WO2012021620A1

WO2012021620A1 - Processes for synthesizing fluorescent carbon nanoparticles and compositions and uses thereof

Info

Publication number: WO2012021620A1
Application number: PCT/US2011/047252
Authority: WO
Inventors: Duck Joo Yang; Abdelaziz Rahy
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 2010-08-10
Filing date: 2011-08-10
Publication date: 2012-02-16

Abstract

A process for synthesizing carbon nanoparticles (CNPs) capable of photoluminescence by direct combustion (i.e., a confined combustion and/or a controlled combustion) of aromatic solvent and the compositions and uses thereof. The CNPs generally have flat, round structure with an average particle size between about 10 nm and about 60 nm, and more generally between about 30 nm and about 60 nm (typically about 50 nm). The CNPs were prepared by a confined combustion of an aromatic compound such as benzene, toluene, xylene, or a mixture thereof, in air. The resulting CNPs have strong photoluminescence. When dispersed in ethanol and excited with 325-nm wavelength, the solution of CNPs exhibited strong photoluminescence at 475 nm with 12%-13% quantum yield.

Description

PROCESSES FOR SYNTHESIZING FLUORESCENT CARBON NANOP ARTICLES AND COMPOSITIONS AND USES THEREOF

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims priority to: provisional United States Patent Application Serial

No. 61/372,455, filed on August 10, 2010, entitled "Processes For Synthesizing Fluorescent

Carbon Nanoparticles By Direct Combustion of Aromatic Solvent and Composition and Uses

Thereof," which provisional patent application is commonly assigned to the Assignee of the present invention and is hereby incorporated herein by reference in its entirety for all purposes.

FIELD OF INVENTION

[0002] The present invention is a process for synthesizing carbon nanoparticles (CNPs) capable of photoluminescence by direct combustion (i.e., a confined combustion and/or a controlled combustion) of aromatic solvent and the compositions and uses thereof.

BACKGROUND

[0003] Carbon is unique among the elements in the vast number and variety of compounds it can form. Without carbon, the basis for life would be impossible. Production of carbon nanoparticles has become an area of increasing interest in material research because they are biocompatible, chemically inert, and can be surface modified. [Hu 2009]. It was discovered that carbon nanoparticles display intense light emission, and it is expected these nanoparticles will yield new insights into practical applications such as in bioimaging [Cao 2007; Ray 2009; Yang 2009], their ability to suppress fluorescence in resonance Raman spectroscopy [Xie 2009], and sensor [Goncalves 2003] and catalyst support in DMFC [Han 2003; Chai 2004].

[0004] To date, a variety of techniques have been developed for fabricating carbon nanoparticles including laser ablation [Hu 2009; Sun 2006], non-thermal plasma [Couranjou 2009], microwave plasma chemical vapor deposition [Yu 2002], microwave of conducting polymers [Zhang 2006], thermal carbonization of bis(2-chloroethyl) amine hydrochloride at 260°C [Bourlinos 2009], arc-in-water method with forced convective jet [Noriaki 2004] and others [Yan 2009; Height 2004]. Liu et al. reported the preparation and fluorescent carbon nanoparticles derived from candle soot. [Liu 2007]. Tian et al. adopted a procedure to synthesize carbon nanoparticles from the combustion soot of natural gas instead of candles. [Tian 2009]. Di Stasio investigated the microstructure of propane-air diffusion -flame soot using TEM. [Di Stasio 2001]. Di Stasio observed three classes of nanoparticles: the class primary particles (20- 50 nm), the sub-primary graphitical particles (6-9 nm), and the elementary particles (<5 nm). [Di Stasio 2001].

[0005] However, these methods have limitations in terms of large scale and economical production because of their harsh synthesis conditions and low production yields. Accordingly, there is the need for a synthesis of carbon nanoparticles with tailored composition and structure, morphology and size using a simple and cheap method.

SUMMARY OF THE INVENTION

[0006] The present invention is a simple and inexpensive method to synthesize nanocarbon materials. Carbon nanoparticles having an average diameter of 50 nm were prepared by combustion of aromatic solvent (such as benzene, toluene, xylene or a mixture) compounds in air. The resulting carbon nanoparticles were found to strongly emit photoluminescence in the visible light when excited with a wide range of wavelength. Particles having narrow particle size distribution (prepared from a mixture of different size particles by a filtration process) improved the fluorescence quantum yield.

