Air filtration media having metal nanoparticle agglomerate adhered thereto, formation thereof, and use thereof

Abstract

Metallic nanoparticle agglomerates can deliver biocidal activity to surfaces on which they are deposited and adhered, such as various air filtration media. Air filtration media can include a plurality of fibers to which a plurality of metallic nanoparticle agglomerates are adhered. The metallic nanoparticle agglomerates can include a plurality of fused, partially fused, or unfused metallic nanoparticles associated with one another on the surface of the plurality of fibers. Suitable metallic nanoparticles for facilitating biocidal activity against various pathogens, such as viruses and bacteria, can include copper nanoparticles and / or silver nanoparticles. Face masks, inline filters, and air filtration systems can integrate the air filtration media.

Description

Background Technology

[0001] The world faces a growing threat from antibiotic-resistant strains (i.e., “superbugs”), which are at least in part untreatable due to the overuse of antibiotics. Other types of resistant microorganisms may present similar problems. Increased population density and efficient public transportation infrastructure further exacerbate the local and global spread of common and emerging diseases.

[0002] Even common bacterial and viral infections can pose serious health risks if effective infection control is not implemented.

[0003] Personal protective equipment (PPE), such as face shields, can be used as part of an infection control program. In particular, in crowded settings where the risk of person-to-person disease transmission is increased, especially where effective social distancing is not achievable, infected and healthy individuals often wear face shields to limit the spread of disease. In healthcare settings, the use of face shields and additional PPE may be even more critical. However, the effectiveness of face shields in reducing infection rates is sometimes limited. Face shields and similar PPE are typically characterized by their “N” rating. For example, an N100-rated face shield can filter particles as small as approximately 0.3 μm. Influenza viruses are smaller than this limit (~0.14 μm), but viral transmission typically occurs through larger respiratory droplets (e.g., approximately 5 μm or larger) produced by coughing or sneezing, meaning they can be effectively filtered by an N100-rated face shield unless the droplets break up upon contact. Furthermore, respiratory droplets evaporate rapidly after being expelled from an individual (i.e., within seconds), allowing free virus to spread in the air. Lower-filtration masks, such as N95 masks, allow up to 5% of larger particles to pass through. Even with N100 masks, the seal around the mouth and nose is often insufficient, allowing infected respiratory droplets to escape or enter through exposed gaps at the mask's edges when coughing or sneezing. As another concern, N100 and N99 masks, and even N95 masks, offer high flow resistance that can cause breathing difficulties, especially for infected individuals already experiencing breathing difficulties. Therefore, the CDC strongly discourages the use of N95 and higher-level masks, particularly by individuals untrained in their use. While lower-level masks may be easier to wear, they may make the wearer more susceptible to infection. Furthermore, the effectiveness of masks in promoting infection control depends on the proper and consistent use of masks by individuals who may encounter easily transmissible pathogens.

[0004] Another potential route of infection from face masks stems from repeatedly removing and reusing contaminated masks during routine use, or simply from repeatedly adjusting them. This type of contamination and disease transmission can occur with any type of face mask, even N100 masks. The high surface area of ​​the mask and the humid environment created by exhaled air passing through it can create a fertile ground for bacteria trapped in the mask, increasing the risk of disease transmission. Trapped viruses, especially those combined with pathogens or non-pathogens, can also pose a contamination hazard in used masks. Furthermore, contaminated masks require careful handling to prevent cross-contamination when worn between different areas. Transfer of pathogens to various touch surfaces due to adjusting a contaminated mask can also cause significant problems. Used masks can also present significant biohazardous waste disposal issues. Other air filtration media (such as HEPA filters, air conditioning filters, HVAC, or aircraft / car cabin filters) can also accumulate pathogens during their use, potentially for months or years, leading to similar problems due to the spread of pathogens already accumulated on the filter media. Attached Figure Description

[0005] The following figures are included to illustrate certain aspects of this disclosure and should not be considered as exclusive embodiments. The disclosed subject matter is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as would occur to those skilled in the art who would benefit from this disclosure.

[0006] Figure 1 and Figure 2 A hypothetical structural diagram of a metal nanoparticle with a surfactant coating is shown.

[0007] Figure 3 An illustrative SEM image of a essentially single copper nanoparticle is shown.

[0008] Figure 4 Illustrative SEM images of copper nanoparticle agglomerates are shown.

[0009] Figure 5 An illustrative SEM image of a copper nanoparticle network obtained after multiple copper nanoparticles are fused together is shown.

[0010] Figure 6A and Figure 6B An illustrative SEM image of copper nanoparticle agglomerates adhered to textile fibers is shown.

[0011] Figure 7 An illustrative SEM image of copper nanoparticle agglomerates adhered to fibers in a cellulose / polyester blend (55:45) is shown, in which the fiber joints are fused together.

[0012] Figure 8 Illustrative photographs show fabrics with copper nanoparticle agglomerates adhering to them during manufacturing (left side of the image) and after prolonged use (right side of the image). Detailed Implementation

[0013] This disclosure generally relates to air filtration technologies, including masks, respirators, inline air filters and similar air filtration systems, and more specifically, to air filter media, including systems and methods associated therewith, which can limit the secondary transmission of disease (once pathogens are captured on them and killed and / or inactivated upon contact with reagents associated with the air filter media).

[0014] As mentioned above, face masks and associated air-filtering media can provide some protection against the spread of viruses, bacteria, and other types of pathogens. However, the risk of secondary infection remains high because pathogens may remain active after use and remain trapped in or on the air-filtering media. These trapped pathogens can frequently spread to various contact surfaces and facilitate secondary infection. In some cases, pathogens small enough may also pass through the air-filtering media.

[0015] This disclosure provides air filter media, such as face masks, respirators, and inline filters, which, for example, can reduce the likelihood of secondary transmission of pathogens captured therein and provide enhanced protection for the wearer or user. Industrial or residential air filtration devices, such as air conditioning filters and other types of air handling systems, can exhibit similar benefits by applying the disclosure herein. In particular, this disclosure describes various types of air filter media impregnated with metals, such as copper and silver, that are biocidally active against various types of pathogens. When pathogens (e.g., viruses and / or bacteria) isolated within the air filter media are exposed to the metal, the metal can kill or inactivate the pathogens, thereby limiting the likelihood of secondary disease transmission and better protecting the wearer or user. In addition to mitigating cross-contamination or transmission of pathogens and providing better protection for the wearer or user, metal incorporation can also limit the hazards of such pathogens after disposal and may, in some cases, reduce waste disposal costs. For example, face masks and other personal protective equipment incorporating suitable metals can be discarded in general waste rather than isolated as biohazardous waste requiring more stringent treatment protocols.

[0016] While incorporating metals into air filter media may be desirable, it can be difficult to achieve in practice using traditional metal incorporation methods. The high melting points of silver and copper make them challenging to incorporate into air filter media. For example, copper forms molten copper at its melting point (1083°C), a temperature completely incompatible with the filter media commonly used in air filtration devices and systems. Silver's melting point is similarly problematic. While micron-sized metal particles or flakes can be produced and incorporated as solids into air filter media, it may be difficult to promote sufficient adhesion of the particles or flakes to provide robust performance. Furthermore, the biocidal activity of micron-sized metal particles or flakes may not be significantly different from that of bulk metal surfaces. Although both silver and copper surfaces exhibit some biocidal activity against certain bacteria and viruses, and in some cases even against antibiotic-resistant bacterial strains, the rate of pathogen inactivation or killing can be quite slow. This slow rate of pathogen inactivation or killing can create the possibility of secondary infection transmission from touched surfaces. For example, coronaviruses can remain active for up to 5 days on surfaces such as glass, polymers, ceramics, rubber, and stainless steel, and for up to 7 days on standard types of surgical masks.

[0017] As a solution to the aforementioned difficulties, this disclosure provides metal nanoparticles, particularly metal nanoparticle agglomerates, as suitable media for introducing metals into conventional air filter media to provide improved biocidal activity and thus infection control. As discussed in further detail below, metal nanoparticles, particularly their agglomerates, offer particularly advantageous configurations for incorporating metals. Given the known biocidal activity of bulk copper and silver surfaces, copper nanoparticles and / or silver nanoparticles can be particularly advantageous metal nanoparticles for delivering biocidal activity to air filter media. The nanoparticle form of these metals can provide a particularly advantageous media for incorporating copper and / or silver into air filter media, particularly air filter media comprising multiple fibers, due to the robust surface adhesion (e.g., for fibers) achievable when agglomerates of these metal nanoparticles are applied to air filter media. Copper and silver nanoparticles can also be used in combination, which can provide complementary biocidal activity against the same or different pathogens that can be targeted or inactivated individually by each metal. Zinc, nickel, titanium and other bioactive metals can also be used in combination with any of these metals (including their respective oxides and / or oxides of copper and / or silver), as well as with other additives that can deliver pathogenic activity to bacteria and / or viruses.

[0018] As further described herein, metal nanoparticles, such as silver and copper nanoparticles, can be readily produced as individual metal nanoparticles and / or their agglomerates, with a size range compatible with their ease of incorporation into the internal phases of air filter media commonly used in air filtration devices and systems. The small size of the metal nanoparticles and their agglomerates allows for easy dispersion throughout the desired portion of the air filter media, or the metal nanoparticles and / or their agglomerates can be distributed in a gradient manner on or near one or more surfaces of the air filter media. Furthermore, due to their high surface energy, the metal nanoparticles may adhere to the air filter media after deposition, providing a robust structure capable of being repeatedly processed during use. Once the metal nanoparticles have reached a high surface energy state, the adhesion of the metal nanoparticles and their agglomerates can involve the formation of chemical bonds.

[0019] Furthermore, an adhesive layer can be incorporated before or simultaneously with the application of metal nanoparticles to the air filter medium to promote improved adhesion of the metal nanoparticles to the air filter medium. The adhesive layer, which may be permanently adhesive, can be applied simultaneously with or separately from the metal nanoparticles. As discussed further below, applying the adhesive layer to the air filter medium or a portion thereof before the metal nanoparticles are deposited on it can provide initial isolation of the metal nanoparticles during loading, followed by further processing to achieve stronger adhesion. As a further advantage, the adhesive can further promote the extended release of active metal substances from the metal nanoparticles or their agglomerates after the metal nanoparticles or their agglomerates have adhered to the surface of the air filter medium. Advantageously, the metal nanoparticles or their agglomerates can be applied to the air filter medium using various spraying techniques, allowing for extensive surface coverage while providing easy control over the degree of metal loading. Alternative deposition techniques for incorporating metal nanoparticles or their agglomerates are also applicable to the disclosure herein.

[0020] The air filter media disclosed herein can advantageously maintain biocidal activity against a variety of pathogens over extended periods (e.g., days to weeks). Furthermore, air filter media with adhering metal nanoparticles or their agglomerates can at least partially self-indicate that they lose their efficacy against pathogens during prolonged use. For example, air filter media with active metal nanoparticle agglomerates thereon can remain black or similarly dark in tone, while exhibiting a lighter color after the biocidal activity decreases (see [link to relevant documentation]). Figure 8 ).

[0021] As used herein, the term "metal nanoparticle" refers to a metal particle with a size of about 250 nm or smaller, particularly about 200 nm or smaller, or about 150 nm or smaller, without any particular mention of the shape of the metal particle. Copper nanoparticles are metal nanoparticles primarily comprising copper, optionally having an oxide coating. Similarly, silver nanoparticles are metal nanoparticles primarily comprising silver, optionally having an oxide coating. The term "metal nanoparticle" herein refers broadly to any metallic structure having at least one size of about 250 nm or smaller, particularly about 200 nm or smaller, or about 150 nm or smaller, and includes other structures that are not substantially spherical in nature, such as metal sheets / discs, metal nanowires, etc. In the disclosure herein, other metal nanostructures may be used as alternatives to or in combination with spherical or substantially spherical metal nanoparticles or their agglomerates.

[0022] The term "metal nanoparticle agglomerate" and its equivalent grammatical form refer to a group of metal nanoparticles having at least one size ranging from about 0.1 μm to about 35 μm, particularly from about 0.1 μm to about 15 μm, and more particularly from about 0.1 μm to about 5 μm. Individual metal nanoparticles in a metal nanoparticle agglomerate can exist within the aforementioned size range, and these individual metal nanoparticles can associate with each other through non-covalent, covalent, or metallic bonding interactions. The term "association" refers to any type of binding force that holds a group of metal nanoparticles together. In some cases, binding forces can be overcome to produce individual metal nanoparticles.

