Nanoplastic removal method and nanoplastic adsorbent

Abstract

One aspect of the present invention pertains to a nano-plastics removal method that includes causing an adsorbent to adsorb nano-plastics under the flow of the present invention, the nano-plastics having an average particle diameter D50 of 100 nm or less, and the adsorbent having a specific surface area of 700 m 2 / g or more.

Description

[Technical Field]

[0001] The present 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 plankton and the bodies of marine organisms, and as a result of their concentration in the food chain, microplastics are accumulating in fish, raising suspicions that we who eat seafood may also be unknowingly ingesting microplastics. Furthermore, it is suspected that tiny nanoplastics float in the air and are ingested by the body when we breathe, and that they are present in beverages and ingested. In fact, recent research has detected nanoplastics in human blood, raising concerns about the potential damage to our health.

[0003] Although the definitions of microplastics and nanoplastics are unclear, they are generally divided by size, with microplastics ranging from 100 nm to 5 mm and nanoplastics up to 100 nm. Microplastics can be removed using ordinary filters, but nanoplastics cannot be removed using commonly used nets and filters, or removal efficiency is low. Patent Document 1 discloses a method for removing nanoplastics using activated carbon as an adsorbent. Non-Patent Document 1 describes the results of research on the removal of nanoplastics using activated carbon. Non-Patent Document 2 describes the results of research on the removal of nanoplastics using sand filtration and activated carbon filtration.

[0004] However, the invention described in Patent Document 1 does not specifically describe how to bring the adsorbent into contact with nanoplastics, and the method described in Patent Document 1 takes a very long time to adsorb nanoplastics, making it difficult to say that it discloses a practical adsorption method. Furthermore, the techniques described in Non-Patent Documents 1 and 2 are silent about removing smaller particles that can slip through biological cell walls or intercellular spaces, such as nanoplastics with an average particle size D50 of 100 nm or less, and have not been shown to be effective in removing nanoplastics with an average particle size D50 of 100 nm or less.

[0005] In view of these problems, the present invention aims to provide a practical nanoplastic removal method that can efficiently remove nanoplastics, and an adsorbent for adsorbing nanoplastics. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Chinese Patent Application Publication No. 113998757 [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 Summary of the Invention

[0008] As a result of intensive research to solve the above problems, the present inventors have found that the above problems can be solved by a method having the following configuration, and have completed the present invention through further research based on this finding.

[0009] That is, a method for removing nanoplastics according to one aspect of the present invention includes adsorbing nanoplastics onto an adsorbent under flow, and the nanoplastics have an average particle diameter D50 of 100 nm or less and a specific surface area of ​​the adsorbent of 700 m 2 / g or more.

[0010] Another aspect of the present invention is a method for removing nanoplastics, which comprises adsorbing nanoplastics onto an adsorbent under liquid flow, wherein the nanoplastics have an average particle diameter D50 of 100 nm or less and a specific surface area of ​​the adsorbent is 700 m 2 / g or more.

[0011] In a further aspect of the present invention, an adsorbent for adsorbing nanoplastics has a specific surface area of ​​700 m 2 / g or more, and is hydrophobic, and the average particle diameter D50 of the nanoplastic is 100 nm or less. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these.

[0013] The nanoplastic removal method according to this embodiment includes adsorbing nanoplastics onto an adsorbent under flow or liquid flow conditions, and the nanoplastics have an average particle diameter D50 of 100 nm or less, and the adsorbent has a specific surface area of ​​700 m 2 / g or more. With this configuration, a practical method for efficiently removing the nanoplastics can be provided.

[0014] <Nanoplastics> In this embodiment, the nanoplastics to be adsorbed and removed are not particularly limited as long as they have an average particle diameter D50 of 100 nm or less. Examples of the nanoplastics include those derived from synthetic resins such as olefins such as polyethylene and polypropylene, esters such as polyethylene terephthalate and polybutylene terephthalate, nylons such as 6-nylon and 6,6-nylon, acrylics such as PMMA, and composites such as ABS. These nanoplastics may be of a single type or multiple types may coexist.

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

[0016] <Adsorbent> Next, the adsorbent used in the nanoplastic removal method of this embodiment will be described. The adsorbent is capable of adsorbing the nanoplastics and has a specific surface area of ​​700 m. 2 / g or more.

