U.S. patent application number 13/073865 was filed with the patent office on 2011-07-28 for organized carbon and non-carbon assembly.
Invention is credited to Sean Imtiaz Brahim, Steven G. Colbern, Leonid Grigorian, Robert L. Gump, Alex E. Moser, Daniel A. Niebauer.
Application Number | 20110183139 13/073865 |
Document ID | / |
Family ID | 38668459 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110183139 |
Kind Code |
A1 |
Grigorian; Leonid ; et
al. |
July 28, 2011 |
ORGANIZED CARBON AND NON-CARBON ASSEMBLY
Abstract
This invention relates generally to organized assemblies of
carbon and non-carbon compounds and methods of making such
organized structures. In preferred embodiments, the organized
structures of the instant invention take the form of nanorods or
their aggregate forms. More preferably, a nanorod is made up of a
carbon nanotube filled, coated, or both filled and coated by a
non-carbon material. This invention is further drawn to the
separation of single-wall carbon nanotubes. In particular, it
relates to the separation of semiconducting single-wall carbon
nanotubes from conducting (or metallic) single-wall carbon
nanotubes. It also relates to the separation of single-wall carbon
nanotubes according to their chirality and/or diameter.
Inventors: |
Grigorian; Leonid;
(Camarillo, CA) ; Colbern; Steven G.; (Fillmore,
CA) ; Moser; Alex E.; (Ventura, CA) ; Gump;
Robert L.; (Camarillo, CA) ; Niebauer; Daniel A.;
(Camarillo, CA) ; Brahim; Sean Imtiaz; (Camarillo,
CA) |
Family ID: |
38668459 |
Appl. No.: |
13/073865 |
Filed: |
March 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11741634 |
Apr 27, 2007 |
7938987 |
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13073865 |
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60796399 |
May 1, 2006 |
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60808096 |
May 24, 2006 |
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60842281 |
Sep 5, 2006 |
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60842543 |
Sep 6, 2006 |
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60874876 |
Dec 14, 2006 |
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Current U.S.
Class: |
428/368 ;
977/744 |
Current CPC
Class: |
C01B 2202/02 20130101;
Y10S 977/734 20130101; Y10S 977/842 20130101; Y10T 428/292
20150115; Y10S 977/75 20130101; C01B 32/18 20170801; C01B 32/178
20170801; C01B 32/168 20170801; Y10S 977/752 20130101; B82Y 30/00
20130101; Y10S 977/742 20130101; Y10S 977/744 20130101; Y10S
977/847 20130101; B82Y 40/00 20130101 |
Class at
Publication: |
428/368 ;
977/744 |
International
Class: |
D01F 8/18 20060101
D01F008/18; D01F 9/12 20060101 D01F009/12 |
Claims
1. An organized carbon and non-carbon assembly comprising a carbon
nanotube filled with a titanium compound, wherein the carbon
nanotube contains titanium carbide in an amount less than about 10
volume percent of the core volume of the carbon nanotubes.
2. The organized carbon and non-carbon assembly of claim 1, wherein
the titanium compound has a formula of
TiH.sub.wB.sub.xN.sub.yO.sub.z, where w varies in the range of 0 to
2, x varies in the range of 0 to 2, y varies in the range of 0 to
1, and z varies in the range of 0 to 2.
3. The organized carbon and non-carbon assembly of claim 1, wherein
the titanium compound is at least about 0.10 weight percent of the
organized assembly.
4. The organized carbon and non-carbon assembly of claim 1, wherein
the titanium compound is at least about 1.00 weight percent of the
organized assembly.
5. The organized carbon and non-carbon assembly of claim 1, wherein
the titanium compound is at least about 4.00 weight percent of the
organized assembly.
6. The organized carbon and non-carbon assembly of claim 1, wherein
the carbon nanotube contains titanium carbide in an amount less
than about 1 volume percent of the core volume of the carbon
nanotubes.
7. The organized carbon and non-carbon assembly of claim 1, wherein
the carbon nanotube contains titanium carbide in an amount less
than about 0.1 volume percent of the core volume of the carbon
nanotubes.
8. The organized carbon and non-carbon assembly of claim 1, wherein
the titanium compound is titanium.
9. The organized carbon and non-carbon assembly of claim 8, wherein
the carbon nanotube is filled and coated with titanium.
10. The organized carbon and non-carbon assembly of claim 1,
wherein the titanium compound is TiN.sub.y, where y varies in the
range of 0 to 1.
11. The organized carbon and non-carbon assembly of claim 10,
wherein the carbon nanotube is filled and coated with
TiN.sub.y.
12. The organized carbon and non-carbon assembly of claim 1,
wherein the titanium compound is TiH.sub.w, where w varies in the
range of 0 to 2.
13. The organized carbon and non-carbon assembly of claim 1,
wherein the titanium compound is TiO.sub.z, where z varies in the
range of 0 to 2.
14. The organized carbon and non-carbon assembly of claim 13,
wherein the carbon nanotube is filled and coated with TiO.sub.z.
Description
[0001] This application is a divisional application of U.S.
application Ser. No. 11/741,634, filed Apr. 27, 2007; which claims
priority to U.S. Provisional Patent Application Nos. 60/796,399,
filed May 1, 2006; 60/808,096, filed May 24, 2006; 60/842,281,
filed Sep. 5, 2006; 60/842,543, filed Sep. 6, 2006; and 60/874,876
filed Dec. 14, 2006; all of which are incorporated herein by
reference in their entirety.
TECHNICAL FIELD
[0002] This invention relates generally to organized assemblies of
carbon and non-carbon compounds. This invention further relates to
methods of making such organized structures. In preferred
embodiments, the organized structures of the instant invention are
made up of nanorods or their aggregate forms. This invention is
further drawn to the separation of single-wall carbon nanotubes. In
particular, it relates to the separation of semiconducting
single-wall carbon nanotubes from conducting (or metallic)
single-wall carbon nanotubes. It also relates to the separation of
single-wall carbon nanotubes according to their chirality and/or
diameter.
BACKGROUND OF THE INVENTION
[0003] There are numerous potential applications of carbon
nanotubes (CNTs) because of their unique mechanical, physical,
electrical, chemical, and biological properties. For example, ultra
low resistance conductors, semiconductors, highly efficient
electron emitters, ultra-strong lightweight fibers for structural
applications, lasers, and gas sensors can all be manufactured by
using CNTs. For reviews of CNT technology, properties, and
applications, see Baughman et al., "Carbon Nanotubes--the Route
Toward Applications", Science, volume 297, pages 787-792 (2002);
Michael J. O'Connell (Editor) "Carbon Nanotubes--Properties and
Applications", CRC Taylor & Francis, New York (2006); Yury
Gogotsi (Editor) "Nanomaterials Handbook", CRC Taylor &
Francis, New York (2006).
[0004] The incorporation of non-carbon materials into CNTs may lead
to even more diverse range of applications, for example, in
improved gaseous storage media or electronic devices. In a
publication entitled "Titanium-Decorated Carbon Nanotubes as a
Potential High-Capacity Hydrogen Storage Medium", Physical Review
Letters, 2005, Vol. 94, article 175501, Yildirim et al. described
that each titanium atom adsorbed on a single-wall CNT (SWCNT) may
theoretically bind up to four hydrogen molecules. Thus,
high-capacity hydrogen storage equipment may be prepared from such
materials, if they were available.
[0005] A variety of synthesis techniques for preparing CNTs exist.
These techniques include for example carbon arc, laser ablation,
chemical vapor deposition, high pressure carbon monoxide process
(HiPco), cobalt-molybdenum catalyst process (CoMoCat). Depending on
the preparation method, CNTs may be metallic and semiconducting. To
improve electrical conductivity of semiconducting CNTs, non-carbon
materials such as metals can be incorporated into CNTs for their
conversion into conducting materials.
[0006] In a publication entitled "Titanium Monomers and Wires
Adsorbed on Carbon Nanotubes: A First Principles Study,"
Nanotechnology, 2006, Vol. 17, pages 1154-1159, Fagan et al.
described that a metallic Ti-wire/tube system may potentially be
obtained by incorporating titanium in a semiconductor SWCNT. As a
result, the electrical conductivity of such materials may reach to
a level comparable or even surpassing that of copper. Such
materials, if available, may aid in the advance of electronic
applications. Fagan et al. also described that the Ti monomer or
wire adsorbed into a SWCNT could be more stable than that adsorbed
on outside surface of the SWCNT.
[0007] Gao et al. in U.S. Pat. Nos. 6,361,861 and 7,011,771
hypothesized the formation of titanium carbide, silicon carbide,
and tantalum carbide core in carbon nanotubes. They disclosed a
method by which TiC filled CNTs were grown on a growth catalyst and
a titanium substrate. Energy Dispersive X-Ray (EDX) analysis of the
nanorods thereby prepared revealed that the cores are cubic
TiC.
[0008] In a publication entitled "Synthesis and Characterization of
Carbide Nanorods," Nature, 1995, vol. 375, pages 769-772, Dai et
al. described that when TiO or Ti+I.sub.2 were reacted with carbon
nanotubes, TiC nanorods were obtained. These nanorods were analyzed
by X-Ray Diffraction (XRD) and found no evidence for presence of
graphitic (nanotube), Ti-metal or Ti-oxide peaks.
[0009] Guerret-Plecourt et al. in a publication entitled "Relation
between Metal Electronic Structure and Morphology of Metal
Compounds Inside Carbon Nanotubes" Nature, 1994, vol. 372, pages
761-765, the arc-discharge method also yielded only TiC filled
CNTs.
[0010] Nagy et al. in a European Patent No. 1 401 763 B1 disclosed
preparation of carbon nanotubes on Ti(OH).sub.4 supported Fe--Co
catalysts. The MWCNTs thereby prepared were later purified and then
analyzed by Proton Induced Gamma Ray Emission and Proton Induced
X-ray Emission. Nagy et al. found no evidence for incorporation of
Ti in the carbon nanotubes. Thus, previous attempts to fill CNTs
with titanium compounds either failed or resulted in formation of
TiC.
[0011] Formation of metal carbides during incorporation of
non-carbon materials may alter the structure of CNTs, resulting in
articles with poor electronic, thermal, chemical and mechanical
properties or articles with properties different than those
targeted. Therefore, this formation should be limited in order to
obtain articles with desired properties.
[0012] With respect to carbon nanotube separation, the
as-synthesized SWCNTs using the existing techniques are not pure.
They may comprise amorphous carbon and metal catalysts. The
as-synthesized SWCNTs may further comprise metallic and
semiconducting carbon nanotubes. Semiconducting SWCNTs are
hereafter abbreviated as s-SWCNTs and metallic SWCNTs as m-SWCNTs.
The as-synthesized SWCNTs may also comprise carbon nanotubes with a
variety of diameters. The relative amount of each component present
in as-synthesized SWCNTs depends on the synthesis process used.
[0013] To utilize their unique properties, the as-synthesized
SWCNTs should be separated into their components. For example, it
may be required to remove the amorphous carbon and the catalyst
from the as-synthesized SWCNTs to utilize their electric
properties. Further separation according to their electrical
conductivities, which depend on their chiralities and diameters,
may also be required if the application is of semiconducting or
conducting type. For example, the use of SWCNTs as transistor
channels requires s-SWCNTs and the use of SWCNTs as conductors for
on-chip connects requires m-SWCNTs. Furthermore, the semiconductor
properties also depend on the diameter of SWCNTs. Their
semiconductor band-gaps decrease with increasing diameter. If they
comprise s-SWCNTs with varying diameters, they will have a band-gap
varying in a wide range. Thus, separation of SWCNTs according to
their diameters may yield s-SWCNTs with semiconductor band-gaps
varying in a narrower and better defined range, making them
suitable for electronic devices based on Schottky barriers.
[0014] In sum, there exists a need for new or improved carbon
nanotube materials with greater purity and superior performance and
methods of making these materials. Also needed are practical
separation procedures to prepare SWCNTs containing size-specific
and/or chiral-specific populations. A size or chirality enriched
population of SWCNTs is useful in the preparation and manufacture
of commercial products or components thereof. They can also be used
as intermediates for preparing other desired products.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic diagram of the types of the organized
carbon and non-carbon assembly of the instant invention.
[0016] FIG. 2 shows the 633 nm excitation Raman spectra of the
starting SWCNTs, the nanorods, the washed and dried nanorods, and
anatase form of titania.
[0017] FIG. 3 shows the scanning electron micrograph of the
starting SWCNTs comprising SWCNT bundles and catalyst
particles.
[0018] FIG. 4 shows the scanning electron micrograph of the
titanium filled and coated SWCNTs.
[0019] FIG. 5 shows the 532 nm excitation Raman spectra of the Ti
filled SWCNTs (dashed line) and the nanorods after oxidization for
about 5 days (solid line).
[0020] FIG. 6 shows the variation of the Raman peak at 145
cm.sup.-1 of the Ti filled SWCNTs as a function of the air exposure
time.
[0021] FIG. 7 shows the transmission electron micrograph of a
TiO.sub.z filled SWCNT bundle.
[0022] FIG. 8 shows the electron diffraction pattern of the
TiO.sub.z filled SWCNT bundle shown in FIG. 7.
[0023] FIG. 9 shows the 532 nm Raman spectrum of the TiO.sub.z
filled SWCNTs.
[0024] FIG. 10 shows the 532 nm excitation Raman spectrum of
TiO.sub.z filled and coated SWCNTs.
[0025] FIG. 11 shows the variation of the Raman peak at 145
cm.sup.-1 of the TiN.sub.y filled SWCNTs as a function of the air
exposure time.
[0026] FIG. 12 shows the variation of the Raman peak at 145
cm.sup.-1 of the TiO.sub.z filled and coated SWCNTs as a function
of the air exposure time.
[0027] FIG. 13 shows the 532 nm excitation Raman spectra of
TiO.sub.z filled and coated SWCNTs taken from the same article but
at two different locations.
[0028] FIG. 14 shows the transmission electron micrograph of Mn
coated and filled SWCNT bundles.
[0029] FIG. 15 shows the transmission electron micrograph of Mn
coated and filled SWCNT bundles.
[0030] FIG. 16 shows the transmission electron micrograph of Ni
coated and filled SWCNT bundles.
[0031] FIG. 17 shows the transmission electron micrograph of Ni
coated and filled SWCNT bundles.
[0032] FIG. 18 shows the transmission electron micrograph of Pd
coated and filled SWCNT bundles.
[0033] FIG. 19 shows the transmission electron micrograph of Pt
coated and filled SWCNT bundles.
[0034] FIG. 20 shows the 633 nm excitation Raman spectra of the
glass coated with a TiN layer, the silicon coated with a TiN layer
and the TiN filled carbon nanotubes (nanorods).
[0035] FIG. 21 shows the 633 nm excitation Raman spectra of the
glass coated with a TiN layer, the silicon coated with a TiN layer
and the TiN filled carbon nanotubes (nanorods).
[0036] FIG. 22 shows the scanning electron micrograph of the TiN
filled carbon nanotubes grown on the Si/TiN/Fe article.
[0037] FIG. 23 shows the scanning electron micrograph of the
nanorod grown on the Si/TiN/Fe article.
[0038] FIG. 24 shows the scanning electron micrograph of the
nanorod grown on the Si/TiN/Fe article.
[0039] FIG. 25 shows the selected area electron diffraction of the
nanorod grown on the Si/TiN/Fe article.
[0040] FIG. 26 shows the weight decrease of starting SWCNTs, Ti
filled SWCNTs and Ti filled and coated SWCNTs as a result of
heating in air.
[0041] FIG. 27 shows the UV-VIS-NIR spectra of the starting SWCNTs,
the precipitate phase and the supernatant phase.
[0042] FIG. 28 shows the 633 nm excitation Raman spectra of the
starting SWCNTs, the precipitate phase and the supernatant
phase.
[0043] FIG. 29 shows fractional abundance of SWCNTs in the starting
SWCNTs and the supernatant phase as a function of SWCNT diameter as
determined by photoluminescence analysis.
[0044] FIG. 30 shows the illustration of two types of halogenated
SWCNTs: (a) the larger diameter tubes, as represented by (7,5) and
(b) the smaller diameter tubes, as represented by (6,5) and (c)
Raman spectra (633 nm excitation) of separated phases before the
removal of intercalated iodine (633 nm excitation). The arrow marks
the polyiodide peaks at about 148 cm.sup.-1. PP is the precipitate
phase and SN is the supernatant phase. The schematic
representations are roughly to the scale.
[0045] FIG. 31 shows the optical transition energies of nanotubes
as a function of radial breathing mode frequency. Circles are for
metallic tubes (E.sub.11.sup.M), while stars are for semiconducting
tubes (E.sub.22.sup.S is below E.sub.11.sup.M, while E.sub.33.sup.S
and E.sub.44.sup.S are above E.sub.11.sup.M). The (n,m) for some
E.sub.22.sup.S and E.sub.11.sup.M are given. The gray lines on
E.sub.22.sup.S and E.sub.R.sup.M and the numbers insides squares
for E.sub.33.sup.S branches indicate SWCNTs with the same (2n+m)
family number. Thick and thin stars are for semiconducting tubes
with (2n+m)mod 3=1 and 2, respectively. The (2n+m)mod 3=0 for
metallic tubes.
[0046] FIG. 32 shows Raman radial breathing modes of the
precipitate phase (a), and the supernatant phase (b) collected with
six excitation wavelengths (nm) shown in the insets; (c) sum
spectra; (d) 458 nm excitation spectra highlighting the small
diameter metallic tubes. The data in (c) were converted from RBM
frequencies (.omega..sub.RBM) to SWCNT diameter units using the
relation d(nm)=218.7/[.omega..sub.RBM(cm.sup.-1)-15.3] found to
work best for CoMoCat nanotubes (see Jorio et al.). PP is the
precipitate phase and SN is the supernatant phase.
[0047] FIG. 33 shows the 647 nm excitation photoluminescence
spectra of the phases. PP is the precipitate phase and SN is the
supernatant phase.
[0048] FIG. 34 shows the 633 nm excitation Raman spectra (a) and
633 nm excitation photoluminescence spectra (b) of the
bromine-separated phases, 633 nm excitation Raman spectra (c) of
the iodine-separated phases. Comparison of (a) with (c)
demonstrates the difference between the bromine- and iodine-based
processes. PP is the precipitate phase and SN is the supernatant
phase.
