KR102432779B1 - One-step synthesized method of black oxide particle - Google Patents

Abstract

The present invention relates to a method for synthesizing black oxide particles, and more particularly, to a method for synthesizing black oxide particles in a unified process. The present invention comprises the steps of preparing a precursor solution by adding a precursor containing metal ions to a solvent; forming the precursor solution in a droplet state using ultrasonic waves; spraying the precursor solution in the droplet state into the inside of a furnace using a carrier gas; and a step of thermally decomposing and oxidizing the droplets in the furnace.

Description

A unified method for synthesizing black oxide particles {ONE-STEP SYNTHESIZED METHOD OF BLACK OXIDE PARTICLE}

The present invention relates to a method for synthesizing black oxide particles, and more particularly, to a method for synthesizing black oxide particles through a unified process.

Environmental purification technology using photocatalyst is a field of advanced oxidation process. This means that when a light source greater than or similar to the band gap energy of the photocatalytic material is irradiated, electrons are excited from the valence band to the conduction band, which results in electrons e ^- ) hole (h ⁺ ) pair is formed and moved to the surface, and superoxide and hydroxyl radical are formed to decompose harmful substances. Photocatalyst technology is a technology attracting attention in the field of water and air purification because it has advantages such as low cost, non-toxicity to the human body, sterilization, effective decomposition power for various organic substances, stability and durability.

Among various materials that can be used as photocatalysts, studies on oxide-based materials having semiconductor properties have been actively conducted. However, in the case of oxides with high-efficiency photocatalytic properties, due to their unique band spacing characteristics, they cannot absorb the visible light region (400 nm to 700 nm) or less, which accounts for about 45% of sunlight, and can not absorb about 5% of the ultraviolet region ( Excitation of electrons is possible only at ~400 nm). In order to solve this problem, cation or anion doping and a technique utilizing a localized surface plasmon phenomenon of a metal have been developed, but the absorption range is limited and the inherent material advantages are reduced.

Recently, black titanium dioxide (Black TiO ₂ ) has been attracting attention as a material capable of solving the above-mentioned problems and capable of a very efficient photocatalytic reaction under sunlight. Black titanium dioxide (Black TiO ₂ ) can be defined as TiO ₂ in which sub-levels are formed inside the band gap by creating surface or internal defects, and is a material capable of absorbing visible light through the formed sub-levels. An excellent property of black titanium dioxide is its oxygen vacancies, which induce an intermediate band in the energy forbidden region and shorten the bandgap, enhancing the area of absorbable light. Oxygen vacancies on the surface promote adsorption of guest molecules and lack of charge due to an electron-deficient environment, thereby enhancing photocatalytic activity. Since then, many researchers have researched to synthesize black oxides by introducing oxygen vacancies in various oxides and to apply them as photocatalysts.

With respect to the method for producing black titanium dioxide, MaO and Chen et al. synthesized black titanium dioxide (Black TiO ₂ ) for the first time by reducing previously synthesized white TiO ₂ in a hydrogen atmosphere for about 3 days (Chen, X., Liu, L., Peter, YY, and Mao, SS, Science, 331 (6018), 746-750 (2011)), many researchers have studied the synthesis and shape control of black oxides by reducing previously synthesized white oxides, further Furthermore, research on optical properties and their applications is in progress. In this related prior art, for example, there is a black titania photocatalyst manufacturing method in which TiO ₂ and Mg powder are mixed to form a mixed powder, and TiO ₂ is reduced by heat treatment (Korean Patent No. 10-179994).

However, in this method, nano-sized white oxide particles must be synthesized in advance and a high-energy-based reduction process is required for a long time, so the process is not only complicated, but also industrial application is difficult because particle growth and strong agglomeration occur during the reduction process. It has limited problems.

Therefore, in order to effectively synthesize a large amount of black oxide, a one-step process in which oxygen vacancies can be efficiently introduced is required. To solve this problem, the concept of forming oxygen vacancies by incomplete oxidation of oxides was introduced. However, no technology has yet reported a unified process using this concept.

Ultrasonic spray pyrolysis is an aerosol process that can economically produce monodispersed sub-micron particles. The ultrasonic spray pyrolysis process has the advantage that it is easy to control the process temperature and the residence time of the droplets, so it is easy to control the physicochemical properties such as crystallinity, crystal structure, and composition of the synthetic particles. It is easy to induce incomplete oxidation in the process of synthesis. However, in the conventional ultrasonic spray pyrolysis process, it is difficult to synthesize nanoparticles due to the limitation of initial droplet size reduction. However, the particles synthesized by the ultrasonic spray pyrolysis process are formed by aggregation of fine primary particles, and the salt-assisted ultrasonic spray pyrolysis process capable of synthesizing nanoparticles by inhibiting aggregation by remaining inactive salts between the primary particles (Salt assisted ultrasonic spray pyrolysis) The synthesis potential of nanoparticles has been sufficiently verified. However, the salt-assisted ultrasonic spray pyrolysis process is complicated and requires a long time to clean residual salts.

