KR20090006449A - Methods of manufacturing carbon nanotube-inorganic oxide nanoparticle composites - Google Patents

Abstract

A method of manufacturing a carbon nanotube-inorganic oxide nano particle complex body is provided to have a very simple process by binding a semiconductor or an insulator oxide nano particle to the carbon nanotube using a method of self-assembly having high selectivity. A method of manufacturing a carbon nanotube - inorganic oxide nano particle complex body comprises steps of: adhering an inorganic oxide nano particle coated to metal salt on a substrate surface; growing the carbon nanotube on the materials; dipping the material in which the carbon nanotube is grown up in water or an aqueous solution and charging the inorganic oxide nano particle; and irradiating an ultraviolet ray in the dipped material, attaching and detaching inorganic oxide nano particle from the material charged by a polarity same with the inorganic oxide nano particle and static-electrically binding the inorganic oxide nano particle to the carbon nanotube charged into opposite polarity with the inorganic oxide nano particle.

Description

Methods of manufacturing carbon nanotube-inorganic oxide nanoparticle composites

1 schematically illustrates a photoinduced self-assembly process of the inorganic oxide nanoparticles of the present invention to the carbon nanotube sidewalls.

FIG. 2 schematically shows the results of self-assembly of inorganic oxide nanoparticles on the sidewalls of carbon nanotubes depending on the type of substrate and the presence or absence of ultraviolet radiation.

3A and 3B show electron microscopic (SEM) analysis photographs of self-assembled composites prepared according to Example 1 and Comparative Example 1 of the present invention. The lower left inset of Figure 3a shows a high resolution transmission microscope (HRTEM) analysis of the TiO ₂ nanoparticles, indicating that the size of the scale bar is 2 nm.

4A, 4B and 4C show electron microscope (SEM) analysis photographs of self-assembled composites prepared according to Example 2, Comparative Example 2 and Comparative Example 3 of the present invention.

5A and 5B show electron microscopic (SEM) analysis photographs of self-assembled composites prepared according to Example 3 and Comparative Example 4 of the present invention.

6A and 6B show electron microscope (SEM) analysis photographs and enlarged photographs of self-assembled composites prepared according to Example 4 of the present invention.

Figure 7 shows an electron micrograph (SEM) analysis of the self-assembled composite prepared according to Example 5 of the present invention.

The present invention relates to a method for producing a composite of carbon nanotube-inorganic oxide nanoparticles. More specifically, the present invention relates to a method for producing a composite of carbon nanotube-inorganic oxide nanoparticles, in which inorganic oxide nanoparticles are self-assembled on sidewalls of carbon nanotubes by photoinduction.

Carbon Nanotube (CNT) is a carbon allotrope made up of carbon present on the earth in a large quantity. It is a substance in which one carbon is combined with another carbon atom in a hexagonal honeycomb pattern of sp ² bond to form a tube. It is an extremely small region of material with a diameter of nanometers (nm = 1 billionth of a meter). Carbon nanotubes have a graphite sheet rounded to a nano-sized diameter and have a sp ² bond structure. Depending on the angle and shape of the graphite surface curling, it is electrically conductive or semiconducting, and carbon nanotubes are single-walled nanotubes or multiwalled nanotubes, depending on the number of bonds in the walls. ), And single-walled nanotubes are called bundles of nanotubes.

Electrical conductivity is similar to copper, and thermal conductivity is like diamond, which is the best in nature. The strength is more than 100 times stronger than steel of the same thickness. Carbon fiber, known to be the thinnest and strongest, can be broken by only 1% strain, while carbon nanotubes can withstand 15% strain. As such, carbon nanotubes have excellent mechanical properties, electrical selectivity, excellent field emission characteristics, high-efficiency hydrogen storage media, and are known as perfect new materials with few defects. Therefore, electron emitters, vacuum fluorescent displays (VFDs), white light sources, field emission displays (FEDs), lithium ion secondary battery electrodes, hydrogen storage fuel cells, nanowires, nanocapsules, nanotweezers, AFM / STM tips, single-electron devices, gas sensors, medical and engineering micro components, and high-performance composites have shown endless applications.

On the other hand, the method of hybridizing independent nanomaterials into a composite is one of the efficient methods for developing functional materials because it may have new properties that have not existed before or a synergistic effect can be achieved than the individual properties of each material. Among many nanocomposites, carbon nanotube-based composites, which are a mixture of carbon nanotubes, polymers, semiconductor quantum dots, transition metal complexes, and wide bandgap metal oxide semiconductors, can be used for solar energy conversion systems and efficient field emission sources. have.

