Adsorbent, method for recovering target substance using adsorbent, and method for manufacturing adsorbent suitable for manufacturing adsorbent

Abstract

The purpose of the present invention is to provide an adsorbent having exceptional adsorption performance, a method for recovering a target substance using the adsorbent, and a method for manufacturing an adsorbent suitable for manufacturing the adsorbent. In order to achieve this purpose, the present invention provides an adsorbent comprising a porous body having a co-continuous structure formed by macropores (2) and a ceramic skeleton (1) that contains mesopores (3), and a sulfur-atom-containing group for modifying the surface of the ceramic skeleton, wherein the amount of the sulfur-atom-containing group contained in the adsorbent is 0.5-3.5 mmol / g, and the water absorption rate of the adsorbent is 8% or higher.

Description

Adsorbent, method for recovering target substances using said adsorbent, and method for manufacturing said adsorbent

[0001] The present invention relates to an adsorbent, a method for recovering a target substance using the adsorbent, and a method for producing the adsorbent suitable for producing the adsorbent.

[0002] From the perspectives of carbon neutrality, SDGs, and the like, technologies related to the reuse or recovery of target substances are attracting attention. Examples of such technologies include technologies for recovering metals or metal ions contained in liquids. Surface-treated particulate porous silica is known as an adsorbent used for recovering target substances such as metals and metal ions. For example, Patent Document 1 describes particulate porous silica having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores. Patent Document 1 also describes that porous silica whose surface is modified with functional groups such as thiol groups is useful for recovering target substances such as metals and metal ions.

[0003] International Publication No. 2017 / 002871

[0004] An object of the present invention is to provide an adsorbent having excellent adsorption performance, a method for recovering a target substance using the adsorbent, and a method for producing the adsorbent suitable for producing the adsorbent.

[0005] The present inventors have discovered that in an adsorbent comprising a porous body having a co-continuous structure formed by a ceramic skeleton including mesopores and macropores, and sulfur atom-containing groups modifying the surface of the ceramic skeleton, the adsorption performance of the adsorbent can be improved by adjusting the amount of sulfur atom-containing groups contained in the adsorbent to 0.5 mmol / g or more and 3.5 mmol / g or less, and adjusting the water absorption rate of the adsorbent to 8% or more, and that the adsorbent can be made to have a high water absorption rate by adjusting the amount of sulfur atom-containing groups contained in the adsorbent to 0.5 mmol / g or more and 3.5 mmol / g or less, and that the adsorbent can ... The present inventors have found that in a method for producing an adsorbent capable of forming a porous body, the hydrophilicity (i.e., water absorption rate) of the adsorbent can be increased by contacting the porous body with a reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups in water, or in an aqueous solution having a pH of 1 to 12, or in a mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 to 12, in which the ratio of the volume of the organic solvent to the volume of the aqueous solution or water is 0.5 or less, thereby improving the adsorption performance of the adsorbent, and have completed the present invention. That is, the present invention encompasses the following inventions.

[0006] [1] An adsorbent comprising a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and sulfur atom-containing groups modifying the surface of the ceramic skeleton, wherein the amount of the sulfur atom-containing groups contained in the adsorbent is 0.5 mmol / g or more and 3.5 mmol / g or less, and the water absorption of the adsorbent is 8% or more. [2] The adsorbent according to [1], wherein the sulfur atom-containing groups comprise thiol groups. [3] The adsorbent according to [1] or [2], wherein the mode pore size of the macropores of the porous body is 200 nm or more and 5,000 nm or less. [4] The adsorbent according to any one of [1] to [3], wherein the ratio of the mode pore size of the macropores of the porous body to the mode pore size of the mesopores of the porous body is 15 or more and 300 or less. [5] The adsorbent according to any one of [1] to [4], wherein the ceramic skeleton contains an element selected from silicon, aluminum, tin, cerium, titanium, and zirconium. [6] The adsorbent according to any one of [1] to [5], wherein the sulfur atom-containing group is capable of adsorbing one or more substances selected from the group consisting of transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16. [7] A method for recovering one or more target substances selected from the group consisting of metals, metal ions, metalloids, and metalloid ions from a solution containing the one or more target substances, the method comprising a step of contacting the solution with the adsorbent according to any one of [1] to [6]. [8] The method according to [7], wherein the one or more target substances are selected from the group consisting of transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16.[9] A method for producing an adsorbent comprising a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and sulfur atom-containing groups that modify the surface of the ceramic skeleton, the method comprising a step of contacting the porous body with a reagent for modifying the surface of the ceramic skeleton with the sulfur atom-containing groups in a solvent, the solvent being water, an aqueous solution having a pH of 1 to 12, or a mixed solution of an organic solvent and either an aqueous solution or water having a pH of 1 to 12, wherein the ratio of the volume of the organic solvent to the volume of the aqueous solution or water is 0.5 or less.

[0007] According to the present invention, there are provided an adsorbent having excellent adsorption performance, a method for recovering a target substance using the adsorbent, and a method for producing the adsorbent suitable for producing the adsorbent.

[0008] FIG. 1 is an enlarged view of a portion of the surface of a porous body according to one embodiment of the present invention.

[0009] <Explanation of Terms> The terms used in this specification will be explained below. The following explanations apply throughout this specification unless otherwise specified.

[0010] <Halogen Atom> Halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0011] <Alkyl Group> The number of carbon atoms in the alkyl group is, for example, 1 to 20, preferably 1 to 10, preferably 1 to 8, more preferably 1 to 6, even more preferably 1 to 5, and still more preferably 1 to 4. The alkyl group may be linear or branched. A linear alkyl group has 1 or more carbon atoms, and a branched alkyl group has 3 or more carbon atoms.

[0012] <Aryl Group> The aryl group is, for example, a monocyclic or polycyclic (for example, bicyclic or tricyclic) aromatic hydrocarbon ring group. The aryl group has, for example, 6 to 14 carbon atoms, preferably 6 to 10 carbon atoms. The polycyclic group may be a fused ring system. Examples of the aryl group include a phenyl group and a naphthyl group. The aryl group is preferably a phenyl group.

[0013] The arylalkyl group is an alkyl group having one or more aryl groups, and the explanations regarding the alkyl group and the aryl group are as described above. The number of aryl groups contained in the arylalkyl group is, for example, 1 to 3, preferably 1 or 2, and more preferably 1.

[0014] The alkylaryl group is an aryl group having one or more alkyl groups, and the alkyl and aryl groups are as described above. The number of alkyl groups contained in the alkylaryl group is, for example, 1 to 3, preferably 1 or 2, and more preferably 1.

[0015] <Alkyloxy Group> The alkyloxy group is a group represented by the formula: —O-alkyl group, and the explanation regarding the alkyl group is as above.

[0016] <Aryloxy Group> The aryloxy group is a group represented by the formula: —O-aryl group, and the explanation regarding the aryl group is as above.

[0017] <Arylalkyloxy Group> The arylalkyloxy group is a group represented by the formula: —O-arylalkyl group, and the explanation regarding the arylalkyl group is as above.

[0018] <Alkylaryloxy Group> The alkylaryloxy group is a group represented by the formula: —O-alkylaryl group, and the explanation regarding the alkylaryl group is as above.

[0019] <Alkylcarbonyl Group> The alkylcarbonyl group is a group represented by the formula: —CO-alkyl group, and the explanation regarding the alkyl group is as above.

[0020] <Arylcarbonyl Group> The arylcarbonyl group is a group represented by the formula: —CO-aryl group, and the explanation regarding the aryl group is as above.

[0021] <Alkyloxycarbonyl Group> The alkyloxycarbonyl group is a group represented by the formula: —CO—O-alkyl group, and the explanation regarding the alkyl group is as above.

[0022] <Aryloxycarbonyl Group> The aryloxycarbonyl group is a group represented by the formula: —CO—O-aryl group, and the explanation regarding the aryl group is as above.

[0023] <Thiol Group> A thiol group is a group represented by the formula: —SH.

[0024] <Alkylthio Group> The alkylthio group is a group represented by the formula: —S-alkyl group, and the explanation regarding the alkyl group is as above.

[0025] <Arylthio Group> The arylthio group is a group represented by the formula: —S-aryl group, and the explanation regarding the aryl group is as above.

[0026] <Arylalkylthio Group> The arylalkylthio group is a group represented by the formula: —S-arylalkyl group, and the explanation regarding the arylalkyl group is as above.

[0027] <Alkylarylthio Group> The alkylarylthio group is a group represented by the formula: —S-alkylaryl group, and the explanation regarding the alkylaryl group is as above.

[0028] <Alkylcarbonylthio Group> The alkylcarbonylthio group is a group represented by the formula: —S-alkylcarbonyl group, and the explanation regarding the alkylcarbonyl group is as described above.

[0029] <Arylcarbonylthio Group> The arylcarbonylthio group is a group represented by the formula: —S-arylcarbonyl group, and the explanation regarding the arylcarbonyl group is as described above.

