WO2010120730A1 - Hazardous substance removing materials, apparatus and methods - Google Patents

Abstract

A hazardous substance removing material and method, and uses and apparatus relating thereto, such as filter masks and other filtering apparatus, are disclosed. The material, in a preferred embodiment, comprises a porous fibrous matrix which is preferably a electrospun, nano fibrous material on which electrosprayed, photocatalytic metal oxide particles, are substantially uniformly deposited.

Description

TITLE: HAZARDOUS SUBSTANCE REMOVING MATERIALS, APPARATUS AND METHODS

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application, which is incorporated by reference herein and claims priority of US Provisional Application No. 61/168,656, filed April 13, 2009 and US Provisional Application No. 61/225,227, filed July 14, 2009.

TECHNICAL FIELD

The present invention relates to hazardous substance removing materials, apparatus and methods particularly suitable for use in air purification applications for breathing in hazardous gaseous environments, and in particular to such hazardous substance removing materials which comprise, for example, a material comprising an air filtering substrate, and apparatus such as a filter mask utilizing the material, and including in particular a replaceable filtering material used in such a mask, as well as methods for the use thereof.

BACKGROUND ART

Methods and materials for removing hazardous substances in gaseous mediums such as in the air, particularly of microbial or viral origin, for example viruses, bacteria, and the like, are well known. There are many types of filtration media and apparatus available using various kinds of filters, or employing techniques such as physical adhesion using adsorbents, and the like.

For example, US Patent Application No. 20060088926, filed April 27, 2006, discloses a method of removing hazardous substances, and hazardous substance removing materials using the same, such as an air cleaning filter, filter masks, and the like. A hazardous substance is removed by using a material in which a support supports an antibody to the substance. Humidity of the ambient atmosphere of the antibody is controlled so that the antibody becomes active, thereby providing a decontamination effect. Also, Japanese Patent Application Laid Open Publication No. 2001 -527166A, a fibrous material is disclosed including a plurality of interwoven threads with a high degree of microfibrillation, wherein at least one thread is derivatized using cyanogen bromide to attach a natural receptor for a virus, or a portion or an analogue thereof, in order to capture a virus. In another disclosure, Japanese Patent Application Laid Open Publication No. 8- 33327 IA describes an antiviral mask composed of a nonwoven fabric with which a tea extract is impregnated and ear stopper strings, wherein the nonwoven fabric with which the tea extract is impregnated is obtained in such a manner that the extract, which is separated and refined from green tea components or black tea components, is dissolved in purified water, is dehydrated lightly, and then dried. This disclosure describes the mask as being of a nonwoven fabric, with which the tea extract is impregnated, thereby to achieve high virus trapping and deactivation performance, and preventing re-entrainment of viruses.

Also, for example, in US Patent No. 6,417,423 Bl, issued July 9, 2002, US Patent No. 6,653,519 B2, issued November 25, 2003, and US Patent No. 7,335,808 B2, issued February 26, 2008, compositions and methods for destroying various biological agents and toxins are disclosed. The compositions comprise finely divided metal oxide or hydroxide nanocrystals, having reactive atoms stabilized on their surfaces, species adsorbed on their surfaces, or are coated with a second metal oxide. In addition, US Patent No. 7,396,569 B2, issued July 8, 2008, discloses methods for the self-assembly of nanoparticles onto a release support that is capable of covalent integration into flexible free-standing films. The nanoparticles may be spaced uniformly or in patterns throughout the films. In US Patent Application Publication No. US 2008/0102136 Al , there are disclosed compositions and methods for destroying biological agents such as toxins and bacteria, wherein the substance to be destroyed is contacted with finely-divided metal oxide or hydroxide nanocrystals. US Patent No. 7,390,760 Bl, issued June 24, 2008, discloses a composite material comprising a plurality of nano fibers intertwined with a plurality of coarse fibers to form one or more layers, which are useful for disposable garments, face masks air filters, and the like. Also, PCT Publication No. WO 2008/063870 Al discloses a filtration device including a filtration medium having a plurality of nano fibers of diameters less than 1 micron formed into a fiber mat in the presence of an abruptly varying electric field, and a device for making a filter material, including an electrospinning element configured to electrospin a plurality of fibers from a tip of the electrospinning element, a collector opposed to the electrospinning element configured to collect electrospun fibers on a surface of the collector, and an electric field modulation device configured to abruptly vary an electric field at the collector at least once during electrospinning of the fibers.

However, the aforementioned methods, materials and apparatus, and others known in the art, for removing hazardous substances in gaseous mediums such as air, which typically involve or have employed a filter or means of physical adhesion using an adsorbent, are largely directed to capture of substances nonspecifically, and have been known to have low effectiveness and to achieve low precision in capturing target substances. Further, in order to avoid re-entrainment or re-floating of removed hazardous substances and to prevent multiplication of the hazardous substances so as not to allow them to serve as a new contaminant source, techniques for sterilizing and deactivating the hazardous substances usually must be incorporated.

SUMMARY OF THE INVENTION

The present invention has as an objective the offering of improvements over the art as described above, by providing hazardous substance removing materials, apparatus and methods which are particularly suitable for use in air purification applications for breathing in hazardous gaseous environments, such hazardous substance removing materials preferably comprising, for example, an air filtering substrate, a filter mask utilizing the substrate, filtering medium employing the material and used in such a mask, and other similar materials and apparatus, as well as methods for the use thereof. The improvements provided by the invention involve the advantageous utilization of the technology disclosed in the following two co-pending US Provisional Patent Applications, the disclosures of which are hereby incorporated by reference into this application in their entirety:

To attain the above objective, the present invention in a preferred embodiment achieves the removal of a hazardous substance in a gaseous environment by utilizing a substrate material, preferably suited for use in a filter, filter mask or other apparatus or device, wherein, upon the substrate material, deposition of metals or metal oxides has been achieved, such as by being electrosprayed onto a substrate, and wherein the substrate is comprised of an electrospun, nano fibrous material on which such electrosprayed and photocatalytic metal oxide particles are uniformly deposited without agglomeration.

Other objectives of the present invention are to provide apparatus and products made by such deposition methods, and uses of the products. The apparatus and products of the present invention may be used, for example, in a process for making filtration devices, which process involves providing a substrate, electro spinning a polymer solution to form a fiber matrix on the substrate and electrospraying metal or metal oxide particles on the fiber matrix. Still another objective is to provide products, and methods of using such products, in various applications such as artificial tissues and scaffolds, electronic applications, such as electronic packaging, sensors, actuators and fuel cells, and filtration systems, such as for the filtration of hazardous gaseous biological and chemical substances in gaseous media such as the air, for example in personal filtration media such as face masks and in biological and chemical protection systems. The materials, apparatus, products and methods provided by the invention are highly effective, by comparison with those of the known art, in avoiding the problems of re-entrainment or re-floating of removed hazardous substances and in preventing multiplication of the hazardous substances, so as not to allow them to serve as a new contaminant source, and thereby mitigating or eliminating the need for conventional techniques for sterilizing and deactivating the hazardous substances. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view schematically showing an air filter according to a preferred embodiment of the present invention.

FIG. 2 is a view schematically showing a mask in use according to a preferred embodiment of the present invention, which can incorporate the air filter shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The principles of the present invention are described herein for illustrative purposes by referencing various exemplary, preferred embodiments thereof. Accordingly, although certain embodiments of the invention are specifically described herein, one of ordinary skill in the art will readily recognize that the same principles are equally applicable to, and can be employed in other apparatuses and methods. Before explaining the disclosed embodiments of the present invention in detail, it is to be understood that the invention is not limited in its application to details of any particular embodiment shown. The terminology used herein is for the purpose of description and not of limitation.

It must be noted that as used herein and in the appended claims, the singular forms "a", "an", and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "a metal oxide" may include a plurality of metal oxides and equivalents thereof known to those skilled in the art, and so forth. As well, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and "having" can be used interchangeably.

Specifically, in a preferred embodiment the present invention achieves the improved removal of a hazardous substance in a gas atmosphere, using a hazardous substance removing material produced as described in the in the following examples, in which a metal oxide deposited fibrous material comprising a substrate, fibers and metal oxide particles, constitute a flexible and porous fibrous matrix on which the metal oxide particles are substantially uniformly deposited on the surface thereof, and wherein the matrix is an electrospun, nano fibrous material on which such electrosprayed and photocatalytic metal oxide particles are substantially uniformly deposited.