Therefore, in order to directly synthesize nanoparticles using the ultrasonic spray pyrolysis process, a new technology capable of suppressing aggregation of primary particles during the process is also required.

Korean Patent No. 10-179994

Chen, X., Liu, L., Peter, Y. Y., and Mao, S. S., Science, 331 (6018), 746-750 (2011)

An object of the present invention is to provide a method for synthesizing black oxide particles based on a unified ultrasonic spray pyrolysis process, which can overcome the limitations of a heat treatment-based reduction method, which is a conventional synthesis method as described above.

Another object of the present invention is to provide a method for synthesizing a nano-sized black oxide by suppressing aggregation of primary particles by adding a decomposable complex agent during the process.

The present invention includes the steps of preparing a precursor solution by adding a precursor and a complexing agent to a solvent in order to solve the above problems; forming the precursor solution in a droplet state using ultrasonic waves; spraying the precursor solution in the droplet state into the inside of a furnace using a carrier gas; and pyrolyzing and oxidizing the droplets inside the furnace.

As the precursor, any one selected from the group consisting of nitrates containing metal ions, acetates, alkoxides, carbonates, and the like may be used.

The metal ions may combine with oxygen to form a metal oxide having a bandgap of 2.5 eV or more and 4.9 eV or less.

The solvent may be any one selected from the group consisting of water, ethanol, methanol, dimethyl sulfoxide, dimethyl acetamide, dimethyl formamide, and the like.

The carrier gas may be at least one inert gas selected from the group comprising nitrogen, helium, argon, and the like.

The lower temperature of the inside of the furnace may be 200 ℃, the upper temperature may be 600 ~ 900 ℃.

In the step of preparing the precursor solution, a complexing agent may be additionally added to the solvent.

The complexing agent may be oxalic acid, citric acid, oleic acid, beta-diketone, or the like.

A molar (mol) ratio of the metal ion added to the solvent and the complexing agent may be 1:1 to 1:20.

The present invention can produce black oxide particles in a unified process based on ultrasonic spray pyrolysis.

In addition, the present invention can continuously manufacture black oxide particles in a unified process.

In addition, the present invention can prepare nano-sized black oxide particles by adding a complexing agent and controlling the temperature during the process.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the ultrasonic spray pyrolysis method used by this invention.
2 is a photograph of black TiO ₂ powder of micro size prepared in Examples 1-1 and 1-2.
3 is a FE-SEM photograph of black TiO ₂ prepared in Examples 1-1 and 1-2.
4 is an XRD analysis result of black TiO ₂ prepared in Examples 1-1 and 1-2.
5 is an O 1s XPS spectrum of black TiO ₂ nanoparticles prepared in Examples 1-1 and 1-2 and general anatase-phase TiO ₂ .
6 is an absorbance analysis result of black TiO ₂ prepared in Examples 1-1 and 1-2.
7 is a schematic diagram showing the nanoparticle synthesis process of adding the complexing agent of Example 2.
8 is an FE-SEM photograph of the particles prepared in Example 2.
9 is an XRD analysis result of the particles prepared in Example 2.
10 is a TEM photograph of BT-900.
11 is an XPS analysis result of BT-900.
12 is a Raman spectroscopy analysis result of BT-900.
13 is an absorbance measurement result of the particles prepared in Example 2 using an ultraviolet-visible spectrophotometer.
14 is a view showing the photocatalytic decomposition efficiency of the particles prepared in Example 2.
15 is a FE-SEM photograph showing the synthesis process of nano-sized particles with or without additives.
16 is an FT-IR spectrum of the precursor solution and particles prepared in Example 2.
17 is a FE-SEM and XRD analysis results of the black ZrO ₂ particles prepared in Example 3.
18 is an absorbance measurement result using the ultraviolet-visible spectrophotometer prepared in Example 3.
19 is a FE-SEM and XRD analysis results of nano-sized black ZrO ₂ particles synthesized by adding a complexing agent in Example 4.
20 is a transmission electron microscope analysis result of nano-sized black and white ZrO ₂ .
21 is an absorbance measurement result of the particles prepared in Example 4 using an ultraviolet-visible spectrophotometer.

The present invention prepares micro- or nano-sized black oxide particles using ultrasonic spray pyrolysis.

Ultrasonic spray pyrolysis is a gas phase synthesis method using a liquid precursor. The ultrasonic spray pyrolysis method can easily prepare a powder having a certain stoichiometric ratio by controlling the composition of the liquid precursor, the process temperature, the internal atmosphere, and the residence time of the droplets, and it is possible to obtain fine particles with high purity and high crystallinity. Also, since it is a gaseous method, it is very free from agglomeration.

