KR100965105B1 - Method of preparating TiO2 Phosphor Composite as Photocatalyst by a sol-gel method - Google Patents

Abstract

Disclosed is a method of manufacturing a titanium dioxide / phosphorescent composite material by coating titanium dioxide (TiO ₂ ) on the phosphor body by a sol-gel method.

The titanium dioxide / phosphorescent composite material prepared according to the method of the present invention has a constant light emitting phosphor even under dark conditions where sunlight is blocked because the titanium dioxide is excited by light emitted from the phosphor to cause a photoreaction. It is an excellent photocatalyst material that can sustain photocatalytic reaction for hours. Therefore, it can be utilized more widely than the current commercially available titanium dioxide material and can be usefully applied to various harmful substances reduction devices, water quality and air purifiers.

Titanium dioxide, sol-gel method, photocatalyst, light emitting material, powder coating

Description

Method of manufacturing titanium dioxide phosphorescent composite material for photocatalyst using sol-gel method {Method of preparating TiO2 Phosphor Composite as Photocatalyst by a sol-gel method}

The present invention relates to a method for producing a photocatalyst titanium dioxide / phosphorescent composite material by coating the photoluminescent powder with titanium dioxide (TiO ₂ ) using a sol-gel method.

Titanium dioxide (TiO ₂ ) is a representative photocatalyst material and generates strong electrons and holes when subjected to ultraviolet rays. It decomposes various environmental pollutants in water and air into harmless carbon dioxide and water. Further, active oxygen, and even if the light can be semi-permanently used because it is very stable chemically himself without change, generated by the photo-reaction (O ^{2 -)} or hydroxyl groups (OH ^-) are chlorine (Cl ₂₎ or ozone ( It has higher oxidizing power than O ₃ ) and has excellent sterilizing power.

Titanium dioxide, however, is a monocomponent material, and because it is a photocatalytic reaction caused by absorption of UV-light (λ ≤ 390 nm) as an excellent photocatalyst or wide bandgap semiconductor (3.2 eV for anatase phase), Absorb only a small amount of UV-light, ˜4%. In addition, glass commonly used as a building exterior material is a representative material that absorbs ultraviolet light well, so the amount of ultraviolet light in the room is extremely small, and thus the photocatalytic efficiency of the room is further lowered, resulting in many restrictions on use. Therefore, when a new photocatalyst material is produced that can cause a photocatalytic reaction even in dark conditions where visible light or light is blocked, its use as various environmental purification materials is expected to be very diverse.

Luminescent materials such as phosphors are excited by absorbing light energy such as sunlight or indoor lighting, and de-excitation in a low energy state to emit light of a specific wavelength. Has the property to In particular, Alkaline earth aluminate-based phosphors are classified as photoluminescent materials because they have the property of emitting light for a long time after absorbing light, and are classified as CaAl ₂ O ₄ : (Eu ^{2 +} , Nd ^{3 +} ) and SrAl ₂ O ₄ :( ^{Eu 2+, Dy 3 +),} BaAl 2 O 4: (Eu 2 +, Dy 3 +) , etc. are representative of the luminous body broad emission spectrum of the green range from violet belonging thereto.

The research trend of TiO ₂ photocatalyst material is mainly divided into (1) improvement of photocatalytic reactivity and (2) development of new photocatalyst material which causes photocatalytic reaction even under visible light. In the first case, a small amount of noble metals such as Pt, Rd, Ag, Au, etc. are doped, and TiO ₂ ultrafine powder is uniformly dispersed in a porous support such as silica or zeolite, or SiO ₂ , ZrO ₂ , (Sr, La Photocatalytic reactivity is improved by bonding with oxides such as TiO _{3 + δ} and the like.

Secondly, some photocatalytic reactions occur under visible light, either by using a die that is sensitive to visible light, or by fabricating TiO ₂ using metal ion implantation, RF magnetron sputtering deposition, or the like. To induce.

However, photosensitizing dyes are extremely limited in use due to their lack of thermal stability, and transition metal ion forced injection methods such as V, Cr, Mn, Fe, and Ni or RF magnetron sputter deposition methods have limitations such as high manufacturing cost and low photoreaction efficiency. There is a difficulty in practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing a titanium dioxide / phosphor photocatalyst composite material of a novel concept in which a photoluminescent powder having luminescent properties is coated with titanium dioxide by a sol-gel method.

