Molecular sieve abstract
A mesoporous alumina molecular sieve and a method of manufacturing
a mesoporous alumina mesoporous alumina molecular sieve of the invention
is produced without using traditionally used additives. Also, because
the size and distribution of the pores can be controlled, the molecular
sieve can be produced simply and economically, producing molecular
sieve with high surface area and thermal stability. Further, a method
of manufacturing an alumina nanotube by using a surfactant and a
use of the alumina nanotube as a hydrogen storage material are provided.
Molecular sieve claims
1. A method of producing a mesoporous alumina molecular sieve,
comprising: mixing a surfactant and an alumina precursor with an
organic solvent to produce a mixture; adding water to the mixture;
hydrothermal synthesizing the mixture with added water; and drying
and calcinating the mixture to remove residual surfactants.
2. The method as claimed in claim 1 wherein the alumina precursor
to water in mole ratio is 1:0.1 to 10.
3. The method as claimed in claim 2 wherein the alumina precursor
to water in mole ratio is 1:1 to 3.
4. The method as claimed in claim 1 wherein the surfactant to
water in mole ratio is 1:0.1 to 10.
5. The method as claimed in claim 1 wherein the surfactant is
a cationic surfactant.
6. The method as claimed in claim 5 where in the cationic surfactant
is represented by chemical formula 1 below: 5wherein R.sub.1 to
R.sub.3 represent substituted or unsubstituted alkyl group with
1 to 4 carbon atoms, R.sub.4 represents substituted or unsubstituted
alkyl group with 8 to 22 carbon atoms, and x represents a halogen
atom, acetate, phosphate, nitrate, or methylsulfate.
7. The method as claimed in claim 1 wherein the alumina precursor
is an aluminum alkoxide.
8. The method as claimed in claim 7 wherein the aluminum alkoxide
is an aluminum-tri-butoxide or an aluminum isopropoxide.
9. The method as claimed in claim 1 wherein the organic solvent
is an alcoholic-based solvent.
10. The method as claimed in claim 9 wherein the organic solvent
is 1-butanol, 2-butanol, 1-propanol or 2-propanol.
11. The method as claimed in claim 1 wherein the hydrothermal
reaction is carried out at 0 to 200.degree. C. for 10 to 100 hours.
12. A mesoporous alumina molecular sieve produced by using any
of the method as claimed in claim 1.
13. A method of producing alumina nanotube, comprising: mixing
a surfactant and an alumina precursor to produce a mixture; adding
water to the mixture; hydrothermal synthesizing the mixture with
added water; and drying and calcinating the mixture to remove residual
surfactants.
14. The method as claimed in claim 13 wherein the alumina precursor
to water in mole ratio is 1:0.1 to 10.
15. The method as claimed in claim 14 wherein the alumina precursor
to water in mole ratio is 1:1 to 3.
16. The method as claimed in claim 13 wherein the surfactant to
water in mole ratio is 1:0.1 to 10.
17. The method as claimed in claim 13 wherein the surfactant is
a cationic surfactant of chemical formula 1 below, an anionic surfactant
of chemical formula 2 below, a nonionic surfactant of chemical formula
3 below, or a neutral surfactant of chemical formula 4 below. 6wherein
R.sub.1 to R.sub.3 represent substituted or unsubstituted alkyl
group with 1 to 4 carbon atoms, R.sub.4 represents substituted or
unsubstituted alkyl group with 8 to 22 carbon atoms, and x represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate. [Chemical
Formula 2]R.sub.5--COOH wherein R.sub.5 represents substituted or
unsubstituted alkyl group with 1 to 22 carbon atoms. [Chemical Formula
3]CH.sub.3(CH.sub.2).sub.30(CH.sub.2CH.sub.2O).sub.n--OH wherein
n represents an integer of 1 to 30. [Chemical Formula 4]R.sub.6--NH.sub.2
wherein R.sub.6 represents substituted or unsubstituted alkyl group
with 8 to 22 carbon atoms.
18. The method as claimed in claim 13 wherein the alcoholic group
of organic solvents is 1-butanol, 2-butanol, 1-propanol or 2-propanol.
19. The method as claimed in claim 13 wherein the hydrothermal
reaction is carried out at 0 to 200.degree. C. for 10 to 100 hours.
20. A method of producing alumina nanotube, comprising: mixing
a surfactant and an alumina precursor with an organic solvent to
produce a mixture; adding water to the mixture; hydrothermal synthesizing
the mixture with added water; and drying and calcinating the mixture
to remove residual surfactants, and further comprising adding a
lithium precursor during producing the mixture or after the calcinating
process.
21. The method as claimed in claim 20 wherein the lithium precursor
and water is added after the calcinating process and further drying
and calcinating to produce an alumina nanotube with lithium, and
again adding the lithium precursor by impregnation method followed
by calcinating process.
22. The method as claimed in claim 20 wherein the lithium precursor
is a lithium hydroxide, halide, nitrate, carbonate or sulfate.
23. The method as claimed in claim 20 wherein the alumina precursor
to the lithium precursor mole fraction is 1:0.1 to 10.
24. The method as claimed in claim 20 wherein the alumina precursor
to mole fraction is 1:0.1 to 10.
25. The method as claimed in claim 20 wherein the alumina precursor
to water mole ratio is 1:1 to 3.
26. The method as claimed in claim 20 wherein the surfactant to
water mole ratio is 1:0.1 to 10.
27. The method as claimed in claim 20 wherein the surfactant is
a cationic surfactant of chemical formula 1 below, an anionic surfactant
of chemical formula 2 below, a nonionic surfactant of chemical formula
3 below, or a neutral surfactant of chemical formula 4 below; 7wherein
R.sub.1 to R.sub.3 represent substituted or unsubstituted alkyl
group with 1 to 4 carbon atoms, R.sub.4 represents substituted or
unsubstituted alkyl group with 8 to 22 carbon atoms, and x represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate. [Chemical
Formula 2]R.sub.5--COOH wherein R.sub.5 represents substituted or
unsubstituted alkyl group with 1 to 22 carbon atoms. [Chemical Formula
3]CH.sub.3(CH.sub.2).sub.30(CH.sub.2CH.sub.2O).sub.n--OH wherein
n represents an integer of 1 to 30. [Chemical Formula 4]R.sub.6--NH.sub.2
wherein R.sub.6 represents substituted or unsubstituted alkyl group
with 8 to 22 carbon atoms.
