Porous body and its production method

The present invention relates to a porous body of an oxide semiconductor used for a photocatalyst, an electrode material of a solar cell, and the like, and a method for producing the same. In particular, the present invention relates to a photocatalyst or a photoelectrode capable of efficiently causing an oxidation / reduction reaction by light irradiation.

When a semiconductor is irradiated with light, electrons having a strong reducing action and holes having a strong oxidizing action are generated, and the molecular species in contact with the semiconductor are decomposed by the redox action. This kind of action of semiconductors is called photocatalytic action, and since the discovery of photodecomposition of water with semiconductor photoelectrodes, the so-called Honda-Fujishima effect, much research has been done as a powerful means of light-to-chemical energy conversion. .. In addition, using this principle, for example, 1) oxidation of organic compounds, 2) organic synthesis such as hydrogenation of unsaturated compounds, 3) removal and decomposition of harmful chemical substances in waste liquid or exhaust gas, 4) sterilization. , 5) Attempts have been made to apply it to the decomposition of dirt.

Such semiconductors (photocatalysts) include titanium dioxide (titania), vanadium pentoxide, zinc oxide, tungsten oxide, copper oxide, iron oxide, strontium titanate, barium titanate, sodium titanate, and sulfide. Cadmium, zirconium dioxide, iron oxide, etc. have been found. Further, it is known that those semiconductors supported by metals such as platinum, palladium, rhodium, and ruthenium as cocatalysts are effective as photocatalysts.

Semiconductor powders have often been used in conventional research on photocatalysts, but in order to link photocatalysts to practical use, it is essential to form a film. Therefore, it is known that it is fixed to resin, glass, or the like, or the semiconductor itself is made into a thin film and used. However, there is a problem that the amount of catalyst itself is not sufficient and the effect cannot be sufficiently exhibited. Further, in order to increase the amount of catalyst, it is sufficient to increase the area of the catalyst layer, but usually there are design restrictions and it is often difficult. On the other hand, in the above-mentioned semiconductors, the n-type semiconductor can be irradiated with light to obtain an electrode-like output. Therefore, it is also used as an electrode material for a wet photocell using a photosensitizing electrolysis phenomenon. In particular, in recent years, the development of dye-sensitized solar cells has been active. The main structure of the semiconductor electrode, which is the working electrode, is a dye-sensitizer adsorbed on the porous semiconductor film. As such a semiconductor material, titanium dioxide (titania), tin oxide, zinc oxide, niobium oxide and the like are used. As the sensitizing dye, a ruthenium complex system and the like are known. This dye-sensitized solar cell has a simple structure and is expected to reduce the cost as compared with the conventional silicon solar cell, but in practical use, improvement of conversion efficiency is the biggest issue.

Therefore, in a photocatalyst or a photoelectrode, in order to obtain higher photoactivity in a small volume, it has been studied to increase the specific surface area of a semiconductor at a low density. That is, making semiconductors porous is being studied.

For example, a method of obtaining a titanium oxide porous thin film photocatalyst having pores having uniform pore diameters on the surface by coating a substrate with titania sol and then heating and firing is disclosed (for example, Japanese Patent No. 2636158).

Alternatively, a method of supporting or coating a photocatalyst on a silica porous body having pores having a diameter of 2 to 50 nm is disclosed (for example, Japanese Patent Application Laid-Open No. 10-151355).

For example, there is disclosed an oxide semiconductor electrode formed on the conductive substrate and having a porous oxide semiconductor layer containing hollow particles made of a metal oxide. Japanese Patent Application Laid-Open No. 2001-76772).<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2001-076772</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2000-319018</text></patcit><patcit num="3"><text>WO98 / 35267</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2003-301283</text></patcit><patcit num="5"><text>Japanese Unexamined Patent Publication No. 3-093634</text></patcit><patcit num="6"><text>Japanese Unexamined Patent Publication No. 5-023637</text></patcit><patcit num="7"><text>Japanese Unexamined Patent Publication No. 63-280748</text></patcit>

<p> However, as in Patent No. 2636158, as a result of diligent studies on a method of heating and firing an organic gel to make it porous, the following problems have been clarified.</p><p> (1) Precursor of oxide semiconductor In the step of firing an organic gel of a polymer, the porous body of the precursor shrinks as it is fired, and the resulting porous oxide semiconductor has a higher density than that of the precursor. There is a tendency for the specific surface area to increase and the specific surface area to decrease.</p><p> (2) Since an organic gel having a network structure is fired, the density and specific surface area of the oxide semiconductor porous body obtained by firing from the organic gel depend on the structure of the organic gel in advance. After obtaining organic gels, it is difficult to control their density and specific surface area.</p><p> Further, when silica is used as a carrier as in JP-A-10-151355, there is a problem that the electrical conduction characteristics are deteriorated because silica is an insulator. In particular, when used as a photoelectrode material, it is necessary to improve the conductivity of the porous body and the electronic network between semiconductor particles in order to improve efficiency.</p><p> Further, since the oxide semiconductor electrode in Japanese Patent Application Laid-Open No. 2001-76772 has a structure in which fine particles are connected to form a hollow, the electronic network between the fine particles may be weak and the electrical conductivity may be low.</p><p> Therefore, a main object of the present invention is to provide a porous body containing an oxide semiconductor in which a more efficient photocatalytic reaction or photoelectrode reaction occurs.</p><p> A further object of the present invention is to provide a method for efficiently producing a porous body containing an oxide semiconductor.</p>

