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Title:
AN APPARATUS AND METHOD FOR RAPID RATE OF TITANIUM DIOXIDE (TIO2) NANOTUBES ARRAYS FORMATION
Document Type and Number:
WIPO Patent Application WO/2012/026799
Kind Code:
A1
Abstract:
The present invention is an apparatus and method for rapid rate of titanium dioxide (TiC>2) nanotube arrays formation. The apparatus (1) for producing titanium dioxide (TiO2) nanotube arrays comprises of an anodization chamber (2), an electrolyte solution (3) acting as an anodization medium, an anodization means characterized by a rectifier (4), an anionic electrode (5) and a cationic electrode (6), an effervescing tube (7) having a plurality of apertures for producing bubbles, a cooling means characterized by a pair of coolant channels having an inlet cooling channel (8) and an outlet cooling channel (9), and a plurality of interval connections (10) in between the inlet cooling channel (8) and outlet cooling channel (9), and an electrolyte circulating means having circulation channels and a pair of circulating channels. The method for producing titanium dioxide (TiO2) nanotube arrays comprises of preparing anionic electrode (5), preparing electrolyte solution (3), performing the anodization process at 25°C of around pH7 for 1 minute and collecting titanium dioxide (TiO2) nanotube arrays from the anionic electrode (5).

Inventors:
SREEKANTAN SRIMALA (MY)
AHMAD ZAINAL ARIFIN (MY)
LOCKMAN ZAINOVIA (MY)
HAZAN ROSHASNORLYZA (MY)
SAHARUDIN KHAIRUL ARIFAH (MY)
LAI CHIN WEI (MY)
Application Number:
PCT/MY2010/000170
Publication Date:
March 01, 2012
Filing Date:
September 14, 2010
Export Citation:
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Assignee:
UNIV SAINS MALAYSIA (MY)
SREEKANTAN SRIMALA (MY)
AHMAD ZAINAL ARIFIN (MY)
LOCKMAN ZAINOVIA (MY)
HAZAN ROSHASNORLYZA (MY)
SAHARUDIN KHAIRUL ARIFAH (MY)
LAI CHIN WEI (MY)
International Classes:
C25C5/02; C01G23/047; C25D11/26; C30B29/16
Domestic Patent References:
WO2008060293A22008-05-22
WO2010080703A22010-07-15
Foreign References:
US20090275143A12009-11-05
US20040194574A12004-10-07
GB2054649A1981-02-18
Other References:
DATABASE WPI Week 200857, Derwent World Patents Index; AN 2008-J72519
Attorney, Agent or Firm:
YIP, Jiun, Hann (Wisma Menjalara Business Avenue Suite 2-8,8th Floor, Jalan 7A/62, Bandar Menjalara Kuala Lumpur, MY)
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Claims:
l/WE CLAIM

1. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, comprising:

an anodization chamber (2);

an electrolyte solution (3) contained in the anodization chamber (2), acting as an anodization medium;

an anodization means characterized by a rectifier (4), an anionic electrode (5) and a cationic electrode (6), wherein the anionic electrode (5) and cationic electrode (6) is electronically connected to the rectifier (4);

a bubbling means characterized by an effervescing tube (7) having a plurality of apertures, connected to an air pump and positioned at the bottom of the anodization chamber (2), for producing bubbles;

a cooling means characterized by a pair of coolant channels having an inlet cooling channel (8) and an outlet cooling channel (9), and a plurality of interval connections (10) in between the inlet cooling channel (8) and outlet cooling channel (9) whereby coolant is introduced into the inlet cooling channel (8), passed by the interval connections (10) and transferred out through the outlet channel (9); and

an electrolyte circulating means characterized by a circulation inlet (12) and a pair of circulating channels (13), whereby the pair of circulating channels (13) are placed at the bottom of the anodization chamber (2), for circulating the electrolyte solution (3) in the anodization chamber (2).

2. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1 , wherein the electrolyte solution (3) is made of preferably but not limited to ethylene glycol, ammonium fluoride and hydrogen peroxide.

3. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance to claim 2, wherein the concentration of ammonium fluoride (NH4F) is preferably but not limited to 5wt%. 4. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance to claim 2, wherein the concentration of hydrogen peroxide (H2O2) is preferably but not limited to 5wt%.

5. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1 , wherein the electrolyte solution (3) preferably fills 80% of the anodization chamber (2).

6. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1 , wherein the cationic electrode (6) is preferably but not limited to solid carbon.

7. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1 , wherein the bubbles formed from the effervescing tube (7) is preferably but not limited to oil free compressed air.

8. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1, wherein the cooling means is preferably made of but not limited to polypropylene. 9. An apparatus (1) for producing titanium dioxide (Ti02) nanotube arrays, in accordance with claim 1 , wherein the coolant is preferably but not limited to water.

10. A method for producing titanium dioxide (Ti02) nanotube arrays, comprises the steps of:

first, preparing anionic electrode (5) by cutting titanium metal into titanium foils with desired dimensions, then cleaning and drying the titanium foils;

second, preparing electrolyte solution (3) by mixing ethylene glycol with ammonium fluoride and hydrogen peroxide until homogenous in a mixing chamber and subsequently, determining pH of the electrolyte solution (3) by using a pH meter;

third, performing the anodization process; and

fourth, collecting titanium dioxide (Ti02) nanotube arrays by washing the anionic electrode (5) with acetone for 1 minute in ultrasonic bath to remove remaining electrolyte solution (3) and to eliminate precipitation formed on the titanium dioxide (Ti02) nanotube arrays, and subsequently placing the anionic electrode (5) in a furnace for annealing process.

