WO2011049085A1 - Photocatalyst containing carbon nitride, method for producing same, and air purification method using the photocatalyst - Google Patents

Photocatalyst containing carbon nitride, method for producing same, and air purification method using the photocatalyst Download PDF

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WO2011049085A1
WO2011049085A1 PCT/JP2010/068385 JP2010068385W WO2011049085A1 WO 2011049085 A1 WO2011049085 A1 WO 2011049085A1 JP 2010068385 W JP2010068385 W JP 2010068385W WO 2011049085 A1 WO2011049085 A1 WO 2011049085A1
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carbon nitride
photocatalyst
graphite
treatment
aqueous solution
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French (fr)
Japanese (ja)
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泰三 佐野
浩士 竹内
信彰 根岸
力 平川
咲子 筒井
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独立行政法人産業技術総合研究所
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Publication of WO2011049085A1 publication Critical patent/WO2011049085A1/en

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    • B01J35/39—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8678—Removing components of undefined structure
    • B01D53/8687—Organic components
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/24—Nitrogen compounds
    • B01J35/613—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/08—Heat treatment
    • B01J37/10—Heat treatment in the presence of water, e.g. steam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/202—Alkali metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/70—Non-metallic catalysts, additives or dopants
    • B01D2255/702—Carbon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/80—Type of catalytic reaction
    • B01D2255/802—Photocatalytic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/70—Organic compounds not provided for in groups B01D2257/00 - B01D2257/602
    • B01D2257/702—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/90—Odorous compounds not provided for in groups B01D2257/00 - B01D2257/708
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/06—Polluted air
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/45—Gas separation or purification devices adapted for specific applications
    • B01D2259/4508—Gas separation or purification devices adapted for specific applications for cleaning air in buildings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/80—Employing electric, magnetic, electromagnetic or wave energy, or particle radiation
    • B01D2259/802—Visible light

Definitions

  • the present invention relates to a photocatalyst, a method for producing the photocatalyst, and an air purification method using the photocatalyst, and more particularly, to a photocatalyst having improved visible light responsiveness.
  • Titanium oxide is a typical example and exhibits a strong photocatalytic activity.
  • 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.
  • Patent Document 1 describes that a photocatalyst exhibiting a high photocatalytic action can be obtained by irradiation with visible light by mixing and baking ammonia or a substance that generates ammonia by heating and a titanium compound.
  • Patent Document 2 describes titanium hydroxide containing 3.3% or more of nitrogen, and a photocatalyst obtained by firing the titanium hydroxide.
  • semiconductors such as tungsten oxide are capable of absorbing visible light because they have a smaller band gap than titanium oxide, and are expected as visible light active photocatalysts (visible light responsive photocatalysts) ( Patent Documents 3 and 4). These visible light responsive photocatalysts often promote their activity using a promoter such as platinum, palladium, or copper compound.
  • Non-patent Document 1 graphite-like carbon nitride has been proposed (Non-patent Document 1). It has been known since the 1980s that this graphite-like carbon nitride powder can be synthesized by pyrolyzing melamine or cyanamide, but the catalytic action has not been studied until recently, and in fact, the graphite-like powder synthesized from melamine Even if carbon nitride is used as it is, there is almost no catalytic activity. However, the literature 1 reports that the activity is improved by supporting platinum or ruthenium and it can be used for water photolysis (hydrogen generation, oxygen generation). ing.
  • non-patent document 2 synthesizes ultrafine-grained graphite-like carbon nitride using silica as a template, and synthesizes graphite-like carbon nitride with a high specific surface area by removing silica with hydrofluoric acid.
  • the photocatalytic activity is not evaluated.
  • titanium oxide decomposes organic substances contained in the adhesive and paint, it is necessary to use an inorganic adhesive or paint that does not contain organic substances when titanium oxide is used. Furthermore, titanium oxide has good compatibility with inorganic materials such as glass and concrete, but has a problem that it has poor compatibility with organic materials.
  • Tungsten oxide-based semiconductors are expected to be visible light-responsive photocatalysts, but their price is about 10 times that of titanium oxide, and the supply is unstable because they are strategic substances. There is also. Further, the graphite-like carbon nitride powder does not have catalytic activity as it is, and some activation means is necessary. However, the activation means using platinum or ruthenium described in Non-Patent Document 1 is expensive, and hydrofluoric acid is used. There is a problem that the synthesis method of Non-Patent Document 2 used is dangerous.
  • the present invention has been made in view of the above circumstances, and provides a photocatalyst obtained by a cheaper and safer method and responsive to not only ultraviolet light but also visible light, and a method for producing the same. It is intended.
  • a photocatalyst comprising, as an active ingredient, powder obtained by subjecting graphite-like carbon nitride powder to an alkali treatment or an acid treatment.
  • the treatment is a heat treatment in an alkaline aqueous solution or an acidic aqueous solution.
  • the present invention it is possible to obtain a photocatalyst by an inexpensive and safe method, and the obtained photocatalyst can utilize the photocatalytic action using visible light even if the ultraviolet light is insufficient in the room. Therefore, titanium oxide and tungsten oxide currently used as photocatalysts can be replaced with inexpensive materials.
  • combination of graphite-like carbon nitride The figure which shows the electron spin resonance (ESR) spectrum of the graphite-like carbon nitride obtained by adding sodium hydroxide aqueous solution and heat-processing at 90 degreeC for 20 hours.
  • strength of the ESR signal observed in g 2.004 vicinity of the ESR spectrum of graphite-like carbon nitride, and the calcination temperature at the time of the synthesis
  • FIG 3 is a powder X-ray diffraction diagram of graphitic carbon nitride.
  • the figure which shows the enlarged part of the main peak in FIG. The figure which shows the profile of the NOx removal test by the graphite-like carbon nitride powder which heat-processed for 90 hours at 130 degreeC by adding sodium hydroxide aqueous solution.
  • the photocatalyst having visible light responsiveness of the present invention is characterized in that its photocatalytic activity is improved by treating graphite-like carbon nitride powder in an alkaline aqueous solution or an acidic aqueous solution. That is, by treating the graphite-like carbon nitride in an alkaline solution or an acidic solution, the specific surface area is increased and the photocatalytic activity is improved.
  • the present invention will be described in more detail using specific measurement results.
  • Graphite-like carbon nitride 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 °C. The resulting yellow powder was ground in a mortar to obtain graphite-like carbon nitride powder.
  • melamine manufactured by Wako Pure Chemical Industries, Ltd.
  • the alkali treatment of graphite-like carbon nitride was performed as follows. 1.0 g of the graphite-like carbon nitride powder and 100 ml of a 0.10 mol / l aqueous solution of sodium hydroxide (Wako Pure Chemical Industries) are placed in a crucible made of Teflon (registered trademark), and sodium hydroxide is utilized using an ultrasonic generator. Was dissolved. At this time, the sodium hydroxide concentration was 0.1 mol / l, and the pH at room temperature was 13. When changing the pH of the solution, the concentration of sodium hydroxide was appropriately changed.
  • a Teflon 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 a predetermined temperature for 20 hours, it was allowed to cool to room temperature. The suspension in the Teflon crucible was centrifuged to obtain a precipitate.
  • the acid treatment of graphite-like carbon nitride was performed as follows. 1.0 g of graphite-like carbon nitride powder obtained by baking the melamine and 100 ml of 0.2 mol / l hydrochloric acid (Wako Pure Chemical Industries) were placed in a Teflon crucible and stirred using an ultrasonic generator. . When changing the pH of the solution, the amount of concentrated hydrochloric acid was appropriately changed.
  • an acid other than hydrochloric acid for example, sulfuric acid or nitric acid
  • concentration of an acid reagent manufactured by Wako Pure Chemical Industries, Ltd.
  • Wako Pure Chemical Industries, Ltd. the concentration of an acid reagent added as appropriate was adjusted so that the hydrogen ion concentration was comparable.
  • a Teflon 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 a predetermined temperature for 20 hours, it was allowed to cool to room temperature. The suspension in the Teflon crucible was centrifuged to obtain a precipitate. The process of washing the precipitate with water by adding 30 ml of water to the precipitate and stirring and centrifuging was repeated several times to obtain acid-treated graphite-like carbon nitride.
  • FIG. 1 shows the specific surface area ( ⁇ ) of graphite-like carbon nitride powder obtained by baking melamine at different temperatures for 2 hours in the production of the above-mentioned graphite-like carbon nitride powder, and the graphite-like carbon nitride powder is hydroxylated.
  • the specific surface area was measured by a multipoint BET method using nitrogen as an adsorbate.
  • FIG. 2 shows the NOx removal rate ( ⁇ ) of the graphite-like carbon nitride powder obtained by baking the melamine at different temperatures for 2 hours, and the aqueous solution of sodium hydroxide (concentration 0.1 mol / wt). It is a figure which shows the relationship between NOx removal rate ((circle)) of the graphite-like carbon nitride powder obtained by adding L) and heat-processing at 90 degreeC for 20 hours, and a calcination temperature. The NOx removal rate was measured as follows.
  • 0.2 g of the treated g-C 3 N 4 was suspended in a small amount of water, the whole amount was 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.
  • the test piece was installed 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.
  • 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 obtained 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.
  • the sample that was not treated with an aqueous sodium hydroxide solution (hereinafter referred to as “NaOH treatment”) showed a low NOx removal rate regardless of the firing temperature.
  • the NOx removal rate was higher than that before the NaOH treatment, and the NOx removal rate was the highest especially around 550 ° C. From these results, in the method for producing graphite-like carbon nitride described above, graphite-like carbon nitride obtained by firing a carbon nitride raw material in the range of 450 ° C. to 650 ° C., preferably 500 ° C. to 600 ° C.
  • the graphite-like carbon nitride having a high photocatalytic activity can be obtained by treating this in an alkaline aqueous solution. Further, as apparent from the results of FIGS. 1 and 2, it was found that the photocatalytic activity does not increase only by increasing the BET area. This is considered to be related to the radical generation ability described below.