SUMMARY OF THE INVENTION
[0049] This invention is directed to an organized carbon and
non-carbon assembly. At a microscopic level, this assembly contains
one or more repeating units that are shorter in one dimension,
typically shorter than 1000 nm. This dimension may also be shorter
than 100 nm or even shorter than 10 nm. A repeating unit may be
partially hollow. For example, the empty portion of the core may be
less than 95, 75, 50, 25, or 10 volume percent. In a preferred
embodiment, a repeating unit takes the form of a nanorod.
[0050] The carbon of the instant invention may be amorphous carbon,
graphite, multi-wall carbon nanotube (MWCNT), single wall carbon
nanotube (SWCNT), or a mixture thereof. The non-carbon of the
instant invention may be metal (or its compounds) or non-metal.
Specific examples of non-carbon materials include magnesium (Mg),
magnesium hydride (MgH.sub.2), magnesium diboride (MgB.sub.2),
magnesium nitride (Mg.sub.3N.sub.2), magnesium oxide (MgO),
strontium (Sr), scandium (Sc), scandium nitride (ScN), yttrium (Y),
titanium (Ti), titanium hydride (TiH.sub.2), titanium nitride
(TiN), titanium diboride (TiB.sub.2), titanium oxide (TiO.sub.2),
zirconium (Zr), zirconium diboride (ZrB.sub.2), zirconium nitride
(ZrN), hafnium (Hf), hafnium nitride (HfN), vanadium (V), vanadium
diboride (VB.sub.2), niobium (Nb), niobium diboride (NbB.sub.2),
niobium nitride (NbN), tantalum (Ta), chromium (Cr), chromium
diboride (CrB.sub.2), manganese (Mn), iron (Fe), cobalt (Co),
nickel (Ni), palladium (Pd), platinum (Pt), boron (B), boron
hydrides, boron nitride (BN), boron oxide (B.sub.2O.sub.3), or a
mixture thereof.
[0051] In some preferred embodiments, an organized carbon and
non-carbon assembly is a nanorod (or its aggregate form) comprising
a carbon nanotube filled, coated, or both filled and coated by a
metal (such as titanium, magnesium), its hydride, boride, nitride,
or oxide, or a mixture (or alloy) thereof. In some embodiments, the
titanium compound fills at least about 0.10, 1.00, or 4.00 weight
percent of the organized assembly and the carbon nanotube and
titanium compound assembly is substantially free of titanium
carbide, for example, less than about 10, 1, or 0.1 volume percent
of the core volume of the carbon nanotube. In other embodiments, an
organized carbon and non-carbon assembly is a nanorod (or its
aggregate form) comprising a carbon nanotube filled, coated, or
both filled and coated by a non-metal (such as boron), its hydride,
boride, nitride, or oxide, or a mixture thereof.
[0052] This invention also provides methods for preparing organized
carbon and non-carbon assemblies. As a first step, a carbon
precursor is reacted with a halogenated precursor to produce a
halogenated intermediate. Halogen is then removed from the
halogenated intermediate to obtain an organized carbon and
non-carbon assembly. If the desired assembly contains a non-carbon
hydride, nitride, oxide, or a mixture thereof, an additional step
of hydrogenation, nitrogenation, and/or oxidation is used after the
halogen removal step.
[0053] The carbon precursor is usually amorphous carbon, graphite,
multi-wall carbon nanotube (MWCNT), single-wall carbon nanotube
(SWCNT), or a mixture thereof. The halogenated precursor typically
comprises a halogenated compound, such as magnesium iodide
(MgI.sub.2), scandium iodide (ScI.sub.3), scandium bromide
(ScBr.sub.3), titanium iodide (TiH.sub.4), titanium bromide
(TiBr.sub.4), vanadium iodide (VI.sub.3), vanadium bromide
(VBr.sub.3), iron iodide (FeI.sub.2), cobalt iodide (CoI.sub.2),
nickel iodide (NiI.sub.2), palladium iodide (PdI.sub.2), platinum
iodide (PtI.sub.2), boron iodide (BI.sub.3), or a mixture thereof.
The amount of the halogenated compound in the halogenated precursor
is at least 0.001 weight %. In other embodiments, the amount of the
halogenated compound in the halogenated precursor is at least 0.01
weight %, 0.1 weight %, 1 weight %, 10 weight %, 50 weight %, or 80
weight %.
[0054] In another embodiment, the halogenated precursor further
comprises a halogen. The halogen is typically iodine, bromine, an
interhalogen compound (such as IBr, ICl.sub.3, BrF.sub.3), or a
mixture thereof. The amount of halogen in halogenated precursor may
be at least 0.001 weight %. In other embodiments, the amount of
halogen in halogenated precursor may be at least 0.01 weight %, 0.1
weight %, 1 weight %, 10 weight %, 50 weight %, or 80 weight %. The
ratio of non-carbon material present in the halogenated precursor
to carbon present in the carbon precursor may be at least 0.01
weight %. In other embodiments, the ratio of non-carbon material
present in the halogenated precursor to carbon present in the
carbon precursor may be 0.01 weight %, 0.1 weight %, 1 weight %, 10
weight %, or 25 weight %. In some embodiments, a halogenated
precursor may comprise more than one type of halogenated
precursors. In other embodiments, a carbon precursor may comprise
more than one type of carbon precursors.
[0055] The reaction between a carbon precursor and a halogenated
precursor may occur at a temperature at which the halogenated
precursor is a liquid. Typically, the reaction temperature is at or
above the melting temperature of a halogenated precursor. In one
embodiment, the carbon precursor and the halogenated precursor may
be reacted at a temperature above 100.degree. C., 150.degree. C.,
or 200.degree. C. for a period longer than 1 minute, 10 minutes, or
20 minutes. After the reaction between a carbon precursor and a
halogenated precursor, a halogenated intermediate is produced.
[0056] Subsequently, halogen is removed from the halogenated
intermediate. The halogen removal step may utilize a suitable
method to reduce the halogen content below 10 weight %. An
effective method involves heating the halogenated intermediate at a
temperature for a sufficiently long period. For example, the
halogen removal step may be carried out at a temperature above
200.degree. C., 300.degree. C., 500.degree. C., or 800.degree. C.
for a period longer than 5 minutes, 10 minutes, 30 minutes, or 1
hour. In one embodiment, this heating may be carried out in a gas
mixture comprising hydrogen at a temperature for a period
sufficient enough to reduce the halogen content of the articles
below 10 weight %. For example, the halogen removal step may be
carried out in a gas mixture comprising at least 0.01 volume % or 1
volume % hydrogen at a temperature above 200.degree. C.,
300.degree. C., 500.degree. C., or 800.degree. C. for a period
longer than 5 minutes, 10 minutes, 30 minutes, or 1 hour. The
heating may be carried out below 1 atmosphere pressure.
[0057] In one embodiment, filled and coated carbon nanotubes (such
as Ti filled and coated SWCNTs) may be prepared by both filling and
coating the carbon nanotube cores by the halogenated non-carbon
precursor (such as a mixture of TiI.sub.4 and I.sub.2), followed by
the removal of halogen.
[0058] In another embodiment, coated carbon nanotubes (such as Ti
coated SWCNTs) may be prepared by coating but not filling the
carbon nanotube cores by the halogenated non-carbon precursor (such
as a mixture of TiI.sub.4 and I.sub.2), and then removing the
halogen. This is achieved by selecting nanotubes having core sizes
smaller than the size of the halogenated precursor.
[0059] In yet another embodiment, the non-carbon filled carbon
nanotubes (such as Ti filled SWCNTs) may be prepared by washing the
halogenated compound coated and filled carbon nanotubes with a
suitable solvent (such as ethanol). This washing removes the
halogenated compound coating, but not the filling at the carbon
nanotube core. Then, after the halogen removal, non-carbon filled
carbon nanotubes (such as Ti filled SWCNTs) are obtained.
[0060] The present invention is further directed to a method for
growing an organized assembly of carbon and the non-carbon and the
product prepared by this method. More specifically, this method
comprises the steps of selecting a substrate, depositing a
metal-layer on the substrate, and growing the organized assembly of
the carbon and the non-carbon material on the metal-layer in an
environment containing an alcohol. In some preferred embodiments,
the substrate may comprise silicon or glass and the metal-layer may
comprise titanium nitride. A chemical environment having ethanol or
additionally having hydrogen may be the preferred growth
environment.
[0061] In some embodiments, growing organized carbon and the
non-carbon assembly may further include depositing a catalyst-layer
on the metal-layer. The catalyst-layer may comprise iron. The
catalyst-layer may be heat-treated in an environment comprising
hydrogen but not any alcohol.
[0062] The present invention is further directed to a method of
separating SWCNTs, comprising the steps of halogenating SWCNTs,
dispersing the halogenated SWCNTs in a medium, and centrifuging the
dispersed SWCNTs to obtain a supernatant and a precipitate phase.
In some embodiments, more than about 85% or 95% of the SWCNTs in
the supernatant may have a diameter larger than a predetermined
size. In other embodiments, the enrichment of a population of
SWCNTs with respect to chirality or diameter in the supernatant may
be a factor of at least about 2.0 or 3.0 compared to the
precipitate phase or at least a factor of about 3.0 or 4.0 compared
to the starting form of SWCNTs. In addition, the population of
SWCNTs in the precipitate phase may be a factor of at least about
2.0 or 3.0 compared to the starting form of SWCNTs. In a preferred
embodiment, the halogen is preferentially intercalated in the cores
of SWCNTs.
[0063] The halogenation step may further include the step of
incorporating SWCNTs by a halogen such as iodine, bromine,
chlorine, fluorine, interhalogen compounds (such as IBr, ICl.sub.3,
BrF.sub.3), and mixtures thereof. Preferably, the halogen includes
iodine, bromine, interhalogen compounds, and mixtures thereof.
[0064] The halogenation step may additionally include the step of
(1) soaking SWCNTs in molten halogens; (2) adding solutions that
contain halogens to SWCNT dispersions; (3) using halogen vapor or
gas; or (4) a combination of these steps.
[0065] The dispersion step may further include (1) high shear
processing of the SWCNTs in a medium such as a liquid; (2) using
surfactants; (3) using carboxy functionalization; (4) using
cellulose derivatives; or (5) a combination of these steps.
Preferably, the dispersion step further includes first preparing a
dispersion of the SWCNTs in a medium such as a liquid and then
further dispersing them in the same medium by high-shear
processing. More preferably, the medium contains a surfactant. The
suitable surfactant may include nonionic or ionic surfactant.
Preferably, the surfactant may contain alkyldiphenyloxide
disulfonate salts, C12/C14-fatty acidethylenediamidethersulfate,
cetyltrimethylammonium bromide, disodium dodecylphenoxybenzene
disulfonate, hexadecyltrimethylammonium p-toluenesulfonate,
n-hexadecyl diphenyloxide disodium disulfonate, octyl phenol
ethoxylate, poly(ethylene oxide) (20) sorbitan mono-oleate, sodium
cholate, sodium diisopropylnaphthalene sulfonate, sodium
2-(1-carboxylatoethoxy)-1-methyl-2-oxoethyl laurate, sodium dodecyl
sulfate, sodium dodecylbenzene sulfonate, Surfynol, N-alkylamines,
and their mixtures.
[0066] The dispersion step may further comprise using a medium that
does not permanently destroy electronic properties of the SWCNTs.
Preferably, the medium may include water, heavy water,
dimethylformamide, dimethylacetamide, formamide, methyl formamide,
hexamethylene phoshphoramide, dimethylsulfoxide, liquid ammonia,
diethylamine, tetrahydrofuran, and mixtures thereof.
[0067] The centrifugation step may further comprise centrifuging at
a high speed. Preferably, the centrifugal force is higher than
about 10,000 g, or more preferably, higher than about 20,000 g. The
centrifugation may continue for longer than 1 hour, preferably
longer than 10 hours, or more preferably longer than 20 hours.
[0068] In one embodiment, the present invention may further
comprise treating halogenated SWCNTs with heat to remove the
halogen from the SWCNTs.
[0069] In another embodiment, the present invention may comprise
treating the supernatant and/or the precipitate phases to remove
the medium, the surfactant, and/or the halogen.
[0070] In yet another embodiment, the present invention may further
comprise a sonication step.
[0071] The present invention is also directed to the size or
chirality enriched SWCNTs separated by the process described
herein.
DETAILED DESCRIPTION OF THE INVENTION
I. Organized Carbon and Non-Carbon Assembly
[0072] This invention is directed to organized assemblies of carbon
and non-carbon materials. These organized structures are made up of
one or more types of a repeating unit and may adopt different
shapes, such as a rod, spherical, semi-spherical, or egg shape. At
least one dimension of the repeating unit is typically smaller than
1000 nm, preferably smaller than 100 nm, or more preferably smaller
than 10 nm. A cross-section of a repeating unit may resemble a
circular, oval, or rectangular shape. Typically, individual
repeating units (or different types of repeating units) aggregate
to nanometer size fragments. In a preferred embodiment, a repeating
unit of this invention may be a nanorod comprising nanocarbon and
non-carbon materials.
[0073] Many forms of carbon are suitable for this invention. These
forms of carbon include for example amorphous carbon, graphite,
MWCNT, SWCNT, or a mixture thereof. In preferred embodiments of
this invention, the carbon may be MWCNT, SWCNT, or a mixture
thereof.
[0074] Many non-carbon materials are suitable for this invention.
For example, a non-carbon material may comprise a metal, metal like
compound, metal nitride, metal oxide, metal hydride, metal boride,
mixture, or alloy thereof. Some examples of a non-carbon material
include magnesium (Mg), magnesium hydride (MgH.sub.2), magnesium
diboride (MgB.sub.2), magnesium nitride (Mg.sub.3N.sub.2),
magnesium oxide (MgO), strontium (Sr), scandium (Sc), scandium
nitride (ScN), yttrium (Y), titanium (Ti), titanium hydride
(TiH.sub.2), titanium nitride (TiN), titanium diboride (TiB.sub.2),
titanium oxide (TiO.sub.2), zirconium (Zr), zirconium diboride
(ZrB.sub.2), zirconium nitride (ZrN), hafnium (Hf), hafnium nitride
(HfN), vanadium (V), vanadium diboride (VB.sub.2), niobium (Nb),
niobium diboride (NbB.sub.2), niobium nitride (NbN), tantalum (Ta),
chromium (Cr), chromium diboride (CrB.sub.2), manganese (Mn), iron
(Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt),
boron (B), boron hydrides, boron nitride (BN), boron oxide
(B.sub.2O.sub.3) and a mixture (or alloy) thereof.
Non-stoichiometric compounds of the non-carbon material are also
within the scope of this invention. In addition, the non-carbon
material may be amorphous or crystalline. The crystalline form
could be distorted, for example by having deficiencies in the
crystal structure. In the instant invention, the non-carbon
material does not comprise a halogen and/or a halogenated
compound.
[0075] In one embodiment, this invention is directed to an
organized carbon and non-carbon assembly comprising a carbon
nanotube filled with a titanium compound that is substantially free
of titanium carbide. For example, the titanium carbide amount may
be less than 10, 1, or 0.1 volume percent of the core volume of the
carbon nanotube. A titanium compound may be titanium, titanium
hydride, boride, nitride, oxide or a mixture thereof. In
particular, a titanium compound may be abbreviated with a formula
TiH.sub.wB.sub.xN.sub.yO.sub.z, where w varies in the range of 0 to
2, x varies in the range of 0 to 2, y varies in the range of 0 to
1, and z varies in the range of 0 to 2. Non-stoichiometric titanium
compounds are also within the scope of this invention. For example,
the titanium compound may be TiO.sub.1.300.
[0076] In another embodiment of this invention, a non-carbon
material comprises a magnesium compound. A magnesium compound may
be magnesium, magnesium hydride, boride, nitride, oxide or a
mixture thereof. In particular, a magnesium compound may be
abbreviated with a formula MgH.sub.aB.sub.bN.sub.cO.sub.d, where a
varies in the range of 0 to 2, b varies in the range of 0 to 2, c
varies in the range of 0 to 2/3, and d varies in the range of 0 to
1. Non-stoichiometric magnesium compounds are also within the scope
of this invention. For example, the magnesium compound may be
MgO.sub.0.500.
[0077] In yet another embodiment of this invention, a non-carbon
material comprises a boron compound. A boron compound may be boron,
boron hydride, nitride, oxide or a mixture thereof. In particular,
a boron compound may be abbreviated with a formula
BH.sub.a'N.sub.b'O.sub.c', where a' varies in the range of 0 to 3,
b' varies in the range of 0 to 1, and c' varies in the range of 0
to 1.5. Non-stoichiometric boron compounds are also within the
scope of this invention. For example, the boron compound may be
BO.sub.1.200.
[0078] The organized assembly of this invention contains only a
limited amount of metal carbides, such as titanium carbide, silicon
carbide, vanadium carbide, tantalum carbide or a mixture thereof.
The metal carbide may be in any form. It may be in a form of
coating, filling or coating and filling. The metal carbide may also
be incorporated to the carbon structure of the carbon nanotube. The
amount of metal carbide may be less than 10 volume percent of the
core volume of the carbon nanotube. The presence and amount of
metal carbides may be determined by using techniques such as XRD,
EDX and Raman spectroscopy.
[0079] As a repeating unit, the non-carbon material may fill, coat,
or both fill and coat the carbon nanotube (CNT). These three cases
are schematically shown in FIG. 1 (a) to (c). In the first case
shown in FIG. 1(a), the non-carbon material fills the core of the
CNT. The articles of the first case are abbreviated hereafter as
"non-carbon material filled carbon," for example, as Ti filled
SWCNTs. In the second case shown in FIG. 1(b), the non-carbon
material coats the CNT. The articles of this case are hereafter
abbreviated as "non-carbon material coated carbon," for example, as
Ti coated SWCNTs. In the third case shown in FIG. 1(c), the
non-carbon material both fills and coats the CNT. The articles of
this case are hereafter abbreviated as "non-carbon material filled
and coated carbon," for example, as Ti filled and coated
SWCNTs.
