JP5582527B2 - Method for producing graphitic carbon nitride - Google Patents

Description

  The present invention relates to graphitic carbon nitride encapsulating metal ions and a method for producing the same.

In recent years, air purification techniques have been studied, and photocatalysts capable of decomposing and removing environmental pollutants by sunlight and room light have attracted attention, and their research has been vigorously conducted.
Titanium oxide is a typical example and exhibits a strong photocatalytic activity. However, since titanium oxide has a large band gap and does not absorb visible light that occupies most of the sunlight and is active only to ultraviolet light, it cannot fully utilize sunlight, and ultraviolet light is extremely weak. There were issues such as not functioning indoors. Therefore, various improvements have been made so that visible light can be used.
For example, a semiconductor such as tungsten oxide can absorb visible light because it has a smaller band gap than titanium oxide, and is expected as a visible light active photocatalyst (visible light responsive photocatalyst) (Patent Document) 1, 2). These visible light responsive photocatalysts often improve their activity using a promoter such as platinum, palladium, or copper compound.

The addition of a metal promoter is generally used to increase the activity of the catalyst, but there are only a few reports on compounds in which carbon nitride and metal ions are combined.
For example, Non-Patent Document 1 proposes the light content of water using graphite-like carbon nitride (hereinafter sometimes referred to as “g-C ₃ N ₄ ”).
It has been known since the 1980s that the powder of g-C ₃ N ₄ can be synthesized by pyrolyzing melamine or cyanamide, but the catalytic action has not been studied until recently, and was actually synthesized from melamine. also uses exactly the _g-C 3 _{N 4,} there is little catalyst activity. The Non-Patent Document 1, to improve the activity by carrying surface platinum and ruthenium g-C ₃ N _4, photolysis of water (hydrogen generation, oxygen generation) is obtained by available to.
Non-Patent Document 2 describes that when carbon nitride synthesized by adding Fe is used, hydrogen peroxide is added, and light is irradiated, benzene is oxidized to phenol.

On the other hand, except for the photocatalyst, several reports have been made on g-C ₃ N ₄ powder.
For example, Non-Patent Document 3 discloses a method for synthesizing g-C ₃ N ₄ having a high specific surface area by synthesizing ultrafine particles g-C ₃ N ₄ using silica as a tene plate and removing silica with hydrofluoric acid. However, photocatalytic activity is not evaluated.
Patent Documents 3 and 4 describe that g-C ₃ N ₄ treated with an aqueous MOH solution (M = K, Na, Li) or mineral acid exhibits excellent fluorescence characteristics or lubrication characteristics. However, there is no description about the catalytic activity.
Furthermore, in Patent Document 5, the metal compound powder of carbon nitride having a layered structure obtained by reacting carbon nitride with a transition metal or an alloy thereof exhibits lubrication characteristics and at the same time a part thereof exhibits paramagnetism. Although described, there is no description of the catalyst.

JP 2009-61426 A JP 2008-149312 A Japanese Patent Laid-Open No. 02-206619 Japanese Patent Laid-Open No. 02-300273 Japanese Patent Laid-Open No. 02-308815 Japanese Patent Application No. 2009-2441049

Kazuhiko Maeda, Kazunari Domen, WANG Xinchen, THOMAS Arne, ANTONIETTI Markus, Yasushi Nishihara Catalytic Conference Discussion Session A Proceedings Vol.102nd, Page.126 (2008.09.23) "Visible light irradiation of carbon nitride (C3N4) Under photocatalytic activity " Xiufang Chen, Jinshui Zhang, Xianzhi Fu, Markus Antonietti and Xinchen Wang J. AM. CHEM. SOC. 2009, 131, 11658-11659, Fe-g-C3N4-Catalyzed Oxidation of Benzene to Phenol Using Hydrogen Peroxide and Visible Light Matthijs Groenewolt, Markus Antonietti; Adbanced Materials 2005, 17, 1789-1792, Synthesis of g-C3N4 Nanoparticles in Mesoporous Silica Host Matrices

