KR100912601B1 - Synthetic method of titanium dioxide photocatalysts to change crystal structure by rate of sulfate and chlorine - Google Patents

Abstract

A synthetic method of a titanium dioxide photocatalyst of which crystalline structure is transformed by sulphate and a chlorine rate is provided to reduce manufacturing cost according to a thermal process by synthesizing the titanium dioxide in low temperature. A synthetic method of a titanium dioxide photocatalyst of which crystalline structure includes the following steps of: synthesizing a titanium tetrachloride aqueous solution having 0.2~3.0M concentration(100); synthesizing a sulphate aqueous solution having 0.1~1.0M concentration by mixing second distilled water and the sulphate(200); synthesizing a titanium dioxide precipitate(300); removing non-reactive organic compounds and remaining reactive by-products; and synthesizing the titanium dioxide photocatalyst(400).

Description

Synthetic method of Titanium Dioxide Photocatalysts to change crystal structure by rate of sulfate and chlorine}

The present invention relates to a method for synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by the ratio of sulphate and chlorine, and more particularly, to synthesize a titanium dioxide photocatalyst by heat treatment at a temperature of 100 ° C. or lower, and to a tetrachloride as a starting material. was added to the chlorine (Cl ^_) and sulfate (sO ₄ ^{2 -)} to adjust the molar ratio of the present invention relates to a method for the synthesis of the titanium dioxide photocatalyst to be easily converted under suitable reaction conditions in a wide variety of crystal structures of titanium dioxide.

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 do not consume and participate directly in the reaction, but provide a mechanism different from the existing photoreaction, satisfying the basic conditions as a general catalyst that can accelerate the reaction rate, as well as irradiating light to the material to be expressed. When used, semiconducting metal oxides or sulfur compounds that absorb ultraviolet light and have strong reducing and oxidizing power are mainly used.

The most widely applied metal oxide for photocatalytic reaction, which plays an essential role in inducing the photochemical reaction, is titanium dioxide. Looking at the photocatalytic reaction mechanism of titanium dioxide, unlike general metal oxides, semiconductor materials such as titanium dioxide are energetic 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, electrons in the titanium dioxide valence band are transferred to the excitde band. This creates a positive hole at the ground level, with electrons empty.

At this time, the light energy required for electron transfer corresponds to two energy levels, and according to the crystal structure of titanium dioxide, the anatase structure is 3.2 eV, the rutile structure is 3.0 eV, and the ruta Titanium dioxide with rutile structure is produced 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 anatase titanium dioxide has a specific surface area. Because of this wide and the active site that can cause surface photoreaction is superior to the rutile structure, most of titanium dioxide for photocatalyst is using anatase structure. Photoreaction can be initiated.

Titanium dioxide is most widely used as a photocatalyst, but recently, the application as a super-aqueous medium is also actively progressed. In the state where the titanium dioxide is not lighted, the surface has hydrophobic properties, but the base state is irradiated with ultraviolet rays of 400 nm or less. The polarization occurs due to the transition of electrons into excited state, and the electron polarization converts the titanium dioxide surface from hydrophobic to hydrophilic. This property is used to make mirrors of wet toilets, car rearview mirrors and other glass products. Commercially available 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, and when used as a paint pigment, it generally has a crystal structure of titanium dioxide because of its good chemical resistance and whiteness. 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 also has a good whiteness rutile titanium dioxide. 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, anatase structure and anatase / rutile mixture are generally used. The structure, and the chemical resistance, corrosion resistance, physicochemical properties of the titanium dioxide and the application of the product to the UV blocker uses a rutile titanium dioxide, which is an anatase structure and rutile of titanium dioxide This is due to the difference in physical properties between the rutile structures.

Conventional titanium dioxide is synthesized 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 ℃ and 1000 ℃ pure titanium dioxide Synthesize

However, in the conventional method of synthesizing titanium dioxide by the sol-gel method or the hydrolysis method, in order to manufacture a pure rutile titanium dioxide, heat treatment is performed on an anatase structure titanium dioxide at a temperature of 700 ° C. or higher. Particle size is increased by mutual agglomeration of adjacent particles by the heat treatment process, and thus the surface area is reduced so that the catalytic activity is reduced. In the high temperature heat treatment process, the production cost is increased as the heat treatment temperature is increased. There is a problem of this deterioration.

The present invention has been made in order to solve the above conventional problems, using titanium tetrachloride as a starting material to control the molar ratio of chlorine (Cl ^_ ) and sulfate (SO ₄ ^2- ) at a low temperature of less than 100 ℃. Through this, an object of the present invention is to easily synthesize a titanium dioxide photocatalyst having a pure anatase structure, an anatase / rutile mixed structure, and a pure rutile structure.