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

[0018] The specific surface area of ​​the adsorbent may be sufficient to exhibit an interaction with the nanoplastics, and is not more than 700 m 2 / g or more, but is preferably 1155m 2 / g~4000m 2 / g, more preferably 1200m 2 / g~3000m 2 / g, more preferably 1250m 2 / g~2500m 2 / g. The specific surface area is 1155 m 2 / g or more, nanoplastics can be sufficiently adsorbed, and nanoplastics can be removed more reliably and efficiently. 2 / g or less, the adsorbent will not be pulverized even when flowed or subjected to liquid passage, and can more reliably have 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 a known method, such as measuring a nitrogen adsorption isotherm and calculating the specific surface area from the resulting adsorption isotherm. More specifically, it can be measured by the method described in the examples.

[0020] The average particle diameter D50 of the adsorbent used in removing nanoplastics under 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 diameter D50 of 1000 μm or less offers the advantage of improving contact efficiency with the adsorbate under flow, thereby providing a method for efficiently removing nanoplastics. Having an average particle diameter D50 of 0.1 μm or more offers the advantage of improving the handleability of the adsorbent.

[0021] The average particle diameter 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 diameter D50 of 1000 μm or less offers the advantage of providing a method that can efficiently remove nanoplastics even under conditions where the contact time with the adsorbate is short, such as under liquid flow. Having an average particle diameter D50 of 0.1 μm or more offers the advantage of providing a method that can efficiently remove nanoplastics without increasing the liquid flow resistance.

[0022] In this embodiment, the average particle diameter D50 of the adsorbent is a value calculated from the particle size distribution (cumulative distribution) measured by a laser diffraction / scattering method, and can be measured, for example, using a wet particle size distribution measuring device (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 nanoplastics, making it easier for the nanoplastics 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 entire adsorbent, including the inner surfaces of the pores.

[0024] To achieve 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. Having the amount of functional groups equal to or less than 1.2 meq / g ensures the hydrophobic interaction between the adsorbent and nanoplastics, enabling efficient removal of nanoplastics. Having the amount of functional groups equal to or greater than 0.01 meq / g allows sufficient water penetration into the adsorbent, resulting in efficient removal of nanoplastics.

[0025] The Boehm method is a known acid-base titration method, and details thereof will be described in the Examples below. This Boehm method can determine the amount of functional groups as the total milliequivalents (meq) of acidic functional groups per unit mass (g) of the adsorbent.

[0026] (Method of manufacturing adsorbent) The method for producing the adsorbent used in the nanoplastic removal method of this embodiment is not particularly limited, but for example, the following will exemplify a production method in which the adsorbent is activated carbon.

[0027] Examples of raw materials for activated carbon include carbonaceous materials. Examples of raw carbonaceous materials include, but are not limited to, plant-based carbonaceous materials (e.g., plant-derived materials such as wood, sawdust, charcoal, fruit shells such as coconut shells and walnut shells, fruit seeds, pulp manufacturing by-products, lignin, and blackstrap molasses), mineral-based carbonaceous materials (e.g., mineral-derived materials such as peat, lignite, brown coal, bituminous coal, anthracite, coke, coal tar, coal pitch, petroleum distillation residue, and petroleum pitch), 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 recycled fiber such as rayon). These carbonaceous materials may be used alone or in combination of two or more.

[0028] Of these carbonaceous materials, coconut shell or phenol resin is preferably used from the viewpoint that a large specific surface area can be easily obtained.

[0029] These carbonaceous materials may be carbonized before use. When carbonization is required, the carbonaceous materials may be carbonized, for example, at a temperature of 400°C to 800°C, preferably 500°C to 800°C, and more preferably 550°C to 750°C, in an environment where oxygen or air is blocked. Thereafter, particle size adjustment may be performed as necessary.

[0030] The above-mentioned carbonaceous material or carbonized carbonaceous material is subjected to an activation treatment. The activation treatment is a process in which pores are formed on the surface of the carbonaceous material, converting it into a porous activated carbon. The activation treatment can be carried out by a method common in the technical field and is not particularly limited, but two types of treatment methods can be mentioned: gas activation treatment and chemical activation treatment. Of these, when used for removing nanoplastics, gas activation treatment is preferred from the viewpoint of leaving less impurities behind.

