WO2021202522A1

WO2021202522A1 - Ultraviolet activated photocatalytic materials for decomposing a chemical compound

Info

Publication number: WO2021202522A1
Application number: PCT/US2021/024875
Authority: WO
Inventors: Ekambaram Sambandan; Bin Zhang; Takuya Fukumura; Satomi GOTO
Original assignee: Nitto Denko Corporation
Priority date: 2020-03-30
Filing date: 2021-03-30
Publication date: 2021-10-07
Also published as: TW202144074A

Abstract

Disclosed herein are photocatalytic elements comprising: a first layer comprising a first photocatalytic material; and a second layer comprising a second photocatalytic material; wherein the second layer is disposed on the first layer. Photocatalytic devices incorporating the photocatalytic elements, and method of making and using the photocatalytic elements are also described herein. The first layer may comprise titania or Pt/K2Ti6013 or alkali metal-containing titanates or mixed oxides of tungsten and titanium.

Description

ULTRAVIOLET ACTIVATED PHOTOCATALYTIC MATERIALS FOR DECOMPOSING A

CHEMICAL COMPOUND

Inventors: Ekambaram Sambandan, Bin Zhang, Takuya Fukumura and Satomi Goto

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 63/001,852, filed March 30, 2020, which is incorporated by reference herein in its entirety.

FIELD

The current disclosure relates to n-type semiconductor material constructs useful in ultraviolet activated photocatalytic applications.

BACKGROUND

Titanium dioxide (T O ), and other titanium-based semiconductors have photocatalytic properties. The energy required to activate these materials is usually in the ultraviolet region of the electromagnetic spectrum. Ultraviolet activated photocatalytic materials, such as K T O , can have higher redox potentials than that of volatile organic compounds (VOC). Thus, activated photocatalysts can enable the oxidative decomposition of VOCs, such as formaldehyde, to CO and H O. It is believed that this is due to wider band gaps and/or deeper valance band positions of the photocatalytic materials as compared to the VOC materials. Many titanium-based photocatalytic materials, however, do not show the desired level of photocatalytic activity necessary for the complete oxidative decomposition of VOCs. Furthermore, many titanium-based photocatalysts have the disadvantage of formation of side products during photocatalysis, which is believed to be responsible for the incomplete mineralization of HCHO by titanium-based photocatalysts. Due to these shortcomings, these materials have not been widely explored for the removal of trace quantity of VOCs in the treatment of air.

There is also a need for photocatalytic materials that have improved performance, such as for the decomposition of volatile organic compounds.

SUMMARY

This disclosure relates to a photocatalytic element comprising: a first layer comprising a first photocatalytic material; and a second layer comprising a second photocatalytic material; wherein the second layer is disposed on the first layer.

Some embodiments include a photocatalytic device comprising the photocatalytic element described herein and a source of electromagnetic radiation, wherein the first layer is disposed between the source of electromagnetic radiation and the second layer. Some embodiments include a method of decomposing a chemical compound, such as a volatile organic chemical, comprising exposing the volatile organic chemical to the photocatalytic element described herein in the presence of an electromagnetic radiation source, wherein electromagnetic radiation from the electromagnetic radiation source has contact with the first layer.

Some embodiments include a method of killing or inhibiting the growth of a virus or bacteria, comprising exposing the virus or bacteria to the photocatalytic element described herein in the presence of an electromagnetic radiation source, wherein electromagnetic radiation from the electromagnetic radiation source has contact with the first layer.

Some embodiments include a method of preparing a photocatalytic element comprising: depositing a second layer comprising a second photocatalytic material upon a substrate, and depositing a first layer comprising a first photocatalytic material upon the second layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing an embodiment described herein.

FIG. 2 is a schematic showing the relationship between conduction energy bands with valence energy bands for various materials.

FIG. 2A is a schematic showing the relationship between conduction energy bands with valence energy bands for various materials.

DETAILED DESCRIPTION

Described herein are photocatalytic materials comprising mixtures of n-type semiconductors that are activated by ultraviolet light. In some embodiments, the photocatalytic materials described herein are useful for having and/or enhancing anti-bacterial activity, anti-viral activity, decomposition of volatile organic compounds (VOC), and/or dye discoloration in aqueous solutions.

Typically, a photocatalytic element comprises a first layer comprising a photocatalytic material, and a second layer comprising a photocatalytic material disposed upon the first layer. The photocatalytic element may be incorporated into a photocatalytic device so that the first layer is disposed between a light source and the second layer. The photocatalytic element or photocatalytic device may further comprise a ceramic support, upon which the second layer is disposed or deposited.

In some embodiments, a photocatalytic may have only a single layer having the composition described herein for the first layer or the second layer.

The photocatalytic element may be incorporated into a photocatalytic device, e.g. for decomposition of VOC, killing or inhibiting growth of bacterial or viruses, or discoloring dyes. This type of device may comprise a source of UV radiation to provide electromagnetic radiation, such as UV or visible radiation to the photocatalytic element described herein. In some embodiments, the first layer of photocatalytic material is in optical communication with the second layer of photocatalytic material. The first layer of photocatalytic material may, for example, be disposed between the source of UV radiation and the second layer of photocatalytic material. In this type of configuration, the first layer of photocatalytic material may be disposed upon the second layer of photocatalytic material. In some embodiments, the UV radiation generated by the source of UV radiation is optically communicated through the first layer of photocatalytic material to affect the second layer of photocatalytic material. For example, if platinum containing photocatalytic material is placed underneath the transition metal oxide layer, the platinum containing photocatalytic material may extract the electrons from the top layer. Platinum may also reduce UV scattering of a top layer (e.g. the first layer) under which the platinum is placed. It is believed that holes will remain in the top layer and electrons will come to the bottom layer and be involved in the decrease in the recombination of the charge carrier.

