U.S. patent application number 10/193105 was filed with the patent office on 2003-03-13 for photocatalyst compositions and methods for making the same.
This patent application is currently assigned to NORITAKE CO., LIMITED. Invention is credited to Hirano, Yuji, Iwata, Misao, Kato, Shinji, Kurobe, Hisanori, Watanabe, Hirokazu.
Application Number | 20030050196 10/193105 |
Document ID | / |
Family ID | 19050459 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030050196 |
Kind Code |
A1 |
Hirano, Yuji ; et
al. |
March 13, 2003 |
Photocatalyst compositions and methods for making the same
Abstract
Photocatalyst compositions may include a photocatalyst layer
formed or disposed on the surface of a porous substrate. A metal
may be disposed on the photocatalyst layer. If the metal is present
predominantly at the surface of the photocatalyst layer, the metal
can be utilized efficiently for photocatalytic reactions. The
photocatalyst composition may be preferably formed by disposing the
photocatalyst layer on the surface of the porous substrate and
depositing the metal predominantly on the surface of the
photocatalyst layer. Photocatalytic filter devices may include
these photocatalyst compositions.
Inventors: |
Hirano, Yuji; (Nagoya-shi,
JP) ; Kato, Shinji; (Nagoya-shi, JP) ;
Watanabe, Hirokazu; (Nagoya-shi, JP) ; Kurobe,
Hisanori; (Nagoya-shi, JP) ; Iwata, Misao;
(Nagoya-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
NORITAKE CO., LIMITED
Nagoya-shi
JP
|
Family ID: |
19050459 |
Appl. No.: |
10/193105 |
Filed: |
July 12, 2002 |
Current U.S.
Class: |
507/238 |
Current CPC
Class: |
B01J 35/04 20130101;
B01J 23/38 20130101; C02F 1/325 20130101; B01D 53/885 20130101;
B01D 2255/802 20130101; C02F 2201/3227 20130101; C02F 2305/10
20130101; B01J 21/063 20130101; B01J 35/004 20130101; A61L 9/00
20130101; C02F 1/78 20130101; C02F 2201/782 20130101; B01J 35/10
20130101; B01J 35/0026 20130101; B01J 37/0018 20130101; B01J 23/755
20130101; B01J 37/0242 20130101; B01J 23/72 20130101; C02F 2209/235
20130101; B01J 23/50 20130101; C02F 1/725 20130101; B01J 23/40
20130101; B01J 21/06 20130101; B01J 37/0215 20130101 |
Class at
Publication: |
507/238 |
International
Class: |
E21B 001/00; E21B
043/28 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 16, 2001 |
JP |
2001-215910 |
Claims
1. A photocatalyst composition comprising: a porous substrate
having a surface, a photocatalyst layer disposed on the surface of
the porous substrate, the photocatalyst layer primarily containing
at least one photocatalytic material and having a surface, and at
least one metal disposed predominantly on or near the surface of
the photocatalyst layer.
2. A photocatalyst composition according to claim 1, wherein the at
least one metal is selected from the group consisting of silver
(Ag), gold (Au), platinum (Pt), palladium (Pd), ruthenium (Ru),
rhodium (Rh), copper (Cu) and nickel (Ni).
3. A photocatalyst composition according to claim 1, wherein at
least 80 wt % of the metal disposed on or near the surface of the
photocatalyst layer is disposed on the surface of the photocatalyst
layer.
4. A pholocatalyst composition according to claim 1, wherein the
metal comprises metal particles having an average particle size of
between 1-100 nm.
5. A photocatalyst composition according to claim 4, wherein at
least 70% by number of the metal particles disposed on or near the
surface of the photocatalyst layer are disposed on the surface of
the photocatalyst layer.
6. A photocatalyst composition according to claim 1, wherein the
porous substrate is a ceramic having a three-dimensional network
structure.
7. A photocatalyst composition according to claim 6, wherein an
average diameter of a backbone of the ceramic is between about 100
.mu.m to 1000 .mu.m.
8. A photocatalyst composition according to claim 6, wherein the
porous ceramic substrate exhibits a light transmissivity of at
least 10% at a thickness of 5 mm.
9. A photocatalyst composition according to claim 6, further having
the following properties: (1) porosity of between about 65% to 99%,
(2) bulk density of about 0.05 g/cm.sup.3 to 60 g/cm.sup.3, and (3)
between 10-30 cells per 25 mm.
10. A photocatalytic filter device comprising: the photocatalyst
composition according to claim 1 and a frame supporting the
photocatalyst composition.
11. A photocatalytic filter device according to claim 10, further
comprising a light source disposed proximally to the photocatalyst
composition and emitting light that activates the photocatalytic
material.
12. A method for making a photocatalyst composition comprising:
disposing a photocatalyst layer substantially comprising a
photocatalytic material on a surface of a porous substrate and
disposing at least one metal predominantly on a surface of the
photocatalyst layer, the metal increasing the photocatalytic
activity of the photocatalytic material.
13. A method according to claim 12, wherein the metal disposing
step further comprises contacting the photocatalyst layer with a
solution containing ions the metal, and irradiating the
photocatalyst layer with light having a wavelength that activates
the photocatalytic material, thereby reducing and depositing the
metal on the surface of the photocatalyst layer.
14. A method according to claim 13, wherein the at least one metal
is selected from the group consisting of silver (Ag), gold (Au),
platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), copper
(Cu) and nickel Ni).
15. A method according to claim 12, further comprising preparing a
ceramic porous structure having a three-dimensional network
structure before the photocatalyst layer disposing step.
16. A method according to claim 15, wherein an average diameter of
a backbone of the ceramic is between about 100 .mu.m and 1000
m.
17. A method according to claim 16, further comprising attaching
ceramic particles to a surface of the backbone of the ceramic.
18. A method according to claim 15, wherein the prepared ceramic
porous substrate satisfies at least one of the following
conditions: (1) porosity of between about 65% to 99%, (2) bulk
density of about 0.05 g/cm.sup.3 to 60 g/cm.sup.3, and (3) between
10-30 cells per 25 mm.
19. A method according to claim 15, wherein the photocatalyst layer
disposing step is performed such that light transmissivity at a
thickness of 5 mm is at least 10%.
20. A composition of matter comprising: a ceramic porous support
having three-dimensional network structure with a backbone having
an average diameter of between about 100-1000 .mu.m, a
photocatalyst material disposed on the backbone of the ceramic
porous support, wherein the ceramic porous support having the
photocatalyst material disposed thereon exhibits a light
transmissivity of at least 10% at a thickness of 5 mm, and metal
particles disposed substantially only on an outer surface of the
photocatalyst material, wherein the metal particles include at
least one metal selected from the group consisting of Ag, Au, Pt,
Pd, Ru, Rh, Cu and Ni and the metal particles have an average
particle size of between about 1-100 nm.
21. A composition of matter according to claim 20, wherein at least
80 wt % of the metal disposed on or near the surface of the
photocatalyst layer is disposed on the surface of the photocatalyst
layer and the ratio of metal particles to photocatalyst material is
between about 0.0005 and 5 wt %.
22. A composition of matter according to claim 21, wherein the
metal particles include at least one of Ag or Cu.
23. A composition of matter according to claim 22, wherein the
composition of matter exhibits the following properties: (1)
porosity of between about 65% to 99%, (2) bulk density of about
0.05 to 60 g/cm.sup.3, and (3) between 10-30 cells per 25 mm.
24. A photocatalytic filter device comprising: the composition of
matter according to claim 23, a frame supporting the composition of
matter and a light source disposed proximally to the composition of
matter according to claim 23 and emitting light having a wavelength
that activates the photocatalytic material.
Description
[0001] This application claims priority to Japanese Patent
Application No. 2001-215910, filed Jul. 11, 2002, the contents of
which are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present teachings relate to compositions comprising a
photocatalytic material (photocatalyst composition) and a metal and
methods for making the same. Photocatalytic filter devices using
these photocatalyst materials are also taught.
