Filter

Abstract

The present invention relates to a filter comprising a free-standing body of non-woven carbon nanotubes that is useful for separating airborne viruses.

Description

[Technical Field]

[0001] The present invention relates to a filter, an air treatment device comprising the filter, and the use of a freestanding non-woven carbon nanotube body in the separation of airborne viruses. [Background technology]

[0002] The presence of airborne viruses is a common risk to public health. The global pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has had a devastating impact on both human lives and the global economy. To combat this in the long term, disease transmission must be hindered by limiting the primary vectors through which the virus spreads. Respiratory liquid aerosols (droplet diameter ≤ 5 μm) are considered to be important primary vectors for many viruses, including coronaviruses, and are generated by coughing, speaking, and exhaled air during breathing. Surgical masks and respirators may offer only limited protection against such viruses.

[0003] Respiratory particles that can enter the lungs pose a risk in indoor environments because they can remain airborne for hours and travel tens of meters by advection and diffusion. These aerosols can contain active SARS-CoV-2 virus particles for at least three hours, leading to high infection rates in enclosed and crowded spaces. To mitigate these risks, air filtration in poorly ventilated (<3 air changes per hour) or predominantly re-aired environments has been proposed as a means to limit the spread of disease. Summary of the Invention

[0004] The present invention is based on the recognition that nonwoven free-standing carbon nanotubes have the desirable function of separating airborne viruses. In particular, nonwoven free-standing carbon nanotubes reduce environmental concentrations of virus particles (e.g., by capturing or inactivating viruses) while allowing high gas flow with low static pressure loss. Therefore, filters incorporating nonwoven free-standing carbon nanotubes can achieve high aerosol filtration efficiency while maintaining low pressure drop. The increased surface area and lower drag on the gas flow due to the "slip" mechanism result in non-zero velocities on the nanotube surfaces. Therefore, smaller nanotube diameters result in better filter performance.

[0005] In a first aspect, the present invention provides a filter capable of separating airborne viruses, the filter comprising: The framework and a free-standing body of non-woven carbon nanotubes mounted on or within a framework.

[0006] The ease with which nonwoven carbon nanotubes can be fabricated facilitates their deployment in effective air filters. Optimization of thickness, mechanical properties (through manufacturing processes), shape, and surface chemistry (e.g., through coatings) makes nonwoven carbon nanotubes a versatile, cost-effective, and high-performance airborne virus barrier solution.

[0007] The framework can be rigid or flexible. The free-standing non-woven carbon nanotube body can be rigid or flexible.

[0008] The filter may be modular (e.g., a cartridge). For this purpose, the framework is rigid. The filter may be part of (e.g., attachable or attached to) an air treatment device. The air treatment device may be a non-medical device such as an air conditioner, air purifier, or air humidifier, or may be a medical device such as a mask, respirator, ventilation device, respirator, or breathing device.

[0009] The filter may be wearable on the face, and may be (or be part of) a mask (e.g., a surgical mask, full face mask or half face mask), helmet, hood or visor.

[0010] The framework may be flexible. The flexible framework may be adjustable and may be adjustable to fit onto facial features.

[0011] The free-standing non-woven carbon nanotube body may be facially wearable (e.g., wearable on a human face) or cranially wearable (e.g., wearable on a human head). The free-standing non-woven carbon nanotube body may be shaped to fit facial features (e.g., human facial features) or cranial features (e.g., human head features). The free-standing non-woven carbon nanotube body may be contoured to fit the face.

[0012] The free-standing non-woven carbon nanotube body is preferably a single wall of non-woven carbon nanotubes.

[0013] The free-standing non-woven carbon nanotube body is preferably a laminate. Multiple layers of non-woven carbon nanotubes may be interdigitated with each other. Multiple layers of non-woven carbon nanotubes may be alternated with multiple layers of porous insulating material.

[0014] It is particularly preferred that the laminate is a bilayer, more preferably a layer of non-woven carbon nanotubes and a layer of porous insulating material.

[0015] The porous insulating material is preferably polyester.

[0016] In a preferred embodiment, the filter comprises: Further provided is a means for inactivating viruses.

[0017] The means for inactivating viruses may be electromagnetic radiation, electrical radiation, microwave radiation, infrared (heat) radiation, ultraviolet radiation, gamma radiation or chemical means.

[0018] The chemical means may be a gas or liquid source. The chemical means may be a source of chlorine, chlorine dioxide, ozone, formaldehyde, or glutaraldehyde. The chemical means may be a source of a high pH or low pH reagent.

[0019] Preferably, the means for inactivating viruses comprises an electric field generator for generating an electric field within the free-standing body of non-woven carbon nanotubes.

[0020] The electric field can be a low voltage field (mV / cm) or a high voltage field (kV / cm). The electric field generator can be a DC or AC power source that can operate in a capacitive or resistive mode. The DC or AC power source can be in an electrical circuit with or without a resistor.

[0021] The electric field generator is preferably AC powered.

[0022] The AC power source may be capable of applying an AC voltage in the range of 0.3 V to 6.0 V. The AC power source may be capable of applying an AC voltage at a frequency in the range of 10 Hz to 20 MHz. The AC power source may be capable of applying an AC voltage at a low frequency (e.g., a frequency in the range of 50 Hz to 500 Hz). The AC power source may be capable of applying an AC voltage at a high frequency (e.g., a frequency in the range of 10 MHz to 20 MHz).

[0023] The ability of CNTs to conduct electrical current at high AC frequencies allows coupling between the virus molecules trapped on the filter and the applied AC current. At sufficiently high frequencies in the microwave range (e.g., 8.3 GHz), dipole-dipole coupling can cause viral inactivation.

[0024] The DC power supply may be capable of applying a DC voltage in the range of 0.1V to 50V, preferably in the range of 0.6V to 3.0V. The DC power supply may be cathodic or anodic. The DC power supply may be capable of applying pulsed DC. The DC power supply may be capable of applying a static DC voltage. The DC power supply may be capable of applying a periodically reversing DC voltage. The DC power supply may be capable of applying a pulsed voltage of fixed polarity. The DC power supply may be capable of applying a pulsed voltage of alternating polarity.

[0025] The electric field generator may be an AC source and a DC source. The electric field generator may be an AC power source and a DC power source. The electric field generator may be switchable between AC and DC.

[0026] Preferably, the means for inactivating viruses comprises a heat generator for generating heat (eg, resistive heat) within the free-standing non-woven carbon nanotube body.

[0027] The heat generator may be capable of raising the temperature of the free-standing body of non-woven carbon nanotubes to a viral inactivation temperature (eg, ≧80° C.).

[0028] The virus may be an aerosolized virus (e.g., a virus transmitted by aerosols or droplets). The virus may be a coronavirus, AAV, Nora, vaccinia, HSV herpes, influenza, or MHV PRRSV. Preferably, the virus is a coronavirus (e.g., COVID-19).

[0029] The non-woven carbon nanotube freestanding bodies can be pristine or functionalized.

[0030] The non-woven carbon nanotube freestanding body can be hydrophobic or hydrophilic.

[0031] The non-woven carbon nanotube free-standing body can be in the form of a fiber, wire, film, ribbon, strand, sheet, plate, mesh, or mat.

[0032] The free-standing non-woven carbon nanotube body may be substantially planar, the free-standing non-woven carbon nanotube body may be substantially annular, or the free-standing non-woven carbon nanotube body may be substantially cylindrical.

[0033] The non-woven carbon nanotube freestanding bodies may be coated or uncoated.

[0034] The free-standing non-woven carbon nanotubes may be coated with a polymer (e.g., a conductive or non-conductive polymer), which may be a thermoplastic or thermoset polymer.

[0035] The non-woven carbon nanotube freestanding body may be coated with a metal or metal oxide, which may be copper oxide.

[0036] In a preferred embodiment, the non-woven carbon nanotube freestanding body is coated with a non-conductive polymer, preferably a fluoropolymer, and more preferably polyvinylidene fluoride (PVDF) or a copolymer or terpolymer thereof.

[0037] The surface density of the freestanding nonwoven carbon nanotubes is 60 gm -2The surface density of the freestanding non-woven carbon nanotubes may be 30 cm or less. -2 The surface density of the freestanding non-woven carbon nanotubes is preferably 20 cm -2 The following are particularly preferred:

[0038] In a preferred embodiment, the areal density of the non-woven carbon nanotube freestanding bodies is 0.1 gm -2 From 14gm -2 is within the range.

[0039] The surface of the free-standing non-woven carbon nanotube body may be substantially uniform. The surface of the free-standing non-woven carbon nanotube body may not be uniform. For example, the surface of the free-standing non-woven carbon nanotube body may be corrugated, wavy, or undulating.

[0040] Preferably, the thickness of the non-woven carbon nanotube freestanding body varies by up to 20%.

[0041] The non-woven carbon nanotube freestanding body may be provided with a polymer core, which may be an elastomeric core or a thermoset or thermoplastic polymer core.

[0042] In a preferred embodiment, a free-standing body of non-woven carbon nanotubes may be attached to a pair of spaced apart electrodes.

[0043] Typically, the filter is 5 kPa -1 to 40 kPa -1 The filter quality factor is in the range of

[0044] The free-standing non-woven carbon nanotube body is (a) introducing a flow of a metal catalyst or a precursor to a metal catalyst into a temperature-controlled flow reactor; (b) introducing a flow of carbon source into a temperature-controlled flow reactor; (c) exposing the metal catalyst or a precursor of the metal catalyst and the carbon source to a temperature range sufficient to generate a particulate metal catalyst and produce carbon nanotubes; (d) transferring the carbon nanotubes as a continuous output through an outlet of a temperature-controlled flow reactor; (e) collecting the continuous effluent in the form of a free-standing or adjustable body of non-woven carbon nanotubes; Preferably, the polymer is obtainable or derived from a process comprising:

[0045] Typically, the particulate metal catalyst is a nanoparticle metal catalyst. The nanoparticles of the nanoparticle metal catalyst preferably have an average diameter (number average diameter, volume average diameter, or surface average diameter) within the range of 1 nm to 50 nm (preferably 1 nm to 10 nm). Preferably, 80% or more of the particles of the nanoparticle metal catalyst have a diameter smaller than 30 nm. It is particularly preferred that 80% or more of the particles of the nanoparticle metal catalyst have a diameter smaller than 12 nm. The concentration of the particulate metal catalyst is 10 6 From 10 10 pieces cm -3 may be in the range of

[0046] Typically, the metal catalyst is one or more of the group consisting of alkali metals, transition metals, rare earth elements (e.g., lanthanides), and actinides. Preferably, the metal catalyst is one or more of the group consisting of transition metals, rare earth elements (e.g., lanthanides), and actinides.