Examples

In the production of a material in accordance with the present invention, a metal or metal oxide suspension is deposited on a substrate by electrospraying. Electrospraying involves generating an electric field between a metal or metal oxide suspension contained, for

example, in a tip of a syringe and a substrate. When the applied electric field strength exceed the surface tension required to release a droplet of the metal or metal oxide suspension from the syringe, a spraying effect, i.e. electrospraying or electrostatic spraying, occurs whereby metal or metal oxide-containing droplets are expelled in a fine mist of atomized particles from the syringe tip.

In an exemplary embodiment of the invention, the applied electric field has a field strength of about 0.25 kV/cm-0.75 kV/cm. In exemplary embodiments of the present invention, the applied electric field strengths may be in the range of from about 0.2 kV/cm to about 4 kV/cm and more preferably, from about 0.3 kV/cm to about 3 kV/cm. The tip-to-collector distance is below about 30 cm, preferably about 20 cm.

Metal and/or metal oxide particles are suspended in a suspension and the suspension is electrosprayed, in order to deposit the particles on the substrate.

Electrospraying is a similar technique to electrospinning but the conditions are such that the suspension is made to spay in a fine mist, atomized particles, rather than as continuous fibers by varying the applied electric field to higher values than are used for electrospinning. Electrospraying has been used as a coating technique in various industries such as the automobile industry. It is desirable, in the present invention, that the metal and/or oxide solid content in suspension is 0.5 % - 20 % of the total suspension weight and, more preferably, the metal and/or metal oxide content 3%-10% of the total suspension weight. Below the lower limit of metal and/or metal oxide concentration in the suspension, the mixture does not expel to deposit onto the electrospun nanofiber. If the metal and/or oxide content in the suspension exceeds the upper limit, the syringe needle is easily clogged to prevent of the ejection of Metal oxide particles.

Metal and/or metal oxide particles may include any metals or metal oxides capable of binding to a surface of fiber-substrate matrix . In an exemplary embodiment, metal oxide particles 4 may have photocatalytic properties. Preferably the photocatalytic metal oxides may be TiOa (titania), ZnO, ZrOa, WO. Other suitable metal oxides include metal oxides with antibacterial properties, such as CaO, MgO, FeO, Fe2O₃, V₂O₅, Mn₂O₃, AbO₃, NiO, CuO, SiOi. Suitable metals are metals with antibacterial properties such as Ag, Zn, Cu and any combination thereof.

The particles used to prepare the spraying suspension may have particle sizes of from about 2 nm to about 1 nm, more preferably, from about 5 nm to about 50 nm and, most preferably, from about 10 nm to about 30 nm. The particle size of the particles used to prepare the suspension influences the particle size of the metal or metal oxide particles deposited on the substrate. Generally, it is desirable to deposit metal and/or metal oxide particles on the substrate having particle sizes of from about 2 nm to about 1 nm, more preferably, from about 5 nm to about 50 nm and, most preferably, from about 10 nm to about 30 nm.

A variety of different materials such as solvents may be used to prepare the particle suspensions. Exemplary solvents include, but are not limited to, deionized water or other polar solvents. The solvent must be capable of suspending a sufficient amount of the metal and/or metal oxide to prepare a suitable sprayable suspension as discussed above. At least one chelating agent such as acetylacetone, ethylacetoacetate, oxalic acid, pentamethylene glycol, phosphonic acids, gluconic acid and diacetone alcohol may be included in the metal oxide suspension in order to enhance the dispersion of the particles in the suspension.

The precise morphologies and physical properties of particles are determined by the selection of the metal and/or metal oxide, specifying the concentration of the metal and/or metal oxide suspension, selecting the conductivity of the solvents used in the suspension and the applied electric field strength. Each of these factors may be varied to produce metal and/or metal oxide particle coatings having different properties.

Preferably, particles are substantially uniformly deposited on substrate matrix , during the electrospraying process. The electrospraying process of the present invention enables a more uniform particle size distribution and avoids substantial agglomeration of the metal oxide particles, by comparison with conventional methods that otherwise may be employed.

In some embodiments, it is desirable to wash the substrate prior to electrospraying the particle suspension thereon in order to enhance the adhesion of the metal and/or metal oxide to the substrate. Washing can be carried out with any suitable solvent including, for example, deionized water and non-aqueous polar solvents like alcohols. Drying may be carried out under conditions that do not damage the substrate, such as drying at ambient temperature.

In some embodiments, it may also be desirable to carry out a surface modification step on the substrate prior to electrospraying and, optionally, after carrying out a washing step. Surface modification is also designed to enhance adhesion of the metal and/or metal oxide to the substrate. Conventional surface modification techniques may be employed, such as treating the substrate with a silica containing solution, and oven drying the treated substrate at a temperature of, for example, 50⁰C - 70⁰C. The surface modification step may employ a binder material that enhances the ability of particles to adhere to substrate. Preferably, the binder material may be stable up to temperatures of at least about 200⁰C. More preferably, the binder may be hydrophilic or may have a hydrophilic functional group. In an exemplary embodiment, the binder material may include at least one silica precursor, such as tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), tetra-w-propoxysilane, tetra-n-butoxysilane, and tetrakis(2- mehoxyethoxy) silane, and organoalkoxysilanes such as methyltriethoxysilane, methyhrimethoxysilane, phenytriethoxysilane, or vinyltriethoxysilane. The binder material is preferably acidic and thus may contain, for example, an inorganic acid such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and suitable organic acids such as acetic acid, dichloroacetic acid, trifluoroacetic acid, benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, ethylbenzenesulfonic acid, benzoic acid, phthalic acid, maleic acid, formic acid and oxalic acid. Also, preferably the pH is in the range of 1-6, and more preferably 2-5.

The substrate may be modified with a binder agent by any conventional coating means, including dip coating or spray coating. Dip coating is preferred because it can coat the whole filter fiber. The resultant coated substrate may then be ultrasonicated and dried.

The resultant deposited material of the present invention is advantageous because it may be highly flexible, thereby enabling the material to be incorporated in movable and bendable structures as well as flexible membranes, such as textiles and fabrics. Additionally, the deposited material may be fabricated to produce any desired pore size, including nanometer or micrometer sized pores suitable for fine filtration applications. The metal oxides of the present invention may also be selected to have photocatalytic properties to enable antimicrobial applications.

In view of these advantages, the deposited materials of the present invention may be used for a wide variety of applications. It is envisioned that products made by the method of the invention may be used for bio medical applications, including without limitation artificial tissues and scaffolds, electronic applications, such as electronic packaging, sensors, actuators and fuel cells, and filtration systems, such as filtration media and biological and chemical protection systems.

The substrate may be fabricated using any suitable means known in the art. The electrospraying process of the present invention may be advantageously incorporated as part of a fabrication method which employs electrospinning of a polymeric material to provide at least a portion of the substrate. In an exemplary embodiment, the substrate material may be a flexible and porous fibrous matrix on which metal and/or metal oxide particles have been deposited, and may be fabricated to have any desired pore size, including micron and nanometer sized pores and may also possess photocatalytic properties. In an exemplary embodiment, the substrate material is an electrospun nano fibrous material electrosprayed with a photocatalytic metal oxide.

The deposited fibrous material can be a composite matrix comprising a substrate, fibers, and metal and/or metal oxide particles, and can be any conventional porous scaffold or mesh structure suitable for supporting and/or binding fibers thereto. In an exemplary embodiment, the substrate can be synthesized from at least one polymeric material, including but not limited to, polypropylene, polyethylene, polycarbonate, polyurethane and, polyester, polybutene, polyisobutene, polypentene, polybutadiene, polyvinyls such as polyvinyl chloride or polyvinyl alcohol, poly(meth)acrylic acid, polymethylmethacrylate (PMMA), polyacrylocyano acrylate, polyacrylonitrile, polyamide, polyester, polystyrene, polytetrafluoroethylene, as well as mixtures thereof.

A variety of suitable support matrices are described in U.S. patent application publication no. US 20080110342, the disclosure of which is hereby incorporated by reference for the purpose of describing suitable support matrices for use in the present invention.

