Adsorbents and adsorption columns

Abstract

To provide an adsorbent that can efficiently remove chemical components from aqueous solutions. [Solution] An adsorbent that adsorbs chemical components in an aqueous solution, wherein the adsorbent contains carbon nanotubes and the G / D ratio of the carbon nanotubes is 10 or less.

Description

[Technical Field]

[0001] This invention relates to an adsorbent and an adsorption column for adsorbing chemical components in an aqueous solution. [Background technology]

[0002] Hot spring water and industrial wastewater can contain harmful elements such as arsenic and boron, which are detrimental to human health and the environment, as well as silicon, which can cause pipe clogging. Arsenic and boron must be removed and reduced to below specified standards before use and discharge. Silicon, on the other hand, is generally not removed before use, leading to frequent pipe clogging and resulting in significant maintenance costs such as internal pipe cleaning and pipe replacement. Therefore, there has been a need for high-performance adsorbents that selectively adsorb harmful elements and other chemical components in hot spring water and industrial wastewater to purify the water quality.

[0003] For example, Patent Documents 1 and 2 propose techniques using activated carbon or chelate polymers having predetermined functional groups as adsorbents. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-258272 [Patent Document 2] Japanese Patent Publication No. 2006-167638 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the conventional technology described above had room for improvement in terms of further increasing the removal rate of chemical components from aqueous solutions.

[0006] Therefore, the present invention aims to provide an adsorbent capable of efficiently removing chemical components from an aqueous solution, and an adsorption column packed with the adsorbent. [Means for solving the problem]

[0007] The inventors diligently conducted research to achieve the above objectives. As a result, the inventors discovered that by using an adsorbent containing carbon nanotubes (hereinafter sometimes abbreviated as "CNT") having a G / D ratio of less than or equal to a predetermined value, chemical components in aqueous solutions can be removed with high efficiency, and thus completed the present invention.

[0008] In other words, the present invention aims to advantageously solve the above problems, and according to the present invention, the adsorbents [1] to [6] below and the adsorption column [7] below are provided.

[0009] [1] An adsorbent that adsorbs chemical components in an aqueous solution, wherein the adsorbent contains carbon nanotubes and the G / D ratio of the carbon nanotubes is 10 or less. In this invention, the "G / D ratio" refers to the ratio of the G-band peak intensity to the D-band peak intensity in a Raman spectrum, and can be measured using the method described in the examples of this specification. Furthermore, in the present invention, "aqueous solution" refers to "a solution mainly composed of water," and "a solution mainly composed of water" means a solution containing 50% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, of water, with the total amount of the solvent excluding solids and solutes being 100% by mass.

[0010] [2] The adsorbent according to [1] above, wherein the carbon nanotube is a surface-modified carbon nanotube.

[0011] [3] The adsorbent according to [1] or [2] above, wherein the chemical component is a metalloid or a compound thereof. In this invention, "metalloid" refers to the six elements boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te).

[0012] 〔4〕The adsorbent according to any one of the above 〔1〕 to 〔3〕, wherein the chemical component contains at least one element selected from the group consisting of boron, silicon, and arsenic.

[0013] 〔5〕The adsorbent according to any one of the above 〔1〕 to 〔4〕, wherein the aqueous solution is hot spring water.

[0014] 〔6〕The adsorbent according to any one of the above 〔1〕 to 〔5〕, which is composed of a self-supporting film containing the carbon nanotubes.

[0015] 〔7〕An adsorption column filled with the adsorbent according to any one of the above 〔1〕 to 〔6〕.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide an adsorbent capable of removing chemical components in an aqueous solution with high efficiency, and an adsorption column filled with the adsorbent.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing the boron concentration, silicon concentration, and arsenic concentration in hot spring water before and after immersion of the adsorbent. [Figure 2] It is a diagram showing the G / D ratio of various CNTs. [Figure 3] It is a diagram showing the relationship between the G / D ratio of CNT and the reduction rate of boron and silicon. [Figure 4] It is a diagram showing the influence of immersion time on the concentrations of boron and silicon. [Figure 5] It is a diagram showing the energy gain when each target component (HBO2, H2SiO3, HASO2) is adsorbed on the surface of CNT or at a one-atom vacancy of CNT.

