Laser-Induced Graphene Filters and Methods of Making and Using Them

Abstract

Virucidal and Microbicidal, Self-Disinfecting Resistive Hot Air Filter, and Methods of Manufacturing and Using the Same. The air filter includes Laser-Induced Graphene (LIG), which is a porous conductive graphene foam formed by photothermal conversion of a polyimide film (or a source of polymer or other LIG precursor material or another source) by a laser source. The LIG in the air filter can capture particulates and bacteria. Bacteria cannot proliferate even when immersed in a culture medium. Through a periodic Joule heating mechanism, the filter easily reaches temperatures above 300 °C. This destroys any microorganisms, including bacteria, and molecules that can cause adverse biological reactions and diseases, such as viruses, pyrogens, allergens, exotoxins, endotoxins, teichoic acids, mycotoxins, nucleic acids, and prions.

Description

[0001] Cross - reference to related applications

[0002] This application claims the benefit of U.S. Patent Application Serial No. 62 / 884,758, titled "Laser Induced Graphene Filters and Methods of Making and Using the Same", filed on August 9, 2019, which is owned by the owner of the present application. This application (including Appendices 1 - 3) is incorporated herein by reference in its entirety. Technical field

[0003] The present invention relates to laser - induced graphene (LIG) filters and methods of preparing and using the same. More specifically, virus - killing and microorganism - killing, self - disinfecting resistive - heating air filters prepared from LIG, and methods of manufacturing and using the same.

[0004] Government rights

[0005] This invention was made with government support under Award No. FA9550 - 14 - 1 - 0111 awarded by the Air Force Office of Scientific Research, U.S. Department of Defense. The U.S. government has certain rights in this invention. Background art

[0006] According to data from the Centers for Disease Control and Prevention (CDC), the probability that a patient in the United States contracts at least one healthcare - associated infection (HAI) is 1 / 31, and 3% of hospitalized patients have one or more HAIs [CDC 2017; Magill 2018]. These numbers may be underestimated due to hospital underreporting. Approximately 10 - 20% of hospital infections are airborne [Eickhoff 1994; Beggs 2003]. These include bacteria, bacterial by - products, and viruses. Another portion of hospital infections is due to contaminants, such as contaminated surfaces and objects, which are formed by the deposition of bacteria, fungi, spores, and various other pathogens in the air carried by droplets, aerosols, and particulate matter [Beggs 2003; Kowalski 2012].

[0007] Current strategies for preventing the spread of airborne pathogens include dilution ventilation, pressurization, directional airflow, disinfection, and filtration [Sehulster 2019; Kowalski 1999]. Dilution ventilation reduces the concentration of the source of infection by exchanging internal air with external air. Pressurization and directional airflow prevent the spread of the source of infection by controlling the air transmission path, while disinfection inactivates the source of infection. Filtration removes the source of infection from the circulation. Pressurization and directional airflow neither remove nor destroy airborne sources of infection and are typically used in combination with filtration and disinfection methods integrated into the air - circulation system [Kowalski 2012].

[0008] Current filtration methods typically use tortuous media containing multiple layers of intertwined fibers [Brown 1993]. Particle capture relies on diffusion, electrostatic attraction, adhesion interception, inertial impaction, and size-exclusion sieving [da Roza 1982]. However, during operation, contaminants accumulate, and the captured microorganisms proliferate in the filter, leading to reduced filtration efficiency, increased energy costs, decreased flow rate, penetration of smaller particles, impaired performance, and downstream air pathogen contamination [Sehulster 2019; Joe 2014; Bonnevie Perrier 2008]. Therefore, air filters need to be replaced regularly, which increases the maintenance cost of filtration equipment and systems.

[0009] The most common air disinfection method is UV-C irradiation [Reed 2010]. However, UV-C requires a critical dose of irradiation to kill bacteria or inactivate viruses. Some microorganisms can survive by repairing the damage, and pathogens attached to particles and present in larger droplets can shield the irradiation [Kowalski 2000]. Light-based filtration systems (such as UV-C, etc.) are "line-of-sight" systems, which means that if the light is not directly exposed to the target of interest (the target may be behind or inside the tortuous filtration structure), the target is not affected by the light. Therefore, UV-C disinfection systems are usually used in series with filtration systems. Ozone, photocatalytic oxidation, and ion generation are alternative disinfection methods available on the market [Bolashikov 2009]. Compared with UV-C, these methods are generally less energy-efficient, more costly, and less effective. Therefore, ultraviolet germicidal irradiation remains the state-of-the-art air disinfection technology at present [Sehulster 2019].

[0010] Current disinfection methods do not destroy biotoxins and by-products of microbial death. Endotoxins, exotoxins, teichoic acids, and mycotoxins can cause adverse reactions in the human body, such as high fever, septic shock, lung injury, autoimmune diseases, and death [Brigham 1986; Danner 1991; Hadidane 1985; Hedayati 2007; Schlievert 1981]. These compounds are difficult to remove, have a high thermal stability of up to 250 °C, and are incredibly potent even at picomolar concentrations or nanogram per kilogram doses [Raetz 2002; Schulster 2012; Tsuji I 1978; Tsuji II 1978]. Thus, although disinfection will kill microorganisms and disrupt virus capsids, toxic products will accumulate as persistent pollutants, and the biological by-products of microbial death can directly provide nutrients for microbial proliferation [Augustowska 2006]. In addition, current disinfection methods offer little protection against highly stable, persistent, and difficult-to-detect proteinaceous infectious particles (prions) [Schulster 2012; WHO 1999; Prusiner 1998]. Although often overlooked, other biological fragments that are not directly toxic to humans have the ability to pose significant risks, such as genetic material fragments, which may contribute to competent bacteria acquiring antibiotic resistance and virulence factors [von Wintersdorff 2016]. Thus, disinfection strategies are often used in combination with filtration, with varying degrees of success.

[0011] Typical object depyrogenation methods include dry heat heating at a temperature of at least 250 °C for an extended period of time [Schulster 2012]. During dry heat heating, endotoxin decomposition is achieved through free radical oxidation at lower temperatures and molecular decomposition at higher temperatures. Decomposition at higher temperatures is usually indiscriminate and does not require any form of catalyst, as almost all biomolecules will rapidly decompose at temperatures above 300 °C. Based on kinetic studies, the time constant for endotoxin concentration log 10 reduction at 250 °C is approximately 300 seconds, which is commonly referred to as the D 1 250℃ -time. The D 1 300℃ -time is approximately 30 seconds, and the D 1 350℃ -time is approximately 3 seconds [Tsuji I 1978; Tsuji II 1978]. Summary of the Invention

[0013] The present invention relates to graphene (LIG) filters and methods for preparing and using the same, and more specifically, to virus inactivation and microbial killing, self-disinfecting resistive heating air filters prepared from LIG, and methods for manufacturing and using the same.

[0014] The present invention is a self-cleaning filter that includes laser-induced graphene (LIG), a microporous conductive graphene foam formed by direct photothermal conversion of a carbon precursor by a commercially available CO 2 laser cutter [Ye2019]. During LIG formation, the photothermal heating of the carbon precursor forces the degassing of non-carbon elements and promotes sp 2 hybridization [Chyan 2018]. To date, LIG has shown good promise in various application fields, such as micro-supercapacitors [Li 2016; Peng 2015”; Lin 2014”], wearable embedded sensors [Stanford I 2019; Carvalho 2018; Sun 2018], triboelectric nanogenerators [Stanford II2019], and electrocatalysis [Zhang I 2018; Zhang II 2018], etc. LIG is also easily doped, chemically functionalized [Ye 2019; Ye 2018], and composite [Luong 2019].

[0015] The conversion of PI into LIG is compatible with roll-to-roll processing and laminate object manufacturing, thus showing the possibility of commercial applications [Luong 2018]. The direct writing ability allows for the formation of various different geometries and configurations, enabling the formation of mechanically robust, free-standing LIG membranes. The microporous filter can simultaneously employ pollutant removal and disinfection strategies.

[0016] The free-standing LIG membrane can capture bacteria, virus-containing particles, and microparticles. It has also been shown that LIG can prevent the proliferation of filtered bacteria, even when immersed in a culture medium. Through the periodic Joule heating mechanism (the filter easily reaches temperatures above 300 °C), the filter destroys the captured bacteria and viruses and exceeds the temperature at which compounds that can sustain life and molecules that may cause adverse biological reactions and diseases, such as virus capsids, pyrogens, pollutants, allergens, exotoxins, teichoic acids, endotoxins, mycotoxins, nucleic acids, and prions, are decomposed. The Joule heating of LIG causes this destruction and decomposition through the carbonization of virus capsids, bacteria, and molecular materials.

[0017] Traditional filters rely on physical cleaning processes or are replaced after particulate matter saturates the filter. For the filters of the present invention, Joule heating enables self-cleaning by simply applying an electric potential across the entire LIG-based filter. This method is particularly useful in hospital environments where microorganisms (such as sepsis-causing microorganisms) persist and are easily transferred from room to room via the air handling system. It also effectively removes virus-containing droplets in indoor living spaces, thus minimizing the opportunity for person-to-person transmission.

