Photocatalyst particles, method for producing photocatalyst particles, and method for recovering photocatalyst particles

Abstract

The photocatalyst particles are polycrystalline particles comprising an oxide selected from the group consisting of MFeO3, M2Fe4O9, and M25FeO39 (wherein M is at least one type selected from the group consisting of Bi, Ga, Ni, Co, and Zn). The coefficient of variation in the aspect ratio of crystal grains constituting the polycrystalline particles is 0.35-1.0.

Description

Technical Field

[0001] This invention relates to a photocatalyst particle, a method for manufacturing the photocatalyst particle, and a method for recycling the photocatalyst particle. Background Technology

[0002] In recent years, the utilization and development of photocatalyst activity has been booming. When photocatalyst particles are irradiated with light, the oxidizing power of holes and the strong reducing power of electrons generated by photoexcitation can be used to decompose and purify harmful substances, deodorize malodorous gases, and sterilize bacteria, thus making them applicable to environmental purification.

[0003] Patent documents 1-4 disclose Bi-containing oxides as photocatalysts.

[0004] Existing technical documents

[0005] Patent documents

[0006] [Patent Document 1] CN104646001 Publication No.

[0007] [Patent Document 2] CN104941662 Publication No.

[0008] [Patent Document 3] CN106807400 Publication

[0009] [Patent Document 4] CN108114736 Publication No. Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The purpose of this invention is to provide a novel photocatalyst particle, its manufacturing method, and its recycling method.

[0012] Methods for solving problems

[0013] [1] A photocatalyst particle having the following properties: selected from MFeO3, M2Fe4O9 and M 25 FeO 39 Photocatalyst particles of polycrystalline oxides from the group consisting of (where M is at least one selected from the group consisting of Bi, Ga, Ni, Co, and Zn),

[0014] The coefficient of variation of the aspect ratio of the grains constituting the polycrystalline particles is 0.35~1.0.

[0015] [2] The photocatalyst particles according to [1], wherein the coefficient of variation of the particle size of the crystal is 0.35~1.0.

[0016] [3] The photocatalyst particles according to [1] or [2], wherein the arithmetic mean of the aspect ratio of the grains is 1.90 to 10.0.

[0017] [4] The photocatalyst particles according to any one of [1] to [3], wherein the particles further comprise at least one metal particle selected from the group consisting of Au, Pd, Ag and Pt supported on the surface of the polycrystalline particles.

[0018] [5] A method for manufacturing photocatalyst particles, comprising the following steps: heating a solution of a salt of at least one metal selected from the group consisting of Bi, Ga, Ni, Co and Zn and an Fe salt to obtain a solution selected from MFeO3, M2Fe4O9 and M 25 FeO 39 The polycrystalline particles of oxides in the group (where M is at least one selected from the group consisting of Bi, Ga, Ni, Co and Zn).

[0019] [6] The method according to [5] further comprises the step of: loading at least one metal particle selected from the group consisting of Au, Pd, Ag and Pt onto the surface of the obtained polycrystalline particles.

[0020] [7] A method for recovering photocatalyst particles, comprising the following steps: recovering the photocatalyst particles from a composition containing the photocatalyst particles described in [1] or [2] using a magnet.

[0021] Invention Effects

[0022] According to the present invention, a novel photocatalyst particle, its manufacturing method and its recycling method are provided. Attached Figure Description

[0023]

【 Figure 1 The image shows the XRD pattern of the particles (BiFeO3) obtained in Example 1.

[0024]

【 Figure 2 The image shows the XRD pattern of the particles (Bi2Fe4O9) obtained in Example 2.

[0025]

【 Figure 3 The image shows a SEM image of the particles (BiFeO3) obtained in Example 1.

[0026]

【 Figure 4 The image shows a SEM image of the particles (Bi2Fe4O9) obtained in Example 2.

[0027]

【 Figure 5 The image shows a SEM image of the particles (BiFeO3) obtained in Comparative Example 1.

[0028]

【 Figure 6 (a) shows the absorption spectra of the particles obtained in Examples 1 and 2. (b) shows the absorption spectrum of the particles obtained in Comparative Example 1.