In order to achieve the above object,

According to one aspect of the invention,

i) preparing a Ti-sol by mixing titanium precursor with 0.05 to 0.3 M in hydrous ethanol;

ii) adding and mixing the phosphor powder to the Ti-sol to coat titanium dioxide on the surface of the phosphor; And

iii) separating the titanium dioxide-coated phosphor, and then heat-treating at 400 to 500 ° C. for 2 to 5 hours.

It is possible to provide a method for preparing a composite material for photocatalyst, in which titanium dioxide (TiO ₂ ) is uniformly coated on the surface of the phosphor.

In addition, according to another aspect of the present invention, it is possible to provide a photocatalyst composite material coated with titanium dioxide (TiO ₂ ) uniformly coated on the surface of the phosphor, which is manufactured by the method.

Hereinafter, the present invention will be described in detail.

In the method for producing a composite material for a photocatalyst of the present invention, first, a phosphorescent material-a phosphor is excited when it receives light, and emits light by itself. A material for which such light emission lasts for a certain time is called a phosphorescent material-CaAl ₂ O ₄ : Eu ^{2 +,} CaCO ₃ as the starting material for the preparation of a ^{_{Nd 3 +: Al 2 O 3}} : Eu 2 O 3: Nd 2 O 3 to 0.97: 1.0: 0.005: 0.01 molar ratio was weighed into the B ₂ O ₃ 3wt% of The powder and ethanol solution were mixed together and mixed with a ball mill for 24 hours.

In the production process of the composite material for the photocatalytic CaAl ₂ O _4: Eu-based, SrAl ₂ O _4: Eu-based, BaAl ₂ O _4: Eu type, ZnS: Cu-based, CaAl ₁₂ O _19: Eu-based, SrAl ₁₂ O ₁₉ : Eu system, BaAl ₁₂ O ₁₉ : Eu system, BaMgAl ₁₀ O ₁₇ : Eu system, SrMgAl ₁₀ O ₁₇ : Eu system, BaMg ₂ Al ₁₆ O ₂₇ : Luminescent body such as Eu can be used without limitation, specific examples of ^{_{CaAl 2 O 4: Eu 2+,}} Nd 3+, SrAl 2 O 4: Eu 2 +, Dy 3 +, BaAl 2 O 4: Eu 2 +, Dy 3 +, CaAl 12 O 19: Eu 2 + system, SrAl ₁₂ O _19: Eu ^{2 +} and the like.

After the ball mill mixing, the mixture was dried at 130 ° C. for 24 hours, and finally mixed powder was placed in an alumina boat and heat-treated at a reaction temperature of 1400 ° C. for 3 hours in a reducing atmosphere of (95% Ar + 5% H ₂ ).

 The present inventors coated the titanium dioxide on the photoluminescent powder prepared as described above using a sol-gel method to produce a titanium dioxide / photoluminescent photocatalyst composite material.

In the above method, first, TBOT (Tetrabutyl titanate, (C ₄ H ₉ O) ₄ Ti) as a titanium precursor is mixed with hydrous ethanol such that 0.05 to 0.3 M, followed by stirring. The hydrous ethanol is not particularly limited, but a mixture of water and ethanol in a volume ratio of 1: 3 to 6 may be used. The coating layer may be formed to an appropriate thickness in the range of the concentration, if it is too low, the coating layer of Ti is too thin or too small, if too high, the coating layer is too thick, rather the photolysis effect is reduced.

The titanium precursor may be used without limitation as long as it can coat the titanium dioxide film by a sol-gel method, for example, TiCl ₄ , Ti (OCH ₂ CH ₃ ) ₄ , Ti (OCH (CH ₃ ) ₂ ) ₄ , ((CH ₃ ) ₂ CHO) ₂ Ti (C ₅ H ₇ O ₂ ) ₂ , Ti (OC ₂ H ₅ ) ₄ , Ti (OCH ₃ ) ₄ , Ti (C ₅ H ₇ O ₂ ) ₂ , and the like. Can be.

