Nitrogen-containing carbon material and its manufacturing method

Abstract

To provide a nitrogen-containing carbon material comprising a pyridine nitrogen atom at a high content ratio.SOLUTION: There is provided a nitrogen-containing carbon material comprising a carbon atom, a nitrogen atom and a halogen atom. A ratio of the number of moles of pyridine nitrogen atom to the total number of moles of nitrogen atom is larger than 59%, and the total content ratio of nitrogen atom is 7 at% or more. Further, the nitrogen-containing carbon material including a condensation polycyclic region where three aromatic rings or more are obtained via condensation is a nitrogen-containing carbon material having a partial structure in which the two pyridine nitrogen atoms are connected via two carbon atoms in the condensation polycyclic region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a nitrogen-containing carbon material and a method for producing the same. [Background technology]

[0002] Carbon materials are expected to be applied in a variety of fields. In particular, nitrogen-containing carbon materials incorporating pyridinic nitrogen atoms are expected to have a variety of applications, such as oxygen reduction catalysts and electrode materials for lithium-sulfur batteries, and many examples of the synthesis of carbon materials containing pyridinic nitrogen atoms have been reported. Non-Patent Document 1 discloses an example in which 4,7-dichloro-1,10-phenanthroline incorporating halogen atoms is calcined at 873 K for the purpose of structural control of the 1,10-phenanthroline skeleton in the carbon material. It was reported that the proportion of pyridinic nitrogen atoms in the nitrogen in the carbon material obtained by this method was 59%. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Masatoshi Murata, Yasuhiro Yamada, Shingo Kubo, Satoshi Sato, Structural Control of Nitrogen-Containing Carbon Materials Using Computational Chemistry (Poster Presentation No. P-09), Graphene and Graphene Oxide Joint Symposium, Akihabara Convention Hall, Tokyo, December 8, 2017 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one aspect of the present disclosure is to provide a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms and a method for producing the same. [Means for solving the problem]

[0005] The first aspect is a nitrogen-containing carbon material containing carbon atoms, nitrogen atoms, and halogen atoms. The nitrogen-containing carbon material is a carbon material in which the ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms is greater than 59% and the total content of nitrogen atoms is 7 at% or more. The nitrogen-containing carbon material is a nitrogen-containing carbon material that includes a fused polycyclic region formed by condensing three or more aromatic rings, and has a partial structure in which two of the pyridinic nitrogen atoms are linked via two carbon atoms in the fused polycyclic region.

[0006] A second aspect is a method for producing a nitrogen-containing carbon material, comprising: preparing a nitrogen-containing aromatic compound having a phenanthroline skeleton and a halogen atom as a substituent; and heating the nitrogen-containing aromatic compound at 200°C or higher and lower than 600°C. [Effects of the Invention]

[0007] According to one aspect of the present disclosure, it is possible to provide a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms and a method for producing the same. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an XPS spectrum of the nitrogen 1s orbital of the nitrogen-containing carbon material according to Example 2. [Figure 2] 1 is an XPS spectrum of the nitrogen 1s orbital of the nitrogen-containing carbon material according to Example 3. [Figure 3] 10 is an XPS spectrum of the nitrogen 1s orbital of the nitrogen-containing carbon material according to Example 5. [Figure 4] 2 is an example of a Raman spectrum of the nitrogen-containing carbon material according to Example 1. [Figure 5] 10 is an example of a Raman spectrum of the nitrogen-containing carbon material according to Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, when a plurality of substances corresponding to each component are present in the composition, the content of each component in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are intended to exemplify nitrogen-containing carbon materials and methods for producing the same in order to embody the technical concept of the present invention, and the present invention is not limited to the nitrogen-containing carbon materials and methods for producing the same shown below.

[0010] nitrogen-containing carbon materials The nitrogen-containing carbon material contains carbon atoms, nitrogen atoms, and halogen atoms. In the nitrogen-containing carbon material, the ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms is greater than 59%, and the total content of nitrogen atoms is 7 at% or more. The nitrogen-containing carbon material contains a fused polycyclic region formed by condensing three or more aromatic rings, and in the fused polycyclic region, it has a partial structure in which two pyridinic nitrogen atoms are linked via two carbon atoms.

[0011] The nitrogen-containing carbon material produced by the production method described below can contain a high content of pyridinic nitrogen atoms. When a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms is applied to, for example, an electrode of a lithium-sulfur battery, the adsorption of lithium polysulfides is promoted, and the shuttle effect of lithium polysulfides is suppressed. This can improve the cycle characteristics of the lithium-sulfur battery. Furthermore, a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms has excellent carbon dioxide adsorption ability. This can be used, for example, as a carbon dioxide sensor. Furthermore, a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms has electrocatalytic activity for redox reactions, and can therefore be used as an electrode for a fuel cell. Furthermore, a nitrogen-containing carbon material containing a high content of pyridinic nitrogen atoms is also suitable for use as a catalyst support, etc.