28. The method as claimed in claim 20 wherein the aluminum precursor
is a aluminum alkoxide.
29. The method as claimed in claim 20 wherein the hydrothermal
reaction is carried out at 0 to 200.degree. C. for 10 to 100 hours.
30. An alumina nanotube produced by the method claim 13.
31. A hydrogen storage material produced by inducing absorption
of hydrogen to the aluminum nanotube of claim 30.
32. A hydrogen storage material of claim 32 wherein the absorption
of hydrogen is carried out while maintaining temperature of a container
holding the nanotube at 298K to 673K and maintaining the pressure
of hydrogen gas at 1 to 10 atmospheric pressure.
33. The hydrogen storage material of claim 32 wherein the container
holding the nanotube is vacuum treated at 373K to 773K prior to
inducing hydrogen adsorption.
Molecular sieve descriptionCROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a 35 U.S.C. .sctn. 371 National Phase
Entry Application from PCT/KR02/01951 filed Oct. 18 2002 and
designating the U.S.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of manufacturing
a mesoporous alumina molecular sieve and an alumina nanotube by
using a surfactant and a use of the alumina nanotube as a hydrogen
storage material.
[0004] 2. Description of the Related Art
[0005] Generally, alumina is considered an important catalyst and
support in industrial processes. A reaction of mesoporous alumina
with uniform porosity, high surface area, chemical stability and
thermal stability is becoming more valuable than existing alumina
with non-uniform pore distribution.
[0006] Various surfactants, such as cationic, anionic, neutral
and nonionic surfactants have been used in producing alumina with
mesopores. Specifically, there have been reports in producing alumina
with mesopores and high surface area, by using a nonionic surfactant,
a sodium dodecyl sulfate and a long chain carboxylic acid.
[0007] However, due to an extremely rapid hydrolysis of alumina
in an aqueous solution, it is difficult to synthesize mesoporous
alumina molecular sieve using a cationic surfactant. Even in the
presence of a surfactant, a hydrated hydroxide in a lamellar form
can be produced. Therefore, additives such as triethanoleamine,
a hydrolysis inhibitor, are added to prevent rapid hydrolysis in
synthesizing mesoporous alumina molecular sieve. Currently, a method
of producing mesoporous alumina molecular sieve with high surface
area, good thermal stability and simple production method is in
demand.
[0008] Hitherto, there have been reports on methods of producing
mesoporous alumina materials with pore structures of a wormhole
or sponge-like motifs by utilizing a supramolecular assembly phenomenon
of a surfactant, but there are no reports on producing alumina nanotube
by using surfactants.
[0009] There have been reports on the reaction of alumina fiber
in a nano-structure, by sol-gel process, in which temperature is
continuously raised until a predetermined cut-off temperature. There
have also been reports on the reaction of alumina nanotube by an
electrochemical anodizing method. However, these processes cannot
produce a large amount of alumina nanotube.
[0010] There has been no report regarding the usage of an alumina
nanotube as a hydrogen storage material.
[0011] Hydrogen is considered an infinite energy source since hydrogen
can be obtained from the earth's water source and it can be recycled
back into water form after combustion. Hydrogen is a clean energy
source since it produces only water, and not environmental pollutants
during combustion. Hydrogen energy can be used in almost all industries,
including transportation and electricity generating systems. However,
a problem in using the hydrogen energy has been raised due to lack
of developments on simple and economical hydrogen storage system.
[0012] Hydrogen can be physically stored in a high-pressure chamber
by compressing the hydrogen beyond 100 atm. But loading the chamber
on a transportational vehicle is extremely dangerous. Also, another
physical storage method involves storing the hydrogen at an extremely
low temperature, below its boiling point (20.3K). However, although
this method allows storing large amount of hydrogen by reducing
the storage volume, the cost of equipments used in maintaining the
low temperature is too high.
[0013] Hydrogen can be chemically stored by using a hydrogen storage
alloy. Although such method efficiently stores hydrogen, with repeated
cycle of storage and release of hydrogen, impurities may enter and
cause deformation of the hydrogen storage alloy, which leads to
a deterioration of the hydrogen storage capacity. Also, because
a metallic alloy is used as the storage medium, the weight per unit
volume increases, thus, it is difficult to load the storage alloy
onto a transportation instrument.
[0014] Another hydrogen storage method is achieved by forcing adsorption
of hydrogen gas on to a solid material. Among such methods, hydrogen
storage by carbon nanotube or nano-structured carbon materials shows
hydrogen storage efficiency exceeding 10 wt. %. However, these results
are difficult to reproduce and many researches are continuing to
overcome problems caused by such method.
[0015] There are ongoing active researches to develop a hydrogen
storage method that reaches at least 6.5 percent by weight of storage
efficiency, which is the target hydrogen storage required by the
US Department of Energy (DOE), while providing stability and economical
efficiency.
SUMMARY OF THE INVENTION
[0016] The present invention provides a mesoporous alumina molecular
sieve with a high surface area and an outstanding thermal stability,
produced in a moderate reaction condition with no other additives
than a surfactant. The invention further provides a method of producing
the same.
[0017] According to an aspect of the present invention, there is
provided a method of producing an alumina nanotube that can be mass
produced in a moderate reaction condition by using a surfactant.
[0018] According to another aspect of the present invention, there
is provided a hydrogen storage method that is more efficient, reliable,
reproducible, and economical than currently available hydrogen storage
methods, by using the alumina nanotube of the foregoing.
[0019] An embodiment of the present invention provides a method
of producing a mesoporous alumina molecular sieve achieved by mixing
a surfactant and an alumina precursor with an organic solvent to
produce a mixture, adding water to the mixture, hydrothermal synthesizing
the mixture with added water, and then drying and calcinating the
mixture to remove residual surfactants.
[0020] The alumina precursor to water mole ratio should be 1:0.1
to 10 for the above embodiment.
[0021] The alumina precursor to water mole ratio should be 1:1
to 3 for the above embodiment
[0022] The surfactant to water mole ratio should be 1:0.1 to 10
for the above embodiment.
[0023] The surfactant is a cationic surfactant for the above embodiment.
