阅读说明：本技术 静电纺碳纳米纤维的制备方法 (Preparation method of electrostatic spinning carbon nanofiber ) 是由 方剑 赵浩阅 宋贝贝 于 2021-08-17 设计创作，主要内容包括：本发明公开了一种静电纺碳纳米纤维的制备方法,包括以下步骤：将聚丙烯腈、微波吸收剂和有机溶剂混合均匀,形成纺丝液,其中,所述纺丝液中聚丙烯腈的含量为8-12wt％,聚丙烯腈和微波吸收剂的质量比为1：(0.1-0.3)。将所述纺丝液进行静电纺丝,得到纳米纤维膜。将所述纳米纤维膜进行热处理,以使所述纳米纤维膜中的聚丙烯腈预氧化,从而得到碳纳米纤维前驱体。将所述碳纳米纤维前驱体在惰性气体氛围中进行微波辐照加热,使得所述碳纳米纤维前驱体中预氧化后的聚丙烯腈碳化,制得碳纳米纤维。本发明制备方法工艺简单、易操作,减少了热传导对能量交换和反应程度的缓解影响,制备过程耗时短,耗能少,工艺绿色环保；生产成本低,有利于工业化批量生产静电纺碳纳米纤维。(The invention discloses a preparation method of electrostatic spinning carbon nanofiber, which comprises the following steps: uniformly mixing polyacrylonitrile, a microwave absorbent and an organic solvent to form a spinning solution, wherein the content of polyacrylonitrile in the spinning solution is 8-12 wt%, and the mass ratio of polyacrylonitrile to the microwave absorbent is 1: (0.1-0.3). And carrying out electrostatic spinning on the spinning solution to obtain the nanofiber membrane. And carrying out heat treatment on the nanofiber membrane to preoxidize polyacrylonitrile in the nanofiber membrane, thereby obtaining the carbon nanofiber precursor. And (3) carrying out microwave irradiation heating on the carbon nanofiber precursor in an inert gas atmosphere to carbonize the pre-oxidized polyacrylonitrile in the carbon nanofiber precursor, thereby preparing the carbon nanofiber. The preparation method has simple process and easy operation, reduces the alleviation influence of heat conduction on energy exchange and reaction degree, has short time consumption and low energy consumption in the preparation process, and has green and environment-friendly process; the production cost is low, and the method is favorable for industrial batch production of the electrostatic spinning carbon nanofibers.)

1. The preparation method of the electrostatic spinning carbon nanofiber is characterized by comprising the following steps:

uniformly mixing polyacrylonitrile, a microwave absorbent and an organic solvent to form a spinning solution, wherein the content of polyacrylonitrile in the spinning solution is 8-12 wt%, and the mass ratio of polyacrylonitrile to the microwave absorbent is 1 (0.1-0.3);

performing electrostatic spinning on the spinning solution to obtain a nanofiber membrane;

carrying out heat treatment on the nanofiber membrane to preoxidize polyacrylonitrile in the nanofiber membrane so as to obtain a carbon nanofiber precursor;

and carrying out microwave irradiation heating on the carbon nanofiber precursor in an inert gas atmosphere to carbonize the pre-oxidized polyacrylonitrile in the carbon nanofiber precursor.

2. The method of preparing electrospun carbon nanofibers according to claim 1, wherein the polyacrylonitrile has a weight average molecular weight of 9-25 ten thousand.

3. The method of claim 1, wherein the microwave absorber comprises one of conductive carbon black, activated carbon, carbon nanotubes, and reduced graphene oxide.

4. The method of claim 1, wherein the organic solvent comprises one or more of nitrogen dimethyl formamide, nitrogen dimethyl acetamide, and dimethyl sulfoxide.

5. The method of preparing electrospun carbon nanofibers according to claim 1, wherein the electrospinning conditions comprise: the receiving distance is 10-20 cm; the advancing speed is 0.5-1 mL/h; the voltage is 12-18 kV; the rotating speed of the roller is 300-1000 rpm.