[0004] 2. Description of the Related Art
[0005] Metal oxides (e.g., semiconductor compounds) such as
titanium dioxide generate electron-hole pairs (i.e., become
polarized) when energy is applied to the metal oxide in excess of
the bandgap (e.g., 3.2 eV for an anatase crystal) of the metal
oxide. These electron-hole pairs may be utilized to provide
photocatalytic effects. For example, Japanese Laid-Open Patent
Publication No. 2001-38218 describes a photocatalytic filter in
which a photocatalyst is disposed on the surface of a porous
ceramic substrate.
[0006] In addition, if a metal (e.g., silver) is disposed on a
substance that is functioning as a photocatalyst (e.g., fine TiO
.sub.2 particles), photocatalytic efficiency can be increased. When
the photocatalyst is polarized, the electron-hole pairs may have
very short lifetimes. In this case, the electron-hole pairs may
recombine and disappear before oxidizing or reducing an externally
supplied substance. Thus, the photocatalyst may not exhibit
photocatalytic activity. This disappearance (i.e., the reduction in
number of electrons and holes) has been a significant factor in
reducing the reaction efficiency of photocatalytic materials.
[0007] However, if a metal (e.g., silver) is disposed on the
photocatalytic substance, the polarization is stabilized and
therefore, photocatalytic efficiency can be increased. For example,
Japanese Laid-Open Patent Publication No. 10-146531 describes a
photocatalyst having fine metal particles in which the
photocatalytic efficiency (photocatalytic activity) was improved by
disposing ultra-fine metal particles on the surfaces of the fine
titanium dioxide particles. Further, Japanese Laid-Open Patent
Publication No. 10-33990 describes a silver-based catalyst in which
silver and/or a silver compound was disposed on the surface of an
alumina powder or another inorganic oxide. In this publication, the
photocatalyst includes a substrate or support (e.g., a honeycomb
structure) made of a ceramic material that has been coated with a
silver-based catalyst.
[0008] As shown in FIG. 18, both the fine metal
particle-photocatalyst described in Japanese Laid-Open Patent
Publication No. 10-146531 and the silver-based catalyst described
in Japanese Laid-Open Patent Publication No. 10-33990 include
particles 90 that comprises metal particles 94 (e.g., silver),
which have been uniformly deposited on substantially the entire
surface of a photocatalytic particle 92, which is a semiconductor
substance such as titanium dioxide. When a substrate or support
(not shown) is coated with a slurry containing the
metal-photocatalyst particles 90 and then fired, a coating layer 96
including the metal particles 94 is formed on the surface of the
substrate, as shown in FIG. 19.
[0009] However, when the coating layer 96 is formed of such
metal-photocatalyst particles 90, a substantial amount of the metal
particles 94 are disposed between adjacent photocatalytic particles
92, as shown in FIG. 19. Therefore, the strength of the coating
layer 96 shown in FIG. 19 tends to be less than the strength of a
photocatalytic layer 98 formed of photocatalytic particles 92 that
are free from metals, as shown in FIG. 20. Furthermore, the surface
properties of the metal-photocatalyst particles 90 are very
different from the surface properties of photocatalytic particles
92 that are free from the metal. Therefore sufficient consideration
should be given to the conditions under which the coating layer 96
is formed in view of the type of metal particles 94 and the amount
of the metal that is disposed on the photocatalytic particle
92.
[0010] In addition, the coating layer 96 contains metal particles
94 that are substantially uniformly disposed throughout the layer
(i.e., both on the surface of the coating layer 96 and within the
interior portion of the coating layer 96). However, under ordinary
conditions for use, sufficient light can not reach the interior
portion of the coating layer 96 in order to sufficiently activate
the photocatalyst material. Therefore, the metal particles 94 that
are disposed within the interior portion cannot effectively be
utilized for photocatalytic purposes. In other words, the amount of
the metal 94 that can be used to increase the photocatalytic
activity of the photocatalyst particles 92 may be significantly
less than the total amount of metal 94. Thus, metal utilization
efficiency is low in the known photocatalytic compositions.
SUMMARY OF THE INVENTION
[0011] It is, accordingly, one object of the present teachings to
provide photocatalyst compositions in which a photocatalyst and a
metal are disposed on a substrate or support in a manner that
enables the metal to be efficiently utilized. It is another object
of the present teachings to provide photocatalytic filter devices
that include such photocatalyst compositions. It is yet another
object of the present teachings to provide methods for making the
photocatalyst compositions.
[0012] In one aspect of the present teachings, photocatalyst
compositions may include a porous substrate A photocatalyst layer
may be disposed or formed on the surface of the porous substrate
and the photocatalyst layer preferably substantially comprises a
photocatalytic substance. Metal or metal particles are disposed
predominantly on the surface of the photocatalyst layer.
[0013] Preferably, most or all the metal (metal particles) is
present at a position within the photocatalyst layer that exhibits
the strongest photocatalytic activity (e.g., the surface of the
photocatalyst layer). In other words, most of the metal is disposed
at a position that can improve or increase the photocatalytic
activity of the photocatalyst material. As a result, the metal
included in the photocatalyst composition can be effectively
utilized.
[0014] In the present specification, the term "porous substrate" is
intended to mean a substrate having pores or hole through which a
fluid can pass, e.g., at atmospheric pressure or at a pressure
higher than atmospheric pressure. For example, preferred porous
substrates may have a three-dimensional structure, such as a
honeycomb structure or a three-dimensional network. Particularly
preferred porous substrates may have a three-dimensional network
structure with pore sizes that allow light to permeate into the
interior portion of the three-dimensional network structure.
[0015] Further, in the present specification, the term "hard porous
substrate" is intended to mean a substrate that does not
significantly deform (e.g., dissolve, expand, etc.) when the porous
substrate contacts an aqueous solvent, such as water or a mixed
solvent based on water, and substantially maintains the
three-dimensional structure of the porous substrate in an aqueous
environment. For example, ceramics having a three-dimensional
network structure may be advantageously utilized as hard porous
substrates.
[0016] In a representative embodiment of the present teachings, at
least one metal (metal particles) of the photocatalyst composition
may be selected from the group consisting of silver (Ag), gold
(Au), platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh),
copper (Cu) and nickel (Ni). If one of these metals is disposed on
the photocatalyst layer, the photocatalytic activity (efficiency)
of the photocatalyst composition may be increased as compared to
photocatalyst compositions that do not include such metals. The
metal is preferably disposed on the photocatalyst layer in the form
of fine metal particles having an average particle size of 100 nm
or less. Such metal particles may significantly increase the
photocatalytic efficiency (photocatalytic activity) of the
photocatalyst material.
[0017] Optionally, photocatalyst compositions of the present
teachings may exhibit a light transmissivity of at least 10% when
the porous substrate (e.g., a substantially plate-shaped porous
material) has a thickness of 5 mm. In photocatalyst compositions
exhibiting such light transmission properties, sufficient light can
permeate into (can be transmitted through) the pores of the porous
substrate in order to efficiently utilize the metal that is present
predominantly on the photocatalyst layer within the interior
portion of the pores of the porous substrate, as well as at the
surface of the photocatalyst layer.
[0018] In another aspect of the present teachings, photocatalytic
filter devices are taught that may include at least one of the
above-described photocatalyst compositions as a primary
photocatalyst material. The present photocatalytic filter devices
may be advantageously utilized, e.g., to purify a fluid by causing
the fluid (e.g., a gas, such as air, or a liquid, such as water) to
flow through the photocatalyst composition (filter portion). For
example, organic substances may be removed from the fluid by
decomposing the organic substances utilizing the photocatalytic
effects of the photocatalyst composition.