As described above, the addition of a metal promoter is generally used for high activation of the catalyst, but there are only a few reports on compounds in which carbon nitride and metal ions are combined (Non-patent Documents 1 and 2). ), Their catalytic activity is not sufficient.
On the other hand, there are a method in which a nitrogen-containing organic compound that is a raw material for carbon nitride and a metal salt that is a metal source are mixed and fired at around 600 ° C. Although it has been reported, a material utilizing the interaction between metal ions and carbon nitride has not been developed. Moreover, the specific surface area of the metal-added carbon nitride was as extremely small as less than 10 m ² / g, and there was almost no activity as a catalyst. Further, a small specific surface area indicates that the particles are large, and it was difficult to use the coating agent.
Furthermore, even when trying to synthesize carbon nitride containing a metal element having a high oxidation activity such as palladium by the method of mixing and firing the above nitrogen-containing organic compound and metal salt, the raw material nitrogen-containing organic compound has a catalytic effect of palladium. The compound containing carbon nitride could not be obtained.

  In Patent Document 5, it is considered that a small amount of Ni is combined with nitrogen or carbon and enters the graphite structure. Thus, it is easily inferred from the study of the metal-inserted graphite, which is a similar compound, that the catalytic activity, optical characteristics, semiconductor characteristics, lubrication characteristics, and the like can be controlled by inserting metal ions between carbon nitride layers. However, since the nitrogen-containing organic compound reacts with the metal or metal compound at a high temperature, only carbon nitride having a small specific surface area can be obtained, and the activity as a catalyst cannot be obtained.

The present invention has been made in view of the present situation, and aims to provide g-C ₃ N ₄ having a large specific surface area and sufficient catalytic activity, and a simple production method thereof. To do.

The inventors of the present invention have made extensive studies to achieve the above-mentioned object, and are a visible light-responsive photocatalyst mainly composed of powder obtained by treating graphite-like carbon nitride powder in an alkaline aqueous solution or an acidic aqueous solution. (Patent Document 6).
The present inventors have further studied and found that the above problem can be solved by using a hydrothermal synthesis technique.
That is, as described above, when a nitrogen-containing organic compound is reacted with a metal or metal compound at a high temperature, only a carbon nitride having a small specific surface area can be obtained. It was considered necessary to achieve the above problems to find out a method of bonding ions, and (ii) a method of increasing specific surface area while bonding carbon nitride and metal ions.
As a result of further examination of the method, a nitrogen-containing organic compound such as melamine or cyanamide was thermally decomposed to prepare g-C ₃ N ₄ , and then reacted with an aqueous solution containing metal ions. It has been found that this can be achieved by inserting it into the layered structure of C ₃ N ₄ .

The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] Graphite with metal ions inserted between layers, characterized by heat- treating graphite-like carbon nitride powder in an aqueous solution of a metal compound selected from metal chloride, metal sulfate, or metal nitrate Of carbon nitride.
[2] The method for producing graphitic carbon nitride according to [1] , wherein metal ions are inserted between layers, wherein the treatment is a heat treatment at 100 to 150 ° C.
[3] The above [1], wherein the metal is any one selected from Li, Na, Mn, Fe, Co, Cu, Zn, Mo, Ru, Pd, Ag, Ba, and Pt [2] A method for producing graphitic carbon nitride in which metal ions are inserted between layers.
[4] The method for producing graphite-like carbon nitride in which metal ions are inserted between the layers according to any one of [1] to [3], wherein the specific surface area of the graphite-like carbon nitride is increased by the treatment. .
[5] Graphite carbon nitride in which metal ions are inserted between the layers is an effective component of the photocatalyst, and metal ions are inserted between the layers according to any one of the above [1] to [4] A method for producing graphitic carbon nitride.

  According to the present invention, it is possible to stably hold various metal ions and to produce a completely new substance having excellent chemical resistance. By the substance obtained by the method, excellent light absorption characteristics, It is possible to provide a novel material having thermocatalytic properties and photocatalytic properties.

