Structure having water purification function by sterilization action, method for producing structure, and method for sterilization and purification

Abstract

To provide a structure having a surface structure capable of sterilizing water only by placing the structure in flowing water and providing water which is not contaminated with bacteria and is safely drinkable. And to provide a method for sterilizing and purifying water only by placing the structure in water.SOLUTION: The structure comprises a base material and a needle-like crystal or a needle-like crystal habit deposited or carried on the solid surface of the base material, wherein the solid surface comprises titanium oxide and the needle-like crystal or the needle-like crystal habit is aragonite comprising calcium carbonate.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a structure that captures bacteria in water or exerts a bactericidal effect by its morphology, and to the use of the same. [Background technology]

[0002] Regarding the morphotoxic effect, which manifests a bactericidal effect depending on the shape, or the so-called mechano-bactericidal effect, it has been reported in recent years that the surfaces of dragonfly and cicada wings are sterile, and that this sterile nano-surface structure exists not only on cicada and dragonfly wings but also on black silicon and the like, and that these nano-surface structures may have a bactericidal effect (Non-Patent Document 1).The bactericidal effect against gram-negative bacteria is strongest for black silicon, followed by dragonfly wings and cicada wings, in that order.

[0003] Black silicon has nanopillars 500 nm high, while cicada and dragonfly wings have nanopillars 240 nm high, and the surface composition of black silicon is mainly silicon oxide, while the surface composition of cicada and dragonfly wings, which are made of chitin, is lipid. The mechanism by which these nanopillars kill bacteria is not described in Non-Patent Document 1, and it is unclear whether the reason black silicon has a stronger bactericidal effect than dragonfly and cicada wings is due to the difference in the shape of the nanopillars or to chemical reasons related to the substances that make up the nanopillars.

[0004] The bactericidal effect of needle-like structures based on mechano-bactericidal effects is not limited to black silicon. Examples include gecko skin (Non-Patent Document 2), nanograss and black diamond nanocones (Non-Patent Document 3), titania nanowires, organic polymers such as PMMA, and gold nanostructures. It is currently believed that when bacteria come into contact with the nanoscale needle-like structures present on the surface of these materials, they are killed by damaging the cell walls.

[0005] The development of technology that applies the bactericidal function of this mechano-bactericidal effect to impart antibacterial properties that are useful to humans is also underway. Patent Document 1 describes the application of antibacterial surfaces with a surface structure that prevents bacterial adhesion to medical devices, household plumbing products, and even marine structures. Furthermore, Patent Document 2 discloses a method for synthesizing nanopillars by anodization for the purpose of providing antifungal properties to the surfaces of devices such as water kettles including coffee makers, lunch boxes, and even heat exchangers, and Patent Document 3 discloses the use of a laminated film of polycarbonate and a synthetic polymer film with nano-sized protrusions to impart bactericidal properties to the surfaces of various molded products. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2011 / 094344 [Patent Document 2] International Publication No. 2016 / 021367 [Patent Document 3] Patent No. 6581159 [Patent Document 4] Patent No. 3275032 [Patent Document 5] Patent No. 3598349 [Patent Document 6] Patent No. 3975270 [Non-patent literature]

[0007] [Non-Patent Document 1] Nature Communications (2013) Doi:10.1038 / ncomms3838 [Non-patent document 2] Acta Biomaterialia (2015) Vol.21, p.109-122 [Non-patent document 3] Biomaterials Science (2018) Vol.6, p.1424-1432 [Non-patent document 4] Appl. Catal. B: Envion. (2019) Vol.242, p.449-459 [Non-Patent Document 5] Nichias Technical Review (2018) No.382, pp.1-6 [Non-patent document 6] In situ X-ray diffraction study of tobermorite formation process, 1st SPring-8 Metal Materials Evaluation Workshop (August 3, 2009) [Non-Patent Document 7] Corrosion Science (1988) Vol.28, p.1177-1181 [Non-patent document 8] Characteristics and Applications of Needle-like Hydroxyapatite, Toagosei Research Annual Report (1999) No.2, p.11-19 [Non-Patent Document 9] Structural similarity between hydroxyapatite and its precursor crystals, Research Report A, College of Industrial Technology, Nihon University (2005) Vol. 38, pp. 35-39 [Non-Patent Document 10] Preparation and Evaluation of Biofunctional Ceramics by Hydrothermal Synthesis - Synthesis and Morphological Control of Hydroxyapatite Crystals -, Report of Hokkaido Industrial Research Institute (2006) Vol.305, pp.159-162 [Non-Patent Document 11] Materials Research Bulletin (1998) Vol.33, p.125-131 [Non-Patent Document 12] Catal. Today (2020) Vol.340, p.334-346 [Non-Patent Document 13] Archives of Toxicology (2019) Vol.93, p.2797-2810 [Non-Patent Document 14] J. Mater. Chem. (2019) Vol.7, p.5725-5731 [Non-Patent Document 15] Biophys. J.(2013) Vol.104, p.835-840 Summary of the Invention [Problem to be solved by the invention]