The Ti-sol solution thus prepared may be used in a coating process as it is, but it is better to use it after aging after leaving it in the air for 24 to 72 hours, preferably 48 hours, in terms of coating degree and uniformity ( 9).

In the coating process, the Ti-sol is coated on the surface of the phosphor body by adding and stirring the phosphor body to the Ti-sol. At this time, the temperature of the Ti-sol is preferably maintained at 40 ~ 60 ℃, pH 6 ~ 8.

On the other hand, in order to minimize deterioration of the photoluminescent body due to moisture absorption in the coating process, the mixing time of the Ti-sol and the photoluminescent body may be shortened to about 30 seconds to 2 minutes, preferably about 1 minute.

Subsequently, the aqueous solution and the powder were separated from the Ti-sol coated phosphor by filtration and vacuum dried at about 60 ° C. for 24 hours to remove residual alcohol and water. It undergoes heat treatment for 2 ~ 5 hours at 400 ~ 500 ℃ to crystallize into anatase TiO ₂ phase. When the heat treatment temperature exceeds 500 ° C, the coated TiO ₂ reacts with a photoluminescent body (eg, CaAl ₂ O ₄ : Eu ²⁺ , Nd ³⁺ ) to generate an intermediate compound (eg, CaTiO ₃ ). The photolysis reaction no longer increases with temperature, and if the heat treatment temperature is less than 400 ° C. or the heat treatment time is too short, the coating layer is anatase-TiO _2. There is a problem that the phase is not sufficiently crystallized. Preferably, heat treatment is performed at 450 ° C. for 3 hours (see FIG. 5).

The scope of the present invention also includes a composite material for photoluminescent-titanium dioxide photocatalyst prepared by the above method.

When a photocatalytic material is coated with titanium dioxide, a photoluminescent material (e.g., Ca-, Ba-, Sr-rare earth alumina-based photoluminescent material) that emits light for a long time upon receiving light, the light is emitted from the photoluminescent material even in a dark state where light is blocked. Titanium dioxide continuously causes photolysis reaction by absorbing light, and even in the presence of light source such as sunlight, titanium dioxide is absorbed and excited by light emitted from photoluminescent body to promote photoreaction. You can do it. In addition, the heterojunction of titanium dioxide with another oxide having a different energy gap causes energy band bending, which reduces the light absorption energy band size of the titanium dioxide, thereby causing photoreaction in the visible light source. In this case, there is an advantage that a visible light source such as an incandescent lamp may be used instead of an ultraviolet light source.

As described above, in the present invention, in the case of the composite material in which the phosphor is coated with titanium dioxide by the sol-gel method, (1) energy band bending occurs when heterojunction is performed with the phosphor oxide having a different energy gap from titanium dioxide. Because of this, the light absorption energy of titanium dioxide is reduced, so that photoreaction may occur even in visible light, so that an incandescent lamp may be used instead of an ultraviolet light source, and (2) the photoluminescent body absorbs light from another light source. By emitting light of a specific wavelength and absorbing the light emitted by the photoluminescent member again, titanium dioxide maximizes the photoreaction efficiency of the titanium dioxide, and (3) the lighted photoluminescent member is constant even in the dark dark field state. Because it emits light for a period of time, the titanium dioxide bonded to the phosphors absorbs luminous light even in the dark, thereby photocatalytic reaction. This can last.

Furthermore, in the case of the phosphor-titanium dioxide composite material according to the present invention, the present invention is applicable to residential / office air purifiers, automobile indoor air purifiers, incinerator noxious gas purifiers, wastewater purification apparatuses, air conditioners, pollution prevention facilities, and the like. More versatile use than commercially available titanium dioxide powder materials.

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are only for illustrating the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited to these examples.

Example  1: by sol-gel method Photoluminescent  Titanium Dioxide Coating

CaCO ₃ : Al ₂ O ₃ : Eu ₂ O ₃ : Nd ₂ O ₃ as a starting material to prepare CaAl ₂ O ₄ : Eu ^{2 +} , Nd ^{3 +} phosphorescent material at a molar ratio of 0.97: 1.0: 0.005: 0.01 Weighed, 3 wt% of B ₂ O ₃ powder and ethanol solution were mixed together and mixed with a ball mill for 24 hours. After mixing, the mixture was dried for 24 hours at 130 ° C. to remove ethanol, and finally the mixed powder was placed in an alumina boat and heat-treated at a reaction temperature of 1400 ° C. for 3 hours in a reducing atmosphere of (95% Ar + 5% H ₂ ).