[0029]

【 Figure 7 For Example 1 (BiFeO3), Example 2 (Bi2Fe4O9), their 1:1 mixtures, and Comparative Example 1 (BiFeO3), a primary reaction kinetic diagram is shown, which plots the methylene blue decolorization ability of the samples relative to the sampling time.

[0030]

【 Figure 8 (a) Ni particles as a reference, (b) BiFeO3 particles of Example 1, (c) Bi2Fe4O9 particles of Example 2, and (d) JH curves of BiFeO3 particles of Comparative Example 1.

[0031]

【 Figure 9 [Photograph of water droplets dropped onto the BiFeO3 particle layer in Example 1.]

[0032]

【 Figure 10 (a) and (b) are photographs of the Bi2Fe4O9 particle layer in Example 1 before and after water droplets were dropped onto it.

[0033]

【 Figure 11 (a) is a graph showing the aspect ratio of the polycrystalline particles of Example 1; (b) is a graph showing the grain size of the polycrystalline particles of Example 1.

[0034]

【 Figure 12 (a) is a graph showing the aspect ratio of the polycrystalline particles of Example 2; (b) is a graph showing the grain size of the polycrystalline particles of Example 2.

[0035]

【 Figure 13 (a) is a graph showing the aspect ratio of the polycrystalline particles of Comparative Example 1; (b) is a graph showing the grain size of the polycrystalline particles of Comparative Example 1.

[0036]

【 Figure 14 (a), (b), and (c) respectively show the SEM images and elemental analysis results of the BiFeO3 polycrystalline particles loaded with Au particles obtained in Example 3 when the Au loading is 0.6wt%, 2.0wt%, and 5.4wt%.

[0037]

【 Figure 15 The graph compares the decomposition activity of MB in BiFeO3 polycrystalline particles of Example 1 with Au loadings of 0.6 wt%, 2.0 wt%, and 5.4 wt% with that of BiFeO3 particles of Example 1 with an Au loading of 0.

[0038]

【 Figure 16 (a) is a photograph showing the state of BiFeO3 polycrystalline particles of Example 1 carrying Au particles being attracted by a magnet in air; (b) is a photograph showing the state of BiFeO3 polycrystalline particles of Example 1 carrying Au particles being attracted by a magnet in water. Detailed Implementation

[0039] (Photocatalyst particles)

[0040] One embodiment involves photocatalyst particles comprising MFeO3, M2Fe4O9, and M 25 FeO 39 The photocatalyst particles of the oxide polycrystalline particles in the group (where M is at least one selected from the group consisting of Bi, Ga, Ni, Co and Zn).

[0041] In other words, the polycrystalline particles are selected from MFeO3, M2Fe4O9 and M 25 FeO 39 Multiple grains of oxide are formed in the group. Grain boundaries exist between the grains. The presence of grain boundaries can be visually determined in SEM images.

[0042] M preferably contains Bi. The atomic ratio of Bi in M ​​is not particularly limited; it can be more than 50% or more than 70%.

[0043] (Crystal composition)

[0044] MFeO3, M2Fe4O9 or M in the grain 25 FeO 39 It can be doped with Ca or Dy.

[0045] (Aspect ratio of grains)

[0046] The aspect ratio r of the grains is defined as follows, based on the individual grains observed in the SEM images of polycrystalline particles.

[0047] r = Major axis of grain / Minor axis of grain

[0048] The major axis refers to the distance between two parallel straight lines that enclose a grain observed in an SEM image at its maximum. The minor axis refers to the distance between two parallel straight lines that enclose a grain observed in an SEM image at its minimum. The major and minor axis directions are not necessarily orthogonal.

[0049] The magnification of the SEM image should be set to observe approximately 100-200 grains. The aspect ratio, i.e., the number of grains, should be set to 100-500.

[0050] (The arithmetic mean of the aspect ratios of the grains)

[0051] The arithmetic mean of aspect ratio r av The definition is as follows.

[0052]

Number 1

[0053]

[0054] There is no particular limitation on the range of the arithmetic mean of the aspect ratio of the grains; it can be above 1.90, above 2.00, above 2.30, below 10.0, or below 9.00.