[0012] In the case of a nitrogen-containing carbon material, for example, some of the carbon atoms constituting the carbon material are considered to be substituted with nitrogen atoms. In other words, the nitrogen-containing carbon material is considered to have a structure in which the carbon material is doped with nitrogen atoms. Carbon materials are mainly sp 2 In this specification, the term "carbon material" refers to a material having a carbon content of 50 at % or more, preferably 55 at % or more, based on the composition ratio determined by elemental analysis, and having a G band (1570 cm) or more, based on the composition ratio determined by elemental analysis. -1 More than 1600cm -1 In addition, carbon materials contain defect structures such as nitrogen atoms, which can cause the D band (1300 cm or less) to be observed. -1 More than 1400cm -1 The G band is generally said to be related to a graphene structure or a chemical structure similar to the graphene structure. The D band reflects the presence of structural defects or functional groups contained in the graphene structure or a chemical structure similar to the graphene structure, and both the G band and the D band can be observed in nitrogen-containing carbon materials. In addition, the D' band (1600 cm) can also be observed in nitrogen-containing carbon materials. -1 More than 1650cm -1 below range), 2D band (2650 cm -1 More than 2750cm -1 below range), D+G band (2800cm -1 More than 3000cm -1 below range) and 2G band (3100cm -1 More than 3300cm -1 The positions of the bands described above in this specification are those observed when the wavelength of the excitation light source is 532 nm.

[0013] The nitrogen atoms that substitute for some of the carbon atoms that make up the carbon material portion of the nitrogen-containing carbon material have sp 2It may contain electrically neutral basal nitrogen present in the basal plane composed of carbon atoms and edge nitrogen present in the edge portion, and may also contain a positively charged quaternary nitrogen atom (QN). The basal nitrogen may take the form shown in any of the following structural formulas (a) to (d) based on its bonding style. The edge nitrogen may take the form shown in any of the following structural formulas (e) to (i) based on its bonding style. The dashed parts in the following structural formulas are sp 2 The resonance structures are shown through the carbon and nitrogen atoms. The basal nitrogen has three sp 2 A tertiary nitrogen atom bonded to a carbon atom with one or two sp 2 These are primary or secondary nitrogen atoms bonded to a carbon atom. They can be distinguished by X-ray Photoemission Spectroscopy (XPS) spectroscopy of the nitrogen 1s orbital.

[0014] [ka]

[0015] [ka]

[0016] Structural formula (a) is a nitrogen-containing structure with one tertiary nitrogen atom located within three six-membered ring structures and is designated T3. Structural formula (b) is a nitrogen-containing structure with one tertiary nitrogen atom located within two six-membered ring structures and is designated T2. Structural formula (c) is a nitrogen-containing structure with one tertiary nitrogen atom located within one six-membered ring structure and is designated T1. Structural formula (d) is a nitrogen-containing structure with one tertiary nitrogen atom located within one five-membered ring structure and is designated T1P.

[0017] Structural formula (e) is a nitrogen-containing structure with a structure similar to a benzene ring, with one secondary nitrogen atom located within a six-membered ring structure, and is called pyridinic nitrogen. Structural formula (f) is a nitrogen-containing structure with one secondary nitrogen atom located within a five-membered ring structure, and is called pyrrolic nitrogen. Structural formula (g) is a nitrogen-containing structure with one secondary nitrogen atom located within a six-membered ring structure, and is called S1. Structural formula (h) is a nitrogen-containing structure consisting of a secondary nitrogen atom without a ring structure, and is called S0. Structural formula (i) is a nitrogen-containing structure consisting of a primary nitrogen atom, and is called NH2. S0 and NH2 are also collectively referred to as amine-type nitrogens. The classification of nitrogen atoms using the above basal nitrogen and edge nitrogen was based on the non-patent document (Y. Yamada, H. Tanaka, S. Kubo, S. Sato, Unveiling Bonding States and Roles of Edges in Nitrogen-Doped Graphene Nanoribbon by X-ray Photoelectron Spectroscopy, Carbon 185 (2021) 342-367.).

[0018] The total content of nitrogen atoms contained in the nitrogen-containing carbon material may be, for example, 7 at% or more. The total content of nitrogen atoms may preferably be 8 at% or more, 9 at% or more, or 10 at% or more. The upper limit of the total content of nitrogen atoms may be, for example, 25 at% or less, preferably 20 at% or less. This makes it possible to suppress a decrease in electrical conductivity in the carbon material. The total content of nitrogen atoms in the nitrogen-containing carbon material is calculated from the elemental analysis value of the nitrogen-containing carbon material. Specifically, the elemental analysis value of each constituent element is divided by the atomic weight to calculate the composition ratio of the nitrogen-containing carbon material, and the total content of nitrogen atoms (at%) can be calculated based on the obtained composition ratio.

[0019] In the nitrogen-containing carbon material, the ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms is, for example, greater than 59%. The ratio of the number of moles of pyridinic nitrogen atoms may preferably be 65% or more, 75% or more, or 85% or more. The upper limit of the ratio of the number of moles of pyridinic nitrogen atoms may be, for example, 99% or less, or 95% or less. The closer the ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms is to 100%, the more the nitrogen-containing carbon material selectively contains pyridinic nitrogen atoms. In other words, the nitrogen-containing carbon material can be said to have excellent structure controllability. The ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms can be analyzed, for example, by measuring the XPS spectrum of the nitrogen 1s orbital using XPS.

[0020] The nitrogen-containing carbon material also contains halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, and the nitrogen-containing carbon material may contain at least one selected from the group consisting of these atoms. Preferably, the halogen atoms may contain at least one selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms. The halogen atoms may be contained in the nitrogen-containing carbon material as a result of the production method described below. The halogen atoms are also considered to be covalently bonded to a portion of the carbon atoms constituting a fused polycyclic region formed by the condensation of three or more aromatic rings, for example.

