CN103936987A - Carbon nanotube composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a carbon nanotube composite material and a preparation method thereof and relates to the technical field of nanomaterial synthesis. The preparation method comprises the following steps: polymerizing ammonium persulfate used as the oxidant and purified multiwalled carbon nanotubes used as a carrier of polyaniline at 0 DEG C ambient temperature to obtain a stable polyaniline/multi-walled carbon nanotubes composite material, and then introducing manganese dioxide under acidic conditions to obtain a manganese dioxide/polyaniline/multi-walled carbon nanotubes composite material. The carbon nanotube composite material is in a tubular structure and polyaniline having particle size of 30-40nm is attached to a tubular body. The electrode made of the multi-walled carbon nanotubes composite material exhibits ideal capacitive properties. The composite material is simple in preparation and has broad application prospect in terms of the super capacitor.

Description

A kind of carbon nanotube composite material and preparation method thereof

technical field

The invention relates to the technical field of synthesis of nanometer materials.

Background technique

Due to their unique structure and physical and chemical properties, conductive polymers can be used as pseudocapacitive electrode materials for supercapacitors. However, its cycle performance is poor, so it is often combined with electric double layer carbon-based materials. By integrating the excellent properties of these two materials, carbon nanotube-loaded conductive polymer composites will occupy great advantages in new nanotechnology applications. Many researchers have reported the composite synthesis process of carbon nanotubes and conductive polymers, the polymers used include polypyrrole, polyaniline and so on.

At present, among many conductive polymers, polyaniline has the characteristics of easy to obtain raw materials, simple synthesis, high conductivity, and unique doping mechanism, and has great development potential in the field of conductive polymers. Due to the high electrical conductivity of carbon nanotubes and the advantages of easily forming a grid structure when combined with polyaniline, the electrical conductivity and mechanical properties of polyaniline can be significantly improved by combining polyaniline with a small amount of carbon nanotubes. Due to the large specific surface area and high porosity of polyaniline nanofibers, considering the modification of manganese dioxide with polyaniline can improve the low electrochemical conductivity of manganese dioxide electrode materials and increase the utilization rate of manganese dioxide. At the same time, the stability and rate performance of the electrode material can be improved. Although the research on polyaniline/manganese dioxide and carbon nanotube/polyaniline binary composites has been reported, the preparation of manganese dioxide/polyaniline/multi-walled carbon nanotube ternary composites and their use as supercapacitor electrodes The material has not been reported yet.

Contents of the invention

The invention provides a manganese dioxide/polyaniline/multi-wall carbon nanotube ternary composite material with simple method and low cost.

The manganese dioxide/polyaniline/multi-wall carbon nanotube composite material of the present invention has the following characteristics: the composite material is in a tubular structure, the outer diameter of the tube body is 20-40 nm, and the particle size attached to the tube body is 30-40 nm. of polyaniline.

From the transmission electron microscope (TEM), it can be observed that the product has the above characteristics, and a layer of polyaniline particles is formed on the surface of the carbon nanotubes in situ, that is, the polyaniline particles are evenly coated on the surface of the carbon nanotubes.

Due to the high electrical conductivity of carbon nanotubes and the advantages of easily forming a grid structure when combined with polyaniline, the electrical conductivity and mechanical properties of polyaniline can be significantly improved by combining polyaniline with a small amount of carbon nanotubes. Polyaniline nanofibers have a large specific surface area and high porosity. Considering the modification of manganese dioxide with polyaniline can improve the low conductivity of manganese dioxide electrode materials, and manganese dioxide can also increase the specific volume of the material. At the same time, the stability and rate performance of the electrode material can be improved. The prepared manganese dioxide/polyaniline/multi-walled carbon nanotube composite electrode shows ideal capacitive properties. The composite material is easy to prepare and has broad application prospects in supercapacitors.

The present invention also proposes a preparation method of the above composite material.

The preparation method is as follows: ammonium persulfate is used as an oxidant, and purified multi-walled carbon nanotubes are used as a polyaniline carrier, and a stable polyaniline/multi-walled carbon nanotube composite material is obtained by polymerization at an ambient temperature of 0 ° C, and then in acidic The manganese dioxide is introduced under the condition to obtain the manganese dioxide/polyaniline/multi-walled carbon nanotube composite material.

