Filter media and systems using the same

Abstract

In some examples, a method of making a filter includes heating a metal substrate to precipitate a first phase from a metal alloy on a surface of the metal substrate, the metal substrate defining a plurality of pores configured to allow a gas to pass through the pores. The metal substrate is a metal alloy comprising a first metal and a second metal. The method further includes growing a plurality of carbon nanotubes (CNTs) on the surface of the first metal of the first phase, and the CNTs are configured to capture at least one particle.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to filtration systems. BACKGROUND

[0002] Filters can be constructed of fibers or porous materials and can remove particulates in a gas stream, such as air, passing through the filter. Particulate matter, including dust, hair, allergens, pathogens, and the like, larger than the pores of the filter can be trapped by the filter media. The efficiency of the filter to remove particulate matter depends on the size of the particulate matter, the pore size and / or pore size distribution of the filter media, and the velocity of the gas flow. SUMMARY

[0003] In some examples, the present disclosure describes a method of making a filter, the method comprising: heating a metal substrate to precipitate a first phase from a metal alloy on a surface of the metal substrate, wherein the metal substrate defines a plurality of pores configured to allow a gas to pass through the pores, wherein the metal substrate comprises a metal alloy, wherein the metal alloy comprises a first metal and a second metal; and growing a plurality of carbon nanotubes (CNTs) on a surface of the first metal of the first phase, wherein the CNTs are configured to capture at least one particle.

[0004] In some examples, the present disclosure describes a filter, the filter comprising: a metal substrate defining a plurality of pores configured to allow a gas to pass through the pores, the metal substrate comprising a metal alloy, the metal alloy comprising a first metal and a second metal; and a plurality of carbon nanotubes (CNTs) grown on a surface of a first phase of the metal substrate, the plurality of CNTs configured to capture at least one particle contained in the gas passing through the metal substrate.

[0005] In some examples, the present disclosure describes a method of detecting a pathogen, the method comprising: capturing, via a filter, a pathogen from a volume of gas flowing through the filter, the filter comprising: a metal substrate defining a plurality of pores configured to allow a gas to pass through the pores, the metal substrate comprising a metal alloy, the metal alloy comprising a first metal and a second metal; and a plurality of carbon nanotubes on a surface of a first phase of the metal substrate, the plurality of carbon nanotubes configured to capture the pathogen; and detecting, via a detector, at least one pathogen captured by the filter.

[0006] In some examples, the present disclosure describes a system for detecting a pathogen, the system comprising: a housing comprising: an inlet configured to allow a gas to enter a conduit, the conduit being in fluid communication with the inlet and configured to define a flow path of the gas within the housing; and an outlet in fluid communication with the conduit and configured to allow the gas to exit the housing; a filter in fluid communication with the conduit and configured to capture the pathogen, the filter comprising: a metal substrate defining a plurality of pores configured to allow the gas to pass through the pores, the metal substrate comprising a metal alloy comprising a first metal and a second metal; and a plurality of carbon nanotubes (CNTs) located on a surface of a first phase of the metal substrate, the plurality of CNTs being configured to capture the virus; and a sensor configured to detect the virus captured by the filter.

[0007] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0008] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

[0009] Figure 1 FIG. 1 is an illustration of an example system showing detection of particles in pressurized air of a cabin of an aircraft using an example carbon nanotube (CNT) filter in accordance with examples of the present disclosure.

[0010] Figure 2 FIG. 2 is an illustration of an example sensor including an example CNT filter in accordance with examples of the present disclosure.

[0011] Figure 3 FIG. 3 is a flowchart of an example method of detecting particles using an example CNT filter in accordance with examples of the present disclosure.

[0012] Figure 4 FIG. 4 is a perspective view of a portion of an example CNT filter in accordance with examples of the present disclosure.

[0013] Figure 5 FIG. 5 is a magnified perspective view of a portion of an example CNT filter substrate prior to CNT growth in accordance with examples of the present disclosure.

[0014] Figure 6 FIG. 6 is a magnified perspective view of a portion of an example CNT filter showing a plurality of CNTs grown on the CNT filter substrate in accordance with examples of the present disclosure.

[0015] Figure 7is a flowchart of an example method of making an example CNT filter in accordance with examples of the present disclosure.

[0016] Figure 8 is a perspective view of an example 3D metal open-cell foam CNT filter in accordance with examples of the present disclosure.

[0017] Figures 9A to 9H shows an example two-dimensional (2D) metal mesh CNT filter in accordance with examples of the present disclosure.

[0018] Figures 10A to 10F is a perspective view of an example three-dimensional (3D) metal open-cell foam CNT filter in accordance with examples of the present disclosure.

[0019] Figures 11A to 11D is a perspective view of an example 2D metal open-cell foam CNT filter in accordance with examples of the present disclosure. DETAILED DESCRIPTION

[0020] In some examples, the present disclosure relates to filters and systems for detecting particles captured by the filters. As described below, example filters can include a metal substrate, such as a two-dimensional (2D) metal mesh substrate, a 2D metal open-cell foam, or a three-dimensional (3D) metal open-cell foam substrate, that includes a plurality of CNTs on a surface of the metal substrate. The metal substrate can be formed of a metal alloy. The metal substrate can be heated to precipitate out or otherwise cause a plurality of phases to be formed from the metal alloy. The phases formed by the heating can be used as one or more sites on the metal substrate at which CNTs can be grown, captured, or otherwise attached, such as chemical vapor deposition (CVD) or other suitable methods for growing and / or attaching CNTs. The metal substrate of the filter can have a pore size large enough to allow a gas, such as air, to pass through the filter without a significant pressure drop, and the CNTs can be patterned, sized, and have a pore and / or interstitial size configured to capture particulate matter, such as dust, hair, allergens, pathogens, such as bacteria and viruses, and the like.

