Hydrophilic carbon nanohorn aggregate and method for producing the same

Abstract

To provide a hydrophilic carbon nanohorn assembly exhibiting excellent dispersibility over a long period of time in an aqueous dispersion medium.SOLUTION: A hydrophilic carbon nanohorn assembly includes a carbon nanohorn assembly with an oxygen-containing functional group introduced at the tip of a carbon nanohorn and includes a cyclodextrin capped and stabilized at the tip of the carbon nanohorn.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hydrophilic carbon nanohorn aggregate dispersible in water, a hydrophilic carbon nanohorn aggregate dispersion containing the hydrophilic carbon nanohorn aggregate, and a method for producing the hydrophilic carbon nanohorn aggregate.

Background Art

[0002] In recent years, nanocarbon materials having a nano-sized size have been found to have various properties including excellent conductivity, and carbon nanotubes, graphene, carbon nanohorn aggregates, etc. have been discovered and studied. Among these, carbon nanohorn aggregates having a spherical structure (for example, Patent Document 1) were known, but in recent years, fibrous structures (for example, Patent Document 2) have also been found. Applications in a wide range of fields are expected, including improving the response speed of sensors and actuators, improving the output of storage batteries and capacitors, and improving the conductivity of rubber and plastic composites.

[0003] Since the carbon nanohorn aggregate at the time of generation is a hydrophobic structure having no hydrophilic group, attempts have been made to modify the carbon nanohorn aggregate to impart hydrophilicity. For example, Non-Patent Document 1 discloses that by oxidizing the tip and side surfaces of carbon nanohorns with hydrogen peroxide, oxygen, etc., the tip and side surfaces of the carbon nanohorns are oxidized, and carboxyl groups and carbonyl groups are added to the tip and side surfaces, thereby improving the dispersibility in water.

[0004] Further, Non-Patent Document 2 discloses that when cyclodextrin is added, cyclodextrin binds to the tip of the nanohorn and acts as a surfactant, enabling the carbon nanohorn aggregate to be dispersed in water.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] [Non-Patent Document 1] M. Zhang et al., ACS Nano, 1, 2007, 265 [Non-Patent Document 2] H. Hanayama et al., Chem Asian J., 2020, 15, 1549 [Summary of the Invention] [Problems to be Solved by the Invention]

[0007] However, in the method described in Non-Patent Document 1, the tip and defect portions of the nanohorns are opened by oxidation, and various substances are incorporated into the inside of the carbon nanohorn aggregate. Therefore, there is a problem that chemical modification reactions for functionalization, catalyst loading, etc. become difficult. In addition, in the method described in Non-Patent Document 2, since the carbon nanohorn aggregate has complete water repellency, it is difficult to be capped, and there is a problem that the yield of the dispersion obtained in about 40 hours is about 27 wt%, and the capping efficiency is poor. Furthermore, since the cap gradually detaches, there is a problem with long-term stability. When the dispersibility in an aqueous solution is poor in this way, there is also a problem that it becomes difficult to remove graphite as an impurity contained during the production of the carbon nanohorn aggregate.

[0008] An object of the present invention is to provide a hydrophilic carbon nanohorn aggregate that exhibits excellent dispersibility over a long period in an aqueous dispersion medium. [Means for Solving the Problems]

[0009] One embodiment of the present invention relates to a hydrophilic carbon nanohorn aggregate having an oxygen-containing functional group introduced at the tip of a carbon nanohorn and a stabilized cyclodextrin that caps the tip of the carbon nanohorn. Another embodiment of the present invention relates to a method for producing a hydrophilic carbon nanohorn aggregate, which includes a step of subjecting a carbon nanohorn aggregate to an oxidation treatment and a step of treating the oxidized carbon nanohorn aggregate with cyclodextrin.

Advantages of the Invention

[0010] According to one embodiment of the present invention, it is possible to provide a hydrophilic carbon nanohorn aggregate that exhibits excellent dispersibility over a long period in an aqueous solution.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0012] Hereinafter, a hydrophilic carbon nanohorn aggregate according to one embodiment of the present invention will be described.

[0013] (Hydrophilic Carbon Nanohorn Aggregate) The hydrophilic carbon nanohorn aggregate of the present embodiment is obtained by performing a weak oxidation treatment on the carbon nanohorn aggregate and then performing a cyclodextrin treatment in an aqueous solution, as described later.