6. The method for preparing electrospun carbon nanofibers according to claim 1, wherein in the step of "heat treating the nanofiber membrane", the heat treatment temperature is 200-280 ℃, the time is 60-120min, and the temperature rise rate is 1-5 ℃/min.

7. The method for preparing electrospun carbon nanofibers according to claim 1, wherein the microwave irradiation heating power is 0.8-1.4 kW; in the microwave irradiation heating process, the temperature of the carbon nanofiber precursor is controlled to be 800-1200 ℃; the microwave irradiation heating time is 10-30 min.

Technical Field

The invention belongs to the technical field of carbon material preparation, and particularly relates to a method for quickly and efficiently preparing electrostatic spinning carbon nanofibers based on a microwave irradiation heating technology.

Background

The carbon nanofiber is a fibrous nano carbon material formed by coiling a plurality of graphite sheets, the diameter of the fibrous nano carbon material is generally 10-500nm, the length of the fibrous nano carbon material is distributed in a range of 0.5-100 mu m, and the fibrous nano carbon material is a one-dimensional carbon material between a carbon nanotube and common carbon fiber. Carbon nanofibers are widely used in the fields of adsorption, filtration, structural reinforcement materials, hydrogen storage, catalysis, energy storage and conversion and the like due to excellent physical and mechanical properties and chemical stability, such as high specific surface area, high length-diameter ratio, high conductivity, low density, high specific modulus, high specific strength, good thermal stability and the like, and attract people's attention.

At present, methods for preparing carbon nanofibers mainly include chemical vapor deposition methods, template methods, electrostatic spinning methods, and the like.

The carbon nano-fiber synthesized by the chemical vapor deposition method has the problem that the pipe diameter uniformity is difficult to control. The chemical vapor deposition method designs the removal of the catalyst, and the removal of the catalyst can damage the fiber structure, and the process has poor expandability and the like.

The template method has complex preparation process, high cost and small yield.

The electrospinning method is favored because of its simple equipment, easy operation, low cost and the ability to continuously produce ultrafine fibers having diameters of several tens of nanometers to several micrometers. Obtaining nanometer fiber protofilament by electrostatic spinning technology, and then obtaining the carbon nanometer fiber by pre-oxidation treatment and carbonization process. Therefore, the high-efficiency control of the diameter and the length of the fiber can be realized by adjusting the spinning parameters, and the optimization of various physical, mechanical and chemical properties of the fiber can also be realized by adjusting the carbonization temperature.

Chongqing et al, the university of Fujian, prepares polyvinyl chloride (PVC) -based carbon nanofibers by utilizing an electrostatic spinning technology in cooperation with a heat treatment process. (Qianqingong et al, a preparation method of PVC-based carbon nanofiber, publication No. CN103409852B) the spinning solution containing PVC is firstly electro-spun into a precursor of PVC-based carbon nanofiber, pre-oxidized in a muffle furnace and then placed in a tube furnace, and calcined for 1-3h at 600-1200 ℃ at the heating rate of 2 ℃/min in the inert gas atmosphere, and finally the PVC-based carbon nanofiber is obtained. Similarly, Wangxinyu et al, university of Tianjin industry, prepares a crosslinked porous carbon nanofiber by utilizing electrostatic spinning in cooperation with a high-temperature carbonization process. (Wangxiangyu et al, a cross-linked porous carbon nanofiber and a preparation method thereof, publication No. CN109082731B) after the electrostatic spinning polyacrylonitrile/linear phenolic resin nanofiber is pre-oxidized, the fiber is carbonized for 1-2h at the temperature of 800-1200 ℃ at the heating rate of 1-5 ℃/min, and finally the specific area is up to 994m²Per g of crosslinked porous carbon nanofibers.

