WO2009048186A1

WO2009048186A1 - Tio2-capsulated metallic nanoparticles photocatalyst enable to be excited by uv or visible lights and its preparation method

Info

Publication number: WO2009048186A1
Application number: PCT/KR2007/004898
Authority: WO
Inventors: Yeon Tae Yu
Original assignee: Industrial Cooperation Foundation Chonbuk National University
Priority date: 2007-10-08
Filing date: 2007-10-08
Publication date: 2009-04-16

Abstract

This invention relates to a TiO2 -capsulated metallic nanoparticle photocatalyst having high activity and exhibiting photocatalytic activity not only under UV light but also under visible light and a method of preparing the same, and particularly, to a TiO2 -capsulated metallic nanoparticle photocatalyst that is able to be excited by UV light or visible light, which includes core metallic nanoparticles and a TiO2 layer formed by coating the surface of the core metallic nanoparticles with TiO2 particles, and to a method of preparing the same.

Description

TIO2-CAPSULATED METALLIC NANOPARTICLES PHO-

TOCATALYST ENABLE TO BE EXCITED BY UV OR VISIBLE

LIGHTS AND ITS PREPARATION METHOD

Technical Field

[1] The present invention relates to a TiO -capsulated metallic nanoparticle pho- tocatalyst having high activity and exhibiting photocatalytic activity not only under UV light but also under visible light and a method of preparing the same, and more particularly, to a TiO -capsulated metallic nanoparticle photocatalyst that is able to be excited by UV light or visible light, which includes core metallic nanoparticles and a TiO layer formed by coating the surface of the core metallic nanoparticles with TiO particles, and to a method of preparing the same. Background Art

[2] Generally, pollutants present in the air are eliminated via an adsorption process, an electrostatic precipitation process, a chemical reaction process, a combustion process, an advanced oxidation process, etc. Air pollutants are classified as gaseous pollutants (harmful gases, offensive odors) and particulate pollutants (dust, ash, microorganisms).

[3] The treatment of the air pollutants varies depending on the type and concentration of the pollutant. In particular, in order to eliminate low-concentration gaseous material present in large amounts in the air, a photocatalyst technique, which is a kind of advanced oxidation process, is preferably used, and the major advantage thereof is that solar light is used as an energy source.

[4] The photocatalyst is responsible for purifying most gaseous pollutants, eliminating liquid particles, such as nicotine or tar, and exhibiting effects of disinfecting microorganisms such as bacteria or viruses.

[5] Purification using a photocatalyst is realized mainly using the strong oxidation power of titanium dioxide obtained by light radiation, and, in some cases, degradation may be generated through reduction, as in the case of ozone. In addition, the case where the photocatalyst is used for air purification is advantageous because chemical materials, which act as a secondary pollution source, are not discharged, and the photocatalyst is non-toxic and is chemically stable, and thus the performance thereof theoretically does not change, even upon extended use.

[6] However, the photocatalyst has the following fundamental problems, despite having the above-mentioned advantages.

[7] In the case of the photocatalyst, the period of time, for which electrons transferred to the conduction band through the radiation of an excitation light source and holes formed in the valence band remain as it is, is estimated to be in the range from tens of

12 Q picoseconds (1x10 sec) to hundreds of nanoseconds (1x10 sec), thus making it difficult to ensure a sufficient period of time for the photocatalyst to react with the pollutant.

[8] Specifically, because the period of time for which the electrons and the holes participate in oxidation-reduction reactions is very short, the photocatalyst does not exhibit sufficient activity. Hence, in order to greatly improve the activity of the photocatalyst, recombination between the electrons transferred to the conduction band and the holes formed in the valence band should be inhibited as far as possible.

[9] Moreover, in the case of the conventional photocatalyst, UV light (200-380 nm) must be used as an excitation light source. However, because UV light amounts to only about 6% of solar light, the use of the photocatalyst is very limited, and furthermore, an additional UV lamp should be provided to induce higher photocatalytic activity.

[10] Thus, it is required to develop a photocatalyst able to be activated by visible light amounting to 52% of solar light, so as to remarkably widen the range of use of the photocatalyst.