<p> The present invention relates to the following porous body and a method for producing the same. 1. A porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface part, 2) the inside is substantially made of a carbon material, and 3) a part or all of the surface part is. A porous body that is an oxide semiconductor. 2. The porous body according to Item 1, wherein the oxide semiconductor is at least one kind of metal oxide. 3. Specific surface area is 100m²Item 2. The porous body according to Item 1, which is / g or more. 4. The porous body according to Item 1, wherein the co-catalyst is supported on the skeleton. 5. The porous body according to Item 4, wherein the oxide semiconductor has a catalytic function and the co-catalyst is in contact with the oxide semiconductor. 6. The porous body according to Item 1, wherein the dye is supported on the skeleton. 7. A porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface part, 2) the inside is substantially made of a carbon material, and 3) a part or all of the surface part is. It is a method for producing an oxide semiconductor / carbon porous body which is an oxide semiconductor. (1) A composite is formed by coating the skeleton with an oxide semiconductor precursor in a carbon precursor-containing wet gel having a network structure skeleton. The first step of obtaining a wet gel, (2) the second step of obtaining a composite dry gel by drying the composite wet gel, and (3) the oxide semiconductor / carbon composite by heat-treating the composite dry gel. A method for producing a porous body, which comprises a third step of obtaining the porous body. 8. The production method according to Item 7, wherein the heat treatment is performed in an atmosphere having an oxygen concentration of 0 to 10% by volume. 9. The production method according to Item 7, wherein the heat treatment is performed in an inert gas atmosphere. Ten. Item 2. The production method according to Item 7, further comprising a step of applying a co-catalyst and / or a dye. 11. The production method according to Item 7, wherein the carbon precursor contains an organic polymer. 12. The production method according to Item 11, wherein the organic polymer is at least one of polyacrylonitrile, polyfurfuryl alcohol, polyimide, polyamide, polyamideimide, polyurethane, polyurea, polyphenol, polyaniline and polyparaphenylene. 13. A porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface part, 2) the inside is substantially made of a carbon material, and 3) a part or all of the surface part is. It is a method for producing a porous body which is an oxide semiconductor. (1) The first step of obtaining a dry gel having a network structure skeleton by drying a carbon precursor-containing wet gel having a network structure skeleton, (2). The second step of obtaining a composite precursor by coating the skeleton with an oxide semiconductor in the dry gel, and (3) heat-treating the composite precursor to obtain an oxide semiconductor / carbon composite porous body. A method for producing a porous body including a third step. 14. Item 3. The production method according to Item 13, wherein the heat treatment is performed in an atmosphere having an oxygen concentration of 0 to 10% by volume. 15. The production method according to Item 14, wherein the heat treatment is performed in an inert gas atmosphere. 16. The production method according to Item 14, further comprising a step of applying a co-catalyst and / or a dye. 17. The production method according to Item 14, wherein the carbon precursor contains an organic polymer. 18. The production method according to Item 17, wherein the organic polymer is at least one of polyacrylonitrile, polyfurfuryl alcohol, polyimide, polyamide, polyamideimide, polyurethane, polyurea, polyphenol, polyaniline and polyparaphenylene. 19. It is a porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface part, 2) the inside is substantially made of a carbon material, and 3) a part or all of the surface part is an oxide. It is a method for producing a porous body which is a semiconductor, and is a first step of obtaining a dry gel having a network structure skeleton by drying a carbon precursor-containing wet gel having a network structure skeleton, and (2) the drying. The second step of obtaining a carbon porous body by carbonizing the gel, and (3) obtaining an oxide semiconductor / carbon composite porous body by coating the skeleton with an oxide semiconductor in the carbon porous body. A method for producing a porous body including 3 steps. 20. The production method according to Item 19, wherein the carbonization treatment is performed in an atmosphere having an oxygen concentration of 0 to 10% by volume. 21. The production method according to Item 19, wherein the carbonization treatment is carried out in an inert gas atmosphere. 22. The production method according to Item 19, further comprising a step of applying a co-catalyst and / or a dye. 23. The production method according to Item 19, wherein the carbon precursor contains an organic polymer. twenty four. Item 23. The production method according to Item 23, wherein the organic polymer is at least one of polyacrylonitrile, polyfurfuryl alcohol, polyimide, polyamide, polyamideimide, polyurethane, polyurea, polyphenol, polyaniline and polyparaphenylene. 25. A solar cell containing the porous body according to item 1 above as an electrode material. 26. A method for producing an oxide semiconductor porous body having a network structure skeleton, in which the skeleton is coated with an oxide semiconductor precursor in a wet gel containing a template material having a network structure skeleton to wet the oxide semiconductor precursor composite. A pretreatment step for obtaining a gel, a drying step for drying the composite wet gel to obtain an oxide semiconductor precursor composite dry gel, and a mold having the network structure skeleton by heat-treating the dry gel in a gas atmosphere containing oxygen. A method for producing a porous body, which comprises a step of removing a material to obtain an oxide semiconductor porous body. 27. A method for producing an oxide semiconductor porous body having a network structure skeleton, in which a wet gel containing a template material having a network structure skeleton is dried to obtain a dry gel containing a template material having a network structure skeleton. The step of coating the skeleton with an oxide semiconductor material to obtain an oxide semiconductor composite precursor, and heat treatment of the composite precursor in a gas atmosphere containing oxygen to remove the template material having the network structure skeleton for oxidation. A method for producing a porous body, which comprises a step of obtaining a physical semiconductor porous body. 28. A method for producing an oxide semiconductor porous body having a network structure skeleton, which is a step of drying a wet gel containing a template material having a network structure skeleton to obtain a dry gel of a template material having a network structure skeleton. A step of solidifying the mold to obtain a template porous body, a step of coating the skeleton with an oxide semiconductor material in the template porous body to obtain an oxide semiconductor / template material composite porous body, and a step of obtaining the network structure skeleton from the composite porous body. A method for producing a porous body, which comprises removing a template material to obtain an oxide semiconductor porous body. 29. A method for producing an oxide semiconductor porous body having a network structure skeleton, wherein the oxide semiconductor precursor is coated on the skeleton in a wet gel containing a template material having a network structure skeleton to obtain an oxide semiconductor precursor composite wet gel. Pretreatment step to obtain, mold material removing step of removing the template material from the composite wet gel to obtain an oxide semiconductor precursor wet gel, drying step of drying the wet gel to obtain an oxide semiconductor precursor dry gel, A method for producing a porous body, which comprises a step of heat-treating the dry gel to obtain an oxide semiconductor porous body. 30. The method for producing a porous body according to any one of Items 26 to 29 above, which further comprises a step of supporting a catalyst. 31. The method for producing a porous body according to any one of Items 26 to 29 above, which further comprises a step of supporting a dye. 32. The method for producing a porous body according to any one of Items 26 to 29 above, wherein the mold material is carbon.</p>

<p> According to the production method of the present invention, an oxide semiconductor-based porous body having a low density and a high specific surface area can be produced. That is, according to the production method of the present invention, it is possible to provide an oxide semiconductor / carbon composite porous body made of an oxide semiconductor material that causes an efficient photocatalytic reaction.</p><p> In particular, in the oxide semiconductor / carbon composite porous body of the present invention, since the core of the network structure skeleton 1 has a carbon material having excellent electrical conduction characteristics, an electrically highly efficient photoelectrode reaction is generated. It becomes possible. That is, since the carbon material and the oxide semiconductor are in contact with each other, not only can electrons be exchanged directly between them, but also if an electronic device is connected to the carbon material via a lead wire or the like, the said Electrons can be exchanged between the electronic device and the oxide semiconductor via the carbon material (and the lead wire), and an electrically highly efficient photoelectrode reaction can be achieved.</p><p> Industrial applicability The porous material of the present invention can be used as a photocatalyst, a photoelectrode, etc. because the oxidation / reduction reaction efficiently occurs by light irradiation. More specifically, it can be used for applications such as solar cells (for example, dye-sensitized solar cells) and photohydrogen generators.</p>

Hereinafter, embodiments of the present invention will be described. First, the structure of the porous body of the present invention will be described with reference to the drawings.<u style="single">1. Porous</u> The porous body of the present invention is a porous body having a network structure skeleton, in which 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially made of a carbon material, and 3) the surface portion. It is characterized in that some or all of them are oxide semiconductors.

The network structure skeleton of the porous body of the present invention may have a three-dimensional network structure. The network structure skeleton is composed of an internal portion and a surface portion.

The interior is essentially made of carbon material. The inside may be densely packed with carbon material, or may have holes formed in a part thereof. The abundance ratio of the pores can be appropriately set according to the desired characteristics of the porous body and the like.

The carbon material is not particularly limited as long as it is carbon or a material containing carbon as a main component. The carbon material obtained by the production method described later is suitable. That is, a carbon material produced by heat treatment from a raw material of the carbon material and / or a carbon material obtained by carbonizing an organic polymer as a carbon precursor can be used. These have the advantage that the structure, properties, etc. of carbon can be arbitrarily controlled depending on the formation conditions, carbonization treatment conditions, and the like.

The carbon material may be either crystalline or amorphous, and may be appropriately set and used according to the use and method of use of the porous body.

A part or all of the surface portion is composed of an oxide semiconductor. As the oxide semiconductor used in the present invention, a material that causes a photocatalytic reaction can be particularly preferably used. For example, titanium dioxide (titania), vanadium pentoxide, zinc oxide, tungsten oxide, copper oxide, strontium titanate, barium titanate, sodium titanate, zirconium dioxide, α-Fe.₂O₃, K₄Nb₆O₁₇, Rb₄Nb₆O₁₇, K₂Rb₂Nb₆O₁₇, Pb_1-xK_2xNbO₆(However, at least one kind of oxide (metal oxide) such as 0 &lt;x &lt;1) can be mentioned.