[0007] Carbon material synthesized by the method shows the following properties:

(i) The carbon nanoparticles generally have flat and round morphology with relatively regular size having an average size between about 10 nm and about 60 nm, and more generally between about 30 nm and about 60 nm. In some embodiments, the average size is between about 40 and about 50 nm. (ii) TEM and SEM imaging shows the carbon nanoparticles look like a cross section of onion.

(iii) The carbon nanoparticles are dispersed well in ethanol and other hydrocarbon solvents but water.

(iv) The carbon nanoparticles have photo-luminescent property. When the carbon nanoparticles were excited at 325 nm, a blue color was emitted with high intensity at 475 nm. Carbon nanoparticles showed a significant shift. Quantum yield was high: 12-13%.

(v) The carbon nanoparticles were found to be mainly carbon with a small amount of hydrogen and oxygen presence (C : H : O = 94.8 : 2.4 : 2.8 by wt%). (This calculates to an atomic ratio of C:H:0 of approximately 46: 1 : 14). The carbon nanoparticles have predominantly carbon in terms of wt%. The hydrogen can be utilized to generate functional groups.

[0008] The carbon nanoparticle material of the present invention can be utilized in a number of applications, including: energy storage (capacitor or electrode in batteries and fuel cells), electronic devices (OLED, solar cells), bio-imaging, imaging for identification, authentication vs. counterfeit, catalyst support, and biological applications.

[0009] Several techniques were previously developed for fabricating carbon nanoparticle collecting (such as soot from candle light (by burning candle wax), natural gas burning, or laser treatment of graphite) are different from the carbon materials of the present invention in terms of composition, particle size, photo-luminescent property, and their potential uses. This included that since the present invention uses aromatic hydrocarbons as feedstock, it is easy to have more carbons having SP₂ state in the carbon materials of the present invention product as compared to the carbons synthesized by the previously developed techniques. [0010] In general, in one aspect, the invention features a method for synthesizing carbon nanoparticles. The method includes selecting an aromatic compound. The method further includes performing a direct combustion of the aromatic compound to form the carbon nanoparticles. The weight percent of carbon in the carbon nanoparticles is at least about 94 wt% of the total weight of the carbon, hydrogen, and oxygen of the nanoparticles. The carbon nanoparticles have an average size between about 10 nm and about 60 nm. The carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

[0011] Implementations of the invention can include one or more of the following features:

[0012] The carbon nanoparticles can have a substantially flat and round morphology.

[0013] The step of direct combustion can include a confined combustion of the aromatic compound.

[0014] The step of direct combustion can include a controlled combustion of the aromatic compound.

[0015] The step of direct combustion can include the direct combustion of the aromatic compound in air.

[0016] The aromatic compound can be a liquid aromatic compound.

[0017] The aromatic compound can be a benzene, an alkylated benzene, or a combination thereof.

[0018] The aromatic compound can be a benzene, a toluene, a xylene, or a combination thereof.

[0019] The carbon nanoparticles can include essentially carbon.

[0020] The carbon nanoparticles can include carbon, oxygen, and hydrogen. The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 94 wt%. The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%.

[0021] The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 94 wt% and about 96 wt%. The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 4 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 3 wt%.

[0022] The weight percent of the oxgen in the carbon, the oxygen, and the hydrocarbon of the carbon nanoparticles can be between about 3 wt% and about 4 wt%.

[0023] The carbon nanoparticles can be essentially carbon, oxygen, and hydrogen.

[0024] The carbon nanoparticles can have an average size between about 30 nm and about

60 nm.

[0025] The carbon nanoparticles can have an average size between about 40 nm and about 50 nm.

[0026] The carbon nanoparticles can have a size between about 10 nm and about 30 nm.

[0027] The carbon nanoparticles can be operable for emitting the blue light having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

[0028] The carbon nanoparticles can be operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

[0029] The carbon nanoparticles can be operable for having a quantum yield of at least about 10%. [0030] The carbon nanoparticles can be operable for having a quantum yield of at least about 12%.

[0031] The quantum yield can be between about 12% and about 13%.

[0032] The method can be performed at room temperature.

[0033] The carbon nanoparticles can be soluble in ethanol. The carbon nanoparticles can be soluble in xylenes. The carbon nanoparticles can be soluble in hexane. The carbon nanoparticles can be soluble in chloroform.

[0034] The carbon nanoparticles can have a BET surface area between about 40 m²/g and about 50 m²/g.

[0035] The carbon nanoparticles can have a point absorption pore volume at P/Po=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

[0036] The carbon nanoparticles can have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

[0037] The carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm.

