阅读说明：本技术 一种表面包覆二氧化铈纳米层的聚酰亚胺纳米纤维膜及其制备方法 (Polyimide nanofiber membrane with surface coated with cerium dioxide nanolayer and preparation method thereof ) 是由 齐胜利 刘克凡 李小刚 田国峰 武德珍 于 2021-11-16 设计创作，主要内容包括：本发明提供了一种表面包覆二氧化铈纳米层的聚酰亚胺纳米纤维膜及其制备方法。首先采用静电纺丝法制备聚酰亚胺纳米纤维膜,并用碱性溶液进行表面刻蚀处理,经过酸化后制备表面羧基化的聚酰亚胺纳米纤维膜,然后将其置于稀氨水中进行铵化；再置于二氧化铈的前驱体溶液中反应,然后用过氧化氢处理,最后经高温热处理从而一步制得表面包覆二氧化铈纳米层的聚酰亚胺纳米纤维膜。二氧化铈纳米层的包覆改善了聚酰亚胺纳米纤维膜的力学性能、热尺寸稳定性、浸润性和耐高温性能。本发明的方法操作过程简单、易于流程化,生产效率高,制备的复合那纤维充分结合了聚酰亚胺和无机层的优势,在锂电池隔膜、催化、过滤、阻燃、除尘等领域具有广阔的应用前景。(The invention provides a polyimide nanofiber membrane with a surface coated with a cerium dioxide nano layer and a preparation method thereof. Firstly, preparing a polyimide nanofiber membrane by adopting an electrostatic spinning method, carrying out surface etching treatment by using an alkaline solution, preparing a polyimide nanofiber membrane with carboxylated surface after acidification, and then putting the polyimide nanofiber membrane into dilute ammonia water for ammonification; then placing the film in a precursor solution of cerium dioxide for reaction, then treating the film with hydrogen peroxide, and finally carrying out high-temperature heat treatment to prepare the polyimide nano-fiber film with the surface coated with the cerium dioxide nano-layer in one step. The coating of the cerium dioxide nano layer improves the mechanical property, the thermal dimension stability, the wettability and the high temperature resistance of the polyimide nano fiber membrane. The method has the advantages of simple operation process, easy process and high production efficiency, and the prepared composite fiber fully combines the advantages of polyimide and an inorganic layer, and has wide application prospect in the fields of lithium battery diaphragms, catalysis, filtration, flame retardance, dust removal and the like.)

1. A preparation method of a polyimide nanofiber membrane with a surface coated with a cerium dioxide nanolayer is characterized by comprising the following steps:

a: dissolving cerium salt in water to obtain a precursor solution of cerium dioxide with the concentration of 0.01-3 mol/L;

b: preparing 3-25 wt% polyamide acid solution from polybasic acid anhydride and polybasic amine through solution condensation polymerization, preparing polyamide acid nanofiber membrane by using an electrostatic spinning method, and performing heat treatment on the polyamide acid nanofiber membrane to obtain the polyimide nanofiber membrane which is completely imidized;

c: b, placing the polyimide nanofiber membrane obtained by the treatment in the step B in an alkaline solution, carrying out surface hydrolysis and ring opening on the polyimide nanofiber membrane, then carrying out acidification in a dilute acid solution to obtain a polyimide nanofiber membrane with a carboxylated surface, and then placing the polyimide nanofiber membrane in a dilute ammonia solution for treatment to obtain a polyimide nanofiber membrane with an aminated surface;

d: placing the polyimide nano-fiber membrane obtained by the treatment in the step C in the precursor solution of cerium dioxide obtained in the step A for reaction, taking out the polyimide nano-fiber membrane, washing the polyimide nano-fiber membrane with deionized water, placing the cleaned polyimide nano-fiber membrane in a hydrogen peroxide solution, and reacting for 1-3 hours;

e: and D, carrying out gradient heating treatment on the nanofiber membrane obtained by the treatment in the step D to obtain the polyimide nanofiber membrane with the surface coated with the cerium dioxide nanolayer.

