Nanocarbon materials

Abstract

To provide a nanocarbon material in which the deterioration of carrier performance over time is suppressed. [Solution] A nanocarbon filament or strip having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant, At least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the nanocarbon filamentous or strip-shaped body, Nanocarbon material having the properties of a nanocarbon material.

Description

[Technical Field]

[0001] This disclosure relates to nanocarbon materials. [Background technology]

[0002] In recent years, thermoelectric generators have become known as solid-state devices that convert thermal energy into electrical energy. Thermoelectric generators are being applied to various applications, such as power supplies for space and thermoelectric conversion modules that operate using body heat (watches, wearable devices, etc.). Furthermore, nanocarbon materials such as carbon nanotube yarn and carbon nanotube ribbon are sometimes used in thermoelectric conversion elements, and various studies are being conducted on nanocarbon materials.

[0003] For example, Patent Document 1 discloses "a functional element in which spun yarn made of a conductive fibrous material is sewn into a sheet-like or strip-like insulating substrate, characterized in that the spun yarn is sewn so as to alternately penetrate the front and back surfaces of the insulating substrate, thereby forming a series cell structure of a π-type thermoelectric conversion element." Patent Document 1 also discloses that "spun yarn is made of a composite material of one or more conductive nanofibers selected from the group consisting of carbon nanotubes (CNTs), carbon nanofibers (CNFs), graphene, graphene nanoribbons, fullerene nanowhiskers, and inorganic semiconductor whiskers, and an insulating or conductive flexible polymer." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2016 / 151634, Patent No. 6529097 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Conventionally, including in Patent Document 1, to impart N-type and P-type conductive regions to nanocarbon materials, conductive dopants are used to dope the nanocarbon material with the respective types of dopants. However, since nanocarbon materials inherently possess P-type conductivity, doping with P-type dopants is sometimes performed to enhance P-type conductivity. However, when oxygen from the atmosphere is adsorbed onto the N-type and P-type conductive regions of the doped dopant, its semiconductivity-imparting ability deteriorates. As a result, the carrier performance of either the N-type or P-type conductive region decreases over time.

[0006] Therefore, the objective of this disclosure is to provide a nanocarbon material in which the deterioration of carrier performance over time is suppressed. [Means for solving the problem]

[0007] The means for solving the problem include the following: <1> A nanocarbon filament or strip having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant, At least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the nanocarbon filamentous or strip-shaped body, Nanocarbon material having the properties of a nanocarbon material. <2> The aliphatic hydrocarbon compound is liquid paraffin. <1> The nanocarbon materials described above. <3> The aromatic hydrocarbon compound is polystyrene. <1> or <2> The nanocarbon materials described above. <4> The P-type dopant and the N-type dopant are dopants having at least one of an aliphatic hydrocarbon group and an aromatic group. <1> ~ <3> Nanocarbon material as described in any one of the items. [Effects of the Invention]

[0008] According to the disclosure, a nanocarbon material capable of suppressing the degradation of carrier performance over time can be provided. [Embodiments for Carrying out the Invention]

[0009] Hereinafter, embodiments that are an example of the disclosure will be described. These explanations and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or lower limit value described in one numerical range may be replaced with the upper limit value or lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or lower limit value of the numerical range may be replaced with the value shown in the examples. Each component in the composition may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition.

[0010] <Nanocarbon Material> The nanocarbon material of the disclosure has at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant, which is a filament or strip of nanocarbon, and at least one adsorption compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds adsorbed on the P-type conductive region and the N-type conductive region of the filament or strip of nanocarbon.

[0011] The nanocarbon material of the disclosure adsorbs the above specific adsorption compound on each region of each conductivity type doped with dopants of each conductivity type in the filament or strip of nanocarbon. Thereby, it becomes difficult for the dopant to come into contact with oxygen adsorbed on the regions of each conductivity type. In addition, the adsorption of oxygen itself on the regions of each conductivity type is suppressed. Therefore, the deterioration of the ability to impart semiconduction is suppressed.