[0021] Examples of the filter can be used in a sensor system configured to determine a presence and / or amount of particles (e.g., viruses) captured on the filter. For example, a presence and / or amount of viruses captured by the filter can be detected via Raman spectroscopy. As described below, the metal substrate can be formed such that the CNTs grown on the metal substrate can be subjected to heating of the metal substrate, and the metal substrate can be heated to destroy the particles captured by the filter. For example, the metal substrate can be heated (e.g., periodically) in order to destroy the captured particles, e.g., to clean the filter.

[0022] In some examples, the system can substantially remove particles, such as organic matter, bacterial particles, viral particles, etc., from a volume of gas via filtration using a filter. For example, a volume of gas can be recirculated through a filter, and a metal substrate can be heated to destroy particles captured by the filter and substantially remove the particles from the volume of gas.

[0023] As the Covid-19 virus has caused significant disruption in many industries, such as commercial aviation, there is a need for means to detect the likelihood of infection at the individual level and at the level of an enclosed space, such as a cabin of an aircraft or the interior of a building. Detecting infected people before boarding an aircraft or entering a building, and detecting air contamination during a flight or while someone is in a building, can go a long way toward establishing confidence that it is safe to travel by air, visit a restaurant, and public buildings, etc.

[0024] In examples, CNTs can be used to filter viruses, e.g., to capture viruses, and Raman spectroscopy can be used to detect the captured viruses. In some examples, a sensor can include a CNT filter and a sensor for testing an individual and / or a volume of gas. For example, the CNT filter and sensor can be housed in a hand-held device. A person can breathe into the device, and if a signature of one or more viruses is detected, the device operator will be informed.

[0025] As such, the CNT filter and sensor can be located in an air management system, such as a building heating, ventilation, and air conditioning (HVAC) system, a vehicle cabin air management system, an environmental control system (ECS), etc. A pump can draw a controlled air flow through the filter, taking an aliquot from the full air flow. The presence and / or amount of one or more viruses captured by the filter element in the air flow can be analyzed periodically or continuously, e.g., via filtration and detection. The titer of the one or more viruses can be determined based on the detection of the one or more viruses. In some examples, the relative risk of viral exposure for an individual exposed to air managed by the air management system (e.g., a passenger in flight, an occupant in a building, etc.) can be determined based on the detection of the one or more viruses. Information related to the virus detection can be communicated in real-time to, e.g., a building manager or security personnel, local emergency responders (police and / or fire departments), an airline, an appropriate agency such as an airport or the Federal Aviation Administration, etc. Appropriate measures can be taken to reduce further exposure and spread of the virus, e.g., evacuation of a building and further testing of occupants, quarantine and further testing of flight passengers upon arrival, diversion of a flight to a more suitable airport, etc.

[0026] In some CNT technologies, CNTs can be grown and / or deposited on catalysts. For example, iron nanoparticles can be CNT catalysts and can be deposited onto the surface of a support structure (e.g., a substrate) and can be sites of growth and / or deposition of CNTs. However, nanoparticles can have associated health and safety risks. For example, nanoparticle catalysts can not have sufficient adhesion to the substrate such that the nanoparticle catalysts and CNTs can separate from the substrate. Separation of nanoparticle catalysts from the substrate can be exacerbated by heating the substrate.

[0027] In some examples, a CNT filter can be formed by forming growth sites on a substrate that can be integral with the substrate itself. For example, a CNT filter can be formed by forming a phase of a metal alloy that includes a catalytic metal of an alloy, forming CNT growth sites as integral parts of the metal alloy substrate structure, and etching the phase to expose the catalytic metal. Such a CNT filter can significantly reduce separation of catalysts and / or CNTs, thereby reducing health and safety risks associated with CNTs separating from a substrate. Additionally, such a filter can reduce health and safety risks by depositing CNTs using a solid metal substrate (such as a mesh and / or open-cell foam) rather than using nanoparticles that are bound to a metal substrate.

[0028] For example, a CNT filter can be constructed using a nickel-aluminum alloy, Alloy 10, or any other suitable metal. In some examples, a solid solution alloy can be etched to remove aluminum, leaving a highly active nickel surface that can be suitable for catalyzing carbon nanotube growth, such as during CVD coating in a hydrocarbon vacuum atmosphere at high temperature. Nickel has corrosion resistance and the advantage of forming a more superior bond with carbon nanotubes than iron. In some examples, a cobalt alloy can be used instead of a nickel alloy. Additionally, the superior bonding / attachment of CNTs to nickel and / or cobalt enables heating of the mesh without debonding the CNTs, for example, heating the metal substrate in order to destroy particles, such as viruses, captured by the filter.

[0029] Figure 1 FIG. 1 is an illustration of an example system 100 that detects particles in pressurized air of a cabin 102 of an aircraft using an example CNT filter in accordance with examples of the present disclosure. The cabin 102 includes an interior environment that houses occupants. Although the illustrated example shows an aircraft cabin and an aircraft ECS, the system 100 can be used with any volume and air or gas management system, such as a building and a building HVAC system. Further, the system 100 can be used in a device with or without an air or gas management system, for example, as a handheld device described further below. For example, a user, such as an aircraft passenger, can breathe into the device housing system 100 and be alerted if particles, such as pathogens, are detected. In some examples, a handheld device that includes the system 100 can be used as a screening device, such as before boarding an aircraft or entering a building.

[0030] The system 100 includes an environmental control system (ECS) 104. The ECS 104 is configured to supply clean, pressurized air to the cabin 102. The ECS 104 includes at least one source of pressurized air 106. The source of pressurized air 106 is configured to generate pressurized air for use in the cabin 102. For example, when the aircraft is on the ground, the air pressure outside the aircraft can be similar or identical to the air pressure within the cabin 102. However, once the air is at a higher altitude, the air pressure outside the aircraft can be significantly lower than the air pressure required for the cabin 102, such that the source of pressurized air 106 can supply pressurized air to the cabin 102. The source of pressurized air 106 can include a variety of air sources, including but not limited to a bleed air source (e.g., one or more compression stages of a gas turbine engine), a load compressor (e.g., directly driven by an auxiliary power unit), a standalone source of pressurized air as a cabin air compressor (e.g., driven by electrical power from an auxiliary power unit), or any other air source capable of supplying air at a sufficiently high pressure to pressurize the cabin 102. The ECS 104 includes at least one air conditioning pack 108. In the process of compressing air, the source of pressurized air 106 can heat the air to a relatively high temperature that is not suitable for direct discharge into the cabin 102. The air conditioning pack 108 is configured to receive pressurized air from the source of pressurized air 106 and cool the pressurized air. Further, the air conditioning pack 108 can include air filtration and / or gas contaminant removal systems.