2. The method according to claim 1, wherein the cerium salt in step a is cerium nitrate, cerium chloride, ammonium cerium nitrate and cerium carbonate, and the concentration of cerium ions in the precursor solution of cerium oxide is preferably 0.05 to 2.5mol/L, particularly preferably 0.1 to 2 mol/L.

3. The preparation method according to claim 1, wherein the alkaline solution in step C is an aqueous solution of one or a mixture of sodium hydroxide, potassium hydroxide and lithium hydroxide, and the concentration of the alkaline solution is 0.5-2 mol/L; the dilute acid solution is any one of acetic acid, trifluoroacetic acid, formic acid, hydrochloric acid and sulfuric acid, and the pH value is adjusted to 5-6; the pH value of the dilute ammonia water is adjusted to 9-13.

4. The method according to claim 1, wherein in step D, the polyamic acid nanofiber membrane is treated in the precursor solution of ceria for 1min to 3h, preferably 2min to 2h, and particularly preferably 10min to 1 h; the concentration of hydrogen peroxide added is 1% -20%, preferably 2% -15%, particularly preferably 3% -10%; the reaction time is 0.5-30min, preferably 1-25 min.

5. The process according to claim 1, wherein the heat treatment time in step E is 0.1 to 5 hours, preferably 1 to 4 hours, the heat treatment conditions are from room temperature to 250 to 400 ℃, preferably 300 to 350 ℃, and the heating rate is 1 to 20 ℃/min, preferably 2 to 10 ℃/min.

6. A polyimide nanofiber membrane having a surface coated with a ceria nano-layer, prepared by the method as set forth in any one of claims 1 to 5.

Technical Field

The invention belongs to the technical field of polyimide nano fiber membranes, and relates to a preparation method of a polyimide nano fiber membrane with a surface coated with a cerium dioxide nano layer and a prepared polyimide nano fiber membrane with a surface coated with a cerium dioxide nano layer.

Background

Since 1991, lithium ion batteries have attracted extensive attention and gained a lot of applications due to their characteristics of high voltage, small size, high energy density, long cycle life, rapid charge and discharge, etc. The nobel chemical prize in 2019 awards scientists who have made outstanding contributions to lithium ion development, and the appearance of lithium ion batteries has changed the life style of people. Battery separators enjoy the reputation of battery "third electrode" and play an important role in the production and use of batteries. This is because various characteristics such as charge and discharge performance, cycle performance, rate performance, and safety performance of the battery are determined by the performance of the separator, and the performance of the separator plays an important role in improving the overall performance of the battery. The separator mainly functions to separate the positive and negative poles of the battery to prevent the battery from being short-circuited due to the contact of the two poles. In addition, the membrane can act as a channel for ions. The polyolefin membrane has good mechanical properties and moderate porosity, but has some problems due to the structural characteristics of the polyolefin membrane: (1) due to the nonpolar nature, the electrolyte has poor wettability and low liquid absorption rate, so that the ionic conductivity and internal resistance of the battery are low, and the production efficiency of the battery is influenced to a certain extent by waiting for the electrolyte to infiltrate the diaphragm after the electrolyte is injected in the production process of the battery. (2) The softening temperature and the melting point (PP is 165 ℃, PE is 135 ℃) of the polyolefin diaphragm are low, and the battery can easily generate local high temperature in the process of high-power charging and discharging, so that the diaphragm is melted and broken, the internal short circuit occurs when the positive electrode and the negative electrode are in contact, and finally the safety accident of the battery is induced. Therefore, the development of a novel lithium ion battery separator with high thermal stability and high electrolyte wettability is an urgent need in the field of lithium ion battery research.