[0047] The metal catalyst is preferably at least one selected from the group consisting of Fe, Ru, Co, W, Cr, Mo, Rh, Ir, Os, Ni, Pd, Pt, Ru, Y, La, Ce, Mn, Pr, Nd, Tb, Dy, Ho, Er, Lu, Hf, Li, and Gd. The metal catalyst is preferably iron.

[0048] The precursor to the metal catalyst may be a metal complex or an organometallic compound. Examples include iron pentacarbonyl, ferrocene, or ferrocenyl derivatives (e.g., ferrocenyl sulfide).

[0049] Preferably, the metal catalyst precursor contains sulfur. Sulfur-containing metal catalyst precursors can promote carbon nanotube growth.

[0050] The precursor of the metal catalyst is preferably a sulfur-containing organometallic. The precursor of the metal catalyst is particularly preferably a sulfur-containing iron organometallic. The precursor of the metal catalyst is more preferably a sulfur-containing ferrocenyl derivative. Furthermore, the precursor of the metal catalyst is more preferably mono-(methylthio)ferrocene or bis-(methylthio)ferrocene.

[0051] The flow rate of the metal catalyst or precursor to the metal catalyst may be from 1 g / hr to 50 g / hr (eg, about 7 g / hr).

[0052] The metal catalyst or metal catalyst precursor may be introduced in step (a) along with a sulfur-containing additive, which may promote carbon nanotube growth. The sulfur-containing additive may be thiophene, iron sulfide, a sulfur-containing ferrocenyl derivative (e.g., ferrocenyl sulfide), hydrogen sulfide, or carbon disulfide.

[0053] In a preferred embodiment, the sulfur-containing additive is a thiophene or carbon disulfide. It is particularly preferred that the sulfur-containing additive is a thiophene.

[0054] In a preferred embodiment, the precursor to the metal catalyst is ferrocene, optionally with a sulfur-containing additive (preferably thiophene or carbon disulfide).

[0055] The flow rate of the sulfur-containing additive may be from 0.1 g / hr to 10 g / hr (eg, about 5 g / hr).

[0056] The metal catalyst or precursor of the metal catalyst introduced in step (a) may be in gaseous, liquid, or solid form. The metal catalyst or precursor of the metal catalyst may be introduced in step (a) along with a non-metallic catalyst modifier or precursor thereof. The non-metallic catalyst modifier may be chalcogen-containing (e.g., sulfur-containing).

[0057] The generation of the particulate metal catalyst may be initiated in step (c) by thermal decomposition or thermal dissociation of the metal catalyst or metal catalyst precursor into metal species (e.g., atoms, radicals, or ions). The generation of the particulate metal catalyst in step (c) may include nucleation, whereby metal species are transformed into nucleated metal species (e.g., clusters). The generation of the particulate metal catalyst may include growth, whereby nucleated metal species are transformed into the particulate metal catalyst.

[0058] The metal catalyst or precursor to the metal catalyst may be introduced (e.g., injected) in step (a) in a linear channel, an axial channel, a spiral channel, a helical channel, a lamellar channel, or a turbulent channel. The metal catalyst or precursor to the metal catalyst may be introduced at multiple locations.

[0059] In step (a), the metal catalyst or precursor to the metal catalyst may be introduced axially or radially into a temperature-controlled flow reactor. The metal catalyst or precursor to the metal catalyst may be introduced axially through a probe or injector.

[0060] The metal catalyst or precursor of the metal catalyst may be mixed with a carrier gas, typically one or more of nitrogen, argon, helium, or hydrogen. The mass flow of the metal catalyst or precursor of the metal catalyst mixed with the carrier gas is typically in the range of 10 lpm to 30 lpm.

[0061] Prior to step (b), the carbon source may be heated.

[0062] Prior to step (b), the carbon source may be subjected to radiative heat transfer by infrared energy, visible light energy, ultraviolet energy or X-ray energy.

[0063] In step (b), the carbon source may be introduced (eg, injected) in a linear channel, an axial channel, a spiral channel, a helical channel, a lamellar channel, or a turbulent channel.

[0064] In step (b), the carbon source may be introduced axially or radially into a temperature-controlled flow reactor. The carbon source may be introduced axially through a probe or injector. The carbon source may be introduced at multiple locations. The carbon source may be an aromatic or aliphatic hydrocarbon, an acyclic hydrocarbon, or a cyclic hydrocarbon (e.g., an alkyne, alkane, or alkene), optionally interrupted by one or more heteroatoms (e.g., oxygen), optionally substituted, and / or optionally hydroxylated. Preferably, the carbon source is an optionally halogenated C 1-6 hydrocarbons (e.g. methane, propane, ethylene, acetylene or tetrachloroethylene), optionally mono-, di- or tri-substituted benzene derivatives (e.g. toluene), or C 1-6 An alcohol (e.g., ethanol).

[0065] The carbon source is methane, optionally (but preferably) in the presence of an aromatic or aliphatic hydrocarbon, an acyclic hydrocarbon or a cyclic hydrocarbon (e.g., an alkyne, alkane or alkene), optionally interrupted with one or more heteroatoms (e.g., oxygen), optionally substituted and / or optionally hydroxylated.

[0066] The carbon source is a C olefin such as methane, ethylene, or acetylene. 1-6 It may also be a hydrocarbon.

[0067] The carbon source may be an alcohol such as ethanol or butanol.

[0068] The carbon source may be an aromatic hydrocarbon such as benzene or toluene.

[0069] In a preferred embodiment, the carbon source is methane, optionally in the presence of propane or acetylene.

[0070] The flow rate of the carbon source may be in the range of 50 sccm to 30,000 sccm (e.g., 2,000 sccm). Typically, in step (b), the carbon source is introduced with a carrier gas such as helium, hydrogen, nitrogen, or argon.

[0071] The flow rate of the carrier gas may be in the range of 1000 sccm to 50000 sccm (e.g., 3000 sccm). In a preferred embodiment, step (a) and step (b) occur simultaneously. For this purpose, the metal catalyst or a precursor of the metal catalyst is preferably suspended or dissolved in the carbon source. It is particularly preferred that the metal catalyst or a precursor of the metal catalyst and the sulfur-containing additive are suspended or dissolved in the carbon source. For example, ferrocene and thiophene may be dissolved in an organic solvent such as butanol, ethanol, benzene, or toluene, and the solution may be introduced (e.g., injected) into a temperature-controlled reactor.

[0072] The carbon nanotubes may be single-walled carbon nanotubes and / or multi-walled carbon nanotubes. In step (c), the structure of the carbon nanotubes may take the form of a 3D continuous network (eg, an aerogel).

[0073] The temperature-controlled flow reactor may be cylindrical or have another shape. The temperature-controlled flow reactor may be substantially vertical or horizontal. Preferably, the temperature-controlled flow reactor is substantially horizontal.

[0074] The walls of the temperature-controlled flow reactor may be selectively cooled by exposure to a cooling liquid such as water, liquid nitrogen, or liquid helium.

[0075] The temperature-controlled flow reactor may be adjusted to provide an axial temperature gradient. The axial gradient need not be uniform (e.g., stepped). The temperature of the temperature-controlled flow reactor may be controlled by resistive heating, plasma, or laser.

[0076] Preferably, the temperature in the temperature-controlled flow reactor is substantially parabolic.

[0077] The temperature range sufficient to generate particulate metal catalyst and to produce carbon nanotubes may range from at least 600°C to 1300°C.

[0078] The temperature-controlled flow reactor may be adapted to introduce reactants through injection nozzles, lances, probes, or multi-orifice injectors (eg, showerhead injectors).

[0079] Step (d) may be performed by mechanical, electrostatic or magnetic forces.

[0080] Step (e) may be performed mechanically, for example, step (e) may be performed on a rotating spindle or drum.

[0081] The process may further include cutting, chopping, shaping, twisting, flattening, stretching, spreading, aligning, bonding, heating, vibrating, or stiffening the freestanding non-woven carbon nanotube body.

[0082] The process may further include chemically modifying the freestanding non-woven carbon nanotube body.

[0083] The process may further comprise densifying the freestanding non-woven carbon nanotube body (e.g., by a factor ranging from 1.5 to 2.5). Densification is typically followed by air drying. Densification may be carried out in an organic liquid. Preferred organic liquids are acetone or methanol.

[0084] The process may further include coating the freestanding non-woven carbon nanotube body.

[0085] The electrical conductivity of the freestanding nonwoven carbon nanotubes is 10 3 S / m to 10 5 It is preferably in the range of 10,000 S / m to 80,000 S / m, and particularly preferably in the range of 10,000 S / m to 80,000 S / m.

[0086] By varying the time of step (e), the areal density of the freestanding non-woven carbon nanotubes may be varied.

[0087] The process may further include mechanically stretching the freestanding body of non-woven carbon nanotubes.

[0088] The average pore size of the non-woven carbon nanotube freestanding body is preferably in the range of 75 nm to 150 nm.

[0089] The pore size distribution of the non-woven carbon nanotube freestanding body is preferably within the range of 75 nm to 150 nm.

[0090] Step (e) may be performed on a bobbin, which may be covered with a porous insulating material to form a free-standing body of non-woven carbon nanotubes in the form of a stack (e.g., a double layer).

[0091] Viewed in a further aspect, the present invention provides an air treatment device comprising a filter as hereinbefore described.

