JP2006281156A - Functional photocatalyst and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a functional photocatalyst which enables to decompose/clean an environmental contaminated substance regardless of daytime and night and to greatly increases a treatment efficiency. <P>SOLUTION: The functional photocatalyst has metallic Pd, originated from a palladium ion (Pd<SP>2+</SP>) aqueous solution, which is deposited on the surface of a photocatalytic (an anatase type) titanium dioxide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a functional photocatalyst obtained by adding another catalytic function to a photocatalyst mainly composed of titanium dioxide.

When titanium dioxide is irradiated with ultraviolet rays, it receives energy exceeding the band gap energy and excites it. In the excited titanium dioxide, electrons in the valence band are excited and transition to the conduction band. The transitioned electrons combine with Ti ⁴⁺ present in the bulk of titanium dioxide to reduce to Ti ³⁺ and combine with abundant oxygen (O ₂ ) in the air to form superoxide (O ₂ ⁻ ). Or combine with hydrogen ions in water to form hydrogen (H ₂ ). Holes remaining in the valence band are combined with superoxide (O ₂ ⁻ ) on the surface lattice of titanium dioxide to be changed to O ⁻ , and further generate so-called active oxygen such as hydroxyl radical or superoxide anion (for example, , See Patent Document 1).

  These series of active oxygen is an effective technology for purifying and preserving the global environment by decomposing environmental pollutants contained in fluids such as exhaust gas and wastewater into water and carbon dioxide without generating harmful substances. It is highly appreciated. Research and development of equipment and facilities for decomposing and purifying environmental pollutants using this technology are progressing rapidly.

  By the way, ultraviolet rays refer to a light wave portion of sunlight having a wavelength of 400 nm or less. Therefore, decomposition and purification of environmental pollutants by ultraviolet irradiation of titanium dioxide is limited to daytime and during sunshine, and sunlight, that is, during periods when ultraviolet irradiation cannot be obtained (such as at night or in cloudy weather) Decomposition and purification are impossible or forced to rely on artificial ultraviolet rays.

  However, the time zone where sunlight, that is, UV irradiation cannot be obtained, is a half year and is halfway between daytime and daytime, and when rain, snowfall, and cloudy weather are added, the majority of the year is exceeded. On the other hand, recent environmental pollution continues to increase regardless of the day and night and the weather, and the demand for the decomposition and purification of pollutants has not been able to keep up with the treatment.

Under these circumstances, the creation of a so-called functional photocatalyst that deposits a general catalytic metal on the surface of photocatalytic titanium dioxide and exhibits catalytic properties regardless of whether it is daytime or nighttime is the decomposition of environmental pollutants.・ Remarkably increase the treatment effect of purification. In addition, sunlight is a natural product, and its use significantly reduces processing costs and is considered to have great economic significance.
JP 11-47611 A

In titanium dioxide (TiO ₂ ), which is excellent as a photocatalyst, there are several problems to be solved first in order to impart a different catalyst characteristic and further increase its use efficiency as a functional photocatalyst. First, titanium dioxide, which is excellent as a photocatalyst, is too fine, does not stick as smooth, scatters in the wind, pollutes the flow, and may become a secondary source of contamination, and prevents further scattering and contamination before use. It is necessary to fix and fix the stool.

  On the other hand, the free persistence of electrons and holes due to ultraviolet irradiation is short, and is at most several pico to several hundred nanoseconds. Therefore, it is desirable that the field of electron transfer by ultraviolet irradiation be a field for the formation of active oxygen as it is, and a field where it is directly mixed with environmental pollutants to be decomposed and purified. For this purpose, it is necessary to prepare a space where the contaminated fluid reaches deep inside the fine fine titanium dioxide and directly acts on the active oxygen provided from the functional photocatalyst.

  On the other hand, zeolite is composed of a dense and firm outer shell and a crystal cavities supported by microcrystals that grow vertically and horizontally. Therefore, by blending this in titanium dioxide and fixing it, the titanium dioxide becomes porous, attracts the contaminated fluid to circulate and acts by mixing directly with the active oxygen generated by the ultraviolet ray or the catalyst. It is thought that it is useful to get a place.