[0008] Non-Patent Documents 1 to 3 indicate that there are various materials with mechano-bactericidal effects, from natural to artificial, but none of these documents are intended to treat bacterial species present in water. This is because the desired function is to prevent bacteria from adhering to the skin and feathers of animals, including insects. Patent Document 3 also describes the application of a synthetic polymer film with a bactericidal surface to the surface of a touch panel display, such as a smartphone, made of polycarbonate, and its application to touch panels installed in hospitals and public places that can be touched by an unspecified number of people.

[0009] Additionally, while some antibacterial surfaces are intended for use in water, their main purpose is to inhibit the formation of biofilms by treating surface-adhering bacteria, and they are not intended to sterilize the water itself. To provide a structure having a surface structure that can sterilize water by simply placing it in running water, thereby making the water safe to drink and free from bacterial contamination, and to provide a method for sterilizing and purifying water by simply placing the structure in water. [Means for solving the problem]

[0010] The present invention relates to a structure having a solid surface that can capture bacteria contained in drinking water, etc., in micron-sized needle-like crystals or needle-like habits precipitated or supported on its surface, and can sterilize them using even smaller nano-sized needle-like crystals or needle-like habits. When water containing bacteria is passed over the surface of the structure of the present invention, the bacteria are captured by the unique needle-like structures and do not flow downstream. Furthermore, the needle-like structures destroy the cell membranes that make up the bacteria, allowing intracellular substances to elute and kill the bacteria.

[0011] Furthermore, when a photocatalytic material is used on the solid surface of a substrate on which needle-shaped structures are precipitated or supported, the active species generated from the photocatalyst upon irradiation with an excitation light source can mineralize the bacteria captured in the needle-shaped structures through photocatalytic decomposition, which, unlike filtration, also provides a technology that avoids the adverse effects of the accumulation of dead bacteria.

[0012] The present invention relates to the following structures (1) to (5) and methods for producing the structures. (1) A structure for water purification, comprising a substrate and needle-shaped crystals or needle-shaped crystal habits precipitated or supported on the solid surface of the substrate, wherein the solid surface is made of titanium oxide, and the needle-shaped crystals or needle-shaped crystal habits are aragonite made of calcium carbonate. (2) The structure according to (1), wherein the substrate is made of titanium oxide. (3) The structure according to (1), wherein the substrate is made of a photocatalytic material other than titanium oxide. (4) A method for manufacturing a structure for water purification comprising a substrate and needle-shaped crystals or needle-shaped crystal habits precipitated or supported on the solid surface of the substrate, the method comprising the steps of passing an aqueous solution of bicarbonate ions and calcium ions through the substrate made of a photocatalyst to precipitate or support the needle-shaped crystals or needle-shaped crystal habits on the solid surface of the substrate, wherein the solid surface is made of titanium oxide, and the needle-shaped crystals or needle-shaped crystal habits are aragonite made of calcium carbonate. (5) A method for manufacturing a structure for water purification comprising a substrate and needle-shaped crystals or needle-shaped crystal habits precipitated or supported on the solid surface of the substrate, the method comprising the steps of passing an aqueous solution containing bicarbonate ions and strontium ions, and sodium ions, potassium ions, or magnesium ions, and a mixed solution of calcium chloride or calcium sulfate through the substrate made of a photocatalyst, thereby precipitating or supporting the needle-shaped crystals or needle-shaped crystal habits on the solid surface of the substrate, wherein the solid surface is made of titanium oxide, and the needle-shaped crystals or needle-shaped crystal habits are aragonite made of calcium carbonate.

