KR100769481B1 - Synthetic method of titanium dioxide photocatalysts to change crystal structure by low heat treatment - Google Patents

Abstract

A synthesizing method of a titanium dioxide photocatalyst is provided to lower the production cost of titanium dioxide and produce a titanium dioxide photocatalyst improved photoactivity, whiteness and ultraviolet intercepting function by controlling concentrations of titanium halide, water and sulfate, and other reaction conditions, and heat-treating titanium dioxide at a temperature of 400 deg.C or less, thereby synthesizing the titanium dioxide photocatalyst. A synthesizing method of a titanium dioxide photocatalyst with crystal structure changed by low temperature heat treatment comprises: a first process of mixing titanium halide with distilled water to synthesize an A solution; a second process of mixing second distilled water with sulfate to synthesize a B solution; a third process(300) of stirring the A solution and the B solution, and heating and refluxing a mixed solution of the A solution and the B solution to synthesize titanium hydroxide; a fourth process(400) of mixing and stirring a basic compound and second distilled water to prepare an aqueous basic solution; a fifth process(500) of titrating the synthesized titanium hydroxide into the prepared aqueous basic solution, and heating and refluxing a mixture of the titanium hydroxide and the aqueous basic solution to obtain a titanium dioxide sediment; and a sixth process(600) of removing solvents and water from the titanium dioxide sediment, removing residual reaction by-products and non-reacted organic matters from the titanium dioxide sediment, and firing the titanium dioxide to synthesize a titanium dioxide photocatalyst.

Description

Synthetic method of Titanium Dioxide Photocatalysts to change crystal structure by low heat treatment

1 is a flow chart showing the synthesis process of titanium hydroxide applied to the present invention

Figure 2 is a flow chart showing the synthesis process of titanium dioxide photocatalyst by low temperature firing process applied to the present invention

3 is an XRD spectrum of various crystal structures of titanium dioxide applied to the present invention.

4 is a graph showing the decomposition rate of congo red at a concentration of 100 mg / L under ultraviolet light by a titanium dioxide photocatalyst having various crystal structures applied to the present invention.

5 is a graph showing the decomposition rate of congo red at 50 mg / L concentration under visible light by titanium dioxide photocatalyst of various crystal structures applied to the present invention.

FIG. 6 is a spectrum analyzed by UV-Vis DR to confirm band gap energy of titanium dioxide having various crystal structures according to the present invention.

* Description of Signs of Main Parts of Drawings *

100. First Process 200. Second Process

300. Third Step 400. Fourth Step

500. The 5th Process 600. The 6th Process

The present invention relates to a method for synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by low temperature heat treatment, and more particularly, to synthesize a titanium dioxide photocatalyst by heat treatment at a temperature of 400 ° C. or less, starting materials titanium halide, water and sulfates. The present invention relates to a method for synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by low temperature heat treatment to control the molar ratio of and convert the crystal structure of titanium dioxide according to reaction conditions.

In general, a photocatalyst is a compound word of photo and a catalyst, which means a catalyst using light or a catalyst for accelerating a photoreaction, and refers to a material that promotes a catalytic reaction using light as an energy source. These photocatalysts not only consumed by directly participating in the reaction, but also provided a mechanism different from the existing photoreaction, satisfying the basic conditions as a general catalyst to accelerate the reaction rate, and irradiating light to a material to be expressed. In this case, semiconducting metal oxides or sulfur compounds which absorb ultraviolet rays and have strong reducing power and oxidizing power are mainly used.

The most widely applied metal oxide for photocatalytic reactions, which plays an essential role in inducing photochemical reactions, is titanium dioxide. In contrast to the photocatalytic reaction mechanism of titanium dioxide, semiconductor materials such as titanium dioxide are energetic unlike general metal oxides. It is characterized by having two bands that do not overlap each other. When light is irradiated on the surface of the titanium dioxide photocatalyst, the electrons in the titanium dioxide valence band are transferred to the excited band. This creates a positive hole at the ground level, with electrons empty.