The principle of the electrostatic spinning technology is as follows: polymer fluid is electrostatically atomized to separate a tiny polymer jet which can run for a long distance. During the movement, as the solvent evaporates, it eventually solidifies into fibers. The liquid drop on the needle head changes from spherical shape to cone shape under the action of electric field, the cone is called as "Taylor cone", the Taylor cone extends from the needle point to polymer fiber filament [8,9] with nanometer diameter, and forms a nanometer fiber film with a certain thickness after a period of time. The fiber morphology is comprehensively influenced by the evaporation rate of the solution, the concentration of the polymer, the spinning distance, the accelerating voltage and the like, and compared with other manufacturing processes, the electrostatic spinning film has smaller thickness and diameter and is more controllable. At present, the electrostatic spinning process can be used for preparing nano fiber materials with various shapes such as coaxial fibers, hollow fibers, porous fibers and the like, and has wide application prospects in the industries of filtration, medical treatment, catalysis, energy and the like.

Polyimide (PI) is a high-performance polymer, the main chain of which contains imide rings, has excellent high and low temperature resistance, excellent mechanical properties, good chemical stability and superior dielectric and irradiation resistance, is one of organic high-molecular materials with the best comprehensive performance, is called as 'solving the problem' and is widely applied to the fields of aviation, aerospace, microelectronics, advanced composite materials and the like. According to the difference of main chain structures, polyimide can be classified into aliphatic PI and aromatic PI, and the aromatic PI has a benzene ring structure on the main chain, so that the comprehensive performance of the polyimide is far better than that of aliphatic polyimide, and the polyimide becomes a high-performance polymer with the highest application degree at present. The polyimide nanofiber membrane prepared by the electrostatic spinning method has the performances of high porosity, flexibility and the like besides the performances of the polyimide, so that the polyimide nanofiber membrane becomes one of the optimal choices of a new-generation high-temperature-resistant and high-safety lithium ion battery diaphragm. The inorganic ceramic is coated on the surface of the polyimide nanofiber, so that the temperature resistance, flame retardance, wettability and strength of the polyimide nanofiber membrane can be further improved, the defect that the inorganic ceramic lacks flexibility is overcome, and the preparation of the polyimide fiber flexible membrane coated with the inorganic ceramic is realized. As a novel ceramic material, the cerium oxide has excellent high-temperature resistance, infiltration performance and flame retardant performance. The invention adopts the organic polymer material polyimide fiber as the matrix and combines with the inorganic material cerium dioxide to prepare the cerium dioxide coated polyimide composite nanofiber membrane, establishes a new method and realizes the controllable coating of the inorganic ceramic layer of the cerium dioxide on the polyimide nanofiber. The composite nanofiber membrane has excellent high temperature resistance, flame retardance, wettability, flexibility, strength and porosity, and can be used as a novel lithium ion battery diaphragm material.

Disclosure of Invention

The invention provides a polyimide nano fiber membrane with a surface coated with a cerium dioxide nano layer and a preparation method thereof.

The polyimide nano fiber membrane with the surface coated with the cerium dioxide nano layer, also called as a polyimide/cerium dioxide composite nano fiber membrane, is characterized in that the surface of the polyimide nano fiber membrane is provided with the cerium dioxide layer, the thickness of the polyimide nano fiber membrane is 5-60 mu m, the diameter of fibers in the polyimide nano fiber membrane is 10-600nm, and the thickness of the cerium dioxide layer is 2-300 nm.

Further, the porosity of the polyimide nanofiber membrane with the surface coated with the cerium dioxide nano-layer is 70% -95%, and preferably 80% -92%.

Further, the thickness of the polyimide nanofiber membrane is preferably 15 to 20 μm.

Further, the diameter of the fiber in the polyimide nanofiber membrane is preferably 20-700nm, and the thickness of the cerium oxide layer is preferably 5-100 nm.