[0038] In general, in another aspect, the invention features carbon nanoparticles. The carbon nanoparticles include carbon, hydrogen, and oxygen. The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 94 wt%. The carbon nanoparticles have an average size between about 10 nm and about 60 nm. The carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

[0039] Implementations of the invention can include one or more of the following features:

[0040] The carbon nanoparticles can have substantially flat and round morphology. [0041] The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%.

[0042] The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 94 wt% and about 96 wt%. The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 4 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 3 wt%.

[0043] The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 3 wt% and about 4 wt%.

[0044] The carbon nanoparticles can have an average size between about 30 nm and about 60 nm.

[0045] The carbon nanoparticles can have an average size between about 40 nm and about 50 nm.

[0046] The carbon nanoparticles can have a size between about 10 nm and about 30 nm.

[0047] The carbon nanoparticles can be operable for emitting the blue light having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

[0048] The carbon nanoparticles can be operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

[0049] The carbon nanoparticles can be operable for having a quantum yield of at least about 10%. [0050] The carbon nanoparticles can be operable for having a quantum yield of at least about 12%.

[0051] The quantum yield can be between about 12% and about 13%.

[0052] The carbon nanoparticles can be made by a process that includes selecting an aromatic compound, and performing a direct combustion of the aromatic compound to form the carbon nanoparticles. The step of direct combustion can include a combustion reaction that is a confined combustion, a controlled combustion, or both.

[0053] The step of direct combustion can include the direct combustion of the aromatic compound in air.

[0054] The aromatic compound can be a liquid aromatic compound.

[0055] The aromatic compound can be a benzene, an alkylated benzene, or a combination thereof.

[0056] The aromatic compound can be a benzene, a toluene, a xylene, or a combinations thereof.

[0057] The carbon nanoparticles can be soluble in ethanol. The carbon nanoparticles can be soluble in xylenes. The carbon nanoparticles can be soluble in hexane. The carbon nanoparticles can be soluble in chloroform.

[0058] The carbon nanoparticles can have a BET surface area between about 40 m²/g and about 50 m²/g.

[0059] The carbon nanoparticles can have a point absorption pore volume at P/P₀=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

[0060] The carbon nanoparticles can have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

[0061] The carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm. [0062] In general, in another aspect, the invention features a method that includes selecting a carbon nanoparticle material. The carbon nanoparticle material includes carbon nanoparticles. The carbon nanoparticles include carbon, hydrogen, and oxygen. The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 94 wt%. The carbon nanoparticles have an average size between about 10 nm and about 60 nm. The carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm. The method further includes using the carbon nanoparticle material in an application. The application is for energy storage, an electronic device, bio-imaging, imaging for identification, authentication, catalyst support, biological application, or a combination thereof.

[0063] Implementations of the invention can include one or more of the following features:

[0064] The carbon nanoparticles can have substantially flat and round morphology.

[0065] The use of the carbon nanoparticle material can include energy storage.

[0066] The type of energy storage can be use in a capacitor, use in an electrode in a battery, use in an electrode in a fuel cell, or a combination thereof.

[0067] The use of the carbon nanoparticle material can include use in an electronic device.

[0068] The electronic device can be an organic light emitting diode or a solar cell.

[0069] The use of the carbon nanoparticle material can include bio-imaging.

[0070] The use of the carbon nanoparticle material can include imaging for identification.

[0071] The use of the carbon nanoparticle material can include authentication.

[0072] The authentication can include identification of a liquid.

[0073] The authentication can include identification of a solid.

[0074] The use of the carbon nanoparticle material can include catalyst support.

[0075] The use of the carbon nanoparticle material can include biological applications.

[0076] The biological application can include a device used in biological applications. [0077] The carbon nanoparticles can have an average size between about 30 nm and about 60 nm.

[0078] The carbon nanoparticles can have an average size between about 40 nm and about 50 nm.

[0079] The carbon nanoparticles can have a size between about 10 nm and about 30 nm.

[0080] The carbon nanoparticles are operable for emitting the blue light can having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

[0081] The carbon nanoparticles can be operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

[0082] The carbon nanoparticles can be operable for having a quantum yield of at least about 10%.

[0083] The carbon nanoparticles can be operable for having a quantum yield of at least about 12%.

[0084] The quantum yield can be between about 12% and about 13%.

[0085] The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be at least about 2 wt%.

[0086] The weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 94 wt% and about 96 wt%. The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 4 wt%. The weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 2 wt% and about 3 wt%. [0087] The weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles can be between about 3 wt% and about 4 wt%.

