JP4135907B2 - Visible light active photocatalyst particles - Google Patents

Description

【００３３】
図１および図２に示したように、ＦＴ−ＩＲの測定結果は、実施例では、波数５８０ｃｍ^-1および３４０ｃｍ^-1において吸収ピークがあり、窒素のみがドープされた比較例とはそのピーク位置は異なることが認められた。
前記吸収ピークは、ドープされた炭素および窒素に基づくものであり、本発明に係る可視光活性型光触媒粒子において特徴的なものである。
【００３４】
また、上記表１に示した評価結果から、窒素および炭素のアニオンをドープした二酸化チタン光触媒粒子（実施例）は、可視光の照射により、ＩＰＡの酸化反応により生成したアセトンガスが検出され、可視光に対する光触媒活性を示すことが認められた。
また、この本発明に係る光触媒は、可視光照射によるアセトンの生成量から、窒素ドープ型の従来品（比較例）よりも優れた光触媒活性を示すことが認められた。
なお、光を照射しない暗条件においては、変化は観察されなかった。
【００３５】
【発明の効果】
以上のとおり、本発明に係る可視光活性型光触媒粒子は、従来の可視光活性型光触媒に比べて、可視光照射に対して高い光触媒活性を示すとともに、その光触媒活性は、安定性、持続性に優れたものである。
このため、本発明に係る可視光活性型光触媒粒子は、その光触媒活性を利用して、有害物質の分解、消臭、抗菌、殺菌、防汚、防曇等の作用を奏することにより、塗料、繊維製品、シックハウス解消剤、工業排水・排ガス等の無害化処理剤、医用材料等の様々な用途に好適に用いることができる。
【図面の簡単な説明】
【図１】実施例および比較例における光触媒粒子についての赤外吸収スペクトルを示したものである。
【図２】実施例および比較例における光触媒粒子についての赤外吸収スペクトルを示したものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to visible light active photocatalyst particles, and more particularly shows activity against visible light irradiation, and uses such photocatalytic activity to decompose, deodorize, antibacterial, disinfect, The present invention relates to visible light activated photocatalyst particles that can be suitably used for paints, textile products, sick house removal agents, detoxification treatment agents such as industrial wastewater and exhaust gas, and medical materials by exhibiting antifouling and antifogging effects. .
[0002]
[Prior art]
Many photocatalysts have semiconducting properties and have a band structure in which a conduction band and a valence band are separated by a band gap having an appropriate width.
When such a photocatalyst is irradiated with light having energy greater than its band gap, electrons in the valence band are excited to the conduction band, generating holes in the valence band and electrons in the conduction band. The holes and electrons generated here cause oxidation / reduction reactions, respectively.
Among them, particularly strong oxidizing power can be used to exert effects such as decomposition, deodorization, antibacterial, sterilization, and antifouling of harmful substances.
Moreover, since it becomes easy to adjust to water due to the super-hydrophilic effect, an anti-fogging effect can be exhibited.
Therefore, taking advantage of the effects as described above, application to paints, fibers, mirrors, medical materials and the like has been proposed, and some of them have already been put into practical use.
[0003]
By the way, in the titanium dioxide photocatalyst, there are mainly anatase type or rutile type crystals, and the band gap of titanium dioxide is 3.2 eV (corresponding to a wavelength of 387.5 nm) or 3.0 eV (wavelength of 413.3 nm). Therefore, as the excitation light, short-wavelength light having a wavelength of 387.5 nm or less or a wavelength of 413.3 nm or less, that is, light other than ultraviolet light was not used.
[0004]
However, in order to efficiently use sunlight, it is preferable that visible light having a wavelength of 400 to 700 nm, which occupies most of it, can be used.
There is also a need for photocatalysts that react not only outdoors but also in spaces where light energy is weak, such as indoor fluorescent lamps.
For this reason, recently, various developments of titanium dioxide exhibiting catalytic activity by irradiation with visible light have been studied for the purpose of efficiently using sunlight and artificial light.
[0005]
For example, Patent Document 1 discloses a method of obtaining visible light activity by forming an oxygen defect by subjecting anatase-type titanium dioxide to hydrogen plasma heat treatment.
Further, it is disclosed that visible light responsiveness can be obtained by doping nitrogen into the crystal lattice of titanium dioxide (see, for example, Patent Documents 2 to 4).