A preparation method of a polyimide nanofiber membrane with a surface coated with a cerium dioxide nanolayer comprises the following steps:

a: dissolving cerium salt in water to obtain a precursor solution of cerium dioxide with the concentration of 0.01-3 mol/L;

b: preparing 3-25 wt% polyamide acid solution from polybasic acid anhydride and polybasic amine through solution condensation polymerization, preparing polyamide acid nanofiber membrane by using an electrostatic spinning method, and performing heat treatment on the polyamide acid nanofiber membrane to obtain the polyimide nanofiber membrane which is completely imidized;

c: putting the polyimide nano-fiber membrane in an alkaline solution for a certain time to hydrolyze and open the surface of the polyimide nano-fiber membrane, then acidifying the polyimide nano-fiber membrane in a dilute acid solution to obtain a polyimide nano-fiber membrane with surface carboxylation, and then putting the polyimide nano-fiber membrane in a dilute ammonia solution with a certain concentration to treat the polyimide nano-fiber membrane with surface ammonification;

d: placing the polyimide nano-fiber membrane obtained by the treatment in the step C in the precursor solution of cerium dioxide obtained in the step A for reaction for a certain time, taking out the polyimide nano-fiber membrane, washing the polyimide nano-fiber membrane with deionized water, placing the polyimide nano-fiber membrane in a hydrogen peroxide solution, and reacting for 1-3 hours;

e: and D, carrying out gradient heating treatment on the nanofiber membrane obtained by the treatment in the step D to obtain the polyimide nanofiber membrane with the surface coated with the cerium dioxide nanolayer.

Further, the cerium salt in step A is cerium nitrate, cerium chloride, ammonium cerium nitrate and cerium carbonate, and the concentration of cerium ions in the precursor solution of cerium oxide is preferably 0.05 to 2.5mol/L, and particularly preferably 0.1 to 2 mol/L.

Further, the electrostatic spinning in step B is a special fiber manufacturing process, and the polymer solution or melt is subjected to jet spinning in a strong electric field. Under the action of the electric field, the liquid drop at the needle head changes from a spherical shape to a conical shape (i.e. a Taylor cone) and fiber filaments are obtained by extending from the tip of the cone, and in this way, polymer filaments with nanometer-scale diameters can be produced. The invention takes the polyamic acid solution as the electrostatic spinning solution, prepares the polyamic acid solution into the nano-fiber through electrostatic spinning, in the process, besides the influence of the spinning concentration on the nanofiber, the necessary spinning parameters are one of the reasons for whether the electrostatic spinning is successful, taking the needle spinning as an example, the voltage is 20-30KV, the propelling quantity is 0.3-0.7 mL/h, an 18-gauge needle head is selected, and the speed of a receiving roller is 300-600 rpm.

Further, the alkaline solution in the step C is an aqueous solution of one or a mixture of several of sodium hydroxide, potassium hydroxide and lithium hydroxide, and the concentration of the alkaline solution is 0.5-2 mol/L; the dilute acid solution is any one of acetic acid, trifluoroacetic acid, formic acid, hydrochloric acid and sulfuric acid, and the pH value is adjusted to 5-6; the pH value of the dilute ammonia water is adjusted to 9-13.

Further, in the step D, the treatment time of the polyamic acid nanofiber membrane in the precursor solution of cerium dioxide is 1min-3h, preferably 2min-2h, and particularly preferably 10min-1 h; the concentration of hydrogen peroxide added is 1% -20%, preferably 2% -15%, particularly preferably 3% -10%; the reaction time is 0.5-30min, preferably 1-25 min.

Furthermore, the heat treatment time of the step E is 0.1-5h, preferably 1-4h, the heat treatment condition is that the temperature is increased from room temperature to 250-400 ℃, preferably 300-350 ℃, and the temperature increasing rate is 1-20 ℃/min, preferably 2-10 ℃/min.

Compared with the prior art, the invention has the following excellent effects:

1. the preparation method establishes a new method, takes the polyimide nano-fiber as a substrate, utilizes a new idea of ammonification after surface alkaline hydrolysis and acidification, and directly treats the composite nano-fiber membrane with hydrogen peroxide after complexing cerium dioxide precursor ions, namely, the preparation of the composite nano-fiber membrane coated with the cerium dioxide inorganic ceramic layer is realized in one step, the process link of post-treatment by finally adding ammonia water in the traditional cerium dioxide generation process is omitted, the steps are simpler, and the controllability is strong.