[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 water vapor, carbon dioxide, air, oxygen, combustion gas, or a mixed gas thereof, using, for example, a fluidized bed, a multi-stage furnace, a rotary furnace, or the like. The heating temperature is not particularly limited and can be appropriately adjusted, for example, to obtain the desired specific surface area of ​​activated carbon. The heating temperature is preferably about 700°C to 1100°C, more preferably about 800°C to 980°C, and even more preferably 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, for example, to obtain the desired specific surface area (700 m) of activated carbon depending on the type, shape, and size of the selected carbonaceous material. 2 / g or more). In consideration of safety and reactivity, the gas partial pressure is preferably carried out using a water vapor-containing gas having a water vapor partial pressure of 10% to 40%. The total pressure of the gas is 1 atmosphere (approximately 0.1 MPa). The gas supply rate is preferably set to, for example, 0.1 L / min to 50 L / min per 100 g of carbonaceous material, and by setting the gas supply rate in this range, the activation reaction can proceed more efficiently.

[0032] The activated carbon obtained by the primary gas activation treatment (hereinafter also referred to as "raw activated carbon" to distinguish it from the activated carbon obtained after the secondary gas activation treatment) may be further subjected to a gas activation treatment (secondary gas activation treatment). When the secondary gas activation treatment is performed, it is preferable to carry out a step of reducing the potassium element in the raw activated carbon and introducing calcium element therein before the secondary gas activation treatment.

[0033] The method for reducing the potassium element is not particularly limited, and examples thereof include washing with a washing solution containing an acid, and replacing the potassium component with another component (for example, a calcium component) by ion exchange.

[0034] The method for incorporating elemental calcium is not particularly limited, and examples thereof include a method of contacting a calcium element source with the raw activated carbon having reduced potassium content. This causes the calcium element source to adhere to the surface and pores of the raw activated carbon. The calcium element content contained in the calcium-incorporated raw activated carbon is preferably 0.1% by mass to 5% by mass. The calcium element content can be calculated by the method described in the Examples below.

[0035] The method for contacting the calcium element source is not particularly limited, and examples thereof include a method of spraying an aqueous solution of the calcium element source onto the raw activated carbon, a method of immersing the raw activated carbon in a solution of the calcium element source, a method of mixing the raw activated carbon with the calcium element source, etc. Among these, the method of spraying an aqueous solution of the calcium element source onto the raw activated carbon is preferred because it allows the calcium element source to be easily and uniformly attached to the surface and pores of the raw activated carbon.

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

[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 furnace, a multi-stage furnace, a rotary furnace, or the like, within the above-mentioned temperature range, in the presence of water vapor, carbon dioxide, air, oxygen, combustion gas, or a mixture thereof.

[0038] The heating temperature, activation time, temperature rise 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 manner as in the primary gas activation treatment described above.

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

[0040] Specifically, the drug activation treatment can be carried out, for example, by the method described in WO 2020 / 179745.

[0041] The activated carbon is preferably in a hydrophobic state or has been subjected to a hydrophobic treatment. The method for hydrophobizing the activated carbon is not particularly limited. For example, in order to prevent oxidation of the activated carbon during the activation treatment described above, the activated carbon may be cooled to a low temperature at the end of the activation treatment and then removed. Alternatively, the activated carbon may be removed by switching the supply gas to a total pressure of 1 atmosphere and a nitrogen partial pressure of about 1 atmosphere (i.e., under a nitrogen atmosphere) at the end of the activation treatment. The method for hydrophobizing the activated carbon is not particularly limited. For example, the activated carbon may be heat-treated under a reducing gas atmosphere or under an inert gas atmosphere. Here, the reducing gas may be, for example, a hydrocarbon gas such as hydrogen, carbon monoxide, or methane, and the inert gas may be, for example, argon, nitrogen, or helium.

[0042] The activated carbon may be washed and dried as necessary. Specifically, when a plant-based carbonaceous material or a mineral-based carbonaceous material such as coconut shell containing impurities such as alkali metals, alkaline earth metals, and transition metals is used as the raw material for the activated carbon, washing may be performed as necessary to remove ash, chemicals, etc. A mineral acid or water is used for washing, and hydrochloric acid, which has a high washing efficiency, is preferred as the mineral acid.

