WO2020190105A2 - Method for preparing carbon material having sp2 hybrid structure with controlled content of pyridinic nitrogen and pyrrolic nitrogen, and carbon material prepared by same - Google Patents

Abstract

The present invention relates to: a method for preparing a carbon material with controlled content of pyridinic nitrogen and pyrrolic nitrogen, comprising the step of bringing a super strong acid into contact with a carbon material having a nitrogen-doped sp2 hybrid structure so as to reduce pyridinic nitrogen and pyrrolic nitrogen while maintaining graphitic nitrogen or quaternary nitrogen present in the carbon material; and a carbon material prepared by same.

Description

Method for producing a carbon material having an SP2 hybrid structure in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled, and a carbon material manufactured thereby

The present invention relates to a method of manufacturing a carbon material having a controlled bond structure of nitrogen doped to an sp2 carbon material in order to improve the electrical conductivity of the carbon material, and to a carbon material manufactured thereby.

Nano-carbon materials such as graphene and carbon nanotubes have low density and high mechanical and electrical properties, so they are being studied in various fields such as energy materials, ultra-high strength materials, and semiconductors. Recently, the electrical properties and chemical properties of nano-carbon materials have been studied. In order to control, a chemical doping method of doping nitrogen, boron, phosphorus, alkali metal, etc. is being studied.

Among various dopants for doping, nitrogen is not only a very common element, but also an element capable of replacing the lattice of sp2 carbon, so it is a dopant having excellent chemical, thermal, and electrical stability. Since this stability is the most suitable property for commercialization, studies have been conducted not only on nanocarbon materials such as graphene, carbon nanotubes, and nanohorns, but also various carbon materials such as carbon fiber and carbon black (KR 10-2014-0054784). .

The carbon material may typically be doped with nitrogen by a chemical vapor deposition method, a nitrogen plasma method, or a heat treatment method. When nitrogen is doped with a carbon material, it can mainly exist in three forms of bonding, which are substituted in the sp2 hexagonal structure of pyridinic nitrogen and pyrrolic nitrogen and carbon doped at the defect or edge. It may be graphitic nitrogen or quaternary nitrogen doped with.

The doping effect of the carbon material may vary depending on the type of nitrogen bonding. First, it is known that pyridine nitrogen and pyrroleic nitrogen have a chemical activity due to having an unshared electron pair and thus have a chemical reaction catalyst effect in energy materials. However, they not only reduce the electron carrier density by localizing electrons, but also break structural symmetry to open the band gap, and thus act as defects from the viewpoint of electrical conduction. On the other hand, it is known that graphitic nitrogen exhibits an n-type doping effect as a nitrogen atom having one more electron than carbon acts as an electron donor, thereby exerting an effect on improving electrical conductivity.

Accordingly, a number of studies have been conducted to control the doped carbon material to have an appropriate bonding form according to the application field, and studies have been conducted to doping nitrogen to improve the electrical conductivity. However, in the existing studies, in addition to graphitic nitrogen, pyridine nitrogen and pyrroleic nitrogen, which are negative in electrical conductivity, are formed together, and thus, a significant effect of improving the electrical conductivity through nitrogen doping has not been achieved (KR 10-2006-0001394).

This can be interpreted as a result of canceling the n-type doping effect of graphitic nitrogen by pyridine nitrogen and pyrrole nitrogen. Therefore, a technique of selectively doping a carbon material with graphitic nitrogen is required.

However, it is very difficult to dope only graphitic nitrogen compared to doping pyridine nitrogen and pyrrole nitrogen in the nanocarbon material. The reason is that pyridine nitrogen and pyrroleic nitrogen are reactions performed at lower energy than graphitic nitrogen. Specifically, unlike graphitic nitrogen that can be doped only with pyridine nitrogen and pyrroleic nitrogen by reacting at low energy in which graphitic nitrogen is not formed, the energy at which graphitic nitrogen is formed involves reactions generated at lower energy. This is because all forms of nitrogen are formed.

Meanwhile, as a method of selectively doping graphitic nitrogen, a method of growing molecules including nitrogen in an aromatic carbon ring in the process of synthesizing a carbon material is known. However, since this method affects the intrinsic morphology of the synthesized material, it can be used to improve the properties of the desired carbon material because it synthesizes a new material with a completely different morphology from the original carbon material. none.

By doping nitrogen through a post-treatment process on the carbon material manufactured according to the existing method, while maintaining the morphology of the carbon material, it is possible to selectively reduce or remove pyridine nitrogen and pyrrole nitrogen to control the bond form of nitrogen. There is a need for a method of improving the electrical conductivity of carbon materials.

An object of the present invention is to contact a carbon material having a nitrogen-doped sp2 hybrid structure with a super strong acid, while maintaining the graphitic nitrogen present in the carbon material, pyridinic nitrogen and pyrrole nitrogen It is to provide a method for manufacturing a carbon material in which the content of pyridine nitrogen and pyrrole nitrogen is controlled, comprising the step of reducing and removing (pyrrolic nitrogen).

Another object of the present invention is to provide a carbon material having a controlled content of pyridine nitrogen and pyrrole nitrogen.

