JP2021169378A - Tubular iron oxide particle, production method thereof, and antibacterial red pigment - Google Patents

Abstract

To provide a production method of a tubular iron oxide particle which gives a tubular structure at a substantial rate with a simple process, and to provide the tubular iron oxide particle thus given, and to provide an antibacterial red pigment, etc. having an excellent color tone and a high antibacterial property.SOLUTION: A production method of a tubular iron oxide particle comprises: an organic sheath production step of cultivating an iron-oxidizing bacterium in a culture solution in a vessel of a cultivation apparatus to produce an organic sheath on an outer periphery part of the bacterium; an iron-containing organic sheath production step of adding at least a trivalent iron compound to the culture solution having the organic sheath produced therein to deposit an iron component to thereby produce an iron-containing organic sheath containing the iron component; a separation step of separating the iron-containing organic sheath from the culture solution; and a heat treatment step of heat-treating the iron-containing organic sheath to produce at least an iron oxide.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing tubular iron oxide particles using iron-oxidizing bacteria, tubular iron oxide particles obtained by the production method, and an antibacterial red pigment containing the same.

As tubular iron oxide particles having a shape different from that of powdered red iron oxide, for example, tubular red iron oxide disclosed in Non-Patent Document 1 is known. This tubular red iron oxide produces tubular iron oxide (constituent element ratio: Fe: Si: P = 73: 22: 5) produced by naturally occurring microorganisms (iron-oxidizing bacterium Leptothrix ochracea). It was obtained by heating at about 800 ° C. in air, and not only exhibits excellent color tone, but also has excellent heat resistance. It is considered that the excellent color tone of this tubular red iron oxide is due to (i) Si solid solution effect, (ii) tubular morphology and the like.

The tubular red iron oxide thus obtained has an almost constant constituent element ratio and the solid dissolved amount of Si or P element does not change. Therefore, the color tone also depends only on the heating temperature, and the heating temperature is constant. , The color does not change.

Therefore, Patent Document 1 describes a step of forming an organic sheath by culturing iron-oxidizing bacteria for the purpose of adjusting the color tone of tubular red iron oxide and imparting catalytic activity, and the obtained organic sheath. Is suspended in an aqueous solution containing iron and other elements to produce iron oxide containing the element, and a method for producing tubular iron oxide particles containing the iron oxide particles has been proposed. Although various iron compounds are exemplified as the iron component to be added in Patent Document 1, only the case where iron powder is used is specifically described as an example.

On the other hand, as a technique utilizing the antibacterial activity caused by a metal element, a method of supporting silver ions on zeolite, silica gel or the like and using them is known (Non-Patent Document 2). In addition, some heavy metals such as Hg and Cd show high antibacterial activity (Non-Patent Document 3), but their use is extremely limited due to their safety problems.

Japanese Unexamined Patent Publication No. 2018-70441

Days and Pigments, 95 (3), 639-643 (2012) Critical Reviews in Microbiology 39, 1-11 (2012) Applied Microbiology and Biotechnology 51, 730-750 (1999)

However, in the conventional method for producing tubular iron oxide particles as described in Patent Document 1, it has been difficult to expand the production scale due to a relatively long process and complicated work. That is, it was necessary to recover the organic sheath formed by the iron oxide bacteria, wash with water, resuspend, and recover and wash the elemental solid-soluble iron oxide sheath in different containers. In addition, although the iron powder used for depositing iron hydroxide on the organic sheath is suitable for the gradual and continuous supply of iron components, the iron deposition process is prolonged and the residual iron powder is removed. The process was essential.

Further, according to the study by the present inventors, when the iron component is deposited in the culture solution, depending on the iron or iron compound used, a tube-shaped structure may not be obtained, and a rod-shaped structure or a tube-shaped structure may be obtained. There is also a problem that it becomes a structure in which a deformed iron component is attached to the outside of the structure, and it becomes difficult to obtain a desired shape and performance.

Therefore, an object of the present invention is, as one aspect, a method for producing tubular iron oxide particles in which a tubular structure can be obtained in a sufficient ratio, and a tubular shape obtained by the production method, although it is a simple process. The purpose is to provide iron oxide particles.

As another aspect, an object of the present invention is a method for producing tubular iron oxide particles having excellent color tone and high antibacterial properties, and tubular iron oxide particles obtained by the production method, and an antibacterial red color containing the same. To provide pigments.

As a result of various studies on iron compounds having different valences to be added when the iron component is deposited in the culture solution, the present inventors obtained a tubular structure in a sufficient ratio from the trivalent iron compound. , It was found that the process could be simplified by this, and the present invention was completed.

That is, the present invention includes the following forms.

(1) A method for producing tubular iron oxide particles.
An organic sheath formation step in which iron-oxidizing bacteria are cultured in a culture solution in a container of a culture device to form an organic sheath on the outer periphery of the bacteria.
An iron-containing organic sheath forming step of producing an iron-containing organic sheath containing the iron component by adding at least a trivalent iron compound to the culture solution produced by the organic sheath and depositing an iron component.
A separation step of separating the iron-containing organic sheath from the culture solution, and
A heat treatment step of heat-treating the iron-containing organic sheath to produce at least iron oxide,
A method for producing tubular iron oxide particles containing.