  • ESR Electron spin resonance
  • the composition of the obtained graphite-like carbon nitride varies depending on the firing temperature, but 0.4 ⁇ x ⁇ 0.6. 1.4 ⁇ y ⁇ 3.1 and 0.1 ⁇ z ⁇ 2.5.
  • the results of X-ray diffraction described later showed that the layered compound was like a graphite-like carbon nitride-like, so that incomplete C 3 with defects such as amino groups was present. N 4 was identified.
  • cyanamide is used as a raw material for carbon nitride, or when cyanamide, melamine, and urea are mixed, almost the same results are obtained, so a raw material for carbon nitride other than melamine may be used. A plurality of carbon nitride raw materials may be mixed.
  • each graphite-like carbon nitride obtained by firing at 520 ° C. to 650 ° C. is subjected to the above-mentioned NaOH treatment to obtain graphite-like carbon nitride having an enhanced photocatalytic activity.
  • Table 1 below shows the measurement results of the NOx removal rate and the BET area with the g-C 3 N 4 powder obtained by the various alkali treatments and acid treatments described above.
  • HCl treatment Treatment with hydrochloric acid (hereinafter referred to as “HCl treatment”) was effective when performed at a hydrochloric acid concentration of 0.2 mol / l (pH ⁇ 1), but was effective at a hydrochloric acid concentration of 0.02 mol / l (pH of about 2).
  • HCl treatment Treatment with hydrochloric acid
  • pH ⁇ 1 hydrochloric acid concentration of 0.2 mol / l
  • the hydrochloric acid concentration of 0.02 mol / l pH of about 2
  • the effect was small at 110 ° C. From this, it is considered that a high hydrogen ion concentration and a temperature exceeding 110 ° C. are necessary.
  • the specific surface area is increased to 20 m 2 / g or more regardless of either the alkali treatment or the acid treatment. It is considered that gC 3 N 4 particles were miniaturized by acid treatment or alkali treatment, and the photocatalyst was remarkably improved.
  • FIG. 5 is a diagram showing visible ultraviolet diffuse reflection spectra of gC 3 N 4 and titanium oxide.
  • a broken line indicates a spectrum of titanium oxide (ST-01), and a dotted line indicates an alkali-treated g-
  • the spectrum of C 3 N 4 the solid line is the spectrum of untreated g-C 3 N 4 .
  • 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.
  • 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 visible light having a longer wavelength (up to about 500 nm). Even when NaOH was added and heat-treated, there was no significant change.
  • FIG. 6 is an X-ray powder diffraction pattern of gC 3 N 4 , which was measured with a RU-300 manufactured by RIGAKU.
  • untreated g-C 3 N 4 deionized water, g-C 3 N 4 and 20 hours of heat treatment at 0.99 ° C.
  • aqueous sodium hydroxide was heated at 0.99 ° C. 20 hours g- C 3 N 4 , g-C 3 N 4 that has been heat-treated at 150 ° C. for 20 hours in an aqueous HCl solution.
  • FIG. 7 is a diagram showing an enlarged portion of the main peak, where the solid line indicates untreated g—C 3 N 4 and the broken line indicates NaOH-treated g—C 3 N 4 . 6 and 7, there is a peak peculiar to the layered compound at 27 to 28 °, and it can be seen from the position of this peak that the average of the layer spacing is calculated to be about 3.3 cm, and is gC 3 N 4 .
  • FIG. 9 even when a sodium hydroxide aqueous solution is added and heated, there is almost no change in the diffraction pattern, but in FIG. 7 where the main peak is enlarged, a slight difference is seen.
  • a sodium hydroxide solution is the best, and a potassium hydroxide solution can also be used.
  • a sodium hydroxide solution having a concentration of 1.4 mol / l was used, most of the g-C 3 N 4 was denatured and the recovery rate was lowered, so the concentration was preferably 1.0 mol / l or less, more preferably Uses an alkaline aqueous solution having a concentration of 0.5 mol / l or less.
  • an aqueous solution of a strong acid can be used, but the pH is preferably 1 or less.
  • the treatment with these aqueous solutions is effective to some extent even at room temperature, but the effect is large when performed at 70 ° C. or higher, but the recovery rate of g-C 3 N 4 decreases when it exceeds 130 ° C. It is preferable to process at a temperature not exceeding ° C. Furthermore, the temperature which does not exceed 110 degreeC is preferable. Since activity does not improve even when heated in pure water, it is necessary to heat-treat in an acidic or alkaline aqueous solution.
  • FIG. 8 is a diagram showing a profile of a NOx removal test using gC 3 N 4 powder that was heated for 90 hours at 130 ° C. with an aqueous sodium hydroxide solution (concentration 0.1 mol / L).
  • FIG. 3 is a view showing a profile of a NOx removal test using g-C 3 N 4 powder which was heated at 150 ° C. for 2 hours with hydrochloric acid (concentration 0.2 mol / L) added.
  • the dotted line indicates the NO concentration
  • the dashed line indicates the NO 2 concentration
  • the solid line indicates the NO x (sum of NO and NO 2 ) concentration
  • the horizontal dotted line indicates the initial concentration of NO x .
  • the concentration of NO decreases while the light is applied, and the concentration returns to the original level when the light irradiation is stopped, indicating that a photocatalytic reaction is occurring.
  • 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.
  • FIG. 10 shows the NOx removal rate of gC 3 N 4 obtained by adding a sodium hydroxide aqueous solution (concentration 0.1 mol / L) and heat-treating at 90 ° C. for 20 hours, and the wavelength of irradiated light.
  • the horizontal axis represents the transmission limit wavelength of the filter. It was confirmed that gC 3 N 4 can use even visible light having a wavelength near 500 nm. Moreover, since the NOx removal rate with a 345 nm filter is higher than the NOx removal rate with a 400 nm filter, it was confirmed that ultraviolet rays can also be used.
  • FIG. 11 is a diagram showing the relationship between the heating temperature and the NOx removal rate when a sodium hydroxide aqueous solution (concentration 0.1 mol / L) is added and heat-treated for 20 hours.
  • the dotted line in the drawing indicates the NO x removal rate if untreated.
  • a high NOx removal rate is exhibited when the temperature is about 90 ° C. to 130 ° C., and may decrease when the temperature reaches 150 ° C.
  • FIG. 12 is a diagram showing the relationship between the heating time and the NOx removal rate when a sodium hydroxide aqueous solution (concentration 0.1 mol / L) is added and heat treatment is performed at 110 ° C. A high NOx removal rate was exhibited in about 20 hours, and decreased when heated for 90 hours.
  • FIG. 13 is a diagram showing the relationship between the heating temperature and the recovery rate when a sodium hydroxide aqueous solution (concentration: 0.1 mol / L) is added and heat-treated for 20 hours.
  • the recovery rate was defined as (g-C 3 N 4 weight after heat treatment) / (weight before heat treatment) ⁇ 100.
  • a part of g-C 3 N 4 is dissolved by the heat treatment, and is refined and cannot be precipitated in the centrifuge, so that the recoverable amount is reduced. Above 110 ° C., the recovery rate was significantly reduced.
  • Figure 14 is the untreated g-C 3 N 4 powder, and an aqueous solution of sodium hydroxide (concentration 0.1 mol / L) was added to the obtained by 20 hours of heat treatment at 90 °C g-C 3 N 4
  • the measurement was performed as follows. 0.2 g of NaOH-treated g—C 3 N 4 was suspended in a small amount of water, the whole amount was 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.
  • the test piece was placed in a photocatalytic reaction vessel shown in JIS R1701-1, covered with a Pyrex lid, and simulated contaminated air containing about 2 ppm of acetaldehyde was circulated at 0.5 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 (GC-14B manufactured by Shimadzu) equipped with an FID type detector. For calibration of the gas chromatograph, 5 ppm acetaldehyde standard gas was used.
  • the CO 2 concentration was measured with an infrared absorption CO 2 meter (41C manufactured by Thermoelectron).
  • FIG. 15 is a graph showing the results of a toluene photocatalytic purification test using g-C 3 N 4 powder obtained by adding HCl and heat-treating at 150 ° C. for 2 hours. The measurement was performed in the same manner as the above-mentioned photocatalytic purification test for acetaldehyde.
  • a gas containing toluene was brought into contact with the photocatalyst without exposure to light, the concentration decreased due to adsorption. The concentration gradually approached the introduced concentration, so when exposed to light, the concentration decreased slightly, and at the same time the generation of CO 2 was confirmed (not shown), indicating that toluene was decomposed.
  • Table 3 shows the results of the toluene removal test.
  • Untreated g-C 3 N 4 powder could not remove (decompose) toluene.
  • the g-C 3 N 4 powder of NaOH treatment, g-C 3 N 4 powder of HCl treatment decomposes the toluene was generate CO 2.
  • the graphite-like carbon nitride powder with improved photocatalytic activity of the present invention can be used as a photocatalytic material by applying it to any substrate, and when this material is used, the energy of light is used to produce air. Can be purified. This material can also be used to decompose acetaldehyde, toluene, and NOx, and can also be used to decompose similar compounds.

Abstract

Disclosed is a photocatalyst which is responsive to visible light and can be obtained at lower cost than conventional photocatalysts by a safe method. Also disclosed is a method for producing the photocatalyst. The photocatalyst which is responsive to visible light is characterized by containing, as an active ingredient, a powder that is obtained by subjecting a graphite-like carbon nitride powder to an alkali treatment or an acid treatment. The alkali treatment or acid treatment is preferably a heat treatment that is carried out in an alkaline aqueous solution or an acidic aqueous solution. A visible light-responsive photocatalyst obtained by the method has a specific surface area of not less than 20 m2/g and significantly improved photoactivity.