[0021] The content of halogen atoms in the nitrogen-containing carbon material may be, for example, 0.01 at% or more and 30 at% or less. The content of halogen atoms may be 0.1 at% or more, 0.3 at% or more, 0.5 at% or more, or 1 at% or more, and preferably 5 at% or less, 3 at% or less, 2 at% or less, or 1.5 at% or less. The content of halogen atoms in the nitrogen-containing carbon material is determined from the difference between the sum of the proportions of carbon, hydrogen, and nitrogen experimentally determined by elemental analysis and the theoretically determined sum (100 wt%) of elemental analysis values.

[0022] In the nitrogen-containing carbon material, the molar ratio of the nitrogen atom content to the halogen atom content (i.e., the number of moles of nitrogen atoms / the number of moles of halogen atoms) may be, for example, 0.3 or more and 2500 or less. The molar ratio of the nitrogen atom content to the halogen atom content may be preferably 1 or more, 2 or more, or 6 or more, and may be preferably 2000 or less, 1500 or less, or 1000 or less.

[0023] The nitrogen-containing carbon material may have a partial structure in which two nitrogen atoms substituting carbon atoms in the carbon material portion constituting the fused polycyclic region are linked via two carbon atoms and are located on the same side of the bond between the two carbon atoms. That is, the fused polycyclic region may have a partial structure consisting of a nitrogen atom, a carbon atom, a carbon atom, and a nitrogen atom, and the two nitrogen atoms may be located on the same side of the double bond between the carbon atoms. That is, the two nitrogen atoms may be located in cis positions. When the two nitrogen atoms are located in cis positions in the nitrogen-containing carbon material, for example, the nitrogen-containing carbon material may have a 1,10-phenanthroline skeleton, a 4,7-phenanthroline skeleton, or a 2,9-phenanthroline skeleton. This allows the nitrogen-containing carbon material to have a high content of pyridinic nitrogen, making it suitable for various applications. Furthermore, when the two nitrogen atoms are located in cis positions in the nitrogen-containing carbon material, it is preferable that the nitrogen-containing carbon material contain a 1,10-phenanthroline skeleton. Nitrogen-containing carbon materials with a 1,10-phenanthroline skeleton are particularly useful in fields such as lithium-sulfur batteries, carbon dioxide sensors, redox reactions, and catalyst supports.

[0024] The presence of a nitrogen-containing carbon material in a 1,10-phenanthroline skeleton can be confirmed by XPS analysis of the 3p orbital of the metal element or the nitrogen 1s orbital, taking advantage of the ease with which the 1,10-phenanthroline skeleton coordinates to metal atoms. Specifically, nitrogen-containing carbon materials with and without coordinated metal atoms are prepared, and the XPS spectrum of the 3p orbital of the metal element or the XPS spectrum of the nitrogen 1s orbital is measured using XPS. Comparing these XPS spectra allows observation of changes in binding energy due to the difference in the electronic state of the nitrogen atom at the 1,10-position depending on whether or not the nitrogen atom is coordinated to a metal atom. In other words, if a change in binding energy can be observed in XPS analysis when a metal atom is coordinated, it can be confirmed that the nitrogen-containing carbon material has a 1,10-phenanthroline skeleton. This can be confirmed by peak separation and fitting, taking into account the change in peak position when the pyridinic nitrogen coordinates to a metal atom. In addition, the peaks observed due to coordination with metal atoms may be analyzed in a complex manner, for example, by combining infrared spectroscopy, etc., in order to distinguish them from nitrogen, which is classified as another type. This makes it possible to distinguish between components necessary for peak separation and unnecessary components. The metal atom to be coordinated may be, for example, at least one selected from the group consisting of iron, cobalt, nickel, and copper. The metal atoms described here may be in the form of a single atom, a metal cluster, or nanoparticles. The coordinated atoms may also be ions. In this case, analysis can be performed in the same manner using XPS analysis.

[0025] Furthermore, the nitrogen atoms in the condensed polycyclic region of the nitrogen-containing carbon material may be pyridinic nitrogen atoms. The presence of such a partial structure further increases the proportion of pyridinic nitrogen atoms. This allows the carbon material to be endowed with properties exhibited by pyridinic nitrogen atoms, such as the adsorption of gas molecules and ionic species, coordination to metal species, and reduction activity for carbon dioxide and oxygen molecules.

[0026] Furthermore, the nitrogen-containing carbon material includes a fused polycyclic region in which three or more aromatic rings are fused. The fused polycyclic region may have a partial structure in which two pyridinic nitrogen atoms are linked via two carbon atoms and are located on the same side of the bond between the two carbon atoms. That is, the nitrogen-containing carbon material may have a partial structure in which the two pyridinic nitrogen atoms are located in cis positions. This partial structure may be, for example, a 1,10-phenanthroline skeleton or a 2,9-phenanthroline skeleton, preferably a 1,10-phenanthroline skeleton. The nitrogen-containing carbon material may have, for example, a partial structure such as the chemical formula shown schematically below.

[0027] [ka]

[0028] In the above chemical formula, X represents a halogen atom, and the dashed line represents a carbon-carbon bond, which is a partial structure. Note that the position of the halogen atom is not limited to the position shown in the above chemical formula.

[0029] Method for producing nitrogen-containing carbon material The method for producing a nitrogen-containing carbon material includes preparing a nitrogen-containing aromatic compound having a phenanthroline skeleton and a halogen atom as a substituent, and a heat treatment step of heat-treating the nitrogen-containing aromatic compound at a temperature of 200°C or higher but lower than 600°C to obtain a carbonized heat-treated product.