At this time, the light energy required to transfer electrons corresponds to two energy levels, and according to the crystal structure of titanium dioxide, the anatase structure is 3.2 eV, the rutile structure corresponds to 3.0 eV, and the ruta Titanium dioxide with rutile structure is manufactured by high temperature heat treatment, so its specific surface area is small and its particle size is large, so it is not suitable as a photocatalyst material that reacts on the surface, whereas titanium dioxide with anatase structure has a specific surface area. Since the active site which is wide and can cause surface photoreaction is superior to rutile structure, most of titanium dioxide for photocatalyst is using anatase structure, and in this case, UV light below 400 nm should be irradiated. Photoreaction can be initiated.

Titanium dioxide is most widely used as a photocatalyst, but in recent years, its application as a superhydrophilic medium has been actively progressed. The surface of the titanium dioxide is hydrophobic in the state in which the titanium dioxide is not illuminated, Polarization occurs as the electrons in the state transition to excited state, and the electron polarization converts the titanium dioxide surface from hydrophobicity to hydrophilicity. Can be commercialized as an anti-fog agent.

The titanium dioxide has been utilized as a white pigment of paint before being applied as a photocatalyst due to its excellent physical and chemical properties such as chemical resistance and corrosion resistance. Among the safest rutile titanium dioxide, another mass consumer of titanium dioxide is used as a raw material for cosmetics, and the women's foundation is also made of rutile titanium dioxide with good whiteness. Is used as a raw material, and even in the case of a sunscreen, titanium dioxide having a rutile structure having fast UV absorption and excellent color is used.

In the case of titanium dioxide, the crystal structure required varies depending on the application field. In order to apply titanium dioxide as a photocatalyst and a superhydrophilic product, an anatase structure and an anatase / rutile mixture are generally used. Using the structure, and the application of titanium dioxide to chemical resistance, corrosion resistance, physicochemical properties and UV blocker, the use of rutile titanium dioxide, which is the anatase structure and ruta of titanium dioxide This is due to the difference in physical properties between the rutile structures.

Conventional titanium dioxide synthesizes titanium dioxide precipitate through hydrolysis in acid using rutile ore, ilmenite, titanium chloride and titanium alkoxide as starting materials, and calcined at a temperature between 400 ° C. and 1000 ° C. to pure titanium dioxide. Synthesize

However, in the case of the synthesis of titanium dioxide by the sol-gel method and the hydrolysis method, in order to manufacture pure titanium tiles, the heat treatment must be performed at 700 ° C. or higher. As a result of agglomeration between adjacent particles, there are various problems such as a decrease in catalytic activity due to a reduction in specific surface area.

The present invention has been made to solve the above conventional problems, by adjusting the concentration of the starting material titanium halide, water, sulfate and other reaction conditions to heat treatment at a temperature below 400 ℃ anatase (anatase) structure, anatase (anatase) Titanium dioxide photocatalyst, which enables the synthesis of titanium dioxide photocatalyst having a mixed structure of rutile and rutile and rutile structure, thereby lowering the manufacturing cost of titanium dioxide and improving photoactivity, whiteness and UV blocking function. The purpose is to provide.

In order to achieve the above object, a first step of synthesizing A solution by mixing a starting material of titanium halide (titanium halide) and distilled water; A second step of synthesizing the B solution by mixing the second distilled water and the sulfate; The solution A was stirred while being mixed dropwise to the solution B at a volume ratio of 1: 0.1 to 0.9, and stirred at a temperature of 4 ° C. for 1 hour, and then the mixed solution of solution A and solution B was mixed in argon and nitrogen gas. A third step of synthesizing titanium hydroxide by refluxing for 2 hours while heating to a temperature of 80 ~ 90 ℃ in a thermostat; A fourth step of preparing a basic aqueous solution by mixing and stirring a basic compound and secondary distilled water; Titanium hydroxide synthesized through the third step was added dropwise to the basic aqueous solution prepared through the fourth step, and maintained at a pH of 8 while heating to a temperature of 80 to 90 ° C. in a thermostat in argon and nitrogen gas. A fifth step of refluxing for 1-2 hours while obtaining a titanium dioxide precipitate; The solvent and water were removed from the titanium dioxide precipitate obtained through the fifth process, the remaining reaction by-products and unreacted organics were removed, and then calcined for 2 to 5 hours while maintaining the temperature below 400 ° C. The sixth step of synthesizing the photocatalyst is to implement a method of synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by a low temperature heat treatment.