[0018] Generally, in one embodiment, the present invention features a method of manufacturing a filter including LIG. The method includes the step of exposing a first side of a polymer-containing sheet to a first laser source. The exposure on the first side results in the formation of laser-induced graphene (LIG) on the first side of the sheet. The LIG is derived from the polymer. The method further includes the step of treating the second side of the sheet. The second side of the sheet is on the opposite side of the first side of the sheet. The LIG on the first side of the sheet and the treating step on the second side provide porosity to the sheet such that air can flow from the first side through the LIG to the second side. At least some of the polymer on the first side of the sheet does not form LIG and is capable of operating to support the LIG formed on the first side.

[0019] Embodiments of the present invention may include one or more of the following features:

[0020] The step of treating the second side of the sheet is a second-side treatment selected from the group consisting of: (a) exposing the second side of the sheet to the first laser source to form LIG on the second side of the sheet, wherein at least some of the polymer on the second side of the sheet does not form LIG and is capable of supporting the LIG formed on the second side; (b) exposing the second side of the sheet to a second laser source to form LIG on the second side of the sheet, wherein at least some of the polymer on the second side of the sheet does not form LIG and is capable of supporting the LIG formed on the second side; (c) exposing the first side of the sheet to the first laser source for a sufficient time to laser the polymer on the second side of the sheet, wherein at least some of the polymer on the second side of the sheet does not form LIG and is capable of supporting the LIG formed on the second side; (d) cutting a grid in the sheet to provide porosity to the sheet such that air can flow from the first side through the LIG to the second side; and (e) combinations thereof.

[0021] The treatment of the second side may include: exposing the second side of the sheet to the first laser source to form LIG on the second side of the sheet. At least some of the polymer on the second side of the sheet may not form LIG and is capable of supporting the LIG formed on the second side.

[0022] The sheet can be located on a laser-reflective surface suitable for the wavelength used to generate LIG (e.g., aluminum suitable for a 10.6 μm laser). During the step of exposing the first side of the sheet to the first laser source, the first laser source can be reflected by the reflective surface to laser the second side of the sheet.

[0023] The treatment of the second side can include: exposing the second side of the sheet to a second laser source to form LIG on the second side of the sheet. At least some of the polymer on the second side of the sheet can remain untransformed into LIG and be capable of supporting the LIG formed on the second side.

[0024] The treatment of the second side can include: exposing the first side of the sheet to the first laser source for a sufficient time to laser the polymer on the second side of the sheet. At least some of the polymer on the second side of the sheet may not form LIG and be capable of supporting the LIG formed on the second side.

[0025] The sheet can be a thin sheet that can be lasered on the second side when the first side is lasered by the first laser source.

[0026] The treatment can include: cutting a mesh in the sheet to provide porosity to the sheet, enabling air to flow from the first side through the LIG to the second side.

[0027] The filter can operate to capture particles or molecules selected from the group consisting of: airborne microorganisms, microbial by-products, microbial-related toxins, viruses, virus capsids, virus capsid droplets, and combinations thereof.

[0028] The method can further include: decomposing the captured particles or molecules by Joule heating.

[0029] The LIG precursor material can be selected from the group consisting of: polymers, carbon-based precursors containing amorphous carbon, and compounds as porous amorphous carbon precursors.

[0030] The compound as a porous amorphous carbon precursor can include an expandable material.

[0031] The LIG precursor material can be a polymer.

[0032] The polymer can be polyimide (PI).

[0033] The sheet can be a polymer sheet.

[0034] The sheet can be a fibrous polymer sheet.

[0035] The polymer can be a LIG precursor polymer.

[0036] The LIG precursor polymer can be selected from the group consisting of: homopolymers, vinyl polymers, step-growth polymers, condensation polymers, polymers made by living polymer reactions, chain-growth polymers, block copolymers, carbonized polymers, aromatic polymers, cyclic polymers, polyimide (PI), polyetherimide (PEI), polyetheretherketone (PEEK), polysulfone, elastomers, rubbers, recycled plastics, polyethylene terephthalate, polytetrafluoroethylene, polyethylene, polypropylene, low-density polyethylene (LPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polybutadiene, poly(styrene-butadiene), polystyrene, polycarbonate, polyamide, polyimide, polyurethane, thermoplastics, thermosets, and combinations thereof.

[0037] The step of exposing the first side can expose the first laser source through a first pattern on the first side.

[0038] The step of treating the second side can include: exposing the second side of the sheet to a second laser source to form LIG on the second side of the sheet. The second laser source can be the same or different from the first laser source. Exposing the second side to the second laser source can expose the second laser source through a second pattern on the second side. The first pattern can be offset from the second pattern.

[0039] The two patterns can be different lattices.

[0040] The first pattern can be a hexagonal pattern, and the second pattern can be a stacked hexagonal pattern.

[0041] The first pattern and the second pattern can each be selected from the group consisting of: hexagons and triangles, squares and parallelograms.

[0042] The first pattern and the second pattern provide a three-dimensional lattice for reinforcement and geometric enhancement.

[0043] The filter is capable of operating to generate heat when pressure is applied across the filter.

[0044] The heat can kill or decompose the trapped particles.

[0045] When pressure is applied across the filter, the filter can operate as an electrostatic filter.

[0046] If the sheet is made of a fibrous polymer, then laser on only one side may be sufficient because the fibrous polymer source is already air-permeable.

[0047] Typically, in another embodiment, the feature of the present invention is an LIG filter, which includes LIG and a polymer capable of supporting the LIG on the first side of the LIG filter. The LIG is on at least the first side of the LIG filter. The LIG filter sheet has a porosity such that the LIG filter can allow air to flow through the LIG on the first side to the second side of the LIG filter. The LIG filter can operate to capture particles selected from the group consisting of: microorganisms in the air, microbial by-products, microbial-related toxins, viruses, virus capsids, their droplets, and combinations thereof.

[0048] Embodiments of the present invention may include one or more of the following features:

[0049] The LIG can be on the second side of the LIG filter. The LIG filter sheet may have a porosity such that the LIG filter can allow air to flow from the first side through the LIG to the second side of the LIG filter.

[0050] The LIG filter can be a filter including LIG prepared by at least one of the above methods.

[0051] The LIG filter can operate to generate heat when pressure is applied across the filter.

[0052] The heat can kill or decompose the captured particles.

[0053] The LIG precursor material can be selected from the group consisting of: polymers, carbon-based precursors containing amorphous carbon, and compounds as porous amorphous carbon precursors.

[0054] The compound as a porous amorphous carbon precursor may include an expandable material.

[0055] The LIG precursor material can be a polymer.

[0056] The polymer can be polyimide (PI).

[0057] Typically, in another embodiment, the feature of the present invention is an LIG film including LIG and a polymer. The LIG film can operate to filter air by capturing airborne particles. The captured particles are selected from the group consisting of: microorganisms in the air, microbial by-products, microbial-related toxins, and combinations thereof. The LIG film can operate to generate heat when a voltage is applied across the entire LIG. The generated heat can be used to kill or decompose the particles.

[0058] Embodiments of the present invention may include one or more of the following features:

[0059] The LIG film can be a filter including LIG prepared by at least one of the above methods.

[0060] The LIG can be on both sides of the LIG film such that air filtration passes through the LIG structures on both sides.

[0061] The LIG film can include an array of carriers made of unlasered polymer material.

[0062] The unlasered polymer material exhibits an AB-stacked hexagonal array pattern.

[0063] The unlasered polymer material can be a stack with at least two patterns.

[0064] The at least two patterns can each be selected from the group consisting of: hexagon and triangle, square and parallelogram.

[0065] The stack with at least two patterns provides a three-dimensional lattice for reinforcement and geometric enhancement.

[0066] The LIG can be made of polyimide.

[0067] The LIG can be made of polysulfone, paper, cotton, wood, or carbohydrate.

[0068] Polysulfone, paper, cotton, wood, or carbohydrate can be flame-retarded with additives.

[0069] The LIG can be made of the following polymers: step-growth polymers, chain-growth polymers, living polymerization polymers, metathesis polymers, vinyl polymers, condensation polymers, or mixtures thereof.

[0070] The trapped particles can cause hospital-acquired infections.

[0071] The trapped particles can be a source of sepsis or viruses.

[0072] The viruses can be selected from the group consisting of: coronavirus, SARS-CoV, MERS-CoV, SARS-CoV-1, and SARS-CoV-2.

[0073] The LIG film can be used to generate heat of at least 70 °C when a voltage is applied across the entire LIG.

[0074] The LIG film can be used to generate heat of at least 150 °C when a voltage is applied across the entire LIG.

[0075] The LIG film can be used to generate heat of at least 250 °C when a voltage is applied across the entire LIG.

[0076] When a voltage is applied across the entire LIG, the LIG film can operate to generate heat, causing the LIG surface to be cleaned by volatilizing the decomposed adsorbate.

[0077] The LIG thin film can operate to generate heat when a voltage is continuously applied across the entire thin film.

[0078] The LIG thin film can operate to generate heat when a voltage is periodically applied across the entire thin film.

[0079] The period can be selected from the group consisting of: hours, minutes, seconds, or fractions of a second.

[0080] The period can be from 1 millisecond to 24 hours.