For example, a photocatalytic device may include, as shown in FIG. 1, photocatalytic element, such as photocatalytic element 10. In this embodiment, photocatalytic element 10 comprises a first layer 12, which comprises a first photocatalytic material, and a second layer 14, which comprises a second photocatalytic material. A source of electromagnetic radiation (e.g. UV, IR, or visible light), such as radiation source 16, is positioned so first layer 12 is between light source 16 and second layer 14. In this way, electromagnetic radiation 18 will contact first layer 12, but may or may not come into contact with second layer 14. In some embodiments, photocatalytic element 10 may further comprise a ceramic support (not shown), upon which the second layer is disposed or deposited.

Generally, the first layer comprises a first photocatalytic material. The first photocatalytic material may include a semiconductor, such as a metal oxide, including a transition metal oxide, and/or an n-type semiconductor. In some embodiments, the first photocatalytic material comprises a plural phase n-type semiconductor. In some embodiments, the first photocatalytic material comprises a single phase n-type semiconductor. The first photocatalytic material may be present in any suitable amount in the first layer, such as at least about 75%, about 75-90%, about 80-95%, about 90-95%, about 90-95%, or about 95-100% of the first layer. Optionally, the first layer may comprise multiple thinner sublayers. For example, the same material may be dip coated plural times providing plural distinct layers of the respective materials.

In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, T O , such as a plural phase T O comprising, e.g. an anatase phase and a rutile phase. In some embodiments In some embodiments, the anatase phase may be about 2.5% to about 97.5%, about 2.5-5%, about 5-10%, about 10-15%, about 15-20%, about 20-25%, about 25-30%, about 30-35%, about 35-40%, about 40-45%, about 45-50%, about 50-55%, about 55-60%, about 60- 65%, about 65-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, about 95-97.5%, or about 83% of the total weight of the T O . In some embodiments, the rutile phase may be about 2.5% to about 97.5%, about 2.5-5%, about 5-10%, about 10-15%, about 15-20%, about 20- 25%, about 25-30%, about 30-35%, about 35-40%, about 40-45%, about 45-50%, about 50-55%, about 55-60%, about 60-65%, about 65-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, about 95-97.5%, or about 17% of the total weight of the T O . In some embodiments, the T O is 80-90% anatase phase and 20-10% rutile phase. In some embodiments, the T O is 83% anatase phase and 17% rutile phase (e.g. P25, sold by Evonik (Parsippany, NJ, USA)). In some embodiments, the titanium oxide may be an anatase titanium oxide only.

In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, substantially only anatase phase T O . For example, for some first photocatalytic materials, the anatase phase is greater than about 95 wt%, greater than about 96 wt%, greater than about 97 wt%, greater than about 97.5 wt%, greater than about 98 wt%, greater than about 98.5 wt%, or greater than about 99.0 wt% of the total weight of the first photocatalytic material. An example of an anatase T O is that sold under the brand name ST-01 by Ishihara Sangyo Kaisha Ltd (Japan). In some embodiments, the anatase phase may be combustion synthesized T O .

In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, Pt/K TieOi . In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, WO₃. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, LhZnThOg. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, KNaTieOi₃. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, IS^TieO^. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, KTio.₅W_1.5O₆. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, 3 mol% WO₃/97 mol% T1O₂. In some embodiments, the first layer, or first photocatalytic material, comprises, consists essentially of, or consists of, ZnO. In some embodiments, the first layer, or first photocatalytic material, comprises a hexatitanate, a septatitanate or an octatitanate.

Generally, the second layer comprises a second photocatalytic material. The second photocatalytic material may include a semiconductor, such as an n-type semiconductor.

A conduction band is a range of electron energies high enough to free an electron from binding with its atom to move freely within the atomic lattice of the material as a "delocalized electron" (see FIGS. 2 and 2A). In semiconductors, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature. The valence electrons are substantially bound to individual atoms, as opposed to conduction electrons (found in semiconductors), which may move more freely within the atomic lattice of the material. On a graph of the electronic band structure of a material, the valence band is generally located below the conduction band, separated from it in insulators and semiconductors by a band gap. In some materials, such as conductors, the conduction band has substantially no discernible energy gap separating it from the valence band. The conduction and valence bands may actually overlap, for example, when the valence band level energy is higher or less negative than the conduction band level energy.

Various materials may be classified by their band gap, e.g., classified by the difference in energy between the valence band and conduction band. In non-conductors (e.g., insulators), the conduction band is much higher energy than the valence band, so it takes too much energy to displace the valence electrons to effectively conduct electricity. These insulators are said to have a non-zero band gap. In conductors, such as metals, that have many free electrons under normal circumstances, the conduction band overlaps with the valence band - there is no band gap - so it takes very little or no additional applied energy to displace the valence electrons. In semiconductors, the band gap is small, on the order of 200 nm to 1000 nm (on the order of 1.24 eV to 6.2 eV). This is believed to be the reason that it takes relatively little energy (in the form of heat or light) to make semiconductors' electrons move from the valence band to another energy level and conduct electricity; hence, the name semiconductor. In some embodiments, the second photocatalytic material has a band gap of at least about 2.8 eV.

