CN1418260A - High yield vapor phase deposition method for large scale single walled carbon nanotube prepration - Google Patents

Abstract

The invention discloses an improved gas phase deposition method for preparing single-walled carbon nanotubes on a metal catalyst carried by airgel. The overall yield of SWCNTs is often at least about 100%, based on the weight of the catalyst, and the reaction time is at least about 30 minutes.

Description

Method for preparing large single-walled carbon nanotubes by high-yield vapor deposition

technical field

The present invention generally relates to a method for preparing single-walled carbon nanotubes (nanotubes) by vapor deposition, wherein the method uses a metal catalyst supported on a carrier. More specifically, _the present invention relates to an improved method in which _the support contains an aerogel, such as _Al2O3 aerogel or _Al2O3 / _SiO2 airgel. The yield of single-walled carbon nanotubes obtained by the improved method is much higher than that obtained by the existing method.

Abbreviation ASB Aluminum tri-sec-butoxide AFM Atomic Force Microscopy (acac) ₂ Di(acetylacetonate) cm cm C °C CVD Chemical Vapor Deposition EtOH Alcohol g g kg kg kg kV kV m ml ml MW molecular weight MWCNT multiwalled carbon nanotube nm nanometer psi pounds per square inch SEM scanning electron microscope SWCNT single walled carbon nanotube sccm standard cubic centimeter per minute STP standard temperature and pressure Tpa terapascal TGA thermogravimetric analyzer TEM transmission electron microscope

Background of the invention

Since Lijima discovered carbon nanotubes in 1991, they have been one of the most actively researched materials in research today. See, lijima, Vol. 354, Nature, pp. 56-58 (1991). Such active research is not very surprising due to the remarkable chemical and physical properties possessed by this material and its potential applications in many different fields.

For example, depending on the number of concentric walls of graphene and the way the graphene is rolled into a cylinder, carbon nanotubes can be conductive like metal or can be semiconductive. See, Dresselhaus et al., Science of Fullerenes and Carbon Nanotubes, Academic Press, San Diego (1996).

Moreover, experiments have shown that individual carbon nanotubes can function as quantum wires and can even be made into room-temperature transistors. See, Tans etc., Vol.386, Nature, pp.474-477 (1997) vis-a-vis quantum wires and Tans etc., Vol.393, Nature, pp.49-52 (1998) vis-a-vis transistors .

Furthermore, carbon nanotubes have been shown to have excellent mechanical properties and chemical stability. The determination of the Young's modulus of the carbon nanotubes by AFM tests and the measurement of thermal vibrations showed values of 1.3 Tpa and 1.8 Tpa respectively, which are higher than those of any other known material. See, Wong et al. Vol.277, Science, pp.1971-1975 (1997) vis-a-vis AFM and Treacy et al., Vol.381, Nature, pp.678-680 (1996) vis-a-visthermal vibrations.

Therefore, due to their chemical stability, excellent mechanical properties, metal-like emission (ballistic) transport properties, and rich variability in electronic properties due to different helicities, carbon nanotubes have become an important component of high-strength composite materials and molecular electronics. Ideal candidates for interconnect and functional devices.

Despite the many unique and technologically important properties of carbon nanotubes, the lack of methods to produce the material in sufficient quantities limits not only the study of fundamental properties, but also more practical developments. The discovery of a low-cost, high-yield method to prepare SWCNTs indeed solves one of the biggest problems the field has faced in the past and opens up opportunities for a variety of applications.

Currently, carbon nanotubes are synthesized by 3 different techniques: (1) arc discharge between two graphite electrodes, (2) CVD by catalytic decomposition of hydrocarbons or CO, and (3) laser evaporation of carbon targets. For CVD, see International Publication No. WO89/07163 to Synder et al.; US 4,663,230 (granted 1987) to Tennent et al.; M. Terrones et al., Nature 388, 52-55 (1997); Z.F.Ren et al., Science 282, 1105 -1107(1998); J.Kong, A.Cassell and H.Dai, Chemical Physics Letters 292, 4-6(1998); J.H.Hafner et al., Chemical Physics Letters 296, 195-202(1998); E.Flahaut et al. , Chemical Physics Letters 300, 236-242(1999); S.S.Fan et al., Science 283, 512-514(1999); H.J.Dai et al., Chemical Physics Letters 260, 471-475(1996); H.M.Cheng et al., Applied Physics Letters 72, 3282-3284 (1998); and A.M. Cassell, J.A. Raymakers, J. Kong and H.J. Dai, Journal of Physical Chemistry B 103, 6484-6492 (1999).

