EP1885647A1 - Article comprising carbon nanotubes and method of using the same for purifying fluids - Google Patents
Article comprising carbon nanotubes and method of using the same for purifying fluidsInfo
- Publication number
- EP1885647A1 EP1885647A1 EP05795204A EP05795204A EP1885647A1 EP 1885647 A1 EP1885647 A1 EP 1885647A1 EP 05795204 A EP05795204 A EP 05795204A EP 05795204 A EP05795204 A EP 05795204A EP 1885647 A1 EP1885647 A1 EP 1885647A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- article
- carbon nanotubes
- chosen
- carbon
- contaminants
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/283—Treatment of water, waste water, or sewage by sorption using coal, charred products, or inorganic mixtures containing them
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/48—Treatment of water, waste water, or sewage with magnetic or electric fields
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/103—Arsenic compounds
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/08—Seawater, e.g. for desalination
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2305/00—Use of specific compounds during water treatment
- C02F2305/08—Nanoparticles or nanotubes
Definitions
- the present disclosure relates to an article for removing contaminants from a fluid, such as a liquid or gas, wherein the article comprises carbon nanotubes.
- the present disclosure also relates to methods of making such an article as well as methods of removing contaminants from fluid using the article.
- the disclosed article is used to produce potable water from waters contaminated with microorganisms or to desalinate salt water.
- Factors to be balanced when treating fluids include the rate of fluid flow, the flow resistance and level of contaminant removal. It would be desirable to have a material that could balance the first two factors, while achieving a higher level of contaminant removal than previously possible.
- nanotechnology materials are that they will enable us to do things not possible with more traditional macro-scale materials, such as fluid purification.
- Many of the current processes can be improved by using articles or filters comprising nanomaterial, such as carbon nanotubes.
- nanomaterial such as carbon nanotubes.
- a mesh including carbon nanotubes a "nanomesh"
- the term “nano” refers to a material or structure whose size is on a scale around one billionth of a meter (i.e., nm), such as on the molecular level.
- nm a meter
- the term “nanotechnology” generally refers to technology that in at least one dimension has a size scale of 1 to 500nm, such as 1 to 100nm, exhibits at least one property or function as a result of the small scale, and is able to control or manipulate individual atoms or molecules.
- an article generally comprised of carbon nanotubes, where at least one carbon nanotube is attached or connected to another carbon nanotube, or to other materials, such as fibers, particles or a substrate.
- Carbon nanotube(s) refer to a nanoscale tubular structure(s) composed of six-member rings of carbon whose bonding patterns create a hexagonal lattice which closes upon itself to form the walls of the cylindrical structure.
- the interconnected structure which is at least partially comprised of nanotubes is referred to herein as a "nanomesh”.
- the article generally comprises carbon nanotubes and may or may not include at least one molecule or cluster attached thereto or located therein, wherein the carbon nanotubes are present in the article in an amount sufficient to reduce the concentration of the contaminants in fluid that come into contact with the article.
- a method of reducing the amount of contaminants in a fluid comprising contacting the fluid with the article as described herein for a time sufficient to separate, remove, immobilize, modify or destroy at least one contaminant from the fluid.
- the method may be used to remove contaminants from water or the air.
- a method of preparing a nanomesh material comprising carbon nanotubes.
- the method comprises mechanical, chemical or irradiative treatments, or any combination thereof, of carbon nanotubes in a medium sufficient to attach at least one functional chemical group to a surface of the carbon nanotube, thereby forming functionalized carbon nanotubes.
- the method further comprises rinsing and/or dispersing the functionalized carbon nanotubes in at least one solvent chosen from aqueous, inorganic, and organic solvents.
- the method further comprises combining multiple types of carbon nanotubes that may have different chemical functionalization, to assist in the removal, destruction, or modification of contaminants.
- the method further comprises mixing the functionalized carbon nanotubes with fibers and at least one solvent to form a suspension of functionalized carbon nanotubes and fibers.
- a nanomesh layer is formed, typically on a porous substrate, by depositing the suspension on the substrate by any standard method, such as vacuum filtration.
- Fig. 1 is a schematic representation of the bonding structure and shape of a single walled carbon nanotube.
- Fig. 2 represents a lattice distortion in a defective carbon nanotube.
- Fig. 3 represents a section of a carbon nanotube functionalized with a carboxyl functional group.
- Fig. 4 represents a filled carbon nanotube.
- Fig. 5 represents a section of a carbon nanotube doped with different atoms.
- Fig. 6 represents a fluid purification device comprising carbon nanotubes wherein the substrate possesses a pleated design.
- Fig. 7 represents a method of depositing carbon nanotubes on a rolled substrate that may be wrapped around a cylinder, block or other bulk material.
- Fig. 8 schematically represents the desalination device showing electrical connection to the nanomesh layers.
- Fig. 9 represents the dynamics of ion motion through a sequence of nanomesh membranes in active mode using both a low-frequency, three-phase AC signal (to drive ion motion) and a higher frequency AC signal (to disrupt the DeBye atmosphere) imposed across the series of nanomesh membranes.
- Fig. 10 schematically demonstrates the neighborhood of ions in a water solution and shows the shielding of charges by the formation of a molecular cloud (DeBye atmosphere) due to the polarized nature of the water molecule.
- Fig. 11 is a flow chart for the process used to manufacture fluid purification devices. This example is specific to the cylindrical substrate, but can be easily generalized to any shape article using any substrate and fiber and/or particle in solution.
- Fig. 12 represents the structure of a cylindrical version of the inventive fluid purification article.
- Fig. 13 represents a flat version of the inventive fluid purification article.
- Fig. 14 is a light microscope image showing nearly uniform bacterial (stained) coverage for untreated solution in Example #1 , sample #1.
- Fig. 15 is a light microscope image showing bacteria (stained) clumped on carbon nanotubes in the nanotube treated solution in Example #1 , sample #2.
- Fig. 16 is a Scanning Electron Microscope (SEM) image showing bacteria with normal cell walls in the absence of nanotubes from Example #1 , sample #1.
- Fig. 17 is an SEM image showing the diffuse and damaged cell wall of a bacteria that has interacted with the nanotubes (in Example #1 , sample #2) which suggests that this interaction is capable of destruction of the bacterial cell.
- Fig. 18 is a schematic of the deposition apparatus for creating a nanomesh on a cylindrical shaped substrate.
- Fig. 19 is a diagram showing an assembled cylindrical fluid purification article.
- Fig. 20 is a photograph of a test desalination device.
- Fig. 21 is a schematic representation of the air membrane testing apparatus.
- Fig. 22 is a SEM micrograph of the self -assembled carbon nanotube/glass fiber nanomesh.
- Fluid is intended to encompass liquids or gases.
- Constants means at least one unwanted or undesired element, molecule or organism in the fluid.
- Removing (or any version thereof) is understood to mean destroying, modifying, or separating contaminants using at least one of the following mechanisms: particle size exclusion, absorption, adsorption, chemical or biological interaction or reaction.
- Chemical or biological interaction or reaction is understood to mean an interaction with the contaminant through either chemical or biological processes that renders the contaminant incapable of causing harm. Examples of this are reduction, oxidation, chemical denaturing, physical damage to microorganisms, bio-molecules, ingestion, and encasement.
- Particle size is defined by a number distribution, e.g., by the number of particles having a particular size.
- the method is typically measured by microscopic techniques, such as by a calibrated optical microscope, by calibrated polystyrene beads, by calibrated scanning probe microscope scanning electron microscope, or optical near field microscope. Methods of measuring particles of the sizes described herein are taught in Walter C. McCrone's et al., The Particle Atlas, (An encyclopedia of techniques for small particle identification), Vol. I, Principles and Techniques, Ed. 2 (Ann Arbor Science Pub.), which are herein incorporated by reference.