[0023] The terms “consolidate,” “consolidation,” and other variations thereof are used interchangeably with the term “fusion” and other variations thereof in this document.

[0024] The term "air filter medium" refers to any porous structure through which air, air components, or gases can pass, preferably wherein the porous structure comprises multiple fibers or fabrics formed therefrom.

[0025] Before discussing the more specific aspects of this disclosure in further detail, a brief additional description of metal nanoparticles and their processing conditions, particularly silver or copper nanoparticles, will first be provided. Metal nanoparticles exhibit many properties that can differ significantly from those of the corresponding bulk metals. One property of metal nanoparticles that is particularly important for processing is the fusion (consolidation) of nanoparticles occurring at their fusion temperature. As used herein, the term "fusion temperature" refers to the temperature at which metal nanoparticles liquefy to exhibit a fused appearance. Consolidation with other metal nanoparticles can readily occur at or above the fusion temperature. As used herein, the terms "fusion," "consolidation," and their other grammatical forms are synonymous with the agglomeration or partial agglomeration of metal nanoparticles to form larger aggregates. Metal nanoparticles within agglomerates can fuse with each other, or individual metal nanoparticles can fuse, thereby forming, in either case, a network of at least partially fused metal nanoparticles.

[0026] Advantageously and surprisingly, metallic nanoparticles, such as silver and / or copper nanoparticles, can adhere to other surfaces even at temperatures far below their fusion temperature, thus allowing bonding with air filter media to occur, as discussed further herein. Depending on the density of the metallic nanoparticles loaded onto the surface of the air filter media and the temperature at which the metallic nanoparticles are treated on the surface of the air filter media, individual metallic nanoparticles may or may not further fuse together when adhered to the air filter media, as disclosed herein. Even more advantageously, metallic nanoparticles can also associate with each other as agglomerates when adhered to the air filter media, wherein individual metallic nanoparticles that may or may not fuse together remain identifiable. Metallic nanoparticle agglomerates can be readily dispersed on and adhere to the air filter media. Advantageously, the agglomeration of metallic nanoparticles can promote retention within the air filter media and, once adhesion to the air filter media has occurred, promote the sustained release of active metallic substances.

[0027] As the size decreases, particularly when the sphere diameter is below about 20 nm, the liquefaction temperature of metal nanoparticles drops sharply from that of the corresponding bulk metal. For example, copper nanoparticles with a size of about 20 nm or smaller can have a melting temperature of about 220 °C or lower, or about 200 °C or lower, compared to the melting point of bulk copper at 1083 °C. Silver nanoparticles below a nanoparticle size of about 20 nm can similarly exhibit a significant deviation from the melting point of bulk silver. Therefore, the consolidation of metal nanoparticles occurring at the melting temperature allows for the fabrication of structures containing bulk metals at significantly lower processing temperatures than when using the bulk metal itself as a starting material. Since air filter media typically exhibit limited heat resistance, metal nanoparticles can provide a particularly effective medium for introducing metals into air filter media. The small particle size of metal nanoparticles facilitates easy dispersion in liquid media for application to air filter media, for example, by spraying processes. Aggregates of metal nanoparticles, whether fused or not but associated, can also be dispersed in a liquid medium for application to the air filter media disclosed herein. These metal nanoparticle aggregates can present a particularly effective form for application to the air filter media disclosed herein because they are readily retained on the air filter media. Once deposited on a suitable air filter media, the metal nanoparticles or their aggregates can be firmly adhered to the air filter media by raising the temperature to at least the fusion temperature. As further described below, the adhesion of metal nanoparticles or their aggregates to the air filter media can even be carried out without raising the temperature above the fusion temperature to form bulk metal, sometimes even at room temperature. Therefore, metal nanoparticle aggregates (where at least a majority of the metal nanoparticles are not fused) can be present in the air filter media disclosed herein. As further discussed herein, adhesion can be further promoted using adhesives.

[0028] Numerous scalable methods have been developed for producing large quantities of metal nanoparticles within a target size range. Most typically, such methods for producing metal nanoparticles involve reducing a metal precursor in the presence of one or more surfactants. The instantaneously separated metal nanoparticles may have a surfactant coating and be separated into multiple nanoparticle agglomerates. The agglomerates can be broken up while retaining the surfactant coating, or the agglomerates can be used directly without further processing. Particularly advantageous metal nanoparticle agglomerates may contain metal nanoparticles with sizes ranging from about 50 nm to about 250 nm. In the case of adhering metal nanoparticles to fibers of an air filter medium, the agglomerates can have an advantageous size range to facilitate distribution by spraying and to promote retention in the air filter medium. Metal nanoparticles or their agglomerates can be separated and purified from the reaction mixture using commonly used separation techniques and processed into formulations suitable for dispersion on air filter media. Once metal nanoparticles have been deposited on the air filter medium, the surfactant coating on the nanoparticles can be removed by gentle heating, airflow, and / or vacuum (any pressure below atmospheric pressure), providing a corresponding increase in surface energy and reactivity to promote adhesion to the air filter medium. Alternatively, the surfactant coating may be lost after prolonged contact with the air filter medium (without additional heating or other treatment), and adhesion to the air filter medium occurs after the surfactant is lost. During this process, the metal nanoparticles may also fuse together, or they may remain in an unfused state. Once the surfactant coating has been removed or lost, the high surface energy generated by the metal nanoparticles can promote adhesion to the air filter medium via chemical bonding. During adhesion to the air filter medium, the metal nanoparticles may or may not fuse together.

[0029] Metal nanoparticle agglomerates with a certain size range, such as those in the range of about 0.1 μm to about 35 μm, or about 0.1 μm to about 15 μm, or about 0.1 μm to about 5 μm, can be advantageous in terms of their ability to be distributed through air filter media (e.g., by aerosol formation or spray droplets). In addition to their ease of distribution and beneficial retention on air filter media, additional benefits can be achieved once the metal nanoparticle agglomerates have lost their surfactant coating or have adhered to the surface of the air filter media by bonding to an adhesive layer. Specifically, metal nanoparticle agglomerates can “detach” individual metal nanoparticles or clusters of metal nanoparticles, which are highly active against a variety of bacteria and viruses. Once released, individual metal nanoparticles or clusters of metal nanoparticles can migrate on the surface of the air filter media but are not released in vivo. By releasing metal nanoparticles differentially from metal nanoparticle agglomerates with a certain size range, the sustained-release characteristics of metal nanoparticles can be achieved to provide prolonged and rapid infection control capabilities. The efficacy over the sustained-release period can be based on the total load of the metal nanoparticle agglomerates per unit area. Therefore, activity against various pathogens can be maintained for several days, such as at least about 3 days, or at least about 5 days, or at least about 7 days, or at least about 10 days, or at least about 14 days, or at least about 21 days, or at least about 30 days. An adhesive layer in contact with the metal nanoparticle agglomerates can further enhance the sustained-release characteristics of the metal nanoparticles to deliver biocidal activity. Suitable adhesives within the adhesive layer are not considered particularly limited and are described in more detail below.

[0030] Once the surfactant coating has been removed or lost from the metal nanoparticles, an oxide coating can be formed on the metal nanoparticles. The oxide-coated metal nanoparticles can also exhibit biocidal activity against bacteria and viruses, both as individual metal nanoparticles and in agglomerates. In some cases, they can be completely converted into metal oxides. Oxidized metal nanoparticles can lead to the formation of reactive and potentially mobile salt compounds on the surface of air filter media. Such salts can include, for example, chlorides, bisulfites, and bicarbonates. For example, chlorides may originate from chloride ions in sweat, exhaled air, or other bodily fluids that may come into contact with the air filter media. The formation of such salts may be particularly prevalent when the metal nanoparticles are exposed to a humid environment, as illustrated with respect to bicarbonate in Reaction 1 below. Conversely, dry conditions can favor the formation of at least a partial oxide coating on the surface of the metal nanoparticles.

[0031] Cu + 1 / 2O₂ + H₂O + 2CO₂ → Cu(HCO₃)₂ (Reaction 1)

[0032] The salt can be a surfactant-stabilized salt complex containing one or more surfactants (e.g., one or more amine surfactants in the case of copper nanoparticles) and a sufficient salt anion to achieve charge balance. The charge-balancing anion can include, for example, halogens, particularly chloride, bisulfite, bicarbonate, lactate, etc. The charge-balancing anion is relatively unstable and can be released to create open coordination sites for binding DNA, proteins, or similar biomolecules, which in some cases can provide biocidal activity against bacteria and viruses. Surfactant-stabilized salt complexes can move relative to each other on the surface of air filter media (even when bound to an adhesive) and provide efficient coverage on the surface of the air filter media (even with low metal nanoparticle loading).

[0033] Any suitable technique can be used to form the metal nanoparticles used in the disclosure herein. Particularly easy techniques for manufacturing metal nanoparticles, particularly for copper nanoparticles, are described in U.S. Patent Nos. 7,736,414, 8,105,414, 8,192,866, 8,486,305, 8,834,747, 9,005,483, 9,095,898, and 9,700,940 (each incorporated herein by reference in its entirety). Similar procedures can be used to synthesize silver nanoparticles. As described therein, metal nanoparticles can be produced in a narrow size range by reducing metal salts in a solvent in the presence of a suitable surfactant system, which may include one or more different surfactants. Suitable surfactant systems are further described below. The customization of the surfactant system, reaction concentration, temperature, and similar factors can determine the size range of the metal nanoparticles obtained from the synthesis of metal nanoparticles. Unbound by any theory or mechanism, surfactant systems are believed to mediate the nucleation and growth of metal nanoparticles, limit surface oxidation of metal nanoparticles (when the surfactant system adheres to them), and / or inhibit extensive aggregation of metal nanoparticles before they are at least partially fused together. As described above, small agglomerates of metal nanoparticles can be formed in many cases and are used in the disclosure herein. Alternatively, metal nanoparticle agglomerates can rupture to form single metal nanoparticles or smaller agglomerates. Suitable organic solvents for dissolving metal salts and forming metal nanoparticles may include, for example, formamide, N,N-dimethylformamide, dimethyl sulfoxide, dimethylacrylurea, hexamethylphosphoramide, tetrahydrofuran, glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, propylene glycol dimethyl ether (proglyme), or polyethylene glycol dimethyl ether. Reducing agents suitable for reducing metal salts and promoting the formation of metal nanoparticles may include, for example, alkali metals in the presence of a suitable catalyst (e.g., lithium naphthalene, sodium naphthalene, or potassium naphthalene) or a borohydride reducing agent (e.g., sodium borohydride, lithium borohydride, potassium borohydride, or tetraalkylammonium borohydride). In non-limiting embodiments, the reduction of metal salts to form metal nanoparticles and their agglomerates can occur in a suitable organic solvent under substantially anhydrous conditions.

[0034] Figure 1 and Figure 2 A hypothetical structural diagram of a metal nanoparticle with a surfactant coating is shown. Figure 1 As shown, the metal nanoparticle 10 includes a metal core 12 and a surfactant layer 14 covering the metal core 12. As described in more detail below, the surfactant layer 14 may contain any combination of surfactants. Figure 2 The metal nanoparticles 20 shown are Figure 1Similar to the metal nanoparticles depicted in the previous section, the difference lies in that a metal core 12 grows around a core 21, which may be the same or a different metal as the core 12. Because the core 21 is deeply embedded within the metal core 12 and is very small in size within the metal nanoparticle 20, it is believed that it will not significantly affect the overall properties of the nanoparticle. The core 21 may contain a salt or a metal, wherein the metal may be the same or a different metal than the core 12. In some embodiments, the nanoparticles may have an amorphous morphology. Figure 1 and Figure 2 This can represent the microstructure of a single copper or silver nanoparticle applicable to the disclosure herein. Figure 3 An illustrative SEM image of a substantially single copper nanoparticle is shown. Figure 4 Illustrative SEM images of copper nanoparticle agglomerates that can be used in the content disclosed herein are shown. Figure 5 An illustrative SEM image of a copper nanoparticle network obtained after multiple copper nanoparticles are fused together is shown. Figure 6A and Figure 6B An illustrative SEM image of copper nanoparticle agglomerates adhered to textile fibers is shown. The copper nanoparticle agglomerates are firmly adhered to the fabric fibers but are not fused together. Figure 7 An illustrative SEM image of copper nanoparticle agglomerates adhered to fibers in a cellulose / polyester blend (55:45) is shown, with the fiber joints fused together. According to this disclosure, bonding with fabric fibers and similar fibers can represent bonding that occurs when metal nanoparticle agglomerates come into contact with multiple fibers within an air filter medium.