[0006]
In the above oxygen-deficient or nitrogen-doped titanium dioxide, it is considered that visible light activity is brought to the titanium dioxide photocatalyst by oxygen-deficient defects or Ti—N bonds.
[0007]
[Patent Document 1]
Japanese Patent No. 3252136 [Patent Document 2]
JP 2001-207082 A [Patent Document 3]
JP 2001-72419 A [Patent Document 4]
JP 2001-190953 A
[Problems to be solved by the invention]
However, the oxygen-deficient and nitrogen-doped photocatalysts described above have problems such as low photocatalytic activity under visible light irradiation and poor stability.
[0009]
The cause of such a technical problem is, for example, that a peak obtained by XPS (X-ray photoelectron spectroscopy) analysis based on a Ti—N bond of nitrogen-doped titanium dioxide disappears in a sample heat-treated in air. Therefore, it is presumed that oxygen deficiency defects or Ti—N bonds are unstable on the particle surface in contact with air.
[0010]
The present invention has been made to solve the above technical problem, and exhibits a high photocatalytic activity for visible light irradiation, and its photocatalytic activity is excellent in stability and sustainability. The object is to provide photocatalyst particles.
[0011]
[Means for solving the problems]
The visible light activated photocatalyst particles according to the present invention have a titanium dioxide component content of 80 wt% or more , a nitrogen anion of 700 wtppm or more and 10,000 wtppm or less, and a carbon of 1/30 or more and 1/3 or less of the nitrogen concentration. It is a particle doped with anions, and the particle size of the particle is 1 μm or less.
The visible light activated photocatalyst particles configured as described above exhibit superior photocatalytic activity compared to conventional visible light activated photocatalysts using oxygen-deficient or nitrogen-doped titanium dioxide, and the photocatalytic activity is It is excellent in stability and sustainability.
[0012]
Further, the visible light activated photocatalyst particles according to the present invention have a titanium dioxide component content of 80 wt% or more , and the spectra measured by Fourier transform infrared spectroscopy have wave numbers of 340 ± 10 cm ⁻¹ and 580 ± 50 cm ^{−. 1} has an absorption peak.
The absorption peak in the Fourier transform infrared absorption spectrum (FT-IR) measured by the KBr method is based on doping with nitrogen and carbon. Therefore, it has excellent photocatalytic activity under visible light irradiation. Is obtained.
[0013]
The visible light active photocatalyst particles preferably exhibit isopropanol oxidation activity under irradiation with visible light having a wavelength of 400 nm or more and 600 nm or less. By showing isopropanol (IPA) oxidation activity, it is confirmed that the visible light active photocatalyst particles according to the present invention exhibit excellent photocatalytic activity for visible light irradiation.
Therefore, the visible light activated photocatalyst particles according to the present invention exhibit the above-mentioned IPA oxidation activity, so that under visible light irradiation, aldehyde gases such as formaldehyde, which are said to cause sick house, and vehicle exhaust gas. It can exhibit excellent functions such as decomposition and removal of environmental pollutants such as NO _x and environmental hormones such as dioxin, which harm human bodies.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The visible light active photocatalyst particles according to the present invention are mainly composed of titanium dioxide, and doped with nitrogen anions of 700 wtppm to 10000 wtppm and carbon anions of 1/30 to 1/3 of the nitrogen concentration. Particles.
Thus, the photocatalyst particles doped with nitrogen and carbon exhibit better photocatalytic activity under irradiation of visible light than conventional oxygen-deficient or nitrogen-doped titanium dioxide photocatalysts. In addition, the photocatalytic activity is excellent in stability and sustainability, and is not easily deactivated even when it comes into contact with air.
In addition, the photocatalytic activity with respect to ultraviolet irradiation also shows the same or better performance as the conventional titanium dioxide photocatalyst.
[0015]
The main component in the visible light active photocatalyst particles is titanium dioxide, and the content thereof is preferably 80 wt% or more, and more preferably 95 wt% or more.
When the content of the titanium dioxide component is less than 80 wt%, sufficient photocatalytic activity cannot be obtained.
Therefore, in the range of less than 20 wt%, composite particles in which other inorganic compounds are mixed can be used as long as the photocatalytic activity of titanium dioxide by visible light irradiation is not impaired.
Examples of the inorganic compound mixed with titanium dioxide include silica, alumina, zirconia, magnesia, zinc oxide and the like.
