JP2002115176A - Porous fiber board supporting photocatalyst and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous fiber board supporting a photocatalyst, capable of synergistically developing the adsorbing function of zeolite and the photocatalytic function of titanium dioxide, performing a photocatalytic reaction on a three-dimensional wide interface and effectively removing NOX, etc. SOLUTION: The porous fiber board supporting a photocatalyst is produced by attaching titanium dioxide fine particles on a zeolite particle, dispersing the zeolite particles in a silica binder and supporting the obtained mixed oxide on the surface of a porous board consisting of an inorganic fiber board, metallic fiber board or inorganic-metallic composite fiber board or between the fibers of the above fiber board. More particularly, the board is produced by dispersing the zeolite particles supporting titanium dioxide fine particles in a solvent, mixing the dispersion with colloidal silica to obtain a coating material, applying the coating material to the surface of a porous board consisting of an inorganic fiber board, metallic fiber board or inorganic-metallic composite fiber board or between the fibers of the above fiber board and heat-treating the product to form a photocatalytic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present _invention, NO _X, SO _X, SPM
(Suspended particulate ma
The present invention relates to a photocatalyst-supported porous fiber plate having a structure in which photocatalyst particles for oxidative decomposition and removal of ter) are uniformly dispersed and supported between the surface of the porous fiber plate and fibers thereof without impairing the photocatalytic reaction.

[0002]

An automobile, factory, containing gas the NO _X or the like to be discharged from the power plant or the like, has been one of the causes of acid rain have a material adverse effect on the environment. NO _X and the like, is also considered as a substance that induces respiratory disorders to the human body. For this reason, various methods for removing harmful gas of the NO _X like in the exhaust gas at the source have been researched and developed, effective removal techniques have been established for once discharged harmful gases It is not at present.

In recent years, there has been proposed a method of converting NO _x and SO _x into nitrates and sulfates by a photocatalytic reaction using a photocatalyst and removing them. When the photocatalyst is irradiated with light having a wavelength having energy equal to or greater than the band gap, electrons are generated in the conductor and holes are generated in the valence band by photoexcitation.
Organic substances, water, harmful gases, etc. are decomposed by the strong oxidizing power of holes. TiO is a substance exhibiting such photocatalysis.
_{2, ZnO, ZrO 2, WO} 3, Fe 2 O 3, FeTiO 3,
Although SrTiO _{3 and the} like are known, the most frequently reported example uses an anatase type titanium dioxide powder as a photocatalyst. In practical use, the photocatalyst powder is coated and fixed on a metal or the like in order to prevent outflow and scattering. As a coating method, for example, a direct coating method introduced in Japanese Patent Application Laid-Open No. Hei 3-8448, photocatalyst particles coated on a metal plate may be used in a coating method.
A method of sintering at a temperature of 0 ° C. or higher, a method of spraying a precursor which becomes a photocatalyst by thermal decomposition onto a substrate heated to a temperature of about 400 ° C., and the like are known.

When titanium dioxide is applied to a metal plate as a photocatalyst to impart photocatalysis, even if the metal plate is uniformly coated with titanium dioxide, the amount of titanium dioxide covered is limited to a practical upper limit. There is a limit to the oxidation resolution of _{X and the} like. Further, in a photocatalytic reaction using a photocatalyst-coated metal plate, for example, NO is oxidatively decomposed into NO ₂ , and further, NO ₂ is decomposed into NO ₃ ⁻ , but most of the intermediate product NO ₂ is NO ₃
^- it will be released into the atmosphere before being oxidatively decomposed on. Therefore, a sufficient NO _x decomposition action may not be exhibited.

[0005] The release into the atmosphere of the NO _X or the like as an intermediate product, known to be able to suppress by temporarily adsorbed by keeping contain a sorbent coating film formed on the surface of the metal plate (JP-A-6-315614). It is also known to use zeolite as an adsorbent and form a coating film by adding it in combination with titanium dioxide (JP-A-7-171408). The present inventors,
Synergistically utilize the photocatalytic function of the adsorption function and titanium dioxide, for effective removal of such NO _X to obtain a photocatalyst-coated coating film capable over a long period of time, the zeolite particles adhered with titanium dioxide particles are dispersed Proposed to form a coating film using silica as a binder (Japanese Patent Application No. 11-3).
No. 38936).