[0035] As described above, the formed metal nanoparticles may have a surfactant coating comprising one or more surfactants on their surface. The surfactant coating may be formed on the metal nanoparticles during the synthesis process. Forming a surfactant coating on the metal nanoparticles during synthesis can desiccate premature fusion of the metal nanoparticles, limit agglomeration to a desired degree or desired agglomerate size, and promote the formation of clusters of metal nanoparticles with narrow size distributions. At least partial loss of the surfactant coating may occur when the metal nanoparticles are heated to the fusion temperature, including at least some loss of low-boiling-point surfactants well below the fusion temperature. If necessary, flowing gas and / or the application of a vacuum (reduced pressure) may further promote surfactant loss, even below the fusion temperature. In some cases, particularly after prolonged contact with the surface of an air filter medium, at least some surfactant loss may occur at room temperature and / or atmospheric pressure. Following surfactant loss, fusion of the metal nanoparticles may occur above or below the fusion temperature. If the uncoated metal nanoparticles remain unfused, they can acquire high surface energy within the air filter medium, which promotes adhesion to the medium, such as to an air filter medium comprising multiple fibers. Once the surfactant coating has been removed, the metal nanoparticles adhere to the air filter medium even below their melting temperature. When heated above the melting temperature, nanoparticle fusion can occur, and the metal nanoparticles become adherent to the air filter medium and adhere to each other. Fusion can also occur between copper and silver nanoparticles when they are impregnated together in the air filter medium.

[0036] Various types of metal nanoparticles, such as copper or silver nanoparticles, can be synthesized by metal reduction in the presence of one or more suitable surfactants. Copper and / or silver may be particularly desirable metals for use in the embodiments of this disclosure because they can promote the killing or inactivation of pathogens when deposited on surfaces. Significantly higher biocidal activity can be achieved when using metal nanoparticles compared to the biocidal activity obtained for bulk metal surfaces. Copper is particularly advantageous due to its low cost. Zinc and zinc oxide can similarly exhibit biocidal activity against bacteria, viruses, and similar microorganisms and can be used in place of copper or silver, or in combination with these metals, in any embodiment disclosed herein. NiO and TiO2 can be used similarly in this regard.

[0037] In various embodiments, the surfactant system present within the metal nanoparticles may include one or more surfactants. The different properties of various surfactants can be used to tune the properties of the metal nanoparticles and their agglomerates. Factors that can be considered when selecting surfactants or combining surfactants for inclusion on metal nanoparticles may include, for example, the ease with which the surfactant is lost from the metal nanoparticles during or before nanoparticle fusion; the nucleation and growth rates of the metal nanoparticles, which affect the nanoparticle size and metal composition; the degree of formation and size of the metal nanoparticle agglomerates, etc. For example, when forming metal nanoparticles, main group metals may require different surfactants than transition metals.

[0038] In some embodiments, amine surfactants or combinations of amine surfactants, particularly aliphatic amines, can be present on the metal nanoparticles. Amine surfactants are particularly suitable for use with copper or silver nanoparticles due to their good affinity for these transition metals. In some embodiments, two amine surfactants can be used in combination with each other. In other embodiments, three amine surfactants can be used in combination with each other. In a more specific embodiment, a primary amine, a secondary amine, and a diamine chelating agent can be used in combination with each other. In yet another more specific embodiment, the three amine surfactants may include a long-chain primary amine, a secondary amine, and a diamine having at least one tertiary alkyl nitrogen substituent. This combination of surfactants can be particularly effective for producing metal nanoparticles within the desired size range. Further disclosure regarding suitable amine surfactants is given below.

[0039] In some embodiments, the surfactant system may include a primary alkylamine. In some embodiments, the primary alkylamine may be C2-C 18 Alkylamines. In some embodiments, the primary alkylamine may be C7-C6. 10 Alkylamines. In other embodiments, C5-C6 primary alkylamines may also be used. Without being bound by any theory or mechanism, the precise size of the primary alkylamine can be balanced between being long enough to provide an efficient antimicelle structure during synthesis and being easily volatilized and / or handled during nanoparticle consolidation. For example, primary alkylamines with more than 18 carbons are also suitable for this embodiment, but they may be more difficult to handle due to their waxy properties. In particular, C7-C... 10 Primary alkylamines can offer a good balance of desired properties, making them easy to use.

[0040] In some implementations, for example, C2-C 18Primary alkylamines can be n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, or n-decylamine. While these are straight-chain primary alkylamines, branched primary alkylamines can also be used in other embodiments. For example, branched primary alkylamines such as 7-methyloctylamine, 2-methyloctylamine, or 7-methylnonylamine can be used. In some embodiments, such branched primary alkylamines may be sterically hindered at their attachment to the nitrogen atom of the amine. Non-limiting examples of such sterically hindered primary alkylamines may include, for example, tert-octylamine, 2-methylpentan-2-amine, 2-methylhexan-2-amine, 2-methylheptan-2-amine, 3-ethyloctan-3-amine, 3-ethylheptan-3-amine, 3-ethylhexan-3-amine, etc. Additional branching may also be present. Without being bound by any theory or mechanism, primary alkylamines are believed to be useful as ligands in metal coordination spheres, but readily dissociate from them during the consolidation of metal nanoparticles.

[0041] In some embodiments, the surfactant system may include a secondary amine. Suitable secondary amines for forming metal nanoparticles may include straight-chain, branched, or cyclic C4-C atoms bonded to the nitrogen atom of the amine. 12 Alkyl groups. In some embodiments, branching can occur on the carbon atom bonded to the nitrogen atom of the amine, thereby creating significant steric hindrance at the nitrogen atom. Suitable secondary amines include, but are not limited to, dihexylamine, diisobutylamine, ditert-butylamine, dinepentylamine, ditert-pentylamine, dicyclopentylamine, dicyclohexylamine, etc. C4-C groups can also be used. 12 Secondary amines outside the scope, but these secondary amines may have undesirable physical properties, such as low boiling point or waxy consistency, which would complicate their handling.

[0042] In some embodiments, the surfactant system may include a chelating agent, particularly a diamine chelating agent. In some embodiments, one or two nitrogen atoms of the diamine chelating agent may be substituted with one or two alkyl groups. When two alkyl groups are present on the same nitrogen atom, they may be the same or different. Furthermore, when both nitrogen atoms are substituted, the same or different alkyl groups may be present. In some embodiments, the alkyl group may be a C1-C6 alkyl group. In other embodiments, the alkyl group may be a C1-C4 alkyl group or a C3-C6 alkyl group. In some embodiments, the C3 or higher alkyl group may be straight-chain or branched. In some embodiments, the C3 or higher alkyl group may be cyclic. Without being bound by any theory or mechanism, it is believed that diamine chelating agents can promote the formation of metal nanoparticles by promoting nanoparticle nucleation.

[0043] In some embodiments, particularly suitable diamine chelating agents may include N,N'-dialkylethylenediamine, especially C1-C4 N,N'-dialkylethylenediamine. Corresponding methyldiamine, propylenediamine, butyldiamine, pentanediamine, or hexamethylenediamine derivatives may also be used. The alkyl groups may be the same or different. Possible C1-C4 alkyl groups include, for example, methyl, ethyl, propyl, and butyl groups, or branched alkyl groups such as isopropyl, isobutyl, sec-butyl, and tert-butyl groups. Illustrative N,N'-dialkylethylenediamines suitable for inclusion on metal nanoparticles include, for example, N,N'-di-tert-butylethylenediamine, N,N'-diisopropylethylenediamine, etc.

[0044] In some embodiments, suitable diamine chelating agents may include N,N,N',N'-tetraalkylethylenediamine, particularly C1-C4 N,N,N',N'-tetraalkylethylenediamine. Corresponding methyldiamine, propylenediamine, butanediamine, pentanediamine, or hexanediamine derivatives may also be used. The alkyl groups may also be the same or different and include those alkyl groups mentioned above. Exemplary N,N,N',N'-tetraalkylethylenediamines suitable for forming metal nanoparticles include, for example, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, etc.

[0045] Surfactants other than aliphatic amines can also be present in surfactant systems. Suitable surfactants in this regard may include, for example, pyridine, aromatic amines, phosphine, thiols, or any combination thereof. These surfactants can be used in combination with aliphatic amines (including those mentioned above), or they can be used in surfactant systems where aliphatic amines are absent. Further disclosures regarding suitable pyridines, aromatic amines, phosphines, and thiols are as follows.

[0046] Suitable aromatic amines can have the formula ArNR 1 R 2 Where Ar is a substituted or unsubstituted aryl group, and R 1 and R 2 Same or different. R 1 and R 2 The aromatic amine can be independently selected from H or alkyl or aryl groups containing 1 to 16 carbon atoms. Illustrative aromatic amines suitable for forming metal nanoparticles include, for example, aniline, toluidine, anisidine, N,N-dimethylaniline, N,N-diethylaniline, etc. Other aromatic amines that can be used in combination with metal nanoparticles will be conceived by those skilled in the art.

[0047] Suitable pyridines may include pyridine and its derivatives. Illustrative pyridines suitable for inclusion on metal nanoparticles include, for example, pyridine, 2-methylpyridine, 2,6-dimethylpyridine, trimethylpyridine, pyridazine, etc. Chelated pyridines, such as bipyridyl chelators, may also be used. Other pyridines that can be combined with metal nanoparticles will be conceived by those skilled in the art.

[0048] Suitable phosphines may have the formula PR3, where R is an alkyl or aryl group containing 1 to 16 carbon atoms. The alkyl or aryl groups attached to the phosphorus center may be the same or different. Illustrative phosphines that may be present on metal nanoparticles include, for example, trimethylphosphine, triethylphosphine, tributylphosphine, tri-tert-butylphosphine, trioctylphosphine, triphenylphosphine, etc. Phosphine oxides may also be used in a similar manner. In some embodiments, surfactants containing two or more phosphine groups (configured to form a chelating ring) may also be used. For example, exemplary chelating phosphines may include 1,2-bisphosphine, 1,3-bisphosphine, and bisphosphines such as BINAP. Other phosphines that can be used in combination with metal nanoparticles will be conceived by those skilled in the art.

[0049] Suitable thiols may have the formula RSH, where R is an alkyl or aryl group having about 4 to about 16 carbon atoms. Exemplary thiols that may be present on metal nanoparticles include, for example, butanethiol, 2-methyl-2-propanethiol, hexanethiol, octylthiol, thiophene, etc. In some embodiments, surfactants containing two or more thiol groups configured to form chelating rings may also be used. Exemplary chelating thiols may include, for example, 1,2-dithiols (e.g., 1,2-ethanethiol) and 1,3-dithiols (e.g., 1,3-propanethiol). Other thiols that can be used in combination with metal nanoparticles can be envisioned by those skilled in the art.

[0050] As described above, a key characteristic of metal nanoparticles is their high surface energy, particularly after the removal of the surfactant coating, which can promote adhesion to air filter media according to the disclosure herein. However, strong adhesion to the air filter media can still be achieved even when the surfactant coating remains intact, particularly when using an adhesive layer. Aggregates of metal nanoparticles, such as silver and / or copper nanoparticles, and optionally zinc, nickel, titanium, or oxides thereof combined with silver and / or copper nanoparticles, can be mixed with solvents in a spray formulation suitable for deposition on air filter media disclosed herein. The spray formulation can be used to promote the introduction of metal into the air filter media before the metal adheres to the surface of the air filter media. In addition to promoting dispersion in a suitable spray formulation, one or more surfactants associated with the metal nanoparticles as a surfactant coating can further promote initial surface adhesion to the air filter media before the surfactant coating is lost and uncoated metal nanoparticles with high surface energy are formed. That is, surfactant coatings can initially hold metal nanoparticle agglomerates in place until a high surface energy state has been reached to promote stronger adhesion and retention of metal nanoparticles on the fibers of the air filter medium.