[0030] <Alkyloxycarbonylthio Group> The alkyloxycarbonylthio group is a group represented by the formula: —S-alkyloxycarbonyl group, and the explanation regarding the alkyloxycarbonyl group is as described above.

[0031] <Aryloxycarbonylthio Group> The aryloxycarbonylthio group is a group represented by the formula: —S-aryloxycarbonyl group, and the explanation regarding the aryloxycarbonyl group is as described above.

[0032] <Alkylene Group and Arylene Group> The alkylene group and the arylene group are divalent functional groups generated by removing one hydrogen atom from an alkyl group and an aryl group, respectively, and the explanations regarding the alkyl group and the aryl group are as described above.

[0033] <One or more substituents> The one or more substituents preferably mean 1 to 3 substituents, more preferably 1 or 2. The one or more substituents can be independently selected from, for example, a hydroxyl group, a carboxyl group, a halogen atom, a phosphate group, an oxo group, an alkyloxy group, an aryloxy group, an arylalkyloxy group, an alkylaryloxy group, and the like.

[0034] <<Porous Body>> The porous body has a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores. Hereinafter, the porous body will be described.

[0035] <Mold and shape of porous body> The mold of the porous body is not particularly limited. Examples of the mold of the porous body include particles, lumps, and molded bodies. Furthermore, the shape of the porous body is not particularly limited. Examples of the shape of the porous body include columnar, spherical (e.g., spherical, elliptical, etc.), needle-like, scaly (flake-like), polyhedral, flat, crushed, and lumpy. Examples of the columnar shape include cylindrical, elliptical, and polygonal prisms (e.g., rectangular, hexagonal, and octagonal prisms). The columnar shape may be a shape in which a part of the cylindrical, elliptical, or polygonal prism is missing.

[0036] When the porous body is in the form of particles, the particle diameter is, for example, 0.5 μm or more and 7.0 mm or less. The particle diameter means the circle-equivalent diameter, that is, the diameter of a circle having an area equal to the area of ​​the particle when viewed in an observation image of the particle (e.g., an SEM image). The particle diameter can be adjusted, for example, by classification.

[0037] When the porous body has a columnar shape, the length is, for example, 1.0 mm or more and 500 mm or less, and the diameter is, for example, 1.5 mm or more and 20 mm or less. The length refers to the dimension in the direction in which the columnar body extends. The diameter refers to the diameter of the end face of the columnar body in the direction in which it extends. When the end face is circular, the diameter refers to the diameter of the circle. When the end face has a shape other than circular, the diameter refers to the diameter of the circle circumscribing the end face.

[0038] <Structure of porous body before modification> The structure of the porous body before modification with sulfur atom-containing groups will be described below with reference to Fig. 1. Fig. 1 is an enlarged view of a portion of the surface of a porous body according to one embodiment of the present invention.

[0039] As shown in FIG. 1, the porous body has a bicontinuous structure formed by a ceramic skeleton 1 containing mesopores 3 and macropores 2 .

[0040] In the porous body, the ceramic skeleton 1 and the macropores 2 each have a continuous three-dimensional network structure and are entangled with each other, thereby forming a co-continuous structure of the ceramic skeleton 1 and the macropores 2. The fact that the porous body has a co-continuous structure of the ceramic skeleton 1 and the macropores 2 can be confirmed by observing the surface or cross section of the porous body with a scanning electron microscope (SEM).

[0041] From the viewpoint of improving the adsorption performance, the mode pore diameter of the macropores 2 is preferably 200 nm or more, more preferably 400 nm or more, and even more preferably 600 nm or more. From the same viewpoint, the mode pore diameter of the macropores 2 is preferably 5000 nm or less, more preferably 4000 nm or less, and even more preferably 3000 nm or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0042] The "most frequent pore size of macropores 2" refers to the most frequent pore size of macropores measured by mercury intrusion porosimetry in the pore diameter range of 50 nm to 500 μm, as described in the Examples below.

[0043] From the viewpoint of improving adsorption performance, the mode pore diameter of the mesopores 3 is preferably 2.0 nm or more, more preferably 5.0 nm or more, and even more preferably 10.0 nm or more. From the same viewpoint, the mode pore diameter of the mesopores 3 is preferably 50.0 nm or less, more preferably 40.0 nm or less, and even more preferably 35.0 nm or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0044] The "modal pore size of mesopores 3" refers to the modal pore size of mesopores measured by the BJH method from a nitrogen adsorption / desorption isotherm, as described in the Examples below.

[0045] From the viewpoint of improving the adsorption performance, the ratio of the most frequent pore size of the macropores 2 to the most frequent pore size of the mesopores 3 is preferably 15 or more, more preferably 20 or more, even more preferably 30 or more, and still more preferably 40 or more. From the same viewpoint, the ratio is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less, and still more preferably 100 or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0046] From the viewpoint of improving the adsorption performance, the specific surface area of ​​the porous body measured by the BET method from the nitrogen adsorption / desorption isotherm is preferably 100 m ２ / g or more, more preferably 120m ２ / g or more, more preferably 130m ２ / g or more. There is no particular upper limit to the specific surface area of ​​the porous body. The method for measuring the specific surface area by the BET method from a nitrogen adsorption / desorption isotherm is as described in the Examples below.

[0047] From the viewpoint of improving the adsorption performance, the total pore volume of the porous body measured by mercury porosimetry is preferably 1.5 mL / g or more and 4.0 mL / g or less, more preferably 1.8 mL / g or more and 3.5 mL / g or less, and even more preferably 2.5 mL / g or more and 3.5 mL / g or less. The method for measuring the total pore volume by mercury porosimetry is as described in the Examples below.

[0048] From the viewpoint of improving the adsorption performance, the porosity of the porous body measured by mercury porosimetry is preferably 70% or more and 90% or less, more preferably 70% or more and 85% or less, and even more preferably 75% or more and 85% or less. The method for measuring the porosity by mercury porosimetry is as described in the Examples below.

[0049] <Material of Porous Body> The ceramics constituting the ceramic skeleton are, for example, oxide ceramics containing a metalloid element or a metal element. The ceramic skeleton 1 may contain one element selected from the group consisting of metalloid elements and metal elements, or may contain two or more elements selected from the group consisting of metalloid elements and metal elements.

[0050] An example of a semi-metallic element is silicon. An example of an oxide ceramic containing silicon is silica (SiO ２ ) are listed.

[0051] Examples of the metal element include aluminum, tin, and transition metal elements such as cerium, titanium, zirconium, vanadium, chromium, iron, cobalt, nickel, palladium, platinum, copper, silver, gold, and zinc. Among these, from the viewpoint of ease of manufacturing the porous body, the metal element is preferably selected from aluminum, tin, cerium, titanium, and zirconium. Examples of oxide ceramics containing aluminum, tin, cerium, titanium, or zirconium include alumina (Al ２ O ３ ), tin oxide (SnO ２ ), ceria (CeO ２ ), titania (TiO ２ ), zirconia (ZrO ２ ) etc.

[0052] The oxide ceramic may further contain, in addition to silicon, aluminum, tin or a transition metal element, an element selected from alkali metal elements such as lithium and sodium, alkaline earth metal elements such as magnesium and calcium, and rare earth elements such as lanthanum, scandium, yttrium and gadolinium.

[0053] <Method for producing porous body> The porous body can be produced, for example, by a method comprising the following steps: (a) a step of producing a polymetalloxane gel by a sol-gel method; (b) a step of forming pores in the skeleton of the polymetalloxane gel produced in step (a); and (c) a step of washing and / or drying the polymetalloxane gel used in step (b) as necessary, and then firing it to produce a ceramic monolith (porous body). Each step will be described below.

[0054] Step (a) In step (a), a polymetalloxane gel is produced by a sol-gel method.

[0055] Polymetalloxane is an inorganic polymer whose main chain structure is a metalloxane bond, which is a bond between a metalloid or metal element and an oxygen atom, i.e., an MO bond (where M represents a metalloid or metal element).

[0056] Examples of metalloid elements represented by M include silicon. Examples of metal elements represented by M include aluminum, tin, cerium, titanium, zirconium, vanadium, chromium, iron, cobalt, nickel, palladium, platinum, copper, silver, gold, and zinc. From the viewpoint of ease of production of the porous body, aluminum, tin, cerium, titanium, or zirconium is preferred.

[0057] The sol-gel method can be carried out according to a conventional method, and an example of the sol-gel method is as follows.

[0058] The sol-gel process includes a sol production step and a gel production step.

[0059] In the sol preparation step, a reaction solution containing a ceramic precursor, a catalyst, and a macropore-forming agent is stirred to prepare a sol.

[0060] The ceramic precursor is not particularly limited as long as it can form a polymetalloxane gel.