[0019] In another aspect of the present teachings, methods are
taught for making the above-described photocatalyst compositions.
In one representative method, a porous substrate may be prepared
(or purchased). Then, a photocatalyst layer made substantially of a
photocatalytic material may be disposed or formed on the surface of
the porous substrate. Thereafter, a metal (metal particles) may be
disposed on the photocatalyst layer such that the metal is present
predominantly at a surface of the photocatalyst layer. The metal
(or a combination of metals) is preferably selected so as to
increase or improve the photocatalytic activity of the
photocatalyst material.
[0020] In one representative embodiment, a photocatalyst layer
containing a photocatalytic substance (e.g., TiO.sub.2, ZnO,
WO.sub.3, Cu.sub.2O or a similar semiconductor compound) is
disposed or formed on the surface of the porous substrate. Then,
the metal is disposed on the surface of the photocatalyst layer.
This representative method enables the metal to be disposed
predominantly at the surface of the photocatalyst layer.
[0021] By disposed or depositing the metal on the surface of the
photocatalyst layer after the photocatalyst layer has been formed
from a photocatalytic substance (e.g., titanium dioxide), a denser
photocatalyst layer can be formed as compared to known
photocatalyst layers formed from an aggregate of metal-carrying
particles. Thus, the photocatalyst layer of the present
photocatalyst composition has excellent mechanical strength.
[0022] Optionally, the metal may be disposed or deposited on the
photocatalyst layer by contacting the photocatalyst layer with a
solution containing the metal and then irradiating the
photocatalyst layer using light having a wavelength that can
activate the photocatalytic substance. When light irradiation is
performed in this manner, the metal (typically metal ions) in the
solution is reduced by the photocatalyst effect of the
photocatalytic substance contained in the photocatalyst layer. As a
result, the reduced metal will be deposited on the surface of the
photocatalyst layer. Accordingly, the metal disposed on the
photocatalyst layer is present predominantly at the surface of the
photocatalyst layer. As noted above, the predominantly present
metal is preferably selected from at least one of Ag, Au, Pt, Pd,
Ru, Rh, Cu and/or Ni.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic view showing a representative
structure of a ceramic substrate.
[0024] FIG. 2 is a cross-sectional view taken along line II-II
shown in FIG. 1.
[0025] FIG. 3 is a schematic view showing the structure of a
ceramic substrate that includes ceramic particles.
[0026] FIG. 4 is a cross-sectional view taken along line IV-IV
shown in FIG. 3.
[0027] FIG. 5 is a schematic cross-sectional view showing a
structure in which a photocatalyst layer is formed on the surface
of the ceramic substrate shown in FIG. 2.
[0028] FIG. 6 is a schematic cross-sectional view showing a
structure in which a photocatalyst layer is formed on the surface
of the ceramic substrate shown in FIG. 4.
[0029] FIG. 7 is a schematic cross-sectional view showing a
photocatalyst composition in which metal particles are present
predominantly at the surface of a photocatalyst layer.
[0030] FIG. 8 shows a representative gas treatment apparatus.
[0031] FIG. 9 is a perspective view showing a photocatalytic filter
that may be utilized as one component of the gas treatment
apparatus shown in FIG. 8.
[0032] FIG. 10 is a plan view showing a photocatalyst module that
may be utilized as one component of the gas treatment apparatus
shown in FIG. 8.
[0033] FIG. 11 is a cross-sectional view taken along line XI shown
in FIG. 10.
[0034] FIG. 12 shows a representative water treatment
apparatus.
[0035] FIG. 13 is a perspective view showing a representative
photocatalyst unit that may be utilized with the water treatment
apparatus of FIG. 12.
[0036] FIG. 14 is a schematic cross-sectional view showing a
photocatalyst treatment device that was used to evaluate the
performance of photocatalyst compositions according to the present
teachings.
[0037] FIG. 15 is a graph showing temporal changes in NO and
NO.sub.2 concentration of a discharged gas according to Example
3.
[0038] FIG. 16 is a graph showing temporal changes in SO.sub.2
concentration of a discharged gas according to Example 4.
[0039] FIG. 17 is a graph showing temporal changes in methyl
mercaptan concentration of a discharged gas according to Example
5.
[0040] FIG. 18 is a schematic cross-sectional view showing the
structure of a known metal-carrying particle.
[0041] FIG. 19 is a schematic cross-sectional view showing a
coating layer formed from known metal-carrying particles.
[0042] FIG. 20 is a schematic cross-sectional view showing a
photocatalyst layer formed of photocatalyst particles on which a
metal is not disposed.
DETAILED DESCRIPTION OF THE INVENTION
[0043] The porous substrate of the present photocatalyst
compositions may comprise metal materials, inorganic materials
and/or organic materials. The terms "porous substrate" and "porous
support" will be utilized interchangeably throughout the present
specification and the intended meaning of these two terms the same.
If the photocatalyst composition will be utilized in an aqueous
medium or environment, the porous substrate preferably does not
significantly deform (e.g., dissolve, expand, etc.) when it
contacts the aqueous medium.
[0044] Representative porous substrates or supports include
non-woven or woven fabrics made of inorganic fibers such as metal
fibers (stainless steel, aluminum, etc.), glass fibers, carbon
fibers or the like, non-woven or woven fabrics made of resin fibers
(e.g., polyurethanes, polyamides, polyesters, or polyolefins), foam
substances made of such resin materials, and porous substances made
of ceramic materials. If the porous substrate comprises or is
substantially made of an organic material, the substrate surface
may preferably be coated with a material having low photocatalyst
reactivity, thereby serving as an undercoating layer, before
forming the photocatalyst layer, which will be further described
below.
[0045] Particularly preferred porous substrates include ceramics
having a three-dimensional network structure (hereinafter "porous
ceramic substrate"). The average diameter of the backbone of such a
ceramic material is preferably between about 100-1000 .mu.m. If the
average diameter of the backbone of such porous ceramic substrates
is at least 100 .mu.m (and more preferably at least 200 .mu.m), the
porous ceramic substrates will have good manufacturing and handling
properties, because these porous ceramic substrates will have
suitable mechanical strength. However, if the average diameter of
the backbone is greater than 1000 .mu.m, it becomes difficult to
appropriately balance the light transmission properties of the
photocatalyst composition (which includes the porous ceramic
substrate) with the surface area per unit volume of the
photocatalyst composition.
[0046] A representative method for making appropriate porous
ceramic substrates will be described as follows. First, a fine
ceramic powder (e.g., one or two or more fine powders comprising
alumina, silica, mullite and the like can be used), a binder
serving as a binding material (e.g., one or more of organic binders
such as dextrin, methyl cellulose, polyvinyl alcohol or the like,
or inorganic binders such as clay, sodium silicate or the like can
be used) and optionally water are mixed and stirred to prepare a
slurry. This slurry serves as a precursor for forming the porous
ceramic substrate. Then, the slurry is impregnated into an organic
porous substance (e.g., a polyurethane foam substance) having a
three-dimensional network structure. Thereafter, the slurry is
dried and fired so that the organic porous substance is decomposed
and the resulting fine ceramic powder is sintered. Thus, as shown
in FIGS. 1 and 2, a porous ceramic substrate 71 having a
three-dimensional structure comprising the sintered fine ceramic
powder is obtained. As shown in FIG. 2, a pore or hole 78 is formed
at positions in which the organic porous substance is
decomposed.