[0030] By using a nitrogen-containing aromatic compound having a phenanthroline skeleton and a halogen atom as a substituent as a raw material for a nitrogen-containing carbon material, a nitrogen-containing carbon material with a high content of pyridinic nitrogen atoms can be efficiently produced. This can be attributed to, for example, the fact that the nitrogen-containing aromatic compound used as the raw material is halogen-substituted, which reduces the energy required for the carbonization reaction and suppresses the collapse of the raw material skeleton. In this specification, the nitrogen-containing aromatic compound having a phenanthroline skeleton also includes materials having a partial structure similar to that of phenanthroline.

[0031] Examples of halogen atoms that the nitrogen-containing aromatic compound serving as a raw material for the nitrogen-containing carbon material has as a substituent include fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc., and include at least one selected from the group consisting of these. The halogen atoms may preferably include at least one selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms. The number of halogen atoms substituted in the nitrogen-containing aromatic compound may be, for example, 1 or more and 8 or less. The number of halogen atoms substituted may preferably be 2 or more, and preferably 4 or less. This allows efficient carbonization to proceed from the portion substituted with halogen atoms while reducing decomposition of pyridinic nitrogen.

[0032] The nitrogen-containing aromatic compound contains at least a pyridinic nitrogen atom. The number of pyridinic nitrogen atoms contained in the nitrogen-containing aromatic compound may be 2 or more and 8 or less per molecule of the nitrogen-containing aromatic compound. The number of pyridinic nitrogen atoms contained may preferably be 6 or less.

[0033] The nitrogen-containing aromatic compound may have other substituents other than halogen atoms. Examples of the other substituents include a hydroxyl group, an alkoxy group, a cyano group, a nitro group, a carboxy group, a formyl group, an alkoxycarbonyl group, a carbamoyl group, a trifluoromethanesulfonyl group, a p-toluenesulfonyl group, and a diazonium group. When the nitrogen-containing aromatic compound has other substituents other than halogen atoms, the number of the other substituents may be, for example, 4 or less, or 2 or less.

[0034] Examples of nitrogen-containing aromatic compounds that can be used as raw materials for nitrogen-containing carbon materials include compounds represented by any of the following general formulas (1a) to (1d): (1a) is 1,10-phenanthroline, (1b) is 1,7-phenanthroline, (1c) is 4,7-phenanthroline, and (1d) is 2,9-phenanthroline.

[0035] [ka]

[0036] In the formula, X represents a halogen atom. n represents the number of halogen atoms substituted and represents a number from 1 to 8. When n is 2 or more, the multiple halogen atoms may be the same or different and may be substituted on the same ring or on different rings. n may preferably be a number from 1 to 6, or 1 to 4.

[0037] It is possible that 1,7-phenanthroline, 4,7-phenanthroline, and 2,9-phenanthroline can be carbonized in two ways: one where the raw materials do not form a six-membered ring and have a structure similar to biphenyl, and the other where the raw materials form a six-membered ring and have a honeycomb structure consisting of benzene rings. The latter form is a graphene structure, and a nitrogen-containing carbon material containing a 1,10-phenanthroline skeleton can be formed. The nitrogen-containing carbon material may also partially contain a structure similar to biphenyl.

[0038] The nitrogen-containing aromatic compound preferably contains at least 1,10-phenanthroline containing a halogen atom as a substituent. By heat-treating 1,10-phenanthroline containing a halogen atom as a substituent, a nitrogen-containing carbon material containing a 1,10-phenanthroline skeleton can be efficiently obtained. The pyridinic nitrogen of 1,10-phenanthroline is easily converted to amine-type nitrogen by thermal decomposition. By containing a halogen atom as a substituent in the nitrogen-containing aromatic compound, carbonization can easily proceed from the portion containing the halogen atom while maintaining a high proportion of the 1,10-phenanthroline skeleton. Furthermore, the nitrogen-containing aromatic compound preferably consists of 1,10-phenanthroline containing a halogen atom as a substituent. This allows for the production of a nitrogen-containing carbon material containing a high content of pyridinic nitrogen.

[0039] Specific examples of the nitrogen-containing aromatic compound include 1,10-phenanthroline derivatives containing a halogen atom as a substituent, but the nitrogen-containing aromatic compound of the present invention is not limited to these. Examples of the nitrogen-containing aromatic compounds include 2-chloro-1,10-phenanthroline, 2-bromo-1,10-phenanthroline, 2-iodo-1,10-phenanthroline, 3-chloro-1,10-phenanthroline, 3-bromo-1,10-phenanthroline, 3-iodo-1,10-phenanthroline, 4-chloro-1,10-phenanthroline, 4-bromo-1,10-phenanthroline, 4-iodo-1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-bromo-1,10-phenanthroline, 5-iodo-1,10-phenanthroline, 4,7-dichloro-1,10-phenanthroline, 4,7-dibromo-1,10-phenanthroline, 4,7-diiodo-1,10-phenanthroline, 4,7-diiodo-1,10-phenanthroline, 4,7-dibromo ... ,10-phenanthroline, 2,9-dichloro-1,10-phenanthroline, 2,9-dibromo-1,10-phenanthroline, 2,9-diiodo-1,10-phenanthroline, 3,8-dichloro-1,10-phenanthroline, 3,8-dibromo-1,10-phenanthroline, 3,8-diiodo-1,10-phenanthroline, 5,6-dichloro-1,10-phenanthroline, 5,6-dibromo-1,10-phenanthroline, 5,6-diiodo-1,10-phenanthroline, 3,5,6,8-tetrachloro-1,10-phenanthroline, 3,5,6,8-tetrabromo-1,10-phenanthroline, 3,5,6,8-tetraiodo-1,10-phenanthroline.