Usually, in order to increase the production efficiency of nanocomposites, suitable organic functional molecules are required as an anchoring group. Such organic functional molecules form unique stable chemical bonds or form noncovalent hybrid materials. According to Patent Publication No. 10-2005-0011867, a linker is used by using a mixture of a carbon nanotube having a carboxylate group introduced into the surface by an acid treatment and a metal nanoparticle having a magnetic molecular assembly layer of a thiol compound formed thereon. A conductive film free from compatibility problems between carbon nanotubes and metal particles by making carbon nanotube-g-metal nanoparticles grafted by using the same, and then dispersing them in an organic solvent or a polymer organic solution and applying and drying them on a substrate. It is disclosed that can be obtained. However, when the electrical properties of the original material are to be maintained, such organic materials act as a negligible energy barrier, thus preventing the synergistic effect. Therefore, there is a need to develop a carbon nanotube-metal hybrid composite free of organic substances.

Patent Publication No. 10-2007-0041024 discloses a method for producing carbon nanotubes for field emission light emitting materials in which transition element metals are coated in nanometer size as an efficient field emission source. This is a step of surface treatment of carbon nanotubes with an acid solution, activation of the surface in (SnCl ₂ + PdCl ₂ ) / HCl solution, immersed in a plating solution containing a compound or a complex containing a transition metal element and coated And oxidizing the transition metal element by thermal oxidation or chemical oxidation.

According to a method recently reported by the present inventors, metal nanoclusters have been directly synthesized on the surface of carbon nanotubes by a spontaneous charge transfer reaction (HC Choi. M. Shim, S. Bangsaruntip, H. Dai, J. Am. Chem. Soc. 2002. 124, 9058). However, according to this method, most transition metal ions are difficult to be reduced by carbon nanotubes due to misalignment of the electrochemical potential, so they are not applicable to transition metals.

Therefore, there is a need for a method of preparing a new carbon nanotube-based composite that can be applied to transition metal nanoparticles without using organic molecules.

The technical problem to be achieved by the present invention is to provide a method for producing a carbon nanotube-inorganic oxide nanoparticle composite which can self-assemble inorganic oxide nanoparticles to a high selectivity on the sidewalls of carbon nanotubes on a substrate without using organic molecules. It is.

One aspect of the present invention to achieve the above technical problem,

Attaching inorganic oxide nanoparticles coated with a metal salt to a surface of the substrate;

Growing carbon nanotubes on the substrate;

Charging the inorganic oxide nanoparticles by immersing the substrate on which the carbon nanotubes are grown in water or an aqueous solution; And

Irradiating the immersed substrate with ultraviolet rays, desorbing the inorganic oxide nanoparticles from the substrate charged with the same polarity as the inorganic oxide nanoparticles, and electrostatically bonding the carbon nanotubes charged with the opposite polarity with the inorganic oxide nanoparticles. It provides a method for producing a carbon nanotube-inorganic oxide nanoparticle composite comprising.

Another aspect of the invention,

Depositing a metal oxide catalyst particle on a surface of the substrate;

Growing carbon nanotubes on the substrate;

Immersing the substrate in water or an aqueous solution in which inorganic oxide nanoparticles are dispersed; And

The immersed substrate is irradiated with UV light to provide a carbon nanotube-inorganic oxide nanoparticle composite manufacturing method comprising electrostatically bonding to carbon nanotubes charged with opposite polarity to inorganic oxide nanoparticles.

Hereinafter, the present invention will be described in more detail.

1 schematically illustrates a process for preparing a carbon nanotube-inorganic oxide nanoparticle composite according to an aspect of the present invention.

The substrate used in the method for producing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention is p-type or n-type doped, Si, Ge, Sn, Se, Te, GaAs, GaN, GaP, GaSb, AlSb, InP , SiC, SiGe, ZnS, CdTe, InGaN, GaAs _1-y P _y , Al _x Ga _1-x As, Hg _x Cd _1-x Te, In _x1 Al _x2 Ga _1-x1-x2 P, In _1-x Ga _x As _y P _1-y , Al _x Ga _1-x As _y Sb _1-y (each x, x ₁ , x ₂ , and y are each independently greater than 0 and less than 1) It may be a semiconductor substrate selected from or a semiconductor substrate coated with an insulating layer thin film. In addition, the insulating layer is preferably formed of one or more selected from the group consisting of silicon oxide, silicon oxynitride, and silicon nitride. The use of the doped substrate is for electrostatic interaction with inorganic oxide nanoparticles which are then charged by ultraviolet irradiation as described below. It is also desirable that all substrates be sonicated with 2-propanol and washed with deionized water before use.

