Microplastic adsorption material and method for recovering microplastics

Abstract

This invention provides a microplastic adsorbent material useful for the collection of microplastics. [Solution] This is an adsorbent material 1 that adsorbs microplastics. It contains magnetic particles 7 within a micelle structure 5 using a surfactant 3, and the hydrophilic portion 3A of the surfactant 3 has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group.

Description

[Technical Field]

[0001] This disclosure relates to a microplastic adsorption material and a method for recovering microplastics. [Background technology]

[0002] A microplastic recovery system capable of selectively recovering microplastics from environmental water has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-113587 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, this technology was not entirely sufficient for collecting microplastics, and new microplastic collection technologies were needed. This disclosure is made in view of the above circumstances and aims to provide a novel microplastic adsorption material and a method for recovering microplastics. This disclosure can be implemented in the following forms. [Means for solving the problem]

[0005] [1] An adsorbent material that adsorbs microplastics, It contains magnetic particles within a micelle structure using a surfactant. The hydrophilic portion of the surfactant is a microplastic adsorbent material having at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group. [2] An adsorbent material that adsorbs microplastics, Magnetic particles are encapsulated within a liposome structure using phospholipids. The hydrophilic portion of the phospholipid has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group, making it a microplastic adsorbent material. [3] The surfactant is a microplastic adsorbent material according to [1], having a hydrocarbon component with 10 to 22 carbon atoms. [4] The phospholipid is a hydrocarbon component having 10 to 22 carbon atoms, as described in [2], for the microplastic adsorption material. [5] The surfactant is a microplastic adsorbent material according to [1] or [3], wherein the surfactant has a composition derived from an unsaturated fatty acid. [6] The microplastic adsorbent material according to [2] or [4], wherein the phospholipid has a composition derived from an unsaturated fatty acid. [7] The magnetic particles have a diameter of 100 nm or less, as described in any of [1] to [6], for the microplastic adsorption material. [8] The magnetic particles are magnetite, the microplastic adsorption material according to any one of [1] to [6]. [9] A method for recovering microplastics, comprising using an adsorption material described in any of [1] to [8] to adsorb and recover microplastics. [Effects of the Invention]

[0006] According to this disclosure, a microplastic adsorbent material useful for the recovery of microplastics is provided. This disclosure provides a method for efficiently recovering microplastics. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of a surfactant. [Figure 2] It is a schematic diagram of the first microplastic adsorption material having a micelle structure. [Figure 3] It is a schematic diagram of a phospholipid. [Figure 4] It is a schematic diagram of the second microplastic adsorption material having a liposome structure. [Figure 5] It is a conceptual diagram explaining the cleaning of magnetic particles. [Figure 6] It is a conceptual diagram explaining the manufacturing method of the first microplastic adsorption material. [Figure 7] It is a conceptual diagram explaining the manufacturing method of a liposome. [Figure 8] It is a conceptual diagram explaining the manufacturing method of the second microplastic adsorption material. [Figure 9] It is a conceptual diagram explaining the function and effect of the first microplastic adsorption material (second microplastic adsorption material).

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the present disclosure will be described in detail. In this specification, for a description using "-" for a numerical range, unless otherwise specified, it shall include the lower limit value and the upper limit value. For example, in the description of "10 - 20", both the lower limit value "10" and the upper limit value "20" shall be included. That is, "10 - 20" has the same meaning as "10 or more and 20 or less". Also, in this specification, the upper limit value and the lower limit value of each numerical range can be arbitrarily combined.

[0009] 1. First microplastic adsorption material 1 The first microplastic adsorption material 1 is an adsorption material that adsorbs microplastics. The first microplastic adsorption material 1 encapsulates magnetic particles 7 in a micelle structure 5 using a surfactant 3 (see FIGS. 1 and 2). The hydrophilic portion 3A of the surfactant 3 has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group.

