Method for producing adsorbing material and method for recovering target substance

Abstract

The present invention addresses the problem of providing a method for producing (regenerating) an adsorbing material or recovering a target substance by adsorbing the target substance to the adsorbing material and then performing a desorption treatment on the target substance, the method being capable of desorbing a sufficient amount of the target substance without using aqua regia in the desorption treatment, and being capable of preventing a decrease in the adsorption performance of the adsorbing material after the desorption treatment. To solve the problem, provided is a method for producing an adsorbing material or a method for recovering a target substance, the method comprising: (1) a step for preparing a second adsorbing material obtained by performing a contact treatment with a target substance-containing liquid on a first adsorbing material which has a co-continuous structure formed by macropores and a ceramic skeleton having mesopores and in which the surface of the ceramic skeleton is modified with a functional group capable of adsorbing a target substance; and (2) a step for obtaining a third adsorbing material or a target substance by performing a contact treatment with an acidic solution excluding aqua regia on the second adsorbing material to desorb the target substance from the second adsorbing material.

Description

Adsorbent manufacturing method and target substance recovery method

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

[0002] From the perspectives of carbon neutrality, SDGs, etc., technologies related to the reuse or recovery of target substances have been attracting attention. Examples of such technologies include technologies for recovering metals or metal ions contained in liquids. Known technologies for recovering metals or metal ions include adsorbents whose surfaces are modified with functional groups (e.g., Patent Documents 1 to 3). The adsorbents can be reused after the adsorbed metals or metal ions are desorbed.

[0003] Japanese Patent Application Laid-Open No. 3-158426 Japanese Patent Application Laid-Open No. 2016-11456 International Publication No. 2017 / 002871 Pamphlet

[0004] The present inventors have found that when a target substance selected from the group consisting of metals, metal ions, metalloids, and metalloid ions is adsorbed onto an adsorbent and then a desorption treatment of the target substance is performed, the adsorption performance of the adsorbent after the desorption treatment may be reduced compared to before the desorption treatment, depending on the conditions of the desorption treatment. Furthermore, the present inventors have found that this tendency is particularly pronounced when the desorption treatment is performed under harsh conditions (for example, when the desorption treatment is performed using aqua regia) in order to increase the amount of the target substance desorbed.

[0005] The decrease in the adsorption performance of an adsorbent after desorption treatment compared to before the desorption treatment becomes a problem when the adsorbent is used repeatedly. Therefore, an object of the present invention is to provide a method for producing (regenerating) an adsorbent or recovering a target substance by adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals, and semi-metal ions onto an adsorbent and then performing a desorption treatment of the target substance, which method can desorb a sufficient amount of the target substance without using aqua regia in the desorption treatment and can prevent a decrease in the adsorption performance of the adsorbent after the desorption treatment.

[0006] In order to solve the above problems, the present invention provides the following method. [1] A method for producing an adsorbent, comprising the following steps: (1A) preparing a second adsorbent by contacting a first adsorbent having a bicontinuous structure formed by a ceramic skeleton having mesopores and macropores, the surface of the ceramic skeleton being modified with functional groups capable of adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals, and semi-metal ions, with a liquid containing the target substance; and (2A) obtaining a third adsorbent by contacting the second adsorbent with an acidic solution excluding aqua regia, thereby desorbing the target substance from the second adsorbent, wherein the percentage of the adsorption amount of the target substance in the second adsorbent prepared in step (1A) relative to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more, and the percentage of the desorption amount of the target substance in step (2A) relative to the adsorption amount of the target substance in the second adsorbent prepared in step (1A) is 70% or more. [2] The manufacturing method according to [1], wherein the contact treatment in step (2A) is carried out at a temperature of 90°C or less. [3] The manufacturing method according to [1] or [2], wherein the acidic solution contains at least one selected from the group consisting of inorganic acids and ammonium salts. [4] The manufacturing method according to any one of [1] to [3], wherein the total concentration of the inorganic acid and ammonium salt contained in the acidic solution is 0.1 mol / L or more and 13 mol / L or less. [5] The manufacturing method according to any one of [1] to [4], wherein the acidic solution contains at least one selected from the group consisting of hydrochloric acid, nitric acid, and ammonium chloride. [6] The manufacturing method according to any one of [1] to [5], wherein the functional group contains at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, a nitrogen-containing heterocyclic group, a thiol group, a sulfo group, a phosphonic acid group, and a carboxyl group. [7] The manufacturing method according to any one of [1] to [6], wherein the ceramic skeleton contains at least one selected from the group consisting of silicon, aluminum, tin, cerium, titanium, and zirconium.[8] The manufacturing method according to any one of [1] to [7], wherein the target substance is 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 recovering a target substance, comprising the steps of: (1B) preparing a second adsorbent by contacting a first adsorbent having a bicontinuous structure formed by a ceramic skeleton having mesopores and macropores, the surface of the ceramic skeleton being modified with functional groups capable of adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals, and semi-metal ions, with a liquid containing the target substance; and (2B) contacting the second adsorbent with an acidic solution excluding aqua regia, thereby desorbing the target substance from the second adsorbent to obtain the target substance, wherein the percentage of the adsorption amount of the target substance in the second adsorbent prepared in step (1B) relative to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more, and the percentage of the desorption amount of the target substance in step (2B) relative to the adsorption amount of the target substance in the second adsorbent prepared in step (1B) is 70% or more.

[0007] According to the present invention, there is provided a method for producing (regenerating) an adsorbent or recovering a target substance by adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals, and semi-metal ions onto an adsorbent and then performing a desorption process on the target substance, which method can desorb a sufficient amount of the target substance without using aqua regia in the desorption process and can prevent a decrease in the adsorption performance of the adsorbent after the desorption process.

[0008] Even when the method of the present invention is repeatedly applied to an adsorbent to manufacture (regenerate) the adsorbent or to recover the target substance, a sufficient amount of the target substance can be desorbed without using aqua regia in the desorption treatment, and a decrease in the adsorption performance of the adsorbent after the desorption treatment can be prevented. Therefore, the method of the present invention is particularly useful when the adsorbent is repeatedly manufactured (regenerated) or the target substance is repeatedly recovered.

[0009] Fig. 1 is an enlarged view of a portion of the surface of an adsorbent according to one embodiment, and Fig. 2 is a schematic view of a flow adsorption device used in Examples and Comparative Examples.

[0010] <Explanation of Terms> The terms used in this specification will be explained below. The following explanations apply throughout this specification unless otherwise specified.

[0011] <Halogen Atom> Halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0012] <Alkyl Group> The number of carbon atoms in the alkyl group is, for example, 1 to 20, preferably 1 to 10, more preferably 1 to 6, still more preferably 1 to 5, and even more preferably 1 to 4. The alkyl group may be linear or branched. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0013] <Aryl Group> The aryl group is, for example, a monocyclic or polycyclic (e.g., bicyclic or tricyclic) aromatic hydrocarbon ring group. The number of carbon atoms in the aryl group is, for example, 6 to 14, preferably 6 to 10. The polycyclic group may be a fused ring group. Examples of the aryl group include a phenyl group and a naphthyl group.

[0014] 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 in the arylalkyl group is, for example, 1, 2, or 3.

[0015] 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 in the alkylaryl group is, for example, 1, 2, or 3.

[0016] <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.

[0017] <Alkylene group> The alkylene group is a divalent functional group formed by removing one hydrogen atom from an alkyl group, and the description of the alkyl group is as described above. Examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, and a decylene group.

[0018] <Arylene Group> The arylene group is a divalent functional group generated by removing one hydrogen atom from an aryl group, and the description of the aryl group is as described above. Examples of the arylene group include a phenylene group, a pentalenylene group, an indenylene group, a naphthalenylene group, an azulenylene group, a phenalenylene group, and a biphenylene group.

[0019] <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 halogen atom, a thiol group, a carboxyl group, a phosphate group, a phosphonate group, a sulfo group, a keto group, an alkyloxy group, an oxo group, etc.

[0020] <Target Substances> Target substances include metals, metal ions, metalloids, and metalloid ions.

[0021] Metals and metalloids include transition metals and metals and metalloids of Groups 13 to 16. Metal ions and metalloid ions include transition metal ions (including rare earth metal ions) and metal ions and metalloid ions of Groups 13 to 16.

[0022] Transition metals 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.

[0023] Rare earth metals include Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0024] Metals and metalloids of Groups 13 to 16 include B, Al, Si, Ga, Ge, As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, Po, and At. Of these, B, Si, Ge, As, Se, Po, At, Sb, and Te are metalloids.

[0025] In view of the high demand for adsorption and recovery, the target substance is preferably selected from precious metals and precious metal ions such as Pt, Pd, Rh, Ru, Ir, Os, Au, Ag, Re, and ions thereof, more preferably selected from Pt, Pd, Rh, Ru, Ir, Os, Au, and ions thereof, and even more preferably selected from Pt, Pd, Rh, Ir, Au, and ions thereof.