The present invention is to prepare a titanium hydroxide (titanium hydroxide) as shown in the formula 1 by the hydrolysis reaction in the aqueous solution state using a titanium halide (titanium halide) as a starting material,

TiX ₄ + 4H ₂ O → Ti (OH) ₄ + 4HX (X = F, Cl, Br)

Next, the titanium dioxide hydrate is produced by the condensation reaction of titanium hydroxide prepared above by Chemical Formula 2,

Ti (OH) ₄ → TiO ₂ (hydrous) + 2H ₂ O

The following is a step for removing organic matter and moisture, and heat treatment at a temperature of 400 ° C. or lower, followed by the oxidation of an anatase structure, a rutile structure, or a mixture of rutile and anatase structures according to Chemical Formula 3 Synthesize titanium.

TiO ₂ (hydrous) → TiO ₂

Hereinafter, a method for synthesizing a titanium dioxide photocatalyst in which a crystal structure is converted by low temperature heat treatment applied to the present invention will be described in detail with reference to the accompanying drawings.

1 is a flow chart showing a synthesis process of titanium hydroxide applied to the present invention, Figure 2 is a flow chart showing a synthesis process of the titanium dioxide photocatalyst by a low temperature firing process applied to the present invention, Figure 3 XRD spectrum of various crystal structures of titanium dioxide to be applied, Figure 4 is a graph showing the decomposition rate of congo red at a concentration of 100 mg / L under ultraviolet light by the titanium dioxide photocatalyst of various crystal structures applied to the present invention, 5 is a graph showing the decomposition rate of congo red at a concentration of 50 mg / L under visible light by titanium dioxide photocatalysts of various crystal structures applied to the present invention, and FIG. 6 is a graph showing titanium dioxide having various crystal structures applied to the present invention. Spectrum analyzed by UV-Vis DR to identify band gap energy is shown and described together.

[Step 1 (mixing process of titanium halide and secondary distilled water)]

The first step is a step of mixing a titanium halide (titanium halide) and distilled water as a starting material to agitate a solution of about 0.2 to 3 M titanium halide (titanium halide), in the present invention, the titanium halide (titanium halide) and The solution prepared by stirring distilled water is called 'A solution' (100).

As shown in FIG. 1, 0.2 to 3 M of the starting material titanium halide 110 is added dropwise to distilled water at a temperature of about 4 ° C. (120), and the titanium halide (titanium halide) is uniform in distilled water. The stirring is performed for at least 20 minutes using a magnetic straw (130).

The titanium halide and the water to be stirred are secondary distilled water. In this case, when the molar ratio of titanium halide (titanium halide) to water is 1: 500 or more, titanium dioxide having an anatase structure is synthesized, and titanium When the molar ratio of titanium halide to water is 1:23 to 500, titanium dioxide of anatase and rutile mixed structure is synthesized, and when the molar ratio of titanium halide to water is 1:23 or less Is synthesized titanium dioxide having a rutile structure.

Titanium halide used as the starting material is very rich in reactivity with oxygen, reacts violently with oxygen in the air, absorbs residual water in the air, and is always in an unstable state in the air to cause hydrolysis. Since the synthesis process can be carried out under anoxic conditions, the experiment is carried out under an argon (Ar) or nitrogen (N) gas atmosphere (140).

[Step 2 (Sulfate Aqueous Solution Manufacturing Process)]

The second step is to prepare a sulfate solution produced by mixing and stirring the secondary distilled water and sulfate salt, in the present invention, the sulfate solution is referred to as 'B solution' (200).