[0061] Examples of ceramic precursors include semimetallic compounds having hydroxyl groups and / or hydrolyzable functional groups (e.g., silicon compounds), metal compounds having hydroxyl groups and / or hydrolyzable functional groups (e.g., aluminum compounds, tin compounds, cerium compounds, titanium compounds, zirconium compounds, etc.). The total number of hydroxyl groups and hydrolyzable functional groups possessed by the ceramic precursor may be 1 or 2, but from the viewpoint of producing a polymetalloxane gel having a highly crosslinked structure with metalloxane bonds (M-O bonds), it is preferably 3 or more, and more preferably 4. When the ceramic precursor has two or more hydrolyzable functional groups, the types of the two or more hydrolyzable functional groups may be the same or different.

[0062] The hydrolyzable functional group is a functional group that is converted into a hydroxy group by hydrolysis. Examples of the hydrolyzable functional group include an alkyloxy group, an acetoxy group, a halide group, and a hydride group, with an alkyloxy group being preferred. The alkyloxy group is preferably an alkyloxy group having 1 to 10 carbon atoms, more preferably an alkyloxy group having 1 to 5 carbon atoms, and even more preferably a methoxy group, an ethoxy group, or a propoxy group. The alkyloxy group may be linear or branched.

[0063] The ceramic precursor may have a functional group other than a hydroxy group and a hydrolyzable functional group. Examples of functional groups other than a hydroxy group and a hydrolyzable functional group include an alkyl group, an alkenyl group, a phenyl group, a phenoxy group, a carboxyl group, an epoxy group, an aldehyde group, a thiol group, an amino group, an acryloyl group, and a methacryloyl group. The alkyl group is preferably an alkyl group having 1 to 10 carbon atoms, more preferably an alkyl group having 1 to 5 carbon atoms, and even more preferably a methyl group, an ethyl group, or a propyl group. The alkyl group may be linear or branched. The alkenyl group is preferably an alkenyl group having 2 to 10 carbon atoms, more preferably an alkenyl group having 2 to 5 carbon atoms, and even more preferably a vinyl group. The alkenyl group may be linear or branched.

[0064] The silicon compound having a hydroxy group and / or a hydrolyzable functional group is preferably an alkyloxysilane. Examples of the alkyloxysilane include tetraalkyloxysilane, trialkyloxysilane, dialkyloxysilane, monoalkyloxysilane, etc., and among these, tetraalkyloxysilane is preferred from the viewpoint of facilitating the hydrolysis reaction and polycondensation reaction. Examples of the tetraalkyloxysilane include tetramethoxysilane and tetraethoxysilane.

[0065] The aluminum compound having a hydroxy group and / or a hydrolyzable functional group is preferably aluminum hydroxide, aluminum alkyl oxide, or the like.

[0066] The tin compound having a hydroxy group and / or a hydrolyzable functional group is preferably tin hydroxide, tin alkyl oxide, or the like.

[0067] The cerium compound having a hydroxy group and / or a hydrolyzable functional group is preferably cerium hydroxide, cerium alkyloxide, or the like.

[0068] The titanium compound having a hydroxy group and / or a hydrolyzable functional group is preferably a titanium alkyl oxide. Examples of titanium alkyl oxides include titanium monoalkyl oxides, titanium dialkyl oxides, titanium trialkyl oxides, and titanium tetraalkyl oxides. Among these, titanium tetraalkyl oxides are preferred from the viewpoint of facilitating the hydrolysis reaction and polycondensation reaction. Examples of titanium tetraalkyl oxides include titanium tetraisopropoxide.

[0069] The zirconium compound having a hydroxy group and / or a hydrolyzable functional group is preferably a zirconium alkyl oxide. Examples of the zirconium alkyl oxide include zirconium monoalkyl oxide, zirconium dialkyl oxide, zirconium trialkyl oxide, and zirconium tetraalkyl oxide. Among these, zirconium tetraalkyl oxide is preferred from the viewpoint of facilitating the hydrolysis reaction and polycondensation reaction. Examples of the zirconium tetraalkyl oxide include zirconium tetraisopropoxide.

[0070] The ceramic precursor may be a metal salt (e.g., aluminum salt, tin salt, cerium salt, etc.) that is converted to a hydroxide by hydrolysis. Examples of aluminum salts include aluminum nitrate, aluminum sulfate, and aluminum chloride. Examples of tin salts include tin nitrate, tin sulfate, and tin chloride. Examples of cerium salts include cerium nitrate, cerium sulfate, and cerium chloride. Of these, aluminum chloride, tin chloride, or cerium chloride is preferred from the viewpoint of facilitating the hydrolysis reaction and polycondensation reaction.

[0071] The catalyst functions as a catalyst for the hydrolysis reaction. Examples of the catalyst include acids and bases. Examples of the acid include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid; and organic acids such as formic acid, acetic acid, oxalic acid, and citric acid. Examples of the base include amines such as sodium hydroxide, potassium hydroxide, aqueous ammonia, sodium carbonate, sodium bicarbonate, and trimethylammonium, ammonium hydroxides such as tert-butylammonium hydroxide, and alkali metal alkyl oxides such as sodium methoxide.

[0072] The macropore-forming agent contributes to the formation of macropores in the ceramic monolith. Examples of the macropore-forming agent include water-soluble polymers and surfactants, among which water-soluble polymers are preferred. The water-soluble polymer induces a sol-gel transition accompanied by a phase separation process (typically spinodal decomposition), and contributes to the formation of a co-continuous structure of the framework phase and the solvent phase in the gel, which in turn contributes to the formation of macropores in the ceramic monolith.

[0073] Examples of water-soluble polymers include polyalkylene glycols such as polyethylene glycol and polypropylene glycol, polyacrylic acid, polyethylene glycol-polypropylene glycol block copolymers, polyvinylpyrrolidone, polystyrene sulfonate sodium salt, and polyallylamine hydrochloride.

[0074] From the viewpoint of efficiently carrying out the phase separation process (typically, spinodal decomposition), the weight average molecular weight of the water-soluble polymer is preferably from 8000 to 15000. The weight average molecular weight is measured by GPC (gel permeation chromatography).

[0075] Examples of surfactants include cationic surfactants such as cetyltrimethylammonium chloride, anionic surfactants such as sodium dodecyl sulfate, and nonionic surfactants such as polyoxyethylene alkyl ether.

[0076] When the ceramic precursor is a semimetallic compound, the reaction solution may contain a mesopore-forming agent. The mesopore-forming agent contributes to the formation of mesopores in the ceramic monolith. Examples of mesopore-forming agents include nitrogen compounds. Examples of nitrogen compounds that can be used as mesopore-forming agents include amide compounds such as urea, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, and N,N-dimethylacetamide; and heterocyclic compounds such as hexamethylenetetramine. Of these, urea is preferred from the viewpoint of efficient mesopore formation.

[0077] The reaction solution may contain one or more solvents. Examples of the solvent include water, an organic solvent, and a mixed solvent of water and an organic solvent. Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, and butanol; and ketones such as acetone and methyl ethyl ketone. When the solvent is a mixed solvent of water and an organic solvent, the content of the organic solvent is preferably 65 mass% or less based on the mass of the mixed solvent.

[0078] From the viewpoint of appropriately controlling the start of the reaction, the reaction solution is preferably prepared by adding the ceramic precursor to a mixture containing the catalyst, the macropore-forming agent, and, if necessary, the mesopore-forming agent. The reaction is initiated by adding the ceramic precursor to a mixture containing the catalyst, the macropore-forming agent, and, if necessary, the mesopore-forming agent.

[0079] The reaction solution may be cooled during stirring. The reaction solution is cooled, for example, so that the temperature of the reaction solution is a temperature at which the sol-gel transition accompanied by a phase separation process (typically spinodal decomposition) easily proceeds, preferably 60°C or less, more preferably 40°C or less. The lower limit is a temperature at which the reaction solution does not freeze, for example, about 1°C.

[0080] For example, when tetramethoxysilane, which is a semimetallic compound having a hydrolyzable functional group, is used as the ceramic precursor, it is preferable to perform the cooling described above.

[0081] The reaction solution turns into a sol as the hydrolysis reaction and polycondensation reaction proceed.

[0082] In the hydrolysis reaction, hydrolyzable functional groups in the ceramic precursor are hydrolyzed to form hydroxy groups. In the polycondensation reaction, metalloxane oligomers are formed by a dehydration condensation reaction between hydroxy groups and a dealcoholization condensation reaction between a hydroxy group and an unhydrolyzed hydrolyzable functional group. For example, when the ceramic precursor is a silicon compound having a hydrolyzable functional group, a siloxane oligomer is formed by a dehydration condensation reaction shown in the following formula (1) and a dealcoholization condensation reaction shown in the following formula (2). In the following formula (2), -OR represents an unhydrolyzed hydrolyzable functional group. ≡Si-OH + HO-Si≡ → ​​≡Si-O-Si≡ + H ２ O...(1) ≡Si-OR + HO-Si≡ → ​​≡Si-O-Si≡ + ROH...(2)

[0083] As the hydrolysis reaction and polycondensation reaction proceed further, nanometer-sized metalloxane oligomer primary particles are formed, and the primary particles aggregate to form secondary particles, thereby converting the reaction solution into a sol.