[0055] (Standard deviation of the aspect ratio of the grains)

[0056] The standard deviation of the aspect ratio r of the grain sd The definition is as follows.

[0057]

Number 2

[0058]

[0059] (Coefficient of variation of the aspect ratio of the grain)

[0060] The coefficient of variation of the aspect ratio of grains is defined as follows.

[0061]

Number 3

[0062]

[0063] In this embodiment, the coefficient of variation of the aspect ratio of the grains ranges from 0.35 to 1.0.

[0064] A coefficient of variation of grain aspect ratio of 0.35 to 1.0 indicates that the grain aspect ratio distribution is relatively wide. The coefficient of variation of grain aspect ratio can be above 0.40, 0.45, or 0.50. The coefficient of variation of grain aspect ratio can be below 0.95, 0.90, 0.85, or 0.80.

[0065] (Grain size, average grain size, standard deviation of grain size, and coefficient of variation of grain size)

[0066] The grain size refers to the arithmetic mean of the major and minor axes of the grain in the SEM image.

[0067] The average grain size refers to the arithmetic mean of the grain sizes of more than 100 grains.

[0068] The coefficient of variation of grain size is defined as the standard deviation of grain size divided by the average grain size.

[0069] The average grain size is not particularly limited; for example, it can be 1 to 1000 nm. The average grain size can be above 2 nm, above 5 nm, above 10 nm, above 20 nm, above 50 nm, above 100 nm, above 150 nm, above 200 nm, below 900 nm, below 800 nm, below 700 nm, below 600 nm, below 500 nm, or below 400 nm.

[0070] There is no particular limitation on the coefficient of variation of grain size, but for example, 0.35 to 1.0 is preferable. The coefficient of variation can also be above 0.30 or above 0.40.

[0071] (Grain shape)

[0072] The shape of the grains is not particularly limited. For example, they can be spherical, rod-shaped, flake-shaped, flower-shaped, amorphous, etc., or they can contain any combination of two or more of these shapes.

[0073] (Average particle size of polycrystalline particles)

[0074] Polycrystalline particles are selected from MFeO3, M2Fe4O9 and M 25 FeO 39 Multiple grains of oxides are formed in the group.

[0075] The particle size of the polycrystalline particles in the secondary particles (aggregates) is not particularly limited; for example, it can be above 1 μm or below 10 μm.

[0076] Furthermore, in this specification, the particle size of polycrystalline particles refers to the arithmetic mean of the major and minor axes of the polycrystalline particles in the SEM image. The average particle size of polycrystalline particles refers to the arithmetic mean of the particle sizes of more than 100 polycrystalline particles.

[0077] (Catalyst loading)

[0078] Photocatalyst particles can have metal particles supported on the surface of polycrystalline particles. The metal in the metal particles can be any one selected from the group consisting of Au, Pd, Ag, and Pt, or an alloy of any combination of these. The surface of the metal particles can be covered with oxides such as silicon dioxide. Such a structure is called a core-shell structure. Examples of core-shell structured metal particles include Au core-silica shell particles and Ag core-silica shell particles.

[0079] The average particle size of the metal particles is not limited and can be set to 1~10nm. The particle size of the metal particles refers to the arithmetic mean of the major and minor axes of the particle in the SEM image. The average particle size of the metal particles refers to the arithmetic mean of the particle sizes of more than 100 particles.

[0080] There is no particular limitation on the loading of metal particles as co-catalysts. For example, the loading of metal particles can be set to 0.2 to 10% of the total mass of polycrystalline particles and metal particles.

[0081] (Ferromagnetic)

[0082] The polycrystalline particles involved in this embodiment are ferromagnetic. Ferromagnetism refers to the presence of a hysteresis loop in the JH curve (magnetization-external magnetic field curve) obtained by VSM measurement or the like. The coercivity HcJ of the polycrystalline particles can also be 1 kOe or more.

[0083] (Ferroelectricity)

[0084] In addition to ferromagnetism, the polycrystalline particles involved in this embodiment also exhibit ferroelectricity. Ferroelectricity refers to the presence of a hysteresis loop in the electric field-polarization curve. The coercive electric field of the polycrystalline particles can also be 1 kV / mm or higher.