[0092] The air treatment device may be for non-medical or medical use.

[0093] The air treatment device may be an air conditioner, an air purifier, an air humidifier, a ventilator, a respirator, a mask, a hood, or a breathing apparatus.

[0094] The filter may be movable through the airflow to be filtered. The filter may be in the form of a belt. The belt may be mounted on a number of rollers in a non-linear arrangement (e.g., a serpentine arrangement).

[0095] The airflow may be moved through a filter. For example, the air treatment device may further include a blower (e.g., a fan) to move the airflow through the filter. The airflow may be recirculated.

[0096] In the mask, the freestanding non-woven carbon nanotubes may be laminated (e.g., bi-layered). The layers of non-woven carbon nanotubes may be interdigitated. Multiple layers of non-woven carbon nanotubes may be interleaved with layers of porous insulating material.

[0097] In masks, the non-woven carbon nanotube freestanding bodies are typically hydrophilic.

[0098] In air conditioners, typically the non-woven carbon nanotube freestanding bodies are hydrophilic.

[0099] Viewed in yet a further aspect, the present invention provides the use of a free-standing non-woven carbon nanotube body as hereinbefore described, or a filter as hereinbefore described, in the separation of airborne viruses. [Brief explanation of the drawings]

[0100] The present invention will now be described in a non-limiting manner with reference to the accompanying figures. [Figure 1] 1 shows the filtration efficiency of a sheet of nonwoven CNT material. [Figure 2] 1 is a cross-sectional view of a first embodiment of a filter according to the present invention. [Figure 3] FIG. 2 is a cross-sectional view of a second embodiment of a filter according to the present invention. [Figure 4] FIG. 10 is a plan view of a third embodiment of a filter according to the present invention. [Figure 5]This paper describes a fourth embodiment of the present invention, a hybrid CNT filter. (a) An adapted direct spinning method using a collection bobbin covered with a polyester backing for in-situ fabrication of a hybrid CNT filter. (b) A diagram illustrating the hybrid CNT filter concept. The hybrid CNT filter can retain SARS-CoV-2 virus particles and aerosols containing them and actively sterilize them through resistive heating generated by applying an electric potential between two electrodes. (c) Photographs showing (i) an upper layer made from a micrometer-thin CNT mat, (ii) a lower layer made from porous polyester, and (iii) the microstructure of the hybrid CNT filter revealed by backlighting. [Figure 6] Permittance and filtration efficiency of CNT filters. (a) Permittance (blue circles, left axis) and penetration rate (red squares, right axis) as a function of areal density. The permeability trend line (blue) has a slope of -0.946, which is in good agreement with the theoretical value of -1. Penetration rate values ​​vary slightly with areal density, with only the 0.1 g m-2 material showing an increase related to microscopic defects. (b) Filtration efficiency as a function of particle size, showing that CNT filters (apart from the 0.1 g m-2 material) exhibit constant filtration efficiency across the entire particle range, without exhibiting a "U"-shaped profile. The filtration efficiency is comparable to that of H13-class HEPA filters. FFP3 mask materials exhibit the standard "U"-shaped behavior both experimentally (solid gray line) and theoretically (dotted gray line) at maximum penetration particle sizes (MPPS) in the hundreds of nanometer range. (c) SEM image showing the CNT filter surface after filtration of an aerosol of Ag nanoparticles (5–120 nm). Brownian motion allows efficient retention of even nanoparticles smaller than the visible pore size (scale bar, 500 nm). (d) SEM image showing polystyrene microbeads (2 μm) deposited on the filter surface. The microparticles are significantly larger than the filter pore size and are mechanically sieved (scale bar, 2 μm). Error bars indicate the standard deviation from at least three different samples. [Figure 7]Electrothermal behavior of the CNT filter. (a) Custom-made heating fixture used for electrothermal experiments. This design allowed for the use of CNT sample strips of various dimensions and ensured robust electrical contact at both ends. (b) Temperature rise (ΔT) as a function of areal power density shows a linear correlation over this temperature range. The slopes are 242.01 °C cm2 W-1 and 272.96 °C cm2 W-1 for the 7 g m-2 free-standing CNT filter and the 0.2 g m-2 polyester-backed hybrid CNT filter, respectively. The dotted-line outlined region encompasses 90% of the data points (±4.65 °C for the 0.2 g m-2 hybrid CNT filter and ±4.42 °C for the 7 g m-2 free-standing CNT filter). (c) The uniformity of the areal heating of the filter as shown by infrared images reveals a homogeneous pattern (inset). Histograms generated by pixel-by-pixel temperature analysis show a mean temperature value of 82°C with standard deviations of 3°C and 6°C for the 7 gm-2 free-standing CNT filter (red bar) and the 0.2 gm-2 hybrid CNT filter (blue bar), respectively. The 0.2 gm-2 hybrid CNT filter (dark red bar), set at a temperature of 130°C, is shown to be nowhere near 100°C. (d) Heating response time shows that it takes 3.54 ± 0.24 seconds to heat the 0.2 gm-2 hybrid CNT filter from 30°C to 70°C (red line), while it takes only 0.48 ± 0.24 seconds to do the same for the 7 gm-2 free-standing CNT filter (blue line). By increasing the set point to 130°C (dark red line), the 0.2 gm-2 hybrid CNT filter exhibits a response speed comparable to that exhibited by the 7 gm-2 free-standing CNT filter. [Figure 8]Virus infectivity due to heat exposure. Results show the residual infectivity level of animal coronaviruses on CNT mats heated to various temperatures or for different times. (a) 5 μL virus-containing droplets were heated for 90 seconds. Reference is based on the infectivity level of the stock solution. RT (room temperature) indicates the infectivity level of samples that were not subjected to active heating. Complete inactivation is observed when the CNT mat is heated to temperatures above 80°C. (b) 0.4 μL virus-containing droplets were heated to a temperature of 80°C. Complete inactivation is observed after 60 seconds. Error bars represent the standard deviation from at least three replicates. [Figure 9]Drying of droplets and aerosols on a heated CNT filter. (a) Images of evaporation of a 0.4 μL droplet on a CNT filter at T = 80 °C over time, τ, taken as the ratio of time to the complete evaporation time, tf. (Top row) Images show the "constant contact radius" (CCR) evaporation model with tf = 15 s and a 1 mm scale bar. (Middle row) Top view of FEM calculations of the droplet surface height, consistent with the experimental conditions. (Bottom row) Cross-sectional view of FEM results for the temperature profile droplet at tf = 19 s. (b) Plot of tf as a function of the initial droplet volume, V0 2 / 3 (corresponding to the initial droplet diameter on the secondary x-axis). The FEM results assume a contact angle of 70°; the upper and lower error bars represent contact angles of 100° and 30°, respectively. The experimental measurements (red circles) are consistent with the FEM results (black squares). The linear correlation (black dotted line) suggests that aerosols (≤5 μm) can evaporate with tf < 1, consistent with the analytical quasi-steady-state Hu and Wu model (Hu, D.; Wu, H. Volume Evolution of Small Sessile Droplets Evaporating in Stick-Slip Mode. Phys. Rev. E 2016, 93, 42805 (https: / / doi.org / 10.1103 / PhysRevE.93.042805)). The colored lines represent different surface concentrations based on filtration time (1 min, 5 min, 15 min, and 60 min are red, orange, blue, and turquoise, respectively). (c) Thermal behavior of the CNT filter as a function of aerosol load, with higher concentrations resulting in lower temperatures. (d) Plot of the measured temperature response of a 0.2 g m-2 hybrid CNT filter to a 5-second flash heating set at 130 °C. [Figure 10]Development and testing of an active filtration unit prototype. (a) Schematic diagram of the prototype unit setup. The prototype unit was placed in a sealed volume (8.7 m). NaCl nanocrystals (with a geometric mean diameter of 119 nm) were introduced into the chamber through a 20-jet impingement atomizer. The aerosol concentration was continuously measured using a condensation particle counter (CPC). (b) Photograph of the structure of the filtration module based on a 0.2 gm hybrid CNT filter. (c) Photograph of the internal components of the prototype unit. Ambient polluted air is sucked into the upper chamber by a centrifugal blower and blown downward into the internal volume of the filtration module. After passing through the outer filter, the air is purified by recycling back to the ambient. (d) Decay plots showing the rapid decay behavior recorded during active filtration at flow rates of 134 m3 hr-1 (blue) and 200 m3 hr-1 (red). It took approximately 15 and 11 minutes to reduce the contaminant number concentration to background using flow rates of 143 m3 hr-1 and 200 m3 hr-1, respectively. The experimental results (solid line) fit well with a theoretical model (dashed line) that accounts for the contaminant reduction rate in a thoroughly mixed, enclosed volume. The filtration reduction rate was separated from the measured overall reduction rate by normalizing it with the natural reduction rate (green line). [Figure 11] Face velocity versus pressure drop. Pressure drop was measured at various face velocities for three different CNT filters (0.1 g m-2, 0.2 g m-2, and 7 g m-2) and an H13 class HEPA filter. Data were collected from at least three samples. The dotted lines represent ±1 standard deviation of the linear regression slope. The slopes are 604.3 m3 hr-1 m-2 kPa-1, 458.1 m3 hr-1 m-2 kPa-1, 183.2 m3 hr-1 m-2 kPa-1, and 10.3 m3 hr-1 m-2 kPa-1 for the H13 HEPA filter, 0.1 g m-2 filter, 0.2 g m-2 filter, and 7 g m-2 filter, respectively. [Figure 12]Filtration efficiency test setup. Ag nanoparticles were generated by a custom particle generator and size-selected by nano-DMA (top). DOS droplets were generated by an impact atomizer and size-selected by AAC (bottom). The aerosol was passed through a CNT filter material mounted in a conductive goblet cassette and sandwiched between an O-ring and a SS mesh. The aerosol that passed through the filter was counted using a CPC. [Figure 13] Filtration efficiency for individual single fiber mechanisms. Individual microfiber filtration efficiency mechanisms (and overall efficiency) are shown by the black curves. Qualitatively show the single fiber efficiency for enhanced diffusion (blue curve) and blocking (red curve) for nanofibers (bundles of CNTs). [Figure 14] Heating response rate of the CNT filters. Heating rate of the dry 0.2 gm-2 and 7 gm-2 CNT filters (solid lines) and the 0.2 gm-2 and 7 gm-2 CNT filters (dotted lines) sprayed with approximately 5 μL of DIW. When coated with water, the response rate was much slower due to the evaporation of water and the heat capacity of the added water. [Figure 15] Percent survival of AAV9 virus due to heat treatment. Results showing the percent survival (relative to the control) of 0.4 μL AAV9-containing droplets heated to a temperature of 80°C on a CNT mat. Results were based on ELISA (gray) and qPCR (black) analysis. The control was based on the genome copies found in the stock solution. RT (room temperature) indicates the infection level of samples that did not undergo active heating. Complete inactivation is observed when the CNT mat is heated for 30 seconds. [Figure 16] Particle size distribution of NaCl aerosol. Size distribution of aerosol atomized in a closed volume. Data (circles) are based on the average of 10 runs. The fit (red line) shows that the geometric mean diameter and geometric standard deviation of the total number are 118.77 nm and 2.08 nm, respectively. [Figure 17]Aerosol reduction rates using different filter types. Reduction rates in a thoroughly mixed room using recirculating air filtration systems with H13 HEPA filters (dashed line), E11 HEPA filters (dotted line), and non-HEPA filters (solid line) with filtration efficiencies of 99.95%, 95%, and 80%, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0101] Example 1 The filtration efficiency of a sheet of nonwoven CNT material was measured and is shown in Figure 1. This revealed that filtration efficiency was high for aerosolized coronavirus-sized particles (which cause Covid-19), but was highly dependent on the face velocity at the filter surface.