[0026] Examples of the forms of metals and metalloids adsorbed to functional groups include metal and metalloid nanoparticles. The metals adsorbed to functional groups may or may not have ligands. The metal ions and metalloid ions adsorbed to functional groups may or may not have ligands.

[0027] <Functional group capable of adsorbing a target substance (sometimes referred to as an "adsorbent functional group" in this specification)> The adsorbent functional group may be capable of adsorbing one type of target substance, or may be capable of adsorbing two or more types of target substances.

[0028] The adsorptive functional group is preferably a functional group containing at least one selected from the group consisting of a nitrogen atom-containing group, a thiol group, a sulfo group, a phosphate group, a phosphonic acid group, a carboxyl group, a hydroxyl group, and a keto group, more preferably a functional group containing at least one selected from the group consisting of a nitrogen atom-containing group, a thiol group, a sulfo group, a phosphonic acid group, and a carboxyl group, and even more preferably a functional group containing at least one nitrogen atom-containing group. The adsorptive functional group may be a functional group composed of at least one selected from the above group. The adsorptive functional group may be a functional group composed of at least one nitrogen atom-containing group.

[0029] The nitrogen atom-containing group is preferably a functional group containing at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group, and more preferably a functional group containing at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, and a nitrilo group. The nitrogen atom-containing group may be a functional group consisting of at least one selected from the above group.

[0030] A primary amino group has the formula: -NH ２ The secondary amino group is represented by the formula: -NHR １ The tertiary amino group is represented by the formula: -NR １ R ２ The quaternary ammonium group is represented by the formula: -N ＋ R １ R ２ R ３ It is expressed as: R １ , R ２ and R ３ are each independently, for example, an alkyl group which may have one or more substituents, an aryl group which may have one or more substituents, an arylalkyl group which may have one or more substituents, an alkylaryl group which may have one or more substituents, etc. The secondary amino group and the tertiary amino group may be an aliphatic amino group or an aromatic amino group, but an aliphatic amino group is preferred. Examples of the aliphatic amino group include R １ a secondary amino group, R １ and R ２ and a tertiary amino group in which both of R and R are alkyl groups which may have one or more substituents. １ a secondary amino group which is an aryl group which may have one or more substituents, an arylalkyl group which may have one or more substituents, or an alkylaryl group which may have one or more substituents; １ and R ２and tertiary amino groups, at least one of which is an aryl group which may have one or more substituents, an arylalkyl group which may have one or more substituents, or an alkylaryl group which may have one or more substituents. The quaternary ammonium group may be an aliphatic ammonium group or an aromatic ammonium group, but an aliphatic ammonium group is preferred. Examples of the aliphatic ammonium group include R １ , R ２ and R ３ and the like. Examples of the aromatic ammonium group include a quaternary ammonium group in which R １ , R ２ and R ３ and a quaternary ammonium group, at least one of which is an aryl group which may have one or more substituents, an arylalkyl group which may have one or more substituents, or an alkylaryl group which may have one or more substituents.

[0031] Examples of secondary amino groups include aliphatic amino groups such as N-methylamino, N-ethylamino, N-propylamino and N-isopropylamino groups, and aromatic amino groups such as N-phenylamino (anilino) groups.

[0032] Examples of the tertiary amino group include aliphatic amino groups such as an N,N-dimethylamino group, an N,N-diethylamino group, an N,N-methylethylamino group, an N,N-dipropylamino group, and an N,N-diisopropylamino group; and aromatic amino groups such as an N,N-diphenylamino group.

[0033] Examples of the quaternary ammonium group include trialkylammonium groups such as trimethylammonium, triethylammonium, and tributylammonium. Examples of the counter ion to the nitrogen atom constituting the quaternary ammonium group include chloride ion, bromide ion, and hydroxide ion.

[0034] An imino group is a divalent group represented by the formula: =NH or -NH-. The imino group may be bonded to one carbon atom by a double bond (i.e., C=NH) or to two carbon atoms by single bonds (i.e., C-NH-C). A secondary amino group (-NHR １ The —NH— in the secondary amino group (—NHR) can be an imino group, but the secondary amino group is preferably a terminal group. １ ) in R １ may have at least one functional group selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group, but preferably does not have such a functional group.

[0035] A nitrilo group is a trivalent group represented by the formula: ≡N or -N<. A nitrilo group may be bonded to one carbon atom by a triple bond (i.e., C≡N), or may be bonded to three carbon atoms by single bonds (i.e., C-N(-C)-C). In the former case, the nitrilo group forms a cyano group (-CN) together with one carbon atom. A tertiary amino group (-NR １ R ２ The -N< in the tertiary amino group (-NR) may be a nitrilo group, but the tertiary amino group is preferably a terminal group. １ R ２ ) in R １ and R ２ may each have at least one functional group selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group, but it is preferable that they do not have such a functional group.

[0036] A nitrogen-containing heterocyclic group is a monovalent group containing at least one (e.g., one, two, or three) nitrogen atom as a ring-constituting atom. In addition to the at least one nitrogen atom, the nitrogen-containing heterocyclic group may contain one or more (e.g., one, two, or three) heteroatoms selected from the group consisting of oxygen atoms and sulfur atoms as ring-constituting atoms. The nitrogen-containing heterocyclic group may be monocyclic or polycyclic (e.g., bicyclic or tricyclic). The number of ring members in a monocyclic nitrogen-containing heterocyclic group is, for example, 3 to 8, preferably 5 or 6. The number of ring members in a polycyclic nitrogen-containing heterocyclic group is, for example, 9 to 14, preferably 9 or 10. The nitrogen-containing heterocyclic group may or may not have aromaticity (i.e., it may be an aromatic heterocyclic group or an aliphatic heterocyclic group). The nitrogen-containing heterocyclic group may have one or more substituents.

[0037] Examples of nitrogen atom-containing heterocyclic groups include 5- or 6-membered monocyclic nitrogen atom-containing heterocyclic groups. Examples of aromatic 5- or 6-membered monocyclic nitrogen atom-containing heterocyclic groups include pyrrolyl, imidazolyl, pyrazolyl, oxazolyl, thiazolyl, isothiazolyl, triazolyl, oxadiazolyl, thiadiazolyl, tetrazolyl, pyridyl, pyridazinyl, pyrimidinyl, and pyrazinyl groups. Examples of non-aromatic 5- or 6-membered monocyclic nitrogen atom-containing heterocyclic groups include pyrrolidinyl, pyrazolidinyl, imidazolidinyl, piperidinyl, piperazinyl, morpholino, and thiomorpholino groups. The non-aromatic 5- or 6-membered monocyclic nitrogen atom-containing heterocyclic group may have one or two unsaturated bonds in the ring, and examples of such nitrogen atom-containing heterocyclic groups include a 1,2-dihydropyridyl group, a 1,4-dihydropyridyl group, and a 1,2,5,6-tetrahydropyridyl group. The 5- or 6-membered monocyclic nitrogen atom-containing heterocyclic group, which may or may not have aromaticity, may be condensed with a benzene ring, and examples of the polycyclic (e.g., bicyclic or tricyclic) nitrogen atom-containing heterocyclic group include an indolyl group, an isoindolyl group, an indazolyl group, a benzimidazolyl group, a benzotriazolyl group, an oxazolopyrimidinyl group, a thiazolopyrimidinyl group, a pyrrolopyridinyl group, a pyrrolopyrimidinyl group, an imidazopyridinyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a cinnolinyl group, a phthalazinyl group, a quinazolinyl group, a quinoxalinyl group, and a naphthyridinyl group.

[0038] The bond of the nitrogen-containing heterocyclic group may be formed by any of the ring-constituting atoms. The bond of the nitrogen-containing heterocyclic group is usually formed by a carbon atom or a nitrogen atom. When the bond of the nitrogen-containing heterocyclic group is formed by a nitrogen atom, the nitrogen-containing heterocyclic group corresponds to a heterocyclic amino group. Examples of aromatic 5- or 6-membered monocyclic heterocyclic amino groups include a 1-pyrrolyl group, a 1-imidazolyl group, a 1-pyrazolyl group, a 3-oxazolyl group, a 3-thiazolyl group, a 1-pyridyl group, a 1-pyridazinyl group, a 1-pyrimidinyl group, and a 1-pyrazinyl group. Examples of non-aromatic 5- or 6-membered monocyclic heterocyclic amino groups (i.e., alicyclic amino groups) include a 1-pyrrolidinyl group, a 1-pyrazolidinyl group, a 1-imidazolidinyl group, a 1-piperidinyl group, a 1-piperazinyl group, a morpholino group, and a thiomorpholino group.

