Nanoplastic removal method and nanoplastic adsorbent

Abstract

This invention provides a practical method for efficiently removing nanoplastics, and an adsorbent for adsorbing nanoplastics. [Solution] The method involves adsorbing nanoplastics onto an adsorbent under flow conditions, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 A method for removing nanoplastics that is 1 / g or more is provided.

Description

[Technical Field]

[0001] This invention relates to a method for removing nanoplastics and an adsorbent for adsorbing nanoplastics. [Background technology]

[0002] In recent years, the impact of microplastics and nanoplastics on living organisms has become a growing concern. These tiny plastics have already been detected in the bodies of plankton and marine organisms, and as a result of concentration through the food chain, microplastics are accumulating in fish, raising suspicions that we, who eat seafood, may be unknowingly ingesting these tiny plastics. Furthermore, it is suspected that even smaller nanoplastics float in the atmosphere and are inhaled through respiration, as well as being present in beverages and ingested. In fact, recent studies have detected nanoplastics in human blood, raising concerns about potential health risks.

[0003] While the definitions of microplastics and nanoplastics are not clearly defined, they are generally distinguished by size: microplastics are defined as particles between 100 nm and 5 mm, and nanoplastics as particles between 100 nm and 5 mm. Microplastics can be removed by general filters, but nanoplastics cannot be removed by commonly used nets and filters, or their removal efficiency is poor. Patent Document 1 discloses a method for removing nanoplastics using activated carbon as an adsorbent. Non-Patent Document 1 describes research results on the removal of nanoplastics using activated carbon. Non-Patent Document 2 describes research results on the removal of nanoplastics by sand filtration and activated carbon filtration.

[0004] However, the invention described in Patent Document 1 does not specifically describe how the adsorbent and the nanoplastic are brought into contact, and the method described in Patent Document 1 has a very long nanoplastic adsorption time, making it difficult to say that a practical adsorption method is disclosed. Furthermore, the technologies described in Non-Patent Documents 1 and 2 do not mention the removal of even smaller particles, such as nanoplastics with an average particle diameter D50 of 100 nm or less, which are small enough to pass through biological cell walls or intercellular spaces, and the effectiveness of removing nanoplastics with an average particle diameter D50 of 100 nm or less has not been confirmed.

[0005] In view of these challenges, the present invention aims to provide a practical method for efficiently removing nanoplastics, and an adsorbent for adsorbing nanoplastics. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Chinese Patent Application Publication No. 113998757 Specification [Non-patent literature]

[0007] [Non-Patent Document 1] Science of the Total Environment, 2021, Vol.791, 148175 [Non-Patent Document 2] Journal of Hazardous Materials, 2022, Vol.436, 129011 [Overview of the project]

[0008] The inventors of the present invention diligently studied to solve the above problems and found that the above problems can be solved by a method having the following configuration. Based on this finding, they further studied and completed the present invention.

[0009] In other words, a nanoplastic removal method according to one aspect of the present invention includes adsorbing nanoplastics onto an adsorbent under flow conditions, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 It is 1 / g or more.

[0010] Another aspect of the present invention relates to a method for removing nanoplastics, comprising adsorbing nanoplastics onto an adsorbent under liquid flow, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 It is 1 / g or more.

[0011] An adsorbent for adsorbing nanoplastics according to a further aspect of the present invention has a specific surface area of ​​700 m² 2 The nanoplastic has a particle size of 100 nm or less, is hydrophobic, and has an average particle diameter D50 of 100 nm or less. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described below, but the present invention is not limited thereto.

[0013] The nanoplastic removal method according to this embodiment includes adsorbing nanoplastics onto an adsorbent under flowing or liquid flow conditions, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 The value is 1 / g or more. This configuration provides a practical method for efficiently removing the nanoplastics.

[0014] <Nanoplastics> In this embodiment, the nanoplastics to be adsorbed and removed are not particularly limited as long as the average particle diameter D50 of the nanoplastics is 100 nm or less. The nanoplastics include, for example, those derived from synthetic resins such as olefin-based ones like polyethylene and polypropylene, ester-based ones like polyethylene terephthalate and polybutylene terephthalate, nylon-based ones like 6-nylon and 6,6-nylon, acrylic-based ones like PMMA, and composite-based ones like ABS. These may be single or a plurality of types may coexist.

[0015] In this embodiment, the average particle diameter D50 means the 50% particle diameter of the volume-based cumulative distribution, and the numerical value of the average particle diameter D50 of the nanoplastics is a value calculated by methods such as the disk centrifugal sedimentation light transmission method, dynamic light scattering method, TEM (transmission electron microscope), etc.

[0016] <Adsorbent> Next, the adsorbent used in the nanoplastics removal method of this embodiment will be described. The adsorbent can adsorb the nanoplastics and is not particularly limited as long as the specific surface area is 700 m 2 / g or more.

[0017] Examples of the adsorbent include activated carbon, mesoporous carbon, zeolite, mesoporous silica, silica gel, porous metal complexes, metal porous bodies, etc. Among these, the adsorbent is preferably activated carbon.

