WO2022040379A1 - System and method to disinfect a room using ultraviolet light and a photocatalyst - Google Patents

Abstract

A disinfection system comprises at least one electric light source configured to emit light into an environment for human occupancy, and a photocatalytic oxidation (PCO) coating is disposed on one or more surfaces of the environment for human occupancy and arranged to be directly or indirectly illuminated by the at least one electric light source. The light includes light in the UVA range and/or light in the violet range. The PCO coating may comprise titanium dioxide. In a corresponding method, the PCO coating is applied to the one or more surfaces using a spray gun, such as a high volume, low pressure (HVLP) spray gun.

Description

SYSTEM AND METHOD TO DISINFECT A ROOM USING ULTRAVIOLET LIGHT AND A PHOTOCATALYST

[0001] This application claims the benefit of U.S. Provisional Application No. 63/068,174 filed August 20, 2020 titled “DISINFECTION SYSTEM AND METHOD FOR AN ENVIRONMENT FOR HUMAN OCCUPANCY INCLUDING ULTRAVIOLET LIGHT EMISSION INTO THE ENVIRONMENT AND PHOTOCATALYTIC OXIDATION COATING”. U.S. Provisional Application No. 63/068,174 filed August 20, 2020 is incorporated herein by reference in its entirety.

BACKGROUND

[0002] The following relates to the disinfection arts, pathogen control arts, bacterial pathogen control arts, lighting arts, and the like.

[0003] Clynne et al., U.S. Pat. No. 9,937,274 B2 issued April 10, 2018 and Clynne et al., U.S. Pat. No. 9,981 ,052 B2 (which is a continuation of U.S. Pat. No. 9,937,274) provide, in some illustrative examples, disinfection systems that includes a light source configured to generate ultraviolet light toward one or more surfaces or materials to inactivate one or more pathogens on the one or more surfaces or materials. [0004] U.S. Pub. No. 2016/0271281 A1 is the published application corresponding to U.S. Pat. No. 9,937,274. U.S. Pub. No. 2016/0271281 A1 is incorporated herein by reference in its entirety to provide general information on disinfection systems for occupied spaces that use ultraviolet light.

[0005] Certain improvements are disclosed.

BRIEF DESCRIPTION

[0006] In some illustrative embodiments disclosed herein, a disinfection system is disclosed. At least one electric light source is configured to emit light into an environment for human occupancy. The light includes light in the UVA range and/or light in the violet range. A photocatalytic oxidation (PCO) coating is disposed on one or more surfaces of the environment for human occupancy and arranged to be directly or indirectly illuminated by the at least one electric light source. [0007] In some illustrative embodiments disclosed herein, a disinfection method comprises: applying a photocatalytic oxidation (PCO) coating on one or more surfaces of an environment for human occupancy; and operating an electric light source to output light into the environment for human occupancy wherein the light includes light in the UVA range and/or light in the violet range and wherein the light directly and/or indirectly impinges on the applied PCO coating.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0009] FIGURE 1 diagrammatically illustrates a disinfection system configured to disinfect an environment for human occupancy.

[0010] FIGURE 2 diagrammatically illustrates an embodiment of a light source of the disinfection system of FIGURE 1.

[0011] FIGURE 3 diagrammatically illustrates an embodiment of an object (illustrative side view of a table) disposed in the environment for human occupancy and modified to incorporate components of the disinfection system of FIGURE 1 .

[0012] FIGURE 4 diagrammatically illustrates a method of installing and operating the disinfection system of FIGURE 1.

[0013] FIGURE 5 diagrammatically shows a high volume, low pressure (HVLP) spray gun suitably used for dispensing the PCO layer in the method of FIGURE 4.

[0014] FIGURES 6-11 present tables of calculated deposition rate parameters as described herein.

[0015] FIGURES 12-16 diagrammatically depict further aspects of combined UVA and PCO layer disinfection in a space for human occupation as described herein.

DETAILED DESCRIPTION

[0016] “Ultraviolet (UV) radiation” or “UV light” pertains to the range between 100 nm and 400 nm, commonly subdivided into UVA, from 320nm to 400 nm; UVB, from 280 nm to 320nm; and UVC, from 100 nm to 280 nm. The violet range of light is 380-450 nm. It will be appreciated that as used herein the term “light” is intended to encompass light in the visible light range (typically considered 400-700 nm) and also UV light, as well as near infrared light (up to about 3000 nm).

[0017] The Actinic UV hazard exposure limit for exposure to ultraviolet radiation incident upon the unprotected skin or eye applies to exposure within a specified time period, which is typically any 8-hour period. To protect against injury of the eye or skin from ultraviolet radiation exposure produced by a broadband source, the effective integrated spectral irradiance (effective radiant exposure, or effective dose), E_s, of the light source shall not exceed 30 J/m². The effective integrated spectral irradiance, E_s, is then defined as the quantity obtained by weighting spectrally the dose (radiant exposure) according to the actinic action spectrum value at the corresponding wavelength. One suitable actinic action spectrum is the published IESNA Germicidal action spectrum.

[0018] U.S. Pub. No. 2016/0271281 A1 discloses disinfection systems that includes a light source configured to generate ultraviolet light toward one or more surfaces or materials in an environment for human occupancy (e.g. a room in a house or building, sometimes referred to herein for brevity as an “occupied space” although it may or may not actually be occupied at any given time) to inactivate one or more pathogens on the one or more surfaces or materials. As disclosed therein, ultraviolet light within or partly encompassing the UVA range (e.g. 280-380 nm inclusive, or in other embodiments 300-380 nm inclusive) is particularly effective for inactivating pathogens, especially bacterial pathogens. Without being limited to any particular theory of operation, it is believed that UVA is typically efficacious in inactivating bacteria by depositing its energy in the outer membrane of the cell, or the cell wall, where the energy of the UVA photon is sufficient to create reactive oxygen species (ROS) or to drive other chemical reactions that may cause enough damage to the cell envelope to kill or inactivate the bacterium.

[0019] However, the efficacy of the UVA radiation in inactivating bacteria is sometimes reduced for bacteria residing on a surface, rather than in an aerosol or otherwise airborne. It is believed that this is due to the surface-bound bacteria being protected by a thin surface water layer and/or other contaminants adhered to the surface (and/or to the bacteria). The efficiency may also be reduced due to the formation of clusters of bacteria wherein those bacteria deep within the cluster may be shielded from the UV irradiation by the outermost bacteria in the cluster; or due to formation of a biofilm wherein a cluster of bacteria form a protective layer surrounding the cluster. Furthermore, UVA radiation is typically less effective for inactivating some other types of pathogens, such as viruses.

