TWI411571B - A method of dispersing carbon nanotubes with silica particles and a dispersion thereof - Google Patents

Abstract

The present invention provides a method for dispersing carbon nanotube with silicon dioxide particles and dispersion so obtained, wherein carbon nanotubes are surrounded by silicon dioxide particles that carry high positive electric charges so as to directly disperse in the aqueous solution. Since the method of the present invention does not undergo covalent bond reaction or use organic solvent, there is no need to functionalize the surface of multi-wall carbon nanotubes, and the carbon nanotubes so obtained can preserve the original excellent property.

Description

Method for dispersing carbon nanotubes with cerium oxide particles and dispersion obtained thereby

The invention relates to a method for dispersing a carbon nanotube by using cerium oxide particles and the obtained dispersion, which can be applied to the fields of composite materials, hydrogen storage materials, electrons, photoelectrics, atomic force microscopes, biosensors and the like.

Due to the excellent properties of carbon nanotubes, many applications have been discussed in recent years. However, the actual products of carbon nanotubes are still few, so far. The reason is as described by De Heer, professor of physics at the Georgia Institute of Technology in the United States. "The carbon nanotubes have not been effectively used after 10 years of discovery. The obstacles are not only the production cost of the carbon nanotubes, but also the dispersion of the application. Limitation and self-assembly capabilities." The key to affecting the dispersibility of carbon nanotubes is that there is a strong van der Waals attraction between the carbon nanotubes, which tends to cause the carbon tubes to gather together and is not easily soluble in aqueous solutions or organic solvents.

The traditional methods of dispersing carbon nanotubes can be roughly divided into two categories: a. covalent modification. This method mainly uses strong acid as a strong oxidant, due to defects in the structure of the carbon nanotubes (such as A five-membered ring or a seven-membered ring) can cut a long carbon tube into a short carbon nanotube of several hundred nanometers. During the reaction, the wall or the end of the carbon nanotube will react accordingly. Oxygen-containing functional groups, including carboxyl groups, carbonyl groups, and alcohol groups, etc., and other literature studies, in which a functional group such as fluorine or an alkane is attached to the side wall of the carbon nanotube without cutting the carbon nanotube. Reduce damage to the structure of the carbon nanotubes. The above-mentioned functionalized carbon nanotubes can be effectively dispersed in an aqueous solution or a different organic solvent, and the types and procedures of the functionalization of the carbon nanotubes are considerably recorded in the literature, and should be considered in the field of application. Select the type of functional group that is desired to be attached to the surface of the carbon nanotube.

Although the covalent bond modification method can effectively disperse the carbon nanotubes, it changes the structure of the carbon nanotubes during the functionalization process, and changes the unique properties of some carbon nanotubes. Subsequent applications were not as expected, so research into non-covalent bond modification methods was developed to disperse the carbon nanotubes.

b. Noncovalent modification Non-covalent bond modification is mainly divided into two kinds, one is based on surfactant as a dispersing agent, the most common is sodium dodecyl sufate (sodium dodecyl sufate, SDS), the carbon nanotubes are first oscillated by ultrasonic waves to destroy the van der Waals attraction between the carbon nanotubes, and the carbon tubes are respectively coated in the micelles formed by the surfactant, and the microcapsules are hydrophobic. The end is internally coated with a carbon nanotube, and the hydrophilic end is externally contacted with the solution to form a stable dispersion.

The other type is mainly a polymer with polar side chains. Commonly used, such as polyvinylpyrolidone (PVP), polystyrene sulfonate (PSS), etc., the dispersion method is also the first to use ultrasonic waves. Oscillation destroys the van der Waals attraction between the carbon nanotubes, and then the main chain of the polymer is wrapped around the carbon nanotubes to form a dispersed nanocarbon tube supramolecular complex, while the polar side chains are Contact with the solution medium to achieve the dispersion effect, the thermodynamic driving force for forming the complex is to exclude the hydrophobic interface between the carbon nanotube wall and the solution medium. This method is also a reversible system, which can replace the solution with a less polar one. Solvents (such as tetrahydrofuran, THF) can cause the winding effect to fail due to changes in the solution system. The dispersion formed by this method can also be regarded as a composite material, which will improve the properties of the carbon nanotube itself and the polymer.

These two non-covalent bond modification methods have little effect on the properties of the carbon nanotubes themselves because they do not destroy the structure of the carbon nanotubes, but in the case of surfactants, because they are detected in biochemical sensors. The presence of surfactants has the potential to cause electrode passivation, detection of signal interference, etc., and polymers can be used as an insulating layer to block these surfactants, but will also slightly reduce the detected current signal.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for dispersing a carbon nanotube with cerium oxide particles, which can effectively reduce the number of steps and preserve the original structure of the carbon nanotube.

