Method for producing n-type nanocarbon filament or strip

Abstract

To provide a method for producing a new N-type nanocarbon filament or strip.SOLUTION: The method for producing the N-type nanocarbon yarn or strip comprises a first step of heating at least a part of the nanocarbon yarn or strip containing the residue of a superacid solution and a second step of doping the heated part of the nanocarbon yarn or strip with an N-type dopant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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 that operate on body heat (wristwatches, wearable devices, etc.). Thermoelectric conversion elements may use 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, which is characterized by being formed 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 the substrate.

[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 onto the endless belt 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 types of 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 base material having thermal insulating properties, and a carbon nanotube yarn formed into a fiber shape from carbon nanotubes and wound spirally around the base material."

[0005] Patent Document 4 describes the process of: "(1) preparing a solution of multi-walled carbon nanotubes in a super acid solvent, wherein the concentration of multi-walled carbon nanotubes in the super acid solvent is selected so that the solution is in a liquid crystalline state; (2) extruding the solution to obtain an extrudate; and (3) removing the super acid solvent from the extrudate; "A method for producing an article comprising well-ordered multi-walled carbon nanotubes, the method comprising: [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-155058 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-17005 [Patent Document 3] International Publication No. 2016 / 151634 [Patent Document 4] Japanese Patent Application Laid-Open No. 2024-5793 [Patent Document 5] Patent No. 5658567 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, including Patent Documents 1 to 5, the mainstream methods for producing nanocarbon filaments or strips having N-type conductivity are to dope a finished nanocarbon filament or strip with an N-type dopant, or to dope a nanocarbon filament or strip treated with a protective agent with an N-type dopant. However, there is also a need for new methods for producing nanocarbon threads or strips having N-type.

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

[0009] The means for solving the problem include the following aspects. <1> a first step of heating at least a portion of the nanocarbon strand or ribbon containing the residue of the super acid solution; a second step of doping the heated portion of the nanocarbon filament or strip with an N-type dopant; A method for producing nanocarbon filaments or strips having N-type. <2> In the first step, the nanocarbon filament or strip is heated as a whole. <1> A method for producing a nanocarbon filament or strip having the N-type described in 1. <3> In the first step, a portion of the nanocarbon filament or strip is heated so that the heated portions and non-heated portions are alternately arranged in the longitudinal direction of the nanocarbon filament or strip. <1> A method for producing a nanocarbon filament or strip having the N-type described in 1. <4> The method for producing a filamentous or带状 nanostructure of N-type carbon nanotubes according to any one of <1> to <3>, wherein the filamentous or带状 nanostructure of the nanocarbon is a filamentous or带状 nanostructure of carbon nanotubes. <5> The method for producing a filamentous or带状 nanostructure of N-type carbon nanotubes according to any one of <1> to <4>, wherein the residue of the superacid solution is sulfur.

Advantages of the Invention

[0010] According to the present disclosure, a novel method for producing a filamentous or带状 nanostructure of N-type carbon nanotubes can be provided.

Brief Description of the Drawings

[0011] [Figure 1] It is a process diagram showing an example of the method for producing a filamentous or带状 nanostructure of N-type carbon nanotubes of the present disclosure.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments which are examples of the present disclosure will be described. These descriptions 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 another numerical range described step by step. Further, 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.

[0013] <Method for Producing a Filamentous or带状 Nanostructure of N-Type Carbon Nanotubes> The method for producing nanocarbon threads or strips having N-type according to the present disclosure includes the steps of: a first step of heating at least a portion of the nanocarbon strand or ribbon containing the residue of the super acid solution; a second step of doping the heated portion of the nanocarbon filament or strip with an N-type dopant; It has.

[0014] In the method for producing nanocarbon filaments or ribbons having N-type conductivity disclosed herein, at least a portion of the nanocarbon filaments or ribbons containing the residue of the superacid solution is heated to cause deoxidation in the heated portion, and the heated portion is then doped with an N-type dopant to obtain the nanocarbon filaments or ribbons having N-type conductivity. Heating the nanocarbon filaments or strips as a whole results in filaments or strips with N-type conductivity throughout. By heating a portion of a nanocarbon thread or strip, 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) is obtained. In other words, in this disclosure, "nanocarbon threads or strips having N-type conductivity" includes both threads or strips having N-type conductivity as a whole and threads or strips having partial regions of N-type conductivity (i.e., threads or strips having regions of both N-type conductivity and P-type conductivity).