(2) The trivalent iron compound is one or more selected from iron (III) sulfate, iron (III) chloride, iron (III) nitrate, iron (III) acetate, and iron (III) citrate. The method for producing tubular iron oxide particles according to (1).

(3) The method for producing tubular iron oxide particles according to (1) or (2), wherein an oxygen-containing gas is supplied into the container of the culture apparatus by bubbling at least in the organic sheath forming step.

(4) The above-mentioned by adding another metal element compound to the culture solution in the iron-containing organic sheath forming step or to the culture solution generated in the iron-containing organic sheath forming step to deposit other metal element components. The method for producing tubular iron oxide particles according to any one of (1) to (3), which produces an iron-containing organic sheath containing an iron component and the other metal element component.

(5) The method for producing tubular iron oxide particles according to (4), wherein the pH is adjusted with a pH adjuster after adding the other metal element compound to the culture solution produced by the iron-containing organic sheath forming step.

(6) The method for producing tubular iron oxide particles according to (5), wherein the other metal element is indium and / or molybdenum.

(7) Tube-shaped iron oxide particles containing trivalent iron oxide and oxides of indium and / or molybdenum.

(8) The tubular iron oxide particle according to (7), which contains a crystal phase of _{α-Fe 2} O ₃ and In ₂ (MoO ₄ ) _3.

(9) An antibacterial red pigment containing the tubular iron oxide particles according to (6) or (7).

According to one aspect of the present invention, a method for producing tubular iron oxide particles in which a tubular structure can be obtained in a sufficient proportion, and tube-shaped iron oxide particles obtained by the production method, although it is a simple process. Can be provided.

According to another aspect of the present invention, a method for producing tubular iron oxide particles having excellent color tone and high antibacterial properties, and the tubular iron oxide particles obtained by the production method, and an antibacterial red pigment containing the same. Can be provided.

It is a photograph showing the state of each step and the corresponding culture solution in Examples 1 to 3, (a) is a flowchart showing each step, (b) is a culture solution after the main culture, and (c) is iron. The culture solution 24 hours after the addition of the source and (d) show the culture solution 24 hours after the addition of the metal salt. The fine morphology and elemental composition of Mo / In-containing BIOX after heating (heating material) are shown, (a) shows an SEM photograph, the inset is an enlarged photograph of the sheath tip, and (b) shows the EDX spectrum, in parentheses. The numerical value of indicates the elemental composition ratio. It is a photograph showing the element distribution in the Mo / In-containing BIOX heating material, (a) is a HAADF image, (b) is an Fe distribution image, (c) is an In distribution image, and (d) is a synthetic distribution image of Fe and In. Is shown. It is a figure which shows the XRD pattern of the Mo / In containing BIOX heating material. It shows the antibacterial activity of the Mo / In-containing BIOX heating material, (a) is a photograph showing the antifilamentous activity against the indicator (Fusarium oxysporum Odoriko strain), and (b) is the antibacterial against Escherichia coli HB101 strain. It is a graph which shows the activity. Here, Mo22 / In16-800: Mo22% / In16% containing BIOX 800 ° C. heating material, Mo22 / In16-600: Mo22% / In16% containing BIOX 600 ° C. heating material, Mo24-600: Mo24% containing BIOX 600 ° C. ℃ heating material, In16-800: 800 ℃ heating material of BIOX containing 16% In, cBIOX-800: 800 ℃ heating material of BIOX containing no other element. It is a graph which shows the photocatalytic activity of the Mo / In-containing BIOX heating material. The plots and vertical bars on the figure indicate the mean (n = 6) and SD values. The abbreviation of the sample is the same as in FIG. 5 (however, TiO ₂ NP: titanium oxide nanoparticles (JRC-TIO-15)). It is a figure which shows the color tone (CIE Lab color chart) of the Mo / In-containing BIOX heating material, (a) shows the chromaticity, and (b) shows the lightness. The abbreviation of the sample is the same as in FIG. 5 (however, MC-55: high-colored red iron oxide (manufactured by Morishita Benji Kogyo)). It is an SEM image photograph which shows the fine form of the product obtained in Experimental Example 1, (a) shows the rod-shaped sheath (I) to which iron oxide particles are attached, and (b) shows the rod-shaped sheath (II). , (C) show a hollow tubular sheath (III), and (d) shows an incomplete hollow sheath (IV) to which iron oxide particles are attached. Here, the inside of parentheses is a classification type, and the scale bar is 2 μm.

Hereinafter, some aspects of the present invention will be described in detail.

As used herein, the term "comprise" also includes the meaning of "essentially consist of" and the meaning of "consist of".

In the present specification, iron oxide produced by iron-oxidizing bacteria may be referred to as "BIOX (Biogenous Iron oxides)", and iron oxide produced by iron-oxidizing bacteria in a natural environment is referred to as "natural BIOX". , Iron oxide produced by culturing isolated iron-oxidizing bacteria is sometimes referred to as "culture system BIOX".