[0014] Fig. 1 schematically shows the structure of the tip of a carbon nanohorn (hereinafter, also simply referred to as the nanohorn tip). It has been shown in Non-Patent Document 2 that the tip of the carbon nanohorn is capped with cyclodextrin by treating the carbon nanohorn aggregate with cyclodextrin. As shown in Fig. 1, it is considered that the tip portion 1 of the carbon nanohorn is capped with cyclodextrin 2. In the present embodiment, the carbon nanohorn has been subjected to a weak oxidation treatment, and an oxygen-containing functional group has been introduced into the nanohorn tip portion 1. Since one cyclodextrin 2 has an OH group (hydroxyl group) as shown in Fig. 1, it interacts with the oxygen-containing functional group of the nanohorn tip portion 1 and is stabilized. Here, "being stabilized" means that, as shown in the examples, even when the aqueous dispersion of the carbon nanohorn aggregate is stored at room temperature (for example, in the range of 20 °C to 30 °C) for one week, the carbon nanohorn aggregate is dispersed. Specifically, "being stabilized by interaction" means that the OH group (hydroxyl group) of cyclodextrin is stabilized by hydrogen bonding with the oxygen-containing functional group of the nanohorn tip. It is well known that the oxygen-containing functional group and the OH group form a hydrogen bond. Also in the present embodiment, it is considered that the capping of cyclodextrin is stabilized by hydrogen bonding, that is, decapping (removal of the cap) is prevented. As shown in the examples, since the hydrophilic carbon nanohorn aggregate of the present embodiment exhibits stable dispersibility over a long period of time, it is strongly presumed that the capping state is stabilized by the above interaction, more specifically, hydrogen bonding, and it is difficult to consider other reasons.

[0015] As described later, the method for manufacturing a hydrophilic carbon nanohorn aggregate according to this embodiment includes a step of subjecting the carbon nanohorn aggregate to an oxidation treatment (in this step, oxygen-containing functional groups are introduced to the tips of the nanohorns) and a cyclodextrin treatment step (the tips of the nanohorns are capped with cyclodextrin and the cyclodextrin is fixed). Further, it can include a step of performing ultrasonic treatment and / or centrifugation treatment to remove impurities. Hereinafter, details will be described together with the method for manufacturing a hydrophilic carbon nanohorn aggregate.

[0016] <Raw material carbon nanohorn aggregate> The carbon nanohorn aggregate used as a raw material may be either a spherical carbon nanohorn aggregate or a fibrous carbon nanohorn aggregate (carbon nanobrush) (Japanese Patent No. 6179678), or a mixture thereof.

[0017] The spherical carbon nanohorn aggregate (hereinafter, sometimes abbreviated as CNHs) is a spherical structure (not necessarily a perfect sphere, but may be an elliptical shape, a donut shape, or other shapes) formed by carbon nanohorn aggregates such as a seed type, a bud type, a dahlia type, a petal dahlia type, and a petal type (graphene sheet structure), either alone or in combination. The seed type is a shape in which almost no or no angular protrusions are observed on the surface of the aggregate, the bud type is a shape in which some angular protrusions are observed on the surface of the aggregate, the dahlia type is a shape in which a large number of angular protrusions are observed on the surface of the aggregate, and the petal type is a shape in which petal-like protrusions are observed on the surface of the aggregate (graphene sheet structure). The morphology and particle size of the generated carbon nanohorn aggregate vary depending on the type and flow rate of the gas. The spherical carbon nanohorn aggregate is described, for example, in Japanese Patent Application Laid-Open No. 2009-190928 (Patent Document 1), and the disclosure content of this document is incorporated herein by reference.

[0018] A single carbon nanohorn is a carbon structure having a conical shape with a tip of a structure wrapped with a graphene sheet sharpened into a horn shape with a tip angle of about 20°, the diameter of the single carbon nanohorn is 1 nm to 20 nm, and the length is 30 nm to 100 nm. In a spherical carbon nanohorn aggregate, the tips are radially aggregated outward. As for the size of the spherical carbon nanohorn aggregate (CNHs), the particle diameter is about 20 nm to 200 nm, preferably about 30 nm to 150 nm.

[0019] The method for producing a spherical carbon nanohorn aggregate is not particularly limited and can be produced by various means. Usually, it can be produced by a laser ablation method using a solid carbon single substance such as graphite as a target in an inert gas atmosphere.

