CN113292066B

CN113292066B - Carbon nanofiber without metal catalyst and preparation method and application thereof

Info

Publication number: CN113292066B
Application number: CN202110608388.3A
Authority: CN
Inventors: 赵相龙; 雍兴华; 孙钰坤; 宋扬; 孟瑞璇; 邵大卫; 陈婷; 李鲁艳; 时术华
Original assignee: Shandong Jianzhu University
Current assignee: Shandong Jianzhu University
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2022-11-22
Anticipated expiration: 2041-06-01
Also published as: CN113292066A

Abstract

The invention discloses a carbon nanofiber without a metal catalyst, a preparation method and application thereof, wherein the preparation method comprises the following steps: the straw is annealed to generate hydrocarbon gas, carbon atoms generated by thermal decomposition of the hydrocarbon gas are transmitted to the surface of downstream charcoal powder by carrier gas to grow carbon nanofibers, and meanwhile, the rough surface of the downstream charcoal powder is used as a catalytic site for catalyzing the growth of the carbon nanofibers. The invention utilizes the straw as the precursor to catalyze and grow the carbon nano-fiber on the surface of the charcoal powder, has the advantages of low cost, reproducibility and mass obtainment, and the whole preparation process does not need a transition metal catalyst nor high-pressure hydrocarbon gas. In addition, after the obtained carbon nanofiber is prepared into a filter membrane by a suction filtration method, the water-in-diesel emulsion can be separated.

Description

Carbon nanofiber without metal catalyst and preparation method and application thereof

Technical Field

The invention relates to a carbon nanofiber without a metal catalyst, and a preparation method and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The carbon nanofiber has the advantages of low density, high conductivity, high mechanical stability and the like, and therefore, the carbon nanofiber has wide application in the fields of oil absorbents, oil-water separation, electrochemical catalyst carriers, super capacitors and the like. At present, the preparation method of the carbon nanofiber mainly comprises electrostatic spinning, carbonization, hydrothermal treatment, microwave irradiation and chemical vapor deposition. The chemical vapor deposition method has advantages of simple operation and low cost, etc. compared to other methods, and thus, the chemical vapor deposition method has been widely studied for preparing carbon nanofibers. The work of Yu et al shows that controlled growth of carbon nanofibers can be achieved by the catalytic action of nickel nanoparticles during chemical vapor deposition (B.Yu, et al. Temperature-dependent chemical state of the nickel catalyst for the growth of carbon nanofibers. Carbon, volume 96, pages 904-910 (2016); B.Yu et al, temperature dependent chemical state of nickel catalyst for the growth of carbon nanofibers. Carbon, volume 96, pages 904-910 (2016)).

However, the inventors have found that this method has a significant disadvantage in that the nickel catalyst inside the carbon nanofibers is difficult to completely remove even by highly corrosive strong acid corrosion, thereby limiting the application fields of such carbon nanofibers.

Disclosure of Invention

In order to solve the defects of the prior art, the invention aims to provide a carbon nanofiber without a metal catalyst, and a preparation method and application thereof, wherein the method can realize low-cost and large-scale production of the carbon nanofiber without the metal catalyst.

In order to achieve the purpose, the technical scheme of the invention is as follows:

on one hand, the preparation method of the carbon nanofiber is characterized in that the straw is annealed to generate hydrocarbon gas, carbon atoms generated by thermal decomposition of the hydrocarbon gas are transmitted to the surface of downstream charcoal powder by carrier gas to grow the carbon nanofiber, and meanwhile, the rough surface of the downstream charcoal powder is used as a catalytic site for catalyzing the growth of the carbon nanofiber.

Experiments show that the growth of the carbon nanofiber can be realized when the annealing temperature of the straw is 500-800 ℃.

In another aspect, a carbon nanofiber is obtained by the above preparation method.

The carbon nanofiber prepared by the method does not contain a metal catalyst, and the adverse effect of impurities of the metal catalyst on the application of the carbon nanofiber can be avoided.

In a third aspect, the carbon nanofiber is applied to the preparation of a filter membrane in an important way.

In a fourth aspect, a filter membrane is prepared from the carbon nanofiber.

In a fifth aspect, a use of the carbon nanofiber or the filter membrane in oil-water separation of emulsion.

The invention has the beneficial effects that:

1. the invention utilizes the straw as the precursor to catalyze and grow the carbon nano fiber without the metal catalyst on the surface of the charcoal powder, has the advantages of low cost, reproducibility and large-scale acquisition, and the whole preparation process does not need a transition metal catalyst nor high-pressure hydrocarbon gas.

