Method for producing n-type nanocarbon fibers or strips

Abstract

A method for producing N-type nanocarbon fibers or strips according to the present invention includes: a first step for heating at least a portion of a nanocarbon fiber or strip including a residue of a super acid solution; and a second step for doping a heated portion of the nanocarbon fibers or strips with an N-type dopant.

Description

Method for producing nanocarbon filaments or strips having N-type

[0001] The present disclosure relates to a method for producing nanocarbon threads or strips having N-type.

[0002] In recent years, thermoelectric power generation elements have become known as solid-state devices that convert thermal energy into electrical energy. Thermoelectric power generation elements have also been applied to, for example, space power supplies and thermoelectric conversion modules (such as wristwatches and wearable devices) that operate on body heat. Thermoelectric conversion elements sometimes utilize nanocarbon filaments or strips, such as carbon nanotube yarns and carbon nanotube ribbons, and various studies have been conducted on nanocarbon filaments or strips.

[0003] For example, Patent Document 1 discloses "a carbon nanotube-containing body, characterized in that it is made by impregnating or coating a part or all of a substrate formed into a thread shape with a dispersion liquid containing carbon nanotubes having semiconducting or metallic properties, and then drying it."

[0004] Patent Document 2 discloses a method for producing carbon nanotube fibers, comprising spraying a mixture containing a hydrocarbon-containing carbon source and a catalyst together with a carrier gas into a production reactor, heating the mixture to produce carbon nanotubes, collecting the produced carbon nanotubes in a sheet form on an endless belt formed by a mesh member of a required width placed in the production reactor, and spinning the sheet-like carbon nanotubes by discharging gas from the inside of the endless belt. Patent Document 3 discloses a functional element in which a spun yarn made of a conductive fibrous material is sewn into a sheet-like or strip-like insulating substrate, the spun yarn being sewn so as to alternately penetrate the front and back surfaces of the insulating substrate, thereby forming a serial cell structure of π-type thermoelectric conversion elements. Patent Document 3 also discloses that "the 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." Patent Document 4 discloses "a thermoelectric conversion module having a heat receiving section and a heat dissipating section, which generates electricity by utilizing the temperature difference between the heat receiving section and the heat dissipating section, the thermoelectric conversion module comprising a substrate having thermal insulation properties, and a carbon nanotube yarn formed into a fiber shape from carbon nanotubes and wound spirally around the substrate."

[0005] Patent Document 5 discloses a method for producing an article containing well-ordered multi-walled carbon nanotubes, comprising: "(1) preparing a solution of multi-walled carbon nanotubes in a super acid solvent, wherein the concentration of the multi-walled carbon nanotubes in the super acid solvent is selected so that the solution is in a liquid crystal state; (2) extruding the solution to obtain an extrudate; and (3) removing the super acid solvent from the extrudate."

[0006] JP 2013-155058 A JP 2016-17005 A International Publication No. 2016 / 151634 A JP 2024-5793 A Japanese Patent No. 5658567 A

[0007] Conventionally, including Patent Documents 1 to 5, the mainstream methods for producing nanocarbon filaments or ribbons having N-type conductivity have been to dope a completed nanocarbon filament or ribbon with an N-type dopant, or to dope a nanocarbon filament or ribbon treated with a protective agent with an N-type dopant. However, there is a need for a new method for producing nanocarbon filaments or ribbons having N-type conductivity.

[0008] Therefore, an object of the present invention is to provide a novel method for producing nanocarbon filaments or strips having N-type.

