KR100676458B1 - Method for synthesis of mesoporous TiO2 and transition metals-impregnated mesoporous TiO2 with visible light activity - Google Patents

Abstract

The present invention relates to a method for synthesizing mesoporous TiO ₂ using a surfactant and impregnating transition metal platinum (Pt) in the pores to produce a photocatalyst having a high activity and high durability in the visible region, the hydrophobic portion of the surfactant By adjusting the length of the mesopores can be adjusted to the intended size, it is possible to synthesize various types of mesopores TiO ₂ such as plate and hexagonal shape depending on the synthesis conditions, in particular impregnated with various transition metals in the pores by concentration It can be characterized by.

The mesoporous TiO ₂ and the transition metal impregnation in the pores according to the present invention can not only maintain the surface of the photocatalyst TiO ₂ by maintaining the surface of the photocatalyst TiO ₂ by impregnating the transition metal in the pores, and further, the transition metal. By the photocatalyst having an active in the visible light region and has an effect that can increase the photoactivity accordingly, to solve the problem of the sustainability and safety of the catalyst, which was a disadvantage in the practical use step at the same time, visible light having high durability and high activity An active photocatalyst can be produced.

Mesopores, TiO2, transition metal impregnation, photocatalyst, visible light activity, sulfuric acid, surfactant

Description

Method for synthesis of mesoporous TiO2 and transition metals-impregnated mesoporous TiO2 with visible light activity}

Figure 1a shows a schematic diagram of the plate-shaped mesoporous TiO ₂ of the present invention.

Figure 1b shows a schematic diagram of the hexagonal mesoporous TiO ₂ of the present invention.

Figure 2a is a curve graph showing the X-ray diffraction analysis (XRD) results of the powder specimens for the plate-shaped mesoporous TiO ₂ obtained in the Example according to the present invention.

Figure 2b shows a TEM image of the plate-shaped mesoporous TiO ₂ obtained in the embodiment according to the present invention.

Figure 3a is a curve graph showing the X-ray diffraction analysis (XRD) results of the powder specimens for the hexagonal mesoporous TiO ₂ obtained in the embodiment according to the present invention.

Figure 3b shows a TEM picture of the hexagonal mesoporous TiO ₂ obtained in the embodiment according to the present invention.

Figure 4 shows a TEM photograph impregnated with a transition metal Pt in the mesoporous TiO ₂ obtained in the embodiment according to the present invention.

The present invention relates to a method for synthesizing various types of mesopores TiO ₂ of TiO ₂ widely used as a photocatalyst and a method for impregnating transition metals in pores. More specifically, the present invention relates to a method of increasing the surface area by synthesizing mesoporous TiO ₂ in plate and hexagonal form by using a surfactant and acidic conditions, and a method of impregnating transition metal (Pt) by concentration in pores. Mesopores using a sol-gel method under an acidic condition using sulfuric acid, a surfactant such as alkyltrimethylammonium bromide or alkyltriethylammonium bromide, and a titanium precursor such as titanium isopropoxide A method of synthesizing TiO ₂ and impregnation method using hexacroroplatonic acid (H ₂ PtCl ₆ · 6H ₂ O) as a precursor of a transition metal, more specifically platinum (Pt), to the pores of the synthesized mesopores TiO ₂ It relates to a method of impregnating platinum nanoparticles by concentration.

The development of mesoporous forms has been active since 1992, when Mobil scientists announced the hexagonal array of mesoporous silica, named MCM-41, resulting in MCM-48, KIT-1, MSU-1, and MCM. Mesoporous silica molecular sieves of various structures with uniform pore sizes were synthesized in the meso region, such as -41 or the same spatial group but larger pore size.

Mesoporous silica molecular sieves are produced primarily from a collection of surfactants using structural derivatives. Among the various mechanisms, the joint mold mechanism proposed by Professor GD Stucky at the University of California, Santa Barbara, is commonly accepted. have. That is, in the present mechanism, a complex composed of a surfactant and a silicate is formed, and a phase change may occur by affecting the structure of the formed complex as the silicate present on the surface of the micelle formed by the surfactant causes a polymerization reaction. Therefore, it is possible to synthesize mesoporous silica molecular sieves having various pore structures and sizes by changing the surfactant or by changing the reaction conditions such as reaction temperature and composition. These mesoporous silica molecular sieves have shown application potential as adsorbents and catalysts, and examples have been reported that they can be applied to various fields such as the production of nanostructured metals and semiconductor materials.