The photoluminescent powder prepared as described above was coated with TiO ₂ to prepare a titanium dioxide / phosphorescent composite powder. Titanium precursor TBOT (Tetrabutyl titanate, ((C ₄ H ₉ O) ₄ Ti, ACROS)) was mixed with hydrous ethanol (water: ethanol = 1: 5) at 0.08∼0.25 molarity (M), followed by stirring The sol was prepared.

The Ti-sol solution prepared above was aged for 48 hours in air, and then phosphorescent powder was added and mixed for about 1 minute to allow Ti-sol to be coated on the surface of the phosphor. The temperature of the Ti-sol in the aging and coating process was maintained at 50 ℃, pH 7.

Subsequently, the Ti-sol-coated phosphor was separated from the aqueous solution and the powder through a filtration process, and vacuum-dried at about 60 ° C. for 24 hours to remove residual alcohol and water. Finally, the coated Ti-sol was heat-treated at about 450 ° C. for 3 hours to crystallize into anatase TiO ₂ phase having photocatalytic properties. 1 shows a flow chart for preparing a titanium dioxide / phosphorescent composite using the sol-gel method.

Experimental Example  One : Phosphor Analysis of Titanium Dioxide Composite Sample

XRD spectra according to the heat treatment temperature of the TiO ₂ -photoluminescent composite material of the present invention prepared by fixing the concentration of TBOT, a precursor material of TiO ₂ , to 0.167 M are shown in FIG. 2. According to this, when the heat treatment temperature is higher than 350 ℃ to produce anatase phase having a photocatalytic property (JCPDS 21-1272).

3 is an XRD analysis result of TiO ₂ -photoluminescent powder prepared by fixing the heat treatment temperature at 450 ℃ and varying the content of TBOT (0.08 ~ 0.25M). According to this, the peak intensity corresponding to TiO ₂ increases as the content of the precursor TBOT increases, indicating that the amount of coated TiO ₂ increases.

Figure 4a is a photograph of the TiO ₂ -photoluminescent powder by TEM, showing that the fine powder layer appears brightly on the surface of the photoluminescent powder irregularly distributed. FIG. 4B is an EDS spectrum measured for the bright part (powder surface part) of the TEM photograph of FIG. 4A. The peak corresponding to the Ti element appears in the 4.5 ~ 5.0 keV region, indicating that the bright portion of the phosphor surface is a TiO ₂ coating layer.

Experimental Example  2 : Phosphor -Decomposition and Analysis of Titanium Dioxide Composites

Photolysis reaction of the phosphor-titanium dioxide composite material prepared in the present invention was carried out by measuring the bleaching state of an aqueous solution of methylene blue (MB), C ₁₆ H ₁₈ CIN ₃ S.

Dilute methylene blue solution (0.05 wt% in water) to distilled water to make an aqueous solution of 1.6 × 10 ^-5 mol / cm ³ , collect about 20ml using a pipette and place it in a clear glass vial container of size 28 × 60mm. Mix 0.5-0.8 g of phosphorescent-titanium dioxide composite powder in a dark room with no light. Subsequently, irradiation is performed with a 60 W-mercury lamp (UV-radiation) and a 100 W white light lamp (Visible radiation). The methylene blue solution is irradiated for a given time, and then, after a certain time elapses after the UV / Vis light source is irradiated (e.g. after 1 hour), about 2ml is collected, centrifuged and centrifuged. The absorption spectrum was measured in a container using a UV / Vis spectrometer.

5 is a result of measuring the photolysis characteristics according to the heat treatment temperature for the TiO ₂ -photoluminescent powder prepared by fixing the concentration of the precursor TBOT to 0.167M under a visible light source (UV-light filtered). The photodegradation reaction of the specimens heat-treated at 450 ° C. was the best, and further increased at temperatures above 500 ° C. As can be seen from the XRD pattern of FIG. 2, it is determined that the crystallization degree of the anatase-TiO ₂ -form having the photocatalytic property is completed at about 450 ° C.