[0009] Means for solving the problems include the following aspects. <1> A method for producing an N-type nanocarbon thread or strip, comprising: a first step of heating at least a portion of a nanocarbon thread or strip containing residue of a super acid solution; and a second step of doping the heated portion of the nanocarbon thread or strip with an N-type dopant. <2> A method for producing an N-type nanocarbon thread or strip according to <1>, in which the entire nanocarbon thread or strip is heated in the first step. <3> A method for producing an N-type nanocarbon thread or strip according to <1>, in which the first step is heating a portion of the nanocarbon thread or strip so that the heated portions and unheated portions are arranged alternately in the longitudinal direction of the nanocarbon thread or strip. <4> The method for producing an N-type nanocarbon thread or ribbon according to any one of <1> to <3>, wherein the nanocarbon thread or ribbon is a carbon nanotube thread or ribbon. <5> The method for producing an N-type nanocarbon thread or ribbon according to any one of <1> to <4>, wherein the residue of the super acid solution is sulfur.

[0010] According to the present disclosure, a novel method for producing nanocarbon threads or strips having N-type can be provided.

[0011] 1 is a process diagram showing an example of a method for producing an N-type nanocarbon thread or ribbon according to the present disclosure.

[0012] An embodiment that is an example of the present disclosure will be described below. These descriptions and examples are intended to illustrate the embodiments and do not limit the scope of the invention. In the numerical ranges described in this specification in stages, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. Each component in the composition may contain multiple corresponding substances. When referring to the amount of each component in a composition, if multiple substances corresponding to each component are present in the composition, the total amount of those multiple substances present in the composition is meant, unless otherwise specified.

[0013] <Method for producing N-type nanocarbon filaments or strips> The method for producing N-type nanocarbon filaments or strips of the present disclosure includes a first step of heating at least a portion of the nanocarbon filaments or strips containing residues of a superacid solution, and a second step of doping the heated portion of the nanocarbon filaments or strips with an N-type dopant.

[0014] In the method for producing nanocarbon threads or strips having N-type conductivity disclosed herein, at least a portion of the nanocarbon threads or strips containing residues of a superacid solution is heated, causing deoxidation in the heating section. Then, the heated section is doped with an N-type dopant, resulting in nanocarbon threads or strips having N-type conductivity. Heating the entire nanocarbon thread or strip results in a thread or strip having N-type conductivity throughout. Heating only a portion of the nanocarbon thread or strip results in a thread or strip having a partial region of N-type conductivity (i.e., a thread or strip having regions of both N-type and P-type conductivity). In other words, in the present disclosure, "nanocarbon threads or strips having N-type conductivity" includes both a thread or strip having N-type conductivity throughout and a thread or strip having a partial region of N-type conductivity (i.e., a thread or strip having regions of both N-type and P-type conductivity).

[0015] Furthermore, the nanocarbon filaments or ribbons containing the residue of the superacid solution have high nanocarbon orientation and high electrical conductivity and mechanical strength properties, so the method for producing the N-type nanocarbon filaments or ribbons disclosed herein can partially convert the highly functional nanocarbon filaments or ribbons into N-type semiconductors.

[0016] In addition, by converting the heated portion of the nanocarbon filament or ribbon containing the residue of the superacid solution into an N-type semiconductor, a fine and well-defined PN junction structure can be formed. As a result, the method for manufacturing the N-type nanocarbon filament or ribbon of the present disclosure can produce nanocarbon filaments or ribbons with high thermoelectric power generation properties.

[0017] In particular, a method for partially doping a completed nanocarbon filament or ribbon with an N-type dopant involves a process of partially applying a liquid material containing the N-type dopant. This process is highly difficult. In comparison, the method for manufacturing an N-type nanocarbon filament or ribbon disclosed herein allows for the easy production of nanocarbon filaments or ribbons with excellent properties.

[0018] Furthermore, in the method of doping an N-type dopant into a nanocarbon filament or strip partially treated with a protective agent, the N-type dopant liquid material penetrates the nanocarbon filament or strip due to capillary action. Therefore, it is difficult to form a fine, well-defined PN junction structure. In contrast, the method of manufacturing an N-type nanocarbon filament or strip disclosed herein allows for the easy formation of a fine, well-defined PN junction structure.

[0019] Each step will be described in detail below.