[0081] The period can be from 5 seconds to 1 minute.

[0082] The captured particles can include microorganisms selected from the group consisting of: bacteria, fungi, and combinations thereof.

[0083] The captured particles include toxins, and the toxins can be endotoxins.

[0084] The captured particles contain viruses, and the viruses can be: coronavirus, SARS-CoV, MERS-CoV, SARS-CoV-1, and SARS-CoV-2.

[0085] Generally, in another embodiment, the present invention features a method that includes the following steps: selecting a LIG thin film including LIG and a polymer carrier. The method further includes the step of using the LIG thin film to capture particles in the air. The captured particles are selected from the group consisting of: microorganisms in the air, microbial by-products, microbial-related toxins, viruses, virus capsids, and combinations thereof. The method further includes the step of applying a voltage across the entire LIG to generate heat. The method further includes the step of using the generated heat to kill or decompose the particles.

[0086] Embodiments of the present invention can include one or more of the following features:

[0087] The LIG thin film can be a filter including LIG prepared by at least one of the above methods.

[0088] The LIG thin film can be at least one of the above LIG filters.

[0089] The LIG thin film can be at least one of the above LIG thin films.

[0090] The LIG thin film can have LIG on one side.

[0091] The LIG thin film can have LIG on one side of a fiber or porous polymer thin film.

[0092] The LIG thin film can have LIG on both sides of the thin film so that air is filtered through the LIG structures on both sides.

[0093] The LIG thin film may include an array of carriers made of unlasered polymer materials.

[0094] The unlasered polymer materials exhibit an AB-stacked hexagonal array pattern.

[0095] The unlasered polymer materials may be a stack with at least two patterns.

[0096] The at least two patterns may each be selected from the group consisting of: hexagon and triangle, square and parallelogram.

[0097] The stack with at least two patterns provides a three-dimensional lattice for reinforcement and geometric enhancement.

[0098] The LIG may be made of polyimide.

[0099] The LIG may be prepared from polysulfone, paper, cotton, wood, or carbohydrates.

[0100] Polysulfone, paper, cotton, wood, or carbohydrates may be flame-retarded with additives.

[0101] The LIG may be made of the following polymers: step-growth polymers, chain-growth polymers, living polymerization polymers, metathesis polymers, vinyl polymers, condensation polymers, or mixtures thereof.

[0102] The captured particles can cause hospital-acquired infections.

[0103] The captured particles can be a source of sepsis.

[0104] The captured particles can be a virus or virus source, including coronaviruses, which further include SARS-CoV, MERS-CoV, SARS-CoV-1, and SARS-CoV-2.

[0105] The step of applying a voltage across the entire LIG can generate heat of at least 70 °C.

[0106] The step of applying a voltage across the entire LIG can generate heat of at least 150 °C.

[0107] The step of applying a voltage across the entire LIG can generate heat of at least 250 °C.

[0108] The step of utilizing the heat may include cleaning the surface of the LIG by volatilizing the decomposed adsorbate.

[0109] The captured particles may include microorganisms selected from the group consisting of: bacteria, fungi, and combinations thereof.

[0110] The captured may include toxins, and the toxins are endotoxins.

[0111] The captured particles can include viruses and / or virus-containing droplets and / or aerosols.

[0112] Generally, in another embodiment, the present invention features a method that includes the steps of: preparing a filter including LIG by laser treating a porous breathable sheet including one or more LIG-forming precursors. The method further includes the step of exposing a first side of the porous breathable sheet to a first laser source. The exposure on the first side results in the formation of LIG on the first side of the sheet. The LIG is derived from a polymer or a carbon-based LIG precursor.

[0113] Embodiments of the present invention can include one or more of the following features:

[0114] The method can further include the step of treating a second side of the porous breathable sheet to form LIG. The second side of the porous breathable sheet can be on the opposite side of the first side of the sheet.

[0115] The porous breathable sheet can be laser treated such that the untransformed portion of the porous breathable sheet is a carrier for the LIG.

[0116] The porous breathable precursor sheet can be selected from the group consisting of: carbon fiber paper, woven carbon fiber fabric, oxidized acrylic (OPAN) felt, activated carbon, carbonized polymer, and combinations thereof.

[0117] The porous breathable precursor sheet can be a porous structure including amorphous carbon.

[0118] The porous breathable precursor sheet can be a porous structure including amorphous carbon.

[0119] The porous structure including amorphous carbon can be a composite material including a polymer.

[0120] The porous breathable precursor sheet can include polymer fibers.

[0121] The porous breathable precursor sheet can include a woven fabric or a non-woven felt. The woven fabric or the non-woven felt can include at least part of the fibers suitable for conversion to LIG.

[0122] The porous breathable precursor sheet can include a breathable open-cell polymer foam.

[0123] The polymer can be selected from the group consisting of: polyimide (PI), polyphenylene sulfide (PSS), polyaramide, cellulose fiber, polyacrylonitrile (PAN), polybenzoxazole (PBO), polyoxazole, phenolic resin, homopolymer, vinyl polymer, polyethylene, polypropylene, linear low density polyethylene, high density polyethylene, step-growth polymer, condensation polymer, polymer made by living polymer reaction, chain-growth polymer, block copolymer, aromatic polymer, cyclic polymer, polyetherimide (PEI), polyetheretherketone (PEEK), polysulfone, elastomer, rubber, poly(styrene-butadiene), crosslinked polystyrene, polyamide, polyimide, thermoplastic material, thermosetting material, and combinations thereof.

[0124] Generally, in another embodiment, the invention features a method that includes the steps of: selecting a porous material coated with one or more LIG precursors. The method further includes: irradiating the porous material coated with one or more LIG precursors with a laser to form a LIG filter comprising LIG and a porous support. The porous support has a porosity such that air can flow through the first side of the LIG filter to reach the second side of the LIG filter.

[0125] Embodiments of the invention may include one or more of the following features:

[0126] The porous material coated with one or more LIG precursors can be selected from the group consisting of: wiremesh, metal foam, porous ceramic plate, polymer foam, polymer filter medium, and porous glass fiber sheet.

[0127] One or more LIG precursors can be selected from the group consisting of: polymers, materials containing amorphous carbon, and substances that form a porous amorphous carbon film upon exposure to heat.

[0128] One or more LIG precursors can include substances that form a porous amorphous carbon film upon exposure to heat, which are expandable materials.

[0129] The method may further include: exposing a first side of a sheet of the porous material coated with one or more LIG precursors to a first laser source. The exposure on the first side of the sheet can form LIG on the first side of the sheet. The LIG can be formed by conversion of one or more LIG precursors coated on the porous material. The porous support can include the untransformed porous material.

[0130] The method may further include treating the second side of the sheet to form LIG on the second side, where the second side is opposite to the first side.

[0131] When a voltage is applied across the entire filter, the LIG filter can operate as an electrostatic filter. When the LIG filter is single-sided, the voltage can be in the plane of the LIG filter. When the LIG filter is double-sided, the voltage can be across the entire LIG filter.

[0132] Brief Description of the Drawings

[0133] Figure 1A is an SEM of LIG.

[0134] Figure 1B is a schematic diagram of a method for laser processing a freestanding LIG filter outside the PI substrate.

[0135] Figures 2A - 2E is a schematic diagram of filter synthesis and basic characteristics. Figure 2A is a schematic diagram of a double-sided laser process that results in the formation of a porous LIG filter supported by a PI lattice. Figure 2B is a schematic diagram of the PI lattice remaining after laser processing. Figure 2C is an optical image of the LIG filter, showing flexibility and mechanical stability. Figure 2D is an SEM image of the LIG filter, showing the LIG blanket and unlasered PI. Figure 2E is the Raman spectrum of the LIG filter at 532 nm.

[0136] Figures 3A - 3C is a cross-sectional SEM image of the LIG filter.

[0137] Figures 4A - 4C is the Raman spectrum and SEM image of a LIG filter derived from a porous precursor carrier (i.e., a nonwoven material made of polyimide P84).

[0138] Figures 4D - 4E is a graph showing the pressure drop of various LIG filters compared to other filters.

[0139] Figure 5A shows a system for a conveyor-based method of producing LIG air filters.

[0140] Figure 5B shows a system for a roll-to-roll method of producing LIG air filters.

[0141] Figures 6A - 6E is a schematic diagram of bacteria capture and subsequent sterilization and depyrogenation by Joule heating. Figure 6A is a schematic diagram of air filtration with a LIG filter installed on a vacuum filtration system with a backing PES test filter. Figure 6B is after filtration by Joule heating Figure 6CSchematic diagram of sterilization and pyrogen removal. Figure 6D It is a schematic diagram of a Joule heating device, where an electric potential is applied across the entire filter for Joule heating. Figure 6E It is an infrared image of a LIG filter Joule heated to 380 °C.

[0142] Figure 7 It is a graph showing the temperature and power of a LIG-based filter heated by Joule heating.

[0143] Figure 8 It is an optical image of a LIG air filter.

[0144] Figures 9A - 9D It shows different geometries, for example, a system with a LIG filter that supports the application of voltage to an electrostatic filter.

[0145] Figure 9E It is shown as Figure 9D A photograph showing multiple parts of the system as shown.