It should be noted that although the electrostatic spinning technology has many advantages for preparing carbon nanofibers, the carbon nanofiber precursor often has the disadvantages of long preparation period, high cost, environmental unfriendliness and the like due to slow temperature rise rate and long annealing time in the high-temperature carbonization process of the traditional tube furnace, and is not favorable for the rapid preparation and further large-scale application of carbon nanofibers.

The heating mode of the conventional tube furnace is to achieve heating by radiating heat of the electric resistance wire to the surface of the heating object. In this process, both the target product and its surrounding environment are heated simultaneously, i.e. this is an overall heating process. This results in a slow rate of temperature rise and requires a long heating time to achieve uniform heating.

Microwave irradiation heating is a local heating method, and is a technology for directly converting electromagnetic energy into heat energy in an irradiation material to realize rapid heating, so that the microwave irradiation heating has ultrahigh heating rate and uniform heating environment, and the energy and time utilization is more efficient. However, the electrospun carbon nanofiber precursor materials, such as polyacrylonitrile-based nanofibers, pitch-based nanofibers, and viscose-based nanofibers, have weak microwave absorption capacity and are difficult to carbonize rapidly.

Based on the above, a rapid, efficient, environment-friendly and low-cost carbonization method is urgently needed to be developed, and the method has important significance for realizing industrialized mass production of the electrospun carbon nanofiber.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides the preparation method of the electrostatic spinning carbon nanofiber, which has the advantages of simple process, easy operation, reduction of the alleviation influence of heat conduction on energy exchange and reaction degree, short time consumption in the preparation process, low energy consumption and green and environment-friendly process; the production cost is low, and the method is favorable for industrial batch production of the electrostatic spinning carbon nanofibers.

The invention discloses a preparation method of electrostatic spinning carbon nanofiber, which comprises the following steps:

uniformly mixing polyacrylonitrile, a microwave absorbent and an organic solvent to form a spinning solution, wherein the content of polyacrylonitrile in the spinning solution is 8-12 wt%, and the mass ratio of polyacrylonitrile to the microwave absorbent is 1 (0.1-0.3);

performing electrostatic spinning on the spinning solution to obtain a nanofiber membrane;

carrying out heat treatment on the nanofiber membrane to preoxidize polyacrylonitrile in the nanofiber membrane so as to obtain a carbon nanofiber precursor;

and carrying out microwave irradiation heating on the carbon nanofiber precursor in an inert gas atmosphere to carbonize the pre-oxidized polyacrylonitrile in the carbon nanofiber precursor.

Preferably, the polyacrylonitrile has a weight average molecular weight of 9 to 25 ten thousand.

Preferably, the microwave absorbent includes one of conductive carbon black, activated carbon, carbon nanotubes, and reduced graphene oxide.

Preferably, the organic solvent comprises one or more of nitrogen-nitrogen dimethylformamide, nitrogen-nitrogen dimethylacetamide and dimethyl sulfoxide.

Preferably, the electrospinning conditions include: the receiving distance is 10-20 cm; the advancing speed is 0.5-1 mL/h; the voltage is 12-18 kV; the rotating speed of the roller is 300-1000 rpm.

Preferably, in the step of carrying out heat treatment on the nanofiber membrane, the heat treatment temperature is 200-280 ℃, the time is 60-120min, and the temperature rise rate is 1-5 ℃/min.

Preferably, the power of the microwave irradiation heating is 0.8-1.4 kW; in the microwave irradiation heating process, the temperature of the carbon nanofiber precursor is controlled to be 800-1200 ℃; the microwave irradiation heating time is 10-30 min.

The invention has the following beneficial effects:

the preparation method of the electrostatic spinning carbon nanofiber adopts microwave irradiation heating to the carbon nanofiber precursor, and the microwave irradiation heating technology can directly convert electromagnetic energy into heat energy in an irradiation material without additional medium for transferring energy. Compared with the traditional heating method, the method for preparing the electrostatic spinning carbon nanofiber based on the microwave irradiation heating technology has a series of advantages of high heating speed, high energy utilization efficiency, low cost, easiness in industrial batch production and the like.