- Non-limiting examples of liquids that may be cleaned using the article described herein include water, foodstuffs, biological fluids, petroleum and its byproducts, non-petroleum fuels, medicines, organic and inorganic solvents, and the liquid forms of hydrogen, oxygen, nitrogen and carbon dioxide, as may be used for rocket propellants or in industrial applications.
- Non-limiting examples of foodstuffs that can be treated with this article comprise animal by-products (such as eggs and milk), fruit juice, alcoholic and nonalcoholic beverages, natural and synthetic syrups, and natural and synthetic oils used in the cooking or food industry [such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e. butter, lard)], or any combination thereof.
- animal by-products such as eggs and milk
- fruit juice such as eggs and milk
- alcoholic and nonalcoholic beverages such as alcoholic and nonalcoholic beverages
- natural and synthetic syrups such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e. butter, lard)
- natural and synthetic oils used in the cooking or food industry such as olive oil, peanut oil, flower oils (sunflower, safflower), vegetable oil, or oils derived from animal sources (i.e. butter, lard)
- sulfites
- Biological fluids that may be decontaminated with the article described herein could be generally derived from an animal, human, plant, or comprise a culture/growth broth used in the processing of a biotechnology or pharmaceutical product.
- the biological fluids which may be cleaned comprise blood (or blood components), serums, and milk.
- Biological reagents used in pharmaceutical products are often quite labile and difficult to sterilize by conventional techniques. Removal of small microorganisms (such as Mycoplasma and viruses) cannot be accomplished by conventional filtration.
- the inventive carbon nanomesh article may be used for viral removal without causing damage to the serum proteins often present and needed in biological reagents.
- the physical and chemical properties of the nanomesh can be controlled to enable removal of contaminants that are created during drug fabrication.
- the inventive article can be used for the sterilization of petroleum products.
- a significant contamination problem is the latent growth of bacteria in petroleum or its derivatives during storage, which has been a problem particularly with aviation fuel. The presence of such bacteria can severely foul and eventually ruin the fuel. Accordingly, a major area of concern in the area of liquid purification is the cleaning bacteria from natural and/or synthetic petroleum products. Natural and/or synthetic petroleum and its byproducts include aviation, automotive, marine, locomotive, and rocket fuels, industrial and machine oils and lubricants, and heating oils and gases.
- another aspect of the present invention includes a method of cleaning the air to remove any of the previously listed contaminants.
- gases that may be cleaned using the article described herein include one or more gases chosen from the air or exhausts from vehicles, smoke stacks, chimneys, or cigarettes.
- the article When used to clean air, the article may take a flat form to provide a greater surface area for air flow. Such flat shapes provide the additional benefit of being able to be easily cut into appropriate shapes for various filter designs, such as those used in gas masks, as well as HVAC systems.
- gases that may be treated according to the present disclosure, such as scrubbed to clean the gas or remove them from exhaust, include argon, acetylene, nitrogen, nitrous oxide, helium, hydrogen, oxygen, ammonia, carbon monoxide, carbon dioxide, propane, butane, natural gas, ethylene, chlorine, ormixtures of any of the foregoing, such as air, nitrogen oxide, and gases used in diving applications, such as Helium/Oxygen mixtures.
- contaminant may actually be a desired product in another.
- the contaminant may contain precious metals or a beneficial pharmaceutical product. Therefore, in one embodiment, it may be beneficial to separate, retain and collect the contaminants rather than just removing and destroying them.
- the ability to "catch and release" desired contaminants, enabling the isolation of useful contaminants or certain reaction byproducts, may be accomplished by tuning the zeta potential and/or utilizing nano-electronic control of the nanomesh article, as described in more detail below.
- Carbon nanotubes generally have two forms: single wall and multi walls.
- Single-wall carbon nanotubes comprises one of these tubular structures so that the inter-connected hexagons line-up with each other.
- Fig. 1 depicts a single walled carbon nanotube.
- these single-walled nanotubes are generally around 1 -2 nm in diameter, similar to human DNA ( ⁇ 2 nm), and usually range from hundreds of nanometers to many microns in length.
- Multi-walled carbon nanotubes comprise many concentric shells of these tubular structures. They can have diameters of tens of nanometers, and can theoretically have lengths up to hundreds of meters.
- the nanomesh described herein can comprise carbon nanotubes attached to each other, or to another material.
- the attachment and/or connection within the nanomesh is a result of forces acting at the nanoscale, non-limiting examples of which are Van der Waals forces, covalent bonding, ionic bonding, geometric constraints, electrostatic, magnetic, electromagnetic, or Casimir forces or combinations thereof.
- the present disclosure also relates to a method of purifying fluid by contacting contaminated fluid with the nanomesh in the article described herein.
- the method of purifying fluid comprises contacting the fluid with a nanomesh, wherein the carbon nanotubes are present in the nanomesh in an amount sufficient to reduce the concentration of at least one contaminant in the fluid that comes into contact with the nanomesh or the interaction zone created by the nanomesh.
- reduce the concentrations of at least one contaminant means a reduction of at least one contaminant to a level below that of the untreated fluid, such as below the maximum contamination levels (MCL) as defined by appropriate regulatory agencies or industrial requirements governing the quality standards of the particular fluid after being treated with the inventive article.
- MCL maximum contamination levels
- One aspect of the present disclosure is related to the use of carbon nanotubes that have a scrolled tubular or non-tubular nano-structure of carbon rings.
- These carbon nanotubes are usually single-walled, multi-walled or combinations thereof, and may take a variety of morphologies.
- the carbon nanotubes used in the present disclosure may have a morphology chosen from horns, spirals, multi-stranded helicies, springs, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology.
- Some of the above described shapes are more particularly defined in M.S. Dresselhaus, G. Dresselhaus, and P. Avouris, eds.
- Carbon Nanotubes Synthesis, Structure, Properties, and Applications, Topics in Applied Physics. 80. 2000, Springer- Verlag; and "A Chemical Route to Carbon Nanoscrolls, Lisa M. Viculis, Julia J. Mack, and Richard B. Kaner; Science, 28 February 2003; 299, both of which are herein incorporated by reference.
- a majority of the carbon nanotubes are distorted by crystalline defects such that they exhibit a greater purification performance than non-distorted carbon nanotubes.
- Crystalstalline defects refers to sites in the tube walls of carbon nanotubes where there is a lattice distortion in at least one carbon ring.
- a "lattice distortion” means any distortion of the crystal lattice of carbon nanotube atoms forming the tubular sheet structure.
- a lattice distortion may include any displacements of atoms because of inelastic deformation, or presence of 5 and/or 7 member carbon rings, or a chemical interaction followed by change in sp 2 hybridization of carbon atom bonds. Such defects or distortions may lead to a natural bend in the carbon nanotube.
- the phrase "exhibit a greater purification performance" means that the nanomesh demonstrates either improvements to the structural integrity of the resultant material, its porosity, its porosity distribution, its electrical conductance, its resistance to fluid flow, geometric constraints, or any combination thereof that lead to an enhancement of contaminant removal.
- greater purification performance could be due to improved and more efficient adsorption or absorption properties of the individual carbon nanotubes.
- the more defects there are in the carbon nanotubes the more sites exist for attaching chemical functional groups.
- increasing the number of functional groups present in the nanomesh should improve the performance of the resulting article.
- the carbon nanotubes may also undergo chemical and/or physical treatments to alter their chemical and/or physical behavior. These treatments are typically done to enable the resulting article to exhibit a greater purification performance, in the sense defined above.
