WO2007001412A2

WO2007001412A2 - Method for purifying carbon nano-onions

Info

Publication number: WO2007001412A2
Application number: PCT/US2005/036348
Authority: WO
Inventors: James M. Howe
Original assignee: University Of Virginia Patent Foundation
Priority date: 2004-10-07
Filing date: 2005-10-07
Publication date: 2007-01-04
Also published as: WO2007001412A3

Abstract

The present invention provides for a novel method of obtaining and purifying carbon nanoparticules, including carbon nano-onions. The present invention provides used diesel oil as a cheap and abundant source of carbon nano-onions and their use in various nanotechnology applications.

Description

COMPOSITIONS AND METHODS FOR LARGE-SCALE PRODUCTION AND USES OF CARBON NANO-ONIONS

Cross Reference to Related Applications This application claims priority under 35 U.S.C. § 119(e) to US Provisional

Application Serial No. 60/616,817, filed October 7, 2004, the disclosure of which is incorporated herein by reference in its entirety.

Field of the Invention The invention relates to a new method for obtaining and for purifying carbon nanoparticles. The invention further relates to an abundant source, method of producing, and uses of carbon nano-onions.

Background of the Invention A tremendous amount of research is currently being performed to develop carbon nanomaterials such as carbon nanotubes and Fullerenes for use in electronic devices, ultra-hard coatings, polymeric thin films, photovoltaic/solar cells, medical imaging, drug delivery, ultracapacitors, broad-band optical limiters and other optical devices, electrospun nano-fibers, MEMS and NEMS devices, adhesives, improved rubbers and polymers, ceramics, alloys, cermets, nanotribology applications, as well as hydrogen and lithium ion storage devices (Georgakilas, et al., J. Am. Chem. Soc, 2003, 125:14268- 14269; U.S. Pat. Nos. 6,162,411, 6,261,455, 6,773,823, and 6,692,718, and U.S. Pat. Pub. Nos. 2004010005, 20050037255, and 200501221309, all of which are incorporated herein by reference in their entirety). One of the most critical aspects in these research and development efforts is the ability to produce large quantities of the carbon nanomaterials reproducibly and affordably. So far, these challenges have limited the widespread applications of carbon nanomaterials.

The soot found in used diesel lubricating oil consists of spherical carbon nano- onions; typically 20 to 40 nanometers in diameter (see Figure 1). They form in the oil during thousands of combustion cycles. Soot will enter the lubrication oil at the rate of approximately 0.005 ounces for every gallon of fuel burned. A truck will burn 1,786 gallons of fuel every 12,500 miles, assuming 7 miles per gallon. During this 12,500 mile oil change interval, more than half a pound (8.75 oz. or 248 grams) of carbon nano- onions will form in the crankcase oil.

These carbon nano-onions are structurally, chemically, and physically different than exhaust soot. The carbon nano-onions found in used diesel lube oil contain approximately 94% carbon, with the balance being oxygen, phosphorous, calcium, and sulfur. The chemical makeup of used lube oil soot is unique and it resembles that of diamond-like carbons, with a mixture of sp, sp2, and sp3 bonding, and with oxygen and sulfur replacing hydrogen. The hardness of used diesel engine oil carbon nano-onions is similar to that of various diamond-like carbons. Carbon nano-onions accumulate in diesel engine oil over time. The longer the oil is used, the large the quantity of carbon nano-onions. Because carbon nano-onions are very hard and tend to aggregate or agglomerate, they become abrasive and cause unwanted diesel engine wear. Carbon nano-onions are also expelled into the atmosphere through diesel engine exhaust. Typical used diesel engine oil contains 75 grams or more of carbon nano-onions per gallon, all of which have roughly the same size and properties.

The structure of large Fullerenic nanostructures has generated considerable attention. Experimental evidence suggests that giant Fullerenes are formed along with smaller Fullerenes in carbon vaporization systems. Carbon clusters up to C₆₃₂, all even numbered and interpreted to be Fullerenes, have been observed in molecular beam mass spectrometer (MBMS) analysis of the vapor from laser vaporization of graphite. Mass spectroscopy of solvent extracts of soot from electrical vaporization of carbon rods showed species interpreted to be C₁₈₈, C_2O8, and C₂₆₆. Transmission electron microscopy (TEM) of crystals consisting largely Of C₆₀ revealed apparently ellipsoidal fullerenes estimated to be about C₁₃₀. Scanning tunneling microscopy (STM) of extracts of soot from electrical vaporization of carbon showed spheres of 1 to 2 nm van der Waals (vdW) diameter which may correspond to fullerenes up to C₃₃₀.

Multiple polyhedral shells separated by about 0.34 nm (close to the interlay er spacing of graphite) and exhibiting spheroidal, elongated and tubular shapes also have been observed by TEM. These multishelled polyhedrons were given the name "nested polyhedrons" because the innermost shell was "nested" within the polyhedral shell of larger dimension. Nested spheroidal polyhedron shells of carbon were first observed by Iijima in carbon deposited from an arc discharge at 10^'7 torr (J. Phys. Chem. 91:3466-7, 1987). The central shells ranged from about 0.1 nm diameter to much larger, some containing one- and two-layered giant Fullerenes equivalent to about C₃₇₀₀ and larger. Subsequently, strikingly spherical onion structures with up to about 70 shells were produced by intense electron-beam irradiation of carbon soot collected from an arc- discharge apparatus.

