JP2017104809A - Method for producing photocatalyst-silica composite molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a photocatalyst-silica composite molding that makes it possible to produce a composite molding having photocatalyst fine particles dispersed in silica by a simple process, and facilitates bulk molding.SOLUTION: A method for producing a photocatalyst-silica composite molding is characterized by mixing silica fine particles, photocatalyst fine particles and organic polymers to obtaine a precursor, before firing the precursor.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a photocatalyst-silica composite molded article suitable as a purifier such as water or air contaminated with harmful chemical substances.

  In recent years, due to increasing interest in environmental issues, pollution of water, soil, air, etc. due to harmful chemical substances (volatile organic compounds, endocrine scattering materials, etc.), which is one of the causes of environmental pollution, is regarded as a problem. There is an increasing need for removal of hazardous chemicals. As a method for removing harmful chemical substances, there is a method for decomposing and removing harmful chemical substances using photocatalytically active fine particles such as titania. For example, a coating film containing photocatalyst fine particles is formed on a substrate surface and used for air purification.

  In order to enhance the decomposition effect of harmful chemical substances by photocatalyst particles, a method of supporting photocatalyst fine particles on the surface of a porous substrate having an adsorption action has been proposed. Examples of the method for supporting the photocatalyst fine particles include a high-frequency sputtering method, a vapor deposition method, an ion plating method, and a method in which a porous substrate is impregnated or coated with a photocatalyst particle dispersion and then heated and fired (for example, Patent Documents). 1-3). However, this method has a problem that it is difficult to increase the amount of photocatalyst fine particles supported on the base material and it is difficult to adjust the amount supported. Therefore, Patent Document 4 proposes a method for obtaining titania-composite porous silica photocatalyst particles by dispersing titania nanoparticles in a solution comprising a triblock copolymer and water glass as a silica source, followed by heating and firing. Yes.

JP 2003-73997 A JP 2002-45650 A Japanese Patent No. 3321733 JP 2014-024041 A

  The method described in Patent Document 4 has a problem that the production process is complicated, and the reaction conditions of the solution must be strictly regulated in order to obtain silica particles having a predetermined structure. Furthermore, the method described in Patent Document 4 has a problem that it is difficult to produce a bulk molded body.

  In view of the above, the present invention provides a method for producing a photocatalyst-silica composite molded body in which a composite molded body in which photocatalyst fine particles are dispersed in silica can be produced by a simple method and bulk molding is also easy. With the goal.

  The method for producing a photocatalyst-silica composite molded article of the present invention is characterized in that a precursor is obtained by mixing silica fine particles, photocatalyst fine particles and an organic polymer, and then the precursor is fired.

  The silica fine particles and the organic polymer are bonded to each other to form a three-dimensional matrix, and a precursor in which the photocatalyst fine particles are dispersed in the matrix is obtained. By calcining the obtained precursor, a photocatalyst-silica composite molded body in which photocatalyst fine particles are dispersed in silica can be obtained. Thus, according to the present invention, it is not necessary to strictly regulate the reaction conditions of the raw material, and the photocatalyst-silica composite molded body can be produced by a relatively simple method. In addition, the photocatalyst-silica composite molded body obtained by the method of the present invention has a porous structure, and has a structure in which photocatalyst fine particles are supported in each pore. Thereby, the site which functions as a catalyst in the molded body increases, and the catalytic effect can be enhanced.

  In the method for producing a photocatalyst-silica composite molded article of the present invention, it is preferable to mix 1 to 100 parts by mass of an organic polymer with respect to 100 parts by mass of the total amount of silica fine particles and photocatalyst fine particles.

  In the method for producing a photocatalyst-silica composite molded article of the present invention, the organic polymer is preferably at least one selected from vinyl resins, acrylic resins and amide resins. By using these organic polymers, a matrix having a three-dimensional structure can be easily formed when mixed with silica fine particles, and a bulk precursor can be easily obtained. Moreover, it becomes easy to obtain a porous photocatalyst-silica composite molded body after firing the precursor.

  In the method for producing a photocatalyst-silica composite molded article of the present invention, the organic polymer is preferably polyvinyl alcohol.