[0031] The system 100 includes at least one particulate sensor 110. The particulate sensor 110 is configured to detect the presence and / or amount of one or more particulates contained within a gas flowing into or out of the cabin 102. The particulate sensor 110 can be configured to detect the concentration of gas contaminants, such as viruses, at different altitudes or flight levels during flight and / or when the aircraft is on the ground. Generally, the particulate sensor 110 can be constructed and / or positioned at any location sufficient to provide an accurate representation of the amount of one or more particulates in the cabin 102. In some examples, the particulate sensor 110 includes a CNT filter including a metal substrate defining a plurality of pores and / or interstices and a plurality of CNT positioned on the metal substrate configured to capture particulates, such as viruses. For example, the particulate sensor 110 can include a CNT filter including a metal substrate containing a metal alloy of, for example, nickel and aluminum. The plurality of CNT can be grown on a surface of a first phase of the metal substrate and configured to capture particulates contained in a gas passing through the pores of the metal substrate, for example, based on particle size.

[0032] The system 100 includes a controller 114. The controller 114 is communicatively coupled to the particle sensor 110 and the ECS 104, and can be configured to receive signals related to particle detection from the particle sensor 110 and send control signals to one or more systems of the ECS 104, such as the pressurized air source 106 and / or the air conditioning pack 108. The controller 114 can include any of a wide variety of devices, including a processor, such as one or more microprocessors, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), or any other equivalent integrated or discrete logic circuitry, as well as any combination of such components, servers, desktop computers, notebook (i.e., laptop) computers, tablets, and the like.

[0033] The controller 114 is configured to control the ECS 104 to maintain adequate conditions within the interior environment of the cabin 102, such as required for personal comfort or legal or industry standards. For example, the controller 114 can be configured to control the pressure, temperature, humidity, air flow rate, or other environmental conditions of the cabin 102 under various aircraft conditions, such as ground operations, passenger load, takeoff, cruise, descent, and landing. The controller 114 can be configured to control the ECS 104 to supply clean, pressurized air to the cabin 102.

[0034] The controller 114 is configured to receive particle detection data from the particle sensor 110. The controller 114 can determine the presence and / or amount of particles based on the detection data including a concentration tolerance of the particle sensor 110. The controller 114 can be configured to determine whether the detected contaminant particles in the cabin 102 exceed a concentration threshold. The concentration threshold can correspond to a maximum allowable particle concentration for a particular contaminant. The controller 114 can be configured to generate an alert and / or an alert signal based on the detection of particles and / or based on the detection of particle concentration exceeding the concentration threshold.

[0035] In response to determining that the particle concentration detection exceeds the particle concentration threshold, the controller 114 can be configured to control one or more contaminant removal systems, e.g., via the air conditioning pack 108. For example, in response to determining that a viral concentration of a virus exceeds a virus threshold in the cabin, the controller 114 can cause cabin air to be recirculated through a contaminant removal system.

[0036] Figure 2 FIG. 1 is a diagram illustrating an example system 100 according to examples of the present disclosure. In the illustrated example, the system 100 includes a cabin 102, a particle sensor 110, an ECS 104, and a controller 114.

[0037] In the illustrated example, the housing 202 can include a filter 204, a sensor 206, a gas conduit 208, a valve 210, a pump 212, a controller 214, an interface 216, and a connector 218. The housing 202 can provide structure for mounting and positioning the filter 204, the sensor 206, the gas conduit 208, and other components of the sensor 200. In the illustrated example, the housing 202 can include a gas inlet 222 and a gas outlet 224, which can be configured to be in fluid communication with a volume of gas. The pump 212 can be configured to move gas through the gas conduit 208. In some examples, the pump 212 can be configured to stop the flow of gas during detection (e.g., by the sensor 206) of particles captured by the filter 204. In some examples, detection of particles captured by the filter 204 can occur while gas is flowing within the gas conduit 208. In the illustrated example, the housing 202 is configured to provide a flow path for gas, e.g., via the gas inlet 222, the gas conduit 208, and the gas outlet 224. The valve 210 can be configured to close or shut off fluid communication between the gas inlet 222 and the conduit 208. In some examples, the valve 210 can be located at any location along the flow path defined by the conduit 208, e.g., before or after the pump 212, and before or after the filter 204. In some examples, the valve 208 can define the gas inlet 222 or the gas outlet 224, and in some examples, the housing 202 can include more than one valve 210, e.g., an inlet valve and an outlet valve that can define the gas inlet 222 and the gas outlet 224, respectively.

[0038] The housing 202 can be configured to house and protect components of the particle sensor 200. For example, the particle sensor 200 can be operated on a vehicle, such as an automotive vehicle and an aircraft, a watercraft, etc., or can be included in a handheld device. The housing 202 can be configured to maintain alignment of measurement geometries, such as the sensor 206 and the filter 204, during particle detection under adverse environmental conditions, such as vehicle operating conditions, e.g., during takeoff, landing, and flight of an aircraft, and during handling conditions, such as accidental dropping of a handheld device that includes the particle sensor 200. Adverse environmental conditions can include flight environmental conditions. For example, adverse environmental conditions can include any vibrations, such as vibrations associated with takeoff, landing, and flight of an aircraft, or vibrations associated with an automotive vehicle or a watercraft.

