JP6301880B2 - Method for synthesizing titanium oxide nanotubes and titanium oxide nanotubes synthesized by this method - Google Patents

Description

  The present invention relates to a method for synthesizing titanium oxide nanotubes and a titanium oxide nanotube synthesized by this method.

  Conventionally, a method for synthesizing a titanium oxide nanotube using a hydrothermal reaction is widely known. For example, Patent Document 1 discloses a method of synthesizing titanium oxide nanotubes from titanium oxide using a hydrothermal reaction.

JP 2014-24732 A

  In the hydrothermal synthesis method described in Patent Document 1, titanium oxide nanotubes are synthesized from titanium oxide by performing a hydrothermal reaction in a state where titanium oxide powder is put into a sodium hydroxide aqueous solution.

  However, in such a method, there is a possibility that the aqueous solution of sodium titanium hydroxide is scattered in the heating and pressurizing vessel used in the hydrothermal reaction, so that the heating and pressurizing vessel is not corroded by strong alkali. It is necessary to coat with a registered trademark of DuPont, the same shall apply hereinafter). In other words, the heating and pressurizing container needs to be made of a material that can not only withstand high temperature and pressure but also withstand chemicals such as alkali.

  In general, in the synthesis of oxide nanomaterials such as titanium oxide nanotubes, hydrothermal synthesis is carried out in a strong alkaline aqueous solution, so that a high temperature and high pressure state is maintained for about 12 hours in a reaction vessel completely sealed with Teflon. Need to be maintained. Therefore, it is necessary to apply Teflon coating and Teflon lining to materials that can withstand high-temperature and high-pressure conditions. In addition to temperature resistance and pressure resistance, chemical resistance is also required, and the materials that can be selected are significantly limited. In addition, there is a problem that it takes a lot of labor and cost to manufacture a heating and pressing apparatus having all of heat resistance, pressure resistance, and chemical resistance.

  The present invention has been made in view of such a problem, and a hydrothermal reaction using a highly erodible liquid such as a strong alkaline aqueous solution without providing chemical resistance to the entire metal heating and pressure vessel. The main object is to provide a heat-pressurized container that can be used. Also provided are a hydrothermal reaction method using the heated and pressurized container, a titanium oxide nanotube synthesis method using the hydrothermal reaction method, and a titanium oxide nanotube synthesized using the titanium oxide nanotube synthesis method. One of the purposes is to provide a heat and pressure vessel that can be used for the synthesis of various oxide nanomaterials.

  The present invention adopts the following means in order to achieve at least one of the above-mentioned main objects.

The method for synthesizing the titanium oxide nanotubes of the present invention comprises:
A synthesis method for synthesizing titanium oxide nanotubes using a heating and pressurizing container in which at least a part of the container is opened and the surface of the container has alkali resistance is housed.
A first step of adding a mixed solution of titanium oxide and aqueous sodium hydroxide solution to the storage container;
A second step of adding water to the heated and pressurized container;
After the first step and the second step, a third step of heating and pressurizing the heated and pressurized container in a sealed state;
Including,
Is.

  In this method of synthesizing titanium oxide nanotubes, the storage container in which the mixed liquid of titanium oxide and sodium hydroxide aqueous solution has alkali resistance on the surface is a case where a mixed liquid containing strong alkali is placed in the storage container. In addition, the possibility that the storage container is eroded by the chemical can be reduced. In addition, at least a part of the storage container is open, sealed in a state where water is put in the heating and pressurizing container, and when the heating and pressurizing note is heated and pressurized, it is generated in the heating and pressurizing container. Water vapor pressurizes the mixed solution in the storage container, and the mixed solution can be maintained in a liquid phase by the vapor pressure. By carrying out like this, if only the surface of a storage container has alkali tolerance, the hydrothermal reaction of the liquid mixture containing a strong alkali can be performed, without providing chemical resistance to the surface of a heating-pressurization container. In addition, by combining a storage container with alkali resistance and a heat and pressure container with pressure resistance and heat resistance performance, a material having either chemical resistance or pressure resistance or heat resistance performance is sufficient. The choice of materials in manufacturing can be improved. In addition, about the method of heating a heating-pressing container here, as long as it is the method of heating internal water, without heating a heating-pressing target object directly, you may use an electrical or a heat medium. Here, “alkali resistance” refers to a property of preventing erosion by alkali, and means having a property of not being eroded by alkali or being hardly eroded by alkali.

