JP6088244B2 - Method for producing carbon-doped photocatalyst - Google Patents

Description

The present invention relates to a method for producing a carbon-doped photocatalyst.

  Titanium oxide is widely known as a photocatalyst that exhibits catalytic action when irradiated with light. When titanium oxide is irradiated with ultraviolet rays, the photocatalytic activity of titanium oxide decomposes harmful substances such as nitrogen oxide, which is a cause of air pollution, and acetaldehyde, which is thought to contribute to sick house syndrome. The Such photocatalytic activity of titanium oxide is expressed by the absorption of ultraviolet rays contained in a part of natural light such as sunlight, incandescent lamps and fluorescent lamps. This is much lower than For this reason, titanium oxide was insufficient as photocatalytic activity under natural light.

  For this reason, a photocatalyst that can be used in the visible light region is desired, and a method of doping titanium dioxide with a transition metal (for example, Patent Document 1), a method of doping titanium dioxide with nitrogen (for example, Patent Document 2), and the like. Proposed.

  However, these methods are complicated, and the photocatalysts produced by these methods are still not fully satisfactory in photocatalytic activity under visible light.

JP-A-9-262482 JP 2007-90336 A

The present invention has been conceived under the circumstances described above, and an object thereof is to provide a method for easily producing a carbon-doped photocatalyst having a higher photocatalytic activity under visible light. .

In the method for producing a carbon-doped photocatalyst provided by the present invention, titanium butoxide is mixed in an ethanol aqueous solution, heated to 150 to 220 ° C. to hydrolyze the titanium butoxide, and dried to be doped with carbon. the first step to obtain an intermediate product, and in order to suppress heat loss of the doped carbon in the intermediate product, and wherein the second step, the including firing the intermediate product at 150 to 300 ° C. To do.

  Preferably, the firing temperature in the second step is 160 to 270 ° C.

  Preferably, the titanium butoxide is titanium tetraisobutoxide.

Preferably, the drying is vacuum drying.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

An example of the manufacturing process of the photocatalyst concerning this invention is shown. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown .

  The manufacturing process of the photocatalyst according to the present invention is shown in FIG. This production method includes a step of preparing an aqueous solution of ethanol which is an example of an organic solvent (S1), a step of mixing titanium butoxide with the aqueous ethanol solution (S2), and a step of hydrothermally reacting the mixture obtained in S2 (S3). ), Centrifuging the first intermediate product obtained in S3 (S4), vacuum-drying the second intermediate product obtained in S4, for example, at 60 ° C. for 12 hours (S5), and S5 A step (S6) of firing the obtained third intermediate product at a predetermined temperature is included.

  As titanium butoxide, titanium tetraisobutoxide is preferably used.

  In S3, the hydrothermal reaction is performed, for example, at 150 to 220 ° C. for 2 hours, and more preferably, the hydrothermal reaction is performed at about 190 ° C.

  In S6, baking is performed at 150 to 300 ° C., for example, for 1 hour, and more preferably baking is performed at 160 to 270 ° C., for example, for 1 hour.

  The photocatalyst produced by such a method exhibits excellent visible light absorption ability. This is presumably because the titanium oxide was effectively doped with the carbon used in the ethanol used as the solvent and the titanium butoxide used as the titanium source.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

[Example 1]
(1) Production of photocatalyst A mixture of 13 ml of titanium tetraisobutoxide and 35 ml of an aqueous ethanol solution (ethanol: water = 30: 5) was placed in a pressure vessel and reacted at 190 ° C. for 2 hours. Subsequently, the product was centrifuged, washed four times with distilled water and ethanol, and vacuum-dried at 60 ° C. for 12 hours (hereinafter, the product at this stage is referred to as “initial product”). Next, this initial product was baked at 265 ° C. for 1 hour to obtain Sample 1. The average particle size of Sample 1 was 11.7 nm.

(2) Nitrogen monoxide (NO) decomposition measurement The photocatalytic activity of Sample 1 obtained by the above method was evaluated by NO gas decomposition measurement at various wavelengths. The decomposition of the NO gas was performed using a flow reactor having an internal volume of 373 cm ³ . In this measurement, 0.2 g of the powder of Sample 1 was placed in a hollow portion of a glass holder (length 20 mm, width 16 mm, depth 0.5 mm), and this glass holder was placed on the center bottom of the reactor. A 450 W high-pressure mercury lamp was used as the light source, and the wavelength of light irradiated to the reactor was adjusted by selecting a filter. As a filter, Pyrex (registered trademark) is used for wavelengths exceeding 290 nm (> 290 nm), Kenko (trade name: L41 Super Pro) is used for wavelengths exceeding 400 nm (> 400 nm), and wavelengths exceeding 510 nm ( For> 510 nm), a Fuji triacetyl cellulose filter was used. As a gas to be circulated in the reactor, a gas (NO concentration 1 ppm) in which nitrogen gas having a NO concentration of 2 ppm and air were mixed at a ratio of 1: 1 was used, and the flow rate of the mixed gas was 200 cm ³ . The NO concentration of the gas that passed through the reactor was measured using a nitrogen oxide analyzer (manufactured by Yanaco, trade name: ECL-88A). FIG. 2 shows the NO decomposition photocatalytic activity when irradiated with light of each wavelength described above.

