JP2005298324A5 - - Google Patents

Description

Porous body and method for producing the same

  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 generating 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 molecular species in contact with the semiconductor are decomposed by the redox action. This action of semiconductors is called photocatalysis, and since the discovery of water photolysis at semiconductor photoelectrodes, the so-called Honda-Fujishima effect, much research has been conducted as a powerful means of light-to-chemical energy conversion. . 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, sulfide. Cadmium, zirconium dioxide, iron oxide and the like have been found. Furthermore, it is known that those semiconductors loaded with a metal such as platinum, palladium, rhodium or ruthenium as a cocatalyst are effective as a photocatalyst.

In the research of conventional photocatalysts, semiconductor powder has been used in many cases, but in order to link the photocatalyst to practical use, it is essential to form a film. For this reason, it is known to fix to a resin, glass or the like, or to use the semiconductor itself as a thin film. However, there is a problem that the catalyst amount itself is not sufficient and the effect cannot be sufficiently exhibited. Further, in order to increase the amount of catalyst, the area of the catalyst layer may be increased, but usually there are restrictions on design and it is often difficult.
On the other hand, the above semiconductor can obtain an electrode-like output by irradiating light to an n-type semiconductor. For this reason, it is used also for the electrode material of a wet photovoltaic cell using a photosensitized electrolysis phenomenon. In particular, in recent years, development of dye-sensitized solar cells has been active. The main structure of the semiconductor electrode, which is the working electrode, is a semiconductor porous film in which a dye sensitizer is adsorbed. As such a semiconductor material, titanium dioxide (titania), tin oxide, zinc oxide, niobium oxide, or the like is used. As the sensitizing dye, a ruthenium complex system or the like is known. Although this dye-sensitized solar cell is expected to be low in cost with a simple structure as compared with a conventional silicon solar cell, improvement of conversion efficiency is the biggest problem in practical use.

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

  For example, a method of obtaining a titanium oxide porous thin film photocatalyst having pores with uniform pore diameters on the surface by coating titania sol on a substrate and then baking it 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, JP-A-10-151355).

For example, an oxide semiconductor electrode comprising a conductive substrate and a porous oxide semiconductor layer formed on the conductive substrate and including hollow particles made of a metal oxide is disclosed ( JP 2001-76772).
JP 2001-077672 A JP 2000-319018 A WO98 / 35267 Japanese Patent Laid-Open No. 2003-301283 JP-A-3-093634 JP-A-5-023637 Japanese Unexamined Patent Publication No. 63-280748

  However, as described in Japanese Patent No. 2636158, the following problems were clarified as a result of intensive studies on a method of heating and baking an organic gel to form a porous body.

  (1) In the step of firing the organic gel of the oxide semiconductor precursor polymer, the precursor porous body contracts as it is fired, and the resulting oxide semiconductor porous body has a density higher than that of the precursor. As a result, the specific surface area tends to decrease.

  (2) Since the organic gel having a network structure skeleton 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. After obtaining organic gels, it is difficult to control their density and specific surface area.

  In addition, when silica is used as a carrier as disclosed in Japanese Patent Application Laid-Open No. 10-151355, there is a problem in that the electric conduction characteristics are deteriorated because silica is an insulator. In particular, when used as a photoelectrode material, it is necessary to improve the electrical conductivity of the porous body and the electronic network between the semiconductor particles in order to increase the efficiency.

  Furthermore, since the oxide semiconductor electrode disclosed in Japanese Patent Application Laid-Open No. 2001-76772 has a structure in which fine particles are connected and become hollow, an electronic network between the fine particles is weak and electrical conductivity may be low.

  Therefore, a main object of the present invention is to provide a porous body including an oxide semiconductor in which a more efficient photocatalytic reaction or photoelectrode reaction occurs.

  A further object of the present invention is to provide a method for efficiently producing a porous body containing an oxide semiconductor.

The present invention relates to the following porous body and method for producing the same .
1 . A method for producing a porous oxide semiconductor body having a network structure skeleton, wherein an oxide semiconductor precursor composite wet gel is formed by coating an oxide semiconductor precursor on the skeleton in a template material-containing wet gel having a network structure skeleton. A template material having the network structure skeleton by obtaining a pretreatment step, drying a composite wet gel to obtain an oxide semiconductor precursor composite dry gel, and heat-treating the dry gel in a gas atmosphere containing oxygen The manufacturing method of the porous body which has the process of removing and obtaining an oxide semiconductor porous body.
2 . A method for producing a porous oxide semiconductor body having a network structure skeleton, wherein a template material-containing wet gel having a network structure skeleton is dried to obtain a template material-containing dry gel having a network structure skeleton, in the dried gel An oxide semiconductor material is coated on the skeleton to obtain an oxide semiconductor composite precursor, and the composite precursor is heat-treated in a gas atmosphere containing oxygen to remove the template material having the network structure skeleton and oxidize A method for producing a porous body having a step of obtaining a porous semiconductor body.
3 . A method for producing a porous oxide semiconductor body having a network structure skeleton, the step of drying a template material-containing wet gel having a network structure skeleton to obtain a dry gel of a template material having a network structure skeleton, and solidifying the dried gel Obtaining a template porous body, coating the skeleton with an oxide semiconductor material to obtain an oxide semiconductor / template material composite porous body, and a template having the network structure skeleton from the composite porous body A method for producing a porous body, wherein the material is removed to obtain an oxide semiconductor porous body.
4 . A method for producing a porous oxide semiconductor body having a network structure skeleton, wherein an oxide semiconductor precursor composite wet gel is formed by coating an oxide semiconductor precursor on the skeleton in a template material-containing wet gel having a network structure skeleton. A pretreatment step for obtaining, a template material removing step for obtaining the oxide semiconductor precursor wet gel by removing the template material from the composite wet gel, a drying step for obtaining the oxide semiconductor precursor dry gel by drying the wet gel, And a method for producing a porous body, comprising a step of heat-treating the dry gel to obtain an oxide semiconductor porous body.
5 . Item 5. The method for producing a porous body according to any one of Items 1 to 4 , further comprising a step of supporting a catalyst.
6 . Item 5. The method for producing a porous body according to any one of Items 1 to 4 , further comprising a step of supporting a dye.
7). Item 5. The method for producing a porous body according to any one of Items 1 to 4 , wherein the template material is carbon.
8). A porous body having a network structure skeleton, wherein 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially hollow, and 3) a part or all of the surface portion is an oxide semiconductor. Is a porous body.

