KR20060102632A - Method for preparing metal oxide nanostructure - Google Patents

Abstract

The present invention uses a carbon black having a surface area of 30 m ² / g or more in the method for producing a metal oxide nanostructure, more specifically, a method for producing a metal oxide nanostructure using carbon thermal reduction (Carbothermal Reduction). By reducing the metal oxide to a gaseous metal efficiently at a relatively low temperature to a method for producing a variety of metal oxide nanostructures.

In the present invention, the metal oxide is preferably a metal oxide having a stoichiometric ratio of MO, M ₂ O ₃ or MO ₂ , wherein M is one or more metal elements, and O is an oxygen atom, most preferably oxidation Zinc, gallium oxide or titanium oxide.

Nanowire, Nanostructure, Metal Oxide, Thermal Reduction, Carbothermal Reduction, Carbon Black

Description

Method for Preparing Metal Oxide Nanostructure

1 is a schematic view of a reactor for the production of metal oxide nanostructures.

Figure 2 is a scanning electron micrograph of the zinc oxide nanostructures prepared by changing the carbon type in the thermal reduction reaction using carbon [(a): graphite used, (b) ~ (e): surface area per unit weight of 100 using carbon black with m ² / g, 200 m ² / g, 800 m ² / g, 1600 m ² / g]

FIG. 3 is a graph of carbon in thermal reduction reaction using carbon and carbon black having a surface area of 100 m ² / g, 200 m ² / g, 800 m ² / g, and 1600 m ² / g, respectively. Graph showing the analysis results of an X-ray photoelectron spectrometer of the zinc oxide nanostructures prepared according to the present invention.

Figure 4 is a scanning electron micrograph of the zinc oxide nanorods prepared according to an embodiment of the present invention.

Figure 5 is a scanning electron microscope photograph taken after the experiment according to a comparative example not according to the present invention.

Figure 6 is a scanning electron microscope photograph of the zinc oxide nanostructures prepared in accordance with an embodiment of the present invention.

Figure 7 is a scanning electron microscope photograph of the zinc oxide nanostructures prepared according to an embodiment of the present invention.

8 is a scanning electron microscope photograph of the gallium oxide (Ga ₂ O ₃ ) nanostructures prepared in accordance with an embodiment of the present invention.

9 is a scanning electron micrograph of the titanium oxide (TiO ₂ ) nanostructures prepared according to an embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

1: quartz tube 2: raw material consisting of a mixture of carbon and metal oxides

3: container of raw materials 4: substrate

The present invention provides a method for producing metal oxide nanostructures having a stoichiometric ratio of metal oxides, preferably MO, M ₂ O ₃ , MO ₂ , where M is one or more metal elements and O is an oxygen atom, Preferably, in the method for producing a metal oxide nanostructure by using carbon thermal reduction (Carbothermal Reduction), the method for producing a metal oxide nanostructure, characterized in that the carbon black having a surface area of 30 m ² / g or more is used. It is about.

Nanostructures of metal oxides, especially metal oxides having a stoichiometric ratio of MO, M ₂ O ₃ , MO ₂ , such as zinc oxide, gallium oxide, titanium oxide, tin oxide, indium oxide, etc., are semiconducting, piezoelectric, ferroelectric, and ferromagnetic. It has a variety of properties. In particular, recent studies have been actively conducted to use such nanostructures in various types of catalysts, transparent conductive films, sensors, photoelectric devices, and energy conversion devices.

Conventional methods for manufacturing metal oxide nanostructures are known, but among them, the method using carbon thermal reduction (Carbothermal Reduction) is simple, inexpensive, and a large amount of powder and carbon powder When mixed and heated to a high temperature, metal oxide nanostructures can be obtained through the reaction steps (a) and (b), and thus, much research has recently been conducted in this field.

Carbothermal Reduction using carbon for the preparation of the metal oxide nanostructures is performed through the following steps.

First, when the metal oxide powder and the carbon powder as a raw material is mixed and heated to a high temperature, the reaction steps (a) and (b) are performed.

M _x O _y (s) + yC (s) → xM (g) + yCO (g) (a)

yCO (g) + M _x O _y (s) → yCO ₂ (g) + xM (g) (b)

In the above scheme, M represents one or more metal elements, and x and y are numbers determined by the valence of the metal.