[0080] The non-carbon material coated or filled and coated carbon
repeating unit may be particularly suitable for preparation of
metal matrix composites. For example, the composites comprising
organized assemblies of the instant invention (such as Ti coated
SWCNTs, Ti filled and coated SWCNTs) with metals such as aluminum
(Al), magnesium (Mg), copper (Cu), steel, and titanium (Ti) may be
prepared. Available methods such as gravity casting, permanent mold
casting, die casting, squeeze casting, investment mold casting and
infiltration casting may be used to prepare such metal matrix
composites: The pressure infiltration casting method disclosed in
U.S. Pat. Nos. 6,148,899, 6,360,809, and 6,776,219 to Cornie et al.
may be particularly useful for preparation of such composites.
[0081] Further, the core of a repeating unit, for example the core
of a SWCNT, may be partially empty. The empty portion of the core
may be in average less than 95, 75, 50, 25, or volume percent. The
volume of the empty space may be determined by using
High-Resolution Transmission Electron Microscopy (HRTEM). The
technique of observation of CNTs by HRTEM is explained in various
publications such as in Brown et al. "High yield incorporation and
washing properties of halides incorporated into single walled
carbon nanotubes", Appl. Phys., 2003, Vol. 76, pages 457-462 and
Sloan et al. "Integral atomic layer architectures of 1D crystals
inserted into single walled carbon nanotubes", Chem. Comm., 2002,
pages1319-1332.
[0082] The coating, filling, or coating and filling by the
non-carbon material may have a continuous or non-continuous form.
For example, they may be in the form of a continuous film deposited
on the outer or inner surface of a SWCNT, islands deposited on the
outer or inner surface of a SWCNT, beads deposited on the surface
of a SWCNT, or particulates deposited in the core of a SWCNT. The
filling and/or coating may distort the shape of the CNT. For
example, non-circular tubes may be obtained as a result of such
distortion.
[0083] The amount of filling and/or coating by the non-carbon
material may be determined by a thermo-gravimetric analysis (TGA)
technique as follows. First, a non-carbon material is incorporated
to a CNT article. Then, this article is inspected by a microscopic
technique such as high resolution transmission electron microscopy
(HRTEM) or high resolution scanning electron microscopy (HRSEM) to
qualitatively determine that whether the incorporation filled
and/or coated the material. Finally, this article is heated in air
to a predetermined temperature range to remove the carbon. Weight
decrease during this heating is measured by a balance. Similarly,
starting CNTs are also heated in air and their weight decrease is
determined. The difference between the weight decrease for the
organized assembly and the weight decrease for the starting CNT is
treated as the amount of incorporation of the non-carbon material.
If there is only filling, this technique yields the filling
amount.
[0084] If the microscopy indicates that there is a coating, this
coating is removed before the heating in air to determine the
filling amount. The coating removal may be achieved by washing the
article with a suitable liquid, such as an organic solvent, acid or
base. For example, alcohols, nitric acid, HCl or like may be used
to remove the coating. Success of removal may be qualitatively
determined by the microscopy. Steps of washing, microscopic
inspection and determination of the weight decrease by heating in
air may be repeated several times to ensure that the coating is
adequately removed.
[0085] An article comprising a coating of the non-carbon material
may also be heated in air. The difference between the weight
decrease of the article comprising a coating of the non-carbon
material and the weight decrease of the same article after the
removal of the coating yields the amount of the coating.
[0086] The organized assembly may contain metal carbides. Their
presence and amount may be determined by using techniques such as
XRD, EDX and Raman spectroscopy. If the metal carbides are found to
be present after such analysis, their amount may be subtracted from
the non-carbon material amount found above to determine the metal
carbide free portion of the non-carbon material.
[0087] The above analysis technique is hereafter abbreviated as
"the TGA based technique".
II. Halide Method
[0088] The instant invention is also directed to methods for
preparing the organized assembly of carbon and non-carbon
materials. In particular, this method comprises the steps of
reacting a carbon precursor with a halogenated precursor to
generate a halogenated intermediate and removing halogen from the
halogenated intermediate to obtain the organized assembly of the
carbon and the non-carbon materials (hereinafter "the halide
method"). If the non-carbon material includes a hydride, nitride,
oxide, or a mixture thereof, the method may further comprise the
step of hydrogenation, nitrogenation, and/or oxidation after the
halogen removal step to obtain a composition comprising (1) carbon
and (2) a non-carbon hydride, boride, nitride, oxide, or a mixture
thereof. In the instant invention, the non-carbon material is not a
halogen.
[0089] Many forms of the carbon precursor are suitable for the
halide method. In a preferred embodiment, these forms of carbon
precursors comprise MWCNT, SWCNT, or a mixture thereof.
[0090] A SWCNT or MWCNT precursor suitable for this invention may
be prepared by any synthesis method. Such methods may include, but
are not limited to, carbon arc, laser vaporization, chemical vapor
deposition (CVD), high pressure carbon monoxide process (HiPco),
cobalt-molybdenum catalyst process (CoMoCat). A SWCNT precursor may
be a mixture of SWCNT precursors prepared by more than one
synthesis method.
[0091] In one embodiment of the halide method, the SWCNT precursor
may be used as purchased. In another embodiment, amorphous carbons
and/or catalysts may be removed from the as-purchased SWCNTs before
the application of the disclosed method. The amorphous carbon
and/or the catalyst removal may be complete or partial. Thus, a
SWCNT precursor may contain any level of amorphous carbon and/or
catalyst. The invention is not limited to any particular method of
removing the amorphous carbon and/or the catalyst from the starting
SWCNTs. As an example, the method disclosed by Delzeit et al. in
U.S. Pat. No. 6,972,056 may be used for this removal.
[0092] A halogenated precursor may comprise a halogenated compound
and a halogen. Examples of the halogenated compound include
magnesium iodide (MgI.sub.2), scandium iodide (ScI.sub.3), scandium
bromide (ScBr.sub.3), yttrium iodide (YI.sub.3), titanium iodide
(TiI.sub.4), titanium bromide (TiBr.sub.4), vanadium iodide
(VI.sub.3), vanadium bromide (VBr.sub.3), molybdenum iodide
(MoI.sub.3), manganese iodide (MnI.sub.2), iron iodide (FeI.sub.2),
cobalt iodide (CoI.sub.2), nickel iodide (NiI.sub.2), palladium
iodide (PdI.sub.2), platinum iodide (PtI.sub.2), boron iodide
(BI.sub.3), lead iodide (PbI.sub.2), bismuth iodide (BiI.sub.3) or
a mixture thereof. Examples of the halogen include iodine, bromine,
an interhalogen compound (such as IBr, ICl.sub.3, BrF.sub.3) or a
mixture thereof.
[0093] Ends of the as-purchased carbon nanotubes are typically
closed, i.e. they are end-capped. The end-caps may prevent direct
filling of cores of the as-purchased carbon nanotubes with the
non-carbon materials. In some previously disclosed filling methods,
the end-caps are removed prior to the filling step by using acids
such as nitric acid or by controlled oxidation at elevated
temperatures. Such end-cap removal methods may cause partial or
excessive removal of carbon and formation of defects, thereby
degrading the useful properties of the carbon nanotubes.
[0094] The presence of the halogen in the halogenated precursor may
aid in filling of the carbon nanotubes with the non-carbon
materials without necessitating a separate end-cap removal step
prior to the filling, thereby simplifying the process. Also, such
filling may be achieved without any degradation of useful
properties of the carbon nanotubes. The presence of halogen may
also increase the amount of filling of carbon nanotubes by
non-carbon materials, thereby improving the yield and desired
properties of the organized assembly. Furthermore, the presence of
halogen may decrease the viscosity of the halogenated precursor,
thereby promoting better infiltration and shorter process
duration.
[0095] Some halogenated compounds may have impractically high
melting points (e.g., 587.degree. C. for FeI.sub.2, 780-797.degree.
C. for NiI.sub.2, 613-638.degree. C. for MnI.sub.2), and if the
reaction is carried out at such high temperatures, the carbon
nanotubes may irreversibly be damaged, diminishing the useful
properties of the organized assembly. However, incorporating
halogens such as bromine with a melting point of -7.3.degree. C. or
iodine with a melting point of 113.6.degree. C. into the
halogenated precursor may substantially reduce the reaction
temperature and prevent any property degradation.
[0096] Thus, there are several advantages of incorporating a
halogen into the halogenated precursor, including achieving filling
with no end-cap removal prior to the filling, increasing the
filling yield, and reducing the reaction temperature and time.
[0097] The amount of the halogenated compound in a halogenated
precursor may be at least 0.001 weight %. In other embodiments, the
amount of the halogenated compound in a halogenated precursor may
be at least 0.01 weight %, 0.1 weight %, 1 weight %, 10 weight %,
50 weight %, or 80 weight %. The amount of halogen in a halogenated
precursor may be at least 0.001 weight %. In other embodiments, the
amount of halogen in a halogenated precursor may be at least 0.01
weight %, 0.1 weight %, 1 weight %, 10 weight %, 50 weight %, or 80
weight %.
[0098] The amount of non-carbon material present in the halogenated
precursor controls the amount of non-carbon material incorporated
into the assembly. Thus, by varying the ratio of the non-carbon
material amount to the carbon precursor, the non-carbon material
content of the final composition can be varied. The ratio of
non-carbon material present in the halogenated precursor to carbon
present in the carbon precursor may be at least 0.01 weight %. In
other embodiments, the ratio of non-carbon material present in the
halogenated precursor to carbon present in the carbon precursor may
be at least 1 weight %, 10 weight %, or 25 weight %.
[0099] As a first process step, a carbon precursor is reacted with
a halogenated precursor. This reaction results in the incorporation
of the carbon precursor with the halogenated precursor to form a
halogenated intermediate. This incorporation may be in any form.
For example, the halogen may be incorporated on the outer or inner
surface or into the chemical structure of the carbon precursor.
This incorporation may be through chemical or physical bonding.
[0100] The reaction between the carbon precursor and the
halogenated precursor may occur at a temperature at which the
halogenated precursor is a liquid. Typically, it is at or above the
melting temperature of the halogenated precursor. In one
embodiment, the carbon precursor and the halogenated precursor may
be reacted at a temperature above 20.degree. C., 100.degree. C.,
150.degree. C., or 200.degree. C. for a period longer than 1
minute, 10 minutes, or 20 minutes.
[0101] In an optional process step, the carbon precursor may be
heated above room temperature to remove volatile compounds, such as
water, before the step of reacting the carbon precursor with the
halogenated precursor. The volatile compound removal may be
achieved by heating the carbon precursor above 100.degree. C. or
200.degree. C. for a period longer than 10 minutes.
[0102] After the reaction between the carbon precursor and the
halogenated precursor, a halogenated intermediate is produced.
[0103] As a second process step, the halogen is removed from the
halogenated intermediate. It is expected that, during the reaction,
the halogenated precursor may open the end caps of the carbon
nanotubes and fill their cores, coat the carbon nanotube, or both
fill (i.e., intercalate) and coat the carbon nanotube. As a result,
the halogenated intermediate may contain halogen, in a free form,
such as iodine, and/or in a form incorporated with the non-carbon
compound, such as TiI.sub.4. The presence of the halogen in the
final assembly in high quantities may deteriorate its properties as
compared to the halogen free assembly. It may be necessary to
reduce the halogen level, for example, below 10 weight %, to obtain
a commercially viable product.
[0104] The halogen removal may be achieved by sublimation,
evaporation, or thermal degradation. The halogen removal may also
be achieved by reacting the halogenated intermediate with a
suitable reactant, for example, hydrogen.
[0105] In particular, the halogen removal step may comprise heating
the halogenated intermediate at a temperature for a period
sufficient enough to reduce the halogen content of the intermediate
below 10 weight %. For example, the halogen removal step may be
carried out at a temperature above 200.degree. C., 300.degree. C.,
500.degree. C., or 800.degree. C. for a period longer than 5
minutes, 10 minutes, 30 minutes, or 1 hour. This heating may be
carried out below 1 atmosphere pressure. In one embodiment, this
heating may be carried out in a gas mixture comprising hydrogen at
a temperature for a period sufficient enough to reduce the halogen
content of the intermediate below 10 weight %. For example, the
halogen removal step may be carried out in a gas mixture comprising
at least 0.01 volume % or 1 volume % hydrogen at a temperature
above 200.degree. C., 300.degree. C., 500.degree. C., or
800.degree. C. for a period longer than 5 minutes, 10 minutes, 30
minutes, or 1 hour. The heating may be carried out below 1
atmosphere pressure. By adjusting these halogen removal conditions,
the level of hydride formation can be controlled and as a result
essentially hydride-free or partially or fully hydrogenated forms
of the non-carbon material may be obtained.
[0106] After the halogen removal step, an organized assembly
comprising a carbon and a non-carbon material (such as metal, metal
like compound, metal boride, or a mixture thereof) is obtained.
Specific examples of such non-carbon material include magnesium
(Mg), magnesium diboride (MgB.sub.2), strontium (Sr), scandium
(Sc), yttrium (Y), titanium (Ti), titanium diboride (TiB.sub.2),
zirconium (Zr), zirconium diboride (ZrB.sub.2), hafnium (Hf),
hafnium nitride (HfN), vanadium (V), vanadium diboride (VB.sub.2),
niobium (Nb), niobium diboride (NbB.sub.2), tantalum (Ta), chromium
(Cr), chromium diboride (CrB.sub.2), manganese (Mn), iron (Fe),
cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), boron (B),
boron nitride (BN), and a mixture thereof.
[0107] For an organized assembly comprising (1) a carbon and (2) a
non-carbon hydride, boride, nitride, oxide, or a mixture thereof,
the method may further include hydrogenation, reaction with boron
compounds, nitrogenation, and/or oxidation of the product after the
halogen removal step. This is an optional step for some hydrides
and borides. For example, if the halogen removal step is carried
out in a gas mixture comprising hydrogen, the non-carbon hydrides
may readily be obtained after the halogen removal without
necessitating this additional step. Also, if the halogenated
precursor includes a boron compound, the borides may also readily
be obtained after the halogen removal step without necessitating
this additional step. The hydrogenation may be carried out above
room temperature in a gas mixture containing hydrogen, ammonia, or
hydrazine. A preferable hydrogenation temperature is below
500.degree. C. In one embodiment of this invention, a hydrogenation
temperature in the range of 100.degree. C. to 300.degree. C. may
also be applied. The reaction with boron compounds may be carried
out by reacting the product with boron hydrides, for example
B.sub.2H.sub.6, B.sub.5H.sub.11. The nitrogenation may be carried
out above room temperature in a gas mixture containing nitrogen,
ammonia, hydrazine, or a mixture thereof. The oxidation may be
carried out at room temperature or above in a gas mixture
containing oxygen. As a result of hydrogenation, reaction with
boron compounds, nitrogenation, and/or oxidation, the assembly
comprising (1) a carbon and (2) a non-carbon (such as metal)
hydride, boride, nitride, oxide, or a mixture thereof is formed.
Some examples of such non-carbon material include magnesium hydride
(MgH.sub.2), magnesium nitride (Mg.sub.3N.sub.2), magnesium oxide
(MgO), scandium nitride (ScN), titanium hydride (TiH.sub.2),
titanium nitride (TiN), titanium oxide (TiO.sub.2), zirconium
nitride (ZrN), hafnium nitride (HfN), niobium nitride (NbN), boron
hydrides, boron nitride (BN), boron oxide (B.sub.2O.sub.3), and a
mixture thereof.
[0108] In one embodiment of the halide method, the organized
assembly comprising non-carbon material filled and coated carbon,
such as Ti filled and coated SWCNT may be prepared by both filling
and coating the carbon nanotube by the halogenated compound. To
achieve the filling, the size of the core should be larger than the
size of the halogenated compound. For example, a halogenated
compound, TiI.sub.4 has a size of about 1 nm. During the
halogenation reaction, this compound can fill the cores of SWCNTs
that have inner diameters larger than 1 nm. Thus, for example,
since the SWCNTs prepared by the carbon arc process have inner
diameters larger than 1 nm, these carbon precursors may be both
filled and coated with TiI.sub.4 and after the removal of iodine,
Ti filled and coated SWCNTs are generated.
[0109] In another embodiment of the halide method, the non-carbon
material coated carbon, such as Ti coated SWCNTs may be prepared by
coating the carbon nanotube by the halogenated compound. To achieve
the coating but not filling, the size of the core should be smaller
than the size of the halogenated compound. For example, a
halogenated compound TiI.sub.4 has a size of about 1 nm and the
SWCNTs prepared by CoMoCat process have inner diameters smaller
than 1 nm. Then, it is expected that during the halogenation
reaction, TiI.sub.4 can coat but not fill the cores of these
SWCNTs. As a result, after the iodine removal, Ti coated SWCNTs may
be produced.
[0110] In yet another embodiment of the halide method, the
non-carbon material filled carbon, such as Ti filled SWCNTs may be
prepared by washing the halogenated compound coated and filled
carbon nanotubes with a suitable solvent, such as ethanol. This
washing may remove the halogenated compound coating, but not the
filling at the carbon nanotube core. Then, after the halogen
removal, Ti filled SWCNTs are produced. This washing may completely
remove the halogenated compound coating if a suitable solvent is
used and/or if the solvent washing step is repeated several times.
This washing may also partially remove the halogenated coating, for
example, thereby incorporating a coating that has a particulate
form to the carbon. The amount of the coating then may be varied by
controlling the solvent type, solvent amount, and number of
repetition of washing steps.
[0111] Thus, by choosing the core size of the carbon nanotube or
incorporating a solvent wash step when the core size is larger than
size of the halogenated compound, the form of non-carbon material
incorporation may be controlled to prepare non-carbon filled,
coated, both filled and coated carbon assemblies, or their
mixtures.
[0112] The TGA based technique described above may be applied to
the halide method to determine the filling and/or the coating
amount as follows. First, a halogenated precursor is incorporated
with a CNT article. Then, the halogenated intermediate is inspected
by microscopy. It was found by such microscopic inspection that
this incorporation typically yields SWCNT articles comprising a
coating of the halogenated precursor. It was also found that such
coating could adequately be removed by washing the halogenated
intermediate with alcohols such as ethanol. After said washing, the
halogen is removed from the halogenated intermediate remained in
the CNT article as a filling. Finally, the washed article is heated
in air to a predetermined temperature range to remove the carbon.
Weight decrease during this heating is measured by a balance. Also,
starting CNTs are heated in air and their weight decrease is
determined. The difference between the weight decrease for the
filled CNT article and the weight decrease for the starting CNTs is
treated as the amount of incorporation of the non-carbon material
as the filling. If the same analysis technique is applied to the
halogenated intermediate with no alcohol washing, the amount of
incorporation of the non-carbon material as the coating and the
filling can be determined.
