JP2009154090A - Silica glass for photocatalyst, and method of preparing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica glass for a photocatalyst, which silica glass is used in a photocatalytic reaction unit and has a characteristic of efficiently converting a wavelength of light not longer than about 250 nm to a longer wavelength of from about 250 nm to about 450 nm and an excellent UV resistance characteristic of hardly losing its catalytic activity after a prolonged exposure to ultraviolet rays, both characteristics being effective for enhancing reaction efficiency of a photocatalyst, and a method of preparing the same. <P>SOLUTION: The silica glass for a photocatalyst is characterized in that the content of a hydroxy (OH) group is not more than 10 weight ppm, a linear transmittance at a thickness of 10 mm and at a wavelength of 245 nm is in a range of from 90.0% to 30.0%, the total content of chlorine and fluorine is not more than 100 weight ppm, and is used in a photocatalytic reaction unit. A method of preparing silica glass for a photocatalyst capable of preparing such silica glass for a photocatalyst as described above is disclosed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to silica glass and a method for producing the same, and more particularly to a silica glass for photocatalyst used in a photocatalytic reaction unit and a method for producing the same.

In recent years, oxide semiconductors, especially titanium dioxide (TiO ₂ ) as a photocatalyst, UV lamps or sunlight as an excitation light source, decomposition using photochemical reactions such as human harmful substances and malodorous substances contained in the atmosphere and water Technology is drawing attention.

As the photocatalyst, a metal ion, a metal complex, or the like is used, but the semiconductor is most frequently used. Semiconductors used as photocatalysts include gallium phosphide (GaP), gallium arsenide (GaAs), cadmium sulfide (CdS), strontium titanate (SrTiO ₃ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), iron oxide (Fe) ₂ O ₃ ), tungsten oxide (WO ₃ ), and the like.

  A semiconductor is usually a nonconductor that does not conduct electricity, but it conducts electricity when exposed to light. The light for that purpose is not limited to any light, but it is necessary that the light has a certain level of energy. This energy is called bandgap energy and is determined by the type of semiconductor. When light having energy greater than this band gap is applied to a semiconductor, electrons flow and a current is generated. Electrons in semiconductors are in the valence band, where electrons cannot move. However, when ultraviolet light with energy above the band gap is applied to the semiconductor, the electrons move to a high energy conduction band. Electric current flows to be able to move. The energy difference between the valence band and the conduction band is a band gap. When electrons move to the conduction band, a hole from which electrons have been removed is formed in the valence band, and this hole has a positive charge and is called a hole. Therefore, electrons and holes can be formed simultaneously, electrons have a strong reducing power, and holes have a strong oxidizing power.

  When most semiconductors are put in water and exposed to light, a reaction called photodissolution occurs that dissolves into cations and anions, so that the semiconductor is not dissolved and cannot be put to practical use. However, titanium oxide does not cause photodissolution in semiconductors, is harmless to humans, is inexpensive, durable and wear-resistant, is abundant in resources, and is easily available, so it is currently used as a photocatalyst. Most of them are titanium oxide.

As a known prior art relating to a photocatalytic reaction device, for example, Patent Document 1 and Patent Document 2 show an exhaust gas treatment device communicated with a combustion exhaust gas discharge passage of an incinerator. This exhaust gas treatment apparatus includes an ultraviolet ray permeable cylinder through which combustion exhaust gas passes, a photocatalyst accommodated in the cylinder, and a light source for exciting the photocatalyst.
The cylinder is a double cylinder composed of an outer cylinder made of quartz glass (hereinafter, quartz glass and silica glass have the same meaning) and an inner cylinder made of quartz glass, and the photocatalyst is made of titanium oxide. It has been shown that silica gel is used as the photocatalyst support, in addition to activated carbon, activated alumina, and porous glass. Since the germicidal lamp and black light are used as the excitation light source, the material of the lamp tube is considered to be quartz glass.

  Patent Document 3 discloses an exhaust gas treatment apparatus that treats environmental pollutants such as dioxins in combustion exhaust gas discharged from an incinerator with a photocatalyst. Among these, it is shown that a plurality of cylinders having ultraviolet transparency are arranged, an ultraviolet light source is arranged inside, and a photocatalyst is arranged outside.

  Patent Document 4 discloses a water purification device that can purify harmful wastewater containing environmental pollutants such as dioxins such as scrubber water in a factory. In this figure, a cylindrical body having optical transparency and containing a photocatalyst therein, and a light source arranged on the outer side of the cylindrical body are shown. Another object of the technology is to provide a water purification device that can easily irradiate the entire photocatalyst with ultraviolet rays, has high purification efficiency, and can be downsized.

However, conventionally used photocatalytic reaction apparatuses (hereinafter also referred to as photocatalytic reaction units) mainly use an ultraviolet lamp using silica glass as a tube material, but the photocatalytic treatment efficiency is low. .
In addition, when the conventional photocatalytic reaction device is used for a long time, problems such as a reduction in processing efficiency of the photocatalytic reaction device occur, and there is a problem in durability.

JP 2001-104752 A JP 2001-104753 A JP 2001-170453 A JP 2003-181475 A

  The present invention has been made in view of such problems, and is a silica glass used in a photocatalytic reaction unit, and in order to improve the reaction efficiency of the photocatalyst, light having a wavelength of about 250 nm or less is about 250 nm to Silica glass for photocatalysts, which can efficiently convert the wavelength to the long wavelength side of about 450 nm, and at the same time, does not deteriorate in performance even when irradiated with ultraviolet rays for a long time, and has excellent properties such as ultraviolet resistance, and It aims at providing the manufacturing method.

  The present invention has been made to solve the above problems, and in silica glass, at least the silica glass has an OH group content of 10 wt. The linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. Provided is a silica glass for photocatalyst characterized in that it is not more than ppm and is used in a photocatalytic reaction unit (claim 1).

Thus, the OH group content is 10 wt. The linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. If it is silica glass for photocatalysts simultaneously satisfying that it is less than or equal to ppm, it is possible to improve the photocatalytic reaction efficiency by converting light of about 250 nm or less from an ultraviolet lamp light source to about 250 nm to 450 nm, High chemical resistance, heat resistance, strength, and high etching resistance to solutions containing acids, alkalis, and salts even when used for long-term photochemical reaction treatment under ultraviolet irradiation It is possible to maintain heat resistance and strength.
Therefore, it can be set as the silica glass suitable for employ | adopting as a photocatalytic reaction unit.

In this case, the silica glass preferably has a linear transmittance in a range of 40.0% to 1.0% at a wavelength of 163 nm having a thickness of 1 mm (Claim 2).
Thus, if the linear transmittance at a wavelength of 163 nm with a thickness of 1 mm is in the range of 40.0% to 1.0%, a silica glass having better chemical resistance can be obtained.

The silica glass has a metal impurity concentration of 50 wt. ppb or less, each concentration of the alkaline earth metal elements Mg and Ca is 10 wt. Less than ppb, each concentration of transition metal elements Cr, Fe, Ni, Cu, Zn is 5 wt. It is preferable that it is below ppb (Claim 3).
As described above, the concentration of the alkali metal elements Li, Na, K is 50 wt. ppb or less, each concentration of the alkaline earth metal elements Mg and Ca is 10 wt. Less than ppb, each concentration of transition metal elements Cr, Fe, Ni, Cu, Zn is 5 wt. If it is ppb or less, wavelength conversion can be performed more effectively, and a silica glass for a photocatalyst having higher UV resistance can be obtained more reliably.

The silica glass is preferably subjected to processing strain removal by annealing using a shielding material for preventing contamination of silica glass and flame polishing using a quartz burner ( Claim 4).
As described above, the silica glass has been subjected to processing strain removal by annealing treatment using a shielding material for preventing impurities from being mixed into the silica glass and flame polishing (fire polish) using a quartz burner. If present, it is possible to obtain a silica glass for a photocatalyst in which processing strain is removed, fine progressive cracks existing in the vicinity of the surface are removed, and contamination of metal impurities in the surface layer portion is more reliably prevented. .