[0085] (bandgap)

[0086] The polycrystalline particles involved in this embodiment can have a band gap of 1.0 to 3.5 eV.

[0087] (Mechanism of action)

[0088] When ultrasonic waves are applied to the photocatalyst particles of this embodiment, or when they are irradiated with ultraviolet or visible light, excited-state species such as OH radicals are generated, thereby decomposing harmful substances such as organic compounds that are components of dirt. In particular, in this embodiment, it can be considered that, since the particles are polycrystalline particles of a specific metal oxide and the coefficient of variation of the aspect ratio of the grains is appropriately controlled, the band gap width is widened, thereby improving the activity as a photocatalyst.

[0089] Furthermore, since polycrystalline particles possess ferromagnetic and ferroelectric properties, they have the effect of suppressing the recombination of charge carriers and holes, which enhances the photocatalyst effect.

[0090] The photocatalyst involved in this embodiment can, for example, be fixed on the surface of a substrate such as metal, ceramic tile, enamel, cement, concrete, glass, fiber, wood, paper, or plastic, and supplied to the photocatalyst for reaction.

[0091] As a fixation method, traditional methods such as sintering the photocatalyst or using binders can be employed. Alternatively, the photocatalyst particles can be shaped into flat, corrugated, honeycomb, spherical, or curved forms after mixing with a binder as needed, and then supplied to the photocatalyst reaction.

[0092] (Method for manufacturing photocatalyst particles)

[0093] A manufacturing method relating to one embodiment of the above-mentioned photocatalyst particles will be described.

[0094] The method for manufacturing photocatalyst particles according to this embodiment includes the following steps: heating a solution of at least one metal salt α selected from the group consisting of Bi, Ga, Ni, Co, and Zn and Fe salt β to obtain a solution of MFeO3, M2Fe4O9, and M... 25 FeO 39 The polycrystalline particles of oxides in the group (where M is at least one selected from the group consisting of Bi, Ga, Ni, Co, and Zn). This process is sometimes referred to as the solvothermal method.

[0095] As a solvent, water, ethylene glycol, etc. can be used, and water is particularly suitable as a solvent, which is the so-called hydrothermal synthesis method.

[0096] The metal salts α and β are not particularly limited and can be nitrates, sulfates, bisulfates, acetates, chlorides, phosphates, hydrogen phosphates, bicarbonates, or carbonates, respectively. Preferably, both metal salts α and β are nitrates.

[0097] Selectively prepare MFeO3, M2Fe4O9 and M 25 FeO 39 In this case, simply set the atomic ratio of M to Fe to 1:1, 2:4, and 25:1 respectively.

[0098] In this process, the solution before heating is first prepared.

[0099] Specifically, metal salts α and β are thoroughly dissolved in a solvent such as water. From the viewpoint of ensuring thorough dissolution of metal salts α and β, the solvent used for dissolution is preferably adjusted to a pH of 3-4 by adding an acid such as nitric acid. For thorough dissolution, appropriate stirring is preferably performed.

[0100] From the viewpoint of appropriately controlling the coefficient of variation of the aspect ratio of the grains, after dissolving the metal salts α and β in the solvent, it is preferable to add an alkali such as KOH to the solution before heating as described later, so as to raise the pH of the solution to 12 or higher.

[0101] The solvent after the addition of a alkali, or before the addition of a alkali, may further contain compounds that produce acids or bases when heated in subsequent processes. An example of such compounds is urea, which, when heated, produces NH4 and carbon dioxide, further increasing the pH of the solution.

[0102] Next, the resulting solution is heated. The heating temperature is not particularly limited, but from the viewpoint of appropriately controlling the coefficient of variation of the grain aspect ratio, it is preferably 130°C or higher, and more preferably 250°C or lower. The temperature is preferably below the critical temperature of the solvent.

[0103] The preferred heating pressure is one that can maintain the solvent in a liquid state during heating. Typically, the solvent is heated to the above temperature in a closed container such as an autoclave, and the pressurized state corresponding to the temperature can be obtained by the saturated vapor pressure of the solvent.

[0104] There is no specific limit to the heating time; it can be set from 60 minutes to 48 hours.