[0013] The present invention also relates to the following method for sterilizing and purifying water (6). (6) A method for sterilizing and purifying water, comprising the steps of placing the structure described in any one of (1) to (3) above in a flow path for water containing fungi or bacteria, flowing the water in the flow path, physically killing the fungi or bacteria by the mechano-sterilizing effect of the needle-shaped crystals or needle-shaped crystal habit, and irradiating the solid surface with light to decompose and remove the fungi or bacteria by the photocatalytic action of the solid surface. [Effects of the Invention]

[0014] The needle-shaped crystals and needle-shaped habit that constitute part of the structure of the present invention are easily produced because they are naturally precipitated or supported on the solid surface of the substrate by repeatedly passing an aqueous solution of a calcium-containing compound over the substrate and drying it. Furthermore, needle-shaped crystals and needle-shaped habit that have been damaged by water flow can be easily restored and repaired by passing natural water containing calcium ions through the water and exposing them to the mineral components in the water. Since the needle-shaped crystals and needle-shaped habit precipitated or supported on the structure of the present invention are crystalline bodies composed of calcium carbonate, apatite, and calcium silicate, when pure water is passed through them, they are expected to gradually lose their habit in a weakly acidic environment due to the influence of carbon dioxide dissolved in the water. However, when the structure of the present invention is expected to be used in developing countries, particularly in the case of purifying drinking water, the water to be treated is often groundwater such as spring water, which usually contains mineral components. Furthermore, when components such as calcium bicarbonate are contained in the water, the effect of repairing the needle-shaped habit damaged by passing water through the structure is apparent, and the structure can be said to have a self-repair function, which is fundamentally different from devices such as filtration devices that lose their function with continued use.

[0015] A major problem with purifying drinking water in developing countries is the high cost of accessing safe water. However, if drinking water is purified using the structure of the present invention, the disinfecting ability is maintained with continued use, which is an advantage not found in conventional water treatment systems. Furthermore, by using a photocatalytic material on the solid surface of the substrate, it becomes possible to mineralize the bacteria captured in the needle-shaped crystals through photocatalytic action.Unlike filtration, it is possible to add a self-repair technology that avoids the adverse effects of dead bacteria accumulation, making it possible to reduce costs. [Brief explanation of the drawings]

[0016] [Figure 1] Electron microscope photographs of needle-like structures made of calcium carbonate (aragonite CaCO3) grown on ceramics, which are an embodiment of the present invention. (a) Magnification: 1000x, (b) Magnification: 5000x. [Figure 2] An electron microscope photograph of calcite crystals, which are the same calcium carbonate as aragonite, growing on ceramics at 1000x magnification. [Figure 3] Laser Raman spectra of (a) aragonite crystals or (b) calcite crystals on a titanium dioxide (TiO2) support. [Figure 4] Electron microscope images of the needle-shaped structures after passing an aqueous solution containing E. coli through them. (a) Magnification: 1000x, (b) Magnification: 5000x [Figure 5] Schematic diagram of a closed circulation device used to evaluate the bactericidal effect of needle-shaped structures on bacteria in water. [Figure 6] This is a diagram showing the change over time in the number of bacteria when water containing E. coli was passed through a tube filled with carriers without needle-shaped structures and carriers with needle-shaped structures, using the closed circulation device shown in Figure 5. Titanium oxide photocatalytic ceramics were used for the solid surface, but the experiment was conducted in the dark to prevent the photocatalytic activity from being expressed. [Figure 7] Micrographs showing the bactericidal effect of E. coli on TiO2 ceramic (top row) or aragonite-supported TiO2 ceramic (bottom row) under static conditions. [Figure 8] The results of determining whether bacteria are viable or dead on the surface of TiO2 ceramic (left) or aragonite-supported TiO2 ceramic (right) after 3 hours of circulation in a closed circulation device under dark conditions are shown using a phase-contrast microscope. [Figure 9]This graph shows the change in bacterial count over time when water containing E. coli was passed through a tube filled with TiO2 ceramic or aragonite-supported TiO2 ceramic using a closed-circulation device. The experiment was conducted in the dark or under UV irradiation. [Figure 10] Figure 9 Field emission scanning electron microscope (FE-SEM) photographs of (a) TiO2 ceramic or (b) aragonite-supported TiO2 ceramic after the experiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] The structure of the present invention is composed of nano- to micron-sized needle-like crystals and has a needle-like habit, which are precipitated or supported on the solid surface of a substrate.

[0018] Since the structure is used for water purification, the substrate of the structure may be made of any material, shape, and size, as long as it is insoluble in water and does not contain elements that are toxic to living organisms.The solid surface of the substrate may also be made of a material that is insoluble in water, does not contain elements that are toxic to living organisms, and allows for the formation of needle-like structures on the surface.The substrate and its solid surface may be made of the same material or different materials, but it is convenient if the substrate on whose solid surface needle-like crystals or needle-like crystal habits made of inorganic oxide ceramic are precipitated or supported is an inorganic oxide ceramic.

