U.S. patent application number 12/868285 was filed with the patent office on 2011-03-03 for method for preparing carbon nanotubes, carbon nanotube films, and electronic devices.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Lian Gao, Hisashi Kajiura, Yongming Li, Jing Sun, Jiaping Wang, Yan Wang, Jing Zhang.
Application Number | 20110052479 12/868285 |
Document ID | / |
Family ID | 43625241 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110052479 |
Kind Code |
A1 |
Kajiura; Hisashi ; et
al. |
March 3, 2011 |
METHOD FOR PREPARING CARBON NANOTUBES, CARBON NANOTUBE FILMS, AND
ELECTRONIC DEVICES
Abstract
A method for preparing carbon nanotubes for synthesizing carbon
nanotubes, fabricating carbon nanotube films and electronic devices
is provided. The method for preparing carbon nanotubes can repair
the defects in side walls of carbon nanotubes under stable
condition easily and prepare carbon nanotubes of excellent
properties. The method utilizes uric acid solution or ammonia water
to treat carbon nanotubes after acidifying the carbon nanotubes by
refluxing with nitric acid. The treatment temperature is, for
example, 25.degree. C..about.90.degree. C., and treatment time is
at least two 2 days. Preferably, the carbon nanotubes are treated
with thionyl chloride solution before being treated with uric acid
solution or ammonia water.
Inventors: |
Kajiura; Hisashi; (Shanghai,
CN) ; Li; Yongming; (Shanghai, CN) ; Wang;
Jiaping; (Shanghai, CN) ; Sun; Jing;
(Shanghai, CN) ; Gao; Lian; (Shanghai, CN)
; Wang; Yan; (Shanghai, CN) ; Zhang; Jing;
(Shanghai, CN) |
Assignee: |
SONY CORPORATION
Tokyo
JP
|
Family ID: |
43625241 |
Appl. No.: |
12/868285 |
Filed: |
August 25, 2010 |
Current U.S.
Class: |
423/447.1 ;
977/742; 977/750 |
Current CPC
Class: |
C01B 32/15 20170801;
B82Y 30/00 20130101; B82Y 40/00 20130101 |
Class at
Publication: |
423/447.1 ;
977/742; 977/750 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2009 |
CN |
CN 200910171619.8 |
Claims
1. A method for preparing carbon nanotubes, comprising: treating
acid-refined carbon nanotubes with a solution of a compound having
an amino group or ammonia water.
2. The method for preparing carbon nanotubes according to claim 1,
further comprising: treating the carbon nanotubes with a solution
of a compound which reacts with a carboxyl group to produce --COCl,
before treating the acid-refined carbon nanotubes with the solution
of a compound having an amino group or ammonia water.
3. The method for preparing carbon nanotubes according to claim 1,
wherein, the compound having an amino group is a compound of which
the amino group reacts with a carboxyl group to substitute the
hydroxyl group in the carboxyl group.
4. The method for preparing carbon nanotubes according to claim 2,
wherein, the compound which reacts with a carboxyl group to produce
--COCl is at least one selected from the group consisting of
SOCl.sub.2, (COCl).sub.2, PCl.sub.3, POCl.sub.3, and PCl.sub.5.
5. The method for preparing carbon nanotubes according to claim 1,
wherein, the treatment with the solution of a compound having an
amino group is performed at a temperature equal to or higher than
25.degree. C. and lower than the boiling point of the solvent of
the solution of a compound having an amino group.
6. The method for preparing carbon nanotubes according to claim 1,
wherein, the treatment with the solution of a compound having an
amino group is performed at a temperature not lower than 25.degree.
C. and not higher than 90.degree. C.
7. The method for preparing carbon nanotubes according to claim 1,
wherein, the carbon nanotubes are single-walled carbon
nanotubes.
8. A method for preparing carbon nanotube films, comprising:
preparing a carbon nanotube film with carbon nanotubes obtained by
treating acid-refined carbon nanotubes with a solution of a
compound having an amino group or ammonia water.
9. The method for preparing carbon nanotube films according to
claim 8, comprising: preparing the carbon nanotubes by treating the
acid-refined carbon nanotubes with the solution of a compound
having an amino group or ammonia water.
10. The method for preparing carbon nanotube films according to
claim 9, further comprising: treating the carbon nanotubes with a
solution of a compound which reacts with a carboxyl group to
produce --COCl, before treating the acid-refined carbon nanotubes
with the solution of a compound having an amino group or ammonia
water.
11. A method for fabricating electronic devices, comprising:
preparing carbon nanotubes or films thereof by treating
acid-refined carbon nanotubes with a solution of a compound having
an amino group or ammonia water; and fabricating the electronic
devices with the carbon nanotube or films thereof.
12. The method for fabricating electronic devices according to
claim 11, comprising: preparing the carbon nanotubes by treating
the acid-refined carbon nanotubes with the solution of a compound
having an amino group or ammonia water.
13. The method for fabricating electronic devices according to
claim 11, comprising: preparing the carbon nanotube films with the
carbon nanotubes which are prepared by treating the acid-refined
carbon nanotubes with the solution of a compound having an amino
group or ammonia water.
14. The method for fabricating electronic devices according to
claim 11, comprising: preparing the carbon nanotubes by treating
the acid-refined carbon nanotubes with the solution of a compound
having an amino group or ammonia water; and preparing the carbon
nanotube films with the carbon nanotubes.
15. The method for fabricating electronic devices according to
claim 14, further comprising: treating the acid-refined carbon
nanotubes with a solution of a compound which reacts with a
carboxyl group to produce --COCl, before treating the acid-refined
carbon nanotubes with the solution of a compound having an amino
group or ammonia water.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority to Chinese Priority
Patent Application CN 200910171619.8 filed in the Japan Patent
Office on Aug. 31, 2009, the entire content of which is hereby
incorporated by reference.
BACKGROUND
[0002] The present application relates to a method for preparing
carbon nanotubes and carbon nanotube films, as well as a method for
fabricating electronic devices, and is applicable to, for example,
the fabrication of various electronic devices utilizing carbon
nanotubes or carbon nanotube films.