[0102] Example 2 Figure 2 is a cross-sectional view of a first embodiment of a filter according to the invention, generally designated by the reference numeral 1. The filter 1 comprises a stack of CNT mats 2, in which individual mats 2a are arranged in an interdigitated pattern and alternate with layers 3 of thin porous insulating material. The filter 1 is in the form of a cartridge that can be mounted in a face mask. Airflow is indicated by double-headed arrows, and viruses are separated by the stack of CNT mats 2. The airflow restriction is proportional to the number of mats 2a and inversely proportional to the gas permeability of the CNTs and insulating layers 3 and the area of ​​each mat 2a and each insulating layer 3.

[0103] A voltage (DC, pulsed DC or low frequency AC) is applied by a voltage source V to inactivate viruses separated by the stack of CNT mats 2. The advantage of using a thin mat 2a and a thin layer 3 of porous insulating material is that the electric field strength (V / mm) across them is greater than the predetermined voltage. A separate sterilization station (using, for example, chlorine as a sterilizing agent) may be provided to allow for long and intense sterilization. Alternatively, a separate heater (e.g., a DC heater) may be provided to raise the temperature to a high temperature (e.g., 100°C).

[0104] The insulating layer 3 is preferably as thin as possible (to provide the highest field strength with the lowest applied voltage) and should have high gas permeability. Candidate materials include thin tissue paper and open-cell foam. Flammable materials require fire resistance, as they could be ignited by a spark (especially if the filter is damaged). As an example, medium-weight tissue paper is 200 μm thick to generate a field strength of 45,000 V / m at 9 V. The insulating layer 3 is preferably chemically resistant to sterilizing gases (e.g., chlorine) so that the filter 1 can be sterilized and reused.

[0105] The applied voltages are (roughly in order of increasing required power supply): a. Static DC voltage b. Periodically reversing DC voltage c. Fixed polarity pulse voltage d. Alternating polarity pulse voltage e. Low frequency (e.g., 50Hz to 500Hz) AC voltage f. AC voltage with higher frequency (e.g. 13.4MHz) It may be one or more of the following.

[0106] The power consumption of the single DC version is very low (probably determined by the degree to which condensation occurs on the insulating layer 3). This may not have a significant impact on indoor use, but could have a significant impact on cold outdoor use (e.g., for paramedics in an ambulance). RF versions are likely to be avoided in clinical environments due to the risk of interference with critical medical electronics. The filter (including the electronics that monitor its operation) can be expected to last a full shift on at least a standard 9V battery (6LR61), which is rechargeable. Supervision functions can include checking for battery voltage leakage current (for wet or contaminated filters), as well as time of use, time since last sterilization, and other safety and management functions. These can be automatically linked to a wireless control system that can record the ID and location of the user.

[0107] Example 3 Figure 3 is a cross-sectional view of a second embodiment of a filter according to the present invention, generally designated by the reference numeral 20. Filter 20 comprises a free-standing cylinder of CNT mats 21 that provides a large filtration area in a compact volume. The cylinder of CNT mats 21 is essentially a "rolled" version of the stack of CNT mats 2 shown in Figure 2. The cylinder of CNT mats 21 comprises individual mats 22a separated by thin layers 23 of porous insulating material.

[0108] Example 4 4 is a plan view of a third embodiment of a filter according to the present invention, generally designated by the reference numeral 41. Filter 41 comprises a CNT mat 42 in an electrical circuit with a voltage source V. Airflow is represented by arrows, and viruses are separated by CNT mat 42.

[0109] Example 5 - Polyester-backed hybrid CNT filter This example concerns a mass-produced air filter using a polyester-backed hybrid CNT mat. Filtration efficiencies are measured up to 99.999% and are available at low areal densities (0.1 gm -2 Ultra-thin mats of CNTs exhibited pressure drops comparable to those of commercially available HEPA filters. The conductive filters self-sterilized by resistive heating for a few seconds at temperatures above 80°C with a thermal flash. At these temperatures, complete inactivation of betacoronaviruses and adeno-associated viruses held on the surface was achieved. A filtration prototype unit (approximately 1.2 m thick) with CNT filter modules was used. 2 ) showed that a rate of 26 air changes per hour achieved 99% air purification in a room for 10 minutes.

[0110] Hybrid CNT mats were fabricated by adapting the floating catalyst CVD (FCCVD) process described in Li, YL; Kinloch, IA; Windle, AH. Direct Spinning of Carbon Nanotube Fibers from Chemical Vapor Deposition Synthesis. Science 2004, 304(5668), 276-278 (see http: / / doi.org / 10.1126 / sciencee.1094982). Testing showed that the air permeability followed a trend related to Darcy's law, while the filter had efficiency comparable to that of a HEPA filter, independent of thickness. In contrast to standard ultrafine fiber filters, no minimum filtration efficiency was detected for any particular particle size. Hybrid CNT filters have high air permeability, high capture efficiency, and low thermal mass. Thermal analysis demonstrated that the hybrid CNT filter can function as a first-order thermal element, and virus inactivation testing confirmed that viral inactivation could be achieved by instantaneous heat exposure. Modeling showed that the adsorbed aerosols easily dried upon application of power, thus achieving efficient energy management.

[0111] (Results and Discussion) Pressure drop Ultra-low areal density (<1gm -2A hybrid CNT mat (Figure 5b) was developed to have a robust structure with high gas permeability. CNT aerogels were spun onto a porous polyester backing (PET open-pore spunlace, NR Spuntech Inc.; see Figure 5) using a continuous, simple process. Upon collection, a thin CNT layer (a few hundred nanometers to a few micrometers thick, see Figure 5c) was constructed on a 0.4 mm-thick porous polyester backing (see Figure 5cii), forming a two-layer hybrid CNT mat (see Figure 5b). The hybrid CNT mat was designed to minimize airflow resistance while maintaining mechanical integrity, ease of operation, and high filtration efficiency. The CNT layer was thin enough to easily transmit light when a visible backlight was used to reveal the microstructure (see Figure 5ciii). An advantage of the synthesis and deposition process is that no post-processing is required, preserving the single-step nature of the process.

[0112] To evaluate the air permeability of the hybrid CNT filter, the pressure drop was measured and the laminar flow through the porous medium was calculated using Darcy's law.

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[0113] When the film thickness and pore length scales are comparable, the thickness of the CNT layer is essentially variable, but the areal density ρ s serves as a reliable surrogate for scaling. The intrinsic permeability of CNTs, in combination with areal density, bulk density, and kinematic viscosity, is a coefficient (filter permittance (k≡Kρ / μρ)) that directly relates to the pressure drop corresponding to the flow rate through the filter. s As expected, the permittance varied inversely with areal density, giving a power law fit with near-unit absolute values ​​(a = -0.95) (see Figure 6). The intrinsic permeability of the material varied for various areal densities (0.1 to approximately 14 gm-2 ) is very stable across samples (K = 6.01 × 10 -17 ±8×10 -19 m 2 ) Therefore, minimizing the thickness of the CNT layer provides a means to reduce the pressure drop for a given flow rate while maintaining filtration efficiency.

[0114] Filtration efficiency A wide range of CNT particle sizes (6-2500 nm) was selected to evaluate their filtration capabilities and find the so-called maximum passing particle size (MPPS). Solid Ag microparticles were used as sample aerosols with sizes ranging from 6 nm to 100 nm, and low-volatility dioctyl sebacate (DOS) oil droplets were used as test aerosols with sizes ranging from 300 nm to 2.5 μm. This range covers typical virus sizes (AAV approx. 20 nm to SARS-CoV-2 approx. 100 nm) to virus-containing aerosolized droplets (approx. 0.5 μm to >5 μm). As shown in Figure 6b, the CNT filter was able to filter a total of 0.2 gm of Ag. -2 At surface densities above 1000 nm, the filtration efficiency is high and nearly constant (>99.95%, the reciprocal of the transmittance) across the range of particle sizes. s ≧0.2gm -2 The CNT filter has an efficiency comparable to that of an H13 class HEPA filter. SEM images show the extremes of particle filtration, from diffusion collection of small particles (e.g., <100 nm, see Figure 6c) to blocking / sticking of larger sized particles (>1 μm, see Figure 6b). In contrast to what is typically observed with standard microfiber filtration media (see FFP3 mask in Figure 6b), which show a minimum in filtration efficiency at MPPS, the hybrid CNT filter does not show MPPS from diffusion to blocking filtration. The penetration values ​​remained constant even when the CNT filter was more than an order of magnitude "thinner." Surface density 0.1 gm -2 Only the thinnest material formed at 1000 nm showed a significant increase in penetration (see Figure 6b). At such low areal densities, imperfections in synthesis or processing can lead to microscopic defects in the CNT mat, causing a significant decrease in filtration efficiency.