  In the method for producing a photocatalyst-silica composite molded article of the present invention, the photocatalyst fine particles are at least one selected from titanium oxide, tin oxide, zinc oxide, vanadium oxide, bismuth oxide, tungsten oxide, iron oxide, and strontium titanate. Preferably there is.

  In the method for producing a photocatalyst-silica composite molded article of the present invention, the photocatalyst fine particles are preferably titanium oxide.

  The precursor for a photocatalyst-silica composite molded article of the present invention is a precursor for a photocatalyst composite molded article containing silica fine particles, photocatalyst fine particles and an organic polymer, and is constituted by bonding silica fine particles and an organic polymer to each other. The photocatalyst fine particles are dispersed in the formed matrix.

  According to the present invention, a composite molded body in which photocatalyst fine particles are dispersed in silica can be produced by a simple method, and bulk molding is also easy.

  The method for producing a photocatalyst-silica composite molded article of the present invention is characterized in that a precursor is obtained by mixing silica fine particles, photocatalyst fine particles and an organic polymer, and then the precursor is fired.

  The average particle diameter (D50) of the silica fine particles is preferably 100 nm or less, particularly preferably 5 to 50 nm. If the average particle diameter of the silica fine particles is too large, the porous property of the photocatalyst-silica composite molded body is lowered, and the catalytic effect is likely to be lowered. Moreover, the sintering state becomes insufficient due to a decrease in the reactivity between the silica fine particles during firing of the precursor, and the resulting photocatalyst-silica composite molded product tends to be inferior in mechanical strength.

  Examples of the photocatalyst fine particles include titanium oxide, tin oxide, zinc oxide, vanadium oxide, bismuth oxide, tungsten oxide, iron oxide (ferric oxide), and strontium titanate. These can be used individually or in mixture of 2 or more types. Of these, titanium oxide having a high catalytic activity effect is preferable. As titanium oxide, nitrogen-doped titanium oxide, oxygen-deficient titanium oxide, or the like can also be used.

  The particle size of the photocatalyst fine particles is not particularly limited, and those having a particle size of micro order to nano order can be used. The particle size is preferably as small as possible from the viewpoint of increasing the contact area between the photocatalyst fine particles and the substance to be decomposed. Accordingly, the average particle diameter (D50) of the photocatalyst fine particles is preferably 10 μm or less, 1 μm or less, particularly 100 nm. The lower limit of the average particle diameter of the photocatalyst fine particles is not particularly limited, but is practically 1 nm or more, particularly 2 nm.

  In the present invention, the average particle diameter (D50) refers to a value measured by a laser diffraction method.

  The mixing ratio of the silica fine particles and the photocatalyst fine particles is not particularly limited, and can be appropriately set in a mass ratio, for example, in the range of silica fine particles: photocatalyst fine particles = 40: 60 to 95: 5. Preferably it is 55: 45-90: 10, More preferably, it is 50: 50-80: 20. If the proportion of silica particles is too large (the proportion of photocatalyst particles is too small), the photocatalytic effect will be insufficient, and if the proportion of silica particles is too small (the proportion of photocatalyst particles is too large), the formation of the silica skeleton will be insufficient. It becomes difficult to obtain a bulk precursor.

  As organic polymers, synthetic polymers such as vinyl resins, acrylic resins, amide resins, and polyethylene oxides; semi-synthetic polymers such as starches and celluloses; chitin, chitosan, casein, gelatin, egg white, starch, And natural polymers such as seaweed, carrageenan, sodium alginate, agar, vegetable viscous material, xanthan gum and bull run. These can be used individually or in mixture of 2 or more types. Among these, it is preferable to use at least one selected from vinyl resins, acrylic resins, and amide resins, and polyvinyl alcohol is particularly preferable. By using these, a matrix having a three-dimensional structure is easily formed when mixed with silica fine particles, and a bulk precursor is easily obtained. Moreover, it becomes easy to obtain a porous photocatalyst-silica composite molded body after firing the precursor.