According to the onset bright, low density, it is possible to produce a porous body having a high specific surface area oxide semiconductor system.

INDUSTRIAL APPLICABILITY The porous body of the present invention can be used for a photocatalyst, a photoelectrode, and the like because an oxidation / reduction reaction occurs efficiently by light irradiation. More specifically, it can be used for applications such as solar cells (for example, dye-sensitized solar cells) and photohydrogen generators.

Embodiments of the present invention will be described below. First, the structure of the porous body of the present invention will be described with reference to the drawings.
1. Porous body The porous body of the present invention is a porous body having a network structure skeleton, wherein 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially hollow, and 3) the surface portion. This is characterized in that part or all of the oxide semiconductor is an oxide semiconductor.

  The network structure skeleton of the porous body of the present invention may be one having a three-dimensional network structure. The network structure skeleton is composed of an inner portion and a surface portion.

The interior is substantially hollow.

Part or all of the surface portion is made of an oxide semiconductor. In particular, a material that causes a photocatalytic reaction can be preferably used for the oxide semiconductor used in the present invention. For example, titanium dioxide (titania), vanadium pentoxide, zinc oxide, tungsten oxide, copper oxide, strontium titanate, barium titanate, sodium titanate, zirconium dioxide, α-Fe ₂ O ₃ , K ₄ Nb ₆ O ₁₇ , Examples include at least one oxide (metal oxide) such as Rb ₄ Nb ₆ O ₁₇ , K ₂ Rb ₂ Nb ₆ O ₁₇ , Pb _1-x K _2x NbO ₆ (where 0 <x <1). it can.

  The porous body of the present invention may contain other components as necessary. For example, a cocatalyst may be included. Examples of promoters 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 use of the porous body, the desired reaction, and the like. The amount of the cocatalyst supported can usually be selected in the range of 0.1 to 20% by weight based on the total weight of the oxide semiconductor and the cocatalyst from the viewpoint of photocatalytic activity.

  Moreover, the pigment | dye may be contained as needed. As the dye, those known as sensitizing dyes can be preferably used. More specifically, it is desirable to use a ruthenium complex system or the like. The amount of the dye supported may be appropriately selected according to the type of the dye used.

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

  Further, the ratio between the inside and the surface portion can be appropriately determined according to the type of the oxide semiconductor, the use of the porous body, and the like.

The bulk density, the BET specific surface area, and the average pore diameter of the porous body of the present invention can be appropriately set depending on the type of oxide semiconductor, the use of the porous body, the usage method, and the like. The bulk density may be appropriately determined from a range of usually 10 kg / m ³ or more and 800 kg / m ³ or less, particularly 50 kg / m ³ or more and 400 kg / m ³ or less. The specific surface area can be appropriately set within the range of usually 50 m ² / g to 1500 m ² / g, particularly 100 m ² / g to 1000 m ³ / g, and more preferably 200 m ² / g to 1000 m ² / g. The specific surface area is a value measured by Brunauer-Emmett-Teller method (hereinafter abbreviated as BET method) which is a nitrogen adsorption method. Moreover, the average pore diameter of the porous body of the present invention can be appropriately determined from the range of usually 1 nm to 1000 nm, particularly 5 nm to 50 nm.

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

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

(1) Reference form 1
The first configuration of the porous body according to the reference embodiment 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 is formed by coating the oxide semiconductor 4 with the network structure made of a dry gel of the carbon material 3 as the core of the skeleton 2.

  The structure of the network structure skeleton 1 is such that the skeleton as shown in FIG. 1 forms a network in the form of 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 aggregation 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 an aggregate of fine particles and has a porous structure having voids between the fine particles. In the structure obtained from the above process, generally, gaps formed by skeletons (skeletons) made of fine particles having a particle diameter of 100 nm or less constitute pores. The pore size is as small as about 1 μm or less. Thereby, as a result of realizing a porosity of 50% or more, a porous body having a high specific surface area can be provided. In particular, in a network structure skeleton formed via a gel as in the present invention, the fine particles are as small as 1 nm or more and 50 nm or less, and the resulting pore size is as small as 100 nm or less. Thus, a porous body having a porosity of 80% or more and a high specific surface area of 100 m 2 / g or more can be obtained.