[0016]
The titanium dioxide has three types of transformations of rutile type (tetragonal system), anatase type (tetragonal system), and brookite type (orthorhombic system), all of which have six oxygen atoms coordinated to the titanium atom. It has a structure where the edges of the distorted octahedron are shared. In the present invention, from the viewpoint of developing photocatalytic activity, a rutile type or anatase type is preferably used, and an anatase type is particularly preferable.
[0017]
In the present invention, visible light active photocatalyst particles are obtained by doping nitrogen and carbon anions into particles mainly composed of titanium dioxide.
The dopant concentration for nitrogen is preferably 700 wtppm or more and 10,000 wtppm or less, and more preferably 1500 wtppm or more and 5000 wtppm or less.
When the concentration of nitrogen is less than 700 wtppm, sufficient photocatalytic activity for visible light irradiation cannot be obtained, and in particular, the rise of initial activity is slow, and the rise gradient is small, depending on the intensity and application of visible light, etc. , It may be difficult to achieve its objectives sufficiently.
The carbon concentration is preferably 1/30 or more and 1/3 or less of the nitrogen concentration from the viewpoint of obtaining sufficient visible light activity.
[0018]
The doping method of the nitrogen and carbon anions is not particularly limited, and a method such as a thermal diffusion method, a laser doping method, a plasma doping method, or an ion implantation method that is usually used in this type of doping is adopted. It does not matter.
Specifically, it can be performed by a method of implanting accelerated ions from a nitrogen anion, a carbon anion source or the like into a titanium dioxide target using an ion implantation apparatus.
Further, solutions containing cyan (HCN), cyanic acid or isocyanic acid (HOCN), lower amines (RNH ₂ , R ₂ NH, R ₃ N), azo, diazo compounds, and the like, and ammonia (NH ₃ ) A method of hydrolyzing a solution-like titanium halide such as titanium chloride (TiCl ₄ ) in a solution containing the above can also be used. Alternatively, in a stream of inert gas such as nitrogen or argon containing cyan, cyanic acid or isocyanic acid, lower amine or the like and ammonia, or in a mixed gas stream of various hydrocarbons and ammonia, It can also be performed by a method of annealing (annealing) titanium.
[0019]
In addition, as described above, nitrogen and carbon topping may be performed by decomposing different compounds. In this case, carbon and nitrogen may be doped simultaneously or sequentially. The timing may be either at the time of particle formation or after the formation depending on the mode.
[0020]
The titanium dioxide (TiO ₂ ) stoichiometrically has 2 moles of oxygen ions bonded to 1 mole of titanium ions.
In the present invention, by doping titanium dioxide having such a stoichiometric chemical composition with nitrogen and carbon anions, oxygen ions bonded to 1 mol of titanium ions are expressed in stoichiometric numbers. It is preferable to have a structure deviating from a certain 2 mol, that is, having a non-stoichiometric number.
It is considered that when titanium dioxide has such a structure, it can exhibit high photocatalytic activity for visible light irradiation.
Specifically, the oxygen ions bonded to 1 mol of titanium ions are preferably 1.9 mol or more and less than 2.0 mol.
[0021]
Therefore, it is preferable that the doped nitrogen anion is bonded to Ti of titanium dioxide in a state where it is in the lattice of the titanium dioxide crystal, that is, in a bonded state of Ti—N—O. Alternatively, oxygen in the titanium dioxide crystal is replaced with nitrogen, and the doped nitrogen anion is in the position of oxygen in the titanium dioxide crystal, that is, in the bonded state of Ti—N—Ti, It is preferably bonded to Ti of titanium dioxide.
Of these bonded states, Ti-N-Ti is more preferable.
[0022]
The particle size of the visible light active photocatalyst particles is 1 μm or less, preferably 0.01 μm or more and 1 μm or less, from the viewpoint of sufficient photocatalytic activity and dispersibility in a solvent. In particular, the primary particles are preferably oblong with a major axis of 10 nm to 100 nm. The major axis of the particles is more preferably about 30 to 40 nm. Since the titanium dioxide photocatalyst particles in such a particle size range are fine particles, they can be suitably used for coating applications.
The primary particles preferably have a minor axis to major axis ratio of about 1: 2 to 4.
[0023]
Further, the visible light activated photocatalyst particles according to the present invention is a spectrum measured by Fourier transform infrared spectroscopy, and has an absorption peak at a wavenumber 340 ± 10 cm ^-1 and 580 ± 50 cm ^-1.