Nested spheres and polyhedral spheroids 5-20 nm in diameter and other polyhedrons of approximately triangular, tetragonal, pentagonal, and hexagonal cross section have also been observed. Nanostructures formed on the cathode during arc- discharge carbon vaporization include tubes with 2 to about 50 nested shells. The tubes are capped by polyhedral domes, sometimes having conical transitions to the cylindrical tube wall. All of these nanostructures contain the feature associated with fullerenes of a structure containing both six-member and five-member carbon rings.

Fullerenes C₆₀ and C₇₀ have been successfully synthesized and collected in flames (Howard et al., Nature 352:139-141, 1991). Evidence of high molecular weight ionic species consistent with an interpretation as being fullerenic structures was observed in low-pressure premixed benzene and acetylene flames (Baum et al., Ber. Bunsenges. Phys. Chem. 96:841-857, 1992). The presence of neutral giant fullerene molecules in flames has not been established, however. Carbon vaporization processes, while capable of making a wide variety of

Fullerenic structures, are very inefficient and not amenable to large scale production of carbon nano-onions. It is desirable to develop a manufacturing process that is efficient and capable of processing large amounts of large spherical Fullerenic nanostructures. There is a long felt need in the art for the development of new sources and methods for purifying carbon nanoparticles and for cheaper purified carbon nano-onions. The present invention satisfies these needs.

Summary of the Invention

The present invention relates to a novel carbon nano-material, an abundant source of said carbon nano-material, a method for large-scale production and purification, and its use in applications including those listed above and others. Called carbon nano-onions, the present invention provides an abundant and reproducible source of extremely hard solid-core spheres containing tightly bound layers of carbon and small quantities of other elements. These spheres are generally 20 to 40 nanometers in diameter. While other methods for producing carbon nano-onions have been attempted, their structure and the limited quantities that can be produced using these other methods distinguishes them from the present invention. The carbon nano-onions of the present invention are far harder than amorphous carbon black and amorphous soot particles made using most combustion processes. In one aspect, the invention provides a cheap and abundant source of carbon nano-onions. In one aspect, the source is used diesel oil.

Typical used diesel engine oil contains 75 grams or more of carbon nano-onions per gallon, all of which have roughly the same size and properties. This source of carbon nano-onions is encompassed by the present invention.

The present invention, as described in the disclosure provided herein, provides a source and procedure for obtaining large quantities of carbon nanoparticles (i.e., soot particles) from used diesel engine oil. It also describes issues related to the logistics and economics of the process as well as recyclability of materials. The resulting carbon nanoparticles may be used in a variety of applications, e.g., as strengthening nanoparticles in organic and inorganic nanocomposites, diamond-like abrasives for polishing and other applications where diamond-like carbon materials are used.

One of ordinary skill in the art will appreciate that other sources of carbon nanoparticles and nano-onions are available other than spent diesel oil and can be used in the methods of the present invention.

In one aspect, the invention provides compositions and methods to obtain and purify carbon nano-onion particulate efficiently and in high purity, and in another aspect, the invention provides high purity carbon nano-onion particulate.

In one embodiment, the present invention provides for the use of used or spent diesel lubricating oil as an abundant source of solid-core, spherical, carbon nano-onions. In one aspect, the used diesel lubricating oil is an abundant source of solid-core, spherical, graphitic carbon nano-onions having a diameter of approximately 10 to 50 nanometers. In one embodiment, purified carbon nano-onions of the invention are of uniform size, composition, and properties. In one aspect, carbon nano-onions of the invention are about 20-40 nm in diameter.

In one embodiment, the purified carbon nano-onions comprise at least about 90% C. In another aspect, the purified carbon nano-onions comprise at least about 92% C. In one aspect, the carbon nano-onions comprise at least about 94% C. In one aspect, the carbon nano-onions comprise a composition of at least about 94% C, with O, Ca, P, and S as the other main elements present in the composition. In another aspect, the carbon nano-onions comprise at least about 96% C. In one aspect of the invention, the carbon nano-onions can be acid treated to remove contaminants, In one aspect, the removed contaminants comprise S, Ca, and P. hi one aspect, the acid is nitric acid. In one aspect, the carbon nano-onions can be alkaline treated to remove contaminants. In one aspect, carbon nano-onions of the invention comprise a hardness of about 1150 ±250 kgf/square mm. hi one aspect, the carbon nano-onions of the invention comprise a surface area of at least about 1,000 m²/gram. hi another aspect, the carbon nano-onions of the invention are able to withstand strong acids.

In one embodiment, the invention provides a process for extracting and purifying carbon nano-onions, said process comprising adding a solvent to used diesel lubricating oil, heating the oilrsolvent mixture, filtering the heated oihsolvent mixture, centrifuging the filtered oihsolvent mixture, heating the post-centrifuge carbon material to dry it and thus remove residual solvent and oil, and pulverizing, ball milling, or sonicating the resulting dried cinder-like carbon material to nano-scale particles. One of ordinary skill in the art would appreciate that the steps need not necessarily be performed in the order described herein, and that the process can be modified. hi one aspect, the solvent is a carbon-based solvent such as toluene, heptane, decane, or chloroform. In another aspect, the solvent is a paraffin solvent such as Norpar™ 12 or Norpar™ 15. In yet another aspect, the solvent is an aliphatic ketone such as methylethyl ketone.

In one embodiment, the invention provides a method for extracting and purifying carbon nano-onions from used diesel lube oil, wherein said process is thin film evaporation. In another embodiment, the invention provides a process for extracting and purifying carbon nano-onions from used diesel lube oil, wherein the process is a distillation process.

