JP2006326530A - Nanoporous titanium oxide membrane and method for treating volatile organic compound using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nanoporous titanium oxide membrane bearing a Group IIIV element such as platinum and a method for removing a volatile organic compound such a methanol using the membrane. <P>SOLUTION: The nanoporous titanium oxide membrane bearing platinum of the invention almost completely decomposes methanol regardless of the methanol supply concentration and shows approximately 100% of carbon dioxide production ratio. A methanol decomposition amount is increased and a carbon dioxide production amount is also greatly increased. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nanoporous titanium oxide film and a method for treating a volatile organic compound using the same, and in particular, a nanoporous titanium oxide film carrying a Group 8 element such as platinum and the like. The present invention relates to a method for decomposing volatile organic compounds such as methanol.

  Volatile organic compounds that easily volatilize in the air at normal temperature and pressure are heavier than water, have a lower viscosity, and are often less degradable. Contaminate. On the other hand, it is released into the atmosphere and is thought to be involved in the generation of oxidants and SPM (suspended particulate matter) through photochemical reactions.

  Volatile organic compounds released into the atmosphere are estimated to be about 1.85 million tons per year in Japan according to the Ministry of the Environment's calculations, and the amount of emissions per unit area is higher than in other countries. Has been. Furthermore, in recent years, contamination of indoor air by chemical substances has become obvious, and health problems such as so-called sick house syndrome and chemical hypersensitivity have attracted attention. For this reason, in order to remove these volatile organic compounds, detoxification technology for volatile organic compounds using titanium oxide having photocatalytic activity has been studied.

  Titanium oxide absorbs light in the ultraviolet region of 400 nm or less, excites electrons in the valence band to the conduction band, and generates holes. Furthermore, holes are believed to react with water or surface hydroxyl groups to generate OH radicals. The generated electrons and holes or OH radicals have a strong reactivity, and their photocatalytic properties have attracted great interest, including decomposition reactions of environmental pollutants.

  On the other hand, titanium oxide is attracting attention as a porous separation membrane material because it does not dissolve in acids other than hydrofluoric acid and concentrated sulfuric acid, alkalis, and organic solvents and has excellent chemical stability.

  So far, the photocatalytic properties of titanium oxide have been evaluated as a fixed bed of titanium oxide powder, a suspension system in aqueous solution, and a titanium oxide coating thin film on a non-porous substrate. In the fixed bed type and suspension systems, there are problems in that the light utilization rate is reduced due to scattering of ultraviolet rays, in the suspension system, separation and recovery of the solution and titanium oxide powder, and in the thin film system, the surface area is small.

  Thus, as shown in FIG. 1, the inventors have proposed a membrane transmission type photocatalytic reaction system that obtains a photocatalytic reaction product on the membrane permeation side by allowing the photocatalytic reaction to occur while passing through the nanopores. (Non-Patent Documents 1 and 2).

  In this system, while the organic matter permeates through the nanopores of titanium oxide, it is considered that the organic matter is adsorbed on the surface of the pore and directly decomposed, or reacts with OH radicals present at high density in the pore, It is thought to have features such as improved photocatalytic reaction speed by convection support, the ability to selectively obtain photocatalytically reacted solution (or gas) on the membrane permeation side, and the combination with molecular sieve function by membrane pores. Yes. In addition, the present inventors have clarified that the system is effective not only in the liquid phase system but also in the photocatalytic decomposition of methanol in the gas phase system (Non-patent Document 3).

Furthermore, it has been reported that the photocatalytic activity is significantly increased by doping titanium oxide with a Group 8 element such as platinum.
Tsuru T, D.Hironaka, T.Yoshioka and M.Asaeda., Sep. Purif.Technol. 25, 307-314,, 2001 Tsuru T, T. Toyosada, T. Yoshioka and M. Asaeda., J. Chem. Eng. Japan, 36, 1063-1069, 2003 Toshinori Tsuru, Takehiro Kan-no, Tomohisa Yoshioka, Masashi Asaeda., Catalysis Today, 82, 41-48, 2003

  However, the above conventional technique has a problem that volatile organic compounds cannot be completely decomposed. That is, since the above membrane permeation type photocatalytic reaction system does not carry a group 8 element such as platinum, holes and electrons generated by light irradiation are recombined inside or on the surface of titanium oxide, and the quantum yield Will fall. Therefore, the improvement of the photocatalytic activity is still insufficient, and the volatile organic compound cannot be completely decomposed and removed.

  The present invention has been made in view of the above problems, and its object is to provide a nanoporous titanium oxide film supporting a Group 8 element such as platinum, and a volatile organic compound such as methanol using the same. The object is to provide a method of removing.

  As a result of intensive studies in view of the above problems, the present inventor has found that a part of the titanium dioxide molecules constituting the nanoporous titanium oxide film in which the film mainly composed of titanium dioxide is supported on the outer surface and / or the inner surface of the substrate. Alternatively, the inventors have found that it is possible to efficiently decompose and remove volatile organic compounds by supporting a metal belonging to Group 8 such as platinum, and the present invention has been completed.