[0015] Furthermore, nanocarbon filaments or ribbons containing the residue of the superacid solution have high nanocarbon orientation and high electrical conductivity and mechanical strength. Therefore, the method for producing 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 of partially applying a liquid material containing the N-type dopant is highly difficult. In contrast, 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] (1st step) In the first step, a nanocarbon filament or strip containing the residue of the superacid solution is prepared (see FIG. 1(A)), and at least a portion of the nanocarbon filament or strip containing the residue of the superacid solution is heated (see FIG. 1(B)). In Figures 1(A) and 1(B), 10A denotes a nanocarbon filament or strip containing residues of the super acid solution, and 12 denotes a heating section.

[0021] - Nanocarbon threads or strips containing residues of super acid solution - The nanocarbon constituting the nanocarbon filaments or ribbons is preferably a carbon nanotube (CNT), that is, the nanocarbon filaments or ribbons are preferably carbon nanotube filaments or ribbons. The carbon nanotube may be a single-walled carbon nanotube (SWCNT) in which one carbon film (graphene sheet) is wound into a cylindrical shape. The carbon nanotube may also be a multi-walled carbon nanotube (MWCNT) such as a double-walled carbon nanotube, a triple-walled carbon nanotube, or a four-walled carbon nanotube in which two graphene sheets are wound concentrically. In consideration of thermoelectric properties, the carbon nanotube preferably has 10 or fewer walls. Single-walled carbon nanotubes are preferred because they tend to provide high thermoelectric properties. Multi-walled carbon nanotubes are preferred because they are inexpensive and easy to mass-produce. A mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes can also be used. Furthermore, the carbon nanotubes may be metallic carbon nanotubes or semiconducting carbon nanotubes, or they may be used in combination. The method for producing carbon nanotubes is not particularly limited. Carbon nanotubes can be produced by arc discharge, chemical vapor deposition (CVD), laser ablation, etc. The carbon nanotubes can be produced by a polymerization method, etc. Commercially available carbon nanotubes may also be used.

[0022] The nanocarbon may be graphene. By placing 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] Residuals of the superacid solution contained in the nanocarbon threads or ribbons include sulfur, phosphorus, halogens (chlorine, fluorine), and the like. The superacid solution may include solutions of Bronsted superacids, Lewis superacids, conjugated Bronsted-Lewis superacids, and the like. Bronsted superacids include perchloric acid, chlorosulfonic acid, fluorosulfonic acid, trifluoromethanesulfonic acid, and the higher perfluoroalkanesulfonic acids (e.g., C2F5SO3H, C4F9SO3H, C5F 11 SO3H, C6F 13 SO3H and C8F 17 SO3H), but are not limited to these. Lewis superacids include, but are not limited to, antimony pentafluoride and arsenic pentafluoride. Bronsted-Lewis superacids include sulfuric acid containing various concentrations of SO3, also known as oleum or oleum. Other Bronsted-Lewis superacids include, but are not limited to, polyphosphate-oleum mixture, tetra(hydrogen sulfate)borate-sulfuric acid, fluorosulfate-antimony pentafluoride (Magic acid), fluorosulfate-SO, fluorosulfate-arsenic pentafluoride, fluorosulfate-hydrogen fluoride-antimony pentafluoride, fluorosulfonic acid-antimony pentafluoride-sulfur trioxide, fluoroantimonic acid, and tetrafluoroboric acid.

[0025] Nanocarbon threads or strips containing residues of superacid solutions are preferably obtained using a wet process (so-called liquid phase process). An example of a wet process is as follows: A super acid solvent of carbon nanotubes is prepared, where the concentration of carbon nanotubes in the super acid solvent is selected so that the solution is in a liquid crystalline state. The solution is extruded to give extrudates, and the super acid solvent is removed from the extrudates. This results in aligned carbon nanotube threads or ribbons.