[0018] The specific surface area of the adsorbent may be a specific surface area sufficient to show an interaction with the nanoplastics and is not particularly limited as long as it is 700 m 2 / g or more, but preferably 1155 m 2 / g to 4000 m 2 / g, more preferably 1200 m 2 / g to 3000 m 2 / g, and even more preferably 1250 m 2 / g to 2500 m 2 / g. When the specific surface area is 1155 m 2By having a specific surface area of ​​4000 m² or more, nanoplastics can be sufficiently adsorbed, and nanoplastics can be removed more reliably and efficiently. 2 By having a particle size of less than / g, the adsorbent does not become micronized even under flowing or liquid conditions, and can more reliably possess sufficient mechanical strength.

[0019] In this embodiment, the specific surface area refers to the BET specific surface area calculated by the nitrogen adsorption method. This specific surface area can be measured by known methods, such as by performing nitrogen adsorption isotherm measurements and calculating it from the obtained adsorption isotherms. More specifically, it can be measured by the method described in the examples.

[0020] The average particle size D50 of the adsorbent used to remove nanoplastics under flow conditions is not particularly limited, but is preferably 0.1 μm to 1000 μm, more preferably 1 μm to 500 μm, even more preferably 10 μm to 200 μm, and particularly preferably 10 μm to 100 μm. Having an average particle size D50 of 1000 μm or less has the advantage of improving contact efficiency with the adsorbate under flow conditions, thus providing a method for efficiently removing nanoplastics. Having an average particle size D50 of 0.1 μm or more has the advantage of improving the handling of the adsorbent.

[0021] The average particle size D50 of the adsorbent used to remove nanoplastics under liquid flow is not particularly limited, but is preferably 0.1 μm to 1000 μm, more preferably 1 μm to 500 μm, even more preferably 10 μm to 200 μm, and particularly preferably 10 μm to 100 μm. Having an average particle size D50 of 1000 μm or less offers the advantage of providing a method for efficiently removing nanoplastics even under conditions of short contact time with the adsorbate, such as under liquid flow. Having an average particle size D50 of 0.1 μm or more offers the advantage of providing a method for efficiently removing nanoplastics without increasing the liquid flow resistance under liquid flow.

[0022] In this embodiment, the average particle size D50 of the adsorbent is a value calculated from the particle size distribution (cumulative distribution) measured by laser diffraction and scattering, and can be measured, for example, by a wet particle size distribution analyzer (Microtrac MT3200) manufactured by Microtrac-Bell.

[0023] The adsorbent is preferably hydrophobic. This configuration has the advantage of increasing the affinity between the adsorbent and the nanoplastic, making it easier for the nanoplastic to be adsorbed onto the adsorbent. In this embodiment, "hydrophobic" refers not only to the hydrophobicity of the surface of the adsorbent, but also to the hydrophobicity of the adsorbent as a whole, including the inner surface of the pores.

[0024] In order to exhibit hydrophobicity, the amount of functional groups in the adsorbent, as measured by the Boehm method, is preferably 0.01 meq / g to 1.2 meq / g, more preferably 0.05 meq / g to 1.0 meq / g, and even more preferably 0.1 meq / g to 0.8 meq / g. When the amount of functional groups is 1.2 meq / g or less, the hydrophobic interaction between the adsorbent and the nanoplastic can be more reliably exhibited, and the nanoplastic can be efficiently removed. When the amount of functional groups is 0.01 meq / g or more, there is the advantage that water penetrates the adsorbent sufficiently, and the nanoplastic can be efficiently removed.

[0025] The Boehm method is a well-known acid-base titration method, and its details are described in the examples below. In this Boehm method, the amount of functional groups can be determined as the total milliequivalent (meq) of acidic functional groups per unit mass (g) of the adsorbent.

[0026] (Method of manufacturing adsorbent material) The method for manufacturing the adsorbent used in the nanoplastic removal method of this embodiment is not particularly limited, but for example, a method for manufacturing the adsorbent when it is activated carbon is given below as an example.

[0027] Examples of raw materials for activated carbon include carbonaceous materials. While not particularly limited, examples of carbonaceous materials include plant-based carbonaceous materials (e.g., wood, wood shavings, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds, pulp manufacturing by-products, lignin, molasses, and other plant-derived materials), mineral-based carbonaceous materials (e.g., peat, lignite, brown coal, bituminous coal, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, petroleum pitch, and other mineral-derived materials), synthetic resin-based carbonaceous materials (e.g., synthetic resin-derived materials such as phenolic resin, polyvinylidene chloride, and acrylic resin), and natural fiber-based carbonaceous materials (e.g., natural fiber-derived materials such as cellulose and regenerated fiber such as rayon). These carbonaceous materials may be used individually or in combination of two or more types.

[0028] Of these carbonaceous materials, coconut shell or phenolic resin is preferred from the viewpoint of easily obtaining a high specific surface area.