  That is, the nanoporous titanium oxide film according to the present invention is a nanoporous titanium oxide film in which a film containing titanium dioxide as a main component is supported on the outer surface and / or the inner surface of the base material, It is characterized in that a part or all of the molecule of (1) carries a metal belonging to Group 8.

  According to the above configuration, the electrons generated by the light irradiation are captured by the metal supported on the titanium dioxide molecules, and the recombination rate between the electrons and the holes generated by the light irradiation is reduced. The lifetime can be extended and the quantum yield can be greatly increased. Therefore, the volatile organic compound can be decomposed very efficiently.

  In the nanoporous titanium oxide film according to the present invention, the metal is preferably platinum. Since platinum is the metal having the highest activity among the elements belonging to Group 8, the quantum yield can be most effectively increased by supporting it on the titanium dioxide molecule. Therefore, the volatile organic compound can be decomposed very efficiently.

  Moreover, in the nanoporous titanium oxide film according to the present invention, the pore diameter of the nanopores of the film is preferably 2 to 25 nm. The permeation mechanism in the nanopore is classified into viscosity, Knudsen flow, and molecular sieve as the pore diameter decreases. In the Knudsen flow in which the contact with the nanopore wall is dominant rather than the collision between molecules, the contact between the volatile organic compound and the titanium oxide pore having photocatalytic activity is dominant and the pore diameter is reduced. It is expected that the decomposition rate of volatile organic compounds will improve as the time elapses.

  The range in which the pore diameter of the membrane is 2 to 25 nm is a range that can be controlled by adjusting the particle size of the colloidal sol, and the permeation mechanism is a range in which a Knudsen flow occurs. Therefore, the decomposition rate of volatile organic compounds can be improved.

  The method for treating a volatile organic compound according to the present invention includes a step of irradiating light to the nanoporous titanium oxide film according to the present invention, and transmitting the volatile organic compound through the nanopores of the nanoporous titanium oxide film. And a step of decomposing the volatile organic compound.

  Since the nanoporous titanium oxide film according to the present invention carries the metal, many electrons generated by light irradiation can be collected in the metal. As a result, the rate of recombination of electrons and holes is reduced, and the electron reaction rate can be increased, so that the photocatalytic activity is significantly increased compared to the case where the metal is not supported. . Therefore, by irradiating the nanoporous titanium oxide film according to the present invention with light and transmitting the volatile organic compound through the nanopores of the film, the volatile organic compound is almost completely decomposed only by allowing it to pass through once. can do.

  In the method for treating a volatile organic compound according to the present invention, the volatile organic compound is preferably methanol, ethanol and / or acetaldehyde. Methanol, ethanol, and acetaldehyde are typical volatile organic compounds. In the method for treating volatile organic compounds according to the present invention, these volatile organic compounds can be efficiently decomposed. Therefore, the influence on the human body and the environment by the above compound can be reduced.

  As described above, the nanoporous titanium oxide film according to the present invention is a nanoporous titanium oxide film in which a film mainly composed of titanium dioxide is supported on the outer surface and / or the inner surface of the substrate, Since some or all of the titanium dioxide molecules carry a metal belonging to Group 8, the decomposition efficiency of volatile organic compounds can be greatly improved as compared with the case where the metal is not carried. There is an effect that can be done.

  Further, the method for treating a volatile organic compound according to the present invention includes a step of irradiating light to nanopores of the nanoporous titanium oxide film according to the present invention, and volatilization into nanopores of the nanoporous titanium oxide film. The step of decomposing the volatile organic compound by allowing the permeable organic compound to permeate is provided, and therefore the effect is that the compound can be almost completely decomposed only by allowing the compound to permeate once.

  An embodiment of the present invention will be described as follows, but the present invention is not limited to this. Hereinafter, a method for treating a nanoporous titanium oxide film and a volatile organic compound (hereinafter referred to as “VOC”) according to the present invention will be described in detail.

(1) Nanoporous titanium oxide film The “nanoporous titanium oxide film” according to the present invention is a film mainly composed of titanium dioxide (also called titania) supported on the outer surface and / or the inner surface of a substrate. A nanoporous titanium oxide film, in which some or all of the titanium dioxide molecules carry a metal belonging to Group 8.

Since the nanoporous titanium oxide film is a film containing titanium dioxide as a main component, it may be composed of only titanium dioxide (TiO ₂ ) or may contain other components. Examples of other components include a trace amount of elements for enhancing the photocatalytic activity of titanium dioxide.

  The base material is made of a material generally used as a filtration device. The shape and the like of the porous material is not particularly limited as long as it is a porous material having an average pore diameter of about 1 μm made of a material generally used as a filtration device. For example, it is preferable to use an inorganic material such as α-alumina or mullite having permeation holes with an average pore diameter of about 1 μm. Among these, α-alumina is preferably used because it has high strength and can be easily subjected to a ground treatment. And the shape can be arbitrary, such as tubular (outer diameter of about 1 cm or more), capillary shape (outer diameter of about 1 to 10 mm), monolith shape (integrated with many holes), flat plate shape, and the like.