[Example 2]
The initial product produced in Example 1 was baked at 165 ° C. for 1 hour to obtain Sample 2. Sample 2 had an average particle size of 11.6 nm. For the NO decomposition measurement, the same apparatus as in Example 1 was used, and the same amount (0.2 g) of Sample 2 as in Example 1 was set in the reactor in the same manner as in Example 1. The supply mode of NO gas and the mode of light irradiation were the same as in Example 1. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown in FIG.

[Comparative Example 1]
The initial product formed in Example 1 was baked at 400 ° C. for 1 hour to obtain Sample 3. Sample 3 had an average particle size of 12.2 nm. For the NO decomposition measurement, the same apparatus as in Example 1 was used, and the same amount (0.2 g) of Sample 3 as in Example 1 was set in the reactor in the same manner as in Example 1. The supply mode of NO gas and the mode of light irradiation were the same as in Example 1. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown in FIG.

[Comparative Example 2]
In this comparative example, the initial product in Example 1 was used as Sample 4. Sample 4 had an average particle size of 11.5 nm. For the NO decomposition measurement, the same apparatus as in Example 1 was used, and the same amount (0.2 g) of Sample 4 as in Example 1 was set in the reactor in the same manner as in Example 1. The supply mode of NO gas and the mode of light irradiation were the same as in Example 1. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown in FIG.

[Comparative Example 3]
In this comparative example, a commercially available titanium oxide powder (manufactured by Degussa, trade name: P25) was used as Sample 5. For the NO decomposition measurement, the same apparatus as in Example 1 was used, and the same amount (0.2 g) of Sample 5 as in Example 1 was set in the reactor in the same manner as in Example 1. The supply mode of NO gas and the mode of light irradiation were the same as in Example 1. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown in FIG.

[Comparative Example 4]
In this comparative example, a mixture of 13 ml of titanium chloride and 35 ml of an aqueous ethanol solution (ethanol: water = 30: 5) was placed in a pressure vessel and reacted at 190 ° C. for 2 hours. The product was then centrifuged, washed 4 times with distilled water and ethanol, vacuum dried at 60 ° C. for 12 hours, and then the product was calcined at 265 ° C. for 1 hour to obtain Sample 6. Sample 6 had an average particle size of 17.2 nm. For the NO decomposition measurement, the same apparatus as in Example 1 was used, and the same amount (0.2 g) of Sample 6 as in Example 1 was set in the reactor in the same manner as in Example 1. The supply mode of NO gas and the mode of light irradiation were the same as in Example 1. The NO decomposition photocatalytic activity when irradiated with light of each wavelength is shown in FIG.

  As can be seen from the measurement data for each sample shown in FIG. 2, the NO decomposition photocatalytic activity in the visible light region in Sample 1 (Example 1) and Sample 2 (Example 2) is 37% NO removal rate, In particular, Sample 1 (Example 1) surpasses the NO decomposition photocatalytic activity of general nitrogen-doped titanium oxide under visible light, but other Samples 3 to 6 (Comparative Examples 1 to 3). For 4), the NO removal rate is all below 20%.

  As described above, the photocatalytic activity of Samples 1 and 2 (Examples 1 and 2) under visible light is such that ethanol used as a solvent in the production process and carbon in titanium butoxide used as a titanium source were oxidized. It is considered that titanium was effectively doped, but the calcination temperature for the initial product in the production process is greatly related to this catalytic activity. That is, when the firing temperature is increased to 400 ° C. (Sample 3, Comparative Example 1), the NO decomposition photocatalytic activity is remarkably lowered, which is considered because the doped carbon is lost by heat. It is done. From the tendency of FIG. 2, it is estimated that the firing temperature for the initial product should be maintained at about 150 to 300 ° C. in order to maintain the NO removal rate as high as about 30% or more.

Claims (4)

A first step of mixing titanium butoxide in an aqueous ethanol solution, heating to 150-220 ° C. to hydrolyze the titanium butoxide, and drying it to obtain a carbon-doped intermediate product; and
A second step of firing the intermediate product at 150 to 300 ° C. in order to suppress heat dissipation of the carbon doped in the intermediate product;
Characterized in including that the method of manufacturing a carbon-doped photocatalyst. The method for producing a carbon-doped photocatalyst according to claim 1, wherein the firing temperature in the second step is 165 to 265 ° C. The method for producing a carbon-doped photocatalyst according to claim 1 or 2, wherein the titanium butoxide is titanium tetraisobutoxide. The method for producing a carbon-doped photocatalyst according to any one of claims 1 to 3, wherein the drying is vacuum drying.

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