According to the preparation method of the electrostatic spinning carbon nanofiber, one of conductive carbon black, activated carbon, carbon nano tubes and reduced graphene oxide is added to serve as a microwave absorbent, the conductive carbon black, the activated carbon, the carbon nano tubes and the reduced graphene oxide have high dielectric properties and short attenuation distance, and have strong response to a microwave electromagnetic field, so that the conversion of microwave energy to heat energy can be realized instantly, and a carbon nano fiber precursor can be rapidly carbonized, and the production efficiency is improved.

According to the preparation method of the electrostatic spinning carbon nanofiber, the microwave absorbent, the polyacrylonitrile and the organic solvent are uniformly mixed and then subjected to electrostatic spinning, so that the microwave absorbent is uniformly dispersed in the interior or on the surface of the nanofiber membrane, and the carbonization effect and efficiency can be improved.

According to the preparation method of the electrostatic spinning carbon nanofiber, the carbon material type microwave absorbent is added, in the microwave radiation heating process, a large amount of Joule heat can be instantly generated by the microwave absorbent, so that the polyacrylonitrile nanofiber can be rapidly carbonized, the carbon material type microwave absorbent has a large specific surface area and excellent conductivity, and after the carbon material type microwave absorbent is uniformly dispersed on a carbon nanofiber membrane, the conductivity and pore structure of the final electrostatic spinning carbon nanofiber are increased, so that the potential application range of the carbon material type microwave absorbent is enriched.

The preparation method of the electrostatic spinning carbon nanofiber has the advantages of simple process, easy operation, quick and efficient carbonization process, and reduction of the influence of heat conduction on energy exchange and reaction degree by special bulk heating, and can quickly obtain the high-conductivity carbon nanofiber by microwave irradiation heating, so that the preparation process is short in time consumption, low in energy consumption and green and environment-friendly in process; the production cost is low, and the method is favorable for industrial batch production of the electrostatic spinning carbon nanofibers.

The carbon nanofiber prepared by the method has controllable structure and property, and carbon nanofiber materials with different fiber diameters, conductive performance and graphitization degrees can be obtained by simply adjusting the proportion of polyacrylonitrile and a microwave absorbent and a microwave carbonization process.

In order to make the aforementioned and other objects, features and advantages of the invention comprehensible, preferred embodiments accompanied with figures are described in detail below.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is SEM images of carbon nanofibers produced in example 1 of the present invention and comparative examples 1 to 3, wherein the A region is the SEM image of PAN/CB-CNF-M10 in example 1, the B region is the SEM image of PAN/CB-CNF-T10 in comparative example 1, the C region is the SEM image of PAN/CB-CNF-T120 in comparative example 2, and the D region is the SEM image of PAN-CNF-T120 in comparative example 3;

FIG. 2 is a Raman spectrum of carbon nanofibers produced in example 1 of the present invention and comparative examples 1 to 3;

FIG. 3 is an SEM image of carbon nanofiber PAN/CB-CNF-M10-2 in example 2 of the invention;

FIG. 4 is an SEM image of carbon nanofiber PAN/CB-CNF-M10-3 in example 3 of the invention;

FIG. 5 is an SEM image of carbon nanofiber PAN/AC-CNF-M10 in example 4 of the invention;

FIG. 6 is an SEM image of carbon nanofiber PAN/MWCNT-CNF-M10 in example 5 of the present invention;

FIG. 7 is an SEM image of carbon nanofibers PAN/rGO-CNF-M10 in example 6 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Step one, preparing spinning solution

Dissolving 0.5g of polyacrylonitrile (PAN, weight average molecular weight of 15 ten thousand) in nitrogen-nitrogen Dimethylformamide (DMF), stirring in water bath at 60 ℃ for 12 hours to obtain a polyacrylonitrile solution with the mass percent of the polyacrylonitrile being 10 wt%, adding 0.15g of conductive Carbon Black (CB) into the polyacrylonitrile solution, magnetically stirring for 2 hours, and then ultrasonically dispersing for 6 hours to obtain a uniformly dispersed spinning solution.