Modes for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. The adsorbent of the present invention is used to remove chemical components from aqueous solutions, such as hot spring water and industrial wastewater.

[0019] (Adsorbent material) The adsorbent of the present invention contains at least CNTs and optionally further contains other components. Hereinafter, the adsorbent of the present invention is characterized in that the G / D ratio of CNTs is 10 or less.

[0020] Furthermore, since the adsorbent of the present invention contains CNTs with a G / D ratio of less than or equal to the above value, chemical components in aqueous solutions can be removed with high efficiency by using this adsorbent. The reason why the above effects are obtained by using the adsorbent of the present invention is not clear, but it is presumed to be as follows.

[0021] First, the inventors' research revealed that CNTs can adsorb various chemical components in aqueous solutions. Furthermore, the inventors' research showed that when comparing the adsorption of chemical components in an aqueous solution onto the CNT surface with the adsorption of chemical components on the CNT surface (e.g., single-atomic vacancies), the latter is energetically more advantageous. In other words, chemical components in an aqueous solution can be adsorbed more stably by defects on the CNT surface (e.g., single-atomic vacancies) than on the CNT surface itself. Therefore, it is thought that the more defects there are on the CNT surface, the greater the amount of chemical components adsorbed onto the CNT. And, since CNTs with a small G / D ratio generally have low crystallinity and are rich in surface defects, it is thought that using CNTs with a small G / D ratio can increase the amount of chemical components adsorbed onto the CNT. For the reasons stated above, it is believed that the adsorbent of the present invention can be used to remove chemical components from aqueous solutions with high efficiency.

[0022] <cnt> As the carbon nanotubes (CNTs), single-walled carbon nanotubes (WNTs), multi-walled carbon nanotubes (WNTs), and mixtures of WNTs and multi-walled carbon nanotubes can be used.

[0023] <<Properties>> [G / D ratio] In this invention, the CNTs used must have a G / D ratio of 10 or less. If the G / D ratio of the CNTs is greater than 10, the number of defects on the CNT surface decreases, and the amount of chemical components adsorbed per unit weight of CNT decreases, thus reducing the removal rate of chemical components in aqueous solution. Preferably, the G / D ratio of the CNTs is 7 or less, more preferably 4 or less, and even more preferably 2.5 or less. If the G / D ratio of the CNTs is 7 or less, the number of defects on the CNT surface increases, and the amount of chemical components adsorbed per unit weight of CNT increases, thus further improving the removal rate of chemical components in aqueous solution. Furthermore, the lower limit of the G / D ratio of the CNTs is not particularly limited and can be, for example, 0.1 or more, or 1 or more. Furthermore, the G / D ratio of CNTs can be adjusted by changing, for example, the type of CNTs used as raw materials, whether or not surface modification treatment is performed, and the type of surface modification treatment. Specifically, the G / D ratio of CNTs can be reduced by applying surface modification treatment to them.

[0024] [BET specific surface area] Furthermore, the CNT used in this invention has a BET specific surface area of ​​100 m². 2 It is preferable that it be 1 / g or more, and 400m 2 It is more preferable that it be 800m or more per gram. 2 It is even more preferable that the BET specific surface area of ​​the CNT is 100m² or more. 2 If the BET specific surface area is greater than or equal to 1g, the amount of chemical components adsorbed per unit weight of CNT increases, further improving the removal rate of chemical components in aqueous solutions. The upper limit of the BET specific surface area of ​​CNTs is not particularly limited; for example, 2000m². 2 / g or less, 1800m 2 / g or less, 1600m 2 It can be less than / g. In this invention, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method, which can be measured using the method described in the examples of this specification.

[0025] CNTs possessing the properties described above can be efficiently produced, for example, by synthesizing CNTs by chemical vapor deposition (CVD) on a substrate having a catalyst layer on its surface. This process involves supplying raw material compounds and a carrier gas to the substrate and dramatically improving the catalytic activity of the catalyst layer by introducing a small amount of oxidizing agent (catalyst activator) into the system (SuperGrowth method; see International Publication No. 2006 / 011655). In this method, the catalyst layer on the substrate surface is formed by a wet process. In the following, CNTs obtained by the SuperGrowth method may be referred to as "SGCNTs".