Description

窒化炭素を含む光触媒及びその製造方法並びに該光触媒を用いた空気浄化方法Photocatalyst containing carbon nitride, method for producing the same, and air purification method using the photocatalyst
　本発明は、光触媒及びその製造方法並びに該光触媒を用いた空気浄化方法に関し、特に、可視光応答性が改良された光触媒に関する。 The present invention relates to a photocatalyst, a method for producing the photocatalyst, and an air purification method using the photocatalyst, and more particularly, to a photocatalyst having improved visible light responsiveness.
　近年、空気浄化を行う技術が研究されており、太陽光や室内光によって環境汚染物質を分解除去することが可能な光触媒が注目され、その研究が精力的に行われている。
　酸化チタンはその代表的なものであり、強力な光触媒活性を示す。しかしながら、酸化チタンは、バンドギャップが大きくて太陽光の大部分を占める可視光が吸収されず、紫外光にのみに活性なため、太陽光を十分に利用することができない、紫外光が極めて弱い室内では機能しない、などの課題があった。そこで、可視光を利用することができるように、いろいろな改良がなされている。
　例えば、特許文献１では、アンモニアまたは加熱によりアンモニアを生成する物質と、チタン化合物を混合して焼成することにより、可視光の照射で高い光触媒作用を示す光触媒が得られるとしている。また、特許文献２では、窒素を３．３％以上含む水酸化チタン、それを焼成して得られる光触媒体が記載されている。 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, Patent Document 1 describes that a photocatalyst exhibiting a high photocatalytic action can be obtained by irradiation with visible light by mixing and baking ammonia or a substance that generates ammonia by heating and a titanium compound. Patent Document 2 describes titanium hydroxide containing 3.3% or more of nitrogen, and a photocatalyst obtained by firing the titanium hydroxide.
　これに対し、酸化タングステンなどの半導体は、酸化チタンと比較してバンドギャップが小さいために可視光を吸収することができ、可視光活性な光触媒（可視光応答性光触媒）として期待されている（特許文献３、４）。これらの可視光応答性光触媒は、白金やパラジウム、銅化合物などの助触媒を利用して活性を促進させることが多い。 On the other hand, semiconductors such as tungsten oxide are capable of absorbing visible light because they have a smaller band gap than titanium oxide, and are expected as visible light active photocatalysts (visible light responsive photocatalysts) ( Patent Documents 3 and 4). These visible light responsive photocatalysts often promote their activity using a promoter such as platinum, palladium, or copper compound.
　また、近年、グラファイト状窒化炭素が提案されている（非特許文献１）。このグラファイト状窒化炭素の粉末は、メラミンまたはシアナミドを熱分解することで合成できることが８０年代から知られているが、触媒作用は近年まで研究されておらず、実際、メラミンから合成されたグラファイト状窒化炭素をそのまま使っても、ほとんど触媒活性はないが、前記文献１では、白金やルテニウムを担持することで活性が向上し、水の光分解（水素発生、酸素発生）に利用できると報告している。 In recent years, graphite-like carbon nitride has been proposed (Non-patent Document 1). It has been known since the 1980s that this graphite-like carbon nitride powder can be synthesized by pyrolyzing melamine or cyanamide, but the catalytic action has not been studied until recently, and in fact, the graphite-like powder synthesized from melamine Even if carbon nitride is used as it is, there is almost no catalytic activity. However, the literature 1 reports that the activity is improved by supporting platinum or ruthenium and it can be used for water photolysis (hydrogen generation, oxygen generation). ing.
　一方、グラファイト状窒化炭素については、非特許文献２に、シリカをテンプレートとして超微粒子のグラファイト状窒化炭素を合成し、シリカをフッ酸で除去することにより、高比表面積のグラファイト状窒化炭素を合成する手法が記載されているが、光触媒活性については評価していない。また、特許文献５、６には、ＭＯＨ水溶液（Ｍ＝Ｋ，Ｎａ，Ｌｉ）或いは鉱酸で処理したものが、優れた蛍光特性或いは潤滑特性を示すことが記載されているが、光触媒活性については何ら記載されていない。 On the other hand, as for graphite-like carbon nitride, non-patent document 2 synthesizes ultrafine-grained graphite-like carbon nitride using silica as a template, and synthesizes graphite-like carbon nitride with a high specific surface area by removing silica with hydrofluoric acid. However, the photocatalytic activity is not evaluated. Patent Documents 5 and 6 describe that a solution treated with an MOH aqueous solution (M = K, Na, Li) or a mineral acid exhibits excellent fluorescence characteristics or lubrication characteristics. Is not described at all.
特開２００２－１６６１７９号公報JP 2002-166179 A 特開２００１－３３５３２１号公報JP 2001-335321 A 特開２００９－６１４２６号公報JP 2009-61426 A 特開２００８－１４９３１２号公報JP 2008-149312 A 特開平０２－２０６６１９号公報Japanese Patent Laid-Open No. 02-206619 特開平０２－３００２３３号公報Japanese Patent Laid-Open No. 02-300273
　前述のとおり、酸化チタンを用いた光触媒においては、窒素をドープすることにより、可視光を利用することができるようにしているが、その効率は未だ低くて充分とはいえず、建材やフィルター、薄膜に加工すると、活性が著しく低下するという問題がある。また、酸化チタンは、接着剤や塗料に含まれる有機物を分解するため、酸化チタンを用いる場合には有機物を含まない、無機系の接着剤や塗料を用いる必要があった。さらに、酸化チタンは、ガラスやコンクリートなどの無機系の材料との相性は良かったが、有機系の材料とは相性が悪いという問題もある。 As described above, in the photocatalyst using titanium oxide, it is possible to use visible light by doping nitrogen, but its efficiency is still low and it cannot be said that construction materials and filters, When processing into a thin film, there exists a problem that activity falls remarkably. In addition, since titanium oxide decomposes organic substances contained in the adhesive and paint, it is necessary to use an inorganic adhesive or paint that does not contain organic substances when titanium oxide is used. Furthermore, titanium oxide has good compatibility with inorganic materials such as glass and concrete, but has a problem that it has poor compatibility with organic materials.
　また、酸化タングステン系半導体は、可視光応答性光触媒として期待されるが、その価格が酸化チタンの約１０倍と、高価であり、また、戦略物質であるために供給が不安定であるという問題もある。
　さらに、グラファイト状窒化炭素粉末は、そのままでは触媒活性がなく、何らかの活性化手段が必要であるが、非特許文献１記載の白金やルテニウムを用いる活性化手段は高価であり、また、フッ酸を用いる非特許文献２の合成方法は危険であるという問題がある。 Tungsten oxide-based semiconductors are expected to be visible light-responsive photocatalysts, but their price is about 10 times that of titanium oxide, and the supply is unstable because they are strategic substances. There is also.
Further, the graphite-like carbon nitride powder does not have catalytic activity as it is, and some activation means is necessary. However, the activation means using platinum or ruthenium described in Non-Patent Document 1 is expensive, and hydrofluoric acid is used. There is a problem that the synthesis method of Non-Patent Document 2 used is dangerous.
　本発明は、上記の事情に鑑みてなされたものであって、より安価でかつ安全な方法で得られ、紫外光のみならず可視光にも応答性を有する光触媒及びその製造方法を提供することを目的とするものである。 The present invention has been made in view of the above circumstances, and provides a photocatalyst obtained by a cheaper and safer method and responsive to not only ultraviolet light but also visible light, and a method for producing the same. It is intended.
　本発明者らは、上記目的を達成すべく鋭意研究を重ねた結果、グラファイト状窒化炭素粉末を、アルカリ処理又は酸処理することにより、光触媒活性を向上できるという知見を得た。
　本発明はこれらの知見に基づいて完成に至ったものであり、本発明によれば、以下の発明が提供される。
［１］グラファイト状窒化炭素の粉末を、アルカリ処理又は酸処理して得られた粉末を有効成分とすることを特徴とする光触媒。
［２］前記処理が、アルカリ性水溶液又は酸性水溶液中での加熱処理であることを特徴とする前記［１］の光触媒。
［３］比表面積が２０ｍ２／ｇ以上であることを特徴とする前記［１］～［２］の光触媒。
［４］可視光応答性を有することを特徴とする前記［１］～［３］の光触媒。
［５］グラファイト状窒化炭素の粉末を、アルカリ処理又は酸処理して光触媒活性を向上させることを特徴とする、グラファイト状窒化炭素を主成分とする光触媒の製造方法。
［６］前記処理が、アルカリ性水溶液又は酸性水溶液中での加熱処理であることを特徴とする前記［５］の光触媒の製造方法。
［７］前記［１］～［４］のいずれかの光触媒を用いて、空気中の汚染物質及び／又は悪臭を分解除去することを特徴とする空気浄化方法。 As a result of intensive studies to achieve the above object, the present inventors have found that the photocatalytic activity can be improved by subjecting the graphite-like carbon nitride powder to an alkali treatment or an acid treatment.
The present invention has been completed based on these findings, and according to the present invention, the following inventions are provided.
[1] A photocatalyst comprising, as an active ingredient, powder obtained by subjecting graphite-like carbon nitride powder to an alkali treatment or an acid treatment.
[2] The photocatalyst according to [1], wherein the treatment is a heat treatment in an alkaline aqueous solution or an acidic aqueous solution.
[3] The photocatalyst according to the above [1] to [2], wherein the specific surface area is 20 m 2 / g or more.
[4] The photocatalyst according to any one of [1] to [3] above, which has visible light responsiveness.
[5] A method for producing a photocatalyst comprising graphite-like carbon nitride as a main component, wherein the graphite-like carbon nitride powder is subjected to alkali treatment or acid treatment to improve photocatalytic activity.
[6] The method for producing a photocatalyst according to [5], wherein the treatment is a heat treatment in an alkaline aqueous solution or an acidic aqueous solution.
[7] A method for purifying air, comprising using the photocatalyst of any one of [1] to [4] to decompose and remove pollutants and / or bad odors in the air.