11 . A method for producing titanium dioxide (Ti02) nanotube arrays in accordance with claim 1 1 , wherein the step of preparing anionic electrode (5) further comprises the steps of:

first, shaping titanium metal into desired sizes and dimensions;

second, immersing said titanium metal into ethanol;

third, sonicating said titanium metal in ultrasonic cleaning bath;

fourth, rinsing said titanium metal with deionized water; and

fifth, drying said titanium metal. 12. A method for producing titanium dioxide (Ti02) nanotube arrays in accordance with claim 12, wherein the titanium metal has a preferable thickness of but not limited to 0.125mm.

13. A method for producing titanium dioxide (Ti02) nanotube arrays in accordance with claim 11 , wherein the step of performing the anodization process further comprises the steps of:

first, filling the anodization chamber (2) with the electrolyte solution (3); second, fixing the anionic electrode (5) to the anionic electrode hanger

(16);

third, hanging the anionic electrode hanger (16) onto a hanging beam (15) where the hanging beam (15) is placed at the grooves of the beam support (14) mounted on the anodization chamber (2);

fourth, commencing the anodization process by switching on the rectifier

(4);

fifth, terminating the anodization process by switching off the rectifier (4); and

sixth, removing the anionic electrode (5) from the electrolyte solution (3).

14. A method for producing titanium dioxide (ΤΊΟ2) nanotube arrays in accordance with claim 14, wherein the anionic electrode hanger (16), hanging beam (15) and beam support (14) are made of preferably but not limited to copper.

15. A method for producing titanium dioxide (Ti02) nanotube arrays in accordance with claim 14, wherein the duration of anodization process is preferably but not limited to one minute. 16. A method for producing titanium dioxide (Ti02) nanotube arrays in accordance with claim 11, wherein condition for the annealing process is preferably but not limited to 400°C for 6 hours.

Description:
AN APPARATUS AND METHOD FOR RAPID RATE OF TITANIUM DIOXIDE (Ti0 2 ) NANOTUBES ARRAYS FORMATION

Technical Field

The present invention relates to an apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotube formation and more particularly an apparatus and method that employ anodization process to form titanium dioxide (Τ1Ό2) nanotubes at a rapid rate.

Background Art

Recently, titanium dioxide (Ti0 2 ) particles have attracted much attention in various industries due to its long term chemical stability, strong oxidizing power, non-toxicity and their low-cost. Titanium dioxide (Ti0 2 );in various forms are used in various applications such as degradation of organic compounds by using titanium dioxide (T1O2) as photocatalyst, photovoltaic applications, gas sensing, elimination of pollutants and others. Due to the growth of the above applications, the production of titanium dioxide (T1O2) grows tremendously as well. Therefore, various fabricating methods for producing various types of titanium dioxide (Ti0 2 ) have been discovered in order to satisfy the demand.

One of the types of titanium dioxide (Ti0 2 ) used in nanotechnology is nano- titanium dioxide (Ti0 2 ). Due to the tremendous growth of nanotechnology, the production of titanium dioxide (Ti0 2 ) nanotube arrays has been growing in a rapid rate. A number of fabricating methods have been used such as electrochemical lithography, photoelectrochemical etching, sol-gel processing, hydrothermal synthesis and template synthesis in order to form nanometer-sized titanium dioxide (Ti0 2 ) tubules, wires, dots and pillars. Another one of the fabricating methods for producing titanium dioxide (Ti0 2 ) nanotube arrays is electrochemical anodization. Electrochemical anodization is the growth of oxide layers on certain metal. However, most of the electrochemical anodization is not suitable in producing large scale titanium dioxide (Ti0 2 ) arrays. This is due to the fact that conventional electrochemical anodization of producing titanium dioxide (Ti0 2 ) nanotubes exposes titanium metal substrate to an acidified fluoride at a voltage range from 100mV to 60V for a period ranging from 1 hour to 24 hours or more with conventional, magnetic or ultrasonic mixing. It is learnt that if the production of large scale titanium dioxide (Ti0 2 ) nanotube arrays on large substrate uses the conventional electrochemical anodization process, the acidified fluoride that has a pH less than 5 will result a high dissolution rate to the titanium dioxide (Ti0 2 ) nanotube arrays and a shorter range of length of the titanium dioxide (ΤΊΟ2) nanotube arrays, which is from 400 to 600nm, will be obtained. Other means that are using organic electrolyte require long hours of formation of titanium dioxide ( " ΠΟ2) nanotube arrays, which is not suitable to be used to produce large scale and optimum titanium, dioxide (T1O2) nanotube arrays. This is due to the fact that long anodization time increases the temperature of the electrolyte solution which in turn affects the formation of the titanium dioxide (Ti0 2 ) nanotube arrays. Moreover, trie use of ultrasonic mixing incurs high maintenance that is not suitable in producing large scale titanium dioxide (ΤιΌ 2 ) nanotube arrays. Therefore, the present invention is used in order to produce large scale and optimum titanium dioxide (Ti0 2 ) nanotube arrays.