It shows the XPS spectrum of _g-C 3 _{N 4} inserting the Ag ions. It is an X-ray diffraction diagram of g-C ₃ N ₄ , (a) is g-C ₃ N _{4 of} raw material, (b) is g-C ₃ N ₄ into which Fe ions are inserted, (c) is Iron-containing carbon nitride obtained by a conventional firing method (reference: Non-Patent Document 1). It shows the XPS spectrum of _g-C 3 _{N 4} inserting the Fe ions. It is an X-ray diffraction diagram of g-C ₃ N ₄ , (a) is g-C ₃ N _{4 of} raw material, (b) is g-C ₃ N ₄ with Pd ion inserted, (c) is A powder obtained by trying to introduce Pd into carbon nitride by a conventional firing method. It shows the XPS spectrum of _g-C 3 _{N 4} which has been inserted a Pd ion. It shows the XPS spectrum of _g-C 3 _{N 4} which has been inserted a Zn ion. X-ray diffraction diagram of the _g-C 3 _{N 4} which inserts the various metal ions. Enlarged view of the vicinity 400eV the XPS spectrum of _g-C 3 _{N 4} which inserts the various metal ions. Enlarged view of the vicinity 290eV the XPS spectrum of _g-C 3 _{N 4} which inserts the various metal ions. Shows various metal ions inserted _g-C 3 _{N 4,} untreated _g-C 3 _{N 4,} and the ultraviolet-visible diffuse reflection spectrum of titanium oxide. It shows the profile of NOx removal test by _g-C 3 _{N 4} powder was inserted Ag.

In the metal carbon nitride compound of the present invention, a metal ion was inserted between layers of g-C ₃ N ₄ by treating graphite-like carbon nitride (g-C ₃ N ₄ ) powder in an aqueous metal compound solution. It is characterized by.
That is, when g-C ₃ N ₄ is treated in an aqueous metal compound solution, the metal ions are inserted between the layers of g-C ₃ N _{4 and} the surface area is increased, and only g-C ₃ N ₄ can be obtained. This is a feature that provides a function that is not possible, and is characterized by the ability to provide metal carbon nitride compounds having various properties since the same metal ion insertion can be performed for various metals.

Hereinafter, although this invention is demonstrated in detail using a manufacture example and a specific measurement result, this invention is not limited by these.
Example 1
(Production of g-C ₃ N ₄ powder)
g-C ₃ N ₄ was synthesized as follows.
30 g of melamine (manufactured by Wako Pure Chemical Industries, Ltd.) is placed in an alumina crucible, covered, baked in an electric furnace at 550 ° C. for 1 hour, the product is ground in a mortar, and then placed in a crucible again for 550 hours. Baked at ℃. The resulting yellow powder was ground in a mortar to obtain g-C ₃ N ₄ powder.
As a result of elemental analysis of the obtained sample, the C / N ratio was 0.67, which was slightly smaller than the theoretical value of 0.75 and the amount of carbon was small, but the result of X-ray diffraction was g-C ₃ N _4. It showed that.
In addition, when cyanamide is used as a carbon nitride raw material, almost the same results are obtained, and therefore a carbon nitride raw material other than melamine may be used.

(Insertion of metal ions into g-C ₃ N ₄ )
0.5 g of the above g-C ₃ N ₄ powder, 0.2 g of silver nitrate, and 5 ml of water were put into a crucible made of Teflon (registered trademark), and silver nitrate was dissolved using an ultrasonic generator. The silver ion concentration at this time is 0.24 mol / l. A Teflon (registered trademark) crucible was placed in a stainless steel jacket and heated while stirring with a magnetic stirrer. The temperature was measured using a thermocouple at the top of the stainless steel jacket, and the temperature was adjusted using a temperature controller, slidac, and mantle heater. After heating at 150 ° C. for 20 hours, it was allowed to cool to room temperature. The suspension in the Teflon (registered trademark) crucible was centrifuged to obtain a precipitate. Add 30 ml of water to the precipitate, stir it, and centrifuge it in an ultracentrifuge (Kubota micro-cooled centrifuge model 3700) (10 minutes at 20000 G) to repeat the process of washing the precipitate with water several times. (Ag) g-C ₃ N ₄ into which ions were inserted was obtained.

In order to confirm that Ag ions were inserted, an X-ray photoelectron spectrum (XPS) of the obtained sample was measured. For the XPS measurement, ESCALAB-220iXL manufactured by FISONS was used, and the spectrum was measured while neutralizing with an electron gun.
FIG. 1 shows the result, and a peak indicating the presence of Ag ions was confirmed in the region of 365 to 378 ev. There are peak shoulders in the vicinity of 370 eV and 376 eV, indicating that there are Ag ions in a special state, which are presumed to be Ag ions existing between the layers of g-C ₃ N ₄ .