[0019] Furthermore, if a photocatalytic material such as titanium oxide is used on the solid surface of the substrate, the photocatalytic action can be used to kill bacteria captured by the needle-shaped crystals and their habits, which not only increases water treatment capacity but also makes it possible to mineralize dead bacteria through photocatalysis, avoiding the negative effects of dead bacteria accumulation, unlike filtration. Test methods for sterilization using this photocatalytic material are described in JIS R1702 "Fine ceramics - Antibacterial test methods and antibacterial effects for photocatalytic antibacterial processed products under light irradiation."

[0020] In the present invention, "sterilization" refers to effectively reducing the number of microorganisms present in water that can grow. In this specification, "bacteria" or "microorganisms" refers to organisms such as bacteria, fungi, protozoa, etc. that are too small to be detected by the naked eye and can be observed using a microscope, etc., but does not include viruses.

[0021] The "nano- to micron-sized needle-shaped crystals and needle-shaped habit of inorganic compound ceramics that are insoluble in aqueous solutions and do not contain elements toxic to living organisms" of the present invention preferably refer to needle-shaped crystals and needle-shaped habit of calcium-containing compounds such as calcium carbonate, apatite, or calcium silicate. Among these, the needle-shaped habit of calcium carbonate is aragonite, which is known to have no ecotoxicity (see Non-Patent Document 13). Furthermore, the term "nano- to micron-sized" refers to lengths of several tens of nanometers to several tens of micrometers. Since the size of bacteria, including fungi, is as large as several tens of micrometers, it is sufficient for the needle to have a length that can capture or pierce them and physically destroy them. Furthermore, Non-Patent Document 15 describes that there is a size of the curvature of the needle tip that is suitable for destroying cell walls, and the aragonite needle-shaped habit closely matches this size.

[0022] To deposit or support aragonite on the solid surface of a substrate, it is necessary to prepare a mixed aqueous solution containing a small amount of strontium ions or an aqueous solution to which ionic species that promote crystallization have been added to a calcium bicarbonate aqueous solution. If even a small amount of strontium ions is dissolved, the calcium carbonate that precipitates or deposits on the solid surface will have an aragonite crystal structure with an acicular crystal habit. On the other hand, if a pure calcium bicarbonate aqueous solution is used, the calcium carbonate that precipitates or deposits on the solid surface will be calcite, which does not have an acicular crystal habit. The structure of the present invention can be produced by repeatedly passing the above mixed aqueous solution over the solid surface of a substrate and then drying it, thereby forming aragonite having an acicular crystal habit on the solid surface. The calcium bicarbonate aqueous solution is preferably at a saturated concentration, but a lower concentration can also be used.

[0023] It is also possible to form needle-like crystals by a similar process using mineral water containing calcium ions instead of the calcium bicarbonate aqueous solution, but the higher the calcium ion concentration, the faster the needle-like crystals will grow. In addition, when an aqueous calcium bicarbonate solution is not used, a mixed solution containing an aqueous sodium bicarbonate solution, an aqueous potassium bicarbonate solution, or an aqueous magnesium bicarbonate solution and calcium chloride or calcium sulfate, and a small amount of strontium ions, is used.

[0024] It is possible to accelerate the growth rate of aragonite by applying a photocatalytic material to a solid surface and continuously irradiating it with light of an excitation wavelength that activates the photocatalyst. This utilizes the calcium carbonate precipitation mechanism that accompanies the photocatalytic decomposition reaction of bicarbonate ions, as described in Non-Patent Document 4.

[0025] For example, when mineral water with a high calcium bicarbonate concentration is passed through a ceramic titanium dioxide photocatalyst while being irradiated with light, needle-shaped aragonite crystals eventually begin to precipitate on the ceramic titanium dioxide photocatalyst. This occurs because bicarbonate ions are converted to carbonate ions by the photocatalytic action, and if calcium ions are also present, they immediately precipitate as insoluble calcium carbonate. Cationic species other than calcium, such as sodium, potassium, and magnesium, also become carbonates through photocatalytic action, but these carbonates are water-soluble, and by shifting to an equilibrium state between carbonate ions and bicarbonate ions, not only do these salts not precipitate, but the concentration of bicarbonate ions does not change before and after the photocatalytic reaction. The concentration of bicarbonate ions decreases before and after the reaction only when calcium ions are present.

[0026] In addition to photocatalytic reactions, it is also possible to accelerate the growth of acicular crystals by increasing the water temperature during aragonite growth above room temperature, which shifts the equilibrium between bicarbonate ions and carbonate ions in the water toward carbonate. This reaction is the same mechanism by which calcium carbonate-containing scale precipitates inside boilers and their pipelines.