  It has been a long time since air pollution was taken up as a social problem. However, air pollution in urban areas is unlikely to decrease at all and remains serious. Originally, in order to fundamentally solve the purification of nitrogen oxides, it is considered indispensable to take measures against its source such as automobiles. However, the path is far away and it has not yet reached decisive technological development.

  An object of the present invention is to obtain a functional photocatalyst that can decompose and purify environmental pollutants without distinction between nighttime and daytime and can significantly increase the processing efficiency. Another object of the present invention is to obtain an apparatus for decomposing and purifying environmental pollutants using this functional photocatalyst. Furthermore, it aims at obtaining the manufacturing method of this functional photocatalyst.

The functional photocatalyst according to the invention described in claim 1 is characterized in that metal palladium derived from an aqueous palladium ion (Pd ²⁺ ) solution is deposited on the surface of photocatalytic (anatase type) titanium dioxide particles. It is.

  The immobilized functional photocatalyst according to the invention described in claim 2 is an immobilized binder in which the zeolite adsorbing the functional photocatalyst according to claim 1 is kneaded with cement and water, or ferrite-based magnetic iron, It is characterized by being fixed to an immobilizing binder made of a metal oxide such as cobalt and titanium, glass or ceramic fired resin.

The functional photocatalyst processing device according to the invention described in claim 3 includes an ultraviolet lamp,
An inner peripheral wall made of an ultraviolet transmitting material surrounding the ultraviolet lamp at the center, an outer peripheral wall made of an ultraviolet transmitting material concentric with the inner peripheral wall, and a pair of plugs closing both ends of the inner peripheral wall and the outer peripheral wall A processing chamber surrounded by a lid,
An intake for guiding the contaminated fluid formed on one lid to the processing chamber;
An outlet for removing the processing fluid formed on the other lid from the processing chamber;
The functional photocatalyst according to claim 1 housed in the processing chamber, or the functional photocatalyst material of the immobilized functional photocatalyst according to claim 2,
The contaminated fluid is circulated from the inlet to the outlet while irradiating the functional photocatalyst material with sunlight from the outside and / or ultraviolet rays from an ultraviolet lamp from the inside.

The method for producing a functional photocatalyst according to the invention described in claim 4 includes a step of immersing photocatalytic (anatase type) titanium dioxide particles in an aqueous solution containing palladium ions (Pd ²⁺ ), and ultraviolet rays in the titanium dioxide particles. And a step of depositing metallic palladium on the surface of titanium dioxide.

  The method for producing a functional photocatalyst according to the invention described in claim 5 is to immobilize the obtained functional photocatalyst obtained in claim 5 on zeolite and knead the adsorbed zeolite with cement and water. The method further comprises a step of fixing a binder, or a metal oxide such as ferritic magnetic iron, cobalt, and titanium, glass or resin to an immobilized binder made of fired ceramic.

  The present invention makes it possible to decompose and purify environmental pollutants without distinguishing between nighttime and daytime, thereby significantly increasing the treatment efficiency. In addition, a device for decomposing and purifying environmental pollutants made using this functional photocatalyst can be obtained. Furthermore, there is an effect that a method for producing this functional photocatalyst can be obtained.

In the present invention, metallic palladium derived from an aqueous palladium ion (Pd ²⁺ ) solution is deposited on the surface of photocatalytic (anatase type) titanium dioxide particles. As a result, it is possible to decompose and purify environmental pollutants without distinguishing between night and daytime, thereby significantly increasing the processing efficiency.

That is, the fine palladium powder is more active as it burns when touched with bare hands, occludes more than 800 times the volume of hydrogen, and discharges it with improved reducibility. For example, carbon monoxide, nitrogen oxides, and hydrocarbons contained in automobile exhaust as a catalyst are converted into harmless nitrogen, carbon dioxide, and water before being discharged. On the other hand, by immersing titanium dioxide (TiO ₂ ) in an aqueous palladium ion (Pd ²⁺ ) solution and irradiating with ultraviolet rays while stirring, electrons are generated and palladium metal is deposited on the surface of titanium dioxide. The

  Titanium dioxide having palladium metal pieces deposited on the surface of the present invention acts as a photocatalyst when irradiated with ultraviolet rays. When ultraviolet irradiation cannot be obtained, palladium acts as a catalyst and functions to decompose and purify environmental pollutants. This makes it possible to decompose and purify environmental pollutants regardless of the presence or absence of irradiation with sunlight, that is, ultraviolet rays. As a result, the processing efficiency and processing time of the functional photocatalyst can be doubled, and an unexpected effect can be expected from its economic effect.