<Example 2>
0.5 g of g-C ₃ N ₄ synthesized by the method described in Example 1, 0.3 g of anhydrous iron chloride (FeCl ₃ ), and 10 ml of water are weighed and placed in a Teflon (registered trademark) crucible. Iron chloride was dissolved using a sonic generator. A Teflon (registered trademark) crucible was placed in a stainless steel jacket and heated at 150 ° C. for 20 hours while stirring with a magnetic stirrer. After allowing to cool to room temperature, the suspension in the Teflon (registered trademark) crucible was centrifuged to obtain a precipitate. 30 ml of water was added to the precipitate and stirred, and the process of washing the precipitate with water was repeated several times by centrifuging with an ultracentrifuge (20000 G for 10 minutes), and g- containing iron (Fe) ions inserted. C ₃ N ₄ was obtained.

FIG. 2 is an X-ray diffraction diagram, (a) is a diffraction diagram of g-C ₃ N ₄ synthesized by the method described in Example 1, and (b) is an insertion of Fe ions of this example. The diffractogram of g-C ₃ N ₄ , (c) is a diffractogram of iron-containing carbon nitride obtained by a conventional firing method (Non-Patent Document 1).
As shown in (a), a main peak near 27.4 ° and an unclear diffraction from 12 to 25 ° can be confirmed. From the position of the main peak, the average of the layer spacing of g-C ₃ N ₄ was calculated to be about 3.3 mm, and it was confirmed that it was g-C ₃ N ₄ which has been conventionally known.
As shown in (b), when Fe ions were added, the 27.4 ° main peak decreased. The decrease in the peak observed here is because the Fe interval is not constant because the Fe ions are randomly inserted between the layers, and the diffraction is weakened by disturbing the periodic structure. The newly generated sharp peak was attributed to iron oxide (α-Fe ₂ O ₃ ), indicating that excess Fe ions were precipitated as iron oxide.
On the other hand, as shown in (c), the iron-containing carbon nitride obtained by the conventional firing method also showed a peak at the same position, but the peak at 27.4 ° was further reduced, and a large amount of iron ions It exists between layers and shows that the periodic structure is further disturbed.
From these results, it was confirmed that when g-C ₃ N ₄ was heated at 150 ° C. in an aqueous solution containing iron ions, g-C ₃ N ₄ containing iron (Fe) ions between layers was obtained.

Further, the introduction of Fe ions was confirmed by measuring the X-ray photoelectron spectrum (XPS) of the obtained sample.
FIG. 3 shows the results. The points indicate measurement points, and the solid line indicates a moving average. A rise indicating the presence of Fe ions was confirmed near 710 ev. It is considered that the intensity is extremely weak because Fe ions are present only between the layers, hardly appear on the surface, and are difficult to detect by XPS having high surface measurement sensitivity.

(Example 3)
As a Pd source, 0.3 g of palladium chloride (PdCl ₂ ) was used, and g-C ₃ N ₄ into which palladium (Pd) ions were inserted was obtained in the same manner as in Example 2.
FIG. 4 is an X-ray diffraction pattern, (a) is a diffraction pattern of g-C ₃ N ₄ synthesized by the method described in Example 1, and (b) is an insertion of Pd ions of this example. The diffractogram of g-C ₃ N ₄ , (c) is a diffractogram of iron-containing carbon nitride obtained by a conventional firing method (Non-Patent Document 1).
When Pd ions were added to the raw material g-C ₃ N ₄ shown in (a), the main peak at 27.4 ° decreased (see (b)), indicating that Pd ions were randomly inserted between the layers. Indicated. A broad peak around 34 ° was attributed to palladium oxide, indicating that excess Pd ions were deposited on g-C ₃ N ₄ as palladium oxide.
Next, an attempt was made to insert Pd ions by a conventional firing method. Melamine and PdCl ₂ were mixed in an agate mortar, placed in an alumina crucible and heated at 550 ° C., and a black powder was obtained. The X-ray diffraction pattern was as shown in (c) of FIG. 7 described later, and did not contain g-C ₃ N ₄ at all. The sharp peaks around 40, 47 and 68 ° are those of metallic palladium. A peak of palladium oxide was also observed at 34 °. It is considered that during heating at 550 ° C., melamine was oxidized and disappeared by the catalytic action of Pd, and Pd itself was reduced to produce metallic palladium.
From these results, it was confirmed that when g-C ₃ N ₄ was heated at 150 ° C. in an aqueous solution containing Pd ions, g-C ₃ N ₄ containing Pd ions between layers was obtained. The method confirmed that g-C ₃ N ₄ into which palladium (Pd) was inserted could not be synthesized.

