KR100816128B1 - Tio2-capsulated metallic nanoparticles for photocatalyst and its preparation method - Google Patents

Abstract

A titanium oxide(TiO2)-capsulated metallic nanoparticle for a photocatalyst and a method for preparing the same are provided to inhibit the recombination of electrons and holes, and therefore to improve the activity of a TiO2 photocatalyst. A titanium oxide(TiO2)-capsulated metallic nanoparticle for a photocatalyst has a core metal nanoparticle size of 1-50 nm and has a titanium oxide coating layer of 1 nm to hundreds of nm on the core metal nanoparticle. The titanium oxide(TiO2)-capsulated metallic nanoparticle is prepared by suspending a highly dispersed metal nanoparticle in a dilute solution of titanium alkoxide complex salt, which is formed by adding triethanolamine as a complexing agent to titanium alkoxide as a starting material to coat the core metal nanoparticle with titanium oxide(TiO2) by a hydrothermal synthesis process. Further, core metal nanoparticle material is one of Au, Ag, Cu, Ni and Co.

Description

TiO2-capsulated metallic nanoparticles for photocatalyst and its preparation method

1 is a model of TiO ₂ encapsulated metal nanoparticles

2 is a mechanism for enhancing photocatalytic activity in TiO ₂ encapsulated metal nanoparticles

Figure 3 is a manufacturing process diagram of TiO ₂ capsule metal nanoparticles

Figure 4 (a) is TiO ₂ capsule-type Au nanoparticles synthesized in [Ti ^{4 +} ] = 0.01mM TTIP / TEOA mixed solution (hydrothermal synthesis temperature 80 ℃)

(b) shows TiO ₂ capsule Au nanoparticles synthesized in [Ti ^{4 +} ] = 0.05mM TTIP / TEOA mixed solution (hydrothermal synthesis temperature 80 ℃)

(c) shows TiO ₂ capsule Au nanoparticles synthesized in [Ti ^{4 +} ] = 0.3mM TTIP / TEOA mixed solution (hydrothermal synthesis temperature 80 ℃)

(d) shows TiO ₂ encapsulated Au nanoparticles synthesized in [Ti ^{4 +} ] = 0.01mM TTIP / TEOA mixed solution (hydrothermal synthesis temperature 140 ℃)

5 is a change in crystal structure of the TiO ₂ capsule metal nanoparticles according to the heat treatment temperature

6 is a photocatalytic activity of TiO ₂ encapsulated metal nanoparticles and conventional TiO ₂ nanoparticles.

In order to improve the activity of the TiO ₂ photocatalyst used to remove gaseous harmful substances (hazardous gases and odors) in the air, the present invention uses 10 to 20 nm of metal nanoparticles as a core material and 1 to several hundred nm of TiO ₂ to the outside. to be coated with the coating layer TiO ₂ encapsulated metal nanoparticles and relates to a method of manufacturing the same, more specifically, the core nanoparticles by ultraviolet light by capturing the electrons of TiO ₂ TiO ₂ encapsulated to enhance the activity of the TiO ₂ photocatalyst A method for synthesizing metal nanoparticles from a complex salt of titanium alkoxide and triethanolamine.

Removal of pollutants present in the air includes adsorption, electrostatic precipitating, chemical reaction, combustion, and advanced oxidation. Air pollutants can be classified into gaseous pollutants (hazardous gases, odors) and particulate pollutants (dust, pollen, bacteria). The treatment of air pollutants varies depending on the type and concentration of pollutants. Especially, low concentration gaseous substances present in large quantities in the atmosphere are most advantageous in the photocatalyst technology, which is a kind of advanced oxidation method, and it is possible to use sunlight as an energy source. It has a big advantage. Most of the gaseous pollutants can be purified by photocatalyst, remove liquid particles of nicotine or tar, and have antibacterial effect against microbial particles such as bacteria or virus. The purifying action is mainly due to the strong oxidative power generated from titanium oxide by light irradiation, but may be decomposed by a reduction reaction such as ozone. Another advantage of using photocatalysts for air purification is that they do not emit chemicals that will be secondary sources of pollution, are non-toxic and photocatalysts are chemically very stable, and therefore theoretically do not change performance over long periods of time.