The porous body of the present invention may contain other components, if necessary. For example, a co-catalyst may be included. Examples of the co-catalyst include metals such as platinum, palladium, ruthenium, gold, copper, tin and zinc; alloys such as platinum palladium, platinum ruthenium and platinum iron; oxides such as nickel oxide, manganese oxide and rhodium oxide. Can be used. These may be appropriately selected according to the intended use of the porous body, the desired reaction, and the like. The amount of the co-catalyst supported can be usually selected in the range of 0.1 to 20% by weight based on the total weight of the oxide semiconductor and the co-catalyst from the viewpoint of photocatalytic activity.

Further, if necessary, a pigment may be contained. As the dye, a dye known as a sensitizing dye can be preferably used. More specifically, it is desirable to use a ruthenium complex system or the like. The amount of the dye carried may be appropriately selected according to the type of dye to be used and the like.

The thickness of the surface portion is not limited, and can be appropriately set according to the intended use, purpose of use, and the like of the porous body. Further, the thickness can be controlled by changing the conditions in the manufacturing method described later.

Further, the ratio of the internal portion to the surface portion can be appropriately determined depending on the type of oxide semiconductor, the use of the porous body, and the like.

The bulk density, BET specific surface area, and average pore diameter of the porous body of the present invention can be appropriately set depending on the type of oxide semiconductor, the application of the porous body, the method of use, and the like. Bulk density is usually 10 kg / m³More than 800kg / m³Below, especially 50 kg / m³More than 400kg / m³It may be appropriately determined from the following range. Specific surface area is usually 50m²/ g or more 1500m²Below / g, especially 100m²/ g or more 1000m³Below / g, further 200m²/ g or more 1000m²It can be set appropriately from the range of / g or less. The specific surface area is a value measured by the Brunauer-Emmett-Teller method (hereinafter abbreviated as BET method), which is a nitrogen adsorption method. Further, the average pore diameter of the porous body of the present invention can be appropriately determined from the range of usually 1 nm or more and 1000 nm or less, particularly 5 nm or more and 50 nm or less.

Further, the shape and size of the porous body of the present invention are not limited, and may be appropriately determined according to the use, purpose of use, etc. of the porous body.

Hereinafter, preferred embodiments of the porous body of the present invention will be described with reference to the drawings.

<u style="single">(1) Embodiment 1</u> The first configuration of the porous body according to the present invention is an oxide semiconductor / carbon composite porous body having a network structure skeleton 1 as shown in FIG. As shown in FIG. 2, the network structure skeleton 1 has a network structure made of a dry gel of carbon material 3 as a core of the skeleton 2, and is coated with an oxide semiconductor 4.

Network structure In the structure of the skeleton 1, the skeletons as shown in FIG. 1 form a network in a three-dimensional network. Such a structure can be made, for example, from the process of obtaining a dry gel via a wet gel. In the case of this process, since the skeleton forms a network structure by agglomeration of fine particles, it can be schematically represented as shown in FIG. When the skeleton is actually observed with an electron micrograph or the like, it can be confirmed that the skeleton is composed of aggregates of fine particles and has a porous structure having voids between the fine particles. In the structure obtained from the above process, the pores are generally formed by gaps formed by skeletons (skeletons) made of fine particles having a particle size of 100 nm or less. The size of the pores is as small as about 1 μm or less. As a result, a porosity of 50% or more can be realized, and as a result, a porous body having a high specific surface area can be provided. In particular, in the network structure skeleton formed via the gel as in the present invention, the fine particles are as small as 1 nm or more and 50 nm or less, and the size of the pores resulting from the fine particles is also as small as 100 nm or less. As a result, the pore ratio is 80% or more, and the specific surface area is 100 m.²It is also possible to obtain a porous body having a high specific surface area of / g or more.

Therefore, in the oxide semiconductor / carbon composite porous body of the present invention, since the oxide semiconductor 4 is coated on the network structure skeleton of the dried gel of the carbon material 3, it is possible to form a porous body having a large specific surface area. .. As a result, it can be applied to highly active photocatalysts. Further, since the core of the network structure skeleton 1 is made of a conductive carbon material, higher electrical efficiency can be realized when it is used as an electrode material for a solar cell or the like.

This can be more reliably achieved by the manufacturing method of the present invention. As one method for producing an oxide semiconductor / carbon composite porous body, in the production method of the present invention, which comprises a step of forming a crystalline oxide semiconductor by heat treatment or the like of a precursor gel of the oxide semiconductor, a mesh of a carbon material is used. Since the structural skeleton 1 has heat resistance, it can play a role as a support for the oxide semiconductor in the heat treatment process and suppress the shrinkage of the porous body during the formation of the oxide semiconductor. As a result, the obtained oxide semiconductor / carbon composite porous body has a low density and a high specific surface area can be achieved.<u style="single">(2) Embodiment 2</u> The second aspect of the porous body according to the present invention is an oxide semiconductor porous body having a network structure skeleton as shown in FIG. As shown in FIG. 3, the surface of this skeleton is made of an oxide semiconductor 6, and the inside thereof is substantially entirely occupied by a hollow portion 7 (space).

In the above structure, in addition to the high specific surface area due to the network structure skeleton which is a dry gel structure, the inside of the skeleton is a hollow portion 7. Since this porous body has a hollow portion, it has a higher specific surface area than the above-mentioned carbon composite porous body. As a result, the porous body can be used as a photocatalyst, a photoelectrode material, etc. with higher activity.

As described above, although the carbon material does not exist in the second embodiment, the porous body of the present invention is particularly preferably one in which the carbon material remains and the inside is partially hollow.<u style="single">(3) Embodiment 3</u> In the third configuration of the porous body according to the present invention, as shown in FIG. 4, in the oxide semiconductor / carbon composite porous body having the network structure skeleton 1 or the oxide semiconductor porous body, the oxide semiconductor having a catalytic function is used. A co-catalyst 9 is supported. In this configuration, since the porous body having a large specific surface area shown in the first or second embodiment is used as a photocatalyst, there are advantages that a larger amount of the co-catalyst can be supported and the reaction active sites can be increased. .. As a result, it can be applied to highly active photocatalysts and the like.

At this time, it is desirable that the co-catalyst exists so as to be in contact with the oxide semiconductor. In the case of the oxide semiconductor / carbon composite porous body of the first embodiment, the cocatalyst may be present on the surface of the oxide semiconductor or between the carbon skeleton and the oxide semiconductor. Further, in the oxide semiconductor porous body of the second embodiment, the co-catalyst may be present on either the outer surface or the inner surface of the skeleton of the oxide semiconductor. In particular, it is preferable that the co-catalyst is present on the surface of the oxide semiconductor in that the chances of contact with the object to be reacted increase and the reactivity becomes higher.<u style="single">(4) Embodiment 4</u> In the fourth configuration of the porous body according to the present invention, as shown in FIG. 4, in the oxide semiconductor / carbon composite porous body or the oxide semiconductor porous body having the network structure skeleton 1, the dye 9 is supported on the oxide semiconductor. Has been done. In this configuration, since the porous body having a large specific surface area shown in the first or second embodiment is used as the photoelectrode, there are advantages such as an increase in the amount of the dye supported and an increase in the reaction active sites. can get. This makes it possible to apply it to electrode materials for dye-sensitized solar cells and the like.

At this time, it is desirable that the dye is present so as to be in contact with the oxide semiconductor. As long as it is the oxide semiconductor / carbon composite porous body of the first embodiment, the dye may be present on the surface of the oxide semiconductor or between the carbon skeleton and the coated oxide semiconductor. Further, in the oxide semiconductor porous body of the second embodiment, the dye may be present on either the outer surface or the inner surface of the skeleton of the oxide semiconductor.