[0029] These carbonaceous materials may be used after carbonization treatment. If carbonization treatment is necessary, the carbonaceous materials can usually be carbonized in an environment that is isolated from oxygen or air, at a temperature of, for example, 400°C to 800°C, preferably 500°C to 800°C, and more preferably 550°C to 750°C. After that, particle size adjustment may be performed as needed.

[0030] The carbonaceous material or carbonized carbonaceous material described above is subjected to an activation treatment. The activation treatment is a process that forms pores on the surface of the carbonaceous material, transforming it into a porous material called activated carbon. The activation treatment can be carried out by methods common in the art and is not particularly limited, but mainly two types of treatment methods can be mentioned: gas activation treatment or chemical activation treatment. Of these, when used for nanoplastic removal, gas activation treatment is preferred from the viewpoint of leaving less impurity residue.

[0031] The gas activation treatment (hereinafter also referred to as "primary gas activation treatment" to distinguish it from the secondary gas activation treatment described later) is a treatment in which a carbonaceous material is heated in the presence of steam, carbon dioxide, air, oxygen, combustion gas, or a mixture thereof, using, for example, a fluidized bed, a multi-stage furnace, or a rotary furnace. The heating temperature is not particularly limited and can be appropriately adjusted, for example, to achieve the desired specific surface area of ​​the activated carbon, preferably at a temperature of 700°C to 1100°C, more preferably 800°C to 980°C, and even more preferably at a temperature of about 850°C to 950°C. The activation time, heating rate, gas partial pressure, and gas supply amount are not particularly limited and can be adjusted according to the type, shape, and size of the selected carbonaceous material, for example, to achieve the desired specific surface area of ​​the activated carbon (700m²). 2 The gas partial pressure should be adjusted as appropriate so that it is 1 / g or more. Considering safety and reactivity, it is preferable to use a water vapor-containing gas with a water vapor partial pressure of 10% to 40% for the gas activation treatment. The total gas pressure is 1 atmosphere (approximately 0.1 MPa). The gas supply rate is preferably 0.1 L / min to 50 L / min per 100 g of carbonaceous material, and this range allows the activation reaction to proceed more efficiently.

[0032] The activated carbon obtained by the primary gas activation treatment (hereinafter also referred to as "raw material activated carbon" to distinguish it from the activated carbon obtained after the secondary gas activation treatment) may be subjected to further gas activation treatment (secondary gas activation treatment). When performing secondary gas activation treatment, it is preferable to perform a step before the secondary gas activation treatment to reduce the potassium element in the raw material activated carbon and to include the calcium element.

[0033] Methods for reducing potassium content are not particularly limited and include, for example, washing with an acid-containing washing solution and replacing potassium components with other components (e.g., calcium components) through ion exchange.

[0034] The method for incorporating the calcium element is not particularly limited, and examples include contacting a calcium element source with the activated carbon raw material in which the potassium element has been reduced. As a result, the calcium element source adheres to the surface and pores of the activated carbon raw material. The calcium element content in the activated carbon raw material containing the calcium element is preferably 0.1% to 5% by mass. The calcium element content can be calculated by the method described in the examples below.

[0035] The method for bringing the calcium element source into contact with the activated carbon is not particularly limited, and examples include spraying an aqueous solution of the calcium element source onto the activated carbon material, immersing the activated carbon material in a solution of the calcium element source, and mixing the activated carbon material with the calcium element source. Among these, the method of spraying an aqueous solution of the calcium element source onto the activated carbon material is preferred because it makes it easy to uniformly adhere the calcium element source to the surface and pores of the activated carbon material.

[0036] The calcium element source is not particularly limited, and for example, a non-water-soluble calcium compound or a water-soluble calcium compound can be used. The calcium element source can be used alone or in combination of two or more types.

[0037] The secondary gas activation treatment can be carried out in the same manner as described for the primary gas activation treatment, for example, using a fluidized bed, a multi-stage furnace, a rotary furnace, etc., within the temperature range, in the presence of steam, carbon dioxide, air, oxygen, combustion gas, or a mixture thereof.

[0038] The heating temperature, activation time, heating rate, gas partial pressure, and gas supply amount in the secondary gas activation treatment are not particularly limited and can be explained in the same way as the primary gas activation treatment described above.

[0039] The aforementioned chemical activation treatment can be carried out by a known method, for example, of mixing an activator such as zinc chloride, calcium chloride, phosphoric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide with a carbonaceous material and heating it under an inert gas atmosphere. The inert gas is not particularly limited, but examples include nitrogen, argon, helium, or mixtures thereof.

[0040] The aforementioned drug activation treatment can be carried out, for example, by the method described in International Publication No. 2020 / 179745.