[0020] (Step 1) In Step 1, a nanocarbon filament or strip containing a residue of a superacid solution is prepared (see FIG. 1(A)), and at least a portion of the nanocarbon filament or strip containing a residue of a superacid solution is heated (see FIG. 1(B)). In FIGS. 1(A) and 1(B), 10A denotes the nanocarbon filament or strip containing a residue of a superacid solution, and 12 denotes a heating portion.

[0021] -Nanocarbon filaments or ribbons containing residues of a superacid solution- The nanocarbon constituting the nanocarbon filaments or ribbons is preferably carbon nanotubes (CNTs). That is, the nanocarbon filaments or ribbons are preferably carbon nanotube filaments or ribbons. The carbon nanotubes may be single-walled carbon nanotubes (SWCNTs) in which one carbon film (graphene sheet) is wound into a cylindrical shape. The carbon nanotubes may also be multi-walled carbon nanotubes (MWCNTs), such as double-walled carbon nanotubes, triple-walled carbon nanotubes, and four-walled carbon nanotubes, in which two graphene sheets are wound concentrically. In consideration of thermoelectric properties, carbon nanotubes with 10 or fewer walls are preferred. Single-walled carbon nanotubes are preferred because they are likely to achieve high thermoelectric properties. Multi-walled carbon nanotubes are preferred because they are inexpensive and have excellent mass productivity. A mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes may also be used. The carbon nanotubes may be metallic carbon nanotubes, semiconducting carbon nanotubes, or a mixture of these. The method for producing the carbon nanotubes is not particularly limited. Carbon nanotubes can be produced by arc discharge, chemical vapor deposition (CVD), laser ablation, or the like. Commercially available carbon nanotubes may also be used.

[0022] The nanocarbon may be graphene. By inserting a carrier between two layers of graphene, graphene can be used as a semiconductor material.

[0023] Other examples of nanocarbons include carbon nanorods, carbon nanowires, graphene, and fullerenes.

[0024] The residue of the superacid solution contained in the nanocarbon filaments or ribbons may include sulfur, phosphorus, halogens (chlorine, fluorine), etc. The superacid solution may include solutions of Bronsted superacids, Lewis superacids, and conjugated Bronsted-Lewis superacids. Bronsted superacids include perchloric acid, chlorosulfonic acid, fluorosulfonic acid, trifluoromethanesulfonic acid, and higher perfluoroalkanesulfonic acids (e.g., C ２ F ５ SO ３ H, C ４ F ９ SO ３ H, C ５ F １１ SO ３ H, C ６ F １３ SO ３ H and C ８ F １７ SO ３ H). Lewis superacids include, but are not limited to, antimony pentafluoride and arsenic pentafluoride. Bronsted-Lewis superacids include various concentrations of SO 2 , also known as oleum or oleum. ３ Other Bronsted-Lewis superacids include polyphosphoric acid-oleum mixture, tetra(hydrogensulfate)borate-sulfuric acid, fluorosulfuric acid-antimony pentafluoride (Magic acid), fluorosulfuric acid-SO ３ , fluorosulfuric acid-arsenic pentafluoride, fluorosulfuric acid-hydrogen fluoride-antimony pentafluoride, fluorosulfonic acid-antimony pentafluoride-sulfur trioxide, fluoroantimonic acid, and tetrafluoroboric acid.

[0025] Nanocarbon filaments or ribbons containing the residue of the superacid solution can be obtained by a wet process (so-called liquid phase process). The wet process can be exemplified by the following process: A superacid solvent for carbon nanotubes is prepared. The concentration of carbon nanotubes in the superacid solvent is selected so that the solution is in a liquid crystal state. The solution is extruded to give extrudates, and the superacid solvent is removed from the extrudates. Aligned carbon nanotube filaments or ribbons are thus obtained.

[0026] However, nanocarbon filaments or strips containing residues of the super acid solution may also be obtained by producing nanocarbon filaments or strips that do not contain residues of the super acid solution using a dry manufacturing method (so-called gas phase method) or the like, and then treating them with the super acid solution.