[0020] One way to address the reduced effectiveness for viruses would be to increase the intensity of the UVA light. However, in the case of an occupied (or possibly occupied) space, this is limited by an upper limit on UVA dose imposed by the Near UV or Actinic UV hazard exposure limits.

[0021] Hence, it is recognized herein that for some applications and use scenarios, it may be desirable to provide a disinfection system that utilizes UVA light (and/or possibly longer-wavelength light, such as violet light) at safe levels for (possible) occupants, while still providing effective surface disinfection of pathogens.

[0022] To provide such a system, it is disclosed herein to employ a synergistic combination of a light source emitting light into the environment for human occupancy in the UVA range (and/or, optionally, the violet range), and one or more photocatalytic oxidation (PCO) coatings applied to one or more surfaces of the environment for human occupancy. Without being limited to any particular theory of operation, it is believed that the PCO layer operates as follows. Nanoparticles of the PCO layer are photocatalyzed by ultraviolet light to produce hydroxyl (-OH) and/or superoxide (O2^_) radicals that are highly reactive with bacteria, viruses, and other pathogens. Hence, the synergistic combination of the UVA light source(s) emitting into the environment for human occupancy together with the PCO layer(s) enables the UVA light to directly inactivate pathogens, especially bacterial pathogens; while the UVA light impinging on the PCO layer(s) indirectly inactivates pathogens in close proximity to the PCO layer surface(s) by way of UVA-induced photocatalytic oxidation.

[0023] In a preferred embodiment, the PCO layer is a titanium dioxide (TiO2) layer. Titanium dioxide has three forms that exhibit photocatalytic oxidation activity: anatase, rutile, and brookite. Of these, anatase TiO2 typically exhibits the strongest photocatalytic oxidation activity; however, a mixture of predominantly anatase TiO2 and a lesser amount of rutile TiO2 has been observed to exhibit stronger photocatalytic oxidation activity than pure anatase TiO2. The mixture should provide the phase separation and bi-phasic separation typically observed when the material is produced using the conventional fuming process, starting with titanium chloride, which produces the advantageous transitional phase titania. See, e.g. Sakar et al., “Insights into the TiC -Based Photocatalytic Systems and Their Mechanisms”, Catalysts 9, 680 (2019). Hence, in some embodiments, the PCO layer is 100% anatase TiO2. In other embodiments, the PCO layer comprises titanium dioxide that is at least 60% anatase TiO2, and more preferably at least 70% anatase TiO2, with the balance of the titanium dioxide of the PCO layer being rutile or another phase of TiO2.

[0024] Predominantly or pure anatase TiO2 is commonly used in air purifiers, in which a UV lamp operates in an enclosed housing with a fan or other air handling system for drawing air in from the room, passing the air over a grid coated with a TiO2 layer, and exhausting the purified air from the enclosed housing. The reactive radicals produced by photocatalytic oxidation of the TiO2 activated by the UV lamp break down volatile organic compounds such tobacco and organic odors. Coatings of predominantly or pure anatase TiO2 is also sometimes used outdoors, where it is activated by ultraviolet and violet components of sunlight to prevent or degrade organic contaminants on exterior walls, roofs, or the like.

[0025] However, there are some difficulties with using PCO layer(s) in conjunction with UVA disinfection lights operating in an indoor environment for human occupancy. The PCO layer in an indoor setting is often not able to be applied during manufacturing of the interior wall or object on whose surface(s) the PCO layer is to be applied. Furthermore, anatase TiO2 is susceptible to damage due to extensive abrasion, and hence may need to be re-applied on occasion, especially on high-contact surfaces such as tabletops, door knobs or instrumentation. A further difficulty is that rutile TiO2 is the thermodynamically stable form; whereas, anatase TiO2 is metastable. Notably, exposure to heat can transform anatase TiO2 into rutile TiO2.

[0026] To address these problems, in some embodiments disclosed herein the PCO layer is coated on the surface or surfaces using a high volume, low pressure (HVLP) spray gun. The material to be applied is suitably TiO2 (predominantly or purely in the anatase form) suspended in a fluid such as water. A HVLP spray gun is connected with high volume air flow (or a high volume flow of another fluid such as nitrogen) and is also connected (directly or by way of a tube) with a container that contains the material to be sprayed (here, the TiO2 nanoparticles suspended in water or another fluid). The material to be sprayed is fed into the HVLP spray gun at low pressure, for example by gravity feed or by diverting a portion of the high-volume air flow into the container to pressurize it to the desired low pressure. The main stream of high-volume airflow is channeled in the nozzle of the HVLP spray gun to intersect the flow of low pressure material as it exits the nozzle of the HVLP spray gun, so as to break the low pressure material into a relatively uniform beam of droplets.

[0027] A HVLP spray gun is typically used for applications such as spraying paint onto a surface. For this task, an HVLP spray gun has the advantages of depositing paint at a relatively high rate of deposition with minimal bounce-back of the paint.

[0028] Herein, it is recognized that a HVLP spray gun has substantial advantages for depositing the PCO film. The low pressure of the TiO2 nanoparticles suspended in water or another fluid, and the lack of heating of this material, enables transferring the purely or predominantly anatase TiO2 nanoparticles onto the surface without inducing transformation of the anatase to rutile TiO2. The low output pressure of the HVLP spray gun also facilitates deposition onto delicate surfaces such as interior walls and/or finished furniture surfaces. Deposition using a HVLP spray gun is also inexpensive and can be performed on substantially any type of surface, in any orientation. The HVLP spray gun can also be used to re-apply the PCO layer at occasional intervals to refresh the PCO layer, e.g. on high contact surfaces, and can be done by personnel without specialized training. If water is used as the suspension fluid, then the water typically evaporates quickly in air after the PCO layer deposition, thereby minimizing its impact on the surface and leaving a pristine layer of anatase TiO2. The material comprising TiO2 nanoparticles suspended in water is also non-toxic.