As used herein, the terms "sheath" and "tube" mean the same shape, meaning a round, elongated hollow shape. As used herein, the term "rod-shaped" means a shape that is round, elongated, and not hollow.

<Manufacturing method of tubular iron oxide particles>
One aspect of the present invention relates to a method for producing tubular iron oxide particles. In this production method, an organic sheath forming step for producing an organic sheath, an iron-containing organic sheath forming step for producing an iron-containing organic sheath containing an iron component, a separation step for separating the organic sheath from the culture solution, and iron oxide are produced. It includes a heat treatment step.

As will be described in detail later, the tubular iron oxide particles are not limited to those containing only iron oxide as a metal oxide component, and include composite iron oxide particles containing oxides of other metal elements.

<Organic sheath formation process>
The organic pod formation step is a step of culturing iron-oxidizing bacteria in a culture solution in a container of a culturing device to generate an organic pod on the outer periphery of the bacterium. Prior to the organic sheath forming step, a pre-culture for increasing the number of bacteria to a certain level or more may be carried out, and in that case, this organic sheath forming step is carried out as the main culture.

The pre-culture is different from the main culture in that it can be carried out on a small scale without using a culture device, and either solid culture or liquid culture may be used, and liquid culture is preferable. The liquid culture in the preculture can be performed by shaking culture, stirring culture, aeration culture and the like.

(Iron oxide bacteria)
The iron-oxidizing bacterium is not particularly limited as long as it produces an organic sheath. Examples of iron-oxidizing bacteria that produce such organic sheaths include Leptothrix sp. And Sphaerotilus sp. Among them, iron-oxidizing bacteria isolated so as to be artificially cultivated can be preferably used. Specific examples of the Leptothrix bacterium include Leptothrix corodini SP-6 strain and Leptothrix corodini OUMS1 strain. Leptoslix corodini OUMS1 strain was released on December 25, 2009 by the National Institute of Technology and Evaluation Patent Microorganisms Depositary Center (2-5-8 Kazusakamatari, Kisarazu City, Chiba Prefecture, Japan (postal code 292-0818)). ), Deposited as accession number NITE P-860. In addition, this strain has now been transferred to an international deposit, and its accession number is NITEBP-860.

(Organic pod)
"Organic sheath" means a sheath-like structure formed outside the cells by iron-oxidizing bacteria belonging to β-proteobacteria such as Leptothrix bacteria and Sphaerotilus bacteria, and this structure is a chain-like bacterium. It is a polymer polymer in which fine fibers composed of heteropolysaccharides and proteins secreted on the outer periphery of the body are densely woven (see Documents 1 to 3 below). In addition, in this specification, the term "organic sheath" may refer to one having iron-oxidizing bacteria inside.
Reference 1: Emerson, D., and Ghiorse, WC (1993) Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6. J. Bacteriol. 175: 7808-7818.
Reference 2: Takeda, M., Makita, H., Ohno, K., Nakahara, Y., and Koizumi, J. (2005) Structural analysis of the sheath of a sheathed bacterium, Leptothrix cholodnii. Int'l. J. Biol. Macromole 37: 92-98.
Reference 3: Kunoh, T., Kunoh, H., and Takada, J. (2015) Perspectives on the Biogenesis of Iron Oxide Complexes Produced by Leptothrix, an Iron-oxidizing Bacterium and Promising Industrial Applications for their Functions. J. Microb. Biochem. Technol. 7: 419-426.
The organic sheath may contain silicon (Si), phosphorus (P), sulfur (S), carbon (C), nitrogen (N), hydrogen (H) and the like derived from the culture medium.

The external shape of the obtained organic sheath is a rod shape having iron-oxidizing bacteria inside, and each shape preferably has an outer diameter of 0.6 to 2 μm and a length of 10 to 1000 μm, and has an outer diameter of 0.8 to 1. It is more preferably 5 μm and 20 to 200 μm in length.

(Culture device)
The culture apparatus is provided with a container (jar, tank, etc.) for storing and culturing the culture solution, and the capacity of the container can be used from 1 to 5 L scale to 100 to 200 L scale.

The culture device preferably includes a stirrer, a temperature control device for the culture solution, a pH control device for the culture solution, an oxygen-containing gas supply mechanism, and a water supply / drainage device. As such a culturing device, a commercially available jar fermenter or a fully automatic microbial culturing device can be used. By using such a culture device, a larger amount of tubular iron oxide particles can be produced as compared with the flask scale.

The oxygen-containing gas supply mechanism of the culture apparatus preferably allows bubbling in the culture solution in the container, and by performing such bubbling, a larger amount of tubular iron oxide particles can be produced.

The dissolved oxygen concentration at the time of bubbling can be appropriately set according to the state of culture.

(Culture conditions)
The culture conditions for the iron-oxidizing bacteria are not particularly limited as long as the organic sheath can be produced, and the type of medium, the culture temperature, the culture time, and the like can be appropriately set according to the type of the iron-oxidizing bacteria and the like. This point is the same for the pre-culture, and the type of medium, the culture temperature, the culture time, and the like can be appropriately set according to the type of iron-oxidizing bacteria and the like.