- the carbon nanotubes may be chemically or physically treated to achieve at least one of the following effects: remove contaminants, add defects, or attach functional groups to defect sites and/or nanotube surface.
- chemical or physical treatment means treating with an acid, solvent or an oxidizer for a time sufficient to remove unwanted constituents, such as amorphous carbon, oxides or trace amounts of by-products resulting from the carbon nanotube fabrication process.
- An example of the second type of chemical treatment is to expose the carbon nanotubes to an oxidizer for a time sufficient to create defect density on the surface of the carbon nanotube.
- the carbon nanotubes comprise atoms, ions, molecules or clusters attached thereto or located therein in an amount effective to assist in the removal and/or modification of contaminants from the fluid.
- the carbon nanotubes described herein may also be treated to alter their properties, as well as the contaminants that may be removed from and/or modified within the fluid.
- the carbon nanotubes are chemically treated with an oxidizer, chosen from but not limited to a gas containing oxygen, nitric acid, sulfuric acid, hydrogen peroxide, potassium permanganate, and combinations thereof.
- Nanotubes which have been treated with an oxidizer can provide unique properties, either in terms of fluid flow, dispersion of nanotubes in the deposition fluid, or from a functionalization perspective (e.g., having the ability to be particularly functionalized).
- “functionalized” refers to a carbon nanotube having an atom or group of atoms attached to the surface that may alter the properties of the nanotube, such as zeta potential. Functionalization is generally performed by modifying the surface of carbon nanotubes using chemical techniques, including wet chemistry or vapor, gas or plasma chemistry, and microwave assisted chemical techniques, and utilizing surface chemistry to bond materials to the surface of the carbon nanotubes. These methods are used to "activate" the carbon nanotube, which is defined as breaking at least one C-C or C- heteroatom bond, thereby providing a surface for attaching a molecule or cluster thereto. As shown in Fig.
- functionalized carbon nanotubes comprise chemical groups, such as carboxyl groups, attached to the surface, such as the outer sidewalls, of the carbon nanotube. Further, the nanotube functionalization can occur through a multi-step procedure where functional groups are sequentially added to the nanotube to arrive at a specific, desired functionalized nanotube.
- the functionalized carbon nanotubes can comprise a non-uniform composition and/or density of functional groups including the type or species of functional groups across the surface of the carbon nanotubes.
- the functionalized carbon nanotubes can comprise a substantially uniform gradient of functional groups across the surface of the carbon nanotubes. For example, there may exist, either down the length of one nanotube or within a collection of nanotubes, many different functional group types (i.e. hydroxyl, carboxyl, amide, amine, poly-amine and/or other chemical functional groups) and/or functionalization densities.
- nanomesh may also be functionalized with chemical groups, decorations or coatings or combinations thereof to change their zeta potential and/or cross-linking abilities and thereby improve the filtration performance of the nanomesh.
- a non-limiting example of performing a specific multi-step functionalization is one that allows the zeta potential of carbon nanotubes to be controlled and improve their ability to remove viruses.
- the carbon nanotubes are refluxed in a mixture of acids. While not being bound by any theory, it is believes that such a process increase the number of defects on the surface of the nanotube, increasing carboxyl functional groups attached to the defect locations, and/or changes the zeta potential of the nanotubes due to the negative charge of carboxyl functional groups in water.
- Carboxyl functionalized nanotubes may then refluxed in a solution of thionyl chloride in a nitrogen atmosphere. Without being held to any theory, it is believes that this acts to convert the previously attached carboxyl functional groups to acyl chloride functional groups. Subsequently, these acyl chloride functionalized nanotubes are refluxed in as solution of ethylenediamine again in a nitrogen atmosphere. It is believed that this reacts with the amine groups on the end of the diamine with the acyl chloride functional group, thereby converting the acyl chloride functional group to a 2-aminoethylamide functional group by replacement of the chlorine atom with one amine group of the diamine.
- the termination of the nanotube functionalization with an amine group will impart a positive charge to the nanotube in water, giving it a positive or less negative zeta potential.
- the foregoing would enable a nanomesh device constructed with nanotubes of this type to specifically target negatively charged contaminants (such as anions, certain molecules, and virus particles) for capture by Van der Waals and/or electrostatic forces, leading to their removal from the contaminant stream.
- carbon nanotubes can also be used for high surface area molecular scaffolding either for functional groups comprised of organic and/or inorganic receptors or to provide structure and support for natural or bioengineered cells [including bacteria, nanobacteria and extremophilic bacteria].
- functional groups comprised of organic and/or inorganic receptors or to provide structure and support for natural or bioengineered cells [including bacteria, nanobacteria and extremophilic bacteria].
- nanobacteria including images of nanobacteria in carbonate sediments and rocks can be found in the following references, which are herein incorporated by reference. R.L. Folk, J. Sediment. Petrol. 63:990-999 (1993), R.H. Sillitoe, R.L Folk and N. Saric, Science 272:1153-1155 (1996).
- the organic and/or inorganic receptors will selectively target the removal of specific contaminants from a fluid stream.
- the natural or bioengineered cells supported by the nanotubes will consume, metabolize, neutralize, and/or bio-mineralize specific biologically-active contaminants. For example, there are specific microorganisms adhered to the nanotubes that can reduce the toxicity of oil spills.
- the carbon nanotubes, the carbon nanotube material, or any subassembly thereof may be treated with radiation.
- the radiation may be chosen from but not limited to exposure from electromagnetic radiation and/or at least one particle chosen from electrons, radionuclides, ions, particles, clusters, molecules or any combination thereof.
- the radiation should impinge upon the carbon nanotube in an amount sufficient to 1 ) break at least one carbon-carbon or carbon-heteroatom bond; 2) perform cross- linking between nanotube-nanotube, nanotube to other nanomesh constituent, or nanotube to substrate; 3) perform particle implantation, 4) improve the chemical treatment of the carbon nanotubes, or any combination thereof.
- Irradiation can lead to a differential dosage of the nanotubes (for example due to differential penetration of the radiation) which causes non-uniform defect structure within the nanomesh structure. This may be used to provide a variation of properties, via a variation of functional groups attached to the carbon nanotubes.
- the carbon nanotubes described herein may also be filled or impregnated with a desired material to achieve certain beneficial properties.
- the terms "filled” or “impregnated” can be used interchangeably, and refer to carbon nanotubes that are at least partially filled with a substance of interest.
- the substance filled or impregnated into the carbon nanotube can typically improve the nanomesh filtration performance and/or specifically re-target its application.
- a non- limiting example is the improvement of filtration through increased nanotube affinity for specific contaminants. For example, if an article is to be used to remove an electronegative contaminant, such as arsenic complexes in water, the carbon nanotubes are first impregnated with an electropositive substance.
- Fig. 4 exemplifies a carbon nanotube that is filled with a substance.
- carbon nanotubes may be modified by coating or decorating with a material and/or one or many particles to assist in the removal of contaminants from fluids or increase other performance characteristics such as mechanical strength, bulk conductivity, or nano-mechanical characteristics.
- coated or decorated carbon nanotubes are covered with a layer of material and/or one or many particles which, unlike a functional group, is not necessarily chemically bonded to the nanotube, and which covers a surface area of the nanotube sufficient to improve the filtration performance of the nanomesh.
- Carbon nanotubes used in the article described herein may also be doped with constituents to assist in the removal of contaminants from fluids.
- a "doped" carbon nanotube refers to the presence of ions or atoms, other than carbon, into the crystal structure of the rolled sheets of hexagonal carbon.
- doped carbon nanotubes means at least one carbon in the hexagonal ring is replaced with a non-carbon atom.