[0029] With reference now to FIGURE 1 , a disinfection system is configured to disinfect an environment 2 for human occupancy, such as an illustrative interior room 2 of a house, building, or the like having a ceiling 4, floor 6, and walls 8. More generally, the environment 2 for human occupancy can be an indoor environment such as a room (which could be a conference room, medical operating room, a hallway, or so forth); or can be a vehicle interior, e.g. an automobile interior, truck interior, an aircraft cabin, a spacecraft interior, a train compartment, or so forth. In these various embodiments, the environment 2 for human occupancy has a floor 6, such as the illustrative floor 6 of the room, the floor of the vehicle or aircraft cabin, or the floor of the train compartment.

[0030] The environment 2 for human occupancy is one which does not typically receive the UV component of sunlight. This can be because it is an indoor location with a limited number of windows, such that sunlight does not enter into the environment 2. Similarly, the environment 2 could be an enclosed standalone shed with few or no windows. Alternatively, in the case of for example a vehicle interior, there may be large windows for admitting sunlight, but those windows may be coated with thin films that block UV radiation from entering the interior of the vehicle, so as to reduce heating of the interior of the vehicle when exposed to direct sunlight. More generally, the environment 2 for human occupancy can be any space that does not receive a UV component of sunlight exceeding the maximum allowed actinic exposure, for example an outdoor space having a ceiling that at least partially blocks direct sunshine, for example a storage area for shopping carts, a carport, a tunnel, a cave, a mine, an amphitheater, a stadium, a dugout, a lean-to, a tarp or tent, a picnic pavilion, or another structure not necessarily classified as a building, but which may be occupied by humans, or any outdoor area that is not instantaneously receiving a UV component of sunlight exceeding the maximum allowed actinic exposure, for example a cloudy or nighttime or seasonally dark environment. In such an environment that does not receive a UV component of sunlight exceeding the maximum allowed actinic exposure, an electric light source of this disclosure may provide UV up to the maximum allowed actinic limit, in combination with any possible sunlight contribution to the actinic limit.

[0031] It will be appreciated that the portion of the environment 2 that is actually occupied by persons is typically the space that is two meters or closer to the floor 6 (sometimes designated as 2.1 meters), which is the expected occupancy in a normal work or home environment. Hence, the disinfection system is typically designed to provide disinfection at a target plane, where the target plane is two meters (or 2.1 meters) or closer to the floor 6. The viral disinfection system includes at least one light source 10 configured to emit light into the environment 2 for human occupancy to inactivate one or more pathogens suspended in ambient air of the environment 2 or residing on surfaces 12 or materials, including human skin. The illustrative at least one light source 10 of FIGURE 1 includes a plurality of ceiling-mounted light sources and a plurality of wall- mounted light sources. More generally, all the light sources could be only ceiling-mounted (as shown), or some or all the light sources could be wall-mounted, supported in lamp holder fixtures, or resting on the floor or on furniture, in coves, suspended from supports, or so forth. The at least one light source 10 preferably includes a plurality of light sources distributed through the environment 2 (e.g. over the entire ceiling 4) so as to apply light to most or all of the ambient air and surfaces in the environment 2.

[0032] The light emitted by the at least one light source 10 preferably is within or at least overlaps the UVA range (320nm to 400 nm). In some embodiments, the UV light source(s) 10 output in the range 280-380 nm inclusive, or in other embodiments 300-380 nm inclusive. Additionally, or alternatively, the at least one light source 10 may emit in the violet range (380-450 nm) or in the combined UVA/violet range. Depending on the type of light source 10, the light may be narrow-band light, e.g. predominantly a single discrete emission line or a set of discrete emission lines, or may be broad-band light. Preferably the intensity of the light emitted by the at least one light source 10 is effective to achieve at least 90% inactivation of the virus pathogen on any surface in the environment within about 8 hours or less. However, the presence of a PCO coating on a surface may enhance the inactivation by about 10x or more, so that surfaces which may have experienced 90% inactivation in 8 hours or less may experience 99% or greater inactivation in 8 hours or less.

[0033] The light source(s) 10 is/are preferably electric light sources, such as light emitting diode (LED) light sources, gas discharge lamps, or the like.

[0034] With reference to FIGURE 2, in some embodiments each light source 10 comprises one or more LEDs 20, for example disposed on a printed circuit board or other substrate 22 and optionally mounted in a housing (not shown). The light source 10 may also include an optional transparent cover plate 24 or the like. The illustrative LEDs 20 are UVA LEDs that emit light with a spectrum whose maximum peak wavelength is in the UVA spectrum. For example, the LEDs 20 may be gallium nitride (GaN)-based LEDs, although other types of UVA-emitting LEDs may be used as the LEDs 20. In some embodiments, there may be as few as a single LED 20 disposed on the substrate 22. The substrate 22 may optionally be coated with a UVA-reflective layer in order to increase the light emission efficiency. Other types of UVA-emitting lamps may be used as the light sources 10, for example as disclosed in U.S. Pub. No. 2016/0271281 A1. When intended for use in the environment 2 for human occupancy during actual occupation by humans, the light source(s) should emit a total dose over a defined time period (sometimes taken as eight hours, corresponding to a typical work shift duration) that is below the actinic dose for that time period. As explained in U.S. Pub. No. 2016/0271281 A1 , intensities of UVA light meeting this actinic limit are still effective for inactivating many airborne and surface-bound pathogens, especially though not limited to bacterial pathogens. Indeed, as disclosed therein, the Actinic UV hazard is less hazardous for wavelengths in the range from about 315 nm to about 380 nm than for longer wavelengths in the range from about 380 nm to about 400 nm at doses required to inactivate pathogens at the 90-99% level.

[0035] With continuing reference to FIGURE 1 , one or more photocatalytic oxidation (PCO) layers 30 are shown coating two walls of the environment 2 and a tabletop of a table 32 disposed in the environment 2. The PCO layers 30 are indicated by hatching in FIGURE 1. More generally, the PCO layers 30 may be disposed on walls of the environment 2, the floor of the environment 2, the ceiling of the environment 2, any combination thereof; and/or on one or more or all of the surfaces of any object disposed in the environment 2. The PCO layer(s) 30 are preferably titanium dioxide (TiO2) layer(s). More preferably, the PCO layer(s) 30 are TiO2 layer(s) in which the TiO2 is at least 60% anatase TiO2, and more preferably is at least 70% anatase TiO2, with the balance being rutile TiO2. In some embodiments, the PCO layer(s) 30 are TiO2 layer(s) in which the TiO2 is pure anatase TiO2. However, other types of PCO materials are contemplated for the PCO layer(s) 30, such as carbon nanoparticles (including nanotubes and fullerine), metals (including gold, silver, and platinum), and metal oxides (such as ZnO2 and WO2). Optionally, a primer (not shown) such as a binder material may be applied before application of the PCO layer(s) 30 to improve adhesion, and/or the PCO layer(s) 30 may incorporate a binder.