In one embodiment, the invention provides a process for extracting and purifying carbon nano-onions, wherein said process includes altering or controlling the surface chemistry of the carbon nano-onions obtained from the source material by the hydrogen termination of their exterior surface. In another embodiment, the process includes altering or controlling the surface chemistry of the carbon nano-onions obtained from the source material by the fluorine termination of their exterior surface. In yet another embodiment, the invention provides a process of altering or controlling the surface chemistry of the carbon nano-onions obtained from the source material by the hydroxyl termination of their exterior surface. In yet a further embodiment, the invention provides a process of altering or controlling the surface chemistry of the carbon nano-onions obtained from the source material by the amine termination of their exterior surface.

In one embodiment, the invention provides for the use of the carbon nano-onions derived from used diesel lube oil in tribological and nano-tribological applications. The carbon nano-onions of the present invention are also useful in other applications, including, but not limited to, electronic devices, ultra-hard coatings, polymeric thin films, photovoltaic/solar cells, medical imaging, drug delivery, ultracapacitors, optical limiters, broad-band optical limiters (including broad band, IR, and NIR regions) and other optical devices, quantum dots, electrospun nano-fibers, MEMS and NEMS devices, adhesives, synthetic rubbers, polymers, ceramic composites, alloys, ceramic metal composites or cermets, metallic glass composites, lithography, aerosols, sputter coating, and as a nano- storage device for hydrogen or lithium.

In one aspect, the carbon nano-onions of the invention are useful as optical limiters, including, but not limited to such optical limiters as cockpit glass and materials and eyeglass lenses. In one aspect, the cockpit glass and materials and eyeglass lenses are useful protection against lasers.

It is an object of the invention to provide a method for producing very large quantities of spherical, solid-core carbon nano-onions that are physically, chemically, and structurally different than Fullerenes, soot, nano-onions and nano-diamonds that are made using other methods. Other aspects and advantages of the present invention are described herein and in the following detailed description of the preferred embodiments thereof.

Brief Description of the Drawings Figure 1 represents an image of an electron micrograph of carbon nano-onions found in used diesel lubricating oil; typically 20 to 40 nanometers in diameter.

Figure 2 graphically illustrates the size distribution of carbon nano-onions purified using a Norpar solvent. The ordinate represents Intensity (%) and the abscissa represents Size (d.nm). Figure 3 graphically illustrates the size distribution of carbon nano-onions purified using a chloroform solvent. The ordinate represents Intensity (%) and the abscissa represents Size (d.nm).

Figure 4 graphically illustrates the results of a cycling test of electrical properties of carbon nano-onions under constant current (0.1 mA/cm²). The ordinate represents Voltage/Current (using volts and mA, respectively) and the abscissa represents Time in hours. Series 1 is indicated by the line with peaks which has two arrows pointing to it and which has the higher of the two "0" indicators on the ordinate. Series 2 is indicated by the lower of the two lines which begins at the lower of the two "0"s on the ordinate.

Figure 5 graphically illustrates the results of a Charge/Discharge capacity test of carbon nano-onions. The ordinate represents Capacity (mAh/g) and the abscissa represents Cycle Number. The filled in black diamonds (♦) represent Series 1 and the filled in black squares (■) represent Series 2.

Figure 6 graphically represents an energy dispersive x-ray spectrum and chemical analysis of typical carbon nano-onion particles obtained from spent diesel oil. An electron energy-loss spectrum from the particles, with the energy of the plasmon peak indicated, is superimposed in the x-ray spectrum. The ordinate of the x-ray spectrum represents counts, and the abscissa represents x-ray energy in KeV. Peaks of the x-ray spectrum are labeled according to element (C, O, P, S, and Ca). For the inset graph representing an electron energy-loss spectrum, the ordinate represents CCD counts and the abscissa represents energy loss in eV. Detailed Description of the Invention

General Description

The invention relates generally to a source and method for purifying carbon nanoparticles, as well as to their use as nanoparticles in a variety of nanotechnology applications.

Abbreviations and Short Forms

"C" represents carbon.

"CNO" means carbon nano-onion.

"H" represents hydrogen. "MBMS" means molecular beam mass spectrometer

"O" represents oxygen.

"STM" means scanning tunneling microscopy

"S" represents sulfur

"TEM" means transmission electron microscope/y "vdW" means van der Waals

Defmitions-

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. As used herein, each of the following terms has the meaning associated with it in this section.

In describing and claiming the invention, the following terminology will be used in accordance with the definitions set forth below.

The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.

The use of the word "detect" and its grammatical variants is meant to refer to measurement of the species without quantification, whereas use of the word "determine" or "measure" with their grammatical variants are meant to refer to measurement of the species with quantification. The terms "detect" and "identify" are used interchangeably herein.

As used herein, an "instructional material" includes a publication, a recording, a diagram, or any other medium of expression which can be used to communicate the usefulness of the invention. The instructional material of the kit of the invention may, for example, be affixed to a container which contains the identified compound or be shipped together with a container which contains the identified compound. Alternatively, the instructional material may be shipped separately from the container with the intention that the instructional material and the compound be used cooperatively by the recipient. As used herein, the term "pulverize" refers to any method for breaking up larger particles or aggregates. For example, pulverize can be a mechanical method. Pulverize includes ball milling and sonicating.

As used herein, the term "purified" and like terms relate to an enrichment of a molecule or compound relative to other components normally associated with the molecule or compound in a native environment. The term "purified" does not necessarily indicate that complete purity of the particular molecule has been achieved during the process. Typically, a compound is purified when at least 10%, more preferably at least 20%, more preferably at least 50%, more preferably at least 60%, more preferably at least 75%, more preferably at least 90%, and most preferably at least 99% of the total material (by volume, by wet or dry weight, or by mole percent or mole fraction) in a sample is the compound of interest.