Step two, preparing the nanofiber membrane

And carrying out electrostatic spinning on the spinning solution to obtain the nanofiber membrane. In the electrostatic spinning process, a stainless steel needle with the inner diameter of 0.51mm is selected, the applied electrostatic voltage is 15kV, the flow rate of the spinning solution is 0.5mL/h, the receiving distance between a metal roller and the needle is 15cm, the rotating speed of the roller is 300rpm, and the spinning time is 5 h.

Step three, preparing carbon nanofiber precursor

And (3) carrying out heat treatment on the nanofiber membrane for 1h at the temperature of 280 ℃ in a blast oven, wherein the heating rate is 2 ℃/min, so that polyacrylonitrile in the nanofiber membrane is pre-oxidized, and the carbon nanofiber precursor is obtained. After heat treatment, the nanofiber membrane has been stabilized.

Step four, preparing the carbon nano fiber

And placing the carbon nanofiber precursor in a cavity of a slide rail type vacuum microwave tube furnace, vacuumizing, continuously introducing nitrogen as protective gas, and performing microwave irradiation heating on the carbon nanofiber precursor in a nitrogen atmosphere to carbonize the preoxidized polyacrylonitrile in the carbon nanofiber precursor. Wherein the microwave power of the microwave irradiation heating is 1.2kW, the heat preservation is started after the temperature reaches 1000 ℃, the slide rail type vacuum microwave tube furnace is closed after the heat preservation is carried out for 10min, so that the carbon nanofiber precursor heated by the microwave irradiation is rapidly cooled to the room temperature in the air and then taken out, and the carbon nanofiber which is marked as PAN/CB-CNF-M10 can be obtained.

SEM analysis of the prepared carbon nanofiber PAN/CB-CNF-M10 showed that CB was uniformly dispersed in the carbon nanofiber prepared in this example, as shown in FIG. 1A.

The average diameter of the fibers was found to be 438. + -.22 nm by selecting 50 fibers at random using the software Image J.

Comparative example 1

As in example 1, the difference is limited to the carbonization treatment of the carbon nanofiber precursor in a conventional tube furnace. Specifically, the method comprises the following steps:

step one, preparing spinning solution

As in example 1.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

And (3) placing the carbon nanofiber precursor prepared in the third step in a traditional tube furnace, keeping the temperature of 1000 ℃ for 10min in a nitrogen atmosphere, raising the temperature at 5 ℃/min, naturally cooling to room temperature, and taking out a sample to obtain the carbon nanofiber which is marked as PAN/CB-CNF-T10.

SEM analysis of the obtained PAN/CB-CNF-T10 showed that the fibers had an average diameter of 445. + -.20 nm as shown in FIG. 1B.

Comparative example 2

As in example 1, the difference is limited to the carbonization treatment of the carbon nanofiber precursor in a conventional tube furnace. Specifically, the method comprises the following steps:

step one, preparing spinning solution

As in example 1.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

And (3) placing the carbon nanofiber precursor prepared in the third step in a traditional tube furnace, keeping the temperature at 1000 ℃ for 120min in a nitrogen atmosphere, raising the temperature at 5 ℃/min, naturally cooling to room temperature, and taking out a sample to obtain the carbon nanofiber, wherein the carbon nanofiber is marked as PAN/CB-CNF-T120.

SEM analysis of the obtained PAN/CB-CNF-T120 showed that the fibers had an average diameter of 432. + -.13 nm as shown in FIG. 1C.

Comparative example 3

As in example 1, the difference was limited to the absence of CB added to the electrospinning solution, and the carbon nanofiber precursor was carbonized in a conventional tube furnace.