[0146] Figures 10A - 10F It is a chart showing graphs of temperature, power, pressure drop, flow rate, cycle stability, and particle capture. Figure 10A It shows the relationship between the pressure drop across the entire LIG filter and the flow rate in the absence of Joule heating. Figure 10B It shows the relationship between the temperature of the LIG filter and the power supplied at different air flow rates. Figure 10C It shows the relationship between the temperature and pressure drop data of the LIG filter. Figure 10D It shows the Joule heating cycle stability of the LIG filter at a constant potential of 15 V for 250 cycles between room temperature and 255 °C. Figure 10E It shows an optical image of water inside a bubbler through which particles from the combustion of five cigarettes flow. Figure 10A It shows the particle size distribution from dynamic light scattering (DLS), which supports the effectiveness of the filter in capturing particles from 0 to 800 nm.

[0147] Figure 11A It is a schematic diagram of the stirring tank system used.

[0148] Figure 11B It is shown as Figure 11A An enlarged illustration of the filter used in the system as shown.

[0149] Figure 11C It is shown before and after Joule heating, Figure 11B An illustration of particulate matter on the filter as shown.

[0150] Figure 12Schematic diagram of dust guidance filtered by the Minimum Efficiency Reporting Value (MERV) 8 filter.

[0151] Figure 13 It is a diagram showing the agitation, annealing, and recovery of the LIG filter containing MERV8 dust.

[0152] Figures 14A - 14C Respectively Figure 13 Photos of the LIG filter used in the process shown before the accumulation of MERV 8 dust (a), after the first round of saturation of MERV 8 dust (b), and after the first round of Joule heating (c).

[0153] Figure 15 It is a diagram showing the agitation, annealing, and recovery of the LIG filter containing bee pollen.

[0154] Figures 16A - 16B They are photos of the LIG filter that was clogged before Joule heating at 300 °C and unclogged after Joule heating at 300 °C, taken Figure 15 after the first round of Joule heating in the process shown.

[0155] Figures 16C - 16F Respectively Figure 15 Photos of the LIG filter used in the process shown after the first round of Joule heating (c), after the second round of Joule heating (d), after four rounds of agitation (e), and after the fourth agitation (f).

[0156] Figure 17 It is a diagram showing the agitation, annealing, and recovery of the LIG filter containing dust collected in a vacuum bag.

[0157] Figures 18A - 18C Respectively Figure 17 Photos of the LIG filter used in the process shown before the second round of agitation (a), after agitation (b), and after Joule heating (c).

[0158] Figures 19A - 19D It is a schematic diagram and result of culturing after air filtration. Figure 19A Schematic diagram of the experimental setup. Figure 19B Schematic diagram of the culturing process. Figure 19C It is a graph of the optical density of the submerged culture medium of the filter without ultrasonic treatment before culturing after 24 hours of incubation. Figure 19D It is a graph of the optical density results after 24 hours of incubation, with bacteria separated from the LIG filter by 2 minutes of ultrasonic waves before culturing. In Figures 19C - 19D , the columns represent the standard deviation of 9 measurements.

[0159] Figure 20 It is a curve graph showing the BET surface area of the LIG filter material.

[0160] Figures 21A - 21B Top view and side view of the LIG filter of the filtration system, respectively.

[0161] Figures 22A - 22F Photographs of various LIG composites for measuring resistance (speed: 5%, power: 15%). Detailed implementation mode

[0162] LIG has attracted much attention because it can simply and quickly synthesize porous graphene films. LIG is synthesized by irradiating a carbon source with a laser. The carbon source is converted into porous graphene in a photothermal manner. The pore size of LIG is about 2 - 10 nm, and at the same time, it has larger micron-sized pores [Lin 2014]. The micron-sized pores in LIG can be seen from the SEM images in Figure 1A . Many of these pores are smaller than the typical requirements of HEPA filters, that is, the size is about 0.3 μm [ASME 2004]. Conveniently, the fabrication of LIG can be carried out using a commercial laser cutter, which can be found in most machine shops. It can be easily transformed into an industrial roll-to-roll system. For example, see the international PCT application No. PCT / US2019 / 068933 filed on December 28, 2019, with the title "Laser-Induced Graphene Composites and Sensors and Methods of Using the Same" ("Tour'933 PCT Application"), which is incorporated herein by reference.

[0163] Method for manufacturing LIG filter material

[0164] In some embodiments of the present invention, to produce an LIG filter, a two-part lasing strategy can be used to convert a polyimide (PI) film 101 into LIG 103. The PI film is lasered on the top side and the bottom side to prepare an LIG free-standing film that allows air to flow through its pores. Figure 1B A schematic diagram of a method for lasering a free-standing LIG filter outside the PI substrate 101 is shown. This method uses a top-side laser 102 and a bottom-side laser 104 to convert the entire thickness of the PI film 101 into LIG 103.

[0165] LIG is synthesized as follows: irradiate a McMaster-Carr Kapton PI 127 μm film with a 10.6 μm 75-watt CO 2 pulse laser in a Universal Laser Systems XLS10MWH laser cutter at a scanning rate of 30 cm / s, a duty cycle of 15%, and an image density of 1000 PPI. AsFigure 2A As shown, laser hexagonal patterns 201 (hexagonal pattern 211 on the top and hexagonal pattern 212 on the bottom) are formed on both sides of the PI film 101, leaving a support grid of PI 101 that imparts mechanical rigidity and strength to the filter while still allowing the LIG 103 to be continuous and conductive.

[0166] During the laser treatment, the PI 101 is fixed to the laser table by capillary adhesion. Since the filter is made by carbonizing the PI 101 into LIG103 through photothermal laser at a temperature of about 2900K (one order of magnitude higher than the temperature required for sterilization and depyrogenation), the filter is default sterile and pyrogen-free before use. The laser area of the filter can be selected as 45mm×45mm. Since the AB stacked hexagonal laser pattern does not allow air to flow at the filter edge and there is a slight offset at the filter edge, the size of the filtration area is approximately equal to the area of the 42mm×42mm 0.22μm polyethersulfone (PES) membrane filter in the Corning TM (Corning TM ) 431097 filtration funnel.

[0167] Similarly, as Figure 2A shown, the PI is laser-treated on both sides, and the alternating AB stacked hexagonal patterns of the PI remain unlasered ( Figure 2B ). Therefore, the filter is an inherent composite material of LIG reinforced by alternating hexagonal PI lattices (similar to the structure of Bernal bilayer graphene). The alternating hexagonal patterns result in excellent rigidity and mechanical strength while maintaining the continuity of the LIG, ensuring high conductivity. However, it should be noted that other patterning geometries can also be used and generally consist of two regular lattices, one pattern on each side, to provide a three-dimensional lattice that imparts reinforcement and geometric enhancement. Since the decomposition temperature of LIG in air is about 575°C, which is higher than the 550°C decomposition temperature of PI in air, the maximum Joule heating temperature of the filter is limited by the PI. But at a test temperature of 380°C, the filter is far below its stability limit.

[0168] As Figure 2C shown in the optical image, the filter can be folded without breaking its structural integrity. The laser scribing of the LIG is a direct writing process, so various geometries and configurations that can be easily adapted to existing HVAC systems can be produced. Figure 2D The SEM image in Figure 2D shows the surface morphology of the LIG, which is highly porous and fibrous. ( Figure 2EThe Raman spectra clearly show the presence of the D, G, and 2D peaks indicating the formation of LIG [Ye2019]. The D band can be generated by the bending of graphene layers in the foam [Dimiev 2016].

[0169] Figures 3A - 3C A cross-sectional image of the LIG filter is shown in Figure 3A It is a cross-sectional image showing the entire thickness of the filter and the inherent morphological gradient of the filter that improves the filtration efficiency. Figure 3B It is a SEM image outside the LIG filter ( Figure 3A magnified image of box 301), showing a blanket of LIG fibers (LIGF) that captures larger particles and aerosols [Duy 2018]. Figure 3C It is a SEM image of a partial LIG filter presenting the LIG structure ( Figure 3A magnified image of box 302), which has tortuous pores of 2.86 - 8.94 nm that allow the capture of bacteria and smaller particles [Lin 2014].

[0170] Various morphologies of LIG are visible. The outer surface of the filter forms a blanket of LIG fibers (LIGF) for capturing larger particles and aerosols ( Figure 3B ). The center of the filter contains porous LIG, which can capture smaller contaminants and bacteria ( Figure 3C ). Both of these morphologies can be formed during the PI laser and have been described previously [Lin 2014; Duy2018]. LIGF is formed due to high laser power and spontaneous degassing, but the deeper laser attenuation in PI leads to the formation of porous LIG [Duy2018]. The morphological gradient helps to extend the service life of the filter because larger particles are removed before smaller particles, thus preventing the blockage of smaller pores. The submicron pores have a high tortuosity and are suitable for capturing microorganisms.