[0027] Crystals that form needle-like habits of calcium silicate include nekoilite, okenite, xonolite, jennite, hillebramdiote, and tobermorite in the wollastonite group, gyrolite and truscottite in the gyrolite group, afwillite in the ν-CS group, and others such as tricalcium silicate hydrate and α-dicalcium silicate hydrate. Using water containing calcium ions and water-soluble silica, a procedure similar to that used to precipitate aragonite can be used to form any of these needle-like habits on a solid surface.

[0028] The main components of natural water are not only calcium but also water-soluble silica (dissolved silica, metasilicic acid). If the needle-like structures are formed using calcium silicate instead of calcium carbonate, it is possible to self-repair any needle-like structures that are damaged during use by passing water containing both calcium ions and dissolved silica through the water. It is known that calcium silicate hydrate is formed by the slow reaction of calcium ions and dissolved silica in the water over time, and it is thought that this mechanism is responsible for the self-repair ability.

[0029] Normally, calcium silicate needle structures do not form in a short time at room temperature and normal pressure, but it is possible to generate calcium silicate crystals on a solid surface in advance by using an autoclave method. This allows calcium silicate to precipitate on the photocatalyst surface, making it possible to apply the self-repair function described above. Details of the calcium silicate synthesis method and precipitation mechanism are described in Non-Patent Documents 5 to 7.

[0030] On the other hand, apatite, which is considered to have excellent biocompatibility among calcium-containing compounds, is also known to partially form needle-like crystals. Although there have been no studies on whether apatite has a self-repair function in natural water, it is thought that it is possible to immobilize needle-like apatite crystals on the surface of titanium dioxide photocatalysts using hydrothermal synthesis methods or other methods to give them a mechano-bactericidal effect, just like aragonite and calcium silicate.

[0031] Among apatites, hydroxyapatite is known for its high biocompatibility and is thought to be non-toxic even if ingested by the human body, making it a promising material for forming needle-like structures. This synthesis method is a hydrothermal synthesis method described in Non-Patent Documents 8 to 10, and it is possible to form needle-like apatite on the surface of solid materials such as titanium oxide photocatalytic materials.

[0032] On the other hand, photocatalytic materials have also been synthesized by depositing biocompatible apatite on solid surfaces such as titanium oxide, with the aim of acting as a blocking layer between the photocatalyst and biological tissue. While this technology is not intended to achieve mechanobactericidal effects, it is believed that if apatite can be formed into needle-like crystals, it may be possible to impart mechanobactericidal effects rather than biocompatibility. Liquid-phase synthesis methods, as described in Patent Documents 4-6 and Non-Patent Documents 11 and 12, have also been investigated for depositing apatite on photocatalysts. This method makes it possible to deposit apatite on solid surfaces in an even milder environment than the hydrothermal synthesis method described above.

[0033] To use the structure of the present invention for sterilizing and purifying water, it is sufficient to place it in running water, and the nano- to micron-sized needle-like crystals on the solid surface will capture and filter out bacteria that flow by. Alternatively, the needle-like crystals can damage the bacterial cell membranes and sterilize the water, thereby sterilizing and purifying the water. Furthermore, when the structure is placed in still water, stirring or shaking the water can more efficiently capture and sterilize bacteria.

[0034] This specification specifically describes a method for manufacturing the structure of the present invention, which is mainly made of a calcium compound having an acicular shape and capable of killing bacteria in water, and a method for killing bacteria in water using this structure. The present invention also relates to the mineralization of killed bacteria when a photocatalytic material is used on the solid surface of the structure of the present invention, the recovery action of acicular shapes damaged by running water due to mineral components in water, the maintenance of the bactericidal function due to the recovery of the acicular shapes, and a method for treating bacteria in water that applies these functions. [Example]

[0035] Hereinafter, with reference to the drawings, we will explain a structure having a bactericidal effect and an aragonite needle structure, which is one embodiment of the structure of the present invention, a method for producing the same, a method for sterilizing water using the structure, and a method for using the structure in combination with a photocatalyst.

[0036] A ceramic titanium dioxide photocatalyst was used as the substrate. When mineral water with a high calcium bicarbonate concentration and trace amounts of dissolved strontium ions was passed through the solid surface of the substrate while irradiating it with light, needle-like crystals of aragonite eventually began to precipitate on the ceramic titanium dioxide photocatalyst. This occurs because bicarbonate ions are converted to carbonate ions by the photocatalytic action, and because calcium ions are also present, they immediately precipitate as insoluble calcium carbonate.