[0027] - Heating Method - The first step may be a step of heating the entire nanocarbon filament or strip under an oxygen atmosphere, or a step of heating a portion of the nanocarbon filament or strip under an oxygen atmosphere. The step of heating a portion of the nanocarbon filament or strip may be, for example, a step of heating a portion of the nanocarbon filament or strip so that heated portions and unheated portions are alternately arranged in the longitudinal direction of the nanocarbon filament or strip. By performing heating so that heated portions that are doped with an N-type dopant and unheated portions that remain P-type due to the residue of the super acid solution are alternately arranged, a nanocarbon filament or strip having a repeated PN junction structure can be easily obtained.

[0028] When the entire nanocarbon filament or strip is heated, heating is performed using, for example, a heating furnace (electric furnace, infrared heating furnace), a hot press, etc. When a portion of the nanocarbon filament or strip is heated, heating is performed using, for example, a laser, a burner, a hot press, etc. In particular, when a laser capable of localized heating is used, nanocarbon filaments or strips having a fine PN junction structure can be easily obtained.

[0029] The heating temperature for the nanocarbon filament or strip is set to a temperature at which deoxidation occurs (for example, 550 to 600° C.).

[0030] (Second Step) In the second step, the heated portion of the nanocarbon filament or strip is doped with an N-type dopant. Specifically, for example, in the second step, it is preferable to immerse the heated nanocarbon filament or strip in an N-type dopant liquid (see FIG. 1(C)). This is because the N-type dopant doping process can be carried out simply and at low cost. After doping, cleaning is carried out. Here, in FIG. 1(C), 10B represents the heated nanocarbon filament or strip, and 14 represents the N-type dopant liquid. However, in the second step, the N-type dopant doping process may also be carried out by a method such as painting or brush painting. By carrying out the N-type dopant doping process, the deoxidized heated portion is converted into an N-type semiconductor and becomes an N-type conductive region.

[0031] The N-type dopant may be a nonionic compound or an ionic compound. In particular, when the solvent of the N-type dopant liquid is water, the N-type dopant is preferably a nonionic compound. On the other hand, when the solvent of the N-type dopant liquid is an organic solvent, the N-type dopant is preferably an ionic compound.

[0032] The nonionic compound is preferably a polyalkyleneimine, which is preferably a polyalkyleneimine having a structural unit with an alkylene group having 1 to 6 carbon atoms (preferably 1 to 4 carbon atoms, more preferably 1 to 2 carbon atoms), and more preferably polyethyleneimine.

[0033] Examples of the ionic compound include alkali metal salts (salts of lithium, sodium, potassium, cesium, etc.) and alkylammonium salts (salts of tetraethylammonium ion, tetrabutylammonium ion, etc.). Among these, alkylammonium halide salts are preferred as the ionic compound, and examples thereof include the following compounds:

[0034]

[0035] From the viewpoint of reducing environmental impact, the solvent for the N-type dopant liquid preferably contains water as a main component. A solvent containing water as a main component may also contain a water-soluble organic solvent such as alcohol (methanol, ethanol, propanol, etc.). Note that "water is the main component" refers to, for example, the proportion of water being 50% by mass (preferably 70% by mass or 90% by mass) or more relative to the total solvent. However, the solvent for the N-type dopant liquid may be mainly composed of an organic solvent. Examples of organic solvents include alcohol (ethanol, propanol, etc.), acetone, methyl ethyl ketone, and butyl acetate. "An organic solvent is the main component" refers to, for example, the proportion of the organic solvent being 50% by mass (preferably 70% by mass or 90% by mass) or more relative to the total solvent.

[0036] Through the above steps, the nanocarbon thread or strip having N-type conductivity of the present disclosure is obtained (see FIG. 1(D)). Here, in FIG. 1(D), 10C denotes the nanocarbon thread or strip having N-type conductivity, P denotes a region of P-type conductivity, and N denotes a region of N-type conductivity. Note that FIG. 1 shows an example of a method for producing a nanocarbon thread or strip having alternating regions of P-type conductivity and N denotes a region of N-type conductivity.