Disclosure of Invention Technical Problem

[11] The present invention has been keeping in mind the above problems occurring in the related art, and provides a TiO -capsulated metallic nanoparticle photocatalyst, whi ch uses, as an excitation light source for TiO , not only UV light but also visible light, and has improved photocatalytic activity compared to conventional photocatalysts, and also provides a method of preparing the same. Technical Solution

[12] According to the present invention, a TiO -capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light may include core metallic nanoparticles and a TiO layer formed by coating the surface of the core metallic nanoparticles with TiO particles.

[13] The core metallic nanoparticles preferably have a particle size of 1-100 nm, and the

TiO layer preferably has a thickness of 1-100 nm.

[14] The core metallic nanoparticles may include one or a mixture of two or more selected from among Au, Ag, Pt, Pd, Cu, Ni, Co, Fe, ZnO, SiO , ZrO, and Al O .

[15] In addition, according to the present invention, a method of preparing a TiO - capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light may include mixing a diluted titanium alkoxide complex solution with a metallic nanoparticle colloidal solution to obtain a mixture, and then subjecting the mixture to hydrothermal synthesis to thus coat metallic nanoparticles with TiO . [16] The metallic nanoparticle colloidal solution preferably includes metallic nanoparticles having a particle size of 1-100 nm.

[17] In the method of the present invention, subjecting the mixture to hydrothermal synthesis is preferably conducted at 40~250°C.

[18] Hereinafter, a detailed description will be given of the TiO -capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light and a method of preparing the same according to the present invention.

[19] According to the present invention, the TiO -capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light includes core metallic nanoparticles and a TiO layer formed by coating the surface of the core metallic nanoparticles with TiO particles.

[20] The core metallic nanoparticles may include one or a mixture of two or more selected from among precious metals, including Au, Ag, Pt and Pd, general metals, including Cu, Ni, Co and Fe, and oxides, including ZnO, SiO , ZrO and Al O .

[21] The particle size of the core metallic nanoparticles is preferably 1-100 nm in order to increase the dispersion of TiO in the coating process and improve the photocatalytic activity of TiO using a surface plasmon phenomenon.

[22] The TiO layer may be formed by adsorbing the TiO particles on the outer surface of the core metallic nanoparticles, as seen in the A type of FIG. 1, or by uniformly layering TiO on the surface of the core metallic nanoparticles, as seen in the B type of FIG. 1.

[23] The thickness of the TiO layer is preferably 1-100 nm. When the coarsening of the

TiO layer progresses further, the TiO layer grows, undesirably decreasing photo- catalytic activity and impeding the dispersion effect of the photocatalyst.

[24] The TiO -capsulated metallic nanoparticle photocatalyst thus structured is advantageous because it exhibits photocatalytic activity not only under UV light but also under visible light, and furthermore, the photocatalytic activity thereof is greatly improved.

[25] The principle by which the photocatalytic activity of the TiO -capsulated metallic nanoparticle photocatalyst is generated under UV light or visible light is based on the high dispersion effect of TiO applied on the surface of the metallic nanoparticles, and is also based on the inhibition effect of recombination between electrons and holes and the effect of improving electron excitation properties, using a surface plasmon phenomenon, and is described in detail below.

[26] [High Dispersion Effect of TiO applied on Surface of Metallic Nanoparticles]

[27] Typically, the activity of the TiO photocatalyst mainly depends on the size of the

TiO crystalline particles. Even if the size of the TiO crystalline particles exhibiting photocatalytic activity is 20 nm or smaller, it is difficult to actually attain the photo- catalytic activity corresponding to the TiO crystalline particle size of 20 nm due to the aggregation of the TiO particles.

[28] Thus, with the goal of synthesizing a highly active TiO photocatalyst, the absorption of a light source, which is an excitation source of electrons, and the adsorption of a reactive material are essentially required, and such a photocatalyst is favorable when having a small crystalline particle size and a spherical shape and maintaining high dispersibility.

