HK1103679B - Multi-layered photocatalyst/thermocatalyst for improving indoor air quality - Google Patents

Description

Multi-layer photocatalyst/thermocatalyst for improving indoor air quality

Background

The present invention relates generally to a multi-layered photocatalyst/thermocatalyst that decomposes ozone and oxidizes gaseous contaminants, including volatile organic compounds, low polarity organic molecules, and carbon monoxide, that adsorb onto a photocatalytic surface to form carbon dioxide, water, and other substances.

Indoor air may include trace amounts of impurities including carbon monoxide, ozone, and Volatile Organic Compounds (VOCs) such as formaldehyde, acetaldehyde, toluene, propionaldehyde, and butene, among others. Absorbent air filters, such as activated carbon, have been used to remove volatile organic compounds from air. When air flows through the filter, the filter blocks the passage of impurities, allowing air free of impurities to flow through the filter. The disadvantage of using filters is that they simply prevent the passage of impurities without destroying them. In addition, air filters are not effective at blocking carbon monoxide and ozone.

Titanium dioxide has been used as a photocatalyst in air purifiers for destroying impurities, particularly polar organic molecules. When titanium dioxide is irradiated with ultraviolet light, photons are absorbed by the titanium dioxide, promoting electrons to pass from the valence band to the conduction band, thereby generating holes in the valence band and adding electrons in the conduction band. The promoted electrons react with oxygen and the holes remaining in the valence band react with water to form reactive hydroxyl radicals. When impurities adsorb onto the titanium dioxide catalyst, the hydroxyl radicals attack and oxidize the impurities to water, carbon dioxide, and other substances.

Titanium dioxide doped or treated with metal oxides increases the effectiveness of the titanium dioxide photocatalyst. However, titanium dioxide and doped titanium dioxide are less effective or ineffective at oxidizing carbon monoxide and low polarity organic molecules as well as decomposing ozone. Carbon monoxide (CO) is a colorless, odorless, toxic gas produced by incomplete combustion of hydrocarbon fuels. Carbon monoxide causes more death than any other poison and may accumulate in the room air due to poor ventilation, smoke extraction or automobile exhaust from the outside air. In the presence of a small amount of carbon monoxide, carbon monoxide poisoning may occur over a long period of time. Sensory organs such as the brain, heart and lungs are most likely subject to hypoxia. The exposure indicated by EPA over an average of eight hours was set at 30 ppm.

Ozone (O)₃) Are contaminants released by equipment that is typically present at the workplace, such as copiers, printers, scanners, etc. Ozone can cause nausea and headache, and can damage nasal mucosa when ozone is irradiated for a prolonged period of time, causing respiratory problems.

Thus, there is a need for a multilayer photocatalyst/thermocatalyst coating that decomposes ozone to oxygen and oxidizes carbon monoxide, low polarity organic molecules, and volatile organic contaminants adsorbed onto the photocatalytic surface to form carbon dioxide, water, and other substances.

Summary of The Invention

The layered photocatalyst/thermocatalyst coating on the substrate purifies the air in a building or vehicle by decomposing and oxidizing any impurities adsorbed onto the coating to form oxygen, water, carbon dioxide, and other substances.

The fan draws air into the air purification system. Air flows through the open channels or passages of the honeycomb. The surface of the honeycomb is coated with a layered photocatalytic/thermocatalytic coating. An ultraviolet light source positioned between successive honeycombs activates the coating.

The coating includes an outer layer of photocatalytic titanium dioxide or metal oxide-supported titanium dioxide for oxidizing volatile organic compounds to carbon dioxide, water, and other substances. A middle layer of photocatalytic precious metal/titanium dioxide coating is located below the outer layer. Below the middle layer is a photocatalytic/thermocatalytic inner layer of nano-dispersed gold on titanium dioxide applied to the honeycomb structure.

When photons of the ultraviolet light are absorbed by the outer layer of titanium dioxide, reactive hydroxyl radicals are formed. When impurities, such as volatile organic compounds, are adsorbed onto the coating, the hydroxyl radicals attack the volatile organic compounds, removing (abstrat) hydrogen atoms from the volatile organic compounds and oxidizing the volatile organic compounds to water, carbon dioxide, and other substances. The thickness of the outer layer is less than 2 microns, which allows photons to penetrate the outer layer to reach the underlying photocatalytic platinum/titanium dioxide layer.