Several prior arts have disclosed applications related to apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotubes formation. One of the prior art is PCT international publication no. 2008/127508 A2 which discloses a method of preparing titania nanotubes that involves anodization of titanium on the presence of chloride ions and at low pH (1-7) in the absence of fluoride! The prior art also includes a kit that is used for preparing the titania nanotubes where the kit comprises of a titanium anode, a cathode and a electrolyte solution that comprises at least mM chloride and has a pH in the range of about 1 to about 7, and the instructions for preparing the titania nanotubes. As compared to the present invention, the prior art is using an electrolyte solution which comprises of chloride instead of fluoride at a low pH range. The prior art is said not suitable to be used in industrially producing titanium dioxide (ΤΊΟ 2 ) nanotube arrays as the production of titania nanotubes bundles break apart at rapid production rate. Therefore, due to the prior art limited applicability, it is said to be not feasible in industrial production of titanium dioxide (Ti0 2 ) nanotube arrays.

PCT international publication no. 2009/015329 A2 has disclosed a method of making nanotubular titania substrate having titanium dioxide (Ti0 2 ) surface that comprises of a plurality of vertically oriented titanium dioxide (Ti0 2 ) nanotube arrays containing oxygen vacancies. The titanium dioxide (Ti0 2 ) nanotube arrays are formed by anodization of a titania substrate in an acidified fluoride electrolyte, which may be conducted in the presence of an ultrasonic field or mixed by conventional mixing. As compared to the present invention, the prior art performs the anodization process in the presence of ultrasonic field, which is not suitable to be used in producing titanium dioxide (TiC½) nanotube arrays industrially as the cost of maintaining a ultrasonic mixer is high. On the other hand, the prior art also mentioned that the electrolyte can be mixed using conventional mixing. However, conventional mixing is also not suitable to be used in this invention as conventional mixing is not convenient to be used in large scale production. Therefore, due to the prior art limited applicability, it is said to be not feasible in industrial production of titanium dioxide (Ti0 2 ) nanotube arrays.

Summary of the invention

In accordance with the present invention, there is provided an apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotubes formation. To date, titanium dioxide (Ti0 2 ) nanotube arrays have been formed using a variety of apparatuses and methods. However, according to journals and researches done lately, anodization process is believed to be one of the methods that are able to produce optimum titanium dioxide (Ti0 2 ) nanotubes arrays. Therefore, the present invention employs anodization process in forming titanium dioxide (Ti0 2 ) nanotubes. Furthermore, the present invention is able to be used industrially to produce large scale titanium dioxide (Ti0 2 ) nanotubes arrays at rapid rate. An anodization process is an electrochemical process of the growth of oxide film on certain metal. The apparatus used in the present invention to perform the anodization process in producing titanium dioxide (Ti0 2 ) nanotubes, comprises of an anodization chamber, an electrolyte solution, an anodization means having a rectifier, an anionic electrode and a cationic electrode, an effervescing tube, a cooling means having an inlet cooling channel, an outlet cooling channel and a plurality of interval connections, and an electrolyte circulating means having a circulation inlet and a pair of circulating channels

In the apparatus, titanium metal is used as the anionic electrode and preferably solid carbon is used as the cationic electrode where both of these electrodes are connected to the voltage source. The voltage source provides voltage for the electrodes to enable the electrochemical process to run. As for the electrolyte solution, it is a solution that includes ethylene glycol (C2H6O2), ammonium fluoride (NH4F) and hydrogen peroxide (H 2 0 2 ).

The effervescing tube has a plurality of apertures and is connected to an air pump to produce bubbles where these bubbles play an important role in obtaining uniform titanium dioxide (Ti0 2 ) nanotubes. As for the cooling means, it is used to maintain an optimum temperature of the electrolyte solution by absorbing the heat generated from the anodization process. In order to absorb the heat of the electrolyte solution, the coolant, which is water, is introduced into the inlet cooling channel, passed through the interval connections between the inlet cooling channel and outlet cooling channel, and is transferred out from the cooling means through the outlet cooling channel. The electrolyte circulating means has a circulation inlet and a pair of circulating channels where the pair of circulating channels is placed at the bottom of the anodization chamber, for circulating the electrolyte solution in the anodization chamber.

As for the method of the present invention, it comprises of four basic steps that include preparing anionic electrode, preparing electrolyte solution, performing anodization process and collecting titanium dioxide (Ti0 2 ) nanotube arrays. To prepare the anionic electrode, titanium metal is used. The titanium metal is first cut into desired dimensions. It is then washed with ethanol in ultrasonic cleaning bath and subsequently washed with deionized water. The titanium metals are then dried and used as anionic electrodes. After that, the electrolyte solution is prepared by mixing ethylene glycol (C 2 H 6 0 2 ), ammonium fluoride (NH4F) and hydrogen peroxide (H2O2). Then, the pH of the electrolyte solution is measured with a pH meter. If the pH of the electrolyte solution is not neutral, small amount of low concentration sodium hydroxide (NaOH) and sulfuric acid (H2SO4) is added in order to make the electrolyte solution to be neutral. The next step is to perform the anodization process under the condition of 25°C at around pH7 for 1 minute. After the anodization process, the titanium dioxide (Ti0 2 ) nanotubes formed on the anionic electrode is collected by washing the anionic electrode with acetone for 1 minute in ultrasonic bath to remove remaining electrolyte solution and to eliminate precipitation formed on the titanium dioxide (Ti0 2 ) nanotubes. Subsequently, the anionic electrode is placed in a furnace for annealing process.