[0115] The high filtration efficiency without obvious MPPS is a result of the hybrid CNT filter's nanostructure (i.e., bundles of several to several tens of CNTs), which is orders of magnitude smaller (10–50 nm) than the ultrafine fibers (0.8–20 μm) used in conventional filters. Conventional filtration curves, such as those for 3M FFP3 filter media (gray dotted line in Figure 6b), show a characteristic minimum filtration efficiency that tends to be 99.97% at 100–500 nm, depending on manufacturer requirements. In this size range, neither Brownian diffusion nor blocking by particles coming within one particle size of the filter fiber is sufficiently effective. Contrary to ultrafine fibers, the stiffness and surface area of ​​CNT filters are greater than conventional fibers, allowing for the overlap of blocking and diffusion modes of filtration (see Figure 13). This leads to a material that does not exhibit MPPS and whose filtration efficiency is entirely determined by the material's imperfections in its uniformity.

[0116] The filter quality factor is a common means of assessing the ratio of filtration efficiency to specific pressure drop,

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[0117] Effective CNT filter and initial reaction heater Because CNTs are electrically conductive, resistive heating can thermally denature captured pathogens, thereby inactivating viral components. To evaluate the heat dissipation ratio of hybrid and free-standing CNT mats, sample strips were mounted in a custom-made heating fixture (see Figure 7a) and analyzed using an infrared thermal camera. Because heat loss is roughly proportional to the surface area, the power dissipation per unit area can be compared at different areal densities and resistances. As can be seen in Figure 7b, the behavior of both mats differs significantly depending on the areal density of the mat (7 and 0.2 gm). -2 ) at 242℃cm 2 W -1 and 273°C cm 2 W -1 The linear dependence of ΔT on the applied power is linear for temperature increases of ΔT < 100°C, with a slope representing the heat-normalized power density. The linear dependence of ΔT on the applied power indicates that heat conduction and heat transfer dominate when the temperature difference between the filter surface and the environment is larger than the heat dissipation (∝ΔT 4 ), but the dominant mechanism of heat loss (∝ΔT 1 ) The higher normalized heat of the hybrid CNT mat suggests that it will lose slightly less heat than the free-standing CNT mat, mainly due to the insulating properties of the polyester backing and the reduced thermal conductivity of the thinner CNT layer. The sample strips used in the analysis are typically 4 Ω (7 gm -2 ) and 150Ω (0.2gm -2 ) and thereby maintains the surface temperature at 80°C. -2 and 0.2 gm -2 For the mat, voltages of 3 V and 16 V were used to generate currents of 0.75 A and 0.11 A, respectively. In most cases, the output was 0.20–0.25 Wcm. -2 It was found that power densities in the range of 100°C can reach and maintain temperatures of 80°C, which is higher than the 70°C required to inactivate viruses such as adeno-associated virus, hepatitis E virus, or SARS-CoV-2.

[0118] To assess the heating uniformity, infrared images were used, as summarized in Figure 7c. The inset shows infrared images of two sample strips at different average temperatures, with histograms showing the temperature per pixel (approximately 100 μm × 100 μm). At an average temperature of 82 °C, the heating uniformity was 7 g cm -2 and 0.2 gcm -2 The heating uniformity of thinner samples was determined by standard deviations of 3°C and 6°C, respectively. -1 K -1 This is due to the larger cross-sectional area of ​​the sintered body. A higher set temperature was also measured to eliminate the lower temperature regions. As can be seen in the dark red histogram, when the setting is adjusted to 130°C, the coldest point does not drop below 100°C.

[0119] The thermal response time provides an upper limit to how quickly the virus can be inactivated. The thermal response was assessed using frame-by-frame analysis of the average temperature on thermal video while heating the sample strips to various setpoints. As can be seen in Figure 7d, at a setpoint of 80 °C, both mats exhibited a thermal capacity of the composite (approximately 800 J kg -1 K -1 ) and low areal heat capacity (<6Jm -2 K -1 ) resulting in ultra-low areal density (0.2 to 7 gm -2 The filter's low heat capacity is preferred because it can reach temperatures sufficient to inactivate viruses with less power consumption, leading to fast and efficient flash sterilization. -2 It took 3.54±0.24 seconds to heat the hybrid CNT mat from 30°C to 70°C (red line), but it took 7 gm -2 The free-standing CNT mat took only 0.48 ± 0.24 seconds (blue line). The slower response of the hybrid CNT is due to the additional thermal inertia of the polyester (approximately a 10-fold increase). However, by increasing the set point to 130 °C (dark red line), the 0.2 gm-2 Hybrid CNT mat is 7gm -2 These results support the idea that by determining the correct heating parameters, a virus inactivation temperature of 70°C or higher can be achieved in less than 1 second, ensuring that heating time is not a limiting factor in the rate of virus inactivation.

[0120] Virus inactivation Cell infectivity tests were performed using a murine coronavirus (MHV-A59), a betacoronavirus (the same group as SARS-CoV-2 and SARS) that can be handled outside a containment level 3 laboratory. Initial experiments were performed to find the "inactivation temperature" at which the virus's infectivity significantly decreased. -2 The free-standing CNT mat was mounted on a heating fixture (see Figure 7a), and a 5 μL droplet containing viruses (concentration approximately 8 × 10) was placed on the mat. 7 infectious units mL -1 ) was pipetted onto the mat. Experiments were performed on a reference sample (a blue disposable lab coat), a control sample (0 V), and four additional samples at different voltages resulting in surface temperatures below 30 °C, 45 °C, 60 °C, and 80 °C (1.3, 2.0, 3.2, and 4.0 V, respectively). As depicted in the control column (0 V) in Figure 8a, the experimental protocol was sufficient to detect virus infectivity using samples obtained from the CNT mat. Even by applying low voltages, a clear decrease in virus infectivity was observed at temperatures below 70 °C (the normal inactivation temperature for SARS-CoV-2 and SARS viruses). This phenomenon suggests that direct surface oxidation may be an additional inactivation mechanism. At an applied potential of 4 V, a four-fold decrease in infectivity was measured down to the limit of detection (VOD). Complete inactivation of the virus at this voltage is the result of the droplets completely evaporating within 90 seconds and directly exposing the virus particles to the CNTs, whose surface temperatures are higher than 70 °C.

[0121] The next series of experiments was conducted to investigate the minimum time required to achieve total inactivation when a voltage of 4 V was applied. In these experiments, smaller virus-containing droplets (0.4 μL) were pipetted onto CNT strips while heating cycles were performed for 5, 10, 15, 30, 45, and 60 seconds. As can be seen in Figure 8b, despite not fully evaporating after 5 seconds, there was a clear decrease in infectivity due to surface oxidation, resulting in a loss of approximately 60% function from the initial viral load. Heating for 30 and 45 seconds resulted in droplet evaporation and significant loss of activity by approximately one order of magnitude. Heating for 60 seconds resulted in complete inactivation (LOD), likely a result of prolonged exposure to the inactivation temperature. Further virus inactivation experiments were performed with adeno-associated virus 9 (AAV9) using the method described above. Complete inactivation of AAV9 contained in a 0.2 μL droplet was achieved after 30 seconds of heating the CNT mat to 80° C. (See FIG. 15).

[0122] These results demonstrate that the resistive heating principle for self-disinfection of CNT filters is effective against SARS-CoV-2 and viruses from the same group. For experimental sensitivity, the droplets used in these experiments were loaded at very high concentrations, much higher than those estimated to be spread by humans. Therefore, in real-life applications, fewer pathogens would be contained, making disinfection to an acceptable level easier. Our results demonstrate that complete inactivation is achievable with millimeter-sized droplets. These droplets require significantly higher energy for evaporation compared with micrometer-sized aerosols (<5 μm). A more theoretical understanding of the kinetics of aerosol evaporation on CNT mats should provide insight into the timeframe required for complete evaporation and complete inactivation of virus-containing aerosols.

[0123] Drying of droplets and aerosols on heated CNT mats The evaporation process of a water droplet bound to a surface was studied using experimental and computational methods. A computational model simulated the diffusion-limited evaporation of a droplet on a heated CNT mat. The model was validated for droplets in a continuous format using optical micrographs of water droplets of a few millimeters to less than one millimeter evaporating on a heated CNT mat (see Figure 9a). Measurements showed that the area of ​​the droplet base remained unchanged for most of the time it evaporated. This suggests that the water droplet on the surface was not affected by the evaporation process. Picknett, RG; Bexon, R. The Evaporation of Sessile or Pendant Drops in Still Air. J. Colloid Interface Sci. 1977, 61(2), 336-350. https: / / doi.org / 10.1016 / 0021-9797(77)90396-4 ) suggests that the evaporation follows the "constant contact radius" (CCR) mode, which is further explained in

[14] . The CCR mode of evaporation is included in the model, which considers convection within the droplet and the diffusion of water vapor from the interface with the surrounding environment.

