Abstract:
A system for treating a surface to prevent or limit offensive odors and/or microbiological activity and improve indoor air quality includes electrostatically charged particles of anatase titanium dioxide and a substrate or surface on which these particles are received. The electrostatic charging of the particles, in conjunction with the substrate being oppositely charged, provides a self-leveling effect to the particles. The particles may be incorporated into an HVAC system defined by ductwork in which untreated air including organic matter flows, is treated, and is ejected as clean air. Methods of treating surfaces or fluids containing organic matter include providing electrostatically charged particles of anatase titanium dioxide and contacting the organic matter therewith to initiate photocatalytic oxidation processes in which the organic matter is broken down into less offensive constituents such as carbon dioxide and water.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to methods and systems for the application of materials to improve indoor air quality and, more particularly, to methods and systems that utilize photocatalytic oxidation to effect the treatment of offensive and undesirable odor-causing elements, inhibit microbial growths, and improve indoor air quality. 
       BACKGROUND OF THE INVENTION 
       [0002]    Various systems for the cleaning and/or deodorizing of surfaces are currently in use. Some systems are generally directed to controlling microbiological particles and other organic constituents via the physical removal of such particles by encapsulating and dispersing the particles which can then be flushed away with water or other solvents. In other systems, chemical agents are used to neutralize or provide some other chemical change to the offending particles. Most often, a system will utilize the combination of neutralization with chemical change and physical removal of the particles. Other systems, particularly those directed to controlling or abating offending odorous emissions, typically mask the particles with perfumes or the like. Still other systems utilize various types of filter media, for example, by promoting the collection of particles in or on material that traps and retains the particles or on surfaces that are ionically charged to attract oppositely charged particles. 
       SUMMARY OF THE INVENTION 
       [0003]    In one aspect, the present invention resides in a treatment system for improving indoor air quality and/or preventing or at least limiting offensive odors and/or microbiological activity such as mold growth or the proliferation of viruses, bacteria, and the like. This system includes particles of anatase titanium dioxide and a substrate or surface on which these particles are received. The titanium dioxide particles are electrostatically charged by being passed between two electrodes prior to deposition on the substrate, thereby charging the particles. The substrate or surface is grounded. Because the particles are similarly charged, they repel each other. However, because the particles are oppositely charged with respect to the substrate, they are attracted to the substrate. The repelling of the particles from each other and the attraction of the particles to the substrate allows the particles to be evenly distributed over the surface of the substrate, thereby exhibiting a self-leveling effect. 
         [0004]    In another aspect, the present invention resides in an HVAC (heating, ventilation, and/or air conditioning) system for the photocatalytic treatment of airborne organic matter. The system is defined by ductwork in which untreated air is directed to flow. The untreated air includes organic matter (microbes, mold, viruses, bacteria, odorous particles, or the like). The ductwork is in communication with a reactor in which particles of titanium dioxide are introduced to provide for the catalytic oxidation of the organic matter, which is collected and removed from the air. The air is then ejected from the reactor as treated air. A light source may be employed with the ductwork to initiate the photocatalytic reaction. 
         [0005]    In another aspect, the present invention resides in methods of treating surfaces and/or organic matter (e.g., volatile organic compounds (VOC)). In these methods, electrostatically charged particles of anatase titanium dioxide are provided. When the particles contact the organic matter, a photocatalytic oxidation process in which the organic matter is broken down into less offensive constituents is initiated. When a surface is treated, the constituents are neutralized by the titanium dioxide. 
         [0006]    One advantage of the present invention is that the electrostatic charge imparted to the titanium dioxide particles causes the particles to repel each other. When deposited onto a grounded or negatively charged surface, the titanium dioxide particles provide a coating that is self-leveling. This coating is therefore more evenly applicable to a surface, which thereby results in a more complete and thorough treatment. Because of the ease with which this coating can be applied, the speed at which surfaces can be treated is vastly improved over methods of the related art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic representation of electrostatically charged particles of the present invention on a negatively charged surface. 
           [0008]      FIG. 2  is a schematic representation of particles being electrically charged as they are ejected from a spraying device. 