2. The carbon nanofiber prepared by the method has excellent hydrophobic/oleophylic performance, so that after the carbon nanofiber filter membrane is prepared by a suction filtration method, only diesel oil in the water-in-diesel emulsion can be selectively allowed to pass through the filter membrane, and the high-efficiency separation of the water-in-diesel emulsion is realized.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.

FIG. 1 is a diagram (a) showing a process of preparing carbon nanofibers and a diagram (b) showing the formation of carbon nanofibers according to example 1 of the present invention;

FIG. 2 is a scanning electron microscope picture and a transmission electron microscope picture of different magnifications of the carbon nanofibers prepared in example 1 of the present invention;

FIG. 3 is an X-ray photoelectron spectrum of the carbon nanofiber prepared in example 1 of the present invention;

FIG. 4 is a scanning electron microscope image of pine charcoal powder prepared in example 1 of the present invention with different magnifications;

fig. 5 is a graph representing the hydrophobic and lipophilic properties of the carbon nanofibers prepared in example 1 of the present invention, wherein a is a picture of water droplets on the surface of the carbon nanofibers, and b is a picture of dichloroethane droplets on the surface of the carbon nanofibers;

FIG. 6 is a representation of the membrane separation of water-in-diesel emulsion using carbon nanofibers according to example 1 of the present invention; a is a picture of the separation process, b is an optical micrograph of the emulsion before separation, and c is an optical micrograph of the filtrate after separation.

FIG. 7 is an optical photograph of commercial diesel fuel and diesel fuel obtained after filtering a water-in-diesel emulsion using a carbon nanofiber filter.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

In view of the fact that the existing method for preparing carbon nanofibers needs to use high-pressure hydrocarbon gas and adopt metal catalysts, and the metal catalysts in the formed carbon nanofibers are difficult to remove, the invention provides carbon nanofibers without metal catalysts, and a preparation method and application thereof.

The invention provides a preparation method of carbon nanofibers, which comprises the steps of annealing straws to generate hydrocarbon gas, conveying carbon atoms generated by thermal decomposition of the hydrocarbon gas to the surface of downstream charcoal powder by carrier gas to grow the carbon nanofibers, and simultaneously taking the rough surface of the downstream charcoal powder as a catalytic site for catalyzing the growth of the carbon nanofibers.

Experiments show that the straw annealing temperature can catalyze the growth of the carbon nano-fiber on the catalytic site at 500-800 ℃.

In order to further reduce the cost of producing carbon nanofibers, in some examples of this embodiment, the charcoal powder is obtained from carbonization of a wood feedstock. The wood raw material is wood powder, wood scraps and the like. Further grinding into powder after carbonization.

In one or more embodiments, the annealing temperature of the straw is 500-800 ℃. The annealing time is 2-5 h. The annealing process needs to be performed in an inert atmosphere, which is provided by nitrogen, helium, argon, xenon, etc., to prevent oxidation.

In some examples of this embodiment, the temperature of the straw annealing is 500-800 ℃.

In some examples of this embodiment, the straw annealing and the carbon nanofiber catalytic growth are both performed in a horizontal tube resistance furnace, the straw is placed in the central high temperature zone of the quartz tube, and the charcoal powder is placed in the edge low temperature zone of the quartz tube. When the annealing temperature of the straw is 600 ℃, the temperature of the charcoal powder is about 400 ℃.

In one or more embodiments, the temperature of the central high temperature zone of the horizontal tube resistance furnace is 550 to 650 ℃. The annealing of the straw can be ensured at the temperature, and the growth temperature of the carbon nanofiber can be ensured.

In another embodiment of the present invention, there is provided a carbon nanofiber obtained by the above-mentioned preparation method.

In a third embodiment of the invention, the carbon nanofiber is applied to the preparation of a filter membrane in a key manner.

In a fourth embodiment of the invention, a filter membrane is provided, which is prepared from the carbon nano-fiber.

In a fifth embodiment of the present invention, there is provided a use of the carbon nanofiber or the carbon nanofiber membrane in oil-water separation in an emulsion.

In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the technical scheme of the present invention will be described in detail below by combining specific examples and comparative examples.

Example 1

Preparation of carbon powder from pine

First, pine wood chips were placed in a quartz tube of a horizontal tube resistance furnace. Then, argon gas was introduced into the quartz tube, and annealing was carried out at a furnace temperature of 600 ℃ for 2 hours. And after the annealing is finished, grinding the obtained charcoal into powder to obtain the pine charcoal powder.

(II) growing carbon nanofibers without metal catalyst

The corn straw powder and the pine charcoal powder are placed in a quartz tube of a horizontal tube type resistance furnace, and the corn straw powder is located in a central high-temperature area of the quartz tube, and the pine charcoal powder is located in a marginal low-temperature area of the quartz tube. Then, argon gas was introduced into the quartz tube at a flow rate of 0.02 liter/min. Next, the furnace temperature was raised to 600 ℃ and held for 1h.