[0020] The fibrous carbon nanohorn aggregate is also called a carbon nanobrush (CNB), and has a structure in which a plurality of carbon nanohorns are radially aggregated and connected in a fibrous shape. This structure resembles the shape of a test tube brush or a mole. The fibrous carbon nanohorn aggregate is different from a structure in which simply a plurality of carbon nanohorns are connected in a row and look fibrous, and can maintain its fibrous shape even when operations such as centrifugation and ultrasonic dispersion are performed.

[0021] The fibrous carbon nanohorn aggregate is formed by further connecting the above spherical carbon nanohorn aggregates with carbon nanohorns, that is, one or more of these carbon nanohorn aggregates are contained in the fibrous structure. The fibrous carbon nanohorn aggregate is described in International Publication No. 2016 / 147909 (Patent Document 2), and the disclosure content of this document is incorporated herein by reference.

[0022] When manufacturing a fibrous carbon nanohorn aggregate, a spherical carbon nanohorn aggregate is also simultaneously produced. The fibrous carbon nanohorn aggregate and the spherical carbon nanohorn aggregate can be separated by their size differences. Furthermore, when impurities other than the carbon nanohorn aggregate are included, they can be removed by methods such as centrifugation, differences in sedimentation rates, and separation by size. Also, by changing the production conditions, it is possible to vary the ratio of the fibrous carbon nanohorn aggregate to the spherical carbon nanohorn aggregate.

[0023] Furthermore, the carbon nanohorn aggregate may contain carbon nanotubes. The carbon structure of this carbon nanohorn may be either single-layer or multi-layer, but a single-layer is preferred.

[0024] The diameter of a single carbon nanohorn is 1 nm to 10 nm, and the length is 30 nm to 80 nm. The fibrous carbon nanohorn aggregate has a diameter of about 30 nm to 150 nm and a length of about 1 μm to 50 μm. The aspect ratio (length / diameter) of the fibrous carbon nanohorn aggregate is 6 to 1700, preferably 50 to 500. The spherical carbon nanohorn aggregate has a diameter of about 30 nm to 150 nm and is of a substantially uniform size.

[0025] The fibrous carbon nanohorn aggregate is characterized by a structure in which highly conductive carbon nanohorns are connected in a fibrous form and have a long conductive path, and thus has high conductivity.

[0026] The method for producing the fibrous carbon nanohorn aggregate is not particularly limited and can be produced by various means. For example, carbon containing a catalyst can be used as a target, and it can be produced by the laser ablation method under a nitrogen atmosphere, an inert atmosphere, or a mixed atmosphere. During the process of cooling the evaporated carbon and the catalyst, a fibrous carbon nanohorn aggregate and a spherical carbon nanohorn aggregate can be obtained. Further, as a method for producing the fibrous carbon nanohorn aggregate, in addition to the laser ablation method, an arc discharge method or a resistance heating method can be used. However, the laser ablation method is more preferable from the viewpoint of continuous generation at room temperature and atmospheric pressure.

[0027] <Oxidation treatment of carbon nanohorn aggregate> The tip of the carbon nanohorn aggregate contains a 5-membered ring or a 7-membered ring structure with higher reactivity than the 6-membered ring. Therefore, by oxidation treatment, that part is preferentially oxidized, and an oxygen-containing functional group is introduced. Examples of the oxygen-containing functional group generated by the oxidation of the carbon ring include, but are not limited to, a carbonyl group, a carboxyl group, a hydroxyl group, a nitro group, a sulfone group, a phenol group, and a functional group containing an ether bond or an ester bond.

[0028] In this embodiment, it is important to perform a weak oxidation treatment, and it is preferable not to perform excessive oxidation. Oxidation treatment starts from the highly reactive 5-membered rings and 7-membered rings that are abundant at the tip. However, in excessive oxidation treatment, oxidation further proceeds, the tip of the nanohorn disappears, and a cap by cyclodextrin cannot be formed. Also, the body of the nanohorn is oxidized to generate pores, and the properties of the bulk of the (hydrophilic) carbon nanohorn aggregate may change, making the intended functionalization impossible.