           [0009]      FIG. 3  is a schematic representation of particles being deposited onto a primer layer disposed on a substrate. 
           [0010]      FIG. 4  is a schematic representation of a system of ductwork in which air is treated using the electrostatically charged particles of the present invention. 
           [0011]      FIG. 5  is a schematic representation of electrostatically charged particles being deposited on a porous bed. 
           [0012]      FIG. 6  is a schematic representation of electrostatically charged particles being sprayed into a chamber for contact with untreated air. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]    As is shown in  FIG. 1 , a system for treating surfaces using photocatalytic oxidation is designated generally by the reference numeral  10  and is hereinafter referred to as “system  10 .” As used herein, the term “treating” means deodorizing and cleaning to produce an effect on indoor air quality. In system  10 , particles  12  are electrostatically charged to have a positive charge such that these particles are attracted to a negatively charged or grounded substrate  14 . The particles  12  are electrostatically charged as the result of being passed through an electrical field generated across electrodes. As the positively charged particles  12  approach the substrate  14 , they are attracted to the surface of the substrate. Moreover, because the particles  12  are all positively charged (or at least mostly positively charged), the particles are attracted to the substrate  14  and repellant of each other, which provides a self-leveling effect and gives a substantially uniform coating of particles. 
         [0014]    In one embodiment, the particles  12  are titanium dioxide particles of the anatase form. Anatase titanium dioxide is capable of oxidizing organic matter. When exposed to UV radiation (e.g., from sunlight or a light source  56 ), the electrons of the titanium dioxide are excited from their ambient energy levels to increased energy levels, which thereby allows for the generation of super oxide ions and hydroxyl radicals. The interactions of super oxide ions and hydroxyl radicals with organic matter facilitate the oxidation of the organic matter. Accordingly, when the particles  12  are coated onto the substrate  14  and come into contact with organic matter (e.g., microbiological particles, microorganisms, bacteria, viruses, mold, mildew, soot, deposits from cigarette and cigar smoke, and the like), the organic matter is oxidized and broken down into less offensive matter. Such less offensive matter may be, but is not limited to, carbon dioxide, water, and the like. 
         [0015]    Although the substrate  14  is generally shown as a flat surface on which the particles  12  are capable of collecting, the present invention is not limited in this regard. For example, the substrate  14  may be a wall, floor, or ceiling on which organic matter has collected and for which treatment is desired. More specifically, the substrate  14  may be drywall (painted or unpainted), masonry, carpeting, tile, millwork, or any other building product. Also, the substrate  14  is not limited to building products, as the particles  12  can be applied to upholstery, tabletops, clothing, drapery, and plastic or polymeric materials such as light switches, keyboards and computer peripherals, touchpads, writing utensils and stationery products, shopping carts, and the like. In any application of particles  12  to a substrate  14 , the particle material (e.g., the titanium dioxide) operates to oxidize organic matter. 
         [0016]    In one embodiment of the present invention, as is shown in  FIG. 2 , the particles  12  are suspended in an aqueous medium and dispensed from a spraying device  20  onto the substrate  14 . The spraying device  20  can be any suitable type of pressure-operated sprayer such as those typically used for spraying water. A nozzle  22  is located at an outlet of the spraying device  20  to control the flow of particles  12  from the spraying device. The nozzle  22  is capable of metering the spray from the spraying device  20  to provide a fine misting of particles to a surface to be treated. 
         [0017]    When the particles  12  are suspended in the aqueous medium, the concentration of titanium dioxide in the medium is about 2 weight percent (wt. %), although higher or lower concentrations may be used without departing from the broader aspects of the present invention. Typically, the particles  12  are nanometer sized particles that are attached to water particles of about 14 microns in diameter. The attractive forces between the water particles and the titanium dioxide particles  12  are about 40 times the force of gravity. 
         [0018]    Electrodes (a positive electrode  26  and a negative electrode  28 ) are located at the outlet of the spraying device  20 . An electrical charge is passed across the electrodes via a battery  29 . The present invention is not limited to the use of a battery for supplying the electrical charge, as other means of doing so (e.g., alternating current) are within the scope of the present invention. 