[0047] Optionally, the porous ceramic substrate may include ceramic
particles that are disposed on the surface of the backbone. In this
case, the porous ceramic substrate will have a rough or uneven
surface due to the ceramic particles. The rough surface may serve
to anchor a photocatalyst layer, as will be further described
below. Further, the rough surface effectively increases the surface
area of the porous ceramic substrate. Therefore, the amount of
photocatalyst per unit volume can be increased. In addition, the
rough surface will increase the surface area per unit volume of the
photocatalyst composition. For ceramic particles, an average
particle diameter of at least 1 .mu.m and at most 100 .mu.m is
preferable, and an average particle diameter of at least 10 .mu.m
and at most 50 .mu.m is more preferable. An average particle
diameter of less than 1 .mu.m will reduce the effect of increasing
the roughness to the porous ceramic substrate. However, if the
average particle diameter is greater than 100 .mu.m, it is
difficult to stably dispose the ceramic particles on the surface of
the porous ceramic substrate.
[0048] Such porous ceramic substrate having ceramic particles
disposed on the surface can be produced in the following manner. An
organic porous substance may be impregnated with the slurry
according to the above-described method for making a porous ceramic
substrate. Then, ceramic particles (one or two or more particles
comprising alumina, silica mullite and the like can be used) are
scattered and attached to the organic porous substance that has
been wetted with the slurry. Thereafter, the ceramic substrate is
dried and fired. As shown in FIGS. 3 and 4, porous ceramic
substrate 71 may include ceramic particles 72 that are disposed
along the surface of backbone 77. In portions of FIG. 3, the
representation of the ceramic particles 72 has been omitted so that
the backbone 77 is exposed for purposes of illustration.
[0049] The main component of the photocatalyst layer disposed on
the surface (i.e., both the inner and outer surfaces of the pores
of the structure) of the porous substrate preferably contains a
material exhibiting photocatalyst activity (e.g., a metal
oxide-based photocatalytic substance). Such photocatalyst materials
may include one, two or more compounds, such as titanium oxide,
tungsten oxide, zinc oxide, vanadium oxide, zirconium oxide and/or
other metal oxides exhibiting photocatalyst activity. Titanium
oxide is a particularly preferred material. Further, the
photocatalyst layer can be formed by preparing a slurry containing
ultra-fine particles of a photocatalytic material as the main
component and an organic or inorganic binder, impregnating a porous
substrate with the slurry, and then drying and firing the porous
substrate.
[0050] FIG. 5 schematically shows a photocatalyst layer 76 disposed
or formed on the porous ceramic substrate 71 shown in FIG. 2. FIG.
6 schematically shows a photocatalyst layer 76 disposed or formed
on the porous ceramic substrate 71 shown in FIG. 4.
[0051] As noted above, the porous substrate with the photocatalyst
layer preferably transmits at least 10% of light through a
thickness of 5 mm, more preferably transmits at least 20%, and even
more preferably transmits at least 30%. Thus, the present
photocatalyst compositions may exhibit a relatively high light
transmissivity (e.g., light transmission of at least 10%, more
preferably at least 20% and even more preferably at least 30%).
There are no particular limitations regarding the upper limit of
the light transmission. However, if the light transmission is
greater than 50%, handling ease of the substrate having a
photocatalyst and/or the mechanical strength retention may be
disadvantageously decreased.
[0052] As noted above, the metal (metal particles) disposed on the
photocatalyst layer may be one or a combination of two or more
transition metals. Preferred examples include Ag, Au, Pt, Pd, Ru,
Rh, Cu and Ni. Precious metals such as Au, Ag, Pt, and Pd are more
preferable, and Ag is even more preferable. These metals can be
disposed in a stable state for a long time, and their catalytic
activity (performance of improving photocatalytic efficiency) can
be maintained for a relatively long time. As a result, the
performance of the photocatalyst composition (photocatalytic
efficiency) can be maintained over a long time.
[0053] Furthermore, metals exhibiting antimicrobial properties,
such as Ag and Cu, may preferably be used in the present
photocatalyst composition. If one or more such metals are utilized,
the growth of microorganisms can be suppressed on the surface of
the photocatalyst composition even when the photocatalyst
composition is not being irradiated (i.e., during the period when
electron-hole pairs are not being generated and polarization is not
present). Therefore, such photocatalyst compositions exhibiting
high antimicrobial properties can prevent microorganisms (e.g.,
bacteria) from growing in or on the photocatalyst composition even
without continuously irradiating the photocatalyst composition.
[0054] As noted above, the metal or metal particles preferably are
substantially all disposed on the surface of the photocatalyst
layer. Thus, at least 70 wt % (more preferably at least 80 wt % and
even more preferably at least 95 wt %) of the metal is present on
and near the surface of the photocatalyst layer. More preferably,
substantially all of the metal is present at the surface of the
photocatalyst layer and substantially no metal is contained within
the interior portion of the photocatalyst layer. Naturally, if
metal is buried deep within the interior portion, the amount of
metal that does not contribute to the photocatalytic activity is
less than the total amount of metal contained within the
photocatalytic composition. Thus, by disposing substantially all
the metal in a position in which the substantially all the metal
contributes to the photocatalytic activity of the photocatalytic
composition, the utilization efficiency of the metal included in
the photocatalyst composition can be high.
[0055] The metal is preferably disposed on the photocatalyst layer
in the form of metal particles. The average metal particle diameter
is preferably 1000 nm or less, more preferably 100 nm or less, and
even more preferably 30 nm or less. When the average particle
diameter is larger than 1000 nm, the photocatalytic effects of the
metal are reduced. There are no particular limitations regarding
the lower limit of the average diameter of a metal particle.
However, it is noted that metal particles having an average
diameter of less than 1 nm are difficult to manufacture and utilize
with current manufacturing techniques.
[0056] At least 70% by number (more preferably at least 80% and
particularly preferably at least 95%) of the metal particles
preferably are present at or near the surface of the photocatalyst
layer. More preferably, substantially all of the metal particles
are present at the surface of the photocatalyst layer (i.e., almost
no metal particles are present within the interior portion of the
photocatalyst layer). The ratio (uneven distribution) of metal that
is present at the surface of the photocatalyst layer and the
average particle diameter of this metal can be easily and reliably
investigated, e.g., by utilizing an electron microscope, such as a
TEM or a similar device.
[0057] In another embodiment of the present teachings, the ratio of
the amount of the metal disposed on the photocatalyst layer with
respect to the amount of the photocatalytic substance contained
within the photocatalyst layer is preferably in the range from
0.001 wt % to 20 wt %, and more preferably in the range from 0.005
wt % to 5 wt %. When the content of the metal is less than these
ranges, the photocatalytic activity is not significantly increased
or improved. On the other hand, when the content of the metal is
higher than these ranges, the metal may reflect or absorb the
externally supplied light. As a result, the amount of light that
reaches the photocatalyst layer may be reduced. In other words,
photocatalytic activity of the metal may be reduced or eliminated,
if too much metal is utilized. Naturally, the amount of metal that
is utilized is preferably minimized in order to reduce production
costs of the photocatalyst material.
[0058] No particular restrictions are placed on the methods for
disposing or depositing the metal on the surface of the
photocatalyst layer. For example, the metal can be disposed
predominantly at the surface of the photocatalyst layer using known
impregnation methods. In one representative, but not limiting
example, a substrate having a photocatalyst layer may be immersed
into an aqueous solution containing a salt (e.g., nitrate,
chloride, sulfate and carbonate) of a metal (e.g., silver). The
substrate may then be dried and subjected to a reduction
treatment.
[0059] In one particularly preferred method, the photocatalyst
layer may be contacted with a solution containing the metal (e.g.,
a metal salt). Then, the photocatalyst layer and the solution are
irradiated with light having a wavelength that will activate the
photocatalytic substance in the photocatalyst layer. For example,
if the photocatalyst is TiO.sub.2, UV rays having a wavelength of
preferably 380 nm or less may be utilized. Hereinafter, this method
will be referred to as a "light irradiation technique" or an
"optical electrodeposition technique". As a further example, a
substrate having a photocatalyst layer may be immersed into a
solution (e.g., an aqueous solvent solution, and typically an
aqueous solution) containing metal ions and then the substrate
having the photocatalyst layer is irradiated with light while being
disposed in the aqueous solution. Thus, the metal ions are then
reduced and precipitated on the surface of the photocatalyst layer.