Further, the X-ray photoelectron spectrum (XPS) of the obtained sample was measured to confirm the introduction of Pd ions.
FIG. 5 shows the result, and a peak indicating the presence of Pd ions was confirmed in the region of 335 to 350 eV. It is broader than the peak of palladium oxide, indicating that Pd ions in a special state exist together with normal palladium oxide (PdO), and exists between the layers of g-C ₃ N ₄ It is estimated that the Pd ion.

Example 4
As a Zn source, 0.2 g of zinc chloride (ZnCl ₂ ) was used, and g-C ₃ N ₄ into which zinc (Zn) ions were inserted was obtained in the same manner as in Example 2.
In the insertion process using ZnCl ₂ , most of g-C ₃ N ₄ is decomposed at 200 ° C., and the recovery rate is extremely low, and the insertion process should be performed at less than 150 ° C.
In order to confirm that Zn ions were inserted, an X-ray photoelectron spectrum (XPS) of the obtained sample was measured.
FIG. 6 shows the result, and a peak indicating the presence of Zn ions centered at 1022 ev was confirmed.

(Example 5)
It was obtained in the same manner g-C ₃ N ₄ which inserted the various metal ions.
When inserting ions other than Examples 1 to 4 (Ag ions, Fe ions, Pd ions, Zn ions), 0.5 g of g-C ₃ N ₄ powder and a metal chloride containing metal ions to be inserted or 0.2 g to 0.3 g of metal sulfate or metal nitrate and 5 ml of water are placed in a Teflon (registered trademark) crucible, and the metal salt is dissolved using an ultrasonic generator, and then 20 ° C. at 150 ° C. After heating for hours, it was allowed to cool to room temperature. The suspension in the Teflon (registered trademark) crucible was centrifuged to obtain a precipitate. 30 ml of water was added to the precipitate and stirred, and the process of washing the precipitate with water was repeated several times by centrifugation (20,000 g for 10 minutes) using an ultracentrifuge (Microcooled Centrifuge Model 3700 manufactured by Kubota). to obtain a _g-C 3 _{N 4} which metal ions are inserted to.
As in the case of ZnCl _{2, in} the case of RuCl ₃ , it was possible to increase the recovery rate by processing at less than 150 ° C.
Figure 7 is a powder X-ray diffraction pattern of the _g-C 3 _{N 4} and _g-C 3 _{N 4} which has been inserted a variety of metal ions.
There is a peak peculiar to the layered compound around 27.4 ° in all the diffraction patterns. From the position of this peak, the average of the layer spacing is calculated to be about 3.3 cm, and it can be seen that the main structure is g-C ₃ N ₄ .
When various metal ions were added, the main peak at 27.4 ° decreased compared to the case where no metal ions were added. The decrease in the peak observed here is because the metal layer is randomly inserted between the layers, so that the layer interval is not constant by 3.3 mm and the diffraction is weakened. When ruthenium ions (Ru) or silver ions (Ag) were added, the main peak was remarkably reduced, and no peaks other than g-C ₃ N ₄ were observed. It was shown that many ions were inserted between the layers compared to other ions, and no metal-like or metal oxide-like Ru or Ag compound was formed.
Even when Cu, Ni, Co, Mn, Pt, or Zn was added, the main peak was slightly reduced, indicating that ions were inserted between the layers. In the case of Cu, a peak of copper oxide was observed, indicating that excessive Cu ions were precipitated as copper oxide. The diffraction peaks observed when other metal ions are used are not caused by metal or metal oxide ions, but are caused by a periodic structure newly formed by insertion of the metal.

FIG. 8 is a diagram showing an X-ray photoelectron spectrum (XPS) of g-C ₃ N ₄ in which various metal ions are inserted, and is an enlarged view of the vicinity of 400 eV involving a nitrogen atom. Compared to _g-C 3 _{N 4} which is not inserted the metal, the peak of the nitrogen has shifted to a higher Binding Energy side (left side in the figure). This indicates that the metal ions are attracting electrons of nitrogen atoms, and it was confirmed that the inserted metal ions interacted with g-C ₃ N ₄ . The interaction was particularly strong with Ru, Pd, Ag, and Zn, moderate with Fe and Cu, and relatively small with Ni.

