TECHNICAL FIELD

The present disclosure relates to a process of preparation of metal oxide-carbon nanotube composite by metal organic chemical vapour deposition (MOCVD). The process of the present disclosure involves simple pathways, takes less time than other processes for making such composites and provides better yield under less stringent reaction conditions than other processes.

The present disclosure also relates to metal oxide-carbon nanotube composite prepared by the process. These metal oxide-carbon nanotube composites are prepared as a homogeneous thin film or obtained as powder composite.

The present disclosure also relates to the application of metal oxide-nanotube composite in catalysis, chemical sensors, energy storage devices and magnetic data storage and other applications.

BACKGROUND

Metal oxide-carbon nanotube (CNT) composites have attracted significant research attention in recent years owing to their potential applications in catalysis, chemical sensors, energy storage devices, magnetic data storage etc. [S. lijima, Nature, 354, 56- 58.(1991); G.G. Wildgoose; C.E. Banks; R.G. Compton, Small, 2, 182-193(2006); P.J.F. Harris, Int. Mater. Rev. 49, 31-43,(2004); H. C. Zeng in Handbook of Organic-Inorganic Hybrid Materials and Nanocomposites; American Scientific Publishers: Stevenson Ranch, CA, 2003; Vol. 2: Nanocomposites, Chapter 4, pp 151-180; Cao Huiqun, Zhu Meifang, Li Yaogang, J. Solid State Chem., 179, 1208-1213(2006)].

Haematite, or a-Fe203, a highly stable, semiconducting, antiferromagnetic oxide has been investigated as photocatalyst, pigment, energy storage devices etc. [ J. Chen, L. Xu, W. Y. Li, X. L. Gou, Adv. Mater. 17, 582,(2005); M.A. Gondal, A. Hameed, Z.H. Yamani, A. Suwaiyan, Chem.Phys. Lett. 5.55,111(2004)].

Recently, a-FeaOa-MWNT composites have been investigated as electrode material for lithium ion batteries [Xin Zhao, Colin Johnston and Patrick S. Grant, J. Mater. Chem., 19, 8755-8760 (2009)].

In general, most of the methods used to prepare metal oxide-carbon nanotube composite (CNT) are multi-step processes which involve the synthesis of the oxide by a chemical route and the addition of pre-synthesized carbon nanotubes, or the catalytic growth of CNTs on the oxide nanoparticles. Currently available methods require more than one step for composite formation, and do not enable film formation on suitable, useful substrates. Depositions of such composite thin films by chemical routes (such as CVD) would normally involve separate precursor sources for each constituent of the composite. (However, metal oxide-CNT composites, either in thin film form or powder form, prepared a CVD process where more than precursor is used, have not yet been reported.) Homogeneous mixing, interfacial adhesion between the constituents of the composite, particle size control of the constituents are the main issues during the synthesis of thin films of such oxide-CNT composites by any available multi-step method. Adhesion of such a composite film to the substrate is an additional issue. Iron oxide-CNT composites are interesting due to their applications in catalysis and energy storage devices. Similarly, composites with oxides of other 3d metals of the periodic table would also be interesting and useful, for the same reasons that iron oxide-CNT composites would be useful (as already enumerated above). Even though Fe304-CNT composites have been synthesized by routes involving multi-step process, Fe203-CNT composites are less well studied. There are no reports on CNT composites with other metal oxides of group 3d. One important and extensively investigated class of electrode materials for supercapacitors is the composite formed by a suitable metal oxide and elemental carbon. Such composites are typically formed in the bulk by mixing the two components thoroughly and, for example, forming relatively thick coatings of such composites using slurry.
Therefore, there is a need for a process that is capable of producing metal oxide- CNT composite in a relatively simple way, which is also a single-step process. The process must be capable of providing high yield and the composite materials obtained should be homogeneous in composition and should have morphology appropriate for a variety of applications. The process must preferably be energy-efficient. The present invention discloses such a single-step process for synthesis of metal oxide-carbon nanotube composite by metal organic chemical vapour deposition (MOCVD). (The abbreviations MOCVD and CVD are used in the rest of this document interchangeably, for convenience, to mean the same process of the present invention.)