These highly useful mesoporous molecular sieves are not limited to mesoporous silica (SiO ₂ ) alone, and the metals that can be synthesized so far are available for Al, Ga, Sn, Sb, V, Fe, Mn, Zr, Hf, W and Nb have been published. However, in the case of TiO _{2 which} is well known as a photocatalyst, mesoporous TiO ₂ of a precisely controlled structure except for the coating form was not synthesized. Making TiO ₂ into mesoporous form, it has been studied by many people because of its high surface area and its applicability. However, until now, the reason why it has not been able to show such a good result is that when the toxic titanium precursor (Ti (OR) ₄ ) meets with water, the polymerization reaction occurs too quickly under acidic conditions with hydrolysis.

For example, in the case of mesoporous silica, when a surfactant is dissolved in water and a silica precursor (Si (OR) ₄ ) is added under acidic conditions, a complex composed of a surfactant and a silicate is formed and present on the surface of the micelle formed by the surfactant. Silicates develop into polymerized sieves in the form of mesopores. However, when the titanium precursor (Ti (OR) ₄ ) is in contact with water, the polymerization reaction takes place so rapidly under acidic conditions with hydrolysis, so it grows into TiO ₂ nanoparticles and is separated from the surfactant to form a mesoporous molecular sieve. It becomes impossible.

In order to overcome the problems caused by the rapid polymerization of titanium precursors, there were cases in which a polymerization inhibitor was added to synthesize the mesoporous TiO ₂ in the form of a coating, but meso precisely controlled in the form of particles. There was no successful synthesis of pore TiO ₂ . Furthermore, the results of impregnating transition metal platinum (Pt) in the pores of mesopores TiO ₂ with precisely controlled particle morphology have not been published.

Accordingly, the present invention provides a method for synthesizing mesoporous TiO ₂ in plate and hexagonal form while inhibiting hydrolysis and polymerization reactions rapidly progressing when the titanium precursor reacts with water under acidic conditions and interacting with a surfactant. I would like to.

In addition, the present invention synthesizes mesopores TiO ₂ in the form of a plate and hexagon, while inhibiting the hydrolysis and polymerization reaction that proceeds rapidly when the titanium precursor reacts with water under acidic conditions and interact with the surfactant, and in the pores It is intended to provide a method for preparing a material impregnated with a transition metal.

In order to achieve the above object, the present inventors repeat various experiments based on the need for a medium to strengthen the interaction with the surfactant to dissolve the titanium precursor in water to obtain a regular and precisely controlled material in the form of mesopores. as a result, the titanium precursor under acidic conditions using sulfuric acid has been used in hydrolysis and polymerization sulfonate group (SO ₄ ^2-) is a TiO ₂ surface causes an interaction between TiO ₂ and the surface active agent that causes a polymerization reaction The present invention has been realized while discovering that it can grow around the active agent to form mesopores.

The present invention solves the problems of mesoporous TiO ₂ , which was able to produce irregular and specific coating forms, and also imparts thermal stability and high activity and high durability of mesoporous TiO ₂ by impregnating transition metals in the pores by concentration. Photocatalysts can be provided.

The present invention relates to a method for synthesizing mesoporous metal oxides whose shape and size are controlled using a surfactant under acidic conditions.

In addition, the present invention relates to a method for synthesizing mesoporous TiO ₂ having pores whose shape and size are controlled by using a surfactant under acidic conditions, and impregnating a transition metal in the pores.

Specifically, in the conventional mechanism for synthesizing mesopores by reacting a surfactant with a metal precursor under acidic conditions, sulfuric acid is added under the acidic conditions and a titanium precursor is added to the metal precursor. That is, the present invention relates to a method for synthesizing mesoporous TiO _2, characterized in that the mesopores are synthesized by reacting a surfactant and a titanium precursor under acidic conditions with sulfuric acid.