FIG. 9 is a view showing an X-ray photoelectron spectrum (XPS) of g-C ₃ N ₄ in which various metal ions are inserted, and is an enlarged view of the vicinity of 290 eV involving carbon atoms. Compared to _g-C 3 _{N 4} which is not inserted the metal is shifted to the peak of the carbon is highly Binding Energy side (left side in the figure). This indicates that the electron density of the carbon atom is lowered due to the insertion of the metal ion. As was observed in the spectrum of the nitrogen atom, were backed in the metal ions are interacting with g-C ₃ N _4.

(Example 6)
To confirm the g-C ₃ N ₄ to the effect due to the interpolated various metal ions, g-C ₃ N ₄ to additives and water were added, the recovery rate (the product upon heating at 0.99 ° C. ÷ the weight of the raw material g—C ₃ N ₄ ) and the specific surface area (BET area). For the measurement of the specific surface area, a multipoint BET method using nitrogen as an adsorbate was used. For the measurement, Autosorb-1 manufactured by Cantachrome was used. About 0.2 g of a sample was placed in a sample holder, deaerated at 120 ° C. for 1 hour, and then the specific surface area was measured.
Table 1 below shows the results.

As is apparent from Table 1, the recovery rate was approximately 100% except when AgNO ₃ and PdCl ₂ were added, and the weight of g-C ₃ N _{4 was} hardly changed.
This indicates that only the metal ions in trace amounts is inserted into the g-C ₃ N _4. When AgNO ₃ having a recovery rate of 112% or PdCl ₂ having a recovery rate of 124% was added, it is considered that a larger amount of silver ions or palladium ions remained in the sample.
Due to the reaction between g-C ₃ N ₄ and metal ions, it was confirmed that the specific surface area (BET area) increased regardless of the type of inserted metal ions, and that g-C ₃ N ₄ was finely divided. In particular, when the insertion of ruthenium ions, in which the increase in the BET area was remarkable, was compared at 110 ° C. and 150 ° C., the BET area of g-C ₃ N ₄ treated at 110 ° C. was 25.0 m ² / g, 150 ° C. Then, it was 67.2 m ² / g. Since it was 7.7 m ² / g before the insertion of ruthenium ions, metal ions were inserted even at 110 ° C., but it was confirmed that the insertion of metal ions was further promoted and refined at 150 ° C. .
Except for the addition of NaCl, which was not effective in promoting the photocatalytic reaction described later, the specific surface area was increased by at least 50% and up to 870% by insertion of metal ions.
On the other hand, the specific surface area of carbon nitride to which Fe ions were added by the conventional firing method (reference: Non-Patent Document 1) was 4.8 m ² / g, and that of Zn was 3.9 m ² / g. It can be seen that the specific surface area is smaller than when no metal ions are added and large particles are formed. This is not preferable for use as a catalyst or battery material.

(Example 7)
The visible ultraviolet diffuse reflectance spectrum of g-C ₃ N ₄ into which various metal ions were inserted was measured. Spectrum of g-C ₃ N ₄ and titanium oxide untreated as a comparison was also measured. Measurement was performed by attaching a diffuse reflection spectrum measurement attachment (ISR-3100) to a visible ultraviolet absorption spectrometer (Shimadzu UV-3600). Barium sulfate was used as a reference substance.
FIG. 10 is a diagram showing the results.
As is clear from FIG. 10, titanium oxide absorbs light of about 400 nm or less and can be used for the photocatalytic reaction, and g-C ₃ N ₄ can absorb longer wavelength visible light (up to about 500 nm).
When Ag ions were inserted, the absorption edge was slightly shifted to the longer wavelength side, indicating that the band gap was reduced. On the other hand, when Zn ions were inserted at 150 ° C., the absorption edge shifted to the short wavelength side, indicating that the band gap was increased. Although illustration is omitted, even when Zn ions were inserted at 110 ° C., the absorption edge was shifted to the short wavelength side, but the shift amount was small. It was found that by reducing the reaction temperature with metal ions, the amount of metal to be inserted can be adjusted, and the light absorption characteristics can also be adjusted. When Pd or Fe ions were inserted, the remaining metal oxide reduced the reflectance over a wide range.
By inserting metal ions as described above, the light absorption characteristics of g-C ₃ N ₄ can be controlled.