[0003] Carbon nanotubes, especially, single-walled carbon nanotubes
(SWNTs) have been arduously investigated and developed due to its
excellent properties in electricity, machinery, magnetism, and
configuration. To date, a plurality of methods, such as laser
ablation process (non-patent document 1), arc discharge process
(non-patent document 2), chemical vapor deposition (CVD) process
(non-patent document 3) and the like have been employed as the
method for preparing single-walled carbon nanotubes. Inevitably,
there are considerable amount of carbon or metal impurities left in
the resulting single-walled carbon nanotubes prepared by these
processes.
[0004] In prior art, the resulting single-wall carbon nanotubes are
refined with an acid to remove the impurities, by chemical
oxidation which involves liquid oxidization (acid treatment,
reflux, etc.) and electrochemical oxidization (non-patent document
4). During the refining process, the structure of SWNTs is often
damaged due to the chemical defects resulted from the refining
(non-patent document 5). Moreover, when the SWNTs are applied to
nanotechnology, in order to disperse or dissolve the SWNTs,
post-treatments such as ultrasonic treatment or drastic chemical
reaction are often necessary (non-patent document 3, 6, 7). During
the post-treatment, additional damages happen to the SWNTs.
[0005] Liu (non-patent document 8), Wang (non-patent document 9),
etc., have reported the method for repairing the structure of SWNTs
having defects by treating the SWNTs in ammonia (NH.sub.3)
atmosphere at 1000.degree. C. After this treatment process, it can
be found that the ratio I.sub.D/I.sub.G of the intensity of band D
(I.sub.D) to that of band G (I.sub.G), which is detected by Raman
spectroscopy, is reduced to not more than 0.01, which shows that
the defects in the side walls of SWNTs have been repaired.
PRIOR ART DOCUMENTS
Non-Patent Documents
[0006] Non-patent document 1: A. Thess, R. Lee, P. Nikolaev, H. J.
Dai, P. Petit, J. Robert, C. H. Xu, Y. H. Lee, S. G. Kim, A. G.
Rinzler, D. T. Colbert, G. E. Scuseria, D. Tomanek, J. E. Fischer
and R. E. Smalley, Science, 1996, 273, 483-487
[0007] Non-patent document 2: S. Iijima, Nature, 1991, 354,
56-58
[0008] Non-patent document 3: J. L. Bahr, J. P. Yang, D. V.
Kosykin, M. J. Bronikowski, R. E. Smalley and J. M. Tour, Journal
of the American Chemical Society, 2001, 123, 6536-6542
[0009] Non-patent document 4: P. X. Hou, C. Liu and H. M. Cheng,
Carbon, 2008, 46, 2003-2025
[0010] Non-patent document 5: J. Zhang, H. L. Zou, Q. Qing, Y. L.
Yang, Q. W. Li, Z. F. Liu, X. Y. Guo anf Z. L. Du, Journal of
Physical Chemistry B, 2003, 107, 3712-3718
[0011] Non-patent document 6: D. Tasis, N. Tagmatarchis, A. Bianco
and M. Prato, Chemical Reviews, 2006, 106, 1105-1136
[0012] Non-patent document 7: D. Tasis, N. Tagmatarchis, V.
Georgakilas and M. Prato, Chemistry, 2003, 9, 4000-4008
[0013] Non-patent document 8: Y. Q. Liu, L. Gao, J. Sun, S. Zheng,
L. Q. Jiang, Y. Wang, H. Kajiura, Y. M. Li and K. Noda, Carbon,
2007, 45, 1972-1978
[0014] Non-patent document 9: Y. Wang, L. Gao, J. Sun, Y. Q. Liu,
S. Zheng, H. Kajiura, Y. M. Li and K. Noda, Chemical Physics
Letters, 2006, 432, 205-208
[0015] Non-patent document 10: J. Chen, M. A. Hamon, H. Hu, Y. S.
Chen, A. M. Rao, P. C. Eklund and R. C. Haddon, Science, 1998, 282,
95-98
[0016] Non-patent document 11: C. Montalbetti and V. Falque,
Tetrahedron, 2005,61, 10827-10852
[0017] Non-patent document 12: J. Jang, J. Bae and S. H. Yoon,
Journal of Materials Chemistry, 2003, 13, 676-681
[0018] Non-patent document 13: P. S. Wharlton and D. H. Bohlen,
Journal of Organic Chemistry, 1961, 26, 3615-&
SUMMARY
[0019] However, the above existing method, which repairs the
defects of the SWNTs by treating in ammonia (NH.sub.3) atmosphere
at 1000.degree. C., is limited in application because a high
temperature treatment at 1000.degree. C. is necessary. Further, as
the ammonia is decomposed into nitrogen gas and hydrogen gas, there
is a risk of explosion due to the hydrogen gas.
[0020] Therefore, the present application is directed to provide a
method for preparing carbon nanotubes, which can easily repair the
defects in the side walls of the acid-refined SWNTs in a stable
condition, and can prepare carbon nanotubes of excellent
properties.
[0021] The present application is further directed in an embodiment
to provide a method for preparing carbon nanotube films, which can
be used to prepare carbon nanotube films of excellent properties,
with carbon nanotubes whose defects in the side walls of the
acid-refined carbon nanotubes are repaired, and who has excellent
properties.
[0022] The present application is still further directed in an
embodiment to provide a method for fabricating electronic devices,
which can fabricate electronic devices of high performance by
utilizing the carbon nanotubes prepared by the above-mentioned
preparation method, or by utilizing the carbon nanotube films
formed of the carbon nanotubes.
[0023] To these ends, the present application provides in an
embodiment a method for preparing carbon nanotubes, which comprises
a step of treating acid-refined carbon nanotubes with a solution of
a compound containing an amino group or ammonia water.
[0024] The present application also provides in an embodiment a
method for preparing carbon nanotube films which prepares the
carbon nanotube films from the carbon nanotubes obtained by
treating acid-refined carbon nanotubes with a solution of compound
containing an amino group or ammonia water.
[0025] Typically, the method for preparing carbon nanotube films
comprises a step of treating acid-refined carbon nanotubes with a
solution of compound containing an amino group or ammonia
water.
[0026] Moreover, the present application provides in an embodiment
a method for fabricating an electronic device, in which carbon
nanotubes or carbon nanotubes films formed of the same are used,
and wherein the carbon nanotubes are prepared by treating the
acid-refined carbon nanotubes with a solution of a compound
containing an amino group or ammonia water.