Both the laser method and the arc method obtain high-quality SWCNTs. However, the problem encountered by these two technologies is the difficulty in increasing the productivity of nanotube materials from the laboratory scale to the industrial scale.

On the other hand, based on published reports, the CVD method clearly presents the best prospects for large-scale production of nanotube materials. This method has been described in 1980 (US4,663,230 by Tennent et al. (granted 1987) and edited by M.S.Dresselhaus, G.Dresselhaus, K.Sugihara, I.L.Spain and H.A.Goldberg in Graphite Fibers and Filaments. M. Cardona et al., Springer Series in MaterialsScience 5 Springer-Verlag, New York (1988) vol.5) reported that various carbon materials such as carbon fibers and multi-walled carbon nanotubes were prepared on a large scale with a higher yield than the laser method and the arc method.

Most recently in 1990, the preparation of SWCNTs by CVD (carbon monoxide or methane) was reported and the preparation of SWCNTs by CVD (benzene or ethylene) mixed with the preparation of bulk MWCNTs was reported. For carbon monoxide CVD, see, H.J. Dai et al., Chemical Physics Letters 260, 471-475 (1996) and P. Nikolaev et al., Chemical Physics Letters 313, 91 (1999). For methane CVD, see, A.M.Cassell, J.A.Raymakers, J.Kong and H.J.Dai, "Large Scale CVD Synthesis of Single-Walled Carbon Nanotubes", Journal of Physical Chemistry B103, 6484-6492 (1999) and E.Flahaut et al., Chemical Physics Letters 300, 236-242 (1999). For benzene CVD see, H.M. Cheng et al., Applied Physics Letters 72, 3282-3284 (1998). For ethylene CVD see J.H. Hafner et al., Chemical Physics Letters 296, 195-202 (1998). Therefore, although the reports of ethylene and benzene each involve SWCNTs, they have the drawback that they are always mixed with a large amount of MWCNTs.

Among these reported CVD methods, only the methane CVD method is reported to produce high-purity and high-quality SWCNT materials. However, the yields of the reported methane CVD processes are low, with the best results so far being 40% overall yield (based on the amount of catalyst with a reaction time of 10-45 min) where _the catalyst was loaded onto _Al2O3 powder or on Al ₂ O ₃ /SiO ₂ powder with a catalyst/support surface area of about 100 m ² /g. See, Cassell et al., supra.

Therefore, a CVD method that provides high quality SWCNTs in a very high yield (eg, at least about 100% with a reaction time of about 30 minutes) would be ideal.

Summary and Purpose of the Invention

Accordingly, the present invention provides a gas phase process _using metal catalysts supported on _aerogels , for example on _Al2O3 aerogels and/or _Al2O3 / _SiO2 aerogels. The catalyst/support used in the present invention is prepared by solvent-gel synthesis followed by removal of the liquid solvent by a drying step selected from supercritical drying, freeze drying and combinations thereof, with supercritical drying being preferred. The method vapor-deposits a carbon-containing compound on a catalyst/carrier. The compound should have a molecular weight of 28 or less, and if the compound has a higher molecular weight, then the compound should be mixed with _H2 . Vapor deposition provides enough heat for a sufficient time to produce SWCNTs on airgel-supported catalysts. These SWCNTs can then be removed from the airgel-supported catalyst if desired. Typically, these SWCNTs can be produced in high yields, eg, about 100% or greater, based on the weight of the catalyst.

Therefore, the object of the present invention is to obtain SWCNTs in a preferred embodiment in a hitherto unobtainable high yield. This yield is much higher than that of the existing CVD method, which has a best yield of about 40% based on the weight of the catalyst.

Thus, it is an advantage that the present discovery provides a method for producing SWCNT materials on a large scale, such as an industrial scale, at low cost.

Having stated some of the objects and advantages of the invention, others will become apparent when the specification and laboratory examples are taken in conjunction with the drawings described below.

Brief description of the drawings

Figure 1 is a graph showing typical TGA yield curves for (a) prepared and (b) purified in air SWCNT materials prepared according to the present method.

Figure 2 is a graph showing the weight gain versus reaction time for the preparation of SWCNT material by the present method using a methane flow of 1158 sccm at 900°C.

Figures 3a and 3b are photographs taken by microscopy showing (a) SEM images (b) TEM images of _SWCNT samples prepared by this method on _Al2O3 airgel-supported Fe/Mo catalysts, respectively. Samples were prepared at about 900°C under methane flow. The flow rate was 1158 sccm. The reaction time was 30 minutes.