(Example 8)
FIG. 11 is a view showing a profile of a photocatalytic NOx removal test using g-C ₃ N ₄ into which Ag ions are inserted. The insertion of Ag ions was performed by the method described in Example 1.
The NOx removal rate was measured as follows.
Ag-inserted g-C ₃ N ₄ (0.2 g) is suspended in a small amount of water, and the entire amount is applied to a glass plate having a width of 50 mm and a length of 100 mm, and dried at 50 ° C. to prepare a photocatalyst test piece. Prepared. The test piece was placed in a photocatalytic reaction vessel shown in JIS R1701-1, covered with a Pyrex (registered trademark) lid, and simulated polluted air containing 1.0 ppm of NO gas was circulated at 1.0 L / min. . The humidity was 6% at 25 ° C. The NO and NO ₂ gas concentrations in the simulated contaminated air coming out of the reaction vessel were measured with a chemiluminescent NOx measuring device (manufactured by MonitorLabs, 8840). Light from a white fluorescent lamp (Toshiba FL10W) was irradiated to the photocatalyst sample piece at an intensity of 6000 Lx through an ultraviolet light removal filter (Sumitex LF-39 manufactured by Sumitomo Chemical), and the photocatalytic action was observed. NOx concentration (the sum of NO gas concentration and NO ₂ gas concentration) is determined and {[NOx concentration when light is not irradiated] − [NOx concentration when light is irradiated]} / {[light is irradiated NOx concentration when not present]} × 100 was defined as the NOx removal rate.

As shown in FIG. 11, the concentration of NO decreases while the light is applied, and the concentration returns to the original level when the light irradiation is stopped. Part of NO becomes NO ₂ and further becomes HNO ₃ and is adsorbed on the photocatalyst and removed from the circulating gas. The area of the portion surrounded by the initial concentration and NOx line corresponds to the removed NOx amount.

Example 9
Table 2 shows the measurement results of NOx removal rate, acetaldehyde removal rate, toluene removal rate, and BET area using photocatalysis by g-C ₃ N ₄ with a metal inserted.
The NOx removal rate was measured in the same manner as the photocatalytic NOx removal test using g-C ₃ N ₄ with the Ag ions inserted therein.

The acetaldehyde removal rate was measured as follows.
A test piece prepared in the same manner as described above was placed in the same photocatalytic reaction vessel as described above, and simulated polluted air containing about 2.0 ppm of acetaldehyde gas was circulated at 1.0 L / min. The humidity was 6% at 25 ° C. The concentration of acetaldehyde in the simulated contaminated air coming out of the reaction vessel was measured with a gas chromatograph equipped with an FID detector (Shimadzu GC-14B). Light from a white fluorescent lamp (Toshiba FL10W) was irradiated to the photocatalyst sample piece at an intensity of 6000 Lx through an ultraviolet light removal filter (Sumitex LF-39 manufactured by Sumitomo Chemical), and the photocatalytic action was observed. {[Acetaldehyde concentration when not irradiating light] − [Acetaldehyde concentration when irradiating light]} / {[Acetaldehyde concentration when not irradiating light]} × 100 was defined as an acetaldehyde removal rate.

Furthermore, the toluene removal rate was measured as follows.
A test piece prepared in the same manner as described above was placed in the same photocatalytic reaction vessel, and simulated contaminated air containing about 1.0 ppm of toluene gas was circulated at 0.50 L / min. The humidity was 6% at 25 ° C. The toluene concentration in the simulated contaminated air coming out of the reaction vessel was measured with a gas chromatograph equipped with an FID detector (Shimadzu GC-14B). Light from a white fluorescent lamp (Toshiba FL10W) was irradiated to the photocatalyst sample piece at an intensity of 6000 Lx through an ultraviolet light removal filter (Sumitex LF-39 manufactured by Sumitomo Chemical), and the photocatalytic action was observed. {[Toluene concentration when not irradiating light] − [Toluene concentration when irradiating light]} / {[Toluene concentration when not irradiating light]} × 100 was defined as the toluene removal rate.

