Mitsubishi Rayon Co., Ltd. (Minato-Ku, Tokyo, JP) secured U.S. Patent 7,645,400 for carbon nanotube compositions and coatings that does not impair the characteristics of the carbon nanotubes and allows the carbon nanotubes to be dispersed or solubilized in a solvent.
The method does not result in separation or aggregation of the carbon nanotubes even during long-term storage. The compositions have superior electrical conductivity, film formability and moldability, and can be easily coated or covered onto a base material. The resulting coated film has superior moisture resistance, weather resistance and hardness.
In order to produce the carbon nanotube coatings, inventor Takashi Saitoh developed a carbon nanotube composition that contains a conducting polymer or heterocyclic compound trimer, a solvent and carbon nanotubes, and may additionally contain a high molecular weight compound, a basic compound, a surfactant, a silane coupling agent and colloidal silica as necessary; a composite having a coated film composed of the composition; and, their production methods.
Although the reason for this is not fully understood, the carbon nanotubes are presumed to be dispersed or solubilized together with the conducting polymer due to mutual adsorption by the conducting polymer and the carbon nanotubes due to the .pi.-.pi. interaction by .pi. electrons.
High molecular weight compounds, plastics, wood, paper, ceramics, fibers, non-woven fabrics, carbon fibers, carbon fiber paper and their films, foams, porous films, elastomers and glass plates can accept a coating of the carbon nanotube composition.
A coated film may be applied to a base material by a method used for ordinary coating. Examples of methods used include coating methods using a gravure coater, roll coater, curtain flow coater, spin coater, bar coater, reverse coater, kiss coater, fountain coater, rod coater, air doctor coater, knife coater, blade coater, cast coater or screen coater, spraying methods such as air spraying or airless spraying, and immersion methods such as dipping.
Bone replacement materials are of increasing importance in the orthopedic, cranio-maxillofacial, and dental fields. Materials that set into solid, calcium-containing mineral products are of particular interest as such products can closely resemble the mineral phase of natural bone and are potentially remodelable. The bone replacement materials are used for repairing fractured bone, strengthening cancerous bone, reinforcing osteoporotic bone, accelerated dental implant anchorage, and the like.
There is a need for a bone replacement material having improved biocompatibility with natural bone. Further needs include a bone replacement material that facilitates the regeneration and growth of bone. Additional needs include a bone replacement material that is biodegradable.
In the treatment of osteoporosis and other bone disorders, it is desirable to deliver therapeutic compounds to the bone. However, it is known that certain substances, although therapeutic, are too toxic to be transported in the human body in free form. For example, fluoride anion (F–) is known to be an active therapeutic agent for osteoporosis, and the only known agent that can generate new bone matrix and new mineral from previously inactive areas. It both improves bone strength and helps prevent fractures. Yet it is too toxic to be administered in free form, such as by injecting NaF in aqueous solution intravenously.
One recently approved treatment for bone disease is a class of chemicals known as biphosphonates. Bisphosphonates bind to bone, slowing osetoporosis and allowing new bone to be formed. However, because this effect is temporary, bone mass is not substantially increased in the long term. Because new bone is not formed, bones are left weakened and prone to later injury.
Hence, bisphosphonates alone are not entirely satisfactory. There remains a need for a suitable compound that inhibits bone resorption and promotes new bone formation so as to produce a net bone gain without adversely affecting the patient. Further, such a compound would be targeted to bone, permitting the release of a therapeutic agent at the site of the bone, and hindering any, potentially harmful release of the agent to the rest of the body.
Professor Lon Wilson in the Dept. of Chemistry has pioneered a new class of drugs for the treatment of osteoporosis and possibly other bone disorders. This medical advancement provides a non-toxic, biologically active composition that is capable of promoting bone growth while simultaneously inhibiting bone resorption, so as to produce a net bone gain. In its most essential design, the drug is comprised of a bisphosphonate group linked to a fullerene molecule. Alternatively, the bisphosphonate group can form chemical bonds directly with the fullerene, or between a linking molecule.
