The present invention relates to carbon nanotubes (CNTs) coated with a functional oxide and a method of fabricating the CNTs coated with a functional oxide.
The present invention was supported by the Information Technology (IT) Research & Development (R & D) program of the Ministry of Information and Communication (MIC) [project No. 2005-S-605-02, project title: IT-BT-NT Convergent Core Technology for advanced Optoelectronic Devices and Smart Bio/Chemical Sensors].
CNTs are macromolecules having a hollow cylindrical shape with a nano size diameter, and are formed by rolling graphite faces having a hexagonal honeycomb shape in which one carbon atom combines with three other carbon atoms. CNTs have unique physical properties, for example, they are light, have electrical conductivity as high as copper, have thermal conductivity as high as diamond, and have tensile strength compatible to steel. CNTs can control electrical properties of metals or semiconductors according to their diameter and wounding shape although they are not doped with a dopant. CNTs can be classified into single walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs) according to rolled shape, and a shape of CNTs in which SWNTs are bundled is referred to as a rope nanotube.
Since CNTs have various physical properties, CNTs can be used as electron emitters, vacuum fluorescent displays (VFDs), field emission displays (FEDs), lithium ion secondary cell electrodes, hydrogen storage fuel cells, nanowires, nano capsules, nano pincettes, AFM/STM tips, single electron transistors, gas sensors, minute parts for medical and technical fields, and high functional composites, etc.
In particular, many studies have been conducted regarding functional CNTs coated with a particular material. Representative examples of such studies are a characteristic study on a high performance field-emission device using CNTs on which a material such as SiO2 or MgO having wide band gap (Whikun Yi et al., Adv. Mater. 14, 1464-1468, 2002) is coated and a study on a field effect transistor including CNTs on which alumina is coated (Lei Fu et al., Adv. Mater. 18, 181-185, 2006).
Meanwhile, nano scale TiO2 is a material widely used as an optical catalyst for environmental purification, a dissolving agent for poisonous organic contaminants, dye sensitive solar cells, and gas sensors and various manufacturing methods have been studied. Representative examples of such studies are a study on sol-gel electrophoresis (Y. Lin et al., J. Phys.: Condens. Matter. 15, 2917-2922, 2003), a study on physical vapour deposition (B. Xiang et al., J. Phys. D: Appl. Phys., 38, 1152-1155, 2005), and a study on thermal evaporation (Jyh-Ming Wu et al., Nanotechnology, 17, 105-109, 2006).
However, TiO2-coated CNTs and a method of fabricating the TiO2-coated CNTs have not yet been reported.
To address the above and/or other problems, the present invention provides CNTs on which TiO2 is uniformly coated so that the CNTs have both physical characteristics of TiO2 nanowire and physical characteristics of CNTs. Such CNTs can be applied to solar cells, field emission display devices, gas sensors, and optical catalysts etc.
According to an aspect of the present invention, there is provided a method of fabricating TiO2-coated carbon nanotubes (TiO2-coated CNTs), comprising: functionalizing CNTs with hydrophilic functional groups; mixing the CNTs functionalized with hydrophilic functional groups in a solution that contains with TiO2 precursors; refining TiO2 precursor-coated CNTs from the solution in which the CNTs and the TiO2 precursors are mixed; and heat treating the refined TiO2-coated CNTs.
The CNTs may be single-walled nanotubes (SWNTs) or multi-walled nanotubes (MWNTs) on which TiO2 precursors are coated.
The functionalizing of CNTs with hydrophilic functional groups may comprise functionalizing the CNTs with carboxyl groups. At this point, the functionalizing of the CNTs with carboxyl groups may comprise refluxing the CNTs in a mixture of sulfuric acid and nitric acid.
The TiO2 precursors may be formed by hydrolysis of a mixed solution in which a titanium alkoxide and alcohol are mixed. At this point, the titanium alkoxide may be titanium n-butoxide Ti[O(CH2)3CH3]4 and the alcohol may be methyl alcohol. The mixed solution of the titanium alkoxide and the alcohol may further comprise a stabilizer, and the stabilizer may be benzoylacetone. The titanium n-butoxide and the benzoylacetone may be mixed in a molar ratio of 1:1.