  Therefore, in the oxide semiconductor / carbon composite porous body of the present invention, since the oxide semiconductor 4 is coated on the network skeleton of the dry gel of the carbon material 3, a porous body having a large specific surface area can be formed. . Thereby, application to a highly active photocatalyst is possible. Moreover, since the core of the network structure skeleton 1 is made of a carbon material having conductivity, higher electrical efficiency can be realized when used as an electrode material for solar cells or the like.

This can be more reliably realized 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 having a step of forming a crystalline oxide semiconductor by heat treatment or the like of a precursor gel of an oxide semiconductor, a network of carbon materials is used. Since the structural skeleton 1 has heat resistance, it can serve as a support for an oxide semiconductor in the heat treatment process, and can suppress 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 can achieve a high specific surface area.

(2) Embodiment 1
A first embodiment 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 portion of the skeleton is made of the oxide semiconductor 6, and the inside is substantially entirely occupied by the hollow portion 7 (space).

  In the above structure, in addition to the high specific surface area due to the network structure skeleton having a dry gel structure, the inside of the skeleton is a hollow portion 7. This porous body has a specific surface area higher than that of the above-mentioned carbon composite porous body due to the hollow portion. As a result, the porous body can be used as a more active photocatalyst, photoelectrode material, or the like.

( 3) Embodiment 2
In the third configuration of the porous material according to the present invention, as shown in FIG. 4, the oxides semiconductor porous body that having a network structure skeleton 1, cocatalyst 9 in the oxide semiconductor having a catalytic function is carried Yes. In this configuration, since the porous body having a large specific surface area shown in Reference Embodiment 1 or Embodiment 1 is used as a photocatalyst, it is possible to secure a larger amount of cocatalyst and to increase reaction active points. There is. This makes it possible to apply to highly active photocatalysts.

At this time, it is desirable that the cocatalyst is present in contact with the oxide semiconductor . The oxide semiconductor porous body according to the first implementation, the cocatalyst may be present in either the outer or inner surface of the oxide semiconductor of the backbone. In particular, a cocatalyst is preferably present on the surface of the oxide semiconductor in terms of increasing the chance of contact with the reactant and increasing the reactivity.

(4) Embodiment 3
In the third configuration of the porous material according to the present invention, as shown in FIG. 4, the oxides semiconductor porous body that having a network structure skeleton 1, the dye 9 is supported on the oxide semiconductor. In this configuration, since the porous body having a large specific surface area shown in Reference Embodiment 1 or Embodiment 1 is used as the photoelectrode, it is possible to increase the amount of the dye supported and to increase the reaction active points. Is obtained. As a result, application to electrode materials for dye-sensitized solar cells and the like becomes possible.

At this time, it is desirable that the dye is present in contact with the oxide semiconductor . The oxide semiconductor porous body according to the first implementation, the dye may be present in either the outer or inner surface of the oxide semiconductor of the backbone.

2. As a method for producing a porous body production method invention of the porous body, it has a limited as long as the structure as described above can be obtained.

(1) First Reference Method The first reference method is a porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface portion, 2) the inside is substantially made of a carbon material, 3) A method for producing an oxide semiconductor / carbon porous body in which a part or all of the surface portion is an oxide semiconductor,
(1) a first step of obtaining a composite wet gel by coating the skeleton with an oxide semiconductor precursor in a carbon precursor-containing wet gel having a network structure skeleton;
(2) a second step of obtaining a composite dry gel by drying the composite wet gel, and (3) a third step of obtaining an oxide semiconductor / carbon composite porous body by heat-treating the composite dry gel. Including.

First Step 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.

  The carbon precursor is preferably an organic polymer material that is carbonized by heat treatment. For example, polyacrylonitrile, polyfurfuryl alcohol, polyimide, polyamide, polyamideimide, polyurethane, polyurea, polyphenol, polyaniline, polyparaphenylene, and the like can be used. These can be used alone or in combination of two or more.

  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. In addition, a gel-like reaction product obtained by reacting these precursor raw materials 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, and glycols such as ethylene glycol and propylene glycol. These may be used alone or in combination of two or more. These may be appropriately selected according to the type of carbon precursor used.

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

  When a carbon precursor material is used, a known material can be used as the material. For example, for polyacrylonitrile, polyfurfuryl alcohol, polyaniline, etc., acrylonitrile, furfuryl alcohol, aniline, etc. can be used as raw materials, respectively. Moreover, when a polyimide is synthesized by a condensation polymerization reaction for forming an imide ring, generally, a tetracarboxylic anhydride compound and a diamine compound can be used. When the polyamide is synthesized by a condensation polymerization reaction for forming an amide bond, generally, a dicarboxylic acid compound, a dicarboxylic acid chloride compound, and a diamine compound can 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 and an aldehyde compound can be used. The raw materials shown here are described for the purpose of using general materials, and are not limited to these raw materials.

  In addition, as these raw materials, the thing containing an aromatic component is preferable at the point that it is easy to be carbonized. In addition, an efficient carbon precursor can be formed by reacting these raw materials together with a catalyst.