[0036] The surfaces that are coated with PCO layers 30 as depicted in FIGURE 1 are arranged to be directly exposed to light output by the light sources 10. This is advantageous because it ensures the directly exposed PCO layers 30 receive activating UVA light so as to be efficiently photocatalyzed by the ultraviolet light to produce hydroxyl (-OH) and/or superoxide (02’) radicals that are highly reactive with bacteria, viruses, and other pathogens. Hence, the PCO coatings 30 operate to inactivate pathogens, especially including but not limited to bacteria and viruses.

[0037] However, in some cases the exposed surfaces may be susceptible to frequent contact that can degrade the PCO layer 30. For example, this may be the case for the tabletop of the table 32. Moreover, it may be desirable to maximize the number of surfaces with PCO coatings to maximize disinfection efficacy. Advantageously, it is recognized herein that even surfaces that are not directly exposed to light output by the light sources 10 may undergo photocatalysis so as to produce reactive radicals. For example, many typical wall and floor surfaces have relatively high reflectivity for ultraviolet light, so that surfaces may indirectly receive light from the light sources 10 at sufficient amounts to activate the PCO coating. As an example, UVA radiation is typically reflected with approximately 10-30% efficiency from common interior building materials (walls, floors, ceilings, textiles, etc.), so that second-bounce irradiances may be ~ 10-30% and third- bounce irradiances may be ~ 1-10% of the direct UVA irradiation, which may not be sufficient to inactivate pathogens.

[0038] For example, with reference to FIGURE 3, the table 32 is shown in an isolation side view. As there seen, the underside of the tabletop is also coated with a PCO coating 30. While the underside is not directly exposed to light output from the light sources 10, it does receive light from the light sources 10 after reflection off the floor 6 and possibly after double-reflection (or even multiple reflection) from the floor 6 and walls 8.

[0039] With reference back to FIGURE 2, a PCO coating 30 may also be coated onto an exterior surface of the transparent cover plate 24 of the light source 10, where it will be directly exposed to the ultraviolet light emitted by the LEDs 20. Advantageously, the PCO coating 30 on the cover plate 24 of the light source 10 may optionally be applied during manufacturing of the light source 10, that is, prior to shipping the manufactured light source 10 to the destination environment 2.

[0040] With reference to FIGURE 4, a method of installing and operating the disinfection system of FIGURE 1 is described. In an optional operation S1 , the light output window (e.g. transparent cover plate 24) of the light source 10 is coated with a PCO layer 30, as diagrammatically shown in FIGURE 2. In an operation S2, the UVA light source(s) 10 is/are installed in the environment 2 for human occupancy, and the intensity of the light source(s) 10 is/are adjusted for occupancy safety in an operation S3, for example so as to comply with a standard such as IEC62471. The adjustment operation S3 may, for example, include taking into account the ceiling height, the spacing of the light sources 10 on the ceiling 4, the time interval over which the environment 2 for human occupancy is expected to be occupied (e.g., eight hour work shift, or some shorter time as might, for example, be the case for a location that is rarely frequented, such as a closet. It will be appreciated that the order of operations S2 and S3 may be reversed, e.g. the light sources 10 may be configured (operation S3) prior to their installation in the environment 2 (operation S2). As an example of this, in some regulatory frameworks it may be desirable or mandatory that the manufacturer of the light source control the configuration process, so that the manufacturer may receive specifications (e.g. ceiling height, light source spacing, et cetera) and configure the light sources 10 per operation S3 before shipping them to the environment 2 for human occupancy for installation per operation S2. Moreover, in some embodiments, the operation S3 may be omitted. For example, it may be that the light sources 10 may be operated only when the environment 2 for human occupancy is unoccupied (for example, using occupancy sensors to detect when the room is occupied and automatically turning off the light sources when occupied and automatically turning on the light sources when not occupied). In this case, the operation S3 may be omitted.

[0041] The disinfection system installation further includes an operation S4 in which the target surfaces in the environment 2 for human occupancy (other than the optional coating of the light output windows of the light sources 10 per operation S1) are coated with the PCO layer 30. In a preferred embodiment, this is done by spraying the PCO coating 30 onto the target surfaces. In a more preferred embodiment, this is done by spraying the PCO coating 30 onto the target surfaces using a high-volume low pressure (HVLP) spray gun. The target surfaces are selected based on factors such as a desire to maximize the total area of coated surfaces in the environment 2, a desire to preferentially (though not necessarily exclusively) coat surfaces that are directly exposed to the ultraviolet (and/or violet) light emitted by the light source(s) 10, the expected adhesion of the PCO coating 30 to the surface, and/or so forth. [0042] Optionally, the operation S4 may include initial application of a primer such as a binder (without TiO2 or other PCO material) to improve adhesion of the PCO layer to the surfaces. Optionally, a binder may be incorporated into the PCO material that is applied to form the PCO coating 30. It may be advantageous to incorporate a binder in order to increase adhesion between the photocatalyst (e.g., TiO2) and the surface to which it is deposited. For example, a binder may be applied to one or more surfaces to form a coating comprising a binder, thus serving as a primer, and subsequently the photocatalytic material may be applied to the coating comprising a binder. In other embodiments, a binder or binder material may be mixed with a photocatalyst material, and the resultant mixture applied to a surface. A combination of both a binder primer and mixing the photocatalytic material with a binder is also contemplated. In some nonlimiting illustrative embodiments, the binder may be opaque (e.g. white), or alternatively may be semi-transparent in the UV region. The binder for use with TiCh may take the form of a Latex primer, for example. In one nonlimiting illustrative embodiment, a mixing ratio between binder material and photocatalytic material (here TiC ) may be 100:1 wt/wt, or more broadly, from 10000:1 to 1 :1 wt/wt (binder to photocatalyst, respectively).