The phrase "reduce particle size to nanoparticle size" as used herein, refers to methods of reducing carbon particle or carbon nano-onion size such as breaking down aggregate particles to smaller aggregates and individual nano-onions. The phrase 'resistant to strong acids or strong bases" as used herein refers to the ability of carbon nano-onions purified from used diesel oil or other sources to be resistant to breakdown or being hollowed out by acid or alkaline treatment.

The phrase 'similar size", as used herein to refer to the size of carbon nano-onions refers to purified carbon nano-onions which fall within a similar size range. In one aspect, the size of the nano-onions within a group of similar size nano-onions varies by about 75 nanometers in diameter. In another aspect, the size of nano-onions within a group varies by about 50 nanometers in diameter. In yet another aspect, the size of nano- onions within a group varies by about 25 nanometers in diameter. In another aspect, the size of nano-onions within a group varies by about 15 nanometers in diameter. In yet another aspect, the size of nano-onions within a group varies by about 10 nanometers in diameter. In a further aspect, the size of nano-onions within a group varies by about 5 nanometers in diameter.

The term "standard," as used herein, refers to something used for comparison. For example, a standard can be a known standard agent or compound which is administered or added to a control sample and used for comparing results when measuring said compound in a test sample. Standard can also refer to an "internal standard," such as an agent or compound which is added at known amounts to a sample and is useful in determining such things as purification or recovery rates when a sample is processed or subjected to purification or extraction procedures before a marker of interest is measured. The term "substantially pure" describes a compound which has been separated from components which naturally accompany it. Typically, a compound is substantially pure when at least 10%, more preferably at least 20%, more preferably at least 50%, more preferably at least 60%, more preferably at least 75%, more preferably at least 90%, and most preferably at least 99% of the total material (by volume, by wet or dry weight, or by mole percent or mole fraction) in a sample is the compound of interest. Purity can be measured by any appropriate method, e.g., in the case of polypeptides by column chromatography, gel electrophoresis, or HPLC analysis. A compound is also substantially purified when it is essentially free of naturally associated components or when it is separated from the native contaminants which accompany it in its natural state. By "used diesel oil" is meant diesel engine lubricating oil which has been subjected to use in a diesel engine. The terms "used diesel oil" and "spent diesel oil" are used interchangeably herein. hi accordance with the present invention, as described above or as discussed in the Examples below, there can be employed conventional chemical and other techniques which are known to those of skill in the art. Such techniques are explained fully in the literature (see, for example, Jao et al., In Proceedings of the International Tribology Conference, vol. 3, pp. 1981-1986 (2001). Nagasaki, Japan: Japanese Society of

Tribologists; Oleshko et al., Microsc. Microanal., 8:350-364 (2002); Kuo et al., SAE, paper No. 981372 (1998); U.S. Patent Nos. 5,985,232, 6,413,487, 6,692,718, 6,740,403, and 6,725,653). There are two main aspects of this invention. The first, is the realization that used diesel engine oil is a cheap, abundant source for purification of carbon nanoparticles with similar sizes and properties. The carbon nanoparticles can be used in a wide range of nanotechnology applications as described herein. Other uses for carbon nanoparticles not described herein are known or may become known. The second aspect is a proposed scheme for extracting the nanoparticles from diesel engine oil. One of skill in the art can imagine many possible alternative methods for extracting soot nanoparticles from diesel engine oil that may be new and patentable.

Used diesel-engine oil contains billions of soot particles, perhaps constituting as much as 10% of the oil volume after prolonged use before the oil is changed. This soot is discarded with the used oil. Given the number of diesel engines currently being used in industrial nations throughout the world, used diesel engine oil appears to be an abundant, continuous source of soot, or carbon nanoparticles.

The invention as described herein provides a process for extracting soot nanoparticles from used diesel engine oil for nanotechnology applications. Since there are many ways in which this might be achieved, it is not so much the methodology, but the idea itself, i.e., that diesel engine oil is an abundant source of carbon nanoparticles, that is the novel and most valuable part of this invention.

In one aspect of the invention, a continuous supply of used diesel engine oil from various sources can be obtained for soot extraction. In another aspect, a collection system can be set up for this relatively cheaply, since most garages, etc., need a place to dispose of used diesel engine oil.

In terms of recyclability and waste disposal, it is desirable to separate the diluent from the used oil after centrifuging, so that it can be mixed with fresh used oil in step 1

(see Examples) and this process can be repeated indefinitely. Various methods for separating a diluent are known to those of ordinary skill in the art and can be implemented without undue experimentation. In contrast to other processes used to make carbon nanomaterials such as carbon nanotubes and carbon onions, the present invention has the advantages of low-cost, high- volume production of carbon nanoparticles with fairly consistent properties.

It is important to note that soot is produced during combustion in all types of engines, so that sources of soot other than diesel engines are also available. Soot emitted from the engine exhaust is also a source of carbon nanoparticles. Because this soot contributes to air pollution and poses a health hazard, in one aspect of the invention, filters can be used to collect soot from engine exhausts as a source of carbon nanoparticles. Carbon nanoparticles prepared according to the techniques of the invention are useful as carbon-based nanocomposite materials for use in air and space vehicles, as abrasives for polishing, can be used where diamond-like carbon is useful because of the inertness of soot and because of the optical properties of soot. The advantages of purifying nanoparticles from soot include, but are not limited to, the low-cost of soot, high-volume production, the simple nanoparticle purification process, and the uniform sizes and properties of the purified carbon nanoparticles.