Consequently, the precipitated metal can be disposed on the surface
of the photocatalyst layer in the form of fine metal particles
having an average particle diameter of about 1 to 10 nm.
[0060] The present light irradiation techniques enable fine metal
particles having an average particle diameter suitable for
improving photocatalytic activity (increasing the reaction
efficiency) to be disposed substantially uniformly along the
surface of the photocatalyst layer. FIG. 7 schematically shows the
photocatalyst composition having metal particles 80 that are
disposed predominantly on the surface of the photocatalyst layer
76.
[0061] The light source for deposition of the metal preferably
emits primarily light having a wavelength (or wavelengths) that
enable(s) the photocatalyst to function appropriately. Naturally,
different types of photocatalyst may require different wavelengths.
For example, a fluorescent lamp, such as a black light, or an
ultraviolet lamp, such as an extra-high pressure mercury lamp or an
extra-low pressure mercury lamp, may be utilized for this process.
When titanium dioxide is used as the photocatalyst, an ultraviolet
lamp is preferably utilized that emits ultraviolet rays having a
wavelength of at least 300 nm and at most 420 nm (e.g., ultraviolet
rays having a peak of at least 360 nm and at most 380 nm).
[0062] In the present light irradiation techniques, the metal is
deposited due to photocatalytic activity at the portion of the
photocatalyst layer that is externally irradiated. Naturally, the
portion that is irradiated at this time will likely correspond to
the portion that is irradiated when the resulting photocatalyst
composition is in use (at the time of light irradiation). In other
words, the portion is irradiated at which the photocatalyst
functions well and increases the photocatalytic efficiency due to
the metal. Therefore, the present light irradiation techniques can
efficiently dispose the metal on the photocatalyst layer.
Consequently, the utilization efficiency of the metal can be
increased and a relatively small amount of the metal can provide a
relatively large effect. Furthermore, the cost of the raw material
for manufacturing the photocatalyst composition can be decreased.
In particular, when precious metals are used as the metal, a
significant reduction of the cost can be expected.
[0063] During light irradiation, the photocatalytic material
contained in the photocatalyst layer can reduce metal ions in the
solution. Therefore, it is not necessary to add an additional
reductant to the solution. However, a reductant may be added to a
solution containing metal ions in order to assist the reduction of
the metal ions by photocatalysis.
[0064] By either the irradiation technique or the impregnation
technique, the substrate having the photocatalyst layer is brought
into contact with the solution (e.g., an aqueous solvent solution)
containing the metal. The substrate having the photocatalyst layer
may be a hard porous substrate, so that the porous substrate is not
substantially deformed by contacting the aqueous solution.
Therefore, in this method, even if the substrate having the
photocatalyst layer contacts the aqueous solution in order to
deposit the metal on the surface of the photocatalyst layer, the
photocatalyst layer is not significantly damaged (i.e., the
photocatalyst layer will not peel off or dislodge from the hard
porous support).
[0065] As noted above, the present photocatalyst compositions
preferably exhibit a light transmissivity of at least 10% at a
thickness of 5 mm. This light ratio indicates the amount of light
that is transmitted through a structure 5 mm deep from the incident
surface with respect to the incident light. More preferably, the
light transmissivity is at least 20% and even more preferably at
least 30%. If the photocatalyst composition exhibits a light
transmissivity of at least 10%, light can be easily transmitted
into the interior portion of the photocatalyst composition.
Therefore, most of the photocatalyst and the metal included in the
photocatalyst composition can be effectively utilized.
[0066] The above-described light transmissivity ranges can be
achieved by satisfying at least one of the following three
conditions (preferably two or more, and more preferably all three
conditions): (1) the porosity is at least 65% and at most 99%
(typically, at least 70% and at most 95%), (2) the bulk density is
at least 0.05 g/cm.sup.3 and at most 0.60 g/cm.sup.3 (typically, at
least 0.15 g/cm.sup.3 and at most 0.50 g/cm.sup.3); and (3) the
number of cells is at least 10 cells per 25 mm (10/25 cm) and at
most 30 cells per 25 mm (30/25 cm). Herein, "the number of cells
(X/25 mm)" indicates the number of cells that intersect a 25 mm
straight line that is drawn along the surface or the cross-section
of a porous ceramic substrate. Naturally, as this number increases,
the pore sizes within the porous ceramic substrate are reduced. For
example, suitable light transmissivity can be achieved by using a
ceramic substrate having a three-dimensional network structure that
satisfies at least one of the conditions (1), (2) and (3)
(preferably two or more, and more preferably all three
conditions).
[0067] A photocatalyst composition having a porosity of 99% or
less, a bulk density of 0.05 g/cm.sup.3 or more and a number of
cells of 30/25 mm or less will exhibit suitable mechanical
strength. Therefore, the photocatalyst will exhibit suitable
manufacturing and handling properties. However, if the
photocatalyst composition has a porosity of less than 65%, a bulk
density of more than 0.60 g/cm.sup.3 and/or a number of cells of
less than 10/25 mm, only a small quantity of light may reach the
interior portion of the photocatalyst composition. In addition, if
such a photocatalyst composition is used as a filter, the pressure
loss may be substantial when a fluid containing a substance to be
treated (fluid to be treated) is passed through the
photocatalyst.
[0068] Representative photocatalytic filter devices may include a
filter that primarily contains one or more of the above-described
photocatalyst compositions. The photocatalytic filter device
optionally may include a supporting frame for maintaining the form
of the photocatalyst composition. Further, an attaching member may
be utilized to attach the photocatalyst composition to a
predetermined position of the supporting frame. A light source may
be provided for irradiating the photocatalyst composition. Further,
a fluid passage defining member may be provided for introducing a
fluid into the photocatalyst composition and a fan or pump may
facilitate efficient passage of the fluid through the photocatalyst
composition. If the filter device is used for treating exhaust
containing a large amount of oil components (e.g., oil particles,
oil smoke, etc.) such as exhaust generated by cooking, a de-oiling
filter may be provided upstream from the photocatalyst composition
in order to filter out oil components contained within the
exhaust.
[0069] FIG. 8 shows a representative gas treatment apparatus, which
is an example of such a photocatalytic filter device. Gas treatment
apparatus 100 may include a light treatment portion 110 having a
photocatalytic filter (photocatalyst composition) 62 and a gas
supply device 120 for supplying a gas 150 that will be treated
(e.g., indoor air) to the light treatment portion 110. The light
treatment portion 110 may include a gas passage (fluid passage
defining member) 112 that communicates with the downstream portion
of the gas supply device 120. A prefilter 114 and a photocatalyst
module 61 also may be disposed within the gas passage 112. The
prefilter 114 is preferably made of non-woven fabrics or a similar
substance and serves to remove (filter) contaminants (e.g., dust)
contained within the gas 150 that will be treated.
[0070] As shown in FIGS. 10 and 11, the photocatalyst module 61 may
include a plurality of (e.g., 12) photocatalytic filters 62 and a
light source 63 for irradiating the photocatalytic filters 62. The
photocatalytic filters 62 may be disposed so as to oppose each
other with the light source 63 interposed therebetween. A frame 64
may integrally support each of these components.
[0071] As shown in FIG. 9, the photocatalytic filters 62 may each
be defined in the form of a flat plate. The photocatalytic filter
62 preferably has a structure in which a photocatalyst layer 76 is
formed, as shown in FIG. 7, on the surface of the porous ceramic
substrate 71 having a three-dimensional structure as shown in FIG.
1. Further, the metal particles 80 are preferably disposed
predominantly on the surface of the photocatalyst layer 76. The
photocatalyst layer 76 may primarily contain titanium dioxide as
the active photocatalyst component. The metal particles 80 may be
silver particles.