As a result of the reaction, M _x O _y (s) powder in the solid state as a raw material is reduced to M (g) in the gas state. The M (g) thus formed is oxidized back to M _x O _y (s) of various nanostructures in a properly designed reactor (see steps (c) and (d) below).

xM (g) + yCO (g) → M _x O _y (s) + yC (s) (c)

yC (s) + yCO ₂ (g) → 2yCO (g) (d)

In the above scheme, M, x and y are the same as described above.

In other words, the process of forming the metal oxide nanostructures through the above reaction steps is called carbon thermal reduction.

In conventional carbon thermal reduction using carbon, graphite has been used as a carbon powder used as a raw material. In this case, the solid phase reaction of M _x O _y (s) and C (s) in the reaction step (a) is not smooth. Therefore, in order to smoothly reduce M _x O _y (s) to M (g), a high temperature reaction was required or an additional gas-controlled feeder had to be added.

In addition, according to the recent literature, single-walled carbon nanotubes may be used to activate the solid phase reaction (reaction step (a)), but single-walled carbon nanotubes are expensive raw materials produced in small amounts. Has a major disadvantage that it is not suitable for mass production. {Ref .: CM Lieber and P. Yang, US005897945A; HT Ng et al . Science 300 , 1249 (2003); D. Banerjee et al . Appl. Phys. Lett. 83 , 2061 (2003); CX Xu et al. Appl. Phys. Lett. 83 , 3806 (2003); ZL Wang, Materials Today 7 , 26 (2004); YH Leung, Chemical Physics Letters 394 , 452 (2004)}.

Therefore, the inventors of the present invention, when manufacturing a metal oxide nanostructure using carbon thermal reduction (Carbothermal Reduction), using carbon black having a low surface area but a large surface area to activate the solid-phase reaction in a variety of forms at relatively low temperatures The present invention was completed by discovering that the metal oxide nanostructure of the compound can be prepared.

The present invention activates the solid phase reaction in the thermal reduction reaction using carbon nanowire, nanorod, nanoplate, nanocomb, nanobelt, nanospring, tetrapod Metal oxide nanostructures having a stoichiometric ratio of MO, M ₂ O ₃ and MO ₂ , such as various metal oxides such as (tetrapod), in particular zinc oxide, gallium oxide, titanium oxide, tin oxide and indium oxide, are produced at relatively low temperatures. It is to provide a method for producing a metal oxide nanostructure that can be.

Hereinafter will be described in detail with respect to the present invention.

The present invention provides a method for producing metal oxide nanostructures having a stoichiometric ratio of MO, M ₂ O ₃ , MO ₂ , such as metal oxides, in particular zinc oxide, gallium oxide, titanium oxide, tin oxide, indium oxide, and more specifically In the method for producing a metal oxide nanostructure by using a carbon thermal reduction reaction (carbothermal reduction), a method for producing a metal oxide nanostructure, characterized in that the carbon black having a surface area of 30 m ² / g or more will be.

In the method of the present invention, carbon black is used as a raw material instead of graphite, which is conventionally used, and mixed with metal oxide powder. Graphite, which has been used in the past, has a surface area per unit weight of less than 10 m ² / g, and the solid phase reaction (reaction step (a)) is not smooth, requiring a high temperature or ancillary gas control supply device.

However, the carbon black used in the present invention has a surface area of 30 m ² / g or more. Therefore, when carbon black is mixed with metal oxide powder and heated, the solid phase reaction between C (s) and M _x O _y (s), which forms M (g), is promoted, compared to graphite, so that the metal oxide nanostructure is relatively low. Can be prepared.

Carbothermal Reduction using carbon is carried out under suitable conditions for the preparation of the desired nanostructure by putting a raw material mixed with carbon black and metal oxide powder having a surface area of 30 m ² / g or more per unit weight in an appropriately designed reactor. do.

1 is a schematic diagram of a reactor having a temperature gradient for preparing a metal oxide nanostructure. Reference numeral 1 denotes a quartz tube, reference numeral 2 denotes a raw material composed of a mixture of carbon powder and metal oxide powder, reference numeral 3 denotes a container of raw material stable at high temperature, and reference numeral 4 denotes a nanostructure of metal oxide. Is the substrate to be formed.