In one embodiment, the carbon nanoparticles of the invention are useful in catalysis. In one aspect, carbon nano-onions are useful as catalysts for increasing the yield of styrene during styrene synthesis. In one aspect, the use of carbon nano-onions increases styrene yield by at least about 25%. In another aspect, use of carbon nano- onions increases styrene yield by at least about 20%. In yet another aspect, the use of carbon nano-onions increases styrene yield by at least about 15%. hi a further aspect, the use of carbon nano-onions increases styrene yield by at least about 5%. In one aspect, the use of carbon nano-onions as catalysts in the production of styrene allows for a decrease in the operating temperature by at least about 200°C. hi another aspect, the use of carbon nano-onions as catalysts in the production of styrene allows for a decrease in the operating temperature by at least about 150°C. In yet another aspect, the use of carbon nano-onions as catalysts in the production of styrene allows for a decrease in the operating temperature by at least about 100°C. In a further aspect, the use of carbon nano-onions as catalysts in the production of styrene allows for a decrease in the operating temperature by at least about 50°C. In one embodiment, the invention provides the use of centrifugation techniques for removing soot from oil.

In one embodiment, the invention provides a centrifuge oil filter, which, inter alia, includes a centrifuge filter housing and a replaceable centrifuge cartridge. In one aspect, the centrifuge oil filter is adapted to remove soot from oil in engine applications.

In one embodiment, a method for separating the carbon nano-onions is to dilute the used diesel lube oil with a petroleum-compatible solvent such as Norpar™ (ExxonMobil), toluene, heptane, chloroform, decane, or other similar solvents to help reduce the viscosity of the oil. The solvent to oil ratio can typically be in a ratio of 1 to 1 to 4 to 1, using as little solvent as practical to reduce the viscosity as much as possible. The solventroil mixture is then typically heated to between 50 to 90°C (higher temperatures may be used, depending on the solvent) and stirred continuously to lower the viscosity, typically close to 1.0 centipoise.

In another embodiment, a technique useful for separating nano-onions from the solventoil mixture employs the use of 2 parts of Norpar 12 to 1 part used diesel lube oil. The 2 to 1 solvent to oil mixture is heated to 60°C, at which point a viscosity of approximately 2.6 centipoise is achieved. The heated solventoil mixture is then filtered using a small pore filter (e.g., Pall Profile II RM1F005H21 0.5 micron filter) to remove larger contaminant particles. Next, the filtered solventoil mixture is centrifuged using a very high-RPM, high g-force and a slow feed rate in order to remove the largest percentage of the carbon nano-onions possible.

The high-speed centrifuge can be a closed-bowl centrifuge, which must be cleaned manually, or a self-cleaning, disk-stack centrifuge. If a closed-bowl centrifuge such as the Sharpies Model AS-26 is used, the wet, black, post-centrifuge material must be removed manually, by using a stainless steel scraper, for example. At this point, the wet, black centrifuged material still contains residual quantities of oil and solvent, so one method for purifying the carbon nano-onions entails baking the wet, post-centrifuge material in atmospheric conditions, or in the presence of an inert gas such as argon at 250°C for 90 minutes. Other options include rinsing the post-centrifuge material in clean solvents, followed by further centrifuging, distillation, or a combination of these methods. What remains after the baking step are small, black, cinder-like chunks of pure carbon nano-onions. The black, cinder-like chucks break apart very easily and can be manually ground using a mortar and pestle, a ball mill, a roller jar, or some other mechanical means. If greater separation of the aggregated carbon nano-onions is desired, a stable colloid can be created using a solvent such as chloroform in a ratio such as 1 milligram of carbon nano-onions to 5 milliliters of chloroform, followed by sonication in a water bath sonicator for one hour. If the centrifuged material does not require drying to remove the residual oil, it can be incorporated directly into a product without a grinding step.

One of ordinary skill in the art will realize that the process can be varied by adjusting such parameters as revolutions per minute of the centrifuge and rotors to regulate the g-force, and various feed rates of the sample. In one aspect, the method of the invention provides high revolutions per minute, with high g-force, and a slow feed rate.

Another source of producing carbon nano-onions envisioned in the present invention is exhaust pipes, mufflers, exhaust filters and other particulate filters used on diesel engine vehicles. These carbon nano-onions can be removed using solvents such as those mentioned above, followed by the purification steps like those outlined herein. The carbon nano-onions found in the exhaust soot are slightly different in structure and hardness and may thus require other kinds of treatment, such as irradiation or some other method to make them harder if extreme hardness is a desired trait. Larger quantities of used diesel lube oil (and thus carbon nano-onions) are available and accessible than exhaust pipes and filters. For example, used diesel lube oil can be obtained and treated in one location such as an oil recycling firm. In addition, the composition and structure of the carbon nano-onions found in the engine oil is unique and thus, so are their chemical and physical properties.