[0105] After heating, the solvent containing the solid is cooled to room temperature, and solid-liquid separation is performed by centrifugation or other methods. The solid is then washed with ethanol, water, etc., and dried as needed to obtain a product selected from MFeO3, M2Fe4O9, and M... 25 FeO 39 The group contains oxide polycrystalline particles.

[0106] (Catalyst loading)

[0107] Metal particles or metal oxide particles that function as co-catalysts can be supported on the surface of the resulting polycrystalline particles as needed.

[0108] To support metal particles on the surface of polycrystalline particles, for example, the polycrystalline particles can be dispersed in a solvent containing a metal salt, and then a reducing agent can be added to the solution to cause the metal particles to precipitate on the surface of the polycrystalline particles. An example of a reducing agent is ethanol.

[0109] When metal oxide particles are supported on the surface of polycrystalline particles, for example, the polycrystalline particles are dispersed in a solvent containing organometallic compounds such as TEOS, and then the metal oxide particles are precipitated on the surface of the polycrystalline particles by adjusting the pH of the solution or by heating and drying.

[0110] (Methods for recovering photocatalyst particles)

[0111] The photocatalyst particle recovery method according to this embodiment includes the following steps: recovering the photocatalyst particles from the composition containing the above-mentioned photocatalyst particles using a magnet.

[0112] Because the photocatalyst particles involved in this embodiment are ferromagnetic, they can be attracted and separated by a magnet. Compared to photocatalyst particles such as titanium dioxide, they are easier to recover from waste materials of photocatalyst products.

[0113] Specifically, it can be used in the following situations: when separating polycrystalline particles from a composition containing polycrystalline particles and a solvent after polycrystalline particle synthesis; when separating polycrystalline particles supported by a cocatalyst from a composition containing cocatalyst-supported crystals and a solvent after supporting polycrystalline particles with a cocatalyst; and when photocatalyst particles are added to wastewater and the photocatalyst particles are recovered after decomposing environmental pollutants.

[0114]

Example

[0115] (Use of medicine)

[0116] Bismuth nitrate (Bi(NO3)3·5H2O, 98%), ferric nitrate (Fe(NO3)3·9H2O, 98%), methanol (98%), tetrachloroauro(III) acid trihydrate (HAuCl4·3H2O, 99.5%), nitric acid (HNO3, 65%) aqueous solution, and methylene blue (MB, ≥95%) were all obtained from Sigma-Aldrich. Potassium hydroxide (KOH, 85%) and urea (99.5%) were purchased from Kanto Chemical Co., Ltd. All reagents were used directly as is, and deionized water (Milipore System, 18.2Ω) was used as the solvent.

[0117] (Example 1) Preparation of BiFeO3 polycrystalline particles

[0118] For BiFeO3, 0.005 mol of Bi(NO3)3·5H2O, 0.005 mol of Fe(NO3)3·9H2O, 0.05 mol of urea, and 2 mL of HNO3 were mixed, and deionized water was added to bring the volume to 20 mL. The mixture was stirred continuously until all chemicals were completely dissolved. Next, the homogenized solution was mixed with 60 mL of 14 M KOH aqueous solution. The resulting mixture was transferred to an autoclave reactor with a polytetrafluoroethylene (PTFE) inner wall and heated at 180 °C for 24 hours. After cooling to room temperature, the product was centrifuged, washed with ethanol and deionized water, and finally dried in an oven at 80 °C to obtain the BiFeO3 particles of Example 1.

[0119] (Comparative Example 1) Preparation of BiFeO3 polycrystalline particles

[0120] Except that the reaction in the autoclave was changed to be heated at 125°C for 24 hours, BiFeO3 particles of Comparative Example 1 were obtained in the same manner as in Example 1.

[0121] (Example 2) Preparation of Bi2Fe4O9 polycrystalline particles

[0122] For Bi₂Fe₄O₉, 0.006 mol of Bi(NO₃)₃·5H₂O, 0.006 mol of Fe(NO₃)₃·9H₂O, 0.1 mol of urea, and 2 mL of HNO₃ were mixed, and deionized water was added to bring the volume to 20 mL. The mixture was stirred continuously until all chemicals were completely dissolved. Next, the homogenized solution was mixed with 60 mL of 10 M KOH aqueous solution. The resulting mixture was transferred to an autoclave reactor with a polytetrafluoroethylene (PTFE) inner wall and heated at 200 °C for 12 hours. After cooling to room temperature, the product was centrifuged, washed with ethanol and deionized water, and finally dried in an oven at 80 °C to obtain granules.