The photocatalytic materials described herein may be used for photochemical decomposition of a volatile organic compound. In the oxidation-reduction reaction of formaldehyde and oxygen, the oxidation of formaldehyde is coupled with the reduction of O . The oxidation potential of formaldehyde is about 2.85 eV. The reduction potential of O is about -0.05 eV. In some embodiments, as a result, a sufficiently large band gap, e.g., 2.85 eV and 0.05 eV, which is about 2.90 eV, would be beneficial in achieving the aforementioned reaction. In addition, the relative positioning of the photocatalytic material's band gap is an important consideration. In some embodiments, the depth of the band gap should be relatively close to that of

can be about at least about +2.85 eV. It is observed that noble metal doping of the metal titanate affects both the conductive band and the valence band of these materials. It is believed that the selection of photocatalytic material that takes these considerations into account provides an improved photocatalytic activity exhibited by the materials, e.g., noble metal doped and/or loaded versions of

may have improved photocatalytic activity as compared to undoped

In some embodiments, the second photocatalytic material may comprise a hexatitanate, a septatitanate and/or an octatitanate. The second photocatalytic material may be a doped or loaded semiconductor material, such as a doped or loaded metal oxide. As used herein, the terms "doped" or "dopant" refer to elements that are incorporated into the crystal lattice of the compound, for example as substituted within defined positions within the crystal lattice or otherwise interstitially included within the crystal. The term "loaded" or "loadant" refers to the non-valent combination, e.g., a physical mixture and/or adjacent disposition of a first material, e.g., the n-type semiconductor material, and a second material, e.g., with co-catalytic materials such as CuO. In some embodiments, the second photocatalytic material may comprise a noble metal dopant.

The second photocatalytic material may comprise a mixed titanate, including a compound that comprises Ti, O and at least another element; e.g., an alkali metal ion, a rare-earth metal ion, niobium, or tantalum. Some metal ions include Ta, Nb, K, Ca, Cu, Mg, or La. In some embodiments, the mixed titanate may be, as non-limiting examples, K₂TIbO_ΐ3, K₄NbeOi₇, K2La2Ti30io and/or M2Ti_n02_n+i where M may be an alkali metal ion (e.g., K, Na, Li, Rb, etc.), and n may be greater than or equal to 5.5, e.g., n = 6, 7, and/or 8. In some embodiments, M may be H. In some examples, M may be a tetraalkylammonium cation, e.g., tetrabutylammonium (TBA). In some embodiments, the mixed titanate has a band gap greater than 2.8 eV. It is believed that a band gap of at least 2.8 eV may provide sufficient energy for oxidation of VOCs (e.g. formaldehyde). When the material has at least a 2.8 eV optical band gap, a charge carrier forms and enables oxidation of the VOC, e.g., formaldehyde. In some embodiments, the mixed titanate may be combustion synthesized. In some examples, a mixed titanate may also be called a metal titanate. In some embodiments, the mixed titanate may be solid state synthesized. In some embodiments, the mixed titanate may be hydrothermally synthesized.

In some embodiments, the mixed titanate of the second photocatalytic material may be doped with a noble metal. In some embodiments, the mixed titanate of the second photocatalytic material may be loaded with a noble metal. In some embodiments, the second photocatalytic material is a metal titanate doped with a noble metal. In some embodiments, the metal titanate may be K2Ti_nO₍2_n+i). In some embodiments, the metal titanate comprises I^TUOg or K2T16O13, and the noble metal comprises silver, gold or platinum. In some embodiments, the metal titanate is

and the noble metal is platinum. In some embodiments, the metal titanate is K2T16O13, and the noble metal is platinum. In some embodiments, the weight ratio of the noble metal may be about 0.001 wt% to about 1.0 wt% of the total weight of the second n-type semiconductor. In some embodiments, the weight ratio of the noble metal (such as gold, silver, or platinum) may be about 0.001-0.005 wt%, about 0.005-0.01 wt%, about 0.01-0.015 wt%, about 0.015-0.02 wt%, about 0.02-0.025 wt%, about 0.025-0.03 wt%, about 0.03-0.035 wt%, about 0.035-0.04 wt%, about 0.04-0.045 wt%, about 0.045- 0.05 wt%, about 0.05-0.055 wt%, about 0.055-0.06 wt%, about 0.06-0.065 wt%, about 0.065-0.07 wt%, about 0.07-0.075 wt%, about 0.075-0.08 wt%, about 0.08-0.085 wt%, about 0.085-0.09 wt%, about 0.09-0.095 wt%, about 0.095-0.01 wt%, about 0.1-0.15 wt%, about 0.15-0.2 wt%, about 0.2- 0.25 wt%, about 0.25-0.3 wt%, about 0.3-0.35 wt%, about 0.35-0.4 wt%, about 0.4-0.45 wt%, about 0.45-0.5 wt%, about 0.5-0.55 wt%, about 0.55-0.6 wt%, about 0.6-0.65 wt%, about 0.65-0.7 wt%, about 0.7-0.75 wt%, about 0.75-0.8 wt%, about 0.8-0.85 wt%, about 0.85-0.9 wt%, about 0.9-0.95 wt%, about 0.95-1 wt%, about 0.001-0.1 wt%, about 0.1-0.2 wt%, about 0.2-0.3 wt%, about 0.3-0.4 wt%, about 0.4-0.5 wt%, about 0.5-0.6 wt%, about 0.6-0.7 wt%, about 0.7-0.8 wt%, about 0.8-0.9 wt%, about 0.9-1 wt%, about 0.001-0.3 wt%, about 0.3-0.6 wt%, about 0.6-1 wt%, about 0.03 wt%, about 0.075 wt%, about 0.15 wt%, or about 0.35 wt% of the total weight of the second n-type semiconductor.