[0006]

The zeolite particles of titanium dioxide fine particles are attached [0005] By forming a silica coating film dispersed in as a binder, effectively the contaminants such as NO _X over a long period of time Although it is possible to obtain a photocatalyst-coated film that can be removed, the surface of the oxidation-removal reaction interface is smaller than that of a three-dimensional one because the material forming the photocatalyst-coated film is a flat plate. It is difficult to say that the oxidative decomposition and removal of the substance is performed efficiently. In particular, there is much room for improvement in purifying the flowing air.

[0007]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and has a photocatalytic substance carried on a porous fiber plate through which the atmosphere passes. That is, the surface of the porous plate made of an inorganic fiber plate, a metal fiber plate or an inorganic / metallic composite fiber plate and between the fibers thereof,
By supporting a mixed oxide in which zeolite particles to which titanium dioxide fine particles are attached are dispersed in a silica binder,
It is an object of the present invention to provide a photocatalyst-supporting porous fiberboard capable of efficiently and oxidatively removing harmful substances in the air over a long period of time and a method for producing the same.

In order to achieve the object, the photocatalyst-supporting porous fiber plate of the present invention comprises an inorganic fiber plate, a metal fiber plate, or a mixed oxide obtained by dispersing zeolite particles to which titanium dioxide fine particles are attached in a silica binder. It is carried on the surface of a porous plate made of an inorganic-metallic composite fiber plate and between the fibers thereof. A glass fiber cloth or glass fiber non-woven fabric is used as the inorganic fiber plate, and SUS or Al material is used as the metal fiber plate. Metal wool is used.
In addition, a cloth or nonwoven fabric in which glass fibers and metal fibers are combined can also be used. Depending on the difference in fiber density, this photocatalyst-supporting porous fiber board is used for various applications such as ventilation fans, air conditioners, air purifiers, and filters for ventilation openings. It also has applications as a sound insulation plate for tunnels and road protection walls.
This photocatalyst-supporting porous fiberboard is prepared by mixing a solvent in which zeolite particles to which titanium dioxide fine particles are adhered is mixed with colloidal silica to prepare a coating, and the inorganic fiberboard, metal fiberboard, or inorganic / metallic It is manufactured by carrying the coating material on the surface of the composite fiberboard and between the fibers and performing a heat treatment to form a photocatalytic layer. The titanium dioxide fine particles can be attached to the surface of the zeolite particles by previously adding to the solvent together with the zeolite particles and stirring.

[0009]

[Action] Zeolites are best adsorbent selective adsorptivity due to selective adsorption and molecular polarity corresponding to the molecular size, it is suitable for the adsorption of such NO _X. Above all, 3-10
The synthetic zeolite having a pore size of Å is, for example, NO, NO
Since the molecular diameters of ₂ or the like is approximately 4 Å, an optimal adsorbent for the NO _X, and the like. However, in the coating film are dispersed zeolite alone, the zeolite as described above is saturated with NO _X, etc., can not adsorb NO _X such that exceeding the saturation point,
Conversely, air emissions, such as NO _X starts.

In this regard, in the photocatalyst-supporting porous fiber board according to the present invention, titanium dioxide fine particles having a photocatalytic function adhere to the surface of zeolite particles dispersed in the coating film. Titanium dioxide particles are to be used in the form attached to the surface of the zeolite particles, without particles mutually agglomerate, made large surface area required for the photocatalytic reaction, the distance between the NO _X or the like adsorbed by the zeolite is extremely Be shorter. Therefore, zeolite NO _X or the like which is adsorbed to are effectively decomposed by the photocatalytic action of titanium dioxide fine particles in a close range, nitrate is removed from the gas phase as the sulphate. Therefore, the effective photocatalytic reaction is maintained over a long period of time, and the adsorption ability of zeolite is restored.
Further, organic substances contained in the SPM are also decomposed by the catalytic action of the titanium oxide, and the intermediate product is adsorbed on the zeolite existing in contact therewith, so that the decomposition proceeds more effectively. Furthermore, in the photocatalyst-supporting porous fiber plate of the present invention, the photocatalyst coating layer spreads not two-dimensionally but three-dimensionally,
Since the oxidative decomposition removal reaction interface by the photocatalyst is greatly increased, air purification can be performed extremely efficiently.