[0113] The coating amount is determined by the TGA based technique
as follows. First, a halogenated precursor is incorporated to a CNT
article. Then, the halogen is removed from the halogenated
intermediate thereby prepared. This removal yields a CNT article
comprising a coating of a non-carbon material. Finally, this
article is heated in air at a predetermined temperature range to
remove the carbon. Difference between the weight decrease of this
article and the weight decrease of the same article after the
removal of the coating yields the amount of the coating.
III. Growth Article Method
[0114] The invention also involves a growth article and the growth
of the organized assembly of the carbon and the non-carbon material
on this article. In one embodiment of this method, the non-carbon
material fills the carbon (i.e. the carbon encapsulates the
non-carbon material).
[0115] The first step of preparing growth article is obtaining a
suitable substrate. The growth article may comprise any solid
substrate suitable for material growth at a high temperature, for
example at a temperature higher than 100.degree. C. or higher than
500.degree. C. Examples of such solid substrates include glasses,
ceramics, metals, and mixtures thereof that can withstand high
growth temperatures without melting, deformation, and/or
decomposition. In one embodiment of the invention, the substrate
may comprise silicon, germanium silicon oxide, quartz, metal oxides
(such as magnesium oxide, zirconium oxide, aluminum oxide), metal
borides (such as titanium diboride), or mixtures thereof.
[0116] The second step of preparing growth article involves
depositing a metal or metal-like compound layer on the substrate.
This layer is hereafter abbreviated as metal-layer. The metal-layer
may comprise metals such as scandium (Sc), yttrium (Y), titanium
(Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb),
tantalum (Ta), chromium (Cr), palladium (Pd), platinum (Pt), alloys
thereof and mixtures thereof. The metal-layer may also comprise
metal-like compounds, such as conductive metal nitrides, conductive
metal borides and mixtures thereof. Examples of conductive metal
nitrides are scandium nitride (ScN), titanium nitride (TiN),
zirconium nitride (ZrN), hafnium nitride (HfN), and niobium nitride
(NbN). Examples of conductive metal borides are titanium diboride
(TiB.sub.2), zirconium diboride (ZrB.sub.2), vanadium diboride,
niobium diboride (NbB.sub.2), and chromium diboride (CrB.sub.2).
Some of the metals such as Si, Zr, and Ti of the metal-layer may be
partially oxidized, for example titanium oxynitride or
TiN.sub.yO.sub.z In a preferred embodiment of this invention, the
metal-layer may comprise metals such as Sc, Ti, V, Cr, nitrides of
these metals (like TiN), borides of these metals, alloys thereof
and mixtures thereof. In another preferred embodiment of this
invention, the metal-layer may comprise TiN.
[0117] If the metal-layer comprises iron, iron-molybdenum, cobalt,
cobalt-molybdenum, nickel, yttrium-nickel, alloys thereof or
mixtures thereof; the amount of such metals in the metal-layer is
less than 10 weight % or even less than 1 weight %.
[0118] The metal-layer may be amorphous or crystalline, including a
distorted crystalline form, such as by having deficiencies in their
crystal structure. Nitrides and borides of the metal-layer may have
non-stoichiometric as well as stoichiometric forms.
[0119] The metal-layer may be deposited on the substrate by any
suitable technique, for example by sputtering, reactive sputtering,
electron beam evaporation, chemical vapor deposition, combinations
thereof and the like. The empty portion of the core of the
organized assembly depends on the thickness of the metal-layer.
Thus, the thickness of this layer may be varied to control the
proportion of the empty space.
[0120] The preparation of the growth article may optionally involve
depositing at least one catalyst layer on the metal-layer. The
catalyst-layer may comprise any material that can catalyze the
formation and growth of the organized assembly. The catalyst-layer
may comprise iron, iron-molybdenum, cobalt, cobalt-molybdenum,
nickel, yttrium-nickel, alloys thereof or mixtures thereof. The
catalyst-layer may be deposited on the metal-layer by any suitable
technique, for example by sputtering, reactive sputtering, electron
beam evaporation, chemical vapor deposition and deposition from
solutions. The catalyst-layer thickness may affect the shape and
dimensions of the organized assembly to be grown. For example, the
catalyst-layer thickness may particularly change the diameter of
the nanorods. Thus, varying the catalyst-layer thickness could
influence the shape and the size of the organized assembly.
[0121] The organized assembly may be grown on the growth article in
an environment containing a carbon source at a temperature above
ambient temperature and at a pressure below atmospheric pressure.
The growth may be carried out for a predetermined growth duration.
The carbon source may be any carbon source that is suitable to
deposit carbon according to the growth article method disclosed in
this invention. The carbon source may be a liquid carbon source
that has sufficient vapor pressure or any gaseous carbon source
with a proviso that the gaseous carbon source is not ethylene. In
U.S. Pat. No. 6,361,861, Gao et al. disclose that the use of
ethylene causes formation of carbon nanotubes filled more than 10%
with carbides of titanium, vanadium, tantalum and mixtures thereof.
In the instant invention, such carbides can not comprise more than
10 volume % of the core volume of the carbon nanotube. Thus, the
use of ethylene as a carbon source is thereby avoided to keep the
carbide formation below 10 volume %, 1 volume %, or even 0.1 volume
% of the core volume of the carbon nanotube.
[0122] In the preferred embodiment, the carbon source may be an
alcohol such as methanol, ethanol, propanol, isopropanol, butanol,
isobutanol or mixtures thereof. The environment may further
comprise an inert gas such as argon, helium, nitrogen, neon, xenon,
krypton or mixtures thereof. The environment may also further
comprise hydrogen.
[0123] The organized carbon and the non-carbon assembly may be
grown on the growth article at a temperature above 100.degree. C.,
above 500.degree. C. or above 700.degree. C. In one embodiment of
this invention, the assembly is grown at about 750.degree. C. In
another embodiment of this invention, the assembly is grown at
about 800.degree. C. The assembly may be grown on the growth
article at a pressure below 500 Torr or 20 Torr. In one embodiment
of this invention, the assembly is grown at about 17 Torr. The
growth duration may be longer than 1 minute or longer than 10
minutes. In one embodiment of this invention, the growth duration
is about 10 minutes. In another embodiment of this invention, the
growth duration is about 30 minutes.
[0124] In one embodiment of this invention, before the step of the
growth of the assembly, the growth article may be heat treated in
an environment containing hydrogen but not any carbon source. This
heat treatment may be carried out to form islands of the catalyst
on the metal-layer. The size of these catalyst islands may affect
the shape and the size of the assembly. For example, the size of
these catalyst islands may particularly control the shape and the
size of the nanorods.
[0125] The size of the catalyst islands may be varied by the heat
treatment conditions (such as heat treatment temperature, duration,
heating rate), heat treatment environment, heat treatment pressure
as well as the thickness of the catalyst-layer. The heat treatment
temperature may be higher than ambient temperature or higher than
700.degree. C. In one embodiment of this invention, the heat
treatment temperature is about 750.degree. C. In another embodiment
of this invention, the heat treatment temperature is about
800.degree. C. The growth article may be heated to the heat
treatment temperature within 0.2 hour or within 1 hour. In one
embodiment of this invention, the growth article may be heated to
the heat treatment temperature at about 0.2 hours. In another
embodiment of this invention, the growth article may be heated to
the heat treatment temperature at about 1 hour. The heat treatment
environment may further comprise at least one inert gas such as
argon, helium, nitrogen, neon, xenon, krypton and mixtures thereof.
The heat treatment may be carried out at a pressure below
atmospheric pressure, below 500 Torr, or below 10 Torr. In one
embodiment of this invention, the heat treatment pressure is about
300 Torr. In another embodiment of this invention, the heat
treatment pressure is about 7 Torr.
[0126] This invention is also directed to devices comprising the
organized carbon and non-carbon assemblies of the instant
invention. These compositions may be used as materials for
preparation of fuel cells, hydrogen storage devices, photovoltaic
cells, catalysts, thermoelectric devices, ultra-low resistance
conductors, and superconductors. For example, Pt filled SWCNTs may
be used as electro catalysts in preparation of fuel cells. The
articles comprising a carbon and Ti, TiN, Mg, B, TiB.sub.2,
MgB.sub.2, or a mixture thereof may be used as hydrogen storage
materials. Also, TiO.sub.2 filled SWCNTs may be used in preparation
of photovoltaic cells or as catalysts for photochemical reactions.
Since the carbon nanotubes have well defined inner (core)
diameters, non-carbon material filled carbon nanotubes may be used
as molecular sieves to limit the reactions to certain molecules
that can fit to the core and to thereby control the reaction to
obtain the desired products.
[0127] The organized assemblies comprising a carbon and a metal
(such as Mg, Sc, Ti, V, Cr), a metal nitride, a metal boride, or a
mixture (or alloy) thereof are particularly useful as intermediates
for preparation of hydrogen storage equipment.
[0128] Another potential application for the articles of this
invention is thermoelectric devices. In general, starting carbon
nanotubes are not considered for thermoelectric applications.
However, their electronic structure may be modified by
incorporation of a non-carbon material to have properties suitable
for thermoelectric applications. The non-carbon materials suitable
for this application include Ti, Zr, Hf, Cr, Re, Fe, Ru, Co, Rh,
Ir, Ni, Pd, Pt, B, or a mixture thereof. It is expected that the
thermoelectric efficiency of the articles comprising such
non-carbon materials may increase due to increasing electrical
conductivity provided by conversion of all carbon nanotubes to
metallic type, increasing free charge carriers caused by having a
different electronic structure, increasing thermopower caused by
the Kondo effect, and/or decreasing thermal conductivity caused by
having increased phonon scattering at the carbon and the non-carbon
material boundary. The presence of the Kondo effect is demonstrated
by Grigorian et al. in a publication entitled "Giant thermopower in
carbon nanotubes: A one-dimensional Kondo system", Phys. Rev. B,
1999, volume 60, pages R11309-R11312.
[0129] The compositions comprising carbon nanotubes and
transitional metals are theoretically predicted to be metallic,
even if the starting carbon nanotubes are semiconducting.
Furthermore, the electrical conductivity of the starting carbon
nanotubes may be enhanced by incorporation of non-carbon materials
to carbon nanotubes. These articles are particularly useful in
preparation of ultra-low resistance conductors. Examples of such
articles are those comprising Ti, TiN, Ni, B, or a mixture thereof.
The articles comprising boron and carbon nanotubes are particularly
expected to have very high electrical conductivity. Moreover, the
articles comprising a carbon and MgB.sub.2 may be used in
preparation of superconducting devices.
IV. Separation Method
[0130] This invention further provides a method for separating the
SWCNTs according to their chirality and/or diameter. This method
comprises halogenating SWCNTs, dispersing the halogenated-SWCNTs in
a medium, and centrifuging said dispersion to supernatant and
precipitate phases. This invention also provides enriched-SWCNTs
according to their chirality and/or diameter.
[0131] The enrichment typically results in the weight percentage of
one type of the SWCNT, characterized by its chirality and/or
diameter, being higher in the separated form of the SWCNT than in
the starting form of SWCNT. The starting form of the SWCNT is
hereafter abbreviated as starting-SWCNT.
[0132] The as-synthesized SWCNTs suitable for this invention may be
prepared by any synthesis method. Such methods may include, but are
not limited to, carbon arc, laser vaporization, chemical vapor
deposition (CVD), high pressure carbon monoxide process (HiPco),
cobalt-molybdenum catalyst process (CoMoCat) and the like. The
as-synthesized SWCNTs may be a mixture of as-synthesized SWCNTs
prepared by more than one synthesis method.
[0133] In one embodiment, the as-synthesized SWCNTs may be used as
the starting-SWCNTs for the separation method disclosed in this
invention. In another embodiment, amorphous carbons and/or
catalysts may be removed from the as-synthesized SWCNTs before the
application of the disclosed separation method. The amorphous
carbon and/or the catalyst removal may be complete or partial.
Thus, the starting-SWCNTs that are separated according to their
chirality and/or diameter by the method of this invention may
contain some level of amorphous carbon and/or catalyst. The
invention is not limited to any particular method of removing the
amorphous carbon and/or the catalyst from the starting-SWCNTs. As
an example, the method disclosed by Delzeit et al. in U.S. Pat. No.
6,972,056 may be used for this removal.
[0134] As a first process step of this invention, the
starting-SWCNTs are halogenated. Many methods exist to incorporate
at least one halogen to the structure of carbon nanotubes. This
incorporation may be in any form. For example, the halogen may be
incorporated on outer or inner surface of the SWCNTs. This
incorporation may be through chemical or physical bonding.
[0135] In one embodiment, the compounds that may be useful for
halogenation of the SWCNTs include iodine, bromine, chlorine,
fluorine, interhalogen compounds (such as IBr, ICl.sub.3,
BrF.sub.3), mixtures thereof and the like. Preferably, useful
halogenation compounds include iodine, bromine, interhalogen
compounds, mixtures thereof and the like.
[0136] The halogenation of SWCNTs may be accomplished by any
suitable methods. One useful halogenation method is disclosed by
Eklund et al. in U.S. Pat. No. 6,139,919. According to this method,
the starting-SWCNTs are halogenated by soaking them in molten
iodine.
[0137] Chen et al. disclose another useful halogenation method in a
publication Nano Letters, Volume 3, No. 9, pages 1245-1249 (2003);
together with the Supporting Information. According to this method,
carbon nanotubes are halogenated by dropwise addition of diluted
bromine or iodine solutions to a surfactant-stabilized aqueous
dispersion of carbon nanotubes.
[0138] Another useful halogenation-method is disclosed by Jacquemin
et al., Synthetic Metals, Volume 115, pages 283-287 (2000).
According to this method, carbon nanotubes are halogenated by
evaporating bromine or iodine at temperatures between 27.degree. C.
and 227.degree. C. under vacuum at a pressure below 10.sup.-6 Torr.
The carbon nanotubes are heated to the same temperature during the
halogenation.
[0139] The halogenated-SWCNTs may also be a mixture of
halogenated-SWCNTs prepared by more than one halogenation
method.
[0140] The halogenation may be carried out at a temperature in the
range of -100.degree. C. to 500.degree. C. In one embodiment, the
halogenation with bromine or iodine may be carried out at a
temperature in the range of 20.degree. C. to 500.degree. C. In
another embodiment the halogenation may be carried out at a
temperature in the range of 20.degree. C. to 200.degree. C. The
halogenation may also be carried out by soaking SWCNTs in at least
one halogen at a temperature equivalent to the melting point of the
said halogen or higher. For example, the melting point of iodine is
about 113.6.degree. C. and the halogenation may be carried out at
about 113.6.degree. C. or a temperature higher than this melting
point. The halogenation with chlorine or fluorine may be carried
out below the ambient temperature. Such halogenation may be carried
out for a duration in the range of 1 minute to 10 hours.
[0141] In another embodiment, after such halogenation, the
halogenated-SWCNTs may be heat-treated at a temperature in the
range of -100.degree. C. to 500.degree. C. This heat treatment may
also be carried out in the range of 20.degree. C. to 500.degree. C.
Yet in another embodiment, the heat treatment temperature may be in
the range of 50.degree. C. to 150.degree. C. This heat treatment
may be carried out for a duration in the range of 1 minute to 10
hours to remove the excess halogen.
[0142] As a second process step of this invention, the
halogenated-SWCNTs are dispersed in a medium, such as a liquid.
This dispersion may be achieved by any suitable dispersion
method.
[0143] One useful method is the high shear processing of the
halogenated-SWCNTs in a medium. Submicron processing
(micro-fluidization) equipments manufactured by MFIC Corporation,
Newton, Mass. may be used to provide the dispersions by high-shear
processing.
[0144] This dispersion may also be achieved by using at least one
surfactant. The surfactant may be any nonionic or ionic surfactant.
Examples of surfactants are alkyldiphenyloxide disulfonate salts
(Dowfax 8390 from Dow Chemical Company), C.sub.12/C.sub.14-fatty
acidethylenediamidethersulfate (from SASOL North America Inc.),
cetyltrimethylammonium bromide (CTAB), disodium
dodecylphenoxybenzene disulfonate (from Dow Chemical Company),
hexadecyltrimethylammonium p-toluenesulfonate (CTAT), n-hexadecyl
diphenyloxide disodium disulfonate (Dowfax 2A1 from Dow Chemical
Company), octyl phenol ethoxylate (Triton-X), poly(ethylene oxide)
(20) sorbitan mono-oleate (Tween 80, from ACROS Organics), sodium
cholate, sodium diisopropylnaphthalene sulfonate (Aerosol OS from
CYTEC Industries Inc.), sodium
2-(1-carboxylatoethoxy)-1-methyl-2-oxoethyl laurate (Ceralution F
from SASOL North America Inc.), sodium dodecyl sulfate (SDS),
sodium dodecylbenzene sulfonate (NaDDBS), Surfynol CT131/324 (from
Air Products and Chemical Inc.), N-alkylamines such as octadecyl
amine, their mixtures and the like. In one embodiment, the
surfactant may be sodium cholate, cetyltrimethylammonium bromide or
mixtures thereof.
[0145] This dispersion may also be accomplished by carboxy
functionalization of the SWCNTs. The method disclosed by
Papadimitrakopoulos in U.S. Patent Application No. 2004/0232073 in
paragraphs [0021] to [0027] may be used for the carboxy
functionalization and the contents of these paragraphs are
incorporated herein by reference. Briefly, this functionalization
may be achieved by immersing the SWCNTs in at least one acid such
as sulfuric acid (H.sub.2SO.sub.4), nitric acid (HNO.sub.3), their
mixtures, and the like for a duration and at a temperature
sufficient to produce the desired level of dispersion. For example,
the carboxy functionalization may be carried out at a temperature
in the range of 40.degree. C. to 100.degree. C., preferably in the
range of 40.degree. C. to 60.degree. C., for at least six hours.
The treatment with oxygen at elevated temperatures, for example at
about 400.degree. C. or treatment with hydrogen peroxide, for
example at a temperature in the range of 40.degree. C. to
100.degree. C. may also achieve the desired carboxy
functionalization level. In one embodiment, the carboxy
functionalization may be followed by surfactant amine
functionalization, as disclosed by the Papadimitrakopoulos
application.