[0051] The produced metal nanoparticles are typically manufactured in the form of large agglomerates, which need to be broken down into smaller agglomerates and / or individual surfactant-coated metal nanoparticles to facilitate use in a variety of applications. Surprisingly, in the disclosure herein, the produced agglomerates, such as those in the 0.1–35 μm size range, particularly those in the 1–15 μm or 1–5 μm size range, are effectively used for spray-dispensing and retention in air filter media. These even larger agglomerates can be retained in air filter media more effectively than individual metal nanoparticles or smaller agglomerates. When such agglomerates adhere to air filter media, their shape may change while remaining bound together in “colonies.” Within the agglomerates, identifiable substructures may exist prior to nanoparticle fusion, such as, but not limited to, flakes 10-50 nm thick with a width of about 100-250 nm, flakes 1-5 nm thick with a width of about 30-50 nm, spheres 100-250 nm wide, metallic nanowires, and any combination thereof. The substructures can have arbitrary shapes, such as squares, triangles, rectangles, polyhedra, circles, and oblongs, and can be crystalline and / or amorphous. For example, elongated structures such as metallic nanowires can have an aspect ratio of at least about 10 or at least about 25. Copper nanoparticles and / or silver nanoparticles may also be combined with pre-fabricated nanowires (e.g., copper nanowires or silver nanowires) and also deposited on the air filter medium. Zinc, nickel, or titanium (particularly in nanoparticle form or their metal oxide form) may also be present in any of these embodiments.

[0052] Therefore, the air filter media of this disclosure may include multiple fibers with multiple metal nanoparticle agglomerates adhered thereto, wherein the metal nanoparticle agglomerates comprise multiple fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surfaces of the multiple fibers. Optionally, the metal nanoparticles may be substantially free of surfactant coating after adhesion to the multiple fibers. In some embodiments, the metal nanoparticles may retain their surfactant coating and / or at least a majority of the metal nanoparticles in the metal nanoparticle agglomerates may remain unfused to each other when adhered to the multiple fibers. As further described herein, in any embodiment herein, the metal nanoparticle agglomerates may be adhered to the air filter media by an adhesive layer.

[0053] In the disclosure herein, metal nanoparticles may include copper nanoparticles, silver nanoparticles, or any combination thereof. Without being bound by any theory or mechanism, it is believed that Cu(0) can be oxidized to Cu(I) in a slow process on an air filter medium, followed by rapid further oxidation to Cu(II). Upon contact with pathogens (e.g., bacteria or viruses), hydroxyl radicals and lipid radicals can be formed, which can disrupt the outer lipid bilayer or protein coat of the virus or bacteria. Furthermore, copper can bind to heteroatoms (e.g., S, N, or P) in amino acids, proteins, DNA, and / or RNA of viruses, bacteria, and other pathogens, leading to inactivation. Metal permeation can also occur within cell membranes or protein coatings, where the metal can inhibit DNA / RNA replication and / or protein transport. Silver nanoparticles may promote bactericidal activity through a similar mechanism.

[0054] The combination of copper and silver nanoparticles can provide specific synergistic effects against pathogens that cannot be adequately treated with a single metal alone. That is, copper and silver nanoparticles can deliver biocidal activity against different pathogens. Furthermore, compared to individual copper or silver nanoparticles, the simultaneous presence of both can achieve enhanced activity against specific pathogens. Unbound by theoretical or mechanistic constraints, these two different types of metal nanoparticles can target different biological pathways and receptors within pathogens, thereby providing more effective killing or inactivation than using either type of metal nanoparticle alone.

[0055] Metal nanoparticles, such as silver nanoparticles and / or copper nanoparticles or aggregates thereof, can be mixed with an atomizable fluid medium in a spray formulation suitable for deposition on an air filter medium disclosed herein. Suitable atomizable fluid media and spray formulations are described in more detail below. Dip coating and similar liquid treatment techniques are also applicable to introducing metal nanoparticles onto the air filter media disclosed herein.

[0056] Spray formulations comprising metal nanoparticle agglomerates, such as silver nanoparticles and / or copper nanoparticles and their agglomerates, can be prepared by dispersing on-the-fly produced or on-the-fly separated nanoparticles in an organic matrix or other medium containing one or more organic solvents, wherein the metal nanoparticle agglomerates can be mixed as well-dispersed solids in the fluid medium. Optionally, the fluid medium may also contain one or more inorganic components, particularly water. As used herein, the term "spray formulation" refers to a fluid composition containing dispersed metal nanoparticles, which can be as individual metal nanoparticles, agglomerated metal nanoparticles, or any combination thereof, suitable for dispensing by spraying. Spray formulations refer to pump-assisted and forced spraying, as well as spraying dispensing using aerosol propellants. Pump-assisted and forced spraying can be dispensed by pressurizing with an inert gas and / or by pressurizing with a mechanical or pneumatic pump.

[0057] Particularly suitable organic solvents that can be present in spray formulations suitable for pumping or pressurized dispensing include C1-C4. 11 alcohols or multiple C1-C 11 Any combination of alcohols. It may also be present in other alcohol-miscible organic solvents. It can be used alone or in combination with one or more alcohols, and is also C1-C. 11 Ketone and aldehyde organic solvents of various sizes are available. Ketone and aldehyde solvents are less polar than alcohols and can help promote the dispersion of metal nanoparticles and / or their agglomerates. For example, low-boiling-point ethers such as diethyl ether, dipropyl ether, and diisopropyl ether are also suitable for promoting the dispersion of metal nanoparticles. One or more glycol ethers (e.g., diethylene glycol, triethylene glycol, etc.), alkanolamines (e.g., ethanolamine, triethanolamine, etc.), or any combination thereof can also be used alone or in combination with one or more alcohols or any other of the aforementioned organic solvents. Various glycol dimethyl ethers can also be used similarly. Water-miscible organic solvents and mixtures of water and water-miscible organic solvents, such as water-organic solvent mixtures containing up to about 50% by volume of water, or up to about 75% by volume of water, or up to about 90% by volume of water, can also be used. During the process of promoting the adhesion of metal nanoparticles to air filter media, the organic solvent can be removed before or after the loss of the surfactant coating.

[0058] In certain embodiments, the spray formulation may contain one or more alcohols; in more specific embodiments, the one or more alcohols may be C1-C64. 11 C1-C4, C4-C 11 Or C7-C 11C1-C4 alcohols are particularly desirable due to their low boiling points, which can facilitate solvent removal after partitioning. In various embodiments, the alcohol may include any monohydric alcohol, dihydric alcohol, or trihydric alcohol. In some embodiments, one or more glycol ethers (e.g., diethylene glycol and triethylene glycol), alkanolamines (e.g., ethanolamine, triethanolamine, etc.), or any combination thereof may be present, either alone or in combination with other alcohols. In some embodiments, multiple glycol dimethyl ethers may be present with one or more alcohols.

[0059] Spray formulations suitable for dispensing by pumping or forced gas pressurization can exhibit viscosity values ​​from about 1 cP to about 500 cP, including from about 1 cP to about 100 cP. Such low viscosity values ​​can be facilitated by spraying driven by mechanical pumping or forced pressurization. The loading of metal nanoparticles in the spray formulations used to produce the above-mentioned viscosity values ​​can range from about 1 wt.% to about 35 wt.%, or about 5 wt.% to about 35 wt.%, or about 10 wt.% to about 25 wt.%, or about 8 wt.% to about 25 wt.%, or about 1 wt.% to about 8 wt.%.

[0060] Spray formulations containing aerosol propellants are also suitable for applying metal nanoparticle agglomerates to air filter media according to the disclosure herein. Such spray formulations may similarly comprise metal nanoparticles or agglomerates thereof dispersed in a fluid medium containing at least an aerosol propellant and optionally other solvents to promote dispersion of the metal nanoparticles therein. Aerosol spray formulations can be considered as a particularly desirable form for distributing metal nanoparticles because aerosol spray cans are widely used and easy to manufacture and transport. Aerosol propellants can provide spray droplets ranging in size from about 10 to 150 μm, while mechanically pumped or forced-pressure spraying can have larger droplet sizes ranging from about 150 to 400 μm.

[0061] Any conventional aerosol propellant can be used in spray formulations, provided that the metal nanoparticle agglomerates (optionally in combination with one or more additional solvents) can be effectively dispersed therein and sprayed from a spray canister. Organic and / or inorganic aerosol propellants can be used. Suitable inorganic aerosol propellants may include, for example, nitrous oxide or carbon dioxide. Suitable organic aerosol propellants may include, for example, volatile hydrocarbons (e.g., ethane, propane, butane, or isobutane), dimethyl ether, ethyl methyl ether, hydrofluorocarbons, hydrofluoroolefins, or any combination thereof. Chlorofluorocarbons and similar compounds may also be used as aerosol propellants, but their use is not preferred due to their ozone-depleting properties. However, chlorofluorocarbons can be satisfactory alternatives where other organic atomizable fluid media may not be effective.

[0062] When using aerosol propellants to promote the dispersion of metal nanoparticle agglomerates, the metal nanoparticle agglomerates can bind directly to the aerosol propellant, or the metal nanoparticles can be dissolved in a secondary fluid medium and subsequently bound to the aerosol propellant in a spray can or similar container. Suitable secondary fluid media may include organic solvents, such as alcohols, glycols, ethers, etc. Any organic solvents used in mechanically pumped or pressurized spray formulations can also be incorporated as a secondary fluid medium into spray formulations containing aerosol propellants.

[0063] Spray formulations containing organic solvents may comprise mixtures of organic solvents that typically evaporate over a specific time period under ambient conditions. In non-limiting embodiments, evaporation may occur within a time period of about 1 min or less, or about 2 min or less, or about 5 min or less, or about 10 min or less, or about 15 min or less, or about 30 min or less. To facilitate evaporation, metal nanoparticles may be dispersed as a concentrate in a higher-boiling-point organic solvent such as C. 10 The metal nanoparticles are first placed in an alcohol, and then mixed with a larger amount of a low-boiling-point organic solvent such as ethanol or diethyl ether (optionally further combined with other organic solvents). High-boiling-point organic solvents can be sufficiently hydrophobic to promote dispersion of the metal nanoparticles in a less hydrophobic and lower-boiling-point organic solvent containing the majority of the organic phase.

[0064] In various embodiments, the size of individual metal nanoparticles disposed on air filter media or present in metal nanoparticle agglomerates in spray formulations may be about 20 nm or larger, more particularly about 50 nm or larger. In particularly suitable embodiments, all or at least about 90%, at least about 95%, or at least about 99% of the metal nanoparticles may be about 20 nm to about 200 nm or about 50 nm to about 250 nm in size. Smaller copper nanoparticles (less than 20 nm) may be more extensively oxidized than larger metal nanoparticles, and the presence of such metal nanoparticles may support the desired degree of oxidation. For example, smaller copper nanoparticles may tend to be more extensively oxidized to CuO or Cu2O, including compounds partially or completely oxidized to them, compared to larger copper nanoparticles with a size greater than 20 nm. Copper nanoparticles within the aforementioned size range (20 nm or larger, or about 50 nm or larger) may provide a coating comprising a mixture of CuO and Cu2O on a metallic copper core, the combination of which may be advantageous for inactivating pathogens on air filter media according to the disclosure herein. Silver nanoparticles within a similar size range can form a coating containing silver oxide on a metallic silver core. When copper and / or silver nanoparticles aggregate and adhere to an air filter medium, the oxide coating can extend over at least a portion of the aggregate surface, leaving an exposed copper or silver metallic surface beneath within the porosity of the aggregate. Larger metallic nanoparticles within the aforementioned size range can retain a significant amount of zero-valent metal to promote biocidal activity, while smaller metallic nanoparticles can form an excess of oxide to promote optimal bioactivity.