　本発明によれば、安価でかつ安全な方法で光触媒を得ることができ、しかも、得られた光触媒は、室内で紫外光が不足していても、可視光を用いて光触媒作用を利用することができるため、現在光触媒として利用されている酸化チタンや酸化タングステンを、安価な材料で代替することができる。 According to the present invention, it is possible to obtain a photocatalyst by an inexpensive and safe method, and the obtained photocatalyst can utilize the photocatalytic action using visible light even if the ultraviolet light is insufficient in the room. Therefore, titanium oxide and tungsten oxide currently used as photocatalysts can be replaced with inexpensive materials.
原料のメラミンを２時間焼成して得られたグラファイト状窒化炭素のＢＥＴ面積、及びさらにＮａＯＨを添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素のＢＥＴ面積と、グラファイト状窒化炭素の合成時の焼成温度の関係を示す図。BET area of graphite-like carbon nitride obtained by firing raw material melamine for 2 hours, and BET area of graphite-like carbon nitride obtained by further adding NaOH to heat treatment at 90 ° C. for 20 hours, and graphite The figure which shows the relationship of the calcination temperature at the time of the synthesis | combination of a shape carbon nitride. 原料のメラミンを２時間焼成して得られたグラファイト状窒化炭素のＮＯｘ除去率、及びさらにＮａＯＨを添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素のＮＯｘ除去率と、グラファイト状窒化炭素の合成時の焼成温度の関係を示す図。NOx removal rate of graphite-like carbon nitride obtained by firing raw material melamine for 2 hours, and NOx removal rate of graphite-like carbon nitride obtained by adding NaOH and heating at 90 ° C. for 20 hours The figure which shows the relationship of the calcination temperature at the time of the synthesis | combination of graphite-like carbon nitride. 水酸化ナトリウム水溶液を添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素の電子スピン共鳴（ＥＳＲ）スペクトルを示す図。The figure which shows the electron spin resonance (ESR) spectrum of the graphite-like carbon nitride obtained by adding sodium hydroxide aqueous solution and heat-processing at 90 degreeC for 20 hours. グラファイト状窒化炭素のＥＳＲスペクトルのｇ＝２．００４付近に観測されたＥＳＲシグナルの積分強度と、グラファイト状窒化炭素の合成時の焼成温度の関係を示す図。The figure which shows the relationship between the integrated intensity | strength of the ESR signal observed in g = 2.004 vicinity of the ESR spectrum of graphite-like carbon nitride, and the calcination temperature at the time of the synthesis | combination of graphite-like carbon nitride. グラファイト状窒化炭素と酸化チタンの可視紫外拡散反射スペクトルを示す図。The figure which shows the visible ultraviolet diffuse reflection spectrum of graphite-like carbon nitride and titanium oxide. グラファイト状窒化炭素の粉末Ｘ線回折図。Fig. 3 is a powder X-ray diffraction diagram of graphitic carbon nitride. 図６におけるメインピークの拡大部分を示す図。The figure which shows the enlarged part of the main peak in FIG. 水酸化ナトリウム水溶液を添加して１３０℃で９０時間加熱処理したグラファイト状窒化炭素粉末によるＮＯｘ除去試験のプロファイルを示す図。The figure which shows the profile of the NOx removal test by the graphite-like carbon nitride powder which heat-processed for 90 hours at 130 degreeC by adding sodium hydroxide aqueous solution. 塩酸を添加して１５０℃で２時間加熱処理したグラファイト状窒化炭素粉末によるＮＯｘ除去試験のプロファイルを示す図。The figure which shows the profile of the NOx removal test by the graphite-like carbon nitride powder which added hydrochloric acid and heat-processed at 150 degreeC for 2 hours. 水酸化ナトリウム水溶液を添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素のＮＯｘ除去率と、照射した光の波長の関係を示す図。The figure which shows the relationship between the NOx removal rate of the graphite-like carbon nitride obtained by adding sodium hydroxide aqueous solution and heat-processing at 90 degreeC for 20 hours, and the wavelength of the irradiated light. 水酸化ナトリウム水溶液を添加して２０時間加熱処理したときの加熱温度とＮＯｘ除去率の関係を示す図。The figure which shows the relationship between heating temperature when adding sodium hydroxide aqueous solution, and heat-processing for 20 hours, and a NOx removal rate. 水酸化ナトリウム水溶液を添加して１１０℃で加熱処理したときの加熱時間とＮＯｘ除去率の関係を示す図。The figure which shows the relationship between heating time when adding sodium hydroxide aqueous solution, and heat-processing at 110 degreeC, and a NOx removal rate. 水酸化ナトリウム水溶液を添加して２０時間加熱処理したときの加熱温度と回収率の関係を示す図。The figure which shows the relationship between heating temperature when a sodium hydroxide aqueous solution is added and heat-processed for 20 hours, and a recovery rate. 未処理のグラファイト状窒化炭素粉末と、水酸化ナトリウム水溶液を添加して９０℃で２０時間加熱処理して得られたグラファイト状窒化炭素粉末による、アセトアルデヒドの光触媒浄化試験結果を示す図。The figure which shows the photocatalyst purification test result of acetaldehyde by the untreated graphite-like carbon nitride powder and the graphite-like carbon nitride powder obtained by adding sodium hydroxide aqueous solution and heat-processing at 90 degreeC for 20 hours. 塩酸を添加して１５０℃で２時間加熱処理して得られたグラファイト状窒化炭素粉末による、トルエンの光触媒浄化試験結果を示す図。The figure which shows the photocatalyst purification test result of toluene by the graphite-like carbon nitride powder obtained by adding hydrochloric acid and heat-processing at 150 degreeC for 2 hours.
　本発明の、可視光応答性を有する光触媒は、グラファイト状窒化炭素の粉末を、アルカリ性水溶液中又は酸性水溶液中で処理することにより、その光触媒活性を向上させることを特徴とするものである。
　すなわち、グラファイト状窒化炭素は、アルカリ性溶液中又は酸性溶液中で処理することで、比表面積が増大し、その光触媒活性が向上する。
　以下、本発明について、具体的な測定結果を用いてより詳細に説明する。 The photocatalyst having visible light responsiveness of the present invention is characterized in that its photocatalytic activity is improved by treating graphite-like carbon nitride powder in an alkaline aqueous solution or an acidic aqueous solution.
That is, by treating the graphite-like carbon nitride in an alkaline solution or an acidic solution, the specific surface area is increased and the photocatalytic activity is improved.
Hereinafter, the present invention will be described in more detail using specific measurement results.
　（グラファイト状窒化炭素粉末の製造）
　グラファイト状窒化炭素は次のようにして合成した。
　メラミン（和光純薬製）３０ｇを、アルミナ製るつぼに入れて蓋をし、５５０℃の電気炉で１時間焼成し、生成物を乳鉢で磨り潰した後、再びるつぼに入れてさらに１時間５５０℃で焼成した。得られる黄色の粉末を乳鉢で磨り潰し、グラファイト状窒化炭素粉末を得た。 (Production of graphite-like carbon nitride powder)
Graphite-like carbon nitride 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 graphite-like carbon nitride powder.
　（グラファイト状窒化炭素のアルカリ処理）
　グラファイト状窒化炭素のアルカリ処理は、次のようにして行った。
　前記のグラファイト状窒化炭素粉末１．０ｇ、０．１０ｍｏｌ／ｌの水酸化ナトリウム（和光純薬）水溶液１００ｍｌを、テフロン（登録商標）製るつぼに入れ、超音波発生器を利用して水酸化ナトリウムを溶解させた。この時の水酸化ナトリウム濃度は０．１ｍｏｌ／ｌ、室温でのｐＨは１３であった。溶液のｐＨを変える場合には水酸化ナトリウムの濃度を適宜変更した。テフロン製るつぼをステンレス製ジャケットに入れ、マグネッチックスターラーで攪拌しながら加熱した。温度はステンレスジャケットの上部で熱電対を用いて測定し、温度調節器、スライダック、マントルヒーターを用いて温度を調節した。所定の温度で２０時間加熱した後、放冷して室温とした。テフロン製るつぼ内の懸濁液を遠心分離し、沈殿物を得た。沈殿物に３０ｍｌの水を加えて攪拌し、超遠心分離機（クボタ製マイクロ冷却遠心機モデル３７００、２００００ｇで１０分）で遠心分離することにより沈殿物を水洗する過程を数回くりかえし、アルカリ処理したグラファイト状窒化炭素を得た。 (Alkali treatment of graphitic carbon nitride)
The alkali treatment of graphite-like carbon nitride was performed as follows.
1.0 g of the graphite-like carbon nitride powder and 100 ml of a 0.10 mol / l aqueous solution of sodium hydroxide (Wako Pure Chemical Industries) are placed in a crucible made of Teflon (registered trademark), and sodium hydroxide is utilized using an ultrasonic generator. Was dissolved. At this time, the sodium hydroxide concentration was 0.1 mol / l, and the pH at room temperature was 13. When changing the pH of the solution, the concentration of sodium hydroxide was appropriately changed. A Teflon 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 a predetermined temperature for 20 hours, it was allowed to cool to room temperature. The suspension in the Teflon crucible was centrifuged to obtain a precipitate. Add 30 ml of water to the precipitate, stir, and repeat the process of washing the precipitate with water several times by centrifuging with an ultracentrifuge (Kubota micro-cooled centrifuge model 3700, 20000 g for 10 minutes), and then alkali treatment Graphitic carbon nitride was obtained.