A first step of synthesizing an aqueous titanium tetrachloride solution having a concentration of 0.2 to 3.0 M by mixing titanium tetrachloride as a starting material and distilled water in order to achieve the above object; A second step of synthesizing an aqueous solution of sulfate having a concentration of 0.1 to 1.0 M by mixing sulfate and secondary distilled water; The aqueous solution of titanium tetrachloride and the aqueous solution of sulfate solution were added dropwise to the aqueous solution of titanium tetrachloride in a volume ratio of 1: 0.01 to 0.5, and stirred. The mixture was stirred for 1 to 2 hours at a temperature of 4 ° C. And a third step of synthesizing the titanium dioxide precipitate by refluxing for 12 to 36 hours while heating to a temperature of 50 ~ 100 ℃ in a thermostatic chamber in nitrogen gas. After removing the solvent and water from the titanium dioxide precipitate obtained through the third process, the water is removed, the remaining reaction by-products and unreacted organics are removed, and then fired for 2 to 5 hours while maintaining the temperature below 400 ° C. The fourth step of synthesizing the titanium dioxide photocatalyst is to implement a method for synthesizing the titanium dioxide photocatalyst in which the crystal structure is converted by the ratio of sulfate and chlorine.

In the titanium dioxide precipitate synthesized through the third process, when the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^{2 −} ) is less than or equal to 1: 0.01, the effect of the sulfate ion is ignored and thus pure rutile When titanium dioxide having a crystal structure is synthesized and the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^{2 −} ) is greater than 1: 0.01 to less than 1.0, the effect of sulfate ions is not ignored and chlorine ions present in the solution. And the anatase / rutile crystal structure of titanium dioxide is synthesized, and the effect of chlorine ion when the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^2- ) is 1: 1.0 or more This is neglected to allow the synthesis of pure titanium anatase crystal structure.

The invention and the titanium tetrachloride as a starting material chlorine (Cl ^_) and sulfate (SO ₄ ^{2 -)} a low temperature heat treatment by pure anatase below 100 ℃ (anatase) structure, the anatase / rutile under conditions to control the molar ratio of (anatase It is possible to synthesize a titanium dioxide photocatalyst having a / rutile) mixed structure and a pure rutile structure, thereby relatively shortening the manufacturing process and synthesizing titanium dioxide at a low temperature, thereby reducing the manufacturing cost according to the heat treatment cost. Since it is manufactured by heat treatment at low temperature and has a relatively large specific surface area compared to the same weight, it can be used as a paint pigment, cosmetics, sunscreen, rubber sensitizer, etc., thereby improving the effectiveness of the product.

Hereinafter, a method of synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by the sulfate and chlorine ratios applied to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a flowchart illustrating a synthesis process of a titanium dioxide photocatalyst applied to the present invention, FIG. 2 is an exemplary diagram of spectrums analyzed by XRD of various crystal structures of titanium dioxide before firing, and FIG. Exemplary spectrum of XRD analysis of various crystal structures of titanium dioxide after firing applied to the present invention.

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 titanium tetrachloride (TiCl ₄ ) as a starting material,

_{TiCl 4 + 4H 2 O → Ti} (OH) 4 + 4H + + 4Cl -

Titanium dioxide hydrate is made by the condensation reaction of titanium hydroxide prepared in Chemical Formula 1 as shown in Chemical Formula 2,

Ti (OH) ₄ → TiO ₂ (hydrous) + 2H ₂ O

The following is a step for removing organic matter and water, and having an anatase structure, an anatase / rutile mixed structure or a rutile structure by the heat treatment at a temperature of 400 ℃ or less Titanium dioxide is synthesized.

TiO ₂ (hydrous) → TiO ₂

In the present invention, various crystal structures such as pure anatase structure, anatase / rutile mixed structure, and pure rutile structure are controlled by controlling the ratio of sulfate and chlorine under low temperature heat treatment at 100 ° C. or lower. The branch is to make it easy to synthesize titanium dioxide, look at the synthesis process of the titanium dioxide photocatalyst, the crystal structure is converted by the sulfate and chlorine ratio implemented by one embodiment of the present invention, as follows.

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

The first step is to prepare a titanium tetrachloride aqueous solution having a concentration of 0.2 ~ 3M by mixing titanium tetrachloride (TiCl ₄ ) and distilled water as a starting material, in the present invention, a solution prepared by stirring the titanium tetrachloride (TiCl ₄ ) and distilled water Is referred to as "A solution".

Titanium tetrachloride (TiCl ₄ ), which is the starting material, was added dropwise to distilled water at a temperature of about 4 ° C. At this time, titanium tetrachloride (TiCl ₄ ) was stirred in the distilled water for 1 to 2 hours to uniformly dissolve the distilled water. Do the work.