However, despite the advantages mentioned above, photocatalysts have the following fundamental problems. In the case of a photocatalyst, the time that the electrons moved to the conduction band and the holes remaining in the valence band by the irradiation of the excitation light source is free from tens of pico seconds (one trillion seconds) to several hundred nano seconds (one billion minutes). It is estimated that it is only 1 second), so it is insufficient to secure time to react with photocatalyst and contaminants. That is, the time for electrons and holes to participate in the redox reaction is so short that the photocatalytic activity is not properly exhibited. Therefore, in order to greatly improve the photocatalytic activity, it is necessary to suppress recombination of electrons moved to the conduction band and holes remaining in the valence band as much as possible.

The present invention was devised to further improve the photocatalytic activity of the existing TiO ₂ , the main object is to place a spherical metal nanoparticles therein to form a TiO ₂ coating layer on the surface of the metal nanoparticles, the TiO ₂ photocatalyst layer by ultraviolet light The core metal nanoparticles trap the electrons generated in the microparticles, thereby inhibiting the recombination of holes and electrons, thereby forming a uniform coating layer of TiO _{2 on} the TiO ₂ encapsulated metal nanoparticle photocatalyst and the metal nanoparticles with enhanced photocatalytic activity. In order to provide a method for producing TiO ₂ encapsulated metal nanoparticles using titanium alkoxide and triethanolamine as a complex salt forming agent.

When described in detail based on the accompanying drawings (Figs. 1, 2 and 3) the present invention for achieving the above technical problem is as follows.

As shown in FIG. 1, the structure of the TiO ₂ encapsulated metal nanoparticles may be represented by two types according to the form of the TiO ₂ coating layer, and metal nanoparticles having a size of 1 to 50 nm may be located therein. 1 to several hundred nm of TiO ₂ photocatalyst particles are adsorbed on the outside, or 1 to several hundred nm of TiO ₂ shell is formed. The Au / TiO ₂ composite nanoparticle photocatalyst of this structure can improve photocatalytic activity by two effects.

The first effect is the high dispersion of TiO ₂ on the surface of the metal nanoparticles. Generally, activity of the TiO ₂ photocatalyst is there is dependent on the size of the TiO ₂ crystal grains, the size of the crystal grains of the TiO ₂ showing the photocatalytic activity is even referred to 20nm because actually TiO ₂ interpersonal agglomeration of the particles of 20nm TiO ₂ It is difficult to obtain photocatalytic activity corresponding to the grain size. For the preparation of highly active TiO ₂ photocatalysts, absorption of the light source, which is the source of electrons, and adsorption of reactants are essential. This type of photocatalyst has advantages in that it has a small grain size, a spherical shape, and high dispersibility. have. In this respect, TiO ₂ encapsulated metal nanoparticles is also because the nanoparticles of TiO ₂ as shown in Fig. 1 being a heterogeneous nucleation is made on metal nanoparticles generated by the mounds oxide of TiO ₂ available from the time, and the internal nano Since the particles are spherical in shape, the external TiO ₂ also has to exhibit spherical particle behavior, so that not only the adsorption of the reactants but also the efficient absorption of the excitation light source can be exhibited, resulting in high activity.

The second effect is the inhibition of recombination of electrons and holes using surface plasmon phenomenon. In the case of the TiO ₂ photocatalyst, as mentioned above, the time when the electrons moved to the conduction band by the excitation light and the holes remaining in the valence band are freely separated. Therefore, in order to improve the activity of the TiO ₂ photocatalyst, it is necessary to suppress recombination of electrons and holes. In the conventional method, a method of slowing the recombination rate between electrons and holes by providing a trap site for trapping electrons between TiO ₂ band gabs by doping heterogeneous elements is used. In the present invention, in order to suppress recombination of electrons and holes, the surface plasmon effect in which electrons accumulate on the surface of metal nanoparticles is used. 2 shows a mechanism for improving the activity of the TiO ₂ photocatalyst by the surface plasmon effect. When the anatase type TiO ₂ receives light below 3.2 eV, electrons in the valence band move to the conduction band. When the nanoparticles such as Au are adjacent, electrons in the conduction band move to the surface of Au nanoparticles with low energy level. Phenomenon occurs. Since it is relatively difficult for electrons moved to the surface of Au to move to TiO ₂ having a high energy barrier, electrons accumulate on the surface of Au during the irradiation of UV (surface plasmon). The recombination rate decreases, and consequently, the photocatalytic activity is improved.

Preparation of TiO ₂ capsule metal nanoparticles was carried out as follows, the manufacturing process is shown in FIG.