[0065] Copper nanoparticles with a size of about 20 nm or smaller can have a melting temperature of about 220°C or lower (e.g., a melting temperature in the range of about 140°C to about 220°C) or about 200°C or lower, which can provide advantages for certain applications, as described above. Silver nanoparticles with a size of about 20 nm or smaller can similarly exhibit melting temperatures significantly different from the corresponding bulk metals. Larger metal nanoparticles (copper or silver nanoparticles) in turn have higher melting temperatures, which may increase rapidly and approach the melting temperatures of bulk metals as the nanoparticle size continues to increase. Depending on the size-based processing and melting temperatures of the metal nanoparticles, they may be fused or not fused within the air filter medium when processed according to the disclosure herein. For example, copper and / or silver nanoparticles may remain substantially unfused when processed according to the disclosure herein, even if their surfactant coating is lost or not. Regardless of whether the metal nanoparticles fuse with each other after the surfactant coating is removed, they can withstand strong adhesion to the air filter medium. As described above, surface oxidation of the metal nanoparticles can occur during this process.

[0066] When deposited on an air filter medium comprising multiple fibers, the metal nanoparticle agglomerates may be primarily located on at least one outer surface of the air filter medium (i.e., on the outer surface layer of the air filter medium) or, when deposited by spray coating, extend to a depth of up to about 3-4 fiber layers in addition to the outer surface layer. For example, a multilayer air filter medium may have metal nanoparticle agglomerates adhered to at least one outer layer (surface) of the air filter medium, and one or more inner layers may contain or not contain metal nanoparticles. In another embodiment, the air filter medium may define a removable insert within a structure without adhered metal nanoparticles. For example, the air filter medium may include a removable insert for a face mask (e.g., a cloth face mask). The insert can be removed to clean the cloth face mask. Due to the presence of the metal nanoparticle agglomerates, the inserts disclosed herein, or any other air filter medium, may be self-sterilizing. When present as an insert or similar structure, the exposed surface of the air filter medium with adhered metal nanoparticle agglomerates may be covered with an outer liner to prevent direct exposure of the metal nanoparticle agglomerates to the wearer. Suitable backings may include porous media, such as woven or nonwoven fabrics without adherent metal nanoparticle agglomerates. Roll-to-roll dip coating and gravure coating can also provide a surface coating of metal nanoparticle agglomerates primarily on the outer surface of the air filter media. Compared to other types of dip coating processes, a primary surface coating ensures effective use of metal nanoparticles to promote biocidal activity, where the metal nanoparticles can be deposited more deeply and significantly within all fiber layers of a multilayer fabric. Metal nanoparticle agglomerates embedded deeper within fiber layers may be ineffective or less effective at delivering biocidal activity because more metal nanoparticle agglomerates are located away from the surface of the air filter media where the load of bacterial or viral pathogens may be higher.

[0067] The loading of metal nanoparticle aggregates on air filter media can range from approximately 0.1 mg / in 2 approximately 10 mg / in 2 or approximately 0.5 mg / in 2 Approximately 5 mg / in 2 or about 1 mg / in 2 Approximately 2 mg / in 2 Or approximately 0.5 mg / in 2 Approximately 3 mg / in 2The coverage density of metal nanoparticle agglomerates on air filter media can be from about 5% to about 95% area, or from about 50% to about 99% area, or from about 60% to about 95% area. Due to the mobility of individual metal nanoparticles or small metal nanoparticle agglomerates detached from the adhered larger metal nanoparticle agglomerates, even coverage densities as low as 3-5% area can be effective for the biocidal activity disclosed herein. When present on air filter media at the aforementioned coverage rates and densities, metal nanoparticles can effectively inactivate a variety of pathogens, including certain bacteria and viruses, generally more effectively than bulk metal surfaces containing the same metal. For example, copper nanoparticles adhered to air filter media and maintaining their nanoparticle form within multiple nanoparticle agglomerates can inactivate / kill viruses in as little as 30 seconds. Kill rates or inactivation rates of up to 100% can be achieved in such a short time. In contrast, bulk copper surfaces may require several hours to achieve the same level of inactivation. Bacteria can be inactivated or killed to similar degrees under various conditions.

[0068] In addition to metal nanoparticle agglomerates or alternative nanostructures, other additives may be incorporated into air filter media and / or spray formulations suitable for producing air filter media according to the disclosure herein. Suitable additives may include, but are not limited to, those capable of generating reactive oxygen species (ROS), which can cause lipid, protein, or DNA damage in microorganisms, ultimately leading to cell membrane damage and cell death. These additives may complement or enhance the biocidal activity delivered by copper nanoparticles, silver nanoparticles, or alternative metal nanoparticles with biocidal activity (e.g., those comprising zinc, nickel, titanium, and / or their oxides).

[0069] NiO can be included as an additive in filter media or in spray formulations suitable for producing filter media. NiO generates ROS very effectively when present at low concentrations. NiO can be effective when included in spray formulations, for example, at an amount of about 0.5% to about 10% of the mass of copper nanoparticles and / or silver nanoparticles (e.g., 0.5 mg to 100 mg NiO), because the submicron particles are distinctly separated from the copper and / or silver nanoparticles. At these loadings, NiO is very effective against certain bacteria, which can extend the biocidal effectiveness of copper or silver. Bismuth, zinc, and tin oxides are equally effective at loadings of about 0.5% to about 10% of the mass of copper and / or silver nanoparticles.

[0070] TiO2 can be included as an additive in filter media or in spray formulations suitable for producing filter media. When the filter media is taken outdoors, TiO2 can catalyze the formation of hydroxyl radicals under UV irradiation (e.g., sunlight). Moisture from the wearer's breath or in the atmosphere can provide a source of moisture for the generation of hydroxyl radicals through photo-oxidation. TiO2 can be present in spray formulations or on air filter media at a loading of about 1% to about 25% of copper nanoparticles and / or silver nanoparticles. TiO2 can also be present in the form of nanoparticles and / or micron-sized particles (e.g., about 100 nm to about 5 μm).

[0071] Copper nanoparticles and / or silver nanoparticles, ZnO, NiO and / or TiO2 can also be used in combination with each other. These additives can be sprayed onto the filter media simultaneously with copper nanoparticles and / or silver nanoparticles (from the same or different spray formulations), or they can be sprayed before or after the copper nanoparticles and / or silver nanoparticles.

[0072] After the spray formulation is deposited onto the filter medium, the solvent and optionally the surfactant can be removed. While solvents and surfactants can be removed under ambient conditions (room temperature and atmospheric pressure), applying at least one of heating, airflow, and / or vacuum (reduced pressure) can accelerate the removal of solvents and surfactants from the air filter medium, resulting in the adhesion of metal nanoparticle agglomerates to the air filter medium. Heating can be performed at any temperature up to or above the melting temperature of the metal nanoparticles, as long as the heating temperature is not so high that the air filter medium itself would be thermally damaged. Therefore, the metal nanoparticles may or may not fuse when adhering to the air filter medium. Furthermore, the heating temperature need not exceed the normal boiling point or reduced pressure boiling point of the surfactant and solvent to promote their removal. In many cases, mild heating well below the boiling points of the surfactant and solvent is sufficient to promote their removal. In a non-limiting embodiment, heating can be performed under flowing nitrogen, air, or other inert gases, or under vacuum, to promote removal. For example, heating the air filter medium in flowing nitrogen or air at a temperature of about 35°C to about 65°C is sufficient to remove solvents and surfactants, thereby distributing the unfused metal nanoparticles as aggregates throughout the air filter medium. Further heating can be performed thereafter if desired to promote the fusion of the metal nanoparticles. In either case, strong adhesion to the air filter medium can be achieved after removing the surfactant from the nanoparticle surface. When heating at higher temperatures, it is desirable to use an inert atmosphere, such as nitrogen, to limit the degradation of the air filter medium and control the amount of surface oxidation occurring on the metal nanoparticles (once the surfactant coating has been removed).

[0073] Once the surfactant coating has been removed from the metal nanoparticles, particularly copper and / or silver nanoparticles, the metal nanoparticles and / or their agglomerates can be subjected to at least partial oxidation. As described above, in the case of copper nanoparticles, the size of the copper nanoparticles and their agglomerates can be selected such that at least some copper metal is retained after oxidation, because the mixture of copper metal (metallic copper) and copper oxide can be beneficial in promoting the inhibition or killing of pathogens. Depending on the size of the silver nanoparticles and how they are treated, the silver nanoparticles may similarly be subjected to varying amounts of surface oxidation. In a non-limiting embodiment, after the surfactant is removed, the copper nanoparticles can form a reaction product in an air filter medium comprising about 25 wt% to about 99 wt% metallic copper or about 45 wt% to about 90 wt% metallic copper, about 0.5 wt% to about 60 wt% Cu₂O, and about 0.1 wt% to about 80 wt% CuO or about 0.1 wt% to about 20 wt% CuO. In more specific embodiments, the amount of metallic copper may be from about 45 wt% to about 90 wt%, or from about 50 wt% to about 70 wt%; the amount of Cu2O may be from about 10 wt% or less, for example from about 0.1 wt% to about 10 wt% or less, or from about 5 wt% to about 10 wt% or less; and the amount of CuO may be from about 1 wt% or less, for example from about 0.1 wt% to about 1 wt%, or from about 0.5 wt% to about 1 wt%. In many cases, Cu2O and CuO can form a coating (shell) with a thickness of about 10 nm or more, or a thickness of 100 nm or more, for example, a thickness of about 100 nm to about 3 μm, on the metal nanoparticles or their agglomerates.

[0074] The silver nanoparticles adhered to the air filter medium may similarly comprise about 25% to about 99% metallic silver, with the balance being Ag2O. Ag2O may similarly exist as a coating (shell) having a thickness of about 10 nm or greater, for example, about 100 nm to about 3 μm.

[0075] In addition to metal nanoparticles and other additives, the spray formulations and air filter media disclosed herein may also contain an adhesive suitable for promoting the adhesion of nanoparticles to fibers within the air filter media. That is, the air filter media disclosed herein may also have an adhesive layer thereon, which can further enhance adhesion to the fibers constituting the air filter media. When an adhesive layer is present, metal nanoparticle agglomerates can adhere to the air filter media even without removal of the surfactant coating. The adhesive layer may be applied together with the metal nanoparticle agglomerates (i.e., in a suitable spray or dip formulation) or may already be present on the air filter media before the metal nanoparticle agglomerates are applied. For this purpose, both contact and non-contact adhesives can be used. Suitable adhesives are well known to those skilled in the art and include conventional epoxy adhesives, nitrile rubber adhesives, acrylic adhesives, styrene-acrylic adhesives, cyanoacrylate adhesives, solvent-based adhesives, aqueous emulsions, etc. The adhesive may be applied at a concentration of about 0.1 mg / in 2 Approximately 0.5 mg / in 2 The adhesive loading is present on the air filter medium. Suitable loading ranges for the adhesive in spray formulations or similar formulations can be from about 0.35 g adhesive / 100 g spray formulation to about 2.75 g adhesive / 100 g spray formulation. The coverage of the adhesive layer on the air filter medium can range from about 50 area % to about 100 area %, or about 60 area % to about 90 area %, or about 75 area % to about 95 area %, or about 90 area % to about 99 area %. The layer thickness of the adhesive layer on the air filter medium can be about 300 nm or less, for example, about 1 nm to about 2 nm, or about 2 nm to about 5 nm, or about 5 nm to about 10 nm, or about 10 nm to about 50 nm, or about 10 nm to about 300 nm. In addition to promoting surface adhesion, the adhesive can also slow down the formation of metal oxides, thereby further modulating the sustained-release characteristics of individual or small agglomerates of metal nanoparticles or their various oxidized forms.

[0076] When an adhesive layer is applied to the surface of an air filter medium, the adhesive may be present in the spray or dip formulation applied to the air filter medium, or the adhesive formulation and the spray or dip formulation containing metal nanoparticles may be applied separately. The adhesive formulation may be applied to the air filter medium first, followed by the spray or dip formulation containing metal nanoparticles, or both the adhesive formulation and the metal nanoparticles may be applied simultaneously. As a further option, the adhesive may be applied to the air filter medium after the metal nanoparticle agglomerates have been deposited onto the air filter medium.