For example, the culture temperature may be usually 15 to 30 ° C, preferably 20 to 25 ° C. The culturing time can be usually about 1 to 4 days, preferably about 2 to 3 days. Examples of the medium include the SGP medium used in the examples.

<Iron-containing organic sheath formation process>
The iron-containing organic sheath forming step is a step of producing an iron-containing organic sheath containing the iron component by adding at least a trivalent iron compound to the culture solution produced by the organic sheath and depositing an iron component. .. As described above, by using the trivalent iron compound, a tubular structure can be obtained in a sufficient ratio when the iron component is deposited on the organic sheath in the culture solution, whereby the culture solution can be used as it is. Therefore, the process up to the formation of the iron-containing organic sheath can be greatly simplified. Further, since a series of steps can be performed in one container, it is also suitable for mass production.

(Trivalent iron compound)
As the trivalent iron compound, one or more selected from iron (III) sulfate, iron (III) chloride, iron (III) nitrate, iron (III) acetate, iron (III) citrate and the like is preferable, and among them, iron (III) sulfate is preferable. , Iron (III) sulfate is more preferable. It is preferable to add these iron compounds as an aqueous solution. The aqueous solution may be added at one time or at intervals.

The concentration of the iron compound in the culture solution after the addition is preferably 1 mM or more, more preferably 5 mM or more, from the viewpoint of the production efficiency of the iron-containing organic sheath. Further, from the viewpoint of suppressing the formation of natural iron oxide particles due to excessive addition, 20 mM or less is preferable, and 10 mM or less is more preferable.

(Culture solution)
As the culture solution, the culture solution obtained in the organic sheath forming step can be used as it is, but it is preferable to add a buffer solution for the purpose of pH adjustment or the like. By such pH adjustment, the iron component can be efficiently deposited on the organic sheath.

As the buffer solution, an acetate buffer solution, a phosphate buffer solution, a citrate buffer solution, a citrate phosphate buffer solution, a borate buffer solution, a Tris buffer solution, and a HEPES buffer solution can be used.

The pH of the culture solution in the iron-containing organic sheath forming step is not particularly limited, and can be appropriately set according to the type of trivalent iron compound and the acid component to be produced. For example, when iron hydroxide is deposited using iron (III) sulfate, pH 3 to 4 is preferable. When other iron compounds are also used, the pH can be appropriately set according to a general precipitation reaction.

(Iron component)
The iron components produced include iron oxyhydroxide represented by α-FeOOH, β-FeOOH, γ-FeOOH, etc., and iron hydroxide having a nearly amorphous structure represented by ferrihydrate. Examples thereof include compounds containing oxygen as a component.

Therefore, the iron-containing organic sheath containing the produced iron component contains such an iron component and a component derived from the organic sheath. That is, as a component derived from the organic sheath, silicon (Si), phosphorus (P), sulfur (S), carbon (C), nitrogen (N), hydrogen (H) and the like can be contained.

(Other metal elements)
By adding another metal element compound to the culture solution in the iron-containing organic sheath forming step or to the culture solution produced in the iron-containing organic sheath forming step to deposit the other metal element component, the iron component and the iron component and An iron-containing organic sheath containing the other metal element component can be produced.

By forming an iron-containing organic sheath containing other metal element components in this way, it is possible to impart functions such as antibacterial action, various catalytic actions, and unique color tones, which cannot be obtained by natural BIOX.

In particular, it is preferable to add the other metal element compound to the culture solution produced by the iron-containing organic sheath forming step, and then adjust the pH with a pH adjuster. By adjusting the pH, other metal element components can be deposited on the organic sheath more efficiently.

Other metallic elements include indium, molybdenum, tungsten, bismuth, aluminum, zirconium, ruthenium, titanium, hafnium, lanthanum, cerium and the like. The other metal elements may be two or more kinds.

Examples of other metal element compounds include chlorides, nitrates, sulfates, oxysulfates, oxides, oxychlorides, and hydrates of these metal elements. Two or more kinds of other metal element compounds may be used at the same time, or may be used sequentially.

Specific compounds include, for example, Na ₂ MoO ₄ , Na ₂ WO ₄ , In (NO ₃ ) ₃ , Bi (NO ₃ ) ₃ , aluminum chloride, aluminum nitrate, aluminum sulfate, potassium aluminum sulfate, zirconium chloride (IV). ), Zirconium oxide, Zirconium oxychloride, Ruthenium chloride (III), Ruthenium chloride (II) Bis (dimethyl sulfoxide), Ruthenium oxide (VIII), RuCl ₂ (CO) ₂ (P (m-C ₆ H ₄ SO ₃ Na) ) ₃ ) ₂ , [(C ₅ R ₅ ) RuCl (PTA) ₂ ] (R = H, Me; PTA = 1,3,5-triaza-7-phosphaadamantane), titanium chloride (III), titanium chloride (IV) ), Titanium oxysulfate, hafnium chloride (IV), hafnium oxide, hafnium oxychloride, hydrates thereof and the like.