In general, the synthesis of anatase type TiO ₂ can be obtained by hydrolysis of titanium alkoxide. By using the hydrolysis reaction of the titanium alkoxide, it is possible to form a TiO ₂ coating layer on the surface of the metal nanoparticles. However, in order to obtain a uniform TiO ₂ coating layer on the surface of the metal nanoparticles, a very slow hydrolysis reaction of titanium alkoxide is required. Because rapid hydrolysis reaction is due to result in the formation of TiO ₂ particulate coarse grain size, rather than forming the TiO ₂ coating layer on the nanoparticle surface. Therefore, in order to suppress the hydrolysis reaction of titanium alkoxide, triethanolamine was used as a complex salt former in the present invention. As the titanium alkoxide, all titanium alkoxides such as titanium methoxide, titanium ethoxide, titanium butoxide and titanium isopropoxide may be used. One of these alkoxides was selected, and a titanium alkoxide complex salt was prepared by mixing titanium alkoxide and triethanolamine in a range of 50 to 90 wt% of a triethanolamine. The titanium alkoxide complex salt showed very stable properties at room temperature, and hydrolysis reaction did not proceed even with addition of water.

In order to form a TiO ₂ coating layer on the surface of the metal nanoparticles, a metal nanoparticle colloid and a titanium alkoxide complex salt dilution solution are prepared. At this time, the metal nanoparticles were selected from the metals such as Au, Ag, Cu, Ni, Co, and the concentration of the metal nanoparticle colloid was adjusted to 0.1 ~ 100mM. Titanium alkoxide complex salt dilution solution was prepared by diluting with ultrapure water so that the concentration of titanium ions is 0.1 ~ 1M. The metal nanoparticle colloidal solution thus prepared was mixed with a titanium alkoxide complex salt dilution solution and hydrothermally treated for 24 hours at a temperature range of 60 to 200 ° C. to prepare TiO ₂ capsular metal nanoparticles. Evaluation of photocatalytic activity of the synthesized TiO ₂ encapsulated metal nanoparticles was performed by decomposition reaction of methanol using an odor meter.

    (2) [Example]

The following describes the present invention through examples.

After dissolving 0.1 g of HAuCl ₄ in 500 mL of ultrapure water and heating it to a boiling point, 100 mL of ultrapure water dissolved in 1 g of Tri-sodium citrate was added as a reducing agent to synthesize Au nanoparticle colloid having a particle diameter of 12 to 15 nm. The low concentration Au nanoparticle colloid is evaporated to make Au nanoparticle colloid with 0.1M Au concentration.

Titanium isopropoxide was used as the titanium alkoxide, and titanium isopropoxide and triethanolamine were mixed at a ratio of 1: 2, and then ultrapure water was mixed with the mixed solution so that 0.5 M was obtained. It was used as a complex salt dilution solution.

In order to coat TiO ₂ on Au nanoparticles, the concentration of the dilute solution of titanium isopropoxide complex salt was adjusted by adding ultrapure water so as to be in the range of 0.01mM to 1mM, and 100ml of the dilution solution made of various concentrations and the colloidal Au nanoparticles 3.3 ml of the mixture was mixed in an autoclave and subjected to hydrothermal treatment for 24 hours.

4 shows representative shapes of TiO ₂ encapsulated Au nanoparticles in the present invention. The shape is changed depending on the amount of titanium ions added during synthesis. These four forms are representative of the TiO ₂ capsular metal nanoparticles obtained in the present invention. Figure 3 (a) shows the TiO ₂ capsule-type metal nanoparticles synthesized in a condition that the concentration of the titanium isopropoxide complex salt dilution solution is 0.01mM and hydrothermal synthesis reaction temperature is 80 ℃. It can be seen that the TiO ₂ coating layer of about 10 nm is formed on the Au nanoparticles of 12 to 15 nm. (B) and (c) of FIG. 3 are TiO ₂ capsular metal nanoparticles obtained by increasing the concentration of the titanium isopropoxide complex salt diluting solution to 0.05 mM and 0.3 mM, respectively. In these cases, some TiO ₂ encapsulated metal nanoparticles are agglomerated but maintain a constant distance between Au nanoparticles. Figure 3 (d) shows the TiO ₂ capsular metal nanoparticles obtained by increasing the concentration of the titanium isopropoxide complex salt dilution solution to 0.01mM and the hydrothermal synthesis temperature to 140 ℃.