[0010] 1.1 Surfactants 3 From the viewpoint of ease of forming the micelle structure 5 and ease of compounding with the magnetic particles 7, the surfactant 3 preferably has a hydrocarbon component 3B with 10 to 22 carbon atoms. If the carbon number is too long, the surfactant 3 tends to become solid, making compounding with the magnetic particles 7 difficult. The hydrocarbon component 3B may be a saturated hydrocarbon chain or an unsaturated hydrocarbon chain. From the viewpoint of ease of forming the micelle structure 5, an unsaturated hydrocarbon chain is preferred for component 3B. As the surfactant 3, one or more selected from the group consisting of fatty acid amides having 14-24 carbon atoms and compounds represented by the following formula (1) are preferred, from the viewpoint of easily encapsulating magnetic particles 7 and enhancing microplastic adsorption capacity. [R(CH3)3N] + Cl - …(1) (R is an alkyl group with 12-18 carbon atoms.) As fatty acid amides having 14-24 carbon atoms, linoleic acid amide and oleic acid amide are preferably used, for example. As the compound represented by formula (1), for example, lauryltrimethylammonium chloride and stearyltrimethylammonium chloride are preferably used.

[0011] 1.2 Magnetic particles 7 The magnetic particles 7 are not particularly limited. Examples of magnetic particles 7 include magnetite, carbonyl iron, γ-iron oxide, manganese ferrite, manganese zinc ferrite, cobalt ferrite, nickel ferrite, and nickel zinc ferrite. Magnetite is preferred as the magnetic particle 7 from the following viewpoints: Magnetite is easy to produce because it consists of iron and oxygen, and it has a low environmental impact because it is an ore called magnetite that exists in nature. In addition, magnetite has a high magnetic flux density, which is advantageous when it comes to recovery. The diameter (particle size) of the magnetic particles 7 is not particularly limited. From the viewpoint of encapsulating the magnetic particles 7 in the micelle structure 5 (or the liposome structure 15 described later), the diameter (particle size) of the magnetic particles 7 is preferably 100 nm or less, more preferably 70 nm or less, and even more preferably 50 nm or less. The lower limit of the diameter (particle size) of the magnetic particles 7 is not particularly limited, but is usually 5 nm. The diameter is measured by observation using a transmission electron microscope.

[0012] 1.3 Method for preparing the first microplastic adsorption material 1 1.3.1 Method for preparing magnetic particles 7 For example, magnetite is prepared as follows: First, iron(II) chloride tetrahydrate and iron(III) chloride hexahydrate are completely dissolved in distilled water. At this time, they are dissolved in a molar ratio that corresponds to the composition ratio of magnetite. Specifically, iron(II) chloride:iron(III) chloride = 1:2. An aqueous ammonia solution (e.g., 28% by mass) is added to the obtained aqueous iron chloride solution and reacted for a predetermined time (e.g., 30 minutes) to obtain magnetic particles 7. To remove unreacted raw materials and by-products other than magnetite, the magnetic particles 7 are collected with a magnet, the reaction solution is removed, and then distilled water is added and the mixture is washed by ultrasonic treatment. After removing the washing solution, the same washing process is repeated. The magnetite remaining after washing is used as magnetic particles 7. Here, we will explain the concept of an example of cleaning with reference to Figure 5. The leftmost figure in Figure 5 shows the state in which magnetite magnetic particles 7 have precipitated in the solution after the reaction. After the magnetite magnetic particles 7 have precipitated, a magnet is used to attract the magnetic particles 7 and discard the excess liquid (see the second figure from the left in Figure 5). Next, distilled water is added and ultrasonic treatment is performed (see the third figure from the left in Figure 5). A magnet is used to attract the magnetic particles 7 and discard the distilled water used for cleaning (see the fourth figure from the left (rightmost) in Figure 5). In this way, the magnetite magnetic particles 7 can be cleaned.