Specifically, the method comprises the following steps:

step one, preparing spinning solution

Dissolving 0.5g of polyacrylonitrile (PAN, weight average molecular weight of 15 ten thousand) in nitrogen-nitrogen Dimethylformamide (DMF), stirring in water bath at 60 ℃ for 12 hours to obtain a polyacrylonitrile solution with the mass percent of 10 wt%, magnetically stirring for 2 hours, and ultrasonically dispersing for 6 hours to obtain a uniformly dispersed spinning solution.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

And (3) placing the carbon nanofiber precursor prepared in the third step in a traditional tube furnace, keeping the temperature at 1000 ℃ for 120min in a nitrogen atmosphere, raising the temperature at 5 ℃/min, naturally cooling to room temperature, and taking out a sample to obtain the carbon nanofiber, wherein the carbon nanofiber is marked as PAN-CNF-T120.

SEM analysis of the obtained PAN-CNF-T120 showed that the fibers had an average diameter of 94. + -.4 nm as shown in FIG. 1D.

Analysis of conductivity and graphitization degree (I) of the carbon nanofibers prepared in example 1 and comparative examples 1 to 3 using a four-probe conductivity tester and a Raman spectrometer, respectively_G/I_D) The results are shown in Table 1 and the Raman spectrum is shown in FIG. 2.

TABLE 1 average fiber diameter, conductivity, and graphitization degree (I) of the carbon nanofibers prepared in example 1 and comparative examples 1-3_G/I_D)

Carbon nanofiber	Average diameter (nm)	Average conductivity (S/m)	IG/ID
				PAN/CB-CNF-M10	438±22	454.79±0.08	0.95
PAN/CB-CNF-T10	445±20	295.70±0.06	0.93
				PAN/CB-CNF-T120	432±13	383.30±0.07	0.98
PAN-CNF-T120	94±4	419.62±0.06	0.99

Example 2

This example is different from example 1 in the amount of the conductive Carbon Black (CB) added. Specifically, the method comprises the following steps:

step one, preparing spinning solution

Dissolving 0.5g of polyacrylonitrile (PAN, weight average molecular weight of 15 ten thousand) in nitrogen-nitrogen Dimethylformamide (DMF), stirring in water bath at 60 ℃ for 12 hours to obtain a polyacrylonitrile solution with the mass percent of the polyacrylonitrile being 10 wt%, adding 0.10g of conductive Carbon Black (CB) into the polyacrylonitrile solution, magnetically stirring for 2 hours, and then ultrasonically dispersing for 6 hours to obtain a uniformly dispersed spinning solution.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

As in example 1.

The carbon nanofiber obtained in this example was designated as PAN/CB-CNF-M10-2.

SEM analysis of the obtained PAN/CB-CNF-M10-2 showed that the fibers had an average diameter as shown in FIG. 3286. + -.11 nm. The average conductivity of PAN/CB-CNF-M10-2 is 430.42 +/-0.07S/M, I_G/I_DThe value was 0.89.

Example 3

This example is different from example 1 in the amount of the conductive Carbon Black (CB) added. Specifically, the method comprises the following steps:

the first step,

Dissolving 0.5g of polyacrylonitrile (PAN, weight average molecular weight of 15 ten thousand) in nitrogen-nitrogen Dimethylformamide (DMF), stirring in water bath at 60 ℃ for 12 hours to obtain a polyacrylonitrile solution with the mass percent of the polyacrylonitrile being 10 wt%, adding 0.05g of conductive Carbon Black (CB) into the polyacrylonitrile solution, magnetically stirring for 2 hours, and then ultrasonically dispersing for 6 hours to obtain a uniformly dispersed spinning solution.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

As in example 1.

The carbon nanofiber obtained in this example was designated as PAN/CB-CNF-M10-3.