[0037] When even a small amount of strontium ions are dissolved in mineral water, the calcium carbonate that precipitates has an aragonite crystal structure with a needle-like crystal habit (Figure 1). However, when a pure calcium bicarbonate aqueous solution is used in a photocatalytic reaction, the calcium carbonate that deposits on the photocatalyst surface becomes calcite, which does not have a needle-like crystal habit (Figure 2). Aragonite and calcite are polymorphs with the same elemental composition but different atomic arrangements, and can be easily distinguished by their different X-ray diffraction and laser Raman spectra (Figure 3).

[0038] The needle-like crystal habit of aragonite on the photocatalyst surface is several hundred nanometers to several tens of micrometers long, as shown in the photograph in Figure 1. Bacteria, including fungi, are at most a dozen micrometers in size, and are long enough to be captured or pierced by the needle-like crystal habit, thereby physically destroying and sterilizing them. Microscopically, the acicular crystal habit precipitates in a very coarse state. Therefore, when the solid surface is a titanium dioxide photocatalyst, organic pollutants (solutes) easily reach the photocatalyst surface when the structure of the present invention is used for water purification. Furthermore, hydroxyl radicals, which are active species generated on the photocatalyst surface, diffuse to a distance of several microns from the photocatalyst surface, which is the tip of the acicular crystal habit. Furthermore, because calcium carbonate does not absorb ultraviolet light in the UV-A region, which is necessary to excite the titanium dioxide photocatalyst, organic pollutants that reach the photocatalyst surface and bacterial tissue captured by the acicular crystal habit are immediately decomposed by photocatalytic oxidation. In other words, the aragonite precipitated on the photocatalyst surface does not substantially inhibit the photocatalytic activity of the solid surface.

[0039] Furthermore, if bacteria are present in the running water, they are filtered out by the needle-like crystal habit of the aragonite, and the needle-like crystal habit of the aragonite destroys the bacterial cell membranes, thereby killing them. If the solid surface is photocatalytic, as mentioned above, hydroxyl radicals and reactive oxygen species generated by photoexcitation diffuse and attack bacteria trapped in the aragonite needle-like crystal habit, thereby killing bacteria. The photocatalytic action of the killed bacteria causes the organic components of the bacterial tissue to be oxidized and decomposed, resulting in mineralization. During this process, calcium ions contained in the continuously flowing mineral water grow as calcium carbonate, using the bacterial species as nuclei. This situation is shown in Figure 4. This experiment was conducted using the closed circulation system shown in Figure 5. In Figure 4(b), finer aragonite needle-like crystals have begun to grow around the large aragonite needle-like crystals that have impaled the bacteria. The mechanism by which aragonite grows around organic matter, including fungi, is described in Non-Patent Document 14.

[0040] The process of sterilization by filtering bacteria into the acicular habit of aragonite or by damaging cell membranes with the acicular habit of aragonite is effective as a technology for treating bacteria contained in water, especially drinking water. Materials with needle structures other than the acicular habit of aragonite that have bactericidal properties are known, such as the group of materials described in the background art above. However, not only are these materials expensive to synthesize, but they are also expected to cause negative physiological effects, such as tumor formation due to biological stimulation, when taken into the body. The structure of the present invention uses a needle-shaped crystal habit made of calcium carbonate, which not only allows for the inexpensive synthesis of antibacterial materials, but also allows the structure to self-repair when damaged by water treatment with the structure by passing water through the structure in an actual environment. Furthermore, the aragonite needle-shaped crystal habit that is released due to damage has the advantage that it dissolves immediately when ingested by the human body, causing no biological effects.

[0041] Figure 6 shows the change in the number of E. coli bacteria when 500 mL of water containing E. coli bacteria (approximately 4000 cfu / mL) was passed through a glass tube filled with approximately 17 g of titanium dioxide ceramics at a rate of 100 mL per minute in the closed circulation system shown in the schematic diagram of Figure 5. Titanium dioxide photocatalytic ceramics were used on the solid surface, but the experiment was carried out in the dark to prevent the photocatalytic activity from being expressed.

[0042] Experiments were conducted using two types of ceramics: one consisting of titanium dioxide only, and one supporting a needle-shaped aragonite crystal habit. Results showed that in an environment without aragonite, the survival rate after three hours was 60%, while in an environment with a needle-shaped aragonite crystal habit, the survival rate was only 19%. It is common technical knowledge that calcium carbonate in aragonite itself is not ecotoxic, so this shows that the presence of a needle-shaped aragonite crystal habit increases the bactericidal rate of E. coli, a result of the mechano-bactericidal effect of the needle-shaped crystal habit.

