Improvement of photocatalytic activity of ferrite-based material under magnetic field

Abstract

The present invention addresses the problem of providing a method for improving photocatalytic performance by using a ferrite material having an easily available element constitution.　The problem is solved by using, as a photocatalyst, ferrite particles having a spinel-type crystal structure, a hexagonal crystal structure, or a garnet-type crystal structure in a magnetic field.

Description

Enhancement of photocatalytic activity of ferrite-based materials under magnetic fields

[0001] The present disclosure relates to the use of ferrite-based materials in the presence of a magnetic field to enhance photocatalytic activity.

[0002] Ferrite-based materials are composed mostly of iron and oxygen, making them inexpensive and readily available. Furthermore, because they are oxides, they are chemically stable and resistant to corrosion. Therefore, they are highly desirable materials for practical use. However, ferrite-based materials, with the exception of the Bi-based materials shown in Patent Documents 1 to 4, have low photocatalytic activity and have not been studied as photocatalysts.

[0003] CN104646001 publication CN104941662 publication CN106807400 publication CN108114736 publication

[0004] An object of the present disclosure is to provide a non-Bi-based ferrite material that exhibits photocatalytic activity.

[0005] The present inventors have found that the photocatalytic activity of a specific ferrite material can be improved by using the material under a magnetic field. This disclosure may include the following inventions: [1] Use of ferrite particles having a spinel-type crystal structure, a hexagonal-type crystal structure, or a garnet-type crystal structure in a magnetic field as a photocatalyst. [2] Use of the ferrite particles according to [1] as a photocatalyst, wherein the ferrite particles exhibit a saturation magnetization of 5 emu / g or more. [3] A magnetic field generating device including magnetic field generating means capable of emitting a magnetic field, wherein a photocatalyst of ferrite particles having a spinel-type crystal structure, a hexagonal-type crystal structure, or a garnet-type crystal structure is provided on the surface of the magnetic field generating means. [4] An information processing device that outputs at least photocatalyst information related to a photocatalyst, magnetic field-related information related to a magnetic field, and photocatalyst-magnetic field-related information indicating the relationship between the photocatalyst-related information and the magnetic field-related information. [5] A photocatalyst application method comprising the steps of providing a photocatalyst of ferrite particles having a spinel crystal structure, a hexagonal crystal structure, or a garnet crystal structure on the surface of a magnetic field generating means capable of emitting a magnetic field. [6] A photocatalyst application method comprising the steps of obtaining a light environment in an application target, obtaining a magnetic field environment in the application target, and providing a photocatalyst of ferrite particles having a spinel crystal structure, a hexagonal crystal structure, or a garnet crystal structure on the application target. [7] A photocatalyst manufacturing method including a quality control step, wherein the quality control step includes the steps of: placing the photocatalyst in a magnetic field environment, applying pollutants to the placed photocatalyst, and irradiating light onto the photocatalyst with the pollutants applied to evaluate the performance of the photocatalyst. [8] A photocatalyst recovery device including a magnetic field generating means.

[0006] According to the present disclosure, a ferrite-based material that can be used as a photocatalyst in a magnetic field can be provided.

[0007] The particles obtained in Example 1 (NiFe ２ O ４ ) obtained in Comparative Example 1. ３ ) obtained in Example 1. ２ O ４) obtained in Comparative Example 1 (BiFeO ３ ) shows SEM images of the particles obtained in (a) Example 1 and (b) Comparative Example 1. The optical absorption spectra of the particles obtained in (a) Example 1 and (b) Comparative Example 1 are shown. The photocatalytic activity of the particles obtained in (a) Example 1 and (b) Comparative Example 1 is evaluated with and without a magnetic field. (a) shows the reference Ni particles, and (b) shows the NiFe particles obtained in Example 1. ２ O ４ particles, (c) BiFeO obtained in Comparative Example 1 ３ This is the JH curve of the particle.

[0008] (Photocatalytic Particles) The ferrite material according to one embodiment is a ferrite particle having a spinel crystal structure, a hexagonal crystal structure, or a garnet crystal structure. The crystal structure of the ferrite particle is specifically MFe ２ O ４ , M'Fe １２ O １９ , and RFe ５ O １２ (wherein M includes at least one selected from the group consisting of Fe, Ni, and Co, M′ includes at least one selected from the group consisting of Ba, Sr, and Pb, and R includes a rare earth element).

[0009] The crystal structure of the ferrite particles may be single crystal or polycrystalline. In the case of polycrystalline, grain boundaries exist between the crystal particles. The presence of grain boundaries can be visually determined in SEM images.

[0010] (Shape of Crystal Particles) The shape of the crystal particles is not particularly limited and may be, for example, spherical, rod-like, flake-like, flower-like, or amorphous, and in the case of polycrystals, may include a combination of any two or more of these shapes.