The purpose of using the purified multi-walled carbon nanotubes in the present invention is to firstly remove the amorphous carbon and catalyst particles in the production process of the multi-walled carbon nanotubes. Technological features of the present invention have:

(1) Using ammonium persulfate as an oxidant, polyaniline was generated in situ on the surface of carbon nanotubes and formed a uniform coating layer. Then manganese dioxide is introduced under acidic conditions to obtain manganese dioxide/polyaniline/multi-walled carbon nanotube composite material. Compared with the usual polyaniline/multi-walled carbon nanotube composite material synthesis route, the method saves preparation reagents and simplifies the production process steps.

(2) Polymerization at 0°C ambient temperature is beneficial to increase the molecular weight of polyaniline and obtain polymers with narrow molecular weight distribution.

(3) The method has easy-to-obtain raw materials and high product reproducibility.

The specific method of purifying multi-walled carbon nanotubes is: disperse multi-walled carbon nanotubes (MWNTs) in HNO ₃ aqueous solution, stir magnetically at the temperature of the mixed system at 120°C, and centrifuge to obtain a precipitate. After centrifugation and washing until the washing solution is colorless, the precipitate in the lower layer is vacuum-dried to obtain purified multi-walled carbon nanotubes. The invention adopts a liquid-phase oxidation method to purify the carbon nanotubes. The liquid-phase oxidation method has relatively mild reaction conditions and is easy to control, and the method greatly reduces the loss rate of samples.

The solvent used for dispersion—the concentration of HNO ₃ aqueous solution was 2.6 M. The greater the concentration of nitric acid, the greater its reaction speed, and the greater the weight loss rate of carbon nanotubes per unit time. In fact, in excess nitric acid solution, after enough time, impurities can be removed. When the concentration of nitric acid exceeds When it is large, because the reaction speed is too fast, the initial reaction is too violent, and more brownish-red _NO gas is produced in the reactor. Therefore, the concentration of nitric acid selected by the present invention is 2.6 M to make the reaction process more moderate.

The specific method for preparing polyaniline/multi-walled carbon nanotubes is: adding aniline solution to the HCl aqueous solution in which the purified multi-walled carbon nanotubes are dispersed, fully stirring evenly under ice-bath conditions to obtain a mixed solution; Add ammonium persulfate solution dropwise, react under stirring conditions, then add acetone to terminate the reaction, wash the precipitate with deionized water and ethanol centrifuge, and vacuum dry the precipitate at 80°C, grind it, and obtain polyaniline/polyaniline walled carbon nanotubes.

In addition, the concentration of the aqueous HCl solution used to disperse the purified multi-walled carbon nanotubes was 1 M, and the mixing ratio of the purified multi-walled carbon nanotubes to the aqueous HCl solution was 0.5 g: 100 mL during dispersion. When doped with a certain concentration of acid, it can effectively prevent the self-assembly and ordered arrangement behavior of the one-dimensional nanostructure. When 1M HCl is added, the formed polyaniline product will be randomly arranged polyaniline nanofibers, which is beneficial to the compounding with carbon nanotubes.

The mass ratio of ammonium persulfate in the ammonium persulfate aqueous solution to the aniline in the aniline solution is 1:1, and the rate of dropping the ammonium persulfate aqueous solution is 1d/3s. Because of the hydrophilicity of APS, it will be dispersed in the continuous water phase, and the polymerization reaction mainly occurs on the surface of the droplet. When the initiator APS is added at a slow rate (3s/d), the density of polymerization centers on the surface of the APS droplet in the solution is low, and at this time only initial polyaniline fibers can be formed in a small range, which is beneficial to the formation of polyaniline and polyaniline. Compounding of carbon nanotubes. If the dropping speed is too fast or the ratio of APS to aniline monomer is increased, the concentration of the initiator will be too high per unit time, causing the aniline monomer to gather in a wide range to form a network structure, which is not conducive to the interaction with carbon nanotubes. complex.

When the mass ratio of ammonium persulfate to aniline in the aniline solution was 1:1, the conductivity of the composite obtained was the highest. The whole reaction system is carried out in the hydrochloric acid medium, and the hydrochloric acid provides the acidity required for the reaction, and enters the polyaniline skeleton in the form of a dopant, endowing it with certain conductivity. Slowly add APS dropwise to avoid overheating of the system reaction. Washing with deionized water and ethanol can respectively wash off the inorganic and organic impurities attached to the product. Water and ethanol have good miscibility and can wash each other. At the same time, ethanol has good volatility. The water and ethanol introduced during the washing of the product can be removed by drying under vacuum conditions.