- carbon nanotubes as described herein could be decorated by a cluster or clusters of atoms or molecules.
- decorated refers to a partially coated carbon nanotube.
- a “cluster” means at least two atoms or molecules attached by any chemical or physical bonding.
- the clusters can exhibit properties of quantum dots resulting in photo-stable, color-tunable, nanocrystal with a wide absorption spectrum and a narrow emission peak.
- Clusters, including quantum dots may be comprised of metals, nonmetals and combinations thereof. These attached clusters may be subsequently photo-activated to remove, disable and/or destroy contaminants.
- a quantum dot is a particle of matter so small that the addition or removal of an electron can be detected, and changes its properties in some useful way.
- a quantum dot is a semiconductor crystal with a diameter of a few nanometers, also called a nanocrystal, that because of its small size behaves like a potential well that confines electrons in three dimensions to a region of a few nanometers.
- the molecules or clusters may also include organic compounds containing at least one protein, including natural polymers composed of amino acids joined by peptide bonds, carbohydrates, polymers, aromatic or aliphatic alcohols, and nucleic or non-nucleic acids, such as RNA and DNA.
- Non-limiting examples of the organic compound may comprise at least one chemical group chosen from carboxyls, amines, arenes, nitriles, amides, alkanes, alkenes, alkynes, alcohols, ethers, esters, aldehydes, ketones, polyamides, polyamphiphiles, diazonium salts, metal salts, pyrenyls, thiols, thioethers, sulfhydryls, silanes, and combinations thereof.
- the nanomesh described herein may also comprise fibers which act to maintain the dispersion (or exfoliation) of the carbon nanotubes during processing.
- Such fibers can be sacrificial (removed from the structure during further processing, such as by chemical or heat treatments) or can remain an integral part of the finished device.
- these fibers typically have a diameter ranging from 1 nm to 1 mm, such as from 10nm to 100 ⁇ m.
- the term "fiber” means an object of length L and diameter D such that L is greater than D, wherein D is the diameter of the circle in which the cross section of the fiber is inscribed.
- the aspect ratio L/D (or shape factor) is chosen ranging, for example, from 2 to 10 9 , such as from 5 to 10 7 and further such as from 5 to 10 6 .
- the fibers that may be used in the composition disclosed herein may be mineral or organic fibers of synthetic or natural origin. They may be short or long, individual or organized, for example, braided, and hollow or solid. They may have any shape, and may, for example, have a circular or polygonal (square, hexagonal or octagonal) cross section, depending on the intended specific application.
- the fibers have a length ranging, for example, from 10nm to 10m, such as from 20 nm to 1 cm. Their cross section may be within a circle of diameter ranging, for example, from 1 nm to 1 mm.
- the fibers can be those used in the manufacture of textiles as derived from bio-mineralization or bio-polymerization, such as silk fiber, cotton fiber, wool fiber, flax fiber, feather fibers, cellulose fiber extracted, for example, from wood, legumes or algae.
- the resorbable synthetic fibers may include: those prepared from glycolic acid and caprolactone; resorbable synthetic fibers of the type which is a copolymer of lactic acid and of glycolic acid; and polyterephthalic ester fibers.
- Nonresorbable fibers such as stainless steel threads may be used.
- the fibers may be chosen from:
- polymeric material chosen from single or multi- component polymers such as nylon, acrylic, methacrylic, epoxy, silicone rubbers, synthetic rubbers, polypropylene, polyethylene, polyurethane, polystyrene, polycarbonates, aramids (i.e. Kevlar ® and Nomex ® ), polychloroprene, polybutylene terephthalate, poly-paraphylene terephtalamide, poly (p-phenylene terephtalamide), and polyester ester ketone, polyesters [e.g. poly(ethylene terephthalate), such as Dacron ® ], polytetrafluoroethylene (i.e.
- Teflon ® polyvinylchloride, polyvinyl acetate, viton fluoroelastomer, polymethyl methacrylate (i.e. Plexiglass ® ), and polyacrylonitrile (i.e. Orion ® ), and combinations thereof;
- At least one carbon nanotube chosen from single walled, double walled or multi-walled carbon nanotubes that have either a nested or non-nested morphology of nano-horns, nano-spirals, nano-springs, dendrites, trees, spider nanotube structures, nanotube Y-junctions, and bamboo morphology or multi- stranded helices;
- a metal oxide nanowire can be prepared by heating metal wires with oxygen in a reaction vessel to a temperature ranging from 230-1000 0 C for a period ranging from 30 minutes to 2 hours.
- the nanowires will grow by using macroscale wires made any metal previously mentioned as a feedstock.
- the resulting metallic oxide nanowires can be in a size ranging from 1 -100 nanometers in diameter, such as 1 -50 nanometers in diameter, including 2-5 nanometers in diameter.
- the surface of the base wire is abraded to provide a roughened surface texture to enable better nanotube adhesion within the nanomesh as well as enhance the purification performance of the article.
- These metal oxide or metal hydroxide nanowires can also be obtained from commercial suppliers.
- the article includes a porous support substrate for depositing the carbon nanotubes using a differential pressure process.
- the porous support substrate may be in any form suitable for the shape of the resulting article, such as a block, tube (or cylinder), sheet or roll, and may comprise a material chosen from ceramic, carbon, metal, metal alloys, or plastic or combinations thereof.
- the substrate comprises a woven or non-woven fibrous material.
- the substrate when the substrate takes the form of sheet, the substrate may be either a flat or planar sheet or in a pleated form (Fig. 6).
- the pleated form being chosen to increase the surface area of the nanomesh exposed to contaminated fluid.
- the substrate is a roll of material on which the nanomesh is deposited.
- the roll may be scrolled through a series of deposition and other processing stations in either a continuous or semi-continuous manner.
- the nanomesh is created by a rolled process, it may be used to wrap around a hollow, porous cylinder, block or other supporting structure to form the filter media as depicted in Fig. 7.
- the porous tubular substrate comprises a carbon material, such as activated carbon (bulk or fiber), the outer surface of which is coated with the carbon nanotubes described herein.
- a carbon material such as activated carbon (bulk or fiber)
- a collection of metal oxide/hydroxide nanowires, made as described above, may also be used as a substrate for the deposition(s) of carbon nanotubes using a differential pressure deposition process.
- the resulting nano-wire/carbon nanotube nanomesh may or may not be treated thermally, mechanically, or chemically to enhance structural integrity and/or improve the purification performance of the article.
- the chemical treatments may include the functionalizing, coating or decoration of the resultant nanomesh with chemical groups, metals, ceramics, plastics, or polymers. Further these chemical treatments may be done so that they the nanomesh article chemically or physically reacts or interacts with contaminants to destroy, modify, immobilize, remove, or separate them.
- the porous support substrate used during the differential pressure deposition process may be either sacrificial or used only temporarily during deposition to form the nanomesh in a method analogous to paper manufacturing.
- Another embodiment of the article comprises multiple nanomesh layers, each of which may be specifically, and independently, tuned through its zeta potential or other means to remove a specific distribution of contaminants or to improve other performance characteristics of the article.
- other means is intended to mean the tuning of specific properties of the nanomesh layer such as its porosity, the contaminant affinity [e.g. functionalization of nanomesh components, specific contaminant(s) receptors], or strength (e.g. binding or cross- linking agents used).
- the nanomesh contains a binding agent (such as polyvinyl alcohol) that acts to improve the filtration performance of the article.
- a binding agent such as polyvinyl alcohol
- Such a binding agent may be introduced into the suspension containing the carbon nanotubes and other nanomesh components prior to the formation of the nanomesh structure.
- the nanomesh can be formed through a process of self assembly.