When adding these compounds, it is preferable to add them as an aqueous solution. The concentration in the culture solution after the addition is usually 0.1 to 100 mM, preferably 0.5 to 20 mM. In addition, the concentration of the other metal element compound in the total amount of the culture solution after the addition can be determined according to the ratio of the target iron element to the other metal element.

(PH regulator)
As the pH adjuster, in addition to the above-mentioned buffer solution, a Na ₂ CO ₃ solution or the like can be used. The pH after the addition is appropriately set according to the types of other metal element compounds and other metal element components to be produced. For _example, the addition of Na _{2 MoO} 4 · 2H 2 O and _{In (NO 3) 3 · 3H} 2 O, when depositing Mo component and In components, as the pH after the addition, the pH3.0~4.5 Preferably, the pH is 3.5 to 4.0, more preferably.

(Deposition operation)
The deposition operation is preferably carried out in a state where the organic sheath is suspended, and the temperature, time and the like can be appropriately set according to the type of iron component to be produced and the like. Further, in order to improve the suspension state, it is preferable to perform a stirring operation or the like.

(Iron-containing organic sheath)
The iron-containing organic sheath is formed into a hollow tubular shape at the same time as iron components such as iron hydroxide are deposited in the organic sheath. Further, when other metal element components are deposited, an iron-containing organic sheath containing an iron component and other metal element components is obtained. The obtained iron-containing organic sheath is usually one in which the iron-oxidizing bacteria inside the organic sheath are killed and desorbed, and can be obtained as if no iron-oxidizing bacteria are present in the iron-containing organic sheath.

The shape of the obtained iron-containing organic sheath is preferably tubular, and the larger the proportion of the tubular shape, the more preferable. The shape of the iron-containing organic sheath is preferably 0.8 to 2 μm in outer diameter, 10 to 1000 μm in length, and 50 to 300 nm in thickness of the tube wall, and 1.0 to 1.2 μm in outer diameter and 20 to 200 μm in length. It is more preferable that the thickness of the tube wall is 100 to 200 nm.

<Separation process>
The separation step is a step of separating the iron-containing organic sheath from the culture solution, and it is preferable to repeat washing and separation. Further, the iron-containing organic sheath may be dried after the separation step.

As a separation step, the culture solution is allowed to stand for a certain period of time to precipitate an iron-containing organic sheath, and then the supernatant is discarded to separate the precipitate, and distilled water or the like is added to the remaining precipitate for washing. However, it is preferable to repeat the operations of precipitation, removal of supernatant, and washing a plurality of times.

When drying, it is preferable to freeze-dry. Pre-drying and freezing may be performed prior to lyophilization.

<Heat treatment process>
The heat treatment step is a step of heat-treating the iron-containing organic sheath to produce at least iron oxide. By performing such a heat treatment, iron hydroxide becomes iron oxide, preferably α-Fe ₂ O ₃ (hematite) is formed, and the iron hydroxide becomes red. Such iron oxide exhibiting a red color can be suitably used as a red pigment.

Further, by heat-treating the iron-containing organic sheath, the organic component contained in the organic sheath can be decomposed and volatilized. Examples of the element thus removed include sulfur (S), carbon (C), nitrogen (N), hydrogen (H) and the like. At least a part of silicon (Si), phosphorus (P) and the like may remain even after the heat treatment.

On the other hand, when the iron-containing organic sheath contains other metal element components, oxides of other metal elements can be produced at the same time. Such an oxide of a metal element can be produced as a nano-dispersed crystal phase or the like together with iron oxide, but it can also be obtained as a composite metal oxide in which at least a part of other metal elements is dissolved in iron oxide. Is. The formation of such a composite metal oxide also corresponds to "at least producing iron oxide" in the present invention.

The heat treatment temperature is preferably 600 to 1000 ° C., more preferably 650 to 950 ° C., further preferably 700 to 900 ° C., and the heat treatment time is preferably 0.1 to 3 hours, more preferably. Is 1 to 2 hours. High a *, b *, and L * values can be obtained depending on the temperature and time of the heat treatment in this range. The heat treatment is usually carried out in the air.

Further, a step of pulverizing iron oxide can also be carried out. By crushing iron oxide, the shape of iron oxide changes from tubular to powder. Grinding can be performed using a known technique. Examples of the crushing device include a pin mill, a hammer mill, a ball mill, a jet mill, a roller mill, and the like.

(Tube-shaped iron oxide particles)
The shape of the tubular iron oxide particles obtained in the heat treatment step is tubular, and the normal size of each shape is that the iron-containing organic sheath has an outer diameter of 0.6 to 1.5 μm and a length of 10 to 10. The thickness of the tube wall is preferably 1000 μm and the thickness of the tube wall is 100 to 300 nm, and more preferably the outer diameter is 0.8 to 1.2 μm, the length is 20 to 200 μm, and the thickness of the tube wall is 150 to 200 nm. This shape is derived from the shape of the organic pod.