[0029] Therefore, as the degree of oxidation, oxygen is preferably 1.0×10 -5 atomic% to 1.0×10 0 atomic%, more preferably 1.0×10 -3 atomic% to 1.0×10 0It is preferably contained in a proportion of atomic %. The ratio of oxygen to carbon can be estimated from, for example, the intensity ratio of O1s and C1s in X-ray photoelectron spectroscopy although various analysis methods can be used.

[0030] The method of this oxidation treatment is not particularly limited, but it can be used in either a gas phase process or a liquid phase process. In the case of a gas phase process, it is carried out in a gas atmosphere such as oxygen, air, hydrogen peroxide, carbon dioxide, carbon monoxide, etc.

[0031] The degree of oxidation can be adjusted by at least one of temperature, time, and gas atmosphere in the oxidation treatment. That is, the degree of oxidation can be adjusted by carrying out the oxidation treatment at different temperatures, and / or different times, and / or different atmospheres. Typically, the degree of oxidation can be increased by carrying out the oxidation treatment at a higher temperature, and / or a longer time, and / or a higher oxygen concentration.

[0032] The oxidation treatment temperature in a gas atmosphere is preferably 250 to 650 °C, more preferably 300 to 500 °C, and even more preferably 300 °C to 400 °C. This is because if the temperature is too low, oxidation hardly occurs, and if it is too high, oxidation is too fast and control becomes difficult. As for the treatment time, although it can be adjusted as appropriate, it is preferably in the range of about 5 to 7 hours at a heating rate of 1 °C / min.

[0033] In the case of a liquid phase process, the oxidation treatment is carried out in a liquid containing an oxidizing substance such as nitric acid, sulfuric acid, hydrogen peroxide, etc. In the case of nitric acid or sulfuric acid, the temperature range is preferably from room temperature to 120 °C. In the case of hydrogen peroxide, it can be used in the temperature range of room temperature to 100 °C, and more preferably 40 °C or higher. In the temperature range of 40 to 100 °C, the oxidizing power acts efficiently. As for the treatment time, although it can be adjusted as appropriate, it is preferably in the range of about 0.5 to 3 hours, for example. Also, when using a liquid phase process, it is more effective to use light irradiation in combination.

[0034] By the above oxidation treatment, oxygen-containing functional groups including carbonyl groups, carboxyl groups, hydroxyl groups, nitro groups, sulfone groups, phenol groups, ether bonds or ester bonds can be added to the tip portions of the carbon nanohorns.

[0035] <Cyclodextrin treatment> By treating the oxidized carbon nanohorn aggregates with a cyclodextrin-containing solution, hydrophilic carbon nanohorn aggregates with the tips of the nanohorns capped with cyclodextrin can be produced. Since oxygen-containing functional groups are introduced at the tip portions of the carbon nanohorn aggregates, the cyclodextrin interacts with the OH groups of the cyclodextrin, specifically forms hydrogen bonds, and the cyclodextrin is immobilized and stabilized.

[0036] Cyclodextrin (hereinafter, may be abbreviated as "CD") is a cyclic oligosaccharide, a non-reducing sugar in which glucose residues are cyclically bonded by α-1,4 bonds, and has a toroidal structure also called an open-ended bucket or crown shape. The inside of cyclodextrin is hydrophobic, but it is water-soluble because it has a large number of OH groups on the outside.

[0037] Examples of cyclodextrin include well-known cyclodextrins such as unsubstituted cyclodextrins containing 6 to 12 glucose units, particularly α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin and / or their derivatives, and / or their mixtures, depending on the difference in the number of glucose units constituting them. α-Cyclodextrin consists of 6 glucose units, β-cyclodextrin consists of 7 glucose units, and γ-cyclodextrin consists of 8 glucose units, and they each have a different cavity size. In the present embodiment, it is preferable to contain at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

[0038] In the cyclodextrin treatment, the oxidized carbon nanohorn aggregate is brought into contact with cyclodextrin in a solution in which cyclodextrin is dissolved. As the dispersion medium, water, or a dispersion medium containing a surfactant, a water-soluble organic solvent, etc. as necessary in addition to water is used.

[0039] The addition amount of cyclodextrin can be appropriately selected, but it is, for example, 0.1 to 50 parts by mass, preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the oxidized carbon nanohorn aggregate. The treatment conditions are not particularly limited, but can be appropriately selected, for example, in the range of 0 to 100 °C, preferably in the range of 10 °C to 70 °C. In one embodiment, for example, the range of 15 °C to 60 °C close to room temperature is preferable. The treatment time can also be appropriately set, but it is, for example, 10 minutes or more, preferably 3 hours or more, and there is no particular upper limit, but it can be carried out, for example, in the range of 10 days or less.