[0123] [XRD Measurement]

[0124] Figure 1 and 2 The XRD patterns obtained by XRD determination of particles (BiFeO3) obtained in Example 1 and (Bi2Fe4O9) obtained in Example 2 under the following conditions are shown.

[0125] Machine used: Rigaku Corporation MiniFlex

[0126] Method: 2θ-θ reflection method

[0127] Using X-rays: Cu-Kα rays

[0128] Scanning speed: 1.00° / minute

[0129] Sampling interval: 0.10°

[0130] Slit width: DS: (variable), SS: 4.2°, RS: 0.3mm

[0131] Depend on Figure 1 The XRD pattern shows that the particles synthesized in Example 1 are BiFeO3. The same determination shows that the particles synthesized in Comparative Example 1 are also BiFeO3.

[0132] Depend on Figure 2 The XRD pattern shows that the particles synthesized in Example 2 are Bi2Fe4O9.

[0133] [SEM Observation]

[0134] Figure 3 and Figure 4 SEM images of the particles obtained from Examples 1 and 2 are shown. Figure 5SEM images of the particles obtained from Comparative Example 1 are shown. It was confirmed that the sample synthesized in Example 1 consisted of polycrystalline particles with a secondary particle size of approximately 1-10 μm, and nanoparticles with a grain size of 1-1,000 nm. It was also confirmed that the sample synthesized in Example 2 consisted of polycrystalline particles with a secondary particle size of approximately 1-10 μm, and nanoparticles with a grain size of 1-1,000 nm. Finally, it was confirmed that the sample synthesized in Comparative Example 1 consisted of polycrystalline particles with a secondary particle size of approximately 1-10 μm, and particles with a grain size of 500-2000 nm.

[0135] [Absorption Spectroscopy Measurement]

[0136] Figure 6 (a) shows the optical absorption spectra of the particles obtained from Examples 1 and 2. The band gap of the sample synthesized in Example 1 was confirmed to be 2.0–2.5 eV. The band gaps of the sample synthesized in Example 2 were confirmed to be 1.53 eV and 2.05 eV. It was confirmed that the photocatalyst particles can absorb visible light.

[0137] Figure 6 (b) shows the absorption spectrum of the particles obtained from Comparative Example 1. The band gap of the sample synthesized in Comparative Example 1 was confirmed to be 2.0 eV to 2.2 eV.

[0138] (Confirmation of photocatalyst activity)

[0139] To evaluate the photocatalytic performance of methylene blue (MB) under visible light in photodecomposition, MB was used as the test contaminant. In a typical procedure, 30 mg of the sample was immersed in an aqueous solution of MB (20 mL, 20 μM) in a quartz tube. After reaching adsorption-desorption equilibrium in the dark for 120 minutes, a photocatalytic adsorption of 500 mW / cm² was applied. 2 A working xenon lamp (LCS-100, 94011A, Newport) was used to irradiate the reaction solution with white light to conduct a photodecomposition experiment of MB. At specified time intervals, 0.2 mL of the reaction solution was drawn and centrifuged to remove all solid particles dispersed in the solution. To determine the MB concentration in the reaction solution, the absorbance of the reaction solution at λ=664 nm was obtained using a UV-vis spectrophotometer (PD-3000UVe, Apel).

[0140] Figure 7The results are primary reaction kinetics obtained by plotting the methylene blue decolorization energy of the samples relative to the sampling time for Examples 1 (BiFeO3), Example 2 (Bi2Fe4O9), their 1:1 mixture, and Comparative Example 1 (BiFeO3). The results show that BiFeO3 of Example 1, Bi2Fe4O9 of Example 2, and the 1:1 weight ratio mixture of BiFeO3 of Example 1 and Bi2Fe4O9 of Example 2 all exhibit photocatalytic activity. On the other hand, the photocatalytic activity of BiFeO3 in Comparative Example 1 is relatively low.