[0077] Air filter media on which metal nanoparticle agglomerates can be applied and adhered according to the disclosure herein are not considered particularly limited. According to the disclosure herein, any conventional air filter media can be treated with metal nanoparticles, particularly copper nanoparticles and / or silver nanoparticles. Illustrative air filter media may include multiple fibers, which may be natural or synthetic fibers, such as cellulose fibers, cotton fibers, glass fibers, or polymer fibers. Suitable polymer fibers may include, but are not limited to, polyester, polypropylene, polystyrene, or any combination thereof. Fiber composition may define a fiber blend to which metal nanoparticle agglomerates are adhered. Suitable air filter media that can be impregnated with metal nanoparticles according to the disclosure herein include, for example, media of N95, N99, or N100 rating. According to the disclosure herein, for example, low-grade face masks such as surgical masks, cloth masks, and dust masks may also have metal nanoparticle agglomerates adhered. Air filter media may be in the form of fabric, tape, sheet, membrane, or any combination thereof. In addition, the air filter medium can be in the form of a removable insert that can be inserted into a face mask (which does not have additional antimicrobial activity delivered to it through the presence of metal nanoparticle agglomerates).

[0078] Fabrics comprising multiple fibers can be woven or nonwoven, single-layered or multi-layered, and / or pleated or unpleated. The term "fabric" refers to the regular or irregular arrangement of individual fibers, which may or may not be further bonded together. Woven fabrics are formed by arranging individual fibers together in a generally regular pattern without bonding the fibers together. Conversely, nonwoven fabrics are formed by arranging individual fibers together and bonding the fibers together through chemical, mechanical, thermal, or solvent treatments. Pleating within an air filter medium can increase the amount of contact surface area with air or gas. Any fabric of the above types is used in the disclosure herein. In certain embodiments, suitable fabrics may be multi-layered, and metal nanoparticle agglomerates may be distributed in a concentration gradient between the multiple layers of the fabric.

[0079] The structure and / or type of air filter media impregnated with metal nanoparticle agglomerates according to the disclosure herein are not considered particularly limited. According to the disclosure herein, air filter media located in face masks (e.g., dust masks and surgical masks), respirators, inline filters for air processors, automotive or aircraft cabin filters, medical filters, biomedical research filters, HEPA filters, etc., can be impregnated with metal nanoparticle (e.g., copper nanoparticles and / or silver nanoparticles) agglomerates to deliver biocidal activity. An air filtration system may include at least one filter comprising the air filter media disclosed herein. In the disclosure herein, the air filter media may include fabrics, which may be woven, nonwoven, and / or meltblown, having different porosities. In some cases, the air filter media may be in the form of an insert.

[0080] The loading of metal nanoparticle agglomerates can be substantially uniform throughout the air filter medium, or the metal nanoparticle agglomerates can be located within the air filter medium or on its outer surface (e.g., within the top 3-4 fabric layers of a multilayer fabric), optionally with an outer liner on the metal nanoparticle agglomerates. For example, for dust masks or similar personal protective equipment, the loading of metal nanoparticle agglomerates within the air filter medium can be from about 100 mg to about 2 g. Larger commercial air filters can contain substantial amounts of agglomerated copper nanoparticles and / or silver nanoparticles. The suitable loading of each metal nanoparticle agglomerate on the air filter medium, based on the total weight of the air filter medium, can range from about 0.5 wt.% to about 20 wt.%, or from about 1 wt.% to about 15 wt.%. Considerations for determining the suitable metal (e.g., copper or silver) loading on the air filter medium include, for example, the expected duration or frequency of use of the air filter medium, and the total airflow passing through the air filter medium during the expected use.

[0081] For example, the mask may include a dome shape, which is adapted to fit snugly around the wearer's face, mouth, and nose. The mask may have a total area of ​​approximately 28-30 square inches, with a copper or silver loading ranging from approximately 0.5 mg / in. 2 Approximately 70 mg / in 2 or approximately 6.5 mg / in 2 Approximately 25 mg / in 2 or approximately 3.5 mg / in 2 Approximately 15 mg / in 2 or approximately 0.5 mg / in 2 approximately 10 mg / in 2 or about 1 mg / in 2 Approximately 2.5 mg / in2 or approximately 3.5 mg / in 2 Approximately 6 mg / in 2 A suitable face mask can be a single layer or comprise multiple layers of air filter media bonded together at the edges. Adhesives may be included to bond the layers together and / or promote the adhesion of metal nanoparticle agglomerates to the air filter media. Copper and / or silver nanoparticles can be sprayed onto the inner layer of the face mask, and then an outer liner can be placed on top of the inner layer of the filter media, such that the outer liner is positioned between the metal nanoparticles and the wearer of the face mask. This arrangement can limit the accidental inhalation of metal nanoparticles and / or additives from the face mask. The air filter media can also be present as an insert placed between the layers of the face mask (e.g., a cloth face mask). Alternatively, the air filter media of the face mask can be single-layered or multi-layered, with at least one outer surface of the air filter media adhered to metal nanoparticle agglomerates. The outer surfaces of the face mask facing away from the wearer and / or facing the wearer can have metal nanoparticle agglomerates adhered to them. Such preparation can be readily incorporated into current manufacturing processes for various types of face masks.

[0082] Inline filters can similarly comprise a multi-layered structure containing agglomerated metal nanoparticles adhered to fibers. For example, the multi-layered structure can comprise pleated or unpleated multi-layered fabrics. An inline filter can include metal nanoparticle agglomerated particles located on the outer surface of the air filter medium, or the metal nanoparticle agglomerated particles can be adhered to one or more inner layers of a multi-layered fabric, which is then covered by an outer liner through which airflow can pass. Similarly, the outer liner can help capture metal nanoparticles that may be accidentally released from the fibers, preventing them from traveling further within air filtration systems incorporating inline filters (such as duct systems in air conditioning systems or piping in gas handling systems).

[0083] In view of the above disclosure, a method for forming an air filter medium with adhered metal nanoparticle agglomerates may include: providing an air filter medium comprising a plurality of fibers; applying a plurality of metal nanoparticle agglomerates to the air filter medium, wherein when applied to the plurality of fibers, the plurality of metal nanoparticle agglomerates comprise a plurality of metal nanoparticles having a surfactant coating thereon; and adhering the plurality of metal nanoparticle agglomerates to the plurality of fibers. Optionally, the method may include removing the surfactant coating from the plurality of metal nanoparticles such that the plurality of metal nanoparticle agglomerates adhere to the plurality of fibers. In other non-limiting embodiments, the metal nanoparticle agglomerates may be adhered to the plurality of fibers by an adhesive layer, in which case the surfactant layer may remain intact. When adhered to the plurality of fibers, the plurality of metal nanoparticles may comprise a plurality of fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surfaces of the plurality of fibers. In non-limiting embodiments, applying the plurality of metal nanoparticle agglomerates to the air filter medium may include spraying a metal nanoparticle formulation onto the air filter medium. When removing surfactant coatings, it may include applying heat, airflow, vacuum, or any combination thereof to the air filter medium after applying multiple metal nanoparticle agglomerates to the air filter medium.

[0084] Airflow, including treatment of exhaled air from a wearer of a face mask or similar personal protective equipment, may include providing an air filter medium of this disclosure; passing the airflow through the air filter medium, wherein the airflow carries a pathogenic load prior to passing through the air filter medium; and reducing, inactivating, or killing one or more pathogens or any combination thereof as the airflow passes through the air filter medium. In a particular embodiment, one or more pathogens may include Covid-19.

[0085] The implementation plan disclosed in this article includes:

[0086] A. Air filter media. The air filter media comprises: multiple fibers to which multiple copper nanoparticles or silver nanoparticles are adhered, wherein the copper nanoparticles or silver nanoparticles are fused, partially fused, or not fused on the fiber surface, and the copper nanoparticles or silver nanoparticles are substantially free of surfactant coating when adhered to the fibers.

[0087] A1. A dust mask containing air filter media A.

[0088] A2. An inline air filter that includes the air filter media of A.

[0089] B. A method for loading copper or silver onto a filter medium. The method includes: providing a filter medium comprising a plurality of fibers; applying a plurality of copper nanoparticles or silver nanoparticles onto the surface of the fibers of the filter medium, the copper nanoparticles or silver nanoparticles comprising a surfactant coating thereon; and removing the surfactant coating from the copper nanoparticles or silver nanoparticles such that the copper nanoparticles or silver nanoparticles adhere to the plurality of fibers.

[0090] Each of implementation schemes A, A1, A2, and B may have any combination of one or more of the following additional elements:

[0091] Element 1: The copper or silver nanoparticles are essentially free of amine coating.

[0092] Element 2: The fibers include cellulose fibers, cotton fibers, polymer fibers, or any combination thereof.

[0093] Element 3: The size range of the copper nanoparticles or silver nanoparticles is from about 20 nm to about 150 nm.

[0094] Element 4: The silver nanoparticles aggregate into multiple copper or silver nanoparticle agglomerates, the size of which ranges from about 1 μm to about 5 μm.

[0095] Element 5: Wherein, when substantially free of surfactant coating, the silver nanoparticles comprise metallic silver and silver oxide, or when substantially free of surfactant coating, the copper nanoparticles comprise metallic copper and one or more copper oxides.

[0096] Element 6: The filter medium also contains silver or copper nanoparticles adhered to multiple fibers.

[0097] Element 7: wherein the copper nanoparticles comprise about 25 wt% to about 99 wt% metallic copper, 0.5 wt% to about 60 wt% Cu2O and about 0.1 wt% to about 20 wt% CuO.

[0098] Element 8: wherein the copper nanoparticles comprise about 45 wt% to about 90 wt% metallic copper, 0.5 wt% to about 60 wt% Cu2O and about 0.1 wt% to about 20 wt% CuO.

[0099] Element 9: The loading of silver nanoparticles on multiple fibers ranges from about 0.5 wt.% to about 20 wt.%.

[0100] Element 10: Applying multiple copper nanoparticles or silver nanoparticles to the filter medium includes spraying a copper nanoparticle or silver nanoparticle formulation onto the filter medium.

[0101] Element 11: Wherein the removal of surfactant coating includes applying heat, vacuum or any combination thereof to the filter medium after applying multiple copper nanoparticles or silver nanoparticles to the filter medium.

[0102] Element 12: The surfactant coating contains one or more amines.

[0103] Element 13: Copper nanoparticles or silver nanoparticles aggregate into multiple copper or silver nanoparticle agglomerates, and when applied to the filter medium, the size of the agglomerates ranges from about 1 μm to about 5 μm.

[0104] As a non-limiting embodiment, exemplary combinations applicable to A, A1, and A2 include: 1 and 2; 1 and 3; 1 and 4; 1, 3, and 4; 1 and 5; 1, 5, and 6; 1, 5, 6, and 7 or 8; 1 and 9; 2 and 3; 2 and 4; 2-4; 2 and 5; 2, 5, and 6; 2, 5, 6, and 7 or 8; 2 and 9; 3 and 4; 3 and 5; 3, 5, and 6; 3, 5, 6, and 7 or 8; 5 and 6; 5-7; 5, 6, and 8; 5 and 9; 5, 6, and 9; 6, 7, and 9; 6, 8, and 9; and 8 and 9. As a further non-limiting embodiment, exemplary combinations applicable to B include, but are not limited to, 2 and 3; 2 and 5; 2, 5 and 6; 2, 5, 6 and 7 or 8; 3 and 5; 3, 5 and 6; 3, 5, 6 and 7 or 8; 5, 6 and 7; 5, 6 and 8; 5 and 9; 5, 6 and 7 or 8; 5, 6 and 9; 6, 7 or 8 and 9, any of which may be further combined with one or more of 10, 11, 12 or 13. Other exemplary combinations applicable to B include, but are not limited to, 2 and 10; 2 and 11; 2 and 12; 2 and 13; 3 and 10; 3 and 11; 3 and 12; 3 and 13; 5 and 10; 5 and 11; 5 and 12; 5 and 13; 5, 6 and 10; 5, 6 and 11; 5, 6 and 12; 5, 6 and 13; 5, 6, 7 or 8 and 10; 5, 6, 7 or 8 and 11; 5, 6, 7 or 8 and 12; and 5, 6, 7 or 8 and 13.

[0105] Other implementation methods disclosed in this document include:

[0106] A'. Air filter medium. The air filter medium comprises: a plurality of fibers with metal nanoparticle agglomerates adhered thereto, the metal nanoparticle agglomerates comprising a plurality of fused, partially fused and / or unfused metal nanoparticles associated with each other on the surfaces of the plurality of fibers.