SUMMARY

The present disclosure relates to a single step process for preparation of a metal oxide-carbon nanotube composite comprising: depositing a metal oxide and carbon nanotubes simultaneously, from a metalorganic compound, preferably a metal beta diketonate complex precursor on a pre-heated substrate with deposition pressure maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes to obtain the metal oxide-carbon nanotube composite.

The present disclosure further relates to metal oxide-carbon nanotube composite synthesized by the process of the present disclosure. These metal oxide-carbon nanotube composites are synthesized as a homogeneous thin film or obtained as powder composite.

The present disclosure also relates to the application of metal oxide-nanotube composite in catalysis, chemical sensors, energy storage devices and magnetic data storage etc.
These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the disclosure, nor is it intended to be used to limit the scope of the subject matter.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other features, aspects, and advantages of the subject matter will become better understood with regard to the following description, appended claims, and accompanying drawings where:

Figure 1 shows X-ray diffraction pattern of a-Fe203-MWNT composite thin film on SS- 316 substrate.

Figure 2 shows Raman spectrum of a-FeaOs -MWNT composite thin film on SS-316
substrate at 10 mW. Figure 3 shows SEM micrograph of a-FeaOa-MWNT composite thin film. Figure 4 shows TEM micrograph of a-FeaOs-MWNT composite thin film obtained by scratching film.

Figure 5 shows X-ray diffraction patterns of films deposited at various pressures at
constant carrier gas flow rate. Figure 6 shows Raman spectrum of thin films deposited at various pressures at constant carrier gas flow rate.

Figure 7 shows Cyclic voltammogram of a-FeiOs-MWNTcomposite in 0.1 M Na2S04. Figure 8 shows Cyclic voltammogram of a-Fe203~MWNTcomposite in 0.1 M Na2S03. Figure 9 shows the SEM micrograph of a composite thin film of cobalt oxide and carbon nanotubes on a stainless steel substrate.

Figure 10 shows the SEM micrograph of a composite of a-Fe203 and carbon nanotubes in powder form.

DETAILED DESCRIPTION

The present disclosure relates to a process of preparation of metal oxide-carbon nanotube composites by metal organic chemical vapour deposition (MOCVD). The process of the present disclosure involves the use of a single precursor, from which both the metal oxide and the carbon nanotube (CNT) originate, thus simplifying the process and reducing the time taken for the process when compared to other processes for making such composites.
The present disclosure also relates to metal oxide-carbon nanotube composite prepared by the process. These metal oxide-carbon nanotube composites are prepared as a homogeneous thin film or obtained as powder composite.

The present disclosure also relates to the application of metal oxide-nanotube composite useful in catalysis, chemical sensors, energy storage devices, and magnetic data storage and other applications.

The present disclosure provides a single step process for preparation of a metal oxide carbon nanotube composite comprising; depositing a metal oxide and carbon nanotubes simultaneously, from metalorganic compound, preferably a metal beta diketonate complex, precursor on a pre-heated substrate with deposition pressure maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes to obtain the metal oxide-carbon nanotube composite.

The substrate used in the process for preparation of a metal oxide carbon nanotube composite thin film can be made of almost any material that is capable of withstanding (without degradation) the elevated temperatures used for the deposition (MOCVD) process. The substrate may specifically be selected from the group consisting of silicon, germanium, gallium arsenide, graphite, aluminium oxide, nickel, stainless steel, cobalt and an alloy consisting of at least one metal selected from a group consisting of iron, nickel, cobalt and steel or combination thereof. The substrate used for the process for preparation of a metal oxide-carbon nanotube composite of the present disclosure is heated in a furnace tube made of a suitable material, such as fused quartz, alumina, mullite, or steel. In a preferred embodiment, the substrate is heated in a quartz tube to a temperature in the range of 500°C to 900°C, preferably 700°C.