[0011] (Crystal particle size, average particle size) The crystal particle size is the arithmetic mean of the major axis and minor axis of the crystal particle in an SEM image. The average crystal particle size is the arithmetic mean of the particle sizes of 100 or more crystal particles. The average particle size in the case of single crystals is not particularly limited, but may be, for example, 1 nm to 1000 nm. The average particle size in the case of polycrystals is not particularly limited, but may be, for example, 1 to 1000 nm. The particle size of crystal particles that are secondary particles (aggregates) is not particularly limited, and may be, for example, 1 μm or more and 10 μm or less.

[0012] (Supporting of promoter) The ferrite particles may have metal particles supported on the surface of the crystal particles. The metal in the metal particles may be any one selected from the group consisting of Au, Pd, Ag, and Pt, or an alloy of any combination thereof. The surface of the metal particles may be covered with an oxide such as silica. This structure is called a core-shell structure. Examples of metal particles with a core-shell structure are Au core-silica shell particles and Ag core-silica shell particles.

[0013] The average particle size of the metal particles is not limited, but can be 1 to 1000 nm. The particle size of the metal particles is the arithmetic mean of the major axis and minor axis of the particles in an SEM image. The average particle size of the metal particles is the arithmetic mean of the particle sizes of 100 or more particles.

[0014] There is no particular limitation on the amount of metal particles that serve as promoters, but for example, the amount of metal particles supported can be 0.2 to 10 mass % relative to the total mass of the ferrite particles and metal particles.

[0015] (Ferromagnetism of Ferrite Particles) The ferrite particles according to this embodiment are preferably ferromagnetic. Ferromagnetic means that a J-H curve (magnetization-external magnetic field curve) obtained by VSM measurement or the like shows a loop with hysteresis. The saturation magnetization of the polycrystalline particles may be 3 emu / g or more, 5 emu / g or more, or 10 emu / g or more.

[0016] (Band Gap) The ferrite particles according to this embodiment may have a band gap of 1.0 to 3.5 eV.

[0017] (Mechanism of Action) The ferrite particles of this embodiment are used in a magnetic field. "In a magnetic field" refers to a magnetic field environment stronger than the normal geomagnetic field (several tens of μT) in the atmosphere. For example, the magnetic field may be 1 mT or more, 10 mT or more, 100 mT or more, 0.5 T or more, or 1 T or more. When the ferrite particles are irradiated with ultraviolet light or visible light in a magnetic field, excited species such as OH radicals are generated, which can decompose harmful substances such as organic compounds that are components of dirt.

[0018] The ferrite particles according to this embodiment can be fixed to the surface of a substrate such as metal, tile, enamel, cement, concrete, glass, fiber, wood, paper, or plastic, and subjected to a photocatalytic reaction. Fixation can be achieved by conventional methods such as sintering the photocatalyst or using a binder. Furthermore, the photocatalyst particles can be mixed with a binder as needed, and molded into a flat, corrugated, honeycomb, spherical, curved, or other shape for use in a photocatalytic reaction.

[0019] (Method for Producing Ferrite Particles) A ​​method for producing the ferrite particles according to one embodiment will be described.

[0020] The ferrite particles according to this embodiment can be synthesized using a breakdown process in which large particles or lumps are mechanically crushed to obtain small particles, or a build-up process in which raw materials are obtained using physical or chemical reactions.

[0021] Equipment used in the breakdown process includes jet mills, ball mills, planetary mills, bead mills, etc. Synthesis methods such as the gas-phase method, liquid-phase method, and solid-phase method are used in the build-up process.

[0022] Gas phase methods include chemical vapor deposition (CVD) methods such as thermal CVD, plasma CVD, and flame methods, and physical vapor deposition (PVD), while liquid phase methods include methods of irradiating physical energy such as spray pyrolysis, laser decomposition, and ultrasonic methods, as well as sol-gel methods, liquid phase reduction methods, and solvothermal methods, and solid phase methods include solid phase pyrolysis, etc. Among these, the solvothermal method is preferred.

[0023] Solvents used in the solvothermal method include water and ethylene glycol, which are used at high temperatures, high pressures, and in supercritical conditions.

[0024] (Supporting of Promoter) If necessary, metal particles or metal oxide particles that function as a promoter can be supported on the surface of the obtained ferrite particles.

[0025] To support metal particles on the surface of ferrite particles, for example, the ferrite particles are dispersed in a solvent containing a metal salt, and then a reducing agent, such as ethanol, is added to the solution to precipitate the metal particles on the surface of the ferrite particles.

[0026] When metal oxide particles are supported on the surface of ferrite particles, for example, the ferrite particles are dispersed in a solvent in which an organometallic compound such as TEOS is dissolved, and then the metal oxide particles are precipitated on the surface of the ferrite particles by adjusting the pH of the solution or by heating and drying, etc.