The photocatalyst-carrying porous fiberboard according to the present invention exerts a remarkable effect particularly when used as a sound insulation wall on a highway where automobiles frequently pass. In other words, on highways, the adsorption and desorption of zeolites is enhanced by the wind pressure fluctuations that occur when cars pass, and the wind pressure fluctuations significantly increase the contact area between the atmosphere and the photocatalyst layer. To excite titanium dioxide as a photocatalyst. As a result, NO _X and the like are effectively removed, highways and the atmosphere around the are purified by the photocatalytic action of titanium oxide.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a method for adhering titanium dioxide particles to zeolite particles, for example, a method in which titanium dioxide particles and zeolite particles are dispersed in an organic solvent and stirred by a ball mill is employed. Titanium dioxide fine particles are preferably anatase type from the viewpoint of photocatalytic activity, and there is no particular restriction on the shape, but fine particles having an average particle size of 50 nm or less are preferable in order to obtain a large effective surface area.

[0013] Naturally the zeolite particles zeolite, although any synthetic zeolite can be used, considering the selective adsorption of such NO _X synthetic zeolite having a pore diameter of 3~10Å is preferred. As the synthetic zeolite, those having an X-type or Y-type crystal structure containing one or more of cations such as K, Na, Mg, Cu, Ag and the like are used. The shape of the zeolite particles is not particularly limited, but preferably has an average particle size of 10 μm or less in order to form a uniform coating film on the surface of the metal plate. When the average particle size exceeds 10 μm, the smoothness of the coating film tends to decrease.

As the organic solvent in which the titanium dioxide fine particles and zeolite particles are dispersed, ethers such as butyl cellosolve and ethyl cellosolve, alcohols such as isopropanol and ethanol, and a mixed solvent thereof are used. For example, a mixed solvent of butyl cellosolve and isopropanol (1: 1) has a high dispersibility and maintains the titanium dioxide fine particles and zeolite particles in a stable suspension state without aggregation. After adding the titanium dioxide fine particles and the zeolite particles to the organic solvent, the titanium dioxide fine particles are adhered to the surfaces of the zeolite particles by stirring using a ball mill or the like. In the stirring, the stirring conditions such as ball weight, stirring speed and stirring time are set so that the titanium dioxide fine particles and the zeolite particles are not crushed and a mechanical adhesion state is obtained between the titanium dioxide fine particles and the zeolite particles. Is done.

After the titanium dioxide particles are adhered to the zeolite particles by stirring, the organic solvent containing the zeolite particles and the titanium dioxide particles is mixed with colloidal silica. As the colloidal silica, for example, an average particle size of 5
A dispersion containing 10 to 50% by mass of silica particles of 150 μm is used. As a colloidal silica mixed dispersion of this type, a dispersion in which a solid component is dispersed in an amount of 10 to 80% by mass is introduced in Japanese Patent No. 2584216.

By mixing an organic solvent containing zeolite particles and titanium dioxide fine particles with colloidal silica, a paint required for forming a coating film having a photocatalytic function is prepared. The paint is preferably titanium oxide: 20 to
40% by mass, zeolite: 1 to 60% by mass, silica: 2
The composition is adjusted to 0% by mass or more. The photocatalytic action of the coating film becomes remarkable at 20% by mass or more of titanium dioxide.
If the titanium oxide is contained in an excessive amount exceeding 0% by mass, cracks easily occur in the coating film. Adsorption capacity of the NO _X such coating film is becomes significant at 1% by mass or more of a zeolite, the amount of the relatively silica excessive addition of zeolite exceeds 60 mass% is reduced, it is formed The adhesion of the coating film to the metal plate surface is reduced. In order to ensure the adhesion of the coating film, 20% by mass or more of silica is required.