- Self assembly means that the nanomesh components arrange themselves into the final nanomesh structure. This is accomplished by controlling the electric, magnetic, chemical and geometric constraints through the choice of functional groups, surface charge distributions, the composition or properties of the dispersive agent, or any combination thereof. For example, adjusting the surface charge distribution of the nanomesh components controls their electrical behavior, which in turn determines how they arrange into the structure of the assembled nanomesh.
- This self assembly may be in any form that leads to an enhanced structural framework within the nanomesh that improves the removal properties, porosity, electrical resistance, resistance to fluid flow, strength characteristics or combinations thereof.
- the above self assembly may be "directed" through the imposition of an external field.
- This applied field works in concert with the properties of any or all of the nanomesh components and/or the fluid in which the components are suspended to guide their assembly into the resulting nanomesh.
- a suspension containing some or all of the components of the nanomesh may be subjected to electromagnetic stimulation during the formation of the nanomesh to achieve a desired component alignment and/or weaving to enhance the fluid purification performance.
- the nanomesh described herein forms a unique nanoscopic interaction zone that uses chemical and physical forces to first attract then to modify or separate microbes and other pathogens from the fluid stream. For example, it is believed that during the sterilization of a fluid, microorganisms come into contact with the nanomesh, causing focused forces to be applied to the microorganisms. These forces first attract, then either cause adherence and/or modification of cells. It is possible that this modification involves disrupting the cell membranes or causing internal cellular damage, thus disabling and/or destroying the microorganisms or their ability to reproduce. In this way, fluids can be effectively sterilized with respect to microorganisms.
- Common microorganisms are in the size range of 1-5 microns long and as such are at least 100 times larger than a nanostructure such as carbon nanotubes.
- Known examples of these organisms include E. coli, Vibrio cholera, Salmonella typhi, Shigella dysenteriae, Cryptosporidium parvum, Giardia lamblia, Entamoeba histolytica, and many others.
- viruses transmitted through water include Polio, Hepatitis A, Rotavirus, Enteroviruses and many others.
- chemical agents include, but are not limited to, ions, heavy metals, pesticides, herbicides, organic and inorganic toxins, and microbial toxins (such as that causing botulism).
- Mechanisms believed to be capable of adsorbing then destroying microorganisms in this nano-regime can act independently or in concert with one another.
- Non-limiting examples of such mechanisms include:
- [0104] Vibrational waves causing either external damage to the cell wall and transport channels and/or internal cellular damage to the DNA, RNA, proteins, organelles, etc.; [0105] • Bubble cavitations from Shockwaves in the liquid around the carbon nanotubes which damage the cell structure; [0106] • Electromagnetic, electrostatic and/or Van der Waals forces which capture and hold biological contaminants; [0107] • Disruption of hydrogen bonding in the vicinity of nanostructures via zeta action causing damage to cell walls and/or DNA; [0108] • Acidification of the environment around the nanostructure, due to specific nanotube functionalizations that attract naturally occurring H + ions in water, which damages cell walls and/or DNA.
- another process of fluid purification is also based on the nanomesh article.
- an electrostatic or electromagnetic field is imposed upon a nanomesh to control the purification of a fluid.
- the imposition of an electric potential across the nanomesh can remove contaminants on the nanoscale. Further, this process can be used in reverse to cleanse the filter article.
- the entire nanomesh can be stimulated with dynamic electromagnetic fields which, when properly adjusted, will excite nanomesh-wide vibrations. These vibrations could have both microorganism damaging effects or induce an ultrasonic self-cleaning effect.
- the utility of the inventive article, in this connection, is that advantage is taken of the high strength, high stiffness (large Young's modulus), high conductivity, and the piezo-electric property of the nanotubes.
- the imposition of a more generalized electromagnetic field can give fluid purification performance that goes beyond existing technologies. For example, in the case of two conducting nanomesh layers, imposing an electric current generates a magnetic field between nanomesh layers (Fig. 8). This field could be tuned to capture all charged particles from a fluid stream.
- a process of liquid desalination is also based on the described nanomesh article.
- One mechanism believed to be capable of desalinating liquid with the described nanomesh is the imposition of a voltage differential between two or more nanomesh membranes.
- one nanomesh membrane carries a positive charge and the other membrane a negative charge.
- the applied potential causes cations to migrate toward the negatively charged membrane and anions to migrate toward the positively charged one.
- Due to the large surface area (1000m 2 /gram) of carbon nanotubes the application a voltage differential across the nanomesh membrane creates a very high capacitance device, thereby creating a efficient, compact, reversible ionic separation zone (i.e. an ion trap).
- a desalination unit could incorporate two or more parallel layers of supported conductive nanomesh that are electrically isolated from each other.
- the two or more layers may be electrically charged in either a static or active mode.
- static mode for example, the nanomesh layers could be oppositely charged to create a salt trap between them.
- active mode device with four or more layers, for example, a four phase signal would be applied to the multi-layer nanomesh structures such that the four legs of the signal are applied to four sequential nanomesh layers. This pattern is repeated every fourth nanomesh layer (Fig. 9). In this way, the charge on each nanomesh layer and across the device indexes sequentially in time from positive to neutral to negative to neutral.
- Done sequentially in time would create, electronically, a moving virtual capacitor within the device which can cause the salt ions to migrate in a direction different than the flow of the water through the device.
- the concentrated salt water would accumulate at the terminus of the virtual capacitor and could be channeled out of a brine port on the device, while the fresh water would pass through the device.
- the desalination device described herein could be designed to take advantage of the biological removal characteristics of the nanomesh structure, as discussed above, to purify the resulting fresh water.
- surfaces susceptible to bio-film formation due to the attachment and growth of contaminating microbes, can be coated with a layer of nanomaterial to prevent either the attachment or subsequent growth of undesirable elements, such as molds, bacteria.
- nanomaterials include elements or compounds having antibacterial properties (such as iodine resin, silver, aluminum oxide, aluminum hydroxide, or triclosan) that are attached to the surface or located within the carbon nanotube or attached to any other nanomesh component.
- Non-limiting examples of contaminants that can be removed from fluid using the disclosed article include, but are not limited to, the following biological agents: pathogenic microorganisms [such as viruses (e.g. smallpox and hepatitis), bacteria (e.g. anthrax, typhus, cholera), oocysts, spores (both natural and weaponized), molds, fungi, conforms, and intestinal parasites], biological molecules (e.g. DNA, RNA), and other pathogens [such as prions and nanobacteria (both natural and synthetic)].
- pathogenic microorganisms such as viruses (e.g. smallpox and hepatitis), bacteria (e.g. anthrax, typhus, cholera), oocysts, spores (both natural and weaponized), molds, fungi, conforms, and intestinal parasites]
- biological molecules e.g. DNA, RNA
- other pathogens such as prions and nanobacteria
- prions are defined as small infectious, proteinaceous particles which resist inactivation by procedures that modify nucleic acids and most other proteins. Both humans and animals are susceptible to prion diseases [such as Bovine Spongiform Encephalopathy (BSE or Mad Cow disease) in cows, or Creutzfeld-Jacob Disease (CJD) in humans].
- BSE Bovine Spongiform Encephalopathy
- CJD Creutzfeld-Jacob Disease
- Nanobacteria are nanoscale bacteria, some of which have recently been postulated to cause biomineralization in both humans and animals. It has further been postulated that nanobacteria may play a role in the formation of kidney stones, some forms of heart disease and Alzheimer's Disease. Further, nanobacteria are also suspected of causing unwanted biomineralization and/or chemical reactions in some industrial processes.