In some embodiments, the second photocatalytic material may comprise a noble metal. In some embodiments, the noble metal may be rhodium, ruthenium, palladium, silver, osmium, platinum or gold. In some embodiments the noble metal may be silver, gold or platinum. In some embodiments the noble metal may be platinum. Nanosized noble metals (e.g. diameters of around 1-20 nm or 5-15 nm) such as platinum may have semiconductor properties, such as larger band gaps (e.g. at least 2.8 eV), and may absorb in the UV-visible range. In some embodiments, the noble metal may be about 0.001 wt% to about 1.0 wt% of the total weight of the second layer, the second photocatalytic material, or the photocatalytic element. In some embodiments, the weight ratio of the noble metal may be about 0.001-0.005 wt%, about 0.005-0.01 wt%, about 0.01-0.015 wt%, about 0.015-0.02 wt%, about 0.02-0.025 wt%, about 0.025-0.03 wt%, about 0.03-0.035 wt%, about 0.035- 0.04 wt%, about 0.04-0.045 wt%, about 0.045-0.05 wt%, about 0.05-0.055 wt%, about 0.055-0.06 wt%, about 0.06-0.065 wt%, about 0.065-0.07 wt%, about 0.07-0.075 wt%, about 0.075-0.08 wt%, about 0.08-0.085 wt%, about 0.085-0.09 wt%, about 0.09-0.095 wt%, about 0.095-0.01 wt%, about 0.1-0.15 wt%, about 0.15-0.2 wt%, about 0.2-0.25 wt%, about 0.25-0.3 wt%, about 0.3-0.35 wt%, about 0.35-0.4 wt%, about 0.4-0.45 wt%, about 0.45-0.5 wt%, about 0.5-0.55 wt%, about 0.55-0.6 wt%, about 0.6-0.65 wt%, about 0.65-0.7 wt%, about 0.7-0.75 wt%, about 0.75-0.8 wt%, about 0.8- 0.85 wt%, about 0.85-0.9 wt%, about 0.9-0.95 wt%, about 0.95-1 wt%, about 0.001-0.1 wt%, about 0.1-0.2 wt%, about 0.2-0.3 wt%, about 0.3-0.4 wt%, about 0.4-0.5 wt%, about 0.5-0.6 wt%, about 0.6- 0.7 wt%, about 0.7-0.8 wt%, about 0.8-0.9 wt%, about 0.9-1 wt%, about 0.001-0.3 wt%, about 0.3-0.6 wt%, about 0.6-1 wt%, about 0.03 wt%, about 0.075 wt%, about 0.15 wt%, or about 0.35 wt% of the total weight of the second layer, the second photocatalytic material, or the photocatalytic element.

Optionally, the second layer may comprise multiple thinner sublayers. For example, the same material may be dip coated plural times providing plural distinct layers of the respective materials. In some embodiments, the second layer, or second photocatalytic layer, comprises, consists essentially of, or consists of, Pt. In some embodiments, the second layer, or second photocatalytic layer, comprises, consists essentially of, or consists of, Pt/TiC> . In some embodiments, the second layer, or second photocatalytic coating may comprise a mixture of rutile titanium oxide and an anatase titanium oxide.

In some embodiments, the second layer, or second photocatalytic material, comprises, consists essentially of, or consists of, anatase phase T O . In some embodiments, for example, the anatase phase is greater than about 95 wt%, greater than about 96 wt%, greater than about 97 wt%, greater than about 97.5 wt%, greater than about 98 wt%, greater than about 98.5 wt%, or greater than 99.0 wt% of the total weight, up to about 100%, of the second photocatalytic material. An example of an anatase T O is that sold under the brand name ST-01 by Ishihara Sangyo Kaisha Ltd (Japan). In some embodiments, the anatase phase may be combustion synthesized T O .

The photocatalytic layer may comprise a support, such as a ceramic support. For example, the second layer may be deposited upon such a support. In some embodiments, the ceramic support may have a honeycombed structure, e.g., plural passageways defined therethrough, for facilitating a high flowthrough rate. In some embodiments, the ceramic support may comprise alumina, silica, or a mixture thereof (e.g. mullite). In some embodiments, the ceramic support may comprise about 25 wt%, about 45 wt%, about 55 wt%, about 65 wt%, about 75 wt% AI O , or any value in a range bounded by any of these values, e.g., 55 wt%. In some embodiments, the ceramic support may comprise about 10 wt%, about 25 wt%, about 35 wt%, about 45 wt%, about 55 wt% S O , or any value in a range bounded by any of these values, e.g., 38 wt%. In some embodiments, the ceramic support may comprise about 1 wt%, about 3 wt%, about 5 wt%, about 7 wt%, about 10 wt% MgO, or any value in a range bounded by any of these values, e.g., 7 wt%. In some embodiments, a plurality of communicating passageways may run through the ceramic support.

In some embodiments, the ceramic support comprises, consists essentially of, or consists of, AI O (e.g., about 50-60% or about 55%), SiC (e.g., about 35-40% or about 38%), and MgO (e.g., about 5-10% or about 7%).