[0039] Examples of target substances suitable for adsorption by primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, imino groups, nitrilo groups, and nitrogen atom-containing heterocyclic groups include Co, Cr, Cu, Fe, Ni, Os, Pd, Pt, Rh, Ru, Au, Ir, W, Zn, V, Mn, and Re.

[0040] Examples of target substances suitable for adsorption by thiol groups include Ag, Co, Cu, Fe, Ir, Ni, Os, Pd, Au, Pt, Rh, Ru, Sc, Zn, and Re.

[0041] Examples of target substances suitable for adsorption by sulfo groups include Cd, Cr, Pb, Zn, Al, Cu, Mn, Sn, Fe, Co, Ni, Ag, and Bi.

[0042] Examples of target substances suitable for adsorption by phosphate groups include In, Al, Bi, Pb, Au, Ir, Pd, Pt, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, and Sn.

[0043] Examples of target substances suitable for adsorption by phosphonic acid groups include In, Al, Bi, Pb, Au, Ir, Pd, Pt, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Cd, and Sn.

[0044] Examples of target substances suitable for adsorption by carboxyl groups include Co, Cr, Cu, Fe, Ir, Ni, Os, Pd, Rh, Ru, Sc, Zn, V, Mn, and Re.

[0045] <First Adsorbent> The first adsorbent has a porous body having a bicontinuous structure formed by a ceramic skeleton having mesopores and macropores, and the surface of the ceramic skeleton is modified with an adsorptive functional group.

[0046] <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.

[0047] 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.

[0048] 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.

[0049] <Structure of porous body before modification> The structure of the porous body before modification with adsorptive functional 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.

[0050] As shown in FIG. 1, the porous body has a bicontinuous structure formed by a ceramic skeleton 1 containing mesopores 3 and macropores 2 .

[0051] 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). The co-continuous structure of the porous body allows efficient adsorption and desorption of the target substance, making it possible to desorb a sufficient amount of the target substance without using aqua regia and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment.

[0052] From the viewpoint of improving the adsorption / desorption performance, the mode pore diameter of the macropores 2 is preferably 0.20 μm or more, more preferably 0.40 μm or more, and even more preferably 0.60 μm or more. From the same viewpoint, the mode pore diameter of the macropores 2 is preferably 5.0 μm or less, more preferably 4.0 μm or less, and even more preferably 3.0 μm or less. Each of these upper limit values ​​may be combined with any of the above-mentioned lower limit values.

[0053] 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.

[0054] From the viewpoint of improving the adsorption / desorption 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.

[0055] 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.

[0056] From the viewpoint of improving the adsorption / desorption 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 33 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.

[0057] From the viewpoint of improving the adsorption / desorption 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.

[0058] From the viewpoint of improving the adsorption / desorption 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.

[0059] From the viewpoint of improving the adsorption / desorption 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.

[0060] <Material of Porous Body> The ceramic that constitutes the ceramic skeleton is, for example, an oxide ceramic containing an element selected from the group consisting of metalloid elements and metal elements. The ceramic skeleton 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.

[0061] An example of a semi-metallic element is silicon. An example of an oxide ceramic containing silicon is silica (SiO ２ ) are listed.

[0062] Examples of metal elements include aluminum, tin, and transition metal elements such as zinc, cerium, titanium, zirconium, vanadium, chromium, iron, cobalt, nickel, palladium, platinum, copper, silver, and gold. Among these, from the viewpoint of ease of manufacturing a porous body, it is preferable that the metal element is selected from the group consisting of 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.

[0063] In addition to silicon, aluminum, tin or a transition metal element, the oxide ceramic may further contain an element selected from the group consisting of 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.

[0064] <Method for producing porous body> The porous body can be produced, for example, by a method described in WO 2022 / 163834, specifically, 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).

[0065] In one embodiment, the ceramic monolith is preferably a silica monolith, which has a bicontinuous structure formed by a silica framework containing mesopores and macropores.

[0066] 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.

[0067] 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.

[0068] The produced ceramic monolith may be pulverized and used as an adsorbent. Pulverization can be carried out according to conventional methods. 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 to 7.0 mm, more preferably 0.5 μm to 5.0 mm, even more preferably 2.0 μm to 4.0 mm, and even more preferably 5.0 μm to 3.0 mm. 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.

[0069] <Surface Modification> In the first adsorbent, the surface of the ceramic skeleton is modified with an adsorptive functional group. The surface of the ceramic skeleton may be modified with one type of adsorptive functional group, or may be modified with two or more types of adsorptive functional groups. The adsorptive functional group may be directly bonded to the surface of the ceramic skeleton, or may be bonded to the surface of the ceramic skeleton via a linker.

[0070] 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 an adsorptive functional group.

[0071] Methods for introducing adsorptive functional groups onto the surface of a ceramic skeleton include, for example, a method for chemically fixing a compound having an adsorptive functional group onto the surface of the ceramic skeleton via a covalent bond, and a method for physically fixing a compound having an adsorptive functional group onto the surface of the ceramic skeleton via a physical interaction such as an ionic bond or a hydrophobic interaction. Examples of methods for chemically introducing adsorptive functional groups onto the surface of a ceramic skeleton include a method for reacting a functional group (e.g., a hydroxyl group) on the surface of the ceramic skeleton with a silane coupling agent having an adsorptive functional group, and chemically fixing the silane coupling agent having an adsorptive functional group onto the surface of the ceramic skeleton.

[0072] In one embodiment, a compound having a nitrogen atom-containing group is fixed to the surface of the ceramic skeleton, thereby modifying the surface of the ceramic skeleton with the nitrogen atom-containing group. Methods for introducing a compound having a nitrogen atom-containing group to the surface of the ceramic skeleton include, for example, chemically fixing a compound having a nitrogen atom-containing group (e.g., a silane coupling agent having a nitrogen atom-containing group) to the surface of the ceramic skeleton via a covalent bond, or physically fixing a compound having a nitrogen atom-containing group to the surface of the ceramic skeleton via a physical interaction such as an ionic bond or hydrophobic interaction. A method for chemically introducing a compound having a nitrogen atom-containing group 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 silane coupling agent having a nitrogen atom-containing group to chemically fix the silane coupling agent to the surface of the ceramic skeleton. The compound having a nitrogen atom-containing group may be fixed to the surface of the ceramic skeleton via a linker. For example, a functional group reactive with a compound having a nitrogen-containing group may be introduced onto the surface of a ceramic skeleton, and then the introduced functional group may be reacted with a compound having a nitrogen-containing group to chemically fix the compound having the nitrogen-containing group to the surface of the ceramic skeleton. A method for introducing a functional group reactive with a compound having a nitrogen-containing group 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 compound having a nitrogen-containing group, thereby 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 compound having a nitrogen-containing group 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.

[0073] As the compound having a nitrogen atom-containing group, an amine compound can be used. The amine compound preferably has at least one nitrogen atom-containing group selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group. The portion of the amine compound other than the nitrogen atom-containing group may be composed of hydrogen atoms and carbon atoms, or may contain one or more other elements (e.g., oxygen atoms, sulfur atoms, halogen atoms, silicon atoms, etc.) in addition to hydrogen atoms and carbon atoms.

[0074] The amine compound may be, for example, at least one selected from the group consisting of monoamines, diamines, triamines, and polyamines. Two or more amine compounds may be used. The amine compound may be a silane coupling agent.

[0075] Examples of the silane coupling agent having at least one nitrogen atom-containing group selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group include silane coupling agents represented by the following formula A, B, or C. Formula A: R ａ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula B: R ａ -R ｄ -NH-R ｅ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula C:R ａ -R ｄ -NH-R ｅ -NH-R ｆ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ

[0076] In Formulas A, B and C, R ａrepresents a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, or a nitrogen atom-containing heterocyclic group; n R ｂ each independently represents an alkyl group, and (3−n) R ｃ each independently represents an alkyloxy group or a halogen group; R ｄ , R ｅ and R ｆ each independently represents an alkylene group, an arylene group, or a combination thereof; and n represents an integer of 0 to 2.

[0077] R ａ is preferably selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, and a nitrogen atom-containing heterocyclic group, and more preferably selected from the group consisting of a primary amino group, a secondary amino group, and a tertiary amino group.

[0078] R ｂ Examples of the alkyl group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0079] R ｃ Examples of the alkyloxy group or halogen group represented by R include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a chloro group, a bromo group, and an iodo group. ｃ Among the alkyloxy groups represented by the formula (I), a methoxy group or an ethoxy group is preferred. ｃ Of the halogen groups represented by the formula (I), a chloro group is preferred.

[0080] R ｄ , R ｅ or R ｆ Examples of the alkylene group represented by the formula (I) include a methylene group, an ethylene group, a propylene group, and a butylene group.

[0081] R ｄ , R ｅ or R ｆ Examples of the arylene group represented by the formula (I) include a phenylene group, a naphthylene group, and a biphenylene group.

