homogenized to obtain a stable dispersion liquid, then the freezing shaping, freeze drying and thermal crosslinking treatment are sequentially performed; finally, the polymer nanoparticles are loaded on the surface of the above product to obtain a three-dimensional nanofiber composite aerogel with a porous network structure, good mechanical stability and excellent adsorption performance. The preparation method of the three-dimensional nanofiber composite aerogel is simple and operable, and can simultaneously and efficiently adsorb and separate anionic and cationic dyes, and has a great application prospect in the fields of treatment of industrial wastewater and remediation of water environment.

[0111] The above is only used for describing the technical idea of the application, and cannot be used to limit the protection scope of the application. Any modification made according to the technical idea of the application on the basis of the technical scheme falls within the protection scope of the claims of the application.

Claims

1. A method for preparing a three-dimensional nanofiber composite aerogel, characterized by, The method comprises the following steps: Step one: mixing electrospinning nanofibers, cellulose nanocrystals, blocked isocyanate and water, and then homogenizing to obtain a dispersion; the mass ratio of the electrospinning nanofibers to the cellulose nanocrystals is 1: (0.25 ~ 0.67); the total mass of the electrospinning nanofibers and the cellulose nanocrystals in the obtained dispersion accounts for 0.6% ~ 2.4% of the dispersion; Step two: sequentially performing freeze forming, freeze drying and thermal crosslinking on the above dispersion to obtain a crosslinked product of electrospinning nanofiber-cellulose nanocrystal composite aerogel; the freeze forming temperature is -80 ~ -40 ℃, and the freeze forming time is 30 ~ 60 min; the freeze drying temperature is -80 ~ -60 ℃, and the freeze drying time is 20 ~ 30 h; the thermal crosslinking temperature is 120 ~ 130 ℃, and the thermal crosslinking time is 1 ~ 2 h; Step three: loading nanoparticles on the above electrospinning nanofiber-cellulose nanocrystal composite aerogel to obtain a three-dimensional nanofiber composite aerogel; the loaded nanoparticles are at least one of polyaniline and polypyrrole.

2. The method for preparing a three-dimensional nanofiber composite aerogel according to claim 1, characterized in that, The electrospinning nanofibers in step one are prepared by mixing one or more of polyacrylonitrile, nylon, cellulose acetate and polyethyleneimine.

3. The method of claim 1, wherein the three-dimensional nanofiber composite aerogel is prepared by the steps of: The addition amount of the blocked isocyanate accounts for 10% ~ 30% of the total mass of the electrospinning nanofibers and the cellulose nanocrystals.

4. The method of claim 1, wherein the three-dimensional nanofiber composite aerogel is prepared by the steps of: In step one, the homogenization speed is 8000 ~ 15000 rpm, and the homogenization time is 5 ~ 20 min.

5. A three-dimensional nanofiber composite aerogel prepared by the method of any one of claims 1 ~ 4.

6. Application of the three-dimensional nanofiber composite aerogel of claim 5 as an organic dye adsorbent.

7. Use according to claim 6, wherein The organic dye includes anionic dyes and cationic dyes. The organic dye includes anionic dyes and cationic dyes.

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