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

[0044] The pulverization treatment can be carried out using a pulverizer commonly used for pulverizing activated carbon. Examples of the pulverizer include high-speed rotary mills such as an aerofoil mill, rod mill, roller mill, hammer mill, blade mill, and pin mill, as well as ball mills and jet mills. The classification treatment can be carried out by a method commonly used for classifying activated carbon, such as classification using a sieve, wet classification, or dry classification. Examples of wet classifiers used for the wet classification include classifiers that utilize the principles of gravity classification, inertia classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers used for the dry classification include classifiers that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification.

[0045] The activated carbon obtained through such a treatment or commercially available activated carbon may be in any form, such as powder, particles, fibers (threads, woven fabric (cloth), or felt), pellets, or spheres, and can be appropriately selected depending on the application. Of these forms, powder is preferred from the viewpoint of high adsorption performance per volume.

[0046] <Method for removing nanoplastics> The nanoplastic removal method according to this embodiment involves adsorbing the nanoplastics onto the adsorbent under flowing conditions. The flowing conditions are not particularly limited, and may be any conditions that allow the adsorbent to have fluidity. For example, a state in which the adsorbent is immersed in a liquid containing the nanoplastics and then shaken can be considered to be under flowing conditions.

[0047] The fluidity of the adsorbent under flow, i.e., the movement speed, 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 movement speed is too slow, the diffusion speed of the adsorbate will be slower than the adsorption speed, and the supply of the adsorbate may not keep up, resulting in insufficient adsorption power. If the movement speed is too fast, the adsorption speed will be slower than the speed at which the adsorbate passes through the surface of the adsorbent, making it difficult to ensure a sufficient amount of adsorption.

[0048] Furthermore, the nanoplastics removal method according to this embodiment includes adsorbing the nanoplastics onto the adsorbent under a liquid-flowing condition. The term "liquid-flowing condition" is not particularly limited, and may refer to conditions under which the liquid containing the nanoplastics is fluid and the adsorbent is fixed. For example, when the adsorbent is packed into a packed bed or is molded with a binder or the like to form a filter, the state in which the liquid containing the nanoplastics is in contact with the adsorbent can be said to be under a liquid-flowing condition.

[0049] The fluidity of the nanoplastic-containing liquid during the liquid flow, i.e., the movement speed, is not particularly limited and is typically 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, and the supply of the adsorbate may not keep up, resulting in insufficient adsorption power. If the movement speed is too fast, the adsorption rate will be slower than the rate at which the adsorbate passes through the surface of the adsorbent, making it difficult to ensure a sufficient amount of adsorption.

[0050] In this embodiment, the liquid containing nanoplastics is water, ethanol, or other liquids that have little effect on the human body. The liquid may contain impurities. There are no particular restrictions on the impurities. For example, the liquid may contain substances that are gaseous at room temperature, such as carbon dioxide, or metal salts, such as sodium chloride or potassium chloride.

[0051] In this embodiment, the temperature at which nanoplastics are removed is not particularly limited and depends on the pressure at which the process is carried out, but is typically carried out at atmospheric pressure in the range of 0°C to 100°C, 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 at which nanoplastics are removed may be anything from reduced pressure to increased pressure. A pressure that is too low is undesirable because the adsorption force of the adsorbent surface decreases due to vaporization of the liquid, while a pressure that is too high is undesirable because it requires special equipment. Therefore, the pressure is usually in the range of 0.1 to 5 atmospheres, preferably 0.5 to 3 atmospheres.

[0053] The amount of nanoplastics removed per gram of the adsorbent is preferably 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 the technology, but the main technologies among them are summarized below.

[0055] The method for removing nanoplastics in a first aspect includes adsorbing nanoplastics onto an adsorbent under flow conditions, wherein the nanoplastics have an average particle diameter D50 of 100 nm or less and a specific surface area of ​​the adsorbent is 700 m 2 / g or more. With this configuration, a practical method for efficiently removing the nanoplastics can be provided.

[0056] In a second aspect, the method for removing nanoplastics comprises adsorbing nanoplastics onto an adsorbent under liquid flow, wherein the average particle diameter D50 of the nanoplastics is 100 nm or less, and the specific surface area of ​​the adsorbent is 700 m 2 / g or more. With this configuration, a practical method for efficiently removing the nanoplastics can be provided.

[0057] A third aspect of the nanoplastics removal method is the same as the first or second aspect, except that the adsorbent is activated carbon. This configuration more reliably provides a practical method for efficiently removing nanoplastics.