In the Fourier transform infrared absorption spectrum measured by KBr method (FT-IR), an absorption peak in the vicinity of a wave number of 340 cm ^-1 and 580 cm ^-1 is observed, which represents that the nitrogen and carbon are doped is there.
By this doped nitrogen and carbon, the Ti—N bond in the visible light active photocatalyst particle according to the present invention is stable, and it can be said that the photocatalytic effect under visible light irradiation is large.
[0024]
The visible light activated photocatalyst particles according to the present invention exhibit oxidation activity of formaldehyde, isopropanol (IPA), etc. under irradiation with visible light.
In particular, a sample in which 0.2 g of the photocatalyst particles are uniformly formed in a 10 cm square is placed in a gas bag having a volume of 1 liter, and the initial isopropanol gas concentration is 1500 ppm ± 150 ppm. After irradiation for 1 hour at an intensity of 0.5 mW / cm ² at a wavelength of 420 nm, the concentration of the produced acetone gas is preferably 500 ppm or more.
When IPA is oxidized, it produces acetone. Further, when the oxidation reaction proceeds, carbon dioxide and water are finally generated. Such an oxidation reaction of IPA is used as one of standard methods for evaluating photocatalytic activity.
[0025]
In general, photocatalytic activity evaluation test method IIb (gas bag B method) of photocatalyst product technical council is used as a method for evaluating photocatalytic activity of titanium dioxide or the like. It is something to evaluate.
On the other hand, in the present invention, in order to evaluate the photocatalytic activity for visible light irradiation, the above-described original evaluation test method is adopted. This makes it possible to clarify that the visible light active photocatalyst particles according to the present invention exhibit excellent photocatalytic activity with respect to visible light irradiation.
[0026]
Hereinafter, specific examples of the evaluation test method for the photocatalytic activity of the visible light active photocatalyst particles according to the present invention will be described.
First, 0.2 g of photocatalyst particles are dispersed in water, and this is applied to a 10 cm × 10 cm quartz glass plate and dried overnight at 50 ° C., which is used as a test sample.
Next, after putting this test sample in a 1 liter Tedlar bag, air containing isopropanol (IPA) vapor is circulated in the tedlar bag for 1 hour to saturate the gas adsorption of the photocatalyst particles.
The IPA gas concentration and the acetone gas concentration in the Tedlar bag are measured by gas chromatography, and a test gas is prepared so that the IPA gas concentration is 1500 ppm ± 150 ppm and the acetone gas concentration is 0 ppm.
The Tedlar bag was irradiated with light having a light intensity of 0.5 mW / cm ^{2 at} a wavelength of 420 nm for 1 hour using a fluorescent lamp equipped with a film that cuts ultraviolet rays having a wavelength of 410 nm or less. The concentration of acetone gas generated by oxidation is measured.
The visible light active photocatalyst particles according to the present invention preferably have an acetone gas concentration of 500 ppm or more at this time, thereby clearly indicating that the photocatalyst exhibits excellent visible light activity. .
[0027]
Promoting action of oxidation of IPA under irradiation of above-described visible light, i.e., IPA exhibit oxidation activity, aldehydes gas such as formaldehyde, which is said to cause sick house, the flue gas NO _X like cars It means having the ability to decompose and remove substances that harm the human body, such as environmental pollutants and environmental hormones such as dioxins, and it can be said that it has an excellent function as a visible light active photocatalyst.
[0028]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.
[Example]
Anatase-type titanium dioxide fine particles doped with 3000 wtppm nitrogen and 150 wtppm carbon (primary spherical particles having a minor axis of about 10 nm and a major axis of about 30 nm) were synthesized to produce photocatalyst particles.
[0029]
About the photocatalyst particle synthesize | combined in the above, the Fourier-transform infrared absorption spectrum (FT-IR) by KBr method was measured.
The apparatus used was a Bruker IFS113V type and a Hitachi 260-50 type Fourier transform infrared spectrophotometer, and the resolution was measured at 4 cm ⁻¹ .
The measurement sample was mixed with KBr in a mortar to form a powder and then pelletized with a tablet molding machine.
The measured spectrum is shown in FIG. 1 and FIG.
[0030]
Moreover, the photocatalytic activity with respect to visible light was evaluated about the said photocatalyst particle. The visible light activity evaluation test was performed by the following method.