[0043] Finally, in an operation S5, the installed and (optionally) adjusted UVA light sources 10 are operated to provide disinfection. This may be done on a specific schedule (e.g., only when the environment 2 is occupied; or only when the environment 2 is unoccupied), optionally using an intensity schedule (e.g. higher intensity when the environment 2 is unoccupied compared with when the environment 2 is occupied, optionally briefly increasing intensity in response to detecting a cough or other audible sound using a microphone that indicates possible expulsion of breath aerosols), or the light sources 10 may be operated continuously at a level that is safe for occupants.

[0044] As diagrammatically indicated in FIGURE 4 by a return arrow S6, optionally the operation S4 may be repeated occasionally to re-coat some or all of the target surfaces with the PCO layer 30. For example, considering the illustrative environment 2 of FIGURES 1-3, the PCO layer 30 coating walls 8, the light cover 24 (FIGURE 2), and the underside of the tabletop (FIGURE 3) may last a long time; whereas, the PCO layer coating the top of the tabletop (FIGURES 1 and 3) may degrade more rapidly due to frequent contact that can rub off or otherwise degrade the PCO coating 30 on the top of the tabletop. Hence, the re-coat indicated by return arrow S6 may entail re-coating only the top of the tabletop frequently, with the walls and underside of the tabletop being re-coated less frequently.

[0045] With reference to FIGURE 5, an illustrative high volume, low pressure (HVLP) spray gun 40 suitably used in performing the PCO layer coating operation S4 is shown in diagrammatic cross-section. The HVLP spray gun 40 includes a nozzle 42 that receives a high-volume airflow 44 and a low-pressure flow of material 46 to be coated, which for performing the operation S4 comprises TiCh nanoparticles suspended in water or another fluid. Preferably, the TiO2 nanoparticles are at least 60% anatase TiCh nanoparticles, and more preferably is at least 70% anatase TiO2 particles, with the balance being rutile TiO2 nanoparticles. The material flow 46 may be provided from a container (not shown; e.g., a plastic or other type of bottle) arranged to deliver the material flow 46 by gravity-feed (i.e., by having the container located above the nozzle 42) or via bypass delivery of a small fraction of the high-volume airflow 44 into the container to pressurize it. In some embodiments, the TiCh nanoparticles are 100% (i.e. pure) anatase TiO2 nanoparticles. The nozzle 42 of the HVLP spray gun 40 includes a flow path 50 through which the material 46 to be sprayed flows and exits at a nozzle discharge orifice 52. The nozzle 42 of the HVLP spray gun 40 further includes flow channels 54 that discharge the high- volume airflow 44 at or near the nozzle orifice 52, and at an angle intersecting the discharge of the material 46 at the orifice 52. The high-volume airflow intersecting the material flow at or near the nozzle orifice 52 operates to break the low-pressure material into a relatively uniform beam of droplets 56.

[0046] HVLP spray coating is preferred as this provides a uniform layer of material which is sufficiently thin so that the water or other suspension fluid evaporates quickly, in a manner that is unlikely to significantly induce conversion of anatase TiCh to rutile TiO2. The transition of anatase typically occurs at temperatures exceeding 500°C or higher, which should easily be avoided using spray coatings utilizing aqueous vehicles. The addition of phosphors also can increase the transition temperature of anatase TiO2 to above 1000°C, while maintaining good photocatalytic properties. The transitional phases of Titania, such as P25, may not be optimal but are a good reference material and are commercially available. However, other coating methods are contemplated, such as other types of spray coating (including air brushes and ultrasonic spray coating), direct painting of the PCO coating with a brush or other implement, electrostatic coating, and/or so forth. [0047] Although not illustrated, it is contemplated to provide fans or other air circulating devices to bring more air into contact with the PCO coating(s) 30 to enhance disinfection efficacy of the PCO coating(s) 30. For example, a fan may be incorporated into the light source 10 of FIGURE 2. Alternatively, the fan or other air circulating device could be a room-wide fan or the like circulating air in the environment 2 as a whole. In some such cases, a pre-existing HVAC system may provide this room-level air circulation.

[0048] In another contemplated variant, the light source 10 may include a total internal reflection (TIR) optic arranged so that contact with the optic acts as an extraction point, causing UVA light to exit the TIR optic, thereby activating the PCO coating at the point it was contacted.

[0049] In yet other variants, high-surface-area objects such as meshes may be coated with the PCO coating 30 and incorporated into the light source 10 or elsewhere, forcing air to pass through or come in contact with the coated object — the high surface area increasing the likelihood of pathogens in the air coming in contact with the activated PCO. Devices that precipitate or flocculate pathogens to increase the likelihood of coming in contact with PCO coated surfaces may be employed, such as cyclonic filters or AC or DC electrostatic devices. The air may additionally or alternatively be forced through a serpentine or other complex path coated with activated PCO to increase the likelihood of pathogens contacting the PCO layer.

[0050] Advantageously, it has been found that under normal circulation the PCO layer 30, if coating all surfaces in the environment 2 for human occupancy, can be expected to inactivate a sufficiently large percentage of (for example 99% or 99.99% of) bacteria within a short period of time, such as one hour. On the other hand, the airborne residency time of viruses is much longer due to their much smaller size and weight. Consequently, while the PCO layer is effective for reducing the bacterial load, additional inactivation of viruses may be desirable.

[0051] In view of the foregoing observations, a further synergistic combination is disclosed herein, namely a disinfection system including the light sources 10 and PCO layers 30, in which the light sources 10 output light in or overlapping the UVA range (e.g., in the range 280-380 nm inclusive, or in other embodiments 300-380 nm inclusive) and also in or overlapping the UVC range (e.g., 200-280 nm inclusive in some embodiments, and more preferably 240-280 nm inclusive). Although UVC light does not strongly activate the PCO layer 30, UVC light is particularly efficacious for disinfecting virus pathogens in an occupied space. For example, a single coronavirus particle is extremely small, having a size of about 0.1 micron in diameter. The particles of many other pathogenic viruses are comparably small, e.g. well under 1 micron in diameter in many cases. As a result, UVC radiation can damage the nucleic acid contained in a coronavirus particle suspended in air very rapidly, e.g. in under one second if a dose ~ 10 J/m² is applied rapidly. By contrast, the short wavelength of UVC light means that its penetration depth in human tissue is small, usually being absorbed in the outer layer of skin or eye tissue. Hence, UVC radiation has less impact on human safety than, for example, UVB radiation, and some regulatory schemes set the dose limit for actinic radiation exposure at 270 nm to 30 J/m² over an eight hour period, with higher doses allowed at other UV wavelengths. While this is a low dose, it provides a window for employing disinfection of occupied spaces by way of UVC light, without posing a safety risk to occupants. In particular, the difference in damage metric for virus particles, which goes with UVC light intensity, versus the damage metric for human tissue, which goes with time-integrated UVC light intensity (that is, a dose, e.g. measured in units of J/m²), can be leveraged to safely inactivate airborne viruses in an occupied environment.