As shown in FIG. 1, sulfates such as (NH ₄ ) ₂ SO ₄ , Na ₂ SO ₄ , and K ₂ SO ₄ are mixed with secondary distilled water 210 to obtain an aqueous solution of sulfate having a concentration of sulfate of 0.1 M to 1.0 M. It is prepared (220) and reacted with the solution A. In this case, when the molar ratio of titanium halide to sulfate is greater than 1: 1.5, pure titanium dioxide having an anatase structure is synthesized. When the molar ratio of titanium halide to sulfate is greater than 1: 1.5, the influence of the molar ratio of titanium halide to water of solution A is negligible because the influence of sulfate is dominant in the reaction to determine the structure of titanium dioxide photocatalyst. Pure titanium anatase structure is synthesized.
In addition, when the molar ratio of titanium halide to sulfate is less than 1: 1.5, since the influence of the molar ratio of titanium halide to water of solution A is dominant, the effect of sulfate is neglected. Depending on the molar ratio of titanium halide to water, anatase structure, a mixture of anatase and rutile, and rutile titanium dioxide are synthesized.

When the concentration of the sulfate prepared in the second step is 1.0 M or more, it is preferable that the reaction is not completed later and the starting material titanium halide is decomposed or the reaction proceeds through another route. The sulfate solution obtained by mixing is arbitrarily called "B solution" in this invention.

[Third Step (Titanium Hydroxide Manufacturing Step)]

The third step is to prepare a titanium hydroxide (300) by mixing and stirring the solution A prepared in the first step and the solution B prepared in the second step (300), as shown in Figure 1 In order to synthesize the titanium hydroxide (titanium hydroxide), the second distilled water and sulphate prepared in the second solution to the solution A prepared by the stirring of titanium halide (titanium halide) and distilled water of the first step through a second step The solution B prepared by the mixing of 200 was mixed dropwise to the solution A (100) using a pipette to be mixed at a volume ratio of 1: 0.1 to 0.9 (310), and solution A for 1 hour at a temperature of 4 ° C. The mixed solution of the solution and B is stirred (320), and the mixed solution 330 of the solution A and B is heated to a temperature of 80 to 90 ° C. in a constant temperature bath 340 in an argon and nitrogen gas atmosphere which is anoxic. (350) reflux for 2 hours (360) titanium hydroxide It synthesizes (titanium hydroxide).

[4th process (basic aqueous solution manufacturing process)]

A fourth process is a process of mixing and stirring a basic compound 410 such as NaOH, KOH, and NH ₄ OH and secondary distilled water 420 (430) to prepare a basic aqueous solution (400), as shown in FIG. As described above, in order to neutralize the titanium hydroxide prepared by the third step 300, the basic aqueous solution is prepared, and the basic aqueous solution is added to the distilled water so that the pH is about 13-14. Then, it is prepared by vigorously stirring for 30 minutes using a stirrer.

[5th process (Titanium dioxide precipitate manufacturing process)]

The fifth step is a step of dropping and stirring the basic aqueous solution 400 in titanium hydroxide, and the basic aqueous solution 400 prepared by the fourth step is prepared by titanium hydroxide. Stirring and dropping into a titanium hydroxide (300) (510) while maintaining a pH of 8 (520) under anoxic conditions in an argon and nitrogen gas (530) for 1 to 2 hours while heating to 80 ~ 90 ℃ Reflux (540) may yield a milky titanium dioxide precipitate.

[Step 6 (Manufacturing Process of Titanium Dioxide Photocatalysts of Various Structures)]

The sixth step is to remove the solvent and the remaining organic matter in the titanium dioxide precipitate, and to prepare a titanium dioxide photocatalyst of various structures (600), as shown in Figure 2 titanium dioxide precipitate obtained in the fifth step ( 500) by using a rotary concentrated evaporator to remove the solvent in the range of 40 ~ 80 ℃ (610), and store the titanium dioxide of various structures for about one day in a vacuum desiccator containing an absorbent (620) to titanium dioxide The included moisture is removed (630).

Pure titanium dioxide with a variety of structures is removed by removing the remaining reaction by-products and unreacted organics (640) and firing at 400 ° C. for 2-5 hours in a tube furnace to run crystallinity (650). Prepare a photocatalyst.

Hereinafter, an experimental example for measuring the crystal structure and photoactivity of titanium dioxide by low temperature heat treatment applied to the present invention will be described.