The metal of the metal salt used in the method for producing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention may be at least one metal selected from the group consisting of Fe, Co, and Ni. This is to promote the growth of carbon nanotubes by the chemical vapor deposition method later.

The inorganic oxide nanoparticles used in the method for preparing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention may be a semiconductor or an insulator oxide, and preferably TiO ₂ or SiO ₂ .

The inorganic oxide nanoparticles used in the present invention can be prepared by a known method and the size of the inorganic oxide nanoparticles is 1 nm to 100 nm on average.

In the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, the step of attaching the inorganic oxide nanoparticles coated with a metal salt on the substrate is a metal salt from a mixed solution of an aqueous solution of a metal salt and an inorganic oxide nanoparticle dispersion. Forming a dispersion of the coated inorganic oxide nanoparticles, and then dip coating the substrate to the mixed solution to attach the inorganic oxide nanoparticles coated with the metal salt on the surface of the substrate, and then drying. . For example, Fe (III) coated with TiO ₂ can be made in a way that was stirred at a constant temperature and time by the addition of FeCl ₃ aqueous TiO ₂ dispersion.

Then, carbon nanotubes are grown on the substrate.

The growth of the carbon nanotubes used in the method for preparing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention is not particularly limited, and may include, but are not limited to, arc-discharge, laser evaporation, and plasma chemical vapor phase. Can be grown by any one method selected from the group consisting of plasma enhanced chemical vapor deposition, thermal chemical vapor deposition, vapor phase growth, electrolysis, flame synthesis. In particular, thermochemical vapor deposition is suitable for synthesizing high purity materials, controlling microstructures, and having a simple apparatus and absolutely advantageous for mass synthesis. When the metal salt coated on the inorganic oxide nanoparticles described above is exposed to high temperature in the thermochemical vapor deposition step, the metal salt is converted into a metal oxide and serves as a starting point of carbon nanotube growth.

In addition, the carbon nanotubes used in the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention are preferably single-walled carbon nanotubes.

Carbon nanotubes grow from inorganic oxide nanoparticles coated with some metal oxide catalysts, only a few of them are the starting point for the growth of carbon nanotubes, and many inorganic oxide nanoparticles remain on the substrate without reacting.

Subsequently, the substrate was immersed in a quartz cuvet containing water or an aqueous solution (specifically, an pH-adjusted aqueous solution by adding acid or base to water) and irradiated with ultraviolet light to the immersed substrate to be the same as the inorganic oxide nanoparticles. The nanocomposite is prepared by desorbing the inorganic oxide nanoparticles from the substrate charged with the polarity and electrostatically bonding the inorganic oxide nanoparticles to the carbon nanotubes charged with the opposite polarity. That is, the present manufacturing process may be divided into two-step photochemical processes in which inorganic oxide nanoparticles are desorbed from the surface of the substrate and then self-assembled at high density on the sidewalls of carbon nanotubes by irradiating ultraviolet rays.

Such an ultraviolet irradiation process may include a step of self-assembling, for example, by irradiating a UV lamp of 100 to 800W for 1 to 10 hours.

Hereinafter, this self-assembly will be described in more detail with reference to FIG. 2.

FIG. 2 schematically shows the results of self-assembly of TiO ₂ nanoparticles on the sidewalls of carbon nanotubes depending on the type of substrate and the presence of UV radiation.

According to the present invention, when the substrate on which the carbon nanotubes are grown is immersed in water or an aqueous solution, the surface of the inorganic oxide nanoparticles exposed to the water phase has a constant charge. In general, the polarity of the surface charge of the inorganic oxide nanoparticles dispersed in water can be predicted from the relationship between the isoelectric point (pI) of the inorganic oxide nanoparticles and the pH of the nanoparticle dispersion. For example, TiO ₂ dispersed in deionized water has a pI of about 6, while TiO ₂ coated on Si or SiO ₂ has an isoelectric point of about 4, which is Si or SiO ₂ with a pI value of 2 to 2.5. Because it is affected. In this case, the surface of the TiO ₂ nanoparticles has a negative charge when the pH exceeds 4, and a positive charge when the pH is less than 4. At this time, since the pH of the aqueous dispersion in which the inorganic oxide nanoparticles are exposed is 5.7, the inorganic oxide nanoparticles have a negative charge beyond the isoelectric point.