The manufacturing method of the present invention removes pyridine nitrogen and pyrroleic nitrogen that reduce electrical conductivity from the nitrogen-doped sp2 carbon material, and at the same time retains only graphitic nitrogen that increases electrical conductivity, effectively increasing the electrical conductivity of the raw material. Can be improved. When applied to fibers or films composed of sp2 carbon-based nano-carbon materials such as graphene or carbon nanotubes, which have been studied recently, it can be applied as an electrically conductive material that can replace metal, so that high-performance new materials are developed. Makes it possible. In addition, since the manufacturing method of the present invention is applied to the post-treatment step while maintaining the previously known doping process, the industrialization cost is low and thus it is very economical.

In addition, in the present invention, when the super acid is contained in the solution and treated, it is a wet process, so it has the advantage of excellent productivity, uniformity, and reproducibility. Moreover, when the super acid is treated, a liquid crystal solution form can be obtained, and thus, it has an effect that can be effectively applied to manufacturing liquid crystal spinning fibers, films, ink, etc. in an additional process.

1 is a diagram schematically showing a reaction according to an embodiment of the present invention.

2 is a diagram showing a liquid crystal carbon nanotube.

3 is a diagram showing a carbon nanotube liquid crystal spinning fiber.

4 is a diagram showing a carbon nanotube film.

5 is a nitrogen-doped carbon nanotube (Pr-CNT), a nitrogen-doped and super acid-treated carbon nanotube (N-CNT), and a nitrogen-doped and super acid-treated carbon nanotube (N _Q -CNT) It is a diagram showing (a) N1s, (b) C1s, and (c) Survey spectra according to the X-ray photoelectron spectroscopy of.

6 is a N1s spectrum according to X-ray photoelectron spectroscopy of carbon nanotubes doped with nitrogen and treated with chlorosulfuric acid (ClSO ₃ H) and carbon nanotubes doped with nitrogen and treated with 98% sulfuric acid (H ₂ SO ₄ (98%)) It is a diagram showing.

7 is a diagram schematically showing a mechanism by which various types of nitrogen doped with sp2 carbon are reduced by strong acids.

Figure 8 is a diagram showing the results of (a,b,d,e,g,h) high-resolution transmission electron microscope and (c,f,i) EDX component analysis results of Pr-CNT, N-CNT, and N _Q -CNT to be.

9 is a diagram showing Raman spectra of Pr-CNT, N-CNT, and N _Q -CNT and analysis thereof.

10 is a diagram showing the results of UV-photoelectron spectroscopy of Pr-CNT, N-CNT, and N _Q- CNT.

11 is a diagram showing (a) specific resistance in the 1.5K to 300K region, (b) specific resistance based on the specific resistance at 300K, and (c) electrical conductivity of Pr-CNT, N-CNT, and N _Q -CNT to be.

Detailed contents for carrying out the present invention will be described as follows. On the other hand, each description and embodiment disclosed herein can be applied to each other description and embodiment. That is, all combinations of various elements disclosed herein fall within the scope of the present invention. In addition, it cannot be said that the scope of the present invention is limited by the specific description described below.

In addition, those of ordinary skill in the art can recognize or ascertain using only routine experimentation a number of equivalents to the specific aspects of the invention described in this application. Also, such equivalents are intended to be included in the present invention.

As an aspect for achieving the above object, the present invention maintains graphitic nitrogen or quaternary nitrogen present in the carbon material by contacting a super acid to a carbon material having a nitrogen-doped sp2 hybrid structure. It provides a method of manufacturing a carbon material in which the content of pyridine nitrogen and pyrrolic nitrogen is controlled, including the step of reducing pyridinic nitrogen and pyrrolic nitrogen.

Specifically, in the present invention, the carbon material having an sp2 hybrid structure may refer to a material containing carbon having an sp2 hybrid structure, and may additionally include carbon of another hybrid structure or additionally include other elements other than carbon. have. The carbon material having the sp2 hybrid structure is selected from the group consisting of carbon nanotubes, graphene, graphene oxide, carbon nanohorns, graphite, polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, carbon black, and activated carbon. There can be more than one. In the present invention, the carbon nanotube may mean a structure in which one or more layers of honeycomb films composed of 　 carbon are sp2　 bonds are formed in a cylindrical shape.

In one experimental example of the present invention, as a carbon material having an sp2 hybrid structure, pyridine nitrogen and pyrrole nitrogen are selectively maintained while maintaining the morphology of the original carbon material by nitrogen doping using carbon nanotubes and then super acid treatment. It was confirmed that the graphitic nitrogen can be selectively doped with a carbon material. However, since the manufacturing method of the present invention is not based on a reaction to a macro morphology based on a plate-shaped sp2 lattice as a unit, but based on a chemical reaction to nitrogen in each atomic unit, the sp2 hybrid structure is The carbon material to have may not be limited to carbon nanotubes.

The carbon material having the sp2 hybrid structure doped with nitrogen in the present invention may be a structure in which the carbon material having the sp2 hybrid structure of the present invention is doped with nitrogen, and is not limited if it is a carbon material doped with nitrogen having an sp2 carbon lattice. Included. The nitrogen may include all of pyridine nitrogen, pyrroleic nitrogen, and graphitic nitrogen, and may include pyridine nitrogen and graphitic nitrogen, or may include pyrroleic nitrogen and graphitic nitrogen, but is not limited thereto. . In addition, doping in the present invention may mean that at least one of the carbon atoms constituting the carbon structure is replaced with a hetero atom. 1 shows an example of a carbon material having a nitrogen-doped sp2 hybrid structure of the present invention.