FIG. 5 shows a thin film obtained by coating the sample of FIG. 4 (b) on a quartz plate and heat-treated at 100 ° C., 200 ° C., 400 ° C., 600 ° C., 800 ° C., and 1,000 ° C. for 3 hours, respectively. This is the result of X-ray diffraction analysis of the crystal structure change of nanoparticles. The diffraction peaks of the (101) plane and (004) plane of anatase were observed at 2θ at around 25.2 ° C and 48 °, and the diffraction peaks of the (111) plane and (200) plane of Au were shown at 38 ° and 44 °. The diffraction peak of anatase did not change significantly with temperature, but the diffraction intensity was greatly improved at 1,000 ℃. The diffraction peak of the Au nanoparticles can be seen that the change in the diffraction peak intensity up to 800 ℃ is very small compared to (a) that is the result of pure Au nanoparticles. From this result, it can be confirmed that the crystal structure of the TiO ₂ coating layer obtained in the present invention is anatase and is a very stable material.

6 is a result of comparing the photocatalytic activity of the TiO ₂ encapsulated metal nanoparticle sol synthesized in the present invention and a conventional commercial TiO ₂ nanoparticle sol (Ishihara Co.). The photocatalytic activity was measured by coating each TiO2 sol on a glass plate and then heat-treating at 400 ° C. for 3 hours, and using methanol as a test gas. 365 nm BLB (Black Light Blue) lamp was used as an excitation light source of a photocatalyst. In the photocatalytic activity test method, a small amount of methanol solution was dropped into the photocatalyst reactor, the methanol concentration in the reactor was uniformed by an odor meter, and the UV lamp was turned on to confirm the odor intensity change of the methanol gas. After 240 minutes of turning on the UV lamp, the deodorization rate of methanol gas was 9.5% for the conventional TiO ₂ nanosol and 17.5% for the TiO ₂ encapsulated nanosol, indicating the photocatalytic activity of the TiO ₂ encapsulated nanosol. You can see that this is about twice as high. In addition, the photocatalytic activity was improved about 1.5 times in the initial reaction.

The present invention relates to the invention of the new type of TiO ₂ encapsulated metal nanoparticles and its manufacturing technology for improving the activity than the conventional TiO ₂ photocatalyst, 1 ~ 1 on the surface of the metal nanoparticles having a diameter of 1 ~ 50 nm Composite nanoparticles having a TiO ₂ coating layer of several hundred nm were synthesized, and the TiO ₂ encapsulated metal nanoparticles developed in the present invention had increased activity from 1.5 to up to 2 times more than the conventional TiO ₂ photocatalyst. The present invention will be able to replace the high performance imported TiO ₂ photocatalyst, which has been used to remove harmful substances in the air, and can further upgrade indoor and outdoor residential environments by increasing the environmental purification effect of the new photocatalyst. In addition, the novel photocatalyst developed in the present invention can be utilized in the field of wastewater treatment as well as air purification, it is possible to expand the field of environmental purification by the photocatalyst. When the product having the environmental purification, antibacterial and self-purifying functions is manufactured using the present invention, the activity of the TiO ₂ capsule-type metal nanoparticles is improved by 1.5 to 2 times compared with the conventional products, thus reducing the amount of photocatalyst used. As a result, cost savings can be expected.

Claims (4)

A core metal and a 1 ~ 50nm size of the nanoparticles, the metal nanoparticle core from 1 to hundreds of TiO ₂ encapsulated metal nanoparticles TiO ₂ have a coating layer on the surface of the nm. TiO ₂ capsule type characterized by suspending highly dispersed metal nanoparticles in a titanium alkoxide complex salt lean solution containing titanium alkoxide as a starting material and triethanolamine as a complex salt former, and coating TiO ₂ on the core metal nanoparticles by hydrothermal synthesis. Method for producing metal nanoparticles. The TiO ₂ encapsulated metal nanoparticle of claim 1, wherein one of Au, Ag, Cu, Ni, and Co is used as the core metal nanoparticle material. The titanium alkoxide according to claim 2, wherein one of titanium methoxide, titanium ethoxide, titanium butoxide, titanium isobutoxide, and titanium isopropoxide is used, and the titanium concentration of the titanium alkoxide complex salt lean solution is 0.01mM ~. A method for producing TiO ₂ capsule metal nanoparticles, wherein the hydrothermal synthesis reaction is performed at a temperature range of 40 ° C. to 250 ° C ..

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