[0084] In the gel production step, the sol obtained in the sol production step is added to a molding mold as needed and then heated to a gelation temperature to produce a polymetalloxane gel. In the gelation step, the hydrolysis reaction and polycondensation reaction proceed further to form a metalloxane polymer, and a sol-gel transition accompanied by a phase separation process (typically spinodal decomposition) is induced to produce a polymetalloxane gel (wet gel). The produced polymetalloxane gel has a co-continuous structure of a skeletal phase and a solvent phase. The skeletal phase is rich in the metalloxane polymer produced by the hydrolysis reaction and polycondensation reaction, and the solvent phase is rich in the solvent. The skeletal phase and the solvent phase each have a continuous three-dimensional network structure and are entangled with each other, thereby forming a co-continuous structure of the skeletal phase and the solvent phase.

[0085] The molding mold is a mold for molding the gel into a desired shape, and examples of materials for the molding mold include synthetic resins such as polystyrene, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate (PC), silicone, and polytetrafluoroethylene (PTFE), and metals such as aluminum and stainless steel.

[0086] From the viewpoint of appropriately forming a co-continuous structure of the skeletal phase and the solvent phase in the gel, the gelation temperature is preferably 20° C. or higher and 80° C. or lower, more preferably 25° C. or higher and 40° C. or lower. The heating time at the gelation temperature is preferably 4 hours or higher and 24 hours or lower.

[0087] Step (b) In step (b), pores are formed in the skeleton of the polymetalloxane gel produced in step (a).

[0088] Pores can be formed in the skeleton of the polymetalloxane gel by a conventional method. When forming pores in the skeleton of the polymetalloxane gel, the polymetalloxane gel produced in step (a) may be reacted with a mesopore-forming agent, if necessary.

[0089] The description of the mesopore-forming agent is the same as above. The mesopore-forming agent may be contained in the polymetalloxane gel produced in step (a), or in the reaction solution containing the polymetalloxane gel and the mesopore-forming agent, or in both. In step (b), pores (pores that will become mesopores in the ceramic monolith) are formed in the gel skeleton. The reaction solution may contain one or more solvents. The description of the solvent is the same as above.

[0090] When the polymetalloxane gel and the mesopore-forming agent are reacted, they may be reacted under heating and reflux.

[0091] The heating temperature during heating under reflux is preferably 50° C. or higher and 120° C. or lower. The heating time during heating under reflux is preferably 1 hour or higher and 36 hours or lower, more preferably 4 hours or higher and 24 hours or lower.

[0092] When a semimetallic compound having a hydrolyzable functional group is used as the ceramic precursor, it is preferable to react the polymetalloxane gel with the mesopore-forming agent under heating under reflux.

[0093] Step (c) In step (c), the polymetalloxane gel subjected to step (b) is washed and / or dried as necessary, and then fired to produce a ceramic monolith.

[0094] Examples of cleaning solutions used for cleaning include water, organic solvents, mixed solvents of water and organic solvents, and aqueous solutions containing acids or bases. Examples of organic solvents include alcohols such as methanol, ethanol, n-propanol, 2-propanol (IPA), and butanol. Examples of acids include hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, acetic acid, formic acid, carbonic acid, citric acid, and phosphoric acid. Examples of bases include sodium hydroxide, potassium hydroxide, ammonia, water-soluble amines, sodium carbonate, and sodium bicarbonate.

[0095] Examples of drying methods include natural drying, heat drying, drying using a low surface tension solvent, drying by freeze sublimation, and supercritical drying.

[0096] In the firing, the firing temperature is preferably from 500° C. to 1000° C., more preferably from 600° C. to 800° C., and the firing time is preferably from 1 hour to 8 hours, more preferably from 3 hours to 5 hours. The firing is usually carried out in an air atmosphere.

[0097] The ceramic monolith has a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores. The ceramic skeleton of the ceramic monolith is formed from the skeleton phase of the polymetalloxane gel, and the macropores of the ceramic monolith are formed from the solvent phase of the polymetalloxane gel.

[0098] In one embodiment, the ceramic monolith is a silica monolith, which has a bicontinuous structure formed by a silica framework containing mesopores and macropores.

[0099] In another embodiment, the ceramic monolith can be an alumina, tin oxide, ceria, titania, or zirconia monolith, which also has a bicontinuous structure formed by a framework of alumina, tin oxide, ceria, titania, or zirconia containing mesopores and macropores.

[0100] The produced ceramic monolith may be molded and used as an adsorbent (e.g., an adsorbent having a columnar shape), or a molded ceramic monolith may be produced using a mold or the like, and used as an adsorbent (e.g., an adsorbent having a columnar shape) either as is or after further molding as needed. For example, a molded ceramic monolith can be produced by using a molding mold for molding a gel into a desired shape in the gel production process. The average diameter of the molded ceramic monolith will be smaller than the average diameter of the mold.

[0101] The produced ceramic monolith may be pulverized and used as an adsorbent. Pulverization can be carried out according to a conventional method. Pulverization can be carried out using, for example, a mortar, a hammer mill, a ball mill, a bead mill, a jet mill, a roller mill, or the like. The particle diameter of the adsorbent after pulverization is preferably 0.5 μm or more and 7.0 mm or less, more preferably 2.0 μm or more and 5.0 mm or less, and even more preferably 5.0 μm or more and 3.0 mm or less. Note that "particle diameter" refers to the circle-equivalent diameter, i.e., the diameter of a circle assumed to have an area equal to the area of ​​the adsorbent after pulverization in an observation image (e.g., an SEM image) of the adsorbent after pulverization.

[0102] The adsorbent of the present invention comprises a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and a sulfur atom-containing group that modifies the surface of the ceramic skeleton. The adsorbent of the present invention will be described below.

[0103] <Surface Modification> The surface of the ceramic skeleton is modified with a sulfur atom-containing group. The surface of the ceramic skeleton may be modified with one type of sulfur atom-containing group, or may be modified with two or more types of sulfur atom-containing groups. The sulfur atom-containing group may be bonded directly to the surface of the ceramic skeleton, or may be bonded to the surface of the ceramic skeleton via a linker.

[0104] The surface of the ceramic skeleton includes the inner and outer surfaces of the ceramic skeleton. The inner surface of the ceramic skeleton includes the inner surfaces of the macropores and mesopores present inside the ceramic skeleton (i.e., not exposed on the outer surface of the ceramic skeleton), and the outer surface of the ceramic skeleton includes the inner surfaces of the macropores and mesopores exposed on the outer surface of the ceramic skeleton. Of the surfaces of the ceramic skeleton, at least the inner surface is preferably modified with a sulfur atom-containing group.

[0105] The sulfur atom-containing group is not particularly limited as long as it is a group containing a sulfur atom. The sulfur atom-containing group may be a monovalent group or a divalent group. Examples of the sulfur atom-containing group include -S ｘ The sulfur atom-containing group is a group containing -S ｘ -, where x is, for example, an integer of 1 to 8, preferably an integer of 1 to 5, and more preferably an integer of 1 or 2. -S ｘ Examples of - include a sulfide group (-S-), a disulfide group (-S-S-), a trisulfide group (-S-S-S-), and a tetrasulfide group (-S-S-S-S-).

[0106] The sulfur atom-containing group is preferably a group containing at least one selected from the group consisting of a thiol group, an alkylthio group which may have one or more substituents, an arylthio group which may have one or more substituents, an arylalkylthio group which may have one or more substituents, an alkylarylthio group which may have one or more substituents, an alkylcarbonylthio group which may have one or more substituents, an arylcarbonylthio group which may have one or more substituents, an alkyloxycarbonylthio group which may have one or more substituents, and an aryloxycarbonylthio group which may have one or more substituents, more preferably a group containing at least one selected from the group consisting of a thiol group and an alkylthio group which may have one or more substituents, and even more preferably a group containing a thiol group. The sulfur atom-containing group may be composed of a group selected from the above group. The arylalkylthio group and the alkylarylthio group may each have a substituent in either the alkyl portion or the aryl portion, or in both.

[0107] In one embodiment, a compound having at least one sulfur atom-containing group (hereinafter sometimes referred to as a "sulfur atom-containing compound") is fixed to the surface of the ceramic skeleton, thereby modifying the surface of the ceramic skeleton with at least one sulfur atom-containing group. Methods for introducing a sulfur atom-containing compound to the surface of the ceramic skeleton include, for example, chemically fixing a sulfur atom-containing compound (e.g., a silane coupling agent having at least one sulfur atom-containing group (hereinafter sometimes referred to as a "sulfur atom-containing silane coupling agent") to the surface of the ceramic skeleton via a covalent bond, and physically fixing a sulfur atom-containing compound to the surface of the ceramic skeleton via physical interactions such as ionic bonds and hydrophobic interactions. A method for chemically introducing a sulfur atom-containing compound to the surface of the ceramic skeleton includes, for example, reacting a functional group (e.g., a hydroxyl group) on the surface of the ceramic skeleton with a sulfur atom-containing silane coupling agent to chemically fix the silane coupling agent to the surface of the ceramic skeleton. The sulfur atom-containing compound may be fixed to the surface of the ceramic skeleton via a linker. For example, a functional group reactive with a sulfur atom-containing compound may be introduced onto the surface of a ceramic skeleton, and then the introduced functional group may be reacted with the sulfur atom-containing compound to chemically fix the sulfur atom-containing compound to the surface of the ceramic skeleton. A method for introducing a functional group reactive with a sulfur atom-containing compound onto the surface of a ceramic skeleton includes reacting a functional group (e.g., a hydroxyl group) on the surface of the ceramic skeleton with a silane coupling agent having a functional group reactive with a sulfur atom-containing compound, and chemically fixing the silane coupling agent to the surface of the ceramic skeleton. Examples of silane coupling agents having a functional group reactive with a sulfur atom-containing compound include silane coupling agents having an epoxy group and / or a haloalkyl group. Examples of silane coupling agents having an epoxy group include 3-glycidyloxypropyltrimethoxysilane. Examples of silane coupling agents having a haloalkyl group include 3-chloropropyltrimethoxysilane.