In the present invention, pyridine nitrogen refers to a nitrogen atom present in a 6-membered heterocyclic compound containing the nitrogen atom, and may be included in an aromatic heterocyclic compound, such as nitrogen of the following formula (1), but nitrogen of formula (2) It may be included in the non-aromatic heterocyclic compound as shown in FIG.

[Formula 1]

[Formula 2]

In the present invention, the pyrroleic nitrogen refers to a nitrogen atom present in the 5-membered heterocyclic compound including the nitrogen atom, and may be included in an aromatic heterocyclic compound, such as nitrogen of the following formula (3), but is not limited thereto.

[Formula 3]

In the present invention, graphitic nitrogen may also be referred to as graphitic nitrogen, and means a nitrogen atom covalently bonded to three or more carbon atoms. Graphitic nitrogen may be a constituent element of a multicyclic compound, for example, as shown in Formula 4 below.

[Formula 4]

In one non-limiting embodiment of the present application, a carbon material selectively doped with graphitic nitrogen is prepared by selectively reducing and removing pyridine nitrogen and pyrroleic nitrogen negative to electrical conductivity in a carbon material having a nitrogen-doped sp2 hybrid structure. And, it was confirmed that the produced carbon material has significantly improved electrical conductivity compared to a carbon material not doped with nitrogen or a carbon material in which pyridine nitrogen and/or pyrroleic nitrogen is not selectively reduced.

The carbon material having the sp2 hybrid structure doped with nitrogen may be prepared by doping the carbon material having the sp2 hybrid structure of the present invention with nitrogen. Nitrogen doping is not limited thereto, but may be performed by one or more methods selected from the group consisting of a plasma treatment method, a chemical vapor deposition method, and a heat treatment method with a nitrogen reactant. Here, the nitrogen reactant includes one or more selected from the group consisting of nitrogen gas, urea, amine, imine, nitrile, pyrrole, diazole, triazole, pyridine, diazine, and triazine. However, it is not limited thereto. In one embodiment of the present invention, nitrogen doping is performed using an induced coupled plasma (ICP), but the present invention is not limited to a specific doping method as long as nitrogen can be doped.

In the present invention, superacids for contacting a carbon material having a nitrogen-doped sp2 hybrid structure means an acid having a stronger acidity than pure sulfuric acid having a Hammett acidity function (H ₀ ) of -12. Specifically, the super strong acid of the present invention may be an acid having H ₀ less than -12, less than -12.5, less than -13, less than -13.5, or less than -13.8, but is not limited thereto.

More specifically, the super strong acid is chlorosulfonic acid (ClSO ₃ H), trifluoromethanesulfonic acid (CF ₃ SO ₃ H), fluorosulfonic acid (HSO ₃ F), carborane acids (Carborane acids), magic acid (FSO ₃ H·SbF ₅ ), fluoroantimonic acid (H ₂ FSbF ₆ ), or a combination thereof, and more specifically, H ₀ is -13.8. It may be a known chlorosulfuric acid.

In one experimental example of the present invention, chlorosulfuric acid is used as a super strong acid to selectively reduce pyridine nitrogen and pyrrole nitrogen without damaging the original morphology of the carbon material, thereby exhibiting n-doping properties and improving electrical conductivity. Confirmed that there is. However, the acid of the present invention is not limited to chlorosulfuric acid and may be included as long as it is a super acid.

In the present invention, the ability to selectively reduce or remove pyridine nitrogen and pyrrole nitrogen while remaining graphitic nitrogen present in the carbon material by super acid treatment is not limited to a specific theory, but will be explained by the following mechanism. Can be (Fig. 6). First, pyridine nitrogen and pyrroleic nitrogen have a non-shared electron pair that can act as a Lewis base, and thus can react with H ⁺ in a strong acidic environment. That is, pyridine nitrogen and pyrroleic nitrogen can be reduced in a strong acidic environment and removed from the sp2 carbon lattice. On the other hand, of the five outermost electrons of graphitic nitrogen, three form sigma bonds with neighboring carbons, the other forms pi bonds with neighboring carbons, and the last one is delocalized as an electron donor or oriented to nitrogen. Because it is regenerated, unlike other nitrogen, it does not have an unshared electron pair that can react with H ⁺ . Therefore, in the case of super acid treatment, pyridine nitrogen and pyrrole nitrogen other than graphitic nitrogen can be removed by reacting with H ⁺ .

In the present invention, a super acid for contacting a carbon material having a nitrogen-doped sp2 hybrid structure may be present in a solution. In this case, the superacid may be present in the solution at a concentration of 10 to 50 mg/mL, 15 to 45 mg/mL, 20 to 40 mg/mL, or 25 to 35 mg/mL, but is not limited thereto. However, when it is present in a concentration of less than 10 mg/mL, the content of the carbon material per unit volume is small, and thus, when a fiber or film is manufactured with the prepared liquid crystal carbon material, the prepared fiber or film may be broken or the strength may be weak. Conversely, when present in a concentration of more than 50 mg/mL, the carbon material may not be sufficiently liquid crystallized, and as a result, the nozzle is clogged in the fiber manufacturing process using liquid crystal or the orientation in the manufactured fiber is lowered, and the strength of the manufactured fiber Can weaken.