[0039] The filter 204 can be a CNT filter including a metal substrate defining a plurality of pores and / or porosities and a plurality of CNTs positioned on the metal substrate that are configured to capture particles, such as viruses. For example, the filter 204 can include a metal substrate comprising a metal alloy of, for example, nickel and aluminum. The plurality of CNTs can be grown on a surface of a first phase of the metal substrate and configured to capture particles contained in a gas passing through the pores of the metal substrate, for example, based on particle size. As used herein with respect to the metal alloy phase, “first” and “second” are used in a nominal sense to facilitate reference to two different phases, and not to refer to a primary phase and a secondary phase of the metal alloy. In some examples, the filter 204 can be substantially similar to one or both of the filters 400 and 800 shown and described below with respect to FIGS. 4A-4B. Figures 4 to 11D

[0040] The sensor 206 can be configured to detect a presence and / or an amount of particles captured by the filter 204. In some examples, the sensor 206 can be a Raman spectrometer configured to illuminate the filter 204 and determine a presence and / or an amount of particles based on characteristics of the particles contained in a received light signal. In some examples, any suitable sensor or sensing method can be used to determine a presence and / or an amount of particles captured by the filter 204.

[0041] The controller 214 can be an electronic controller including processing circuitry. For example, the controller 214 can include a processor and / or other processing circuitry and computer-readable storage media encoded with instructions for causing the valve 210 to open and close, for causing the pump 212 to move gas through the conduit 208, for causing the sensor 206 to perform measurements to detect particles captured by the filter 204, for causing the metal substrate of the filter 204 to be heated so as to destroy particles captured by the filter 204, and / or for communicating with external devices via the interface 216. In some examples, the controller 214 can be connected to the interface 216. The interface 216 can be configured to enable communication between the controller 214 and external devices, for example, via any suitable wired or wireless communication. The particle sensor 200 can include a connector 218. The connector 218 can be configured as a communication connector, for example, a wired communication connection, and / or a connector for receiving power. The particle sensor 200 can receive power via any suitable wired or wireless technology.

[0042] ​In some examples, the particulate sensor 200 can be a handheld device. For example, a user, such as an aircraft passenger, can breathe into the particulate sensor 200 through the inlet 222. The controller 214 can be configured to open the valve 210 when a person breathes into the inlet 222. In other examples, a user and / or operator can press a button or otherwise mechanically cause the valve 210 to open when breathing into the inlet 222. The pump 212 can move the user’s breath through the conduit 208, or the pump 212 can be omitted and the user’s exhalation can move the user’s breath through the conduit 208, the filter 204, and the outlet 224. If particulates are detected, such as described below, the user and / or operator can be alerted.

[0043] The controller 214 can be configured to determine a presence and / or amount of particulates captured by the filter 204 based on one or more measurements performed by the sensor 206. In some examples, an external device can determine a presence and / or amount of particulates captured by the filter 204 based on one or more measurements performed by the sensor 206, such as via signals corresponding to the one or more measurements sent to the external device via the interface 216.

[0044] Figure 3 is a flowchart of an example method of detecting particulates according to the techniques of this disclosure. While the method 300 is described with respect to the particulate sensor 200, in other examples, the method 300 can be used with other sensors.

[0045] The controller 214 can cause the valve 210 to open and the pump 212 to cause a gas, such as air, to move through the conduit 208 to draw the gas in through the inlet 222 and out through the outlet 224, thereby collecting a sample of a portion of the gas in fluid communication with the gas inlet 222 by causing the gas to move through the filter 204 (302).

[0046] The filter 204 can capture particulates, such as pathogens, from the gas flowing through the conduit 208 (304). For example, the filter 204 can include a metal substrate, such as a 2D metal mesh or a 3D metal open-cell foam, configured to allow the gas to pass through the pores of the mesh or foam without a substantial pressure drop across the filter 204. The filter 204 can include a plurality of CNTs grown on a surface of the metal substrate and configured to capture particulates, for example, based on size.

[0047] The controller 214 can cause the sensor 206 to detect particles captured by the filter 204 (306). For example, the sensor 206 can be a Raman spectrometer configured to illuminate the filter 204 based on characteristics of particles contained in a received light signal and determine a presence and / or amount of the particles. For example, the sensor 206 can illuminate the filter 204 with a substantially monochromatic laser. The light can interact with one or more particles of one or more particle types captured by the filter 204. For example, the laser can interact with molecular vibrations, phonons, or other excitations of the one or more particles, resulting in inelastic scattering (e.g., Raman scattering) of the laser and a shift in energy (e.g., and frequency) of the inelastically scattered laser. The shift in energy provides information about vibrational modes of the one or more captured particles, and can provide a “structural fingerprint” of the captured particles such that different types of particles can be identified and distinguished based on detected Raman scattering. For example, an amount of scattered light as a function of wavelength can be detected, e.g., a spectrum of the scattered light can be detected via a spectrometer. Spectra of different types of particles can produce different spectral features in a spectrum captured by a detector of the Raman spectrometer. Based on the particle type, the spectrum can have peaks and valleys (e.g., large or small amounts of light at particular wavelengths and / or wavelength bands). In some examples, particles can be distinguished by their spectral differences, including peaks and valleys at different wavelengths, peaks and valleys with different full-width-at-half-maximum (FWHM) or half-width-at-half-maximum (HWHM) peak widths, different amounts of light at one and / or more same wavelengths and / or energy levels, etc. In some examples, viruses can be distinguished from other pathogens, particles, or other viruses based on spectral differences due to Raman shifts caused by different proteins of the virus.

[0048] In some examples, the controller 214 can cause the sensor 206 to detect particles at a particular point, location, region, area, position, etc. of the filter 204. In some examples, the controller 214 can cause the sensor 206 to detect particles at multiple points, locations, regions, areas, positions, etc. of the filter 204, e.g., in order to spatially “scan” the filter 204 to detect particles. In some examples, the controller 214 can cause the sensor 206 to detect particles at one or more locations on the filter 204 multiple times. For example, the controller 214 can cause the sensor 206 to detect particles at one or more locations on the filter 204 at 100 times / second (e.g., 100 hertz (Hz), 10 Hz, 1 Hz, once / minute, once / ten minutes, once / hour, once / day, or at any other detection rate).