[0041] The activated carbon is preferably in a hydrophobic state or has been subjected to a hydrophobic treatment. The method for making the activated carbon hydrophobic is not particularly limited, and examples include cooling the activated carbon to a low temperature at the end of the activation treatment and removing the activated carbon in order to suppress oxidation of the activated carbon in the activation treatment described above, or switching the supply gas to a nitrogen partial pressure of about 1 atmosphere at a total pressure of 1 atmosphere (i.e., under a nitrogen atmosphere) at the end of the activation treatment and removing the activated carbon. The method for hydrophobic treatment of the activated carbon is not particularly limited, and examples include heat treatment of the activated carbon under a reducing gas atmosphere or heat treatment under an inert gas atmosphere. Here, the reducing gas is, for example, hydrocarbon gases such as hydrogen, carbon monoxide, and methane, and the inert gas is, for example, argon, nitrogen, and helium.

[0042] The activated carbon may be washed and dried as needed. Specifically, for example, if plant-based carbonaceous materials such as coconut shells or mineral-based carbonaceous materials containing impurities such as alkali metals, alkaline earth metals, and transition metals are used as raw materials for activated carbon, it may be washed as needed to remove ash, chemicals, etc. Mineral acids or water can be used for washing, and hydrochloric acid is preferred as the mineral acid because it has high washing efficiency.

[0043] The activated carbon may be subjected to grinding and / or classification as needed. Specifically, for example, it can be subjected to grinding and / or classification to obtain a desired average particle size D50 of the activated carbon.

[0044] The aforementioned grinding process can be carried out using a grinding device commonly used for grinding activated carbon. Examples of such grinding devices include high-speed rotating mills such as erofort mills, rod mills, roller mills, hammer mills, blade mills, and pin mills, as well as ball mills and jet mills. The aforementioned classification process can be carried out using methods commonly used for classifying activated carbon, such as sieve classification, wet classification, and dry classification. Examples of wet classifiers used in the aforementioned wet classification include classifiers that utilize principles such as gravity classification, inertia classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers used in the aforementioned dry classification include classifiers that utilize principles such as sedimentation classification, mechanical classification, and centrifugal classification.

[0045] The activated carbon obtained through this process, or commercially available activated carbon, may be in any form, such as powder, particulate, fibrous (thread, woven cloth, felt), pellet, or spherical, and can be appropriately selected depending on the application. Of these forms, powder is preferred from the viewpoint of high adsorption performance per unit volume.

[0046] <Methods for removing nanoplastics> The nanoplastic removal method according to this embodiment includes adsorbing the nanoplastic onto the adsorbent under flow conditions. The term "under flow conditions" is not particularly limited and can be any condition under which the adsorbent exhibits fluidity. For example, a state in which the adsorbent is added to a liquid containing the nanoplastic and shaken can be considered to be under flow conditions.

[0047] The fluidity, or movement speed, of the adsorbent under the aforementioned flow conditions is not particularly limited, but is usually in the range of 0.1 cm / s to 100 m / s, preferably 0.5 cm / s to 90 m / s, and more preferably 1 cm / s to 50 m / s. If the movement speed is too slow, the diffusion rate of the adsorbate will be slower than the adsorption rate, so the supply of adsorbate may not keep up, and sufficient adsorption force may not be achieved. If the movement speed is too fast, the adsorption rate will be slower than the rate at which the adsorbate passes over the surface of the adsorbent, making it difficult to ensure a sufficient amount of adsorption.

[0048] Furthermore, the nanoplastic removal method according to this embodiment includes adsorbing the nanoplastic onto the adsorbent under liquid flow. The condition under liquid flow is not particularly limited, and is sufficient as long as the liquid containing the nanoplastic is fluid and the adsorbent is fixed. For example, when the adsorbent is filled into a packed bed or molded into a filter using a binder, the state in which the liquid containing the nanoplastic is in contact with the adsorbent can be said to be under liquid flow.

[0049] The fluidity, or migration speed, of the liquid containing the nanoplastic under the aforementioned liquid flow is not particularly limited, and is usually in the range of 0.1 cm / s to 100 m / s, preferably 0.5 cm / s to 90 m / s, and more preferably 1 cm / s to 50 m / s. If the migration speed is too slow, the diffusion rate of the adsorbate will be slower than the adsorption rate, so the supply of adsorbate may not keep up, and sufficient adsorption force may not be achieved. If the migration speed is too fast, the adsorption rate will be slower than the rate at which the adsorbate passes over the surface of the adsorbent, making it difficult to ensure a sufficient amount of adsorption.

[0050] In this embodiment, the liquid containing the nanoplastic is a liquid that has little effect on the human body, such as water or ethanol. The liquid may contain impurities. These impurities are not particularly limited, and for example, the liquid may contain gaseous substances at room temperature such as carbon dioxide, or metal salts such as sodium chloride or potassium chloride.

[0051] In this embodiment, the temperature for removing nanoplastics is not particularly limited and depends on the operating pressure, but is usually in the range of 0°C to 100°C at atmospheric pressure, preferably in the range of 1°C to 90°C, and more preferably in the range of 4°C to 80°C.

[0052] In this embodiment, the pressure used to remove nanoplastics can be either reduced pressure or increased pressure. Pressures that are too low are undesirable because they reduce the adsorption force on the adsorbent surface due to the vaporization of the liquid, while pressures that are too high are undesirable because they require special equipment. Therefore, the process is usually carried out in the range of 0.1 to 5 atmospheres, preferably in the range of 0.5 to 3 atmospheres.