The super acid of the present invention may be a true solvent made of a carbon material. Accordingly, the manufacturing method of the present invention can obtain a carbon material liquid crystal at the same time as the super acid treatment process, and since this liquid crystal can be directly radiated or filmed, there is a great advantage that it can be effectively utilized as a macro assembly with only a very simple process. In one experimental example of the present invention, it was confirmed that chlorosulfuric acid can be used as a super acid capable of selectively reducing pyridine nitrogen and pyrrole nitrogen, and can be used as a strong solvent for carbon nanotubes.

In the present invention, the step of reducing pyridine nitrogen and pyrroleic nitrogen is 6 hours or more, 8 hours or more, 10 hours or more, 12 hours or more, 15 hours or more, 18 hours or more, 21 hours or more, 24 hours or more, 36 hours or more. It may be carried out by contacting a solution containing a super acid for a period of time, but is not limited thereto. However, when contacting for more than 12 hours, the selective reduction effect of pyridine nitrogen and pyrrole nitrogen is excellent in the nitrogen-doped carbon material, and when contacted for more than 36 hours, the carbon material has excellent liquid crystalline properties, resulting in fibers and films. It can be conveniently used in the manufacture of, etc.

In one non-limiting experimental example of the present invention, it was confirmed that pyridine nitrogen and pyrroleic nitrogen can be selectively removed by contacting a super acid with a carbon material for 12 hours, and in another experimental example, a super acid was added for 36 hours. It was confirmed that selective reduction can be performed by contacting the carbon material, and at the same time, the carbon material has a liquid crystal phase and can be processed into fibers or films using this.

The manufacturing method of the present invention can selectively reduce pyridine nitrogen and pyrrole nitrogen present in a nitrogen-doped sp2 structured carbon material, through which only graphitic nitrogen functioning as an electron donor remains in the carbon material, As the density can be increased, as a result, it is possible to provide a carbon material having improved electrical conductivity. The electrical conductivity of the carbon material with controlled contents of pyridine nitrogen and pyrroleic nitrogen prepared according to the present invention is the carbon material before nitrogen doping and the content of pyridine nitrogen and pyrrole nitrogen by super acid treatment after nitrogen doping. This can be improved compared to the carbon material before it is controlled. Specifically, the electrical conductivity of the carbon material in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled is 50%, 70%, 90%, 95%, 100%, 105%, 110% compared to the carbon material before nitrogen doping. , Or it may be improved by more than 120%, and the content of pyridine nitrogen and pyrroleic nitrogen is 100%, 120%, 140%, 160%, 180% compared to the carbon material before being controlled by super acid treatment after nitrogen doping , 185%, 190%, 195%, 200%, 205%, 210%, 215%, 220%, 225%, or may be improved by more than 230%, but is not limited thereto. Moreover, the manufacturing method of the present invention also maintains the existing doping process and is a post-treatment method, thus minimizing process introduction cost. In one non-limiting experimental example of the present invention, the carbon material in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled was increased to 2.2 times (i.e., 120% improvement) of the carbon material not doped with nitrogen, and was doped with nitrogen. It was confirmed that the pyridine nitrogen and pyrroleic nitrogen were selectively increased by 3.3 times (ie, 230% improvement) of the non-reduced carbon material, and the electrical conductivity was remarkably improved.

In another aspect, the present invention provides a carbon material in which the contents of pyridine nitrogen and pyrrole nitrogen are controlled. The carbon material in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled can be prepared according to the manufacturing method of the present invention described above. The thus produced carbon material selectively contains graphitic nitrogen, which increases electrical conductivity by selectively reducing or removing pyridine nitrogen and pyrrole nitrogen, and thus has n-doped properties and can exhibit excellent electrical conductivity. Moreover, since the carbon material of the present invention maintains the unique morphology of the carbon material even in the process of super acid treatment, it can have a desired morphology while having improved physical properties.

In addition, when the super acid is present in the solution as a strong solvent for the carbon material and is treated on the carbon material, the carbon material thus produced has a liquid crystal phase and can be directly radiated or filmed.

Hereinafter, the present invention will be described in more detail based on Examples and Experimental Examples. These examples are for illustrative purposes only, and in order to confirm the effect of sp2 carbon, the effect of the present invention is confirmed through single-walled carbon nanotubes, one of the materials with the highest sp2 carbon ratio among carbon materials. I did. It will be apparent to those of ordinary skill in the art that the scope of the present invention is not construed as being limited by these examples.

Example 1: Preparation of carbon nanotubes doped with nitrogen and treated with super acid

Among the carbon materials, single-walled carbon nanotubes (hereinafter, SWCNT; TUBALL ^TM , carbon>99%) having a high carbon ratio based on sp2 were used as the carbon material.

Then, in the same reactor, SWCNT powder (0.5 ~ 2 g) was treated with ICP (100 W 20 min) in an N ₂ (50 ~ 250 sccm) atmosphere and doped with nitrogen. For uniform doping of SWCNT, the reaction chamber was continuously rotated (50 rpm) and mixed during all plasma treatments. As described above, pyridine nitrogen (N _Py ), pyrroleic nitrogen (N _Pyrr ), and graphitic nitrogen (N _Q ) were mixed to obtain a prepared nitrogen-doped SWCNT.

After it stirred for then mixed in a ratio of chlorosulfuric acid and 30 mg / mL of nitrogen-doped CNT in Dry room moisture-3, by selectively reduced to the N _Py and N _Pyrr of nitrogen doped SWCNT, N _Py and A carbon nanotube doped with N _Q in which N _Pyrr was selectively reduced was obtained.

