JP3678606B2 - Metal-modified apatite and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to apatite. More specifically, the present invention relates to a metal-modified apatite that can express a photocatalytic function in addition to the biocompatibility and adsorption characteristics exhibited by apatite, and is particularly useful in the field of electronics. The present invention also relates to a method for producing such metal-modified apatite.
[0002]
[Prior art]
Semiconductor materials such as titanium oxide are known to exhibit a photocatalytic function. That is, in such a semiconductor material, when it absorbs light energy having a wavelength corresponding to the band gap between the valence band and the conduction band, excitation causes the electrons in the valence band to move to the conduction band, and holes in the valence band. Will occur. In the conduction band, it is assumed that some material (for example, organic matter) is adsorbed on the surface of the semiconductor material, and the electrons transferred to it move to the organic matter on the surface of the semiconductor material to reduce it. In the valence band, The holes generated there take the electrons and oxidize the organic matter. In particular, in titanium oxide, since holes in the valence band have a very strong oxidizing power, there is an ability to finally decompose organic matter into water and carbon dioxide. Utilizing such a photocatalytic function (oxidative decomposition function) of titanium oxide, a titanium oxide film has been used as an antibacterial agent, bactericidal agent, deodorizing agent, environmental purification agent, and the like. However, since titanium oxide itself does not have the property of adsorbing any substance on its surface, there is a limit to the oxidative decomposition function that can be obtained.
[0003]
On the other hand, calcium hydroxyapatite Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ (hereinafter also referred to as CaHAP) is a main component of living hard tissues such as teeth and bones, and easily exchanges ions with various cations and anions. Therefore, it has high biocompatibility and adsorption properties. Therefore, calcium hydroxyapatite has been actively researched for a wide range of applications, including medical materials such as artificial tooth roots, artificial bones, and artificial organs, as well as chromatography adsorbents, chemical sensors, ion exchangers, and catalysts. It is coming. Calcium hydroxyapatite has an ability to specifically adsorb organic substances such as proteins.
[0004]
Recently, the electrical characteristics of semiconductor materials such as titanium oxide are not particularly intended for application in the field of electronics, but two types of materials as described above, namely, semiconductor materials such as titanium oxide and Development and research of products that can effectively bring out the characteristics of both by combining calcium phosphate compounds such as CaHAP have been carried out.
[0005]
For example, in JP-A-6-172113, at least one metal compound of Ti, Zr or Zn is provided on the surface of a hardly soluble phosphate (preferably hydroxyapatite) carrying at least silver ions as antibacterial ions. An antibacterial agent characterized by having a coating interposed therein is disclosed. Japanese Patent Laid-Open No. 10-33921 discloses amorphous calcium phosphate (preferably containing crystal water) in a base material (preferably paper, woven fabric, non-woven fabric or plastic foam) formed into a sheet shape. Tricalcium phosphate) and an optical semiconductor composition (preferably, titanium oxide, cadmium sulfide, etc.) dispersed or else the amorphous calcium phosphate and the optical semiconductor composition are bonded to such a substrate. The filter is characterized by being bonded via
[0006]
More recently, in Japanese Patent Application Laid-Open No. 10-244166, a base material such as activated carbon, activated alumina, silica gel, glass, foam ceramics, foam plastic is prepared, and a film made of titanium oxide is formed on the surface of the base material. Alternatively, an environmental purification material characterized in that a substrate made of titanium oxide particles is prepared, and the surface of the titanium oxide film or titanium oxide particles is coated with porous calcium phosphate (preferably hydroxyapatite, fluorinated apatite, etc.). Specifically, materials for removing bad odor, decomposing and removing harmful substances or dirt in the air, treating waste water, sterilizing water, and the like are disclosed. Such an environmental purification material is formed by immersing a substrate with a titanium oxide film or titanium oxide particles in a simulated body fluid whose composition, pH, etc. are adjusted so that a porous calcium phosphate film is easily formed. be able to. However, this environmental purification material has a structure in which the surface of the titanium oxide film or particle is coated with calcium phosphate, so that even though the coating is porous, it is satisfactory in the underlying titanium oxide. A photocatalytic function high enough to be obtained cannot be expressed. That is, since a sufficient amount of light does not reach the titanium oxide, the titanium oxide remains inactive, which may cause a decrease in oxidative decomposition efficiency. In addition, the organic matter adsorbed on the calcium phosphate coating on the titanium oxide is likely to remain on the surface of the coating without moving to the titanium oxide because of the strong adsorption power of the coating. It does not suffer from oxidative degradation by photocatalyst. As a result, since adsorption equilibrium is eventually reached, the adsorptive power of the calcium phosphate coating to organic matter and the like is significantly reduced.