[0108] In the compound having at least one sulfur atom-containing group, the portion other than the sulfur atom-containing group may be composed of hydrogen atoms and carbon atoms, or may contain one or more other elements (e.g., oxygen atoms, nitrogen atoms, halogen atoms, silicon atoms, etc.) in addition to hydrogen atoms and carbon atoms.

[0109] As the compound having at least one sulfur atom-containing group, one or more compounds may be used, or two or more compounds may be used. The compound having at least one sulfur atom-containing group may be a silane coupling agent.

[0110] Examples of silane coupling agents containing at least one sulfur atom-containing group include silane coupling agents represented by formula A, B, C, D, or E. Formula A: R ａ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula B: R ａ -R ｄ -Si(-O-(R ｅ -O) ｍ -R ｆ ) ｎ (-R ｃ ) ３－ｎ Formula C: Si(-R ｇ ) ｑ (-R ｈ ) ３－ｑ -R ｉ -S ｘ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula D: Si(-O-(R ｊ -O) ｐ -R ｋ ) ｑ (-R ｈ ) ３－ｑ -R ｉ -S ｘ -R ｄ -Si(-O-(R ｅ -O) ｍ -R ｆ ) ｎ (-R ｃ )３－ｎ Formula E: Si(-R ｇ ) ｑ (-R ｈ ) ３－ｑ -R ｉ -S ｘ -R ｄ -Si(-O-(R ｅ -O) ｍ -R ｆ ) ｎ (-R ｃ ) ３－ｎ

[0111] In Formula A, R ａ represents a monovalent sulfur atom-containing group, R ｂ each independently represents an alkyl group, R ｃ each independently represents an alkyloxy group or a halogen atom, R ｄ represents an alkylene group, an arylene group, or a combination thereof; and n represents an integer of 0 to 2.

[0112] In Formula B, R ａ , R ｃ , R ｄ and n are as defined in formula A, and R ｅ each independently represents an alkylene group; R ｆ each independently represents an alkyl group, and m represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably an integer of 1 or 2.

[0113] In Formula C, R ｂ , R ｃ , R ｄ and n are as defined in formula A, and R ｇ each independently represents an alkyl group, R ｈ each independently represents an alkyloxy group or a halogen atom, R ｉ represents an alkylene group, an arylene group, or a combination thereof; q represents an integer of 0 to 2; and x represents an integer of 1 to 8, preferably an integer of 1 to 5, and more preferably an integer of 1 or 2.

[0114] In Formula D, R ｃ , R ｄ and n are as defined in formula A, and R ｅ , R ｆ and m are as defined in formula B, and R ｈ, q and x are defined as in formula C, and R ｊ each independently represents an alkylene group; R ｋ each independently represents an alkyl group, and p represents an integer of 1 to 5, preferably an integer of 1 to 3, and more preferably an integer of 1 or 2.

[0115] In formula E, R ｃ , R ｄ and n are as defined in formula A, and R ｅ , R ｆ and m are as defined in formula B, and R ｇ , R ｈ , R ｉ , q and x have the same meanings as in formula C.

[0116] R ａ is preferably a group selected from the group consisting of a thiol group, an alkylthio group which may have one or more substituents, an arylthio group which may have one or more substituents, an arylalkylthio group which may have one or more substituents, an alkylarylthio group which may have one or more substituents, an alkylcarbonylthio group which may have one or more substituents, an arylcarbonylthio group which may have one or more substituents, an alkyloxycarbonylthio group which may have one or more substituents, and an aryloxycarbonylthio group which may have one or more substituents, more preferably a group selected from the group consisting of a thiol group and an alkylthio group which may have one or more substituents, and even more preferably a thiol group.

[0117] R ｂ , R ｆ , R ｇ or R ｋ Examples of the alkyl group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0118] R ｃ or R ｈ Examples of the alkyloxy group or halogen atom represented by R include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a chlorine atom, a bromine atom, and an iodine atom. ｃ or R ｈThe alkyloxy group represented by R is preferably a methoxy group or an ethoxy group. ｃ or R ｈ The halogen group represented by the formula (I) is preferably a chlorine atom.

[0119] R ｄ , R ｅ , R ｉ or R ｊ Examples of the alkylene group represented by the formula (I) include a methylene group, an ethylene group, a propylene group, and a butylene group.

[0120] R ｄ or R ｉ Examples of the arylene group represented by the formula (I) include a phenylene group, a naphthylene group, and a biphenylene group.

[0121] R ｄ or R ｉ Examples of the combination of an alkylene group and an arylene group represented by the formula include groups represented by the formula: -X-Y-, -Y-X-, -X-Y-X-, or -Y-X-Y-, where X represents an alkylene group and Y represents an arylene group.

[0122] R ｄ or R ｉ The alkylene group, arylene group, or combination thereof represented by the formula (I) may have one or more substituents.

[0123] Examples of the silane coupling agent represented by formula A include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltriethoxysilane.

[0124] Examples of the silane coupling agent represented by formula B include ethoxy(3-mercaptopropyl)bis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silane.

[0125] Examples of the silane coupling agent represented by formula C include bis(3-(triethoxysilyl)propyl)tetrasulfide and bis(3-(triethoxysilyl)propyl)disulfide.

[0126] Generally, the greater the amount of functional groups introduced onto the surface of the adsorbent, the better the adsorption performance. However, when sulfur atom-containing groups are introduced onto the surface of a ceramic skeleton, if the amount of introduced sulfur atom-containing groups is too large, the hydrophobicity of the adsorbent increases. When the hydrophobicity of the adsorbent increases, it becomes difficult for a solution containing the target substance to reach the pores, and the introduced functional groups cannot be effectively utilized, resulting in a decrease in adsorption performance. Therefore, from the viewpoint of effectively improving the adsorption performance of the adsorbent, the amount of sulfur atom-containing groups contained in the adsorbent is 0.5 mmol / g or more and 3.5 mmol / g or less, based on the mass of the adsorbent. From the viewpoint of more effectively improving the adsorption performance of the adsorbent, the amount of sulfur atom-containing groups contained in the adsorbent is preferably 1.0 mmol / g or more and 3.5 mmol / g or less, more preferably 1.0 mmol / g or more and 3.0 mmol / g or less, based on the mass of the adsorbent, even more preferably 1.5 mmol / g or more and 3.0 mmol / g or less.

[0127] The "amount of sulfur atom-containing groups" means the amount of one type of sulfur atom-containing group when the adsorbent contains one type of sulfur atom-containing group, and means the total amount of the two or more types of sulfur atom-containing groups when the adsorbent contains two or more types of sulfur atom-containing groups. Furthermore, the "amount of sulfur atom-containing groups" means the amount converted to sulfur atoms. The amount of sulfur atom-containing groups can be measured according to a conventional method. For example, the amount of sulfur atom-containing groups can be measured by the method described in the Examples below.

[0128] The sulfur atom-containing group is capable of adsorbing, for example, one or more species selected from the group consisting of transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16.

[0129] Transition metals and transition metal ions include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Zn, Cd, Hg, and rare earth metals and ions thereof.

[0130] Rare earth metals and rare earth metal ions include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu and ions thereof.

[0131] Group 13-16 metals and metalloids and ions thereof include B, Al, Si, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, Po, and At and ions thereof, of which B, Si, Ge, As, Se, Po, At, Sb, and Te are metalloids.

[0132] In order to more effectively improve the adsorption performance of the adsorbent, it is preferable that the target substance to be adsorbed by the sulfur atom-containing group is one or more selected from the group consisting of Cu, Ag, Au, Pd, Pt, Bi, Se, and As.

[0133] <Water absorption rate> When the hydrophobicity of the adsorbent is high, it becomes difficult for the solution containing the target substance to reach the pores, and the introduced functional groups cannot be effectively utilized, resulting in a decrease in adsorption performance. Therefore, it is preferable that the adsorbent has low hydrophobicity, i.e., has high hydrophilicity.