In the method for producing mesoporous TiO ₂ of the present invention, a sulfonate group (SO) of sulfuric acid is used to react a surfactant having a structure such as Chemical Formula 1 or Chemical Formula 2 with a titanium precursor and increase the interaction between the surfactant and the titanium precursor. ₄ ^2- ). In the formula of the following surfactant, n (natural number) has a range of 10-20, and preferably 13, 15, or 17. The sulfonate group of the present invention enhances the interaction of the surfactant with the titanium precursor, allowing the titanium precursor to undergo polymerization while auditing the surfactant, making it possible to produce mesoporous TiO ₂ .

CH ₃ (CH ₂ ) _n N (CH ₃ ) ₃ ⁺ Br ^- n = 10 ~ 20

CH ₃ (CH ₂ ) _n N (CH ₂ CH ₃ ) ₃ ⁺ Br ^- n = 10 ~ 20

Preferably the surfactant of the present invention is a tetradecyltrimethylammonium Bromide (Tetradecyltrimethylammonium Bromide), hexadecyltrimethylammonium Bromide (octadecanetrimethylammonium Bromide) and octadecane trimethylammonium Bromide (Octadecyltrimethylammonium group Bromide) having a structure of Formula 1 The structure of Formula 2 may be selected from the group consisting of Tetradecyltriethylammonium Bromide, Hexadecyltriethylammonium Bromide and Octadecanetriethylammonium Bromide.

The sulfonate group (SO ₄ ^2- ) added to sulfuric acid according to the method of the present invention results in the interaction between the surfactant and the titanium precursor to increase the mutual attraction. Specifically, the titanium precursor is hydrolyzed when it meets with water and the polymerization reaction occurs in an acidic state. The sulfonate group (SO ₄ ^2- ) acts as an intermediary for strong interaction with the cation of the active agent amine group (RN (CH ₃ ) ₃ ⁺ ), growing crystals around the surfactant in the form of mesoporous Crystals are synthesized. Specifically, the present invention includes adding sulfuric acid at a molar ratio of 45 to 50: 1, preferably at a molar ratio of 48: 1. In the present invention, the pH of the reactor in which the synthesis takes place is preferably 0.8 to 2.0.

In addition, the present invention is a method for synthesizing a mesoporous metal oxide by reacting a surfactant and a metal precursor under acidic conditions, wherein 1.0 to 1.5 M sulfuric acid is added under acidic conditions, the molar ratio of the surfactant and sulfuric acid is 45-50 Adding a surfactant if possible.

In addition, the manufacturing method of the mesoporous TiO ₂ of the present invention includes a method for synthesizing various types of mesopores according to the molar ratio of the titanium precursor and the surfactant. Specifically, in the present invention, the molar ratio of the titanium precursor and the surfactant may be added in a ratio of 1: 1 to 7: 1 to provide mesoporous TiO ₂ of a desired form.

Specifically, when the molar ratio of the titanium precursor and the surfactant is controlled at the same ratio, since the interaction occurs at 1: 1, the mesoporous TiO ₂ having a plate-like shape as shown in FIG. 1a is synthesized, and when the molar ratio of the titanium precursor is increased, In order to increase the interaction with the surfactant, it grows in a spherical shape, and hexagonal mesopores as shown in FIG. 1B are formed. The molar ratio of titanium precursor and surfactant for synthesizing hexagonal mesoporous TiO ₂ is preferably 5: 1.

In addition, in the present method, the adjustment of the pH of the reactor reacting with the titanium precursor and the surfactant has an important meaning. The structure of the mesopores is different depending on the pH. This is because the acid concentration not only affects the polymerization of the titanium precursor, but also greatly influences the interaction between the surfactant and TiO ₂ polymerized depending on the concentration of sulfonate group (SO ₄ ^2- ) with the acid concentration. Because it's crazy. The pH concentration at which the mesoporous TiO ₂ of the present invention can be synthesized is 0.8 to 2.0, preferably 1 to 1.5, and most preferably 1.3.

Preferably, the present invention provides a method for synthesizing a mesoporous metal oxide by reacting a surfactant with a metal precursor under acidic conditions, wherein the surfactant: titanium precursor: sulfuric acid: water is 1: 5: 48: 2057 mol ( mol) addition in ratio.