- contaminants that can be removed from fluid using the disclosed article include, but are not limited to noxious, hazardous or carcinogenic chemicals comprised of natural and synthetic organic molecules (such as toxins, endotoxins, proteins, enzymes, pesticides, and herbicides), inorganic contaminants (such as heavy metals, fertilizers, inorganic poisons) and ions (such as salt in seawater or charged airborne particles).
- noxious, hazardous or carcinogenic chemicals comprised of natural and synthetic organic molecules (such as toxins, endotoxins, proteins, enzymes, pesticides, and herbicides), inorganic contaminants (such as heavy metals, fertilizers, inorganic poisons) and ions (such as salt in seawater or charged airborne particles).
- Applications of the cleaned fluid, specifically clean water include potable water, irrigation, medical and industrial.
- potable water irrigation, medical and industrial.
- de- ionized water for industrial processes including, but not limited to, semiconductor manufacturing, metal plating, and general chemical industry and laboratory uses.
- the chemical compounds that may be removed from fluid using the article described herein are removal target atoms or molecules that include at least one atom or ion chosen from the following elements: antimony, arsenic, aluminum, selenium, hydrogen, lithium, boron, carbon, oxygen, calcium, magnesium, sulfur, chlorine, niobium, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, germanium, bromine, strontium, zirconium, yttrium, molybdenum, rhodium, palladium, iodine, silver, cadmium, indium, cesium, tin, barium, lanthanum, tantalum, beryllium, copper, fluoride, mercury, tungsten, iridium, hafnium, rhenium, osmium, platinum, gold, mercury, thallium, lead, bismuth, polonium, radon
- Another aspect of the present disclosure relates to a method of making a nanomesh material to be used in an article for removing contaminants from fluid, such as a nanomesh material comprises functionalized carbon nanotubes.
- the general process for making a nanomesh comprising functionalized carbon nanotubes and treated glass fibers eventually used in a cylindrical article is described in Fig. 11. It is noted, however, that the following process can be used to describe the fabrication of any shape article wherein carbon nanotubes are mixed, or not, with an additional substance prior to deposition.
- the "Treated Glass Fiber” described in step 2 would simply be replaced with another substance chosen from any described herein and the substrate described in step 4 would simply change from "cylindrical carbon block” to any desired material and shape, such as a flat woven substrate, when used in an air purification device.
- Fig. 12 is a side perspective of an article comprising a hollow tube of activated carbon having a nanomesh of carbon nanotubes thereon.
- the contaminated fluid flows through the outer wall of the tube with the purified fluid exiting the device from the interior of the hollow tube.
- Fig. 13 is a representation of a flat or planar purification device. 1. Preparation of Functionalized Carbon Nanotubes
- One process for preparing functionalized carbon nanotubes generally comprises an initial sonication of commercially available carbon nanotubes in a solvent.
- Such carbon nanotubes include multi-wall carbon nanotube powder made by any chemical process, such as Chemical Vapor Deposition (CVD) oven process that typically has a purity >95% by weight, and characteristic dimensions of 500nm-50 ⁇ m in length, such as 10-20 ⁇ m, and 2-200 nm in diameter.
- CVD Chemical Vapor Deposition
- the carbon nanotubes are treated in acid, chosen from but not limited to nitric, sulfuric, hydrochloric, and/or hydrofluoric acid or combination thereof.
- acid chosen from but not limited to nitric, sulfuric, hydrochloric, and/or hydrofluoric acid or combination thereof.
- these acids can be used individually to wash the carbon nanotubes, or be used in various combinations.
- the carbon nanotubes are first washed in nitric acid and then washed in hydrofluoric acid.
- the carbon nanotubes are washed in sulfuric acid after being washed in nitric acid.
- the acid wash is performed to remove any contaminants, such as amorphous carbon, or catalyst particles and their supports which may interfere with the surface chemistry of the nanotube, and producing functional groups (such as carboxyl, for example) attached to the defect locations on the surface of the carbon nanotubes.
- contaminants such as amorphous carbon, or catalyst particles and their supports which may interfere with the surface chemistry of the nanotube, and producing functional groups (such as carboxyl, for example) attached to the defect locations on the surface of the carbon nanotubes.
- This functionalization also provides hydrophilicity to the carbon nanotubes, which is thought to improve the filtration performance of the resulting article.
- the carbon nanotubes are then subjected to a final distilled water rinse, and suspension in an appropriate dispersant, such as distilled water, or an alcohol, such as ethanol or isopropanol.
- an appropriate dispersant such as distilled water, or an alcohol, such as ethanol or isopropanol.
- sonication, stirring and heating is employed throughout this functionalization process to maintain adequate dispersion of the nanotubes while cleaning.
- the process of making a nanomesh for use in the described article comprises mixing the previously described functionalized carbon nanotubes with metal oxide (such as iron oxide) or metal hydroxide (such as iron hydroxide) treated (either coated or decorated) fibers as disclosed herein.
- metal oxide such as iron oxide
- metal hydroxide such as iron hydroxide
- the preparation of such metal oxide or metal hydroxide treated glass fibers may comprise mixing a metal oxide or metal hydroxide containing solution with commercially available glass fibers, such as fibers having a diameter ranging from 0.2 ⁇ m-5 ⁇ m.
- the process comprises stirring the glass fibers with a mixture of distilled water and colloidal metal oxide or metal hydroxide solution for a time sufficient to treat the glass fibers.
- the treated fibers may then be dried in an oven.
- the ingredients used to make the suspension comprise the functionalized carbon nanotube solution and the metal oxide or metal hydroxide treated fibers prepared in the previously mentioned processes.
- the functionalized carbon nanotubes are first dispersed in an appropriate medium, such as water or ethanol, by sonication.
- the metal oxide or hydroxide treated glass fibers are separately dispersed in a container, again in an appropriate medium, such as water or ethanol. These separate dispersions are then mixed to form a suspension of functionalized carbon nanotubes and metal oxide or metal hydroxide treated fibers.
- the structure of the final nanomesh may comprise different layers of functionalized carbon nanotubes and metal oxide or metal hydroxide treated glass fibers. These different layers are formed from distinct suspension made from different ratios of carbon nanotubes and treated glass fiber. 4. Deposition of Carbon Nanomesh
- the procedure for depositing the functionalized carbon nanotube/treated fiber mixture including, but not limited to, metal oxide or metal hydroxide coating of any of the fibers disclosed here in.
- the nanomesh can be made from the carbon nanotube/treated fiber mixture using a differential pressure deposition or direct assembly.
- the deposition process uses differential pressure across the substrate to deposit the functionalized carbon nanotube/metal treated fiber suspension onto a carbon block substrate.
- the pressure difference applied across the substrate is such that the pressure is lower inside the substrate block. This differential pressure forces the fluid comprising the suspension to flow through the substrate, depositing carbon nanotube/glass fiber mixture on the outer surface of the substrate, thereby forming the nanomesh. 5.
- the coated substrate is covered with a porous protective paper and a coarse plastic netting to protect the nanomesh material. End caps are then attached and the edges of the nanomesh sealed to prevent fluid circumventing the nanomesh.
- This assembly is then incorporated into an outer housing which is sealed to form the article for removing contaminants from a fluid.
- An example of such a final, nanomesh-containing, filter assembly prior inside an outer plastic housing is shown in Fig. 19.
- the carbon nanomesh filters are capable of removing more than 7 logs of a bacterial contaminant (E. coli) and more than 4 logs of a surrogate for viral agents (the MS 2 bacteriophage). These removal capacities exceed the requirements for bacterial removal and the recommended levels of viral removal specified by the US-EPA (Guidance Manual for Compliance with the Filtration and Disinfection Requirements for Public Water Systems Using Surface Water, U.S. Environmental Protection Agency, March 1991 ). Independent testing of the inventive article, it has confirmed that the article satisfies the basic standards for water purification in the United States.