[0134] The hydrophilicity of an adsorbent can be evaluated based on the water absorption rate of the adsorbent. The higher the water absorption rate of the adsorbent, the higher the hydrophilicity of the adsorbent. From the viewpoint of effectively realizing an improvement in the adsorption performance of the adsorbent, the water absorption rate of the adsorbent is 8% or more. From the viewpoint of more effectively realizing an improvement in the adsorption performance of the adsorbent, the water absorption rate of the adsorbent is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, and even more preferably 100% or more. The upper limit value is not particularly limited. The upper limit value may be 500% or less, 400% or less, or 300% or less. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0135] The water absorption rate of an adsorbent is measured as follows. The adsorbent is dried under reduced pressure, and the weight of the adsorbent after drying under reduced pressure is measured. Specifically, the pressure is reduced to 100 Pa or less, the adsorbent is dried at 40°C for 1 hour, and the weight of the adsorbent after drying under reduced pressure is measured. Next, 200 mg of the adsorbent after drying under reduced pressure is placed in a mesh basket and suspended in a 200 mL beaker containing 125 mL of pure water. At this time, the mesh basket is suspended in the beaker so that the entire adsorbent is immersed in the pure water. Next, the pure water in the beaker is stirred at 350 rpm for 30 minutes at 25°C. After stirring, the mesh basket is removed, and any water adhering to the mesh basket is wiped off to prevent the adsorbent from coming into contact with water after removal. Next, the weight of the adsorbent after immersion is measured, and the water absorption rate is calculated based on the following formula. Water absorption rate (%)={(weight of adsorbent after immersion)−(weight of adsorbent after drying under reduced pressure)} / (weight of adsorbent after drying under reduced pressure)×100

[0136] As described above, when sulfur atom-containing groups are introduced onto the surface of a ceramic skeleton, if the amount of introduced sulfur atom-containing groups is too large, the hydrophobicity of the adsorbent increases and the adsorption performance decreases. Therefore, the amount of sulfur atom-containing groups contained in the adsorbent is adjusted to 0.5 mmol / g or more and 3.5 mmol / g or less, based on the mass of the adsorbent. However, simply adjusting the amount of sulfur atom-containing groups contained in the adsorbent within the above range is difficult to achieve the desired water absorption rate. In addition to adjusting the amount of sulfur atom-containing groups contained in the adsorbent within the above range, in the method for producing an adsorbent, the porous body and a reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups are contacted in water, in an aqueous solution having a pH of 1 to 12, or in a mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 to 12, where the ratio of the volume of the organic solvent to the volume of the aqueous solution or water is 0.5 or less. This easily achieves the desired water absorption rate. The method for producing an adsorbent will be described later.

[0137] <<Method for Producing Adsorbent>> The method for producing an adsorbent of the present invention is a method for producing an adsorbent comprising a porous body having a bicontinuous structure formed by a ceramic skeleton containing mesopores and macropores, and sulfur atom-containing groups that modify the surface of the ceramic skeleton, and includes a step of contacting the porous body with a reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups in a solvent.

[0138] As a reagent for modifying the surface of the ceramic skeleton with a sulfur atom-containing group, for example, a compound having at least one type of sulfur atom-containing group, preferably a silane coupling agent having at least one type of sulfur atom-containing group, more preferably a silane coupling agent represented by formula A, B, C, D, or E, can be used. One type of reagent may be used, or two or more types of reagents may be used.

[0139] In the step of contacting the porous body with a reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups in a solvent, the mixture containing the porous body, the reagent, and the solvent is heated, for example, at a temperature of 40°C to 100°C, preferably 60°C to 100°C, and more preferably 80°C to 100°C, for a time of, for example, 1 hour to 12 hours, preferably 2 hours to 10 hours, and more preferably 4 hours to 8 hours, thereby modifying the surface of the ceramic skeleton with sulfur atom-containing groups. After modifying the surface of the ceramic skeleton with sulfur atom-containing groups, the adsorbent is separated from the mixture using a solid-liquid separation method such as filtration, and the separated adsorbent is washed with a washing liquid such as pure water. The washed adsorbent is then dried, thereby obtaining the final product, the adsorbent.

[0140] The solvent used when contacting the porous body with the reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups is water, an aqueous solution having a pH of 1 to 12, or a mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 to 12, in which the ratio of the volume of the organic solvent to the volume of the aqueous solution or water is 0.5 or less. This allows the reaction of modifying the surface of the ceramic skeleton with sulfur atom-containing groups to be carried out quickly.

[0141] As the water, for example, pure water, ion-exchanged water, distilled water, reverse osmosis water (RO water), etc. can be used.

[0142] From the viewpoint of efficiently modifying the surface of the ceramic skeleton with sulfur atom-containing groups, the aqueous solution having a pH of 1 to 12 is preferably an aqueous solution having a pH of 2 to 10, more preferably an aqueous solution having a pH of 3 to 7.

[0143] An aqueous solution having a pH of 1 to 12 can be prepared by adding an acid or a base to pure water. The acid to be added can be selected from, for example, acetic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc. The acid to be added is preferably acetic acid. The base to be added can be selected from, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, trimethylamine, triethylamine, etc. The base to be added is preferably selected from sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate. In one embodiment, the aqueous solution having a pH of 1 to 12 is an aqueous acetic acid solution.

[0144] When a mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 to 12 is used to contact a porous body with a reagent for modifying the surface of the ceramic skeleton with sulfur atom-containing groups, a large ratio of the volume of the organic solvent to the volume of the aqueous solution or water in the mixed solution increases the hydrophobicity of the produced adsorbent, resulting in a decrease in the adsorption performance of the produced adsorbent. Therefore, from the viewpoint of increasing the hydrophilicity (i.e., water absorption) of the produced adsorbent, it is preferable that the ratio of the volume of the organic solvent to the volume of the aqueous solution or water in the mixed solution is small. Specifically, this ratio is 0.5 or less. This ratio is preferably 0.3 or less, more preferably 0.1 or less. The lower limit is not particularly limited as long as it exceeds 0. The "volume of organic solvent" refers to the volume of one organic solvent when the mixed solution contains one organic solvent, and refers to the total volume of the two or more organic solvents when the mixed solution contains two or more organic solvents. An aqueous solution having a pH of 1 to 12 does not contain an organic solvent. Therefore, the ratio of the volume of the organic solvent to the volume of the aqueous solution in an aqueous solution having a pH of 1 to 12 is 0.

[0145] Examples of the organic solvent include alcohol solvents such as monohydric alcohols (e.g., chain aliphatic alcohols such as methanol, ethanol, n-propanol, and 2-propanol; cyclic aliphatic alcohols such as cyclobutanol, cyclopentanol, and cyclohexanol; and aromatic alcohols such as benzyl alcohol and phenylethyl alcohol), dihydric alcohols (e.g., ethylene glycol, diethylene glycol, propylene glycol, and dipropylene glycol), and polyhydric alcohols (e.g., glycerin, diglycerin, triglycerin, and tetraglycerin); ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and propylene glycol monomethyl ether; Examples of suitable solvents include polyhydric alcohol derivatives such as tetrahydrofuran, 2-methyl-tetrahydrofuran, cyclopentyl methyl ether, dibutyl ether, 1,4-dioxane, methyl tert-butyl ether, diisopropyl ether, dimethoxyethane, and diglyme; ketone solvents such as acetone, methyl ethyl ketone, and diethyl ketone; ester solvents such as methyl acetate and ethyl acetate; halogenated hydrocarbon solvents such as dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, and chlorobenzene; aromatic hydrocarbon solvents such as toluene and xylene; and aliphatic hydrocarbon solvents such as hexane and heptane. In one embodiment, the mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 to 12 is a mixed solvent of ethanol and an aqueous solution or water having a pH of 1 to 12.

[0146] The method for producing an adsorbent of the present invention can produce an adsorbent that is highly hydrophilic (i.e., has a high water absorption rate), and is therefore suitable for producing the adsorbent of the present invention.

[0147] <Effects and Uses of Adsorbent> The adsorbent of the present invention has excellent adsorption performance due to the effects of the bicontinuous structure formed by the ceramic skeleton containing mesopores and macropores, the effects of the amount of sulfur atom-containing groups being 0.5 mmol / g or more and 3.5 mmol / g or less, and the effects of a water absorption rate of 8% or more. The adsorption performance can be evaluated based on the adsorption rate (the percentage of the amount of the target substance adsorbed by the adsorbent relative to the amount of the target substance initially contained in the solution) calculated from the amount of the target substance adsorbed by the adsorbent when a solution containing the target substance is contacted with the adsorbent for a certain period of time. The adsorption performance can also be evaluated based on the adsorption rate calculated by dividing the amount of the target substance adsorbed by the adsorbent by the certain period of time when a solution containing the target substance is contacted with the adsorbent.

[0148] The adsorbent of the present invention is useful as an adsorbent for adsorbing one or more target substances selected from the group consisting of metals, metal ions, semi-metals, and semi-metal ions, and can be used to recover one or more target substances.