Alternative methods to separate the carbon nano-onions from used diesel lube oil can be envisioned, such as those used in the oil recycling business, distillation, cracking, and fractionation. Again, these are examples or illustrations only and should not be construed as being limited to these examples, but rather should be construed to encompass any and all variations which become evident as a result of the teaching provided herein. The invention further provides methods to remove contaminants from purified carbon nano-onions. Carbon nano-onions purified as described herein can be subjected to other techniques including, but not limited to, acid and alkaline treatments. As described in the examples, nitric acid and sulfuric acid can be used to remove contaminants. For example, nitric acid has been used to remove S, Ca, and P (see

Examples), hi addition, hydrogen peroxide (alkaline) can be used to treat purified carbon nano-onions to remove contaminants (see Examples). Acid and alkaline concentrations can vary, depending on the particular acid or base used the particular contaminant to be removed, hi one aspect, the concentration may be as much as about 50%. In another aspect, the concentration may be as much as about 40%. In yet another aspect, the concentration may be as much as about 30%. In a further aspect, the concentration may be as much as about 20%. In yet another aspect, the concentration may be as much as about 15%. In another aspect, the concentration may be as much as about 10%. In yet another aspect, the concentration may be as much as about 5%. In one aspect, the treatment is for a time period of up to twenty-four hours or more. In another aspect, the treatment is for up to 18 hours. In one aspect, the samples are sonicated during acid and alkaline treatment.

In one embodiment, strong acid or alkaline treatment of purified carbon nano- onions of the present invention does not alter the structure of the carbon nano-onions. That is, the carbon nano-onions remain solid after treatment, as opposed to carbon black nano-particles which do not hold up to exposure to nitric acid and can become hollow upon such treatment.

Various methods are available for characterizing carbon nano-onions of the invention. These include electron microscopy, energy dispersive spectroscopy, x-ray powder diffraction, electron microdiffraction, x-ray microanalysis, MALDI mass spectrometry, and various methods for use in electronic and magnetic measurements.

The invention should not be construed to be limited solely to the assays and methods described herein, but should be construed to include other methods and assays as well. One of ordinary skill in the art will know that other assays and methods are available to perform the procedures described herein. Without further description, it is believed that one of ordinary skill in the art can, using the preceding description and the following illustrative examples, make and utilize the present invention and practice the claimed methods. The following working examples therefore, specifically point out the preferred embodiments of the present invention, and are not to be construed as limiting in any way the remainder of the disclosure.

Experimental Examples

The invention is now described with reference to the following Examples. These Examples are provided for the purpose of illustration only and the invention should in no way be construed as being limited to these Examples, but rather should be construed to encompass any and all variations which become evident as a result of the teaching provided herein.

The extraction of soot particles from diesel engine oil is described in four steps below. It is important to realize that there are many potential variations on this process, many of which have not been explored, but which might improve the output, reproducibility and recyclability of the process. Other processes for extraction, such as filtering, precipitation, etc., and other sources of carbon nanoparticles are also available.

Extraction Procedure:

1) Used diesel engine oil is mixed with a diluent, such as heptane, to decrease the viscosity of the oil. The ratio of diluent to oil will depend on a number of factors, such as the chemical used for dilution, the length of time used for centrifuging, etc. These features would be optimized for a given process, typically using as little diluent and time as possible in the process.

2) The oil/diluent mixture is then centrifuged in a tube or bowl using commercially available ultracentrifuges at a speed of about 10,000 to about 100,000 revolutions per minute, depending on other conditions such as the rotor or centrifuge used. Typically, 17,000 revolutions per minute are used. Such a speed produces a force of about 20,000 xg. This causes the soot particles to settle and collect at the bottom of the tube or bowl. The rate at which settling occurs depends on the centrifuge speed, mixture viscosity, particle sizes, etc., and centrifuging may last for several hours. After centrifuging, the remaining liquid is decanted from the tube or bowl.

3) A small amount of fresh diluent is then added to the tube or bowl and they are ultrasonicated to clean the soot nanoparticles, break up agglomerates, and disperse them in the diluent. This solution is then ultracentrifuged as in step 2), but for a shorter time. The process is repeated several times.

4) The final soot is removed from the tube or bowl and dried in an oven for several hours at ~50°C to evaporate any residual diluent, and stored in a dry environment.

Unique problems are encountered when one attempts to separate nanoparticles from any viscous fluid, especially on a large scale, continuous-flow basis, and when the viscous fluid also contains nanoparticles that are not desired (i.e. contaminants).

In one experiment for separating the carbon nano-onions, the used diesel lube oil was diluted with a petroleum-compatible solvent, Norpar™ (Exxon-Mobil), to help reduce the viscosity of the oil, using 2 parts of Norpar 12 to 1 part used diesel lube oil. The 2 to 1 solvent to oil mixture was heated to 60°C, at which point a viscosity of approximately 2.6 centipoise was achieved. The heated solvent:oil mixture was then filtered using a small pore filter (e.g., Pall Profile II RM1F005H21 0.5 micron filter) to remove larger contaminant particles. Next, the filtered solventroil mixture was centrifuged using a very high-RPM, high g-force and a slow feed rate in order to remove the largest percentage of the carbon nano-onions possible. Samples were then oven-dried at about 50⁰C.

Following the purification procedure, the samples were then subjected to an analysis to determine the size distribution of the nano-onions. The values and conditions for the analysis included toluene as a dispersant, viscosity (cP) of 1.6300, dispersant RI of 1.42, material RI of 1.59, material absorption of 0.01, 25°C, count rate (kcps) of 332.9, 60 second duration, 1.25 measurement position (mm), and attenuator at 6. The results (see Figure 2) include a Z-average (d.nm) of 185, PdI of 0.256, intercept of 0.942, and peak values as shown in Table 1. Table 1.