[0146] Cellulose derivatives may also be used as dispersants for
the SWCNTs. An example of such use is described by Minami et al.,
Applied Physics Letters, Volume 88, article 093123 (2006) (an
online publication).
[0147] The examples of dispersion processes described above, i.e.
the high-shear, the surfactant, the carboxy functionalization and
the cellulose derivative processes may be used alone or in
combination. If they are applied in combination, these dispersion
processes may be used in any order. For example, the surfactant may
be added after the halogenation step and before the dispersion
step. Or, in another embodiment, the surfactant may also be added
after the dispersion by the high shear processing step and before
the centrifugation step.
[0148] The dispersion may be achieved in any medium that does not
permanently destroy semiconducting and metallic properties of the
SWCNTs. Such medium includes water, heavy water (deuterium oxide or
D.sub.2O), dimethylformamide (DMF), dimethylacetamide (DMAC),
formamide, methyl formamide, hexamethylene phoshphoramide,
dimethylsulfoxide (DMSO), liquid ammonia, diethylamine,
tetrahydrofuran (THF), mixtures thereof and the like. In one
embodiment the medium may be water, heavy water or mixtures
thereof.
[0149] The efficiency of separation may depend on dispersing SWCNT
bundles down to individual nanotubes. Practically, it may be
difficult to break down all SWCNT bundles to individual nanotubes
and thereby obtain a complete dispersion. Thus, enrichment rather
than a full separation of SWCNTs may be expected.
[0150] As a third step of this invention, the dispersed SWCNTs are
centrifuged. This centrifugation may be carried out at high speeds
that can achieve high centrifugal forces, for example higher than
10,000 g, or higher than 20,000 g. The duration of the
centrifugation may be longer than 1 hour, 10 hours, or 20 hours. At
the end of the centrifugation, the SWCNT dispersion is separated
into supernatant and precipitate phases. The supernatant phase may
be separated from the precipitate phase by a careful decantation of
the supernatant phase. One of these phases could be enriched with
respect to the chirality and/or the diameter of the SWCNTs. These
phases may be used as centrifuged to manufacture useful commercial
products.
[0151] In one embodiment, these two phases further may be processed
to remove the medium, the surfactant, and/or the halogen from the
supernatant or the precipitate phase. This fourth step is an
optional process step. The medium may be removed by simple
evaporation. The surfactant or the halogen may be removed by
heating at elevated temperatures, for example at temperatures
higher than 200.degree. C., higher than 300.degree. C. or higher
than 500.degree. C. In one embodiment, the medium, the surfactant,
and the halogen removal may be achieved in vacuum. The vacuum
pressure may be lower than 10 Torr, 1 Torr, or 0.01 Torr. The
SWCNTs dispersed in the supernatant phase also may be recovered by
changing the pH of the dispersion resulting in precipitation of
SWCNTs and by the further processing to remove the medium, the
surfactant, and/or the halogen, as described above.
[0152] In another embodiment, the sonication may be applied before,
after, or during any process step described above to aid successful
dispersion of the SWCNTs. This fifth step is an optional process
step. The sonication may be carried out for a duration of at least
1 minute or 15 minutes.
[0153] Any or a combination of the above five process steps may be
repeated at least once to further enrich the supernatant or the
precipitate phases for their s-SWCNT or m-SWCNT content.
[0154] The samples obtained from the supernatant and the
precipitate phases may be analyzed to determine their enrichment
level with respect to the chirality and/or the diameter of the
SWCNTs. Several analysis techniques, such as Raman spectroscopy,
ultraviolet-visible-near infrared spectroscopy (UV-VIS-NIR) and
electrical conductivity measurements may be applied to determine
the chirality enrichment. A photoluminescence (PL) technique could
be applied to determine the diameter enrichment. To assess any
enrichment, it is necessary to characterize SWCNT (n,m) population.
This task may be achieved by using a combination of Raman and
photoluminescence spectroscopies. Multiple excitation wavelengths
may be required due to strongly resonant nature of both SWCNT Raman
and photoluminescence spectra. See Rao et al., Science, volume 275,
pages 187-191 (1997); O'Connell et al., Science, volume 297, pages
593-596 (2002); and Fantini et al., Phys. Rev. Lett., volume 93,
article 147406 (2004). This approach has been used to quantify
(n,m) population of the starting CoMoCat SWCNTs and it was
disclosed that (6,5) and (7,5) nanotubes together may account for
about 60% of the starting-SWCNTs. See Jorio et al., Phys. Rev. B,
volume 72, article 075207, pages 1-5 (2005).
[0155] During the halogenation of SWCNTs, the halogen may
preferentially fill (i.e. intercalate) empty cores of the SWCNTs
depending on an atomic, ionic, or molecular size of the halogen
species and inner diameters of the SWCNTs. The SWCNTs that have
inner diameters larger than the size of the halogen species may be
filled with halogen, whereas those that have smaller diameters may
not be filled. As a result, SWCNTs filled with a halogen may carry
more positive charge per carbon atom as compared to those free of a
halogen. Thereby, those SWCNTs filled with and those free of the
halogen may interact differently with ionic surfactants and this
difference may be utilized to separate SWCNTs into distinct phases
according to their diameter.
[0156] For example, commercial CoMoCat material comprises
predominantly (6,5) and (7,5) SWCNTs with diameters of about 0.757
nm and about 0.829 nm, respectively. See Bachilo et al., J. Am.
Chem. Soc., volume 125, pages 11186-11187 (2003). According to Fan
et al., Phys. Rev. Lett., volume 84, pages 4621-4624 (2000), the
SWCNT wall thickness may be about 0.350 nm. Then the inner
diameters d.sub.in of (6,5) and (7,5) SWCNTs may be estimated to be
about 0.407 and about 0.479 nm, respectively. These values are
comparable to diameters of large ions such as iodine, which has a
diameter d.sub.I of about 0.432 nm. Since
d.sub.in(6,5)<d.sub.I<d.sub.in(7,5), iodine may be expected
to intercalate into interior of (7,5) SWCNTs, but not (6,5)
SWCNTs.
[0157] Then, a diameter-based separation of larger nanotubes
(d.sub.in>d.sub.I) with iodine-filled interior from smaller
(d.sub.in<d.sub.I) empty ones may be achieved. The outcome may
be related to about 32 picometer difference in SWCNT diameters.
From the experimental results disclosed below, the thickness of
pi-electronic cloud of SWCNT walls may be estimated to be in the
range of 0.350 to 0.367 nm. This mechanism may open new avenues for
manipulating SWCNTs with unprecedented picometer-scale
precision.
[0158] The interior space of SWCNTs may be filled with iodine. See
Fan et al. "Atomic Arrangement of Iodine Atoms inside Single-Walled
Carbon Nanotubes", Phys. Rev. Lett., 2000, Vol. 84, pages
4621-4624; Grigorian et al., Phys. Rev. Lett., volume 80, pages
5560-5563 (1998); Bendiab et al., Phys. Rev. B, volume 69, article
195415 (2004); and Chancolon, et al., J. Nanosci. Nanotech., volume
6, pages 82-86 (2006). Typically, SWCNT diameters may be relatively
large (d>1.2 nm and d.sub.in>0.85 nm) providing ample room to
accommodate the intercalated species inside these nanotubes. The
intercalated iodine may form negatively charged polyiodide chains,
(I.sub.3).sup.- and (I.sub.5).sup.-, residing both outside and
inside positively charged SWCNTs. See Fan et al., Grigorian et al.,
and Bendiab et al.
[0159] However, atomic size limitations may become prominent when
smaller diameter SWCNTs (such as CoMoCat material) are used for
intercalation. With respect to iodine, these nanotubes may fall
into one of two categories depending on their diameter: in larger
(d.sub.in>d.sub.I) tubes, iodine ions may occupy two sites, both
outside and inside nanotubes, whereas the smaller
(d.sub.in<d.sub.I) tubes may accept iodine only at the outside
site (as disclosed below in Example 25 and shown in FIG. 30a, b).
One difference between the two types may be the total amount of
transferred charge, i.e., the first type may have more iodine and,
consequently, may carry more positive charge per carbon atom as
compared to the second type. Thereby, these two types may be
expected to interact differently with ionic surfactants, and this
difference may be utilized to separate them into two distinct
phases.
[0160] Such diameter separation of SWCNTs based on the size of
molecule or atom and the inner diameters of SWCNTs is not
restricted to halogens. SWCNTs may be filled with other molecules
or atoms that have sizes larger or smaller than those of halogens
to preferentially fill the empty cores of the SWCNTs to achieve a
diameter separation for larger or smaller size SWCNTs. For example,
SWCNTs that are synthesized by HiPCo process have inner diameters
varying in the range of 0.8 nm to 1.4 nm. The HiPCo SWCNTs that
have inner diameters larger than about 1.0 nm may be filled with a
molecule or atom that has a size of about 1 nm. Then, the SWCNTs
that have inner diameters larger than about 1 nm may be separated
from those that have inner diameters smaller than about 1 nm.
[0161] For example, TiI.sub.4 has a size of about 1 nm. It fills
the inner cores of SWCNTs with inner diameters larger than 1 nm
when it is reacted with SWCNTs in the presence of I.sub.2. The
iodine may later be removed from the SWCNTs, forming SWCNTs filled
with titanium. Then, by having a suitable ionic surfactant,
titanium-filled SWCNTs may be separated from empty ones.
[0162] By having suitable combinations of atoms or molecules with
different sizes that may fill the empty cores of SWCNTs, further
separation of SWCNTs according to their inner diameter may be
achieved, thereby narrowing the diameter distribution range of the
enriched SWCNT phases.
[0163] The present invention is further directed to a novel
population of size or chirality enriched SWCNTs, for example, a
population containing substantially pure conducting SWCNTs, a
population containing substantially pure semiconducting SWCNTs, a
population containing substantially pure small diameter SWCNTs, or
a population containing substantially pure large diameter SWCNTs.
Preferably, a substantially pure population may contain a
population of more than 95% of SWCNTs larger than or smaller than a
predetermined size. More preferably, the population may include
more than 95% of SWCNTs with diameters larger than about 0.800 nm.
The novel population may also be substantially free of amorphous
carbon and catalyst.
[0164] There may be other secondary separation mechanisms that
affect the separation method of the instant invention. An example
of such secondary mechanism is as follows. A surfactant used for
the dispersion may have a shorter molecular length and thereby may
not fully envelop the larger diameter SWCNTs. Thus, the surfactant
due to its length may adequately be effective only for smaller
diameter SWCNTs. This was observed earlier for pristine CoMoCat
material and attributed to preferential suspension of smaller
diameter tubes by surfactant in the supernatant phase, while larger
diameter tubes were incorporated into the precipitate phase, as
disclosed by Jorio et al. in a publication entitled "Quantifying
carbon nanotube species with resonance Raman scattering", Phys.
Rev. B, volume 72, article 075207 (2005).
[0165] Because of such secondary mechanisms, after the
centrifugation, some fraction of the larger diameter SWCNTs may
undesirably go to the precipitate phase joining the smaller size
SWCNTs instead of remaining in the supernatant phase. If the
fraction of such larger diameter SWCNTs in the precipitate phase is
large enough to degrade quality of the enrichment of the
precipitate phase, another surfactant with a longer molecular
length may be chosen for the dispersion to improve the
enrichment.
[0166] Furthermore, the SWCNTs that have diameters too large for
some surfactants may constitute a small fraction of some
commercially available SWCNTs. For example, the fraction of the
SWCNTs larger than about 0.9 nm is about 10 weight % of the
starting SWCNTs purchased from SouthWest NanoTechnologies, Norman,
Okla., under a tradename SWeNT, with a catalog number Grade
S-P95-02-DRY, as shown in FIG. 29. Therefore, even if some portion
of the larger than 0.9 nm diameter fraction goes to the precipitate
phase, it may not significantly affect the overall enrichment level
of the precipitate phase with the smaller diameter SWCNTs.
[0167] Also, in an optional process step, the precipitate phase
that may comprise smaller diameter SWCNTs and very large size
SWCNTs caused by secondary mechanisms may be further separated into
at least two fractions. For example, if starting SWCNTs purchased
from SouthWest NanoTechnologies are used, the precipitate phase
thereby obtained may comprise one fraction with diameters smaller
than about 0.8 nm and the other with diameters larger than about
0.9 nm. This phase may be further separated into two fractions as
follows. First halogen is removed from the precipitate phase by
heating in vacuum to a predetermined temperature. Then the SWCNTs
thereby obtained are dispersed in water by using a suitable
surfactant, such as a non-ionic surfactant. It is expected that
after the centrifugation of this dispersion, the SWCNTs with
diameters smaller than about 0.8 nm are recovered in the
supernatant phase, while those with diameters larger than about 0.9
nm in the precipitate phase. As a result, after this optional
separation step, the starting SWCNTs are finally separated into
three fractions, where the first fraction comprises SWCNTs with
diameters smaller than about 0.8 nm, the second one with diameters
in the range of about 0.8 nm to about 0.9 nm, and the third one
with diameters larger than about 0.9 nm.
[0168] The invention is illustrated further by the following
examples that are not to be construed as limiting the invention in
scope to the specific procedures or products described in them.
EXAMPLES
Example 1
Ti Filled SWCNT Articles
[0169] In this example, the single-wall carbon nanotubes (SWCNTs)
were filled with titanium (Ti). SWCNTs were purchased from Carbon
Solutions Inc. (Riverside, Calif.) with a catalog number P2-SWNT.
They were manufactured by using the arc process. These SWCNTs are
designated as "starting SWCNT." A Raman spectrum of the starting
SWCNTs was obtained by using a Raman spectrometer, manufactured by
Horiba Jobin Yvon (Edison, N.J.) at a laser excitation wavelength
of about 633 nm. The Raman spectrum shown in FIG. 2 as a solid line
had two strong signals, one at about 176 cm.sup.-1, which was
caused by their radial breathing mode, and another at about 1600
cm.sup.-1, which was caused by their tangential mode and called as
G band (not shown). These were typical signals for SWCNTs.
[0170] The starting SWCNTs were processed as follows. The SWCNTs,
weighed about 23 mg, were placed in a 50 ml three-necked round
bottom Pyrex flask, which was equipped with a heating mantle, a
thermocouple, and an addition arm. The flask was connected to a
vacuum system through a liquid nitrogen trap.
[0171] The titanium iodide crystals (TiI.sub.4) used in this
Example were purchased from Aldrich with a catalog number 41,
359-3. The iodine crystals (I.sub.2) were purchased from Aldrich
with a catalog number 20, 777-2. TiI.sub.4 (about 1.0 gram) was
mixed with I.sub.2 (about 1.0 gram) in a nitrogen-filled glove box
and placed in the flask addition arm. The end of the addition arm
was covered to protect the mixture from atmospheric moisture. The
addition arm was then taken out of the glove box and connected to
the reaction flask. Thus, the SWCNTs and the TiI.sub.4/I.sub.2
mixture initially were kept in separate locations in the flask.
[0172] After the connection, the flask was immediately evacuated to
a pressure below 1 Torr. The contents of the flask were then heated
to about 150.degree. C. in vacuum for about 15 minutes to remove
volatile species from the SWCNTs. After this heating, the vacuum
valve was closed and the TiI.sub.4/I.sub.2 mixture was poured on
the SWCNTs by tipping the addition arm. The heating was continued
in order to melt the TiI.sub.4/I.sub.2 mixture and soak the SWCNTs
in the melt as follows. First, after the mixture was poured, the
flask was heated to about 200.degree. C. within about 6 minutes.
Then, it was further heated to about 275.degree. C. within about 12
minutes. Upon reaching about 275.degree. C., the vacuum valve was
opened to remove some un-reacted TiI.sub.4/I.sub.2 by evaporation
into the cold trap. The heating was continued in vacuum at about
275.degree. C. for about 1 hour. The contents of the flask were
then cooled to room temperature by cutting power to the heating
mantle. At this step, the nanorods comprised TiI.sub.4/I.sub.2
coated and filled SWCNTs.
[0173] This article was processed to remove TiI.sub.4 and I.sub.2
coating by an ethanol washing step as follows.
[0174] After the cooling, the flask was transferred to the glove
box filled with nitrogen, and the article was washed with ethanol
(Aldrich, catalog number 45, 984-4) to further remove un-reacted
TiI.sub.4/I.sub.2 mixture. The nanorods were first mixed with about
25 ml ethanol to prepare a suspension. This suspension was then
centrifuged at a centrifugal force of about 10,000 g for about 15
minutes to obtain a supernatant phase and a precipitate phase. The
supernatant phase was carefully removed by using a pipette and
discarded. This washing step was repeated once. The precipitate
phase was then transferred back to the glove box and it was dried
at about 25.degree. C. to remove residual ethanol. The precipitate
phase was characterized by 633 nm Raman spectroscopy. In the
ethanol washing step, the centrifugation step may be replaced with
a filtration step to recover the nanorods from the suspension. At
this step, the nanorods comprised TiI.sub.4/I.sub.2 filled
SWCNTs.
[0175] The TiI.sub.4/I.sub.2 filled SWCNTs were processed to remove
iodine by a heat treatment step as follows.
[0176] The precipitate phase was then placed in a quartz tube,
which was inserted in a tube furnace. The tube was sealed,
connected to a vacuum system and evacuated to about 30 mTorr
pressure. The furnace was then heated to about 500.degree. C.
within one hour. The heating was continued at about 500.degree. C.
for about 30 minutes.
[0177] After this heating period, a gas mixture consisting
essentially of about 3% hydrogen and about 97% argon was introduced
into the quartz tube and the pressure was raised to about 10 Torr.
The heating was further continued at a furnace temperature of about
500.degree. C. for about two hours at about 10 Torr in the flowing
gas mixture, after which the furnace was cooled to room
temperature. The Ti filled SWCNTs were thereby obtained.
[0178] It was observed by eye that the nanorods comprised black and
orange granules. Some of the granules were mechanically separated
according to their color by using a microscope. The orange and
black granules were separately characterized by using the Raman
spectrometer.
[0179] The Raman spectrum of the black granules, shown in FIG. 2
with hollow circles, had a strong signal at about 176 cm.sup.-1,
suggesting that the carbon nanotubes preserved their carbon
structure after the halogen removal step. A Raman spectrum of an
anatase TiO.sub.2 is also shown in FIG. 2 with a broken line. The
anatase TiO.sub.2 sample had a very strong signal at about 157
cm.sup.-1, with three ancillary peaks at about 410 cm.sup.-1, 532
cm.sup.-1, and 651 cm.sup.-1. These peaks were not present for the
black granules, indicating that the anatase titania was not present
in them in quantities detectable by Raman spectroscopy.