<u style="single">2. Manufacturing method of porous body</u> The method for producing the porous body of the present invention is not limited as long as the above structure can be obtained, but the following methods 1 to 4 can be particularly preferably adopted.<u style="single">(1) First method</u> The first method is a porous body having a network-structured skeleton, in which 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially made of a carbon material, and 3) a part of the surface portion. Alternatively, it is a method for producing an oxide semiconductor / carbon porous body which is entirely an oxide semiconductor, and (1) coating the skeleton with an oxide semiconductor precursor in a carbon precursor-containing wet gel having a network structure skeleton. The first step of obtaining the composite wet gel, (2) the second step of obtaining the composite dry gel by drying the composite wet gel, and (3) the oxide semiconductor by heat-treating the composite dry gel. / Including the third step of obtaining a carbon composite porous body.

<u style="single">1st process</u> In the first step, a composite wet gel is obtained by coating the skeleton with an oxide semiconductor precursor in a carbon precursor-containing wet gel having a network structure skeleton.

As the carbon precursor, an organic polymer material that is carbonized by heat treatment is preferable. For example, polyacrylonitrile, polyfurfuryl alcohol, polyimide, polyamide, polyamideimide, polyurethane, polyurea, polyphenol, polyaniline, polyparaphenylene and the like can be used. These can be used in one kind or two or more kinds.

As the carbon precursor-containing wet gel, for example, a solution or dispersion obtained by dissolving or dispersing a separately synthesized precursor in a solvent can be used. Further, the gel-like reaction product obtained by reacting the raw materials of these precursors in a solvent can be used as it is as a carbon precursor-containing wet gel.

Examples of the solvent include water, alcohols such as methanol, ethanol, propanol and butanol, glycols such as ethylene glycol and propylene glycol, and the like. These can be used alone or in admixture of two or more. These may be appropriately selected depending on the type of carbon precursor to be used and the like.

In this case, the concentration of the above solution or dispersion can be appropriately set according to the type of wet gel to be used, the type of solvent, and the like.

When a raw material for a carbon precursor is used, a known raw material can be used as the raw material. For example, in polyacrylonitrile, furfuryl alcohol, polyaniline and the like, acrylonitrile, furfuryl alcohol, aniline and the like can be used as raw materials, respectively. Further, when the polyimide is synthesized by a polycondensation reaction for forming an imide ring, an anhydrous tetracarboxylic dian compound and a diamine compound can be generally used. When the polyamide is synthesized by a polycondensation reaction that forms an amide bond, a dicarboxylic acid compound, a dicarboxylic acid chloride compound, and a diamine compound can generally be used. As the polyurethane, a diol compound such as a polyol and a diisocyanate compound can be used. As the polyurea, a diisocyanate compound can be used. As the polyphenol, a phenol compound, an aldehyde compound and the like can be used. The raw materials shown here are described to the effect that general ones are used, and are not limited to these raw materials.

As these raw materials, those containing an aromatic component are preferable in that they are easily carbonized. Further, by reacting these raw materials together with a catalyst, an efficient carbon precursor can be formed.

Hereinafter, a case where a polyphenol wet gel is used as the carbon precursor-containing wet gel will be described as an example. Examples of the method for obtaining a wet gel include a method in which a polyphenol raw material is synthesized by a sol-gel reaction in a solvent to form a wet gel. At this time, a catalyst can be used if necessary. In this formation process, the raw materials react in the solvent to form fine particles of polyphenol, and the fine particles gather to form a network structure skeleton 1 to form a wet gel. Specifically, the composition of the raw material and the solvent which are predetermined solid components is determined. If necessary, a catalyst, a viscosity modifier, or the like is added to the solution prepared to that composition, and the mixture is stirred, and cast, coated, or the like to obtain a desired usage pattern. After a certain period of time elapses in this state, the solution gels and becomes a wet gel. Further, if necessary, an aging treatment may be performed for the purpose of aging the wet gel, controlling the pores, and the like.

As raw materials for polyphenols, phenol compounds such as phenol, cresol, resorcin (1,3-benzenediol), catechol, fluoroglycinol, novolac-type phenol resin, resole-type phenol resin, and phenols such as salicylic acid and oxybenzoic acid are used. Examples include carboxylic acids and the like. Examples of the aldehyde compound as a condensing agent include formaldehyde, acetaldehyde, furfural and the like, as well as paraformaldehyde and hexamethylenetetramine which generate formaldehyde by heating. As the condensation catalyst, a base catalyst and / or an acid catalyst can be used. The base catalyst mainly proceeds with an addition reaction such as a methylol group, and the acid catalyst mainly proceeds with a polyaddition condensation reaction such as a methylene bond. Base catalysts include hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide; carbonates of alkali metals such as sodium carbonate and potassium carbonate, as well as catalysts for the production of general phenolic resins such as amine and ammonia. Can be used. As the acid catalyst, for example, sulfuric acid, hydrochloric acid, phosphoric acid, oxalic acid, acetic acid, trifluoroacetic acid and the like can be used. Further, as the solvent, it is sufficient that the raw material can be dissolved to form a polyphenol gel. For example, in addition to water, alcohols such as methanol, ethanol, propanol and butanol, glycols such as ethylene glycol and propylene glycol and the like can be mentioned. These can be used alone or in combination of two or more.

Examples of the oxide semiconductor include those used in the porous body of the present invention. The precursor thereof is not particularly limited as long as it is a material that becomes a predetermined oxide semiconductor by heat treatment. For example, it can be appropriately selected from metal alkoxide, metal salt and the like.

The coating method with the oxide semiconductor precursor is not particularly limited. For example, a) a method of impregnating a carbon precursor-containing wet gel with a solution or dispersion obtained by dissolving or dispersing an oxide semiconductor precursor in a solvent, and b) using a carbon precursor-containing wet gel as a raw material for an oxide semiconductor. Examples thereof include a method of producing an oxide semiconductor precursor from a raw material in the wet gel after impregnation.

As the method a) above, a solution or dispersion obtained by dissolving or dispersing an oxide semiconductor precursor in a solvent is used, and a carbon precursor-containing wet gel is immersed in the solution or dispersion. By this step, the polymer adheres to and is coated on the skeleton portion of the network structure. For example, titania (TiO as an oxide semiconductor precursor)₂) The precursor is a sol state of fine particles polymerized by hydrolysis using titanium methylphenoxide, titanium n-monoxide, titanium n-propoxyside, titanium triisopropoxyside tri-n-butylstannoxide, etc. as raw materials. Titanium precursors can be obtained. In this method, the wet gel holds the solution or dispersion inside, and these precursors are complexed because they are adsorbed or aggregated on the skeleton and remain on the skeleton when dried. Further, when a wet gel containing a solution in which the precursor is dissolved is immersed in a solvent poor for the polymer, the precursor is precipitated and coated on the skeleton. The method of coating the oxide semiconductor precursor on the skeleton is not limited to these.

The method b) is a method in which a wet gel of a carbon precursor is immersed in a solution in which a raw material of an oxide semiconductor precursor is dissolved, and the oxide semiconductor precursor is synthesized inside the gel. According to this method, since the precursor is synthesized inside the network structure skeleton 1, it is possible to obtain a composite wet gel in which the oxide semiconductor precursor is not physically eluted, which is particularly effective in the present invention. This is one of the methods. For example, as a raw material for the titania precursor, for example, titanium methylphenoxide, titanium n-monoxide, titanium n-propoxide, titanium triisopropoxide tri-n-butylstannoxide, titanium tetraisopropoxide or the like can be used. it can. By reacting these raw materials together with a catalyst, an efficient oxide semiconductor precursor can be formed.

The amount of the oxide semiconductor precursor used may be such that the coating layer has a desired thickness.<u style="single">2nd process</u> In the second step, the composite wet gel is dried to obtain a composite dry gel.