[0012] From the above, the nanocarbon material of the present disclosure suppresses the degradation of carrier performance over time. Here, as a technique for preventing the dopant from coming into contact with oxygen, a technique of providing a coating layer on the filamentous or带状 body of nanocarbon to inhibit the oxidation adsorption itself by the coating layer is also conceivable. However, in this technique, when damage and peeling of the coating layer occur, the oxygen inhibition ability decreases, and it is difficult to achieve suppression of the degradation of carrier performance over time. On the other hand, the nanocarbon material of the present disclosure adsorbs the above specific adsorption compound that prevents the dopant from coming into contact with oxygen to the filamentous or带状 body of nanocarbon, so the adsorption compound is difficult to detach over time. Therefore, compared with the technique of providing a coating layer, the nanocarbon material of the present disclosure has a high ability to suppress the degradation of carrier performance over time.

[0013] Hereinafter, the details of the nanocarbon material will be described.

[0014] (Filamentous or带状 body of nanocarbon) The filamentous or带状 body of nanocarbon has at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant.

[0015] -Nanocarbon- As the nanocarbon constituting the filamentous or带状 body of nanocarbon, carbon nanotubes (CNTs) are preferable. That is, as the filamentous or带状 body of nanocarbon, it is preferable that it is a filamentous or带状 body of carbon nanotubes. Carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) in which a single carbon film (graphene sheet) is wound into a cylindrical shape. Carbon nanotubes may also be multi-walled carbon nanotubes (MWCNTs), such as double-walled, triple-walled, or quadruple-walled carbon nanotubes, in which two graphene sheets are wound concentrically. Considering thermoelectric properties, carbon nanotubes with 10 layers or less are preferable. Single-walled carbon nanotubes are preferable because they easily provide high thermoelectric properties. Multi-walled carbon nanotubes are preferable because they are inexpensive and easy to mass-produce. Single-walled and multi-walled carbon nanotubes can also be used in combination. Furthermore, carbon nanotubes may be metallic carbon nanotubes, semiconducting carbon nanotubes, or a mixture of both. The method for producing carbon nanotubes is not particularly limited. Carbon nanotubes can be produced by methods such as arc discharge, chemical vapor deposition (CVD), and laser ablation. Commercially available carbon nanotubes may also be used.

[0016] Nanocarbon may also be graphene. By inserting carriers between two layers of graphene, graphene can be used as a semiconductor material.

[0017] Other examples of nanocarbons include carbon nanorods, carbon nanowires, graphene, and fullerenes.

[0018] -Dopant- One method for doping nanocarbon filaments or strips with a dopant is to immerse the heated nanocarbon filaments or strips in a dopant solution. This method allows for simple and low-cost doping. After doping, washing is performed. However, doping with a dopant may be performed by methods such as application or brushing.

[0019] --Type P Dopant-- P-type dopants refer to dopants in which the Seebeck coefficient is positive in the filamentous or strip-like regions of the doped nanocarbon, and include nonionic compounds or ionic compounds. In particular, when the solvent of the P-type dopant solution is water, a nonionic compound is preferred as the P-type dopant. On the other hand, when the solvent of the P-type dopant solution is an organic solvent, an ionic compound is preferred as the P-type dopant.

[0020] Examples of nonionic compounds that are P-type dopants include tetracyanoquinodimethane (TCNQ) derivatives (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, 2,5-dimethyl-7,7,8,8-tetracyanoquinodimethane, 2-fluoro-7,7,8,8-tetracyanoquinodimethane, 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane, etc.), Benzoquinone derivatives (2,3-dichloro-5,6-dicyano-p-benzoquinone, tetrafluoro-1,4-benzoquinone, etc.) Quinosaline derivatives (5,8H-5,8-bis(dicyanomethylene)quinoxaline, dipyradino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonnitrile, etc.) Examples include 9H-carbazole, 9H-carbazole-4-ol, and pyrazine.

[0021] Examples of ionic compounds that are P-type dopants include perchlorate ions (ClO2). 4- ), permanganate ion (MnO 4- ), iodate ion (IO 3- ), thiocyanate ion (SCN - ), hexafluorophosphate ion (PF 6- ), tetrafluoroborate ion (BF 4- ), trifluoromethanesulfonate anion (TfO - ), bis(trifluoromethanesulfonyl)amine anion (TFSI- ) Iodide ion (I - ) Bromide ion (Br - ) Chloride ion (Cl - ) Nitrate ion (NO 3- ) or tosylate ion (Tos - ) and metal salts thereof. Examples of the metal salts include silver salts and copper salts.