The ultrasonic spray pyrolysis method used in the present invention can be divided into an ultrasonic spray step, a pyrolysis step, and a collection step, and a schematic diagram thereof is shown in FIG. 1 . First, a solution of a desired precursor is prepared, and the solution is introduced into the tube at the lower end to which the ultrasonic terminal is connected using a syringe pump. Microdroplets of the solution introduced by the ultrasonic terminal having a constant frequency are made, and the microdroplets move into the furnace preheated by the carrier gas. The preheated furnace in the pyrolysis zone is divided into two zones. In the first zone, the solvent of microdroplets is evaporated, and in the second zone, oxide crystallization proceeds. Factors affecting the size, crystallinity and shape of the synthesized powder are the temperature of this second region and the residence time in the furnace. When setting the crystallization temperature, the time for the sprayed droplets to pass through the preheated furnace is only a few seconds, so in general, the temperature of the furnace is controlled to be higher than the pyrolysis temperature of the raw material precursor.

In the present invention, adding a precursor containing metal ions to a solvent to prepare a precursor solution; forming the precursor solution in a droplet state using ultrasonic waves; spraying the precursor solution in a droplet state into the inside of a furnace using a carrier gas; and pyrolyzing and oxidizing the droplets in the furnace.

Hereinafter, each step will be described in detail.

preparing a precursor solution by adding a precursor containing metal ions to a solvent

Conventionally, in order to prepare a black oxide, a preformed white oxide is used as a starting material, but in the present invention, a black oxide can be prepared from a precursor by a unified process.

The precursor may be any one selected from the group consisting of nitrates, acetates, alkoxides, carbonates, and the like containing metal ions.

The metal ion is not particularly limited as long as it combines with oxygen to form a metal oxide having a bandgap of 2.5 eV or more and 4.9 eV or less, for example, Zn, W, Ti, Zr, Ga, etc. have.

The solvent is a solvent capable of dissolving a precursor containing metal ions, and may be, for example, methanol, ethanol, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), dimethyl acetamide (DMA), or the like.

In general, the particle size and distribution of particles synthesized by ultrasonic spray pyrolysis is predominantly influenced by the microscopic droplet size generated by ultrasonic vibration. The droplet size can be created finely by increasing the frequency of the ultrasonic vibrator. However, from this point of view, synthesizing nano-sized particles requires a lot of cost. Therefore, this obscures the advantages of ultrasonic spray pyrolysis and limits the industrial advantages. In order to economically synthesize nanoparticles, a salt-assisted ultrasonic spray pyrolysis process has been studied, but it required several washing and drying steps to remove the salt, which may lead to agglomeration and low yield of the synthesized particles.

In the present invention, in order to directly synthesize nano-sized black oxide particles and to solve the problems of ultrasonic spray pyrolysis, the concepts of coordination bonds and organometallic compounds are introduced. The present inventors focused on the precipitation (precipitation) and decomposition of organometallic compounds caused by the metal complexing agent formed between the metal precursor and the organic ligand during the ultrasonic spray pyrolysis process. Additionally, the synthesis of nano-sized black oxide particles was attempted by blocking the inflow of oxygen from the outside to inhibit oxidation and controlling the decomposition rate and crystallization rate of the precipitate (precipitate). Thereafter, the size, shape, optical properties and photocatalytic properties of the synthetic particles were analyzed by various methods. In addition, the effect of complexing agents on the synthesis of nano-sized particles was systematically investigated. The complexing agent can form nano-sized particles by inhibiting aggregation of primary particles during the thermal decomposition process.

The solvent may be any one selected from the group consisting of ethanol, methanol, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), dimethyl acetamide (DMA), and the like.

To the solvent, oleic acid, citric acid, oxalic acid, beta diketone, etc. may be further added as a complexing agent. The molar (mol) ratio of the added metal ion to the complexing agent may be 1:1 to 1:20. By the amount of the complexing agent within the above range, the size of the formed black oxide particles can be adjusted to 40nm ~ 5um.

The beta diketone is, 2,4-pentanedione, 3-methyl-2,4-pentanedione, 3-isopropyl-2,4-pentanedione, 2,2-dimethyl-3,5-hexadione, 4 ,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione and the like.

Forming the precursor solution in a droplet state using ultrasonic waves

The ultrasonic terminal has a predetermined frequency (for example, 1.5 to 1.7 MHz), and mechanical energy is transmitted to the precursor solution by ultrasonic vibration, whereby droplets are formed on the surface of the solution.

Spraying the precursor solution in the droplet state into the inside of a furnace using a carrier gas

The formed droplets move into the furnace using a carrier gas.

The carrier gas is at least one inert gas selected from the group comprising nitrogen, helium, argon and the like. It is preferable that the supply flow rate of the carrier gas is about 100 ml/min to 10 L/min.

The droplet is pyrolyzed and oxidized inside the furnace

The pyrolysis and oxidation phase is divided into two regions. In the first region, the solvent of the microdroplets is evaporated and precipitation of the solid phase is caused. In the second region, decomposition and crystallization of the precursor and complexing agent proceed. The temperature of the first region for evaporating the solvent is 200°C, and the temperature of the second region where crystallization is performed is 400 to 1200°C.