  The nanoporous titanium oxide film according to the present invention is preferably formed directly on the base material as described above by a sol-gel method or a CVD method. Since the nanoporous titanium oxide film preferably has a uniform pore diameter as much as possible, it is preferable to produce the film using a sol-gel method in which the pore diameter can be easily controlled.

  Here, the sol-gel method refers to a method for producing a precursor that uses a liquid colloidal solution of a metal salt to obtain a gel by subsequent heat treatment (JIS Industrial Terminology Dictionary 5th Edition, page 1294).

  In the sol-gel method, the pore diameter of the nanoporous titanium oxide film can be controlled by adjusting the particle diameter of the colloidal sol. The particle size of the colloidal sol can be controlled by the condensation polymerization reaction temperature when preparing the colloidal solution.

  The nanoporous titanium oxide film varies depending on the shape of the substrate, but can be produced on the outer surface, the inner surface, or both the inner and outer surfaces of the substrate. Furthermore, decomposition of VOC may be handled by one porous film, or a plurality of films prepared by different methods on different surfaces of the base material or different base materials may be used.

  Moreover, although the aspect of carrying | supporting a nanoporous titanium oxide film to the base material is not specifically limited, From a viewpoint of improving the efficiency of a photocatalytic reaction, it is preferable to carry | support uniformly to a base material.

  FIG. 2 is a schematic view of a nanoporous titanium oxide film formed into a tube shape. In FIG. 2, for example, a nanoporous titanium oxide film based on α-alumina is connected to a glass tube using a glass raw material. One side of the glass tube is closed, and the other is a permeate that has passed through the film. Open for recovery.

  Some or all of the titanium dioxide molecules carry a metal belonging to Group 8. A metal belonging to Group 8 can extend the lifetime of holes as described above, and can greatly increase the quantum yield. Examples of metals belonging to Group 8 include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum is particularly preferably used because it has the highest activity.

  The method for supporting the metal on the titanium dioxide molecule is not particularly limited, and a conventionally known method can be used. For example, an impregnation method that is a method of immersing a support in a solution containing a catalyst and drying, a photo evaporation method that is a method of supporting metal by reducing and evaporating metal ions at a reduction site formed by light irradiation, and the like are used. be able to. The “supporting” refers to a state in which a catalytic substance is placed on some kind of substance.

  In one embodiment, in the nanoporous titanium oxide film according to the present invention, the pore diameter of the nanopores of the film is preferably 2 to 25 nm. Since the mean free path of VOC such as methanol is considered to be several tens of nanometers, the permeation mechanism of the VOC of the nanoporous titanium oxide film having the pore diameter of 2 to 25 nm is that the flow field structure is intermolecular collision. Of the collisions with the molecular boundaries, the Knudsen flow mainly involves collisions with the molecular boundaries, and the contact between the VOC and the nanopores having photocatalytic activity is dominant. The range of the pore diameter of 2 to 25 nm is a range that can be arbitrarily controlled by adjusting the particle size of the colloidal sol.

  Therefore, by setting the pore diameter of the membrane to 2 to 25 nm, a Knudsen flow can be created, and the contact frequency between titanium dioxide carrying metal and VOC can be increased, so that the decomposition rate of VOC is improved. Can be made. Further, the pore diameter is preferably small. As the pore diameter is smaller, the contact efficiency between the photocatalytically active site and the VOC in the pore is increased, so that the decomposition rate of VOC can be further improved.

  The mean free path is an average of the distance traveled until a molecule collides with another molecule and then collides with another molecule.

  In a nanoporous titanium oxide film not supporting a metal such as platinum, holes and electrons generated by light irradiation are recombined inside or on the surface of titanium dioxide. That is, such an electronic reaction process becomes a rate-limiting reaction. On the other hand, since the nanoporous titanium oxide film according to the present invention carries a metal belonging to Group 8 such as platinum, many electrons generated by light irradiation can be collected in the metal. As a result, the rate of recombination of electrons and holes is reduced, and the electron reaction rate can be increased, so that the photocatalytic activity is significantly higher than that of nanoporous titanium oxide films that do not support metals such as platinum. It has become expensive.

  For example, as shown in the examples described later, the nanoporous titanium oxide film not supporting the metal was able to completely photocatalytically decompose about 100 ppm of methanol, but decomposed as the methanol supply concentration increased. The rate decreased, the production rate of carbon dioxide, a complete oxide, decreased, and the amount of formaldehyde, a harmful intermediate product, increased. On the other hand, a nanoporous titanium oxide film supporting platinum can decompose methanol almost completely regardless of the methanol supply concentration, and can decompose methanol to almost 100% carbon dioxide without forming formaldehyde. It was.