[0088] The carbon nanoparticles can be soluble in ethanol. The carbon nanoparticles can be soluble in xylenes. The carbon nanoparticles can be soluble in hexane. The carbon nanoparticles can be soluble in chloroform.

[0089] The carbon nanoparticles can have a BET surface area between about 40 m²/g and about 50 m²/g.

[0090] The carbon nanoparticles can have a point absorption pore volume at P/Po=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

[0091] The carbon nanoparticles can have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

[0092] The carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm.

[0093] The foregoing has outlined rather broadly the features and technical advantages of the invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0095] FIGURES 1A-1C show photographic images of the steps in the preparation of carbon nanoparticles from combustion of aromatic solvent. FIGURE 1A is a photographic image showing a confined combustion of an aromatic solvent. FIGURE IB is a photographic image showing the carbon soot that was formed. FIGURE 1C is a photographic image showing the carbon soot collected.

[0096] FIGURE 2A is a photographic image showing the carbon soot after dispersal in a solvent.

[0097] FIGURE 2B and FIGURE 2C are photographic images showing the fluorescence of the carbon nanoparticles of the present invention.

[0098] FIGURE 3A is a photographic image of other filtrate solutions formed by embodiments of the present invention. FIGURE 3B is a photographic image showing these filtrate solutions under UV exposure, which show blue color fluorescence. FIGURE 3C is a photographic image showing these filtrate solutions after UV exposure was discontinued, which also show blue color fluorescence.

[0099] FIGURES 4A-4D are TEM images of carbon nanoparticles of an embodiment of the present invention.

[00100] FIGURE 5 is an SEM images of carbon nanoparticles of an embodiment of the present invention.

[00101] FIGURE 6 is a graph that shows the photo luminescence spectra of the carbon nanoparticles of an embodiment of the present invention at room temperature, which were recorded with the excitation wavelength set at 325 nm. [00102] FIGURE 7 is a graph that shows that the photoemission of the carbon nanoparticles of an embodiment of the present invention shift in different media (ethanol, xylene, hexane, and chloroform (tri-chloromethane)).

[00103] FIGURE 8 is a graph that shows the Raman spectrum of the as-produced carbon nanoparticles of an embodiment of the present invention.

[00104] FIGURE 9 is a graph that shows the thermo gravimetric analysis (TGA) of the as- produced carbon nanoparticles of an embodiment of the present invention.

DETAILED DESCRIPTION

[00105] The present invention is a new method to obtain carbon nanoparticles by direct combustion of an aromatic solvent (such as benzene, toluene, or xylene or a mixture thereof) in air, such as a confined combustion performed in a confined space (such as a glass container). In embodiments of the present invention, the majority of the product resulting from the combustion is deposited in the wall of the container (i.e., with yield around 45 wt%). Only a small amount was deposited on the bottom. Since the combustion process can be continued until the solvent is completely consumed and no complex apparatus is needed, the present technique could be scalable for mass production.

[00106] In embodiments of the present invention, carbon soot (aggregates of carbon nanoparticles ("CNPs")) was collected after a confined combustion of benzene, toluene, xylene or a mixture, in air. FIGURE 1A is a photographic image showing a confined combustion of an aromatic solvent in vessel 102. "Confined" combustion is a combustion reaction in a confined vessel. Confined combustion reactions generally occur with flammable fluid-air mixtures or from the dispersion of a cloud of combustible dust in air. FIGURE IB is a photographic image showing carbon soot 103 that was formed by such a combustion process. FIGURE 1C is a photographic image showing the carbon soot 103 collected in a container 104 (such as a glass container like a Pyrex® jar). Alternatively, or in addition, the combustion can be a "controlled" combustion, i.e., a combustion reaction in which the temperature and composition of the reactants are carefully controlled, thereby tailoring the rate at which the flammable material and oxygen react.

[00107] The as-prepared samples were dispersed in solvent (ethanol), which solution is shown in FIGURE 2A. The solution was then filtered (such as by using 0.45 μιη filter). A light yellow filtrate was collected. As shown in FIGURES 2B-2C, when the filtrate was exposed to UV irradiation, the filtrate showed blue fluorescence {i.e., blue color fluorescence under UV exposure).

[00108] FIGURE 3A is a photographic image of filtrate solutions 301 and 302 formed by embodiments of the present invention. FIGURE 3B is a photographic image showing filtrate solutions 301 and 302 under UV exposure and showing blue color fluorescence. FIGURE 3C is a photographic image showing that filtrate solutions 301 and 302 continued to exhibit blue color fluorescence after UV exposure was discontinued.