[0058] A fourth aspect of the nanoplastics removal method is the nanoplastics removal method of any one of the first to third aspects, wherein the adsorbent has an average particle size D50 of 1000 μm or less. This configuration provides a method that can efficiently remove nanoplastics even under conditions where the contact time between the liquid containing nanoplastics and the adsorbent is short, such as when the liquid is passed through the adsorbent.

[0059] A fifth aspect of the nanoplastics removal method is the nanoplastics removal method of any one of the first to fourth aspects, wherein the adsorbent is hydrophobic. This configuration increases the affinity between the adsorbent and the nanoplastics, making it easier for the nanoplastics to be adsorbed onto the adsorbent. This makes it possible to more reliably provide a practical method for efficiently removing nanoplastics.

[0060] A sixth aspect of the nanoplastic removal method is the nanoplastic removal method of any one of the first to fifth aspects, wherein the amount of functional groups in the adsorbent measured by the Boehm method is 1.2 meq / g or less. This configuration makes it possible to more reliably exert hydrophobic interactions between the adsorbent and the nanoplastics. As a result, it is possible to more reliably provide a practical method for efficiently removing the nanoplastics.

[0061] In the seventh aspect, the adsorbent for adsorbing nanoplastics has a specific surface area of ​​700 m 2 / g or more, and the nanoplastics are hydrophobic and have an average particle size D50 of 100 nm or less. This configuration increases the affinity between the adsorbent and the nanoplastics, making it easier for the nanoplastics to be adsorbed onto the adsorbent, thereby enabling the nanoplastics to be removed efficiently.

[0062] In an eighth aspect, the adsorbent for adsorbing nanoplastics is the same as the adsorbent for adsorbing nanoplastics as in the seventh aspect, except that the amount of functional groups in the adsorbent measured by the Boehm method is 1.2 meq / g or less. This configuration has the advantage of more reliably exerting hydrophobic interactions between the adsorbent and the nanoplastics, allowing the nanoplastics to be removed efficiently. [Example]

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

[0064] The average particle diameter D50, specific surface area, and amount of functional groups of the adsorbent described below were measured as follows.

[0065] <Measuring method for adsorbents> [Average particle diameter D50] The adsorbent to be measured was mixed with a surfactant and ion-exchanged water to prepare a dispersion, and the average particle diameter D50 of the adsorbent was measured by the absorption method using a laser diffraction / scattering particle size distribution analyzer (MT3200, manufactured by Microtrac-Bell Co., Ltd.). The concentration of the dispersion was adjusted to fall within the measurement concentration range displayed by the instrument. In addition, Wako Pure Chemical Industries, Ltd.'s "Polyoxyethylene (10) Octylphenyl Ether" was used as the surfactant when preparing the dispersion, and an appropriate amount was added to prevent the generation of bubbles that would affect the measurement. The analysis 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 Remaining 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 Enhanced Filter; Disabled Flow rate: 50% Ultrasonic output: 40W Ultrasonic time: 180 seconds The particle size at which the cumulative volume distribution obtained by particle size distribution measurement reaches 50% was defined as the average particle size D50.

[0067] [Specific surface area] Using a Microtrac-Bell BELSORP-mini, 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 was measured at 77 K. The obtained adsorption isotherm was analyzed using the multipoint method according to the BET equation, and the specific surface area of ​​the adsorbent was calculated from the straight line in the relative pressure region of P / P0 = 0.01 to 0.1 of the obtained curve.

[0068] [Functional group amount] The amount of surface functional groups on the adsorbent was measured by a known hydrochloric acid titration method based on H.P. Boehm, Advan. Catal., 1966, 16, 179, etc. Specifically, a 0.1 N ethanol solution was prepared as a test solution using sodium ethoxide (Kojundo Chemical Laboratory Co., Ltd.). 0.5 g of the adsorbent to be measured was added to 25 mL of this test solution and stirred at 25°C for 24 hours. After stirring, the test solution and the adsorbent were separated by centrifugation. 10 mL of the test solution was sampled and subjected to neutralization titration using an "888 Titrando" (Metrohm, Switzerland) with 0.1 N hydrochloric acid, with the pH reaching 4.0 as the endpoint. The sample titer was then determined. A blank test was also performed using a solution containing no sample, and the blank titer was also determined. The amount of surface functional groups was calculated using the following formula (1).