2. The polyimide coaxial coating cerium dioxide nanofiber membrane prepared by the invention has the advantages of excellent high temperature resistance (capable of bearing high temperature of 500 ℃), thermal dimensional stability (shrinkage rate of 0 at 310 ℃), wettability (a contact angle with electrolyte is about 13 ℃), flame retardance and the like, high porosity (the highest contact angle can reach 92%), high strength (the highest contact angle can reach 50MPa) and the like, combines the dimensional performance of polyimide and the flame retardance and wettability of cerium dioxide ceramic, has the potential of serving as a novel high-performance lithium battery diaphragm, and is a novel organic-inorganic composite material.

3. The polyimide nanofiber membrane coaxially coated with the inorganic ceramic can be prepared by utilizing the characteristic that active groups contained on the surface of PI subjected to alkaline hydrolysis ring opening can complex cations, and compared with a multilayer diaphragm prepared by a coating method, the nanofiber membrane has a more uniform fiber structure, lighter weight and better electrolyte wettability.

4. The process equipment requirement for preparing the polyimide coaxial coating cerium dioxide nano-fiber membrane is easy to meet, the process is simple, the operation is simple and convenient, the repeatability is high, and the controllable preparation of nano-fiber membranes with different nano-fiber diameters and different thicknesses and the controllable coating of cerium dioxide on the surface of the fiber membrane can be realized by adjusting the process parameters.

Drawings

FIG. 1 is a scanning electron micrograph of a polyimide/ceria composite nanofiber membrane prepared according to example 1, the left image being 30000 times and the right image being 1000 times at magnification;

FIG. 2 is a scanning electron micrograph of a polyimide/ceria composite nanofiber membrane prepared according to example 2, the left image of the magnification being 20000 times, and the right image being 1000 times;

FIG. 3 is a scanning electron micrograph of a polyimide/ceria composite nanofiber membrane prepared according to example 3, the left image of the magnification being 20000 times, and the right image being 1000 times;

fig. 4 is a scanning electron microscope image of the polyimide/ceria composite nanofiber membrane prepared according to example 4, with a magnification of 20000 times on the left and 2000 times on the right.

Fig. 5 is a scanning electron microscope image of the polyimide/ceria composite nanofiber membrane prepared according to example 5, with a magnification of 30000 times on the left and 2000 times on the right.

FIG. 6 is a scanning electron micrograph of a polyimide nanofiber membrane prepared as in example 1, at 50000 times on the left and 2000 times on the right at magnification.

FIG. 7 is a scanning electron micrograph of ash obtained by calcining the polyimide/ceria composite nanofiber membrane prepared in example 1 at a high temperature of 900 ℃ for 1.5 hours, the left image being 30000 times and the right image being 2000 times.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Example 1

Preparing a PMDA/ODA system polyamide acid nano-fiber membrane, performing thermal imidization to obtain a polyimide nano-fiber membrane, firstly etching the polyimide nano-fiber membrane in 0.1mol/L potassium hydroxide solution, adding 7ml of glacial acetic acid, dripping 10 drops of dilute ammonia water, then placing the polyimide nano-fiber membrane in 1mol/L cerium dioxide precursor solution, adding 5ml of hydrogen peroxide solution, and finally performing thermal treatment to obtain the polyimide/cerium dioxide composite nano-fiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; placing the obtained polyamide acid fiber membrane in a heating furnace, and heating at a speed of 2 ℃/minGradually heating to 300 ℃ and keeping for 2h to prepare the polyimide nanofiber membrane. (2) 20ml of deionized water and 25ml of absolute ethyl alcohol are weighed and mixed evenly in a beaker. 14.68g of cerium nitrate is weighed, added into a mixed solvent of ethanol and deionized water, and stirred to be fully dissolved, so as to obtain a precursor solution of cerium dioxide. (3) The polyimide nano fiber membrane is placed in 0.1mol/L potassium hydroxide solution for etching for 1min, and then placed in 1mol/L cerium dioxide precursor solution for 1 h. (4) Adding 5ml of glacial acetic acid to adjust the pH value to 5, then adding 10 drops of dilute ammonia water to adjust the pH value to 9 (5), and then adding measured 7.87ml of H₂O₂Fully reacting for 20min, taking out and airing. (5) And (3) placing the nanofiber membrane obtained by the previous step in a drying oven at 400 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with cerium dioxide, wherein the morphology of the obtained fiber is shown in figure 1. The polyimide/ceria composite nanofiber membrane prepared in example 1 had a shrinkage of 0 and a tensile strength of 35.9MPa when it was held at 400 ℃ for 1 hour.