Below, the case where a polyphenol wet gel is used as a carbon precursor containing wet gel is demonstrated as an example. Examples of a method for obtaining a wet gel include a method in which a raw material of polyphenol is synthesized by a sol-gel reaction in a solvent and is converted into a wet gel. At this time, a catalyst can be used as needed. In this formation process, polyphenol fine particles are formed while the raw materials react in a solvent, 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 that are predetermined solid components is determined. If necessary, a catalyst, a viscosity modifier or the like is added to the solution prepared to the composition, and the mixture is stirred to obtain a desired form of use by casting, coating, or the like. When a certain period of time elapses in this state, the solution gels and becomes a wet gel. If necessary, an aging treatment may be performed for the purpose of aging a wet gel, controlling pores, and the like.

  The raw materials for polyphenols include phenols such as phenol, cresol, resorcin (1,3-benzenediol), catechol, phloroglicinol, novolac-type phenol resin, resol-type phenol resin, and other phenol compounds such as salicylic acid and oxybenzoic acid. Examples include carboxylic acid. Examples of the aldehyde compound that is a condensing agent include formaldehyde, acetaldehyde, furfural, and the like, as well as paraformaldehyde, hexamethylenetetramine, and the like that generate formaldehyde by heating. As the condensation catalyst, a base catalyst and / or an acid catalyst can be used. The base catalyst mainly proceeds an addition reaction such as a methylol group, and the acid catalyst mainly proceeds a polyaddition condensation reaction such as a methylene bond. Base catalysts include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate, as well as catalysts for producing general phenol resins such as amines 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. Moreover, as a solvent, the raw material should just melt | dissolve and a polyphenol gel can be formed. For example, in addition to water, alcohols such as methanol, ethanol, propanol and butanol, and glycols such as ethylene glycol and propylene glycol can be used. These can be used individually or in mixture of 2 or more types.

  Examples of the oxide semiconductor include those used in the porous body of the present invention. The precursor 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 alkoxides, metal salts and the like.

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

  As the method a), a solution or dispersion obtained by dissolving or dispersing the oxide semiconductor precursor in a solvent is used, and the carbon precursor-containing wet gel is immersed in the solution or dispersion. By this step, the polymer adheres to the skeleton of the network structure and is coated. For example, titania (TiO2) precursor as an oxide semiconductor precursor is made from titanium methylphenoxide, titanium n-monooxide, titanium n-propoxide, titanium triisopropoxide tri-n-butylstannoxide, etc. By hydrolysis, a titania precursor in a sol state of polymerized fine particles can be obtained. In this method, the wet gel retains the solution or dispersion therein, and these precursors are adsorbed or agglomerated on the skeleton, and are combined to form a residual skeleton when dried. Further, when a wet gel containing a solution in which the precursor is dissolved is immersed in a poor solvent for the polymer, the precursor is deposited and coated on the skeleton. Note that the method for coating the skeleton with the oxide semiconductor precursor is not limited thereto.

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 the 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 difficult to physically elute, which is particularly effective in the present invention. 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 may be used. it can. It is to be noted that an efficient oxide semiconductor precursor can be formed by reacting these raw materials together with a catalyst.

  The amount of the oxide semiconductor precursor used may be such that the coating layer has a desired thickness.

Second Step In the second step, a composite dry gel is obtained by drying the composite wet gel.

  It does not specifically limit as a drying method. For example, in addition to normal drying methods such as natural drying, heat drying, and vacuum drying, supercritical drying methods, freeze drying methods, and the like can also be used. Generally, if the amount of solid components in the wet gel is decreased in order to increase the surface area of the dried gel and reduce the density, the gel strength decreases. In addition, simply drying 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 a drying means. Thereby, shrinkage of the gel during drying, that is, densification can be effectively avoided. Even in a normal drying means for evaporating a solvent, gel shrinkage during drying can be suppressed by using a high-boiling solvent for slowing the evaporation rate or controlling the evaporation temperature. Moreover, shrinkage | contraction of the gel at the time of drying can also be suppressed by performing the water repellent process etc. on the surface of the solid component of a gel with respect to a wet gel, and controlling surface tension.

  In the supercritical drying method or the freeze drying method, by changing the phase of the solvent from the liquid state, the solvent can be dried without eliminating the gas-liquid interface and applying stress to the gel skeleton due to surface tension. For this reason, the shrinkage | contraction of the gel at the time of drying can be prevented, and the porous body of a low density dry gel can be obtained. In the present invention, it is particularly preferable to use the supercritical drying method.

  As a solvent used for supercritical drying, a solvent retained by a wet gel can be used. If necessary, it is preferable to substitute 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 which directly make the solvent a supercritical fluid, carbon dioxide, water and the like. Or you may substitute by organic solvents, such as acetone, isoamyl acetate, and hexane which are easy to elute 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 conditions are set to a critical pressure of 8.09 MPa or more and a critical temperature of 239.4 ° C. or more, and the pressure is gradually released in a constant temperature state. 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 a constant temperature in the same manner, and then dried to a gaseous state. I do. For example, when the solvent is water, drying is performed at a critical pressure of 22.04 MPa or higher and a critical temperature of 374.2 ° C. or higher. As the time required for drying, it suffices to pass a time required for the solvent in the wet gel to be replaced at least once by the supercritical fluid.

Third Step In the third step, an oxide semiconductor / carbon composite porous body is obtained by heat-treating the composite dry gel.

  The heat treatment temperature can be appropriately determined depending on the type of oxide semiconductor (precursor), desired physical properties, and the like, generally within a range of 300 ° C. to 1200 ° C. (especially 450 ° C. to less than 1000 ° C.). .