The drying method is not particularly limited. For example, in addition to the normal drying method of natural drying, heat drying, and vacuum drying, a supercritical drying method, a freeze drying method, and the like can also be used. In general, if the surface area of the dry gel is increased and the amount of solid components in the wet gel is reduced in order to reduce the density, the gel strength is lowered. In addition, simply drying the gel often causes the gel to shrink due to stress during solvent evaporation. In order to obtain a dry gel having excellent porous performance from the wet gel, supercritical drying or freeze drying can be preferably used as the drying means. As a result, shrinkage of the gel during drying, that is, densification of the gel can be effectively avoided. Even in a normal drying means for evaporating a solvent, shrinkage of the gel during drying can be suppressed by using a high boiling point solvent for slowing the evaporation rate or by controlling the evaporation temperature. Further, the shrinkage of the gel during drying can be suppressed by controlling the surface tension of the wet gel by subjecting the surface of the solid component of the gel to a water repellent treatment or the like.

In the supercritical drying method or freeze-drying method, the solvent can be dried by changing the phase state from the liquid state to eliminate the gas-liquid interface and without giving stress to the gel skeleton due to surface tension. Therefore, shrinkage of the gel during drying can be prevented, and a porous body of a low-density dried gel can be obtained. In the present invention, it is more preferable to use the supercritical drying method.

As the solvent used for supercritical drying, the solvent held by the wet gel can be used. Further, if necessary, it is preferable to replace it with a solvent that is easy to handle in supercritical drying. Examples of the solvent to be substituted include alcohols such as methanol, ethanol and isopropyl alcohol that directly make the solvent a supercritical fluid, as well as carbon dioxide and water. Alternatively, it may be replaced with an organic solvent such as acetone, isoamyl acetate, or hexane, which is easily eluted with these supercritical fluids.

Supercritical drying can be performed in a pressure vessel such as an autoclave. For example, when the solvent is methanol, the critical condition is that the critical pressure is 8.09 MPa or more, the critical temperature is 239.4 ° C or more, and the pressure is gradually released while the temperature is constant. For example, when the solvent is carbon dioxide, the critical pressure is 7.38 MPa or more, the critical temperature is 31.1 ° C or more, and the pressure is released from the supercritical state at the same constant temperature to make it a gas state and dry. .. For example, when the solvent is water, the drying is performed at a critical pressure of 22.04 MPa or higher and a critical temperature of 374.2 ° C or higher. The time required for drying may be at least one time during which the solvent in the wet gel is replaced by the supercritical fluid.

<u style="single">Third step</u> In the third step, the composite dry gel is heat-treated to obtain an oxide semiconductor / carbon composite porous body.

The heat treatment temperature is generally within the range of 300 ° C or more and 1200 ° C or less (particularly 450 ° C or more and less than 1000 ° C), as appropriate according to the type of oxide semiconductor (precursor), desired physical properties, etc. Can be determined.

For example, in the case of a titania precursor, anatase formation begins to proceed at about 500 ° C or higher, so the test is carried out at 500 ° C or higher. From the viewpoint of working time efficiency, a temperature of about 600 to 700 ° C is preferably suitable. The upper limit of the heating temperature may be equal to or lower than the heat resistant temperature of the carbon material of the network structure skeleton 1. For example, a dry gel made of carbon material shrinks slightly at about 600 ° C, but at 1200 ° C or higher, graphitization begins to progress and the shrinkage increases, so the firing temperature may be selected according to the degree of shrinkage suppressing effect. In particular, it is desirable to bake at less than 1000 ° C.

The atmosphere of the heat treatment is not limited, and may be any of the air, an oxidizing atmosphere, a reducing atmosphere, an inert gas atmosphere, a vacuum, and the like. In particular, considering combustion and the like, when the temperature is set high, it is preferable to perform it in a low-concentration oxygen atmosphere. More specifically, it is desirable to create an atmosphere in which the oxygen concentration is 0 to 10% by volume. More preferably, it is in an inert gas atmosphere or in vacuum. In particular, it is most preferably in an inert gas atmosphere. As the inert gas, various gases such as nitrogen, argon and helium can be used.<u style="single">(2) Second method</u> The second method is a porous body having a network-structured skeleton, in which 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially made of a carbon material, and 3) a part of the surface portion. Alternatively, it is a method for producing a porous body which is entirely an oxide semiconductor. (1) The first step of obtaining a dry gel having a network structure skeleton by drying a carbon precursor-containing wet gel having a network structure skeleton. (2) The second step of obtaining a composite precursor by coating the skeleton with an oxide semiconductor in the dry gel, and (3) the oxide semiconductor / carbon composite porous by heat-treating the composite precursor. Includes a third step to obtain the body.

<u style="single">1st process</u> In the first step, a wet gel containing a carbon precursor having a network structure skeleton is dried to obtain a dry gel having a network structure skeleton.

As the wet gel, the same wet gel as that shown in the first method can be used. Further, the drying method can be carried out in the same manner as the drying in the second step of the first method.

<u style="single">2nd process</u> In the second step, a composite precursor is obtained by coating the skeleton with an oxide semiconductor in the dry gel.

As the oxide semiconductor, various oxide semiconductors mentioned in the first method can be used.

The coating method of the oxide semiconductor is not particularly limited, and in the present invention, there are roughly two methods, that is, a method of forming an oxide semiconductor precursor in a liquid phase and then firing it, and a method of forming an oxide semiconductor in a gas phase. It can be used characteristically. More specifically, 1) a method of coating the oxide semiconductor precursor on the skeleton and then heat-treating it to form an oxide semiconductor, 2) a method of applying an oxide semiconductor to the skeleton by a vapor phase method, etc. are applied. it can.

The method 1) above can be carried out according to the first method. Further, the heat treatment of the oxide semiconductor precursor may be carried out in combination with the heat treatment of the third step of the second method, or may be separately heat-treated. In either case, the heat treatment conditions may be in accordance with the third step of the first method.

The methods 2) above are, for example, c) a method of forming an oxide semiconductor precursor in a gas phase in a dry gel of a carbon precursor and then performing a heat treatment, and d) directly forming an oxide semiconductor in a dry gel of a carbon precursor. A method of forming and covering with a gas phase can be adopted.

As the vapor phase method itself, a known method can be adopted. For example, a general method such as chemical vapor deposition (CVD) or physical vapor deposition (PVD) may be used, and a method of vaporizing or evaporating an oxide semiconductor or its raw material by heating or the like may be adopted. it can.

The method (c) above is, for example, a method of vaporizing a raw material of an oxide semiconductor precursor, introducing the raw material into a dry gel, and reacting the raw material in the dry gel to produce an oxide semiconductor precursor. For example, in the case of forming titania as an oxide semiconductor, it is a method in which raw materials such as titanium tetrachloride, titanium methylphenoxide, and titanium n-monoxide are filled in a dry gel as vapor and then polymerized. This oxide semiconductor precursor can form an oxide semiconductor by further heat treatment.

The method d) above is a method of directly forming an oxide semiconductor on the skeleton of a dried gel by a vapor phase method using a raw material of an oxide semiconductor. This method is advantageous in that heat treatment is not required as compared with the method c) above. For example, when forming titania, titanium tetrachloride, metallic titanium or the like may be used as a starting material and oxidized by heat, plasma, ions, light, a catalyst or the like. Alternatively, titanium oxide can be targeted and coated on the dry gel by a method such as sputtering or laser ablation. In order to proceed with crystallization in the dry gel, the heating method has high controllability and can be preferably used. At this time, as an advantage of growing in the gas phase, there is a feature that the treatment can be performed at a lower temperature than that of firing.

<u style="single">Third step</u> In the third step, the composite precursor is heat-treated to obtain an oxide semiconductor / carbon composite porous body.