[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 thread or strip in an oxygen atmosphere, or a step of heating a portion of the nanocarbon thread or strip in an oxygen atmosphere. An example of the process of heating a portion of a nanocarbon filament or strip is a process of heating a portion of the nanocarbon filament or strip so that heated portions and non-heated portions are arranged alternately in the longitudinal direction of the nanocarbon filament or strip. By heating the nanocarbon fibers or strips with repeated PN junction structures, it is easy to obtain nanocarbon fibers or strips with repeated PN junction structures by alternating heated areas that are doped with N-type dopants with unheated areas that remain P-type due to the residual super acid solution.

[0028] When the nanocarbon filament or strip is heated in its entirety, a heating furnace (electric furnace, infrared heating furnace), a hot press, or the like is used for heating. When a part of the nanocarbon filament or strip is heated, the heating is performed using, for example, a laser, a burner, a hot press, or the like. In particular, by using a laser capable of localized heating, nanocarbon threads or strips having fine PN junction structures 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] (2nd process) In the second step, the heated portion of the nanocarbon thread or ribbon is doped with an N-type dopant. Specifically, for example, in the second step, it is preferable to immerse the heated nanocarbon filament or ribbon in an N-type dopant solution (see FIG. 1(C)). This is because the doping process with the N-type dopant can be carried out easily and at low cost. After doping, the nanocarbon filament or ribbon is then washed. In FIG. 1(C), 10B denotes a heated nanocarbon filament or strip, and 14 denotes an N-type dopant liquid. However, in the second step, the doping treatment with the N-type dopant may be carried out by a method such as coating or brush coating. By performing a doping process with an N-type dopant, the deoxidized heated portion is converted into an N-type semiconductor, becoming an N-type conductive region.

[0031] N-type dopants include non-ionic compounds and ionic compounds. In particular, when the solvent of the N-type dopant liquid is water, a nonionic compound is preferred as the N-type dopant. On the other hand, when the solvent for 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. The polyalkyleneimine 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, alkyl ammonium halide salts are preferred as the ionic compounds, and the following compounds are exemplified:

[0034] [ka]

[0035] From the viewpoint of reducing the environmental load, the solvent of the N-type dopant liquid preferably contains water as a main component. The solvent containing water as a main component may contain a water-soluble organic solvent such as alcohol (methanol, ethanol, propanol, etc.). Note that "water is the main component" means 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 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, butyl acetate, etc. "Mainly composed of an organic solvent" means 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.

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

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

[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 by mass.

[0039] <Example 1: Conversion of carbon nanotube filaments into N-type semiconductors by desulfurization through 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 filament was heated in a heating furnace at 600° C. for 3 hours, and then immersed in an N-type dopant solution within 24 hours and left for 24 hours or more. 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 filament 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, and the generated thermoelectric power was measured using a thermoelectric property measuring device to calculate the Seebeck coefficient.

[0040] Example 2: Formation of a fine PN junction structure in a carbon nanotube filament by local 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 portion of the carbon nanotube linear body to be desulfurized with a fiber laser, the body was immersed in an N-type dopant solution within 24 hours and left for 24 hours or more. The linear carbon nanotube body was taken out of the N-type dopant solution and washed with acetone. Thereafter, the Seebeck coefficient of the laser-irradiated portion (heated portion) of the obtained carbon nanotube filament was measured, and it was found to be −57 (μV / K), indicating N-type semiconductor properties. Furthermore, the non-laser irradiated portion (non-heated portion) of the obtained carbon nanotube filament maintained the P-type semiconductor properties. It was confirmed that by irradiating the material with a laser at regular intervals and heating it, fine PN junction structures (approximately 1 mm apart) can be formed within a single carbon nanotube filament. [Explanation of symbols]

[0041] 10A Nanocarbon threads or strips containing residues of superacid solutions 10B Heated nanocarbon filaments or strips Nanocarbon threads or strips with 10C N type 12 Heating section 14 N-type dopant solution

Claims

1. a first step of heating at least a portion of the nanocarbon thread or ribbon containing the residue of the super acid solution; a second step of doping the heated portion of the nanocarbon filament or ribbon with an N-type dopant; A method for producing nanocarbon filaments or strips having N-type.

2. 2. The method for producing an N-type nanocarbon filament or strip according to claim 1, wherein the first step heats the entire nanocarbon filament or strip.

3. A method for producing an N-type nanocarbon filament or strip 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. 2. The method for producing an N-type nanocarbon thread or ribbon according to claim 1, wherein the nanocarbon thread or ribbon is a carbon nanotube thread or ribbon.

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

Images