[0013] 1.3.2 Method for preparing micelles Micelles are prepared by dissolving surfactant 3 in a solvent such as water. From the viewpoint of limiting micelle concentration, the content of surfactant 3 in the solution generally needs to be 0.2 mM or higher. Although it is necessary to calculate this for each molecular weight of the surfactant used, generally, 0.006 parts by mass or more and 0.03 parts by mass or less per 100 parts by mass of solvent is preferred, 0.007 parts by mass or more and 0.02 parts by mass or less is more preferred, and 0.008 parts by mass or more and 0.015 parts by mass or less is even more preferred. If surfactant 3 remains undissolved, it can be dissolved by raising the temperature of the aqueous solution to above the melting point of surfactant 3, or by ultrasonically treating the aqueous solution. Alternatively, it can be dissolved by mixing it with alcohol such as ethanol.

[0014] 1.3.3 Method for preparing the first microplastic adsorption material 1 A magnetic particle liquid 8 containing magnetic particles 7 and a micelle liquid 10 containing micelles are mixed to form a mixed solution 12A. By allowing the mixed solution 12A to stand, the magnetic particles 7 and micelles are compounded to obtain the first microplastic adsorbent material 1 (see Figure 6). In this case, silicone oil, heptane, or α-olefin may be used as the dispersion medium. In that case, the dispersion medium may be added to the mixed solution 12A and stirred.

[0015] 1.4 Effects of the First Microplastic Adsorption Material 1 As schematically illustrated in Figure 9, when the first microplastic adsorbent material 1 is introduced into water indicated by symbol 31, in which microplastics indicated by symbol P are dispersed, the microplastics are adsorbed onto the first microplastic adsorbent material 1. At this time, the first microplastic adsorbent material 1 may be stirred in the water. By attracting the first microplastic adsorbent material 1, which has the microplastics adsorbed onto it, to a magnet (north or south pole), the microplastics in the water can be recovered. Therefore, using the first microplastic adsorbent material 1 can improve water pollution caused by microplastics. The first microplastic adsorbent material 1 has a surfactant 3 as a component. The hydrophilic portion 3A of the surfactant 3 has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group, and can be cationized. Therefore, the first microplastic adsorbent material 1 can also be cationized and positively charged. For this reason, it is presumed that the first microplastic adsorbent material 1 can efficiently adsorb microplastics that tend to be negatively charged by utilizing electrostatic adsorption. Furthermore, if the surfactant 3, which is a component of the first microplastic adsorption material 1, has a hydrocarbon component 3B with a carbon number of 10 to 22, which has a high affinity for microplastics, the microplastic adsorption capacity will be increased. Furthermore, since the first microplastic adsorbent material 1 has a micelle structure 5, it has high dispersibility in water. Furthermore, since the first microplastic adsorption material 1 contains magnetic particles 7 within its micelle structure 5, the first microplastic adsorption material 1 that has adsorbed microplastics can be recovered using a magnet. In other words, microplastics can be easily recovered using the first microplastic adsorption material 1. Furthermore, if magnetite is used for the first microplastic adsorption material 1, it is composed of naturally occurring materials, and even if it were to leak out, the impact on the environment would be small.

[0016] 2. Second microplastic adsorption material 11 The second microplastic adsorption material 11 is an adsorption material that adsorbs microplastics. The second microplastic adsorbent material 11 encapsulates magnetic particles 7 within a liposome structure 15 using phospholipid 13 (see Figures 3 and 4). The hydrophilic portion 13A of the phospholipid 13 has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group.

[0017] 2.1 Phospholipids 13 From the viewpoints of the ease of forming the liposome structure 15 and the ease of complexing with the magnetic particles 7, the phospholipid 13 preferably has a hydrocarbon constituent 13B having 10 to 22 carbon atoms. If the number of carbon atoms is too long, the phospholipid 13 tends to become solid, making it difficult to complex with the magnetic particles 7. The hydrocarbon constituent 13B may be a saturated hydrocarbon chain or an unsaturated hydrocarbon chain. From the viewpoint of lowering the melting point of the phospholipid 13 and facilitating the formation of the liposome structure 15, the constituent 13B is preferably an unsaturated hydrocarbon chain. As the phospholipid 13, from the viewpoints of being able to easily encapsulate the magnetic particles 7 and enhancing the microplastic adsorption ability, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (C 41 H 78 NO8P, DOPE), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine (C 41 H 82 NO8P, DSPE), 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (C 37 H 74 NO8P, DPPE), and 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (C 33 H 66 NO8P, DMPE), and one or more selected from the group consisting thereof are preferred. Among these phospholipids 13, DOPE is particularly preferred because it has a structure derived from an unsaturated fatty acid and thus has a low melting point, making it easy to form liposomes.