[0149] The one or more target substances can be selected from the group consisting of, for example, transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16. Among these, in view of the high demand for adsorption and recovery, the one or more target substances are preferably selected from the group consisting of transition metals excluding rare earth metals, metals and metalloids of Groups 13 to 16, and ions thereof. Examples of the form of the metals and metalloids adsorbed by the adsorbent of the present invention include metal nanoparticles and metalloid nanoparticles. The metals, metalloids, metal ions, and metalloid ions adsorbed by the adsorbent of the present invention may or may not each have a ligand.

[0150] <<Method for recovering target substance>> The method for recovering target substance of the present invention is a method for recovering one or more target substances from a solution containing one or more target substances selected from the group consisting of metals, metal ions, metalloids, and metalloid ions (hereinafter referred to as "liquid to be treated"), and includes a step of contacting the liquid to be treated with the adsorbent of the present invention.

[0151] When a liquid to be treated is brought into contact with the adsorbent of the present invention, one or more target substances contained in the liquid to be treated are adsorbed by the adsorbent of the present invention, thereby making it possible to recover one or more target substances from the liquid to be treated.

[0152] Examples of the liquid to be treated include wastewater discharged from a plant or the like, and wastewater containing valuable metals discharged from a metal refining process. The liquid to be treated usually contains water. The wastewater or wastewater may be pretreated as necessary before being brought into contact with the adsorbent of the present invention.

[0153] The one or more target substances contained in the liquid to be treated can be selected from the group consisting of, for example, transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16. Among these, from the viewpoint of the high demand for adsorption and recovery, it is preferable that the one or more target substances be selected from the group consisting of transition metals excluding rare earth metals, metals and metalloids of Groups 13 to 16, and ions thereof.

[0154] Examples of methods for contacting the liquid to be treated with the adsorbent of the present invention include a method of immersing the adsorbent of the present invention in the liquid to be treated, a method of passing the liquid to be treated through a column packed with the adsorbent of the present invention, etc. The liquid can be passed through, for example, using a liquid feed pump.

[0155] The adsorbent of the present invention is particularly useful when recovering each target substance from a liquid to be treated in which the concentration of each target substance is low (for example, the concentration of each target substance is 0.1 ppm or more and 5000 ppm or less, particularly 0.1 ppm or more and 100 ppm or less).

[0156] The present invention will be explained in more detail below based on examples and comparative examples, but the scope of the present invention is not limited by these examples and comparative examples.

[0157] Example 1 (1) Preparation of Silica Monolith 8.67 g of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH), 7.80 g of urea, and 86.7 g of an aqueous acetic acid solution (acetic acid concentration: 6.06% by mass) were added to a 150 mL reaction vessel and stirred at room temperature for 10 minutes. The reaction vessel was placed in an ice bath, and the reaction solution was cooled with stirring for 15 minutes. 44.7 g of tetramethoxysilane was added to the cooled reaction solution, and the mixture was stirred for 30 minutes while cooling in the ice bath. The reaction solution was heated in a 30°C warm bath and then left to stand overnight in an incubator at 30°C to prepare a polysiloxane gel.

[0158] The resulting polysiloxane gel was then added to a separate reaction vessel containing 30 mL of 3 mol / L urea water, and the mixture was heated under reflux for 12 hours. After the reaction was completed, the resulting polysiloxane gel was washed with water and dried for 12 hours in a dryer set at 60°C. After drying, the gel was fired at 600°C for 5 hours in an air atmosphere to produce a silica monolith. The produced silica monolith was pulverized and classified to obtain a silica monolith with a particle size of 100 μm or more and 300 μm or less.

[0159] (2) Observation by Scanning Electron Microscope When the surface structure of the silica monolith obtained in (1) above was observed by a scanning electron microscope (JSM-7900F manufactured by JEOL), it was confirmed that the silica monolith had a bicontinuous structure formed by a silica skeleton and macropores.

[0160] (3) Measurement of specific surface area and most frequent pore size of mesopores The specific surface area and most frequent pore size of mesopores of the silica monolith obtained in (1) above were measured using a specific surface area and pore size distribution measuring device (BELSORP-miniX manufactured by Microtrac-Bell). For a silica monolith that had been degassed under reduced pressure at 400°C for 3 hours, the amount of nitrogen adsorption and desorption at a temperature of 77K was measured using liquid nitrogen by a multipoint method to obtain an adsorption and desorption isotherm, and the specific surface area and most frequent pore size were calculated based on the adsorption and desorption isotherm. The specific surface area was calculated by the BET method, and the most frequent pore size was calculated by the BJH method.

[0161] The BJH method is a method for analyzing the distribution of pore volume relative to the diameter of pores assumed to be cylindrical in accordance with the standard Barrett-Joyner-Halenda model (for details, see J. Amer. Chem. Soc., 73, 373, 1951, etc.). In the present invention, pores having diameters ranging from 2 to 200 nm were analyzed.

[0162] (4) Measurement of total pore volume, most frequent pore size of macropores, and porosity The total pore volume, most frequent pore size of macropores, and porosity of the silica monolith obtained in (1) above were measured by mercury intrusion porosimetry using a mercury porosimeter (AutoPore IV 9520 manufactured by Micromeritics). In the mercury intrusion porosimetry, pressure was applied to the pores of the silica monolith to infiltrate mercury, and the pore volume and specific surface area were determined from the pressure and the amount of mercury intruded. The pore diameter was calculated from the relationship between the pore volume and the specific surface area when the pores were assumed to be cylindrical. In the present invention, mercury intrusion porosimetry was used to analyze a range of pores having a diameter of 50 nm to 500 μm. The measurement was carried out under the following conditions and procedures.

[0163] (Measurement conditions) Mercury parameters Advancing contact angle: 130.0° Receding contact angle: 130.0° Surface tension: 485.0 mN / m (485.0 dynes / cm) Mercury density: 13.5335 g / mL Low pressure parameters Exhaust pressure: 50 μmHg Exhaust time: 5.0 minutes Mercury injection pressure: 0.0035 MPa Equilibration time: 10 seconds High pressure parameters Equilibration time: 10 seconds Injection volume: adjusted to 25% or more and 90% or less Measurement environment: 20°C

[0164] (Measurement procedure) (i) Weigh out approximately 0.5 g of sample and place it in the sample cell, then enter the weighed value. (ii) Measure the range of 0.0048 to 0.2068 MPa in the low-pressure section. (iii) Measure the range of 0.2068 to 255.1060 MPa in the high-pressure section. (ii) and (iii) were performed automatically using the software provided with the device.

[0165] The results of (3) and (4) above are shown in Table 1.

[0166]

[0167] (5) Preparation of thiol-containing silica monolith adsorbent 4.08 g of 3-mercaptopropyltrimethoxysilane, which had been stirred at room temperature for 1 hour, 35 mL of an aqueous acetic acid solution (pH 3.3), and 5.0 g of the silica monolith obtained in (1) above were added to a reaction vessel, and the mixture was left to stand at room temperature for 30 minutes, followed by heating at 80°C for 4 hours to prepare a thiol-containing silica monolith adsorbent. The thiol-containing silica monolith adsorbent was separated from the solution by filtration, washed with 500 mL of pure water, and dried to obtain 6.89 g of a thiol-containing silica monolith adsorbent.

[0168] (6) Measurement of sulfur atom content The sulfur atom content contained in the thiol-containing silica monolith adsorbent obtained in (5) above was quantified using a carbon / sulfur analyzer (EMIA-Expert manufactured by Horiba, Ltd.), and the sulfur atom content was taken as the thiol group content.

[0169] (7) Measurement of Water Absorption The thiol-containing silica monolith adsorbent obtained in (5) above was dried under reduced pressure, and the weight of the adsorbent after drying under reduced pressure was measured. Specifically, the pressure was reduced to 100 Pa or less, and the adsorbent was dried at 40°C for 1 hour. The weight of the adsorbent after drying under reduced pressure was measured. Next, 200 mg of the adsorbent after drying under reduced pressure was placed in a mesh basket and suspended in a 200 mL beaker containing 125 mL of pure water. At this time, the mesh basket was suspended in the beaker so that the entire adsorbent was immersed in the pure water. Next, the pure water in the beaker was stirred at 350 rpm for 30 minutes at 25°C. After stirring, the mesh basket was removed, and the water adhering to the mesh basket was wiped off with a paper wiper. Next, the weight of the adsorbent after immersion was measured, and the water absorption was calculated based on the following formula. Water absorption rate (%)={(weight of adsorbent after immersion)−(weight of adsorbent after drying under reduced pressure)} / (weight of adsorbent after drying under reduced pressure)×100

[0170] The results of (6) and (7) above are shown in Table 2.