Example 2: Preparation of carbon nanotubes doped with nitrogen and treated with super acid

After preparing nitrogen-doped CNTs under the same conditions as in Example 1, after mixing with chlorosulfuric acid and stirring for 12 hours instead of 3 days, chlorosulfuric acid was treated under the same conditions as in Example 1, and N _Py and N CNTs in which _Pyrr was selectively reduced were prepared.

Example 3: Preparation of carbon nanotube liquid crystal spinning fiber doped with nitrogen and treated with super acid

A liquid crystal spun fiber was prepared using the CNT subjected to the super acid treatment of Example 1. Specifically, CNT in a solution state having a liquid crystal phase mixed with chlorosulfuric acid was sprayed through a nozzle to acetone in the coagulation tank at a pressure of 10 to 30 G and a rate of 0.01 to 1 mL/min using a syringe pump to form fibers. Then, it was wound in water of a second coagulation bath, and then dried at 100° C. for 12 hours.

Example 4: Preparation of carbon nanotube film doped with nitrogen and treated with super acid

According to the blade coating method, a carbon nanotube film was prepared by dropping the CNT liquid crystal spinning fiber of Example 3 on a glass substrate, and then aligning the CNTs by covering and pushing it with another glass substrate. The obtained film is shown in FIG. 4.

Comparative Example 1: Carbon nanotubes not doped with nitrogen

Single-walled carbon nanotubes (hereinafter, SWCNT; TUBALL ^TM , carbon>99%) were purchased and used as received.

Comparative Example 2: Preparation of carbon nanotubes doped with nitrogen and not treated with super acid

Nitrogen-doped CNTs were prepared under the same conditions as in Example 1, and then nitrogen-doped and N _Py and N _Pyrr were not reduced by not _performing super acid treatment.

Comparative Example 3: Preparation of carbon nanotubes doped with nitrogen and treated with an acid other than a super acid

A carbon nanotube was prepared under the same conditions as in Example 2, except that 98% sulfuric acid was used instead of the super acid.

Comparative Example 4: Preparation of carbon nanotube liquid crystal spinning fiber not doped with nitrogen

In order to confirm the effect of improving the electrical conductivity of nitrogen doping, a carbon nanotube liquid crystal spinning fiber not doped with nitrogen was prepared. Specifically, SWCNT was mixed with chlorosulfuric acid at a ratio of 30 mg/mL and stirred for 3 days to obtain a solution state SWCNT solution having a liquid crystal phase, which was fiberized under the same conditions as in Example 3, wound up, and dried. .

Comparative Example 5: Preparation of carbon nanotube liquid crystal spinning fiber doped with nitrogen and not treated with super acid

In order to confirm the effect of the selective reduction effect of nitrogen on the electrical conductivity, a carbon nanotube liquid crystal spinning fiber was prepared under the same nitrogen doping conditions as in Example 1 and not treated with a super acid.

Specifically, SWCNT was mixed with chlorosulfuric acid at a ratio of 30 mg/mL and stirred for 3 days to obtain a solution state SWCNT solution having a liquid crystal phase, which was fiberized under the same conditions as in Example 3, wound up, and dried. . The prepared carbon nanotube fibers were subjected to ICP treatment under the same conditions as in Example 1 and doped with nitrogen. Through this, a nitrogen-doped carbon nanotube liquid crystal spinning fiber was prepared by _mixing N _Py , N _Pyrr , and N _Q.

Comparative Example 6: Preparation of a carbon nanotube film not doped with nitrogen

A carbon nanotube film was prepared in the same manner as in Example 4, except that the CNT liquid crystal spinning fiber of Comparative Example 4 was used instead of the CNT liquid crystal spinning fiber of Example 3.

Comparative Example 7: Preparation of carbon nanotube film doped with nitrogen and not treated with super acid

A carbon nanotube film was prepared in the same manner as in Example 4, except that the CNT liquid crystal spinning fiber of Comparative Example 5 was used instead of the CNT liquid crystal spinning fiber of Example 3.

Experimental Example 1: Confirmation of production of carbon nanotube liquid crystal phase, liquid crystal spinning fiber, and film

CNT (LC-Pr-CNT) in which CNT of Comparative Example 1 was mixed with chlorosulfate and CNT (LC-N _Q -CNT) in a state in which the nitrogen-doped CNT in Example 1 was mixed with chlorosulfate are shown in FIG. Done. As can be seen in FIG. 2, it can be seen that CNT is dissolved in chlorosulfuric acid to form a liquid crystal phase. In addition, the CNT liquid crystal spun fiber obtained in Example 3 is shown in FIG. 3, and the CNT film obtained in Example 4 is shown in FIG.

Through this, it was confirmed that when using chlorosulfuric acid, the CNT has a liquid crystal phase, so that processing into a liquid crystal spinning fiber or film has an advantageous advantage.

Experimental Example 2: Confirmation of selective reduction effect of pyridine nitrogen and pyrrole nitrogen according to nitrogen doping and super acid treatment

In order to check whether N _Py and N _Pyrr are selectively reduced while maintaining N _Q by nitrogen doping and super acid treatment, nitrogen-doped carbon nanotubes (Comparative Example 1; Pr-CNT), nitrogen doped and super acid treatment Carbon nanotubes that were not (Comparative Example 2; N-CNT), and nitrogen-doped and super acid-treated carbon nanotubes (Example 1; N _Q- CNT) were compared through X-ray photoelectron spectroscopy and shown in FIG. Done. Specifically, the CNTs of Comparative Example 1, Comparative Example 2, and Example 1 were evenly coated on a Cu substrate in a powder state, and then measured using [Thermo Scientific, ESCALAB 250Xi] to perform XPS analysis.