Measurement and analysis methods

1) FE-SEM (Field emission-scanning electron microscopy)

FE-SEM analysis was performed to confirm the shape and size of the synthesized particles, and the equipment used was JSM-7500F manufactured by JEOL of Japan. The measurement was performed with an acceleration voltage of 10 kV, and the magnification was measured from 5000 times to 100000 times.

2) XRD (X-ray diffraction)

XRD analysis was performed to determine the crystallinity of the synthesized particles. XRD analysis can obtain information about crystallinity or the structure of a material by irradiating a sample with X-rays at a certain angle and measuring the intrinsic diffraction angle and intensity diffracted from the grating. The equipment used was X'pert ³ powder manufactured by PANaltycal of the Netherlands, and Cu-Ka rays (λ=1.5406Å) were used for X-rays, and 4° per minute was measured from 2θ=10 to 90°. The obtained diffraction pattern was analyzed against JCPDS card information.

3) TEM (Transmission electron microscopy)

TEM analysis was performed to confirm the detailed shape of the collected particles and the disorder layer and crystallinity of the surface, and the selected area electron diffraction (SAED) pattern of the sample was analyzed to determine the crystal phase. After the sample was dispersed in ethanol, a very small amount was collected, prepared on a copper grid, and dried at room temperature for at least one day. The equipment used is a JEM-2100F manufactured by JEOL of Japan.

4) Raman spectroscopy

In order to confirm the increase in the disorder of the crystal structure due to the effect of oxygen vacancies, analysis was performed with a Raman spectrophotometer. The equipment used was LabRAM HR-800 UV-Visible-NIR manufactured by HORIBA JOBIN YVON in Japan.

5) XPS (X-ray photoelectron spectroscopy)

XPS analysis was performed to confirm the change in the chemical bonding state of the oxide surface due to oxygen vacancies. When oxygen vacancies are introduced, a number of incomplete bonds (dangling bonds) on the surface increase, and bonds with -OH groups mainly increase. The peak observed prominently around 531.0 eV in the XPS O 1s spectrum is known as a general feature that appears as the chemical bonding state of black TiO ₂ changes. The equipment used was ESCALAB 250, a product of Thermo scientific in the United States.

6) UV-VIS spectrophotometer

A UV-VIS spectrophotometer was used to analyze the optical properties of the synthesized sample, and the wavelength band was measured from 200 nm to 1400 nm to determine the absorption range from ultraviolet to near infrared. The control group was selected as a white oxide produced by heat-treating the synthesized particles in the atmosphere. The equipment used was UV-2600 manufactured by SHIMADZU of Japan.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following examples are only preferred examples of the present invention, and the present invention is not limited to the following examples at all.

Example 1. Micro-sized black titanium dioxide particles

Example 1-1.

The sample was synthesized by ultrasonic spray pyrolysis, and the solution used was added to 100 ml of absolute ethanol (Ethyl alcohol, Pure, Sigma aldrich, 200 proof, ACS reagent, >99.5%) of titanium tetra isopropoxide at a concentration of 100 mM. was manufactured by The solution was stirred at room temperature at 300 rpm for 24 hours, and the solution injection rate was fixed at 1.2 ml/min. The frequency of the ultrasonic terminal generating micro-droplets was set to 1.7 MHz, and the carrier gas for moving the micro-droplets into the preheated furnace was flowed at a rate of 2 L/min using N ₂ (99.999%). The temperature of the lower part of evaporating the solvent was fixed at 200 °C, and the upper temperature was set at 500 °C, and the shape, size, crystallinity and photocatalytic properties of black titanium dioxide according to the temperature difference were measured. Hereinafter, the synthesized particles may be referred to as BTM-500 depending on the crystallization temperature.

Example 1-2.

Black titanium dioxide was prepared in the same manner as in Example 1-1, except that the upper temperature was set to 900°C. Hereinafter, the synthesized particles may be referred to as BTM-900 depending on the crystallization temperature.

Measurement Example 1-1. Change of color according to temperature

The photos of the powders prepared in Examples 1-1 and 1-2 are shown in FIG. 2 . 2A is a BTM-500, (B) is a BTM-900, (C) is a P25 manufactured by Degussa. BTM-500 showed a light gray color, and BTM-900 synthesized at high temperature changed to a darker gray color close to black. When compared with the color of Degussa's P25 shown in (C) of FIG. 2 , it is estimated that oxygen vacancies on the surface have been formed as it is gray rather than white.

Measurement example 1-2. Microstructure analysis using scanning electron microscope (FE-SEM)

The microstructures of the particles prepared in Examples 1-1 and 1-2 were analyzed through FE-SEM, and the results are shown in FIG. 3 . 3 (A) and (C) are BTM-500, (B) and (D) are BTM-900. As a result of observation, the size of the particles was confirmed to be about 0.5 to 1.5 μm, and also exhibited a spherical shape.