Platinum deposited on the surface of titanium dioxide enhances the separation of charge carriers and reduces the rate of recombination of electrons and holes. Platinum is also an excellent thermal catalyst. It is believed that platinum may further oxidize the photocatalytic oxidation intermediate to carbon dioxide and water.

Carbon monoxide may diffuse through the porous layer and reach the inner layer. At room temperature, the gold/titanium dioxide layer oxidizes carbon monoxide to carbon dioxide. When carbon monoxide is adsorbed on the coating, the gold acts as an oxidation catalyst and lowers the energy barrier of the carbon monoxide, oxidizing the carbon monoxide to carbon dioxide in the presence of oxygen.

In an environment where ozone concentration is high, a fourth manganese oxide/titanium dioxide layer is applied to the honeycomb structure under the inner layer. Ozone can also diffuse through the porous layer and reach the inner layer. When ozone is adsorbed on the manganese oxide/titanium dioxide coating, the manganese oxide decomposes the ozone to molecular oxygen at room temperature or slightly elevated temperatures due to the heat generated by the ultraviolet light.

These and other features of the present invention will be best understood from the following specification and drawings.

Brief Description of Drawings

The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the generally preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 illustrates an enclosed environment, such as a building, vehicle or other structure, including an indoor space and an air conditioning system;

FIG. 2 illustrates an air purification system of the present invention;

FIG. 3 illustrates a honeycomb structure of the air purification system;

FIG. 4 illustrates a first embodiment of the layered photocatalyst of the present invention;

FIG. 5 illustrates a second embodiment of the layered photocatalyst of the present invention;

fig. 6 illustrates another embodiment of an air purification system.

Detailed description of the preferred embodiments

Fig. 1 schematically illustrates a building, vehicle or other structure 10 including an indoor space 12, such as a room, office or vehicle passenger compartment, such as a car, train, bus or airplane. The air conditioning system 14 heats or cools the indoor space 12. Air in the indoor space 12 is drawn into the air conditioning system 14 through a path 16. The air conditioning system 14 varies the temperature of the air 16 drawn from the indoor space 12. If the air conditioning system 14 is operating in a cooling mode, the air is cooled. Or if the air conditioning system 14 is operating in a heating mode, the air is heated. The air then returns to the indoor space 12 through the path 18, changing the temperature of the air in the indoor space 12.

Fig. 2 schematically illustrates an air purification system 20 for purifying air in a building or vehicle 10 by oxidizing impurities, such as volatile and semi-volatile organic compounds, carbon monoxide to water, carbon dioxide, and other substances. For example, the volatile organic compound may be an aldehyde, a ketone, an alcohol, an aromatic compound, an alkene, or an alkane. The air purification system 20 will also decompose ozone into oxygen. The air purification system 20 may purify air before it is drawn into the air conditioning system 14 along path 16, or it may purify air exiting the air conditioning system 14 before it is blown back into the indoor space 12 of the building or vehicle 10 along path 18. The air purification system 20 may also be a stand-alone unit that is not used with the air conditioning system 14.

The fan 34 draws air into the air purification system 20 through the inlet 22. The air flows through a particle filter 24 which filters out dust or any other large particles by preventing the flow of these particles. The air then flows through a substrate 28, such as a honeycomb structure. In one example, the honeycomb 28 is made of aluminum or an aluminum alloy. Fig. 3 schematically illustrates a front view of a honeycomb 28 having a plurality of hexagonally-shaped open channels or passages 30. The surfaces of the plurality of open channels 30 are coated with a layered photocatalytic/thermocatalytic coating 40.

As shown in fig. 4, the coating 40 of the present invention comprises at least 3 layers. Preferably, the coating 40 has about 0.5-1mg/cm on the honeycomb 28²The amount of the supported catalyst. The coating 40 includes an outer layer 42 of titanium dioxide or metal oxide doped titanium dioxide. The outer layer 42 is effective to oxidize volatile and semi-volatile organic compounds such as aldehydes, ketones, alcohols, aromatics, alkenes, or alkanes. Titanium dioxide is an effective photocatalyst for the oxidation of volatile organic compounds to carbon dioxide, water and other substances. Outer layer 42 has an effective thickness (less than 2 microns) and porosity. That is, outer layer 42 is capable of allowing other impurities, such as low polarity organic compounds, carbon monoxide, and ozone, that are not oxidized by outer layer 42 to diffuse through outer layer 42 and adsorb on the layers below outer layer 42.