[0026] <<Surface-modified CNTs>> Here, as the CNTs, the raw material CNTs produced by the above method may be used as is, or surface-modified CNTs obtained by modifying the surface of the raw material CNTs may be used. From the viewpoint of further increasing the removal rate of chemical components in the aqueous solution, it is preferable to use surface-modified CNTs. The reason why the removal rate of chemical components in the aqueous solution is improved by using surface-modified CNTs is not entirely clear, but it is presumed to be as follows. As mentioned above, it is thought that the lower the crystallinity of the CNTs and the more defects there are on the CNT surface, the greater the amount of chemical components adsorbed onto the CNTs. Furthermore, when surface modification is applied to the raw material CNTs, the number of defects on the CNT surface (e.g., single-atomic vacancies) increases, which is thought to increase the amount of chemical components adsorbed onto the CNTs. In addition, it is presumed that hydrophilic functional groups such as carboxyl groups and hydroxyl groups are generated on the surface of surface-modified CNTs, as will be discussed later. The presence of hydrophilic functional groups on the CNT surface makes it easier for aqueous solutions to penetrate not only the surface of the CNTs but also into the interior of the CNTs, which is thought to increase the amount of chemical components adsorbed onto the CNTs. The combined effect of this increase in defects on the CNT surface and the hydrophilic effect is thought to further improve the removal rate of chemical components from aqueous solutions when using surface-modified CNTs.

[0027] Surface modification treatments for raw material CNTs include, for example, energy ray irradiation treatments such as corona discharge treatment, plasma treatment, electron beam irradiation treatment, and ultraviolet irradiation treatment; and chemical treatments such as strong acid treatment. Among these, energy ray irradiation treatment is preferred, and plasma treatment is more preferred.

[0028] Plasma treatment can be carried out, for example, by known low-temperature plasma treatment. The treatment apparatus is not particularly limited, and known internal electrode or external electrode types can be used, but the external electrode type is preferred because it does not contaminate the electrodes. The treatment conditions such as treatment pressure, power supply frequency and treatment output are not particularly limited and can be selected as appropriate. The plasma generating gas is not particularly limited, but organic or inorganic gases can be used as appropriate, either alone or in a mixture of two or more. Examples of such gases include oxygen, nitrogen, hydrogen, ammonia, methane, ethylene, and carbon tetrafluoride. Among these, oxygen, nitrogen, and carbon tetrafluoride are preferred.

[0029] In plasma treatment, it is preferable to stir the raw material CNTs. Since raw material CNTs are usually used as dry powder, the plasma may not reach all of them. In this invention, stirring means turning them over or agitating them, and it means moving the raw material CNTs during treatment in order to perform plasma treatment uniformly. The simplest method is to remove the material after plasma treatment, stir it, and then perform plasma treatment again. A method of performing plasma treatment while stirring continuously or intermittently is also possible.

[0030] The conditions for plasma processing vary depending on the plasma generating gas and discharge type used, and cannot be generalized, but for example, a power output of 10-400W and a gas pressure of 5-150Pa are preferable. The processing time can be selected as appropriate, but the irradiation time (or the sum of the irradiation times for each intermittent irradiation) is usually 1 to 600 minutes, preferably 10 to 500 minutes, and more preferably 100 to 400 minutes.

[0031] As described above, the surface of the raw material CNT is plasma-treated. By appropriately selecting the treatment conditions, only the surface layer of the raw material CNT can be mildly treated, and excessive structural damage can be suppressed. Various functional groups are formed on the surface of the resulting surface-modified CNT, depending on the type of plasma generating gas used. When oxygen is used as the plasma generating gas, the functional groups formed on the surface of the surface-modified CNT include oxygen-containing functional groups such as hydroxyl groups, carbonyl groups, and carboxyl groups. When nitrogen is used as the plasma generating gas, the functional groups formed on the surface of the surface-modified CNT include nitrogen-containing functional groups such as nitro groups and amine groups. When carbon tetrafluoride is used as the plasma generating gas, the functional groups formed on the surface of the surface-modified CNT include fluorine-containing functional groups such as fluoro groups, trifluoromethyl groups, and fluorocarbonyl groups. Furthermore, surface-modified CNTs may have only one of the above-mentioned functional groups, or they may have multiple of the above-mentioned functional groups.