Measurement example 1-3. Crystal structure analysis using X-ray diffraction analysis (XRD)

The results of XRD analysis of the particles prepared in Examples 1-1 and 1-2 are shown in FIG. 4 . 4 (A) is a BTM-500, (B) is a BTM-900. The obtained diffraction pattern was compared with JCPDS card information to confirm that it was anatase-phase TiO ₂ (JCPDS #21-1272), and it was confirmed that rutile-phase TiO ₂ (JCPDS #21-1276), a high-temperature stable phase, was not observed. It was confirmed that the intensity of the peak increased as the synthesis temperature increased, which is confirmed from the anatase-phase TiO ₂ (101) peak with 2θ of 25.281°. The intensity of the observed peak is very high, and in BTM-900, it is possible to identify the peaks in various details, so the crystallinity is very good. Also, by looking at the difference in peak intensity between BTM-500 and BTM-900, it can be confirmed that the crystallinity increases as the temperature of the crystallization section increases.

Measurement example 1-4. Confirmation of the presence of oxygen vacancies by X-ray photoelectron spectroscopy (XPS)

5 shows the O 1s XPS spectrum of BTM-900 and general anatase-phase TiO ₂ . 5(A) is BTM-900, (B) is anatase-phase TiO ₂ of 10 nm size, which is a product of MKnano of Canada, which is commercially available. In general TiO ₂ , the main peak appears around 529.6 eV, and in black titanium dioxide, the main peak appears after 530 eV due to defect movement. Looking at (A) of FIG. 5, which is the spectrum of BTM-900, the main peak appeared at about 530.5 eV, and the peak after 532 eV, which is known as the peak of oxygen adsorbed such as Ti-OH, is higher than that of the control group (B). observed. The peak appearing in this region is known as the main characteristic of black TiO ₂ and is known to appear due to the introduction of oxygen defects. Since the peak due to oxygen defects is observed very high, it can be seen that black titanium dioxide having a large amount of oxygen vacancies or internal defects is synthesized.

Measurement example 1-5. Absorbance Measurement Using Ultraviolet-Visible Spectrophotometer

In order to find out whether BTM-500 and BTM-900 match the optical properties of known black titanium dioxide, absorbance was measured using an ultraviolet-visible spectrophotometer, and the results are shown in FIG. 6 . In the case of BTM _- 900 particles, absorption in the visible ray region was exhibited, and as shown in FIG. A bandgap smaller than 3.0~3.2eV can be seen.

From the results of Example 1, it can be confirmed that the black titanium dioxide particles are directly synthesized by controlling the thermal decomposition reaction and the process atmosphere of the TTIP precursor, thereby inhibiting the oxidation of titanium dioxide.

Example 2. Black Titanium Dioxide with Nano Size

The sample was synthesized by ultrasonic spray pyrolysis, and the precursor solution was 100mM titanium tetraisopropoxide in 100ml absolute ethanol (Ethyl alcohol, Pure, Sigma aldrich, 200 proof, ACS reagent, >99.5%) in the same manner as in Example 1. It was prepared by adding the concentration, and citric acid was added as a complexing agent in a predetermined molar ratio with the metal ion. The solution was stirred at room temperature at 300 rpm for 24 hours, and the solution injection rate was fixed at 1.2 ml/min. The frequency of the ultrasonic terminal generating micro-droplets was set to 1.7 MHz, and the carrier gas for moving the micro-droplets into the preheated furnace was introduced at a rate of 2 L/min using N ₂ (99.999%). The temperature of the lower part for evaporating the solvent was fixed at 200 °C, and the temperature of the crystallization section (upper part) was fixed at 900 °C. Hereinafter, the generated particles were denoted as BT-900, and overall information of the synthesis method is shown in FIG. 7 .

Measurement Example 2-1. Microstructure Analysis Using Scanning Electron Microscopy (SEM)

The microstructure of BT-900 was analyzed through FE-SEM, and the results are shown in FIG. 8 . The shape was spherical and showed a free form from agglomeration. The size of the synthesized nanoparticles was confirmed to be about 10 to 30 nm.

Measurement example 2-2. Crystal structure analysis using X-ray diffraction analysis (XRD)

The results of XRD analysis of BT-900 are shown in FIG. 9 . The obtained diffraction pattern was compared with JCPDS card information to confirm that it was anatase-phase TiO ₂ (JCPDS #21-1272), and a phase transition to rutile-phase TiO ₂ (JCPDS #21-1276), a high-temperature stable phase, was also observed. This shows that complex structures of anatase and rutile phases can be synthesized when the process is carried out at a higher temperature.

The average particle size can be obtained by using the full width at half maximum of the peak obtained through X-ray diffraction analysis and Scherrer's equation. Scherrer's expression is:

Here, d is the particle size, λ is the wavelength of X-rays (Cu-Ka=1.5406 Å), b is the half width of the obtained peak, and θ is the diffracted scattering angle (Bragg angle). The synthesized particles were calculated to have a size of 13.7 nm. This means the size of the primary particles constituting the synthesized nanoparticles.