The light source 32 located between successive honeycombs 28 activates the photocatalytic coating 40 on the surface of the open channels 30. As shown, the honeycomb 28 and the light source 32 alternate in the air purification system 20. That is, there is a light source 32 between each honeycomb 28. Preferably, the light source 32 is an ultraviolet light source that generates light having a wavelength in the range of 180 nanometers to 400 nanometers.

The light source 32 is turned on to activate the outer layer 42 on the surface of the honeycomb 28. When a photon of ultraviolet light is absorbed by outer layer 42, an electron is excited from the valence band to the conduction band, creating a hole in the valence band. The electrons excited into the conduction band are captured by oxygen. The holes in the valence band react with water molecules adsorbed on the outer layer 42 to form reactive hydroxyl groups.

When the volatile organic compound is adsorbed onto outer layer 42, the hydroxyl groups attack the volatile organic compound, removing (abstrat) hydrogen atoms from the volatile organic compound. In this process, hydroxyl radicals oxidize the volatile organic compounds and produce water, carbon dioxide, and other substances.

Preferably, the photocatalyst is titanium dioxide. In one example, the titanium dioxide is Millennium titanium dioxide, Degussa P-25, or equivalent titanium dioxide. However, it should be understood that other photocatalytic materials or combinations of titanium dioxide and other metal oxides may be used. For example, the photocatalytic substance may be Fe₂O₃，ZnO，V₂O₅，SnO₂Or FeTiO₃. Alternatively, other metal oxides may be mixed with the titanium dioxide, such as Fe₂O₃、ZnO、V₂O₅、SnO₂、CuO、MnO_x、WO₃、Co₃O₄、CeO₂、ZrO₂、SiO₂、Al₂O₃、Cr₂O₃Or NiO.

Alternatively, if the outer layer 42 is a metal oxide supported titanium dioxide, the titanium dioxide of the intermediate layer 44 may be supported with a metal compound, such as WO₃，ZnO，CdS，SrTiO₃，Fe₂O₃，V₂O₅，SnO₂，FeTiO₃，PbO，Co₃O₄，NiO，CeO₂，CuO，SiO₂，Al₂O₃，Mn_xO₂，Cr₂O₃Or ZrO₂。

An intermediate layer 44 of catalytically active metal supported on titanium dioxide or a single layer of titanium dioxide photocatalyst treated with a very highly dispersed catalytically active metal is applied underneath the outer layer 42. Preferably, the titania is loaded with a group VIII noble metal, such as rhodium, ruthenium, palladium, iridium, osmium or platinum. However, the titanium dioxide may be loaded with copper, silver, rhenium, gold, or the like. More preferably, the metal is selected according to the desired substrate for the catalyst. Thus, if more than one metal is used, the metals can be dispersed into very small single metal containing nanocrystals or very small mixed metal clusters. Typically, the catalytic metal used for this function is platinum. The catalytically active metal may also be a metal alloy or an intermetallic compound.

The catalytically active metal supported on the titanium dioxide intermediate layer 44 has a high degree of reactivity with low polarity organic compounds. Platinum deposited on the surface of titanium dioxide enhances the separation of charge carriers and reduces the rate of recombination of electrons and holes. Platinum is also an excellent thermal catalyst. It is believed that platinum can further oxidize the photocatalytic oxidation intermediate to carbon dioxide and water. Low polarity organic molecules have an increased affinity for platinum. When the low-polarity organic compound is adsorbed on the platinum, the platinum retains the low-polarity organic compound on the coating layer 40 to perform hydroxyl oxidation, which oxidizes the low-polarity organic compound to carbon dioxide in the presence of oxygen.

Platinum dispersed on titanium dioxide exhibits photocatalytic properties for low impurity concentrations, e.g., less than 50 ppm. The photocatalytic oxidation rate of ozone, ethylene and butane is greater for the case where platinum is supported on titanium dioxide than when titanium dioxide is used alone. The photocatalytic oxidation rate for ozone and butane is twice that for platinum supported on titanium dioxide and between 2 and 14 times that for ethylene.

The rate of photocatalytic oxidation of ethylene depends on the humidity and ethylene concentration. Surprisingly, the photocatalytic oxidation of these impurities increases with increasing water vapor. In contrast, these impurities decrease with increasing humidity when photocatalytic oxidation is carried out with titanium dioxide alone.