[0032] <Other ingredients> Other components that can be incorporated into the adsorbent of the present invention are not particularly limited, as long as they do not significantly impair the desired effect. Examples of other components include solvents such as water and various organic solvents; polymer components; additives such as antioxidants; and metal catalyst particles such as copper, platinum, and palladium. These components may be used individually or in combination of two or more in any ratio.

[0033] Furthermore, the adsorbent of the present invention can take any form as long as it contains CNTs, but it may be in the form of an aggregate of CNTs such as a self-supporting membrane, or in the form of CNTs supported on a carrier. When CNTs are in the form of an aggregate such as a self-supporting membrane or supported on a carrier, known binders may be used.

[0034] <Freestanding membrane> Here, a self-supporting membrane refers to a membrane that can maintain its shape even without the presence of another support. A self-supporting membrane can be obtained, for example, by coating a dispersion containing the adsorbent of the present invention onto any support, drying the resulting coating, and removing the support. Alternatively, if the support is porous, the self-supporting membrane can be obtained by filtering the dispersion containing the adsorbent of the present invention through the support, drying the resulting filtrate, and removing the support. The self-supporting membrane of the present invention may also be obtained as a self-supporting membrane with a support attached.

[0035] The support material is not particularly limited as long as it can sufficiently fix the self-supporting film during its manufacture and can be easily removed after the film has been formed. Examples include synthetic resin sheets such as PTFE (polytetrafluoroethylene) sheets and PET (polyethylene terephthalate) sheets, and porous sheets such as cellulose, nitrocellulose, filter paper, and alumina.

[0036] When applying a dispersion onto a support, known coating methods can be used. Examples of coating methods include dipping, roll coating, gravure coating, knife coating, air knife coating, roll knife coating, die coating, screen printing, spray coating, and gravure offset.

[0037] When drying the resulting coating or filter, known drying methods can be employed. Examples of drying methods include hot air drying, hot roll drying, and infrared irradiation. The drying atmosphere can be selected as appropriate, such as air, an inert gas such as nitrogen or argon, or a vacuum.

[0038] <Aqueous solution> Aqueous solutions containing chemical components are not particularly limited as long as water is the main component. Examples of aqueous solutions include hot spring water, industrial water and industrial wastewater, tap water, and well water (spring water). Among these, hot spring water is preferred. Hot spring water includes, for example, hot spring source water, hot spring wastewater, and hot spring raw water diluted with water for cooling.

[0039] <<Chemical components>> The chemical components in the aqueous solution that can be adsorbed by the adsorbent of the present invention are not particularly limited, but semimetals and their compounds are preferably mentioned. Examples of semimetals include boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and tellurium (Te). Examples of compounds of semimetals include, for example, boron-containing compounds such as metaboric acid (HBO2), boric acid (H3BO3), borax (NaB4O7), borate ion (B(OH4) - ), fluoboric acid (HBF4), etc.; silicon-containing compounds such as metasilicic acid (H2SiO3), SiO3 2- , orthosilicic acid (H4SiO4), etc.; arsenic-containing compounds such as metaarsenic acid (HAsO2); and the like. Among those described above, boron, silicon, arsenic, boron-containing compounds, silicon-containing compounds, and arsenic-containing compounds are preferred, and metaboric acid, metasilicic acid, and metaarsenic acid are more preferred. Note that the chemical components in the aqueous solution may be only one kind or two or more kinds.