[0171] In another embodiment of the present invention, a breathable porous sheet containing a polymer or carbon-based LIG precursor is converted into LIG. An example of a sheet of porous precursor material includes a nonwoven felt composed of polyimide fibers. The felt is irradiated with a 10.6 μm 75 watt CO 2 pulsed laser with a duty cycle of up to 30%, and laser-induced graphene is obtained. Figure 4A The Raman spectra of the laser-treated polyimide felt are shown, which clearly show the D, G, and 2D peaks indicating the formation of LIG. Figure 4B The SEM images in Figures 4B - 4C show the highly porous nature of the LIG surface morphology. Cross-sectional images of the LIG filter (nonwoven polyimide material before and after laser) are shown in Figures 4D - 4EShows the pressure drop characteristics of various P84 nonwoven LIG filters compared to other filter materials. Figure 4D Curves 401 - 406 therein show N95 masks, surgical masks, uncoated P84, coated P84, uncoated P84 LIG, and coated P84 LIG. Figure 4E Curves 411 - 414 therein show surgical masks, N95 masks, LIG on coated P84, and surgical masks and LIG P84 nonwovens together.

[0172] Different from embodiments using solid polymer sheets, LIG air filters can be produced from porous sheets by laser on only one side without specific patterning. In contrast, porosity needs to be created on solid sheets by converting both sides into porous LIG or first cutting a grid in the solid sheet. This further eliminates the need for pattern alignment on both sides of the sheet and allows for maintaining a continuous porous support.

[0173] Due to these advantages, the method of manufacturing air filters by laser on porous substrates can be well used in embodiments of automated manufacturing of LIG air filters. Examples of automated manufacturing include, but are not limited to: passing a porous sheet through a laser exposure area on a conveyor belt, or using a roll - to - roll conveyance method to perform the same operation ( Figures 5A - 5B ).

[0174] Figure 5A Shows a system 500 utilizing a conveyor - based method for producing LIG air filters. The conveyor belt 504 moves via rollers 505 to move the conveyor belt in the direction of arrow 506. A sheet 501 of porous LIG precursor material (e.g., made of a polymer such as polyimide) is moved by the conveyor belt and then lasered using laser 503 to form LIG 502 supported on the unlasered LIG precursor material 501.

[0175] Figure 5B Shows a system 510 for a roll - to - roll method of producing LIG air filters. A roll 516 of LIG precursor material 511 (e.g., made of a polymer such as polyimide) is unwound and moved via rollers 515 so that the LIG precursor material 511 can be lasered using laser 513 to form LIG 512 supported on the unlasered LIG precursor material 511. The LIG 512 supported on the unlasered LIG precursor material 511 is then collected by winding onto a roll 517.

[0176] Filtration system using LIG

[0177] Compared to typical fiber filters, LIG filters are unique in that LIG exhibits moderate electrical conductivity, enabling the filter to perform Joule heating through electrical power dissipation.Figures 6A - 6C Shows the working principle of the self - sterilizing LIG - based filter. The filter test setup is as Figure 6A shown. The vacuum filtration system 600 includes a LIG filter 602. An air stream 604 can flow through this filter into the chamber 601 and out through a filter 603 (e.g., a 0.22 - μm PES filter) to the vacuum section 605.

[0178] The LIG filter 602 is mounted on the vacuum filtration system 600 and is serially backed by a 0.22 - μm pore - tested PES membrane 603. The PES membrane 603 captures the contaminants passing through the LIG filter 602 and provides a way to characterize the effectiveness of the LIG filter 602. When the LIG filter 602 is subjected to an air stream, microorganisms and contaminants (e.g., mold spores, bacteria, particulates, and endotoxins) are embedded in the LIG. See Figure 6B . SEM imaging and Raman spectroscopy show no signs of LIG particles being released from the filter and traveling downstream to the PES membrane. The LIG filter can then be Joule - heated to a temperature far exceeding the pathogen - killing temperature ( Figure 6C ).

[0179] A schematic of the Joule - heating process is shown in Figure 6D . A DC power supply is used to apply an electric potential across the filter. The dissipation of electrical energy results in resistive heating. An infrared image showing the thermal distribution on the LIG filter is shown in Figure 6E . The filter easily exceeds 380 °C and the thermal distribution is very uniform.

[0180] What is unique about this air filter is that LIG is a conductive material. A sheet resistance of ∼5 Ω / sq has been demonstrated [Chyan 2018]. When a sufficient voltage is applied across the entire LIG filter, Joule heating causes the filter temperature to rise rapidly, which can incinerate the trapped particulates such as bacteria, endotoxins, and viruses. The bactericidal temperatures for bacteria and endotoxins in dry air are 150 °C and 250 °C respectively [Jenneman 1986]. The temperature at which the viral capsid is inactivated is a much lower temperature, less than about 3 seconds at 150 °C. Using a DC power supply, the LIG material can be rapidly Joule - heated to 250 °C in about 6 seconds with a power consumption of about 0.8 W / cm 2 . Figure 7 Shows the relationship between the temperature of the LIG - based filter and the applied power. This enables the rapid incineration of the trapped particulates, so the LIG - based air filter is considered self - cleaning. Conveniently, the PI supporting the free - standing LIG film is stable in air up to 550 °C. This is much lower than the required bactericidal temperature, so the film will be very stable over time.

[0181] Figure 8 Shows an optical image of the LIG filter subjected to 25 days of continuous air flow.

[0182] The conductivity of the LIG air filter also allows the LIG filter to operate in an electrostatic mode, thus enhancing particle capture. Applying an electric potential across the entire LIG filter can capture charged particles. In a single-sided LIG air filter, a voltage can be applied in the plane of the filter sheet. In a double-sided LIG filter, a voltage can be applied across the entire filter such that the first side of the LIG filter can carry more positive or negative charge compared to the second side of the LIG filter on the other side of the sheet. The application of charge shows a decrease in the permeability of bacterial particles through the filter. Figures 9A - 9D Different geometries are shown, for example, a system with a LIG filter 902 across which a voltage 903 is applied to support an electrostatic filter 901 (P84 polyimide fiber, Evonik Fibers GMBH, Lenzing, Austria). Figures 9C - 9D The system includes spacers 904. Figure 9E is shown as Figure 9D a photograph of multiple parts of the system as shown.

[0183] Table I shows the relationship between the reduction in colony-forming units of Pseudomonas aeruginosa (P. aeruginosa) and Figures 9A - 9D the geometries shown and the electric potential applied in systems without using LIG (P84 polyimide fibers of single and double layer thicknesses). In Table 1, at an air flow rate of 10 liters per minute, the bacterial passage rate (%) is normalized with respect to a system without any test filter.

[0184] Table I:

[0185]

[0186] NT – Not tested

[0187] Relationship between temperature, power, air flow rate and pressure drop

[0188] Important parameters for filter characterization include flow rate, pressure drop, and particle capture ability. The effective flow rate of a filter reflects the rate at which air can be effectively filtered through the filter. The pressure drop across the filter represents the resistance of the filter to the air flow and is related to the power consumption required to drive the air through the filter. The figure of merit (Q) of an air filter is typically defined as in Equation 1:

[0189] Q = -In(P) / Δp (I)

[0190] where P is the particle permeability defined as the downstream particle concentration divided by the upstream particle concentration, and ΔP is the pressure drop across the filter [Brown 1993]. At a given air flow rate, a low pressure drop and high particle capture efficiency are desired.

[0191] The relationship between the pressure drop across the entire LIG filter and the air flow rate at room temperature is shown as Figure 10A follows. The filter exhibits a pseudo-linear relationship between the air flow and the pressure drop, which is common in particulate-trapping air filters. The effect of the air flow rate on the Joule heating ability of the LIG filter is characterized by Figure 10B the following. Specifically, the relationship between the temperature and the electrical power curve of the filter while withstanding air flows from 0 to 25 liters per minute was recorded (curves 1001 - 1006 correspond to 0, 5, 10, 15, 20, and 25 liters per minute, respectively).

[0192] At relatively low flow rates (0 and 5 liters per minute), no substantial effect on the temperature - power relationship was observed, and a temperature decrease with low supply power was observed at high flow rates. However, the temperature - power curves show an S-shaped behavior at higher flow rates, indicating that even at relatively high flow rates, increasing the power can partially compensate for the temperature decrease.

[0193] The relationship between the pressure drop across the entire LIG filter and the filter temperature at different flow rates is shown in Figure 10C (curves 1011 - 1016 correspond to 0, 5, 10, 15, 20, and 25 liters per minute, respectively). As expected, the pressure drop increases with increasing flow rate. It was also observed that the pressure drop increases with increasing temperature. This is due to the negative thermal expansion coefficient of graphene [Yoon 2011]. As the temperature increases, the LIG shrinks, the pore size decreases, and the air flow resistance increases.

[0194] Shrinking is beneficial for several reasons. When the filter is Joule heated, shrinking enhances the ability of the LIG to capture and incinerate the trapped contaminants. Similarly, as the temperature increases, shrinking improves the electrical contact within the LIG and reduces the resistivity of the material, making heating increasingly easier. Shrinking reduces the air flow, resulting in less energy loss during heating and enabling higher temperatures to be reached, thus leading to the S-shaped behavior observed in the temperature - power curves.