[0027] The method for preparing the electronic devices comprises,
for example, a step of treating the acid-refined carbon nanotubes
with a solution of a compound having an amino group or ammonia
water; or comprises a step of preparing carbon nanotube films from
the carbon nanotubes which are treated with a solution of a
compound containing an amino group or ammonia water; or comprises
both of the two steps.
[0028] In the present application, the acid-refined carbon
nanotubes refer to those carbon nanotubes which are treated by
refluxing with acid, such as nitric acid, and the carbon nanotubes
are featured with carboxyl group (--COOH) bonded to the side walls
of the acid-refined carbon nanotubes. Basically, the carbon
nanotubes can be synthesized by any suitable method. Specifically,
various methods such as laser ablation process, arc discharge
process, and chemical vapor deposition (CVD), etc., can be used.
Compounds containing an amino group which reacts with a carboxyl
group (--COOH) to substitute the hydroxyl group (--OH) of the
carboxyl group are typically used as the compounds containing an
amino group (--NH.sub.2). Thus the amino group of the compound
containing an amino group needs to be easily dissociated in the
solution of the compound containing the amino group. As described
above, --COOH is boned to the side walls of the acid-refined carbon
nanotubes. Thus, if the carbon nanotubes are treated with the
solution of the compound containing an amino group, then the amino
group reacts with the carboxyl group bonded to the carbon nanotubes
and substitutes the hydroxyl group of the carboxyl group, and the
--COOH is transformed into --CONH.sub.2. During this process, the
defects of the side walls of carbon nanotubes can be repaired. The
compound containing an amino group is preferably, for example but
not limited to, carbamide (NH.sub.2CONH.sub.2). Ammonia water is
the aqueous solution of gaseous ammonia (NH.sub.3), and has the
same function as the solution of the compound containing an amino
group.
[0029] Preferably, the present application further includes a step
of treating carbon nanotubes with a solution of a compound, which
reacts with carboxyl to form --COCl, before treating the carbon
nanotubes with the solution of a compound containing an amino group
in an embodiment. If the carbon nanotubes bonded with carboxyl are
treated with the solution, the carboxyl bonded to the carbon
nanotubes transforms into --COCl. If the resulting carbon nanotubes
boned with --COCl are treated with the solution of a compound
containing an amino group, then --COCl boned to the carbon
nanotubes transforms into --CONH.sub.2. The compound which reacts
with carboxyl group to produce --COCl is preferably at least one
selected from the group consisting of thionyl chloride
(SOCl.sub.2), oxalyl chloride ((COCl).sub.2), phosphorus
trichloride (PCl.sub.3), phosphorus oxychloride (POCl.sub.3), and
phosphorus pentachloride (PCl.sub.5).
[0030] Generally, the treatment with the solution of a compound
containing an amino group is performed at a temperature equal to or
higher than 25.degree. C. and lower than the boiling point of the
solution of a compound containing an amino group, and typically not
less than 25.degree. C. and not higher than 90.degree. C., but not
limited thereto. Generally, the treatment with the solution of a
compound which reacts with a carboxyl group to form --COCl is
performed at a temperature equal to or higher than 25.degree. C.
and lower than the boiling point of the solution of a compound
containing an amino group. Typically, the temperature for treating
with ammonia water is preferably set at a comparative low
temperature for inhibiting ammonia from evaporating.
[0031] Typically, the carbon nanotubes are single-walled carbon
nanotubes, but also can be multilayer carbon nanotubes. And
typically, the carbon nanotube films are single-walled carbon
nanotube films, but also can be multilayer carbon nanotube films.
The diameter and length of the carbon nanotubes forming the carbon
nanotube films are not specifically limited.
[0032] The carbon nanotubes or carbon nanotube films can be applied
to various electronic devices. As such electronic devices, field
emission components, field effect transistors (FETs) (including
thin film transistors (TFTs)), single electron transistors,
molecular sensors, solar cells, photovoltaic components, light
emitting components, memories, etc. Also, carbon nanotube films can
be used, for example, as thin film electrodes or transparent
electrodes.
[0033] According to the present application as described above in
an embodiment, the defects in the side walls of the carbon
nanotubes during acid refining can be repaired by treating with a
solution of a compound containing an amino group or ammonia water.
Typically, the treatment is performed at a temperature low to
100.degree. C. or below, and a stable condition without a strong
acid, thus the carbon nanotubes are prevented from being severed or
the like. Furthermore, the treatment can be easily and efficiently
performed. Especially, by treating the carbon nanotubes with a
solution containing the compound which reacts with carboxyl group
on the side walls of the carbon nanotubes to form --COCl before
treating with the solution of a compound containing an amino group,
the reaction utilizing the compound containing an amino group is
made happen more easily, and lowering of the treatment temperature
and shortening of the treatment time for treating with the solution
of a compound containing an amino group can be realized.
[0034] According to the present application in an embodiment, the
defects in the side walls of the acid-refined carbon nanotubes can
be repaired easily under a stable condition, and it is easy to
fabricate nanotubes with excellent properties and without defects.
Moreover, the carbon nanotube films with excellent properties can
be easily fabricated with those carbon nanotubes. Further, these
carbon nanotubes or carbon nanotube films can be used to fabricate
high performance electronic devices.