Detailed description of the invention

The present invention provides single-walled carbon nanotubes using a novel gas phase process in which specific catalysts/supports are used in the deposition of carbonaceous compounds. In a preferred embodiment, the present invention provides a surprising increase in the yield of single-walled carbon nanotubes compared to prior methods using powder supports.

The term "single-walled carbon nanotubes" means well known in the art. Furthermore, it is not intended to exclude, with respect to the present method, that small amounts, eg <1%, of multi-walled carbon nanotubes can be produced at the same time.

Suitable carbon-containing compounds may be vaporous at STP or may be compounds which can be converted to vapor under the reaction conditions. Preferably, the compound has a molecular weight of 28 or less. Examples are CO, _CH4 , and combinations thereof. If the molecular weight of the compound is greater than 28, such as benzene (MW=78) or ethylene (MW=30), then the compound should be mixed with _H2 , such as 50% by volume of _H2 .

To practice the preferred embodiment at a high yield of about 100% or greater, a sufficient flow rate of the carbonaceous compound should be used and may be from about 900 seem to about 1300 seem.

Sufficient time may be from about 0.25 hour to about 7 hours. A sufficient temperature may be from about 750°C to about 1000°C. The yield can be about 200%, about 300%, or higher.

Suitable catalysts are any metal catalysts known in the art of preparing nanotubes. Preferred metal catalysts may be Fe/Mo, Fe/Pt and combinations thereof. A suitable carrier is any aerogel which the term means in the art, usually prepared by drying, for gelling with air as the dispersant. The airgel carrier may be a pulverized carrier converted into an aerogel by known methods. As discussed in detail below, drying may be supercritical or may be freeze drying, but is not intended to include drying resulting in a xerogel. A preferred airgel support may be Al ₂ O ₃ airgel support, Al ₂ O ₃ /SiO ₂ airgel support and combinations thereof.

As shown in Fig. 1, the yield of SWCNT materials was determined by heating the as-prepared SWCNT materials in TGA under flowing air. The overall yield of SWCNT material, calculated by dividing the weight loss between 300 °C and 700 °C by the weight remaining at 700 °C, is shown in % weight gain on the vertical axis and temperature on the horizontal axis , where the SWCNT material was burned in air, the weight remainder at 700 °C was assumed to be the weight of the catalyst and support material.

Purification of material prepared by this method was also investigated. Due to the high amorphousness of the airgel support prepared in this method, the removal of catalyst and support from SWCNT material becomes quite easy. The support can be removed by stirring in dilute HF acid, refluxing in another dilute acid such as _HNO3 , or refluxing in dilute base such as NaOH solution. Figure 1 shows the TGA results of the material refluxed in 2.6M _HNO3 for about 4 hours, followed by filtration.

As shown in Figure 2, for a typical growth time of about 60 minutes at about 900°C, the average yield using the catalyst/support was about 200%. The maximum yield (weight gain) was found to be about 600% at about 6.5 hours of growth. This method shows that the yield is significantly better than that previously reported by A.M.Cassell, J.A.Raymakers, J.Kong, H.J.Dai, Journal of PhysicalChemistry B 103, 6484-6492 (1999) Kong, Cassell and Dai, ChemicalPhysics Letters 292, 4-6 (1998) ) reported value.

As shown in Figures 3a and 3b, the quality of the as-prepared SWCNTs was characterized by SEM imaging and TEM imaging.

More specifically, as shown in Fig. 3a, the SEM image of the as-prepared SWCNT material shows very clear fibers entangled in the mesh network. The diameter of the fibers was shown to be from about 10 to about 20 nanometers. It is mentioned that the SEM images are of the as-grown material, without purification prior to imaging.

Moreover, as shown in Fig. 3b, the TEM images of the SWCNT material show that the fibers observed in the SEM images are actually bundles of single-walled carbon nanotubes. The diameter of the nanotubes, as determined from high resolution TEM images, is about 0.9 to about 2.7 nm.

Both SEM and TEM images show that SWCNT materials have the same properties as laser method (see, A.Thess et al., Science 273, 483-487 (1996) and T.Guo, P.Nikolaev, A.Thess, D.T.Colbert and R.E.Smalley, Chemical Physics Letters243, 49-54 (1995)) and arc method (see, M.Wang, X.L.Zhao, M.Ohkohchi and Y.Ando, Fullerene Science & Technology 4, 1027-1039 (1996) and C.Journet et al., Nature 388 , 756-758(1997)) prepared high-quality single-walled carbon nanotubes with similar characteristics.