[0082] R ｄ , R ｅ or R ｆExamples 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.

[0083] R ｄ , R ｅ and R ｆ The alkylene group, arylene group, or combination thereof represented by the formula (I) may have one or more substituents.

[0084] The monoamine preferably has one nitrogen atom-containing group selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group. Examples of the monoamine include silane coupling agents represented by Formula A, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-(N-phenyl)aminopropyltrimethoxysilane, and 3-(4-pyridyl)propyltrimethoxysilane.

[0085] The diamine preferably has two nitrogen-containing groups selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen-containing heterocyclic group. The two nitrogen-containing groups may be the same or different. Examples of the diamine include silane coupling agents represented by Formula B. Examples of the silane coupling agents represented by Formula B include 3-(2-aminoethylamino)propyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, and N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride.

[0086] The triamine preferably has three nitrogen atom-containing groups selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, and a nitrogen atom-containing heterocyclic group. The three nitrogen atom-containing groups may be the same or different. Examples of triamines include silane coupling agents represented by formula C, such as 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane.

[0087] The polyamine preferably has four or more nitrogen atom-containing groups selected from the group consisting of primary amino groups, secondary amino groups, tertiary amino groups, quaternary ammonium groups, imino groups, nitrilo groups, and nitrogen atom-containing heterocyclic groups. The four or more nitrogen atom-containing groups may be the same or different. Examples of polyamines include polyalkyleneimines, polyvinylamines, and polyallylamines.

[0088] Examples of polyalkyleneimines include polymers obtained by polymerizing one or more alkyleneamines by a conventional method. The polyalkyleneimine may also be a polymer obtained by reacting a polymer obtained by polymerizing one or more alkyleneamines by a conventional method with a desired compound to chemically modify the polymer. The polyalkyleneimine may be linear or branched. Examples of polyalkyleneimines include triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, polyethyleneimine, polypropyleneimine, and polybutyleneimine.

[0089] The weight average molecular weight of the polyalkyleneimine is, for example, 146 to 30,000, preferably 146 to 15,000, more preferably 146 to 5,000, and even more preferably 146 to 1,800. The weight average molecular weight of the polyvinylamine is, for example, 174 to 25,000, and preferably 174 to 6,000. The weight average molecular weight of the polyallylamine is, for example, 230 to 150,000, preferably 230 to 15,000, more preferably 230 to 8,000, and even more preferably 230 to 5,000. The weight average molecular weight can be measured, for example, by gel permeation chromatography (GPC) using polystyrene as a standard substance.

[0090] In one embodiment, a compound having a sulfo group (hereinafter referred to as "first compound") is fixed to the surface of the ceramic skeleton, thereby modifying the surface of the ceramic skeleton with a sulfo group. The above description regarding the method for introducing a compound having a nitrogen atom-containing group onto the surface of the ceramic skeleton also applies to the method for introducing a first compound onto the surface of the ceramic skeleton, unless otherwise specified. When applied, "compound having a nitrogen atom-containing group" is read as "first compound."

[0091] In one embodiment, a compound having a thiol group (hereinafter referred to as "second compound") is fixed to the surface of the ceramic skeleton, thereby modifying the surface of the ceramic skeleton with a thiol group. The above description regarding the method for introducing a compound having a nitrogen atom-containing group onto the surface of the ceramic skeleton also applies to the method for introducing a second compound onto the surface of the ceramic skeleton, unless otherwise specified. When applied, "compound having a nitrogen atom-containing group" is read as "second compound."

[0092] As a method for modifying the surface of the ceramic skeleton with a sulfo group, a method may be adopted in which a second compound is fixed to the surface of the ceramic skeleton and then a thiol group contained in the second compound is converted to a sulfo group. The conversion of a thiol group to a sulfo group can be carried out according to a conventional method. The conversion of a thiol group to a sulfo group can be carried out, for example, by the method described below. Even if the compound fixed to the surface of the ceramic skeleton does not initially contain a sulfo group, if the compound is derivatized so that it ultimately contains a sulfo group, this is included in the phrase "the surface of the ceramic skeleton is modified with a sulfo group by fixing a compound having a sulfo group to the surface of the ceramic skeleton."

[0093] The portion of the first compound other than the sulfo group and the portion of the second compound other than the thiol group may each 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. As the first compound and the second compound, one or more compounds may be used, or two or more compounds may be used. The first compound and the second compound may be used in combination. As the first compound and the second compound, a silane coupling agent may be used.

[0094] Examples of the silane coupling agent containing a sulfo group include silane coupling agents represented by Formula D or E. Formula D:R ｇ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula E:R ｇ -R ｄ -Si(-O-(R ｈ -O) ｍ -R ｉ ) ｎ (-R ｃ ) ３－ｎ

[0095] Examples of silane coupling agents containing a thiol group include silane coupling agents represented by formula F or G. Formula F:R ｊ -R ｄ -Si(-R ｂ ) ｎ (-R ｃ ) ３－ｎ Formula G:R ｊ -R ｄ -Si(-O-(R ｈ -O) ｍ -R ｉ ) ｎ (-R ｃ ) ３－ｎ

[0096] In Formula D, R ｇ represents a sulfo group, and R ｂ , R ｃ , R ｄ and n has the same meaning as in formulae A to C.

[0097] In formula E, R ｇ , R ｃ , R ｄ and n has the same meaning as in formula D, and R ｈ each independently represents an alkylene group; R ｉ 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.

[0098] In formula F, R ｂ , R ｃ , R ｄ and n has the same meaning as in formula D, and R ｊ represents a thiol group.

[0099] In formula G, R ｃ , R ｄ and n has the same meaning as in formula D, and R ｈ , R ｉ and m are defined as in formula E, and R ｊ is synonymous with formula F.

[0100] R ｈ Examples of the alkylene group represented by the formula (I) include a methylene group, an ethylene group, a propylene group, and a butylene group.

[0101] R ｉExamples of the alkyl group represented by the formula (I) include a methyl group, an ethyl group, a propyl group, and a butyl group.

[0102] Examples of the silane coupling agent represented by formula D include 3-(trimethoxysilyl)-1-propanesulfonic acid.

[0103] Examples of the silane coupling agent represented by formula E include 3-(dimethoxy(2-methoxyethoxy)silyl)-1-propanesulfonic acid.

[0104] Examples of the silane coupling agent represented by formula F include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropyltriethoxysilane.

[0105] Examples of the silane coupling agent represented by formula G include ethoxy(3-mercaptopropyl)bis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silane.

[0106] The amount of adsorbent functional groups contained in the first adsorbent is preferably 0.10 mmol / g to 6.0 mmol / g, more preferably 0.10 mmol / g to 5.0 mmol / g, even more preferably 1.0 mmol / g to 4.0 mmol / g, and even more preferably 1.0 mmol / g to 3.0 mmol / g, based on the mass of the first adsorbent. The term "amount of adsorbent functional groups" refers to the amount of one type of adsorbent functional group when the first adsorbent contains one type of adsorbent functional group, or the total amount of two or more types of adsorbent functional groups when the first adsorbent contains two or more types of adsorbent functional groups. The amount of adsorbent functional groups can be measured according to conventional methods.

[0107] When the adsorptive functional group is a nitrogen atom-containing group, the amount of the nitrogen atom-containing group means the amount of nitrogen atoms derived from the nitrogen atom-containing group (i.e., the amount converted into nitrogen atoms). The amount of the nitrogen atom-containing group can be measured according to a conventional method. For example, the amount of the nitrogen atom-containing group can be measured by the method described in the examples below.

[0108] When the adsorptive functional group is a sulfo group, the amount of sulfo groups means the amount of sulfur atoms derived from the sulfo group (i.e., the amount in terms of sulfur atoms). The amount of sulfo groups can be measured according to a conventional method. For example, the amount of sulfo groups can be measured by the method described in the examples below.

[0109] When the adsorptive functional group is a thiol group, the amount of thiol groups means the amount of sulfur atoms derived from the thiol groups (i.e., the amount in terms of sulfur atoms). The amount of thiol groups can be measured by a conventional method.

[0110] When the adsorptive functional group is a phosphate group, the amount of the phosphate group means the amount of phosphorus atoms derived from the phosphate group (i.e., the amount in terms of phosphorus atoms). The amount of the phosphate group can be measured by a conventional method.

[0111] When the adsorptive functional group is a phosphonic acid group, the amount of the phosphonic acid group means the amount of phosphorus atoms derived from the phosphonic acid group (i.e., the amount calculated as phosphorus atoms). The amount of the phosphonic acid group can be measured by a conventional method.

[0112] When the adsorptive functional group is a carboxyl group, the amount of carboxyl groups means the amount of carbon atoms derived from the carboxyl groups (i.e., the amount converted into carbon atoms). The amount of carboxyl groups can be measured by a conventional method.