[0124] Figure 9a shows good agreement in time between the measured and modeled evaporation processes for the measured 0.4 μL water droplet. The small overestimation of the evaporation time for the model (19 s) compared to the experimental result (15 s) can be explained by modeling the uncertainty due to the lack of water penetration into the CNT mat. The agreement between experiment and theory for 0.1 μL, 0.4 μL, 1 μL, and 5 μL is visualized in Figure 9b, where the red circles (experimental) confirm the black squares (modeled). This result is consistent with the documented power-law time scaling for the CCR evaporation kinetics (evaporation time t f and the initial volume V0 is t f ∝V0 2 / 3(The relationship is based on the CCR power law (black dotted line). The evaporation time for microdroplets and nanodroplets is estimated to be less than a few milliseconds. These results agree well with the analytical quasi-steady-state model by Hu and Wu described above for evaporation of small droplets deposited under constant temperature conditions. The results derived for an interface temperature of approximately 70 °C lie between the 50 °C and 70 °C isotherm of Hu and Wu's model, depicted by the green line (Figure 9b). While the model required adjustment to better fit the present situation, where constant volumetric heat is generated by the CNT mat at a known rate, such agreement provides certainty for application.

[0125] After establishing the validity of the model, other parameters affecting evaporation time were evaluated. The filtration time, which directly affects the aerosol surface concentration, has a significant effect on evaporation time. As can be seen in Figure 9b, higher aerosol surface concentrations (represented by the red-to-orange, red-to-blue, and red-to-turquoise boxes) result in longer evaporation times, as the initial 5 μm diameter aerosol is reached in a few seconds. As depicted in Figure 9c, the simulations showed that the energy flow to each surface-bound droplet decreases as more droplets are captured by the CNT mat. This reduced energy flow results in lower droplet interfacial temperatures and longer evaporation times. However, as can be seen from the dynamic thermal behavior (Figure 7d) and shown in Figure 9b, even though the evaporation timescale is on the order of hundreds of milliseconds, all aerosol should be fully evaporated within 5 s of a 130 °C flash pulse (yellow region). Once all aerosols have completely evaporated, viral particles are directly exposed to surface temperatures above 80 °C, which have been shown to inactivate modeled viruses. These results suggest that viral inactivation can be achieved using a short pre-pulse, thereby ensuring high thermal efficiency of active filter systems. They also suggest appropriate timescales for optimization between flash heating intervals and pulse durations to balance energy consumption and viral inactivation of filters during use.

[0126] Performance evaluation of the prototype unit The ability to produce CNT mats in large quantities enabled the construction of a prototype unit with a full-scale hybrid CNT filtration module that fits into a conventional recirculation filter unit. As shown in Figure 10a, the prototype unit was designed to draw in ambient air using a centrifugal blower (RG175 / 2000, ebm-papst UK) and direct the air outward through a cylindrical filter module. The filtered air was then recycled back into the ambient air, reducing the concentration of airborne particles and droplets in the environment. As shown in Figure 10b, the filtration module was constructed with a cylindrical stainless steel mesh approximately 1.2 m thick, with the CNT layer facing inward to provide mechanical support. 2 0.2gm -2 The hybrid CNT mat was fabricated by attaching a filtration unit to the module (see Figure 10c). As shown in Figure 10a, the filtration unit was attached to the module at a sufficient concentration (approximately 3 × 10) to serve as a model aerosol. 5 #cm -3 After introducing NaCl nanocrystals, the particle efficiency decreased with the enclosed volume (approximately 8.0 m 3 The nanocrystal aggregate geometric mean diameter was adjusted to approximately 120 nm (Figure 16) to match the typical MPPS of the filter media, thereby representing the sample aerosols of most interest (approximating the size of the SARS-CoV-2 pathogen). To evaluate the efficiency of purifying enclosed environments, two flow rates (143 m) were used, corresponding to 16 and 23 air changes per hour (ACH) of the internal volume, consistent with current guidelines for isolation rooms (>12 ACH). 3 hr -1 and 200m 3 hr -1) was used to operate the prototype unit. The rate of reduction of suspended particles was monitored using a concentration particle counter. To properly separate the reduction rate due to functioning filtration from the overall rate, the natural reduction rate (caused by leakage, diffusion losses) was subtracted from the overall reduction rate. Figure 10d shows a characteristic rapid reduction. Filtration alone reduces the background level (approximately 6.5 × 10 3 #cm -3 ) to reduce the number concentration of pollutants to 143 m 3 hr -1 and 200m 3 hr -1 Using a flow rate of 1000 m / s, it took approximately 15 and 11 minutes, respectively. By extrapolation of the green line, the natural decay should be similar within approximately 350 minutes. The experimental results (solid line) agreed well with the theoretical model (dotted line), which assumes that the suspended particles are well mixed within the enclosed volume (see Equation S9). The slight deviations were due to very low particle concentrations (<3 × 10) caused by small leakage from the surrounding environment into the enclosed volume. 2 #cm -3 These overall results demonstrate the promising application of hybrid CNT mats in full-scale filtration systems.

[0127] (Conclusion) The results show that the active virus hybrid CNT filter exhibits excellent filtration efficiency (HEPA H13 level) while maintaining low pressure drop. The filter can be flash-heated to 130°C within a few seconds to inactivate all viruses. The large filtration module (approximately 1.2 m) incorporated into the prototype unit 2 They showed that equipping a ventilated air conditioner with a filter can reduce air pollution by a factor of ten within minutes. Deployed in poorly ventilated or crowded environments (e.g., offices, public transport, leisure and entertainment venues), such units could have a significant impact on combating the spread of airborne viruses, such as COVID-19 and seasonal influenza, which have imposed a collective social burden of $87.1 billion in the United States alone.

[0128] (Measurement method) Filtration efficiency and SEM images Filtration efficiency tests were performed on disk-shaped samples (d = 25 mm) inserted into conductive blank cassettes (Sure cassette blanks, SKC). The conductive enclosure was essential to minimize electrostatic losses, especially for particles smaller than approximately 50 nm. To ensure a robust mounting and circumferential seal, the disk samples were sandwiched between a stainless steel mesh support and a silicone rubber O-ring (OD = 25 mm; ID = 20 mm). Tests were performed using particles with mobility diameters ranging from 6 to 2500 nm. Tests performed within the 6 to 100 nm range used Ag nanoparticles generated by a custom-built particle generator, which produces silver vapor that later condenses back into nanoparticles. The silver was present in a quartz sample tube mounted in a dedicated furnace. The generator was heated to a temperature range of 1280–1320 °C and operated under a nitrogen flow of 2.2–2.5 standard liters per minute (slpm; HEPA-filtered, BOC). Ag nanoparticles were sorted into nearly monodisperse mobility diameters of 6 nm, 10 nm, 15 nm, 25 nm, 50 nm, 75 nm, and 100 nm using a differential mobility analyzer (DMA) with a 3085 DMA column and a 3080 electrostatic classifier. Analyses performed in the 100–2500 nm range used dioctyl sebacate (DOS, Sigma-Aldrich, purity ≥90%) aerosol droplets produced with a single-jet impingement nebulizer (CH Technologies) operating at 0.5–1 slpm of nitrogen flow. DOS droplets were sorted into nearly monodisperse mobility diameters of 300 nm, 500 nm, 1000 nm, and 2500 nm using an aerodynamic aerosol classifier (AAC). Because the AAC uses the particle's aerodynamic diameter to classify particles, a proper conversion from aerodynamic diameter to mobility diameter was required (see below), as shown in Equation S6. The Ag particle concentrations and DOS particle concentrations downstream of the cassettes were analyzed with TSI Ultrafine Condensation Particle Counters (UCPC) 3025A and 3776, respectively (see Figure 12). Particle concentration measurements were performed for each selected size in a specific order: (1) an empty cassette run used as a blank test; (2) a cassette run with a polyester backing (for hybrid filters); and (3) a cassette run with the designated CNT filter.Each measurement was repeated on three different samples through a 0.3 slpm nitrogen flow filtration cassette. Filtration efficiency was calculated using the following equation:

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[0129] Two CNT filter mats were prepared for SEM imaging. The first was prepared by collecting aerosolized Ag nanoparticles (size range: 5-120 nm) for 45 minutes. The second was generated by using 10 μL droplets of 2 μm aqueous suspension polystyrene beads (Merck) diluted 1:100 with deionized water (DIW). The droplets were air-dried at ambient temperature. The filter surfaces were imaged using a MIRA3 field emission gun SEM (Tescan). Imaging was performed at a working distance of 3-5 mm using an ET SE detector at an accelerating voltage of 1 kV (polystyrene beads) and an In-Beam SE detector at an accelerating voltage of 5 kV (Ag nanoparticles). No conductive layer was added.

[0130] (filter pressure drop) Filter pressure drop tests were performed using the same disk-shaped samples and cassettes described above. The volumetric flow rate was controlled from 0.1 slpm to 6 slpm using a mass flow controller (Alicat), and suction was provided by a scroll vacuum pump (nXDS, Edwards). The pressure drop across the filter was measured using a differential pressure manometer (HD750, Extech Instruments) connected to the inlet and outlet of the cassette. All measurements were corrected by subtracting the inherent pressure drop of an empty filter cartridge.

[0131] (Electrothermal analysis) Electrothermal analysis of freestanding and hybrid CNT mats was performed using a FLIR T650 infrared camera (640 × 480 px resolution, 7.5–14 μm spectral sensitivity, 24 mm f / 1.0 optics) and a custom-built heating fixture. The fixture consisted of a sample holder with two adjustable, parallel brass rod electrodes capable of clamping samples of different sizes (75–120 mm in length and up to 50 mm in width) (Figure 7a). The electrodes were connected to the terminals of a DC power source (EX2020R, AIM-TTI instruments). To minimize the effects of forced convection due to occasional air currents, the fixture was placed in a deep glass container without using any fans or blowers near the ongoing experiment.

[0132] Temperature versus power measurements were recorded by manually adjusting the voltage applied to a 75 × 10 mm CNT sample strip, while the camera's built-in software measured the average temperature of a 420 × 55 pixel square. At each setpoint, current was recorded directly from the power supply console. The voltage step size and maximum voltage depended on the sample's resistance (which is inversely proportional to its areal density). Each experiment was repeated on at least three different samples. Still images collected during the heating experiments were used to assess sample heating uniformity using both "FLIR Tools" software for qualitative visual inspection and a custom MatLab script for pixel-by-pixel quantitative analysis (code included in the SI Appendix) to export pixel temperature information from the images.