Highly dispersed platinum particles on the surface of titanium dioxide can reduce the rate of recombination of electrons and holes and increase the photocatalytic activity of the coating. Preferably, the platinum particles are less than 5 nanometers in size, forming platinum islands of about 1.0 to 1.5 nanometers. The preferred platinum loading is 0.1% to 5.0%.

The intermediate layer 44 has an effective thickness and porosity. That is, the intermediate layer 44 can allow other impurities, such as carbon monoxide and ozone, that are not oxidized by the intermediate layer 44 to pass through the intermediate layer 44 and adsorb on the layer below the intermediate layer 44.

A thermally catalyzed inner layer 46 is applied to and deposited on the surface of the honeycomb 28 below the intermediate layer 44. The inner layer 46 is either gold nano-dispersed on titanium dioxide, gold on a mixed metal oxide including titanium dioxide, gold on titanium dioxide with other metal oxides supported on the surface, or gold containing mixed metal clusters.

At room temperature, the inner layer 46 oxidizes carbon monoxide to carbon dioxide. When carbon monoxide is adsorbed on the coating, the gold acts as an oxidation catalyst and lowers the energy barrier of the carbon monoxide, oxidizing the carbon monoxide to carbon dioxide in the presence of oxygen. Thus, the inner layer 46 acts as a thermal catalyst.

The oxidation of carbon monoxide occurs mainly at the peripheral interface of the gold particles. Carbon monoxide is adsorbed either on the surface or at surrounding sites of gold to form carbonyl species. Oxygen is adsorbed on the gold/titanium dioxide surface. It is believed that oxygen is adsorbed onto the surrounding interface. The carbonyl species at the peripheral location react with oxygen to form an oxy-gold-carbon monoxide complex. The complex is decomposed to produce carbon dioxide.

Preferably, the gold particles are less than 3 nanometers in size. The size of the gold particles is also critical for the activity of carbon monoxide oxidation in terms of its thermocatalytic function, depending on the gold from which the nanoparticles are formed.

The titanium dioxide may also be loaded with metal oxides to further enhance the thermal catalytic effect of the inner layer 46. Gold particles have a tendency to migrate to the surface of the titanium dioxide to form large clusters. The effectiveness of inner layer 46 may be reduced by migration of the gold particles. By supporting a metal oxide on the surface of titanium dioxide, the metal oxideThe compounds can separate the gold particles and prevent them from migrating to form clusters, thereby increasing the effectiveness of the inner layer 46. Preferably, metal oxides are used to fix the gold particles on the surface of the titanium dioxide. In one example, the metal oxide is at least WO₃、ZnO、CdS、SrTiO₃、Fe₂O₃、V₂O₅、SnO₂、FeTiO₃、PbO、Co₃O₄、NiO、CeO₂、CuO、SiO₂、Al₂O₃、Mn_xO₂、Cr₂O₃Or ZrO₂One kind of (1).

This may also include titania or titania treated with a monolayer of another metal oxide having titania modified with individual points containing one or more, but typically less than 12, atoms of another metal to be oxidized, such as iron, cobalt and rhenium, which serve to anchor the gold particle sites below 3 nanometers. The surface dopant sites surrounded by titanium dioxide or its treated metal monolayer act as surface energy potential holes that inhibit free movement of gold.

The inner layer 46 has an effective thickness and porosity. That is, inner layer 46 is capable of allowing other impurities, such as ozone, that are not oxidized by inner layer 46 to pass through inner layer 46 and adsorb on any layers below inner layer 46.

As shown in fig. 5, a thermocatalytic fourth layer 48 may be applied directly on the honeycomb 28, under the inner layer 46, in an environment where ozone concentration is high. The fourth layer 48 is a manganese oxide/titanium dioxide ozone destruction catalyst. At room temperature, the fourth layer 48 decomposes ozone to oxygen.

Manganese oxide is effective for the decomposition of ozone at ambient temperature. Manganese oxide facilitates the decomposition of ozone into adsorbed surface oxygen atoms. These oxygen atoms then combine with ozone to form adsorbed peroxides that can be desorbed as molecular oxygen. When ozone is adsorbed on manganese oxide, manganese oxide functions as a site for adsorbing free ozone by lowering the energy barrier required for ozone decomposition. Thus, in the presence of ozone alone, manganese oxide (including manganese oxide and promoter-doped manganese oxide) generates oxygen.

If a fourth layer 48 is used, the fourth layer 48 is applied to the honeycomb 28, the inner layer 46 is applied to the fourth layer 48, the middle layer 44 is applied to the inner layer 46, and the outer layer 42 is applied to the middle layer 44.

After passing through the honeycomb 28, the purified air exits the air purifier through an outlet 36. The wall 38 of the air purification system 20 is preferably lined with a reflective material 42. The reflective material 42 reflects ultraviolet light onto the surfaces of the open channels 30 of the honeycomb 28.

In addition, detailed descriptions of the coating method are disclosed in the co-pending patent application serial No. 10/449,752 entitled "tungsten oxide/titanium dioxide photocatalyst for improving indoor air quality", filed on 30/5/2003, in the co-pending patent application serial No. 10/464,942 entitled "bifunctional manganese oxide/titanium dioxide photocatalyst/thermal catalyst for improving indoor air quality", filed on 19/6/2003, and in the co-pending patent application serial No. 10/465,025 entitled "bifunctional gold/titanium dioxide photocatalyst/thermal catalyst for improving indoor air quality", filed on 19/6/2003, the disclosures of which are incorporated herein by reference in their entireties. See also pending patent application serial No. 10/64,942 for information on bifunctional manganese oxide/titanium dioxide photocatalysts/thermocatalysts. See also pending patent application serial No. 10/465,024 for information on bifunctional gold/titanium dioxide photocatalysts/thermocatalysts.

Fig. 6 illustrates another example of an air purification system 50. In this example, air flows first through the first honeycomb 52, through the second honeycomb 54, and then through the third honeycomb 56 having a manganese oxide/titanium dioxide coating. One of the first honeycomb 52 and the second honeycomb 54 has a titanium dioxide coating or a metal oxide doped titanium dioxide coating. The metal oxide may be WO₃、ZnO、SrTiO₃、Fe₂O₃、V₂O₅、SnO₂、FeTiO₃、PbO、Co₃O₄、NiO、CeO₂、CuO、SiO₂、Al₂O₃、Mn_xO₂、Cr₂O₃Or ZrO₂. The metal oxide doped titanium dioxide coating oxidizes impurities, such as volatile organic compounds and semi-volatile organic compounds, to water and carbon dioxide. The other of the first honeycomb 52 and the second honeycomb 54 has a gold/titanium dioxide coating for oxidizing carbon monoxide to water and carbon dioxide. The manganese oxide/titanium dioxide coating decomposes ozone into oxygen and water.

By using a honeycomb with a metal oxide doped titanium dioxide coating, a honeycomb with a gold/titanium dioxide coating, and a third honeycomb 54 with a manganese oxide/titanium dioxide coating, carbon monoxide, ozone, volatile organic compounds, and semi-volatile organic compounds can be oxidized and destroyed. Thus, the air purification system 50 including the metal oxide doped titanium dioxide coated honeycomb, the gold/titanium dioxide coated honeycomb, and the manganese oxide/titanium dioxide coated honeycomb 60 can function the same as a layered coating having the manganese oxide/titanium dioxide layer 48, the gold/titanium dioxide layer 46, and the metal oxide/titanium dioxide layer 42.

It should be understood that the honeycombs 52, 54, and 56 may be present in any order. However, ozone is a strong oxidant and can promote the photocatalytic oxidation process. Therefore, it is preferred that the air eventually flow through the metal oxide doped titanium dioxide honeycomb 56. Alternatively, the air purification system 50 includes more than one first cell structures 52, second cell structures 54, and third cell structures 56.

While a honeycomb 28 has been illustrated and described, it should be understood that the photocatalytic/thermocatalytic coating 40 may be applied on any structure. The voids in the honeycomb 28 are generally hexagonal in shape, but it should be understood that other void shapes may be used. When impurities adsorb onto the photocatalytic/thermocatalytic coating 40 of the structure in the presence of a light source, the impurities are oxidized into water, carbon dioxide, and other substances.

The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. However, since a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (24)

1. A purification system, comprising:

a substrate; and

a layered catalytic coating applied on the substrate, the layered catalytic coating comprising a photocatalytic first coating, a photocatalytic metal-supported metal compound second coating, and a thermocatalytic third coating;

wherein the thermocatalytic third coating comprises gold particles on a metal oxide, the metal oxide being one of titanium dioxide, a mixed metal oxide comprising titanium dioxide and titanium dioxide loaded with a second metal oxide, and the gold particles having a size below 3 nanometers.

2. The purification system as recited in claim 1 wherein said first coating is one of titanium dioxide and metal compound-supported titanium dioxide.