The deposited fibrous material further includes fibers, preferably formulated as nanofibers. The fibers may form a web that is supported by and bound to the substrate. The fibers may be synthesized from any suitable polymer capable of adhering to or being supported by substrate. In an exemplary embodiment, the polymer may include polyamides, such as polyamide 11 and polyamide 12, polyvinyl acetate), poly(vinylidene fluoride), polyvinyl pyrrolidone), poly(ethylene oxide), poly(acrylonitrile), poly(caprolactone), poly(methyl methacrylate), polycarbonate, polystyrene, polysulfone, acrylonitrile/butadiene copolymer, cellulose, cellulose acetate, chitosan, collagen, DNA, fibrinogen, fibronectin, nylon, poly(acrylic acid), poly(chlorostyrene), poly(dimethyl siloxane), poly(ether imide), poly(ether sulfone), poly(ethyl acrylate), poly(ethyl vinyl acetate), poly(ethyl-co-vinyl acetate), polyethylene terephthalate), poly(lactic acid-co-glycolic acid), poly(methyl methacrylate), poly(methacrylic acid) salt, poly(methyl styrene), poly(styrene sulfonic acid) salt, poly(styrene sulfonyl fluoride), poly(styrene-co-acrylonitrile), poly(styrene-co-butadiene), poly(styrene-co-divinyl benzene), poly( vinyl alcohol), poly(vinyl chloride), polyacrylamide, polyaniline, polybenzimidazole, poly(dimethylsiloxane-co- polyethyleneoxide), poly(etheretherketone), polyethylene, polyethyleneimine, polyimide, polyisoprene, polylactide, polypropylene, polyurethane, poly(vinylidene fluoride), poly(vinylpyrrolidone), poly(2-hydroxyethyl methacrylate) (PHEMA), proteins, SEES copolymer, silk (natural or synthetically derived), styrene/isoprene copolymer and combinations or polymer blends thereof. Polymer blends may be employed as long as the two or more polymers are soluble in a common solvent or mixed solvent system. Examples of possible polymer blends include poly(vinylidene fluoride)-blend-poly(methyl methacrylate), polystyrene-blend-poly(vinylmethylether), poly(methyl methacrylate)- blend-poly(ethyleneoxide), poly(hydroxypropyl methacrylate)-blend poly(vinylpyrrolidone), poly(hydroxybutyrate)-blend-poly(ethylene oxkie), protein blend- polyethyleneoxide, polylactide-blend-polyvinylpyrrolidone, polystyrene-blend-polyester, polyester-blend-poly(hydroxyethyl methacrylate), polyethylene oxide)-blend poly(methyl methacrylate), poly(hydroxystyrene)-blend-poly(ethylene oxide)) and combinations thereof.

In an exemplary embodiment, suitable fibers for use in the present invention may be fabricated by electrospinning a polymer solution onto the surface of the substrate to form a web of fibers. This process involves generating an electric field between a polymer solution contained in a tip of a syringe and the substrate. When the applied electric field strength exceeds the surface tension of a droplet of the polymer solution to be released from the syringe, the solution is ejected in a random spinning motion. The electric field applied in an exemplary embodiment of the invention has a field strength in the range of about 0.2 kV/cm to about 4 kV/cm and more preferably, of about 0.3 kV/cm to about 3 kV/cm. As the polymer solution is projected towards the substrate, the solvent in the polymer solution evaporates before collecting on the substrate, thereby producing long continuous polymer fibers deposited on the substrate. The polymer solution may include any polymer or polymer mixtures, preferably the above listed polymers, and corresponding solvents to dissolve said polymers. Alternatively or in addition thereto, the solution may include polymers which have been melted. Optionally, the solution may also include any additives or filler suitable for forming fibers by electiospinning. In an exemplary embodiment, the additives or fillers may be added to change the resultant fiber size and quality. For example, the addition of trace amounts of salts and/or surfactants may increases solution conductivity and the charge accumulation at the tip of the electiospinning device, generating greater stretching forces and smaller diameter fibers. Surfactants may also reduce the surface tension of the polymer allowing for smaller fibers. In an exemplary embodiment, the surfactants may include, but are not limited to, tetrabutyl ammonium chloride (TBAC), cesium dodecyl sulfate (CsDS), sodium dodecyl sulfate (SDS), tetramethyl ammonium dodecyl sulfate (TMADS), tetraethyl ammonium dodecyl sulfate (TEADS), tetiapropyl ammonium dodecyl sulfate (TPADS), tetrabutyl ammonium dodecyl sulfate (TBADS) and octylphenol poly(ethylene glycol ether) and the salts may include, but are not limited to, lithium chloride, sodium nitrate, calcium chloride, sodium chloride, formates, acetates, propionates, malates, maleates, oxalates, tartrates, citrates, benzoates, salicylates, phthalates, stearates, phenolates, sulfonates, and amines, as well as mixtures thereof.

In one embodiment of the present invention, polymer concentration in the electiospinning solution may influence the properties of the electrospun fibers. Concentrations from 2 wt% to 30 wt%, based on the total weight of the polymer solution, may be suitable for the present invention with a more preferred range of about 4 wt% to about 20 wt%.

A variety of suitable methods for electiospinning polymer fibers are described in, for example, U.S. patent application publication no. US 20080110342, the disclosure of which is hereby incorporated by reference for the purpose of describing suitable electiospinning methods for electrospinning polymers.

Electrospinning may be used to synthesize fibers with diameters ranging from several nanometers to several micrometers, depending upon the electiospinning conditions and selected polymer solution. In an exemplary embodiment, the fibers are nanosized fibers of about 100 nm to about 2 nm, more preferably 500 nm to about 1 nm. The precise morphologies and physical properties of the fibers can be determined by polymer selection, specifying the concentration of the polymer solution, selecting the conductivity of the solvents used in the polymer solution and selection of an applying an electric field strength, needle diameter of syringe and injection speed of polymer solution. Each of these factors may be varied to fabricate polymeric fibers having different properties.

In another embodiment, the present invention relates to metal and/or metal oxide deposited materials. In an exemplary embodiment, particles may be substantially uniformly distributed on a surface of the matrix and/or have a relatively narrow particle size distribution indicating that the particles do not substantially agglomerate into large particles. Usually, in the case of dip coating, the particle size of deposited metal oxide particles on the filter substrates is at least 100 nm due to agglomeration. On the other hand, metal oxides deposited by electrospraying usually have particle sizes of below 100 nm and, more preferably, below 50 nm. Also, electrospraying results in more uniformly deposited metal oxides on the substrate.

In one embodiment, the present invention relates to filtration materials made by a process of the present invention wherein the fibrous portion of the substrate is fabricated by electrospinning and the metal and/or metal oxide is applied by electrospraying. In such filtration devices, electrospraying allows the particles to be distributed such that they do not substantially block or prevent the flow of air through the pores of fiber-substrate matrix. Preferably, the particles are nanosized powder particles which provide a layer of fine coating over the fiber-substrate matrix. Therefore, the resultant matrix has a smaller pore size and larger specific surface area as compared to a fiber-substrate matrix prepared by dip coating metal oxide particles onto the substrate, as well as compared to many conventional filtration systems.

Of these various applications, the invention can be particularly beneficial for filtration systems, specifically antimicrobial filtration systems. The material of the present invention can be synthesized as a nanofibrous matrix, which when coated with nanosized metal and/or metal oxide particles, is capable of fine filtration. The material can then be formulated as, applied to or incorporated in a textile or fabric to contain or filter out undesirable particles and pollutants. In an exemplary embodiment, a photocatalytic metal oxide is deposited on a nano fibrous material having a large specific surface area for antimicrobial activity. The photocatalytic metal oxide particles may function to contain, inhibit or render ineffective bacteria, viruses and other microorganisms. When the photocatalytic metal oxide is illuminated by visible or ultra violet light having a higher energy than its band gaps, the valence electrons in the photocatalytic metal oxide will excite to the conduction band, and the electron and hole pairs will form on the surface and bulk inside of the metal oxide photocatalyst. These electron and hole pairs generate oxygen radicals, O²", and hydroxyl radicals, OH", after combining oxygen and water, respectively. Because these chemical species are unstable, when the organic compounds contact the surface of the photocatalyst, it will combine with O²" and OH", respectively, and turn into carbon dioxide (CO2) and water (H2O). Through the reaction, the photocatalytic metal oxide is able to decompose organic materials, such as odorous molecules, bacteria, viruses and other toxic or harmful microorganisms, in the air.

The antimicrobial activity of the photocatalyst involves oxidative damage of the cell wall where the photocatalytic metal oxide contacts the microorganism. Upon penetration of the cell wall, the photocatalytic metal oxides may gain access to and enable photooxidation of intracellular components, thereby accelerating cell death.