It is a benefit of this present invention to provide an apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation that is able to form longer titanium dioxide (Ti0 2 ) nanotubes arrays with uniform thickness on large substrate. It is another benefit of this present invention to provide an apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation that is able to form longer titanium dioxide (Ti0 2 ) nanotubes arrays under a neutral condition. It is still another benefit of this present invention to provide an apparatus and method for rapid rate of titanium dioxide (ΤΊΟ2) nanotubes arrays formation that has an electrolyte solution of ethylene glycol (C2H6O2) with ammonium fluoride (NH 4 F) of fluoride concentration of 5wt% and hydrogen peroxide (H 2 0 2 ) of concentration of 5wt% which is capable of producing titanium dioxide (Ti0 2 ) nanotubes arrays with diameter of 46nm and length of 2.25pm within 1 minute of anodization process, where the hydrogen peroxide (H 2 0 2 ) plays an important role in producing OH radicals that increases the dissolution of Ti and increases the oxidation rate and consequently forming titanium dioxide (Ti0 2 ) nanotubes arrays at rapid rate.

It is yet another benefit of this present invention to provide an apparatus and method for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation that uses carbon as an alternative for cationic electrode. Brief Description of Drawings

A complete understanding of the present invention may be obtained by reference to the accompanying drawing, when considered in conjunction with the subsequent, detailed description in which: Figure 1 is the perspective view of the apparatus for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation.

Figure 2 is the side cross-sectional view of the apparatus for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation. Figure 3 is the front cross-sectional view of the apparatus for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation.

Figure 4 is the schematic diagram of the apparatus for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation.

Figure 5 is the flow chart diagram of the method for rapid rate of titanium dioxide (ΤΊΟ2) nanotubes arrays formation. Figure 6 is the flow chart diagram for the steps of preparing the anionic electrode.

Figure 7 is the flow chart diagram for the steps of performing the anodization process. Figure 8 is the FESEM images of titanium dioxide (Ti0 2 ) nanotubes arrays obtained with anodization time of 1 minute in 90wt% of ethylene glycol (C 2 H 6 0 2 ) with hydrogen peroxide (H 2 0 2 ) and ammonium fluoride (NH 4 F) at 60V by bubbling means. Detailed Description of Drawings

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures.

Referring to figure 1 to figure 4, they are showing an apparatus (1) for rapid rate of titanium dioxide (Ti0 2 ) nanotubes arrays formation. Generally, the formation of titanium dioxide (Ti0 2 ) nanotubes arrays is achieved by anodization of pure titanium foil in an electrolyte solution. However, various factors are considered in order to obtain optimum titanium dioxide (Ti0 2 ) nanotubes arrays. In this invention, an apparatus for developing optimum titanium dioxide (Ti0 2 ) nanotubes arrays are provided where the apparatus (1) comprises of an anodization chamber (2), an electrolyte solution (3) filled in the anodization chamber (2), acting as an anodization medium, an anodization means characterized by a rectifier (4), an anionic electrode (5) and a cationic electrode (6), wherein the anionic electrode (5) and cationic electrode (6) is electronically connected to the rectifier (4), a bubbling means characterized by an effervescing tube (7) having a plurality of apertures, connected to an air pump and positioned at the bottom of the anodization chamber (2), for producing bubbles, a cooling means (8) characterized by a pair of coolant channels having an inlet channel (9) and an outlet channel (10), and a plurality of interval connections (11) in between the inlet channel (9) and outlet channel (10) whereby coolant is introduced into the inlet channel (9), passed through the interval connections (11) and transferred out through the outlet channel (10), and an electrolyte circulating means characterized by a circulation inlet (12) and a pair of circulating channels (13), whereby the pair of circulating channels (13) are placed at the bottom of the anodization chamber (2), for circulating the electrolyte solution (3) in the anodization chamber (2).

The anodization chamber (2) is an open chamber that is preferably made of polypropylene, where it is chosen to be used due to its inertness to the electrolyte solution (3). However, other materials can be used to construct the anodization chamber (2) as long as the material is inert towards the electrolyte solution (3). At the initial stage of anodization, a compact layer of titanium dioxide (Ti0 2 ) forms on the titanium metal. This is initial process is known as passivation process titanium (Ti) and the chemical reaction is stated in reaction 1. At this stage, the field assisted dissolution dominates chemical dissolution as the electric field across the electrode is very high. The field assisted dissolution polarizes and weaken the Ti-0 bond resulting in dissolution of oxide. As a result, pits will start to form randomly on the surface of the oxide which will act as pore nucleation centre. As the process continues, chemical dissolution takes over field assisted dissolution. During chemical dissolution, pits will grow into various sizes and depths. The pore growth of the pits is assisted by fluorine content in the solution to produce ion TiF 6 2" as a result of localized chemical dissolution, where the mechanism is represented by reaction 2. As the process continues, the oxide layer at the bottom of the pore is subjected to chemical dissolution and becomes thinner with time. This leads to a higher field at the bottom of the pore that drives further oxidation and field assisted dissolution where Ti comes out of the metal and dissolve in solution. The hydrogen peroxide (H 2 0 2 ) in the electrolyte is noticed to accelerate the Ti dissolution, which is indicated by intense yellow colour of the electrolyte solution. Reaction 3 and 4 shows the reaction of the hydrogen peroxide (H 2 0 2 ), which is a powerful oxidant, with metal-titania interface producing titanium dioxide (Ti0 2 ) layer. The growth and propagation of the pores is anticipated to occur inward titanium. This then leads to the formation of discrete, hollow-like cylindrical oxide which will then be developed into nanotubular structures of titanium dioxide (Ti0 2 ). However, in order to obtain a high aspect ratio and optimum titanium dioxide (Ti0 2 ) nanotubes arrays, various factors have to be considered where the factors include the type of electrolyte solution used, concentration of hydrogen peroxide (H 2 0 2 ), concentration of ammonium fluoride (NH 4 F), voltage of the anodization, time of the anodization, temperature of the anodization, and more.