[0195] Thermal cycle stability

[0196] The results of the thermal cycling stability test of the LIG filter are shown in Figure 10D the following. No decomposition was observed within 250 cycles up to 255 °C, where a potential of 15 V was applied for 5 seconds at a constant rate and then switched off for 5 seconds to allow the filter to cool to room temperature. Subsequently, the filter was heated for 30 minutes under the same conditions to test the extended Joule heating thermal stability. The extended Joule heating of the LIG filter sample confirmed the constant thermal stability. Finally, the filter was subjected to heating at 380 °C for 1 hour, and no signs of degradation were observed due to the significant thermal stability of the LIG and PI.

[0197] Due to the low heat capacity of LIG, the heating and cooling rates are very fast. The amount of time required to heat to 255 °C is approximately 5 seconds, and the amount of time required for the filter to cool to room temperature is approximately 5 seconds. The low heat capacity is crucial for filter efficiency because the filter does not require a large amount of energy for heating, thus helping to achieve high temperatures in a short time with low power consumption. At the same time, the amount of waste heat transferred to the air and finally discharged through air conditioning is also reduced. As the temperature increases, the current increases by approximately 4.5% because the conductivity of LIG increases with temperature, so real-time temperature monitoring can be carried out by measuring the resistance. The decomposition temperature of LIG in air is approximately 575 °C, and its thermal stability in air is higher than that of PI, whose decomposition temperature in air is approximately 550 °C. As determined by TGA, the filter is stable below 560 °C. Therefore, the operating peak temperature of the Joule-heated LIG filter should be limited to <500 °C to prevent thermal degradation.

[0198] Particle pollutant capture test

[0199] Particles are generated by cigarette combustion and passed through the LIG filter to determine the efficiency of capturing submicron particles. The filtered air is bubbled through water to capture the airborne particulates and analyzed by dynamic light scattering (DLS).

[0200] Optical images of water used to capture airborne particulates ( Figure 10E ) show that the unfiltered air (in container 1021) contains more particulates than the filtered air (in container 1022), as indicated by the change in the color of the solution. DLS is used to estimate the concentration of particles captured in the bubbler. See Figure 10F , and curves 1031 - 1032 represent unfiltered and with filter respectively. Over all particle size ranges, the filter blocked most of the particles (more than 86% for 0 - 500 nm). Some smaller particles were able to penetrate the filter, although the observed size range was small enough to penetrate a high-efficiency particulate air (HEPA) filter.

[0201] However, since most bacteria, fungi, aerosols, virus-containing aerosols, allergens, and pathogen-carrying particulate matter are usually micron-sized, finer filtration does not provide a substantial improvement for medical application protection [Kowalski 2012]. The filtration efficiency can be easily improved by adding filter layers, folding the filter, or chemical functionalization, although the latter may make the operating temperature more restricted. Based only on size exclusion screening without considering any other capture mechanisms, the filter will effectively block pollen, spores, and dust particles and will thus effectively eliminate common allergens [Sublett 2010].

[0202] Reusability / Joule heating

[0203] The LIG filter is purposefully coated with different materials and subjected to Joule heating to test its reusability. Figure 11A Shown is a stirring tank system 1100 that is used to coat the filter with a test medium, and the chart data shows the recovery of the filter. System 1100 includes a stirring tank 1101 having a fan 1102 (e.g., a 12V fan) for manual particulate saturation of particles 1103 and a vacuum filtration system 1104 that includes a LIG filter 1105. An enlarged view of the LIG filter 1105 is as Figure 11B shown. The LIG filter 1105 can be a non-corrugated monolithic LIG 1106 with a silver conductor 1107. The vacuum filtration system 1104 can use a conduit 1108 to allow air flow to create a vacuum. System 1100 also includes a pressure gauge H009 for air pressure readings and a power supply 1110. Figure 11C Shown are the particulate matter on the LIG filter 1105 before Joule heating (LIG filter 1105a) and after Joule heating (LIG filter 1105b). A PES filter is not required in system 1100.

[0204] MERV 8 dust

[0205] The Minimum Efficiency Reporting Value (MERV) is designed to assist in filter rating. The MERV rating table can be found at http: / / www.mechreps.com / PDF / Merv_Rating_Chart.pdf, and some various different filters are rated as follows:

[0206] Spun fiberglass filters (MERV 1 - 4): These filters are inexpensive and disposable, will trap 80% of particles 50 microns and larger, and impede 25% of particles 3 to 10 microns. Many manufacturers recommend these filters as the minimum protection against dust and dirt accumulation on fan motors, heat exchangers, and other surfaces. They filter out large particles to protect furnace components, provide maximum air flow, but do not filter out tiny harmful pollutants that affect people's health.

[0207] Disposable pleated paper or polyester filters (5 - 8 MERV): These medium-sized filters can capture 80% to 95% of particles 5 microns and larger. They cost four times as much as spun fiberglass filters but provide better filtration.

[0208] Electrostatic filters (2 to 10 MERV): They use self-charging fibers to attract particles out of the air. A standard-sized disposable folded version sells for about $10 (e.g., 16 inches x 25 inches x 1 inch). The washable version (4 to 10 MERV, usually not folded) sounds like a good way to save money, but the quality varies with cost. The better-quality ones can last up to 8 years. These filters must be completely dried after washing to avoid mildew or mold growth, so a convenient trick is to buy two and then spin them out for cleaning.

[0209] Disposable folded high-MERV filters (11 to 13 MERV): High-efficiency filters can capture particles as small as 0.3 microns, such as bacteria and some viruses. The two- to five-inch-thick filters are fixed in a box-like housing mounted on the air handler and can last up to a year. Variations in the filter design cycle can increase the price.

[0210] High-Efficiency Particulate Air (HEPA) filters: This is truly high-end filtration that can filter out particles as small as 0.3 microns. HEPA filters severely restrict airflow and can only be matched with compatible systems.

[0211] For MERV 8 filters, the dust spot efficiency is 30 - 35, and the arrestance is greater than 90%. The typical controlled contaminants for MERV 8 filters are particles with a size of 3.0 to 10.0 pm. The typical applications and limitations of MERV 8 filters are commercial buildings. The typical air filter / cleaner type for MERV 8 filters is a folded filter, which is usually disposable, has an extended surface area, is thick, has a cotton-polyester blend medium, and a cardboard frame.

[0212] Figure 12 The dust guide 1200 of the MERV 8 filter is shown. The dust guide 1200 is a high-velocity air cone system where air containing dust is blown into the cone through the duct 1201. Then the air is filtered using the MERV 8 filter 1202, which will provide filtration against mold spores, pollen, pet dander, and dust mite debris. Through this system, particles are captured in the filter 1202.

[0213] The dust guide 1200 is used to capture dust from outdoor sources on the filter 1202. Subsequently, the filter 1202 is cut into squares and backloaded into the box system 1100. Then clean air (laboratory quality) is used to blow the particles captured in the MERV filter (referred to as MERV8 dust) onto the LIG filter 1105.

[0214] Figure 13 Illustration showing agitation, annealing, and recovery of the LIG filter 1105 containing MERV8 dust within a series of cycles. Figures 14A - 14C The LIG filter 1105 is shown before MERV 8 dust accumulation, after the first round of saturation with MERV 8 dust, and after the first round of Joule heating. Figure 13 It shows that the air pressure increases significantly after media agitation. Although it does not return to the initial level, there is a significant recovery. Since the non-combustible substances in the air remain blocked in the filter, it cannot be restored to the original level.

[0215] Bee pollen

[0216] Joule heating can effectively reduce the blockage of organic substances such as bee pollen. Bee pollen is one of the most well-known apitherapeutics, and its chemical composition depends to a large extent on the plant source, geographical source, and other factors (e.g., climatic conditions, soil type, bee race, and activities). In the composition of bee pollen, there are about 250 substances, including amino acids, lipids (triglycerides, phospholipids), vitamins, macro and micronutrients, and flavonoids.

[0217] Figure 15 It shows the agitation, annealing, and recovery of the LIG filter material rapidly aged with bee pollen. (Agitation involves two 12-volt fans that circulate air in a closed box with the media stacked inside. In the case of bee pollen, the surface of the box needs to be tapped or the box shaken so that the fans can blow the bee pollen around. The density of bee pollen is (~0.68 g / cm 3 ). Figures 16A - 16B It shows the filter that was blocked before Joule heating at 300 °C and unblocked after Joule heating at 300 °C obtained after the first round of Joule heating, respectively. Figures 16C - 16F It shows the LIG filter after the first round of Joule heating, the LIG filter after the second round of Joule heating (and a bee pollen foam sheet can be seen and formed), the LIG filter after four rounds of agitation, and the LIG filter after the fourth agitation (and bee pollen falling off the filter can be seen), respectively.

[0218] Filter blockage leads to an increase in the pressure drop across the entire filter and an increase in energy consumption. Joule heating incinerates the trapped particles and reduces the pressure drop to "regenerate" the filter (i.e., unclog the filter). This regeneration of the filter can achieve energy savings throughout the life cycle of the filter.

[0219] After three rounds of oversaturation / agitation / annealing, the recovery is obvious. However, as graphene seems to adhere moderately to the annealed bee pollen, the bee pollen starts to heat the sheet and peel off from the filter, resulting in filter damage and showing more recovery than the initial pressure value, and finally damage occurs.