A preferred method of synthesis of a fullerene-based bisphosphonated drug includes attachment of a water-solubilizing group, and attachment of a therapeutic agent. A plurality of fluorine atoms, as a therapeutic agent, are bound to one hemisphere the fullerene, thus hindering toxicity. Further it is believed that fluorine anion is released over time at the surface of the bone, due partly to the basic and nucleophilic environment of bone’s surface.
It is known that fluorine anion generates new bone matrix and new mineral from previously inactive areas. It is envisioned that polyfluorobisphosphonated fullerenes, as bimodal drugs, can deliver the two bisphosphonate and F– components to bone in a single, non-toxic “package” that is easily absorbed in the gastrointestinal tract.
Professor Wilson's research program involves bringing carbon nanotechnology to the fields of biology and medicine. The nanoparticle "building blocks" of this program are fullerenes (C60), endohedral metallofullerenes (M@C60), and ultra-short (20 nm long) single-walled carbon nanotube capsules (US-tubes). Externally, these carbon nanostructures are being chemically derivatized to make them biocompatible and cell-specific through peptide and antibody targeting. Internally, the nanostructures are being loaded with materials of medical interest for diagnostic and therapeutic medicine.
Other materials of interest include Fe2O3 and Gd3+ ions for magnetic resonance imaging (MRI), I2 molecules for X-ray computed tomography (CT) imaging and alpha-particle radionuclides (Ac3+-225 and At-211) for alpha-radioimmunotherapy of single-cell cancers. Cancer therapies are also being developed that take advantage of superparamagnetic nanostructures, such as Gd3+@US-tubes, that are simultaneously diagnostic (MRI-guided) and therapeutic (magnetic hyperthermia) agents in a single package. All these carbon nanostructures, with their medical cargos, are designed to be among the first intracellular agents, since the future of medicine will involve the early detection of disease at the cellular level when it is most treatable.
Nanoengineered materials promise great advances in medicine, and, working with colleagues at various medical centers, our goal is to bring key, high-performance materials to the clinic as soon as possible.
Rice reports a patent application has been filed to cover the use of fullerenes for the treatment of osteoporosis.
Contact: Brian Phillips, Rice University Office of Technology Transfer Tel: 713-348-6278 Brian.j.phillips@rice.edu
Invention Abstract: Fullerenes for the Treatment of Osteoporosis Technology ID: #20025 Investigator: Professor Lon Wilson
The Hewlett-Packard Company has developed a maskless method of patterning a carbon nanotube layer on a substrate with a laser beam. The laser beam is directed onto the surface of a carbon nanotube layered on a substrate. Relative movement between the laser beam and the first surface is caused, thereby forming at least one cavity feature on the substrate layered with a thin film of carbon nanotubes.
In U.S. Patent Application 20090311489, HP inventors Lynn Sheehan (Barndarrig, IE), Kevin Dooley (Blessington, IE) and Rory Jordan (Dublin, IE) detail a system and method for direct write patterning of carbon nanotube thin films for flexible, transparent, electronics applications using laser ablation. The system provides for large area, high resolution, patterning of carbon nanotube films. The patterning method is more efficient than other methods, such as photolithographic processes, since the patterning may be accomplished in one process step as opposed to multi-step photolithographic processes
The carbon nanotube film to be patterned is first produced by filtering a fixed quantity of the dispersion through a nitrocellulose membrane. After the film is set, the surfactant is removed via solvent washing. The membrane containing the nanotube film is then transferred to a substrate, and dried for 2 hours at 90.degree. C. The membrane is removed by dissolving the membrane in a suitable solvent, such as acetone. A number of solvent baths may be performed to ensure that the membrane is totally removed. This process results in a carbon nanotube film on a substrate, which can then be patterned into desired features. The thickness of the nanotube film can be controlled by changing the concentration of tubes in the solution.