[0171]

[0172] 60 mg of the thiol-containing silica monolith adsorbent obtained in (5) above was immersed in 30 mL of an aqueous solution (Pd 100 ppm, pH = 1) prepared by diluting palladium standard solution (Pd1000) (manufactured by Kanto Chemical Co., Inc.) 10 times with dilute nitric acid, and the mixture was stirred at 25°C for 1 hour. After the reaction was completed, the silica monolith adsorbent was separated by filtration, and the amount of palladium contained in the resulting filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The percentage of the amount of palladium adsorbed by the silica monolith adsorbent relative to the amount of palladium initially contained in the aqueous solution (hereinafter referred to as the "adsorption rate of palladium element") was calculated. The calculated adsorption rates of palladium element are shown in Table 3. In Table 3, the adsorption rate of palladium element is referred to as "Pd adsorption rate."

[0173] 60 mg of the thiol-containing silica monolith adsorbent obtained in (5) above was immersed in 30 mL of an aqueous solution (Bi 100 ppm, pH = 1) prepared by diluting bismuth standard solution (Bi1000) (manufactured by Kanto Chemical Co., Ltd.) 10 times with dilute nitric acid, and stirred at 25 ° C. for 1 hour. After the reaction was completed, the silica monolith adsorbent was separated by filtration, and the amount of bismuth contained in the obtained filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The adsorption rate of bismuth element calculated in the same manner as the adsorption rate of palladium element is shown in Table 3. In Table 3, the adsorption rate of bismuth element is referred to as "Bi adsorption rate."

[0174] 60 mg of the thiol-containing silica monolith adsorbent obtained in (5) above was immersed in 30 mL of an aqueous solution (As 10 ppm, pH = 1) prepared by diluting arsenic standard solution (As1000) (manufactured by Kanto Chemical Co., Ltd.) 100 times with dilute hydrochloric acid, and the mixture was stirred at 25 ° C. for 1 hour. After the reaction was completed, the silica monolith adsorbent was separated by filtration, and the amount of arsenic contained in the obtained filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The adsorption rate of arsenic, calculated in the same manner as the adsorption rate of palladium, is shown in Table 3. In Table 3, the adsorption rate of arsenic is referred to as "As adsorption rate."

[0175] 60 mg of the thiol-containing silica monolith adsorbent obtained in (5) above was immersed in 30 mL of an aqueous solution (Se 10 ppm, pH = 1) prepared by diluting selenium standard solution (Se1000) (manufactured by Kanto Chemical Co., Ltd.) 100 times with dilute nitric acid, and stirred at 25 ° C. for 1 hour. After the reaction was completed, the silica monolith adsorbent was separated by filtration, and the amount of selenium contained in the obtained filtrate was analyzed using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation). The adsorption rate of selenium, calculated in the same manner as the adsorption rate of palladium, is shown in Table 3. In Table 3, the adsorption rate of selenium is referred to as "Se adsorption rate."

[0176]

[0177] [Example 2] A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in the preparation of the adsorbent was changed to 1.02 g. The results are shown in Tables 1 to 3.

[0178] Example 3 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in preparing the adsorbent was changed to 2.04 g. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, and therefore is indicated as "-" in Table 2, but from the results of Examples 2 and 4, it can be estimated that the water absorption rate is 8% or more.

[0179] [Example 4] A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in preparing the adsorbent was changed to 3.06 g. The results are shown in Tables 1 to 3.

[0180] Example 5 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in preparing the adsorbent was changed to 5.11 g. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, and therefore is indicated as "-" in Table 2, but from the results of Examples 1 and 4, it can be estimated that the water absorption rate is 8% or more.

[0181] [Example 6] A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in preparing the adsorbent was changed to 7.15 g. The results are shown in Tables 1 to 3.

[0182] Example 7 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH) used in the preparation of the silica monolith was changed to 9.97 g. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, and therefore is indicated as "-" in Table 2, but from the results of Example 1, it can be estimated that the water absorption rate is 8% or more.

[0183] Example 8 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of polyethylene glycol 10000 (manufactured by SIGMA-ALDRICH) used in the preparation of the silica monolith was changed to 7.08 g. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, and therefore is indicated as "-" in Table 2, but from the results of Example 1, it can be estimated that the water absorption rate is 8% or more.

[0184] Example 9 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the heating reflux time in 3 mol / L urea water was changed to 5 hours in the preparation of the silica monolith. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, so it is indicated as "-" in Table 2, but from the results of Example 1, it can be estimated that the water absorption rate is 8% or more.

[0185] Example 10 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the heating reflux time in 3 mol / L urea water was changed to 24 hours in the preparation of the silica monolith. The results are shown in Tables 1 to 3. Note that the water absorption rate was not measured, and therefore is indicated as "-" in Table 2, but from the results of Example 1, it can be estimated that the water absorption rate is 8% or more.

[0186] [Comparative Example 1] A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in preparing the adsorbent was changed to 0.51 g. The results are shown in Tables 1 to 3.

[0187] Comparative Example 2 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the amount of 3-mercaptopropyltrimethoxysilane used in the preparation of the adsorbent was changed to 12.25 g. The results are shown in Tables 1 to 3.

[0188] Comparative Example 3 A thiol-containing silica monolith adsorbent was prepared and evaluated in the same manner as in Example 1, except that the acetic acid aqueous solution (pH 3.3) was replaced with a mixed solution of ethanol and acetic acid aqueous solution (pH 3.3) (volume ratio 1:1). The results are shown in Tables 1 to 3.

[0189] Comparative Example 4 Evaluation was carried out in the same manner as in Example 1 using commercially available thiol-containing silica SiliaMetS Thiol(SH) Metal Scavenger (manufactured by SiliCycle). The results are shown in Tables 1 to 3. SiliaMetS Thiol(SH) Metal Scavenger does not have a co-continuous structure. Note that the specific surface area, most frequent macropore diameter, most frequent mesopore diameter, total pore volume, porosity, and water absorption were not measured, and therefore are indicated as "-" in Tables 1 and 2.

[0190] Comparative Example 5 A thiol-containing silica adsorbent was prepared and evaluated in the same manner as in Example 4, except that 5.0 g of commercially available silica Wakogel C-200 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of the prepared silica monolith in the preparation of the adsorbent. Wakogel C-200 does not have a bicontinuous structure. The results are shown in Tables 1 to 3. Note that the specific surface area, most frequent macropore diameter, most frequent mesopore diameter, total pore volume, porosity, and water absorption were not measured, and therefore are indicated as "-" in Tables 1 and 2.

[0191] Comparative Example 6 A thiol-containing silica adsorbent was prepared and evaluated in the same manner as in Comparative Example 2, except that 5.0 g of commercially available silica Wakogel C-200 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of the prepared silica monolith in the preparation of the adsorbent. The results are shown in Tables 1 to 3. The specific surface area, most frequent diameter of macropores, most frequent diameter of mesopores, total pore volume, porosity, and water absorption were not measured, and therefore are indicated as "-" in Tables 1 and 2.

[0192] 1...Ceramic skeleton 2...Macropores 3...Mesopores

Claims

1. An adsorbent comprising a porous body having a bicontinuous structure formed by a ceramic skeleton including mesopores and macropores, and sulfur atom-containing groups modifying the surface of the ceramic skeleton, wherein the amount of the sulfur atom-containing groups contained in the adsorbent is 0.5 mmol / g or more and 3.5 mmol / g or less, and the water absorption rate of the adsorbent is 8% or more.

2. The adsorbent of claim 1, wherein the sulfur atom-containing group comprises a thiol group.

3. The adsorbent according to claim 1 or 2, wherein the most frequent pore size of the macropores of the porous body is 200 nm or more and 5000 nm or less.

4. The adsorbent according to claim 1 or 2, wherein the ratio of the most frequent pore size of the macropores of said porous body to the most frequent pore size of the mesopores of said porous body is 15 or more and 300 or less.

5. The adsorbent of claim 1 or 2, wherein the ceramic framework comprises an element selected from silicon, aluminum, tin, cerium, titanium and zirconium.

6. The adsorbent according to claim 1 or 2, wherein the sulfur atom-containing group is capable of adsorbing one or more species selected from the group consisting of transition metals including rare earth metals, metals and metalloids of Groups 13 to 16, transition metal ions including rare earth metal ions, and metal ions and metalloid ions of Groups 13 to 16.

7. A method for recovering one or more target substances selected from the group consisting of metals, metal ions, metalloids and metalloid ions from a solution containing the one or more target substances, the method comprising a step of contacting the solution with the adsorbent described in claim 1 or 2.

8. The method of claim 7, wherein the one or more target substances are selected from the group consisting of transition metals, including rare earth metals, Group 13-16 metals and metalloids, transition metal ions, including rare earth metal ions, and Group 13-16 metal and metalloid ions.

9. A method for producing an adsorbent comprising a porous body having a bicontinuous structure formed by a ceramic skeleton including mesopores and macropores, and sulfur atom-containing groups that modify the surface of the ceramic skeleton, the method comprising a step of contacting the porous body with a reagent for modifying the surface of the ceramic skeleton with the sulfur atom-containing groups in a solvent, the solvent being water, or an aqueous solution having a pH of 1 or more and 12 or less, or a mixed solution of an organic solvent and an aqueous solution or water having a pH of 1 or more and 12 or less, wherein the ratio of the volume of the organic solvent to the volume of the aqueous solution or water is 0.5 or less.