[0040] As described above, the oxygen-containing functional group at the tip of the carbon nanohorn aggregate and the hydroxyl group of cyclodextrin interact, specifically, are immobilized by hydrogen bonding, and a stabilized hydrophilic carbon nanohorn aggregate is obtained. By obtaining hydrophilicity, the dispersibility in an aqueous medium is improved.

[0041] <Ultrasonic treatment, and / or centrifugation step> In order to disperse the hydrophilic carbon nanohorn aggregate obtained in this way even better, after the cyclodextrin treatment, ultrasonic treatment is preferably performed in the liquid as it is, or in a different liquid, preferably an aqueous solution, after recovering the hydrophilic carbon nanohorn aggregate. At this time, a treatment device such as a bath type in which ultrasonic waves are applied from the outside of the container holding the liquid, or a chip type in which a chip-type oscillator is inserted into the container can be used, but a bath type that is simple and does not allow impurities to mix in is preferable. The frequency and treatment time can be appropriately set, but the frequency is preferably 28 KHz to 100 KHz, and the treatment time is preferably 5 minutes to 30 minutes.

[0042] Furthermore, if necessary, a centrifugation process may subsequently be performed to remove impurities such as graphite from the carbon nanohorn aggregate.

[0043] The hydrophilic carbon nanohorn aggregate thus obtained has a low impurity content and no pores are formed on the surface of the body portion, so it is also suitable for functionalizing hydrophilic carbon nanohorn aggregates using catalyst carriers or chemical modification groups.

[0044] The hydrophilic carbon nanohorn aggregate obtained in this embodiment has extremely excellent dispersibility in water. In the case of a spherical carbon nanohorn aggregate, in the particle size distribution determined by the dynamic light scattering method, in a dispersion liquid using water as a dispersion medium, 90% by mass or more, preferably 95% by mass or more, more preferably 98% by mass or more of the hydrophilic carbon nanohorn aggregate has a particle size of 400 nm or less.

[0045] The hydrophilic carbon nanohorn aggregate according to the present invention can be used in various applications. Since the carbon nanohorn aggregate is excellent in conductivity, catalytic activity, adsorption / absorption properties, and thermal conductivity, for example, it can be applied to a wide range of applications such as electrode materials for lithium-ion batteries, fuel cells, capacitors, electrochemical actuators, air batteries, solar cells, electromagnetic shields, thermal conduction sheets, heat dissipation sheets, protective sheets, filters, absorbents, etc.

Example

[0046] Examples are shown below to explain the present invention in more detail, but the present invention is not limited by the following examples.

[0047] <Example 1> (Step 1: Production of CNHs) A carbon nanohorn aggregate (CNHs) was produced by the CO 2 laser ablation method. First, a sintered round bar carbon as a solid carbon substance was placed in a vacuum vessel, and the laser power density was 30 kW / cm under an Ar atmosphere 2 and the target rotation speed was 2 rpm under the condition of CO 2The solid carbon material was irradiated with laser light at room temperature for 30 minutes. The soot material thus obtained was observed by a transmission electron microscope (TEM), and it was confirmed that it had a carbon nanohorn aggregate structure.

[0048] (Step 2: Production of oxCNHs) A carbon nanohorn aggregate (oxCNHs) with the tip of the nanohorn oxidized and an oxygen-containing group introduced was produced by heating the CNHs produced in Step 1 in a tabletop muffle furnace (KDFS70) in an air atmosphere in the range of 300°C to 400°C for 4 to 7 hours.

[0049] (Step 3: Production of CD-oxCNHs) A hydrophilic carbon nanohorn aggregate (CD-oxCNHs) capped with cyclodextrin was produced as follows. First, 20 mg of the oxCNHs produced in Step 2 was put into 80 mL of water, and ultrasonic dispersion treatment was performed for 15 minutes to prepare an oxCNHs dispersion. Next, 5 mg of γ-CD was added, and the mixture was stirred at 40°C for 12 hours. Then, ultrasonic treatment was performed for 15 minutes, and centrifugation was performed at 3000 rpm for 20 minutes. Subsequently, filter washing was performed using a filter with a pore size of 200 nm to wash away excess γ-CD, and CD-oxCNHs were produced.