[0040] Specific examples of nitrogen-containing aromatic compounds, such as 1,7-phenanthroline, 2,9-phenanthroline, and 4,7-phenanthroline, each containing a halogen atom as a substituent, are shown below, but the nitrogen-containing aromatic compounds of the present invention are not limited to these. Nitrogen-containing aromatic compounds include 3-bromo-1,7-phenanthroline, 5-bromo-2,9-phenanthroline, and 2-bromo-4,7-phenanthroline.

[0041] The nitrogen-containing aromatic compound may be purchased or produced by a known method. The nitrogen-containing aromatic compound substituted with a halogen atom can be produced, for example, by a halogen substitution reaction of an available halogenated nitrogen-containing aromatic compound, a halogenation reaction of a nitrogen-containing aromatic compound, or the like.

[0042] Nitrogen-containing carbon materials can be produced by heat-treating and carbonizing a nitrogen-containing aromatic compound. Carbonization here refers to heat-treating a nitrogen-containing aromatic compound to produce a carbon material with a carbon content of 50 at% or more and in which the G band is observed in Raman spectroscopy. The carbon content here is determined from the composition ratio determined by elemental analysis. It is believed that heat-treating a nitrogen-containing aromatic compound can abstract, for example, halogen atoms, hydrogen atoms, etc. from the nitrogen-containing aromatic compound, resulting in the formation of new carbon-carbon bonds, thereby carbonizing the compound.

[0043] The heat treatment temperature for heat treating the nitrogen-containing aromatic compound may be, for example, in the range of 200°C or higher and lower than 600°C. The heat treatment temperature may be preferably 230°C or higher, 250°C or higher, 280°C or higher, or 300°C or higher, and may be preferably 550°C or lower, 500°C or lower, 450°C or lower, or 400°C or lower. When the heat treatment temperature is within the above range, the structural controllability of the phenanthroline skeleton can be further improved. This tends to increase the content of pyridinic nitrogen atoms.

[0044] The heat treatment of the nitrogen-containing aromatic compound can be carried out, for example, by raising the temperature from room temperature to a predetermined heat treatment temperature and maintaining the predetermined heat treatment temperature for a predetermined heat treatment time. The temperature rise rate may be, for example, from 1°C / min to 30°C / min, preferably from 5°C / min to 15°C / min. The heat treatment time may be, for example, from 30 minutes to 24 hours, preferably from 30 minutes to 6 hours.

[0045] The heat treatment of the nitrogen-containing aromatic compound may be carried out under sealed tube conditions. By carrying out the heat treatment under sealed tube conditions, for example, sublimation of the raw material compound can be suppressed. The heat treatment of the nitrogen-containing aromatic compound may be carried out under reduced pressure. By carrying out the heat treatment under reduced pressure, for example, side reactions due to gases generated during carbonization can be suppressed. The reduced pressure conditions in the heat treatment may be, for example, 50 Pa or less, preferably 30 Pa or less, more preferably 10 Pa or less, and particularly preferably 1 Pa or less. The lower limit of the reduced pressure conditions may be, for example, 0.1 Pa or more.

[0046] The heat treatment of the nitrogen-containing aromatic compound may be carried out by contacting the nitrogen-containing aromatic compound with a powder or a substrate and heat-treating the compound at a temperature of 200°C or higher but lower than 600°C. Alternatively, the heat treatment of the nitrogen-containing aromatic compound may be carried out by supporting the nitrogen-containing aromatic compound on a powder or a substrate and heat-treating the compound at a temperature of 200°C or higher but lower than 600°C. The material of the powder or substrate may be, for example, copper, nickel, cobalt, platinum, gold, or the like, which exhibits catalytic activity. This allows the pyridinic nitrogen atoms to bond with the powder or substrate, thereby reducing the decomposition of the pyridinic nitrogen atoms during heat treatment. The particle size of the catalytic metal powder may be, for example, 1 nm or higher but 300 nm or lower, or 50 nm or higher but 100 nm or lower. The material of the powder or substrate may be graphite, carbon black, carbon nanotubes, activated carbon, silica, alumina, glass, or the like.

[0047] The method for producing a nitrogen-containing carbon material may further include, after the heat treatment step, a pulverizing step of pulverizing the heat-treated product, a purification step of purifying the heat-treated product, and the like.

[0048] The purification step may include a first purification step for removing impurities from the heat-treated product obtained and a second purification step for removing residual metals that cannot be completely removed in the first purification step. The residual metals can be removed using, for example, an acid, a chelating agent, a metal scavenger, or the like.