First, 0.2 g of the photocatalyst particles synthesized as described above was dispersed in water, applied to a 10 cm × 10 cm quartz glass plate, and dried overnight at 50 ° C., which was used as a test sample.
Next, after putting this test sample in a 1 liter Tedlar bag, air containing isopropanol (IPA) vapor was circulated in the tedlar bag for 1 hour to saturate the gas adsorption of the photocatalyst particles, thereby preparing a test gas. .
When the gas concentrations of IPA and acetone of this test gas were measured by gas chromatography (Shimadzu GC-8A, column: Shimadzu packed column SBS-100), IPA was 1500 ppm and acetone was not detected (ND).
Then, the Tedlar bag was used with a fluorescent lamp (Toshiba FLR20S, W / M) equipped with a film (UV Guard UGP20WL10, manufactured by Fuji Photo Film Co., Ltd.) that shields ultraviolet rays having a wavelength of 410 nm or less, and the light intensity at a wavelength of 420 nm was 0. The light of 5 mW / cm ² was irradiated for 5 hours. Every 30 minutes from the start of irradiation, the IPA gas concentration and the concentration of acetone gas generated by the oxidation of IPA were measured.
The results are shown in Table 1.
[0031]
[Comparative example]
For conventional nitrogen-doped titanium dioxide fine particles (manufactured by Company A) (primary particle size of 5 to 10 nm), Fourier transform infrared absorption spectra (FT-IR) were measured in the same manner as in the above Examples.
The measured spectrum is shown in FIG. 1 and FIG.
In addition, the nitrogen-doped titanium dioxide fine particles were also evaluated for photocatalytic activity with respect to visible light in the same manner as in the above examples.
The results are shown in Table 1.
[0032]
[Table 1]

[0033]
As shown in FIGS. 1 and 2, the measurement results FT-IR, in the embodiment, there is an absorption peak at a wavenumber 580 cm ^-1 and 340 cm ^-1, the peak position from the comparative example in which only nitrogen is doped Were found to be different.
The absorption peak is based on doped carbon and nitrogen, and is characteristic in the visible light active photocatalyst particles according to the present invention.
[0034]
Further, from the evaluation results shown in Table 1 above, the titanium dioxide photocatalyst particles doped with nitrogen and carbon anions (Examples) detected acetone gas generated by the oxidation reaction of IPA by visible light irradiation, and visible. It was found to exhibit photocatalytic activity for light.
In addition, it was confirmed that the photocatalyst according to the present invention exhibited a photocatalytic activity superior to that of a conventional nitrogen-doped product (comparative example), based on the amount of acetone produced by visible light irradiation.
Note that no change was observed in the dark conditions where no light was irradiated.
[0035]
【The invention's effect】
As described above, the visible light active photocatalyst particles according to the present invention exhibit higher photocatalytic activity to visible light irradiation than conventional visible light active photocatalysts, and the photocatalytic activity is stable and durable. It is an excellent one.
For this reason, the visible light active photocatalyst particles according to the present invention use the photocatalytic activity to exhibit the action of decomposition, deodorization, antibacterial, sterilization, antifouling, antifogging, etc. of harmful substances, It can be suitably used for various applications such as textile products, sick house eliminating agents, detoxification treatment agents such as industrial wastewater and exhaust gas, and medical materials.
[Brief description of the drawings]
FIG. 1 shows infrared absorption spectra of photocatalyst particles in Examples and Comparative Examples.
FIG. 2 shows infrared absorption spectra of photocatalyst particles in Examples and Comparative Examples.

Claims (3)

The content of the titanium dioxide component is 80 wt% or more , and is a particle doped with an anion of nitrogen of 700 wtppm or more and 10000 wtppm or less and an anion of carbon of 1/30 or more and 1/3 or less of the nitrogen concentration, A visible light active photocatalyst particle having a particle size of 1 μm or less. Visible light activity characterized in that the content of titanium dioxide component is 80 wt% or more , and the spectrum measured by Fourier transform infrared spectroscopy has absorption peaks at wave numbers of 340 ± 10 cm ⁻¹ and 580 ± 50 cm ^−1. Type photocatalytic particles. The visible light active photocatalyst particles according to claim 1 or 2, which exhibit isopropanol oxidation activity under irradiation with visible light having a wavelength of 400 nm to 600 nm.

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