Ti 4+ + H 2 0 2 →Ti0 2 + 2H + (reaction 1) Ti0 2 + 6NH 4 F + 2H + → [TiF 6 ] 2" + H 2 0 2 + 6NH 4 + (reaction 2)

2Ti0 2 + H 2 0 2 + 2e " -→· Ti 2 0 3 + H 2 0 + 0 2 (reaction 3)

Ti 2 0 3 + H 2 0 2 -> 2Ti0 2 + H 2 0 + 2e " (reaction 4) The chemical composition of electrolyte solution (3) used in this invention is preferably but not limited to the mixture of ethylene glycol (C 2 H 6 0 2 ), ammonium fluoride (NH 4 F) and hydrogen peroxide (H 2 0 2 ) where the preferable concentration for both ammonium fluoride (NH 4 F) and hydrogen peroxide (H 2 0 2 ) are 5wt%. A variety of electrolyte solutions (3) such as organic electrolyte and aqueous-based electrolyte may also be used in the anodization process. However, in order to obtain optimum titanium dioxide (Ti0 2 ) nanotube arrays, organic electrolyte is preferably used as major drawbacks are observed in the use of aqueous-based electrolyte. One of the major drawbacks of using aqueous-based electrolyte is that it requires the pH of the solution to be less than 5 and thus this speeds up the etching process at the top of the titanium dioxide (ΤΊΟ2) nanotube arrays due to the presence of water in the electrolyte. Also, the presence of water causes pH burst and thus producing titanium dioxide (Ti0 2 ) nanotube arrays with rough surfaces. Furthermore, the growth rate of titanium dioxide (Ti0 2 ) nanotube arrays is higher using organic electrolyte as compared to those of using aqueous-based electrolyte solution. Moreover, by using organic electrolyte solution, more uniform pore diameters and smother walls of the titanium dioxide (Ti0 2 ) nanotube arrays are produced. The organic electrolytes that may be used in this invention are such as glycerol (C3H 5 (OH)3), ethylene glycol (C 2 H 6 0 2 ), formamide (CH 3 NO), dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). In this invention, the organic electrolyte that is preferably used is ethylene glycol (C 2 H 6 0 2 ). As for ammonium fluoride (NH 4 F), it is an fluoride ion (F " ) provider where fluoride ions (F ~ ) are used essentially for pore formation of the titanium dioxide (Ti0 2 ) nanotubes where the formation goes through the diffusion of fluoride ions (F " ) and simultaneously effusion of [TiF 6 ] 2" . The presence [TiF 6 ] 2~ ions leads to chemical dissolution of titanium dioxide (Ti0 2 ) layer whereby fluoride ions (F " ) in the electrolyte solution attack the interface and allow the ions of the electrolyte solution to penetrate into interface and accelerate the pore growth. When the fluoride content is lower than 1.5 wt%, the chemical dissolution is expected to be low and the dissolution in the vertical direction into titanium bulk can hardly happen where the tube formation cannot be initialized and there is only a compact oxide layer on titanium surface. The use of optimum amount of fluoride ions (F " ) in the electrolyte would enhance the chemical dissolution which forms pores of titanium dioxide (Ti0 2 ) nanotube arrays at a faster rate. It is observed that 5wt% is the preferable concentration for formation of titanium dioxide (Ti0 2 ) nanotube arrays at a rate of 2250nm/min. Yet, a high concentration of fluoride ion (F " ), which is more than 5wt%, will lead to a high chemical dissolution at the top of the titanium dioxide (Ti0 2 ) nanotube arrays where the titanium dioxide (Ti0 2 ) nanotube arrays will tend to be short and finally deform or etch away when it exceeds 10wt%.