[0024] The cationic surfactant is of chemical formula 1 below;
1
[0025] wherein R.sub.1 to R.sub.3 represent substituted or unsubstituted
alkyl group with 1 to 4 carbon atoms, R.sub.4 represents substituted
or unsubstituted alkyl group with 8 to 22 carbon atoms, and x represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate.
[0026] The alumina precursor should be an aluminum alkoxide, for
example, aluminum-tri-butoxide or an aluminum isopropoxide.
[0027] According to an embodiment of the present invention, the
organic solvent should be a solvent belonging in an alcoholic group
of organic solvents such as 1-butanol, 2-butanol, 1-propanol or
2-propanol.
[0028] According to an embodiment of the present invention, the
hydrothermal reaction is carried out at 0 to 200.degree. C. for
10 to 100 hours.
[0029] Another embodiment of the present invention provides a mesoporous
alumina molecular sieve produced by using any the methods described
in the foregoing.
[0030] Another embodiment of the present invention provides a method
of producing alumina nanotube achieved by mixing a surfactant and
an alumina precursor with an organic solvent to produce a mixture,
adding water to the mixture, hydrothermal synthesizing the mixture
with added water, and then drying and calcinating the mixture to
remove residual surfactants.
[0031] According to an embodiment of the present invention, lithium
precursor may be added during the mixing the surfactant and the
alumina precursor step or after the drying and calcinating process.
The lithium precursor and water is added after the calcinating process
to induce ion exchange and further dried and calcinated to produce
an alumina nanotube with lithium seed and again adding the lithium
precursor by impregnation method followed by calcinating process.
[0032] According to another embodiment of the present invention,
the lithium precursor may be lithium hydroxide, halide, nitrate,
carbonate or sulfate.
[0033] According to another embodiment of the present invention,
the alumina precursor to the lithium precursor mole fraction is
1:0.1 to 10. Even more preferably 1:1 to 3 mole fraction.
[0034] According to another embodiment of the present invention,
the alumina precursor to surfactant to water mole ratio is 1:0.1
to 10:0.1 to 10.
[0035] According to another embodiment of the present invention,
the surfactant should be a cationic surfactant of chemical formula
1 below, an anionic surfactant of chemical formula 2 below, a nonionic
surfactant of chemical formula 3 below, or a neutral surfactant
of chemical formula 4 below; 2
[0036] wherein R.sub.1 to R.sub.3 represent substituted or unsubstituted
alkyl group with 1 to 4 carbon atoms, R.sub.4 represents substituted
or unsubstituted alkyl group with 8 to 22 carbon atoms, and x represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate.
[0037] [Chemical Formula 2]
R.sub.5--COOH
[0038] wherein R.sub.5 represents substituted or unsubstituted
alkyl group with 1 to 22 carbon atoms.
[0039] [Chemical Formula 3]
CH.sub.3(CH.sub.2).sub.30(CH.sub.2CH.sub.2O).sub.n--OH
[0040] wherein n represents an integer of 1 to 30.
[0041] [Chemical Formula 4]
R.sub.6--NH.sub.2
[0042] wherein R.sub.6 represents substituted or unsubstituted
alkyl group with 8 to 22 carbon atoms.
[0043] According to another embodiment, the aluminum precursor
should be an aluminum alkoxide, for example, aluminum-tri-butoxide
or an aluminum isopropoxide.
[0044] According to another embodiment, the hydrothermal reaction
should be carried out at 0 to 200.degree. C. for 10 to 100 hours.
[0045] According to an embodiment of the present invention, there
is provided an alumina nanotube produced by the above methods.
[0046] According to another embodiment of the present invention,
there is provided a hydrogen storage material produced by inducing
adsorption of hydrogen to the aluminum nanotube.
[0047] The hydrogen storage material, wherein the adsorption of
hydrogen is carried out while maintaining temperature of a container
holding the nanotube at 298K to 673K and maintaining the pressure
of hydrogen gas at 1 to 10 atmospheric pressure. The hydrogen storage
material of above wherein the container holding the nanotube is
vacuum treated at 373K to 773K prior to inducing hydrogen adsorption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] 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:
[0049] FIG. 1 is a TEM photograph and SADP pattern of an alumina
nanotube produced according to Example 2-6 of the invention;
[0050] FIG. 2a are HR-TEM photographs of an alumina nanotube with
lithium, produced according to Example 2-10 of the invention
[0051] FIG. 2b are TEM photographs of an alumina nanotube with
lithium, produced according to Example 2-10 of the invention;
[0052] FIG. 3 is a TEM photograph of an alumina nanotube with lithium,
produced according to Example 2-14 of the invention;
[0053] FIG. 4 represents a diagram for a constant volume system
to test the hydrogen storage capacity of the alumina nanotube;
[0054] FIG. 5 is a graph depicting the result of hydrogen storage
capacity experiments of the alumina nanotube with lithium produced
in Example 10 under constant pressure (2.7 atmospheric pressure)
but at different temperatures.
[0055] FIG. 6 depicts the results of .sup.1H NMR showing the adsorption
and desorption of hydrogen at 2.7 atmospheric pressure and room
temperature of the alumina nanotube with lithium produced in Example
10;
[0056] FIG. 7 is a TEM photograph of mesoporous alumina molecular
sieve produced according to Example 1-5 of the invention; and
[0057] FIG. 8 is a graph depicting the X-ray diffraction pattern
of the mesoporous alumina molecular sieve produced according to
Example 1-4 of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0058] The invention provides a method of producing a mesoporous
alumina molecular sieve by using a surfactant and an alumina precursor
in a moderate reaction condition.
[0059] In the method of producing mesoporous alumina molecular
sieve according to the present invention, the hydrolysis rate of
an alumina precursor can be controlled simply by using a surfactant
and water mixed in a stoichiometric ratio in an alcohol-based organic
solvent, even without commonly used additives such as triethanolamine.
As a result, the production of hydrate hydroxides, caused by rapid
hydrolysis, can be minimized. Also, by manipulating the reaction
condition and the length of the surfactant's tail, the size and
distribution of the mesopores of the alumina molecular sieve can
be controlled.