The metalorganic compound used in the process for preparation of a metal oxide carbon nanotube composite is a compound of either iron, cobalt, or nickel, or a metalorganic compound wherein more than one of these metals is present. Any metalorganic compound, which has direct metal-oxygen bonds within its molecular structure, may be used as the precursor for the MOCVD process of the present invention. In particular, metal beta-diketonate complexes may be used as precursors to obtain metal oxide-CNT composites described in this invention. The metal beta diketonate complex used in the process described herein for the preparation of metal oxide-carbon nanotube composites is either iron acetyl acetonate or cobalt (II) acetyl acetonate. Such acetyl acetonates are often abbreviated as acac's, for example, Fe(acac)3, ferric acetyl acetonate, which has been used to obtain the results described herein. The metal beta diketonate complex, ferric acetyl acetonate, is a crystalline compound, which may be vaporized (sublimated) at a temperature in the range of 140°C - 200 °C, preferably at 158°C, for preparation of the iron oxide-carbon nanotubes (CNTs) composite.

An embodiment of the present disclosure provides a single step process for preparation of a metal oxide-carbon nanotube composite comprising; depositing a metal oxide and carbon nanotubes simultaneously, from a metal beta diketonate complex precursor on a pre-heated substrate with deposition pressure maintained between 5 torr and 700 torr, preferably 10 torr, and deposition time between 1 minute and 120 minutes to obtain the metal oxide-carbon nanotube composite.

Yet another embodiment of the present disclosure provides a single step process for preparation of a metal oxide-carbon nanotube composite comprising; depositing a metal oxide and carbon nanotubes simultaneously, from a metal beta diketonate complex precursor on a pre-heated substrate with deposition pressure maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes, preferably 30 minutes, to obtain the metal oxide-carbon nanotube composite. It will be appreciated that the deposition time will affect the thickness of the deposition; longer the deposition time, thicker will be the deposit; and shorter the deposition time, thinner will be the deposit.

Further an embodiment of the present disclosure provides a single step process for preparation of a metal oxide-carbon nanotube composite comprising; depositing a metal oxide and carbon nanotubes simultaneously, from a metal beta diketonate complex precursor on a pre-heated substrate in the ambience of an inert gas selected from argon, helium, neon, krypton, xenon or nitrogen, preferably argon, with deposition pressure maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes to obtain the metal oxide-carbon nanotube composite.

In still another embodiment of the present disclosure, the CVD process described herein results in a metal oxide-CNT composite powder material, wherein the proportion of the metal oxide and CNT in the composite powder material can be varied by varying the substrate temperature, the substrate material, the pressure in the furnace tube, and by choosing a metalorganic compound which has in its molecular structure a larger or smaller proportion of carbon. In one particular embodiment, the process of the present disclosure provides metal-oxide-CNT composite wherein the composition range of 100% metal oxide to 100% MWNTs, with any mixed composition of oxide and MWNTs in between, for example, 50% oxide and 50% MWNTs.

In one aspect, the metal oxide-multiwall carbon nanotubes (MWNTs) composite prepared by the process of the present disclosure has the metal oxide and the carbon nanotubes in the range of 100% metal oxide to 100% carbon nanotubes.