[29] Accordingly, in the TiO -capsulated metallic nanoparticle photocatalyst of the present invention, as seen in FIG. 1, the TiO nanoparticles undergo heterogeneous nuclear production on the metallic nanoparticles, thus making it possible to realize high dispersion of TiO from the time of production. Further, because the shape of the metallic nanoparticles, which are positioned internally, is a sphere, the TiO positioned on the metallic nanoparticles shows a spherical particulate behavior, which thus enables the adsorption of the reactive material and the efficient absorption of the excitation light source, resulting in high activity.

[30] [Inhibition Effect of Recombination between Electrons and Holes using Surface

Plasmon Phenomenon]

[31] In the case of the TiO photocatalyst, the period of time, for which the electrons transferred to the conduction band by the excitation light and the holes formed in the valence band remain as it is, is very short. Therefore, in order to increase the activity of the TiO photocatalyst, there is a need to inhibit the recombination between the electrons and the holes.

[32] A conventional method provides a trap site which is able to capture electrons in the

TiO band gaps through doping of heterogeneous elements to thus decrease the recombination rate between the electrons and the holes. In contrast, in the present invention, the recombination between the electrons and the holes is intended to be inhibited using a surface plasmon phenomenon of accumulating electrons on the surface of the metallic nanoparticles.

[33] FIG. 2 illustrates a mechanism for improving the activity of the TiO photocatalyst using a surface plasmon phenomenon.

[34] When anatase type TiO is exposed to light of 3.2 eV or less, electrons are transferred from the valence band to the conduction band. In this case, when metallic nanoparticles such as Au are adjacent thereto, a phenomenon, in which the electrons of the conduction band are transferred to the surface of the metallic nanoparticles, such as Au, having a low energy level, occurs.

[35] As such, it is relatively difficult to move again the electrons transferred to the surface of the metallic nanoparticles, such as Au, to TiO having a high energy barrier. Accordingly, during the radiation of UV light, a phenomenon (a surface plasmon phenomenon) in which the electrons accumulate on the surface of Au occurs, thus decreasing the recombination rate of electrons and holes, consequently improving pho- tocatalytic activity.

[36] [Effect of Improving Electron Excitation using Surface Plasmon Phenomenon]

[37] Because the electrons accumulated on the TiO -capsulated Au nanoparticles (by a surface plasmon phenomenon) are present near the conduction band of TiO , they may be easily excited through the radiation of light having a low energy wavelength, such as visible light. Hence, the TiO -capsulated metallic nanoparticles exhibit photo- catalytic activity even in the visible light range.

[38] Next, a method of preparing the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention is described below.

[39] The method of preparing the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention includes mixing a diluted titanium alkoxide complex solution with a metallic nanoparticle colloidal solution to obtain a mixture which is then subjected to hydrothermal synthesis to thus coat the metallic nanoparticles with TiO , thereby preparing a TiO -capsulated metallic nanoparticle photocatalyst.

[40] The diluted titanium alkoxide complex solution is prepared by mixing titanium alkoxide with a complexing agent to form a titanium alkoxide complex, which is then diluted with ultrapure water.

[41] Examples of the titanium alkoxide include all titanium alkoxides, including titanium methoxide, titanium ethoxide, titanium butoxide, and titanium isopropoxide.

[42] The complexing agent is used to inhibit the hydrolysis of titanium alkoxide so as to form a uniform TiO layer on the metallic nanoparticles, and examples thereof include triethanolamine, ethanolamine, diethanolamine, triethanolamine, methyldiamine, dimethyleneamine, trimethyleneamine, and triethylenetetramine.

[43] Specifically, anatase type TiO may be synthesized through the hydrolysis of titanium alkoxide. The hydrolysis of titanium alkoxide enables the formation of the TiO layer on the metallic nanoparticles. However, the formation of a uniform TiO layer on the surface of the metallic nanoparticles requires that titanium alkoxide be hydrolyzed very slowly. This is because fast hydrolysis results in the formation of coarse particulate TiO , rather than the formation of the TiO layer on the surface of the nanoparticles. Thus, with the aim of inhibiting the hydrolysis of titanium alkoxide, titanium alkoxide should be mixed with the complexing agent, such as triethanolamine.