The quartz tube is mounted in a tubular high temperature furnace, with a gradient in the direction of decreasing temperature from A to B. The container 3 containing the raw material is usually in the range of 1000 to 1400 ^° C. if the carbon is graphite, and the substrate 4 is suitably positioned at a lower temperature, depending on the desired structure, or in some cases, the container. It may be located above (3). In the reactor configured as described above, the metal oxide of the raw material 2 is deprived of oxygen by carbon and is reduced to a gaseous state M (g) to move along a temperature gradient to form a metal oxide nanostructure on the substrate 4. In addition, even when the substrate 4 is positioned on the container 3 without a temperature gradient, M (g), which is also reduced to a gaseous state, forms a nanostructure on the substrate in the state of a metal oxide.

In the method of the present invention, the mixing ratio of the carbon black and the metal oxide powder depends on the reaction temperature, that is, the heating temperature of the raw material container and the temperature on the substrate, the type of the metal oxide nanostructure to be manufactured, the surface area of the carbon black used, the heating time, and the like. It does not necessarily need to be limited to the specific range in the mixing ratio, Preferably it exists in the range of 10: 1-1:10 (weight ratio).

In addition, the carbon black used in the present invention should have a surface area of 30 m ² / g or more. If the surface area of the carbon black is less than 30 m ² / g, the function of activating the solid phase reaction is weak and it becomes difficult to proceed the reaction at a low temperature of the desired degree. Preferably the surface area of the carbon black is advantageously between 100 and 2500 m ² / g.

In the method of the present invention, a container containing a raw material, which is a mixture of carbon black and metal oxide powder, in a conventional method, a relatively low temperature of 600 to 1,000 ^o C or less, in which nanostructures of metal oxides such as zinc oxide are difficult to form. The metal oxide nanostructure may be formed even by heating in the range.

In the process of the invention, the heating temperature of the vessel is advantageously present in the range of 600 ^° C. to 1500 ^° C. If the heating temperature is less than 600 ^o C, even though carbon black having a large surface area is used, the degree of formation of the metal oxide nanostructures is insignificant. If the heating temperature is more than 1500 ^o C, energy consumption is high, and the metal oxide nanostructures are rather This is because it may be reduced.

Heating time of a container changes with reaction conditions, and is not specifically limited.

The temperature of the substrate also depends on the type of metal oxide nanostructure to be formed, the heating temperature of the raw material container, the mixing ratio of the raw materials, the surface area of the carbon black, and the like, and is not particularly limited.

As the substrate, a substrate may be used in the group consisting of a semiconductor substrate commonly used such as Si and Ge, a glass substrate, a GaN having a structure similar to ZnO, a sapphire substrate, and an oxide substrate such as ZnO or MgO. Preferably, Si, Sapphire, GaN substrates are advantageous.

When the metal oxide nanostructure is manufactured by thermal reduction using carbon, a metal catalyst may be deposited on a substrate for efficient production thereof. As the metal catalyst, any one of those commonly used in the art may be used. Preferably, at least one selected from the group consisting of Au, Cu, Pt, Pd, Ir, and Co is used.

In the process of the invention, a separate gas supply does not necessarily have to be present.

If the method of the present invention is a method for producing a metal oxide nanostructure by thermal reduction reaction using carbon, can be applied regardless of the type of metal oxide, more specifically, titanium, zirconium, hafnium, vanadium, niobium, tantalum , Chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, osmium, cobalt, nickel, copper, zinc, scandinium, yttrium, lanthanum, lanthanum-based elements (e.g., cerium, prazeodymium, Neodymium, promethium, samarium, pyrodium, gadolinium, terbium, disprogium, holium, erbium, turrium, iterbitum and lutetium), boron, aluminum, gallium, indium, thallium, And oxides of at least one metal element selected from the group consisting of silicon, germanium, tin, lead, magnesium, calcium, strontium and barium.

Preferably it can be applied to metal oxides having a stoichiometric ratio of MO, M ₂ O ₃ , MO ₂ . Here, M may be a single metal element or a mixed state of two or more metal elements.

More preferably, the metal oxide is advantageously zinc oxide, gallium oxide, titanium oxide, tin oxide, indium oxide, and more particularly in the case of zinc oxide, gallium oxide, titanium oxide. Most preferably the method of the present invention is better applied when producing zinc oxide nanostructures.

The metal oxide nanostructures prepared according to the method of the present invention are nanowires, nanorods, nanoplates, nanocombs, nanobelts, nanosprings, nanosprings, Various forms of shapes, such as tetrapod, can be selectively taken.