[0040] When the aqueous solution contains boron and / or boron-containing compounds, the boron concentration in the aqueous solution (total concentration of boron and boron-containing compounds) is usually 0.1 to 1000 mass ppm, preferably 0.5 to 300 mass ppm, more preferably 1 to 100 mass ppm. When the aqueous solution contains silicon and / or silicon-containing compounds, the silicon concentration in the aqueous solution (total concentration of silicon and silicon-containing compounds) is usually 1 to 9000 mass ppm, preferably 10 to 5000 mass ppm, more preferably 100 to 1000 mass ppm. When the aqueous solution contains arsenic and / or arsenic-containing compounds, the arsenic concentration in the aqueous solution (total concentration of arsenic and arsenic-containing compounds) is usually 0.001 to 100 mass ppm, preferably 0.01 to 10 mass ppm, more preferably 0.05 to 5 mass ppm.

[0041] (Adsorption column) The adsorption column of the present invention is filled with the adsorbent material of the present invention described above. The adsorption column of the present invention typically comprises an inlet, a body, and an outlet, with the body being filled with the adsorbent material of the present invention. Furthermore, since the adsorption column of the present invention is filled with the adsorbent of the present invention, chemical components in aqueous solutions can be removed with high efficiency by using the adsorption column of the present invention. The adsorption column of the present invention may also include parts other than the inlet, main body, and outlet.

[0042] The adsorption column of the present invention can be used, for example, as follows. First, an aqueous solution containing a chemical component is introduced into the inlet of the adsorption column. The aqueous solution introduced into the inlet comes into contact with the adsorbent packed in the main body, and the chemical component in the aqueous solution is adsorbed by the adsorbent. After that, the aqueous solution that has passed through the main body of the adsorption column is discharged from the outlet of the adsorption column. Because the chemical component has been adsorbed by the adsorbent packed in the main body of the aqueous solution discharged from the adsorption column, the chemical component content is reduced compared to the aqueous solution before it was introduced into the adsorption column.

[0043] The material of the adsorption column of the present invention is not particularly limited, and known resins, metals, etc., can be used. Furthermore, the method of filling the main body of the adsorption column with the adsorbent is not particularly limited, and known methods can be used.

[0044] (Method for removing chemical components from aqueous solutions) The following describes a method for removing chemical components from an aqueous solution using the adsorbent of the present invention (hereinafter sometimes simply referred to as the "removal method"). The removal method of the present invention typically includes at least a step (contact step) of bringing the adsorbent of the present invention into contact with an aqueous solution containing the target chemical component. Furthermore, since the method for removing chemical components from an aqueous solution of the present invention uses the adsorbent of the present invention as the adsorbent that adsorbs the chemical components in the aqueous solution, it is possible to remove the chemical components from the aqueous solution with high efficiency. Furthermore, the removal method of the present invention may include steps other than the contact step (other steps).

[0045] <Contact process> The method of contact between the adsorbent and the aqueous solution in the contact process is not particularly limited. For example, the adsorbent and the aqueous solution can be brought into contact by immersing the adsorbent in the aqueous solution. Alternatively, the adsorbent and the aqueous solution may be brought into contact by passing the aqueous solution through the adsorption column of the present invention described above. Furthermore, the contact between the adsorbent and the aqueous solution may be performed only once or repeated multiple times.

[0046] When immersing an adsorbent in an aqueous solution, the contact time between the adsorbent and the aqueous solution is preferably 1 minute or more, more preferably 5 minutes or more. If the contact time between the adsorbent and the aqueous solution is greater than or equal to the above value, the removal rate of chemical components in the aqueous solution can be further increased. The upper limit of the contact time is not particularly limited and can be, for example, 72 hours or less, or 36 hours or less.

[0047] Furthermore, when the adsorbent is immersed in an aqueous solution, the concentration of the adsorbent in the immersion solution is preferably 0.1 g / L or more, more preferably 1 g / L or more, and even more preferably 5 g / L or more. If the concentration of the adsorbent in the immersion solution is equal to or greater than the above values, the removal rate of chemical components in the aqueous solution can be further increased. The upper limit of the adsorbent concentration is not particularly limited and can be, for example, 100 g / L or less, or 50 g / L or less.

[0048] <Other processes> Other steps include, for example, a step to remove the adsorbent from the aqueous solution after the contact step (removal step). The method for removing the adsorbent from the aqueous solution is not particularly limited, and for example, a filtration method using filter paper can be used. [Examples]

[0049] The present invention will be described in detail below based on test examples, but the present invention is not limited to these test examples. In the following description, "%" and "parts" used to express quantities refer to mass unless otherwise specified. In the test examples, various measurements and evaluations were performed using the following methods.