The specific method for preparing manganese dioxide/polyaniline/multi-wall carbon nanotubes is: after polyaniline/multi-wall carbon nanotubes and potassium permanganate aqueous solution are stirred and reacted, the precipitate is taken by centrifugal washing with deionized water and ethanol, and then Manganese dioxide/polyaniline/multi-walled carbon nanotube composite material was obtained by drying and grinding at 50°C. Manganese dioxide is introduced under acidic conditions, and the manganese dioxide/polyaniline/multi-walled carbon nanotube composite material is obtained through the in-situ redox reaction of potassium permanganate and polyaniline. Compared with the existing synthesis route of manganese dioxide/polyaniline composite material, the preparation reagent is saved and the production steps are simplified. The raw material of the method is easy to obtain, and the product has high reproducibility. The obtained manganese dioxide/polyaniline/multi-wall carbon nanotube composite material has high stability and has broad application prospects in supercapacitors.

The concentration of the above-mentioned potassium permanganate aqueous solution is preferably 0.01-0.06 M.

The concentration of potassium permanganate has a great influence on the morphology of composite materials. In the case of fixing the content of polyaniline/multi-walled carbon nanotube composite material at 0.05 g, the concentration of potassium permanganate solution was controlled at 0.01M-0.06 M, and the amount of manganese dioxide increased with the increase of potassium permanganate concentration. Increase. When the concentration of potassium permanganate solution is small, the thickness of the outer surface of polyaniline does not increase significantly. When the concentration of potassium permanganate solution is 0.02 M ~ 0.04 M, it can be seen that a layer of manganese dioxide particles is distributed on the surface of polyaniline, and the thickness of the coating layer gradually increases. When the concentration of potassium permanganate solution reaches 0.05 M and 0.06 M, not only a thick layer of manganese dioxide particle layer is covered on the surface of polyaniline, but also there are self- Agglomerated manganese dioxide particles.

Description of drawings

Figure 1 is a TEM photo of the purified carbon nanotubes, and the scale bar is 100 nm.

Figure 2 is the TEM photo of the prepared polyaniline/multi-walled carbon nanotube composite material, and the scale bar is 100 nm.

Figure 3 is the TEM photo of the prepared manganese dioxide/polyaniline/multi-walled carbon nanotube composite material, and the scale bar is 100 nm.

Detailed ways

The terms used in the present invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art.

The present invention will be described in further detail below in conjunction with specific examples and with reference to data. It should be understood that these examples are only for illustration of the present invention, but not to limit the scope of the present invention in any way.

In the following examples, various procedures and methods not described in detail are conventional methods well known in the art.

Preparation process steps:

1. Purification of carbon nanotubes: Add MWNTs into a round-bottomed flask filled with 50 mL of 2.6 M HNO ₃ aqueous solution, magnetically stir and reflux at 120°C for 24 hours to completely react the system, and then centrifuge the reaction system containing the precipitate Finally, the precipitate is obtained, and then washed by centrifugation until the washing liquid is colorless, and then the lower layer of precipitate is vacuum-dried to obtain purified multi-walled carbon nanotubes.

The morphology of the purified carbon nanotubes is shown in Fig. 1 .

It can be seen from Figure 1 that the purified multi-walled carbon nanotubes have a tubular structure.

2. Preparation of polyaniline/multi-walled carbon nanotube composite material: Weigh 0.5 g of carbon nanotubes into 100 mL of 1M HCl aqueous solution and stir for 0.5 h until uniform dispersion.

Put the above HCl aqueous solution container containing carbon nanotubes in an ice bath, then add 2.0 g of aniline monomer solution into the container, stir for 0.5 h until uniform dispersion, and then add ammonium persulfate containing 2.0 g of ammonium persulfate The aqueous solution was added dropwise to the above mixed system at a rate of one drop every 3s, and then fully stirred for 6h until the reaction of the system was complete.

After the reaction was complete, acetone was added to terminate the reaction.

Then deionized water and ethanol were used to centrifuge and wash three times, and then the precipitate was vacuum-dried at 80 °C for 24 h, and then ground to obtain polyaniline/multi-walled carbon nanotube composites.