Diam. (nm) % Intensity Width (tan)

Peak l: 234 97.5 141

Peak 2: 4700 2.5 784

Peak 3: 0.00 0.0 0.00

Next, a sample was purified in chloroform and the size distribution of the carbon nano-onions was determined as described above. The values and conditions for the analysis included chloroform as a dispersant, viscosity (cP) of 0.5300, dispersant RI of 1.443, material RI of 1.59, material absorption of 0.01, 25°C, count rate (kcps) of 221.1, 70 second duration, 1.25 measurement position (mm), and attenuator at 5. The results (see Figure 3) include a Z-average (d.nm) of 153, PdI of 0.143, intercept of 0.957, and peak values as shown in Table 2.

Table 2.

Diam. (nm) % Intensity Width (nm)

Peak l: 182 100 81.3

Peak 2: 0.00 0.0 0.0

Peak 3: 0.00 0.0 0.00

In another set of experiments, purified carbon nano-onions were tested for their electrical properties. Figure 4 demonstrates the results of a constant current cycling test. It should be noted that there is a sloping insertion reaction, with Li added as voltage drops, and that there is a single phase reaction with no obvious staging reactions (see Figure 4). Figure 5 demonstrates the results of experiments to determine charge/discharge capacities of carbon nano-onions. There was 79% irreversible capacity, that is, 79% of the Li added during the first reaction never came back. The value for the first discharge was 666.5 mAh/g and for the first charge it was 138 mAh/g. The carbon was found to have poor capacity retention and no obvious insertion plateaus. The cycling profile was similar to a hard carbon.

The results described above regarding efforts to reduce nano-agglomeration in various solvents demonstrate the reduction of the average diameter of nano-agglomerates to 153 nanometers in chloroform (following 1 hour of water-bath sonication) and an average diameter of 185 nanometers in toluene (following 1 hour of water-bath sonication).

To further examine purity and elemental content following the purification process of the invention, carbon nanoparticles were purified from spent diesel oil as described above. A small amount of purified sample was dispersed in a solvent (i.e., toluene) and applied dropwise on a standard holey carbon film. The carbon film with added sample:solvent mixture was then inserted directly into a transmission electron microscope outfitted with an energy dispersive x-ray analysis system. The analysis was performed at 200.0 KeV at 10 eV per channel. An EDXS spectrum, which has superimposed in the field an EELS spectrum, is provided in Figure 6. Peaks of the x-ray spectrum are labeled according to element (C, O, P, S, and Ca). The results of the analysis are quantified in Tables 3 and 4. The Weight % total of the elements listed in

Tables 3 and 4 was 100%.

Table 3. X-ray analysis of carbon nanoparticles purified from diesel oil

Element Weight % Std. Dev. Atomic %

C 93.45 1.2 96.09

O 3.85 0.05 2.97

P 0.32 0.00 0.13

S 0.95 0.05 0.37

Ca 1.42 0.07 0.44 Table 4. X-ray analysis of carbon nanoparticles purified from diesel oil

Element k-Ratio Intensity FWHM CeV) ROI (net)

C 0.9482 6065.6 129.5 8790.43

O 0.0292 419.3 121.5 436.14 P 0.0039 83.7 124.3 91.88

S 0.0083 256.6 126.8 251.84

Ca 0.0104 389.1 133.8 354.50

The inset graph of Figure 6 represents an electron energy-loss spectrum. Chemical alteration of carbon nano-onion composition-

Methods are available for altering the composition of the purified carbon nano- onions of the invention described above, including acid treatment and alkaline treatment of purified carbon nano-onions. To this end, carbon nano-onions were prepared as described in the Examples herein and then subjected to nitric acid treatment to remove contaminants. It was found that nitric acid treatment removes the S, Ca, and P, leaving only C and O. Furthermore, such treatment did not change the structure of the carbon nano-onions. In addition, nitric acid, sulfuric acid, and hydrogen peroxide (up to 30%) treatments for up to 18 hours, with sonication, have been used effectively to remove contaminants without altering the structure of the carbon nano-onions (results not shown).

In summary, the invention disclosed herein provides a rich source of carbon nanoparticles (i.e., used diesel engine oil) and demonstrates a new method for purifying carbon nanoparticles from used diesel engine oil, for use in nanotechnology applications.

The invention should not be construed to be limited solely to the assays and methods described herein, but should be construed to include other methods and assays as well. One of skill in the art will know that other assays and methods are available to perform the procedures described herein.

Headings are included herein for reference and to aid in locating certain sections. These headings are not intended to limit the scope of the concepts described therein under, and these concepts may have applicability in other sections throughout the entire specification. The disclosures of each and every patent, patent application, and publication cited herein are hereby incorporated herein by reference in their entirety.

While this invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention may be devised by the previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. The appended claims are intended to be construed to include all such embodiments and equivalent variations. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

ClaimsWhat is claimed is:

1. A method for purifying carbon nano-onions, said method comprising obtaining a sample comprising carbon nano-onions, adding a solvent to said sample to form a solventrsample mixture, heating said solventrsample mixture, filtering said heated solventrsample mixture, centrifuging said filtered solventrsample mixture to remove said solvent and precipitate carbon material containing carbon nano-onions, heating said carbon material, and pulverizing said heated carbon material to reduce particle size to nanoscale particle size, thereby purifying carbon nano-onions.

2. The method of claim 1, wherein said solvent and said sample are mixed in a range of ratios from about 0.1 parts of solvent to 1.0 part of sample to about 10.0 parts of solvent to 1.0 parts of sample.