　（グラファイト状窒化炭素の酸処理）
　グラファイト状窒化炭素の酸処理は、次のようにして行った。
　前記のメラミンを焼成して得られたグラファイト状窒化炭素粉末１．０ｇ及び０．２ｍｏｌ／ｌの塩酸（和光純薬）１００ｍｌを、テフロン製るつぼに入れ、超音波発生器を利用して攪拌した。溶液のｐＨを変える場合には濃塩酸の量を適宜変更した。塩酸以外の酸、例として硫酸や硝酸、を用いる場合には、同程度の水素イオン濃度となるように適宜加える酸試薬（和光純薬製）の濃度を調節した。テフロン製るつぼをステンレス製ジャケットに入れ、マグネッチックスターラーで攪拌しながら加熱した。温度はステンレスジャケットの上部で熱電対を用いて測定し、温度調節器、スライダック、マントルヒーターを用いて温度を調節した。所定の温度で２０時間加熱した後、放冷して室温とした。テフロン製るつぼ内の懸濁液を遠心分離し、沈殿物を得た。沈殿物に３０ｍｌの水を加えて攪拌し、遠心分離することにより沈殿物を水洗する過程を数回くりかえし、酸処理したグラファイト状窒化炭素を得た。 (Acid treatment of graphite-like carbon nitride)
The acid treatment of graphite-like carbon nitride was performed as follows.
1.0 g of graphite-like carbon nitride powder obtained by baking the melamine and 100 ml of 0.2 mol / l hydrochloric acid (Wako Pure Chemical Industries) were placed in a Teflon crucible and stirred using an ultrasonic generator. . When changing the pH of the solution, the amount of concentrated hydrochloric acid was appropriately changed. When using an acid other than hydrochloric acid, for example, sulfuric acid or nitric acid, the concentration of an acid reagent (manufactured by Wako Pure Chemical Industries, Ltd.) added as appropriate was adjusted so that the hydrogen ion concentration was comparable. A Teflon 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 a predetermined temperature for 20 hours, it was allowed to cool to room temperature. The suspension in the Teflon crucible was centrifuged to obtain a precipitate. The process of washing the precipitate with water by adding 30 ml of water to the precipitate and stirring and centrifuging was repeated several times to obtain acid-treated graphite-like carbon nitride.
　図１は、前述のグラファイト状窒化炭素粉末の製造において、メラミンを異なる温度で２時間焼成して得られたグラファイト状窒化炭素粉末の比表面積（□）、及びそのグラファイト状窒化炭素粉末に水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素粉末の比表面積（○）と、焼成温度の関係を示す図である。
　なお、比表面積の測定には窒素を吸着質として用いる多点ＢＥＴ法を利用した。測定にはカンタクローム社製Ａｕｔｏｓｏｒｂ-１を用いた。約０．２ｇの試料を試料ホルダーに入れ、１２０℃で１時間脱気処理をした後、ＢＥＴ面積を測定した。
　図１から、より高温で焼成することにより、ＢＥＴ面積の大きなグラファイト状窒化炭素粉末を調製することができることが分かる。 FIG. 1 shows the specific surface area (□) of graphite-like carbon nitride powder obtained by baking melamine at different temperatures for 2 hours in the production of the above-mentioned graphite-like carbon nitride powder, and the graphite-like carbon nitride powder is hydroxylated. It is a figure which shows the relationship between the specific surface area ((circle)) of the graphite-like carbon nitride powder obtained by adding sodium aqueous solution (concentration 0.1 mol / L), and heat-processing at 90 degreeC for 20 hours, and a calcination temperature.
The specific surface area was measured by a multipoint BET method using nitrogen as an adsorbate. 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 BET area was measured.
From FIG. 1, it can be seen that a graphite-like carbon nitride powder having a large BET area can be prepared by firing at a higher temperature.
　図２は、前記のメラミンを異なる温度で２時間焼成して得られたグラファイト状窒化炭素粉末のＮＯｘ除去率（□）、及びそのグラファイト状窒化炭素粉末に水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素粉末のＮＯｘ除去率（○）と、焼成温度の関係を示す図である。
　なお、ＮＯｘ除去率の測定は次のようにして行った。
　０．２ｇの前記処理したｇ－Ｃ３Ｎ４を少量の水に懸濁させ、幅５０ｍｍ、長さ１００ｍｍのガラス板に全量を塗布し、５０℃で乾燥させて光触媒試験片を調製した。試験片をＪＩＳ　Ｒ１７０１－１に示された光触媒反応容器に設置し、パイレックス（登録商標）製のフタをして、ＮＯガスを１．０ｐｐｍ含む模擬汚染空気を１．０Ｌ／ｍｉｎで流通させた。湿度は２５℃で６％とした。反応容器から出てくる模擬汚染空気中のＮＯおよびＮＯ２ガス濃度を、化学発光式のＮＯｘ測定器（ＭｏｎｉｔｏｒＬａｂｓ社製８８４０）で測定した。白色蛍光灯（東芝製ＦＬ１０Ｗ）の光を、紫外光除去フィルター（住友化学製スミペックスLF-39）を通して、６０００Ｌｘの強度で光触媒試料片に照射し、光触媒作用を観測した。ＮＯｘ濃度（ＮＯガス濃度とＮＯ２ガス濃度の和）を求め、｛［光を照射していないときのＮＯｘ濃度］－［光を照射したときのＮＯｘ濃度］｝／｛［光を照射していないときのＮＯｘ濃度］｝×１００をＮＯｘ除去率とした。 FIG. 2 shows the NOx removal rate (□) of the graphite-like carbon nitride powder obtained by baking the melamine at different temperatures for 2 hours, and the aqueous solution of sodium hydroxide (concentration 0.1 mol / wt). It is a figure which shows the relationship between NOx removal rate ((circle)) of the graphite-like carbon nitride powder obtained by adding L) and heat-processing at 90 degreeC for 20 hours, and a calcination temperature.
The NOx removal rate was measured as follows.
0.2 g of the treated g-C 3 N 4 was suspended in a small amount of water, the whole amount was 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. The test piece was installed 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 obtained 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.
　図２に示すとおり、水酸化ナトリウム水溶液による処理（以下、「ＮａＯＨ処理」という。）をしていない試料では、焼成温度によらず低いＮＯｘ除去率を示した。ＮａＯＨ処理後の試料の場合には、ＮａＯＨ処理前よりも高いＮＯｘ除去率を示し、特に５５０℃付近で最もＮＯｘ除去率が高くなった。
　これらの結果から、先に記載したグラファイト状窒化炭素の製造方法において、窒化炭素の原料を、４５０℃から６５０℃、好ましくは５００℃から６００℃の範囲で焼成することにより得たグラファイト状窒化炭素を、アルカリ性水溶液中で処理することにより、光触媒活性の高いグラファイト状窒化炭素を得られることが分かる。
　また、図１及び２の結果から明らかなように、ＢＥＴ面積が大きいだけでは光触媒活性は大きくならないことが分かった。このことは、次に述べるラジカル生成能力も関係していると考えられる。 As shown in FIG. 2, the sample that was not treated with an aqueous sodium hydroxide solution (hereinafter referred to as “NaOH treatment”) showed a low NOx removal rate regardless of the firing temperature. In the case of the sample after the NaOH treatment, the NOx removal rate was higher than that before the NaOH treatment, and the NOx removal rate was the highest especially around 550 ° C.
From these results, in the method for producing graphite-like carbon nitride described above, graphite-like carbon nitride obtained by firing a carbon nitride raw material in the range of 450 ° C. to 650 ° C., preferably 500 ° C. to 600 ° C. It can be seen that the graphite-like carbon nitride having a high photocatalytic activity can be obtained by treating this in an alkaline aqueous solution.
Further, as apparent from the results of FIGS. 1 and 2, it was found that the photocatalytic activity does not increase only by increasing the BET area. This is considered to be related to the radical generation ability described below.
　（グラファイト状窒化炭素の電子スピン共鳴（ＥＳＲ）のスペクトル）
　水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して９０℃で２０時間加熱処理することにより得られたグラファイト状窒化炭素の電子スピン共鳴（ＥＳＲ）スペクトルを、日本電子製ＴＥ３００ＥＳＲスペクトロメーターを用いて液体窒素温度で測定した。
　図３は、その結果を示すものであり、暗所でも不対電子の存在を示すＥＳＲシグナル強度がｇ＝２．００３～２．００５付近に観測された。可視光を５分間照射するとＥＳＲシグナル強度が増大し、不対電子の量が増大したことを示した。さらに、光の照射を中止すると、ＥＳＲシグナルは暗所での強度に戻った。このように、可視光の照射により、光触媒反応を開始させる不対電子の量が増大することが確認された。 (Electron spin resonance (ESR) spectrum of graphitic carbon nitride)
An electron spin resonance (ESR) spectrum of graphite-like carbon nitride obtained by adding a sodium hydroxide aqueous solution (concentration 0.1 mol / L) and heat-treating at 90 ° C. for 20 hours was measured using a JEOL TE300 ESR spectrometer. And measured at liquid nitrogen temperature.
FIG. 3 shows the result, and an ESR signal intensity indicating the presence of unpaired electrons was observed in the vicinity of g = 2.003 to 2.005 even in the dark. Irradiation with visible light for 5 minutes increased the ESR signal intensity, indicating an increased amount of unpaired electrons. Furthermore, when the light irradiation was stopped, the ESR signal returned to the intensity in the dark place. Thus, it was confirmed that the amount of unpaired electrons for initiating the photocatalytic reaction is increased by irradiation with visible light.
　図４は、前記のメラミンを異なる温度で２時間焼成して得られたグラファイト状窒化炭素粉末について、前記と同様にして測定した、ｇ＝２．００４付近に観測されたＥＳＲシグナルの積分強度と、焼成温度の関係を示すものである。
　５５０℃付近で焼成して得られたグラファイト状窒化炭素に比較的多くの不対電子が存在し、不対電子が存在しやすい性質を有していることが確認された。 FIG. 4 shows the integrated intensity of the ESR signal observed around g = 2.004, measured in the same manner as described above for the graphite-like carbon nitride powder obtained by firing the melamine at different temperatures for 2 hours. This shows the relationship of the firing temperature.
It was confirmed that the graphite-like carbon nitride obtained by firing at around 550 ° C. has a relatively large number of unpaired electrons and has the property that unpaired electrons are likely to exist.