         [0019]    As is shown in  FIG. 3 , prior to the particles  12  being sprayed onto the substrate  14 , a primer coat  15  can optionally be applied to the substrate  14  to facilitate the adherence of the particles. This primer coat  15  comprises encapsulated titanium dioxide particles and, more particularly, titanium dioxide particles that are suspended in a gel. The primer coat  15  is applied in the same or a similar manner as in embodiments in which the particles  12  are applied to the substrate  14  without the primer coat  15 . 
         [0020]    In another embodiment of the present invention, as is shown in  FIG. 4 , the particles  12  can be introduced into an HVAC (heating, ventilation, and/or air conditioning) system of a building. The present invention is not limited to buildings, however, as the particles can be introduced into similar systems such as those characteristic of motor vehicles (such as cars, airplanes, buses, trains, and the like) as well as other enclosed areas (such as subway tunnels and the like). 
         [0021]    In a system of ductwork, which is designated generally by the reference numeral  30  and hereinafter referred to as “ductwork  30 ,” untreated air (shown at arrow  32 ) is drawn or forced through an inlet  36 . The inlet  36  may include a filter  38  that separates and removes dust and other particulate matter as well as larger organic matter from the untreated air  32  as the air enters the ductwork  30 . The present invention is not so limited, however, as the inlet  36  may include only a grate or the like that prevents larger debris from entering the ductwork  30 . 
         [0022]    The untreated air  32  is drawn into the ductwork  30  via a fan  40  or other apparatus capable of providing for the convective flow of air. An air flow speed detector  42  is located in the ductwork  30  to ascertain the speed of air flow through the ductwork. Both the fan  40  and the air flow speed detector  42  are in electrical communication with each other through a microprocessor  46  such that closed loop control of the air speed through the ductwork  30  is maintained. 
         [0023]    As the air passes through the ductwork  30 , the untreated air  32  is drawn into a reactor  50  and photocatalytically treated via electrostatically charged, photocatalytic titanium dioxide particles  12  and the light source  56 . Electrical communication between the reactor  50  and the microprocessor  46  allows for closed loop control of treated air  60  as it exits the reactor. The treated air  60  is then ejected from the ductwork  30 . 
         [0024]    As is shown in  FIG. 5 , in one embodiment, the reactor  50  comprises the electrostatically charged titanium dioxide particles  12  impregnated into or otherwise disposed on a web or the like to provide a porous bed  62  having an inlet surface  64  and an outlet surface  66 . The untreated air  32  is received on the inlet surface  64  and, as it passes through the porous bed  62 , deposits organic matter therein on the inlet surface where such organic matter is attracted to and brought into contact with the titanium dioxide particles  12 . As the untreated air  32  is received on the inlet surface  64  where the organic matter engages the titanium dioxide particles  12 , the particles are exposed to light from the light source  56 , which initiates the photocatalytic reaction of the titanium dioxide thus effectively destroying the undesirable constituents of the organic matter. The destroyed constituents of the organic matter are collected on and remain on the porous bed  62 , and the air then exits the porous bed from the outlet surface  66  as treated air  60 . 
         [0025]    As is shown in  FIG. 6 , in another embodiment, the reactor  50  comprises a spray of titanium dioxide particles  12  into a chamber  63  into which the untreated air  32  is drawn or forced. The particles  12  are sprayed from spraying devices  20  that impart electrostatic charges to the particles, thereby causing them to be attracted to oppositely charged particles of organic matter in the untreated air  32 . The electrostatic charge causes the particles  12  to stick to the organic matter. The light source  56  effects the photocatalytic reaction of the titanium dioxide to destroy the undesirable constituents of the organic matter. A reactor filter  68  is located in the reactor  50  to facilitate the collection of agglomerated particles of titanium dioxide and organic matter. Once the particles  12  agglomerate with the organic matter and are removed from the air stream, the treated air  60  is ejected from the reactor  50 . 
         [0026]    Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of the appended claims.