[0053] Preferably, the amount of nanoplastic removed per gram of the adsorbent is 0.45 mg / g-adsorbent or more, and more preferably 0.5 mg / g-adsorbent or more.

[0054] As described above, this specification discloses various aspects of technology, the main technologies among them are summarized below.

[0055] The first embodiment of the nanoplastic removal method includes adsorbing nanoplastics onto an adsorbent under flow conditions, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 The value is 1 / g or more. This configuration provides a practical method for efficiently removing the nanoplastics.

[0056] A second embodiment of the nanoplastic removal method includes adsorbing nanoplastics onto an adsorbent under liquid flow, wherein the average particle size D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m². 2 The value is 1 / g or more. This configuration provides a practical method for efficiently removing the nanoplastics.

[0057] In the third embodiment, the nanoplastic removal method is the nanoplastic removal method in the first or second embodiment, wherein the adsorbent is activated carbon. With this configuration, a practical method that can efficiently remove the nanoplastic can be provided more reliably.

[0058] The nanoplastic removal method in the fourth embodiment is the nanoplastic removal method in any one of the first to third embodiments wherein the average particle size D50 of the adsorbent is 1000 μm or less. With this configuration, it is possible to provide a method that can efficiently remove nanoplastics even under conditions where the contact time between the liquid containing the nanoplastics and the adsorbent is short, such as under liquid flow conditions.

[0059] The fifth embodiment of the nanoplastic removal method is the nanoplastic removal method in any one of the first to fourth embodiments, wherein the adsorbent is hydrophobic. With this configuration, the affinity between the adsorbent and the nanoplastic is increased, and the nanoplastic is more easily adsorbed onto the adsorbent. Therefore, a practical method that can efficiently remove the nanoplastic can be provided more reliably.

[0060] The nanoplastic removal method in the sixth embodiment is a nanoplastic removal method in any one of the first to fifth embodiments wherein the amount of functional groups of the adsorbent, as measured by the Boehm method, is 1.2 meq / g or less. With this configuration, it is possible to more reliably exert the hydrophobic interaction between the adsorbent and the nanoplastic. Therefore, a practical method that can efficiently remove the nanoplastic can be provided more reliably.

[0061] The adsorbent for adsorbing nanoplastics in the seventh embodiment has a specific surface area of ​​700 m² 2 The nanoplastic has a particle size of 100 nm or less, is hydrophobic, and has an average particle size D50 of 100 nm or less. With this configuration, the affinity between the adsorbent and the nanoplastic is increased, and the nanoplastic is easily adsorbed onto the adsorbent, so that the nanoplastic can be removed efficiently.

[0062] The adsorbent for adsorbing nanoplastics in the eighth embodiment is the adsorbent for adsorbing nanoplastics in the seventh embodiment, wherein the adsorbent has a functional group content of 1.2 meq / g or less as measured by the Boehm method. This configuration makes it possible to more reliably exert hydrophobic interactions between the adsorbent and the nanoplastic, and has the advantage of efficiently removing the nanoplastic. [Examples]

[0063] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0064] The average particle size D50, specific surface area, and functional group content of the adsorbent described later were measured as follows.

[0065] <Method for measuring adsorbents> [Average particle diameter D50] A dispersion was prepared by mixing the adsorbent to be measured with a surfactant and ion-exchanged water. The average particle size D50 of the adsorbent was measured by absorption using a laser diffraction / scattering particle size distribution analyzer (Microtrac-Bell "MT3200"). The concentration of the dispersion was adjusted to fall within the measurement concentration range displayed by the instrument. Polyoxyethylene (10) octylphenyl ether, manufactured by Wako Pure Chemical Industries, Ltd., was used as the surfactant during dispersion preparation, and an appropriate amount was added to avoid generating bubbles or other issues that could affect the measurement. The analytical conditions are shown below.

[0066] (Analysis conditions) Number of measurements: 1 Measurement time: 30 seconds Distribution display; volume Particle size classification; standard Calculation mode; MT3000 Solvent name; WATER Upper measurement limit: 1408μm, lower measurement limit: 0.243μm Remaining ratio: 0.00 Passage ratio: 0.00 Residual ratio setting; disabled Particle permeability; absorption Particle refractive index; N / A Particle shape;N / A Solvent refractive index: 1.333 DV value: 0.0500~0.2000 Transmittance (TR);0.730~0.920 Extended filter; disabled Flow rate: 50% Ultrasonic output: 40W Ultrasound duration: 180 seconds The average particle diameter D50 was defined as the particle size at which the cumulative volume-based distribution obtained from particle size distribution measurements reached 50%.

[0067] [Specific surface area] Using a BELSORP-mini manufactured by Microtrac-Bell Co., Ltd., the adsorbent to be measured was heated at 300°C for 3 hours under a nitrogen stream (nitrogen flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the adsorbent at 77K was measured. From the obtained adsorption isotherms, a multipoint analysis was performed using the BET formula, and the specific surface area of ​​the adsorbent was calculated from the straight line in the relative pressure region P / P0 = 0.01 to 0.1 of the obtained curve.