[0050] <Comparative Example 1> (Production of CD-CNHs) A carbon nanohorn aggregate (CD-CNHs) capped with cyclodextrin without oxidizing the carbon nanohorn aggregate was produced as follows. First, 20 mg of the CNHs produced in Step 1 of Example 1 was put into 80 mL of water, and ultrasonic dispersion treatment was performed for 15 minutes. Next, 5 mg of γ-CD was put into the CNHs dispersion, and the mixture was stirred at 40°C for 12 hours. Then, ultrasonic treatment was performed for 15 minutes, and then centrifugation was performed at 3000 rpm for 20 minutes. Subsequently, filter washing was performed using a filter with a pore size of 200 nm to wash away excess γ-CD, and the CD-CNHs of the comparative example were produced.

[0051] The particle size distributions obtained by the dynamic light scattering method for FIGS. 2(a) to (c) are shown for the CD-oxCNHs produced in Example 1 (FIG. 2(a)), the CD-CNHs produced in Comparative Example 1 (FIG. 2(b)), and the oxCNHs produced in Step 2 of Example 1 (FIG. 2(c)).

[0052] From FIG. 2(a), it can be seen that in CD-oxCNHs, the nano-horn particles are dispersed as almost primary particles, but from FIG. 1(b), it can be seen that in CD-CNHs, the nano-horn particles are aggregated. Also, from FIG. 1(c), it can be seen that the oxidized oxCNHs have a wide range of dispersed nano-horn particles and aggregated nano-horn particles.

[0053] FIG. 3 is a graph showing the TGA results of CD-oxCNHs. From FIG. 3, it can be seen that after centrifugation and filter washing, impurities are removed and only the weight loss of CD and CNHs remains.

[0054] 1 mg each of oxCNHs, CD-CNHs, and CD-oxCNHs was collected and dispersed in 10 mL of water. FIG. 4 is a photograph showing the dispersion states of the (a) 10 minutes later and (b) 10 hours later of the oxCNHs, CD-CNHs, and CD-oxCNHs dispersions from the left. At 10 hours shown in FIG. 4(b), all except CD-oxCNHs aggregated and precipitated. Also, CD-oxCNHs showed no change even after one week, thus it became clear that they exist stably in a highly dispersed state.

[0055] Although the present invention has been described with reference to the embodiments and examples above, the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

[0056] Some or all of the above embodiments may also be described as follows in the appended claims, but the disclosure of the present application is not limited to the following appended claims.

[0057] (Appended Claim 1) A carbon nanohorn aggregate having an oxygen-containing functional group introduced at the tip of the carbon nanohorn, and a stabilized cyclodextrin that caps the tip of the carbon nanohorn, and A hydrophilic carbon nanohorn aggregate having the same.

[0058] (Appendix 2) The hydrophilic carbon nanohorn aggregate according to Appendix 1, wherein the cyclodextrin is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof.

[0059] (Appendix 3) The hydrophilic carbon nanohorn aggregate according to Appendix 1 or 2, wherein the oxygen-containing functional group is introduced by subjecting the tip of the carbon nanohorn to an oxidation treatment.

[0060] (Appendix 4) A hydrophilic carbon nanohorn aggregate dispersion containing water and the hydrophilic carbon nanohorn aggregate according to any one of Appendices 1 to 3.

[0061] (Appendix 5) The hydrophilic carbon nanohorn aggregate dispersion according to Appendix 4, wherein in the particle size distribution determined by the dynamic light scattering method, 90% by mass or more of the hydrophilic carbon nanohorn aggregate has a particle size of 400 nm or less.

[0062] (Appendix 6) A step of subjecting the carbon nanohorn aggregate to an oxidation treatment, and A step of treating the oxidized carbon nanohorn aggregate with cyclodextrin, and A method for producing a hydrophilic carbon nanohorn aggregate, comprising the same.

[0063] (Appendix 7) The method for producing a hydrophilic carbon nanohorn aggregate according to Appendix 6, wherein the oxidation treatment step is a step of introducing an oxygen-containing functional group at the tip of the carbon nanohorn.

[0064] (Appendix 8) The method for producing a hydrophilic carbon nanohorn aggregate according to Appendix 7, wherein the treatment step with the cyclodextrin is a step of capping the tip of the carbon nanohorn with the cyclodextrin and fixing the cyclodextrin.