[0072] Referring back to FIGS. 10 and 11, the frame 64 may comprise
an anti-corrosion metal, such as stainless steel, in the form of a
box and may include openings on opposing sides. A plurality of
(e.g., 6) photocatalytic filters 62 may be arranged within the same
plane, and may be supported by a lattice frame 68 in order to form
a flat plate-like filter unit 69. Two filter units 69 may be
attached to the openings provided on the opposite sides of the
frame 64. A plurality of light sources 63 held by the frame 64 may
be disposed in parallel to each other between the filter units 69.
In the photocatalyst module 61 having this structure, the
photocatalytic filters 62 are exposed to the outside from the
openings on the opposite sides of the frame 64. The gas that will
be treated passes through the photocatalyst module 61 via the two
layered photocatalytic filters 62. In this embodiment, four
ultraviolet lamps are used as the light sources 63.
[0073] The gas supply device 120 shown in FIG. 8 may include a fan
(not shown) disposed within a casing 122. When the fan is driven,
the gas 150 can be drawn in from an inlet 124 of the casing 122.
The drawn gas 150 then flows from an outlet 126 to the gas passage
112 (light treatment portion 110). Thereafter, the gas 150 passes
through the prefilter 114 and then through the photocatalytic
filters 62 disposed within the photocatalyst module 61. Thus, the
photocatalytic filters 62 capture any contaminants that remain
within the gas 150. Furthermore, odorous components contained
within the gas 150 will contact the photocatalyst layer 76 disposed
on the surface of the photocatalytic filters 62. The contaminants
and odorous components are then photolyzed due the photocatalytic
activity of titanium dioxide, which may be the main component of
the photocatalyst layer 76. Thus, the gas 150 is converted into
purified air 152 and is discharged to the outside.
[0074] As shown in FIG. 8, a post treatment unit 116 may be
provided downstream from the photocatalyst module 61. The post
treatment unit 116 may preferably include a device that can purify
(or deodorize) the gas 150 by a process other than photocatalytic
activity. For example, a filter having an adsorption function using
activated carbon can be used as the post treatment unit 116.
[0075] In another embodiment of the present teachings, FIG. 12
shows a water treatment apparatus 200, which is another
representative photocatalytic filter device according to the
present teachings. The water treatment apparatus 200 may include a
light treatment portion 220 and an ozone supply portion 240. The
light treatment portion 220 may include a treatment bath 222 made
of quartz for storing water 250 that will be treated. The
photocatalytic filter 62 may be accommodated within the treatment
bath 222. Further, an ultraviolet lamp 224 may be disposed to the
side of the treatment bath 222. A power source 226 is connected to
the ultraviolet lamp 224. When the ultraviolet lamp 224 is turned
on, the photocatalytic filter 62 is irradiated with ultraviolet
rays via the side wall of the treatment bath 222. The
photocatalytic filter 62 may have a flat plate-like shape and may
be disposed so as to face the side wall (surface that is irradiated
with ultraviolet rays) of the treatment bath 222.
[0076] The ozone supply portion 240 may include an ozone generator
242. Dry air 252 is first supplied to the ozone generator 242 in
order to increase the ozone content and then is supplied to the
treatment bath 222 via an ozone supply passage 244. An air
diffusing tube 246 may be connected to the terminal end of the
ozone supply passage 244. The air difusing tube 246 may be
submerged in the water 250 that will be treated, which is disposed
within the treatment bath 222. The diffusing tube 246 preferably
generates small bubbles 254 containing ozone that pass through the
water 250 that will be treated. A flow meter 248 may be disposed
within the ozone supply passage 244 in order to monitor of the flow
rate of the gas supplied from the ozone generator 242.
[0077] The water 250 that will be treated may contain contaminants
(e.g., organic substances such as proteins, amino acids, and/or
saccharides) and is disposed within the treatment bath 222 in which
the photocatalytic filter 62 has been accommodated. The ultraviolet
lamp 224 is turned ON in order to irradiate the photocatalytic
filter 62 with ultraviolet rays. As a result, the contaminants in
the water 250 will be photolyzed due to the photocatalytic activity
of the titanium dioxide, which preferably may be the primary
component of the photocatalyst layer. Thus, the treated water 250
can be purified. As indicated above, small bubbles 254 containing
ozone are preferably injected into the water 250 via the air
diffusing tube 246, because purification can be increased by
combining the photocatalytic activity and contaminant degradation
(ozonolysis) using ozone. The above-described water treatment
apparatus 200 is particularly suitable for purifying water 250 that
has a relatively high transparency.
[0078] FIG. 13 shows a representative photocatalyst unit 300 that
can be utilized within another water treatment apparatus. The
photocatalyst unit 300 may include a water passage tube 312 through
which the water 250 to be treated will flow. A plurality of
disk-shaped photocatalytic filters 62 may be spaced from each other
within the water passage tube 312. The photocatalytic filters 62
may preferably be disposed perpendicular to the longitudinal axis
of the water passage tube 312. In addition, a plurality of (e.g.,
four in this example) ultraviolet lamps 314 may be accommodated
within the water passage tube 312. The ultraviolet lamps 314 may
extend through the plurality of photocatalytic filters 62 along the
longitudinal axis of the water passage tube 312. The ultraviolet
lamps 314 are connected to a source power (not shown). When the
ultraviolet lamps 314 are turned ON, the water 250 is supplied to
the water passage tube 312 and passes through the photocatalytic
filters 62, and any contaminants in the water 250 will photolyzed,
thereby purifying the water 250.
[0079] The photocatalyst unit 300 can be also used as a component
of a gas treatment apparatus. In this case, a gas that will be
treated is supplied to the passage tube 312.
[0080] Each of the additional features and method steps disclosed
above and below may be utilized separately or in conjunction with
other features and method steps to provide improved photocatalytic
compositions and methods for making and using the same. Detailed
representative examples of the present teachings, which examples
will be described below, utilize many of these additional features
and method steps in conjunction. However, this detailed description
is merely intended to teach a person of skill in the art further
details for practicing preferred aspects of the present teachings
and is not intended to limit the scope of the invention. Therefore,
combinations of features and steps disclosed in the following
detailed description may not be necessary to practice the present
teachings in the broadest sense, and are instead taught merely to
particularly describe representative and preferred embodiments of
the present teachings, which will be explained below in further
detail with reference to the figures. Of course, features and steps
described in this specification may be combined in ways that are
not specifically enumerated in order to obtain other usual and
novel embodiments of the present teachings and the present
inventors contemplate such additional combinations.
EXAMPLE 1
Manufacture of a Photocatalyst Composition (1)
[0081] 446.5 g of fine ceramic powder (fine alumina powder), 16.0 g
of talc, 36.5 g of Kibushi clay (a type of sedimentary clay), 155 g
of water and 12.5 g of a dispersant were put into a 2 liter pot
mill made of polyethylene. Further, alumina balls having a diameter
of 10 mm were put up to about 1/3 of the pot mill and the mixture
was stirred for 5 hours. Then, 127.1 g of an organic binder
(product name "CERAMO TB-01" manufactured by Dai-ichi Kogyo Seiyaku
Co., Ltd.) were added to the mixture in the pot mill and stirred
for 20 hours. This solution was utilized as a slurry for forming a
porous ceramic substrate.
[0082] An organic porous substance having a three-dimensional
network structure (polyurethane foam in this example) was
impregnated with the slurry. Then, the polyurethane foam (product
name "MF-13" manufactured by INOAC Corp.) was lifted out of the
slurry and excess slurry was removed by pressing with a roller. The
slurry lodged within the voids of the polyurethane foam was blown
out with a spray so as to eliminate clogging of the voids. The
polyurethane foam containing the slurry as dried at 70.degree. C.
for 24 hours and then fired at 1600.degree. C. for one hour. This
firing decomposed the polyurethane foam and sintered the alumina
fine powder contained in the slurry. As a result, a porous ceramic
substrate having a three-dimensional network structure was
produced.