Comparative example 1

Preparing the PMDA/ODA system polyamide acid nanofiber membrane, and performing thermal imidization to obtain the polyimide nanofiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 350 ℃ at the heating speed of 4 ℃/min, and keeping for 1h to obtain the polyimide nanofiber membrane. The polyimide nanofiber membrane prepared in comparative example 1 has a shrinkage of 0.3% and a tensile strength of 13.3MPa when it is incubated at 400 ℃ for 1 hour.

Example 2

Preparing a PMDA/ODA system polyamide acid nano-fiber membrane, performing thermal imidization to obtain a polyimide nano-fiber membrane, firstly etching the polyimide nano-fiber membrane in 0.1mol/L potassium hydroxide solution, adding 7ml of glacial acetic acid, dripping 10 drops of dilute ammonia water, then placing the polyimide nano-fiber membrane in 1mol/L cerium dioxide precursor solution, adding 5ml of hydrogen peroxide solution, and finally performing thermal treatment to obtain the polyimide/cerium dioxide composite nano-fiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2 hours to obtain the polyimide nanofiber membrane. (2) 20ml of deionized water and 25ml of absolute ethyl alcohol are weighed and mixed evenly in a beaker. 14.68g of cerium nitrate is weighed, added into a mixed solvent of ethanol and deionized water, and stirred to be fully dissolved, so as to obtain a precursor solution of cerium dioxide. (3) The polyimide nano fiber membrane is placed in 0.1mol/L potassium hydroxide solution for etching for 30s, and then placed in 1mol/L cerium dioxide precursor solution for 1 h. (4) Adding 5ml of glacial acetic acid to adjust the pH value to 5, then adding 10 drops of dilute ammonia water, adjusting the pH value to 9 (5), then adding 7.87ml of H2O2, fully reacting for 20min, taking out and airing. (5) And (3) placing the nanofiber membrane obtained by the previous step in a drying oven at 400 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with cerium dioxide, wherein the morphology of the obtained fiber is shown in figure 2. The polyimide/ceria composite nanofiber membrane prepared in example 2 had a shrinkage of 0 and a tensile strength of 33.6MPa when it was incubated at 400 ℃ for 1 hour.

Comparative example 2

Preparing the PMDA/ODA system polyamide acid nanofiber membrane, and performing thermal imidization to obtain the polyimide nanofiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 350 ℃ at the heating speed of 4 ℃/min, and keeping for 1h to obtain the polyimide nanofiber membrane. The polyimide nanofiber membrane prepared in comparative example 2 has a shrinkage of 0.3% and a tensile strength of 13.3MPa when it is incubated at 400 ℃ for 1 hour.