Subsequently, surface charges are generated on the substrate by irradiation with ultraviolet rays. For example, in the case of doped Si, a small number of charge carriers are known to increase substantially on the surface with light irradiation. Negative charges accumulate on the substrate surface. As a result, when the substrate is p-type Si, the attached TiO ₂ detaches from the surface of the substrate by electrostatic repulsion. The concentration of the TiO ₂ nanoparticles desorbed from the substrate into deionized water after ultraviolet irradiation from one embodiment according to the present invention was analyzed by ICP / Mass spectroscopy (Perkin-Elmer, ELAN DRC-e), and 1.69 × 10 ^-3. It has a concentration of mg / L, which is simply desorbed TiO ₂ when soaked in deionized water. It is twice the concentration of 0.85 × 10 ⁻³ mg / L, the concentration of nanoparticles.

Second, the surface of the carbon nanotubes attached to the substrate as the ultraviolet light is irradiated causes the negative charge (or positive charge) accumulated on the underlying substrate surface to increase the hole (h +) (or electron) concentration in the carbon nanotubes. It is self-assembled in such a way that the inorganic oxide nanoparticles charged with negative charges (or positive charges) desorbed from the surface of the substrate by being charged with positive charges (or negative charges) and carbon nanotubes by electrostatic attraction. For example, TiO ₂ is desorbed from the p-type Si substrate in accordance with the above-described ultraviolet irradiation, and the carbon nanotubes increase the hole concentration by the negatively charged substrate so that the surface is positively charged. As a result, the negatively charged TiO ₂ is coupled to the sidewall of the positively charged inductively charged carbon nanotubes by electrostatic attraction.

On the other hand, if the n-type Si substrate is used instead of the p-type, the polarity is reversed, so that electrostatic attraction acts between the substrate and the inorganic oxide nanoparticles, so that the inorganic oxide nanoparticles are not detached from the substrate and can be self-assembled on the sidewall of the carbon nanotubes. none. In this case, if the pH of the aqueous dispersion is lower than the isoelectric point of the inorganic oxide nanoparticles, the surface of the inorganic oxide nanoparticles can be self-assembled by the above method since the surface of the inorganic oxide nanoparticles is charged with a positive charge. The pH of the aqueous dispersion can be adjusted by using an aqueous solution prepared by adding acid or base to water.

Therefore, in the method for preparing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, in order to self-assemble the inorganic oxide nanoparticles on the sidewalls of the carbon nanotubes, when the pH of the aqueous dispersion is greater than the isoelectric point of the inorganic oxide, the substrate is p. It is preferable that it is a type Si, whereas when the pH of an aqueous dispersion is smaller than the isoelectric point of an inorganic oxide, it is preferable that the said base material is n type Si. In other words, carbon nanotubes and inorganic oxide nanoparticles are combined by electrostatic interaction by appropriately selecting the type of inorganic oxide nanoparticles, the pH condition of the aqueous dispersion and the type of the substrate, and inducing polarity of the substrate and carbon nanotubes by ultraviolet rays. To prepare a composite.

In the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, ultraviolet rays may be irradiated for 1 hour to 10 hours, preferably 4 hours. If it is too short than the minimum time, it is difficult for a sufficient self-assembly process to occur, and if it is too long than the maximum time, there is a problem that productivity is reduced due to an increase in process time.

According to another aspect of the present invention, carbon nanotubes capable of self-assembling inorganic oxide nanoparticles with high selectivity on sidewalls of carbon nanotubes by supplying externally without attaching the inorganic oxide nanoparticles to the substrate surface before self-assembly- The present invention relates to a method for preparing an inorganic oxide nanoparticle nanocomposite. According to the above production method, the process may be further simplified by omitting the step of attaching the inorganic oxide nanoparticles coated with the metal salt on the surface of the substrate of the present invention.

The manufacturing method is to first deposit the metal oxide catalyst particles on the surface of the substrate. It may use known methods (see HC Choi, S. Kundaria, DW Wang, A. Jarvey, Q. Wang, M. Rolandi, H. Dai, Nano Lett. 2003, 3, 157), which is described later on Is to activate the growth of carbon nanotubes.

The substrate used in the method for producing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention is p-type or n-type doped, Si, Ge, Sn, Se, Te, GaAs, GaN, GaP, GaSb, AlSb, InP , SiC, SiGe, ZnS, CdTe, InGaN, GaAs _1-y P _y , Al _x Ga _1-x As, Hg _x Cd _1-x Te, In _x1 Al _x2 Ga _1-x1-x2 P, In _1-x Ga _x As _y P _1-y , Al _x Ga _1-x As _y Sb _1-y (each x, x ₁ , x ₂ , and y are each independently greater than 0 and less than 1) It may be a semiconductor substrate selected from or a semiconductor substrate coated with an insulating layer thin film. In addition, the insulating layer is preferably formed of one or more selected from the group consisting of silicon oxide, silicon oxynitride, and silicon nitride. The use of the doped substrate is for electrostatic interaction with inorganic oxide nanoparticles which are then charged by ultraviolet irradiation as described above. It is also preferred that all substrates be treated with 2-propanol ultrasonically and washed with deionized water prior to use.