[0018] 2.2 Magnetic particles 7 In the second microplastic adsorption material 11, regarding the "magnetic particles 7", the description in the column of the "first microplastic adsorption material 1" is applied as it is, and the description thereof is omitted. That is, the "magnetic particles 7" described in the item of the "first microplastic adsorption material 1" is applied as it is.

[0019] 2.3 Manufacturing method of the second microplastic adsorption material 11 2.3.1 Manufacturing method of magnetic particles 7 In the second microplastic adsorption material 11, the explanation for "method for producing magnetic particles 7" is the same as that given in the section for "first microplastic adsorption material 1," and is omitted from this description. In other words, the "1.3.1 Method for producing magnetic particles 7" explained in the section for "first microplastic adsorption material 1" is applied as is.

[0020] 2.3.2 Method for producing liposomes Phospholipid 13 is dissolved in an organic solvent to obtain a phospholipid solution 14. The content of phospholipid 13 in the phospholipid solution 14 needs to be calculated for each molecular weight of phospholipid used, but it is preferably 0.03 parts by mass or more and 0.2 parts by mass or less, more preferably 0.04 parts by mass or more and 0.15 parts by mass or less, and even more preferably 0.06 parts by mass or more and 0.08 parts by mass or less, per 100 parts by mass of solvent (organic solvent). This phospholipid solution 14 is placed in a container such as a test tube (see the leftmost figure in Figure 7). Only the organic solvent is evaporated in the container to form a thin film of phospholipid 13 on the inner wall of the container (see the second figure from the left in Figure 7). A predetermined amount of distilled water indicated by symbol 16 is added to the container and allowed to stand to dissolve the phospholipid 13 in the water to obtain a liposome solution 18 (see the third and fourth figures from the left in Figure 7). If phospholipid 13 is poorly soluble in water, it can be dissolved by raising the temperature of the solution to 40°C or above, or by adding cholesterol. Furthermore, the liposome solution 18 may be frozen with liquid nitrogen and thawed at room temperature multiple times to homogenize the size of the liposomes. To equalize the size of the liposomes, the liposome diameter can be made uniform by passing the solution through a filter with a desired aperture diameter.

[0021] 2.3.3 Method for preparing the second microplastic adsorption material 11 A magnetic particle solution 8 containing magnetic particles 7 and a solution containing liposomes (liposome solution 18) are mixed to form a mixture 12B. By allowing the mixture 12B to stand, the magnetic particles 7 and liposomes are compounded to obtain a second microplastic adsorbent material 11 (see Figure 8). In this case, silicone oil, heptane, or α-olefin may be used as the dispersion medium. In that case, the dispersion medium may be added to the mixture 12B and stirred.