Measurement example 2-3. Microstructure Analysis by Transmission Electron Microscopy (TEM)

A microstructure photograph of BT-900 analyzed through a transmission electron microscope is shown in FIG. 10 . 10A shows a selected area electron diffraction (SAED) pattern of BT-900. The synthesized particles have a spherical shape and have a size of about 10 nm to 30 nm. As a result _of confirming the interplanar distance between the gratings through the TEM image at high magnification shown in FIG. It can be seen that the crystallinity is excellent from the very clear . The change in the interplanar distance is a result of the decrease in structural regularity due to the introduced oxygen vacancies.

In addition, it can be confirmed that a disorder layer in which a lattice is not clearly visible is present on the surface, which is a typical characteristic of black titanium dioxide. This layer appears due to the introduction of surface oxygen vacancies or defects, which cause the band spacing of TiO ₂ to be reduced. Therefore, nanoparticles were directly synthesized by ultrasonic spray pyrolysis, and it is judged that the color of the synthesized black titanium dioxide was changed due to oxygen vacancies and defects as in other known results.

Measurement example 2-4. Confirmation of the presence of oxygen vacancies by X-ray photoelectron spectroscopy (XPS)

11 shows the O 1s XPS spectrum of BT-900. As a comparison group, TiO ₂ powder (WT900) changed to white by heat treatment of BT-900 particles in the air was used. The results were similar to those of BTM-900 previously, and the main peak was shown at 530.1 eV, which was consistent with the known binding peak of most black titanium dioxide. The 531.4 eV peak is the peak of adsorbed oxygen such as Ti-OH, and the 531.4 eV peak of the black titanium dioxide synthesized by ultrasonic spray pyrolysis is larger than that of the control, confirming that it is the effect of oxygen vacancies.

Measurement example 2-5. Crystal structure analysis using Raman spectroscopy

Raman spectroscopy was performed to check whether a change in the Raman spectrum peak was observed while structural regularity was reduced due to surface oxygen vacancies peculiar to black titanium dioxide, or whether other phases not confirmed by XRD existed, and the results are shown in FIG. 12 shown in

According to reports from several studies synthesizing black titanium dioxide, the main peak of black titanium dioxide appears around 152 cm ^-1 shifted to the right rather than 144 cm ^-1 of white TiO ₂ . This 144 cm ^-1 peak is a peak of the Ti-O-Ti bond inside TiO ₂ , and the shift of the peak appears as Raman scattering changes due to defects present in the synthesized particles. In the Raman spectrum, the peak appearing toward the rear wavelength band is a bond existing on the surface, and the peak in the vicinity of about 640 cm ^-1 is known as the peak of the Ti-O-Ti bond existing on the surface.

Looking at the Raman spectrum of black titanium dioxide synthesized at 900°C by ultrasonic spray pyrolysis, it can be seen that the main peak is present in the vicinity of about 152.6 cm ^-1 and the peak in the rear wavelength band is not clearly observed. Since the lattice of anatase-phase TiO ₂ with excellent crystallinity exists inside, the main peak of black titanium dioxide could appear, and the peak was not accurately observed in the wavelength band after the surface bonding peak appeared due to the influence of oxygen vacancies on the surface.

Measurement example 2-6. Absorbance Measurement Using Ultraviolet-Visible Spectrophotometer

In order to evaluate the optical properties of black titanium dioxide synthesized by ultrasonic spray pyrolysis, absorbance was first measured using an ultraviolet-visible spectrophotometer, and the results are shown in FIG. 13 . As a comparison group, TiO ₂ powder (WT900) changed to white by heat treatment of BT-900 particles in the air was used.

The heat-treated particles as a control did not absorb any light of 400 nm or less in the visible ray region, but the black titanium dioxide of the present invention showed a tendency to absorb the visible ray region and the near-infrared region. In addition, as a result of calculating the band gap using the Kubelka-Munk equation, it can be confirmed that the band gap of the existing white TiO ₂ is smaller than the band gap (3.0~3.2 eV).

Measurement example 2-7. Evaluation of photocatalytic properties

In order to confirm the photocatalytic properties of black titanium dioxide particles synthesized by ultrasonic spray pyrolysis, a photochemical decomposition experiment was conducted using 100 ml of methylene blue solution diluted to 1x10 ^-5 M in DI water in visible light with P25 as the control group. proceeded. For the black titanium dioxide sample, BT-900 was used, and 0.05 g was added into the solution. In order to equilibrate the physical adsorption-desorption equilibrium between the sample and methylene blue, it was placed in a dark room for 150 minutes and then light irradiation was started. After irradiation, 1.5 ml of the solution was collected every 30 minutes and absorbance was measured with an ultraviolet-visible spectrophotometer, and the results are shown in FIG. 14 . P25 showed almost no photocatalytic properties, and BT-900 showed photocatalytic properties in the region below visible light. White TiO ₂ generally does not exhibit photocatalytic properties in the visible light range because it hardly absorbs the visible light range with a band interval of 3.0 to 3.2 eV, and the photocatalytic properties were very poor as shown in FIG. 14 . It was confirmed that BT-900 had a high physical adsorption rate, which is presumed to be caused by a difference in surface charge due to the countless oxygen vacancies on the surface or an increase in the physical adsorption power of the sample.