The metal of the metal oxide catalyst particles used in the method for producing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention may be any one metal selected from the group consisting of Fe, Co, and Ni, or a mixture thereof. This is to promote the growth of carbon nanotubes by the chemical vapor deposition method later.

The inorganic oxide nanoparticles used in the method for preparing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention may be a semiconductor or an insulator oxide, and preferably TiO ₂ or SiO ₂ .

The inorganic oxide nanoparticles used in the present invention can be prepared by a known method and the size of the inorganic oxide nanoparticles is 1 nm to 100 nm on average.

In the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, the step of depositing the metal oxide catalyst particles on the surface of the substrate is immersed and stirred in the aqueous solution of the metal salt or metal salt and hydroxyl amine and then It is preferred to include the step of firing at a temperature of 600 to 1000 ℃ for 1 to 10 minutes. For example, after immersing the Si substrate in an aqueous solution mixed with a certain concentration of FeCl ₃ and NH ₂ OH and stirred for a certain time, spontaneous deposition of nanoparticles occurs, which is calcined for 5 minutes at a temperature of 800 ℃ Fe ₂ O ₃ The metal oxide catalyst particles can be deposited on the surface of the Si substrate by a method of converting the same into a Si substrate.

Then, carbon nanotubes are grown on the substrate.

The growth of the carbon nanotubes used in the method for preparing the carbon nanotube-inorganic oxide nanoparticle composite according to the present invention is not particularly limited, and may include, but are not limited to, arc-discharge, laser evaporation, and plasma chemical vapor phase. Can be grown by any one method selected from the group consisting of plasma enhanced chemical vapor deposition, thermal chemical vapor deposition, vapor phase growth, electrolysis, flame synthesis. In particular, thermochemical vapor deposition is suitable for synthesizing high purity materials, controlling microstructures, and having a simple apparatus and absolutely advantageous for mass synthesis.

In addition, the carbon nanotubes used in the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention are preferably single-walled carbon nanotubes.

Subsequently, the substrate is immersed in a quartz cuvet containing water or an aqueous solution in which inorganic oxide nanoparticles are dispersed and irradiated with ultraviolet rays to the carbon nanotubes which are charged with opposite polarity to the inorganic oxide nanoparticles. Nanocomposites are prepared by direct bonding. One mechanism of self-assembly of inorganic oxide nanoparticles is as follows. Some of the inorganic oxide nanoparticles in the dispersion adhere to the immersed substrate and the nanoparticles are charged either positively or negatively depending on the pH of the dispersion. As described above, the surface charge is then generated by the ultraviolet irradiation and the same polarity-charged nanoparticles attached to the substrate are detached from the surface of the substrate by electrostatic repulsion and at the same time opposed to the substrate by the substrate. Polar charges are self-assembled by electrostatic attraction on the sidewalls of the induced carbon nanotubes. According to another mechanism, the inorganic oxide nanoparticles in the dispersion may be self-assembled by electrostatic attraction by ultraviolet irradiation without being attached to the substrate after being charged as described above. The manufacturing method according to the present invention may occur by either or both of the above two mechanisms.

Such an ultraviolet irradiation process may include a step of self-assembling, for example, by irradiating a UV lamp of 100 to 800W for 1 to 10 hours.

In the method for preparing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, the inorganic oxide nanoparticles are self-assembled on the sidewalls of the carbon nanotubes so that when the pH of the aqueous dispersion is greater than the isoelectric point of the inorganic oxide, the substrate is p-type. Si is preferable, whereas when the pH of the aqueous dispersion is smaller than the isoelectric point of the inorganic oxide, it is preferable that the substrate is n-type Si. In other words, carbon nanotubes and inorganic oxide nanoparticles are combined by electrostatic interaction by appropriately selecting the type of inorganic oxide nanoparticles, the pH condition of the aqueous dispersion and the type of the substrate, and inducing polarity of the substrate and carbon nanotubes by ultraviolet rays. To prepare a composite. The pH of the aqueous dispersion can be adjusted by using an aqueous solution prepared by adding acid or base to water.

In the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, ultraviolet rays may be irradiated for 1 hour to 10 hours, preferably 4 hours. If it is too short than the minimum time, it is difficult for a sufficient self-assembly process to occur, and if it is too long than the maximum time, there is a problem that productivity is reduced due to an increase in process time.