[00109] As discussed above, large quantities of carbon nanoparticles were collected from the wall of the container. FIGURES 4A-4D show TEM images of the as-produced carbon nanoparticles collected from the container wall. FIGURE 5 shows a TEM image of the as- produced carbon nanoparticles collected from the container wall.

[00110] The TEM images were recorded using a JOEL Company Instrument (Model: 2100) operating at 200 KV. Sample preparation for the imaging was done by ultrasonically dispersing the particles in ethanol and using the solution; the particles were deposited on a copper grid coated with carbon film. The morphology of the sample was determined by using a Zeiss-LEO Model 1530 variable-pressure field-effect scanning electron microscope, and the dried sample for SEM was prepared by coating each sample on a carbon conductive grid. [00111] From FIGURES 4A-4B and FIGURE 5, it can be seen that the sample are aggregated nanoparticles having round morphology with relatively regular size. Based on statistical analysis of several samples of the present invention, the average size of the nanoparticles was found to be about 50 nm. Generally, the carbon nanoparticles have an average size between about 30 and about 60 nm. In some embodiments, the average size is between about 40 and about 50 nm.

[00112] FIGURES 4C-4D show a multi-shell concentric circle structure. Yan et al. reported the synthesis of carbon nanoparticles (CNPs) 3-6 nm, carbon anions 30-80 nm, and carbon nanoropes using commercial mesophase pitch as carbon precursor and a block copolymer PI 23 through solution phase synthesis below 200°C [Yan 2007]. It is believed that CNPs of about 50- nm size having flat, round structure are a new composition and further believed that the processes of the present invention are the first process that yields CNPs of about 50-nm size having flat, round structure. Still further, it is believed that CNPs of about 50-nm size having flat, round structure have not been reported to date.

[00113] CNPs samples (after filtration) were dried at 120°C for testing carbon, oxygen, and hydrogen percent. Based on elemental analysis of the CNP sample (Galbraith Laboratory), the CNP samples were found to be mainly carbon with a small amount of hydrogen and oxygen presence (C : H : O = 94.8 : 2.4 : 2.8 by wt%). It is believed that the resulting CNPs synthesized in the present invention may be related to the assembly of the aromatic molecules in liquid. At the same condition, the confined combustion of non-aromatic hydrocarbon compound such as hexane was found to produce only a very small amount of amorphous carbon. It is further believed that the π-π stacking interaction among aromatic compounds in liquid resulted in the formation of the nanoparticles via a self-assembly and polymerization to the CNPs having flat, structure (and generally having no sharp edges).

[00114] It has been reported that carbon nanoparticles have to be surface-passivated in order to become highly photoactive, having strong photo luminescence in the visible and infrared spectral regions [Cao 2007]. As-prepared nanocarbons were insoluble in water, so they relatively hydrophobic in nature. However when the sample was sonicated in ethanol, it was dispersable and filterable through a 0.45 μιη filter. As discussed above and shown for example in FIGURES 2B-2C, and 3A-3C, a light yellow filtrate was collected, which filtrate showed blue color fluorescence under UV exposure.

[00115] FIGURE 6 shows the photoluminescence of the carbon nanoparticles at room temperature with peak intensity at 475nm (shown on emission curve 602) with the excitation wavelength at 325 nm (shown on excitation curve 601). The CNPs of the present invention do not need to be passivated to be photoactive. Luo et al. reported that in order to have fluorescence from carbon material, there need to be oxygen atoms in the carbon material [Luo 2009]. Elemental analysis of a CNP sample of the present invention showed that it has oxygen, and FTIR also shows that it has the C=0 group corresponding to the 1720 cm-1 absorption peak. A broad photoluminescence peak can be seen at 490 nm. The CNPs of the present invention, in addition to fluorescing in the visible light, are essentially non-photobleaching and retain their fluorescence indefinitely. Even quantum dots, which exhibit longer lifetimes, will ultimately photobleach. However, the CNPs of the present invention have very stable photoemission over many hours under UV light with quantum yields of 12-13%. The "quantum yield" is the number of photons emitted divided by the number of photons absorbed. For materials that are primarily carbon, quantum yields greater than about 10% is high. Accordingly, the CNPs of the present invention have a high quantum yield property. This property allows one to modulate this emission for sensor application. The CNPs of the present invention remained stable for many hours, under even high illumination conditions - i.e., they do not exhibit the blinking most fluorophors exhibit.