[0068] [Functional group amount] The amount of surface functional groups in the adsorbent was measured by a known hydrochloric acid titration method based on H.P. Boehm, Advan. Catal., 1966, 16, 179, etc. Specifically, first, a 0.1N ethanol solution was prepared as the measurement solution using sodium ethoxide manufactured by Kojun Chemical Laboratory Co., Ltd. 0.5g of the adsorbent to be measured was added to 25mL of this measurement solution and stirred at 25°C for 24 hours. After stirring, the measurement solution and adsorbent were separated by centrifugation, and 10mL of the measurement solution was taken and neutralized by titration with 0.1N hydrochloric acid using Metrohm AG's "888Titrando" in Switzerland, with the titration endpoint being the point at which the pH becomes 4.0, to determine the sample titration volume. Meanwhile, a blank test was performed with a solution without the sample, and the blank titration volume was also determined, and the amount of surface functional groups was calculated using the following formula (1).

[0069] Surface functional group content (meq / g) = {Blank titration volume (mL) - Sample titration volume (mL)} × 0.1 × f (hydrochloride factor) / Weight of adsorbent used (g) × 25 (mL) / 10 (mL) (1)

[0070] <Adsorbent material> The adsorbent used in this embodiment is as follows:

[0071] [Adsorbent 1] Carbonaceous raw material was bituminous coal, and a carbonized product was obtained by carbonization at 650°C. 600g of the obtained carbonized product was placed in a furnace, and a mixed gas with a partial pressure of 15% water vapor, 11% carbon dioxide, and 74% nitrogen was supplied to the furnace at a total gas pressure of 1 atmosphere and a flow rate of 80 L / min. The product was activated at 880°C for 3 hours. After that, the supplied gas was switched to a gas with a partial pressure of 100% nitrogen, and the product was treated at 880°C for 1 hour. The resulting activated product was washed in 1N hydrochloric acid, desalted using deionized water, and then dried at 120°C. The resulting dried product was sieved through a 10-35 mesh sieve (JIS standard) to obtain adsorbent 1.

[0072] [Adsorbent material 2] Adsorbent 1 was crushed using a ball mill to obtain powdered adsorbent 2 with a D50 of 49.3 μm.

[0073] [Adsorbent material 3] Char made from coconut shells of the Philippines was fed into a rotary kiln, and activation treatment was carried out at 850°C by supplying propane combustion gas and steam to achieve a water vapor partial pressure of 35%. The specific surface area of ​​the resulting activated carbon was 1141 m². 2 It was / g.

[0074] The raw activated carbon was washed in 0.3N hydrochloric acid, desalted using deionized water, and then dried at 120°C. Next, 500g of the obtained washed activated carbon was sprayed with an aqueous calcium nitrate solution (23g calcium nitrate tetrahydrate, 117g deionized water), and then dried in a 120°C dryer for 5-7 hours. The calcium element content of the obtained calcium element-containing activated carbon was measured as follows and found to be 0.8% by mass.

[0075] (Calcium element content) First, a calibration curve was created for the potassium and calcium content of standard solutions of known concentrations.

[0076] Next, the raw activated carbon, which had been pulverized to have an average particle size of 20 μm or less, was dried at 115 ± 5°C for 3 hours, and then 0.1 g was placed in a designated container. To this container, 10 mL of nitric acid (60.0-62.0% by mass) was added and mixed, and then the sample was pretreated at 210°C for 1 hour using a microwave sample pretreatment device (MARS 6, manufactured by CEM Japan Co., Ltd.) to decompose the raw activated carbon.

[0077] The obtained solution was removed, and deionized water was added to make a total volume of 200 mL to prepare the measurement solution. This solution was then analyzed using a multi-type ICP emission spectrometer (Shimadzu Corporation "ICPE-9820"). The concentrations of metal elements were determined from the obtained values ​​and the created calibration curve, and the calcium content was determined using the following formula (2).

[0078] Calcium element content (mass%) = ((Calcium element concentration [mg / L] × 10) -3 (×0.2[L]) / (Mass of raw activated carbon [g]))×100 (2)

[0079] Next, 450 g of the obtained calcium-containing activated carbon was placed in a fluidized bed furnace, and a mixed gas with a partial pressure of 15% water vapor, 11% carbon dioxide, and 74% nitrogen was supplied to the furnace at a total gas pressure of 1 atmosphere and a flow rate of 108 L / min. Activation was carried out at an activation temperature of 920°C to achieve an activation yield of 18.5%. After that, the supply gas was switched to a gas with a partial pressure of 100% nitrogen, and the treatment was carried out at 920°C for 1 hour. The obtained activated product was washed in 1N hydrochloric acid, desalted using deionized water, and then dried at 120°C. After drying, the obtained adsorbent was pulverized in a ball mill to obtain powdered adsorbent 3 with a D50 of 58.6 μm.