The laser is an 11 W diode pumped solid state pulsed ultraviolet (UV) laser operating at 60 kHz. The laser generates UV laser light with a wavelength of less than 400 nm, and the wavelength is tied to energies that are equal to or higher than the bond energy of the material to be patterned The interaction between the carbon nanotube layer in substrate and the pulsed UV radiation results in the dissociation of certain chemical bonds in the carbon nanotube molecules, fragmenting it into smaller units. Above a specific threshold energy, carbon nanotube fragments are ablated from the surface of substrate. The amount of material that is ablated increases with increasing laser power.
A computer that contains pattern information also includes laser power control information, which defines the laser power that is to be used at the various points in the pattern followed by the laser beam. Based on the stored pattern information, a controller is configured to cause system to scan the laser beam over the substrate in any desired pattern, and form cavity features (e.g., channels or microchannels) in the substratein a single process step by modifying the laser power above and below the ablation threshold while scanning the laser beam across the substrate. The laser patterning performed by the Hewlett-Packard system provides a reduction in process steps, compared to conventional photolithographic processes, as it provides for the patterning of features in carbon nanotube films without the need for photo-masks and the associated develop processes.
Since their discovery in 1991, carbon nanotubes (CNTs) have attracted considerable attention from researchers because of their unique electrical, mechanical, and thermal properties. The remarkable electrical properties of carbon nanotubes make them ideal candidates for applications such as sensors, interconnects, transistors, and flat panel displays. These properties provide an opportunity to develop high performance flexible, transparent electrodes for use in various products. However, for successful implementation into products such as flexible electronics, it is desirable to have methods to deposit and pattern carbon nanotubes over large areas, at high resolution, and with processing temperatures that are compatible with plastics. In order to take advantage of the potential electrical and optical properties of carbon nanotubes, manufacturers will have to be able to pattern the materials into common electronic circuitry forms.
Inkjet printing of carbon nanotubes directly onto a substrate in a desired pattern has been previously proposed. However, such a process has the disadvantages of ink formulation for the carbon nanotubes, resolution limitations, and insufficient attachment to the substrates. Patterning techniques based on substrate and carbon nanotube chemistry interactions have also been previously proposed. This process has the disadvantages of very complicated chemical science, inconsistent results for pattern fill, and the need to pattern the attach chemical prior to attaching the carbon nanotubes.
Photolithographic processes have also been proposed. Such processes have the disadvantage of requiring several photolithographic and plasma etch steps to complete the desired pattern. Another proposal is to use laser trimming of carbon nanotubes using a copper mask system. This laser trimming method can produce patterns of carbon nanotubes defined by the copper grid mask. This method has the disadvantages that only patterns defined by the copper grid can be produced, and the laser exposure needs to be uniform over the area being patterned.
Hewlett-Packard inventors believe their use of laser patterning overcomes the limitations of the above processes.
SouthWest NanoTechnologies Inc. (SWeNT), a leading manufacturer of single-wall and specialty multi-wall carbon nanotubes (CNT), has been awarded two prestigious grants from the Oklahoma Center for the Advancement of Science and Technology (OCAST). The Oklahoma Nanotechnology Initiative is the focal point for information on nanotechnology in the state. OCAST contracts with The State Chamber of Oklahoma to manage the Oklahoma Nanotechnology Initiative (ONI).
The first is an Oklahoma Applied Research Support (OARS) grant. The topic is "Next Generation LED Lighting with CNT Printed Electrodes." SWeNT will use the OCAST grants to develop a new generation of single-walled carbon nanotubes with higher electrical conductivity and transparency than is currently available commercially.
"Improved nanotubes developed under the OARS grant will enable printed LED lighting products that consume one third the energy of fluorescent bulbs," explains David Arthur, SWeNT CEO. "Furthermore, the carbon nanotubes we develop for LED lighting will also be used in a wide range of other pioneering applications including photovoltaics, super-capacitors, batteries and displays."