[0069] Amount of surface functional groups (meq / g) = {blank titration volume (mL) - sample titration volume (mL)} × 0.1 × f (hydrochloric acid factor) / weight of adsorbent used (g) × 25 (mL) / 10 (mL) (1)

[0070] <Adsorbent> The adsorbents used in this example are as follows:

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

[0072] [Adsorbent 2] Adsorbent 1 was pulverized in a ball mill to obtain powdered adsorbent 2 having a D50 of 49.3 μm.

[0073] [Adsorbent 3] Char made from coconut shells from the Philippines was placed in a rotary kiln, and activation treatment was carried out at 850°C by supplying propane combustion gas and steam so that the steam partial pressure was 35%. The specific surface area of ​​the obtained raw activated carbon was 1141 m. 2 / g.

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

[0075] (Calcium element content) First, calibration curves for the contents of potassium and calcium elements were prepared from standard solutions of known concentrations.

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

[0077] The resulting solution was taken out, and ion-exchanged water was added to make a 200 mL measurement solution, which was then analyzed using a multi-type ICP emission spectrometer (Shimadzu Corporation, "ICPE-9820"). The metal element concentrations were calculated from the obtained values ​​and the prepared calibration curve, and the calcium element content was calculated using the following formula (2).

[0078] Calcium element content (mass%) = (calcium element concentration [mg / L] x 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 of 15% water vapor partial pressure, 11% carbon dioxide partial pressure, and 74% nitrogen partial pressure was fed into 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%. The feed gas was then switched to a gas with a 100% nitrogen partial pressure, and treatment was carried out at 920 °C for 1 hour. The obtained activated product was washed with 1N hydrochloric acid, desalted with ion-exchanged 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 4] 576.9 g (100 parts by mass based on dry solid content) of pine sawdust (moisture content: 48% by mass) was mixed with 564.7 g (160 parts by mass based on dry solid content (concentration: 100% by mass)) of an aqueous phosphoric acid solution (concentration: 85% by mass) (mass ratio of phosphoric acid to sawdust (phosphoric acid / sawdust) = 1.6). The mixture was heated in a circulation dryer set at 175°C so that the mass loss rate from the reference solid content mass (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 the temperature was raised to 300°C at a rate of 4°C / min while circulating air at a rate of 25 mL / min per 1 g of the mixture, and the mixture was maintained at this temperature for 3 hours to carry out oxidation.

[0082] Next, the flow 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 nitrogen at 25 mL / min per 1 g of the mixture, and then calcined by holding the temperature at that temperature for 2 hours. The resulting calcined product was washed with water, dried at 120°C, and then pulverized in a ball mill to obtain powdered adsorbent 4 with a D50 of 55.1 μm.

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

[0084] [Adsorbent 6] Silica gel "Wakogel LP-60" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. was used as the adsorbent 6. Note that D50=50.2 μm.

[0085] The specific surface area, average particle diameter D50, and amount of functional groups of the above adsorbents 1 to 6 were measured by the above-mentioned methods. The results are shown in Table 1.

[0086] [Table 1]

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

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

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

[0090] The dispersion thus shaken 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 was measured at a wavelength of approximately 262 nm using a 10 mm cell with a UV absorption spectrometer "UV-1800" manufactured by Shimadzu Corporation, and the residual polystyrene nanoparticle concentration was determined using a calibration curve prepared as described below. The amount of polystyrene nanoparticles removed per 1 g of adsorbent (mg / g-adsorbent) was then calculated. The particle density of polystyrene nanoparticles was assumed to be 1.05 g / mL in order to calculate the amount removed.

[0091] As a blank test, a standard particle dispersion diluted to a polystyrene nanoparticle concentration of 0.0011% was used, and the absorbance at a wavelength of around 262 nm was measured using a 10 mm cell with a UV absorption spectrometer "UV-1800" manufactured by Shimadzu Corporation, 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. The absorbance of each standard series was then measured in the same manner as above to determine the concentration of each polystyrene nanoparticle. A calibration curve was then created using these absorbances as the standard.

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

[0094] For Examples 1 to 4 and Comparative Examples 1 and 2, the absorbance at around 262 nm, the concentration of residual polystyrene nanoparticles, and the amount of nanoplastics removed, which were measured and calculated as described above, are shown in Table 2.