[0113] <Method for converting thiol groups to sulfo groups> In one embodiment, the method for converting thiol groups to sulfo groups includes the following steps: (e) modifying the surface of the ceramic skeleton of a porous body with thiol groups; and (f) converting the thiol groups to sulfo groups. This method is advantageous in that the amount of sulfo groups can be easily adjusted.

[0114] Step (e) can be carried out by contacting the porous body with a reagent (hereinafter referred to as the "first reagent") for modifying the surface of the ceramic skeleton of the porous body with a thiol group in a first solvent.

[0115] As the first reagent, for example, a compound having a thiol group, preferably a silane coupling agent having a thiol group, more preferably a silane coupling agent represented by formula F or G can be used.

[0116] As the first solvent, for example, water, an aqueous solution, a mixed solution of an organic solvent and an aqueous solution or water, or the like can be used.

[0117] The aqueous solution can be prepared by adding an acid to water. The acid can be selected from, for example, acetic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, etc. Among these, acetic acid is preferred. The concentration of acetic acid in the aqueous solution is, for example, 0.01% by mass or more and 5.0% by mass or less.

[0118] Examples of organic solvents that can be used include alcohol-based solvents such as methanol, ethanol, and propanol; ether-based solvents such as tetrahydrofuran and 2-methyl-tetrahydrofuran; ketone-based solvents such as acetone and methyl ethyl ketone; ester-based solvents such as methyl acetate and ethyl acetate; halogenated hydrocarbon-based solvents such as dichloromethane and chloroform; aromatic hydrocarbon-based solvents such as toluene and xylene; and aliphatic hydrocarbon-based solvents such as hexane and heptane.

[0119] The temperature when the porous body and the first reagent are brought into contact with each other in the first solvent is, for example, 60° C. or higher and 100° C. or lower. The time for which the porous body and the first reagent are brought into contact with each other in the first solvent is, for example, 2 hours or higher and 24 hours or lower.

[0120] After the surface of the ceramic skeleton of the porous body is modified with thiol groups, the thiol-modified porous body is separated from the reaction mixture using a solid-liquid separation method such as filtration. The separated porous body is washed with a cleaning solution such as pure water, dried, and then used in step (f).

[0121] Step (f) can be carried out by contacting the thiol group-modified porous material obtained in step (e) with a reagent for converting the thiol group to a sulfo group (hereinafter referred to as the "second reagent") in a second solvent.

[0122] The second reagent may be, for example, an oxidizing agent such as hydrogen peroxide, nitric acid, or metachloroperbenzoic acid. An aqueous solution containing an oxidizing agent may be used as the second reagent. The aqueous solution containing an oxidizing agent may be prepared by adding the oxidizing agent to water. When an aqueous solution containing hydrogen peroxide is used as the second reagent, the hydrogen peroxide concentration in the aqueous solution is, for example, 10.0% by mass or more and 60.0% by mass or less.

[0123] The second solvent may be, for example, water. When hydrogen peroxide or an aqueous solution containing hydrogen peroxide is used as the second reagent, the hydrogen peroxide concentration in the second solvent is, for example, 5.0% by mass or more and 30.0% by mass or less.

[0124] The temperature when the thiol group-modified porous material and the second reagent are brought into contact with each other in the second solvent is, for example, 40° C. or more and 80° C. or less. The time for which the thiol group-modified porous material and the second reagent are brought into contact with each other in the solvent is, for example, 0.5 hours or more and 12 hours or less.

[0125] After converting the thiol groups contained in the thiol group-modified porous material to sulfo groups, the sulfo group-modified porous material is separated from the reaction mixture using a solid-liquid separation method such as filtration. The separated porous material is washed with a cleaning solution such as pure water and then dried. In this way, the sulfo group-modified porous material can be obtained.

[0126] In another embodiment, the sulfo-modified porous body can be produced by a method including a step of directly modifying the surface of the ceramic skeleton of the porous body with sulfo groups. For example, the method described in RSC Adv. 2017, 7, pp. 56559-56565 can be used as such a method. According to the method described in this document, the surface of the ceramic skeleton of the porous body can be directly modified with sulfo groups by adding chlorosulfonic acid to the porous body and stirring the mixture.

[0127] <<Method for Producing Adsorbent>> The method for producing an adsorbent of the present invention includes steps (1A) and (2A). Steps (1A) and (2A) will be described below.

[0128] <Step (1A)> Step (1A) is a step of preparing a second adsorbent obtained by contacting a first adsorbent with a liquid containing a target substance (hereinafter referred to as "liquid to be treated").

[0129] The liquid to be treated contains a target substance that can be adsorbed by the adsorptive functional group of the first adsorbent. The liquid to be treated may contain one type of target substance or two or more types of target substances.

[0130] Examples of the liquid to be treated include waste liquid discharged from a plant or the like, and wastewater containing valuable metals discharged from a metal refining process, a metal plating process, etc. The liquid to be treated usually contains water. The waste liquid, wastewater, etc. may be pretreated as necessary and then contacted with the first adsorbent.

[0131] Examples of methods for contacting the liquid to be treated with the first adsorbent include a method of immersing the first adsorbent in the liquid to be treated and a method of sending the liquid to a column packed with the first adsorbent. When the method of immersing the first adsorbent in the liquid to be treated is used, the second adsorbent is separated from the liquid to be treated by solid-liquid separation such as filtration and then subjected to step (2A). When the method of sending the liquid to a column packed with the first adsorbent is used, the second adsorbent may be removed from the column after the end of the liquid transfer and then subjected to step (2A), or it may be subjected to step (2A) without being removed from the column after the end of the liquid transfer (i.e., in the state of the column packed with the second adsorbent). The liquid transfer can be performed, for example, using a liquid transfer pump. The liquid transfer may be performed continuously or intermittently.

[0132] When the liquid to be treated is brought into contact with the first adsorbent, the target substance contained in the liquid to be treated is adsorbed onto the first adsorbent, resulting in a second adsorbent. The second adsorbent contains the first adsorbent and the target substance adsorbed to the first adsorbent. The second adsorbent may contain one type of target substance or two or more types of target substances.

[0133] It is generally known that setting the contact treatment temperature higher increases the adsorption efficiency. The temperature when the liquid to be treated is brought into contact with the first adsorbent is not particularly limited, but may be, for example, 25°C or higher, 40°C or higher, or 50°C or higher, from the viewpoint of the treatment cost associated with temperature control and the adsorption efficiency. The upper limit may be, for example, 90°C or lower, or 70°C or lower. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0134] In step (2A), in order to efficiently desorb a sufficient amount of the target substance from the second adsorbent by contacting the second adsorbent with an acidic solution other than aqua regia, it is necessary for the second adsorbent to contain a sufficient amount of the target substance. Therefore, the percentage of the adsorption amount of the target substance in the second adsorbent prepared in step (1A) relative to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more. This percentage is preferably 55% or more, more preferably 60% or more, even more preferably 65% ​​or more, and even more preferably 70% or more. The upper limit is 100%.

[0135] The "saturated adsorption amount of the target substance on the first adsorbent" means the amount (g) of the target substance adsorbed on the first adsorbent from the start of contact treatment between the liquid to be treated and the first adsorbent until the concentration of the target substance in the liquid to be treated after contact with the first adsorbent becomes the same as the concentration of the target substance in the liquid to be treated before contact with the first adsorbent. The "amount (g) of the target substance adsorbed on the first adsorbent" means the amount (g) of one type of target substance adsorbed on the first adsorbent when one type of target substance is adsorbed on the first adsorbent, or the total amount (g) of the two or more types of target substances adsorbed on the first adsorbent.

[0136] For example, in the case where the liquid to be treated is brought into contact with the first adsorbent by feeding the liquid to a column filled with the first adsorbent, and the liquid to be treated that has passed through the column is collected in a collection container, the feeding is stopped when the concentration of the target substance in the liquid to be treated that has passed through the column becomes the same as the concentration of the target substance in the liquid to be treated before passing through the column, and the total amount of the target substance in the liquid to be treated that has been collected in the collection container from the start to the end of the feeding is measured, and the saturated adsorption amount of the target substance in the first adsorbent can be calculated based on the following formula: Saturated adsorption amount of the target substance in the first adsorbent = (total amount of the target substance in the liquid to be treated that has been supplied to the column from the start to the end of the feeding) - (total amount of the target substance in the liquid to be treated that has been collected in the collection container from the start to the end of the feeding).

[0137] The "amount of the target substance adsorbed on the second adsorbent prepared in step (1A)" means the amount (g) of the target substance adsorbed on the first adsorbent by the contact treatment in step (1A) (i.e., from the start to the end of the contact treatment). The meaning of the "amount (g) of the target substance adsorbed on the first adsorbent" is the same as above.