The following formula was used to calculate the decomposition efficiency and its rate, and the results are shown in (B) of FIG. 14 . Equation C was calculated by setting the absorbance value of 663 nm, which shows the highest absorbance.

Photocatalytic degradation efficiency (%) = (C ₁ -C)/C ₁ x 100

Here, C ₁ is the absorbance at 663 nm measured just before light irradiation after the adsorption-desorption equilibrium is achieved, and C is the value measured by taking a sample every 30 minutes and measuring for a total of 120 minutes. In addition, C _o and C are the concentrations at the initial stage and after a specific reaction time (t) of the reaction organic material, respectively, and k _app is a pseudo-first-order rate constant. This rate constant is affected by reaction conditions such as temperature and pH, and the larger this value, the greater the efficiency of the catalyst.

From the photocatalytic decomposition efficiency shown in FIG. 14(A), it was confirmed that black titanium dioxide synthesized by ultrasonic spray pyrolysis showed photocatalytic properties in the region below visible light. This is because the band structure is changed due to the formation of synthetic oxygen vacancies and absorption of light with wavelengths below visible light is possible. A graph for obtaining a numerical speed value is shown in (B) of FIG. 14 . BT-900 exhibited a rate constant (k _app ) of 1.13x10 ^-2 and a rate constant 35 times faster than that of P25.

In order to check the effect of the added complexing agent on the size of the synthesized particles, the particles were synthesized in the same manner as in Example 2 except for the addition of the complexing agent and the crystallization temperature, and the FE-SEM analysis results are shown in FIG. 15 . (A), (B) and (C) are particles synthesized at 375 ^o C, 400 ^o C, and 450 ^o C, respectively, by adding a complexing agent. On the other hand, (D), (E) and (F) are particles synthesized at the same temperature without adding a complexing agent. From the results of FIG. 15 , it can be confirmed that when a complexing agent is added, the size is changed to nano-sized particles through a decomposition process. On the other hand, when no complexing agent was added, no change in particle size according to temperature was observed.

16 shows the FT-IR spectral results of the solution and synthesized particles, and confirms the decomposition temperature of the chemically bound residue and the organic material. 16 (A) shows the FT-IR spectrum of the precursor solution, and it is observed that new peaks are formed at 1527 cm ^-1 and 1605 cm ^-1 when a complexing agent (OA in FIG. 16 (A)) is introduced. . Compared with the reference data in which the titanium ion and the complexing agent are combined, it is assumed that the titanium precursor and the complexing agent are chemically bound and there is a residual organic material that does not bind. Figure 16 (B) shows the FT-IR spectrum of the particles after ultrasonic spray pyrolysis. The peaks at 1527 cm ⁻¹ and 1605 cm ⁻¹ observed in the precursor solution were maintained up to 450° C., indicating the decomposition of free organic matter not bound to titanium ions and precipitation of organometallic compounds bound to titanium ions. In addition, the decrease in this peak suggests that the organic material can be sufficiently decomposed in an oxygen-free atmosphere.

From the results of Example 2, it was confirmed that nano-sized particles could be synthesized by inhibiting aggregation of primary particles when citric acid was added as one of the complexing agents mentioned above.

Example 3. Micro-sized black zirconia particles

The sample was synthesized by ultrasonic spray pyrolysis in the same way as the synthesis process of black peat, and the solution used was zirconium nitrate in absolute ethanol (Ethyl alcohol, Pure, Sigma aldrich, 200 proof, ACS reagent, >99.5%) of 100 mM concentration was added. The solution was stirred at room temperature at 300 rpm for 24 hours, and the solution injection rate was fixed at 1.2 ml/min. The frequency of the ultrasonic terminal generating micro-droplets was set to 1.7 MHz, and the carrier gas for moving the micro-droplets into the preheated furnace was flowed at a rate of 2 L/min using N ₂ (99.999%). The temperature of the lower part for evaporating the solvent was fixed at 200 °C, and the upper temperature was set at 800 °C to measure the shape, size, and crystallinity of black zirconia.

Measurement example 3-1. Analysis results of scanning electron microscope (SEM) and X-ray diffraction analysis (XRD)

The microstructure of the synthesized particles was analyzed through FE-SEM, and the results are shown in FIG. 17 . Similar to black titanium dioxide, it was spherical in shape and exhibited a form free from agglomeration.

In addition, the X-ray diffraction pattern was compared with the JCPDS card information to confirm that it was a square ZrO ₂ (JCPDS #49-1642). However, it is thought that the intensity and clarity of each diffraction peak decreased as the regularity of the crystal structure decreased due to the introduction of oxygen vacancies.

Measurement example 3-2. Absorbance Measurement Using Ultraviolet-Visible Spectrophotometer

In order to investigate the change in optical properties due to the introduction of oxygen vacancies, absorbance was measured using an ultraviolet-visible spectrophotometer, and the results are shown in FIG. 18 . Unlike the existing white ZrO ₂ , it can be clearly confirmed that a sub-energy level is formed within the band gap due to the introduction of oxygen vacancies, so that absorption of visible and near-infrared light is possible.