- MS 2 bacteriophage which is commonly used as a surrogate in assessing a devices virus removal capabilities for drinking water, is a male specific, single stranded RNA virus, with a diameter of 0.025 ⁇ m and an icosahedral shape. Its size and shape are similar to other waterbome viruses such as the polio and hepatitis viruses, although the MS 2 bacteriophage is not a human pathogen.
- E. coli suspension was made by using a sterile, biological loop (commercially available) to remove a loop full of the reconstituted stock [obtained from American Type Culture Collection (ATCC), stock culture ATCC #25922] which was streaked on a commercially available blood agar plate. This plate was then incubated for 12-18 hours at 36 9 C, removed from the incubator and examined for purity.
- ATCC American Type Culture Collection
- ATCC #25922 stock culture ATCC #25922
- the carbon nanotubes were treated with nitric acid solution to remove contaminants (such as amorphous carbon, or catalyst particles and their supports which may interfere with the surface chemistry of the nanotube), increase the number of crystalline defect sites in the nanotubes and to attach carboxyl chemical group to these defect sites.
- This functionalization also provided a hydrophilic behavior to the carbon nanotubes.
- the treatment was performed by mixing 250mg of purified nanotubes in a total volume of 35ml of concentrated nitric acid in a centrifuge tube, shaking well and sonicating in a Cole Parmer 8851 Sonicator at full power for 10 minutes in 50°C water bath. The nitric acid/carbon nanotube mixture was then centrifuged at 2,500 rpm until the supernatant was clear (6-10 minutes) and then the supernatant was decanted. The nitric acid treatment was repeated, but with 20 minutes of sonication.
- nitric acid treated carbon nanotubes were then water washed by suspending them in 35ml total volume distilled water, sonicating (as above) for 10 min, centrifuging (as above), then decanting the supernatant. This water wash was repeated until the pH was at least 5.5 (-3-4 times), sonicating for 5 min each time.
- Test Solutions [0149] The E. co// suspension, prepared as outlined above, was then divided into two equal parts.
- the untreated solution (Test Solution #1 ) was prepared by diluting one of the divided E. co// suspensions with distilled water to attain an E. coli concentration of -2x10 9 cfu/ml (2:5 dilution).
- the other solution (Test Solution #2) was prepared by adding 25 mg of functionalized nanotubes to the other divided E. coli suspension. This solution was then diluted with distilled water to achieve the same concentration of E. coli as in Test Solution #1. This dilution resulted in a concentration of carbon nanotubes in Test Solution #2 of 625 ppm.
- Test Solutions #1 and #2 were simultaneously sonicated with a Branson-2510 Sonicator for 3 min. These Test Solutions were then centrifuged in a commercially available centrifuge at 2500 rpm for 2 minutes to form pellets, and the supernatant decanted leaving 1 ml of supernatant behind. The pellets of Test Solutions #1 and #2 were then used to make two samples (#1 and #2) described below.
- Sample #1 was prepared by placing a drop of the test solution free of carbon nanotubes (Test Solution #1 ) on a commercially available glass microscope slide (American Scientific Products, Micro Slides, plain, Cat. M6145, size 75 x 25 mm that was cleaned with sulfuric acid and rinsed with distilled water) and refrigerated at 4°C for 19 hours. After refrigeration, atomic force microscopy (AFM) analysis was performed (without fixation) using a Veeco Dimension 3100 Scanning Probe System in tapping mode to investigate the sample.
- AFM atomic force microscopy
- Sample #1 was also thermally fixed (by brief exposure to an open flame) and then stained (with Gram Crystal Violet dye) followed by a water wash. Light microscopy was performed using an Olympus light microscope at 100Ox magnification and under immersion oil. Digital images were made with an Olympus DP10 CCD.
- Sample #2 Carbon Nanotube Treated
- Sample #2 was prepared by placing (and smearing) a drop of the carbon nanotube/E. contest solution (Test Solution #2) on a glass microscope slide as described above. The sample was thermally fixed, stained, and light microscopy was conducted as for Sample #1 above. Sample #2 was then placed in a refrigerator at 4°C for 19 hours, after which time it was removed and AFM analysis (as described above) was conducted as for Sample #1. Sample #2 was returned to the refrigerator for an additional 24 hours, after which time light microscopy was again conducted.
- Sample #1 (suspension of bacteria without carbon nanotubes) showed E. coli bacterial cells uniformly distributed over the entire surface of the slide (Fig. 14). The image further shows that the bacteria had well-defined edges, suggesting that the bacteria cells were intact. No changes in their shape were found after 2 days stored in a dry state in the refrigerator.
- sample #1 There were numerous individual bacterial cells present over the entire slide for the sample without carbon nanotubes (Sample #1 ) bacterial cells were absent from most of the slide for the sample with carbon nanotubes (Sample #2). As shown in Fig. 15, any bacteria that were present in the latter case were tightly packed around the carbon nanotubes, indicating that the carbon nanotubes were capturing and holding the bacteria.
- Sample #1 demonstrated E. coli closely packed together. As shown in Fig. 16, the bacterial cells of normal cells have sharp boundaries. The decrease in size and packing density of bacteria was seen in the AFM image of sample #1 before heat treatment and optical image of this sample after heat treatment.
- Sample #2 showed some cells in the vicinity of the nanotubes, with the boundary of the E. coli cell walls being diffused and/or damaged. In fact, after mixing with the nanotubes, some of the E. coli cells disintegrated beyond the point of recognition. The presence of some diffused E. coli fragments was also seen in the vicinity of the nanotubes.
- Fig. 17 shows a scanning electron micrograph (SEM) image of a bacterial cell that burst upon interaction with a carbon nanotube.
- a suspension was prepared using a solution of functionalized carbon nanotubes and iron hydroxide treated glass fibers previously prepared as described above.
- 5g of the functionalized carbon nanotubes (carboxylated through the nitric acid wash procedure described in Example #1 ) were suspended in 1 liter of water and placed in a room temperature water bath in a Cole Parmer 8851 Sonicator and sonicated at full power for 20 minutes.
- Four liters of distilled water were added to the sonicated, functionalized carbon nanotubes/water mixture to yield a concentration of 1 mg functionalized carbon nanotubes per 1 ml water.
- Approximately 100ml of Fe decorated glass fiber solution was placed in a separate container and diluted to 1 liter with distilled water. This mixture was blended in a commercial blender for 5 minutes.
- the structure of the final nanomesh was achieved by depositing a layer of the functionalized carbon nanotubes/iron hydroxide coated glass fiber mixture onto a carbon block substrate.
- FIG. 18 The procedure for depositing the functionalized carbon nanotube/iron hydroxide coated or decorated glass mixture is schematically represented in Fig. 18.
- a filter assembly was made by loading a cylindrical carbon block onto a perforated mandrel.
- the deposition chamber was filled with the carbon nanotube/glass fiber suspension (5:8 ratio).
- the filter assembly was connected to vacuum tubing leading to a Franklin Electronics Varian TriScroll vacuum pump and then was submerged in the filled deposition chamber.
- the vacuum pump attached to the filter assembly was turned on and the entire suspension was drawn through the carbon filter substrate under vacuum, depositing a nanomesh on its outer surface.
- the deposited filter assembly was removed from the deposition chamber, remained connected to the vacuum pump and the deposited nanomesh filter assembly was dried under vacuum for 1 -2 hours in a drying oven set at 50° C within a nitrogen atmosphere.