[0138] For example, when the contact treatment in step (1A) is carried out by feeding the liquid to be treated into a column packed with a first adsorbent, and the liquid to be treated that has passed through the column is collected in a collection container, the total amount of the target substance in the liquid to be treated that is collected in the collection container from the start to the end of liquid feeding can be measured, and the amount of the target substance adsorbed by the second adsorbent can be calculated based on the following formula: Amount of the target substance adsorbed by the second adsorbent = (Total amount of the target substance in the liquid to be treated that is supplied to the column from the start to the end of liquid feeding) - (Total amount of the target substance in the liquid to be treated that is collected in the collection container from the start to the end of liquid feeding).

[0139] The amount of the target substance adsorbed to the first adsorbent and the amount of the target substance in the liquid to be treated can be measured using, for example, an ICP emission spectrometer.

[0140] <Step (2A)> Step (2A) is a step of subjecting the second adsorbent to a contact treatment with an acidic solution excluding aqua regia (sometimes referred to as a "desorption treatment" in this specification) to desorb the target substance from the second adsorbent, thereby obtaining a third adsorbent. Hereinafter, the acidic solution excluding aqua regia may be simply referred to as the "acidic solution."

[0141] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, it is preferable that the acidic solution contains at least one selected from the group consisting of inorganic acids and ammonium salts.

[0142] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, the inorganic acid preferably contains at least one selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, and boric acid, and more preferably contains at least one selected from the group consisting of hydrochloric acid and nitric acid. When the desorption treatment is performed using the inorganic acid, it is possible to prevent the desorption treatment from causing deterioration of the adsorptive functional groups contained in the third adsorbent and resulting in a decrease in the adsorption performance of the third adsorbent.

[0143] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, the ammonium salt preferably contains at least one selected from the group consisting of ammonium chloride, ammonium sulfate, and ammonium carbonate, and more preferably contains ammonium chloride. When the desorption treatment is performed using the above ammonium salt, it is possible to prevent the desorption treatment from causing deterioration of the adsorptive functional groups contained in the third adsorbent and resulting in a decrease in the adsorption performance of the third adsorbent.

[0144] The solvent contained in the acidic solution may be, for example, water.

[0145] In this specification, aqua regia refers to a mixture of concentrated hydrochloric acid and concentrated nitric acid. The ratio of the volume of concentrated hydrochloric acid to the volume of concentrated nitric acid in aqua regia is, for example, 1.5 to 4.0.

[0146] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, the total concentration of the inorganic acid and ammonium salt contained in the acidic solution is preferably 0.1 mol / L to 13 mol / L, more preferably 0.5 mol / L to 8.0 mol / L, and even more preferably 1.0 mol / L to 6.0 mol / L. When the total concentration is within the above range, it is possible to prevent the desorption treatment from causing deterioration of the adsorptive functional groups contained in the third adsorbent and resulting in a decrease in the adsorption performance of the third adsorbent. When the acidic solution contains one substance selected from the group consisting of inorganic acids and ammonium salts, the total concentration refers to the concentration of the one substance. When the acidic solution contains at least two or more substances selected from the group consisting of inorganic acids and ammonium salts, the total concentration refers to the total concentration of the two or more substances.

[0147] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, the contact treatment in step (2A) is preferably carried out at a temperature of 90°C or less, more preferably 70°C or less, and even more preferably 60°C or less. The lower limit is not particularly limited as long as it is a temperature at which the acidic solution does not freeze. The lower limit may be, for example, 1°C or more or 20°C or more. Each of these lower limits may be combined with any of the above-mentioned upper limits.

[0148] Examples of methods for contacting the second adsorbent with the acidic solution include immersing the second adsorbent in the acidic solution and pumping the acidic solution into a column packed with the second adsorbent. When the method of immersing the second adsorbent in the acidic solution is used, the third adsorbent is separated from the acidic solution by solid-liquid separation such as filtration and then used. When the method of pumping the acidic solution into a column packed with the second adsorbent is used, the third adsorbent may be removed from the column after the pumping is completed and used, or it may be used without being removed from the column after the pumping is completed (i.e., in the state of a column packed with the third adsorbent). At least one target substance contained in the acidic solution can be recovered according to conventional methods. The recovered at least one target substance may be subjected to treatments such as separation, concentration, and purification according to conventional methods. The pumping can be performed, for example, using a pumping pump. The pumping may be performed continuously or intermittently.

[0149] From the viewpoint of desorbing a sufficient amount of the target substance in step (2A) and preventing a decrease in the adsorption performance of the adsorbent after the desorption treatment, the contact treatment in step (2A) is preferably carried out using an acidic solution of 1 L / kg or more per mass of the second adsorbent. The upper limit is not particularly limited. The upper limit may be, for example, 200 L / kg or less.

[0150] When the second adsorbent is contacted with an acidic solution, at least one target substance is desorbed from the second adsorbent to obtain a third adsorbent. One target substance or two or more target substances may be desorbed from the second adsorbent.

[0151] In order to prevent a decrease in the adsorption performance of the third adsorbent, it is necessary to desorb a sufficient amount of the target substance from the second adsorbent in step (2A). This is because if the target substance remains adsorbed to the adsorptive functional groups contained in the third adsorbent, the adsorption performance of the third adsorbent will decrease. Therefore, the percentage of the amount of the target substance desorbed in step (2A) relative to the amount of the target substance adsorbed in the second adsorbent prepared in step (1A) is 70% or more. This percentage is preferably 75% or more, more preferably 80% or more, and even more preferably 85% or more. The upper limit is 100%. When this percentage is within the above range, a decrease in the adsorption performance of the third adsorbent can be prevented. Therefore, the third adsorbent can adsorb a sufficient amount of the target substance.

[0152] The meaning of "the amount of the target substance adsorbed on the second adsorbent prepared in step (1A)" is the same as above.

[0153] The "amount of target substance desorbed in step (2A)" means the amount (g) of the target substance desorbed from the second adsorbent due to the contact treatment in step (2A) (i.e., from the start to the end of the contact treatment). The "amount (g) of target substance desorbed from the second adsorbent" means the amount (g) of desorbed target substance when one type of target substance is desorbed from the second adsorbent, or the total amount (g) of desorbed target substance when two or more types of target substances are desorbed from the second adsorbent.

[0154] For example, when the contact treatment in step (2A) is carried out by feeding an acidic solution into a column filled with a second adsorbent, and the acidic solution that has passed through the column is collected in a collection container, the total amount of the target substance in the acidic solution collected in the collection container from the start to the end of feeding can be measured, and this can be used as the amount of target substance desorbed in step (2A).

[0155] The amount of the target substance in the acidic solution can be measured using, for example, an ICP emission spectrometer.

[0156] After step (2A), the third adsorbent may be washed using a washing liquid such as water.

[0157] When desorption treatment is performed under harsh conditions (e.g., using aqua regia) in order to increase the amount of desorption of the target substance, the adsorption performance of the adsorbent after the desorption treatment is significantly reduced. In contrast, according to the adsorbent manufacturing method of the present invention, a sufficient amount of the target substance can be desorbed without using aqua regia in step (2A), and the adsorption performance of the third adsorbent obtained in step (2A) can be prevented from being reduced.

[0158] <<Method for recovering target substance>> The method for recovering a target substance of the present invention includes the following steps: (1B) a step of preparing a second adsorbent obtained by contacting a first adsorbent with a liquid containing the target substance; and (2B) a step of contacting the second adsorbent with an acidic solution excluding aqua regia, thereby desorbing the target substance from the second adsorbent and obtaining the target substance.

[0159] The percentage of the amount of the target substance adsorbed in the second adsorbent prepared in step (1B) relative to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more. The percentage of the amount of the target substance desorbed in step (2B) relative to the amount of the target substance adsorbed in the second adsorbent prepared in step (1B) is 70% or more.

[0160] The method for recovering a target substance of the present invention can be carried out in the same manner as the method for producing an adsorbent of the present invention, except that the target substance is obtained in step (2B).

[0161] The above explanation regarding the method for producing an adsorbent of the present invention also applies to the method for recovering a target substance of the present invention, unless otherwise specified. When applying, "Step (1A)" should be read as "Step (1B)" and "Step (2A)" should be read as "Step (2B)."

[0162] <Production 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 a 6.06% by mass aqueous acetic acid solution were added to a 150 mL reaction vessel and stirred at room temperature (25°C) 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 solution 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 produce a polysiloxane gel.

[0163] 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 mixture 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 850 μm or less.

[0164] (2) Observation by Scanning Electron Microscope When the surface structure of the silica monolith obtained in (1) above was observed with a scanning electron microscope (JSM-7900F manufactured by JEOL), it was confirmed that the silica monolith had a bicontinuous structure.

[0165] (3) Measurement of specific surface area and most frequent pore size of mesopores Measurement of the specific surface area and most frequent pore size of mesopores was carried out 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.

[0166] 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.