  Therefore, it can be said that the nanoporous titanium oxide film according to the present invention is very effective for decomposing and removing VOC existing in the atmosphere, and not only an air purifier but also an air conditioner filter or an air purifier filter. Etc. can be used.

(2) VOC processing method The VOC processing method according to the present invention includes a step of irradiating light to nanopores of the nanoporous titanium oxide film according to the present invention, and a nanopore of the nanoporous titanium oxide film. Disassembling the VOC by allowing the VOC to pass therethrough.

  The nanopores only need to have a pore diameter that can pass through the gaseous VOC. However, since the Knudsen flow can be created as described above, the pore diameter is 2 to 25 nm. Preferably, the pore diameter is preferably as small as possible in order to increase the contact efficiency between the photocatalytically active site and the VOC in the pores.

  The type of VOC is not particularly limited since it is considered that adverse effects on the human body and the environment can be prevented by decomposing and removing those present in the atmosphere. Examples of the target for decomposition and removal include VOCs contained in industrial raw materials, solvents and the like.

  For example, methanol, ethanol, acetaldehyde, formaldehyde, hexane, heptane, octane, nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, 2,4-dimethylpentane, benzene, toluene, ethylbenzene, m, p- Xylene, o-xylene, styrene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, 1,2,4,5-tetramethylbenzene, α-pinene , Limonene, dichloromethane, trichloroethylene, tetrachloroethylene, chloroform, 1,1,1, -trichloroethane, 1,2-dichloroethane, carbon tetrachloride, chlorodibromomethane, p-dichlorobenzene, ethyl acetate, butyl acetate, n-butanol, Acetone, methyl ethyl ketone, methyl isobuty Ketone, nonanal, decanal, etc. may be subject to decomposition and removal.

  In addition, the VOC may be permeated through the nanopores alone or as a mixture.

  The step of irradiating the nanoporous titanium oxide film with light is a step of causing photocatalytic reaction by irradiating the nanoporous titanium oxide film according to the present invention with light. Irradiation light is not particularly limited, but titanium dioxide absorbs light in the ultraviolet region of 400 nm or less, and excites electrons in the valence band to generate a hole to generate holes. It is preferable to do.

  The irradiation is performed, for example, by irradiating the surface of the nanoporous titanium oxide film with ultraviolet light using an ultraviolet lamp. As the ultraviolet irradiation means, black light as an ultraviolet lamp is preferably used, but a mercury lamp, a xenon lamp, or the like can also be used.

  FIG. 1 is a schematic diagram showing a process of decomposing the VOC by allowing the VOC to permeate through the nanopores of the nanoporous titanium oxide film. In the VOC processing method according to the present invention, a photocatalytic reaction can be obtained on the membrane permeation side by allowing the photocatalytic reaction to occur while allowing the VOC to pass through the nanopores.

  Since the nanoporous titanium oxide film carries a metal belonging to Group 8 such as platinum as described above, the decomposition efficiency of VOC is greatly improved.

  VOCs are oxidatively decomposed while passing through the nanopores due to the holes generated in the nanoporous titanium oxide film by light irradiation. At this time, the metal captures electrons generated by light irradiation and extends the lifetime of holes, so that the oxidative decomposition of VOC is enhanced as compared with the case where the metal is not supported. As a result, the VOC can be almost completely decomposed by passing the VOC once through the nanopore.

  In addition, according to the VOC processing method of the present invention, it is possible to decompose organic substances (fouling substances) that clog pores by filtration. This makes it possible to decompose the fouling material and restore the permeation flux of the membrane without the need for a washing step such as membrane washing or backwashing, which has been indispensable in the prior art. It is.

  FIG. 3 is a schematic diagram showing an outline of the photocatalytic film type reactor 1 for carrying out the VOC processing method according to the present invention.

  As shown in FIG. 3, the photocatalytic membrane reactor 1 includes a gas cylinder 11, a mass flow 12, a bubbling device 13, a preheater 14, a light source 15, a nanoporous titanium oxide film 16, a membrane cell 17, a valve 18, and a thermocouple 19. The gas chromatography 20 and the bypass line 21 are provided.

  The nanoporous titanium oxide film 16 is mixed with the air supplied from the gas cylinder 11 in the bubbling device 13 and transmits the VOC heated by the preheater 14. As described above, the nanoporous titanium oxide film 16 is a nanoporous titanium oxide film in which a film containing titanium dioxide as a main component is supported on the outer surface and / or the inner surface of the base material. A part or all of these molecules carry a metal belonging to Group 8.

  The gas cylinder 11 is a cylinder filled with air, and supplies air to the bubbling device 13. The mass flow 12 is for adjusting the flow rate of the air supplied to the bubbling device 13. The bubbling device 13 is filled with VOC, and mixes the compound and the air supplied from the gas cylinder 11 to form steam. The preheater 14 is for heating the steam to the photocatalytic reaction temperature.

  The light source 15 is for irradiating the nanoporous titanium oxide film 16 with light, and black light is preferably used as described above. However, a mercury lamp, a xenon lamp, or the like can also be used. .