[00116] FIGURE 7 shows that the photoemission of carbon nanoparticles shifts in different media (ethanol, xylene, hexane, and chloroform (tri-chloromethane), as shown in curves 701-704, respectively). One way to explain this emission shift is the solvatochromism, which is the change in nanoparticle photo emission due to a change in solvent polarity. It has been found that, in more polar solvent, such as ethanol, carbon nanoparticles of the present invention exhibit a blue shift. UV-vis spectrum of the carbon nanoparticles dispersion in ethanol showed no absorption peak in the visible range, which is consistent with carbon material.

[00117] Curve 802 of FIGURE 8 shows the Raman spectrum of the as-produced carbon nanoparticles of the present invention. This Raman spectrum shows the presence of the typical G-band at 1594 cm^"1 and D-band at 1347 cm^"1, which usually correspond to the E_2g nodes of graphite and disordered graphite respectively. The intensity ratio (I_D/IG), which is often used to correlate the structural purity of graphite, also indicates that the carbon nanoparticles are composed of mainly nanocrystalline material. [Ray 2009; Ferrari 2000].

[00118] As shown in FIGURE 9, thermal gravimetric analysis (TGA) shows a significant thermal stability consistent with the formation of carbon materials. As shown in curve 902 (for graphene) graphene is stable in air until 600°C, and at higher temperature it oxidizes to C0₂. As shown in curve 901 (for CNPs of the present invention), the CNPs of the present invention begin to oxidize at 550 °C, approximately 50°C lower than graphene. In materials science, the specific surface area of macroscopic samples of powders or porous materials is routinely determined by the measurement of gas adsorption (generally N₂ at 77K) and calculations using the Brunauer- Emmett-Teller (BET) isotherm. Due to its nanometric size, the CNPs of the present invention have a specific surface area of 44 m²/g. The pore structures were analyzed further by the BJH method from N₂ adsorption-desorption isotherm. The results of the BET and BJH analysis of CNPs of the present invention are summarized in Table 1 below. Table 1

(Characteristics of carbon nanoparticles samples by N₂ BET)

[00119] As discussed herein, the BET surface area, the single point absorption pore volume at P/Po=0.99, the t-Plot micro pore volumne, and BJH desorption average pore diameter are characteristics of the carbon nanoparticles samples measured by N₂ BET adsorption measurement at 77K.

[00120] As shown above, embodiments of the present invention include methods to synthesize flat, round carbon nanoparticles having an average size of around 50 nm. In other embodiments, carbon nanoparticles having an average diameter in the 10-30 nm range were obtained. In still further embodiments, carbon nanoparticles having an average diameter in the 30-60 nm range (and in some instances in the 40-50 nm range) were obtained. The resulting carbon nanoparticles were found to strongly emit photoluminescence in the visible when excited at a range of 275-375 nm wavelength.

[00121] The CNPs were found to emit strong fluorescence in the visible range, with peak intensity at 475 nm when excited with a wide wavelength range with high excitation at 325 nm with 12-13% quantum yield. It is believed that the reason the CNPs have photoluminescence is the oxygen presence in the CNPs.

[00122] Due to their properties, CNPs of the present invention can be utilized in a number of applications, including: energy storage (capacitor or electrode in batteries and fuel cells), electronic devices (OLED, solar cells), bio-imaging, imaging for identification, authentication vs. counterfeit, catalyst support, and biological applications.

[00123] The examples provided herein are to more fully illustrate some of the embodiments of the present invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute exemplary modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[00124] All patents and publications referenced herein are hereby incorporated by reference. It will be understood that certain of the above-described structures, functions, and operations of the above-described embodiments are not necessary to practice the present invention and are included in the description simply for completeness of an exemplary embodiment or embodiments. In addition, it will be understood that specific structures, functions, and operations set forth in the above-described referenced patents and publications can be practiced in conjunction with the present invention, but they are not essential to its practice. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without actually departing from the spirit and scope of the present invention.

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Claims

WHAT IS CLAIMED IS:

1. A method for synthesizing carbon nanoparticles comprising:

(a) selecting an aromatic compound; and

(b) performing a direct combustion of the aromatic compound to form the carbon nanoparticles, wherein

(i) the weight percent of carbon in the carbon nanoparticles is at least about 94 wt% of the total weight of the carbon, hydrogen, and oxygen of the nanoparticles,

(ii) the carbon nanoparticles have an average size between about 10 nm and about 60 nm, and

(iii) the carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm and about 375 nm.

2. The method of Claim 1, wherein the carbon nanoparticles have a substantially flat and round morphology.

3. The method of Claim 1, wherein the step of direct combustion comprises a confined combustion of the aromatic compound.