[0027] The ferrite particles according to this embodiment have ferromagnetic properties, so they can be separated by being attracted to a magnet. Compared to photocatalyst particles such as titanium oxide, they are easier to recover from waste photocatalyst products.

[0028] The ferrite particles according to the present embodiment may be used together with a binder resin of a paint in a magnetic field, or may be provided in the form of a composite of the ferrite particles and a resin, or in the form of a composition in which the ferrite particles and a resin are dissolved or dispersed in a solvent.

[0029] (Magnetic Field Generator) Another embodiment is a magnetic field generator including a magnetic field generating means capable of generating a magnetic field, and a ferrite particle photocatalyst provided on the surface of the magnetic field generating means. The magnetic field generating means may be any means capable of generating a magnetic field, and examples thereof include, but are not limited to, electromagnets, permanent magnets, Helmholtz coils, etc. Examples of magnetic field generating devices including a magnetic field generating means include, for example, a scrap iron crane equipped with an electromagnet or the like at the tip of the crane, and a medical device that generates a magnetic field, such as an MRI device.

[0030] (Information Processing Device) Another embodiment is an information processing device that outputs at least photocatalyst information related to a photocatalyst, magnetic field-related information related to a magnetic field, and photocatalyst-magnetic field-related information indicating the relationship between the photocatalyst-related information and the magnetic field-related information. The photocatalyst information includes information on the structure and physical properties of the photocatalyst, such as, but not limited to, a crystal structure, light absorption characteristics, and photocatalytic activity. The magnetic field-related information includes, but is not limited to, a means for generating a magnetic field and the strength of the magnetic field. Examples of information processing devices that output photocatalyst-magnetic field-related information indicating the relationship between the photocatalyst-related information and the magnetic field-related information include a web server and a database server.

[0031] (Photocatalyst Application Method) Another embodiment is a photocatalyst application method that includes a step of providing a ferrite particle photocatalyst on the surface of a magnetic field generating means. Also, a photocatalyst application method that includes a step of obtaining a light environment in the application target, a step of obtaining a magnetic field environment in the application target, and a step of providing a ferrite particle photocatalyst on the application target is not particularly limited. Furthermore, the step of obtaining a light environment may involve exposing the target to sunlight (natural light) or illuminating it with lighting such as LED lighting.

[0032] (Method for manufacturing photocatalyst) Another embodiment is a method for manufacturing a photocatalyst that includes a quality control step. The quality control step includes the steps of placing the photocatalyst in a magnetic field environment, applying contaminants to the placed photocatalyst, and irradiating the photocatalyst with light to evaluate the performance of the photocatalyst. The quality control step can ensure the production of the photocatalyst, and may include performing a performance test on the photocatalyst.

[0033] (Photocatalyst recovery device) Another embodiment is a photocatalyst recovery device including a magnetic field generating means. An electromagnet or the like can be used as the magnetic field generating means to recover ferrite particle photocatalysts. The specific configuration of the recovery device is not particularly limited, and it is sufficient that it includes a magnetic field generating means.

[0034] (Chemicals used) Bismuth nitrate (Bi(NO ３ ) ３ ・5H ２ O, ≥ 98%), iron nitrate (Fe(NO ３ ) ３ ・9H ２ O, ≥ 98%), nickel sulfate (NiSO ４ ・6H ２ O, ≧98%), nitric acid (HNO ３ , 65%) and malachite green oxalate (MG, ≥90%) 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 as received, and deionized water (Milipore System, 18.2 Ω) was used as the solvent.

[0035] (Example 1) NiFe ２ O ４ Preparation of polycrystalline particles 0.005 mol NiSO ４ ・6H ２ O, 0.01 mol of Fe(NO ３ ) ３ ・9H ２ 0, 1 g urea, 2 mL HNO ３, and 18 mL of deionized water were mixed. Then, 30 mL of 14 M KOH aqueous solution was mixed. The resulting mixture was transferred to an autoclave reactor lined with polytetrafluoroethylene and heated at 180 °C for 24 hours. After cooling to room temperature, the resulting product was centrifuged, then washed with ethanol and deionized water, and finally dried in an oven at 80 °C. The sample was then placed in a muffle furnace and heated at 700 °C for 2 hours to obtain the particles of Example 1.

[0036] (Comparative Example 1) BiFeO ３ Preparation of polycrystalline particles 0.005 mol Bi(NO ３ ) ３ ・5H ２ O, 0.005 mol Fe(NO ３ ) ３ ・9H ２ 0, 0.05 mol urea, 2 mL HNO ３ The mixture was mixed and then deionized water was added to a final volume of 20 ml. Continuous stirring was performed until all chemicals were completely dissolved. The homogenized solution was then mixed with 60 mL of 14 M KOH aqueous solution. The resulting mixture was transferred to a polytetrafluoroethylene-lined autoclave reactor and heated at 180°C for 24 hours. After cooling to room temperature, the resulting product was centrifuged, washed with ethanol and deionized water, and finally dried in an oven at 80°C to obtain particles of Comparative Example 1.