[0180] The rutile form of TiO.sub.2 had Raman signals at about 141
cm.sup.-1, about 235 cm.sup.-1, about 444 cm.sup.-1, and about 607
cm.sup.-1, when measured by using a laser at a wavelength of about
633 nm. The SiC had Raman signals at about 260 cm.sup.-1, about 420
cm.sup.-1, about 605 cm.sup.-1, and at about 607 cm.sup.-1, when
measured by using a laser at a wavelength of about 633 nm, as
disclosed by Lohse et al. in a publication entitled "Raman
spectroscopy as a tool to study TiC formation during controlled
ball milling", J. Applied Physics, 2005, volume 97, pages 114912-1
to 114912-7. As shown in FIG. 2, the Raman spectrum of the black
granules did not have peaks belonging to the rutile TiO.sub.2 nor
SiC, indicating that the black granules were essentially free of
these compounds.
[0181] The black granules were further analyzed by a transmission
electron microscope (TEM), manufactured by JEOL Inc. (Peabody,
Mass.) with a model number JEOL2010 HRTEM. Before this analysis,
the black granules were mixed with 5 milliliter isopropanol and
then sonicated for 30 minutes to have dispersion. This dispersion
was later deposited on a TEM grid for analysis. This analysis
indicated that the black granules comprised nanorods. The selected
area electron diffraction analysis done by using the TEM revealed
that nanorod shells comprised carbon and nanorod cores comprised
titanium. The nanorods were essentially free of TiO.sub.2,
TiH.sub.4, or iodine. The TEM micrographs revealed that there was
no titanium coating on SWCNTs. It was thereby accepted that, during
the solvent washing step, the halogenated precursor coating was
substantially removed from the SWCNTs, preventing formation of a
titanium coating.
[0182] Thus, the Raman and TEM analysis results indicated that the
black granules comprised titanium filled SWCNT nanorods.
[0183] The orange granules showed a strong titanium oxide
(TiO.sub.2) Raman signal, with no detectable carbon nanotube
signal. This result suggested that the orange granules were formed
due to residual un-reacted halogenated titanium precursor.
[0184] The black granules were mixed with about 15 ml of about 3
g/l solution of cetyltrimethylammonium bromide (CTAB) with D.sub.2O
and the resultant mixture was sonicated for about 20 minutes, using
a high-power horn sonicator. A solid product was recovered from the
mixture by first evaporation of volatile matter at about
100.degree. C. and then heating the dried granules at about
500.degree. C. in a vacuum pressure of about 30 mTorr for about 1
hour to remove CTAB. The Raman spectrum of these nanorods, shown in
FIG. 2 with hollow stars, had a strong signal at about 176
cm.sup.-1, suggesting that the SWCNTs preserved their carbon
structure after this washing and drying process. No titanium oxide
Raman signal was observed. This result confirmed that the Ti filled
SWCNT articles were thereby obtained.
Example 2
Ti Filled SWCNT Articles
[0185] This example was carried out in the same manner as described
in Example 1, except that about 82 mg of SWCNT was used instead of
about 23 mg of SWCNT, 1.8 grams of TiI.sub.4 and 1.8 grams of
I.sub.2 were used instead of 1 gram of TiI.sub.4 and 1 gram of
I.sub.2, and that the experiment was conducted with minimal
exposure to the external environment. There were only black
granules, but no orange granules after the halogen removal step,
indicating that an article consisting essentially of Ti filled
SWCNTs was successfully obtained.
Example 3
Ti Filled and Coated SWCNT Articles
[0186] In this example, the SWCNTs were both filled and coated with
titanium (Ti). This example was carried out in the same manner as
described in Example 2, except that the contents of the reaction
flask were heated at about 275.degree. C. for about 15 to 20
minutes prior to opening the vacuum valve and that the ethanol
washing step was not carried out after the preparation of the
article comprising TiI.sub.4/I.sub.2 coated and filled SWCNTs.
Thus, after the cooling of the flask, TiI.sub.4/I.sub.2 coated and
filled SWCNTs were directly placed in a quartz tube, which was
inserted in a tube furnace. The Ti filled and coated SWCNTs were
thereby obtained.
[0187] A micrograph of the starting SWCNT obtained by scanning
electron microscopy (SEM), is shown in FIG. 3. This precursor
comprised SWCNT bundles where each bundle was an aggregate of a few
dozen of SWCNTs. The particles shown in this micrograph are the
metal catalysts used for the SWCNT formation and growth. FIG. 4
shows an SEM micrograph of the Ti filled and coated SWCNT articles.
From the scale bars, it was estimated that the titanium formed a
coating on both individual SWCNTs and SWCNT bundles, with a
thickness varying in the range of 7 nm to 17 nm.
Example 4
Ti Coated SWCNT Articles
[0188] In this example, the SWCNTs were coated with titanium (Ti).
This example was carried out in the same manner as described in
Example 3, except that SWCNTs purchased from SouthWest
NanoTechnologies (Norman, Okla.), under a tradename SWeNT, with a
catalog number Grade S-P95-O.sub.2-DRY were used as starting
SWCNTs, instead of the SWCNTs purchased from Carbon Solutions Inc.
They were manufactured by using the CoMoCat process and purified to
remove the catalysts and graphitic carbon.
[0189] These SWCNTs comprise predominantly (6,5) and (7,5) SWCNTs
with diameters of about 0.757 nm and about 0.829 nm, respectively.
See Bachilo et al., ""Narrow (n,m)-Distribution of Single-Walled
Carbon Nanotubes Grown Using a Solid Supported Catalyst", J. Am.
Chem. Soc., 2003, Vol. 125, pages 11186-11187. According to Fan et
al., "Atomic Arrangement of Iodine Atoms inside Single-Walled
Carbon Nanotubes", Phys. Rev. Lett., 2000, Vol. 84, pages
4621-4624, the SWCNT wall thickness may be about 0.350 nm. Then the
inner diameters d.sub.in of (6,5) and (7,5) SWCNTs was estimated to
be about 0.407 nm and about 0.479 nm, respectively. Since TiI.sub.4
has a size of about 1 nm, this molecule may not fill, but coat the
starting SWCNTs. It is thereby accepted that the articles prepared
in this example comprise the Ti coated SWCNTs.
Example 5
TiO.sub.z Filled SWCNT Articles
[0190] In this example, TiO.sub.z filled SWCNTs were prepared,
where z varies in the range of 0 to 2. This example was carried out
in the same manner as described in Example 2, except that after the
iodine removal step, i.e. after the furnace was cooled to a room
temperature, the gas mixture consisting essentially of about 3%
hydrogen and about 97% argon was replaced with air and the article
was oxidized for a predetermined time at room temperature.
[0191] After a certain oxidation time interval, the nanorods were
analyzed to determine their TiO.sub.2 content. This analysis was
carried out by using the Raman spectrometer manufactured by Horiba
Jobin Yvon at a laser excitation wavelength of about 532 nm. The
results are shown in FIG. 5. The Raman spectrum of the Ti filled
SWCNTs, shown as dashed lines, had two peaks one at about 153
cm.sup.-1 and the other at about 168 cm.sup.-1. As oxidation
proceeded, one strong peak at about 145 cm.sup.-1 and three
ancillary peaks at about 395 cm.sup.-1, about 514 cm.sup.-1, and
about 637 cm.sup.-1 gradually appeared. These peaks are due to
anatase form of TiO.sub.2. The spectrum of the nanorods oxidized
for about 5 days is shown in FIG. 5 as a solid line.
[0192] The intensity of the strong Raman peak at about 145
cm.sup.-1 due to anatase TiO.sub.2 was monitored as a function of
air exposure time. The results were plotted as a function of the
oxidation time, as shown in FIG. 6. These results demonstrated that
Ti filling may be controllably oxidized to prepare articles
comprising TiO.sub.z filled SWCNTs, where z varies in the range of
0 to 2. The value of z may controllably be varied by varying the
oxidation time.
[0193] A TEM micrograph of a single TiO.sub.z filled SWCNT bundle
is shown in FIG. 7. The electron diffraction patterns of this
article, shown in FIG. 8, confirmed that this bundle comprised
TiO.sub.2. This result suggested that dark lines in the bundles,
observed in FIG. 7, are caused by TiO.sub.z filling. The TEM
micrographs suggested that there was no titanium coating. Then, it
was accepted that the solvent washing substantially removed the
halogenated precursor coating.
[0194] It is expected that the Ti may be completely oxidized to
TiO.sub.2 by prolonging the oxidation time.
Example 6
TiO.sub.z Filled SWCNT Articles
[0195] This example was carried out in the same manner as described
in Example 2, except that after the iodine removal step, i.e.,
after the furnace was cooled to a room temperature, the gas mixture
consisting essentially of about 3% hydrogen and about 97% argon was
replaced with air and the article was oxidized for about 30 minutes
after the furnace temperature reached to about 300.degree. C. A
Raman spectrum of this article is shown in FIG. 9. The two peaks,
one at about 153 cm.sup.-1 and the other at about 168 cm.sup.-1,
belonging to Ti filled SWCNTs, were masked in this spectrum with
the presence of an intense peak at about 145 cm.sup.-1. This
intense peak and three ancillary peaks at about 395 cm.sup.-, about
514 cm.sup.-1, and about 637 cm.sup.-1 indicated that the titanium
filling was converted into the TiO.sub.z filling after about 30
minutes of oxidation. This experiment demonstrated that the
oxidation time may be decreased by increasing the oxidation
temperature.
Example 7
TiO.sub.z Filled and Coated SWCNT Articles
[0196] In this example, TiO.sub.z filled and coated SWCNTs were
prepared. This example was carried out in the same manner as
described in Example 3, except that after the iodine removal step,
i.e., after the furnace was cooled to a room temperature, the gas
mixture consisting essentially of about 3% hydrogen and about 97%
argon was replaced with air and the article was oxidized for two
hours at about 500.degree. C. TiO.sub.z filled and coated SWCNTs
were thereby prepared.
[0197] The Raman spectrum of the TiO.sub.z filled and coated SWCNTs
acquired at a laser excitation wavelength of about 532 nm is shown
in FIG. 10. Characteristic peaks at about 147 cm.sup.-1, about 397
cm.sup.-1, about 514 cm.sup.-, and about 637 cm.sup.-1 are
consistent with anatase form of TiO.sub.2. This article also had a
Raman peak at about 1592 cm.sup.-1 corresponding to the G-band of
the SWCNTs (not shown in FIG. 10). The peak around 483 cm.sup.-1
was a non-repeatable spurious peak and thereby ignored.
Example 8
TiN.sub.y Filled and Coated SWCNT Articles
[0198] In this example, TiN.sub.y filled SWCNTs were prepared,
where y varies in the range of 0 to 1. This example was carried out
in the same manner as described in Example 3, except that after the
iodine removal step, i.e., after the furnace was cooled to room
temperature, the gas mixture consisting essentially of about 5%
hydrogen and about 95% argon was replaced with nitrogen and the
article was nitrogenated as follows. First, the material was heated
from room temperature to about 500.degree. C. within 20 minutes at
a pressure of less than 40 mTorr and held at about 500.degree. C.
for about 30 minutes under the same pressure. Then, a gas mixture
of about 5% hydrogen and about 95% argon was introduced at a gas
flow rate of about 100 cm.sup.3/min at a temperature of about
500.degree. C. and the pressure was raised to about 10 Torr. After
this step, the temperature was increased from about 500.degree. C.
to about 600.degree. C. within 30 minutes. At about 600.degree. C.,
the gas flow rate was reduced to about 50 cm.sup.3/min while the
pressure was maintained at about 10 Torr. Then nitrogen was
introduced and the pressure in the tube was adjusted to a pressure
of about 20 Torr. And this gas treatment was continued for about 2
hours at about 600.degree. C. The hydrogen-argon gas flow was then
stopped and only the nitrogen was allowed to flow for about 2 more
hours at about 600.degree. C. Finally, the furnace was cooled to
room temperature in nitrogen. TiN.sub.y filled and coated SWCNT
articles were thereby prepared.
[0199] The TiN.sub.y filled and coated SWCNT article was exposed to
air at room temperature for about 24 hours. The Raman spectrum was
recorded periodically during this time. The intensity of the Raman
peak at about 145 cm.sup.-1 was monitored as described in Example
5. FIG. 11 shows the corresponding oxidation profile. Negligible
change in the intensity of this peak indicated that this article
was resistant to the oxidation and stable in air. Because the
oxidation of titanium did not occur, it was accepted that the
titanium was nitrogenated to TiN.sub.y during this nitrogenation
treatment.
Example 9
TiO.sub.z Filled and Coated SWCNT Articles
[0200] In this example, TiO.sub.z filled and coated SWCNTs were
prepared. First, TiN.sub.y filled and coated SWCNTs were prepared
in the same manner as described in Example 8. Then, these nanorods
were heated to about 600.degree. C. under a pressure of less than 4
mTorr and kept at this temperature for about 2 hours. After this
heating step, the nanorods were cooled to room temperature and
oxidized in air in the same manner as described in Example 5.
TiO.sub.z filled and coated SWCNT articles were thereby
prepared.
[0201] The oxidation profile of the material was followed by Raman
spectroscopy measurement as described in Example 5. The results,
shown in FIG. 12, were similar to that observed with the TiO.sub.z
filled SWCNT articles described in Example 5. These results further
demonstrated Ti metal or TiN.sub.y may be controllably oxidized to
TiO.sub.z. FIG. 13 shows the Raman spectra of the TiO.sub.z filled
and coated SWCNT articles acquired at a laser excitation wavelength
of about 532 nm. Two spectra were taken from the same article but
at two different locations. One spectrum corresponded to an anatase
form of TiO.sub.2 (about 401 cm.sup.-1, about 518 cm.sup.-1 and
about 640 cm.sup.-1) and the other to a rutile form of TiO.sub.2
(about 254 cm.sup.-1, about 430 cm.sup.-1 and about 616 cm.sup.-1).
This result indicated that TiO.sub.2 filling and coating comprised
a mixture of anatase and rutile phases.
Example 10
TiH.sub.w Filled SWCNT Articles
[0202] In this example, TiH.sub.w filled SWCNTs were prepared,
where w varies in the range of 0 to 2. First, Ti filled SWCNTs were
prepared in the same manner as described in Example 2. Then, these
nanorods were placed in an air-free chamber and heated to about
650.degree. C. in vacuum for at least 2 hours to remove volatile
compounds. After the removal of volatile compounds, the temperature
was decreased to about 500.degree. C. and the chamber was
pressurized to about 500 Torr with hydrogen. The nanorods were
hydrogenated by keeping them at this temperature for at least one
hour. Finally, the hydrogenated nanorods were cooled to a room
temperature. TiH.sub.w filled SWCNT articles were thereby
prepared.
[0203] These nanorods were later heated to a temperature in the
range of 400.degree. C. to 650.degree. C. to release the hydrogen
from the nanorods. The hydrogen evolution was followed by using a
mass spectrometer. The evolution started at about 200.degree. C.
and became considerable at about 400.degree. C. The total amount of
hydrogen evolved from the nanorods indicated that at least 80% by
weight of titanium was hydrogenated, i.e., forming TiH.sub.0.800.
This result demonstrated that Ti filled SWCNTs may be used in
preparation of hydrogen storage devices and the hydrogen evolution
may be achieved at temperatures as low as 200.degree. C.
Examples 11 to 16
Metal Filled and Coated SWCNT Articles
[0204] In these examples, the starting SWCNTs were filled with
various metals in the same manner as described in Example 2, except
that iodides of Mn, Fe, Co, Ni, Pd, or Pt were used instead of
TiI.sub.4. The articles comprising Mn filled and coated SWCNTs, Fe
filled and coated SWCNTs, Co filled and coated SWCNTs, Ni filled
and coated SWCNTs, Pd filled and coated SWCNTs, or Pt filled and
coated SWCNTs were thereby prepared.
[0205] Micrographs, taken by Scanning Transmission Electron
Microscopy (STEM), of the Mn filled and coated SWCNTs are shown in
FIGS. 14 and 15, Ni filled and coated SWCNTs in FIGS. 16 and 17, Pd
filled and coated SWCNTs in FIG. 18, and Pt filled and coated
SWCNTs in FIG. 19. Dark lines observed in the SWCNT bundles were
accepted to be due to the non-carbon filling and dark spots on the
SWCNT bundles were the non-carbon coating.
[0206] These micrographs indicated that the ethanol washing did not
completely remove the halogenated precursors and as a result,
non-carbon coatings that had particulate forms were incorporated to
the SWCNTs.
[0207] This example demonstrated that the process disclosed in
Example 2 may be used to incorporate various metals to SWCNTs. It
further demonstrated that the amount of non-carbon compound may be
controlled.
Example 17
Preparation of the Si/TiN/Fe Growth Article
[0208] In this example, silicon wafers were first coated with the
metal-layer comprising TiN and then coated with the catalyst-layer
comprising iron by using a magnetron sputtering equipment
manufactured by Denton Vacuum (Moorestown, N.J.) with a model
number DV502. The silicon wafers were cleaned in three steps as
follows. In a first cleaning step, a 100 millimeter diameter
silicon wafer was cut into about 10 millimeters x about 100
millimeters strips. These strips were placed in a 4 to 5 weight
percent detergent/water solution and sonicated for about 5 minutes.
These strips then were washed with deionized water for at least one
minute and finally dried by blowing dry nitrogen gas. In a second
cleaning step, a solution was prepared to contain deionized water,
hydrogen peroxide, and ammonium hydroxide with a volume ratio of
5:1:1 respectively. The silicon strips cleaned in the first step
were placed in this solution and heated at about 80.degree. C. for
at least 20 minutes. These strips then were washed with deionized
water for at least one minute and finally dried by blowing dry
nitrogen gas. In a third cleaning step, a solution was prepared to
contain about 7 volume percent hydrofluoric (HF) acid/water
solution. The silicon strips cleaned in the second step were placed
in this solution and kept in it for 30 to 35 seconds. These strips
then were washed with deionized water for at least one minute and
finally dried by blowing dry nitrogen gas.