On the other hand, the present invention includes a method for controlling the size of the pores by adjusting the length of the hydrophobic portion of the surfactant. Specifically, since the synthesized mesoporous TiO ₂ pores are composed of a surfactant, a large length of hydrophobicity can be made by adjusting the length of the hydrophobic portion (the alkyl chain) of the surfactant to make pores of large size. The use of surfactants with short lengths allows the synthesis of small pores. In fact, when adding a surfactant of n = 15 in the formula of the present invention than the case of n = 13 to synthesize larger pores, by adjusting the number of n in the present invention can be synthesized pores of the desired size Provide a method.

The present invention includes a mesoporous TiO ₂ and a method for producing the impregnated transition metal by impregnating the transition metal in the pores of the synthesized mesoporous TiO ₂ . Specifically, the mesopores synthesized by the method of the present invention have a surfactant in the pores and thus cannot be used as a catalyst per se. Therefore, if the surfactant is removed by solvent or calcination method, the transition metal precursor is impregnated into the pores using capillary phenomenon, and then reduced by using a high temperature or a reducing agent. This is possible. Preferably, the present invention includes platinum (Pt) as a transition metal.

According to the present invention, it is possible to prepare mesoporous TiO ₂ in a precisely controlled form according to the molar ratio of the surfactant and the titanium precursor, the acid concentration and the sulfonate concentration, and furthermore, a transition metal in the mesoporous TiO ₂ pores, preferably Preferably impregnated with platinum (Pt) it is possible to improve the photoactivity of the photocatalyst.

As mentioned above, features of the present invention and other advantages will become more apparent from the embodiments described below. However, the present invention is not limited to the following examples.

<Example>

Example 1 Synthesis of Surfactant

This embodiment is for illustrating the synthesis of the surfactant represented by the formula (1) or (2).

100 mL of acetonitrile solution was placed in a two-necked flask equipped with a temperature controller, and 10 mL of 1-bromtetradecane solution was added to the solution. After the reactants were completely dissolved, trimethylamine was added at a ratio of 1: 1.5 mol.

Subsequently, after sending reaction temperature to 80 or more for 10 hours, the solvent was blown enough. The obtained surfactant was recrystallized from chloroform and ethyl acetate (Ethylacetate) by adding a solvent in a ratio of 1: 3. Recrystallization was carried out three or more times.

Comparative Example 1

In the same manner, 1-bromerhexadecane (1-Bromotehexadecane) and 1-bromeroctadecane (1-Bromooctadecane) were repeated using trimethylamine and triethylamine.

Example 2 Mesoporous TiO of Plate Structure ₂ Synthesis of

In a 1000 mL plastic bottle with a lid, 1 g of the surfactant obtained in Example 1 was dissolved in 100 mL of 1.3 M sulfuric acid solution, followed by stirring until it was sufficiently dissolved in a stirrer. Subsequently, after lowering the temperature of the reactor to 0 ° C. and over 1 hour, titanium isopropoxide was slowly added by adjusting the ratio of 1: 1 mole of the surfactant. After the addition, the lid of the plastic bottle was closed and shaken vigorously three to four times at 10 minute intervals. After leaving at room temperature for 5 hours or more, the composite was filtered using a filter, and then sufficiently washed with 300 mL of distilled water. The resulting product was placed in an 80 ° C. oven and dried for at least 2 hours, and the dried sample was calcined at 350 ° C. or 400 ° C. for 3 hours to remove the structural derivative (surfactant).

Comparative Example 2: Hexagonal Mesoporous TiO ₂  synthesis

It is the same as the experimental content described above, but was synthesized by adjusting the molar ratio of titanium precursor and surfactant to 5: 1.