[0049] In some examples, the controller 214 and / or the external device can determine the presence and / or amount of particles captured by the filter 204 based on one or more measurements performed by the sensor 206 (e.g., one or more light spectra of one or more particles detected by the sensor 206). In some examples, the controller 214 and / or the external device can qualitatively determine the amount of particles. For example, the controller 214 can determine whether the amount of particles captured by the filter 204 at a first time is greater than and / or less than the amount of particles captured by the filter 204 at a second time based on one or more light spectra detected at the first time and one or more light spectra detected at the second time.

[0050] In some examples, the controller 214 and / or the external device can compare peaks and valleys of detected light spectra to a threshold value, and can determine and record the light spectra as a positive or negative value with respect to the presence of particles. In some examples, the controller 214 and / or the external device can use such threshold values to determine whether individual points, locations, regions, zones, positions, etc. of a scan of the filter 204 contain particles. In other words, based on the detected light spectra, the controller 214 and / or the external device can determine a spatial image of the presence and / or amount of particles captured by the filter 204. In some examples, the controller 214 and / or the external device can determine a particle load, a particle flux, a filtration rate of particles, etc. based on the spatial image of the presence and / or amount of particles captured by the filter 204 based on the detected light spectra.

[0051] In some examples, any suitable sensor or sensing method can be used to determine the presence and / or amount of particles captured by the filter 204, and the controller 214 and / or the external device can determine the presence and / or amount of particles captured by the filter 204 by any suitable method.

[0052] In some examples, the particles can include dust, hair, allergens, pathogens, etc. For example, the particles that can be captured by the filter 204 and detected by the sensor 206 can include pathogens, such as bacteria, viruses, or any microorganism that can cause disease. In some examples, the particles can include a pathogen, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), for example, a coronavirus that causes coronavirus disease 2019 (COVID-19) or any other coronavirus.

[0053] After the sensor 206 detects the presence and / or amount of particles, the controller 214 can cause the metal substrate of the filter 204 to heat in order to destroy the particles, e.g., pathogens, captured by the filter 204 (308). For example, the filter 204 can be connected to a power source, and the controller 214 can cause the power source to apply a voltage and / or current to the metal substrate of the filter 204 to resistively or joule heat the metal substrate to destroy the captured particles. Unlike a catalyst deposited on a surface of a substrate, because the CNTs of the filter 204 can grow on catalyst sites that are part of a metal alloy, the CNTs and catalyst can be heated without the CNTs detaching, e.g., the CNTs can remain attached during heating in order to destroy the captured particles. In some examples, the metal substrate and / or CNTs can be heated to at least about 60 degrees Celsius (°C), or at least about 150 °C, or about 200 °C, or at least about 250 °C. In some examples, the metal substrate and / or CNTs can be heated to a temperature and for an amount of time in order to destroy the particles without initiating oxidation of the carbon of the CNTs. In other words, the metal substrate can be heated to a high enough temperature and for a time sufficient to destroy the particles, but not heated to a low enough temperature and for a time sufficient to avoid and / or reduce oxidation of the CNTs. In some examples, heating the metal substrate in order to destroy the particles can “clean” the filter 204, e.g., enable subsequent detection of the presence and / or amount of particles. For example, the controller 214 can cause the pump 212 to remove the gas from the conduit 208, and can cause the valve 210 to close so that gas does not flow through the filter 204. The metal substrate of the filter 204 can be heated in order to destroy the particle or particles captured by the virus. The controller 214 can then cause the method 300 to repeat to obtain a second detection of the particles.

[0054] In some examples, destroying the particles via heating the metal substrate can inactivate, kill, denature, or degrade the particles. Generally, heating the metal substrate to a higher temperature can inactivate, kill, denature, or degrade the particles in a shorter period of time. For example, biological macromolecules can denature in a temperature range of 50 °C to 100 °C, which can be reversible, and can take a long time to “kill” a biological pathogen. Biological macromolecules can begin to degrade at 150 °C to 200 °C, e.g., a biological macromolecule can completely change a chemical into a simpler and / or more stable organic in a very short time. The products of the degraded macromolecule can be gaseous, like methane, hydrogen, or can remain on the filter 204 as a simpler stable solid, like sugar. In some examples, if the metal substrate is heated in order to denature and / or degrade a biological pathogen, the Raman peaks associated with the biological pathogen can disappear from the detected spectrum.

[0055] In some examples, heating the metal substrate to destroy the particles can "clean" a volume of gas, e.g., reduce and / or remove an amount of particles in a volume of gas. For example, the controller 214 can cause the metal substrate to be heated to destroy particles (e.g., pathogens) captured by the filter 204 while causing the pump 212 to cause gas in a volume of gas to flow through the conduit 208. In some examples, the heating and gas flow can be continuous, and the gas can be circulated through the conduit 208. In some examples, the sensor 206 can continuously detect the presence and / or amount of particles captured by the filter 204, where the filter 204 can be at any temperature. In other words, the filter 204 can capture and destroy particles while the sensor 206 continuously detects, e.g., monitors, the presence and / or amount of particles captured by the filter 204. In some examples, the sensor 206 can detect the presence and / or amount of particles captured by the filter 204 over a period of time, and the sensor 206, or the controller 214, or an external device, can determine an amount of particles in a volume of gas based on the presence and / or amount of particles detected over the period of time.

[0056] Figures 4 to 6 Different views of an exemplary CNT filter 400 are shown at different magnifications and at different steps in the process of making the CNT filter 400. The CNT filter 400 is shown relative to Figures 4 to 6 are described.