[0209] After the third cleaning step, the silicon strips were
placed on a rotatable table in a sputtering deposition chamber. The
silicon strips on the rotatable table were positioned in the range
of 3 cm to 7 cm beneath a circular planar DC magnetron with about 5
cm diameter target attached to its face. At least 99.9 weight
percent pure titanium (Ti) target was used for the sputtering. The
chamber was closed and evacuated. It then was pressurized to about
3.5 millitorr total pressure by providing about 0.5 millitorr
nitrogen and about 3.0 millitorr argon. The plasma was formed by a
DC magnetron energized at about 376 volts giving about 150 watts
applied power to the magnetron. The sample table was rotated with a
speed of about 15 rpm. After the formation of the plasma, the
shutter covering the rotatable table was opened and the TiN layer
was deposited on the silicon strips by reactive sputtering for
about 30 minutes. The thickness of the TiN layer was measured by a
profilometer manufactured by Veeco Instruments Incorporated
(Woodbury, N.Y.) with a model number DEKTAK3030FT. The thickness
was determined to be about 172.0 nanometers.
[0210] After the determination of the TiN layer thickness, the
silicon strips were placed on the rotatable table in the sputtering
chamber. An iron target was prepared as follows. A low carbon steel
stock was cut to form a disk with a diameter of about 50.8
millimeter and a thickness of about 1.6 millimeter. A hole was
machined at the center of this disk. Then, a graphite disk with a
diameter of about 25.4 millimeter and a thickness of about 1.6
millimeter was placed in this hole forming the iron target. The
titanium target was replaced with the iron target. The chamber was
closed and evacuated. It then was pressurized to about 7.0
millitorr total pressure by providing argon. The plasma was formed
by a DC magnetron energized at about 373 volts giving about 100
watts applied power to the magnetron. The sample table was rotated
with a speed of about 15 rpm. After the formation of the plasma,
the shutter was opened and the iron layer was deposited on the
silicon strips for about 95 seconds. The thickness was determined
to be about 8.1 nanometers as measured by the profilometer.
[0211] As a result, a layered growth article structure of Si/TiN/Fe
containing a silicon substrate, a TiN layer, and an iron (Fe) layer
was obtained.
Example 18
Preparation of the Glass/TiN Growth Article
[0212] In this example, a borosilicate glass slide (glass) was
coated with a TiN layer in the same manner as described in Example
17, except that the iron layer was not deposited on the TiN layer.
Thus, the article obtained in this example had a layered structure
of glass/TiN. This article was then analyzed by a Raman
spectrometer, manufactured by Horiba Jobin-Yvon, Edison, N.J.,
under a catalog name LabRamHR Raman Microscope at a laser
excitation wavelength of about 633 nm. The analysis results are
shown in FIGS. 20 and 21.
Example 19
Preparation of the Si/TiN Growth Article
[0213] In this example, a silicon wafer was coated with a TiN layer
in the same manner described in Example 17, except that the iron
layer was not deposited on the TiN layer. Thus, the article
obtained in this example had a layered structure of Si/TiN. This
article was then analyzed by the Raman spectrometer. The analysis
results are shown in FIGS. 20 and 21.
Example 20
TiN Filled Carbon Nanorods
[0214] In this example, the nanorods were grown on the Si/TiN/Fe
growth article prepared in Example 17 by using a chemical vapor
deposition (CVD) technique as follows. The Si/TiN/Fe article was
placed in a quartz tube. The inner pressure of the tube was reduced
to about 300 Torr. At this pressure, the inner atmosphere of the
tube was replaced with an atmosphere consisting essentially of
about 3% hydrogen and about 97% argon. The quartz tube was
electrically heated from an ambient temperature to about
800.degree. C. within about 0.2 hour. When the temperature reached
to about 800.degree. C., the inner pressure was reduced to about 7
Torr. At this step, the atmosphere consisted essentially of about
3% hydrogen and about 97% argon.
[0215] Prior to heating the quartz tube, a steel bottle was filled
with ethanol and placed in a water bath. This bottle then was
connected to the gas supply line of the quartz tube through a stop
valve and a needle valve. The water bath was heated to about
100.degree. C., while the stop valve was kept closed. When the
quartz tube reached to the temperature of about 800.degree. C. and
the inner pressure was reduced to about 7 Torr, the stop valve was
opened to provide ethanol vapor to the inner volume of the quartz
tube. By using the needle valve attached to the steel bottle, the
total inner pressure of the quartz tube was controlled at about 17
Torr, thereby keeping the partial pressure of the ethanol at about
10 Torr in the growth environment.
[0216] The ethanol vapor flowing over the Si/TiN/Fe article caused
the growth of the nanorods. The stop valve attached to the steel
valve was kept open for about 30 minutes. Finally, the valve was
closed, the furnace heating was shut off, and the Si/TiN/Fe article
was cooled to the ambient temperature in an atmosphere consisting
essentially of about 3% hydrogen and about 97% argon.
[0217] The Si/TiN/Fe article was analyzed by a scanning electron
microscope (SEM), manufactured by JEOL Inc. (Peabody, Mass.) with a
model number JSM6401F. As shown in FIG. 22, the nanorods were grown
on the Si/TiN/Fe article. These nanorods had straight elongated
structures. These nanorods were then analyzed by the Raman
spectrometer. The analysis results are shown in FIGS. 20 and
21.
[0218] As shown in FIG. 20, the Raman spectra of the nanorods had
two large peaks, one at about 1,325 cm.sup.-1 and the other at
about 1,600 cm.sup.-1, while those of the glass/TiN article
prepared in Example 18 and the Si/TiN article prepared in Example
19 did not have peaks at these wavelengths. These two peaks were
assigned to as D-band and G-band of graphitic carbon respectively,
as well known in the prior art. This result indicated that the
nanorods grown on the Si/TiN/Fe article comprise carbon.
[0219] As shown in FIG. 21, the Raman spectra of the glass/TiN
article had three peaks, one in the range of 210 cm.sup.-1 to 230
cm.sup.-1, the second in the range of 300 cm.sup.-1 to 310
cm.sup.-1, and the third at about 550 cm.sup.-1. The nanorods as
well as the Si/TiN article had similar three peaks, indicating that
the nanorods also comprised TiN. However, the peak appeared at
about 550 cm.sup.-1 for the glass/TiN article shifted to about 560
cm.sup.-1 for the Si/TiN article and to about 610 cm.sup.-1 for the
nanorods. There was a peak at about 440 cm.sup.-1 for the nanorods.
A small peak appeared for the Si/TiN article in the range of 420
cm.sup.-1 to 440 cm.sup.-1. In a publication entitled "Raman
Scattering, Superconductivity, and Phonon Density of States of
Stoichiometric and Non-stoichiometric TiN", Physical Review B,
1978, Vol. 17, No. 3, pages 1095-1101, Spengler et al. described
that a perfect TiN crystal does not have a Raman scattering, but
any deviation from this perfect structure, for example presence of
any vacancies in the lattice, may cause the Raman scattering. The
more the deviation, the more pronounced the Raman scattering will
be. Then, as shown in FIG. 21, the peaks appearing in the range of
550 cm.sup.-1 to 610 cm.sup.-1, 210 cm.sup.-1 to 230 cm.sup.-1, and
300 cm.sup.-1 to 310 cm.sup.-1 indicated that the TiN of the
present invention was not a perfect TiN crystal. The TiN of the
nanorods had a considerable deviation from that of the perfect TiN
crystal structure, as evidenced from the peak appeared at about 440
cm.sup.-1 for the nanorods.
[0220] The nanorods were further analyzed by a transmission
electron microscope (TEM), manufactured by JEOL Inc. (Peabody,
Mass.) with a model number JEOL2010 HRTEM. Before this analysis,
the nanorods were scraped off of the surface of the growth article
into about 5 milliliters of isopropanol and then sonicated for
about 30 minutes to obtain a dispersion. This dispersion was later
dispensed on a TEM grid for analysis. The following results were
obtained by this analysis. An example of a nanorod is shown in FIG.
23. The high magnification of this nanorod was shown in FIG. 24.
This nanorod had a different structure at its edge than that at its
core. The edge had a layered structure forming a shell around a
well ordered crystal structure at the nanorod core. The selected
area electron diffraction analysis done by using the TEM revealed
the crystal structure of the core. One example of the selected area
diffraction micrographs is shown in FIG. 25. According to this
analysis, the core had lattice parameters of a=4.88 .ANG., b=3.42
.ANG., and c=3.08 .ANG.. These TEM results indicated that the shell
with layered structure may comprise carbon and the core with well
ordered crystal structure may comprise TiN. Since standard TiN had
a cubic structure with a lattice parameter of a=b=c=4.236 .ANG.,
the TiN that formed the core may be distorted under the strain
caused by the carbon shell.
Example 21
Ti Filled SWCNT Articles
[0221] In this example, the single-wall carbon nanotubes (SWCNTs),
purchased from Carbon Solutions Inc. (Riverside, Calif.) with a
catalog number P2-SWNT were filled with titanium (Ti). The starting
SWCNTs were processed as follows. The SWCNTs, weighed about 500 mg,
were placed in a 50 ml three-necked round bottom Pyrex flask, which
was equipped with a heating mantle, a thermocouple, a magnetic
stirrer, a reflux condenser and two addition arms. The flask was
connected to a vacuum system through a liquid nitrogen trap.
[0222] The titanium iodide crystals (TiI.sub.4) used in this
example were purchased from Aldrich with a catalog number 458449.
The bromine (Br.sub.2) was purchased from Aldrich with a catalog
number 470864. TiI.sub.4 (about 2.2 gram) was placed in the flask's
first addition arm in a nitrogen-filled glove box. The end of the
addition arm was covered to protect the mixture from atmospheric
moisture. The addition arm was then taken out of the glove box,
connected to the reaction flask. Br.sub.2 (about 5 milliliter) was
then placed in the second addition arm. Stirring was begun and
about 4 milliliter Br.sub.2 quickly added to the flask containing
SWCNTs. The SWCNT and Br.sub.2 mixture was then heated to a
temperature in the range of 40.degree. C. to 59.degree. C. After
heating at this temperature for about 1 hour, the remaining about 1
milliliter of Br.sub.2 was added to the flask. After heating and
mixing at this temperature for about 1 more hour, TiI.sub.4 was
slowly added to the mixture within about 5 minutes. The
SWCNT/Br.sub.2/TiI.sub.4 mixture was heated and stirred at the same
temperature for about 2 more hours. After this halogenation
reaction, a distillation condenser was connected to the flask, the
mixture was heated to a temperature of about 200.degree. C. within
20 minutes, thereby removing Br.sub.2 from the mixture by
evaporation. The flask was then cooled to a temperature below
100.degree. C. and remaining Br.sub.2 was removed under vacuum for
about 5 minutes. Finally, the flask was cooled to room temperature,
transferred to a nitrogen-filled glove box, and the halogenated
SWCNT intermediate was removed from the flask.
[0223] The intermediate was washed as follows. First, the
intermediate was placed into a centrifuge tube, about 25 milliliter
absolute ethanol (Aldrich Cat. No. 459836) was added on the
intermediate, and the mixture was centrifuged at a centrifugal
force of about 10,000 g for about 15 minutes. After the
centrifugation, the supernatant was carefully separated from the
precipitate. This ethanol addition, the centrifugation and the
supernatant separation process were repeated for four more times.
Finally, the precipitate obtained after this process was dried
overnight in the glove box. It was assumed that this washing
completely removed the TiI.sub.4 coating, leaving behind only
TiI.sub.4 filled SWCNTs.
[0224] After this washing, the intermediate was placed in a quartz
cuvette, transferred to a graphite vacuum furnace and the furnace
was evacuated to a pressure below 50 mTorr. The furnace was then
heated at about 10 Torr pressure in a gas mixture of about 5%
hydrogen with Ar flowing at a rate of about 3.5 liters/minute as
follows. The furnace was first heated to about 300.degree. C. with
a rate of about 300.degree. C./hour and kept at this temperature
for about 0.5 hour, then heated to about 600.degree. C. with a rate
of about 300.degree. C./hour and kept at this temperature for about
3 hours, finally cooled to room temperature with a rate of about
300.degree. C./hour. The Ti filled SWCNT article was thereby
prepared.
[0225] Another article was prepared in the same manner described
above in this example, except that this article was not washed. The
Ti filled and coated SWCNT article was thereby prepared.
[0226] The amount of Ti filling and/or coating was determined by
the TGA based technique described as follows. The Ti filled SWCNT
article, the Ti filled and coated SWCNT article, and a starting
SWCNTs were heated in air between room temperature and 800.degree.
C. with a heating rate of about 2.degree. C./minute and the weight
decrease was determined by using a balance. The results are shown
in FIG. 26. After the heating, the starting SWCNTs left about 10.25
weight % residue, the Ti filled SWCNT article about 17.53 weight %
residue and the Ti filled and coated SWCNT article about 34.53
weight % residue. The weight difference between the Ti filled SWCNT
article and the starting SWCNTs, i.e. 17.53%-10.25%=7.28% was
treated as due to TiO.sub.2 filling or 4.36% Ti. The weight
difference between the Ti filled and coated SWCNT article and the
starting SWCNTs, i.e. 34.53%-10.25%=24.28% was treated as due to
TiO.sub.2 filling and coating or 14.53% Ti. The amounts of titanium
filling and titanium filling and coating were thereby
determined.
[0227] This TGA technique indicated that the starting SWCNTs were
filled in this example with titanium forming an article comprising
SWCNTs filled with about 4.36 weight % titanium. It also indicated
that an article comprising SWCNTs filled and coated with about
14.53 weight % titanium were prepared.
Example 22
Preparation of Halogenated-SWCNTs
[0228] The starting-SWCNTs used in this example were purchased from
SouthWest NanoTechnologies, Norman, Okla., under a tradename SWeNT,
with a catalog number Grade S-P95-O.sub.2-DRY. These SWCNTs were
manufactured by using CoMoCat process and purified to remove the
catalysts and graphitic carbon.
[0229] The starting-SWCNTs were dispersed in sodium
cholate-D.sub.2O solution by sonication and then were analyzed by
an ultraviolet-visible-near infrared (UV-VIS-NIR) spectrometer,
manufactured by Varian, Walnut Creek, Calif., under a catalog name
Cary 500 Scan. The spectrum of the starting-SWCNTs thereby obtained
was shown in FIG. 27. The starting-SWCNTs dispersed in sodium
cholate-D.sub.2O solution by sonication also were analyzed by a
Raman spectrometer, manufactured by Horiba Jobin-Yvon, Edison,
N.J., under a catalog name LabRamHR Raman Microscope at a laser
excitation wavelength of about 633 nm. The Raman spectrum of the
starting-SWCNTs was shown in FIG. 28.
[0230] The starting-SWCNTs, weighed in the range of 50 milligrams
to 100 milligrams, were placed at the bottom of a 150 ml round
bottom flask that had an addition arm. Iodine crystals, weighed in
the range of 2 grams to 4 grams, were placed in the flask's
addition arm. Thus, the starting-SWCNTs and the iodine initially
were kept in separate locations in the flask.
[0231] The flask was connected to a vacuum system through a liquid
nitrogen trap. The flask was first evacuated to a pressure below 1
Torr. Then, the contents of the flask were heated to a temperature
in the range of 120.degree. C. to 150.degree. C. in vacuum to
remove volatile species from the starting-SWCNTs. After this
heating, the vacuum was shut off and the iodine crystals were
poured on the starting-SWCNTs by tipping the addition arm. The
heating was continued to melt the iodine crystals and soak the
starting-SWCNTs in the molten iodine. The heating was further
continued for 2 to 15 minutes after the immersion of the
starting-SWCNTs in the molten iodine. The halogenated-SWCNTs with
iodine thereby were obtained.
[0232] After the halogenation step, the halogenated-SWCNTs were
heat treated at a temperature in the range of 50.degree. C. and
80.degree. C. for a duration in the range of 1 to 5 hours to
partially sublime iodine from the halogenated-SWCNTs. The heat
treated halogenated SWCNTs thereby were obtained.
Example 23
Dispersion of Halogenated-SWCNTs
[0233] First, about 5 milligrams of the heat treated
halogenated-SWCNTs obtained in Example 22 were mixed with about 25
ml solution containing about 20 grams per liter sodium cholate in
deuterium oxide (D.sub.2O). This mixture was sonicated for a
duration in the range of 20 to 30 minutes to prepare a
dispersion.
[0234] The halogenated-SWCNT dispersion was then micro-fluidized,
using an M110Y Microfluidizer manufactured by MFIC Corporation. The
250 micrometer and the 87 micrometer diamond interaction chambers
were used in series. Processing pressure was in the range of 23,000
psi to 26,500 psi. The dispersion was passed through the
interaction chambers 11 times. The dispersed-SWCNTs thereby were
obtained.
Example 24
Centrifugation to Obtain Supernatant and Precipitate Phases
[0235] The dispersion was divided up into about 50 ml aliquots and
placed in centrifuge tubes. The dispersion was then centrifuged at
a centrifugal force of about 20,000 g for about 7.5 hours to obtain
a supernatant phase and a precipitate phase. The supernatant phase
was separated from the precipitate phase by carefully decanting the
supernatant phase into another tube. The supernatant phase was
analyzed by the UV-VIS-NIR spectrometer and the Raman spectrometer.
The results were shown in FIGS. 27 and 28. The precipitate phase
was first annealed at about 500.degree. C. for about 2 hours in
vacuum of about 0.1 Torr to remove iodine and then dispersed in
sodium cholate-D.sub.2O solution by sonication and finally analyzed
by the UV-VIS-NIR spectrometer and the Raman spectrometer. The
results were shown in FIGS. 27 and 28.
[0236] The starting-SWCNTs and the supernatant phase also were
analyzed to determine their diameter distribution by
photoluminescence spectroscopy. This technique was disclosed in
detail by Bachilo et al. in a publication entitled
"Structure-Assigned Optical Spectra of Single-Walled Carbon
Nanotubes", Science, volume 298, pages 2361-2366 (2002). The
starting-SWCNTs were dispersed in sodium cholate-D.sub.2O solution
by sonication before the analysis. The supernatant phase obtained
after centrifugation was used in the photoluminescence analysis
with no further processing. The diameter distributions of the
starting-SWCNTs and the supernatant phase were shown in FIG.
29.