Example 4. Black Zirconia with Nano Size

The sample was synthesized by ultrasonic spray pyrolysis in the same way as the synthesis process of black peat, and the solution used was zirconium nitrate in absolute ethanol (Ethyl alcohol, Pure, Sigma aldrich, 200 proof, ACS reagent, >99.5%) of 100 mM It was prepared by adding the concentration, and as a complexing agent, citric acid was added with a metal ion in a predetermined molar ratio. The solution was stirred at room temperature at 300 rpm for 24 hours, and the solution injection rate was fixed at 1.2 ml/min. The frequency of the ultrasonic terminal generating micro-droplets was set to 1.7 MHz, and the carrier gas for moving the micro-droplets into the preheated furnace was flowed at a rate of 2 L/min using N ₂ (99.999%). The temperature of the lower part to evaporate the solvent was fixed at 200 °C, and the process was carried out by setting the temperature of the upper part to 800 °C.

Measurement Example 4-1 Analysis result of scanning electron microscope (SEM) and X-ray diffraction analysis (XRD)

The microstructure of the synthesized particles was analyzed through FE-SEM, and the results are shown in FIG. 19 . The synthesized black zirconia nanoparticles were spherical in shape similar to black titanium dioxide nanoparticles, exhibited aggregation-free appearance, and were confirmed to have a size of about 40 nm.

In addition, the X-ray diffraction pattern was compared with the JCPDS card information to confirm that it was a square ZrO ₂ (JCPDS #49-1642). However, it is thought that the intensity and clarity of each diffraction peak decreased as the regularity of the crystal structure decreased due to the introduction of oxygen vacancies.

Measurement example 4-2. Microstructure Analysis by Transmission Electron Microscopy (TEM)

A photograph of the microstructure of black zirconia analyzed through a transmission electron microscope is shown in FIG. 20 . As a control, white zirconia particles (W-ZrO ₂ ) obtained by heat-treating the synthesized nanoparticles in an atmospheric atmosphere at 600 ^o C for 1 hour were used. All inserted SAED (selected area electron diffraction) patterns were confirmed to be ZrO ₂ , and it can be confirmed that a disorder layer in which a lattice is not clearly visible, which is characteristic of a typical black oxide, exists on the surface of black zirconia. On the other hand, in the case of white zirconia, which was further oxidized through heat treatment in the atmosphere, the lattice was clearly observed up to the surface of the particles. Therefore, it is judged that the color of the black zirconia synthesized by ultrasonic spray pyrolysis was also changed due to oxygen vacancies and defects, as in other known results.

Measurement example 4-3. Absorbance Measurement Using Ultraviolet-Visible Spectrophotometer

In order to investigate the change in optical properties due to the introduction of oxygen vacancies, absorbance was measured using an ultraviolet-visible spectrophotometer, and the results are shown in FIG. 21 . Unlike white ZrO ₂ , black ZrO ₂ showed clear absorption in the sub-visible region, and through this, sub-energy levels were formed within the band gap due to the introduction of oxygen vacancies, clearly confirming that absorption of visible and near-infrared rays is possible. can do.

Claims (10)

preparing a precursor solution by adding a precursor containing metal ions to a solvent;
forming the precursor solution in a droplet state using ultrasonic waves;
spraying the precursor solution in the droplet state into the inside of a furnace using a carrier gas; and
pyrolyzing and oxidizing the droplets inside the furnace;
The precursor is an alkoxide containing a metal ion,
The solvent is any one selected from the group comprising methanol, ethanol, DMSO (dimethyl sulfoxide), DMF (dimethyl formamide) and DMA (dimethyl acetamide),
In the step of preparing the precursor solution, a complex agent is further added to the solvent, and the complexing agent is any one selected from the group consisting of oxalic acid, oleic acid, citric acid and beta-diketone black oxide particles (Black Oxide particles) manufacturing method. delete The method of claim 1,
The metal ions combine with oxygen to form a metal oxide having a bandgap of 2.5 eV or more and 4.9 eV or less. delete The method of claim 1,
The carrier gas is at least one inert gas selected from the group consisting of nitrogen, helium and argon. Method for producing black oxide particles. The method of claim 1,
A method of producing black oxide particles, wherein the lower temperature inside the furnace is 200 °C, and the upper temperature is 600 to 900 °C. delete delete The method of claim 1,
The beta diketone is 2,4-pentanedione, 3-methyl-2,4-pentanedione, 3-isopropyl-2,4-pentanedione, 2,2-dimethyl-3,5-hexadione and 4 , 4,4-trifluoro-1-(2-naphthyl)-1,3-butane ion method for producing any one selected from the group consisting of black oxide particles (Black Oxide particles). 10. The method of claim 9,
A method for producing black oxide particles, wherein the molar ratio of the metal ion and the complexing agent added to the solvent is 1:1 to 1:20.

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