　（グラファイト状窒化炭素の元素分析）
　窒化炭素の原料を５５０℃で焼成して得られたグラファイト状窒化炭素の元素分析を行った。その結果、組成をＣ３Ｎ４＋ｘＨｙＯｚと表記すると、ｘ＝０．５２、ｙ＝１．７４．ｚ＝０．１７と求められた。Ｃ／Ｎ比は０．６６であり、完全なＣ３Ｎ４（ｘ＝ｙ＝ｚ＝０）の理論値の０．７５よりも小さかった。
　また、窒化炭素の原料の焼成温度を５２０℃～６５０℃の間で変化させると、得られたグラファイト状窒化炭素の組成は、焼成温度によって差があるが、０．４＜ｘ＜０．６、１．４＜ｙ＜３．１、０．１＜ｚ＜２．５の範囲にあった。
　いずれの場合も、後述のＸ線回折の結果（図６、７参照）は、グラファイト状窒化炭素様の層状化合物であることを示したので、アミノ基などの欠陥が存在する不完全なＣ３Ｎ４であると同定された。
　また、窒化炭素の原材料としてシアナミドを用いた場合や、シアナミドとメラミンと尿素を混合した場合にも、ほぼ同様の結果が得られたことから、メラミン以外の窒化炭素の原材料を用いても良いし、複数の窒化炭素の原材料を混合しても良い。 (Elemental analysis of graphitic carbon nitride)
Elemental analysis of graphitic carbon nitride obtained by firing a carbon nitride raw material at 550 ° C. was performed. As a result, when the composition is expressed as C 3 N 4 + x H y O z , x = 0.52, y = 1.74. It was determined that z = 0.17. The C / N ratio was 0.66, which was smaller than the theoretical value 0.75 of perfect C 3 N 4 (x = y = z = 0).
Further, when the firing temperature of the carbon nitride raw material is changed between 520 ° C. and 650 ° C., the composition of the obtained graphite-like carbon nitride varies depending on the firing temperature, but 0.4 <x <0.6. 1.4 <y <3.1 and 0.1 <z <2.5.
In either case, the results of X-ray diffraction described later (see FIGS. 6 and 7) showed that the layered compound was like a graphite-like carbon nitride-like, so that incomplete C 3 with defects such as amino groups was present. N 4 was identified.
Also, when cyanamide is used as a raw material for carbon nitride, or when cyanamide, melamine, and urea are mixed, almost the same results are obtained, so a raw material for carbon nitride other than melamine may be used. A plurality of carbon nitride raw materials may be mixed.
　次に、前記５２０℃～６５０℃で焼成して得られた、それぞれのグラファイト状窒化炭素に、前述のＮａＯＨ処理をして光触媒活性が高められたグラファイト状窒化炭素を得、それらについて、元素分析を行ったところ、０．４８＜ｘ＜０．５５、１．４＜ｙ＜２．７、０．３＜ｚ＜０．７の範囲にあった。
　これらの結果から、完全なＣ３Ｎ４の組成（ｘ＝ｙ＝ｚ＝０）よりも、やや窒素が過剰であり、水素と酸素を含んだ組成のグラファイト状窒化炭素様の化合物がより高い光触媒活性を有していることが分かった。 Next, each graphite-like carbon nitride obtained by firing at 520 ° C. to 650 ° C. is subjected to the above-mentioned NaOH treatment to obtain graphite-like carbon nitride having an enhanced photocatalytic activity. As a result, 0.48 <x <0.55, 1.4 <y <2.7, and 0.3 <z <0.7.
From these results, the graphite-like carbon nitride-like compound of the composition containing hydrogen and oxygen is slightly higher than the complete composition of C 3 N 4 (x = y = z = 0). It was found to have photocatalytic activity.
　以上のことから、以下に述べる各実施例では、窒化炭素の原料を５５０℃で焼成して得られたグラファイト状窒化炭素を用いた。
　なお、以下、本明細書において、グラファイト状窒化炭素を、単に「ｇ－Ｃ３Ｎ４」と表記こととするが、前述の不完全な組成のｇ－Ｃ３Ｎ４を含むものとする。 From the above, in each Example described below, graphite-like carbon nitride obtained by firing a carbon nitride raw material at 550 ° C. was used.
Hereinafter, in this specification, the graphitic carbon nitride, but simply to be referred to as "g-C 3 N 4" is intended to include g-C 3 N 4 incomplete composition described above.
　下記の表１は、前記の種々のアルカリ処理及び酸処理で得られたｇ－Ｃ３Ｎ４粉末による、ＮＯｘ除去率とＢＥＴ面積の測定結果を示すものである。 Table 1 below shows the measurement results of the NOx removal rate and the BET area with the g-C 3 N 4 powder obtained by the various alkali treatments and acid treatments described above.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１から明らかなように、従来の方法で得られる、未処理のｇ－Ｃ３Ｎ４（添加物無し）のＮＯｘ除去効率は３．９％だった。水のみを加えて加熱しても、ＮＯｘ除去率は向上しなかった。ＮＯｘ除去試験の結果の詳細については、後に図で示す。
　各種の添加物を加え、加熱処理を約２０時間行い、得られた沈殿を水で洗浄して光触媒試料を得たところ、高いＮＯｘ除去率が得られた。特に、水酸化ナトリウム水溶液を加えて９０℃～１３０℃で加熱処理すると、３０％以上の高いＮＯｘ除去活性が得られた。
　ＮａＯＨ処理の後は、蒸留水で試料を洗浄したほうが、高いＮＯｘ除去率が得られた。これは、Ｎａイオンが多量に残っていると、ＮＯｘの酸化が阻害されると考えられる。ただし、洗浄回数が少なくても、ＮａＯＨ処理をする前より明らかにＮＯｘ除去率が高められているため、洗浄は必須ではないと思われる。また、８回水洗した試料の除去率は低かったので、洗いすぎると除去率が低下すると思われる。
　塩酸による処理（以下、「ＨＣｌ処理」という。）は、塩酸濃度０．２ｍｏｌ／ｌ（ｐＨ＜１）で行うと効果があったが、塩酸濃度０．０２ｍｏｌ／ｌ（ｐＨ約２）では効果が見られなかった。ｐＨ＜１の場合でも、１１０℃では効果が小さかった。このことから、高い水素イオン濃度と１１０℃を超える温度が必要であると考えられる。
　これらの処理によって、ＮＯｘ除去率が増大する時には、アルカリ処理、酸処理のいずれかによらず、比表面積が２０ｍ２／ｇ以上に増大していた。酸処理やアルカリ処理によりｇ－Ｃ３Ｎ４粒子が微小化され、光触媒が著しく向上したと考えられる。 As is apparent from Table 1, the NOx removal efficiency of untreated g-C 3 N 4 (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. Details of the results of the NOx removal test will be shown later in the drawings.
Various additives were added, heat treatment was performed for about 20 hours, and the resulting precipitate was washed with water to obtain a photocatalyst sample. As a result, a high NOx removal rate was obtained. In particular, when a sodium hydroxide aqueous solution was added and heat-treated at 90 ° C. to 130 ° C., a high NOx removal activity of 30% or more was obtained.
After the NaOH treatment, a higher NOx removal rate was obtained by washing the sample with distilled water. This is considered that oxidation of NOx is inhibited when a large amount of Na ions remain. However, even if the number of times of cleaning is small, the NOx removal rate is clearly higher than before the NaOH treatment, and thus cleaning is not considered essential. Moreover, since the removal rate of the sample washed with water 8 times was low, it seems that the removal rate is lowered if it is washed too much.
Treatment with hydrochloric acid (hereinafter referred to as “HCl treatment”) was effective when performed at a hydrochloric acid concentration of 0.2 mol / l (pH <1), but was effective at a hydrochloric acid concentration of 0.02 mol / l (pH of about 2). Was not seen. Even at pH <1, the effect was small at 110 ° C. From this, it is considered that a high hydrogen ion concentration and a temperature exceeding 110 ° C. are necessary.
When the NOx removal rate is increased by these treatments, the specific surface area is increased to 20 m 2 / g or more regardless of either the alkali treatment or the acid treatment. It is considered that gC 3 N 4 particles were miniaturized by acid treatment or alkali treatment, and the photocatalyst was remarkably improved.
　図５は、ｇ－Ｃ３Ｎ４と酸化チタンの可視紫外拡散反射スペクトルを示す図であって、図中、破線は、酸化チタン（ＳＴ－０１）のスペクトル、点線は、アルカリ処理したｇ－Ｃ３Ｎ４のスペクトル、実線は、未処理ｇ－Ｃ３Ｎ４のスペクトルである。可視紫外吸収スペクトロメータ（島津製ＵＶ－３６００）に、拡散反射スペクトル測定用アタッチメント（ＩＳＲ－３１００）を取り付けて測定した。参照物質には硫酸バリウムを用いた。
　図から明らかなように、酸化チタンは約４００ｎｍ以下の光を吸収して光触媒反応に利用でき、ｇ－Ｃ３Ｎ４はより長い波長の可視光（約５００ｎｍまで）を吸収できる。ＮａＯＨを添加して加熱処理しても、大きく変化はしなかった。 FIG. 5 is a diagram showing visible ultraviolet diffuse reflection spectra of gC 3 N 4 and titanium oxide. In the figure, a broken line indicates a spectrum of titanium oxide (ST-01), and a dotted line indicates an alkali-treated g- The spectrum of C 3 N 4 , the solid line is the spectrum of untreated g-C 3 N 4 . 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.
As is apparent from the figure, 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 visible light having a longer wavelength (up to about 500 nm). Even when NaOH was added and heat-treated, there was no significant change.