Another object of the present invention is to provide a dispersion of a carbon nanotube that retains the original structure and properties of the carbon nanotube and enhances its applicability.

The method for dispersing a carbon nanotube by using cerium oxide particles is to mix positively charged cerium oxide particles with a carbon nanotube in an inorganic solvent, so that the carbon nanotubes are surrounded by cerium oxide particles to achieve The effect of dispersion is obtained, and a dispersion of a carbon nanotube is obtained accordingly.

The positively charged cerium oxide particles are preferably mixed with the carbon nanotubes in a manner that is ultrasonically oscillated. The carbon nanotube of the present invention may be a multi-walled carbon nanotube or other type of carbon nanotube; the content of the carbon nanotube is usually less than 40 mg/mL, preferably less than 20 mg/mL.

The diameter of the cerium oxide is 1 to 50 nm, preferably 10 to 15 nm; the pH of the aqueous cerium oxide particle solution is usually less than 3, preferably about 2; the concentration of the aqueous cerium oxide particle solution is usually less than 15 wt. %, preferably 1 to 10 wt%.

The inorganic solvent of the present invention may be water or other suitable inorganic solvent.

The method for dispersing a carbon nanotube of the present invention is to disperse a carbon nanotube in an aqueous solution by means of a non-covalent bond and a non-organic solvent modification. After it is added to the carbon nanotube by using a positively charged aqueous solution of nanoparticle, the nanoparticle with high charge will surround the carbon nanotube, and finally the nanoparticle will be charged with the same charge. The carbon nanotubes are uniformly dispersed in the aqueous solution.

The medicines used in the preferred embodiments of the present invention include: 1. Multi-walled carbon nanotubes, having a purity of about 99%, manufactured by TECO.

2. Ceria suspension: colloidal silica, a suspension aqueous solution of cerium oxide coated with cerium oxide particles, with a positive charge, 30 wt%, manufactured by DuPont under the trade name LUDOX CL.

3. Hydrogen chloride: purity of about 96%, manufactured by SHOWA.

4. Sodium Hydroxide: Purity is about 35%, manufactured by OSAKA.

Example 1

a. preparing an aqueous solution of cerium oxide particles (1 wt%) and adjusting its pH value to 2 with hydrogen chloride (0.1 M); b. adding a multi-layered wall carbon nanotube to an aqueous solution of cerium oxide particles to form a carbon nanotube a mixture of 5 mg/mL; c. Fully disperse the multi-walled carbon nanotubes in an aqueous solution of cerium oxide particles using an ultrasonic oscillator, and let stand for several days to observe the oxidation of the multi-walled carbon nanotubes The dispersion in the aqueous solution of cerium particles.

Comparative example 1~5

The procedure of Example 1 was repeated except that the pH of the aqueous solution of cerium oxide particles was adjusted to 3, 4, 5, 6, and 7 with hydrogen chloride (0.1 M) and sodium hydroxide (0.1 M), respectively, as shown in Table 1. .

Examples 2 to 3 and Comparative Example 6

The procedure of Example 1 was repeated except that the content of the multilayered wall carbon nanotubes was changed to 10 mg/mL, 20 mg/mL, and 40 mg/mL, respectively, as shown in Table 1.

Comparative Example 7

The procedure of Example 2 was repeated, except that step a used deionized water containing no cerium oxide particles, and the multi-walled nanotubes of step b were 5 mg/mL, as shown in Table 1.

Examples 4 to 6 and Comparative Examples 8 to 9

The procedure of Example 4 was repeated, but the content of the multi-walled carbon nanotubes of step b was 20 mg/mL, and the weight percentage of the cerium oxide particles was changed to 2 wt%, 5 wt%, 10 wt%, 15 respectively. Wt%, 30 wt%, as shown in Table 1.

The dispersion effects of the above examples and comparative examples are illustrated by photographs and microscopic analysis, and are summarized in Table 1.

A. Effect of pH value of aqueous solution of cerium oxide particles on dispersion effect From Example 1 and Comparative Examples 1 to 5, multi-layered wall carbon nanotubes (5 mg/mL) at different pH values of cerium oxide particle aqueous solution (1 wt The dispersion in %) is shown in Figures 1 and 2.

1 is the dispersion after ultrasonic oscillation for 1 hour: (a) pH = 2; (b) pH = 3; (c) pH = 4; (d) pH = 5; (e) pH = 6 (f) pH=7; after ultrasonic vibration for 1 hour, it was found that the multilayered-walled carbon nanotubes were uniformly dispersed in each aqueous solution without any precipitation.

Figure 2 shows the dispersion after standing for 24 hours: (a) pH = 2; (b) pH = 3; (c) pH = 4; (d) pH = 5; (e) pH = 6; ) pH = 7. After standing for 24 hours, it can be clearly seen that the multi-walled carbon nanotubes are still uniformly dispersed in the solution in the aqueous solution of cerium oxide particles (a bottle) of pH=2; and the oxidation at pH=3~7 In the aqueous solution of cerium particles (b~f bottle), delamination or precipitation may occur, indicating that the multi-walled carbon nanotubes are clustered together. It is understood that the pH of the aqueous solution of the cerium oxide particles (1 wt%) dispersed multi-walled carbon nanotubes (5 mg/mL) should be less than 3, preferably about 2.

B. Effect of the amount of multi-layered wall carbon nanotubes added From Examples 1 to 3 and Comparative Examples 6 to 7, different amounts of multi-layered wall carbon nanotubes were used in an aqueous solution of cerium oxide particles (pH = 2, 1 wt%). The dispersion is shown in Figures 3 and 4.

Figure 3 shows the dispersion after 1 hour of ultrasonic oscillation: (a) 5 mg/mL multi-walled nanotubes dispersed in deionized water at pH=2; (b) 5 mg/mL; (c) 10 mg (d) 20 mg/mL; (e) 40 mg/mL multi-walled nanotubes dispersed in an aqueous solution of cerium oxide particles; after ultrasonic vibration for 1 hour, it was found that the multi-walled carbon nanotubes were uniformly dispersed. In each aqueous solution, no precipitation occurred.

Figure 4 shows the dispersion after 72 hours of standing: (a) 5 mg/mL multi-walled nanotubes dispersed in deionized water; (b) 5 mg/mL; (c) 10 mg/mL; 20 mg/mL; (e) 40 mg/mL multi-walled nanotubes were dispersed in an aqueous solution of cerium oxide particles.

After standing for 72 hours, in Comparative Example 7, it was found that in the aqueous solution of pH=2 deionized water (a bottle), the multi-walled carbon nanotubes quickly aggregated to form a precipitate, which proved that the multilayered-walled carbon nanotubes were Dispersion in the aqueous solution of cerium oxide particles is indeed due to the influence of cerium oxide particles, and does not effectively disperse the multi-walled carbon nanotubes due to the change in the pH value of the solution.

In Examples 1 to 3, 5~20 mg/mL multi-walled carbon nanotubes were added to the cerium oxide particle aqueous solution (b~d bottle), which remained well dispersed after 72 hours, without precipitation. Occurrence and uniform dispersion can last for about two weeks.

However, in Comparative Example 6, 40 mg/mL multi-walled carbon nanotubes were added to the aqueous solution of cerium oxide particles (e-bottle), and stratification was apparent after 72 hours, and the multi-layered nano-crystals could not be effectively dispersed. Carbon tube, the reason is that the amount of multi-walled carbon nanotubes (40 mg / mL) has exceeded the content of the aqueous solution of cerium oxide particles (pH = 2, 1wt%), multi-walled carbon nanotubes Aggregation can no longer maintain a uniform dispersion.

Through the above results, an aqueous solution of cerium oxide particles (pH = 2, 1 wt%) can disperse a multi-walled carbon nanotube having a content of less than 40 mg/mL; preferably less than 20 mg/mL.

C. Effect of weight percentage of cerium oxide particles From Examples 3 to 6 and Comparative Examples 8 to 9, dispersion of multi-walled nanotubes (20 mg/mL) in aqueous solutions of different weight percentages of cerium oxide particles The situation is shown in Figures 5 and 6.

Figure 5 is the weight percentage of cerium oxide particles in the dispersion after 1 hour of ultrasonic oscillation: (a) 1; (b) 2; (c) 5; (d) 10; (e) 15; (f) 30 Wt%. After 1 hour of ultrasonic vibration, it was found that the multi-walled carbon nanotubes were uniformly dispersed in each aqueous solution without any precipitation.

Figure 6 is the dispersion after 72 hours of standing, the weight percentage of cerium oxide particles: (a) 1; (b) 2; (c) 5; (d) 10; (e) 15; (f) 30 Wt%. After standing for 72 hours, 1 to 10 wt% of cerium oxide particle aqueous solution (a~d bottle) can be found to work well for dispersing multi-walled carbon nanotubes (20 mg/mL).

The 15 wt% aqueous solution of cerium oxide particles (e bottle) obviously has delamination, which means that excessive cerium oxide particles are not conducive to the dispersion of multi-walled carbon nanotubes. That is, the upper limit of the concentration of the aqueous cerium oxide particle solution should be less than 15% by weight; preferably from 1 to 10% by weight.

As for the 30 wt% aqueous solution of ceria particles (f bottle), it is solidified because the weight percentage of the ceria particles is too high, resulting in the gelation of the aqueous solution after the addition of the multi-walled carbon nanotubes. .

D. Transmission electron microscopy analysis Using a transmission electron microscope (TEM) (JEM-200CX from, JEOL), the surface morphology of the carbon nanotubes before and after dispersion was observed, and it was confirmed whether the cerium oxide particles were surrounded. On the surface of the carbon nanotubes. Figure 7 is a multi-layered wall carbon nanotube (a) before dispersion; (b) TEM pattern after dispersion.

It can be seen from Fig. (a) that the multi-walled carbon nanotubes are gathered together to form a bundle. From the figure (b), it can be seen that the multi-walled carbon nanotubes are dispersed one by one, which proves that the cerium oxide particles can indeed disperse the multi-walled carbon nanotubes, and the surface of the multi-walled carbon nanotubes is also The presence of nanoparticles is observed, indicating that the cerium oxide particles do surround the multi-layered wall carbon nanotubes. From the partial enlarged view of Fig. (b), it can be seen that the cerium oxide particles have a particle diameter of about 10 to 14 nm, and the multilayered wall carbon nanotubes have a diameter of about 40 nm, which clearly shows that the cerium oxide particles surround Living around a multi-walled carbon nanotube.

E. Atomic force microscopy analysis using atomic force microscope (AFM) (SPA-400 multiple function units together with SPI-3800N, Seiko) tapping scanning mode to observe the surface morphology and confirmation of carbon nanotubes before and after dispersion Whether the cerium oxide particles surround the surface of the carbon nanotubes. Figure 8 is a multi-layered wall carbon nanotube (a) before dispersion; (b) 2-D pattern of AFM after dispersion.

Figure (a) shows the surface topography of a single multi-walled carbon nanotube. It can be clearly seen that the multi-walled carbon nanotube is a straight tube with a diameter of 40 nm. The morphology is consistent with the arc discharge method and has straightness. The characteristics of the rod-shaped and structurally intact defects are quite different from those of the multi-layered wall carbon nanotubes prepared by the chemical vapor deposition method of the low-temperature process and having a curved shape and many defects.

A single multi-walled carbon nanotube surrounded by cerium oxide particles is also scanned by atomic force microscopy to obtain the figure (b). It is obvious that the cerium oxide particles are surrounded by the multilayered carbon nanotubes, and the particle diameter is also At about 10~15 nm, it is consistent with the results of the transmission electron microscope. It is known from Figure (b) that the single-walled nano-carbon nanotubes surrounded by cerium oxide particles have a diameter of about 100 nm, which is much larger than the diameter of the multi-walled carbon nanotubes. It was demonstrated that the cerium oxide particles surround the multi-layered wall carbon nanotubes.

By atomic force microscopy and transmission electron microscopy analysis, it can be proved that the positively charged cerium oxide particles do surround the multi-walled carbon nanotubes. Moreover, since the cerium oxide particles have a positive charge, a repulsive force is generated between them, so that the multilayered wall carbon nanotubes can be uniformly dispersed in the aqueous solution of the cerium oxide particles. Such a non-covalent bond and a non-organic solvent can effectively reduce the number of operating steps and retain the original excellent properties of the carbon nanotubes, which can be utilized in many industries.

Figures 1 and 2 show the dispersion of multi-walled nanotubes in aqueous solutions of cerium oxide particles at different pH values.

Figures 3 and 4 show the dispersion of different amounts of multi-walled nanotubes in an aqueous solution of cerium oxide particles.

Figures 5 and 6 show the dispersion of multi-walled nanotubes in aqueous solutions of different weight percentages of cerium oxide particles.

Figure 7 is a TEM image of the multilayered wall carbon nanotubes before and after dispersion.

Figure 8 is a 2-D pattern of the AFM before and after the dispersion of the multilayered wall carbon nanotubes.

Claims (10)

A method for dispersing a carbon nanotube by using cerium oxide particles by mixing a cerium oxide particle coated with a positively-charged metal oxide with a carbon nanotube in an inorganic solvent having a pH of less than 3 The carbon nanotubes are surrounded by the cerium oxide particles to achieve the effect of dispersion. The method of claim 1, wherein the positively charged metal oxide is aluminum oxide. The method of claim 1, wherein the carbon nanotubes are less than 40 mg/mL. The method of claim 1, wherein the concentration of the cerium oxide particles is less than 15 wt%. The method of claim 1, wherein the inorganic solvent is water. A carbon nanotube dispersion comprising a surface coated with a positively charged metal oxide cerium oxide particle, a carbon nanotube, and an inorganic solvent having a Ph value of less than 3, wherein the carbon nanotube is coated with the cerium oxide Surround the particles. The dispersion of claim 6, wherein the positively charged metal oxide is aluminum oxide. The dispersion of carbon nanotubes as described in claim 6 wherein the content of the carbon nanotubes is less than 40 mg/mL. The dispersion of carbon nanotubes according to claim 6, wherein the concentration of the cerium oxide particles is less than 15 wt%. The dispersion of carbon nanotubes according to claim 6, wherein the inorganic solvent is water.