In the method for preparing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, the concentration of the inorganic oxide nanoparticle dispersion is 0.5 to 1.5 ppm and preferably 1 ppm. If the concentration of the dispersion is below the minimum concentration, the self-assembly density is low, and if the concentration is above the maximum concentration, a thick film of inorganic oxide nanoparticles may be formed.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the technical idea of the present invention is not limited to the following examples.

Example  1: p type Si On board  Carbon Nanotubes- TiO ₂  Preparation of Nanoparticle Composite

25 mL of titanium tetraisopropoxide (TTIP, Aldrich) was added dropwise to 300 mL of deionized water whose pH was adjusted to 1 by HNO ₃ . The dispersion was then aged at 80 ° C. for 8 hours with continued stirring and left at room temperature for 7 days. The resulting TiO ₂ nanoparticles were confirmed by high resolution transmission electron microscopy (HRTEM) and the average diameter was 7 nm. Then 17.9 μL of 0.1 M FeCl ₃ aqueous solution was added to the TiO ₂ nanoparticle dispersion, and stirred for 2 hours to prepare a dispersion of Fe (III) / TiO ₂ catalyst.

TiO ₂ nanoparticles (Fe (III) / TiO ₂ ) coated with Fe (III) in the dispersion prepared in this manner were transferred onto a Si substrate by a dip coating method and then dried using nitrogen gas. The used Si substrate was a Si (111) substrate doped with boron and had a resistivity of 1 Ω · cm. Then, single-wall carbon nanotubes were grown by supplying CH ₄ , H ₂ , C ₂ H ₄ gas at 1000 ° C. at 900 ° C. under a chemical vapor deposition (CVD) system on Si substrates. The Si substrate containing the TiO ₂ nanoparticles and single-walled carbon nanotubes was then immersed in a quartz cuvet containing 100 mL of deionized water. The final pH of the dispersion was measured at about 5.7. Next, ultraviolet (480 W, ultra-high pressure mercury lamp, USHIO Inc.) was irradiated for 4 hours at room temperature to prepare a carbon nanotube-inorganic oxide nanoparticle composite. The result is shown in FIG. 3A.

Example  2: p type Si On board  Carbon Nanotubes- SiO ₂  Preparation of Nanoparticle Composite

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 1, except that SiO ₂ nanoparticles (Aldrich, average diameter = 15 nm) were used instead of TiO ₂ . The result is shown in FIG. 4A.

Example 3: Preparation of carbon nanotube-Ti O ₂ nanoparticle composite on p-type Si substrate covered with Si O ₂ thin film

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 1 except that the SiO ₂ / Si substrate was used as the substrate. The used SiO ₂ / Si substrate is a 500 nm thick SiO ₂ insulating layer thin film deposited on the p-type Si substrate of Example 1 by thermal evaporation. The result is shown in FIG. 5A.

Example 4 Preparation of Carbon Nanotube-TiO ₂ Nanoparticle Composites on a p-type Si Substrate by Direct Ti ₂ O ₂ External Supply

Fe ₂ O ₃ catalyst nanoparticles prepared on a p-type Si substrate by a conventional method (HC Choi, S. Kundaria, DW Wang, A. Jarvey, Q. Wang, M. Rolandi, H. Dai, Nano Lett. 2003 , 3, 157) to supply 1000, 500 and 20 sccm of CH ₄ , H ₂ , C ₂ H ₄ gas at 900 ° C. under chemical vapor deposition (CVD) system on the p-type Si substrate, respectively. Single-walled carbon nanotubes were grown, then immersed in a cuvet containing an aqueous dispersion containing 1 ppm of TiO ₂ nanoparticles, and UV (480 W, ultra-high pressure mercury lamp, USHIO Inc.) at room temperature for 4 hours. Irradiation during the preparation of carbon nanotube-inorganic oxide nanoparticle composite. The results are shown in FIGS. 6A and 6B.

Example 5 TiO Dispersed in Basic Aqueous Solution ₂  Carbon Nanotubes-TiO on p-type Si Substrates by Direct Supply ₂  Preparation of Nanoparticle Composite

Carbon nanotubes were prepared in the same manner as in Example 4, except that TiO ₂ having a negative charge was used on the surface prepared in basic condition of pH = 11 instead of TiO ₂ prepared in acidic condition. Inorganic oxide nanoparticle composites were prepared. The results are shown in Figures 7a and 7b.

Comparative Example 1 Carbon Nanotubes-TiO on a p-type Si Substrate Without Ultraviolet Rays ₂  Preparation of Nanoparticle Composite

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 1, except that the mixture was left at room temperature for 4 hours without irradiation with ultraviolet rays. The results are shown in Figure 3b.