[0049] (Application example) A fuel cell may contain a nitrogen-containing carbon material according to the present disclosure. An electrode of a lithium-sulfur battery may contain a nitrogen-containing carbon material according to the present disclosure. A carbon dioxide sensor may contain a nitrogen-containing carbon material according to the present disclosure. A catalyst support may contain a nitrogen-containing carbon material according to the present disclosure. A carbon dioxide adsorbent may contain a nitrogen-containing carbon material according to the present disclosure. [Example]

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0051] (Synthesis Example 1 of Nitrogen-Containing Aromatic Compound) Synthesis of 2,9-diiodo-1,10-phenanthroline (29-DIP) 2,9-Dichloro-1,10-phenanthroline (498 mg, Tokyo Chemical Industry Co., Ltd.) and sodium iodide (900 mg, Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a Schlenk tube. After replacing the atmosphere in the Schlenk tube with nitrogen, a 55 wt% aqueous solution of hydroiodic acid (12 ml, Fujifilm Wako Pure Chemical Industries, Ltd.) was added and the reaction was carried out at 80°C for 24 hours. After the reaction was completed, the reaction mixture was filtered under suction, and the solid crude product was washed with distilled water (150 ml) and 2-propanol (30 ml, Kanto Chemical Co., Ltd.). The crude product was dissolved in dimethyl sulfoxide (35 ml, Kanto Chemical Co., Ltd.) and filtered through a membrane. After that, an aqueous solution of potassium iodide (535 mg, Sigma-Aldrich) dissolved in distilled water (20 ml) was added and the mixture was stirred at room temperature for 30 minutes. The precipitated crystalline white solid was collected by filtration, washed with distilled water (50 ml) and 2-propanol (30 ml, manufactured by Kanto Chemical Co., Inc.), and dried under reduced pressure to obtain purified 2,9-diiodo-1,10-phenanthroline (710 mg).

[0052] (Synthesis Example 2 of Nitrogen-Containing Aromatic Compound) Synthesis of 4,7-diiodo-1,10-phenanthroline (47-DIP) 4,7-Dichloro-1,10-phenanthroline (500 mg, Tokyo Chemical Industry Co., Ltd.) and sodium iodide (900 mg, Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a Schlenk tube. After replacing the atmosphere in the Schlenk tube with nitrogen, 55 wt% aqueous hydroiodic acid solution (12 mL, Fujifilm Wako Pure Chemical Industries, Ltd.) was added and the reaction was carried out at 80 °C for 12 hours. After the reaction was completed, distilled water (30 mL) was added to the reaction mixture and the mixture was suction filtered. The solid crude product was washed with distilled water (150 mL) and 2-propanol (3 mL, Kanto Chemical Co., Ltd.). After washing, the crude product was dissolved in dimethyl sulfoxide (80 mL, Kanto Chemical Co., Ltd.) and filtered through a membrane. This was mixed with an aqueous potassium iodide solution prepared by dissolving potassium iodide (900 mg, Sigma-Aldrich Co.) and potassium hydroxide (350 mg, Kanto Chemical Co., Ltd.) in distilled water (50 mL) and stirred at room temperature for 30 minutes. The precipitated needle-like white solid was collected by filtration, washed with distilled water (350 ml) and 2-propanol (30 ml, manufactured by Kanto Chemical Co., Ltd.), and dried under reduced pressure to obtain purified 4,7-diiodo-1,10-phenanthroline (540 mg).

[0053] (Synthesis Example 3 of Nitrogen-Containing Aromatic Compound) Synthesis of 2,9-dibromo-1,10-phenanthroline (29-DBP) 2,9-Dichloro-1,10-phenanthroline (750 mg, Tokyo Chemical Industry Co., Ltd.) was placed in a Schlenk tube. The atmosphere in the Schlenk tube was then replaced with nitrogen, and phosphorus tribromide (5 mL, Sigma-Aldrich) was added. The mixture was then reacted at 170°C for 6 hours. After the reaction, distilled water was added to the Schlenk tube while it was ice-cooled, and the reaction mixture was neutralized with sodium carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.). The reaction mixture was filtered under suction, and the resulting crude product was washed with distilled water (500 mL) and ice-cooled methanol (3 mL, Kanto Chemical Co., Ltd.). The washed crude product was dried under reduced pressure, dissolved in methanol (190 mL, Kanto Chemical Co., Ltd.) by heating, and allowed to stand at 4°C for recrystallization to yield purified 2,9-dibromo-1,10-phenanthroline (625 mg).

[0054] (Synthesis Example 4 of Nitrogen-Containing Aromatic Compound) Synthesis of 5,6-dibromo-1,10-phenanthroline (56-DBP) 1,10-Phenanthroline (1.1 g, manufactured by Tokyo Chemical Industry Co., Ltd.), 30% fuming sulfuric acid (9 ml, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and bromine (0.3 ml, manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed under ice cooling and reacted in a stainless steel pressure vessel at 120°C for 22 hours. After the reaction was completed, distilled water (380 ml) was added while cooling on ice to adjust the pH to 3. The reaction mixture was filtered under suction, and the resulting crude product was extracted with dichloromethane (250 ml, manufactured by Kanto Chemical Co., Ltd.) and washed with distilled water. The collected organic layer was dried over magnesium sulfate (manufactured by Fujifilm Wako Pure Chemical Co., Ltd.), and the solvent was distilled off. The residue was dissolved in ethanol (20 ml, manufactured by Kanto Chemical Co., Ltd.) by heating and then allowed to stand at 4°C for recrystallization to obtain purified 5,6-dibromo-1,10-phenanthroline (560 mg).

[0055] (Preparation of nitrogen-containing aromatic compounds) The nitrogen-containing aromatic compounds used in Synthesis Examples 1 to 4 of the nitrogen-containing aromatic compound and in Example 8 were commercially available products (manufactured by Tokyo Chemical Industry Co., Ltd.). The nitrogen-containing aromatic compound used in Example 8 was a commercially available product (manufactured by Sigma-Aldrich). Only in Example 10 described below, commercially available 4,7-dibromo-1,10-phenanthroline was purified to obtain the nitrogen-containing aromatic compound.