SWeNT also received funds to engage three interns under the Faculty and Student Intern Partnership program, in response to SWeNT's proposal for "Undergraduate Internships in Advanced Nanotechnology. "This grant will allow these interns to gain real-world research experience helping to develop innovative advanced materials."
"OCAST's support for our employment of interns to assist us in new technology development will help us on the OARS activity as well as other research activities we have planned," says Arthur. "Both SWeNT and the student interns will have much to gain from this program." OCAST is a state agency established to foster innovation in existing and developing businesses in Oklahoma. Ricardo Prada-Silvy with Southwest NanoTechnologies (SWeNT) Inc. will direct student interns in nanotechnology research. Plans call for hiring three interns for projects currently underway at SWeNT which is an internationally recognized firm with a focus on nanotechnology development. Award: $59,910 for two years
"We're very pleased with and grateful for this continued support from our state represented by these two grants. SWeNT would not be a leading carbon nanotubes producer today without OCAST support," Arthur explains.
Fulcrum SP Materials (Herzliah Pituach, Israel) reports it has signed a collaboration agreement with Arkema Inc. concerning the development of high performance composite parts with improved damage resistance. Arkema will contribute its multiwall carbon nanotubes (CNTs) technology and Fulcrum will bring its propriety protein base interface and dispersion technology for CNTs. The objective of the project is to develop a technology allowing the grafting of CNTs on 2 dimensional or 3 dimensional woven fabrics such as Carbon fibers. Such reinforced fabrics will be used to produce advanced composite parts for applications in aeronautics or other industrial applications.
Fulcrum's technology was invented by Professor Oded Shoseyov and Professor Arie Altman both from the Robert H. Smith Faculty of Agriculture, Food & Environment at The Hebrew University of Jerusalem, and was licensed to Fulcrum for further development, by Yissum, the technology transfer arm of the Hebrew University.
Advanced composites are advanced structural materials, such as carbon fibers and Kevlar, in a matrix such as epoxy resin. Stronger and lighter then conventional materials such as steel and aluminum, they are being used in aero-space, sports, ballistics and clean-tech applications. The aspiration for higher strength to weight ratioandlightweight, fuel-saving technologies, as well as the search for environment-friendly products, creates a tremendous demand for new technologies in the market of advanced composites. The global market size of for composite materials was $21.5 Billion and is expected to reach $53 Billion in 2014.
For the past three years, Arkema has been involved in major development programs designed to assist companies seeking innovation by using nano-structured materials. Arkema, as a world leader in nano-structured materials, and a producer of carbon nanotubes (CNT), has established a large number of partnerships in various sectors for applications requiring enhanced performance in terms of electrical conductivity, thermal conductivity, and mechanical strength.
"Fulcrum's innovative technology of bonding carbon nanotubes directly to the fabric such as carbon fiber, is unique and if successful, could set new standards in advanced composites markets," said Moshe Kelner, President of Arkema in Israel.
"We welcome the agreement with Arkema, this cooperation will enable Fulcrum to reach a wider base of applications and customers with our ground breaking technology," said Nimrod Litvak, Fulcrum's CEO.
Arkema, a global chemical company and France’s leading chemicals producer, reports sales of $9 billion and holds leadership positions in its principal markets with internationally recognized brands. Arkema has 15,000 employees in over 40 countries and six research centers located in France, the United States and Japan.
Fulcrum is a nanotechnology company aiming to commercialize the use of nano-particles in the fast growing market of composite materials. Fulcrum's proprietary platform technology utilizes genetically engineered proteins to create self-assembly nano-structures with ground breaking, innovative properties. The first developed nano-structures include carbon nanotubes (CNT) bound to fabrics such as Carbon fabric and Kevlar and CNT reinforced polymers (epoxy resins).