In Fig. 5(a), it can be seen that N-CNTs have an asymmetrical N1s peak. This means that several types of nitrogen peaks are convolutional. Thus, after obtaining raw data minimizing the noise of the N1s peak, the results of deconvolution of the N-CNT and NQ-CNT spectra into three types of detailed spectra having a Gaussian distribution are shown together. N-CNT showed three dominant peaks: N _Py (398.4 eV), N _Pyrr (399.8 eV), and a small amount of N _Q (401.0 eV). On the other hand, N _Q -CNT showed only a single peak of N _Q without other convolutional peaks due to the symmetrical complete Gaussian distribution. Through this, it was confirmed that N _Py and N _Pyrr were selectively removed while _leaving N _Q by super acid treatment.

The removal reaction of N _Py and N _Pyrr by acid can be understood by the same mechanism as in FIG. 6 (FIG. 6 shows only the reduction reaction of nitrogen for convenience, and the process of reducing unsaturated bonds of carbon is not shown in FIG. 6). Specifically, looking at the mechanism, N _Py and N _Pyrr doped on sp2 carbon lattice have Louis-Base characteristics because they have a lone pair of electrons, and these lone pairs act as protonation sites in a rich Proton environment such as chlorosulfate to form unsaturated bonds. Branches are continuously reduced by Proton along with carbon (Figs. 6(a) and 6(b)). The very high Proton environment becomes a driving force that can irreversibly _advance the reactions of N _Py and N _Pyrr . On the other hand, in N _Q , three of the five electrons are involved in bonding with carbon, and the other electron is involved in bonding by sp2 hybrid orbital, and the last one electron is delocalized in π ^* state as a carrier. It forms a coupling with the surrounding carbon and plays two roles of being localized. Accordingly, the electrons of N _Q do not form an unshared electron pair, and have a property of being chemically inert to Proton (Fig. 6(c)). Consequently, according to this mechanism, nitrogen It is understood that on the doped CNTs N _Py and N _Pyrr are removed and only N _Q remains.

Meanwhile, in FIG. 5(b), it can be seen that C1s is chemically shifted by the change in Fermi level of the surrounding carbon by the reduction of N _Py and N _Pyrr . When N _Py and N _Pyrr , which delocalize electrons, are introduced into the sp2 lattice of carbon, nitrogen itself has a negative charge (which does not mean n-type doping), but the surrounding carbons have a positive charge. The lowered electron concentration in carbon increases the bonding force between the nucleus and core level electrons, causing C1s to chemically move toward higher binding energy. In fact, in Fig. 5(b), N-CNTs containing N _Py and N _Pyrr have a high binding energy (284.50 eV) compared to Pr-CNT (284.38 eV) or N _Q -CNT (284.28 eV). You can see that it moves. This means that when several forms of nitrogen are doped, the effects of the more dominant bonding forms, N _Py and N _Pyrr , are greater. On the other hand, since only N _Q acting as an electron donor exists in CNT (N _Q -CNT) after selective reduction, it can be confirmed that the downshift is due to the increased fermi-level of carbon.

In addition, in the Survey Spectrum of FIG. 5(c), the relative ratio of constituent elements was confirmed. In N-CNT, it can be seen that the N1s (400 eV) signal, which was not present in Pr-CNT, appears, and this can be observed in N _Q CNT. Here, it can be seen that the O1s (533 eV) of N _Q -CNT is maintained at a similar level despite the treatment with chlorosulfuric acid, which is unlikely to be known that nitrogen-doped CNTs are oxidized in a strong acidic environment such as sulfuric acid. Shows that the reduction reaction is possible without chemical damage.

Through this, it was confirmed that the carbon-containing material was doped with nitrogen and then treated with super acid to selectively reduce N _Py and N _Pyrr while maintaining N _Q without chemical damage.

Experimental Example 3: Confirmation of selective reduction of pyridine nitrogen and pyrrole nitrogen by nitrogen doping and acid treatment other than super acid

To confirm the effect of acid treatment other than super acid on pyridine nitrogen and pyrrole nitrogen of nitrogen-doped carbon nanotubes, nitrogen-doped and super acid-treated carbon nanotubes (Example 2) and nitrogen-doped super acid The carbon nanotubes (Comparative Example 3) treated with an acid other than this were compared through X-ray photoelectron spectroscopy. Specifically, after evenly coating the CNTs of Example 2 and Comparative Example 3 in a powder state on a Cu substrate, XPS analysis was performed by measuring using [Thermo Scientific, ESCALAB 250Xi], and as a result, the XPS N1s spectrum is shown in FIG. Indicated.

As a result of the analysis, it was confirmed that in the carbon nanotubes doped with nitrogen and treated with chlorosulfuric acid (ClSO ₃ H), N _Py and N _Pyrr were selectively reduced by chlorosulfuric acid treatment, and only N _Q remained. On the other hand, in carbon nanotubes doped with nitrogen and treated with 98% sulfuric acid (H ₂ SO ₄ (98%)), N _Py remains in addition to N _Q by sulfuric acid treatment, so N _Py and N _Pyrr are selectively reduced and removed. It was confirmed that it was not.