The heat treatment method may be the same as the heat treatment in the third step of the first method. In particular, the heat treatment atmosphere is preferably an atmosphere in which the oxygen concentration is 0 to 10% by volume. Among them, it is more preferably in an inert gas atmosphere or in a vacuum, and most preferably in an inert gas atmosphere.<u style="single">(3) Third method</u> The third method is a porous body having a network-structured skeleton, in which 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially made of a carbon material, and 3) a part of the surface portion. Alternatively, it is a method for producing a porous body which is entirely an oxide semiconductor. (1) The first step of obtaining a dry gel having a network structure skeleton by drying a carbon precursor-containing wet gel having a network structure skeleton. (2) The second step of obtaining a carbon porous body by carbonizing the dry gel, and (3) the oxide semiconductor / carbon composite by coating the skeleton with an oxide semiconductor in the carbon porous body. The third step of obtaining a porous body is included.

<u style="single">1st process</u> In the first step, a wet gel containing a carbon precursor having a network structure skeleton is dried to obtain a dry gel having a network structure skeleton.

As the carbon precursor-containing wet gel, the same wet gel as that used in the first method can be adopted. The method for drying the wet gel may be carried out according to the drying method in the second step of the first method.

<u style="single">2nd process</u> In the second step, the dry gel is carbonized to obtain a carbon porous body.

The method of carbonization may be the same as the heat treatment in the third step of the first method. In particular, it is desirable that the atmosphere of the carbonization treatment is an atmosphere in which the oxygen concentration is 0 to 10% by volume. Among them, it is more preferably in an inert gas atmosphere or in a vacuum, and most preferably in an inert gas atmosphere.

<u style="single">Third step</u> In the third step, an oxide semiconductor / carbon composite porous body is obtained by coating the skeleton with an oxide semiconductor in the carbon porous body.

The method of coating the carbon porous body with the oxide semiconductor may be the same as that of the second step of the second method.<u style="single">(4) Fourth method</u> The present invention includes a fourth method of carrying out a step of further applying a co-catalyst or a dye in the above-mentioned first to third methods. The step of supporting the co-catalyst or the dye on the porous body of the present invention will be described.

As the co-catalyst or the dye, those used in the porous body of the present invention (the ones listed above) can be used respectively.

The means for applying the co-catalyst or the dye is not particularly limited, and it may be carried out according to a known method. For example, 1) a method of supporting using a colloid, 2) a method of supporting a co-catalyst or a dye precursor and then reducing it with a reducing agent such as hydrogen, 3) a method of calcining the co-catalyst or the dye precursor, etc. There is a method of supporting a catalyst on the body.

As the precursor, any material that finally gives a co-catalyst or a dye can be used. For example, a metal salt or the like can be used as a precursor of the co-catalyst. When a catalyst or a precursor of a dye is used, a treatment for catalyzing or sensitizing the dye may be carried out after the support. These methods may be appropriately selected depending on the desired co-catalyst or dye, the type of material used, and the like.

The step of applying the catalyst or the dye (or a precursor thereof) may be carried out at any stage of the first method to the third method. For example, 1) a method of adding a wet gel of a carbon material or a carbon precursor, 2) a method of forming a wet gel of a carbon material or a carbon precursor and applying it to the surface thereof, and 3) an oxide semiconductor precursor. There are a method of imparting in a step after forming, 4) a method of imparting in a step after forming an oxide semiconductor porous body, and the like.

The amount of the co-catalyst or dye supported can be appropriately determined according to the properties of the porous body, the type of co-catalyst or dye to be used, the application, and the like.<u style="single">(5) Fifth method</u> The first to fourth methods may include a step of removing a part of the carbon material which is the network structure skeleton or a precursor thereof. By such a step, a porous body having pores in a part of the carbon material can be obtained more reliably.

In the step of removing the carbon material or the carbon precursor, the carbon material or the carbon precursor is removed from the porous body in which the network structure skeleton 1 of the carbon material or the carbon precursor and the oxide semiconductor precursor or the oxide semiconductor are composited. Use the method. The means for removing is not limited, and for example, treatments such as evaporation, sublimation, and elution can be performed. In particular, in the present invention, heat treatment is suitable because the removal of the carbon material and the firing and crystallization of the oxide semiconductor material can be performed at the same time. As a method of heat treatment, carbon material is burned in an atmospheric gas containing oxygen (for example, in the atmosphere) to produce CO.₂The temperature at which the gas becomes gas may be heated to about 500 ° C. or higher. The upper limit of the heating temperature may be within the heat-resistant temperature of the oxide semiconductor material of the network structure skeleton 1. For example, in the case of titania, when the temperature exceeds 800 ° C, the firing temperature is about 800 ° C or less because the structure is a mixture of rutile type or amorphous having low photocatalytic activity instead of anatase type having photocatalytic activity. Is preferable.

By further advancing the heat treatment as described above, all of the carbon material can be removed. The porous body obtained in this case is an oxide semiconductor porous body.

Hereinafter, preferred embodiments of the production method of the present invention will be shown.

<u style="single">(Embodiment 5)</u> The first method (first method) for producing an oxide semiconductor / carbon composite porous body or an oxide semiconductor porous body according to the present invention comprises the basic steps shown in FIG.

As a basic step, after forming a wet gel having a network structure skeleton 1 of a carbon material, an oxide semiconductor precursor is formed on the wet gel, and the oxide semiconductor precursor is heat-treated to form a crystalline oxide. This is a method of making a semiconductor. That is, a step of synthesizing a wet gel of a carbon material from a carbon raw material, and a step of coating the obtained wet gel of a carbon material with an oxide semiconductor precursor in a liquid phase to obtain a composite wet gel of the oxide semiconductor precursor. It comprises a step of drying the composite wet gel of the oxide semiconductor precursor to obtain a composite dry gel, and then a step of heat-treating to obtain a porous body.

Here, by performing the heat treatment step in an inert gas atmosphere, an oxide semiconductor / carbon composite porous body can be obtained. In this manufacturing method, since the network structure skeleton 1 of the carbon material has a role as a support for maintaining the structure when the oxide semiconductor precursor is heat-treated, the porous body of the precursor shrinks as the heat treatment is performed. It is possible to suppress the phenomenon of heat treatment. As a result, it is possible to suppress an increase in density when the precursor is changed to a crystalline oxide semiconductor, and it is possible to suppress a decrease in specific surface area.

Alternatively, by performing the heat treatment step in a gas atmosphere containing oxygen, the carbon material having the network structure skeleton 1 can be removed to obtain an oxide semiconductor porous body. In this production method, since the network structure skeleton 1 is formed from the oxide semiconductor material, it is possible to form an oxide semiconductor porous body having a large specific surface area. Further, since the hollow portion exists inside the network structure skeleton 1, the surface area can be improved. Thereby, an oxide semiconductor porous body having a low density and a large specific surface area can be obtained. This porous body can be effectively used as a photocatalyst or a photoelectrode material.

The above steps are basic, and additional steps such as solvent substitution, catalyst formation, and surface treatment may be included in each step.<u style="single">(Embodiment 6)</u> The second method (second method) for producing the oxide semiconductor / carbon composite porous body or the oxide semiconductor porous body according to the present invention comprises the basic steps shown in FIG.

As a basic step, an oxide semiconductor precursor is formed on a dry gel obtained by forming a network structure skeleton 1 of a carbon material, and the oxide semiconductor precursor is heat-treated to form a crystalline oxide semiconductor. The method. That is, a step of synthesizing a wet gel of a carbon material from a carbon raw material, a step of drying the obtained wet gel of a carbon material to obtain a dry gel of a carbon precursor, and a step of coating a dry gel with an oxide semiconductor material and oxidizing it. It comprises a step of forming a product semiconductor composite precursor and a step of heat-treating the obtained oxide semiconductor composite precursor to obtain a porous body.