[0095] [Table 2]

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

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

[0098] As a blank test, the standard particle dispersion was diluted to a polystyrene nanoparticle concentration of 0.0009%, and the absorbance at a wavelength of around 262 nm was measured using a 10 mm cell with a UV absorption spectrometer "UV-1800" manufactured by Shimadzu Corporation, and the result was 0.020 (Table 3, blank test 2).

[0099] For Comparative Examples 3 to 6, the absorbance at around 262 nm, the concentration of residual polystyrene nanoparticles, and the amount of nanoplastics removed were measured and calculated using the same methods as in Example 1. Table 3 shows the results.

[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 particle size standard particle 3020A (polystyrene guaranteed average particle size: 23±2 nm standard particles, particle concentration 1 wt% dispersion) was taken, and diluted to a particle concentration of 0.001% using ultrapure water in a 1 L measuring flask) was used as test water, and the sample was collected at 7.2 mL / min and space velocity (SV) of 560 h -1 Under the conditions above, water (liquid) was passed through the column packed with Adsorbent 1 in an upflow manner.

[0103] The dispersions after 10 minutes of flow, 30 minutes of flow, and 60 minutes of flow were each filtered using a 0.45 μm "Minisart" (registered trademark) syringe filter manufactured by Sartorius, and the filtrate was collected in a PP centrifuge tube (2 x 50 mL). The collected filtrate was measured for absorbance at a wavelength of approximately 262 nm using a 10 mm cell with a UV absorption spectrometer "UV-1800" manufactured by Shimadzu Corporation. The residual polystyrene nanoparticle concentration was then determined using the calibration curve prepared in Example 1. Furthermore, the amount of polystyrene nanoparticles removed per 1 g of adsorbent (mg / g-adsorbent) after 10 minutes, 30 minutes, and 60 minutes of flow was calculated. The particle density of polystyrene nanoparticles was assumed to be 1.05 g / mL in order to calculate the amount of removal. The absorbance at around 262 nm, the concentration of residual polystyrene nanoparticles, and the amount of nanoplastic particles removed, which were measured and calculated in this manner, are shown in Table 4.

[0104] [Table 4]

[0105] <Consideration> From Tables 1 and 2, the specific surface area is 700m 2 It was found that in Examples 1 to 4, in which nanoplastics were removed under flow using adsorbents 1 to 4 with a densitometric concentration of 0.1% or more, a sufficient amount of nanoplastics could be removed.

[0106] On the other hand, the specific surface area is 700m 2 Even when Adsorbents 1 and 2 with a saturation of 0.1% or more were used, in Comparative Examples 3 and 4, in which nanoplastics removal was carried out under static conditions without shaking, a sufficient amount of nanoplastics could not be removed.

[0107] Specific surface area is 700m 2 In Comparative Examples 1, 2, 5, and 6, in which nanoplastics were removed using Adsorbents 5 and 6 with a densitometric value of less than 1 / g, a sufficient amount of nanoplastics could not be removed under either flow or static conditions.

[0108] From Tables 1 and 4, the specific surface area is 700m 2 In Example 5, in which nanoplastics were removed by passing a liquid through the adsorbent 1 having a densitometric value of 0.1% or more, it was found that a sufficient amount of nanoplastics could be removed.

Claims

1. Adsorbing nanoplastics onto an adsorbent under flow conditions; The average particle size D50 of the nanoplastic is 100 nm or less, The specific surface area of ​​the adsorbent is 700 m ２ / g or more, The adsorbent has an average particle diameter D50 of 1000 μm or less, A method for removing nanoplastics, wherein the amount of functional groups in the adsorbent measured by the Boehm method is 1.2 meq / g or less.

2. The method comprises adsorbing nanoplastics onto an adsorbent under liquid flow, The average particle size D50 of the nanoplastic is 100 nm or less, The specific surface area of ​​the adsorbent is 700 m ２ / g or more, A method for removing nanoplastics, wherein the amount of functional groups in the adsorbent measured by the Boehm method is 1.2 meq / g or less.

3. The method for removing nanoplastics according to claim 1 or 2, wherein the adsorbent is activated carbon.

4. The nanoplastics removal method according to claim 2, wherein the adsorbent has an average particle diameter D50 of 1000 μm or less.

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

6. Specific surface area is 700m ２ / g or more, the amount of functional groups measured by the Boehm method is 1.2 meq / g or less, and the polymer has hydrophobicity. An adsorbent for adsorbing nanoplastics with an average particle diameter D50 of 100 nm or less.

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