Through this, it was confirmed that, unlike sulfuric acid, superacids such as chlorosulfuric acid can be removed by selectively reducing both N _Py and N _Pyrr in a nitrogen-doped carbon material.

Experimental Example 4: Checking whether the structure of carbon nanotubes is changed according to nitrogen doping and super acid treatment

In order to check whether the structure of the carbon nanotubes is changed by nitrogen doping and super acid treatment, the same CNT powder as in Experimental Example 2 was subjected to [FEI] through High Resolution Transmission Electron Microscopy (HR-TEM). -Titan G3, Cs-Corrector + Monochromator equipped, 80kV], and EDX component analysis (Super-X, 4-SDD system) in the HAADF-STEM mode of the same equipment is shown in FIG. The specimen was prepared by dispersing in ethanol using a bath type sonicator, and dropping it onto a lacey carbon grid.

As a result of the analysis, it can be seen that Pr-CNTs have high crystallinity without visible defects (FIG. 7(a)), and they exist in bundles by van der Waals force (FIG. 7(b)). In addition, it was confirmed that the N-CNT did not change or distort the shape of the Bamboo-like CNT despite the introduction of nitrogen (FIG. 7(d)). However, some point defects (yellow arrows) were observed on the sidewall of the carbon nanotube, which is likely to be the location where N _Py and N _Pyrr exist. As a result of EDX analysis, it can be seen that nitrogen (red), which was not seen in Pr-CNT (Fig. 7(c)), is uniformly distributed in the CNT bundle (carbon; blue) in N-CNT (Fig. 7(f)). there was.

On the other hand, N _Q -CNT retains the point defects due to the _voids of the removed N _Py and N _Pyrr as it is, but unzipping does not proceed further and maintains the cylindrical CNT structure (Fig. 7(g)), It can be seen that it has nitrogen distributed inside the bundle (Fig. 7(i)).

Through this, it was _confirmed that nitrogen doping and super acid treatment selectively reduced N _Py and N _Pyrr while maintaining the unique structural characteristics of CNTs.

Experimental Example 5: Confirmation of change in doping characteristics of carbon nanotubes according to nitrogen doping and super acid treatment

In order to confirm the effect of nitrogen doping and super acid treatment on the doping properties of carbon nanotubes, Raman and UV-photoelectron spectroscopy (UPS) for the CNT films of Examples 4, 6, and 7 Was measured. The results are shown in FIGS. 9 and 10.

9(a) is a Raman spectrum that occurs at 1000 ~ 3000 cm ^-1 , the strongest peak observed at 1580 ~ 1600 cm ^-1 , G-band (graphitic mode), D observed at 1300 ~ 1350 cm ^-1 -band (defect-induced mode), and finally, two strong peaks of 2D-Band (double resonance mode) observed at 2550 ~ 2700 cm ^-1 are shown. Fig. 6(b) shows the R value (I _G / I _D ratio), which is the ratio of the peak intensity of the G-band to the peak intensity of the D-band, from the Raman spectrum, and shows the crystallinity through the R-value. Able to know. A high R value means that the D-band peak intensity is low, which means that it has high crystallinity. For example, when nitrogen having a shorter bond length is doped in the sp2 lattice of CNTs, the D-band increases due to crystallinity reduction due to symmetry breaking, and accordingly, the R-value decreases. N-CNT can be confirmed by having a lower R value than Pr-CNT. On the other hand, although structural point defects remain in N _Q -CNT after removal of N _Py and N _Pyrr by super acid treatment (Fig. 7), it can be seen that the R value is increased compared to N-CNT. This suggests that N _Py and N _Pyrr , which delocalize electrons, have a greater influence on the increase in the _disorder (D-band) of carbon lattice than the effects of nitrogen and substituted hydrogen and structural _vacancy .

In Fig. 9(c), it can be seen that the 2D band visible near 2700 cm ^-1 exhibits a large shift according to the bonding type of nitrogen. The 2D band is very sensitive to the carrier density of the π valence band of CNT, and specifically, it is up shifted in p-type doping and down shifted in n-type doping. Considering that the shift of the G-band was within 1 cm ^-1 , it can be seen that the shift of the 2D band is very distinct from 1 to 9 cm ^-1 . At all wavelengths of 488, 514, and 785 nm, and _Py N N In N-CNT is the high rate of _Pyrr while the 2D band showed p-type characteristics to blue shift, the N _Q N _Q -CNT only doped 2D It was confirmed that the band shifted red to show n-type characteristics.

The doping characteristics of CNTs can also be confirmed through a valence-level spectrum of UV-photoelectron spectroscopy (UPS) (FIG. 10). Specifically, it can be seen a work function (Φ) of the material using a 2 ^nd cut-off edge may appear on parts of the peak. Compared with Pr-CNT, as the p-type characteristics of N _Py and N _Pyrr , which have higher ratios in N-CNT, are larger than the n-type characteristics of N _Q , which have a lower ratio, the Fermi level is lowered and thus Vacuum- As a result of the increase in the energy gap to the level, it can be seen that it has a higher work function than that of Pr-CNT. However, since N _Py and N _Pyrr were removed from N _Q -CNT by acid, the Fermi level increased only under the influence of the electron donor N _{Q and} the work function decreased (5.46 eV -> 4.59 eV), and accordingly, N _Q- It was confirmed that CNTs showed n-type doping characteristics, and this tendency to decrease the work function by N _Q is consistent with the theoretically calculated research results.