As is apparent from Table 2, the NOx removal efficiency of carbon nitride (without additive) obtained by the conventional method was 3.9%. Even when only water was added and heated, the NOx removal rate did not improve.
On the other hand, when g-C ₃ N ₄ into which various metal ions of the present invention were inserted was used, higher NOx removal was obtained than when no additive metal was used. In particular, a sample in which silver ions and zinc ions were inserted obtained NOx removal activity that was three times higher. On the other hand, insertion of Na ions and Mn ions had little effect. Details of the results of the NOx removal test will be shown later in the drawings.
In the removal test of acetaldehyde and toluene, the effect of insertion of silver ions was also observed. With acetaldehyde, the removal rate was improved up to twice that without the additive. In toluene decomposition, toluene could not be removed at all without additives, but the removal performance improved to a state where toluene could be decomposed by insertion of silver ions. This is considered to be because the g-C ₃ N ₄ particles were miniaturized by adding metal ions and heating, and the photocatalytic reaction rate was significantly improved.
Although the test was not conducted because the heat resistance temperature of the used container was 150 ° C., the heat resistance of g-C ₃ N ₄ was 520 ° C. or higher, and the recovery rate was almost 100% even at 150 ° C. (Table Since it is 1) and has not been decomposed at all, it is easily assumed that metal ions can be inserted up to the supercritical water temperature of 375 ° C. within the allowable temperature range of the container.

Further, as described in Patent Document 6, after hydrothermal treatment in an alkaline aqueous solution, further addition of silver nitrate and insertion of silver ions increased the NOx removal rate to 23%.
From this, it is considered that a plurality of acid treatments, alkali treatments and metal ion insertions may be mixed, or a plurality of metal ions may be mixed. However, in the case of adding an acid or an alkali, it is necessary to adjust the temperature appropriately because g-C ₃ N ₄ is easily decomposed during the hydrothermal treatment.

As a result of examining the effect of adding the metal compound of the second period to the sixth period to carbon nitride, it was confirmed that the metal belonging to any period improved photocatalytic activity and the specific surface area. The 8th-12th group of the 5th period showed a high effect. In terms of atomic number, 30 to 47 elements showed a high effect. Also, any of chloride, nitrate and sulfate was effective. In particular, ruthenium chloride and iron chloride were effective in increasing the specific surface area. However, when Ru was added, NO gas and acetaldehyde adsorbed remarkably, and the photocatalytic reaction could not be measured (Table 2).
The NOx removal rate by carbon nitride to which Fe ions were added by a conventional firing method (reference: Non-Patent Document 2) was 0.6%, and when Zn was added, NOx could not be removed at all. The reason is considered to be that the specific surface area is extremely small and that the properties of the semiconductor deteriorated due to the reaction of the metal at a high temperature.

By applying g-C ₃ N ₄ with improved activity of the present invention to a certain substrate, it can be used as a photocatalytic material. When this material is used, air is purified by utilizing the energy of light. can do. This material can also be used for the decomposition of acetaldehyde, toluene, NOx, as well as the decomposition of malodorous substances, air pollutants, or other similar compounds such as oxygenated hydrocarbons, aromatic hydrocarbons, reactive inorganic gases, etc. Can also be used.

Claims (5)

Graphite-like carbon nitride in which metal ions are inserted between layers, characterized by heat- treating graphite-like carbon nitride powder in an aqueous solution of a metal compound selected from metal chloride, metal sulfate, or metal nitrate Manufacturing method. The method for producing graphitic carbon nitride having metal ions inserted between layers according to claim 1, wherein the treatment is a heat treatment at 100 to 150 ° C. 3. The metal according to claim 1, wherein the metal is any one selected from Li, Na, Mn, Fe, Co, Cu, Zn, Mo, Ru, Pd, Ag, Ba, and Pt. A method for producing graphitic carbon nitride in which metal ions are inserted between layers. The method for producing graphite-like carbon nitride having metal ions inserted between layers according to any one of claims 1 to 3, wherein the specific surface area of the graphite-like carbon nitride is increased by the treatment . The graphite-like carbon nitride with metal ions inserted between layers according to any one of claims 1 to 4, wherein the graphite-like carbon nitride with metal ions inserted between the layers is an effective component of a photocatalyst. A method for producing carbon nitride.