Figure 6 shows the results of measuring the photolysis characteristics of the TiO ₂ -photoluminescent powders of which the amount of precursor TBOT was changed under a visible light source and heat-treated at 450 ° C., respectively. According to this, commercial TiO ₂ Although the powder (P-25, Degussa) hardly reacted, the TiO ₂ -photoluminescent powder prepared in the present invention can be seen that the photolysis reaction occurs well, and the sample with the added concentration of 0.167M of precursor TBOT is the highest photolysis. The characteristics are shown. In particular, at 0.167M, the decomposition rate was nearly 70% after 3.5 hours of visible light irradiation, and almost all of the decomposition was completed after 5.5 hours of irradiation.

FIG. 7 is a graph comparing photodegradation characteristics of commercial TiO ₂ powder and TiO ₂ -photoluminescent powder to which precursor TBOT 0.167M was added using a UV-light light source. P-25 reacts as fast as the initial 2.5 hours after UV-irradiation, almost all of the decomposition was done 5.5 hours ago. In contrast, the TiO ₂ -phosphorescent powder with 0.167M of precursor TBOT added, the initial photolysis rate was slower than that of commercial P-25 TiO ₂ powder, which is equivalent to the amount of TiO ₂ coated for commercial methylene blue solution. _It is thought to be a difference which occurs because it is relatively much smaller than ₂ powders, and thus the total specific surface area that can be involved in the reaction is low.

8 is an emission spectrum of samples prepared by varying the amount of precursor TBOT. Samples coated with TiO ₂ showed lower emission values than pure phosphorescent powders, and as the amount of TBOT increased, the amount of coated TiO ₂ increased and the emission intensity decreased. However, even when the TiO ₂ layer is coated, the photoluminescent body maintains a certain degree of luminescence property, which indicates that light emitted from the photoluminescent material excites TiO ₂ coated on the surface to promote the photolysis reaction. As illustrated in FIG. 7, when the concentration of the precursor TBOT is more than 0.167M, the photodegradation rate is lowered, which may be interpreted as the intensity of light emitted from the photoluminescent body decreases when the TiO ₂ coating layer is increased. . Therefore, it can be seen that the highest photolysis property can be seen at an appropriate TBOT concentration (0.167M) in which the amount of the coating layer TiO ₂ and the intensity of light emitted from the photoluminescent body can maintain a complementary relationship with each other.

Another mechanism by which TiO ₂ -phosphorescent composites cause photoreactions under visible light is the expansion of the absorption band due to heterojunction between two oxides with different energy band gaps. According to the literature and the paper, the heterojunction CdS / TiO ₂ , Bi ₂ S ₃ / TiO ₂ reported that the photodegradation reaction occurs well even in the visible light wavelength range. In the present invention, when TiO ₂ and phosphorescent materials (CaAl ₂ O ₄ : Eu ^{2 +} , Nd ^{3 +} , SrAl ₂ O ₄ : Eu ^{2 +} , Dy ^{3 +} , etc.) having different energy band gaps are bonded together, The energy band structure is deformed at the interface, so that photolysis reaction is possible even under visible light.

FIG. 9 shows that Ti-sol having a precursor TBOT concentration of 0.167 M and a aging time of 0 to 72 hours was coated on CaAl ₂ O ₄ : Eu ^{2 +} and Nd ^{3 +} powder, respectively. The results of measurement of photodegradation characteristics of the TiO ₂ -photoluminescent powder heat-treated at 450 ° C. under a visible light source are shown. The photodegradation rate increases with the aging time until the aging time of the Ti-sol reaches 48 hours, and after that time, it does not increase any more. Therefore, the aging treatment of the Ti-sol improves the photodegradation rate of the TiO ₂ -photoluminescent body, and the optimum aging period is about 48 hours.

The photocatalyst composite material prepared by the present invention is a heterogeneous bonding of photoluminescent materials and titanium dioxide having different energy bands, thereby deforming the energy band structure of the bonding interface, so that the photocatalytic reaction may occur even under visible light such as indoor lighting. The reaction efficiency is increased. In addition, the photocatalytic reaction may occur continuously in a dark condition in which light is blocked because some titanium dioxide may be excited by light emitted from the phosphor.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above embodiments, but may be embodied in various forms, and those skilled in the art to which the present invention pertains. It will be appreciated that the present invention may be embodied in other specific forms without changing the technical spirit or essential features of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

1 is a flow chart of manufacturing a titanium dioxide / phosphorescent composite using a sol-gel method according to an embodiment of the present invention.