(Use)
When the tubular iron oxide particles _{contain α-Fe 2} O ₃ (hematite), they exhibit a red color, so that they can be suitably used as a red pigment. As for the color of the tubular iron oxide particles, a * (reddish) is preferably 25 or more, more preferably 30 to 50, b * (yellowish) is preferably 25 or more, more preferably 30 to 50, L * (lightness). Is preferably 30 or more, and more preferably 40 to 50. The parameters L *, a *, and b * here are defined in the color space called the CIE1976 L * a * b * color system recommended by the International Commission on Illumination (CIE) in 1976, and are implemented. It can be measured by the method described in the example.

When used as a pigment, it preferably contains at least one element selected from the group consisting of aluminum (Al), zirconium (Zr), titanium (Ti) and hafnium (Hf). It also preferably contains indium and / or molybdenum.

When the tubular iron oxide particles further contain indium and / or molybdenum, especially _{when they contain crystal phases of α-Fe 2} O ₃ and In ₂ (MoO ₄ ) ₃ , the color tone of red iron oxide is significantly improved. Not only that, it is equipped with antibacterial activity and photocatalytic activity in addition to it.

<Tube-shaped iron oxide particles>
One aspect of the present invention relates to tubular iron oxide particles containing trivalent iron oxides and oxides of indium and / or molybdenum. The tubular iron oxide particles preferably contain a crystal phase of _{α-Fe 2} O ₃ and In ₂ (MoO ₄ ) _3.

Such tubular iron oxide particles, which can be obtained by the production method of the present invention, not only significantly improve the color tone of red iron oxide, but are also equipped with antibacterial activity and photocatalytic activity.

In the composition of such tubular iron oxide particles, the element ratio of iron in the particles is 50 to 90% in atomic% (here, atomic% of major elements other than oxygen, carbon, nitrogen and hydrogen). It is preferable that the total of the above is 100, which is the same in the description of this paragraph below), and more preferably 60 to 80%. The element ratio of indium is preferably 0 to 20% in atomic%, more preferably 10 to 30%. The element ratio of molybdenum is preferably 0 to 20% in terms of atomic%, more preferably 10 to 30%. Further, it may contain silicon, phosphorus and the like.

When tubular iron oxide particles _{contain crystal phases of α-Fe 2} O ₃ and In ₂ (MoO ₄ ) ₃ , oxygen based on stoichiometry is added according to the atomic% range of each of the above metal elements. May contain.

<Antibacterial red pigment>
One aspect of the present invention relates to an antibacterial red pigment containing tubular iron oxide particles containing a trivalent iron oxide and an oxide of indium and / or molybdenum. The tubular iron oxide particles preferably contain a crystal phase of _{α-Fe 2} O ₃ and In ₂ (MoO ₄ ) _3.

Such tubular iron oxide particles not only significantly improve the color tone of red iron oxide, but are also equipped with antibacterial activity and photocatalytic activity. The composition of the antibacterial red pigment is preferably the same as that of the above-mentioned tubular iron oxide particles.

Hereinafter, some aspects of the present invention will be specifically described with reference to examples and the like, but the technical scope of the present invention is not limited thereto.

Experimental Example 1 (Optimization of conditions for depositing iron components on the organic sheath)
See Minerals 5, 335-345 (2015) in 20 ml SGP (Silicon-Glucose-Peptone) liquid medium in which cells of Leptoslix corodini OUMS1 strain (hereinafter referred to as "OUMS1 strain") were placed in a 50 ml sterile centrifuge tube. ], And shake culture (preculture) at 20 ° C. and 70 rpm for 3 days. After that, it was aseptically added to 1.5 L of SGP liquid medium contained in a mini jar fermenter (M-1000, manufactured by Tokyo Rika Kikai Co., Ltd.), and stirred and cultured at 20 ° C. and 80 rpm for 2 days while bubbling air. By (main culture), agglomerates (organic sheaths) of rod-shaped sheaths composed of organic components were prepared. The composition of the SGP liquid media used, glucose 1g, peptone _{1g, Na 2 Si0 3 · 9H} 2 O 0.2g, CaCl 2 · 2H 2 O 0.044g, MgSO 4 · 7H 2 O 0.041g, Na 2 HPO _{4 · 12H 2 O 0.076g, KH} 2 PO 4 · 2H 2 O 0.02g, HEPES 2.838g, distilled water 1000 ml, was pH 7.0.

The iron source shown in Table 1 was added to the culture solution containing the organic sheath obtained above so as to have a final concentration of 10 mM, and the mixture was stirred at 20 ° C. and 80 rpm for 24 hours to form iron hydroxide in the organic sheath. At the same time as depositing, an iron-containing organic sheath (hereinafter referred to as "BIOX") formed into a hollow tubular shape was produced. In the case where the pH was adjusted with an acetate buffer, an acetate buffer (pH 4.2) having a final concentration of 10 mM was added in addition to the iron source. Table 1 shows the pH after the addition of the iron source and the fine form (classification type) of the product.

As a result, as shown in Table 1, product samples classified into I to IV according to the type of fine form were obtained. That is, as shown in FIG. 8, I.I. Rod-shaped sheath with iron oxide particles attached, II. Rod-shaped sheath, III. Hollow tubular sheath, IV. Those classified as incomplete hollow sheaths to which iron oxide particles were attached were obtained. Therefore, it was clarified that adding about 10 mM iron (III) sulfate to the organic sheath suspension in the presence of an acetate buffer is suitable for forming tubular iron oxide particles.