[0060] The mesoporous alumina molecular sieve of the invention
is produced by mixing a surfactant and an alumina precursor in an
organic solvent to form a mixture. Afterwards, water is slowly added
to the mixture, followed by hydrothermal reaction, drying and calcination
processes to remove residual surfactants.
[0061] As a surfactant, any of the surfactants commonly used in
the field may be used. However, preferably, a cationic surfactant
is used and more preferably, a cationic surfactant as represented
by the following Chemical Formula 1 is used. 3
[0062] wherein R.sub.1 to R.sub.3 represent substituted or unsubstituted
alkyl group with 1 to 4 carbon atoms, R.sub.4 represents substituted
or unsubstituted alkyl group with 8 to 22 carbon atoms, and X represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate.
[0063] Examples of the cationic surfactant of the Chemical Formula
1 include CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).sub.3Br (wherein
n is 12 14 16 or 18) and CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).sub.3Cl
(wherein n is 12 14 16 or 18). Since the size of a mesopore depends
on the length of the cationic surfactant's tail, an appropriate
cationic surfactant with desired tail length may be chosen in producing
mesopores with a predetermined size.
[0064] Preferably, the amount of surfactant is 0.1 to 10 mole per
1 mole of alumina precursor. At an amount of less than 0.1 mole
ratio, the surfactant may not effectively form micelle structures
and at an amount greater than 10 mole ratio, it is not cost effective
to use such surplus amount of surfactants.
[0065] As an alumina precursor, any commonly used material in the
field may be used. However, preferably, an aluminium alkoxide, such
as aluminium tri-sec-butoxide and aluminium isopropoxide is used.
[0066] In conventional methods, the alumina precursor such as aluminum
alkoxide undergoes rapid hydrolysis, forming hydrated hydroxide
so that additives are used to restrain hydrolysis. However, in the
present invention, the hydrolysis rate can be controlled simply
by adding water, without adding additives.
[0067] Preferably, the amount of water for hydrolysis is in a stoichiometric
ratio to the alumina precursor. Preferably, water is added slowly
into a mixture of an alumina precursor and a surfactant in an organic
solvent. Also preferably, the stoichiometric ratio of water to aumina
precursor is 0.1 to 10 mole of water per 1 mole of alumina precursor
and more preferably 1 to 3 mole of water per 1 mole of alumina precursor.
At an amount less than 0.1 mole ratio, an effective hydrolysis of
aluminium precursor is unlikely to take place, and at an amount
greater than 10 mole ratio, the hydrolysis rate would increases
due to large amount of water, making the formation of uniform mesopores
difficult.
[0068] Preferably, the organic solvent for the invention is an
alcohol-based organic solvent, such as 1-butanol, 2-butanol, 1-propanol
and 2-propanol.
[0069] In the process of the invention for preparing a molecular
sieve, the mixture of a surfactant and an aluminium precursor in
an organic solvent is added with water and then is subjected to
hydrothermal reaction. The purpose of the hydrothermal reaction
is to form an alumina mesopore precursor by a dehydration reaction
of the mixture. Preferably, temperature during the reaction is 0
to 200.degree. C. and the reaction lasts 10 to 100 hours.
[0070] After the hydrothermal reaction, drying and calcination
processes are carried out to produce a mesoporous alumina molecular
sieve. Preferably, the drying process is carried out at a room temperature
or at a sufficiently high temperature to effectively remove un-reacted
materials and solvents. The temperature may vary according to the
amount of added water and solvents. The purpose of the calcination
process is to remove residual surfactants. Preferably, the process
is carried out at an inert atmosphere or at an air atmosphere for
1 to 10 hours at 200 to 800.degree. C.
[0071] Unlike conventional methods, the present method allows for
the production of mesoporous alumina molecular sieve with controlled
pore size and pore distribution. Also, because the hydrolysis rate
is slow, formation of hydrated hydroxide is suppressed, resulting
in homogenized formation of the mesoporous alumina molecular sieve.
Further, it is economical since additives are not used.
[0072] The invention further includes a method of producing an
alumina nanotube by using a surfactant, an alumina precursor and
water in a moderate condition, without solvents or additives.
[0073] In the present invention, an alumina nanotube is produced
by a surfactant and water mixed in a stoichiometic ratio without
using solvents or additives. The synthetic reaction is performed
at a temperature of approximately 150.degree. C. or lower to encourage
simple drying of the mixture and separation of the product.
[0074] The invention further includes an alumina nanotube with
lithium. The lithium can be added simultaneously or following the
alumina nanotube reaction. When adding lithium after nanotube reaction,
ion-exchange method or impregnation method is used to incorporate
lithium into the alumina nanotube.
[0075] The alumina nanotube of the invention weighs less and is
better capable of safely storing large amount of hydrogen compared
to other hydrogen storage materials that use hydrogen storage alloy
or carbon nanotubes. Further, the alumina nanotube of the invention
can be applied for use in a secondary lithium battery.
[0076] The method of producing the alumina nanotube includes mixing
a surfactant and an alumina precursor to create a mixture; adding
water to the mixture, followed by hydrothermal reaction and drying
and calcinating processes to remove residual surfactants.
[0077] As the surfactant for the above process, preferably, a cationic
surfactant of Chemical Formula 1 an anionic surfactant of Chemical
Formula 2 a non-ionic surfactant of Chemical Formula 3 or a neutral
surfactant of Chemical Formula 4 as depicted below are used. 4
[0078] wherein R.sub.1 to R.sub.3 represent substituted or unsubstituted
alkyl group with 1 to 4 carbon atoms, R.sub.4 represents substituted
or unsubstituted alkyl group with 8 to 22 carbon atoms, and X represents
a halogen atom, acetate, phosphate, nitrate, or methylsulfate.
[0079] [Chemical Formula 2]
R.sub.5--COOH
[0080] wherein R.sub.5 represents substituted or unsubstituted
alkyl group with 1 to 22 carbon atoms.
[0081] [Chemical Formula 3]
CH.sub.3(CH.sub.2).sub.30(CH.sub.2CH.sub.2O).sub.n--OH
[0082] wherein n represents an integer of 1 to 30.
[0083] [Chemical Formula 4]
R.sub.6--NH.sub.2
[0084] wherein R.sub.6 represents substituted or unsubstituted
alkyl group with 8 to 22 carbon atoms.