The photocatalytic element or photocatalytic device may be characterized by its ability to degrade a volatile organic compound, such as formaldehyde, in the present of a light source, such as ultraviolet light. For example, formaldehyde degradation may be determined by measuring the decrease or percentage loss of the initial formaldehyde concentration, e.g., ranging from 0% loss to 100% loss over time, or by measuring the formation of carbon dioxide (CO ), or percentage increase of the concentration of CO , e.g., ranging from 0% to 100% formation of CO (based on the amount of carbon in the initial formaldehyde concentration) over time. Degradation of the volatile organic compound (e.g. formaldehyde) may be determined, e.g. for a period of about 1 minute to 10 hours, e.g., 30 minutes, 1 h, or 2 h. During the measurement, the photocatalytic material may be exposed to ultraviolet light, such as a UV LED of single wavelength 365 nm having, e.g. 10 mW/cm² power, or e.g. Loctite UV of broad wavelength between 300 and 420 nm having, e.g. 15 mW/cm² of power. In some embodiments, the degradation is at least about 50%, about 50-55%, about 55-60%, about 60- 65%, about 65-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, about 95-100%, or about 100% of the initial amount of organic compound, such as formaldehyde, after exposure to the UV activated heterogeneous material. In some embodiments, the formation of CO is at least about 10%, e.g., about 10-100%, about 10-50%, about 50-55%, about 55-60%, about 60-65%, about 65-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, about 95- 100%, or about 100% of the initial amount of the organic compound, such as formaldehyde, after exposure to the UV activated heterogeneous material.

The photocatalytic element or photocatalytic device may be used in a method of decomposing a volatile organic chemical such as a hydrocarbon, e.g. a Ci-₆ alkyl, including methane, ethane, propane, butane, etc., a Ci-₆ alkene, a Ci-₆ alkyne, an aldehyde, e.g. a Ci-₆ aldehyde, including formaldehyde, a thiol including ethyl mercaptan, methyl mercaptan, dimethyl sulfide, diethylsulfide, dimethyl disulfide, diethyl disulfide, carbon disulfide, etc., an amine including a Ci-₆ amine, a ketone such as a C ketone including acetone, a carboxylic acid such as a Ci-₆ carboxylic acid, including formic acid, acetic acid, butyric acid, etc., a Ci-₆ ester, a Ci-₆ ether, etc. This method includes exposing the volatile organic chemical to the photocatalytic element, e.g. the first layer or second layer of the photocatalytic element, in the presence of electromagnetic radiation, e.g. a source of IR, UV, and/or visible radiation. In some embodiments, the electromagnetic radiation, such as UV radiation, comes into contact with the first layer. For example, the first layer may be positioned between the source of electromagnetic radiation, such as UV radiation, and the second layer.

The electromagnetic radiation, such as UV radiation, to which the volatile organic compound and the photocatalytic element (e.g. the first layer and/or the second layer) are exposed, may be provided by a source (such as an LED source, e.g. a UV LED) that has a power of about 0.1-50 mW/cm², about 0.1-5 mW/cm², about 5-10 mW/cm², about 10-20 mW/cm², about 20-30 mW/cm², about 30-40 mW/cm², about, 40-50 mW/cm², about 6-8 mW/cm², or about 7 mW/cm², or an equivalent amount of UV radiation from another source such as the sun. The volatile organic compound may be exposed to the electromagnetic radiation, such as UV radiation, for any suitable amount of time to decompose the volatile organic compound, such as about 1 min to 24 hours, about 1-5 min, about 5-30 min, about 30-60 min, about 60-90 min, about 90-120 min, about 120-150 min, about 150-180 min, about 180- 210 min, about 210-240 min, about 240-270 min, about 270-300 min, about 300-330 min, about 330- 360 min, about 360-390 min, about 390-420 min, about 420-450 min, about 450-480 min, about 480- 510 min, about 510-540 min, about 540-570 min, about 570-600 min, about 5-12 hours, about 12-18 hours, about 18-24 hours, or longer.

In some embodiments the electromagnetic radiation is in a wavelength range of about 300-

420 nm.

In some embodiments, the method (e.g. exposing the volatile organic compound to the photocatalytic element in the presence of electromagnetic radiation such as UV radiation) is effective in degrading at least about 10%, about 10-50%, about 50-55%, about 55-60%, about 60-65%, about 65-70%, about 70-75%, about 75-80%, about 80-85%, about 85-90%, about 90-95%, about 95-100%, or about 100% of the initial amount of a volatile organic compound.

In some embodiments, the photocatalytic element or device described herein may be anti bacterial (light and dark); anti-viral; can decompose volatile organic compounds (VOC); and/or can discolor food additive dyes. Suitable non-limiting examples of food additive dyes include Natural Blue Colored powder (Color Maker, Anaheim, California, USA) and/or FD&C blue No. 2 synthetic food additive dye food additive dye (Synthetic blue colored powder, Chromatech, Inc., Michigan, USA).

The photocatalytic element or device described herein may also increase the performance (level of effectiveness) relative to other photocatalytic compositions.

Those of ordinary skill in the art recognize ways to determine whether a heterogeneous material discolors food additives or dyes. One example of determining the discoloration of food additive dyes can be by measuring the decrease or percentage loss of the initial amount of food dye additive over time. In one example, the food additive can be a natural anthocyanin food additive dye or an FDC food additive dye. In some embodiments, the discoloration of food dye additives can be from 0% to 60% after 5 hours under a blue LED emitting at 455 nm with 45 mW/cm² power. In some embodiments, the degradation is at least 25%, at least 30%, at least 40%, at least 50%, and/or at least 60% of the initial amount of the natural anthocyanin food additive dye after exposure to the heterogeneous material.