  The membrane cell 17 is a reaction chamber to which a mixed vapor of VOC and air is supplied. A nanoporous titanium oxide film 16 is fixed in the membrane cell 17. The membrane cell 17 may be a stable substance that does not cause a photocatalytic reaction or reacts with VOC and is made of a substance that can transmit light. For example, quartz or Pyrex (registered trademark) is preferably used.

  When the mixed vapor enters the nanopores of the nanoporous titanium oxide film 16 and the nanoporous titanium oxide film 16 is irradiated with light, a photocatalytic reaction occurs. That is, OH radicals are generated at a high density in the nanoporous titanium oxide film 16 by the energy of light, and VOC reacts with the OH radicals and is oxidatively decomposed. In some cases, VOC is adsorbed on the surface of the nanopore and directly decomposed.

  In the VOC processing method according to the present invention, the VOC is oxidatively decomposed by such a process. Since the nanoporous titanium oxide film carries a metal belonging to Group 8 such as platinum as described above, the VOC can be almost completely oxidized and decomposed, and the gas completely purified on the membrane permeation side. Can be obtained.

  In addition, as shown in the examples described later, the nanoporous titanium oxide film not supporting the metal has a decomposition rate that decreases as the supply concentration of VOC increases, but the nanoporous titanium oxide supporting the metal In the method according to the present invention using a membrane, a high decomposition rate can be maintained regardless of the supply concentration of VOC, so that the oxidative decomposition of VOC can be performed very efficiently.

  The valve 18 is for switching the gas flow path. The thermocouple 19 is for measuring the temperature of the nanoporous titanium oxide film 16. The gas chromatography 20 is for performing composition analysis of the oxidatively decomposed VOC. The bypass line 21 is for adjusting the concentration of the supplied VOC.

  Note that the present invention is not limited to the configurations described above, and various modifications are possible within the scope of the claims, and technical means disclosed in different embodiments are appropriately combined. Embodiments obtained in this manner are also included in the technical scope of the present invention.

  The present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to this. Those skilled in the art can make various changes, modifications, and alterations without departing from the scope of the present invention. The production of the nanoporous titanium oxide film, the measurement of the nanopores of the produced nanoporous titanium oxide film, the loading of platinum on the nanoporous titanium oxide film, and the photocatalytic reaction were performed as follows.

(Preparation of nanoporous titanium oxide film)
The nanoporous titanium oxide film was produced by a sol-gel method. Titanium isopropoxide (hereinafter referred to as “TTIP”) was used as a starting material. TTIP was mixed with isopropyl alcohol (hereinafter referred to as “IPA”) as a dispersion medium and hydrochloric acid as a catalyst, and then a predetermined amount of water was added, followed by hydrolysis at about 4 ° C. for 1 hour. The composition ratio (molar ratio) of the starting solution was TTIP / IPA / water / hydrochloric acid = 1/140/4 / 0.4.

  After hydrolysis, a titanium dioxide colloidal sol was prepared by aging at a predetermined temperature (20 to 50 ° C.) for 10 hours (Non-patent Document 1). The particle size of the titanium dioxide colloidal sol can be controlled by this aging temperature, and the particle size measured by the dynamic light scattering method was about 30 to 100 nm. The particle size was measured with a dynamic light scattering photometer (ELS800, manufactured by Otsuka Electronics Co., Ltd.).

  As the substrate, a porous α-alumina tube (pore diameter: 1 μm, length: 9 cm, outer diameter: 1 cm) was used. First, titanium dioxide fine particles (ST-41, manufactured by Ishihara Sangyo Co., Ltd., particle size 200 nm) and a commercially available titanium dioxide sol solution (STS-01, manufactured by Ishihara Sangyo Co., Ltd.) are supported on the α-alumina tube. As a result, an intermediate layer was formed. Thereafter, a titanium dioxide colloidal sol (Non-patent Document 1) was coated stepwise in order from a colloid having a larger particle size and baked to prepare a nanoporous titanium oxide film. The firing was performed in an air atmosphere at a temperature of 450 ° C. for 15 minutes or longer.

(Measurement of nanopores in nanoporous titanium oxide film)
The nanopores of the produced nanoporous titanium oxide film were measured using nanopalm porometry (NanoPermPorometer, manufactured by Seika Sangyo Co., Ltd.). Nano palm porometry is a method in which nitrogen and hexane vapor are supplied to a porous body, and the pore diameter is measured by blocking nitrogen permeation by capillary condensation of the vapor component.

(Platinum supported on nanoporous titanium oxide film)
Platinum was supported on the nanoporous titanium oxide film by using a photo evaporation method. First, in a test tube, the ultra-pure water H ₂ PtCl 6 · _{6H 2 O} dissolved was prepared solution nanoporous titanium oxide films on not carrying a platinum (total solution weight of about 19.0g of) Soaked. Nitrogen was passed through the solution at about 20 × 10 ⁻⁶ m ³ / min for 30 minutes, and then the nanoporous titanium oxide film was irradiated with black light (350 nm, 4 W) for 10 to 120 minutes. The initial concentration of H ₂ PtCl ₆ .6H ₂ O was 0.6 mol / m ³ or 1.9 mol / m ³ .