[0035] Additional features and advantages are described herein, and
will be apparent from the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0036] FIG. 1 is a photograph in substitution for a picture showing
a TEM image of the SWNTs which have been acid-refined by refluxing
in nitric acid according to Example 1 corresponding to the first
embodiment;
[0037] FIG. 2 is a photograph in substitution for a picture showing
a TEM image of the SWNTs which have been treated directly with
NH.sub.2CONH.sub.2 solution according to Example 1 corresponding to
the first embodiment;
[0038] FIG. 3 is a photograph in substitution for a picture showing
a TEM image of the SWNTs which have been treated with
NH.sub.2CONH.sub.2 solution after treated with SOCl.sub.2 solution
according to Example 2 corresponding to the second embodiment;
[0039] FIG. 4 is a schematic figure showing the results obtained by
measuring the Raman spectra of the acid-refined SWNTs, the SWNTs
treated directly with NH.sub.2CONH.sub.2 solution, and the SWNTs
treated with NH.sub.2CONH.sub.2 solution after treated with
SOCl.sub.2 solution according to Examples 1 and 2 respectively
corresponding to the first and second embodiments;
[0040] FIG. 5 is a schematic figure showing the TG-DTA curves of
the acid-refined SWNTs according to Example 2 of the second
embodiment;
[0041] FIG. 6 is a schematic figure showing the TG-DTA curves of
the SWNTs treated with NH.sub.2CONH.sub.2 solution after treated
with SOCl.sub.2 solution according to Example 2 of the second
embodiment;
[0042] FIG. 7 is a schematic figure showing the results obtained by
measuring the FT-IR spectra of the acid-refined SWNTs, the SWNTs
treated directly with NH.sub.2CONH.sub.2 solution, and the SWNTs
treated with NH.sub.2CONH.sub.2 solution after treated with
SOCl.sub.2 solution according to Examples 1 and 2 respectively
corresponding to the first and second embodiments;
[0043] FIG. 8 is a schematic figure showing the results obtained by
measuring the dispersion concentration of the acid-refined SWNTs,
the SWNTs treated directly with NH.sub.2CONH.sub.2 solution, and
the SWNTs treated with NH.sub.2CONH.sub.2 solution after treated
with SOCl.sub.2 solution according to Examples 1 and 2 respectively
corresponding to the first and second embodiments; and
[0044] FIG. 9 is a schematic figure showing the defect repair
mechanism of the SWNTs of NH.sub.2CONH.sub.2 solution treatment
according to Example 1 corresponding to the embodiment.
DETAILED DESCRIPTION
[0045] The present application will be disclosed below with
reference to the figures according to an embodiment as follows:
[0046] 1. the first embodiment (carbon nanotubes and the method for
preparing the same)
[0047] 2. the second embodiment (carbon nanotubes and the method
for preparing the same)
[0048] 3. the third embodiment (carbon nanotube films and the
method for preparing the same)
1. The First Embodiment
Carbon Nanotubes and the Method for Preparing the Same
[0049] In the first embodiment, carbon nanotubes are synthesized
with known methods of prior art. In particular, the carbon
nanotubes can be synthesized with, for example but not limited to,
laser ablation process, arc discharge process, CVD process,
etc.
[0050] Then the carbon nanotubes synthesized as described above are
refined with acid by known methods. In particular, the acid
refining is performed, for example, by refluxing the carbon
nanotubes with nitric acid (HNO.sub.3). During the acid refining,
the circlewise arranged carbon atoms in the side walls of carbon
nanotubes are oxidized into carboxyl groups (--COOH), which lead to
defects.
[0051] Next, the carbon nanotubes refined with acid as described
above are treated with the solution of a compound containing an
amino group (--NH.sub.2) or ammonia water. In particular, the
solution or ammonia water is mixed with the carbon nanotubes. With
such a treatment, the carboxyl group bonded to the side walls of
the carbon nanotubes reacts with the amino group of the compound in
the solution or the ammonia in the ammonia water, and the hydroxyl
group (--OH) of the carboxyl group is substituted by the amino
group, thus the carboxyl group transforming into --CONH.sub.2,
which will be removed from the carbon nanotubes eventually. Thus,
the defects in the side walls of the carbon nanotubes are repaired
by the above series of processes. The solvent of said solution can
be selected from known solvents according to requirements. In
particular, for example but not limited to, water can be employed
as the solvent. The treatment temperature is selected according to
requirements, typically a temperature equal to or higher than the
room temperature (for example, 25.degree. C.) and lower than the
boiling point of the solvent of the solution, and preferably a
temperature at least 10.degree. C..about.20.degree. C. lower than
the boiling point. In particular, the treatment temperature ranges,
for example, from 25.degree. C. to 90.degree. C., The treatment
time is selected according to requirements, usually in connection
with the treatment temperature and between 1 day and 10 days.
[0052] Next, the carbon nanotubes treated with the solution of a
compound containing an amino group or ammonia water are washed with
water, separated by centrifugal separation or filtration
separation, and then dried.
[0053] Thus the desired carbon nanotubes are obtained.
[0054] According to the first embodiment, the defects occurred in
the side walls of the acid-refined carbon nanotubes can be easily
and almost completely repaired under a stable condition, and the
carbon nanotubes of excellent properties and without defects can be
obtained. The carbon nanotubes can be used to, for example, various
electronic devices, thereby electronic devices of high performance
can be realized.
2. The Second Embodiment
Carbon Nanotubes and the Method for Preparing the Same
[0055] In the second example, firstly, the carbon nanotubes are
synthesized and refined with acid in the same way as that of the
first embodiment.
[0056] Next, the carbon nanotubes refined with acid as described
above are treated with the solution containing a compound which
reacts with the carboxyl group to produce --COCl. In particular,
for example, the solution is mixed with the carbon nanotubes. With
the treatment, the carboxyl group (--COOH) bonded to the side walls
of the carbon nanotubes reacts with the compound contained in the
solution, and the hydroxyl group (--OH) contained in the carboxyl
group is substituted by Cl, producing --COCl. The solvent of the
solution can be selected from various known solvents according to
requirements. The treatment temperature is selected according to
requirements, typically a temperature equal to or higher than the
room temperature (for example, 25.degree. C.) and lower than the
boiling point of the solvent of the solution, and preferably is a
temperature at least 10.degree. C..about.20.degree. C. lower than
the boiling point. In particular, the treatment temperature ranges,
for example, from 25.degree. C. to 90.degree. C., and generally, a
commonly low temperature is enough. The treatment time is selected
according to requirements, in connection with the treatment
temperature, and generally between 1 day and 10 days.
[0057] Next, after being treated with the solution containing a
compound which reacts with a carboxyl group to produce --COCl, the
carbon nanotubes are treated, in the same manner as in the first
embodiment, with the solution of a compound containing an amino
group or ammonia water. With the treatment, the --COCl bonded to
the side walls of the carbon nanotubes reacts with the compound
contained in the solution or the ammonia of the ammonia water, and
the Cl in the --COCl is substituted by the amino group, which
produces --CONH.sub.2. Thus, before being treated with the solution
of a compound containing an amino group or ammonia water, the
carbon nanotubes are treated with the solution containing the
compound which reacts with the carboxyl group to produce --COCl,
facilitating the reaction of the solution of a compound containing
an amino group or the ammonia water (non-patent document 10,
11).