  The degree of deposition of palladium in the present invention is sufficient if palladium is supplemented with sufficient active oxygen to decompose and purify environmental pollutants when UV irradiation cannot be obtained. In addition, it is not preferable to coat and deposit the entire surface of titanium dioxide because it inhibits the photocatalytic action of titanium dioxide when irradiated with ultraviolet rays. As a preferable precipitation, although it is empirical, it is sufficient to deposit the surface of the titanium dioxide particles sparsely, that is, about 15 to 30% of the total surface area visually.

  The functional photocatalyst of the present invention does not need to be particularly finely sized, and may be an irregular size obtained by general chemical treatment. However, if the fine particles soaked in an aqueous palladium ion solution are used as they are, they do not function sufficiently as functional photocatalysts because they contain moisture and adhere, so it is necessary to dry them before use. It was. On the other hand, active oxygen generated by ultraviolet irradiation of titanium dioxide facilitates decomposition of organic substances than water. Therefore, organic substances have been made unsuitable as binders for immobilizing titanium dioxide. However, although the fluororesin is an organic substance, specific resistance as a binder of titanium dioxide has been confirmed, and in applications that require exceptional flexibility, for example, the functional photocatalytic sheet can be used under the condition that it is replaced upon deterioration. It can also be used as a binder. Accordingly, as a preferred embodiment of the present invention, there is disclosed a material in which a zeolite adsorbed with a particulate catalyst and a fluorine resin as a binder are kneaded and formed into a sheet shape to form an antioxidant sheet.

  In addition, as a binder for fixing titanium dioxide, for example, it may be fixed by kneading with cement or water, or may be fixed with a ceramic obtained by firing glass, resin, and metal oxide. Even if the contact area with titanium dioxide is increased by blending, the active oxygen generated by the irradiation of ultraviolet rays and the contaminants taken in from the outside are mixed and acted, so that it is considered to function sufficiently. Therefore, as another preferred embodiment of the present invention, the zeolite adsorbed with the particulate catalyst is a fixed binder in which cement and water are kneaded, or metal oxides such as ferritic magnetic iron, cobalt, and titanium, Disclosed is a glass or resin fixed to a fixed binder made of fired ceramic.

  In the present invention, as a treatment apparatus using a functional photocatalyst, an ultraviolet lamp; an inner peripheral wall made of an ultraviolet transmitting material surrounding the ultraviolet lamp as a center, and an outer periphery made of an ultraviolet transmitting material concentric with the inner peripheral wall A processing chamber surrounded by a wall and a pair of lid portions closing both ends of the inner peripheral wall and the outer peripheral wall; an intake port for introducing the contaminated fluid formed in one lid portion to the processing chamber; An outlet for removing the processing fluid formed in the lid from the processing chamber; and the functional photocatalyst according to claim 1 or the functionality of the immobilized functional photocatalyst according to claim 2 accommodated in the processing chamber. A photocatalyst material; and circulates the contaminated fluid from the inlet to the outlet while irradiating the functional photocatalyst with sunlight from the outside and / or ultraviolet rays from an ultraviolet lamp from the inside.

So-called active oxygen such as hydroxyl radical and superoxide anion is generated from the functional photocatalyst irradiated with ultraviolet light, and directly acts on the contaminating organic substances to be oxidized, decomposed or purified. These reactions start with a reaction that reduces water (4H ₂ O) (4H ⁺ → 2H ₂ ) and a reaction that oxidizes (4OH → O ₂ + 2H ₂ O). By absorbing light, titanium dioxide becomes electrons and holes. When the generated electrons are combined with oxygen, super oxidants (O ₂ ⁻ ) are generated, and when they are combined with protons (H ⁺ ), hydrogen atoms are generated. However, super oxidants are easily generated from the affinity between oxygen and protons. Naturally, protons are generated, and hydrogen is generated in the absence of oxygen.