3. The purification system as recited in claim 2 wherein said first coating is a titanium dioxide coating supported by a metal compound, said metal compound being WO₃、ZnO、CdS、SrTiO₃、Fe₂O₃、V₂O₅、SnO₂、FeTiO₃、PbO、Co₃O₄、NiO、CeO₂、CuO、SiO₂、Al₂O₃、Mn_xO₂、Cr₂O₃And ZrO₂At least one of (1).

4. The purification system as recited in claim 3 wherein said metal compound is FeTiO₃、PbO、CeO₂And Al₂O₃At least one of (1).

5. The purification system as recited in claim 1 wherein said first coating has a thickness of less than 2 microns.

6. The purification system as recited in claim 1 wherein said second coating is a catalytically active metal supported on titanium dioxide.

7. The purification system as recited in claim 6 wherein said catalytically active metal is one of a metal alloy and an intermetallic supported on said titanium dioxide.

8. The purification system as recited in claim 6 wherein said catalytically active metal is a group VIII noble metal.

9. The purification system as recited in claim 8 wherein said group VIII noble metal is one of rhodium, ruthenium, palladium, iridium, osmium and platinum.

10. The purification system as recited in claim 6 wherein said catalytically active metal is one of silver and rhenium.

11. The purification system as recited in claim 1 wherein said second coating oxidizes low polarity organic molecules.

12. The purification system as recited in claim 1 wherein said third coating oxidizes carbon monoxide.

13. The purification system as recited in claim 1 wherein said third coating is applied over said substrate, said second coating is applied over said third coating, and said first coating is applied over said second coating.

14. The purification system as recited in claim 1 further comprising a manganese oxide/metal oxide layer applied on said substrate and said third coating is applied on said manganese oxide/metal oxide layer, said second coating is applied on said third coating and said first coating is applied on said second coating.

15. The purification system as recited in claim 14 wherein said manganese oxide/metal oxide layer is manganese oxide and promoter doped manganese oxide/titanium dioxide.

16. The purification system as recited in claim 14 wherein the manganese oxide/metal oxide layer decomposes ozone.

17. The purification system as recited in claim 1 further comprising a light source for activating said layered catalytic coating and said layered catalytic coating oxidizes contaminants that adsorb onto said layered catalytic coating when activated by said light source.

18. The purification system as recited in claim 17 wherein said light source is an ultraviolet light source.

19. The purification system as recited in claim 17 wherein photons from said light source are absorbed by said layered catalytic coating to form reactive hydroxyl radicals, said reactive hydroxyl radicals oxidizing said impurities in the presence of oxygen and water.

20. The purification system as recited in claim 17 wherein said impurity is at least one of a volatile organic compound and a semi-volatile organic compound that is at least one of an aldehyde, a ketone, an alcohol, an aromatic compound, an alkene, and an alkane.

21. The purification system as recited in claim 1 wherein said first coating, said second coating and said third coating are porous.

22. A fluid purification system, comprising:

a vessel having an inlet and an outlet;

a porous substrate within the container;

means for drawing fluid into the container through the inlet, flowing the fluid through the porous substrate, and discharging the fluid from the container through the outlet;

a layered catalytic coating applied on the substrate, the layered catalytic coating comprising a first coating of a photocatalytic metal oxide, a second coating of a photocatalytic noble metal-supported metal oxide, and a third coating of a thermocatalytic metal oxide, and the third coating being gold particles on the metal oxide, and the gold particles having a size below 3 nanometers; and

an ultraviolet light source for activating the catalytic coating, photons from the ultraviolet light source being absorbed by the layered catalytic coating to form reactive hydroxyl radicals that, when activated by the ultraviolet light source, oxidize impurities in the fluid adsorbed onto the layered catalytic coating in the presence of water and oxygen.

23. The fluid purification system as recited in claim 22 wherein said fluid is air.

24. A method of decontamination, comprising the steps of:

applying a layered catalytic coating applied on a substrate, the layered catalytic coating comprising a photocatalytic first coating, a photocatalytic metal-supported metal compound second coating, and a thermocatalytic third coating, the third coating being gold particles on a metal oxide, and the gold particles having a size below 3 nanometers; and

activating the layered catalytic coating;

forming reactive hydroxyl groups;

adsorbing impurities onto the layered catalytic coating;

oxidizing the impurities with the hydroxyl groups;

reducing the oxidation energy barrier of carbon monoxide in the impurities with the gold particles of the third coating; and

the carbon monoxide is then oxidized.