  After irradiation with black light, the nanoporous titanium oxide film was rinsed with distilled water, dried at room temperature for 30 minutes, and then dried at 100 ° C. for 90 minutes. The concentration of supported platinum was determined by ICP analysis, and the amount of platinum supported on the nanoporous titanium oxide film was calculated from the concentration difference before and after irradiation with black light.

(Photocatalytic reaction)
A nanoporous titanium oxide film 16 (10φ × 90 mm) was used, and 4 to 8 black lights (350 nm, 4 W) were used as the light source 15. As the VOC component, methanol, ethanol or acetaldehyde was used, the air flow rate was 100 to 500 cc / min, the VOC concentration was 100 to 12000 ppm, the water vapor concentration was 600 to 25000 ppm, and the reaction temperature was 80 to 110 ° C.

  The VOC concentration was adjusted by the mass flow 12, and the water vapor concentration was adjusted to four types according to the temperature of the bubbling device 13 (0 ° C., 30 ° C.), the sweep method and the bubbling method. Two gas chromatographies 20 were used for the analysis. GC1 (column: PorapakT) analyzed methanol, formaldehyde, water, formic acid, ethanol, and acetaldehyde, and GC2 (column: Gascropack54) quantified carbon dioxide. .

[Example 1: Nanoporous titanium oxide film]
FIG. 4 shows a cross-sectional SEM image of the nanoporous titanium oxide film produced by the above method. As shown in FIG. 4, an intermediate layer having a thickness of about several μm was observed on the outer surface of the substrate, and a colloid coating layer having a thickness of 1 μm or less formed thereon was observed. Therefore, the titanium dioxide layer is considered to be about several μm including the intermediate layer. A thin film of titanium dioxide was prepared on a quartz plate, and the ultraviolet transmittance of the titanium dioxide thin film was measured using UV / Vis spectra (Jasco, V-570). As a result, the transmittance at a wavelength of 350 nm exhibited by a titanium dioxide layer having a thickness of 1 μm was estimated to be about 30%. Therefore, in a colloid coating layer that exhibits separation selectivity, ultraviolet light irradiated from black light is It is thought that it has almost penetrated.

FIG. 5 shows the measurement results of the pore size distribution of the nanoporous titanium oxide film. As can be seen from FIG. 5, the pore diameter at which the nitrogen permeability made non-dimensional with the permeability of dry nitrogen shows 50% can be controlled to about 2 nm to 17 nm. This pore size was controlled by the particle size of the colloidal sol used for coating. The transmittance of dry nitrogen was in the range of 1 to 2 × 10 ⁻⁵ mol / s / m ² / Pa.

  In addition, since the intermediate layer of these films is coated using titanium oxide fine particles having a particle diameter of 200 nm, the pore diameter of the intermediate layer is estimated to be in the range of several tens of nm. Therefore, it can be said that the pore diameter shown in FIG. 5 indicates the pore diameter of the colloid coating layer.

  FIG. 6 shows the measurement results of the pore size distribution of the nanoporous titanium oxide film before and after platinum support. The pore diameter before platinum support was about 16 nm, but the pore diameter decreased to 10 nm after 120 minutes of irradiation with black light.

FIG. 7 shows the relationship between the average pore diameter of the nanoporous titanium oxide film and the photodeposition time on the platinum deposition amount. As shown in FIG. 7, the pore diameter decreased with the progress of photoevaporation time, the amount of platinum deposited increased, and both of them tended to approach a certain value. The initial concentration of chloroplatinic acid was 1.95 mol / m ³ and 0.61 m ³ , but the deposition amount of platinum gradually approached a constant value regardless of the initial concentration. This is considered to be due to the fact that when black is formed on the film surface, the black light is not transmitted and the photo-deposition is completed.

[Example 2: Decomposition of methanol by nanoporous titanium oxide film according to the present invention]
FIG. 8 (a) shows the relationship between the reaction amount and the methanol concentration in the nanoporous titanium oxide film according to the present invention. FIG. 8 (b) shows the relationship between the reaction rate and the methanol concentration for the nanoporous titanium oxide film according to the present invention. The oxidative decomposition process of methanol is expressed as methanol → formaldehyde → formic acid → carbon dioxide, and harmful formaldehyde is generated in the oxidative decomposition process.

  As shown in FIG. 8A, the nanoporous titanium oxide film according to the present invention on which platinum is supported decomposes methanol almost completely regardless of the methanol supply concentration, and the carbon dioxide production rate is also almost 100%. showed that. In addition, the amount of methanol decomposed increased, and the amount of carbon dioxide produced increased greatly. From this, it can be seen that platinum loading is extremely effective for methanol oxidative decomposition reaction.