[0167] (4) Measurement of total pore volume, most frequent pore size of macropores, and porosity Using a mercury porosimeter (AutoPore IV 9520 manufactured by Micromeritics), the total pore volume, most frequent pore size of macropores, and porosity were measured by mercury intrusion porosimetry. In 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 pores having a diameter of 50 nm to 500 μm. The measurement was performed under the following conditions and procedures.

[0168] (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

[0169] (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.

[0170] The results of (3) and (4) above are shown in Table 1.

[0171]

[0172] (5) Preparation of nitrogen atom-containing group-modified silica monolith adsorbent 5.0 g of the silica monolith obtained in (1) above was added to a reaction vessel, 35 mL of pure water, and 3.73 g of 3-aminopropyltrimethoxysilane were added, and the mixture was heated to reflux at 100°C for 4 hours. The silica monolith was separated from the solution by filtration, washed with 500 mL of pure water, and dried to obtain 6.44 g of nitrogen atom-containing group-modified silica monolith adsorbent. 3-aminopropyltrimethoxysilane is a compound represented by the formula: NH ２ -CH ２ CH ２ CH ２ -Si(-OCH ３ ) ３ The nitrogen atom-containing group-modified silica monolith adsorbent obtained by using 3-aminopropyltrimethoxysilane has a primary amino group (-NH ２ ) is included.

[0173] (6) Measurement of the amount of nitrogen atom-containing groups The amount of nitrogen atoms contained in the silica monolith adsorbent obtained in (5) above was quantified using an oxygen, nitrogen, and hydrogen analyzer ONH836 manufactured by LECO Japan LLC, and the quantified amount of nitrogen atoms was used as the nitrogen atom-containing group (-NH ２ The amount of nitrogen atom-containing groups (-NH ２ The amount of ) was 2.8 mmol / g based on the mass of the silica monolith adsorbent.

[0174] <Production Example 2> (1) Preparation of nitrogen atom-containing group-modified silica monolith adsorbent A nitrogen atom-containing group-modified silica monolith adsorbent was prepared by surface modification in the same manner as in Production Example 1(5), except that 4.63 g of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane was used instead of 3-aminopropyltrimethoxysilane. N-(2-aminoethyl)-3-aminopropyltrimethoxysilane has the formula: NH ２ -CH ２ CH ２ -NH-CH ２ CH ２ CH ２ -Si(-OCH３ ) ３ The nitrogen atom-containing group-modified silica monolith adsorbent obtained using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane has a primary amino group (—NH ２ ) and an imino group (—NH—).

[0175] (2) Measurement of the amount of nitrogen atom-containing groups The amount of nitrogen atoms contained in the silica monolith adsorbent obtained in (1) above was quantified using an oxygen, nitrogen, and hydrogen analyzer ONH836 manufactured by LECO Japan, LLC, and the quantified amount of nitrogen atoms was taken as the amount of nitrogen atom-containing groups contained in the silica monolith adsorbent. The amount of nitrogen atom-containing groups contained in the silica monolith adsorbent was 2.4 mmol / g, based on the mass of the silica monolith adsorbent.

[0176] <Production Example 3> (1) Preparation of sulfo group-modified silica monolith adsorbent 2.04 g of 3-mercaptopropyltrimethoxysilane that had been stirred at room temperature for 1 hour, 35 mL of an aqueous acetic acid solution (acetic acid concentration: 0.1% by mass), and 5.0 g of the silica monolith obtained in Production Example 1(1) 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 group-modified silica monolith. The thiol group-modified silica monolith was separated from the solution by filtration, washed with 500 mL of pure water, and dried to obtain 5.91 g of a thiol group-modified silica monolith.

[0177] 3.0 g of the obtained thiol group-modified silica monolith, 15 mL of hydrogen peroxide solution (hydrogen peroxide concentration: 30% by mass), and 15 mL of pure water were added to a reaction vessel and heated at 60°C for 1 hour to convert the thiol groups to sulfo groups, thereby producing a sulfo group-modified silica monolith. The sulfo group-modified silica monolith was separated from the solution by filtration, washed with 500 mL of pure water, and dried to obtain 3.09 g of sulfo group-modified silica monolith.

[0178] (2) Measurement of the amount of sulfo groups The amount of sulfur atoms contained in the sulfo group-modified silica monolith was measured using a carbon / sulfur analyzer (EMIA-Expert manufactured by Horiba, Ltd.), and the measured amount of sulfur atoms was taken as the amount of sulfo groups contained in the sulfo group-modified silica monolith. The amount of sulfo groups contained in the silica monolith adsorbent was 1.9 mmol / g, based on the mass of the silica monolith adsorbent.

[0179] Example 1 (1) First Adsorption Treatment (Measurement of Saturated Adsorption Amount and Production of Second Adsorbent) 0.125 g of the silica monolith adsorbent (first adsorbent) obtained in Production Example 2 was packed into a column (diameter 4.0 mm, length 100 mm), and the column was connected to a liquid delivery pump via a piping tube, thereby producing the flow adsorption apparatus shown in FIG. 2 .

[0180] At room temperature (25°C), an iridium chloride solution containing 100 ppm of iridium was pumped through the column at a flow rate of 0.2 mL / min using a pump, and the solution that passed through the column was collected in a collection container. The solution was collected in 10 mL portions. The solution was pumped until the iridium concentration in the collected solution reached 100 ppm.

[0181] The total amount of iridium element in the recovered solution was measured using an ICP optical emission spectrometer (SPECTROGREEN FMD46 manufactured by Hitachi High-Tech Science Corporation), and the amount of iridium element adsorbed on the silica monolith adsorbent (second adsorbent) after the first adsorption treatment was calculated based on the following formula: Amount of iridium element adsorbed on silica monolith adsorbent after the first adsorption treatment = (Total amount of iridium element in the solution supplied to the column from the start to the end of liquid delivery) - (Total amount of iridium element in the solution recovered in the recovery container from the start to the end of liquid delivery).

[0182] The amount of iridium element adsorbed on the silica monolith adsorbent after the first adsorption treatment was converted into the amount of iridium element adsorbed per kg of the silica monolith adsorbent (hereinafter referred to as "iridium adsorption amount").

[0183] The amount of iridium element adsorbed on the silica monolith adsorbent after the first adsorption treatment was taken as the saturated adsorption amount of iridium element on the silica monolith adsorbent.

[0184] The percentage of the amount of iridium adsorbed on the silica monolith adsorbent after the first adsorption treatment relative to the saturated amount of iridium adsorbed on the silica monolith adsorbent (hereinafter referred to as "iridium adsorption rate") was calculated. The iridium adsorption rate after the first adsorption treatment was 100%.

[0185] (2) First desorption treatment (production of third adsorbent) The silica monolith adsorbent (second adsorbent) after the first adsorption treatment was subjected to a desorption treatment using the same flow adsorption apparatus as used in the first adsorption treatment.

[0186] At room temperature (25°C), 24 mL of an aqueous ammonium chloride solution (ammonium chloride concentration: 5.0 mol / L) was delivered to the column at a flow rate of 0.2 mL / min using a delivery pump, and the solution that passed through the column was collected in a collection container.

[0187] The total amount of iridium element in the recovered solution was measured using an ICP emission spectrometer (PS3520 UVDD manufactured by Hitachi Corporation), and this was taken as the amount of iridium element desorbed in the first desorption treatment.

[0188] The percentage of the amount of iridium element desorbed in the first desorption treatment relative to the amount of iridium element adsorbed on the silica monolith adsorbent after the first adsorption treatment (hereinafter referred to as "iridium desorption rate") was determined.

[0189] (3) First Washing Treatment After the first desorption treatment, 10 mL of pure water was pumped into the column using a liquid pump to perform a washing treatment.

[0190] (4) Second Adsorption Treatment In order to confirm that the adsorption capacity had not decreased after the desorption treatment, a second adsorption treatment was performed on the silica monolith adsorbent (third adsorbent) after the first cleaning treatment in the same manner as the first adsorption treatment, and the iridium adsorption amount and iridium adsorption rate in the second adsorption treatment were determined. Note that, when determining the iridium adsorption amount and iridium adsorption rate in the second adsorption treatment, the amount of iridium adsorbed on the silica monolith adsorbent after the first adsorption treatment was taken as the saturated adsorption amount of iridium on the silica monolith adsorbent.

[0191] (5) Second Desorption Treatment The silica monolith adsorbent after the second adsorption treatment was subjected to a second desorption treatment in the same manner as the first desorption treatment, and the iridium desorption rate in the second desorption treatment was determined.

[0192] (6) Second Cleaning Treatment After the second desorption treatment, a second cleaning treatment was carried out in the same manner as the first cleaning treatment.