[0052] To provide for combined UVA and UVC emission, some of the LEDs 20 of the light source of FIGURE 2 can be UVA-emitting LEDs and some UVC-emitting LEDs, e.g. AIGaN-based LEDs. Alternatively, if multiple light sources 10 are provided, e.g. as shown in FIGURE 1 , then some of the light sources 10 can include exclusively UVA- emitting LEDs while other light sources 10 can include exclusively UVC-emitting LEDs (or, the UVC light sources may be low pressure mercury lamps or other UVC emitters). In some embodiments, the light emitted by the UVC LEDs is effective to produce an actinic dose at a target plane in the environment of 30 J/m² or less over an eight hour period, where the target plane is two meters (or 2.1 meters) or closer to a floor of the environment for human occupancy. However, if both UVA and UVC LEDs are operating together in an occupied environment, then the combined actinic dose generated by both the UVA and UVC LEDs should be below the actinic limit. As previously noted, this can be determined by the effective integrated spectral irradiance (effective radiant exposure, or effective dose), E_s, of the light source, which should not exceed 30 J/m² The effective integrated spectral irradiance, E_s, is defined as the quantity obtained by weighting spectrally the dose (radiant exposure) according to the actinic action spectrum value at the corresponding wavelength, e.g. using the published IESNA Germicidal action spectrum. For example, the light emitted by the at least one light source 10 (whether this is a UVA-only light source or a combination of UVA and UVC light sources) produces an actinic dose at a target plane in the environment over an eight hour period that is below an actinic limit, where the target plane is 2.1 meters or closer to a floor of the environment for human occupancy. A benefit of operating both UVA and UVC LEDs in combination with PCO-coated surfaces in an occupied environment is that the UVC may strongly inactivate viruses while airborne, and the UVA-activated PCO may strongly inactivate viruses on the PCO-coated surfaces after the precipitate from the air onto the surfaces, or are deposited directly onto the surfaces.

[0053] It should be noted that the limitations on maximum light output of the light sources 10 in any of the embodiments disclosed herein that are imposed by the actinic limit are only applicable if the light sources 10 are to be operated while the environment 2 for human occupancy is actually occupied, or at least may be occupied. On the other hand, if the disinfection system includes occupancy sensors to reliably detect when the environment 2 is occupied, then the light sources 10 may be operated above the actinic limit when the occupancy sensors indicate the environment 2 is unoccupied. The occupancy sensors may, for example, include one or more of: motion sensors such as a passive infrared (PIR) motion sensors, microwave motion sensors, ultrasonic motion sensors, a camera-based motion sensors, and/or so forth; a microphone which detects occupancy based on detected vocalization; and/or so forth. To ensure reliable determination of when the environment 2 is unoccupied, in some embodiments at least two occupancy sensors are used (in some variant embodiments further required to be of different sensor types or modes of operation), and the determination of whether the environment 2 is occupied or unoccupied is based on some combination of the outputs of the two or more sensors, e.g. all sensors must agree the environment 2 is unoccupied or alternatively using a voting scheme.

[0054] However, UVC radiation may be of reduced efficacy for inactivating viruses that are bound to a surface.

[0055] Hence, the disclosed synergistic combination of light sources 10 emitting both UVA and UVC light and the PCO coating 30 provides inactivation of all of: airborne bacteria (predominantly due to the UVA light); airborne viruses (predominantly due to the UVC light); and surface-bound bacteria and viruses (predominantly due to the PCO layer 30 activated by the UVA or UVC light).

[0056] In the following, an analysis is provided of the effectiveness of the PCO layer 30 in the indoor setting for disinfection purposes. The typical size range of viruses is about 0.02 to 0.25 pm. The typical size range of bacteria is about 0.2 to 3 pm. The typical size range of fungi is about 3 to 30 pm. See, e.g. Wladyslaw Kowalski, Ultraviolet Germicidal Irradiation Handbook (Springer-Verlag Berlin Heidelberg 2009) (hereinafter “Kowalski 2009”). From 2009 Liu, Particle Deposition onto Enclosure Surfaces, The Aerospace Corporation, CONTRACT NUMBER FA8802-09-C-0001 , the deposition rate onto the walls, floor and ceiling of particles suspended in the air can be calculated as a function of time given the diameter (or characteristic length) of the airborne particle and the dimensions of the space.