[0058] Next, in the same manner as in the first embodiment, the
carbon nanotubes treated with the solution of a compound containing
an amino group or ammonia water are washed with water, separated by
centrifugation or filtration, and then dried.
[0059] Thus, the desired carbon nanotubes are obtained.
[0060] According the second embodiment, apart from the advantages
of the first embodiment, other advantages are also obtained. For
instance, before being treated with the solution of a compound
containing an amino group or ammonia water, the carbon nanotubes
are treated with the solution containing a compound which reacts
with carboxyl group to produce --COCl, so as to realize the
lowering of the temperature or the shortening of the time of the
treatment of the solution of a compound containing an amino group
or ammonia water.
Example 1
[0061] Example 1 is an example corresponding to the first
embodiment.
[0062] The SWNTs synthesized by chemical vapor deposition (CVD)
process are used as the SWNTs. The SWNTs used in the present
invention are available from Chengdu Institute of Organic Chemistry
of Chinese Academy of Sciences (CIOC), which are synthesized by CVD
process at 1000.degree. C. using methane (CH.sub.4) as the raw
materials and CoMo as the catalyst.
[0063] The SWNTs are refined with acid by refluxing with 2.6 M
nitric acid (HNO.sub.3) at 140.degree. C. for 48 hours to remove
impurities.
[0064] Next, 1 g NH.sub.2CONH.sub.2 is dissolved in 2 ml water to
prepare NH.sub.2CONH.sub.2 solution.
[0065] Then, 20 mg of SWNTs refined with acid as described above is
mixed with the NH.sub.2CONH.sub.2 solution, then is treated with
ultrasound in water bath for 1 min. Then the SWNTs are treated in
the NH.sub.2CONH.sub.2 solution at 25.degree. C..about.90.degree.
C. for not less than 2 days.
[0066] Next, thus obtained admixture is filtered, rinsed and
dried.
[0067] Thus the desired SWNTs is obtained.
[0068] The recovery ratio of the SWNTs is not less than 95%.
Example 2
[0069] Example 2 is an example corresponding to the first
embodiment.
[0070] The SWNTs synthesized by chemical vapor deposition (CVD)
process are used as the SWNTs. The SWNTs used in the present
invention are available from Chengdu Institute of Organic Chemistry
of Chinese Academy of Sciences(CIOC), which are synthesized by CVD
process at 1000.degree. C. using methane (CH.sub.4) as the raw
materials and CoMo as the catalyst.
[0071] The SWNTs are refined with acid by refluxing with 2.6 M
nitric acid (HNO.sub.3) at 140.degree. C. for 48 hours to remove
impurities.
[0072] Next, 20 ml SOCl.sub.2 and 1 ml DMF (N,N-dimethylformamide)
are mixed to prepare the SOCl.sub.2 solution.
[0073] Next, 100 mg of SWNTs refined with acid as described above
is mixed with SOCl.sub.2 solution and stirred at 25.degree. C. for
24 hours, so that the SWNTs react with the SOCl.sub.2 solution (See
non-patent Document 10)
[0074] Next, the obtained admixture is rinsed with THF
(tetrahydrofuran), then dried in vacuum at room temperature, thus
the SWNTs whose side walls are bonded with --COCl are obtained.
[0075] Next, NH.sub.2CONH.sub.2 solution is obtained by dissolving
1 g NH.sub.2CONH.sub.2 in 2 ml water.
[0076] Next, 20 mg of SWNTs whose side walls are bonded with --COCl
obtained as described above are mixed with the NH.sub.2CONH.sub.2
solution, and is treated with ultrasound in water bath for 1 min.
Then the SWNTs are treated in the NH.sub.2CONH.sub.2 solution at
25.degree. C..about.90.degree. C. for not less than 2 days.
[0077] Next, thus obtained admixture is washed with water,
separated by centrifugation or filtration, and then dried.
[0078] Thus the desired SWNTs is obtained.
[0079] The recovery ratio of the SWNTs is not less than 95%.
[0080] In order to evaluate the effects of SOCl.sub.2
solution-based pre-treatment, two SWNTs samples are compared, with
one obtained by treating with SOCl.sub.2 solution and then dipping
in the solution of NH.sub.2CONH.sub.2 contained in a transparent
vessel at 60.degree. C., the other obtained by directly dipping and
treating in the solution of NH.sub.2CONH.sub.2 contained in a
transparent vessel at 60.degree. C. As a result, the volume of the
first sample is three times as that of the second one. This is
because the NH.sub.2CONH.sub.2 treatment after the SOCl.sub.2
treatment results in sufficient stripping of the SWNT bundles, thus
reducing the diameter of the bundles (non-patent document 10). The
stripping of the SWNT bundle is considered to enable to increase
the whole surface area of the SWNTs in NH.sub.2CONH.sub.2 solution,
as a result, the contact area between the acid-refined SWNTs and
NH.sub.2CONH.sub.2 solution is increased, and the reaction is sped
up. Moreover, in the case where the acid-refined SWNTs are treated
with SOCl.sub.2 solution, and then dipped and treated in
NH.sub.2CONH.sub.2 solution of 60.degree. C. in a transparent
vessel, the SWNTs exist in the whole volume of NH.sub.2CONH.sub.2
solution. Obviously, the contact area between the acid-refined
SWNTs and NH.sub.2CONH.sub.2 solution increases and thus the
reaction becomes faster as the temperature of NH.sub.2CONH.sub.2
solution treatment, which is performed after treating the SWNTs
with SOCl.sub.2 solution, becomes higher. Moreover, in the case
where the acid-refined SWNTs are directly dipped and treated in
NH.sub.2CONH.sub.2 solution, the color of the supernatant in the
transparent vessel becomes dark yellow, on the contrary, in the
circumstance where the acid-refined SWNTs are treated with
SOCl.sub.2 solution, and then dipped and treated in
NH.sub.2CONH.sub.2 solution at 60.degree. C., the color of the
supernatant in the transparent vessel does not change. This is
because the pretreatment of SOCl.sub.2 solution makes the reaction
of SWNTs with NH.sub.2CONH.sub.2 solution accelerated, which
prevents the generation of the intermediate products.