  After preparing silica fine particles, photocatalyst fine particles and organic polymer, these are mixed. The mixing ratio is 1 to 100 parts by weight, 2 to 50 parts by weight, 5 to 40 parts by weight, particularly 10 to 30 parts by weight of the organic polymer with respect to 100 parts by weight of the total amount of silica fine particles and photocatalyst fine particles. It is preferable. When it is out of the range of the mixing ratio, it becomes difficult to obtain a bulk precursor. From the viewpoint of mixing each component homogeneously, the silica fine particles and the photocatalyst fine particles, which are solid components, are dispersed in a dispersion medium to produce a solid component dispersion, and separately, an organic polymer is dissolved in a solvent to obtain a high organic content. After preparing the molecular solution, it is preferable to mix the solid component dispersion and the organic polymer solution.

  Examples of the dispersion medium used for the solid component dispersion include organic dispersion media such as alcohol and water. It is preferable that the content of the solid component in the solid component dispersion is appropriately adjusted within a range of, for example, 1 to 20% by mass, and further 5 to 10% by mass. The solid component dispersion can be obtained, for example, by mixing for about 0.5 hour to 1 day using a ball mill such as a planetary ball mill.

  Examples of the solvent used for the organic polymer solution include organic dispersion media such as alcohol and water. In addition, when using polyvinyl alcohol as an organic polymer, since polyvinyl alcohol is water-soluble, it is preferable to use water as a solvent. In this case, since the solid component dispersion and the organic polymer solution are mixed later, it is preferable to use water as a dispersion medium used for the solid component dispersion. The content of the organic polymer in the organic polymer solution is preferably adjusted as appropriate in the range of, for example, 1 to 20% by mass, and more preferably 5 to 10% by mass. The organic polymer solution can be obtained, for example, by stirring for 6 hours or more using a ball mill such as a planetary ball mill.

  The solid component dispersion obtained as described above and the organic polymer solution are mixed at a predetermined ratio, and stirred for, for example, 0.5 hours or more to obtain a solid component-organic polymer mixed solution. In addition, when an ultrasonic wave is applied during stirring, the dispersion state of the solid component can be improved. Moreover, by controlling the mixed solution to be acidic (for example, pH 1 to 5, particularly about pH 2 to 4), the moldability of the precursor is improved, or a porous photocatalyst-silica composite molded body is obtained after the precursor is fired. It becomes easy.

  The solid component-organic polymer mixed solution obtained above is poured into a molding container and dried to obtain a precursor (cast molding). As the molding container, for example, a resin container made of fluorine-based resin, polypropylene, or the like can be used, but a fluorine-based resin container is preferable because of its excellent releasability. In order to maintain the shape, a load may be applied to the liquid surface of the mixed solution during drying. The drying temperature is not particularly limited, but is usually room temperature. The drying time depends on the size of the precursor, but is preferably 3 days or more, particularly preferably 5 days or more.

  In addition to cast molding, molding methods such as injection molding, extrusion molding, sheet molding, and screen printing may be used.

  By calcining the precursor, a photocatalyst-silica composite molded body is obtained. The precursor is preferably baked after first removing the organic polymer by a degreasing step.

  The degreasing step is preferably performed at a temperature at which the organic polymer is sufficiently decomposed, and is preferably about 600 to 700 ° C, for example. In order to make it difficult for the organic polymer component to remain inside the precursor, it is preferable that the rate of temperature increase from the degreasing temperature to the main firing temperature is as low as possible (for example, 1 to 5 ° C./min).

  The temperature of the main baking step is preferably about 700 to 1200 ° C. so that the silica fine particles are sufficiently bonded. When titania is used as the photocatalyst fine particles, the firing temperature is preferably about 900 ° C. or lower. If the calcination temperature is too high, titania transitions from the anatase structure to the rutile structure, so that the activity effect of the photocatalyst tends to decrease.

  The photocatalyst-silica composite molded body obtained by the method of the present invention has a porous structure, and has a structure in which photocatalyst fine particles are supported in each pore. As a result, the number of sites functioning as a catalyst in the molded body increases, and the catalytic effect can be enhanced. From the viewpoint of increasing the specific surface area of the molded body and increasing the amount of photocatalyst fine particles supported, it is preferable that the pore size is small. For example, the pore size in the photocatalyst-silica composite molded article is preferably 100 nm or less, particularly preferably 50 nm or less. Note that if the pore size is too small, harmful chemical substances to be purified are less likely to enter, and therefore it is preferably 1 nm or more, particularly 5 nm or more.

  Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to these examples.

  Table 1 shows Examples (Sample Nos. 1 to 9) and Comparative Examples (Sample No. 10) of the present invention.

(1) Manufacture of photocatalyst-silica composite molded body In the mass ratio shown in Table 1, silica fine particles (Silica, fumed, average particle diameter 7 nm, manufactured by ALDRICH) and titania fine particles (P25, manufactured by Nippon Aerosil Co., Ltd.) which are photocatalyst fine particles. An average particle diameter of 21 nm) was introduced into ion-exchanged water and stirred for 1 hour or longer under ultrasonic waves to obtain a dispersion in which silica fine particles and photocatalyst fine particles (solid component) were uniformly dispersed. In addition, the quantity of ion-exchange water was adjusted so that the ratio of the solid component in a solid component dispersion liquid might be 8 mass%.

  Polyvinyl alcohol (PVA) (manufactured by Wako Pure Chemical Industries, Ltd., saponification degree: 78 to 82 mol%) was put into ion-exchanged water and stirred at 50 ° C. for 12 hours or more to obtain a uniform aqueous PVA solution. In addition, the quantity of ion-exchange water was adjusted so that the ratio of PVA in PVA aqueous solution might be 8 mass%.

  Next, the solid component dispersion and the PVA aqueous solution were mixed so as to have a mass ratio of 8: 2 (that is, 25 parts by mass of PVA with respect to 100 parts by mass of the solid component), and then stirred for 1 hour under ultrasonic waves to be solid. A component-PVA mixture was obtained. The obtained solid component-PVA mixture was cast into a fluororesin (polytetrafluoroethylene) container and sufficiently dried at room temperature for 7 days or more to obtain a precursor. The precursor was degreased at 600 ° C., and then fired at the temperature shown in Table 1, to obtain a bulk photocatalyst-silica composite molded body. Comparative Example No. No. 10 used the above titania fine particles as they were.

(2) Water quality purification test 0.5 g of each sample was added to a methylene blue solution having a concentration of 5 mg / L in a quartz cell and irradiated with ultraviolet rays (wavelength 365 nm). After 1 hour, 2 hours, and 5 hours, the shade of the methylene blue solution was observed and evaluated in five stages. Note that “5” was a hue before ultraviolet irradiation, and “1” was colorless and transparent. The results are shown in Table 1.

  As is apparent from Table 1, it can be seen that the photocatalyst-silica composite molded body of the example can decompose methylene blue and purify water quality in a short time as compared with the titania fine particles as a comparative example.

  The photocatalyst-silica composite molded article produced by the method of the present invention is suitable as a purification agent for water, soil, air, etc. contaminated with harmful chemical substances.

Claims (7)

  A method for producing a photocatalyst-silica composite molded article, comprising: obtaining a precursor by mixing silica fine particles, photocatalyst fine particles and an organic polymer; and calcining the precursor.   The method for producing a photocatalyst-silica composite molded article according to claim 1, wherein 1 to 100 parts by mass of the organic polymer is mixed with 100 parts by mass of the total amount of the silica fine particles and the photocatalyst fine particles.   The method for producing a photocatalyst-silica composite molded article according to claim 1 or 2, wherein the organic polymer is at least one selected from vinyl resins, acrylic resins, and amide resins.   The method for producing a photocatalyst-silica composite molded article according to claim 3, wherein the organic polymer is polyvinyl alcohol.   The photocatalyst fine particles are at least one selected from titanium oxide, tin oxide, zinc oxide, vanadium oxide, bismuth oxide, tungsten oxide, iron oxide, and strontium titanate. The manufacturing method of the photocatalyst-silica composite molded object as described in any one.   The method for producing a photocatalyst-silica composite molded article according to claim 5, wherein the photocatalyst fine particles are titanium oxide. A precursor for a photocatalyst composite molded article containing silica fine particles, photocatalyst fine particles and an organic polymer,
A precursor for a photocatalyst-silica composite molded article, wherein the photocatalyst fine particles are dispersed in a matrix composed of the silica fine particles and the organic polymer bonded to each other.