On the other hand, in the functional photocatalyst, when electrons are combined with oxygen (O ₂ ), superoxide (O ₂ ⁻ ) is generated and combined with protons (H ⁺ ) to form hydrogen atoms (H). However, considering the electron affinity between oxygen and proton, superoxide is more likely to be generated, and hydrogen is generated in the absence of oxygen.

  On the other hand, the organic matter is more easily oxidized than water, and when the concentration is increased, the probability that holes are used for the oxidation of the organic matter increases, and the recombination rate between carriers decreases. Thus, it is considered that the transfer of electrons to oxygen molecules at the reduction site becomes the rate-determining factor of the entire photocatalytic reaction under the condition that holes are sufficiently consumed. In other words, by facilitating the transfer of electrons to oxygen molecules, so-called active oxygen, such as highly reactive hydroxyl radicals and superoxide anions, required to increase the efficiency of photocatalytic reactions and proceed with oxidation reactions, is created, causing environmental pollution. It is thought that the decomposition and purification of substances will be accelerated.

  As a result, the major feature of functional photocatalysts is that the oxidizing power of holes is stronger than the reducing power of excited electrons, and the adsorbed water present on the surface of the functional photocatalyst is oxidized by the holes, resulting in a highly oxidizing hydroxy group. It becomes a radical, which reacts with organic matter. Further, when oxygen is present, radicals of the organic intermediate and oxygen molecules cause a chain reaction to decompose the organic matter and finally become water and carbon dioxide.

  Nitrogen dioxide contained in the atmosphere receives sunlight and separates into nitrogen monoxide and atomic oxygen and combines with oxygen molecules to form ozone. Moreover, the formed ozone immediately reacts with nitric oxide to form nitrogen dioxide and oxygen molecules, so that in the presence of only nitrogen oxides, ozone or the total amount of nitrogen dioxide does not increase, and water or adsorption Nitrogen oxide is converted into nitric acid or nitrous acid by circulating the product, and is dissolved and adsorbed to be removed from the atmosphere.

  By the way, it is considered that these series of actions are a photocatalyst in the atmosphere and a reaction in the presence of the catalyst, and superoxide anions are largely involved. In this way, the process of electron transfer to oxygen molecules at the reduction site under the conditions where holes are sufficiently consumed determines the overall reaction of the photocatalytic reaction and facilitates the transfer of electrons to oxygen molecules. Efficiency can be increased. In this regard, it can be solved by using a functional photocatalyst, titanium dioxide, a catalyst, and palladium in combination. Note that sulfur oxides in the atmosphere can be treated on the same principle as in the case of nitrogen oxides, and can be removed from the atmosphere.

  Traditionally, floor tiles, soap sticking to toilets, fats such as dirt, calcium and magnesium ions in water, and soaps of urea, as the main stains in bathrooms and toilets, or urea bacteria Organic substances that can be decomposed into A photocatalyst tile is one of these disassembled and removed. Many of the photocatalytic tiles are baked with titanium dioxide on the surface, and metal oxides and urea decomposition products are decomposed and removed by active oxygen generated by the ultraviolet irradiation. However, bathrooms, toilet facilities, and pipes are not necessarily conscious of sunlight incident from a certain direction, and ultraviolet rays reach the toilet bowls and tub wraps for installation and maintenance for each purpose and application. In addition, things that are placed directly block sunlight, that is, ultraviolet rays completely, and titanium dioxide baked on this part does not function, and it is considered that there is a difference in soil decomposition and purification such as metal soap and urea decomposition organic matter It is done.

  In contrast, tiles coated and baked with the functional photocatalyst of the present invention generate a series of active oxygens such as hydroxyl radicals and superoxide anions with or without UV irradiation to decompose and purify organic contaminants. Therefore, it is possible to maintain cleanliness by uniformly decomposing and purifying the pollutants on the entire surface.

Example 1. Production of Functional Photocatalyst Titanium dioxide particles were immersed in an aqueous solution containing palladium ions (Pd ²⁺ ), and the titanium dioxide fine particles were irradiated with ultraviolet rays to deposit metallic palladium on the titanium dioxide surface to obtain a functional photocatalyst. In order to proceed stably, it is effective to add phosphonate as a reducing agent, ethylenediamine as a complexing agent of palladium ion (Pd ²⁺ ), and thiodiglycolic acid as a stabilizer. In this case, the factors that greatly affect the deposition rate are the concentration of (Pd ²⁺ ) and the bath temperature, and the deposition rate increases in proportion to the concentration of (Pd ²⁺ ), and increases with increasing bath temperature. Moreover, when the coprecipitation of phosphorus is seen, it increases in proportion to the 0.2th power of the phosphonate concentration as a reducing agent, and the value decreases as the pH increases. Incidentally, in this invention, it implemented at pH 6-8 and bath temperature 50 degreeC.

Example 2 Decomposition / Purification Device FIG. 1 is an explanatory view showing an embodiment of a functional photocatalyst treatment device for decomposing / purifying environmental pollutants. In the figure, the functional photocatalyst treatment apparatus 1 has two large and small Pyrex (trade name) glass cylinders with the same center line and both ends, and is sealed with a top lid 6 and a bottom lid 4 at both ends. Thus, a photocatalyst processing chamber 2 that is a space between the large and small cylinders and an ultraviolet lamp chamber 3 that is a small cylindrical space are formed.

  The photocatalyst treatment chamber 2 houses a functional photocatalyst ball 10 in which a natural zeolite powder having a functional photocatalyst adsorbed thereon is fixed to a fixed binder processed into a spherical shape. An artificial ultraviolet lamp 12 is installed in the ultraviolet lamp chamber 3. When processing the fluid containing the contaminant, a liquid or gas fluid containing the contaminant is introduced from the contaminated fluid intake 5 of the bottom lid 4 and circulated to the treatment fluid outlet 7 of the top lid 6. Active oxygen generated from the functional photocatalyst by irradiation of ultraviolet rays from the outside and artificial ultraviolet rays from the inside, and the contaminated fluid to be circulated together are attracted to the zeolite internal space to decompose and purify contaminated organic substances.

  The functional photocatalyst ball 10 is accommodated in a stainless steel wire mesh cage (not shown) or the like and held in the processing chamber 2. Incidentally, the stainless steel wire mesh cage is adjusted according to the inner and outer circumferences of the processing chamber 2, and the functional photocatalyst ball 10 is incorporated and stored in the processing chamber 2. A functional photocatalyst sheet can be used in place of the functional photocatalyst ball 10 depending on the state of the contaminated fluid.

  The fluid contaminated with the pollutant is taken into the processing chamber 2 from the intake 5 of the lower lid 4, comes into contact with the functional photocatalyst ball 10, the water level is raised by the subsequent contaminated fluid, and the outlet 7 of the top lid 6. Discharged from.

  The air was collected in a fixed container, the blank values of nitrogen monoxide, nitrogen dioxide, and nitric oxide contained in it were clarified, and then the environmental pollutant decomposition and purification device shown in FIG. 1 was repeatedly circulated and passed through. Thereafter, the values of nitric oxide, nitrogen dioxide and nitric oxide contained in the decomposed and purified air were measured. Incidentally, the nitrided oxide contained in the air at the measurement location, and the results of decomposition and purification were as follows.

  Outside air was sampled on the street side where automobiles reciprocate frequently, and the following blank values were obtained. The blank values of nitric oxide, nitrogen dioxide, and nitric oxide were 4.6 to 4.9, 0.3 to 0.5, and 4.9 to 5.6 ppm, respectively. On the other hand, this outside air is continuously circulated for 24 hours by using an environmental pollutant decomposition / purification treatment device using a functional photocatalyst ball as a decomposition / purification agent, and residual pollutants, nitric oxide, nitric oxide Was measured. As a result, each value was 1.5-1.7, 0.1-0.3, 1.6-1.9 ppm. This value corresponds to about one third of the blank value, and it seems that the efficiency is poor depending on the idea. However, it is useful to decompose and purify the pollutants that continuously decrease to this extent, and it is considered to be sufficiently practical.