　図６は、ｇ－Ｃ３Ｎ４の粉末Ｘ線回折図であり、ＲＩＧＡＫＵ製ＲＵ－３００で測定した。図中、下から順に、未処理ｇ－Ｃ３Ｎ４、イオン交換水中、１５０℃で２０時間加熱処理したｇ－Ｃ３Ｎ４、水酸化ナトリウム水溶液中、１５０℃で２０時間加熱したｇ－Ｃ３Ｎ４、ＨＣｌ水溶液中、１５０℃で２０時間加熱処理したｇ－Ｃ３Ｎ４を示す。
　図７は、そのメインピークの拡大部分を示す図であり、実線は、未処理ｇ－Ｃ３Ｎ４、破線は、ＮａＯＨ処理したｇ－Ｃ３Ｎ４を示す。
　図６、７から、２７～２８°に層状化合物に特有のピークがあり、このピークの位置から層間隔の平均は約３．３Åと算出され、ｇ－Ｃ３Ｎ４であることが分かる。図９において、水酸化ナトリウム水溶液を加えて加熱しても回折図にはほとんど変化が見られないが、メインピークを拡大した図７では、わずかに差が見られる。ピークの低角側の回折強度が減少しており、層間隔の大きな成分が、ＮａＯＨ処理により取り除かれている。この結果と、比表面積が増大した結果から、凝集しているｇ－Ｃ３Ｎ４の中で、層間隔が大きく弱い部位が、ＮａＯＨ処理によって破壊され、微細化されたことが分かる。 FIG. 6 is an X-ray powder diffraction pattern of gC 3 N 4 , which was measured with a RU-300 manufactured by RIGAKU. In the figure, in order from the bottom, untreated g-C 3 N 4, deionized water, g-C 3 N 4 and 20 hours of heat treatment at 0.99 ° C., aqueous sodium hydroxide was heated at 0.99 ° C. 20 hours g- C 3 N 4 , g-C 3 N 4 that has been heat-treated at 150 ° C. for 20 hours in an aqueous HCl solution.
FIG. 7 is a diagram showing an enlarged portion of the main peak, where the solid line indicates untreated g—C 3 N 4 and the broken line indicates NaOH-treated g—C 3 N 4 .
6 and 7, there is a peak peculiar to the layered compound at 27 to 28 °, and it can be seen from the position of this peak that the average of the layer spacing is calculated to be about 3.3 cm, and is gC 3 N 4 . In FIG. 9, even when a sodium hydroxide aqueous solution is added and heated, there is almost no change in the diffraction pattern, but in FIG. 7 where the main peak is enlarged, a slight difference is seen. The diffraction intensity on the low angle side of the peak is reduced, and the component having a large layer spacing is removed by NaOH treatment. From this result and the result of the increase in specific surface area, it can be seen that in the agglomerated gC 3 N 4 , the portion where the layer spacing is large and weak was destroyed and refined by NaOH treatment.
　以上のとおり、本発明に用いるアルカリ性水溶液としては、水酸化ナトリウム溶液が最も良く、水酸化カリウム溶液も用いることができる。１．４　ｍｏｌ／ｌの濃度の水酸化ナトリウム溶液を用いると、大部分のｇ－Ｃ３Ｎ４が変質して回収率が低下したため、好ましくは１．０　ｍｏｌ／ｌ以下の濃度、さらに好ましくは０．５　ｍｏｌ／ｌ以下の濃度のアルカリ性水溶液を用いる。酸性水溶液としては、強酸の水溶液が使用できるが、ｐＨ１以下にすることが好ましい。
　また、これらの水溶液による処理は室温で行ってもある程度効果があるが、７０℃以上で行うと効果が大きいが、１３０℃を超えるとｇ－Ｃ３Ｎ４の回収率が低下するため、１５０℃を超えない温度で処理することが好ましい。さらに１１０℃を超えない温度が好ましい。純水中で加熱しても活性は向上しないので、酸性またはアルカリ性水溶液中で加熱処理する必要がある。 As described above, as the alkaline aqueous solution used in the present invention, a sodium hydroxide solution is the best, and a potassium hydroxide solution can also be used. When a sodium hydroxide solution having a concentration of 1.4 mol / l was used, most of the g-C 3 N 4 was denatured and the recovery rate was lowered, so the concentration was preferably 1.0 mol / l or less, more preferably Uses an alkaline aqueous solution having a concentration of 0.5 mol / l or less. As the acidic aqueous solution, an aqueous solution of a strong acid can be used, but the pH is preferably 1 or less.
In addition, the treatment with these aqueous solutions is effective to some extent even at room temperature, but the effect is large when performed at 70 ° C. or higher, but the recovery rate of g-C 3 N 4 decreases when it exceeds 130 ° C. It is preferable to process at a temperature not exceeding ° C. Furthermore, the temperature which does not exceed 110 degreeC is preferable. Since activity does not improve even when heated in pure water, it is necessary to heat-treat in an acidic or alkaline aqueous solution.
　（ＮＯｘ除去試験）
　以下、ＮＯｘ除去試験の結果を図に示す。
　図８は、水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して、１３０℃で９０時間加熱処理したｇ－Ｃ３Ｎ４粉末によるＮＯｘ除去試験のプロファイルを示す図であり、図９は、塩酸（濃度０．２ｍｏｌ／Ｌ）を添加して、１５０℃で２時間加熱処理したｇ－Ｃ３Ｎ４粉末によるＮＯｘ除去試験のプロファイルを示す図である。
　図中、点線は、ＮＯ濃度、１点破線は、ＮＯ２濃度、実線は、ＮＯｘ（ＮＯとＮＯ２の和）濃度、水平の点線は、ＮＯｘの初期濃度を示している。
　いずれの場合も、光を当てている間ＮＯの濃度が低下し、光照射を止めると濃度が元に戻ることから、光触媒反応が起こっていることが分かる。ＮＯの一部はＮＯ２になり、さらにＨＮＯ３となって光触媒に吸着し、流通ガス中から取り除かれる。初期濃度とＮＯｘの線で囲まれた部分の面積が、取り除かれたＮＯｘ量に相当する。 (NOx removal test)
The results of the NOx removal test are shown in the figure below.
FIG. 8 is a diagram showing a profile of a NOx removal test using gC 3 N 4 powder that was heated for 90 hours at 130 ° C. with an aqueous sodium hydroxide solution (concentration 0.1 mol / L). FIG. 3 is a view showing a profile of a NOx removal test using g-C 3 N 4 powder which was heated at 150 ° C. for 2 hours with hydrochloric acid (concentration 0.2 mol / L) added.
In the figure, the dotted line indicates the NO concentration, the dashed line indicates the NO 2 concentration, the solid line indicates the NO x (sum of NO and NO 2 ) concentration, and the horizontal dotted line indicates the initial concentration of NO x .
In either case, the concentration of NO decreases while the light is applied, and the concentration returns to the original level when the light irradiation is stopped, indicating that a photocatalytic reaction is occurring. 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.
　図１０は、水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して９０℃で２０時間加熱処理することにより得られたｇ－Ｃ３Ｎ４のＮＯｘ除去率と、照射した光の波長の関係を示した図である。光源として２００Ｗのキセノンランプを用い、短波長の光をカットオフするフィルターのカットオフ波長を変えながら、ＮＯｘ除去率を測定した。横軸はフィルターの透過限界波長を示す。ｇ－Ｃ３Ｎ４は５００ｎｍ付近の波長の可視光までを利用できることが確認された。また、４００ｎｍのフィルターでのＮＯｘ除去率よりも３４５ｎｍのフィルターでのＮＯｘ除去率が高いことから、紫外線も利用できることが確認された。 FIG. 10 shows the NOx removal rate of gC 3 N 4 obtained by adding a sodium hydroxide aqueous solution (concentration 0.1 mol / L) and heat-treating at 90 ° C. for 20 hours, and the wavelength of irradiated light. FIG. Using a 200 W xenon lamp as the light source, the NOx removal rate was measured while changing the cutoff wavelength of a filter that cuts off short-wavelength light. The horizontal axis represents the transmission limit wavelength of the filter. It was confirmed that gC 3 N 4 can use even visible light having a wavelength near 500 nm. Moreover, since the NOx removal rate with a 345 nm filter is higher than the NOx removal rate with a 400 nm filter, it was confirmed that ultraviolet rays can also be used.
　図１１は、水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して２０時間加熱処理したときの加熱温度とＮＯｘ除去率の関係を示す図である。なお、図中の点線は、未処理の場合のＮＯｘ除去率を示している。
　図から明らかなように、９０℃から１３０℃程度が高いＮＯｘ除去率を示し、１５０℃になると低下する場合がある。 FIG. 11 is a diagram showing the relationship between the heating temperature and the NOx removal rate when a sodium hydroxide aqueous solution (concentration 0.1 mol / L) is added and heat-treated for 20 hours. The dotted line in the drawing indicates the NO x removal rate if untreated.
As is apparent from the figure, a high NOx removal rate is exhibited when the temperature is about 90 ° C. to 130 ° C., and may decrease when the temperature reaches 150 ° C.
　図１２は、水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して１１０℃で加熱処理したときの加熱時間とＮＯｘ除去率の関係を示す図である。
　２０時間程度で高いＮＯｘ除去率を示し、９０時間加熱すると低下した。 FIG. 12 is a diagram showing the relationship between the heating time and the NOx removal rate when a sodium hydroxide aqueous solution (concentration 0.1 mol / L) is added and heat treatment is performed at 110 ° C.
A high NOx removal rate was exhibited in about 20 hours, and decreased when heated for 90 hours.
　図１３は、水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して２０時間加熱処理したときの加熱温度と回収率の関係を示す図である。回収率は（加熱処後のｇ－Ｃ３Ｎ４重量）／（加熱処理前の重量）×１００で定義した。
　加熱処理により一部のｇ－Ｃ３Ｎ４が溶解するとともに、微細化されて遠心分離器では沈殿させることができないため、回収できる量が減少する。１１０℃を超えると、回収率は著しく低くなった。 FIG. 13 is a diagram showing the relationship between the heating temperature and the recovery rate when a sodium hydroxide aqueous solution (concentration: 0.1 mol / L) is added and heat-treated for 20 hours. The recovery rate was defined as (g-C 3 N 4 weight after heat treatment) / (weight before heat treatment) × 100.
A part of g-C 3 N 4 is dissolved by the heat treatment, and is refined and cannot be precipitated in the centrifuge, so that the recoverable amount is reduced. Above 110 ° C., the recovery rate was significantly reduced.