  The platinum decomposition yielded a methanol decomposition rate of almost 100% and showed a tendency toward complete oxidation in which methanol was oxidized to almost carbon dioxide.

[Example 3: Ethanol decomposition and acetaldehyde decomposition by nanoporous titanium oxide film according to the present invention]
FIG. 9 shows the concentration dependency when ethanol is supplied to the nanoporous titanium oxide film according to the present invention and the result of comparison with the nanoporous titanium oxide film not supporting platinum. (A) shows the relationship between the reaction amount and the supply ethanol concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the supply ethanol concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum.

  FIG. 10 shows the concentration dependence when acetaldehyde is supplied to the nanoporous titanium oxide film according to the present invention and the result of comparison with a nanoporous titanium oxide film not supporting platinum. (A) shows the relationship between the reaction amount and the supplied acetaldehyde concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the supplied acetaldehyde concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum.

Here, the supported amount of platinum in the nanoporous titanium oxide film is estimated to be 8.4 × 10 ⁻⁵ g from FIG.

First, when the behavior of the decomposition reaction when the nanoporous titanium oxide film according to the present invention is used is compared with the result of the nanoporous titanium oxide film not supporting platinum, when the VOC is ethanol, the ethanol conversion rate is greatly increased. As a result, the selectivity of acetaldehyde and carbon dioxide was greatly decreased and increased, confirming the improvement of decomposition characteristics by supporting platinum on the nanoporous titanium oxide film.
Similarly, when VOC was acetaldehyde, the acetaldehyde conversion rate increased and the formaldehyde and carbon dioxide selectivity tended to decrease and increase, respectively.

[Example 4: Behavior of decomposition characteristics of VOC]
In Example 3, the behavior of the VOC decomposition characteristics by changing the supply VOC concentration while fixing the air flow rate was examined. In Example 4, the behavior of the VOC decomposition characteristics was examined by fixing the supplied VOC concentration and changing the air flow rate, that is, changing the residence time.

  FIG. 11 shows the result of comparing the residence time dependency when the supplied VOC is ethanol and acetaldehyde between the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. . (A) shows the relationship between the reaction rate and the residence time for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the residence time for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum.

  Here, the residence time was calculated using the volume (thickness 1 mm) of the alumina support tube. In FIG. 11, the broken line represents the result of the nanoporous titanium oxide film according to the present invention, and the solid line represents the result of the nanoporous titanium oxide film not supporting platinum.

  Regarding the residence time dependency in the nanoporous titanium oxide film according to the present invention, the acetaldehyde selectivity is the largest at the minimum residence time that can be measured, and the residence time decreases as the residence time value increases. It was found that almost complete oxidation was maintained at about 0.7 seconds. It was also found that the ethanol conversion rate was maintained at 100% throughout.

  In addition, the behavior of the acetaldehyde generation rate in the nanoporous titanium oxide film not supporting platinum has a maximum and is convex upward, while that in the nanoporous titanium oxide film according to the present invention is downwardly convex. I found out that

  The difference in behavior may be considered as follows. First, the nanoporous titanium oxide film according to the present invention has better decomposition performance than that of the nanoporous titanium oxide film not supporting platinum. It is conceivable that the oxidation proceeds toward complete oxidation when the residence time is shorter than that of the membrane. Therefore, it is considered that the right side portion of the behavior of the acetaldehyde decomposition rate in the nanoporous titanium oxide film not supporting platinum, that is, the portion showing the tendency toward complete oxidation is shifted to the left.

[Comparative Example 1: Methanol decomposition reaction using nanoporous titanium oxide film not supporting platinum]
FIG. 12 shows the change over time in the concentration of methanol, carbon dioxide, formaldehyde, and water after passing through the nanoporous titanium oxide film not supporting platinum at various methanol supply concentrations.

  In the region shown in FIG. 12 (1), the methanol concentration supplied to the nanoporous titanium oxide film was adjusted to about 100 ppm using the bypass line 21. The light source is irradiated with ultraviolet light using black light, and the center temperature of the nanoporous titanium oxide film is kept at about 110 to 120 ° C. by radiant heat. In the region shown in (2) of FIG. 12, when the supplied methanol was completely permeated through the nanoporous titanium oxide film, the methanol concentration after permeation through the nanoporous titanium oxide film decreased to almost zero.

  On the other hand, in the region shown in (2) of FIG. 12, the concentration of water increased from 750 ppm to 900 ppm and the concentration of carbon dioxide increased from 450 ppm to 550 ppm as compared to the region shown in (1) of FIG. Formaldehyde was not detected. This is because the raw material methanol was supplied to the nanopores of the nanoporous titanium oxide film by forced convection and permeated through the pores with photocatalytic activity in a uniform residence time, so that a high decomposition rate was obtained. Conceivable.