[0080] [Adsorbent material 4] 576.9 g (100 parts by mass in terms of dry solids) of pine sawdust (moisture content 48% by mass) and 564.7 g (160 parts by mass in terms of dry solids (concentration 100% by mass)) of phosphoric acid aqueous solution (concentration 85% by mass) were mixed (mass ratio of phosphoric acid to sawdust (phosphoric acid / sawdust) = 1.6). The mixture was heated in a circulating dryer set to 175°C until the mass reduction rate from the standard solids content (100 parts by mass + 160 parts by mass = 260 parts by mass) was 16.0% by mass. Heating was carried out for approximately 5 hours with stirring every hour.

[0081] The resulting mixture was placed in a tube furnace, and oxidation was carried out by increasing the temperature to 300°C at a rate of 4°C / min while circulating 25 mL / min of air per gram of the mixture, and holding the temperature for 3 hours.

[0082] Next, the flowing gas was switched from air to a gas with a partial pressure of 100% nitrogen, and the mixture was heated to 500°C at a rate of 4°C / min while flowing 25 mL / min of nitrogen per gram of the mixture, and held for 2 hours to perform calcination. The resulting calcined product was washed with water, dried at 120°C, and then pulverized in a ball mill to obtain a powdered adsorbent 4 with a D50 of 55.1 μm.

[0083] [Adsorbent material 5] Char made from coconut shells of the Philippines was placed in a rotary kiln, and activation treatment was carried out at 850°C by supplying propane combustion gas and steam to achieve a water vapor partial pressure of 35%. The resulting activated product was crushed in a ball mill to obtain a powdered adsorbent 5 with a D50 of 55.3 μm.

[0084] [Adsorbent material 6] As the adsorbent 6, we used silica gel "Wako Gel LP-60" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. The D50 value was 50.2 μm.

[0085] Table 1 shows the results of measuring the specific surface area, average particle size D50, and functional group content of the above adsorbents 1 to 6 using the method described above.

[0086] [Table 1]

[0087] <Test Example 1> [Example 1] The nanoplastic removal performance of adsorbent 1 under fluid conditions was confirmed as follows.

[0088] First, 1 mL of Thermo Fisher Scientific's particle size standard particle 3020A (polystyrene guaranteed average particle size: 23 ± 2 nm standard particle, particle concentration 1 wt% dispersion) was taken, and diluted to a particle concentration of 0.001% by making up the volume in a 1 L volumetric flask using ultrapure water.

[0089] Then, 0.5 g of adsorbent 1 and 100 mL of diluted standard particle dispersion were added to a 200 mL Erlenmeyer flask, and the flask was shaken at 25°C for 24 hours (shaking amplitude 4 cm, shaking frequency 160 times).

[0090] The dispersion, shaken as described above, was filtered using a 0.45 μm "Minisart" (registered trademark) syringe filter manufactured by Sartorius, and the filtrate was collected in two 50 mL PP centrifuge tubes. The absorbance of the collected filtrate at a wavelength of approximately 262 nm was measured using a 10 mm cell with a Shimadzu UV-1800 UV absorber, and the residual polystyrene nanoparticle concentration was determined using a calibration curve created as described later. The amount of polystyrene nanoparticles removed per gram of adsorbent (mg / g - adsorbent) was then calculated. In calculating this removal amount, the particle density of polystyrene nanoparticles was assumed to be 1.05 g / mL.

[0091] As a blank test, a standard particle dispersion diluted to a polystyrene nanoparticle concentration of 0.0011% was measured for absorbance at a wavelength of approximately 262 nm using a 10 mm cell with a Shimadzu UV-1800 UV spectrometer, and the result was 0.025 (Table 2, Blank Test 1).

[0092] (Calibration curve creation method) The standard particle dispersion prepared above was diluted with ultrapure water to prepare several standard series. Next, the absorbance of each standard series was measured immediately using the same procedure as above to determine the concentration of polystyrene nanoparticles, and a calibration curve was created using their absorbances as a reference.

[0093] [Examples 2-4, Comparative Examples 1-2] The nanoplastic removal performance of adsorbents 2-6 under flow conditions was confirmed in the same manner as in Example 1, except that the adsorbents listed in Table 2 (adsorbents 2-6) were used as adsorbents.

[0094] Table 2 shows the results for absorbance around 262 nm, residual polystyrene nanoparticle concentration, and nanoplastic removal amount, which were measured and calculated as described above for Examples 1-4 and Comparative Examples 1-2.

[0095] [Table 2]

[0096] [Comparative Example 3] In the same procedure as in Example 1, the nanoplastic removal performance of adsorbent 1 under static conditions was confirmed, except that instead of shaking at 25°C for 24 hours, the material was left to stand at 25°C for 24 hours.

[0097] [Comparative Examples 4-6] In the same procedure as in Example 1, the nanoplastic removal performance of adsorbents 2, 5-6 under standing conditions was confirmed, except that instead of shaking at 25°C for 24 hours, the samples were left to stand at 25°C for 24 hours, and the adsorbents used were those listed in Table 3 (adsorbents 2, 5-6).