  In addition, since the boiling point of the mixed liquid of titanium oxide and sodium hydroxide aqueous solution is higher than the boiling point of water, when the heated and pressurized container is heated and pressurized, water will be vaporized before the mixed liquid. The inside of the heating and pressurizing container is in a vaporized atmosphere of water. By doing so, water vapor that has entered at least part of the inside of the storage container pressurizes the liquid mixture in the storage container, and the liquid mixture can be maintained in a liquid phase by the vapor pressure.

  In the method for synthesizing titanium oxide nanotubes of the present invention, the volume of water may be 30% to 80% of the internal volume of the heating and pressurizing vessel. By doing so, bumping of the mixed solution can be prevented in advance, and the possibility that the mixed solution will be scattered in the heating diffusion container can be reduced. For this reason, for example, even when the mixed solution contains a highly erodible solution such as a strong alkali, it is possible to perform a hydrothermal reaction without requiring chemical resistance on the surface of the heated and pressurized container. A heated and pressurized container can be provided. For example, when the predetermined amount is less than 30% of the capacity of the reaction vessel, the effect of water is small, and the possibility that the liquid mixture cannot be maintained in a liquid phase due to the water vapor pressure increases. If the volume is larger than 80%, the pressure in the reaction vessel may increase rapidly due to the expansion of water, which is not preferable.

  In the titanium oxide nanotube synthesis method of the present invention, the temperature and pressure inside the heating and pressurizing vessel and the storage vessel in the third step may be a saturation temperature and a saturated vapor pressure of the water. . By doing so, since the water is kept in a saturated vapor state, the liquid surface of the mixed solution is covered with the saturated vapor of water, and the possibility that the mixed solution is scattered can be reduced. In addition, if only the surface of the storage container has chemical resistance, the hydrothermal reaction of the liquid mixture containing the erodible component can be performed without imparting chemical resistance to the surface of the heated and pressurized container. .

  In the titanium oxide nanotube synthesis method of the present invention, the aqueous sodium hydroxide solution may have a concentration of 7 mol / L or more, and the pH of the mixed solution may be maintained at 13 or more. At this time, the pH is preferably 13 or more, more preferably 7 mol / L (hereinafter referred to as “7M”) or more, more preferably 13 or more, and more preferably 15 M or more of water. More preferably, the pH is set to 13 or more with sodium oxide. Moreover, it is not limited to an aqueous sodium hydroxide solution, and may be, for example, an aqueous potassium hydroxide solution, an aqueous lithium hydroxide solution, an aqueous rubidium hydroxide solution, or an aqueous cesium hydroxide solution. When synthesizing titanium oxide nanotubes under such conditions, the conventional method may cause scattering of a highly concentrated strong alkaline aqueous solution that is highly erodible. However, by using the method for synthesizing titanium oxide nanotubes of the present invention, it is possible to synthesize titanium oxide nanotubes without subjecting the inner surface of the heated and pressurized container to alkali resistance treatment. By doing so, the method for synthesizing the titanium oxide nanotubes of the present invention can be performed using a part of the existing heating and pressurizing vessel.

  In the method for synthesizing titanium oxide nanotubes of the present invention, when the mixed liquid is heated and pressurized, the mixed liquid may be pressurized at a pressure of 0.2 to 0.6 megapascal. At this time, the pressure is preferably 0.1 to 0.6 megapascal, preferably 0.2 to 0.6 megapascal, preferably 0.17 to 0.48 megapascal, It is more preferably 0.25 megapascal or more and 0.35 megapascal or less. In the case of synthesizing titanium oxide nanotubes under such conditions, in the conventional method, there is a possibility that a highly concentrated sodium hydroxide aqueous solution having a strong erodibility may be scattered. Although it is necessary to perform treatment, by using the titanium oxide nanotube synthesis method of the present invention, it is possible to synthesize titanium oxide nanotubes without performing alkali resistance treatment on the inner surface of the heating and pressurizing vessel. By doing so, the method for synthesizing the titanium oxide nanotubes of the present invention can be performed using a part of the existing heating and pressurizing vessel.