- the fully assembled filter article was comprised of a central carbon filter core coated with the functionalized carbon nanotube nanomesh and covered by a porous protective paper held in place with cylindrical plastic netting. This cartridge was capped and the edges of the nanomesh sealed to prevent fluid circumventing the nanomesh and placed into an outer housing to create the final product (Fig. 19). Effectiveness of Cylindrical Purification Article:
- a bacterial assay was conducted by challenging the nanomesh, made in accordance with the present example (Example 2), with a challenge fluid of reconstituted E. coli stock culture ATCC #25922.
- This challenge fluid was made by using a sterile biological loop (commercially available) to remove a loop full of the reconstituted stock and streaking it on a commercially available blood agar plate. This plate was then incubated for 12-18 hours at 36 s C. The culture was then removed from the incubator and examined for purity.
- Example 3 Fabrication of a Flat Purification Article [0173] Analogously to Example 2, a flat nanomesh was made from commercially available purified carbon nanotubes and a non-woven, fused, polypropylene fabric substrate.
- a challenge test was run following the same procedures as in Example 2, except that the composition of the challenge solution was -1x10 8 cfu/ml of E. coli. A total of 100 ml (total -1x10 10 cfu) of this challenge solution was drawn through the carbon nanomesh/substrate material using a differential pressure of -0.25 psi. A control filtrate was obtained by passing the E. coli challenge filtrate through a commercially available 0.45 micron Millipore filter. The test challenge filtrate was not concentrated. The resulting filtrates, of the control and the challenge, were then analyzed with a commercially available spectra-photometer to determine the presence of protein and DNA.
- the fuel/water/bacteria challenge filtrate sample was allowed to separate into its fuel - water components, and four test samples were obtained from each component. Each test sample was plated on agar. Samples were then incubated to analyze bacteria growth at 37 0 C and samples were incubated at room temperature to analyze mold growth. No bacteria or mold culture growth was observed on the challenge filtrate test plates after incubating the samples for 24 and 48 hours. The control samples presented vigorous colonies of bacteria and mold growth after incubation at 24 and 48 hours. The results confirm that the carbon nanomesh, made in accordance with the present example (Example 3), was a barrier to bacteria in fuel for it accomplished removal of bacteria and mold from the fuel beyond the limits of detection with testing protocols.
- a flat nanomesh device was made from commercially available, purified, carbon nanotubes and a non-woven, fused, 0.5 oz/yd 2 carbon tissue paper substrate.
- the construction of this device utilized a process of self assembly of the nanomesh, as defined above.
- Specific electropositive and electronegative functional components were used to enable this self assembly.
- the carbon nanotubes were functionalized with amine groups which caused them to be electropositive (i.e. positive zeta potential) when dispersed in water.
- the glass fibers were decorated with iron hydroxide clusters that caused them to be electronegative when dispersed in water. As shown in Fig. 22, when the two suspensions were combined, the nanotubes wrapped around the glass fibers due to electrical forces.
- the dehydrated nanotubes were suspended in 500ml of ethylenediamine and sonicated for 20 hours at 60 0 C in a nitrogen atmosphere.
- the ethylenediamine was distilled off and the sample washed with 0.1 M hydrochloric acid, filtered and rinsed repeatedly with distilled water until a neutral pH is reached.
- the rinsed amine functionalized carbon nanotubes were then dried in an oven at 100 0 C for 24 hours.
- Example #4 The flat purification device constructed in the present example (Example #4) using the amine functionalized carbon nanotubes and iron hydroxide decorated glass fibers was tested for biological removal as in described in the Tests of Effectiveness for Example #3 [test a) E. coli and b) MS-2 bacteriophage]. These tests demonstrated that the self-assembled nanomesh article achieved a removal capability for bacteria and virus of over 8 logs and 7 logs, respectively.
- a 64 layer, flat nanomesh device was made from: commercially available purified, functionalized carbon nanotubes; glass fibers measuring 100- 500nm in diameter and 300-500 ⁇ m in length; a solution of 0.0125% by weight of polyvinyl alcohol with a molecular weight of 20,00Og in distilled water; 1.5 oz/yard cellulose filter paper as an insulator; a non-woven, fused, 0.5 oz/yard 2 conductive carbon tissue paper substrate; silver-imbedded conductive and insulating epoxies; a plastic, non-conductive housing; and a power supply to supply 1.5V DC across each neighboring pair of conducting nanomesh layers.
- This carbon nanotube/glass fiber suspension was deposited on a 5"x5" area of a 5.5"x5.5" sheet of 0.5 oz/yard 2 carbon tissue paper using differential pressure of ⁇ 1 psi. Four 2" diameter discs were cut from this 5"x5" nanomesh sheet, thereby completing 4 layers of the 64 layer, 2" diameter device (32 of the 64 layers are conductive, the others are insulating). [0196] An electrical lead was attached to each conductive nanomesh layer using a silver-filled conductive epoxy. All conductive nanomesh layers were sandwiched between insulating layers and these "sandwiches" were then stacked with the electrical leads being equally spaced azimuthally (i.e.
- a dynamic retention test was performed, wherein a differential DC voltage of 4.OmV was applied to each of 16 neighboring pairs of conductive nanomesh layers (i.e. even numbered nanomesh layers were positively charged and odd numbered layers were negatively charged).
- a saline challenge solution of 1 g of sodium chloride dissolved in 1000 ml of distilled water (1%o salinity) was used to test the efficacy of the device. In one pass through the device, 1.6% of the salt was removed. This removal rate was equivalent to 0.52 g of salt per g of carbon nanotubes. This represented a 23% increase in salt removal over the static device, showing that even a very weak voltage enhanced the removal of salt ions from a water solution, thereby demonstrating the nano-electric removal effect. Further enhancement of the salt removal will certainly be achieved as the DC voltages are increased and AC signals, which disrupt the DeBye atmosphere, are imposed.
- a flat air membrane filter was constructed using functionalized carbon nanotubes (carboxylated through the nitric acid wash as described in
- Example #1 The procedure suspended 25mg of these functionalized nanotubes in 25ml of distilled water and sonicated for 10 minutes in a Branson Model 900B Sonicator in a water bath at room temperature. This solution was then diluted to 4 liters with distilled water and polyvinyl alcohol was added so that a concentration of 0.125% polyvinyl alcohol by weight was achieved. The suspension was then mixed for 3 minutes at speed setting 3 with an UltraTurrax T18 Basic immersion blender. The nanomesh was created by deposition on a 5"X5" area of a 5.25"X5.25" square piece of porous, polymeric substrate using a differential pressure filtration process with a differential pressure of ⁇ 1 psi. Test of Effectiveness of Air Membrane Article:
- Biological removal testing was performed on the membrane to determine its effectiveness. Two 2.5" discs were cut from the square membrane and were mounted between two flat metal rings of 2" ID, 2.5" OD. One disc was used to measure the pressure drop versus flow speed curves for the membrane article device, while the other was used for biological removal testing. The bio- removal testing was done by mounting the filter disc in a 2" ID cylindrical wind tunnel (schematically shown in Fig. 21 ) which was capable of testing the capture efficiency of bacterial spores of Bacillus subtilis, a widely accepted surrogate for biological agents but not a human pathogen, making it safe for laboratory testing.
- the testing entailed releasing the bacterial spores upstream of the filter disc through an aerosolizer and capturing the fraction that passed through the filter in a fluid-filled, all-glass impinger at the downstream end of the testing apparatus.
- a controlled set of experiments were performed to estimate the spore retention of the testing apparatus. In this biological testing, we achieved over 6 logs of removal of Bacillus subtilis spores. Further, we were able to determine that removal of biological agents is independent of the removal of non-biological particles and of the filter's resistance to air flow.
Abstract
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