[0056] Example 1 A glass tube was charged with 60 mg of 2,9-dichloro-1,10-phenanthroline (29-DCP; manufactured by Tokyo Chemical Industry Co., Ltd.) as a nitrogen-containing aromatic compound and dried under reduced pressure at 120°C for 1 hour. The glass tube was then sealed with a gas burner while still under reduced pressure to a length of approximately 7 cm, producing an ampoule. The ampoule was placed in a tubular electric furnace, and the temperature was increased from room temperature (approximately 25°C) to 400°C at a rate of 10°C / min, followed by heat treatment for 1 hour to obtain a carbonized body. After the heat treatment, the carbonized body was recovered, finely ground in an agate mortar, and then heated under reduced pressure at 300°C for 1 hour to remove raw materials and low-molecular-weight components, thereby obtaining a sample of the nitrogen-containing carbon material of Example 1.

[0057] (Examples 2 to 14) Each sample of the nitrogen-containing carbon material was obtained in the same manner as in Example 1, except that a nitrogen-containing aromatic compound shown in Table 1 was used instead of 2,9-dichloro-1,10-phenanthroline and the heat treatment temperature was changed as shown in Table 1.

[0058] The meanings of the abbreviations in Table 1 are as follows: 1,10-Phen: 1,10-phenanthroline 29-DCP: 2,9-dichloro-1,10-phenanthroline 29-DBP: 2,9-dibromo-1,10-phenanthroline 29-DIP: 2,9-diiodo-1,10-phenanthroline 47-DCP: 4,7-dichloro-1,10-phenanthroline 47-DBP: 4,7-dibromo-1,10-phenanthroline 47-DIP: 4,7-diiodo-1,10-phenanthroline 38-DBP: 3,8-dibromo-1,10-phenanthroline 3568-TBP: 3,5,6,8-tetrabromo-1,10-phenanthroline 56-DBP: 5,6-dibromo-1,10-phenanthroline 5-CP: 5-chloro-1,10-phenanthroline

[0059] (Comparative Example 1) A sample of Comparative Example 1 was obtained in the same manner as in Example 1, except that 1,10-phenanthroline (1,10-Phen; manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of 2,9-dichloro-1,10-phenanthroline.

[0060] evaluation Composition and nitrogen content The compositions and nitrogen contents of the samples obtained in Examples 1 to 14 were evaluated as follows. The proportions of carbon, nitrogen, and hydrogen in the samples were analyzed by elemental analysis using the combustion method. Carbon was obtained by analyzing the amount of carbon dioxide, hydrogen by analyzing the amount of water, and nitrogen by analyzing the amount of nitrogen gas. The weight percentage (wt%) of each element obtained by elemental analysis was divided by its atomic weight to determine the composition ratio. Since phenanthroline contains 12 carbon atoms, the composition ratio was calculated assuming that 12 carbon atoms were contained. The atomic weight percentage (at%) of nitrogen was obtained from the obtained composition ratio. The results of the nitrogen content (at%) are shown in Table 1.

[0061] Pyridinic nitrogen atom content The content of pyridinic nitrogen atoms in the nitrogen atoms of the samples obtained in Examples 1 to 14 was evaluated as follows.

[0062] First, the XPS spectrum of the nitrogen 1s orbital was measured using XPS. -5 The measurements were performed in a vacuum chamber at 100 Pa. XPS spectra were measured using an AXIS-ULTRA DLD (Shimadzu Corporation). XPS measurements were performed at room temperature using a sample mounted on carbon tape. The measurement conditions were as follows: MgKα radiation (dual anode) light source, emission current 10 mA, anode voltage 10 kV, pass energy 40 eV, measurement range converted to bond energy 385 eV to 409 eV, and number of accumulations 10. For samples that charge up during XPS spectrum measurement, a neutralization gun was used under neutralization conditions of a filament current of 1.75 A, charge balance 3.0 V, and filament bias 1.0 V.

[0063] The obtained XPS spectrum of the nitrogen 1s orbital was analyzed as follows. First, the measured photoelectron kinetic energy was converted to binding energy. The background was removed by assuming a Shirley background, and peak separation and fitting were performed. Peak separation was performed assuming peak tops at at least the binding energy of pyridinic nitrogen at 398.0 eV, the binding energy of basal nitrogen (T1) at 399.5 eV, and the binding energy of basal nitrogen (T2, T3) at 400.1 eV. These binding energies were used to set a Voigt function, and fitting was performed by adding an asymmetry function. The full width at half maximum of each peak was set to 1.5 eV. The content of pyridinic nitrogen was obtained by the ratio of the total area of ​​the XPS spectrum of the nitrogen 1s orbital to the area of ​​the XPS spectrum of the nitrogen 1s orbital derived from pyridinic nitrogen. An example of peak separation is shown in Figures 1 and 2. The pyridinic nitrogen atom content estimated by XPS for each of Examples 1 to 14 is shown in Table 1. In Examples 3 to 6 and 8 to 14, amine-type nitrogen (SO, NH) was added to the peak separation and fitting. The binding energy of the amine-type nitrogen was assumed to have a peak top at 398.9 eV. The full width at half maximum of each peak used in peak separation was set to 1.5 eV. In Examples 4 to 11, 13, and 14, quaternary nitrogen (QN) was added to the peak separation and fitting. The binding energy of the quaternary nitrogen was assumed to have a peak top at 401.2 eV. The full width at half maximum of each peak was set to 1.5 eV.