[0193] (7) Third Adsorption Treatment In order to confirm that the adsorption capacity had not decreased after the second desorption treatment, the silica monolith adsorbent after the second cleaning treatment was subjected to a third adsorption treatment in the same manner as the first adsorption treatment, and the iridium adsorption amount and iridium adsorption rate in the third adsorption treatment were determined. Note that, when determining the iridium adsorption amount and iridium adsorption rate in the third adsorption treatment, the amount of iridium adsorbed on the silica monolith adsorbent after the first adsorption treatment was taken as the saturated adsorption amount of iridium on the silica monolith adsorbent.

[0194] (8) Third Desorption Treatment The silica monolith adsorbent after the third adsorption treatment was subjected to a third desorption treatment in the same manner as the first desorption treatment, and the iridium desorption rate in the third desorption treatment was determined.

[0195] (9) Third Cleaning Treatment After the third desorption treatment, the third cleaning treatment was carried out in the same manner as the first cleaning treatment.

[0196] The results are shown in Table 2. Note that the iridium desorption rate may exceed 100% due to the influence of measurement errors inherent in the device. When the iridium desorption rate exceeds 100%, it is expressed as "100". Similarly, in other examples, when the desorption rate exceeds 100%, it is expressed as "100".

[0197]

[0198] Example 2 The same procedure as in Example 1 was carried out, except that the concentration of ammonium chloride used in the desorption treatment was changed to 3 mol / L. The results are shown in Table 3.

[0199]

[0200] Example 3 The same procedure as in Example 1 was carried out, except that 12 mol / L hydrochloric acid was used instead of ammonium chloride in the desorption treatment. The results are shown in Table 4.

[0201]

[0202] Example 4 The same operations as in Example 1 were performed, except that the silica monolith adsorbent used was changed to that prepared in Production Example 1, the solution delivered in the adsorption treatment was changed to a palladium nitrate solution containing 100 ppm of palladium, and the acidic solution used in the desorption treatment was changed to 12 mol / L hydrochloric acid, which was delivered at 60°C. The palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 1. The results are shown in Table 5. When the palladium adsorption rate exceeded 100%, it was represented as "100." Similarly, in other examples, when the adsorption rate exceeded 100%, it was represented as "100." The reason the adsorption rate exceeded 100% is presumed to be because the saturated adsorption amount was lower than the theoretical maximum adsorption amount calculated from the amount of functional groups modified on the surface.

[0203]

[0204] Example 5 The same operations as in Example 4 were carried out, except that the acidic solution used in the desorption treatment was changed to 6 mol / L hydrochloric acid, and the palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 4. The results are shown in Table 6.

[0205]

[0206] Example 6 The same operations as in Example 4 were carried out, except that the acidic solution used in the desorption treatment was changed to 3 mol / L nitric acid, and the palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 4. The results are shown in Table 7.

[0207]

[0208] Example 7 The same operations as in Example 4 were carried out, except that the acidic solution used in the desorption treatment was changed to 0.5 mol / L nitric acid, and the palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 4. The results are shown in Table 8.

[0209]

[0210] Example 8 The same operations as in Example 4 were carried out, except that the temperature of the desorption treatment was changed to 80° C., and the palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 4. The results are shown in Table 9.

[0211]

[0212] Example 9 The same operations as in Example 4 were carried out, except that the acidic solution used in the desorption treatment was changed to a 5 mol / L aqueous ammonium chloride solution and the temperature of the desorption treatment was changed to 25° C. The palladium adsorption amount, palladium adsorption rate, and palladium desorption rate were determined in the same manner as in Example 4. The results are shown in Table 10.

[0213]

[0214] Example 10: A column (4.0 mm in diameter, 100 mm in length) was packed with 0.100 g of the silica monolith adsorbent (first adsorbent) obtained in Production Example 3 instead of 0.125 g of the silica monolith adsorbent (first adsorbent) obtained in Production Example 2; the solution used in the adsorption treatment was changed to a lead nitrate solution containing 100 ppm of lead, which was delivered at a flow rate of 0.15 mL / min at 25°C; and the acidic solution used in the desorption treatment was changed to 1 mol / L nitric acid, which was delivered at a flow rate of 0.15 mL / min at 25°C. The lead adsorption amount, lead adsorption rate, and lead desorption rate were determined in the same manner as in Example 1. The results are shown in Table 11. A lead adsorption rate exceeding 100% was indicated as "100." Similarly, in other examples, an adsorption rate exceeding 100% was indicated as "100." The reason why the adsorption rate exceeds 100% is presumed to be because the saturated adsorption amount is lower than the theoretical maximum adsorption amount calculated from the amount of functional groups modified on the surface.

[0215]

[0216] Example 11 The same operations as in Example 10 were carried out, except that the acidic solution used in the desorption treatment was changed to 6 mol / L hydrochloric acid, and the amount of lead adsorption, the lead adsorption rate, and the lead desorption rate were determined in the same manner as in Example 10. The results are shown in Table 12.

[0217]

[0218] Comparative Example 1 The same operations as in Example 1 were carried out, except that the acidic solution used in the desorption treatment was changed to aqua regia (the volume ratio of concentrated hydrochloric acid to concentrated nitric acid was 3), and the iridium adsorption amount, iridium adsorption rate, and iridium desorption rate were determined in the same manner as in Example 1. The results are shown in Table 13. Note that the adsorption amount significantly decreased in the second adsorption treatment, so the test was terminated at this point.

[0219]

[0220] Comparative Example 2 The same operations as in Example 1 were carried out, except that the column was packed with an ion exchange resin (Amberlite (trademark) IRA904Cl, manufactured by DuPont) instead of the silica monolith adsorbent, and the iridium adsorption amount, iridium adsorption rate, and iridium desorption rate were determined in the same manner as in Example 1. The results are shown in Table 14. Note that the iridium desorption rate in the first run was lower than 70%, and the iridium adsorption amount in the second run tended to decrease compared to the examples, so the test was terminated at this point.

[0221]

[0222] DESCRIPTION OF SYMBOLS 1: Ceramic skeleton 2: Macropores 3: Mesopores 60: Flow adsorption device 61: Column 62: Piping tube 63: Liquid transfer pump 64: Collection container

Claims

1. A method for producing an adsorbent comprising the following steps: (1A) preparing a second adsorbent by contacting a first adsorbent having a bicontinuous structure formed by a ceramic skeleton having mesopores and macropores, the surface of the ceramic skeleton being modified with a functional group capable of adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals and semi-metal ions, with a liquid containing the target substance; and (2A) obtaining a third adsorbent by contacting the second adsorbent with an acidic solution excluding aqua regia, thereby desorbing the target substance from the second adsorbent, wherein the percentage of the adsorption amount of the target substance in the second adsorbent prepared in step (1A) relative to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more, and the percentage of the desorption amount of the target substance in step (2A) relative to the adsorption amount of the target substance in the second adsorbent prepared in step (1A) is 70% or more.

2. The method according to claim 1, wherein the contact treatment in step (2A) is carried out at a temperature of 90°C or less.

3. The manufacturing method according to claim 1 or 2, wherein the acidic solution contains at least one selected from the group consisting of inorganic acids and ammonium salts.

4. The manufacturing method according to claim 1 or 2, wherein the total concentration of the inorganic acid and the ammonium salt contained in the acidic solution is 0.1 mol / L or more and 13 mol / L or less.

5. The manufacturing method according to claim 1 or 2, wherein the acidic solution contains at least one selected from the group consisting of hydrochloric acid, nitric acid and ammonium chloride.

6. The method according to claim 1 or 2, wherein the functional group comprises at least one selected from the group consisting of a primary amino group, a secondary amino group, a tertiary amino group, a quaternary ammonium group, an imino group, a nitrilo group, a nitrogen atom-containing heterocyclic group, a thiol group, a sulfo group, a phosphonic acid group and a carboxyl group.

7. The manufacturing method according to claim 1 or 2, wherein the ceramic skeleton contains at least one element selected from the group consisting of silicon, aluminum, tin, cerium, titanium and zirconium.

8. The method according to claim 1 or 2, wherein the target substance is 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 recovering a target substance, comprising the steps of: (1B) preparing a second adsorbent by contacting a first adsorbent having a bicontinuous structure formed by a ceramic skeleton having mesopores and macropores, the surface of the ceramic skeleton being modified with a functional group capable of adsorbing a target substance selected from the group consisting of metals, metal ions, semi-metals and semi-metal ions, with a liquid containing the target substance; and (2B) contacting the second adsorbent with an acidic solution excluding aqua regia to desorb the target substance from the second adsorbent and obtain the target substance, wherein the percentage of the adsorption amount of the target substance in the second adsorbent prepared in step (1B) to the saturated adsorption amount of the target substance in the first adsorbent is 50% or more, and the percentage of the desorption amount of the target substance in step (2B) to the adsorption amount of the target substance in the second adsorbent prepared in step (1B) is 70% or more.

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