Experimental Procedures

Titania deposited nano fibrous material of the present invention was synthesized according to the following method. A polypropylene filter substrate was washed and cleaned by dipping into a deionized water and polar solvent mixture. It was subsequently dried at ambient temperature before being dip coated in a silica binder solution. The substrate was then ultrasonicated and dried in an oven at about 50⁰C to about 70⁰C. A solution of 2 grams of polyamide 11 in 48 g of formic acid/dichloromethane of 30 ml equal volume amount was prepared. This solution was heated on a heating plate while stirring. This polyamide solution was then electrospun onto the silica coated substrate at an applied electric field strength of about 1 kV to about 30 kV, to produce polyamide nano fibers. Nanosized titania particles of about 10 nm to about 15 nm in diameter were then suspended in a suspension with deionized water and ethanol 50:50 (w/w) and electrosprayed onto the polyamide nanofϊbers. The titania particles were electrosprayed using an applied electric field strength of about 5 kV to about 15 kV. Titania particles were applied to the same substrate as was used as described above using a dip coating process similar to that described in Kenawy, E.R. and Y.R. Abdel-Fattah (2002) "Antimicrobial properties of modified and electrospun poly( vinyl phenol)." Macromolecular Biosciences 2(6): 261-266. It was found that significant agglomeration of the titania occurred as a result of this process leading to a non-uniform distribution of titania on the substrate, as well as the formation of larger agglomerated titania particles. The formation of the larger agglomerated particles is disadvantageous since it decreases the effective surface area of the titania available to provide antimicrobial activity relative to smaller particles of the same amount of titania.

The preparation of a titania dispersion useful in the present invention can be as described below. The dispersion can be prepared in a three step process that involves a first solvothermal preparation of titania particles, a second preparation of titania particles by hydrolysis and a subsequent step of blending the titania particles made by the solvothermal and hydrolysis processes.

The Solvothermal Process

The solvothermal process provides a higher degree of anatase crystallinity and a higher concentration of the titania. In contrast, the hydrolysis process provides a more uniform participate dispersion. In an exemplary embodiment, the invention is directed to a novel method for synthesizing a transparent and photocatalytic titania dispersion that is characterized by substantially uniformly dispersed nanometer titania particles having anatase crystalline structures. The solvothermal step of the present invention is designed to effectively proprogate anatase structure titania particles. Solvothermal preparation of titania is known and various solvothermal processes are described in, "Titanium Dioxide Nanomaterials: Synthesis, Properties, Modification and Applications," Chen, Xiaobo and Mao, Samuel S., Chem. Rev., 2007,107, 2891-2959, the disclosure of which is hereby incorporated by reference for the discussion of the production of titania nanomaterials by solvothermal processes.

The solvothermal step of the present invention involves preparing a solution of a titania precursor in a suitable solvent, such as non-aqueous polar solvent or mixtures of non- aqueous polar solvents. In order to enhance visible light efficiency, metal ions such as Fe³⁺, Cr³⁴, In³⁺, W⁶*, Nb⁵⁺, canbe introduced as dopants into the TiO₂ structure. Also, metal or metal oxides of Pt, Ru, Ni, Cu, Fe, can be impregnated. Therefore, the precursors for these materials, for example, platinum tetrachloride (PtCU), nickel nitrate, etc. may also be included in the solution. Any titania precursor or titania precursor complex may be incorporated in the solution. In an exemplary embodiment, the titania precursor and the synthesized titania dispersion may have photocatalytic properties. For example, the titania precursors, such as titanium isopropoxide, titanium butoxide, and other titanium alkoxides, titanium chloride, titanium nitrate, titanium sulfate, titanium amino oxylate, titanium trichloride, tetrabutoxytitanate, titanium tetraethoxide or a combination thereof, may be used to synthesize photocatalytic titanias.

The method is capable of synthesizing a nontoxic, water insoluble, highly oxidizing, UV and/or visible light activated photocatalytic titania particles. In an exemplary embodiment, the titania precursor may be present in the solution in an amount less than about 20% by weight of the solution, more preferably in an amount of about 1% to about 10% by weight of the solution.

Additional compounds, such as acids, bases or combinations thereof, may be added to the titania precursor solution to adjust the pH. In an exemplary embodiment, the pH of the mixture is sufficiently low to break down the titania particles, thereby producing small titania particles. The added compound may be used to establish a pH level equal to or less than about 6, preferably, about 1-6, more preferably, equal to or less than about 4, and most preferably, about 2 - 4. In an exemplary embodiment, the compound may be any inorganic acid, such as nitric acid, hydrochloric acid, sulfuric acid, orthophosphoric acid, perchloric acid or organic acid such as acetic acid, pentanoic acid, butanoic acid, propaneic acid, oleic acid, carboxylic acid, linoleic acid or a combination thereof. Additives may be optionally included in the mixture. In an exemplary embodiment, the additives may enhance antimicrobial activity of the dispersion. For example, silver precursors or other antimicrobial agents may be added to the mixture. The commonly used Ag precursor: silver nitrate, silver chloride.

Optionally, the mixture may also include any binding agent capable of facilitating or enhancing the binding or application of the synthesized titania dispersion to any desired surface or substrate. Preferably, the binding agent may be stable up to temperatures of at least about 200⁰C. More preferably, the binding agent may be either hydrophilic or may have a hydrophilic functional group. The binding agent may alternatively be added to the metal oxide dispersion. Most preferably, the binding agent facilitates the uniform dispersion of titania particles in a dispersion and/or uniform deposition of the titania dispersion on a substrate, and in an exemplary embodiment, the binding agent may include at least one silica compound or precursor, such as tetraethylorthosilicate (TEOS) or tetramethyl orthosilicate (TMOS), tetra-n- propoxysilane, tetra-n-butoxysilane, and tetrakis (2-mehoxyethoxy) silane, and organoalkoxysilanes such as methyltriethoxysilane, methyltrimethoxysilane, methyl tri-n- propoxysilane, phenyltriethoxysilane, or vinyltriethoxysilane.

The binding material is preferably acidic and thus, may contain, for example, an inorganic acid. The binding agent may be capable of facilitating coupling without further modifying the surface or substrate to be coated with the titania dispersion.

Subsequently, the titania precursor solution may be stirred and simultaneously heated.

Preferably, the solution is heated to a temperature of about less than 200⁰C, more preferably, about 150⁰C to about 200⁰C, and most preferably about 150⁰C to about 170⁰C and is prepared under a pressure of about 10 atmospheres to about 20 atmospheres, preferably about 10 atmospheres to about 17 atmospheres for less than about 5 hours, more preferably about 2 hours to about 3 hours. Temperatures and pressures below this range are insufficient to induce chemical interaction, and temperatures and pressures above this range cause large particle coagulation and increase the risk of explosion. From this pressurized heating step, titania particulates may be precipitated in the titania precursor solution. In an exemplary embodiment, the resultant product contains from about 1% to about 15% by weight of titania particles, based on the total weight of the reaction mixture, more preferably in an amount of about 0.3 wt% to about 5 wt%, based on the total weight of the reaction mixtures. Notably, the synthesized product has a high concentration of titania, and an increased crystallinity and Brunauer-Emmett-Teller (BET) specific surface area. The degree of crystallinity may be varied by adjusting the pH of the solution and/or the reaction temperature and pressure of the solvothermal reaction. In an exemplary embodiment, the solvothermal synthesis may produce fine nanosized titania particles of from about 2 nm to about 100 nm, more preferably, from about 5 nm to about 50 nm, and, most preferably, from about 10 nm to about 30 nm. Additionally, due to the added binder material, the solution may readily adhere to any surface or substrate.

The Hydrolysis Method

The dispersion of the titania prepared by a solvothermal process can be improved as follows, by conducting a second synthesis of titania by hydrolysis and then combining the hydrolysis product with the solvothermal product. Thus, the present invention can also nvolve the step of synthesizing titania particles by hydrolysis of at least one titania precursor in solution. The production of titania by hydrolysis is also known and various hydrolysis processes, also referred to as hydrothermal processes, are described in, "Titanium Dioxide Nanomaterials: Synthesis, Properties, Modification and Applications," Chen, Xiaobo and Mao, Samuel S., Chem. Rev., 2007,107, 2891 -2959, the disclosure ofwhich is hereby incorporated by reference for the discussion of the production of titania nanomaterials by hydrothermal processes.

In the hydrolysis step, a solution is prepared from water and a titania precursor. Any titania precursor or titania precursor complex may be incorporated in the solution. In an exemplary embodiment, the titania precursor and the synthesized titania may have photocatalytic properties. For example, the titania precursors, such as titanium isopropoxide, titanium alkoxide, titanium chloride, titanium nitrate, titanium sulfate, titanium ammo oxylate, titanium isoproxide or a combination thereof, may be used to synthesize photocatalytic titania. The hydrolysis step is also capable of synthesizing a nontoxic, water insoluble, highly oxidizing, UV and/or visible light activated photocatalytic titania. In an exemplary embodiment, the titania precursor may be present in the solution in an amount less than about 20% by weight of the solution, more preferably in an amount of about 3% to about 10% by weight of the solution.

If necessary, deionized water may be added to the mixture to initiate hydrolysis and functions to maintain a dispersion of the titania photocatalyst. In an exemplary embodiment, water is present in an amount of about 50% to about 80 % by weight of the solution, more preferably in an amount of about 65% to about 75% by weight of the solution.