The morphology of polyaniline/multi-walled carbon nanotube composites is also affected by the concentration ratio of aniline monomer and carbon nanotubes. While the content of carbon nanotubes was fixed at 2.0 g, the content of aniline monomer (0.5-3.0 g) was changed, and the morphology of polyaniline/multi-walled carbon nanotube composites was different, which indicated that polyaniline and multi-walled carbon There is mainly physical adsorption between nanotubes. When the content of aniline monomer is 2.0 g, the carbon nanotubes act as templates, which serve as the gathering place for polyaniline nucleation, and the aniline grows on the surface so that the polyaniline covers the surface of the carbon nanotubes more uniformly, forming a shape Looks better.

The morphology of the composite material is shown in Fig. 2.

It can be seen from Figure 2 that a uniform layer of polyaniline particles is attached to the surface of the tubular carbon nanotubes.

3. Preparation of manganese dioxide/polyaniline/multi-wall carbon nanotube composite material: add 0.05g polyaniline/multi-wall carbon nanotube to the Erlenmeyer flask, and add high manganese with a concentration of 0.01-0.06M to it at one time Potassium acid aqueous solution was stirred at room temperature for 10 min. The obtained solution was then centrifuged three times with deionized water and ethanol, dried in a constant temperature drying oven at 50 °C for 12 h, and then ground to obtain a sample.

When the concentration of the potassium permanganate aqueous solution was 0.03M, the morphology of the manganese dioxide/polyaniline/multi-walled carbon nanotube composite sample was obtained as shown in Figure 3.

It can be seen from Figure 3 that the diameter of the outer tube of carbon nanotubes is about 20-40 nm and the particle size of polyaniline is 30-40 nm through the observation of transmission electron microscope (TEM), and the composite material after polymerization is still well maintained. The tubular structure of carbon nanotubes.

Claims (9)

1. a manganese dioxide/polyaniline/multi-walled carbon nanotube composite material, is characterized in that, described composite material is tubular structure, and the external diameter of tube body is 20～40 nm, is attached with particle diameter on tube body It is polyaniline with a thickness of 30-40 nm. 2. the preparation method of manganese dioxide/polyaniline/multi-wall carbon nanotube composite material as claimed in claim 1 is characterized in that with ammonium persulfate as oxygenant, with the multi-wall carbon nanotube of purification as the carrier of polyaniline, A stable polyaniline/multi-wall carbon nanotube composite material is obtained by polymerization at an ambient temperature of 0° C., and then manganese dioxide is introduced under acidic conditions to obtain a manganese dioxide/polyaniline/multi-wall carbon nanotube composite material. 3. The preparation method according to claim 2, characterized in that: the multi-walled carbon nanotubes are dispersed in the _HNO3 aqueous solution, and after the temperature of the mixing system is 120° C. under magnetic stirring, the precipitate is obtained after centrifugation , and then centrifuged and washed until the washing solution is colorless, and then the lower layer of precipitate is vacuum-dried to obtain purified multi-walled carbon nanotubes. 4. The preparation method according to claim 3, characterized in that: the concentration of the _HNO3 aqueous solution is 2.6 M. 5. preparation method according to claim 2, is characterized in that: add aniline solution in the HCl aqueous solution that is dispersed with the multi-walled carbon nanotube of purification, fully stir under ice-bath condition, obtain mixed solution; Add ammonium persulfate aqueous solution dropwise to the solution, react under stirring conditions, then add acetone to terminate the reaction, wash the precipitate with deionized water and ethanol by centrifugation, and vacuum dry and grind the precipitate at 80°C to obtain polyaniline / Multi-walled carbon nanotubes. 6. preparation method according to claim 5, is characterized in that: the concentration of the HCl aqueous solution of the multi-walled carbon nanotubes that is used for dispersion purification is 1M, when dispersing, the multi-walled carbon nanotubes of purification and HCl aqueous solution The mixing ratio is 0.5g: 100mL. 7. preparation method according to claim 5 is characterized in that: the mass ratio of ammonium persulfate in described ammonium persulfate aqueous solution and aniline in aniline solution is 1: 1, and the speed of dripping ammonium persulfate aqueous solution is 1d /3s. 8. the preparation method according to claim 2 is characterized in that: after polyaniline/multi-walled carbon nanotube and potassium permanganate aqueous solution stirring reaction, get sediment with deionized water, ethanol centrifugal washing, then through 50 °C drying and grinding to obtain manganese dioxide/polyaniline/multi-walled carbon nanotube composite material. 9. preparation method according to claim 8 is characterized in that: the concentration of described potassium permanganate aqueous solution is 0.01～0.06M.