In order to form a coating film provided with a photocatalytic function on the surface of an inorganic fiber plate, a metal fiber plate, or an inorganic / metallic composite fiber plate and between fibers thereof, titanium dioxide fine particles and zeolite are coated on the surface of the coating film. It is important that is exposed. As a method of forming such a coating film, there are a spray method, a sol-gel method, a physical vapor deposition method, a powder coating method, an immersion method and the like. Above all, the immersion method is easy to form a coating film exposing titanium dioxide fine particles and zeolite,
Since the paint loss is small and the adhesion efficiency is high, the coating cost is also low.

The material of the inorganic fiberboard, metal fiberboard, or inorganic / metallic composite fiberboard on which the coating film is formed is not particularly limited, but may be glass fiber cloth, glass fiber nonwoven fabric, SUS or Al. Use is made of a fiberboard made of glass, cloth, nonwoven fabric, or the like in which glass fibers are combined with SUS or Al metal fibers. Preferably, a glass fiber cloth or nonwoven fabric is used because the fiber diameter is small and the surface area can be increased, and light can be efficiently applied to the photocatalyst because light transmission and scattering occur. Prior to painting, degreasing, washing,
Pretreatment such as pickling, chromate treatment, and phosphate treatment is performed as necessary. Further, a primer layer may be formed in advance. The primer layer has the function of improving the adhesion of the photocatalyst layer. A coating containing titanium dioxide fine particles and zeolite particles is applied to the surface of the fiberboard at a coating amount of 0.5 μm or more in dry film thickness. The film thickness of less than 0.5 [mu] m, there is a case where the photocatalytic action of such oxidative decomposition and removal of such sufficient NO _X is not expressed.

The solvent is removed by heat treatment from the surface of the inorganic fiber plate, the metal fiber plate, or the inorganic / metallic composite fiber plate and the coating applied between the fibers. When the material is an inorganic fiberboard or an inorganic / metallic composite fiberboard, if the heat treatment temperature is set to 150 to 400 ° C., the solvent is completely removed from the coating film, and the photocatalyst, zeolite and silica are firmly strengthened. A bonded coating is formed. When the material is a metal fiber plate, the heat treatment temperature can be increased to 800 ° C., and the production can be performed by a short heat treatment. If the heat treatment temperature is too low or the heat treatment is performed for a short time, a part of the solvent remains between the titanium dioxide fine particles and the zeolite particles, and the tendency tends to have a bad influence on the photocatalytic reaction and the adsorption action. Further, the condensation polymerization of the colloidal silica is insufficient, and the adhesion of the coating film tends to be insufficient. However, when the material contains an inorganic material, the strength of the material is reduced at a heat treatment temperature exceeding 400 ° C. When the material is a metal fiber plate, if it exceeds 800 ° C., the crystal structure of titanium dioxide changes, and the photocatalytic activity decreases.

[0020]

Example: A photocatalyst-supporting fibril plate having a thickness of 0.22 m
A glass fiber cloth having a weight of 11.0 g / m ² in m was used. After defatting the fibrous plate for forming a coating film, a silica-based coating material in which zeolite particles to which titanium dioxide fine particles are adhered is dispersed, and anatase-type titanium oxide fine particles, zeolite particles, silica A photocatalytic layer of a mixed oxide containing particles was formed. The paint used was prepared by adding anatase-type titanium dioxide fine particles having an average particle diameter of 7 nm and synthetic zeolite particles having an average particle diameter of 2 μm to a mixed solvent (1: 1) of butyl cellosolve / isopropanol, and stirring for 30 minutes with a ball mill. Prepared by mixing. The adhesion amount of the obtained photocatalyst layer was 40 g / m ² .

[0021]

[Comparative Example] SUS304 with a plate thickness of 1.4 mm as an original plate
A photocatalyst-coated layer plate was prepared in the same manner as in Example except that a flat plate was used. The adhesion amount of the obtained photocatalyst layer is 40 g / m
^{Was 2} .