[44] Further, the diluted titanium alkoxide complex solution is preferably obtained by diluting the complex solution with ultrapure water, so that the titanium ion concentration is 0.1-1 M. In the case where the titanium ion concentration exceeds 1 M, the hydrolysis rate is increased, thus making it difficult to obtain the TiO -capsulated metallic nanoparticle photocatalyst. [45] The metallic nanoparticles of the metallic nanoparticle colloidal solution may include one or a mixture of two or more selected from among precious metals, including Au, Ag, Pt and Pd, general metals, including Cu, Ni, Co and Fe, and oxides, including ZnO, SiO , ZrO and Al O . The particle size of the metallic nanoparticles is preferably 1-100 nm. When the coarsening of the TiO layer progresses further, the TiO layer grows, undesirably decreasing photocatalytic activity and impeding the dispersion effect of the photocatalyst.

[46] The mixture of the diluted titanium alkoxide complex solution and the metallic nanoparticle colloidal solution is subjected to hydrothermal synthesis, thereby synthesizing the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention.

[47] The hydrothermal synthesis is preferably conducted at 40~250°C for 6-48 hours to form a TiO layer having excellent crystallinity. Advantageous Effects

[48] According to the present invention, the TiO -capsulated metallic nanoparticle photocatalyst has greatly improved photocatalytic activity, and, in particular, exhibits superior photocatalytic activity not only under UV light but also under visible light, compared to conventional TiO photocatalysts.

[49] The TiO -capsulated metallic nanoparticle photocatalyst of the present invention may substitute for conventional high-performance imported TiO photocatalysts for use in the removal of harmful materials from air, and furthermore, may exhibit high environmental purification effects to thus improve indoor and outdoor housing environments.

[50] Further, because the photocatalyst according to the present invention does not essentially require a UV lamp, thanks to its high photocatalytic activity under visible light, it may be widely used in environmental purification fields, including air purification, wastewater treatment, etc., and for products having various disinfecting and self-purification functions. Brief Description of the Drawings

[51] FIG. 1 illustrates the structure of a TiO -capsulated metallic nanoparticle photocatalyst according to the present invention;

[52] FIG. 2 schematically illustrates a mechanism for improving the activity of the TiO photocatalyst using a surface plasmon phenomenon;

[53] FIGS. 3 to 6 illustrate 300,000 magnified TEM photographs of the TiO -capsulated metallic nanoparticle photocatalysts of Examples 1 to 4;

[54] FIG. 7 illustrates a TEM photograph of the TiO -capsulated metallic nanoparticle photocatalyst of Example 5; [55] FIG. 8 illustrates the results of X-ray diffraction of the TiO -capsulated metallic nanoparticle photocatalyst, depending on the thermal treatment temperature; [56] FIG. 9 illustrates the results of activities of the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention and a conventional TiO nanoparticle photocatalyst; [57] FIG. 10 illustrates the UV-visible light absorption spectrum of the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention and a pure TiO photocatalyst; [58] FIG. 11 illustrates the degradation rate of acetaldehyde in the presence of the TiO - capsulated metallic nanoparticle photocatalyst according to the present invention under visible light; and [59] FIG. 12 illustrates the degradation rate of methyl orange in the presence of the TiO

-capsulated metallic nanoparticle photocatalysts of Examples 6~8.

Mode for the Invention [60] [Example 1]

[61] Titanium alkoxide, for example, titanium isopropoxide, and a complexing agent, for example, triethanolamine, were mixed at a ratio of 1:2, after which the mixture solution was mixed with ultrapure water so as to make a titanium ion concentration of

0.01 mM, thus obtaining a diluted titanium alkoxide complex solution. [62] 0.1 g of HAuCl was dissolved in 500 ml of ultrapure water, heated to the boiling

4 point thereof, and then added with 100 ml of ultrapure water in which 1 g of trisodium citrate as a reducing agent was dissolved, thus synthesizing an Au nanoparticle colloid having a particle size of 12-15 nm, which was then evaporated, thereby obtaining an Au nanoparticle colloid having an Au concentration of 0.1 M.