[0022] 2.4 Effects of the second microplastic adsorption material 11 In the case of the second microplastic adsorbent material 11, microplastics in water can be recovered in the same way as the effects of the first microplastic adsorbent material 1 explained in Figure 9. In other words, using the second microplastic adsorbent material 11 can improve water pollution caused by microplastics. This effect can be explained by changing "first microplastic adsorbent material 1" to "second microplastic adsorbent material 11" in Figure 9. The second microplastic adsorbent material 11 is composed of phospholipid 13. The hydrophilic portion 13A of the phospholipid 13 has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group, and can be cationized. Therefore, the second microplastic adsorbent material 11 can also be cationized and positively charged. For this reason, it is presumed that the second microplastic adsorbent material 11 can efficiently adsorb microplastics that tend to be negatively charged by utilizing electrostatic adsorption. Furthermore, if the phospholipid 13, which is a component of the second microplastic adsorption material 11, has a hydrocarbon component 13B with a carbon number of 10 to 22, which has a high affinity for microplastics, the microplastic adsorption capacity will be increased. Furthermore, since the second microplastic adsorbent material 11 has a liposome structure 15, it has high dispersibility in water. Furthermore, since the second microplastic adsorbent material 11 contains magnetic particles 7 within its liposome structure 15, the second microplastic adsorbent material 11 that has adsorbed microplastics can be recovered using a magnet. In other words, microplastics can be easily recovered using the second microplastic adsorbent material 11. Furthermore, if magnetite is used for the second microplastic adsorption material 11, it is composed of naturally occurring materials, and even if it were to leak out, the impact on the environment would be small.

[0023] 3. Methods for collecting microplastics The method for collecting microplastics uses at least one of the first microplastic adsorbent material 1 and the second microplastic adsorbent material 11. The microplastic recovery method of this embodiment can effectively recover microplastics and effectively improve water pollution caused by microplastics. [Examples]

[0024] The present disclosure will be further illustrated by examples. Experiments 1, 2, 3, 4, and 5 are examples. Experiments 6, 7, 8, and 9 are comparative examples.

[0025] 1. Fabrication of magnetic particles Magnetite was prepared as follows: First, iron(II) chloride tetrahydrate and iron(III) chloride hexahydrate were completely dissolved in distilled water. At this time, they were dissolved in a molar ratio that corresponds to the composition ratio of magnetite. Specifically, iron(II) chloride:iron(III) chloride = 1:2. A 28% by mass aqueous ammonia solution was added to the obtained iron chloride aqueous solution and reacted for 30 minutes to obtain magnetic particles. To remove unreacted raw materials and by-products other than magnetite, the magnetic particles were collected with a magnet, the reaction solution was removed, and then distilled water was added and the particles were washed using ultrasonic treatment. After removing the washing solution, the same washing process was repeated 10 times. The magnetite remaining after washing was used as magnetic particles.

[0026] 2. Preparation of microplastic adsorption materials (1) Preparation of microplastic adsorption materials for Experiments 1 and 2 Each surfactant (raw material for micelles) listed in Table 1 was dissolved in water to prepare a micelle solution containing micelles. 20 g of water was used for every 1.86 mg of surfactant. A microplastic adsorbent material was obtained by mixing a magnetic particle liquid containing magnetite with a micelle liquid containing micelles, and allowing the mixture to stand to composite the magnetite and micelles.

[0027] [Table 1]

[0028] (2) Preparation of microplastic adsorption materials for Experiments 3, 4, and 5 A phospholipid solution was prepared by dissolving each phospholipid (the raw material for liposomes) listed in Table 1 in chloroform. 2 ml of chloroform was used for every 13 mg of phospholipid. The phospholipid solution was placed in a test tube. Only the organic solvent was evaporated within the test tube, forming a thin film of phospholipid on the inner wall. 20 g of distilled water was added to the test tube, and the mixture was allowed to stand to dissolve the phospholipid in the water, obtaining a liposome solution. A magnetic particle liquid containing magnetite and a liposome liquid containing liposomes were mixed to form a mixture, and by allowing the mixture to stand, the magnetite and liposomes were compounded to obtain a microplastic adsorbent material.

[0029] (3) Preparation of microplastic adsorption materials for Experiments 6 and 7 A phospholipid solution was prepared by dissolving each phospholipid (raw material for liposomes) listed in Table 1 in chloroform. 2 ml of chloroform was used for every 13 mg of phospholipid. The phospholipid solution was placed in a test tube. Only the organic solvent was evaporated within the test tube, forming a thin film of phospholipid on the inner wall. 20 g of distilled water was added to the test tube, and the phospholipid was dissolved in the water by standing to obtain a liposome solution. The liposomes prepared in this way were used as a microplastic adsorption material.