[0022]

[Evaluation Test Example, Test pieces were cut out from each photocatalyst-coated plate produced by the method shown in Comparative Examples were subjected to the resolution test NO _X. In the NO _X resolution test, 50 mm
Two test pieces of × 100 mm were put in a quartz glass reaction vessel, and purified air containing 50 ppm of NO and 1 ppm of NO (1.
5 l / min) into the reaction vessel and from the outside of the reaction vessel 0.5 m
Ultraviolet light of W / cm ² (wavelength 365 nm) was irradiated for 5 hours. The conditions of this evaluation are severe conditions as the evaluation of the NO _X resolution. In this condition, NO contained in the purified air flowing out of the reaction vessel, measuring the concentration of NO _X, etc. NO _2, were calculated NO _X density reduction rate according to the following equation from the change of the NO _X concentration before and after the test . NO _X density decrease rate (%) = (before test NO _X concentration - NO _X concentration after test) / ○ those × 100 NO _X density decrease rate (NO _X density before the test) is 50% or more, When the NO _X concentration reduction rate is 25% or more and less than 50%,
_{If the} rate of decrease in _X concentration is less than 25%, the result is indicated by ×, and NO _X
The resolution was evaluated.

[0023]

[0024] With regard to NO _X resolution, as seen in the survey results in Table 1, the photocatalyst supporting fiber plate according to the present invention showed a NO _X resolution both excellent photocatalytic coated metal plate of Comparative Example in the NO _X resolution was poor. The difference was thus generated to the NO _X resolution, since the surface area of the substrate is different from the present invention and comparative example embodiment, the adhesion amount of deposited oxide titania fine zeolite, and significance of the increase in the light irradiation area It shows.

[0025]

As described above, the photocatalyst-supporting porous fiber plate of the present invention comprises a mixed oxide obtained by dispersing zeolite particles, on which titanium dioxide fine particles are previously adhered, in a silica binder, an inorganic fiber plate, and a metal fiber. Since it has a structure supported on the surface of the fiberboard, or the surface of the inorganic-metallic composite fiberboard and the fibers, NO _{X and the} like adsorbed on the zeolite particles are secured at a close distance to the titanium dioxide fine particles,
Photocatalytic action of titanium dioxide fine particles are used in the decomposition and removal of such effectively NO _X. Moreover, since the photocatalyst NO _X or the like which is attracted by the reaction is decomposed and removed, it no zeolite particles is saturated with NO _X, etc., adsorption ability of the zeolite particles is maintained over a long period of time. Further, the area of the decomposition removal reaction interface can be greatly increased. As a result, decomposition and removal by adsorption and photocatalytic reactions such as NO _X is performed very efficiently, it is used as the porous fiberboard help environmental cleanup. Above all, when used as a highway noise barrier, the degree of contact between the air and the porous fiberboard and the N
Adsorption of O _X like is promoted, decomposition and removal functions such as NO _X is further improved.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) A61L 9/16 F term (reference) 4C080 AA05 AA07 BB02 CC01 CC07 HH05 JJ05 KK08 LL03 MM02 MM04 NN06 QQ03 4D048 AA02 AA06 AA14 AB01 AB03 BA06X BA06Y BA07X BA07Y BA11X BA11Y BA12X BA12Y BA39X BB08 EA01 4G069 AA03 AA08 AA09 AA11 BA02A BA02B BA02C BA04A BA04B BA07A BA07B BA14A BA14B BA14C BA17 BA48A CA13 CA13 AA13 CA13 ACA13 CA13 ACA

Claims (2)

[Claims] 1. A mixed oxide obtained by dispersing zeolite particles to which titanium dioxide fine particles are attached in a silica binder, is supported on the surface of an inorganic fiber plate, a metal fiber plate or an inorganic / metallic composite fiber plate and between the fibers. A photocatalyst-supporting porous fiber plate, characterized in that: 2. A coating material is prepared by mixing a solvent in which zeolite particles to which titanium dioxide fine particles are adhered with colloidal silica to prepare a coating material, and the surface of an inorganic fiber plate, a metal fiber plate or an inorganic / metallic composite fiber plate is prepared. And a method for producing a photocatalyst-supporting porous fiberboard, wherein the coating material is supported between fibers and subjected to a heat treatment to form a photocatalyst layer.