[0043] <Experiment demonstrating mechano-sterilization effect> We conducted an experiment to determine whether aragonite could exert its mechano-bactericidal effect even under static conditions, and the results are shown in Figure 7. The images show the surface of TiO ceramic (Figure 7, top panel) or aragonite-supported TiO ceramic (Figure 7, bottom panel) placed in a petri dish filled with approximately 5000 cfu / mL of E. coli K-12 after 16 hours of incubation. Scanning electron microscopy (SEM) revealed that in the TiO-only system, E. coli bacteria remained intact and dispersed on the surface (top left). In the aragonite-supported system, protoplasmic material was released from the cell wall puncture site (bottom left). The cell membrane was then stretched by the nanoneedles, and these membranes then formed aggregates. These aggregates eventually became the nuclei for the precipitation of the aragonite needle-like crystals shown in Figure 4. Confocal microscopy revealed that live bacteria covered the TiO surface on the TiO-only surface (top center and top right), whereas in the aragonite-supported system, the total number of bacteria was low, with relatively few live bacteria and a relatively large number of dead bacteria (bottom center and bottom right).

[0044] <Bactericidal effect under dark conditions> The closed circulation system shown in Figure 5 was used. A glass tube (300 mm diameter x 10 mm I.D.) filled with TiO ceramic or aragonite-supported TiO ceramic was connected to the closed circulation system, and 250 mL of water containing approximately 5000 cfu / mL of E. coli K-12 was circulated for 3 hours under dark conditions. The results of the subsequent determination of bacterial viability on the TiO surface (observed using a phase-contrast microscope) are shown in Figure 8. In the TiO2 ceramic-only system shown on the left in Figure 8, both live bacteria (upper left) and dead bacteria (lower left) cover the TiO2 surface, but in the aragonite-supported system shown on the right in Figure 8, the number of live bacteria (upper right) was very small, and the number of dead bacteria (lower right) was almost undetectable. If the aragonite needle-like crystal habit was simply trapping the E. coli in the flowing water, the number of bacteria on the surface (both live and dead) should be greater than on the flat TiO2 ceramic, but almost no live or dead bacteria were observed in this phase-contrast microscope observation.

[0045] The reason for this is that with a phase-contrast microscope, the protoplasm inside the bacteria is stained, causing live bacteria to emit green fluorescence and dead bacteria to emit red fluorescence, which is then observed. Because this experiment was conducted in water, as is clear from the SEM image in Figure 7, the protoplasm of dead bacteria that should have been stained dissolves into the water, leaving only a small number of live bacteria visible, making it difficult to observe the dead bacteria. Furthermore, as explained in Figure 6, the number of bacteria steadily decreased during the three-hour circulation period, which clearly indicates a mechanical sterilization effect.

[0046] <Bactericidal effect when used in combination with photocatalyst> Changes in the number of E. coli K-12 cells under dark conditions and UV light irradiation using TiO2 ceramic photocatalysts and aragonite needle-shaped habit supported ceramic photocatalysts (250 mL, flow rate 100 mL / min, UV-A intensity 2 mW / cm 2 ) is shown in Figure 9. Under dark conditions, the rate of bacterial reduction using TiO2 ceramic alone was slow (natural attrition), but the bactericidal effect of the photocatalytic action associated with UV light irradiation increased the bacterial removal rate by three times. The aragonite needle-shaped crystalline habit supported TiO2 ceramic photocatalyst showed a bacterial removal rate 1.3 times faster than that of the TiO2 ceramic photocatalyst under UV irradiation, even under dark conditions. These results show that the acicular crystal habit exhibits a processing ability based on a mechano-sterilization effect, independent of catalytic reactions. UV irradiation further increases the sterilization rate by three times. These results indicate that the sterilization effect is synergistically enhanced by supporting aragonite compared to photocatalytic sterilization using TiO2 alone.

[0047] Furthermore, these surfaces were observed using a field emission scanning electron microscope (FE-SEM), which can obtain high-resolution images (Figure 10). On the reference ceramics, there was no change in the morphology of the E. coli (A), but on aragonite, most of the E. coli observed were destroyed (B), and it was rare to observe E. coli retaining their original morphology.

[0048] Although only E. coli was used in this experiment, it is possible that larger microorganisms, such as protozoan cysts, could be captured if the aragonite crystal habit becomes larger. The cysts of amoebic dysentery, a protozoan that is a worldwide drinking water problem that must be solved, are said to be about 15 microns in diameter, and it is possible that aragonite could be used to treat microorganisms larger than these bacteria. The habit size of aragonite makes it possible to capture these microorganisms, and it is thought that cysts can be removed from flowing water.