[0057] Figure 4 is a perspective view of a portion of an exemplary CNT filter 400 according to an example of the present disclosure. The CNT filter 400 includes a metal substrate 402 having a plurality of pores 404 (only a single pore is labeled in the figure). Figure 4

[0058] In some examples, the metal substrate 402 can be formed of an alloy including at least a first metal and a second metal. For example, the metal substrate 402 can be formed of a metal alloy including a nickel-based alloy or a superalloy, such as a nickel-aluminum (NiAl) alloy. Suitable alloys can include, but are not limited to, Alloy 10, Inconel 718, Inconel 713LC, MAR 247, MAR 246, MAR 200, PWA 1480, PWA 1484, Rene N4, B1900, Inconel 625, a cobalt-aluminum alloy, a cobalt-iron alloy, any superalloy that can precipitate nickel, aluminum, or titanium gamma prime phases through heat treatment, or any other suitable metal alloy. In some examples, a suitable alloy can be a nickel or cobalt-based alloy including at least 3% aluminum.

[0059] ​As described below, the alloy of the metal substrate 402 can be selected such that the first phase precipitates out of the second phase of the alloy in a spatial pattern. The metal substrate 402 can be further selected such that the first phase can be etched (e.g., via chemical etching) to remove alloy elements and / or metals and leave "islands" of different alloy elements and / or metals in the spatial pattern, which can serve as growth sites for CNTs.

[0060] In the illustrated example, the metal substrate 402 can be referred to as a 2D metal mesh, which allows air to pass through the holes 404. In some examples, the metal substrate 402 can be a 3D metal open-cell foam, such as Figure 8 As illustrated. In some examples, the CNT filter 400 can be substantially similar to the CNT filter 204, and the size of the holes 404 can be set such that the CNT filter 400 does not cause a significant pressure drop in air flow (e.g., air) through the holes 404. For example, the metal substrate 402 can have a density of at least 5, a density of at least 9, a density of at least 20, a density of at least 30, a density of at least 40, or any other density. In some examples, the "strands," "fibers," "struts," etc. can have an effective diameter of at least 0.5 mm, an effective diameter of at least 0.75 mm, an effective diameter of at least 1.0 mm, an effective diameter of at least 2.0 mm, an effective diameter of at least 3.0 mm, or any other effective diameter. In some examples, the holes 404 can have an effective diameter of at least 0.1 mm, an effective diameter of at least 0.3 mm, an effective diameter of at least 0.6 mm, an effective diameter of at least 0.8 mm, an effective diameter of at least 1.0 mm, an effective diameter of at least 2.0 mm, an effective diameter of at least 3.0 mm, or any other effective diameter.

[0061] In some examples, the metal substrate 402 formed as a 2D metal mesh can be formed by laser cutting, stamping, or any other suitable method. In some examples, the metal substrate 402 formed as a 3D metal open-cell foam can be formed by reticulated foam coating, lost polymer casting, adding a foaming agent to a slurry of metal powder and sintering, or by any other suitable method.

[0062] Figure 5 is a magnified perspective view of a portion of the surface of an exemplary CNT filter 400 metal substrate 402 prior to CNT growth according to an example of the present disclosure. Figure 5A plurality of first phase regions 502 of a metal alloy, including, for example, a metal base 402 of the metal alloy precipitated out of the metal alloy by heating the metal alloy. As shown, the first phase regions 502 form discrete "islands" on a surface of the metal alloy base 402, which are surrounded by a second phase 504, for example, in a spatial pattern 506. For example, the metal base 402 can be a nickel-aluminum alloy (e.g., a Ni-Al superalloy). The composition of the alloy can be selected such that, when the alloy base is heated, a γ' phase can precipitate out of the alloy. As used herein with respect to phases of a metal alloy, "first" and "second" are used in a nominal sense to facilitate reference to two different phases, and not to refer to a primary phase and a secondary phase of the metal alloy.

[0063] As described below, in some examples, the metal base 402 can be etched after heating. For example, the metal base 402 can be chemically etched to remove aluminum from the first phase regions 502 (e.g., γ' phase regions) of the spatial pattern 506, leaving a high activity nickel surface in the spatial pattern 506 to catalyze growth of CNTs.

[0064] In some examples, the spatial pattern 506 dictates characteristics of CNT growth. For example, the size, shape, and spacing of the spatial pattern 506 can dictate the size, shape, length, and distribution of CNTs grown on the spatial pattern 506. In some examples, the spatial pattern can include a distribution of sizes, shapes, and spacings. For example, the spatial pattern 506 can include a plurality of first phase regions 502 that are approximately rectangular, and the spacing between the first phase regions 502 can be about 10 nm to about 500 nm. In some examples, the spacing between the first phase regions 502 can dictate, for example, the spacing or separation between CNTs at an early stage of CNT growth, while the growth is columnar.

[0065] The first phase regions 502 can include a distribution of sizes, for example, one or both of the lengths of the first phase regions 502 can be about 10 nm to about 2 μΜ. In some examples, the planar distribution of the first phase regions 502 can include at least 50% of the surface area of the metal base 402. The planar distribution of the first phase regions 502 can include at least 75% of the surface area of the metal base 402, the planar distribution of the first phase regions 502 can include at least 95% of the surface area of the metal base 402, or any other surface area of the metal base 402. In some examples, the CNT filter 400 can include other sizes and ranges of sizes of the first phase regions 502, and other spacings and ranges of spacings between the first phase regions 502.

[0066] The first phase regions 502 can include nickel or cobalt. For example, the first phase regions 502 can be nickel aluminide, such as Ni3Al. In some examples, the first phase regions 502 can include at least 70 percent by weight (wt.%) of nickel, at least 86 wt.% of nickel, at least 90 wt.% of nickel, or any other wt.% of nickel.

[0067] In some examples, the second phase 504 can be a solid solution of nickel and other elements in an alloy. For example, the second phase 504 can be a nickel-aluminum or cobalt-aluminum composition that is different from the first phase regions 502.

[0068] Figure 6 is a magnified perspective view of a portion of an example CNT filter 400 according to examples of the present disclosure, showing a plurality of CNTs 602 grown on a metal base 402 of the CNT filter 400. In some examples, the size, density, and spatial distribution of the CNTs correspond to the shape, size, and spacing distribution of the spatial pattern 506 of the first phase regions 502. In some examples, the CNTs 602 include a plurality of CNT pores, such as spacing between adjacent CNTs. In some examples, the CNT pores can be sized to capture certain particles, such as pathogens. For example, the CNT pores can be about 5 nm to about 500 nm, and can be configured to capture viruses.