[0220] Indoor dust

[0221] The dust collected from the bag of a standard vacuum cleaner was also filtered using an LIG filter. The dust (referred to as "indoor dust") was directly agitated into the LIG filter by squeezing the dust through the holes in the bag by hand to allow the dust particles to escape.

[0222] Figure 17 Show the agitation, annealing, and recovery of the LIG filter containing indoor dust. After annealing the indoor dust particles from the vacuum bag, no recovery was found. The material picked up by vacuum contained a large amount of glass or silica and was not annealed within the temperature range of ~350 °C used by Joule heating. Figures 18A - 18C Respectively Figure 17 Photographs of the LIG filter used in the process shown before the second agitation (a), after agitation (b), and after Joule heating (c).

[0223] Bacterial capture and culture results

[0224] Figure 19A Show the experimental setup for determining the efficacy of the LIG filter in capturing and killing airborne bacteria. The vacuum filtration system 1900 includes an LIG filter 1902 through which an air stream 1904 can flow into a chamber 1901 and out through a filter 1903 (e.g., a 0.22 μm PES filter) for evacuation 1905. A control filtration system 1910 is also shown Figure 19A in which it has a similar setup except that it does not include the LIG filter 1902.

[0225] The LIG filter 1902 was installed on a commercially available vacuum filtration system and subjected to an air stream 1904 at a rate of 10 liters per minute for ninety hours. The time-dependent incubation of airborne bacteria captured by the filter showed that the bacteria underwent a lag phase, an exponential phase, and a stationary phase within the 24-hour incubation time. Therefore, the incubation after 24 hours was used to determine whether the filter was exposed to or had captured bacteria.

[0226] Air passed through the LIG filter at the same flow rate and duration as the control filtration funnel. A control 0.22 μm PES membrane (labeled PES A in the control filtration system 1910). A PES membrane labeled PES B (vacuum filtration system 1900) was in series with the LIG filter, and subsequent culturing of PES B showed whether bacteria passed through the LIG filter during operation.

[0227] Figure 19BIt is a schematic diagram of the cultivation process. The relevant filter 1911 is immersed in the broth medium 1912, and after cultivation, the bacterial proliferation is detected using the optical density measurement of the obtained culture 1915 over time.

[0228] Figure 19C It is a bar graph of the optical density of the medium. The 90-hour air flow filters are incubated in the medium for 24 hours (the LIG filter, PES A, PES B, LIG heated filter, and sterile LIG are shown in columns 1921 - 1925 respectively). It is observed that no bacterial growth occurred in all samples except the PES control filter (PES A) that underwent a comparable flow rate and duration, indicating the presence of bacteria in the air.

[0229] Repeat this experiment, but before incubating for 24 hours, gently sonicate the filter in the medium for 2 minutes. As Figure 19D shown (and the LIG filter, PES A, PES B, LIG heated filter, and sterile LIG are shown in columns 1931 - 1935 respectively), subsequent bacterial growth was observed in the PES A filter and the non-Joule heated LIG filter. Therefore, due to the antibacterial encapsulation surface properties of LIG, even when the filter is immersed in the medium, the bacteria captured by the LIG filter will inhibit proliferation [Luong2019; Singh 2017].

[0230] There was no bacterial growth in the medium incubated with the PES test filter sample (PES B) in series with the LIG filter, indicating that the LIG filter successfully prevented bacteria from reaching PES B, and PES B remained sterile. No bacterial growth was observed on the sonicated Joule heated LIG filter sample, indicating that Joule heating at 300 °C successfully killed the bacteria.

[0231] It was also observed that between four 24-hour trials, the optical density of the PES A filter containing the medium was roughly the same, indicating that gentle sonication does not kill bacteria. In subsequent trials, after observing the exponential phase of the PES A and non-Joule heated LIG filters, the additional incubation time of the filters exceeded 130 hours, showing no bacterial proliferation in the Joule heated LIG or PES B, indicating that these filters are sterile within the experimental range.

[0232] Polysaccharide carbonization demonstration

[0233] Bacterial endotoxins are usually lipopolysaccharides (LPS), which are structural components of the outer leaflet of the outer membrane of Gram-negative bacteria. They are released during bacterial death and contain long-chain glycan polymers (also known as O antigens) that are attached to a core oligosaccharide, which in turn is bound to lipid A [Rietschel 1994]. The major physiological immune responses to endotoxins, such as high fever and septic shock, can be attributed to the lipid A portion of LPS. Generally, endotoxins require long-term heating above 250 °C to decompose. However, above 300 °C, log 10 the decomposition rate accelerates to a second time scale [Tsuji I 1978; Tsuji II 1978].

[0234] Since the thermal stability of starch is comparable to that of the carbohydrate portion of LPS [Aggarwal 1998; Liu 2009], it was demonstrated that starch was carbonized by Joule heating LIG to determine whether the surface exceeded the temperature required to decompose LPS. When 1.10 W·cm -2 was supplied to the filter, the surface temperature reached 300 °C within <5 s, and the starch spread on the filter surface decomposed rapidly within <1 minute. Since the internal temperature of the heating element is usually higher than the surface temperature, this indicates that the surface is hot enough to carbonize the polysaccharide. The previously demonstrated maximum stable extended heating temperature of 380 °C is sufficient to degrade almost all biomolecules within seconds, including prions, mycotoxins, endotoxins, exotoxins, teichoic acids, and nucleic acids, etc.

[0235] Virus capture and destruction

[0236] Figure 20 The BET surface area of LIG-3.6W is shown. This indicates that LIG has a large surface area of approximately 342 m 2 / g and abundant nanopores with high tortuosity (pore size distributions at 2.36 nm, 3.68 nm, 5.37 nm, and 8.94 nm). Therefore, LIG is particularly suitable for the diffusion and adsorption capture of virions as well as aerosols generated by coughing and sneezing that may contain virions or other pathogens. The subsequent Joule heating reaches a temperature sufficient to destroy the components that make up the virus, such as nucleic acids, proteins, lipids, and carbohydrates. Therefore, the same filter can also be used in masks, personal protective equipment, and HVAC systems to prevent the spread of airborne infectious diseases.

[0237] Other materials are equally suitable for suitable substances used to produce LIG for filtration applications, including polyimide, PEEK, PES, paper, and cloth in the form of thin films, membranes, sheets, foams, fibers, fabrics, and textiles.

[0238] LIG filtration system

[0239] Figures 21A - 21B The shown framework is a demonstration of LIG air filtration. Figures 21A - 21B Top and side views of an example of the LIG filtration framework device 2100 of the filtration system are shown respectively. Figure 21A The following layout is shown: a glass frame 2101, nylon bolts and nuts 2102 (nylon bolts and nuts with airtight gaskets), LIG 2103, a copper strip 2104 (under the glass), excess polyimide 2105, an exposed copper strip 2106, and alligator clips 2107 (or other connectors for electrical contact). Figure 21B A side view of the exposed electrode is shown, demonstrating the position of the electrical contact points matching the exposed electrode.

[0240] In the LIG filter 2100, the filter captures and then anneals the particles captured in the filter. In order for graphene to anneal the captured particles, LIG requires electrodes. Using electrodes trapped between the LIG filter and a high-temperature resistant insulator framework allows the electrodes to provide rigid support for the graphene. The nature of the graphene formed by LIG is fibrous and touch-sensitive. Using flat electrodes (such as copper) pressed against the graphene between the frame and LIG helps to maintain contact. Other methods may dry out and crack, or may be too thick, resulting in separation from the interior of the HVAC system during vibration. This electrode application method is an annealing method.

[0241] LIG 2103 lasers both sides of the selected material in the required pattern. LIG 2103 is placed between two frames 2101 made of the selected material, and copper electrodes are embedded to allow periodic annealing. LIG 2103 is exposed to the central element, and the frame presses the copper against the graphene. Nylon screws 2102 provide the pressing of the frame 2101, helping to achieve an airtight seal and pressing the electrodes against the graphene. The frame 2101 has the ability to have a fully glass face as a rigid variant of LIG 2103, which has electrodes laminated between low-density polyethylene. This also shows a rigid air filter, which is designed to be placed in an air filtration vent. As long as the glass can withstand the stress generated during assembly, it is expandable.

[0242] Various electrodes all present different resistance readings and achieve benefits similar to those of the copper strip. These materials are applicable options optimized and tested with the fabricated filters to meet the required performance.

[0243] For other electrode information related to its application to the LIF filter, see the Tour’933 PCT application, which is incorporated herein by reference.

[0244] The measured resistance

[0245] Figures 22A - 22FPhotographs of various LIG composites for measuring resistance (speed 5%, power 15%), which started at 210 ohms before 1000 bending tests. Figures 22A - 22F Applicable to the following materials with measured resistance: (a) copper – 270 Ω, (b) copper – 268 Ω, (c) aluminum – 650 Ω, (d) silver paint – 320 Ω, (e) hammered tin-lead solder – 650 Ω, and (f) 2-1 ultrafine graphite – high-temperature RTV – 500 Ω.

[0246] Use

[0247] The LIG filter of the present invention can capture contaminants and microorganisms and self-clean through Joule heating. The filter is applicable to hospitals for reducing hospital infections transmitted through air, droplets, aerosols, and particulate-matter-transmission modes. The LIG filter overcomes the challenges of traditional HVAC filters and disinfection methods. Self-sterilization through Joule heating can prevent microbial proliferation on the filter and subsequent downstream contamination.