  The titanium oxide nanotube of the present invention is a titanium oxide nanotube synthesized using any one of the above-described titanium oxide nanotube synthesis methods. Since this titanium oxide nanotube is synthesized using the above-described titanium oxide nanotube synthesis method, the titanium oxide nanotube can be synthesized without subjecting the inner surface of the heating and pressurizing vessel to alkali resistance treatment. For this reason, it is not necessary to give chemical resistance to the inside of the heating and pressurizing vessel in order to synthesize titanium oxide nanotubes, and the degree of freedom in selecting the material of the reaction vessel can be increased. In addition, since a titanium oxide nanotube can be synthesized using a part of an existing heating and pressure vessel, a large amount of titanium oxide nanotubes can be synthesized.

FIG. 1 is a schematic diagram showing an outline of the configuration of the heating and pressurizing container 20. FIG. 2 is a photograph taken with a transmission electron microscope. FIG. 3 is a photograph of titanium oxide nanotubes synthesized under the conditions of Example 1 to Example 3. FIG. 4 is a photograph of titanium oxide nanotubes synthesized under the conditions of Example 4 to Example 6.

  In describing an example of a method for synthesizing a titanium oxide nanotube of the present invention, FIG. 1 is used to illustrate an outline of the configuration of a heating and pressurizing vessel 20 that is an example of a hydrothermal reactor used in the method of synthesizing a titanium oxide nanotube of the present invention. I will explain. FIG. 1 is a schematic diagram showing an outline of a configuration of a heating and pressurizing container 20 which is an example of an embodiment of the present invention. As shown in FIG. 1, the heating and pressurizing container 20 stores a storage container 32 in which a mixed liquid containing titanium oxide and a sodium hydroxide aqueous solution is stored in a sealable reaction container 30. When performing the hydrothermal reaction, water 34 having a lower boiling point than the liquid mixture is added to the reaction vessel 30, and the reaction vessel 30 is heated and pressurized using a heating / pressurizing device (not shown). Hydrothermal reaction can be performed. A plurality of storage containers 32 may be stored in the reaction container 30. At this time, the mixed solutions stored in the plurality of storage containers 32 may all be the same or different. As described above, since a plurality of storage containers can be stored in one reaction container, a hydrothermal reaction can be performed with a plurality of storage containers in which samples are divided even when a hydrothermal reaction of a large amount of samples is performed. The hydrothermal reaction can be carried out under more uniform conditions as compared with the case where the hydrothermal reaction is carried out in a large storage container that can contain a large amount of sample.

  The reaction container 30 is a stainless steel sealable container and can store one or more storage containers 32. The reaction container 30 can contain water 34 inside the reaction container 30 with the storage container 32 stored and outside the storage container 32, and the water 34 and the storage container 32 are put in the reaction container 30. And can be sealed. In this state, the inside of the reaction vessel 30 can be maintained in a high temperature and high pressure state by heating and pressurizing the reaction vessel 30 using a heating / pressurizing device (not shown). The reaction vessel 30 may be provided with various measuring machines such as a thermometer. In this way, the temperature conditions in the reaction vessel 30 can be measured from the outside. The shape of the reaction container 30 is not particularly limited as long as it can be sealed with the storage container 32 and water inside. The material is not limited to stainless steel, and various materials can be used as long as they can withstand high temperature and high pressure conditions. In addition, about various measuring instruments with which the reaction container 30 is equipped, what is necessary is just to have heat-resistant pressure resistance, and alkali tolerance is not required.

  The storage container 32 is a resin container having a surface coated with Teflon coating or Teflon lining, and an upper portion thereof is opened. For this reason, after being left in the reaction container 30 and sealed, the reaction container 30 and the storage container 32 have the same pressure atmosphere because the upper part of the storage container 32 is opened. Below. Further, since the surface is subjected to Teflon coating or Teflon riding, the possibility of being eroded by chemicals can be reduced even when a solution containing a strong acid or strong alkali is stored. The storage container 32 may be made of Teflon or Teflon liner.

  Next, an example of the hydrothermal reaction method and the titanium oxide nanotube synthesis method of the present invention will be described using the hydrothermal reaction method using the heated and pressurized container 20 as an example.

  First, as a storage container 32, a Teflon reaction container was filled with titanium oxide powder (manufactured by Sakai Chemical Industry Co., Ltd., product number: SA-120) and a 10M sodium hydroxide aqueous solution in a weight ratio of 1:10. Next, the storage container 32 is allowed to stand in a stainless steel autoclave known as the reaction container 30, and water having a capacity of 30% with respect to the internal volume of the storage container 32 is placed in the storage container 32. Sealed. Subsequently, the storage container 32 was heated with heated oil, and this state was maintained at 145 ° C. to 150 ° C. for 20 hours. At this time, since the upper portion of the storage container 32 is open, the storage container 32 is filled with water vapor that has been evaporated into the reaction container 30 up to the liquid level.

Subsequently, the product in the storage container 32 was collected and observed with a transmission electron microscope. The result is shown in FIG. From this figure, a tubular nano-sized product having a diameter of about 10 nanometers and a length of about 500 nanometers was confirmed. As a result of XRD and XRF analysis and non-surface area measurement of this nano-sized product, this tube-shaped nano-sized product was converted into titanium oxide (Na ₂ Ti ₃ O ₇ and H ₂ Ti having anatase structure of titanium oxide). ₃ O ₇ intermediate). The specific surface area was found to be a ^{10 m} 2 / g of 10 times or more a specific surface area of the titanium oxide powder before the reaction with 100 to 400 m ² / g.

  This result has the same characteristics as the product reported in the conventional method for producing titanium oxide nanotubes, and the inside of the reaction vessel 30 was observed in detail. It was also confirmed that was not scattered. From this result, it is possible to synthesize a titanium oxide nanotube similar to a conventional titanium oxide nanotube by leaving the storage container 32 opened at the top in the reaction container 30 and heating and pressurizing it with water in it. it is obvious.

  The reason why the titanium oxide nanotube similar to the conventional method can be synthesized by the hydrothermal reaction of the present invention is not clear, but the inventors consider as follows.

  In the hydrothermal reaction method of the present embodiment, the water in the reaction vessel 30 is heated to bring the water into a saturated steam state. At this time, the titanium oxide powder is precipitated in an aqueous sodium hydroxide solution, and the aqueous solution of sodium hydroxide is held in the liquid phase by the vapor pressure drop under the condition of the saturated vapor pressure of water.

  That is, the titanium oxide in the alkaline aqueous solution state is not saturated until it is pressurized with the saturated water vapor pressure, and is held in the liquid phase state, so that it is in a sealed state in the storage container. In addition, in the present invention, the saturated water vapor pressure can be used not only for the purpose of heating and pressurization but also for the purpose of sealing the storage container, so it is considered that the same titanium oxide nanotubes as in the conventional method could be synthesized. Thus, since the storage container is sealed with water vapor, so that the sodium hydroxide aqueous solution is sealed in the storage container, the reaction container has temperature and pressure resistance against water. Just do it.

  Furthermore, when the storage container is open, there is no difference in pressure between the storage container containing the sodium hydroxide aqueous solution and the reaction container. For this reason, it is not necessary to make a pressure resistant container, and it is only necessary to separate water and an aqueous sodium hydroxide solution. For this reason, the storage container does not need a strong Teflon autoclave container having chemical resistance, temperature pressure resistance, and pressure pressure resistance as in the conventional case, and a thin, simple resin container is sufficient.

  Next, by applying actual physical property values, it is shown that the aqueous sodium hydroxide solution is retained in the liquid phase by the saturated water vapor pressure of water. In general, the vapor pressure drop of the aqueous solution is proportional to the solute molarity of the solute, and the degree T of increase in the boiling point of the aqueous solution compared to the boiling point of the pure solvent with the vapor pressure drop is expressed by the following equation (1). In the following formula (1), Kb is a predetermined constant, and mb is the molar concentration of the solute.

  The physical properties of water and sodium hydroxide are applied to the formula (1), and the vapor pressure curves of the derived water and the aqueous sodium hydroxide solution of each concentration (5, 10, 15 M) are shown in Tables 1 and 2 below. Table 1 is a vapor pressure curve of water and a sodium hydroxide aqueous solution of each concentration, with the vertical axis representing temperature and the horizontal axis representing vapor pressure. Each graph shows, in order from the top, a 15 M aqueous sodium hydroxide solution (D), a 10 M aqueous sodium hydroxide solution (C), a 5 M aqueous sodium hydroxide solution (B), and water (A). Yes.

  Table 2 below shows the vapor pressure curves of water and aqueous sodium hydroxide solution of each concentration, with the vertical axis representing the vapor pressure and the horizontal axis representing the temperature. Each graph shows water (A), 5M aqueous sodium hydroxide solution (B), 10M aqueous sodium hydroxide solution (C), and 15M aqueous sodium hydroxide solution (D) in order from the top. Yes.

  As shown in Table 1, for example, under the condition of 0.2 megapascal, the boiling point of a 10M sodium hydroxide aqueous solution is 5.8 ° C, and when it is 0.3 megapascal, it is 6.3 ° C. You can see that it is rising. Conversely, when compared at the same temperature, as shown in Table 2, the vapor pressures of the pure solvent and the 10M aqueous sodium hydroxide solution are 0.2 megapascal and 0.15 megapascal, respectively, at 120 ° C. At a certain temperature, the water is saturated, but the aqueous sodium hydroxide solution remains in the liquid phase, and the aqueous sodium hydroxide solution is always pressurized due to the saturated vapor pressure of the water, and is confined in the liquid phase. I understand. From the above, it is clear from the calculation that the difference between the saturated vapor pressure of water and the vapor pressure of the sodium hydroxide aqueous solution functions as the upper lid of the storage container that is the titanium oxide nanotube production container.

  Here, the pH change of the aqueous sodium hydroxide solution before and after heating and pressurization at each concentration of the aqueous sodium hydroxide solution is shown in Table 3 below. Table 3 shows the heat and pressure when a sodium hydroxide aqueous solution at a concentration of 0.2M, 0.4M, 0.6M, 0.8M, and 1.0M is heated and pressurized at 145 ° C. to 150 ° C. for 20 hours. It is the table | surface which showed the change of pH before and behind. As apparent from this table, the maximum pH before and after changes only 0.04, almost no external water is mixed in the sodium hydroxide aqueous solution, and the sodium hydroxide aqueous solution is scattered outside. It is clear that this is not the case. In other words, it can be said that it is clear that the aqueous sodium hydroxide solution is confined in a liquid phase state by water vapor.

  The example of the synthesis method which synthesize | combined the titanium oxide nanotube using the synthesis method of the titanium oxide nanotube of this invention is shown below.

Example 1
Titanium oxide powder (manufactured by Sakai Chemical Industry Co., Ltd., product number: SA-120) and 10M aqueous sodium hydroxide solution are placed in a 1:10 weight ratio in a Teflon reaction container, and the storage container 32 is statically placed in a known stainless steel autoclave. Then, 30% of water with respect to the inner volume of the storage container 32 was put into the storage container 32, and the storage container 32 was sealed. Subsequently, the storage container 32 was heated with heated oil, and this state was maintained at 145 ° C. to 150 ° C. for 20 hours. At this time, since the upper portion of the storage container 32 is open, the storage container 32 is filled with water vapor that has been evaporated into the reaction container 30 up to the liquid level.

  Subsequently, the product in the storage container 32 was sampled and observed with a transmission electron microscope. The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (the axial length of the titanium oxide nanotubes) of 180.6 nanometers and a specific surface area of 156.62 square meters / gram were synthesized.

(Example 2)
Titanium oxide nanotubes were synthesized under the same conditions as in Example 1 except that the weight ratio of the titanium oxide powder and sodium hydroxide aqueous solution placed in a Teflon reaction vessel was 1.5: 10, and a transmission electron microscope was prepared. The product was observed at The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (the axial length of the titanium oxide nanotubes) of 199.16 nanometers and a specific surface area of 152.83 square meters / gram were synthesized.

(Example 3)
Titanium oxide nanotubes were synthesized under the same conditions as in Example 1 except that the weight ratio of titanium oxide powder placed in a Teflon reaction vessel to a sodium hydroxide aqueous solution was 1: 5, and produced with a transmission electron microscope. Things were observed. The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (the axial length of the titanium oxide nanotubes) of 197.52 nm and a specific surface area of 98.687 square meters / gram were synthesized.

Example 4
Titanium oxide powder (manufactured by Sakai Chemical Industry Co., Ltd., product number: SA-120) and 10M aqueous sodium hydroxide solution are placed in a 1:10 weight ratio in a Teflon reaction container, and the storage container 32 is statically placed in a known stainless steel autoclave. Then, 30% of water with respect to the inner volume of the storage container 32 was put into the storage container 32, and the storage container 32 was sealed. Subsequently, the storage container 32 was heated with heated oil, and this state was maintained at 158 ° C. for 20 hours. At this time, since the upper part of the storage container 32 is open, the storage container 32 is filled with water vapor evaporated from the water contained in the reaction container 30 up to the liquid level, and the pressure is 0.48. It was megapascal.

  Subsequently, the product in the storage container 32 was sampled and observed with a transmission electron microscope. The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (length in the axial direction of the titanium oxide nanotubes) of 50 to 200 nanometers and a diameter of 10 to 20 nanometers were synthesized.

(Example 5)
Titanium oxide nanotubes were synthesized under the same conditions as in Example 4 except that the temperature heated with heating oil was 129 ° C., and the product was observed with a transmission electron microscope. The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (length in the axial direction of the titanium oxide nanotubes) of 500 to 1000 nanometers and a diameter of 10 to 20 nanometers were synthesized. In addition, since heating is performed in a closed system, the pressure is 0.25 megapascal by setting the temperature to 129 ° C.

(Example 6)
Titanium oxide nanotubes were synthesized under the same conditions as in Example 4 except that the temperature heated with heated oil was 120 ° C., and the product was observed with a transmission electron microscope. The result is shown in FIG. From this figure, it was confirmed that titanium oxide nanotubes having an average particle diameter (length in the axial direction of the titanium oxide nanotubes) of 500 to 1000 nanometers and a diameter of 10 to 20 nanometers were synthesized. Since the heating is performed in a closed system, the pressure is 0.17 megapascals by setting the temperature to 129 ° C.

  From the above results, it was confirmed that the titanium oxide nanotubes can be synthesized under any conditions.

  INDUSTRIAL APPLICABILITY The present invention can realize mass synthesis of oxide nanomaterials such as titanium oxide nanotubes that can be generated by a hydrothermal reaction using a strong alkaline aqueous solution with an initial capital investment as low as possible.

  20 ... Heated and pressurized container, 30 ... Reaction container, 32 ... Storage container, 34 ... Water.

Claims (6)

A synthesis method for synthesizing titanium oxide nanotubes using a heating and pressurizing container in which at least a part of the container is opened and the surface of the container has alkali resistance is housed.
A first step of putting a mixed liquid of titanium oxide and aqueous sodium hydroxide into the storage container;
A second step of adding water to the heated and pressurized container;
After the first step and the second step, a third step of heating and pressurizing the heated and pressurized container in a sealed state;
Including,
A method for synthesizing titanium oxide nanotubes. The capacity of the water is 30% or more and 80% or less of the content of the heated and pressurized container,
The method for synthesizing a titanium oxide nanotube according to claim 1. The temperature and pressure inside the heated and pressurized container and the storage container in the third step are the saturation temperature and saturated vapor pressure of the water,
A method for synthesizing a titanium oxide nanotube according to claim 1 or 2. The temperature of the mixed solution in the third step is not more than the saturation temperature in the saturated vapor pressure condition of the water,
The method for synthesizing a titanium oxide nanotube according to any one of claims 1 to 3. The sodium hydroxide aqueous solution has a concentration of 7 mol / L or more,
The pH of the mixed solution is maintained at 13 or more,
The method for synthesizing a titanium oxide nanotube according to any one of claims 1 to 4. The pressurization to the mixed solution in the third step is a pressure of 0.2 megapascal or more and 0.6 megapascal or less,
The method for synthesizing a titanium oxide nanotube according to any one of claims 1 to 5.

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