[0022] --N-type dopant-- The N-type dopant means a dopant having a negative value of the Seebeck coefficient in the region of the filamentous or带状 body of the doped nanocarbon, and examples thereof include non-ionic compounds or ionic compounds. In particular, when the solvent of the N-type dopant solution is water, a non-ionic compound is preferable as the N-type dopant. [[ID=Element 23]]On the other hand, when the solvent of the N-type dopant solution is an organic solvent, an ionic compound is preferable as the N-type dopant.

[0023] The non-ionic compound as the N-type dopant is preferably a polyalkyleneimine. The polyalkyleneimine preferably has a structural unit having an alkylene group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably

[0024]

[0024] Examples of the ionic compound as the N-type dopant include alkali metal salts (such as salts of lithium, sodium, potassium, or cesium), and alkylammonium salts (such as salts of tetraethylammonium ion or tetrabutylammonium ion). Among these, the ionic compound is preferably an alkylammonium halide salt, and examples thereof include the following compounds.

[0025]

Chemical formula

[0026] It should be noted that there may be some inaccuracies in the translation due to the complexity of the chemical and technical terms. It is recommended to double-check with a professional in the relevant field for more accurate understanding. Examples of N-type dopants include complexes of alkali metal salts and cyclic ethylene oxides. Ions found in alkali metal salts include hydroxyl ions (OH) - ), alkoxy ions (CH3O - CH3CH2O - i-PrO - and t-BuO - (etc.), thioions (SH) - and alkylthioions (CH3S - and C2H5S - etc.), cyanuryl ions (CN - ), carboxyl ion (CH3COO - Examples include: Examples of alkali metals contained in alkali metal salts include lithium, sodium, and potassium. Examples of cyclic ethylene oxides include crown ethers.

[0027] Examples of N-type dopants include phosphine compounds such as triphenylphosphine, trioctylphosphine, and 1,3-bis(diphenylphosphine)propane.

[0028] --Suitable Dopant-- If P-type and N-type dopants have structures similar to those of aliphatic hydrocarbon compounds or aromatic hydrocarbon compounds used as adsorbents, the deterioration of their carrier performance over time is more easily suppressed. Therefore, it is preferable that the P-type dopant and N-type dopant are dopants (polyalkyleneimines, triphenylphosphines, etc.) having at least one of an aliphatic hydrocarbon group (such as an alkylene group) and an aromatic group (such as a phenyl group).

[0029] --Dopant Solution-- From the viewpoint of reducing environmental impact, the solvent of the dopant solution preferably contains water as its main component. The solvent containing water as its main component may also contain water-soluble organic solvents such as alcohols (methanol, ethanol, propanol, etc.). Note that "water as the main component" means, for example, that the proportion of water is 50% by mass (preferably 70% by mass, or 90% by mass) or more of the total solvent. However, the solvent of the dopant solution may have an organic solvent as its main component. Examples of organic solvents include alcohols (ethanol, propanol, etc.), acetone, methyl ethyl ketone, and butyl acetate. Having an organic solvent as the main component means, for example, that the proportion of the organic solvent is 50% by mass (preferably 70% by mass, or 90% by mass) or more of the total solvent.

[0030] (adsorbed compound) The adsorbent compound is at least one selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds. The adsorbed compound is preferably selected from nonpolar compounds that do not affect the semiconductivity-conducting ability of the dopant, do not have polar groups, and do not undergo dopant reactions. Polar groups include acidic polar groups (carboxyl groups, carboxylic acid bases, sulfo groups, sulfonic acid bases, phosphate groups, phosphate bases, formyl groups, phenol groups (phenolic hydroxyl groups), etc.), neutral polar groups (hydroxyl groups, amide groups, cyano groups, etc.), and basic polar groups (amino groups, imino groups, quaternary ammonium groups, etc.).

[0031] -Aliphatic hydrocarbon compounds- Examples of aliphatic hydrocarbon compounds include saturated and unsaturated hydrocarbon compounds such as liquid paraffins, isoparaffins, α-olefin oligomers, and polybutenes.