[0141] (Confirmation of the magnetic properties of the particles)

[0142] The magnetic properties of the particles were evaluated using a vibrating sample magnetometer (VSM). Specifically, measurements were performed at 23°C using a TM-VSM1530-HGC-D manufactured by Tamagawa Corporation. The scan rate was 200 Oe / s, and the scan range was 1.5T. 0.07 g (BiFeO3 particles from Example 1) or 0.15 g (Bi2Fe4O9 particles from Example 2) of particles were placed in a φ5 mm epoxy sample holder for VSM evaluation.

[0143] Figure 8 (a) shows the JH curves of Ni particles as a reference, (b) shows the BiFeO3 particles of Example 1, (c) shows the Bi2Fe4O9 particles of Example 2, and (d) shows the BiFeO3 particles of Comparative Example 1. Similar to (a), hysteresis loops were also observed in (b), (c), and (d), confirming that they are ferromagnetic.

[0144] Water contact angle measurement method (confirmation of superhydrophilicity)

[0145] The water contact angles of BiFeO3 particles in Example 1 and Bi2Fe4O9 particles in Example 2 were measured using an automated contact angle measuring device (SImage AUTO 100, Excimer Co., Ltd.). First, approximately 20 mg of particles were placed on a glass substrate, and the particle layer was planarized while ensuring that a portion of the area was completely covered by the BiFeO3 or Bi2Fe4O9 particle layer. A 5 μL volume of water droplet was dispensed into the area completely covered by the BiFeO3 or Bi2Fe4O9 particle layer. A side view photograph of the droplet was then acquired. The acquired images were then analyzed, and the contact angles were quantified using software built into the contact angle measuring device.

[0146] Figure 9 This is a photograph taken after water droplets were dropped onto the BiFeO3 particle layer in Example 1.

[0147] Figure 10(a) and (b) are photographs of the Bi2Fe4O9 particle layer before and after water droplets were dropped onto it in Example 2, respectively.

[0148] The contact angle of the BiFeO3 particles in Example 1 was less than 10°, and the contact angle of the Bi2Fe4O9 particles in Example 2 was less than 10°.

[0149] (Determination of the aspect ratio and particle size of the grains that make up the polycrystalline particles)

[0150] Based on the SEM images of the polycrystalline particles, the aspect ratio and particle size of 100 grains were determined. According to the above definitions, the arithmetic mean of the aspect ratio, the coefficient of variation of the aspect ratio, the average particle size, and the coefficient of variation of the particle size were measured. The results for Example 1, Example 2, and Comparative Example 1 are shown in Table 1.

[0151] Table 1

[0152]

[0153] also, Figure 11 (a) is a graph showing the aspect ratio of the polycrystalline particles of Example 1. Figure 11 (b) is a graph showing the grain size histogram of the polycrystalline particles of Example 1.

[0154] Figure 12 (a) is a graph showing the aspect ratio of the polycrystalline particles of Example 2. Figure 12 (b) is a graph showing the grain size histogram of the polycrystalline particles of Example 2.

[0155] Figure 13 (a) is a graph showing the aspect ratio of the polycrystalline grains of Comparative Example 1. Figure 13 (b) is a graph showing the grain size histogram of the polycrystalline particles of Comparative Example 1.

[0156] (Example 3) Preparation of BiFeO3 polycrystalline particles of Example 1 supported on Au particles

[0157] Similar to Example 1, 60 mg of the obtained BiFeO3 particles were dispersed in a solution containing 30 mL of deionized water and 15 mL of ethanol, followed by the addition of 600 μL of 1 M NaOH solution. Ethanol was used as a reducing agent to promote Au deposition on BiFeO3. After heating the slurry to 50°C, 150–750 μL of 10 mM HAuCl4 solution was added to adjust the amount of Au modified on the BiFeO3. The solution was stored at 50°C for 3 hours. The BiFeO3 polycrystalline particles carrying Au particles were centrifuged, washed with deionized water and ethanol, and then dried in an oven at 80°C for later use. The Au content was evaluated using an energy-dispersive X-ray diffraction (EDX, EMAX EX-250, HORIBA) system mounted on a scanning electron microscope (SEM, S-4300 SE, Hitachi).