4. The method of Claim 1, wherein the step of direct combustion comprises a controlled combustion of the aromatic compound.

5. The method of Claim 1, wherein the step of direct combustion comprises the direct combustion of the aromatic compound in air.

6. The method of Claim 1 , wherein the aromatic compound is a liquid aromatic compound.

7. The method of Claim 1, wherein the aromatic compound is selected from the group consisting of benzenes, alkylated benzenes, and combinations thereof.

8. The method of Claim 1, wherein the aromatic compound is selected from the group consisting of benzenes, toluenes, xylenes, and combinations thereof.

9. The method of Claim 1 , wherein the carbon nanoparticles consists essentially of carbon.

The method of Claim 1 , wherein

(a) the carbon nanoparticles comprise carbon, oxygen, and hydrogen,

(b) the weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 94 wt%;

(c) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%; and

(d) the weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%.

11. The method of Claim 10, wherein

(a) the weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 94 wt% and about 96 wt%;

(b) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 2 wt% and about 4 wt%; and (c) the weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 2 wt% and about 3 wt%.

12. The method of Claim 11, wherein the weight percent of the oxygen in the carbon, the oxygen, and the hydrocarbon of the carbon nanoparticles is between about 3 wt% and about 4 wt%.

13. The method of Claim 10, wherein the carbon nanoparticles consist essentially of carbon, oxygen, and hydrogen.

14. The method of Claim 1, wherein the carbon nanoparticles have an average size between about 30 nm and about 60 nm.

15. The method of Claim 1, wherein the carbon nanoparticles have an average size between about 40 nm and about 50 nm.

16. The method of Claim 1, wherein the carbon nanoparticles have a size between about 10 nm and about 30 nm.

17. The method of Claim 16, wherein the carbon nanoparticles are operable for emitting the blue light having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

18. The method of Claim 16, wherein the carbon nanoparticles are operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

19. The method of Claim 1, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 10%.

20. The method of Claim 1, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 12%.

21. The method of Claim 20, wherein the quantum yield is between about 12% and about 13%.

22. The method of Claim 1 , wherein the method is performed at room temperature.

23. The method of Claim 1, wherein

(a) the carbon nanoparticles are soluble in ethanol;

(b) the carbon nanoparticles are soluble in xylenes;

(c) the carbon nanoparticles are soluble in hexane; and

(d) the carbon nanoparticles are soluble in chloroform.

24. The method of claim 1, wherein the carbon nanoparticles have a BET surface area between about 40 m²/g and about 50 m²/g.

25. The method of claim 1, wherein the carbon nanoparticles have a point absorption pore volume at P/P₀=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

26. The method of claim 1, wherein the carbon nanoparticles have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

27. The method of claim 1, wherein the carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm.

28. Carbon nanoparticles comprising

(a) carbon;

(b) hydrogen; and

(c) oxygen, wherein

(i) the weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 94 wt%,

(iv) the carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

29. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a substantially flat and round morphology.

30. The carbon nanoparticles of Claim 28, wherein

(a) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%; and

(b) the weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%.

31. The carbon nanoparticles of Claim 30, wherein

(b) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 2 wt% and about 4wt%; and

(c) the weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 2 wt% and about 3 wt%.

32. The carbon nanoparticles of Claim 31, wherein the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 3 wt% and about 4 wt%.

33. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have an average size between about 30 nm and about 60 nm.

34. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have an average size between about 40 nm and about 50 nm.

35. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a between about 10 nm and about 30 nm.

36. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles are operable for emitting the blue light having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

37. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles are operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

38. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 10%.

39. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 12%.

40. The carbon nanoparticles of Claim 39, wherein the quantum yield is between about 12% and about 13%.

41. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles are made by a process comprising the steps of:

(a) selecting an aromatic compound; (b) performing a direct combustion of the aromatic compound to form the carbon nanoparticles;

(c) the step of direct combustion comprises a combustion reaction selected from the group consisting of confined combustion, controlled combustion, and combinations thereof.

42. The carbon nanoparticles of Claim 41, wherein the step of direct combustion comprises the direct combustion of the aromatic compound in air.

43. The carbon nanoparticles of Claim 41, wherein the aromatic compound is a liquid aromatic compound.

44. The carbon nanoparticles of Claim 41, wherein the aromatic compound is selected from the group consisting of benzenes, alkylated benzenes, and combinations thereof.