[0065] (Appendix 8a) The method for producing a hydrophilic carbon nanohorn aggregate according to any one of Appendices 6 to 8, further including a step of performing ultrasonic treatment and / or centrifugation treatment.

[0066] (Appendix 9) The method for producing a hydrophilic carbon nanohorn aggregate according to any one of Appendices 6 to 8, wherein in the oxidation treatment step, the degree of oxidation is adjusted by at least one of temperature, time, and gas atmosphere.

[0067] (Appendix 9a) The method for producing a hydrophilic carbon nanohorn according to Appendix 9, wherein the gas atmosphere contains at least one gas selected from oxygen, air, hydrogen peroxide, carbon dioxide, and carbon monoxide.

[0068] (Appendix 10) In the oxidation treatment step, the oxidation is performed such that the degree of oxidation contains oxygen at a ratio of 1.0×10 -5 ~1.0×10 0 atomic %. The method for producing a hydrophilic carbon nanohorn aggregate according to any one of Appendices 6 to 9.

Explanation of Reference Numerals

[0069] 1 Tip of the carbon nanohorn 2 Cyclodextrin

Claims

1. A carbon nanohorn aggregate having an oxygen-containing functional group introduced at the tip of the carbon nanohorn, and cyclodextrin that caps the tip of the carbon nanohorn, wherein the cyclodextrin is stabilized in a state where it caps the tip of the carbon nanohorn by a hydrogen bond between the oxygen-containing functional group and the OH group of the cyclodextrin, and A hydrophilic carbon nanohorn aggregate having the same.

2. The hydrophilic carbon nanohorn aggregate according to claim 1, wherein the cyclodextrin is at least one selected from the group consisting of α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin, and derivatives thereof.

3. The hydrophilic carbon nanohorn aggregate according to claim 1 or 2, wherein the oxygen-containing functional group is introduced by subjecting the tip of the carbon nanohorn to an oxidation treatment.

4. A hydrophilic carbon nanohorn aggregate dispersion containing water and the hydrophilic carbon nanohorn aggregate according to any one of claims 1 to 3.

5. The hydrophilic carbon nanohorn aggregate dispersion according to claim 4, wherein in the particle size distribution determined by the dynamic light scattering method, 90% by mass or more of the hydrophilic carbon nanohorn aggregate has a particle size of 400 nm or less.

6. Performing an oxidation treatment by a gas phase process in which the carbon nanohorn aggregate is brought into contact with a gas selected from the group consisting of oxygen, air, hydrogen peroxide, carbon dioxide, and carbon monoxide, or performing an oxidation treatment by a liquid phase process in which the carbon nanohorn aggregate is brought into contact with a liquid containing an oxidizing substance, an oxidation treatment step, and A cyclodextrin treatment step of bringing the oxidized carbon nanohorn aggregate and cyclodextrin into contact with each other in a solution in which cyclodextrin is dissolved, and A method for producing a hydrophilic carbon nanohorn aggregate, including the same.

7. The method for producing a hydrophilic carbon nanohorn aggregate according to claim 6, wherein the oxidation treatment step is carried out at a temperature of 250 to 650 °C in the case of oxidation treatment by a gas phase process, and in the case of oxidation treatment by a liquid phase process, it is carried out in a temperature range of room temperature to 120 °C, whereby an oxygen-containing functional group is introduced at the tip of the carbon nanohorn.

8. In the treatment step using the cyclodextrin, the tip of the carbon nanohorn is capped with the cyclodextrin, and the cyclodextrin is fixed in a state of capping the tip of the carbon nanohorn by a hydrogen bond between the oxygen-containing functional group introduced into the tip of the carbon nanohorn and the OH group of the cyclodextrin. The method for producing a hydrophilic carbon nanohorn aggregate according to claim 7.

9. In the oxidation treatment step, the degree of oxidation is adjusted by at least one of temperature, time, and gas atmosphere. The method for producing a hydrophilic carbon nanohorn aggregate according to any one of claims 6 to 8.

10. In the oxidation treatment step, the oxidation degree is such that oxygen is contained in a proportion of 1.0×10 －５ to 1.0×10 ０ atomic percent with respect to the total carbon, and the oxidation treatment is performed. The method for producing a hydrophilic carbon nanohorn aggregate according to claim 9.

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