[0248] The LIG filter can capture bacteria and prevent proliferation even when immersed in a culture medium. Through a periodic Joule heating mechanism, the filter eliminates particles on the filter surface, destroys the captured bacteria, and exceeds the temperature at which life-sustaining compounds and molecules that may cause adverse biological reactions and diseases thermally decompose, such as pyrogens, contaminants, allergens, exotoxins, teichoic acids, endotoxins, mycotoxins, nucleic acids, and prions.

[0249] This material can be used in medical institutions such as hospitals because infections caused by bacteria and endotoxins in hospitals affect approximately 5% of all inpatients. It is believed that approximately 20% of healthcare-associated infections (HAIs) are airborne [Kowalski 2016]. Many bacteria are transported between rooms through air ducts. Traditional HEPA filters in air ducts need to be scrubbed or replaced after the filter becomes saturated. The LIG-based air filter of the present invention can be periodically Joule heated to incinerate the captured bacteria and endotoxins. This will destroy the captured particulates, thereby reducing infectious substances transmitted through air ducts.

[0250] In addition to being used in a medical environment, LIG filters can also be used in other applications where it is necessary to incinerate airborne microorganisms to prevent biological warfare or terror agents in the air. LIG filters are also suitable for reducing the risk of pathogen transmission in transportation systems such as commercial airplanes, trains, and buses to prevent the long-distance spread and transfer of diseases carried and introduced by high-volume passengers from different sources. Similarly, the filter can be used to protect animals, plants, fungi, and other organisms from diseases in agricultural, veterinary, zoological, and research environments. In the same way, the filter can protect biological laboratories from contamination.

[0251] The LIG air filter can be used to capture viruses, viruses in aerosolized droplets, and easily inactivate the viruses because the inactivation temperature of the viruses is typically 3 seconds at 150 °C. This includes coronaviruses.

[0252] The geometry of the LIG air filter can be changed to provide the most effective particle capture for specific applications. In addition, adjusting the laser parameters during LIG synthesis can change the pore size distribution.

[0253] In some embodiments, it may not be necessary to use a bilateral LIG film. In this alternative embodiment, spaces can be cut in the PI film for air to pass through. However, the LIG grid covers one or both sides and if the mesh is thick enough, the capture rate of microorganisms and viruses is still very high.

[0254] In addition, other materials can be used to fabricate LIG, such as paper, wood, polysulfone, and various chain-growth, step-growth, and living polymer systems, including condensation polymers and vinyl polymers. In addition, for example, other materials can be selected from the group consisting of homopolymers, vinyl polymers, step-growth polymers, condensation polymers, polymers made by living polymer reactions, chain-growth polymers, block copolymers, carbonized polymers, aromatic polymers, cyclic polymers, polyimide (PI), polyetherimide (PEI), polyetheretherketone (PEEK), polysulfone, elastomers, rubbers, recycled plastics, polyethylene terephthalate, polytetrafluoroethylene, polyethylene, polypropylene, low-density polyethylene (LPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), polybutadiene, poly(styrene-butadiene), polystyrene, polycarbonate, polyamide, polyimide, polyurethane, thermoplastics, thermosets, and combinations thereof.

[0255] While embodiments of the present invention have been shown and described, those skilled in the art can make variations thereto without departing from the spirit and content of the present invention. The embodiments and examples described herein are for illustrative purposes only and are not intended to be limiting. Many variations and modifications of the present invention disclosed herein are possible and are within the scope of the present invention. The scope of protection is not limited by the description listed above, but is only defined by the appended claims, and the scope of the claims includes all equivalent content of the subject matter of the claims.

[0256] The contents of all patents, patent applications, and publications cited herein are incorporated herein by reference in their entirety, and they provide exemplary, procedural, or other details supplementary to the content described herein.

[0257] Quantities and other numerical data may be given in the form of ranges. It should be understood that the use of such range forms is for convenience and brevity only, and should be interpreted flexibly to include not only the values explicitly listed as the limits of the range, but also all individual values or sub-ranges included within that range, as if each value and sub-range had been explicitly listed. For example, a numerical range of about 1 to about 4.5 should be interpreted to include not only the explicitly listed limits of 1 to about 4.5, but also individual values such as 2, 3, 4 and sub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies to ranges involving only one value, such as "less than about 4.5", which should be understood to include all of the above values and ranges. In addition, this interpretation applies regardless of the width of the range or feature described. The symbol "~" is the same as "about / approximately".

[0258] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of the present invention pertains. Although any methods, devices, and materials similar or equivalent to those described herein can also be used to implement or test the subject matter of the present disclosure, representative methods, devices, and materials are described.

[0259] In accordance with long-standing patent law practice, the terms "a" and "an" when used in this application (including the claims) mean "one or more / one or more kinds".

[0260] Unless otherwise specified, all numerical values representing the contents of various components, reaction conditions, etc. used in this specification and the claims should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise specified, the numerical parameters used in this specification and the appended claims are approximate values and can vary according to the desired properties to be achieved by the present disclosure.

[0261] As used herein, the terms "about" and "substantially" when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage, cover variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1% compared to the specific amount, and such variations are suitable for practicing the methods disclosed herein.

[0262] As used herein, the terms "substantially perpendicular" and "substantially parallel" refer, respectively, to variations within ±10° of the perpendicular and parallel directions in some embodiments, within ±5° of the perpendicular and parallel directions in some embodiments, within ±1° of the perpendicular and parallel directions in some embodiments, and within ±0.5° of the perpendicular and parallel directions in some embodiments.

[0263] As used herein, the term "and / or" when used in a list of entities means that the entities may be present alone or in combination. Thus, for example, the phrase "A, B, C, and / or D" includes A, B, C, and D alone, and also any and all combinations and sub - combinations of A, B, C, and D.

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Claims

1. A method of manufacturing a filter comprising LIG, wherein, the method comprises the following steps: (a) exposing a first side of a sheet comprising a LIG precursor material to a first laser source, wherein, (i) the exposure on the first side causes the formation of LIG on the first side of the sheet, and (ii) the LIG is derived from the LIG precursor material; (b) treating a second side of the sheet, wherein, (i) the second side of the sheet is on the opposite side of the first side of the sheet, (ii) the step of treating the second side comprises: exposing the second side of the sheet to a second laser source to form LIG on the second side of the sheet, (iii) the second laser source is (A) the first laser source or (B) a laser source different from the first laser source, (iv) the LIG on the first side of the sheet and the LIG on the second side of the sheet are adjacent and provide porosity to the sheet such that the sheet is a LIG filter capable of allowing air to flow from the first side through the LIG to the second side, (v) by the step of exposing the first side of the sheet comprising the LIG material to the first laser source, some of the LIG precursor material on the first side does not form LIG, and the LIG precursor material on the first side that does not form LIG is capable of operating to support the LIG formed on the first side, and (vi) by the step of exposing the second side of the sheet comprising the LIG material to the second laser source, some of the LIG precursor material on the second side does not form LIG, and the LIG precursor material on the second side that does not form LIG is capable of operating to support the LIG formed on the second side.

2. The method according to claim 1, wherein, the first laser source and the second laser source are the same laser source.

3. The method according to claim 1, wherein, the filter is capable of operating to capture particles or molecules selected from the group consisting of: viruses, airborne microorganisms, microbial by-products, microbial-related toxins, viruses, virus capsids, virus capsid droplets, and combinations thereof.

4. The method according to claim 3, the method further comprises: decomposing the captured particles by Joule heating.

5. The method according to claim 1, wherein, the LIG precursor material is selected from the group consisting of: polymers, carbon-based precursors comprising amorphous carbon, and compounds as porous amorphous carbon precursors.

6. The method according to claim 1, wherein, the LIG precursor material is a polymer.

7. The method according to claim 1, wherein, the step of exposing the first side exposes the first laser source through a first pattern on the first side.

8. The method according to claim 7, wherein, (a) exposing the second side to the second laser source exposes the second laser source through a second pattern on the second side; and (b) the first pattern is offset from the second pattern.

9. The method according to claim 1, wherein, when a voltage is applied across the entire filter, the filter is capable of operating to generate heat.

10. A LIG filter, which comprises: (a) a first LIG, wherein the first LIG is on a first side of the LIG filter; (b) a second LIG, wherein the second LIG is on a second side of the LIG filter, adjacent to the first LIG; and (c) A LIG precursor material that supports a first LIG on a first side of the LIG filter and a second LIG on a second side of the LIG filter, wherein, (i) The LIG filter sheet has a porosity such that the LIG filter allows air to flow through the first LIG on the first side to the second side of the LIG filter and flow through the second LIG on the second side of the LIG filter; and (ii) The LIG filter is capable of operating to capture particles selected from the group consisting of viral particles, airborne microorganisms, microbial by-products, microbial-related toxins, and combinations thereof.

11. The LIG filter according to claim 10, wherein, When a voltage is applied across the entire filter, the LIG filter is capable of operating to generate heat.

12. The LIG filter according to claim 11, wherein, The heat can kill or decompose the captured particles.

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