Experimental Example 1 (XRD Measurement)

Experimental Example 1 is to measure the XRD (X-ray diffraction) of the titanium dioxide photocatalyst in order to confirm the crystal structure according to the reaction conditions of the titanium dioxide photocatalyst synthesized in the first to sixth step, Table 1 below Figure 3 shows the measurement conditions of the XRD data for measuring the XRD, Figure 3 shows the crystal structure of the titanium dioxide photocatalyst synthesized by varying the molar ratio of titanium halide to water and sulfate in the first step and the second step It is a graph (spectrum) analyzed by XRD.

Parameters Value Start angle 20.00 End angle 80.00 Step size 0.04 Time per step 0.50 Used radiation Cu K _a

As a result of the measurement with the basic measurement conditions shown in Table 1, as shown in FIG. 3, the higher the concentration of titanium halide (titanium halide), the higher the rutile (rutile) weight fraction in titanium dioxide. Properly adjusting the molar ratio of titanium halide to water and sulfate in the first and second steps of the invention will produce titanium dioxide photocatalysts of various structures under low temperature heat treatment conditions of 400 ° C. or less. It becomes possible.

Experimental Example 2 (photolysis experiment)

Figures 4 and 5 show the reaction time of the reaction time of congo red by titanium dioxide and rutile 17%, 51%, 91% and 100% titanium dioxide photocatalyst of pure anatase structure in ultraviolet and visible light, respectively. As a graph showing the results of analysis with a UV-Vis spectormeter, it is used as a red dye to investigate the photoactivity in the ultraviolet light for the titanium dioxide photocatalysts of various structures synthesized by the first to sixth process. Congo red is about 100 mg / L as standard and 50 mg / L congo red is used as a standard material. .

As shown above, after the condensation of the red dye dye congo red 100 mg / L concentration of the various structures prepared by the precipitation method under the ultraviolet light source using a titanium dioxide light irradiation, these photocatalysts by congo Degradation curves of the red solution show 21% and 16% catalytic activity, respectively, compared to pure titanium anatase photocatalysts, which are commercially used titanium dioxide containing 17% and 51% rutile structures. It can be seen that this improvement.

The decomposition test of 50 mg / L congo red with titanium dioxide photocatalysts of various structures synthesized by the first to sixth steps under the visible light irradiation by installing the ultraviolet filter is shown in FIG. Similar to the results of the experiments, it can be seen that the activity of the catalyst containing a certain amount of rutile structure is superior to that of the pure anatase structure catalyst.

However, when 60 mg of congo red at 50 mg / L concentration was photolyzed under visible light irradiation for 60 minutes, the relative activity difference of the catalyst having a rutile fraction of 17% for pure anatase structure catalyst was 78 As a percentage, the catalytic activity of the visible light source is superior to that of the ultraviolet light.

As can be seen from the above results, it can be seen that TiO ₂ containing a rutile structure is much more catalytically active in ultraviolet and visible light sources than titanium dioxide having anatase structure, which is commonly used. In the light source, it can be seen that the activity is improved by 78% or more than the anatase structure catalyst.

As shown in FIG. 3, when the first to sixth processes are manufactured, crystal structure conversion of titanium dioxide can be performed by detailed reaction conditions, which affects the produced titanium dioxide activity.

As such, the photocatalytic activity of titanium dioxide, which contains about 10% to 50% of the rutile structure, is superior to that of the pure anatase structure of titanium dioxide, which is widely used commercially. This is because titanium dioxide having a structure exhibits catalytic activity by absorbing light in the visible region, which will be described in detail through Experimental Example 3.

Experimental Example 3 (UV-Vis DR Spectrum of Titanium Dioxide)

As shown in FIG. 6, it can be seen that as the rutile structure increases in the crystal structure of the titanium dioxide photocatalyst, the absorption spectrum shifts to the long wavelength region, and the dioxide produced by the first to sixth steps The higher the rutile structure ratio in the titanium photocatalyst, the higher the activity in the long wavelength. As shown in FIGS. It can be seen that the activity is excellent.