[0083] The porous ceramic substrate was immersed in a photocatalyst
slurry (product name "STS-01" manufactured by Ishihara Sangyo
Kaisha, Ltd.), excess slurry was removed by spraying, and dried at
200.degree. C. Thus, a photocatalyst layer containing a
photocatalyst (titanium dioxide) as the main component was formed
on the surface of the porous ceramic substrate. The photocatalyst
slurry used in this example contained fine particles of
anatase-type titanium dioxide (photocatalyst) that were
mono-dispersed in an aqueous medium.
[0084] Next, fine silver particles were deposited on the surface of
the photocatalyst layer. More specifically, an aqueous silver
nitrate solution (silver nitrate concentration of 9.3 mmol/m.sup.3
(9.3.times.10.sup.-3 mmol/liter)) was placed in a quartz cell and
the substrate having the photocatalyst layer was immersed in the
quartz cell. Then, the pH of the aqueous silver nitrate solution
was adjusted to about pH 6.3 using a 0.4 normal(M) KOH aqueous
solution and the aqueous solution was stirred for 30 minutes.
Thereafter, oxygen in the quartz cell was removed by bubbling
nitrogen through the aqueous solution. Then, the substrate having
the photocatalyst layer in the quartz cell was irradiated with
ultraviolet light having a wavelength of 365 nm for one hour using
a 500 W high-pressure mercury lamp. Thereafter, the substrate
having the photocatalyst layer was lifted out of the aqueous silver
nitrate solution, washed, and then dried at 110.degree. C. for 3
hours in a drying oven. As a result, a photocatalyst composition
(sample 1) was produced with the fine silver particles disposed on
the surface of the photocatalyst layer.
EXAMPLE 2
Manufacture of a Photocatalyst Composition (2)
[0085] A photocatalyst composition (sample 2) was produced in the
same manner as in Example 1 except for the following difference.
Specifically, the aqueous silver nitrate solution having a silver
nitrate concentration of 9.3 mmol/m.sup.3 was replaced with an
aqueous silver nitrate solution having a silver nitrate
concentration of 46 mmol/m.sup.3 (4.6.times.10.sup.-2 mmol/liter).
The amount of the fine silver particles disposed on the substrate
having the photocatalyst layer was thus controlled by the
concentration of the silver nitrate.
[0086] Table 1 shows the silver nitrate concentration of the
aqueous silver nitrate solution used in Examples 1 and 2, the
amount (average of the entire photocatalyst composition) of fine
silver particles per unit volume of the resulting photocatalyst
composition (samples 1 and 2), and the ratio (in weight) of the
amount of the disposed fine silver particles to the weight of the
photocatalyst (titanium dioxide). The amount of the disposed fine
silver particles and the ratio thereof with respect to the weight
of the photocatalyst were calculated based upon measured values
obtained by measuring the amount of Ag that remained in the aqueous
silver nitrate solution after the substrate having the
photocatalyst layer was lifted out. This measurement was performed
using an inductive coupling plasma emission analysis apparatus
(ICP-AES).
1 TABLE 1 Silver nitrate Amount of Ag concentration deposited
Ag/TiO.sub.2 (mmol/m.sup.3) (mg/cm.sup.3) (wt %) Example 1 9.3 5.0
.times. 10.sup.-3 0.014 Example 2 46 2.5 .times. 10.sup.-2
0.072
[0087] Observation using an electron microscope confirmed that
substantially all fine silver particles were deposited on the
surface of the photocatalyst layer in both samples 1 and 2. The
average particle diameter of the fine silver particles was 3
nm.
[0088] Further, both samples 1 and 2 exhibited light transmissivity
of 30% or more at a thickness of 5 mm. The light transmissivity of
each sample was measured according the following process. A black
light (product name "FL10BLB" manufactured by Toshiba Lighting
& Technology Corporation providing wavelengths of 300 to 420 nm
and a peak wavelength 360 nm) was placed 7 cm from the surface of
the samples. An ultraviolet intensity meter (product name "UM-10"
manufactured by Minolta Co., Ltd.) was placed in contact with the
back surface of the sample and the intensity of the ultraviolet
rays that were transmitted through the samples was measured. Light
transmissivity was calculated based upon the ratio of the intensity
when the sample was interposed between the black light and the
ultraviolet intensity meter to the intensity when the sample was
not interposed between them, as follows:
Light transmissivity (%)={(intensity measured when the sample is
interposed)/(intensity measured when the sample was not
interposed)}.times.100
[0089] Both samples 1 and 2 satisfied the following three
conditions: (1) the porosity was at least 65% and at most 95%; (2)
the bulk density was at least 0.15 glcm.sup.3 and at most 0.60
g/cm.sup.3; and (3) the number of cells was at least 10/25 mm and
at most 30/25 mm. Herein, the porosity was calculated from the
volume, the mass and the density of the sample. The bulk density
was calculated from the volume and the mass of the sample. Further,
the number of cells was measured by observation using an optical
microscope.
EXAMPLE 3
Evaluation of Purification Performance of the Photocatalyst
Composition (1)-NO Removal Performance
[0090] As shown in FIG. 14, a photocatalyst treatment device 40 was
prepared with a main member 42, a window plate 45 and a black light
50 as a light source. An inlet 43 and an outlet 44 were defined on
the side faces of the main member 42. The upper opening of the main
member 42 was closed by the window plate 45 made of quartz glass.
Thus, an interior passage 46 leading from the inlet 43 to the
outlet 44 was defined within the photocatalyst treatment device 40.
A height adjusting plate 48 having a thickness of 10 mm was set on
the bottom surface of the interior passage 46 and a sample
(photocatalyst composition) 49 was mounted thereon when
measurements were performed. The black light 50 was disposed above
the window plate 45. Nitrogen monoxide gas having a NO
concentration of 1.0 ppm (diluted with air) and a relative humidity
of 50% at 25.degree. C. was supplied from the inlet 43 at a rate of
3 liters/min. Gas (discharged gas) exhausted from the outlet 44 was
introduced into a chemiluminescence NO.sub.x meter (not shown) in
order to measure the NO and NO.sub.2 concentrations.
[0091] The measurements were performed as follows. The sample 49
having a length of 50 mm, a width of 50 mm and a thickness of 13 mm
was mounted on the height adjusting plate 48. The samples were the
photocatalyst composition (sample 1) produced in Example 1 and the
photocatalyst composition (sample 2) produced in Example 2. For
comparison, the substrate having the photocatalyst layer obtained
in the process of producing the photocatalyst composition in
Example 1 (comparative sample 1: silver is not disposed on the
photocatalyst layer) was also evaluated.
[0092] First, nitrogen monoxide gas was allowed to flow through the
interior passage 46 for 10 minutes, and it was confirmed that the
NO concentration of the discharged gas reached 0.9 ppm or more.
Thereafter, the black light 50 was turned ON and the NO
concentration and the NO.sub.2 concentration of the discharged gas
were measured over time. FIG. 15 shows the results of this
measurement. As seen in FIG. 15, in comparative sample 1 in which
silver particles are not included, after 10 minutes had passed from
turning ON the black light, the NO concentration increased with
time. This result indicates that the NO removal performance of the
comparative sample 1 was reduced as time elapsed. On the other
hand, in samples 1 and 2, in which silver particles were included,
the NO concentration of the discharge gas remained low (0.6 ppm or
less), regardless of the amount time that had passed after the
black light was turned ON. This result indicates that the NO
removal performance of the samples was maintained throughout the
measurement period. Further, less NO.sub.2 was produced (NO.sub.2
concentration of the discharged gas) in samples 1 and 2 than in the
comparative sample 1. This result indicates that in samples 1 and
2, NO is efficiently converted to NO.sub.3.sup.-(and the generation
of NO.sub.2 was suppressed).