[0133] Dynamic heating and cooling of the samples were characterized by recording thermal videos while manually switching the power source on and off. The voltage was selected so that the sample reached a stable temperature of approximately 80 °C (or 130 °C). A Matlab script (SI Appendix) was used to extract the average temperature of the sample (of a 420 px × 55 px crop of the frame) and the timestamp of each frame of the video. For each case, results from a minimum of 10 heating (and cooling, if relevant) cycles were averaged to obtain replicate results.

[0134] (Virus heat inactivation and infectivity testing) Tests were performed with a surrogate murine coronavirus (MHV-A59), a betacoronavirus in the same group as SARS and SARS-CoV-2. The dedicated host cells were grown for a week and plated in 96-well plates. 1 mL aliquots of medium were prepared for elution. 7 gm -2 The CNT strip was attached to a dedicated heating fixture (Fig. 7a). Approximately 8 × 10 CNTs were placed in a protein-rich solution with a volume of 5 μL or 0.2 μL. 7 infectious units mL -1 Droplets containing concentrations of (TCID50) were pipetted along the strip (four drops total). The droplets were left to rest for a short time to allow natural absorption. The CNT strips were heated for 90 seconds at various temperatures (RT, 30°C, 45°C, 60°C, 80°C) or at 80°C for various heating times (0, 5, 10, 15, 30, 45, 60 seconds) (for 0.2 μL droplets). Control experiments were performed in blue disposable lab coats (which do not absorb water). The CNT strips were divided into four parts, transferred to elution tubes, vortexed for 10 seconds, and left to stand until titration. Eight 10-fold dilutions of each biological replicate were performed in medium containing dextran. The medium in the 96-well plates containing the cells was replaced with medium containing 2% FCS and DEAE dextran (to promote infection). 50 μL of virus dilution was transferred to four rows of a 96-well plate containing cells. Cells were cultured at 37°C and 5% CO for 3–5 days. Plates were scored for cytopathic effect (CPE).

[0135] (Droplet evaporation - experiments and modeling) Experiment to visualize the evaporation process of droplets 110 x 40 mm, 7 gm -2 The test was performed on a CNT sample of 0.255 Wcm. The sample was placed on the strip heating fixture described above with a gauge length of 75 mm. -2The sample was heated to an average temperature of 80 °C by applying a voltage of 4.35 V, passing a current of 1.76 A, equivalent to an areal power density of 1000 kJ / cm². DIW droplets were pipetted onto the surface at volumes of 0.1 μL, 0.4 μL, 1 μL, and 5 μL. Each evaporation test was repeated at least three times. Images and videos of droplet evaporation were captured using a Dino-Lite AM4113T USB microscope (AnMo Electronics Corporation) at a magnification of ×45. Image analysis was performed using Dino-Lite software.

[0136] A computational model was developed using COMSOL Multiphysics (version 5.5) to simulate the diffusion-limited evaporation of a water droplet on a CNT mat. The model employed a 2D axisymmetric geometry that circulated a cylindrical domain containing the CNT mat, the water droplet, and the surrounding air. To reduce the influence of evaporation on the surrounding conditions, the total height of the domain was 1600 times the height of the droplet, which was kept constant at 25 °C and 60% relative humidity. To match the relative length scales used during the experiments, the radius of the domain was 40 times the base radius of a 0.4 μL droplet, unless otherwise specified. Further details about other simulation parameters, along with the rate-limiting physics and boundary conditions used in the simulation, are provided in the Supporting Information below (see Section 5).

[0137] (Performance evaluation of a CNT filter-based prototype) The filtration unit was installed in a 8 m² volume, made of Plexiglas and interconnected with a Rexroth frame (BOSCH). 3A background scan of the particle concentration in the chamber was performed before each measurement. A 20-jet impingement nebulizer (CH Technologies) was placed on the floor of the chamber and filled with 20% w / w NaCl (>99.7%, Fisher Scientific) in DIW solution (volume 300 mL). Nitrogen (HEPA filtered, BOC) was delivered to the nebulizer through an MFC at a flow rate of 37 slpm, atomizing the solution and filling the chamber with NaCl nanoparticles with an aggregate mean diameter and geometric standard deviation of 118.77 nm and 2.08 nm, respectively (see Figure 16). Filtration experiments were performed at a flow rate of 143 m 3 hr -1 and 200m 3 hr -1 Experiments were performed without any active filtration to determine the natural rate of decline. After a two-minute aerosolization period, the flow rate to the nebulizer was stopped and the filter unit was turned on. Each experiment was repeated at least three times. All particle concentration measurements were performed using a TSI-UCPC Model 3776.

[0138] ( Supplementary information ) 1. Pressure drop The Darcy behavior of the CNT filter was evaluated by comparing the pressure drop across the CNT filter with flow rates of 0.1 slpm, 0.3 slpm, 0.5 slpm, 1.0 slpm, 1.5 slpm, 3 slpm, and 6 slpm, with a surface area of ​​3.14 × 10 -4 m 2 The correlation between the face velocity through the CNT filter and the surface velocity normalized by the 20 mm disc diameter was evaluated. According to Darcy's law and Equation 1 (see above), there should be a linear correlation between them, and indeed such behavior was observed at 0.1 gm -2 , 0.2gm -2 and 7gm -2 The slopes of these trend lines (0.1 gm) are plotted in Figure 11 for the 0.1 gm sample. -2 of sample, 0.2 gm -2 of sample and 7gm -2 For each sample, 458.1 m 3 hr -1 m-2 kPa -1 , 183.2m 3 hr -1 m -2 kPa -1 and 10.3 m 3 hr -1 m -2 kPa -1 ) is the permittance value (k) as defined in the text. The variance in pressure drop for each filter type across the three different samples is small. This results in a small standard deviation in the permittance values, which is graphed as the dotted line. The method was to generate these trend lines and evaluate their slopes, which was then used to calculate the permittance values ​​for all samples. As a reference, a commercial class H13 HEPA filter (Camfil) was examined. As can be seen in Figure 11, the permittance (slope) of the commercial filter was calculated to be 604.3 m 3 hr -1 m -2 kPa -1 "These results demonstrate that with further optimization, it is possible to create a hybrid CNT filter that retains the filtration efficiency of HEPA but does not result in a higher pressure drop. This would allow filtration system manufacturers to utilize the original design and simply replace commercially available HEPA filters with hybrid CNT filters."

[0139] The specific air permeability K of CNTs can be calculated using the linear equation shown below:

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[0140] 2. Filtration efficiency Nanoparticle size selection is most commonly performed by selecting a property known as mobility (B), which is related to the particle diameter.

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[0141] Also, the aerodynamic diameter (d a Modern techniques have also been developed to classify particles by a property known as a density of 1000 kg / m that has the same settling velocity as the particle in question. 3 Since a large, low-density particle can have the same settling velocity as a smaller, denser particle, it follows that the d a includes the density as well as the physical dimensions of the particle. From Hinds, W.C.A. Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles; Wiley, 1999, the settling velocity (V TS ) can be used to relate a particle's aerodynamic diameter to its mobility diameter:

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[0142] To select particles sized at or above 100 nm that are nearly monodisperse, an aerosol classifier (AAC) was used in this study. Because the AAC selects by aerodynamic diameter, these diameters were converted to mobility diameters so that results such as filtration efficiency could be directly linked to results using DMA. For example, a mobility diameter of 2500 nm corresponds to a DOS particle (ρ = 914 kg / m 3 ), the equivalent aerodynamic diameter was calculated to be 2387 nm. The AAC was then programmed to select particles with a mobility (and physical) diameter of 2500 nm, allowing classification of particles with a mobility (and physical) diameter of 2500 nm. Under the test conditions, the two dominant filtration mechanisms were interception and diffusion. The former occurs when particles follow the gas flow passing less than a particle radius from the filter fibers, contacting and retaining the particles. Diffusion filtration occurs when particles diverge from the gas flow within the filter and contact the filter media via Brownian motion. Interception naturally captures larger particles most efficiently, since they rarely follow the flow unless they come within a particle radius of any filter fiber. Conversely, diffusion can capture smaller particles efficiently, since smaller particles move faster than larger particles via Brownian motion. Therefore, small particles can easily diverge from the flow and come into contact with nearby filter media. Conventional filters exhibit a characteristic minimum filtration efficiency between 100 and 500 nm (Figure 13). Within this size range, neither the diffusion nor the cutoff curves overlap, resulting in a "U"-shaped profile of the overall filtration efficiency curve, with a minimum located at the so-called maximum particle passing size (MPPS). However, a unique feature of CNT networks compared to conventional filter media is the orders of magnitude smaller diameter of the fibers (i.e., bundles of approximately 10 CNTs). Because the surface area of ​​the fibers is so large, even relatively large particles can be captured by diffusion (blue CNT diffusion curve). Similarly, the gaps and spaces between fibers are smaller than in conventional filters, so particles must be very small to avoid capture by cutoff (red CNT cutoff curve). This is a rather peculiar behavior of filtration efficiency—there is no size range where the mechanism is significantly ineffective, and the characteristic U-shaped profile of filtration efficiency is not observed.

[0143] 3. electrothermal analysis To better demonstrate the effectiveness of the CNT filter as a fast-response heating element, which efficiently uses resistive heating to evaluate the collected aerosols rather than heating the filter material, a series of additional experiments were performed. In these experiments, a CNT strip (75 × 10 cm) mounted in a heating fixture (Figure 7) was sprayed with approximately 5 μL of deionized water (DIW) at room temperature using an airbrush (Gocheer). The strip (0.2 gm -2 and 7gm -2 ) was heated to a set point of 80°C (as described above) and the evaporation process was thermally recorded. A time-lapse analysis was performed (as described above) to measure the time it took for the sample to reach the endpoint temperature, as shown in Figure 14. -2 For the free-standing CNT filter, the heating time from 30 to 75°C increased ten-fold (from 0.48 to 4.98 seconds) relative to the "dry" material, and the heating time for the 0.2 gm filter under the same parameters increased ten-fold (from 0.48 to 4.98 seconds). -2 The resistance heating energy was increased by a factor of two for the hybrid CNT filter, indicating that due to the low thermal inertia of the CNT filter, most of the resistive heating energy is not wasted by heating the backing or water coating the surface, rather than heating the CNT layer itself.