Example 3

Preparing a PMDA/ODA system polyamide acid nano-fiber membrane, performing thermal imidization to obtain a polyimide nano-fiber membrane, firstly etching the polyimide nano-fiber membrane in 0.1mol/L potassium hydroxide solution, adding 7ml of glacial acetic acid, dripping 10 drops of dilute ammonia water, then placing the polyimide nano-fiber membrane in 1mol/L cerium dioxide precursor solution, adding 5ml of hydrogen peroxide solution, and finally performing thermal treatment to obtain the polyimide/cerium dioxide composite nano-fiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; temperature of spinningDegree: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2 hours to obtain the polyimide nanofiber membrane. (2) 20ml of deionized water and 25ml of absolute ethyl alcohol are weighed and mixed evenly in a beaker. 14.68g of cerium nitrate is weighed, added into a mixed solvent of ethanol and deionized water, and stirred to be fully dissolved, so as to obtain a precursor solution of cerium dioxide. (3) The polyimide nano fiber membrane is placed in 0.1mol/L potassium hydroxide solution for etching for 10s, and then placed in 1mol/L cerium dioxide precursor solution for 1 h. (4) Adding 5ml of glacial acetic acid to adjust the pH value to 5, then adding 10 drops of dilute ammonia water to adjust the pH value to 9 (5), and then adding measured 7.87ml of H₂O₂Fully reacting for 20min, taking out and airing. (5) And (3) placing the nanofiber membrane obtained by the previous step in a drying oven at 400 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with cerium dioxide, wherein the morphology of the obtained fiber is shown in figure 3. The polyimide/ceria composite nanofiber membrane prepared in example 3 had a shrinkage of 0 and a tensile strength of 30.9MPa when it was incubated at 400 ℃ for 1 hour.

Comparative example 3

Preparing the PMDA/ODA system polyamide acid nanofiber membrane, and performing thermal imidization to obtain the polyimide nanofiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 350 ℃ at the heating speed of 4 ℃/min, and keeping for 1h to obtain the polyimide nanofiber membrane. The polyimide nanofiber membrane prepared in comparative example 3 has a shrinkage of 0.3% and a tensile strength of 13.3MPa when it is incubated at 400 ℃ for 1 hour.

Example 4

Preparing a PMDA/ODA system polyamide acid nano-fiber membrane, performing thermal imidization to obtain a polyimide nano-fiber membrane, firstly placing the polyimide nano-fiber membrane in 1mol/L potassium hydroxide solution for etching, adding 7ml glacial acetic acid, dripping 10 drops of dilute ammonia water, then placing the polyimide nano-fiber membrane in 1mol/L cerium dioxide precursor solution, adding 5ml hydrogen peroxide solution, and finally performing thermal treatment to obtain the polyimide/cerium dioxide composite nano-fiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2 hours to obtain the polyimide nanofiber membrane. (2) 20ml of deionized water and 25ml of absolute ethyl alcohol are weighed and mixed evenly in a beaker. 14.68g of cerium nitrate is weighed, added into a mixed solvent of ethanol and deionized water, and stirred to be fully dissolved, so as to obtain a precursor solution of cerium dioxide. (3) The polyimide nano fiber membrane is placed in 0.1mol/L potassium hydroxide solution for etching for 10s, and then placed in 1mol/L cerium dioxide precursor solution for 1 h. (4) Adding 5ml of glacial acetic acid to adjust the pH value to 5, then adding 10 drops of dilute ammonia water to adjust the pH value to 9 (5), and then adding measured 7.87ml of H₂O₂Fully reacting for 20min, taking out and airing. (5) The last step is processed to obtainAnd (3) placing the obtained nanofiber membrane in a drying oven at 400 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with cerium dioxide, wherein the morphology of the obtained fiber is shown in figure 4. The polyimide/ceria composite nanofiber membrane prepared in example 4 had a shrinkage of 0 and a tensile strength of 30.6MPa when it was incubated at 400 ℃ for 1 hour.

Comparative example 4

Preparing the PMDA/ODA system polyamide acid nanofiber membrane, and performing thermal imidization to obtain the polyimide nanofiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 350 ℃ at the heating speed of 4 ℃/min, and keeping for 1h to obtain the polyimide nanofiber membrane. The polyimide nanofiber membrane prepared in comparative example 1 has a shrinkage of 0.3% and a tensile strength of 13.3MPa when it is incubated at 400 ℃ for 1 hour.