[0050] <G / D ratio> Using a microscopic laser Raman spectrophotometer (manufactured by Thermo Fisher Scientific, product name "Nicolet Almega XR"), the Raman spectrum of CNT was measured. Then, regarding the obtained Raman spectrum, the intensity of the G-band peak observed near 1590 cm -1 and the intensity of the D-band peak observed near 1340 cm -1 were determined, and the G / D ratio was calculated. <BET specific surface area> In accordance with JIS Z8830, using a BET specific surface area measuring device (manufactured by Mount Tech Co., Ltd., HM model-1210), the BET specific surface area (m 2 / g) of CNT was measured. <Boron concentration and silicon concentration> The boron concentration and silicon concentration in the aqueous solution were measured using inductively coupled plasma mass spectrometry (hereinafter abbreviated as "ICP-MS"). Specifically, after immersing the adsorbent in the aqueous solution for a certain period of time, the immersion solution was filtered through filter paper, and the boron concentration and silicon concentration in the filtrate were measured using "Agilent 7850" of Agilent. At this time, in order to be below the detection upper limit value of ICP-MS, the filtrate was diluted 1 / 1000 and measured. In addition, experimental instruments such as glass test tubes and beakers are made of borosilicate glass and have an inappreciable influence on the detection of boron and silicon, so polypropylene conical tubes were used. For the same reason, when weighing the sample, the experiment was also carried out using a micropipette instead of a volumetric flask or the like. <Arsenic concentration> The arsenic concentration was measured by ICP-MS and colorimetric method. The measurement of the arsenic concentration by ICP-MS was carried out in the same manner as the measurement of the above boron concentration and silicon concentration. In addition, for the measurement by the colorimetric method, an arsenic concentration simple inspection kit (manufactured by MI Tech Co., Ltd.) was used.

[0051] (Test Example 1) <Material> Hot spring water A and hot spring water B were used as aqueous solution samples. As an adsorbent, SGCNT (manufactured by Zeon Corporation, product name "ZEONANO(registered trademark) SG101"; G / D ratio: 3.21; BET specific surface area: 1350 m²) 2 (A CNT containing 90% or more single-walled carbon nanotubes was used.) <Method> 0.6 g of SGCNT was immersed in 6 mL of hot spring water A for 24 hours. The immersion solution was then filtered through filter paper, and the boron and silicon concentrations in the filtrate were evaluated according to the method described above. The same experiment was performed three times, and the mean and standard deviation were calculated. The boron and silicon concentrations in the hot spring water A before immersion were evaluated in the same manner. 0.08 g of SGCNT was immersed in 50 mL of hot spring water B for 24 hours, and the immersion solution was filtered through filter paper. The arsenic concentration in the filtrate was evaluated according to the method described above. The arsenic concentration in hot spring water B before immersion was evaluated in the same manner. <Result> The results are shown in Figure 1. The error bars in Figure 1 indicate the standard deviation. From Figure 1, it can be seen that the boron, silicon, and arsenic concentrations in the hot spring water were significantly reduced by CNT immersion.

[0052] (Test Example 2) <Material> As for CNTs, SGCNTs and e-DIPS (manufactured by Meijo Nanocarbon Co., Ltd.; product name "MEIJO eDIPS"; G / D ratio: 30.1; BET specific surface area: 750 m²) 2 The study used SGCNTs (containing 90% or more single-walled carbon nanotubes) and surface-modified carbon nanotubes (SGCNTs) that had been plasma-treated. Plasma treatment was performed using the following procedure: 5g of SGCNTs was spread thinly on the stage of a plasma treatment apparatus (manufactured by Kai Semiconductor Co., Ltd., product name "Rotating Tabletop Vacuum Plasma Apparatus YHS-DΦS"), and plasma irradiation was performed for 360 minutes using CF4 gas, N2 gas, or O2 gas under treatment conditions of 200W power, 40Pa gas pressure, and 4sccm flow rate. Hot spring water A was used as the aqueous solution sample. <Method> The G / D ratio of various CNTs was evaluated according to the method described above. The results are shown in Figure 2. Furthermore, 0.06 g of each type of CNT was immersed in 6 mL of hot spring water A for 24 hours, and the boron and silicon concentrations in hot spring water A before and after immersion were evaluated according to the method described above. The reduction rate (%) was then calculated according to the formula: Reduction rate (%) = {(Concentration before immersion - Concentration after immersion) / Concentration before immersion} × 100. The relationship between the G / D ratio and the reduction rate is shown in Figure 3. <Result> Figure 3 shows that the smaller the G / D ratio of CNTs, the higher the rate of reduction of boron and silicon tends to be. Therefore, it can be seen that the smaller the G / D ratio of CNTs, the more efficiently boron and silicon can be removed from aqueous solutions.