Normally, nanowires have a diameter of 10 to 50 nm and a length of 100 nm or more, nanorods have a diameter of 50 nm to 200 nm, a length of 100 nm or more, and a nanoplate having a thickness of 50 nm or more and a width of 1 μm or more. Has In addition, the nano-comb is a nano-comb is a form in which the nanorods or nanowires are arranged in a comb-tooth form on the nanoplate.

Hereinafter, experimental examples and preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

Experimental Example 1

This experimental example relates to an experiment showing the surface area effect of carbon. Zinc oxide powder was selected as the metal oxide powder to test the surface area effect of carbon.

In a reactor having a structure as shown in FIG. 1, a Si substrate is placed on a container of raw materials, and 0.2 g of raw materials mixed with carbon (graphite or carbon black) and zinc oxide powder in a 1: 1 (weight ratio) ratio is 30 ^° C. in air at 30 ^° C. The experiment was performed to produce a zinc oxide nanostructure without a separate gas supply by heating for a minute. At this time, the substrate used was made of Si, the temperature of the substrate was 800 ^° C. Carbon black was used to have a surface area per unit weight of 100 m ² / g, 200 m ² / g, 800 m ² / g, and 1600 m ² / g, respectively.

Results of the zinc oxide nanostructures formed on the substrate are shown in FIGS. 2 and 3. Figure 2 is a scanning electron micrograph showing the surface area effect of carbon (a) is the case of using graphite having a surface area of 3 m ² / g, (b) ~ (e) are each 100 m ² / surface area per unit weight It is a photograph about the reaction product when the carbon black which is g, 200 m <^2> / g, 800 m <^2> / g, and 1600 m <^2> / g is used as a raw material.

In FIG. 2A, no zinc oxide nanostructures were formed, and only nanoparticles of Au used for efficient production of zinc oxide nanostructures were observed. However, FIG. 2 (b), in which carbon black having a surface area of 100 m ² / g is used, shows that some zinc is applied to the surface of the substrate to form nano domains. In this case, the metal catalyst is mixed with the case where it is not reacted with the nano domains, and thus, zinc coating is not sufficient under the present experimental conditions. Figure 2 (C) is a case of using a carbon black having a surface area of 200 m ² / g, it can be seen that most of the surface is coated with zinc compared to Figure 2 (b). In Figure 2 (d) when using the carbon black surface area of 800 m ² / g when the nano rods (Nanorod) is the use of carbon black shows that some form, and finally, a specific surface area of 1600 m ² / g to the surface of the substrate In Figure 2 (e) shows that the nanorods started to grow in Figure 2 (d) is much more grown. Therefore, FIG. 2 shows that zinc oxide nanostructures can be efficiently produced when carbon black having a large surface area is used as a raw material, and zinc oxide nanostructures are more efficiently formed as the surface area of carbon black increases.

3 is an X-ray photoelectron spectroscopy (XPS) analysis result of the nanostructure shown in FIG. 2 (horizontal axis: unit m ² / g (where G means graphite), and vertical axis: unit atom) %], Which clearly shows the tendency of more Zn atoms to be applied to the surface of the substrate as the surface area of carbon used as raw material increases. Therefore, the surface area effect of carbon on the nanostructure formation shown in Figure 2 was confirmed once again through XPS analysis.

Example 1

Nanostructures of zinc oxide were prepared on a Si substrate on which a metal catalyst Au having a size of 10 to 20 nm was deposited. In this experiment, 0.2 g of a raw material with a mixture of carbon black and ZnO powder having a surface area of 800 m ² / g and ZnO powder at a temperature range of 850 ^o C, much lower than the temperature range of 1000 to 1400 ^o C, was used. It was carried out by heating for a minute. At this time, the temperature of the substrate was 650 ~ 850 ℃. 4 is a scanning electron micrograph showing the zinc oxide nanorods formed as a result of this experiment, (A) and (B) are measured at 20,000 times and 100,000 times magnification, respectively. The zinc oxide nanorods formed at this time had a diameter of 50 to 150 nm and a length of about 1 μm.