Comparative Example 2: Carbon Nanotubes-SiO on p-type Si Substrate Without Ultraviolet Rays ₂  Preparation of Nanoparticle Composite

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 2, except that the mixture was left at room temperature for 4 hours without irradiation with ultraviolet rays. The results are shown in Figure 4b.

Comparative example  3: pH P-type under conditions of 1 Si On board  Carbon Nanotubes- SiO ₂ Preparation of Nanoparticle Composite

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 2, except that the pH of the inorganic oxide nanoparticle composite was adjusted to 1 using 1 M aqueous HCl solution. The result is shown in FIG. 4C.

Comparative example  4: n type Si On board  Carbon Nanotubes- TiO ₂  Preparation of Nanoparticle Composite

A carbon nanotube-inorganic oxide nanoparticle composite was prepared in the same manner as in Example 1, except that a Si substrate doped with phosphorus was used. The Si (100) substrate doped with phosphorus had a resistivity of 1 Ω · cm. The result is shown in FIG. 5B.

evaluation

Hereinafter, the analysis results of the composites prepared according to Examples 1 to 5 and Comparative Examples 1 to 4 will be described with reference to FIGS. 3 to 7.

The state of the carbon nanotube-inorganic oxide nanoparticle composites prepared according to Example 1 and Comparative Example 1 was investigated using a scanning electron microscope (SEM) and a high resolution transmission electron microscope (HRTEM), respectively, and the results are shown in FIG. 3A. And as shown in FIG. 3B.

Referring to this, first, from the high-resolution transmission microscope (HRTEM) analysis picture inserted in the lower left of Figure 3a it can be seen that the TiO ₂ prepared by a known method has a diameter of 7 nm on average. In addition, the composite of Example 1 shown in Figure 3a was found to be self-assembled on the sidewall of the single-walled carbon nanotubes with high density after the TiO ₂ nanoparticles are detached from the substrate surface. On the other hand, in the composite of Comparative Example 1 shown in Figure 3b was not irradiated with ultraviolet light, no self-assembly was observed. In other words, the irradiation of ultraviolet rays can be seen as an important active source of self-assembly.

The state of the carbon nanotube-inorganic oxide nanoparticle composites prepared according to Example 2, Comparative Example 2, and Comparative Example 3 was investigated using a scanning electron microscope (SEM), and the results are shown in FIGS. 4A, 4B, and 4, respectively. As shown in Figure 4c.

Referring to this, the composite of Example 2 shown in Figure 4a is easily detached from p-type Si due to the low isoelectric point (pI ~ 2) of SiO ₂ when irradiated with UV light in deionized water of pH = 5.7 single-walled carbon nano It was found that self-assembly occurred well on the side wall of the tube. On the other hand, when the ultraviolet light is not irradiated under the same conditions as in Comparative Example 2 shown in Figure 4b, no self-assembly was observed. In addition, when the pH of the aqueous solution is 1 from the result of the Comparative Example 3 shown in Figure 4c is lower than the isoelectric point of SiO ₂ because the surface of the substrate is charged with a positive charge, self-assembly did not occur.

The state of the carbon nanotube-inorganic oxide nanoparticle composites prepared according to Example 3 and Comparative Example 4 was investigated using a scanning electron microscope (SEM), and the results are shown in FIGS. 5A and 5B, respectively.

Referring to this, as in the composite of Example 3 shown in FIG. 5A, even in the case of p-type Si covered with a 500 nm SiO ₂ insulating layer thin film, self-assembly of TiO ₂ nanoparticles was observed, although not high density. I could see. Such substrates have a lower negative charge density than the induced negative charge of the pure p-type Si surface. On the other hand, when the n-type substrate was used as the composite of Comparative Example 4 shown in FIG. 5B, it was observed that the TiO ₂ nanoparticles were indiscriminately integrated on the substrate without self-assembly on the single-walled carbon nanotubes. .

The state of the carbon nanotube-inorganic oxide nanoparticle composite prepared according to Example 4 was investigated using a scanning electron microscope (SEM), and the results are shown in FIGS. 6A and 6B.

Referring to this, the self-assembled TiO ₂ to some extent can be observed.

The state of the carbon nanotube-inorganic oxide nanoparticle composite prepared according to Example 5 was investigated using a scanning electron microscope (SEM), and the results are shown in FIG. 7.

Referring to this, one can also observe self-assembled TiO ₂ . In this case, the pH of the dispersed aqueous solution contained in the cuvette is adjusted to 11, so that the surface of the nanoparticles has a negative charge. In addition, since the carbon nanotubes coated on the p-type Si substrate by ultraviolet irradiation have a positive charge, self-assembly may be directly generated by electrostatic attraction to produce a carbon nanotube-TiO ₂ nanoparticle composite.