[0069] The CNTs 602 can be grown on the first phase regions 502, for example, via a catalyst of the first phase regions 502. The CNTs 602 can be single-walled or double-walled CNTs. In some examples, the CNTs 602 can have a diameter of at least 10 nm, a diameter of at least 25 nm, a diameter of at least 50 nm, or any other diameter. The CNTs 602 can have a length of at least 10 mm, a length of at least 100 mm, a length of at least 1 mm, a length of at least 3 mm, or any other length.

[0070] Figure 7 is a flowchart of an example method 700 of preparing an example CNT filter according to examples of the present disclosure. The method 700 can be used, for example, to prepare any of the filters 204 and / or CNT filters 400.

[0071] A metal base of a CNT filter including a metal alloy can be heated so as to precipitate a first phase from a second phase of the metal alloy in a spatial pattern (702). For example, the metal base 402 can be heated so as to precipitate the first phase regions 502 in the spatial pattern 506 surrounded by the second phase regions 504. In some examples, the first phase regions are gamma prime phase and include only nickel and aluminum or cobalt and aluminum.

[0072] After heating, the metal substrate can be etched to remove the metal from the precipitated first phase (704). For example, the metal substrate 402 can include a nickel-aluminum or cobalt-aluminum superalloy that is heated to precipitate the gamma prime phase of the alloy in the spatial pattern 506. The aluminum can be removed via chemical etching, leaving behind catalytic metal nickel (or cobalt) on the surface of the first phase region 502 in the spatial pattern 506. In some examples, the etching can be performed at room temperature.

[0073] In some examples, the first phase region 502 can be the gamma prime phase of the alloy in the spatial pattern 506 and can consist essentially of at least 70 wt% nickel or cobalt, at least 86 wt% nickel or cobalt, or at least 90 wt% nickel or cobalt. In some examples, the etching removes the aluminum from the first phase region 502, and after etching, the first phase region 502 can consist essentially of at least 95 wt% nickel or cobalt or at least 99 wt% nickel or cobalt. In some examples, the catalytic metal on the surface of the first phase region 502 is part of the structure of the metal substrate 402.

[0074] In other words, and in a similar manner, the resulting catalytic metal (e.g., nickel, cobalt, or any suitable CNT catalyst) is analogous to a primer that is part of the surface, which is primed to facilitate the adhesion of a coating or material to be adhered to the surface, rather than a primer that is coated on the surface. In the case of a coated primer, there are two possible failure bonds, the bond between the surface and the primer, and the bond between the primer and the material intended to adhere to the surface via the primer. Similarly, a CNT filter that includes a catalyst that is coated and / or deposited on a substrate has two possible failure bonds, the bond between the substrate and the catalyst and the bond between the catalyst and the CNTs grown on the catalyst. In contrast, a catalyst included in a phase of an alloy that is precipitated out of a second phase of the alloy as described herein is part of the structure of the metal substrate. Thus, one of the potential bond failure is eliminated, and there is only one possible failure bond, the bond between the CNTs and the catalyst, which can generally be a very high strength bond.

[0075] After etching, CNTs can be grown on the catalyst in the spatial pattern (706). For example, the highly active nickel, cobalt, or other suitable catalytic metal in the spatial pattern 506 can catalyze the growth of CNTs during CVD coating in a hydrocarbon vacuum atmosphere at high temperature. In some examples, nickel and cobalt can be corrosion resistant and can facilitate superior bonding to CNTs compared to iron.

[0076] Figure 8is a perspective view of an exemplary 3D metal open-cell foam CNT filter 800 according to examples of the present disclosure. The CNT filter 800 includes a metal base 802 that includes a plurality of cells 804, e.g., alternatively referred to as voids 804 (in Figure 8 only a single cell / void is labeled in

[0077] In some examples, the material and composition of the metal base 802 can be substantially similar to the metal base 402 described above. For example, the metal base 802 can be formed of an alloy including at least a first metal and a second metal, such as a nickel-based alloy, a superalloy such as Alloy 10, a nickel- or cobalt-based alloy, a nickel-aluminum alloy, a cobalt-aluminum alloy, or any other suitable metal alloy.

[0078] Similar to the metal base 402, the alloy of the metal base 802 can be selected such that the first phase precipitates out of the second phase of the alloy in a spatial pattern. The metal base 802 can be further selected such that the first phase can be etched (e.g., via chemical etching) to remove alloy elements and / or metals and leave “islands” of different alloy elements and / or metals in the spatial pattern that can serve as growth sites for CNTs as described above.

[0079] In the example shown, the metal base 802 can be referred to as a 3D metal open-cell foam that allows air to pass through the cells 804. In some examples, the CNT filter 800 can be substantially similar to the CNT filter 204, and the size of the cells 804 can be set such that the CNT filter 800 does not cause a significant pressure drop of the gas flow (e.g., air) through the cells 804.

[0080] In the example shown, a gas passing through the CNT filter 804 can pass through a plurality of cells 804 and can be in fluid communication with a plurality of “strands,” “fibers,” “struts,” etc. of the metal base 802 that define the cells 804. In contrast, a gas passing through the 2D metal mesh CNT filter 400 can pass through a single cell (assuming no backflow or cyclonic flow) and be in fluid communication with a single strand, fiber, strut, etc. of the metal base 402. In some examples, the 3D metal open-cell foam CNT filter 800 can capture more particles for a given cross-sectional area flow path of the gas compared to the 2D metal mesh filter 400. In some examples, the sensor 206 is able to detect particles captured within the space of the 3D metal open-cell foam CNT filter 800, e.g., the illumination light of a Raman spectrometer can propagate within the entire space of the 3D metal open-cell foam CNT filter 800 via multiple reflections off the surface of the metal base 802, and Raman scattered light can propagate from the space of the 3D metal open-cell foam CNT filter 800 to the detector of the sensor 206 via multiple reflections off the surface of the metal base 802.