[0081] Next, the evaluation results of the SWNTs prepared by
Examples 1 and 2 will be described.
[0082] Now, the SWNTs just being refined with acid by refluxing
with 2.6 M HNO.sub.3 at 140.degree. C. for 48 hours are referred to
as "newly acid-refined SWNTs". And the SWNTs of Example 1, which
are treated with NH.sub.2CONH.sub.2 solution after being refined
with acid by refluxing with 2.6 M HNO.sub.3 at 140.degree. C. for
48 hours, are referred to as "Sample 1". the SWNTs of Example 2,
which are treated with SOCl.sub.2 solution, and then
NH.sub.2CONH.sub.2 solution after being refined with acid by
refluxing with 2.6 M HNO.sub.3 at 140.degree. C. for 48 hours, are
referred as "Sample 2".
[0083] FIGS. 1-3 show the TEM images of newly acid-refined SWNTs,
sample 1 and sample 2 respectively. According to FIGS. 1-3,
impurities (amorphous carbon, multi-layer carbon nanotubes,
nanometer graphite particles, metal impurities, etc.) can be found
in the newly acid-refined SWNTs, and on the contrary, almost no
impurity can be found in sample 1 and sample 2. Thus it can be
considered that the impurities of newly acid-refined SWNTs are
substantially removed by the treatment of Examples 1 and 2.
Moreover, it can be found there is almost no change in the length
of SWNTs of samples 1 and 2, compared with the newly acid-refined
SWNTs. This means that the SWNTs of Examples 1 and 2 have not be
severed because the treatment of Examples 1 and 2 employs
chemically stable NH.sub.2CONH.sub.2 and is conducted at low
temperature and stable condition.
[0084] Table 1 shows the results of element analysis of the newly
acid-refined SWNTs, sample 1 and sample 2 by energy dispersive
X-ray spectroscopy (EDS).
TABLE-US-00001 TABLE 1 element sample Carbon (mol %) Oxygen (mol %)
newly acid-refined 95.83 4.17 SWNTs Sample 1 98.38 1.62 Sample 2
98.70 1.30
[0085] According to table 1, the sum of carbon content (mol %) and
oxygen content (mol %) is 100% for any of the newly acid-refined
SWNTs, sample 1 and sample 2, and no other element besides carbon
and oxygen is detected. This implies that NH.sub.2CONH.sub.2 and
SOCl.sub.2 for the treatment in Examples 1 and 2 have neither
bonded with the SWNTs by covalent bond or non-covalent bond, nor
been adsorbed to the surfaces of SWNTs. The NH.sub.2CONH.sub.2 and
SOCl.sub.2 are completely washed out and removed during the
filtration. For the newly acid-refined SWNTs, sample 1 and sample
2, carbon contents respectively are 95.83 mol %, 98.38 mol %, 98.70
mol %, and oxygen content respectively are 4.17 mol %, 1.62 mol %,
1.30 mol %. Here, the oxygen comes from the carboxyl group bonded
to the side walls of the acid-refined SWNTs. Compared to the newly
acid-refined SWNTs, the oxygen content of sample 1 and sample 2
subjected to the treatment of Example 1 and Example 2 are greatly
reduced, which implies that the carboxyl groups in Sample 1 and
Sample 2 are greatly reduced, thus it can be concluded that the
defects in Sample 1 and Sample 2 are significantly reduced. The
oxygen content in Sample 2 is less than that in Sample 1, which
indicates that SOCl.sub.2 has an effect of further reducing the
carboxyl groups bonded to the side walls of the acid-refined
SWNTs.
[0086] To determine the differences between the newly acid-refined
SWNTs and the SWNTs of Sample 1 and Sample 2, Raman spectroscopy is
obtained, which is an effective method in detecting defects in
SWNTs. In particular, Renishaw Micro Raman spectrometer having an
excitation wavelength of 633 nm is used to record the Raman
spectroscopy of the SWNTs.
[0087] Thus obtained Raman spectroscopy is shown in FIG. 4, in
which, Curve (a) is the Raman spectra of the newly acid-refined
SWNTs, Curve (b) is the Raman spectra of Sample 1, while Curve (c)
is the Raman spectra of Sample 2. There are two main regions in the
typical Raman spectra of the SWNTs, which respectively are D band
near 1330 cm.sup.-1 corresponding to disordered graphite layers and
the conjugated system destroy degree, and G band near 1590
cm.sup.-1 corresponding to the stretching vibration of tangential
C--C bond. The ratio (I.sub.D/I.sub.G) of D band intensity I.sub.D
to G band intensity I.sub.G is a measurement of covalent bond shift
or defects in the side walls, which is a common practice
(non-patent document 8). Due to the damage in the side walls of the
SWNTs caused by the oxidization effect of nitric acid which is a
strong acid, I.sub.D of newly acid-refined SWNTs is observable. The
ratio I.sub.D/I.sub.G for newly synthesized SWNTs is 0.03.
TABLE-US-00002 TABLE 2 sample I.sub.D/I.sub.G Newly acid-refined
SWNTs 0.2719 Sample 1 0.050 Sample 2 0.010
[0088] Table 2 shows the I.sub.D/I.sub.G values of newly
acid-refined SWNTs, sample 1 and sample 2.
[0089] According to Table 2, I.sub.D/I.sub.G is 0.2719 for the
newly acid-refined SWNTs, on the contrary, the ratio is greatly
reduced for sample 1 and sample 2, and is 0.050 for sample 1 and
0.010 for sample 2. Based on this, it can be concluded that the
SWNTs of sample 1 and sample 2 subjected to the treatment of
Example 1 and Example 2 almost have no defect, and the graphite
structure with defects in the newly acid-refined SWNTs has almost
been completely repaired. Moreover, I.sub.D/I.sub.G of sample 2 is
reduced more than that of sample 1, which indicates that SOCl.sub.2
has effects in helping repair the defects of SWNTs with defects.
The result of Raman spectra is consistence with the result of
element analysis.