The metal oxide-carbon nanotube composite obtained by the process of the present disclosure is in form of a powder composite material or a homogenous thin film. The metal oxide-carbon nanotube composite obtained by the process of the present disclosure is a metal oxide-multiwall carbon nanotube composite or a metal oxide-single wall carbon nanotube composite.
Still another embodiment of the present disclosure provides a process for preparation of an iron oxide-carbon nanotube composite, comprising: depositing small crystals of an oxide of iron and carbon nanotubes simultaneously from iron acetyl acetonate precursor on a pre-heated steel substrate with deposition pressure maintained between 5 torr and 700torr, deposition time between 1 minute and 120 minutes to obtain the iron oxide- carbon nanotube composite, wherein the oxide of iron is ferric oxide (Fe203) or magnetite (Fe304); and the iron acetyl acetonate is selected from ferrous acetylacetonate or ferric acetylacetonate.
Yet another embodiment of the present disclosure provides a process for preparation of an iron oxide-carbon nanotube composite, comprising: depositing small crystals of an oxide of iron and carbon nanotubes simultaneously from iron acetyl acetonate precursor on a pre-heated steel substrate in the ambience of an inert gas selected from argon, helium, neon, krypton, xenon, or nitrogen, preferably argon, with deposition pressure maintained between 5 torr and 700 torr, deposition time between 1 minute and 120 minutes to obtain the iron oxide-carbon nanotube composite, wherein the oxide of iron is ferric oxide (Fe203) or magnetite (Fe304); and the iron acetyl acetonate is selected from ferrous acetylacetonate or ferric acetylacetonate.

In a further embodiment, the present disclosure provides a single-step process for preparation of a metal oxide-carbon nanotube composite comprising: depositing a metal oxide and carbon nanotubes simultaneously, from metalorganic compound, preferably a metal beta diketonate complex, by transporting it into the heated zone of a furnace tube through the flow of an inert gas over the heated metalorganic compound. The inert gas, known as the carrier gas, may be selected from the group of argon, nitrogen, helium, krypton, or xenon, or a mixture of one or more of these inert gases. The pressure in the heated zone (furnace tube) is maintained between 5 torr and 700 torr, and the transport of vapours is continued for the time duration between 1 minute and 120 minutes, so as to obtain the metal oxide-carbon nanotube composite. The deposition pressure (that is, pressure in the furnace tube) is maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes, to obtain the metal oxide-carbon nanotube composite. The carbon nanotubes formed by the process of the present disclosure are single-walled, multiwalled, or a mixture of single- and multiwalled CNTs.

In a different embodiment of the present disclosure, the CVD process (for the formation of a composite film or composite powder) is carried out in the presence of a small amount of an oxidant gas (such as oxygen) or a reductant gas (such as hydrogen). The determination of whether to use such gases depends on the proportion of carbon in the molecular structure of the metalorganic precursor compound.

The process for synthesis of metal oxide-multiwall carbon nanotube composite by metal organic chemical vapor deposition (MOCVD) disclosed herein is a single-step process, wherein both the metal oxide and the CNT, which together form the composite, originate in the molecular structure of a single metalorganic compound, thus obviating the need for the use of more than one precursor for the formation of the metal oxide-CNT composite. This feature of the present disclosure simplifies the process and simplifies the apparatus required for the formation of the said composite, thereby resulting in a reduction of the cost of the CVD process.

Because of the use of a single precursor for the formation of the metal oxide-CNT composite, the single-step process for preparation of metal oxide-carbon nanotube composites of the present invention leads to more homogeneous compositions on a scale (nanometer-scale) not easily achieved by other methods. This is likely to mean better performance of any device based on such a composite. Compositional homogeneity can be retained even as composition is varied to achieve different material characteristics and, hence, different possible applications.

The present disclosure provides a metal oxide-carbon nanotube composite prepared by the process of the present disclosure wherein the metal oxide-carbon nanotube composite is a multiwalled carbon nanotube composite or a single-walled carbon nanotube composite. The oxide of cobalt in these composites is C03O4.

The metal oxide-multiwall carbon nanotubes (MWNTs) composite prepared by the process of the present disclosure can be used for in catalysis, chemical sensors, energy storage devices and magnetic data storage etc. These devices are made possible by the intimate, homogeneous, tailored composites of the present disclosure.