[0032] -Aromatic hydrocarbon compounds- Examples of aromatic hydrocarbon compounds include benzene, polycyclic aromatic compounds, and polynuclear aromatic hydrocarbon compounds.

[0033] Polycyclic aromatic compounds are compounds in which two or more aromatic rings are fused together. Examples of polycyclic aromatic compounds include naphthalene, fluorene, phenanthrene, anthracene, triphenylene, tetraphenylene, pyrene, chrysene, and tetracene. Polycyclic aromatic compounds may also be derivatives of these compounds in which halogen groups or aliphatic hydrocarbon groups (such as alkyl groups having 1 to 10 carbon atoms) are substituted.

[0034] Polynuclear aromatic hydrocarbon compounds are compounds that contain two or more aromatic rings, which are linked to each other by carbon-carbon bonds or by linking groups such as methylene groups, ethylene groups, vinylene groups, and ethynylene groups. Examples of polycyclic aromatic compounds include biphenyls and terphenyls. Polycyclic aromatic compounds may also be derivatives of these compounds in which halogen groups or aliphatic hydrocarbon groups (such as alkyl groups having 1 to 10 carbon atoms) are substituted.

[0035] Aromatic hydrocarbon compounds may be compounds in which two or more of the above-mentioned benzene, polycyclic aromatic compounds, and polynuclear aromatic hydrocarbon compounds are linked by carbon-carbon bonds, or linked via linking groups such as methylene groups, ethylene groups, vinylene groups, and ethynylene groups.

[0036] Aromatic hydrocarbon compounds also include aromatic hydrocarbon polymers such as polystyrene.

[0037] Among these, from the viewpoint of suppressing the deterioration of carrier performance over time, the adsorbent compounds are preferably aliphatic hydrocarbon oils that are liquid at 25°C, such as liquid paraffin (paraffin with the highest purity from which impurities such as aromatic hydrocarbons and sulfur compounds have been removed); aromatic hydrocarbon monomers with 3 to 6 aromatic rings, such as anthracene and benzopyrene; and aromatic hydrocarbon polymers, such as polystyrene, with liquid paraffin and polystyrene being more preferred. The adsorbent compound may be used alone or in combination of two or more.

[0038] Here, the confirmation that the adsorbed compound is adsorbed onto the nanocarbon filament or strip is as follows: For example, secondary ion mass spectrometry (SIMS) can be used to determine whether or not the target adsorbed compound is detected, thereby confirming that the compound is adsorbed onto the nanocarbon filamentous or strip-like material.

[0039] -Method for adsorption of adsorbed compounds- A preferred method for adsorbing a compound onto a nanocarbon filament or strip (in the conductive region of each type) is, for example, immersion in a coating solution in which the adsorbed compound is dispersed or dissolved in a solvent (water or an organic solvent, etc.), a liquid of the adsorbed compound that is liquid at room temperature (25°C), or a liquid in which the adsorbed compound has been liquefied by heating (for example, heating up to 150°C). This is because the adsorption treatment of the adsorbed compound can be carried out simply and at low cost. After the adsorption treatment, washing may or may not be performed. In addition, the adsorption treatment of the adsorbed compound may be carried out by methods other than immersion, such as coating or brush application.

[0040] (Application) The carbon materials disclosed herein can be applied to a variety of uses. For example, the carbon material of this disclosure can be suitably applied as a carbon material for connecting thermoelectric elements in a thermoelectric conversion module. Furthermore, the carbon materials disclosed herein are also suitably applicable to semiconductor applications. [Examples]

[0041] Examples are described below, but this disclosure is not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" all refer to mass.

[0042] <Example 1> Carbon nanotube filaments (hereinafter referred to as "CNT filaments") were doped with polyethyleneimine. After doping, the N-type CNT filaments were immersed in liquid paraffin as an adsorbent compound for 24 hours, and then washed and dried with n-hexane. When the Seebeck coefficient of the N-type CNT yarn treated with liquid paraffin was measured immediately after obtaining it, the initial Seebeck coefficient was -65.1 (μV / K). Meanwhile, the obtained liquid paraffin-treated N-type CNT yarn was left in the air at room temperature (25°C) to check the change in the Seebeck coefficient over time. As a result, the Seebeck coefficient after 4 months was -71.5 (μV / K), indicating that it maintained its N-type properties.

[0043] <Comparative Example 1> When the Seebeck coefficient of the N-type CNT yarn obtained in Example 1 was measured without immersion in liquid paraffin, the initial Seebeck coefficient was -65.1 (μV / K). On the other hand, when the Seebeck coefficient of the obtained N-type CNT yarn was examined over time in the same manner as in Example 1, the Seebeck coefficient decreased by 60-30% after about one month (from -65 (μV / K) to -40--10 (μV / K)). Then, after four months, the Seebeck coefficient became +2 (μV / K), resulting in a conversion to P-type.

[0044] <Example 2> Water-soluble oil-treated N-type CNT yarn was obtained in the same manner as in Example 1, except that a water-soluble oil (a compound whose main skeleton is an aliphatic hydrocarbon having hydroxyl groups and some ether groups at the terminal groups) was used as the adsorbent compound. The Seebeck coefficient of the water-soluble oil-treated N-type CNT yarn was then investigated at the initial and temporal stages.

[0045] <Example 3> Carbon nanotube filaments (hereinafter referred to as "CNT filaments") were doped with triphenylphosphine. After doping, the N-type CNT filaments were immersed for 24 hours in an acetone solution of polystyrene as an adsorbent compound, and then washed and dried with acetone. When the Seebeck coefficient of the polystyrene-treated N-type CNT yarn obtained immediately was measured, the initial Seebeck coefficient was -40 (μV / K). Meanwhile, the obtained polystyrene-treated N-type CNT yarn was left in the atmosphere at room temperature (25°C) to check the change in the Seebeck coefficient over time. As a result, the Seebeck coefficient after 3 weeks was -17 (μV / K), indicating that the N-type properties were maintained.

[0046] <Comparative Example 2> When the Seebeck coefficient of the N-type CNT yarn obtained in Example 1 was measured without immersion in a polystyrene acetone solution, the initial Seebeck coefficient was -40 (μV / K). On the other hand, when the Seebeck coefficient of the obtained N-type CNT yarn was examined over time in the same manner as in Example 4, the Seebeck coefficient was +30 to +20 (μV / K) after one week, and then +30 to +20 (μV / K) after two weeks, indicating a shift to the P-type.

[0047] <Example 4> N-type carbon nanotube (CNT) yarns, after doping, were immersed in a water-soluble oil (the same water-soluble oil as in Example 3) as an adsorbent compound for 24 hours, followed by washing and drying with n-hexane to obtain water-soluble oil-treated N-type carbon nanotube (CNT) yarns, in the same manner as in Example 4. The Seebeck coefficients of the water-soluble oil-treated N-type carbon nanotube (CNT) yarns were then examined at the initial and temporal stages.

[0048] The Seebeck coefficient was measured as follows: One end of a CNT yarn was heated to create a temperature difference between the two ends of the sample. The resulting thermoelectric voltage was then measured using a thermoelectric property measuring device, and the Seebeck coefficient was calculated.

[0049] [Table 1]

[0050] From the above results, it can be seen that the carbon material of this embodiment shows less variation in the Seebeck coefficient between the initial stage and over time compared to the carbon material of the comparative example. This demonstrates that the carbon material in this embodiment exhibits suppressed deterioration of carrier performance over time.

Claims

1. A nanocarbon filament or strip having at least one of a P-type conductive region doped with a P-type dopant and an N-type conductive region doped with an N-type dopant, At least one adsorbed compound selected from the group consisting of aliphatic hydrocarbon compounds having 20 or more carbon atoms and aromatic hydrocarbon compounds, adsorbed on the P-type conductive region and the N-type conductive region of the nanocarbon filamentous or strip-shaped body, Nanocarbon material having the properties of a nanocarbon material.

2. The nanocarbon material according to claim 1, wherein the aliphatic hydrocarbon compound is liquid paraffin.

3. The nanocarbon material according to claim 1, wherein the aromatic hydrocarbon compound is polystyrene.

4. The nanocarbon material according to claim 1, wherein the P-type dopant and the N-type dopant are dopants having at least one of an aliphatic hydrocarbon group and an aromatic group.

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