The TiO2 precursors are refined to remove large particles of TiO2 precursors by filtering the mixed solution in which a titanium alkoxide and alcohol are mixed. The concentration of TiO2 may be controlled using alcohol when the TiO2 precursors are refined.
The mixing of the CNTs functionalized with hydrophilic functional groups in a solution that contains with TiO2 precursors may further comprise performing ultra-sonication of the mixed solution. The ultrasonication may be performed for 12 to 24 hours.
The refining of TiO2 precursor-coated CNTs may comprise filtering the mixed solution using a filter paper, and may further comprise drying the TiO2-coated CNTs in the air after refining the TiO2-coated CNTs using a filter paper.
In the mixing of the CNTs functionalized with hydrophilic functional groups in a solution that contains TiO2 precursors, the CNTs functionalized with hydrophilic functional groups may be mixed in the solution that contains refined TiO2 precursors in a mixing concentration (kg/1) in the range of 0.005% to 0.015%.
The heat treating of the refined TiO2-coated CNTs may be performed at a temperature in the range of 300° C. to 700° C.
As described above, CNTs are functionalized with hydrophilic carboxyl groups, TiO2 precursors are synthesized, the TiO2 precursors and the CNTs are mixed, and then, CNTs on which the TiO2 precursors are coated (TiO2-coated CNTs) are formed by ultrasonification and heat treating. The TiO2-coated CNTs formed in this manner have both the characteristics of CNTs and TiO2 nanowires, and thus, can have wide industrial applicability such as solar cells, field emission display devices, gas sensors, or optical catalysts.
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
According to the present invention, a method of fabricating TiO2-coated carbon nanotubes (TiO2-coated CNTs) includes, functionalizing CNTs with hydrophilic functional groups, mixing the CNTs functionalized with hydrophilic functional groups in a solution that contains with TiO2 precursors, refining TiO2 precursor-coated CNTs from the solution in which the CNTs and the TiO2 precursors are mixed, and heat treating the refined TiO2-coated CNTs.
The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the following descriptions, it is understood that when a layer is referred to as being ‘on’ another layer or substrate, it can be directly on the other constituent element, or intervening a third constituent element may also be present. Also, in the drawings, the thicknesses of layers and regions are exaggerated for clarity, and like reference numerals in the drawings denote like elements. Terms used in the descriptions are to explain the present invention, and do not confine the meanings and the range of the present invention.
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In the present embodiment, TiO2-coated CNTs coated on a silicon substrate or a copper grid are obtained, however, in another embodiment of the present invention, the alcohol solution 20 that contains the TiO2-coated CNTs 16′ is dried and heat treated at a temperature in the range of 300° C. to 700° C., for example 500° C. for approximately 10 hours, and thus, the powder TiO2-coated CNTs are obtained.
X-Ray Diffraction Analysis
Raman Spectroscopy Analysis
Also, in order to confirm the stability of a TiO2-coated CNT solution (a solution in which TiO2 precursors are uniformly coated on surfaces of CNTs), Raman spectroscopic analyses were performed with respect to a synthesized solution (specimen 1) that was aged for 22 days from the operation 1d and a synthesized solution (specimen 2) that was aged for 1 day. As described in the above embodiment, the specimens 1 and 2 were formed in thin films after coating on silicon substrates and heat treating them. The result of Raman spectroscopic analyses were shown in
Transmission Electron Microscopic (TEM) Analysis
Scanning Electron Microscopic (SEM) Analysis
Various process variables were controlled in order to synthesize CNTs on which TiO2 is uniformly coated. In each process, a product of TiO2-coated CNTs was observed using a SEM.
As described above, CNTs are functionalized with hydrophilic carboxyl groups, TiO2 precursors are synthesized, the TiO2 precursors and the CNTs are mixed, and then, CNTs on which the TiO2 precursors are coated (TiO2-coated CNTs) are formed by ultrasonification and heat treating. The TiO2-coated CNTs formed in this manner have both the characteristics of CNTs and TiO2 nanowires, and thus, can have wide industrial applicability such as solar cells, field emission display devices, gas sensors, or optical catalysts.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
Number | Date | Country | Kind |
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1020070026775 | Mar 2007 | KR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/KR2008/001549 | 3/19/2008 | WO | 00 | 3/18/2010 |