[0053] (Test Example 3) <Material> SGCNT (unmodified surface) and activated carbon were used as adsorbents. In addition, hot spring water A and elemental solutions of boron or silicon (prepared by diluting the chemicals to a concentration similar to that of the hot spring water) were used as aqueous solution samples. <Method> 0.6 g of SGCNT or activated carbon was immersed in 6 mL of hot spring water A, and the boron and silicon concentrations in hot spring water A were evaluated before immersion, 5 minutes after immersion, and 24 hours after immersion according to the method described above. The same experiment was performed three times, and the mean and standard deviation were calculated. Furthermore, the same experiment was conducted using an elemental solution of boron or silicon instead of hot spring water A. <Result> The results are shown in Figure 4. From Figure 4, it can be seen that SGCNT has a higher removal rate of boron and silicon than activated carbon. Furthermore, it can be seen that the removal rate of boron and silicon is higher with a 24-hour immersion time than with a 5-minute immersion time.

[0054] (Test Example 4) <Method> Using density functional theory (DFT), the energy (E) of the system in which the target components (HBO2, H2SiO3, HAsO2) are adsorbed on CNTs is determined. CNT+atom,mol ), the energy (E) of a system in which CNTs exist independently CNT ), and the energy (E) of the system in which the target component exists independently. atom,mol The following calculations were performed. Two types of CNTs were used: a CNT model without single-atom vacancies and a CNT model with single-atom vacancies. The energy gain (ΔE) was then calculated according to the following formula. JPEG2026046081000001.jpg9170<Result> Figure 5 shows the energy gain and the state in which each target component is adsorbed onto a single-atomic vacancy. As shown in Figure 5, the energy gain is negative whether the target component is adsorbed on the CNT surface or onto a single-atomic vacancy in the CNT. Therefore, the energy evaluation by first-principles calculations also confirms that the target component can be adsorbed on both the CNT surface and the single-atomic vacancy in the CNT. Furthermore, Figure 5 shows that when the target component is adsorbed on the CNT surface, compared to when it is adsorbed on a single-atomic vacancy in the CNT, the absolute value of the energy gain (ΔE) is larger in the latter case. A larger absolute value of the energy gain indicates that the target component is adsorbed more stably. Therefore, it is suggested that the target component is adsorbed more stably on a single-atomic vacancy in the CNT than on the CNT surface. [Industrial applicability]

[0055] According to the present invention, it is possible to provide an adsorbent that can efficiently remove chemical components from an aqueous solution, and an adsorption column packed with the adsorbent.< / cnt>

Claims

1. An adsorbent that adsorbs chemical components in an aqueous solution, The adsorbent material contains carbon nanotubes, An adsorbent in which the G / D ratio of the carbon nanotubes is 10 or less.

2. The adsorbent according to claim 1, wherein the carbon nanotube is a surface-modified carbon nanotube.

3. The adsorbent according to claim 1, wherein the chemical component is a metalloid or a compound thereof.

4. The adsorbent according to claim 1, wherein the chemical component contains at least one element selected from the group consisting of boron, silicon, and arsenic.

5. The adsorbent according to claim 1, wherein the aqueous solution is hot spring water.

6. The adsorbent according to claim 1, comprising a self-supporting membrane containing the carbon nanotubes.

7. An adsorption column filled with the adsorbent described in any one of claims 1 to 6.

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