The BIOX obtained using iron (III) sulfate was heated in the air at 800 ° C. for 2 hours to obtain a heating material (heat-treated product: tubular iron oxide particles). Regarding this, the fine morphology was observed and the element composition ratio was measured by the SEM-EDX method. As a result, it was found that the heating material maintained a hollow tubular sheath shape having a diameter of about 0.8 μm (tube wall thickness of about 0.1 μm). Moreover, it was shown that the chemical composition was Si = 6, P = 4, S = 6, Fe = 94 (at%).

Example 1 (Preparation of organic sheath derived from iron-oxidizing bacteria)
Inoculate the cells of the OUMS1 strain into 20 ml of SGP (silicon-glucose-peptone) liquid medium [see Minerals 5, 335-345 (2015)] in a 50 ml sterile centrifuge tube and shake at 20 ° C. and 70 rpm for 3 days. Cultured (precultured).

After that, it was aseptically added to 1.5 L of SGP liquid medium contained in a mini jar fermenter (M-1000, manufactured by Tokyo Rika Kikai Co., Ltd.), and stirred and cultured at 20 ° C. and 80 rpm for 2 days while bubbling air. By (main culture), agglomerates (organic sheaths) of rod-shaped sheaths composed of organic components were prepared (FIG. 1 (b)). The composition of the SGP liquid media used, glucose 1g, peptone _{1g, Na 2 Si0 3 · 9H} 2 O 0.2g, CaCl 2 · 2H 2 O 0.044g, MgSO 4 · 7H 2 O 0.041g, Na 2 HPO _{4 · 12H 2 O 0.076g, KH} 2 PO 4 · 2H 2 O 0.02g, HEPES 2.838g, distilled water 1000 ml, was pH 7.0.

Example 2 (Deposition of iron component on the organic sheath)
To the culture solution containing the organic sheath obtained above, an acetate buffer (pH 4.2) was added so that the concentration after addition was 10 mM, and Fe ₂ (SO) was added so that the concentration after addition was 7.6 mM. ₄ ) _{By adding 3} and stirring at 20 ° C. and 80 rpm for 24 hours, iron hydroxide was deposited in the organic sheath, and at the same time, an iron-containing organic sheath (BIOX) formed into a hollow tubular shape was prepared (FIG. 1 (Fig. 1). c)). The main elemental compositions (excluding C, H, O) of this BIOX by the SEM-EDX method are Fe = 84, Si = 6, P = 4, S = 6 (at%, average value n = 10). rice field.

Example 3 (Deposition of other elements on the iron-containing organic sheath)
As concentration after _{Na 2 MoO} 4 · 2H 2 O and added so that the concentration after addition to the culture medium becomes 10mM containing ferrous organic sheath obtained above is _{5mM In (NO 3) 3 ·} 3H _{After adding 2} O, the pH was adjusted to 3.5-4.0 using a 1000 mM Na ₂ CO ₃ solution, and the mixture was stirred at 20 ° C. and 80 rpm for 24 hours (FIG. 1 (d)).

Then, the supernatant was discarded, and the operation of washing the remaining precipitate with 10 times the amount of distilled water was repeated three times, and then a Mo / In-containing BIOX powder was prepared using a freeze-dryer. About 4.8 g of Mo / In-containing BIOX was obtained from the 1.5 L volume of organic sheath suspension.

Example 4 (fine form and elemental composition of Mo / In-containing BIOX heating material)
The culture system BIOX containing Mo and In was heated in the air at 800 ° C. for 2 hours to obtain a heating material (heat-treated product: tubular iron oxide particles) of BIOX containing Mo / In. Regarding this, the fine morphology was observed and the element composition ratio was measured by the SEM-EDX method. As a result, it was found that the heating material maintained a hollow tubular sheath shape having a diameter of about 0.8 μm (tube wall thickness of about 0.1 μm) (FIG. 2A). Further, it was shown that the chemical composition was Si = 4, P = 2, Mo = 22, In = 16, Fe = 56 (at%) (FIG. 2 (b)).

Example 5 (Distribution of major elements in the heating material of Mo / In-containing BIOX)
The elemental distribution of Mo / In-containing BIOX in the heating material was analyzed by STEM-EDS. As a result, it was inferred that Fe oxide and In oxide having a diameter of 50 to 100 nm each formed a nanocomplex structure (Fig. 3).

Example 6 (Crystal phase of Mo / In-containing BIOX heating material)
The crystal phase of the Mo / In-containing BIOX 800 ° C. heating material was analyzed by the powder XRD method. As a result, _{it was clarified that it mainly consisted of the crystal phases of α-Fe 2} O ₃ and In ₂ (MoO ₄ ) ₃ (Fig. 4).