FIG. 10 exemplifies an external appearance of a vertically aligned double-walled carbon nanotube bulk structure obtained through growth by chemical vapor deposition (CVD) apparatus developed at AIST's Nanotube Research Center as shown in U.S. Patent Application 20090297846.
Japanese researchers at the National Institute of Advanced Industrial Science and Technology (AIST) Nanotube Research Center (Ibaraki, JP) reveal a process to selectively produce aligned double-walled carbon nanotube bulk structure in U.S. Patent Application 20090297846. The process is capable of "realizing high purity, large scaling and patterning, an aspect of which has not hitherto been achieved," say inventors Kenji Hata Takeo Yamada. Motoo Yumura, and Sumio Iijima.
The process can produce double-walled carbon nanotube, characterized by having an average outer diameter of 1 nm or more and 6 nm or less and a purity of 98 mass % or more can be produced in bulk. According to the process it is possible to produce a double-walled carbon nanotube and its bulk structure with high selectivity and high efficiency by extremely simple means inclusive of control of the particle size of fine particles of the catalyst metal, control of the thickness of a catalyst metal thin film enabling to realize it and the presence of an oxidizing agent such as water vapor in the reaction system.
The height (length) of the vertically aligned double-walled carbon nanotube varies depending upon the use; its lower limit is 0.1 .mu.m, and its upper limit is not particularly limited, from the viewpoint of actual use, it is preferably between 2.5 mm to 10 cm or more. In addition, it is possible to prolong the life of the metal catalyst, realize the efficient growth thereof at a high growth rate and achieve mass production. Also, the carbon nanotube grown on a substrate can be easily peeled off from the substrate or catalyst.
The inventors say, it is to be especially emphasized that according to the production process, the double-walled carbon nanotube coexisting with a single-walled carbon nanotube (SWCNT) and a multi-walled carbon nanotube of three or more, its proportion of presence following the growth can be freely selected and controlled by controlling the particle size of the catalyst metal and further the thin film of the catalyst metal. For example, the proportion of the double-walled carbon nanotube can be selectively controlled at 50% or more, 80% or more, and further 85% or more.
On the other hand, it is also possible to increase the proportion of the single-walled carbon nanotube or the multi-walled carbon nanotube of three or more walls. According to such control, the behavior of its application is largely expanded. The aligned double-walled carbon nanotube bulk structure can be expected to have various applications in heat dissipators, heat conductors, electric conductors, reinforcing materials, electrode materials, batteries, capacitors or super capacitors, electron emission elements, adsorbing agents, optical elements and in semiconductor devices.
The patterning method for semiconductor devices may be a wet process or a dry process. For example, in addition to patterning using a mask, patterning using nanoimpirnting, patterning using soft lithography, patterning using printing, patterning using plating, patterning using screen printing and patterning using lithography are all possible. As shown in FIG. 1, a thin film of a metal catalyst having a strictly controlled thickness is first provided on a substrate. For example, an iron chloride thin film, an iron thin film prepared by sputtering, an iron-molybdenum thin film, an alumina-iron thin film, an alumina-cobalt thin film and an alumina-iron-molybdenum thin film can be enumerated.
A carbon nanotube chemical vapor deposition (CVD) equipment is used with an apparatus for feeding an oxidizing agent to grow the DWNT. It is not particularly limited with respect to configuration and structure of other reaction apparatus and reactors for achieving the CVD method. Any of known conventional apparatus such as a thermal CVD furnace, a heating furnace, an electric furnace, a drying furnace, a thermostat, an atmospheric furnace, a gas replacement furnace, a muffle furnace, an oven, a vacuum heating furnace, a plasma reactor, a micro plasma reactor, an RF plasma reactor, an electromagnetic wave heating reactor, a microwave irradiation reactor, an infrared ray irradiation heating furnace, an ultraviolet ray heating reactor, an MBE reactor, an MOCVD reactor and a laser heating apparatus can be used.