[0081] In some examples, a ratio of a volume of the metal substrate 802 to a volume of the pores 804 in a total space of the CNT filter 800 can be less than about 30%. In some examples, the metal substrate 802 / pore 804 volume ratio can be less than about 10%, less than about 5%, or less than about 1%. In some examples, the metal substrate 802 can be formed via casting, powder metallurgy, a cast process, advanced manufacturing, or by any other suitable method. For example, the metal substrate 802 can be cast with an open-cell polyurethane foam skeleton.

[0082] Figures 9A to 9H Figures 10A to 10F and Figures 11A to 11D is a perspective view of an exemplary CNT filter according to examples of the present disclosure.

[0083] Figures 9A to 9H is a perspective view of exemplary 2D metal mesh CNT filters 900A-900H according to examples of the present disclosure. In some examples, the 2D metal mesh CNT filters 900A-900H can be substantially similar to the 2D metal mesh CNT filters 400 described above with only different mesh geometries, as shown.

[0084] Figures 10A to 10F is a perspective view of exemplary 3D metal open-cell foam CNT filters 1000A-1000F according to examples of the present disclosure. In some examples, the 3D metal open-cell foam CNT filters 1000A-1000F can be substantially similar to the 3D metal open-cell foam CNT filters 800 described above with only different open-cell foam geometries, as shown.

[0085] Figures 11A to 11D is a perspective view of exemplary 2D metal open-cell foam CNT filters 1100A-1100D according to examples of the present disclosure. In some examples, the 2D metal open-cell foam CNT filters 1100A-1100D can be substantially similar to any of the 2D metal mesh CNT filters 400 and 900A-900H or the 3D metal open-cell foam CNT filters 800 and 1000A-1000F described above with only different open-cell foam geometries, as shown. For example, any of the 2D metal open-cell foam CNT filters 1100A-1100D can be a 2D metal mesh that extends in a direction perpendicular to the 2D area of the mesh, e.g., a “thick” 2D mesh. In some examples, the pores of the 2D metal open-cell foam CNT filters 1100A-1100D can be considered “tubes” that extend in the perpendicular direction and have the same cross-sectional shape along the perpendicular direction.

[0086] Various examples have been described. These and other examples are within the scope of the following claims.​

Claims

1. A method of making a filter, the method comprising: heating a metal substrate to precipitate a first phase from a metal alloy on a surface of the metal substrate, wherein the metal substrate defines a plurality of pores configured to allow a gas to pass through the pores, wherein the metal substrate comprises a metal alloy, wherein the metal alloy comprises a first metal and a second metal, the metal alloy selected from a nickel-aluminum alloy or a cobalt-aluminum alloy, wherein the first metal comprises one of nickel and cobalt, the first phase being a gamma prime phase of the metal alloy; etching the metal substrate to remove the second metal from the first phase after the heating; and growing a plurality of carbon nanotubes on the surface of the first metal of the first phase, wherein the carbon nanotubes are configured to capture at least one particle.

2. The method of claim 1, wherein the metal substrate comprises one of a two-dimensional metal mesh, a two-dimensional metal open-cell foam, or a three-dimensional metal open-cell foam.

3. The method of claim 1, wherein the metal substrate is configured to allow the gas to pass through the pores and there is no pressure differential from one side of the filter relative to another side of the filter.

4. The method of claim 1, wherein the metal alloy comprises a nickel aluminum alloy and the first metal is nickel and the second metal is aluminum, wherein the first phase is a gamma prime phase of the nickel aluminum alloy, wherein etching the metal substrate comprises chemically etching the metal substrate to remove the aluminum from the gamma prime phase, leaving nickel as active sites for the carbon nanotubes, wherein growing the plurality of carbon nanotubes comprises growing the plurality of carbon nanotubes via chemical vapor deposition.

5. The method of claim 4, wherein the carbon nanotubes define a plurality of pores in a range of 5 nm to 500 nm.

6. A filter made by the method of any one of claims 1-5, the filter comprising: a metal substrate defining a plurality of pores configured to allow a gas to pass through the pores, the metal substrate comprising a metal alloy, the metal alloy comprising a first metal and a second metal, the metal alloy selected from a nickel-aluminum alloy or a cobalt-aluminum alloy; and a plurality of carbon nanotubes grown on a surface of a first phase of the metal substrate, the plurality of carbon nanotubes configured to capture at least one particle contained in the gas passing through the metal substrate.

7. The filter of claim 6, wherein the first phase is precipitated out of the metal alloy in a predetermined spatial pattern, wherein the first phase is configured to catalyze growth of the plurality of carbon nanotubes.

8. A system for monitoring a pathogen, the system comprising: a housing comprising: an inlet configured to allow a gas to enter a conduit, the conduit in fluid communication with the inlet and configured to define a flow path of the gas within the housing; and an outlet in fluid communication with the conduit and configured to allow the gas to exit the housing; a filter disposed within the housing, the filter comprising: a metal substrate defining a plurality of pores configured to allow the gas to pass through the pores, the metal substrate comprising a metal alloy, the metal alloy comprising a first metal and a second metal, the metal alloy selected from a nickel-aluminum alloy or a cobalt-aluminum alloy; and a plurality of carbon nanotubes grown on a surface of a first phase of the metal substrate, the plurality of carbon nanotubes configured to capture at least one particle contained in the gas passing through the metal substrate. A filter prepared by the method of any one of claims 1-5, the filter being in fluid communication with the conduit and configured to capture the pathogen, the filter comprising: a metal substrate defining a plurality of pores configured to allow a gas to pass through the pores, the metal substrate comprising a metal alloy comprising a first metal and a second metal, the metal alloy selected from a nickel-aluminum alloy or a cobalt-aluminum alloy; and a plurality of carbon nanotubes located on a surface of the first phase of the metal substrate, the plurality of carbon nanotubes configured to capture a virus; and a sensor configured to detect the virus captured by the filter.

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