The silica glass for a photocatalyst is a carrier supporting a photocatalyst material among the members constituting the photocatalytic reaction unit, a photocatalyst housing container in which the photocatalyst material is supported on the carrier, an ultraviolet lamp tube for a light source, It can be used for at least one of an ultraviolet lamp window for a light source and an ultraviolet reflector.
As described above, the silica glass for photocatalyst according to the present invention is a support for supporting a photocatalyst material among members constituting a photocatalyst reaction unit, a photocatalyst housing container for supporting a photocatalyst material, and a light source. It can be used for ultraviolet lamp tubes, ultraviolet lamp windows for light sources, ultraviolet reflectors, and the like. And if it is a photocatalytic reaction unit equipped with such a member using silica glass for photocatalyst, the photocatalytic reaction efficiency is improved by converting the wavelength of light of about 250 nm or less from the ultraviolet lamp light source to about 250 nm to 450 nm. be able to. In addition, even when used for photochemical reaction treatment under long-term UV irradiation, it is possible to prevent the performance of silica glass from being deteriorated, so long-term operation is suppressed by suppressing the reduction in processing capacity and durability. It can be performed.

  The present invention also relates to a method for producing a silica glass for photocatalyst used in a photocatalytic reaction unit, wherein at least silica powder is used as a raw material, and the silica powder raw material is heated in a temperature range of 500 ° C to 1000 ° C. A step of dehydrating, a step of producing a transparent silica glass ingot by electrically heating and melting the silica powder subjected to the heat dehydration treatment in an atmosphere containing at least hydrogen, and the transparent silica glass ingot having a predetermined shape A process for removing the processing strain by an annealing process using a shield material for preventing impurities from being mixed into the silica glass, and a process for removing the processing strain. A step of assembling the silica glass into a shape used in the photocatalytic reaction unit. Law provides (claim 6).

  If it is the manufacturing method of the silica glass for photocatalysts by such a process, the OH group density | concentration of the silica glass to manufacture can be adjusted to an appropriate range, chlorine and a fluorine are hardly contained, and the linear transmittance of the light of wavelength 245nm is obtained. It can be adjusted to an appropriate range. As a result, it is possible to improve the photocatalytic reaction efficiency by converting the light of about 250 nm or less from the ultraviolet lamp light source to about 250 nm to 450 nm, and the performance is not easily deteriorated even by long-time ultraviolet irradiation. A silica glass for a photocatalyst having excellent resistance to irradiation can be produced.

The present invention also relates to a method for producing a silica glass for photocatalyst used in a photocatalytic reaction unit, comprising at least a step of synthesizing a white soot body by a flame hydrolysis method using a silicon compound as a raw material, The step of subjecting the soot body to heat dehydration treatment in an atmosphere containing at least hydrogen and at least one of chlorine and fluorine, and the white soot body subjected to heat dehydration treatment under a vacuum of 10 ² Pa or less A step of forming a transparent silica glass ingot by electrically heating and melting, a step of processing the transparent silica glass ingot into a predetermined shape, and preventing impurities from being mixed into the silica glass in the shape-processed silica glass A process for removing processing strain by annealing using a shielding material, and silica glass from which the processing strain has been removed as the photocatalyst To provide a method of manufacturing a photocatalytic silica glass, which comprises a step of assembling the shape used in the response unit (claim 7).

  According to the method for producing a silica glass for a photocatalyst including such steps, the contents of OH groups, chlorine, and fluorine of the silica glass to be produced can be adjusted to an appropriate range, and the linear transmittance of light having a wavelength of 245 nm can be obtained. It can be adjusted to an appropriate range. As a result, the photocatalytic reaction efficiency can be improved by converting the wavelength of light of about 250 nm or less from the ultraviolet lamp light source to about 250 nm to 450 nm, and the performance is not easily deteriorated even by prolonged ultraviolet irradiation. A silica glass for a photocatalyst having excellent resistance to irradiation can be produced.

In these cases, the silica glass to be produced has an OH group content of 10 wt. ppm or less, a linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. It is preferable to make it ppm or less (claim 8).
If it is a manufacturing method of the silica glass for photocatalysts mentioned above, OH group content will be 10 wt. ppm or less, a linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. Silica glass for photocatalyst having a ppm or less can be produced, and the photocatalytic reaction efficiency can be improved by converting the wavelength of light of about 250 nm or less from an ultraviolet lamp light source to about 250 nm to 450 nm. It can be set as the silica glass for photocatalysts excellent in property.

Moreover, in the manufacturing method of the silica glass for photocatalysts based on this invention, the annealing process with respect to the silica glass which processed the said shape is carried out in an electrical resistance heat processing furnace, Al and / or Zr are 10-1000 wt. It is preferable to use at least one of ppm-containing silica glass plate, Si single crystal plate, and Si polycrystalline plate (Claim 9).
As described above, the annealing treatment for the silica glass whose shape has been processed is performed by using Al and / or Zr of 10 to 1000 wt. If at least one of the ppm-containing silica glass plate, Si single crystal plate, and Si polycrystal plate is used, it is possible to more effectively prevent metal impurities from being mixed into the silica glass for photocatalyst to be produced. it can.

The method for producing a silica glass for a photocatalyst preferably further includes a step of performing flame polishing using a quartz burner after at least the step of processing the transparent silica glass ingot into a predetermined shape. Item 10).
As described above, in the method for producing a silica glass for photocatalyst according to the present invention, if further flame polishing (fire polish) is performed, not only the progressive cracks existing on the surface portion are removed and the strength is improved, but also silica. The optical properties of the glass can be further improved, and if a quartz burner is used during this flame polishing, it is possible to effectively prevent metal impurities from being mixed into the surface of the silica glass during the flame polishing. be able to.

As described above, the silica glass for photocatalyst according to the present invention can efficiently convert the incident light of about 250 nm or less to the long wavelength side of about 250 nm to 450 nm, thereby improving the reaction efficiency of the photocatalyst. Can be made. In addition, damage to silica glass due to ultraviolet irradiation can be reduced, and even when ultraviolet irradiation is performed for a long time, occurrence of a decrease in strength, a decrease in transmittance, and the like can be suppressed.
Moreover, if it is a manufacturing method of the silica glass for photocatalysts according to this invention, the above silica glass for photocatalysts with high light wavelength conversion efficiency and excellent ultraviolet resistance can be manufactured.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
As described above, in the conventional photocatalytic reaction apparatus, an ultraviolet lamp using silica glass as a tube material is used as a light source, but there are problems such as low processing efficiency of the photocatalyst. In addition, when the conventional photocatalytic reaction unit is used for a long time, the processing efficiency of the photocatalytic reaction unit is lowered and the durability is low.

In order to solve these problems, the present inventor has conducted the following studies.
Conventionally, the photocatalytic reaction apparatus used is an ultraviolet lamp made of silica glass as a tube material. Generally, the ultraviolet lamp has an ultraviolet light of about 150 nm to about 450 nm (and light in the visible region). However, since ultraviolet light having a wavelength of about 250 nm or less is easily absorbed by oxygen, it is difficult to use in photocatalytic reaction. In actual photocatalytic reaction, light having a wavelength of about 250 nm or more is used. Mainly contributing. Therefore, in order to promote the photocatalytic reaction, it was necessary to strongly generate light having a wavelength of about 250 nm to 450 nm. In other words, in addition to the original light having a wavelength of about 250 nm or more, if light having a wavelength of about 250 nm or less can be used for the photocatalytic reaction without being absorbed by oxygen or the like, the photocatalytic reaction efficiency can be improved. And if the wavelength of light of about 250 nm or less can be wavelength-converted to about 250 nm to 450 nm, it was considered that the photocatalytic reaction efficiency can be improved.

  The present inventors conducted further diligent studies and experiments, and a preferable combination of physical properties of silica glass for a photocatalytic reaction apparatus has an OH group content of 10 wt. ppm or less, the linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. It was found that it is below ppm. And by combining these three physical properties, it is possible to improve the photocatalytic reaction efficiency by converting the light of about 250 nm or less from the ultraviolet lamp light source to about 250 nm to 450 nm, and at the same time, the initial chemical resistance, heat resistance, It has been found that the strength can be increased and high etching resistance can be maintained with respect to a solution containing acid, alkali and salt even in the operation of the photocatalytic device for a long time, and heat resistance and strength can be maintained, The present invention has been completed.

  Hereinafter, the present invention will be described in more detail with reference to the drawings, but the present invention is not limited thereto.

  A preferred combination of physical properties for the silica glass for photocatalyst has an OH group content of 10 wt. ppm or less, the linear transmittance at a wavelength of 245 nm when the thickness of the silica glass is 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. It is to satisfy three items below ppm at the same time.

(About OH group content, chlorine and fluorine content)
Silica glass is composed of a continuous network structure (network structure) of silicon Si and oxygen O, but OH groups, fluorine (F), and chlorine (Cl) serve as terminal portions (network terminators) of this network structure. It is. When used as a silica glass for photocatalysts, the silica glass material is exposed to ultraviolet irradiation. When an appropriate amount of OH groups are present in the silica glass, the Si—O—Si bond angle approaches the stable angle, and the network structure of the silica glass is stabilized. This has the effect of reducing the generation of absorption bands that cause large absorption in the ultraviolet region, such as the e-prime center (E'Center), and is due to ultraviolet irradiation such as a decrease in intensity and a decrease in transmittance caused by ionization. Damage can be suppressed.

  Therefore, the silica glass used under ultraviolet irradiation generally has, for example, 1000 wt. A low concentration of OH groups, such as about ppm or less, may be contained. However, if the content of the network terminator is too large, the chemical resistance is lowered, and the etching rate of the silica glass is increased when it comes into contact with a solution containing at least one of acid, alkali, and salt.

Therefore, in the silica glass for a photocatalyst of the present invention, the OH group content (concentration) is 10 wt. ppm or less. The OH group concentration is 5 wt. If it is less than or equal to ppm, the chemical resistance is further improved, which is more preferable.
For the same reason, in the silica glass for a photocatalyst of the present invention, the total content of fluorine and chlorine is 100 wt. ppm or less, preferably 50 wt. ppm or less.

In addition, the control of the OH group concentration is, for example, in the case of producing silica glass as a transparent silica glass ingot by electrically heating and melting high-purity silica powder as will be described later, the atmospheric pressure at the time of heating and melting, and the type of contained gas In particular, it is possible by changing the amount of water. In addition, when producing a transparent silica glass ingot by producing a white soot body by an oxyhydrogen flame hydrolysis method such as silicon tetrachloride SiCl ₄ raw material as will be described later, and subsequently heating the zone in a vacuum furnace, This can be achieved by changing and controlling the flow rate ratio of oxygen and hydrogen during body synthesis, or by controlling the atmospheric gas and pressure during the heating and melting of the white soot body.

The chlorine content can be controlled by controlling the degree of vacuum and temperature during the dehydration treatment of the white soot body in the oxyhydrogen flame hydrolysis method of the SiCl ₄ raw material described later. More specifically, while dehydrating the white soot body, first, the furnace is preliminarily calcined at about 500 to 1000 ° C. while degassing water H ₂ O and chlorine after 1300 to 1600 while hydrogen or chlorine is contained in the furnace. ℃ about, when vitrified under a vacuum of 10 2 ^Pa, it is possible to reduce the chlorine content.

  In addition, as described later, the fluorine content can be controlled by heating the white soot body at a temperature of about 200 to 800 ° C. in a fluorine-containing atmosphere. By setting the fluorine gas concentration of the silica glass low, the fluorine content of the silica glass can be lowered.

(About the transmittance of light having a wavelength of 245 nm)
Further, in the present invention, as described above, a 10 mm-thick double-sided parallel optical polished surface at a wavelength of 245 nm (light energy is 5.0 eV) (surface accuracy value λ / 20 or less in 633 nm optical interferometer measurement in a 20 mm diameter area) ) In the range of 90.0% to 30.0%. Moreover, it is more preferable to set it as the range of 80.0%-50.0%.
For example, a high-purity silica powder raw material described later is electrically heated and melted, and the produced OH group content is 10 wt. ppm or less and the total content of chlorine and fluorine is 100 wt. Some silica glasses produced in a reducing atmosphere having a composition of ppm or less contain oxygen deficiency-related defects, and such silica glasses show absorption near a wavelength of 245 nm.

In particular the absorption band with an absorption peak near wavelengths 245nm are generally referred to as so-called B ₂ band Schottky defect type. Representative examples of B ₂ band has an absorption peak at 247nm (5.02eV) has _{B 2} alpha band, emission band is generated showing peaks at 280nm (4.42eV) and 450 nm (2.74 eV) by photoexcitation. In addition, there is a B ₂ β band, an absorption peak at 240 nm (5.15 eV), and emission peaks at 290 nm (4.24 eV) and 390 nm (3.16 eV). Hereinafter, this light absorption and light emission phenomenon at different wavelengths is referred to as a light wavelength conversion phenomenon.

  Due to this light wavelength conversion phenomenon, when this silica glass is used as the material constituting the photocatalyst device, the wavelength of about 150 nm to about 250 nm ultraviolet light generated from the ultraviolet lamp light source is converted to about 250 nm to about 450 nm. Reaction efficiency can be improved.

  In this light wavelength conversion phenomenon, when silica glass is irradiated with high-power ultraviolet rays for a long time or heated at a high temperature for a long time in an oxygen-containing atmosphere, the conversion efficiency may be lowered. However, the OH group content in the silica glass is 10 wt. By keeping it at ppm or less, it is possible to suppress a decrease in conversion efficiency.

In addition, the linear transmittance at a wavelength of 163 nm (light energy: 7.6 eV) at a thickness of 1 mm double-sided parallel optical polished surface (surface accuracy value λ / 20 or less in a 633 nm optical interferometer measurement in a 20 mm diameter area) is 40.0. % To 1.0% is preferable, and 30.0% to 5.0% is more preferable.
For example, a white soot body is synthesized by a flame hydrolysis method using a silicon compound described later as a raw material, and then the white soot body is dehydrated under an atmosphere gas containing at least one of hydrogen, chlorine, and fluorine. It is an oxygen deficiency related defect observed in a synthetic vitrified synthetic silica glass, and shows absorption near a wavelength of 163 nm.
Silica glass exhibiting this absorption band exhibits better chemical resistance (etching resistance to solutions and gases containing acids, alkalis, salts, etc.) than those not exhibiting this absorption band. Although the detailed mechanism is unknown, it is presumed that the presence of Si—Si bonds improves the chemical resistance. Further, the silica glass showing the absorption band, since it is the same oxygen-deficient related defects and B ₂ band is presumed to increase the wavelength conversion phenomenon.

(About the purity of silica glass)
The silica glass for a photocatalyst according to the present invention is preferably highly pure from the surface layer portion to the inside.

  The silica glass for photocatalysts depends on the physical properties of the material to be treated, but is in contact with normal temperature or high temperature corrosive exhaust gas or waste water under ultraviolet irradiation, and for a long time while receiving stress from the material to be treated. Used under conditions that are severe for the material.

  If silica glass contains alkali metal element, alkaline earth metal element, or transition metal element at a concentration higher than a certain level, recrystallization occurs due to the phase transition of silica glass to microcrystals such as cristobalite. This tends to cause so-called white devitrification. As a result, the ultraviolet light transmittance of 400 nm or less is lowered, and the strength such as bending strength is lowered.

In order to prevent recrystallization, it is necessary to reduce the content of impurity metal elements in the entire silica glass. In particular, it is necessary to maintain the surface layer portion of the silica glass with high purity. Specifically, each concentration of Li, Na, K, Mg, Ca, Cr, Fe, Ni, Cu, and Zn is 100 wt. It is preferable to set it to ppb or less.
Further, each of the alkali metal elements Li, Na, and K is 50 wt. ppb or less, and each of the alkaline earth metal elements Mg and Ca is 10 wt. ppb or less, and each of transition metal elements Cr, Fe, Ni, Cu, Zn is 5 wt. It is particularly preferable to set it to ppb or less. Further, each of the alkali metal elements Li, Na, and K was added at 10 wt. ppb or less and each of the alkaline earth metal elements Mg and Ca is 5 wt. ppb or less and each of the transition metal elements Cr, Fe, Ni, Cu, Zn is 1 wt. More preferably, it is ppb or less.

  Further, with such high purity, the wavelength conversion to the longer wavelength side visible light region (that is, the wavelength region of about 500 nm to about 600 nm that does not contribute to the photocatalytic action) generated by mixing of impurities is increased. It can also be prevented.

  In order to keep the surface layer portion in high purity, it is necessary to produce not only the raw material of silica glass but also the transparent silica glass base material in the stage before processing into a predetermined shape with high purity, and further, as silica glass for photocatalyst It is necessary to prevent process contamination in various processing processes such as processing such as cutting and grinding, heat treatment in an electric furnace, and etching cleaning treatment using a hydrofluoric acid solution. Details of this method will be described later.

  Below, the method to manufacture the silica glass for photocatalysts which has the above characteristics is demonstrated.

(Manufacturing method 1)
FIG. 1 shows a method for producing a transparent silica glass ingot by an electric heating and melting treatment of silica powder as an example of the method for producing a photocatalyst silica glass according to the present invention.

First, as shown to Fig.1 (a), a silica powder is prepared (process 1-a).
Various silica powders can be used at this time, but it is preferable to make the silica powder as highly pure as possible. Specifically, synthetic silica powder synthesized from high-purity silica raw material or high-quality natural quartz powder is subjected to high-purification treatment multiple times at about 600 to 900 ° C. in an atmosphere containing hydrogen chloride HCl gas, etc. Purified silica powder or the like can be used.

Next, as shown in FIG.1 (b), a silica powder raw material is heat-dehydrated in the temperature range of 500 to 1000 degreeC (process 1-b).
By this step, mainly OH groups can be adjusted.

Next, as shown in FIG. 1 (c), the silica powder that has been heat-dehydrated is electrically heated and melted in an atmosphere containing at least hydrogen, thereby producing a transparent silica glass ingot (step 1-c). ).
Under such a reducing atmosphere, the final OH group concentration is 10 wt. It is made to become below ppm.
In this way, the OH group concentration is 10 wt. A transparent silica glass ingot of ppm or less can be synthesized while suppressing the metal impurity concentration to a low level. The total content of chlorine and fluorine is 100 wt. ppm or less.

Next, as shown in FIG.1 (d), the transparent silica glass ingot produced at process 1-c is processed into a defined shape (process 1-d).
The processing method is performed by molding, cutting, grinding, welding, adhesion, polishing, washing, and the like, and is not particularly limited, but prevents process contamination as much as possible.

  Next, as shown in FIG. 1 (e), processing strain removal by annealing treatment using a shielding material for preventing impurities from being mixed into the silica glass is performed on the silica glass shaped in step 1-d. Perform (step 1-e).

As a shielding material at this time, aluminum Al is 10 to 1000 wt. A silica glass plate containing ppm is preferred. In addition to Al, zirconium Zr was added in an amount of 10 to 1000 wt. You may contain about ppm. If such an Al-doped silica glass plate or the like is used as a shielding material, it is possible to effectively prevent metal impurities from being mixed into the silica glass to be heat-treated, as disclosed in Japanese Patent No. 3393063. The shield material may be a Si single crystal plate, a Si polycrystalline plate, or the like. The reason why mixing of metal impurities is prevented by using these is not always clear, but in the case of silica glass doped with Al, a part of the Si element in the silica glass network structure is replaced by Al. It is presumed that the element fixes and absorbs impurity cations such as Na ⁺ , K ⁺ and Li ^{+ in} the form of ionic bonds. Further, in the case of a Si single crystal or Si polycrystal, it is presumed that the Si elements are densely arranged as a crystal structure, thereby preventing the diffusion and penetration of impurity elements.
The processing strain removal by the annealing treatment is an essential process for improving the strength of the various processed silica glass for photocatalyst.

Specific examples of the annealing furnace used in this step are shown in FIGS.
An annealing furnace (electric heating furnace) 10 shown in FIG. 3 includes a chamber 11 and a heater 12 such as a molybdenum silicide heater in which a heat insulating material such as a high-purity alumina board is stretched. FIG. 3 shows an example in which a single crystal silicon wafer as a shielding material is used as the hearth material 13 and an Al-doped silica glass as a shielding material is used as the shielding chamber 14.
The to-be-heated body 15 is the silica glass which performed the said shape processing process.

An annealing furnace 20 shown in FIG. 4 includes heaters 22a and 22b such as a molybdenum disilicide heater in a chamber 21 in which a heat insulating material such as a high-purity alumina board is stretched. The heaters 22a and 22b may be arranged vertically as shown in FIG.
FIG. 4 shows an example in which a single crystal silicon wafer as a shielding material is used as the hearth material 23, and Al or Zr-doped silica glass as a shielding material is used as the cylindrical shielding tube 24.
The heat-treated body 25 is silica glass that has been subjected to the shape processing.

In addition to the above steps, flame polishing (fire) for the purpose of dissolving and removing progressive fine cracks existing on the surface of various processed silica glass for photocatalysts, as well as improving strength and light transmission. This flame polishing is preferably performed using a quartz burner from the viewpoint of preventing process contamination as described above. Usually, a metal burner is used for flame polishing. However, when a metal burner is used, metal contamination occurs at a depth of 30 μm from the surface of the silica glass, particularly from the surface. By subjecting this to flame polishing using a quartz burner, metal contamination of the surface layer of silica glass can be prevented.
The flame polishing may be performed after the annealing treatment for removing the processing strain, but may be performed at any stage as long as at least the transparent silica glass ingot is processed into a predetermined shape.

Next, as shown in FIG.1 (f), the silica glass which removed the process distortion at process 1-e is assembled in the shape used for a photocatalytic reaction unit (process 1-f).
The shape processed here is not particularly limited. For example, among the members constituting the photocatalytic reaction unit, a photocatalyst body storage container that exhibits a photocatalytic action, an ultraviolet lamp tube for a light source, an ultraviolet lamp window for a light source, an ultraviolet reflection It can be processed and assembled into a plate or the like, and can also be processed into a carrier carrying a photocatalytic material.

  The silica glass for photocatalysts based on this invention can be manufactured through the above processes. And if it is a manufacturing method of such a silica glass for photocatalysts, 10 wt. ppm or less, linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. ppm or less.

The silica glass for photocatalysts of the present invention can also be produced as follows.
(Manufacturing method 2)
FIG. 2 shows a method for producing a transparent silica glass base material (transparent silica glass ingot) as an example of a method for producing a photocatalyst silica glass according to the present invention, after once synthesizing a white soot body.
First, as shown to Fig.2 (a), a white soot body is synthesize | combined by the flame hydrolysis method which uses a silicon compound as a raw material (process 2-a).
As a silicon compound used as a raw material, a high-purity silicon compound such as silicon tetrachloride SiCl ₄ is used, and white at a relatively low temperature (about 500 to 800 ° C.) by flame hydrolysis using oxyhydrogen gas or propane gas. An opaque soot body is produced.
At this time, the flow rate ratio of oxygen and hydrogen is adjusted, and the OH group content of the finally produced silica glass is 10 wt. It is made to become below ppm.
It is preferable to use a silicon compound as a raw material with as high a purity as possible.

Next, as shown in FIG. 2 (b), the white soot synthesized in step 2-a is subjected to heat dehydration treatment in an atmosphere containing at least hydrogen and containing at least one of chlorine and fluorine ( Step 2-b).
By this step, the OH group concentration can be greatly reduced. In particular, the OH group concentration can be more efficiently reduced under an atmosphere containing either chlorine or fluorine. However, in the present invention, the chlorine and fluorine concentrations in the atmosphere are preferably set to a certain level or less in order to reduce the chlorine and fluorine contents. For example, a hydrogen-containing atmosphere in which the flow rate ratio of chlorine (or fluorine) is 10% or less at atmospheric pressure is preferable.

Next, as shown in FIG. 2 (c), the heat-dehydrated white soot body is electrically heated and melted under a vacuum of 10 ² Pa or less to obtain a transparent silica glass ingot (step 2-c). .
Thus, by setting the pressure of the atmospheric gas to a vacuum of 10 ² Pa or less, the contents of OH groups, chlorine, and fluorine contained in the silica glass can be surely set within the appropriate range.
As described above, by the steps 2-b and 2-c, the OH group content is 10 wt. ppm, and the total content of chlorine and fluorine is 100 wt. A transparent silica glass ingot having a ppm or less can be synthesized while suppressing the metal impurity concentration to a low level.

  Subsequent steps are performed on the transparent silica glass ingot thus produced, and the step of processing the transparent silica glass ingot shown in FIGS. 2D, 2E, and 2F into a predetermined shape (step 2). -D), a process of removing processing strain by annealing using a shielding material for preventing impurities from being mixed (process 2-e), a flame polishing process, and a process of assembling silica glass into a shape used for a photocatalytic reaction unit (Step 2-f) and the like can be performed in the same manner as in Production Method 1.

  The photocatalytic reaction unit employing the silica glass for photocatalyst according to the present invention contributes to the photocatalytic reaction by converting the wavelength of about 250 nm or less from the ultraviolet lamp light source to about 250 nm to 450 nm. Since the intensity of light having a wavelength of about 250 to 450 nm can be increased, the photocatalytic reaction efficiency can be improved. In addition, even when used for photochemical reaction treatment under long-term UV irradiation, it is possible to prevent the performance of silica glass from being deteriorated, so long-term operation is suppressed by suppressing the reduction in processing capacity and durability. It can be performed.

  FIGS. 5 and 6 show examples of specific examples of the photocatalytic reaction unit that can use the silica glass for photocatalyst according to the present invention.

FIG. 5 shows an example of a photocatalytic reaction unit of a type in which an object to be processed is passed through a photocatalyst body filled in a reaction chamber. 5A is a schematic cross-sectional view as viewed from the side of the photocatalytic reaction unit, and FIG. 5B is a schematic cross-sectional view along the AA ′ plane in FIG. 5A.
The photocatalytic reaction unit 30 includes an ultraviolet lamp 31 having a silica glass lamp tube and an ultraviolet reflecting plate 32 on the outside and a photocatalytic reaction chamber 33 filled with a photocatalyst 35 inside. Indicated. In addition, the photocatalytic reaction unit 30 may include a pressure-proof reinforcing fin 34 for reinforcing the internal pressure of the photocatalytic reaction chamber 33. In addition, an exhaust gas introduction pipe 36 that introduces exhaust gas into the photocatalytic reaction chamber 33, a processing gas discharge pipe 37 that discharges the processed gas from the photocatalytic reaction chamber 33, and the like are provided.

  In such a photocatalytic reaction unit 30, the ultraviolet light emitted from the ultraviolet lamp 31 is directly or directly reflected by the ultraviolet reflecting plate 32 to irradiate the photocatalytic body 35 in the photocatalytic reaction chamber 33. An object to be processed is passed through the photocatalytic reaction chamber 33 by the exhaust gas introduction pipe 36, the processing gas discharge pipe 37, and the like, and is purified by the action of the photocatalyst contained in the photocatalyst body 35.

  And the silica glass for photocatalysts of this invention can be used for the material of the lamp tube of the ultraviolet lamp 31, the reflective surface protection material of the ultraviolet reflector 32, the photocatalyst reaction chamber 33, the pressure | voltage resistant reinforcement fin 34, etc. The photocatalyst 35 can also be used as a carrier on which titanium dioxide is supported.

FIG. 6 shows a photocatalytic reaction unit 40 in which an ultraviolet lamp is arranged at the center of the photocatalyst body as an example of the pollutant gas purification apparatus. A silica glass chamber 42 covered with a metal chamber 41, for example, having a spiral partition plate 42a serves as a reactor. In addition, an ultraviolet lamp 43 is disposed at the center thereof. The photocatalyst body 45 is filled in the silica glass chamber 42. While irradiating the photocatalyst 45 with ultraviolet rays by the ultraviolet lamp 43, the pollutant gas is introduced from the pollutant gas inlet 46, and the pollutant gas is purified by passing through the photocatalyst 45, and the purified gas is removed from the purified gas outlet 47. Let it drain. The partition plate 42a may be omitted, but by arranging such a spiral partition plate 42a in the reactor, the gas passage distance in the photocatalyst body can be increased, and the pollutant gas purification process is effective. Can be done automatically.
The ultraviolet lamp 43 is not limited as long as it can irradiate light including ultraviolet rays having a wavelength of 400 nm or less. However, in order to efficiently irradiate ultraviolet rays, a high pressure mercury lamp, a low pressure mercury lamp, an excimer lamp, a light emitting diode, and a laser are used. It is preferable to use a diode or the like.

  The silica glass for photocatalyst of the present invention is used as a material for the lamp tube of the ultraviolet lamp 43, the silica glass chamber 42 including the spiral partition plate 42a, the contaminated gas inlet 46, the purified gas outlet 47, and the like. it can. The photocatalyst 45 can also be used as a carrier on which titanium dioxide is supported.

In the above specific example, the photocatalytic reaction unit as a purification device having an ultraviolet lamp is exemplified, but even a photocatalytic reaction unit using a photocatalytic reaction by ultraviolet rays contained in sunlight is used for the photocatalyst according to the present invention. Silica glass can be used without any problem, and the photocatalytic reaction efficiency can be improved by converting the wavelength of light of about 250 nm or less contained in light to about 250 nm to 450 nm.
Moreover, it is also possible to use the silica glass for photocatalysts based on this invention about all the members made from a silica glass which comprise a photocatalytic reaction unit. For example, the silica glass of the present invention may be used for an ultraviolet lamp tube for a light source or a window.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.
Example 1
According to the method for producing a silica glass for a photocatalyst by an electric heating melting method using silica powder as a raw material as shown in FIG. 1, a silica glass was produced as follows. The raw silica powder is an example of natural quartz powder.

(Made to ingot)
First, using high-quality natural quartz powder as a starting material powder, 90 kg of high-quality natural quartz powder with a particle size of 50 to 200 μm is heat-treated in an atmosphere containing hydrogen chloride gas HCl at 800 to 1000 ° C. And purified to high purity. Next, the highly purified quartz raw material powder was subjected to heat degassing treatment at 700 ° C. for 1 hour at a vacuum degree of 10 ² Pa or less (step 1-a).

Next, this highly purified raw material powder is put into a tungsten (W) crucible, which is placed in a high purity vacuum furnace of a stainless steel jacket and a tungsten mesh heater, and the furnace is sealed and gradually evacuated. Then, the pressure was set to 10 Pa or less, and degassing was performed by heating at a temperature of 800 ° C. for 1 hour. Next, the inside of the furnace was set to 100% helium He gas, 10 ⁵ Pa (substantially the same as atmospheric pressure), and was evacuated again to 10 ² Pa (step 1-b).

Next, it was held at 1750 ° C. for 1 hour by electrical resistance heating, and then cooled to room temperature. As the temperature increased, the atmospheric pressure was kept constant at 10 ² Pa, and when the temperature reached 1750 ° C., a nitrogen gas atmosphere containing about 10 ⁵ Pa of hydrogen H ₂ gas at 10% was used. Thereafter, it was cooled and taken out from the vacuum furnace to obtain a cylindrical transparent silica glass ingot (base material) having dimensions: 200 mm in diameter and 900 mm in length (step 1-c). Subsequently, in order to remove contamination on the outer surface portion, etching treatment and cleaning with pure water were performed with a 50% aqueous solution of hydrofluoric acid HF.

(Processing into physical property evaluation samples)
Next, this transparent silica glass ingot was cut and ground and polished to process each physical property evaluation sample (corresponding to Step 1-d).
In addition, the dimensions (length x width x thickness) of each sample are
Chlorine, fluorine, and impurity element concentration analysis samples (dimensions 30 × 30 × 30 mm),
Sample for measuring OH group concentration (dimension 30 × 30 × t10 mm),
Sample for measuring transmittance (dimensions 30 × 30 × t10 mm, 30 × 30 × t1 mm)
Sample for acid resistance evaluation test (size 50 × 50 × t1 mm),
Sample for alkali resistance evaluation test (dimensions 50 × 50 × t1 mm),
Sample for salt tolerance evaluation test (dimensions 50 × 50 × t1 mm),
Sample for wavelength conversion effect test (dimensions 10 × 10 × t70mm)
It was.
Further, a plurality of other samples for evaluation and a set of silica glass parts for assembling a photocatalytic reaction vessel as shown in FIG. 6, specifically, a part for assembling a silica glass chamber 42 including a spiral partition plate 42a. And a set of parts such as an ultraviolet lamp 43 (step 1-d).

(Heat treatment to remove processing strain (annealing))
The sample for evaluation and the set of parts for the photocatalytic reaction vessel were subjected to heat treatment for removing processing strain in an annealing furnace equipped with a shielding material as shown in FIG. 3 (step 1-e).
First, a single crystal silicon wafer was laid as a hearth plate 13 in an air atmosphere electric heating furnace 10 using a high-purity alumina refractory material. Further, a dome-shaped silica glass container (shield chamber) 14 as shown in FIG. 3 was placed thereon. The silica glass container is made of 100 wt. ppm and zirconium Zr of 10 wt. The doped silica glass was doped with ppm and had an impurity shielding effect.
And it kept at 1150 degreeC for 10 hours in the electric furnace of a high purity alumina heat insulating material in air | atmosphere, Then, it cooled to 1000 degreeC with the temperature-fall rate of 10 degreeC / hour, and carried out natural cooling to room temperature after that.

  A silica glass photocatalytic reaction unit (photocatalytic reaction vessel) having a diameter of 10 cm and a length of 30 cm was assembled from a set of parts for the photocatalytic reaction vessel (step 1-f) while finely adjusting the shape.

(Example 2)
The silica glass for photocatalyst was manufactured by the method passing through the white silica soot body as shown in FIG.

(Synthesis of soot body)
Silicon tetrachloride SiCl ₄ gas with a purity of 99.9999 wt% is fixed at ₂ L / min in terms of room temperature 25 ° C., oxygen O ₂ gas is ₂ to 20 L / min, and hydrogen H ₂ gas is 6 to 60 L / min. The white soot body containing an OH group was prepared by adjusting the carrier gas to argon Ar and introducing it into a silica glass burner for synthesis (step 2-a).
Next, an atmosphere heat treatment was performed at 500 ° C. for 3 hours in a 10 ⁵ Pa atmosphere (approximately atmospheric pressure) of nitrogen gas N ₂ 90%, hydrogen gas H ₂ 9%, and hydrogen chloride HCl 1% (step 2-b). ).

(Production of transparent silica glass ingot)
The soot body is installed in a stainless steel vacuum electric furnace equipped with a cylindrical graphite heater, the inside of the electric furnace is set to a vacuum of 10 ² Pa or less, and the heating zone at a temperature of 1550 ° C. is slowly extended from below to above. By melting while moving, a transparent silica glass ingot having a dimension diameter of 200 mm × length of 1000 mm was produced (step 2-c).

  Subsequently, the processing to the silica glass sample for evaluation, the photocatalyst reaction vessel and member set production, the processing strain removal, and the reaction unit assembly for the photocatalyst (steps 2-d to 2-f) are performed in the case of Example 1 (step 1-). d to step 1-f).

(Example 3)
The silica glass for photocatalyst was manufactured by the method passing through the white silica soot body as shown in FIG.
(Synthesis of soot body)
A white soot body containing an OH group was produced in the same manner as in Example 2 (step 2-a).

(Fluorine F dope, dehydration treatment)
The white soot body containing the OH group was subjected to F doping and dehydration treatment in a gas atmosphere containing 1% silicon tetrafluoride SiF _{4 at} 10 ⁵ Pa (approximately the same as atmospheric pressure) at 400 ° C. (step 2). -B).

(Production of transparent silica glass ingot)
The soot body is installed in a stainless steel vacuum electric furnace equipped with a cylindrical graphite heater. The electric furnace is evacuated to 10 ² Pa or less, and the heating zone at a temperature of 1550 ° C. is slowly moved from below to above. While melting, a transparent silica glass ingot having a diameter of 200 mm and a length of 1000 mm was produced (step 2-c).

  Subsequently, processing into a silica glass sample for evaluation, production of a set of photocatalytic reaction vessels, removal of processing strain, and assembly of photocatalyst reaction vessels (steps 2-d to 2-f) were performed in the same manner as in Examples 1 and 2. went.

(Comparative Example 1)
As described below, silica glass was produced by a conventional production method based on the oxyhydrogen flame Bernoulli method using natural quartz powder as a raw material.

(Preparation of natural quartz raw material powder)
About 90 kg of natural quartz powder adjusted to a particle size of 50 to 200 μm was prepared.
(Oxyhydrogen flame Bernoulli melting)
The above raw material powder was introduced into an oxyhydrogen flame Bernoulli burner at a constant supply amount, and was deposited in a layered manner on the target on the lower high-purity graphite disc while being melted. Thereafter, a transparent fused silica glass ingot was taken out to obtain a disk-like glass having a diameter of 300 mm × height of 300 mm. Next, in order to remove contamination on the outer surface portion, etching treatment and cleaning treatment with pure water were performed with an HF aqueous solution.

  Subsequently, processing into a silica glass sample for evaluation, production of a set of photocatalytic reaction containers, removal of processing strain, and assembly of a reaction unit for photocatalyst were performed in the same manner as in each example.

(Comparative Example 2)
As described below, silica glass containing fluorine in a high concentration was produced by a method through a white soot body.

(Synthesis of white soot)
First, a white soot body was synthesized by the same method as in Examples 2 and 3.
(Fluorine F dope treatment)
Next, the white soot body synthesized above was F-doped at 300 ° C. under a gas atmosphere containing 10% SiF _{4 at} 10 ⁵ Pa (approximately the same as atmospheric pressure).
(Heated and melted transparent glass)
The F-doped white soot body is placed in a stainless steel vacuum electric furnace equipped with a cylindrical graphite heater, heated and melted under the same atmospheric temperature conditions as in Example 3, and a transparent silica having dimensions of 200 mm in diameter and 300 mm in length. A glass ingot was produced.

  Subsequently, processing into a silica glass sample for evaluation, production of a set of photocatalytic reaction vessels, removal of processing strain, and assembly of the photocatalyst reaction vessel were performed in the same manner as in each example.

(Comparative Example 3)
As described below, silica glass containing OH groups and chlorine at high concentrations was produced by a method through a white soot body.

(Synthesis of white soot)
First, white soot bodies were synthesized by the same method as in Examples 2 and 3 and Comparative Example 2.
(Heated and melted transparent glass)
Then, without performing dehydration, the white soot body was placed in a stainless steel vacuum electric furnace equipped with a cylindrical graphite heater, and the pressure inside the electric furnace was reduced to 10 ⁴ Pa (about 0.1 atm). While melting at a temperature of 1500 ° C. while slowly moving from below to above, a transparent silica glass ingot having a size of 200 mm in diameter and 300 mm in length was produced.

  Subsequently, processing into a silica glass sample for evaluation, production of a set of photocatalytic reaction containers, removal of processing strain, and assembly of a reaction unit for photocatalyst were performed in the same manner as in each example.

About each silica glass manufactured by Examples 1-3 and Comparative Examples 1-3 manufactured above, various physical-property evaluation was performed as follows.
First, various physical property evaluation methods as silica glass will be described.

(OH group concentration)
Concentration analysis was performed by infrared absorption spectrophotometry of a 30 × 30 × t10 mm silica glass sample subjected to double-sided parallel optical polishing. Concentration conversion was according to the following document. The lower limit of quantification is 1 wt. ppm.
D. M.M. Dodd and D.D. B. Fraser, Optical determination of OH in fused silica, Journal of Applied Physics, Vol. 37 (1966) P.I. 3911.

(Chlorine concentration analysis)
After the silica glass pulverized pieces were dissolved in an HF aqueous solution, concentration analysis was performed by a turbidimetric method using AgNO ₃ addition. The lower limit of quantification is 5 wt. ppm.
(Fluorine concentration analysis)
After the silica glass pulverized pieces were dissolved in an aqueous NaOH solution, concentration analysis was performed by an ion electrode method. The lower limit of quantification is 10 wt. ppm.

(Impurity metal element concentration, surface layer contamination analysis)
A silica glass sample 30 × 30 × 30 mm for impurity analysis was placed in a fluororesin container, and an etching dissolution treatment of a surface layer of 30 μm was performed with an HF aqueous solution. Next, the solution was dried to make an acidic solution of nitric acid, and then Li, Na, K, Mg, Ca, Cr, Fe, ICP emission spectrometry (ICP-AES) or ICP mass spectrometry (ICP-MS). Ten elemental analysis of Ni, Cu, and Zn was performed. Therefore, the obtained analysis value is an average concentration of a portion (surface layer 30 μm portion) from the surface to a depth of 30 μm.

(Impurity metal element concentration, internal bulk purity analysis)
A glass piece equivalent to 1 g is cut out from a substantially central part of a silica glass sample for impurity analysis 30 × 30 × 30 mm, etched with HF aqueous solution and washed with pure water, and then the remaining glass piece is completely dissolved in HF aqueous solution. went. Next, the solution was dried to prepare an acidic solution of nitric acid, which was prepared as an analysis solution. Then, the 10 elemental analysis was performed on this solution by ICP-AES method and ICP-MS method.

(Wavelength 245 nm transmittance measurement)
Apparent linear light transmittance (%) at a wavelength of 245 nm was measured by ultraviolet absorption spectrophotometry of a 30 × 30 × t10 mm silica glass sample subjected to double-side parallel optical polishing. The repeat measurement accuracy of the same sample was within ± 0.1%.
(Wavelength 163 nm transmittance)
Apparent linear light transmittance (%) at a wavelength of 163 nm was measured by vacuum ultraviolet absorption spectrophotometry of a 30 × 30 × t1 mm silica glass sample subjected to double-sided parallel optical polishing. The repeat measurement accuracy of the same sample was within ± 0.1%.

(Acid resistance test)
Ten silica glass samples of 50 × 50 × t1 mm that were mirror-polished on both sides were prepared, a sufficient amount of 96% sulfuric acid H ₂ SO ₄ aqueous solution was filled in a fluororesin container, and 10 samples were set therein. The sample was dissolved in the air at 30 ° C. for 100 hours while stirring the sulfuric acid solution. Next, the sample was taken out and the weight loss of the sample was determined with a precision weighing scale, and the amount of dissolution per area (g / m ² ) was determined.

(Alkali resistance evaluation test)
Ten double-side mirror-polished 50 × 50 × t1 mm silica glass samples were prepared, a sufficient amount of 10% sodium hydroxide NaOH aqueous solution was filled in a fluororesin container, and 10 samples were set therein. The sample was dissolved in the atmosphere at 30 ° C. for 100 hours while stirring the sodium hydroxide solution. Thereafter, a sample was taken out, weight reduction was determined, and the dissolution amount per area (g / m ² ) was determined.
(Salt tolerance evaluation test)
Ten 50 × 50 × t1 mm silica glass samples that were mirror-polished on both sides were prepared. A fluororesin container was filled with a sufficient amount of 10% sodium chloride NaCl solution, and 10 samples were set therein. The sample was dissolved in the air at 50 ° C. for 100 hours while stirring the sodium chloride solution. Thereafter, a sample was taken out, weight reduction was determined, and the dissolution amount per area (g / m ² ) was determined.

In addition, the photocatalytic reaction vessel assembled in each example and comparative example was used to actually irradiate an ultraviolet lamp, and the photocatalytic reaction efficiency was measured.
However, the photocatalyst body used in a unified manner for each example and each comparative example was prepared by the following method for comparison between each example and each comparative example.

(Preparation of fibrous high-purity silica support)
The OH group is 250 wt.% By the soot method of oxyhydrogen flame hydrolysis using high purity silicon tetrachloride as a raw material. A high-purity transparent synthetic silica glass containing ppm was prepared. By cutting this synthetic silica glass, 20 rod-shaped synthetic silica glasses having a size of about 3 mm × 10 mm square and a length of 1 m were produced. Next, these 20 silica glass rods are set as raw material rods in a fiber manufacturing apparatus, softened and stretched by flame heating with a first gas burner to form thick fibers having a diameter of about 200 to 300 μm, and subsequently with a second gas burner. Wool having a diameter of about 4 to 10 μm was produced by jet blow while softening and stretching to form thin fibers by flame heating. The diameter of the wool could be controlled by controlling the feed speed of the synthetic silica glass as the raw material rod, the fiber pulling speed, the flame amount and the temperature control. After the wool was housed in a winder, it was cut so as to have a length of about 500 to 1000 mm, and mixed to prepare a cottony and massive fibrous high-purity silica carrier. The fiber curl radius was 50-100 mm.

(Photocatalyst film formation treatment by dip coating method (dip coating method))
Reagents such as titanium alkoxide as a photocatalyst source of titanium oxide, ethyl alcohol as a solvent, and polyethylene glycol as a stabilizer were mixed to prepare a dip coating solution. Next, the fibrous high-purity silica carrier previously prepared and the dip coating liquid in the container are put separately in a pressure-resistant glove box, and then the fibrous silica carrier is used while reducing the pressure in the glove box to 10 ³ Pa or less. Was degassed, and then the carrier was put into a dip coating solution while being returned to normal pressure and immersed in a titanium compound solution. After repeating this dip coating operation 5 times, it was taken out from the glove box, placed in an electric furnace, and baked at 450 ° C. for 1 hour to obtain a transparent film. Thereafter, when this transparent film was examined by X-ray diffraction analysis or the like, it was confirmed that it was anatase-type titanium oxide (TiO ₂ ), and it was observed by a scanning electron microscope (SEM) or the like. It consists of ultrafine particles of titanium oxide having a diameter of about 5 to 10 nm, has pores of about 2 to 3 nm, and a specific surface area of about 100 m ² / g.
In this way, a fibrous photocatalyst was produced in which a material (titanium oxide) that serves as a photocatalyst was coated on a fibrous silica glass support.

(NOx (nitrogen oxide) purification test)
The evaluation fibrous photocatalyst produced as described above was placed in a reaction vessel.
In order to evaluate the purification capacity of the photocatalyst, a nitrogen oxide (NOx) decomposition experiment was performed using an evaluation apparatus such as the conceptual diagram shown in FIG. Specifically, nitric oxide (NO) was used as NOx.
Specifically, the photocatalytic reaction unit 40 has a structure as shown in FIG. 6. An ultraviolet lamp 43 is passed through the center of the silica glass chamber 42 assembled in each example and each comparative example, and a fibrous photocatalyst is surrounded by the ultraviolet lamp 43. The body 45 is arranged.
In addition, air gas cylinder 61, NO100 wt. The system includes a NOx gas cylinder 62 through which ppm standard gas can flow, a pressure regulator 63, a mass flow controller 64, various valves 65, a NOx concentration meter 66, an exhaust fan 67, and the like.
The outer dimensions of the reaction vessel are 11 cm in diameter and 32 cm in length, the outer diameter of the photocatalyst housing silica glass chamber is 10 cm, the inner diameter is 3 cm, the length is 30 cm, the volume is about 2 L, and the input amount of the fibrous photocatalyst is 400 g.

The experimental conditions are as follows.
(1) In order to stabilize adsorption, the NOx gas flow is changed to a NO concentration of 1 wt. The measurement was performed at a ppm flow rate of 60 ml / min for 30 minutes.
(2) Next, the ultraviolet lamp (ultra-high pressure mercury lamp) in the reaction vessel was turned on, and the average ultraviolet intensity in the 150 nm to 450 nm region on the lamp surface was 1 mW / cm ² .
In this state, NOx gas flow, NO concentration 1 wt. A continuous decomposition operation at ppm, gas flow rate of 180 ml / min, temperature of 25 ° C., relative humidity of 50% and 5 hours was performed, and NO decomposition experiment by photocatalysis was performed.

The evaluation of NOx decomposition performance was performed based on the numerical value calculated by the following formula (1).
NOx decomposition rate (%) = 100 × {(NO initial concentration wt.ppm) − (NO purification concentration wt.ppm)} / (NO initial concentration wt.ppm) Equation (1)
A NO decomposition rate of 80% or more was evaluated as ○, 80% to 50% as Δ, and less than 50% as ×.

  The results of various physical property evaluations and NOx purification tests are summarized in Table 1 below.

The silica glasses of Examples 1 to 3 had higher etching resistance to acid, alkali, and salt aqueous solutions than Comparative Examples 1 to 3.
Moreover, when the photocatalyst reaction container produced with the silica glass of Examples 1-3 was used, compared with the case of Comparative Examples 1-3, the decomposition | disassembly performance of NO was high.

Moreover, the light wavelength conversion effect of the silica glass manufactured by each Example and each comparative example was evaluated as follows.
(Optical wavelength conversion effect test)
A low-pressure mercury lamp light (input power 40 W) that generates a wavelength of 254 nm is mainly irradiated to a prismatic sample having a size of 10 × 10 × 70 mm and having a mirror-finished surface of 10 × 10 × 70 mm produced in each example and each comparative example. The relative emission intensity was determined by measuring the converted light on the long wavelength side with a spectrophotometer, and is shown in Table 2. The relative light emission intensity was shown as the relative intensity with the peak intensity of the fluorescence spectrum (light emission by the impurity element) in the vicinity of 500 to 600 nm in Comparative Example 1 being 100.

  The relative emission intensity around 270 to 300 nm and the relative emission intensity around 380 to 450 nm of the silica glass produced in Examples 1 to 3 are higher than those in Comparative Examples 1 to 3, and the light wavelength conversion effect by the silica glass of the present invention is high. It turns out that it is obtained.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

It is a flowchart which shows an example of the manufacturing method of the silica glass for photocatalysts which concerns on this invention. It is a flowchart which shows another example of the manufacturing method of the silica glass for photocatalysts which concerns on this invention. It is a schematic sectional drawing which shows typically an example of the electric heating furnace which comprised the shielding material which can be applied to the silica glass for photocatalysts of this invention. It is a schematic sectional drawing which shows typically another example of the electric heating furnace which comprised the shielding material which can be applied to the silica glass for photocatalysts of this invention. It is the cross-sectional schematic which shows an example of the photocatalyst reaction unit which can use the silica glass for photocatalysts which concerns on this invention. It is the cross-sectional schematic which shows another example of the photocatalyst reaction unit which can use the silica glass for photocatalysts which concerns on this invention. It is an example of the apparatus which evaluates the processing capability of a photocatalyst body, and is the schematic which showed the NOx purification test apparatus used by the Example and the comparative example.

Explanation of symbols

10 ... Electric heating furnace, 11 ... Chamber, 12 ... Heater,
13 ... hearth material, 14 ... shield chamber, 15 ... silica glass,
20 ... Electric heating furnace, 21 ... Chamber, 22a ... Upper heater, 22b ... Lower heater,
23 ... hearth material, 24 ... shield tube, 25 ... silica glass,
30: Photocatalytic reaction unit,
31 ... UV lamp, 32 ... UV reflector,
33 ... Photocatalytic reaction chamber, 34 ... Pressure-resistant reinforcing fin, 35 ... Photocatalyst body,
36 ... exhaust gas introduction pipe, 37 ... treatment gas discharge pipe,
40: Photocatalytic reaction unit,
41 ... Metal chamber,
42 ... Silica glass chamber, 42a ... Spiral partition plate,
43 ... UV lamp, 45 ... Photocatalyst,
46 ... Pollutant gas inlet, 47 ... Purified gas outlet,
61 ... Air gas cylinder,
62 ... NOx gas cylinder (NO100wt.ppm standard gas),
63 ... Pressure regulator, 64 ... Mass flow controller,
65 ... Valve, 66 ... NOx concentration meter, 67 ... Exhaust fan.

Claims (10)

  In the silica glass, at least the silica glass has an OH group content of 10 wt. The linear transmittance at a wavelength of 245 nm with a thickness of 10 mm is in the range of 90.0% to 30.0%, and the total content of chlorine and fluorine is 100 wt. Silica glass for photocatalyst characterized by being not more than ppm and used in a photocatalytic reaction unit.   The silica glass for a photocatalyst according to claim 1, wherein the silica glass has a linear transmittance in a range of 40.0% to 1.0% at a wavelength of 163 nm having a thickness of 1 mm.   The silica glass has a metal impurity concentration of 50 wt.% For each of the alkali metal elements Li, Na, and K in each of the portion from the surface to 30 μm and the inner portion thereof. ppb or less, each concentration of the alkaline earth metal elements Mg and Ca is 10 wt. Less than ppb, each concentration of transition metal elements Cr, Fe, Ni, Cu, Zn is 5 wt. The silica glass for a photocatalyst according to claim 1 or 2, wherein the silica glass is ppb or less.   The silica glass is subjected to processing strain removal by annealing treatment using a shielding material for preventing contamination of silica glass and flame polishing using a quartz burner. The silica glass for photocatalysts as described in any one of Claims 1 thru | or 3.   The silica glass for photocatalyst is a carrier supporting a photocatalyst material among the members constituting the photocatalytic reaction unit, a photocatalyst housing container in which the photocatalyst material is supported on the carrier, an ultraviolet lamp tube for a light source, and a light source The silica glass for a photocatalyst according to any one of claims 1 to 4, which is used for at least one of an ultraviolet lamp window and an ultraviolet reflector. A method for producing a silica glass for photocatalyst used in a photocatalytic reaction unit, comprising at least:
Using silica powder as a raw material, and heat dehydrating the silica powder raw material in a temperature range of 500 ° C. to 1000 ° C .;
A step of producing a transparent silica glass ingot by electrically heating and melting the heat-dehydrated silica powder in an atmosphere containing at least hydrogen; and
Processing the transparent silica glass ingot into a predetermined shape;
For the processed silica glass, removing the processing strain by annealing using a shielding material to prevent impurities from being mixed into the silica glass;
And a step of assembling the silica glass from which the processing strain has been removed into a shape used for the photocatalytic reaction unit. A method for producing a silica glass for photocatalyst used in a photocatalytic reaction unit, comprising at least:
A step of synthesizing a white soot body by a flame hydrolysis method using a silicon compound as a raw material;
A step of subjecting the white soot body to heat dehydration treatment in an atmosphere containing at least hydrogen and containing at least one of chlorine and fluorine;
A step of obtaining a transparent silica glass ingot by electrically heating and melting the heat-dehydrated white soot body under a vacuum of 10 ² Pa or less;
Processing the transparent silica glass ingot into a predetermined shape;
For the processed silica glass, removing the processing strain by annealing using a shielding material to prevent impurities from being mixed into the silica glass;
And a step of assembling the silica glass from which the processing strain has been removed into a shape used for the photocatalytic reaction unit.   The silica glass to be produced has an OH group content of 10 wt. ppm or less, a linear transmittance of 90.0% to 30.0% at a wavelength of 245 nm with a thickness of 10 mm, and a total content of chlorine and fluorine of 100 wt. The method for producing a silica glass for a photocatalyst according to claim 6 or 7, wherein the concentration is not more than ppm.   In the electric resistance heat treatment furnace, the silica glass having the processed shape is annealed with Al and / or Zr of 10 to 1000 wt. The silica glass for a photocatalyst according to any one of claims 6 to 8, wherein the silica glass plate contains at least one of ppm-containing silica glass plate, Si single crystal plate, and Si polycrystal plate. Manufacturing method.   The method for producing a silica glass for a photocatalyst according to any one of claims 6 to 9, further comprising a flame using a quartz burner at least after the step of processing the transparent silica glass ingot into a predetermined shape. The manufacturing method of the silica glass for photocatalysts which has the process of grind | polishing.

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