On the other hand, hydrogen peroxide (H 2 0 2 ) is also used in the mixture of the electrolyte solution (3). Hydrogen peroxide (H 2 0 2 ) herein contributes HOO " and H + ions where the HOO " ions play a role of oxygen provider and H + is used in the formation of [TiF 6 ] 2" complexes. Besides, in the presence of the hydrogen peroxide (H 2 0 2 ), the OH- radicals are formed and speed the dissolution of titanium to accelerate the formation of titanium dioxide (Ti0 2 ) nanotube arrays. It is also known that donation of oxygen is more difficult in organic electrolyte such as ethylene glycol because it is strongly bound to the carbon atom by a double bonding. This reduces the tendency to form oxide layer. Therefore, the hydrogen peroxide (H 2 0 2 ) is used in enhancing the formation of oxide layer by contributing HOO " which eventually is a good oxygen provider. With a low concentration of hydrogen peroxide (H 2 0 2 ), the H + in the electrolyte solution is not sufficient enough to speed up the reaction 2 in building optimum titanium dioxide (Ti0 2 ) nanotube arrays. On the other hand, if the concentration of hydrogen peroxide (H 2 0 2 ) is high, the H + in the electrolyte solution (3) will be high, causing dissolution at the top part of the titanium dioxide (Ti0 2 ) nanotubes. It is observed that by using a concentration of hydrogen peroxide (H2O2) of 10wt%, the top part of the titanium dioxide (Ti0 2 ) nanotubes starts to etch away. With a hydrogen peroxide (H 2 0 2 ) concentration of 5wt%, it is observed that the titanium dioxide (ΤΊΟ2) nanotubes formed are optimum, with an aspect ratio of 49.45 within 1 minute of anodization. Therefore, the concentration of hydrogen peroxide (H 2 0 2 ) that is preferably used in the electrolyte solution (3) is 5wt%. As mentioned earlier, the electrolyte solution (3) is a mixture of ethylene glycol (C 2 H 6 0 2 ), ammonium fluoride (NH 4 F) and hydrogen peroxide (H 2 0 2 ). Before being used, the ethylene glycol (C 2 H 6 0 2 ) is first filled into a mixing chamber. Then, ammonium fluoride (NH 4 F) solution is added into ethylene glycol (C2H6O2) and is stirred for 30 minutes to homogenize the mixture. After that, hydrogen peroxide (H2O2) is added into the mixture and stirred for another 30 minutes for the same purpose. The pH of the mixture is determined using a pH meter. If the pH of the mixture is acidic, sodium hydroxide (NaOH) is added accordingly in order to bring the pH of the mixture to neutral. On the other hand, if the pH of the mixture is alkaline, then adequate amount of sulfuric acid will be added in order to bring the pH of the mixture to neutral. This is done due to the fact that during the anodization process, the formation of titanium dioxide (Ti0 2 ) nanotube arrays produces H + ions which make the mixture of electrolyte solution (3) acidic. If an acidic electrolyte solution is used, a high concentration of H + ions causes high rate of chemical etching, resulting in shorter titanium dioxide (Ti0 2 ) nanotubes. On the other hand, if an alkaline electrolyte solution is used, a low concentration of H + ions causes a low rate of pit formation. Once the mixing is completed, the electrolyte solution (3) is pumped from the mixing chamber to the anodization chamber (2). As the anodization chamber (2) is an open chamber, only approximately 80% of the anodization chamber (2) is required to be filled with the electrolyte solution (3). The remaining spaces left will be used to accommodate the anionic electrodes (5). If too much of electrolyte solution (3) is filled into the anodization chamber (2), the introduction of anionic electrodes (5) will cause the electrolyte solution (3) to overspill. In order for the anodization process to occur, a rectifier (4) is supplied to the apparatus (1 ). In this invention, the rectifier (4) is electrically connected to the cationic electrodes (6) and anionic electrodes (5). The rectifier (4) can be any type of source provided that it is able to produce electric power that is capable of establishing constant voltage to the anionic electrode (5) and cationic electrode (6). It is an added advantage if the rectifier (4) is a source that can be altered momentarily so that the voltage can be sweeped during the early stage of anodization process. The voltage used in the anodization process is one of the factors to be controlled in order to obtain optimum titanium dioxide (Ti0 2 ) nanotube arrays. It controls the field assisted oxidation process and the field assisted dissolution process of the anodization process and this varies the diameter and the length of the titanium dioxide (Ti0 2 ) nanotube arrays. In this invention, the optimum voltage supplied to the anodization process is 60V. It is observed that in the Ti anodization for 60 minutes in the optimum electrolyte, the aspect ratio for 60V, 50V, 40V and 30V are 86.36, 57.14, 40.00 and 27.27 respectively. As mentioned earlier, voltage affects the diameter of the titanium dioxide (Ti0 2 ) nanotube arrays. The diameter of the titanium dioxide (Ti0 2 ) nanotube arrays obtained using 60V, 50V, 40V and 30V are 110nm, 105nm, 100nm and 80nm and the length are 2.25pm, 4pm, 6pm and 9.5pm respectively. As for the cationic electrode (6), the preferred material used is carbon. In numerous prior arts, various materials such as platinum, carbon, tantalium, aluminium, stanum or tin, cuprum, cobalt, ferum or iron, nickel and wolfram or tungsten have been used. However, only iron, stainless steel, aluminium and carbon are chosen to be investigated, which they are lower in cost compared to the above mentioned. As this invention is used to produce large scale titanium dioxide (Ti0 2 ) nanotube arrays, high cost materials such as platinum or nickel will not be feasible to be used. Due to the stability and high aspect ratio of carbon, it is preferably used in this invention compared to all the above mentioned materials. In this invention, carbon electrodes are shaped into panels where these panels are mounted onto the walls of the anodization chamber (2) and are electrically connected to the rectifier (4).

In order to compare the effect of cationic material towards the anodization process, different materials such as aluminium, stainless steel, iron and carbon are used as cationic electrode (6) in anodization process of 60 minutes anodization time in 85% glycerol and 15 % water at 60V for 1 hour. It is observed that by using stainless steel as cationic electrode (6), the aspect ratio obtained is much lower compared to those using carbon, iron and aluminium. The use of stainless steel as cationic electrode (6) resulted in short titanium dioxide (Ti0 2 ) nanotube arrays with an average length of 700 nm, and nonuniform wall. Besides, the diameter of the titanium dioxide (Ti0 2 ) nanotube arrays seem to be nonuniform at the bottom and top of the titanium dioxide (Ti0 2 ) nanotube arrays, which results in conical shape type of titanium dioxide (Ti0 2 ) nanotube arrays. It is apparent that the thickness of the wall is very small, which is approximately 5 to 10 nm. With this thickness, the wall can no longer support themselves and thus collapse in certain region due to low stability. The aspect ratio obtained from aluminium cationic electrode is identical to carbon cationic electrode. However, it is observed that the top surface of the titanium dioxide (Ti0 2 ) nanotube arrays is similar to those using stainless steel. The wall at the bottom of these titanium dioxide (Ti0 2 ) nanotube arrays seems to be stable but the top seems to be failing to sustain its stability, hence collapsed. Although the aspect ratio obtained is identical to carbon, the stability of titanium dioxide (Ti0 2 ) formed using aluminium is a lot lower compared to those using carbon. As for the use of iron as the cationic electrode (6), it resulted in the formation of well-organized titanium dioxide (Ti0 2 ) nanotube arrays with high aspect ratio. However, the stability of iron is lower as compared to carbon. It is observed that the mass loss of iron after anodization process is 46pg/cm 2 /h while the mass loss for carbon is 1.5pg/cm 2 /h. By comparing the use of carbon cationic electrode with other cathode materials, carbon has a desirable aspect ratio with larger tube diameter of 100nm and longer tube length of 2.0pm. Therefore carbon is preferably used in this invention compared to all the above mentioned materials. Furthermore carbon's performance is equally good as platinum whereby titanium dioxide (ΤΊΟ2) nanotube arrays with similar aspect ratio are obtained with both electrodes. However, by comparing between platinum and carbon, carbon will be more cost saving as the cost for using platinum as the cationic electrode (6) will be much higher than carbon. Therefore, carbon is preferably used in this invention compared to all the above mentioned materials.