45. The carbon nanoparticles of Claim 41, wherein the aromatic compound is selected from the group consisting of benzenes, toluenes, xylenes, and combinations thereof.

46. The carbon nanoparticles of Claim 28, wherein

(a) the carbon nanoparticles are soluble in ethanol;

(b) the carbon nanoparticles are soluble in xylenes;

(c) the carbon nanoparticles are soluble in hexane; and

(d) the carbon nanoparticles are soluble in chloroform.

47. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a BET surface area between about 40 m²/g and about 50 m²/g.

48. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a point absorption pore volume at P/P₀=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

49. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

50. The carbon nanoparticles of Claim 28, wherein the carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm.

51. A method comprising:

(a) selecting a carbon nanoparticle material, wherein the carbon nanoparticle material comprises carbon nanoparticles comprising

(i) carbon,

(ii) hydrogen, and

(iii) oxygen, wherein

(A) the weight percent of the carbon in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 94 wt%,

(B) the carbon nanoparticles have an average size between about 10 nm and about 60 nm, and

(C) the carbon nanoparticles are operable for emitting blue light when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm; and (b) using the carbon nanoparticle material in an application selected from the group consisting of energy storage, electronic devices, bio-imaging, imaging for identification, authentication, catalyst support, biological applications, and combinations thereof.

52. The method of Claim 51 , wherein the carbon nanoparticles have a substantially flat and round morphology.

53. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises energy storage.

54. The method of Claim 53, wherein the type of energy storage is selected from the group consisting of use in a capacitor, use in an electrode in a battery, use in an electrode in fuel cell, and combinations thereof.

55. The method of Claim 51, wherein the use of the carbon nanoparticle material comprises use in an electronic device.

56. The method of Claim 55, wherein the electronic device is selected from the group consisting of organic light emitting diodes and solar cells.

57. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises bio-imaging.

58. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises imaging for identification.

59. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises authentication.

60. The method of Claim 59, wherein the authentication comprises identification of a liquid.

61. The method of Claim 59, wherein the authentication comprises identification of a solid.

62. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises catalyst support.

63. The method of Claim 51 , wherein the use of the carbon nanoparticle material comprises biological applications.

64. The method of Claim 63, wherein the biological application comprises a device used in biological applications.

65. The method of Claim 51 , wherein, the carbon nanoparticles have an average size between about 30 nm and about 60 nm.

66. The method of Claim 51, wherein the carbon nanoparticles have an average size between about 40 nm and about 50 nm.

67. The method of Claim 51, wherein the carbon nanoparticles have a size between about 10 nm and about 30 nm.

68. The method of Claim 51, wherein the carbon nanoparticles are operable for emitting the blue light having a wavelength between about 425 nm and about 550 nm when the carbon nanoparticles are excited using an excitation wavelength between about 275 nm to about 375 nm.

69. The method of Claim 51, wherein the carbon nanoparticles are operable for having a highest peak of emitting the blue light at around 475 nm when the carbon nanoparticles are excited using an excitation wavelength of about 325 nm.

70. The method of Claim 51, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 10%.

71. The method of Claim 51, wherein the carbon nanoparticles are operable for having a quantum yield of at least about 12%.

72. The method of Claim 71, wherein the quantum yield is between about 12% and about 13%.

73. The method of Claim 51 , wherein

(a) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%; and (b) the weight percent of the hydrogen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is at least about 2 wt%.

74. The method of Claim 73, wherein

(b) the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 2 wt% and about 4 wt%; and

75. The method of Claim 74, wherein the weight percent of the oxygen in the carbon, the oxygen, and the hydrogen of the carbon nanoparticles is between about 3 wt% and about 4 wt%.

76. The method of Claim 51 , wherein

(a) the carbon nanoparticles are soluble in ethanol;

(b) the carbon nanoparticles are soluble in xylenes;

(c) the carbon nanoparticles are soluble in hexane; and

(d) the carbon nanoparticles are soluble in chloroform.

77. The method of claim 51, wherein the carbon nanoparticles have a BET surface area between about 40 m²/g and about 50 m²/g.

78. The method of claim 51, wherein the carbon nanoparticles have a point absorption pore volume at P/P₀=0.99 between about 0.09 cm³/g and about 0.10 cm³/g.

79. The method of claim 51, wherein the carbon nanoparticles have a t-plot micro pore volume between about 0.01 cm³/g and about 0.02 cm³/g.

80. The method of claim 51, wherein the carbon nanoparticles have a BJH desorption average pore diameter (4V/A) between about 8 nm and about 10 nm.