[0237] The results shown in FIGS. 27-29 obtained by the use of
three different analysis techniques indicated that the
starting-SWCNTs were separated according to their diameter. The
UV-VIS-NIR absorption at different wavelengths was caused by the
SWCNTs having different diameters. The spectrum of the
starting-SWCNTs had a composite peak at about 1,000 nm (FIG. 27).
This composite peak was caused by the optical transitions across
the band-gap of s-SWCNTs. Since the band-gap depended on diameter;
this peak comprised several components corresponding to s-SWCNTs of
different diameters. In the supernatant-SWCNT, this peak appeared
at about 960 nm, while in the precipitate-SWCNT at about 1,040 nm.
Thus, according to the UV-VIS-NIR spectra, the supernatant phase
and the precipitate phase comprised SWCNTs having different
diameters.
[0238] Similarly, peak positions of the Raman spectra were also
diameter dependent. See also Yu et al. in a publication entitled
"(n,m) Structural Assignments and Chirality Dependence in
Single-Wall Carbon Nanotube Raman Scattering" J. Phys. Chem. B,
volume 105, pages 6831-6837 (2001). The starting-SWCNTs had three
Raman peaks, at about 1,310 cm.sup.-1, about 1,549 cm.sup.-1, and
about 1,592 cm.sup.-1 (FIG. 28). The supernatant-SWCNTs also had
three peaks. Two of them, one at about 1,310 cm.sup.-1 and the
other at about 1,592 cm.sup.-1, did exist for that of the
starting-SWCNTs. However, the third peak for the supernatant-SWCNTs
appeared at a different location: about 1,556 cm.sup.-1. The
precipitate-SWCNTs also had three peaks. One of them, at about
1,549 cm.sup.-1, did exist for that of the starting-SWCNTs. Two of
the peaks for the precipitate-SWCNTs appeared at different
locations, one at about 1,300 cm.sup.-1 and the other at about
1,588 cm.sup.-1. Such Raman spectra shifts were indicative of the
enrichment of the supernatant-SWCNTs according to their
diameter.
[0239] The diameter distribution determined by the
photoluminescence technique further supported the finding that the
supernatant (or the precipitate) phase was enriched according to
the SWCNT diameter (FIG. 29). The starting-SWCNTs had diameters
varying in the range of 0.650 to 1.400 nm. The diameters smaller
than 0.78 nm contributed more than 40% of the starting-SWCNTs. In
contrast, more than 95% of the supernatant-SWCNTs had diameters
larger than 0.78 nm, indicating that the supernatant phase was
enriched with larger diameters.
Example 25
Atomic Size-Limited Intercalation into Single Wall Carbon
Nanotubes
[0240] In this example, a diameter-based separation of larger
nanotubes (d.sub.in>d.sub.I) with iodine-filled interior from
smaller (d.sub.in<d.sub.I) empty ones is disclosed. Here,
d.sub.in stands for inner diameter of individual carbon nanotubes
and d.sub.I for the ionic diameter of iodine. First, about 20
milligrams of starting-SWCNTs (purchased from SouthWest
NanoTechnologies) were degassed in the reaction chamber by heating
to about 140.degree. C. in vacuum (about 1 Torr) for about 20
minutes. Next, the vacuum pump was disconnected, and the reaction
was carried out by adding iodine powder (about 10 grams) and
heating the mixture at about 150.degree. C. for about 30 minutes.
Then, temperature was decreased down to about 100.degree. C. and
the vacuum pump was connected again (about 1 Torr) to remove
unreacted iodine by keeping the halogenated SWCNTs at this
temperature for about 2 hours. By weight uptake measurement, it was
estimated that final composition was approximately IC.sub.12,
consistent with the literature (Grigorian et al.). The halogenated
SWCNTs were thereby obtained.
[0241] The halogenated SWCNTs were first dispersed in water by
using cetyltrimethylammonium bromide (CTAB) as surfactant and then
further dispersed in water by high shear mixing using the M110Y
Microfluidizer (22 passes through the interaction chambers at about
26,500 psi pressure), and finally centrifuged at about 20,000 g
(Fisher 21000R) for about 4 hours. The resulting supernatant phase
was carefully separated from the precipitate phase by decanting.
Both phases were consequently heated in vacuum (about 10.sup.-2
Torr) at about 500.degree. C. for about 4 hours to remove
intercalated iodine and the surfactant.
[0242] Raman spectra were measured using a Dilor XY
triple-monochromator equipped with a N.sub.2-cooled charge coupled
device (CCD) detector. Measurements were performed in a
backscattering configuration with a microscope objective lens of
80.times.. As excitation sources, 6 laser lines from an ArKr laser
and 10 laser lines from a dye laser were used. The dye laser was
pumped by a 6 W Ar laser, using the DCM Special in the range of
654.5 nm (1.90 eV) to 612.1 nm (2.03 eV) and the Rhodamine 6G dyes
in the range of 605.0 nm (2.05 eV) to 567.9 nm (2.18 eV). The six
ArKr laser lines were: 647 nm (1.92 eV), 568 nm (2.18 eV), 514.5 nm
(2.41 eV), 488 nm (2.54 eV), 476.5 nm (2.60 eV), and 457.9 nm (2.71
eV). The 633 nm excitation wavelength spectra were measured using
Horiba Jobin Yvon Aramis Raman spectrometer. The Raman
spectrometers were calibrated for absolute intensity. For frequency
adjustments, the spectrometer was calibrated during the measurement
procedure, every time the excitation laser energy was changed. In
addition, for each laser excitation energy, Si substrate spectra
were acquired as reference. The data were analyzed using the Origin
software, OriginLab Corporation, Northampton, Mass. (for visual
comparative analysis and figure preparations) and the PeakFit
software, Systat Software Incorporated, San Jose, Calif. (for
quantitative analysis). In the PeakFit software, the non-Raman
related baselines were removed, and the spectra were fitted using a
sum of Lorentzians. From the fitting procedure the radial breathing
mode frequencies, linewidths, intensities and integrated areas were
extracted. The photoluminescence (PL) spectra were measured at 647
nm with a SPEX 750M spectrometer equipped with a 600 l/mm grating
blazed at about 1000 nm and a Princeton Instruments OMA V InGaAs
linear diode array detector. The excitation laser power was set to
about 10 mW and focused onto the sample using a 10.times. Mituoyo M
Plan Apo NIR objective lens with a working distance of about 30.5
nm, and emission was collected by the same objective lens in a
backscattering configuration. The spectral resolution of the system
was about 1 nm. The dispersions for PL and some Raman measurements
were prepared by sonicating SWCNT powders mixed with CTAB
surfactant in deionized water (about 200 milligrams SWCNT and about
3 grams of CTAB per liter of water). The outer diameters of SWCNT
were calculated as d=(a.sub.CC/.pi.) {3(n.sup.2+nm+m.sup.2)}, where
a.sub.CC=0.142 nm is the C-C distance, and .pi.=3.1415. The ionic
diameter values of halogens were adopted from Pauling publication
entitled "The Nature of the Chemical Bond" (Cornell Univ. Press,
Ithaca, N.Y., 1960), page 514. The (n,m) assignment procedure was
based on FIG. 31 where the optical transition energies (E.sub.ii,
i=1, 2, 3 . . . labeling the optical transition level) are plotted
as a function of radial breathing mode (RBM) frequency
(.omega..sub.RBM) that is proportional to the inverse tube diameter
(1/d) for every (n,m) tube. This plot is the basis for the (n,m)
assignment of the resonance Raman signals. The RBM signal for a
given (n,m) SWCNT is only observed when the laser excitation energy
approaches the electronic transition energy for this (n,m) SWCNT.
The RBM signal is stronger when the incoming light (the laser
excitation energy) matches exactly the resonance energy, or when
the scattered light (the laser excitation energy minus the RBM
energy for a Stokes process) matches the electronic transition
energy.
[0243] Specific excitation energies were selected to achieve
resonance with metallic and semiconducting tubes in the full range
of diameter distribution, so that diameter and/or chirality
separation enrichment can be determined. Specific excitation
energies were also selected to achieve full resonance with the
semiconducting (n,m) tubes that are preferentially produced by the
CoMoCat process, i.e. the (6,5) and (7,5) SWCNTs. Resonance profile
with a quasi-continuous set of laser excitation lines was performed
to assure full resonance has been obtained. Another reason of
specific excitation energy selection was to achieve full resonance
with the metallic (n,m) tubes that are preferentially produced by
the CoMoCat process, i.e. the (7,4) and (6,6) SWCNTs that have
diameters similar to the (6,5) and (7,5) SWCNTs, respectively.
[0244] An ArKr laser and a dye laser with tunable energy were used
for the population analysis. The transition energies are strongly
dependent on many-body effects (electron-electron and electron-hole
interactions). And the many-body effects are strongly dependent on
the environment dielectric constant. To have more accurate
information on the specific (n,m) SWCNT population, resonance Raman
maps were analyzed at the energies where the (6,5) and (7,5) SWCNTs
get into resonance. For the SWCNT powder measurements, the laser
power at the samples was kept at about 1 mW to avoid heating
effects. The use of higher power levels in solid samples was
observed to change the large/small diameter population ratio in the
sample, indicating comparatively larger heat induced damage of
smaller diameter (more reactive) tubes.
[0245] Highly accurate comparative analysis of population for
specific (n,m) SWCNTs can be performed based on the resonance
profiles obtained with the dye laser. Raman scattering efficiency
depends on (n,m) indices, so that direct comparison of RBM
intensities (I.sub.RBM) of different (n,m) nanotubes is not
correct. Variation in RBM intensity of particular (n,m) SWCNTs in
different samples is mostly related to SWCNT concentration in the
sample. For a comparative analysis, the relative intensities of
different (n,m) tubes should be compared within the same sample.
For example, in the starting CoMoCat material, it was found that
I.sub.RBM=37 for (7,5) and 36 for (6,5) tubes. In the precipitate
phase, I.sub.RBM=74 for (7,5) and 65 for (6,5) tubes, and in the
supernatant phase, I.sub.RBM=148 for (7,5) and 57 for (6,5) tubes.
Comparison of the relative intensities shows that the (7,5) to
(6,5) SWCNT ratio is almost the same for the starting material
(37/36=1.0) and the precipitate phase (74/65=1.1), but it is
significantly higher in the supernatant phase (148/57=2.6). These
data indicate an enrichment of the supernatant phase with (7,5)
tubes by a factor of 2.6 as compared to the precipitate phase.
[0246] The six ArKr laser excitation lines cover resonances for
both metallic and semiconducting SWCNTs in the entire diameter
range in the CoMoCat SWCNT material. For each of these excitation
lines, the RBM spectra were fit with a sum of Lorentzians assigned
to specific (n,m) tubes, and the integrated areas were then summed
up separately for metallic and semiconducting SWCNTs (Table 1).
These data include both powders and dispersions in water with CTAB
surfactant.
TABLE-US-00001 TABLE 1 Metal-to-semiconductor ratios Solution
Powder Sample % metal % semiconductor % metal % semiconductor
Starting-SWCNT 58 42 59 41 Precipitate Phase 48 52 62 38
Supernatant Phase 50 50 58 43
[0247] Note that these numbers reflect only relative Raman
intensities and not the actual metal-to-semiconductor molecular
ratio due to the dependence of the Raman signal intensity on (n,m).
The metallic-to-semiconducting character of the Raman response in
the fractions exhibited small variations, but no clear evidence for
enrichment of the fractions with either metallic or semiconducting
tubes was observed.
[0248] Raman spectra of both phases before the removal of
intercalated iodine (FIG. 30c) show a strong peak at about 148
cm.sup.-1, due to intercalated polyiodides, in addition to the
peaks in the range of 180 to 350 cm.sup.-1, due to SWCNT radial
breathing modes (RBM). For assignment of these peaks, see Fan et
al. and Rao et al. No Raman peaks attributable to unreacted,
molecular iodine were observed. The polyiodide-to-SWCNT ratio as
estimated from the relative intensities of respective Raman peaks
was about two times higher in the supernatant phase as compared to
the precipitate phase, indicating that the supernatant phase had
more intercalated iodine per SWCNT. These Raman spectra can not be
used for separation assessment because the resonance conditions
change when SWCNTs are charged. Moreover, these changes may be
different for the supernatant and precipitate phases as they carry
different amount of charge per carbon. The 148 cm.sup.-1 peak
disappeared entirely after vacuum heating at about 500.degree. C.
for about 2 hours, confirming complete removal of the intercalated
iodine.
[0249] RBM frequencies are inversely proportional to nanotube
diameters (Rao et al. and Jorio et al.), and can therefore be used
to determine diameter distribution in the separated phases after
removal of intercalated iodine. The results obtained earlier for
starting CoMoCat material (Jorio et al.) provided a guide on
selecting several specific excitation wavelengths to cover all
major SWCNT species. At each excitation wavelength, only a few
SWCNTs of all present in the sample are in resonance and contribute
to Raman intensity. Accordingly, the RBMs at each wavelength are
different as they represent different SWCNTs (FIG. 32a, b). To
obtain representative RBM intensity distribution over the entire
sample, these spectra were added up for each phase (FIG. 32c).
[0250] The RBM intensity distributions around the boundary of about
290 cm.sup.-1 or d of about 0.78 nm clearly indicate a
diameter-based separation in the phases (FIG. 32c). In particular,
the precipitate phase is enriched with diameters smaller than about
0.78 nm, and supernatant phase with diameters larger than about
0.78 nm SWCNTs. Note that the data in FIG. 32c represent both
metallic and semiconducting nanotubes, so both these populations
exhibit the same boundary between the phases.
[0251] In the range below about 250 cm.sup.-1, higher RBM
intensities were systematically observed in the precipitate phase
as compared to the supernatant phase (FIG. 32c), indicating that
SWCNTs with diameters larger than about 0.9 nm went preferentially
to the precipitate phase. This was observed earlier for pristine
CoMoCat material and attributed to preferential suspension of
smaller diameter tubes by surfactant, as disclosed by Jorio et al.
in a publication entitled "Quantifying carbon nanotube species with
resonance Raman scattering", Phys. Rev. B, volume 72, article
075207 (2005).
[0252] As a next step, resonance profiles were measured for small
diameter semiconducting SWCNTs. Using these data, relative
intensities of each (n,m) tubes may be determined under full
resonance condition. Comparison of these relative intensities
revealed that (6,5), (8,3), and (6,4) SWCNTs were enriched in
precipitate, and (7,5) SWCNTs in supernatant phases. For metallic
nanotubes, the boundary was found to be between (7,4) and (6,6)
SWCNTs enriched in the precipitate and supernatant phases,
respectively (FIG. 32d).
[0253] These results place the semiconducting boundary between
(8,3) and (7,5) SWCNTs with diameters of about 0.782 and about
0.829 nm, respectively, and about 0.047 nm (or 47 pm) difference in
diameters. For metallic tubes, the boundary was found to be between
(7,4) and (6,6) SWCNTs enriched in precipitate and supernatant
phases, respectively (FIG. 32d). Taking into account the diameters
of the metallic SWCNTs, i.e., d of about 0.814 and about 0.755 nm
for (6,6) and (7,4) SWCNTs, respectively, the boundary can be
further narrowed down to about 32 pm difference between d(8,3) and
d(6,6) SWCNTs.
[0254] Additional information on SWCNT separation was obtained from
PL spectra where the relative intensities of (8,3), (6,4), and
(9,1) SWCNTs can be compared to those of (7,5) and (7,6) SWCNTs
(FIG. 33). The Raman and PL cross sections for individual SWCNTs
are different, and PL offers independent conformation of Raman
data. Enrichment of the precipitate phase with (8,3), (6,4), and
(9,1) SWCNTs, and the supernatant phase with (7,5) and (7,6) SWCNTs
was observed, consistent with the Raman results.
[0255] Summarizing, the combined Raman and PL data provided
evidence that SWCNTs were separated into two phases according to
their diameters: i.e., SWCNTs with diameters equal to and smaller
than about 0.782 nm went to the precipitate phase, and SWCNTs with
diameters equal to or larger than about 0.814 nm went to the
supernatant phase. Then, it was expected that (1) SWCNTs that were
large enough to accommodate iodine in their interior (supernatant
phase) were separated from the smaller ones with empty interiors
(precipitate phase), and (2) the separation boundary was determined
by the relation between SWCNT inner diameter and intercalated
iodide ion diameter, about 0.432 nm.
Example 26
Atomic Size-Limited Intercalation into Single Wall Carbon
Nanotubes
[0256] In this example, a diameter-based separation of larger
nanotubes (d.sub.in>d.sub.Br) with bromine-filled interior from
smaller (d.sub.in<d.sub.Br) empty ones is disclosed. Here,
d.sub.Br is ionic diameter of bromine. This example was carried out
in the same manner disclosed in Example 25 except that the
halogenation was carried out using bromine at about 30.degree. C.,
followed by vacuum heating at about 30.degree. C. for about 2
hours.
[0257] With ionic diameter of about 0.390 nm, bromine ion is
expected to fit inside (6,5) SWCNTs in contrast to iodine ion,
thereby moving the separation boundary towards the smaller SWCNT
diameters. The main difference in the RBM modes is the decrease of
the (6,4) intensity in the precipitate phase as compared to the
supernatant phases (FIG. 34) indicating enrichment of the
precipitate phase with (6,4) nanotubes. The (9,1) nanotubes that
have the same diameter as (6,5), as well as (6,5), (8,3), and (7,5)
tubes, are all enriched in the supernatant phase. The separation
boundary in this case lies between the (6,4) and (6,5) tubes, i.e.,
d=0.692 and 0.757 nm. This result suggests that the proposed
mechanism based on the size of the halogen and the inner diameter
of the SWCNTs may be used to separate SWCNTs according to their
diameter.
[0258] It is expected that interiors of larger (d>1.22 nm)
nanotubes may accommodate several iodide chains side by side giving
rise to new boundaries between single and multiple intercalated
ions per cross section. An interesting implication may be the
creation of sets of discretely charged nanotube species (e.g., as
in FIG. 30a, b) with potential use as logic elements for molecular
electronics.
[0259] In summary, a new method was demonstrated for diameter-based
separation where SWCNTs with filled interior were separated from
the empty ones. The separation boundary may be tuned with
picometer-scale discrimination by selecting geometric size of
intercalant species.
[0260] Although a number of embodiments of the invention have been
described above, those of ordinary skill in the art will appreciate
that various modifications can be made without departing from the
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
* * * * *