Homogeneous composite thin films of metal oxide and multi-walled carbon nanotubes (MWNTs) have been prepared in a novel, single-step process by metal-organic chemical vapor deposition (MOCVD), using metal beta diketonate complexes - as precursor. Such metal beta diketonate compounds contain direct metal-oxygen bonds, together with hydrocarbon or other organic moieties. The deposition of carbon in the form of multi¬walled nanotubes in copious amounts is a surprising result, because it is well known in the art that the formation of CNTs in a CVD process requires the presence of a fine metal catalyst, namely, iron, nickel, or cobalt. The present invention involves no such metal catalyst, and it is surmised that the metal beta diketonate compounds being employed act as both the catalyst and the carbon source.
Argon used in the process of the present disclosure as the carrier gas is at a flow rate in the range of 10 to 40 sccm. However, this is specific to the CVD system employed in arriving at this invention, and does not limit the scope of this invention because it is well known that the process parameters used in a CVD process vary from one CVD system to another, depending on whether the process chamber (furnace tube) is larger or smaller, and whether the CVD system is hot-walled or cold-walled, and so forth. For example, the flow rate of the carrier gas is usually higher (for a given process) in a larger CVD reactor than in a smaller CVD reactor.
As is well known in the relevant art, CVD processes (including MOCVD) can be scaled up to produce large-area coatings of uniform thickness and composition, as well as to obtain uniform coatings on substrates of arbitrary shape. This enables the use of such coatings in different applications.

The CVD apparatus and the process may also be engineered to produce larger or smaller amounts of the metal oxide-CNT powder composite material.

The process for synthesis of metal oxide-multiwall carbon nanotubes (MWNTs) composite by metal organic chemical vapor deposition (MOCVD) is a single step process.

The single step process for preparation of a metal oxide-carbon nanotube composite leads to more homogeneous compositions on a scale (nanometer-scale) not easily achieved by other methods. This is likely to mean better performance of any device based on such a composite. Compositional homogeneity can be retained even as composition is varied to achieve different material characteristics and, hence, different possible applications.

The CVD processes (including MOCVD) can be scaled up to produce large-area coatings of uniform thickness and composition, as well as uniform coatings on substrates of arbitrary shape. This enables the use of such coatings in different applications.

An embodiment of the present disclosure provides an iron oxide-carbon nanotube composite prepared by a process of the present disclosure wherein the iron oxide-carbon nanotube composite is a multiwalled carbon nanotube composite or a single-walled carbon nanotube composite.

Another embodiment of the present disclosure provides a cobalt oxide-carbon nanotube composite prepared by a process of the present disclosure wherein the cobalt oxide-carbon nanotube composite is a multiwalled carbon nanotube composite or a single- walled nanotube composite.

The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to be restrictive or to imply any limitations on the scope of the present disclosure.

EXAMPLES

The disclosure will now be illustrated with working examples, which is intended to illustrate the working of disclosure and not intended to be restrictive or to imply any limitations on the scope of the present disclosure.

EXAMPLE 1

The Chemical Vapor Deposition (CVD) precursor, iron acetyl acetonate, ((Fe(CH3CH(CO)2CH3)3), [abbreviated as Fe(acac)3], a subliming crystalline solid, was synthesized and purified using procedure known in the art. The formation of the said CVD precursor was confirmed using mass spectroscopy, infrared spectroscopy and elemental analysis. The substrate used was stainless steel (SS316) pieces, measuring about 10 mm x 10 mm, and ~1 mm in thickness. The stainless steel pieces were cleaned in soap solution followed by washing with distilled water, methanol, and acetone, in that sequence. The substrate and precursor were loaded into the quartz tube (CVD reaction chamber or furnace tube) and the precursor vaporizer, respectively. They were heated to desired temperature by resistive heating, under accurate feedback control of temperature. The precursor was heated in the vaporizer to 158° C, a temperature selected by measuring the precursor sublimation characteristics, and the vapors were carried by argon to the deposition chamber. The film depositions were carried out over a range of conditions, wherein the pressure in the CVD chamber and carrier gas flow rate were varied, while keeping the substrate temperature constant, as also the duration of deposition (Table 1). After the deposition was concluded by terminating precursor flow, the substrate was allowed to cool to room temperature under flowing argon. Thus, a-Fe203-MWNT (multi wall carbon nanotubes) composite films were obtained. By varying one of the CVD process conditions, namely the reactor pressure, the proportion of the oxide and the CNT in the resulting film can be varied.