[63] 100 ml of the diluted titanium alkoxide complex solution and 3.3 ml of the Au nanoparticle colloid were mixed, placed in an autoclave, and then subjected to hy- drothermal synthesis at 8O⁰C for 24 hours, thus completing a TiO -capsulated metallic nanoparticle photocatalyst as shown in the TEM photograph of FIG. 3.

[64] From the TEM photograph of FIG. 3, a TiO layer about 10 nm thick can be seen to be formed on the Au nanoparticles having a particle size of 12-15 nm.

[65]

[66] [Example 2]

[67] Unlike Example 1, 100 ml of the diluted titanium alkoxide complex solution having a titanium ion concentration of 0.05 mM and 3.3 ml of the Au nanoparticle colloid were mixed, placed in an autoclave, and then subjected to hydrothermal synthesis at 8O⁰C for 24 hours, thus completing a TiO -capsulated metallic nanoparticle photocatalyst as shown in the TEM photograph of FIG. 4. [68] From the TEM photograph of FIG. 4, it can be seen that the TiO -capsulated metallic nanoparticle photocatalyst was partially agglomerated, but the Au nanoparticles were arranged at regular intervals.

[69]

[70] [Example 3]

[71] Unlike Example 1, 100 ml of the diluted titanium alkoxide complex solution having a titanium ion concentration of 0.3 mM and 3.3 ml of the Au nanoparticle colloid were mixed, placed in an autoclave, and then subjected to hydrothermal synthesis at 8O⁰C for 24 hours, thus completing a TiO -capsulated metallic nanoparticle photocatalyst as shown in the TEM photograph of FIG. 5.

[72]

[73] [Example 4]

[74] Unlike Example 1, 100 ml of the diluted titanium alkoxide complex solution having a titanium ion concentration of 0.01 mM and 3.3 ml of the Au nanoparticle colloid were mixed, placed in an autoclave, and then subjected to hydrothermal synthesis at 14O⁰C for 24 hours, thus completing a TiO -capsulated metallic nanoparticle photocatalyst as shown in the TEM photograph of FIG. 6.

[75]

[76] [Example 5]

[77] Unlike Example 1, 100 ml of the diluted titanium alkoxide complex solution having a titanium ion concentration of 10 mM and 3.3 ml of the Au nanoparticle colloid including Au nanoparticles having an average particle size of 60 nm were mixed, placed in an autoclave, and then subjected to hydrothermal synthesis at 180⁰C for 24 hours, thus completing a TiO -capsulated metallic nanoparticle photocatalyst as shown in the TEM photograph of FIG. 5.

[78] From the TEM photograph of FIG. 7, a TiO layer about 50-80 nm thick having excellent crystallinity can be seen to be formed on the Au nanoparticles having a particle size of 40-50 nm.

[79]

[80] [Examples 6-8]

[81] Unlike Example 5, 100 ml of the diluted titanium alkoxide complex solution having a titanium ion concentration of 10 mM and 3.3 ml of the Au nanoparticle colloid including Au nanoparticles having an average particle size of each of 50 nm, 25 nm, and 15 nm were mixed, placed in an autoclave, and then subjected to hydrothermal synthesis at 18O⁰C for 24 hours, thus synthesizing capsulated metallic nanoparticle photocatalysts having the different Au core particle sizes of Examples 6-8.

[82]

[83] [X-ray Diffraction Test] [84] The TiO -capsulated metallic nanoparticle photocatalyst of Example 2 was applied on a quartz plate to thus obtain a thin film, which was then subjected to thermal treatment for 3 hours at temperatures of 100⁰C, 200⁰C, 400⁰C, 600⁰C, 800⁰C and 1,000⁰C. Thereafter, in order to measure the change in the crystalline structure of the TiO layer and the Au nanoparticles, an X-ray diffraction test was conducted. The results are shown in FIG. 8.