The fact that the SEM image only shows nanotubes and not the amorphous carbon overcoat indicates that the catalyst/support surface is essentially completely covered with nanotube material. However, in the TEM images, eg for samples with a weight gain, ie yield, higher than about 300%, an outer layer of amorphous carbon is observed, which can be removed during and/or after SWCNT production.

Furthermore, this method reflects that the drying method of the wet gel (as discussed in the laboratory examples below) is an essential step in the preparation of high performance catalysts on airgel supports as used in this method. Drying may be performed by supercritical drying, such as by _CO2 supercritical drying, or by ethanol supercritical drying, or may be by freeze drying, such as by freeze drying with water, and combinations thereof.

However, it is not intended to include drying that results in xerogels. Fricke, Aerogels, Springer-Verlag, Berlin, Heidelberg, New York, Tokyo (1986) and N. Husing, U. Schubert, Angew. Chem. Int. Ed. 37, 22-45 (1998) discussed (i.e. about STP) evaporation of the liquid solvent will shrink the gel due to the collapse of the porous structure by the force of surface tension from the liquid/gas interface within the pores of the gel, and this shrinkage will significantly reduce the total surface area and pore volume, the dry material is often referred to as a xerogel.

On the other hand, during supercritical drying at a temperature much greater than STP and a pressure much greater than STP, the liquid solvent in the wet gel enters a supercritical state, for example under a blanket of carbon dioxide. Therefore, there is essentially no liquid/gas interface within the pores during drying. The original porous structure in the wet gel is thus substantially maintained in the final dry catalyst/aerogel.

Also, as more and more nanotubes grow on the surface of the airgel-supported catalyst, carbonaceous compounds, ie methane or carbon monoxide in the examples below, become more difficult to disperse onto the catalyst/support. Furthermore, since amorphous carbon deposition was observed on nanotubes at longer growth times as mentioned above in the discussion of Figures 3a and 3b, this carbon overcoat further reduces the rate of diffusion of carbonaceous compounds to the catalyst/support. This overburden explains why the growth rate decreases with time as shown in Figure 2.

In summary, a new method has been found for the preparation of single-walled carbon nanotubes using a catalyst/support format that can be used in vapor phase deposition methods, preferably in greater yields than obtainable by existing methods. This yield increase is usually by _a factor of at least 2.5, and often 5, compared to similar catalysts supported on _Al2O3 powder.

Lab Example Materials

All materials used in the laboratory examples were research grade materials obtained from various suppliers.

Aluminum tri-sec-butoxide (hereinafter abbreviated as ASB), Fe ₂ (SO ₄ ) ₃ .4H ₂ O and bis(acetylacetonato)dioxomolybdenum (hereinafter abbreviated as MoO ₂ (acac) ₂ ) were purchased from Sigma / Aldrich Chemicals.

Reagent grade nitric acid, ammonium hydroxide and ethanol were purchased from VWR Scientific Products.

High purity methanol, carbon dioxide and hydrogen were supplied by National Welders Inc. Embodiment 1 catalyst/carrier preparation

The catalyst/support was prepared using the solvent-gel technique reported in D.J.Suh and J.T.Park, Chemistry of Materials 9, 1903-1905 (1997) followed by supercritical drying. Optionally some samples were dried by freeze drying.

In a routine test, 23 g of ASB were dissolved in 200 ml of ethanol as liquid solvent in a round bottom flask under reflux. Then, 0.1 ml of concentrated _HNO3 , diluted with 1 ml of water and 50 ml of ethanol, was added to the mixture.

The resultant was refluxed for 2 hours until a clear solution was formed, then _1.38 g _Fe2 ( _SO4 ) _3.4H2O and 0.38 g _MoO2 (acac) ₂ were added to the mixture. The amounts of Fe and Mo were selected so that the molar ratio of Mo:Fe:Al=0.16:1:16. After refluxing for more than 2 hours, the mixture was cooled to room temperature, and then 5 ml of concentrated _NH4OH , diluted with 5 ml of water, was added to the mixture with vigorous stirring in order to encourage the dissolved metal salts to form nanoscale hydroxide particles and attach on airgel. Forms a gel within minutes.

The resultant was left to age for about 10 hours, after which a supercritical drying step was performed under the following conditions.