Table 1: One of the ranges of CVD conditions employed

EXAMPLE 2

Characterization of a-FeiO^-MWNT composite by X-ray diffraction:

The a-Fe203-MWNT composite films prepared in Example 1 were characterized by powder X-ray diffraction (Bruker D8 Advance instrument, with Cu-Ka X-ray source).

Figure 1 shows the X-ray diffraction pattern of the films deposited at 700°C, at a chamber pressure of 10 torr, under a carrier gas (argon) flow rate of 30 seem. The pattern features two prominent peaks corresponding to the (104), (110) planes of a-Fe203, with considerable broadening due to the nanocrystalline nature of the oxide.

EXAMPLE 3

Characterization of a-Fe^O^-MWNT composite by Raman Spectroscopy:

The a-Fe203-MWNT composite films prepared in Example 1 were characterized by Raman spectroscopy (LabRam HR-Raman and MicroPL using 514 nm laser).

Figure 2 depicts the Raman spectrum taken with a lOOX microscope objective at a laser power 10 mW. To be consistent with the XRD data identifying the deposition of a- Fe203, the Raman spectrum should feature 7 phonon lines, namely, two Aig modes (225 and 498 cm"') and five Eg modes (245, 293, 299, 411 & 612 cm"'). [D.L.A. de Faria, S.Venancio Silva and M.T.de Oliveira, J.Raman Spectroscopy,28, 873-878(1997)]. However, the Raman shift in the film deposited at 10 torr correspond to 219, 287, 406, 494, 606 cm"'. That is, the peaks are shifted towards lower wave numbers, and the peaks have increased line widths, as can be seen fi-om figure 2. Furthermore, the Raman spectrum of this film grown at 10 torr also contains peaks characteristic of carbon nanotubes, viz., the tangential mode corresponding to the Raman-allowed optical mode E2g of 2-D graphite centered at 1586 cm''(G-band), and a peak centered around 1342 cm''(D- band), mainly due to the defects present.

As CVD chamber pressure is varied at a fixed flow rate of argon, the composition of the deposited film composition changes firom being purely Fe203 to MWNT/Fe203 composite to mainly MWNTs. In figure 5 and figure 6, a comparison of the X-ray diffraction patterns and of the Raman spectra, corresponding to the films deposited at various pressures is shown. Films deposited at 5 torr shows sharp XRD peaks corresponding to a-Fe203, with no D, G peaks, characteristic of MWNTs, are present in the Raman spectrum. As deposition pressure is increased to 30 torr, the resulting films show no Raman peaks characteristic of MWNTs as shown in figure 6.

This example illustrates that, by choosing a suitable CVD process parameter such as the reactor pressure, it is possible to alter the proportion of metal oxide and CNT in the resulting composite.

EXAMPLE 4

Characterization of a-Fe2O3-MWNT composite by Scanning Electron Microsocopy:
The a-Fe203-MWNT composite films prepared in Example 1 were characterized by scanning electron microscopy (Quanta LV/ESEM at 25kV) and by transmission electron microscopy. The typical SEM micrographs of the films grown on stainless steel SS316 substrates are as shown in figure 3. The observed microstructures are in accordance with the findings from XRD and Raman spectroscopy, that Fe203 nanoparticles are deposited along with CNTs. The oxide particles seem to decorate CNT walls as can be seen from TEM micrographs of the composite in figure 4.