[0007]
[Problems to be solved by the invention]
In view of the current state of the prior art as described above, the object of the present invention is to further develop the catalytic function exhibited by various apatites including calcium hydroxyapatite and to express a novel catalytic function, and At the same time, an object of the present invention is to provide a metal-modified apatite that is particularly useful in the field of electronics, which can maintain an excellent adsorption property for a specific adsorbed substance such as an organic substance derived from apatite over a long period of time.
[0008]
Another object of the present invention is to provide a method by which the excellent metal-modified apatite according to the present invention can be produced easily and with high reliability.
[0009]
[Means for Solving the Problems]
The present inventors have recently synthesized apatite such as calcium hydroxyapatite and a metal oxide having a photocatalytic action by a method different from the conventional technique, that is, metal ions in the apatite crystal ( For example, a compound at the atomic level consisting of ion exchange of a part of a calcium oxide (in the case of calcium hydroxyapatite) with a metal ion of a metal oxide having a photocatalytic action (for example, titanium ion in the case of titanium oxide). It was discovered that the above-mentioned problems can be solved by using technology.
[0010]
One aspect of the present invention is a metal-modified apatite formed by a coprecipitation method, wherein a metal oxide having a photocatalytic action is formed by ion exchange in an apatite crystal structure. It is in.
In another aspect of the present invention, the metal-modified apatite of the present invention is produced by adding a predetermined amount of metal ions of a metal oxide to constituent ions of the apatite. In the method for producing metal-modified apatite, it is prepared by coprecipitation in the presence of
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The metal-modified apatite and the method for producing the metal-modified apatite according to the present invention will be described as follows with respect to preferred embodiments thereof. It should be understood that the present invention is not limited to the following embodiments.
In the metal-modified apatite according to the present invention, the apatite constituting the main body can basically be represented by the following general formula.
[0012]
A _x (BO _y ) _z X
In the above formula, A represents various metal atoms such as Ca, Co, Ni, Cu, Al, La, Cr, Fe, and Mg, B represents an atom such as P and S, and X represents a hydroxyl group. (—OH), a halogen atom (for example, F, Cl) and the like. Examples of such apatite are apatite, hydroxyapatite, fluoroapatite, chloroapatite, tricalcium phosphate, calcium hydrogen phosphate and the like, although not limited to those listed below. The apatite that can be suitably used in the practice of the present invention is hydroxyapatite in which X in the above formula is a hydroxyl group, and more preferably, X in the above formula is a hydroxyl group and A is calcium (Ca). Calcium hydroxyapatite (CaHAP), that is, Ca ₁₀ (PO ₄ ) ₆ (OH) ₂ . Therefore, the following description of the apatite of the present invention will be described with reference to CaHAP.
[0013]
In the metal-modified apatite of the present invention, apatite and a metal oxide having a photocatalytic action are combined at the atomic level by a coprecipitation method, whereby a part of the metal ions in the apatite crystal is converted into a metal oxide having a photocatalytic action. It is characterized by ion exchange with metal ions. Thereby, as schematically shown in FIG. 1, the apatite region 3 which is an adsorption site a of a specific adsorbed substance (not shown) such as an organic substance and the metal which is an adsorbed substance decomposition site b depending on the photocatalytic action The oxide region 4 can coexist on the same crystal plane at an atomic level scale, and therefore, the adsorption and decomposition of the adsorbed substance can be performed simultaneously and uniformly and efficiently. Further, the ion exchange method based on the coprecipitation method employed in the present invention is a titanium oxide crystal exhibiting photocatalytic activity in the production of a titanium oxide film by the sol-gel method employed in the prior art referred to above. In contrast to the fact that a heat treatment at a high temperature of around 500 ° C. is necessary to achieve the structure, the heat treatment is unnecessary and the crystal structure of the metal oxide exhibiting photocatalytic activity is not formed. It is possible to realize excellent photocatalytic activity.