First, the catalyst/support wet gel was sealed in a high pressure vessel, which was then cooled to about 0°C and pressed to fill the vessel with liquid _CO2 at about 830 psi (about 59.4 kg/cm ² ). Perform a solvent exchange step in order to exchange the ethanol liquid solvent in the gel with liquid _CO by flushing the vessel with liquid _CO for a period of time.

Then, the vessel is heated to about 50°C to about 200°C, above the critical temperature of CO ₂ (31°C), and the pressure is maintained at about 1500 psi to 2500 psi (about 106.4 kg/cm ² -176.8 kg/cm ² ), It is above the critical pressure of _CO2 (1050 psi, 74.8 kg/ ^cm2 ). The system was maintained at these conditions for a period of time, after which the pressure was slowly reduced while the temperature was kept constant.

Finally, the temperature was lowered to room temperature. Then, each catalyst (in the metal hydroxide form) on the airgel support was calcined at 500° C. for 30 minutes, thereby being converted into the metal oxide form. It was then converted to the metallic form by reduction in _H2 at 900°C for 30 minutes before being used for SWCNT growth. The pressure at this stage was about 830 psi (about 59.4 kg/cm ² ). Each catalyst/support prepared in this manner was a catalyst supported on a highly porous, very fine, free-flowing aerogel with a surface area of about 500 m ² /g to about 600 m ² /g.

Alternatively, instead of _CO2 , some samples were supercritically dried with ethanol or dried by freeze drying as follows.

Ethanol supercritical drying: Use a 100ml high pressure and high temperature container. Add at least 35ml of wet gel to the container. Before heating, the system was _flushed with N to drive out the air. The whole system is then sealed and heated. After the temperature reached 260 °C, the system was kept at this temperature for 30 minutes, after which EtOH was slowly released. The release observation takes about 15 minutes. Then, the system was cooled slowly and the airgel-supported catalyst was removed. The yield of such nanotubes was similar to that of drying with _CO2 .

Freeze-drying: The ethanol in the wet gel is replaced with water by solvent exchange. Then, samples were frozen with liquid nitrogen and placed in a freeze dryer (Freezone Plus 6, Labconco, Kansas City, Missouri, United States of America). It took several days to dry the sample completely and the yield was lower than that with _CO2 . SWCNT growth

SWCNTs were fabricated in a simple vapor deposition facility consisting of a tube furnace and gas flow control. In a typical growth experiment, approximately 50 mg of the catalyst/support sample was placed in an alumina boat within a quartz tube. Each sample was individually heated to reaction temperature under Ar flow at a flow rate of 100 seem, then Ar was converted to _H2 (ca. 100 seem flow) for 30 minutes, followed by methane flow (ca. 1000 seem) for 30 minutes. Each sample was heated at each temperature of about 800°C, about 850°C, about 900°C, and about 950°C.

The reaction was allowed to proceed for the required time, after which the methane flow was turned off and the Ar flow was turned on and the temperature was lowered to room temperature. Each resultant was then weighed and characterized.

characterize

SWCNT samples were fully characterized using TEM imaging and SEM imaging.

TEM imaging was performed on a Philip CM-12 microscope operated at 100 kV. Samples for TEM imaging were prepared by sonicating approximately 1 mg of material in 10 ml of methanol for 10 min and drying a few drops of the suspension on a clean carbon grid.

SEM imaging was performed on a Hitachi S-4700 microscope with an electron beam energy of 4 kV by placing the as-grown material on a conductive carbon tape.

The yield of SWCNT material relative to the catalyst was determined on a thermogravimetric analyzer (model SDT 2960 from TA Instruments) under flowing air at a heating rate of 5 °C/min. As described in Figure 1, the observed yield by TGA was 100.2%.

Example II

The steps of Example 1 were essentially repeated, except that during SWCNT growth, the methanol flow time was about 60 minutes (instead of about 30 minutes) and the temperature was about 900°C (instead of about 800°C, about 850°C, about 900°C °C and different temperatures of about 950 °C), the flow rate was about 1158 sccm (instead of about 1000 sccm). The yield by TGA was about 200%.

Embodiment III (comparison)

The catalyst/support was also made from the same _Al2O3 wet gel, only dried _differently , resulting in a xerogel. The airgel-supported catalyst showed a yield of high-purity SWCNTs of about 200% under methane flow at about 900°C for about 60 minutes, as reported in Example I. On the other hand, xerogel-supported catalysts showed <5% weight gain under the same conditions.

Example IV

As for the Fe/Mo catalyst supported on _Al2O3 airgel, the procedure was repeated, except _this time the Fe/Mo catalyst was loaded onto _SiO2 airgel prepared by a similar method.