The anionic electrode (5) is made of titanium metal which can be shaped into different sizes and dimension according to the desired size and dimension. However, the titanium metal is preferred to have a thickness of 0.125mm. After shaping the titanium metal into a desired size and dimension, it is immersed into ethanol and subsequently sonicated in an ultrasonic cleaning bath. Next, the titanium metal is rinsed with deionized water and dried for use in further matter. In this invention, after the preparation, the anionic electrode (5) is suspended onto an anionic electrode hanger (16) where the anionic electrode hanger (16) is hanged on a hanging beam (15) and dipped into the electrolyte solution (3). The hanging beam (15) is either placed horizontally or vertically on the grooves of beam support (14) mounted on the edge of the anodization chamber (2), depending on the amount of anionic electrodes (5) needed to be dipped into the electrolyte solution (3). The material used to construct the hanging beam (15) and beam support (14) is copper. Other material can also be used as long as the voltage is able to pass through the hanging beams (15) and beam support (14) to the anionic electrode (5). Other than using pure titanium metal or titanium alloy in the anodization process, titanium metal or titanium alloy can also be placed on other substrates to be anodized, where the size of the substrate used is dependant on the size of the anodization tank.

Another feature found in the anodization chamber (2) is cooling means where the cooling means is characterized by a plurality of cooling channels having an inlet cooling channel (8), an outlet cooling channel (9) and a plurality of interval connections (10). The inlet cooling channel (8), outlet cooling channel (9) and interval connections (10) are made of polypropylene where polypropylene is chosen due to its inertness towards the electrolyte solution (3). The main function of the cooling means is to reduce and maintain the temperature of the electrolyte solution (3). In order to reduce and maintain the temperature, coolant is introduced into the cooling means where the coolant chosen is water. Water is preferably chosen as a coolant due to its high specific capacity compared to other liquids. In order to reduce and maintain the temperature of the electrolyte solution (3), chilled coolant is introduced into the inlet cooling channel (8) where the coolant is than passed through the interval connections (10). Upon passing through the interval connections (10), the coolant absorbs heat from the electrolyte solution (3). The coolant with absorbed heat is then transferred out through the outlet cooling channel (9). Coolant with specific temperature can be introduced into the cooling means in order to obtain or maintain desired temperature. If the temperature of the electrolyte solution (3) is high, a coolant with a low temperature will be introduced. However, other coolant such as air or any other media can be used as long as it is a heat absorbent that is able to absorb generated heat from the electrolyte solution and maintain the temperature of the electrolyte solution.

Further another feature found in the anodization chamber (2) is the bubbling means which is characterized by an effervescing tube (7) that has a plurality of apertures. The effervescing tube (7) is placed at the bottom of the anodization chamber (2). An effervescing inlet channel (11) is connected to an air pump where the air pump supplies air through the effervescing inlet channel (11) to the effervescing tube (7) to produce bubbles, and controls the velocity of the air bubbles produced. The air pump supplies oil free compressed air to the effervescing tube (7) where the air passes through the apertures and enters the electrolyte solution (3) as bubbles. The bubbles that are produced from the effervescing tube (7) are used to homogenize the electrolyte solution (3) which is a mixture solution. Other homogenizing means that can also be used are such as magnetic stirring, ultrasonic mixing and conventional stirring.