  For example, in the case of a titania precursor, anatase formation starts to proceed at about 500 ° C. or higher, and therefore, it is performed at 500 ° C. or higher. From the viewpoint of working time efficiency, a temperature of about 600 to 700 ° C. is preferable. Moreover, the upper limit of heating temperature should just be below the heat-resistant temperature of the carbon material of the network structure frame | skeleton 1. FIG. For example, the dry gel of the carbon material slightly shrinks at about 600 ° C., but at 1200 ° C. or higher, graphitization starts to progress and the shrinkage increases. Therefore, the firing temperature may be selected depending on the degree of the shrinkage suppressing effect. It is particularly desirable to bake at less than 1000 ° C.

  The atmosphere for the heat treatment is not limited, and may be any of air, oxidizing atmosphere, reducing atmosphere, inert gas atmosphere, vacuum, and the like. In particular, considering combustion and the like, it is preferable that the temperature be set high in a low-concentration oxygen atmosphere. More specifically, it is desirable that the atmosphere has an oxygen concentration of 0 to 10% by volume. More preferably, it is in an inert gas atmosphere or in a vacuum. In particular, an inert gas atmosphere is most preferable. As the inert gas, various gases such as nitrogen, argon, and helium can be used.

(2) Second Reference Method The second reference method is a porous body having a network structure skeleton, 1) the skeleton is composed of an inside and a surface portion, and 2) the inside is substantially made of a carbon material, 3) A method for producing a porous body in which part or all of the surface portion is an oxide semiconductor,
(1) 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;
(2) a 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 thereby heat-treat the oxide semiconductor / carbon composite porosity. Including a third step of obtaining a body.

First Step In the first step, a dry gel having a network structure skeleton is obtained by drying a carbon precursor-containing wet gel having a network structure skeleton.

The said wet gel can use the thing similar to the wet gel shown by the 1st reference method. Also, the drying method can be carried out in the same manner as the drying in the second step of the first reference method.

Second Step 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 reference method can be used.

  The method for coating the oxide semiconductor is not particularly limited. In the present invention, there are two main methods: a method in which an oxide semiconductor precursor is formed in a liquid phase and then firing, and a method in which an oxide semiconductor is formed in a gas phase. It can be used characteristically. More specifically, 1) a method in which an oxide semiconductor precursor is coated on the skeleton and then heat-treated to form an oxide semiconductor, and 2) a method in which an oxide semiconductor is imparted to the skeleton by a vapor phase method are applied. it can.

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

  The above method 2) includes, for example, c) a method in which an oxide semiconductor precursor is formed in a gas phase in a dry gel of a carbon precursor and then heat treatment, and d) an oxide semiconductor directly in the dry gel of a carbon precursor. It is possible to adopt a method of forming and coating in the gas phase.

  In addition, a well-known method can be employ | adopted for the gaseous-phase method itself. 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 employed. it can.

  The method c) is, for example, a method in which a raw material of an oxide semiconductor precursor is vaporized, introduced into a dry gel, and reacted in the dry gel to generate an oxide semiconductor precursor. For example, when titania is formed as an oxide semiconductor, a raw material such as titanium tetrachloride, titanium methylphenoxide, or titanium n-monoxide is vaporized and charged into a dry gel before polymerization. This oxide semiconductor precursor can form an oxide semiconductor by further heat treatment.

  The method d) is a method in which an oxide semiconductor is directly formed on a skeleton of a dry gel by a vapor phase method using an oxide semiconductor raw material. This method is advantageous in that no heat treatment is required as compared with the method c). For example, when titania is formed, titanium tetrachloride, metal titanium, or the like is used as a starting material and may be oxidized by heat, plasma, ions, light, a catalyst, or the like. Alternatively, the dried gel can be coated with a technique such as sputtering and laser ablation using titanium oxide as a target. In order to advance crystallization in a dry gel, the method by heating has high controllability and can be preferably used. At this time, as an advantage of growing in the vapor phase, there is a feature that the treatment can be performed at a low temperature as compared with the firing.

Third Step In the third step, an oxide semiconductor / carbon composite porous body is obtained by heat-treating the composite precursor.

The heat treatment method may be the same as the heat treatment in the third step of the first reference method. In particular, the heat treatment atmosphere is preferably an atmosphere having an oxygen concentration of 0 to 10% by volume. Among these, it is more preferable to be in an inert gas atmosphere or vacuum, and most preferable to be in an inert gas atmosphere.

(3) Third Reference Method The third reference method is a porous body having a network structure skeleton, wherein 1) the skeleton is composed of an interior and a surface portion, and 2) the interior is substantially composed of a carbon material, 3) A method for producing a porous body in which part or all of the surface portion is an oxide semiconductor,
(1) 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;
(2) a second step of obtaining a carbon porous body by carbonizing the dried gel; and (3) an oxide semiconductor / carbon composite by covering the skeleton with an oxide semiconductor in the carbon porous body. A third step of obtaining a porous body;
including.

First Step In the first step, a dry gel having a network structure skeleton is obtained by drying a carbon precursor-containing wet gel having a network structure skeleton.

The carbon precursor-containing wet gel may be the same as the wet gel used in the first reference method. What is necessary is just to implement the drying method of a wet gel according to the drying method of the 2nd process of a 1st reference method.

Second Step In the second step, a carbon porous body is obtained by carbonizing the dried gel.