The titanium tetrachloride (TiCl ₄ ) and the water to be stirred using secondary distilled water, in this case the concentration of the titanium tetrachloride solution is about 0.2 ~ 3.0M, when the concentration of the titanium tetrachloride solution is more than 3.0M As the reaction proceeds very rapidly, it is difficult to control the titanium dioxide crystal structure, which may cause undesirable results.

Titanium tetrachloride (TiCl ₄ ) used as the starting material reacts violently with oxygen in the air, absorbs the remaining water in the air, and remains in an unstable state in the air so as to cause hydrolysis. Is to be carried out under anoxic conditions, but the experiment is carried out in an argon (Ar) or nitrogen (N) gas atmosphere.

[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".

Sulfates such as (NH ₄ ) ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ are mixed with the secondary distilled water to prepare a sulfate solution having a sulfate concentration of 0.1 to 1.0 M. The sulfate concentration is 1.0 M. In this case, it is preferable to pay attention because the reaction proceeds rapidly in the titanium dioxide precipitate production step of the third step.

[3rd process (titanium dioxide precipitate manufacturing process)]

The third step is to prepare a titanium dioxide precipitate by mixing and stirring the solution A prepared in the first step and the solution B prepared in the second step, and in order to synthesize the titanium dioxide precipitate, titanium tetrachloride (TiCl ₄ ) The solution A prepared by stirring the distilled water and the solution B prepared by stirring the sulfate and distilled water were stirred with a pipette so as to be mixed at a volume ratio of 1: 0.01 to 0.5 with a pipette, and stirred at a temperature of 4 ° C. for 1 to 2 hours. While the mixed solution of solution A and solution B is stirred, the solution of solution A and solution B is heated to a temperature of 50 to 100 ° C. in an incubator in an argon (Ar) and nitrogen (N) gas atmosphere, which is anoxic conditions. Reflux for ˜ 36 hours to synthesize a titanium dioxide precipitate.

When the titanium dioxide is chlorine (Cl ^_) increases the content of ions under acidic conditions, rutile (rutile) and the crystal structure is synthesized, a sulfate (SO ₄ ^{2 -)} when the content of the ion is increased, anatase by steric hindrance Because of the tendency to form (anatase) crystal nuclei, an anatase crystal structure is synthesized.

In mixing the A solution prepared by stirring titanium tetrachloride (TiCl ₄ ) with distilled water and the B solution prepared by stirring sulfate and distilled water, the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^{2 −} ) is 1: 0.01 or lower case, chlorine (Cl ^_) ion impact is relatively sulfate by (SO ₄ ^{2 -)} the sulfate because it largely acts more influenced by the ion (SO ₄ ^{2 -)} an effect on the ion is ignored these conditions In is synthesized titanium dioxide having a pure rutile crystal structure.

When the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^{2 −} ) is greater than 1: 0.01 to less than 1.0, the effect on sulphate (SO ₄ ^{2 −} ) ions can no longer be ignored. It is competing with Cl ^_ ) ions, whereby titanium dioxide having an anatase / rutile mixed structure is synthesized under these conditions.

The chlorine (Cl ^_) for sulfate (SO ₄ ^{2 -)} a molar ratio of 1: 1.0, sulfate (SO ₄ ^{2 -)} or more are affected by ion zoom is effected prior to impact of relatively chlorine (Cl ^_) ion Under these conditions, titanium dioxide with a pure anatase crystal structure is synthesized because the influence by chlorine (Cl ^_ ) ions is ignored.

[Step 4 (Manufacturing Process of Titanium Dioxide Photocatalysts with Various Structures)]

The fourth step is to remove the solvent and the organic matter remaining in the titanium dioxide precipitate, to prepare a titanium dioxide photocatalyst of various crystal structures, the solvent is removed from the titanium dioxide precipitate obtained in the third step using a vacuum filter In order to remove residual impurities, it is washed several times with distilled water, and titanium dioxide of various crystal structures is stored in a vacuum desiccator containing a moisture absorbent for one day to remove moisture contained in titanium dioxide.

The remaining reaction by-products and unreacted organics are removed, and then fired at 400 ° C. for 2 to 5 hours in a tube furnace to increase crystallinity, thereby preparing pure titanium dioxide photocatalyst having various crystal structures.

Hereinafter, an experimental example of the crystal structure of titanium dioxide converted by the sulfate and chlorine ratios applied to the present invention will be described.

Experimental Example (XRD Measurement)

Experimental Example was measured 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 fourth process, Table 1 below will showing the measurement conditions of the XRD data, 2 and 3 are chlorine in a third step (Cl ^_) and sulfate (SO ₄ ^{2 -)} to measure the XRD crystals of titanium dioxide photocatalyst composite by varying the mole ratio of structure 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

The table has the basic measurement conditions shown in the first measurement result, the chlorine in the third step of the present invention (Cl ^_) and sulfate (SO ₄ ^{2 -)} by properly adjusting the molar ratio of 2, and as shown in Figure 3 of the Titanium dioxide photocatalysts of various crystal structures can be prepared under low temperature heat treatment conditions of 100 ° C or lower.