[0090] In Example 1 and Example 2, the influences of treatment
temperature of NH.sub.2CONH.sub.2 solution on the repair of SWNTs
are investigated. To this end, the treatment is performed
respectively at 25.degree. C., 60.degree. C., and 90.degree. C.,
and the treatment time is 8 days. The results are shown in Table 3,
wherein, sample 1 (90.degree. C.), sample 1 (60.degree. C.), and
sample 1 (25.degree. C.) denote samples that the SWNTs treatment
using NH.sub.2CONH.sub.2 solution as Example 1 are respectively
performed at 90.degree. C., 60.degree. C., and 25.degree. C., while
sample 2 (90.degree. C.), sample 2 (60.degree. C.), and sample 2
(25.degree. C.) denotes samples that the SWNTs treatment using
NH.sub.2CONH.sub.2 solution as Example 2 are respectively performed
at 90.degree. C., 60.degree. C., and 25.degree. C.
TABLE-US-00003 TABLE 3 sample I.sub.D/I.sub.G Newly acid-refined
SWNTs 0.2719 Sample 1 (90.degree. C.) 0.0567 Sample 1 (60.degree.
C.) 0.1952 Sample 1 (25.degree. C.) 0.2312 Sample 2 (90.degree. C.)
0.0100 Sample 2 (60.degree. C.) 0.0205 Sample 2 (25.degree. C.)
0.1256
[0091] As shown in Table 3, for sample 1, I.sub.D/I.sub.G of newly
acid-refined SWNTs is 0.2719, on the contrary, the ratio is greatly
reduced to for sample 1 (25.degree. C.), sample 1 (60.degree. C.)
and sample 1 (90.degree. C.), and is 0.2312 for sample 1
(25.degree. C.), 0.1952 for sample 1 (60.degree. C.) and 0.0567 for
sample 1 (90.degree. C.). And for sample 2, I.sub.D/I.sub.G of
newly acid-refined SWNTs is 0.2719, on the contrary, the ratio is
greatly reduced to for sample 2 (25.degree. C.), sample 2
(60.degree. C.) and sample 2 (90.degree. C.), and is 0.1256 for
sample 2 (25.degree. C.), 0.0205 for sample 2 (60.degree. C.) and
0.0100 for sample 2 (90.degree. C.). Based on this, it can be
concluded that the higher the treatment temperature is, the better
the repair effect is. Moreover, it can be seen that I.sub.D/I.sub.G
of sample 2 is much smaller than that of sample 1 when comparing at
the same treatment temperature. This is because the SOCl.sub.2
solution treatment performed before the NH.sub.2CONH.sub.2 solution
treatment increases the defect repair effects for the SWNTs. Or, by
treating with SOCl.sub.2 solution before treating with
NH.sub.2CONH.sub.2 solution, the treatment temperature of
NH.sub.2CONH.sub.2 solution required for achieving an identical
I.sub.D/I.sub.G value is significantly reduced.
[0092] In Example 2, the influences of treatment time of
NH.sub.2CONH.sub.2 solution on the defect repair of SWNTs are
investigated. To this end, the treatment temperature is set at
90.degree. C., while treatment times respectively are 2 days, 4
days, 6 days and 8 days. The results are shown in Table 4, wherein
sample 2 (2 days), sample 2 (4 days), sample 2 (6 days) and sample
2 (8 days) respectively denote the samples that the SWNTs treatment
using NH.sub.2CONH.sub.2 solution as Example 2 are respectively
performed for 2 days, 4 days, 6 days and 8 days.
TABLE-US-00004 TABLE 4 sample I.sub.D/I.sub.G Newly acid-refined
SWNTs 0.2719 Sample 2 (2 days) 0.1387 Sample 2 (4 days) 0.0598
Sample 2 (6 days) 0.0194 Sample 2 (8 days) 0.0100
[0093] As shown in FIG. 4, I.sub.D/I.sub.G of newly acid-refined
SWNTs is 0.2719, on the contrary, the ratio is greatly reduced for
sample 2 (2 days), sample 2 (4 days) and sample 2 (6 days), and is
0.1387 for sample 2 (2 days), 0.0598 for sample 2 (4 days), 0.0194
for sample 2 (6 days), and almost 0 for sample 2 (8 days). Based on
this, it can be concluded that the longer the treatment time is,
the better the repair effect is.
[0094] The qualities of the newly acid-refined SWNTs and the SWNTs
of sample 2 are evaluated by differential thermal analysis and
thermogravimetry (TG-DTA). FIG. 5 shows TG and DTA results of newly
acid-refined SWNTs. FIG. 6 shows TG and DTA results of sample 2
(90.degree. C.). The TG-DTA measurement is performed as follows: 10
mg of the obtained sample is heated at speed of 5.degree. C./min,
air is used as ambient atmosphere, and an empty platinum tray is
used as reference.
[0095] According to FIGS. 5 and 6, the newly acid-refined SWNTs
begin to oxidize at T=380.degree. C., while the sample 2
(90.degree. C.) treated with SOCl.sub.2 solution begins to oxidize
at T=485.degree. C. Based on this, it can be concluded that the
SWNTs, which are treated with SOCl.sub.2 solution before being
treated with NH.sub.2CONH.sub.2 solution, becomes difficult to be
oxidized. This implies that the defects of the side walls of the
SWNTs of sample 2 (90.degree. C.) are more sufficiently
repaired.
[0096] Fourier Transform Infrared Spectroscooy (FT-IR) is employed
to evaluate the newly acid-refined SWNTs, sample 1 and sample 2,
wherein the FT-IR is conducted by using FTIR spectrometer (Bio-Rad
FTS-185). The obtained FTIR spectra are shown in FIG. 7 and the
intensities of FTIR spectra are normalized so as to obtain
identical I.sub.G. Table 5 shows the vibration frequencies of the
peaks of FTIR spectra of newly acid-refined SWNTs (non-patent
document 5, 12).
TABLE-US-00005 TABLE 5 Absorption band/cm.sup.-1 attributes 1060
C--C--O ring stretching vibration, C--C--C asymmetric stretching
vibration 1540 --C.dbd.C--stretching vibration 1650 stretching
vibration of C.dbd.O boned with H 1699 C.dbd.O
[0097] It is evident that the stretching vibration of C.dbd.O boned
with H and the stretching vibration of C.dbd.O originates from the
carbonyl group (C.dbd.O), which is caused by the chemical
oxidization due to the nitric acid used for acidifying the SWNTs.