In the method for producing a carbon nanotube-inorganic oxide nanoparticle composite according to the present invention, the semiconductor or insulator oxide nanoparticles can be bonded to the carbon nanotubes by self-assembly with high selectivity only by UV irradiation without using organic molecules. The process is very simple and economical. The carbon nanotube-inorganic oxide nanoparticle composite thus made may be used in photocatalyst and high efficiency photovoltaic devices.

Claims (16)

Attaching inorganic oxide nanoparticles coated with a metal salt to a surface of the substrate; Growing carbon nanotubes on the substrate; Charging the inorganic oxide nanoparticles by immersing the substrate on which the carbon nanotubes are grown in water or an aqueous solution; And Irradiating ultraviolet light to the immersed substrate to desorb the inorganic oxide nanoparticles from the substrate charged with the same polarity as the inorganic oxide nanoparticles and electrostatically bonding the carbon nanotubes charged with the opposite polarity to the inorganic oxide nanoparticles. Carbon nanotubes-inorganic oxide nanoparticles composite manufacturing method. Depositing a metal oxide catalyst particle on a surface of the substrate; Growing carbon nanotubes on the substrate; Immersing the substrate in water or an aqueous solution in which inorganic oxide nanoparticles are dispersed; And Irradiating ultraviolet rays to the immersed substrate, and electrostatically bonding to carbon nanotubes charged with opposite polarity to inorganic oxide nanoparticles. [Claim 3] The method of claim 1 or 2, wherein the metal of the metal salt is at least one member selected from the group consisting of Fe, Co, and Ni. The substrate of claim 1 or 2, wherein the substrate is p-type or n-type doped, Si, Ge, Sn, Se, Te, GaAs, GaN, GaP, GaSb, AlSb, InP, SiC, SiGe, ZnS, CdTe , InGaN, GaAs _1-y P _y , Al _x Ga _1-x As, Hg _x Cd _1-x Te, In _x1 Al _x2 Ga _1-x1-x2 P, In _1-x Ga _x As _y P _1-y , Al _x Ga _1-x As _y Sb _1-y (each x, x ₁ , x ₂ , and y each independently has a value greater than 0 and less than 1) Carbon nanotube-inorganic oxide nanoparticle composite production method. The method of claim 4, wherein the substrate is coated with an insulating layer. The method of claim 5, wherein the insulating layer is formed of at least one selected from the group consisting of silicon oxide, silicon oxynitride, and silicon nitride. The method of claim 1, wherein attaching the inorganic oxide nanoparticles coated with the metal salt to the surface of the substrate comprises mixing and stirring an aqueous solution of the metal salt and the inorganic oxide nanoparticle dispersion to form the inorganic oxide nanoparticle dispersion coated with the metal salt. ; Method of manufacturing a carbon nanotube-inorganic oxide nanoparticles composite, characterized in that it comprises the step of dip coating the substrate to the dispersion (dip coating) to dry. The method of claim 2, wherein the depositing of the metal oxide catalyst particles on the surface of the substrate is performed by immersing and stirring the substrate in an aqueous solution of a metal salt or a metal salt and hydroxyl amine, and then calcining at a temperature of 600 to 1000 ° C. for 1 to 10 minutes. Carbon nanotubes-inorganic oxide nanoparticles composite manufacturing method comprising the step of. The method according to claim 1 or 2, wherein the inorganic oxide is a semiconductor or an insulator. 3. The method of claim 1, wherein the inorganic oxide is TiO ₂ or SiO _{2. 4} . According to claim 1 or 2, wherein the carbon nanotubes (arc-discharge), laser evaporation (laser evaporation), plasma enhanced chemical vapor deposition (plasma enhanced chemical vapor deposition), thermal chemical vapor deposition (thermal chemical vapor deposition) Method for producing a carbon nanotube-inorganic oxide nanoparticle composite, characterized in that the growth by any one method selected from the group consisting of deposition, vapor phase growth, electrolysis, and flame synthesis method . The method of claim 1 or 2, wherein the carbon nanotubes are single-walled carbon nanotubes. The method of claim 1 or 2, wherein the pH of the aqueous solution is greater than the isoelectric point of the inorganic oxide and the substrate is p-type Si. The method according to claim 1 or 2, wherein the pH of the aqueous solution is smaller than the isoelectric point of the inorganic oxide and the substrate is n-type Si. The method of claim 1 or 2, wherein the ultraviolet light is irradiated for 1 hour to 10 hours. The method of claim 2, wherein the concentration of the inorganic oxide nanoparticle dispersion is 0.5 to 1.5 ppm.

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