The carbonization method may be the same as the heat treatment in the third step of the first reference method. In particular, the atmosphere for the carbonization treatment is desirably an atmosphere having an oxygen concentration of 0 to 10% by volume. Among these, it is more preferable to be in an inert gas atmosphere or vacuum, and most preferable to be in an inert gas atmosphere.

Third Step In the third step, an oxide semiconductor / carbon composite porous body is obtained by coating the skeleton in the carbon porous body with an oxide semiconductor.

The method for coating the carbon porous body with the oxide semiconductor may be the same as in the second step of the second reference method.

(4) Fourth reference The present invention includes in the first reference method to third reference method, the fourth reference method for further performing the step of applying the co-catalyst or dye. The step of supporting a promoter or a 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 (listed above) can be used.

  The means for imparting a cocatalyst or dye is not particularly limited, and 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 cocatalyst or a dye precursor and then reducing with a reducing agent such as hydrogen, 3) porous by firing of a cocatalyst or a dye precursor, etc. There is a method of loading a catalyst on the body.

  As the precursor, any material can be used as long as it is a material that finally gives a promoter or a dye. For example, a metal salt or the like can be used as a precursor of the promoter. In the case of using a catalyst or a dye precursor, a catalyst or sensitizing dye may be applied after the support. These methods may be appropriately selected according to the desired cocatalyst or dye, the type of material used, and the like.

You may implement the process of providing a catalyst or a pigment | dye (or those precursors) in any step of a 1st reference method-a 3rd reference 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 the wet gel to the surface thereof, 3) an oxide semiconductor precursor There are a method of applying in the step after forming, 4) a method of applying in the step after forming the oxide semiconductor porous body, and the like.

The amount of the cocatalyst or dye supported can be appropriately determined according to the properties of the porous body, the type of cocatalyst or dye used, the application, and the like .

The porous oxide semiconductor according to the present invention removes a part of the carbon material having a network structure skeleton or a precursor thereof from the oxide semiconductor / carbon composite porous body obtained by the first reference method to the fourth reference method. the step of including. By this step, a porous body having pores in a part of the carbon material can be obtained more reliably.

  The step of removing the carbon material or the carbon precursor removes the carbon material or the carbon precursor from the porous body in which the carbon material or the network structure skeleton 1 of the carbon precursor and the oxide semiconductor precursor or the oxide semiconductor are combined. Use the method. The means for removing is not limited, and for example, processes such as evaporation, sublimation, and elution can be performed. In particular, in the present invention, the heat treatment is suitable because the removal of the carbon material and the firing and crystallization of the oxide semiconductor material can be performed simultaneously. As a heat treatment method, heating may be performed to about 500 ° C. or more as a temperature at which the carbon material burns to become CO 2 gas in an atmosphere gas containing oxygen (for example, in the air). The upper limit of the heating temperature may be in the range of the heat resistance temperature of the oxide semiconductor material of the network structure skeleton 1. For example, in the case of titania, if the temperature exceeds 800 ° C., the structure is not anatase type having photocatalytic activity but a rutile type or amorphous material having low photocatalytic activity, and the firing temperature is about 800 ° C. or less. It is preferable.

  In addition, all the carbon materials can be removed by further proceeding with the heat treatment as described above. 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 described.

(Embodiment 4 )
First manufacturing method of the oxides semiconductor porous body that involved in the present invention (first method) consists of the basic steps shown in FIG.

  As a basic process, 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 carbon material from a carbon raw material, a step of coating the obtained wet gel of carbon material with an oxide semiconductor precursor in a liquid phase to obtain a composite wet gel of oxide semiconductor precursor The method includes a step of drying a composite wet gel of an oxide semiconductor precursor to obtain a composite dry gel, and a step of subsequent heat treatment to obtain a porous body.

By performing the heat treatment step in a gas atmosphere containing oxygen, it is possible to remove the carbon material having a network structure skeleton 1 to obtain an oxide semiconductor porous body. In this manufacturing method, since the network structure skeleton 1 is formed from an oxide semiconductor material, an oxide semiconductor porous body having a large specific surface area can be formed. Furthermore, since a hollow part 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 replacement, catalyst formation, and surface treatment may be included in performing each step.

(Embodiment 5 )
The second method of manufacturing oxides semiconductor porous body that involved in the present invention (second method) basically consists of steps shown in FIG.

  As a basic process, 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. Is the method. That is, a step of synthesizing a wet gel of carbon material from a carbon raw material, a step of drying the obtained wet gel of carbon material to obtain a dry gel of a carbon precursor, and an oxide semiconductor material coated on the dry gel to oxidize A step of forming a solid semiconductor composite precursor, and a step of obtaining a porous body by heat-treating the obtained oxide semiconductor composite precursor.

By performing the heat treatment step in a gas atmosphere containing oxygen to give an oxide semiconductor porous body by removing the carbon material having a network structure skeleton 1. In this manufacturing method, since the network structure skeleton 1 is formed from an oxide semiconductor, an oxide semiconductor porous body having a large specific surface area can be formed. Furthermore, since a hollow part exists in the network structure skeleton 1, a high specific surface area can be obtained. Thereby, 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 replacement, catalyst formation, and surface treatment may be added to perform each step.

(Embodiment 6 )
A third method of manufacturing oxides semiconductor porous body that involved in the present invention (method 3) consists of the basic steps shown in FIG.