Polar solvents may optionally be added to the titania precursor prior to hydrolysis. Any polar solvents capable of improving the dispersion of the titania particles may be used. In an exemplary embodiment, the polar solvent may be an organic, non-aqueous solvent. Preferably, the polar solvent may include ethyl alcohol, isopropyl alcohol, methyl alcohol, acetone, dichloromethane, tetrahydrofuran, ethylacetate, ethers, demethylformamide or a combination thereof.

Additional compounds, such as acids, bases or combinations thereof may be added to the mixture to control the pH level of the mixture. In an exemplary embodiment, the pH of the mixture is sufficiently low to dissolve or break down the titania particles, thereby producing small titania particles. The added compound may be used to establish a pH level equal to or less than about 6, preferably, about 1 -6, more preferably, equal to or less than about 4, and most preferably, about 2-5. In an exemplary embodiment, the compound may be any inorganic acid, such as nitric acid, hydrochloric acid, sulfuric acid orthophosphoric acid, perchloric acid or an organic acid such as acetic acid, pentanoic acid, butanoic acid, propanoic acid, oleic acid, carboxylic acid, linoleic acid or a combination thereof.

Optionally, the mixture may also contain various additives such as binder materials and chelating agents. In an exemplary embodiment, the mixture may include an additive, such as a chelating agent, which may function to reduce titania particle size, enhance dispersion stability, improve solubility, and induce catalytic action, and/or render the product transparent. Preferably, the chelating agent may include acetylacetone, ethylacetoacetate, oxalic acid, pentamethylene glycol (1,5-pentanediol), phosphonic acid, gluconic acid, diacetone alcohol, amino acids, butanedioic acid or combinations thereof Usually, the added amount of chelating agent is within a molar ratio of 0.01-1 of chelating agent to titanium precursor, and more preferably a molar ration of 0.01-0.3 of chelating agent to titanium precursor.

The solution may be subsequently reacted at a temperature of about 60⁰C to about 150⁰C, more preferably in an amount of about 70⁰C to about 100⁰C for about 6 hours to about 15 hours, more preferably for about 9 hours to about 13 hours. The mixture may then be subsequently agitated and cooled to about room temperature, to produce titania by hydrolysis of the titania precursor.

The resultant titania containing product contains from about 5 % to about 20 % by weight of titania, based on the total weight of the reaction mixture, more preferably from about 8 % to about 15 % by weight of titania, based on the total weight of the reaction mixture. Notably, the titania particles are uniformly dispersed and may be easily applied to any substrate surface. In an exemplary embodiment, the resulting titania particles may be nanosized, preferably having a diameter of from about 5 nm to about 50 nm, more preferably, having a diameter of from about 10 nm to about 30 nm. Additionally, the reaction product may be transparent, or alternatively may have any color, to enable various coating applications.

Combining the Solvothermal and Hydrolysis Titania Dispersions

The resulting titania dispersions produced by the solvothermal process and hydrolysis process are subsequently blended together to produce a titania dispersion characterized by both a high degree of anatase crystalline structure as well as a substantially uniform dispersion of titania particles. In an exemplary embodiment, the titania dispersions synthesized by the solvothermal process and the hydrolysis process may be blended in a ratio of about 10:1 to about 1:2, more preferably, about 5:1 to about 2:1.

Optionally, water may be added to this mixture in order to improve the appearance, manufacture and application of the titania dispersion. After mixing, the dispersion may optionally be agitated. The synthesized titania dispersion is advantageous because it has a stable and uniformly dispersed high concentration of anatase crystalline titania particles. Furthermore, the dispersion may be photocatalytic, transparent and have a high binding affinity. In an exemplary embodiment, the titania colloid is an environmentally friendly, easily manufactured, inexpensive, highly photoactive uniform dispersion of nanosized titania particles in a transparent dispersion that may be activated under visible or ultra violet light.

The blended titania dispersion may then be applied to a substrate using any conventional means, including coating, such as spray coating, dip coating, spin coating, CVD (chemical vapor deposition), PVD (physical vapor deposition), electrostatic coating. The dispersion may be applied to any substrate surface, including both solid as well as porous membranes, such as fabrics and textiles. Alternatively, the titania dispersion may be incorporated in a liquid based or viscous medium, such as concrete, that may be used for construction or otherwise fabricate a structure.

In view of these advantages, the titania dispersion utilized in the present invention, characterized by its high photoactalytic activity, stability and superior particle dispersion, may be used to enable the present invention to have a wide variety of applications. In one embodiment, it is envisioned that the highly oxidant solution may be used for clean energy generation by splitting water to produce hydrogen and oxygen. Alternatively, it may be used for various decontamination applications. For example, the solution may enable environmentally safe oxidization of volatile organic compounds, malodorous materials, harmful gas emissions and other environmental pollutants from various sources, including vehicles as well as industrial plants. Thus, the photocatalytic solution enables the invention to be used to sterilize, decompose, decontaminate and/or purify harmful or malodorous materials in any medium, including any structural surface, in the air and/or in a liquid using visible light and/or ultraviolet light irradiation, and may be used decontaminate glass, tile, and metal surfaces as well as purify water and air, or directly placed on a substrate surface or on a contaminant to begin decontamination upon exposure to ultraviolet light or visible light.

Alternatively, the solution may be incorporated in a paint, coating, or liquid mixture which is then applied to another substrate to be decontaminated. For example, the titania photocatalyst may be mixed with concrete or paint to oxidize nitrogen oxides (NOx) or sulfur oxides (SOx), which cause acid rain. Air pollutants may therefore be removed by coating or constructing roads and buildings with paints and/or coatings containing photocatalytic titania particles. Such coatings may also provide anti-fogging applications.

Additionally, the solution may also enable antimicrobial, namely antifungal, antimicrobial or antiviral, and other biological decontamination and sterilization applications, by light irradiation. In an exemplary preferred embodiment of the present invention, the photocatalytic antimicrobial solution may be particularly useful for constructing filtration systems, such as masks, or the solution may be coated on or incorporated in a nano fibrous matrix capable of fine filtration. Preferably, the matrix may be a textile or fabric capable of containing or filter out undesirable particles and pollutants.

Alternatively, in accordance with the invention the solution may be coated on any surface to create a self-cleaning sterile surface area, which may be useful for hospitals, pharmaceutical plants, food preparation areas, waste collection areas, waste treatment plants, and other areas requiring germ control.

In an exemplary embodiment, the invention may include photocatalytic titania dispersion coated on a substrate having a large specific surface area for antimicrobial activity. The photocatalytic titania particles may function to contain, inhibit or render ineffective bacteria, viruses and other microorganisms. When the photocatalytic titania is illuminated by visible or ultra violet light having a higher energy than its band gaps, the valence electrons in the photocatalytic titania will excite to the conduction band, and the electrons and hole pairs will form on the surface and bulk inside of the photocatalyst. These electron and hole pairs generate oxygen radicals, O²", and hydroxyl radicals, OH", after combining oxygen and water, respectively. Because these chemical species are unstable, when the organic compounds contact the surface of the photocatalyst, it will combine with (V and OH", respectively, and turn into carbon dioxide (CO2) and water (H2O). Through the reaction, the photocatalytic titania is able to decompose organic materials, such as odorous molecules, bacteria, viruses and other toxic or harmful microorganisms, in the air, on a substrate surface or in a liquid medium.

In one embodiment, a titania dispersion useful in the present invention may be synthesized by mixing two titania dispersions prepared by a solvothermal process and by hydrolysis as follows. During the solvothermal process, a mixture was prepared by adding about 19 g of a 67% concentrated nitric acid compound, and about 63 g of deionized water to about 3 L of a 95% concentrated ethyl alcohol compound. The mixture was agitated while the components were added. About 100 g of 99.9 % concentrated titanium

tetraisopropoxide (TTIP) was then added drop by drop to the mixture, comprising about 1 % by weight of the solution, and the mixture was stirred for over 2 hours to induce hydrolysis. After mixing, the solution was then pressure sealed in an autoclave having a magnetic stirrer as well as a gauge and means for controlling temperature and pressure. The rotational speed of magnetic stirrer was set to 1,000 rpm, and autoclave was programmed to heat the solution to about 170 ⁰C at a rate of about 5 ⁰C /min. The reactor temperature was maintained at about 170 ⁰C for about 3 hours, and the pressure within the autoclave was maintained at about 16 atmospheres. The reactor was subsequently cooled down to ambient room temperature, and the resulting ivory colored titania dispersion was removed.