Here, the heat treatment step is carried out in an inert gas atmosphere to obtain an oxide semiconductor / carbon composite porous body. In this production method, since the network structure skeleton 1 of the carbon material has a role as a support for maintaining the structure when the oxide semiconductor precursor is heat-treated, the porous body of the precursor shrinks as the heat treatment is performed. Can be suppressed. As a result, it is possible to suppress an increase in density when the precursor is changed to a crystalline oxide semiconductor, and it is possible to suppress a decrease in specific surface area.

Alternatively, by performing the heat treatment step in a gas atmosphere containing oxygen, the carbon material having the network structure skeleton 1 is removed to obtain an oxide semiconductor porous body. In this production method, since the network structure skeleton 1 is formed from the oxide semiconductor, it is possible to form an oxide semiconductor porous body having a large specific surface area. Further, since the hollow portion exists inside the network structure skeleton 1, a high specific surface area can be obtained. As a result, an oxide semiconductor porous body having a low density and a large specific surface area can be obtained. Such a porous body can be effectively used as a photocatalyst or a photoelectrode material.

The above steps are basic, and steps such as solvent substitution, catalyst formation, and surface treatment may be added to each step.<u style="single">(Embodiment 7)</u> The third method (third method) for producing the oxide semiconductor / carbon composite porous body or the oxide semiconductor porous body according to the present invention comprises the basic steps shown in FIG. 7.

The basic step is a method of forming an oxide semiconductor in a gas phase in a carbon porous body obtained by forming a network structure skeleton 1 of a carbon material. That is, a step of synthesizing a wet gel of a carbon material from a carbon raw material, a step of drying the obtained wet gel of a carbon raw material to obtain a dry gel of a carbon precursor, and a step of carbonizing the dry gel to obtain a carbon porous body. , An oxide semiconductor / carbon composite porous body is obtained through a step of forming an oxide semiconductor material in a gas phase in a carbon porous body. As a method for forming an oxide semiconductor in a gas phase, as described above, i) a method of forming an oxide semiconductor precursor in a gas phase and then heat-treating in an inert gas atmosphere, ii) a direct oxide semiconductor. A method of forming or the like can be adopted.

In this manufacturing method, the network structure skeleton 1 of the carbon material functions as a support for maintaining the structure when the oxide semiconductor precursor is heat-treated, so that the porous body of the precursor shrinks as the heat treatment is performed. Can be suppressed. As a result, it is possible to suppress an increase in density when the precursor is changed to a crystalline oxide semiconductor, and it is possible to suppress a decrease in specific surface area. In particular, when an oxide semiconductor is directly formed in the gas phase, it is advantageous because distortion such as shrinkage due to heat treatment of the precursor is unlikely to occur.

Further, a part of the carbon material having the network structure skeleton 1 can be removed from the obtained oxide semiconductor / carbon composite porous body. The removing step includes a heat treatment step in a gas atmosphere containing oxygen. In this production method, since the network structure skeleton 1 is formed from the oxide semiconductor material, the specific surface area can be made larger than that of the porous body in which the carbon material is densely packed. Thereby, a porous body having a lower density and a larger specific surface area can be obtained. This porous body can be effectively used as a photocatalyst or a photoelectrode material.

In this case, it is possible to further proceed with heat treatment and the like to remove all of the carbon material. In this case, a porous body of an oxide semiconductor can be obtained. In the case of producing the oxide semiconductor porous body, since the carbon material (that is, the inside) is completely absent, a mold material can be used instead of the carbon material. The mold material is not limited as long as it can be removed while maintaining the surface portion. For example, silica or the like can be suitably used as a mold material. In this case, silica and the like can be removed by etching.

The above steps are basic, and steps such as solvent substitution, catalyst formation, and surface treatment may be added to each step.

<u style="single">(Embodiment 8)</u> Another method for producing a porous oxide semiconductor according to the present invention comprises the basic steps shown in FIG.

As a basic step, an oxide semiconductor precursor is formed on a wet gel of a carbon material having a network structure skeleton 1, and then the carbon material existing as the core of the network structure skeleton 1 is removed to form a porous oxide semiconductor. Is a way to get. That is, a step of synthesizing a wet gel of a carbon material from a carbon raw material, and a step of coating the obtained wet gel of a carbon material with an oxide semiconductor precursor in a liquid phase to obtain a composite wet gel of the oxide semiconductor precursor. , A step of removing the carbon material from this composite wet gel to obtain an oxide semiconductor precursor wet gel, a step of drying the wet gel of the oxide semiconductor precursor to obtain a dry gel, and then heat treatment to obtain a porous body. Consists of the process of obtaining.

In this production method, since the network structure skeleton 1 is formed from the oxide semiconductor material, it is possible to form an oxide semiconductor porous body having a large specific surface area. Further, since the hollow portion exists inside the network structure skeleton 1, the surface area can be improved. As a result, an oxide semiconductor porous body having a low density and a large specific surface area can be obtained. Such a porous body can be effectively used as a photocatalyst or a photoelectrode material. In this case, since all of the carbon material is removed, a mold material other than the carbon material can be used. As the mold material, the material listed in the seventh embodiment can be preferably used. Further, in the eighth embodiment, as in the seventh embodiment, the porous body of the present invention can be produced by removing a part of the carbon material.

Examples will be shown below, and the features of the present invention will be described in more detail. However, the scope of the present invention is not limited to the examples.

&lt;&lt; Example 1 &gt;&gt; First, a wet gel using a polyphenol-based polymer as a carbon precursor was synthesized. Wetting of polyphenols solidified by gelling an aqueous solution of raw materials prepared so that resorcinol (0.3 mol / L), formaldehyde and sodium carbonate have a molar ratio of 1: 2: 0.01 using water as a solvent. I got a gel.

Subsequently, in a wet gel of polyphenols, a composite wet gel of titania precursor was formed. The titania precursor was obtained by immersing the above-mentioned polyphenol wet gel in a raw material aqueous solution prepared by diluting titanium tetraisopropokioside with absolute ethanol and adding triethanolamine and water to impregnate the inside of the gel skeleton. The titania precursor was coated on the skeleton of the wet gel, left at room temperature and at about 80 ° C for 2 days each.

Subsequently, the composite wet gel in which the titania precursor was formed inside the gel was dried. The drying method was carried out by supercritical drying after replacing the solvent inside the wet gel with acetone to obtain a composite dry gel of the titania precursor from which the solvent inside was removed. As the conditions for supercritical drying, carbon dioxide was used as a drying medium, and after 4 hours had passed under the conditions of a pressure of 12 MPa and a temperature of 50 ° C., the pressure was gradually released to atmospheric pressure, and then the temperature was lowered to obtain a dry gel. At this time, the sizes before and after drying were almost the same, and there was almost no shrinkage. Apparent density is about 220kg / m³The vacancy rate was about 90%. In addition, the specific surface area measured by the BET method, which is a nitrogen adsorption method, is approximately 800 m.²It turned out to be a high value of / g.

Finally, the composite dry gel of the titania precursor was calcined to obtain a titania / carbon composite porous body. After leaving the composite dry gel in a nitrogen atmosphere at 100 ° C for 1 hour, 200 ° C for 1 hour, 300 ° C for 1 hour, 400 ° C for 1 hour, and 500 ° C for 1 hour. On the contrary, the temperature was lowered at 400 ° C for 1 hour, 300 ° C for 1 hour, 200 ° C for 1 hour, and 100 ° C for 1 hour, and then slowly cooled to room temperature. At this time, the size of the dried gel before and after firing was about 90% in length. Apparent density is about 300kg / m³The vacancy rate was about 80%. The specific surface area measured by the BET method, which is a nitrogen adsorption method, is approximately 450 m.²It was confirmed that it had a high value of / g.