The present invention adjusts the concentration of the starting material titanium halides, sulfates and other reaction conditions to obtain a titanium dioxide having a pure rutile structure and a mixed structure of rutile / anatase at a temperature of 400 ℃ or less By making it possible to synthesize, it is possible to reduce the heat treatment cost, and it is possible to synthesize rutile titanium dioxide by heat treatment at 400 ℃ to increase the specific surface area up to 30㎡ / g. When used as a physical property sensitizer for barriers and rubbers, the specific surface area to the same weight is large, so that the effectiveness of titanium dioxide can be improved in a small amount.

In addition, when applied as a photocatalyst, the photocatalytic activity of titanium dioxide in which rutile is present at a ratio of 17% is about 16% and 78% at ultraviolet and visible light, respectively, than titanium dioxide having pure anatase structure. Under the conditions, the decomposition efficiency of organic matter is increased, so that it can be applied to various fields such as environmental purification, antifouling, sterilization, and building materials.In particular, the catalytic activity is improved by about 78% in visible light than commercial titanium anatase structure. It can be applied as a photocatalyst showing high efficiency in sunlight.

Claims (4)

A first step of synthesizing an A solution by mixing a starting material titanium halide and distilled water; A second step of synthesizing the B solution by mixing the second distilled water and the sulfate; The solution A was stirred while being mixed dropwise to the solution B at a volume ratio of 1: 0 to 0.9, and stirred at a temperature of 4 ° C. for 1 hour, and then the mixed solution of solution A and solution B was dissolved in argon and nitrogen gas. A third step of synthesizing titanium hydroxide by refluxing for 2 hours while heating to a temperature of 80 ~ 90 ℃ in a thermostat; A fourth step of preparing a basic aqueous solution by mixing and stirring a basic compound and secondary distilled water; Titanium hydroxide synthesized through the third step was added dropwise to the basic aqueous solution prepared through the fourth step, and maintained at a pH of 8 while being heated to a temperature of 80 to 90 ° C. in a thermostat in argon and nitrogen gas. A fifth step of refluxing for 1-2 hours while obtaining a titanium dioxide precipitate; The solvent and water were removed from the titanium dioxide precipitate obtained through the fifth process, the remaining reaction by-products and unreacted organics were removed, and then calcined for 2 to 5 hours while maintaining the temperature below 400 ° C. And a sixth step of synthesizing the photocatalyst. The method of synthesizing a titanium dioxide photocatalyst, wherein the crystal structure is converted by a low temperature heat treatment. The method of claim 1, Solution A synthesized by the first step is produced by mixing and stirring 0.2-3 M of titanium halide, which is a starting material, with distilled water at 4 ° C., with a molar ratio of titanium halide (titanium halide) to water of 1: 500. In the above case, titanium dioxide having an anatase structure is synthesized, and when the molar ratio of titanium halide to water is 1:23 to 500, titanium dioxide having a mixture of anatase and rutile is synthesized. When the molar ratio of titanium halide to water is 1:23 or less, a method of synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by low temperature heat treatment is characterized in that titanium dioxide having a rutile structure is synthesized. The method of claim 1, Solution B synthesized by the second process is to produce a sulfate solution of the concentration of 0 ~ 1.0 M by mixing sulphate in the second distilled water, if the molar ratio of titanium halide (titanium halide) to sulphate 1: 1.5 or more The effect of the molar ratio of titanium halide to water in the solution is ignored, resulting in the synthesis of pure titanium dioxide with an anatase structure, and when less than 1: 1.5, the effect of sulfate is ignored so that the titanium halide of solution A is ignored. According to the molar ratio of halide) to water, the crystal structure is converted by low temperature heat treatment, characterized by the synthesis of anatase structure, anatase and rutile mixed structure, and rutile titanium dioxide. Method for synthesizing titanium dioxide photocatalyst. The method of claim 1, The basic aqueous solution synthesized by the fourth step is a basic compound such as NaOH, KOH and NH ₄ OH and secondary distilled water is mixed and stirred, optionally mixed one or overlapping to prepare a basic aqueous solution of pH 13-14 A method for synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by low temperature heat treatment, which is added dropwise to titanium hydroxide synthesized through a third process and maintained at pH 8.

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