The weight gain of the catalyst on _SiO2 airgel was about 10% under the same conditions (methane flow at about 900°C for about 60 minutes). Therefore, it is clear that although the SiO ₂ airgel support plays a role (i.e. about 10%), the method of the present invention preferably uses an Al ₂ O ₃ airgel or Al ₂ O ₃ /SiO ₂ airgel support to obtain further excellent (ie, a weight gain of about 100% or greater).

Example V

The procedure of Example I was essentially repeated, except this time CO was substituted for _CH4 . Likewise, the temperature of the CO stream was about 850°C and the CO flow rate was about 1200 sccm for about 200 minutes. The result was a yield of about 150%.

Example VI

Basically repeat the steps of Example 1, except that Al ₂ O ₃ /SiO ₂ is used as the airgel carrier instead of Al ₂ O ₃ as the airgel carrier. Essentially the same result is obtained, except that a more amorphous carbon is present.

Embodiment VII (contrast)

It is believed that the more amorphous carbon produced in Example VI is due to, as a comparison, the _Al2O3 / _SiO2 airgel (without any metal catalyst) being tested with methane at ₉₀₀ °C for 30 minutes and thus converting the methane become amorphous carbon.

It will be understood that changes may be made in various details of the invention without departing from the scope of the invention. Moreover, the foregoing description has been presented for purposes of description only and not limitation, and the invention is defined by the appended claims.

Claims (18)

1. A method for preparing single-walled nanotubes, comprising: depositing a carbon-containing compound on a supported catalyst containing a metal catalyst and an airgel carrier under gas-phase conditions, and simultaneously forming a single-walled catalyst on an airgel-supported catalyst. Wallized carbon nanotubes were heated under the reaction conditions of temperature and time. 2. The method of claim 1, wherein said carbon-containing compound has a molecular weight of 28 or less. 3. The method of claim 2, wherein said carbonaceous compound is selected from the group consisting of methane, carbon monoxide, and combinations thereof. 4. The method of claim 1, wherein said carbon-containing compound has a molecular weight greater than 28 and the compound is mixed with hydrogen. 5. The method of claim 4, wherein said carbon-containing compound is selected from the group consisting of ethylene, benzene, and combinations thereof. 6. The method of claim 1, wherein the metal catalyst is selected from the group consisting of Fe/Mo, Fe/Pt, and combinations thereof. 7. The method of claim 1, wherein the airgel support is _{selected from the group consisting of Al2O3 airgel support} , _Al2O3 / _SiO2 airgel support, and combinations thereof. 8. The method of claim 1, wherein said depositing is performed at a sufficient flow rate of the carbonaceous compound, sufficient time and sufficient heat to obtain a yield of at least about 100% based on the weight of the catalyst. 9. The method of claim 8, wherein said sufficient flow rate is from about 900 seem to about 1300 seem. 10. The method of claim 1, wherein the airgel-supported catalyst has a surface area of from about 500 ^m2 /g to about 600 ^m2 /g. 11. The method of claim 1, wherein the airgel-supported catalyst is dried by drying selected from the group consisting of supercritical drying, freeze drying, and combinations thereof. 12. The method of claim 11, wherein said supercritical drying is selected from the group consisting of _CO2 supercritical drying, ethanol supercritical drying, and combinations thereof. 13. The method of claim 11, wherein said freeze-drying is freeze-drying using water. 14. The method of claim 1, wherein said sufficient heating provides a temperature of from about 750°C to about 1000°C. 15. The method of claim 1, wherein said sufficient time is at least about 0.25 hours. 16. The method of claim 1, wherein said yield is at least about 100%. 17. The method of claim 1, further comprising separating the single-walled carbon nanotubes from the airgel-supported catalyst. 18. A method of preparing single-walled carbon nanotubes, comprising depositing a carbon-containing compound on a supported catalyst comprising a metal catalyst and an airgel carrier under gas-phase conditions, wherein the carbon-containing compound is selected from the group consisting of methane, carbon monoxide, and combinations thereof, The metal catalyst is selected from Fe/Mo, Fe/Pt and combinations thereof, and the airgel carrier is selected from Al ₂ O ₃ airgel supports, Al ₂ O ₃ /SiO ₂ airgel supports and combinations thereof, and the airgel supported The catalyst is dried by drying selected from supercritical drying, freeze drying, and combinations thereof, and the deposition is carried out under sufficient flow of the carbonaceous compound for sufficient time and sufficient heat to achieve at least about 100% by weight of the catalyst yield.

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