[0014]
Although FIG. 1 shows an example of the high-functional composite material 10 in which the metal-modified apatite 2 is formed as a thin film on the base material 1, the embodiment of the present invention is not limited to this. That is, as will be described below, the metal-modified apatite of the present invention may not have a base material, or it may be used temporarily only when a metal-modified apatite thin film, film, sheet or the like is produced. They may be removed after their production is complete.
[0015]
Further, in the metal-modified apatite of the present invention, it is easy to mix the apatite region and the metal oxide region at the atomic level on the same crystal plane, particularly from FIG. 2 showing the surface structure model of Ti ion-exchanged CaHAP. Will be able to understand.
According to the present invention, when a part of metal ions in an apatite crystal is ion-exchanged with a metal ion of a metal oxide having a photocatalytic action, the metal oxide having a photocatalytic action is known to be useful in this technical field. Various metal oxides can be used, but preferably, oxides of metals such as titanium, zirconium, iron, and tungsten can be used, and more preferably, oxides of titanium, that is, TiO _2. Can be used. Therefore, in the following description, the present invention will be described with particular reference to the use of TiO ₂ .
[0016]
According to the knowledge of the present inventors, when ion exchange is performed using a metal oxide, the metal ion content of the metal oxide can be widely changed depending on the desired result, Usually, the ratio to the metal ion in the apatite crystal is 15 mol% at the maximum, and even if it exceeds 15 mol%, a more remarkable effect cannot be expected. The content of metal ions is generally preferably in the range of 3 to 11 mol% in terms of the ratio of metal ions such as Ca ions, and most preferably around 10 mol% or less.
[0017]
The metal-modified apatite of the present invention can be provided in various shapes and dimensions depending on its use, production conditions, and other factors. Suitable shapes include, for example, particles, tablets, rods, plates, blocks, sheets, films, thin films and the like. In addition, when this apatite is a sheet, a film, a thin film, etc., those materials may be used alone, or in combination with a base material in order to constitute a highly functional composite structure, You may use it in the form coat | covered on the single side | surface or both surfaces of the base material. The substrate used here is not limited to those listed below, but for example, paper (including synthetic paper), woven or non-woven fabric, wood, glass, metal, ceramics, plastic, etc. Other examples include foils, films, sheets, and plates of various materials. These substrates may be porous as necessary. The metal-modified apatite of the present invention can be advantageously used particularly in the form of a thin film formed on the surface of the substrate.
[0018]
As described above, the metal-modified apatite of the present invention characterized in that the metal oxide is formed in the apatite crystal structure is preferably a predetermined amount of metal ions of the metal oxide, that is, its The starting material can be added in advance to the constituent ions of apatite, that is, the starting material, and synthesized by coprecipitation in the presence of both.
[0019]
The method for producing the metal-modified apatite according to the present invention can be easily understood from FIG. 3 showing the first half of the production process of Ti ion-exchanged CaHAP. Ie:
A predetermined amount of a starting material of CaHAP, that is, calcium nitrate, and a starting material of titanium oxide, that is, titanium sulfate, is mixed with the decarbonized pure water. The the predetermined amount when, preferably, an amount such case, the _{X metal = Ti / (Ti +} Ca) = 0.03~0.11 ( molar ratio) that it was the X _metal. Although this rule is shown for the case where the metal atom to be exchanged is Ti and the metal atom of the apatite (corresponding to A of the apatite previously shown in the general formula) is Ca, this is possible in the practice of the present invention. This rule is effective for other metal combinations. Further, the total concentration of the metal such as Ti and the metal such as Ca is preferably adjusted to be 0.1 mol. Next, phosphoric acid is added to the resulting mixture, and ammonia water is further added to adjust the pH. The pH at this time is preferably about 9. Subsequently, the resulting suspension is preferably aged at 100 ° C. for 6 hours and further filtered. When the precipitate separated by filtration is washed with pure water and further dried, the target Ti ion-exchanged CaHAP can be obtained. This may be used as it is, or may be used after it is applied to an appropriate substrate according to a coating method such as spin coating, a vapor deposition method such as sputtering, or other methods to form a thin film.