&lt;&lt; Comparative Example 1 &gt;&gt; For comparison, a wet gel of the titania precursor alone was obtained under the conditions described in Example 1. Drying was also carried out under the same conditions as in Example 1 to obtain a dried gel of the titania precursor. At this time, the size before and after drying was about 95% in length. Apparent density is about 150kg / m³The vacancy rate was about 90%. In addition, the value of the specific surface area measured by the BET method, which is a nitrogen adsorption method, is about 500 m.²It was found to have a high specific surface area of / g.

Further, this was calcined under the same conditions as in Example 1 to obtain a titania porous body. At this time, the size of the dried gel before and after firing was about 70% in length. When combined with drying, it shrank to about 65%. Apparent density is about 550kg / m³The vacancy rate was about 40%. In addition, the value of the specific surface area measured by the BET method, which is a nitrogen adsorption method, is about 150 m.²It was / g.

As described above, in the conventional wet gel of titania precursor as in Comparative Example 1, the shrinkage during drying is small, but the shrinkage during firing is large. On the other hand, by combining with the carbon wet gel as in Example 1, shrinkage during firing could be suppressed and the specific surface area could be increased.

&lt;&lt; Example 2 &gt;&gt; A composite dry gel of titania precursor prepared under the same conditions as in Example 1 was obtained. By heat-treating this composite dry gel in the air, the carbon skeleton was evaporated and titania was crystallized and promoted to anatase crystal system to obtain a titania porous body. The heat treatment conditions are as follows: leave at 100 ° C for 1 hour, leave at 200 ° C for 1 hour, then leave at 300 ° C for 1 hour, then leave at 400 ° C for 1 hour, and leave at 500 ° C for 1 hour. Then, on the contrary, the temperature was lowered at 400 ° C for 1 hour, 300 ° C for 1 hour, 200 ° C for 1 hour, and 100 ° C for 1 hour, and then slowly cooled to room temperature. Before and after the heat treatment, the size shrank to about 70% in length, but the apparent density was about 100 kg / m.³Small and specific surface area is about 800m²A high value of / g was obtained. It was confirmed by electron microscope observation that this titania porous body had a hollow structure.

&lt;&lt; Example 3 &gt;&gt; First, a wet gel was synthesized using a polyphenol-based polymer as a carbon precursor under the conditions described in Example 1. Next, the obtained polyphenol wet gel was washed with ethanol (solvent replacement) and then supercritically dried with carbon dioxide to obtain a dried polyphenol gel. The conditions for supercritical drying were also the same as in Example 1.

Subsequently, a dry gel of polyphenol was coated with the titania precursor. The titania precursor is prepared by diluting titanium tetraisopropokioside with absolute ethanol and adding triethanolamine, water and polyethylene glycol to the raw material aqueous solution prepared by immersing the above polyphenol dry gel in the gel skeleton. Impregnated. The titania precursor was coated on the skeleton of the dried gel after being left at room temperature for 2 days.

Further, the dry gel coated with the titania precursor was calcined in a nitrogen atmosphere to obtain a titania / carbon composite porous body. The firing conditions were the same as in Example 1. At this time, the size of the gel before and after firing was about 85% in length. Apparent density is about 300kg / m³And the specific surface area is about 450m²It was a high value of / g.

&lt;&lt; Example 4 &gt;&gt; A composite gel coated with a titania precursor prepared under the same conditions as in Example 3 was obtained. By heat-treating this composite gel in the air, the carbon skeleton was evaporated and the crystallization of titania was promoted to obtain a titania porous body. The firing conditions were the same as in Example 2. Before and after the heat treatment, the size shrank to about 70% in length, but the apparent density was about 100 kg / m.³Small and specific surface area is about 800m²A high value of / g was obtained. It was confirmed by electron microscope observation that this titania porous body had a hollow structure.

&lt;&lt; Example 5 &gt;&gt; First, a wet gel using a polyimide polymer as a carbon precursor was synthesized. A 1 wt% N-methylpyrrolidone solution of polyamic acid synthesized from pyromellitic anhydride and 4,4'-oxydianiline was placed in a container and gelled to obtain a solidified polyamic acid wet gel.

Subsequently, this polyamic acid wet gel was used to obtain a polyimide dry gel as a carbon precursor by the following two methods.

In the first method, the polyamic acid wet gel was immersed in a solution of acetic anhydride and pyridine to carry out chemical imidization. This polyimide wet gel was dried to obtain a polyimide dry gel A.

In the second method, the polyamic acid wet gel was dried to obtain a dry gel. This dried gel was thermally imidized at 300 ° C. under a nitrogen atmosphere to obtain a polyimide dried gel B.

The obtained polyimide dry gels A and B were carbonized at 600 ° C. in a nitrogen atmosphere to obtain a carbonized carbon porous body. Both of the dried gels A and B were able to obtain carbon porous bodies in the same manner.

Further, titania was formed in the network structure skeleton 1 in the obtained carbon porous body. The carbon porous body is installed in a vacuum film forming apparatus, and titanium tetrachloride gas is discharged and plasma is formed by a high frequency of 13.56 MHz and a power of 200 W. Titania is formed in the carbon porous body whose temperature is adjusted to 200 ° C. / A carbon composite porous body was obtained. It was confirmed by X-ray diffraction that the produced titania had an anatase crystal structure. The apparent density of this titania / carbon composite porous material is about 220 kg / m.³With little shrinkage, the specific surface area by the BET method is about 600 m.²High values were obtained with / g. &lt;&lt; Example 6 &gt;&gt; The titania / carbon composite porous body prepared in Example 5 was heat-treated in the air under the same conditions as in Example 2 to obtain a titania porous body. This apparent density is about 100kg / m³Small, its specific surface area is 900m²A high value of / g was obtained. This titania porous body was also confirmed to have a hollow structure by electron microscope observation, and it is considered that a high specific surface area was achieved by the effect.

&lt;&lt; Example 7 &gt;&gt; A platinum catalyst was supported on the titania / carbon composite porous body A prepared in Example 1 and the titania porous body B prepared in Example 2 by the following method.

The platinum salt was supported by impregnating the porous bodies A and B with a 3 mmol / L ethanol solution of chloroplatinic acid. Sodium borohydride was added to this at room temperature to support a catalyst composed of platinum particles. The amount of catalyst supported is approximately 0.2 mg / cm, respectively.², Approximately 0.35 mg / cm²Therefore, the amount of the porous body B having a large specific surface area was larger.

<figref num="1">FIG. 1 is a schematic diagram for explaining a network structure skeleton in the porous body of the present invention.</figref><figref num="2">FIG. 2 is a cross-sectional view showing a network structure skeleton in the oxide semiconductor / carbon composite porous body of the present invention.</figref><figref num="3">FIG. 3 is a cross-sectional view showing a network structure skeleton in the porous oxide semiconductor of the present invention.</figref><figref num="4">FIG. 4 is a schematic view showing another example of the porous body of the present invention.</figref><figref num="5">FIG. 5 is a process diagram showing an example of a method for producing a porous body obtained in the present invention.</figref><figref num="6">FIG. 6 is a process diagram showing another example of the method for producing a porous body obtained in the present invention.</figref><figref num="7">FIG. 7 is a process diagram showing an example of a method for producing a porous body obtained in the present invention.</figref><figref num="8">FIG. 8 is a process diagram showing another example of the method for producing a porous body obtained in the present invention.</figref>

Code description

1 mesh structure skeleton 2 skeleton 3 carbon material 4 oxide semiconductor 6 oxide semiconductor 7 hollow part 8 porous network structure skeleton 9 supported cocatalyst or dye