[0085] Examples of cationic surfactants of Chemical Formula 1 include
CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).sub.3Br (n is 12 14 16 or
18), CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).sub.3Cl (n is 12 14
16 or 18). The size of a mesopore depends on the length of the cationic
surfactant's tail. Therefore, a cationic surfactant with an appropriate
tail length may be chosen depending on the desired size of the mesopore.
[0086] Examples of anionic surfactants of Chemical Formula 2 include
CH.sub.3(CH.sub.2).sub.10COOH, CH.sub.3(CH.sub.2).sub.12COOH and
CH.sub.3(CH.sub.2).sub.14COOH and CH.sub.3(CH.sub.2).sub.16COOH.
[0087] Examples of nonionic surfactants of Chemical Formula 3 include
CH.sub.3(CH.sub.2).sub.15--(CH.sub.2CH.sub.2O).sub.2--OH, CH.sub.3(CH.sub.2).sub.15--(CH.sub.2CH.sub.2O).sub.10--OH
and CH.sub.3(CH.sub.2).sub.15--(CH.sub.2CH.sub.2O).sub.20--OH.
[0088] Examples of neutral surfactants of Chemical Formula 4 include
CH.sub.3(CH.sub.2).sub.11NH.sub.2 CH.sub.3(CH.sub.2).sub.13NH.sub.2
and CH.sub.3(CH.sub.2).sub.15NH.sub.2.
[0089] The surfactants of the foregoing may be used alone or in
a combination. Preferably, the amount is 0.1 to 10 mole of the surfactant
per 1 mole of the aluminum alkoxide precursor. If the amount of
the surfactant is less than 0.1 mole ratio, the surfactant cannot
effectively form micelle structures and when the amount is greater
than 10 mole ratio, it is not cost effective to use such surplus
amount of surfactants.
[0090] As an alumina precursor, any commonly used material in the
field may be used. However, preferably, an aluminium alkoxide is
used. Examples include aluminium tri-sec-butoxide and aluminium
isopropoxide.
[0091] Such alumina precursor, such as aluminum alkoxide, undergoes
rapid hydrolysis, forming a hydrated hydroxide, so that additives
are used to restrain hydrolysis. However, in the present invention,
the hydrolysis rate can be controlled simply by adding water, without
adding additives.
[0092] Preferably, the amount of water used in hydrolysis is determined
according to the stoichiometric ratio to the alumina precursor.
Preferably, water is added slowly into a mixture of an alumina precursor
and a surfactant in an organic solvent. Also preferably, the stoichiometric
ratio of water to alumina precursor is 0.1 to 10 mole of water per
1 mole of alumina precursor and more preferably 1 to 3 mole of water
per 1 mole of alumina precursor. At an amount less than 0.1 mole
ratio, it is difficult for an effective hydrolysis of aluminium
precursor to take place, and when the amount is greater than 10
mole ratio, the rate of hydrolysis increases due to large amount
of water, making the formation of uniform mesopores difficult.
[0093] In the process of the invention for preparing a molecular
sieve, the mixture of a surfactant and an aluminium precursor in
an organic solvent is added with water and then subjected to hydrothermal
reaction. The purpose of the hydrothermal reaction is to form an
alumina mesopore precursor from the dehydration reaction of the
mixture containing the surfactant, aluminium precursor and the organic
solvent. Preferably, the temperature during the reaction is 0 to
200.degree. C. and the reaction lasts 10 to 100 hours.
[0094] After the hydrothermal reaction, drying and calcination
processes are carried out to produce a mesoporous alumina molecular
sieve. Preferably, the drying process is done at a room temperature
or at a sufficiently high temperature to effectively remove un-reacted
materials and solvents. The temperature may vary according to the
amount of added water and solvents. The purpose of the calcination
process is to remove residual surfactants. Preferably, the process
is done at an inert atmosphere or at an air atmosphere for 1 to
10 hours at 200 to 800.degree. C.
[0095] The invention further includes an alumina nanotube with
lithium. The lithium can be added simultaneously or after the alumina
nanotube reaction. When adding lithium after the alumina nanotube
reaction, ion-exchange method or impregnation method is used to
incorporate lithium into the alumina nanotube.
[0096] Lithium can be effectively added during nanotube reaction
by adding lithium precursor while the surfactant, alumina precursor
and water are being mixed. Preferably, the amount of lithium precursor
is 0.1 to 10 mole per 1 mole of alumina precursor and more preferably,
1 to 3 mole per 1 mole of alumina precursor. Also preferably, the
lithium precursor is lithium hydroxide, halide, nitrate, carbonate
or sulfate. If the amount is less than 0.1 mole ratio, an effective
chemical bonding between lithium precursor and alumina precursor
is difficult to obtain, and at an amount of greater than 10 mole
ratio, an effective chemical reaction may not occur because of the
small amount of aluminium precursor compared to the lithium precursor.
[0097] Besides adding the lithium precursor during the alumina
nanotube reaction as described in the foregoing, lithium precursor
may be added after the alumina nanotube has been produced.
[0098] In order to add lithium precursor to a pre-produced alumina
nanotube, a lithium precursor is added to impose ion exchange of
the lithium precursor in the aqueous solution of the nanotube, followed
by drying and calcinating processes to create an alumina nanotube
with a lithium seed. Afterwards, another impregnation process with
lithium precursor is imposed to produce alumina nanotube with lithium.
[0099] A radical as defined in the invention to be a substituted
or unsubstituted alkyl group with 1 to 4 carbon atoms includes such
radicals in linear or branched forms, and one or more of the radicals
may be substituted with a halogen atom, hydroxy group, carboxyl
group, cyano group or amino group. Examples of such radicals include
methyl, ethyl, n-propyl, isopropy, n-butyl, isobutyl, sec-butyl
and t-butyl.
[0100] A radical as defined in the invention to be a substituted
or unsubstituted alkyl group with 1 to 22 carbon atoms includes
such radicals in linear or branched forms, and one or more of the
radicals may be substituted with a halogen atom, hydroxy group,
carboxyl group, cyano group or amino group. Examples of such radicals
include methyl, ethyl, n-propyl, isopropy, n-butyl, isobutyl, sec-butyl,
t-butyl, pentyl, isoamyl, hexyl, octyl, isooctyl, nonyl, lauryl,
myristyl, cetyl and stearyl.