  In the regions shown in (3), (4), and (5) of FIG. 12, the methanol supply concentration was adjusted to 1100 ppm, 4400 ppm, and 2300 ppm, respectively. The methanol concentration and the carbon dioxide concentration changed stepwise, and reached a steady state in a relatively short time. That is, it became clear that the photocatalytic reaction of methanol occurred. Formaldehyde, an intermediate product for complete oxidation, was not detected when the feed methanol was at a low concentration, but was detected when the feed methanol was at a high concentration.

  FIG. 13 shows the methanol concentration dependence of the reaction rate (methanol decomposition rate, formaldehyde production rate, carbon dioxide production rate) and reaction rate (methanol conversion rate, formaldehyde selectivity, carbon dioxide selectivity). The methanol decomposition rate was determined from the product of the difference between the concentration on the inlet side and the concentration on the permeate side of the nanoporous titanium oxide film and the air flow rate. The methanol decomposition rate, carbon dioxide production rate, formaldehyde production rate Is the ratio of the respective reaction rate to the methanol decomposition rate.

  When the feed methanol concentration was low, the methanol decomposition rate and carbon dioxide production rate were high and the formaldehyde production rate tended to be low. Moreover, as the methanol concentration increased, the amount of methanol decomposition gradually decreased, and the amount of formaldehyde generated gradually increased. Methanol decomposition rate and formaldehyde production rate showed a similar tendency.

  As described above, when a nanoporous titanium oxide film not supporting platinum is used, the decomposition rate of methanol and the carbon dioxide production rate decrease as the supply methanol concentration increases, and the high formaldehyde production rate is maintained. From this, it was shown that the proportion of intermediate products increased and methanol was not completely oxidized. The decrease in the rate of complete oxidation is thought to be because the photocatalytically active sites were occupied by competitive adsorption by the raw material methanol and the intermediate product formaldehyde.

  As described above, the nanoporous titanium oxide film according to the present invention is a nanoporous titanium oxide film in which a film containing titanium dioxide as a main component is supported on the outer surface and / or the inner surface of the base material. Since some or all of the titanium dioxide molecules carry a metal belonging to Group 8, volatile organic compounds such as methanol can be decomposed very efficiently.

  Therefore, this invention can be utilized for the filter of an air conditioner, the filter of an air cleaner, etc., for example.

It is a schematic diagram which shows the process of decomposing | disassembling VOC by making VOC permeate | transmit the nanopore of a nanoporous titanium oxide film. It is a schematic diagram of the nanoporous titanium oxide film | membrane shape | molded in the tube shape. It is a schematic diagram which shows the outline of the photocatalyst film | membrane type reactor 1 for enforcing the processing method of VOC which concerns on this invention. 1 shows a cross-sectional SEM image of a nanoporous titanium oxide film according to the present invention. The measurement result of the pore diameter distribution of the nanoporous titanium oxide film which concerns on this invention is shown. The measurement result of the pore diameter distribution of the nanoporous titanium oxide film before and after platinum support is shown. The relationship between the average pore diameter of a nanoporous titanium oxide film and the photoevaporation time exerted on the platinum deposition amount is shown. (A) shows the relationship between the reaction amount and the supply methanol concentration in the nanoporous titanium oxide film according to the present invention. (B) shows the relationship between the reaction rate and the supply methanol concentration for the nanoporous titanium oxide film according to the present invention. (A) shows the relationship between the reaction amount and the supply ethanol concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the supply ethanol concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (A) shows the relationship between the reaction amount and the supplied acetaldehyde concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the supplied acetaldehyde concentration for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (A) shows the relationship between the reaction amount and the residence time for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. (B) shows the relationship between the reaction rate and the residence time for the nanoporous titanium oxide film according to the present invention and the nanoporous titanium oxide film not supporting platinum. In Comparative Example 1, methanol, carbon dioxide, formaldehyde, and water at various methanol supply concentrations change with time after passing through a nanoporous titanium oxide film that does not support platinum. In Comparative Example 1, the reaction rate (methanol decomposition rate, formaldehyde production rate, carbon dioxide production rate) and reaction rate (methanol conversion rate, formaldehyde selectivity, carbon dioxide selectivity) are dependent on methanol concentration.

Explanation of symbols

1 Photocatalytic membrane reactor 16 Nanoporous titanium oxide membrane

Claims (5)

  The film mainly composed of titanium dioxide is a nanoporous titanium oxide film supported on the outer surface and / or the inner surface of the base material, and some or all of the titanium dioxide molecules belong to Group 8 A nanoporous titanium oxide film characterized by carrying a metal.   The nanoporous titanium oxide film according to claim 1, wherein the metal is platinum.   The nanoporous titanium oxide film according to claim 1 or 2, wherein the nanopores of the film have a pore diameter of 2 to 25 nm. Irradiating the nanoporous titanium oxide film according to any one of claims 1 to 3 with light;
And a step of decomposing the volatile organic compound by allowing the volatile organic compound to permeate through the nanopores of the nanoporous titanium oxide film.   The said volatile organic compound is methanol, ethanol, and / or acetaldehyde, The processing method of the volatile organic compound of Claim 4 characterized by the above-mentioned.