Example 7 (Antibacterial activity of Mo / In-containing BIOX heating material)
First, in order to investigate the hyphal activity of the Mo / In-containing BIOX heating material, a mycelial piece of the ascomycete Fusarium oxysporum Odoriko strain (or Botrytis cinerea SAS53 strain) was placed in the center of a 10-fold diluted PDA plate medium. After arranging the test sample powder in a streak pattern around it, the elongation and growth of hyphae were investigated under irradiation with a fluorescent lamp (10 W) at 24 ° C. As a result, it was found that the elongation of hyphae was remarkably suppressed in the case of the Mo / In-containing BIOX exothermic material (600 ° C. and 800 ° C.) (FIG. 5 (a)).

In addition, for the purpose of testing antibacterial activity, 0.5 mg / ml of a test sample was added to ^{a bacterial solution (1-2 x 10 6 cfu / ml) of Escherichia coli HB101 strain, and the mixture was stirred at 24 ° C. by darkening.} While (120 rpm), the change in the viable cell count over time was investigated by the dilution plate method.

As a result, in the test group treated with the Mo / In-containing BIOX heating material (800 ° C.), the reduction rate of the viable cell count was significantly higher than that in the other test groups, so that the sample had a high bactericidal action. It was revealed to have (Fig. 5 (b)).

Example 8 (Photocatalytic activity of Mo / In-containing BIOX heating material)
The photocatalytic activity of the Mo / In-containing BIOX heating material was tested by the removal rate of methylene blue (MB) under visible light irradiation. That is, 0.5 mg / ml of the test sample was added to a 20 μM MB solution, and the change over time in the MB concentration was separated under irradiation with a white LED light source (600 kLux, 400 nm-780 nm, LA-HDF158A, Hayashi-Repic). It was measured using a photometer. The test was repeated twice in two series.

The removal rate of MB was calculated by _{(C 0-} C _t ) / C _{0 x 100.} Note that C ₀ and C _t represent MB concentrations in the centrifugal supernatant after the equilibrium adsorption treatment of MB and after light irradiation for t hours, respectively. As a result, under the present test conditions, the Mo / In-containing BIOX heating material almost completely removed MB within 24 hours, indicating that the sample had a certain degree of photocatalytic activity (FIG. 6).

Example 9 (Color tone of the heating material of BIOX containing Mo / In)
In order to evaluate the color tone of each heat-treated sample, a spectrocolorimeter (CM-2600d, Konica-Minolta) was used to spectroscopically analyze the reflected light (including the normal reflected light) with respect to the irradiation of the D65 standard light source. A commercially available high-colored Bengala MC-55 (Morishita Benji Kogyo Co., Ltd.) was used as a comparative control.

As a result, the Mn / In-containing BIOX 800 ° C. heating material (cBIOX-Mo22 / In16-800) had significantly higher saturation and brightness (L ^* = 48.3, a ^* = 37) as compared with other samples. .2, b ^* = 42.5) was shown (Fig. 7).

According to the disclosure of the present specification, it is possible to produce tubular iron oxide particles equipped with antibacterial activity and photocatalytic activity in addition to significantly improving the color tone of conventional red iron oxide. This is expected to lead to the expansion of the range of use of red iron oxide. In addition, the disclosed manufacturing method is superior to the conventional method in terms of shortening and convenience of the work process, and is suitable for scale expansion in terms of system configuration. Therefore, it is suitable for mass production for commercial use. Will be easier to migrate.

Claims (9)

A method for producing tubular iron oxide particles.
An organic sheath formation step in which iron-oxidizing bacteria are cultured in a culture solution in a container of a culture device to form an organic sheath on the outer periphery of the bacteria.
An iron-containing organic sheath forming step of producing an iron-containing organic sheath containing the iron component by adding at least a trivalent iron compound to the culture solution produced by the organic sheath and depositing an iron component.
A separation step of separating the iron-containing organic sheath from the culture solution, and
A heat treatment step of heat-treating the iron-containing organic sheath to produce at least iron oxide,
A method for producing tubular iron oxide particles containing. Claim 1 in which the trivalent iron compound is at least one selected from iron (III) sulfate, iron (III) chloride, iron (III) nitrate, iron (III) acetate, and iron (III) citrate. The method for producing tubular iron oxide particles according to. The method for producing tubular iron oxide particles according to claim 1 or 2, wherein oxygen-containing gas is supplied into the container of the culture apparatus by bubbling at least in the organic sheath forming step. By adding another metal element compound to the culture solution in the iron-containing organic sheath forming step or to the culture solution generated in the iron-containing organic sheath forming step to deposit the other metal element component, the iron component and the iron component and The method for producing tubular iron oxide particles according to any one of claims 1 to 3, wherein an iron-containing organic sheath containing the other metal element component is produced. The method for producing tubular iron oxide particles according to claim 4, wherein the pH is adjusted with a pH adjuster after adding the other metal element compound to the culture solution produced by the iron-containing organic sheath forming step. The method for producing tubular iron oxide particles according to claim 5, wherein the other metal element is indium and / or molybdenum. Tubed iron oxide particles containing trivalent iron oxide and oxides of indium and / or molybdenum. The tubular iron oxide particle according to claim 7, which comprises a crystal phase of α-Fe ₂ O ₃ and In ₂ (MoO ₄ ) _3. The antibacterial red pigment containing the tubular iron oxide particles according to claim 6 or 7.

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