Those of ordinary skill in the art recognize ways to determine whether a heterogeneous photocatalytic material maintains higher activity, e.g., the better performance of the heterogeneous material. The photocatalytic decomposition of formaldehyde was performed employing photocatalyst which had a top layer comprising T O (P25) and a bottom layer comprising Pt of the present disclosure (Table 2)(e.g., 12.78% at 15 min and 36.07% at 60 min), while substantially higher activity was observed when employing known photocatalyst P25 (see Table 2).

The following embodiments are contemplated by the inventors:

Embodiment 1. A photocatalytic element comprising: A first layer of a photocatalytic material; and A second layer of a photocatalytic material, wherein the first material is interposed between a radiation source and the second layer and the second material has band gap of at least 2.8 eV.

Embodiment 2. The photocatalytic element of embodiment 1, wherein the first photocatalytic material comprises a metal oxide.

Embodiment s. The photocatalytic element of embodiment 1, wherein the first photocatalytic material comprises at least 75% wt of the first layer.

Embodiment 4. The photocatalytic element of embodiment 2, wherein the first photocatalytic material comprises titanium oxide.

Embodiment 5. The photocatalytic element of embodiment 2, wherein the titanium oxide is a mixture of a rutile titanium oxide and anatase titanium oxide.

Embodiment 6. The photocatalytic element of embodiment 2, wherein the titanium oxides comprise a single phase anatase titanium oxide.

Embodiment ?. The photocatalytic element of embodiment 1, wherein the second photocatalytic material comprises a hexatitanate, a septatitanate or a octatitanate.

Embodiment s. The photocatalytic element of embodiment 1, wherein the second photocatalytic material comprises a noble metal dopant or loading.

Embodiment s. The photocatalytic element of embodiment 1, wherein the second photocatalytic material comprises a noble metal loadant.

Embodiment 10. The photocatalytic element of embodiment 1, further comprising a ceramic support material.

Embodiment 11. A method for making a photocatalytic element comprising: providing a honeycombed ceramic substrate; creating a first catalytic coating upon the ceramic substrate, the first catalytic coating having a band gap of at least 2.8 eV; and creating a second catalytic coating upon the first catalytic coating, the first catalytic layer comprising at least 75 wt% of a metal oxide.

Embodiment 12. The method of embodiment 11, wherein the first photocatalytic coating comprises a hexatitanate, a septatitanate or an octatitanate.

Embodiment 13. The method of embodiment 11, wherein the second photocatalytic coating comprises a mixture of rutile titanium oxide and an anatase titanium oxide.

Embodiment 14. A photocatalytic element made according to embodiments 11-13. Embodiment 15. A method of decomposing a chemical compound, comprising exposing the chemical compound to a photocatalytic material of embodiment in the presence of ultraviolet radiation.

Embodiment 16. A photocatalytic element for positioning before a radiation source, the material comprising:

A first layer of a first photocatalytic material; and

A second layer of a second photocatalytic material, wherein the first layer of first photocatalytic material is interposed between a radiation source and the second layer of second photocatalytic material, and the second material has band gap of at least 2.8 eV, and the second material can be noble metal, and the photocatalytic element can be a multilayer structure.

Embodiment 17. The photocatalytic element of embodiment 16, wherein the first photocatalytic material comprises at least 75% wt of the first layer.

Embodiment 18. The photocatalytic element of embodiment 16, wherein the first photocatalytic material comprises a metal oxide.

Embodiment 19. The photocatalytic element of embodiment 18, wherein the first photocatalytic material comprises titanium oxide.

Embodiment 20. The photocatalytic element of embodiment 19, wherein the titanium oxide comprises an anatase titanium oxide.

Embodiment 21. The photocatalytic element of embodiment 20, wherein the titanium oxide is a mixture of a rutile titanium oxide and anatase titanium oxide.

Embodiment 22. The photocatalytic element of embodiment 16, wherein the second photocatalytic material comprises a hexatitanate, a septatitanate, an octatitanate, a KTio_. W _. O , a L ZnTiaOg, or a L MgTigOg.

Embodiment 23. The photocatalytic element of embodiment 16, wherein the second photocatalytic material comprises a noble metal.

Embodiment 24. A photocatalytic device, the photocatalytic device comprising the photocatalytic element of embodiments 16-23 and a ceramic support material.

Embodiment 25. A method for making a photocatalytic element comprising:

Providing a ceramic substrate,

Creating a second catalytic coating upon the ceramic substrate, the first catalytic coating having a band gap of at least 2.8 eV; and/or or the ceramic coating having noble metals selected from Pt, Pd, Ag, Au, Rh; and

Creating a first catalytic coating upon the second catalytic coating, the first catalytic layer comprising at least 75 wt% of a metal oxide. Embodiment 26. The method of embodiment 25, wherein the first photocatalytic coating comprises a hexatitanate, a septatitanate or a octatitanate, a KTio. W . O , a L ZnTigOg, or a LhMgT Og

Embodiment 27. The method of embodiment 25, wherein the first photocatalytic coating comprises a mixture of rutile titanium oxide and an anatase titanium oxide.

Embodiment 28. A photocatalytic element made according to any of embodiments 25-

27.

Embodiment 29. A method for decomposing a volatile chemical compound, wherein the volatile chemical compound is exposed to the photocatalytic material of embodiment 16, 17, 18, 19, 20, 21, 22, or 23; and the photocatalytic material is activated with an ultraviolet radiation source.