[0107] A1'. A face mask containing the air filter medium of A'.

[0108] A2'. An inline air filter that includes the air filter media of A'.

[0109] A3'. An air filtration system comprising at least one filter, the filter comprising the air filter media of A'.

[0110] B'. A method for forming an air filter medium. The method includes: providing an air filter medium comprising a plurality of fibers; applying a plurality of metal nanoparticle agglomerates to the air filter medium, wherein, when applied to the plurality of fibers, the plurality of metal nanoparticle agglomerates comprises a plurality of metal nanoparticles having a surfactant coating thereon; and adhering the plurality of metal nanoparticle agglomerates to the plurality of fibers; wherein the plurality of metal nanoparticle agglomerates comprises a plurality of fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surfaces of the plurality of fibers.

[0111] C': A method for processing airflow. The method includes: providing an air filter medium comprising a plurality of fibers to which a plurality of metal nanoparticle agglomerates are adhered, the metal nanoparticle agglomerates comprising a plurality of fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surfaces of the plurality of fibers; passing an airflow through the air filter medium having a pathogenic load prior to passing through the air filter medium; and reducing, inactivating, or killing one or more pathogens or any combination thereof as the airflow passes through the air filter medium.

[0112] Each of implementation schemes A', A1', A2', A3', B', and C' may have any combination of one or more of the following additional elements:

[0113] Element 1': The air filter medium is multi-layered, and at least one outer layer of the air filter medium is adhered with metal nanoparticle agglomerates.

[0114] Element 2': Wherein the air filter medium defines a removable insert for the mask.

[0115] Element 3': The metal nanoparticles in the metal nanoparticle agglomerates include copper nanoparticles, silver nanoparticles, or any combination thereof.

[0116] Element 4': The metal nanoparticle agglomerates also contain NiO, ZnO, TiO2 or any combination thereof.

[0117] Element 5': The plurality of fibers include cellulose fibers, cotton fibers, polymer fibers, glass fibers, or any combination thereof.

[0118] Element 6': wherein at least most of the metal nanoparticles in the metal nanoparticle agglomerate have a size range of about 20 nm to about 250 nm or about 50 nm to about 250 nm.

[0119] Element 7': wherein the size range of the metal nanoparticle agglomerates is from about 0.1 μm to about 35 μm, or wherein when applied to an air filter medium, the size range of the metal nanoparticle agglomerates is from about 0.1 μm to about 35 μm.

[0120] Element 8': The metal nanoparticles therein are silver nanoparticles containing metallic silver and a silver oxide coating.

[0121] Element 9': Wherein the metal nanoparticles are copper nanoparticles, which contain metallic copper and a coating containing Cu2O, CuO or any combination thereof.

[0122] Element 10': wherein the copper nanoparticles comprise about 25 wt% to about 99 wt% metallic copper, about 0.5 wt% to about 60 wt% Cu2O and about 0.1 wt% to about 20 wt% CuO or about 0.1 wt% to about 80 wt% CuO.

[0123] Element 11': wherein the copper nanoparticles comprise about 45 wt% to about 90 wt% metallic copper, about 0.5 wt% to about 60 wt% Cu2O and about 0.1 wt% to about 20 wt% CuO or about 0.1 wt% to about 80 wt% CuO.

[0124] Element 12': Wherein, based on the total weight of the air filter media, the loading of metal nanoparticles on multiple fibers ranges from about 0.5 wt.% to about 20 wt.%.

[0125] Element 13': where multiple fibers together define a woven fabric, a nonwoven fabric, or any combination thereof.

[0126] Element 14': wherein the woven or nonwoven fabric is multilayered, and the metal nanoparticle agglomerates are distributed in a concentration gradient between the multilayers of the woven or nonwoven fabric.

[0127] Element 15': The metal nanoparticles are essentially free of surfactant coating after adhering to multiple fibers.

[0128] Element 16': wherein at least most of the metal nanoparticles in the metal nanoparticle agglomerate are not fused together.

[0129] Element 17': The air filter media is self-sterilizing.

[0130] Element 18': Multiple metal nanoparticle agglomerates are adhered to multiple fibers through an adhesive layer.

[0131] Element 19': Applying multiple metal nanoparticle agglomerates to an air filter medium includes spraying a metal nanoparticle formulation onto the air filter medium.

[0132] Element 20': The method further includes removing the surfactant coating from the plurality of metal nanoparticles, such that the plurality of metal nanoparticle agglomerates adhere to the plurality of fibers.

[0133] Element 21': wherein removing the surfactant coating includes applying heat, airflow, vacuum, or any combination thereof to the air filter medium after applying a plurality of metal nanoparticle agglomerates to the air filter medium.

[0134] Element 22': Wherein the surfactant coating contains one or more amines.

[0135] Element 23': wherein at least most of the metal nanoparticles in the metal nanoparticle agglomerate are not fused together.

[0136] As a non-limiting embodiment, exemplary combinations applicable to A', A1', A2', A3', and C include, but are not limited to, 1' and 3'; 1', 3', and 4'; 1' and 6'; 1' and 7'; 1', 9', and 10' or 11'; 1' and 14'; 1' and 16'; 1' and 17'; 1' and 18'; 1' and 22'; 1' and 23'; 3' and 6'; 3' and 7'; 3', 9', and 10' or 11'; 3' and 14'; 3' and 16'; 3' and 17'; 3' and 18'; 3' and 22'; 3' and 23'; 6' and 7'; 6', 9', and 10' or 11'; 6' and 14'; 6' and 16'; 6' and 1 7'; 6' and 18'; 6' and 22'; 6' and 23'; 7', 9' and 10' or 11'; 7' and 14'; 7' and 16'; 7' and 17'; 7' and 18'; 7' and 22'; 7' and 23'; 9', and 10' or 11'; 9' and 14'; 9' and 16'; 9' and 17'; 9' and 18'; 9' and 22'; 9' and 23'; 14' and 16'; 14' and 17'; 14' and 18'; 14' and 22'; 14' and 23'; 6' and 17'; 16' and 18'; 16' and 22'; 16' and 23'; 18' and 22'; 18' and 23'; and 22' and 23'. Any of the above, optionally in further combination with one or more of 19'-23', applies to B'.

[0137] To facilitate a better understanding of this disclosure, the following preferred or representative embodiments are provided. These embodiments should not be construed as limiting or restricting the scope of the invention.

[0138] Example

[0139] Agglomerates of copper nanoparticles (size range 50-250 nm) with a monolayer of amine surfactant on their surface (agglomerate size 1-35 μm) are adhered to a 55 / 45 cellulose / polyester blend fabric with an average fiber diameter of about 10 μm using an epoxy resin adhesive. This can be accomplished by spraying a suitable ink or dye formulation onto the fibers, or by dip coating or gravure coating using commercial methods. The adhesive layer is about 20-50 nm thick, with the metal nanoparticle agglomerates partially embedded in the adhesive layer, most of which remains exposed. The agglomerates cover about 20-50% of the fiber surface. The copper loading on the fabric ranges from about 1.2 mg / in. 2 Approximately 2.7 mg / in 2 Depending on size, some agglomerates can partially remove the surfactant layer, leading to partial oxidation and the formation of a mixture of copper, Cu₂O, and CuO on the surface of the fibrous fabric. The ratio of copper to oxides can range from 1% to 10%. Over time, oxidation and dissolution gradually cause the initial deep reddish-brown to fade to a lighter yellowish-green. Figure 8 Illustrative photographs are shown of fabrics with copper nanoparticle agglomerates adhering to them during manufacturing (left side of the image) and after prolonged use (right side of the image). The nanoparticle-loaded fabrics were then subjected to various stability and toxicological tests specified below.

[0140] Agglomerates of copper nanoparticles (sizes ranging from 20-150 nm) with partially removed monolayer amine surfactants on their surface (agglomerate size 5-15 μm) are adhered to a 30 / 70 cellulose / polyester fabric blend with an average fiber diameter of about 10 μm using an epoxy resin adhesive. This can be accomplished by spraying a suitable ink or dye formulation onto the fibers, or by dip coating or gravure coating using commercial methods. The adhesive layer is about 50-100 nm thick, with the metal nanoparticle agglomerates partially embedded in the adhesive layer, most of which remains exposed. The agglomerates cover about 30-70% of the fiber surface. The copper loading on the fabric ranges from about 2.3 mg / in. 2 Approximately 4.5 mg / in 2 Depending on size, some agglomerates may be completely or partially oxidized, resulting in a mixture of copper, Cu₂O, and CuO on the fiber surface. The ratio of copper to oxides can range from 5% to 25%.

[0141] Agglomerates of copper nanoparticles (size range 50-250 nm) with a monolayer of amine surfactant on their surface (agglomerate size 1-35 μm) are adhered to a 55 / 45 cellulose / polyester fabric blend with an average fiber diameter of about 10 μm using a styrene-acrylic block copolymer adhesive. This can be accomplished by spraying a suitable ink or dye formulation onto the fibers, or by dip coating or gravure coating using commercial methods. The adhesive layer is about 100-250 nm thick, with the metal nanoparticle agglomerates partially embedded in the adhesive layer, most of which remains exposed. The area coverage of the agglomerates on the fiber surface is about 10-35%. The copper loading on the fabric ranges from about 1.7 mg / in. 2 Approximately 3.5 mg / in 2 Depending on size, some agglomerates can be completely or partially oxidized, resulting in a mixture of copper, Cu₂O, and CuO on the surface of the fibrous fabric. The ratio of copper to oxides can range from 5% to 15%.

[0142] Agglomerates of copper nanoparticles (size range 50-200 nm) with a monolayer of amine surfactant on their surface (agglomerate size 1-35 μm) are adhered to 100% polypropylene fabric (meltblown) with an average fiber diameter of about 10 μm using an epoxy adhesive. This can be accomplished by spraying a suitable ink or dye formulation onto the fiber, or by dip coating or gravure coating using commercial methods. The adhesive layer is about 35-150 nm thick, with the metal nanoparticle agglomerates partially embedded in the adhesive layer, most of which remains exposed. The agglomerates cover about 5-30% of the fiber surface. The copper loading on the fabric ranges from about 0.7 mg / in. 2 Approximately 1.6 mg / in 2 Depending on size, some agglomerates may be completely or partially oxidized, resulting in a mixture of copper metal, Cu2O, and CuO on the fiber surface. The ratio of copper metal to oxides can range from 1% to 5%.

[0143] Agglomerates of copper nanoparticles (size range 35-200 nm) with a monolayer of amine surfactant on their surface (agglomerate size 3-25 μm) are adhered to 100% cotton fabric with an average fiber diameter of about 10 μm using a styrene-acrylic block copolymer adhesive. This can be accomplished by spraying a suitable ink or dye formulation onto the fiber, or by dip coating or gravure coating using commercial methods. The adhesive layer is about 50-150 nm thick, with the metal nanoparticle agglomerates partially embedded in the adhesive layer, most of which remains exposed. The area coverage of the agglomerates on the fiber surface is about 40-75%. The copper loading on the fabric ranges from about 2.7 mg / in. 2Approximately 4.5 mg / in 2 Depending on size, some agglomerates may be completely or partially oxidized, resulting in a mixture of copper metal, Cu₂O, and CuO on the fiber surface. The ratio of copper metal to oxides can range from 3% to 25%.

[0144] Agglomerates of copper nanoparticles (size range 20-150 nm) with a monolayer of amine surfactant on their surface were mixed with CuO particles (size 35-100 nm) at a weight ratio of 25-50%. The agglomerates (size 5-15 μm) were adhered to a 30 / 70 cellulose / polyester fabric blend with an average fiber diameter of approximately 10 μm using an epoxy resin binder. This could be accomplished by spraying a suitable ink or dye formulation onto the fibers, or by dip coating or gravure coating using commercial methods. The binder layer was approximately 50-200 nm thick, with the agglomerates partially embedded in the binder layer, most of which remained exposed. The area coverage of the agglomerates on the fiber surface was approximately 30-70%. The copper / copper oxide loading on the fabric was approximately 1.3 mg / in. 2 Approximately 2.4 mg / in 2 .