During hydrolysis, about 1 kg of deionized water was poured into a 5 L vessel. A mixture of about 111.65 g of a 99.9 % concentration of tetraisopropoxide (TTIP) and about 65g of a 99 % concentration of acetylacetone was added drop by drop to the water and agitated for over 30 min to prepare the mixture for hydrolysis. Acetylacetone was added as a chelating agent to control the hydrolysis reaction and to suppress particle agglomeration and growth. The reaction temperature was controlled by a heating mantle/heating jacket and set to about 90⁰C. After agitating for about 2 hours, about 9.8 g of a 67% concentrated nitric acid solution was added to the solution and stirred for about 2 hours. The reaction mixture was then cooled to ambient room temperature while stirring for about 12 hours to synthesize a yellowish titania dispersion.

The titania slurries produced by the solvothermal process and hydrolysis were then blended with deionized water in a ratio of about 5 : 1 :4 by weight and agitated vigorously to produce a transparent and uniformly dispersed titania photocatalyst dispersion.

In one embodiment, a titania dispersion useful in the present invention may be synthesized by mixing two titania dispersions prepared by a solvothermal process and by hydrolysis as follows. During the solvothermal process, a mixture was prepared by adding about 25 g of a 67% concentrated nitric acid compound and about 246 g of deionized water to about 3 L of 99% concentrated isopropanol. The mixture was agitated while the components were added. About 200 g of a 99.9% concentrated titanium tetraisopropoxide (TTIP) was then added drop by drop to the mixture, comprising 2% by weight of the solution, and the mixture was stirred for over 2 hours to induce hydrolysis.

After mixing, the solution was then pressure sealed in an autoclave having a magnetic stirrer as well as a gauge and means for controlling temperature and pressure. The rotational speed of magnetic stirrer was set to 1,000 rpm, and autoclave was programmed to heat the solution to about 160 ⁰C at a rate of about 5 ⁰C /min. The reactor temperature was maintained at about 160 ⁰C for about 3 hours, and the pressure within the autoclave was maintained at about 15 atm. The reactor was subsequently cooled down to ambient room temperature, and the resulting white colored titania dispersion was removed.

During hydrolysis, 1 kg of deionized water was poured into a 5 L vessel. About 355.3 g of a 99.9% concentration of tetraisopropoxide (TTIP) was added drop by drop to the water and agitated for over 30 min to prepare the mixture for hydrolysis. About 50 g of a 98% concentrated oxalic acid compound was added as a chelating agent to control the hydrolysis reaction and to suppress particle agglomeration and growth. The reaction temperature was controlled by a heating mantle/heating jacket and set to about 90 ⁰C.

After agitating for about 2 hours, about 6.3 g of a 67% concentrated nitric acid was added to the solution and stirred for about 2 hours. The reaction mixture was then cooled to ambient room temperature while stirring for about 12 hours to synthesize the titania dispersion.

The titania slurries produced by the solvothermal and hydrolysis steps were then blended with deionized water in a ratio of about 2: 1 :5 by weight and agitated vigorously to produce a titania photocatalyst dispersion. In one embodiment, a titania dispersion useful in the present invention may be synthesized by mixing two titania dispersions prepared by a solvothermal process and by hydrolysis as follows. During the solvothermal process, about 63 g of deionized water was added to about 1.5 L of a 95% concentrated ethyl alcohol solution, and the mixture was stirred. A second mixture of about 22 grams of deionized water, about 15O g of ethyl alcohol and about 14 g of a 5% concentrated hydrochloric acid was added drop by drop to a vessel containing another mixture of about 61 g of tetramethyl orthosilicate (TMOS), about 500 g of ethyl alcohol and about 8.9 g of 5 wt% dilute phenolic resin in alcohol. This solution was agitated for over 30 minutes. The two mixtures were subsequently mixed together and agitated. A mixture of about 100 g of a 99.9% concentrated titanium tetraisopropoxide (TTIP) and about 500 g ethyl alcohol was also added drop by drop to the mixture. A 67% concentrated nitric acid solution was added to adjust the pH level of the solution to about 2-3. The final mixture was stirred for over 2 hours to induce hydrolysis.

After mixing, the solution was then pressure sealed in an autoclave having a magnetic stirrer as well as a gauge and means for controlling temperature and pressure. The rotational speed of magnetic stirrer was set to 1,000 rpm, and autoclave was programmed to heat the solution to about 160 ⁰C at a rate of about 5 ⁰C /min. The reactor temperature was maintained at about 160 ⁰C for about 3 hours, and the pressure within the autoclave was maintained at about 17 atmospheres. The reactor was subsequently cooled down to ambient room temperature, and the resulting white colored titania dispersion was removed. During hydrolysis, about 355.3 g of a 99.9% concentration of tetraisopropoxide (TTIP) was poured into a 5 L reactor filled with about 1 kg of deionized water. The mixture was agitated for over 30 minutes to prepare the mixture for hydrolysis. About 50 g of a 98% concentrated oxalic acid compound was added as a chelating agent to control the hydrolysis reaction and to suppress particle agglomeration and growth. The reaction temperature was controlled by a heating mantle/heating jacket and set to about 90 ⁰C. After agitating for about 2 hours, about 6.3 g of a 67% concentrated nitric acid was added to the solution and stirred for about 2 hours. The reaction mixture was then cooled to ambient room temperature while stirring for about 12 hours to synthesize the titania dispersion. The titania dispersions produced by the solvothermal process and hydrolysis were then blended with deionized water in a ratio of about 2: 1 :3 by weight and agitated vigorously to produce a titania photocatalyst dispersion.

In one embodiment, a dispersion useful in the present invention may be synthesized by mixing two titania dispersions prepared by a solvothermal process and by hydrolysis as follows. During the solvothermal process, a mixture was prepared by adding about 26 g of a 67% concentrated nitric acid compound, about 2 g of a 99.9% concentrated silver nitrate compound and about 95 g of deionized water to about 3 L of a 95% concentrated ethyl alcohol. The mixture was agitated while the components were added. About 150 g of a 99.9% concentrated titanium tetraisopropoxide (TTIP) was then added drop by drop to the mixture, comprising 1.5% by weight of the solution, and the mixture was stirred for over 2 hours to induce hydrolysis. After mixing, the solution was then pressure sealed in an autoclave having a magnetic stirrer as well as a gauge and means for controlling temperature and pressure. The rotational speed of magnetic stirrer was set to 1,000 rpm, and autoclave was programmed to heat the solution to about 160 ⁰C at a rate of about 5 ⁰C /min. The reactor temperature was maintained at about 160 ⁰C for about 3 hours, and the pressure within the autoclave was maintained at about 16 atm. The reactor was subsequently cooled down to ambient room temperature, and the resulting gray colored titania dispersion was removed. During hydrolysis, about 1 kg of deionized water was poured into a 5 L reactor. A mixture of about 177.7 g of a 99.9% concentration of tetraisopropoxide (TTIP) and about 33.3 g of a 96% concentration of pentamethylene glycol was added drop by drop to the water and agitated for over 30 min to prepare the mixture for hydrolysis. Acetylacetone was added as a chelating agent to control the hydrolysis reaction and to suppress particle agglomeration and growth. The reaction temperature was controlled by a heating mantle/heating jacket and set to about 90 ⁰C. After agitating for about 2 hours, about 8.1 g of a 67% concentrated nitric acid solution was added to the solution and stirred for about 2 hours. The reaction mixture was then cooled to ambient room temperature while stirring for about 1 2 hours to synthesize the titania dispersion. The titania slurries produced by the solvothermal process and hydrolysis were then blended with deionized water in a ratio of about 3:1 :5 by weight and agitated vigorously to produce a titania photocatalyst dispersion.

The photocatalytic activity of the titania dispersions synthesized as described above were analyzed by testing their deodorization, anti-fungal, anti-bacterial and self- cleaning properties. The results demonstrated that titania dispersions of the present invention have a high photocatalytic activity.

Deodorization Experiment

The level of photocatalytic activity of the titania dispersions [produced as described above was measured by evaluating deodorization activity. To evaluate the deodorization properties a dispersion was tested with acetaldehyde, a malodorous volatile organic compound. A 1 Ox 10 cm² glass plate was coated with a prepared titania dispersion and dried at about 70⁰C to about 120⁰C over a period of about 2 hours. The plate was subsequently cooled to ambient room temperature. Prior to exposure to the acetaldehyde, the titania coated plate was illuminated with UV-A light having a light intensity of about 1.0 mW/cm² over a period of about 3 hours. The titania coated plate was then placed within a 5 L - Tedlar™ bag, which was slit open. The bag was then tightly sealed using a heat sealer. Subsequently, a vacuum pump was used to extract air of inside from an opening of the bag; thereafter the opening was closed.