FIG. 2 is a schematic view of a production apparatus for producing double-walled carbon nanotube or an aligned double-walled carbon nanotube bulk structure.
Figure 13 is a tunneling electron microscope (TEM) photographic image obtained by peeling off the vertically aligned double-walled carbon nanotube from its substrate using a pair of tweezers, dispersing it in a solution, placing it on a grid of an electron microscope (TEM) and observing it by an electron microscope (TEM). It is noted that neither the catalyst nor amorphous carbon is incorporated in the obtained carbon nanotube. The double-walled carbon nanotube of pictured is 99.95 mass % in a non-purified state
Frequently, the availability of materials limit the research and development of applications, and SWNTs are no different, where their mass production is the key factor in establishing a CNT industry. The Nanotube Research Center is committed to and actively engaged in developing methods for mass production of economical, pure, and high quality SWNTs based on its Super Growth methods. The Center is running a 5 year/ $20million national project to pursue this goal. For SWNTs to become a widely used industrial material, the cost must be reduced to the level of classic carbons, such as activated carbon or carbon-fibers. This translates to a 100-fold to 1000-fold reduction in production cost in the future. They believe that this problem will eventually be solved by the very high growth efficiency of Super-growth that can already produce more than 1 g of SWNTs in ten minutes on a A4 (20x30cm) substrate.
National Institute of Advanced Industrial Science and Technology (AIST) Nanotube Research Center AIST Tsukuba Central 5 1-1-1 Higashi Tsukuba Ibaraki 305-8565 Japan TEL : +81-29-861-4654 FAX : +81-29-861-4654
In U. S. Patent 7,634,337, Snap-On Incorporated (Pleasant Prairie, WI) inventors Steven Brozovich and Robert Hoevenaar disclose a programmable vehicle or engine diagnostic tool that includes an interface for receiving a signal relating to a performance parameter of the vehicle or engine, a user interface, and a central processing unit, for processing the signal to generate information for presentation to the user. To facilitate fast boot yet enable re-programming of the diagnostic tool, the system utilizes a non-volatile random access memory main memory for the processor based tool, to store the programming for execution by the central processing unit. Disclosed examples of suitable memories include magnetoresistive random access memory (MRAM), carbon nanotube random access memory (CN-RAM) and programmable metallization memory cell (PMC) memory.
Snap-On’s diagnostic system includes a non-volatile nano random access memory (NNRAM) coupled to the central processing unit. The NNRAM serves as random access main memory for the central processing; and programming is stored in the NNRAM. The programming consists of an operating system and at least one vehicle or engine diagnostic application program for execution by the central processing unit directly from the NNRAM memory serving as the random access main memory for the central processing unit. The execution of the programming directly from the NNRAM by the central processing unit controls the processing operation of the central processing unit with regard to one or more vehicle or engine diagnostic functions of the system.
According to the Brozovich and Hoevenaar, NNRAM or the like allows the tool designer/ manufacturer to provide the desired programmability (something that would be lost if a standard ROM were used which would also be fast for OS and application memory). The fast access time and fast read/write (R/W) times of NNRAM or the like make the boot time minimal, since the tool runs the software programming right out of the non-volatile main memory, eliminating the time required to download into fast RAM from Flash or a hard disk drive. This allows an altering of the system architecture in that the memory no longer needs separation into two areas, nonvolatile (slow) RAM and fast SRAM (static RAM) or PSRAM (pseudostatic RAM). Hence, this new architecture also should be cheaper and smaller and typically have longer battery life because of reduced memory circuitry.