[0145] Aggregates of copper nanoparticles (size range 20-250 nm) with a monolayer of amine surfactant on their surface were mixed with CuO particles (size 35-100 nm) at a weight ratio of 25-50% and with NiO or ZnO at a weight ratio of 2-10%. The aggregates (size 5-15 μm) were adhered to a 30 / 70 cellulose / polyester fabric blend with an average fiber diameter of about 10 μm using an epoxy resin binder. This could be accomplished by spraying a suitable ink or dye formulation onto the fibers, or by dip coating or gravure coating using commercial methods. The binder layer was about 50-150 nm thick, with the aggregates partially embedded in the binder layer, most of which remained exposed. The area coverage of the aggregates on the fiber surface was about 20-50%. The total metal / metal oxide loading on the fabric was about 1.3 mg / in. 2 Approximately 2.4 mg / in 2 .

[0146] Stability test. A 6”×6” fabric sheet was tumbled in water for 8 hours. Only 1.4% by weight of usable copper (0.54 mg) was released into the water.

[0147] Shedding was also determined by exposing the fabric to simulated breathing conditions (facial velocity airflow of 8.4 m / min and 40.8 m / min) and analyzing the released copper in the filter trap using SEM or EDS. Shedding tests did not show any detectable release of copper from the fabric.

[0148] VOCs. When tested under standard conditions, no volatile organic compounds (VOCs) from the group of 70 standard VOCs were detected released from the fabric.

[0149] Direct exposure to cell growth medium was performed. First, a piece of fabric was immersed in supplemented cell growth medium for up to 1 hour, then removed. Subsequently, Vero cells or Calu-3 lung epithelial cells were immersed in cell growth medium and incubated overnight in a CO2 incubator. Cell viability was determined by assessing ATP production using a luminescence assay. The luminescence assay did not show substantial changes in cell viability.

[0150] Efficacy. The fabric was tested for efficacy against a group of bacterial and viral pathogens. This group of bacteria included Gram-positive bacteria, Gram-negative bacteria, antibiotic-resistant bacteria, bacteriophages representing non-enveloped viruses, enveloped viruses (e.g., H1N1 influenza, H3N2 influenza, and SARS-CoV-2), and non-enveloped viruses such as feline calicivirus. In all cases, a kill rate of >99% was observed within 30 seconds and maintained full efficacy for 15 days with repeated daily exposures. For Staphylococcus aureus (ATCC 6538), Enterobacter aerogenes (ATCC 13048), Pseudomonas aeruginosa (ATCC 15442), methicillin-resistant Staphylococcus aureus MRSA (ATCC 33592), and Escherichia coli O157:H7 (ATCC 35150), efficacy was >99.9% within a 2-hour standard EPA exposure time. Over a 30-day period, the fabric maintained essentially 100% of its original efficacy against repeated viral inoculation (27M PFU; H1N1, H3N2, and feline calicivirus) or bacterial loads introduced into the fabric. Under visible wear conditions, after months of high daily contact use and moisture exposure, the fabric maintained >99.9% efficacy against Staphylococcus aureus and Klebsiella pneumoniae. Within 24 hours, it achieved near 100% inactivation against human wound pathogens such as Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), and Staphylococcus epidermidis.

[0151] Unless otherwise stated, all figures representing the amount of an ingredient, properties such as molecular weight, reaction conditions, etc., used in this specification and related claims should be understood to be modified by the term "about" in all cases. Therefore, unless stated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations varying with the desired properties sought to be obtained according to embodiments of the invention. At least, and not in an attempt to limit the application of the equivalence principle to the scope of the claims, each numerical parameter should be interpreted at least according to the number of significant figures reported and by applying ordinary rounding techniques.

[0152] This document presents one or more illustrative embodiments incorporating features of this disclosure. For clarity, not all features of the physical implementation are described or illustrated in this application. It will be understood that in the development of physical implementations incorporating this disclosure, numerous implementation-specific decisions must be made to achieve the developer's objectives, such as complying with system-related, business-related, governmental-related constraints, and other constraints, which vary and occasionally depend on the implementation method. While the developer's efforts may be time-consuming, such efforts will be a routine task for those skilled in the art who benefit from this disclosure.

[0153] Therefore, this disclosure is well suited to achieving the stated objects and advantages, and those inherent therein. The specific embodiments disclosed above are merely illustrative, as modifications and practices can be made to this disclosure in different but equivalent ways that will be apparent to those skilled in the art who have benefited from the teachings herein. Furthermore, no limitation is intended to be made on the details of the constructions or designs shown herein, except as described in the appended claims. It will thus be apparent that changes, combinations, or modifications can be made to the specific illustrative embodiments disclosed above, and all such changes are considered to be within the scope and spirit of the invention. The disclosure herein can be appropriately practiced in the absence of any elements not specifically disclosed herein and / or any optional elements disclosed herein. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, compositions and methods may also be described as “consistently composed of various components and steps” or “composed of various components and steps.” All quantities and scopes disclosed above may vary to some extent. Whenever a numerical range with a lower and upper limit is disclosed, any quantity falling within that range and any scope of inclusion is specifically disclosed. In particular, each range of values ​​disclosed herein (in the form of “about a to about b” or equivalently “about a to b” or equivalently “about ab”) should be understood as listing each quantity and range contained within a broader range of values. Furthermore, unless the patentee expressly and clearly defines otherwise, the terms in the claims have their ordinary, common meaning. Additionally, the indefinite articles “a” or “an” used in the claims are defined herein as indicating one or more elements introduced therein.

Claims

1. An air filter medium comprising: Multiple fibers, wherein multiple metal nanoparticle agglomerates are adhered to the multiple fibers, and when applied to the multiple fibers, the multiple metal nanoparticle agglomerates comprise multiple metal nanoparticles having a surfactant coating thereon, and the multiple metal nanoparticle agglomerates contain additives for generating reactive oxygen species. The metal nanoparticle agglomerates comprise multiple fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surfaces of the plurality of fibers. The metal nanoparticles in the aforementioned metal nanoparticle agglomerates include copper nanoparticles, silver nanoparticles, or any combination thereof; and The loading of metal nanoparticle agglomerates deposited on the surface by spraying the formulation ranges from 0.1 mg / in. 2 Up to 10 mg / in 2 The coating density is such that the spray formulation comprises a plurality of metal nanoparticle agglomerates dispersed in an organic matrix containing one or more organic solvents and an additive for generating active oxygen.

2. The air filter medium according to claim 1, wherein the additive for generating active oxygen comprises NiO, ZnO, TiO2 or any combination thereof.

3. The air filter medium according to claim 1, wherein the plurality of fibers comprises cellulose fibers, cotton fibers, polymer fibers, glass fibers, or any combination thereof.

4. The air filter medium according to claim 1, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate have a size range of 50 nm to 250 nm.

5. The air filter medium according to claim 1, wherein the size range of the metal nanoparticle agglomerates is 0.1 μm to 35 μm.

6. The air filter medium according to claim 1, wherein the metal nanoparticles are silver nanoparticles comprising a metallic silver and a silver oxide coating.

7. The air filter medium according to claim 1, wherein the metal nanoparticles are copper nanoparticles comprising metallic copper and a coating, wherein the coating comprises Cu2O, CuO, or any combination thereof.

8. The air filter medium according to claim 7, wherein the copper nanoparticles comprise 25% to 99% by weight of metallic copper, 0.5% to 60% by weight of Cu₂O, and 0.1% to 80% by weight of CuO.

9. The air filter medium according to claim 7, wherein the copper nanoparticles comprise 45% to 90% by weight of metallic copper, 0.5% to 60% by weight of Cu₂O, and 0.1% to 80% by weight of CuO.

10. The air filter medium according to claim 1, wherein the loading of metal nanoparticles on the plurality of fibers is from 0.5 wt.% to 20 wt.% based on the total weight of the air filter medium.

11. The air filter medium of claim 1, wherein the plurality of fibers together define a woven fabric, a nonwoven fabric, or any combination thereof.

12. The air filter medium of claim 11, wherein the woven or nonwoven fabric is multilayered, and the metal nanoparticle agglomerates are distributed in a concentration gradient between the multilayers of the woven or nonwoven fabric.

13. The air filter medium of claim 1, wherein the metal nanoparticles are substantially free of surfactant coating after adhering to the plurality of fibers.

14. The air filter medium of claim 1, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate are not fused together.

15. The air filter medium according to claim 1, wherein the air filter medium is self-sterilizing.

16. The air filter medium according to claim 1, wherein the plurality of metal nanoparticle agglomerates are adhered to the plurality of fibers by an adhesive layer.

17. A face mask comprising the air filter medium according to claim 1.

18. The face mask of claim 17, wherein the air filter medium is multilayered, and at least one outer surface of the air filter medium is adhered with metal nanoparticle agglomerates.

19. The face mask of claim 17, wherein the air filter medium defines a removable insert for the face mask.

20. An inline filter comprising the air filter medium according to claim 1.

21. An air filtration system comprising at least one filter, said filter comprising the air filter medium according to claim 1.

22. A method for producing an air filter medium exhibiting biocidal activity, the method comprising the steps of: Provides air filter media comprising multiple fibers; A sprayable formulation is provided, wherein the sprayable formulation comprises a plurality of metal nanoparticle agglomerates dispersed in an organic matrix containing one or more organic solvents and an additive for generating active oxygen, wherein when applied to the plurality of fibers, the plurality of metal nanoparticle agglomerates comprise a plurality of metal nanoparticles having a surfactant coating thereon. and A sprayable formulation comprising the plurality of metal nanoparticle agglomerates and the additive for generating active oxygen is sprayed onto the air filter medium to cause the plurality of metal nanoparticle agglomerates to adhere to the plurality of fibers. The plurality of metal nanoparticle agglomerates comprise a plurality of fused, partially fused, and / or unfused metal nanoparticles associated with each other on the surface of the plurality of fibers.

23. The method according to claim 22, wherein the metal nanoparticles in the metal nanoparticle agglomerate include copper nanoparticles, silver nanoparticles, or any combination thereof.

24. The method of claim 22, further comprising: The surfactant coating is removed from the plurality of metal nanoparticles, causing the aggregates of the plurality of metal nanoparticles to adhere to the plurality of fibers; The removal of the surfactant coating includes heating the air filter medium at a temperature of 35°C to 65°C in flowing nitrogen or air after adhering the plurality of metal nanoparticle agglomerates to the plurality of fibers.

25. The method of claim 22, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate have a size range of 50 nm to 250 nm.

26. The method of claim 22, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate are not fused together.

27. The method of claim 22, further comprising: An adhesive layer is applied to the air filter medium, wherein the adhesive layer has a thickness of 300 nm or less, and wherein the sprayable formulation adheres to the adhesive layer.

28. The method of claim 22, wherein the sprayable formulation exhibits a viscosity value of 1 cP to 100 cP.

29. The method of claim 22, wherein the loading of metal nanoparticles in the sprayable formulation is in the range of 1 wt.% to 35 wt.%.

30. The method of claim 22, wherein the sprayable formulation further comprises an aerosol propellant.

31. A method comprising: An air filter medium exhibiting biocidal activity is provided, said air filter medium being prepared by the method of claim 22; The airflow passes through the air filter medium, the airflow carrying a pathogenic load before passing through the air filter medium; and The pathogen load is reduced, or one or more pathogens or any combination thereof are inactivated or killed when the airflow passes through the air filter medium.

32. The method according to claim 31, wherein the metal nanoparticles in the metal nanoparticle agglomerate include copper nanoparticles, silver nanoparticles, or any combination thereof.

33. The method of claim 31, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate have a size range of 50 nm to 250 nm.

34. The method of claim 31, wherein at least a majority of the metal nanoparticles in the metal nanoparticle agglomerate are not fused together.

35. The method of claim 31, wherein the plurality of metal nanoparticle agglomerates are adhered to the plurality of fibers by an adhesive layer, wherein the adhesive layer has a thickness of 300 nm or less.

36. The method of claim 35, wherein the adhesive layer slows down the generation of metal oxide substances, thereby adjusting the sustained-release characteristics of the active metal in the metal nanoparticle agglomerates.

37. The method of claim 31, wherein the air filter medium changes color when the biocidal activity of the metal nanoparticles adhered to the air filter medium changes.

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