[0144] 4. Virus inactivation Additional virus inactivation studies were performed with the AAV9 virus serotype. AAV9 was chosen because it is considered a stable virus (see Bennett, A.; Patel, S.; Mietzsch, M.; Jose, A.; Lins-Austin, B.; Jennifer, C.Y.; Bothner, B.; McKenna, R.; Agbandje-McKenna, M. Thermal Stability as a Determinant of AAV Serotype Identity. Mol. Ther. Clin. Dev. 2017, 6, 171-182). The AAV9-CMV-eGFP (Vector Biolabs) virus stock was inactivated at a stock concentration of 6.3 × 10 13 A 0.2 μL drop of AAV9 solution was added to 7 gm -2 Pipette 2 µL of volume onto the CNT strips, totaling 1.26 x 10 11 Each CNT strip contained 100 genome copies (GC). The strips were mounted in a custom-made heating fixture (Figure 7a) and heated to 80°C (minimum temperature) for 0 s (room temperature, RT), 30 s, 60 s, and 90 s. Each sample was run in triplicate. The area of ​​the strip containing the droplet was excised and placed in a 15 mL centrifuge tube containing 5 mL of FreeStyle 293 medium. A control medium containing 2 μL of AAV9 stock solution was prepared at a dilution ratio of 1:1000. All aliquots were stored at -80°C prior to analysis. AAV virus titer was performed using an AAV Real-Time PCR Titer Kit (Takara Cat#6233) according to the kit instructions, and intact AAV9 was quantified using an AAV Titer ELISA (ProGen Cat#PRAAV9). As can be seen in Figure 15, removal of AAV9 from CNT strips was achievable using the method described above, and complete inactivation of AAV9 was achieved already after 30 seconds of heating, as verified by both qPCR and ELISA.

[0145] 5. Drying of droplets and aerosols on heated CNT mats A computational model was developed to simulate the diffusion-limited evaporation of water droplets on a CNT mat. It was first validated with experimental results of droplet drying and used to predict typical drying times of aerosol droplets. A simplified pseudo-steady-state analytical model under isothermal conditions was also used to validate the results (see Hu and Wu, above).

[0146] COMSOL Model Features Computational simulations were performed using the commercially available software COMSOL Multiphysics. The model employed a 2D axisymmetric geometry that circulated into a cylindrical domain containing the CNT mat, a water droplet, and surrounding air. To reduce the influence of ambient conditions, the total height of the domain was 1,600 times the droplet height and was kept constant at 25 °C and 60% relative humidity. To match the relative length scales used during the experiments, the radius of the domain was 40 times the base radius of the 0.4 μL droplet, unless otherwise specified.

[0147] Volume density is approximately 500 kgm -3 That is, 7gm -2 The CNT filter sample is estimated to be 10 μm thick. The specific heat capacity is 800 JK. -1 kg -1 (Masarapu, C.; Henry, LL; Wei, B. Specific Heat of Aligned Multiwalled Carbon Nanotubes. Nanotechnology 2005, 16(9), 1490-1494. ( https: / / doi.org / 10.1088 / 0957-4484 / 16 / 9 / 013 )), the in-plane and out-of-plane thermal conductivities are 130 Wm -1 K -1 and 0.11Wm -1 K -1(Zhang, X.; Tan, W.; Smail, F.; Volder, M. De; Fleck, N.; Boies, A. 2018, 29(36), 365708. (See http: / / doi.org / 10.1088 / 1361-6528 / aacd7b).

[0148] Assumptions We assumed that the droplets are small enough to ignore the effects of gravity and maintain a constant contact radius and spherical cap shape throughout the evaporation time. A moving mesh method was used to model the geometric deformation of the gas-liquid interface by assuming an average value of the surface moisture flux. We also assumed that curvature, Stefan flow, and velocity effects are negligible (see Semenov, S.; Starov, V.M.; Rubio, R.G.; Velarde, M.G. Computer Simulations of Evaporation of Pinned Sessile Droplets: Influence of Kinetic Effects. Langmuir 2012, 28(43), 15203-15211). The model incorporates evaporative cooling and Marangoni convection driven by the temperature gradient at the gas-liquid interface.

[0149] Adjusting physical properties and boundary conditions No-slip and no-flux boundary conditions were applied at both the liquid-solid and gas-solid interfaces, and the incompressible Navier-Stokes equations were used to model the flow in both liquid phases. Diffusion-limited transport of water vapor away from the liquid-gas interface was described by a transport equation for low-concentration species in the air domain. The moisture content was set to ambient conditions at the top and radial region boundaries. A no-flux boundary condition was applied at the gas-solid interface, and the gas-liquid interface was assumed to be in vapor-liquid equilibrium. The heat transfer equation was applied to all three phases. The top and radial region boundaries were set to a fixed temperature. The bottom region boundary was subject to natural convection with a length scale of 40 mm, the width of the mat used in the experiment. Both sides of the mat released heat by radiation, with emissivity measured in units of . The CNT mat was supplied with input power, and the value of the input power was determined so that the steady-state temperature reached 80 °C without evaporation, consistent with the results shown in Figure 7d.

[0150] Simulation of evaporation time as a function of aerosol droplet surface concentration In addition to the base case model above, the effect of the surface concentration of aerosol droplets was also studied. Assuming that the filter captures all incoming droplets and that no evaporation occurs outside of the active thermal cycle, the surface concentration of aerosol droplets at the start of active heating can be derived under "worst case" conditions. In other words, the evaporation time required in this situation is a reliable estimate.

[0151] The normal experimental operating conditions are a flow rate (Q) of 120 m 3 h -1 and total area (A) 1.235m 2 The droplet concentration in the air (c) was calculated as 1 cm 3 We assumed a particle size of 1 particle per 1000 m2, which is the upper limit of the aerosol concentration produced by talking and coughing people (Johnson et al. Modality of Human Expired Aerosol Size Distributions. J. Aerosol Sci. 2011, 42(12), 839-851. (https: / / doi.org / https: / / doi.org / 10.1016 / j.jaerosci.2011.07.009)).h ) was chosen to be 1, 5, 15, or 60 min. When converted into an input parameter of the model, the surface concentration was determined by the length scale (R S ) by using the average area per droplet, a single droplet simulation can represent the total evaporation time required to dry the filter after each collection cycle. At higher surface concentrations, each droplet occupies a smaller area, and therefore less power is used for evaporation. The results are shown in Table S1.

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[0152] 6. Performance evaluation of a prototype filtration unit A 20-jet impingement atomizer filled with 20% w / w NaCl (>99.7%, Fisher Scientific) dissolved in DIW solution was placed in a closed test volume (8.0 m 3 ) was used to generate model aerosols in the atmosphere. To analyze the size distribution of the NaCl nanocrystals, in situ particle measurements were performed using a TSI Smart Mobility Particle Sizer 3080 (SMPS) system, which includes a TSI Ultrafine Condensation Particle Counter 3776 (UCPC) and a TSI Differential Mobility Analyzer 3085 (DMA). Figure 16 shows the average of 10 collected size distribution data (circles), which, when fitted (line), indicate a total particle concentration of 6.39 x 10 5 cm -3 The aggregate geometric mean diameter and geometric standard deviation (CMD) were 118.77 nm and 2.08 nm, respectively. The CMD closely matches the size of a single SARS-CoV-2 virus particle, making it more realistic for studies aimed at assessing the system's ability to prevent COVID-19 transmission.

[0153] To better understand the behavior of the filtration system, a basic numerical model was developed to solve for the aerosol attenuation rate within a confined volume. The model assumes a completely sealed and perfectly mixed room relative to the environment. Based on this, Equation S8:

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[0154] Due to the nature of air recirculation filtration systems, the filters do not require extremely high filtration performance compared to single-pass based units (i.e., personal masks or process gas supply lines). The use of the above model allowed for a sensitivity analysis of how filtration efficiency affects contaminant reduction over time. The ACH value used in this simulation (22.99 hr -1 ) is the flow rate (200m) used to test the basic prototype unit. 3 hr -1 ) and room size (8.0m 3 ) As can be seen in Figure 17, the time it took for the H13 HEPA filter (green dashed line) to purify the room to 99% was less than 10% faster compared to the lower grade E11 HEPA filter (blue dotted line). Using a non-HEPA filter (red line) increases this time by only 25%.

Claims

1. The framework and a free-standing body of non-woven carbon nanotubes mounted on or within a framework; and a means for inactivating the virus, A filter capable of separating airborne viruses, wherein the means for inactivating the viruses comprises an electric field generator for generating an electric field within the freestanding nonwoven carbon nanotube body, and inactivates the viruses by resistive heating.

2. 10. The filter of claim 1, wherein the electric field generator is an AC power source.

3. 3. The filter of claim 1, wherein the freestanding non-woven carbon nanotube body is a single layer of non-woven carbon nanotubes.

4. 4. The filter according to claim 1, wherein the non-woven carbon nanotube free-standing body is a laminate.

5. 5. The filter of claim 4, wherein the laminate is a bilayer.

6. 6. The filter of claim 5, wherein the bilayer is a layer of non-woven carbon nanotubes and a layer of porous insulating material.

7. 7. The filter of claim 6, wherein the porous insulating material is polyester.

8. The surface density of the nonwoven carbon nanotube freestanding body is 0.1 gm －２ From 14gm －２ 8. The filter of claim 1, wherein the .lambda.

9. An air treatment device comprising a filter according to any one of claims 1 to 8.

10. 10. The air treatment device of claim 9, which is an air conditioner, an air purifier, an air humidifier, a ventilator, a ventilation system, a respirator, a mask, or a breathing apparatus.

11. 11. Use of a free-standing non-woven carbon nanotube body according to any one of claims 1 to 10 or a filter according to any one of claims 1 to 10 in separating airborne viruses.

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