Table 2 below shows the XRD measurement results of titanium dioxide before and after firing shown in FIGS. 2 and 3, and synthesized by controlling the molar ratio of chlorine (Cl ^_ ) and sulfate (SO ₄ ^{2 −} ). In order to confirm the composition of each crystal structure from the XRD analysis results of the rutile (rutile) peaks and the anatase (anatase) peaks are summarized numerically.

No. As-synthesized Calcined (after firing) I _A I _R Fraction of ruitle (%) Fraction of anatase (%) I _A I _R Fraction of ruitle (%) Fraction of anatase (%) a 0 1,734 100.0 0.0 0 3,022 100.0 0.0 b 85 1,244 94.8 5.2 340 2,888 91.4 8.6 c 269 1,059 83.1 16.9 663 2,000 79.0 21.0 d 856 598 46.6 53.4 2,695 909 29.7 70.3 e 981 392 33.3 66.7 2,557 502 19.7 80.3 f 1,233 306 23.7 76.3 2,923 359 13.3 86.7 g 1,422 132 10.4 89.6 3,273 108 4.0 96.0 h 1,988 0 0.0 100.0 3,404 0 0.0 100.0 i 2,214 0 0.0 100.0 3,176 0 0.0 100.0

The composition of the crystal structure according to the synthesis conditions can be obtained from the following formula.

[Calculation 1]

Fraction of rutile (%) =

[Calculation 2]

Fraction of anatase (%) = 100-Fraction of rutile

Titanium dioxide is a ceramic crystal having a variety of crystal planes, I _A in the formula 1 represents the intensity of the peak diffracted in the 101 planes of the anatase (anatase) crystal structure, I _R is 110 planes rutile crystal structure will represent the intensity of the peak that is diffracted in, chlorine (Cl ^_) and sulfate (SO ₄ ^{2 -)} in the third step of the present invention from the results in Table 2 by properly controlling the molar ratio of a, to prepare the titanium dioxide of the various structures It can be seen that the composition can also be precisely formulated.

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

Figure 2 is an illustration of the spectrum of XRD analysis of various crystal structures of titanium dioxide before firing applied to the present invention

Figure 3 is an illustration of the spectrum of XRD analysis of various crystal structures of titanium dioxide after firing applied to the present invention

* Description of Signs of Main Parts of Drawings *

100. First Process 200. Second Process

300. Third Step 400. Fourth Step

Claims (2)

A first step of synthesizing an aqueous titanium tetrachloride solution having a concentration of 0.2 to 3.0 M by mixing titanium tetrachloride and distilled water as starting materials; A second step of synthesizing an aqueous solution of sulfate having a concentration of 0.1 to 1.0 M by mixing sulfate and secondary distilled water; The aqueous solution of titanium tetrachloride and the aqueous solution of sulfate solution were added dropwise to the aqueous solution of titanium tetrachloride in a volume ratio of 1: 0.01 to 0.5, and stirred. The mixture was stirred for 1 to 2 hours at a temperature of 4 ° C. And a third step of synthesizing the titanium dioxide precipitate by refluxing for 12 to 36 hours while heating to a temperature of 50 ~ 100 ℃ in a thermostatic chamber in nitrogen gas. After removing the solvent and water from the titanium dioxide precipitate obtained through the third process, the water is removed, the remaining reaction by-products and unreacted organics are removed, and then fired for 2 to 5 hours while maintaining the temperature below 400 ° C. And a fourth step of synthesizing the titanium dioxide photocatalyst. The method of claim 1, In the titanium dioxide precipitate synthesized through the third process, When the molar ratio of chlorine (Cl ^_ ) to sulfate (SO ₄ ^{2 −} ) is less than or equal to 1: 0.01, the effect of the sulfate ions is ignored and pure titanium dioxide having a pure rutile crystal structure is synthesized. Chlorine (Cl ^_) for sulfate (SO ₄ ^{2 -)} in a molar ratio of 1: 0.01 has been exceeded less than ~1.0 compete with chloride ions present in the do not override the effect of the sulfate ion solution anatase / rutile ( Titanium dioxide of anatase / rutile) crystal structure is synthesized, Chlorine (Cl ^_) for sulfate (SO ₄ ^{2 -)} a molar ratio of 1: not less than 1.0, characterized in that the override the influence of the chloride ion synthesis of pure anatase (anatase) of titanium dioxide in the crystalline structure sulfate and A method for synthesizing a titanium dioxide photocatalyst in which the crystal structure is converted by a chlorine ratio.

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