Through this, it was _confirmed that carbon nanotubes in which N _Py and N _Pyrr were not reduced _exhibit p-type characteristics, while carbon nanotubes selectively reduced N _Py and N _Pyrr according to the present invention _exhibit n-type characteristics. Could

Experimental Example 6: Confirmation of the effect of improving the electrical conductivity of carbon nanotubes by super acid treatment

Figure 11(a) shows the Temperature Dependent Specific Resistance of N-CNT fibers measured at low temperature through the 4-Probe method. Interestingly, in spite of the hetero atom doping effect, the N-CNT fiber (blue color) mixed with N _Py and N _Pyrr showed a tendency to increase the electrical resistance rather than the Pr-CNT. This can be considered to be due to the decrease in electron density due to the N _Py and N _{Pyrr acting} as electron localization and scattering sites during the electrical conduction process. On the other hand, the N _Q -CNT fiber (red color) showed a tendency to decrease in electrical resistance compared to Pr-CNT, which can be seen as a result of an increase in the carrier density as N _Q acts as an electron donor.

In FIG. 11(b), through a plot of R/R _300K , it is possible to confirm the tendency of electric resistance change according to temperature. In the low-temperature region of 1.5K to 100K, the electrical resistance generally decreases with the increase in temperature, which can be seen as an effect of the increase in electron carriers due to temperature. In the case of N-CNT, since the concentration of electrons is insufficient, it can be seen that the dependence of these electron carriers decreases than that of Pr-CNT. This is because the concentration of the initial electron carriers increased due to doping and the relatively metallic properties increased. to be. The viscosity at which electrical resistance increases more rapidly due to scattering between Electron-Electron or Electron-Phonon after 150K, supports the increase in metallic properties after doping.

In Figure 11 (c), nitrogen-doped Pr-CNT liquid crystal spinning fiber (Comparative Example 4), nitrogen-doped and super acid-treated N-CNT liquid crystal spinning fiber (Comparative Example 5), and nitrogen-doped and super acid-treated It shows the electrical conductivity of the N _Q -CNT liquid crystal spinning fiber (Example 3).

It can be seen that the electrical conductivity of the N _Q -CNT fiber of Example 3 is 2.2 times that of the Pr-CNT fiber of Comparative Example 4 and 3.3 times that of the N-CNT fiber of Comparative Example 5, which is significantly improved.

Through this, the carbon material produced according to the present invention maintains the unique morphology of the carbon material, while selectively reducing or removing pyridine nitrogen and pyrroleic nitrogen that negatively affects electrical conductivity, and at the same time improving electrical conductivity. It was confirmed that the electrical conductivity of the carbon material can be improved by maintaining the nitrogen.

Claims (11)

1. By contacting a super acid to a carbon material having a nitrogen-doped sp2 hybrid structure, while maintaining the graphitic nitrogen present in the carbon material, pyridinic nitrogen and pyrrolic nitrogen are obtained. Comprising the step of reducing,

   A method for producing a carbon material in which the content of pyridine nitrogen and pyrrole nitrogen is controlled.
2. The content of pyridine nitrogen and pyrroleic nitrogen according to claim 1, further comprising a preparation step of preparing a carbon material having an sp2 hybrid structure doped with nitrogen by doping a carbon material having an sp2 hybrid structure with nitrogen. Controlled carbon material manufacturing method.
3. The method of claim 2, wherein the carbon material having the sp2 hybrid structure is carbon nanotube, graphene, graphene oxide, carbon nanohorn, graphite, polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, carbon black, and activated carbon. The method for producing a carbon material in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled, including at least one selected from the group consisting of.
4. The method of claim 2, wherein the preparation step is performed through one or more methods selected from the group consisting of a plasma treatment method, a chemical vapor deposition method, and a method of heat treatment with a nitrogen reactant, pyridine nitrogen and pyrrole nitrogen. Method for producing a carbon material with a controlled content of.
5. The method of claim 4, wherein the nitrogen reactant is selected from the group consisting of nitrogen gas, ureas, amines, imines, nitriles, pyrroles, diazoles, triazoles, pyridines, diazines, and triazines. The method for producing a carbon material containing at least one, wherein the content of pyridine nitrogen and pyrroleic nitrogen is controlled.
6. The method of claim 1, wherein the superacid is present in a solution, wherein the contents of pyridine nitrogen and pyrrole nitrogen are controlled.
7. The method of claim 6, wherein the concentration of the super acid in the solution is 10 to 50 mg/mL, wherein the content of pyridine nitrogen and pyrrole nitrogen is controlled.
8. The method of claim 6, wherein the reducing step is carried out by contacting the solution for a period of 12 hours or more, wherein the content of pyridine nitrogen and pyrroleic nitrogen is controlled.
9. A carbon material in which the content of pyridine nitrogen and pyrrole nitrogen is controlled, prepared by the method of any one of claims 1 to 8.
10. A carbon material prepared by the method of claim 7 and having a liquid crystal phase, in which the content of pyridine nitrogen and pyrrole nitrogen is controlled.
11. The method of claim 9, wherein the carbon material is not doped with nitrogen; Or a carbon material in which the content of pyridine nitrogen and pyrroleic nitrogen is controlled in which the electrical conductivity is increased compared to the carbon material in which nitrogen is doped and pyridine nitrogen and pyrroleic nitrogen are not reduced.

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