[0101] A radical as defined in the invention to be a substituted
or unsubstituted alkyl group with 8 to 22 carbon atoms includes
such radicals in linear or branched forms, and one or more of the
radicals may be substituted with a halogen atom, hydroxy group,
carboxyl group, cyano group or amino group. Examples of such radicals
include octyl, isooctyl, nonyl, lauryl, myristyl, cetyl and stearyl.
[0102] The invention will now be described more fully with reference
to examples. This 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.
EXAMPLES
Example 1-1 to 1-5
[0103] The method of synthesizing a mesoporous alumina molecular
sieve is as follows.
[0104] In 70 ml of 1-butanol, CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).sub.3--
-Br (n=12 14 or 16) as a cationic surfactant and aluminum tri-sec-butoxide
as a alumina precursor as listed in Table 1 were mixed under stirring
until a uniform mixture is obtained. To the mixture, distilled water
was slowly added. The mole ratio of the mixture was 0.5:1:2 for
surfactant:aluminum tri-sec-butoxide:distilled water, respectively.
After the mixture was stirred until a uniform mixture was obtained,
the obtained mixture in a gel form was moved into a Teflon-lined
autoclave container, and hydrothermal reaction was carried out for
24 hours at temperatures listed in Table 1. Afterwards, the product
was washed with ethanol several times, the product was dried at
room temperature for 16 hours and followed by another 5 hours of
drying at 110.degree. C. Then, a calcination process was carried
out at 500.degree. C. and at atmospheric pressure for 4 hours to
remove any residual surfactant, thereby producing the mesoporous
alumina molecular sieve. The mesopore distribution is shown in Table
1. Also, the TEM photograph of the mesoporous alumina molecular
sieve in Examples 1-5 is shown in FIG. 7. FIG. 7 shows that a comparatively
uniform mesopore has a similar structure as a worm-hole distribution.
1TABLE 1 BET Specific Surfactant Temp. Time Surface area BJH Pore
size CH.sub.3(CH.sub.2).sub.n-1N(CH.su- b.3).sub.3--Br (.quadrature.)
(h) (m.sup.2/g) (nm) Example 1-1 n = 12 100 24 429 4.5 Example 1-2
n = 14 100 24 241 6.5 Example 1-3 n = 16 RT 24 310 7.2 Example 1-4
n = 16 100 24 337 6.7 Example 1-5 N = 16 150 24 401 4.8
[0105] As Table 1 illustrates, the surface areas of mesoporous
alumina molecular sieves range between 241 to 429 m.sup.2/g. The
BET surface area and BJH pore size of the mesoporous molecular sieves,
determined by nitrogen isotherm absorption test, were dependent
upon reaction temperature and the tail length of the surfactants.
As reaction temperature was raised from room temperature to 423K,
the pore size decreased from 7.2 nm to 4.8 nm, and the pore distribution
became narrower. Also, the pore size increased with an increase
in the tail length of the surfactants. Therefore, it can be inferred
that by manipulating the condition during reaction process, the
size of the pore can be controlled.
[0106] FIG. 8 illustrates the representative small angle and wide
angle X-ray diffraction patterns of the mesoporous alumina molecular
sieve produced according to Example 1-4 of the invention. XRD pattern
of the small angle, which is known to be closely related to the
distribution of the pores of the mesoprous alumina, showed only
a single peak, which is an indication of irregular mesopore structure.
The wide angle X-ray diffraction analysis indicates the correspondence
between the mesoporous alumina molecular sieves and the bulk gamma-alumina
peaks. These results indicate that the mesoporous alumina molecular
sieves of Example 1-4 are composed of oxidized aluminium or aluminium
oxyhydroxide with low crystallinity.
[0107] The pore structure of the mesoporous alumina molecular sieve
of Example 1-4 showed high uniformity, however, clear repetitive
arrangements of the pore structures were not shown. Such irregular
pore connectivity is considered to be similar to a worm-hole or
a sponge like structure, often found in the mesopores of silica
alumina. Although a consistent arrangement over a wide range is
not shown, as the small angle X-ray diffraction analysis illustrates,
a single strong peak indicates that each of the pore channels possesses
consistent distribution.
[0108] High resolution NMR allows for a structural analysis of
aluminum in a mesoporous alumina molecular sieve. For the present
invention, .sup.27Al MAS (Magic angle spinning), CPMAS (Cross Polarization
Magic Angle Spinning), MQMAS (Multiple Quantum Magic Angle Spinning)
NMR experiments were performed for the molecular sieves of Examples
1-1 to 1-5 in regards to each of the tail lengths. The results
showed two clear resolution .sup.27Al NMR peaks, which indicate
the presence of nonequivalent magnetic Al centers. The two peaks
are known to represent aluminum sites with tetrahedral and octahedral
structures, respectively. Around 33 ppm, a weak NMR peak was observed,
and this was a 5-coordinated aluminum site. .sup.27Al CPMAS (Cross
Polarization Magic Angle Spinning) NMR showed three clear peaks
at 72 33 and -1 ppm. This is due to the increase in the center
of the 5-coordinated aluminum due to a cross polarization effect.
In other words, due to magnetization transfer from proton to aluminum,
the corresponding NMR peak of 5-coordinated aluminum increased.
There had been reports that such 5-coordinated aluminum center can
function as a Lewis acid. Therefore, it can be assumed that the
5-coordinated aluminum center in the molecular sieve synthesized
by using a cationic surfactant contains an electron receiving group.
[0109] The mesoporous alumina molecular sieve synthesized according
to the invention has similar structure to a worm-hole structure
while having a high surface area, thermal stability and different
coordinated aluminum sites than conventional molecular sieves.
Examples 2-1 to 2-5
[0110] Production of Alumina Nanotube
[0111] As illustrated in Table 2 CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3).su-
b.3--Br (N=12 14 or 16), as a cationic surfactant, and aluminum
tri-secondary-butoxide as an alumina precursor were mixed under
stirring until an uniform solution was obtained. Distilled water
was slowly added to the solution. The mole ratio of such solution
was 0.5:1:2 for surfactant:aluminum tri-secondary-butoxide:distilled
water, respectively. After the solution was further stirred until
it became uniform, the resulting solution, in a gel form, was moved
into a Teflon-lined autoclave container, and was subjected to hydrothermal
reaction for 24 hours at temperatures listed in Table 1. Afterwards,
the product was washed with ethanol several times, and then the
product was dried at room temperature for 16 hours and for another
5 hours at 110.degree. C. Then, after 4 hours of calcinating process
at 500.degree. C. and at atmospheric pressure to remove residual
surfactant, an alumina nanotube composed of oxidized aluminum was
obtained.