Embodiment 30. The method of embodiment 29, wherein the ultraviolet radiation source has a wavelength region between about 300 nm and about 420 nm and a power of about 0.5 to 20 mW/cm².

Embodiment 31. The method of embodiment 30, wherein the ultraviolet radiation source has a wavelength of about 365 nm and a power of about 7 mW/cm².

Embodiment 32. The method of embodiment 29, 30, or 31, wherein the volatile chemical compound is formaldehyde, and the photocatalytic material decomposes at least 85% of the formaldehyde in hours of exposure.

EXAMPLES

Example 1(a). Synthesis of an n-type semiconductor (Ex-1) Aqueous Combustion Synthesis of K₂Ti₆0g 30 g solution of Titanium(IV) bis(ammonium lactatojdihydroxide (titanium lactate [Tyzor LA], Sigma Aldrich, St. Louis, MO, USA), 3 g potassium acetate (20% excess amount) (Sigma Aldrich, St. Louis, MO, USA) and 5 g ammonium nitrate (Sigma Aldrich, St. Louis, MO, USA) were dissolved in a glass beaker (250mL volume). This clear solution was heated in the preheat muffle furnace at 500 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to a fused silica container and then, the powder was annealed at 1000 °C for 12 hrs to get a single phase and crystalline K₂T1₄O₉ powder.

Example 1(b). Synthesis of a doped n-type semiconductor (Ex-2) Aqueous Combustion Synthesis of 0.348 wt% Pt in K T O

30 g Tyzor LA (Titanium precursor), 3 g potassium acetate (20% excess amount) (Sigma Aldrich, St. Louis, MO, USA), 0.0365 g platinum ammonium nitrate (Sigma Aldrich, St. Louis, MO, USA) and 5 g ammonium nitrate (Sigma Aldrich, St. Louis, MO, USA) were dissolved in a glass beaker (250 mL volume). This clear solution was heated in the preheat muffle furnace at 500 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to fused silica container and then, the powder was annealed at 1000 °C for 12 hrs to get a Pt doped K T O powder.

Example 1(c). Synthesis of a doped n-type semiconductor (Ex-3) Aqueous Combustion Synthesis of 0.15 wt% Pt in K Ti C

30 g Tyzor LA (Titanium precursor), 3 g potassium acetate (20% excess amount), 0.0183 g platinum ammonium nitrate and 5 g ammonium nitrate were dissolved in a glass beaker (250mL volume). This clear solution was heated in the preheat muffle furnace at 500 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to fused silica container and then, the powder was annealed at 1000 °C for 12 hrs to get a Pt doped powder.

Example 1(d). Synthesis of a doped n-type semiconductor (Ex-4) Aqueous Combustion Synthesis of 0.075 wt% Pt in K T O

30 g Tyzor LA (Titanium precursor), 3 g potassium acetate (20% excess amount), 0.00938 g platinum ammonium nitrate and 5 g ammonium nitrate were dissolved in a glass beaker (250 mL volume). This clear solution was heated in the preheat muffle furnace at 500 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to fused silica container and then, the powder was annealed at 1000 °C for 12 hrs to get a Pt doped powder

Example 1(e). Synthesis of a doped n-type semiconductor (Ex-5) Aqueous Combustion Synthesis of 0.03

30 g Tyzor LA (Titanium precursor), 3 g potassium acetate (20% excess amount), 0.00469 g platinum ammonium nitrate and 5 g ammonium nitrate were dissolved in a glass beaker (250mL volume). This clear solution was heated in the preheat muffle furnace at 500 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to fused silica container and then, the powder was annealed at 1000 °C for 12 hrs to get a Pt doped powder

Example 1(f). Synthesis of a doped n-type semiconductor (Ex-6) Aqueous Combustion Synthesis of 0.075 wt% Pt in K Ti i

30 g of Tyzor LA (Titanium precursor), 2 g potassium acetate (20% excess amount), 0.007 g platinum ammonium nitrate and 5 g ammonium nitrate were dissolved in a glass beaker (250mL volume). This clear solution was heated in the preheat muffle furnace at 430 °C until the combustion was over. The combustion reaction lasted for at least 15 minutes. Then, the voluminous powder was transferred to an alumina container. The powder was then annealed at 1000 °C for 12 hrs to get a Pt doped K₂TieOi powder

Example 2(a). Synthesis of an n-type semiconductor physical mixture (Comparative Ex-1) Acoustic Mixing of K₂Ti₄0₉ & Ti0₂ (P 25)

About 0.7 g undoped

(Ex-1), made as described in Example-l(a) above, and 0.7 g Ti0₂ (fumed Ti0₂ sold under the name Aeroxide P 25, Evonik, Parsippany, NJ, USA) were mixed for 3 min using a setting of acoustic intensity 40% (Lab AM [Acoustic Mixer] Resodyn Acoustic Mixers, Inc., Butte, MT, USA). 130 mg of the mixed powder was sonicated in 2.6g water in a water bath for 30 min. Then, the 130 mg of the suspended powder was dispersed in a petri dish of 60 mm x 15 mm while evaporating at 120 °C.

Example 2(c). Comparative Example 1 (CE-1) Synthesis of an P25 only semiconductor dispersion

CE-1 (P 25, Evonik) was prepared without additional purification in a manner similar to that of Example 2(a), except that no K₂Ti₄0₉ was added to the powder to be dispersed.

Example 2(d). Comparative Example 1 (CE-2) Synthesis of an ST-01 only semiconductor dispersion

CE-2 (ST-01) was prepared without additional purification in a manner similar to that of Example 2(a), except that only K₂TieOi was added to the powder to be dispersed.