　図１４は、未処理のｇ－Ｃ３Ｎ４粉末、及び水酸化ナトリウム水溶液（濃度０．１ｍｏｌ／Ｌ）を添加して９０℃で２０時間加熱処理して得られたｇ－Ｃ３Ｎ４粉末による、アセトアルデヒドの光触媒浄化試験結果を示す図である。
　測定は次のようにして行った。０．２ｇのＮａＯＨ処理したｇ－Ｃ３Ｎ４を少量の水に懸濁させ、幅５０ｍｍ、長さ１００ｍｍのガラス板に全量を塗布し、５０℃で乾燥させて光触媒試験片を調製した。試験片をＪＩＳ　Ｒ１７０１－１に示された光触媒反応容器に設置し、パイレックス製のフタをして、アセトアルデヒドを約２ｐｐｍ含む模擬汚染空気を０．５Ｌ／ｍｉｎで流通させた。湿度は２５℃で６％とした。反応容器から出てくる模擬汚染空気中のアセトアルデヒド濃度を、ＦＩＤ式検出器を備えたガスクロマトグラフ（島津製ＧＣ－１４Ｂ）で測定した。ガスクロマトグラフの校正には５ｐｐｍのアセトアルデヒド標準ガスを用いた。ＣＯ２濃度は赤外吸収式のＣＯ２計（Ｔｈｅｒｍｏｅｌｅｃｔｒｏｎ社製４１Ｃ）で測定した。白色蛍光灯（東芝製ＦＬ１０Ｗ）の光を、紫外光除去フィルター（住友化学製スミペックスLF-39）を通して、６０００Ｌｘの強度で光触媒試料片に照射し、光触媒作用を観測した。このフィルターにより、３８０ｎｍ未満の紫外光の強度は、０．１％未満になる。｛［光を照射していないときのアセトアルデヒド濃度］－［光を照射したときのアセトアルデヒド濃度］｝/［光を照射していないとアセトアルデヒド濃度］×１００をアセトアルデヒド除去率とした。
　光照射を時間ゼロで開始すると、水酸化ナトリウム水溶液を添加して加熱処理して得られたｇ－Ｃ３Ｎ４粉末を用いた場合（△）にはアセトアルデヒド濃度が低下し、同時にＣＯ２が発生し、光触媒反応によりアセトアルデヒドがＣＯ２にまで酸化された。一方、未処理のｇ－Ｃ３Ｎ４を用いた場合（○）にはほとんどアセトアルデヒド濃度が低下せず、ＣＯ２の発生量も少なかった。 Figure 14 is the untreated g-C 3 N 4 powder, and an aqueous solution of sodium hydroxide (concentration 0.1 mol / L) was added to the obtained by 20 hours of heat treatment at 90 ℃ g-C 3 N 4 It is a figure which shows the photocatalyst purification test result of acetaldehyde by powder.
The measurement was performed as follows. 0.2 g of NaOH-treated g—C 3 N 4 was suspended in a small amount of water, the whole amount was 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. The test piece was placed in a photocatalytic reaction vessel shown in JIS R1701-1, covered with a Pyrex lid, and simulated contaminated air containing about 2 ppm of acetaldehyde was circulated at 0.5 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 (GC-14B manufactured by Shimadzu) equipped with an FID type detector. For calibration of the gas chromatograph, 5 ppm acetaldehyde standard gas was used. The CO 2 concentration was measured with an infrared absorption CO 2 meter (41C manufactured by Thermoelectron). 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. With this filter, the intensity of ultraviolet light of less than 380 nm is less than 0.1%. {[Concentration of acetaldehyde when not irradiated with light] − [Concentration of acetaldehyde when irradiated with light]} / [Concentration of acetaldehyde when irradiated with no light] × 100 was defined as an acetaldehyde removal rate.
When light irradiation is started at time zero, the concentration of acetaldehyde decreases when g-C 3 N 4 powder obtained by adding a sodium hydroxide aqueous solution and heat-treating (Δ), and at the same time, CO 2 is reduced. Acetaldehyde was oxidized to CO 2 by photocatalysis. On the other hand, when untreated g—C 3 N 4 was used (◯), the acetaldehyde concentration was hardly lowered and the amount of CO 2 generated was small.
　同様にして塩酸（濃度０．２ｍｏｌ／Ｌ）を添加して、１５０℃で２０時間加熱処理して得られたｇ－Ｃ３Ｎ４によるアセトアルデヒドの光触媒浄化試験を行い、表２に結果をまとめた。
　アセトアルデヒド除去率は、ＮａＯＨ処理をした試料で４．９％、ＨＣｌ処理をした試料で１４．９％、未処理のｇ－Ｃ３Ｎ４試料で０．３％だった。ＣＯ２発生量についても、水酸化ナトリウム水溶液または塩酸を添加した試料で有意に高い値を示し、光触媒活性が向上したことをした。 Similarly, a photocatalytic purification test of acetaldehyde with g-C 3 N 4 obtained by adding hydrochloric acid (concentration 0.2 mol / L) and heat-treating at 150 ° C. for 20 hours was conducted, and the results are summarized in Table 2. It was.
The removal rate of acetaldehyde was 4.9% for the sample treated with NaOH, 14.9% for the sample treated with HCl, and 0.3% for the untreated g-C 3 N 4 sample. The amount of CO 2 generated was also significantly higher in the sample to which an aqueous sodium hydroxide solution or hydrochloric acid was added, indicating that the photocatalytic activity was improved.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　図１５は、ＨＣｌ添加して１５０℃で２時間加熱処理して得られたｇ－Ｃ３Ｎ４粉末による、トルエンの光触媒浄化試験結果を示す図である。
　測定は、前述のアセトアルデヒドの光触媒浄化試験と同様にして行った。
　光を当てない状態でトルエンを含むガスを光触媒に接触させると吸着により濃度が減少した。徐々に濃度が導入濃度に近づいてきたので光を当てると、わずかだが濃度が減少し、同時にＣＯ２の発生が確認され（図省略）、トルエンが分解されたことを示した。
　表３に、トルエン除去試験結果を示す。
　未処理のｇ－Ｃ３Ｎ４粉末はトルエンを除去（分解）できなかった。一方、ＮａＯＨ処理をしたｇ－Ｃ３Ｎ４粉末と、ＨＣｌ処理をしたｇ－Ｃ３Ｎ４粉末はトルエンを分解し、ＣＯ２を発生した。 FIG. 15 is a graph showing the results of a toluene photocatalytic purification test using g-C 3 N 4 powder obtained by adding HCl and heat-treating at 150 ° C. for 2 hours.
The measurement was performed in the same manner as the above-mentioned photocatalytic purification test for acetaldehyde.
When a gas containing toluene was brought into contact with the photocatalyst without exposure to light, the concentration decreased due to adsorption. The concentration gradually approached the introduced concentration, so when exposed to light, the concentration decreased slightly, and at the same time the generation of CO 2 was confirmed (not shown), indicating that toluene was decomposed.
Table 3 shows the results of the toluene removal test.
Untreated g-C 3 N 4 powder could not remove (decompose) toluene. On the other hand, the g-C 3 N 4 powder of NaOH treatment, g-C 3 N 4 powder of HCl treatment decomposes the toluene was generate CO 2.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　本発明の光触媒活性を向上させたグラファイト状窒化炭素の粉末を、何らかの基材に塗布することで、光触媒材料として利用することができ、この材料を用いると、光のエネルギーを利用して、空気を浄化することができる。また、この材料は、アセトアルデヒド、トルエン、ＮＯｘの分解に利用でき、類似の化合物の分解にも使える。 The graphite-like carbon nitride powder with improved photocatalytic activity of the present invention can be used as a photocatalytic material by applying it to any substrate, and when this material is used, the energy of light is used to produce air. Can be purified. This material can also be used to decompose acetaldehyde, toluene, and NOx, and can also be used to decompose similar compounds.

Claims (7)

  1. 　グラファイト状窒化炭素の粉末を、アルカリ処理又は酸処理して得られた粉末を有効成分とすることを特徴とする光触媒。 A photocatalyst comprising, as an active ingredient, powder obtained by subjecting graphite-like carbon nitride powder to an alkali treatment or an acid treatment.
  2. 　前記処理が、アルカリ性水溶液又は酸性水溶液中での加熱処理であることを特徴とする請求項１に記載の光触媒。 The photocatalyst according to claim 1, wherein the treatment is a heat treatment in an alkaline aqueous solution or an acidic aqueous solution.
  3. 　比表面積が２０ｍ２／ｇ以上であることを特徴とする請求項１又は２に記載の光触媒。 The photocatalyst according to claim 1 or 2, wherein the specific surface area is 20 m 2 / g or more.
  4. 　可視光応答性を有することを特徴とする請求項１～３のいずれか１項に記載の光触媒。 The photocatalyst according to any one of claims 1 to 3, which has visible light responsiveness.
  5. 　グラファイト状窒化炭素の粉末を、アルカリ処理又は酸処理して光触媒活性を向上させることを特徴とする、グラファイト状窒化炭素を主成分とする光触媒の製造方法。 A method for producing a photocatalyst comprising graphite-like carbon nitride as a main component, wherein the graphite-like carbon nitride powder is subjected to alkali treatment or acid treatment to improve photocatalytic activity.
  6. 　前記処理が、アルカリ性水溶液又は酸性水溶液中での加熱処理であることを特徴とする請求項５に記載の光触媒の製造方法。 The method for producing a photocatalyst according to claim 5, wherein the treatment is a heat treatment in an alkaline aqueous solution or an acidic aqueous solution.
  7. 　請求項１～４のいずれか１項に記載の光触媒を用いて、空気中の汚染物質及び／又は悪臭を分解除去することを特徴とする空気浄化方法。 An air purification method comprising decomposing and removing pollutants and / or odors in the air using the photocatalyst according to any one of claims 1 to 4.
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