EXAMPLE 5

Electrochemical characterization of a-Fe203-MWNT composite films was carried out in the three-electrode configuration at room temperature on an electrochemical analyzer (Eco Chemie PGSTAT302N). Platinum foil was used as counter electrode and standard calomel electrode,Ag/AgCl was used as reference electrode in 0.1 M Na2S04 and O.1M Na2S03 electrolyte solution, respectively.

Figure 7 and figure 8 shows the cyclic voltammograms obtained at a scan rate of 5 mV/s when a Fe203-CNT composite film was used as electrode material, employing O.IM Na2S04 and O.IM Na2S03 as the electrolyte, respectively.

The CV curve corresponding to the composite thin film electrode shows nearly rectangular behaviour in sodium sulphate electrolyte and the capacitance was deduced to be 4 F/g (figure 7). However, when O.IM Na2S03 is the electrolyte (figure 8), it is evident from the voltammogram, that some redox reactions also take place at the electrode, together with the double layer capacitive action. Due to non-rectangular shape of the voltammogram, the average capacitance was calculated from following equation [Hui Pan, Chee Kok Poh, Yuan Ping Feng, and Jianyi Lin, Chem. Mater. 19, 6120-6125(2007)].

Cave=q/(AVm)=l/0.9mv of 0.9 /(V)dV, where m=loading, v is the scan rate, and of 0.9 i(V)dV corresponds to the area under the CV curve. The capacitance was calculated to be 163 F/g.

EXAMPLE 6

The stainless steel pieces measuring about 10 mm x 10 mm, and ~1 mm in thickness were cleaned in soap solution followed by washing with distilled water, methanol, and acetone, in that sequence. The substrate and precursor, namely Fe(acac)3, were loaded into the quartz tube and the precursor vaporizer, respectively. They were heated to desired temperature by resistive heating, under accurate feedback control of temperature. The precursor was heated in the vaporizer to 158° C, a temperature selected by measuring the precursor sublimation characteristics, and the vapors were carried by argon to the deposition chamber, as in example 1. Further details of the CVD conditions employed in Example 6 are listed in Table 2.

Table 2: CVD conditions employed in Example 6

The CVD process carried out under the conditions listed in Table 2 results in a composite powder material in which both FeaOs and multi-walled carbon nanotubes (MWNTs) are present, as in Figure 6.

EXAMPLE 7

The stainless steel pieces measuring about 10 mm x 10 mm, and ~1 mm in thickness were cleaned in soap solution followed by washing with distilled water, methanol, and acetone, in that sequence. The substrate and precursor, namely cobalt(II) acetylacetonate or Co(acac)3, were loaded into the quartz tube and the precursor vaporizer, respectively. They were heated to desired temperature by resistive heating, under accurate feedback control of temperature. The precursor was heated in the vaporizer to 170° C, a temperature selected by measuring the precursor sublimation characteristics, and the vapors were carried by argon to the deposition chamber, as in example 1. CVD was carried out under conditions shown in Table 3.
Table 3: CVD conditions employed in Example 7
The resulting film is a composite, in which both C03O4 and MWNTs are present, which is shown in Fig.9.

EXAMPLE 8

Table 4: CVD conditions employed in Example 8

Using process conditions given in Table 4 above, and using ferric acetyl acetonate as the precursor, a powder composite material made of a-FeaOa and CNTs was obtained. This is shown in Fig. 10.

The present invention and equivalent thereof have many advantages, including those which are described below.

a. The process is quick, consumes a relatively small amount of energy and time than other techniques for the formation of metal oxide-CNT composites, wherein CNTs and the metal oxide are produced by separate processes and then mixed together.

b. The process is capable of producing metal oxide-multiwall carbon nanotubes (MWNTs) composite of desired composition in a single step, using a single precursor, reducing the complexity of the apparatus required for producing composite materials of the kind described in this invention. The metal oxide-multi wall carbon nanotubes (MWNTs) composite films produced by the process are homogeneous in composition, and can be produced over large substrate areas and over substrates of arbitrary shape.

c. The process of the present disclosure may be employed to produce thin films of the metal oxide-CNT composite, or the composite material in powder form.

d. The process of the present disclosure obviates the need for a fine powder metal catalyst that is required for the formation of CNTs in CVD processes described in the prior art.
e. The process of the present disclosure may be used to prepare composites of CNT with the oxides of different metals, namely, iron, nickel, and cobalt or a combination thereof
f The process may also be used to obtain metal oxide-single wall carbon nanotubes composites.