SEM analysis of the obtained PAN/CB-CNF-M10-3 showed that the fibers had an average diameter of 311. + -.12 nm as shown in FIG. 4. The average conductivity of PAN/CB-CNF-M10-3 is 533.46 +/-0.1, I_G/I_DThe value was 0.87.

Example 4

This example is different from example 1 in that the microwave absorbent in this example is 0.15g of Activated Carbon (AC). Specifically, the method comprises the following steps:

step one, preparing spinning solution

Dissolving 0.5g of polyacrylonitrile (PAN, weight average molecular weight of 15 ten thousand) in nitrogen-nitrogen Dimethylformamide (DMF), stirring in water bath at 60 ℃ for 12 hours to obtain a polyacrylonitrile solution with the mass percent of 10 wt%, adding 0.15g of Activated Carbon (AC) into the polyacrylonitrile solution, magnetically stirring for 2 hours, and then ultrasonically dispersing for 6 hours to obtain a uniformly dispersed spinning solution.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

As in example 1.

The carbon nanofiber obtained in this example was designated as PAN/AC-CNF-M10.

SEM analysis of the obtained PAN/AC-CNF-M10 showed that the fibers had an average diameter of 352. + -.26 nm, as shown in FIG. 5. The average conductivity of PAN/AC-CNF-M10 was 338.40. + -. 0.09S/M, I_G/I_DThe value was 0.71.

Example 5

This example is different from example 1 in that the microwave absorber in this example is 0.15g of multi-walled carbon nanotubes (MWCNTs). Specifically, the method comprises the following steps:

step one, preparing spinning solution

Firstly, 0.15g of multi-walled carbon nanotube (MWCNT) is uniformly dispersed in DMF (dimethyl formamide) through ultrasonic and stirring, then 0.5g of polyacrylonitrile (PAN, weight-average molecular weight is 15 ten thousand) is added, stirring is carried out in a water bath at 60 ℃ for 12 hours, then ultrasonic dispersion is carried out for 2 hours, and uniformly dispersed spinning solution is obtained, wherein the mass percentage of the polyacrylonitrile in the spinning solution is 10 wt%.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

As in example 1.

The carbon nanofiber obtained in this example was designated as PAN/MWCNT-CNF-M10.

SEM analysis of the obtained PAN/MWCNT-CNF-M10 showed that the average fiber diameter was 376. + -.22 nm, as shown in FIG. 6. The average conductivity of PAN/MWCNT-CNF-M10 was 471.61. + -. 0.05S/M, I_G/I_DThe value was 1.08.

Example 6

The difference between this embodiment and embodiment 1 is that the microwave absorber in this embodiment is 0.125g of reduced graphene oxide (rGO). Specifically, the method comprises the following steps:

step one, preparing spinning solution

Firstly, 0.125g of reduced graphene oxide (rGO) is uniformly dispersed in DMF (dimethyl formamide) through ultrasonic and stirring, then 0.5g of polyacrylonitrile (PAN, weight average molecular weight is 15 ten thousand) is added, stirring is carried out in water bath at 60 ℃ for 12 hours, then ultrasonic dispersion is carried out for 2 hours, and uniformly dispersed spinning solution is obtained, wherein the mass percentage of polyacrylonitrile in the spinning solution is 10 wt%.

Step two, preparing the nanofiber membrane

As in example 1.

Step three, preparing carbon nanofiber precursor

As in example 1.

Step four, preparing the carbon nano fiber

As in example 1.

The carbon nanofiber obtained in the embodiment is recorded as PAN/rGO-CNF-M10.

SEM analysis of the prepared PAN/rGO-CNF-M10 showed that the fibers had an average diameter of 180. + -.11 nm as shown in FIG. 7. The average conductivity of PAN/rGO-CNF-M10 is 439.81 +/-0.04S/M, I_G/I_DThe value was 1.03.

The principle and the implementation mode of the invention are explained by applying specific embodiments in the invention, and the description of the embodiments is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.