The process is shown in fig. 1a, the corn stalk powder generates hydrocarbon gas due to annealing, and the hydrocarbon gas is pyrolyzed into carbon atoms. These carbon atoms are then transported by argon gas to the surface of the pine charcoal powder. Since the pine charcoal powder has rough surfaces, these rough surfaces act as catalytic sites to catalyze the growth of carbon nanofibers.

The prepared product is shown in fig. 1b, which shows that a large amount of carbon nanofibers are grown on the surface of the pine charcoal powder.

The microstructure of the carbon nanofiber is shown in fig. 2, and fig. 2a and 2b show that the carbon nanofiber has a curved and twisted morphology; figure 2c shows that the carbon nanofibers are a solid fiber structure.

The X-ray photoelectron spectrum (fig. 3) of the carbon nanofiber shows that the carbon nanofiber prepared in this example only contains carbon elements, and does not contain any metal elements.

The scanning electron micrograph of the pine charcoal powder is shown in FIG. 4. Fig. 4a shows that the surface of the pine charcoal powder is very rough, and fig. 4b shows that the surface of the pine charcoal powder contains a large number of ribs (as indicated by arrow 1) and tips (as indicated by arrow 2). This suggests that these rough surfaces are beneficial as nucleation sites for carbon nanofibers during chemical vapor deposition to catalyze the growth of carbon nanofibers.

The characterization picture of the hydrophobicity and oleophilicity of the carbon nanofiber surface is shown in fig. 5. In fig. 5a, the contact angle of the water drop is about 140 °, indicating that the carbon nanofiber has superior hydrophobicity. In FIG. 5b, the dichloroethane contact angle is about 0, indicating that the carbon nanofibers have excellent oleophilic properties.

The carbon nanofibers were made into a filter membrane by suction filtration method and the filter membrane was used to separate water-in-diesel emulsion, and as shown in fig. 6, it can be seen from fig. 6a that the emulsion became transparent and clear filtrate after passing through the filter membrane. Since the carbon nanofibers have excellent hydrophobic and lipophilic properties, this suggests that the filter membrane prohibits the water droplets in the emulsion from passing through the filter membrane, while allowing the diesel oil in the emulsion to pass through the filter membrane. Fig. 6b and 6c show that the emulsion contained a large number of water droplets before filtration and no water droplets were present in the filtrate after filtration, further demonstrating that the carbon nanofiber filter membrane inhibits the passage of water droplets in the emulsion, thereby achieving the separation of the water-in-diesel emulsion.

FIG. 7 is an optical photograph of commercial diesel fuel and diesel fuel obtained after filtering a water-in-diesel emulsion using a carbon nanofiber filter. It can be seen that the filtered diesel is much clearer and more transparent. This indicates that carbon nanofiber filtration membranes can be fully used to remove water impurities from commercial diesel.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of carbon nanofibers without metal catalysts is characterized in that straws are annealed to generate hydrocarbon gas, carbon atoms generated by thermal decomposition of the hydrocarbon gas are transmitted to the surface of downstream charcoal powder by carrier gas to grow the carbon nanofibers, and meanwhile, the rough surface of the downstream charcoal powder is used as a catalytic site for catalyzing the growth of the carbon nanofibers;

wherein the straw annealing temperature is 500-800 ℃, the annealing time is 2-5 h, and the annealing process needs to be carried out in an inert atmosphere;

wherein, the annealing of the straws and the catalytic growth of the carbon nanofibers are both carried out in a horizontal tube type resistance furnace, the straws are placed in a central high-temperature area of a quartz tube, and charcoal powder is placed in an edge low-temperature area of the quartz tube;

the temperature of the horizontal tubular resistance furnace is 500-800 ℃;

preparing a filter membrane from the carbon nanofibers by a suction filtration method, and using the filter membrane for separating the water-in-diesel emulsion;

the charcoal powder is obtained by carbonizing a wood raw material;

the charcoal powder surface contains a large number of edges and tips, and the particles are in micron-sized.

2. The method of preparing carbon nanofibers without metal catalyst as claimed in claim 1, wherein the inert atmosphere comprises any one of nitrogen, helium, argon, xenon.

3. The method for preparing carbon nanofibers not containing a metal catalyst according to claim 1, wherein the carbonization temperature is 500 to 800 ℃.

4. A carbon nanofiber obtained by the production method according to any one of claims 1 to 3.

5. Use of the carbon nanofibers according to claim 4 in the preparation of a filtration membrane.

6. A filter membrane prepared from the carbon nanofiber as set forth in claim 4.

7. Use of the carbon nanofibres according to claim 4 or the filter membrane according to claim 6 for oil-water separation in an emulsion.