[0112] Table 2 represents the reaction conditions (the tail length
of surfactants, reaction temperature) for producing the alumina
nanotubes.
2 BET BJH Surfactant(Cationic) Temp. Specific Surface Area Pore
size (CH.sub.3(CH.sub.2).sub.n-1N(CH.s- ub.3).sub.3--Br) (.quadrature.)
Time (h) (m.sup.2/g) (nm) Example 1-1 n = 12 100 72 256 3.0 Example
2-2 n = 14 100 72 328 3.8 Example 2-3 n = 16 RT 72 293 3.4 Example
2-4 n = 16 100 72 389 3.6 Example 2-5 n = 16 150 72 385 3.8
[0113] The results in Table 2 indicate that with an increase in
the carbon chain in the tail of the surfactants and temperature,
the pore size and the surface area increase.
Examples 2-6 to 2-9
[0114] Production of Alumina Nanotube
[0115] Various surfactants (cationic, anionic, nonionic, neutral)
with 16 carbon chains in the tail length were used to produce alumina
nanotubes. The mixing ratio was same as for the examples 2-1 to
2-5 in that 0.5:1:2 for surfactant, aluminum tri-secondary-butoxide,
respectively, were used.
[0116] FIG. 1 represents the TEM photograph and SADP pattern of
the alumina nanotube produced by Example 2-6
3 TABLE 3 Temp. BET Specific Surface Area BJH Pore Size Surfactant
(.quadrature.) Time (h) (m.sup.2/g) (nm) Example 2-6 CH.sub.3(CH.sub.2).sub.15N(CH.sub.3).sub.-
3--Br 150 72 385 3.8 Example 2-7 CH.sub.3(CH.sub.2).sub.14COOH 150
72 282 2.8 Example 2-8 CH.sub.3(CH.sub.2).sub.15NH.sub.2 150 72
300 2.8 Example 2-9 CH.sub.3(CH.sub.2).sub.15--(PEO).sub.2--OH 150
72 445 3.0
[0117] The results in Table 3 show that when surfactants with same
tail length of carbon chain were used, the alumina nanotube of the
present invention showed higher surface area than other conventionally
used commercial bulk alumina.
Examples 2-10 to 2-13
[0118] Production of Alumina Nanotube with Lithium
[0119] In order to produce an alumina nanotube with lithium, a
cationic surfactant (CH3(CH2)n-.sub.1N(CH.sub.3).sub.3Br, n=16)
or nonionic surfactant (--CH.sub.3(CH.sub.2).sub.n-1--C.sub.6H.sub.5--(PEO).sub.x--,
OH, n=8 x=8) as a surfactant, aluminum tri-secondary-butoxide as
aluminum precursor, and lithium hydroxide, lithium chloride or lithium
carbonate as lithium precursor, and water as a solvent were mixed
according to Table 4. The mole ratio was 0.5:1:1:2 for surfactant:aluminum
precursor:lithium precursor:water, respectively. After the mixture
was stirred until a uniform solution was obtained, the obtained
solution was poured into a Teflon-lined autoclave container, and
was subjected to hydrothermal reaction for 72 hours at 423K. Afterwards,
ethanol was used to wash the product several times, and the product
was dried at 383K. Then, after 4 hours of calcinating process at
773K and at atmospheric pressure to remove residual surfactant,
an alumina nanotube with lithium was obtained.
[0120] Table 4 illustrates the reaction conditions (reaction temperature,
type of surfactant, type of lithium precursor) for the production
of alumina nanotubes with lithium.
4TABLE 4 BET Specific BJH Pore Lithium Temp. Time Surface Area
Size Precursor Surfactant (K) (h) (m.sup.2/g) (nm) Example 2-10
LiOH CH.sub.3(CH.sub.2).sub.15N(CH.sub.3).sub.3--Br 423 72 128 4.0
Example 2-11 LiCl CH.sub.3(CH.sub.2).sub.15N(CH.sub.3).sub.3--Br
423 72 234 6.2 Example 2-12 Li.sub.2CO.sub.3 CH.sub.3(CH.sub.2).sub.15N(C-
H.sub.3).sub.3--Br 423 72 137 10.0 Example 2-13 LiOH CH.sub.3(CH.sub.2).sub.7--C.sub.6H.sub.5--(PEO).sub.8--OH
423 72 136 3.0
[0121] FIG. 2a represents HR-TEM photographs of an alumina nanotube
with lithium, produced according to Example 2-10 of the invention.
[0122] FIG. 2b represents TEM photographs of an alumina nanotube
with lithium, produced according to Example 2-10 of the invention.
[0123] FIGS. 2a and 2b indicate that the alumina nanotube is composed
of bundle of lower nanotubes and the structure was confirmed by
molecular simulation.
Example 2-14
[0124] Production of Alumina Nanotube with Lithium
[0125] In producing an alumina nanotube with lithium, a lithium
precursor may be added on to an already produced alumina nanotube
by post-treatment.
[0126] First, a cationic surfactant (CH.sub.3(CH.sub.2).sub.n-1N(CH.sub.3)-
.sub.3Br, n=16) as a surfactant, aluminum tri-secondary-butoxide
as aluminum precursor and water as a solvent were mixed together.
The mole ratio was 0.5:1:2 for surfactant:aluminum precursor:water,
respectively. After the mixture was stirred until a uniform mixture
was obtained, the resulting solution was poured into a Teflon-lined
autoclave container, and was subjected to hydrothermal reaction
for 72 hours at 423K. Afterwards, the product was washed with ethanol
several times, and then dried at 383K. Then, after 4 hours of calcinating
process at 773K and at atmospheric pressure to remove any residual
surfactant, an alumina nanotube was obtained.
[0127] To the alumina nanotube, lithium is added to create a derivative
of alumina nanotube with added lithium as described below.