[0037] (Applications) The N-type nanocarbon filaments or strips obtained by the manufacturing method of the present disclosure can be used in a variety of applications. For example, the N-type nanocarbon filaments or strips can be suitably used as nanocarbon filaments or strips that connect thermoelectric conversion elements of a thermoelectric conversion module. In addition, the N-type nanocarbon filaments or strips can also be suitably used in semiconductor applications.

[0038] Examples will be described below, but the present disclosure is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0039] Example 1: Conversion of Carbon Nanotube Filaments to N-Type Semiconductors by Desulfurization via Total Heating Carbon nanotube filaments manufactured using chlorosulfonic acid as a superacid solution and an N-type dopant solution (solute: polyethyleneimine, solvent: 2-propanol, concentration: approximately 20 wt %) were prepared. The carbon nanotube filaments were heated in a 600°C furnace for 3 hours, then immersed in the N-type dopant solution within 24 hours and left for at least 24 hours. The carbon nanotube filaments were removed from the N-type dopant solution and washed with 2-propanol. The Seebeck coefficient of the resulting carbon nanotube filaments was then measured and found to be -40 (μV / K), indicating N-type semiconductor properties. The Seebeck coefficient was measured as follows. One end of the carbon nanotube filament was heated to generate a temperature difference between both ends of the sample. The resulting thermoelectric power was measured using a thermoelectric property measurement device, and the Seebeck coefficient was calculated.

[0040] Example 2: Formation of Fine PN Junction Structures in Carbon Nanotube Filaments by Localized Laser Heating. Carbon nanotube filaments manufactured using chlorosulfonic acid as a superacid solution and an N-type dopant solution (solute: triphenylphosphine, solvent: acetone, concentration: approximately 1 mol / L) were prepared. After irradiating the carbon nanotube filaments with a fiber laser at a portion to be desulfurized, the filaments were immersed in the N-type dopant solution within 24 hours and left for at least 24 hours. The carbon nanotubes were removed from the N-type dopant solution and washed with acetone. The Seebeck coefficient of the laser-irradiated portion (heated portion) of the resulting carbon nanotube filament was then measured, resulting in a value of -57 (μV / K), indicating N-type semiconductor properties. Furthermore, the non-laser-irradiated portion (unheated portion) of the resulting carbon nanotube filament maintained P-type semiconductor properties. This confirmed that fine PN junction structures (approximately 1 mm apart) could be formed within a single carbon nanotube filament by irradiating the filaments with a laser at regular intervals and heating them.

[0041] The reference numerals are explained as follows: 10A: nanocarbon thread or strip containing residue of super acid solution 10B: heated nanocarbon thread or strip 10C: nanocarbon thread or strip having N-type 12: heating portion 14: N-type dopant solution

[0042] The disclosure of Japanese Patent Application No. 2024-112022 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing nanocarbon filaments or strips having an N-type conductivity, comprising: a first step of heating at least a portion of the nanocarbon filaments or strips containing residues of a superacid solution; and a second step of doping the heated portion of the nanocarbon filaments or strips with an N-type dopant.

2. A method for producing an N-type nanocarbon filament or strip as described in claim 1, wherein the first step heats the entire nanocarbon filament or strip.

3. A method for producing a nanocarbon filament or strip having N-type as described in claim 1, wherein in the first step, a portion of the nanocarbon filament or strip is heated so that the heated portions and non-heated portions are arranged alternately in the longitudinal direction of the nanocarbon filament or strip.

4. A method for producing an N-type nanocarbon thread or strip according to claim 1, wherein the nanocarbon thread or strip is a carbon nanotube thread or strip.

5. The method for producing nanocarbon threads or strips having N-type according to claim 1, wherein the residue of the super acid solution is sulfur.

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