Comparative Example 1

This experiment is the result of a control experiment of Example 1. This experiment was carried out under the same conditions as in Example 1 using conventional graphite (surface area: 3 m ² / g) rather than carbon black having a surface area of 800 m ² / g. 5 is a scanning electron micrograph showing the results of this experiment, (a) and (b) are measured at 20,000 times and 100,000 times magnification, respectively. Unlike FIG. 4, which is the result of Example 1, no zinc oxide nanostructures were formed, and only the shape of Au catalyst having a size of 10 to 50 nm originally present on the Si substrate was shown.

Example 2

In this example, the experiment was carried out under the same reaction conditions as in Example 1 except for using carbon black having a surface area of 800 m ² / g, heating the raw material at 950 ^° C., and controlling the temperature of the substrate as follows. Zinc oxide nanostructures were formed. 6 is a scanning electron micrograph showing the results of this experiment, when the temperature of the substrate is 930 ℃ (A) zinc oxide nanowires, (900) (Zn) zinc oxide nano pins Formed.

Example 3

In this embodiment, carbon black having a surface area of 800 m ² / g is used, and a raw material having a weight ratio of carbon black and ZnO 1: 4 is heated at 1050 ^° C., except that the temperature of the substrate is controlled as follows. The experiment was performed under the same reaction conditions as in Example 1 to form a zinc oxide nanostructure. 7 is a scanning electron micrograph showing the results of this experiment, when the temperature of the substrate is 950 ~ 1000 ℃ (A) zinc oxide nano comb teeth, 930 ~ 970 ℃ ((B)) oxidation Zinc tetrapod was formed.

Example 4

In this embodiment, carbon black having a surface area of 1600 m ² / g is used, gallium oxide (Ga ₂ O ₃ ) powder is used instead of zinc oxide, and raw materials are heated at 1,000 ^o C. Experiments were performed under the same reaction conditions to form gallium oxide nanostructures. 8 is a scanning electron micrograph showing the results of this experiment, (a) and (b) are measured at 20,000 times and 100,000 times magnification, respectively. It can be seen that rod-shaped gallium oxide having a thickness of about 20 nm was formed.

Example 5

In this embodiment, carbon black having a surface area of 1600 m ² / g is used, titanium oxide (TiO ₂ ) powder is used instead of zinc oxide, and the same reaction as in Experiment 1 except that the raw materials are heated at 1,000 ^° C. Experiments were performed under the conditions to form a titanium oxide nanostructure. Figure 9 is a scanning electron micrograph showing the results of this experiment, (a) and (b) are measured at the magnification of 5000 times and 10 million times, respectively. Triangular titanium oxide nanoplatelets were formed together with the titanium oxide nanorods having a thickness of about 20 nm.

As can be seen from the above experimental results, the present invention of preparing a metal oxide nanostructure using carbon black having a large surface area of carbon has an effect of forming a metal oxide nanostructure even though the reaction temperature can be lowered by at least 150 ^o C or more. Can be. In addition, the method of the present invention can be usefully used for the production of various metal oxide nanostructures.

Since carbon black is a relatively inexpensive raw material, there is an advantage in that the manufacturing cost of the metal oxide nanostructure may be significantly lowered in the present invention.

Claims (6)

A method for producing a metal oxide nanostructure using carbon thermal reduction using carbon, the method for producing a metal oxide nanostructure, characterized in that carbon black having a surface area of 30 m ² / g or more is used. The metal oxide nanostructure of claim 1, wherein the metal oxide has a stoichiometric ratio of MO, M ₂ O _3, or MO ₂ , wherein M is one or more metal elements, and O is an oxygen atom. Manufacturing method. The method of claim 1 or 2, wherein the carbon black has a surface area of 100 m ² / g to 2,500 m ² / g. The method of claim 1 or 2, wherein the carbon black and the metal oxide powder are mixed and used in a weight ratio of 1:10 to 10: 1. The method for producing a metal oxide nanostructure according to claim 1 or 2, wherein the carbon black is heated at a temperature range of 600 ° C or higher. The metal oxide nanostructures of claim 1 or 2, wherein the metal oxide nanostructures have a diameter of 10 to 50 nm and a length of 100 nm or more, a nanorod of 50 nm to 200 nm and a length of 100 nm or more, and a thickness of 50 nm or more. A method for producing a metal oxide nanostructure, characterized in that the nanoplate having a width of 1 μm or more, or the nanorods or nanowires in the form of nanocombs arranged in a comb-tooth shape on the nanoplate.

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