  The basic process is a method of forming an oxide semiconductor in a gas phase on 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 the carbon raw material to obtain a dry gel of a carbon precursor, a step of carbonizing the dry gel to obtain a carbon porous body The oxide semiconductor / carbon composite porous body is obtained through the step of forming the oxide semiconductor material in the gas phase in the carbon porous body. As described above, as a method for forming an oxide semiconductor in a gas phase, i) a method in which an oxide semiconductor precursor is formed in a gas phase and then heat-treated in an inert gas atmosphere, and ii) a direct oxide semiconductor is formed. A forming method or the like can be employed.

  In this manufacturing method, when the network structure skeleton 1 of the carbon material heat-treats the oxide semiconductor precursor, the porous body of the precursor shrinks as it heat-treats in order to serve as a structure-supporting support. Can be suppressed. Accordingly, an increase in density when the precursor is changed to a crystalline oxide semiconductor can be suppressed, and a decrease in specific surface area can be suppressed. In particular, when an oxide semiconductor is directly formed in a gas phase, it is advantageous because distortion such as shrinkage due to heat treatment of the precursor hardly occurs.

Furthermore, it removes a portion of the carbon material having a network structure skeleton 1, using the resultant oxide semiconductor / carbon composite porous body. As this removal process, there is a heat treatment process in a gas atmosphere containing oxygen. In this manufacturing method, since the network structure skeleton 1 is formed from the oxide semiconductor material, the specific surface area can be increased as compared with a 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, to remove all of the carbon material further advanced heat treatment, Ru obtain a porous body of an oxide semiconductor. In the case of manufacturing an oxide semiconductor porous body, since there is no carbon material (that is, inside), a template material in place of the carbon material can be used. 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 template material. In this case, silica or the like can be removed by etching.

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

(Embodiment 7 )
Another method for manufacturing a porous oxide semiconductor according to the present invention includes the basic steps shown in FIG.

  As a basic process, 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 body. Is the way to get. That is, a step of synthesizing a wet gel of carbon material from a carbon raw material, a step of coating the obtained wet gel of carbon material with an oxide semiconductor precursor in a liquid phase to obtain a composite wet gel of oxide semiconductor precursor The step of obtaining the oxide semiconductor precursor wet gel by removing the carbon material from the composite wet gel, the step of drying the oxide semiconductor precursor wet gel to obtain the dry gel, and then the heat treatment to obtain the porous body It consists of the process of obtaining.

  In this manufacturing method, since the network structure skeleton 1 is formed from an oxide semiconductor material, an oxide semiconductor porous body having a large specific surface area can be formed. Furthermore, since a hollow part 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. 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 materials listed in Embodiment 7 can be suitably used. In the eighth embodiment, similarly to the seventh embodiment, the porous body of the present invention can be manufactured by removing a part of the carbon material.

  The features of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to the examples.

<< Reference Example 1 >>
First, a wet gel using a polyphenol polymer as a carbon precursor was synthesized. A raw material aqueous solution prepared using resorcinol (0.3 mol / L), formaldehyde and sodium carbonate in a molar ratio of 1: 2 to 0.01 using water as a solvent was gelled and solidified. A wet polyphenol gel was obtained.

  Subsequently, a composite wet gel of titania precursor was formed in a polyphenol wet gel. The titania precursor was impregnated into the skeleton of the gel by immersing the polyphenol wet gel in a raw material aqueous solution prepared by diluting titanium tetraisopropoxyside with absolute ethanol and adding triethanolamine and water. The titania precursor was coated on the wet gel skeleton by standing at room temperature and about 80 ° C. for 2 days, respectively.

  Subsequently, the composite wet gel in which the titania precursor was formed inside the gel was dried. The drying method was performed by supercritical drying after substituting the solvent in the wet gel with acetone to obtain a composite dry gel of titania precursor from which the solvent was removed. Supercritical drying was performed using carbon dioxide as a drying medium, and after 4 hours under conditions of a pressure of 12 MPa and a temperature of 50 ° C., the pressure was gradually released to lower the temperature, and then the temperature was lowered to obtain a dry gel. At this time, the size before and after drying was almost the same, and it was hardly contracted. The apparent density was about 220 kg / m3, and the porosity was about 90%. Moreover, it turned out that the specific surface area measured by BET method which is a nitrogen adsorption method is a high value of about 800 m <2> / g.

  Finally, the titania precursor composite dry gel was fired to obtain a titania / carbon composite porous body. The composite dried gel is left in a nitrogen atmosphere at 100 ° C. for 1 hour, left at 200 ° C. for 1 hour, left at 300 ° C. for 1 hour, left at 400 ° C. for 1 hour, left at 500 ° C. for 1 hour, and conversely at 400 ° C. The temperature was lowered at 300 ° C. for 1 hour, 200 ° C. for 1 hour, and 100 ° C. for 1 hour, and then gradually cooled to room temperature. At this time, the size of the dried gel before and after firing was about 90% in length. The apparent density was about 300 kg / m3, and the porosity was about 80%. Further, it was confirmed that the specific surface area measured by the BET method which is a nitrogen adsorption method has a high value of about 450 m <2> / g.