2 is an XRD pattern according to the heat treatment temperature of the TiO ₂ -photoluminescent composite prepared by fixing the concentration of Ti-sol TBOT to 0.167M.

Figure 3 is a TiO ₂ sol prepared by changing the concentration of Ti- TBOT to 0.08 ~ 0.25M - an XRD pattern of the luminous body composite material - a TiO ₂ powder with a heat treatment the luminous body 450 ℃.

4A is a photograph of a TiO ₂ -photoluminescent powder observed by TEM, and FIG. 4B is an EDS spectrum measured for a bright part (powder surface part) of the TEM photograph.

5 is a result of measuring the photodegradation characteristics (absorption constant with exposure time) according to the heat treatment temperature for the TiO ₂ -photoluminescent powder prepared by fixing the amount of Ti- precursor TBOT to 0.167M under a visible light source.

FIG. 6 shows the results of measuring photodegradation characteristics (absorption coefficient according to exposure time) of TiO ₂ -phosphorescent powders which were changed in the amount of Ti-precursor TBOT under visible light and heat-treated at 450 ° C., respectively.

FIG. 7 shows photodegradation characteristics (absorption coefficient according to exposure time) for commercial TiO ₂ powder (P-25) and TiO ₂ -luminescent powder to which Ti-precursor TBOT 0.167M is added in the present invention using an ultraviolet light source. This is the result of comparing one data.

8 is an emission spectrum (light intensity according to wavelength) of TiO ₂ -photoluminescent powder samples prepared by varying the amount of Ti precursor precursor TBOT.

9 is a result of measuring the photolysis characteristics of the TiO ₂ -photoluminescent powder under visible-light light source according to the aging time (Ti-sol).

Claims (7)

i) preparing a Ti-sol by mixing titanium precursor with 0.05 to 0.3 M in hydrous ethanol; ii) adding and mixing the phosphor powder to the Ti-sol to coat titanium dioxide on the surface of the phosphor; And iii) separating the titanium dioxide-coated phosphor, and then heat-treating at 400 to 500 ° C. for 2 to 5 hours. Method of manufacturing a composite material for a photocatalyst is uniformly coated with titanium dioxide (TiO ₂ ) on the surface of the phosphor. The method of claim 1, wherein the titanium precursor is TiCl ₄ , Ti (OCH ₂ CH ₃ ) ₄ , Ti (OCH (CH ₃ ) ₂ ) ₄ , ((CH ₃ ) ₂ CHO) ₂ Ti (C ₅ H ₇ O ₂ ) ₂ , Ti (OC ₂ H ₅ ) ₄ , Ti (OCH ₃ ) ₄ And Ti (C ₅ H ₇ O ₂ ) _{2 A} method for producing a composite material for a photocatalyst selected from the group consisting of. According to claim 1, wherein the phosphor is CaAl ₂ O ₄ : Eu system, SrAl ₂ O ₄ : Eu system, BaAl ₂ O ₄ : Eu system, ZnS: Cu system, CaAl ₁₂ O ₁₉ : Eu system, SrAl ₁₂ O ₁₉ : Eu-based, BaAl ₁₂ O ₁₉ : Eu-based, BaMgAl ₁₀ O ₁₇ : Eu-based, SrMgAl ₁₀ O ₁₇ : Eu-based and BaMg ₂ Al ₁₆ O ₂₇ : Eu-based composite material for the photocatalyst selected from the group consisting of Way. The method according to claim 1, further comprising aging the Ti-sol in the atmosphere for 24 to 72 hours before step ii). The method of claim 1, wherein the coating time of step ii) is 30 seconds to 1 minute. The method according to claim 1, further comprising the step of drying the residual alcohol and water of the titanium dioxide-coated phosphor, before the heat treatment of the titanium dioxide-coated phosphor, in step iii). A composite material for photocatalyst prepared by the method of claim 1, wherein titanium dioxide (TiO ₂ ) is uniformly coated on the surface of the phosphor.

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