Example 5

Preparing a PMDA/ODA system polyamide acid nano-fiber membrane, performing thermal imidization to obtain a polyimide nano-fiber membrane, firstly etching the polyimide nano-fiber membrane in 0.5mol/L potassium hydroxide solution, adding 7ml of glacial acetic acid, dripping 10 drops of dilute ammonia water, then placing the polyimide nano-fiber membrane in 1mol/L cerium dioxide precursor solution, adding 5ml of hydrogen peroxide solution, and finally performing thermal treatment to obtain the polyimide/cerium dioxide composite nano-fiber membrane. (1) 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1 are weighed, the ODA is completely dissolved in 30ml of N, N-Dimethylformamide (DMF) solvent, the mechanical stirring is carried out, and ice water is added to the mixture after the ODA is completely dissolved in the DMFUnder the bath condition, PMDA is added step by step to obtain polyamic acid solution with moderate viscosity, the polyamic acid solution is filled into a 20ml syringe after being mechanically stirred for 2 hours, and the polyamic acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 2 hours to obtain the polyimide nanofiber membrane. (2) 20ml of deionized water and 25ml of absolute ethyl alcohol are weighed and mixed evenly in a beaker. 14.68g of cerium nitrate is weighed, added into a mixed solvent of ethanol and deionized water, and stirred to be fully dissolved, so as to obtain a precursor solution of cerium dioxide. (3) The polyimide nano fiber membrane is placed in 0.1mol/L potassium hydroxide solution for etching for 10s, and then placed in 1mol/L cerium dioxide precursor solution for 1 h. (4) Adding 5ml of glacial acetic acid to adjust the pH value to 5, then adding 10 drops of dilute ammonia water to adjust the pH value to 9 (5), and then adding measured 7.87ml of H₂O₂Fully reacting for 20min, taking out and airing. (5) And (3) placing the nanofiber membrane obtained by the previous step in a drying oven at 400 ℃ for heat preservation for 2h to obtain the polyimide nanofiber membrane with the surface coated with cerium dioxide, wherein the morphology of the obtained fiber is shown in figure 5. The polyimide/ceria composite nanofiber membrane prepared in example 5 had a shrinkage of 0 and a tensile strength of 33.9MPa when it was incubated at 400 ℃ for 1 hour.

Comparative example 5

Preparing the PMDA/ODA system polyamide acid nanofiber membrane, and performing thermal imidization to obtain the polyimide nanofiber membrane. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4, 4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, filling the polyamic acid solution into a 20ml injector, and preparing the polyamic acid fiber membrane by using an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are spinning voltage: 29 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 18; receiving roller rotating speed: 500 rpm; receiving distance: 20 cm. Placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; and (3) placing the obtained polyamide acid fiber membrane in a heating furnace, gradually heating to 350 ℃ at the heating speed of 4 ℃/min, and keeping for 1h to obtain the polyimide nanofiber membrane. The polyimide nanofiber membrane prepared in comparative example 1 has a shrinkage of 0.3% and a tensile strength of 13.3MPa when it is incubated at 400 ℃ for 1 hour.

Experimental tests show that, by comparing the scanning electron microscope images of the pure polyimide nanofiber membrane in fig. 6 with the scanning electron microscope images of the ceria-coated polyimide composite nanofiber membrane in fig. 1 to 5, the fiber surface of the pure polyimide nanofiber membrane can be clearly seen to be smooth, and the rough surface coating structure can be observed on the surface of the composite nanofiber, namely, the ceria nano layer is tightly coated on the surface of the polyimide fiber. FIG. 7 is a scanning electron microscope image of ash obtained by calcining the ceria-coated polyimide composite nanofiber membrane prepared in example 1 at a high temperature of 900 ℃ for 1.5 hours. The existence of ceria is demonstrated by the observation that there is still material remaining and the morphology of the fibers after high temperature calcination at 900 ℃ is shown in the figures, and the phenomena of figures 1-7 show that we have successfully prepared polyimide/ceria composite nanofiber membranes.