[0057] FIGURES 6-11 present tables of thusly calculated deposition-rate parameters, where particles of diameter 0.01 to 0.3 pm represent small to large viruses, and diameters 0.1 to 3 pm represent small to large bacteria. FIGURE 6 describes four typical room sizes (small office, conference room, ballroom, and gym or lobby) across the range of interest for indoor disinfection lighting, where the ratio of surface area (assuming 4 walls + floor + ceiling, and no other surfaces) to the volume, SA/, is the geometric factor that determines the deposition rate from the volume onto the surfaces. Clearly, if there are additional surfaces in the space, e.g. furniture, then the ratio S/V will be larger. Therefore, the S/V with no objects inside the room should be considered to be a minimum value for S/V, and the deposition rates calculated here would also be minimal rates. FIGURES 7 and 8 summarize the percentage of airborne particles that are deposited onto the surfaces after periods of 1 hour and 8 hours, respectively. FIGURE 9 shows the additional deposition provided by a low amount of mechanical ventilation (air changes per hour, ACH, of 2.4/hr), with an 8-hour elapsed exposure time. The enhancement of the deposition rate of particles from the volume of air to the surfaces is given to be about 4x in going from an ACH of 0.8/hr to an ACH of 2.4/hr in Fig. 4 of 2009 Liu, thus the enhanced deposition rates in FIGURE 9 vs. FIGURE 8. This 4x enhancement of particle deposition onto surfaces due to a mild amount of air movement suggests that the inclusion of a fan in the environment to direct the motion of air towards a surface that is coated with PCO and irradiated with UVA may considerably enhance the overall disinfection rate in the environment. Furthermore, it may be advantageous for the fan-driven air motion to be generally away from a potentially susceptible likely occupant location (e.g., a desk that is likely to be occupied) and especially in a direction that avoids moving airborne pathogens from the vicinity of one likely occupant location (which might potentially be an infected person) to another likely occupant location (which might potentially be a person susceptible to infection). Generally, a vertical motion of air will provide such advantage. For example, a fan may direct air upward into the upper room, above the head space of individual occupants, where high intensities of UV (due to closeness to the ceilingmounted light sources 10, see FIGURE 1 ) may disinfect the air before returning the air downward into the occupancy zone in the environment. In contrast, in the present disclosure which includes the PCO layers 30 (see FIGURE 1 ), since the dose of UV is below the allowed actinic limit, and the UV is irradiated generally downward from a ceiling fixture directly exposing the occupants in the environment, as well as irradiating the floor and other horizontal surfaces, if such surfaces are coated with PCO (that is, if PCO layers 30 coat surfaces at occupancy level), then the enhanced inactivation is realized. Therefore, a fan that directs air generally downward in combination with surfaces coated with PCO and irradiated by UVA at dose levels below the actinic limit will provide an enhanced inactivation of airborne and surface pathogens in the occupied environment. FIGURE 10 extends the additional deposition provided by a low amount of mechanical ventilation (air changes per hour, ACH, of 2.4/hr), with a 24-hour elapsed exposure time. FIGURE 11 is a calculation of the incremental log removal rate of the pathogens from the air onto the surfaces based on the percent deposition from FIGURE 10 (at 24 hours, with ACH = 2.4/hr ventilation), indicating that for bacteria of 1 pm, an additional removal of about 0.7 to 1 .0 log is obtained due to deposition onto surfaces in smaller rooms. For bacteria larger than 1 pm, the removal rate can be several log . If each surface is coated with the PCO layer 30 and irradiated with sufficient UVA light, providing a high log kill once the bacteria alights onto the surface, then the log deposition rate of the airborne bacteria is equivalent to an enhancement of the log inactivation rate of the bacterial in air due to the UVA.

[0058] With reference now to FIGURES 12-16, some further aspects of combined UVA and PCO layer disinfection in a space for human occupation are described. In general, FIGURES 12-16 depict a diagrammatic side view of the environment 2 for human occupancy, including the ceiling 4, walls 8, and floor 6. A single ceiling-mounted diagrammatic light source 10 is shown in FIGURES 12-15, while FIGURE 16 includes both a ceiling-mounted light source 10 and a wall-mounted light source 10, the latter being disposed on the left-hand wall 8 from the vantage of FIGURE 16. A single representative object 31 (and more particularly the table 32 in the example of FIGURE 14) is disposed in the environment 2. In FIGURES 12-16,

[0059] With reference to FIGURE 12, the light source 10 emits UVA light 70 that travels within the fixture of the light source 10 and the environment 2 in which the light source 10 is installed. Some portion of the UVA light 70 may interact with pathogens that are present on surfaces of the space, or objects 31 within the space, or fluids such as air within the space, inactivating or reducing these pathogens. These interactions are indicated by filled star symbols. The PCO coating 30 is applied to the outside of the light source 10 (as also shown in FIGURE 2). Some portion of the UVA light 70' interacts with the PCO coating 30 to create reactive oxygen species (ROS), which inactivates or reduces pathogens on the coated surface or in fluids adjacent to the surface. This PCO-mediated disinfection at surfaces coated with the PCO layer 30 is indicated by open star symbols.

[0060] With reference to FIGURE 13, the arrangement of FIGURE 12 is shown but with the addition of an air circulating device 72 (e.g., a fan 72) that produces air movement 74. Air circulation devices 72 may be employed to bring more air into contact with the PCO-coated surface to be cleaned or disinfected, further enhancing the effectiveness of the PCO coating 30. Devices may be employed to alter or regulate the humidity of the air to increase the effectiveness of the disinfection. The air circulating device(s) 72 may or may not be a part of the UVA-generating device. (For example, the air circulating device(s) 72 may be pre-existing HVAC fans or blowers).

[0061] With reference to FIGURE 14, the illustrative object is the table 32 with a PCO layer 30 coating the underside of the table 32 (also shown in FIGURE 3; the embodiment of FIGURE 14 omits the PCO layer coating the top of the table 32 shown in FIGURE 3). UVA radiation is typically reflected with around 10-30% efficiency from common interior building materials (walls, floors, ceilings, textiles, etc.), so that first-bounce irradiances may be around 10-30% and second-bounce irradiances may be around 1 -10% of the direct UVA irradiation, which may not be sufficient to inactivate pathogens. If a surface that is not exposed to direct irradiation but is exposed to first-bounce or second-bounce (or more bounces) irradiation is coated with PCO (e.g. the PCO coating 30 on the underside of the table 32 as shown in FIGURE 3, optionally also coating shadowed legs of the table or more generally any surface not exposed to direct UVA radiation), then the UVA irradiance may be sufficient to inactivate pathogens on the PCO-coated surfaces.

[0062] With reference to FIGURE 15, the PCO coating 30 may instead - or in addition - be applied to surfaces of the environment 2, e.g. the left-hand wall 8 of the environment 2 is shown in FIGURE 15 as including a PCO layer 30 (see also PCO layer 30 on two walls 8 shown in FIGURE 1 ) and/or to surfaces of objects 31 in the environment 2 (see also PCO coating 30 on the tabletop of the table 32 shown in FIGURES 1 and 3) allowing enhanced disinfection on those surfaces. These surfaces may in addition be coated with materials that enhance the UVA reflectivity of the surface, allowing the UVA light to reflect off of these surfaces onto other objects or surfaces that may or may not be coated with PCO. Air may be circulated around or forced onto the coated surfaces in the room (by fan, synthetic jet, or the like; not shown in FIGURE 15 but shown and described with reference to FIGURE 13) to increase disinfection effectiveness. Alternatively, if these surfaces are made from or covered with a PCO-coated permeable surface, air may be forced through them. The coated surfaces or objects may include air-permeable textile sheets or wall partitions, air vents or other HVAC components, by way of non-limiting illustrative example.