It is observed that by using bubbling means, the aspect ratio obtained is higher than the one using magnetic stirring where the aspect ratio for bubbling and magnetic stirring is 92.09 and 86.36 respectively. Furthermore, the diameter and length of the titanium dioxide (Ti0 2 ) obtained is higher as compared to the one using magnetic stirring. The diameter and length of the titanium dioxide (Ti0 2 ) obtained from bubbling is 107nm and 9.9μηη respectively whereby the diameter and length of the titanium dioxide (Ti0 2 ) obtained from magnetic stirring is 105nm and 9.5 m respectively. The structure of the titanium dioxide (Ti0 2 ) nanotube arrays obtained using bubbling means is uniform throughout the surface compared to those formed using magnetic stirring. Moreover, the cost of using magnetic stirring is higher as compared to those using bubbling means which only includes effervescing tube (7) and air pump. In addition, bubbling means is simpler to manage and maintain as compared to magnetic stirrer. Therefore, bubbling means is preferably used in this invention. Also found in the anodization chamber (2) is the electrolyte circulating means which is characterized by a circulation inlet (12) and a pair of circulating channels (13), whereby the pair of circulating channels (13) are placed at the bottom of the anodization chamber (2). The purpose of this electrolyte circulating means is to circulate the electrolyte solution (3) in the anodization chamber (2). Before starting the anodization process, electrolyte solution (3) is filled into the anodization chamber (2) using this electrolyte circulating means. Electrolyte solution (3) is pumped into the anodization chamber (2) through the circulation inlet (12) and circulating channels (13) until the anodization chamber (2) is 80% filled. As the anodization chamber (2) is an open chamber, only 80% of the anodization chamber (2) is filled in order to accommodate the anionic electrodes (5). At the bottom of the anodization chamber (2), holes are constructed on the wall of the anodization chamber (2) to drain the electrolyte solution (3) out at the end of the anodization process. Referring to figure 5, it is showing the flow chart of the method for producing titanium dioxide (Ti0 2 ) nanotube arrays. The first step of the method is to prepare the anionic electrode (5). As mentioned earlier, the anionic electrode (5) used in this invention is titanium metal. However, the titanium metal has to be processed earlier before being used. After preparing the anionic electrode (5), the next step is to prepare the electrolyte solution (3). Also as mentioned earlier, the electrolyte solution (3) is a mixture of ethylene glycol (C 2 H 6 0 2 ), ammonium fluoride (NH 4 F) and hydrogen peroxide (H2O2). The mixture is prepared by first filling ethylene glycol (C2H6O2) into the mixing chamber. Then, ammonium fluoride (NH F) is added into the ethylene glycol (C 2 H 6 0 2 ) and stirred homogenously for 30 minutes. Thereafter, hydrogen peroxide (H 2 0 2 ) is added into the mixture and stirred homogenously for another 30 minutes. The pH of this mixture of electrolyte solution (3) is then determined using a pH meter. As in this invention, the pH of the electrolyte solution (3) required is neutral and therefore, if the electrolyte solution is acidic, sodium hydroxide (NaOH) is added adequately in order to bring the electrolyte solution (3) to neutral. On the other hand, if the electrolyte solution (3) is alkaline, sulfuric acid (H 2 SO is added adequately in order to bring the electrolyte solution (3) to neutral. After mixing, the electrolyte is filled into the anodization chamber (2). After preparing the electrolyte solution (3), the subsequent step is to perform the anodization process. The anodization process is performed under a specific condition where the condition is preferably but not limited to 25°C at around pH7 for 1 minute. At about 1 minute after the anodization process started, it is observed that titanium dioxide (Ti0 2 ) nanotube arrays are formed. Therefore in this invention, the anodization process is terminated after one hour and the anionic electrode (5) is removed from the electrolyte solution (3). The next step is to collect the titanium dioxide (Ti0 2 ) nanotubes by washing the anionic electrode (5) with acetone for 1 minute in ultrasonic bath in order to remove remaining electrolyte solution (3) and to eliminate precipitation formed on the titanium dioxide (Ti0 2 ) nanotubes. Subsequently, the anionic electrode (3) is placed in a furnace for annealing process.

Referring to figure 6, it is showing the flow chart diagram for the steps of preparing the anionic electrode (5). In this invention, titanium metal is used as anionic electrode (5). However, the titanium metal has to be processed before using it as anionic electrodes (5). The preferable thickness of titanium metal used in this invention is 0.125mm. The first step of the preparation is to shape the titanium metal into desired size and dimensions. Then, the titanium metal is immersed into ethanol and subsequently sonicated in ultrasonic cleaning bath. Thereafter, the titanium metal is rinsed with deionized water and dried later on. The dried titanium metal can then be used as anionic electrode (5).

Referring to figure 7, it is showing the flow chart diagram for the steps of performing the anodization process. The first step of performing the anodization process is to fill the anodization chamber (2) with electrolyte solution (3). As mentioned earlier, the anodization chamber (2) is an open chamber and therefore, the anodization chamber (2) is not fully filled with the electrolyte solution (3). After that, the anionic electrodes (5) are fixed onto the anionic electrode hanger (16). Then, the anionic electrode hanger (16) is hanged onto a hanging beam (15) where the hanging beam (15) is placed at the grooves of the beam support (14) mounted on the anodization chamber (2). The hanging beams (15) can be placed either horizontally or vertically on the grooves of the beam support (14) depending on the amount of anionic electrodes (5) used. Consequently, the anionic electrode (5) will be fully suspended in the electrolyte solution (3). As the anionic electrode hanger (16), hanging beam (15) and beam support (14) are made of preferably but not limited to copper, voltage is easily transferred through the anionic electrode hanger (16), hanging beam (15) and beam support (14). Thereafter, the anodization process is commenced by switching on the voltage source (4). The anodization process is performed at a preferably but not limited condition of 25°C at around pH7 for 1 minute. Subsequently, the anodization process is terminated by switching off the rectifier (4). Soon after switching off the rectifier (4), the anionic electrode (5) is removed out from the electrolyte solution (3).

Referring to figure 8, it is showing the FESEM images of titanium dioxide (Ti0 2 ) nanotube arrays obtained at 1 minute in 90wt% of ethylene glycol electrolyte containing 5wt% of hydrogen peroxide (H2O2) and 5wt% of ammonium fluoride (NH 4 F) at 60V by bubbling means. In the figure, the first image is showing top view of the titanium dioxide (Ti0 2 ) nanotube arrays formed in 1 minute whereby the second image is showing cross-sectional view of the titanium dioxide (Ti0 2 ) nanotube arrays formed in 1 minute. At about 1 minute after the anodization starts, titanium dioxide (Ti0 2 ) nanotube arrays are formed with diameter of 45.5nm and length of 2.25μηι. It is observed that the rate of formation of these titanium dioxide (Ti0 2 ) nanotube arrays is 2250nm/min, which is considered as a rapid rate of formation.