[0098] As a blank test, a standard particle dispersion diluted to a polystyrene nanoparticle concentration of 0.0009% was measured using a 10 mm cell with a Shimadzu UV-1800 UV absorber at a wavelength of approximately 262 nm, and the result was 0.020 (Table 3, Blank Test 2).

[0099] Table 3 shows the results for Comparative Examples 3 to 6, including absorbance around 262 nm, residual polystyrene nanoparticle concentration, and nanoplastic removal amount, which were measured and calculated using the same method as in Example 1.

[0100] [Table 3]

[0101] <Test Example 2> [Example 5] A filtration capacity test was conducted by packing 0.46 g of adsorbent 1 into a stainless steel column with a diameter of 6.2 mm, a height of 25.4 mm, and an internal volume of 0.77 mL, and confirming the nanoplastic removal performance of adsorbent 1 under liquid flow.

[0102] Specifically, the standard particle dispersion used in Example 1 (1 mL of Thermo Fisher Scientific's standard particle size 3020A (polystyrene guaranteed average particle size: 23 ± 2 nm standard particles, particle concentration 1 wt%) was taken, diluted to a particle concentration of 0.001% in a 1 L volumetric flask using ultrapure water) was used as the test water, with a flow rate of 7.2 mL / min and a space velocity (SV) of 560 hr. -1 Under these conditions, water (liquid) was passed through the column packed with adsorbent 1 in an upflow manner.

[0103] The dispersions after passing through the solution for 10 minutes, 30 minutes, and 60 minutes were filtered using a Sartorius 0.45 μm "Minisart" (registered trademark) syringe filter, and the filtrates were collected in PP centrifuge tubes (50 mL x 2). The absorbance of the collected filtrates at a wavelength of approximately 262 nm was measured using a Shimadzu UV-1800 UV spectrometer with a 10 mm cell. The residual polystyrene nanoparticle concentration was then determined using the calibration curve created in Example 1. Furthermore, the amount of polystyrene nanoparticles removed per gram of adsorbent (mg / g - adsorbent) after passing through the solution for 10 minutes, 30 minutes, and 60 minutes was calculated. In calculating the above removal amounts, the particle density of polystyrene nanoparticles was assumed to be 1.05 g / mL. Table 4 shows the results of the absorbance, residual polystyrene nanoparticle concentration, and nanoplastic particle removal amount at around 262 nm, which were measured and calculated in this manner.

[0104] [Table 4]

[0105] <Consideration> From Tables 1 and 2, the specific surface area is 700 m². 2 In Examples 1-4, where nanoplastics were removed under flow conditions using adsorbents 1-4 with an adsorbent content of 1-4 / g or more, it was found that a sufficient amount of nanoplastics could be removed.

[0106] On the other hand, the specific surface area is 700 m² 2 Even when using adsorbents 1 and 2 with a concentration of 1 / g or more, comparative examples 3 and 4, in which nanoplastic removal was performed under static conditions without shaking, were unable to remove a sufficient amount of nanoplastic.

[0107] Specific surface area of ​​700 m² 2 In Comparative Examples 1, 2, 5, and 6, where nanoplastic removal was performed using adsorbents 5-6 with a concentration of less than / g, a sufficient amount of nanoplastic could not be removed under either flowing or static conditions.

[0108] From Tables 1 and 4, the specific surface area is 700 m². 2 In Example 5, where nanoplastic removal was performed under liquid flow using adsorbent 1 with a concentration of 1 / g or more, it was found that a sufficient amount of nanoplastic could be removed.

Claims

1. This includes adsorbing nanoplastics onto an adsorbent under flow conditions. The average particle size D50 of the aforementioned nanoplastic is 100 nm or less. The specific surface area of ​​the adsorbent is 700 m². ２ A method for removing nanoplastics that is 1g or more.

2. This includes adsorbing nanoplastics onto an adsorbent under liquid flow conditions. The average particle size D50 of the aforementioned nanoplastic is 100 nm or less. The specific surface area of ​​the adsorbent is 700 m². ２ A method for removing nanoplastics that is 1g or more.

3. The nanoplastic removal method according to claim 1 or 2, wherein the adsorbent is activated carbon.

4. The method for removing nanoplastics according to claim 1 or 2, wherein the average particle size D50 of the adsorbent is 1000 μm or less.

5. The method for removing nanoplastics according to claim 1 or 2, wherein the adsorbent is hydrophobic.

6. The nanoplastic removal method according to claim 1 or 2, wherein the amount of functional groups in the adsorbent measured by the Boehm method is 1.2 meq / g or less.

7. Specific surface area is 700 m² ２ An adsorbent for adsorbing nanoplastics that are hydrophobic, have an average particle size D50 of 100 nm or less, and have a concentration of 1 / g or more.

8. The adsorbent according to claim 7, wherein the amount of functional groups measured by the Boehm method is 1.2 meq / g or less.

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