[0063] With reference to FIGURE 16, the light source(s) 10 may be incorporated into walls 8, ceiling 4, floor 6, or surfaces of other objects such as tables or countertops. This is shown in FIGURE 16 as light sources 10 incorporated into the ceiling 4 and left-hand wall 8; see also FIGURE 1 showing light sources 10 mounted on the ceiling 4). The light source(s) 10 may employ a TIR optic where contact with the optic acts as an extraction point, causing UVA light to exit the TIR optic, thereby activating the PCO at the point it was contacted.

[0064] These various embodiments may be variously combined. In various embodiments, the PCO layer(s) 30 may be applied to one or more internal surfaces of the light source(s) 10, and air may be forced through the fixture of the light source to come in contact with these surfaces to be disinfected. The air may be moved a fan, by a synthetic jet, by natural convection, or by some other method. The light source(s) 10 (or some subset thereof) may act as an air supply or return vent as part of the space’s HVAC system, disinfecting air as it is exchanged in the space. High-surface-area objects such as meshes may be coated with PCO and incorporated into the light source(s), forcing air to pass through or come in contact with the coated object — the high surface area increasing the likelihood of pathogens in the air coming in contact with the activated PCO. Devices that precipitate or flocculate pathogens to increase the likelihood of coming in contact with PCO coated surfaces may be employed, such as cyclonic filters or AC or DC electrostatic devices. The air may be forced through a serpentine or other complex path coated with activated PCO to increase the likelihood of pathogens coming in contact with the path surfaces.

[0065] The present disclosure has been described with reference to exemplary embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS:

1 . A disinfection system comprising: at least one electric light source configured to emit light into an environment for human occupancy wherein the light includes light in the UVA range and/or light in the violet range; and a photocatalytic oxidation (PCO) coating disposed on one or more surfaces of the environment for human occupancy and arranged to be directly or indirectly illuminated by the at least one electric light source.

2. The disinfection system of claim 1 wherein the at least one light source comprises one or more light emitting diodes (LEDs) emitting light with a spectrum whose maximum peak wavelength is in the UVA spectrum.

3. The disinfection system of any one of claims 1 -2 wherein the PCO coating comprises titanium dioxide (TiO2).

4. The disinfection system of claim 3 wherein the TiO2 of the PCO coating comprises at least 60% anatase TiO2 with the balance of the TiO2 being one or more TiO2 phases other than anatase TiO2.

5. The disinfection system of claim 3 wherein the TiO2 of the PCO coating comprises at least 70% anatase TiO2 with the balance of the TiO2 being one or more TiO2 phases other than anatase TiO2.

6. The disinfection system of claim 3 wherein the TiO2 of the PCO coating comprises pure anatase TiO2 or a mixture of anatase TiO2 and rutile TiO2 with bi-phasic separation.

7. The disinfection system of any one of claims 1 -2 wherein the PCO coating is disposed on one or more walls of the environment for human occupancy.

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8. The disinfection system of any one of claims 1 -2 wherein the PCO coating is disposed on one or more or all of the surfaces of at least one object disposed in the environment for human occupancy.

9. The disinfection system of any one of claims 1 -2 wherein the light emitted by the at least one light source produces an actinic dose at a target plane in the environment for human occupancy over an eight hour period that is below an actinic limit, wherein the target plane is 2.1 meters or closer to a floor of the environment for human occupancy.

10. The disinfection system of any one of claims 1 -2 wherein the light emitted by the at least one light source further includes light in the UVC spectrum.

11 . The disinfection system of any one of claims 1 -2 wherein the environment for human occupancy is an indoor environment.

12. The disinfection system of claim 11 further comprising: an air circulating device arranged to flow air vertically upward or downward in the indoor environment.

13. The disinfection system of any one of claims 1 -2 wherein the environment for human occupancy is a vehicle interior.

14. A disinfection method comprising: applying a photocatalytic oxidation (PCO) coating on one or more surfaces of an environment for human occupancy; and operating an electric light source to output light into the environment for human occupancy wherein the light includes light in the UVA range and/or light in the violet range and wherein the light directly and/or indirectly impinges on the applied PCO coating.

15. The disinfection method of claim 14 wherein the PCO coating comprises titanium dioxide (TiCh).

16. The disinfection method of claim 15 wherein the TiCh of the PCO coating comprises at least 60% anatase TiO2 with the balance of the TiO2 being one or more TiO2 phases other than anatase TiO2.

17. The disinfection method of claim 15 wherein the TiO2 of the PCO coating comprises at least 70% anatase TiO2 with the balance of the TiO2 being one or more TiO2 phases other than anatase TiO2.

18. The disinfection method of claim 15 wherein the TiO2 of the PCO coating comprises pure anatase TiO2 or a mixture of anatase TiO2 and rutile TiO2 with bi-phasic separation.

19. The disinfection method of any one of claims 15-18 wherein the applying includes applying TiO2 nanoparticles suspended in a fluid on the one or more surfaces of an environment for human occupancy using a high volume, low pressure (HVLP) spray gun.

20. The disinfection method of claim 19 wherein the fluid comprises water.

21. The disinfection method of any one of claims 14-18 wherein the PCO coating further comprises a binder.

22. The disinfection method of claim 21 further comprising applying a binder layer without TiO2 prior to the applying of the PCO coating.

23. The disinfection method of claim 14-18 further comprising applying a binder layer without TiO2 prior to the applying of the PCO coating.

24. The disinfection method of any one of claims 14-18 wherein the applying includes applying the PCO coating on the one or more surfaces of an environment for human occupancy using a spray gun.

25. The disinfection method of any one of claims 14-18 wherein the applying includes applying the PCO coating on the one or more surfaces of an environment for human occupancy using a high volume, low pressure (HVLP) spray gun.

26. The disinfection method of any one of claims 14-18 wherein the operating includes operating the electric light source to output the light into the environment for human occupancy to produce an actinic dose at a target plane in the environment for human occupancy over an eight hour period that is below an actinic limit, wherein the target plane is 2.1 meters or closer to a floor of the environment for human occupancy.

27. The disinfection method of any one of claims 14-18 wherein the light output into the environment for human occupancy further includes light in the UVC spectrum.

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