As seen in FIG. 7, there is no peak corresponding to the stretching
vibration of C.dbd.O boned with H and the stretching vibration of
C.dbd.O in sample 1 and sample 2, thus it can be concluded that
there is no C.dbd.O. Therefore, no C.dbd.O group exists after the
treatment of example 1 and 2, which means that the C.dbd.O in
sample 1 and sample 2 has been reduced by NH.sub.2CONH.sub.2. The
conclusion is consistent with those of EDS analysis and Raman
analysis. Moreover, according to FIG. 7, there is no other peak
observed in sample 1 and sample 2, which implies that the carbonyl
group bonded to the newly acid-refined SWNTs has been removed from
the SWNTs without transforming into other organic groups.
[0098] In order to evaluate the integrity of the SWNTs of sample 1
and sample 2 treated with NH.sub.2CONH.sub.2 solution, the newly
acid-refined SWNTs, sample 1 and sample 2 are dispersed in 1 wt %
sodium dodecyl benzene sulfonate (SDBS) solution, treated with horn
ultrasound for 1 hour, then centrifugated for 2 times (13000 rpm,
30 mins). UV-Vis-NIR absorbances at 550 nm are measured, and the
values for newly acid-refined SWNTs, sample 1 and sample 2 are
respectively 0.31, 0.12 and 0.10. The result indicates that for the
SWNTs treated with NH.sub.2CONH.sub.2 solution, the concentration
of SWNTs is reduced by at least three times, in other words, the
SWNTs of sample 1 and sample 2 treated with NH.sub.2CONH.sub.2
solution are difficult to be dispersed. Obviously, it is resulted
from the reduction of defects in the SWNTs of sample 1 and sample
2. Treating the SWNTs in ammonia at 1000.degree. C. will repair the
structure of the SWNTs with defects and confirm the reduction of
the dispersancy of SWNTs (non-patent documents 8 and 9). The
concentration of the SWNTs of sample 2 is less than that of sample
1, thus it can be reconfirmed that the pre-treatment with
SOCl.sub.2 solution is helpful in reducing the defects in
SWNTs.
[0099] As described above, in Embodiments 1 and 2, the defects
occurred in the acid-refined SWNTs are repaired by amino group
(--NH.sub.2). Although the mechanism for reducing the defects of
SWNTs according to the treatment of Example 1 and 2 is still
unveiled, the present invention gives the following
explanation.
[0100] FIG. 9 shows a simple and reliable reaction path of the
carboxyl reductive reaction using NH.sub.2CONH.sub.2 solution. It
is well known that the carboxyl group reacts with
NH.sub.2CONH.sub.2 to produce acidamide by heating. In the process
that acid-refined SWNTs reacts with NH.sub.2CONH.sub.2 solution,
SWNT-CONH.sub.2 is firstly formed as an intermediate. The existence
of the amino group explains the color change of the supernatant,
since the aroma amine shows a color. The color of the acid-refined
SWNTs treated with NH.sub.2CONH.sub.2 solution at 90.degree. C. is
much clearer than that of the sample treated with
NH.sub.2CONH.sub.2 solution at 60.degree. C., which is possibly
resulted from the accelerated decomposition of SWNT-CONH.sub.2
through a further reaction when treating with NH.sub.2CONH.sub.2
solution at a higher temperature. Because no intermediate is
detected after rinsing and drying, it is considered to be
instable.
[0101] The further amido-based reductive reaction of
SWNT-CONH.sub.2 to desorb organic groups and obtain SWNTs of intact
structure happens in the way of well known Wharton reaction
(non-patent document 13). That is to say, the ketone group of the
intermediate is firstly reduced by the amino group generated from
the hydrolyzation of NH.sub.2CONH.sub.2 solution. The new
intermediate decomposes and releases nitrogen gas (N.sub.2), and
the SWNTs are finally obtained. In which case, SOCl.sub.2 not only
activates the carboxyl group but also accelerates the reaction
between the acid and the amine.
3. The Third Embodiment
Carbon Nanotube Film and the Method for Preparing the Same
[0102] In the third embodiment, the carbon nanotubes obtained from
the first embodiment and the second embodiment are used to prepare
carbon nanotube films.
[0103] That is to say, in the third embodiment, the carbon
nanotubes obtained from the first embodiment and the second
embodiment are used to prepare carbon nanotube films on a substrate
(not shown) according to the well known method. In particular, as
the method for fabricating carbon nanotube films, many methods can
be used, such as drop casting, spin casting, air brushing, dip
casting, Langmuir-Blodgett method and filtration method.
[0104] The carbon nanotubes dispersion, which utilizes a surfactant
to make the carbon nanotubes separated from each other and well
dispersed in the liquid, is typically used during preparing the
carbon nanotube films. As the surfactant, anion surfactants, cation
surfactants, amphoteric surfactants, and nonionic surfactants can
be utilized, wherein, anion surfactants are preferred. The anion
surfactants can be, for example, sodium dodecylsulfate (SDS),
sodium dodecyl benzene sulfonate (SDBS), sodium dodecanesulfonate
(SDSA), etc.
[0105] As the substrate for preparing carbon nanotube films,
various substrates can be selected according to requirements. In
particular, for example, the glass substrates, quartz substrates,
silicon substrates (especially those have oxidation film (SiO.sub.2
film) formed on the surface) can be use as the substrates. And as
the flexible substrates, various plastic substrates can be used.
The plastic substrates formed from, for example but not limiting
to, polyethylene terephthalate, polyethylene, polypropylene,
polystyrene, polycarbonate or the like can be used as the plastic
substrates. As the transparent substrates, the transparent plastic
substrate made of polyethylene terephthalate or the like can be
used.
[0106] According to the third embodiment, the carbon nanotubes of
excellent properties prepared by the first embodiment and the
second embodiment can be utilized to prepare carbon nanotube films
of excellent properties. The carbon nanotube films can be used, for
example, as conductive films or transparent conductive films. The
sheet resistance of the conductive films or the transparent
conductive films can be reduced to at most 60% of that of prior
art. The conductive films and transparent conductive films can be
applied to, for example, the thin film electrodes or transparent
electrodes of various electronic devices, so as to realize high
performance electronic devices.
[0107] It should be appreciated, for example, that the values, raw
materials, equipments and processes given in the foregoing
embodiments and examples are simply exemplary and can be changed
according to requirements.
[0108] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *