KR20060112858A - Process for preparing titanate and titanium oxynitride - Google Patents

Abstract

Provided are a method for mass-preparing a titanate of nano structure having high specific surface area and easily controlled nano-form, with low cost and high efficiency, and a method for preparing a titanium oxynitride having high specific surface area which exhibits high optical activity at region of visible rays by using the titanate. The method for preparing a titanate comprises hydrothermally synthesizing a mixture solution formed by mixing titanium precursor and ammonia water with solvent. The titanium precursor is at least one selected from the group consisting of titanium oxysulfate, titanium sulfate, titanium alkoxide, and titanium halide. Amount of the ammonia water is 2-25 mol based on 1 mol of the titanium precursor. The solvent is a distilled water, an alcohol, or mixture thereof. Amount of the solvent is 50-500 mol based on 1 mol of the titanium precursor. The reaction temperature and time of the hydrothermal synthesis are 80-200 deg.C and 0.1-10 hours, respectively. The method for preparing the titanium oxynitride comprises firing the titanate prepared by the method.

Description

Process for preparing titanate and titanium oxynitride

Figure 1a shows a TEM picture of the nanostructured titanate according to Example 2 of the present invention.

Figure 1b shows a SAED pattern of the nanostructured titanate according to Example 3 of the present invention.

Figure 2 shows a TEM image of titanium oxynitride nanostructures according to Example 4 of the present invention.

Figure 3 shows the XPS analysis spectrum in the nitrogen 1s region of the nanostructured titanate and titanium oxynitride according to Examples 3 and 4 of the present invention.

Figure 4a shows a TEM picture of the nanostructured titanium oxide according to Example 5 of the present invention.

Figure 4b shows a SAED pattern of the titanium oxide of the nanostructures according to Example 6 of the present invention.

5 shows XRD patterns of nanostructure oxides according to Examples 1 to 6 of the present invention.

6 shows UV / visible-diffusive reflectance spectra of nanostructured titanates and titanium oxynitrides according to Example 8 of the present invention.

FIG. 7 is a graph showing photodegradation activity of isopropyl alcohol in the visible region of titanate and titanium oxynitride having nanostructures according to Example 8 and Comparative Examples 1 and 2 of the present invention.

The present invention relates to a method for producing titanate and titanium oxynitride, and more particularly, to a method for producing nanostructured titanate and titanium oxynitride having a high specific surface area.

In general, titanium oxide is not only an important catalyst and support for many industrial processes, but also has many applications such as solar cell materials, hydrogen production, humidity sensors, self-cleaning, environmental pollutant purification, and sterilization. to be. In particular, titanium oxynitride (TiO ₂ -xN _x ) partially nitrided in titanium oxide exhibits photocatalytic properties of absorbing visible light in the visible region to decompose organic materials.

In these various fields, the control of the size, shape and structure of the titanium oxide is very important. Conventional nanostructured titanium oxide was prepared using an aluminum membrane (Anodic Aluminum Membrane, AAO) or an organic gel (organo-gel) as a structural derivative. However, such a manufacturing method has problems in increasing production cost and mass production since it is necessary to use a structural derivative. In the case of the AAO method, it is difficult to control the structure of the nano size because the control of the size of the nano structure depends on the size of the aluminum membrane. have.

Recently, a method for producing a titanate-structured nanotube by hydrothermal synthesis in a high concentration of NaOH solution has been described (Chem. Eur. J. 2003, 9, 2229-2238; Chem. Phys. Lett., 2003, 380, 577-582; Langmuir 1998, 14, 3160-3163), but the manufacturing method using the crystalline titanium oxide such as titanium oxide occupies a large proportion of the material, and exhibits photoactivity in the visible region of titanium oxynitride There is a problem that is difficult to manufacture.

Meanwhile, conventional titanium oxynitride uses titanium alkoxide or chloride form as a titanium precursor, titrates ammonia water in an alcohol solvent to form a titanium gel, and then flows ammonia gas at a high temperature of 500 ° C. or higher to prepare titanium oxynitride. come. This process also has the disadvantage of having a relatively small specific surface area of 100m ² / g and the inconvenience of having to carry out the cost of the alkoxide type inorganic precursor and the nitriding reaction with ammonia gas at high temperature.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a manufacturing method capable of mass-producing a titanate of nanostructures having easy control of nano shapes and having a high specific surface area at low cost and high efficiency.

Another object of the present invention is to provide a method for producing a high specific surface area of titanium oxynitride having high photoactivity in the visible region using the titanate.

Another technical problem to be achieved by the present invention is to provide a photocatalyst including the titanate.

Another technical problem to be achieved by the present invention is to provide a photocatalyst including the oxynitride.

The present invention to achieve the above technical problem,

It provides a method for producing a titanate comprising the step of hydrothermally (hydrothermal) a mixture solution of a titanium precursor and ammonia water mixed with a solvent.

Titanium oxysulfate, titanium sulfate, titanium alkoxide, titanium halide, etc. can be used as said titanium precursor.

The molar ratio of the ammonia is preferably 2 to 25 moles based on 1 mole of the titanium precursor.

Distilled water, alcohol, or a mixture thereof may be used as the solvent, and the content thereof is preferably 50 to 500 moles based on 1 mole of the titanium precursor.

The hydrothermal synthesis temperature is preferably 80 to 200 ℃.

The hydrothermal synthesis time is preferably 0.1 to 10 hours.

The titanate has a form of nanosheets, nanofibers, nanorods, nanoparticles, and the like in the form of nanostructures.

The specific surface area of the titanate is preferably 370 to 520 m ² / g.

The present invention to achieve the above other technical problem,

It provides a method for producing titanium oxynitride comprising the step of firing the titanate obtained in the above-described manufacturing method at 200 to 500 ℃ for 0.1 to 10 hours.

The specific surface area of the titanium oxynitride is preferably 300 to 380 m ² / g.

The titanium oxynitride has a form of nanosheets, nanofibers, nanorods, nanoparticles, and the like in the form of nanostructures.

The present invention to achieve the above another technical problem,

It provides a photocatalyst comprising the titanate or titanium oxynitride.

Hereinafter, the present invention will be described in more detail.

The present invention provides a method for producing a large amount of nanostructured titanate under relatively mild conditions, a method for producing titanium oxynitride by further calcining the obtained titanate, and a photocatalyst comprising the same.

The titanate according to the present invention is obtained by hydrothermal synthesis of a mixture solution obtained by mixing a titanium precursor and ammonia water with a solvent.

Titanium oxysulfate, titanium sulfate, titanium alkoxide, titanium halide, etc. may be used as the titanium precursor. For example, TiOSO ₄ xH ₂ O x H ₂ SO ₄ available from Aldrich, Fluka, Junsei may be used. have.

Examples of a material capable of forming a salt with the titanium precursor include ammonia water and ammonium chloride, and as the ammonia water, a 28-30% aqueous solution may be used.

The molar ratio of the titanium precursor and ammonia water may be 2 to 25 mol, preferably 5 to 15 mol of the ammonia water (in the case of 28 to 30% aqueous solution) based on 1 mol of the titanium precursor. If the molar ratio of the ammonia water is 2 mol or less, there is a problem that the nanostructure is not formed, and if the molar ratio exceeds 25 mol, there is a problem in that a material having a nanostructure forms a stack.

Such titanium precursor and ammonia water are mixed and used in a solvent. As such a solvent, distilled water, alcohol or a mixture thereof can be used. Such a solvent may use about 50 to about 500 moles based on 1 mole of the titanium precursor, and if it is out of the above range, it is considered difficult to have an effective nanostructure, but it is necessarily limited within this range due to the nature of the solvent. It will be apparent to those skilled in the art that the present invention is not intended.

In preparing a mixture solution by mixing the titanium precursor and ammonia water in a solvent, it is more preferable that the stirring process is performed so that the mixture is obtained in a gel state and they become a more homogeneous mixture. Such a stirring process is sufficient if the mixture is sufficient to ensure proper homogeneity, and can usually be performed for about 10 minutes to about 3 hours. In addition, the ammonia water may be mixed with the titanium precursor at the same time, may be added in small portions in the stirring process, and may be mixed in small portions after the stirring process after the initial mixing. Among them, in order to obtain a more homogeneous mixture, a small amount of ammonia water is mixed with a titanium precursor in advance in a solvent, followed by stirring, and then a method of slowly dropping a certain amount of ammonia water will be preferred. The final composition of this mixture is as described above.

After obtaining a homogeneous mixture, a hydrothermal synthesis step is performed. In this hydrothermal synthesis step, the reaction temperature and the reaction time serve as the main control factors. The reaction temperature applied in the hydrothermal synthesis step according to the present invention is preferably about 80 to 200 ℃, preferably 100 to 150 ℃ which is a relatively weak temperature range. If the hydrothermal synthesis temperature is less than 100 ° C., sufficient hydrothermal synthesis is not obtained. If the hydrothermal synthesis temperature is more than 150, nanoparticles may be formed instead of oxides having nanostructures, which is undesirable. Suitable reaction time in the hydrothermal synthesis step according to the present invention is 10 to 100 hours, preferably 24 to 72 hours. If the reaction time is less than 10 hours, sufficient hydrothermal synthesis cannot be obtained, and if it exceeds 100 hours, there is little effect of hydrothermal synthesis on the excess reaction time.

By hydrothermal synthesis that satisfies the above conditions, the titanium precursor reacts with ammonia water to form titanate, followed by further washing the pH of the filtrate to neutrality using distilled water or the like. After neutralization, the filtrate is further filtered to further wash with ethanol, and then dried in a vacuum drying oven to form nanostructured titanate. The nanostructured titanate thus formed may have the form of nanosheets, nanofibers, nanorods, nanoparticles, etc., which may be affected by the number of moles of the reaction or the temperature of the reaction, regardless of the number of moles of the reaction. Nanoparticles are formed below < RTI ID = 0.0 > C, < / RTI > Below) or nanopipes (ratio 10 or more) may be formed.

The titanate obtained in the hydrothermal synthesis step as described above has a high specific surface area, and has a specific surface area of 370 to 520 m ² / g based on the BET specific surface area.

The present invention can produce titanium oxynitride by using the titanate obtained by the above-described process, the manufacturing process of such titanium oxynitride includes the step of firing the titanate prepared above.

The firing process is preferably performed at a temperature of 200 to 500 ° C., preferably 300 to 500 ° C., and when it is out of the temperature range, there is a problem that sufficient baking cannot be obtained. In addition, the time for which the firing process is performed may be performed for 0.1 to 10 hours, preferably 1 to 4 hours, and if the firing time is less than 0.1 hour, sufficient firing may not be obtained, and in case of exceeding 10 hours There is a problem that it is not economical because the effect of the firing time is not obtained.

Such a firing process is already included in the titanate, such as ammonia groups, they can be vaporized in the firing process does not require a step of injecting a separate ammonia gas, it can be carried out in a normal atmosphere atmosphere is more economical Can be.

The calcination process removes moisture, hydroxyl groups, and ammonia groups remaining in the titanate, thereby obtaining titanium oxynitride. In particular, the titanium oxynitride obtained by calcining the titanate as described above has a high specific surface area, and thus has a value of 250 to 380 m ² / g based on the BET specific surface area.

In addition, the titanium oxynitride according to this process is obtained in the form of anatase particles, the structure has the form of nanosheets, nanofibers, nanorods, nanoparticles and the like.

The titanium oxynitride has a high specific surface area and thus has high catalytic activity and thus can be used in various fields. In particular, the titanium oxynitride has an optical property of absorbing light in the visible light region of 420 nm or more. Can be.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, which are intended to describe the present invention in more detail, but the present invention is not limited thereto.

Examples 1 to 3

Method for synthesizing nanostructured titanate is as follows. After mixing 28-30% aqueous ammonia and titanium precursor titanium oxalate (available from Aldrich; TiOSO ₄ xH ₂ O xH ₂ SO ₄ ) in a constant amount of distilled water and stirring it for a uniform mixture for at least 1 hour, Aqueous ammonia was slowly added dropwise. This molar composition of the mixture is made uniform _{TiOSO 4 xH 2 O xH 2 SO} 4: NH 4 OH: H 2 O is 1: 500 was adjusted to -: - 50 2 25.

The gel mixture formed after stirring was transferred to an autoclave vessel and subjected to a hydrothermal process for 24 to 72 hours at a hydrothermal synthesis temperature of 100 to 135 ° C. The product thus obtained is first washed several times with distilled water until the pH of the filtrate becomes neutral, and when the neutral filtrate is filtered, the product is washed two or more times with ethanol, and then vacuum dried oven at 70 to 80 ° C. Dried at least one day. TEM images of the nanostructured ammonium titanate thus prepared are shown in Table 1 below for FIGS. 1A and 1B and their tissue properties. From the TEM photographs of FIGS. 1A and 1B, it can be seen that ammonium titanate according to the present invention has structural features such as (nanosheet and nanopipe).

# Hydrothermal Synthesis Condition BET specific surface area (m ² / g) Pore volume (m ³ / g) BJH pore size (nm) Molar ratio Temperature ( ^o C) / hour (h) Example 1 1: 5: 50 120/72 374 0.56 4.0 Example 2 1: 10: 70 120/72 459 0.65 3.8 Example 3 1: 15: 80 120/72 512 0.72 3.7

According to Table 1, it can be seen that ammonium titanate according to the present invention has a high BET specific surface area, and the pore volume and the BJH pore volume are fine.

Example 4

The ammonium titanate prepared in Example 1 was calcined in an air atmosphere at a temperature of 400 ° C. for 1 to 4 hours to remove the remaining water, hydroxyl groups, and ammonia groups, thereby obtaining titanium aoxynitride having an anatase structure. The TEM photograph of the titanium oxynitride having the nanostructure thus prepared is shown in FIG. 2, and its tissue characteristics are shown in Table 2 below. From the TEM photograph of FIG. 2, it can be seen that the titanium oxynitride according to the present invention is converted from the titanate structure to the anatase structure of the titanium oxide.

And XPS analysis results for the nitrogen element analysis in the titanium oxynitride is shown in FIG. As can be seen from the XPS analysis of FIG. 3, the nitrogen species (398.9 eV) in the case of titanium oxynitride was titanium oxynitride in comparison with the ammonium titanate obtained in Example 3 in the case of the titanium oxynitride obtained in Example 4. Although present in the nitride structure, ammonium titanate shows that some of the N Species are nitrogen species coordinated with titanium (400.5 eV) in the structure of the titanate or nitrogen species (398.8 eV) derived from ammonia ions. Can be.

# Hydrothermal Synthesis Condition BET specific surface area (m ² / g) Pore volume (m ³ / g) BJH pore size (nm) Molar ratio Temperature ( ^o C) / hour (h) Example 4 15 120/72 Firing temperature: 400 Firing time:> 1h 377 0.61 3.5

From the results in Table 2, it can be seen that the titanium oxynitride according to the present invention has a high BET specific surface area and a fine pore volume and a BJH pore size.

Examples 5-6

After mixing 28-30% ammonia water and titanium oxalate, a titanium precursor, in a constant amount of distilled water and stirring it for a uniform mixture for at least 1 hour, a predetermined amount of ammonia water is slowly added dropwise. This molar composition of the mixture is made uniform _{TiOSO 4 xH 2 O xH 2 SO} 4: NH 4 OH: H 2 O is 1: 500 was adjusted to -: - 50 2 25. After stirring, the formed gelled mixture was transferred to an autoclave vessel and subjected to a hydrothermal process for 24-72 hours at 140-150 ° C., a hydrothermal synthesis temperature. The product thus obtained is first washed several times with distilled water until the pH of the filtrate becomes neutral, and when the neutral filtrate is filtered, the product is washed two or more times with ethanol. Drying in a vacuum drying oven at 70-80 ° C. for at least one day. TEM photographs of the titanium oxide having the nanostructures thus prepared are shown in FIGS. 4A and 4B, and their tissue characteristics are shown in Table 3 below. From the TEM photographs of FIGS. 4A and 4B, it can be seen that ammonium titanate according to the present invention shows the shape of the nanorod structure.

division Hydrothermal Synthesis Condition BET specific surface area (m ² / g) Pore volume (m ³ / g) BJH pore size (nm) Molar ratio Example 5 15 185 0.41 3.5 Example 6 15 65 0.35 -

The results of Table 3 indicate that the nanorods and nanoparticles are formed as the synthesis is performed at 140 ° C. and 150 ° C., respectively, so that inorganic materials having a small specific surface area are synthesized compared to the nanosheets or nanopipes synthesized at 100 to 135 ° C. Able to know.

Example 7

XRD patterns of the nanostructured titanium oxide prepared as in Examples 1 to 6 are shown in FIG. 5. From the results of FIG. 5, it can be seen that the XRD pattern (crystal structure) of titanium oxide having a nanostructure does not change when hydrothermal synthesis is performed by changing the molar ratio of titanium and ammonia water. Only shape is the transformation from nanosheets to nanopipes. However, when the molar ratio of titanium to ammonia water is fixed to 15 and the hydrothermal synthesis temperature is changed from 120 to 150 ° C., the crystal structure is changed from titanium oxide to oxynitride (ananatase type).

Example 8

Titanium oxynitride prepared as in Example 4 has an optical characteristic of absorbing light in the visible region and a photocatalyst characteristic of decomposing isopropyl alcohol by absorbing light in the visible region of 420 nm or more. Absorption of light in the visible light region was confirmed by UV / visible diffuse reflection spectrum as shown in FIG. As shown in FIG. 7, titanate was not able to confirm photodegradation activity for isopropyl alcohol, whereas in the case of titanium oxynitride, it was confirmed that at least half of the initial concentration of isopropyl alcohol was removed within 1 hour. have.

Comparative Example 1

Comparative experiments were performed using Degussa titania P25 in the same manner as in Example 8. The results do not show photoactivity in the visible region as shown in FIG. 7.

Comparative Example 2

In the same manner as in Example 8, the comparative results of the preparation of the titanium oxynitride prepared by the Asahi (human) research team previously reported in Science ( Science , 2001, 293, 269-271) are shown in FIG. Shown in Compared with the titanium oxynitride prepared by the present invention, it showed low photoactivity in visible light.

The titanate prepared according to the present invention may prepare nanostructured titanium oxides capable of controlling the shape of nanosheets, nanofibers, nanorods, nanoparticles, etc. by controlling the molar ratio of the ammonia water and the titanium precursor and the hydrothermal synthesis temperature. In the present invention, a low-cost, high-efficiency manufacturing method capable of producing a high specific surface area of titanium oxynitride by preparing a nanostructured titanate in a relatively low temperature hydrothermal synthesis process and firing it in an air atmosphere. In addition, the low cost enables mass production, which is expected to be utilized in various environmental purification fields such as decomposition of volatile organic substances in the atmosphere under visible light.

Claims (16)

A method for producing a titanate, characterized in that it comprises the step of hydrothermally (hydrothermal) a mixture solution of titanium precursor and ammonia water mixed with a solvent. The method of claim 1, wherein the titanium precursor is at least one selected from the group consisting of titanium oxysulfate, titanium sulfate, titanium alkoxide, and titanium halide. The method of claim 1, wherein the content of the ammonia water is 2 to 25 moles based on 1 mole of the titanium precursor. The method for producing titanate according to claim 1, wherein the solvent is distilled water, alcohol, or a mixture thereof. The method of claim 1, wherein the content of the solvent is 50 to 500 moles based on 1 mole of the titanium precursor. The method according to claim 1, wherein the reaction temperature of the hydrothermal synthesis step is 80 to 200 ℃. The method of claim 1, wherein the reaction time of the hydrothermal synthesis step is 0.1 to 10 hours. The method of claim 1, wherein the form of the titanate is nanosheets, nanofibers, nanorods, or nanoparticles. The method of claim 1, wherein the titanate has a BET specific surface area of 370 to 520 m ² / g. 10. A method for producing titanium oxynitride, comprising calcining a titanate obtained by the process according to any one of claims 1 to 9. The method for producing titanium oxynitride according to claim 10, wherein the firing temperature of the firing step is 200 to 500 ° C. The method for producing titanium oxynitride according to claim 10, wherein the firing time of the firing step is 0.1 to 10 hours. The method of claim 10, wherein the titanium oxynitride has a BET specific surface area of 300 to 380 m ² / g. The method of claim 10, wherein the titanium oxynitride is in the form of nanosheets, nanofibers, nanorods, or nanoparticles. A photocatalyst comprising a titanate obtained by the production method according to any one of claims 1 to 9. A photocatalyst comprising titanium oxynitride obtained by the manufacturing method according to any one of claims 10 to 14.

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