[0158] Figure 14 (a), (b), and (c) respectively show SEM images and elemental analysis results of BiFeO3 polycrystalline particles of Example 1 with Au loadings of 0.6 wt%, 2.0 wt%, and 5.4 wt%.

[0159] Figure 15 This is a graph comparing the decomposition activity of MB in BiFeO3 polycrystalline particles of Example 1 with Au loadings of 0.6 wt%, 2.0 wt%, and 5.4 wt% to that of BiFeO3 polycrystalline particles of Example 1 with an Au loading of 0. The steps are the same as described above. The photocatalyst activity of the Au-loaded particles is further improved.

[0160] (Recycling based on the magnetic force of photocatalyst particles)

[0161] (1) Approximately 20 mg of BiFeO3 polycrystalline particles from Example 1, loaded with Au particles, were placed in a φ10 mm glass container. When a neodymium magnet (model: TN22-21K-1P, size: 22 mm × 21 mm × 5 mm, adsorption force: 70.56 N, manufactured by Trusco) was brought close to the glass container, the particles inside the glass container were clearly adsorbed to the side of the inner wall. A photograph of this state is shown below. Figure 16 As shown in (a).

[0162] (2) Pure water was added to the glass container containing the BiFeO3 polycrystalline particles of Example 1 loaded with Au particles, bringing the water level to 20 mm. To ensure uniform distribution of the BiFeO3 polycrystalline particles of Example 1 loaded with Au particles in the solution, the mixture was placed in an ultrasonic homogenizer. Subsequently, a neodymium magnet was placed near the glass container. At the instant the neodymium magnet came into contact with the glass container, some of the BiFeO3 polycrystalline particles of Example 1 loaded with Au particles were immediately adsorbed onto the side of the inner wall. After maintaining the magnet configuration for 15 minutes, a large number of BiFeO3 polycrystalline particles of Example 1 loaded with Au particles were adsorbed onto the side of the inner wall near the neodymium magnet, and the solution became transparent. The photograph at this time is shown below. Figure 16 As shown in (b).

[0163] [Note]

[0164] The photocatalyst particles disclosed herein possess photocatalytic performance under visible light, with energy efficiency exceeding that of existing photocatalysts such as titanium dioxide. Therefore, they can contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs).

[0165] • Goal 9: "Build infrastructure for industrial and technological innovation".

Claims

1. A photocatalyst particle, characterized in that, It possesses components selected from MFeO3, M2Fe4O9, and M 25 FeO 39 The photocatalyst particles are polycrystalline particles of oxides in the group, wherein M is at least one selected from the group consisting of Bi, Ga, Ni, Co, and Zn. The coefficient of variation of the aspect ratio of the grains constituting the polycrystalline particles is 0.35~1.

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2. The photocatalyst particles according to claim 1, wherein, The coefficient of variation of the grain size is 0.35~1.

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3. The photocatalyst particles according to claim 1 or 2, wherein, The arithmetic mean of the aspect ratio of the grains is 1.90 to 10.

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4. The photocatalyst particles according to claim 1 or 2, wherein, It further comprises at least one metal particle selected from the group consisting of Au, Pd, Ag and Pt, supported on the surface of the polycrystalline particles.

5. A method for manufacturing photocatalyst particles, characterized in that, The process includes the following steps: heating a solution of a salt of at least one metal selected from the group consisting of Bi, Ga, Ni, Co, and Zn with an Fe salt to obtain a solution selected from MFeO3, M2Fe4O9, and M... 25 FeO 39 The polycrystalline particles of oxides in the group, wherein M is at least one selected from the group consisting of Bi, Ga, Ni, Co and Zn.

6. The method according to claim 5, wherein, The process further includes the following step: loading at least one metal particle selected from the group consisting of Au, Pd, Ag and Pt onto the surface of the obtained polycrystalline particles.

7. A method for recovering photocatalyst particles, characterized in that, The process includes the following step: recovering the photocatalyst particles from a composition containing the photocatalyst particles according to claim 1 or 2 using a magnet.

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