[85] Near 2Θ of 25.2⁰C and 48°, the diffraction peaks of the (101) plane and (004) plane of the anatase were observed, and at 38° and 44°, the diffraction peaks of the (111) plane and (200) plane of Au were observed. The diffraction peak of the anatase was not greatly changed depending on the change in the temperature, and the diffraction intensity was remarkably improved at 1,000⁰C. The diffraction peaks of the Au nanoparticles at 38°and 44°showed very small changes in the intensity of the diffraction peak up to 800⁰C. From these results, the crystalline structure of the TiO layer obtained in the present invention can be confirmed to be anatase and very stable to heat.

[86]

[87] [Photocatalytic Activity Test]

[88] Each of the TiO -capsulated metallic nanoparticle photocatalyst sol (containing 0.5 g of TiO ) of Example 2 and a TiO nanoparticle sol (containing 0.5 of TiO ), available from Ishihara Sangyo, Japan, was applied on a glass plate and was then subjected to thermal treatment at 400⁰C for 3 hours to thus serve as a test sample.

[89] The photocatalytic activity test was conducted by placing each test sample in a photocatalytic reactor, dropping a small amount of methanol solution in the reactor, ascertaining that the methanol concentration in the reactor was constant by means of an odor monitor, and then turning on a UV lamp to thus detect the odor level of methanol gas using the odor monitor.

[90] As the UV lamp, which is an excitation light source of the photocatalyst, a 365 nm

BLB (Black Light Blue) lamp was used.

[91] The activities of the TiO -capsulated metallic nanoparticle photocatalyst sol

(containing 0.5 g of TiO ) of Example 2 and the TiO nanoparticle sol (containing 0.5 of TiO ) available from Ishihara Sangyo, Japan were determined. The results are shown in FIG. 9.

[92] 240 min after the UV lamp was turned on, the odor removal rate of the methanol gas was determined to be 9.5% in the case of the conventional TiO nanosol and 17.5% in the case of the TiO -capsulated nanosol, as seen in FIG. 9. As the results, the photocatalytic activity of the TiO -capsulated metallic nanoparticle photocatalyst sol according to the present invention was improved about two times, compared to the conventional TiO nanosol. Further, in the initial reaction, the photocatalytic activity was improved about 1.5 times.

[93]

[94] [UV-Visible Light Absorption Spectrum Test]

[95] The UV- visible light absorption spectrum of each of the TiO -capsulated metallic nanoparticle photocatalyst of Example 5 and a pure TiO photocatalyst was measured. The results are shown in FIG. 10.

[96] As seen in FIG. 10, the pure TiO exhibited the absorption properties only in the

UV light range of 250~380 nm, whereas the TiO -capsulated metallic nanoparticle photocatalyst exhibited the absorption properties not only in the UV light range (200-400 nm), but also in the visible light range (400-700 nm).

[97] In the UV-visible light absorption spectrum, the 330 nm peak was caused by the anatase type TiO , and the absorption peak of 600 nm was a unique absorption peak of the Au nanoparticles. Thus, from the results of analysis of the UV-visible light absorption spectrum, the excitation behavior of electrons by visible light may be described as follows. Specifically, it is concluded that the Au nanoparticles absorb light near 600 nm so that the energy of electrons present on the surface of the Au nanoparticles is increased to thus excite the electrons, and the electrons thus excited are transferred to the conduction band of TiO by the absorption of visible light having a wavelength of 380-600 nm, thereby exhibiting the photocatalytic activity.

[98]

[99] [Test of Measurement of Degradation Rate of Acetaldehyde]

[100] The TiO -capsulated metallic nanoparticle photocatalyst sol (containing 0.5 g of

TiO ) of Example 5 was applied on a glass plate and was then subjected to thermal treatment at 400⁰C for 3 hours to thus serve as a test sample.

[101] The test sample was placed in the photocatalyst reactor, after which the degradation rate of acetaldehyde as a reactive gas, having an initial concentration adjusted to 100 ppm, was measured over time. The results are shown in FIG. 11. As the UV light source, a 365 nm BLB (Black Light Blue) lamp was used, and as the visible light source, a metal halide lamp of 175 watts was used.

[102] As seen in FIG. 11, P25, available from Deggusa, Germany, under visible light showed a degradation rate (b of FIG. 11) of about 0%, which was the same as the degradation rate (a of FIG. 11) in an empty reactor having no photocatalyst under visible light, and thus did not exhibit photocatalytic properties under visible light.