[0020]
The metal-modified apatite according to the present invention is particularly useful in the field of electronics. Specifically, the metal-modified apatite is used in a display device such as a PDP installed in a restaurant or public facility, and is maintenance-free due to a self-cleaning effect. be able to. Further, it can be used for peripheral devices of a computer, such as a keyboard, a mouse, a housing, and the like, to prevent adhesion of dirt such as hand dust. Furthermore, it can be used for optical components (mirrors, lenses, etc.) used inside touch panels, printers, etc., and light intensity attenuation caused by dirt adhering to the optical components can be suppressed.
[0021]
【Example】
The present invention will be described below with reference to the embodiments thereof. It should be understood that the present invention is not limited to the following examples.
Example 1
Preparation of Ti ion-exchanged CaHAP Prepare 1 liter (L) of pure water treated with decarbonation gas, and in a nitrogen atmosphere, 0.1 mol of calcium nitrate and different amounts of titanium sulfate solution with respect to the pure water. Mixed and stirred. In this case, the addition amount of titanium sulfate is such that X _metal = Ti / (Ti + Ca) is 0, 0.01, 0.03, 0.1, 0.5, in order to investigate the influence of the Ti amount in the obtained composite material. It changed so that it might be set to 0.8 (molar ratio). Further, the total concentration of Ti and Ca was 0.1 mol. Next, 0.06 mol of phosphoric acid was added to the obtained mixture, and 15 mol / L of ammonia water was further added to adjust the pH to 9.00. Subsequently, the resulting suspension was transferred to a Teflon ^TM bottle followed by aging for 6 hours at 100 ° C.. The suspension in which the precipitate was formed was filtered, and the fractionated precipitate was washed with 5 L of pure water and further dried in a dry oven at 70 ° C. for 12 hours. CaHAP without Ti ion exchange (hereinafter also referred to as CaHAP) and Ti ion exchanged CaHAP (hereinafter also referred to as Ti-CaHAP) were obtained.
Example 2
Characterization of CaHAP and Ti-CaHAP Using the CaHAP and Ti-CaHAP prepared in Example 1 as samples, TEM, XRD, XPS and FT-IR were characterized. The results will be described below.
(1) Observation of crystal form The form of each sample was observed using a transmission electron microscope (TEM) manufactured by JEOL. It is confirmed that the sample with Ti addition amount, that is, X _{metal up} to 0.1 is composed of uniform particles, and the crystal structure of HAP is maintained as the Ti addition amount increases, and the shape is elliptical. It was confirmed that the shape changed from needle to needle. Furthermore, when X _metal exceeds 0.1, it has been clarified that HAP rod-like giant particles and amorphous particles that are considered to be titanium phosphate hydrate are produced.
(2) Evaluation of crystallinity The crystallinity of each sample was further evaluated by XRD (X-ray diffraction). As a result, as shown in the graph of FIG. 4, it was confirmed that the crystallinity was lowered as the Ti addition amount increased.
(3) Surface analysis From the surface analysis of each sample by XPS (using a Perkin-Elmer photoelectron spectrometer) and the surface analysis by FT-IR (using a Perkin-Elmer FT-IR apparatus), Ti ions are Although it exists a lot in the inside of the particle, it became clear that X _metal = 0.1 exists as Ti—OH on the surface of some particles. FIG. 5 is a graph showing the FT-IR spectrum of each sample.
[0022]
From the evaluation results as described above, it has been clarified that Ti ion exchange into HAP can be effectively performed in samples up to the vicinity of X _metal = 0.1. Moreover, it is clear that this conclusion can be similarly applied not only to Ti—CaHAP particularly confirmed in this example, but also to other metal-modified apatites included in the scope of the present invention.