[0037] [XRD Measurement] FIGS. 1 and 2 show the particles (NiFe ２ O ４ ) and the (BiFeO ３ The XRD chart obtained by XRD measurement of the sample was shown below under the following conditions: Instrument used: MiniFlex manufactured by Rigaku Corporation Method: 2θ-θ reflection method X-ray used: Cu-Kα ray Scan speed: 1.00° / min Sampling interval: 0.10° Slit width: DS: (variable), SS: 4.2°, RS: 0.3 mm

[0038] From the XRD chart of FIG. 1, it can be seen that the particles synthesized in Example 1 are NiFe. ２ O ４ It became clear that...

[0039] From the XRD chart of FIG. 2, the particles synthesized in Comparative Example 1 were BiFeO ３ It became clear that...

[0040] 3 and 4 show SEM photographs of the particles obtained in Example 1 and Comparative Example 1. It was confirmed that the sample synthesized in Example 1 was polycrystalline particles with a secondary particle diameter of about 1 to 10 μm, and that the crystal particles were nanoparticles with a diameter of 1 to 1,000 nm. It was confirmed that the sample synthesized in Comparative Example 1 was polycrystalline particles with a secondary particle diameter of about 1 to 10 μm, and that the crystal particles were nanoparticles with a diameter of 1 to 1,000 nm.

[0041] 5 shows the optical absorption spectra of the particles obtained in Example 1 and Comparative Example 1. The band gap of the sample synthesized in Example 1 was confirmed to be 1.8 to 2.7 V. The band gap of the sample synthesized in Comparative Example 1 was confirmed to be 2.0 to 2.5 V.

[0042] (Confirmation of photocatalytic activity) To evaluate the photocatalytic performance under visible light in the photodegradation of malachite green (MG), MG was used as a test pollutant. In a typical procedure, 30 mg of a sample was immersed in an aqueous MG solution (20 mL, 20 μM) in a quartz tube. After achieving adsorption-desorption equilibrium in the dark for 120 minutes, the reaction solution was exposed to 500 mW / cm ２ White light was irradiated from a xenon lamp (LCS-100, 94011A, Newport) operating at 1000 W, and photodecomposition experiments of MG were performed with and without the addition of a samarium magnet (saturation magnetization 0 T to 0 T). Specifically, a magnetic field environment was created by stirring the aqueous solution with a samarium magnet stirrer placed in a quartz tube immersed in the sample. At designated time intervals, 0.2 mL of the reaction solution was extracted 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 measured using a UV-vis spectrometer (PD-3000UVe, Apel).

[0043] FIG. 6 shows the results of Example 1 (NiFe ２ O ４ ) and Comparative Example 1 (BiFeO ３) shows a first-order reaction plot in which the malachite green decolorization ability of the sample was measured with and without a samarium magnet (magnetic field) and plotted against the sampling time.

[0044] (Confirmation of magnetic properties of particles) 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 Seisakusho Co., Ltd. The scanning speed was 200 Oe / s and the scanning range was 1.5 T. 0.10 g (NiFe ２ O ４ ), 0.07g (BiFeO ３ The particles were placed in a φ5 mm epoxy sample holder for VSM evaluation.

[0045] FIG. 7(a) shows the Ni particles as a reference, and (b) shows the NiFe particles of Example 1. ２ O ４ particles, (c) BiFeO of Comparative Example 1 ３９ The JH curves of the particles show that, as in (a), a hysteresis loop was observed in (b), confirming that the particles were ferromagnetic.

[0046] [Additional remarks] The photocatalytic particles disclosed herein can have excellent photocatalytic activity in a magnetic field, and can contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Build resilient infrastructure, promote inclusive and sustainable industrialization, foster innovation and infrastructural resilience."

Claims

1. Use of ferrite particles having a spinel, hexagonal or garnet crystal structure as a photocatalyst in a magnetic field.

2. Use of ferrite particles as a photocatalyst according to claim 1, wherein the ferrite particles exhibit a saturation magnetization of 5 emu / g or more.

3. A magnetic field generating device comprising a magnetic field generating means capable of generating a magnetic field, and a photocatalyst of ferrite particles having a spinel crystal structure, a hexagonal crystal structure, or a garnet crystal structure provided on the surface of the magnetic field generating means.

4. An information processing device that sends out at least photocatalyst information related to a photocatalyst, magnetic field-related information related to a magnetic field, and photocatalyst-magnetic field-related information indicating the relationship between the photocatalyst-related information and the magnetic field-related information.

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