[0128] As a lithium precursor, LiNO.sub.3 was used. In the already
produced alumina nanotube, 0.5 wt % of LiNO.sub.3 per 1 g of the
alumina nanotube and 100 ml of water were added to allow ion exchange
for 3 hours at a room temperature. The resulting product was filtered,
washed with distilled water, and dried for 12 hours at 373K. The
dried material was calcinated at 623K for 5 hours and at an air
atmosphere for 2 hours. After the material reached 573K, it was
treated with oxygen for 2 hours to obtain an alumina nanotube with
added lithium seed.
[0129] In the resulting alumina nanotube with added lithium seed,
5 wt % of LiNO.sub.3 was added again by an impregnation process
followed by a calcinations process at 623K and at an air atmosphere
to produce an alumina nanotube with lithium.
[0130] FIG. 3 depicts the TEM photograph of the alumina nanotube
with lithium.
Example 2-15
[0131] Hydrogen Storage by Using Alumina Nanotube
[0132] In Example 2-10 hydrogen storage capacity was tested by
using the alumina nanotube with lithium.
[0133] FIG. 4 illustrates schematical view of the equipment used
to perform hydrogen storage experiments. The equipment is fixed
volume equipment having a hydrogen gas storage container (4) (83.52
ml) and a sample container (6) (15.02 ml), where samples are to
be added.
[0134] For hydrogen storage test, 0.1 g of alumina nanotube with
lithium as produced by Example 2-10 is inserted in the sample container
(6) of FIG. 4. Then, vacuum pump (5) was connected to the container
and all other valves were closed. By using the vacuum pump, all
foreign substances in the sample were discharged. For the process,
by using temperature controller (7), the temperature of the electrical
furnace was preheated to a range between 473K and 673K and then
reduced to 298K-673K for the hydrogen storage test. After the temperature
was set, all valves were closed, and then vacuum pump (5) was turned
on.
[0135] After the temperature of the entire system was set to the
appropriate hydrogen storage experiment temperature (298K-673K)
and stabilized, the pressure control regulator was set to a constant
pressure (2.7 atm). Afterwards, hydrogen storage container was filled
with hydrogen, and when the pressure was stabilized, the reading
on transmeter (3) was recorded. After recording readings at various
pressures, the value of the pressure transmeter (3) was calibrated.
Afterwards, it was confirmed that no gas escaped from the entire
system.
[0136] For the hydrogen storage test, hydrogen with ultrahigh purity
(99.999%) in predetermined pressure (2.7 atm) was injected into
the hydrogen container (6). The readings on the pressure transmeter
indicator were recorded with time.
[0137] The amount of hydrogen absorbed in an alumina nanotube was
assessed by the decreased value in the pressure. FIG. 5 shows the
amount of hydrogen adsorbed under a constant pressure (2.7 atm)
but at different temperatures. From FIG. 5 it can be inferred that
the hydrogen adsorption speed and hydrogen storage capacity clearly
increase with the increase in the temperature. At a temperature
above 473K, the hydrogen storage capacity was similar for all samples
(approximately 8.8 wt %).
[0138] Also, FIG. 5 shows that when hydrogen adsorbed (approx.
8.8 wt %) at 473K, was re-vacuumed at 673K to be detached and readsorption
test was carried out, a smooth desorption and readsorption processes
of hydrogen were possible.
Experimental Example
[0139] The adsorption and desorption processes of the hydrogen
during hydrogen storage Experiment of 2-15 was confirmed by .sup.1H
NMR and shown in FIG. 6.
[0140] "a" represents the result of .sup.1H NMR at room
temperature, before hydrogen storage, but after vacuum treatment,
which showed that there was no hydrogen adsorption. "b"
represents the result of .sup.1H NMR after 45 hours of hydrogen
storage test at room temperature and at 2.7 atmospheric pressure,
which showed hydrogen adsorption. Afterwards, the adsorbed hydrogen
was re-vacuumed and deabsorbed and .sup.1H NMR confirmed a complete
desorbed as shown in "c." Then, "d" showed that
the hydrogen readsorption had taken place.
[0141] The above examples and experimental examples show that the
hydrogen storage capacity by the alumina nanotubes produced according
to the present invention, even in a mild environment (temperature
and pressure), the hydrogen storage efficiency (approximately 8.8
wt. %) was higher than other commonly used hydrogen storage materials
and also showed smooth adsorption and desorption reactions. Accordingly,
the alumina nanotube produced according to the invention is considered
a safe and economical hydrogen storage medium.
[0142] Theoretically, the hydrogen storage capacity of a hydrogen
storage unit using a metal hydride is considered to be high, depending
on the type of the metal (e.g. 10.6 wt % for LiAlH.sub.2). However,
ordinarily, it is known that an actual metal hydride only shows
approximately 5 wt. % of hydrogen storage capacity. Recently, there
had been a report of high hydrogen storage capacity by using a carbon
nanotube (approx. 20 wt. %). However many researchers are refuting
the reproducibility of such result since most of other reports show
approximately 5 wt % of hydrogen storage capacity at an extremely
high pressure (approx. 100 atm). Therefore, a new hydrogen storage
medium using the alumina nanotube of the present invention can be
useful.
[0143] As discussed above, the alumina nanotube produced by the
present invention has the following advantages: compared to other
production of carbon materials having nano structures, alumina nanotube
production is simple and produces large quantity; the absorption
and de-absorption can be easily controlled by manipulating temperature
and pressure during the use as a hydrogen storage material; the
inner structure does not easily change form even after repeated
adsorption-desorption reactions, thereby providing a structural
stability; and by proven accuracy and reproducibility, it provides
great use as clean hydrogen energy source.
[0144] The mesoporous alumina molecular sieve of the invention
is produced by using a cationic surfactant without using traditionally
used additives. Also, because the size and distribution of the pores
can be controlled, the molecular sieve can be produced simply and
economically, producing molecular sieve with high surface area and
thermal stability.
[0145] Further, the alumina nanotube of the invention, can be mass-produced
in a mild condition, compared to other commonly used methods of
nanotube production. The alumina nanotube can be used as a hydrogen
storage material since it can effectively store and safely transport
comparatively large amount of hydrogen in a small volume. Further,
it can be used in a lithium secondary battery.
[0146] 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. |