[0093] The amount of NO fixed to the photocatalyst composition in
the form of nitrate ions (NO.sub.3.sup.-) was obtained from the
difference between the NO amount supplied from the inlet 43 and the
total amount of NO and NO.sub.2 discharged from the outlet 44
during measurement. Based upon this information, the ratio
(NO.sub.3.sup.-fixation ratio) of the NO fixed to the photocatalyst
composition with respect to the supplied NO was calculated. Table 2
shows these results. The NO.sub.3.sup.-fixation ratio of samples 1
and 2 was at least 15 times greater than the NO.sub.3 fixation
ratio of comparative sample 1.
2 TABLE 2 NO.sub.3.sup.-fixation ratio (%) Sample 1 26.9 Sample 2
19.6 Comparative Sample 1 1.3
EXAMPLE 4
Evaluation of Purification Performance of the Photocatalyst
Composition (2)-SO.sub.2 Removal Performance
[0094] The nitrogen monoxide gas that was used in Example 3 was
replaced by sulfur dioxide gas having a SO.sub.2 concentration of
1.0 ppm (diluted with air) and a relative humidity of 50% at
25.degree. C. and was supplied at a rate of 3 liters/min. The
discharged gas from the outlet 44 was introduced into an
ultraviolet spectrophotometric SO.sub.2 meter. Other aspects of
Example 4 are the same as Example 3.
[0095] A sample was mounted on the interior passage 46 and sulfur
dioxide gas was allowed to flow through the sample for 2 hours.
Thereafter, the black light 50 was turned ON for one hour and then
was turned off. In this example, the SO.sub.2 concentration of the
discharged gas was also measured over time during a period when the
black light 50 was not turned ON, and the SO.sub.2 adsorption
ability of the photocatalyst composition was investigated. FIG. 16
shows the results of the measurement. As shown in FIG. 16, before
the black light was turned ON, in comparative sample 1, the
SO.sub.2 concentration of the discharged gas gradually increased.
This result indicates that the SO.sub.2 removal performance
(adsorption ability) decreased as the time elapsed. On the other
hand, in samples 1 and 2, the SO.sub.2 concentration of the
discharge gas was maintained low, and SO.sub.2 purification
performance (adsorption performance) was maintained.
[0096] The amount of SO.sub.2 adsorbed by the photocatalyst
composition was calculated based upon the difference between the
amount of SO.sub.2 supplied from the inlet 43 and the amount of
SO.sub.2 discharged from the outlet 44 during the measurement
period. Thereafter, the ratio (SO.sub.2 adsorption ratio) of the
SO.sub.2 adsorbed by the photocatalyst composition with respect to
the supplied SO.sub.2 was calculated. Table 3 shows these results.
Table 3 indicates that the SO.sub.2 purification performances of
samples 1 and 2 are better than comparative sample 1
3 TABLE 3 SO.sub.2 adsorption ratio (%) Sample 1 43.1 Sample 2 41.7
Comparative Sample 1 37.7
EXAMPLE 5
Evaluation of Purification Performance of the Photocatalyst
Composition (3)-Methyl Mercaptan Removal Performance
[0097] The nitrogen monoxide gas that was used in Example 3 was
replaced with methyl mercaptan gas having a methyl mercaptan
concentration of 1.0 ppm (diluted with air) and a relative humidity
of 50% at 25.degree. C., and was supplied at a rate of 3
liters/min. The discharged gas from the outlet 44 was collected in
a fluoroplastic gas bag, and the methyl mercaptan concentration was
measured with a gas detecting tube. Other aspects of Example 5 were
the same as Example 3.
[0098] A sample was mounted on the interior passage 46 and methyl
mercaptan gas was allowed to flow through it for 10 minutes. It was
confirmed that the methyl mercaptan concentration of the discharged
gas reached about 1.0 ppm. Thereafter, the black light 50 was
turned ON and the methyl mercaptan concentration of the discharged
gas was measured over time. FIG. 17 shows the results of this
measurement. As shown in FIG. 17, in comparative sample 1 in which
silver is not contained, the methyl mercaptan concentration of the
discharged gas was equal to the supplied gas, which indicates that
the methyl mercaptan is not significantly decomposed. On the other
hand, in samples 1 and 2, the methyl mercaptan concentration of the
discharge gas was lower (about 0.8 ppm) than the supplied gas,
which indicates that the methyl mercaptan was decomposed.
[0099] The amount of methyl mercaptan removed by the photocatalyst
composition was calculated based upon the difference between the
methyl mercaptan amount supplied from the inlet 43 and the methyl
mercaptan amount discharged from the outlet 44 during the
measurement period. Thereafter, the ratio (methyl mercaptan removal
ratio) of the methyl mercaptan removed by the photocatalyst
composition with respect to the supplied methyl mercaptan was
calculated. Table 4 shows these results.
4 TABLE 4 Methyl mercaptan removal ratio (%) Sample 1 15 Sample 2
22 Comparative Sample 1 0
EXAMPLE 6
Evaluation of Antibacterial Properties (1)
[0100] An E. Coli suspension (strain: E. Coli K-12, the number of
cells (in 0.1 ml): 6.times.10.sup.8) in an amount of 0.1 ml was
added to sample 1 and sample 1 was irradiated with ultraviolet
light at an intensity of 1200 .mu.W/cm.sup.2 (360 nm) for 30
minutes. Then, sample 1 was immersed in a brain heart infusion
(BHI) medium and the medium was cultured at 37.degree. C. in an
incubator for 16 hours. The medium that had been subjected to
culturing was collected and applied to a BHI agar medium in a petri
dish. Thereafter, this petri dish was cultured at 37.degree. C. in
an incubator for 10 hours. After the culturing ended, no colonies
of E. Coli were observed in the petri dish.
EXAMPLE 7
Evaluation of Antibacterial Properties (2)
[0101] The antibacterial properties were evaluated in the same
manner as in Example 6, except for the following difference. An E.
Coli suspension was added to sample 1 in the same manner as in
Example 6. Then, instead of irradiating sample 1 with ultraviolet
light, sample 1 was shielded from light using aluminum foil. After
the culturing ended, no colonies of E. Coli were observed in the
petri dish.
COMPARATIVE EXAMPLE 1
Evaluation of Antibacterial Properties (3)
[0102] The antibacterial properties were evaluated in the same
manner as in Example 6 (i.e., with ultraviolet irradiation for 30
minutes), except that sample 1 was replaced with comparative sample
1 (silver was not contained). After the culturing ended, no
colonies of E. Coli were observed in the petri dish.
COMPARATIVE EXAMPLE 2
Evaluation of Antibacterial Properties (4)
[0103] The antibacterial properties were evaluated in the same
manner as in Example 7 (i.e., without ultraviolet irradiation),
except that sample 1 was replaced with comparative sample 1 (silver
was not contained). After the culturing ended, 240 colonies of E.
Coli were observed in the petri dish.
[0104] Table 5 collectively shows the results of Examples 6 and 7
and Comparative Examples 1 and 2. Sample 1 contains silver, which
exhibits antibacterial properties. Therefore, sufficient
antibacterial properties are also exhibited, even if ultraviolet
irradiation is not performed. Therefore, when sample 1 is used with
a photocatalytic filter device, it is not necessary to continuously
operate the apparatus in order to prevent growth of microorganisms
(e.g. bacteria). Consequently, operating costs can be reduced.
5 TABLE 5 UV ray Antibacterial properties Sample irradiation
(number of colonies) Example 6 Sample 1 (silver 30 min. 0
contained) Example 7 Sample 1 (silver blocked 0 contained) Compar-
Comparative Sample 1 30 min. 0 ative (silver not contained) Example
1 Compar- Comparative Sample 1 blocked 240 ative (silver not
contained) Example 2
* * * * *