Example 3
Evaluation of photocatalytic activity CaHAP (X _metal = 0) and Ti-CaHAP (X _metal = 0.1) prepared in Example 1 were respectively pressed into tablets having the same specific surface area and used as samples. A sealed desiccator substituted with synthetic air was prepared, and a sample and acetaldehyde (CH ₃ CHO) vapor were introduced until the gas phase concentration reached 200 ppm. Next, ultraviolet light having a light quantity of 2.12 mW was irradiated for 24 hours from above the desiccator, and thereafter, ultraviolet light having the same light quantity was irradiated for 24 hours at intervals of 24 hours. The concentration of acetaldehyde gas and its decomposition carbon dioxide generated by the (CO ₂₎ in the desiccator was measured by gas chromatography, for samples consisting CaHAP (X _metal = 0) results plotted in FIG. 6, also For the sample made of Ti-CaHAP (X _metal = 0.1), the results plotted in FIG. 7 were obtained. In each figure, curve I and curve II indicate the concentrations of acetaldehyde gas and carbon dioxide gas, respectively, and ON and OFF indicate the timing of irradiation with ultraviolet light and irradiation stop, respectively.
[0023]
As understood from the results plotted in FIG. 6 and FIG. 7, in the case of the sample made of CaHAP (X _metal = 0) as a comparative example, an increase in the concentration of carbon dioxide gas due to irradiation with ultraviolet light is almost recognized. could not. Although the carbon dioxide concentration was slightly increased by the first irradiation with ultraviolet light, it was adsorbed in the sample from the beginning because there was no change even with the second irradiation with ultraviolet light. It is understood that it is derived from carbon dioxide. On the other hand, in the case of a sample made of Ti-CaHAP (X _metal = 0.1), which is an example of the present invention, there is a significant increase in the concentration of carbon dioxide gas every time ultraviolet light is irradiated, resulting in excellent photocatalytic activity. It became clear to have.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to further develop the catalytic function exhibited by various apatites including calcium hydroxyapatite to express a novel photocatalytic function, and at the same time, derived from apatite. In addition, it is possible to provide a metal-modified apatite capable of maintaining excellent specific adsorption characteristics for a specific adsorbed substance such as an organic substance over a long period of time. Further, according to the present invention, it is also possible to provide a method by which the excellent metal-modified apatite according to the present invention can be produced simply and with high reliability.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a preferred example of a highly functional composite material containing metal-modified apatite according to the present invention.
FIG. 2 is a schematic diagram showing a surface structure model of Ti ion exchanged CaHAP according to the present invention.
FIG. 3 is a flow sheet showing the first half of the production process of Ti ion-exchanged CaHAP according to the present invention.
FIG. 4 is an X-ray diffraction diagram of Ti ion exchanged CaHAP particles according to the present invention.
FIG. 5 is an FT-IR spectrum diagram of Ti ion-exchanged CaHAP particles according to the present invention.
FIG. 6 is a graph plotting gas chromatographic results for a sample made of CaHAP (X _metal = 0).
FIG. 7 is a graph plotting the results of gas chromatography for a sample made of Ti—CaHAP (X _metal = 0.1).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base material 2 ... Metal-modified apatite film | membrane 3 ... Apatite area | region 4 ... Metal oxide area | region 10 ... High functional composite material

Claims (4)

Apatite part of the calcium in the crystal structure has been replaced by titanium titanium oxide having a photocatalytic activity, substitution of calcium by the titanium, which was done by ion-exchange based on coprecipitation, the free of crystal structure of the titanium oxide, and metal-modified apatite having a photocatalytic function, characterized in that the calcium titanium and the apatite of the titanium oxide is incorporated at the atomic level. 2. The metal-modified apatite according to claim 1 , wherein the titanium ions are contained in an amount of 10 mol% or less with respect to calcium ions in the apatite crystals. The metal-modified apatite according to claim 1 or 2 , wherein the apatite is calcium hydroxyapatite. Some of the calcium apatite crystal structure has been replaced by titanium titanium oxide having a photocatalytic activity, does not include the crystal structure of the titanium oxide, and calcium of the apatite and titanium of the titanium oxide A method for producing a metal-modified apatite having a photocatalytic function in which is incorporated at an atomic level,
The replacement of calcium with titanium is performed by ion exchange based on a coprecipitation method, and the starting material of the titanium oxide is previously used as the starting material of the apatite, and the molar ratio of titanium ions to calcium ions is Ti / (Ti + Ca) = A method for producing a metal-modified apatite, characterized in that the metal-modified apatite is prepared by coprecipitation in the presence of both in an amount of 0.03 to 0.11 .

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