In U.S. Patent 7,632,569, Rice University researchers disclose a high yield, single step method for producing large quantities of continuous macroscopic carbon fiber from single-wall carbon nanotubes using inexpensive carbon feedstocks at moderate temperatures. The production method also includes steps for purifying a mixture of single-wall carbon nanotubes and amorphous carbon contaminate. Purification includes the steps of heating the mixture under oxidizing conditions sufficient to remove the amorphous carbon, followed by recovering a product that is at least about 80% by weight of single-wall carbon nanotubes, according to inventors Richard E. Smalley (deceased), Daniel T. Colbert, Hongjie Dai, Jie Liu, Andrew G. Rinzler, Jason H. Hafner, Ken Smith, Ting Guo, Pavel Nikolaev and Andreas Thess.
A method for producing tubular carbon molecules of about 5 to 500 nm in length is also disclosed. The method includes the steps of cutting single-wall nanotube containing-material to form a mixture of tubular carbon molecules having lengths in the range of 5-500 nm and isolating a fraction of the molecules having substantially equal lengths. The nanotubes may be used, singularly or in multiples, in power transmission cables, in solar cells, in batteries, as antennas, as molecular electronics, as probes and manipulators, and in composites.
The purification process comprises heating the SWNT-containing felt under oxidizing conditions to remove the amorphous carbon deposits and other contaminating materials. In a preferred mode of this purification procedure, the felt is heated in an aqueous solution of an inorganic oxidant, such as nitric acid, a mixture of hydrogen peroxide and sulfuric acid, or potassium permanganate. Preferably, SWNT-containing felts are refluxed in an aqueous solution of an oxidizing acid at a concentration high enough to etch away amorphous carbon deposits within a practical time frame, but not so high that the single-wall carbon nanotube material will be etched to a significant degree. Nitric acid at concentrations from 2.0 to 2.6 M have been found to be suitable. At atmospheric pressure, the reflux temperature of such an aqueous acid solution is about 120.degree. C.
The nanotube-containing felts can be refluxed in a nitric acid solution at a concentration of 2.6 M for 24 hours. Purified nanotubes may be recovered from the oxidizing acid by filtration through, e.g., a 5 micron pore size TEFLON filter, like Millipore Type LS. Preferably, a second 24 hour period of refluxing in a fresh nitric solution of the same concentration is employed followed by filtration.
Refluxing under acidic oxidizing conditions may result in the esterification of some of the nanotubes, or nanotube contaminants. The contaminating ester material may be removed by saponification, for example, by using a saturated sodium hydroxide solution in ethanol at room temperature for 12 hours. Other conditions suitable for saponification of any ester linked polymers produced in the oxidizing acid treatment will be readily apparent to those skilled in the art. Typically the nanotube preparation will be neutralized after the saponification step. Refluxing the nanotubes in 6M aqueous hydrochloric acid for 12 hours has been found to be suitable for neutralization, although other suitable conditions will be apparent to the skilled artisan.
After oxidation, and optionally saponification and neutralization, the purified nanotubes may be collected by settling or filtration preferably in the form of a thin mat of purified fibers made of ropes or bundles of SWNTs, referred to hereinafter as "bucky paper." In a typical example, filtration of the purified and neutralized nanotubes on a TEFLON membrane with 5 micron pore size produced a black mat of purified nanotubes about 100 microns thick. The nanotubes in the bucky paper may be of varying lengths and may consist of individual nanotubes, or bundles or ropes of up to 10.sup.3 single-wall nanotubes, or mixtures of individual single-wall nanotubes and ropes of various thicknesses. Alternatively, bucky paper may be made up of nanotubes which are homogeneous in length or diameter and/or molecular structure due to fractionation as described hereinafter.
The purified nanotubes or bucky paper are finally dried, for example, by baking at 850.degree. C. in a hydrogen gas atmosphere, to produce dry, purified nanotube preparations.
The conditions may be further optimized for particular uses, but this basic approach by refluxing in oxidizing acid has been shown to be successful. Purification according to this method will produce single-wall nanotubes for use as catalysts, as components in composite materials, or as a starting material in the production of tubular carbon molecules and continuous macroscopic carbon fiber of single-wall nanotube molecules.