A gaseous mixture containing about 100 ppm of acetaldehyde was then collected and introduced into the bag. The bag containing the titania coated plate and acetaldehyde gas was subsequently exposed to UV-light at an intensity of about 1 mW/cm² over a period of about 2 hours using a 40 W black light blue lamp. The gas inside the bag was monitored every 10 min after light irradiation, and the concentration of the acetaldehyde gas inside the bag was measured using a gas chromatography equipped flame ionized detector.

The deodorization efficiency was found to increase with UV light irradiation time. After 2 hours, the concentration of acetaldehyde steadily decreased to below 20 ppm. Therefore, the experiment demonstrated that the titania dispersions have superior photocatalytic activity in view of its ability to break down acetaldehyde gas.

Anti-fungal Experiment

The level of photocatalytic activity of the titania dispersions prepared for use in the present invention was measured by evaluating anti-fungal activity. To evaluate the anti-fungal properties of a titania dispersion prepared as described above, the dispersion was tested by exposure to a fungi culture. Several coats of the titania dispersion were applied to sets of

6 wallpaper sheets having a dimension of about 5x5 cm². The sheets were subsequently dried at about 60 ⁰C for 30 min.

A fungi culture was also created using about IL of deionized water, about 3.0 g of ammonium nitrate, and about 1.0 g of potassium dihydrogen phosphate, about 0.5 g of magnesium sulfate, about 0.25 g of potassium chloride, about 0.002 g of iron sulphate, and about 25 g of agar. A 1.0 ml blended fungal spore suspension was then uniformly streaked on a plate, and the prepared titania coated sheet was placed in the center of the plate. 0.05ml of the blended pore fungal suspension was again uniformly streaked on the plate. After covering, the plate was allowed to incubate for 14 days at a temperature of about 28 ± 2°C and humidity of over 95 %.

The plates were monitored over the 14 day period according to a 3 tiered fungicide index that evaluates the ripeness of the agar fungi. A score of 3 represents that no amount of agar cultured fungus was observed on the titania coated sheet. A score of 2 represents that agar cultured fungus was observed on the titania coated sheet but did not exceed 1 /3 of the titania coated sheet. A score of 1 represents that agar cultured fungus was observed on the titania coated sheet and exceed 1/3 of the titania coated sheet. After 4 weeks of incubation, every tested titania coated sheet was evaluated as having a fungicide index of 3. Therefore, the experiment demonstrated that the titania dispersions have superior photocatalytic activity in view of the highly effective fungicide activity.

Antibacterial Experiment

The level of photocatalytic activity of titania dispersions useful in the present invention was measured by evaluating antibacterial activity. To evaluate the antibacterial properties of the titania dispersions prepared as described above, such a dispersion was tested by exposure to E. CoIi. The titania dispersion was coated on an array of plates. The titaniacoated plates were then sterilized by heating the plates to 150 ⁰C for a 30 minute period. A 10 ml E. CoIi solution was incubated at a temperature of about 35 ⁰C for about 24 hours. The E. CoIi solution was then re-suspended in deionized water and diluted to a concentration of about 2*10⁵ colony forming unit (CFU)/ml. The diluted E. CoIi solution was then dropped onto the titania coated plates and quickly covered with an air tight cover film.

The plates were irradiated under a 15 W black light blue UV lamp at an intensity of about 1.0 mW/cm² over a period of about 2 hours. The plates were then rinsed with 0.15 M saline solution to collect any surviving E. CoIi. 1 ml of the collected E. CoIi was then plated on a petri dish and cultured at a temperature of about 37 ⁰C for a period of about 24 hours, and the surviving survival E. CoIi were counted. Before UV irradiation, colonies of E. CoIi were visibly present. After UV irradiation, all traces of the cultivated E. CoIi colonies were destroyed. Therefore, the experiment demonstrated that the titania dispersions have superior photocatalytic activity in view of the highly effective antibacterial activity.

Self-Cleaning

The level of photocatalytic activity of the titania dispersions useful in the present invention was measured by evaluating their self-cleaning capabilities. To evaluate the self-cleaning properties of such a titania dispersion, the dispersion was tested by evaluating their ability todegrade methylene blue (CieHigCINsS). About 100 ml of a titania dispersion prepared as described above was blended with about 100 ml of methylene blue and then vigorously stirred in the dark for about 1 hour using a magnetic stirrer. The dispersion, having an initial methylene blue concentration of about 3.2xlO^Λ mol/l, was then exposed to UV illumination. The dispersion was maintained at ambient room temperature and at a pH level of about 6, using sodium hydroxide. Degradation of methylene blue over time was then measured under this established environmental condition.

About 50 ml of the dispersion was then poured into a petri dish and irradiated using a 40 W black light blue UV-A lamp having a light intensity of about 1.0 mW/cm² for about 1 hour. The light intensity was controlled using an UV-radiometer (Konica Minolta UM- 360). The degree of methylene blue degradation was observed over time with the naked eye. Prior to exposure to UV light, the dispersion had a pervasive blue color. After UV irradiation, the dispersion was transparent and showed no blue coloration. Therefore, the experiment demonstrated that the titania dispersions have superior photocatalytic activity in view of their ability to degrade methylene blue.

The foregoing examples have been presented for the purpose of illustration and description and are not to be construed as limiting the scope of the invention in any way. The scope of the invention is to be determined solely from the claims appended hereto.

In accordance with the present invention, removal of the hazardous substance in a gas phase atmosphere can be attained with high effectiveness and precision. In addition, the present invention provides the function of largely sterilizing and deactivating a target hazardous substance selected, and therefore it is generally unnecessary to incorporate further techniques for sterilizing and deactivating the hazardous substance for use in conjunction with the materials and apparatus provided by the invention.

It is to be appreciated that in manufacture of the hazardous substance removing material of the present invention, as described above, the support comprising a porous fibrous matrix is preferably a electrospun, nano fibrous material on which such electrosprayed and photocatalytic metal oxide particles are substantially uniformly deposited, such that the optimum effectiveness of the invention, also as described above, is achieved.

Preferred compositions, materials and methods for the manufacture of the hazardous substance removing material of the present invention are described in detail in the foregoing description and accordingly in accordance with the invention, novel methods and compositions have been disclosed for producing the novel hazardous substance removing material of the invention. The methods can preferably involve preparing a titania dispersion by blending two different titania dispersions synthesized by a solvothermal process and a hydrolysis process. The novel compositions, comprising the titania dispersion, have a plurality of titania particles substantially uniformly dispersed therein, and can be blended to provide a high concentration of titania with an anatase crystalline structure, thereby to provide the desired level of photocatalytic activity, and also permitting the preparation of transparent titania dispersions. The compositions thus obtained can be used to provide the advantages of the present invention as described. According to the present invention, methods are also disclosed for electrospraying nanosized metal or metal oxide particles onto a substrate, and materials produced thereby are disclosed such as a metal oxide deposited fibrous material comprising a substrate, fibers and metal oxide particles. Such a material may be a flexible and porous fibrous matrix on which metal oxide particles may be uniformly deposited on a surface thereof. In a particularly preferred exemplary embodiment, an electrospun, nano fibrous material on which such electrosprayed, photocatalytic metal oxide particles are uniformly deposited without agglomeration, is contemplated.

Accordingly, it is contemplated that in accordance with the present invention the hazardous material can be removed with the single use of the hazardous substance removing material of the invention, which is particularly advantageous when used in a personal filtration apparatus such as a mask worn on the face, such as shown in FIG. 2. A hazardous substance removing material of the present invention is thus capable of being used in a gaseous atmosphere and attains highly precise removal of a hazardous substance in such atmosphere to be captured. In addition, the metal oxides utilized as described herein can themselves have a function of sterilizing and deactivating some types of hazardous substances, therefore, it may be unnecessary to incorporate further techniques for sterilizing and deactivating the hazardous substance.

It is to be appreciated that the hazardous substance removing material of the present invention is not limited to the embodiments particularly illustrated or described in detail herein, and can be incorporated into and used in many different forms of apparatus, such as for example and without limitation:

Disposable masks N95 masks

HVAC filters

Home filters

Humidifier filters

Surgical masks Surgical masks with shields

Hoods

Air purifying respirators

Negative pressure masks

Coveralls Gowns

Surgical Scrubs

Patient gowns

Laboratory coats

Physician's coats Nursing uniforms Tissues Towels Bed sheets Blankets Pillows

It is also to be appreciated that the hazardous substance removing material of the present invention can be used for various decontamination applications, for example, for environmentally safe oxidization of volatile organic compounds, malodorous materials, harmful gas emissions and other environmental pollutants from various sources, including vehicles as well as industrial plants.