Example 3: Mesoporous TiO Impregnated with Transition Metal (Pt) ₂ Synthesis of

At least one of the mesoporous TiO ₂ , acetone solvent from which the surfactant has been removed, is completely dissolved in a beaker, and then 14.7 mg of hexachloroplatonic acid (H ₂ PtCl ₆ .6H ₂ O) is used as a platinum precursor, and 72 μl of After dissolving in acetone, 0.05 g of mesoporous TiO ₂ was mixed and mixed uniformly. After the solution is mixed enough to enter the pores, put it in the 333 K oven for 6 hours to evaporate and dry the acetone sufficiently. Put the dried sample in a U-shaped reactor and raise the hydrogen gas to 573K for 4 hours at room temperature. The platinum precursor was reduced while maintaining at 2 hours. The flow rate of the flowed hydrogen gas was 0.36 Lmin-1g-1, and the MnO / SiO ₂ trap was passed through to purify the pure hydrogen gas from which oxygen impurities were removed. After reduction, the mixture was vacuumed at 573 K for 2 hours to remove hydrogen remaining in the reactor.

Mesoporous TiO ₂ Structural analysis

Synthesis of mesoporous TiO _{2 according to} the present invention was analyzed by XRD and confirmed by TEM image.

(1) XRD measurement

X-ray powder diffraction analysis is the most common analytical method for structural analysis of materials. The pore structure of the mesoporous TiO ₂ material synthesized in this study could be analyzed using X-ray diffraction analysis. The X-ray powder diffraction pattern was measured while changing at 0.01 ° 2θ intervals using a Rigaku diffractometer (miniflex, 30 kV, 15 mA) using Cu Ka radiation (λ = 0.1541 nm) as an X-ray source. The measurement range was measured at 1 ° per minute (1 ° min ⁻¹ ) at 1 ° <2θ <6 °. Analysis of the peaks shown in XRD of FIG. 2A shows that the mesopores TiO ₂ having a plate-like structure were formed by the peaks of (100), (200) and (300) forms. Analyzing the XRD peak of FIG. 3a, it can be calculated that the peak consists of (100), (110), (200), etc., and it was found that mesoporous TiO ₂ having a hexagonal structure was formed.

(2) TEM measurement

The synthesized mesoporous TiO ₂ was characterized by transmission electron microscopy. Transmission electron microscopy images were obtained using a Phillips CM20 apparatus (100 kV). For transmission electron microscopic analysis, 0.03 g of mesoporous TiO ₂ was dispersed in 20 g of acetone and sonicated for 30 minutes to prepare a dispersion solution. The carbon film-treated copper grid was contacted with the analytical solution for several seconds, and then dried at room temperature to prepare a TEM specimen. In FIG. 2B, the mesoporous TiO ₂ having a plate-like structure is synthesized, and FIG. 3B shows that the mesoporous TiO ₂ having a hexagonal shape is synthesized.

As described above, according to the present invention, the mesopores TiO ₂ having various pore sizes and structurally plate-shaped and hexagonal forms can be synthesized by controlling the molar ratio of the surfactant and the titanium precursor and pH using sulfuric acid. The pores may be impregnated with transition metal Pt in nanoscale.

The mesoporous TiO ₂ synthesized in this way has a wide surface area and high photoactivity by transition metals, so it is excellent as a photocatalyst. Especially, it can be used as a photocatalyst having activity in visible light because it can impregnate transition metal Pt by concentration. It can act as a catalyst with high durability.

Claims (12)

A method of synthesizing mesoporous metal oxides by reacting a surfactant with a metal precursor under acidic conditions, wherein the amount of sulfuric acid is added to form an acidic condition of pH 0.8 to 2.0, and the formula (I) or formula (II) The molar ratio of the surfactant having a structure of) and sulfuric acid is 45 to 50, the molar ratio of the molar ratio of the surfactant and the titanium precursor is 1: 1 to 1: 7 of the mesoporous TiO ₂ Synthesis method. Formula 1: CH ₃ (CH ₂ ) _n N (CH ₃ ) ₃ ⁺ Br ^- n = 10 to 20 Formula 2: CH ₃ (CH ₂ ) _n N (CH ₂ CH ₃ ) ₃ ⁺ Br ⁻ n = 10 to 20 delete delete delete delete delete delete delete Claim 1, wherein the mesoporous synthetic method of the visible light response mesoporous TiO _2, characterized in that the TiO ₂ to remove the surfactant, and was impregnated with a platinum precursor synthesized according to the. delete delete delete

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