[0049] In this way, under bright conditions where photocatalytic activity is expressed, by using a structure with aragonite needle-like crystal habits and a photocatalytic material on the solid surface, it is possible to simultaneously exert the bactericidal activity due to the photocatalytic effect. For example, by using titanium oxide, which is inexpensive, highly active, and harmless, as the photocatalytic material, it is possible to sterilize water by photocatalysis during good weather during the day, and to sterilize using the needle-like structure during bad weather and at night.

[0050] By introducing a photocatalytic water treatment device using the structure of the present invention to rural communities in developing countries that do not have access to safe water, it will be possible to supply safe water using only sunlight irradiation. Furthermore, not only in developing countries but also in Japan, when the supply of drinking water is cut off during a disaster, it will be possible to purify river water, leftover bath water, etc. to a drinkable level.

[0051] (Addendum) (Note 1) A structure in which nano- to micron-sized needle-shaped crystals or needle-shaped crystal habits of inorganic compound ceramics that are insoluble in aqueous solutions and do not contain elements that are toxic to living organisms are precipitated or supported on the surface of a solid substrate. (Appendix 2) The structure according to (1) above, wherein the inorganic compound ceramic is a calcium-containing compound. (Appendix 3) The structure according to (1) or (2) above, wherein the calcium-containing compound is calcium carbonate, apatite, or calcium silicate. (Appendix 4) A structure according to any one of (1) to (3) above, wherein the solid surface is a surface having an inorganic compound ceramic that is insoluble in an aqueous solution system and does not contain elements that are toxic to living organisms. (Appendix 5) A structure according to any one of (1) to (4) above, characterized in that the needle-shaped crystals and needle-shaped crystal habit have a bactericidal effect of entangling bacteria floating in water and / or stimulating and / or destroying bacterial cell membranes. (Appendix 6) The structure according to any one of (1) to (5) above, wherein the solid surface has photocatalytic activity. (Appendix 7) The structure according to (6) above, which can decompose and remove bacteria by photoexcitation. (Appendix 8) The structure according to any one of (1) to (7) above, wherein the needle-like crystals and needle-like crystal habit damaged by the water flow are restored by passing natural water containing calcium ions through the structure. (Appendix 9) A method for sterilizing and purifying water, characterized by placing the structure according to any one of (1) to (8) above in water.

Claims

1. A structure for water purification, comprising: a substrate; and needle-like crystals or needle-like crystal habits deposited on or supported on a solid surface of the substrate; the solid surface is made of titanium oxide; The needle-shaped crystals or needle-shaped crystal habits are aragonite structures made of calcium carbonate.

2. 2. The structure according to claim 1, wherein the substrate is made of titanium oxide.

3. The structure according to claim 1 , wherein the substrate is made of a photocatalytic material other than titanium oxide.

4. A method for manufacturing a water purification structure comprising a substrate and needle-like crystals or needle-like crystal habits precipitated or supported on a solid surface of the substrate, The method includes a step of passing an aqueous solution containing bicarbonate ions and calcium ions through the substrate made of a photocatalyst, and depositing or supporting needle-like crystals or needle-like crystal habits on the solid surface of the substrate, the solid surface is made of titanium oxide; A method for producing a structure for water purification, wherein the needle-like crystals or needle-like crystal habit are aragonite made of calcium carbonate.

5. A method for manufacturing a water purification structure comprising a substrate and needle-like crystals or needle-like crystal habits precipitated or supported on a solid surface of the substrate, The method comprises a step of passing an aqueous solution containing bicarbonate ions and strontium ions, and sodium ions, potassium ions, or magnesium ions, and a mixed solution of calcium chloride or calcium sulfate through the substrate made of a photocatalyst, thereby precipitating or supporting needle-like crystals or needle-like crystal habits on the solid surface of the substrate, the solid surface is made of titanium oxide; A method for producing a structure for water purification, wherein the needle-like crystals or needle-like crystal habit are aragonite made of calcium carbonate.

6. A step of placing the structure according to any one of claims 1 to 3 in a flow path of water containing fungi or bacteria; flowing the water through the flow path; physically killing the fungi or bacteria by the mechanobactericidal effect of the needle-shaped crystals or needle-shaped crystal habit; and irradiating the solid surface with light to decompose and remove the fungi or bacteria by the photocatalytic action of the solid surface.

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