The material of the invention also can be used to sterilize, decompose, decontaminate and/or purify harmful or malodorous materials in any gaseous medium, and also in antimicrobial, antifungal or antiviral, and other biological decontamination applications. In a preferred exemplary embodiment, the material provided by the invention can be particularly useful for constructing filtration systems, such as masks.

In another exemplary embodiment, the nano fibrous matrix of the material provided by the invention is capable of fine filtration, and preferably, the matrix comprises a textile or fabric capable of containing or filtering out undesirable particles and pollutants which may be useful for hospitals, pharmaceutical plants, food preparation areas, waste collection areas, waste treatment plants, and other areas requiring germ control.

In an especially preferred embodiment, the material of the invention may comprise a photocatalytic titania dispersion coated on a substrate having a large specific surface area for antimicrobial activity, and also may comprise a silver-titanium dioxide dispersion. The photocatalytic titania particles may function to contain, inhibit or render ineffective bacteria, viruses and other microorganisms, such as, for example, at least one and even more than one hazardous substance selected from bacteria, fungi, viruses, and allergens. Specifically, the bacteria may include, for example, Staphylococcus (Staphylococcus aureus, Staphylococcus epidermidis, and the like), Micrococcus, Bacillus anthracis, Bacillus cereus, Bacillus subtilis, Propionibacterium acnes, and the like as Gram-positive bacteria, and Pseudomonas aeruginosa, Serratia marcescens, Burkholderia cepacia, Streptococcus pneumoniae, Legionella pneumophilia, Mycobacterium tuberculosis, and the like as Gram-negative bacteria. The fungi may include, for example, Aspergillus, Penicillius, and Cladosporium. The viruses may include, for example, influenza viruses, coronavirus (SARS virus), adenovirus, and rhinovirus. The allergens may include, for example, pollens, mite allergens, and cat allergens. The photocatalytic titania particles exhibit high effectiveness against the foregoing hazardous substances by being bacteriostatic while also acting to substantially sterilize and deactivate viruses and allergens.

The apparatus or device in which the hazardous substance removing material of the present invention is employed may include an indicator for detecting the activity degree of the rate and/or extent of decontamination or removal of the hazardous substance, and outputting a signal when the detected rate becomes lower than a predetermined activity degree. If such an indicator is present, it can be bonded or otherwise attached either to the material of the invention or to a support for the material of the invention, such as a fibrous support, such that whether the material of the invention can be effectively used or should be replaced can be readily recognized. Especially, if a color of the indicator changes when the detected rate becomes lower than the predetermined activity degree, such judgments can be done at a glance. One skilled in the art can conceive of various indicators that can be used in conjunction with the present invention, and which operate to produce readings by such means as pH change, temperature increase, dynamic stress, and the like.

The following examples are provided by way of illustration of the present invention, but are not to be construed as limitations thereon in any way.

EXAMPLE 1 The hazardous substance removing material of the invention may be used as an air filter for an air conditioner and an air purification system. With the air filter, a hazardous substance specifically can be captured in the ambient air, and therefore, highly precise air purification in which a hazardous substance or substances to be captured can be specified, and is performed by appropriate selection of the material to have a function of sterilizing and deactivating some kinds of hazardous substances, thereby making it unnecessary to combine techniques for sterilizing and deactivating a target hazardous substance.

EXAMPLE 2

Referring now to the Figures, FIG. 1 shows a filter (10) for airborne hazardous substances, utilizing the hazardous substance removing material of the invention, which, in one preferred embodiment, can be incorporated into a mask. The mask includes a substantially rectangular-shaped mask body (11), which is designed to accept and hold the filter (10). FIG. 2 shows such a mask in use, according to a preferred embodiment of the present invention. The mask includes a mask body (11) and ear support strings (12) that connect paired ends of the minor sides of the mask body (11), around the head of the user (13).

The mask body (11) is comprised of a support of fibrous material composed of an air permeable outer cloth (14) in which gauze woven fabrics are piled, a net- like air permeable inner cloth (15) forming a pocket inside the air permeable outer cloth (14), and the hazardous substance removing material of the invention (10) arranged inside the pocket. In the mask shown, when the ability of the material (10) to remove the hazardous substance becomes low, it can be increased only by replacing the hazardous substance removing material (10). With the use of the mask, air purification in a gaseous atmosphere and highly precise, particular air purification, in which a specified hazardous substance is to be captured and removed, can be performed. Thus, the material provided by the instant invention can have a function of sterilizing and deactivating some kinds of hazardous substances, and therefore, it may be unnecessary to combine the techniques for sterilizing and deactivating a target hazardous substance.

Moreover, preferably the hazardous substance removing material (10) is interposed between the air permeable outer and inner cloths (14, 15) and the air permeable inner cloth (15) has higher air permeability than the air permeable outer cloth (14), resulting in greater efficiency of the material since it is not directly exposed to the breath of the user (13).

It is to be appreciated, however, that the hazardous substance removing material (10) of the invention, while shown as being replaceable in the mask in the above example, may comprise the mask body itself which may be replaceable as needed.

EXAMPLE 3

In another preferred embodiment of the present invention, the following composition can be sprayed, such as by conventional electrospraying techniques, onto the material (10) of the invention. The composition comprises a silver-titanium dioxide dispersion, and includes titanium dioxide (Degussa P25), Silver Nitrate (AgNO₃), Nitric Acid (HNO₃), de-ionized water and sodium dodecyl sulphate (SDS), and can be produced utilizing the following procedure:

1. Add nitric acid to de-ionized water until the pH is between 4 and 5

2. Add TiO₂ to the solution above in a weight ratio of TiO₂: water = 1 : 100

3. Add silver nitrate to the solution above so that it makes up approximately 0.1% of the solution in weight

4. Agitate the solution above for 5 minutes so that it mixes thoroughly

5. Add sodium dodecyl sulphate (SDS) so that it makes up approximately 0.1% of the solution in weight

6. Sonicate the resulting solution for 30 minutes. 7. Add ethanol to the solution so that it makes up approximately 2.0% of the solution in weight

8. Illuminate this solution with a light (e.g. fluorescent) while agitating continuously for 4 hours

9. Sonicate the solution for 30 minutes.

It has been found that the foregoing preferred embodiment of the invention is especially advantageous for the removal of hazardous substances in interior environments, such as those in office buildings wherein fluorescent lighting is utilized.

As previously stated, the foregoing description and examples have been presented only for the purposes of illustration and description, and are not to be construed as limiting the scope of the present invention in any way, which scope is to be determined solely from the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A hazardous substance removing material comprising a fibrous matrix on which metal oxide particles are substantially uniformly deposited on the surface thereof.

2. The hazardous substance removing material of claim 1, wherein said matrix is an electrospun, nano fibrous material.

3. The hazardous substance removing material of claim 1, further comprising a support for said hazardous substance removing material.

4. The hazardous substance removing material of claim 1, wherein said metal oxide particles are electrosprayed.

5. The hazardous substance removing material of claim 1, wherein said metal oxide particles are substantially uniformly deposited on the surface of said matrix.

6. The hazardous substance removing material of claim 1, wherein said metal oxide particles are photocatalytic.

7. The hazardous substance removing material of claim 3, wherein the support is a fibrous material.

8. The hazardous substance removing material of claim 1 or claim 3, further comprising an indicator capable of detecting an activity degree of removal of the hazardous substance and outputting a detectable signal when a detected activity degree becomes lower than a predetermined activity degree.

9. The hazardous substance removing material of claim 1 or claim 3, further comprising a silver-titanium dioxide composition.

10. The hazardous substance removing material of claim 8, wherein said indicator is bonded to the support of claim 3.

11. The hazardous substance removing material of claim 8, wherein said indicator changes in color when a detected activity degree becomes lower than the predetermined activity degree.

12. A method for removing a hazardous substance, which method comprises using the hazardous substance removing material claimed in any of claims 1 through 11.

13. An air filter, comprising the hazardous substance removing material of any of claims 1 through 11.

14. A mask, comprising the hazardous substance removing material of any of claims 1 through 11.

15. The mask of claim 14, in which a support supports the hazardous substance removing material.

16. The mask of claim 15, wherein the hazardous substance removing material is interposed between a pair of air permeable outer and inner cloths and the air permeable inner cloth has higher air permeability than the air permeable outer cloth.

17. Apparatus comprising the hazardous substance removing material of any of claims 1 through 11, which apparatus is selected from the group of products consisting of : Disposable masks, N95 masks, HVAC filters, Home filters, Humidifier filters, Surgical masks, Surgical masks with shields, Hoods, Air purifying respirators, Negative pressure masks, Coveralls, Gowns, Surgical Scrubs, Patient gowns, Laboratory coats, Physician's coats, Nursing uniforms, Tissues, Towels, Bed sheets, Blankets, and Pillows.