Example 3
After adsorbing the functional photocatalyst obtained in Example 1 with natural zeolite powder, this was mixed in an aqueous dispersion of polytetrafluoroethylene as a fluororesin so as to have a solid content ratio of 40% by weight, A paste-like kneaded product was obtained. The kneaded product was dried at 120 ° C. to obtain a catalyst sheet containing 40% by weight of a functional photocatalyst. (Please check the difference from the actual one)

The resulting catalyst sheet was used to measure the effect of pollutant decomposition and purification. Fig. 2 shows the mixing of nitrogen monoxide (NO) at a rate of 1 ppm for a flow rate of 500 cm ³ / min in a pollutant decomposition / purification device made using 200 cm ² of ceramic sole containing functional photocatalyst (40%). The results obtained through continuous communication for one week.

  As shown in the figure, during the week, naturally, the daytime with UV irradiation and the night without UV irradiation were repeated alternately, but the decomposition and purification curves of nitric oxide were not stepped curves and were smooth. Curve. This is considered to indicate that the functional photocatalyst continuously decomposed and purified the pollutants regardless of day or night. Incidentally, the value obtained by subtracting the nitrogen oxide decomposition / purification concentration from the nitrogen oxide supply concentration corresponds to the treatment amount of nitric oxide.

It is explanatory drawing which shows one Embodiment of the functional photocatalyst processing apparatus which decomposes | disassembles and purifies an environmental pollutant. It is explanatory drawing which shows the decomposition | disassembly result of the nitric oxide of the catalyst sheet | seat of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Functional catalyst processing apparatus 2 ... Processing chamber 3 ... Light source chamber 4 ... Bottom cover 5 ... Population 6 ... Top cover 7 ... Outlet 10 ... Photocatalyst ball (functional photocatalyst)

Claims (5)

A functional photocatalyst characterized in that metal palladium derived from an aqueous palladium ion (Pd ²⁺ ) solution is deposited on the surface of photocatalytic (anatase type) titanium dioxide particles.   The zeolite adsorbed with the functional photocatalyst according to claim 1 baked an immobilized binder in which cement and water are kneaded, or a metal oxide such as ferritic magnetic iron, cobalt, and titanium, glass or resin. An immobilized functional photocatalyst characterized by being fixed to an immobilized binder made of ceramic. With UV light,
An inner peripheral wall made of an ultraviolet transmitting material surrounding the ultraviolet lamp at the center, an outer peripheral wall made of an ultraviolet transmitting material concentric with the inner peripheral wall, and a pair of plugs closing both ends of the inner peripheral wall and the outer peripheral wall A processing chamber surrounded by a lid,
An intake for guiding the contaminated fluid formed on one lid to the processing chamber;
An outlet for removing the processing fluid formed on the other lid from the processing chamber;
The functional photocatalyst according to claim 1 housed in the processing chamber, or the functional photocatalyst material of the immobilized functional photocatalyst according to claim 2,
A functional photocatalyst treatment apparatus that circulates a contaminated fluid from an inlet to an outlet while irradiating the functional photocatalyst material with sunlight from the outside and / or ultraviolet rays from an ultraviolet lamp from the inside. A step of immersing photocatalytic (anatase type) titanium dioxide particles in an aqueous solution containing palladium ions (Pd ²⁺ ) and a step of irradiating the titanium dioxide particles with ultraviolet rays to deposit metallic palladium on the titanium dioxide surface were provided. The manufacturing method of the functional photocatalyst characterized by the above-mentioned. The obtained functional photocatalyst is adsorbed on zeolite, and the adsorbed zeolite is kneaded with cement and water, or a fixed binder, or ferritic magnetic iron, cobalt, titanium and other metal oxides, glass or resin. The method for producing a functional photocatalyst according to claim 4, further comprising a step of fixing to a fixed binder made of a fired ceramic.

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