<< Comparative Example 1 >>
For comparison, a wet gel with a single titania precursor was obtained under the conditions described in Reference Example 1. Drying was also performed under the same conditions as in Reference Example 1 to obtain a dried titania precursor gel. At this time, the size before and after drying was about 95% in length. The apparent density was about 150 kg / m ³ and the porosity was about 90%. Moreover, it turned out that the value of the specific surface area measured by BET method which is a nitrogen adsorption method has a high specific surface area of about 500 m < ² > / g.

Further, this was fired under the same conditions as in Reference Example 1 to obtain a titania porous body. At this time, the dimension of the dried gel before and after firing was about 70% in length. When combined with drying, it contracted to about 65%. The apparent density was about 550 kg / m ³ and the porosity was about 40%. Moreover, the value of the specific surface area measured by the BET method which is a nitrogen adsorption method was about 150 m ² / g.

As described above, in the conventional titania precursor wet gel 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 a carbon wet gel as in Reference Example 1, shrinkage during firing could be suppressed, and the specific surface area could be increased.

"Example 1"
A composite dry gel of titania precursor produced under the same conditions as in Reference Example 1 was obtained. The composite dried gel was heat-treated in the atmosphere to evaporate the carbon skeleton and crystallize titania to promote the anatase crystal system, thereby obtaining a titania porous body. The heat treatment conditions were as follows: 100 ° C. for 1 hour, 200 ° C. for 1 hour, 300 ° C. for 1 hour, 400 ° C. for 1 hour, 500 ° C. for 1 hour, and then 400 C. for 1 hour, 300.degree. C. for 1 hour, 200.degree. C. for 1 hour, and 100.degree. C. for 1 hour, and then gradually cooled to room temperature. Before and after the heat treatment, the size shrank to about 70% in length, but the apparent density was as small as about 100 kg / m ³ and the specific surface area was also high as about 800 m ² / g. This titania porous body was confirmed to have a hollow structure by electron microscope observation.

<< Reference Example 2 >>
First, under the conditions described in Reference Example 1, a wet gel was synthesized using a polyphenol polymer as a carbon precursor. Next, after washing the obtained polyphenol wet gel with ethanol (solvent substitution), supercritical drying with carbon dioxide was performed to obtain a polyphenol dry gel. The supercritical drying conditions were the same as in Example 1.

  Subsequently, a titania precursor was coated on a dried polyphenol gel. The titania precursor is prepared by diluting titanium tetraisopropoxyoside with absolute ethanol, adding triethanolamine, water and polyethylene glycol, and immersing the polyphenol dry gel in the gel skeleton. Impregnated. The titania precursor was coated on the skeleton of the dried gel by standing at room temperature for 2 days.

Further, the dried gel coated with the titania precursor was baked 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. The apparent density was about 300 kg / m ³ and the specific surface area was a high value of about 450 m ² / g.

Example 2
A composite gel coated with a titania precursor produced under the same conditions as in Reference Example 2 was obtained. The composite gel was heat-treated in the atmosphere to evaporate the carbon skeleton and promote the crystallization of titania, thereby obtaining a titania porous body. The firing conditions were the same as in Example 1 . Before and after the heat treatment, the size contracted to about 70% in length, but the apparent density was as small as about 100 kg / m ³ and the specific surface area was also high as about 800 m ² / g. This titania porous body was confirmed to have a hollow structure by electron microscope observation.

<< Reference Example 3 >>
First, a wet gel using a polyimide polymer as a carbon precursor was synthesized. A 1% by weight 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, a polyimide precursor gel of carbon precursor was obtained from this polyamic acid wet gel by the following two methods.

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

  In the second method, the polyamic acid wet gel was dried to obtain a dry gel. This dry gel was subjected to thermal imidization at 300 ° C. in a nitrogen atmosphere to obtain polyimide dry gel B.

  The obtained polyimide dry gels A and B were carbonized at 600 ° C. in a nitrogen atmosphere to obtain a carbonized porous carbon body. Both of the dried gels A and B were able to obtain a carbon porous body 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 placed in a vacuum film forming apparatus, titanium tetrachloride gas is formed by discharge plasma with a high frequency of 13.56 MHz and power of 200 W, titania is formed in the carbon porous body adjusted to 200 ° C., and titania. / A carbon composite porous body was obtained. The produced titania was confirmed to have an anatase crystal structure by X-ray diffraction. The apparent density of this titania / carbon composite porous body was about 220 kg / m ³ and there was little shrinkage, and the specific surface area by the BET method was about 600 m ² / g and a high value was obtained.

Example 3
The titania / carbon composite porous body produced in Reference Example 3 was heat-treated in the atmosphere under the same conditions as in Example 2 to obtain a titania porous body. This apparent density was as small as about 100 kg / m ^3, and the specific surface area was as high as 900 m ² / g. This titania porous body is also confirmed to have a hollow structure by electron microscope observation, and it is considered that a high specific surface area is achieved by the effect.

Example 4
Carrying a platinum catalyst in the following way titania porous body B was created manufactured in Example 1.

The platinum salt was supported by impregnating the porous body B in a 3 mmol / L ethanol solution of chloroplatinic acid. To this, sodium borohydride was added at room temperature to carry a catalyst composed of platinum particles. Catalyst loading was about 0.35 mg / cm ^2.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Network structure frame | skeleton 2 Frame | skeleton 3 Carbon material 4 Oxide semiconductor 6 Oxide semiconductor 7 Hollow part 8 Network structure frame | skeleton of porous body 9 Supported promoter or pigment | dye

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