Although the subject matter has been described in detail with reference to certain embodiments thereof, other embodiments are also possible. As such, the spirit and scope of the present invention disclosed should not be limited to the description of the preferred embodiments contained therein.

We Claim:

1. A single step process for preparation of a metal oxide-carbon nanotube composite comprising:

depositing a metal oxide and carbon nanotubes simultaneously, from a metal beta diketonate complex precursor on a pre-heated substrate with deposition pressure maintained between 5 torr and 700 torr, and deposition time between 1 minute and 120 minutes to obtain the metal oxide-carbon nanotube composite.

2. The process as claimed in claim 1, wherein the substrate is selected from the group consisting of silicon, germanium, gallium arsenide, graphite, aluminium oxide, nickel, stainless steel, cobalt and an alloy consisting of at least one metal selected from a group consisting of iron, nickel, cobalt and steel or combination thereof.

3. The process as claimed in claim 1, wherein the deposition pressure is 5 torr to 700 torr and the duration of deposition of the vaporized precursor on the substrate is 1 minute to 120 minutes.

4. The process as claimed in claim 1, wherein an oxidizing gas, such as oxygen, or a reducing gas, such as hydrogen, is introduced into the reaction chamber so that the composition of the gaseous ambient of the reaction chamber is made of an inert gas to the extent of at least 90 volume present.

5. The process as claimed in claim 1, wherein the metal in the metal beta diketonate complex is selected from iron, cobalt, or nickel, or combinations thereof.
6. The process as claimed in claim 1, wherein the metal oxide-carbon nanotube composite is in form of a powder composite material or a homogenous thin film..

7. The process as claimed in claim 1, wherein the metal beta diketonate complex is iron acetyl acetonate.

8. The process as claimed in claim 1, wherein the metal beta diketonate complex is cobalt(II) acetyl acetonate.

9. The process as claimed in claim 1, wherein the metal oxide-carbon nanotube composite obtained is a metal oxide-multiwall carbon nanotube composite or a metal oxide-single wall carbon nanotube composite.

10. The process for preparation of an iron oxide-carbon nanotube composite as claimed in claim 1, comprising:

depositing small crystals of an oxide of iron and carbon nanotubes simultaneously, from iron acetyl acetonate precursor on a pre-heated steel substrate with deposition pressure maintained between 5 torr and 700 torr, deposition time between 1 minute and 120 minutes to obtain the iron oxide-carbon nanotube composite, wherein the oxide of iron is ferric oxide (Fe203) or magnetite (Fe304); and the iron acetyl acetonate is selected from ferrous acetylacetonate or ferric acetylacetonate

11. The process as claimed in claim 10, wherein the iron oxide-carbon nanotube composite is an iron oxide-multiwall carbon nanotube composite or an iron oxide- single wall carbon nanotube composite.

12. The process as claimed in claim 1, wherein the deposition of the metal oxide on the substrate is conducted in the ambient of an inert gas selected from argon, helium, neon, krypton, xenon, or nitrogen, or combinations thereof

13. A metal oxide-carbon nanotube composite prepared by a process as claimed in any of the preceding claims wherein the metal oxide-carbon nanotube composite is a multiwalled carbon nanotube composite or a single-walled carbon nanotube composite.

14. The metal oxide-carbon nanotube composite as claimed in claim 13 wherein the metal oxide OS iron oxide or cobalt oxide.

15. The composite as claimed in claims 13 or 14 wherein the metal oxide and the carbon nanotubes is in the range of 100% metal oxide to 100% carbon nanotubes.