3. The method of claim 2, wherein said ratio is about 4.0 parts of solvent to about 1.0 part of sample.

4. The method of claim 1, wherein said solvent:sample mixture is heated in a range from about 50°C to about 90⁰C.

5. The method of claim 4, wherein said heated solventrsample mixture is filtered using a small pore filter.

6. The method of claim 5, wherein said small pore filter has a pore size of about 0.5 microns.

7. The method of claim 5, wherein said filtered solventrsample mixture is centrifuged at high revolutions per minute, with high g-force, and a slow feed rate.

8. The method of claim 7, wherein said revolutions per minute are about 30,000 revolutions per minute.

9. The method of claim 7, wherein the centrifuge is a closed-bowl centrifuge.

10. The method of claim 1, wherein said precipitated carbon material comprising carbon nano-onions is heated at about 250⁰C for about 90 minutes.

11. The method of claim 10, wherein said precipitated carbon material containing carbon nano-onions is heated at atmospheric conditions or in the presence of an inert gas.

12. The method of claim 1, wherein said solvent is selected from the group consisting of a carbon-based solvent, a paraffin solvent, an aliphatic ketone solvent.

13. The method of claim 12, wherein said carbon-based solvent is selected from the group consisting of toluene, heptane, decane, and chloroform.

14. The method of claim 12, wherein said paraffin solvent is Norpar™12 or Norpar™15.

15. The method of claim 12, wherein said aliphatic ketone is methylethyl ketone.

16. The method of claim 1, wherein said particle size is from about 5 nanometers in diameter to about 250 nanometers in diameter.

17. The method of claim 16, wherein said particle size is from about 10 nanometers in diameter to about 50 nanometers in diameter.

18. The method of claim 1, wherein said method is selected from the group consisting of thin film evaporation and distillation. '

19. The method of claim 1, wherein said sample is selected from the group consisting of used diesel lube oil, soot from exhaust pipes, soot from mufflers, and filters used on diesel engine vehicles.

20. The method of claim 19, wherein said sample is used diesel oil.

21. The method of claim 20, wherein said purified carbon nano-onions are spherical, solid-core, and multishell carbon nano-onions.

22. The method of claim 21, wherein said purified carbon nano-onions are of uniform size, composition, and properties.

23. The method of claim 22, wherein said size comprises a range of sizes from about 10 nanometers in diameter to about 50 nanometers in diameter.

24. The method of claim 23, wherein said size comprises a range of sizes from about 20 nanometers in diameter to about 40 nanometers in diameter.

25. The method of claim 22, wherein said composition comprises at least about 90% C.

26. The method of claim 25, wherein said composition comprises at least about 94% C.

27. The method of claim 26, wherein said composition further comprises elements selected from the group consisting of O, Ca, P, and S.

28. The method of claim 22, wherein said carbon nano-onions comprise a hardness of about 1150 ±250 kgf/square mm.

29. The method of claim 22, wherein said carbon nano-onions comprise a surface area of at least about 1 ,000 m²/gram.

30. The method of claim 22, wherein said carbon nano-onions are resistant to strong acids.

31. The method of claim 22, wherein said carbon nano-onions are resistant to strong bases.

32. The method of claim 1, wherein the surface chemistry of said carbon nano-onion is altered by a method selected from the group consisting of hydrogen termination of the exterior surface of said carbon nano-onion, fluorine termination of the exterior surface of said carbon nano-onion, hydroxyl termination of the exterior surface of said carbon nano- onion, and amine termination of the exterior surface of said carbon nano-onion.

33. A method of removing contaminants from the purified carbon nano-onions of claim 1, said method comprising treating said purified carbon nano-onions with an acid or a base.

34. The method of claim 33, wherein said acid is nitric acid or sulfuric acid.

35. The method of claim 33, wherein said base is hydrogen peroxide.

36. Purified carbon nano-onions obtained by a method comprising obtaining a sample comprising carbon nano-onions, adding a solvent to said sample to form a solventrsample mixture, heating said solvenfcsample mixture, filtering said heated solvent:sample mixture, centrifuging said filtered solventsample mixture to remove said solvent and precipitate carbon material containing carbon nano-onions, heating said carbon material, and pulverizing said heated carbon material to reduce particle size to nanoscale particle size.

37. The purified carbon nano-onions of claim 36, wherein said sample is spent diesel oil.

38. A method of using the purified carbon nano-onions of claim 1, wherein said method is selected from the group of applications consisting of tribological, nano-tribological, electronic device, ultra-hard coating, polymeric thin film, photovoltaic/solar cell, medical imaging, drug delivery, ultracapacitor, optical limiter, broad-band optical limiter, optical device, quantum dot, electrospun nano-fiber, MEMS device, NEMS device, adhesive, synthetic rubber, polymer, ceramic composite, alloy, ceramic metal composite, cermet, metallic glass composite, lithography, aerosol, sputter coating, and a nano-storage device.

39. The method of claim 38, wherein said optical limiter is selected from the group consisting of cockpit glass, cockpit glass materials, and eyeglass lenses.

40. The method of claim 39, wherein said cockpit glass, cockpit glass materials, and eyeglass lenses are useful for preventing laser damage.

41. The method of claim 40, wherein said laser damage is eye damage.

42. A cheap source of abundant carbon nanoparticles, wherein said carbon nanoparticles comprise spherical, solid-core, and multishell carbon nanoparticles, further wherein said carbon nanoparticles comprise uniform size, composition, and properties.

43. The source of claim 42, wherein said source is used diesel oil.

44. A kit for use in purifying carbon nano-onions, said kit comprising a sample comprising carbon nano-onions, an instructional material, and an applicator for the use thereof.