[103] However, the TiO -capsulated metallic nanoparticle photocatalyst sol of Example 5 exhibited a degradation rate (c of FIG. 11) of 100% after 120 min under visible light, and also a degradation rate (d of FIG. 11) of 90% after 180 min under UV light. The reason why the degradation rate under visible light is higher is assumed to be that the output of the radiated visible light source is higher than the UV light source. [104] The P25, conventionally available from Deggusa, Germany, did not exhibit photo- catalytic activity under visible light, whereas the TiO -capsulated metallic nanoparticle photocatalyst sol of Example 5 exhibited superior photocatalytic activity under visible light.

[105] In addition, in order to test the photocatalytic activity, the TiO -capsulated metallic nanoparticle photocatalyst sol (containing 0.5 of TiO ) of Example 5 was applied on a glass plate and then used as a test sample without thermal treatment. As the results, 160 min after the initiation of measurement, the degradation rate of acetaldehyde reached 100%.

[106] In this way, when the TiO -capsulated metallic nanoparticle photocatalyst according to the present invention is prepared through high-temperature hydrothermal synthesis, the crystallinity of TiO is excellent, and furthermore, high photocatalytic activity is ensured even without additional thermal treatment.

[107]

[108] [Test of Measurement of Degradation Rate of Methyl Orange]

[109] Using the TiO -capsulated metallic nanoparticle photocatalysts of Examples 6 to 8, the degradation of methyl orange was tested. In a 250 ml beaker, 100 ml of a methyl orange solution having an initial concentration of 0.03 mM and 20 mg of the TiO - capsulated metallic nanoparticle photocatalyst were mixed and then subjected to ultrasonic dispersion for 10 min for uniform dispersion of the photocatalyst. Further, for uniform dispersion of the TiO -capsulated metallic nanoparticle photocatalyst and physical adsorption equilibrium of methyl orange, a mixing process was conducted for 30 min using a magnetic stirrer. As the UV light source, a 365 nm BLB (Black Light Blue) lamp was used, and as the visible light source, a metal halide lamp of 175 watts was used. The test results are shown in FIG. 12.

[110] As is apparent from FIG. 12, it can be seen that the photocatalytic activity was greatly increased when the particle size of the Au core was decreased. In particular, in the case where the particle size of the Au core was 15 nm as in c of FIG. 12, the degradation rate was approximately 100% after a reaction time of 50 min. Industrial Applicability

[111] According to the present invention, the photocatalyst has high photocatalytic activity under visible light and thus does not essentially require a UV lamp, and therefore may be used in environmental purification fields, including air purification, wastewater treatment, etc., and for products having various disinfecting and self- purification functions.

Claims

[1] A TiO -capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light, comprising core metallic nanoparticles and a TiO layer formed by coating a surface of the core metallic nanoparticles with TiO particles.

[2] The TiO -capsulated metallic nanoparticle photocatalyst according to claim 1, wherein the core metallic nanoparticles have a particle size of 1-100 nm.

[3] The TiO -capsulated metallic nanoparticle photocatalyst according to claim 2, wherein the TiO layer has a thickness of 1-100 nm.

[4] The TiO -capsulated metallic nanoparticle photocatalyst according to any one of claims 1 to 3, wherein the core metallic nanoparticles comprise one or a mixture of two or more selected from among Au, Ag, Pt, Pd, Cu, Ni, Co, Fe, ZnO, SiO , ZrO, and Al O .

[5] A method of preparing a TiO -capsulated metallic nanoparticle photocatalyst able to be excited by UV light or visible light, comprising mixing a diluted titanium alkoxide complex solution with a metallic nanoparticle colloidal solution to obtain a mixture, and then subjecting the mixture to hydrothermal synthesis to thus coat metallic nanoparticles with TiO .

[6] The method according to claim 5, wherein the metallic nanoparticle colloidal solution comprises metallic nanoparticles having a particle size of 1-100 nm.

[7] The method according to claim 5 or 6, wherein the subjecting the mixture to hydrothermal synthesis is conducted at 40~250°C.