[0064] FIG. 1 shows the results of measuring the XPS spectrum of the nitrogen 1s orbital in the nitrogen-containing carbon material of Example 2. From the results of peak separation, it was confirmed that the pyridinic nitrogen atom content was 94%. FIG. 2 shows the results of measuring the XPS spectrum of the nitrogen 1s orbital in the nitrogen-containing carbon material of Example 3. From the results of peak separation, it was confirmed that the pyridinic nitrogen atom content was 84%. FIG. 3 shows the results of measuring the XPS spectrum of the nitrogen 1s orbital in the nitrogen-containing carbon material of Example 5. From the results of peak separation, it was confirmed that the pyridinic nitrogen atom content was 81%.

[0065] [Table 1]

[0066] As shown in Table 1, it was confirmed that a nitrogen-containing carbon material with a high nitrogen content can be obtained by using a nitrogen-containing aromatic compound having a phenanthroline skeleton and a halogen atom as a substituent as a raw material. It was also confirmed that a nitrogen-containing carbon material with a high content of pyridinic nitrogen atoms can be obtained. Note that, in the sample of Comparative Example 1, only the generation of an oily substance was confirmed, and no nitrogen-containing carbon material was obtained, so composition analysis was not performed. In addition, 1 As a result of H-NMR (Nuclear Magnetic Resonance) measurement, it was found that a compound containing amine-type nitrogen was present in the sample of Comparative Example 1. This is thought to indicate that carbonization did not proceed in Comparative Example 1, and the raw material was thermally decomposed. 1 H-NMR measurements were performed using a nuclear magnetic resonance spectrometer (JNM-ECA500; manufactured by JEOL Ltd.) under measurement conditions of a resonance frequency of 500 MHz and a pulse width of 7.11 μsec.

[0067] Raman spectroscopy The Raman spectra of the samples obtained in Examples 1 and 3 were measured using a microscopic laser Raman spectrophotometer (NRS-4500; manufactured by JASCO Corporation). The wavelength of the excitation light source was 532 nm. The laser intensity was 0.3 mW. The objective lens magnification was 100x. The exposure time was 10 or 20 seconds, and the number of integrations for each spectrum measurement was 10. The results are shown in Figures 4 and 5. Each spectrum was normalized to the peak showing the maximum intensity.

[0068] From the results of Raman spectroscopy, 1300cm -1 More than 1400cm -1 The following range and 1570cm -1 More than 1600cm -1Peaks were confirmed in the following ranges. These reflect the D band and G band, and it was presumed that the samples obtained in Examples 1 and 3 were carbonized.

[0069] Example 15 Commercially available 3,5,6,8-tetrabromo-1,10-phenanthroline (Sigma-Aldrich) was prepared as a nitrogen-containing aromatic compound. 20 mg of 3,5,6,8-tetrabromo-1,10-phenanthroline and 400 mg of copper particle powder (Sigma-Aldrich) with particle sizes of 60 to 80 nm were placed in a glass tube and dried under reduced pressure at 180°C for 1 hour. The glass tube was then sealed with a gas burner while still under reduced pressure to a length of approximately 7 cm to prepare an ampoule. The ampoule was placed in a tubular electric furnace and heated from room temperature (approximately 25°C) to 450°C at a rate of 10°C / min for heat treatment, yielding a carbonized product. The ampoule was then opened, and the carbonized product was recovered. The recovered carbonized product was then subjected to reduced pressure at 380°C for 1 hour to remove raw materials and low-molecular-weight components, yielding a sample of the nitrogen-containing carbon material of Example 15. The obtained sample was subjected to XPS analysis and peak separation in the same manner as in Examples 1 to 14. Peak separation and fitting confirmed that the content of pyridinic nitrogen atoms was at least higher than 59%.

Claims

1. a nitrogen-containing carbon material containing carbon atoms, nitrogen atoms, and halogen atoms, the nitrogen-containing carbon material has a total content of nitrogen atoms in its composition of 7 at% or more; the nitrogen-containing carbon material contains, as the nitrogen atoms, a pyridinic nitrogen atom and a basal nitrogen atom; the ratio of the number of moles of pyridinic nitrogen atoms to the total number of moles of nitrogen atoms is greater than 59%, the nitrogen-containing carbon material contains a fused polycyclic region formed by condensing three or more aromatic rings, The nitrogen-containing carbon material has a partial structure in which two of the pyridinic nitrogen atoms are linked via two carbon atoms in the fused polycyclic region.

2. 2. The nitrogen-containing carbon material according to claim 1, wherein the content of the halogen atoms is 0.01 at % or more and 30 at % or less.

3. 3. The nitrogen-containing carbon material according to claim 1, wherein the halogen atom comprises at least one selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom.

4. A nitrogen-containing carbon material described in any one of claims 1 to 3, wherein the partial structure includes a structure in which the two pyridinic nitrogen atoms are arranged on the same side of the bond between the two carbon atoms.

5. preparing a nitrogen-containing aromatic compound having a phenanthroline skeleton and a halogen atom as a substituent; a method for producing a nitrogen-containing carbon material, the method comprising: heat-treating the nitrogen-containing aromatic compound at a temperature of 200°C or higher but lower than 600°C to carbonize it;

6. The method according to claim 5, wherein the halogen atom comprises at least one selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom.

7. The method according to claim 5 or 6, wherein the nitrogen-containing aromatic compound comprises 1,10-phenanthroline having a halogen atom as a substituent.

8. The manufacturing method according to claim 5 , wherein the heat treatment is carried out under reduced pressure.

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