Example 3. Separate layering of ST-01 semiconductor and Ti0₂ materials on Ceramic Material

Monolayer Dip coating procedure:

Sufficient deionized water was added to a given amount of Ti0₂ (P25) photocatalyst (Evonik, Parsippany, NJ, USA) to create a 20 wt.% Ti0₂ photocatalyst (e.g. P25) in aqueous slurry. The resultant slurry was then usually probe sonicated for 30 min to disperse the photocatalyst in water. Then, a 1 cm cube of honeycomb ceramic support (AI₂C [55%], Si0₂ [38%], MgO [7.0 %], Elite Ceramics Industrial Co., Ltd, Beijing, PRC) of size 1 cm by 1cm by 1cm in size (which was pre-annealed at 400 °C for 30 min under ambient atmosphere. The pre-annealed cube was then dipped/submerged into the slurry and removed from the slurry immediately. Excess slurry was removed by hand-held squeeze bulb air blower. The coated cube was then It was dried on a hot plate at 150 °C for 30 min. This cycle of dip coating and dried was repeated until the photocatalytic coating total weight was about of 80 mg (photocatalyst amount). The repeated dip coated cube filter with about 80 mg of photocatalytic material. Finally, the photocatalyst coated filter was annealed at 400 °C for 30 min.

Bilayer and multilayer Dip coating procedure:

Other embodiments of coated supports were made in a manner similar to that described above except that after a first layer of a selected material achieved the desired amount, e.g., 20 mg, a second material coating was deposited upon the first completed layer, then annealed similarly at 400 °C for 30 min. The coatings were varied as set forth in Table 1. Finally, the photocatalyst coated filter was annealed at 400 °C for 30 min.

Table 1 below summarizes photocatalyst amount after the number of cycle of coating procedure. Table 1: Photocatalyst coating achieved by dip coating in the aqueous slurry followed by annealing at 400°C

Example 4. Experimental set-up 1 for photocatalysis (Ex-IA and CE-1) The PCcat coated filter made as described above, was sealed in 5 LTedlar bag and the bag was filled with 1.5 L air (0.5 L/min for 3 min) and 1.5L (0.5 L/min for 3 min) standard formaldehyde VOC gas (17.52 ppm + N balance gas). Initial and final formaldehyde concentrations were estimated using GASTEC tube (91L) and during the photocatalysis, CO was monitored using PP system. UV LED source with 7 mW/cm² power was used to study UV photodecomposition of Formaldehyde. The wavelength region between 300 and 420 nm was used from UV LED The results are summarized in Table 2 below. Table 2 summarizes filters evaluation results by gas bag static method:

Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. The terms "a," "an," "the" and similar referents used in the context of describing the present disclosure (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or representative language (e.g., "such as") provided herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of any claim. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the present disclosure.

Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

Certain embodiments are described herein, including the best mode known to the inventors for carrying out the present disclosure. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the present disclosure to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.

In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, byway of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.

Claims

1. A photocatalytic element comprising: a first layer comprising a first photocatalytic material; and a second layer comprising a second photocatalytic material; wherein the second layer is disposed on the first layer.

2. The photocatalytic element of claim 1, wherein the second photocatalytic material is a noble metal.

3. The photocatalytic element of claim 1 or 2, wherein the first layer comprises T O .

4. The photocatalytic element of claim 1 or 2, wherein the first layer comprises Pt/K TieOi _.

5. The photocatalytic element of claim 1 or 2, wherein the first layer comprises WO _.

6. The photocatalytic element of claim 1 or 2, wherein the first layer comprises LhZnT Os_.

7. The photocatalytic element of claim 1 or 2, wherein the first layer comprises KNqTίbO _.

8. The photocatalytic element of claim 1 or 2, wherein the first layer comprises Na₂Ti₆0i_3.

9. The photocatalytic element of claim 1 or 2, wherein the first layer comprises KTio.₅W_1.5O₆.

10. The photocatalytic element of claim 1 or 2, wherein the first layer comprises WO in an amount of about 3 mol% and T O in an amount of about 97 mol%_.

11. The photocatalytic element of claim 1 or 2, wherein the first layer comprises ZnO.

12. The photocatalytic element of claim 1, 2, 3, 4, 5, 6, 1 , 8, 9, 10, or 11, wherein second photocatalytic material has a band gap of at least 2.8 eV.

13. A photocatalytic device, comprising the photocatalytic element of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, and a source of electromagnetic radiation, wherein the first layer is disposed between the source of electromagnetic radiation and the second layer.

14. A method of decomposing a volatile organic chemical, comprising exposing the volatile organic chemical to the photocatalytic element of claim 1 in the presence of an electromagnetic radiation source, wherein electromagnetic radiation from the electromagnetic radiation source has contact with the first layer.

15. The method of claim 14, wherein the electromagnetic radiation is ultraviolet radiation.

16. The method of claim 14, wherein the electromagnetic radiation is supplied by a source having a power of about 1 to about 50 mW/cm².

17. The method of claim 14, wherein the electromagnetic radiation is equivalent to the amount of electromagnetic radiation supplied by an LED source having a power of about 1 to about 50 mW/cm².

18. A method of preparing a photocatalytic element comprising: depositing a second layer comprising a second photocatalytic material upon a substrate, and depositing a first layer comprising a first photocatalytic material upon the second layer.

19. The method of claim 18, wherein the substrate is a honeycombed ceramic substrate.