[0030] (4) Preparation of microplastic adsorption material for Experiment 8 Each surfactant (raw material for micelles) listed in Table 1 was dissolved in water to prepare a micelle solution containing micelles. 20 g of water was used for every 1.86 mg of surfactant. The micelles thus prepared were used as a microplastic adsorption material.

[0031] (5) Preparation of microplastic adsorption material for Experiment 9 As shown in Table 1, magnetite was used directly as the microplastic adsorption material.

[0032] 3. Evaluation Method Water (100g) was placed in a beaker, and microplastics (0.01g) were dispersed in the water. Various microplastic adsorbent materials (20g) were added to this dispersion and stirred. After stirring, a permanent magnet was brought close to the outside of the beaker, and the contents of the beaker were observed visually.

[0033] 4. Evaluation Results The evaluation results are shown in Table 1. In experiments 1, 2, 3, 4, and 5, microplastics were adsorbed onto the microplastic adsorbent materials. Furthermore, in experiments 1, 2, 3, 4, and 5, it was confirmed that the microplastic adsorbent materials that had adsorbed microplastics were attracted to magnets. Thus, microplastics could be easily recovered using these microplastic adsorbent materials. Table 1 also shows the evaluation results of the ease of micelle formation or liposome formation. When the surfactant or phospholipid had an unsaturated hydrocarbon chain, micelle formation or liposome formation was easy.

[0034] In experiments 6, 7, and 8, microplastics were adsorbed onto the microplastic adsorbent material. However, in experiments 6, 7, and 8, the microplastic adsorbent material that had adsorbed the microplastics was not attracted to the magnet. Therefore, even using these microplastic adsorbent materials, it was not easy to recover the microplastics.

[0035] In Experiment 9, microplastics were not adsorbed by the microplastic adsorption material. Therefore, even using this microplastic adsorption material, it was not easy to recover the microplastics.

[0036] 5. Effects of the Examples According to this embodiment, a microplastic adsorbent material useful for the recovery of microplastics is provided. This embodiment provides a method for efficiently recovering microplastics.

[0037] The present invention is not limited to the embodiments detailed above, and various modifications or changes are possible within the scope of the claims of the present invention. [Explanation of Symbols]

[0038] 1 ...First microplastic adsorption material 3. Surfactants 3A…part 3B...Component part 5. Micellar structure 7...magnetic particles 8...Magnetic particle liquid 10...Micelle solution 11. Second microplastic adsorption material 12A…Mixed liquid 12B…Mixed liquid 13. Phospholipids 13A...part 13B...Component part 14. Phospholipid solution 15…Liposome structure 18…Liposome solution

Claims

1. An adsorbent material that adsorbs microplastics, It contains magnetic particles within a micelle structure using a surfactant. The hydrophilic portion of the surfactant is a microplastic adsorbent material having at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group.

2. An adsorbent material that adsorbs microplastics, Magnetic particles are encapsulated within a liposome structure using phospholipids. The hydrophilic portion of the phospholipid has at least one of a primary amino group, a secondary amino group, and a quaternary ammonium group, making it a microplastic adsorbent material.

3. The microplastic adsorbent material according to claim 1, wherein the surfactant has a hydrocarbon component with 10 to 22 carbon atoms.

4. The microplastic adsorbent material according to claim 2, wherein the phospholipid has a hydrocarbon component with 10 to 22 carbon atoms.

5. The microplastic adsorbent material according to claim 1, wherein the surfactant has a composition derived from an unsaturated fatty acid.

6. The microplastic adsorbent material according to claim 2, wherein the phospholipid has a composition derived from an unsaturated fatty acid.

7. The microplastic adsorption material according to claim 1 or claim 2, wherein the magnetic particles have a diameter of 100 nm or less.

8. The microplastic adsorption material according to claim 1 or claim 2, wherein the magnetic particles are magnetite.

9. A method for recovering microplastics, comprising using the adsorption material described in claim 1 or claim 2 to adsorb and recover microplastics.

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